Wp J. £L Pill ^tbrarg QH40I NORTH CAROLINA STATE UNIVERSITY LIBRARIES S00953631 R MATTC"RTATifi study o: THIS BOOK IS DUE ON THE DATE INDICATED BELOW AND IS SUB- JECT TO AN OVERDUE FINE AS POSTED AT THE CIRCULATION DESK. MAR 1 1982 f % AUG 5*4997 s MATERIALS FOR THE STUDY OF VARIATION TREATED WITH ESPECIAL REGARD TO DISCONTINUITY IN THE ORIGIN OF SPECIES. BY WILLIAM BATESON, M.A. FELLOW OF ST JOHN'S COLLEGE, CAMBRIDGE Pontoon : MACMILLAN AND CO. AND NEW YOKE. 1894 [All Eights reserved.] Cambridge : PRINTED BY C. J. CLAY, M.A., AND SONS, AT THE UNIVERSITY PRESS. PREFACE. This book is offered as a contribution to the study of the problem of Species. The reasons that have led to its production are as follows. Some years ago it was my fortune to be engaged in an investi- gation of the anatomy and development of Balanoglossus. At the close of that investigation it became necessary to analyze the meaning of the facts obtained, and especially to shew their bear- ing upon those questions of relationship and descent which modern morphology has attempted to answer. To this task I set myself as I best might, using the common methods of morphological argument and interpretation, and working all the facts into a scheme which should be as consistent as I could make it. But the value of this and of all such schemes, by which each form is duly ushered to its place, rests wholly on the hypothesis that the methods of argument are sound. Over it all hung the suspicion that they were not sound. This suspicion seemed at that time so strong that in preface to what I had to say I felt obliged to refer to it, and to state explicitly that the analysis was under- taken in pursuance of the current methods of morphological criticism, and without prejudging the question of possible or even probable error in those methods. Any one who has had to do such work must have felt the same thing. In these discussions we are continually stopped by such phrases as, " if such and such a variation then took place and was favourable/' or, " we may easily suppose circumstances in which such and such a variation if it occurred might be beneficial," and the like. The whole argument is based on such assumptions as these — assumptions which, were they found in the arguments of Paley or of Butler, we could not too scornfully ridicule. " If," say we with much circumlocution, " the course of Nature followed the p S J^- VI PREFACE. lines we have suggested, then, in short, it did." That is the sum of our argument. Were we all agreed in our assumptions and as to the canons of interpretation, there might be some excuse, but we are not agreed. Out of the same facts of anatomy and development men of equal ability and repute have brought the most opposite conclusions. To take for instance the question of the ancestry of Chordata, the problem on which I was myself engaged, even if we neglect fanciful suggestions, there remain two wholly incompatible views as to the lines of Vertebrate descent, each well supported and upheld by many. From the same facts opposite conclusions are drawn. Facts of the same kind will take us no further. The issue turns not on the facts but on the assumptions. Surely we can do better than this. Need we waste more effort in these vain and sophistical disputes ? If facts of the old kind will not help, let us seek facts of a new kind. That the time has come for some new dej)arture most naturalists are now I believe beginning to recognize. For the reasons set forth in the Introduction I suggest that for this new start the Study of Variation offers the best chance. If we had before us the facts of Variation there would be a body of evidence to which in these matters of doubt we could appeal. We should no longer say " if Variation take place in such a way," or " if such a variation were possible ; " we should on the contrary be able to say " since Variation does, or at least may take place in such a way," ''' since such and such a Variation is possible," and we should be expected to quote a case or cases of such occurrence as an observed fact. To collect and codify the facts of Variation is, I submit, the first duty of the naturalist. This work should be undertaken if only to rid our science of that excessive burden of contradictory assumptions by which it is now oppressed. Whatever be our views of Descent, Variation is the common basis of them all. As the first step towards the systematic study of Variation we need a compact catalogue of the known facts, a list which shall contain as far as possible all cases of Variation observed. To carry out such a project in any completeness may be impossible ; but were the plan to find favour, there is I think no reason why in time a consider- able approach to completeness should not be made. PREFACE. Vll Difficulty has hitherto arisen from the fact that Variation is not studied for its own sake. Each observer has some other object in view, and we are fortunate if he is good enough to mention in passing the variations he has happened to see in following his own ends. From the nature of the case these observations must at first be sporadic, and, as each standing alone seems to have little value, in the end they are unheeded and lost. If there were any central collection of facts to which such observations might from time to time be added, and thus brought into relation with cognate observations, their value would at once appear and be preserved. To make a nucleus for such a collection is the object of the present work. The subject treated in this first instalment has been chosen for the reasons given in the text. Reference to facts that could not be included in this section of the evidence has as far as possible been avoided, but occasionally such reference was necessary, especially in the Introduction. It was my original purpose to have published the facts with- out comment. This course would have been the most logical and the safest, but with hesitation it was decided to add something of the nature of analysis. I do this chiefly for two reasons. First, in starting a method one is almost compelled to shew the way in which it is to be applied. If it is hoped that others may interest themselves in the facts, it is necessary to shew how and why their interest is asked. In the old time the facts of Nature were beautiful in themselves and needed not the rouge of speculation to quicken their charm, but that was long ago, before Modern Science was born. Besides this, to avoid the taint of theory in morphology ' is impossible, however much it may be wished. The whole science is riddled with theory. Not a specimen can be described without the use of a terminology coloured by theory, implying the accept- ance of some one or other theory of homologies. If only to avoid misconception matters of theory must be spoken of. It seemed at first also that the meaning of the facts was so clear that all would read it alike ; but from opportunities that have occurred for the discussion of these matters I have found that it is not so, and reluctantly I have therefore made such com- ments as may serve to bring out the chief significance of the Vlll PREFACE. phenomena, pointing out what they shew and what they do not shew, having regard always to deficiencies in the evidence. That this is a dangerous course I am aware. But in any discussion of a problem in the light of insufficient knowledge the real danger is not that a particular conclusion may be wrong, for that is a transient fault, but rather that the facts themselves may be so distorted as to be valueless to others when the conclusions that they were used to shew have been discarded. This danger I have sought indifferently to avoid by printing the facts as far as possible apart from all comment, knowing well how temporary the worth of these comments is likely to be. I have thus tried to avoid general statements and have kept the descriptions to particular cases, unless the number of similar cases is great and an inclusive description is enough. Each separate paragraph relating a fact has been as far as possible isolated and made to stand alone ; so that if any one may hereafter care to go on with the work he will be able to cut out the discarded comments and rearrange the facts in any order preferred, inserting new facts as they come to hand. Most of these facts are numbered for reference. The numbers are distrib- uted on no strict system, but are put in where likely to be useful. For almost every fact stated or mentioned one reference at lea>t is given. When this is not the case the fact is either notorious, or else the result of my own observation. In collecting evidence I have freely used the collections of former writers, especially those of Geoffroy St Hilaire, Ahlfeld, and Wenzel Gruber, but unless the contrary is stated, each passage referred to has been seen in its original place. By this system I hope I have avoided evidence corrupted by repetition. Several well known conceptions, notably that of the presence of order in abnormality, first formulated by Isidore Geoffroy St Hilaire, have been developed and exhibited in their relation to recent views. The professed morphologist will note that many of the state- ments are made on authority unfamiliar to him. I have spared no pains to verify the facts wherever possible, and no case has been admitted without remark if there was reason to doubt its authen- ticity. So long as skilled zoologists continue to neglect all forms that are abnormal the student of Variation must turn to other sources. This neglect of the Study of Variation may be attributed in PREFACE. IX great measure to the unfortunate circumstance that Natural History lias come to be used as a vehicle for elementary education, a purpose to which it is unsuited. From the conditions of the case when very large classes are brought together it becomes necessary that the instruction should be organized, scheduled, and reduced to diagram and system. Facts are valued in proportion as they lend themselves to such orderly treatment ; on the rest small store is set. By this method the pupil learns to think our schemes of Nature sufficient, turning for inspiration to books, and supposing that by following his primer he may master it all. In a specimen he sees what he has been told to see and no more, rarely learning the habit of spontaneous observation, the one lesson that the study of Natural History is best fitted to teach. Such a system reacts on the teacher. In time he comes to forget that the caricature of Nature shewn to his pupils is like no real thing. The perspective and atmosphere that belong to live nature confuse him no more. Two cases may be given in illustration. Few animals are dissected more often than the Crayfish and the Cockroach. Each of these frequently presents a striking departure from the normal (see Nos. 83 and 625) in external characters, but these variations have been long unheeded by pupil and by teacher; for though Desmarest and Brisout published the facts so long ago as 1848, their observations failed to get that visa of the text-books without which no fact can travel far. It is especially strange that while few take much heed of the modes of Variation or of the visible facts of Descent, every one is interested in the causes of Variation and the nature of " Heredity,'" a subject of extreme and peculiar difficulty. In the absence of special knowledge these things are discussed with enthusiasm. even by the public at large. But if we are to make way with this problem special know- ledge is the first need. We must know what special evidence each group of animals and plants can give, and this specialists alone can tell us. It is therefore impossible for one person to make any adequate gathering of the facts. If it is to be done it must be done by many. At one time I thought that a number of persons might perhaps be induced thus to combine ; but though I hope hereafter some such organized collection may be made, it is perhaps necessary that the first trial should be single-handed. X PREFACE. As I have thus been obliged to speak of many things of which I have no proper knowledge each section must inevitably seem meagre to those w 7 ho have made its subject their special study, and I fear that many mistakes must have been made. To any one who may be willing to help to set these errors right, I offer thanks in advance, " humbly acknowledging a work of such concern- ment unto truth did w T ell deserve the conjunction of many heads." In the course of the work I have had help from so many that I cannot here give separate thanks to each. For valuable criticisms, given especially in connexion with the introductory pages, I am indebted to Mr F. Darwin, Dr C. S. Sherrington, Dr D. MacAlister, Mr W. Heape, Mr G. F. Stout, Dr A. A. Kanthack and particularly to Mr J. J. Lister. I have to thank the authorities of the British Museum, of the Museum of the Royal College of Surgeons, of the Musee d'Histoire Naturelle in Paris, and of the Museums of Leyden, Oxford, Rouen, New T castle-upon-Tyne, of the Ecole Veterinaire at Alfort, and of the Dental Hospital for the great kindness that they have shewn me in granting facilities for the study of their collections. In particular I must thank Mr Oldfield Thomas of the British Museum for much help and advice in con- nexion with the subject of Teeth. I am also greatly obliged to Messrs Godman and Salvin for opportunities of examining and drawing specimens in their collections. To many others who have been good enough to lend specimens or to advise in particular cases my obligations are acknowledged in the text, but I must especially express my gratitude to Dr Kraatz of Berlin, to Dr L. von Heyden of Frankfurt, and to M. H. Gadeau de Kerville of Rouen for the large numbers of valuable insects wuth which they entrusted me. My best thanks are due to Dr A. M. Norman for many useful suggestions, for the loan of specimens and for the kindly interest he has taken in my work. My friend Mr H. H. Brindley has very kindly given me much assistance in determining and verifying several points that have arisen, and I am particularly indebted to him for permission to give an account of his very interesting and as yet unpublished observations on the variation and regeneration of the tarsus in Cockroaches. Through the help of Dr David Sharp I have been enabled to introduce much valuable evidence relating to Insects, a subject of PREFACE. XI which without his assistance I could scarcely have spoken. It is impossible for me adequately to express my obligation to Dr Sharp for his constant kindness, for the many suggestions he has given me, and for the generosity with which he has put his time and skill at my service. It is with especial pleasure that I take this opportunity of offering my thanks to Professor Alfred Newton for the encourage- ment and sympathy he has given me now for many years. As many of the subjects treated involve matters of interpret- ation it should be explicitly declared that though help has been given by so many, no responsibility for opinions attaches to anyone but myself unless the contrary is stated. The blocks for Figs. 18, 19, 25, 13:3, 161 and 185 (from Proc Zool. Soc.) were very kindly given by the Zoological Society of London; that for Fig. 28 (from Trans. Path. Soc.) by the Pathological Society; and for Fig. 140 which is from the Descent of Man I am obliged to the kindness of Mr F. Darwin. Figs. 5 B, 5 c, and 77 were supplied by the proprietors of Newman's British Butterflies, and Figs. 5 A, 82 and 84 by the proprietors of the Entomologist. The sources of other figures are acknowledged under each. Those not thus acknowledged have been made from specimens or from my own drawings or models by Mr M. P. Parker, with the exception of a few specially drawn for me by Mr Edwin Wilson. The work was, as I have said, begun in the earnest hope that some may be led thereby to follow the serious study of Variation, and so make sure a base for the attack on the problems of Evolution. Those who reject the particular inferences, positive and negative, here drawn from that study, must not in haste reject the method, for that is right beyond all question. That the first result of the study is to bring confusion and vagueness into places where we had believed order established may to some be disappointing, but it is best we deceive ourselves no longer. That the problems of Natural History are not easy but very hard is a platitude in everybody's mouth. Yet in those days there are many who do not fear to speak of these things with certainty, with an ease and an assurance that in far simpler problems of chemistry or of physics would not be endured. For men of this stamp to solve difficulties may be easy, but to feel Xll PREFACE. difficulties is hard. Though the problem is all unsolved and the old questions stand unanswered, there are those who have taken on themselves the responsibility of giving to the ignorant, as a gospel, in the name of Science, the rough guesses of yesterday that tomorrow should forget. Truly they have put a sword in the hand of a child. If the Study of Variation can serve no other end it may make us remember that we are still at the beginning, that the com- plexity of the problem of Specific Difference is hardly less now than it was when Darwin first shewed that Natural History is a problem and no vain riddle. On the first page I have set in all reverence the most solemn enuntiation of that problem that our language knows. The priest and the poet have tried to solve it, each in his turn, and have failed. If the naturalist is to succeed he must go very slowly, making good each step. He must be content to work with the simplest cases, getting from them such truths as he can, learning to value partial truth though he cheat no one into mistaking it for absolute or universal truth; remembering the greatness of his calling, and taking heed that after him will come Time, that "author of authors," whose inseparable property it is ever more and more to discover the truth, who will not be deprived of his due. St John's College, Cambridge. 29 December, 1893. CONTENTS. INTRODUCTION. SECT. 1. The Study of Variation 2. Alternative Methods ..... 3. Continuity or Discontinuity of Variation 4. Symmetry and Meristic Eepetition 5. Meristic Variation and Substantive Variation 6. Meristic Repetition and Homology 7. Meristic Repetition and Division . 8. Discontinuity in Substantive Variation : Size 9. Discontinuity in Substantive Variation : Colour and Colour-Patterns 10. Discontinuity in Substantive Variation : Miscellaneous Examples 11. Discontinuity in Meristic Variation: Examples .... 12. Parallel between Discontinuity of Sex and Discontinuity in Variation 13. Suggestions as to the nature of Discontinuity in Variation . 11. Some current conceptions of Biology in view of the Facts of Variation 1. Heredity. 2. Reversion. 3. Causes of Variation. 4. The Variability of "useless" Structures. 5. Adaptation. G. Natural Selection. PAGE 1 6 13 17 22 28 33 36 42 r,i GO 66 68 75 PART I. MERISTIC VARIATION Linear Series ..... Radial Series ..... Bilateral Series ..... Secondary Symmetry and Duplicity . CHAPTER I. Arrangement of Evidence CHAPTER II. Segments of Arthhopoda 87—422 jj;5_447 448—473 171— 56G 83 91 XIV CHAPTER CHAPTER CHAPTER CHAPTER III. IV. V. VI. CHAPTER VII CONTENTS. Vertebra and Ribs Spinal Nerves Variation in Arthropoda Cpletopoda, Hirudinea and Cestoda Branchial openings of Chordata and struc- tures IN CONNEXION WITH THEM . 1. Ascidians. 2. Cyclostomi. 3. Cervical Fistula? and Super- numerary Auricles in Mammals CHAPTER VIII. Mammjs CHAPTER IX. Teeth Preliminary. Primates. Canidae. Felidas. Viverridas. Muste lidae. Pinnipedia. Marsupialia. Selacbii. Radulse of Buccinum CHAPTER X. Teeth— Recapitulation CHAPTER XI. Miscellaneous Examples .... Scales. Kidneys; Renal Arteries; Ureters. Tentacles and Eyes of Mollusca. Eyes of Insects. Wings of Insects. Horns of Sheep, Goats and Deer. Perforations of shell of Haliotis. CHAPTER XII. Colour-Markings Ocellar Markings. Simultaneity of Colour-Variation in Parts repeated in Linear Series (Larvae of Lepidoptera : Chitonidae) CHAPTER XIII. Minor Symmetries: Digits . Cat. Pp. 313—324. Man and Apes. Pp. 324—360. Increase in number of digits, p. 324. Cases of Polydactylism associated ivith change of Symmetry. A. Digits in one Successive Series, p. 326. B. Digits in two homologous groups forming "Double-hands," p. 331. Complex cases, p. 338. Polydactylism not associated ivith change of Symmetry, p. 344. (1) A. Single extra digit external to minimus, p. 345. (1) B. Single extra digit in other positions, p. 349. (2) Duplication of single digits, p. 349. (3) Combinations of the foregoing, p. 352. (4) Irregular examples, p. 353. Reduction in number of phalanges, p. 355. Syndactylism, p. 356. Absence of digits and representation of two digits by one, p. 358. Horse, pp. 360 — 373. Extra digits on separate metacarpal or meta- tarsal, p. 361. More than one digit borne by metacarpal III., p. 369. Intermediate cases, p. 371. Artiodactyla, pp. 373—390. Polydactylism in Pecora, p. 373. Poly- dactylism in Pig, p. 381. Syndactylism in Artiodactyla, p. 383. Birds, pp. 390—395. Possibly Continuous numerical Variation in digits : miscellaneous examples, pp. 395 — 398 (Chalcides. Cistudo. Rissa. Erinaceus. Elephas.) Inheritance of Digital Variation. Association of Digital Variation with other forms of Abnormality. PAGE 102 129 146 156 171 181 195 265 274 288 311 CONTEXTS. XV CHAPTER XIV. Digits: Recapitulation CHAPTER XV. Minor Symmetries: Segments in Appendages CHAPTER XVI. Radial Series Coelenterata. Pedicellariae of Echinoderms. Cell-Division. CHAPTER XVII. Radial Series: Echinodermata CHAPTER XVIII. Bilateral Series CHAPTER XIX. Further Illustrations of the Relationship between Right and Left Sides CHAPTER XX. Supernumerary Appendages in Secondary Symmetry Introductory. — The Evidence as to Insects. CHAPTER XXI. The Evidence CHAPTER XXII. CHAPTER XXIII. CHAPTER XXIV. CHAPTER XXV. Appendages in Secondary Symmetry . as to Crustacea. Duplicity of Appendages in Arthropoda . Secondary Symmetry in Vertebrates. Re- marks on the Significance of Repetition in Secondary Symmetry : Units of Repe- tition Double Monsters Concluding Reflexions PAGE 400 410 423 432 448 4G3 474 525 539 553 559 567 INDEX OF SUBJECTS, p. 576. INDEX OF PERSONS, p. 593. CORRIGENDA. p. 23, line 5. For " and that in " read " and in." p. 27, line 29. For " appear" read " appears." p. 37, line 18. For " their " read " the." p. 54. Note 2. For "xxviii" read "xx." p. 55. Parra is now known not to have affinities with the Eallidae. p. 141. In description of Fig. 15 insert "After Solgee." p. 151, line 2 and p. 153, Note. For "W. B." read "G. B." p. 198. For " Pinnipediae" read "Pinnipedia." For "Dent." read "Deuf." p. 212. In description of Fig. 40 delete " p l of the left side is in symmetry with two teeth on tbe right side." The figure is correct. p. 281, 15th line from bottom. Delete " and perhaps all." p. 382. For "W. H. Benham" read "W. B. Benham." p. 429. For " Banyul's " read " Banyuls." p. 473, 4th and 6th lines from bottom. For " Tornaria" read " Balanoglossus" p. 526. Delete the heading " (1) Clear cases of Extra Parts in Secondary Symmetry." Note to p. 461, Note 718. As to union of eyes in Bees, see further, Ditteich, Zeit. f. Ent., Breslau, 1891, xvi. p. 21, and Cook, A. J., Proc. Amer. Ass., 1891, p. 327. Note to p. 468, Note 2. In connexion with Giard's observation the following fact should be given. Since this Chapter was printed I have had an opportunity of examining a sample of Flounders taken in the shallow water off Bournemouth. Of 23 specimens seen alive, all but about half a dozen were more or less blotched with shades of brown on the " blind " side. In five the brown was more extensive than the white. The eyes and dorsal fins were normal. The fishmonger who shewed them to me said that the Flounders in that place were generally thus blotched, and that those seen were a fair sample. In estimating the significance of Cunningham's experiment (p. 467) this fact should be remembered. INTRODUCTION. All flesh is not the same flesh : but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of bird?. SECTION I. The Study of Variation. To solve the problem of the forms of living things is the aim with which the naturalist of to-day comes to his work. How have living things become what they are, and what are the laws which govern their forms ? These are the questions which the naturalist has set himself to answer. It is more than thirty years since the Origin of Species was written, but for many these questions are in no sense answered yet. In owning that it is so, we shall not honour Darwin's memory the less ; for whatever may be the part which shall be finally assigned to Natural Selection, it will always be remem- bered that it was through Darwin's work that men saw for the first time that the problem is one which man may reasonably hope to solve. If Darwin did not solve the problem himself, he first gave us the hope of a solution, perhaps a greater thing. How great a feat this was, we who have heard it all from child- hood can scarcely know. In the present work an attempt is made to find a way of attacking parts of the problem afresh, and it will be profitable first to state formally the conditions of the problem and to examine the methods by which the solution has been attempted before. This consideration shall be as brief as it can be made. The forms of living things have many characters: to solve the problem completely account must be taken of all. Perhaps no character of form is common to all living things; on the contrary their forms are almost infinitely diverse. Now in those attempts to solve the problem which have been the best, it is this diversity of form which is taken as the chief attribute, and the attempt to solve the general problem is begun by trying to trace the modes by which the diversity has been produced. In the shape in which it has been most studied, the problem is thus the Fftor * AFY l B. ii n n i\\\\ooo 2 THE PROBLEM OF SPECIES. [ixtrod. problem of Species. Obscurity has been brought into the treat- ment of the question through want of recognition of the fact that this is really only a part of the general problem, which would still remain if there were only one species. Nevertheless the problem of Species is so tangible a part of the whole that it is perhaps the best point of departure. For our present purpose we cannot begin better than by stating it concisely. The forms of living things are diverse. They may neverthe- less be separated into Specific Groups or Species, the members of each such group being nearly alike, while they are less like the members of any other Specific Group. [The Specific Groups may by their degrees of resemblance be arranged in Generic Groups and so on.] The individuals of each Specific Group, though alike, are not identical in form, but exhibit differences, and in these differences they may even more or less nearly approach the form characteristic of another Specific Group. It is true, besides, that in the case of many Specific Groups which have been separated from each other, intermediate forms are found which form a continuous series of gradations, passing insensibly from the form characteristic of one Species to that characteristic of another. In such cases the distinction between the two groups for purposes of classification is not retained. The fact that in certain cases there are forms transitional between groups which are sufficiently different to have been thought to be distinct, is a very important fact which must not be lost sight of; but though now a good many such cases are known, it remains none the less true that at a given point of time, the forms of living things may be arranged in Specific Groups, and that between the immense majority of these there are no transitional forms. There are therefore between these Specific Groups differences which are Specific. No definition of a Specific Difference has been found, perhaps because these Differences are indefinite and hence not capable of definition. But the forms of living things, taken at a given moment, do nevertheless most certainly form a discontinuous series and not a continuous series. This is true of the world as we see it now, and there is no good reason for thinking that it has ever been otherwise. So much is being said of the mutability of species that this, which is the central fact of Natural History, is almost lost sight of, but if ever the problem is to be solved this fact must be boldly faced. There is nothing to be gained by shirking or trying to forget it. The existence, then, of Specific Differences is one of the characteristics of the forms of living things. This is no merely subjective conception, but an objective, tangible fact. This is the first part of the problem. sect. I.] INTRODUCTION. 3 In the next place, not only do Specific forms exist in Nature, but they exist in such a way as to fit the place in Nature in which they are placed; that is to say, the Specific form which an organism has, is adapted to the position which it fills. This again is a relative truth, for the adaptation is not absolute. These two facts constitute the problem : I. The forms of living things are various and, on the whole, are Discontinuous or Specific. II. The Specific forms, on the whole, fit the places they have to live in. How have these Discontinuous forms been brought into exist- ence, and how is it they are thus adapted ? This is the question the naturalist is to answer. To answer it completely he must find (1) The modes and (2) The causes by which these things have come to pass. Before considering the ways in which naturalists have tried to answer these questions, it is necessary to look at some other phenomena characteristic of Life. We have said that at a given moment, or point of time, the specific forms of living things com- pose a discontinuous series. The element of time thus intro- duced is of consequence, and leads to important considerations. For the condition of the organized world is not a fixed condition, but changes from moment to moment, and that which can be pre- dicated of its condition at one moment may not at any other point of time be true. This process of change is brought about partly by progressive changes in the bodies of the individuals themselves, hut chiefly by the constant succession of individuals, the parents dying, their offspring succeeding them. It is then a matter of observation that the offspring born of parents belonging to any one Specific Group do as a rule conform to that Specific Group themselves, and that the form of the bodv, the mechanisms and the instincts of the offspring, are on the whole similar to those which their parents had. But like most general assertions about living things this is true not absolutely but relatively only. For though on the whole the offspring is like the parent or parents, its form is perhaps never identical with theirs, but generally differs from it perceptibly and sometimes materially. To this pheno- menon, namely, the occurrence of differences between the structure, the instincts, or other elements which compose the mechanism of the offspring, and those which were proper to the parent, the name Variation has been given. We have seen above that the two leading facts respecting the forms of living things are first that they shew specific differen- tiation, and secondly that they are adapted. To these we may now add a third, that in the succession from parent to offspring there is, or may be, Variation. It is upon the fact of the exist- ence of this phenomenon of Variation that all inductive theories of Evolution have been based. 1—2 4 A POSTULATE. [introd. The suggestion which thus forms the common ground of these theories is this : — May not the Specific Differences between Species and Species have come about through and be compounded of the individual differences between parent and offspring ? May not Specific Differentiation have resulted from Individual Variation ? This suggestion has been spoken of as the Doctrine of Common Descent, for it asserts that there is between living things a community of descent. In what follows it will be assumed that this Doctrine of Descent is true. It should be admitted from the first that the truth of the doctrine has never been proved. There is never- theless a great balance of evidence in its favour, but it finds its support not so much in direct observation as in the difficulty of forming any alternative hypothesis. The Theory of Decent in- volves and asserts that all living things are genetically connected, and this principle is at least not contrary to observation ; while any alternative hypothesis involves the idea of Separate Creation which by common consent is now recognized as absurd. In favour of the Doctrine of Common Descent there is a balance of evidence: it is besides accepted by most naturalists ; lastly if it is not true we can get no further with the problem : but inasmuch as it is unproven, it is right that we should explicitly recognize that it is in part an assumption, and that we have adopted it as a pos- tulate. The Doctrine of Descent being assumed, two chief solutions of the problem have been offered, both starting alike from this common ground. Let us now briefly consider each of them. A. Lamarck's Solution. So many ambiguities and pitfalls are in the way of any who may try to re-state, in a few words, the theory propounded in the Philosoplvie Zoologique, that it is with great diffidence that the following account of it is given. Lamarck points out that living things can in some measure adapt themselves both structurally and physiologically to new circumstances, and that in certain cases the adaptability is present in a high degree. He suggests that by inheritance and perfection of such adaptations they may have become what they are, and that thus specific forms and mechanisms have been produced, as it were, by sheer force of circumstances. On this view it is assumed that to the demands made on it by the environment the organism makes an appropriate structural and physiological response ; in other words, that there is in living things a certain tension, by which they respond to environmental pressure and fit the place they are in, somewhat as a fluid fits a vessel. This is not, I think, a misrepresentation of Lamarck's theory. It amounts, in other words, to a proposal to regard organisms as machines which have the power of Adaptation as one of their fundamental and inherent qualities or attributes. sect, l] introduction. 5 Without discussing this solution, we may oote that it aims at being a complete solution of both (1) The existence and persistence of differing forms, {'!) The fact that the differing forms are adapted fco different conditions ; and (3) The causes of the Variation by which the diversity baa occurred. B. Darwin's Solution. Darwin, without suggesting causes of Variation, points out that since (1) Variations occur — which they are known to do — and since (2) some of the variations are in tin- direction of adaptation and others are not — which is a necessil v — it will result from the conditions of the Struggle for Existence that those better adapted will on the whole persist and the less adapted will on the whole be lost. In the result, therefore, there will be a diversity of forms, more or less adapted to the states in which they are placed, and this is very much the observed condition of living things. We may note that this solution does not aim at being a com- plete solution like Lamarck's, for as to the causes of Variation it makes no suggestion. The arguments by which these several solutions are supported, and the difficulties which are in the way of each, are so familiar that it would be unprofitable to detail them. On our present knowledge the matter is talked out. Those who are satisfied with either solution are likely to remain so. It may be remarked however that the observed cases < one who has ever tried to realize the complexity of the relations between an organism and its surroundings, the infinite variety of the consequences which every detail of structure and every shade of instinct may entail upon the organism, the precision of the correla- tion between function and the need for it, and above all the mar- vellous accuracy with which the- presence or absence of a power or a structure is often compensated among living beings — no one can reflect upon these things and be hopeful that our quantitative estimates of utility are likely to be correct. But in the absence of such correct and final estimates of utility, we must never use the utility of a structure as a point of departure in considering the manner of its origin ; for though we can see that it is, or may be, useful, yet a little reflexion will shew that it is, or may be, harmful, but whether on the whole it is useful or on the whole harmful, sect, in.] INTRODUCTION. 1 3 can only be guessed at. It thus happens that we can only gel an indefinite knowledge of Adaptation, which for the purposes of our problem is not an advance beyond the original knowledge that organisms are all more or less adapted to their circumstanc< -. No amount ot" evidence of the same kind will can-)' us beyond this point. Hence, though the Study of Adaptation will alwaysremain a fascinating branch of Natural History, it is not and cannot be a means of directly solving the problem of the origin of Species. SECTION III. Continuity oh Discontinuity of Variation. What is needed, then, is evidence of a new kind, for do amount of evidence of the kinds that have been mentioned will take us much beyond our present position. We need more know- ledge, not so much of the facts of anatomy or development, as of the principles of Evolution. The question to be considered is how such knowledge may be obtained. It is submitted that the Study of Variation gives us a chance, and perhaps the only one, of arriving at this knowledge. But though, as all will admit, a knowledge of Variation lies at the root of all biological progress, no organized attempt to obtain it has been made. The reason for this is not very clear, but it apparently proceeds chiefly from the belief that the subject is ton difficult and complex to be a profitable field for study. However this maybe, the fact remains, that since the first brief treatment of the matter in Animals and Plants under Domestication do serious effort to perceive or formulate principles of Variation has been made, and there is before us nothing but the most meagre ami superficial account of a few of its phenomena. Darwin's firsl collection of the facts of Variation has scarcely been increased. These same facts have been arranged and rearranged by each successive interpreter: the most various and contradictory pro- positions have been established upon them, and they have been strained to shew all that it can possibly he hoped that they will shew. Any one who cares to glance at the works ot' those who have followed Darwin in these fields mav assure himself ot' this. So far, indeed, are the interpreters of Evolution from adding to this store of facts, that in their hands the original -t<> take on the new characters as for one. If the manner of development of Repeated Parts is considered, this fact will not seem surprising. For all these parts arise from the undifferentiated tissues by a process of Division, and what- ever characters were potentially present in the undifferentiated tissues may appear in the parts into which it subsequently divides. A somewhat loose illustration will perhaps make this more clear. Everyone knows the rows of figures which children cut out from folded paper. There are as many figures as folds, each figure being alike if the folds coincide. If the paper is pink, all the figures are pink ; if the paper is white, all the figures are white, and so on. If blotting-paper is used, and one blot is dropped on the folded edges, the blot appears symmetrically in all the figures. So also any deviation in the lines of cutting appear in all the figures ; a whole row of soldiers in bearskins may be put into helmets by one stroke of the scissors. Of course it is not meant to suggest that the process of division by which parts of the body are pro- duced bears any resemblance to that by which the figures are cul out, but merely to illustrate the fact that since it is by a proc- ss of Division of an undifferentiated mass that the Repeated Parts are produced, so the characters of these Repeated Parts depend upon the characters which were present in the original mass and upon the modes by which the parts were divided out from it. Summary of Sections I to I r At this point it will be well briefly to recapitulate the pre- ceding Sections. We are proposing to attack the problem of Species by studying the facts of Variation. Of the facts of Variation in general we have selected a particular group upon which to begin this study. The group of variations thus chosen are those which relate to Number of parts, Division, Repetition, and the other phenomena which are 28 METAMERIC SEGMENTATION. [introd. to be included under the term Meristic. With variations in quality and Substance it is not at present proposed to deal, except in so far as it is necessary to refer to them in their relation to the phenomena of Merism, and in illustration of the structural possi- bilities or necessities which in the body follow as corollaries upon the existence of Meristic Repetition. It has also been proposed to limit the consideration to Varia- tions which are Discontinuous. As has been already stated, Dis- continuous Variations may belong to the Meristic Group or to the Substantive, but it is to the former that attention will first be directed. SECTION VI. Meristic Repetition and Homology. In what has gone before, the two conceptions now introduced, namely the distinction of Variations into Meristic and Substan- tive, and into Continuous and Discontinuous, have been sketched in outline. The significance of the facts which follow will be made more evident if these two conceptions are now more fully developed in some of their aspects. Under the name Merism I have proposed to include all pheno- mena of Repetition and Division, whenever found and in whatever forms occurring, whether in the parts of a body or in the whole. The consequences of the admission of this proposition are con- siderable and should be fully realized ; for on recognition of the unity of these phenomena it is possible to group together a number of facts whose association will lead to simplification of some morphological conceptions, and to other results of utility. That the phenomena of Merism form a natural group is in some respects a familiar idea, but in its fullest expression it is as yet not generally received, still less have the consequences which it entails been properly appreciated. Every one who has gone even a little way into morphological inquiry has met some of the difficulties to which we shall now refer. It is with respect to the phenomena of Segmentation that these difficulties are most familiar, and it is in this connexion that they may be best discussed. Segmentation is a condition which reaches its highest development in Vertebrates, the Annelids, and the Arthropods, and it is in these groups that it has been most studied. In them it appears as a more or less coincident Repetition of elements belonging to most of the chief systems of organs along an axis corresponding to the long axis of the body. To segmentation of this kind the name ' Metameric ' has been given, and by many morphologists the attempt has been made, either tacitly or in words, to separate such Metameric Segmen- tation from other phenomena of Repetition elsewhere occurring. sect, vi.] INTRODUCTION. 29 It has thus been attempted to distinguish the Repetitions which occur along the long axis of the body from those occurring along the long axis of appendages, such as for example the joints of antennae or of digits, and some have even gone so far as to regard the Segmentation of the Vertebrate tail as a thing different in kind from that of the trunk itself. It would be apart from our present purpose to recur to these subjects, were it not that this suggestion of the existence of a difference in kind between Meta- meric Segmentation and other Repetitions has led to several notable errors in the interpretation of the facts of morphology and in the application of these facts to the solution of the problems of Descent. In order to lay a sound foundation for the study of Meristic Variation these errors must be cleared away, and to do this it is necessary to break down the artificial distinction between the phenomena of Metameric Segmentation and other cases of Repetition of Parts, so that the whole may be seen in their true relations to each other. When this is done, the mutual relations of the facts of Meristic Variation will also become more evident. The first difficulty which has been brought into morphology by the suggestion that Metameric Segmentation is a phenomenon distinct in kind, is one which has coloured nearly all reasoning from the facts of Morphology to problems of phylogeny. For the existence of Metameric Segmentation in any given form is thus taken to be one of its chief characters, and, as such, is allowed pre- dominant weight in considering the genetic relations of these forms. By the indiscriminate though logical extension of this principle the conclusion has been reached that Vertebrates are immediately connected with, or have arisen by Descent from Annelids, or from Crustacea and the like, for the Repetition in these forms is closely similar. Others again, being struck with the resemblance between the Repetition of Parts along the radial axes of Starfishes and those which occur along the long axes ot" Annelids have hazarded the conjecture that perhaps this resem- blance may indicate the actual phylogenetic history of these Repetitions. Though such speculations as these are little better than travesties of legitimate theory, some of them still command interest if not belief. 1 All alike are founded on the assumption that resemblances between the manner and degree in which Repe- tition occurs are unlikely to have arisen save by community oi Descent. A broader view of Meristic phenomena will shew that 1 These modern "Instances" recall many that once were famous but are now- forgotten. For example : Item non absurda est similitudo et conformitas ilia, ut homo sit tanquam planta inversa. Nam radix nervorum et facultatum animalium est caput; parte* autem seminales sunt infima, nan computatis < .rtremitatibus tihi- arum et brachiorum. At in planta, radix [qua irutar capitis est) regulariter infimo loco collacatur ; scmitia autem supremo. BACON, Nov. Org. Lib. II. 27. In «0fl computatis extremitatibus, amateurs of Instantije Confohmes may still find matter for warning. 30 HOMOLOGY. [istrod. this assumption is unfounded ; for so far are the expressions of it which are called Metamerism from standing alone, that it is almost impossible to look at any animal or vegetable form without meeting phenomena of Repetition which differ from Metamerism only in degree or in extent. Between these Repetitions and Metameric Repetitions it is impossible to draw any line, and the Meristic Variations of all will therefore be treated together. This error in the estimate of the value of Metamerism as a guide to phylogeny is one by which the evidence of Variation is only indirectly affected. The other errors now to be mentioned are of a much more serious nature, for they concern the general conception of the nature of Homology which is the basis of all morphological study. In introducing the method of the Study of Variation I have said that it can alone supply a solid foundation for inquiry into the manner by which one species arises from another. The facts of Variation must therefore be the test of phylogenetic possibility. Looking at organs instead of species, we shall now see that the facts of Variation must also be the test of the way in which organ arises from organ, and that thus Variation is the test of Homo- logy. For the statement that an organ of one form is homologous with an organ of another means that there is between the two some connexion of Descent, and that the one organ has been formed by modification of the other, or both by modification of a third. The precise way in which this connexion exists is not defined, and indeed has scarcely ever been considered, though such a consideration must sooner or later be attempted. We must for the present be content with the belief that in some un- defined way there is a relationship between ' homologous ' parts, and that this is what we mean when we affirm that they are homologous. We have however assumed that the transition from one form to another takes place by Variation. If therefore we can see the variations we shall see the precise mode by which the descent is effected, and this must be true of the parts or organs as it is true of the whole body. In like manner then as the Study of Variation may be hoped to shew the way by which one form passes into another, so also may it be hoped that it will shew how r the organs of one form take on the shape of the homologous organs of another. In the absence of the evidence of Variation reasoning as to Homology rests solely on conjecture, and assumptions have thus been made respecting the nature of Homology which have coloured the whole of morphological study. Of these, two demand attention now. I. As to Homology between the Members of one Series. We saw above (page 29) how the resemblance between Repetitions sect, vi.] INTRODUCTION. 31 occurring in divers forms has led to the belief that those forms had a common descent: in a somewhat similar way it has hap- pened that the resemblance between individual members of a series of Repeated Parts has led to the belief that they must originally have been alike, and that they have been formed by differentiation of members originally similar. Many who would hesitate thus to formulate such a belief nevertheless have taker part in inquiries which can succeed only on the hypothesis that this has been the history of such parts. Of this nature are the old attempts to divide the skull into vertebrae, recognizing the several parts of each ; the modern disquisitions on the segmenta- tion of the cranial nerves ; the attempts to homologize the several phalanges of the vertebrate pollex and hallux with the several phalanges of the other digits ; similar attempts to trace the precise equivalence of the elements of the carpus and tarsus, and many other quests of a like nature. In all these it is assumed that there is a precise equivalence to be found with enough searching, and that all the members of such series of Repetitions were originally alike. If the series of ancestors were before us it is expected that this would be seen to have been the case. In the light of the facts of Variation this assumption will be seen to be a wrong one, and these simple views of the Repetition and Differen- tiation of members in Series must be given up as inadequate and misleading, even though there be no other to substitute. II. As to the individuality of Members of Series. In seeking to homologize a series of parts in one form with a series of parts in another, cases often occur in which the whole series of the one is admittedly homologous with the whole series of the other. In such cases the question arises, can the principle of Homology be extended to the individual members of the two Series? If the two Series each contain the same number of members this question is a comparatively simple one, for it may be assumed that each member of the Series is the equivalent or Homologue of the member which in the other Series occupies the same ordinal position. If however the number of members differs in the tw<> Series, how is the equivalence to be apportioned ? This is a question again and again arising with regard to Meristic Series such as teeth, digits, phalanges, vertebrae, nerves, vessels, mammae, colour-markings, the parts of the flower, and indeed in almost every system whether of animals or plants. To decide this question there are still no general principles. But though we yel know nothing as to the steps by which Meristic Variation proceeds, there is nevertheless a received view by which the interpretation of the phenomena is attempted, and though in the case of each system of organs the application of the principle is different, yel the principle applied is essentially the same. Thus to compare the members of Series containing different members it is first assumed that the series consisted ancestrally of 32 INDIVIDUALITY OF MEMBERS OF SERIES, [introd. some maximum number, from which the formula characteristic of each descendant has been derived by successive diminution. Here, again, I do not doubt that many who employ this assumption would hesitate to make it in set terms, but nevertheless it is the logical basis of all such calculations. Now this hypothesis involves a definite conception of the mode in which Variation works, and it is most important that this should be realized clearly. For if it is true that each member of a Series has in every form an individual and proper history, it follows that if we had before us the whole line of ancestors from which the form has sprung, we should then be able to see the history of each member in the body of each of its progenitors. In such a Series the rise of an individual member and the decline of another should then be manifest. Each would have its individual history just as a Fellowship in a College or a Canonry in a Cathedral has an individual history, being handed on from one holder to his successor, some being suppressed and others founded, but none being merged into a common fund. In other words, according to the received view of the nature of these homologies, it is assumed that in Variation tlie individuality of each member of a Meristic Series is respected. The difficulty in applying this principle is notorious, but when the evidence of Variation is before us the cause of the difficulty will become evident. For it will be found that though Variation may sometimes respect individual homologies, yet this is by no means a universal rule; and as a matter of fact in all cases of Meristic Series, as to the Variation of which any considerable body of evidence has been collected, numerous instances of Varia- tion occur, in which what may be called the stereotyped or tra- ditional individuality of the members is superseded. This error in the application of the principle of Homology to individual members of Meristic Series has arisen almost entirely through want of recognition of the unity of Meristic Repetition, wherever found. In the case of a series of parts among which there is no perceptible Differentiation, no one would propose to look for individual Homologies. For example, no one consid* rs that the individual segments in the intestinal region of the Earth- worm have any fixed relations of this kind ; no one has proposed to homologize single leaves of one tree with single leaves on another ; it is not expected that the separate teeth of a Roach have definite homologies with separate teeth of a Dace, for such expectations would be plainly absurd. But in series whose mem- bers are differentiated from each other the existence of such in- dividuality is nevertheless assumed. To take only one case: a whole literature has been devoted to tin- attempt to determine some point in the vertebral column or in the spinal nerves from which the homologies of the segments may bo reckoned. This is a problem which in its several forms has been widely studied. Some sect, vi.] INTRODUCTION. 33 have attempted to solve it by starting from the lumbar plexus, while others have begun from the brachial. In the case of Birds this question is reduced to an absurdity. Which vertebra «>f a Pigeon, which has 15 cervical vertebrae, is homologous with the first dorsal of a Swan which has 26 cervicals ? To decide these questions the only possible appeal is to the facts of Variation, and judged by these facts the whole inquiry comes to an end, for it is seen at once that the expectation is founded on a wrong con- ception of the workings of Variation. No one, as has been said above, would attempt such an inquiry if the series were un- differentiated, for this individuality would not be expected in such a Series ; but to suppose that it does exist in a differentiated Series of parts, is to suppose that with Differentiation the ordinal individuality of the members has become fixed beyond revision. This supposition the Study of Variation will dispel. Here, as in the preceding case of the theoretical doctrine of Serial Homology, the current view is far too simple and far too human. Though the methods of Nature are simple too, yet their simplicity is rarely ours. In these subjective conceptions of Homology and of Variation, we have allowed ourselves to judge too much by human criterions of difficulty, and we have let our- selves fancy that Nature has produced the forms of Life from each other in the ways which we would have used, if we had been asked to do it. If a man were asked to make a wax model of the skeleton of one animal from a wax model of the skeleton of another, he would perhaps set about it by making small additions to and subtractions from its several parts; but the natural process differs in one great essential from this. For in Nature the body of one individual has never been the body of its parent, and is no1 formed by a plastic operation from it; but the new body is made again new from the beginning, just as if the wax model had gone back into the melting-pot before the new model was begun. SECTION VII. Meristic Repetition and Division. Before ending this preliminary consideration of ftferism it is right that we should see other aspects of the matter. What fol- lows is put forward in no sense as theory or doctrine but simply as suggesting a line of thought which should be in the minds of any who may care to pursue the subject further or to study the evidence. It is perhaps only when it is seen in connexion with its possible developments that the magnitude of the subject can be fully felt. b. 3 34 ASEXUAL REPRODUCTION. [introd. Iii the treatises on Comparative Anatomy which belong especi- ally to the beginning of this century, the idea constantly recurs that the series of segments of a metamerically segmented form do in some sort represent a series of individuals which have not detached themselves from each other. Seen in the light of the Doctrine of Descent this resemblance or analogy has been taken as a pos- sible indication that the segmented forms may actually have had some such phylogenetic history as this. By similar reasoning the Metazoa have been spoken of as " Colonies " of Protozoa. Now though we need not allow ourselves to be drawn away into these and other barren speculations as to phylogeny, we may still note the substance of fact which underlies them. For it is now recognized that between the process by which the body of a Kais is metamerically segmented, and that by which it divides into a chain of future " individuals," no line can be drawn : that the process of budding, or of stabilization, by which one form gives rise to a number of detached individuals, is often indistinguishable from the process by which a near ally gives rise to a connected colony, and that the two processes may even be interchangeable in the same form; finally that the process of division of a fertilized ovum by the first cleavage plane may be in some essentials com- parable with the division of a Protozoon into two new individuals. All these are now commonplaces of Natural History. With what justice these considerations may have been applied to the problems of phylogeny we need not now inquire, but to the interpretation of the facts of Variation they have an application which ought not to be neglected. If, then, as is admitted, there is a true analogy between the process by which new organisms may arise asexually by Division, and the process by which ordinary Meristic Series are produced, it follows that Variation, in the sense of difference between offspring and parent, should find an analogy in Differentiation between the members of a Meristic Series. Applied to the case of asexual re- production there seems no good reason for denying this analogy. It is of course an undoubted fact that in the asexual reproduction of many forms Variation is rare, though the sexually produced offspring of the same forms are very variable. In plants this is familiar to everyone, though the extension of the same principle to animals rests chiefly on inference. Nevertheless in plants bud- variation, both Meristic and Substantive, happens often, and the division of a plant into two dissimilar branches may well be coin- pared to the production of dissimilar offspring by one parent : in- deed, if the processes of Division are admitted to be fundamentally the same, this conclusion can scarcely be escaped. In one more aspect this subject may be considered with profit. It is, as we have seen, believed that the division of an ovum into two segmentation-spheres is not a process essentially different SECT, vii.] INTRODUCTION. 35 from the division of certain Protozoa into two " individuals." In conceiving the manner of Variation in such Protozoa we have little or no fact to guide us, but this much is obvious : that for the introduction of a variety as the offspring of a given species, ii La necessary either that the two parts into which the unicellular organism divided should have varied equally, and that the division should thus be a symmetrical division (in the full sense of qualitative as well as formal symmetry); or that the division should be asymmetrical, the resulting parts being dissimilar, in which case one may conceivably belong to the type and the other be a Variety. If Variation has ever occurred in the reproduction of animals of this class it must have occurred on one or both of these plans. Returning to the segmentation of the Metazoan ovum we have the well-known results of Roux and others, shewing that, in certain species, the first 1 cleavage-plane divides the body into the future right and left halves. In such cases then on the analogy of the Protozoon, the right and left halves of the body are in a sense comparable with the two young Protozoa, and though each half is hemi-symmetrical, it is in this way the equivalent of a separate organism. This suggestion, which is an old one. receives support from many facts of Meristic Variation, especially from the mode of formation of homologous Twins and "double Monsters which are now shewn almost beyond doubt, to arise from the division of one ovum 2 . But besides the evidence that each half of the body may on occasion develop into a whole, evidence will be given that one half may vary in its entirety, independently of the other half. Such Variation may be one of sex. taking the form of Gynandromorphy, so well-known among Lepidoptera, in which the secondary sexual characters of one side are male, those of the other being female; or it may happen that the difference between the two sides is one of size, the limbs and organs of one side being smaller than those of the other; or lastly the Variation between the two sides may be one that has been held characteristic of type and variety or even of so-called species and species 3 . These matters have been alluded to here as things which a student of the facts of Variation will do well to bear in mind. I' is difficult to see the facts thus grouped without feeling the 1 Often it is the second cleavage-plane (if any) which corresponds with the future middle line. - The well-known evidence relating to this subject will be spoken of later. The view given above, which is now very generally received, finds BUpporl in the striking observations of Diuesch, lately published (Zt. f. w. ZooL, L891, Lin. p. 160). Working with eggs of Echinus, Driesch found that if the first two segmentation- spheres were artificially separated, each grew into :i Beparate Pluteut; if tin- separation was incomplete, the result was a double-monster, united by homologous surfaces. Similar experiments attended by similar results have since been made on Ampkioxus by E. B. Wilson, Anat. An:., vn. 1892, p. 732. :} Evidence of such abrupt Variation between the two sides of the body belongs for the most part to the Substantive group. 3—2 36 SUBSTANTIVE VARIATION : EXAMPLES. [introd. possibility that the resemblance between the two sides of a bilaterally symmetrical body may be in some essentials the same as the resemblance between offspring of the same parent, or to use an inclusive expression, that the resemblance between the members of a Meristic Series may be essentially the same as the resemblance and relationship between the members of one family ; that the members of a row of teeth in the jaw, of a row of peas in a pod, of a chain of Salps, or even a litter of pigs, all resulting alike from the processes of Division, may stand to each other in relationships which though different in degree may be the same in kind. If reason shall appear hereafter for holding any such view as this, the result to the Study of Biology will be profound. For if it shall ever be possible to solve the problem of Symmetry, which may well be a mechanical one, we shall thus have laid a sure foundation from which to attack the higher problem of Variation, and the road through the mystery of Species may thus be found in the facts of Symmetry. SECTION VIII. Discontinuity in Substantive Variation: Size. From the subject of Merism and the thoughts which it suggests, we now r pass to another matter. The first limitation by which we proposed to group Variations was found in the characters which they affect : the second relates to the magnitude, or as I shall call it, the Continuity of the variations themselves. And though for many a conception has no value till it be cast in some finite mould, my aim will be rather to describe than to define the meaning of the term Continuity as applied to Variation. In dealing w r ith a subject of this obscurity, where the outlines are doubtful, an exact mapping of the facts cannot be made and ought not to be attempted; but I trust that from the present indications, vague though they are, some larger and more definite conception of Discontinuity in Variation may shape itself hereafter by a process of natural growth. For this reason I shall as far as possible avail myself of examples rather than of general expres- sions, whether inclusive or exclusive. To those who have studied the recent works of Galton, the conceptions here outlined will be familiar. In the chapter on " Organic Stability " in Natural Inheritance, the matter has been set forth with charming lucidity, and what follows will serve chiefly to illustrate the manner in which the facts of Natural History correspond with the suggestions there made. In the ease of most species it is a matter of common knowledge sect, viii.] INTRODUCTION. 37 that though no two individuals are identical, there are many which in the aggregate of their characters nearly approach each other, constituting thus a normal, from which comparatively few differ widely. In such a species the magnitude of these differences is proportional to the rarity of their occurrence. Now this, which is a matter of common experience, has been shewn by Galton to be actually true of several quantities which in the case of Man are capable of arithmetical estimation. In the cases referred to it has thus been established that these quantities when marshalled in order give rise to a curve which is a normal curve of Frequency of Error. Taking for instance the case of stature, Galton's statistics shew that for a given community there is a mean stature, and the distribution of the statures of that community around the mean gives rise to a Curve of Error. In this case the individuals of that community in respect of stature form one group. Now in the case of a collection of individuals which can be separated into two species, there is some character in respect of which, when arranged by their statistical method, the individuals do not make one group but two groups, and the distribution of each group in respect of that character cannot be arranged in one Curve of Error, though it may give rise to two such curves, each having its respective mean. For example, if in a community tall individuals were common and short individuals were common, but persons of medium height were rare, the measurements of the Stature of such a community when arranged in the graphic method would not form one Curve of Error, though they might and probably would form two. There would thus be a normal for the tall breed, and a normal for the short breed. Such a community would, in respect of Stature, be what is called dimorphic. The other case, in which the whole community, grouped according to the degrees in which they display a given character, forms one Curve of Error, may conveniently be called monomorphic in respect of that character. By considering the possible ways in which such a condition of dimorphism may arise in a monomorphic community, one of the uses of the term Discontinuity as applied to Variation will be made clear. Considering therefore some one character alone, in a specie which is monomorphic in respect to that character, individuals possessing it in its mean form are common while the extremes are rare; while if the species is dimorphic the extremes are common and the mean is rare. Now the change from the mono- morphic condition to the dimorphic may have been effected with various degrees of rapidity: for the frequency of the occurrence of the mean form may have gradually diminished, while that <>f the extremes gradually increased, through the agency of Natural Selection or otherwise, in a long series of generations; or on the other hand the diminution in the relative numbers of the mean individuals may have been rapid and have been brought about in 38 HORNS OF BEETLES. [iNTROD. a few generations by a few large and decisive changes, whether of environment or of organism. Referring to the curve of Distribution formed in the graphic method of displaying the statistics, during the monomorphic period the curve has one apex corresponding with the greatest frequency of one normal form, but in the dimorphic period the curve has two apices, corresponding with the comparative frequency of the two extremes, and the comparative rarity of the mean form. The terms Continuous or Discontinuous are applicable to the process of transition from the monomorphic to the dimorphic state according as the steps by which this change was effected are small or large. The further meanings of Discontinuous Variation will be explained by the help of examples. The first cases refer to Sub- stantive Variation 1 , and we may conveniently begin by examining a case of Variation in a character which is easily measured arith- metically. Among beetles belonging to the Lamellicorn family there are numerous genera in which the males may have long horns arising from various parts of the head and thorax 2 . These horns may be n in Fig. 1. Side-views of the Lamellicorn beetle, Xylotrupe* gideon. Legs not represented. I, High male, II, Medium male, III, Low male. 1 In referring thus to evidence as to Substantive Variation, I find myself in tin- difficulty mentioned in the Preface. For it is necessary to allude to matters which cannot be properly treated in this first instalment of facts. In order, however, that the one introductory account may serve for all the evidence together, such allusion is inevitable and I can only trust that full evidence as to Substantive Variation may be produced before long. 2 For particulars of this subject with illustrations, see Descnit of Man, 1st ed.. vol. i. pp. 309 — 372. A detailed account of this and the succeeding example in the case of the Earwig was given by Mr Brindley and myself in P. Z. N.. 1893. SECT. VIII.] INTRODUCTION. 39 of very great size, as in the well-known Hercules beetle ( Dynastes here ales) and others. The females of these forms are usually without horns. In such genera it is commonly found that the males are not all alike, but some are of about the size of the females and have little or no development of horns, while others are more than twice the size of the females and have enormous horns. These two forms of male are called " low ' and " high ' males respectively. In many places in the Tropics such beetles abound, both " high ' : and "low" males occurring in the same locality. An admirable example of this phenomenon is seen in Xylotrujpes gideon, of which a " high," " low," and medium male are shewn in profile in Fig. 1. Of this insect a very large number were kindly given to me by Baron Anatole von Hiigel, who collected them at one time, in one locality, in Java. In this species there is one cephalic and one thoracic horn, placed in the positions shewn in the figure. Fig. 1, I shews a "high' male, II is a medium, and in a "low' : male. In the gathering received there were 342 males. My friend, Mr H. H. Brindley, has made careful measurements of the lengths of the horns of these specimens and has constructed the diagram, Fig. 2. In this each dot represents an individual, and the abscissae shew the measurements of the length of the cephalic horn. For clearness these measurements are represented as of twice the natural size. So far as the numbers go the result shews that the most frequent forms are Fig. 2. Diagram representing the frequency of the lengths of cephalic horn in male Xylotrupea gideon. M, the mean case ; M' the mean value. The abscissas give lengths of cephalic horn in lines. 40 FORCEPS OF EARWIGS. [introd. the moderately low and the moderately high, the forms of mean measurement being comparatively scarce. It is true that the numbers are few, but so little heed is paid to phenomena of this kind that material is difficult to obtain and the present oppor- tunity was indeed wholly exceptional 1 . But taking the evidence for what it is worth, the comparative scarcity of " medium " males in that particular sample is clear, and so far the form is dimorphic, and has two male normals. Now such a condition may have arisen in several ways. First, in the past history of the species there may have been a time when the males were horned and were monomorphic, the " medium" form being the most frequent, and the present dimorphic condition may have been derived from this, either continuously or discon- tinuously as described above for the case of Stature. Secondly, the dimorphism may date from the first acquisition of the horns, and this character may perhaps have always been distributed in the dimorphic way. In this case the term Discontinuous would be applicable to the Variation by which the groups of "high" and "low' males have been severally produced. I am not acquainted with evidence as to the course of inheritance in these cases, and I do not know therefore whether both " high" and " low" males may be produced by one mother. If this should be shewn to be the case, it would suggest that the separation of the males into two groups was a case of characters which do not readily blend, and are thus exempt from what Galton has called the Law of Regression 2 . In the case of a somewhat similar structure found in the Common Earwig (Forjicula auricularia) the dimorphism is still more definite. In the autumn of 1892 on a visit to the Fame Islands, a basaltic group off the coast of Northumberland, it was found that these islands teem with vast quantities of earwigs. The abundance of earwigs was extraordinary. They lay in almost continuous sheets under every stone and tussock, both among the sea-birds' nests 1 * and by the light-keepers' cottages. Among them Fig. 3. I, High were males of the two kinds shewn in Fig. 3 ; the male, II, Low male one or high male having forceps of unusual length, of Common Earwig th Qther Qr j j b - the common f orm . {horticula auricu- x . . . . ' . ° . , P laria) from the It appears that the high male is known trom many Fame Islands. places in England and elsewhere and that it was made into a distinct species, F. forcipata, by 1 In the Lucanidffi, of which the Stagbeetle (L. cervus) is an example, a similar phenomenon occurs, the "high" and "low" males being distinguished by the degree of development of the mandibles. No suihcient number of male Stagbeetles has yet been received to warrant any statement as to the frequency of the various types of males. 2 Natural Inheritance, pp. 88 — 110. SECT. VIII.] INTRODUCTION. 41 Stevens 1 though by later authorities* 2 the species has not been retained. A large sample of Earwigs collected in a Cambridge garden contained 163 males of which 5 would come into the high class, but the great abundance of high males at the Fames seems to be quite exceptional. With a view to a statistical determination of the frequency of the high and low forms 1000 of these Earwigs were collected 1»\ Miss A. Bateson, the whole being taken at random on one day from three very small islands joined to each other at low tide. Of the 1000 specimens 583 proved to be mature males with elytra fully developed, no specimen with imperfect elytra being included in this number 3 . On measuring the length of the forceps to the nearest half mm. and grouping the results in the graphic method the curve shewn in Fig. 4 was produced. The figures on the Fig. 4. Curve shewing frequency of various lengths of forceps of male Earwigs {F. auricularia) from the Fame Islands. Ordinate*, numbers of individuals \ abseissie, lengths of forceps in mm. ordinates here shew the numbers oi individuals, those on the abscissae giving the length of the forceps in millimetres. As there 1 Stevens, Brit. Ent. 1835, vi. p. 6, PI. xxvm. fig. 4. 2 Fischer, Orthop. Euro})., 1853, p. 74; Bkunnek von Wattinwyj, Prodr. d. europ. Orthop., 1882, p. 12. 1 For particulars in evidence of the maturity of these specimens see /'. '/.. Sf., 1893. 42 COLOUR. [iNTROD. shewn the smallest length of forceps was 25 mm., and the greatest 9 mm., the greatest frequency being grouped about 3*5 mm. and 7 mm. respectively. The mean form having forceps of moderate length is comparatively rare. The size of the forceps of the females scarcely varies at all, probably less than 1 mm. in the whole sample. The number of cases is enough to fairly justify the acceptance of these statistics and it is not likely that a greater number of cases would much alter the shape of the curve. Here, therefore, is a group of individuals living in close communion with each other, high and low, under the same stones. No external circum- stance can be seen to divide them, yet they are found to consist of two well-marked groups. Before leaving these examples special attention should be di- rected to the fact that the existence of a complete series of indivi- duals, having every shade of development between the "lowest" and the " highest " male, does not in any way touch the fact that the Variation may be Discontinuous ; for we are concerned not with the question whether or no all intermediate gradations are possible or have ever existed, but with the wholly different question whether or no the normal form has passed through each of these intermediate conditions. To employ the metaphor which Gal ton has used so well — and which may prove hereafter to be more than a metaphor — we are concerned with the question of the positions of Organic Stability; and in so far as the intermediate forms are not or have not been positions of Organic Stability, in so far is the Variation discontinuous. Supposing, then, that the "high" and " low " males should become segregated into two species — a highly improbable contingency — these two species would have arisen by Variation which is continuous or discontinuous according to the answer which this question may receive. SECTION IX. Discontinuity in Substantive Variation : Colour and Colour-Patterns. From the consideration of Discontinuity in the Variation of a character, size, which may be readily measured arithmetically, we pass to the more complex subject of Discontinuous Variation in qualities which are not at once capable of quantitative estimation. In this connexion the case of colour- variation may be profitably considered. Nature abounds with examples of colour-polymor- phism, and in numerous instances such Variation is discontinuous. Of such discontinuous Variation in colour I shall speak under two heads, considering first variations in colours themselves and sect, ix.] INTRODUCTION. }:> secondly variations in colour-patterns. As it is not proposed to give the evidence as to Substantive Variation in this volume, a few examples must suffice to shew the use of the term Dis- continuity as applied t<> these Colour- variations. I. Colours. The case of the eye-colour of Man may well be mentioned first, as it has been studied statistically by Galton In this case the facts clearly shewed that certain types of eye-colour are relatively common and that intermediates between th< se types are comparatively rare. The statistics further shewed that in this respect inheritance was alternative, and that the different types of eye-colour do not often blend in the offspring. " If one parent has a light eye-colour and the other a dark eye-colour, some of the children will, as a rule, be light and the rest dark ; they will seldom be medium eye-coloured, like the children of medium eye-coloured parents. 1 " Colour dimorphism of this kind is very common among animals and plants. It is well known, for example, among beetles. Several metallic blue beetles have bronze varieties of both sexes, living together in the same locality. A familiar instance of this dimor- phism occurs in the common Pliratora vitellince. Again in the Elaterid beetle, Corymbites cupreus, there is a similar dimorphism in both sexes, the one variety having elytra in larger part yellow- brown, while the elvtra of the other are metallic blue. This blue variety was formerly reckoned a distinct species, G. ceruginosus. In the latter case I am informed by Dr Sharp, who has had a large experience of this species, that no intermediate between these two varieties has been recorded, and in the case of the Phratora the occurrence of intermediates is very doubtful. An- other common example of colour dimorphism is seen in Telephorus livid us y the "sailor" of "soldiers and sailors." This beetle inav be found in large numbers, about half being slaty in colour ( var. disj)ar), while the remainder have the yellowish colour which coleopterists call "testaceous." Such instances may be multi- plied indefinitely. When the whole evidence is examined it will be found that different colours are liable to different discontinuous variations; as instances may be mentioned black and tan in dogs ; olive-brown or green and yellow in birds, &c.' J ; grey and cream- 1 Natural Inheritance, p. 1H9. 2 A specimen of the green Ring Parakeet [PaUeornU torquatua) at the Zoological Society's Gardens was almost entirely canary-yellow in 1890. Since that date it has become more and more "ticked" with green feathers. A Green Woodpecker (Picas riridis) is described, having the feathers of the runi]> edged with red instead of yellow, the normally green feathers of the three lower rows of wing-coi and the back were pointed with yellow. J. H. Gubnby, Zoologist, xi. p. •"■- I am indebted to Mr Gnrney for the loan of a coloured drawing of this specimen. Another example is described as being entirely canary-yellow, with the exception <>t a few feathers on the cap, which were purple-red. Dk Bktta, Mater. i<> r una fauna Veronese, p. 174. For this reference I am indebted to Prof. Newton. Specimen <>f Common Bunting whitish yellow. Edwabo, ZawL, 6492 ; Sedge Warbler canary- yellow. Bird, Zool., 3G32. The Canary itself is a similar case. An Eel gamb<> yellow. Gurnet, Zool., 3599. 44 RED AND YELLOW. [introd. colour in mice and cygnets 1 ; red and blue in the eggs of many Copepoda 2 , the tibiae of Locusts 3 , the hind wings of the Crimson Underwing (Catocala nupta) 4 , &c. Another case of blue as a variety of scarlet is the familiar one of the flower of the Pim- pernel (Anagallis arvensis). Discontinuous colour-variation of this kind is one of the commonest phenomena in nature, but to advance the subject materially it is necessary for a large mass of evidence tc^be produced. This cannot now be attempted, but in order to bring out the close relation between these facts and the problem of Species I propose to dwell rather longer on one special section of the evidence which must serve to exemplify the rest. The case which I propose to take is that of certain yellow, orange, and red pigments. For brevity I shall present the chief facts in the first instance without comment. 1. Colias edusa (Clouded Yellow) is usually orange-yellow, having a definite pale yellow female variety, helice, which is not recognized as occurring in the male form. A specimen is figured having the right side helice and the left edusa. Fitch, E. A., Entomologist, 1878, xli. p. 52, PI. fig. 11. This was an authentic specimen, for Mr Fitch tells me that it was taken by his son and seen alive by himself. A specimen having one wing white and the rest orange is recorded by Morris, Brit. But., p. 13. Intermediates between edusa and helice must be exceedingly rare. Oberthur records two such specimens and says that Staudinger took a similar one at Cadiz. For this intermediate he proposes a new name, helicina. Bull. Soc. Ent. Fr. (5), x. p. cxlv. 1 In this case I can affirm the alternative character of the inheritance. For several years a pair of swans kept by St John's College, Cambridge, have produced cygnets, some of which have been of the normal grey, while others have been fawn- colour, a condition which Prof. Newton tells me has been thought characteristic of the " Polish " swan, a putative species. None of these cygnets are intermediate in colour, and all accmire the full white adult plumage, but the feet of the fawn-coloured cygnets remain pale in colour. Now the father of these has pale feet and was doubtless himself a fawn-coloured cygnet ; the hen is normal. The cock formerly belonged to Dr Clifford, who kindly told me that the cygnets of this bird by a different hen were also thus diverse. A pair of these were given to Sir John Gibbons, who informs me that "from these there has been a brood every year, and always I think one of the cygnets has been white or nearly so, the others being of the usual colour." One of Dr Clifford's birds was also given to the late Mrs Gosselin of Blakesware, to whom I am indebted for descriptions of and feathers from several fawn-coloured cygnets which were its offspring. A similar case on the Lake of Geneva is re- corded by Fauvel, Rev. ZooL, 1869, p. 334, and another in the Zool. Gardens at Amsterdam, by Newton, Zool. Rec, 1869, p. 99. 2 This is well known to collectors of fresh-water fauna, and I have repeatedly seen the same phenomenon in species of Diaptomue, especially D. asiaticus, in the lakes of W. Siberia. Among thousands of individuals with red-brown egg-sacs, will often occur a few specimens having the egg-sacs of a brilliant turquoise-blue. In this connexion compare the case of the Crayfish [Astacus fluviatilis), which turns scarlet on being boiled, and which, like the Lobster, not uncommonly appears in a full blue variety. 3 Caloptemu spretus with hind tibia? blue instead of red, Dodge, Can. Ent., 1878, x. p. 105 ; Melanoplus paekardii, having hind tibia? red instead of bluish, Bruner, Can. Ent., 1885, xvn. p. 18. For reference to these observations I am indebted to Cockereel, Ent. , 1889, xxii. p. 127. 4 Win ik. Ent., 1889, xxn. p. 51. Compare the fact that in another species of Catocala (C. fraxini), the Clifden Nonpareil, the hind wings are normally bluish. sect, ix.] INTRODUCTION. 45 A curious specimen, apparently a male, having the colour of hdice was kindly shewn me by Mr F. H. Waterhouse. The light marks which in the female are present on the dark borders of the fore-wing are only represented by one minute light mark on each fore-wing. In most if not all of the edusa group of Colias, there is a pale aberration of the female, corresponding to the helice variety of < zdusa. Elwes, Tr. Ent. Soc, 1880, p. 134. In the same paper is a full account of the geographical distribution of the several species and colour-varieties of Colias. Colias hyale (Pale Clouded Yellow) is normally sulphur-coloured. Nearly white varieties and a variety with the field rich sulphur colour, and the apical marginal patches red, are recorded in several works. 2. Gonepteryx rhamni (The Brimstone) is sulphur-yellow in the male, and greenish-white in the female. There is a spot in each wing, and the scales covering this on the upper side are bright orange. Gonepteryx cleopatra, a S. European species, is like the above in the hind-wings, while the field of the fore-wings is flushed with orange of exactly the tint of that on the spots of G. rhamni. There are several records in entomological literature alleging the capture of "G. cleopatra" in Britain, e.g. Proc. Ent. Soc., 1887, p. xliii. In addition to these there are records of specimens of G. rhamni more or less flushed with orange ; e.g., a specimen at Aldershot with orange spots on fore-wings as in cleopatra, Proc. Ent. Soc, 1885, p. xxiv. Mr Jenner "Weir said he had seen a specimen in Ingall's collection, intermediate between rhamni and cleopatra. ibid. A male of G. rhamni taken at Beckenham had the costal margin of each fore-wing broadly but unequally suffused with bright rose- colour or scarlet, and the right posterior wing was marked in like manner. The insect was thus marked when captured. Bicknell, Proc. Ent. Soc, 1871, p. xviii. 3. Anthocharis (Euchloe) cardamines (The Orange Tip), in the male has the fore-wings tipped with orange on both sides, while in the female these orange tips are absent. The field in both is white In entomological literature are many records of variations in the extent and depth of the orange markings on upper or under side, or both (cp. Zoologist, xiii. 4562; Proc Ent. Soc, 1S70, p. ii. ; Mosley, Illustrations of British Lepidoptera ; Haworth ; Boisduval ami many others), but with these we are not immediately concerned. A specimen is figured in which the orange spots were completely represented by yellow. Mosley, Illustrated Brit. Lep. The white of the field is replaced by primrose or lemon yellow in several Continental forms. These have been described as species under the names eupheno, belia, euphenoides, gruneri, &c. A local variety of A. eupheno is described from Mogador, where it was found common at a little distance from the town. The female was much larger than the type, resembling the male in markings and in shape of the fore-wings. The orange blotch, instead of being con- fined to tip of the fore-wing as normally, extends to the discoidal spot and is usually bounded by a black band, sometimes suffusing the whole tip of the wing. The colour of the field varies from pure white to pale lemon: the hind-wings are always yellower than in the type, in some 46 RED AND YELLOW. [ixtrod. specimens being nearly as yellow as those of the male. Mr M. C. Oberthiir supplied a specimen from Central Algeria which was inter- mediate between the type and this variety. Leech, J. H., P. Z. S., 1886, p. 122. 4. Amongst Lepidoptera the change from red to yellow is very common. A case of Vanessa atalarda, having the red partially replaced by yellow, is figured in Entom., 1878, xi. p. 170, Plate. Varieties of Arctia caja, Callimorpha dominula, C. hebe, C. hera, C. jacoboece, Zygcena filipendulce, Z. minos, tfcc, with yellow instead of red, are to be seen in many collections. See especially Ochsexheimer, Schm. v. Europa, 1808, n. p. x, also p. 25, and many other authors. A chalk-pit at Madingley, Cambridge, has long been known to collectors as a locality for the yellow Z. filipendulce (Six-spot-Burnet); see Eat. Mo. Mag. xxv. p. 289. In some of these the yellow is tinged with red, but it is commonly a very distinct variety. A variety of the Red Underwing (Catocala nupta) with brownish-yellow in the place of the red, is figured by Exgramelle, Papill. d'Eur., PL cccxxn. The evidence relating to this subject is very extensive, and concerns many genera and species besides those named above. 5. Pericrocotus flammeus (an Indian Fly-catcher) is grey and yellow in the female, and black and orange-red in the male. The young male is grey and yellow like the female. An adult male is described in which the grey had been fully replaced by black, but the yellow remained, not having been replaced by red. R. G. "Wardlaw Ramsay, P. Z. S., 1879, p. 765. See also Legge, Birds of Ceylon, I. p. 363, for description of male in transitional plumage. Curiously enough the change from red to yellow and from light yellow to dark is no less common among plants, though it can scarcely be supposed that the substances concerned are similar. 1. y'' n -cognized as belonging to a given locality, or they may be trifling, and appreciable only when a large number of individuals arc gathered But apart from these differences of form and texture there are a great number of colour-varieties of which the following are the three chief whole-coloured forms, viz. white, dark purple-brown, and yellow. In addition to these there are banded forms, and the bands may be coloured with any two of the three colours men- tioned above. Among the banded forms there are two distinct sorts of banding, in the one there are very many fine bands and in the other there are a few broad bands. In most localities these colour- varieties may all be found ; though in some places, especi- ally where the water is foul, as at Plymouth, the shells are greatly corroded and the colours, if originally present, are obscured. Speaking however of localities in which colour- varieties are to be seen at all, several may generally be found together. If any one will take the trouble to gather a few hundreds of these shells and will set himself to sort them into groups according to their colours, he will find that the majority fall naturally into groups of this kind ; and that those which cannot be at once assigned to groups but fall intermediately between the groups are com- paratively few. I have seen this at many places on the English coast; in Yorkshire, Norfolk, Suffolk, Kent, Sussex, Dorsetshire. Devonshire, Cornwall, &c. In several localities I have found pairs belonging to different colour-varieties breeding together, and there is therefore no reasonable doubt that these colour- variations do not freely blend, but are discontinuous. The statements here made with regard to P. lapillus hold in almost the same way for Littorina rudis, but in this case the number of colour-types is larger. In L. rudis I have occasionally seen specimens of which the upper part belonged to one colour- type, and the lower to another, the transition occurring sharply at one of the varices. In these cases the shell appears to have been injured and is possibly renewed. One of the commonest British Lady-birds (Coccuwlla decern - ■punctata) is an extremely variable form. A great number <>f its varieties may be found together, ranging from forms with small black spots on a red field to forms in which the field is black with a few red spots. But in spite of the great diversity there are certain types which are again and again approached, while the intermediates are comparatively scarce. The following case, well known to entomologists, may he mentioned here. The Painted Lady (Pyrameis cardui) is found in the typical form over the i utile extent of every continent, with the exception of the Arctic regions and possibly 8. America. A special form of it (var. kerakawi) is found in Australia an 1 New Zealand, bnt the other large islands south of Asia possess the normal type. The Latter is also found in the Azores, Canaries, Madeira and St Helena. This butterfly lias been taken on the snowdevel in the Alps; and in X. America, though it may he regarded as one of the commonest butterflies in the elevated centra] district, it is most abundant at a level of 7000—8000 feet. It has been taken on Arapahoe Teak, between 11,000 B. 4 50 COLOUR-PATTERNS. [INTEOD. and 12,000 feet (from Scxdder, Butterflies of X. America, i. pp. 477 — 480). Of this insect, which is a very constant one, a certain striking aberration has been found, always as a great rarity, in many lands. In this aberration the markings are almost entirely rearranged. It is said to have been first described by Eambur under the name var. Elymi, but this description I have never found. (The reference quoted is Annales des Sci. d' observation, Paris, 1829, Vol. n. PL v.) As often happens with Variation, without coloured figures description is almost useless, but tbe figures referred to are very accessible. In a British specimen of this aberration the white bars are absent from the anterior costae and a series of white fusiform blotches are present along the marginal border; two abnormal white spots are also present near the anal angle, thus continuing the series down the wing (fig. 5, a.). The hind- wings are equally aberrant. The two large dark spots which are usually on the disk between the median nervure and the inner margin are altogether wanting. Between each of the nervures of the hind-wing is a white spot, whereas in the normal form there is no white spot at all on the hind-wings. These white spots on the hind-wings form a row parallel to the border of the wing and, as it Fig. 5. A. Clark's specimen of P. cardui, var. ehjmi from I'.ut. 1880. B. Newman's specimen. Brit. But., p. 64. C. P. cardui, normal, also from Newman, Brit. But., p. 64. SECT, ix.] INTRODUCTION. 51 were, continue the series of white spots borne by the anterior rings. [Underside not described.] This specimen was reared from a larva found near the river I Clapton Park. Clark, J. A., Entomologist, 1880, xm. p. 73, fig. A coloured figure of the same specimen, Mosley, S. L., PI. 8, fig. H. A form very closely similar to the above is figured in black and white by Newman from a specimen in IngalFs collection (fig. 5, n). [This is apparently the specimen given in Zoologist, p. H304.] Newman, British Butterflies, p. 01, liji. A British specimen which nearly approaches this aberration in the absence of the white bars on the costae and in the absence of the black transverse bar i- recorded. In it each of the sub-marginal rows of black spots on the posterior wings is drawn, containing a white spot. In this specimen the In-own-red of the type v. presented by rose-colour. Newman, Entomologist, 1*73, p. 345, fig. Another specimen closely resembling this aberrant form is described from New South Wales. Olliff, A. S., Proc. Linn. Hoc, N. 8. W., S. 2, in. p. L250. Another specimen closely resembling the above was taken at Graham's Town, S. Africa, and is mentioned by Jenner Weir, Entomologist, 1889, xxn. p. 7:;. Another specimen is figured in which the hind-wings are marked as in tie- above, but the anterior wings, though strongly resembling this aberration in the general disposition of the colours, yet differ in details, the chief points of difference being that the white costal bar is only partially obliterated and the white spots on the anal angles of the fore- wings are not developed. [This specimen was in Kaden's collection and was presumably European. J Heurich-Schaffer, Bd. i. p. 41, PI. 35, tigs. 157 and 158. A description is given of an aberrant form taken at King William's Town, S. Africa, which " closely resembled that figured by Herrich-Schaffer."' Tbimen, R., South-African Butterflies, i. p. 201. A specimen (British) resembling the above, but lacking the white spots on the anal angles of the fore- wings and having the marginal row on the hind-wing light- coloured, but not quite white, is figured by Mosley, Pt. in. PI. 3, fig. 3. Two specimens were taken in New Jersey, U.S.A., which are stated to have conformed to this aberration. Si'reckkr, Cat. N. Amer. Macrolepidop., p. 187. Another British specimen generally resembling Herrich-S chaffer's figure is represented by Mosley, PI. 8, fig. 4. In all the above specimens the resemblance, as far at least as the upper surface is concerned, is considerable. With the exception of Herrich-Schaffer's example, the undersides are not figured, but from the descriptions it may he gathered that they also resembled each other though probably not so closely as the upper surfaces. The resemblance between the underside of the Australian specimen an I that figured by Herrich-Schaffer must have been very close. "Intermediate between these extreme sports and the normal form are tin examples taken at Cape Town in 1866, 1878 and 1874 — the first by myself in which the fore-wing markings are scarcely affected, hut the hind-wing spots are minutely ocellate and externally prolonged, so as to be confluent with tie ing row of lunules." Tkimen, ibid. pp. 201, 202. Another aberration, a Belgian specimen, resembles •* Elijmi" in kind but differs from it in degree. In it also the while bars are absent from the costflB, and tin- brown and black markings of the anterior wings are rearranged in almost exactly the same manner. The posterior wings are modified u> a much less extent and the normal row of black spots between the nervines remains, while only the first and second of the series of white spots is present, the former being very slight. In this individual the markings of the underside also resemble the alienation generally, but it retains the four ocelli of the type. Die DoNCEEL, II. Doni kikk. Ann. S oVEnt. Beige, 1878, xxi. p. 10, Plate. A specimen, also Belgian, is described in which the two anterior win J8 n -liihle Herrich-Schaffer's figure in lacking the white bars on the costal and in the arran nient of the black and ground colour. In neither of them are the whit. of the anal angles (found in the British ami Australian sp scimens) present. The white markings at the apex of the anterior wings differ on the two sides, being in both of them unlike the type and an approach v> the aberrations in question, hut the degree to which they are developed differs markedly, being greatesl on the right si The left posterior wing resembles the aberration in having the -ix abnormal white spots, but less emphasized than in the figures quoted above; in general colour this wine is darker than the type. The right posterior wing, however, has Qone of the white spots of the aberration, and differs from the type only in being more suffused with 4- 2 52 COLOUR-PATTERNS. [iNTBOD. black. To recapitulate, the two anterior and the left posterior wing resemble generally, though not entirely, the aberration, while the right posterior wing is nearly normal. A specimen is described from Ekaterinoslav, S. Russia, which resembles this aberration in wanting the black transverse band and in the disposition of the apical white spots. A trace of the white costal bar remains on the costal border. On the underside of this specimen the ocelli were placed in a pale rose-coloured band. (Name proposed, aberration, inornata). Bramsox, K. L., Ann. Soc. Ent. France, S. 6, vi. 1886, p. 284. Besides the rare aberration " var. Elymi" there is a variety sometimes found in Europe, which in Australia is so constant and definite that it has been regarded as a species. The following may be quoted respecting its occurrence in Australia, where it is common : " There is in abundance about Melbourne and in many other parts of Australia a Cynthia with the general appearance and habit of G. cardui, so closely represented that every entomologist I know refers it to that species. The Australian species differs from the European one constantly, however, in having the centres of the three lower round spots on the posterior wings bright blue, and having two other blue spots on the posterior angles of the same wings, the corresponding parts of the European form being black." For this form the name C. kershawi is proposed. M'Cot, F., Ann. and May. of Nat. Hist., Ser. 4, i. 1868, p. 76. See also Olliff, A. S., Proc. Linn. Soc, N. S. W., Ser. 2, in. p. 1251. The notices of its occurrence in Europe are as follows. In 1884 Mr Jenner Weir exhibited a specimen of P. cardui, taken in the New Forest. Three of the five black spots in the disk of the upper side of the hind-wings had blue pupils ; he pointed out that the specimen thus approached the Australian form, P. kershawi. Proc. Ent. Soc, 1884, p. xxvii. Olliff, loc. cit., states that he has taken a specimen having these blue markings at Katwijk, in Holland. In the case given, the evidence certainly suggests that these various forms of aberration are grouped round a normal form of aberration, just as the individuals of the type are grouped round its normal. One example of a similar discontinuity in a melanic varia- tion may profitably be given. I have taken this opportunity of referring to such a case, as the general evidence of melanic variations goes on the whole to shew that they are not commonly discontinuous, and further evidence on this point would be most valuable. To appreciate the evidence Butler's coloured plate should be referred to. Terias. A well-marked group of butterflies of this genus allied to T. hecabe, is found in Japan. It contains forms of great diversity in amount of black border which occurs on the outer margins of the fore- and hind-wings. The remainder of the wings is lemon-yellow. The black border may be confined to the tip of the fore-wings, or may there occupy a considerable area and be extended along the whole outer margin of both wings. The form with the least black is called T. man- ihirina, that with the most, is called T. mariesii, and the intermediate form is called T. anemone. Upwards of 150 specimens, all from Nikko, were examined; these ranged between the two extremes, and were found to form a continuous series. Butler states that "the absence of six of them, referable only to two gradations, would at once leave the three species as sharply defined as any in the genus." [In the case of these butterflies, there are thus three groupsof va net ies, two extreme groups and one mean group ; intermediates between these sect, ix.] INTRODUCTION. 53 are comparatively rare. Butler suggests that these intermediate forma should be regarded as hybrids, even in the absence of experimental evidence. This view is of course dependent on the truth of the belief that such a discontinuous occurrence of variations is anomalous.] Twenty specimens of the species T. bethesaba and thirty-nine of T. jaegeri (both from Japan), were also examined. The former pre- sented no variations whatever, and the latter only vary in the yellower or redder tint on the under surface of the secondaries. Butler, A. G., Trans. Ent. Sob, 1880, p. 197, PL vi. Compare the following : Terras constantia. Twenty-five pupae, all found together on the same twigs at Teapa, Tabasco, Mexico, by Mr H. H. Smith. The butterflies from these are in Messrs Godman and Salvin's collection, who kindly allowed me to examine them. The amount of black border on both wings varies much, nearly though not quite so much as in the cases figured by Butler. In the lightest the apex of the fore-wing alone is black, and there is no black on the hind-wing in 9 specimens ; of the remaining 16 some have a well-defined black border to the hind-wing, while in the rest (about 6) this border is slight. This case is a particularly interesting one, as the specimens were associated and presumably belonged to one brood. ev For another beautiful case of discontinuous Variation in pattern I am indebted to Dr D. Sharp. The Cambridge Univer- sity Museum lately received a series of 38 specimens of Kallima inachys, the well-known butterfly whose folded wings resemble a dead leaf with its mid-rib and veinings. The underside of this butterfly is sometimes marked with large blotches and flecks of irregular shape, which, as has often been noted, resemble the patches of discoloration caused by fungi in decaying Leaves. Dr Sharp pointed out to me that the specimens examined fell naturally into four groups according to the coloration of the underside. In the first group the field is nearly plain, though the tint varies in individuals. The "mid-rib" is strongly marked in this and all the groups, but the "veinings" are absent or very slightly marked in the first group : 18 specimens. In the second group the ground is almost plain, but it bears numerous strongly marked black-speckled spots, of forms which though irregular in outline are closely alike, and occupy the same positions in all the six specimens, being scarcely if at all represented in any of the others. In the third group the dark bars representing "veins' are strong, but the field is nearly uniform : 10 specimens. In the fourth group, of four specimens, the ground-colour is darkened in such a way as to leave large and definite blotches of light colour in particular places. Of these specimens three have the veinings very strongly marked, while the fourth is without them. Into these four groups the specimens could be unhesitatingly separated, though in each group many individual differences 54 MISCELLANEOUS EXAMPLES. [iNTBOD. occurred. Xo marked variation in the upper-sides was to be seen. These specimens were all from the Khasia hills, Assam, but there was of course no evidence that all were flying together. One of the most interesting examples of discontinuous Variation in colour-patterns is the case of ocellar markings or eye-spots. Upon this subject nothing need here be said as the evidence will be given in detail in the course of this volume (see Chap. XIII.). SECTION X. Discontinuity in Substantive Variation. — Miscellaneous Examples. Of the discontinuous occurrence of Substantive Variation, the manifestations are many and diverse. We have seen that in such features as size, colour, and colour-patterns, Variations may be discontinuous, and a form may thus result, differing markedly from the type which begot it. Variation in the proportions or the constitution of essential parts may no less suddenly occur. The range of these phenomena is a large one, but for the purposi - of this Introduction a few examples must suffice in general illustration of their scope. A discontinuous variation which is familiar to all is that of " reversed" varieties, especially of Molluscs and Flat-fishes. Such varieties are formed as optical images of the body of the type. In both of the groups named, some species are norm ally right-handed, others being normally left-handed, while as individual variations reversed examples are found. In Molluscs this is not peculiar to Gasteropods with spiral shells, but may occur also both in Lima- cidse (slugs) 1 and in Lamellibranchs" 2 . Such variation is commonlj discontinuous, and the two conditions are alternative. The fact that the reversed condition may become a character of an estab- lished race is familiar in the case of Fnsus antiquus. This shell is found in abundance as a fossil of the Norwich Crag, such specimens being normally left-handed, though the same species at the present day is a right-handed one. Of the left-handed form a colon)- was discovered by MacAndrew on the rocks in Vigo Bay 8 . It was there associated with certain ether shells proper to the Norwich Crag. This discovery seemed to Edward Forbes to be so remarkable that he looked on it as corroborative evidence of a special connexion between the fauna of Vigo Bay and the Crag fossils 3 . Jeffreys had the same variety from Sicily 4 . 1 For example, a sinistral Avion, Baudon, Jour. ,<>> case in which there had been this hereditary character, the others having been of accidental occurrence. Such bircls are sometimes called 'Emu' fowls." Lkwis Wright, IllvM. Book of Poultry, 1886, p. 230. Of many domestic animals, for example, the goat, eat and rabbit, varieties with long, silky hair are familiar under the name of "Angoras." Very similar breeds of guinea-pigs are kept, to which the name " Peruvian " is given. In this connexion the capture of a mouse {Mm musculus) with long, black, silk-like hair is interesting 1 , as shewing that such a total variation may occur as a definite phenomenon without Selection. 1 Cocks, W. P., Tram. Cornwall Polytech. Soc, L852. Like other animals, mice have of course often been found black. For instance, a number of black mice were found in Hampstead-down Wood. Hkwktt, Y\\. '/.oo\. Jour. iv. p. 348. 56 HAIR. [iNTROD. As to the partial nakedness of the skin of many animals (Man, &c.), several suggestions have been made. It has been variously supposed that the covering of hair has been gradually lost by Man, in correlation with the use of clothes ; with the heat of the sun ; for ornamental purposes under sexual selection l ; or perhaps as a protection from parasites 2 . Various suggestions Have also been made to explain the persistence of hair at the junction of the limbs and on the head and face. To a con- sideration of the origin of nakedness, the evidence of Variation in some measure contributes, and though the bearing is not very direct, it may illustrate the futility of inquiries of this kind made without regard to the facts of Variation. Mouse (Mus musculus) : male and pregnant female found in a straw-rick at Taplow ; both were entirely naked, being without hairs at all, excepting only a few dark-coloured whiskers. The skin was thrown up into numerous prominent folds, transversely traversing the body in an undulating manner. This condition of the skin obtained for them the name of " Rhinoceros mice." The ears were dark or blackish, the tail ash-coloured, and the eyes black, indicating that they were not albinos. The exfoliations from the skin were examined microscopically but no trace of hair-follicles was found, nor any suggestion of disease. The animals were active and healthy. The young ones, when born, were similar to the parents. The teeth were normal. In the Museum of the College of Surgeons is a precisely similar specimen which was found in a house in London. Gaskoix, Proc. Zool. Soc, 1856, p. 38, Plate. Three specimens of the common Mouse ( Mus musculus) were caught in the town of Elgin. The whole bodies of these three creatures "were completely naked — as destitute of hair and as fair and smooth as a child's cheek. There was nothing peculiar about the snout, whiskers, ears, lower half of the legs and tail, all of which had hair of the usual length and colour. They had eyes as bright and dark as in the common variety At least two others were killed in the same house where these were found." Gordon, G., Zoologist, 1850, viii. p. 2763. Shrew. (Sorex sp.) "whole of upper surface of head and body destitute of hair, and skin corrugated like that of Naked Mice figured in P. Z. S., 1856 ;" sent to Brit. Mus. by Mr P. Garner. Gray, J. E., Ann. and Mag. of X. II., 1869, S. 4, iv. p. 360. In connexion with these cases, the following fact is interesting : Heterocephalus is a genus of burrowing rodent from S. Africa. It contains two species, of which one is about the size of a mouse and the other is rather larger. They are characterized by possessing an apparently hairless skin which is on the head and body of a wrinkled and warty nature. On closer inspection the skin is seen to be furnished with tine scattered hairs, but there is no general appearance of a hairy covering. There is no external ear in these animals. Oldfikld Thomas, P. Z. S., 1885, p. 845, Plate LIV. Naked horses have often been exhibited. Such a horse caught in a 1 C. Darwin, Descent of Man, i. p. 142. 2 Belt, Naturalist in Nicaragua; see also Hudson, Naturalist in La Plata, 1892. sect, x.] INTRODUCTION. 57 semi-feral herd in Queensland was described by Tegetmeikr, Field, xlviii. 1876, p. 281. The skin was black and like india-rubber. Careful examination shewed no trace of hair, or any opening of a hair-follicle. In Turkestan, in the year 1886, I heard of one thus travelling, but failed to see it. ' Hairless' dogs in S. America remain distinct (Belt, I. c. ). Of discontinuous Substantive Variation in bodily proportions a single example must suffice. Among domestic animals of many kinds, races are known in which the bones of the face do not grow to their full size, while the bones of the jaw are, or may be, of normal proportions. Familiar examples of this are the bull-dog, the pug, the Japanese pug, the Niata cattle of La Plata 1 , some short-faced breeds of pigs, and others. In the case of these domestic animals the part which Selection has taken in their pro- duction is unknown, and the magnitude of the original variations cannot be ascertained. It is nevertheless of interest to notice that parallel variations have occurred in distinct forms, and I think that this is to some extent evidence that the variations were from the first definite and striking. As regards the dogs even, there is a presumption that the short face of at least the Japanese pug arose independently from that of the common, or Dutch pug (as it used to be called), but as to this the evidence is insufficient. Among the dogs' skulls found in ancient Inca inter- ments, a skull was found having the form of the bull-dog. Nehring, Kosmos, 1884, xv. As these remains belong to a period before the European invasion, it is most probable that this bull-dog breed arose independently of ours. Apart however from domestic animals there is evidence as to the origin of short-faced breeds. This evidence, which is not so well-known as it deserves to be, is provided by the occurrence of a similar variation in fishes. Darwin in speaking of the evidence as to Niata cattle makes allusion to the case of fishes in a note 2 , quoting Wyman as to the cod, which occurs in a form known to fishermen as the " bull-dog " cod. The interest of this obser- vation is increased by the fact that it does not stand alone, but similar variations have been seen in the carp, chub, minnow, pike, mullet, salmon and trout. In the last-named there is even evidence of the establishment of a local race having this singular character. Carp (Ci/prinus carpio). " Bull-dog"-headed Carp have often boon described. The face ends more or less abruptly in front of the eyes, while the lower jaw has almost its normal length. The front part of the head is bulging and prominent, giving the fish an appearance which several authors compare to that of a monumental dolphin. A u f ood figure of such a specimen is given by G. St Hilaibe, Hist, des Anom., ed. 1837, i. p. 9G, where a full account of the older literature of the 1 C. Darwin, Animals and Plants under Domestication, 2nd edition, i. p. 92. - Ibid., p. 93, note. 58 BULL-DOG HEADS. [iNTROD. subject may be found. Inasmuch as carp are largely bred in ponds on the continent, there is in this case some suggestion that unnatural conditions may be concerned, but this suggestion does not apply to other cases of the same Variation. Otto, Lehrb. path. Anat., I. § 129, states that in the ponds of Silesia such fish are not rare. See also Voigt, Mag. f. d. Naturk., ill. p. 515. Cyprinus hungaricus : specimen from the Danube similarly formed. The forehead was protuberant and bulged in front of the eyes so that its anterior border was almost vertical. The attachments of the mandible are carried forward in such a manner that the mandible itself was directed upwards almost at right angles to the body. [Good figure.] Steindachner, Verh. zool.-bot. Ges. Wien, 1863, xm. p. 485, Plate. [Several other types of Variation in the heads of Cyprinoids occur, but cannot be described here.] Chub {Leuciscus dobula = cephalus) : specimen having anterior part of head rounded "like a monumental dolphin/' The body was normal, measuring 33 cm. in length. Landois, Zoo/. Garten, 1883, XXIV. p. 298. Minnow (Phoxinus ton's) specimen having a snout like a pug ("mnsratt f peach-stones producing nectarine-trees, and of nectarine-stones producing peach-trees — of the same tree bearing peaches and nectarines — of peach-trees suddenly producing by bud-variation nectarines (such nectarines reproducing nectarines by seed), as well as fruit in part nectarine and in part peach, — and, lastly. of one nectarine-tree first bearing half-and-half fruit and subsequent ly true peaches" 1 . After disposing of alternative hypotheses he concludes that "we may confidently accept the common view that the nectarine is a variety of the peach, which may be pro- duced either by bud- variation or from seed." In this case the evidence is complete. The variation from peach to nectarine or from nectarine to peach may be total. If less than total, the fruit may be divided into either halves or quarters so that for each segment the Variation i> total -till. Of inter- mediate forms other than these divided ones, we have in this case 1 Animals and Plants under Dom€8tication t cd. 2, i. p. 362. 2 Ibid., p. 362, quoting from Loudon's Hard. Mag, L828, p. •">:>. The case of a Royal George peach which produced a fruit. " three parts of it being peach and one part nectarine, quite distinct in appearance as well a< in flavour." The lin« ~ of division were longitudinal. 60 RADIAL REPETITION. [introd. no evidence : it is therefore a fair presumption that they are either rare or non-existent; and that the peach-state and the nectarine-state are thus positions of " Organic Stability," between which the intermediate states, if they are chemical ami physical possibilities, are positions of instability. These examples of Discontinuity in Substantive Variation must suffice to illustrate the nature of the phenomena. It will be seen that the matters touched on cover a wide range, and the evidence relating to them must be considered separately and at length. Such a consideration I hope in a future volume to attempt. SECTION XI. Discontinuity ix Meristic Variation: Examples. Inasmuch as the facts of Meristic Variation form the substance of this volume, it is unnecessary in this place to do more than refer to the manner in which they exhibit the phenomenon of Dis- continuity. One or two instances must suffice to give some sug- gestion of this subject, detailed consideration being reserved. Parts repeated meristically form commonly a series, which is either radial or linear, or disposed in some other figure derived from or compounded of these. For the purpose of this preliminary treatment an instance of Discontinuous Variation in each of these classes may be taken. 1. Radial Series. Variations in the number of petals of actinomorphic flowers exhibit the Discontinuity of Meristic Variation in perhaps its simplest form. Phenomena of precisely similar nature will hereafter be de- scribed in animals, but such variations in flowers are so common and so accessible that reference to them may with profit be made. In Fig. 7 such an example is shewn. It represents a Tulip having the parts of the flower formed in multiples of four, instead of in multiples of three as normally. Variation of this kind may be seen in any field or hedgerow 1 . Meristic Variation is here presented in its greatest simplicity. Such a case may well serve to illustrate some of the phenomena of Discontinuity. 1 For full literature and lists of cases see especially Masters, Vegetable Teratoid;/ //. s. v. PolyphyUy. It is perhaps unnecessary to refer to the fact tbat the numerical changes here spoken of are quite distinct from those which result from an assumption by the members of one series or whorl of the form and characters proper to other whorls. SECT. XI.] INTRODUCTION. 61 A form with four segments occurs as the offspring of a form with three segments. Such a Variation, then, is discontinuous Fig. 7. Diagram of the flower of a Tulip having all the parts in -4. because a new character, that of division into four, has appeared in the offspring though it was not present in the parent. This new character is a definite one, not less definite indeed than that of division into three. It has come into the strain at one step of Descent. Instances in which there is actual evidence of such descenl are rare, but there can be no question that these changes do commonly occur in a single generation, and, indeed, in many plants, as for example Lysimachia (especially L. nemorum), flowers having all the parts in -4 or in -6 may be frequently seen on plants which bear likewise normal flowers with the parts in -5. Now such a variation as this of the Tulip illustrates a pheno- menon which in the Study of Variation will often be met. We have said that the variation is discontinuous, meaning thereby that the change is a large and decided one, but it is more than this ; it is not only large, it is complete. The resulting form possesses the character of division into four no less completely and perfectly than its parent possessed the character of division into three. The change from three to four is thus perfected : from the form with perfect division into three La sprung a form with perfect division into four. This is a case of a total or perfect Variation. This conception of the totality or perfection of Variation is one which in the course of the study will assume great importance, and it may be best considered in the simple case of numerical and Meristic Variation before approaching the more complex questioo of the nature of totality or perfection in Substantive Variation. The fact that a variation is perfect at once leads to the (pus- 62 RADIAL REPETITION. [introd. tion as to what it might be if imperfect. Between the form in -3 and the form in -4 are intermediates possible? and if possible, do they exist ? Now by choosing suitable species of regular flowers, individual flowers may no doubt be found in which there are three large segments and one small one ; or two normal segments and a third divided into two, making four in all. Such flowers are firstly rare, while cases of perfect transformation are common. But be- sides their rarity there is, further, a grave doubt whether they are in any true sense intermediate between the perfect form in -3 and the perfect form in - 4. After this again it must be asked whether or no they do as a matter of fact occur as intercalated steps in the descent of the form in -4 from the form in -3 '. To the last ques- tion a general negative may at once be given ; for though there is abundant evidence that Meristic Variations of many kinds and in several degrees of completeness may be seen in the offspring of the same parent, yet any one member of such a family group may shew a particular Variation in its perfection, and the occurrence of an}- intermediate in the line of Descent is by no means necessary for the production of the perfect Variation. To answer the former question, whether or no forms imperfectly divided into four parts are in reality intermediate between those in -3 and those in -4, a knowledge of the mechanics of the process of Division is required. Such knowledge is as yet entirely wanting, and discussion of this matter must therefore be prema- ture. With much hesitation I have decided to make certain reflexions on the subject, which will be found in an Appendix to this work. These may perhaps have a value as suggestions to others, though from their theoretical nature they can find no place here. There is however another class of cases which are intermediate in a different way. In the Tulip described above the quality of division into 4 was present in all the floral organs. This is not always the case, for a Meristic Variation may be present in one series of organs, though it is absent in some or all of the others, and this is a phenomenon frequently recurring. Nevertheless, though only partially distributed, a Variation may still be dis- played in its totality in the parts wherein it is present. The parts of a single whorl, the calyx for example, may undergo a complete Variation, while the corolla and other parts are un- changed. In the same way single members of a radial series, as a petal for example, may undergo a complete Variation while the other members of the series are unchanged. The same will be shewn hereafter to be true of animals also. For instance, the normal number of the parts in the disc of Aurelia is four, but the whole body may be divided instead into Bix or some other number of parts. Examples are also found in which the parts of one-half or of one quadrant are arranged in the new number, while the remainder is normal; and. as in flowers, SECT. XI.] INTRODUCTION. <;:; this new Dumber may prevail in some or in all of those systems of organs which are disposed around the common centre. 2. Linear Series. Before speaking further of the totality or perfection of Varia- tion it will be well to give an illustration of Discontinuous Meristic Variation as it occurs in the case of a linear series of parts. AlS such an illustration the case of the variation in the number of joints in the tarsus of the Cockroach (Blatta) may be taken. This variation has been the subject of very full investigation l>v Mr H. H. Brindley. The tarsus of the Cockroach is normally divided into five joints, but in about 25 per cent, of B. americana (and in a smaller proportion of several other species) the tarsus of one or more legs is divided into only four joints, though the total length may be the same as that of the corresponding leg of the other side, Fig. 8. Between the five-jointed form of tarsus and the four-jointed form no single case in any way intermediate was seen. The whole 11 Fig. 8. Tarsi of the third pair of legs in a specimen of Blatta americana, I. the left tarsus, having the normal, or 5- jointed form; II. the right tarsus, having the 4-jointed form. evidence will be given in full in the proper place and raises many questions of great interest; but that which is important to our present consideration is the fact that the Variation is hero un- doubtedly discontinuous, arising suddenly as a total or perfect Variation, from the rive-jointed form to the four-jointed, ffere the variation, though total as regards the limb in which it is present, is not total as regards all the legs taken together. For commonly only a single leg had a four-jointed tarsus, and only one specimen was met with in which all six legs thus varied, and one specimen only shewed the variation in five legs. In speaking of such a Variation as a perfect Variation several things are meant. First, it is meant that the tarsus of the new pattern is as distinctly divided into four joints as the normal is into five. In 64 LINEAR REPETITION. [ixtrod. addition to this the statement that the varying limb is perfect conveys a number of ideas that cannot be readily formulated ; for example, that the joints are to all appearance properly proportioned and serviceable, shewing no sign of unfitness: they have in fact much the same appearance as they have in those of the Orthoptera in which the tarsus is normally four-jointed. But besides these attributes, which though useful enough for ordinary description are still in their nature formless and of no precise application, there is another which in the case of these varying legs we are entitled to make. We have said that these four-jointed tarsi are to all appearance normal, save for the number of the joints. Now the measurements which, at my suggestion, Mr Brindley has been kind enough to make, entitle us to go beyond this, and to assert that the four-jointed, tarsus has another character bv reason of which it is actuallv in a sense a "normal" form. A brief considera- tion of this will clearly illustrate the meaning of the term "per- fection" applied to Variation. We saw above that in a monomorphic form, the frequency with which, in respect of any given character, it departs from its mean condition follows a curve of Frequency of Error. This is, indeed, what is meant by the statement that the mean condition is a normal. Taking the five-jointed tarsus, measurements shewed that the ratio of the length of any given joint to the length of the whole tarsus varied in this way about a moan value. Measurement of the joints of the four-jointed form shewed that the ratios which they bear to the total length of their respective tarsi vary in a similar way about their mean values, and that there is thus a "normal" four-jointed condition just as there is a "normal" five- jointed condition. In the same way, then, that the ratio of the length of each of the five joints to that of the whole tarsus is not always identical but exhibits small variations, so the ratios of the several joints of the four-jointed tarsus to the length of the whole tarsus also vary, but in each case the ratio has a mean value which is approached with a frequency conforming to a curve of Error. The measurements established also another fact which is of consequence to an appreciation of the nature of totality in Variation. It not only appeared that the departures from the mean value of these ratios in the four-jointed variety were dis- tributed about the mean in the same way as those of the five- jointed form, but it was also shewn that the absolute varia- tions from the mean values of these ratios were not on the whole greater in the four-jointed tarsi than in the five-jointed tarsi. In other words, the four-jointed tarsus occurring thus sporadically, as a variety, is not less definitely constituted than the five jointed type, and the proportions of its several joints are not less constant. It is scarcely necessary to point out that sect, xi.] INTRODUCTION. 65 these facts give no support to the view that the exactness or perfection with which the proportions of the normal \m\i\ are approached is a consequence of Selection. It appears rather, that there are two possible conditions, the one with five joints and the other with four, either being a position of Organic Stability. Int.* either of these the tarsus may fall; and though it is still conceivable that the final choice between these two may have been made by Selection, yet it cannot be supposed that the accuracy and com- pleteness with which either condition is assumed is the work of Selection, for the "sport" is as definite as the normal. This interesting case of Meristic Variation in the tarsus of the Cockroach illustrates in a striking way the principle which is perhaps the chief of those to which the Study of Variation at the outset introduces us. We are presented with the phenomenon of an organ existing in two very different states, between which no intermediate has been seen. Each of these states is definite and in a sense perfect and complete ; for the oscillations of the four- jointed form around its mean condition are not more erratic than those of the normal form. Now when it is remembered that just such a four-jointed condition of the tarsus is known as a normal character of many insects and especially of some Orthoptera, it is, I think, difficult to avoid the conclusion that if the four-jointed groups are descended from the five-jointed, the Variation by which this condition arose in them was of the same nature as that seen as an individual Variation in Blatta ; that as the modern pheno- menon of the individual Variation which we see, so thai pasl phenomenon of the birth of a four-jointed race, was definite and complete, and that the change whose history is gone, like the change to be seen to-day, was no gradual process, but a Discon- tinuous and total Variation 1 . 1 Since this Section was written it has seemed possible that the account Riven above may be found to need an important modification. It is well known that Blatta, in common with many other Orthoptera, has the power of reproducing the antennae and legs after amputation or injury, and we have made 80me observations shewing that the tarsi of these regenerated legs sometimes, if not always, contain four joints. The question therefore arises whether the 4-jointed tarsus la a truly congenital variation, and not rather a variation introduced in the process of regeneration, somewhat after the manner of a bad- variation. To determine this point a considerable number of immature specimens were examined, and it was found that the percentage of individuals with 4-jointed tarsi is considerably Less in the young than in the adult. These facts lend support to the view that the 4-jointed condition is not congenital. A quantity of individuals were also hatched from the egg-cocoons, and among them there has thus far been found no ease of 4-jointed tarsus. On the other hand the total number thus hatched is not yet sufficient to create any strong probability that none are ever batched in the 4-jointed state. We have also seen the 4-jointed tarsus in three very young in- dividuals, which, to judge from their total length, must have been newly hatched. The statistics shew besides that the abnormality is distinctly commoner p females than in males, and that it is commoner in the legs of the 2nd pair than in the 1st, and much more common in the 3rd pair of legs than in the 2nd. These facts some- what favour the view that the variation may be congenital. It seems also ex- ceedingly improbable that in the specimen with all the tarsi 4-jointed. the six legs could each have been lost and renewed. There seems on the whole to be a pre- B. 5 66 SEX AND VARIETY. [introd. SECTION XII. Parallel between Discontinuity of Sex and Discontinuity in Variation. The application of the term Discontinuity to Variation must not be misunderstood. It is not intended to affirm that in dis- continuous Variation there can be between the variety and the type no intermediate form, or that none has been known to occur, and it is not even necessary for the establishment of Discontinuity that the intermediate forms should be rare relatively to the perfect form of the variety, though in cases of discontinuous Variation this is generally the case ; but it is rather meant that the perfect form of the variety may appear at one integral step in Descent, either without the occurrence of intermediate grada- tions, or at least without the intercalation of such graduated forms in the pedigree. In the case of the tarsus of Blatta we have seen an example of a total and complete Variation affecting single members of a series of repeated parts, not collectively, but one or more at a time 1 . Such an instance of a Meristic Variation occurring in a state which is total as regards members of a series but not total as regards the whole series finds many parallels among Substantive Variations, as, for example, that of the Crab (Cancer par/ ants) bearing the right third maxillipede fashioned as a chela, while the left third maxillipede was normal. Variations of this nature in plants are of course well known to all. At a previous place (Section vn.) allusion was made to the familiar but very curious analogy between members of a series of Meristic parts and separate organisms. The facts of Variation bring out this analogy in many singular ways, and in speaking of the totality of Variation it is necessary to bear these facts in mind. Not only are there abundant instances of independent division or multiplication of single members of Meristic series, but as has been said, single members of such series may thus inde- pendently and singly undergo qualitative or Substantive Variation, being treated in the physical system of the body as though they were separate units. In Variation, therefore, though it will be sumption that the variation may at least sometimes be congenital. Supposing however that this shall be found hereafter not to be the case, I do not thiuk that the deductions drawn from the facts will be less valid. The conclusions as to the definiteness of the two types, and the relationships of the several parts of each to the several parts of the other, would still hold good. There are besides in other forms, instances of similar numerical Variation, as for example, in the number of joints in the antennae of Prionidae, where the hypothesis of change on renewal is impossible, from which a similar argument might be drawn ; but on the whole I have preferred to leave the account as it stands, taking the case of Blatta as an example, because it is easily accessible and because, from the fewness of the joints concerned, the issues are singularly clear. 1 See Note at the end of Section xi. sect, xii.] INTRODUCTION. G7 found that members of Meristic series may vary simultaneously and collectively — and this is one of the most important generaliza- tions which result from the Study of Variation — yet it is also true that in Variation single members of such series may vary independently and behave as though they possessed an " in- dividuality" of their own. If ever it shall be possible to form a conception of the physical processes at work in the division and reproduction of organisms, account must be taken of both of these phenomena. I know no way in which the nature of Discontinuity in Varia- tion and the position of intermediate forms may be so well illus- trated as by the closely parallel phenomenon of Sex. In the case of Sex in the higher animals we are familiar with the existence of a race whose members are at least dimorphic, being formed either upon one plan or upon the other, the two plans being in ordinary experience alternative and mutually exclusive. Between these two types, male and female, there are nevertheless found intermediate forms, "hermaphrodites," occurring in the higher animals at least, as great rarities. Now though these inter- mediate forms perhaps exist in gradations sufficiently fine to supply all the steps between male and female, it cannot be supposed that the one sex has been derived from the other, and still less that the various stages of hermaphroditism have been passed through in such Descent. Besides this, even though there is an accurate correspondence or homology between the several organs which are modified upon the one plan in the male and upon another in the female, and though this homology is such as to suggest, were we comparing two species, that the one had been formed from the other, part by part, yet by the nature of the case such a view is here inadmissible: for firstly it is im- possible to suppose that either sex has at any time had the organs of the other in their completeness, and secondly it is clear that any hypothetical common form, by modification of which both may have arisen, must have been indefinitely remote and could certainly not have possessed secondary sexual organs bearing any resemblance to those now seen in the higher forms. All this has often been put, but the application of it to Variation is of considerable value. For in the case of Sex there is an instance of the existence of two normals and of many forms intermediate between them, occurring in a way which precludes the supposition that the intermediates represent stages that have ever occurred in the history of the two forms. In yet another way Sex supplies a parallel to Variation. As we know, the sexes are discontinuous and occur commonly in their total or perfect forms. Now just as members of a Meristic seri« - may present total variations independently of each other, so may single members of such a series present opposite secondary sexual characters, which may nevertheless be in each case complete. 68 NATURE OF DISCONTINUITY. [introd. The best known instance of this is that of gynandromorphic insects, in which the characters of the whole or part of one side of the body, wings and antennae, are male, while those of the other side are female. Remarkable instances of a similar pheno- menon have been recorded among bees and will be described later. As is well known, the organs and especially the legs of the sex- less females or workers are formed differently from those of the drones, but there are cases of individuals having some of the parts and appendages formed on the one plan arid some on the other. Thus in these individuals, which are in a sense inter- mediate between workers and drones, the characters of the two sexes may still be not completely blended, the male type pre- vailing in some parts, and the female in others. In the Dis- continuity of Substantive Variation will be found examples of imperfect blending of variety and type closely comparable with this case of the imperfect blending of Sex. SECTION XIII. Suggestions as to the natuke of Discontinuity in Variation. The observations at the end of Section XI, regarding the Dis- continuity of Meristic Variation lead naturally to certain reflexions as to the nature of Discontinuous Variation in general. In tin- case of the Cockroach tarsus, there given, it appeared that just as the structure of the typical form varies about its mean condition, so the structure of the variety varies about another mean condition. This fact, which in the given instance of Meristic Variation is so clear, at once suggests an inquiry whether this is not the usual course of Discontinuous Variation, and, indeed, whether Discon- tinuity in Variation does not mean just this, that in varying the organism passes from a form which is the normal for the type to another form which is a normal for the variety. Such transitions plainly occur in many cases of Meristic Variation, and in a consider- able number of Substantive Variations there will be found to be indications that the phenomenon is similar. It is true that at the present stage of the inquiry the evidence has the value rather of suggestion than of proof, but the suggestion is still very decided and it is scarcely possible to exaggerate the importance of even this slender clue. In stating the problem of Species at the beginning of this inquiry it was said that the forms of living things, as we know them, constitute a discontinuous series, and it is with the origin of the Discontinuity of the series that the solution of the main problem is largely concerned. Now the evidence of Discontinuous Variation suggests that organisms may vary abruptly from the sect, xiii.] INTRODUCTION. G9 definite form of the type to a form of variety which has also in some measure the character of definiteness. Is it not then possible that the Discontinuity of Species may be a consequence and ex- pression of the Discontinuity of Variation \ To declare at the present time that this is so would be wholly premature, but the suggestion that it is so is strong, and as a possible light on the whole subject should certainly be considered. In view of such a possible solution of one of the chief parts of the problem of Species it will be well to point out a line of inquiry which must in that event be pursued. If it can be shewn that the Discontinuity of Species depends on the Discontinuity of Variation, we shall then have to consider the causes of the Dis- continuity of Variation. Upon the received hypothesis it is supposed that Variation is continuous and that the Discontinuity of Species results from the operation of Selection. For reasons given above (pp. 15 and 1G) there is an almost fatal objection in the way of this belief, and it cannot be supposed both that all Variation is continuous and also that the Discontinuity of Species is the result of Selection. With evidence of the Discontinuity of Variation this difficulty would be removed. It will be noted also that it is manifestly impossible to suppose that the perfection of a variety, discontinuously and suddenly occurring, is the result of Selection. No doubt it is conceivable that a race of Tulips having their floral parts in multiples of four might be raised by Selection from a specimen having this character, but it is not possible that the perfection of the nascent variety can have been gradually built up by Selection, for it is, in its very beginning, perfect and symmetrical. And if it may be seen thus clearly that the perfection and Symmetry of a variety is not the work of Selection, this fact raises a serious doubt that perhaps the similar perfection and Symmetry of the type did not owe its origin to Selection either. This consideration of course touches only the part that Selection may have played in the first building up of the type and does not affect the view that the perpetuation of the type once constituted, may have been achieved by Selection. But if the perfection and definiteness of the type is not due to Selection but to the physical limitations under which Variation proceeds, we shall hope hereafter to gain some insight into the nature of these limitations, though in the present state of zoological study the prospect of such progress is small. In the observations which follow I am conscious that the bounds of profitable specu- lation are perhaps exceeded, and I am aware that to many this may seem matter for blame; but there is, in my judgment, a plausibility in the views put forward, sufficient at least to entitle them to examination. They are put forward in no sense as a formulated theory, but simply as a suggestion {'or work. It is, besides, only in foreseeing some of the extraordinary possibilities 70 MECHANICAL. [introd. that lie ahead in the Study of Variation, that the great value of this method can be understood. It has been seen that variations may be either Meristic or Substantive, and that in each group discontinuous and definite variations may occur by steps which may be integral or total. We are now seeking the factors which determine this totality and define the forms assumed in Variation. In this attempt we may, by arbitrarily confining our first notice to very simple cases, recog- nize at least two distinct factors which may possibly be concerned in this determination. Of these the first relates to Meristic Variation and the second to Substantive Variation. 1. Possible nature of the Discontinuity of Meristic Variation. Looking at simple cases of Meristic Variation, such as that of the Tulip or of Anrelia, or of the Cockroach tarsus, there is, I think, a fair suggestion that the definiteness of these variations is deter- mined mechanically, and that the patterns into which the tissues of animals are divided represent positions in which the forces that effect the division are in equilibrium. On this view, the lines or planes of division would be regarded as lines or planes at right angles to the directions of the dividing forces ; and in the lines of Meristic Division we are perhaps actually presented with a map of the lines of those forces of attraction and repulsion which determine the number and positions of the repeated parts, and from which Symmetry results. If the Symmetry of a living bod} wore thus recognized as of the same nature as that oi any sym- metrical system of mechanical forces, the definiteness of the sym- metry in Meristic Variation would call for no special remark, and the perfection of the symmetry of a Tulip with its parts divided into four, though occurring suddenly as a " sport," would be recog- nized as in nowise more singular than the symmetry of the type. Both alike would then be seen to owe their perfection to me- chanical conditions and not to Selection or to any other gradual process. If reason for adopting such a view of the physics of Division should appear, the frequency with which in any given form a particular pattern of Division or of Symmetry recurs, would be found to be determined by and to be a measure of the %J stability of the forces of Division when disposed in that particular pattern. It will of course be understood that in these remark- no suggestion is offered as to the causes which determine whether a tissue shall divide into four or into three, but merely as to the conditions of perfection of the division in either case. It will also be clear that though the symmetry of a flower or of any other tissue depends also on symmetrical growth, it is primarily dependent on the symmetry of its primary divisions, upon which symmetrical growth and secondary symmetrica] divisions follow. •sect, xiii.] INTRODUCTION. 71 It would be interesting and I believe profitable to examine somewhat further the curiously close analogy between the sym- metry of bodily Division and that of certain mechanical systems by which close imitations both of linear and of radial segmentation can be produced ; and though to some this might seem overdaring, the possibility that the mechanics of bodily Division are in their visible form of an unsuspected simplicity is so far-reaching that it would be well to use any means which may lead others to ex- plore it. And even if at last this suggestion shall be found to have in it no other element of truth, it would still be of use as a forcible presentation of the fact, which when realized can hardly be doubted, that among the factors which combine to form a living body, the forces of Division may be distinguished as in their mani- festations separable from the rest and forming a definite group. For, already (Section V.) it has been pointed out that the patterns of Division or Merism may be changed, while the Substance of the tissues presents to our senses no difference. The recognition of this essential distinctness of the Meristic forces will, I believe, be found, to supply the base from which the mechanics of growth will hereafter be attacked. The problems of Morphology will thus determine themselves into problems in the physiology of Division, which must be recognized together with Nutrition, Respiration and Metabolism, as a fundamental property of living protoplasm. To sum up : there is a possibility that Meristic Division may be a strictly mechanical phenomenon, and that the perfection and Symmetry of the process, whether in type or in variety, may be an expression of the fact that the forms of the type or of the variety represent positions in which the forces of Division are in a condition of Mechanical Stability. 2. Possible nature of the Discontinuity of Substantive Variation. Passing from the phenomena of Division and arrangement to those of constitution or substance we are, as has been said, again presented with the phenomenon of discontinuous or total Varia- tion, and we must seek for causes which may perhaps govern and limit this totality, and in obedience to which the Variation is thus definite. Now as in the case of Meristic Variation, by arbitrarily limiting the examination to those cases which seem the simplest it appears that there is at least an analogy be- tween them and certain mechanical phenomena, bo by similarly restricting ourselves to very simple cases there will be seen to be a similar analogy between the discontinuity of some Sub- stantive Variations and that of chemical discontinuity. It is on the whole not unreasonable to expect that the definitem — of at least some Substantive Variations depends ultimately on the discontinuity of chemical affinities. To take but one instance, 72 CHEMICAL. [introd. that of colour, we are familiar with the fact that the colours of many organic substances undergo definite changes when chemi- cally acted on by reagents, and it is not suggested that the defmiteness and discontinuity of the various colours assumed is dependent on anything but the defmiteness of the chemical changes undergone. The changes of litmus and many vegetable blues to red on treatment with acids, of many vegetable yellows to brown on treatment with alkalies, the colours of the series of bodies produced by the progressive oxidation of biliverdin are familiar examples of such definite colour-variations. With facts of this kind in view, the conclusion is almost forced on us that the defmiteness of colour-variation is a conse- quence of the defmiteness of the chemical changes undergone. No one doubts that the orange colouring matter of the variety of the Iceland Poppy (P. nudicaule) is a chemical derivative from the yellow colouring matter of the type. It is not ques- tioned that in such cases a definite alteration in the chemical conditions in which the pigment is produced determines whether the flower shall be orange or yellow ; and I think it is reasonable to expect that the frequency with which the flowers are either yellow or orange as compared with the rarity of the intermediate shades is an expression of the fact that the yellow and orange forma of the colouring matter have a greater chemical stability than the intermediate forms of the pigment, or than a mixture of the tun pigments. If then it should happen, as we may fairly suppose it might, that the orange form were to be selected and established as a race, it would owe the defmiteness of its orange colour and the precision of its tint, not to the precision with which Selection had chosen this particular tint, but to the chemical discontinuity of which the originally discontinuous Variation was the expression. To pass from the case of a sport to that of Species, it is well known that of the man}* S. African butterflies of the genus Euchloe ( = Anthocharis, Orange-tips), some have the apices or tips of the fore-wings orange-red (for example, E. danae), while in others they are purple (for example, E. ione). Upon the view that the transition from orange to purple, or vice verm, had been continuously effected by the successive Selection of minute variations, we are met bv all the difficulties we know so well. Why is purple a good colour for this creature ? If purple is a good colour and red is a good colour, how did it happen that at some time or other all the intermediate shades were also good enough to have been selected ? and so on. These and all the cognate difficulties are opened up at once, and though they have been met in the fashion we know, they have scarcely been over- come. But at the outset this view assumes that every inter- mediate may exist and has existed, an assumption which i- gratuitous and hardly in accordance with the known fact thai chemical processes are frequently discontinuous. When besides sect, xiil] INTRODUCTION. 73 this it is known that Variation may be discontinuous, I submit that it is easier to suppose that the change from red to purple was from the first complete, and that the choice offered to Selec- tion was between red and purple ; and that the tints of the purple and of the red were determined by the chemical properties of the body to which the colour is due. This case is a particularly interesting one in the light of the fact that, as Mr F. G. Hopkins has lately shewn me, this purple colour, dissolved in hot water, leaves on evaporation a substance which gives the murexide reaction and cannot as yet be distinguished from the substance similarly derived from the orange or yellow colouring matters of Pieridae in general. As was stated above, Mr Hopkins has shewn that these yellows are acids, allied to mycomelic acid, a derivative of uric acid, and therefore of the nature of excret- ory products. Whether the purple body is related to the yellow or to the orange as a salt is to an acid, or otherwise, cannot yel be affirmed ; but if the difference between them is a chemical difference, which can hardly be doubted, there is at least a pre- sumption that the discontinuity of these colours in the several species, is an expression of the discontinuity of the chemical properties of this body. The possibility that from such bodies a series of substances might perhaps by suitable means be pre- pared in such a way as to represent many or even all intermediate shades, does not greatly affect the suggestion made; for even in such series it is almost certain that points of comparative stability would occur, and Discontinuity would be thus introduced. The case of Colour has been taken in illustration because it is the simplest and most intelligible example of the possibility that the Discontinuity of some Substantive Variations is d. 'tor- mined by the Discontinuity of the chemical processes by which the structures are produced. It is true that perhaps no Bpecies has been rightly differentiated by colour alone, but colour is still one of the many characters which go to the distinguishing of a species, and it is precisely one of the characters whi s significance and delimitation by Natural Selection is most obscure. Moreover by the fact that in the case of these yellow and red Pieridye the colours are of an excretory nature, we are reminded that Variation in colour may be an index of serious changes in the chemical economy of the body, and that when an animal is said to be selected because it is red or because it is purple, the real source of its superiority may be not its red colour or its purple colour, but other bodily conditions of which th< colours are merely symptoms. By those who have attempted to reconcile the phenomena of Colour with the hypothesis of Natural Selection this fact is too often overlooked. But though it may reasonably be supposed that much of the Discontinuity of Variation and some of the Discontinuity of 74 ANALOGY OF DISEASE. [introd. Species arise through discontinuous transition from one state of mechanical or chemical stability to another state of stability, there nevertheless remain large classes of discontinuous variations, and of Specific Differences still more, whose Discontinuity bears no close analogy with these. To these phenomena inorganic Nature offers no parallel. We may see that they are discontinuous and that their course is in some way controlled, but as to the nature of this control we can make no guess. Though the resemblance may be misleading, it is neverthe- less true that in living Nature there are other phenomena, those of disease, which present a Discontinuity closely comparable with that of many variations. In problems of disease we meet again the same problem which we meet in Variation, namely, changes which may be complete or specific, though occurring so suddenly as to exclude the hypothesis that Selection has been the limiting cause. All this is familiar to everyone who has considered the problem of Species. For though, like discontinuous variations, the manifestations of specific disease are not always identical, but differ in intensity and degree, varying about a normal form, still these manifestations maybe specific in the sense in which the term is used with reference to the characters of Species. If we exclude those diseases whose specific characters are now known to be the result of the invasion of specific organisms, there still remain very many which are known and recognized by definite and specific symptoms produced in the body, though there is as yet no evidence that they are due to specific organisms. [Of course if it were shewn that these diseases also result from the action of specific organisms, they then only present to us again the original problem of Species ; for if the definiteness, or Species, of a disease is due to the definiteness, or Species, of the micro-organism which causes it, the cause of that definiteness of the micro-organism remains to be sought, and we are simply left with a particular case of the general problem of Species.] But in the meantime we can see that the manifestations are specific ; and while we do not know that they result from causes themselves specific, the nature of the control in obedience to which they are specific is unknown. The parallel between disease and Variation may be mis- leading, but this much at least may fairly be learned from it : that the system of an organized being is such that the result of its disturbance may be specific. And in the end it may well be that the problem of Species will be solved by the study of pathology ; for the likeness between Variation and disease goes far to support the view which Virchow has forcibly expressed, that " every deviation from the ty pe of the parent animal must have its foundation on a pathological accident 1 ." 1 E. Virchow, Journal of Pathology, I. 1892, p. 12. sect, xiv.] INTRODUCTION. 75 SECTION XIV. Some current conceptions of Biology in view of the facts of Variation. Enough has now been said to explain the aim of the Study of Variation, and to shew the propriety of the choice of the facts of Meristic Variation as a point of departure fur that study. Before leaving this preliminary consideration, reference to some cognate subjects must be made. It has been shewn that in view of the facts of Variation, some conceptions of modern Morphology must be modified, while others must be abandoned. With the recognition of the sig- nificance of the phenomena of Variation, other conceptions of biology will undergo like modifications. As to some of these a few words are now required, if only to explain methods adopted in this work. 1. Heredity. It has been the custom of those who have treated the subject of Evolution to speak of " Heredity ' : and "Variation" as two antagonistic principles ; sometimes even they are spoken of as opposing "forces." With the Study of Variation, such a description of the pro- cesses of Descent will be given up, even as a manner of speaking. In what has gone before I have as far as possible avoided any use of the terms Heredity and Inheritance. These terms which have taken so firm a hold on science and on the popular fancy, have had a mischievous influence on the development of bio- logical thought. They are of course metaphors from the descent of property, and were applied to organic Descent in a time when the nature of the process of reproduction was wholly mis- understood. This metaphor from the descent of property is inadequate chiefly for two reasons. First, by emphasizing the fact that the organization of the offspring depends on material transmitted to it by its parents, the metaphor of Heredity, through an almost inevitable confusion of thought, suggests the idea that the actual body and consti- tution of the parent are thus in some way handed on. No one perhaps would now state the facts in this way, but something very like this material view of Descent was indeed actually de- veloped into Darwin's Theory of Pangenesis. From this sugges- tion that the body of the parent is in some sort remodelled into that of the offspring, a whole series of errors arc derived Chief among these is the assumption that Variation must necessarily be a continuous process; for with the body of the parent to start from, it is hard to conceive the occurrence of discontinuous change. Of the deadlock which has resulted from the attempt 76 REVERSION. [introd. to interpret Homology on this view of Heredity, I have already spoken in Section VI. Secondly, the metaphor of Heredity misrepresents the essential phenomenon of reproduction. In the light of modern investiga- tions, and especially those of Weismann on the continuity of the germ-cells, it is likely that the relation of parent to offspring, if it has any analogy with the succession of property, is rather that of trustee than of testator. Hereafter, perhaps, it may be found possible to replace this false metaphor by some more correct expression, but for our present purpose this is not yet necessary. In the first exami- nation of the facts of Variation, I believe it is best to attempt no particular consideration of the working of Heredity. The phenomena of Variation and the origin of a variety must necessarily be studied first, while the question of the perpetua- tion of the variety properly forms a distinct subject. Whenever in the cases given, observations respecting inheritance are forth- coming they will be of course mentioned. But speaking of dis- continuous Variation in general, the recurrence of a variation in offspring, either in the original form or in some modification of it, has been seen in so many cases, that we shall not go far wrong in at least assuming the possibility that it nun/ nappear in the offspring. At the present moment, indeed, to this state- ment there is little to add. So long as systematic experiments in breeding are wanting, and so long as the attention of naturalists is limited to the study of normal forms, in this part of biology which is perhaps of greater theoretical and even practical im- portance than any other, there can be no progress. 2. Reversion. Around the term Reversion a singular set of false ideas have gathered themselves. On the hypothesis that all perfection and completeness of form or of correlation of parts is the work of Selection it is difficult to explain the discontinuous occurrence of new forms possessing such perfection and completeness. To account for these, the hypothesis of Reversion to an ancestral form is proposed, and with some has found favour. That this suggestion is inadmissible is shewn at once by the frequent occur- rence by discontinuous Variation, of forms which though equally perfect, cannot all be ancestral. In the case of Veronica and Liiuiria, for example, a host of symmetrical forms of the floral organs may be seen occurring suddenly as sports, and of these though any one may conceivably have been ancestral, the same cannot be supposed of all, for their forms are mutually exclusive. On Veronica buxbaumii, for instance, are many symmetrical tlowers, having two posterior petals, like those of other Scrophu- larinese : these may reasonably be supposed to be ancestral, but sect, xiv.] INTRODUCTION. 77 if this supposition is made, it cannot be made again for the equally perfect forms with three petals, and the rest 1 . The hypothesis of Reversion to account for the Symmetry and perfection of modern or discontinuous Variation is made through a total misconception of the nature of Symmetry. There is a famous passage in the Descent of Man, in which Darwin argues that the phenomenon of double uterus, from its perfection, must necessarily be a Reversion. "In other and rarer cases, two distinct uterine cavities are formed, each having its proper orifice and passage. No such stage is passed through during the ordinary development of the embryo, and it is difficult to believe, though perhaps not impossible, that the two simple, minute, primitive tubes could know how (if such an expression may be used) to grow into two distinct uteri, each with a well- constructed orifice and passage, and each furnished with numerous muscles, nerves, glands and vessels, if they had not formerly passed through a similar course of development, as in the case of existing marsupials. No one will pretend that bo perfect a structure as the abnormal double uterus in woman could be the result of mere chance. But the principle of reversion, by which Long-lost dormant structures are called back into existence, might serve as the guide for the full development of the organ, even after the lapse of an enormous interval of time-." Descent of Man, vol. I. pp. 123 and 124. This kind of reasoning has been used by others again and again. It is of course quite inadmissible; for by identical reason- ing from the perfect symmetry of double monsters, of the si ugh- eye of the Cyclopian monster, and so on, it might be shewn th.it Man is descended from a primitive double vertebrate, from a one-eyed Cyclops and the like. For other reasons it is likely enough that double uterus was a primitive form; but the per- fection and symmetry of the modern variation to this form is neither proof nor indication of such an origin. Such a belief arises from want of knowledge of the facts of Meristic Variation, and is founded on a wrong conception of the nature of symmetry and of the mechanics of Division. The study of Variation shews that it is a common occurrence for a part which stands in the middle line of a bilaterally symmetrical animal, to divide into two parts, each being an optical image of the other: and thai conversely, parts which normally are double, standing as optical images of each other on either side of such a middle line may 1 For a full account of such facts, see a paper by Miss A. Bateson and myself On Variations in Floral Symmetry. Journ. Linn. Soc, xxvui. p, 386. 2 This extraordinary passage is scarcely worthy of Darwin's penetration. If read in the original connexion it will seem strange that it should have been allowed to stand. For in a note to these reflexions on Reversion [Descent, i. i>. L25) Darwin refers to and withdraws his previously expressed view that supernumerary digits and mamma? were to be regarded as reversions. This view had been based on I perfection and symmetry with which these variations reproduce the structure of putative ancestors. It was withdrawn because Gegenbaur had shewn that poly* dactyle limbs often bear no resemblance to those of possible ancestors, and I extra mammae may not only occur symmetrically and in places where they are normal in other forms, but also in several quite anomalous situations. In the light of this knowledge it is strange that Darwin should have continued to regard the perfection and symmetry of a variation as evidence that it is a Reversion. 78 CAUSES OF VARIATION. [introd. be compounded together in the middle line forming a single, symmetrical organ. It would probably help the science of Biology if the word 'Reversion' and the ideas which it denotes, were wholly dropped, at all events until Variation has been studied much more fully than it has yet been. In the light of what we now know of the process of repro- duction the phrase is almost meaningless. We suppose that a certain stock gives off a number of individuals which vary about a normal ; and that after having given them off, it begins to give off individuals varying about another normal. We want to say that among these it now and then gives off one which approaches the first normal, that shooting at the new mark it now and then hits the old one. But all that we know is that now and then it shoots wide and hits another mark, and we assume from this that it would not have hit it if it had not aimed at it in a bygone age. To apply this to any other matter would be absurd. We might as well say that a bubble would not be round if the air in it had not learned the trick of round- ness by having been in a bubble before : that if in a bag after pulling out a lot of white balls I find a totally red one, this proves that the bag must have once been full of red balls, or that the white ones must all have been red in the past. Besides the logical absurdity <»n which this use of the theory of Reversion rests, the application of it to the facts of \ a nation breaks down again and again. I have already mentioned some cases of this, but there are manv others of a different class. For instance, it will be shewn that the percentage of extra molars in the Anthropoid Apes is almost the highest reached among mammals. On the usual interpretation, such teeth are due to Reversion to an ancestral condition with 4 molars, and on less evidence it has been argued that a form frequently shewing such " Reversion " is older than those which do not. From this reason- ing it should follow that the Anthropoids are the most primitive form, at least of monkeys. It is surely time that these brilliant and facile deductions wore no more made in the name of science. 3. Causes of Variation. Inquiry into the causes of Variation is as yet, in my judgment, premature. 4. The Variability of" useless" Structu?*es. The often-repeated statement that "useless" parts are especially variable, finds little support in the facts of Variation, except in as far as it is a misrepresentation of another principle. The examples taken to support this statement are commonly organs standing at the end of a Meristic Series of parts, in which sect, xiv.] INTRODUCTION. 79 there is a progression or increase of size and degree of development, starting from a small terminal member. In such cases, as that of the last rib in Man, and several other animals, the wisdom-teeth of Man, etc., it is quite true that in the terminal member Variation is more noticeable than it is in the other members. This is, I believe, a consequence of the mechanics of Division, and has no connexion with the fact that the functions of such terminal parts are often trifling. Upon this subject something will be said later on, but perhaps a rough illustration may make the meaning more clear at this stage. If a spindle-shaped loaf of bread, such as a " twist," be divided with three cuts taken at equal distances, in such a way that the two end pieces are much shorter than the middle ones, to a child who gets one of the two large middle pieces the contour-curves of the loaf will not matter so much ; but to a child who gets one of the small end bits, a very slight altera- tion in the curves of the loaf will make the difference between a fair-sized bit and almost nothing, a difference which the child will perceive much more readily than the complementary difference in the large pieces will be seen by the others. An error in some measure comparable with this is probably at the bottom of the statement that useless parts are variable, but of course there are many examples, as the pinna of the human ear, which are of a different nature. It is unnecessary to say that for any such case in which a part, apparently useless, is variable, another can be produced in which some capital organ is also variable ; and conversely, that for any case of a capital organ w r hich is lit t If subject to Variation can be produced a case of an organ, which though trifling and seemingly "useless," is equally constant. With a knowledge of the facts of Variation, all these trite generali- ties will be forgotten. o. Adaptation. In examining cases of Variation, I have not thought it neces- sary to speculate on the usefulness or harmfulness of the variations described. For reasons given in Section II, such speculation, whether applied to normal structures, or to Variation, is barren and profitless. If any one is curious on these questions of Adaptation, he may easily thus exercise his imagination. In any case of Variation there are a hundred ways in which it may 1»' beneficial, or detrimental. For instance, if the " hairy" variety of the moor- hen became established on an island, as many strange varieties have been, I do not doubt that ingenious persons would invite us to see how the hairiness fitted the bird in some special way tor life in that island in particular. Their contention would he hard t<> deny, for on this class of speculation the only limitations are those of the ingenuity of the author. While the only test of utility is the success of the organism, even this does not indicate the utility 80 NATURAL SELECTION. [ixtrod. of one part of the economy, but rather the nett fitness of the whole. 6. Natural Selection. In the view of the phenomena of Variation here outlined, there is nothing which is in any way opposed to the theory of the origin of Species " by means of Natural Selection, or the preserva- tion of favoured races in the struggle for life." But by a full and unwavering belief in the doctrine as originally expressed, we shall in no way be committed to representations of that doctrine made by those who have come after. A very brief study of the facts will suffice to gainsay such statements as, for example, that of Claus, that "it is only natural selection which accumulates those altera- tions, so that tliey become appreciable to us and constitute a varia- tion which is evident to our senses 1 ." For the crude belief that living beings are plastic conglomerates of miscellaneous attributes, and that order of form or Symmetry have been impressed upon this medley by Selection alone ; and that by Variation any of these attributes may be subtracted or any other attribute added in indefinite proportion, is a fancy which the Study of Variation does not support. Here this Introduction must end. As a sketch of a part of the phenomena of Variation, it has no value except in so far as it may lead some to study those phenomena. That the study of Variation is the proper field for the development of biology there can be no doubt. It is scarcely too much to say that the study of Variation bears to the science of Evolution a relation somewhat comparable with that which the study of affinities and reactions bears to the science of chemistry: for we might almost as well seek for tin- origin of chemical bodies by the comparative study of crystallo- graphy, as for the origin of living bodies by a comparative study of normal forms. 1 Text-book of Zoology, Sedgwick and Heathcote's English translation, vol. i. p. 148. In the original the passage runs: " erst die naturliche Zuchtwahl haufi und verstarkt jew Abweichungen in dem Masse dass sie fur mis wahmehmbar werden und eine in die Augen fallende Variation bewirken." C. Claus, Lehrb. d. Zool., Ed. 2, 1883, p. 127, and Grundztige der Zoologie, 1880, Bd. i. p. 90. The italics are in the original. PART I. MERISTIC VARIATION. B. CHAPTER I. ARRANGEMENT OF EVIDENCE. The cases of Meristic Variation, here given, illustrate only a small part of the subject. The principles upon which these have been chosen may be briefly explained. It was originally intended to give samples of the evidence relating to as many different parts of the subject as possible, so that the ground to be eventual lv covered might be mapped out, leaving the separate sections of evidence to be amplified as observations accumulate. This plan would be the most logical and perhaps in the end the most useful, but for several reasons it has been abandoned. I have chosen ;i different course, first, because during the progress of the work opportunities occurred for developing special parts of the evidence; secondly, since isolated observations have no interest for most persons, it is more likely that the importance of the subject will be appreciated in a fuller treatment of special sections, than in a general view of the whole ; and lastly, because as yet the attempt to make an orderly or logical classification of the phenomena <>f Merism, however attractive, must be so imperfect as to be alm<»M worthless. For these reasons I have decided to treat more fullv a few sections of the facts, hoping that in the course of time similar treatment may be applied to other sections also. The sections have been chosen either because there is a fairly large body <>t evidence relating to them, or on account of the importance or novelty of the principles illustrated. As far as possible I have described each case separately, in terms applicable specially to it, deductions or criticism being kepi apart. The descriptions are written as if for an imaginary cata- logue of a Museum in which the objects might be displayed 1 . This system, though it entails repetition, has, I believe, advantag - which cannot be attained when the descriptions are given in a comprehensive and continuous form. In speaking of subjects, such as supernumerary mamma 1 , or cervical Rstulse, where the evidence has been exhaustively treated by others, and upon which 1 can add nothing, it has not seemed necessary to follow this system, and in such cases connected abstracts are given. 1 Cases of special importance are marked by an asterisk. 6—2 84 MERISTIC VARIATION. [part i. As the evidence here presented consists, as yet, only of speci- men chapters in the Natural History of Meristic Variation, and does not offer any comprehensive view of the whole subject, no strict classification of the facts is attempted. The evidence of Meristic Variation relates essentially to the manner in which changes occur in the number of members in Meristic series. Such numerical changes may come about in two ways, which are in some respects distinct from each other. For instance, the number of legs and body-segments in Peripatus edivardsii varies from 29 to 34 1 : here the variation in number must be a manifestation of an original difference in the manner of division or segmentation in the progress of development. The change is strictly Meristic or divisional. On the other hand, change in number may arise by the Substantive Variation of members of a Meristic series already constituted. For example, the evidence will shew that the number of oviducal openings in Astacus may be increased from one pair to two or even three pairs. Here the numerical variation has come about through the assumption by the penultimate and last thoracic appendages, of a character typically proper to the append- ages of the antepenultimate segment of the thorax alone. Now there is here no change in the number <»f segments composing the Meristic series, but by Substantive Variation the number of openings has been increased. The case of the modification of the antenna of an insect into a foot, of the eye of a Crustacean into an antenna, of a petal into a stamen, and the like, are examples of the same kind. It is desirable and indeed necessary that such Variations, which consist in the assumption by one member of a Meristic series, of the form or characters proper to other members of the series, should be recognized as constituting a distinct group of phenomena. In the case of plants such Variation is very common and is one of the most familiar forms of abnormality. Masters, in his treatise on Vegetable Teratology 2 , recognizes this phenomenon and gives to it the name "Metamorphy," adopting the word from Goethe. As Masters says, so long as it is only proposed to use the word in Teratology, no great confusion need arise from the fact that the same term and its derivatives are used in a different sense in several branches of Natural History. But if, as I hope, the time has come when the facts of what has been called '"Tera- tology" will be admitted to their proper place in the Study of Variation, this confusion is inevitable. In this study, besides, this particular kind of variation will be found to be especially impor- tant and I believe that in the future its significance and the mod,' of its occurrence will become an object of high interest. For this reason it is desirable that the term which denotes it should not lead to misunderstanding, and I think a new term is demanded. 1 Sedgwick, A., Quart. Jour. Micr. Sri., 1888, xxvm. p. 467. 2 Masters, M. T., Vegetable Teratology, p. 239. chap. I.] ARRANGEMENT OF EVIDENCE. 85 For the word 'Metamorphy' I therefore propose to substitute the term Homoeosis, which is also more correct; for the essential phenomenon is not that there has merely been a change, but that something has been changed into the likeness of something else In the cases given above, the distinction between Homceotic Variation and strictly Meristic Variation is sufficiently obvious, but many numerical changes occur which cannot be referred with certainty to the one class rather than to the other. Such cas are for the most part seen in Vertebrates: for in them what may be called the fun da mental numbers of the segments are not consti- tuted with the definiteness found in Arthropods or in the Annelids, and several Meristic series of organs are disposed in numbers and positions independent of, or at least having no obvious relation bo those of the other Meristic series. The number and positions of mammae, or stripes, for instance, need not bear any visible relation to the segmentation of the vertebrae &c. The repetition of mem- bers of such a series may thus not coincide with, or occur in mul- tiples of the segmentation of other parts in the same region. When such is the case, when the segmentation of one series of organs bears no simple or constant geometrical relation to the segmenta- tion of other systems, it is not always possible to declare whether a numerical change in one of the systems of organs belongs properly to the first or the second of the classes described abow. It is likely enough that in such a case as that of mammas there may sometimes be an actual Meristic division and subsequent separation of the tissues already destined to form the mamma?, occurring in such a way that each comes to take up its final position, and indeed the numerous cases in which such division has been imperfectly effected go far to prove that this is the case. But, on the other hand, it is not possible to know that the division did no1 occur before any tissue was specially differentiated off to form mammae, and that the separation may be as old even as the division of the mamma? of the right side from those of the left, a process which almost beyond question occurs in the segmentation of the ovum. The distinction between these two alternatives is thus one rather of degree than of kind, and it is only in such forms as the Arthropods, the floral organs of some Phanerogams and the like, where the members of the several Meristic series have definite numbers, or coincide with each other, that this distinction is easily recognized. For this reason 1 do not think it well to at tempt to carry out any classification of the evidence based on this dis- tinction. In the foregoing remarks I am aware that a very large question, which lies at the root of all accurate study of Meristic Variation, has been passed over somewhat superficially, but I scarcely think a fuller treatment possible in the present state of knowledge of the physics of Division, and in the absence of thorough observation of the developmental history of those tissues which ultimately 86 MERISTIC VARIATION. [PABT I. become differentiated to form members of such non-coincident or independent Meristic series. Some years ago 1 , in the course of an argument that Balanoglossus should be considered as representing some of the ancestral characters of Chordata, I had occasion to refer to some of these difficulties, and especially to the different characters of the two kinds of segmentation ; that of the Annelids, in which the repetitions of the organs belonging to the several systems are coincident, and, on the other hand, that of the Chordata, for example, in which this coincidence may be irregular or partial. At that time I was of opinion that these two sorts of segmentation may, in certain cases, have had a different phylogenetic history, and have resulted from processes essentially distinct. It appeared to me that we should recognize that, in the Annelids on the one hand, segmentation of the various systems of organs had been coincident from the beginning, while in the Chordata the segmentation had been progressive and had arisen by segmentation or repetition of the organs of the several systems independently. The reasons for this view were derived chiefly from the fact that it is possible to arrange the lower Chordata in order of progressive segmen- tation of the several systems. In particular such treatment was shewn to be applicable to the central nervous system, the vertebral column and the mesoblastic somites, and in these cases it was maintained that the evidence of the lower forms of Chordata goes to shew that segmen- tation had occurred in these systems one after another, and that their segmentation was not derived from a form having a complete repetition of each part in each segment : that these forms, in fact, shewed us tin- history of this progress from a less segmented form to one more fully segmented. The views then set forth have met with little acceptance. Those who are occupied with the search for the pedigree of Vertebrates still direct their inquiries on the hypothesis, expressed or implied, that in the ancestral form there was a series of complete segments, each containing a representative of each system of those organs which in the present descendants appear in series. It is thus supposed that each segment of the primitive form must have been a kind of least common denominator of the segments of its posterity. The possibility that the segmentation of Vertebrates may have arisen progressively is, indeed, scarcely considered at all. Though in the light of the study of Variation, it now seems to me that the discussion of these questions must be indefinitely post- poned, and that there are radical objections to any attempt to interpret the facts of anatomy and development in our present ignorance of Variation, I have seen no reason to depart from the view expressed in the paper referred to : that interpreted by the current methods of morphological criticism, the facts go to shew that the segmentation of the Chordata differs essentially from that of the Annelids drc, and that it has arisen by progressive segmentation of the several systems of an originally unsegmented form. T<> those who hold as Dohrn, Gaskell. Marshall and others have done, that the evolution of Vertebrates has 1 Quart. Jour. Micr. Set, 1886. chap. I.] ARRANGEMENT OF EVIDENCE. 87 been a progress from a more fully segmented form to forms less seg- mented, I would again point out that this view is in direct opposition to the indications afforded by the lower Chordata, which are less and not more segmented than the higher forms. The hypothesis of an ancestor made up of complete segments is resorted to because it is felt to be difficult to conceive the progressiva building up of a segmented form, but on appeal to the facts of Variation the evidence will clearly shew that Repetition of parts previously (wilt- ing is a quite common phenomenon; that such repetition may occur in almost any system of organs; and lastly that such new repetitions may be coincident in the several systems. To argue moreover that these repetitions, for instance that of oviducal apertures in Astacus, of mammas or cervical ribs in mammals are "reversions," leads to ab- surdity, for on the same reasoning, the occurrence, in the Crab, of a third maxillipede formed as a chela, would shew that these appendages had been originally chehe, that the occurrence of petaloid sepals shews that the sepals had originally been petals, and so forth. These considerations will suffice to illustrate the great difference of degree, if not of kind, which probably exists between these two kinds of segmentation, that which arises by the repetition of bud- like segments, each containing parts of many systems on the one hand, and the progressive and separate segmentation of the several systems on the other. For reasons already given, however, I shall not attempt in this first collection of evidence to separate the facts on these lines. Though some cases can at once be seen to be strictly Meristic while others are plainly Homceotic, many cannot be affirmed to belong to the one group rather than to the other. There is, besides, a serious doubt whether perhaps after all, Homceotic Variation even in its most marked forms, may Dot ultimately rest on and be an expression of a change in the pro- cesses of Division, and be thus, at bottom, strictly Meristic also. In our present ignorance of the physics of Division, this doubt cannot be satisfied, and therefore it will be best to make no definite separation between the two classes of variations, though whenever the nature of a given variation is such that it may at once be recognised as Homceotic, it will be well to specify this. In the absence of a more natural classification, the material has been roughly arranged with reference to the geometrical disposition and relations of the structures concerned. In the Introduction, Section IV. p. 21, reference was made to the (aft that the Symmetry of an organism may be such as to include all the parts into one system of Symmetry, and for such a system the term Major Symmetry was proposed. Systems of this kind are seen in the Vertebrates and Echinoderms, for example. On the other hand systems of Symmetry occur in limbs and other separate parts of organisms, in such a way that each such system is either altogether or partially geometrically complete and symmetrical in itself. For example, the toe of a Horse, the arm of a Starfish, the 88 MERISTIC VARIATION. [part I. \ eye-spots of some Satyrid butterflies, &c, are each in themselves nearly symmetrical. To these separate systems of Symmetry the term Minor Symmetry will be applied. Minor Symmetries may or may not be compounded into a Major Symmetry. Between these there is of course no hard and fast line. In each class of Symmetry, Meristic Repetition may occur, and the repeated parts then stand in either I. Linear or Successive Series. II. Bilateral or Paired Series. III. Radial Series. Parts meristically repeated may thus stand in one or more geometrical relations to each other, and the first part of the evidence of Meristic Variation will be arranged in groups according as it is in one or other of these relations that the parts are affected. In each group cases affecting Major Symmetry will be given first, and those affecting Minor Symmetries will be taken after. As it is proposed to arrange the facts of Meristic Variation in groups corresponding with these three forms of Meristic Repetition, it will be useful to consider briefly the nature of the relation in which the members of such series stand to each other, and the characters distinguishing the several kinds of series. Reduced to the simplest terms, the distinction may be thus expressed. In the Linear or Successive series the adjacent parts of any two consecutive members of the series are not homologous, but the severally homologous parts of each member or segment form a successive series, alternating with each other. For example, the anterior and posterior surfaces of such a series of segments may be represented by the series A ,AP, AP, AP, P. The relation of any pair of organs in Bilateral Symmetry differs from this, for in that case each member of the pair jwesents to its fellow of the opposite side parts homologous with those which it* fellow presents to it, each being, in structure and i>osition, an optical image of the other. The external and internal surfaces of such a pair may therefore be represented thus : E 1,1 E. If the manner of origin of these two kinds of Repetition be considered, it will be seen that though both result from a process of Division, yet the manner of Division in the two cases is very different. For in the case of division to form a paired structure, the process occurs in such a way as to form a pair of images, of which similar and homologous parts lie on each side of the plane of division ; while, in the formation of a chain of successive fluents, each plane of division passes between parts which are dissimilar, and whose homology is alternate. The distinction between these two kinds of Division is of course an expression of the fact that the attractions and repulsions from which Division chap. I.] ARRANGEMENT OF EVIDENCE. 89 results are differently disposed in the two cases. It is further to be observed that the distinction, though striking, is nevertheli & one of degree, for the two kinds of Division pass gradually into each other. By one or other of these two modes, or by a combin- ation of both, all Meristic Series of Repetitions are formed In Radial series, the Major Symmetry is built up by radial divisions of the first kind, producing segments whose adjacent parts are homologous, and related to each other as images. Each of these segments is therefore bilaterally symmetrical about a radial plane. There is no succession between the segments, and in a perfectly symmetrical series, Successive or Linear repetitions can only occur in Minor Systems of Symmetry. The considerations here set forth, though well known, have an importance in the interpretation of the evidence, for the connexion between the geometrical relations of organs and their Meristic Variations is intimate. An arrangement of the facts with reference to these geometrical relations cannot, of course, be absolute, for it is clear that a Bilateral Symmetry, containing Linear Repetitions may be derived from a Radial Symmetry, and that these figures cannot be precisely delimited from each other; nevertheless this plan of arrangement has still several advantages. Chief among these is this : that it brings out and emphasizes the fact that the possible, or at least the probable Meristic Variations of such parts depend closely on the r/eometrical relation in which they stand. This is, perhaps, in a word, the first great deduction from the facts of Meristic Variation. The capacity for, and manner of Meristic Variation appear to depend not on the physiological nature of the part, on the system to which it belongs, on the habits of the organism, on the Deeds or exigencies of its life, but on this fact of the geometrical position of the parts concerned. Linear series are liable to certain sorts of Variation, Bilateral Series are liable to other sorts of Variation, and Radial Series to others again. As 1 have ventured to hint before, the importance of all this lies in the glimpse which is thus afforded us of the essential nature of Meristic Division and Repetition. Such interdependence between the geometrical re- lations, or pattern, in which a part stands, and the kinds of Variation of which it is capable, is, I think, a strong indication that in Meristic Division we are dealing with a phenomenon which in its essential nature is mechanical. Since this is a thing of the highest importance, it will be useful to employ a system which shall give it full expression. Evidence as to Meristic Variation in cell-division and in the segmentation of ova will bespoken of in connexion with the Varia- tion of Radial and Bilateral series. The second section of evidence is less immediately relevant to the problem of Species; nevertheless it bears bo closely on the nature of Merism and on the mechanics of Physiological Division, 90 MERISTIC VARIATION. [part i. that in any study of this subject reference to it cannot be omitted. The evidence in question relates first to abnormal repetition of limbs or other peripheral structures, (which in the normal form are grouped into and form part of a system of Symmetry,) such ab- normal repetitions occurring in such a way as to lie outside tin's normal system of Symmetry and unbalanced by any parts within it. This phenomenon occurs in many forms, especially in bilateral animals, and may be exceptionally well studied in the case of supernumerary limbs in Insects and in supernumerary chelte in Crabs and Lobsters. It will be shewn that such extra parts generally, if not always, make up a Secondary system of Symmetry in themselves ; and the way in which such a Secondary system is related to the normal or Primary system of Symmetry of the body from which they spring, constitutes an instructive chapter in the study of Meristic Variation. More extensive repetitions of this class, when affecting the axial parts of the body, give rise to the well-known Double and Triple Monsters, which, as has often been said, reproduce in tin- higher animals phenomena which, under the name of fission, are commonly seen in the lower forms. The general evidence as to these abnormalities is so accessible and familiar that it need not be detailed here, and it will therefore be enough to give an outline of its chief features and to point out the bearing of this class of evidence on the subject of Meristic Variation in general. CHAPTER II. meristic variation of parts repeated in linear ob successive series. Segments of Arthropoda. Individual Variation in the fundamental number of members constituting a Linear Series of segments can only be recognized in those forms which at some definite stage in their existence cease to add to the number of the series. Hence in a large proportion of the more fully segmented invertebrates this phenomenon cannot be studied, for in many of these, as for instance in Chilognatha and in most of the Chaetopoda the formation of new segments is not known to cease at any period of life, but seems to continue in- definitely. On the other hand, while in Insecta, and in Crustacea excepting the Phyllopods, the fundamental numbers are definite, no case of individual Variation in them has been observed. Between these two extremes, there are animals in certain classes, for example, Peripatus, some of the Chilopoda among Myriapods, Aphroditidae among Annelids, and sonic of tin- Hran- chiopoda among Crustacea, in which the number of segments do< a not increase indefinitely during life, but is nevertheless not so immutable as in the Insects and the majority of Crustacea. In the forms mentioned, certain numbers of segments, though not the same for the whole family, are characteristic of certain genera, as in the case of the Chilopoda (excepting I reophilidae), or of certain species, as in some of the Peripati. But besides this, in some oi the forms named, e.g., the Geophili and Peripatus edwardsii, indi- vidual Variation has been recorded among members of the same species. It is unfortunate that for many of the forms in which Variation of this kind possibly takes place no Bufficienl observa- tion on the point has been made, but as examples of a phenomenon which, on any hypothesis, must have played a chief part in the evolution of these animals, the few available instances are oi in- terest. *1. Peripatus. The number of segments which have claw-bearing ambulatory legs differs in different species of this genus. Y\ hile, 92 MERISTIC VARIATION. [part i. moreover, in some of the species the number appears to be very constant for the species, in the case of others, great individual variation is seen to occur. Sedgwick's observations in the case of P. edwardii shew conclusively that these variations cannot be ascribed to difference in age. There is besides no ground for sup- posing that increase in the number of legs occurs in any species after birth, and it is in fact practically certain that this is not the case. In Peripatus capensis, which was exhaustively studied by Sedgwick, the appendages arise in the embryo successively from before backwards, the most posterior being the last to appear, and the full number is reached when the embryo arrives at Sedgwick's Stage G. The following is taken from the list constructed by Sedgwick from all sources, including his own observations. As the bibliography given by him is complete and easily accessible it is not repeated here, and the reader is referred to Sedgwick's monograph for reference to the original authorities. Sedgwick, A., Quart. Jour. Micr. Sci. xxviii., 1888, pp. 431 — 493. Plates. South African Species. P. capensis : 17 pairs of claw-bearing ambulatory legs (Table Mountain, S. Africa). P. balfouri : 18 pairs of legs, of which the last pair is rudiment- ary (Table Mountain, S. Africa). Sedgwick has examined more than 1000 specimens from the Cape, and has only seen one specimen with more than 18 pairs of legs. This individual had 20 pairs, the last pair being rudiment- ary. It closely resembled P. balfouri, but differed in the number of legs and in certain other details (q. v.); Sedgwick regarded this form provisionally as a variety of P. balfouri. P. mosleyi : 21 and 22 pairs of legs: near Williamstown, S. Africa. The specimens with 22 legs were two in number and were both females. They differed in certain other particulars from the form with 21 legs, but on the whole Sedgwick regards them as a variety of the same species. P. brevis (DE Blainville): 14 pairs of legs. (This species not seen by Sedgwick.) Other species from S. Africa which have been less fully studied are stated to have 19, 21 and 22 pairs of legs respectively. In all South African forms, irrespective of the number of legs, the generative opening is subterminal and is placed behind the last pair of fully developed legs (between the 18th or rudimentary pair in P. balfouri). Sedgwick, pp. 440 and 451. Australasian Species. P. v one- Zealand ice. 15 pairs of legs. New Zealand. P. leuckartii. 15 pair of legs. Queensland. In both of these species the generative opening is between the last pair of legs. (Sedgwick, p. 486.) chap, il] SEGMENTS OF ARTHROPOD A. 93 Neotropical Species. In all the Neotropical Species which have been at all fully ex- amined, the number of legs varies among individuals of the same species. P. edward&ii: number of pairs of legs variable, the smallest number being 29 pairs, and the greatest number being 34. Males with 29 and 30 pairs of legs. The females are larger, and have a greater number of legs than the males. The new-born young differ in the same way. From 4 females each having 29 legs, seven embryos were taken which were practi- cally fully developed. Of these, 4 had 25) legs, 2 had 34, 1 had 32. An embryo with 29 and one with 30 were found in the same mother. An embryo, quite immature, but possessing the full number of legs, was found with a larger number of legs than one which occupied the part of the uterus next to the external opening. (Caracas. | Peripatus demeraranus : 7 adult specimens had 30 pairs of legs; 6 had 31 pairs; 1 had 27 pairs. Out of 13 embryos ex- amined, 7 have 30 pairs and 6 had 31. (Demerara.) Peripatus trinidadensis : 28 to 31 pairs of ambulatory legs. (Trinidad.) Peripatus torquatus : 41 to 42 pairs. (Trinidad.) Specimens of other less fully known species are recorded as having respectively, 19, 28, 30, 32, 36 pairs of legs, &c. In the Neotropical Species, irrespective of the number of legs, the generative opening is placed between the legs of the penulti- mate pair. (Sedgwick, p. 487.) Peripatus (jidiformis?) from St Vincent: six specimens ex- amined. Of these, 1 specimen had 34 pairs of legs, 2 had 32 pairs. 1 had 30 pairs, and 1 had 29 pairs. Pocock, R. I., Nature } 1892, xlvi. p. 100. In connexion with the case of Peripatus, the following evidence may be given, though very imperfect and incomplete. 2. Myriapoda. Chilognatha. Variation in the number of segments composing the body in this division of Myriapoda cannot be observed with certainty; foritisnotpossibletoeliniin.it.' changes in number due to age, nevertheless the manner in which this increase occurs has a bearing on the subject. In Jidus terrestris the number of segments is increased al each moult by growth of new segments between the lately formed antepen- ultimate segment and the permanent penultimate segment At each of the earlier moults six new segments are here added: in Blaniulua the number thus added is four, and in Polydesmus? two fresh segments are formed at each of the earlier moult-. In each of these forms the number added is the same at each of the earlier moults. Newport, G., Phil. Trans., 1841, pp. 129 and 130. Chilopoda. The number of Leg-bearing Begments differs in the several genera of Chilopoda, but except in the Gkophilidse the number proper to each genus is a constant character. For instance in Lithobiw 94 MERISTIC VARIATION. [part i. this number is 15; in Scolopendra it is 21; in Scolopendrops, 23; in Cryptops 21, &c. In Geophilidse, however, the total number of moveable segments is much larger, ranging from about 35 to more than 200. Though not characteristic of genera, the number seems within limits to mark each particular species. It was found that male Geophili have fewer segments than the female. The males of Arthronomalus longicornis have 51 or 52 leg-bearing segments, while females usually have 53 or 54. Full- grown females of Geophilus terrestris have 83 or 84 pairs of legs and segments, and the males of the same species have 81 or 82. In a large Neapolitan species, Geophilus Icevigatus Bruhl. 1 the variation is rather greater. In eight males the number varied between 96 and 99; in eleven females, between 103 and 107. Of two female Geophilus sulcatus one individual had 136 and the other 140. Newport, G., Trans. Linn. Soc, xix. 1845, p. 427, &c. [In some of the Chilopoda 1 an increase in the number of segments takes place after the larva hatches, but the variations mentioned above are recorded as occurring in fully formed specimens independently of changes due to age.] In the foregoing cases, a fact which is often met in the Study of Variation is well seen. It often happens that in particular genera or in particular species, a considerable range of Meristic Variation is found, while in closely allied forms there is little or none. Examples of this are seen in the variability of the Geophi- lidae as compared with the other Chilopoda, and in the neo-tropical species of Peripatus which vary in the number of legs, while P. balfouri, for instance, is very constant. It will !».• noticed that in both these cases, the absolute numbers of parts repeated are con- siderably higher in the variable than in the constant forms. But though such cases have given rise to general statements that series of organs containing a small number of members are, as such, less variable than series containing more members, these statements require considerable modification ; for it is not difficult to give instances both in plants and in animals, where series made up of a small number of members, shew great meristic variability. The bearings of these cases on the nature of Meristic Repetition and the conception of Homology will be considered hereafter. Here, however, it may be well to call attention to the fact that we have now before us cases in which various but characteristic num- bers of legs or segments differentiate allied species or genera ; that in assuming the truth of the Doctrine of Descent, we have ex- pressed our belief that in each case the species with diverse num- bers are descended from some common ancestor. In the evolution of these forms, therefore, the number has varied : this on the one hand. On the other hand, in GeopJtilus and in Peripatus, we see 1 According to Newport (Trans. Linn. Soc. xix. 1845, p. 268), all Myriapoda .acquire a periodical addition of segments and legs, but according to later observi i a this is not true of all the Chilopodu. chap. II.] SEGMENTS OF ARTHROPODA. 95 contemporary instances of the way in which such a change at its origin may be brought about. Though there are several things to be gained by study of these instances, one feature of them calls for attention now, namely, the definiteness of the variations recorded. The change from a form with one number to a form with another number here shews itself not as an infinitesimal addition or sub- traction, but as a definite, discontinuous and integral change, pro- ducing it may be, as in Peripatus edwardsti, a variation amounting to several pairs of legs, properly formed, at one step of Descent. This will not be seen always to be the case, but it is none the less to be noted that it is so here. Among Insects I know no case of such individual variation in the fundamental number of segments composing the body. Among Crustacea two somewhat remarkable examples must be mentioned, though it will be seen that both of them belong to categories very different from that with which we are now concerned. But in- asmuch as they relate to the general subject of Meristic Variation they should not be omitted. 3. Carcinus maenas. The abdomen of these crabs consists normally of seven segments, including the last or telson. In the female the divisions between all these seven are very distinct. The abdomen of the normal male is much narrower than that of the female, and in it the divisions between the 3rd, 4th and 5th segments are obliterated. Males, however, which are inhabited by the Rhizo- cephalous parasite Sacculina do not acquire these sexual characters, and in them there are distinct divisions between the 3rd, -4th and 5th segments. (Fig. '.• c. I Fig. 9. A. Abdomen of Carcinus mamas, female, normal. B. Abdomen of male, normal. C. Abdomen of male infested by Sacculina. After Giabb and Bonnier. In male Carcinus mamas inhabited by the Entoniscian parasite, Fori union, a similar deformity may occur, but is often very much less in extent, sometimes being only apparent in a slight alteration in the contour of the sixth abdominal Bomite. In specimens of Portunus, Platyonyckus, Pilummu and Xantho inhabited by Knto- niscians, no change was observed. Giahd and Bonne b comment on the remarkable fact that the change in the sexual characters effected by Sacculina is greater than that resulting from the presence of Entoniscian- ; for since the latter are more internal parasites, preventing the growth of and actually replacing generative entirely or in part, it might have been expected that the conseqnenoes of their presence would be more profound. . A., and Bonnibb, J., Contrib. a L'e'tnde des Bopyriens, Travaux de Vinst. zool. de Lille et p. . of which a description is known to me, and the remainder of Artemia. All the sp* of Branchipus collected are quite clearly defined both in the male and the female, and have certainly nothing to do with the Artemia. Of the latter some preliminary account may now be given, as the tacts bear on Schmankewitsch'a problem. Omitting those which were badly preserved and those which do not contain adults, there remain twenty-eight samples, satisfactorily preserved with corrosive Bublima from as many localities. Of these, eight contain males, all of them having the 1 Bull. Imp. Soc. Sat. Moscou, 1834, vxx. p. 152. 2 Mem. Ac. Sci. P€t. t 1837. in. p. 395. B. 7 98 MERISTIC VARIATION. [part I. distinctive characters of A. salina. It is difficult to speak with confidence as to the species of an Artemia from the female alone, but by careful comparison I can find no point of structure which differentiates any of the remainder from the females found with males, and I therefore regard them as all of the same species, A. salina. The waters were of many kinds, some being large salt lakes, while others were small salt ponds or even pools. The specific gravities of these waters varied from 1-030 to 1-215, and judging from the results of the analysis of six samples, the composition of the waters is also very different. The specific gravities were measured in the field with a hydrometer reading to -005, and on comparing these readings with the de- terminations of the Sp. G. of the samples brought home it appears that they were approximately correct, and I think therefore that these rough readings are fairly trustworthy. As to the composition of the waters not analyzed, nothing can be said with much confidence. As the analyses shew, some of these lakes contain chiefly chlorides, others chiefly sulphates, and so on. In a few {e.g. xxix) there is a great quantity of sodium carbonate, so much that the water was strongly alkaline and felt soapy to the hands. This can generally be recognized on the spot in various ways. The first point raised by Schmankewitsch's work is that of the caudal fins. Among my samples I have every stage between the large fins with some twenty bristles, down to the condition with no distinct fin or bristles. The following table gives the results as regards the number of bristles on the caudal fins, and this Bristles on single No. in Catalogue Sp. G. caudal fin. Eggbearing ? ? only Remarks XXIX. 1-030 10 to 24 Analyzed. Strongly alkaline. 5 > sp. 5 > 5 > sp.? B. cuculliger B. torquatus ditto Bradypus sp. sp. sp. C 9 9 9 9 9 9 9 9 8 9 9 9 9 9 8 8 8 D L 15 4 15 4 15 4 15 4 15 4 5 14 4 14 4 16 3 15 3 15 4 s 6 6 6 5 5 5 6 7 Struthers 3 6 6 15 4 14 4 5 15 15 C 5 + 8 + 9? 12 10 11 9 11 9? 11 Coll. Surg. 3428. 9 10 C 8 minute c. r. rt. C 9 large c. r. both sides (one lost). jD 15 moveable r. rt., fixed on 1. Camb. Mus. C 9 no rib. Coll. Surg. 3427. Brit. Mus. 919 a. Brit. Mus. 52. 9. 20. 5. C 9 c. r. h in. long. Univ. Coll. Loud. frt. ^ n Oxford Mus. Coll. Surg. 3422. 7th sacral onlv ankylosed in part. Brit. Mus. 46. 10. 16. 14. C 9 small rib-like horn on 1. Mus. Med.-Chir. Acad. Petersb. Gruber 2 . Gruber's private collection' 2 . C 8 may have borne rib on rt. il. free c. r. 1st thoracic complete, rt. c. r. ankylosed. 1st thor. A in. long, like a c. r. ; ankylosed. C 9 has pair short c. r. Brit. Mus. «>21 b. Gruber 2 . Brit. Mus. 47. 4. 6. 5. j 3 specimens from Brazil said to have 8 cervicals. No detailed account \ given. I)E BliAINVILLE 4 . 1 Flower, W. H., Mammals, Living and Extinct, 1891, p. 183. 2 Gruber, Mem. Imp. Ac. Sci. Pet. Ser. vn., xiii. 1869, no. 2, p. 31. 3 Struthers, Jour. Anat. Phys., 1875, p. 48 note. de Blainville, Osteogr., Psc. v., pp. 27, 28 and 64. In the place cited, de Blainville gives C 9, D 16, L 3, S 6, C 9—11 as the normal, but he does not say in how many specimens this formula was seen. I have therefore been unable to tabulate this observation. It will be seen that D 16 is quite exceptional, but as it occurred in the Coll. Surg, specimen no. 3422 it was described by Owen as the normal, and this statement has been copied by many authors, perhaps by de Blainville. 5 Fourth lumbar ankylosed to sacrum by tr. proc. 120 MERISTIC VARIATION. SUMMARY OF 40 CASES: Welcker 1 . [part i. Brady pus C D L 10 14 (14 4 4 ) C 10 no c. r. 2 cases 2 , * 10 < or or > C 10 with c. r. of fair size. On C 9 c. r. very (15 3 ) 3 cases. y small or absent. (15 4 ) 29th is 1st sacral. 9 1 or or } 9 cases. 16 3 ) / 9 15 3 15 cases, j C° usually with) 28th fa x L 9 14 4 o cases. \ c. r. 21 cases. \ 9 14) s i C 9 has either large c. r. or complete r. ) 27th or or > 5 cases. (This normal in B. tor- > is 1st 8 15) i quatus: once in B. cuculliger.) ) sacral. (c. r., cervical rib. C 6 , C 7 , &c, sixth, seventh cervical vertebra, &c.) 45. Choloepus. C 7 D 23 L 3 S 8 4 C. didactylus CoZi. Surg. 3435. it 7 24 3 7 Oxford. ii 7 23 4 5 CoZZ. Swrp. 3427 {Catalogue). ii 7 23 3 7 6 Coll. Surg. 3424. sp. 6 24 3 6 5 Cambridge. sp. 6 23 3 9 3or4 Brit. Mm. 65. 3. 4. 5. sp. 6 22 4 8 5 CZmv. CoZZ. Bond. sp. 6 21 3 8 5? Brit. Mm. 1510 o. C. hoffmanni 6 22 5 8 5? JBrZf. Mus. 1510 c. ii 6 21 4 7 5 CoZZ. S»r#. 3439. C. hoffmanni ? 6 3 23 2 7 4? Brit. Mus. 80. 5. 6. 84. SUMMARY OF 9 CASES: Welcker 4 . C D + L C. didactylus ii C. hoffmanni ii 7 7 6 6 6 C 27 26 27 26 25 1st sacral is the 35th. 2 cases. 1st sacral is the 34th. 2 cases. 1st sacral is the 34th. 1 case. 1st sacral is the 33rd. 1 case. 1st sacral is the 32nd. 3 cases. 1 Welcker, Zool. Anz. 1878, i. p. 294. 2 This includes the celebrated specimen (in natural ligaments) described by Rapp, Anat. Unters. d. Edent., Tubingen, ed. 1843, p. 18. 3 This specimen is labelled C. didactylus, but coming from Ecuador and having this formula is probably C. hoffmanni. (Compare Thomas, O., P. Z. S., 1880, p. 492.) In it C 6 bears cervical rib articulating with shaft of the first thoracic rib. 4 Zool, Anz. 1878, i. p. 295. 5 In a specimen in Leipzig Museum, no. 459, the 6th cervical bears large ribs, of which the right nearly reaches the sternum, so that Welcker says that there are only 5 true cervical vertebras. In another of these specimens there is a cervical rib on C 6 measuring 19 mm. chap, iil] VERTEBRA AND RIBS : BRADYPODID^E. 121 On this evidence several comments suggest themselves. First it should be noted that the Bradypodidae strikingly exemplify the principle which Darwin has expressed, that forms which have an exceptional structure often shew an exceptional frequency of Variation. Among Mammals the Sloths are peculiar in having a number of cervicals other than 7, and from the tables given it will be seen that both the range and the frequency of numerical Variation is in them very great, not only as regards the cervicals, but as regards the vertebra? generally. As concerning the correlation between Variation in the several regions, Welcker points out that his results go to shew that there is such a relation, and that when the sacrum is far back, the ribs also begin further back, or at least are less developed on the cervicals. As he puts it. with a long trunk there is a long neck. This is a very remarkable conclusion, and it must be admitted that it is, to some extent, borne out by the additional cases given above. The connexion, however, is very irregular. For instance, the Cambridge specimen of Brady pus, though the 29 th is the 1st sacral, has had cervical ribs of good size on the 9th vertebra, and even has a small one on the 8th. But taking the whole list together, Welcker's generalization agrees with the great majority of cases. Expressed in the terms defined above, we may therefore say that backward Homoeosis of the lumbar segments is generally, though not quite always, correlated with backward Homoeosis of the cervicals, and vice versa. It will be seen further that this Variation concerns every region of the spine, and that even in the total number of prae-sacral vertebrae there is a wide range of variation, viz. from 27 to 29 in Bradypus (52 specimens) and from 30 to 34 in Cholozpus (20 specimens). Perhaps no domestic mammal shews a frequency of variation in the fundamental number of segments com- parable with this. In this connexion it may be observed that the absolute number of dorso-lumbars in Clwl&pus (25 — 27) is ex- ceptionally large amongst mammals ; but this is not the case in Bradypus. If the case of Bradypus stood alone, some would of course recognize the occurrence of cervical ribs on the 9th and 8th ver- tebrae as an example of atavism, or return to the normal mam- malian form with 7 cervicals. The occurrence of normal ribs on the 7th in Gholoepus and the occasional presence of cervical ribs on the 6th vertebra in this form, even reaching nearly to the sternum as in Welcker's Leipzig case, obviate the discussion of this hypo- thesis. We have, then, in the Bradypodidae an example of mammals in which the vertebrae undergo great Variation as regards both their total number and their regional distribution. As the tables shew this is no trifling thing, concerning merely the number of the caudal vertebrae, the detachment of epiphyses which may then be 122 MERISTIC VARIATION. [part i. called ribs, or some other equivocal character, but on the contrary it effects besides changes in the number of pras-sacral segments, that is to say, of large portions of the body, each with their proper supply of nerves, vessels and the like, producing material change in the mechanics and economy of the whole body : this moreover in wild animals, struggling for their own lives, depending for their existence on the perfection and fitness of their bodily organiz- ation. Carnivora. The following cases, though few, have an interest as exemplifying vertebral Variation in another Order. Felis domestica. In all the skeletons of Felidje that I have examined the formula is C 7, D 13, L 7, S 3. A specimen of the domestic Cat having C 7, D 14, L 7 is described by Struthers. The change of articular processes from dorsal to lumbar was completed between the 18th and 19th vertebra? but the posterior zygapophyses of the 17 th, though of the dorsal type, have to some extent the characters of a transition-joint. As is stated below, the change in the domestic Cat normally occurs between the 17th and 18th. In this case therefore with increase in numbers of ribs the position of the articular change has varied. This case is described by Struthers, J. Anat. Phys., 1875, p. 64, Note, but the description there given differs in some respects from that stated above, which is taken from a letter kindly written by Professor Struthers in answer to my inquiries. There is here forward Homceosis in the development of ribs on the 21st vertebra, in the alteration in position of the articular change, and in the fact that the 28th is not united to the sacrum. As seen in some other cases, therefore, with forward Homceosis the number of presacral vertebrae is increased ; but as usual owing to the equivocal nature of caudal vertebra? it is not possible to state that the total number of vertebra? is greater. Canis vulpes. Normally, C 7, D 13, L 7 ; articular change from dorsal to lumbar between 17th and 18th. Specimen having C 7, D 14, L 6, in which further the articular change occurs partly between the 17th and 18th. and partly between the 18th and 19th. In Mus. Coll. Sure/. Edin. Information as to this specimen was kindly sent me by Professor Struthers. Jackal. Specimen having C 7, D 13, L 8 instead of 7. Articular change as usual between 17th and 18th. Struthers in litt. Canis familiaris. Case of cervical rib on left side borne by 7th cervical. This rib was lh in. long and articulated with a tubercular elevation on the 1st thoracic rib of the same side. The remaining ribs and vertebra? were normal, [fully described] Gruber, W., Arch. f. Anat. Phys., u. wiss. Med., 1867, p. 42, Plate. [In connexion with the foregoing observations it may be mentioned that the articular change does not take place in the same place in all Felida?. In 4 specimens of F. leo, 2 of F. tigris and 2 of F. pardus, in Edinburgh, and in one Lion and one Tiger in Cambridge the lumbar type begins between the 18th and 19th as in Struther's abnormal Cat chap, in.] vertebrae: reptilia. 123 above described ; but in 4 F. domestica, and 2 F. catus in Edinburgh, I F. domestica, 1 F. catus, 1 F. concolor and 1 Cyncelurus jubatus in Cambridge the change is between the 17th and 18th. For informa- tion as to the Edinburgh specimens, I am indebted to Professor Struthers.] 50. Galictis vittata. Specimen from Parana had 16 pairs of ribs, I I true and 5 false ; 5 lumbar, 2 sacral and 2 1 caudal vertebra?. A specimen from Brazil had only 15 pairs of ribs and the same number of lumbar and sacral vertebra?. Burmeister, Heise durch d. La Plata-Staaten, Halle, 1861, II. p. 409. [This is therefore another case of forward Homceosis, (as manifested in the presence of an additional pair of ribs) associated with an increase in the number of pra?sacral vertebra?.] 51. Halichcerus grypus. Phocida? generally have C 7, D 15, L 5. Specimen of H. grypus having C 7, D 15, L 6 at Berlin. The an- terior of the six lumbars bears a rudimentary rib about 5 cm. in length on the left side. The 28th vertebra is here detached from the sacrum giving S 3, but generally it is united to it, giving S 4. Nehring, A., Sitzb. naturf. Fr. Berlin, 1883, pp. 121 and 122. There is here therefore a forward Homceosis in the development of a rib on the 23rd, and also in the detachment of the 28th from the sacrum. Reptilia. 52. Mr Boulenger kindly informs me that though the number of ventral shields (which is the same as that of the vertebra?) is as a rule very variable in the several species of Snakes as a whole, there is nevertheless great difference in the degree of variability. A case of maximum variation is that of Polyodontophis subpunctatus, in which the number of ventral shields has been observed to vary from 151 to 240 (Boulenger , Fauna of Brit. India; Reptilia ko,. 1890, p. 303). 53. On the other hand the range of variation in Tropidonotus natrix is unusually small. Among 141 specimens examined the number of ventral shields varied from 162 to 190 (Straucii, Mem. Ac. Sci. Pet., 1873, xxl, No. 4, pp. 142 and 144). *54. Gavialis gangeticus. In this animal there are normally present 24 presacral vertebra? and 2 sacrals, the first caudal being the 27th. This vertebra has a peculiar form, being biconvex. Specimen de- scribed having 25 presacrals, 2 sacrals, the 28th being the first caudal. Baur, G., J. of Morph., IV., 1891, p. 334. In this case Baur argues that since the first caudal is clearly recognizable by its peculiar shape, this vertebra must be "homologous" in the two specimens and he considers that a vertebra must have been "intercalated" at some point anterior to the first caudal by a process similar to that seen in Python (see No. 7). In liis judgment this has occurred between the 9th and 10th vertebra 1 , but no reason for this view is given. On the system here adopted, this would be spoken of as a case of forward Homoeosis. 55. Heloderma. The first caudal in the normal form may be dis- tinguished by having a perforation in the small rib connected with 124 MERISTIC VARIATION. [part I. it. In this it is peculiar. Four specimens shewed the following arrangements : — II. horridum Xo. 1. First caudal is the 36th vertebra (Troschel). ditto No. 2 37th (Baur). //. suspectum No. 1 38th (Shufeldt). ditto No. 2 39th (Baur). Baur, G., J. of Morph. iv. 1891, p. 335. Batrachia. 1 Rana temporaria. In the normal frog there are nine separate vertebrae in addition to the urostyle. A specimen is described by Bourne having 10 free vertebras (Fig. 11, III.). The axis and third vertebra bore tubercles upon the transverse pro- cesses, perhaps representing a partial bifurcation of the kind described in No. 58. The ninth vertebra was abnormal in having zygapophyses, and in that its centrum presented two concavities Figure 11. Vertebral columns of Frog (Rana temporaria), after Bourne. I. Specimen having transverse processes borne by the atlas, together with other abnormalities described in text No. 58. II. Normal Vertebral Column. III. Specimen having ten free vertebra?, described in text, No. 56. 1 I regret that the paper bearing on this subject lately published by Adolphi, Morph. Jahrb., 1892, xix. p. 313, appeared too late to permit me to incorporate the valuable facts it contains. chap, ill.] VERTEBRAE: BATRACHIA. 125 for articulation with a tenth vertebra. The right zygapophysis was well formed and articulated with the tenth, but the left was rudimentary. The tenth vertebra itself had an imperfect centrum and the neural arch though complete was markedly asymmetrical. Posteriorly its centrum presented two convexities for articulation with the urostyle. [For details see original figures.] Bourne, A. G., Quart. J. Micr. Sci., xxiv. 1884, p. 87. This is a case of some importance as exhibiting Meristic Variation in a simple form. Of course, as Bourne says, we may say that in this specimen the end of the urostyle has been segmented off and that it is composed of " potential " vertebra?, and as he also remarks, it is interesting in this connexion to notice that some Anura, e.g. Discoglossus, present one or two pairs of transverse processes placed one behind the other at the proximal end of the urostyle. But this description is still some way from expressing all that has happened in this case ; for beyond the separation .of a tenth segment from the general mass of the urostyle there is Substantive Variation in the ninth vertebra in correlation with this Meristic Variation. For the ninth has devel- oped a zygapophysis and has two concavities behind, like the vertebra? which in the normal frog are anterior to the ninth. There is therefore a forward Homoeosis, associated with an increase in number of segments, just as there is in such a case as that of Man (No. 20) or in that of Galictis vittata (No. 50). It is also interesting in this case to see that the actually last free vertebra here, though it is the 10th, has two convex articular sur- faces behind like the 9th, which is the last in the normal frog, thus shewing a similar forward Homoeosis. Now applying the ordinary conception of Homology to this case, we may, as Bourne says. prove that the 9th in it is homologous with the 9th in a normal frog for its transverse processes are enlarged in the characteristic manner to carry the pelvic girdle. But similarly we may prove also that the tenth in this case is homologous with the ninth of the normal, for its centrum has the peculiar convexities characterizing the last free vertebra. Baur's proof that the first caudal was homologous in the two specimens of Gavialis (see No. .54) rested on the same class of evidence, and for the moment is satisfying, but as here seen this method though so long established leads to a dead-lock. Upon this case it may be well to lay some stress, for the issues raised are here so easily seen. Besides this the imperfect condition of the extra vertebra enables us to sec the phenomenon of increase in a transitional state, a condition rarely found. In the instances recorded in Gavialis (No. 54), owing to the perfection and completeness of the variation, the characters of the 1st caudal are definitely present in the 28th though normally proper to the 27th, and therefore it may be argued that the 28th here is the 27th of the type. The frog here described shews that in this conclusion other possibilities are not met. On the analogy 126 MERISTIC VARIATION. [part i. of several cases already given, it is not impossible that if the variation seen in this frog had gone further, the 10th vertebra might alone support the ilium (cp. Nos. 57 and 60) and thus present the characters of the normal 9th in their completeness. If this change had taken place, we should have a case like that of Gavialis, and there would be nothing to shew that the new 10th vertebra was not the 9th of the normal. The truth then seems to be that owing to the correlation between Meristic Variation pro- ducing change in number, and simultaneous Substantive Variation producing a change of form or rather a redistribution of characters, the attempt to trace individual homologies must necessarily fail ; for while such determination must be based either on ordinal position or on structural differentiation, neither of these criterions are really sound. As I have tried to shew, the belief that they are so depends rather on preconception than on the facts of Variation. '57. A male specimen of It. temporaria <£ with ten free vertebras is described by Howes. In this case the 9th had a posterior zygapophysis on the left side only. Upon the left side the transverse process of the 9th w r as not larger than that of the 8th and did not support the ilium, which on the left side was entirely borne by the large transverse process of the 10th. On the light side the transverse processes of both 9th and 10th were developed to support the ilium, neither being in itself so large as that of the 10th on the left side. The 9th was concave in front instead of convex as usual, and thus the 8th which is normally biconcave is convex behind. The posterior faces of both 9th and 10th bore two convexities such as are normal to the 9th. The urostyle was normal, having well-developed apertures for exit of the last pair of spinal nerves. Howes, G. B., Anat. Ariz., I. 1886, p. 277, figures. In this case the departure from the normal, exemplified by No. 56, has gone still further, and the new 10th vertebra bears the ilium wholly on the left side and in part on the right. The con- dition is thus again intermediate between the normal and a com- plete transformation of the 9th into a trunk vertebra and the introduction of a 10th to bear the ilium (as in No. 60). As regards the homologies of the vertebras, the same issues are ao-ain raised which were indicated in regard to No. 56. 58. Rana temporaria: Case in which transverse processes were present in the atlas vertebra and the transverse processes of several of the vertebra? were abnormal (Fig. 11, I.). The atlas possessed well- developed transverse processes. In the axis the transverse processes are directed forwards instead of backwards, and that of the left side presents an indication of bifur- cation at its extremity. The third vertebra possessed two pairs of transverse processes which are joined together for two-thirds of their length. The fourth chap, in.] vertebrae: recapitulation. 127 vertebra presents a transverse process on the right side which is bifur- cated at its extremity. The remaining vertebra, though slightly asymmetrical, present no special peculiarity, except that the neural arch of the ninth vertebra is feebly developed. Bourne, A. G., Quart. Jonrn. Micr. Sci., 1884, xxiv., p. 86, Plate. There is here backward Homoeosis of the atlas, the only case of the kind I have met with 1 . The reduplication of the transverse processes of the third vertebra should be studied in connexion with the cases of double vertebrae in Python (No. 7) and the cases of bifid rib (in Man, No. 12), for they present a variation perhaps inter- mediate between these two phenomena. Bombinator igneus. In this form there is a considerable range of variation in the development of the transverse processes for the attachment of the pelvic girdle. 59. Gotte figures a specimen in which the flat expanded transverse processes have a similar extent on the two sides, but while that on the right side is made up of the processes of the 9th and 10th vertebne (in about the proportions of two to one), that on the left side is entirely formed by the transverse process of the 10th vertebra. Gotte, Entiv. d. Unke, Atlas, PI. xix., fig. 346. *60. Sardinian specimen figured in which the processes for the attach- ment of the pelvic girdle seem to be composed entirely by those of the 10th vertebra while those of the 9th are not developed. Gene, J., Mem. Reale Ac. cli Torino, S. 2, i., PI. v., fig. 4. 61. Specimen figured in which both transverse processes of 9th and of the 10th are almost equally developed to carry the pelvic girdle. Camerano, L., Atti R.Ac. Sci. Torino, 1880, xv.,fg. 3. 62. Specimen in which the left transverse process of the 9th bears the pelvic girdle on the left side, and the right transverse process of the 10th bears it on the right side, while the corresponding processes of the opposite sides were not developed. Similar case recorded in Alytes obstetricans by Lataste, Rev. int. des Sci., m., p. 49, 1879 [not seen, W.B.] ; ibid. Jig. 4. 63. Specimen in which the transverse processes of the 9th alone were developed to carry pelvic girdle, but the proximal end of the urostyle was laterally expanded more than usual, ibid. p. 7, Jig. 3. [Case of hypertrophy of coccyx, ibid. Jig. 6; ad hoc v. Bedriaga. Zool. Anz., 1879, il, p. 664; Camerano, Atti R. Ac. Sci. Torino, xv„ p. 8.] Recapitulation of important features of Variation as seen in the vertebral column. I. As regards fact. 1. The magnitude of the variations. 2. The rarity of imperfect vertebne. 3. The phenomenon of imperfect Division of vertebras and ribs. Adolphi, I. c, p. 352, PI. xn. fig. 3 gives an account of a specimen of Bufo variabilis in which the atlas bore a transverse process on the left side only. In this specimen the first two vertebrae were united and their total length was reduced. 128 MERISTIC VARIATION. [part i. 4. The frequency of substantial if imperfect bilateral sym- metry in the variations, but the occasional occurrence of asymmetry also. 5. The special variability of some types, e.g. Simia satyrus ; the Bradypodida? ; Bombinator igneus. 6. The evidence that this variability may occur without the influence of civilization or domestication. II. As regards principle. 1. The occasional, though not universal, association of for- ward Homceosis with increase in number and of back- ward Homoeosis with reduction in number. 2. The frequent correlation between Variation in several regions, such correlated Variation being sometimes unilateral. 3. The impossibility of applying a scheme of Homology between individual segments. CHAPTER IV. Linear Series — continued. Spinal Nerves. The spinal nerves compose a Meristic Series in many respects similar to that of the vertebrae. As between the vertebra*, so between the spinal nerves, there is differentiation according to the ordinal succession of the members, certain distributions and func- tions being proper to nerves in certain ordinal positions. The study of the way in which Variation occurs in this series is one of great interest, but unfortunately it is extremely complicated. For while as regards vertebrae the distribution of structural differentiation can be recognized on inspection, in the spinal nerves to obtain a true knowledge of the arrangement in any one case physiological investigation or at least elaborate and special methods of dissection are needed. Though it is therefore impossible to introduce any account which should at all adequately represent the great diver- sity of possible arrangements, it is nevertheless necessary to refer briefly to the chief results attained by these methods and to the principles which have been detected in the Variation of the nerves. It must of course be foreign to our purposes to examine the many diversities of pattern produced by the divisions and anastomoses of nerve-cords in the formation of plexuses, &c, and we must confine our consideration to cases of Variation in the distribution of dif- ferentiation among the spinal nerves, that is to say, in the segmen- tation of the nervous system in so far as it may be judged from the arrangement of spinal nerves. Some conception of the magnitude and range of Variation found in single species of Birds may be gained by reference to the beau- tiful researches of Furbringer 1 . A table is given by Fiirbringer, shewing the number and serial position of the spinal nerves which take part in the formation of the brachial plexus in 07 species of 1 Fiirbringer's memoirs are of such magnitude and completeness that I have felt it to be somewhat of an impertinence to attempt to make selection from them : and it must be remembered that from the isolated and typical cases here given, only a distorted view of the evidence can be gained. As regards this subject, therefore, reference to the original work is especially needed. B. 9 130 MERISTIC VARIATION. [part I. 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X ^2 CD CC cc •: CO , c3'_ ^ d ^ o? llial CS 5-1 a fi, O CD c3 M CD = C8 ^ O CO 2 s o CO o a CO CD CO S CD « i'rj r. . a C 9? si 5S s s S'cj S3 P-iPh <1 Si CD 1h CO CO CC 'cc 2, P S3 -g Si CD ■ Si +3 ^ ° 3 CO O =s p'S ° s « 2 >>^3 w OPhO CO 1-3 03 c3 S > 2 .-i CO P-i CD 2 si Si ^3 "2 co C3 rl Sh ~, C3 i— l ^ 03 Sh O c3 CO s9 S3 a o o o - o o CD ^< ffl 1-1 Si CO A O oo CHAP. IV.] SPINAL NERVES! BIRDS. 131 > X > X > X > I— I X HH X X > X X > 1— 1 XI X i-5 i— i r— 1 X X r-H X X X X X X X 1— 1 X H-H r— ( 1— 1 > X >>> XXX > X ►V* ^ ls> K> K> K> k*^ K> k^H S/H ^ ^ S^ s> ^ s^ ^ HHHHHHHHHHHHHHHHHHHHHH K> S**H S> S^ K^ *^ K/H Kj4 K> K/"* S*"H h^ *^A S/* S^ ^v* *^ S^ Sx* S^ h^ S^ r— 1 r-H r-H r-H — 1 r— 1 r— 1 1— 1 h-t HHHH i— i i— ( — 1— 1 HH HH HH HH — — i r-H X k A K^d ^A K> K*H S^ K*H SyH K/H Kyt ^V* S^ S^ S^ *V< *^ ^^ S**H K> K> K> ►v* XII. K> K> S> S> K*^ >S/H ^ ^ K^ S/H k> K> k> K^< S/* S> S*^ ^vH S^ S/* ^ hH HH H- * HH r— ! (-H 1— 1 r-H r-H hH 1— 1 r— 1 X s^ ^ ^ s> nnrsn X XX X **• X X X X* X W S3 00 a CO 3 • 00 & ^•l-t • l-l : s o " c3 p M 5^ . _ c3 o CD . N tfi * a r-J • i— < 5 - - r- CJ V. c o vulgaris imulgus e 1 " 03 - tO rvus abys elus apus 3 medius •r — g 2 - s "3b 00 us corone us pilaris R " *■ - - a, - r 3 *5 CC += HH f3 - s M H CJ O t. 3 cT o PvS i CS o £ U mo Ph mop- C o OH ^* a CO to •fH JH o . CD « J2 & -«-a L o CD ^ CD 00 ^ 03 ?t •+» t« a CD «o S *^ CD oo to e fl b u « a S CD ^3 P5 -H» W <4-l o o 125 to P3 SJ « r> ::=> fe Fh T3 r>i ^3 Fh O c f=H a> "^— ' > • FH be 1 Mr R. Assheton sends me word of a similar specimen found among 80 of both sexes; Prof. W. B. Howes of another among 144 of both sexes. 154 MERISTIC VARIATION. [part i. In all cases of supernumerary oviducal openings the normal open- ings were also present. These cases are in addition to those received from Mr Benham. So far, therefore, the cases of extra opening amount to over 3 per cent, of females examined. Of 714 males examined, only one was abnormal, having no trace of a generative opening on the right side, the vas deferens ending blindly and hanging free in the thoracic cavity. There was no female opening in this specimen, and the abdominal appen- dages had the form characteristic of the male on both sides. The base of the last thoracic leg on the right side bore no enlargement for the genital opening, but was plain and like that of the pen- ultimate leg 1 . In cases of females which lacked one of the openings, the basal joint for the leg which should have been dilated and perforated for the opening, was undilated and resembled the basal joint of a penultimate leg. The oviduct upon the imperforate side was more or less aborted and hung loosely in the thoracic cavity. In the abnormal females with extra oviducal openings, the oviduct divides generally into two just before it enters the legs, the fork being placed at the level between them. In some few cases no branch of the oviduct could be traced to the extra open- ing. In one specimen the extra opening led into a short tube which ended blindly, not communicating with the oviduct. The specimen (4) with extra openings on the penultimate and last legs had thus in all six oviducal openings. Those in the normal position on the antepenultimate legs were of normal size, those on the next pair were smaller but still of fair size, while those on the last pair of thoracic legs were very small, that on the left side being the smallest and admitting only a fair-sized bristle. In this specimen the single oviduct of each side forked in its peripheral third, giving a duct to each of the first two pairs of openings, but I failed to find any connexion between it and the openings on the last thoracic legs, which were very short blind sacs. In all cases of extra oviducal opening the basal joint of the leg is expanded like those of the normal antepenultimate legs, the degree of expansion being proportional to the size of the opening. The normal openings are always the largest, but the extra ones are sometimes almost as large and would easily allow the passage of ova, but occasionally they are too small to let an egg through. As regards principles of Homoeotic Variation illustrated by these cases, three points should be especially remarked : 1 Compare the following : Astacus fluviatilis. Amongst 1500 specimens 3 were found in which the tubercle through which the green gland opens was entirely- absent. The opening itself was not formed and the green gland of the same side was absent. In another specimen the opening was deformed, probably owing to some mutilation. In this and the previous cases the green gland of the other side was considerably enlarged. Strahl, C, Midler's Archiv fiir Anat. u. Phys., 1859, p. 333,^. chap, v.] HOMCEOSIS IN ARTHROPOD A . 155 1. That this Variation may be bilaterally symmetrical, but that the evidence goes to shew that it is more often uni- lateral. 2. That there is a clear succession between the several oviducal openings, those of the antepenultimate legs being the largest, the penultimate the next, and those of the last legs the smallest. 3. That Homceosis may occur between segments which are not adjacent, as in the case of extra oviducal openings on the last thoracic legs, none being formed on the penultimate (No. 84). 4. That the Variation may be perfect. With the foregoing, the following evidence may be compared, though it is very doubtful whether it properly belongs here 1 . 86. Cheraps preissii [an Australian freshwater Crayfish, nearly allied to Astacusj. Of seven specimens received one was a normal male and three were normal females. The other three had on the basal joint of the third [antepenultimate] pair of legs a round opening, having the size and shape and situation of the normal female openings. These apertures were closed with soft substance. The fifth legs bore the usual male openings, from which the ends of the ductus ejacula- torius protruded. The coiled spermatic ducts were normal ; but no ovary was found and no internal structure was connected with these female openings, von Martens, E., Sitzb. Ges. naturf. Fr. Berlhi, 1870, p. 1. 87. Astacus pilimanus J, a single specimen, and A. braziliensis J, a specimen collected by Hensel in Southern Brazil, a similar opening was found on the third pair of legs ; but in other specimens of these forms there was only a slight though sharply defined depression in the chitinous covering at this point, von Martens, E., I.e. 1 See also Nicholls, ~R.,Phil Trans., 1730, xsxvi. p. 290, figs. 3 and 4 describing a Lobster {Homarus vulgaris) having male organs on the left side and female organs on the right. CHAPTER VI. linear series — continued. Ch^etopoda, Hirudinea and Cestoda. Imperfect Segmentation \ Though from the circumstance mentioned at the beginning of Chapter n, that the total number of segments in the Annelids is generally indefinite, true Meristic Variation cannot be easily re- cognized in this group, there is nevertheless a remarkable group of cases of imperfect segmentation, in which by reason of the incom- pleteness of the process of Division, the occurrence of Variation is at once perceived. The following cases were all originally described by Cori, who speaks of them as instances of "intercalation" of segments. For reasons sufficiently explained in the Chapter on Vertebras, there are objections to the use of this term, if only as a mode of expression, and the evidence concerning these cases has therefore been re-cast. *88. Lumbricus terrestris : the 46th segment having the form shewn in Fig. 21, I. being normal on the right side, but double on the left. Internally a septum divided the two parts a and a from each other. Each of them contained a nephridium, setae, &c. Cori, C. J., Z.f. w. Z. t liv. 1892, p. 571, fig. 1. *89. Specimen having, in the region close behind the clitellum, three consecutive segments, each resembling that just described. Of these the first was double on the right side, the second on the left, and the third on the right again. Fig. 21, II. shews the internal structure, the nephridia and other jmrts having doubled in each of the doubled half-segments. Cori, /. c, p. 572, fig. 2. 90. Lumbriconereis : case similar to the first case in Lumbricus, Fig. 21, III. Cori, C. J., I c, p. 572, fig. 4. 91. Halla parthenopeia. A specimen 50 cm. long presented numerous abnormalities of which two are represented in Fig. 21, IV. At the point marked a the lines of division between the segments 1 Numerous facts illustrating this subject are given in a recent paper by Buchanan, F., Q. J. M. S., 1893. CHAP. VI.] ANNELIDS. 157 enclose a small spindle-shaped island of tissue. Three segments lower a wedge-shaped half-segment is similarly formed. At Fig. 21. Examples of imperfect segmentation in Annelids (after Com). I. Lrimbricus terrestris (No. 88). II. L. terrestris (No. 89), as seen when laid open on the dorsal side. III. Lumbriconereis (No. 90). IV. Halla parthenopeia (No. 91). N, nephridium ; Np, nephridial pores; D, alimentary canal; dG, dorsal vessel; vG, circular vessel. The letters a, b, c, &c. indicate the parts belonging to the respective segments. another point in the same animal (not shewn in Fig. 21) one of the segments was partly divided into two in the right dorso- lateral region. Com, p. 572, figs. 8 and 9. Spiral Segmentation \ 92. Lumbricus terrestris. Fig. 22, I. A shews a part of an Earthworm seen from the dorsal side, the ventral side being- normal in appearance. By following the groove indicating the plane of the septum between b and c on the right side to the ventral surface, it could be traced to the left side between b and c, so across the dorsal surface, between c and d on the right side, across the ventral surface and between c and d on the left, reach- ing nearly to the middle dorsal line again. This is shewn dia- grammatically in Fig. 22, I. B. 93 A simpler case affecting one segment only is shewn in Fig. ' 22, II. 94. Another specimen exhibited a similar arrangement near the tail-end (Fig. 22, III.). The lettering of the figure sufficiently explains the course of the spiral septal plane. [Cori does not state that the septa internally formed a spiral division, but it can scarcely be doubted that they did so, following the external groove, 1 Further observations on this subject have been lately published by Morgan, T. H., Journ. of Morph., 1892, p. 245, and by Buchanan, F., Q. J. M. S., 1893. 158 MERISTIC VARIATION. [part I. like the spiral valve of an Elasmobranch's intestine.] Cori, Z.f. w. Z. t Liv. 1892, p. 573, figs. 5, 6 and 7. * I B Fig. 22. Spiral segmentation in Lumbricus terrestris. I, A, the case No. 92 ; I, B, diagrammatic representation. II, A, the case No. 93 ; II, B, diagrammatic representation. III, the case No. 94. (After Cori.) Two other cases described by Cori may be mentioned here, though there is a presumption that they are not really examples of Variation in the segmentation along the axis of a Primary Symmetry, but rather belong to the class of Secondary Symmetries. They are alluded to here as it is convenient to illustrate this distinction by taking them in connexion with the examples just given. 95. Hermodice carunculata. (Fig. 23, III.) Between two normal segments is what seems at first to be a segment double on the left side with two complete sets of parapodia, but imperfectly divided on the right (left of figure), the septal groove stopping short before it reaches the parapodial region. The lower half on this side is re- presented with a normal ventral ramus of the parapodium, but the ventral ramus in the upper was itself partially doubled, having in particular two cirri Cv. I. and Cv. II. and two branches of setae. The condition of the dorsal ramus is not described. Of course without seeing this specimen it is impossible to say more than this, but the figure strongly suggests that the division between the two halves of this parapodium was a division into images and not into successive segments. The figure represents the lower cirrus Cv II. as standing in the normal position for the cirrus, on the posterior limb of the parapodium, but the anterior cirrus is distinctly shewn as placed on the anterior limb of the elevation and anterior to the bristles. If this were actually the case, this double parapodium must be looked on as a kind of bud, with a distinct Secondary Symmetry of its own. Described afresh from Cori, C. J., Z.f. w. Z., liv. 1892, p. 574, fig. 3. CHAP. VI.] ANNELIDS. 159 96. Diopatra neapolitana. In the middle of a specimen 35 cm. long was an arrangement somewhat similar to the above. The part marked ci CM TIT Fig. 23. I. The case of Diopatra neapolitana (No. 96) from the side. II, the same looking upon the parapodia. C I. C II, the two supernumerary cirri. III. The case of Hermodice carunculata No. 95. Cv, cirrus of ventral branch of parapodium ; Cd. dorsal cirrus ; Cv. I, Cv. II, the two cirri borne on the super- numerary parapodium. (After Cobi.) V was cut off as shewn in Fig. 23, I., it bore a normal cirrus, and the other part of the segment, marked b, bore two cirri and two bunches of bristles. The figure does not indicate that there was any relation of images between these two parts, but this would scarcely appear in this case unless specially looked for. Described afresh from Com, C. J., I.e., p. 573, figs. 10 and 11. In considering the evidence as to Secondary Symmetries reference to these cases will again be made. Generative organs of Earthworms 1 . The number and ordinal positions of the primary and accessory generative organs and of their ducts differ in the several classifi- catory groups of Earthworms. In the evolution of these forms it may therefore be supposed that Variation in these respects has occurred. To this subject the following evidence relates. The difficulty which was mentioned in the case of Variation in ver- tebrae, that there is no. clear distinction between Homceotic and strictly Meristic Variation, will here also be met, inasmuch as the total number of segments in these forms is indeterminate ; but 1 For information and references on this subject I am indebted to Mr F. E. Beddard and Mr W. B. Benham. 160 MERISTIC VARIATION. [part i. probably we shall be right in regarding the majority of these variations as Homceotic. Lumbricus. Throughout this genus there is normally a single pair of ovaries, placed in the 13th segment, on the posterior surface of the septum between the 12th and 13th segments. The following cases of supernumerary ovaries are recorded : 97. Lumbricus turgldus : specimen having an extra pair of ovaries in the 14th 1 segment. 98. Specimen having an extra ovary on the right side in the 14th segment. 99. L. purpureus: specimen having an extra ovary on the left side in the 14th segment. In all these cases the extra ovaries were in size, form and position like the normal ovaries. There was no extra oviduct or receptaculum ovorum, but the normal ovaries and oviducts were present as usual. Bergh, R. S., Zeit. f wiss. ZooL, XLiv. 1886, p. 308, note. 100. Allolobophora sp. [partly = Lumbricus, the common Earth- worm] : specimen having, in all, seven pairs of ovaries ; viz. a pair in the 12th, 13th, 14th, 15th, 16th, 17th and 18th segments. Of these all except the pair of the 13th segment are supernumerary. Each of these ovaries was placed on the posterior face of a septum in the usual position. The three anterior pairs in shape, structure and position closely resembled the normal structures. Of these the most anterior were slightly the largest. The four posterior pairs were smaller and resembled the ovaries of a very young or immature worm, but on examination all were found to contain ova. The normal pair of oviducts were present and no extra ovi- ducts could be found, though carefully sought for. Woodward, M. F., P. Z. S. } 1892, p. 184, Plate xiil •101. Lumbricus herculeus, Savigny (= L. agricola, HofTmeister), having an asymmetrical arrangement of the generative organs, &c. On the left side the arrangement was normal ; the ovary being in the 13th segment, the oviducal opening in the 14th, and the open- ing of the vas deferens in the 15th segment (Fig. 24). On the right side each of these structures was placed in the segment anterior to that in which it is normally found : the right ovary was in the 12th, the external opening of the right oviduct was in the 13th, and the external opening of the right vas deferens was in the 14th segment. The spermathecse were normal on the left side, being placed in the 9th and 10th segments, but on the right side one spermatheca only was present, that of the 9th segment. The vesiculse seminales were present as usual in the 9th and 11th segments, but there was no vesicula in the 12th 1 In Bergh's enumeration the ordinal number of these segments is one less than in that commonly used : the latter system is adopted above. CHAP. VI. ANNELIDS. 161 segment on the right side, while that of the left side was fully Right Left (normal) Fig. 24. Lumbricus herculeus, having the generative organs of the right side one segment higher than usual. A, external view from below. B, view of the organs from above, spth, sperrnathecae ; ov, ovary; as, oesophagus ; cat, calciferous glands. After Ben ham. formed. It is remarkable that in this case, the calciferous gland of the 12th segment was absent on the right side. [I am indebted to Mr Benham for an opportunity of examining this specimen.] Benham, W. B., Ann. & Mag. N. H., 1891, Ser. 6, VII. p. 257, PI. in. Another specimen presented the same variations as the fore- going, both as regards the asymmetrical arrangement of the genital pores and the absence of the calciferous gland : but in it there were vesiculae seminales on the right side in segments 10 and 11, but none in segment 9 ; and there was a spermatheca on the right side in segments 8 and 9. [In the normal form the spermatheca? are in segments 9 and 10, so that, in this individual in the matter of the spermathecse as well as of the genital pores, structures were formed in particular segments which are normally found one segment lower down.] Bexham, W. B., in litt., March, 1891. 11 B. 162 MERISTIC VARIATION. [part I. 103. Table shewing position of ovaries in forms having two or more pairs of ovaries, and in the Variations found (slightly altered from M. F. Woodward, P. Z. S., 1892): Segments A canthodrilus Kclipidrilus Eudrilus Lumbricus terrestris (normal) L. herculeus (? = teirestris) Benham's \ 1. 2 specimens (rt. I., turgidus Bergh's spec, (abnorm.) do. do. do. (abnorm.)... J ' L. purpureus do. do. (abnorm.)... J .' AUolobophora sp. (Common Earthworm, abnorm.) Perionyx (two pairs, varying from 9 — 16).. Phreodrilus Ph reoryctes l Vrochceta 9 10 11 12 13 14 15 X X? X X X X ! I X X X X X X X X X X X X X X X X 16 1 17 X X X X X X 18 x 104. AUolobophora sp. [> 11 „ . 6,7,8 13, 14 16 12 (2 specs.) 8, 9, rt. ; 9, 10, 1. 14 18 1) 13 8, 9, rt.; 9, 10, 1. 14, 15 18 >> 14 (1 spec.) 8, 9 15, 17 21 1) 15 15, 16 18 Though the position of both varied greatly, the male pores were always posterior to the female ones. In some specimens certain of the segments were only divided from each other on one side of the body, being confluent on the other. For example in Var. No. 14, segments 11 and 12 and also segments 18 and 19 were only divided from each other on the left side (cp. Nos. 88—91). Out of 430 individuals 15 variations in these structures were seen; of 12 of these variations single specimens only were found, but two specimens occurred with each of the other three forms oi variation. In a single case a nephridium was found nearer to the dorsal line in one segment than in the adjacent segment. Many of the conditions here occurring as variations are found normally 11—2 164 MERISTIC VARIATION. [part I. in other genera and species. 1886, p. 308, figs. Beddard, F. E., Proc. Zool. Soc, A _2 A. 5 j8 _8_ 12. n_ 12 13 11 15 16 17 18 10 20 '^ \-v ^ Fig. 25. Perionyx excavatus. Diagrams shewing some of the variations in respect of the number and positions of the openings of the spermathecre and generative pores. From Beddard, P. Z. S., 1886. Perionyx griinewaldi, Michaelsen. Normally a pair of male genital pores on the 18th segment, and a single oviducal opening for the two oviducts in the middle line of the 14th segment. 107. In two specimens a different arrangement was found. One of these had the oviducal opening in the 15th segment [position of male openings not specified and presumably normal]. 108. The other had two oviducal openings, one in the 13th and one in the 14th segment [not stated whether these openings were median or lateral, nor whether each of them was a double structure as of course the normal female opening is]. In this specimen the male openings also were placed anteriorly to their normal position, being in the 17th segment. Michaelsen, Jahrb. d. Hamburg, wiss. Anstalt, 1891, viii., p. 34. Allurus. In Terricolse generally, the £ pores are on the 15th, and the $ pores on the 14th, as in the common Earthworm. 109. Allurus tetraedrus, a widely distributed form, has £ pores on the 13th and $ pores on the 14th, the £ pores being thus in front of the ^ pores as a specific character. Under the name Allurus dubius Michaelsen described two specimens having the male pores on the 14th instead of on the 13th, and the £ pores on the 15th instead of on the 14th, each being thus one segment in advance of its normal place [backward Homceosis]. Michaelsen, W., Jahrb. Hamb. wiss. Anst., 1890, vie, p. 7 ; see also Arch. f. Naturg., 1892, lviii., p. 251. Compare No. 111. 110. Besides these is a batch of 8 specimens of A. tetrdedrus, loc. un- known, 6 specimens had both £ and $ pores in the 14th. Clitellum began in 23rd, tuberc. pubert. in 24th. These specimens are thus intermediate between A. hercynius, which has the pores as in Lum- CHAP. VI.] HIRUDINEA. 165 bricus, and A. tetraedrus. Michaelsen, W., Arch. f. Naturg., 1892, lviil, p. 251, Allurus putris : specimen having J 1 pores on 13th (instead of 15th) as an abnormality; in it the other external generative organs (and doubtless the internal also) were 2 segments higher than usual, the J pore being on the 12th instead of 14th. Tuberc. pubert 26 — 28. Michaelsen, Jahrb. Hamburg, wiss. Anst., 1891, vin., p. 8. Compare No. 109. Allurus sp. : specimen having 1. side normal ; right side, £ pore in 12th, % in 11th, clitellus and tuberc. pubert. one segment higher than usual. Ibid. Enchytrceid^e. J 1 pore generally in the 12th segment. In Buchholzia appendicidata (Buch.) it is on the 8th, as a specific character. In Pachydrilus sphagnetorum (Vejd.) it is either on the 8th or on the 9th, according to individual variation, the other parts being then disposed as follows : cf pore on 8th S pore on 9th Ovaries on dissep Vas def. in front of dissep. c? pore 7/8 8/9 8/9 9 9/10 10 9 and \ 10 6/7 7/8 7/8 8 8/9 9 8 and \ 9 Oviduct on dissep ? pore Clitellum Michaelsen, W., Arch./, mikr. Anal, 1888, xxxr. p. 493 ; see also Jahrb. Hamb. wiss. Ansl, vii. p. 8. Perichaeta hilgendorfi, n. sp. Mich. 7 specimens. Variation in number of spermathecal openings, as follows. 5 specimens had 2 pairs in the groove between segments 6/7 and 7/8; 1 specimen had 3 pairs, between 5/6, 6/7 and 7/8; 1 specimen had only one, on the left side between 6/7, which corresponded internally to a single spermatheca [other variations also observed in these specimens, q.v.]. Michaelskn, W., Arch. f. Nature/., 1892, lviii. p. 236. Perichaeta fortoesi (an Earthworm from New Guinea). In this animal a pair of spermatheca? is placed in the 8th segment and another pair in the 9th. Two specimens only have been examined and in both of these an additional spermatheca was found on the left side, internal to the other. In one individual the 5th sperma- theca was in the 8th segment, and in the other it occurred in the 9th. Beddaki>, F. E., Proc. Zool. Soc, 1890, p. 65, Plate. Aiiolobophora lissaensis. Similar variation in spermatheca 1 , Michaelsen, W., Jahrb. Hamb. wiss. Anst., vin., 1891, p. 19. HlRUDINEA. Hirudo medicinalis. The number of pairs of testes is variable, but 9 pairs most often found. Of 31 specimens of this species, 21 had 9 pairs, 6 had 10 pairs, and 4 had 9 on one side and 10 on the other. Chworostansky, C, Zool. Anz., 1886, p. 4-AG. 166 MERISTIC VARIATION. [part I. 118. Hirudo officinalis : of 7 specimens, 5 had 9 pairs of testes, 1 had 10 pairs, and though in the 7th specimen there were 2 pairs, the vas deferens of the last pair of testes ended blindly. Ibid. 119. Hirudo medicinalis, Fairly often the vas deferens is prolonged beyond the 9th testis, and having passed through rive annuli, ends in a glandular mass of irregular form. Case given in which the 7 last testes of right side were absent or only represented by amorphous material, the testes of the left side being abnormally large. Ebrard, Nouv. monopr. des Sangsues vied., Paris, 1857, p. 9'.). *120. Hirudo officinalis : an individual having a supernumerary penis, and vesicula seminalis of the right side, in the 5th somite. vs 2 Fig. 26. Case of Hirudo officinalis, No. 120. p l , penis in normal position ; p 2 , supernumerary penis ; vs, the usual vesicula? seminales ; vs' 2 , supernumerary vesicula seminalis. (From a diagram sent to me by Mr Gibson.) The normal penis in the sixth segment was fully formed and into it opened on either side a vas deferens, provided with a vesicula seminalis as usual. But the vesicula of the right side gave off in addition a vas deferens, which passed forwards into the fourth segment and there enlarged into another vesicula seminalis. This additional vesicula was connected by a duct with a supernumerary penis placed and opening in the middle of the fifth segment. The parts of the left side as well as the female organs were normal. [I have to thank Mr Gibson for furnishing me with a diagram (Fig. 26) supplementing the published account.] Gibson, R. J. Harvey, Nature, 1887, xxxv., p. 392. Aulastoma gulo (Horse Leech). In this form as is usual among the Gnathobdellidce there are from 9 to 12 pairs of tes- chap, vi.] ANNELIDS : RECAPITULATION. 167 ticular sacs which communicate with a tortuous vas deferens on each side which together enter a single penis. The paired ovaries are placed behind this and the oviducts unite to form a common vagina. 121. In a specimen found amongst a large series investigated, each vas deferens opened by a separate penis, of which the most an- terior opened in the 20th annulus and the posterior in the 25th. The female apparatus was similarly divided. One ovary was placed near the penis in the 25th annulus and from it a vagina passed down to open with the penis. The other ovary, with a similar vagina, lay in the 30th annulus. Asper, G., Zool. Anz., 1878, I, p. 297. Recapitulation of evidence as to Oligoch^eta and Hirudinea. Variation in these two groups appears in such similar modes that points of special consequence in both may conveniently be spoken of together. 1. As elsewhere seen, so here, there are forms, e.g., Perionyx excavatus or Pachydrilus sphagnetorum, shewing great variability, while others, the common Earthworm for instance, rarely vary. 2. Both forward and backward Homceosis may occur ; a form normally having the r example, a segment with two pores measured IS mm. in Length 170 MERISTIC VARIATION. [parti. [instead of about 20 mm.), and one with five pores measured 28 mm. (instead of 50 mm.). L., p. 571. 120. T.-rnia. < [noted by Leuckart from ELelueb of a Tan i a having generative on the *ur/ace of the Begments. Leuckart himself has never seen :ui example of this variation. [Original reference not found] L., p. 570, Note. 127. Taenia solium and T. saginata. Specimens are known having two generative pores opposite each other at the same level. In such cases each l7 I . 12 s . TaDnia solium in which the pores are normally alternating, may be found with symmetrically developed pores; and on the contrary, T. elliptica in which they are normally symmetrical, may occur with an asymmetrical arrangement. L., pp. 353 and 529. [29 T. saginata: in a chain of about 6'5 metres in length, and containing some (150 joints, there was found a single, heart- Bhaped, supernumerary joint like those described; a single joint was found with two genital pores, one being on each lateral border about the same level. The largest number of consecutive joints having the genital pores on the same side was six. Tuckermax, F., Zool. Anz., xi., L888, p. ( .»4. [30 Taenia coenurus. Specimen observed by Leuckart in which the last s or 10 segments shewed a transposition of the generative organs, those which usually lie at the distal end being placed at the proximal. This change of position was especially seen in the case of organs engaged in the preparation of the ova. The proximal proglottides of this individual were normal. The trans- ition segment between these two regions contained two simple vesiculae Beminales and two marginal papillae which were on opposite Bides; but in spite of the resemblance of these structures to genital pores, neither opening, nor cirrus, nor vasa deferentia could be distinguished. L., p. 504. 131. A.mongst chains of normal proglottides it is not rare to find a segment containing male organs only. L., p. 504. Speaking generally, slight abnormalities are far more common than great ones. Nearly every specimen of Tapeworm has in- dividual peculiarities, and these generally repeat themselves in the same chain of proglottides. This repetition of the same abnormality in different parts of the chain is also the rule for the greater abnormalities also. L.. pp. 529, 572 and 573. CHAPTER VII. linear series — continued. BRANCHIAL OPENINGS OF CHORDATA AND STRUCTURES IN CONNEXION WITH THEM. Under the general heading of Variation of branchial openings facts will be given relating to the following subjects. I. Variation in the patterns formed by the bars, vessels and stigmata of the branchial sac in Ascidians. II. Variation in the number of gill-sacs in Cyclostomi. III. Abnormal openings in the cervical region of Mammals, known as " cervical fistula 3 ," and external appendages called " cer- vical auricles," or " supernumerary ears," present sometimes in connexion with such openings. With reference to the two first subjects the evidence is only fragmentary, but the instances recorded seem to be of sufficient consequence to warrant their introduction in illustration especially of the magnitude and definiteness of Variation. Variations affecting the opercular opening in Amphibia are mentioned in connexion with Bilateral Series. I. Ascidians. Transverse vessels of Branchial Sac. 132. Ascidia scabra. Branchial sac in one specimen shewing abnormal and irregular structure owing to branching of transverse vessels. The resulting appearance is entirely peculiar. Herdmax, W. A., J. Linn. Soc. (Zool.), 1881, xv., p. 284, PI. xvii., fig. 3; also p. 330. 133. Ascidia virginea (O. F. Miiller): a case of great irregularity exactly similar to the above. Ibid., p. 330. 134. Ctenicella lanceplani. Branchial sac may present characters due to variations in disposition of transverse vessels etc., which assume three distinct patterns or marked varieties. Lacaze-Duthieks, Arch, Zool. Exp., S. 1, Vol. vi., p. 619, Vol. xxxiii., rigs. 9 — 11. 172 MKIMSTIO VARIATION. [part i. '13"). Ascidia plebeia (Alder): branchial sac has very characteristic appearance and Lb very constant in the size of meshes, papillae &c. One point La liable to variation: as a rule the transverse vessels are of the same calibre, but in several specimens every fourth vessel is much wider than the intervening three. Herdmax, p. 331. Stiqmata and Meshes. 136. Ciona intestinalis : meshes vary but according to no apparent method: 5 Btigmata in ;i mesb normal; 4 and G met with frequently; 10 the utmost seen. Herdman, p. 332. 1 ;> >7. Ascidia aspersa. In typical specimens, transverse vessels all same size, the meshes being square and undivided, but individuals occur in which many (not all) of these square meshes are divided by delicate transverse vessels into pairs of oblong areas. Herdmax, p. 332. L38. Styela grossularia. The genus Styela is characterized by the presence of branchial folds, normally four on each side, but in this 3pecies the folds are almost obsolete, being entirely wanting on the left side and reduced to a single slight inward bulging on the right side, bearing internal longitudinal bars. This fold is separated from the dorsal lamina by a broad space without internal longitudinal bars. A similar wide space is present on the left side of the dorsal lamina, and two others on the vertebral edcje of the sac, one on each side of the endostyle. These spaces vary in size in individuals. They commonly contain 1G stigmata, but numbers down to 12 were frequent and in one case 10 only were present: only once more than 16 observed, and in that case tliere were 28. Number of internal longitudinal bars on fold varies from 6 to 9, generally 8 or 9. Herdmax, p. 330. Id considering the significance of these cases with reference to the origin of Species it is to be remembered that the characters of the branchial sac, the sizes of the transverse vessels, shape of meshes and the number of stigmata they contain are held to be of the first importance for the classification of Ascidians; but Herd- man finds that while they are highly characteristic in some species they are qoI so in others 1 . II. Cyclostomi. L39. Myxine glutinosa. In this genus there are normally six pairs of branchial pouches. I am indebted to Professor Weldon for an account of a specimen dissected by him in which there were seven pairs of these pouches. On the left side all the seven pouches were distinct and separate, each having a separate open- 1 The olfactory tubercle in Ascidians may have a different form and position in different individuals of the same species, but the range of variation changes according to the species. Molgula was found to be the most constant, Ascidia virginea and A. plebeia the most variable forms. Herdman, Pwc. R. Phys. Soc. Edin., vi., p. 267, figs.; also id., Proe. Lit. Phil. Soc. Liverpool, xxxvm. p. 313, Pis. i. and ii. Variation respecting the atrial pore will be considered in connexion with Bilateral Repetition. CHAP. VII.] CYCLOSTOMT. 173 ing from the oesophagus and a separate aortic arch supplying it. On the right side the sixth and seventh pouches were practically * r D asu Fig. 27- Myxine glutinosa ; specimen having seven pairs of branchial sac-. Diagram shewing branchial sacs, heart and aortic arches from the dorsal surface. On the right side the sixth and seventh branchial sacs were partially confluent. D. oes., ductus cesopJiageus. (From a drawing kindly lent by Prof. Weldon.) confluent though each had a separate oesophageal opening and a separate arch from the aorta. In the drawing, for which I am also indebted to Professor Weldon, the oesophageal openings are not shewn. 40. Bdellostoma. In this genus the number of branchial sacs is variable, different numbers being found in different species and individual variation also occurring. The generic name Heptatrema was originally given by Dum£ril from the presence of seven gill-sacs. In 1834 Joh. MtJLLER, finding that this character is not constant proposed the name Bdellostoma. Of three Cape specimens examined by him one had seven gill-sacs on each side, one had six on each side, and one had six on the right side and seven on the left. To these he gave the names B. hepta- trema, B. hexatrema and B. heterotrema respectively (Abh. k. Ah Wiss. Berlin, 1834, pp. 66, 67 and 79, Taf. VII.). Further observa- tion has shewn that the number of gill-sacs in the Cape Bdello- stoma is liable to individual variation, some specimens having six while others have seven. The name B. cirrhatum (GtJNTHER, Gat. Brit Mus., viii. 1870, p. 511) includes these and the New Zealand specimens. As to the relative frequency of specimens with six or seven pairs or with an asymmetrical arrangement I have no in- formation. A collection lately brought from the Cape by Sedgwick includes one specimen with six pairs and several with seven pairs. 174 MEKISTIC VARIATION. [part i. 141. B. polytrema : single specimen from Chili, badly preserved but apparently having fourteen pairs of gill-openings. GuNTHEJt I. c, p. 512. Specimen having 14 gill-openings on left side and 13 on right. Sciinkii.ki:. A., Arch. f. iWaturg., xnvi. 1S80, p. 115 (cp. Putnam, Proc. Bost X. 11. &, xvi. L873, p. 1G0). /;. bischoffii: single specimen, 10 gill-openings on each side. ibid. Ammoccetes : having eighl branchial openings on each side instead of Beven, the normal number. The shape of the mouth of this specimen was also abnormal, being described as somewhat square. [No satis- factory description.] Eowabo, Thomas, Zoologist, xvi., p. 60D7. 142. In connexion with individual Variation in the number of gill- sacs in Myxinoids it should be borne in mind that in Petro- myzon there are normally seven pairs of gill-sacs. The case of the Notidanidse may also be mentioned in this connexion. Among Selachians the Notidanidse are peculiar in having a number of gill- slits other than rive, and of them liexanchits has six pairs, while Heptanchus has seven 1 . III. Cervical Fistula and Supernumerary Auricles ix Mammals. Though the evidence of this subject is well known and has often been collected, it may be convenient to give here some abstract of the facts in so far as the phenomena of Variation are illustrated by them. Since cervical fistula? have been believed to result from the persistence of the embryonic branchial clefts, they may properly be considered in relation to the general question of Variation in the number of gill-slits, while the development of external appendages, perhaps serially homologous with the external ears, directly concerns the subject of Meristic Variation. Man. The subject has been studied by many observers, espe- cially by Aschersox 2 , and by Heusixger 3 , who brought together and abstracted 4(i cases, being all that had been described in Man up to LS(j4. G. Fischer 4 gives a full list of the literature of the subject up to 1870, with an analysis of 65 cases. A further paper by Heusixger 5 contains a general account of these structures as they are found in Man and in the domestic animals. Additional cases, together with a general discussion of the subject, especially in relation to fistula? on the external ears, were given by Sir James 1 Balanoglossus. In five species with which I am acquainted, the number of pill-bars and slits varies in proportion to the size of the body, and as it is not unlikely that these animals continue to grow throughout life, it is probable that the number of branchiae is always increasing by formation of new gill-slits at the posterior end of the branchial region. The same is probably true of Amphioxus. 2 Ascherson, BefistulU colli congenitis, Berlin, 1832. 3 Heusinger, Anh. f. Path. Anat. u. Phys., 1864, xxix. 4 Fischer, G., Dent. Ztsch.f. Chirurg., 1873. 8 Heusinger, Deut. Ztsch. f. Thierm., 1878. * chap, vil] CERVICAL FISTULA. 175 Paget 1 in 1878. Lastly, the whole evidence as to cervical fistulas and the structures associated with them has been fully collected up to 1889 and tabulated by Kostanecki and Mielecki-, who also discuss in detail the relations of these abnormalities to the facts of development. The following account is taken from these sources. For figures the reader is referred to the original memoirs. 143. Cervical fistuke are generally known as orifices placed in the region of the neck, leading into a sinus of greater or less extent, varying in size from a mere pit to a duct some inches in length. In the greater number of cases the sinus ends blindly, but in about a third of recorded cases (K. and M.) it passes inwards to open into the pharynx, forming thus a communication between the pharyngeal cavity and the exterior. Such passages are spoken of as complete cervical fistulas, those which have an external but no internal opening being external incomplete fistuke. Besides these there are cases of diverticula from the pharynx or oesophagus which do not reach the exterior, and these are known as internal incomplete fistula?. Cervical fistuke are more commonly present on one side only, but in a good many cases they have occurred on both sides. According to Fischer they are more common on the right side than on the left. The following statistics are given by him. 65 persons had 79 fistuke : 51 unilateral, 14 bilateral: 20 complete, 53 without an opening to the pharynx: of the unilateral cases 33 were on the right and 13 on the left : 34 in males, 30 in females. There was evidence of heredity in 21 cases. The external opening is very small and may either be on the surface of the skin or elevated on a minute papilla. Sometimes it is covered by a small flap of skin as with a valve, in other cases it is placed as a fissure between two lips. The positions in which the ex- ternal openings of cervical fistula? are found are very variable, but in the great majority of cases the opening is close to the middle line in the neighbourhood of the sterno-clavicular articulation, generally from a few lines to an inch above it, on either the inner or the outer border of the sterno-cleido-mastoid muscle. In rarer cases the external opening is placed at the level of the middle of the cricoid cartilage, and is sometimes just behind the angle of the jaw. These positions are not however at all precisely maintained, but vary a good deal in different cases. When the external opening is in the higher situation and the fistula is complete, a sound may then be passed into the pharynx, but when the external opening is low, the duct when present passes upwards covered by skin only, in a straight line so far as the upper limit of the larynx, at which point it turns at a sharp angle upwards and inwards. For this reason it is not possible in such cases to follow the course to the pharynx by means of a sound, but in some of them the presence of an internal opening has been proved by the injection of fluids having colour or taste. The position of the internal openings is also variable, and from the nature of the case has been accurately 1 Paget, Sir J., Trans. Med. Ghir. Soc, lxi., 1878. - Von Kostanecki und Yon Mielecki, Arch. f. path. Anat. u. Phys., cxx. and csxi. 176 MEIilSTIC VARIATION. [part i. determined in comparatively few instances. In a case dissected by Neuhopek 1 there was a fistula on each side, the external opening of the right was \ in. from the middle line and 7 lines above the clavicle, that of the left was 3 — 4 lines higher and further from the middle line. The right internal opening was on the posterior border of the pharyngo-palatine muscle, behind the cornu of the hyoid near the tonsil, tin- left internal opening being rather higher than the right. Internal openings ol such fistulas have also been seen on the edge of the areas pharyngo-palatinus, also in the neighbourhood of the root of the tongue. Seidel 9 gives a case in which there were two fistulas, the one on the right side in the upper position, and the other in the middle line at about the same level, but whether either of these communicated with the pharynx could not be made out. The twin-brother of the -ante infant had a single minute fistula. The ducts of cervical fistulas are usually of greater calibre than the external openings but they are rarely wider than a fine quill. The walls are tough and the lining epithelium is sometimes flat and some- times ciliated. The degree to which the walls are sensitive differs in different cases. The external opening is described in several instances as having a reddish colour. In three cases of the presence of branchial fistulas in female patients, it is recorded that the external openings became inflamed during the menstrual periods. From the point of view of the naturalist the chief interest of cervical fistula? arises in connexion with the question of their mor- phology. Since the time of Ascherson the view has been commonly accepted that these structures arise by persistence of embryonic gill- clefts, and some of the recent writers 3 on the subject have gone so far as to apportion the various forms of cervical fistula? among the several gill-clefts from the first to the fourth, according to the situations of the external openings, giving diagrams shewing the regions occupied by each. As Kostanecki and Mielecki point out, this apportionment is quite arbitrary; for in the development of the neck the external in- vaginations for all the clefts behind the hyoid arch become included in the sinus cervicalis of Rabl (sinus pra?cervicalis of His), which is eventually closed by the growth of the opercular process from the hyoid arch. The external opening of a cervical fistula may thus represent a part of the sinus cervicalis still left open, but it cannot on the ground of its position be referred to any gill-cleft in particular. ►Such reference could only be properly made on the ground of the position of the internal opening and the course of the duct in relation to structures whose relation to the visceral clefts is known. More- over owing to the way in w r hich the 3rd and 4th clefts are shifted inwards by the formation of the sinus cervicalis, Kostanecki and .Mielecki consider that they are practically excluded. The same authors after an analysis of the cases in which the position of the internal opening has been properly ascertained, come to the conclusion that in all these it falls within the region of the 2nd visceral sac 1 Neuhofer, M., Ueb. d. angeb. Hatefistel, Inaug. Diss., Munich, 1847. 2 Seidel, J., Defist. colli cungen., Inaug. Diss., Breslau, 1863. 3 Sutton, J.Bland, Lancet, 1888, p. 308; Cusset, Et ude sur Vappareil branchial, &c, Paris, 1887. chap, vii.] CERVICAL AURICLES. 177 (hyo-branchial). Besides they point out that the evidence in the few cases in which the course of the duct has been traced, shewed that it passed between the external and internal carotids. In their judgment, therefore, cervical listuhe are all to be referred to the second (hyo-bran- chial) cleft. Next it is to be remembered that according to many observers (especially His) there is at no period a complete connexion between the outer gill-clefts and the evagination from the pharynx or branchial sacs, but the membrane separating these chambers is stated by them never to be broken down. If this account is accepted, it is, as Kostanecki and Mielecki have said, necessary to suppose that in the case of any complete cervical fistula a communication between the exterior and the pharynx has arisen by some abnormal occurrence. This is illustrated by reference to the normal condition of the first or hyo-mandibular cleft. Here the auditory meatus represents an external incomplete fistula, and the Eustachian tube an internal incomplete fistula, the two being separated by the tympanic membrane. In a single case given by Virchow 1 a complete passage existed congenitally in this position, together with great abnormality in position and forin of the external ear. From the evidence it may thus on the whole be concluded that incomplete external fistula? result from imperfect closure of the sinus cervicalis, and that incomplete internal fistula? may arise by persistence of one of the branchial sacs, but it is doubtful whether many cases of the latter properly belong to the category of branchial fistula? at all. Supernumerary A iwicles. 144. Abnormal appendages attached to the neck have been described by several observers, and by those who have discussed the subject of cervical fistula? some account of these appendages is generally given. In the neighbourhood of the external ears, especially near the anti- tragus, such structures having the form of small warts or flaps of skin are not very uncommon. Their presence is generally associated with deformity of the external ear, and often with what are known as "aural fistula? 2 ." In the region of the neck, supernumerary auricles 1 Virchow, Arch. path. Anat. u. Phys.. 1865, xxxn. 2 Aural fistulae are spoken of by many writers as being of the same nature as cervical or branchial fistulae. Tbey are blind ducts or pits, opening on some part of the external ear and are nearly always associated with other abnormalities either in the form of the ear or defective hearing, <>1.. xi. p. 172 (two figures). 6 Sutton, J. 13., Evolution and Disease, pp. 84 and 85. 7 Goubaux, Bee. de Med. Veter., Ser. 3, ix. p. 335. 8 Figured by Sutton, I.e., p. 87. CHAPTER VIII linear series — continued. MAMMAE. Some of the phenomena of Meristic Variation are well seen in the case of mammae 1 , and especially in the modes by which increase in the number of these organs takes place. The facts regarding these variations in Man have so often been collected that it is scarcely necessary to detail them again. For our present purposes it will be sufficient to give a recapitulation of the chief observations in so far as they illustrate the pheno- mena of Variation. The most important collections of the evidence on this subject are those of Puech 2 , Leichtexstern 3 , and Williams 4 , from whose papers references to all cases recorded up to 1890 maybe obtained. Besides these, Bruce 5 has given a valuable account of a consider- able number of new cases together with measurements and statis- tical particulars. These accounts contain almost all that is known on the subject but additional reference will be made to original authorities in a few special cases. In Man supernumerary mammae or nipples nearly always occur on the front of the trunk, being usually placed at points on two imaginary lines drawn from the normal nipples, converging in the direction of the pubes. These lines may thus be spoken of as the :t Mammary lines." It is with reference to supernumerary ma mm* occurring on these lines that the subject of mammary variations is chiefly important to the study of Meristic Variation. In addition to these, however, there are a few well authenticated examples .if mammae placed in parts of the body other than the mammary Lines and of these some mention must be made hereafter. 1 It will be understood that facts as to variations consisting in absence of mammae or nipples and other such changes do not come within the scope of this volume, but belong rather to the province of Substantive Variation. 2 Puech, Lea Mamelles et leurs anomalies, Paris, 187<>. 3 Leichtensterx, Virch. Arch.f.patk. Anat. u. Pin/*., 1878, i.xxin. p. 222. This collection was apparently made independently from that of Puech. 4 Williams, W. Roger, Jour. Anat. Phys., 1891, xxv. p. 22-"). 5 Bhuce, J. Mitchell, Jour. Anat. Plnja., lsTK, xin. p. 425. 182 MERIST1C VARIATION. [part i. In the great majority of cases (over 90 per cent., Leichten- STERN l ) of mammae placed on the mammary lines, the supernumer- ary structures are below the normal ones, being then as a rule in- ternal to them, while those found above the normal mammae are less common and are external to the normal mammae. The di- stance separating the normal from the supernumerary mammae (lifters greatly in different cases, and most conditions have been - 11 intermediate between a stage in which the nipple is bifid, and that in which completely separate supernumerary mammae are pre- sented. It is of consequence to observe that there appears to be no case in which a supernumerary mamma is so large as the nor- mal mamma of the same individual. The degree to which supernumerary structures of this nature are developed is very various. They may be fully formed mammae with nipples, in the female capable of function ; while in other cases, on the contrary, they may either consist of nipples only, having no distinguished glandular tissue of mammary character in connexion with them, or they may be tumours of mammary cha- racter without nipples or even definite ducts. Between these >Mveral conditions there is no sharp distinction. It appears there- fore that there are two rudimentary or imperfect conditions possi- ble : either supernumerary nipples without recognizable mammary glands, shading off into small warty elevations of uncertain charac- ter, and on the other hand redundant portions of mammary gland without nipples. The latter may be partially connected w r ith the normal mammae or quite separate from them. All these states of imperfection are much more common than the complete super- numerary mammae. Fully formed supernumerary mammae have been found above the normal mammae and also below them, the latter being the more frequent position. For those found on the mammary lines the axilla is the highest position and the upper part of the abdo- minal wall the lowest. Of the rudimentary forms, the mammary tumours without nipples occur usually if not always above and ex- ternal to the normal mammae, being generally in or near the axilla. The supernumerary nipples however are in the great majority of cases below and internal to the normal ones. Small supernumerary nipples are quite common in Man, but the statistics of different observers £ive various results. Bruce found in 2311 females 14 cases ('605 per cent.), and in 1645 males 47 cases (2"857 per cent.). These persons were patients at the Brompton Hospital for Consumption and were not specially ex- amined with a view to this inquiry. Among 315 such persons examined for the purposes of these statistics, 24 cases were seen (7'6 per cent.), 1 being male and 5 female. In 8 cases two extra nipples were present, and one doubtful case of three extra nipples 1 Not including mammary tumours without nipples in the axilke. CHAP. VIII.] MAMMAE. 183 was seen. Bruce regards 7*6 as for various reasons rather too hio-h o o a proportion. In a recent paper Bardelebex however states that among 2736 recruits examined with regard to supernumerary nip- ples, 637 cases (23'3 per cent.) were seen, 219 being on right side 248 on left side, and 170 on both sides. The discrepancy between these statistics no doubt arises through want of agreement as to the inclusion of cases in which the extra nipples are very rudimen- tary. It seems to be clearly shewn that the abnormality is commoner in men than in women, and there is some evidence that it is more frequent on the left side than on the right (Bruce, Leichtex- sterx and Bardelebex). It is also well established that super- numerary nipples are much more commonly present as single than as paired structures, and that when paired they are by no means always at the same level on the two sides. Cases of the presence of supernumerary mamma? as paired structures symmetrically placed are nevertheless sufficiently numerous. Organs of this na- ture may also occur simultaneously on the same side of the bod}* at different levels. For example in one of Leichtexsterx's cases, a small secreting supernumerary mamma with a nipple was pre- sent in the left axilla, while there was also another supernumerary nipple on the lower border of the left breast. The greatest num- ber of supernumerary nipples occurred in a case described by Neu- GEBAUER 1 , represented in Fig. 29. In this patient there were on each side three supernumerary nipples above the normal ones, and Fig. 20. Diagram of a case of four pairs of supernumerary nipples in human female. The normal breasts raised to shew the lowest pair. (After Nedgebaueb.) 1 Neugebaueb, F. L., Gentralb.f. Gyndk., 1886, p. 729. 184 MERISTIO VARIATION. [part i. «»ne on each side below them. The latter were concealed by the pendent breasts. When the child was being snckled milk oozed from each of the uppermost or axillary nipples, but from the remaining six supernumerary nipples milk could only be extracted l>v pressure. The flowing of milk from supernumerary nipples when the child is at the normal breasts, has often been observed. A few references to cases exhibiting the several features above mentioned may be of use. 149. Bifid nipple, the same on each breast [plane of division not specified]. Duval, 1>" Mamelon et de son aureole, Paris 1861, P-90. 150. Two nipples on the same areola, bilaterally symmetrical. The two nipples stood in the mammary line defined above. Tiedemann, Ztsck.f Physiol, v.. L833, p. 110, Taf. i. fig. 3. 151. Cases are given by Charcot and le Gendre, Gaz. vied, de Paris, 1859, p. 773, in which an extra nipple was placed external to the normal one on the same breast. In one of these the extra nipple had no areola. Leichtenstern (p. 253) in quoting these cases, speaks of them as instances of supernumerary nipples on the same level as the normal ones, but this is not expressly stated in the original account, which does not, as I think, exclude the possibility that the supernumerary nipples were above and external to the normal ones. Two functional nipples with separate areolae on the left breast, which nevertheless was not larger than that of the light side, ibid. The same authors mention another case in which such a second nipple had no areola ; the mother of patient stated to have been the same. See also SlNETY, Gaz. wed. de Paris, 1887. p. 317 (full description and measurements). In this ease the supernumerary nipple was placed below 7 the normal one. 152. A case in which three nipples were placed on each breast is given by PAULLINUS, Miscell. Curios., &c, 1687, Decur. ii. Ann. v. Append, p. 40. The case is given on the authority of Prackel and the three nipples are said to have been arranged in an equi- lateral triangle, the normal being above at the apex, and the two others at the same level below. The description and the figure accompanying it do not however justify complete confidence in this observation, and indeed the contributions of Paullinus to the Miscellanea Curiosa contain so much of the marvellous that they should not be accepted without hesitation. The same may be said of the case of five nipples each having an areola quoted by Percy and Laurent, Diet. Sci. med., xxxiv. p. 517, .9. v. " Multi- mamme." The authority for this case is a letter of Hannseus to Borrichius, dated 1675. I have not found any observation of this class of abnormality later than the seventeenth century, but it is of course quite possible that cases may occur in which the nipples are distributed on the breast otherwise than along the mammary lines. CHAP. VIII.] MAMMAE. 185 153. Supernumerary mamma with nipple in axilla, Leichtenstern, p. 245, and others. 154. Supernumerary mamma above and external to the normal ones. Numerous cases; see especially case of two bilaterally symmetrical mammae in this position, Shannon, Dubl. Med. Jour., 1848, v. p. 26Q,Jig. [figure repeated by Ahlfeld, Williams &c.]; also similar case, Quinquaud, Rev. photogr. des hop., 1870, p. 10. 155. Supernumerary mammae below and internal to normal ones: numerous cases, see Leichtenstern, &c. In nearly all these the Fig. 30. Supernumerary nipples and mammae of different sizes in human female. (After Bruce.) supernumerary organs are close to the normal mamma'. A few examples of such structures on the upper part of the abdominal wall are known, e.g., Tarnier in his edition of Cazeaux, Traite de Vart des Accouchements, 1870, ed. 8, p. 86. In the male several such cases are recorded, e.g., Bruce, J. Anat. Phys., XIII. 1879, p. 446, PL Examples of this kind in the female are shewn in Fig. 30 (after Bruce) and in the male in Fig. 31 (after Leichtenstern ). 156. Mammary tumours in the axilla are described by Champneys, Med. Chir. Trans., 1886, lxix. p. 419, as of common occurrence in lying-in women. These structures are of various sizes and without any nipple, pore, or duct. The secretion was obtained by squeez- ing the lump and oozed through the skin at the situations of the sebaceous follicles. In this manner both colostrum and milk were obtained, following each ether as in the normal mammae. Similar observations in single cases have been made by many writers. 157. Redundant mammary tissue of this kind connected with, and thus forming an axillary extension of the normal mammae, CAME- RON, Jour, Anat. Phys., 1879, XIII. p. 149; also Notta, Arch, de Tocologie, 1882, p. 108. 186 MERISTIC VARIATION". [part I. *1 K 158. Two pairs of supernumerary mamma- below the normal ones, DE MORTILLET, Bull. Soc. d'Anthrop., L883, Ser. 3, vi. p. 458. An Fig. 31. Supernumerary mammae in the male, symmetrical and asymmetrical. (After Leichtenstern.) important case of a man having two pairs of supernumerary mammae on the mammary lines. There was a gradual diminution in size from the highest to the lowest, the latter being a little above the level of the umbilicus. Each pair was at the same level. 159. Four pairs of supernumerary nipples (ten in all) are recorded only in Neugebaxter's patient, already mentioned. Three of the supernumerary pairs were above the normal ones, and the other pair below them. As seen in Fig. 29 the nipples of each pair did not stand in the case of each pair at precisely the same levels, and between those of the lowest pair there was a considerable differ- ence of level, that on the left side being at some, distance below the normal breast, while that on the right side was on its lower border. In a few cases the supernumerary nipple is described as having been perpendicularly below the normal one, and it is likely that such cases must be looked on as exceptions to the general rule that the mammary lines converge posteriorly; but it is not impos- sible that even in some of them the supernumerary nipple might have been found to be rather nearer the middle line if this point had been specially inquired into. The foregoing examples are given as selected illustrations of the several facts, and for full lists of cases the reader is referred to the works already mentioned. ICO. Of supernumerary mammae placed in parts of the body other than the mammary line some mention must be made, though those of them chap, viii.] MAMMAE. 187 tliat are authentic have no close bearing on the subject of Meristic Variation. There are firstly two often quoted cases 1 in the Miscellanea Curiosa in which mammae are said to have been present on the back, but as has already been remarked, many of the stories told in this collection are clearly fabulous, and this is especially true of the contri- butions of Paullinus. Both these records are given at second hand and the first case (Paullinus) is said to have been seen in 1564, more than a hundred years before the date of the account. Helbig's accounts of things seen by himself are generally trustworthy, but in this case lie is only repeating what w T as told to him by a Polish noble about a woman seen in Celebes. There are no modern cases on record. There is however indisputable evidence of the presence of a mammary gland on the thigh (especially Robert's case ; for references to several accounts of this see Leichtenstern, p. 255); on the cheek, Bartii, Arch. f. path. Anat. u. Phys., 188, p. 569; on the acromion, Klob, Ztsch. f. K. K. Ges. d. Aerzte in Wien, 1858, p. 815; in the labium majus, Hartung, Ueb.einen Fall von Mamma Accessoria, Inaug. Diss., Erlangen, 1875. In the two last cases the mammary nature of the gland was proved by microscopic examination. In Earth's case of a mamma on the cheek the microscopical investigation did not give a certain result (q. v.). As Leichtenstern shewed, the case of inguinal mamma, mentioned by Darwin and others, really related to Robert's case of a femoral mamma. In 1885, however, Blaxchard (Bull. Soc. d'Anthrop., 1885, p. 230) stated that Testut had lately seen such a case and was about to publish an account of it, but this has not yet appeared (1892). Most writers on the subject have accepted cases of supernumerary mamma placed anteriorly in the middle line. These are given by Percv and Laurent, Diet. Sci. med., xxxiv., 1819, on the authority of several different persons. One case was seen by themselves (p. 526), and in it the third mamma stood below and between the other, forming a triangle with them. In another case given on the authority of Goi;i:i: there are said to have been a pair of extra mammae below the normal ones, and a fifth between the supernumeraries. In view of the fact that many paired organs may by Variation occur compounded in the middle line, there is nothing incredible in these accounts, nevertheless there is, so far as I know, no recent observation of such an occur- rence in the case of mammse, and with the one exception (which is very briefly described), the accounts given are at second hand". It is moreover not clear that the words used ll ai(-tlr#*nHit et an milieu des deux autres" do not mean simply below and between the other two. The case contributed by Gorre is nevertheless given in great detail and cannot lightly be set aside. Before speaking of the bearing of these facts on morphological conceptions it is necessary to refer to some of the phenomena of 1 Paullinus, Miscell. Curios., &c., Dec. ii., Ann. iv. 1686, p. 203, Appendix, giving a case said to have been seen in 1564; also Otto Helbig, ibid., Dec. i., Ann. ix. and x., pubd. 1693, p. 45(j. 2 Williams (p. 235) quotes Baktels, Arch. f. Anat, 1872, p. 306, as alluding to such a case, but I do not think that the passage is meant to convey this meaning. 188 MERISTIC VARIATION. [part I. mammary Variation in other mammals. In connexion with the case of Man it may be mentioned that supernumerary mamma below and internal to the normal ones has been seen in Macacus and in Cercopithecus patas, Sutton. J. B., Intern. Jour, of Med. Sci., 1889, XCVII. pp. 2o2 and 253; in the Orang-utan, Owen, Con/p. A nut., iii. p. 780. In many mammals the number of the mammae is very inconstant even within the limits of species and from the facts seen in such cases deductions may be drawn which arc at once instructive as to the nature of mammarv Variation and have an application to the morphology of Meristic Series in general, of these I shall give examples taken from three species. '161. The first is that of the cow's udder. Normally the cow has four teats of about equal size. Not unfrequently there are six teats, of which four are large and may be said in the usual parlance t<» be the " normal " ones, and two are small and placed posteriorly to the others. A case of this kind is shewn in Fig. 32, II. Commonly these extra teats give no milk, but in many cases they have been known to do so. Their size and position vary greatly; sometimes they are placed near the other teats as shewn in the figure, but I have seen them very high up, almost in the fold between the udder and the thighs. Very frequently, however, there is only one extra teat making five in all, such an extra teat being so far as I know, always on Fig. 32. Supernumerary teats in two heifers. I. The third teat is completely separate on the left side, but on the right side is united with the second. (The cleft between the two is incorrectly represented as a sharp line ; there was no such sharp line of demarcation; the skin being very slightly depressed in this place.) II. Teats of the third pair both completely separate. CHAP. VIII.] MAMMAE. 189 *162. one side of the udder. The sketch given in Fig. 32, I. was taken from a heifer having an arrangement intermediate between the condition with four teats and that with six. As the figure shews, on the left side there were three complete teats but on the right side the third teat was incompletely separated from the second. This third teat was joined to the second for its whole length but had a separate pore. The animal which belonged to the St John's College Dairy Farm was unfortunately sold before the first calf was born, so 1 had no opportunity of seeing whether milk was given by both these teats. The significance of such a case will afterwards appear. In many mammals, such as the pig, rabbits, cats and dogs, the mammae are distributed in two mammary lines along the ventral surface. The number of the mamma? in such cases is noto- riously variable, and in some respects this variation is interesting and has a bearing on questions of the nature of Meristic Repetition. If a number of such animals be examined it will be found that as a rule there are the same number of glands on the two sides, and that they are arranged in pairs, those of each pair standing at the same level or nearly so. Nevertheless departures from this ar- rangement are very frequent. Individuals are in the first place commonlv found with a different number of mammae on the two sides, and in such cases it is interesting to observe that together w T ith the difference in the number of mammas on the two sides V V Fig. 33. Diagram of nipples in a male Bull-dog. On right side, four ; on left, five ; the two anterior and two posterior being almost at the same levels. umb. umbilicus. The dotted line shews the outline of the thorax. 190 MERISTIC VARIATION. [part i. there is generally if aot always a disturbance in the paired arrange- 1G3. ment. A simple case of t his kind occurring in the dog is represented in Fig. 33. The animal is a male bulldog lately in my possession. On the right side there arc four nipples, while on the left there are five. The most anterior on each side stand almost at the same level on the thorax. The second on each side are almost at the same distance below them, that on the left side being J in. higher. Similarly the most posterior nipples stand on each side at almost exactly the same level od the sheath of the penis, the total length from the first to the last nipple on each side being practically the same. On the left however there are two nipples placed between the second and the last, but on the right there is only one. This one nipple stands at a level not far from the middle between the old and 4th of the other side, making as it were a complement to or balance with them. 164. Thirty-five young pigs examined with regard to these questions gave the following results. They belonged to five litters (30 pure- bred Tarn worths ; 5 cross-bred, out of Berkshire sow, sire unknown). These pigs were all quite young, about a fortnight old, and conse- quently there was no displacement due to functional development of the glands. M.AMHLM. Right. Left. Pigs. A. 6 — regular! v arranged in pairs 3 B. 7 — 7 ditto 10 C. 7 — 7 ditto 5th rudimentary 1 D. 8 — (S ditto 4th rudimentary 3 E. 7 — 8 all paired exc. 1. 4th rudimentary 2 F. 7 — 8 1. 4th rudimentary, 1. 3rd and 5th displaced... 1 I 1 . 7 — 8 rt. 2nd balances 1. 2nd and 3rd 1 H. 8 — 71. 2nd balances rt. 2nd and 3rd 1 I. 8 - — 7 1. 3rd balances rt. 3rd and 4th 1 K. 6-7 rt. 1st balances 1. 1st and 2nd 1 L. 6—7 l.-2nd rudimentary 1. 1st and 3rd displaced... 1 M. 6 — 7 all paired exc. 1. 4th rudimentary 1 X. 7 — 7 altogether irregular 4 O. 6 - - 6 ditto 2 P. 7 — 6 ditto 1 Q. 7 — 8 ditto 1 R. 8 — 7 ditto 1 Total 35 The animals in groups D and E, except one of the latter, be- longed to the same litter. In them a small rudimentary nipple stood between the 3rd and 5th, but the latter were not spaced out for it, being no further apart than any of the others. The measure- chap, viil] MA1DLE : COMMENT. 191 ments of the distances between the nipples on one side in one of these cases were, in inches, 1^, 1, T %, ^, ji, ±£ , j* , the rudimentary nipple standing ^ in. from either of its neighbours. In the I) O i o o o O I Ol Ol 1 o 2 j O _> 02 .2 O O O 3 O 2 ■4 O ° " , 30 04 0-5 °4 3 3 O 4 O 5 olO O* O O .5 O ° o 4 05 O O , ~ O O O O 5 O 06 OO O O 7 o o 8 6 o o 7 7 a o 8 6 o o 7 6 o o 7 E F G K L Fig. 34. Diagrams of nipples in very young pigs. Letters refer to groups in No. 164. group this was found on both sides, but in the E group on one side only, as in the figure (Fig. 34). Comment on foregoing evidence. On looking at a series of cases like those roughly illustrated in the diagrams, one is tempted to inquire as to the factors which determine the positions of these mammae and nipples. Though such an inquiry must lead to small definite results it may not be unprofitable to point out some deductions which may be made from the facts. I take this opportunity as a good one for illus- trating the position here adopted with respect to the theory of Reversion, and for discussing certain features of the phenomena of Division. The mammary glands form an example of a class of Meristic organs which are distributed in series along a body already seg- mented, but whose positions have no obvious coincidence with the fundamental segmentation. In the case of the pig, for instance, it would doubtless be found that the mamma; bear more or less definite relations to particular vertebrae, but they are not limited to such positions as the ribs or spinal nerves must be. The seg- mentation of the mammae is thus a segmentation, or serial arrange- ment, superadded upon that of the vertebra 1 . The question to be considered is. what determines the points at which mammae are to be formed ? In the paper to which reference has been made, Williams has contended for the view that each somite bore originally a pair of mammae; and we may remark that if this were so the problem of the segmentation of the mammae would be the same as that of the 192 MERISTIC VARIATION, [part i. general segmentation of the trunk. The same author then argues that the appearance of supernumerary nipples or mammae along the mammarv lines is a reversion to an ancestral condition, and a figure is given, shewing the places at which mamma? are on this view believed to have been placed, definite ordinal numbers being- assigned to each. Against this suggestion may be urged those ob- jections to appeals t<» the hypothesis of reversion which were men- tioned in the Introduction (Section XII.), but in addition to these there are a number of objections applying specially in the case of mammary Variation. The view that supernumerary mammae are reversions rests on the frequency and definiteness with which they occupy certain positions. But though they do occur more often in some positions than in others they are in no sense limited to these positions, for they may stand anywhere, at least upon the mammary lines. To justify the view that the positions of super- numerary mammae are definite it is necessary to exclude the cases of bifid nipple, of multiple nipples on the same breast, and of axil- lary extensions of the mammae, all which phenomena would then be looked on as belonging to a class different from that of actual supernumerary mammae. In the argument referred to, this course is actually adopted. The acceptance of such a view leads to great difficulty. For example, in Neugebauer's case (see Fig. 29), Williams considers that the posterior nipples of the two sides be- long to different pairs, and have consequently different homologies, because they stand at different levels. Such distinctions are, I believe, unreal. It is surely impossible to suppose that the Repetition seen in the udders of the two cows in Fig. 32 is a phenomenon different in the two cases. In the one there are two extra teats in symmetrical positions, equally spaced out from the second teats ; in the other there is a third teat on one side and a double second or posterior teat on the other. Surely it is clear that the double condition of this teat represents an im- perfect phase of a process perfected on the other side. If further proof were needed it may be found in the fact already mentioned, that the mammae of the pig and other such animals, may be the same in number even on the two sides, but nevertheless stand quite irregularly and without any visible arrangement into pairs. The existence of these cases in which no order of form or regul- arity can be traced may seem at first sight to be an insuperable objection to any attempt at the detection of principles in the ar- rangement of the mammae. There is however the fact that many, and indeed in must forms the majority of individuals do shew an orderly and paired arrangement, and the further fact that of those cases which depart from this, a certain number present appear- ances which suggest that this departure has come about in a regular way. Though the irregular cases remain, something would be gained if we could comprehend any of the elements on which the regularity depends. The case of regularity and symmetry, in a chap, viil] MAMM.£ : COMMENT. 193 sense, includes the cases of irregularity. The difficulty is to under- stand the causes of regularity and of symmetry ; but if we could be sure of these it would not be hard to conceive disturbances result- ing in irregularity. In the pigs are found, first, cases of six on both sides in pairs, and also of seven on both sides in pairs ; besides these there were cases of 6 — 7 and of 7 — 8. Of these there were some in which two on one side stood in positions which geometrically balanced that of one of the other side, the others being arranged in pairs. In such cases the appearances suggest that there has been a division of one mamma to form two, and that the two have then separated or travelled apart. The division of organs into two is of course a common occurrence, and may naturally be supposed to be a pheno- menon of the same nature as the division of single cells. The case of mamma? is perhaps instructive inasmuch as it bears witness to the fact that such division must take place at a remotely early period in development. For while in cases to be given hereafter of division, for example, between teeth, it may be supposed that the travelling apart of the two resulting teeth is mechanical, in the sense that the two growing teeth may simply push apart from each other just as two cartilage- cells, &c, may separate by the concen- tric deposition of material, the separation cannot be supposed to occur in the mamma? by these late changes, but the process of mechanical separation, though the same in kind as that in the case of teeth, must be conceived as beginning early in the history of segmentation. At this point a circumstance, very often to be seen in other cases, should be mentioned. When an organ, single on one side, corresponds geometrically with two organs on the other side, each of the latter is frequently of the same size and developed to a like extent as the single one of the other side. This of course would be expected on the hypothesis that the division of organs is a pheno- menon similar to the division of cells, that is to say, not merely a division, but a reproduction. But the supposition of division of single members of the series is not sufficient to account for all the facts of Variation seen. We have to consider not only the case in which one organ of one side balances two of the other. We have to deal also with the cases of six on each side and seven on each side all corresponding in pairs. In these there is no indication that there has been a division of a single member on each side. The spacing is regular in each case and there is no obvious crowding at any part of the series. Even if therefore in the former case there is a suggestion that the genus of single mamma? have divided into two at a period of develop- ment after the series of mamma? was constituted as a series, there is no such suggestion in the present case. We must, I think, in the latter suppose that the existences of all the mamma?, whether b. 13 194 MERISTIC VARIATION. [part I. six or seven, are determined together. How or at what stage such determination is made, there is no direct evidence to shew. The various arrangements seen suggest then that the relative positions occupied by the mammae depend partly on the number that are present, and that the position of each mamma is to some extent dependent on the position of other mamma?, especially of its neighbours. In this connexion the cases F and L are interesting- ones (Fig. 34). In L for example, the 1st on the left is at a higher level than the 1st on the right. It is succeeded by a rudimentary 2nd having none on the same level on the other side. The left 3rd is behind the right 2nd, but posterior to this point the nipples are approximately paired. These appearances suggest that the dis- placement of the 1st and 3rd on the left are in some way connected with the presence of the rudimentary left 2nd. Similarly in F the left 3rd and 5th are spaced out for the rudimentary 4th. From its position and small size it might fairly be supposed that this is a " supernumerary " organ, for at all events it is visibly different from the others : but in the case of seven on each side in pairs, no one mamma rather than another can be pointed out as obviously supernumerary when compared with a similar series of six. It seems therefore that of the factors determining the relative posi- tions of the mamma? along the mammary lines, the number of the mamma? is one, and that the positions of the mamma? are in some way and to a limited extent correlated with each other. That there are other factors at work, also, is sufficiently shown by the exist- ence of cases of apparently utter irregularity. In seeking to go beyond this and inquire as to the way in which this correlation is brought about there is, in the present state of knowledge of the mechanics of Division, not much to be gained. Reference may be made to recent observations published in abstract by O. Schultze 1 . According to him there is in young- embryos of several mammals (Pig 1*5 cm. long; Rabbit 13 — 14 days, &c.) a ridge running along the dor so-lateral aspect on each side and at points upon this the mamma? and nipples are even- tually formed. (The formation of the true nipples is preceded by the raising of. the epidermis into small elevations, "primitive teats," which afterwards disappear.) The two mammary lines are by subsequent changes and growth of the body brought into the ventro-lateral position. The question of the position of the mamma? therefore resolves itself into this : what determines the positions at which mammary centres, to borrow the word used in the case of bone, are to be formed on the mammary lines ? In a subse- quent place I shall contend that the facts given are only intelli- gible on the view that the forces determining the points of growth of mamma? are compounded into one system of forces. But to the question what are these forces there is no answer. 1 0. Schultze, Anat. Anz., 1892, vn. p. 265, since published in full {Verh. d. phys.-med. Gee. zu WUrzburg, xxyi. 1893, p. 171, Pis.). CHAPTER IX. linear series — continued. Teeth. From the consideration of numerical Variation in mammae we may proceed to an examination of like phenomena in the case of the teeth of vertebrates. The modes of Variation in these organs are, as might be expected, in many ways similar, but several cir- cumstances combine to make the Variations of teeth more com- plicated than those of mammae. Teeth arise developmentally by special differentiation at points along the jaws, much as the mammae arise by differentiation at points along the mammary lines ; and as in the case of mammas, so in the case of teeth, we are concerned first with changes in the number of points at which such differentiation takes place, and next with the general changes or accommodations which occur in the series in association with numerical changes. As in mammas, so also in teeth, numerical Variation may occur sometimes by the division of a single member of the series into two, and sometimes by a reconstitution of at least a considerable part of the series. Between the case of mammas and that of teeth, there is how- ever an important point of distinction. The series of mamma? is practically an undifferentiated series. There is between mammae standing in one mammary line no obvious qualitative differentia- tion. Though not all identical in structure, the differences between them are of size and of quantity, not of form or quality. If such qualitative difference is present it must be trifling. In con- sidering Variation in mammae we have thus to deal only with changes in number, and with the geometrical and perhaps mecha- nical question of the relative positions of the mammae. The teeth of most Vertebrates, however, are differentiated to form a series of organs of differing forms and functions, and the study of Variation in teeth may thus be complicated by the occurrence of qualitative changes in addition to simply numerical ones. In teeth, in fact, there are not only Meristic variations, but Substantive variations 13—2 196 MERISTIC VARIATION. [part i. also ; and thus, as in the case of vertebrae, for instance, in any given example of a numerical change qualitative changes must be looked for too. As a preliminary to the consideration of evidence relating to the Variation of teeth it may be useful to call attention to certain peculiarities of teeth considered as a Meristic Series. In the Introduction, Section V, it was pointed out that in order to get any conception of the Evolution of parts repeated in an animal, the fact of this Repetition must be recognized, and it must be always remembered that we are seeking for the mode in which not one part but a series of similar parts has been produced. The simplest case to which this principle applies is that of organs paired about the middle line, and in the steps by which such parts have taken on a given form it is clear that similar variations must have occurred on the two sides. In the absence of evidence it might be supposed either that such variations had occurred little by little on the two sides independently, or on the other hand, that Variation had come in symmetrically and simultaneously on the two sides. Upon the answer given to this question the success of all attempts to form a just estimate of the magnitude of the integral steps of Variation depends. In many examples already given it has now been shewn that though in the case of paired organs Variation may be asymmetrical, yet it is not rarely symmetrical, and in part the question has thus been answered. In the evidence that remains many more cases of such sym- metrical variations will be described, and it may be taken as established that when the organs stand in bilateral symmetry, that is to say, as images on either side of a middle line, their Varia- tion may be similar and symmetrical. The teeth present this problem of the Variation of parts stand- ing as images, in an unusual and peculiar w T ay. For in the case of teeth we have to consider not only the steps by which the right and left sides of each jaw have maintained their similarity and symmetry, but in addition the further question as to the relation of the teeth in the upper jaw to those in the lower jaw. There are many animals in which there is very great difference between the upper and lower rows of teeth, and it must of course be remembered that perhaps in no animal are the teeth in the upper jaw an exact copy of those in the lower, but nevertheless there is often a substantial similarity between them, and in such cases we have to consider the bond or kinship between the upper and lower teeth whereby they have become similar or remained so. For it may be stated at once that there is some evidence that the teeth in the upper and lower jaws may vary similarly and simul- taneously, though such cases are decidedly rare, especially in numerical Variation, and are much less common than symmetrical Variation on the two sides of the same jaw. chap. IX.] TEETH I PRELIMINARY. 197 In speaking of the relation of the series of the upper jaw to that of the lower jaw as one of images., it must be remembered that the expression is only very loosely applicable. In particular it should be noticed that though in so far as the lower teeth are a copy of the upper ones the resemblance is one of images, yet the teeth which resemble each other do not usually stand opposite to each other in the bite, but members of the upper series alternate with those of the lower. The incisors, as a rule, however, and the back teeth of a certain number of forms do bite opposite each other, and in them the relation of images is fairly close. The importance of the recognition of the relation of images as subsisting between the teeth of the upper and lower jaws will be seen when this case is compared with that of the two sides of the body. For ordinary bilateral symmetry is, as has already been suggested, an expression of the original equality and similarity of the two halves into which the ovum was divided by the first cleavage-plane, or by one of the cleavages shortly succeeding upon this. The fact that the two halves of the body are images of each other is thus both an evidence and a consequence of the fact that the forces dividing the ovum into two similar halves are equal and opposite to each other. The bilateral symmetry of Variation is thus only a special case of this principle. In view of the fact that the teeth in the upper and lower jaws may vary simultaneously and similarly, just as the two halves of the body may do, it seems likely that the division of the tissues to form the mouth-slit must be a process in this respect comparable with a cleavage along the future middle line of the body. It is difficult, however, to realize the actual occurrence of such a process of division in the case of the slit forming the original stomodoeum, and this difficulty is increased by the recent observations of Sedgwick 1 to the effect that in the Elasmobranchs examined by him the mouth-slit first appears as a longitudinal row of pores. If this is so the relation of images must exist in the case of the mouth, not only in respect of the two sides of the slit, but also in respect of the anterior and posterior extensions of the slit. But whatever may be the processes by which the tissues bounding the mouth of a vertebrate come apart from each other, the result is clearly in many cases to produce an anterior series of organs in the upper jaw, related to a posterior series of organs in the lower jaw, much in the same way that the right side of a jaw is related to the left of the same jaw. This relation may appear as has been stated, not only in the normal resemblances between the upper and lower teeth, but also in the fact that similar and simultaneous Variation is possible to them. In another respect the Repetition of teeth may differ from that of other Linear Series already considered. In many animals, the 1 Sedgwick, A., Quart. Jour. Micr. Sci., 1892, p. 570. 198 MEMSTIC VARIATION. [part i. Pike, the Alligator, or the Toothed Whales, for example, the teeth stand in a regular and usually continuous series, differing from each other chiefly in size, ranging from small teeth in front, through large teeth, and often down to small teeth again at the back of the jaw. Such a 'homodont' series as a rule passes through only one maximum. Most mammals, however, are 'heterodont,' that is to say, the teeth can be distinguished into at least two groups, the incisors and canines on the one hand, and the pre- molars and molars on the other ; and in a large number of animals having this arrangement the anterior members of the series of premolars and molars are small, increasing regularly in size from before backwards, reaching a maximum usually in some tooth anterior to the last. Though instances will be given of Variation, and especially of reduplication, occurring in most of the teeth, even in those which stand well in the middle of the series of back- teeth, such as the upper carnassials of the Cat, or the fourth pre- molars of the Seal, yet on the whole Variation in heterodont forms is more common at the anterior and posterior ends of the series of back-teeth. In view of this fact it is of some importance to recognize that the small members at the beginning of the pre- molar series are as regards their relatively small size, in the con- dition of terminal members of series, and exhibit the variability of terminal members almost as much as the last molars. With these remarks by way of preface, evidence as to the numerical Variation of teeth in certain groups will be given in full. This account will for the most part be confined to a brief description of the conditions presented by the specimens. In the next chapter the principles which may be perceived to underlie these facts and the general conclusions to which they appear to lead will be separately discussed. The evidence here given relates to certain selected groups 1 of Mammals, and chiefly to the Primates (excepting Lemuroidea), Car- nivora (CanidaB, Felidse, Viverridse, Mustelidse and Pinnipedise), and Marsupialia (Phalangerida?, Dasyurida^, Didelphyidas, part of Macro- podidae, &c). The facts to be given relate chiefly to increase in number of teeth. In the case of terminal members of series, such as the most anterior premolar or the last molar, some reliable facts as to cases of absence were found, but for the most part the evidence as to the absence of teeth is ambiguous and each case requires separate treatment. The evidence is in this chapter arranged according to the 1 Evidence as to the dental variations of Man is not here introduced. Con- siderable collections of such facts have been made by Magitot {Anom. du syst. dent.), Brscn (Dent. Monats. f. Zahnh. 188fi, iv.), and others, and illustrative specimens are to be found in most museums. I do not know that among these human variations are included phenomena different in kind from those seen in other groups, except perhaps certain cases ot teeth united together, a condition rarely if ever recorded in other animals. chap, ix.] TEETH ! PRELIMINARY. 199 zoological position of the groups concerned. In several cases variations of similar nature were seen in different groups ; cases of this kind will be brought into association in the next chapter. As regards nomenclature I have in the main followed the common English system, numbering both the premolars and molars from in front backwards. In one respect I have departed from the practice now much followed. It has seemed on the whole better that the premolar which in any given jaw stands first, should be called p 1 , even though in certain cases there may be reasons for doubting whether it is the true homologue of the p 1 of other cases 1 . Theoretical views of this kind can only at best be used as a substitute for the obvious nomenclature in a few re- stricted cases, such as that of the Cat, in which by the application of the methods of reasoning ordinarily adopted in Comparative Anatomy the first upper premolar would be looked on as the equivalent of p 2 in the Dog. There are, however, few who would feel confident in extending this reasoning to many other cases, that of Man, for instance, and I believe it is on the whole simpler to number the teeth according to their visible and actual relations. As I have already attempted to shew in another place 2 , in the light of the facts of Variation, it is to be doubted whether in their varia- tions teeth do follow those strict rules of individual homology by which naturalists have sought to relate the arrangements in dif- ferent types with each other. The material examined has consisted chiefly of specimens in the British Museum and the Museums of the College of Surgeons, Leyden, Oxford and Cambridge, the Paris Museum of Natural History, and some smaller collections. I have to thank the authorities of these several museums for the great kindness I have received from them; and in particular I must express my indebtedness to Mr Oldfield Thomas, of the British Museum, for the constant help and advice which he has given me, both as regards the subject of teeth generally and especially in examining the specimens in the British Museum 3 . PRIMATES. S0111D.E. The Anthropoid Apes (Orang, Chimpanzee, and Gorilla). *165. The teeth of the three large Anthropoids arc perhaps more variable, both in number and position, than those of any other 1 In cases where confusion might arise any change from common nomenclature is notified in the text. 2 Proc. Zool. Soc, 1892, p. 102. :i In the following descriptions B.M. stands for British Museum; C.S.M. lor Museum of the Boyal College of Surgeons; CM., O.M., U.C.M., Leyd. M., P.M., for the Cambridge, Oxford, University College London, Leyden and Paris Museums respectively. 200 MERISTIC VARIATION. [part i. group of mammals of which I have been able to examine a con- siderable number. In different collections 142 normal adult skulls were seen and 12 cases of extra teeth. Of these one was a case of extra incisor (Gorilla, No. 186), one of anomalous teeth (Gorilla, No. 187), and the remainder molars. Thus far therefore there are nearly 8 per cent, cases of extra teeth. This figure is remarkable in comparison with the rarity of such cases in Hylobates (51 skulls seen, all normal), and the like rarity in other Old World monkeys (42-S normals and 2 cases of extra teeth). Simia satyrus (Orang-utan). Normal adult skulls seen, 52. Supern itinerary molars. 166. Adult male haying additional posterior molar (m 4 ) behind and in series with the normal teeth, on both sides in upper jaws and on left side in lower jaw. In each case the in 4 is rather smaller than ??i 3 , but all are well formed, having each four cusps and the normal complement of fangs, viz., one in front and one behind in the lower jaw, and two on outer and one on inner side in upper jaw. On right side of lower jaw there is no trace of additional molar, though there is almost as much room for it as on the left side. C. M., 1160, D, described by Humphry, G. M., Jour. Anat. Phys., 1874, p. 140, Plate. 16/. Female (Borneo) having six cheek-teeth in each upper jaw and in right lower jaw [doubtless a case like the foregoing] mentioned by Peters, W., Sitzungsb. naturf. Fr. Berlin, 1872, p. 76. 1G8. Specimen with large alveolus on each side for w\ L. M., 24. 169. Specimen (Borneo) having m 4 in right lower jaw, behind and in series with the normal teeth. The tooth is of rather small size, but is regular in position and form. B. M., 3, m. 170. Specimen having a right ^ more than half the size of m :i - U. C. M., E, 253. 171. Specimen having supernumerary molar on each side in lower jaw. Mayer, Arch. f. Nature/., 1849, 1. xv. p. 356. 172. Similar case. Fitzinger, Sitzungsb. math. — nat. CI. Ak. Wien, 1853, i. p. 436. Similar case. Bruhl, Zar Kenntniss des Orangkopfes, Wien, 1856. [] refers to the case described by Fitzinger.] Molar absent. 173. Specimen "remarkable for absence of the upper right third molar and for absence of nasal bones, which are greatly reduced in some other specimens." C. S. M., 44. See Catalogue Mus. Coll. Surg. 1884. The other teeth are all normal and fully formed. Variations in position of teeth. Though not directly pertaining to the subject here considered, the following examples of consider- chap, ix.] TEETH : ORAXG. 201 able departure from the normal arrangement may be perhaps usefully introduced in illustration of the peculiar variability of the dentition of the group. *174. A skull from Borneo in the Oxford University Museum (num- bered 2043 a) has the following extraordinary arrangement. All the teeth are normal and in place except the second premolar of each side in the upper jaw. On both sides there is a large diastema between p 1 and «^. The diastema on the left side is of about the same size as the normal second premolar, but that on the right side is considerably too small for a normal tooth. The singularity of this specimen lies in the fact that the missing tooth of the right side is present in the skull, but instead of being in its proper place it stands up from the roof of the mouth within the arcade immediately in front of the right canine and almost exactly on the level of the second incisor, being in the premaxilla, at some distance in front of the maxillary suture. That this tooth is actually the second premolar which has by some means been shifted into this position there can be no doubt whatever. It has the exact form of the normal second premolar, and is of full size. It stands nearly vertically but is a little inclined towards the outside. The canine is by the growth of this tooth slightly separated from the second incisor, and the first premolar is consequently pushed also somewhat further back. Hence it happens that the diastema for the second premolar on the right side is not of full size. This should be understood, as it might otherwise be imagined that the contraction was due to a complementary increase in the size of the other teeth, of which there is no evidence. On the left side of the palate there was a very slight ele- vation at a point homologous and symmetrical with that at which the second premolar of the right side was placed. As it seemed possible that the missing tooth of the left side might be concealed beneath this elevation, a small piece of bone was here cut away, with the result that a tooth of about the same size and formation as f; was found imbedded in the bone. In this case therefore the second premolar of the right side and of the left side have travelled away from their proper positions and taken up new and symmetrical positions in the palate, anterior to the canines. The facts of this case go to shew that the germ of a tooth contains within itself all the elements necessary to its development into its own true form, provided of course that nutrition is unrestricted. This might no doubt be reasonably expected ; but since the forms of organs and of teeth in particular are by some attributed to the mechanical effects of growth under mutual pressure, it may be well to call special attention to this case, which goes far to disprove such a view. 175. Specimen having the teeth of the two sides in the lower jaw in extraordinarily asymmetrical disposition. The bone of the jaw does 170. 177 202 MERISTIC VARIATION. [part I. not seem to have been broken, but there appears to have been disease of the articulations of the mandibles. B. M., S6, 12, 20, 10. Specimen in which "position of the left upper canine is abnormal. It is displaced backwards and lies to the outer side of the first premolar, which it has pushed towards the middle line." C. S. M., 41 (see Catalogue). Case in which upper right canine occupies a position within and on a level with the first premolar, which is pushed outwards. C. S. M., 40, A. Troglodytes niger, calvus, &c. (Chimpanzee). Normal adult skulls seen. 35. Supernumerary molars. *178. Specimen having on right side in upper jaw a very small square tooth behind m*, in the arcade (Fig. 35) ; and in the left upper 1 ms m 3 V *, m m.z Fig. 35. Posterior right upper molars of Chimpanzee. I. The case No. 178 {Coll. Surg. Mus., No. 1). II. A normal Chimpanzee of approximately the same size. jaw an empty alveolus in the similar place, shewing clearly that a similar tooth has been present : lower jaw normal. C. S. M., 1. 179. Specimen in which teeth all gone, but alveoli exist behind those of the normal teeth on both sides in upper jaw, and there is little doubt that there was here a fourth molar on each side. C. S. M., 9. 180. Specimen in which teeth all gone, but alveoli shew clearly that there was a fourth upper molar on right side ; evidence on left side inconclusive : lower jaw gone. C. S. M., 12. 181. Specimen of T. calvus having an extra mS in lower jaw on right side. This tooth is about one quarter of the size of m z , resembling that in case No. 178. This specimen is in the private collection of Prof. Milne Edwards, who w r as so kind as to shew it to me. Gorilla savagei (Gorilla). Normal adult skulls seen, 55. CHAP. IX.] TEETH I GORILLA. 203 Supernumerary molars. *182. Specimen having m i behind and in series with the others on both sides in lower jaw and on right side in upper jaw. On left side both teeth are square and somewhat worn, but the right m* is a curious conical tooth. Gallery of P. M., A, 505, described by Gervais, P., Journ. de ZooL, in. p. 164. PL 183. Two cases of four molars in each upper jaw. Magitot, Anom. du syst. dent., p. 100, PL v. tig. 8. [Of these one is in collection of Dr Auzoux; the other is No. 121 in P. M., but as I did not see it when examining the collection it is not reckoned in the statistics given above.] Similar case, Hensel, Morph. Jahrb., v. p. 543. 184. Specimen having supernumerary molar which had not quite pierced bone [no statement as to position]. Wyman, Jeffries, Proc. Boston ]S T . H. S\, v. p. 160. 185. Specimen having extra molar in crypt on each side in upper jaw behind m 3 . L. M., 3. Super n umerary incisor. Fully adult male from Congo having an extra incisor in lower , There are thus five incisors in lower jaw (Fig. 36), of which * 186. jaw Fig. 36. Lower incisors and canines of Gorilla No. 186. .r, y and z are three central incisors. The upper figure shews the tooth y as seen from the side. (Specimen in Coll. Surg. Mus., 21, A.) one, presumably the supernumerary, stands almost exactly in the middle line. This tooth is turned half round, so that the plane of its chisel stands obliquely. The teeth are all well formed and none belong to the milk-dentition, for the milk-teeth are much smaller and of different form. I did not succeed in satisfying myself that the central tooth is certainly the super- numerary. The second incisors are in place on each side and are quite distinct, and the right first incisor is similarly normal. 204 MERISTIC VARIATION. [part i. But whether the oblique tooth, or the tooth between it and the right i l , should be rather considered supernumerary cannot be declared with certainty. Probably this is one of the cases, of which more will be said hereafter, in which both teeth replace the normally single i 1 . C. S. M. 21, A. ^37 Anomalous extra teeth. A lower jaw in the Museum of the Odontological Society "having two supernumerary teeth embedded in the hone beneath the coro- noid process and sigmoid notch. Originally only a small nodule of enamel was visible on the inner surface of the right ascending ramus, just external to the upper extremity of the inferior dental canal. On cutting away the bone this nodule was found to be a portion of a supernumerary tooth having a conical crown and a single tapering root. Lying above it, another supernumerary tooth was discovered, of which there had previously been no sign whatever. This was likewise exposed by removing the superjacent bone, and found to be a larger tooth with a conical crown and three long narrow roots. The teeth were lying parallel to each other, with their crowns pointing upwards and backwards, so that they could hardly under any circumstances have been erupted in the alveolar arch." Trans. Odont. Soc, 1887, xix. p. 206, fig. Specimen having fragment of a tooth imbedded in bone between left lower canine and p 1 ; perhaps a fragment of a milk-tooth P.M., A, 506. [Two specimens in the stores of the P.M. shew great irregularities in the arrangement of the teeth; but in both cases so many teeth had been lost during life that a satisfactory description of the abnormalities cannot now be given.] Hylobates (Gibbons). Normal specimens seen, 51. No abnormal case known to me. Old World Monkeys other than Anthropoid Apes. 188. Of the genera Semnopithecus, Colobus, Nasalis, Cercojnthecus, Cercocebus, Macacus and Cynocephalus ; 419 normal specimens examined. Only two had definite supernumerary teeth, but in one other case it was possible that extra molars had been present. Supernumerary molars. 189. Cynocephalus porcarius, having large extra molar behind and in series in each upper jaw. The two teeth are of the same pattern precisely. In lower jaw there is on each side a large space behind m 3 , but there is no tooth in it. O. M., 2011, b. 190. Macacus rhesus, old male, having a fourth molar in place in right lower jaw. The tooth does not stand up fully from the bone. On the same side in the upper jaw there is also a fourth molar, but was entirely enclosed in bone and was only found by cutting away the side of the maxilla by way of exploration. B. M., 30, c. 191. Macacus radiatus, having small and fairly definite depression behind m} in each jaw. These depressions seem to be perhaps the alveoli of teeth but it cannot be positively stated that extra molars have been present. C.S.M., 145. 192. Abnormal arrangement. Only one case of considerable irregularity of arrange- ' ment seen, viz., Cercopithecus lalandii (C. S. M. 113), case in which lower canines are recurved and pass behind the upper ones. See Cat. JIus. Coll. Surg. chap, ix.] TEETH : ATELES. 205 New World Monkeys. *193. In the species of Cebida? and especially in Ateles supernumerary teeth arc rather common, eight cases being found in 284< skulls, or nearly 3 per cent, (in addition to cases recorded by others). Of American monkeys belonging to other genera 92 skulls were seen, all being normal. Some cases of absence of the third molar were seen in Ateles, which are interesting in connexion with the fact that there are normally only two molars in Hapalidse. Cebid.e : normal formula i J, c\, p f , m§. Chrysothrix, normal adults, 5. Cebus, normal adults belonging to about ten species, 66. Supernumerary molars. 194. Cebus robustus : supernumerary molar in each upper jaw giving p f , m 4; de Blainville, Laurent's Annal. d'Anat. etPhys., 1837, i. p. 300°, PL viii. fig. 6. 19o. c variegatus : small tubercular molar in right lower jaw behind m?. The extra tooth is cylindrical and peg-like, having about Jth the diameter m?. Leycl. Mus. 8, Cat. 11. Ateles : normal adult skulls, belonging to several species, 60. Supern umerary molars. *196. A. pentadactylus : extra molar in series behind m d in both upper and lower jaws on right side, in each case a small round tooth. P. M., A, 1505. This specimen described by de Blainville Laurent's Ann. d'Anat, et Phys., 1837, I. p. 300, PL VIII. rig. 5: mentioned also by Geoffroy St Hilaire, Anom. d'Organ., i. p. 660. 197. A. vellerosus : extra molar on left side in lower jaw behind m 3 , as a fully-formed and well-shaped tooth, but not so large as m<. B. M., 89. 12. 7. 1. 198. Ateles sp. : extra molar on left side in lower jaw. Magitot, Anom. du syst. dent, p. 101, No. 6. Supernumerary premolars. *199. Brachyteles hemidactylus [a genus doubtfully distinct from Ateles] : specimen from S. America having 1. upper series and all lower series normal. In place of right upper p l are two teeth (Fig. 37). These two teeth are similar to each other and for want of space they bulge a little out of the arcade. Each is in size and shape very like normal £\ having a sharp cusp and a flat internal part to the crown. Both teeth are slightly rotated in opposite directions, so that the cusp of the anterior is antero- 206 MERISTIC VARIATION. [part I. lateral instead of lateral, while the cusp of the posterior is postero- Fig. 37. Surface view of upper jaw of Brackyteles hemidactylus, described in No. 199. From skull in Brit. Mux., 42, a. lateral. These two teeth stand thus in somewhat complementary positions. B. M., 42, a. *200. Ateles marginatus : wild specimen from river Cupai, has 4—4 3—3 P O O ' O — O m 3—3' ■m? m 3 Fig. 38. Surface view of upper teeth of Ateles marginatum, specimen described in No. 200, and side view of both jaws together. The specimen is in Brit. 3Ius., 1214, b. chap, ix.] TEETH : ATELES. 207 that is to say, an extra premolar on each side in the upper jaw, the lower jaw being normal. The four upper premolars are perfectly formed, large teeth, in regular series on both sides. As a conse- quence the lower canines bite on and partly behind the upper canines. There was nothing to suggest that any one of these teeth was supernumerary, rather than another (Fig. 38). B. M.. 1.214, b. Supernumerary incisor. 201. Ateles ater : specimen from Peruvian Amazon : in right upper jaw there is a large alveolus for i 2 , which is gone, while a third incisor stands between this and the canine. This third incisor bites on lower canine, and lower p 1 of the same side bites in front of the upper canine. B. M., 1108, d. 202. Ateles paniscus : extra incisor in upper jaw. Rudolphi, Anat.-phys. Abh., 1802, p. 145. Absence of molars (cp. No. 209). Inasmuch as^f, m% is the normal formula for the Hapalidae, the following cases of absence of m 3 in Ateles are interesting. There was in no case any doubt that the skulls were fully adult, and there was no suggestion that the absent tooth had been lost. *203. Ateles marginatus : specimen from the Zoological Society's menagerie, bones rough and unhealthy-looking, but skull well formed and certainly not very young, has no m 3 in either jaw, giving 3 3 2 2 the formula p — , m~ — -, as in Hapalidse. There is no space in the jaw behind m 2 , and in the upper jaw the bone ends there almost abruptly. 204. A. melanochir : Caraccas specimen, having no posterior m 2 on either side in upper jaw. The lower series normal, but the jaws are somewhat asymmetrical, so that the lower posterior right m 3 is behind the level of its fellow of the other side. B. M., 4s. 10. 26. 3. 205. A. variegatus : wild specimen, having lower m 3 absent on both sides. Left *f is also absent, but has been almost certainly present. CM., 1098, B. Mycetes : of various species, adult normals, 81. Supernumerary molar. 206. M. niger : supernumerary molar in the right upper jaw. The arrangement is peculiar. So far as m- the teeth are normal. Behind and in series with m 2 there is a large tooth, a good deal larger than the normal m 3 , and having rather the form of m* than of m 3 . Its form is, however, not precisely that of m 2 , for the middle or fifth cusp is rather anterior to the centre of the tooth. 208 M ERISTIC VARIATION [rART I. instead of being posterior to it as usual. Outside this tooth is another, standing out of the arcade, having the size and almost the form of normal m*. B. M., 749, c. (Fig. 39). This case may be an example of one of two principles which will be in the next chapter pointed out as operating in the case Fig. 39. Mycetes niger, No. 20(i ; right upper molars. Brit. Mus., 7-49, c. of dental Variation. Eitlier m 2 may have divided into two, both standing in series, and the normal m s may have been pushed out of the arcade in connexion with this reduplication ; or the tooth standing outside may represent an addition to the normal series, and in that case the tooth standing as m z in the series may be a representation of m z , raised to the normally higher condition of m 2 in correlation with the presence of an extra tooth in the series, in the way shewn to occur in other cases (see Chapter x., Section 7). Between these alternative possibilities I cannot decide. Super n u merary premolar. 207. Mycetes niger : between and internal to p}_ and $P on left side there is a premolar. This is probably a supernumerary one, but the jaw is so much diseased that the relations are not distinct. B. M., 749, d. 208. Callithrix, normal adults, 22. (In B.M., 51, b on both sides rn? is separated by a narrow diastema from m?. The appearances suggest that possibly a small rudimentary tooth may have stood between them, but this is quite uncertain). Nyctipithecus : 1 1 normals. 209. Pithecia : 1 1 normals. Specimen having no right m*^, and apparently this tooth was not about to be formed, for the dentition is otherwise complete. C. M., 1094, a. (Cp. Xo. 202.) Lagothrix, 6, Chiropotes, 1, Ouakaria, 3 normals respectively. Hapalid.e. In this group m 3 is normally absent ; and no specimen having this tooth or any other dental abnormality was seen. Of adult normal skulls 33 were seen, belonging to various species. chap, ix.] TEETH : CAXID^E. 209 CARNIVORA. Canid.e. The evidence of the Variation of teeth in Canidae is divided into three groups according as it concerns (1) incisors, (2) pre- molars, (3) molars. No case specially relating to the canines is known. In each of these groups the cases relating to (A) ivild Canidae are taken first, and those relating to (B) domestic Dogs afterwards. Of wild specimens of the genus Canis (including the Fox) 289 skulls were seen, and amongst them were 11 cases of super- numerary teeth, about 3*5 per cent, (besides many recorded cases). Of 216 domestic Dogs (including Pariahs, Esquimaux, &c.) 10 had supernumerary teeth, or 7 "4 per cent, (besides many re- corded cases). I have not included skulls of edentulous breeds, in which the original condition of the teeth cannot be told with certainty. Statistics of the occurrence of supernumerary teeth are given by Hexsel, Morph. Jahrb., 1879. Among 345 domestic Dogs in his collection there are 28 cases of one or more extra molars, 12 cases of extra premolar, and 5 cases of extra incisor. [If therefore no two of these cases refer to the same skull, there were in all 45 cases of extra teeth in 345 skulls, or 13 per cent. It is not stated that the collection was not strictly promiscuous, but it may be anticipated that this figure is rather high.] An analysis of Hensel's cases will be given in the sections relating to the particular teeth. The usual dentition of the genus Canis is if, c\, p\, m%. The Wild Dog of Sumatra, Java and India, C. javanicus and C. primcevus (by some considered as one species) have in': 7 ami have been set apart as a genus under the name Cuon (HODGSON, Calcutta Jour. N. H., 1842, ii. p. 205). The genus Icticijon differs in having normally ??ij. The genus Otocyon on the contrary has usually ??if. Of the variations to be described in Canis the most notable are (1) cases of i 4 —^ ; (2) cases of extra premolar, common in upper, very rare in lower jaws ; (3) cases of ^ 3 or m*, and one case of in J giving the formula characteristic of Otocyon. In several instances a con- siderable increase in the size of »£ or m* is found associated with the presence of ™?_ or m* respectively. An interesting group of cases of extra molars was found in 0. cancrivorus, in which this abnormality seems to be common. The frequent absence of p 1 in the Esquimaux dogs is worth notice. Absence of m? is common in Dogs, but absence of «^ is rare. In Otocyon one case of m± is recorded, and in let icy on one example has m\ instead of m\. b. 14 210 MERISTIC VARIATION. [part I. I. Variation in Incisors and Canines. A. Wild Caxid^e. No case of extra incisor known to me. Two cases of absent incisor, viz. 210. [Canis] Vulpes pennsylvanica, Brit. Columbia, having ' \ o ' a PP aren tly i l has nut been present on either side. B. M., 1402, b. 211. Canis vulpes: only 5 incisors in lower jaw, with no trace of alveolus for the sixth. Schaff, E., Zool, Gart, 1887, xxviil p. 270. B. Dogs. 212. Dog (resembling Bloodhound) : four incisors on each side in upper jaw. The externals, i 3 , normal, but no evidence as to which of the other teeth supernumerary. Leyclen Mus. 213. Thibetan Mastiff, Nepal: sockets for four teeth on each side in pmx. Teeth all gone. Alveoli of two sides nearly symmetrical. In absence of the teeth it cannot be positively stated that this is not a case of persistent milk-teeth, but this seemed unlikely. B. M., 166, g. 214. Mastiff: four teeth on each side in front of canines; from form of teeth probably case of persistent milk-canines. Lower jaw gone. O. M., 1749. 215. Dog : on right, sockets for three teeth in addition to ? 3 which is in place. These three sockets all smaller than the normal ones, and socket for upper right canine also slightly reduced in size. Odont. Soc. Mus. 216. Dog : small skull in my possession, has in place of right & two alveoli, both at the same level, divided by a thin bony septum, the one internal to the other: left &_ is in place and normal: lower jaw gone. 217. Among 345 Dogs' skulls four had extra upper incisor on one side, and one skull had perfectly formed fourth upper incisor on both sides. This tooth smaller than third incisor. Hensel, I. c, p. 534. Several cases of 7 or 8 incisors in upper jaw, teeth being usually asymmetrical. Nehring, Sitzb. not. Fr. BerL, 1882, p. 67. 218 In lower jaw such cases much rarer. Supernum. lower in- cisor on one side, one case [? in 650 skulls], Nehring, ibid. ; also a Dog (cJiien chinois-japonais), 4 incisors in each lower jaw. Magitot, An. syst. dent, p. 81. Case of divided incisor. 219. Bulldog : right i~ with very wide crown; main cusp partially bifid, as if intermediate between single and double condition. Morph. Lab. Cambridge. Similar case kindly sent to me by Prof. G. B. Howes. chap, ix.] TEETH: CANIDyE. 211 3 — 3 220. Absence of incisor is very rare in Dog. One case of i- — given by Hexsel, I. c. p. 534. (Hensel observes that this gives the formula for incisors of Enhydris [Latax]; he also calls attention to fig. of Enhydris with three lower incisors in Owen, Odontogr., PI. 128, fig. 12, but as this is not mentioned as an anomaly in text, it is very doubtful.) 221. Dog having the upper canine imperfectly divided into two on each side as shewn in Fig. 39. The plane of division was at right Fig. 39. Eight and left profiles of Dog having the canines partially divided. angles to the line of the alveolus so that the two parts of each canine stood in the plane of the series of teeth. The division was more complete on the right side than on the left. The lower canines were normal. This specimen was kindly sent to me by Mr J. Harrison. II. Variation in Premolars. Several distinct variations were found in the premolars of Canidse. A number of cases shew five upper premolars instead of four, and the question then arises whether the extra tooth is due to the division of a single tooth, or to reconstitution of the series 1 . The occurrence of a fifth premolar in the lower jaw is much rarer, only three or four cases (Wolf (2) and Greyhound (? 2)) being known to me. The following other forms of Variation oc- curred. In C. mesomelas, No. 228, an extra tooth stood internal to fP, and was perhaps a duplicate of this tooth. One case of bifid p^ was seen, and two cases in which p 2 had apparently divided to form two single-rooted teeth (0. viverrinus, No. 227 and a Sledge-dog, No. 237). A few examples of absence of p 1 deserve notice. Lastly, though really an example of Substantive Variation, I have included a curious case of possibly Homceotic variation of p^ into the partial likeness of the carnassial (No. 245). 1 On this point see Chapter x. Sections 3 and 5. 14—2 212 MERISTIC VARIATION. [part I. Increase in number of Premolars. A. Wild Canid^e. 222. C. dingo : specimen having two closely similar teeth between p* and the canine in each upper jaw 1 . Both the teeth had the form and size of a premolar. This not a case of persistent milk-tooth, Nehring, A., Sitzb. naturf. Fr. Berlin, 1882, p. 66. C. dingo : on right side p] is in place, and there is an alveolus for second tooth of about same size. On left side P 1 is rather small. L. M. C. lateralis, Gaboon. On 1. side p^ is single, but on rt. side there are two almost identical teeth between P^ and the canine : of these the most anterior is level with, but slightly smaller than, left £. (Fig. 40) B. M., 1689, a, (See Mivart, P. Z. 3., 1890, p. 377.) 223. 224. 225. 226. 227. 228. 229, Fig. 40. Cants lateralis, No. 224. View of canines and front premolars of the upper jaw. p l of the left side is in symmetry with two teeth on the right side. C. vulpes : in 142 skulls, one case of two teeth between p z and canine (sc. five premolars) in left upper jaw. Hensel, I. c, p. 548. In C. vulpes the root of p 1 is not rarely partly divided into two by a groove of variable depth. The division is sometimes nearly com- plete, as in C. S. M., 651. C. mesomelas : two teeth between p 2 and canine in left lower jaw, anterior the larger. Doxitz, Sitzb. naturf. Fr. Berl., 1869, p. 41. Division of p' 2 C. viverrinus : left p? represented by two teeth, each having one root. Of these the anterior is tubercular, while the posterior is rather long from before backwards. Anterior premolars normal. L. M. (Compare Sledge-dog, No. 237.) Reduplication of p*. C. mesomelas : inside right upper p 3 is a supernumerary tooth which nearly resembles p A , but is a little smaller; lower jaw normal. C. S. M., 643. (See Nos. 226 and 247.) C. lupus: in addition to irregularities in position of teeth, there is a doubtful appearance as of an alveolus inside left P^ which is displaced outwards. C. S. M., 624. 1 Mivart, I.e., by mistake quotes this case as one of extra teeth above and below. CHAP. IX.] TEETH : CANID^E. 213 Partially bifid premolar. 230. ^* vu lP es • right v\ has three roots and a partially double crown with two cusps (Fig. 41). The whole crown is pyramidal, the labial face being parallel to the arcade and the three roots stand each at one angle of the base : left pj normal; lower jaw missing. B. M., 175, o. Jh Iji l [ Fig. 41. Teeth of Fox (C. vulpes) described in No. 230. The separate view- shews the right first premolar removed, seen from the labial side. Extra premolar in lower jaw. 231. C. lupus : two teeth between p 2 and canine in lower jaw on right side, one case: and the same on left side also, one case. These two occurred in 27 Wolf skulls seen by Hexsel, Morph. Jahrb., 1879, v. p. 548. B. Domestic Dogs. *232. Dog : between F 2 and canine on rt. side there are two teeth, each shaped like a normal £\ the anterior being somewhat the larger. This seen in two cases, figured in Fig. 42, II. and III. right m Fig. 42. Profiles of canines and anterior premolars in three dogs having two teeth on one side in symmetry with one tooth on the other. I. C. S. M., 570. II. and III. Skulls in Cambridge Univ. Morph. Lab. Lower jaws absent. The property of the Zool. Lab., Cambridge (cp. G. lateralis, No. 224). 233. Spaniel : similar case, left side, Fig. 42, I. C. S. M,, 570. 214 MERISTIC VARIATION. [part i. 5 5 234. Dog : large skull, having^ =--, all the normal teeth being o — o in place, of proper form and size, standing evenly without crowding. O. M, 1780. 235. Dogs. In 3 t5 skulls were 1 1 cases of supernumerary premolar in the upper jaw. viz. on both sides, 1 case, on right side, 7 cases, on left side, 3 cases. These were all cases described by Hensel as instances of the presence of "p b " of his notation, i.e. a tooth between p ] and canine. Hensel, Morph. Jahrb.f 1879, v. p. 546. Out of 650 skulls, including Hensel's ."U">, 18 had two anterior premolars as described, on both sides in upjDer jaw. Nehring, Sitzb. naturf. Fr. BerL, 1882, p. 6Q. English Spaniel: outside and anterior to right & is a worn stump, probably of an extra tooth (?). B. M., KJG, j. 236. Deerhound : tiro alveoli where p~i should be; probably two distinct teeth stood here, but it is possible that the two alveoli were for distinct roots of a single tooth. C. M., 991, B. Division of r p~. 237. Sledge-dog, Greenland : all teeth normal except left upper p 2 . This tooth normally of course has two roots. Here it is represented by two distinct teeth, each having one root. The anterior has a fairly sharp cusp, but the posterior has a rounded crown. The teeth are in perfectly good condition and do not look worn. They are separated from each other by a considerable diastema. It appears clear that instead of the normal p* } two distinct teeth have been formed. 0. M., 1787 (compare C. viverrinus, No. 227). Absence of Premolars. A. Wild Canid.e. 236. C corsac : fi absent on both sides without trace. Giebel, Jirouits Kl. u. Orel., Mamm. p. 196, Xote. 239. c. occidentalis : p absent on both sides. C. S. M., 629. 240. C. vulpes : in 142 skulls : P^ absent from both sides 1 case, do. „ „ left „ 1 „ do. „ ,, right „ 1 ,, p 1 » „ both „ 1 „ do. „ „ left „ 2 „ do. „ ,, right „ 2 „ Hensel, Morph. Jahrb., 1879, p. 548. A doubtful case of absence of left p. B. M., 175, c. chap, ix.] TEETH : CANID.E. 215 241. C. (Nyctereutes) procyonoides : p^ absent on both sides with- out trace in B. Ms, 186, e; and absent on right side in B. M., 186, d. On the contrary B. M. 186 a and b and C. S. M., 672, are normal. The following cases of absent premolars were doubtful : C. dingo : right v^ and left J^. C. S. M. C. antarcticus: p l above and below on left side. C. S. M., 635. B. Domestic Dogs. 242. From the nature of the case it is not often possible to say with con- fidence that p 1 has not been present in a given skull, but from the material examined this variation appears to be rather rare. In 216 skulls, excepting those of Esquimaux dogs, I only saw two clear cases in which the bones were smooth, without trace of alveolus, viz. "Danish" Dog: p~i absent on both sides, O. M., 1786. Terrier: p} absent on both sides. C. S. M., 579. Many others doubtful. According to Hensel, however, absence of p l is common, and he states that in 345 skulls the following occurred : 1^ absent on both sides 5 cases, do. ,, ,, one 4 ,, pi ,, ,, both frequently, do. ,, ,, one 9 cases, p 1 absent on both sides and F 1 on one side, 1 case. Jforph. Ja/trb., 1879, p. 546. [This is of course a far higher frequency than was found by me, but perhaps discrepancy arises from difference in reckoning the evidence of absence.] Two doubtful cases of absence of p were seen in Dogs. *243. Esquimaux Dogs: absence of p l quite common, the following skulls being all of the breed that I have seen. Normals, withp~, only two specimens. Specimens with nop 1 , above or below, the canines in such cases standing close to p 1 , three cases, viz. B. M., 58. 5. 4. 96; B. M., 166, a; C. S. M., 542. £ absent on left side and pi on both sides, C. M., 1000, c. pi absent both sides and pi absent on left side, L. M. p^ and pi both absent from right side; left normal, O. M., 1789. p~ l absent on left side, B. M., 166, r, 3. p~ l absent on right side, B. M., 166, t, 2. The partial establishment of a character of this kind in a breed, which, if selected at all, has been selected for very different qualities, is rather interesting. It need scarcely be remarked that the partial loss of this tooth cannot in the Esquimaux dog have occurred in connexion with an enfeebled habit of life, as might perhaps be supposed by some in the case of the edentulous lap-dogs. As will be shewn in the next section, absence of the front premolars is a common character in the dogs of the ancient Incas, but in them the posterior molars are also frequently absent. There is no special reason for supposing that the Esquimaux dogs came originally from America, but it may be worth recalling as a suggestion, that according to anthropologists the relations •2 1 6 MERISTIC VARIATION. [part i. of the Esquimaux are rather with American tribes than with Europeans. If this were established, it would be not unlikely thai the Esquimaux dogs might be descended from dogs domesti- cated in America before the coming of Europeans, and so far belong rathe]- with the Inca dogs than with ours 1 . *244. Inca Dogs. The domestic dogs from the Inca interments, be- longing to a period before the coming of the Spaniards, have been investigated by Xehrinr. Of nine skulls not one had the full number of teeth and there was no case of supernumerary teeth. Sometimes the anterior premolar was absent, sometimes a posterior molar, and in soiih' cases both. The formulas were as follows: 4—4 ' ; 4-3' m 2- -2 . — o 4 — 4 ^3-3' 7)1 2- 3- _9 — 1 case. 4—4 ' ; 3-3' m 2- 3- _9 — ~1 3 cases — o 4 — 4 *3-3' m 9 — 9 -J -1 , — - 1 case. -2 4 — 3 7)1 2- 2- -2 - — - 1 case. -2 3 — 3 ^3—3' 7)1 9_ 3- _9 — 2 cases — o The dogs were all of moderate size, and none shewed any defects in the form of teeth, which were all strong and sound. Nehring, A., A'osntos, 1884, xv. p. 94. Variation (J Homceotic) in form of third Premolar. 245. Dog : large breed. In the upper jaw on both sides the third premolar, instead of having only two roots, has a third internal root, thus somewhat resembling the carnassial. The crown of the tooth very slightly changed. This is not a case of persistent milk-tooth, which though a three- rooted tooth, is very different. C. S. M., 558. III. Variation in Molars. Supernumerary molars are not rare in Canidae. In all cases seen by me these teeth are single-rooted, round-crowned, rather tubercular teeth, placed behind m? or m? as the case may be. HENSEL 1 has observed that if m± occurs, then m? which is normally single-rooted, not infrequently has a double root, though the same variation may occur when there is no m 4 present. Conversely, when ///'• is absent, not a rare variation, then rn? is often of a 1 Bartlett, arguing chiefly from habits, considers the Esquimaux dogs to be domesticated wolves, and says that they often breed with the wolf. P. Z. S., 1890, p. 47. - Hexsel, Morph. Jahrb., 1879, v. p. 539. chap, ix.] TEETH : CANIDyE. 217 size below the normal, having a single root and a crown slightly- developed, like that of m*. This reduced condition of ~m* may also occur in cases in which m Ti is not absent. These observations of Hensel's, which are of great consequence to an appreciation of the nature of Repetition, I can fully attest, and similar cases of Variation in adjacent teeth associated with the presence of a supernumerary were seen in other animals also. A. Wild Canid.e. Supernumerary Molars. 246. CJ. lupus: 26 normals seen. Specimen from Courland having supernumerary m? on left. In this specimen m? is rather ab- normally large on both sides, and the lower third molar, on the left side, viz. that on which the upper jaw has an extra tooth, is larger than right m? } but it is not larger than usual. C. M., 976, M. Hexsel, I. c, p. 548, saw 27 skulls, none having extra molar, but one specimen known to him had a right m?. 247. C. mesomelas J (a Jackal): small, bitubercular left w^. Doxitz, Sitzb. naturf. Ft. Berlin, 1872, p. 54. (See Nos. 226 and 228.) The S. American Canidce {Lycalopex group) are remarkable for the frequency with which they possess extra molars, as the following cases (C. azarcv, vetulus, magellanicus and cancrivorus) testify. Flower and Lydekker 1 speak of the occasional presence of ™? in G. cancrivorus, but the evidence taken together seems rather to shew that there is a general variability at the end of the molar series in both jaws in these species ; for not only is *J}? found, but in some cases m* also, while in one instance there was an 'odontome,' or rather a complex of 4 small teeth attached to m 3 . 248. O- vetulus, Brazil : specimen having an extra molar in right lower jaw (Fig. 44, 1.). The posterior part of ^ is slightly pushed outwards and a very small extra tooth stands behind and partly internal to it. Right m 3 is slightly larger than left nfi and differs from it also a little in pattern. The extra tooth has one large and about three smaller blunt cusps on its crown, and might be described as a small representation of the larger m* seen in other cases. B. M., 84. 2. 21. 1 (mentioned by Mivart 2 , Monogr. Canidce). *249. Canis azarae : Brazilian specimen having a large super- numerary molar (w 3 ) in each upper jaw placed in series with the others. In this specimen the great enlargement of »£ is very 1 Mammals, Living and Extinct, 1891, p. 540. 2 In the same place Mivart mentions a case of m? in " C. cancrivorus" but I have not seen it. Perhaps this reference is to van der Hoeven's case (No. 249) which was by Burmeister named C. cancrivorus (see Huxley, P. Z. S., 1880, p. 268). 218 MERISTIC VARIATION. [part I. noticeable on both sides, and this tooth is present as a large tooth with apparently three roots. In the lower jaw there is no extra booth, but the molars are considerably larger than those of a 2.30. *251. 2") 2 Fig. 43. ( 'anis \ , m\, B. M., 185, a. /<{, m~ i, B. M., 185, b. yj, rnf, C. S. M., 533. (See Flower, P. Z. S., 1880, p. 71.) 25G. Otocyon megalotis [ = lalcmdii and coffer]: the usual formula is />;}, m : j, that is, one molar more than the Dog in each jaw. It occurs in 4 skulls at B. M. and in 2 at C. S. M. One specimen has in adcli- 4 — 4 tion an extra molar of good size in each upper jaw, giving on — — j. 4 — 4 In this case m? is enlarged also on both sides. C. S. M., 675 (see Cat, Mus. Coll. Surg., Arc). Three specimens having mf mentioned by Doxitz, Sit-.h. naturf. Fr. Berlin, 1872, p. 54. B. Domestic Dogs. Super n itinerary Mola rs. 257. Dogs. In 345 skulls the following 28 cases occurred, chiefly in large breed- : "^ on both sides and v? on one side, 1 case. "^ on both sides 2 cases. mP on one side 9 cases. '» :: and ]n* on one side only 2 cases. m* on both sides 6 cases. m 4 on one side only 8 cases. Hensel, Morpk. Jahrb., 1879, v. p. 538. CHAP. IX.] TEETH I CANID.E. 221 In addition to these, wi 3 and m* absent on both sides, 1 case. This was the only case in 860 skulls of Canis, of which about 650 were Dogs. The formula in it is thus that of Otocyon or the fossil Amphicyon. Nehring, Sitzb. naturf. Fr. Berlin, 1882, p. 66. In 216 skulls seen by me there were 8 cases of extra molars, viz. : — 258. Sheep dog : left m 3 . C. S. M., 587; Bulldog : left m 3 . B. M., 166 s; Dog from New Zealand, having left m\ left m* being larger than right m». C. M., 1000; Bhotea Mastiff: m+ on right B. M., 166, f.; Pointer: lefty. C. M., 1000, A; Dog: right Ji? Carnb. Morph. Lab.; Pariah : m 4 has been present on both sides, also a small stump below ^ and p 2 , possibly part of a milk-tooth. B. M., 166, §, ni\. Of wild species, 27 8 adult skulls having no extra teeth were seen, and 8 cases of extra teeth (nearly 3 per cent.): of domestic Cats, 35 adults without, and 3 cases with extra teeth (so far, about 9 per cent.). Aj3 in Canidte so in Felidae, there is a remarkable group of cases of variation in the anterior premolars. In the normal a small anterior premolar stands in the upper jaw, and commonly it is oiK'-rooted, sometimes two-rooted (cases given); but there is no small anterior premolar in the lower jaw. Cases of variation consisting in the presence of two small premolars above are common 1 , just as there are often two small anterior premolars in the Dog. There are besides a few cases of the presence of a small anterior premolar in the loiver jaw, but they are rather rare, and curiously enough there seems to be no case of the coincidence of these two variations in the same skull. As already stated, in describing cases, the small anterior pre- molar in the upper jaw will be here spoken of as p^, though no suggestion that it is the homologue of the Dog's p^_ is meant. In a few species p^_ is most commonly absent (cases given). There are some curious cases of duplicates of large premolars (Cat) and one of duplicate canine (Tiger), also a few of supernumerary molar. Though so small, and biting on no tooth of the lower jaw, n& is nearly always in place even in old skulls (Hexsel). Variation in Incisors. No quite satisfactory case of numerical variation in incisors of Felidae known to me. The following should however be mentioned. 203. F - lynx : two extra teeth in premaxillai. Bight incisors normal; sockets for left incisors normal. Outside left f and close to canine is an extra tooth of good size, and in same place on right is a socket for a similar tooth. Since they are in pre- maxillffi these teeth are probably not persistent milk-canines. Lower canines bite in front of the extra teeth. B. M., 1156, a. Incisors absent. 9(34_ F. pardalis: i l and fl absent on left side. As regards the lower jaw the tooth may have been present, and been lost, but left £ has probably never been present. It is especially notable that left f is larger than right f, but there is no indication that £ is compounded with it. B. M., 1068, a. F. chate [?= pardalis]: doubtful if i 1 has been present on either side. B. M., 55. 12. 26. 178. 2Qr>. Cynaelurus jubatus : no trace of right P ; same skull has no p^\ lower jaw ' normal. B. M., 135,/. 1 For discussion of such cases see Chapter x. Section 5. CHAP. IX.] TEETH I FELID^E. 223 Anterior Premolars {supernumerary). Upper Jaw. 266. F. pardus : right P^ single and normal; on 1. side two such teeth, both standing at level anterior to right P 1 . The anterior is of same size as right p^, the posterior is rather smaller. B. M., 87. 4. 25. 1. 267. F. eyra : two small anterior premolars in left upper jaw, Baird, U. S. and Mex. Bound. Swrv., Pt. 2, PI. xni. figs. 2, a and 2, c [anomaly not mentioned in text]. *268. F. catus, Athens. Two small anterior premolars in upper jaw both sides (Fig. 40, I.), small and standing close together. On rt. anterior the larger, on 1. posterior the larger. B. M., 47. 7. 22; 2. * 269. 270. 271. 272. Fig. 46. Left-hand figure : upper jaw of F. catus, No. 268. Eight-hand figure : upper jaw of F. inconspicua, No. 269. F. inconspicua (= torquata). Rajpootana. Two small an- terior premolars in upper jaw both sides ; both small, diastema between them. Posterior is nearly in contact with "jt) 3 ", while anterior is only a little behind canine (Fig. 46, II.). B. M., 85. 8. 1. 26. (Another specimen has p^_ as large single-fanged tooth.) F. domestica (out of 38 skulls) : internal to and rather behind left p} is an almost identical copy of it, though rather smaller. Not a milk-tooth. C. S. M., 414. Out of 252 skulls two anterior premolars on Ijoth sides, 4 cases ; on right, 2 cases; on left, 1 case [none specially described]. Hensel, Morph. Jahrb., 1879, v. p. 553. F. caligata, Socotra : outside right p} t a small extra tooth. In this specimen )j} on each side has two roots. B. M., 857, b. Doubtful cases of extra upper anterior premolar, F. pardus, C. S. M. 365 ; F. leo, C. S. M. 308. Lower Jaw. 273. F. concolor : a supernumerary anterior premolar on both sides present, Berl. Anal. Mus., 3678. Hensel, ibid. F. catus or mani- culata : ditto. Frank/. Mils., Hensel, ibid. F. catus : ditto, on left side, closely resembling^ 1 . Two cases, B. M., 1143 and 1143, a. 274. F. domestica : (in 252 skulls) a supernumerary premolar on both sides, just in front of and nearly same size as the usual "P 2 ," one case ; on left, as a very small tooth midway between canine and "p*" one case; on right, rather larger than in foregoing and nearer to "//-'," one case. Hensel, ibid. 275. F. tetraodon: alveolus for small anterior premolar in right lower jaw; but as this fossil form very rare, uncertain whether normally 224 MERISTIC VARIATION. [part i. present in the species, de Blainville, Osteogr., Atlas, PI. xvi. Feles fossiles. Variations- in size of P^. 27(3. r. pardus : j£ sometimes two-rooted, as C. S. M., 360 (African); more often one-rooted, as C. S. M., 304, Arc: many gradations between these. In B. M., 115, q right i± extraordinarily large, left normal. Minute alveolus external and posterior to each of these ; on left side a small worn stump ['? of milk-tooth] in this alveolus. 277 r. domestica : />} two-rooted C. S. M. 40'J and B. M., 127, q ; on right side two- ' rooted B. M. 127, 8. F. catus C. S. M. 401 and F. minuta (Borneo) B. M., 122,/, P 1 partially two-rooted. F. caligata, see above, No. 272. F. chaus: left p} very small, right p] fair size. B. M. 131, e. F. jaguarondi, ditto, B. M. Absence of p 1 . In the following cases it appeared that p^ had not been present. 278. F. catus. both sides, a cave-skull, Hexsel, I. c. ; left side only, Caucasus, B. M. 1113, m ; F. tigris, Hexsel, F. onca, both sides, B. M. 117, c ; F. xnanul, ditto, B. M. 1863, a; F. nebulosa, ditto, two cases [? normal for species] B. M.; F. rubi- ginosa. Malacca, ditto, B. M., 1856, a; F. chaus: both sides in domesticated specimen from India, B. M. ; and in B. M. 58. 5. 4. 69, similar specimen, this tooth is small on left, absent on right; F. brachyurus, absent both sides, B. M. ; F. cbinensis, right absent, B. M., 70. 2. 18. 25; F. javanensis, left absent, B. M. 1641, a (but in B. M. 1309, b, p} is particularly large). F. domestica : in 252 skulls v^ nl Kent both sides 6 times, and one side, once (in 2 cases anterior deciduous tooth remained on both sides in upper jaws of adults) Hexsel, /. c. p. 552; in 38 skulls seen by me, n} absent both sides, 2 cases ; right side in one case (Manx, C. S. M., 428, a). In the following species the absence of vl was so frequent as to call for special notice. 279. Cynaelurus jubatus : of 8 skulls 3 (2 African) were like Cat, having 2^ both sides; p 1 absent both sides, 3 cases, B. M., 135,/. and 0. S. M. — ; left p^ absent, right very small, C. S. M., 441; right ;/ absent []]. B. M., 135, c. 280. F. caracal : out of 8 skulls only 4 had any indication that i^ 1 might have been present, and in these it was doubtful. 281. Lynx : of Lynxes of possibly different species, 17 skulls have no .P 1 , a skull marked "Lynx borealis" B. M., 1230, a has a small, worn stump as p 1 on each side. 2S2. F- pajeros ( =pampana) i Chili: 2 skulls only known to Hensel, I c, both without^. This tooth absent in B. M. 126 and 126, c; but in one specimen seen, right p^ absent but left p} of good size. Partial division (?) of lower premolar. Two cases relate to this subject. The first lower premolar of Felidse is a two-rooted tooth of well-known form. In the first of the following cases it bore an extra talon and root ; in the second there w r as a small extra root on the internal face. (Cp. C. vulpes, No. 230.) 283. F. tigris : anterior right lower premolar has a thin supernumerary root on internal side of the tooth at the level between the two normal roots. This tooth in form resembled a milk-carnassial to some extent, but it was certainly not one of the normal milk-teeth. C. S. M., 333. CHAP. IX.] TEETH : FELID^E. 225 *284. F. fontanieri (see No. 290): anterior premolar of right lower jaw has additional talon on internal and anterior surface (Fig. 47). This B C Fig. 47. Veils fontanieri, No. 284. A. The normal anterior premolar of the left lower jaw. B. The corresponding tooth of the right side from above. C. The same from the lingual side. portion has a separate root, and stands somewhat apart from rest of crown, looking like a partially separated tooth. B. M., 90. 7. 8. 1. Duplicate Teeth. 285. F- tigris: on right side, two canines in the same socket, both of large size, the anterior being the smaller; neither is a milk-tooth. Mus. Odont. Soc. 28C. F. domestica : having a large supernumerary tooth in each upper jaw. The extra tooth was in each case a small but accurate copy of the carnassial tooth (Fig. 48) of its own side. In each Fig. 48. The teeth in upper jaw of Cat, No. 286. case the extra tooth stood internally to the carnassial tooth, ex- tending from the level of the middle of the carnassial tooth to the level of the middle of the molar. B. M., 83. 3. 10. 1. 287. Specimen having a tooth in the upper jaw closely resembling the second premolar ("ju 3 " auctt.) internal to and between it and the carnassial. The internal tooth is slightly smaller than the second pre- molar 1 (Fig. 49). C. S. M., 414. 1 In this case, it is not possible to say strictly that either of the two teeth " is " the normal second premolar, rather than the other. B. 15 226 MERISTIC VARIATION. [part I. 288. Specimen having a small tooth internal to the middle of the lower [?side] carnassial (»?): the extra tooth was here divided into two cusps so that it was a copy of the carnassial. Iensel, I. c. rK/ ^ ~& Fig. -49. Plan of teeth in upper jaw of Cat, No. 287. The two teeth marked with crosses are separately shewn, that on the right being the external. 289. Specimen having a tooth like the last, but not so distinctly divided into two cusps, internal to posterior end of lower carnassial [?side]. ibid. Supernumerary Mo lars. Cases like the last cannot be clearly separated from cases of true extra molars in series, such as the following. It is remarkable that no case of supernumerary upper molar in series seems to be known in Felidas. In the Tiger and other species the upper molar is sometimes single- and sometimes double-rooted. '290. F. fontanieri : a species nearly allied to the Leopard (F. jxirdus), inhabiting the Kiu-Kiang, a geographically isolated region of X. China. Only two skulls are known, and each of them pre- sents an abnormality in dentition (see No. 284). Skull having supernumerary tubercular tooth in series (nfi) behind the left lower molar (m l ). B. M., 1490, a. 291. r - pardalis: "^2 on left side. Hensel, Morph. Jahrb., 1879, v, p. 541. F. tigrina : tubercular ^2 on left side. Schlegel, P. Z. S., 1866, p. 419. r. lynx : ditto [? side}. Magitot, A nom. syst. dent., p. 103. F. domestica : "supernumerary permanent molar in lower jaw" [no particulars]. Wtman, J., Proc. Boston N. H. S., V, p. 160. F. pardus : doubtful indication that a left m 2 has been present. C. M., 933, F. Absent Molar. F. leo : ml absent on both sides, and there is no space for it behind the upper carnassials. B. M., 3043. The only case seen in all Felidas examined. F. domes- tica : "^ absent [? both sides]. Hensel, /. c, p. 541. chap, ix.] TEETH : VIVEKRID^E. 227 VIVERRIDJE. Of the Viverrida?, Herpestes and Crossarchus are the only genera represented in collections in quantity sufficient to repay study of their dental variations. In the teeth of these two genera, however, variation is considerable and appears in some interesting forms. In Herpestes there is first some evidence of variability in the number of the incisors, including one case of extra incisor. Next the facts respecting the presence or absence of the anterior pre- molar are of some consequence, both as illustrating the general variability and modes of Variation of this tooth, and also be- cause the normal presence or normal absence of the anterior pre- molar is one of the characteristics of different species, which shew a progression in this respect. There is one case which should probably be looked on as an example of duplicate anterior pre- molar. There are besides two cases of duplicates of large premolars, but of true supernumerary molars in series only one case was seen. Another specimen shewed what is perhaps partial division of a molar. Of 130 skulls, five had supernumerary teeth, not including cases of unusual presence of anterior premolar. Incisors. The following cases shewed departure from the normal i 1 292. Herpestes gracilis : an extra incisor in lower jaw. ^ and P in place and clearly recognizable on both sides, but between the two second incisors are three small teeth, all of about the same size and shape. Neither of these is a milk-tooth, for the milk-teeth are dis- tinctly different both in size and form. There was no evidence to shew which tooth was the supernumerary one. B. M., 826, a. *293. H. nipalensis J" : only four incisors in lower jaws. This is a re- markably clean and sound skull. The four incisors stand close together, filling up the whole space between the two lower canines. There is no reasonable doubt that only four lower incisors have been present. It is difficult to see that any of the four incisors exactly corresponds with ■ any of the normal teeth; for while the two lateral teeth are of about the same size as normal p, they have a different position, arising from the outer sides of the jaw, slightly in front of the roots of the canines, whereas normal P arises internal to the other incisors. To what extent the alteration in position is correlated with the change in number cannot be affirmed. B. M. 146, m. *294. H. persicus : only four incisors in lower jaw. Judging from general appearances it seemed that T l was missing from both sides. The teeth stand in a close series between the canines, which are nearer together than in normal specimens. The consequence of this to the arrangement of the bite is curious. The left lower canine bites in its normal place, between the upper canine and &; but the right lower canine bites in front of the upper ^, which is displaced backwards 15—2 228 MERISTIC VARIATION. [part i. towards the right upper canine. The whole anterior part of the lower jaw is thus twisted a little towards the left side. Besides these two definite cases of absence of incisors, in the following instances there was a presumption that the absence was due to variation, but a definite state- ment cannot be made. H. smithii: only four incisors in lower jaw. B. M., 1435, a. H. gracilis: doubtful casu of absence of p on both sides. B. M., 789, b. H. nyula : doubtful if right £ has been present. B. M. Anterior Premolars. In the great majority of both Asiatic and African species of Her- pestes the anterior premolar (;/) is normally present in both jaws, and in these species 6 cases of absent ^ were seen. When present it is a tootli of small but still considerable size. It appeared from the specimens that pi in the species H. gracilis (Africa generally), and both l^_ and y in H. galera (E. Africa) are commonly absent. As in other cases of absence of teeth the question arises whether the absence is due to age or accident, or on the other hand to original deficiency. This question cannot be definitely answered, but some considerations touching it should be mentioned. First, as has been said, the tooth when present is of moderate size: though small, it is quite large enough to be functional, and is in no sense rudimentary. In his synopsis of the genera, Thomas 1 says of Herpestes, " Premolars ± (if only 3 in either jaw, a diastema always present)." There is however no reason for supposing that the presence or absence of p l is determined by chance. From the fact that a tooth is small, it by no means follows that it is often lost. To any one handling large numbers of skulls, instances of the contrary must be familiar. .A case in the Otters well illustrates this point. In Lutra vulgaris upper p l is a small tooth, and from its singular position internal to the canine, it might be supposed that the development of the canine might easily push it out; yet in 41 skulls of Lutra vulgaris, only 1 case of absence of P^ was seen. Of L. cinerea on the contrary six skulls are without p] ; but as in two young skulls it is present on both sides, there is thus a strong presumption that in this species the tooth is lost with maturity. The frequent absence in the one species and the constant presence in the others points to a difference in organization between them. When p 1 is missing in a skull, though we are not entitled to infer that it has not been present, still the fact of its presence in one case and of its absence in another is on the face of it an indication that between the two there is a difference or Variation, but whether the Variation lay in the number of teeth originally formed or in the mode in which they were affected by subsequent growth is uncertain. In the specimens to be described the absence of p l in certain individuals or species is no less definite than its presence in the others, and that which is a variation in one species will be seen to be the rule in others. As regards the presence of p x the specimens thus make a progressive series. Most species having^, but p± as a variation; H. gracilis (and pulverulentus) having p± normally, but pj as a variation and p o — o 1 Thomas, 0., on the African Mungooses, P. Z. S., 1882, p. 62. chap, ix.] TEETH I HERPESTES. 229 also as a variation ; and lastly //. galera having p^ normally but shew- 3 4 4 4 ing a case of p-~- and another of p- ~ . Lastly, all specimens of Crossarchus seen had p^. Of species commonly having p±, 91 such skulls and the following cases of absence of jJ l were seen : *295. H - ichneumon, 9 normals: ^i absent both sides. B. M. ; on left, C. M., 965, D. H. griseus, 21 normals : pi absent on right, two cases. B. M., 145, k and m. H. smithii. 6 normals: pi absent both sides. B. M., 979, b; on left side, B. M. 84. 6. 3. 13. 296. H. gracilis on the contrary shewed j^i m 8 specimens, p 1 present both sides once, B. M., 789, a ; left pi absent once. B. M., 789, b. H. pulverulentus : p± in 2 specimens. 297. H. galera : pf in 7 skulls, one being quite young: p 1 is present in all four places, in one young skull making pf, B. M., 148, d; pi and p} both present and well developed on right side in old skull. On the left there is ample room for them. B. M., 79, a, P} present on both sides and alveolus for pi on right. B. M., 148, I. Crossarchus : 13 skulls assigned to 4 species, all had pf • Case of two Anterior Premolars. 298. H. microcephalus : on right side two teeth like p^, crowded together, others normal. Leyd. M. Compare JRhinogale melleri (an 5 Q African Mungoose) of which only known skull (in B. M.) has p j -. The appearance here is that a tooth unlike and rather larger than p^ stands in front of it on each side (see Thomas, I.e., pp. 62 and 84). Supernumerary Large Premolars. Taken together the two following cases are important as illustrating the difficulty of drawing any sharp distinction between cases of dupli- cates of particular teeth and cases of extra teeth in series. They should be read in connexion with the cases of F. domestica (No. 286), Helictis orientalis (No. 312), Vison liorsfieldii (No. 311), Ommatophoca 7'ossii (No. 320), Plioca grcenlandica (No. 324), &c. *299. Herpestes gracilis: supernumerary tooth in right lower jaw (Fig. 50). On comparing the teeth of this specimen with those of Fig. 50. Bight lower jaw of Herpestes gracilis, No. 299. View from labial side ; ground-plan of the jaw ; separate view of the tooth + . C, the canine. other Herpestes in which jp is present it is quite certain that no tooth in the abnormal jaw corresponds with p. The foremost of its pre- molars on both sides clearly has the form of $K The next teeth have the correct form of p*. In the left lower jaw the next tooth is p; but 230 MERISTIC VARIATION. [part I. on the right side immediately in succession to j? but slightly within the arcade is another tooth (marked + in the figure), which is very nearly a copy of p*, though a little smaller. On the outside of the jaw and behind this tooth is a normal p. From its singular position outside the series, this tooth might easily be taken for a supernumerary one though its form clearly shews it to be a natural p* displaced, while two teeth having the form of p* stand in succession. B. M., 63. 7. 7. 18. (mentioned 'by Thomas, P. Z. S., 1882, p. 62). 300. H. ichneumon (Andalusia): in one of the upper jaws between and internal to l^ and i^ 3 is a 3-rooted tooth (not a milk-tooth) which in size and shape is about intermediate between P^ and p\ Leyd. M. Molars. The only cases of noticeable variation in molars were both in the same species, Crossarchus zebra. Of this species six skulls were seen, four normal, and also the two following, the first being a case of extra molar on each side, the next a case of increase in size and complex variation in w 2 , on the left side suggesting a partial divi- sion of this tooth. f 301. Crossarchus zebra : small but well-formed additional molar in upper jaw on each side, making pf, m\. (Fig. 51, III.) Teeth unfortunately all much worn, so that it is not possible to determine whether any of the molars differ from their normal forms in corre- lation with the existence of these extra teeth ; but as far as size is concerned, there was no sign of such change, ^ and »£ being of the usual size. B. M., 73. 2. 24. 18 mentioned by Thomas, P. Z. S., 1882, pp. 61 and 89. Fig. 51. Crossarchus zebra. I. Posterior upper molars of No. II. A normal specimen, right upper jaw. III. Upper jaw of No. 301. 302. chap, ix.] TEETH : MUSTELINE. 231 302. C. zebra: all teeth normal except second molars in the upper jaws on each side, which depart from the normal in the following manner. Right ^ has a small extra cusp (Fig. 51, I.) on its outer side, making four instead of three as usual (cp. figure of normal, Fig. 51, II.). The left ™? is very extraordinary. It is rather less than twice the size of its fellow of the other side (Fig. 51, 1.). The crown is of an irregularly elliptical form, the long axis being oblique. The posterior and anterior faces are marked by a shallow groove, giving an appearance of imperfect division into two teeth. The total number of cusps is greater than twice that borne by the other, but from the irregularity of the surface it is not possible to speak more precisely. For fear of injury the tooth was not extracted, so that the number of roots cannot be specified. B. M., 82. 5. 26. 1. 303. H. ichneumon (Egypt), having no right m 2 - Leyd. Mus. MUSTELIDiE 1 . The evidence of dental Variation in this family is at present too small in amount to be of much value. It is chiefly interesting in so far as it relates to cases of the occurrence in one genus or sub-family, of a formula characteristic of another. Variations of this class, con- sisting in the presence of or absence of the anterior premolar or last molar, are in some of the forms very common. As will be suggested in the next chapter, some of these, for example, the variations in p 1 in the Badger, have a certain importance as giving some measure of the magnitude which a tooth may have when the species is, as it were, oscillating between the possession and loss of the tooth in question. Amongst Mustelidse there were two cases of supernumerary large premolars, probably reduplicatory. A nterior Premo lars. Mustela (Martens), normally p±, m%. Seen in adult skulls of various species [M . peunanti, mattes, foina, zibellina, Jlavigula, americana), 62: also the following: 3Q4 M. foina :], mk. Normal adults (G. barbara 8, vittata 4, alla- mo it'll 2), 14 specimens. *306. Gr. barbara, having minute extra anterior premolar (making 4) in each lower jaw. B. M., 839, f. In 28 skulls Hensel found the following variations in premolars, the molars being always ?/*.!• p - — , viz. the normal, 12 cases o — o 3—3 „ '■■1=2 6 » 3—3 , ' ; 3-2 3 53 3—3 * 2-3 9 - 1 5) 2 3 3 2 4 4 2 2 3 4 ;i]s ° J ' J^2 ,P 3~r3' P 2--r P 2~~3' 7 ' 3^3 ea ° h ™ ° ne CaSG ' Taken together therefore there were 12 normals with j>%, 16 cases of greater or less reduction, and 2 cases of increase. Hensel 1 , Saugethiere Sud-Brasiliens, p. 83. 307. G - vittata: p 1 may be absent, especially from upper jaw. Bukmeister, Reise durch d. La Plaata-Staten, Halle, 1861, n. p. 409 [this variation not seen by Hensel]. Poccilogale: p|, m{. 3 specimens. Mephitis : p!}, mh. 9 specimens. 308. Conepatus: p$, m$. 12 specimens. Conepatus is the S. American representa- tive of Mephitis, and normally differs from it in having one premolar less in upper jaw. This tooth is sometimes present as a minute tooth making p% . Sometimes on the contrary there is a premolar less in the lower jaw, giving p\. Coues, Fur-bearing Animals of N. Amer., p. 192 and Note. In addition to the 12 normals mentioned two cases of pf were seen, viz. C. mapurito, B. M., 88. 11. 25. 8, and C. chilensis, B. M. 829, a. In the former the anterior premolar is of good size, but in the latter it is very rudimentary. Another case mentioned by Baibd, Mamm. of N. Amer., p. 192. Mydaus : pf, ml. 4 specimens. *309. Meles : commonly pj-, m\. In M. taxus, the common Badger, p } is frequently absent from one or more places. Of 36 skulls only 16 had p* in all jaws, 7 have it in each lower jaw and 2 had no such tooth in either jaw. In remaining cases it was sometimes absent on right, sometimes on left, sometimes from above and sometimes from below. Some of these cases may be due to senile changes but this was certainly not so in all. Absence from lower jaw seems the most common. Hensel, Morph. Jahrb., 1879, v. p. 550. Of genus Meles the following were seen by myself. + means pre- sence, — absence of p l . 1 The numbers given by Hensel are the totals of p + m, but he states that the variation always concerned the small anterior premolars next the canines. CHAP. IX.] TEETH : MUSTELID^E. 233 Upper jaw Lower jaw ji. i Cases right left r" right left Meles ta.riis + + + + 3 )> )j - - + j- 16 >5 »1 - - ? ? 1 ») 11 — — — — 1 )) )J + - 4- + 3 il/. ana kirn ) + + + 1 25 2 Japan ) M. chinensis 3 Taxidea : p% , mj. 7 specimens. IVIellivora : p% , m^-. 7 specimens. Helictis: p±, m\. 6 specimens. Ictonyx ( = Zorilla) : p%, m\. 14 specimens. 310. Lutra. The Otters for the most part have p±, mh. The anterior premolar of the upper jaw is a small tooth standing internal to the canine, but in the common Otter its presence is most constant. In the Oriental L. cinerea, and the Neo-tropical L.feUna on the contrary this tooth appears to be more frequently absent than present. The follow- ing table gives the results of examination of a series of skulls. + signifies presence, — absence of p\ Lutra vulgaris 11 11 ,, macrodus 11 11 ,, cinerea '» >j ,, Sumatra na ,, capensis ii ii ,, maculicollis ,, felina ii ii >) )> ,, sp. (S. America) »j ii ii ii right left Cases + + 40 — + 1 + + 11 — 2 (1 old ; 1 young) + + 2 (young) — — 6 + + 4 + + 1 — — 1 + + 1 + + 3 — — 3 + — 2 + + 14 — — 1 + ~ 1 In L. cinerea ( = leptonyx) the absence of l^_ is associated with a more forward position of p^, of which the anterior border is then level with the posterior border of the canines 1 . 1 See Flower and Lydekker, Mammals, Living and Extinct, p. 568, Fig. 261. 234 MEBISTIC VARIATION. [part I. Large Premolars. 311. Putorius (labelled " Vison Horsfieldii"): at the place in which the right lower posterior premolar ("j7 4 ") should stand there are two such teeth at the same level. They are almost identical, but the inner -A Fig. 52. Putorius, No. 311, right lower jaw, ground-plan of teeth and profile views of two teeth at the same level. Upper figure is the internal tooth. (upper in figure) is slightly the smaller (Fig. 52). B. M., 823, a. 312. Helictis orientalis, Java: having supernumerary two-rooted tooth internal to and between p 2 and f£. This extra tooth is almost a copy of if (Fig. 53). B. M., 824, a. Fio. 53. Helictis orientalis, No. 312. Surface view of upper jaw and a representation of the right upper teeth as seen from inside. Molars. 313. Putorius: Hensel, Morph. Jahrb., v. 1879, p. 540, states that he has several skulls of Fcetorius putorius with an extra upper molar on one side in a rudimentary condition. Giebel, Bronn's Kl. u. Ord., p. 18G, Taf. xv. figs. 1, 2 and 3, figures a specimen of "Putorius typus" having a fairly well developed extra upper molar on each side making m# instead of m\. Probably both these accounts refer to P. fcetidus. 314. Lutra platensis: supernumerary molar on one side of upper jaw. Such a tooth normally present on both sides in L. valetoni, a fossil form. Von Heuglin, Nov. Act. Leop. Car. Cces., xxix. p. 20. Lutra * chap, ix.] TEETH : PINNIPEDIA. 235 sp., S. America, B. M., 85. 11. 23. 1, has small alveolus behind?^ on each side. 315. Mellivora (= Ratelus): similar case. Vox Heuglix, ibid. 31(3. Meles taxus has normally m\. Skull from Quarternary diluvium of Westeregeln has small alveolus behind right w^ and left m 7 -. Another fossil skull has m§. Nehring, Arch. f. Anthrop. x. p. 20. [1 Small alveolus behind left m* in B. M., 211, L] 31/. Lutra: case of absence of ^a; Mustela : ^ may be absent. Hensel, I. c. PINNIPEDIA. With reference to dental Variation in Otariidae and Phocidse there is a considerable quantity of evidence. Id some of the species the frequency of abnormalities is remarkably great. Among the most interesting examples are two cases of reduction in the number of incisors, both occurring in Phoca barbata. These cases are especially important in connexion with the fact that the Seals are exceptional among Carnivores in having a number of incisors other than §, and that among the different sub-families of Seals there is diversity in this respect. Taken together, the cases of Variation in the premolars and molars of Seals illustrate nearly all the principles observed in the numerical Variation of teeth. In both premolars and molars there are examples of the replacement of one tooth by two, and in some of these the resulting teeth stand in series while in others they do not. Besides these there are numerous instances of extra pre- molars and molars belonging to various categories. As regards the frequency of extra teeth in Seals it may be mentioned that of Phocidae 139 normals were seen, and 11 cases of supernumerary teeth ; of Otariida? 121 normals and 5 cases of super- numerary teeth. From the simplicity of the normal dentition and from the diversity of the variations presented, the evidence as to the teeth of Seals may conveniently be studied by those who are interested in the phenomena of Variation without special knowledge of the subject of mammalian dentition. Incisors. It will be remembered that of Phocidae the sub-family Phocinae (like Otariidae) has normally if, while the Monachinae have if and the Cystophorinas i \. Of Phocinae of various genera and species 105 skulls having if were seen, and in addition the two following. 318. Phoca barbata. Greenland: skull having i\ on both sides (Fig. 54). This skull is a particularly good one and is neither very old nor very young. The teeth stand regularly together and there is no lacuna between them. There is no reasonable doubt that an incisor is absent from each side of each jaw. The shape of the 236 MERISTIC VARIATION. [part i. premaxillae is different from that seen in other specimens of Phoca, and, doubtless in correlation with the absence of the two upper Fig. 54. Incisors and canines of Phoca barbata, No. 318. incisors, the width of the premaxillae is considerably less than in specimens having the normal dentition. B. M., 90. 8. 1. 6. 319. P« barbata: in left upper jaw are three normal incisors; but on the right side the incisors have been lost. The alveoli, however, shew plainly that only two incisors had been present. Of these the outer one in size agrees with P, being a large alveolus equal to that of i"3 of the other side, but the second alveolus, occupying the place of i l and i 2 , is also a large alveolus, scarcely smaller than that for R It appears therefore that in this specimen a single large tooth stood in place of i 1 and %K A lower jaw placed with this skull was normal, but it was not certain that it belonged to the skull. O.M., 1724. Premolars and Molars. Normal arrangement. In Phocidae there are normally five teeth behind the canines in each jaw, and according to the received accounts, of these teeth 4 are premolars and one is a molar, giving p f> m p T ne Otariidae on the other hand have generally p |, m f , but both the two upper molars stand at a level behind that of the lower molar, so that the posterior molar, w* 2 is placed so far back that it meets no tooth in the lower jaw. Some of the Otariidae, however, as 0. californiana, do not possess such a pos- terior tooth, and have only m {. 0. stelleri is peculiar in the fact that it also has only one upper molar, but this tooth is separated by a large diastema from p 4 , and stands in the position character- istic m 2 of the other Otariidae. Hence it may be supposed that ^ is really absent while »& 2 is present. Amongst the cases will be found some of the presence in Pho- cidas, especially Halichoerus, of an extra molar placed in the usual position of »£ in the Otariidae. But lest any one should think it manifest that this is an example of Reversion to the Otarian con- dition, attention is called to cases of such an extra molar in the Otariidse also. Similarly there are instances of absent molar in those Otariidae which have m f , leaving m -j- ; and of these cases one occurs in such a way as to leave the peculiar diastema between CHAP. IX.] TEETH : PINNIPEDIA. 237 * P^ and the molar, referred to above as characteristic of 0. stelleri (see No. 342). The cases are grouped in an arbitrary collocation, according as it seemed desirable that particular variations should be studied together. In the sections dealing with premolars, Phocidae are not separated from Otariida 1 . First Premolar. 320. Ommatophoca rossii, an Antarctic Seal. Of this form only two skulls are known, both in the British Museum. One of these (B. M., 324, b.) has the arrangement usually found in Phocidae, namely, five teeth behind the canines in each jaw, giving the formula .2—2 1 — 1 5—5 *2ZT2' fl I— I>^ + m 5=5 (on the analogy of other Seals p|, m\). The other specimen is exceedingly remarkable (Fig. 55). In it the incisors and canines Fig. 55. Ommatophoca rossii, No. 320, teeth of the upper jaw. are as in the first specimen, but the first tooth behind the canines on both sides in the lower jaw and on the right side in the upper jaw, has a very peculiar form, having a deep groove passing over the whole length of the tooth, on its outer and inner sides. These grooves extend from the tip of the root along both sides of the crown, and thus imperfectly divide each tooth into an anterior and 238 MEBISTIC VARIATION. [part i. a posterior half. The cusp of each tooth is also divided by the grooves so as to form two small cusps. Each of these teeth is therefore an imperfectly double structure, and may be described as being just half-way between a single tooth and two teeth. These teeth are shewn in Fig. 56. Fig. 56. Ommatophoca rossii, No. 320. The anterior premolars of upper and lower jaws from the side. (The left lower and right upper teeth were not extracted.) On the left side in the upper jaw, as the vis-a-vis to one of these double teeth, there are actually two complete teeth, of very similar but not identical form, as shewn in Fig. 56. Each stands in a distinct alveolus, the two being separated by a bridge of bone. The dental formula of this skull, taken as it stands, is therefore p' i' m n T> f° r snlce the bigeminous teeth are not com- pletely divided, they must be reckoned as single teeth. 321. Cystophora cristata : internal to and slightly in front of p 1 on each side in the upper jaws is an extra tooth. These extra teeth are alike in form but are rather smaller than jp\ C. M., 895. 322. Cystophora cristata (label, Phoca cristata): internal to right upper p^ is an alveolus for a small one-rooted tooth. In the corre- sponding situation in the left lower jaw there is such an extra tooth in place. Leyd. M. 323. Zalophus lobatus ( = Otaria lobata): left 2^ smaller than right j^, and between the canine and the left F 1 there is a supernumerary tooth, smaller than left P 1 . (The same skull has another extra tooth outside and between F* and i^, see below No. 333.) Leyd. M. [P. vituUna: alveolus for left #] much larger than that for rt. v l \ the latter tooth is in place, hut left & is missing. C. M., 902.] Large Premolars. 324. P« groenlandica : in the position in which left upper p*> should stand there are two whole and complete teeth, each as large as normal p^. Fig. 57). The two stand perfectly in series, and owing to the wide CHAP. IX.] TEETH : PINNIPEDIA. 239 gaps normally existing between the teeth in this species there is no crowding. Between these two teeth there are slight differences of 325, Fig. 57. Phoca groenlandtca, No. 324. Left and right profiles. This figure was kindly drawn for me by Mr J. J. Lister. form, and the posterior is rather the larger. On both sides w^ is in place and at the same level. Both the two teeth in place of p^ bite be- tween p* and ™} of the lower jaw. On the right side F* is normal and m^ is also normal but P^ is a very large and thick tooth, and its main cusp is cloven, giving it the appearance of imperfect division into two. In this case therefore p^ on the one side may be supposed to have divided into two perfect and nearly similar teeth, while on the right side this division is begun but not completed. Leyd. M. Otaria ursina £ : supernumerary premolar in left upper jaw. This is a curious case. The right upper and both lower jaws are normal. On comparing the left upper series of 7 teeth with the right series which has 6 normal teeth, it is seen firstly that the two molars of each side are alike in form and stand at their proper levels (Fig. 58). Fig. 58. Otaria ursina, No. 325, seen from left side. 1, 2, 3, 4, first to fourth lower premolars ; 5, lower molar. Next, the two posterior premolars of each side (f* and F 4 ) agree so nearly that there is no reasonable doubt that they are not concerned in the variation. Anterior to this there is difficulty, for whereas p l and p 2 are normal and in place on the right side, there are three teeth on the left side to balance them. These three teeth moreover are so nearly alike that it is impossible to say that either of them is 240 MEMSTIC VARIATION. [part I. * definitely the extra tooth. The first premolars of each side are almost exactly alike, and the second and third of the left side are each very like the second on the right side (p 2 ), so that it might be said that p 2 was represented by two teeth on the left side; and as seen in Fig. 58 the second and third on the left side bite between f- and p of the lower jaw, as the normal p 2 would do. This is however accomplished by the backward displacement of p*. Probably therefore this should be looked on as a case of division of P^, but there is no proof that the three first premolars of the left side are not collectively equivalent to the first two of the right side. C. M., 911, f. 326. P. grcenlandica : the second upper right premolar is represented by two teeth, each of which has two roots; the two teeth stand at the same level in the arcade, the inner one being rather smaller. On the left side the second upper premolar is incompletely double, the crown being partially divided by an oblique constriction into an anterior and internal portion and a larger posterior and external part. The former has one root and the latter two. P. M., A, 2897. 327. Otaria jubata : left upper p 3 a bigeminous tooth something like the anterior premolars of Ommatophoca (No. 320). In this animal all the premolars and molars are one-rooted and have single conical crowns. The abnormal tooth is formed as it were of two such simple teeth imperfectly divided from each other through their whole length, the plane of division being transverse to the jaw. The teeth of the two sides are not alike and in particular the posterior lower m} is much smaller than the right. The skull has been much mended and the position of some of the teeth is not very certain, but the above- mentioned facts are correct. C S. M., 975. oZo. Otaria cinerea : supernumerary tooth in upper jaw on both sides. The extra tooth in each case stands within the arcade, internal to the Fig. 59. Otaria cinerea, No. 328. A diagram of the positions of the upper teeth, and profiles of the teeth standing internal to each m*. 5th tooth behind the canine (sc. »^), which is pushed outwards by it. The extra tooth of the left side (Fig. 59) is a little larger and at a level rather anterior to that of the left extra tooth. C. M., 911 **. CHAP. IX.] TEETH .* PINNIPEDIA. 241 *329. P. vitulina : having a supernumerary tooth in each jaw on the right side. This is a somewhat remarkable case. In both jaws the extra tooth does not stand in series with the others but is placed within the arcade (Fig. 59, + + ). That of the upper jaw is a curved tooth with one large median cusp and a small cusp anterior to and posterior to it, having somewhat the form of p* of the lower jaw. This tooth stands within the arcade at a level between that of l^ and F 5 which are pushed outward by it. The extra tooth of the lower jaw in shape closely resembles that of the upper jaw, but is slightly larger, having very much the size and shape of the lower right jp. In position this extra tooth does not stand between p 2 and p 3 like the upper supernum- erary, but is placed ivithin the arcade and p and p* which are some- what separated by it. C. M., 903. [Judged by the ordinary rules of dental homology, the two extra teeth are not homologous, for the upper one is between p 2 and p-\ while the lower one is between p and p 4 . But when the jaws are put together it appears that the two extra teeth are opposite to each other almost exactly, the large cusp of the lower one being in the bite scarcely at all posterior to the large cusp of the upper. The tooth of the lower jaw is thus almost exactly the image or reflexion of the tooth in the upper jaw.] Fig. 60. Phoca vitulina, No. 329 ; view of upper teeth from the surface, and an imaginary profile of the upper and lower teeth of the right side seen from within. 330. Otaria ursina : this skull in bad condition. The Catalogue (1884) states that between F 2 and l^ on both sides and between P^ and nfl on both sides there was a small supernumerary tooth, in all, four extra teeth in the upper jaw. The anterior supernumeraries are in place and one rather smaller than v\ The posterior supernumeraries are lost, but from the alveoli they must have been of fair size, though not so large B. 16 242 MERISTIC VARIATION. [Px^rt i. as lA In each case the extra tooth is placed a little within the arcade though the adjacent teeth are also spaced out for it. This skull has been a good deal mended. C. S. M., 990. 331. Phoca grocnlandica : in right upper jaw p^ is smaller than the corresponding tooth of the left side, though it is two-rooted as usual. Between it and pI there is a small, peg-like, supernumerary tooth. Both p^ and the extra tooth bite between pi and m 1 of the lower jaw. Leyd. M. 332. P. grocnlandica: supernumerary tooth with two roots placed internally to and between left & and m\ The last molars stand at the same level on the two sides. B. M.,328, i. 333. Zalophus lobatus: in right upper jaw a supernumerary tooth placed on the outside of the arcade on a level with the interspace between p* and p 4 . This tooth resembles p 4 or m 1 . On the left sidep 1 is smaller than on right side and a supernu- merary tooth which is still smaller stands between p^ and the canine. Leyd. M. [given above, No. 323]. 334. P. vitulina: in right lower jaw a supernumerary tooth inside the arcade, between pi and pi. In size and form it agrees very nearly with the first premolar of the right lower jaw: other teeth normal. C. M., 903, F. 335. 3P. vitulina: in front of p* on left side the teeth are all lost but there has been some irregularity, probably a supernumerary tooth level with pi : also behind right nfl there is a small tubercular nodule of bone which may perhaps cover a supernu- merary molar. C. S. 31., 1064. Molars. 336. P. vitulina : on left side there is a small supernumerary molar placed behind »^. This tooth stands in the line of the arcade (Fig. 61) Fig. 61. Phoca vitulina No. 336, a profile of the left teeth in the bite as seen from within. but is turned so that its greatest width is set transversely to the jaw. In the lower jaw of the same side there is a supernumerary tooth placed internally to m l . This tooth has two roots and three cusps, and is therefore not a copy of m 1 , which has 4 — 5 cusps. C. S. M., 1067. '337. Halichoerus grypus : of 47 skulls seen, 12 have one or more supernumerary molars. One case of p% , m§. Nehring, Sitzb. naturf. Fr. Berlin, 1883, p. 110. 2 2 Of 34 skulls in Greifswald Museum there were 3 cases of m ^ , and five cases of m\ on one side only. Ibid., 1882, p. 123. Of 11 skulls seen by myself two individuals (C. M.) have an extra molar on left side. In these cases the extra teeth are placed at a considerable distance behind »£ as they are in Otaria. [In addition to these Gray figures a skull with m\ but without allusion to this fact in the text. Hand-list of Seals in B. M., 1874, PL vil] chap, ix.] TEETH : UNGULATA. 243 A skull having left ml two-rooted, right ml being much less so. C. S. M., 1059. 338. •P- groenlandica : minute supernumerary molar on each side in upper jaw making m'f . P. M., A. 2898. 339. Zalophus californianus, an Eared Seal not far removed from tar la. but having p + mi instead of ~. The five back teeth are arranged as a rule in a continuous series, but sometimes there is a small space between the last molar and the penultimate [cp. 0. stelleri], and occa- sionally they are all slightly and evenly spaced. One case of p + m £ on both sides and two cases of p + m£ on one side only. In these the extra teeth were behind the (normally) last molar and smaller than it. being without the accessory cusps seen in that tooth. Allen, J. A., J\\ Amer. Pinnipeds, 1880, pp. 209, 224 and 226. 340. Z. lobatus : one specimen having p + w^f on right and £ on left, Leyd. M. [in addition to 3 specimens with the normal £]. 7 — 7 341. Callorhinus ursinus : normally £> + m£; one case having o — o and one case with - -. Allen, I. c, p. 224 (cp. No. 343). o — o deduction in numbers of molars. q 5 342. Arctocephalus australis, normally p + mf : one case of „ — . General statement made that in cases of absence of a tooth it is the antepenultimate molar which is missing [not described in a specific case]. Allen, I. c, p. 224. 343. Callorhinus ursinus, normally £; 2 cases of i. Allen, I. c. (cp. No. 341). 344. Otaria jubata, normally 4: one specimen having 4- on both sides, Leyd. M.; one specimen having right 4 left 4. Leyd. M. Cystophora cristata: only one molar, viz. left ^ present; from the state of the bones it seemed possible that the others had not been formed, but this is quite uncertain. C. S. M., 1101. Macrorhinus leoninus: doubtful if the molars had been present. C. S. M. 1109. UNGULATA. As to the occurrence of Variation in the dentition of Ungulates 1 have no statistics, but a certain number of miscellaneous cases have been collected from different sources. Most of the cases relate to domestic animals and are given on the authority of Morot and Goubaux. Perhaps the most interesting evidence is that regarding the change of form in the "canines" of the Sheep. These teeth of course have normally the shape of incisors, but in the cases described by Morot they had more or less of the character of canines. This evidence, though belonging properly to the Sub- stantive class, is introduced here on account of its close relation to some general aspects of variation in teeth. 1G— 2 244 MERISTIC VARIATION. [part i. * It is noticeable that there is so far no case of an incisor appear- ing in the upper jaw of Ruminants. The evidence is divided into two groups, the first relating to incisors and canines, the second to premolars and molars. Incisors and Canines. 345. Elephas africanus g : the left tusk imperfectly doubled. The root of this tooth was double 1 , one root being outer and the other inner. The half of the tusk arising from the outer root twisted round and over the other half so that at the other end it lay above and internal to it. The structure of the tusk was essentially double, but the two parts were more or less blended together in the middle third. The ex- ternal ends were separate, but broken and somewhat deformed. Friedlowsky, A., Sitzungsb. d. K. Ak. Wien, 1868, lix. i. p. 333. Plate. 346. Horse. Supernumerary incisors common. Magitot, Anom. Syst. dent., p. 104, Plates. Numerous specimens in Museum of Veterinary School at Alfort. 347. Specimen having 12 upper incisors and 12 lower incisors belonging to the permanent dentition. Goubaux, Pec. med. vet., 1854, Ser. 4, I. p. 71. Similar observation, Lafosse, Cours Hippiatrique, 1772, p. 32. 348. Extra teeth of more or less irregular form placed behind upper incisors very common : many specimens in museum at Alfort. Speci- men having left ^ as a double structure, the two halves not being separated. (Alfort Mus.) Magitot, /. c, PI. xix. fig. 25. Absence of incisor in Horse is rare. Goubaux, who has largely studied the subject, knew no case of absence of any tooth in Horse, /. c. 349. Skeleton of Cart-mare in C. M. has only two incisors on the left side in the upper jaw. The teeth stand evenly and without break or trace of any other incisor having been present. There is no sufficient indication to shew which of the incisors is missing, but the two incisors present agree most nearly with i 2 and i 3 . This specimen was first pointed out to me by Mr S. F. Harmer. (See also case given by Kudolphi, Anat.-phys. Abh., 1802, p. 145.) *350. Mare of common breed, foaled March, 1876, having in the upper jaw no i 3 in either milk or permanent dentition, and in the lower jaw no permanent P. In the upper jaw there were only 4 milk incisors, which were subsequently replaced by 4 permanent incisors. Animal seen by Morot in Apr. 1880 ; it then had 4 per- manent incisors in the upper jaw, but no i 3 . In the lower jaw permanent i 1 and i- were in place, together with i 3 of the milk series on each side. As Morot remarks it is still possible that the other incisors might appear. Dam normal; half-sister abnormal, given in next case. Morot, Bull. Soc. med. vet., 1885, Ser. 7, n. p. 125. *351. Mare out of same mother as last case, by another sire, foaled Apr. 1877, had only 4 milk-incisors in upper jaw. Seen by Morot at 3 years old, had then the teeth of lower jaw normal, viz. permanent i 1 , and milk i 2 and i 3 all in place. In upper jaw were permanent i 1 and milk i 2 on each side. The right milk /- on the external side had a light groove parallel to the long axis of the tooth, suggesting that it might be a double structure, but the groove was very slight and the crown was single. At five years old this animal had the normal 6 lower incisors, but in the upper jaw left i 3 was absent. On the other hand a well-formed supernumerary tooth stood behind right i 3 , right i 2 being partly rotated. Ibid., p. 127. 1 See also a curious case of "nine tusks " imperfectly described by Chapmax, J., Travels in Interior of S. Africa, n. p. 98. chap, ix.] TEETH : TJNGULATA. 245 352. Ass : ( $ some 20 yrs. old) on right side in upper jaw were two canines, one in front of the other in the same alveolus. Morot, Rec. med. vet., 1889, Ser. 6, vn. p. 480. Another somewhat similar case, ibid. 353. Cow : in j}lace of right p, two third incisors placed side by side. Morot, Bull, et mem. Soc. med. vet., 1886, p. 321. Goat, 4 — 5 weeks old ; supernumerary lower incisor placed be- tween the two median incisors which rose above it. This tooth stood transversely so that its edge lay exactly in the long axis of the head. Morot, /. c. 354. Sheep : extra incisor on left side. (Alfort Mus.). Goubaux, Rec. med. vet., 1854, Ser. 4, I. [Several other cases.] Abnormal form of Canines in Sheep. 355. In the lower jaw of the Sheep there are on each side 4 incisi- form teeth, arranged in close series without any diastema. Of these the outermost, known in veterinary works as " corner teeth," are considered by zoologists as representing canines. The corner teeth or canines have been found in a considerable number of cases actually shaped like canines instead of like the incisors as usual. These teeth have been found presenting this modification in several degrees, but in order to gain a fair view of the matter it is necessary to read the evidence in its entirety. The facts given were founded on 18 animals, 15 ewes and 3 males [whether rams or wethers not stated]. In these 18 cases there were 28 individual teeth of abnormal form. Of these 14 were conical with a point either sharp or rounded ; 7 were conical with a bifid point ; 5 were cuneiform ; 1 was cylindrical with a surface shaped like an ass' hoof; 1 was pyramidal. In 8 specimens the abnormality was unilateral and in 10 it was bilateral, but in the latter the corner teeth of the two sides were frequently of differing forms [details given]. Morot, Bull. Soc. med. vet., 1887, p. 166. Pig". No case of Variation in incisors met with. [This is perhaps singular in connexion with the fact that the Peccaries (Dicotyles) have i -§.] 356. Dicotyles torquatus (normally £§) : two specimens having 3 2 i-= ; in one of them i* of the side having the extra tooth is deformed. o — o Another young skull of Dicotyles also had 3 incisors on left side. Hensel, Sdugetldere Sild-Brasiliens, p. 94. Molars. 357. Horse: supernumerary molars exceedingly rare; case of such a tooth in left upper jaw, behind and in series with the others. Goubaux, Rec. med. vSt. } 1854, Ser. 4, i. p. 71, same case, figured by Magitot, /. c, PI. v. fig. 9. * 246 MERISTIC VARIATION. [part i. *358. Ass : thoroughbred Spanish she-ass, in the Museum of the Royal College of Surgeons, has a large supernumerary molar on each side in series in the upper jaw, and a similar tooth in the left lower jaw. The same skull has the first premolar also present on each side in the upper jaw, as is not unfrequently the case in Equidse. All four canines are present as minute teeth. The dental formula for this skull is therefore ,3_3 l_i 4_4 4 — 1 tK ^3=3 C r=Ti^3=3 m 4^3 =45 ' 359. Auchenia lama : specimen having a suj>ernumerary (fourth) molar in the lower jaw [? on both sides]. This tooth was fully formed and resembled the normal last molar. In the upper jaw T was a small alveolus behind ?/i 3 , for another tooth which was not present in the specimen. Rutimeyer, L., Vers, einer nattirl. Geschichte des Binder, Zurich, I. p. 55, Note. 360. Cervus axis $ : specimen having a supernumerary grinder placed on the inside of the normal series on the left side of the upper jaw. In the lower jaw of the same specimen the following supernumerary teeth : (1) a small, compressed accessory tooth on both sides placed internally to m? ; and (2) behind the large three-fold sixth molar was a smaller two-fold tooth which had caused a displacement of the 6th molar. Donitz, Sitzungsb. d. naturf. Fr., Berlin, 1872, p. 54. 361. Cervus rufus : having supernumerary (4th) premolar on one side in lower jaw. Hensel, Morph. Jahrb., v. p. 555. 362. Ox : supernumerary upper molar on left side. Magitot, I. 3 ") between upper p 1 and p 4 is generally absent, and in the lower jaw there are usually only two "intermediate" teeth. The following table shews the variations seen in 58 skulls and 7 lower jaws wanting skulls (including 43 1 Leyden skulls described by Jentink, I. c). Small upper Intermediate Cases. premolar teeth in 1. j. A Leyden Other Total r > r \ right left right I left (Jentink) Museums + 1 lr. jaw — — 1 1 2 1 3 — — 1 2 2 2 - — 2 1 2 3 + 2 lr. jaws — — 2 2 27 1 8 35 + 4 lr. jaws — — 3 2 2 2 - - 3 3 2 2 1 In one of these 1. P l + - 2 3 1 1 absent (see No. 370) — + 3 3 1 1 + + 2 1 1 1 + + 2 3 1 1 + + 3 2 2 2 + + 3 3 2 1 4 + + 4 3 1 1 58 1 Not including the case, Leyd. Mm., 153 (Jentink, I.e., p. 91), in which the "small" upper premolar is stated to be absent as an abnormality. As p 3 is usually absent in the species, probably this refers to p 1 . 254 MEEISTIC VARIATION. [part I. The above includes six skulls from Waigiu, the individual peculiarities of which are given below : 3 3 1 1 + 3 3 1 1 B. M., 61. 12. 11. 18. + + 2 3 1 1 + + 3 2 1 1 + + 3 3 1 1 B. 21. , 61. 12. 11. 17. + + 4 3 1 1 The great variability of these skulls from the island of Waigiu is very remarkable. The 4 Leyden specimens were described by Jen- TINK 1 . In one of these there was besides no left upper 2nd molar, which was entirely absent without trace, leaving a diastema between m 1 and m 3 . In connexion with the variations of the dentition of P. maculatus in Waigiu the following singular circumstance should be mentioned. In all other localities the male P. maculatus alone is spotted with white, the female being without spots, but in Waigiu the females are spotted like the males 2 . This curious fact was first noticed by Jextixk (I. c, p. 111). In the other species of Phalanger no case of special importance met with; but since in P. ursinus p x is normally (4 skulls seen) two-rooted, it may be of interest to note that such a two-rooted condition of p l was seen on both sides as a variation in P. ornatus, B. M., 1317, b (2 other specimens having single-rooted p x ). * 378. Trichosurus vulpecula ( = Phalangista vulpina). The typical form of this species is Australian, while the large variety, fuliginosa, is peculiar to Tasmania. In the typical form no instance of absence of P^ seen in 17 specimens examined. All possessed this tooth on each side, and though varying a good deal in size, it was in every case well- formed and functional, never being in a condition which could be called rudimentary. Of the Tasmanian variety fuliginosa, 18 specimens (8 in B. M., 10 in C. M.) were examined. In 6 F 1 was present on both sides. 1 right side only. 1 left. 2 p 1 was absent altogether. C. M., 14 k and I. Nevertheless in every case in which this tooth is present it is a large tooth of about the size of the canines. In one case P^ is two-rooted on each side, as (Thomas, Cat. Marsup., p. 186) in the Celebesian Phalan- ger ursinus. C. M., 14 a, Hobart Town, Tasmania. Of the "intermediate" teeth in lower jaw one only is usually present, being 1 The small premolar was accidentally described in the paper referred to as being between the canine and p 4 , instead of between the anterior premolar and p A . Jentink, in litt. 2 Compare the converse case of Hepialus humuli (the Ghost Moth), of which, in all other localities, the males are clear white and the females are light yellow- brown with spots; but in the Shetland Islands the males are like the females, though in varying degrees. See Jenner Weir, Entomologist, 1880, p. 251, PI. CHAP. IX.] TEETH : DASYURIDJE. 255 close to the large incisor. In two cases (C. M., 15 p and h, pi-ob. both Australian) there are two intermediate teeth, one near the incisor, the other near fi. 379. Pseudochirus. Of various species 29 skulls shew no numerical variation in upper series. The number of "intermediate" teeth in lower jaw is very variable, 2 on each side being the most frequent, but 1 and 3 being also common. P. pere- grinus, Upper Hunter E., B. M., 41, 1182, has 2 intermediate teeth in left lower jaw, but on the right side one partially double intermediate tooth. (See also No. 371.) Petaurus : 25 skulls shew no numerical variation in upper series. In this genus the number of small teeth in the lower jaw is remarkably constant. In addition to p* there were 3 small teeth on each side in 380. all cases seen except two, viz. — P. breviceps var. papuanus (8 normals): right side normal; left lower jaw has 4 teeth besides^ 4 (Fi^. 66). B. M. 5 77. 7. 18. 19. Bight Left Fig. 66. Petaurus breviceps, No. 380. Lower jaws in profile: on right side three intermediate teeth, on left side four. 381. Another specimen has, in addition to ~j?,four small teeth in each lower jaw. There is a small diastema between the 3rd and 4th. B. M., 42. 5. 26. 1. [no skull]. 382. Dactylopsila trivirgata : 3 specimens have upper series normal. In addition one has an extra tooth in left upper jaw between i^ and canine. This tooth somewhat resembles but is rather smaller than the canine, near and slightly internal to which it stands [? reduplicated canine]. B. M., 1197, d. (3) Premolars and molars of Dasyuridse and Didelphyidse. Thylacinus, 19 normals; Sarcophilus, 9 normals, no abnormal known to me. Dasyurus, 37 normals (4 species). 383. D. geoffroyi : specimen in which p 4 in right lower jaw has its crown partially divided into two, the plane of division being at right angles to the jaw. C. M., 39, a. 256 MERISTIC VARIATION. [part I. 384. D. viverrinus : rigKfc upper m 4 slightly larger than the left, which is normal. C. M., 38, g. *385. D- maculatus, Tasmania, having a supernumerary molar in left upper jaw, and on both sides in the lower jaw. The fourth molar in the upper jaws is increased in size in a remark- able manner ( Fig. <>7, B and C). This case requires detailed description. In Fig. 67, A, a normal right upper jaw is shewn. It belongs to a specimen considerably larger than the abnormal one, but the latter, Mr Thomas tells me, is a good deal smaller than the normal size of the species. In the normal there are two small pre- molars ( p 1 and p 9 of Thomas), and behind these, four molars. The molars increase in size from the first to the third, which is by far the largest. Behind the third is the fourth molar, which is much smaller than the others, having the peculiar flattened form shewn in the Figure 67, A. Fig. 67. A. Eight upper jaw of normal Dasyurus maculatus (shewn as far as the canine) for comparison with the variety. (N.B. The latter is considerably smaller.) B. Upper jaw of D. maculatus, No. 385. C. Lower jaw of the same specimen. On comparing the abnormal skull with a normal one it is seen that the two premolars and first three molars on each side are unchanged. Behind the third molar on the right side there is a single tooth ; but this, instead of being a thin tooth like normal ™ 4 , is considerably larger and the longitudinal measure- ment in the line of the jaw is not very much less than the transverse measurement. In the right upper jaw therefore the number of the teeth is unchanged. On the left side, behind the third molar, there is a square tooth (w* 4 ) of good size, about equal in bulk to half w 3 , while behind this again there is another tooth, _^ 3 , which is a thin CHAP. IX.] TEETH : DASYURID^E. 257 386, and small tooth having nearly the form and size of normal w 4 . The lower series is alike on both sides, each having an extra molar behind m" 4 (Fig. 67, C). The two extra teeth are well formed, being as long but not quite so thick as m*. B. M., 41, 12, 2, 3. In Cat. Marsup. Brit. Mus., 1888, p. 265, note, Thomas refers to this skull, and describes it as an instance of an additional molar inserted between m 3 and m 4 on the left side above and on both sides below. This view is of course based on the resemblance that the extra »»? of the left side bears to a normal mt and on the fact that the left w 4 is like no tooth normally present. In the light however of what has been seen in other cases of super- numerary molars a simpler view is possible. For in cases in which a supernumerary molar is developed behind a molar which is normally a small tooth, the latter is frequently larger than its normal size. In the present case it appears that on the right side ™ 4 has been thus raised from a small tooth to be a tooth of fair size, while on the left side the change has gone further, and not only is ««* promoted still more, but a supernumerary ra 5 is developed as well. It is interesting to note that this ft& is a small tooth, very like normal ^_ 4 , and it thus may be said to be beginning at the stage which m^ generally reaches. In the lower jaw wf is added without marked change in ~m± ; for mF is normally a large tooth and has, as it were, no arrears to be made up. Mr Thomas, to whom I am indebted for having first called my attention to this remarkable case, allows me to say that he is prepared to accept the view here suggested. Phascologale. In the upper jaw normally 3 premolars, by Thomas reckoned as p\ p 3 and p*. Between the first and second ("p 3 ") there is sometimes, but not always, a small space, and in the following case a supernumerary tooth was present in this position. Phascologale dorsalis, (Fig. 68) having an extra premolar between the first and second in the left upper jaw : rest normal. B. M., 1868, b. Thomas, O., Phil. Trans., 1887, p. 447, PL 27, figs. 7 and 8. In the lower jaw ~jfi is often small and may be absent. As Thomas has observed, the size of p 4 in the upper and lower jaws maintains a left ri/fht reversed Fig. 68. Phascologale dorsalis, No. 386. Teeth of left upper jaw from canine to first molar; below, the teeth of the right side reversed (after Thomas). b. 17 258 MERISTIC VARIATION. [part i. fairly regular correspondence. Within the limits of one species p* may 387. shew great variation ; for instance, of Phascologale fiavipes 7 specimens were seen ; in 1 jT 1 was absent, in 2 it was small, in 2 mode- rate, and in 2 it was large. 388. Didelphys : 79 specimens normal. One specimen alone, D. lanigera, Colombia, B. At., 1733, b, was abnormal, having no m 4 in either upper or lower jaws. D. opossum (one specimen, B. M.) had right n* larger than the left. (4) Molars of certain Macropoclidae. The following evidence relates to the genera Bettongia, Potorous and Lagorchestes. In these forms the molars are normally four in each jaw. As Thomas observes (Cat. Marsup. Brit. Mus., p. 105, note), in Bettongia cases of fifth molar occur, but on the other hand cases of non- eruption of m 4 occur also. The variations seen in the three genera were as follows. 4 4 Bettongia penicillata : 8 specimens have m . ; in 7 of them m 4 is small (in B. M., 279, j, ™^ is very minute; but in B. M., 278, m, the lower m* is large). *389. 1 specimen °. has m 4 in left lower jaw only, this tooth being small. B. M., 279, a. *onn i • x. 1.2.3.0.5 — 1.2.3.0.0 _ , ., *390. 1 specimen has m = — s — = — - — = = — - — =- — . In both upper laws r 1.2.3.4.5 — 1.2.3.4.0 rr J there is a small empty crypt behind m 3 , and on right side behind this again there is a minute tubercular tooth not represented on the other side. B. M., 279, b. 4 — 4 B. cuniculus : 2 specimens have m- - . 391. 1 specimen has no left v?. B. M., 982, c. 5 5 *392. 1 specimen has m— — = ; in upper jaws m 5 very small in crypts, but o — o in lower jaws they are of good size. B. M. 51. 4. 24. 7. 4 4 B. lesueri : 13 specimens have m - (in one of them on 4 very small. B. M., 277, g). 5 5 393. 1 specimen has m , m 5 being minute and lying in crypts. B. M., 41, 1157. 4 4 394. Potorous (Hypsiprymnus): mj- in 5 specimens of P. tri- dactylus and in 2 of P. platyops. A single specimen of P. gilberti has no right upper m\ B. M., 282, b. 395. Lagorchestes. In this genus m 4 is present and is a large tooth, not materially smaller than m s . Nevertheless it commonly falls short of the other teeth and remains partly within the jaw. This was the case in 10 skulls of L. leporoides and L. conspicillatus. In one skull of L. leporoides, m 4 stood at the same height as the other teeth. I see no reason to suppose that all the other skulls were young, and it seems more likely that this imperfect eruption of m 4 is characteristic. chap, ix.] TEETH : RHINOPTERA. 259 Selachii. Some features characteristic of Meristic Variation are well seen in the case of the teeth of Sharks and Rays. Of these fishes there are many having little differentiation between the separate rows of teeth. In these a distinct identity cannot be attributed to the several rows, and numerical Variation is quite common. But besides these there are a few forms whose teeth are differ- entiated sufficiently to permit a recognition of particular rows of teeth in different specimens, and to justify the application of the term "homologous'' to such rows. Nevertheless with such differentiation Meristic Variation does not cease. In the following examples it will be seen further that in such Variation there may be not merely a simple division of single teeth but rather a recasting of the whole series, or at least of that part of it which presents the Variation, for the lines of division in the type may correspond with the centres of teeth in the variety. These cases also exemplify the fact that variations of some kinds are often only to be detected when in some degree im- perfect ; for if the divisions in No. 396 for instance had taken place similarly on both sides, it would have been difficult to recognize that this was a case of Variation. Rhinoptera jussieui (= javanica) : specimen in which the number and arrangement of the rows of teeth is different on the two sides, as shewn in Fig. 69, upper diagram. The dis- position on the right side of the figure is normal, that on the left being unlike that of any known form. Specimen in B. M. described by Smith Woodward, Ann, and Mag. N.H., Ser. 6, vol. i. 1888, p. 281, fig. As Woodward points out, the rows of plates on the left side may be conceived as having arisen by division partly of the plates of the central row and partly from the lateral row, marked I. But if this be accepted as a repre- sentation of the relation of the normal to the abnormal, in the way indicated by the lettering, the plates of the row marked b, for instance, must be supposed each to belong half to one rank and half to a lower rank. The same applies to the plates in the row I b. By whatever cause therefore the points of develop- ment of the teeth are determined, it is clear that the centres from which each of the teeth in the rows I b and b was de- veloped were not merely divided out from centres in the normal places but have undergone a rearrangement also. With change of number there is also change of pattern. The tessellation on the abnormal side is so regular and definite that had it existed in the same form on both sides the specimen might readily have become the type of a new species. There is indeed in the British Museum a unique pair of jaws in both of which (upper and lower) a very similar tessellation 17—2 260 MERISTIC VARIATION. [part I. occurs in a nearly symmetrical way. This specimen is described as Rhinoptera potyodon, but it is by no means unlikely that it T Th la Oc Ob wM lL £ HLUL Oa M M jt m Fig. 69. Upper figure ; Rhinoptera jussieui, No. 396, after Smith Woodwakd,. from whom the lettering is copied. Middle figure, Rhinoptera, sp., No. 397. Lower figure Rhinoptera javanica, No. 398, after Owen. is actually a Variation derived from the usual formula of Rhino- ptera. It is figured by Gunther, Study of Fishes, 1880, p. 346. Fig. 133. *QQ7 39/. Rhinoptera sp. incert. : teeth as in middle diagram, Fig. 69. On the left side three rows of small lateral teeth, while on the right side two of these rows are represented by one row, which in one part of the series shews an indication of division. C. S. M. {Hunterian Specimen). CHAP. IX.] TEETH I SELACHII. 261 398. Rhinoptera javanica : the row of teeth marked I is one side single, but on the other side is represented by two rows. Fig. 69, lower diagram. Owen, Odontography, PI. 25, Fig. 2. C. S. M. (Hunterian specimen). 399. Cestracion philippi : an upper jaw having the teeth disposed as in the figure (Fig. 70). C. S. M. Fig. 70. Upper jaw of Cestracion philippi, No. 399. 400, On comparing the teeth of the two sides it will be seen first that the rows do not correspond individually, and secondly that they do not at all readily correspond collectively. Assuming that the rows marked 4 on each side are in correspondence (which is not by any means cer- tain) several difficulties remain: for right 5th is larger than left 5th, but left 6th and 7th together are larger than right 6th; right 7th is about the same size as left 8th, but right 8th is larger than left 9th. The proportions in the figure were carefully copied from the specimen. " Cestracion sp." [so labelled, but probably not this genus] : lower jaw as in Fig. 71. On the right side the second row of large plates is represented by two rows, properly fitting into each other, but on the left side the plates of the inner side are completely 262 MERISTIC VARIATION. [part I. divided, but the division is gradually lost towards the middle of the jaw and the external plates are without trace of division. C. S. M. Fig. 71. The lower jaw of a Selachian, No. 400. The proximal ends shewn (enlarged). The right is reversed for comparison with the left. RADUL.E of a Gasteropod. * The following example of Meristic Variation in the teeth of a Molluscan odontophore may be taken in connexion with the subject of teeth, though the structures are of course wholly different in nature. For information on this subject I am in- debted to the Rev. A. H. Cooke. Generally speaking the number and shapes of the radular teeth are very characteristic of the different classificatory divi- sions. There are however certain forms in which a wide range of Variation is met with ; of these the case of Buccinum undatum is the most conspicuous. 401. Buccinum undatum. In most specimens the number of denticles on the central plate is 5 — 7 and on the laterals 3 — 4. In 27 specimens from Hammerfest and Vardo the teeth were as follows : — Lateral plates. Cases. 4 8 4 12 4 2 4 1 4 1 3 & 4 1 3& 4 1 4 & 5 1 Central plate. 5 6 7 6—8 9 6 7 8 from Friele, Jahrb. deut mat. Ges., VI. 1879, p. 257. CHAP. IX.] RADUL^E I BUCCINUM. 263 *402. The range of Variation may be still greater than this, the number of centrals being sometimes as low as 3. Fig. 72 shews the different conditions found. In it eight varieties are shewn, M/vWV. IV VI Fig. 72. Variations in odontophore of Buccinum undatum. I. Three centrals (Labrador). II. Four centrals. III. Five centrals, approxi- mately symmetrical bilaterally. IV. Five centrals, not symmetrical ; the two external centrals on one side almost separate, correspond with a bifid denticle on the other side (Labrador). V. Six complete centrals (Labrador). VI. Seven centrals (Lynn). VII. Nine almost distinct centrals. VIII. Eight centrals ; laterals asymmetrical (4 and 5). I. II. IV. — VI. from photographs made and kindly lent by Mr A. H. Cooke. III. VII. VIII. after Friele. I. II. IV. — VI. being taken from Mr Cooke's specimens, III. VII. and VIII. from Friele's figures. As thus seen, in these variations considerable symmetry may be maintained. This symmetry and defmiteness of the varieties in the cases with 3 and 4 centrals is especially noteworthy, in- asmuch as these are abnormal forms and have presumably arisen discontinuously. As also seen in the figure, e.g. IV. and VI. this symmetry is not universal, and may be imperfect. The specimen shewn in VIII. is remarkable for the asymmetry of the lateral plates, which have 4 and 5 denticles respectively. In connexion with the subject of symmetrical division interest attaches to cases like that shewn in Fig. 72, IV. in which on the 264 MEBISTIC VARIATION. [part i. outside of the central plate a pair of almost wholly separate denticles on one side correspond with a large, imperfectly divided denticle of the other side. A very similar specimen is figured by Friele, Norske Nordhavs-Exp., viii. PL v. fig. 16. The number found in one part of the radula is usually main- tained throughout the whole series, but this is not always so. A case in which the number of centrals at the anterior end of the radula was 6, and at the posterior end 8, is given by Friele, Norske Nordhavs-Exp., 1882, viii. p. 27, Taf. v. fig. 17. CHAPTER X. Linear Series — continued. Teeth — Recapitulation. In this chapter I propose to speak of those matters which seem to have most consequence in the foregoing evidence as to the Variation of Teeth. Each of the following sections treats of some one such subject, specifying the cases which chiefly illustrate it. It will be understood that the sections do not stand in any logical collocation but are simply arranged consecutively. The treatment given is of course only provisional and suggestive, being intended to emphasize those points which may repay investigation. The subjects which especially call for remark are as follows : (1) The comparative frequency of dental Variation in differ- ent animals. (2) Symmetry in Meristic Variation of Teeth. (3) Division of Teeth. (4) Duplicate Teeth. (5) Presence and absence of Teeth standing at the ends of series (first premolars, last molars). (6) The least size of particular Teeth. (7) Homceotic Variation in terminal Teeth when a new member is added behind them. (8) Reconstitution of parts of the Series. (1) The comparative frequency of dental Variation in different animals. The total number of skulls examined for the purpose of this inquiry was about 3000. From so small a number it is clearly impossible to make any definite statement as to the relative frequency of Variation in the different orders, but some indications of a general character may be legitimately drawn. First, the statistics very clearly shew that while dental Varia- tion is rare in some forms, it is comparatively frequent in others, but there is no indication that this frequency depends on any condition or quality common to these forms. Setting aside examples of the coming and going of certain small and variable 266 MERISTIC VARIATION. [part i. teeth, the animals shewing the greatest frequency of extra teeth were the domestic Dogs, the Anthropoid Apes and the Phocidse. Attention is especially called to the fact that the variability of domestic animals is not markedly in excess of that seen in wild forms. From the hypothesis that Variation is uncontrolled save by Selection, there has sprung an expectation, now fast growing into an axiom, that wild animals are, as such, less variable than domesticated animals. This expectation is hardly borne out by the facts. It is true that, so far as the statistics go, supernumerary teeth were more common in domestic Dogs than in wild Canidse, and though the number of Cats seen was small, the same is true in their case also as compared with wild Felidse. But though it is true that the domestic Dog is more variable in its dentition than wild Doofs, it is not true that it is much more variable than some other wild animals, as for instance, the Anthropoid Apes or the genus Phoca. The doctrine that domestication induces or causes Variation is one which will not, I think, be maintained in the light of fuller evidence as to the Variation of wild animals. It has arisen as the outcome of certain theoretical views and has received support from the circumstance that so many of our domesticated animals are variable forms, and that so little heed has been paid to Variation in wild forms. To obtain any just view of the matter the case of variable domestic species should be com- pared with that of a species which is variable though wild. The great variability of the teeth of the large Anthropoids, appearing not merely in strictly M eristic and numerical Variation, but also in frequent abnormalities of position and arrangement, is striking both when it is compared with the rarity of variations in the teeth of other Old World Monkeys and the comparative rarity of great variations even in Man. If the Seals or Anthropoids had been domesticated animals it is possible that some persons would have seen in their variability a consequence of domestication. When the evidence is looked at as a whole it appears that no generalization of this kind can be made. It suggests rather that the variability of a form is, so far as can be seen, as much a part of its specific characters as any other feature of its organization. Of such frequent Variation in single genera or species some curious instances are to be found among the facts given. Of Canis cancrivorus, a S. American Fox, the majority shewed some abnormality. Of Felis fontanieri, an aberrant Leopard, two skulls only are known, both showing dental abnormalities. In Seals only four cases of reduplication of the first premolar were seen, and of these two were in Cystopliora cristata. The number of cases of abnormality in the genus Ateles is very large. Of six specimens of Crossarchus zebra, two shew abnormalities. Of the very few skulls of Myrmecobius seen, two shew an abnormal num- ber of incisors. Three cases of Variation were given in Canis mesomelas, not a very common skull in museums. On the other chap, x.] TEETH : SYMMETRY. 267 hand the rarity of Variation in the dentition of the Common Fox (G. vulpes) is noteworthy, especially when compared with the extraordinary frequency of Variation in the molars of S. American Foxes. The constant presence of the small anterior premolar in the upper jaw of Otters (Lutra) of most species, as compared with the great variability of the similar tooth in the Badgers (Meles) and in other species of Otters, may also be mentioned. The evidence given in the last chapter should not, I think, be taken as indicating the frequency of dental Variation in Mammals generally. The orders chosen for examination were selected as being those most likely to supply examples of the different forms of dental Variation, and it is unlikely that the frequency met with in them is maintained in many other orders. (2) Symmetry in Meristic Variation of Teeth. With respect to bilateral Symmetry an examination of the evidence shews that dental Variation may be symmetrical on the two sides, but that much more frequently it is not so. The in- stances both of bilaterally symmetrical Variation, and of Variation confined to one side are so many that examples can be easily found in any part of the evidence. Besides these there are a few cases in which there is a variation which is complete on one side, while on the other side the parts are in a condition which may be regarded as a less complete representation of the same variation. Such cases are Ommato- phoca rossii No. 320, Phoca gramlandica No. 324, Dasyurus macu- latus No. 385, Ganis lupus No. 246, G. vetulus No. 248, &c. In the remarks preliminary to the evidence of dental Variation, reference was made to a peculiarity characteristic of the teeth considered as a Meristic Series of parts. As there indicated, the teeth are commonly repeated, so as to form a symmetry of images existing not only between the two halves of one jaw, but also to a greater or less extent between the upper and lower jaws. It was then mentioned that cases occur in which there is a similar Varia- tion occurring simultaneously in the upper and lower jaws of the same individual. Such similar Variation may consist either in the presence of supernumerary teeth, or in the division of teeth, or in the absence of teeth. It should, however, be noticed that examples of Variation thus complete and perfect in both jaws are comparatively rare. Speaking generally, it certainly appears from the evidence that similar Variation, (1) on one side of both jaws, or (2) on both sides of one jaw and on one side of the other, or (3) on both sides of both jaws are all rare. Of these three the following examples may be given : — Of (1), Macacus rhesus No. 190, Ateles pentadactylus No. 196, Esquimaux dog No. 243, Phoca vitulina No. 329. 268 MERISTIC VAKIATIOX. [part i. Of (2), Simla satyrus No. 106, Dasyurus maculatus No. 385, E. asinus No. 352. Of (3), Dog Xo. 257, Bettongia cuniculus, No. 392, Ateles margi- natus No. 203, Phoca barbata No. 318, Ommatophoca rossii No. 320. Of these, further examples may be seen in the evidence given regarding the anterior premolars of Galictis barbara, Meles, and Herpestes. (3) Division of Teeth. Among the cases of increase in number of teeth are many in which by the appearances presented it may be judged that two teeth in the varying skull represent one tooth in the normal, and have arisen by the division of a single tooth-germ. Of such division in an incomplete form several examples have been given. The plane of division in these cases is usually at right angles to the line of the jaw, so that if the division were complete, the two resulting teeth would stand in the line of the arcade. Incomplete division of this kind is seen in the first premolar of Ommatophoca rossii No. 320, in the fourth premolar of Phoca groenlandica No. 324, in the incisors of Dogs No. 219, in the canine of Dog No. 221, in the lower fourth premolar of Dasyurus geoffroyi No. 383. The plane of division is not however always at right angles to the jaw, but may be oblique or perhaps even parallel to it, though of the latter there is no certain case. Cases of division in a plane other than that at right angles to the jaw are seen in C. vulpes No. 230, Phalanger orientalis No. 368, Phoca groenlandica No. 326 and doubtfully in a few more cases. The existence of the possibility of division in these other planes is of some consequence in considering the phenomenon of duplicate teeth standing together at the same level in relation to that of the presence of duplicate teeth in series. Beyond this also it may be anticipated that if ever it shall become possible to distinguish the forces which bring about the division of the tooth-germ, the relation of the planes of division to the axis of the Series of Repe- titions will be found to be a chief element. (4) Duplicate Teeth. Teeth standing at or almost at the same level as other teeth which they nearly resemble may conveniently be spoken of as duplicate teeth, though it is unlikely that there is a real distinc- tion of kind between such teeth and those extra teeth which stand in series. Duplicate teeth were seen in Felis domestica Nos. 286 and 287, Ganis mesomelas No. 228, Herpestes ichneumon No. 300, [Putorius] Vison horsfieldii No. 311, Helictis orientalis No. 312, Cystop)iora cristata No. 322, and perhaps in some other cases. That these cases are not separable on the one hand from examples of extra teeth in series may be seen from Herpestes gracilis No. 299, Cystophora cristata No. 321 [compare with No. 322], Brachy teles chap, x.] TERMINAL TEETH. 269 hemidactylas No. 199 [compare with Ateles rnarginatus No. 200]. PJioca vitulina No. 336 ; and that on the other hand they merge into cases of supernumerary teeth standing outside or inside the series, and whose forms do not correspond closely to those of any tooth in the series, may be seen by comparison with Otaria iwsina No. 325, Phoca vitulina No, 329, Phalanger orientalis No. 372. Though in some cases the shapes of duplicate teeth make a near approach to the shapes of normal teeth, yet they are never exactly the same in both, and teeth whose forms approach so nearly to those of other teeth in the series as to suggest that they are duplicates of them and that they may have arisen by multipli- cation of the same germ, cannot be accurately distinguished from extra teeth whose forms agree with none in the normal series. (5) Presence and Absence of Teeth standing at the ends of Series (first premolars, last molars): the least size of particular Teeth. Of the cases of numerical Variation in teeth the larger number concern the presence or absence of teeth standing at the ends of Series. As was mentioned in introducing the subject of dental Variation, in many heterodont forms the teeth at the anterior end of the series of premolars and molars are small teeth, standing to the teeth behind them as the first terms of a series more or less regularly progressing in size. Not only in teeth but in the case of members standing in such a position in other series of organs, e.g. digits, considerable frequency of Variation is usual. Variability at the ends of Series is manifested not only in the frequency of cases of absence of terminal members, but also in the frequency of cases of presence of an extra member in their neigh- bourhood. An additional tooth in this region may appear in several forms. It may be a clear duplicate, standing at the same level as the first premolar (e.g. Cat, No. 270). On the other hand, as seen in the Dogs (Nos. 232 and 233) there may be two teeth standing between the canine and (in the Dog) the second pre- molar. The various possibilities as to the homologies of the teeth may then be thus expressed. The posterior of the two small teeth may correspond with the normal first premolar, and the anterior may be an extra tooth representing the first premolar of some possible ancestor having five premolars; or, the first of the two premolars may be the normal, and the second be intercalated (see No. 224) ; or, both the two teeth may be the equivalent of the normal first premolar ; lastly, neither of the two may be the precise equivalent of any tooth in the form with four premolars, Of these possibili- ties the first is that commonly supposed (Hexsel and others) to most nearly represent the truth. But the condition seen in cases where there is an extra tooth on one side only, as in the Dogs figured (Fig. 42), strongly suggests that neither of the two teeth strictly corresponds with the one of the other side. Seeing that in such cases the single tooth of the one side stands often at the level 270 MERISTIC VARIATION. [part i. of the diastema on the other, it seems more likely that the one tooth balances or corresponds to the two of the other side, which may be supposed to have arisen by division of a single germ. On the other hand since the two anterior premolars found in such cases are not always identical in form and size, either the anterior or the posterior being commonly larger than the other, there is no strict criterion of duplicity, and it is clearly impossible to draw any sharp distinction between cases of duplicity of the first pre- molar and cases in which the two small premolars are related to each other as first and second. These two conditions must surely pass insensibly into each other. If the case of the teeth is com- pared with that of any other Linear series in which the number of members is indefinite, as for example that of buds on a stem, the impossibility of such a distinction will appear. A good illustration of this fact may often be seen in the arrangement of the thorns on the stems of briars. For large periods of the stem both the angular and linear succession of the thorns of several sizes may be exceed- ingly regular ; but it also frequently happens that a thorn occurs with two points, and on searching, every condition may sometimes be found between such a double thorn and two thorns occurring in series, having between them the normal distinctions of form or size. Very similar phenomena may be seen in the case of the strong dermal spines of such an animal as the Spiny Shark (Echi- norhinus spinosus). These structures are of course from an anato- mical standpoint closely comparable with teeth. In them, spines obviously double, triple or quadruple, are generally to be seen scattered among the normal single spines, but between the double condition and the single condition, it is impossible to make a real distinction. The remarks made as to the first premolars apply almost equally to the last molar. See Phoca vitulina No. 336, Mycetes niger No. 206, Man, Magitot, Anom. syst. dent, PI. v. figs. 4, 5 and 6, Canis cancrivorus Nos. 251 and 252, Crossarchus zebra No. 302. (6) The least size of 'particular Teeth. What is the least size in which a given tooth can be present in a species which sometimes has it and sometimes is without it ? In other words, what is the least possible condition, the lower limit of the existence of a given tooth ? This is a question which must suggest itself in an attempt to measure the magnitude or Dis- continuity of numerical Variation in teeth. The evidence collected does not actually answer this question completely for any tooth, but it shews some of the elements upon which the answer depends. In the first place it is seen at once that the least size of a tooth is different for different teeth and for different animals. chap, x.] LEAST SIZE OF TEETH. 271 Considered in the absence of evidence it might be supposed that any tooth could be reduced to the smallest limits which are histo- logically conceivable ; that a few cells might take on the characters of dental tissue, and that the number of cells thus constituting a tooth might be indefinitely diminished. Indeed on the hypothesis that Variation is continuous this would be expected. Now of course there is no categorical proof that this is not true, and that teeth may not thus occur in the least conceivable size, but there is a good deal of evidence against such a view. The facts on the whole go to shew that teeth arising by Variation in particular places, at all events when standing in series in the arcade, have a more or less constant size on thus appearing. Within limits it seems also to be true that the size in which such a tooth appears has in many cases a relation to the size of the adjacent teeth and to the general curves of the series. For example in the Orang, the series of molars does not diminish in size from before backwards, and extra molars when present are, so far as I know, commonly of good size, not wholly disproportionate to the last normal molar. The same is I believe true in the case of the Ungulates. In the Dogs however the series of lower molars diminishes rapidly at the back, and the extra molars added at the posterior end of the series are of a correspondingly reduced size. As presenting some ex- ception to this rule may be mentioned two cases in the Chimpanzee, Nos. 178 and 181 and the case of Cebus robustus No. 194, in each of which the extra molar is disproportionately small. The principle here indicated is of loose application, but speaking generally it is usual for an extra tooth arising at the ends of series to be of such a size as to continue the curves of the series in a fairly regular w T ay. It would at all events be quite unparalleled for an extra tooth arising at the end of a successively diminishing series, as the Dog's lower molars, to be larger than the tooth next to it, and with the exception of cases of duplicate anterior pre- molars (see Dogs Nos. 232 and Cat No. 268) I know no such case. In these besides, the anterior tooth is very slightly larger than its neighbour, and it should be remembered that the first premolar, though the terminal member of the series of premolars, is not actually a terminal tooth. Examples have been given of animals which seem to be oscil- lating between the possession and loss of particular teeth, the first premolar of the Badgers, p 1 of some species of Otter, &c. In these cases we are not yet entitled to assume because in a given skull the tooth is absent, that it has never been formed in it, though this is by no means unlikely, but as already pointed out (p. 22sary to suppose that the variations by which this form has departejj from the ordinary Hippocampi had occurred separately, and that -each spine had separately developed its tag of skin, the number of variations and selections to be postulated would be enormous ; but probably no such supposition is needed. We are, as I think, entitled to expect that if we had before us the line of ancestors of Phyllopteryx, we should see that many and perhaps all of the spines which are thus modified in different parts of the body had simultaneously broken out, as we may say, into tags of skin, just as the feathers of the Moor-hen (Gallinula chloropus) 5 may collectively take on the " hairy " form, or as, to take the case 1 Animals and Plants under Domestication, ed. 1885, n. chap. xxv. 2 As D,*$*vin mentions, simultaneity in the variations of the hair may be mani- fested in size and texture as well as in colour. A bay horse was lately exhibited at the Westminster Aquarium standing 16£ hands, having the hair of both mane and tail of prodigious length. The longest hairs of the mane measured 14 ft. and those of the tail 13 ft. It did not appear that the hair of the fetlocks or bo ly was unusual in character, but these were kept closely clipped and nothing could be affirmed on this point. 3 By the courtesy of Professor L. Vaillant I was enabled to examine a number of specimens of the singular breeds uf Gold-fish from China in the Paris Museum of Natural History. Some of these are characterized by the great length both of the appendicular fins and of the caudal fin also. Measurement shewed that there was a substantial correspondence between the lengths of these parts, those with long appendicular fins having also very long tails. The correlation between these parts is not however universal in Gold-fishes, and in many of the ordinary "Telescope" Gold-fish the tail may be longer than that of a common Gold-fish of the same size, though the length of the appendicular fins be not exceptional (v. infra). 4 Gunther, Study of Fishes, 1880, p. 682, fig. 309. 5 See Introduction, p. 55. 310 MERISTIC VARIATION. [part i. of Radial Series, the petals of a flower may all together take on the laciniated condition 1 . Further study will indeed probably lead to the recognition of a principle which may be thus expressed : that jxtrts which in any one body are alike, which have, that is to say, undergone similar Variation in the past, may undergo similar variations simid- taneously; a principle which, if true at all, is true without regard to the morphological position of the parts in question. 1 For cases see Masters, Vegetable Teratology, 1869, p. 67. CHAPTER XIII. linear series — continued. Minor Symmetries : Digits. All the cases considered in the foregoing chapters have il- lustrated Variation of parts whose repetition is disposed in Linear Series along the chief axis of the body, being thus arranged directly and immediately with reference to the Major Symmetry of the body. We have now to consider cases of the Meristic 'Variation of parts which are also repeated in Linear Series but normally possess in some degree the property of symmetry partially completed within the limits of their own series, thus forming a Minor Symmetry. Of Linear repetitions thus occurring there is a great diversity, and evidence will here be produced regarding two of the chief examples, namely, the digits of vertebrates and the segmentation of antennae and tarsi of Insects. In each of these groups of organs the parts are frequently formed in such a way as to make an approach to symmetry, about one or more axes within the limits of the appendage to which they belong. This fact will be found to lead to conse- quences apparent in the manner in which numerical Variation takes place in limbs of the various types. In these Minor Symmetries Linear Repetition may occur in two forms : there may be repetitions of digits or other parts in lines forming an angle with the axis of an appendage ; and there may be repetitions in the form of joints &c. along the axis of the appendage itself. The cases of Variation in number of joints in the appendages of Insects are chiefly interesting as examples of manifest Dis- continuity in Variation, and from the conclusions which they suggest as to the supposed individuality of segments. This latter question arises also in considering the relation of the two pha- langes of the pollex and hallux to the three phalanges of the other digits, but the evidence which can be gained from a study 312 MERISTIC VARIATION. [part i. of Variation with reference to this question is so intimately con- nected with the subject of the variation of digits in general that it cannot be considered apart. Other cases referring to repetitions in the line of the axis of appendages will be taken in a subsequent chapter. In studying numerical Variation in the digits of certain animals, especially the Horse and the Pig, we shall meet with forms of Variation which are peculiar to structures having a bilateral symmetry. In examining the evidence as to Meristic Variation of Bilateral Series further reference to these cases will have to be made, but it appears simplest to describe the facts in the first instance in connexion with the subject of digits. From the evidence as to Meristic Variation in digits I propose to make a selection, taking certain groups of cases having a direct and obvious bearing on the general problems of Variation. It will be understood and should be explicitly stated that unless the contrary is declared the principles of form which can be per- ceived as operating in special cases are not of universal appli- cation in the Variation of digits, but are enuntiated as applying only to the special cases in which they are perceived. In the human subject, for example, cases of polydactylism will be quoted which when arranged together form a progressive series illus- trating the establishment of a novel and curious Symmetry ; but though these cases are valuable as illustrations of the way in which the forces of Division and growth can dispose themselves to produce a symmetrical result, yet it must always be borne in mind that very many variations of the digits have been seen in Man, whether consisting in increase in number of digits or in decrease, of which the result is almost shapeless. The case of polydactyle Cats is thus especially interesting from the fact that in this animal the polydactyle condition, though differing in degree of expression in various specimens, yet, in the greater number of cases, occurs in ways which may be interpreted as modifications of one plan, or rather of one plan for the hind foot and of another for the fore foot. I arrange the evidence primarily according to the animal con- cerned, Cat, Man and Apes, Equidye, Artiodactyles, &c. To these are added a few facts as to digital variations in Birds, but from the scantiness of the evidence and the difficulty of determining the morphology of the parts I have not found it possible to give a profitable account of these phenomena in other vertebrates below Mammalia. In most of the groups increase in number of digits may be seen to occur in several distinct ways ; and, just as in the case of teeth, mammae, &c, it is possible to recognize cases of division of single members of series, and cases of addition to the series chap, xiil] DIGITS : CAT. 313 either at one of its ends (often associated with remodelling of other members of the series) or in the middle of the series. Reduction in number of digits, or ectrodactylism as it is often called, is usually so irregular in the manner of its occurrence that little could be done as yet beyond a recitation of large numbers of cases amongst which no system can be perceived. For the present therefore the interest of these observations for the student of Variation is comparatively small and they are for the most part omitted. To the irregularity of ectrodactylism in general certain cases of syndactylism are a marked exception and of these an account will be given. After stating the morphological evidence as to numerical Variation in digits in the several groups, reference will be made to some collateral points of interest concerning such variations. There is a good deal of evidence respecting the recurrence of digital variations in those lines of descent wherein they have appeared. Facts of this kind have been frequently seen in the case of Man, and other examples are known in the Cat, the Pig, the Ox, Deer, Sheep, &c. References to these cases will be given. It will be seen that the facts contained in this section of evidence are of consequence rather as indicating the limits set on Variation, and from their bearing on the question of the nature of Symmetry and of Homology, than from any more direct appli- cation to the problem of Species, but even this cannot be said with much confidence. There are in certain groups limbs such as the pes of Macro- podidse or that of Peramelidae whose appearance forcibly recalls what is seen in some teratological cases and the possibility that they may have had such a sudden origin may well be kept in view 1 . Cat. The apprehension of the chief features in the evidence as to digital variation in the Cat will be made more easy if a general account of the subject be given as a preliminary. In order to understand the peculiar phenomena seen in the limbs of poly- dactyle cats certain points of normal structure are to be re- membered. Of these the most important relate to the claws and their disposition with regard to the second phalanx ; for it is by this character that the relation of digits to the symmetry of the limb may be determined. 1 In the case named this is all the more likely from the circumstance that according to Thomas, Cat. Marsup. Brit. 2Ius., p. 220, there is reason for supposing that the extraordinary condition of the digits II and III was attained independently in these two groups. 314 MERISTIC VARIATION. [part i. Hind foot. The phenomena seen in the case of the hind foot are in some respects simpler than those of the variations in the fore foot, and for this reason they may conveniently be described first. If the phalanges of the index of the hind foot, for example, be examined, it will be seen that the proximal phalanx is nearly bilaterally symmetrical about a longitudinal axis, but that the second phalanx is deeply hollowed out upon the external or fibular side. Into this excavation the ungual phalanx is withdrawn when the claw is in the retracted position. The retraction is chiefly effected by a large elastic ligament running from the outside of the distal head of the second phalanx and inserted into the upper angle of the last phalanx (see Owen, Anat. and Phys. of Vert., III. p. 70, fig. 36). The same plan is found in the digits II to V both of the fore foot and of the hind foot. By this asymmetrical re- traction of the claw a digit of the right side may be differentiated at a glance from one of the left side, for the claw is retracted to the right side of a right digit and to the left side of a left digit. The importance of this fact will be seen on turning to the evidence, for it is found that with variation in the number of digits there is a correlated variation in their symmetry. With respect to the tarsus little need be said. The proximal part of the tarsus contains three bones, the calcaneum, astragalus and navicular. The distal row consists of four bones, the cuboid and three cuneiform bones. In the majority of polydactyle cats that I have seen in which the tarsus is affected, the cuboid is normal and the ecto-cuneiform is also normal and recognizable ; internal to the latter there are three small cuneiforms articulating with the navicular instead of two, making four cuneiforms in all. In some specimens there is no actual separation between the two innermost of these cuneiforms, but the lines of division between them are clearly marked. In the normal hind foot of the Cat there are four fully formed toes, commonly regarded as II, III, IV and V, each having three phalanges. In the place where the hallux would be there is a small cylindrical bone articulating at the side of the internal cuneiform. As usually seen, all the four digits are formed on a similar plan, each having its claw retracted to the external or fibular side of the second phalanx, the four digits of a right foot being all right digits and those of left feet being all left digits. The rudimentary hallux has of course no claw. Starting from this normal as the least number of digits, it will be found that a large proportion of cases are such that they may be arranged in an ascending or progressive series. In this series the following Conditions have been observed. In the schematic representations of the limbs the words 'Eight' or 'Left' signify that a digit is shaped as a right or as a left. The Roman numeral chap, xiil] digits: cat. 315 indicates that the digit to which it is assigned has the tarsal or carpal relations of the digit so numbered in the normal. For brevity each is described as a right foot. I. The normal, consisting of four three-phalanged digits, each retracting its claw to the external, viz. right side, and a rudimentary hallux with no claw. In this foot therefore the digits enumerated from the external side are Eight. Eight. Eight. Eight. Eudiment. V IV III II I II. Five digits, each with three phalanges. Of these the minimus and annularis borne by a normal cuboid are normal and are formed as right digits. The medius is borne by a normal ecto- cuneiform and is also a true right digit. Internal to this is a full- sized digit having the relations of an index and borne by a bone placed as a middle cuneiform. But the claw of this digit cannot be retracted to the external side of the limb, for the second phalanx is not excavated on this side. There is on the contrary a slight excavation on the internal side of the second phalanx, but this is very incomplete and the claw cannot be fully retracted, being in fact almost upon the middle line of the digit when bent back. This digit is thus intermediate between a right and a left. Nevertheless it is truly the index of this right foot, for it has the tarsal relations of an index. Internal to this digit is another, which by all rules of homology should be the hallux, but it has three phalanges and is fashioned as a left digit, retracting its claw to the left (internal) side of the digit. This digit (Fig. 85, II, d 1 ) is borne jointly by two cuneiforms, c 1 and c 2 , as shewn in the figure. There is thus one cuneiform more than there is in the normal. In this foot therefore the digits enumerated from the external side are as follows : — Eight. Eight. Eight. Indifferent. Left. V IV III II I Such a specimen is No. 472, right pes. Between this state and the normal I have as yet met no inter- mediate. It might perhaps have been expected that a foot having four three-phalanged digits and a hallux with two phalanges would be a common form of variation. Such a condition has not however been seen, so far as I know. III. The foot shewn in Fig. 85, 1 exemplifies the next condition. In it the three external digits, which are structurally the minimus, annularis and medius of a normal foot are normal in form, position and manner of articulation with the tarsus. Internal to the medius are three digits, of which the innermost has two phalanges (Fig. 85, I, d l ) and a claw which cannot be retracted, like the pollex of the normal fore foot. The other digits, d 3 and d 2 , are fashioned as left digits, retracting their claws to the internal or left side of the limb. It will be seen that of them d 3 has the 316 MERISTIC VARIATION. [part I. relations to the tarsus which an index should have. The tarsus is as in the last Condition. In the specimen seen, c 1 and c 2 were not actually separate from each other, but there was a distinct line of division between them. Here then the digits enumerated from the external side are as follows : — Eight. Eight. Eight. Left. Left Hallux-like V IV III II digit digit IV. The stage next beyond the last is shewn in Fig. 87, II. [The drawing is from a left foot.] Here there are six digits, each with three phalanges. The three externals are normal and true rights as before. The other three are all formed as lefts. Tarsus as before. This foot may be represented thus : — Eight. Eight. Eight. Left. Left Left V IV III II digit digit As far as I have seen the last or fourth Condition is the com- monest. There are doubtless many variants on these plans. No. 477 is an especially noteworthy modification of the third Condition and the cases of the hind feet in No. 478 must also be specially studied as not conforming truly to either Condition. Forefoot. I. The normal right fore foot has four digits II — V each with three phalanges all differentiated as rights, and a pollex with two phalanges, the last being non-retractile but bearing a claw. It may be represented thus : — Eight. Eight. Eight. Eight. Pollex. V IV III II I Departures from this normal are more irregular than they are in the case of the hind foot. Those given in this summary being only a selection. For the others the evidence must be examined. II. One specimen, No. 474, has the four external digits normal. The pollex however has three phalanges and is formed as a digit of the other side, thus : — Eight. Eight. Eight. Eight. Left. V IV III II I III. The next Condition seen was as follows: — Eight. Eight. Eight. Eight. V IV III II d tj Q -2 a 2 03 it Cj rt O CO Left Indifferent digit digit IV. In the majority of polydactyle cats the manus 1ms the digits II — V normal in shape and symmetry. Internal to the digit II are two digits more or less united in their proximal parts ; sometimes the metacarpal only, sometimes the metacarpal and first phalanx are common to both. Of these two digits the external, chap, xiil] digits: CAT. 317 that is, the one next to the digit II, is in some degree shapeless and imperfect, but the external branch is as a digit of the other side in form. Internal to this double digit is a seventh digit, sometimes with two phalanges, sometimes with three, but in either case the claw is as a rule non-retractile, and the digit is in this respect not differentiated as either right or left. Such a manus may be thus represented (cp. Fig. 86 a left manus) : — Eight. Right. Right. Right. Amorphous Left Indifferent V IV III II digit digit digit / As regards the carpus its changes are like those of the tarsus. When there are six metacarpals there are three carpals in the distal row internal to the magnum. That next the magnum may be supposed to be trapezoid, and the other two may be spoken of as first and second trapezium. In correspondence the length of the scapho-lunar is increased. No comment can increase the interest of these curious facts. In the pes, as has been stated, with change in the number of digits there is change in the grouping and symmetry of the series of digits, and in particular the digit having the relations of the index or digit II is formed as the optical image of its neighbour III instead of forming a successive series with it. There is thus a new axis of symmetry developed in the limb, passing between the parts which form the digits II and III of the normal. The evidence of the above statements may now be given. r 472. Cat having the digital series of each extremity abnormal, being that preserved in the Coll. Surg. Mus., Teratological Catalogue, 1872, Nos. 305 and 306. Right pes (Fig. 85, II). Digits III, IV and V normal right digits. Internal to these are two digits each having three phalanges and claws. That lettered d 1 is formed as a left digit but d 2 is al- most indifferent, the second phalanx being slightly hollowed on the inside. Internal to the external cuneiform there are three small bones, of which the inner two together bear the digit d 1 . [This is the Condition II of the pes.] Left pes has the same structure as the right so far as can be seen from the preparation (in which the muscles remain). The digits III, IV and V are normal left digits, but internally to them there are two digits each with three phalanges, of which the external is an indifferent digit, while the internal is formed as a right. [Condition II of the pes.] Left manus. The digits II, Til, IV and V are normal. But the carpal of the distal series (trapezoid) which bears the digit II is imperfectly separated from a similar bone placed internal to it. This second part of the trapezoid bears a metacarpal which articulates with a full-sized digit of three phalanges formed as a right digit. From the external side of the first phalanx of this 318 MERISTIC VARIATION. [part I. digit there is given off a rudimentary digit, which has however a complete claw, but its bones do not differentiate it as right or left. II ect cijl Fig. 85. I. Right pes of Cat No. 473, shewing condition III of the pes. II. Right pes of Cat No. 472 shewing Condition II of the pes. as, astragalus, c 1 , c-, c 3 , three ossifications representing the ento- and meso- cuneiforms of the normal, cb, cuboid, clc, calcaneum. d 1 — cZ 6 , the digits numbered from the inside, ect, cu, ecto-cuneiform. nav, navicular. (From specimens in Coll. Surg. Mus.) The " pollex", d\ has two phalanges and is rather slender. The trapezium which bears it is not separated from the scaphoid. (Fig. 86). [Condition IV of the manus.] Right manus. This is exactly like the left manus so far as can be seen from the dissection, except for the fact that the rudimentary digit borne by the large digit external to the "pollex" is much more reduced than in the case of the left manus. The digit which supports it is fashioned as a left digit. [Condition IV of the manus.] 473. Cat having digital series of all feet abnormal, being the specimen in Mus. Coll. Surg., Teratol. Catalogue, 306 B. CHAP. XIII.] DIGITS : CAT. 319 Right pes. The digits III, IV and V (Fig. 85, I) are normal and are fashioned as right digits. The cuboid and external Fig. 86. Left manus of Cat No. 472, shewing Condition IV of the manus. cu, cuneiform, d 1 — d 7 , digits numbered from the inside, m, magnum, sclu, scapho-lunar. Tp, trapezoid. (From a specimen in Coll. Surg. Mus.) cuneiform (cb and ect. cu) are also normal. Internally to the ex- ternal cuneiform there is a long flat bone which is grooved in such a way as to divide it into three parts (c 1— 3 ) and each of these bears a digit. Of these digits, d 2 and d 3 have each three phalanges, but d l has only two phalanges and may therefore be called a hallux. The digits d 2 and d 3 are fashioned not as right digits but as left digits, and their claws are thus retracted towards the internal side of the second phalanges, which are hollowed out to admit of this. The bones of the hallux are not thus differentiated as right or left, for the claw is not retractile. The navicular is enlarged in correspondence with the presence of the fourth cuneiform element and the astragalus and calcaneum are normal. (Fig. 85, 1). [Con- dition III of the pes.] Left pes. This foot is almost exactly like the right. As in it, the digits III, IV and V are normal and are left digits. Internal to this are three digits, viz. a hallux and two long digits with three phalanges which are both made as right digits. The bones of this foot have not been cleaned. [Condition III of the pes.] Right manus. This is formed on the same plan as the manus of the last animal, differing from it in details of the carpus, chiefly in the presence of two separate trapezial elements. The four digits on the external side, II — V are shewn by their claws to be true 320 MERISTIC VARIATION. [part I. right digits. They articulate in a normal way with the trapezoid, magnum and unciform, and are thus clearly II, III, IV and V. The metacarpals of the " pollex " and of the double digit corre- sponding to d' 2 and d 3 of Fig. 86 articulate with two separate carpal bones of the distal row. The external of these bears a rather thick metatarsus which peripherally gives articulation to two digits. Of these the internal is well formed and bears a claw which slides up on its internal side, and thus shews it to be formed as a left digit. The other is misshapen in its proximal phalanx which perhaps contains two phalangeal elements compounded together and aborted ; hence the relation of this digit to the symmetry of the limb is not apparent. The claw and last phalanx are well formed. The innermost carpal bone is nearly normal and bears an almost normal " pollex." [Condition IV of the manus.] Left manus. This foot has not been dissected, but from ex- amination it appears that the digits II, III, IV and V are normal like those of the right manus. As in it, there is a " pollex " with two proper phalanges, but the metacarpal of the " pollex " is in its proximal part united with the metacarpal of an imperfectly double digit corresponding to d 2 and d 3 of Fig. 86. The division between the two parts of this double digit is not so complete in the left manus as it is in the right and from external examination it appears that the phalanges of the two are not separate. There are two claws of which one is rudimentary and the pads of the two are separated only by a groove. There is nothing to indicate .whether these digits are formed as right or left digits. [Approaches Con- dition IV of the manus.] *474. Cat having supernumerary digits. This specimen belonged to the strain of polydactyle Cats observed by Mr Poulton (see No. 480) and I am indebted to Mr J. T. Cunningham for an oppor- tunity of examining it. Left manus. Five digits, the normal number. The " pollex ' however is a long digit, composed of three phalanges, which reaches very nearly to the end of the index. The claw of this digit is not retracted to the outside of the second phalanx, like that of a normal digit, but to the inside, and the chief elastic ligament is on the inside of these joints instead of being on the outside as in a normal digit. This pollex therefore may be said to be fashioned as a right digit, bearing the same relation to the others as a right limb bears to the left. The flexors and extensors of this digit were fully developed. The carpal series was normal. [Condition II of the manus.] Right manus. Six digits fully formed, one bearing an additional nail on the third digit from the inside. Beginning from the outer or ulnar side, there are four normal right digits, placed and formed as V, IV, III and II respectively. Internal to these are two digits, the outermost having three phalanges, being shaped as a left digit and bearing a minute supernumerary nail in the skin chap, xiii.] digits: CAT. 321 external to the normal nail. The innermost digit has two pha- langes, and is formed like a normal pollex, excepting that its claw was very deep and looked as if it were formed from the germs of two claws united and curving concentrically. The carpus as regards number of elements was normal, but the trapezium and trapezoid were both of rather large size, and the pollex articulated partly with the trapezium but chiefly with the downward process on the radial side of the scapho-lunar. [This approaches Condition IV of the manus, but in it the external of the two united digits is only represented by the minute extra nail.] Left pes. Six digits, each having three phalanges. The three outer digits were formed as left digits, but the three inner digits were shaped like right digits. The internal cuneiform is double the normal size, but is not divided into two pieces. It bears the two internal digits, of which the innermost is ankylosed to it. [Condition IV of the pes.] Compare Fig. 87, II. Right pes. Same as the left, except for the fact that the two internal digits are completely united in their metacarpals and first phalanges, and the cuneiform series consists of four bones, two of which correspond to the internal cuneiform of double size described in the left foot. (Compare Fig. 85, I, c 1 and c 2 .) [Condition IV of the pes, save for the union of the metacarpals of the two internal digits.] 475. Kitten belonging to Mr Poulton's strain (see No. 480) and kindly lent by him to me for examination. The specimen was very young and the carpus and tarsus were not dissected. Left manus. Six digits, all with three phalanges. The two internal digits are separated by a space from the others so as to form a sort of lobe. The claw of the innermost digit is re- tracted on the top of the second phalanx and not to the side, so that this digit is not differentiated either as a right or a left. The next digit is a right and the four external digits (II, III, IV and V) are normal lefts. [Condition III of manus.] Right manus. Same as left. Left pes. Same as left pes of No. 474 [sc. Condition IV oi the pes]. Right pes : same as the left [Condition IV of the pes]. 476. Cat having its extremities abnormal, the property of the Oxford University Museum and kindly lent for examination; bones only preserved. Right pes. Like the left pes of No. 474, but c 1 not separated from c 2 . [Condition IV of pes.] Left pes. Like the right, but c 1 separate from c'\ [Condition IV of pes.] Right manus. The four external digits II — V normal. The double digit like that of No. 472. The innermost digit with thn b. 21 322 MERISTIC VARIATION. [part I. phalanges, but the claw not retracted to one side more than to the other. [Condition IV of the manus.] Left manus. The same as the right. [Condition IV of the manus.] *477. Cat having all extremities abnormal, also the property of the Oxford University Museum. Left pes. Like the left pes of case No. 474 [sc. Condition IV of the pes] represented in Fig. 87, II. Right pes a peculiar case (Fig. 87, I). The digits V, IV and III are normal right digits. The digit II marked 3 in the figure is e.cu Fig. 87. Hind feet of Cat No. 477. I. Eight pes not truly conforming to any of the Conditions numbered. II. Left pes shewing the ordinary form of Condition IV of the pes. Lettering as in Fig. 85. (From a specimen in Oxford Univ. Mus.) very slightly differentiated as a right digit, but the excavation on the external side is very slight, and the claw when retracted is almost on the middle of the second phalanx. The digit 2 of the figure is a left, and internal to it is a three-phalanged digit of which the claw is not retracted into any excavation. [Not conforming to any of the Conditions specified.] 478. Cat having all feet abnormal, kindly lent to me by Mr Oldfield Thomas. chap, xiil] digits : cat. 323 Left pes. Digits V, IV, III normal lefts. The next internally (II) is a three-phalanged digit formed as a right. The next is a thick three-phalanged digit with a partially double nail and double pad. This is not differentiated as either right or left. The innermost digit is a two-phalanged hallux-like digit, not differentiated as right or left. [Not conforming to any condition in my scheme.] Right pes. The same as the left except that the digit II is only slightly differentiated as a left. The next has a double nail, and the innermost is hallux-like as described for the other foot. [Not conforming to any condition of my scheme.] Right manus. As in No. 472. "Pollex" with two phalanges. [Condition IV of the manus.] Left manus. Same as right, but the " pollex ' : is only repre- sented by a single bone not differentiated or divided into meta- carpal and phalanges and bearing no claw. [Approaches Condition IV of the manus.] 479. Cat. A left pes bearing abnormal digits. The digits II, III, IV and V are normal and are true left digits. Internal to these are two metatarsals which are united centrally and peripherally but are separate in their middle parts. These two metatarsals by their common distal end bear amorphous phalanges belonging to three digits. There are two large claws and one rudimentary one. [For details the specimen must be seen.] The navicular bone is divided into two distinct bones, of which one carries the external cuneiform and a small cuneiform for the digit II, the metatarsal of which is rather slender and compressed in its proximal part. The internal part of the navicular bone bears two cuneiforms, one for each part of the united metatarsals. The digits borne by these metatarsals are so misshapen that it is not possible to say anything as to their symmetry. Mus. Coll. Surg., Terat, Catal., No. 306 A. [This specimen does not conform to any of the Conditions of my scheme.] *480. In the case of the Cat the polydactyle condition has been observed by Poulton (Nature, xxix. 1883, p. 20, figs. ; ibid., XXXV. 1887, p. 38, figs.) to recur frequently in the same strain. A female cat had six toes on both fore and hind feet. The mother of this cat had an abnormal number of toes not recorded. The grandmother and great-grandmother were normal. Two of the kittens of the 6-toed cat had seven toes both on the fore and hind feet [no 7-toed pes among specimens examined 1 »y me]. Many families produced by the 6-toed cat, and among them only two kittens with 7 toes on all feet, but between this and the normal numerous varieties seen. The abnormality is not in all cases sym- metrical on the two sides of the body. The pads of the different toes are sometimes compounded together. In some cases an extra pad was present on the hind foot behind and interior to the central pad. The second pad was sometimes distinct from the central pad and sometimes was united with it. [From the figures it appears that the secondary 21—2 324 MERISTIC VARIATION. [part I. central pad in the pes bore to the digits internal to the axis of sym- metry a relation comparable with that which the chief central pad bears to the digits III — V, but the secondary central pad is at a higher level than the primary one.] It was especially noted that the details in the arrangement of the pads were inherited in several instances. The history of the descendants of the 6-toed cat was followed and a genealogical tree is given shewing that the abnormality has been present in a large proportion of them. This was observed in five generations from the original 6-toed cat, so that including the mother of the 6-toed cat the family has contained polydactyle members for seven generations. It may reasonably be assumed that in most of these cases the fathers of these kittens have been normal cats and a good deal of evidence is adduced which makes this likely. It was observed also that some normal cats belonging to this family gave birth to polydactyle kittens. In the later period of the life of the original 6-toed cat she gave birth to kittens which were all normal. I know no case of reduction in number of digits or of syndac- tylism in the Cat. Man and Apes. Increase in number of Digits. Increase in the number of digits occurs in Man in many forms. Among them may be distinguished a large group of cases differing among themselves but capable of being arranged in a progressive series like that described in the Cat. These cases are all examples of amplification or j3roliferation of parts internal to the index of the manus. Taking the normal as the first Condition, the next in the progress is a hand having the digits II — V normal, but the thumb with three phalanges, or as the descriptions sometimes say, " like an index." (Condition II.) In the next condition a two-phalanged digit is present internal to the three-phalanged " thumb." (Condition III.) In the next Condition the digit internal to the three-phalanged " thumb " has itself three phalanges. (Condition IV.) A variant from this oc- curred in the left hand of a child (No. 488) of parent having hands in Condition IV. In the child the right hand was in Condition IV, but in the left there were the usual four digits II — V, and internal to them two complete digits, each of three phalanges, but of these the external had a small rudimentary digit arising from the meta- carpus. Hence the hand may be described as composed of two groups, the one containing four and the other three digits. In one case, No. 490, the right hand was in Condition IV, but the left hand was advanced further. For in it the metacarpal of the innermost digit bore a 2-phalanged digit internally to its 3-phalanged digit. This may be considered as a Condition V. chap, xiil] DIGITS : MAN. 325 The number of phalanges in the digits in these Conditions may be represented thus. The || marks the metacarpal space. (The hand is supposed to be a right.) Condition I 2 | 33 3 3 II 3 | 3333 „ III 2 3 | 3 3 33 n IV 3 3 | 3333 v 2 3 3 | 3 33 3 Distinct from these Conditions are the states sometimes described as " double-hand." In the full form of this there are eight digits, each of three phalanges. The eight digits are arranged in two groups, four in each group. The two groups stand as a complementary pair, the one being the optical image of the other ; or in other words, the one group is right and the other is left. Besides the double-hand with eight digits there are also forms of double-hand with six digits, arranged in two groups of three and three. Lastly, there are cases of double-hand having seven fingers, an external group of four and an internal group of three. Thus expressed these cases seem to come very near that mentioned as a variant on Condition IV, but in one and perhaps both of these double-hands there was in the structure of the fore- arm and carpus a great difference from that found in the only recorded skeleton of Condition IV. At first sight it would naturally be supposed that these double- hands in one or all kinds stand to the other Conditions in the some relation that Condition IV of the pes in the Cat does to the other polydactyle conditions in the Cat. But the matter is complicated by the fact that the evidence goes to shew that in the human double-hands the bones of the arm and carpus may be modified, and in Dwight's example of seven digits (No. 489) at all events, and perhaps in other double-hands, an ulna-like bone takes the place of the radius, or in other words, the internal side of the fore-arm is fashioned like the external side. In the polydactyle cats the bones of the fore-arm were normal, as are they also substantially in cases of the human Conditions III and IV, which have been dissected. Further, in some of the human cases of eight digits the abnormality was confined to one hand, which is never the case in the higher condition of polydactylism in the Cat, so far as I know. These circumstances make it necessary to recognize the possibility that some at least of the human double-hands are of a different nature from the lower forms of polydactylism. This subject will be spoken of again after the evidence as to the variation of digits has been given (Chap. xiv. Section (4).) 326 MERISTIC VARIATION. [part I. In addition to cases more or less conforming to schemes that can be indicated are several which cannot be thus included. These will be duly noticed when the more schematic cases have been described. That any of the cases can be arranged in a formal sequence of this kind is perhaps surprising, and the relations of some of the Conditions, II and III for instance, to each other must at once recall the principle seen already in other examples of addition of a member at the end of a successive series of parts, notably in the case of Teeth (see p. 272). It was then pointed out that when a new member is added beyond a terminal member whose size is normally small relatively to that of the normal penultimate, then the member which is normally terminal is raised to a higher condition. Now this same principle is seen in Condition III of the polydactyle manus. Attention must nevertheless be forthwith called to the fact that a two-phalanged digit 1 may be present internal to the thumb (usually arising from it) though the thumb has still but two phalanges. But generally these cases may properly be described as examples of duplicity of the thumb ; and as was well seen in the case of Teeth, any member of a series may divide into two though the rest of the series remain unaltered. Duplicity of a member without reconstitution of the series is to be recognized as one occurrence, and change in number associated with reconstitu- tion of other members especially, of adjacent members, is another. In Teeth and other Meristic series these two phenomena are both to be seen, though as was pointed out (p. 270) they pass insensibly into each other. Another feature to be specially mentioned in this preliminary notice is the difference in the manner in which the higher forms of polydactylism appears in the human foot from that seen in the human hand. In the hand there is this strange group of cases forming a progress from the normal hand to Condition V, besides the distinct series of double-hands. Polydactyle feet on the con- trary do not in Man, so far as they have been observed (with the doubtful exception of Nos. 499 and 500), develop a new symmetry. Cakes of Polydactylism associated with Change of Symmetry. A. Digits in one Successive Series. '481. Man having a "supernumerary index" on each hand. Left hand. No" thumb " present. In its stead there is a digit having three phalanges which " performs its office." The middle phalanx was abnormally short. The first intermetacarpal space was not great. [Degree of opposability not stated.] Right hand. In addition to four normal fingers there was a three-jointed digit 1 A case in which a 3-phalanged digit was placed on the radial side of the pollex is mentioned by Windle, Jour. Anat. Plnjs.. xxvi. p. 440, but has not yet been described. No other such case is known to me. This perhaps should be classed with double-hands. Cp. No. 502. CHAP. XIII.] DIGITS : MAX. 327 482, which could be opposed to them and could perform all the move- ments of flexion, &c. Internal to this three-jointed digit was a rudimentary thumb having only one phalanx and no nail. [Re- lations of metacarpals to each other not particularly described.] Guermonprez, F., Rev. des mal. de Venfance, iv. 1886, p. 122, figs. [Left hand Condition II; right hand almost Condition III.] Girl having a three-jointed thumb, resembling a long fore- finger. Annandale, Diseases of the Fingers and Toes, p. 29, PI. II. fig. 19. [Condition II.] 483. Man having a thumb with three phalanges on each hand. Feet normal. In the thumbs the metacarpal is 2 j- in. long; the first phalanx If in., being longer than usual. The second phalanx is longer on the radial side than on the external side, causing the distal phalanx to curve towards the index. On the internal it measures J- in., in the middle | in., and on the ulnar side \ in. The distal phalanx is 1 in. long. When the left thumb is straightened it passes \ in. beyond the joint between the 1st and 2nd phalanx of the index. In the right hand the thumb scarcely reaches that joint. The utility of the thumb is not impaired. A maternal aunt had a similar thumb on right hand. Struthers, Edin. New Phil. Journ., 1863 (2), p. 102, PI. n. fig. 6. [Both hands Condition II.] *484. Father and three children, each having 3-phalanged thumbs shaped as indices and not opposable. [Full description q.v.~\ Paternal grand- mother had double-thumb. Farge, Gaz. hebd. de med. et chir., Ser. 2. ii. 1866, p. 61. *485. Man having the following abnormalities of the digits. (Fig. 88). Right hand. The number of digits was normal, but the Fig. 88. Right and left hands of No. 485. Right hand in Condition II; Left hand in Condition III. (After Windle.) 328 MERISTIC VARIATION. [part I. * ±86, radial digit or thumb had three phalanges in addition to the meta- carpal, all the articulations being moveable. Relatively to the others their digit was placed as a thumb. Left hand. The digit corresponding with the thumb was composed of three phalanges like that of the right side, and though finger-like in form it was functionally a thumb. On the radial side of this 3-jointed digit there was a supernumerary digit composed of two phalanges articu- lating with the metacarpal bone of the 3-jointed thumb. This supernumerary digit had a well-formed nail. The 3-jointed thumb of the left hand was longer than that of the right hand (measure- ments given), Windle, B.C. A., Journ. of Anat. xxvi. 1891, p. 100, PL II. [Right hand, Condition II ; left hand, Condition III.] Man having 3 phalanges in the thumb of the left hand together with a supernumerary digit. (Fig. 89.) This case in several respects resembles the left hand of the subject described by Windle. The four fingers were normal. The thumb stood in its normal relations to them, but was finger-like in form, having three phalanges in addition to the metacarpal. On the radial side of Fig. 89. Bones of left hand of No. 486, shewing Condition III. (After Rijkebusch.) this 3-phalanged digit there was a supernumerary digit, having two phalanges and a separate metacarpal, which articulated with the head of the metacarpal of the thumb and the trapezium. In the carpus of this hand there was a supernumerary bone which is described as an os centrale. The bones and muscles of this limb CHAP. XIII.] DIGITS : MAN. 329 are described in detail. The thumb and the supernumerary digit were closely webbed together and were very slightly moveable. Specimen first described by Rukebusch, Bijdr. tot de Kennis der Polydactylie, Utrecht, 1887, Plates, and subsequently by Spronck, Arch, neerl, XXII. 1888, p. 235, PL VI. — IX. [Condition III.] *487. Woman having 6 digits on each hand and foot as follows. In each hand the thumb has three phalanges, and internal to it articulating with the same metacarpal is an extra digit having two phalanges [measurements given] webbed to the three-phalanged thumb. [Con- dition III of the manus.j Right foot has six complete metatarsals and digits very regularly set, one of them being internal to but longer than the hallux which has two phalanges as usual. The digit internal to it has also two phalanges. Left foot has also an extra digit with two phalanges longer than the hallux, placed internal to and articulating with the metatarsal of the hallux which has two phalanges as usual. Many members of family polydactyle [particulars given]. Struthers, Edin. New Phil. Jour., 1863 (2), p. 93. [Note in this case that in the feet the digits added internally to hallux are greater than it, and they thus stand as the largest terms in the series, the other members being Successive to them. The series thus does not decline from the hallux both internally and externally in the way seen in most other cases of extra digits on the internal side of the limb.] 488. Man having six digits, each with three phalanges, on each hand. d 1 Fig. 90. Bones of right hand of No. 488 shewing Condition IV. n 1 and n 2 represent the scaphoid, lu, lunar, c, cuneiform, tm, trapezium. td, trapezoid, m, magnum, u, unciform. ac l , ac 2 are supernumerary bones. (After Eudinoer.) 330 MERISTIC VARIATION. [part I. The digits were arranged in two groups, which were to some extent opposable to each other. The digits II, III, IV and V stood in their normal positions and were properly formed. In the place where the thumb should stand there were two digits, each with three pha- langes. Of these the external (rf 2 ) was of about the length and form of the index finger while the internal, d 1 , was a good deal shorter and more slender. The bones of the carpus are shewn in Fig. 88. The scaphoid was represented in the right hand by two bones n 1 and n 2 , and there were two accessory bones, ac 1 and ac 2 placed in the positions shewn. The two hands were almost exactly alike, save for slight differences in the carpal bones [see original figures], and for the fact that in the left hand the internal of the two digits of the radial group was rather more rudimentary. Rudinger, Beitr. zur Anat. des Gehororgans, d. venosen Blutbahnen d. Schddelhohle, sotuie der ilberzdhligen Finger, Miinchen, 1876, Plate. [Both hands in Condition IV.] 489. A female child born to the last case, No. 488, had the right hand in the same condition as that of the father, while the left hand differed from it in the presence of an additional rudimentary finger arising from the ulnar side of the digit d\ This additional finger bore a nail but it appeared to consist of two joints only and to be attached to the metacarpus by ligamentary connexions. Rudinger, ibid. [Right hand in Condition IV ; left hand depart- ing from the Conditions enumerated. Compare with manus of Cat, Fig. 84] 490. Man. Rigid hand bore six digits and metacarpals. The most external digit was a normal minimus, succeeded by digits IV and III webbed together. Next to III there was an index. Internal to this and separated from it by a small metacarpal space was a 3-phalanged long digit much as in Windle's case, No. 481, and internal to it is a 2-phalanged thumb of nearly normal form like that of No. 485. Left hand bore seven digits but six metacarpals. Minimus normal. IV, III and II webbed together. Internal to II was a 3-phalanged digit much as in the right hand ; but internal to this there was a metacarpal bearing two digits, an external having 3 phalanges and an internal having 2 phalanges. Each foot had six digits and six metatarsals (q. v.). Redescribed from the account and figures given by Gruber, Bull. Ac. Sci. Pet., xvi. 1871, p. 359, figs. [Right hand Condition IV, left hand Con- dition V.] 491. Child having six fingers on each hand. The fingers were united together. In the thumb [? both] there were three phalanges and the length of the thumb was as great as that of the "other fingers." Dubois, Arch, gener. de Med., 1826, Ann. iv. T. xi. p. 148; this case is quoted by Geoffroy St Hilaire, Hist, des Anom., i. p. 227, Note. [? Condition IV.] 491, d. New-born male child having on the right hand two "thumbs" each with three phalanges. Oberteufer, J. G., Stark's Arch. f. Gebnrtsh., 1801, xv. p. 612. [Con- dition IV.] (No more cases known to me.) * CHAP. XIII.] DOUBLE-HAND. 331 B 1 . Digits in two homologous groups, forming "Double-hands." *492. Double-hand I. Seven digits in two groups of four and three. Male : left arm abnormal, having seven digits arranged in two groups, the one an external group of four normal digits, and the other an internal group of three digits 2 . (Fig. 91.) Described from a dried specimen in Mus. of Harvard Med. School. The man was a machinist and found the hand not merely very useful to him in his business, but he also thought that it gave him advantages in playing the piano. " The fore-arm consists of the normal left ulna and of a right one in the place of a radius. The left one shews little that calls for comment, excepting that there is a projection outward at the place of the lesser sigmoid cavity to join a corresponding projection from the other ulna. The upper surface of this projection articulates with the humerus. At the lower end the styloid process is less prominent than usual, and the head rather broad. The right or extra ulna is put on hind side before, that is, the back of the olecranon projects forward over the front and outer aspect of the humerus. If the reader will place his right fore-arm on the outer side of the left one he will see that it is necessarv for the I ; ■ : . . . i* ho ■ '• II Fig. 91. I. The left band of No. 492 from the dorsal surface. II. The humerus and two bones of the fore-arm at the elbow of the same c 0, olecranon. O 2 , the secondary " olecranon ". I, the inner condyle of the humerus. I 2 , the second or external " inner condyle." (After Dwight.) ulna to be thus inverted if the thumbs are to toucli and the palms to be continuous. This olecranon is thinner, flatter, and longer than normal. The coronoid process is rudimentary. From the side of this process and from the shaft just behind it arises the projection already 1 Every case known to me is given. 2 This is the case reported by Jackson, to Bost. Soc. of Med. hup.. 1852. 332 MERISTIC VARIATION. [part I. referred to which meets a similar one from the normal ulna [Fig. 89, II]. On the front of this there is a small articular surface looking forward which suggests a part of the convexity of the head of the radius. The upper articular surface shews a fissure separating it from the side of the olecranon which is not found in the normal ulna. These projections which touch each other are held together by a strong interosseous liga- ment. The lower end of this ulna is very like the other, only somewhat broader. The mode of union of the lower ends could not be seen without unwarrantable injury to the specimen. There can hardly have been any definite movement between these bones. Perhaps the ligaments may have permitted some irregular sliding, but it is impossible to know. These bones have been described first because their nature is very clear and, once understood, is a key to the more difficult interpretation of the lower end of the humerus." The upper end of the humerus presented nothing noteworthy. A detailed description and figures are given, from which it appears that the lower end of the humerus had such a form as might be produced by sawing off the greater part of the external condyle and applying in place of it the internal condyle of a right humerus. The carpus seen from the dorsal side had the structure shewn in the diagram (Fig. 92). The proximal row consisted of three bones besides the two pisiforms (p l and p 2 ). There was a cuneiform at either side of the wrist, and between them a bone evidently composed of a pair of semilunars, having a slight notch in its upper border. At each end of Fig. 92. Diagram of the carpal bones in the left hand of No. 492 from the dorsal surface. pis 1 , cu 1 , u 1 , m 1 , pisiform, cuneiform, unciform and magnum of the external or normal half of the band consisting of four fingers ; pis*, cu 2 , u 2 , m 2 , the similar bones for the internal group of three fingers. Zu 1+2 , the compounded lunar elements corresponding to the two groups, x, bone placed as trapezoid. (After Dwight.) the second row is an unciform bearing the middle and ring fingers. Next came two ossa magna very symmetrically placed, each bearing the metacarpal of a medius. Between these is a bone which Dwight states chap, xiil] double-haxd. 333 to have clearly represented the trapezoid of the left hand, bearing an index finger. The metacarpals and phalanges needed no description. The muscles are described in detail [^.v.]. Some of the features in the distribution of the arteries and nerves are of interest, and 1 transcribe Dwight's account in full. It appears that, like the bones, the vessels and nerves proper to the radial side of a normal left arm have in a measure been transformed into parts proper to the ulnar side of a right arm. "The Arteries. The brachial divides at about the junction of the middle and lower thirds of the humerus. The main continuation, which is the ulnar proper, runs deeply under the band thought to represent the pronator radii teres, to the deep part of the fore-arm where it gives off the interosseous. Above the elbow there is a branch running backward between the internal condyle and the olecranon. The inter- osseous branches are not easy to trace. There seems to be an anterior interosseous and three branches on the back of the forearm, one running on the membrane and one along each bone. At least two of them share in a network on the back of the carpus. Having reached the hand the ulnar artery runs obliquely across the palm to the cleft between the two sets of fingers, supplying the four normal fingers and the nearer side of the extra middle finger. The other branch of the brachial crosses the median nerve and runs, apparently superficially, to the outer side of the fore- arm. It supplies the little and ring fingers and the corre- sponding side of the middle finger of the supernumerary set. There is no anastomosis in the palm between the superficial branches of the two arteries. Each gives off a deep branch at the usual place, which forms a deep palmar arch from which some interosseous arteries spring. There is also an arterial network over the front of the carpal bones. The arteries of the deep parts of the hand cannot all be seen. The Nerves. The ulnar nerve proper pursues a normal course and supplies the palmar aspect of the little finger and half the ring finger of the normal hand. Near the wrist it gives off a very small posterior branch, which is not well preserved, but which seems to have had less than the usual distribution. The median nerve is normal as far as the elbow, running to the inner side of the extra condyle. It is then lost in the dried fibers of the flexor sublimis, from which it emerges in two main divisions near the middle of the fore-arm. The inner of these soon divides into two, of which one supplies the adjacent sides of the ring and middle fingers and the other those of the middle and index fingers of the normal hand. The outer division of the median supplies the outer side of the index and both sides of the extra middle finger and one side of the extra ring finger. One of the branches to the index gives off a dorsal branch, and there is a doubtful one for the extra middle finger. The musculo-spiral nerve passes behind the humerus as usual. A nerve which is undoubtedly continuous with it emerges from the hardened muscles over the fused outer condyles. It seems to be the radial branch changed into an ulnar. It runs with the extra ulnar artery to the hand and sending a deep branch into the palm, goes to the ring linger. There is a detached branch on the other side of the little finger which in all probability came from it. The deep branch sends a twig along the metacarpal bone of the ring finger. It probably 334 MERISTIC VARIATION. [part i. supplied the side of the ring linger left unprovided for, but this is uncertain. Assuming this to have been the case, each ulnar nerve supplies the palmar surface of one finger and a half, the median supply- ing the remaining fingers of both hands. Unfortunately no dorsal branches except those mentioned have been preserved." Dwight, T., Mem. Boston Soc. of JV. H.. 1892, Vol. iv. No. x. p. 473, Pis. xliii and xliv. [This is a case of high significance. We shall come back to it hereafter. Meanwhile it will be noted that in it we meet again the old difficulty so often presented by cases of Meristic Variation. In this fore-arm there is already one true ulna. Internal to it is another bone also formed as an ulna. We may therefore, indeed we must, call it an ulna. But is it an " ulna " ? To answer this we must first answer the question what is an ulna? Similarly, is the second pisiform a "pisiform," or is the second ulnar nerve an c< ulnar " nerve ? These questions force themselves on the mind of anyone who tries to apply the language of orthodox morphology to this case, but to them there is still no answer. Or, rather, the answer is given that an " ulna," a " pisiform " and the like are terms that have no fixed, ideal meaning, symbols of an order that we have set up but which the body does not obey. An " ulna " is a bone that has the form of an ulna, and a " pisiform " is that which has the form of a pisiform. If we try to pass behind this, to seek an inner and faster meaning for these conceptions of the mind, we are attempting that for which Nature gives no warrant : we are casting off from the phenomenal, from the things which appear, and we set forth into the waste of metaphysic] 493. Boy having abnormalities in the left hand as follows. The four outer fingers II — V are normal in form and proportions. Internal to these is firstly an opposable digit with a single metacarpus and single proximal phalanx but having two distal phalanges side by side webbed together. Internal to this partially double thumb are two digits in series, each with a metacarpal and three phalanges, respectively re- sembling the annularis and minimus of a right hand. Struthers, Edin. New Phil. Jour., 1863 (2), p. 90, PI. n. fig. 5. [Not representing any of the Conditions.] 494. Male infant, one year and five months, examined alive, having the right hand abnormal, possessing seven digits, arranged in two groups, an ulnar group of four and a radial group of three. Each digit had three phalanges, but the ring and middle fingers of the ulnar group are webbed in the region of the proximal phalanges. The ulnar group seemed to articulate with the carpus in the usual way. The radial group probably formed joints with more than one facet on the trapezium, and possibly also with a surface on the lower end of the radius. It did not seem that the carpal bones were increased in number, for the right wrist had the same circumferential measurement as the left, which was normal. The lower end of the ulna did not seem to articulate normally with the carpus. The elbow was also abnormal, and it seemed "as if the ulna were dislocated inwards." Ballantyne, J. W., Edin. Med. Jour., 1893, cdli. p. 623, fig. [Possibly this condition approached to that found in the last cases.] 495. CHAP. XIII.] DOUBLE-HAND. 335 Double-hand II. Eight digits in two groups of four and four. Woman (examined alive) having eight fingers in the left hand arranged as follows (Fig. 93). With the exception of the left arm the body was normal. The limb was very muscular. The shoulder- joint was natural. The external condyloid ridge of the humerus was strongly defined. The muscles and tendons of the fore-arm were so prominent that it was not easy to decide whether there was a second radius or ulna, but Murray eventually came to the Fig. 93. Left hand of No. 495. (After Murray.) conclusion that there was no such extra bone. The fore-arm could be only partially flexed. The eight fingers were arranged in two groups of four in each, one of the groups standing as the four normal fingers do, and the other four being articulated where the thumb should be. There was no thumb distinguishable as such, but it is stated that there was a protuberance on the dorsal side of the hand, between the two groups of fingers, and this is con- sidered by Murray to represent the thumbs, for according to his view the limb was composed of a pair of hands compounded by their radial sides. In the figure of the dorsal aspect which is given by Murray taken from a photograph, this protuberance cannot be clearly made out. The four radial fingers in size and shape appeared to be four fingers of a right hand. In the radial group of fingers, the" middle "and" jring " fingers (6 and 7) were webbed as far as the proximal joints, and the movements of the fingers of this group were somewhat stiff and imperfect. Between the t \v< » gn nips of fingers there was a wide space as between the thumb and index of a normal hand, and the two parts of the hand could be opposed to each other and folded upon each other. The power of inde- pendent action of the fingers was very limited. No single finger could be retained fully extended while the other seven fingers were flexed, but if both " index " fingers (4 and 5) were extended, 336 MERISTIC VARIATION. [part I. the other six fingers could be flexed, or the four fingers of either group together with the " index " of the other group may be extended, while the other three are flexed. The " index " fingers could not be flexed while the other fingers were extended, nor can the " little fingers " be extended while the others were flexed. Murray, J. Jardine, Med. Chir. Trans., 1863, xlvi. p. 29, PL n. 496. Female child, five weeks, having a hand of eight digits on the right side (Fig. 94). The digits were disposed in two groups of four in each. [No further r*0^" Fig. 94. Right hand of No. 496. (After Giraldes.) description.] Giraldes, Bull. soc. de Chirurg., Paris, 1866, Ser. 2, vi. p. 505, fig. The same case referred to again, Giraldes, Mai. Chir. des Enfants, 1869, p. 42, Jig. 49^ Female child having right hand almost exactly like Murray's case, but without ' syndactylism. The two halves could be folded on each other. The four extra digits articulated with an imperfect metacarpal which was annexed to the normal meta- carpal [of the index]. Fumagalli, C, Annal. Univers. di Med. Milano, 1871, vol. ccxvi. p. 305, fig. Girl's right hand having eight fingers, represented in a wax model. Langalli, La scienza e lapratica, Pavia, 1875 [Not seen : abstract from Dwight, I. c], 498. Double-hand III. Six digits in two groups of three and three. Man having abnormalities of left arm as follows (Fig. 95). The left hand was composed of six digits with three phalanges, which were disposed in two groups of three digits in each. The two middle digits were the longest (d 3 and c/ 4 ), and the length of the digits on either side of them diminished regularly. The appear- ance was as of a hand composed of the middle, ring and little fingers of a pair of hands united together. The two groups of fingers were to some extent opposed to each other and all the digits could be flexed and extended. The digit d 3 though single in its peripheral parts articulated with two metacarpals, its proxi- mal phalanx having two heads. Upon the radial side of the CHAP. XIII.] DOUBLE-HAND. 337 carpus of this hand there was a soft tumour about 2'5 cm. in height, resembling a cyst with a firm wall. Fig. 95. Dorsal and palmar aspects of the left hand of No. are numbered from the inside. (After Jolly.) 498. The digits The structure of the bones of the arm and fore-arm could not be made out with certainty in the living subject, but it appeared that the humerus was formed by two bones partially united together. As regards the skeleton of the fore-arm an ulna could be felt extending from the upper arm to the processus styloideus. The existence of a radius could not be made out with certainty, but a second bone could be felt which was in very close connexion [with the ulna]. Jolly, Tnternat. Beitr. z. wiss. Med., 1891. 499. Male child, three years old, twin with a normal female child, having all extremities abnormal. Right hand. Six metacarpals arranged in two groups of three in each group. Each bore a three-phalanged digit, none resembling a thumb. The first and sixth were alike, resembling a minimus, while the two median fingers resembled middle fingers. On the radial side the three digits were completely united together. The next was five, and the two external to this were also united. Left hand. Like the right, but all the fingers united together in two groups of three in each group. Feet. Each foot had nine metatarsals and nine digit-, the central being like a hallux and having two phalanges perhaps, but thicker than a hallux. The externals were like minimi. The four toes on each side of the " hallux " were united two and two. The tarsus was of about double size. The right leg was shorter than the left. Gherixi, A.,Gaz. med. ital.-lombard., 1874, No. .31. p. 401, figs. B. 22 338 MERISTIC VARIATION. [part I. Complex and irregular cases of Polydactylism associated with Change of Symmetry. *500. Man (examined alive) having abnormalities in the digits of hands and feet (Fig. 96). The case is very briefly and inadequately described, but the condition was apparently as follows. Right hand. Beginning from the ulnar side, there were three normal digits (6, 5, 4). Beyond the third of these, which must be ») '/] > ■i) f] / > si 1 ;t jr 6 ft loJ 5 J J v 3 2 ~3 * Fig. 96. Hands and feet of No. 500. (After Kuhnt.) chap, xiii.] COMPLEX POLYDACTYLISM : MAN. 339 regarded as the medius, there were two complete digits (3, 2) each having three phalanges : and on the radial side of the innermost of these digits there was a stump-like rudiment (1), apparently representing another digit. [This case therefore differed from those of Win die and Rijkebiisch in the fact that both the digits internal to the medius (m) were disposed as though they belonged to a left hand, and Kuhnt, in fact, states that each hand was, as it were, composed of parts of a pair of hands, thus agreeing with Jolly's case, No. 499.] Left hand. In this hand there were only five digits, each of which had three phalanges. None of them was fully opposable, but that on the radial side (1) could to some extent be moved as a thumb. Of these five digits the middle one was the longest, and on each side of it there were two similar digits, those next to the middle finger being the longest and those remote from it being a good deal shorter and having the form of little fingers, which Kuhnt considers them to have been. [This hand is perhaps in Condition II.] Right foot. The hallux (2, 3) was of abnormal width and its bones were to some extent double, the ungual phalanx being completely so. [The nail however is drawn as a single structure and the double character of the toe was not apparent in its external appearance.] On the internal (tibial) side of the hallux there were two supernumerary toes (1, 1) having, so far as could be ascertained, a single metatarsus. The number of phalanges in these toes is not distinctly stated. Left foot. The hallux (3, 4) was to some extent double, like that of the right foot. Internally to it were two supernumerary toes (1, 2) having apparently a common metatarsal. [Of these the most internal is represented as being very wide and resembling a hallux, but this feature is not mentioned in the description and the number of phalanges is not given]. [It is greatly to be regretted that no fuller account of this important case is accessible. According to Kuhnt's view each hand and each foot were structurally composed of parts of a complementary pair of hands and feet. As regards the hands the facts agree witli this description and with what has been seen in other cases, but the condition of tin 1 feet is more doubtful, and without more knowledge of the details no opinion can be given. It should be remembered that the original description is very brief and Dr Kuhnt offers an apology for the im- perfection of the figures.] Kuhnt, Virch. Arch, f path. Anat. u. Phy8., lvi. 1872, p. 268, Taf. vi. 501. Case of a foot with eight toes, stated to have resembled Kuhnt's case (No. 501). Ekstein, Prager Wochens., No. 51, 1891. 502. Man whose right arm beside the normal hand bore an extra thumb and finger. The two thumbs were united and had a common meta- carpal joint. They were of equal size. They were flexed and extended together and had the power of spreading apart. The extra finger was beyond the extra thumb and was shaped like an index. Besides the radius and ulna of the normal arm there was an extra radius on the outer [1 internal] side of the normal radius. This bone had a joint of its own at its elbow. The wrist was broad, suggesting the presence or' additional bones. Nothing is said of a metacarpal bone for the new index. Carre, Seance publ. de la soc. rog. <1> Mid., Ghir. et Pharm. de o 340 MEMSTIC VARIATION. [part i. Toulouse, 1838, p. 28. [Not seen by me. Abstract taken from D wight, I.e., vide No. 492. Cp. p. 326, Xote.] 503. Girl, new-born, having the left foot "double," bearing eleven toes. The left labium majus was twice as large as the right, and the left leg and thigh were much thinner than the corresponding parts on the right side [measurements given]. The extra parts were all on the planter side of a foot which had toes of nearly normal shapes and sizes. This foot was bent into a position of extreme talipes equino-varus, and the great toe was bent so that it pointed inwards at right angles to. the metatarsal. Upon the plantar side of this foot there was a series of six well- formed, small toes, arranged in a series parallel to that of the 'normal' five, and having their plantar surfaces in opposition to those of the latter. Of the series of six toes that facing the normal little toe exactly resembled it. The second was the longest of the six, but did not resemble a great toe. The third and fourth were equal in length, the fifth and sixth being shorter, as are the external toes of a normal foot. None of the toes were webbed. Bull, G. J., Boston Med. and Sury. Jour. 1875, xciii. p. 293, fig. [This figure copied by Ahlfeld. Missb. d. Menschen, PI. xx. fig. 2.] [The case described by Graxdix, Amer. Jour, of Obstetrics, 1887, xx. p. 425, Jig., is probably a case of a pair of limbs composing a Secondary Symmetry attached to and deforming the limb belonging to the Primary Symmetry and corresponding with that of the other side. The nature of this case will be better understood when evidence as to the manner of constitution of Secondary Symmetries has been given.] "504. Macacus sp. A monkey, full-grown, having nine toes on the left foot ; right foot normal, upper extremities not preserved. The specimen is described as No. 307 in the Catalogue of the Terato- logical Series (1872) in the Mus. Coll. Surg. (Hunterian specimen). Though I am disposed to agree in the main with the view of the nature of the specimen given in the Catalogue it is not in my judgment possible to decide confidently in favour of this view to the exclusion of all others. For this reason the specimen is here described afresh. This is the more necessary as the account of the Catalogue is incorrect in some particulars. Extra parts are present in the limb and in the pelvic girdle. (Figs. 97 and 98.) The names to be given to the parts depend on the hypothesis of their nature which may be preferred. In general terms it may be stated that the ventral or pubic border of the girdle and the internal (tibial) border of the limb are nearly normal. The external (fibular) border of the limb is also normal, but between these there are in addition to the normal parts other structures, whose true nature is somewhat uncertain. The appearances may be realized best in the following way. Sup- pose that two similar left feet lie in succession to each other, the " posterior " having its hallux next to the minimus of the "anterior/' so that the digits read I, II, III, IV, V, I, II, III, IV, V. Now if the two feet could interjDenetrate so far that the minimus of the " anterior " foot took the place of the hallux of the " posterior," this chap, xiii.] POLYDACTYLE FOOT : MaCCLCUS. 341 second hallux not being represented, the condition of this specimen would be nearly produced. In the same way the left pelvic girdle is just what it would be if two left innominate bones were placed in succession, the ischium of the " anterior " superseding the pubis of the posterior. As in the foot, so in the innominate, of the portions which coincide the parts belonging to the anterior are alone represented. Something very like this was seen in the case, for instance, of the imperfect division of vertebrae in Python, No. 7. The chief difficulty attending this view of the nature of the case is the fact that as regards the tarsus the "anterior" foot h'- .g* It- 4&} .fib 1 Fig. 97. Macacus, No. 50-1, left leg. C. S. M. 307. 7* 1 , head by which femur articulates. lr, supernumerary head (?). gt, great tro- chanter. gt 2 , " posterior " great trochanter. It, lesser trochanter, t, tibia, fib 1 , " anterior fibula." fib 2 , "posterior" fibula (?). clc, calcaneum. As, astragalus, nav, navicular. nav 2 , supposed second navicular, c 1 — c 6 , six cuneiform bones, c 3 , the ecto-cuneiform of "anterior" foot, cb, cuboid. 'C3 342 MERISTIC VARIATION. [part I. lacks the external (fibular) parts of a tarsus, viz. the cuboid and calcaneum. There is a cuboid, cb, and a calcaneum, c, for the "posterior" foot, but none for the " anterior." The bone c 3 might of course be called a cuboid ; but if this is a cuboid there is no ecto-cuneiform for the anterior foot. The account given in the Catalogue avoids these difficulties by the statement that each foot has three cuneiforms and a cuboid, declaring that there is a second cuboid between the two sets of cuneiforms. This is nevertheless incorrect, for the whole distal series in the tarsus contains onlv seven bones and not eight. The mistake has no doubt arisen by counting c s twice over. The Catalogue is also in error in neglecting the fact that the tarsal articulation of the digit 2 is quite abnormal. Similarly in the crus, there is no good reason to affirm that the boney^ 1 is a fibula rather than a tibia. The Catalogue regards it as a second tibia, but I incline to speak of it as the fibula of the ' anterior ' foot following the view already indicated. As I have said, the leg is almost normal in the structure of its external border and almost normal in its posterior border, but between these the nature of the parts is problematical. All that can be done is to describe the parts as they are seen. Beginning at the external (fibular) border of the foot there is a nearly normal series of three digits, 9, 8, 7, fashioned as V, IV and III I II Fig. 98. I. Innominate bone of Macacus, No. 504. i\ p, is 1 , t 1 , of 1 , ilium, pubis, ischium, ischial tuberosity and obturator foramen of the supposed anterior part of the girdle; the parts marked 2 being the corresponding structures of the supposed posterior part. II. Details of tarsus of the same. Digits numbered 1 — 9 from the inside. A, astragalus, c, calcaneum. n 1 . navicular of "anterior" foot. n\ navicular of "posterior" foot, cb, cuboid, c 1 — c F ', six bones placed as cuneiforms. chap, xiii.] POLYDACTYLE FOOT : MoCOCUS. 343 respectively, the V and the IV articulating with the cuboid (cb) and the III with an external cuneiform, c 6 , as usual. There is a middle cuneiform, c 5 , bearing a digit, 6, which is almost exactly formed as a II. Internal to this point the parts can only be named with hesitation. The tarsal bone, c 4 , of the distal series internal to c 5 is shaped like another c 5 , but the digit which it bears rather resembles a minimus. This is succeeded by a tarsal bone, c 3 , shaped like the external cunei- form, c 6 , but it bears a digit of the length suited to an annularis. Internal to this are two tarsal bones of the distal row, c 2 and c\ which bear three digits, 1, 2, and 3. Of these the most internal is undoubtedly an internal cuneiform ; it bears firstly a slender but otherwise normal hallux with two phalanges, and secondly, it contributes (abnormally for an internal cuneiform) to the articulation of a digit, 2, which is thinner than all the others and resembles rather a minimus than an index. The digit, 2, also articulates with c 2 which chiefly supports the third digit. Between the metatarsals of the digits 5 and 6 there is a considerable space, owing to the fact that the head of the metatarsal of 6 is pro- longed upwards like that of a normal metatarsal V. In addition to those described are four other tarsal bones : firstly, a calcaneum c, which is rather smaller than that of the normal right leg. It articulates with the cuboid, cb, with the astragalus, A, and with the bone, n 2 . The astragalus is very large in its transverse dimension but its length is less than that of the normal astragalus. Peripherally it bears two bones, firstly, a navicular, n\ and secondly. a bone of uncertain homology, marked n 2 in Fig. 96. The navicular articulates with c\ c 2 and c 3 , together with the bone n 2 . The latter, ri 2 , articulates with c 3 , c 4 , c 5 , c 6 , and also with the cuboid, cb, the astragalus and calcaneum and navicular. From its form and relations it is probably a second navicular. The bones of the crus are three. Firstly, a tibia, lib., which is rather thinner than the normal bone and is somewhat bowed inwards. Passing as a chord to the curve of the tibia there is a thin bone, fib . which is tendinous in its upper part. External to this, articulating with the external condyle of the femur there is a third bone. ji/>\ which has nearly the form and proportions of a normal fibula. All three bones articulate with the large astragalus. There is a small patella. The femur is about half as thick again as that of the right leg. Its head is nearly normal in form, articulating with the rather shallow acetabulum. The lesser trochanter and the internal border of the femur are nearly normal. Anteriorly and externally there are the following parts. Upon the external border there is a projecting callosity, clearly being a great trochanter in its nature. Internal to this there is a knob- shaped, rounded protuberance, which in texture so closely resembles the head of a femur that it is almost certainly of this nature. h is rounded and smooth as though for articulation with an acetabulum, though it stands freely. Between this tuberosity and the real head of the femur there is a third tuberosity, apparently representing the end of the great trochanter of that limb which lias been spoken of as "anterior." The peripheral end of the femur is nearly normal on its inner side, while on the outside it is considerably enlarged. The ex 344 MERISTIC VARIATION. [part i. ternal condyle is thus much larger than that of the normal femur, but there is in it only a very slight suggestion of a division into two parts. The innominate bone has an ilium which anteriorly is normal, but which posteriorly enlarges and to some extent divides into two parts, V and i 2 . Of these the ventral part, i\ unites with a nearly normal pubis, p, and bounds the shallow acetabulum with which the femur articu- lates. The rest of this acetabulum is made up by the ischium, is 1 , of the "anterior" limb, which together with the pubis bounds an obturator foramen, of 1 . Dorsal to these parts the ilium has a partly separated portion, i 2 , which forms part of the wall of a cavity apparently repre- senting the acetabulum of the "posterior" limb. Dorsal to this a complete ischium arises which bears a normal ischial tuberosity and curves round a second smaller obturator foramen, of 2 . In so far as the foregoing description involves conceptions of homology it is merely suggestive, but the structure of the innomi- nate bone leaves little doubt that the nature of the parts is much as here described. Nevertheless the appearance of the digits 5 and 6 and of the tarsal bones c 3 to c 6 somewhat suggests that there is a symmetry about an axis passing between the digits 5 and 6 ; but if 5 were a minimus and if 6 were fashioned as an index, which it is, the appearance of a relation of images would to some extent exist in any case. This appearance is however confined to the dorsal aspect of the foot and is not present on the plantar aspect. This case, if the view of it proposed be true, differs from other examples of double-hand (e.g. Nos. 491 to 499) in that the Repe- tition is Successive and is not a Repetition of images ; for the digits stand I, II, III, IV, V, II, III, IV, V, and not V, IV, III, II, [I], II, III, IV, V as in those other cases. In this respect it is so far as I know unique. Those who have treated the subject of double-hand generally make reference to the following records. Kueff, De conceptu, Frankfurt, 1587, PI. 41 ; Aldro- vandi, Monstr. Hist., 1642, p. 495 ; Kerckrixg, Obs. anat., Amst. 1670, Obs. xx. PL, but the descriptions are scarcely such as to be useful for our purpose. A case quoted by Dwight, Mem. Bost. Soc.of N. H., iv. No. x. p 474, from du Cauroi, Jour. des Scavans, 161)6, pub. 1697, p. 81 [originally quoted by Mor.vxd and misquoted by many subsequent authors], is probably not an example of double-hand (see No. 522). Cases of Polydactylism in Man and Apes not associated with definite change of Symmetry. From the evidence as to polydactylism in general the foregoing cases have been taken out and placed in association as exhibiting the development of a new system of Symmetry in the limb. It will have been noticed that in all of them the external (ulnar or fibular) parts of the limb remain unchanged, and the parts not represented in the normal are on the internal (radial or tibial) sides. In the remaining cases of polydactylism, which constitute the great majority, there is no manifest change in the general symmetry of the limb. chap, xiil] DIGITS : MAN. 345 These general phenomena of polydactylism have been observed from the earliest times and the literature relating to the subject is of great extent. Most cases known up to 1869 [not including Struthers' cases] were collected by Fort, Difformites des Doigts, Paris, 1869, and independently by Grubeu, Bull. Ac. Sci. Pet, xv. 1871, p. 352 and p. 460, and good collections of references have subsequently been published, especially by Fackexheim. Jen. Zeits., XXII. p. 343. Of the whole number of cases the majority fall into a few types, and a great part of the evidence may thus be easily summarized and illustrated by specimen-cases. The forms of polydactylism thus constantly recurring may be dealt with conveniently under the following heads. (1) Addition of a single digit, complete or incomplete. A. external to minimus, in series with the other digits. B. in other positions. (2) Duplication of single digits, especially of the pollex and hallux. (3) Combinations of the foregoing. Besides these are a certain number of cases not included in the above descriptions, and of them an account will be given under the heading (4) Irregular examples. As bearing upon the frequency of the several forms of poly- dactylism it may be stated that in this irregular group are included all cases which I have met with that exhibit any feature of importance in departure from the cases otherwise cited. For the purpose of this list I have examined every record of polydactyl- ism to which access could be obtained. (1) A. Single extra digit external to minimus in hand or foot. (a) Incomplete form. This is one of the commonest forms of extra digit. In the great majority of such cases the extra digit is not complete from the carpus or tarsus but arises from the metacarpal or metatarsal, less often from one of the phalanges, of the minimus. The attachment may be either by a direct articulation upon the side of one of these bones, or they may give off a branch bearing the extra digit. In a not uncommon form of the variation the extra digit has no bony attachment to the hand, but is a rudimentary structure hanging from some part of the minimus by a peduncle. Of these several forms the following are illustrative cases. -A' Extra digit hanging from minimus hi/ a peduncle. Nanus. Annandale", Diseases of Fingers and Toes, 1865, p. 30, PI. n. fig. 20; Tarnier, Bull. Soc. de Chir., Paris, vi., 1866, p. 487; and numerous other examples. Pes. Bcsch, quoted by Grcber, I.e., p. 470: this form in the pes is rare. 346 MERISTIC VARIATION. [part I. 506. Extra digit arising from one of the phalanges of minimus. Axxandale, I.e. ; Otto, Monstr. sexc. Descr., Taf. xxv. fig. 7; Cramer, Wochens. f. d. ges. Heilkunde, 1834, No. 51, p. 809; Gaillard, Gaz. med,, 1862. This form seems to be comparatively scarce. 507. Extra digit arising from metacarpus or metatarsus of minimus. The great majority of cases are of this nature but exhibit many differences of degree. The articulation may be on the side of the metacarpus V (see Morand. Mem. Ac. Sci. Paris, 1770, p. 142, fig. 4; Coll. Surg. Mus., Catal, Teratol. Ser.', 1872, No. 308, and numerous other cases), or of the metatarsus V (see Grurer, I. c p. 476, Note 28) but in the pes this is less common. Frequently also the articulation of the extra digit is on the head of the metacarpus V (Gaillard, I. c.) or metatarsus V (Mus. Coll. Surg., Terat. Ser., No. 310). In the foregoing cases the extra digit articulates immediately with the side or head of metacarpal or metatarsal, but sometimes in the manus and often in the pes the digit articulates at the end of a branch given off by the metacarpus (Morand. ibid., fig. 3, and numerous other records), or by the metatarsus (Morand, /. c; Struthers, Edin. New Phil. Jour., 1863 (2), p. 89; Meckel, J. F., Handb. d. path. Anat., ii. Abth. 1, p. 36, and many more. 5 OS Hylobates leuciscus (Fig. 99) having an extra digit in the left manus arti- culating externally with the metacarpus V and in the right manus articulating with a branch from it. Mus. Coll. Surg., Teratol. Ser., No. 307, A. Fig. 99. Hylobates leuciscus, No. 508, minimus of right and left manus bearing a supernumerary digit articulating with the metacarpals. (From specimen in Coll. Surg. Mus.) (b) Complete digit having metacarpus or metatarsus external to minimus. Extra digits external to the minimus are occasionally complete, having a metacarpal or metatarsal and three phalanges, standing truly in series with the other digits, but to judge from the records this complete form is decidedly rare. In the first of the following examples given it should be noted that the digit standing fifth, CHAP. XIII.] DIGITS : MAX. 34; that is to say, as minimus, was itself rather longer than it should be in the normal, thus illustrating the principle with regard to the. Variation of a small terminal member of a Meristic Series on becoming penultimate which was predicated especially in regard to Teeth (see p. 272). In Morand's case the interesting feet of th< partial assumption by the sixth digit of anatomical characters proper to the minimus is commended to the attention of the reader. *i .09. *r 510. Girl : one extra digit on the external side of each hand. The normal little fingers are rather longer than usual and the extra lingers have nearly the same length. Each has three phalanges. Neither of the extra fingers can be moved separately from the finger adjacent to it. In the left hand the extra finger is borne on a supernumerary meta- carpal which lies parallel with the normal metacarpal V. Each extra digit can be opposed to the pollex. In the right hand the extra finger is borne on the enlarged head of the fifth metacarpal. Beraxger, Bull. Soc. d > A?ithrop., Paris, 1887, Ser. 3, x. p. 600. Man (parents normal, one brother had six digits on each extremity, six other members of family normal) having an extra digit external to minimus on both hands (Fig. 100) and both feet, in series with the normal digits. Left hand: unciform abnormally large, having two articular facets, one for the metacarpal of the fifth and the other for that of the sixth digit. The sixth metacarpal bears a digit of three phalanges of which the second and third were very short. [It does not appear that V was of increased length.] Bight hand : metacarpals normal in number, but the fifth is very thick, having in its peripheral third on the external R L Fig. 100. Palmar views of the bones of the hands of No. 510. (After Otto and Mokand.) 348 M ERISTIC VARIATION. [part i surface an articulation for a short digit of three phalanges, the second and third being very small. Feet : well formed ; cuboid of size greater than the normal, bearing the proximal end of two united fifth and sixth metatarsals. Each of these is separate peripherally and bears a digit [of 3 phalanges to judge from the figure (fig. 6)] in series with the normal toes, but shorter than the minimus. Muscles. In the left hand the sixth digit was fully supplied with muscles. There were two extra interossei and the extensor communis sent tendons to the sixth digit. The abductor, the flexor brevis and the flexor ossis metacarpi which in the normal are proper to the minimus were all inserted into the sixth digit instead. In the right hand the extensor communis gave a tendon to the sixth, which also possessed a proper abductor, but the fifth had no special extensor. Of the flexors the sublimis gave a tendon to each of the digits index, medius and annularis, none to the fifth, but a small slip to the sixth. The flexor profundus gave four tendons as usual, but from that going to the fifth a small tendon passes off laterally and piercing the sublimis is inserted as usual. In both feet the muscles were similar. The extensor longus gave a tendon to the sixth digit, and the extensor brevis does not. The flexor longus has four tendons as usual, none going to the sixth digit ; the flexor brevis has four normal tendons and an extra one for the sixth. The two tendons proper to the fifth (minimus) go to the sixth. The interossei are normal and there are only two lumbricales, one for the second digit and one for the fourth. Morand 1 , Mem. de V Acad. Roy. des Sci., Paris, 1770, p. 142, Figs. 1, 2, 4, 5 and 6. [The condition of the muscles in regard to the fifth and sixth digits in this case is worthy of special attention. If the morphologist will here propose to himself the question which is the extra digit, he will find it unanswerable. In the right hand, judging from the bones, it may seem evident that the fifth with its complete metacarpal is the minimus and that the sixth is a new structure ; but the condition of the feet and the right hand taken with that of the left, make a series or progression from which the similarity of the variation in each of the three states is evident; hence, if it is thought that the most external digit in the right hand is the extra part, it must also be held that the external or sixth digit in the left hand is the extra digit. But this digit in respect of its muscles has some of the points of structure peculiar to a minimus, while the fifth digit or supposed minimus on the contrary is without these characters. Hence neither digit is the minimus. Just as in the Condition III (see p. 326) of the hand, we saw that on the presence of a digit internal to the pollex, the pollex itself may be promoted to be a fingerdike digit with three phalanges, so may the fifth digit be partially fashioned as a more 1 The .similar descriptions and figures given by Otto, I.e., PI. xxv. figs. 9 — 11, Seerig, Vb. angeb. Verwachs. d. Finger u. Zelien, Ammon, Die angeb. Kr. d. Mensch., all refer, I believe, to this one original case of Morand's, though the fact is not stated and though several authors (Gruber, &c.) quote thern as separate cases. Seerig states that his figures are from preparations in the Breslau Museum. These figures agree exactly with those of Otto, which again agree closely with those of Morand but give more detail as to the carpi, taken no doubt from the actual specimens which had been acquired by the Breslau collection. I have therefore copied Otto's figures, though taking the important descriptions from Morand. chap. XIII.] DOUBLE-THUMBS : MAX. 349 central digit on the presence of a digit external to it. If therefore it be still called the "minimus" this term can only be applied to it by virtue of its ordinal position. ' For other cases of complete digits in this position see Auvard, Arch, de Tocologie xv. 1888, p. 633; Marsh, Lancet, 1889 (2), p. 739. (1) B. Single extra digit in other positions. Apart from cases of extra digit external to the minimus, cases of duplication of the pollex or hallux (to be considered below), and cases of extra digits internal to the pollex or hallux associated with change of symmetry of the digital Beries, the remaining cases of single extra digit are very few. In other words, it is with digits as with Meristic series in general, when a new member is added, the addition taking place in such a way that homologies may be recognized, it is most often at on* the ends of the series that the addition is made. Cases of extra digits in other positions are in Man and Apes very rare, and even in some of the few recorded < of a new digit arising on the inner side of the minimus (No. 511) it should be re- membered that this inner digit is judged to be the extra one rather than the outer mainly by reason of its smaller size. I can only give particulars of few such cases, and of the remainder no details are available. *511. Simia satyrus (Orang-utan), having a rudimentary extra digit arising from the internal side of the minimus of each hand: feet normal. In the left manus the minimus has all joints moveable as usual ; the first phalanx is normal, but the second is bent outwards nearly at right angles, thus making room for an extra digit arising from the first phalanx and directed inwards. This digit is fixed and has no articulation and no nail, but it is in its outer part bent back again towards the minimus with which it is webbed. The structure in the right manus is almost the same but the extra digit is larger and in its outer part free from the minimus, bearing a nail. Bolau, Verh. naturw. Ver. Hamburg, 1879, N. P. in. p. 119. 512. Woman: left pes bearing an extra digit articulating by an imperfect metatarsal with outside of metatarsal of IV. The extra digit stands obliquely to the others, sloping outwards and being attached by ligaments to the normal V. [The Cata- logue states that the extra digit resembles a right digit, but I see no sufficient evidence of this.] C. S. M., Ter. Cat. 312. [A case perhaps similar to foregoing is briefly quoted by Gruber, I.e., p. 471, note 83, as being in the Vienna Museum of Anatomy.] 512(2. Child: left metacarpal IV bore a supernumerary digit on external side. This digit was shorter than the digit IV and was completely webbed to it. Broca, *ki «)7 >r., 1863 (2), p. 87; Boulian, Rec. de Mem. de Mid. milit., 1865, Ser. 3, xiii. p. 67, jigs.); and besides this there are several examples in which one hand bore a clear pair of double-thumbs, while in the other hand there is an extra radial digit in succession to the normal thumb (e.g. 352 MERISTIC VARIATION. [part i. Fackexheim, I.e., p. 359, fig. iv.). Thus do the two conditions pass into each other, though some cases are clearly cases of duplicity and some are clearly cases of extra digit in Succession 1 , I know no case of unmistakeable duplicity in any digit but pollex or hallux ; but no doubt a good many cases of extra digit arising from the minimus may be of this nature (e.g. Annandale, PI. ill., fig. 28), though it is more likely that the extra digit is in Succession. In digits other than I or V the only case of possible duplicity known to me as occurring in a limb not exhibiting one of the complex conditions of polydactylism, are those of Streng ( Viertelja.hr sschrift f prakt. Heilk.. xlix. 1856, p. 178; original not seen by me; quoted by Gruber, p. 476), being a case apparently of double medius on one metacarpal ; and of Dusseau, Cat. Mus. Vrolik, No. 518, two terminal phalanges on right medius (together with double thumb ; six fingers on left hand and peripheral duplicity of hallux in each foot). Accompanied by numerical Variation in other parts of the digital series such cases of duplicity are known in a few other cases. (3) Combinations of the foregoing. Limbs not rarely present the forms of polydactylism already named in combination. Such combination may be found in the same limb, or one or more limbs may present one form, while another form may be found in the other limb or limbs. Of these combinations the following- three cases will be sufficient illustration. Case of double hallux on each foot, and rudimentary digit attached by peduncle to the minimus of each hand. 516. A female member of a polydactyle family [particulars given] had an abortive supernumerary finger attached by a peduncle to the little finger of each hand. In the feet the two great toes were each partially double. In the left great toe the individual phalanges could be felt and there were two nails. In the great toe of the right foot the adjacent sets of phalanges were inseparably united by their lateral borders, forming one bone, which was correspondingly broadened. There was only one nail which was notched in the middle of its free border. Mum, J. S., Glasgow Med. Jour., 1884, N. S. xxi. p. 420, Plate. Case of each extremity with double pollex or hallux and rudimentary digit attached to minimus. 517. Female infant having thumb of each hand double, the two sets of bones lying in the same skin and connective tissue. In the right hand the nails and phalanges of each were quite distinct, but it was not certain whether the metacarpals were separate or not. In the left hand the nails were not completely separate and the phalanges of the two thumbs were less distinctly separate. To the first phalanx of the little finger of each hand was appended a rudimentary bud- like finger, hanging by a peduncle. The feet resembled the hands. From the inner border of the metatarsal of each great toe there proceeded a well-formed thumb-like toe with two phalanges. This toe was set at right angles to the great toe and could be flexed and to some extent opposed. On the external border of the right foot there was a small extra little toe hanging by a peduncle from the metacarpal V. In the left foot the supernumerary little toe was bound up with the normal little toe for its whole length. Hagenbach, E., Jahrb.f. Kinderheilk., xiv. 1879, p. 234,^*. [Cp. No. 514.] 1 Compare with the largely similar series of phenomena seen in the foot of the Dorking fowl (v. infra). But in it if the two hallucal digits are not a true pair it is most commonly the inner that is the largest, conversely, to the general rule in the extra digits arising from the pollex in Man. chap, xiil] IRREGULAR POLYDACTYLISM : MAX. 353 Case of double hallux in combination ivith extra digits on external side. 518. Man in Middlesex Hospital, 1834, having on the right foot two toes articulating with the first metatarsal, and ou the left foot two toes articulating with the first metatarsal, and also two toes articulating with the fifth metatarsal. From the ulnar side of one of his hands two fingers had been removed. In each hand the middle and ring fingers were adherent throughout their length, as also were all the toes, except the minimi. Five brothers and three out of four sisters of this man had six toes on each foot and six fingers on each hand. The other sister had seven toes on one foot and six on the other, and had two extra fingers on each hand. London Med. Gaz., 1834, April, p. 65, figs. (4) Irregular examples. Thus far we have considered cases of polydactylisra that can be in some degree brought into order and included in general descriptions. There remain a small number of irregular cases each presenting special features which make general treatment inapplicable. These cases are instances of extremities, mostly feet, having seven, eight or nine digit-. The descriptions of these cases are for the most part fragmentary, and as the bones have been examined in only one of them (Moraxd) so far as I am aware, the relations of the digits to each other and to the limb are obscure. Speaking generally in these irregular examples there is an appearance of division, possibly of duplication, of several digit-. It should be noticed also that in some of them (e.g. Blasius, No. 520) the digits did not lie evenly in one plane but were in a manner bunched up so as to overlie each other. In such a case it would be interesting to know whether the digits originally grew in one plane and were afterwards shifted during growth, or whether the original Repetition was thus irregular. As all these cases differ from each other an adequate account of them could only be given at great length, and by reproducing the original descriptions in full, together with such figures as are attainable. For these reasons it would not be profitable to introduce them here, though in a study of the nature of Meristic Repetition it is important to remember that these irregular cases exist. As illustrative of several cases I have appended an account of two complex cases in the foot and of one in the hand, giving references to such others as I am acquainted with. 19*. Girl, set. 6, having abnormal toes on the left foot as follows (Fig. 103). The total number of toes on the left foot was nine. From the position and form it appeared that the digits (6—9) representing II, III, IV and V were normal, bat upon th< radial side of these instead of a single hallux there were five toes. ( >f these 1 and 2 were imperfectly separated, articulating with the first metatarsal bj their first phalanges, which were united to form a common proximal head. Bach had a distinct second phalanx and in general form resembled a great toe having a separate nail. The second metacarpal bore firstly a pair of toes, 3 and 4, which were still less separate from each other than 1 and 2, the biridity being oonfined to the soft parts. These two toes had one proximal and one distal phalanx in oommon. The second metatarsal also bore an external digit, 5, which in form ratlin reaembli d a normal third digit, being considerably shorter than »'• [and presumably oontaining three phalanges]. The toes 1, 2, 3 and 4 were found alter amputation to be devoid of muscles and presented onlv the terminations of the tlexor and extensor tendons b. 23 354 MERISTIC VARIATION. [part i. having their normal insertions. The toes 1 and 2 were supplied by the same flexor tendon which bifurcates and passes to be inserted into the ultimate phalanx of each / H Fig. 103. Foot of No. 519. (After Athol Johnson.) by a separate slip. The vinculum by which it is attached is common to the two bones. Johnson, Athol A., Trans. Path. Soc, ix. 1858, p. 427, fig. 520. Male infant having supernumerary toes on the left foot, The tarsus and meta- tarsus were abnormally wide. The hallux appeared externally to be divided into two. This duplicity was most marked in the second phalanx and appeared in a slight infolding of the skin. The nail also shewed traces of duplicity. Next to the hallux were two toes which were bent upwards and inwards. Of these the one overlay the other. The uppermost was found after excision to have two sets of phalangeal bones enclosed in the same skin ; these two articulated with a single metatarsal bone. The lower toe was thought by Blasius to represent the digit II. Next to this there was a rudimentary digit with a slightly developed nail. After excision it was found that this toe contained a cartilaginous basis which was partly segmented into two phalanges and articulated with a metatarsal. External to this rudimentary toe were three normal toes, representing as Blasius supposes, the digits III, IV and V. External to the putative V was another digit of the same size and shape. Blasius, v. SiebohVs Jour. f. Geburtsh., xiii. 1834, p. 131, figs. 1 and 2 ; figures copied in Ahlfeld, Jlissb. d. Mensch., Taf. xx. fig. 11. [This foot appears to contain parts of ten digits.] 521. Child having polydactyle hands as follows. In each hand the fingers were webbed to the tips, each minimus having an extra nail. In the right hand the pollex was triplicate, having three sets of phalanges and three nails, the whole being in a common integument. In the left hand the pollex was duplicate, having two sets of phalanges webbed together and two nails. Each member thus formed a prehensile paw. In right foot little toe webbed to next toe. Some (not all) of brothers and sisters had similar hands : father and grandfather had similar hands : mother and grandmother normal. Harker, J., Lancet, 1865 (2), p. 389, ^.g. 522. The following are other examples of irregular polydactylism : Morand, Mem. Ac. Sci. Paris, 1770, p. 139, figs. 8 and 9. (The same redescribed from Morand's figure by Delplanque, Etudes Teratol., n. Douai, 1869, p. 67, PI. v. ; and again by Lavocat, Mem. Ac. Sci. Toulouse, v. 1873, p. 281, PI. i., who takes a different view.) Gruber, Mem. Ac. Sci. Pet., Ser. vn. Tom. n. No. 2 (fig. copied in Bull. Ac. Sci. Pet., xv. 1871, fig. 6, and by Ahlfeld, Missb. d. Mensch., PI. xx. fig. 20). Gruber, Bull. Ac. Sci. Pet., xv. 1871, p. 367, figs. 4 and 5. Otto, I.e., PI. xxvi. figs. 8 — 11. Froriep, Neue Notizen, d)c., Weimar, No. 67, 1838, iv. p. 8, figs. 4 — 8 (very brief account of important case, copied by Ahlfeld and others). Du Cauroi, Jour, des Scavans, 1696 (pub. 1697), p. 81 (quoted first by Morand, afterwards wrongly quoted by many writers. Dwight, Mem. Bost. N. H. S., iv. chap, xiil] REDUCTION OF DIGITS : MAX. 355 No. x. p. 474, supposes that this is a case of double-hand, palm to palm (as No. 503), but the original probably means that two adjacent thumbs and two adjacent annu- lares were united, the digits being all in one plane). Popham, Dull. Quart. J. of Med. Sci., xliv. 1867, p. 481. Dusseau, Cat. JIus. Vrolik, 1865, p. 457 (very brief, see p. 352). Graxdelemext, Gaz. des hop., 1861, p. 553. Lisfraxc (see Schm. Jahrb., xn. 1836, p. 263). Eorberg, Jour. f. Kinderkr., xxxv. 1860, p. 426. Mabjoltn, Bull. Soc. de Chir., 1866, Ser. 2, vi. p. 505, jig. (probably case of double- hand). Annandale, Bis. of Fingers and Toes, 1865, p. 39 (eight metatarsals on a foot possibly associated with change of Symmetry). Ibid., p. 35, figs. 41 and 49 (pollex with two sets of phalanges but three nails, together with extra digit external to V). Cp. No. 521. Heyxold, Vireh. Arch., 1878, lxxii. p. 502, PL vn. Mason, F., Trans. Path. Soc., 1879, xxx. p. 583 (foot having eight metatarsals and nine digits). Melde, Ft., Anat. Unters. eines Kindes mit beiders. Befekt d. Tibia u. Poly- dactylic an Hdnden u. Fiisseti, Inaug. Diss., Marburg, 1892 (important). REDUCTION IN NUMBER OF DIGITS. Though in reduction of digits the course of Variation is generally irregular and the result often largely amorphous there are still features in the evidence which may be of use to us, and a few selected cases are of some interest. These features will be sjDoken of under the three following heads, though for a general view of the subject reference must be made to teratological works. (1) Reduction in number of phalanges. ( 2 ) Syndactylism. (3) Ectrodactylism. (1) Reduction in number of phalanges. As in certain cases of polydactylism it appeared that increase in the number of phalanges in the thumb could be regarded as a step in the direction of increase in the number of digits, so a reduction may be thought to be a step towards diminution in the number of digits. But though many cases of reduction in number of phalanges are recorded, there is in them nothing which suggests that they may be fitted into a series of gradual reduction comparable with the series of gradual increase already described. It is indeed chiefly as illustrating the possible completeness and perfection of Variation that these phenomena have a direct bearing on the subject of Meristie Variation, The following case is chosen as being especially regular and symmetrical. *523. ^ an having only one phalanx in each hallux, and two in each of the other fingers and toes. The hands were almost exactly alike. The thumb had a short metacarpal fin: long, and one phalanx (11 in.), the joint between them being loose as if composed of soft tissue. Uy the length of the metacarpal (Sin.) the index is longer than the other digits. The next two metacarpals have only half that length. The metacarpal of V is l.lin. long, but from its obliquity does not project so far as that of IV. The proximal phalanx of the index measnn I , mediae I:, annularis 1, minimus 1^. The distal phalanx in index and middle |, ring and little | in. In left hand the distal phalanx of index is proportionally short. r. Except the index all the dibits present their usual proportions. The feet are well formed as far as distal ends of metatarsals. The toes are short, pulpy and loosely articulated. Each has two phalanges except the hallux, which has only cue. This case was a twin with a normal male. An elder brother and younger sister have the 23—2 356 MERISTIC VARIATION. [part i. digits similarly formed, but in the last the feet are also turned in. Struthers. Edin. New Phil. Jour., 1863 (2), p. 100. As an example of similar and simultaneous Variation in both extremities this is an instructive case. (2) Syndactylism. Under this name have been described those cases in which two or more digits are to a greater or less extent united together. In their bearing on the morphology of Repeated Parts some of these variations are very instructive. It will be found that the impor- tant considerations in this evidence may be divided into two parts. Of these the first concerns the manner of the variation and the second to the position in which it is most commonly found. The manner of union betiveen digits. In many cases of union of digits the limb is amorphous ; with these we have now no special concern. In simpler examples the digits may be of normal form but some or all of them may be united by a web of integument for a part or the whole of their length. (For records of such cases see Fort, Axxaxdale, &c). *524. But besides these cases of webbing are many in which the union may be of a much more intimate character. Taking the cases together a progressive series may be arranged shewing every condition, beginning from an imperfect webbing together of the proximal phalanges to the state in which two digits are intimately united even in their bones, and perhaps even to the condition in which two digits are represented by a single digit (see No. 529). That the latter condition represents a phase in this series of variations does not seem to be generally recognized by those who have dealt with the subject but it is impossible to exclude it. The lower conditions of this variation are sufficiently illustrated by Fig. 104, I and II (from Anxaxdale, Diseases of Fingers and Toes, figs. 39 and 33), shewing cases of medius and annularis partially com- bined for the whole of their length. A higher condition is shewn in Fig. 104, III, in which the same digits are united so closely that their external appearance suggests that only four digits are present in the hand. In this specimen (Anxaxdale, I. c, p. 14) there were neverthe- less five metacarpals, but the first phalanges of III and IV were united peripherally and bore a second and third phalanx and one nail common to them both. The same author (I. c. fig. 44) gives an illustration of such a set of bones from Otto 1 . The following cases are interesting as occurring in Apes. *525. Pithecia satanas (Monkey) : young male having the third and fourth digits of the hand on each side completely connected by a fold of nude skin. The remain- ing digits of the hands and feet were normal. Forbes, W. A., P. Z. S., 1882, p. 442. 526. Macacus cynomologus : specimen having the fifth finger of the right hand represented by a rudiment only. On dissection the first phalanx of the fifth finger was found to be enclosed with that of the fourth. All the fingers of the abnormal (right) hand were somewhat misshapen and bore several exostoses. [? congenital variation] Fbiedlowsky, A., Verh. zool. hot. Ges. Wien, 1870, xx. p. 1017, Plate. 1 I have failed to find the original of this figure in Otto's works. CHAP. XIII.] UNION OF DIGITS : MAN. 357 Before going further certain points are to be noted. First, the union as shewn in the figures is a union or compounding as of optical I D IV Fig. 104. Cases of syndactylism. I, II and III. A progressive series illus- trating degrees in the union of medius and annularis in the hand. IV. Case of union of index and medius of the foot. The union is incomplete peripherally. (After Axxandale.) images in Bilateral Series, and is not like that of parts in Succc»m\ <■ Series. Next, the union of the bones is more complete /» rxphi rally and less complete centrally. The latter is a rule very commonly observed in cases of the union of the bones of digits both in Man ami other mam- mals. This statement is made without prejudice to the other let that in the least state of syndactylism as manifested by union of the Bofl parts, it is the most central phalanges which are united. Such a case of partial union between II and T FT in the foot' is shewn in Pig. 1" 1. I V (Axnaxdale, /. c, fig. 34). The rule that in the Lowest condition o! syndactylism of the bones it is commonly at the periphery thai the union is most complete is also difficult bo understand in connexion with 1 Compare several remarkable cases of this variation in one family, lb Clkbo, M€m. hoc. Linn. Normandie, ix. p. xxvi. 358 MERISTIC VARIATION. [part i. the fact that the division of digits in the lowest forms of polydactylism appears also first in the peripheral phalanges. These phenomena appear to be in contradiction to each other, and I am not aware that the fact of the appearance of the digits early in the development of the limb throws any light on the difficulty. The number of digits which may be thus united is not limited to two, and examples of intimate union between three and even four digits are common. The position of union. *527. Those who have treated of this subject do not, so far as I am aware, notice the fact that the phenomenon of Syndactylism most frequently affects particular digits. From an examination of the recorded cases it appears that in the hand there is a considerable preponderance of cases of union between the digits III and IV. I regret that I have not material for a good analysis of the evidence on this point, but I may mention meanwhile that in a collection taken at random of some thirty-five cases of hands having only two digits united (chiefly those given by Fort and Annandale) over 25 are cases of union of the digits III and IV ' ; in only one were the digits I and II united ; the digits II and III in 1 4 cases ; the digits IV and V in 1 3 cases. *528. On the other hand if two digits in the foot are united they are nearly ahvays II and III. If in the hand three digits are joined they may be either III, IV and V, or (perhaps less commonly) II, III and IV. In cases of union of all the digits II to V, the digits III and IV are often much more intimately united than the others, and are often recorded as having a common nail, while II and V have separate nails. This question of the comparative frequency of the different forms of syndactylism would probably repay full investigation, and to the study of the mechanics of Division it would clearly be important. In the meantime may be noted the fact that the evidence suggests the possi- bility that we have here to do with a case of union of parts which are related to each other as optical images, and that the digits II to V of the hand constitute an imperfect Minor Symmetry within themselves. The fact that the subjects of most frequent union in the foot are the digits II and III, not the digits III and IV as in the hand, may be connected with the fact that the hallux stands to the foot in a different geometrical relation from that which the pollex bears to the hand and that consequently the axes of Symmetry are different in it. (3) Absence of digits (Ectrodactylism). In the conditions already described though the digits are not all clearly divided from each other yet no one wdiole digit can be supposed to be absent. Even in the specimen shewn in Fig. 104, II, from the presence of separate metacarpals III and IV the identity of the several digits is still easily recognized. These simplest cases however by no means exhibit all the phenomena. From a large group of cases the three following are chosen as each illustrating a distinct possibility. 1 Owing to the ambiguity of some records as to the similarity of the condition in the right and left hands I cannot give exact numbers. chap, xiil] ONE DIGIT STANDING FOR TWO. 359 Upon the morphological questions arising out of these facts comment will be made when the whole subject of numerical Variation of digits is discussed. *x 529. Representation of digits II and III of the pes by one digit. Man having four digits in the right foot as shewn in Fig. 105. The calcaneum. astragalus, navicular, first (internal) cuneiform and cuboid were normal. The navicular had on its peripheral surface three facets as usual. The second and third cuneiforms were completely united to form one bone which bore no traces of its double nature as shewn in the figure (c 2 + c 3 ). The peripheral surfaces of both form one plane. Taking the four digits in order, the minimus has its normal form and tarsal relations. The digit next to it has the normal form and relations of a dijnt IV. n+m Fig. 105. Bones of the right foot of No. 529. I, apparently representing index and medius. IV, annularis. hallux. 11^- III, digit V, minimus, a, astra- c 3 , bone apparently representing the middle and external cuneiforms. (After Gruber.) galus. sc, navicular, cb, cuboid, c 1 , internal cuneiform, c 2 *x 530, Internal to this is a metatarsal of abnormal thickness articulating with the single bone presumably representing the external and middle cuneiforms. This metatar- sus presented no trace of duplicity. It bore a digit of three phalanges of more than normal thickness but otherwise normal. The hallux was normal, having two pha- langes. Each of the other digits had three phalanges, but the 2nd and 3rd phalai. of the minimus were ankylosed. Of the muscles, the transversalis pedis, one of the lumbricales, one of the inter- ossei dorsales and one of the interossei plantares were absent. The extensor and flexor longus each had three tendons. [Detailed description of bones and soft parts given.] Gruber, W., Virch. Arch. f. path. Anat. u. PJn/s., 1869, xi.yii. [p. :>04. PI. VIII. Single digit articulating with the cuboid [probably a ease of representation of digits IV and V by one digit]. Man having four digits on the left foot as follows. The foot is well form The digits I, II and III are normal and have normal tarsal relations. The fourth digit has a well-formed metatarsal and three phalanges. The hones are perhaps rather more robust than those of a normal fifth digit, but the nit tatarsal has the normal tuberosity at the base strongly developed. This metatarsal articulates with a cuboid of somewhat reduced size having only onv articular facet on it- peripheral surface. The other parts were all normal, and even in the muscular BVstem only a trifling abnormality was found. Parents normal. Stkintiiu.. C. P., Virch. Arch, f. path. Anat. u. Phys., 1887, cix. p. 347. 360 MEMSTIC VARIATION. [part l Reduction of digit IV of pes. '531. [This case is introduced here for comparison with the last.] A left foot having abnormalities as follows. Calcaneum, astragalus, internal cuneiform normal in size and shape. The second cuneiform is rather broader than usual, but the surface which it presents to the internal cuneiform has all the characters of a middle cunei- form. External to this middle cuneiform is only one large tarsal bone in the distal row. This bone presents no clear sign of duplicity, but from its form and relations it appeared that it represented both the cuboid and the ecto-cuneiform. The hallux and digit II have approximately normal relations. The large cuboid-like bone bears externally a metatarsal agreeing in shape with a metatarsal V ; and internal to this the same tarsal bone bears another metatarsal which upon its external side gives off yet another metatarsal of reduced size. Each of the five metatarsals bore a digit, but the digits of the minimus and of the slender IV were webbed together. [Full details given.] Brenner, A., Virch. Arch. f. path. Anat. u. Phys., 1883, xciv. p. '23, PL ii. 532. Besides these simpler cases there are very many recorded instances of reduction in number of digits in which the identification of the parts is quite uncertain. From the point of view of the naturalist it is worthy of remark that even in some of the cases departing most widely from the normal form the limb though having only three or perhaps two digits still presents an approach to a symmetry. Examples of this kind are given by Guyot-Daubes {Rev. d' Anthropoid 1888, xvn. p. 541, figs.) and by Fotherby (Brit. Med. Jour., 1886 (1), p. 975 figs. ) and many more. Fotherby's record is interesting as relating to a family among whose members feet bearing only two opposable claw-like digits of irregular form recurred for five generations. Evi- dence relating to limbs of this kind is so obscure that it is not possible as yet to make deductions from it, but there seems to be a general agreement among anatomists that when two digits only remain one of them has the characters of a minimus. Reference must be made also to the fact that in cases of absence of radius the pollex is almost always absent. This seems to be established in very many cases. The only examples of a pollex present in the absence of a radius known to me are that of (jruber, Virch. Arch. f. path. Anat. u. Phys. 1865, xxxn. p. 211, and that of Geissendorfer, Zur Casuistik d. congen. Radiusclefectes, Munch. 1890. Horse. Variation in the number of digits in the Horse 1 has been repeatedly observed from the earliest times. The mode of occur- rence of the change is by no means always the same, but on the contrary several distinct forms of Variation may be recognized. On inspection the cases may be divided into two groups. A. Cases in which the extra digit (or digits) possesses a distinct metacarpal or metatarsal. B. Cases in which the large metacarpal or metatarsal (III) gives articulation to more than one digit. Besides these I have placed together in a third group (C) two very remarkable cases which cannot be clearly assigned to either of the other groups. These instances are of exceptional interest from the fact that in them is exhibited a condition intermediate between those of the other two groups. We have seen repeatedly that 1 In the Mule two cases have been recorded, but in the Ass I know no instance of polydactylism. Describing a polydactyle horse seen on a journey in Rio Grande von Jhering (Kosjjios, 1884, xiv. p. 99) states that he believes polydactyle horses to be much more common in S. America than in Europe, and that most persons who have travelled much in that country have met with cases. Mules between the jackass and mare are bred in great numbers, but he had heard of no case in a mule. chap, xiil] digits: horse. 361 Meristic Variation may take place by division of single members of Series, a phenomenon well seen in the B group ; and we have also seen many cases of numerical Variation by addition to the Series associated with a reconstitution, or more strictly a redistribution of differentiation amongst the members of the series thus newly constituted ; but here in these rare examples of the C group the nature of the parts is such that it cannot be predicated that the change is accomplished by either of these methods exclusively. From such cases it follows that the two processes are not really separable, but that they merge into each other. (Compare the similar facts seen in regard to teeth p. 269, and mammae p. 1.93.) A. Extra digits borne by distinct metacarpal or METATARSAL. The cases in this group may be subdivided as follows : (1) Two digits, one being formed by the development of the digit II. a. Only three metacarpals or metatarsals (II — IV) as usual. Common form : fore and hind limb. b. Four metacarpals (? I — IV). Common form : anato- mically described in fore limb only. c. Five metacarpals (? I — V). Single case in fore limb. (2) Tivo digits, one being formed by development of the digit IV. Rare. (3) Three digits; the digits II and IV both developed. Rare. (4) Two digits; the digits II and IV both developed, III aborted. Rare. It will appear from the evidence that though the same varia- tion is often present in the limbs of both sides this is not always so. The fore and hind limbs also sometimes vary similarly and simultaneously, but in other cases they do not. Different forms of numerical Variation are also sometimes found on the two sides, and not rarely the variation in the fore limb is different from that in the hind limb. (1) Two digits, one formed by development of the digit II. a. Three metacarpals or metatarsals only. To this division and to the next, (1) b, belong the greal majority of cases of polydactylism in the Horse. Unfortunately most of the records have .been made from living animals and contain do anatomical description: in the absence of such particulars it is not possible to know r whether a given case belongs to this division or to the next, and it thus is impossible to determine the relative frequency with which the two forms occur. The following are given as specimen cases. 362 MERISTIC VARIATION. [part I. Forefoot *533. Horse of common breed, having a supernumerary digit on the inner side of the right fore foot (Fig. 106). Humerus and radius: no noticeable variation. Ulna a little more developed than usual ; lower end slightly broken, having probably reached to lower fourth of radius. The part of the inferior and external tuberosity of the radius which is usually supposed to represent the ulna is larger than in the normal form. Fig. 106. Right fore foot of Horse, No. 533. A. The leg seen from in front. B. The carpal bones enlarged. M, magnum, sc, scaphoid, u, unci- form. t' 2 , trapezoid, t 1 , supernumerary bone not found in normal, represent- ing trapezium. IV, the metacarpal re- presenting digit IV. Ill and II, meta- carpals bearing those digits respec- tively. (After Arloing.) Carpus consisted of eight bones, instead of seven as usual. Scaphoid much larger than normal ; lunar, cuneiform and pisiform normal. In the lower row the magnum and unciform have normal relations, but in the place of the normally single trapezoid are two bones, one anterior (f), the other posterior (t 1 ). These together bear the enlarged inner metacarpal (II). The posterior of these bones had a short pyramidal process lying beside the inner meta- carpal. This process was partially constricted off and is regarded by chap, xiii.] DIGITS : HORSE. 363 Arloing as a representative of the metacarpal I, the carpal portion of the bone being the trapezium. The outer metacarpal (IV) was perhaps slightly larger than usual. The inner metacarpal (II) was greatly enlarged at its central end, articulating with the tw r o bones t 1 and t' 2 , and partly with the magnum. In its central part this metacarpal was fused with the large metacarpal (III) and above is united to it by ligamentous fibres. Below r it again separates from the large metacarpal and is enlarged, bearing an additional digit of three phalanges, the lowest bearing a hoof. [This hoof is not curved towards the large hoof as in many specimens described, but is convex on both sides, resembling the hoof of an ass.] The large central metacarpal was flattened on the side adjacent to the enlarged metacarpal II. The muscles, nerves and vessels are fully described (q. v.). Arloing. M. S., Ann. Sci. Nat, ZooL, Ser. V. T. vm. pp. 61 — 67, PL 534. Foal having two toes on each fore foot. The father and mother of this foal w r ere both of the "variete chevaline comtoise." The foal in question was the only one which this mare dropped and she died two months afterwards. The foal w T as in nowise abnormal excepting for the peculiarity of the fore feet. The carpus was normal and the external metacarpal was rudimentary as usual and ends in a small knob. The internal metacarpal is thicker than the external one and bears a digit of three phalanges, the terminal phalanx bearing a small hoof. This hoof is curved outwards towards the normal hoof. The ligaments and tendons of the foot did not suffice to keep it stiff, and as the animal walked, it not only touched the ground with the hoof but also with the posterior surface of the phalanges. This led to inflammation of the foot, in consequence of which the foal was killed. CORNEVIN, Nouveaux cas de didactylie chez le chevcd, Lyons (1882?). [Xote that this case differs from the last in the fact that the carpus was normal.] A similar case in the right forefoot is given by Kitt. Dent. Ztsch. f. Thiermed., 1886, xn. Jahresb., 1884 — 5, p. 57, Jig. Hind foot. Among the many accounts of polydactyle horses I know none which gives an anatomical description of a case of a fully developed digit II in the hind foot. The following case, indeed, is the only one known to me in which an}^ facts respecting the condition of the tarsus of a polydactyle horse have been ascertained. In it, as will be seen, the digit II was not fully developed. 535. Horse having the metatarsal II enlarged and bearing a rudimentary ' digit (Fig. 107 B and C). In the left hind foot the arrangement was as shewui in Figs. B and C. The metatarsal II was enlarged an. 1 articulated with "two united cuneiform bones" [presumably one bone with indica- tions of duplicity]. Internal to this digit was a " first cuneiform bone," but the digit I was not developed. The metatarsal II bore peripherally a rudiment of a digit as shewn in the figure. The right hind foot was similar to the left but it is stated that the "three small cuneiform 364 MERISTIC VARIATION. [part I. bones'' were serjarate 1 , as shewn in Fig. 107 C. The fore feet of the same animal were in the condition described in (1) h. [See No. 537.] Marsh, 0. C, Am. Jour. Sci., xliii 1892, pp. 340 and 345. s'l " mr iv Fig A. B. C. 107. Limb bones of a polydactyle horse. Left fore foot. No. 537. Left hind foot. No. 535. Tarsus of right hind foot from the inside. three bones placed as m, magnum. No. 535. n, navicular, cb, cuboid. 4, ecto-cuneiform. 1, 2, 3, cuneiforms, td, trapezoid, tm, trapezium, u, unciform. I, II, III, IV, numerals affixed to the metacarpals on the hypothesis that these are their homologies. Cp. Fig. 108, which is lettered on a different hypothesis. (After Marsh.) b. Four metacarpals. This condition is a higher manifestation of the variation seen in the cases just given. In No. 533 the digit II was developed and in addition the trapezium had appeared ; in the cases now to be 1 Marsh introduces this case in support of a contention that these variations are of the nature of Reversion. Upon the same page appears the statement that "in every specimen examined, where the carpal or tarsal series of bones were preserved and open to inspection, the extra digits were supported in the usual manner," I. c, p. 345 : this assertion is hardly in agreement with the previously stated fact that the metatarsal II is supported by two cuneiform bones. On p. 349 Marsh comments on the presence of five bones in the distal row of the tarsus, and from the expres- sions used it is implied that five such bones had been met with in other polydactyle hind feet. A number of alternative explanations are proposed ; (1) that the five tarsals correspond "to those of the reptilian foot"; (2) that the first may be a " sesamoid " ; (3) that the first may be a remnant of the first metatarsal, for such a rudiment " apparently exists in some fossil horses." With conjectures of this class morphologists are familiar. Into their several merits it is impossible to inquire, but it may be mentioned that the real difficulty is not the presence of the cuneiform marked 1, but the fact that the tarsal element of the digit II seems to have been double, and that the digits in reality are not supported in the usual manner. CHAP. XIII.] DIGITS : HORSE. 3G5 given the digit II is extensively developed and the trapezium bears a splint bone representing the metacarpal I, like that which in the normal represents the digit II. This is a phenomenon illustrating the principle seen in the case of teeth and other parts in series (see p. 272), namely, increase in the degree of development of the normally last member of a series correlated with the appear- ance of a new member beyond it. Nevertheless the same cases have sometimes been described (e.g. Gatal. Mus. Coll. Surg.) on a different hypothesis. This is illustrated by the lettering of Fig. 108. On this other view the innermost carpal is considered to be the trapezoid and its splint-bone is regarded as the original metacarpal II. The second digit, ac, and its tarsal bone are supposed to be " accessory ' : or "intercalated." To these terms it is difficult to attach any definite meaning. The proposal that some digits are to be reckoned in estimating homologies and that others are to be omitted is arbitrary, and, if allowed, would make nomenclature dependent on personal choice. It is, as has been often pointed out in foregoing chapters, simpler to number the parts in order as they occur and to accept the visible phenomena as the safest index of the methods and possibilities of Variation. Nevertheless, to illustrate the point at issue I have introduced two cases of the same Variation, the one, No. 536, lettered on the view advocated by the Catalogue of the College of Surgeons, &c, the other, Xo. 537. 108. Eight fore foot of Horse No. 530 from acta Fig. behind. The upper surfaces of the carpal bones of the distal row are separately shewn above. Specimen in Coll. Surg. Mus., Ter. Cat., 304. T, trapezoid, if, magnum. U, unciform. ci! metacarpal (IV being developed, bearing a digit. (After V\'<>"I»-Mason.) Ill 368 MERISTIC VARIATION. [part i. Wehenkel, I. c, p. 15, mentions a similar specimen in the Museum of the Veterinary School at Berlin described by Gurlt, Mag. f. gesam. Thierh., 1870, p. 297 [not seen, W. B.]. (3) Three digits [1 the digits II and IV being both developed]. Examples of this variation are alluded to by many authors but I know of no anatomical description. The following are all very im- perfectly described. 541. Foal (foetus): left manus having three sub-equal digits; right manus two digits and rudiments of a third more developed than usual. Hind feet normal. Geoffroy St Hilaire, Ann. Sci. Nat., xi. 1827, p. 224. Similar case, Bredin, Froriep , s Notizen, xvm. p. 202. 542. Horse from Texas, having extra digit on inside of each manus, and an extra digit both on the outside and on the inside of each pes [external view only]. Marsh, Am. Jour. Sci., xliii. 1892, p. 344, fig- ~- 543. Horse with both splint-bones bearing digits in each foot. Franck, Handb. d. Anat., Stuttg., 1883, p. 228. (4) Two digits ; the digits II and IV both developed, III aborted wholly or in part. Mention of these cases must be made in illustration of the possibilities of Meristic Variation, but the parts were in all three instances so misshapen that the animals could not have walked. 544. Foal having two toes on each foot, the developed toes belonging to the metacar- pals and metatarsals II and IV, while the normally large III was not developed at all in the fore feet and was in the hind feet represented by a wedge of bone only. Hind feet. Left. Bones of leg and tarsus said to have been normal. Metatarsal III represented by a wedge of bone fixed between the greatly developed metatarsals II and IV. The wedge-like bone 5 cm. wide at upper end, having usual tarsal rela- tions. Its length about the same as its width. Laterally it is united to the metatarsals II and IV which curved round it till they met, and then curve away from each other again. Each was about 20 cm. long and bears a misshapen digit consisting of a proximal phalanx and a hoof-bearing distal phalanx. A small nodule of bone attached to the proximal phalanx may or may not represent part of a middle phalanx. Bight. Very similar to left, but the wedge-like III was rather broader — [for details see original]. Fore feet. More misshapen and less symmetrical than hind feet : metacarpal III not developed at all. The metacarpals II and IV curved towards each other and crossed, giving an unnatural appearance to the feet. Eight foot. Cuneiform and lunar united, and upon the surface of the bone formed by their union there was a groove occupied by two parts of the tendon of the anterior extensor metacarpi passing to mcp. II and IV respectively. Pisiform and scaphoid normal [this is not clear from the figure]. Magnum absent. Unciform and trapezoid abnormal only in respect of their relations, for whereas they should articulate with the magnum they do not do so, for both magnum and mcp. Ill are not represented. Metacarpal II was 11 cm. long, mcp. IV being 19 cm. long. Each bore a digit with a hoof; the digit IV having a proximal and a distal phalanx connected by a fibrous cord instead of a middle phalanx. The digit II had a rudimentary distal phalanx only. Left foot like the right, but with the mcp. and digit II more fully developed. [Muscles fully described. It may perhaps be thought that there is not sufficient proof that the developed digits are actually those normally represented by the splint-bones II and IV, but the condition of the hind feet is practically conclusive that this is the right interpretation.] Wehenkel, La Poly dacty lie chez les Solipedes, from J. de la soc. r. des sci. vied, de Bruxelles, 1872, Plate. 545. Foal, in which the right anterior leg possessed two metacarpals and digits. The radius, ulna and proximal series of carpal bones were normal. In the distal series only two bones were present, viz., an inner bone corresponding to the trapezoid, and a magnum. There was no separate bone corresponding to the CHAP. XIII.] DIVISION OF DIGIT I HORSE. 369 546. unciform, but in its stead, the head of the outer metacarpal was continued upwards to articulate with the cuneiform. Between the heads of the two metacarpals was an irregularly quadrate bone which articulated with the magnum in the place where the large metacarpal (III) should be. This bone however only extended a little way, articulating at its outer end with a notch in the external metacarpal. [This i- the author's view, but the figure strongly suggests that this quadrate bone may have been originally in connexion with the external metacarpal and that it may have been separated from it by fracture. If this were so, the large metacarpal would then not be represented by a separate bone at all.] The outer metacarpal distally bore three phalanges of irregular shape, flexed backwards and outwards. The inner metacarpal articulated solely with the trapezoid. Peripherally it bore a callosity which was due to the healing of a fracture. The phalanges of the inner metacarpal were three, but the first was reduced in length, while the second was elongated and bent in a sinuous manner. The ungual phalanx of this toe was cleft. [The author regards this case as analogous to the foregoing one, No. 544, that is to say, as an instance of development of the normally rudimentary lateral metacarpals to the exclusion of the large one (III), and he considers therefore that the large metacarpal (III) is only represented by the quadrate ossification which lay between the two developed metacarpals.] Ercolani, G. B., Mem. della Ace. Sci. d. Istituto di Bologna, S. 4, T. in. 1881, p. 760, Tav. i.fig. 11. Foal in which the feet were all very abnormal. In the two fore feet the meta- carpal of the normal toe (III) was very little developed, being however somewhat larger on the left side than it was on the right. It bore no digit. The external metacarpal bone (IV) of each fore foot attained a considerable length and bore a small hoof-bone. In the left fore foot the inner metacarpal was present but reduced ; in the right foot it was absent. Bight hind foot also had the external metacarpal developed and bearing three small phalanges, but the central metacarpal (III) was fairly developed, bearing however only two phalanges. Left liind foot was amor- phous. Boas, J. E. V., Deut. Ztschr. f Thiermedecin, vn. pp. 271 — 275. [For full description, measurements and figures see original.] B. Cases in which metacarpal III gives articulation to MORE THAN ONE DIGIT. These cases are clear examples of the representation of a Bingle digit by two. It will be seen besides that the two resulting digits may stand to each other in the relation of optical images (see Fig. 110) and do not form a Successive Series, thus following the common method of division of structures possessing the property of Bilateral Symmetry in some degree (cp. p. 77). All cases of this variation known to me occurred in the fore limb. *z o47. Foal: a right fore foot figured from a specimen in the collection of the Veterinary School of Copenhagen (Fig. 110) has two complete digits articulating with a single normal metacarpal bone. The two digits are symmetrically developed ; each consists of three phalanges and bears a hoof. These two hoofs are well formed and curve to- wards each other like those of Artiodactyles. Boas, J. E. V., Deut. Ztschr. f. Thiermedecin, vii., p. 277, Taf. xi.,jiy. 9. 548. Two fore feet of a foal, each being Irregularly and unequally bifid. Boas, ibid., jigs. 7 and ^. B. t.rt inf Fio. IK'. Bight for.' foot of Bora No. 547. Mcp, peripheral cml of metacarpal III. est, external side. int. internal Bide i After Boas.) 24 370 MERISTIC VARIATION. [part I. 549. Filly, two-year old, which had been born with left fore foot cleft like that of the Ox. Each of the two toes had three phalanges, which were completely separate as far up as the metacarpophalangeal joint. The division externally was carried to the same extent as in the Ox. The lower end of the great metacarpal III felt as if bifurcated like that of the Ox, so as to give separate articular support to the two toes. Upper parts normal. The lesser metacarpals, II and IV, felt through skin, seemed to terminate rather lower down in left foot than in right, but this was uncertain. Animal examined alive. No attempt at shoeing had been made, and hoofs * 550. having become elongated forwards larger was much larger or New Phil. Jour.. had had their points sawn off. The whole foot more spread than the other. Struthers, J., Edin 1863, pp. 279 and 280. Horse: right fore foot having phalanges bifid (Fig. 111). The limb was normal as far as the distal end of the metatarsal, except for some exostoses. The proximal phalanx was short and of great width; in its lower third it divided into two divergent parts, the divergence being more marked on the posterior face than on the anterior. Each of these diverging processes bears a complete second and third phalanx. The third phalanges each bear hoofs, which are convex on the outer sides but lit together on the opposed surfaces, the external hoof being slightly concave on its inner face, while the internal is slightly convex. On the plantar surface, each toe bore a half -frog. The two large sesamoids, normally present in the Horse, are in this specimen united along their inner borders to form a single bone, which was placed behind the upper part of the proximal phalanx. Two small sesamoids lay behind the third phalanx. A good deal of exostosis had taken place in all the phalangeal bones. Arloing, M. S., Ann, Sci. Nat., Ser. V., Tome vin. pp. 67—69, PI. 551. Mb Sla Fig. 111. Right fore foot of Horse No. 550, from in front. sc, scaphoid, tp, 552. Foal : in right fore foot the large metacarpal divided into two parts, each bearing a separate digit. The proximal row of the carpus consisted of four normal bones, but the distal row was composed of two bones only. The external splint-bone (IV) was of normal proportions, but the internal splint-bone (IIj had almost completely disappeared. The large metacarpal (III) divided in its peripheral third into trapezoid. II, III, two equal cylindrical branches, each of which bore a digit IV, metacarpals. Ilia, composed of three phalanges and bearing a crescentic HI 6, internal and hoof. These two digits were bent across each other in a external sets of pha- shapeless way. Delplanque, Mem. Soc. centr. cVAgric. langes representing du Dep. du Nord, s. 2, ix. Douai, 1866—18(37, p. 295, PL III. fig. 5. Mule, having two distinct toes on each fore foot. The hoofs were shaped like those of the Ox. They were of unequal length. Jolt, Comptes Eendus, 1860, p. 1137. [Perhaps a case belonging to this section.] the digit III of the normal. (After Abloing.) chap, xiii.] DIGITS OF HORSE : SPECIAL CASES. 371 C. Intermediate casks. m trf flWml i* IV T We have now seen cases of increase in number of digits oc- curring by addition to the series, and cases occurring by division of III. It may at first sight seem impossible that there can be any process intermediate between these two. Nevertheless the word sufficiently nearly describes the condition of at least the first of the following cases, and is to some extent applicable to the second also. If the condition shewn in Fig. 112 be compared with those in Figs. 106 and 110 it will be seen that it is really inter- mediate between them. *553. Horse (young): right manus with internal supernumerary digit. The bones are not in place, but have been attached with wires. The condition is as follows. The distal series of carpus remains ami is normal or nearly so. Of the splint-bones, the inner (mcp. II) is thicker than the outer mcp. IV, but it is very little longer. The large metacarpal (III) is almost, but not quite, bilaterally symmetrical about its middle line. In the distal epiphysis the asymmetry is distinct, the internal side of the epiphysis being less developed than the external side. This epiphysis bears a large digit of three phalanges, but instead of being bilaterally symmetrical, like the normal toe of the Horse, each of the joints is flattened on the internal side, the flattening increasing from the first to the third phalanx. The hoof is greatly flattened on its inner face. Internally to the epiphysis of the digit III there is a separate small bone, representing the distal end of an inner metacarpal. This bone bears a digit with two phalanges, and a hoof which is flat on the side turned towards the •other hoof, like that of a calf, though it only reaches to the top of the larger hoof. The first phalanx of this digit is imperfectly divided by a suture into two parts. This division is not that of the epiphysis from the shaft. This extra digit may be thought to be that of mcp. II, but it is clear that it was in part applied to mcp. III. Note also that mcp. Ill is modified in correlation with its presence. Coll. Surg. Mas., in Terat Cat., No. 301. The foregoing case well illustrates the inade- quacy of the view on which an individuality is attributed to members of the digital series. The smaller digit in it is as regards Fig, 112, Bight maims of :i hoi No. ").*)3, from behind, m, magnum. I i tra- pezoid. », unciform. (From a -inrirnen the Sym- in Coll. Surg. Mus.). oi •> _ 1 — 372 MERISTIC VARIATION. [part I. metry of the limb complementary to the larger digit. It is a partial substitute for the inner half of the digit III. If the visible Symmetry of the limb is an index of mechanical relations in which the parts stood to each other in the original division of the manus into digits it is possible that there may have been a mechanical equivalence between the two digits. 554. Mule (between jackass and mare): foetus of about nine months having super- numerary digits. Hind limbs normal. Fore limbs normal as far as peripheral ends of metacarpals. Each manus consisted of three digits. Eight. Metacarpals II and IV normal splint-bones. Metacarpal III normal as far as line of union with its distal epiphysis. The inner part of the sheath of the epiphysis is continued into a rod of fibro-cartilage which supports an extra toe. This rod of cartilage contains a small ossification which represents, as it were, the proximal phalanx of this internal supernumerary toe. Its outer end bears a small second pbalanx, and this bears a small distal phalanx which was covered by a hoof. This extra toe, therefore, is internal to the main continuation of the leg, commences from the line of union between the large metacarpal and its epiphysis, and has three phalangeal joints. The epiphysis of the large metacarpal supports a normal first phalanx with which the second phalanx articulates. This second phalanx is enlarged iuternally [details obscure] to bear a small extra nodule of cartilage which appears to be of the nature of an extra toe. The second phalanx also bears a large third (ungual) phalanx. This ungual phalanx together with the minute supernumerary toe borne by the second phalanx are together encased in a common hoof, but the hoof is divided by a groove into two distinct lobes, corresponding with the division between the two digits which it contains. The whole foot, therefore, has one free internal toe and one large toe bearing a small internal one, which are enclosed in a common hoof. Left fore foot. Fig. 113. The small, lateral metatarsals II and IV, and the large central metatarsal III are normally constructed ; but from the inner side of the sheath of the large metatarsal, upon the line of union between the bone and its epiphysis, arises a fibro-cartilaginous rod, which contains an ossification representing the proximal phalanx of a supernumerary toe (lettered II in fig.). This rod of tissue in its proximal portion is represented in the figure as abutting on, but distinct from the end of the inner small, lateral metatarsal. It bears a cartilaginous second phalanx, containing a small ossification, which articulates with a terminal (ungual) phalanx covered by a hoof. The distal end of the large metatarsal articulates with a large first phalanx, which at its proximal end is of normal width. At about its middle point this phalanx bifurcates into two parts, of which the inner, Ilia, is short and ends a little beyond the point of bifurcation : it bears an ungual phalanx only, which is encased in a hoof. The outer iimb (III b) of the bifurcated first phalanx bears an elongated second phalanx of somewhat irregular shape which carries a larger ungual phalanx covered by a separate hoof. In this foot, therefore, there is an inner toe consisting of three phalanges attached to the inside of the large metatarsal : next, the proximal phalanx of the large toe is divided longitudinally into two parts, bearing (1) an internal toe having only the ungual phalanx and hoof; (2) an outer toe which has a second and third (ungual) phalanx. In the case of both feet, the hoof and ungual phalanx of the outer toe are turned inwards, having an external curved edge and an internal straight edge; but the two inner toes in each case are turned outivards, having their outer edges straight and their inner edges curved. Jolt, A. et Lavocat, N., Mem. de VAc. des Sci. de Tou- louse, S. 4, Tome in., 1853, p. 364, Plates. [Authors regard this case as proof of Fig. 113. Left fore foot of Mule No. 554. IV, the external splint-bone. Ill, the chief metacarpal. Ilia, Illb, internal and external rudi- mentary digits borne by HI. II, a super- numerary digit at- tached to the inner side of III. (After Joly and Lavocat.) •chap, xiii.] DIGITS OF HORSE : SPECIAL CASES. 373 truth of certain views of the phylogeny of the Horse and employ a system of nomen- clature based on these views. This is not retained in the abstract here given.] ARTIODACTYLA. In the domesticated animals of this order digital Variation is not rare, being in the case of the Pig especially common. Such variation has been seen in the Roebuck and Fallow Deer, but not in any more truly wild form so far as I am aware. These varia- tions may take the form either of polydactylism or of syndactylism. Of the former a few cases are known in Ox, Sheep, Roebuck Fallow Deer, and many cases in the Pig ; syndactylism has been seen only in the Ox and in the Pig. The absence of cases of syndactylism in the Sheep is a curious instance of the caprice with which Variation occurs. The phenomena of polydactylism in Pecora may conveniently be taken separately from the similar phenomena in Pigs. Polydactylism in Pecora. At the outset one negative feature in the evidence calls for notice. It is known that in the embryo Sheep rudiments of meta- carpals II and V exist 1 which afterwards unite with III and IV. In view of this fact it might be expected by some that there would be found cases of Sheep and perhaps Oxen polydactyle by develop- ment of the digits II or V. In the Sheep only one case (No. 555) is known that can be possibly so interpreted; and in the I ).\ there is no such case unless Nos. 557, 558, and 559 should be held by any to be examples of the development of II, a view attended by many difficulties. The two following examples are the only ones known t<> nit- in which there can be any question of reappearance of a lost digit, but in neither is the evidence at all clear. *555. Sheep. Some specimens of a small Chilian breed had an extra digit on the hind foot. It was not present in all individuals and was not seen to be inherited; but normal parents were observed to have offspring thus varying. [From the description given I cannot tell whether the extra digit was internal or external. Also, though said to have been on the hind foot, in describing the bones the cannon-bone is twice called metacarpus; probably this is a slip for metatarsus.] The digit was only attached by skin. It contained a bent bone, of which the upper segment was 20 mm. long, the lower 13 mm. Proximally the 1 Rosenberg, Z. f. w. Z., 1873, xxiii. pp. 126—182,^. It. Ac. Sometimes these rudiments remain fairly distinct ;it the proximal end of the eannon-bone, especially of the fore foot. See Xatiicsius, Die Sehafiucht, L880, pp. 187 and 1 13, figs. 374 MERISTIC VARIATION. [part I. cartilaginous head of this bone rested in a pit on the tendon of the flexor brevis digitorum at the level of the end of first third of the cannon-bone, and peripherally it bore an end-phalanx and claw-like hoof, properly articulating. No splint-bones present. [Other details given : it was suggested that the bent bone re- presented an extra ' metacarpal ' and first and second phalanx.] Von Nathusius, H., Die Schafzucht, 1880, p. 143. 556. Capreolus caprea (Roebuck), 2 yr. old, killed in district of Betzenstein, having a slender fifth digit on the inside of each fore foot. In the left there was a small, conical metacarpal element, bearing a digit with three phalanges. The right extra digit had a longer metacarpal piece with epiphysis, but in it there were only two phalanges. Each bore a hoof of about the size of those of II or V. The hoofs curved outwards. Bau- muller, C, Abh. naturh. Ges. Numb., ix. 1892, p. 53, PL Other cases of polydactyle Pecora mostly fall into two groups : (1) Examples of limbs having three digits borne by a large cannon-bone made up of three metatarsal or metacarpal elements, grouped in one system of Symmetry. The axis of Symmetry is then deflected from the normal position, and instead of falling between two digits it approaches more or less to the central line of the middle of the three digits. The degree to which this change of Symmetry takes place corresponds irregularly with the extent to w r hich the innermost digit is developed. This form is known in the Ox only [? Goat]. (2) Limbs in which the series of digits has two more or less definite axes of Minor Symmetry. Both of the systems of Sym- metry thus formed are in addition arranged about one common axis of Symmetry. The nature of this condition will be discussed later. It occurs in Ox, Sheep, Roebuck and Deer. (1) Three digits in one system of Symmetry. *557. Calf. Right manus (Fig. 114) having three digits borne by a single cannon-bone. This is an old specimen of unknown history which was kindly sent to me by Mr W. L. Sclater for examination. Of the carpal bones only the distal row remains, containing a trap- ezoido-magnum and unciform not differing visibly from the normal. The cannon-bone spreads at about its middle into three sub-equal parts, each ending in a separate articular head bearing a trochlear ridge. Between these articular surfaces the only point of difference was that in that of the middle digit (b), the trochlear ridge was rather nearer to the outer surface of the joint, not dividing it into two halves as usual (see figure). The foramen for entrance of the nutrient vessel was in the channel between the external and middle digits. This channel was very slightly deeper than the corresponding channel between the middle and inner digits. Each articular head bore a digit, well formed, CHAP. XIII.] DIGITS : PECORA. 375 of approximately similar lengths, having a hoof. The [hoofs of the outer and inner digits curved to the middle line of the limb, like the -n for Fig. 114. Eight fore foot of a Calf, No. 537. I. The whole foot seen from behind. II. The bones from behind. tpM. trapezoido-magnum. imc, unciform, n, for., nutrient foramen. J", dotted outline shewing position of supposed rudiment of digit V. Sesamoids not shewn. normal hoofs of a cloven-footed animal, but the hoof ol the central toe was convex on both sides. The two accessory hoofs were in place, one on each side as shewn in the figure. The whole manus was very nearly symmetrical about the middle line of this digit. It was notice able that the out^r and inner hoofs were both father narrow in propor- tion to the length of the limb, but the whole width y>i the fool was rather greater than it should be. The small bone considered to repre sent the digit A' articulates with the unciform as usual, being of normal size. Each of the three digits was supplied with flexor and extensor tendons. 558. Heifer having three fully developed toes on each hind limb. The right hind foot described (Fig. 115). The calcaneum, astragalus and cuboido-navicular presented no special abnormality. The cuneiform 376 MERISTIC VARIATION. [part I. Uc 559. series usually consisting of two pieces in the Ox, were here represented by one piece (c and c 3 ), though externally the bone seemed to be in two pieces. The internal portion (c) approximately corresponding in posi- tion with the normal ento-cuneiform was imperfectly and irregularly divided by a groove into two parts. The metatarsus or cannon-bone at its proximal end was almost normal, but from about its middle it spread out into three parts as shewn in the figure, each part ending in an articular surface and bearing a digit, but the trochlear ridge for the innermost digit (ac) was not quite so large as those for the others. From the skeleton it seems clear that this innermost digit could not have reached the ground. Of the three hoofs the middle one was the largest, the other two being nearly equal to each other in size. The outermost hoof curved inwards, and the innermost hoof curved outwards. The middle hoof also curved outwards, but less so than that of a normal digit III, being rather flatter underneath, and having its two edges more nearly symmetrical. The accessory hoofs ('ergots' of French writers) were " in their usual place, on either side of and behind the foot." This speci- men was originally described by Goodman, Ne- ville, Jour. Anat. Phys., 1868, Ser. 2, i. p. 109. The skeleton of the foot is in the Cambridge University Museum of Pathology. In answer to my inquiries Mr G. Daintree of Chatteris, the owner of this animal, kindly gave me the following information. This cow was bought in 1861 and from her a three- toed strain arose, of which about ten generations were pro- duced. The three-toed condition appeared in both males and females, but no three-toed bull was kept, so that the descent was wholly through females. About two in three calves born of this strain had three toes. In one case only were there three toes on the fore feet. The third toe was never walked on. The breed was got rid of because it was at last represented only by males, the last being sold in 1887. The beasts were as good as any other cattle of the same class. Calf. ally resembling the last case is nearly normal. The middle digit is very thick, and is somewhat twisted and flexed. Its ungual phalanx is not specially curved in either direction but it is not truly symmetrical. The innermost digit is thin and short and its ungual phalanx is the hypothesis that not much curved. In this specimen there is a HI and IV represent , . •■ j j, ,. . . . ,, ,. . , . these dibits ot the decided appearance or division in the distal epi- norma i and that ac physis of the metacarpal of the middle digit is an accessory digit. (?III). Coll. Surg. Mus., Terat. Series, No. 300. gener- Left manus having three digits, ?he external digit uan Km) Fig. 115. Right hind foot of heifer, No. 558. As, astragalus. clc, calcaneum. c, c s , parts of a large united bone repre- senting cuneiforms. Ill, IV, ac, letters affixed to illustrate chap. XIII.] DIGITS : PECORA. 377 The following two cases are jjerhaps of the same nature as the foregoing. 560. Goat having three digits in each manus, described by Geoffroy St Hilaire, Hist, des Anom. i. p. 689. The description states that a supernumerary toe was placed between the two normal toes. The middle toe was one-third of the size of a normal toe, but the lower part of the foot was larger than usual. This case was probably like No. 557 ; for from the shapes of the lateral hoofs that case also might seem to an observer at first sight to be an example of a toe " intercalated " between two normal toes. But in No. 5G0 the middle digit was reduced. 561. Calf having a small supernumerary toe 'placed between the digits of the right manus.' This toe had a hoof and seemed externally to be perfect, but on dissection it was found to contain no ossification, but was entirely composed of fibrous tissue and fat. Ercolani, Mem. Ac. Bologna, S. 4, in. p. 772. [Probably case like last, the middle digit being still less developed.] This case is probably distinct from the others given. 562. Calf: right fore foot having three complete metacarpals, each bearing a digit of three phalanges. The two outer were disposed as in the normal, but the innermost metacarpal was quite free from the others and its digit stood off from the others [not grouping into their symmetry as in preceding cases] and having an ungual phalanx [of ? pyramidal shape]. Delplanque, Etudes Teratol., Douai, 1869, n. p. '63, PI. II. Jigs. 2 and 3. [It is difficult to determine the relation of this case to the others and I am not sure that I have rightly understood the form of the inner digit ; but since this digit seems to be outside the Minor Symmetry of the limb it is almost impossible to suppose that it can really be the digit II reappearing. I incline to think that it is more likely that this digit belongs to a separate Minor Symmetry. Compare the similar phenomena in Pigs, No. 570.] On the foregoing cases some comment may be made. It may be noted that the two first (Nos. 557 and 558) present two stages or conditions of one variation. In No. 557 all three digits reach the ground and the change of Symmetry is completed ; in No. 558 the internal digit is not so large in proportion and the plane of Symmetry is not deflected so far. As to the morphology of the three digits in these cases three views are open on the accepted hypotheses. First, the internal digit (if it be admitted to be the supernumerary) may be simply a developed II. The existence of the normal accessory hoofs practically negatives this suggestion, for there can be little doubt that one of them represents II (v. infra, No. 579). The condition of the cuneiforms in No. 558 suggests further that an element is introduced into the cuneiform series between the almost normally formed ento-cuneiform and the ecto-cuneiform. But if this new element is the middle cuneiform, then the internal digit (Fig. 115, ac) may still be II. But the innermost ergot is II in the normal. Or is the inner ergot in this case I, and is this once more a case of tin- development of a normally terminal member, II, and of the addition . of I beyond it in correlation, as we saw in the Horse (see p. 364) ? That such a correlation may exist is unquestionable, and it is not clear that these cases are not examples of it. But even if this principle be adopted here as a means of bringing these cases into harmony with received conceptions it will presently be seen that it still will not reconcile some other cases, notably those of the presence of supernumerary digits in a Minor Symmetry apart from that of the normal series. Yet if the conception of the digits as 378 MERISTIC VARIATION. [part I. endowed with individuality be not of universal application, we shall not save it even if by ingenuity we may represent the facts of the present case as in conformity with its conditions. On the other hand it may be suggested that there is a division of some one digit, and undoubtedly in No. 559 there is a sugges- tion that the innermost digit and the central digit are both formed by division of III. But in the first place this view cannot so easily be extended to Nos. 557 and 558, for in them there is practically no indication that the digits are not all independent and equivalent. The circumstance that the nutrient vessel enters between the external and middle digits may perhaps be taken to shew that they are III and IV ; but this vessel, if single, must necessarily enter in one or other of the interspaces and there is no reason for supposing that, were there an actual repetition of a digit, the vessel must also be doubled, though doubtless repetition of vessels commonly enough occurs with repetition of the organs supplied. Next, the Symmetry of the foot, the development of the middle digit to take a median place, the position of the accessory hoofs, one on either side equidistant from the middle line of the manus, all these are surely indications that this limb was from the first developed and planned as a series of three digits, and not as a series of two digits of which one afterwards divided. The series has a new number of members, and each member is in correlation with the existence of the new number remodelled. It is no part of the view here urged to deny that a single digit, like any other single member of a series, may divide into two (or even into three) for this phenomenon is not rare. Probably enough No. 559 is actually a case of such a division of the digit III. But here in digits as in mammae, teeth, &c, the evidence goes to shew that there is no real distinction between the division of one member to form two, and that more fundamental reconstitution of the series seen in No. 557, for the state of No. 558 is almost halfway between them. In it we almost see the digit III in the act of losing its identity. (2) Limbs with digits in two systems of Minor Symmetry (Double-foot). In dealing with these there are difficulties. The cases are examples of limbs of Calves or Sheep hearing four or rive digits arranged in two groups either of two and two, or of two and three. The members of each group curve towards each other in such a w r ay that each group has a separate axis of Symmetry (Figs. 117 and 118). In several such cases the two groups are related to each other as right and left. Of these facts two different views are possible. For first, a limb of this kind may be a structure like the double-hands seen in Man (pp. 331 to 337), for it is certain that an almost completely symmetrical series of parts is in those cases formed by proliferation of a series normally hemi-symmetrical, how r ever unexpected this phenomenon may be. On the other hand it might be argued that one of the groups of digits represents the normal, and that the other group is supernumerary. chap, xiii.] DOUBLE-FOOT I PECORA. 379 For, as will be hereafter shewn at length in the case of Insects, super- numerary appendages may grow out from a normal appendage and are then a pair, being formed as a right and a left, composing a separate Secondary Symmetry. On the first view the digits of each group are in symmetry with each other like those of the normal limb, the two groups also balancing each other like the halves of a double-hand: on the other view one of the groups would be supposed to be made up of a right and a left digit III, or of a right and a left digit IV. The possibility of the second view being true arises of course in the Artiodactyles from the fact that in them the normal digits compose a bilateral Minor Symmetry. There is nevertheless little doubt that the former account is the right one and that neither group is a Secondary Symmetry ; for were either of the groups really in Secondary Symmetry the supposed super- numerary group should contain at least parts of four digits. Lastly, some of the cases, as No. 566, are clearly of the nature of double limbs, both groups having a common axis of Symmetry. A further difficulty arises from the fact that most of these double limbs are old specimens cut off from the trunk. There is therefore no proof that such a limb is not that of a polymelian in Geoffroy St Hilaire's sense. In other words, though it is practically certain that neither of the groups of digits is itself a system of Secondary Symme- try it is quite possible, and in some cases likely that the whole limb is of this nature. In cases of duplicity, especially of posterior duplicity, the two limbs of one or both of the united bodies frequently form a compound structure somewhat resembling one of the double limbs here under consideration. Hence it is not possible to include with confid- ence great numbers of cases of double limbs described by various writers or preserved in museums, for it is rarely that particulars re- garding the rest of the animal are to be had. This difficulty applies to almost all cases known to me and they are therefore given with this caution. This objection of course does not apply to such a case as No. 564. The following few cases will sufficiently illustrate the different forms of limbs included in this section. They consist of two chief kinds ; first, limbs like Nos. 563 and 566, in which both groups contain two digits, and secondly, cases like No. 567, in which one of the groups contains three digits, recalling the state described in the last section (cp. Nos. 558 and 559). Besides these there are some cases of amor- phous extra digits not here related. 563. Cow, full-grown, right fore foot with four digits arranged in two groups of two, as sbewn in fig. 116. The carpus not preserved. No particulars as to the rest of the animal. This specimen is in the Museum of Douai and is described in detail by Dklplanque, Etudes Teratologiques, n. Douai, 1869, p. 30, PI. I. [The possibility that this may be a limb of a pygomelian is not excluded.] *564. Cervus dama (Fallow Deer). A female having each hind foot double. The division occurs in the upper part of the tarsus, which gradually diverges into two separate tarsi [? metatarsi] and two separate feet. This doe had for several successive years dropped a fawn with the same malformation, though she had been served by several bucks. Ward, Edwin, Proc. Zool. Soc, 1874, p. 90. 565. Two cases, a Roebuck and a Deer, mentioned by Geoffroy St Hilaire {Hist, des Anom., I. p. 697) are probably of this nature. 380 MERISTIC VARIATION. [part I. Fig. 116. Specimen stated by Delplanque to have been the ri^bt foot of a Cow (see No. 563). (After Delplanque.) Sheep, having four toes, each having three phalanges, on each posterior limb (Fig. 117). In each case the toes were arranged as two pairs, the hoofs of each pair being turned towards each other. Each foot had four united metatarsals, marked off from each other by grooves on the surface of the bone, the division between the metatarsals of each pair of toes being clearly marked at the peripheral ends of the bones. In the case of each foot there were parts of a pair of tarsi arranged in a symmetrical and com- plementary manuer about the middle line of the limb. In each tarsus there was a large bone having the structure of two calcanea, a right and a left, united posteriorly ; the upward prolongation, proper to the calcaneum, was present on each side of this bone and projected upwards on each side of the tibia. The astragalus of each foot was similarly a bone double in form, uniting in itself the parts of a right and left astragalus. The left foot had a single fiat bone below the astragalus, representing as it were two naviculars fused together ; and four bones in a distal row, representing presumably two cuboids, and two cuneiform elements. In the right foot also there was a single bone below the astragalus, and four other bones arranged in a way slightly different from that of the other foot. Ercolani, ibid., p. 773, Tav. n. figs. 7 and 8. Fig. 117. Bones of left hindjfoot of a Sheep, No. 566 [q. v.] copied from Ercolani. clc, clc, the two calcanea. a + a 2 , bone representing the two astragali, n + n' 2 , tbe two naviculars, cb, cb, the two cuboids. CHAP. XIII.] DOUBLE-FOOT : PECORA. 381 [A case given by Ebcolani (I. c, p. 783, Tav. 11., figs. 9 and 10) of similar duplicity in a lamb seems to be very possibly a case of double monstrosity. In this animal the hind limbs were altogether absent.] 567. Calf, having five digits on one manus. There is nothing to shew positively whether this specimen is a right or a left, and it is even possible that it is part of a polymelian 1 . Carpal bones gone. Metacarpals four, disposed in two pairs. One pair bear the digits d 4 and d 5 (Fig. 110), which have a common proximal joint. Their ungual phalanges curve towards each other, forming a Minor Symmetry like those of a normal Calf. The other two metacarpals bear three digits ; two (d 3 and d 2 ) articulate with one metacarpal having a divided epiphysis. The other metacarpal bears a digit (d 1 ) of full size curving towards d' 2 . The ungual phalanges of d 2 and d 3 are nearly straight [cp. Nos. 558 and 559.] C. S. M., Terat. Ser., No. 299. 568. Calf: left hind foot similar case : inner group of tico toes curving towards each other and an outer group of three toes of which the middle one was almost bilaterally symmetrical while the hoofs of the other two were each turned towards it. Five metatarsals united but marked out clearly by grooves. Tarsus much as in No. 566. Ercolani, 7. c, p. 774, Tav. i. fig. 8. 569. Calf: left hind foot a somewhat different case, Drew, Commercium Litterarium, Nuremberg, 1736, p. 225, Taf. in. fig. 2. [Description meagre, but figure good. Beginning from the inside the five toes turned (1) outwards, (2) outwards, (3) inwards, (4) outwards, (5) inwards, respectively. There were only four metatarsals, (3) and (4) being both borne on one metatarsal.] POLYDACTYLISM IX THE PlG. Fig. 118. Manus of a Calf. No. 567. d\ d 2 , d 3 , group of three digits [? internal] ; d 4 , d\ group of two digits [? external]. 570. Of the great numbers of feet of poly- dactyle pigs recorded or preserved in museums all I believe are fore feet. No case of a polydactyle hind foot is known to me in the pig. All the cases are examples of proliferation upon the internal side of the digital series. With very few exceptions the variation takes one of two forms, consisting either in the presence of a single digit internal to the digit II, or in the presence of tivo digits, either separate or partially compounded, in this position. A very few cases depart from these conditions 2 . The condition is very usually the same or nearly the same in both fore feet. One extra digit, internal to digit II. Such a digit may either have a separate bone for its articulation in one or both rows of the carpus (as Ercolani, /. c, PI. I. fig. 3), or it may articulate with a half-separated extension of the trapezoid (as Coll. Surg. Mus., Ter. Ser., 297 A), or with the metacarpal or other part of digit II (very common), sometimes simply branching from this digit without an articulation. In no case of which good accounts are to be 1 The Catalogue gives no indication on these points. 2 For example a 1. fore foot in which the -metacarpal of II. bears a rudimentary digit on each side of the digit II, three in all. Ebcolani, Mem. Ac. Bol., 1881, PL I, fig. 1. 38: 9 MERISTIC VARIATION. [part I. had does such a digit group itself into the Symmetry of the normal manus ; but it stands apart, or is bent or adducted behind the other digits, having a hoof which is irregularly pyramidal, curving in neither direction especially. Such a digit has generally three phalanges, and is of about the size of digit II, though not rarely it is large in size approaching more nearly to III than to II (as Coll. Surg. Mus., Ter. Ser. t 297). Two extra digits internal to digit II % This condition is not less common than the last. The two extra digits are borne either by two separate extra carpal bones (Fig. 119, c\ c 2 ), or by one carpal imperfectly divided (Ercolani, I. c, PI. I., Jig. 6); or the metacarpals of the extra digits simply articulate against the carpo-metacarpal joint of II (as in a specimen in my own possession). The extra digits may be double throughout, or the two may be com- pounded in their proximal parts (Ercolani, I. c, PL i., fig. 5 ; also case in Oxford Mus. 1 , 1506, a, in which the two extra digits were ill-formed and of unequal size, having a common metacarpal). Fig. 119 shews such a pair of extra digits in their most complete form. The central part of the metacarpal of II has either never ossified or has been absorbed. As bearing on the question of the relations of parts in Meristic Repetition the fact of most importance is the circumstance that the digits III and IV retain their normal Symmetry, but the two • I II Fig. 119. Left manus of a Pig, No. 571. I. View from in front. II. View from inside to shew the convergence of d 1 and d 2 towards each other. d 1 , d 2 , two extra digits placed internally, c 1 , c 2 , two extra carpal bones with which they articulate, sc, scaphoid, lu, lunar, cu, cuneiform, t, trapezoid, m, magnum, u, unciform. d z — d 6 , the digits II, III, IV, V. 1 For note of this specimen I am indebted to Mr W. H. Benbam. chap, xiil] DIGITS : PIG. 383 extra digits form another Minor Symmetry of their own. It is perhaps worth noting that the metacarpal of the digit lettered d a in the form of its head is nearly the optical image of that of III (d*), but this resem- blance may be misleading and must not be insisted on. Coll. Surg. Mus., Ter. Ser., 298. 572 Wild Boar. Two cases, apparently resembling the foregoing are described, from external examination only, in the wild boar by Geoffroy St Hilaire, Hist, des Anom., 1. p. 696. Syndactylism in Artiodactyla. This phenomenon is known in the Ox and is common in the Pig. In all cases the variation consists in a more or less complete union or absence of division between the digits III and IV. Among the many records of digital variation in the Pig no case relates to union between a lateral and a chief digit, but it is always the two chief digits III and IV that are united. (Compare the case of Man, p. 358.) In this case there is therefore an absence of a division in the middle plane of a bilateral Minor Symmetry, and the parts that remain united are related to each other as optical images. The phenomenon is thus the exact converse of the variation consisting in a division along a plane of bilateral sym- metry which was seen in the Horses Nos. 547 and 550. As was remarked in speaking of similar variations in Man, it is to be noticed that if the union is incomplete, as it commonly is, the peripJteral parts are the least divided, the division becoming more marked as the proximal parts are approached. In the normal Sheep according to Rosenberg 1 the metacarpals II and V are distinct in the embryonic state, afterwards completely uniting with III and IV. The same is presumably true of the Ox ; but whether this be so or not, the digits II and V are in the normal adult not represented by separate bones in the hind foot, and in the fore foot V only is represented by the rudimentary * bone articulating with the unciform. Unusual interest therefore attaches to the observations made by Bo AS and by Kitt of the development of lateral metacarpals and metatarsals (II and V) in Calves having III and IV united. Note also that in two of Kitt's cases there was not only a development of lateral digits but also indications of a division occurring in them. Besides this, in the right fore foot of one solid-hoofed Pig (No. 585) there is a slight appearance of duplicity in the ungual phalanx of the lateral digit V. On the other hand the reduction of accessory hoofs {ergots) in Landois' case, No. 582, seems to be an example of a contrary phenomenon ; for the connexion between the developed lateral metacarpals and metatarsals in Kitt's case (No. 579) must be taken as evidence that the accessory hoofs do really represent II and V. 1 Rosenberg, A., Z.f. w. Z., 1873, xxm. pp. 126 — 132, figs. 14, &c. 384 M ERISTIC VARIATION. [part i. *573. Ox. Young ox having the two digits of the right fore foot completely united together. At the lower extremity of the large double metacarpal (III and IV) of the normal limb a deep cleft is present, which separates the two articular extremities of the bone. In this specimen this cleft was represented only by a sort of antero-posterior channel, at the bottom of which there was a slight groove, which was all that remained as an indication of the original double nature of the bone. At the back of this metacarpal there were only three sesamoids instead of four, and in the central one there was not the slightest trace of duplicity. This sesamoid was placed opposite to the channel above mentioned. The two first phalanges were entirely united, but the vestiges of this fusion could be seen both before and behind and also in the two articular surfaces by which the bone was in contact with the metacarpal. The same was true of the second phalanges. The third phalanges however were so completely fused and so reduced in size that they had the appearance of a single bone. The two small sesamoids were similarly united. The general appearance of this limb was remarkably like that of the Horse. Barrier, Rec. mecL veter., 1884, Ser. 6, Tome 13, p. 490. [No particulars given as to the condition of the other feet of the same animal.] 574. Ox having right fore foot with a single large metacarpal and one splint-bone [? Y]. The peripheral end of the metacarpal had two articular surfaces closely compressed together, and these two surfaces bore but one digit of three phalanges and one hoof like that of a Foal. The preparation was an old one, and with regard to the accessory hoofs there was no indication that could be relied on. Kitt, Dent. Ztschr. f. Thierm., XII. 1886, Jahresb., 1884—5, p. 62, Case No. III. 575. Calf: each foot having only one hoof. The phalanges, sesamoids, meta- carpals and metatarsals, were all normal and the hoofs alone were united. The cavity of the hoof was divided internally into two chambers, which were more distinct in front than behind. Externally each hoof was slightly bifid in front, but the soles of the feet were without trace of division. Morot, C, Bull, de la Soc. de vied, vet., 1889, Ser. vn. T. vi. p. 39. Case I. 576. Calf: killed at 10 weeks old. The left fore foot alone was abnormal, having only one hoof. Viewed from without, this hoof was like that of a young ass, but it bore a slight median depression, which was about 3 cm. wide and only 1 to 2 mm. deep, which was all that remained to shew its double structure. Internally the cavity of the hoof was single, but a horny ridge was present on the inside in the region of the depression. The two unequal phalanges were peripherally united into a single bone, but were separate centrally, and the two parts were not quite symmetrical [details given]. The other parts were nearly normal. Morot, C, I. c, Case 2. *577. Ox. In a newly-born calf the following abnormalities were seen. In the right fore foot there was a small well formed metacarpal bone on the outside of the normal paired metacarpals, and a similar but more rudimentary structure was also present on the inside of the limb. The additional outer metacarpal bore two small phal- angeal cartilages, and with them had a length of about 10 cm., but the supernumerary metacarpal on the inner side was more rudimentary and bore no trace of phalangeal structures. The toes chap, xiii.] syndactylism: ox. 385 borne by the normal metacarpal of the right fore foot were ab- normal, inasmuch as the second and third phalanges were united together. The first pair of phalanges were separate, but their outer ends were modified so as to articulate with the single second phalanx. The distal (third) phalanx bore a groove indicating its double origin, but the second phalanx was without any such groove, and was to all appearance a single structure. The left fore foot also bore an outer and an inner supernumerary metacarpal, but in this case it was the inner supernumerary meta- carpal which attained the greatest size. This inner metacarpal bore two small phalangeal bones, while the outer extra metacarpal was more rudimentary and had no phalanges. The phalanges of the two normal toes were separate in the left foot, but though the bones were of the ordinary formation the two toes were enclosed in a common hoof. Boas, J. E. V., Morph. Jahrb., 1890, p. 530, figs- Boas also states that in the museum of the Agricultural School of Copenhagen are several instances of united toes in the fore foot of the Ox, and that in all these specimens the outer metacarpals (II and V) are larger than they are in normal specimens, but are not so much developed as in the case just described. Boas, I.e. 578. A case [sc. Ox (?)] is also mentioned in which the two normal toes of the hind foot were united, and the median and distal parts of the metatarsals II and V were developed, though they are absent in the normal form. Boas, I.e. *579. Calf having the digits of each foot united and bearing a single hoof. The carpus and tarsus were not seen. Fore foot. The chief digits, III and IV, were completely united in the fore limbs and bore a single hoof, but, in addition to this variation, the metacarpals of the lateral digits, II and V, were developed and ossified. The length of metacarpal II was 9 cm. and its thickness at the proximal end was T5 cm. Metacarpal Y had a length of 8 cm. and a maximum thick- ness of 1*3 cm. at the proximal end. The metacarpal of the united digits, III and IV, measured 13 cm. in length. The metacarpal V was slightly bifid at its distal extremity, and here presented two articular surfaces. With the internal of these there articulated a bone measuring 2 cm. by 0-5 cm., and attached by fibrous tissue to the end of this bone there was a cartilaginous nodule. The external end of metacarpal V bore a rod-like piece of cartilage, 1 cm. in length. This and the cartilaginous nodule of the other part of the digit together formed the basis of one of the accessory hoofs (ergots), but the horny covering itself was divided by a deep cleft into two imperfectly separate parts. To the metacarpal of II was loosely articulated a bone 2*5 cm. in length, to which a nodule of cartilage was attached. The end of this digit was covered by an accessory hoof, which was imperfectly double like that of V and contained a second cartilaginous nodule, which was distinct from the first and was not supported by any proximal bone. The union between the digits III and IV was complete, and the re- b. 25 386 MERISTIC VARIATION. [part i. suiting structure with its hoof was like that of the Horse. The artic- ulations were perfectly mobile. At the ruetacarpo-phalangeal joint there were two sesamoids only. [With this division in the lateral digits on fusion of III and IV compare Pig, No. 585.] Hind foot. The digits III and IV were united as in the fore feet, but the single hoof was more pointed. The metatarsals II and V were developed. The latter was 12-7 cm. long, and was united to the large metatarsal above, but was free below, and was joined by a liga- ment to its accessory hoof. That of II began in the middle of the metatarsus, being cartilaginous and of about the thickness of a goose- quill ; it was connected with the accessory hoof by a ligament only. Kitt, Dent. Z. f Thierm., xil, 1886, Jahresb. 1884-85, p. 59, Case No. I, Jin. *580. Calf. Three of the feet had each one large digit (III and IV) formed much as in the last case. But in the dried preparation it could be seen that in each of these feet there were four accessory hoofs, and connected with them several ossicles irregularly placed, re- presenting phalanges 1 and 2 connected by ligaments with lateral metacarpals. The fourth foot [which 1] had only three accessory hoofs, but the phalanges 1 and 2 of the digits III and IV were partially separated from each other, and there were two distal phalanges, one for each digit ; but instead of being side by side, they were placed one behind the other, both being encased in a single hoof. Kitt, I.e., p. 61, Case No. II. 581. Calf. A right fore foot having the two chief digits (III and IV) represented by one digit with one hoof. The distal end of the common metacarpal had two articular surfaces in close contact which bore a digit in which there were only slight traces of duplicity. The meta- carpal of the digit V was represented by two small bones, one beside the upper and one beside the lower end of the large metacarpal. These two ossicles were connected together by a ligament which is prolonged downwards as far as the accessory hoof, and contains two nodules of cartilage. On the median side of the foot there is no rudiment of the metacarpal II, but the accessory hoof contains a nucleus of partly ossified cartilage. Kitt, I.e., p. 63, Case IV. 582. Calf having a single hoof on each fore foot. In external appearance, the hoof was a single structure, but its anterior portion shewed two projections which sug- gested that it was really a double structure. The outer accessory hoof was present on the right foot in a very much reduced form, but the corresponding structure of the inner side of the foot was entirely absent, and a marked ' turning-point ' in the hairs (Haancirbel) indicated the place where it should normally have been de- veloped. In the left foot the accessory hoofs were in the same condition as in the right foot, but the ' turning-point ' was not formed at all. There were no skeletal structures corresponding to the accessory hoofs. The skeleton of left fore foot was prepared. In it the metacarpal was 125 mm. long, having a deep cleft on its anterior face, indicating the line of union of the two metacarpals. The two articular heads, which in a normal animal of the same age are separated from each other by about 5 mm., are in this specimen united by the inner edges of their anterior borders. The proximal phalanges formed a single bone, 32 mm. long. The division between the two bones was visible as a cleft on the anterior surface, in which place the two ossifications were distinctly separated from each other ; on the posterior surface the union between the two is continued for half the length. The second phalanges formed a typically single bone, as did also the distal phalanges which bore the hoof. The foramina for the two nutrient arteries of the two toes remained double and entered the single bone, one on each CHAP. XIII.] SYNDACTYLISM : PIG. 387 583. side. Landois, H., Verh. d. naturh. Ver. d. preuss. Rheitil., Bonn, 1881, S. 4, vin. p. 127. Pig. " Solid-hoofed " pigs have been mentioned by many writers from the time of Aristotle. The fact that they have been reported as occurring in many parts of the world makes it likely that the variation has often arisen afresh. The first case (No. 583) is the only instance of complete union of III and IV in the pig that is known to me. The variation is most commonly simultaneous in fore and hind feet. As seen, it occurs in many degrees. Several specimens not separately mentioned below are in the Coll. Surg. Mus. and other collections. A fore foot and a hind foot of the same individual, in which the two chief digits were completely united, viz. represented by a single series of bones. In each case the two chief metacarpals and metatarsals (III and IV) were respectively represented by a single large bone, and with each a single digit of three phalanges articulated. The bones of these digits were straight, and not curved as they are in an ordinary foot in which two toes are present. There was not the slightest trace of duplicity, and the lateral digits were placed symmetrically on either side. The sesamoids were two in number A B Fig. 120. Bones of feet of solid-hoofed Pig, No. 583, from specimens in the Museum at Alfort, described by Barrier. A. Left manus from in front. B. Left manus from behind. C. Left pes from in front. The numbers II and V indicate the digits so numbered in the normal. 25—2 388 MERISTIC VARIATION. [part i. instead of four. The carpus and tarsus appear to have also been changed in connexion with this unification of the digits, for in the distal series at least the normal number of bones was not present. [The feet had been cut off across the tarsus and carpus before being received. By kind permission of the authorities at Alfort I examined these specimens and made the sketches in Fig. 118. I could not satisfactorily identify the bones of carpus and tarsus. The proximal parts were covered by a large exostosis.] The extensor of the phalanges ended in three tendons only, and the same was true of the deep and superficial flexors. The central tendon in each case however shewed signs of its double nature. Barrier, Rec. mid. ve'ter., 1884, Ser. 6, Tom. xiii. p. 491. 584 A skeleton of a solid-hoofed pig exists in the Museum of the Royal College of Surgeons of Edinburgh which was presented by Sir Neil Menzies of Rannoch, Perthshire. Inquiries instituted by Struthers (1863) elicited the following facts. " The solid-hoofed pig has been well known and abundant on the estates of Sir Neil Menzies at Rannoch for the last forty years. Most, if not all of them, were black. They were smaller than the ordinary swine, and seem to have had shorter ears. They liked the same food and pasture as the common swine, and showed no antipathy to herd with them. They were more easily fattened, though they did not attain so large a size as the ordinary swine ; their flesh was more sweet and tender, but some of the Highlanders had a prejudice against eating the flesh of pigs which did not " divide the hoof," unaware apparently that the Mosaic prohibition applied to all pigs. A male and female of the solid-hoofed kind w T as brought to Rannoch forty years ago, by the late Sir Neil Menzies, which was the commencement of the breed there ; but I have not been able to learn Avhere they were brought from. Although they did not breed faster than the common kind, they multiplied rapidly, in consequence of being preserved, so that the flock increased to several hundred. " At first, care was taken to keep them separate, on purpose to make them breed with each other, but after they became numerous they herded promiscuously with the common swine. As might be expected in a promiscuous flock, some of the young pigs had solid and some cloven feet, but I am unable as yet to say whether any definite result was ascertained as to the effect of crossing ; whether any experi- ments were tried as to crossing ; or whether after the promiscuous herding, some of the pigs of the same brood presented cloven and some solid hoofs. " No pig was ever known there with some of its feet solid and some cloven ; nor, so far as is known, was there any instance of young born with cloven feet, when both parents were known to be solid- hoofed. The numbers diminished — for what cause is not apparent ; so that last year there was only one or two — one of them a boar, which died ; and now the solid-hoofed breed appears to be extinct in Rannoch." 585. " Fore foot. — The distal phalanges of the two greater toes are re- presented by one great ungual phalanx, resembling that of the Horse, CHAP. XIII.] SYNDACTYLISM : PIG. 389 but longer in proportion to its breadth. The middle phalanges are also represented by one bone in the lower two-thirds of their length, presenting separate upper ends for articulation with the proximal phalanges. The proximal phalanges are separate through their entire length. The whole foot above the middle phalanges presents the usual arrangement and proportions in the hog." Middle Phalanges. "There is no symphysis or mark indicating a line of coalescence of the two phalanges. The surface across the middle is somewhat irregularly filled up to nearly the level of each lateral part. Each half of the phalanx, as indicated by the notch between the separate upper ends, has the full breadth of the proximal phalanx above it." Distal Phalanx. The middle part of this is raised above the lateral parts, and is partially separated from them by a fissure on each side, giving it an appearance as of the union of three bones. The end of the phalanx is notched like that of the horse ; it bears no trace of symphysis. ' ' The ungual phalanx of one of the lesser internal toes of the fore foot presents a bifurcation reaching half the length of the phalanx." See Fig. 121. I. II. Fig. 121. I. A right fore foot of a solid-hoofed Pig, No. 585, from in front. The ungual phalanx of the digit V is bifid [cp. Nos. 579 and 580]. (After Struthers.) II. Middle digits of foot of solid-hoofed Pig, No. 587. .r, an extra ossification wedged in between the phalanges of III and IV. (After Elliott Coues.) " Hind foot. In the hind foot only the distal phalanx is single.... There is no trace of double origin to the bone." Struthers, J., Edin- burgh New Phil. Jourii., 1863, pp. 273— 279, Jigs. 586. A P air of solid-hoofed pigs received by Zoological Society of London from Cuba * in 1876. The sow gave birth to a litter of six [the solid-hoofed boar being presumably the father]. The six young were three males and three females. The hoofs wen solid like those of the parents in two males and one female : in the others the hoofs were cloven as in the normal pig. The feet of one of the solid-hoofed males of thi> litter were dissected, and it was found that "the proximal and second phalanges are separated as usual, whilst at the extreme distal ends of the ungual phalanges 390 MERISTIC VARIATION. [part i. these bones are completely fused together ; and, further, a third ossicle was developed at their proximal ends, where they are not completely united, between and above them " [cp. No. 587]. " It might have been imagined that the deformity was simply the result of an agglutination along the middle line of the two completely-formed digits ; but such is not the case, the nail-structure being absent in the interval, where it is replaced by bone with a transverse cartilage below it. The nail is con- tinued straight across the middle line of the hoof, as in the horse." Garbod, A. H., Proc. Zool. Soc, 1877, p. 33. 587. Domestic pigs having the two central hoofs compounded into a single solid hoof have been known to occur several times in America. The two other toes remain distinct in these cases. A breed of pigs having this character is said to have been established in Texas, which transmits this peculiarity in a definite way. In this breed the peculiarity is said to have been so firmly established that "no tendency to revert to the original and normal form is observable in these pigs." A cross between a solid-hoofed boar and an ordinary sow is said to produce a litter of which the majority shew the peculiarity of the male parent. " On the sole of the hoof, there is a broad, angular elevation of horny substance, apex forward, and sides running backward and outward to the lateral borders of the hoof, the whole structure being curiously like the frog of the horse's hoof. In fact it is a frog, though broad, flattened, and somewhat horseshoe-shaped, instead of being narrow, deep and acute as in the actual frog of the horse. This arcuate thickening of the corneous sub- stance occupies about the middle third of the whole plantar surface of the foot." The terminal phalanges are united together, and above this single bone is another independent ossification lying between the second phalanges of the two digits, which remain distinct. [Cp. No. 586.] Coues, Elliott, Bull. XI. S. Geol. Geogr. Surv., iv. p. 295, fig. 588. Case resembling the above reported from Sioux City, Iowa, in which these pigs were bred for some time and were advertised for sale, with the statement that they were also of superior quality. Other cases given from different parts of the United States. In one of these it is stated that one hind foot was thus formed [the others being presumably normal]. Auld, R. O, Amer. Nat., 1889, xxiii. p. 447, fig. 589. Fig. In all four feet the digits III and IV partially united and covered by one hoof. The metacarpals and first phalanges were separate in each case but the second and third phalanges of the two digits were united together. The common hoofs were not compressed laterally, as in some of the cases seen in the Calf, and the small digits II and V were unmodified. Kitt, Deut. Zt. f. Thierm., xn. 1886, Jahresb., 1884-85, p. 64, Case IV, figs. POLYDACTYLISM IN BlRDS 1 . The whole number of cases of Polydactylism recorded in birds generally is small. The phenomena however seen in the Dorking fowl are well worthy of attention and have scarcely been adequately treated. I propose here to give an account of this case, mentioning instances seen in other birds and indicating so far as may be their relation to the facts of the Dorking. Five-toed fowls have been known from very early times. The character is now most definitely associated with the Dorking, though it is also considered necessary in Houdans for show purposes. It is likely that the latter breed derived the fifth toe from the Dorking. Fifth toes may often be seen to occur in other breeds, but I cannot quote a satisfactory record of their appearance in pure strains. In the foot of an ordinary four-toed fowl the hallux articulates with the tarso-metatarsus by a separate metatarsal. The hallux in such a foot most often has two phalanges. In its commonest form the five- toed foot departs from this normal in the fact that the hallucal meta- 1 See also the case of Rissa, p. 396. chap, xiii.] DIGITS I BIRDS. 391 tarsus bears two digits instead of one. The morphological nature of these digits is obscure. Some have judged that one of them is .1 " prse-hallux ; " Cowper ' sees in the internal toe the true hallux, and argues that the digit commonly called the hallux is really the index ; Howes and Hill 2 consider that the normal hallux has split into these two digits. The diversity of these views comes partly from an insuffi- ciency of the area of fact over which the inquiry has been extended, for it will be found that the conditions are very various and shade off imperceptibly in several directions. As in all cases of Meristic Series, the first question relates to the position of these digits in the system of Symmetry of the limb. Are they in a Successive Series with the other digits, or do they balance them ? Are they in Succession to each other or do they balance each other as images 1 Turning to the facts with these considerations in view it will be seen that no general answer can be given, but that the condition is sometimes of the one kind and sometimes of the other. For there are not merely two conditions, a four-toed and a live-toed, but there is a whole series of conditions and according to the cases chosen so may the question be answered. By examining a few score of fowls' feet many sorts may be seen. 590. (1) The most usual five-toed foot is that figured by Cowpeb (I.e., p. 2-19), in which the metatarsal of the hallux bears two digits, an outer one of two phalanges and an inner of three phalanges. For pur- poses of description let us call the outer the hallux. In this foot then the hallux is the least digit, and the members of the digital series increase in size on either side of it. 591. (2) But not rarely is found a state like the last save that the inner digit is borne by the proximal phalanx of the hallux. This is very common. The two digits may then be about equal in size, or more often the hallux is the smaller. 592. (3) Hallux more or less perfectly divided into two digits with a common base, having (a) two, or (b) three phalanges (as in Howes' case Fig. 5). This state is practically that of the human "double-thumb" (see p. 350), and, just as in that phenomenon, the duplicity may be of various extent, often affecting only the nail and distal phalanx. f ><•- tween the two parts of such a double digit there is often that relation as of optical images found in human double-thumb, the curvatures of the two parts being equal and opposite. But if both digits are of good - and are separate up to the metatarsal this equality is rarely it ever found, and one of the digits, generally the innermost, is the larger. In this condition therefore there is a Succession from the hallux to the inner digit just as in (1). So the condition of double-hallux, that is to say the representation of one member of a series by two members in bi- lateral symmetry, shades off' imperceptibly into the condition in which a new member is formed in Succession to the terminal member. It should be noted that this case presents a remarkable difference from that seen in the like cases of variation on the radial Bide of the hand of Man. In Man the states of true double-thumb are just as in the Fowl; but if there is a difference or Succession between the two parts 1 Jour. Anat. Phys., xx. p. 593; and xxm. p. 242. - Ibid., xxvi. p. 31)5, jigs. 392 MERJSTIC VARIATION. [pam I. it is the external l which is the greater, being in several cases a three- phalanged digit shaped like an index (see No. 486). Nevertheless in the Fowl it is the internal which is the greater. The conditions in the following cases are not far removed from those named above. 593. Archibuteo lagopus (Rough-legged Buzzard): specimen in good condition shot near Mainz, being otherwise normal. The toes of the left foot were placed as usual in a bird of prey, but on the outside 2 of the hind toe was a much smaller accessor}- toe. This accessory toe was attached to the hind toe almost as far as the base of the claw of the latter. The claw of the accessory toe was half the size of that of the hind toe. In the left leg the muscles of the thigh and shank were less developed than usual. Toes of right foot abnormally arranged, being all directed forwards. The three normally anterior toes were on the inside of the series, and the toe which should properly be single and directed posteriorly was double and was directed anteriorly. These abnormally disposed toes were not functional. The right leg was much more developed than the left, and it seemed as if the bird had habitually stood on the right leg. vox Reichenau, W., Kosmos, 1880, vn. p. 318. 594. Gallinula chloropus (Moorhen): specimen killed in Norfolk in 1846. "Each of the hind toes possessed a second claw, which in the right foot merely springs from about the middle of the true toe, but in the left is attached to a second toe, which proceeds from the original one, about half-way from its junction with the tarsus." Extra toe and claw in each case attached outside 2 of the true hind toe. Guexey, J. H., and Fishek, W. R., Zoologist, 1601. Guinea-hen having double hallux ; of the two digits the external 2 was the longer. Geoffroy St Hilaire, Hist, cle Anom., i. p. 695. Division of digits II and III. 595. Anas querquedula, L. (Garganey Teal): wild specimen having the left foot abnormally formed. In it there was no toe occupying the place of the hallux, but the digits II and III [using the common nomenclature] were partially bifurcated. In the digit III, the extremity only was divided, but each part bore a separate nail and there was no web between these secondary digits, which were somewhat irregular in form. The digit II divided in about its middle into two nearly similar digits, which were united by a web. The nails of these digits were hypertrophied. Erco- laxi, Mem. Ace. Bologna, S. iv. T. in. p. 804, Tav. in. fig. 1. 596. (4) From the condition seen in (3) it might be supposed that duplicity of the hallux is the least possible step in the progress of the four-toed form towards the five-toed. It is only one of the least possi- ble steps. For in a few cases upon the base of the digit recognizable as the hallux, and standing in the normal place of the hallux, may be found a minute rudiment of a digit, sometimes with a nail, sometimes without. Between this and the well-formed fifth toe all conditions exist. There are thus, as usual in the numerical variations of Meristic Series, two least conditions, one being found in duplicity of a single member, the other taking the form of addition of a rudimentary member beyond the last member. 597. Passing now from the simpler conditions of the variation to the more complex, several distinct states may be mentioned. The diverg- ence from the normal may be greater either by the presence of two extra digits, or by change in the position of the extra digit or digits. 1 The only case to the contrary is that mentioned by Wixdle, Jour. Anat. Phys , xxvi. p. -440, in which a three-phalanged digit stood on the radial side of a pollex. This ease has not been described. See pp. 326 and 352. 2 In reading these records it should be remembered that owing to the backward direction of the hallux the apparent outside is morphologically inside, and probably this is meant in each case. chap, xiii.] DIGITS : BIRDS. 393 Tico extra digits are said to be not uncommon in the Dorking but I have myself seen only one case. A foot of this kind is figured by Cowper 1 , and in it the appearance is as of an extra digit of three joints ( ? all phalanges) arising internally and proximally to the hallucal metatarsal, which already bears two small and sub-equal digits. In the case seen by myself there was one large internal digit with three phalanges sepa- rately articulating with the tarso-metatarsus, and the hallucal metatarsus bore a digit divided peripherally, bearing two nails related as images. Here therefore there was a double hallux, and internal to it a separate digit. 598. The evidence regarding extra digits in other positions, though small in amount, is of importance as a light on the morphology of these repeti- tions of digits. We have seen that the ordinary extra digit is, with the hallux, borne on the hallucal metatarsal. In one of Howes' cases (I. c. figs. 2 and 3) this metatarsal instead of simply articulating with the shank of the tarso-metatarsal ivas continued up to articulate also with the tibio-tarsus. From this state the condition in which a separate digit (or digits) articulates with the tibio-tarsus only is not far removed. Of this condition I know no detailed account in the Dorking, though it is referred to by Lewis Wright 2 , but I have met with the following cases in other birds. • 599. Aquila chrysaetos (Golden Eagle): having two extra toes borne by right metatarsus [left foot is not described]. The two extra toes attached to upper part of the back of the metatarsus. Each bears a full-sized claw which was curved backwards and upwards. One of the toes bore six scutella on the morphologically upper surface and four on the plantar surface. The other toe, which was more completely united to the metatarsus along its whole length, bore only a single scutellum on the plantar surface. The rest of the foot was normal. Jackel, A. J.. Zool. Gart., xv. 1874, p. 141, fig. 600. Pheasant: right foot bearing a thin and deformed digit articulating internally with the distal end of tibio-tarsus. Hallux normal. Left not seen. Specimen received from Mr W. B. Tegetmeier. (301. Pheasant: each leg bears a large extra digit of irregular form attached to the middle of anterior surface of tibio-tarsus. The two legs almost exactly alike, but in one the digit is firmly and in the other loosely attached to tibio-tarsus. Specimen kindly sent by Mr Tegetmeier. 602. Buteo latissimus S , having extra digit on right leg. the toe was well formed, with two phalanges, bearing perfectly formed claw, loosely attached internally to tibio-tarsus just above articulation with tarso-metatarsus. Coale, H. K., Auk, 1887, iv. p. 331, fig. [Cp. No. 593.] 603. Turkey having two imperfectly separate digits [? images] attached to process of tibio-tarsus. Two cases differing in degree: hallux normal. Ercolani, Mem. Ac. Bologna, Ser. iv. in. PI. in. figs. 2 and 3. 604. Pheasant: somewhat similar case, in which two such digits were similarly placed, but one was large and the otber small. Ibid., fig. 4. 605. Larus leucopterus. For the following case I am indebted to Professor R. ' Ridgway, Curator of the Department of Birds, in the United States National 1 Cowper, J., Joum. Anat. Phys., xxm. p. 249. 2 "Perhaps the most difficult point in judging Dorkings, however, La to watch against malformations of the feet which have been fraudulently removed ; for the abnormal structure of the Dorking foot is very apt to run into still more abnor- mal forms, which disqualify otherwise fine birds for the show-pen. Birds are not unfrequently produced which possess three back toes, or have an extra toe high ap the leg; or, in the case of the cock, with supernumerary spurs, which have been known to grow in every possible direction We have on two occasions seen prizes awarded to birds which shewed unquestionable traces of such amputation...." The Illustrated Book of Poultry, 1886, p. 331. 394 MERISTIC VARIATION. [part I. Museum. The specimen is No. 76,221 in that collection, marked "Greenland, Sept. 1877 ; Loc. Kumlien." The accompanying figures were kindly made for me A B Fig. 122. Larus leucopterus, No. 605. A. Eight foot seen from in front. B. The same from the internal side. C. Left foot from in front. From a drawing of specimen in U. S. Nat. Mus., kindly made for me by Prof. Eidgway's direction. under Professor Eidgway's supervision and sufficiently shew its structure (Fig. 122). [It will be seen that the hallux in A, the right foot, appears on the outside; this I conceive is due to partial rotation to shew the abnormal toes.] Besides these there are a few amorphous cases of extensive repetition of digits in birds. These facts shew how fruitless a work it is to try to find a general statement which shall include all the cases. There is an almost unbroken series of conditions starting from either duplicity of the hallux, or from the presence of an internal rudimentary chap, xiii.] DIGITS : LIZARD. 395 digit, up to a condition somewhat resembling that of " double- hand " in Man. If the first digit behind the hallux is the prae- hallux, what are the digits on the tibio-tarsus ? If on the other hand the appearance of an extra digit internal to the supposed hallux is to be evidence that this " hallux ,: is the index, it may equally be argued that if two digits come up internal to the " hallux " then the supposed hallux is the medius, and so on inde- finitely. Again, though with Howes and Hill we may accept the cases of double-hallux as evidence that an extra digit may appear by division of the hallux, which is indisputable, we must equally accept the cases Nos. 597 and 598 as evidence that extra digits may grow directly from the tarsus or even from the tibia, though the hallux remain single and unchanged. And between these two there is no line of distinction ; they pass into each other. Do not these things suggest that we are looking for an order that does not exist ? Is it not as if we should try to name the branches of a tree in their sequences ? Possibly Continuous numerical Variation in Digits : miscellaneous examples. Under this heading are placed in connexion a few cases of great interest. Whatever may be held as to the relation to the problem of Species of the phenomena hitherto described, it can scarcely be doubted that the following are instances of Variation which at least may be of the kind by which new forms are evolved. Great interest would attach to a determination whether the reduction of the digits in these cases is a' continuous or a discon- tinuous process, but unfortunately these phenomena have been statistically studied by no one, and it is not possible to do more than make bare mention of the fact that such Variation is known to occur. There is no statistical evidence as to whether the indivi- duals in any one locality may not fall into groups, dimorphic or polymorphic in respect of the degree to which the digits are developed (compare the case of the Earwig, Introduction, p. 40). As an inquiry into the Continuity of Variation such an investiga- tion would be exceptionally valuable. In the case, for instance, of Cistudo mentioned below, such a statistical inquiry should surely not be hard to make. *606. Chalcides. This is a genus of Lizards belonging to the family Scincidse. In several genera of this family the limbs are reduced or absent, differences in this respect being frequent among species of the same genera. (See Boulenger, Catalogue of Lizards in Brit. Mus., 1887, m. pp. 398, &c.) Mr Boulenger kindly shewed me a number of Lizards of the ..... genus Chalcides from the shores of the Mediterranean basin which strongly resemble each other in colour and general appearance, but which contained almost a complete series of conditions in respect 396 MERISTIC VARIATION. [part i. of the development of the limbs and digits, ranging from C. ocellatus and C. bedriagce with pentadactyle limbs fairly developed, through C. lineatus (tridactyle) and 0. tridactylus to C. guentheri in which the limbs are minute conical rudiments. Amongst the species of this series great individual variations occur. 607. Chalcides mionecton : normally four digits on each foot. A specimen in Brit. Mus. kindly shewn to me by Mr Botjlenger has on each hind foot five digits. 608. C. sepoides : Mr Botjlenger tells me that the normal num- ber of digits on each foot is five, but that specimens occur having four digits on each foot. 609. Cistudo. This genus includes the North American Box- turtles as defined by Agassiz (N. Amer. Testudinata, Gontrib. to N. H. of U. S., I. p. 444). These animals are widely distributed to the E. of Rocky Mountains. On the hind feet of some of them there are three digits, while others have four. Gray (P. Z. S., 1849, p. 16) described two Mexican specimens which agreed in having three large claws on the hind foot with no appearance of a fourth claw, and even scarcely any rudiment of the fourth toe, which was then believed to be present in the other members of the genus. To this three-toed form he gave the generic name Onychotria, but in Brit. Mus. Cat, 1855, he gave up this name as a generic distinction, describing the Mexican form as Cistudo mexi- cana, giving three toes on the hind foot as a definite character. Agassiz in 1857 (I.e.) divided Cistudo into four species, giving to the Mexican form the name C. triunguis, and he states that the western and south-western type is remarkable for having almost universally only three toes on the hind feet. The toe which is missing is the outer toe and " it fades away so gradually that the genus Onycliotria cannot stand." The form found from New England to the Carolinas is called by Agassiz G. virginea = C. Caro- lina, and he states that he received a three-toed specimen from N. Carolina which agreed in all other respects with those from New England. Putnam (Proc. Boston, N. H. S., x. p. 65) stated that the three- toed form found in the South is only a variety of C. virginea, and that he had seen two specimens which had three toes on one hind foot and four on the other. 610. Rissa 1 . The common Kittiwake (R. tridactyla) as found in 1 In illustration of the possible bearing of these facts on the problem of Species reference may be made to the fact that among birds there are several examples of species differing from their near allies by reason of the absence of the hallux. Speaking of this feature in Jacamaraleyon tridactyla, Sclater observes: "In the present bird we meet with another example of the same character [viz. a monotypic form], and with one, perhaps, more isolated in its structure than any of those above mentioned, Jacamaraleyon being notably different from all other members of the Galbulidae in the absence of the hallux. At the same time we must be careful not to put too high a value upon this at first sight seemingly important chap. xiii. j DIGITS : K1TTIWAKE, ELEPHANT, &C. 397 this country and in N. Atlantic has no hallux, but only a small knob without a nail in its place. No variation in respect of this digit is recorded 1 . Birds not distinguishable from the Atlantic Kittiwake occur in the North Pacific, but amongst these Pacific specimens birds are found occasionally as rarities having a hallux " as large as it is in any species of Larus " (Coues, p. 640). This feature also exhibits gradatious. Specimens are described by Coues and also by Saunders having the hallux including the nail 2 in. long, with a perfect claw. These are given as extreme examples. Saunders remarks that this hallux is small for the size of the bird, stating that another species of similar size, L. canus, had a hallux '5 in. long. Of these specimens of R. tridac- tyla from Alaska one had the nail of the hallux developed, though less so than in the extreme case. Saunders states further that the variation is not always equal in extent on both feet of the same individual : he considers that the extreme form is probably rare and local. Coues, E., Birds of North-West (U. S. Geol. Surv. Terr.), 1874, p. 646; and Saunders, Howard, P. Z. 8., 1878, pp. 162—64. 611. Rissa brevirostris : a species from the N. Pacific distinct from R. tridactyla shews a similar variation in the development of the hallux, though in a smaller degree. A specimen has no claw on right hind toe and only minute speck on left ; another has no hind nail whatever ; another has small black nails of unequal size on the two hind toes. Saunders, H., I. c, p. 165. (312. Erinaceus. E. europceus has a large hallux, while in E. diadema- tus it is only 4 mm. in length, and in E. albiventris it is normally absent in adults. An adult female S. albiventris had a minute hallux in the left hind foot, represented by a claw and ligamentous structures, the rjhalanges being absent 2 . In a female a few months old a minute hallux with usual number of phalanges was present on both sides. The presence or absence of a hallux has often been considered a suffi- cient ground for the formation of a new genus. Dobson, G. E., P. Z. &, 1884, p. 402. 613. Elephas. In both the Indian and African elephant the number of digits represented by bones is five, both in the fore and the hind foot. The number of hoofs differs in the two species. The African elephant has normally four on the fore foot and three character, as the same feature occurs as is well known, not only in certain genera of other allied families (such as Alcedinidre and Picida}), but even in a genus of Oscines (Cholornis), in which group the foot- structure is generally of a very uniform character." Sclater, P. L., Monograph of t he Jacamars and Puff-Bird* t 1879 -82, p. 50. 1 Mr A. H. Evaxs has called my attention to a recent paper by Clarke (Ibis, 1892, p. 442) giving an account of a minute rudiment of the hallux in embryos of R. tridactyla from Scotland. 2 Compare facts as to the loss of the hallux in Mungooses (Herpestida 1 ), Thomas. O., P. Z. S., 1882, p. 61. 398 MERISTIC VARIATION. [part I. on the hind foot, and I am not aware that variations from this number have been seen. In the Indian elephant there is variation, and though I cannot give any complete account of the matter the following particulars may be of interest. According to Buffox the ' Elephant ' has generally five hoofs on both fore and hind feet, but sometimes there are four, or even three 1 . He gives a particular case of an Indian elephant with four hoofs on each foot, both fore and hind feet. Tachard 2 , to whom Buffon refers, was desired by the French Academy to notice on his journey in Siam, whether elephants had hoofs, and he states that all that he saw had five on each foot. Possibly the four- toed variety does not occur in Siam. I am indebted to Mr W. T. Blanford for the information that the natives of India attach importance to the number of hoofs, and also for the following references. Hodgson 3 gives a sketch of elephants with four hoofs on each foot, marked " Elephas Tndicus, var. isodactylus nob., Hab. the Saul forest," together with the following note : " The natives of Nepal distinguish between the breeds with four toes [sic] on all the feet and those with five to four toes." Sanderson 4 speaking of this says that some elephants have but sixteen hoofs, the usual number being five on each fore foot and four on each hind foot ; and that in the native opinion 'a less number than eighteen hoofs in all disqualifies the best animals.' Forsyth 5 also alludes to the same fact. Taken together these accounts seem to shew that five on the fore foot and four on the hind foot is the most usual number, but that both the number on the fore foot may diminish to four and that on the hind foot may increase to five. Several text-books mention the subject but I know no statistics regarding it. In view of the different number characteristic of the African elephant this variation has some interest. In particular it would be of use to know whether the variation exhibits Discontinuity, and also to what extent it is symmetrical. Inheritance of digital Variation. 614. Recurrence of digital Variation in strains or families is frequent, but though many observations on the subject have been made no guiding principle has been recognized. To the general statement that digital Variation, whether taking the form of poly dactyl ism or other- 1 Buffon, Hist. Nat., xxviii. p. 201. The mention of three hoofs must I think refer to the African species, which Buffon does not distinguish from the Indian. In the Cambridge Museum (Catal. 699) is an old preparation of the skin of an elephant's foot having three hoofs. This is declared by the Catalogue to be the fore foot of an Indian elephant. Perhaps this is a mistake. 2 Tachard, Voy. de Siam, 1687, p. 233. 3 Hodgson, B. H., Mammals of India, MS. in Zool. Soc. Library. 4 Sanderson, G. P., Wild Beasts of India, p. 83. 5 Forsyth, J., Highlands of India, 1872, p. 286. chap, xiii.] INHERITANCE OF DIGITAL VARIATION. 399 wise, does very commonly appear in the offspring or kindred of the varying individuals I can add nothing. It should be mentioned that though in families exhibiting digital Variation the forms that the change takes may differ (in some cases widely even among individuals nearly related) yet on the whole the variation, if recurring at all, more often recurs in a like form. This holds good apart from the rarity of the particular form of variation. The facts described by Farge (I.e., infra) are exceptionally interesting in this connexion. In the family described by him duplicity of the thumbs occurred in the paternal grandmother, while the father and three children had their thumbs of the three-phalanged form as in No. 483. This case strikingly illustrates the well-known principle that Meristic variability may appear in the same strain or family under forms morphologically very dissimilar. Attention is also called to the circumstance that in the case of the three toes in the ox (No. 558) the descent was wholly through females, and the same was almost certainly true in the polydactyle cats (No. 480). In the case of the syndactyle pigs the evidence of maintenance of the variation in the strain is very clear (No. 584). See also No. 564. As regards digital Variation in Man the following are the best genealogical accounts : Anderson, Brit. Med. Jour., 1886 (1), p. 1107. Billot, Mem. vied, milit., 1882, p. 371. Boyd-Campbell, Brit. Med. Jour., 1887, p. 154. Fackenheim, Jen. Zte., 1888. Fotherby, Brit. Med. Jour., 1886 (1), p. 975. Furst (see Canst. Jahresb., 1881, p. 283). Harker, Lancet, 1855(2), p. 389. Lucas, Gm/s Hosp. Rep., xxv., p. 417. Morand, Mem. Ac. Sci., 1770, p. 140. Muir, Glasg. Med. Jour., 1884. Pott, Jahresb. d. Kinderh., xxi., p. 392. Potton 1 quoted by Gruber from de Bansi . Bull. Soc. d'Anthrop., 1863, iv. p. 616. Struthers, Edin. Neio Phil. Jour., 1863(2), pp. 87 et seqq. Wolf, Berl. klin. Wochens., 1887, No. 32. Farge, Gaz. hebd. de med. et chir., Ser. 2, n. 1866, p. 61. Case given Loud. Med. Gaz., 1834, p. 65. Association of digital Variation with other forms of Abnormality. (315, In the great majority of cases of polydactylism the rest of the bod} is normal, the limb or limbs varying alone. There are however a cer- tain number of examples of polydactylism in association with other abnormalities ; as for instance with phocomely, cyclopia, double uterus, hare-lip, defective dentition, defect of tibia, - 26—2 404 MERISTIC VARIATION. [part I. but its own external parts may more or less balance its own inter- nal parts. This relation differs greatly in different animals, the Minor Symmetry being nearly complete in the Artiodactyles and in the Horse, but much less so in the human manus and pes, &c. The matter now for consideration is the influence or consequences of the existence of this symmetry in the Meristic Variation of digits ; and conversely the light which the observed phenomena of Variation throw on the nature of that relation of symmetry. It will be seen that in some points the two halves of a bilaterally symmetrical limb behave just as do the two halves of the bilaterally symmetrical trunk, while in other points their manner of Varia- tion is different. Thus, the digit III of the Horse may divide into two halves related to each other as images, bearing hoofs flattened on their adjacent edges ; that is to say, the two resulting parts are formed not as copies of the undivided digit, but as halves of it, a condition never seen in division occurring anywhere but in the middle line of a bilateral Symmetry. In the syndactyle feet of the Pig or the Ox the converse pheno- menon exists ; for the digits III and IV, which normally stand as images of each other, are here wholly or in part compounded to form a digit to which the uncompounded digits are related as halves. Thus far the connexion between the geometrical relations of the digits and the modes of their Variation is clear and simple, and does not differ from that maintained in the Major Symmetry. But in proceeding further there is difficulty. If, for instance, the manus or pes of a Horse possesses within itself the properties of a bilateral Symmetry, then the splint-bone II may be supposed to be in symmetry with the similar bone IV. It would therefore be expected that on the occasion of the develop- ment of II to be a full digit, the splint-bone IV would at least not unfrequently develop, thus exhibiting that similarity and simul- taneity of Variation which we have learnt to expect from parts in symmetry with each other. Nevertheless such an occurrence seems to be extremely rare. Then arises a further question: if the digit II develop simultaneously, say in the two fore feet, would the mechanical conditions of which Symmetry is the outward expression be satisfied without a corresponding change in the digit IV of the fore feet ? Is the frequent absence of symmetry in the variation of the halves of the Minor Symmetry in any way connected with the possibility that the two Minor Symmetries together may be maintaining their relations to each other as parts of a Major Symmetry ? Of course as to this we know nothing, but the existence of this double relation should be remembered. In several other phenomena of digital Variation the influence of Symmetry is to be suspected. Reference may first be made to the series of changes seen in the Cat's hind foot in correlation with chap, xiv.] SYMMETRY IN DIGITAL VARIATION. 405 numerical change. The bones of this pes do not normally exhibit any very clear bilateral symmetry \ Yet on the appearance of new digits the foot is reconstituted and its parts are, to use a metaphor, c deposited ' in a system of bilateral symmetry a whose completeness is proportional to the degree of development of the new digits. What may be the meaning of this extraordinary fact one cannot yet guess. The fancy is constantly presented to the mind that there is in the normal foot a condition of strain, that the balance between the right foot and the left is a condition of imperfect stability, and that upon the introduction of some unknown disturbance this balance is upset and each foot settles down as a separate system. But I see no way of testing this fancy and no way of following it further. Still more complex are the facts seen in the human hand. There is here first the fairly complete series of conditions ranging from the normal, through the three-phalanged thumb up to the several Conditions in which extra digits upon the internal side of the limb seem to have sprung up to balance the four normal digits ; but on the contrary there is the exceptional case of the Macacque's foot (No. 504) where the extra parts are, as I believe, external. (Besides these there are the wholly distinct series of "double- hands," which will be spoken of below.) The former cases taken alone would certainly suggest that there is an imperfect balance or system of symmetry subsisting between the thumb and the four fingers of the normal manus, but to this suggestion there are numerous difficulties which need hardly be detailed in this preliminary glance at the phenomena. With more confidence it can be maintained that the pollex and perhaps the hallux of Man is in itself a Minor bilateral Sym- metry, apart from the four fingers, for it may divide into equal parts related as images. The same is true of the hallux of the Dorking (p. 390), and probably of the extra digit or digits some- times arising from the tibio-tarsus of the Turkey for example (see No. 603). Besides this the facts of the frequent syndactylism between the digits III and IV of the human manus, taken in connexion with the phenomena of the Pig and Ox, suggest that the four fingers may have among themselves again a relation of the nature of Symmetry. 1 In the normal pes, though all the claws are retracted to the outside of the second phalanges, yet the claws of digits III and IV rest close together, that of III being external to its pad, while that of IV is internal to its pad, forming, so far, a relation of images between these two digits. In the polydactyle foot it is a remark- able feature that, though the bones are in symmetry about an axis passing between II and III, the relation of the claws of III and IV to their pads remains almost normal, still giving a superficial appearance of symmetry between these two digits. (In the polydactyle pes the pads are mostly rather narrower.) 2 It will be remembered that this symmetry appears not merely in the lengths of the several digits but in the manner of retraction of the claws and in the corre- sponding form of the second phalanges, three digits being fashioned (in the case of six perfect digits) as right digits and three as lefts. 406 MERISTIC VARIATION. [part i. It has been mentioned that there is some evidence to shew that in the human pes it is the digits II and III which are most frequently syndactyle, even up to the point of being (in No. 529) apparently represented by a single digit, and in this connexion it will be remembered that in the polydactyle pes of the Cat it is also between these digits that the new axis of Symmetry falls. These scanty allusions to the possible influences which Sym- metry may exercise over Meristic Variation of digits will suffice to indicate the nature of the problem to those who may care to examine it. It is with hesitation that so indefinite a matter is spoken of at all. Nevertheless it is likely that if any one can find a way of interpreting these indications the result will be con- siderable. (5) Duplicity of limbs. In the evidence as to the digits of Man facts were given respecting the state known as Double-hand, and some similar cases were referred to in Artiodactyles. In these instances the digital series, and to some extent the limb, is in its new shape made up of the external parts of a pair of limbs compounded together in such a way that there is a partial duplicity of the limb, the two halves being more or less exactly complementary to each other and related as images 1 . This phenomenon in its perfect form must be essentially distinct from the other cases of increase in number of digits ; for in the double-hands the limb developes an altogether new bilateral symmetry (see especially No. 492). Between cases of duplicity in limbs and the other forms of polydactylism confusion can only arise when the nature of the parts is ambiguous. As has been stated, in all certain cases of double-limbs the two are compounded by their internal or pneaxial borders, but the case of Macacque No. 504 was peculiar in the fact that there was in it a presumption that the two limbs were not a pair but in Succession. In Arthropoda there are a very few cases of true duplicity in appendages comparable with the double-hands. These cases will be dealt with hereafter. 1 The fact that a structure naturally hemi-syminetrical, needing the limb of the other side to balance it, may on occasion develop as a complete symmetry is most paradoxical, but no other interpretation of the facts seems possible. The phenome- non is of course comparable with that observed by Driesch in the eggs of Echinus, where eacb half-ovum developed into a whole larva on being separated from the other half-ovum (see p. 35, Note). It will be shewn that in almost every case in which such an appearance is found in the extra appendages of Insects this appear- ance is misleading, and that the extra parts have a Secondary Symmetry of their own ; but no such way through the difficulty is here open. chap, xiv.] DISCONTINUITY IN DIGITAL VARIATION. 407 (6) Homceotic Variation in terminal digits token a new member is added beyond them. This is a principle that has been several times seen in Meristic Variation, and in Chapter x. Section 7, it was treated of at length in the case of teeth. Some few illustrations of the same principle occur among the evidence as to digits. It has been seen for in- stance how that, upon the appearance of an extra digit on the radial side, the digit which stands in the position of pollex may have three phalanges and resemble an index (No. 485, &c). Similarly it was found that upon the formation of a large digit externally to the minimus the digit standing in the ordinal position of the minimus may have an increased proportional length (No. 509). Still more important is Morand's case (No. 510), in which the most external digit had muscles proper to a minimus, while the digit standing in the ordinal position of the minimus was without them. The cases of extra digit in the Horse (No. 536, &c.) still more clearly illustrate the principle, if the view of the nature of those cases taken in the text be received. It should be expressly stated that in digits, as in teeth, it is not always that the terminal member is promoted on becoming penultimate. Such promotion is indeed rather exceptional in digits, but the fact that it may occur is none the less a phenome- non of great significance. (7) The absence of a strict distinction between duplicity of a given digit and other forms of addition to the Series. This subject has been so often spoken of in connexion with special cases that it is unnecessary here to make more than brief allusion to it. The same principle was shewn to be true of teeth (p. 270) and of mammae (p. 193), and there is little doubt that it is true of Meristic Series generally. Facts illustrating the matter in relation to digits will be found in the evidence as to duplication of pollex and hallux in Man (p. 351), as to duplication of the hallux in the Fowl (p. 391), in the evidence of cases in the Horse of variation intermediate between division of III and development of II (p. 371), and in the cases of three-toed Cows (p. 377). In almost all the animals in which any considerable range of digital Variation is to be seen it is possible to find a series of cases making an insensible transition from true duplicity, or division into two equivalent parts whose positions and forms are such that they maybe reasonably looked upon as both representing a normally single member, up to the condition in which while the series contains a greater number of members, each member nevertheless stands in a regular Succession to its neighbour. Upon the proper understanding of this proposition and upon the recognition of its truth hang those corollaries before enuntiated 408 MERISTIC VARIATION. [part i. touching the false attribution of the character of individuality to members of Meristic Series. (8) Discontinuity in digital Variation. The evidence that the Meristic Variation of digits may be discontinuous is often rather circumstantial than direct. If for example in the case of the Horse any one chooses to suppose that every polydactyle horse had in its pedigree an indefinitely long- series of ancestors in which the size of the extra digit progressively increased, it would not be easy to produce direct evidence that this was not the fact. But as regards the human examples such evi- dence is abundant, many of the most marked cases being the offspring of normal parents and there can be no reasonable doubt that the same would be found true of other animals. But it may fairly be replied that until it shall have been shewn that formations like those described as variations may be estab- lished in a natural race or species the contention that the Varia- tion of digits may be discontinuous is so far weakened. To this I would reply by referring to the case of Cistudo, Chalcides, and the other similar examples ; for though in respect of these forms the evidence is sadly imperfect yet it plainly indicates that very distinct and palpable variation may be found between different individuals. And since it is actually known that there may in these points be considerable differences between the two sides of the body it may safely be assumed that at least the same differ- ences may occur between parent and offspring. We may therefore take it that there is in these cases some Discontinuity of Variation, though until some one shall have examined statistically such cases as that of the Box-turtles or of the Kittiwakes, as to the magnitude of the Discontinuity it is not possible to speak. If hereafter Discontinuity shall be shewn to occur in many such cases it will be difficult to resist the sugges- tion that similar numerical diversity elsewhere characterizing the digital series of various forms may have come about by similarly discontinuous Variation. (9) Relation of the facts of digital Variation to the problem of Species. This relation is both direct and indirect : direct, inasmuch as some of the conditions seen to occur as variations are not far removed from those known as normals in other forms ; and indi- rect, since those strange and paradoxically regular dispositions of digits which are found among the variations bear witness to the influence of the principles of Symmetry, and prove that there are modes in which Variation may be controlled and may produce a result which has the quality of regularity and order of form independently of the guidance of Natural Selection. chap, xiv.] DIGITAL VARIETY AXD SPECIES. 409 Of actual variations from the arrangement of digits character- istic of one form to that characteristic of another there are as ye1 scarcely any examples. The cases given on pp. 395 to 39S being the most evident. For the rest, that is to say examples of arrangements happen- ing as variations matching no normal, some may say in haste that with their like Zoology has no concern. It would be convenient if those who make this careless answer (as many do) would mark the point at which it is proposed to begin this rejection of the evidence of Variation. Few perhaps realize how impossible it is to give a real meaning to these distinctions. As regards digits, for instance, I suppose that no one who holds the doctrine of Common Descent would refuse to admit the evidence of Variation as to the hallux of Hedgehogs (No. 612) as exemplifying the way in which species may be built up — if indeed species are built up of varia- tions at all. And if this case is admitted, by what criterion shall we exclude cases of the formation of a hallux in the Dog ? But if these are not excluded it is difficult to shew good reason for not admitting the case of the three-phalanged digit placed as a hallux in the Cat (No. 472) with all the curious series of which that is only the first term. Are we quite sure that because there is no Carnivore with a three-phalanged hallux therefore such a creature could not exist in nature ? Still more difficult is it to shew cause why duplicity of the hallux should be set apart as a variation not capable of being perpetuated or of becoming part of the specific- characters of an animal, seeing that there is actual evidence both in the case of the Dorking fowl and in the St Bernard dog that it may become at least an imperfectly constant character. In connexion with the subject of this section many suggestions with special bearing on particular cases, both positive and negative, will strike every reader. In the present imperfect state of the evidence it would be premature to pursue these. It may however be well to mention that several writers, especial ly Joly and Lavocat (No. 554). have seen in the cases of divided digit III in the Horse an indication that the digit III of the Horse corresponds with the digits III and IV of the Artiodactyles. The evidence as to syndactylism between these two digits in Ox and Pig would probably be considered t<» give support to the same view. But while we may note that the relations of the digits with the carpus and tarsus of these forms, were comparative evidence absent, should absolutely prevent any one from seriously maintaining such an opinion, nevertheless the fact that such closely similar systems of Symmetry may thus aris< independently of each other is of interest. CHAPTER XV. linear series — continued. Minor Symmetries : Segments in Appendages. Meristic Repetition along the axes of appendages is very like that along the axis of the body. Just as particular numbers of segments or repetitions along the axis of Major Symmetry charac- terize particular forms, so particular numbers of joints characterize particular appendages. Such numbers frequently differentiate species, genera, or other classificatory divisions from each other. In the evolution of these forms therefore there must have been change in these numbers. Those who are inclined to the view that Variation is always continuous do not perhaps fully realize the difficulty that besets the application of this belief to the observed facts of normal structure. For in those many groups whose genera or species may be distinguished from each other by reason (amongst other things) of difference in the number of joints in some particular appendage or appendages, will any one really maintain that in all these the process by which each new number has been intro- duced was a gradual one ? To take a case : even were evidence as to the manner of such Variation wanting, would it be expected that the Longicorn Prionidae, most of which have the unusual number of 12 antennary joints, did, as they separated from the other Longicorns which have 11 joints, gradually first acquire a new joint as a rudiment which in successive generations in- creased ? Or, conversely, did the other Longicorns separate from a 12-jointed form by the gradual "suppression" of a division or of a joint ? If any one will try to apply such a view to hundreds of like examples in Arthropods, of difference in number of joints in appendages of near allies — forms that by the postulate of Common Descent we must believe to have sprung from a common ancestor — he will find that by this supposition of Continuity in. Variation he is led into endless absurdity. Surely it must be clear that in many such cases to suppose that the limb came through a phase in which one of its divisions was half-made or chap, xv.] JOINTS OF ANTENNAE. 411 one of its joints half-grown, is to suppose that in the comparatively near past it was an instrument of totally different character from that which it has in either of the two perfect forms. But no such supposition is called for. With evidence that transitions of this nature may be discontinuously effected the difficulty is removed. The frequency of Meristic Variation in appendages is much as it is in the case of body-segments. On the one hand there are series containing high total numbers of repetitions little differentiated from each other (e.g. the antennas of the Lobster), and in these Meristic Variation is common ; on the other hand in series containing few segments much differentiated from each other, such Variation, though not unknown, is rare. Of the latter a few instances are here offered. That the} 7 are so few may perhaps be in part attributed to the little heed that is paid to observations of this class. Records of this kind might indeed be hoped for in the works of those naturalists to whom the title " systematic " has been given ; but unfortunately the attention of these persons has from the nature of the case been drawn rather to features whereby species may be kept apart than to facts by which they might be brought together. From the lack therefore of records of such variations their absence in Nature must not lightly be assumed. To quote but one case : in the common Earwig the numbers and forms of the antennary joints are exceedingly variable, but in many special treatises on Orthoptera, I cannot find that this variability is spoken of, and if alluded to at all the only notice is given in the form "antennas 13- or 14-jointed." Antennae of Insects. Prionid,e. I am indebted to Dr D. Sharp for the information that the number of antennary joints in certain Prionidse varies. In Longi- corns generally the number of joints is constantly 11. Dr G. H. Horn of Philadelphia who is specially acquainted with this group, has kindly written to me that of six species of N. American Prioni four species have 12 antennary joints constantly in both sexes. Besides these he gives the following cases of Variation. It will be seen that in both of these the normal number is much greater than it is in the other species 1 . *61G. Prionus imbricornis : females have very constantly 18 joints; males have 18 to 20. A male in Dr Sharp's collection has only 17 joints in each antenna. 1 In Prionus imbricornis and P. fissicornis doubt may be felt whether the trifid apex should be reckoned as one joint or as two, but this applies equally to each individual. I have counted it as one. 412 MEMSTIC VARIATION. [part t. *617. Prionus fissicornis: the female has 25, and the male 27 — 30, the note on the preceding species applying here. 618. Polyarthron. A Prionid beetle, in which the male has curious many-jointed feather-like antennae, according to Serville has always 47 joints, but Thomson (Syst. Ceramb., 1866, p. 284) says the number varies with the species and individually. A male in Dr Sharp's col- lection has 45 joints in each antenna and a female has 31 in each. 619. Lysiphlebus is a Braconid (Hymenoptera) parasite on Aphides. From a colony of Aphides on a bush of Baccharis viminalis 121 speci- mens of Lysiphlebus were reared : of these 57 were males and 64 were females. The number of joints in the antennae varied as follows : Males. 1 4 joints 18 specimens. 15 37 16 1 .... 15 on one side and 16 on the other 1 Females. 12 7 13 54 14 1 12 on one side and 1 3 on the other 2 In those having a different number of joints in the right and left antenna?, the last joint of the antenna which contained the fewest joints was longer than the last joint of the antenna with the larger number of joints. Nevertheless this relation did not hold throughout : for example in the case of the male with 16 joints, the last joint was of the same length proportionally as that of the males with only 14 joints. As a rule the specimens with fewer antennary joints are smaller than the others. Variations were also seen in coloration, in the proportional length of the tarsi, and in the presence or absence of the transverse cubital nervure, but none of the characters divided the sample consistently, it was therefore inferred that the individuals belonged to one species of Lysiphlebus, (L.citraphis, Ashm.) From another colony of Aphides living on a rose-bush 58 specimens of Lysiphlebus were bred, and no characters were found by which these could be separated from those bred from the Aphis of Baccharis. In the case of the second sample the joints of antennae were as follows : Males. 14 joints 10 specimens. 15 19 14 on one side and 1 5 on the other 2 Females. 12 2 13 25 CHAP. XV.] ANTENNAE : BEETLE. 413 The number of antennary joints is employed as a specific character in the classification of Lysiphlebus by Ashmead, Proc. U. S. Nat. Mus., 1888, p. 664). Coquillet, D. W., Insect Life, 1891, Vol. in. p. 313. *620. Donacia bidens. (Phyt.) A female found by Dr D. Sharp at Quy Fen in company with many normal specimens had in each antenna eight joints instead of eleven as in the normal. As shewn in the figure (Fig. 123) the antennae of the two sides were exactly Fig. 123. Donacia bidens ? . I. Normal antennae, eleven joints in each. II. Abnormal specimen, having eight joints in each antenna. No. 620. alike, and the insect was normal in all other respects. I am much obliged to Dr Sharp for shewing me this specimen. Forficula auricularia, the common Earwig. In the various species of Forficula the number of joints in the antenna? differs, the numbers 11, 12, 13 and 14 being all found as normals in different species 1 . As regards F. auricularia most authors give 14 as the number of antennary joints. Serville 2 gives 13 or 14. A number of adult earwigs examined by myself with a view to this question shewed that there is great diversity in regard to the number of antennary joints. The whole matter needs much fuller investigation but the preliminary results are interesting. The commonest number is 14, which occurs in perhaps 70 — 80 per cent. The next commonest is 13, which was seen in a considerable number, while 12, and even 11 occur in exceptional cases. Different numbers were frequently found on the two sides. 1 Brunner von Wattenwyl, Prodr. eur. Orth., 1882. The number in F. auri- cularia is given by Brunner as 15, but I have never seen this number. It is no doubt an accidental error. The same mistake is repeated by Shaw, E., Ent. Mo. Mag., 1888—89, xxv. p. 358. 2 Suites a Buffon: Orthop., 1839. 414 MERISTIC VARIATION. [part I. * As is usual with appendages the whole length of the antenna? differed a good deal independently of the number of joints. 621. On comparing antennas with different numbers it seemed that the proportional length of the first two joints was nearly the same in all, but in the third joint there was great difference, as shewn in Fig. 124. The left antenna in Fig. 124, I may be taken to be the normal form with 14 joints. In it both 3rd and 4th joints are small. The right antenna of the same specimen has 13 joints and in most of the 13-jointed antenna? the arrange- Fig. 124. Various forms of antennas of adult Earwigs {Forficula auricularia), all from one garden and taken at one time. I. Specimen having the left antenna normally 14-jointed, and the right 13-jointed. No. 621. II. Both antennae 13-jointed. No. 622. III. Both antennae 12-jointed. No. 623. IV. Bight antenna normally 14-jointed ; left antenna 12-jointed. No. 624. Note that the rights and lefts are arranged as marked by letters r and I. The antennae were so fixed for drawing in order to bring them side by side after the bend from the first joint. This figure was drawn with the camera lucida by Mr Edwin Wilson. ment was much as shewn in this figure. As shewn, the 3rd joint especially is here rather longer than in the 14-jointed form, but several of the peripheral joints are also a little longer, so that chap, xv.] antenna: earwigs. 415 though the 13-jointed antenna is not as a whole so long as the 14-jointed antenna of the same individual it is longer than its first 13 joints. 622. But besides the common 13-jointed form occasional specimens are as shewn in Fig. 124, II. Here both antennae are 13-jointed, the 3rd joint being much longer, and the 4th a little longer than the corresponding joints of the normal with 14 joints. Two specimens were seen having this structure in both antennas, thus presenting a difference which, did it occur in a form known from but few specimens, would assuredly be held to be of classificatory importance. 623. In another case (Fig. 124, III) each antenna contained only 12 joints, the 3rd, 4th and 5th being all of greater length than in the normal. 624. Fig. 124, IV shews a case in which there was on the right side a normally 14-jointed antenna but that of the left side was 12-jointed, agreeing nearly with those in Fig. 124, III. In considering these facts the possibility that some or all the abnormal states may result from or be connected with regenera- tion must be remembered ; but from the frequency of the varia- tions, from their diversity, and from the fact that symmetrically varying individuals are not rare, it is on the whole unlikely that all can owe their origin to regeneration. It will besides be noticed that it is in the proximal joints that the greatest changes are seen, and it must surely be rarely that these are lost by mutila- tion. The difficulty — indeed the futility — of attempting to adjust a scheme of individuality among such series of segments must here be apparent to all. We can see the change in number and the change in proportions, and we are doubtless entitled to affirm that the differences between these several kinds of antennae are reached by changes occurring chiefly in the neighbourhood of the 3rd and 4th joints ; but not only is there no proof that the changes are restricted to these joints, but the appearances suggest that there are correlated changes in many, and. perhaps in all of the joints. Tarsus of Blatta 1 . : 625. Among the families of the class Orthoptera the number oi tarsal joints differ. In Forficularia the number of tarsal joints 1 In connexion with variation in the number of joints in legs I may mention the case of Stenopterus rufus ? (Longicorn) described by Gadbatj de Kkkville as having each tibia divided into two parts by an articulation [Le Naturaliste, 1889, B. 2, xi. p. 9, fig.)} but upon examination it proved that each tibia had been sharply bent at each of these points, and there was no real articulation. I have to thank M. Gadeau de Kerville for lending me this insect together with many interesting specimens of which mention will be made hereafter. 416 MERISTIC VARIATION. [part I. is 3, in Blattodea, Mantodea and Phasmodea 5, in Acridiodea 3, in Locustodea 4, in Gryllodea 2 or 3 1 . The fact, originally observed by Brisout de Barneville 58 , that in various species of Blattidse the number of tarsal joints may vary from five to four is therefore of considerable importance in a consideration of the manner in which these several forms have been evolved from each other. The species in which Brisout observed this variation were ten in number and belonged to four genera of Blattidse. At my suggestion Mr H. H. Brindley has made an extended investigation of the matter and a preliminary account of the results arrived at was given in the Introduction (p. 63). It was found that of Blatta americana 25% of adults have one or Fig. 125. I. Normal five-jointed left tarsus of Blatta americana. tarsus of the same having four joints. n II. Right more tarsi 4-jointed. In Blatta orientalis these cases amounted to 15°/o > an d of 102 B. germanica examined, 16 had one or more 4-jointed tarsi. The abnormality occurred sometimes in one leg and sometimes in another, being more frequent in the legs of the second pair than in those of the first, and much more frequent in the third pair than in either. In some specimens legs of the two sides were symmetrically affected, but this was exceptional. Only one specimen has hitherto been met with having all the tarsi 4-jointed. There was a slightly greater frequency in females than in males. When the examination of these abnormal tarsi was begun it was supposed that the variation was congenital, but as explained in a note to the Introduction (p. 65) doubt subsequently arose as to this. It is well known that Blattidse like many other Orthoptera have the power of renewing the appendages after loss, and Mr Brindley found by experiment that when the tarsus of Blatta orientalis is renewed after mutilation the resulting tarsus is 4-jointed. It was also found that 4-jointed tarsi were much more frequent in adults than in the young. The question therefore arises, is the 4-jointed tarsus ever congenital 1 1 From Bbunneb von Wattenwyl, Prodr. europ. Orthop., 1882. • Ann. ent. soc. France, s. 2, vi. 1848, Bull., p. xix. CHAP. XV.] tarsus of Blatta. 417 To this question a positive answer cannot yet be given ; but as about 200 young B. orientalis have since been hatched from the egg and no 4-jointed tarsus was found among them, while in every instance of regeneration the new tarsus had four perfect joints, there is now a presumption that the variation does not occur congenitally. On the other hand it should be mentioned that the 4-jointed tarsus was seen in 3 specimens, found by Mr Brindley, which by their size would be judged to have been newly hatched. But even if the variation shall hereafter be found to be sometimes congenital it is certain that this occurrence must be very rare, and there can be no doubt that in the majority of cases the 4-jointed tarsus has arisen on regeneration 1 . As mentioned in the Introduction, the existence of the 4-jointed tarsus, whatever be the manner of its origin, raises two questions. Of these the first is morphological, relating to the degree to which the joints exhibit the property of individuality, and the second is of a more general nature, relating to the application of the theory of Natural Selection to such a case of discontinuous change. The interest of the case in its bearing on both of these questions arises from the Discontinuity, which was complete. All the tarsi seen were either 5-jointed or 4-jointed, and in none of the latter was any joint ever rudimentary, or any line of articulation imperfectly formed (except in a single specimen having a deformed tarsus). There were 5-jointed tarsi and 4-jointed tarsi : between them nothing. Following the usual methods of Comparative Anatomy it must be asked which of the 5 joints is missing in the 4-jointed tarsus'? With reference to this question careful measurements of the separate joints were made by Mr Brindley in 115 cases of 4-jointed tarsi occurring in legs of the third pair in B. americana; and for comparison the separate joints of 115 normal 5-jointed third tarsi of the same species were also measured. (It is clear that the legs compared must belong to the same pair, 1st, 2nd or 3rd, for there is considerable differentiation between them. From this circumstance it was comparatively difficult to obtain a large number of cases, and hence the smallness of the whole number measured. But though of course statistics respecting a larger number would be more satisfactory there is no reason to think that by exami- nation of a greater number of cases the result would be materially affected.) In the two sets of tarsi the total length of each tarsus was reduced to 1-000, the lengths of the joints being correspondingly reduced. The arithmetic means of the ratios of the several joints to the whole lengths of the tarsi to which they belonged was as follows : Five-jointed form. 1st joint •532 2nd joint •156 3rd joint •095 4th joint •019 5th joint ■168 Four-jointed form. 1st joint •574 2nd joint •183 3rd joint •061 4th joint •179 1 The circumstance that in Mr Brindley's observations the variation was in all species more frequent in females than in males, and that the frequency differed in b. 27 418 MEEISTIC VARIATION. [part i. The evidence derived from these numbers lends no support to the expectation that any one particular joint of the 5-jointed form is missing from the 4-jointed, or that any one joint of the 4-jointed form corresponds with any two joints of the 5-jointed ; for if the numbers are treated with a view to either of these hypotheses it will be found impossible to make them agree with either. It appears rather that the four joints of the 4-jointed form collectively represent the five joints of the normal. The other question upon which the statistics bear has already been stated in the Introduction. In any appendage the ratio of the length of each joint to the whole length of the appendage varies ; but if it varies about one normal form it will be possible to find a normal or mean value for this ratio, and the frequency with which other values of the same ratio occur will be inversely proportional to the degree in which they depart from the normal value. The curve representing the frequency of occurrence of these values will then be a normal Curve of Error. The form of this curve will indicate the constancy with which the normal proportions of the tarsal joints are approached. If the proportional lengths of the tarsal joints vary little then the curve representing the frequency of their departure from their normal value will be a steep curve, but if these proportions are very variable and have little constancy, then the curve will be flatter. The probable error will thus in the case of each value be a measure of the constancy with which it conforms to its normal proportions. As explained in the Introduction, upon the hypothesis that all constancy of form is due to the control of Natural Selection, it would be anticipated that the 4-jointed tarsus, if a variation, would be very much less constant in the proportions of its joints than the 5-jointed tarsus. It was however found that as a matter of fact the proportions of the joints of the 4-jointed form were very nearly as constantly conformed to as those of the joints of the normal tarsus. The evidence of this is as follows. The total length of the 5-jointed tarsus being L, and t 1 , t 2 , &c. being the lengths of its several joints, I, T 1 , T 2 , &c. representing t l T 1 the same measurements in the 4-jointed form, the ratios — &c, — &c, represent J-J v the proportional length of the several joints in each case. The values of these ratios were then arranged in ascending order in their own series and the measures occupying the positions of the first, second, and third quarterly divisions noted 1 (indicated hereafter by Q 1 , M and Q 3 respectively). The probable error or t 1 T 1 variation of each ratio y , — , &c. will then be represented by the expression Q3_ Ql — - . Inasmuch as the joints are of different lengths, to compare the results each must be converted into percentages of the mean length of the joint concerned. These results are set forth in the accompanying tables. the different pairs of legs may seem to point to the existence of some control other than the simple chances of fortuitous injury. As regards the latter point it is not unlikely that the legs of the third pair, being longer and less protected, may be more often mutilated than the others. 1 As described by Galton, F., Proc. Roy. Soc, 1888-9, xlv. p. 137. CHAP. XV.] tarsus of Blatta. 419 Five-jointed tarsus. t l «-' t* t* t 5 L L L T* L Q l •521 •152 •095 •046 •162 M •529 •156 •099 •049 •168 Mean error as percentage of M •535 1-3 •160 2-6 •101 3-0 •051 5-0 •174 3-6 Four-jointed tarsus. T 1 rp'2 T i T i I I I I Q 1 •565 •178 •060 •172 M •575 •183 •064 •177 Q 3 Mean error as percentage of M •584 1-6 •189 3-0 •068 6-2 •183 3-1 It is thus seen that the percentage variation of the ratios of the several joints to the total length is very little greater in the case of the abnormal than it is in the normal tarsus. As regards the longer joints these results are probably a trustworthy indication of the amount of Variation, but in the case of the shorter joints the errors of observation must no doubt be so great in proportion to the smallness of the lengths to be measured that no reliance should be placed on results obtained from them. As evidence that in spite of the small number of instances examined the general result is satisfactory it may be mentioned that the mean Q 3 + Qi obtained as the value of — ^r— agrees fairly well in each case both -j with the value of M, the middlemost value, and also with the arith- metic mean given above. It may therefore be taken that the curve is regular and the series nearly uniform. The correlations between the lengths of the joints and that of the whole tarsus have also been examined by Mr Brindley using the method proposed by Galton I.e., the results closely agreeing with those obtained by the ordinary method here described 1 . If the 4-jointed tarsus be a congenital variation the sig- nificance of the fact that the abnormality is in its constancy to its normal hardly less true than the type-form must be apparent 1 It is hoped that a fuller account of this subject will be given separately. I am indebted to Mr F. Galton for advice kindly given when this investigation was begun, and Mr Alfred Harker has most obligingly given much help in connexion with it. 27—2 420 MERISTIC VARIATION. [part i. to all. Yet even if, as now seems likely, the 4-jointed tarsus be not a congenital variation but is rather a result of regenera- tion, there is still difficulty in reconciling the now established fact that the form of the regenerated part, though different from the normal, is scarcely less constant, with any hypothesis that the constancy of the normal is dependent upon Selection. If it were true that the smallness of the mean variation of the t 1 ..." ratio y , which is ultimately the measure of the constancy and Li truth to type of the 5-jointed tarsus, is really due to Selection and to the comparative prosperity of specimens whose tarsal pro- portions departed little from the normal, to what may we ascribe T l the smallness of the mean variation of the ratio -j- ? Are we to suppose that the accuracy of the proportions of the regenerated tarsus is due to the Natural Selection of individuals which in renewing their tarsi conformed to this one pattern ? We are told that the struggle for existence determines every detail of sculpture or proportions with such precision that in- dividuals which fall short in the least respect are at a disad- vantage so great as to be capable of being felt in the struggle, and so decided as to lead to definite and sensible effects in Evolu- tion. If this is so, should we not expect that individuals which had suffered such a comparatively serious disadvantage as the loss of a leg or of a tarsus, would be in a plight so hopeless that even though some of them may survive, renew the limb and even breed, yet, as a class, by reason of their mutilation they must rank with the unfit ? Nevertheless we find not only that there is a mechanism for renewing the limb, but that the renewal is performed in a highly peculiar way ; that in fact the structure newly produced differs from the normal just as species differs from species, and is scarcely less true and constant in its pro- portions than the normal itself. Now if this exactness in the proportions of the renewed limb is due to Selection, it must be due to Selection working among the mutilated alone ; and of them only among such as re- newed the limb ; and of them only among such as bred. Moreover if the accuracy of the form of the renewed tarsus is due to Selection working on fortuitous variations in the method of renewal, and not to any natural definiteness of the variations, the number of selections postulated is already enormous. But this vast number of selections must by hypothesis have all been made from amongst the mutilated — a group of individuals that would be supposed to be at a hopeless disadvantage 1 . 1 The same dilemma is presented in all cases where a special mechanism or device exists (and must be supposed to have been evolved) only in connexion with regeneration. An instance is to be seen in the Lobster's antenna. As is well known the antennary filament of the Lobster when lost is renewed not as a straight out- chap, xv.] RADIAL JOINTS OF COMATUL^E. 421 One or more of the hypotheses are thus clearly at fault. A natural, and I believe a true comment will occur to every one : that probably the injured insects are not at any serious disad- vantage, and that these mutilations perhaps make very little difference to their chances. But can we admit that the loss of a leg matters little, and still suppose that the definiteness and accuracy of the exact proportions of the tarsal joints makes any serious difference ? The hypothesis, therefore, that the smallness of the mean variation in the proportional lengths of the tarsal joints of the 4-jointed tarsus has been gradually achieved by Selection is un- tenable, whether that 4-jointed tarsus be a product of regenera- tion or a congenital variation. But if the accuracy with which the abnormal conforms to its type be not due to a gradual Selec- tion, with what propriety can we refer the similar accuracy of the normal to this directing cause ? Kadial joints in Arms of Comatul^e. The number of radial joints above the basals up to the division of the rays in Crinoids is usually constant in the genera. In Antedon and Actinometra there are normally three such joints, the third radial being the axillary, and none of these bear pinnules. Both increase and decrease in the number of radials has been observed, but variations from this number are rare, more so than variations in the number of rays. Carpenter, P. H., Chall. Rep., xxvi. Pt. lx. p. 27. Antedon alternata: specimen having in one ray four radials, none bearing pinnules or united by syzygy. ibid., PL xxxu.fig. 6. Encrinus gracilis (fossil) : in one ray four radials. Wagner, Jen. Ztschr., 1887, xx. p. 20, PI. ii. fig. 13. Antedon remota, A. incerta, Actinometra parvicirra (Fig. 126); one specimen of each of these species had one ray with only two radials. Carpenter, I.e., PL xxix. fig. 6; PL xviii. fig. 4; PL lxi. fig. 1. Fig. 126. Actinometra parvicirra, No. 628. Specimen having only two radials in the ray marked x. (From P. H. Carpenter.) growth, as the other appendages are, but when formed again it is coiled up in a tight conical spiral which cannot be extended at all, but is kept firmly in place by the shortness of the skin on the inner curvature. (For figure see Howes, Jour. Anat. Phys., xvi. p. 47.) During the process of regeneration the antenna is very soft, and were it extended it would from its great length be much exposed to injury. At the next moult after renewal the new antenna is drawn out as a straight filament like the normal, and its skin then hardens with that of the rest of the body. This strange manner of growth occurs only on regeneration. It is hard to believe both 422 MERISTIC VARIATION. [part i. Metacrinus. Some species have normally 5, others normally 8 radials. If there are 5, the 2nd and 3rd are united by syzygy and bear pinnules; but if there are 8, both 2nd and 3rd, and the 5th and 6th are thus united and bear pinnules. In Plieatocrinus the number of radials is two, and this is also the case in one or two fossil Comatulas. Pentacrinus has normally three radials like Antedon. 629. Pentacrinus mulleri: specimen having in one ray four radials, the 2nd and 3rd united by syzygy, though bearing no pinnules. Carpenter, I.e.; and Chall. Rep. xi. Pt. xxxii. p. 311, PI. XY.Jig. 2. (1) that the number of individuals that have lost antennae — a serious injury one may judge — and have renewed them, and have bred, can have been enough to lead to the establishment by Selection of a distinct and highly special device to be invoked solely on the occasion of mutilation of an antenna ; and also (2) that the least detail of normal form is of such consecpience as to be rigorously maintained by Selection. CHAPTER XVI. Radial Series. Little need be said in preface to the facts of Meristic Varia- tion in Radial Series. In them phenomena analogous to those of the Variation in Linear Series are seen in their simplest form. Just as in Linear Series the number of members may be changed by a reconstitution of the whole series so that it is impossible to point to any one member as the one lost or added, so may it be in the Meristic Variation of Radial Series: and again as in Linear Series, single members of the series may divide. Be- tween these there is no clear line of distinction. Next, as in Linear Series, Variation, whether Meristic or Substantive, may take place either in single segments (quadrants, sixths, &c), or simultaneously in all the segments of the body. For instance, a single eye may be divided into two, or there may be duplicity simultaneously occurring in all the eyes of the disc (see No. b'34) and so on. These phenomena are here illustrated by facts as to the Meristic Variation of Hydromedusae and of Aurelia. The latter is exceptionally variable and in its changes exhibits important features. Together with these facts as to Variation in Major Symmetries is given an instance of similar Variation in the pedicellarise of an Echinid, and it will be seen that in this case of a Minor Symmetry the change is perfect and altogether comparable with those found in Major Symmetries of similar geometrical configuration. The best field for the study of the variations of Radial Series is of course to be found in plants ; and in the Meristic Variations of radially symmetrical flowers precisely similar phenomena may be easily seen. 424 MERISTIC VARIATION. [part 1. I. CCELENTERATA. *630. Sarsia mirabilis 1 : normally four radial canals, &c. (Fig. 127. I and III). Out of many hundreds of N. American specimens two were found with six radial canals, six ocelli, and six tentacles, Fig. 127. Sarsia mirabilis. I and III, the normal form, with four radii, from below and from above. II and IV, an abnormal form with six radii, from below and from above respectively. (From Agassiz.) symmetrically arranged (Fig. 127, II and IV). These specimens were of larger absolute size than the normals. Agassiz, L., Mem. Amer. Ac. Sci., iv. p. 248, PI. v. fig. 5. 1 Sarsia is the medusa of the Gymnoblastic Hydroid Syncoryne. chap, xvi.] RADIAL SERIES : JELLY-FISH. 425 'G31. Sarsia sp. Among many thousands examined on the east coast of Scotland one was found having six radial canals, six ocelli and six tentacles. Romanes, G. J., Jour. Linn. Soc, Zool., xii. p. 527. '632. Sarsia sp. A single specimen having five complete segments: the only abnormality met with amoog thousands of naked-eyed medusae observed, ibid., xiii. p. 190. There is perhaps in the whole range of natural history no more striking case of the Discontinuity and perfection of Meristic Variation. Is it besides a mere coincidence, that the specimens presenting this variation, so rare in the free-swimming Hydromedusse, should have been members of the same genus ? 633. Clavatella (Eleutheria) prolifera. This form has a medusa which creeps about on short suctorial processes borne by the tentacles. The number of these tentacles varies from 5 to 8. In the specimens examined by Krohn 1 the number was 6. Most of Claparede's 2 speci- mens had 8. Filippi 3 found that the majority had 6 arms, but 15 per cent, had 7. Those examined by Hincks 4 never had more than 6. Filippi considered that the difference in number was evidence that his specimens were of a species different from Claparede's. I examined many of this form at Concarneau and found six the commonest number in the free medusae, but those still undetached frequently had 5, possibly therefore the number increases with development. [See also Cladonema radiatum, &c. Hincks, I.e., p. 65, &c] Claparede states that the 6-armed specimens had 6 radial canals, but the 8-armed usually had four though occasionally six, but never eiidit canals. In this case note not only the frequent occurrence of Meristic Variation, but also the suggestion that particular numbers of tentacles are proper to particular localities. '634. Normally there is a single eye at the base of each arm. Claparede figures (I.e. p. 6, PL i. fig. 7 a) a case of duplicity of an eye, and says that specimens occur in which each eye is doubled, so that there are two eyes at the base of each arm instead of one. 635. Stomobrachium octocostatum (.ZEquoridae) : variety found in Cromarty Firth, |rds of size represented by Forbes (Monogr. Br. Naked-eyed Medusce); ovaries bluish instead of orange, and without denticulated margins. Tentacles arranged in double series, long and short alternating, while in the type the series is single. The number of large tentacles same as in type. Each smaller tentacle bears vesi- cular body at base, without pigment or visible contents. The same variety figured by Ehrenberg, Abh. Ah. Berl., 1835, Taf. vin. fig, 7. Romanes, G. J., Jour. Linn. Soc. xn. p. 526. [Simultaneous Variation of the several segments.] With Nos. 634 and 635 compare the fact that in Tiarops poly- 1 Arch. f. Naturg., 1861, p. 157. 2 Beob. iib. Anat. u. Entw. Wirbelloscr Thiere, 1863, p. 5. 3 Mem. Ac. Torino, S. 2, xxiii. p. 377. 4 Brit. Hyd. Zoophytes, 1868, p. 71. 426 MERISTIC VARIATION. [part i. diademata there are normally as a specific character four diadems between each pair of radial tubes, making in all sixteen instead of eight, which is the usual number in the genus. Romanes, G. J., Jour. Linn. Soc. Zool., XII. p. 525. *636. Aurelia aurita. This form exhibits an exceptional frequency of Meristic Variation. In the normal there are 16 radial canals, 4 oral lobes, 4 generative organs and 8 lithocysts. The de- partures from this normal form have been described in detail by Ehrenberg 1 and by Romanes 2 . Meristic Variation in Aurelia may occur in two distinct ways, first in the degree to which there is complete separation between the generative sacs, and second in actual numerical change. Imperfect division of generative sacs. In the commonest form of Aurelia there are four generative organs each distinct from its neighbours, but in some specimens the generative epithelium is continuous all round the mouth, and there is then one continuous generative chamber, though opening by 4 openings as usual. (Such absence of complete sepa- ration between some of the generative organs is not rarely seen in cases of numerical Variation, v. infra.) Though the epithelium is then continuous it does not form a true circle, but is sacculated to form 4 (as normally) 3, 6, or some other number of incompletely separated parts. Ehrenberg (I. c, p. 22) saw a case in which there were 6 such sacculations, three on each side being united and having one generative pouch, but each of these pouches opened by 3 openings. There was thus a bilateral symmetry, each half containing three lobes of ovarian epithelium incompletely separated from each other. Complete union of all the generative organs was very rare. The specimens differ greatly with regard to the degree to which the generative epithelium is folded off, and in the shapes of the generative organs. Commonly the generative epithelium is of a horse-shoe form, the two limbs of the horse-shoe not meeting each other; but in some specimens the two limbs may be to various degrees approximated, so that each generative organ is kidney-shaped or even roughly circular. (Cases figured by Ehrenberg, I.e., PI. n.) [Here note the Simultaneous Variation of the single quadrants.] Numerical Variations. Of these the most striking and also the most frequent are variations consisting in a perfect and symmetrical change in the fundamental number of segments composing the disc. Normally there are four quadrants (Fig. 128, I). Varieties are found having only half the usual number of organs, the disc being made up of two halves, each contain- ing one generative organ (Fig. 128, IV). Other symmetrical varieties having three, and six, as their fundamental numbers are shewn in Fig. 128, V, and II. These figures are from Romanes. Symmetrical forms having five segments and eight segments are described and figured by Ehrenberg. As to the comparative frequency of these forms facts are given below. In each of them all the parts normally proper to one quadrant are repeated in each segment of the disc, the number of parts being greater or less than the normal in correspondence with the funda- mental number of the specimen. 1 Ehrenberg, C. G., Abh. k. Ah. Wiss., Berlin, 1835, pp. 199—202, Plates. 2 Romanes, G. J., Jour. Linn. Soc., Zool., xn. p. 528, and xm. p. 190, Pis. xv. and xvi. CHAP. XVI.] radial series : Aurelia. 427 Next, the number of certain organs may vary independently of other organs. For example as seen in Fig. 128, VI the radial canal Fig. 128. Diagrams of various forms of Aurelia aurita, slightly simplified from Eojianes. I. The normal. II. Symmetrical form with 6 radii. III. Two additional chief radial canals in opposite interradii (where manubrial lobes also were bifid) and substitution of two canals for one in another interradius. IV. Form with two generative organs. V. Form with three generative organs. VI. Symmetrical form in which the intergenital canals are all doubled, the others remaining single. VII. Apparently upper half-disc arranged as for a symmetry of four, lower half for a symmetry of six. VIII. One of the quadrants tripled (?). IX. Form resembling VI. except that in one quadrant the intergenital canal is not doubled. The descriptions are not altogether those of Romanes. normally lying in a plane between each pair of generative organs may in each quadrant be represented by two canals, and in correspondence with this change the number of marginal organs is proportionately changed in the quadrants affected. But besides these changes symmetrically carried out in eacli quadrant or in the whole disc, one or more quadrants or a half-disc may vary inde- pendently. For example Fig. 128, VII, shews a specimen in which the two upper quadrants are normal but the lower half-disc is primarily divided into three. (In the case figured the parts of the lower half-disc 428 MERISTIC VARIATION. [part i. are not quite accurately distributed). Similarly a particular quadrant may be represented by two sets of parts or by three sets (Fig. 128, VIII), the other three quadrants being normal or nearly so. I have seen a case also in which the chief symmetry was arranged as for three seg- ments (having 3 oral lobes), but one of the three segments was imper- fectly divided into two. In a case of 6 segments, 3 on one side may be large and the other 3 small, somewhat as in Fig. 128, VIII, but the whole disc was not circular, the radius on the side of the large segments being the greater. In the figures (after Romanes) all the discs are represented as circles, but my own experience was that when there was not a truly symmetrical distribution of the generative organs the half quadrant or other segment in which the number of parts was greatest bulged out- wards, thus exemplifying the general rule that when an organ divides the two resulting parts are together larger than the undivided organ. Besides those specified, there are also irregular cases, e.g., specimens with 3 generative organs but 4 oral lobes and other parts in multiples of 4, but as Ehrexberg says in such cases it is generally possible to detect that one of the generative organs is larger than the others or even partially double. He also saw cases otherwise arranged in a symmetry of 6, but having 22 chief radial canals instead of 24, &c. Also 14 radial canals (instead of 12) were found in some cases of 3 generative organs. As everyone will admit, it is impossible in regular threes, sixes, tfcc. to say that any particular segment is missing or is added rather than another. Comparative frequency of the several forms. *637. Among thousands of individuals seen by Ehrenberg only two were 8-rayed, 15 — 20 were 6-rayed, some 20 — 30 were 5- and 3-rayed, the remainder being 4-rayed. In percentages, 90 are 4-rayed, 3 are 3-rayed 3 are 5-rayed, 2 are 6-rayed and 2 have other numbers. The result of an attempt to ascertain these percentages in a great shoal of Aurelia washed ashore on the Northumberland coast on 4 Sept. 1892 is given below. The radial canals were not counted, and the numbers apply strictly to the generative sacs only. It will be seen that the proportion of abnormals is lower than that given by Ehrenberg. 2 generative sacs symml. : 3 oral lobes in 4 unbroken cases ...10 (O^ /,) 2 large, 1 small : 3 or. lobes 1 normal 1735 3 large, 1 small : 5 or. lobes 1 3 4 4 4 5 5 6 6 6 6 6 2 large, 2 small : 3 lobes 1 symmetrical 5 lobes in one 2 not quite symmetrical 1 sym. : 6 lobes in 2 unbroken cases 7 (0'39°/ o ) not symmetrical 1 4 large, 2 small 1 4 large, 2 united : 6 lobes in 1 unbroken ... 2 3 large, 3 small : 6 lobes 1 1763 CHAP. XVI.] RADIAL SERIES : PEDICELLARI^E. 429 There were therefore 1735 normals, 19 symmetrical varieties and 9 irregulars. It will be noted not only that the symmetrical varieties are comparatively frequent, but also that the several forms of irregu- larity were seen for the most part in single specimens only. II. PEDICELLARI.E OF ECHINODERMS. The number of jaws in the pedicellarias differs in different forms of Echinoderms, and I am indebted to Professor C. Stewart for information concerning them. In Asteroidea the number of jaws is usually two, but in Luidia savignii the normal number of jaws is three. In the Echinoidea the number of jaws is usually three, but in Asthenosoma the normal number is four. 638. Dorocidaris papillata : number of jaws in pedicellariae I I Fig. 129. Peclicellariae of Dorocidaris papillata. I. Normal form with three jaws. II. A pedicellaria with four jaws from the abactinal region. (From Prof. Stewart's specimens.) normally three as in Fig. 129, I, but occasionally four in pedi- cellarise of the abactinal region, as in Fig. 129, II. [Note that the variety is perfect and symmetrical.] For this fact I am obliged to Professor Stewart, who kindly allowed this figure to be made from his preparations. 639. Luidia ciliaris : pedicellariae nearly all with three jaws ; but on Roscofif specimens a few having two jaws occur on the borders of the ambulacral groove. In Banyul's specimens none such were found in this position, but there is one in almost all the marginal intervals. CuE"not, Arch. zool. exp., S. 2. V. bis, p. 18. 640. Asterias glacialis : occasionally ^ree-jawed pedicellariae like those of Luidia are found among the normal two-jawed pedi- cellarise. Cu£not, I. c, p. 23. 430 MERISTIC VARIATION. [part III. Cell-Division. *G41. It was purposed at this point to have introduced an account of Meristic variations observed in the manner of division of nuclei and cells ; but I have found that, to give adequate representation of these facts even in outline, it would be necessary not only to treat of a very complex subject with which I have no proper acquaintance, but also greatly to enlarge the scope of this work. But were no word said on these matters, indications most useful as comment on the nature of Meristic Variation at large would have to be foregone ; and unwilling that these should be wholly lost I shall venture briefly to allude to so much of the matter as is needful to shew some ways in which the facts of abnormal cell- division can be used in reference to the wider question of Meristic Variation. We have been dealing with cases of Radial repetition, and we have seen that with Variation in the number of parts the result may still be radially symmetrical. It therefore becomes of interest to note that in the case of abnormal cell-division the result of numerical change may in like manner be radially symmetrical. Cells which should normally contain two centrosomes and which should divide into two parts have been seen to contain three centro- I II Fig. 130. Triasters. I. Tripolar division of nucleus in embryonic tissue of Trout (after Henneguy 1 ). II. Triaster from mammary carcinoma. Centrosomes not shewn (from F lemming 2 ). somes (Fig. 130) prior to division into three parts, and the tri- angle formed by the three centrosomes may be equiangular just as may be the triangle of the segments of the abnormal Aurelia (Fig. 128, V), or of the jaws of the normal pedicellaria of Dorocidaris (Fig. 129). It is, I imagine, difficult to suppose that the radial symmetry of each of these series of organs is 1 Heknegut, Jour, de VAnat. et Phys., 1891, p. 397, PI. xix. fig. 9. 2 Flemming, Zelhubstanz, Kern u. Zelltheilung, 1882, PI. viii. fig. v. after Martin, Virch. Arch., 1881, lxxxvi. PI. iv. chap, xvi.] SYMMETRY IN TRI ASTERS. 431 different in its nature, or indeed that it is anything but a visible expression of the equality of the strains tending to part each segment from its neighbours. (The case of the triaster is taken as the simplest and most plainly symmetrical, but examples of cells with greater numbers of centrosomes, sometimes dividing symmetrically, have also been seen.) For our purpose this fact is first of use as a demonstration of the absurdity of an appeal to " Reversion " as a mode of escape from the admission that variations in Radial Symmetry may be total and perfect though the new number of segments is one which presumably never occurred in the phylogeny ; for we need scarcely expect that even conspicuous defenders of the doctrine that all perfection must have been continuously evolved, will plead that the cells of every tissue in which a triaster is found did once normally divide with three poles. Yet if it be once granted that the symmetry of these abnormal forms is a sudden and new departure from the normal, it will not be easy to put the other cases on a different footing. Though we have repudiated all concern with the causes of ab- normality, mention may be made of the fact that multipolar figures, both regular and irregular, have been observed to result from the action of reagents {e.g. quinine, Hertwig 1 ). Such figures are of course well known especially in the case of carcinomatous growths, and as Hertwig observes, from the resemblance of these figures to those artificially induced by chemical means it seems possible that these pathological appearances may also be the result of some chemical stimulus. But whatever be the immediate or directing causes of abnormalities in cell-division, or of those other abnormalities in the segmentation of Radial Series of larger parts, and whether any of the causes in the several cases be similar or different, we can scarcely avoid recognition that the resulting phenomena are closely alike 2 . 1 0. Hertwig, Die Zelle u. d. Geivebe, 1893, pp. 192—198. 2 See also a case of the presence of triasters in two bilaterally symmetrical tracts of the blastoderm of Loligo [v. infra). CHAPTER XVII. Radial Series: Echinodermata. As seen in the majority of adult Echinoderms the repeated parts are arranged with a near approach to a Radial Symmetry and it is thus convenient to consider their Meristic Variations in that connexion. But it must of course always be remembered that in their development these repetitions are in origin really a Successive Series and not a Radial Series. The segments are not all identical (as, in appearance at least, they are in many Ccelenterates &c), but are morphologically in Succession to each other, though there may be little differentiation between them. In the case therefore of Variation in the number of segments, resulting in the production of a body not less symmetrical than the normal body, there must be in development a correlated Variation among the several members like that seen in so many cases of additions to the ends of Linear Series. This circumstance should be kept in view by those who seek in cases of numerical Variation, in Echinoderms to homologize separate segments of the variety with those of the type, hoping to be able to say that such a radius is added, or such other missing. As in other animals, this has been attempted in Echino- derms, and though I know well that in the complex subject of Echinoderm morphology I can form no judgment, yet it is difficult to suppose that the same principles elsewhere perceived would not be found to hold good for Echinoderms also. All that is here proposed is to give abstracts of facts as to Variation in the numbers composing the Major Symmetries. It will of course be remembered that though the fundamental number in Echinoderms is most commonly five, other numbers also occur as normals, {e.g. four in the fossil Tetracrinus, six in some Ophiurids, &c. Examples will be given of total change from five to four and to six, and so on. It is besides not a little interesting that of the normally 4-rayed Tetracrinus both o -rayed and 3-rayed varieties should be known. Besides the examples of total Variation there are a few cases of incomplete Variation in which there is a fair suggestion that chap, xvil] RADIAL SERIES : HOLOTHURIOIDEA. 433 a particular ray is reduced in size (Nos. 680 and 681, &c). There are also two cases of imperfect division of a ray in an Echinid (Nos. 688, &c), while in Asteroids &c. this condition is common. It is of importance to observe that just as in Linear Series abnormal divisions of members of the series are commonly transverse to the lines of Repetition, so in radial forms the divisions of rays are commonly radial. The evidence is complicated by the fact that in many Echinoderms extensive regeneration can occur, and in some genera reproduction by division of the disc and subsequent regeneration is almost certainly a normal occurrence 1 . Never- theless it cannot be doubted that the variation seen in Echini, in Asterina, in the discs and stems of Crinoids, &c, are truly congenital. Similarly, though in Asterias &c. reduction in the number of arms might otherwise be thought to be due to mutila- tion, it cannot be so in Echini &c. HOLOTHURIOIDEA. Cucumaria planci : among 150 half-grown specimens found at Naples five were 6-rayed. Ludwig, H., Zool. Anz., 1886, IX., p. 472. [These specimens are described in detail.] To determine which is "the intercalated ray" the following ingenious reasoning is offered, and as a good practical illustration of the conception of the individuality of segments as applied to an Echinoderm we may well consider it. 1 It is likely that several of the Ophiurids and Asteroids which normally have more than 5 arms undergo such fission. Lutken ((Efvers. Dansk. vid. Selsk. Fork., 1872, pp. 108—158 : tr. Ann. and Mag. N. H., 1873, S. 4, xn. pp. 323 and 391) gave an account of this phenomenon. Ophiothela isidicola (Formosa) generally has 6 arms, rarely equal, usually 3 large opposite to 3 small ; specimens common with only 3 arms, with appearance as if corresponding half-disc cut off. There can be no doubt that the animal divides and that the other 3 arms are renewed. The same phenomenon has been seen in other small 6-armed Ophiurids, especially of genus Ophiactis, but Liitken never saw any trace of it in any normally 5- rayed species of the genus. There are indications that the division occurs once when the animal is very small and again when it is adult or nearly so. In Ophiocom._. and e x of the usual nomenclature, as shewn in Fig. 133. For details see original description. *6G9. Encrinus liliiformis : amongst other abnormalities case given in which one of the radii bore only one arm. V. Strom- beck, Palceont, IV. p. 169, PL xxxi. fig. 3. 668. CHAP. XVII.] ASTEROIDEA. 439 ASTEROIDEA. 670. Symmetrical change in number of rays is common in some of the forms. Asterias rubens and A. glacialis are frequently seen with 6 or with 7 arms symmetrically arranged, and I have , mouth anus Fig. 133. Antedon rosacea having two arms abnormally divided. Tbe figure A shews the relations of the two abnormal arms, b 2 and e lt to the mouth and anus. B shews the arm b 2 . (From Proc. Zool. Soc.) 440 MEBISTIC VARIATION. [part i. seen one with 8. Individuals with 4 arms occur, but are much less common than those with 6. I have seen Asterina gibbosa with 4 rays, and a specimen (Scilly) given me by Mr S. F. Harmer has 6 rays, of which 2 are a little nearer together than the others (suggesting division of a ray). Mr E. W. MacBride tells me that he has seen several 6-rayed specimens of this species. Mr E. J. Bles kindly tells me that he dredged a 4-rayed Porania pulvillus in the Clyde estuary. There appeared to be no trace of a fifth ray and the specimen was as nearly as possible sym- metrical. The following cases exhibit special points. 671. Asterias glacialis : specimen with 8 rays possessed 3 madre- porites. Couch, J., Charlesworttis Mag. of N. R., 1840, iv. p. 34. (372. Asterias rubens : G-rayed specimens frequent atWimereux. In several of these there are two sand-canals terminating at a common madreporite. Giard, A., Comptes rendus, 1877, p. 973; cp. id. C. R. soc. bid., 1888, p. 275. 673. Partial division of an arm is fairly common in Asteroids, but less common I believe than the total variation in number, though I know no statistics on this point. For a figure of Asterias (Hippasterias) equestris L. with a bifid arm, presenting no appearance as of regener- ation see Tiedemann, Zeitschr.f Phys., 1831, iv. p. 123, Plate 1. The two following are peculiar cases. 6 / 4. Cribrella oculata : one of the arms bearing a branch, not as a radius, but about (in dried specimen) at right angles to the normal arm, the property of Prof. C. Stewart, who kindly shewed it to me. 675. Porania pulvillus, Gray (a Starfish): Specimen 5 cm. in diame- ter, having five short rays. The ray opposite the madreporite when viewed from the aboral surface is seen to be distinctly bifurcated at 1/ v^i.'i\\ & \ Mm* &*& a *~-s s. Fig. 134. Porania pulvillus, No. 675, having the arm opposite the madreporite abnormally divided as shewn at x and y. (From a sketch kindly sent by Prof. Hbbdmak.) chap, xvii.] ECHINOIDEA. 441 about 1 cm. from its termination. The ambulacral groove of (Fig. 134) this abnormal ray divides into two branches at a distance of 2 cm. from the edge of the mouth. One of these branches runs along one of the forks of the ray to its extremity without further complication ; but the other branch, belonging to the second fork, divides again 2 mm. from the first bifurcation, so as to form two tracts which unite with one another 3 mm. further on, thus inclosing a small piece of the ordi- nary integument in an ambulacral area. Finally, this ambulacral area divides once more close to the tip of the ray. There are no signs of injury or disease in the specimen. Hekdman, W. A., Nature, 1886, xxxi. p. 596. [I am indebted to Professor Herdman for the accom- panying diagram of this specimen.] ECHINOIDEA. In the Echinoids there are (1) cases of total Variation to a 4-rayed form with 4 ambulacra and 4 interambulacra 1 : (2) cases of partial or total disappearance of a definite ambulacrum or interambulacrum, which can be named either because part of it is present, or because two sets of similar plates thus become adjacent: (3) a case of total variation to a 6-rayed form : (4) cases of imperfect reduplication of a radius, thus forming an imperfectly 6-rayed form. (1) Total Variation to a Grayed form. 676. Cidarites coronatus?: 4-rayed regular specimen (Fig. 135). Meyer, A. B., Nova Acta G. L. C, xvm. 1836, p. 289, PL xm. Fig. 135. Cidarites coronatus ? No. 676, a regularly 4-rayed specimen from oral surface. (From A. B. Meyer.) *677 # Echinoconus (Galerites) subrotundus : 4-rayed specimen in Woodwardian Mus. (Fig. 136). The ambulacral and interambulacral areas are relatively wider than in a normal of the same size, the space of the areas that are wanting being as it were shared among those that are present. Apical disc roughly rectangular, and seems to be com- posed of 4 perforated basals (genitals) and 4 perforated radials (oculars). The basal plate corresponding to the posterior unpaired interambulacral area is perforated, though normally imperforate. Statement made that 1 CuiNOT, Arch, tie Biol., 1891, xi. p. 632, says that Echinoconus vulgaris has been seen with only three radii, but no authority is given. 442 MERISTIC VARIATION. [part I. the parts missing are those which lie on the left side of a line drawn through the middle of the anterior single ambulacrum and the posterior na 1 * >-// .... '^ ■/■':[: < vv 1 v- -•■/ •> • • L ' -< r~ V -. Fig. 136. Echinoconus subrotundus having 4 rays, No. 677. (From Roberts, Geol. Mag., 1891.) 1. View of apical system. 2. Seen from side. 3. From apex. 4. From below. aa, anterior ambulacrum [?]. mp, madreporite. ai, anal interradius. The parts are lettered after Roberts. unpaired interambulacrum, but it is not possible to say which of the paired areas of this side are wanting, as the pores in the ambulacral plates round the peristome are indistinctly shewn. Roberts, T., Geol. Mag., 1891, Dec. ill., vni. p. 116, figs. 678. Discoidea cylindrica : a 4-rayed specimen, absolutely sym- metrical. There are only 4 oculars corresponding with the 4 ambu- lacra. Cotteau, G., Pal. /rang., 1862 — 67, VII. p. 31, PI. 1011, figs. 6 and 7. [This is exactly like Roberts' case No. 677 and is illustrated by beautiful figures (q.v.). Cotteau in describing it says that the anterior ambulacrum is wanting. It is difficult to see any sufficient reason for the determination that this ambulacrum in particular is wanting. For in this case there are only 4 sets of interambulacral plates as well as 4 ambulacral areas in perfect symmetry. The anus of course lies between two ambulacra ; and as the whole number is even and the radii are symmetrically arranged, there is thus no ambu- lacrum in the plane of the anus. Hence the suggestion that it is the anterior ambulacrum which is wanting. But if by Variation an Echinid has 4 symmetrical radii it would always seem that the chap, xvii.] ECHINOIDEA. 443 anterior ambulacrum was missing, whether it be the anterior ambu- lacrum, or the left anterior, or the left posterior that is wanting, or even if all 4 new ambulacra correspond with all 5 of the normal.] (379. Amblypneustes sp. (S. Australia): four specimens, each with four ambulacra [no description or statement as to symmetry]. Haacke, Zool. Anz., 1885, p. 505. (See No. 687.) (2) Partial or total disajipearance of a definite ambulacrum or inter ambulacrum. *680. Echinus melo, having only four complete ambulacral areas (Fig. 137). The specimen is not spherical, for the apical system is warped over in one direction and the oral pole is pulled in an opposite direction, while the shell is much higher in the region of the apical system than it is at the opposite side. There are only four ocular plates, which are subequal, the madreporic plate and the plate opposite to it being some- what larger than the other two. The genital plates are also four. Only four ambulacral areas leave the apical system, and at that point they are almost symmetrically disposed. Lower down however a triangular series of plates bearing ambulacral pores is intercalated between the plates of one of the interambulacral systems which it divides into two. This intercalated series is of course the representa- tive of the ambulacral area which is wanting at the apex of the shell. The five ambulacra are nearly symmetrically disposed round the oral surface just as theyb^r ambulacra are round the apical system. This transition from a tetramerous to a pentamerous symmetry is effected by complementary changes in the amount of divergence of the rays as they pass down the shell. Examination shews that the ambulacrum which is thus partially absent is the right posterior. Philippi, Arch. f. Naturg., in. p. 241, Plate. 681. Amblypneustes formosus : a 4-rayed specimen having a somewhat asymmetrical test. One of the interambulacral regions is abnormally wide, and at about 9 plates down the side of the test in this region a wedge-shaped piece composed of several partially distinct plates bearing 7 pairs of ambulacral pores. This fragment doubtless represents the deficient ambulacral area. The apical system consists of 10 plates. The two genital plates of the abnormal area are reduced in size, and the ocular plate between them is abnormally large. Consider- ing the madreporic plate as indicating the right anterior interambula- crum, it appears that it is the left anterior ambulacrum which is thus deficient. The height of the shell at the abnormal side is less than at the other. Bell, F. Jeffrey, Jour. Linn. Soc, xv. p. 126, Plate. In each of the foregoing the missing ambulacrum is actually at some place represented by plates of ambulacral character, and the shape of the test is greatly changed in correlation with the partial disappearance of the radius. The following cases differ, in that in them one ambula- crum is wholly wanting in the affected radius, and the interambulacra are contiguous with each other. Curiously enough in two of these specimens the symmetry is changed little or not at all. The cases in Hemiaster were all Algerian fossils l . 1 Besides those here given in the text, Gauthier in the same place describes an interesting case of symmetrical reduction in the two posterior ambulacra of Hemiaster africanus. * 444 MERISTIC VARIATION. [part I. II Fig. 137. Echinus melo, No. 680, having the right posterior ambulacrum partially absent, a, anterior ambulacrum, ra, la, right and left anterior ambu- lacra, rp, Ip, right and left posterior ambulacra. I. View from apex. II. View from oral surface. (From Philippi.) chap, xvil] ECHINOIDEA. 445 g§2 # Hemiaster batnensis : specimen in which the left posterior ambulacrum is not present, and the ambulacral groove is only indicated by a shallow depression, beyond which there are some rounded pores which continue the ambulacral area beyond the fasciole. The corre- sponding ocular seems to be absent. The test is of normal form, but the median suture of the right posterior interambulacrum is not quite straight. Gauthier, M. V., Comptes rendus de I'Ass. pour Vav. des sci., 1885, xiii. p. 258, PL vn. fig. 1. ' (383. H. batnensis : very similar case of absence of right anterior ambulacrum and corresponding genital and ocular plate, ibid., fig. 3. (384. Hemiaster sp. : left anterior ambulacrum wanting and is gone without trace. There are only 4 oculars and 3 genitals. In corre- spondence with this variation there is considerable change in symmetry of the test, which is irregular, the anterior and right anterior ambu- lacra being deflected from their normal courses. [See details.] Ibid., figs. 4 and 4 bis. [Here, where there is a clear differentiation between the several ambulacra, it is doubtless possible to affirm that such a definite ambulacrum is missing, for the two interambulacra are left adjacent to each other.] 685. Echinus sphaera (O. F. Miiller): specimen described in which the left posterior interambulacral series of plates is almost entirely absent. The details of the structure are as follows : the genital plate which stands at the head of the left posterior interambulacrum is reduced in size in all directions ; but the two ocular plates which should be separated by it are somewhat enlarged, bearing several extra tuber- cles, and meet together peripherally to the genital plate. The series of interambulacral plates which should begin from this genital plate are represented by a rudimentary row of small tubercles : the ambulacral systems which are normally separated by these plates are consequently almost contiguous. The rudimentary interambulacral series widens somewhat at a short distance from the apical series and forms a small island of interambulacral structure bearing 4 large tubercles. Beyond this, viz. at a point placed about ^ the distance from the apex to the oral surface, the two ambulacra again unite and are continued as a single ambulacrum of double width. Doxitz, W., Midler's Arch, f Anat. u. Phys., 1866, p. 406, PI. xi. (3) Case of total Variation to a Q-rayed form. *686. Galerites albogalerus(P) : a regularly 6-rayed specimen having six symmetrical ambulacra and interambulacra (Fig. 138). Meyer, A. B., Nova Acta Ac. Cces. Leop. Gar., xvm. 1836, p. 224, PI. xiii. Fig. 138. Galerites albogalerus, No. 686. A six-rayed specimen. (After Meyer.) 446 MERISTIC VARIATION. [part I. (387. Amblypneustes (S. Australia): 6-rayed specimen [no description or statement as to symmetry]. Haacke, W., Zool. Anz., 1885, p. 505. (See No. 679.) (4) Cases of imperfect reduplication of a radius. '688. Amblypneustes griseus : having one of the ambulacra doubled (Fig. 139); the apical system was normal. The width of the anterior ambulacral region was almost double that of the others : it contained two ambulacra lying side by side, each, as usual, composed of a double row of plates with an ambulacral area and two poriferous zones. The is.aPca Fig. 139. Amblypneustes griseus, No. 688. Specimen having the anterior ambulacrum doubled. I. The test seen from the apex. II. Details of anterior ambulacrum shewing combined poriferous zones between A and A. The dotted line bisects the ambulacrum of double width. (After Stewart.) areas and external poriferous zones are like those of a normal ambula- crum ; but the poriferous zones which touch one another are fused together, with the pores irregularly arranged. The combined porifer- ous zones are not quite equal to the sum of two normal ones. The whole of this area, formed of the union of two ambulacra, projects as a ridge which is continued down the whole of the side of the shell. Stewart, C, Jour. Linn. Soc, xv. p. 130, PI. 689. Hemiaster latigrunda : right posterior ambulacrum double, the two resulting ambulacra are closely adjacent peripherally and a small interambulacral area is formed between them in their more central parts. There are 6 oculars but no extra genital. Gauthier, /. c, tigs. 5 and 5 bis. 690. Hemiaster batnensis : right anterior ambulacrum double, the two ambulacra are in contact through all their length. Cotteau, Pal. frarig., 1869, p. 150, PI. xx., and Gauthier, I. c. [For interesting evidence as to variation in the number of genital pores on the costals in several genera of Echini, see Lambert, Bull. Soc. Yonne, 1890, xliv. Sci. chap, xvil] ophiuroidea. 447 nat., p. 34; also Gauthier, Comptes rendus Ass. fr. pour Vav. Sci., Toulouse, 1887, and other references given by these authors.] Ophiuroidea. Individuals with various numbers of arms are often seen, especially in the genera Ophiothela, Ophiocoma, Ophiacantha and Ophiactis, and in many of the species there are most usually six arms. In these forms the evidence as to Meristic Variation is complicated by the circumstance that in several of them change in the number of arms may take place in the ontogeny, by division and subsequent regeneration (see note on p. 433). CHAPTER XVIII. Bilateral series. Of the organs repeated in Linear Series whose variations have been illustrated, many are bilaterally repeated also ; but thus far we have considered them only in their relations as members of Linear Series. It now remains to examine the variations which they exhibit in virtue of their relation to each other as members of a Bilateral Series. Meristic Variation in this respect is manifested in two ways. A normally unpaired organ standing in the middle line of a bi- lateral symmetry may divide into two so as to form a pair of organs ; and conversely, a pair of organs normally placed apart from each other on either side of a middle line may be com- pounded together so as to form a single organ in the middle line. In animals and plants nothing is more common than for different forms to be distinguished from each other by the fact that an organ standing in the middle line of one is in another represented by two organs, one on either side. The facility there- fore with which each of these two conditions may arise from the other by discontinuous Variation is of considerable importance. Admirable instances of the bearing of this class of evidence upon the question of the origin of Species are to be seen in zygomorphic flowers. Veronica for example differs from the other Scrophulariacea? especially in the fact that it has only one posterior petal, instead of two posterior petals one on each side of a middle line. But there is evidence not only that forms having normally two posterior petals may as a discontinuous variation have only one such petal, placed in the middle line, but also that the single posterior petal of Veronica may as a variation be completely divided into two. Similarly the single anterior petal of Veronica may also as a variation be divided into two, thus giving three posterior and two anterior petals as in for example Salpiglossis 1 . In these cases, which might be indefinitely multiplied, 1 An account of several discontinuous variations in the structure of zygomorphic corollas was given by Miss A. Bateson and myself. Jour. Linn. Soc, 1892, xxvm., Botany, p. 386. chap, xviii.] BILATERAL REPETITION. 449 there is thus a clear proof that so far as the variations in number and symmetry are concerned, the transition from the one form to the other may be discontinuous. Analogous phenomena in animals are so familiar that general description of them is for the most part not needed, and an account will only be given of a few less known examples both of union and of division of such parts. Besides these strictly Meristic Variations in the amount of separation between the two halves a few examples are introduced in further illustration of the relationship that subsists between the two halves of a bilateral animal. In considering the evidence both of median union and of division it must be remembered that the germs of most of the organs in question are at some time of their developmental history visibly double, and that when organs that should normally unite to form single median structures are found double in older stages, this duplicity is strictly speaking only a persistence of the earlier condition. But to appreciate this comment it should be extended. For, in every animal in which at some period of the segmentation of the ovum, the plane of one of the cleavages corresponds with the future middle line, all median organs must in a sense be paired in origin, and the distinction between paired and median organs is thus seen to be only one of the degree or amount of separation between the symmetrical halves. Nevertheless the evidence of Variation bears out the expectation that would be formed on examination of normal diversities between species or larger groups both in animals and plants, namely that whenever structures are geometrically related to each other as optical images, insta- bility may shew itself as Variation in the degree to which such parts unite with or separate from each other. It is remarkable that this instability appears as much in the case of organs bi- laterally symmetrical about an axis of Minor Symmetry as it does in the parts paired about the chief axis of Symmetry of the whole body. Examples of such Variation in bilaterally symmetrical parts of a Minor Symmetry have been already given in the case of the feet of the Horse and of the converse phenomenon in the feet of Artiodactyles (q.v.). A good illustration of the way in which duplicity about an axis of Minor Symmetry may pass into the unpaired condition is seen in the case of ocellar markings on bilaterally symmetrical feathers. By comparing different feathers on several species of Polyplectron, Darwin found that it was possible to find most of the gradations between the complete duplicity shewn in Fig. 140, I, where each half of the feather bears an almost symmetrical ocellus, and the partially confluent condition shewn in Fig. 140, II, which is not far removed from the state of the ocellus in the Peacock's tail-coverts, where the whole ocellus has no peripheral b. 29 450 MERISTIC VARIATION. [part I. indentation and is very nearly symmetrical about the rachis of the feather, though each of its halves has no axis of symmetry. I II Fig. 140. I. Part of tail-covert of Polyplectron chinquis, with the two ocelli of nat. size. II. Part of tail-covert of Polyplectron malaccense, with the two ocelli partially confluent, of nat. size. (From C. Darwin, Descent of Man, 1871, n. p. 139, figs. 54 and 55.) Attention should be called to the fact that abnormal division along a middle line may in many cases represent one of two different pheno- mena which are not readily distinguishable. For when a normally single organ is represented by two, standing on either side of a middle line it is often possible that there may be not only a division of the organ but a partial duplicity of the axis. These two conditions are of course morphologically distinct ; for in the case of division of the organ only, the two parts are still in symmetry about the original axis of Major Symmetry of the body, but in the case of duplicity of the axis there are two equivalent axes of symmetry, about which each half is separately symmetrical. But though this distinction is in a sense a real one it cannot be applied to cases of duplicity occurring in any organ whose halves assume a bilaterally symmetrical form when sepa- rate. For example in the case of the foot of the Horse, or of the hjemal spines &c. of Gold-fishes (v. infra), when division occurs, each of the two halves is only hemi-symmetrical, and this duplicity is no more evidence that the axis is double than is the ordinary double condition of the vertebrate kidney; but in the case of duplicity of the central neural canal in Man for instance, or in the case of the tail-spine of Limulus described below, it is not clear that there is not a partial duplicity of the axis. Division or absence of union in Middle Line. Most of the organs which in a vertebrate stand in a median position have been seen more or less often in a divided condition. chap, xviii.] MEDIAN DIVISION: GOLD-FISHES. 451 Examples of such division in the middle line were, I believe, first put together by Geoffroy St Hilaire, and a very full collection of the evidence seen in Man is given by Ahlfeld 1 . The organs most often divided are the sternum, neural arches, uterus, penis, &c, and of these, specimens may be seen in any patho- logical collection. Organs more rarely divided are the tongue 2 , epiglottis 3 , uvula 4 , and central neural canal 5 . The following are special cases of variation consisting in a median division. Division of caudal and anal fins in Gold-fishes. •691. Cyprinus auratus (Gold-fish). The following account of the multiple fins of Gold-fishes in China and Japan is taken chiefly from Pouchet 6 and Watase 7 . There is evidence to shew that these animals were first imported to Japan from China. Three distinct breeds of Gold-fishes are kept in Japan. The first, called " Wakin " has a slender body closely resembling that of the common carp. The second "Maruko or Ranckiu" has a very short body, being in some cases almost globular in shape and in it the dorsal fin is generally entirely absent. The head is usually disfigured by rough-looking protuberances of the skin which often attain a considerable size. The third or "Riukin" has a short body with a rounded ab- domen. Of all the breeds, this has the most beautiful tail which is very large and often longer than the rest of the body. Gold-fish breeders of the present day can freely produce the " Riukin" or "Maruko " from the " Wakin." Various intermediate forms between the above-mentioned breeds exist. In all gold-fishes, irrespective of the breed to which they belong, the tail-fin is, above all other parts, subject to the greatest varia- tion. It is to be found in one of the following three states ; (1) It is vertical and normal. (2) It may consist of two separate halves ; each of these halves is to all appearance a complete tail and the two tails pass backwards side by side, but are united dorsally at the point where they join the body. (3) The two tails thus formed are united by their dorsal edges to a variable degree and their lower edges may be bent outwards, so that the two combined tails come to be spread out into a three-lobed, nearly horizontal fin. 1 Ahlfeld, F., Mush. d. Menschen, 1880. 2 Partsch, Brest. Arztl. Ztsch., 1885, No. 17 ; Pooley, Amer. Jour., 1872, N.S., cxxvi. p. 385 [from Ahlfeld, p. 119]. 3 Manifold, W. H., Lancet, 1851(1), p. 10; French, Ann. Anat. Surg. Soc. Brooklyn, N. Y., 1880, ii. p. 271 [not seen], from Cat. Libr. Surg. -gen. U. S. Army. 4 Trelat, Gaz. des H6p. t 1869, No. 125 [for others v. Ahlfeld, Abschn. n. p. 175], 5 Wagner, J., Mull. Arch. Anat. Phys., 1861, p. 735, PI. xvn. A. 6 Pouchet, G., Jour, de Vanat. et phys., vn. p. 561, PI. xvu. 7 Watase, S., Jour. Imp. Coll. Sci. Tokio, i. p. 217, Plates. 29—2 452 MERISTIC VARIATION. [part I. Besides the caudal fin, the anal fin undergoes remarkable Fig. 141. Caudal and anal fins of Gold-fish (Cyprinus auratus). I. Normal tail, seen from side. t>, dorsal lobe, d, ventral lobe. II. Abnormal form divided as far as the notochord. v' v', two ventral lobes, d' d\ two dorsal lobes. III. Abnormal form, the two ventral lobes, v' v', separate. IV. Pen- ultimate vertebra of normal Carp (C. carpio). n.s, neural spine, h.s, haemal spine. V. Penultimate vertebra of a Gold-fish with trilobed caudal fin. h'.s', double haemal spine. VI. Diagram of transverse section through region of anal fin of normal Gold-fish. VII. Similar section through a specimen having the anal fin doubled, i.s, interhaernal spine. /. r, fin ray. n, bony nodule. i.s',f'.r', n', corre- sponding parts doubled. (After Watase.) variation. It is either median and normal ; or it may be distinctly paired (Fig. 141, VII). There are all stages of caudal and anal fins, intermediate be- tween the normal and the completely paired states. Thus the tail-fin with its lower portion alone in a double state, or the anal fin with either its anterior or posterior portion double and the remainder single, is of quite common occurrence. These different conditions of the two fins combine in various ways in different individuals thus giving rise to manifold varieties of form. This doubling of the tail-fin consists essentially in a longi- tudinal splitting of the morphologically lower lobe of the tail. The first step in the process of doubling is seen in the case of gold-fishes in which there is a slight longitudinal groove in the chap, xviil] MEDIAN DIVISION : GOLD-FISHES. 453 ventral margin of the tail-fin. This groove may be extended up through all the rays of the lower lobe of the tail, which then consists of two tails side by side. The small dorsal lobe, which lies above the notochord, is never involved in the jwocess, but always remains single. There is therefore in this case no doubling of the axis of the body. Examination of the skeleton shews that in those fishes which have two tails the haemal spines of the last three vertebrae are longitudinally split 1 and diverge to carry the two tail-fins (Fig. 141, V). Pouchet lays stress on the fact that the size of each of the paired tails is greater than that of the normal tail of a Gold-fish ; but as Watase states that in the variety "Riukin" the tail may be as long as the body, it is clear that this hypertrophy may exist without any repetition. In cases where the anal fin is doubled the process is exactly the same, resulting from a longitudinal splitting of the rays of which it is composed. This may only affect the outermost parts of the fin or may be carried up further so as to divide the inter- hsemal spines, in which case the two anal fins arise from the body wall at separate points and diverge from each other. Pouchet, who has extensively studied the history of Gold-fishes in Europe, believes that it is almost certain that those which were brought to Europe in the eighteenth century were all more or less of the double-tailed order. He refers especially to the figure given by Linnaeus 2 representing the double-tailed form as a normal. Pouchet states that the evidence goes to shew that this anomalous race is not maintained in China by any rigid selec- tion. He quotes a Chinese encyclopaedia to the effect that the double-tailed Gold-fish is found in running streams, and gives the evidence of Kleyn 3 , a missionary in China during the eighteenth century, who states that "In fluvio Sleyn Gyprini sunt qui caudam habent trifurcam et a piscatoribus Leid-brassen vocantur, quasi diceres aliorum Cyprinoram conductor es." Though the duplicity of the hasmal spines may be unaccompanied by other variations it should be noticed that the extraordinary "Telescope ' , Gold-fish not unfrequently has also the double tail-fin. In the Telescope Gold-fish the eyes project from the orbit to a greater or less extent, in the extreme form being entirely outside the head and attached by a small peduncle only. The various forms of abnormal Gold-fishes are generally to be seen in large quantities in the shops of the dealers in aquariums &c. which abound near the Pont Neuf in Paris. One of these dealers told me that he bred considerable numbers of them every year, and that in fish from the same parents there was little uniformity, many normals being produced for one that shewed any of the extreme variations. It is recorded that of the Gold-fish hatched in Sir Robert Heron's menagerie about two in five were deficient in the dorsal fin and two in a hundred or rather more had a "triple" [sc. three-lobed as described above] tail-fin, and as many have the anal 1 It should be observed that there is no want of original union between the hasmal spine3, for these close in the haemal canal as usual. The phenomenon is thus altogether different from that of spina bifida in the neural spines. 2 Fauna suecica, 17-15, p. 331, PI. II. 3 Kleyn, Miss., v. p. 62, Tab. xm. fig. 1 [not seen], quoted by Baster, Opusc. subsec, Harl., 1762, p. 91, note. 454 MERISTIC VARIATION. [part I. fin doubled. The deformed fishes were separated from the others but did not produce a greater proportion of varying offspring than the normals (Ann. Mag. N. H., 1842, p. 533). For a magnificent series of plates illustrating the various forms of Gold- fishes see Billardon du Sauvigny, Hist. nat. des Dorades de la Chine, Paris, 1780. [In Brit. Mus. copy text wanting ; I do not know if it ever appeared.] Division of median structures in Coleoptera. The following list includes every case known to me. I. Epistome. 692. Anisoplia floricola (Lam.): Algerian specimen having the epistome (chaperon) completely divided into two parts in the middle line. Attention is called to the fact that this is a normal character in certain genera of Lamellicorns, for example, Diphucephala and Inca. Fairmaire. L., Ann. Soc. ent. France, 1849, Ser. 2, VII. Bull., p. lx. II. Pronotum 1 . In Coleoptera the pro-thoracic shield or pronotum is normally a single plate continuous from side to side. The following is a list of cases in which this structure w r as composed of two lateral parts. In Nos. 695 and 706 the division was not completed through the whole length of the shield. The two halves were in most cases symmetrical, but in Nos. 700 and 703 they were unequal. As is shewn by No. 704 &c, there is in these variations more than a mere fault of union between two chitinous plates, for in this case the adjacent or inner edges of the plates were beset with yellow hairs such as occur on the anterior and posterior margins of the normal pronotum. In No. 703 again the adjacent edges of the two plates are everted and form definite margins. 693. Melolontha vulgaris (Lam.), prothoracic shield consists of two symmetrical pieces which do not meet in the dorsal middle line. The prothorax is greatly reduced in length and the head con- sequently is almost in contact with the scutellum (Fig. 142, I). Kraatz, G., Deut. ent. Ztschr., 1880, p. 341.. PL u. fig. 8. Fig. 142. Melolontha vulgaris, the Cockchafer, two cases of division of prono- tum. (After Kraatz. ) 1 With these cases compare the following : Hydrobius fuscipes, specimen having pronotum formed into three lobes, one being central, and two lateral. The lateral lobes projected from each side as considerable expansions. Kraatz, G.,Deut. ent. Ztschr., 1889, p. 222, fig. 21. chap, xviii.] MEDIAN DIVISION: BEETLES. 455 694. A male, closely similar case (Fig. 140, II., ibid., 1877, xxr. v .5l,Taf.i.fig.2. 695. A male in which the pronotum was similarly divided, but the division was not quite complete, de la Chavigxerie, Ann. Soc. ent. Finance, 1846, Ser. 2, iv., Bull., p. xviii., PL II., fig. II. 696. An almost identical specimen (male). Mocquerys, Coleop. anorm., 1880, p. 140, fig. [Now in the Rouen Museum, where I have examined it.] 697. Another case ; extent of division not specified. Staxxius, Milll. Arch. Anat. Phys., 1835, p. 304. 698. Oryctes nasicornis £ (Lam.) : anterior part of pronotum divided into two parts by a longitudinal suture : posterior part of pronotum undivided. Head normal, ibid., PL V. fig. 7. 699. Onitis bison (Lam.) : pronotum divided in the middle by a longitudinal suture, the lateral pieces being raised up. ibid. 700. Heterorhina nigritarsis (Lam.) : specimen in the Hope Col- lection at Oxford having the pronotum completely divided into two somewhat unequal halves, of which the left is the largest. The posterior angle of each of the pieces does not occupy its normal position, but lies internal to the outer border of the elytron. Owing to this disposition the mesothorax is exposed for a short distance on each side and for a considerable extent in the centre. 701. Attelabus curculionides (Rhyn.) : specimen of moderate size ; head, elytra and legs normal. Structure of prothorax peculiar in that the two lateral halves do not meet in the middle line, leaving betwixt them a membranous space. The prothorax is shortened and the head is pushed back into the thorax as far as the level of the eyes. The edges of the plates of the prothorax are well formed and properly finished. Scutellum present, but is not at all concealed by the prothorax. Drechsel, C, Stettiner ent. Ztg., 1871, xxxii. p. 205. 702. Chrysomela fucata (Phyt.) : Pronotum divided centrally into two parts, each of which is triangular. The parts of the head and scutellum which should be covered by the thoracic shield are thus exposed. Krause, Stettiner ent, Ztg., 1871, xxxir. p. 137. 703. Telephorus nigricans (Mai.) : the pronotum is divided into two unequal halves. The left half is nearly twice as large as the right, and projects beyond the middle line, covering a part of the right side of the prothorax. The right portion is small and very concave. Both of these two parts of the pronotum are everted at their edges to form a definite margin. The margins are con- tinued all round each piece, and thus two margins are adjacent in the contiguous parts of the plates. This specimen was kindly lent to me by M. H. Gadeau de Kerville. 704. Carabus scheidleri: thorax dorsally covered by two com- pletely separate and symmetrical plates, whose inner edges are beset with yellow hairs [as the anterior and posterior margins 456 MERISTIC VARIATION. [part i. normally are]. The rest of the animal was normal. Kraatz, G., Berl. ent. Ztschr., 1873, xvn. p. 430, fig. 705. Carabus lotharingus : thoracic shield divided in centre to form two triangular pieces which only unite at a single point. The head is drawn back into the thorax. Duponchel, Ann. Soc. ent. France, 1841, S. 1, X., Bull, p. XX., PL 706. Lixus angustatus (Rhyn.): thoracic shield partially divided, present a deep emargination both before and behind [description not quite clear]. Doue, Ann. Soc. ent, France, 1851, ix. Bull., p. LXXXII. III. Metasternal plates. ~07. Rhizotrogus marginipes $ (Lam.) having the abdomen de- formed in a svmmetrical manner. Looked at from the ventral surface the metasternal plates are seen to be divided in the middle line by a deep depression so that the abdomen consists superficially of two lobes ; these two lobes are united together in the last segment in which the metasternal plate is undivided. The two lobes are of equal size and the longitudinal depression which divides them is shewn in the figure to be regularly and sym- metrically formed. The animal is otherwise normal. [No dis- section was made.] Baudi, L. V., Bull. Soc. Ent. Ital., 1877, ix., p. 220, fig. IV. Pygidium. 708. Melolontha vulgaris (Lam.) : pygidium bifid, two cases. Kraatz, G., Deut. ent. Ztschr., 1880, p. 342, PL II., figs. 4 and 4 a; and ibid., 1889, p. 222, PL I., fig. 19. ■j-qq A case of "double proboscis 1 ' is recorded in Sphinx ligustri. The specimen was a pupa, and through the pupal skin it could be seen that the two mandibles had not united to form the single proboscis, but were divaricated. Kraatz, Deut. nit. Ztschr., 1880, xxiv., p. 345, rig. Miscellaneous cases of doubtful nature. T 1 0. Ascidians. Prof. W. A. Herdman tells me that he has several times met with Ascidians having a supplementary lateral atriopore. He regards this as a retention of a larval character, since in the young there are two atriopores which in normal individuals afterwards unite dorsally. 711, Limulus polyphemus : large specimen found at Fort Macon, N. Carolina, having a forked caudal spine (Fig. 143). This variation is Fig. 143. Limulus polyphemus No. 711, having forked caudal spine. (After Packard.) chap, xviii.] MEDIAN DIVISION : MISCELLANEOUS. 457 probably very rare. Packard, A. S., Mem. Bost. N. II. S., 1872, n. p. 201, .$7. 712. Palamnaeus borneensis (Scorpion) : specimen in which the terminal poison-spine was double, as shewn in Fig. 144. The two halves were not quite equal and there was no opening of a poison-gland on the shorter spine. This specimen, which is in the Brit. Mus. was kindly shewn to me by Mr R. I. Pocock. Chirocephalus £ : specimen hav- ing the generative sac with two horns instead of one. [Normally there is only one such horn which forms a median downward prolongation of the ovisac. No further description.] Provost, B., Mem. sur les Chirocephales, p. 232 ; in 71; Jurine's 1820. Hist, des Monocles. Geneva, Fig. 144. Double poison-spine of a Scorpion {Palamncem borne- ensis). I. From dorsal side. II. From ventral side. ??, the spine which bore the openings of the poison-glands. 714. Buccinum undatum. A number of specimens were formerly obtained from Sandgate in Kent 1 , having the operculum double. Sometimes the two opercula were separate, sometimes united. Many specimens of this variation are in the collection of Dr A. M. Norman, who kindly shewed them to me. The shells and opercula alone remain and consequently it is not now possible to determine the position of the line of division relatively to the morphological planes of the animal ; but, from the fact that in several instances the two opercula were related to each other as images, it seems likely that the division was in the longitudinal median plane, though this must be uncertain. Moreover in one of Dr Norman's specimens, from the fragment of dried flesh adhering, it appeared that the apex of the foot might have been bifid. Four cases are shewn in Fig. 145. In two of them (I and II) there is a fairly close relation of images, while in III this relation is less clear and in IV it is practically destroyed, though it is of course quite possible that this may be the result of unequal growth. Several of these opercula are much contorted and without any very definite shape. II I w. HE Fig. 145. Cases of duplicity in operculum of Buccinum undatum, from specimens in the collection of Dr A. M. Norman. I and II nat. size. Ill and IV enlarged. Ill and IV were kindly drawn for me by Mr J. J. Lister. 1 See Jeffreys, J. G., Ann. Mag. N. H., 1860 (2), p. 152. 458 MERISTIC VARIATION. [part i. It was intended to have introduced here some account of the curious and very rare cases in which, for a greater or less region of the spine, corresponding half-vertebrae, on either side of the middle line, are not united together in their proper order, but I fear this would be too great a digression. For references on the subject see Leveling, Obs. anat. rarior., Norimb., 1787, Fsc. 1, cap. in. p. 145, Tab. v.; Sandifort, Mils, anat, Leyden, 1835, IV. p. 74. PL clxxviii. ; Reid 1 , Jour, of Anat., 1887, xxi. p. 76, fig.; Guy's Hosp. Rep., 1883, p. 132. Union or absence of Division in the Middle Line. This phenomenon is the converse of that described above. Examples of median union are found in many organs of different kinds. In vertebrates such union is especially well known in the case of the eyes, the ears, and the posterior limbs, producing the cyclopic, synotic and symmelian conditions respectively. Each of these is of some interest to the student of Variation by reason of the symmetry and perfection with which the union takes place. In the cyclopian the degree to which the two eyes are com- pounded presents all shades intermediate between the perfect duplicity of the normal and the state in which the eye-balls are united in the middle line of the forehead and have one circular cornea 2 . These variations are closely comparable with those of the eye-spots on feathers referred to on p. 449 ; for there also all stages are seen between a pair of eye-spots placed one on either side of a middle line and complete union to form one eye-spot bisected by the middle line. There is of course no normal vertebrate having the eyes thus united in the middle line, but as Meckel has remarked, the case of the cyclopian is not essentially different from that of the Cladocera in which the compound eyes, paired in other Crustacea, are united to form a single median eye. The cases No. 718 and 719 of median union of the compound eyes of Bees may also be considered in this connexion. A very similar series of variations occurs in regard to the ears of vertebrates, which in the synotic or cephalotic condition are compounded in the middle line to a varying degree 3 . Such union of the ears is especially common in the Sheep, cyclopia being most frequent in the Pig. Dareste 4 states that the first beginning of the cyclopian condi- tion appears in the Chick as a precocious union of the medullary folds in the region of the fore-brain, occurring before the optic vesicles are fully formed from it. The degree to which the union of the eyes is complete then depends on the earliness with which the folds begin to meet relatively to the time of budding off of the optic vesicles. Dareste 5 also declares that the cephalotic state is similarly first indicated by a premature union of the folds in the region of the medulla, taking place 1 A ease in Man, resembling No. 7. 2 For an extensive collection of cases illustrating the various degrees of cyclopia see especially Ahlfeld, Missb. d. Mensch., Abschn. n. 1882. 3 For figures see e.g., Otto, Mus. anat. path. Vratisl., PI. i. fig. 5, PI. in. fig. 2 (Lambs) ; Guerdan, Monats.f. Geburtsk., x. p. 176, PI. i. (Man) and many more. 4 Comptes rendus, 1877, lxxxiv. p. 1038. 5 I. c, 1880, xc. p. 191. chap, xviil] MEDIAN UNION : KIDNEYS. 459 before this part of the brain has widened out. In this way the auditory involutions are approximated. This account however cannot apply to all cases of union of ears; for the compounded ears are sometimes on the ventral side of the neck, as in Guerdan's case 1 . The body of the symmelian ends posteriorly in an elongated lobe made up of parts of the posterior limbs compounded together by homo- logous parts. The two femora are usually united to form a single bone, the tibiae are separate and the two limbs are again compounded in the tarsal region. The axial parts posterior to the hind limbs are always greatly aborted 2 . Union of the kidneys in the middle line (Fig. 146), forming the " horse-shoe kidney " of human anatomists, is a similar phenome- non. As to the mode of development of this variation I know no evidence. Usually the kidneys together form a single horse-shoe shaped mass of glandular tissue, the union being posterior 3 ; very Fig. 146. Kidneys united in the condition known as "horse-shoe" kidney (Man). In this specimen there were three renal arteries on each side. (From Guy's Hosp. Rep., 1883.) 1 See note 2, p. 458. 2 See especially, Meckel. Arch. Anat. Phys., 1826, p. 273; Geoffroy Si Hilaire, Hist, des Anom., ed. 1837, n. p. 23; Gebhard, Arch. Anat. Phys., l^ss, Anat. Abth., p. 164 (good fig.). To the determination of the morphology of the hind limb the structure of the symmelian monster is of unique importance, but I do not know that it has had the notice it deserves from comparative zoologists. From the manner of union of the parts of the two limbs may be obtained a positive proof of the morphological relations of the surfaces of the two limbs to each other. In a symmelian the feet are united by their fibular borders, the minimi being adjacent, the halluces exterior, and the combined plantar surfaces ventral. The great trochanters are dorsal, being often united into one in the dorsal middle line, and the patellae are also dorsal, being also not rarely partly compounded. From these facts, even were other indications wanting, we have a proof that if the hind limbs were laid out in their original morphological relations to each other (as the tail-fins of a Crayfish may be supposed to be) the halluces would be external and anterior, the minimi internal and posterior, the flexor surfaces of the thigh and crus and the plantar surface of the (human) foot would be ventral and the extensor surfaces of the thigh and crus and the dorsum of the (human) foot would be dorsal. This is of course affirmed without prejudice to any question of phylogeny ; but that these must be the ontogenetic relations of the parts is clearly proved by the symmelian. 3 Sometimes anterior, e.g. Odin, Lyon mid., 1874, No. 12 [from Constat?* Jahresb., 1874, i. p. 19] ; and Freund, Beitr. z. Geburtsh. u. Gyn., iv. 1875 [from Canstatt's Jahresb., 1875, p. 340]. 460 MERISTIC VARIATION. [part I. rarely the posterior ends of the kidneys are joined by a bridge of ligamentous tissue 1 . A remarkable case, in which the union of the two kidneys was very complete and only indications of duplicity remained, is given by Pichaxcourt, Gaz. hebd., 1879, p. 514. *7 715 Illustrative Cases. To these familiar instances are added a few less generally known. Capreolus caprea (Roebuck): specimen having the two horns compounded in the middle line, forming a common beam for almost the lower half of the horn (Fig. 147). This specimen was exhibited among a large series of abnormal horns in the German Exhibition beld in London 1891. Casts of it are in the Brit. Mus. and Camb. Univ. Mus. 2 . * >v ' Fig. 147. A Roebuck (Capreolus caprea) Xo. 705, having the horns com- pounded to form one. 716. Limax agrestis : specimen having the upper tentacles united into one in the middle line. The eyes were paired as usual. Forbes and Haxley, Hist. Brit. Moll, iv. p. 288 and I. PI. JJJ, fig. 4. 1 See Gruber, Virch. Arch., 1865, xxxn. p. 111. The original is at Darmstadt. chap, xviii.] MEDIAN UNION: EYES. 461 717. Helix hispida : specimen in which the tentacles were united together. They were adherent throughout, excepting for a slight cleft at the end, about one line in length. A shallow longitudinal suture was visible between the two. The animal and shell were otherwise normally formed. Roberts, G., Science Gossip, 1886, xxii. p. 259. *718. Apis mellifica (Honey-bee): a worker having the two com- pound eyes continued up so as to unite on the top of the head (Fig. 148). The union between the eyes of the two sides was com- plete. There was no trace of any groove or division between them and the resulting structure was perfectly symmetrical. In a normal the three simple eyes are arranged in a triangle between CE~~~^1 Fig. 148. A worker Bee (Apis mellifica) No. 708, having the two compound eyes united across the middle line, seen from in front, and from the side. CE, the united compound eyes. Oc, a single structure representing the three simple eyes of the normal. (After Stannius.) the upper edges of the compound eyes, but in this specimen they were united into a single structure which was symmetrically placed in the middle line in front of the united compound eyes (Fig, 148, Oc). The body thus formed by the union of the simple eyes was a round projection beset with long yellowish hairs. In a normal male the compound eyes are much larger and are in contact with each other at the top of the head, but the division between them is sharply defined. In a normal worker, however, the compound eyes are widely separated. The facetting and the hairs on these eyes were normal and the animal was in all other respects properly formed. STANNIUS, Muller's Arch, Anal Phys., 1835, p. 297, PI. '719. Apis mellifica having the compound eyes completely and symmetrically fused. This individual was either a young and abnormally developed queen, or else a worker. Its structure was in several respects abnormal. The third pair of legs are like those of the workers, as is shewn by the structure of the first joint of the tarsus, the brush of hairs on the outside of the leg is not so 462 MERISTIC VARIATION. [part i. much developed as in the workers, and this feature suggested that perhaps the specimen may be a young and abnormal queen. The abdomen is small and seems to have been arrested in its develop- ment, but its shape is that of the abdomen of the workers. The last segment of the abdomen is elongated, triangular, and slightly grooved in the middle of the posterior border, so as to permit the passage of the sting. The wings are more like those of a queen or worker than those of a male ; for in the latter they generally greatly exceed the abdomen in length. The thorax is small, narrow, and contracted more than in the normal form, being also less convex. The space between the wings is less than in a fully developed bee. The antennas are mutilated, but seem to have been normal ; but their last joints are slightly reddish brown as they are in females, whether workers or queens, and not black as they are in drones. The two compound eyes were completely fused together in the middle line, across the place in which the simple eyes ought to be found. The simple eyes are not present at all. Lucas, H., Ann. Soc. Entom. France, S. 4, viii. 1868, p. 7: 37, PI. CHAPTER XIX. bilateral series — continued. Further illustrations of the Relationship between Right and Left Sides. I. Variations in Segmentation of the Ovum of Loligo. The following facts, taken from Watase 1 , are introduced in further illustration of the mode of occurrence of bilaterally symme- trical M eristic Variation. *720. Loligo pealei. In the blastoderm the nucleus is placed eccen- trically, being rather nearer to the posterior pole, as shewn in Fig. a. v. Fig. 149. Diagrams illustrating variations in segmentation of a Squid. (Loligo pealei). I. Normal unsegmented ovum, n, the nucleus eccentrically placed. A, anterior. P, posterior. L, left. R, right. II, III, and IV. The shaded portions shew areas in which in some specimens nuclear division was precocious. V. In the two shaded areas triasters occurred in one specimen. VI. The hlastomeres of the shaded areas in one specimen were not divided from each other. 1, 2, 3, successive planes of division, ar, anterior right quadrant, pr, posterior right quadrant. ar', pr', &c. areas separated off by the third segmentation-furrow. (After Watase.) 1 Watase, S., Jour, of Morph., iv. 1891, p. 247, Plates. 464 MERISTIC VARIATION. [part I. 149, I. The first furrow, 1, 1, divides the blastoderm into two halves and corresponds with the future longitudinal middle line. The second furrow, 2, 2, is at right angles to this, dividing the blastoderm into anterior and posterior halves, and the third furrow, 3, 3, passes as shewn in Fig. 149, V. In the subsequent segmentations various irregularities were seen in single eggs, some of the variations being bilaterally sym- metrical while others were confined to a particular half or to a particular quadrant. For example, in some ova the nuclei of the cells formed from the left half of the blastoderm, excepting those next the median axis posteriorly (Figs. 149, II and 150, I), began to divide before those of the right side and reached an advanced stage of karyokinesis while the nuclei of the right half were still resting. The nuclei of each half kept time very nearly (for details see original figures). This curious variation was seen in three (perhaps four) ova all taken from one mother. In another the nuclei of the two anterior quadrants al, ar, in their divisions kept ahead of those of the posterior quadrants. Fig. 149, IV. represents an ovum in which the nuclei of the right posterior quadrant on the contrary divided before those of the 3 other quadrants. Another variation is shewn in Figs. 149, VI and 150, II. There the four blastomeres shaded had either been never fully divided from each other or had subsequently fused together symmetrically on each side. / IT Fig. 150. Variations in segmentation of ovum of Loligo pealei. I. Case in which the nuclei of cells of the left half of the blastoderm began to divide pre- cociously. II. Case in which the blastomeres of the areas ar' and al' were not distinct from each other. (After Watase.) Fig. 149, V, illustrates another remarkable Meristic variation which symmetrically affected the portions shaded. In both of these shaded segments the nuclei divided into three by triple karyokinesis, forming " triasters." chap, xix.] LATERAL HOMOEOSIS. 465 II. Homoeosis in cases of normal Bilateral Asymmetry. In proportion as an animal is bilaterally symmetrical the right side is an image of the left. Nevertheless in many substantially symmetrical forms there is asymmetry in the condition of some one or more organs present on both sides. (This asymmetry, in the cases to be considered, is of course distinct from that due to asymmetrical disposition of unpaired viscera, such as the heart and liver of vertebrates, &c.) In several of these cases there is evidence that both sides may on occasion assume the form normally proper to one only. Some one will no doubt be prepared with the suggestion that these variations are reversions : with this suggestion I shall deal after the facts have been recited. Spiracle of Tadpole. 721. Pelobates fuse us : a tadpole, 7 cm. long, having two spiracles symmetrically placed (Fig. 151), one on the right side and the other on the left 1 . [No details given.] H^ron-Royer, Bull. soc. zool. Fr. t ix. Fig. 151. A tadpole of Pelobates fuscus, having, as a variation, two spiracular openings, No. 721. (After Heron-Royek.) 1884, p. 162, j%. [In the normal there is only one spiracle, that of the left side. In Pipa and Dactylethra two spiracles are normally present. See Wyman, Proc. Bost. N. H. S., ix. p. 155; Wilder, Am. Nat.y 1877, xi. p. 491 ; Boulenger, Bull. soc. zool. Fr., 1881, vi. p. 27. Tusk of Narwhal. 722. Monodon monoceros (Narwhal). In normal males the left tusk alone is developed while the right remains abortive in its alveolus. In the female both tusks are in this rudimentary condition. No reliable record (1871) of a specimen having the right tusk only developed, but in eleven cases from various sources the two tusks were both developed, and in several of these the two were of about equal length. The normal asymmetry of the skull is not affected by the presence or absence of the teeth. Clark, J. W., P. Z. S., 1871, p. 42, figs, (full literature); see also Turner, W., Jour. Anat. Phys., 1871, p. 133 and 1874, p. 516. Ovary and oviduct of Fowl. It might be anticipated that development of the right ovary and oviduct in birds would be a frequent form of Variation, but as a matter of fact very few such cases are recorded. In consideration of 1 In the same place is recorded a case of a tadpole of this species having the spiracle on the right side instead of the left, perhaps a case of situs inversus. b. 30 466 MERISTIC VARIATION. [part i. the large numbers of birds, wild and domesticated, annually dissected in laboratories it may perhaps be concluded that these variations are exceedingly rare 1 . 728. Hen having a small right ovary in addition to the left ovary. The left oviduct was normal, but the left ovary was partially transformed into sacculated tissue. [Full histological details of the structure of both ovaries given.] The hen had partly assumed the plumage of the cock, having four sickle-feathers and other characters proper to the male. Brandt, Z.f. w. Z., xlviii. 1889, p. 134, Pis. 724. Hen having a normal left oviduct and in addition a partially developed right oviduct which formed a large thin-walled cyst dis- tended with gas. C. S. M., Ter. Cat., 1872, 455. Proboscis-pore of Balanoglossus and ivater-pores of larvce of Asterias. ♦725. Balanoglossus kowalevskii. The anterior or proboscis-body- cavity is continued backwards into the proboscis-stalk as two hollow horns. In this and most other species the left of these alone acquires an opening to the exterior at the proboscis-pore. In B. kupfferi alone there are two such pores, one opening into each of the two horns 2 . A specimen of B. kowalevskii in which both horns thus opened to the exterior was seen by Morgan, T. H., Jour, of Morph., 1891, v. p. 442. 72G. Asterias vulgaris. The Bipinnaria larva as commonly seen resembles the usual Tornaria in having a left water-pore only. In several larvae 3| to 4 days old the presence of two such water-pores, a right and a left, symmetrically placed, has been observed by Field and Brooks. The right pore subsequently closes. This condition is be- lieved by Field to represent not a variation but a normal phase of development [though further confirmation is needed]. Field, G. W., Q. J. M.S., 1893, xxxiv. p. 110, PL xiv. figs. 22 and 23. Variations in Flat-fishes. A curious series of variations bearing on the relations of the right side to the left occur in Pleuronectidse. The evidence on this subject was collected by Steenstrup 3 in 1863. Flat-fishes are normally coloured on the upper side and are without chromatophores in the skin of the lower side 4 . Variations in colour occur in two ways ; the upper side may be white like the lower, or on the contrary the lower side may be coloured like the upper. The former change cannot well be distinguished from other cases of albinism 5 and does not call for special notice here. 1 In view of the cases of the Crayfish and the Cockroach mentioned in the Preface, much stress cannot be laid on this consideration. 2 Spengel, J. W., Mitth. zool. Stat. Neap., 1884, v. p. 494, PI. xxx. fig. 2. 3 Steenstrup, Overs, k. Dansk. vid. Selsk., 1863, p. 145, abstr. by Wyville Thomson, Ann. and Mag. X. H., 1865 (1), p. 361. 4 In some species the coloured side is normally the right, in others the left, reversed specimens being common in some species (P. Jlesus), rare in others. The reversed condition concerns only the head, skin, muscles, &c, and there is no transposition of the internal viscera. 5 Evidence collected by Steenstrup. Gottsche (Arch. f. Naturg., 1835, n. p. 139) states that P. platessa is not rarely wholly white on both sides. I have never chap, xix.] FLAT-FISHES. 467 The converse variation, by which the lower side assumes the colour of the upper side is important in several aspects. Interest has of late been drawn to this subject especially through an experiment recently made by Cunningham 1 , who found that of a number of young flat-fishes reared in a vessel illuminated by mirrors from below, some became partially marked with pigmented patches on the lower side. The suggestion was made that this pigmentation was induced by the direct action of light. It is of course impossible here to enter into the theoretical questions raised in connexion with this subject and this account will be confined to description of the colour- variation as seen in nature and of the singular variation in structure commonly associated with it. Mr Cunningham has obligingly advised me in connexion with this subject. Pigmentation of the lower side has been seen in Rhombus maocimus, R. Icevis, Pleuronectes flesus, P. platessa, P. oblongus, Solea vulgaris [?] and probably other forms. Attention is drawn to one feature in these changes which from our standpoint has an important bearing. When the underside of a flat-fish is pigmented, it is often not merely pigmented in an indefinite way but it is coloured and marked just as the upper side is. There are, I know, many specimens upon whose undersides a brownish yellow tint is either generally diffused or restricted to patches, but when there is pigment of a deeper shade, as in all the well marked cases of the variation, the colour and markings are closely like those of the upper side. For example, a Plaice (P. platessa) sent to me by Mr Dunn of Mevagissey is fully coloured over the posterior half of the lower side ; but there is not merely a general pigmentation, for the coloured part of the lower side is marked ivith orange markings exactly like those of the upper side. More than this : it was found by passing pins vertically through the body that there was in the case of most of the spots a close correspondence in position behveen those of the upper and those of the loiver side. There were 13 spots on the coloured part of the lower side, which extended slightly beyond the line of greatest width. Of these, 13 spots on body and fins coincided exactly with those of the upper side ; 2 coincided nearly ; 2 were not repres- ented on the upper side ; and 2 spots of the upper side were not represented on the lower. From these facts it is clear that in " double " flat-fishes we have an instance of symmetrical variation of one half of the body into more or less complete likeness of the other half, resembling other cases of Homceosis in Bilateral Series already noticed. This is made the more evident by the fact that in the two best described specimens of "double" Turbot (No. 727) not merely did the lower side resemble the upper side in point of colour, but upon it were also present the bony tubercles normally proper to the dark side, being only slightly less well developed on the lower side than on the upper. succeeded in seeing an entirely white specimen, though individuals partially white on the upper side are not rare. See also Zool, pp. 4596, -1914. Zeugopterus puncta- tus white on both sides, Day, Brit. Fishes, n. p. 19. 1 Cunningham, J. T., Proc. Roy. Soc, 1893. 30—2 468 MERISTIC VARIATION. [part I. (Such a development of tubercles 1 on the lower side may however occur without any correlated change of colour.) It is also stated that in the " double " turbots the muscles of the lower side are thicker than they normally are, thus approximating to the upper side, a feature that may be taken as an indication that the manner of swimming is different from that of normals. A flat-fish having pigmentation on the lower side does not necessarily present any other abnormality' 2 . The Plaice, for in- stance, just mentioned, was, colour apart, quite normal. But some specimens of flat-fishes darkly coloured below present in addition a very singular structural variation. This consists essen- tially in the presence of a notch of greater or less depth occurring below the anterior end of the dorsal fin above the eye (Fig. 1 52). By this cleft the anterior end of the dorsal fin is separated from the back of the head and is borne on a process or horn project- ing anteriorly so as to continue the contour of the body above the Fig. 152. Head of a Brill (Rhombus Icevis) having the dorsal fin separated from the head as described in the text. (From Yarrell.) 1 The literature relating to discontinuous variations consisting in the presence of bony tubercles upon the blind side of Rhombi is extensive. See especially Demidoff, Voy. dans la Russie Merid., 1840, in. p. 534, Pis. 28, 29 and 30. Steixdachner, Sitzb. Ak. Wiss. Wien, 1868, lvii. (1), p. 714. Rathke, Mem. Ac. Sri. P6t. t 1837, in. p. 349. Gunther, Cat. Brit. Mm. Fishes, iv. p. 409. These cases will not be confounded with those of supposed hybrids between R. maximus and R. lavis, which bear upon both sides scales of various sizes. - I know no detailed description of a flat-fish wholly pigmented on the underside, having the dorsal fin normal, but numerous authors (Gottsche, Duhamel, &c.) make mention of such cases. Since this chapter was written I have seen two recent papers on the subject by Giard (Comptes rend. Soc. Biol, 1892, S. 9, iv. p. 31 and Nat. Sci., 1893, p. 356) contributing further evidence on the subject and giving new cases in the Turbot. According to Giard, of flounders (P.Jiesus) at Wimereux 3 °/ are fully coloured on the blind side, in addition to many that are piebald. This must be a very much higher proportion of abnormal specimens than is found in English fisheries. chap, xix.] FLAT-FISHES. 469 head. Steenstrup states that the variation has, he believes, been observed in all flat-fishes 1 except the Halibut (Hippoglossus). In several but not all cases of this abnormality the eye belong- ing to the lower side was not placed in its normal position on the upper surface, but stood in an intermediate position on the top of the head, so that it could be partially seen in profile looked at from the " blind " side. It seems possible that the pigmentation of the " blind " side is in some way correlated with some abnormal delay in the shifting of the eye and a consequent continuation of the power of receiving visual sensations from this side. The abnormality of the dorsal fin is in accordance with this suppo- sition. To understand the nature of this condition it must be remem- bered that the form of the flat-fish is derived from the usual "round" form by two principal changes. (1) By a twisting of the head the eye is brought over from the blind side to the upper side. (2) The dorsal tin is extended forwards above the eye thus shifted ; for as Steenstrup and Traquair 2 have shewn, this anterior extension of the dorsal fin is not in the morphological middle line. It is in fact an anterior repeti- tion of the series of dorsal fin-rays along the new contour-line of the body, and occurs irrespective of the fact that the tissues with which it is there associated are not median at all. Steenstrup and Traquair shewed plainly that it is insufficient to suppose that there is a twisting of the head, for this does not explain the presence of the dorsal fin in the position in which it is found, curving along that which ivas once the side of the head. Traquair sug- gested that these relations could be attained by two processes ; ( 1 ) a twisting of the head so as to bring over the eye from the future "blind" side, and (2) a forward growth of the dorsal fin along that which is then the upper contour-line of the head. These processes have now been actually seen by Agassiz 5 in several Pleuronectidre. The first observation of a specimen at the stage when the eye is on the top of the head and the dorsal fin is not yet extended, seems to be that of Malm 4 and there can be little doubt that the normal development proceeds in this way 5 . It has been pointed out by many writers that if the upper eye were to remain in an intermediate position on the top of the head, and the dorsal fin were then to grow forwards, arching over it, the condition of these abnormal forms would be reached. That this is what has actually occurred in them seems likely. A number of difficult questions are thus raised as to the histological 1 The evidence as to the Sole seems to be doubtful (v. infra). 2 Traquair, Trans. Linn. Soc, 1865, xxv. p. 2(33. 3 Agassiz, Proc. Amer. Ac. Sci. 1878, xiv. p. 1, Pis. 4 Malm, (Efvers. k. Sven. Vet. Ac, 1854, p. 173, see Ann. and Man. N. H. 1865 (1), p. 366. 5 Allusion should be made to the fact that in the genus " Plagusia" the dorsal fin acquires its forward extension at a time before the shifting of the eye occurs. When the time for this change comes the eye of the future bliud side passes under the dorsal fin and above the skull, through the tissues from one side of the head to the other. This was first observed by Steenstrup, and afterwards by Agassiz in great detail and the fact can hardly now be questioned. This mode of development is peculiar to " Plagusia" though when Steenstrup wrote he expected that the same would be found to occur in other Pleuronectidse. 470 MERISTIC VARIATION. [part I. processes by which the dorsal fin comes to stand where it does. We are accustomed to think of the repetition of the fin-rays as being an expression of the fundamental segmentation of the trunk, accessory to it no doubt, but still of the same nature and histologically dependent upon it. The extension of this repetition along the morphological side of the face is thus an anomaly. Further comment on the nature of the variation will be made after the chief cases have been given. *727. Rhombus maximus (Turbot). Two specimens respectively 9 in. 9 lines and 7 in. 6 lines in length, 7 in. 6 lines, and 5 in. 6 lines broad. Both sides of a similar coffee-brown colour. The smaller had a yellowish white spot, about 1 in. square, on the operculum of the lower side. The colour was more uniform than usual and the dark spots normally found on the fins of the Turbot were absent. Both sides irregularly beset with horny tubercles, only slightly more developed on the upper than on the lower sides. Fine scales were also found deep in the skin of both sides. All fins except the dorsal were normal in form and position. The dorsal fin was anteriorly detached from the head, being borne on a horn-like projection. The separation between the head and dorsal fin was continued backwards as a semi-circular notch to a level behind the eyes. Upon many of the fin-rays of the dorsal, anal and caudal fins there were 1 — 7 small knotty elevations of the size of poppy-seed. In the smaller specimen these elevations were smaller, and on the caudal fin absent. The left eye had its normal posi- tion, but the right eye [of "blind" side] was placed on the top of the head, but in such a position that it could scarcely have seen any thing not directly over it. [See further details given.] Schleep, Isis, 1829, p. 1049, PL in. Similar specimen Couch, Fishes Brit. Isl., in. p. 157. Dried speci- mens in Brit. Mus., Newcastle Mus., &c. *728. Very good figures of such a Turbot are given by Duhamel du Monceau (Traite general des Pesches, 1777, III. Sect. ix. p. 262, PI. III. figs. 3 and 4). The under side was of nearly the same colour as the upper and the tubercles generally found on the upper side only were present on the lower side also, though of smaller size. A slight notch separated the dorsal fin from the head ; but the upper eye is figured as in its normal place, not being on the top of the head, and it w T ould of course be invisible from the "blind" side. [This important case is referred to by Steenstrup, but seems to be unknown to others, who attribute the separation of the dorsal fin to the persistence of the eye on the top of the head.] 729. A young turbot, similarly coloured on both sides, having the eyes still symmetrical, swimming on edge, is figured by McIntosh, Fishes of St. Andrews, 1875, PI. vi. figs. 5 and 6. Prof. Mcintosh kindly informed me that these "double" individuals swim on edge much longer than usual. 730. Rhombus laevis (Brill). Specimen presenting similar characters. The lower (rt.) side of a uniform dark colour with exception of a white patch on operculum. The right pectoral fin was whitish. The under side was rather darker than the upper and the mottling present on the upper side was entirely absent from the under side, which was without marking or spot. This is very probably a post- chap, xix.] FLAT-FISHES. 471 mortem change. Right pelvic fin dark, but the left was whitish, speckled with black. Nostrils normal. The eye of the right (blind) side was placed almost entirely on the left side, but not completely so, for it could be seen to some extent in profile from the right side. The notch separating the dorsal fin from the head was rounded, and extended to about the level of the posterior margin of the left eye. There were about 6 chief fin-rays borne by the prominence above the eye. The fish seemed to be in all respects healthy and well grown. Paris Mils., numbered #90 #310. [This specimen was kindly shewn to me by Prof. Vaillant.] Similar specimen, also having white patch on operculum Duhamel du Monceau, 7. c. See also Fig. 152, from Yarrell, Brit. Fishes, 3rd ed., i. p. 613. The specimen described by Donovan (Brit. Fish., 1806, iv. PI. xc.) under the name " Pleuronectes cy clops" was in Steenstrup's opinion a young Brill having this variation. In this specimen the right eye is seated on the top of the head and is seen in profile from the right side. The right side was coloured like the left, but was not so dark. The dorsal fin began behind the right eye. This specimen was found in a rock-pool "inveloped in a froth" said to have resembled cuckoo-spit. 731. Zeugopterus punctatus (Muller's Topknot). This fish is very liable to mal- formations of the anterior end of the dorsal fin, causing it to form an arch over the eyes. Yarrell (quoting Couch), Brit. Fish., 3rd ed., i. p. 6-18. 732 "Platessa oblonga" De Kay (American Turbot) ; specimen having both sides darkly coloured; upper eye placed on the top of the head; dorsal fin separated by a notch. Storer, Mem. Amer. Ac. Sci., vm. p. 396, PI. xxxi. fig. 2 b. 733. Pleuronectes platessa (Plaice) : specimen completely and similarly pigmented on both sides far from rare. In a specimen thus coloured the ' tubercula capitis ' were as strongly marked on the one side as on the other. In several examples the anterior end of the dorsal fin was separated, from the head, Gottsche, Arch. f. Naturg., 1835, n. 1, p. 139. 734 Pleuronectes nesus (Flounder) : several specimens found at Birkenhead, having ' a deep notch of this kind above the eyes. These fishes were 'very dark brown (almost black) on both sides.' In the length of the fins these examples differed somewhat from the Flounder, Higgins, Zoologist, 1855, p. 4596, fig. Specimen of this kind figured by Traquair, Trans. Linn. Soc, 1865, xxv. p. 288, PI. xxxi. figs. 8 and 9. See also Nilsson, Skandin. Fauna: Fiskama, Lund, 1855, p. 621; Couch, Brit. Fishes, 1864, in. p. 198. 735. Solea vulgaris. Many authors mention Soles coloured on both sides, but I know no good description of one. Yarrell (I. c, p. 669) says "we have not seen the Solea Trevelyani of Ireland (Sander's News-letter, 16th April, 1850). It is dark-bellied and is described as bearing a projection on the head like the monstrosity figured on p. 643." Duhamel du Monceau (/. c, PL I. figs. 3 and 4) represents a sole darkly coloured on both sides. The dorsal fin is shewn in its normal state, not separated from the head. No special description is given, and as the author does not state that he had himself seen such a sole the figure was perhaps not drawn from an actual specimen. A sole with the under side piebald is described in Zool. x. p. 3660. In connexion with this evidence Steenstrup refers to a small flat- fish, Hippoglossus pinguis, found in a few localities in Scandinavian waters, having a form almost intermediate between a "flat" and a "round" fish. The eye of the "blind" side is exactly on the top of the head and can be seen in profile from the blind side. The blind side is nearly as muscular as the upper side, and its skin is yellowish-brown in colour and is only slightly paler than that of the upper side. The dorsal fin begins behind the eye, not arching over it. Steenstrup looked on this creature as representing in a normal form the "double condition presented as a variation in the cases we have been speaking of. See description and figures in Smit's edition of Fries, Ekstrom and Sundevall's Hist, of Scand. Fishes, 1893, pp. 416 and 417. Smit makes a new genus, Platysomatichthys, for this animal. 472 MERISTIC VARIATION. [part i. Comment on the foregoing cases. In the cases preceding many will no doubt see manifest examples of Reversion. There is a sense in which this view must be true, for it can scarcely be questioned that if we had before us the phylogenetic series through which the Flat-fishes, the Narwhal, &c. are descended, it would be seen that each did at some time have a bilaterally symmetrical ancestor. But, for all that, in an unqualified description of the change as a reversion the significance of the facts is missed. By the state- ment that a given variation is a reversion it is meant that in the vary- ing individual a form, once the normal, reappears. The statement more- over is especially intended to imply that the definiteness and magnitude of the step from normal to variety is due to the circumstance that this variety was once a normal. It is meant, in fact, that the great- ness of the modern change can be explained away by the suggestion that in the past, the form now presented as a variation, was once built up by a gradual evolution, and that though in its modern appearance there is Discontinuity, yet it was once evolved gradually. Now the attempt to apply this reasoning, especially to the case of the "double " Flat-fishes, leads to difficulty. "We may admit that in so far as the varieties are bilaterally symmetrical they represent a normal. Their bilateral symmetry, as a quality apart, may be an ancestral character, if any one is pleased so to call it. But that in the contem- porary resumption of a bilateral symmetry we have in any further sense a reappearance of an ancestral form is very unlikely. First it might be fairly argued that it is improbable that there was ever a typical flat-fish having ori'both sides the peculiar pigmentation of the present upper sides of the Pleuronectidse of our day. Such a creature would be highly anomalous. But even if in strictness we forego the assumption that since the evolution of Flat-fishes there has never been an ancestor fully pigmented on both sides, there still remains the difficulty that each species may in the "double" state have upon its lower side the specific colour proper to its own upper side. A notable instance of this has been mentioned in the Plaice (p. 467); and here not only was the pigmentation of the lower side, as far as it went, like that of the upper, but the spots were even almost bilaterally symmetrical. It is true that the lower side does not in every case copy the upper in colour, but it may do so ; and, in proportion as it does so in different species, so far at least are the changes not simply revers- ions ; for the several patterns of Turbot, Plaice &c. are mutually ex- clusive and it can hardly be supposed that each species had separately a "double" ancestor having the present specific pattern on both sides. The outcome of this reasoning is to shew that the hypothesis of Reversion in the strict sense is an insufficient account of the actual variation in these Flat-fishes, and in the production of these varying forms there is thus a Discontinuity over and above that which can be ascribed to Reversion. The facts stated in connexion with the Plaice (p. 467), especially the symmetry of the spots, probably indicate the real nature of this Discontinuity, and raise a presumption that in the new resemblance of the lower side to the upper we have a phenomenon of Symmetry resembling that Homceosis shewn to occur between parts in chap, xix.] LATERAL HOMCEOSIS : COMMENT. 473 Linear Series. In the Flat-fish the right side and the left have been differentiated on different lines, as the several appendages of an Ar- thropod have been, but on occasion the one may suddenly take up all or some of the characters, whether colour, tubercles or otherwise, in the state to which they have been separately evolved in the other. What may be the cause leading to this discontinuous change we do not know. That it is often associated with a delay in the change of position of the eye of the " blind " side seems clear from the frequent detachment of the dorsal fin in these cases. But it should be borne in mind that even in such examples the eye may still eventually get to its normal place, though probably it was delayed in the process and so led to detachment of the fin. Taken with the fact that the young " double " turbots swim on edge longer than the normals it must be concluded that the bilateral symmetry of colour is associated with reluctance or delay in the assumption of the asymmetrical state, but more than this cannot be affirmed. I do not urge that the same reasoning should be applied in other cases, but the possibility must be remembered. In the Narwhal, for instance, it is perhaps unlikely that there was ever an ancestor which had two tusks developed to the extent now reached by the left tusk of the male ; but if there ever were any such form, it is hard indeed to suppose that it could have been connected with the present species by a series of successive normals in which the right tusk gradually diminished while the left was of its present size. On the whole it seems more likely that when the right tusk now develops to be as long as the left, it is taking up at one step the state to which the left has been separately evolved. However this may be, the fact that such Homoeosis is possible should be kept in view in considering the meaning of such cases as that of a Tornaria with two water-pores. For while on the one hand we may suppose that Balanoglossus kupfferi with its normal pair of water- pores is the primitive state and that the varying Tornaria is a revers- ion, on the other hand B. kupfferi may be a form that has arisen by a Homceotic variation from the one-pored form, and of this variation Balanoglossus No. 725 may be a contemporary illustration 1 . 1 The following interesting example of a similar Variation has appeared since these pages were set up. Eledone cirrhosa : specimen having not only the third left arm developed as a hectocotylus, as usual, but the third right arm also. The right had 57, the left 66 suckers, but otherwise they were alike. Appellof, A., Bergens Museums Aarbog, 1893, p. 14. CHAPTER XX. Supernumerary Appendages in Secondary Symmetry. Introductory. — The Evidence as to Insects. Of all classes of Meristic variations those consisting in repeti- tion or division of appendages are by far the most complex and the most difficult to bring into system. There is besides no animal which normally presents the condition seen in the varia- tions about to be described, though there may be a true analogy between them and phenomena found in colonial forms. It has nevertheless seemed well to introduce some part of this evidence here for two reasons. First the subject is a necessary continuation of the evidence as to digits, which would otherwise be left incom- plete ; secondly it will be shewn that though many of the cases are irregular and follow no system that can be detected, there remain a large number of cases (being, indeed, the great majority of those that have been well studied) whose form-relations can be put in terms of a simple system of Symmetry. Thus not only are we introduced to a very remarkable property of living bodies, but also the way of future students of Variation may be cleared of a mass of tangled facts that have long been an obstacle ; for on apprehen- sion of the system referred to it will be seen that cases of repeti- tion in Secondary Symmetry are distinct from those of true Variation within the Primary Symmetry and may thus be set apart. Arrangement of evidence as to Repetition of Appendages. In the first instance I shall give the evidence as to Secondary Symmetries in Insects and Crustacea, prefacing it with a prelimin- ary account of the system of Symmetry obeyed by those cases which I shall call regular, and explaining the scheme of nomen- clature adopted. Besides the regular cases of extra parts in Secondary Symmetry there are many irregular examples which cannot be shewn to conform to the system set forth. Of all but a few of these, details are not accessible, and of the rest many are chap, xx.] SECONDARY SYMMETRY: PRELIMINARY. 475 mutilated or so amorphous that the morphological relations of the surfaces cannot be determined. Over and above these there remain a very few cases of Repetition of parts of appendages where the arrangement is cer- tainly not in Secondary Symmetry, but is of a wholly different nature, exemplifying in Arthropods that duplicity of limbs already seen in the human double-hands (p. 331) and in the double-feet of Artiodactyles (p. 378). Genuine cases of this kind are excessively rare ; but owing to hasty examination great numbers of cases have been described as instances of duplicity, though in reality the supernumerary parts in them can be shewn to be of paired struc- ture. To emphasize the distinctness of these cases they will be made the subject of a separate consideration. Logically they should of course be treated before the Secondary Symmetries ; but their essential features may be understood so much more readily if the latter are taken first that I have decided to change the natural order. In continuation of the evidence as to Secondary Symmetry in Arthropods will be given a brief notice of similar phenomena in vertebrates. This evidence is comparatively well known and accessible and I shall attempt no detailed account of it, referring to the facts chiefly with the object of shewing how the principles found in Arthropods bear on the vertebrate cases. It will then be necessary to consider how repetitions in Second- ary Symmetry are related to other phenomena of Repetition. Lastly something must be said with regard to the bearing of these facts on the general problems of Natural History. Preliminary account of paired Extra Appendages in Secondary Symmetry (Insects). Supernumerary appendages in Insects are not very un- common, perhaps 120 cases of this kind being recorded 1 . Nearly all known examples are in beetles, but this may be due to the greater attention paid to the appendages in that order. They do not seem to appear more often in one family than in another, but perhaps the rarity of instances in Curculionidye is worth noting. They are found in both sexes, in all parts of the world, and in species of most diverse habits. Supernumerary parts may be antenna?, palpi or legs. (Extra wings are probably in some respects distinct. They have al- ready been considered. See p. 281.) Extra appendages may be either outgrowths from the body in the neighbourhood of the part repeated, or, as in the great majority of cases, they occur as outgrowths from an appendage, extra legs growing from normal legs, extra antenna: from antenna 1 , &c. In every case there are two essentials to be determined : first the constitution 1 Not including some 110 cases of alleged duplicity of appendages given later. 476 MERISTIC VARIATION. [part L of the extra parts, and secondly the symmetry or relation of form subsisting on the one hand between the extra parts themselves, and on the other between the extra parts and the normal parts. In few cases of extra appendages arising from the body itself have these essentials been adequately ascertained. For brevity I shall describe the phenomena as seen in extra legs. The same description will apply generally to the antennae. Recorded cases of extra palpi are very few, but probably are not materially different. Structure of Paired Extra Legs. The parts composing extra legs do not as a rule greatly differ from those of the normal legs which bear them. Though in many instances extra legs are partially deformed, they are more often fairly good copies of the true leg. Not rarely the extra parts are more slender or a little shorter than the normal appendage, but in form and texture they are real appendages, presenting as a rule the hairs, spurs, &c. characteristic of the species to which they belong. The next point is especially important. The parts found in extra legs are those parts which are in the normal leg peripheral to the point from which the extra legs arise, and, as a rule no more. Though in extra legs parts may be deficient or malformed, structures which in the normal leg are central to the point of origin of the extra legs are not repeated in them 1 . For instance, if the extra legs spring from the trochanter they do not contain parts of the coxa, if from the second tarsal joint, the first tarsal joint is not represented in them, and so on. Extra legs may arise from any joint of the normal leg, and are not much commoner in the peripheral parts than in the central ones, but there is a slight preponderance of cases be- ginning from the apex of the tibia. It is rather remarkable that cases of extensive repetition are not much less rare than others, the contrary being for the most part true of the limbs of vert- ebrates. It does not appear that extra legs arise more commonly from either of the three normal pairs in particular. Supernumerary legs of double structure are sometimes found as two limbs separate from each other nearly or quite from the point of origin, but in the majority of cases their central parts may be so compounded together that they seem to form but one limb, and the essentially double character of the limb is not then conspicuous except in the periphery. For example it frequently happens that the femora of two extra legs are so compounded together that they seem to have only a single femur in common, 1 Particular attention is therefore called to one case of extra antennas, which did actually contain parts normally central to the point of origin. (See No. 804.) chap, xx.] SECONDARY SYMMETRY I PRELIMINARY. 477 and careless observers have often thus declared them to be two legs with one femur. Similarly the two tibiae or the two tarsi may be more or less compounded. In the case of Silpha nigrita (No. 769), the two extra legs which arose from a femur were compounded throughout their length, having a compound tibia and tarsus (see Fig. 167). Even in cases when the two extra legs appear to arise separately it will generally be found that they articulate with a double compound piece of tissue which is supernumerary and is fitted into the joint from which they appear to arise. This is especially common in cases of two extra tarsi, which seem to spring directly from a normal tibia. As a matter of fact in all such cases these extra tarsi articulate with a supernumerary piece of tissue, as it were let into, and com- pounded with, the apex of the normal tibia. These bodies are themselves double structures, composed of parts of two tibiae. In determining the morphology of the limbs they are of great importance, but unfortunately they are not generally mentioned by those who describe such formations. But though extra parts are generally present in the leg centrally to the point from which the extra legs actually diverge, it should be expressly stated that if this point is in the periphery of the leg, the central joints are normal : if for example, there are two extra tarsi, there may be parts of two extra tibial apices, but the base of the tibia, the femur, &c. are single and normal. Symmetry of Paired Extra Legs. To appreciate what follows it is necessary to have a distinct conception of the normal structure of an insect's leg, and to understand the use of the terms applied to the morphological surfaces. If the leg of a beetle, say a Carabus, is extended and set at right angles to the body, the four surfaces which it presents are respectively dorsal, ventral, anterior and posterior. In the femur, tibia and tarsus the dorsal is the extensor, and the ventral is the flexor surface. The anterior surface is seen from in front and the posterior from behind. (The terms ' internal ' and ' external ' are to be avoided as they de- note different surfaces in the different pairs.) Difficulty as to the use of terms arises from the fact that as the beetle walks or is set in collections, the legs are not at right angles to the body but are rotated on the coxa?, so that the plantar surface of the first pair of legs is turned forwards, but the plantar surfaces of the second and third pairs are turned backwards 1 . 1 Attention is directed to the fact that in a beetle there is a complementary relation not only between the legs of the right and left sides but also imperfectly between the legs of the first pair and those of the second and third pairs, which are in some respects images of the first leg of their own side. For instance, in Gerambyx (see Fig. 160) the trochanter of the fore leg is kept in place by a process of the coxa which goes down behind it, but the corresponding process in the second and third legs is in front of each trochanter. Again in Melolontha &c. the tibial serrations of 478 MERISTIC VARIATION. [part I. Extra legs may arise from airy one of the morphological surfaces, but more often their origin is in a position intermediate between them, e.g., antero-ventral, or postero-dorsal. The next question is that of the determination of parts which are extra from the parts which are normal. Two extra legs spring from a normal leg. The appearance is often that of a leg single proximally, but triple peripherally. All three limbs are often equally developed and at first sight it might well be supposed that the three collectively represent the single leg of the normal. In many cases of Meristic Variation I have contended that the facts are only intelligible on the view that there has been such collective representation. But in these Secondary Symmetries this supposition is [? always] inadmissible. On closer examination it is generally more or less easy to see that the three legs do not arise in the same way, but that one arises as usual while the other two are, as it were, ingrafted upon it. It is thus possible in all but a very few cases to determine the normal leg from the others by tracing the surfaces from apex to base, when it will be found that some surface of the normal is continuous throughout the appendage while those of the extra legs end abruptly at some part of the normal leg. Nearly always besides, as has been mentioned, the extra legs are more or less compounded together at their point of origin even if separate peripherally. In a few very exceptional cases it happens that one of the extra appendages is compounded with the normal and not with the other extra appendage. A remarkable case of this in an antenna may be seen in Melolontha, No. 800, and in a leg in Platycerus caraboides, (q.v.) We have now to consider the positions of the paired extra legs in regard to the normal leg and in regard to each other. At first sight their dispositions seem entirely erratic ; but though it is true that scarcely two are quite identical in structure, yet their divers structures may for the most part be reduced to a system. This system, though far from including every case, still includes a large proportion and even the remainder do not much depart from it except in very few instances. The comprehension of the general system will also greatly help to make the aberrant cases appreciated with comparatively few words. For simplicity therefore, the con- sideration of exceptional cases will be deferred and the principles stated in a general form. It will be remembered that we are as yet concerned only with doable extra legs. When extra appendages, arising from a normal appendage, are thoroughly relaxed and extended, the following rules will be the first legs curve backwards, but those of the other legs curve forwards. This circumstance is mentioned lest it might be thought to have been neglected in what follows, but this complementary relation has nothing to do with that which will be shewn to exist between the extra legs. chap, xx.] SECONDARY SYMMETRY : RULES. 479 found to hold good with certain exceptions to be hereafter specified. I. The long axes of the normal appendage and of the two extra appendages are in one plane : of the two extra appendages one is therefore nearer to the axis of the normal appendage and the other is remoter from it. II. The nearer of the two extra appendages is in structure and position formed as the image of the normal appendage in a plane mirror placed between the normal appendage and the nearer one, at right angles to the plane of the three axes; and the remoter append- age is the image of the nearer in a plane mirror similarly placed between the two extra appendages. Transverse sections of the three appendages taken at homo- logous points are thus images of each other in parallel mirrors. As the full significance of these principles may not be at once seen it may be well to add a few words of general description. The relation of images between the extra legs is easy to understand. They are a complementary pair, a right and a left. This might indeed be pre- dicted by any one who had considered the matter. The other principles, which concern the relations of the extra legs to the normal leg, are more novel. For first it appears not that either of the extra legs indifferently may be adjacent to the normal, but that of the extra pair the adjacent leg is that which is formed as a leg of the other side of the body. If therefore the normal leg bearing the extra legs be a right leg, the nearer of the extra legs is a left and the remoter a right. This principle holds in every case of double extra appendages of which I have any accurate knowledge, where the struc- ture of the parts is such that right limbs can be distinguished from left. But perhaps of greatest interest is the fact that the inclination of the surfaces of each extra leg to those of its fellow and to those of the normal are determined with an approach to uniformity in the manner described. These principles of arrangement may be made clear by a simple mechanical device (Fig. 153). A horizontal circular disc of wood has an upright rod fixed in its centre. This rod passes through one end of a vertical plate of wood which can be turned freely upon it as an axle, so as to stand upon any radius of the horizontal circle. The head of the axle bears a fixed cog-wheel. In the vertical wooden plate are bored two holes into which two rods each bearing a similar cog-wheel are dropped, so that each can rotate freely on its own axis. The three cog-wheels are geared into each other. They must have the same diameter and the same number of teeth. Three wax models of legs are fixed on the head of each wheel as shewn in Fig. 153. In that figure, R represents the apex of the tibia and tarsus of a normal right leg. The anterior surface is dark, and the posterior is white. The anterior and posterior spurs of the tibia are shewn at A and P. SL and SR represent the two supernumerary legs, SL being a left, SR a right. (They are supposed to arise from the leg R at some proximal point towards which they converge.) When the wooden plate is put so that the arrow points to the word "Posterior" on the disc, the models will then take the positions they would have if they arose from the posterior surface, all the ventral surfaces coming into one plane. If the arrow be 480 MERISTIC VARIATION. [part I. set to "Ventral" the two supernumeraries will turn their dorsal surfaces to each other, and so on. The model SL thus rotates twice on its own axis for each Fig. 153. A mechanical device for shewing the relations that extra legs in Secondary Symmetry bear to each other and to the normal leg from which they arise. The model R represents a normal right leg. SL and SR represent respect- ively the extra right and extra left legs of the supernumerary pair. A and P, the anterior and posterior spurs of the tibia. In each leg the morphologically anterior surface is shaded, the posterior being white. R is seen from the ventral aspect and SL and SR are in Position VP. revolution round R, but the surfaces of the model SR always remain parallel to those of the model R. In every possible position therefore each model is the image of its neighbour in a mirror tangential to the circle of revolution. In the figure the models have the position they should have if arising postero-ventrally. Here the plantar surface of SL is at right angles to the plantar surfaces of the other two legs. Since at each radius the relative position of the legs differs, it is possible to define these positions by naming the radius. This will be done as shewn in Fig. 154. In this diagram imaginary sections of the legs are shewn in the various positions they would assume at various radii. The central thick outline shews a section of the normal leg, a longer process distinguishing the anterior surface from the posterior. The radii are drawn to various points D, A, V, P, representing the dorsal, anterior, ventral and posterior positions respectively. In- termediate positions may be marked by combinations, DA, VVP, &c, using the system employed in boxing the Compass. On several of the radii ideal sections of the extra legs are shewn in thin lines, the shaded one being the nearer and the plain one the remoter. M 1 and M 2 shew the planes of the imaginary mirrors. The manner in which the pair of extra limbs are compounded with each other in their proximal parts, and with the normal limb at their chap, XX.] SECONDARY SYMMETRY : SCHEME. 481 point of origin is most extraordinary. It does not appear that the surfaces compound together along any very definite line or that the II Fig. 154. Diagrams of the relations of extra legs in Secondary Symmetry at various positions relatively to the normal leg from which they arise. The legs are represented in transverse section, the morphologically anterior side of each heing indicated by the longer spur. The section of the normal leg, in which the radii converge, is shewn with a thick black line. The section of the nearer extra leg in Diagram I is shaded, while the remoter is blank. The radii shew them in various positions, anterior, posterior, dorsal, ventral, iv/c. relatively to the normal leg. M 1 , the plane of reflexion between the nearer extra limb and the normal. M' 2 , plane of reflexion between the nearer and the remoter extra limbs. Diagram II is constructed in the same way to illustrate special cases of extra legs arising anteriorly or posteriorly. If the two extra legs diverge from each other centrally to the tibial apex each tibial apex is then complete, as on radius A of Diagram I. In Diagram II are shewn two degrees of composition of the two tibial apices, illustrating how, in cases of complete composition, the extra parts may consist wholly of two morphologically posterior or anterior surfaces according as they arise posteriorly or anteriorly to the normal leg. (See for instance Nos. 750 and 764.) line of division between the several limbs is determined by the normal structure of the limbs. The homologous parts seem to be compounded at any point, almost as an object partly immersed in mercury com- pounds with its image along the line to which it is immersed, where- ever that line may be. b. 31 482 MERISTIC VARIATION. [part i. From this some curious results follow. For instance, if two extra limbs arise anteriorly and are separate at their tibial apices, they bear four spurs as shewn at radius A in the upper diagram of Fig. 154. But if the two are fully compounded at the tibial apices in the anterior position the compounded limb will only have two spurs, both being shaped as anterior spurs (as shewn in the lower diagram) and con- versely for the posterior position (see No. 764). The parts, in fact, where the pair may be supposed to interpenetrate (dotted in the diagrams) are not represented. Those who have described these phenomena have in consequence often made the following error. Observing a limb giving off' a morpho- logically double limb with a common proximal part subsequently sepa- rating into its two components, they speak of this as a "primary and secondary dichotomy." When the facts are understood it is clear that there is no dichotomy between the extra legs and the normal, for the parts are not equivalent and the normal is undivided. Such are the principles followed. It ivould not be true to assert that these rules are followed with mathematical jyrecision, but in the main they hold good. Special attention will be given to cases departing from them, bat the number of such cases is small. The cases of slight deviation from the schematic positions are besides mostly those of extra limbs in the Positions A and P, and generally the deviation in them takes the same form, causing the ventral surfaces of the extra parts to be inclined to each other downwards at an obtuse angle instead of forming one plane. In all cases possible I have examined the specimens myself, and I am under obligation to numerous persons who have very generously given me facilities for doing so. Amongst others I am thus greatly indebted to M. H. Gadeau de Kerville, Dr G. Ivraatz and Dr L. von Heyden for the loan of many valuable insects, and also to Messrs Pennetier, Giard, Dale, Mason, West- wood, Waterhouse, Janson, Harrington, Bleuse, &c. In this part of the work I am under especial obligation to Dr D. Sharp, for without his cooperation it would not have been possible for me to have undertaken the manipulations needed. He has most kindly given up his time to the subject, and in the case of almost every one of the specimens examined at Cambridge I have had the benefit of his help and advice. Of cases not seen by me few are described in detail sufficient to warrant a statement as to the planes in which the parts stood, but sometimes the figures give indications of this. Some of the accounts are quite worthless, merely recording that such an insect had two extra legs : in such cases I have thought it enough to give the reference and the name of the insect for statistical purposes. But every case known to me is here re- corded : there has been no rejection of cases. The cases will be taken in order of the Positions, beginning CHAP. XX.] EXTRA LEGS : POSITION V. 483 with the Position V and taking the other radii in order, going round against the hands of a watch. Cases of Extra Legs in Secondary Symmetry. (1) Position V. *736. Carabus scheidleri % : pair of extra legs having a common femoral^ portion arising from the trochanter of the right fore leg (Fig. 155). This case is of diagrammatic simplicity. The troch- Fig. 155. Carabus scheidleri, No. 736. The normal right fore leg, R, bearing an extra pair of legs, SL and SR', arising from the ventral surface of the coxa, C. Seen from in front. (The property of Dr Kraatz.) anter bears a normal leg (R) articulating as usual. Immediately ventral to this articulation there is a second articulation upon a small elevation. This bears a double femur made up of jDarts of a pair of femora compounded by their dorsal borders. The double femur has thus two structurally ventral surfaces opposite to each other. The apex presents two articular surfaces in the same plane as that of the normal leg, each bearing a tibia, both tibiae flexing in the same vertical plane. Since the double femur of the extra legs stands vertically downwards at right angles to the normal femur, it will be seen that both the extra tibiae flex upwards, but one of them is a left leg (SL), bending to meet the normal leg, while the other is a right (SR') } bending towards the ventral surface of the body. The tibia of the left extra leg is a little shorter than that uf the normal, and the tibia of the right extra leg is a little longer than it. All three tarsi are thinner than a normal tarsus; and the claws are a good deal reduced in the case both of the normal and the right extra leg, while in the left extra leg they are absent altogether. This is an example of a pair of extra legs arising 31—2 484 MERISTIC VARIATION. [part i. in the position marked V in the Scheme and having precisely the relations there shewn. Specimen first described by Kraatz, G., Berl. ent. Zt., 1873, p. 432, fig. 9. I am greatly indebted to Dr Kraatz for an opportunity of examining it. 737. Carabus marginalis : penultimate joint of left hind tarsus is en- larged and presents two articular surfaces, a proximal one on the ventral surface, and another at the apex. The latter bears the normal last joint with its claws. From the proximal articular surface arises a thick joint shorter than the normal last joint, bearing at its apex two pairs of claws set back to back, as in the Position "V. Specimen rede- scribed from Kraatz, G., Deut. ent. Zt., 1880, xxiv. p. 344, PI. n. fig. 29. 738. Carabus granulatus the large posterior spur of left middle tibia bearing extra parts. LT, EPS & LPS. singh of suture b is seen (Specimen the iding posteriorly i u± ana jlt correspo and between the two extra s P ur Fs of normal, x, x, line tarsi represents their two between these two spurs The limb is . i ill from the posterior surface - posterior spurs. 1 he double property of Dr Kraatz.) nature of this spur is seen when it is examined from the anterior side, for upon that surface it is marked by a longitudinal ridge-like suture. This specimen was first described by Kraatz, JJeut. ent. Zt, 1876, xx. p. 378, fig. 13, and I am indebted to Dr Kraatz for an opportunity of examining it. Galerita africana (Carab.) : (Fig. 163) right middle leg normal as far as the last tarsal joint, which bears three additional claws arising dorsally to the normal pair. The extra claws are three in number, two of them being small and standing at the anterior border of the limb, while at the posterior border there is one claw of larger size. This larger claw is really a double structure, which is clearly shewn by the 496 MERISTIC VARIATION. [part i. presence of two channels on its concave surface. Position of origin is therefore D, while the inclination of the extra pairs of claws to each other is about that required A. Fig. 163. Galerita africana, No. 758. Apex of right middle tarsus. A, anterior. P, posterior. V, ventral. (Specimen in Rouen Mus.) for the position DDA ; for the planes of the two pairs are not parallel but incline to each other at an acute angle. Specimen originally described by Mocquerys, Col. unarm. , p. 64, fig. (6) Position DP. 759. Pyrodes speciosus (Longic.) ; having two supernumerary legs articulating with the thorax by a common coxal joint, which is distinct from the coxa of the left middle leg, but is enclosed in the same socket with it. In this remarkable case the normal leg is complete, though slightly pushed towards the middle line. The socket in the mesothorax is enlarged posteriorly and dorsally so as to form an elongated, elliptical articulation, which lies ob- liquely, so that its ventral end is anterior to its dorsal end. The anterior and ventral end is occupied by the coxa of the normal leg, while the coxal joint of the two extra legs fills the space dorsal and external to it. Both are capable of being moved independently in the relaxed insect. The extra legs articulate with their coxa by a common double trochanter which has two apices, from which point the legs are distinct. Their position is dorsal and posterior to the normal leg, being practically that marked DP in the Scheme, and the relative positions of the extra legs are very nearly those indicated for the Position DP. The leg nearest the normal leg is of course a right leg in structure, and its plantar and a little of its structurally anterior surfaces are turned posteriorly. On the other hand, the remoter leg is a true left leg and the ventral surface of its femur is placed almost exactly horizontally. All three legs are complete, but they are a little shorter and more slender than the middle leg of the other side. This specimen is in the Hope Collection at Oxford. CHAP. XX.] EXTRA legs: position dp. 497 * 7 gO. Carabus irregularis J ; left middle leg and right hind leg bear- ing supernumerary tarsal portions. In the left middle leg, Fig. 164, I, the 2nd tarsal joint is short and thick ; the 3rd joint is partially double, as shewn in the figure. One of its apices bears a tarsus of reduced size, and the other apex, which is postero-dorsal, bears a double tarsus having common 4th and 5th joints. The 5th joint of the latter bears two pairs of claws which curve ventrally and partly towards each other. The figure I shews the appearance from the ventral or concave side of the claws, while the figure II is drawn from the convex or dorsal side. The disposition and small number of the spines on the ventral side of the extra 5th joint shew that the ventral surfaces are partly suppressed, and in fact that the surfaces which are adjacent in the extra tarsi are in part ventral surfaces. This view is also borne out by the direction and curvature of the claws. Eelatively to each other and to the normal the extra parts have nearly the Position DP. 7-° III Fig. 164. Carabus irregularis. I. Semi-diagrammatic view of left middle leg from antero-ventral surface. I 1 , the claws of normal left tarsus, r, I 2 , claws of extra tarsi compounded together. lh l , hair marking the dorsal surface between the claws. A, anterior. P, posterior. II. Dorsal view of apex of extra tarsus rh, Ur, two hairs marking dorsal surfaces. III. Dorsal view of right hind leg. c'c', c"c", claw-like spines, perhaps representing extra claws. (Specimen the property of Dr Kraatz.) The right hind tarsus has the form shewn in Fig. 164, III. The 3rd, 4th and 5th joints are not fully separated from each other. Both the 4th and 5th joints bear extra parts, but their nature is obscure. The 5th joint is partly double, and the anterior part bears two shapeless claw-like spines (c'c). The 4th joint bears a similar pair of claw-like b. 32 498 MEBTSTIC VARIATION. [part i. structures of smaller size (c"c"). Probably these should be considered as rudiments of extra tarsi ; but if this view is correct, it appears that two extra tarsi are present, arising from different joints. For the loan of this specimen I am indebted to Dr G. Kraatz, who first described and figured it in Deut. ent. Z&, 1877, XXI. pp. 57 and 63, tig. 27. •rgj Chrysomela graminis (Phy tophagi) : the femur of the right middle leg bears a supernumerary pair of legs attached to the posterior and dorsal side of its apex. At this point' there is an articulation with which the single proximal part of the extra pair of tilme articulates. This- piece, which is common to the two super- numerary tibia?, is a sub-globular, amorphous mass from which the two tibia? diverge. " Each of the two tibia? bears a complete tarsus, except that the most posterior has only one claw. In colour the two supernumerary tarsi differ from the normal, being brown instead of metallic green, but the tibia? are normal in colour. From the shape of the articulations and the arrangement of the pubescence, it is clear that the surfaces of the legs which are naturally adjacent are constructed as posterior surfaces, and the forms of the two are complementary to each other, the hindmost of the extra legs being formed as a left leg, while the foremost is a right leg. As the}' stand, however, the two tibia? are not in the same position relatively to the body, for the foremost is placed normally, having its plantar surface turned downwards, but the hindmost is rotated so that its plantar surface is partially turned forwards. The relative positions are nearly those marked DP in the Scheme, but the most posterior tarsus is more rotated than it should be according to that diagram. This condition may be to some degree connected with the presence of the amorphous growth at the base of the extra tibia?. This specimen was kindly lent for description by Dr Mason. 762. Fimelia interstitialis (Tenebrion.) : left posterior femur bears two super- numerary tibia? arising from the postero-dorsal surface of its apex. These two are a pair, for the tibia nearest to the normal tibia is a right tibia, the remoter being a left. The adjacent surfaces are chiefly anterior surfaces in structure, but the ventral surfaces are inclined to each other at an obtuse angle. The position of the extra legs is almost that marked DP in the Scheme, but the inclination of the ventral surfaces of the extra legs is rather more acute than it would be in the Position DP. The tarsi are all broken off. Specimen originally described by Mocqvekys, Col. anorm., p. 44, fig. 7Q3 Acinopus lepelletieri (Carab.): two extra legs arising from posterior surface of base of femur of /. middle leg. From position it seems that the most anterior is the normal, but this is doubtful. The arrangement is nearly that of Position DP, but as one of the femora is constricted and bent, the relations are rather irregular. Specimen first described by Mocquerys, Col. anorm., p. 41, Jig. (7) Position P. *764. Silis ruficollis^ (Malacoderm) : right anterior femur bearing a supernumerary limb (Fig. 165). The coxa and trochanter normal. The femur is of about twice the antero-posterior thickness of a normal femur and at its apex presents two articulations in the same horizontal plane. Of these the anterior bears a normal tibia and tarsus, but the posterior bears an extra tibia which appears at first sight to be a single structure. This tibia is more slender than the normal one and is provided with four tarsal joints, the terminal one being withered and without claws. Upon closer examination it is found that this extra tibia is in reality made of the posterior surf aces of a paii; of tibice not separated from each other. In this case the morphological duplicity of the extra tibia is capable of proof. For, as shewn in Fig. 165, II, the normal tibia is not bilaterally symmetrical about its middle line. On the contrary the anterior surface is differentiated from the CHAP. XX.] EXTRA LEGS : POSITION P. 499 posterior by several points. This may be seen in the spurs at the apex of the tibia, for the anterior spur (a) is long, but the a- II II III Fig. 165. Silts ruficollis, No. 764. I. The right anterior leg seen from ventral surface, a, anterior, p, posterior. This figure was drawn with the microscope and is reversed. II. Detail of apex of tibia of the anterior or normal tibia, shewing a, the anterior, and p, the posterior sjjurs. III. Similar detail of apex of the tibia of the extra limb, shewing p' and p", two structurally posterior spurs. posterior (p) is short (as is usual in the front leg of many beetles). The hairs on the surface of the tibia are also directed asymmetri- cally and the parting or division between them is not median, but is nearer to the anterior border (see figure). But in the extra part there is no such differentiation, and botli surfaces are structurally posterior surfaces. The hairs part in the middle, and both spurs (p, p") are formed as posterior spurs. This extra structure is therefore made up of the two posterior borders of a right and a left tibia compounded together in Position P. (See diagram, Fig. 165, II.) This specimen was found by Dr Sharp amongst a number of insects collected by myself in his company at Wicken Fen on Sunday 1 , July 26, 1891. Such a case taken in connexion with others {e.g. Xo. 801 ) makes it certain that many cases of supposed " single ' : extra appendages are really examples of double extra parts. 1 A day or two before, the manuscript of this part of the subject had been put by with the remark that no good opportunity of thoroughly investigating a case of " single" extra leg had occurred, but that it could scarcely lie doubted that traces of duplicity would be found in them. Considering the great rarity of extra ap- pendages in Insects, and remembering that even of the whole number very few are of the supposed " single " order, I have thought the occurrence of this capture a coincidence of sufficient interest to be worthy of mention. Dr Sharp tells me thai amongst all the beetles that have gone through his hands only one case of extra appendage (No. 755) was seen. 32—2 500 MERISTIC VARIATION. [part I. 765. Scarites pyracmon (Carab.). At base of posterior face of the trochanter of left normal front leg, immediately above the cotyloid articulation was implanted an elongated lanciform joint. This joint was directed backwards and represented a pair of trochanters com- pounded by their anterior surfaces. With each of the two apices of this double trochanter was articulated a complete leg, in all respects formed as an anterior leg. The two moved as a complementary pair. [Details given. This is one of the earliest and best described cases. AsMUSS 1 in quoting it points out that the description and figure plainly shew that the two extra legs were a pair, a right and a left, respect- ively. They were in fact a pair, arising from the posterior surfaces of the normal leg, and presenting their anterior surfaces to each other.] Lefebvkk, A., Gu&rin's Mag. de ZooJ., 1831, Tab. 40. 766. Geotrupes mutator (Lainellicorn) : two supernumerary limbs arising from femur of right anterior leg. Femur greatly widened, upon posterior border giving off a large prominence which divides into two processes at right angles to each other. Each of these processes bears a normal tibia and tarsus, but the foremost of these tibiae is shaped as a left tibia, having its serrated border placed anteriorly, while the other extra tibia is formed as a right tibia, having its serrated border placed 'posteriorly. [The pair of limbs arise from the posterior surface of the normal limb and have their anterior surfaces adjaceut, as in Position P.] FRiVALDsm:, J., Term. Fuzetek., 1886, x. p. 79, PI. 76/. Pterostichus lucublandus ? (Carabidre): third tarsal joint of left middle leg at apex presents wide articular surface. On this stands a triple 4th joint, made up of a single anterior portion, bearing the rest of the normal tarsus and a posterior portion, double in structure, the two parts being completely united. The single anterior part of this 4th joint bears a normal 5th joint with claws. The double posterior part of the 4th joint bears a pair of separate 5th joints, each having a pair of claws. Of these the anterior is perfect, but the peripheral part of the posterior 5th joint is crumpled, so that its claws are twisted out of position, but at its base it stands exactly as the normal 5th joint, and as the 5th joint of the anterior extra tarsus, all three being in the same horizontal plane. These extra parts, therefore, are in the Position marked P in the Scheme and have the relations there indicated for that position. This specimen was kindly lent to me by Mr Harrington, who first described it Can. Ent., 1890, xxn. p. 124. (8) Positions VPP to VVP. *768. Ceroglossus valdiviae, Chili (Carabidse): left anterior tibia bearing a pair of supernumerary legs. The tibia widens, and in its middle part gives off posteriorly and ventrally a wide branch having the form of a pair of tibial apices compounded together. The double tibia bears two tarsi (Fig. 166, B! , L') having a common proximal joint, but these have unfortunately been broken, two joints being missing from the one and three from the other. The legs are a right and left as usual, and they stand in the relative positions marked VPP in the Scheme. This is a very simple and striking case, for the animal is of good size and the parts are well formed. The two tibial spurs which are adjacent in the two extra tibiae are compounded so as to form a double spur with two points as shewn in the figure. As shewn for the Position 1 Monstrositates Goleopterorum, 1835, p. 44, PI. chap, xx.] EXTRA LEGS : POSITION VPP. 501 VPP in the Scheme, the compounded parts of the extra ap- pendages, viz., the double tibia and the double first tarsal joint have two complete ventral surfaces inclined to each other at an obtuse angle, while there are only two halves of dorsal surfaces. Fig. 166. Ceroglossw valdivia, No. 768. Left anterior tibia with extra parts seen from the ventral surface. L, the normal left tarsus. R' and L', the extra tarsi, compounded in their proximal joint. A, anterior. P, posterior. Xote that the anterior spur of the normal is curved and that the double spur representing the two anterior spurs of the extra tibial apices has thus a bifid point. (Specimen the property of Mr E. W. Janson.) Similarly there are two structurally posterior surfaces, but no structurally anterior surfaces, for these are adjacent and un- developed. This specimen was kindly lent by Mr E. \V. Janson. 769. Silpha nigrita (Heteromera): from right middle femur arises a pair of legs which are completely united as far as the apex of the last tarsal joint. The point of origin of the supernumerary limbs is on the anterior and ventral border of the femur. The form of the extra limbs is shewn in Fig. 167. The surfaces V and V are structurally ventral surfaces. They are turned chiefly forwards, but are inclined to each other at an acute angle. The surfaces, therefore, which arc adjacent in this pair of legs, and which are consequently obliterated, arc chiefly the morphologically anterior surfaces and to some extent the dorsal surfaces. The plantar or ventral surfaces of the last tarsal joints are inclined to each other rather more obtusely than those of the tibiae, 80 that the curvatures of the two pairs of claws are very nearly turned forwards as well as away from each other. This is not fully brought out in the figure. The position of origin is about VP, but the claws are in Position VPP. Specimen first described and figured by MoCQUERYS, Col. anorm., p. 43, fig. 502 MERISTIC VARIATION. [part I. Fig. 167. Silpha nigrita, No. 769. Right middle femur bearing a compounded pair of extra legs. V, ventral surface of nearer extra leg. V, ventral surface of the remoter extra leg. (In Rouen Mus.) 770. Tenthredo solitaria (Sawfly): tibia of right middle leg divides in peripheral third to form two branches, of which the anterior bears the normal tarsus. The posterior branch arises from the postero-ven- tral surface of the normal and bears a double tarsus consisting of the posterior parts of a pair compounded in Position VP, almost exactly. Tibial spurs as in Fig. 166. The compound tarsus has only 4 joints, the 5th being apparently broken off. In Cambridge Univ. Mus., history unknown. 771. Telephorus rusticus (Malacoderm) : tibia of left middle leg dilated and somewhat deformed in its peripheral portion. It presents two apical processes, the one anterior and the other posterior. The anterior of these bears a normal, backwardly directed tarsus, but the posterior process bears two tarsi by separate articulations. The anterior of these two tarsi is directed forwards to face the tarsus of the other apex, but the posterior tarsus is backwardly directed. [From its attitude it is clear that the middle of these tarsi is a structure complementary to one of the others, but there is no evidence to shew whether it is a pair to the anterior or to the posterior. Position either VPP, or DAA, pro- bably the former.] Kraatz, Deut. ent. Zt., 1880, p. 344, fig. 33. 772. Anthia sp. (Carabidae) : left posterior tibia bearing two supernumerary tarsi. The postero-ventral side of the apex of the tibia is dilated so as to form a triangular projection, causing the point of articulation of the normal tarsus to be raised upwards. The projection bears two tarsi of which the posterior curves downwards and backwards, being fashioned as a left tarsus while the anterior curves forwards and slightly upwards being a right tarsus. These two tarsi have unfortunately been broken but were presumably complete. The whole apex of the tibia bears five spurs instead of two, but the relation of the spurs to the separate tarsi was not clear. The chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES. 503 tarsi are very nearly in the Position VPP. Specimen very kindly lent by Mr E. W. Janson. 773. Julodis aequinoctialis (Buprestida?) : the extra legs arise from the posterior and ventral side of the base of the tibia of left middle leg. They are a pair, and are compounded together by their lateral and dorsal surfaces in such a way that the morphologically ventral surfaces of the two are almost in contact along the anterior border of the compound limb. The ventral surfaces here converge at an acute angle. The two extra legs are compounded together throughout the tibiae and first 4 tarsal joints. The 5th tarsal joints are free, but only one of them remains. The former presence of the other is only shewn by a socket. The normal tibia is con- stricted and bent at one point so that it does not stand in its normal position. The femoro-tibial articulation is rigid. This is a case of a pair of legs compounded as in the position marked VVP in the Scheme but the point of origin is more nearly that of VPP. Specimen originally described by Mocquerys, Col. anorm., p. 47 Jig. 774 Metrius contractus (Carab.) Esch.: specimen in which the middle left femur ' bears an incomplete pair of legs in addition to the normal one. The femur is of normal length. The tibia of the normal leg is articulated with the end of the femur as usual, but is somewhat shorter, stouter and more curved than the tibia of the corresponding leg of the other side. A supernumerary tibia arises from the posterior [and ventral ?] side of the femur a short distance within the apex, and is articulated with it by a separate cotyloid cavity ; the two articular cavities for the two tibia? are confluent, being connected by a groove. The end of this tibia is dilated at its outer end, and bears two articular surfaces, one on each side ; with each of these surfaces, a complete tarsus is articulated, nearly normal in form but somewhat stouter than a normal tarsus. There are four terminal spurs to this tibia, two being below the outer tarsus and two being below the inner tarsus. [It therefore seems that this tibia is made up of parts corresponding with the ventral side of a right tibia and the ventral side of a left tibia, and it is hence probable that if the dis- position of the claws of the tarsi had been examined, it would have been found that they too were a pair, one being a right foot and the other a left. Position probably VVP.] Jayne, H. V., Trans. Amer. Ent. Soc, 1880, vin. p. 156, PL iv. figs. 3 and 3 a . 775 Aromia moschata ? (Longicorn) : right anterior coxa bearing a pair of super- numerary legs having trochanter and the proximal half of the femur in common. The normal leg and the extra ones were all somewhat reduced in size but were complete. The extra leg adjacent to the normal is a left leg. [From the figure it appears that the legs arose in the Position P, or VPP, and their relative positions seem to have been those indicated in the Scheme. Of course it is not possible to state this definitely without examination, but it is clear that there was at least no great departure from the position shewn in the Scheme.] It is remarked that in this specimen the right mandible was abnormally small. Kolbe, H. J., Naturw. Wochens., 1889, iv. p. 169, Jigs. (9) Two cases not conforming to the Scheme. Two cases of double supernumerary tarsi require separate con- sideration. The arrangement in both of these cases departs from chat which is usually followed, but it will be seen that there is considerable though imperfect agreement between the two ex- ceptions. Both of these occur in the anterior legs of males of the genus Galathus, and it happens that in the normal form the apex of the tibia presents a considerable modification from the simple structure of other beetles. This modification affects the anterior legs only, and is found in several genera of Carabidae, being especially pronounced in Calathus. 504 MERISTIC VARIATION. [part i. In order to appreciate the nature of these cases it is necessary that the anatomy of the parts should be understood. The apex of the tibia in the simple form, e.g. the second or third leg in Carabus, bears two large articulated spurs. The two spurs are ventral to the articulation of the tarsus, and one of them is placed at the anterior border of the tibial apex while the other is posterior. In these unmodified legs both spurs are placed at the same level in the limb, so that the bases of both are in the same transverse section (cp. Fig. 166). In the forms presenting the sexual modification, the anterior spur is of some- what small size but occupies the same position relatively to the other parts that it does in a simple leg. The posterior spur however, which is large, does not stand at the same level on the tibial apex, but has, as it were, travelled up the tibia so that it stands at a considerable distance central to the apex, and instead of marking the posterior border of the limb it is placed nearly in the middle of the actual ventral surface. A long channel runs from the posterior spur to the anterior one, and the appearances suggest that the modified form is reached by a deformation of the original apical surface, which is twisted so that the posterior spur is thus drawn up into the secondary position. In the fore leg of a male Carabus the beginning of such a change can be seen, but in Pterostichus and especially in Calathus it reaches a maximum. The change may be briefly described by saying that a section to include the two spurs must be taken in a plane which is oblique to the long axis of the limb instead of transverse to it. As a result of this modification the morphological surfaces of the anterior tarsus of Calathus &c. have a peculiar disposition relatively to the same surfaces of the tibia when compared with other forms. Commonly the ventral surface of the tarsus is parallel to a line taken through the bases of the spurs, but owing to the rotation of the posterior spur into its secondary position this plane is here oblique to the ventral surface of the tarsus. These points will be at once evident if the front leg of a male Calathus is examined. It was laid down as a principle generally followed in cases of double extra appendages, that the three terminations, when ex- tended, stand in the same plane, and the chief feature which distinguishes the two following cases is that the three termina- tions are not in one plane. Moreover, though the two supernumerary tarsi are a com- plementary pair, and together with the normal tarsus are arranged as a series of images, yet in order to produce the arrangement of the present cases the planes of reflexion would not be parallel to each other (as in Fig. 154) but inclined in the manner to be described. CHAP. XX.] EXTRA LEGS : CALATHUS. 505 g a *77G. Calathus graecus g (Carabiclre) : left anterior tibia bearin pair of supernumerary tarsi compounded together. The diagram, Fig. 169, I, shews, in projection, the relations of the parts round the tibial apex. As lias been explained, the posterior spurs P 1 , P 2 and P 3 are really much central to the apex, but they are here represented as it* they were projected upon the apex. The head of the tibia is produced posteriorly into a long and narrow process which is formed of the united parts of the two extra limbs and bears the articulation common to the two extra tarsi. The two tarsi stand with their ventral surfaces almost at right angles to each other, but the united dorsal surfaces are almost in a continuous plane. The fifth joints alone are separate, that of RT being small (Fig. 168). RT, Fig. 168. Calathus gracus, No. 776. Left anterior tibia bearing a double extra tarsus. L2\ normal tarsus. RT, L'T, extra pair of tarsi. LAS, LPS, normal anterior and posterior spurs. L'A'S', L'P'S', anterior and posterior spurs belonging to L'T. RAS, RPS, anterior and posterior spurs belonging to RT. x, .v, dotted line indicating plane of morphological division between extra tarsi, .r.v, .vx, plane of division between the normal and RT. (Specimen the property of Dr Kraatz.) In studying this case one source of confusion should be specially referred to. It is seen that though the origin of the extra tarsi is posterior to the normal tarsus, the extra tarsi are as a fact united along their morphologically posterior borders. Nevertheless the position of the spurs shews that it is the anterior surfaces which are morphologically adjacent to each other, for the spurs are arranged in the series A'P', PA 2 , A 3 P 3 , and the union of the posterior borders of the tarsi is a result of the modification in the form of the tibia consequent on the rotation of the posterior spur. To produce the arrangement here seen, the planes of reflexion would be M 1 and M 2 respectively, and these are almost at right angles to each 506 MEBJSTIC VARIATION. [part t. other. The present case therefore is very different from those hither- to described, for in them the planes of reflexion were nearly or quite parallel. Whether this difference in the Symmetry of the extra parts may be connected with the departure of the normal tibia from its own customary symmetry cannot be affirmed, but such a possibility should be borne in mind. This specimen was kindly lent to me by Dr G. Kraatz, who first described it in Deut. ent. Zt., 1877, xxi. p. 62, fig. 23. Dorsal t 3 Posterior A/2 I II Posterior Anterior Fig. 169. I. Ground-plan of tibial apex of Calathus grams, No. 776. II. Similar ground-plan of the tibial apex of Calathus cisteloides, No. 777. In each case the spurs are conceived as projected upon one plane, t 1 , the normal tarsus. A 1 , P 1 , its anterior and posterior spurs, t 2 , A 2 , P 2 , similar parts of nearer extra tarsus, t 3 , A 9 , P s , similar parts of remoter extra tarsus. M 1 , plane of reflexion between t 1 and t 2 . M 2 , plane of reflexion between i 2 and t 3 . Calathus cisteloides ^ (Carabidae): right anterior tibia bearing a pair of supernumerary tarsi compounded together. In this case the extra parts were anterior to the normal tarsus. The parts were arranged as in the diagram, Fig. 169, II, which is a projection of the tibial apex. The apex is produced anteriorly so as to form a wide expansion which bears the common articulation for the double tarsus. This produced portion is of course formed by the composition of parts of a pair of tibiae. It is noticeable that the three tibial apices which enter into the formation of the general apex are in one respect not actually images of each other. For the angular distances between A 1 and P 1 , and between A 2 and P 2 , are exceedingly small, being far less than in a normal tibia of the species, and in fact the grooves running from each anterior spur to the corresponding posterior one are almost paral- chap, xx.] EXTRA LEGS I UNCONFORMABLE CASES. 507 lei to each other and to the long axis of the tibia. The tarsi f and f' separate in the first joint. The relative positions are shewn in the diagram, and it is thus seen that the planes of reflexion M x and M 2 are inclined to each other at an acute angle. This specimen was kindly lent to me by Dr L. von He yd ex and was first described and figured by Mocquerys, Col. anorm., 1880, p. 65, Jig. It is difficult to observe the two foregoing cases without sus- pecting that the fact that they deviate from the normal symmetry of extra parts may be connected with the normal modification of the anterior tibia in these Carabidw. It should be remembered that the tibia and tarsus of the unmodified leg of a beetle are very nearly bilaterally symmetrical about the longitudinal median plane of the limb, but in this leg of these forms the symmetry is lost. Possibly then the upsetting of the ordinary rules for the Symmetry of extra parts may follow on this modification. The difference between the two cases moreover is possibly due to the fact that in one the extra parts are on the posterior surface of the leg, while in the other they are on the anterior. Since the normal limb is not bilaterally symmetrical it is reasonable to expect that the results would differ in the two cases. One other case of a pair of extra tarsi in the fore leg of a male Calathus is re- corded (No. 777 a), but insufficiently described. It is to be hoped that a few cases of extra tarsi in the fore leg of male Calathus or Pterostichus may be found, and it is very possible that such a case even in Carabus would help to clear up these points. 777 a. Calathus fulvipes 3 (Carabidre) : tibia of right fore leg bears pair of extra tarsi. [Fig. and description inadequate.] Perty, Mitth. not. Ges. Bern, 1866, p. 307, Jig. 5. (10) Nine other cases departing from the Schematic Positions. Each of these needs separate consideration. *778. Platycerus caraboides (Lucan.) : left hind tarsus has form shewn in Fig. 170. The terminal joint had only one claw. R and L' are presumably the extra pair, but it will be seen that they arise at separate places from the 3rd tarsal joint. Otherwise, they stand approximately in Position V. Described originally by Mocquerys, Col. anorm., p. 67, Jig. 779. Philonthus ventralis (Staphylinidse): third joint of right posterior tarsus bearing supernumerary termi- nation of double structure. The apex of the third joint is enlarged, and at a point anterior and slightly dorsal to the articulation of the normal fourth joint the super- raboides, No. 778. Left bind tarsus from posterior surface. L, the presumably normal apex, has only one median claw. R and L', arise separately from the 3rd joint. (In Houen Mus.) 508 MEMSTIC VARIATION. [part i. numerary parts arise. The fourth and fifth joints of the supernumerary tarsi are of double structure, but are not separated from each other. The double fifth joint bears two pairs of claws, of which the two adja- cent members are compounded together at their bases. The plane in which one pair of claws stands is about at right angles to the plane in which the other pair is placed, the opposed surfaces being ventral surfaces. Stated in terms of the Scheme on p. 481, the supernumerary tarsi are placed as in the position DDA, whereas their position of origin is DA A. It is noticeable that the normal fifth joint does not stand quite in its usual jDosition, but is a little twisted so that it par- tially turns its ventral surface in an anterior direction. This specimen was described and figured by Fauvel, Rev. d'Fnt., 1883, n. p. 93, PI. ii. No. l'. It was kindly lent to me by M. Bleuse, to whom it belongs. 780. Alaus sordidus (Elateridae) : Ceylon, femur of right middle leg bears two supernumerary legs arising from its postero-dorsal surface. All three legs are somewhat abnormal in form and the principal femur is partly shrivelled at its base. At a point on the postero-dorsal sur- face about halfway from the apex there is a large, irregular boss from which the two extra femora diverge. Of these that wdiich is nearest to the normal leg may be distinguished as a left leg by the planes of movement of its tibia and tarsus, while the remoter leg is a right leg. The tarsus of the latter is broken but was probably complete. The surfaces which the extra legs present to each other are structurally anterior surfaces, but the relative positions of the three legs do not correspond with any of the positions shewn in the Scheme. It should however be noticed that this fact may be connected with the presence of the amorphous thickening at the point of origin of the extra femora. Specimen in Hope Collection first described and figured by AVestwood, Oriental Entomology, PL XXV. fig. 9, and mentioned Proc. Linn. Soc. 1847, p. 346. 781. Clythra quadripunctata (Phyt,): left anterior trochanter bears two supernumerary legs. Both the normal leg and the two extra ones are complete. The position of the latter is very peculiar ; for, arising from the anterior surface of the trochanter, they turn their structurally dorsal surfaces towards the anterior surface of the normal leg, which thus stands between them, one of them being above it and the other ventral to it. Of these that which is placed dorsally is structurally a right leg, while the lower one is a left, like the normal one. Both the extra legs are also partly rotated so that their ventral surfaces are partially directed upwards. From these facts it appears that the position of these extra legs relatively to the normal one does not correspond with any of the positions indicated in the Scheme, and it did not seem to be possible to refer this deviation from the usual arrangement to any special malformation of any of the parts. Speci- men originally described by Mocquerys, Col. anorm., p. 42, fig. 782. Clytus liciatus (Long.) : right tibia reduced and thickened, being- shapeless and bent. Its apex presents two articulations, the one anterior and the other posterior, the latter bearing a normal, 4-jointed tarsus. The anterior articulation bears a slender double tarsus, the two parts of which are compounded in the 1st, 2nd, and 3rd joints but separate in the 4th or terminal joints. The supernumerary tarsi are very chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES. 509 slender and the whole thickness of their common proximal joint is even less than that of the proximal joint of the normal tarsus. The ac Fig. 171. Clytus liciatus, No. 782. I. View of right tibia. II. Detail of the extra parts, from plantar surface, ac, ac, claws supposed to be morphologically anterior, pc, rudiments supposed to represent posterior claws. III. Enlarged view of the end of the normal tarsus. (The property of Dr Kraatz.) terminal joints of the extra tarsi are well formed, but they each bear only one fully developed claw, the claw of the adjacent side of each being only represented by a rudimentary knob. It appears at first sight that these extra tarsi are at their origin from the tibia only a single appendage and that their double nature only begins from the third joint. This however is not the case, for there are five spurs on the tibia, together with a small brown knob which perhaps represents the sixth spur. The tibia is greatly misshapen and the arrangement of the spurs is so amorphous that I did not succeed in determining their morphological relations. This specimen was kindly lent by Dr Kraatz, having being first described by him in Berl. ent. Zt., 1873, xv r n. p. 433, figs. 1 7 and 17 a. 783. Cryptohypnus riparius (Elater.). The tibia of the right anterior ler the lamellae are continuous upon their ventral aspect : therefore the surfaces which are adjacent in the extra right and left clubs, and by which they are compounded together, are partly ventral surfaces. This is approximately Position DP of the Scheme. Left Antenna. Second joint thickened and presenting three articulations as follows. 1. a peripheral articulation bearing the normal club ; 2. a ventral articulation bearing a 4th joint and club composed of 3 formless lamellae ; 3. a dorsal articulation bearing a small cylindrical joint only. The shape and formation of these extra parts is so indefinite that their morphology could not be determined. For the loan of this specimen I am indebted to Dr L. v< »x Heyden, who first described it in Deut ent. Zt. y 1881, XXV, p. 10"), fig. 1. 796. Rhizotrogus aequinoctialis (Lain.) : 4-th joint of right antenna bears a supernumerary structure projecting forwards and lying in the same horizontal plane as the normal club. This structure is lanceolate in form and its outer surface is in texture similar to the external surfaces of a normal club. On the ventral aspect it presents a simple ridge, but on the dorsal side its outer coating is divided by a spindle-shaped slit through which part of the internal structure protruded. The edges of this opening and the protruding portion of the interior bear a few hairs. There can be little doubt that this supernumerary body repre- sents an imperfectly formed pair of cluhs, and that it is in fact a more rudimentary condition of the parts found in No. 795. Specimen origi- nally described and tigured by Mocquerys, Col. anorm., p. 1 •>,./?'#. 797. Llchnanthe vulpina (Lam.) : right antenna bears in addition to normal club a small spherical club made up of three joints, arising from posterior border of a l<>n^ 518 MERISTIC VARIATION. [part i. joint apparently representing the normal 4th, 5 th, and 6th joints not segmented from each other. [As this supernumerary part is in itself symmetrical it probably con- tains within itself parts of a pair of clubs compounded in Position P. Cp. No. 795.] Jayne, H. F., Trans. Amer. Ent. Soc, 1880, vm. p. 158, PI. iv. fig. 8. 798. Polypbylla decemlineata (Lamellicorn). A specimen in which the right antenua bears a partially double supernumerary branch in addition to the normal antenna. This additional structure articulates with the second joint of the antenna by means of a single large joint. This joint carries a double club consisting of two sets of lamellae, seven being in each set. The two sets of lamellae are united at their bases at an angle of forty-five degrees. The plane of the normal club is per- pendicular to that of the abnormal ones. The normal club itself is Ath shorter than that of the other side. [The details of the structure of this specimen are difficult to follow and the reader is referred for further particulars to the description and figures given in the original.] Jayne, H. F., Trans. Amer. Ent. Soc, 1880, vm. p. 158, Ji(]s. (b) The extra parts arising from the normal at separate points. 99. Odontolabis stevensiij (Lucanidae). As the repetition in this specimen is almost complete and the relations of the parts fairly clear though in some respects peculiar, a detailed account will be useful. The body, legs, &c. are normal, save that the back of the head and thorax have been crushed by some accident. The antennae are both abnormal in the way shewn in Fig. 176. The condition will be better understood if the normal antenna is first described. *7 r i Fig. 176. Odontolabis stevensii, No. 799. The liead seen from below, and enlarged views of the two antennae. R, right. L, left. There is some doubt as to which of the branches is the normal and which the supernumeraries. See description in text. The normal antenna of Odontolabis is much like that of its ally Lit can us cervus, the Stag-beetle. It is made up of 10 joints composing three parts differentiated from each other. The first, or " scape, ' : is a single joint as long as the rest of the antenna. It widens a little from its central end or base towards the apex, and is slightly flattened from above downwards. The second part, or " funiculus," has six simple joints. The last three joints form the club. They are flattened from above down- wards and lie in a horizontal plane. The anterior (" inner ") border of each of these three joints is produced into flat ex- pansions, covered with sensory pores, which together form a series of serrations along the anterior border. When in its natural chap, xx.] EXTRA ANTENNAE ARISING TOGETHER. 519 position the serrated border of the right antenna faces towards the left side, and that of the left is turned towards the right. The structure of the abnormal specimen is as follows. Left Antenna. Scape normal. Its plane however is not quite horizontal as usual, but is a little oblique, the anterior border being slightly higher than the posterior. In the funiculus the 1st and 2nd joints (2nd and 3rd of the whole antenna) are a little thicker than usual but otherwise normal. The 3rd joint of the scape is enlarged and presents at its apex two sockets, each bearing a continuation as shewn in the figure. The two sockets are not in a horizontal plane, but their plane is oblique and nearly at right angles to the plane of the scape, the socket bearing the branch l l being the higher. It is important that the precise re- lations of these parts should be clearly understood. This outer socket of the 3rd funicular joint bears the branch l\ made up of three more funicular and three club-joints, turning their serrated border in the direction of the rigid antenna : I 1 is therefore structurally a left antenna. Its surface is of the same nature as that of a normal antenna, but its size is a little smaller. It is in an oblique plane inclined to the horizontal at about 45 . the posterior (outer) border being the higher. The inner socket of the 3rd funicular joint bears a cylindrical joint not quite fully segmented off from the next joint peripheral to it. These two are 4th and 5th funiculars. The 5th again presents two sockets, bearing respectively the branches I 2 and I 3 . The branch I 2 has one small joint (6th funicular) and three club-joints, turning their serrated border towards I 1 . This branch is therefore structurally a right antenna. It stands in the same oblique plane as I 1 , the serrated border being the higher. In size it also agrees with l\ being rather smaller than the normal. The branch I 3 is a normal left in size and shape, and it lies in a horizontal plane. Here therefore there is a left antenna and a pair, one a right and the other a left. Which then is the normal, I 1 or I 3 ? Inas- much as I 3 and P arise by a common stalk it may seem that they are the extra pair and that I 1 is the normal. We have now seen in many cases that extra parts in Secondary Symmetry are compounded together as P and I 2 are here. But considering the fact that I s is of normal size and in the normal horizontal plane, whereas I 1 and I- are both smaller and are in an oblique plane complementary to each other, I incline to the view thai if one branch is the normal, it is I 3 , and that / l and I- are the extra pair in Secondary Symmetry, though tlieij do not arise to- gether. They are then nearly in Position DPP, but depart from that position in the fact that I 1 is not horizontal (cp. No. 757). If I 1 and I 2 are really the extra parts, in the fact that they do not arise together, but spring separately from different points on the normal, w r e meet with a condition rarely seen, but that 520 MERISTIC VARIATION. [part t. this is a possible condition is proved beyond doubt by the succeeding case. Right Ante)i int. Scape precisely as in left antenna. The 1st funicular (2nd antennary) has two sockets at its apex, placed like those on the 3rd funicular of the left side, the anterior socket being the lower and the posterior socket being the higher. The anterior socket bears a normal right antenna, ?- 3 . The posterior bears the structure shewn in the figure. This appendage has unfortunately been broken, but enough remains to suggest the original structure. It consists of five funicular and a 1st club- joint. The 5th joint of the whole funiculus bears a large socket looking downwards and forwards, its other socket looking back- wards and upwards. From the former the original continuation has been lost. The latter bears the 6th funicular and its 1st club-joint, this again having an empty socket. The plane of the two sockets of the 5th funicular is oblique to the horizon, like that of I 1 and I' 2 . Though it is clearly im- possible to shew how this antenna was in its unbroken state, we may note that if it were continued in the way suggested by the dotted lines it would have borne a complementary pair of clubs, r 1 and r 2 , like I 1 and I' 2 of the other side, placed like them in an oblique plane nearly corresponding with DPP of the Scheme. This specimen was kindly entrusted to me by M. Henri Gadeau de Kerville. He tells me that he believes a description of it has already appeared, but this I have failed to find. I have therefore ventured to describe it again, with apologies to the original describer. The specimen bears a label in the hand- writing of the late Major Parry and was no doubt in his cele- brated collection of Lucanidse. 800. Melolontha vulgaris : right antenna bearing a pair of incomplete supernumerary antennae (Fig. 177). The first joint is normal ; it bears a second joint of singular form, consisting of a long anterior branch, and a short posterior branch i the length of the anterior. The anterior bears two clubs in the manner shewn in the figure (Fig. 177). Of these Fig. 177. Melolontha vulgaris, No. 800. Lettered according to the view that R is the normal right club. L, the supernumerary left, and R' the supernumerary right. (From Wesmael.) * 801, chap, xx.] EXTRA ANTENNA ARISING SEPARATELY. 521 one (E) is inwardly directed and is as wide as, but only | the length of a normal club. The posterior of the two clubs (L) is directed back- wards and has only four lamellae which are apparently united together. The other small club (R') is also composed of only four lamella? which are similarly united together. In both L and R the middle lamellae shew traces of further subdivision. The figure represents the three clubs as being all in one plane, but the club R' is really below /,, which stand- up from the normal antenna. It is mentioned that some of the tarsi were mutilated or defective. [Here L and R' are clearly a complement- ary pair, though separately arising from the normal. It will be observed that as in Lereboullet's case (No. 790) the second joint, which is common to two clubs, is greatly elongated.] Wesmael, Bull. Ac. Belg., 1850, xvi. 2, p. 382, fig. Navosoma sp. (Longic.) Left antenna abnormal. The joints of the normal are a little flattened from above downwards and are nearly elliptical in section. But the anterior border is differentiated from the posterior by the presence of two elongated patches of tissue covered with sensory pores. The two patches are both on the anterior border, one being* on the dorsal surface and one on the ventral, separated from each other by a chitinous ridge. Upon the general surface of the peripheral joints of the antennae are several other such patches, but none are so distinct as those of the anterior border. The abnormal left antenna has the form shewn in Fig. 1 78. So far as the 8th joint it does L'*R L'+R' Fig. 178. Navosoma, No. 801. Left antenna seen from below. Lettered on the view that R and L' are the extra parts. S, sensory patch. (In Hope Collection.) not differ from the normal. The 9th and 10th joints have besides their chief patches of sensory pores (S) on the anterior border, an additional patch (L' + R') posterior to the chief patch. But up to the 10th joint there is no vertical division. The 10th joint however has two articular surfaces, anterior and posterior, in the same horizontal plane. The posterior bears an apical (11th) joint of normal form, having anteriorly a sensory patch. But the apical joint borne by the anterior articular surface has two such sensory patches, an anterior and a posterior. This joint therefore contains in itself parts of a pair of joints. It is not quite fully segmented off from the 10th joint. Nevertheless it is difficult to suppose that the anterior joint is the extra pair in Secondary Symmetry, for its anterior patch, Ls, seems to continue the normal series of patches, S, S, etc. Therefore the patches R and L' seem to be the patches of the extra pair, though one of them is on a separate joint and the other is applied to the normal. Taken with the case of Odontolabis No. 799 and Mehlontha No. 800, this 522 MERISTIC VARIATION. [part i. must, I think, be judged to be a possible account, and in this case R and L' are, as regards symmetry, in Position P. It is of course possible that Ls and R are really the extra pair in Position A, but the presump- tion is rather the other way 1 . Specimen in Hope Collection at Oxford. (2) Cases of double extra antennce, Symmetry unknown. 802. In none of the following can any confident statement be made as to the symmetrical relations of the parts, Several of the cases I have myself seen, but I noticed no clear indications as to their symmetry. A good many of them however were ex- amined before I was fully alive to the importance of these matters in the case of filamentous antennae, and perhaps if they were studied with proper regard to the question of symmetry more might be made of them. Many cases that follow r are mutilated or partly amorphous, and of almost all the descriptions are very imperfect. For our purpose some value attaches to these records as evidence of the distribution of such abnormalities, and to any person who may hereafter pursue the subject a fairly com- plete list of the references may be of use. To this therefore I shall confine myself; for on reviewing the abstracts that I have made of these examples it is clear that they only give the results of superficial examination. Speaking generally, in these cases, from some one joint of an antenna there arises either a pair of extra antennae compounded for a greater or less extent of their proximal parts, or two extra antennae distinct from their point of origin. The letters R and L indicate the side affected, and the number following is approximately that of the joint from w r hich the extra parts spring. In the greater number of sound cases the three branches lie in or nearly in a horizontal plane and are, I anticipate, in Positions A or P. Cases which seem from the indications to conform to the Scheme are marked ||. Mutilated or partially amorphous cases are marked J. Blaps attenuata (Het.) R3 Mocquerys, Coleopteres anormaux, 1880, p. 5, Jig. ' || Malachius marginellus L2 ibid., p. 7, fig. (Mai.) Timarcha tenebricosa R9 ibid., p. 13, fig. (Phyt.) Clytus tricolor (Long.) L7 ibid.' 2 , p. 19, fig. * X C. arcuatus LI ibid., p. 20, fig. Calopteron reticulatum LI ibid., p. 25, fig. (Mai.) Carabus monilis (Car.) L3 ibid., p. 3, fig. ' C. auronitens L7 ibid., p. 9, fig. ■ Ftinus latro (Ptin.) L5 ibid., p. 8, Jig. Elater murinus (Elat.) L2 Ann. and Mag. of N. H., 1831, iv. p. 476. Zonites praeusta (Het.) E3 Stannius, Mull. Arch. f. Anat. Phys., 1835, p. 303. 1 This is perhaps too strongly put. 2 Description and figure incorrect. Apical joint of extra branch is bifid. chap, xx.] EXTRA ANTENNA : OBSCURE CASES. 523 Helops cacruleus (Het.) R5 Dendarus hybridus (Het.) L 4 : Scraptia fusca (Het.) L 5 : Carabus sacheri (Car.) R7 Fimelia scabrosa (Het.) R 2 Anchomenus sex punctatus L 6 (Car.) Calosoma investigator R 5 (Car.) Dromrcolus barnabita L 5 (Eucn.) Carabus arvensis L 4 Shringe, Ann. Soc. Linn, de Lyon, 1836, PI. Romano, Atti Ac. sci. Palermo, 1845, N. S., i. fig. Rouget, Ann. soc. ent. France, 1849, S. •_'. vii. p. 437. Letzner, Jahresb. schles. Ges. f. vaterl. Kultur, 1854, p. 86. Blackmore, Proc. Ent. Soc, 1870, p. xxix. Kraatz, Dent. ent. Zt., 1877, xxi. p. 56, fig. 19. ibid., 1889, xxxm. p. 221, fig. von Heyden, ibid., 1881, xxv. p. 108, jig. 16. Specimen kindly lent by M. A. Fauvel. 803. Meloe violaceus ? : between rigbt eye and tbe base of the right antenna arise two supernumerary antenna from the head. Of these one has 3 joints and the other has one. Kraatz, Bent. ent. Zt., 1877, xxi. p. 57, PI. i.fig. 22. 804. The following example is mentioned here, though its nature is quite obscure. In it there is a suggestion that parts of two extra antennae are present, but the extra parts seem to be peri- pheral to the parts which they repeat. As my stay in Rouen was short I was not able to give as much time to this specimen as I should have wished \ Melolontha vulgaris ^ : left antenna abnormal. This case differs wholly from any other that I know of. I can only describe it in a most tentative way. The appearance when the lamella' were cleaned and separated was as shewn in Fig. 179. Joints 1 — 8 are fairly normal, but peripheral to this place there were Fig. 179. Left antenna of Melolontha vulgaris, No. 804. The numbers air set in tentative suggestion of the possible nature of the parts. (In Rouen Mas.) 1 This antenna was when I saw it covered with mould and dirt. In washing it I accidentally detached it from the head, but I mounted it again carefully with the specimen. 524 MERISTIC VARIATION. [part i. a number of lamellae, some like normal lamellae, others quite irregular. As far as I could make out, the divisions were as shewn in the figure, and I have affixed numbers to the several parts in illustration of their possible nature. The appearance suggests that there is an irregular repetition of a pair of clubs peripheral to the normal antenna, but I can form no opinion as to the morphology of the parts. Originally described by MoCQUERYS, Col. an arm., 1880, p. 12, fig. [Description and figure altogether misleading.] Paired extra Palpi. 805. Bembidium striatum (Carabidae) : left maxillary palp arises by a first joint enlarged towards its apex, bearing three separate terminal joints instead of one. Of these joints one stands apart on a small process of the first joint, but the other two are placed close together, on either side of the apex of the first joint, and diverge from each other at about a right angle. Jacquelix-Duval, Ann. Soc. Ent. France, 1850, Ser. 2, viii. p. 533, Plate xvi. 806. Helops sulcipennis (Het. ): supernumerary, partially double apical joint arises from the 2nd joint of right maxillary palp. It is set on at right angles to the plane of the normal palpus. Jayxe, H. F., Trans. Amer. Ent. Soc., 1880, viii. p. 1QI, jig. 14. 807. Euprepia purpurea (Arctiidse): a specimen in which the right wings and antenna were male and the left wings and antenna female, is declared to have possessed an extra pair of palpi. [No sufficient description of this extraordinary occurrence is given; and as the repetition of the palpi is only incidentally mentioned, it may be doubted whether a full examination was made.] Freyer, C. F., Beitr. zur Schmetterlingshunde, 1845, Vol. v, p. 127, Tab. 458, Jig. 4. CHAPTER XXL Appendages in Secondary Symmetry — continued. The Evidence as to Crustacea 1 . The facts as to Secondary Symmetries in Crustacea are so similar to those already detailed in Insects that, were it not for their value as confirmation of the principles indicated, it would be scarcely necessary to describe them at large. Some few of the cases have besides a special interest, as in them may be seen rudimentary or bud-like structures apparently presenting the lowest condition of paired parts in Secondary Symmetry. Precisely as in Insects there are a number of cases (including those last mentioned) where it would at first sight be supposed that the extra parts are single, but on inspection most of them prove double. Nevertheless there remain some few where this cannot be shewn, and strange as it may seem, these must be admitted to be genuine examples of duplicity of limbs. Of them a special account will be given in another chapter. There are besides, as in Insects, a considerable number of cases in which the nature of the parts is not clear, though the majority of such cases are not examples of extra parts, but are normal appendages mutilated or deformed. One specimen (No. 821) is the only case known to me in which tivo pairs of supernumerary parts arise from one append- a s e - Another (No. 827) is unique in the fact that according to the description three separate appendages are repeated upon a single appendage. It is not clear that this is in any strict sense an instance of Secondary Symmetry, but for convenience it is taken in this chapter. 1 Useful bibliography given by Faxon, Harv. Bull., 1880—1, vm. p. 271. 526 MERISTIC VARIATION. [part i. Of the whole number, two affect antennas, four are in non- ehelate ambulatory legs, one is in a chelate ambulatory leg and the rest, being the great majority, are all in chelae. With reference to these extra parts several false views have from time to time been held. For example, in some of the commonest cases there is an extra pair of dactylopodites, or of indices, curving towards each other. The extra parts may then greatly resemble the dactylopodite (or " pollex ") and index of a normal chela, and many authors have not unnaturally supposed that the extra parts were actually an extra pair of forceps re- peating those of the normal chela. This may easily be shewn to be an error, from the fact that it is often possible by some slight structural difference between the pollex and the index to detect that both extra parts are either both pollices or both indices. But the fullest disproof of this supposition is found in the fact that the great majority of the phenomena will be readily seen to conform to the principles enuntiated for Secondary Sym- metries in Insects (p. 479). A good many authors from the time of Rosel vox Rosexhof 1 onwards have said that these cases are a result of injury, or of regeneration after injury. For this belief I know no ground. It should be remembered as an additional difficulty in the way of this belief, that when the limb of a Crab or Lobster is injured it is usually thrown off bodily, while the extra parts most often spring from the periphery of the chela. But since, according to Heixekex 2 , such mutilated parts are sometimes retained, this must not be insisted on. In the case of an ambulatory leg the surfaces may be named as in an insect (without any suggestion that these names denote true homologies between the surfaces so named). In describing chelae I propose to use the following arbitrary terms. The border upon which the dactylopodite articulates is the pollex-border, the opposite border being the index-border. It should be noted that in the Crab the pollex-border is superior, but in a Lobster 3 it is internal. (1) Clear cases of Extra Parts in Secondary Symmetry. A. Legs. *808. Palinurus vulgaris : left penultimate ambulatory leg bore two supernumerary legs (Fig. 180). Coxopodite of great width. The basipodite had three articular surfaces as shewn in Figure 180, 1 Eosel von Rosenhof, Insekten-Belustigung ', 1755, in. p. 344. 2 Heineken, Zool. Jour. 1828—29, iv. p. 284. 3 It is worth noticing that in the chela of a Scorpion though a close copy of that of a Decapod, the arrangement is reversed, the articulated pincer being external. chap, xxl] SECONDARY SYMMETRY : CRUSTACEA. 527 each bearing a complete leg. When seen by me the leg marked L' was lost. Normal tytl Fig. 180. Palinurus vulgaris, No. 808. Left penultim ate walking leg. (After Leger.) * I could not quite satisfy myself as to which of the three was the normal, but it was clear that R' was in form a right leg and that the other two were lefts. If the leg L' is the normal, it has been pushed out of place by a pair of extra legs in Posi- tion DAA, but if R' and U be the extra legs, then the most anterior leg is the normal and has been pushed out of place by a pair in Position VPP. For an opportunity of examining this specimen, I am obliged to the courtesy of Prof. A. MlLNE EDWARDS. Originally described and figured by Leger, M., Ann. Sci. Nut., ZooL, 1886, S. vii. I, p. Ill, PI. 6. 809. Lithodes arctica : 2nd leg on right side has terminal joint as shewn in Fig. 181, II. If E be the normal then K and L are a pair in Position Y, but if B! be the normal then R and L' are a pair in Position D. Attention called to the sreat diminution in size of all three termi- nations as compared with the normal (Fig. 181, I). Original description, Herklots, J. A., Bijdr. tot J. h. Genootsch. Sat. Art is Mag., 1852, iv. p. 37, PI. ; repeated Arch, neerl., 1870, v. p. 410, PI. xi. 810. Cancer pagurus : last left leg closely like last case [in Position D]. Richard, Arch. Zool. exp., 1893, p. 102, fy. 811. Carcinus maenas : 2nd amb. leg as in Fig. 181, III. A pair of 528 MERISTIC VARIATION. [part I. compounded extra points in Position J). Duns, Proc. jR. PJiys. Soc. Edin., ix. p. 75, PL Fig. 181. I. Lithodes arctica, normal terminal joint of ambulatory leg. II. Second right leg of No. 809. (Both after Herklots.) III. Carcinus mcenas, No. 811, second ambulatory leg. (After Duns.) P, normal terminal point. P', P", extra terminal points in Position D. B. Chelate Appendages. (a) Two extra dactylopodites and double extra index. 812. Eriphia spinifrons $ : specimen of unusually large size, normal but for left chela shewn in Fig. 182, I and II 1 . The chela bore normal left dactylopodite, LD, and index, LI ; also, upon pollex-border the structures shewn. These consisted of two dactylopodites, R'D, L'D, working opposite each other on a com- pounded double index, R'l\ L'l, which had two toothed borders, one for each of them. This is therefore a pair of chelae repeated in Position D [if indeed the dactylopodite mark the dorsal surface]. Taken from Herklots, Arch, neerl., 1870., v. p. 412, PL XI. 1 In connexion with this case Herklots states that the rt. chela in the normal is the larger and otherwise differs from the left (1 in 8 being reversed in this respect). It does not seem from the figure that there was such differentiation between the extra pair, but in future cases this point should be looked for. chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA. 529 813. Astacus fluviatilis : about 3 years old according to Sou- beiran's (Camp. Rend. 1865, lx. p. 1249) account. Right chela ap- parently deformed by injury or disease. Left chela had all normal Fig. 182. I and II. Eriphia spinifrons, No. 812. I. A view of the left chela. II. An enlarged view of the extra parts from the other side. LD, LI, normal lift dactylopodite and index. R'D, L'D, right and left extra dactylopodites. R'l, LI, right and left extra indices not separated from each other. (After Herklots.) III. Cheliped of Homarus americanus, No. 811. (After Faxon.) I), I. normal dactylopodite and index. D', D", extra dactylopodites. I', I", perhaps an indication of double extra indices. IV. Astacus fluviatilis, No. 813, left chela. L, normal left dactylopodite. R'D, L'D, right and left extra dactylopodites. L'l + R'I, left and right extra indices not separated from each other. (After Maggi.) parts and in addition the structure shewn in Fig. 182, IV upon the pollex-border of propodite. Here was a boss, separated by a groove. It was observed that the structure was that of a rt. and 1. dactylopodite working upon a double index [as in last case]. Structure of muscles, fully described, was also in agree- ment with the view that the extra parts were a complementary B. 3-1 530 MERISTIC VARIATION. [part I. 814 815. pair [similarly in Position D]. Maggi, L., Rend. R. 1st. Lomb., 1881, xiv. p. 333,^5. Homarus americanus : small cheliped as shewn in Fig. 182, III. It bears normal dactylopodite (D) and index (7), but this part is bent almost at rt. angles. From the outer angle arise the parts shewn. Apparently U and D" are a complementary pair of extra dactylopodites in Position D. The piece I' + I' is not described ; from the figure it seems possible that it may represent parts of the indices proper to D' and D". Case given by Faxon, Harv. Bull, 1880—1, vm. p. 261, PI. II. fig. 2. Cancer pagurus : right chela as shewn in Fig. 183. This is a case of some complexity. The figure will best make it clear. The dactylo- podite D' is single and so also is the index P. D is a double dactylo- podite, and F having teeth on two sides may be judged to be a double index. But if D' and P are the normal chela they each stand opposite Fig. 183. Cancer pagurus, No. 815. Eight chela seen from the apex, and from the outside. The lettering is arranged on the hypothesis that 1)' is the normal dactylopodite, P the normal index. D, the double extra dactylopodite, P', small double extra index. (From Proc. Zool. Soc.) the pincers to which they do not belong. Nevertheless I see no other interpretation possible. (This case is curiously like that of the tarsal claws in Rhizotrogus No. 786.) Specimen incorrectly described by myself, P. Z. S., 1890, p. 581, fig. 2. C. 816. Cancer pagurus : right chela in a condition not far removed from r that of the last case, le S£n£chal, Bull. Soc. Zool. France, 1888, p. 123, figs- 817. Uca una: a chela having complex repetition of parts somewhat as in No. 815. Jaeger, G., Jahresh. d. Ver. vaterl. JVaturk, 1851, xvn. p. 35, PL i. figs. 12 and 13. Perhaps of this nature is the case in Astacus fiuviatilis, Eoesel v. Kosenhof, Ins.-Belust., in. Tab. L.x.fig. 28. (b) Two extra dactylopodites arising from normal dactylo- podite. *818. To this and the next division belong the great majority of chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA. 531 cases of repetition of parts in Crustacea. Including examples recorded by various authors and specimens in different Museums there are nearly fifty cases of this class known to me. Indjpx Fig. 184. Three cases of two extra dactylopodites arising from a normal dactylopodite. I. Left chela of Carcinus mamas in Brit. Mus. II. Left chela of C. mcenas after Lucas, Ann. Soc. ent. France, S. 2, n. p. 42, PL I. Jig. 2. III. Right chela of Homarus, after van Beneden, Bull. Ac. Belg., S. 2, xvn. p. 371. Fig. 185. Cancer pagurus. Two chela? of the kind specified in No. 818, described by myself in Proc. Zool. Soc, 1890, p. 581, whence figs, are taken. 34—2 532 MERISTIC VARIATION. [part I. The various simple forms taken are illustrated by the eight cases shewn in Figs. 184, 185 and 186. It will be seen that when such extra processes arise on the toothed border of the dactylo- podite they turn their smooth borders to each other, but when 819 Fig. 186. Homarus americanus. Three chela whose dactylopodites bear double extra dactylopodites. I. A left. II. A left. III. A right. R, normal right. L, normal left. R', extra right. L\ extra left. (From Faxon.) they arise on the smooth border they turn their toothed borders to each other, thus fulfilling the conditions of the Scheme given at p. 481. Though from the close agreement between the three prongs in some of the specimens it is not always possible to tell the normal dactylopodite with certainty, it will be seen that in these the rules hold whichever of the two possible prongs be supposed to be the normal. Astacus leptodactylus : left chela has dactylopodite as shewn in Fig 187, II. Presumably D is the normal pushed out of place, and D' and D" are the two extra dactylopodites. They are so placed that none meets the index. Karoli, J., Term. Filzetek, 1877, i. p. 53, PI. II. chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA, 533 7? I Jl Fig. 187. I. Cancer pagurus, No. 820, right chela. Specimen in Coll. Surg. Mus. II. Astacus leptodactylus, left chela, after Karoli. 820. Cancer pagurus : somewhat similar case in rt. chela (Fig. 187, I) ; but here the normal, R, stands in its normal place. In Coll. Surg. Mus. •821. Homarus americanus : dactylopodite only of right chela preserved. It is bent sharply downwards, out of the plane of the " hand," and bears upon its upper surface two pairs of blunt, toothed processes [probably being rudiments of two pairs of extra dactylopodites]. Faxon, I.e., p. 261, PL II. fig. 1. 822. Homarus americanus : dactylopodite {a) bent upwards and outwards, crossing index without meeting it (Fig. 188). From the smooth border of dactylopodite arise two toothed processes Fig. 188. Homarus americanus, No. 822, left chela, a, normal point of dactylopodite. b, c, extra points. (After Faxon.) (b and c) curving towards index. [I take it that this is some- thing like the cases of Position A in Insects (p. 4M) but from the original figure the relations cannot be quite decided.] Faxon. I.e., p. 260, PI. I. fig. 15. 534 MERISTIC VARIATION. [part I. (c) Two extra indices arising from a normal index. *823. This again is a fairly common form, though much less frequent pi Fig. 189. I. Right chela of Homarus americanas. R', L', right and left extra indices not separated from each other. (After Faxon.) II. Homarus vulgaris, right chela in Brit. Mus. III. H. vulgaris, right chela bearing extra double index. R' and L', not separated. (After Lucas, I. c.) R' V i. n Fig. 190. I. Left chela of Carcinus mcsnas, indices only shewn, d, place of articulation of dactylopodite. In Coll. Surg. Mus. II. A similar case in Homarus americanus, after Faxon. L, normal left index. R', L' y extra right and left indices. chap, xxi.] SECONDARY SYMMETRY [ CRUSTACEA. 535 than the last. The cases known to me amount to about ten or fifteen. Seven cases are illustrated in Figs. 189, 190, and 191. Fig. 191. Two cases of extra indices in Cancer pagurus. I. In Coll. Surg. Mus. II. After le Senechal. R, normal right index. L, normal left. R', L', extra rights and lefts. (d) Simple processes, probably being rudimentary extra pairs of indices or of dactylopodites. *824. Many such are described, but of few can anything be said with confid- ence. A comparatively simple case is shewn in Fig. 19:2, where there is a decided suggestion that the process L' + R' is morphologically a pair of indices that have not separated from each other but stand compounded by their toothed borders. On comparing this case with for instance, Fig. 191, II, it will be seen that the two conditions might readily pass into each other in the way so often seen in Insects. Other cases of a more doubtful cha- racter are shewn in Fig. 193. Though in each the nature of the extra part is obscure, it is probable that they are all rudimentary states of the repetitions described. The alternative view that they are single repetitions certainly can- ,i i- j . n £ • ' ji„ mu puber from le Senechal. Bull. not be applied to all, for m many the Soc / XlluL ,,,.„„,,, l88 8, m... p. 125. extra process, though in the plane ot the L , normal index. L' + ll\ ?pair index and dactylopodite, is similar on of extra indices in Position V. Fig. 192. Left chela of Porta- 536 MEKISTIC VARIATION. [part I. m Fig. 193. I. Eight chela of C. pagurus in Coll. Surg. Mus. E, right index. II. Similar specimen whose dactylopodite bears x, a supernumerary process. In Coll. Surg. Mus. III. Astacus fluviatilis, left chela bearing ,r, a supernumerary process. EI, ED, right index and dactylopodite. (After Lucas.) both its faces in this plane. There is however no doubt that the distinction between these cases and true duplicity is hard to trace and possibly enough it is not really absolute. 825. -A- s eac h case differs from the others I give a list of those not in private col- lections 1 . The ? indicates that the case perhaps approaches the condition of true duplicity. D, dactylopodite. I, index. Tiedemann, Meckel's Arch., 1819, v. p. 127, PL u. Jig. 2. Jaegek, G., Jahresh. Ver. vaterl. Naturk., 1851, xvn. p. 35, PL i. fig. 7. id., Meckel's Arch., 1826, p. 95, PL n. fig. 3. Eosel v. Eosenhof, Ins.-Belust., in. p. 314, fig. 31. ibid., fig. 30. Lucas, Ann. soc. ent. Fr., 1814, Ser. 2, n. p. 45, PL i. fig. 6. Faxon, Harv. Bull., vm. p. 259, PL i. fig. 11. ibid., PL i. fig. 6. Eichard, Ann. sci. nat., 1893, p. 106. Coll. Surg. Mus. Coll. Surg. Mus. E, right. L, left. . Astacus fluviatilis EI ? A. fluviatilis EI A. fluviatilis A. fluviatilis LD EI '.' A. fluviatilis A. fluviatilis (Fig. 193, in.) LI LI Homarus americanus H. americanus '? Cancer pagurus C. pagurus (Fig. 193, i.) C. pagurus (Fig. 193, n.) LI ED LD LI LD (e) Exceptional Gases. *826. Homarus americanus : Right chela. Meropodite sub- cvlindrieal instead of flattened ; peripherally divides into two parts each bearing an articulated appendage as shewn in Fig. 194. [The appendage R is a normal chela. What is B! + 1/ ? Faxon, carefully describing the case, thinks that R! + U is a rudimentary and reversed copy of R, and that the case is one of duplicity. But from the particulars given, and especially from the circum- stance that the carpopodite was " much more spiny ,; than the normal, I think it likely that R' + U is morphologically a double structure formed of a pair of carpopodites compounded together. 1 With these may perhaps be mentioned the following : Apus cancriformis, having upon the 40th foot a second small flabellum shaped like the normal flabellum. The bract was greatly reduced in size. Lankestek, E. E., Q.J. M.S., 1881, xxi. p. 350, PL xx. fig. 12. [In explanation of Plate the abnormal foot is called the 30th.] chap, xxi.] CRUSTACEA : EXCEPTIONAL CASES. 537 Without having seen the specimen it is impossible to say much, but the parts should be examined with a view to this possibility. I conceive that the large spine marked by Faxon &p' stands on 1B' + L' Fig. 194. Homarus americanus, No. 826. A right chela. (After Faxon.) the morphologically middle line between the two extra half- meropodites.] Faxon, Harv. Bull VIII. p. 262, PI. II. fig. G. *827. Astacus fluviatilis $ : large adult. /. Abdomen wide in comparison with slender chelae: otherwise normal except left chela. This was formed as in Fig. 195. All normal except carpopodite, from which arose a fixed piece seeming to be an extra misshapen carpopodite, bearing three extra chelce, L', R and x. [R! and L' are a clear pair of images L' being right and left respectively. But between R' and the normal L there is the third extra chela x. As to the nature of this nothing can be said. Whether it is a left or a right cannot be told from fig. So far as I know, Fk;. 195. A$tacu» fluviatilis $Ho. this case is unique. Full description 82 ?, 1(,ft chela. /.. the normal. 7/ . on j w,^nm,^,.^v,4.„ • • • • i L>', presumaMv extra right and lelt and measurements given in original, oh ^ *, exta-a chela of uncertain q. V.] CANTONI, Rend. R. 1st, Lomb., nature. (After Cantoui.) 1883, xvi. p. 771,^. 538 MERISTIC VARIATION. [part I. C. Antenna}. *82S. Palinurus vulgaris : right antenna bore three complete filaments. So far as last spiny joint (merocerite) normal. Of this joint the peripheral portion much enlarged, presenting two articulations. The most posterior bore a normal carpocerite and fila- ment (Fig. 196, 1). The anterior articulation bore a double carpo- cerite with two filaments (II and III). As author points out, II is structurally a left antenna. [By the kindness of M. Alphonse Milne Edwards I have been allowed to examine this specimen. I am not sure that I succeeded in correctly determining the surfaces of the extra antennae, for the basal parts were not veiy fully formed ; but according to my determination their relations differed markedly „,«„„., . , r ,1 r f»j_i o l- j.* Fig. 196. Proximal parts of the right from those of any of the Schematic antenna of Pa Unurm vulgaris, No. 828. positions, for while the position I, the normal. II, extra left. Ill, extra of origin is VVA the two extra ri g ht - ( After L eg er antennae stand very nearly in the Position DA.] sci. nat, ZooL, 1886, S. 7, i. p. 109, PI. 6. *829. Astacus fluviatilis : exopodite of left antenna (Fig. 197) bears two supernumerary points, R' and L', which seem to have been inserted upon the internal border of the normal exopodite. Stamatt, G., Ball. Soc. Zool. France, 1888, xm. p. 199,^. Amorphous Cases. As has been stated, there are many cases, recorded or preserved, in which the nature of the parts cannot be made out. The majority of these are, I believe, injured or deformed limbs, and not cases of repetition of parts. Nevertheless of the latter class there are un- tiUs paving extra points to , exopodite of left antenna. R, doubtedly some amorphous cases, though they normal right. L, normal left. are far less common than regular ones, even R', L', extra right and left. as normal structures are more common in their (After Stamati.) regular shapes than in a deformed state. I mention the following as being, I think, the earliest record of abnormalities of this class. 830. Homarus : left chela having irregular process on inner border of dactyl opodite, and two irregular processes on inner border of index. [No description.] Bernhardus a Berniz, Miscell. Curios., Jena, n. 1671, p. 175, Obs. ci. PI. L£ger, A nn. Fig. 197. Astacus fiuvia- CHAPTER XXII. Duplicity of appendages in Arthropoda. That there should be such a thing as a limb double in the sense in which the following are double, has always seemed to me most strange. We know that a segment of an Annelid, or a vertebra, may be on one side of the body divided to form two segments or two vertebrae (as in No. 88 or No. 7) while on the other side of the middle line the segment is single. This is in keeping with all that we know of Division of parts in Linear Series. So might we suppose that a parapodium, or a rib, or perhaps a limb-bud might divide into two ; but the two half- segments or half- vertebrae are in Succession to each other, and are not complementary images of each other as these double- limbs are. That a parapodium may divide into two Successive para- podia is possible enough, though, apart from division of the segment bearing it, I know no clear case. But it may be stated at once that in Arthropods and Vertebrates such a phenomenon as the representation of one of the appendages by two identical appendages standing in Succession is unknown. No right arm is ever succeeded on the same side of the body by another arm properly formed as a right, and no Crustacean has two right legs in Succession, w T here one should be. The only cases at all approaching this state are those of Macacus No. 504 (q. r.), a case that must be interpreted with great hesitation ; and of the Frogs described by Cavanna and by Kingslev, also doubtful cases (see Chapter xxm). But though such repetition is probably unknown and is perhaps against Nature, there are still these strange double-limbs: fcwo limbs, always I believe imperfect, placed not in Succession, but as complementary images of each other, more or less exact. These we have seen in the hand of Man and in the feet of Artiodactvles; we have now to study them in Insects and in Crustacea 1 . 1 With mistrust I name cases in Amphibia and Fishes, perhaps of tin's nature. Lissotrjton punctatus (Newt): left pes having 10 digits in two groups, ('» and 4. Coll. Surg. Mas., Ter. Sei\. 293, a [not dissected]. Protopterus annectens : rt. 540 MERISTIC VARIATION. [part i. On the morphology or significance of duplicity in limbs I can make no comment beyond the few remarks given on p. 406. It is just possible that in Nos. 832 to 834 the duplicity of the chela or of the index is a division in the middle line of a Bilateral Minor Symmetry ; for some chelae are peripherally very nearly symmetrical about the plane of the dactylopodite and index. In Arthropods double-limbs are no less rare than in Vert- ebrates, for though in various works there are some scores of cases to be found, the great majority may be safely rejected as being almost certainly cases of double extra parts in Secondary Symmetry having their duplicity disguised as we saw it in Nos. 750, 764, or 801. By most of those who have dealt with these things the possibility of disguised duplicity in the extra part has been unheeded ; and ignorant of the special difficulties of these cases they have thus set down specimens as examples of duplicity of appendages at a casual glance. For this reason therefore I shall only give particulars of those few cases which are better established or otherwise of special interest, letting the rest follow as a list of references. It will not be forgotten that whenever an extra part is in itself symmetrical it always may be a double structure, and the special application of this fact to cases of extra filamentous an- tennas must in particular be borne in mind. Crustacea. *831. Hyas araneus : a left chela having the form shewn in Fig. 198, II and III. Fig. 198, I shews a normal left chela of this species from the outside in the same position as II. In the abnormal specimen the dactylopodite D is normal save that pectoral fin double, the division being in a horizontal plane, so that the two filaments were dorsal and ventral to each other [cp. No. 503]. Albrecht, Sitzb. Ak. Wiss. Bed., 1886, p. 545, PL vi. Silurus glanis : extra fin attached to pelvic girdle and partly to rt. pelvic fin. Warpachowski, Anat. Anz., 1888, in. p. 379, fig. Rana esculenta : left hind foot double ; rt. not seen [a very clear case]. Ercolani, Mem. Ace. Bologna, 1881, S. 4, in. p. 812, PI. iv.fig. 11. ' In Kaiidae a group of cases of extra fin are known. They are upward projections from the dorsal surface near the middle line. They are often spoken of as " dorsal ' : 7902 fins, but in the only case I have seen (Paris Mus. N. H., —^ , kindly shewn me by Prof. L. Vaillant) the attachment is not really median but is slightly oblique, and seems, from external examination, to spriug from some part of the pectoral girdle ('? left scapula). See Lacepede (who named such a fish "Raja cuvieri"), Hist. not. des Poiss., 1798, i. p. 141, PL vn.; Neill, Mem. Wern. Soc., 1808, i. p. 554; Moreau, Poiss. de la France, 1881, i. p. 206. In these fishes the real dorsal fins were in the proper place (though in some species they may be far forward, Forskal, Descr. Anim. in itin. Orient., 1775, i. p. 18). This repetition is of course quite distinct from that other curious and also Discontinuous variation in which the pectorals are partly divided into two lobes (R. clavata, Yarrell, Brit. Fish., eel. Richardson, 1859, ii. p. 585) ; or are separated from the head so as to project like horns on either side, as in last case ; and also in R. clavata, Yarrell, ibid. ; p. 384 ; Day, Brit. Fish., n. p. 345, PL clxxi. fig. 2; in R. batis, Day, l. c., p. 337; in R. asterias, Bureau, Bull. soc. zool. France, 1889, xiv. p. 313, fig. chap, xxn.] DOUBLE APPENDAGES : ARTHROPODA. 541 its point is rather worn. Where the index should be, there is a great eminence, bearing apically a second articulated dactylo- podite D\ complementary to D. Between the two dactylopodites Fig. 198. Hyas araneus. I. A normal left chela. II. The left chela of No. 831 from the outside. III. The same from the inside. D, normal dactylo- podite. D', extra dactylopodite. j, normal index, f, a small index toothed on both sides. (In Brit. Mus.) at the inner side of the eminence there is a fixed short process, j', which is toothed upon both the edges which it presents to the two dactylopodites. Round the articulation of 1)' are setae like those round the place of articulation of D. Specimen in Brit. Mus., kindly shewn to me by Mr R. I. Pocock. 832. Cancer pagurus : right chela. Dactylopodite and index each double in the way shewn in Fig. 199. Each is toothed on the side presented to the other half-pincer. Note that there is no proof that one or other of these points is not a pair compounded in Position A or P, but since both seemed equally to diverge from the normal plane of the propodite this is most unlikely. Specimen in Museum of Newcastle- upon-Tyne. 833. Homarus americanus : right chela shewn in Fig. 200, I. Two dactylo- podites separately articulating. Index bifid at apex and bearing two rows of teeth, one on each edge. Dactylopod- ites did not meet index. Faxon, Harv. Bull, vin. p. 260, PL I. fig. 13. 834. ? Hyas sp. Right chela. Dactylopodite single and in normal plane. Two separate and similar indices, each toothed as usual, Fig. l'J'.l. Ki-ht i-h. hi of Cancer pagurus, No. 832. I>\ D 2 , two partially Beparate dactylopodites. I 1 , 1-, two partially separate indices. (In Newcastle Mus.) 542 MERISTIC VARIATION. [part I. Fig. 200, I. Homarus americanus, right chela, No. 833. (After Faxon.) II. Lupa dicantha, left chela, No. 836. LI), LI, left dactylopodite and index. x, supernumerary index. (After Lucas.) making angle of about 45° with each other. This angle almost exactly bisected by the plane in which dactylopodite moves. Bell Collection, Oxford. 835. Maia squinado : from inner side of base of index of right chela arises a second index as shewn in Fig. 201. It is about half as large as the supposed normal index. The latter is dis- placed outwards. Dactylopodite moves in ap- proximately normal plane, missing both indices and falling between them. Specimen kindly lent by Prof. C. Stewart. Fig. 201. Right chela of Maia squinado, No. 835. The following are cases very similar to Nos. 834 and 835. 836. Lupa dicantha, left chela (Fig. 200, II). Lucas, Ann. Soc. eat. ' France, 1844, S. 2, II. p. 43, PI. i. fig. 1. 837. C. pagurus, right chela, 2 cases, le Sknechal, Bull. Soc. Zool. France, 1888, xm. p. 125, Jig. 2. 838. Xantho punctulatus, left chela (Fig/ 202) in which the index divided at about its middle to form two similar and equally diverging blunt processes. Herklots, Arch, neerl, 1870, v. p. 410, PI. x. 839. Homarus americanus : right chela bearing an extra index. Dactylopodite does not meet the normal index. [Very doubtful if of same nature as foregoing cases.] Faxon, I.e., PL I. fig. 14. The following cases are exceptional. 840. Homarus vulgaris : right chela has coxopodite single ; but basi- chap, xxil] DOUBLE APPENDAGES : ARTHROPODA. 543 Fig. 202. Xantlw punctulatw. Two views of left chela of No. 838, shewing the division of the index. (After Herklots.) podite is wrinkled and has two apical articulations, each bearing a small chela ; both are soft and not calcined, having articulations indicated by furrows only. [No information as to planes.] Richard, Ann. Sci Nat., 1893, p. 106. 841. Homarus americanus : right chela having a short articulated process below the dactylopodite moving in plane at right angles to it. [?a double structure]. Faxox, Haw. Bull., viii. PI. i. fig. 12. 842. H. americanus : toothless process articulating beloiv dactylopo- dite, moving in plane at right angles to its plane of motion. It articu- lates upon a separate process given by the propodite. [It is difficult to suppose that this extra process can be double.] Faxon, I. c , PI i fig. 16. Mr G. Dimmock of Canobie Lake, N. H. has kindly sent rue word of a Gelasimus having a chela of very anomalous form. Both index and dactylopodite are said to have been bifid, but the plane of division was at right angle* to the plane of the dactylopodite and index, so that all four points were in one plane. This specimen has unfortunately been destroyed ; but Mr Dimmock tells me that the arrangement was certainly thus, and that the unusual difficulty of bringing this case into agree- ment with others was recognized in examining it. INSECTS. Among the following 110 cases which all either have been or might be called cases of " duplicity ,J of legs, antenna-, or palpi, there is, I think, not one clear case of unmistakeable duplicity, such as for instance those of the chela? in Nos. 831 or 832. They should thus be considered as cases in which bhe extra parts have not been or cannot be shewn to be double, rather than as examples of proved duplicity of normal appendag 3. In every case that I have myself properly examined, it is either possible to prove the duplicity of the extra parts; or else essential features {e.g. spurs &c.) by which a right appendage may be told from a left are wanting. Nevertheless the few straight- forward cases of double-limbs in Crustacea k«-i-j» one alive to the possibility that some of these also may be the same. The most probable cases of true duplicity of limbs are Nos. 844, JS40 and 85 I . 544 MERISTIC VARIATION. [part I. *843. 1. Legs. Prionus californicus (Longic.) : each femur bore two tibiae and tarsi : both maxillary palps and also the left labial palp were partially double (Fig. 203). [No statement as to right labial palp. This shewn in fig. much thicker than left, but on com- S44. Fig. 203. Jayne.) Prionus californicus, No. 843, having extra legs and palpi. (After paring with a specimen it seems to be of normal thickness.] In some of the legs the two tibise are compounded at their bases, in others they articulate separately. [Several details given ; and in particular, enlarged views of the palpi and of the bases of the tibiae. But as no details are given regarding the apices and apical spurs of the tibia3 nothing can be said as to symmetry. It will be remembered that we have already had a case of a Prionus, No. 750, which similarly was supposed to have two of its legs double ; but there by means of the tibial spurs it was shewn that the extra part was in Secondary Symmetry. Possibly enough the same could here be shewn. It is much to be hoped that this specimen can be traced.] Jayne, H. F., Trans. Anier. Ent. Soc. y 1880, viii. p. 159, fig. 12. Allantus sp. (Tenthred., Sawfly) : extra leg borne by coxa of right middle leg. This coxa is imperfectly double, bearing two separate trochanters. Of these the anterior bears a small leg which, though ill formed, is complete in all its parts, but has the tarsal joints of abnormally small size. The posterior trochanter bears a leo; of full size. Its femur curves forwards and then backwards. The femur of the smaller curves for- chap, xxil] DOUBLE APPENDAGES : INSECTS. 545 wards, but its tibia curves backwards. The femora are so twisted that I failed to determine the symmetry of these 1<-l;s ; and while it was clear that neither was a normal left it was equally doubtful whether either was shaped as a right. Of all cases in Insects this is one of the nearest to the condition of true duplicity. Hope Collection, Oxford. 845. Carabus intricatus : middle right femur is partially bifid, pre- senting two apices in the same horizontal plane. The anterior apex bears a tibia and tarsus of nearly normal form. The other apex bears a tibia and tarsus of full length but much more slender than a normal one. This leg was ill-formed. The tibia bore no spurs, and there was no indication as to its symmetry, and nothing shewed that it was a right or a left leg. It is stated in the original description that the two legs could be separately moved and that both assisted in locomotion. Originally described by Mocquerys, Col. anorm., p. 45, ^y. f 846. Melolontha vulgaris : right anterior leg divided to form two legs. The femur dilates in peripheral third to form two apices, each bearing a tibia. These two tibiae are at right angles to the femur and are together in the same straight line, the one pointing forwards and the other backwards, each tibia turning its ventral or flexor surface towards the femur. The anterior tibia carries a tarsus of 4 joints with claws, while the posterior tibia lias a normal tarsus of live joints. For a figure of this specimen and particulars concerning it I am in- debted to Professor Alfred Giard. 847. Leptura testacea (Longic.): in tarsus of left middle leg the 2nd joint presents two apices (Fig. 204). The posterior bears normal 3rd and 4th (terminal) joints with a proper pair of claws. The anterior apex bears a narrow 7 3rd and 4th joint, the latter having only a single median claw [cf. No. 848]. Kraatz, Deut. ent. Zt., 1876, xx. p. 378, fig. 14. 848. Tetrops praeusta (Longic.) : right anterior femur widened towards apex, which presents two articulations in same horizontal plane. Each of these bears a tibia. The post- erior tibia and tarsus are complete in all respects, but they flex downwards and back- wards. The anterior tibia has a normally 4-jointed tarsus, but the apical joint bears only one claw, and there is no sign of muti- lation [cp. No. 847]. Were it not for the closely similar case of Silis No. 764 there would be no reason to doubt that this is a true case of duplicity, but that example shews how masked may be the doubleness of extra parts ; and though I could not prove either of these legs to be double I feel no certainty that one of them is not double. Specimen very kindly lent for descrip- tion by Mr F. H. YVateruouse. b. 35 Fig. 204. Leptura tes- tacea, No. SIT. Tarsus of left middle Leg from the plantar surface. (The pro- perty of Dr Kraatz.) 546 MERISTIC VARIATION. [part i. 849. Chlaenius holosericus (Carab.): left anterior tibia enlarged and dividing close to base into two branches of similar form and length [curving towards each other], botli equally furnished with hairs and bearing spines characteristic of the species. Anterior branch bears a complete tarsus like that of a leg of the other side, but posterior branch bears only one tarsal joint. Camerano, Atti Ac. Sci. Torino, 1878, xiv. fig. 850. Brachinus crepitans (Carab.): 3rd joint of right posterior tarsus enlarged ; 4th joint divides to form two apices (Fig. 205), each bearing- separate 5th joint in same horizontal plane. Each of these has a pair *.Q^ Fig. 205. Eight hind foot of Brachinus crepitans, No. 850. A, anterior. P, posterior. E, the supposed normal right apex. (In Rouen Mus.) of claws curving ventralwards. The two apical joints are not identical, the anterior being the shorter and continuing the general direction of the tarsus. I could not determine the symmetry. When examined by me the specimen was intact, but in cleaning it I broke this abnormal leg. First described by Mocquerys, Col. anorm., 1880, p. 63, fig. The two following cases differ from the rest in that the extra leg arose from the body separately from the normal leg. Among the cases of extra limbs in Secondary Symmetry were a few in which the coxa of the extra limbs was in the same socket as the coxa of a normal leg, though not united to it ; but in the first, and perhaps in both of the two cases that follow, the extra leg was wholly separate. The first case, No. 851, is the only one of the kind that I have seen. *»^ 851. Tenthredo ignobilis (Tenthred., Sawfly) : extra leg arising from 2?rothorax, on the left side of the body, at some distance behind the proper left anterior leg. Behind the anterior legs the prothorax of a normal specimen presents ventrally an elevation on each side of the middle line ; the point of origin of the extra leg is about halfway between this elevation and the socket of the coxa of the normal left anterior leg. The specimen had been a good deal injured by being- pinned very nearly through the point of origin of the extra leg, and on relaxing the specimen and attempting to restore the parts to their former positions I unfortunately broke off the extra leg from the body 1 . The leg is fairly well formed, but is a little shorter and a good 1 The specimen has been mended as nearly as possible in the position originally occupied by the leg. As it may pass hereafter into other hands, it may be well to chap, xxii.] SUPPOSED CASES OF DOUBLE LEG. 54' deal more slender than the normal anterior leg. Owing to the slighl degree to which the anterior legs of this insect are structurally differen- tiated from the middle legs, it cannot be positively stated that the extra leg is in form an anterior or a middle leg, but in size and general conformation it approaches very nearly to that of an anterior leg. It is complete in all its joints, having normal ciliation and claws, but the spurs are entirely absent from the apex of the tibia and probably have never been formed. This is an unfortunate circumstance; for, ina much as the anterior spur of a normal anterior tibia in this specie- is markedly differentiated from the posterior spur, it would have been easy to determine the surfaces of this leg had the spins been present. As it is, the matter cannot be positively decided, and it must sutlice to say that the general form of the leg and the shape and curvat are of its joints are such as to make it appear to be fashioned as an anterior leg and as a leg of the side upon which it occurs, namely, the left. This specimen was most kindly lent for description by Mr C. W. Dale, of Glanville's Wootton, Dorsetshire. It is the specimen mentioned in Ann. and Mag., 1831, iv. p. 21. 352. Elater variabilis (Elat.): complete extra leg articulating by separate coxa close to right anterior leg. Germar, E. F., May. cU r Ent., II. p. 335, PI. i. fig. 12. [This case has been copied by many authors. The figures represent the right fore leg and the extra one as normal right legs, but they are not sufficiently detailed to give con- fidence that this was so. If the specimen still exists it is to be hoped that it may be properly described.] o ko This is a list of all remaining cases in which it is in any way possible that there is duplicity of a leg. The point of origin is shewn approximately. * , seen by myself. J, partly amorphous or mutilated. 0, no description. R, right. L, left, tr., trochanter, f, femur, tb, tibia, ts, tarsus. * % Osmoderma eremita 1 (Lamell.) L 1. c. Mallodon sp. (Longic.) R 3. c. Pasimachus punctulatus (Carab.) L 2. tr. Broscus vulgaris (Carab.) R 1. tr. Agonuxn sexpunctatum (Carab.) R 3. f. % Carabus septemcarinatus £ R3. f. J Carabus nemoralis L 3. f. Carabus creutzeri ? L 1. f. Procrustes coriaceus' 2 (Carab.) R3. f. IVIeloe coriaceus (Het.) L 1. f. Carabus helluo R 1. f. Trichodes syriacus (Cleriche) R 1. f. X Chrysomela haemoptera (Phyt.) ? 3. f. 1— ii. Mocquerys, Col. anorm., p. 40, fig. ibid., p. 50, fig. Jayne, Trans. Amer. Ent. Soc., 1880, yiii. p. 150, PI. iv. fig. I. Imhoff, Ber. Vale nut. Get. Basel, 1838, in. p. 3. Schneider. Jahresb. scJdes. (?< -. vaterl. Kultur, I860, p. L29. Kraatz, Dent. cut. Zt., 1*77. xxi. p. 57, PI. i.fig. 32. Otto, Herm., Term.fuzetek, 1*77, i. p. 52, PI. ii. Kk.vatx, /. c, fig. 31. MOCQUEBYS, /. «'., )'. ">■">. fig. Staxnius, Mail. A n-li. . I wit.I'h >/■<.. 1835, i>. 3( >!'>,. //'.l), and Melolontha hippocastani, No. 795, where such extra parts were present on both antennae, suggesting that the similarity of the repetition of the two sides is due to the relation of Symmetry between the right side and the left. But against this view may be mentioned the cases Prionus coriarius, No. 750, and Carabus irregularis, No. 760, where two legs of the same side each bore extra parts, and the Lobster, No. 821, having two pairs of extra points on one dactylopodite. These cases suggest that bilateral simultaneity in such repetition may perhaps represent merely a general capacity for this form of repetition. The case of Prionus calif orm'c us, No. 843, would no doubt bear on this question, but unfortunately the facts in that case are scarcely well enough known to justify comment. 1 A case is given by Faxon {llarv. Bull., vin. PI. n. fig. 8) of Callinectes has- tatus in which the left lateral horn of the carapace, instead of being simple as in normal specimens, had three spines. It is just possible that two of these may have been in Secondary Symmetry. All other cases known to me arc in appendicular parts. 558 MERISTIC VARIATION. [part i. One further point remains to be spoken of. We have said that a system of parts in Secondary Symmetry is in a sense analogous with a bud, but in one respect the condition of these parts differs remarkably from all phenomena of budding or reproduction that are seen elsewhere. In a bud the various organs always present the same surfaces to each other, or in other words, the planes of division always pass between similar surfaces. In Secondary Symmetries this is not the case. As illustrated by the diagram on p. 481, the extra parts may present to each other, or remain compounded by any of their surfaces, whether anterior, posterior, or otherwise. This seems to be altogether unlike anything ever met with in animals and plants. It is as if in a bud on a plant two leaves on opposite sides of the axis could in their origin indifferently present any of their surfaces to each other. It will be remembered that the symmetry cannot be the result of subsequent shiftings, but must represent the original manner of cleavage of the two extra limbs from each other. We must there- fore conceive that in the developing rudiment of the two extra limbs either surface may indifferently be external, the polarity being ultimately determined by the relation of the bud or rudiment to the limb which bears it. CHAPTER XXIV. Double Monsters. Of the evidence as to double and triple " monstrosity ' and of the classification of the various forms no account can be given here. This may be found in any work on general teratology. In this chapter are put together a few notes on points respecting these formations of interest to the naturalist, and having relation to what has gone before. It is now a matter of common knowledge that in animals [and plants] division may occur in such a way that two or more bodies may be formed from what is ostensibly one fertilized ovum (cp. multipolar cells). But by a similar division, imperfectly effected, the resulting bodies instead of being complete twins or triplets may remain united together, frequently having a greater or less extent of body in common. In other words, speaking of simple cases in bilateral animals, the whole body, resulting from the development, may contain more than one bilaterally complete group of those parts which normally constitute the Primary Sym- metry of an " individual." If well developed, the component groups are most often united by homologous parts, so that there is a geometrical relation <>t' images between the groups together, forming the compound struc- ture, the whole being one system of Symmetry. Concerning the relations of the several parts of such a system to each other numerous questions of interest arise, but with these it is not now proposed to deal. To those unacquainted with facts of this class it may be of use to point out in the fewest words the direction in which this importance lies. It arises, briefly, from the fact that in the resemblance between a pair of homologous twins, win fcher wholly or partially divided, there is once again an illustration of the phenomenon of Sym- metry, and of the simultaneous Variation of structures related to each other as sym- metrical counterparts. The frequency of close resemblance between twins is a matter of common know- ledge. If it be true that such twins may result from the development of one ovum— a fact that cannot be doubted in face of the complete series of stages intermediate between total and partial duplicity — the resemblance between these twins is then of the same nature as that subsisting between the two halves of any other bilaterally symmetrical system. A wide field of inquiry is thus opened up. for, as suggested in the Introduction (p. 30) if the very close resemblance of twins to each other is a phenomenon dependent on Symmetry of Division, the less close resemblance betw een members of families may be a phenomenon similar in kind. 560 MERISTIC VARIATION. [part i. It will be remembered that the resemblance between twins is a true case of similar and simultaneous Variation of counterparts. This is clearly proved by the fact that when distinct Meristic Variations are exhibited by one twin they are not rarely present in the other also. Cases of this simultaneous Variation are familiar to all who have studied this subject. A useful list of examples in completely separate twins is given by Windlk 1 . One of the best known cases in twins incompletely separated, is that of the Siamese Twins-, who had each only eleven pairs of ribs (instead of twelve). Reference must lastly be made to a particular corollary which may naturally be deduced from the fact that the bodies of incompletely separated twins are grouped as a single system of Symmetry. If the whole common body were bilaterally sym- metrical, one twin must be the optical image of the other. But if the organs of one twin be normally disposed, the organs of the other must be transposed in completion of the Symmetry. This theoretical expectation is in part borne out by the facts. With a view to this question Eichwald 3 examined the evidence as to thoracopagous double monsters (including xiphopagi, &c), and found that in almost every case one of the bodies shewed some transposition of viscera, though to a varying extent 4 . There are nevertheless a few cases even of thoracopagi where neither body ex- hibits any transposition 5 . Moreover, contrary to natural expectation, it does not appear that in ordinary cases of completely separate twins either twin has its viscera transposed; and conversely, of 152 cases of transposition collected by Kuchenmeister only one could be shewn to have been a twin 6 . It seems therefore that the frequency of transposition in double monstrosity depends in some way upon the maintenance of the connexion between the twins; and that if the separation be completed early, as it must be supposed to be in cases of homologous twins born separate, then both bodies as a rule develop upon the normal plan, like the bodies of multiple births of other animals. But as the evidence now stands there is no reason to suppose that individuals with transposition of viscera, born as single births, have ever had a counterpart any more than individuals whose viscera are normally placed, tempting as it is to imagine that both may have had some counterpart which in the ordinary course does not develop. For the present we need not go beyond the fact that between complete duplicity resulting in " homologous twins," and the least forms of axial duplicity, consisting in a doubling of either extremity of the longitudinal axis almost all possible degrees have been seen 7 . By persons unfamiliar with abnormalities it 1 Windle, B. C, Jour. Anat. Phys., xxvi. p. 295. 2 For full abstracts of all evidence relating to this case, see Kuchenmeister, Die angeb. Verlagerung d. Eingeweide d. Menschen, Leipzig, 1883, p. 201. 3 Eichwald, Pet. med. Ztsch., 1870, No. 2, quoted from abstr. Virch. u. Hirsch, Jahresb., 1871, p. 167. 4 Eichwald supports the view that in these cases it is the right twin which shews the transposition. As Kuchenmeister (I. c.) points out, this cannot by the nature of the case be a universal rule ; for the relative position of xiphopagous twins may result singly from the way in which they happen to be laid by the mother or the midwife. Of the Siamese Twins, besides, it was Chang, the left twin, in whose body there were indications of transposition. The twins may also remain face to face. The expression " right twin " must always need further definition, and it should be qualified as the right when the livers are adjacent, or when the hearts are adjacent, as the case may be. Whether the rule is wholly or partially true for either of these positions seems to be very doubtful. 5 For example, Bottchee, Dorpater med. Ztschr., n. p. 105, quoted from V. u. II., Jahresb., I. c. In the specimen Terat. Cat. Coll. Surg. Mus., 1872, No. 114, there is no transposition, but here the hearts were not separate. 6 1. c., p. 268. One, however, was a child of a mother who had before borne twins, I. c, p. 313. 7 The fact that some of the degrees are much more common than others has an obvious bearing on the question of Discontinuity, which might with profit be pur- sued. A statistical examination as to the angles at which the bodies are most frequently inclined to each other would also probably lead to an interesting result. chap, xxiv.] AXIAL DUPLICITY: BEPTILES. 561 is sometimes supposed that axial duplicity is a phenomenon more or less peculiar to Man and to domesticated animals [and plants], and the occurrence is looked on as a part of thai Meristic in- stability which is ascribed to absence of the control of a Btrict and Natural Selection. This view is far from Bound Such phenomena have on the contrary been found in many classes of animals, vertebrate and invertebrate, and the unquestionable frequency in domesticated animals may in great measure be fairly attributed to the comparative ease with which the births of these creatures can be observed. As considerations of tin- kind have weight with many it has seemed worth while to give references to examples taken from a variety of different groups, shewing not only that such compound bodies may be produced in wild animals, but also that they may sometimes be able to carry on the business of life without artificial help. In Mammals and Birds I do not know an authentic case of a double monster that had grown up in the wild state. *865. In Reptiles many such cases are known and are referred to by most of the older writers. Of Snakes having complete or partial duplicity, nearly always of the head, some twenty cases are recorded. Several of these were animals of good size, and must have had aD independent existence for some considerable time. Some of the cases have special points of interest, but into these it is not now proposed to enter. As bearing on the question of the frequency of Meristic Variation in families and strains attention is called to the circumstance that Mitchill's three specimens were all found in one brood of 120 which were taken with the mother. The following is a list of records of snakes having the head whollv or partially double. Coluber constrictor. Wyman, J., Proc. Bost. X. II. S., 1862, ix. p. 193, fg. Coluber constrictor. Mitchill, S. L., Amer. Jour, of Sri., x. 1826, p. 48, PI. (3 specimens). Ophibolus getulus. Yarrow, Amer. Xat., 1878, xn. p. 470. Pityophis. ibid., p. 264. Pelamis bicolor. [Remarkable case 1 : the duplicity appearing only in the fact that there were 4 nasal plates instead of 2, each with a nostril] Boettger, 0., Per. iib. d. Seuck. nat. Ges. in Frank/, a. J/., 1890, p. lxxiii. In the remainder the species is not clear. Redi, Osserv, int. agli anim. viventi, &c, 1778, p. 2, Tav. i. [very good account]; LaceVkde, Hist. nat. des Serpens, n. 1789, p. 482; Bancroft, Nat Hist, of Guiana, 1769, p. 214, PL; Laxzoxi, Miscell. curios., 1690, Obs. « i.wi. p. 318, Fig. 36; Boston Soc. Med. Imp., Catal. of Mas.. No. 856, quoted from Wyman, /. c. ; Edwards, Nat. Hist, of Birds, dfcc, Pt. iv. 1751, p. 207, PI. ; Dorxer, Zoo!. Gart., 1873, xiv. p. 407 : Coll. Surg. Mus., Terat. Cat, 1872, Nos. 24—27. 1 Compare with Mitchill's two last cases, and also with a case ill Alytes ob- stetricans. Herox-Royer, Bull. Soc. Zool. France, 1884, ix. p, 164, B. 36 562 MERIST1C VARIATION. [part I. EC TV Fig. 207. Chrysemys picta, 2 or 3 days old. I, II, normal. Ill and IV, two- headed specimen. In the latter the nuchal and two pygal plates are normal. Be- tween them are 12 plates on each side, 11 being the most usual number. Among the costals an extra plate is wedged in on the rt. First vertebral divided by suture ; fifth is made up of 4 irregular plates. In the plastron there is a doubling of the gular plate. The rt. femoral has a suture. (From Barbour.) chap, xxiv.] AXIAL DUPLICITY: IX VERTKIiKATKS. 563 See also, Geoffroy St. Hilaire, Hist, des a num., ed 1838, 11. p. 197; Dumeril et Bibron, Erpdt generate, 1884, vi. p, 209. 866. Duplicity of the head is less common in Lizards, but several examples are known. See Geoffkoy St. HlLAlBB, I c, p. 195: Con Paris, 1869, S. 3, v. p. 136, etc. *867. In Chelonia also are several such instances. See Edwards, N1, p. lMm 1 , ; .Mnniii.i, /. ,-. ; BaBBOUB, E. H., Amer. Jour, of $ci., 1888, S. 3, xxxvi. p. 227, PL v. The lasi i particularly interesting case from the circumstance that the behaviour during life was observed to some extent, though only a popular account is given. The two heads seemed to act independently, and it is said that there was no concerted action between the feet of the two sides. Barbour's figures are reproduced in Fig. 207. In fish-hatching establishments double monstrosity is of frequent occurrence among young Salmon and Trout. A two-headed embryo of a Shark is preserved in Coll. Surg. Mus. {Terat. Cat. 1 s 7l', No. 22 The following cases relate to invertebrates. Chaetopoda. Duplicity in this Class has been often seen, but that any of the cases are truly congenital cannot be stated. There is evidence that in many Annelids regeneration 1 both of head or tail may freely occur, and it is quite possible that the second head or second tail may have grown out from an injured place, though of this there is no actual proof. In cases of posterior bifurcation each tail generally contains all the parts proper to the normal, but in Xo. S71 one of the tails was without the terminal cirri usual in the species. So far as can be gathered from the evidence it does not appear that the two con- tinuations of the body have always the same number of segments, which might perhaps be expected were both the result of a natural division of the developing body. On the other hand, they do seem generally to have a nearly equal development, and are almost always (in cases of double tails, at least) fairly equal in length, which would not be anticipated if one only were a new growth. Moreover, if the double tail is in some way due to regeneration one would expect to find such duplicity in its minor conditions much more commonly. Into the details of the structure it is not now proposed to enter, and indeed of most of the cases there is little to be told. The evidence is mentioned here simply in further proof of the power of these indiv- iduals, thus greatly departing from the normal of their species, to maintain themselves with no apparent difficulty. It will be noticed that the species concerned are most various, and include not only Errant ia, but two cases also in Serpulida?. The literature of the subject was collected by Collin ', and a list of the references was independently collected and published with abstracts by Andrews 3 . This list, with a few additions, was republished by Friend 4 . Though many of the accounts are imperfect they are referred 1 The evidence on this point does not come within the scope of this work. References to it may be obtained from Akdbbws, Zeppelin, Taenia ccenurus : specimen whose head had 6 suckers instead of 4, and 32 hooks instead of 28. Proglottides were 3-sided prisms, in section triangular. Longitudinal vessels 6 instead of 4, two being in each angle. Absolute size of head greater than normal. This abnormal 566 MERISTIC VARIATION. [part i. form is known to occur in many kinds of Tapeworms, and especially in Cysticerci. Leuckart, Parasiten d. Menschen, pp. 501 — 2, cp. p. 577. [Case withfii'e suckers mentioned, ibid., p. 578.] In another form of abnormality the chain of segments has three longitudinal flanges, formed, as it were, by the union of two chains of proglottides having one edge in common. Head not found, but several cases known. Genital openings in one case all upon the common edge. Leuckart, ibid., p. 574. Cp. Cobbold, Trans. Path. Soc, xvn. p. 438; Levacher, Comptes Yendus, 1841, xm. p. 661. 882 Bifurcated chains of proglottides have also been seen, e.g. specimen of TaBnia (cysticerci) tenuicollis, which bifurcated several times in terminal portion, though normal in front of this. Momez, Bull. >Sci. du No rd, x. p. 201. See also Taenia saginata ? Leuckart, I. c, p. 573. Brachiopoda. 883. Acanthothyris spinosa (Rhynchonellida^): case of duplicity I u Fig. 209. Acanthothyris spinosa, No. 883. Case of duplicity. (From P. Fischer.) I. Seen from ventral valve. II. Looking between the valves. as shewn in Fig. 209. Fischer, P., Jour, de Conchyl. S. 3, xix. p. 343, PL xm. figs 4—7. HOLOTHURIOIDEA. 884. Cucumaria acicula : specimen made up of two individuals cohering laterally at posterior ends. Schmeltz, Verh. d. Ver. f. naturw. Unterhaltung, Hamb., 1877, iv. p. XV. 885. Cucumaria planci : case of second mouth and ring of tenta- cles borne on a lateral bud-like projection. Ludwig, H., Z.f. w. Z., liii. Supp. p. 21, PI. v. 886. Ccelenterata. Forms which are commonly simple, such as Actinia or Sagartia, are rarely found with two discs seemingly due to incomplete division, which in these forms may take place longitudinally [?] as well as by ordinary budding. Gosse, P. H., Sea-Anemones, p. xxi., &c. See also Guyon, Zoologist, p. 7026, fig. Similar occurrences, not distinguishable from budding, have been seen in Medusas, e.g., Phialidium variabile, Davidoff, Zool. Anz., iv. p. 620, fig.; Gastro- blasta raffaeli, Lang, A., Jen. Ztseiir., xix. p. 735. An interesting case of this kind * was seen in Cordylophora lacustris. Several polystomatous specimens were found on a particular mass of Cordylophora, but were not found on all colonies gathered with this mass and had not been seen previously in specimens from the same locality. [Further particulars.] Price, H., Q. J. M. S„ 1876, p. 23, figs. Protozoa. Double and triple monstrosity has been seen in several Foraminifera, see e.g., Dawsox, Canad. Nat., 1^70, p. 177, figs.; Balkwit>l and Wright, Trans. B. Irish Ac, 1885, xxviii. p. 317, PL xiv., &c. [As to cases in Stentor, see Balbiani, J. de Vanat., 1891, No. 3, but these are doubtless examples of regeneration and duplicity following injury.] CHAPTER XXV. Concluding Reflexions. To attempt at this stage any summary of conclusions would be misleading. The first object of this work is not to set forth in the present a doctrine, or to advertise a solution of the problem of Species, but rather to bring together materials that may help others hereafter to proceed with the solution of that problem. A general enumeration of particular conclusions is therefore to be avoided. Indeed, from the scantiness of the evidence, its present value is chiefly in suggestion, and the facts must therefore be themselves still studied in detail. The reader must interpret as he will. But, as often happens, that which may not shew the right road is enough to shew that the way taken has been wrong, and so is it with this evidence. Upon the accepted view it is held that the Discontinuity of Species has been brought about by a Natural Selection of particular terms in a continuous series of variations. Of the difficulties besetting this doctrine enough was said in the introductory pages. These difficulties have oppressed all who have thought upon these matters for themselves, and they have caused some anxiety even to the faithful. And if in nice of the difficulties reasonable men have still held on, it has not been that the obstacles were unseen, but rather that they have hoped a way through them would be found. Now the evidence, of which a sample has been here presented, gives hope that though there be no way through the difficulties, there is still perhaps a way round them. For since all the difficulties grew out of the assumption that the course of Variation is continuous, with evidence that Variation maybe discontinuous, for the present at least the course is clear again. Such evidence as to certain selected forms of variations has I submit, been given in these chapters, and so tar a presumption is created that the Discontinuity of which Species is an expression has its origin not in the environment, nor in any phenomenon of Adaptation, but in the intrinsic nature of organisms themselves, manifested in the original Discontinuity of Variation. But this evidence serves a double purpose. Though some may 568 MERISTIC VARIATION. [part I. doubt whether the variations here detailed are such as go to the building of Specific Differences (a doubt which, it must be granted, does fairly attach to some part of the evidence), yet the existence of sudden and discontinuous Variation, the existence, that is to say, of new forms having from their first beginning more or less of the kind of perfection that we associate with normality, is a fact that disposes, once and for all, of the attempt to interpret all per- fection and definiteness of form as the work of Selection. The study of Variation leads us into the presence of whole classes of phenomena that are plainly incapable of such interpretation. The existence of Discontinuity in Variation is therefore a final proof that the accepted hypothesis is inadequate. If the evidence went no further than this the result would be of use, though its use would be rather to destroy than to build up. But besides this negative result there is a positive result too, and the same Discon- tinuity which in the old structure had no place, may be made the framework round which a new structure may be built. For if distinct and "perfect" varieties may come into existence discontinuous!)', may not the Discontinuity of Species have had a similar origin ? If we accept the postulate of Common Descent this expectation is hard to resist. In accepting that postulate it was admitted that the definiteness and Discontinuity of Species depends upon the greater permanence or stability of certain terms in the series of Descent. The evidence of Variation suggests that this greater stability depends primarily not on a relation between organism and environment, not, that is to say, on Adaptation, but on the Discontinuity of Variation. It suggests in brief that the Discontinuity of Species results from the Discontinuity of Variation. This suggestion is in a word the one clear and positive indica- tion borne on the face of the facts. Though as yet it is but an indication, there is scarcely a problem in the comparison of structures where it may not be applied with profit. The magnitude and Discontinuity of Variation depends on many elements. So far as Meristic Variation is concerned, this Discontinuity is primarily associated with and results from the fact that the bodies of living things are mostly made up of repeated parts — of organs or groups of organs, that is to say, which exhibit the property of "unity," or, as it is generally called, "individuality." Upon this phenomenon depends the fact that Meristic Variation in number of parts is often integral, and thus discontinuous. The second factor that most contributes to the Discontinuity of Variation is Symmetry, manifesting its control in the first place directly, leading often to a result that we recognize as definite and perfect because it is symmetrical. But besides this direct control that we associate with Symmetry, other erfects greatly contributing to the magnitude of Variation chap, xxv.] CONCLUDING REFLEXIONS. 569 can be traced to a factor not clearly to be distinguished from Symmetry itself. For, as has been explained, Symmetry, whether Bilateral or Radial, is only a particular case of that phenomenou of Repetition of Parts so universally characteristic of living bodies ; and that resemblance between two counterparts, which we call Bilateral Symmetry, is akin to the resemblance between parts repeated in Series, though, as is shewn by their geometrical re- lations, the processes of division by which the parts were originally set off, must be in some respects distinct. Bilateral Symmetry <>t Variation is thus only a special case of the similar and simul- taneous Variation of repeated parts. The greatness of the observed change from the normal is often largely due to this possibility of simultaneity in Variation, the change thus manifesting itself not in one part only, but in many or all of the members of a series of repeated parts. Instances of such similar and simultaneous Variation of serial parts in animal- have now been given. Examples still more marked may be seen abundantly among plants. A variation, for example, in the form or degree of fission of the leaf, slight perhaps by itself, when taken up and repeated in every leaf in its degree, constitutes a definite and conspicuous distinction. Everyone has observed this common fact. Few illustrations of it are more evident than that of the common Hawthorn. In a quickset hedge soon after the leaves begin to unfold almost each separate plant can be recognized even at a distance, and its branches can be traced by their special character-, by the shapes and tints of the leaves, by the angles that they make with the stem, by the manner of unfolding of the buds, and - forth. These variations, sometimes slight in themselves, by their similarity and simultaneity build up a conspicuous result. The phenomenon of serial resemblance is in fact an expression of the capacity of repeated parts to vary similarly and simul- taneously. In proportion as in their variations such parts retain this capacity the relationship is preserved, and in proportion as it is lost, and the parts begin to vary independently, exhibiting differentiation, the relationship is set aside. It will be noticed that to render the converse true we must extend the conception of Serial Homology in special cases to organs not commonly regarded as serially homologous with each other, but which having assumed some common character thereafter may vary together (cp. p. :*()!»). In the power of independent Variation, members of series once more exhibit the property of "unity" that we have already noticed as appearing in the manner in which the number of the members is changed. ' The fact that members of series should hi' capable of varying as "individuals" is paradoxical. Such members, teeth, digits, segments of Arthropods, and the like, are each made up of various tissues endowed with miscellaneous functions and d i ss imil ar in their morphological nature. Nevertheless each group is capable 570 MERISTIO VARIATION. [part I. of independent division and of separate Variation. Single digits for instance may thus be independently hypertrophied as a whole, single segments or single appendages or pairs of appendages may be differ- entiated in some special way, and so forth. At this point reference may again be made to that extraordinary Discontinuity of Variation appearing in what I have called Ho- mceosis, so strikingly seen in the few Arthropod cases given (p. 146), and so common in flowering plants. In these changes a limb, a floral segment, or some other member, though itself a group of miscellaneous tissues, may suddenly appear in the likeness of some other member of the series, assuming at one step the condition to which the member copied attained presumably by a long course of Evolution. Many times in the course of this work we have had occasion to consider the modifications in the conception of Homology demanded by the facts of Variation. It is needless to speak further of this matter here, and the reader is referred to pp. 125, 191, 269, 394 and 417, where the subject is discussed in relation to Linear Series of several kinds, and to the facts given in Chapter XVI and at p. 433 bearing on the same questions in their application to Radial Series. The outcome of these considerations shews, as I think, that the attribution of strict individuality to each member of a series of repeated parts leads to absurdity, and that in Variation such individuality may be set aside even in a series of differentiated members. It appears that the number of the series may be in- creased in several ways not absolutely distinct, that a single member of the series may be represented by two members, that a terminal member may be added to the series, and also that the number of the members may change, no member precisely corre- sponding in the new total to any one member of the old series : in short, that with numerical change resulting from Meristic Variation there may be a redistribution of differentiation. But though this is, in my judgment, a fact of great consequence, its relation to the Study of Variation is merely incidental. It is not so much that to enlarge the conception of Homology so as to include the phenomena of Meristic Variation is a direct help, as that to maintain the old view is a hindrance and keeps up an obstacle in the way of any attempt to apprehend the real nature of the phenomena of Division, and hence of Meristic Variation. So long as it is supposed that each member of a series of repeated parts is literally individual, it is impossible to form any conception of Division that shall include the facts of Meristic Variation, for in Variation it is found that the members are divisible. It is an unfortunate thing that the study of Homology has been raised from its proper place. The study of Homologies was at first undertaken as a means of analyzing the structural evidences of relationship, and hence of Evolution. This is its proper work and chap, xxv.] CONCLUDING REFLEXIONS. 571 use ; but the pursuit of this search as an aim in itself has led to confusion, and has tended to conceal the fact that there are pheno- mena, to which the strict conception of individual Homology is not applicable. This exaggerated estimate of the fixity of the relationship of Homology has delayed recognition of the Discontinuity of Meristic Variation, and has fostered the view that numerical Variation must be a gradual process. This view the evidence shews to be wrong, as it was also im- probable. Brief allusion may be made to three separate points of minor un- importance. It is perhaps true that, on the whole, series containing large num- bers of undifferentiated parts more often shew Meristic Variation than series made up of a few parts much differentiated, but throughout the evidence a good many of the latter class are nevertheless to be seen. Reference may be made to a point that might with advantage be examined at length. The fact that Meristic Variation may take place suddenly leads to a deduction of some importance bearing on the expect- ation that the history of development is a representation of the course of Descent. In so far as Descent may occur discontinuously it will, I think, hardly be expected that an indication of the previous term will appear in the ontogeny. For example, if the four-rayed Tetracrinus may suddenly vary to both a five-rayed and also to a three-rayed form (see p. 437) it is scarcely likely that either of these should go through a definitely four-rayed stage; and if the origin of the four-rayed form itself from the five-rayed form came similarly as a sudden change, it would not be expected that a five-rayed stage would be found in its ontogeny. Similarly, if a flower with rive regular segments arise as a sport from a flower with four, it would not, I suppose, be expected that the fifth segment would arise in the bud later than the other four. I suggest these examples from Radial Series, as in them the question is simpler, but similar reasoning may be applied to many cases of Linear Series also. It will be noted that the attempt to apply to numerical variations the conception of Variation as an oscillation about <>n> mean is not easy, difficulty arising especially in regard to the choice of a unit for the estimation of divergence. In few cases can facts be collected in quantity sufficient even to sketch the outline of such an investigation : but, to judge from the scanty indications available, it seems that in cases of numerical change variations to numbers greater than the normal number, and to numbers less than it are not generally of equal frequency. Probably no one would expect that they should be so. As was stated in the Introduction, wo arc concerned here with the manner of origin of variations, not with tin- manner of their perpetuation. The latter forms properly a (list ind subject. We may note however, in passing, how little do the lew known facta bearing on this part of the problem accord with those ready-made 572 MERISTIC VARIATION. [part i. principles with which we are all familiar. Upon the special fallacy of the belief that great Variation is much rarer in wild than in domesticated animals we have often had occasion to dwell. As was pointed out in the discussion of the evidence on Teeth (p. 266) this belief arises from the fact that domesticated animals are for the most part variable, and that w r e have every opportunity of ob- serving and preserving their variations. To compare rightly their variability with that of wild animals choice should be made of animals that are also variable though wild. Taken in this way the comparison is fair, and as I have already said, if we examine the variation in the vertebrae of the Sloths, in the teeth of the Anthro- poid Apes, in the colour of the Dog-whelks {Purpura lapillus), &c, we find a frequency and a range of Variation matched only by the most variable of domesticated animals. It is needless to call attention to the fact that in hardly any cases even of extreme variations in wild creatures is there evidence that the animal was unhealthy, or ill nourished, or that its economy was in any visible way upset ; but in almost every example, save for the variation, the body had the ajDpearance of normal health. After all that has been said few perhaps will still ask us to believe that the fixity of a character is a measure of its importance to the organism. To try to apply such a doctrine in the open air of Nature leads to absurdity. Let one more case be enough. I go into the fields of the North of Kent in early August and I sweep the Ladybirds off the thistles and nettles of waste places. Hun- dreds, sometimes thousands, may be taken in a few hours. They are mostly of two species, the small Coccinella decempunctata .or variabilis and the larger C. septempunctata. Both are exceedingly common, feeding on Aphides on the same plants in the same places at the same time. The former (G. decempunctata) shews an ex- cessive variation both in colours and in pattern of colours, red- brown, yellow-brown, orange, red, yellowish-white and black, in countless shades, mottled or dotted upon each other in various ways. The colours of pigeons or of cattle are scarcely more variable. Vet the colour of the larger G. septempunctata is almost absolutely constant, having the same black spots on the same red ground. The slightest difference in the size of the black spots is all the variation to be seen. (It has not even that dark form in which the black spreads over the elytra until only two red spots remain, which is to be seen in C. bipunctata.) To be asked to believe that the colour of G. septempunctata is constant because it matters to the species, and that the colour of C. decempunctata is variable because it does not matter, is to be asked to abrogate reason. But the significance of the facts does not stop here. When, looking further into the variations of 0. decempunctata it is found that most of its innumerable shades of variation are capable of being grouped round some eight or ten fairly distinct types, surely chap, xxv.] CONCLUDING REFLEXIONS. 57 3 an expectation is created in the mind that the distinctness of these forms of varieties, all living [and probably breeding] together, may be of the same nature as the distinctness of Species : and since it is clear that the distinctness of the varieties is not the work of separate Selection we cannot avoid the suspicion that the same may be true of the specific differences too. An error more far-reaching and mischievous is the doctrine that a new variation must immediately be swamped, if I may use the term that authors have thought fit to employ. This doctrine would come with more force were it the fact that as a matter of experience the offspring of two varieties, or of variety and normal, does usually present a mean between the characters of its parents. Such a simple result is, I believe, rarely found among the facts of inheritance. It is true that with regard to this part of the problem there is as yet little solid evidence to which we may appeal, but in so far as common knowledge is a guide, the balance of experience is, I believe, the other way. Though it is obvious that there are certain classes of characters that are often evenly blended in the offspring, it is equally certain that there are others that are not. In all this we are still able only to quote case against case. No one has found general expressions differentiating the two classes of characters, nor is it easy to point to any one character that uniformly follows either rule. Perhaps we are justified in the impression that among characters which blend or may blend evenly, are especially certain quantitative characters, such as stature : while characters depending upon differences of number, or upon quali- tative differences, as for example colour, are more often alternative in their inheritance. But even this is very imperfectly true, and as appeared in the case of Earwigs (p. 40) there may be a definite dimorphism in respect of a character which to our eye is simply quantitative. Nevertheless it may be remembered that it is especially by differences of number and by qualitative differences that species are commonly distinguished. Specific differences are less often quantitative only. But however this may be, whatever may be the meaning of alternative inheritance and the physical facts from which it results, and though it may not be possible to find general expressions to dis- tinguish characters so inherited from characters that may blend, it is quite certain that the distinctness and Discontinuity of many characters is in some unknown way a part of their nature, and is not directly dependent upon Natural Selection at all. The belief that all distinctness is due to Natural Selection, and the expectation that apart from Natural Selection there would be a general level of confusion, agrees ill with the facts of Variation. We may doubt indeed whether the ideas associated with that flower of speech, "Panmixia," are not as false to the laws of Hie as the word to the laws of language. 574 MERISTIC VARIATION. [part I. But beyond general impression, in this, the most fascinating part of the whole problem, there is still no guide. The only way in which we may hope to get at the truth is by the organization of systematic experiments in breeding, a class of research that calls perhaps for more patience and more resources than any other form of biological inquiry. Sooner or later such investigation will be undertaken and then we shall begin to know. Meanwhile, much may be done to further the Study of Varia- tion even by those who have none of the paraphernalia of modern science at command. Many of the problems of Variation are pre- eminently suited for investigation by simple means. If we are to get further with these problems it will be done, I take it, chiefly by study of the common forms of life. There is no common shell or butterfly of whose variations something would not be learnt were some hundreds of the same species collected from a few places and statistically examined in respect of some varying character. Any- one can take part in this class of work, though few do. At the present time those who are in contact with the facts and material necessary for this study care little for the problem, or at least rarely make it the first of their aims, and on the other hand those who care most for the problem have hoped to solve it in another way. These things attract men of two classes, in tastes and tempera ment distinct, each having little sympathy or even acquaintance with the work of the other. Those of the one class have felt the attraction of the problem. It is the challenge of Nature that calls them to work. But disgusted with the superficiality of "naturalists" they sit down in the laboratory to the solution of the problem, hoping that the closer they look the more truly will they see. For the living things out of doors, they care little. Such work to them is all vague. With the other class it is the living thing that attracts, not the problem. To them the methods of the first school are frigid and narrow. Ignorant of the skill and of the accurate, final knowledge that the other school has bit by bit achieved, achievements that are the real glory of the method, the "naturalists" hear onlv those theoretical conclusions which the laboratories from time to time ask them to accept. With senses quickened by the range and fresh air of their own work they feel keenly how crude and inadequate are these poor generalities, and for what a small and conventional world they are devised. Dis- appointed with the results they condemn the methods of the others, knowing nothing of their real strength. So it happens that for them the study of the problems of life and of Species becomes associated with crudity and meanness of scope. Beginning as naturalists they end as collectors, despairing of the problem, Turning for relief to the tangible business of classification, account- ing themselves happy if they can keep their species apart, caring chap, xxv.] CONCLUDING REFLEXIONS. 575 little huw they became so, and rarely telling ns how they may be brought together. Thus each class misses that which in the other is good. But when once it is seen that, whatever be the truth as to the modes of Evolution, it is by the Study of Variation alone that the problem can be attacked, and that to this study both classes of observation must equally contribute, there is mice more a place for both crafts side by side: for though many things spoken ..f in the course of this work are matters of doubt or of controversy, of this one thing there is no doubt, that if the problem of Species i^ to be solved at all it must be by the Study of Variation. INDEX OF SUBJECTS. Acanthoderes nigricans, double (?) leg, 548 Acanthodrilus, double tail, 565 Acanthothyris, double monster, 566 Accessory hoofs of Ox, connected with supernumerary digits, 285 Acherontia atropos, colours of larva?, 304, 305 Acinopus lepelletieri, extra legs, 498 Actinometra, variation in number of radial joints, 421; 4-rayed specimen, 437 ; 6-rayed, 437 Adaptation, Study of, as a method of solving problems of species, 10; logical objection to the method, 12 ; speculations as to, avoided, 79; of species, approximate only, 11 Adimonia tanaceti, double (?) antenna, 550 Agabus uliginosus, double (?) leg, 548 Agestrata dehaanii, extra legs, 491 Agonum sexpunctatum, double (?) leg, 547; riduum, double (?) antenna, 550 Agra catenulata, extra legs, 512 Akis punctata, double (?) antenna, 551 Alans sordidus, extra legs, 508 Aleochara mcesta, extra legs, 488 Allantus, extra appendage, 544 Allolobophora, generative organs of, 160, 162, 165 ; duplicity of head and tail, 565 ; lissaensis, spermathecae, 165 Allurus, generative organs of, 164, 165; putris, 165; hercynius, tetraedrus, 164 Alytes, vertebras, 127; axial duplicity, 561 Amblypneustes, 4-rayed, 443; 6-rayed, 446; partial reduction of a ray, 443; partial duplicity of a ray, 446 Ammoccetes, alleged case of eight pairs of gill-openings, 174 Ampedus ephippium, double (?) antenna, 551 Amphicyclus (Holothurian), tentacles not in multiples of five, 435 Amphimallus solstitialis, extra antenna?, 515 Amphioxus, number of gill- slits, 174. Anagallis arvensis, colour- variation, 44 Anas querquedula, division of digits, 392 Anchomenm sexpunctatus, extra antenna?, 523; double (?) antenna, albipes, an- gusticollis, 550 Angora breeds, 55 Anisoplia floricola division of epistome, 454 Annelids, segmentation compared with that of Chordata, 86; imperfect seg- mentation, 156; spiral segmentation, 157 ; variation in generative organs, 159 ; axial duplicity, 563 Anomala junii, extra antenna?, 515 A user, spinal nerves, 130, 133 Antedon, variation in number of radial joints, 421; 4-rayed specimen, 436; 6-rayed specimen, 437; abnormal branching, 438 Antenna developed as foot, 146, 147 Anteuna?, variation in number of joints, Prionida?, 411; Polyarthron, 412; Lyriphlebus, 412; Donatio,, 413; Forficuhi, 413 extra, in Secondary Symmetry, 513-522 ; symmetry un- known, 522; arising from head, 551 supposed double, 548 Anthia, extra legs, 502 Antkocharis cardamines, colour-varia- tion, 45 eupheno, 45 ; ione, 72 Anthropoid Apes, Variation in Verte- bra?, 116; teeth, 199; digits, 349 Aphodius, extra legs, 494 Apis mellifica, union of compound eyes, 461 Appendages, joints of, 410 supernumerary, arrange- ment of evidence, 474 in Secondary Symmetry, 475 ; mechanical model illustrating relations, 480; duplicity of, 406, 539 Apteryx, brachial plexus, 130 Apus, extra fiabellum, 536 Aquila chrysaetos, extra digits, 393 Archibuteo lagopus, extra digit, 392 Arctia, colour-variation, 46 Arctocephalus australis molars, 243 Arge pherusa, eye-spots, 295 Avion, sinistral, 54 Aromia moschata, extra legs, 485, 503, 512 ; double (?) antenna, 3 cases, 551 Artemia, salina and milhausenii, 96; gracilis, 100; relation to Branchipus, 96 ; segmentation of abdomen, 100 Arteries, renal, 277; in a case of double- hand, 333 Arthronomalus, number of segments, 94 Arthropoda, variation in number of segments, 87; Homoeosis in append- ages, 146; axial duplicity, 565 Articular processes, change from dorsal to lumbar type, 109 ; variations in position of change, 110, 112, 114, 117, 122 INDEX OF SUBJECTS. 577 Artiodactyla, polydactylism, 373; syn- dactylism, 383 ; teeth, 245, 246 Ascidia plebeia, specimens having every fourth vessel of branchial sac dilated, 172 Ascidians, variation in branchial struct- ures, 171, 172; extra atriopore, 456 Ass, canines, 245 ; molars, 246 ; absence of digital variation in, 360 Astaeus fluvidtilis, colour-variation, 44 variation in number of oviducal open- ings, 84, 152 absence of male open- ing, 154 absence of oviducal opening, 152, 153 absence of opening from green gland, 154 extra chela?, 529, 537 extra processes from chela?, 536 repetition of exopod- ite of antenna, 538 A. leptodactylus, extra dactylopodites, 532 A. pilimanus and braziliensis, apparent presence of female opening in males, 155 Aster ias, variation of pedicellariae, 429; arms, 439 with 8 rays and 3 madreporites, 440; extra water-pore, 466 polaris, normally 6-rayed, 433 problema, tenuispina, undergo fission, 433 Asterina, 4-raved and 6-rayed specimens, 440 Asteroidea, arms, 439-441 Ateles, teeth, 205, 206, 207 Atriopore, extra, in Ascidians, 456 Attelabus, division of pronotum, 455 Aulastoma gulo, asymmetrical variation in generative organs, 167 Aurelia aurita, Meristic Variation of, 426 ; statistics as to, 428 Auricles, cervical, in Man, 177; in Pig, 179; in Sheep and Goats, 180; are repetitions of ears, 180 Baer, von, Law of, 8; its proper scope, 9; probably not applicable to cases of Discontinuous Meristic Variation, 571 Balance between mamma?, 189 ; between teeth, 213 Balanocrinus, 4-rayed specimens, 436 Balanoglossus, two methods of develop- ment, 9 ; number of gill-slits, 174 ; extra proboscis-pore, 466 ; supposed relation to Chordata, 86 Batrachia, extra limbs, 554; spinal nerves, 141; vertebra?, 124; extra B. atrial opening, 465; axial duplicitv, 561 Bdell08tQma t individual and specific variations in number of gill-sacs, 173, 174 cirrhatum, heptatrema, heterotrema, hexatrema, 173; btichoffi,polytrema, 174 Beech, fern -leaved, 25 Bees, hermaphrodite, 68 ; union of eyes, 461 ; antenna modified as foot, 147 Beetles, variation of horns, 38; an- tenna?, 411, 413; extra ap- pendages in Secondary Sym- metry, 475; legs, 483; an- tenna?, 513; palpi. 524; di- vision of pronotum. 455 supposed double leg.-,, 544 ; sup- posed double antennas, 51s ; supposed double palpi, 551 Benibidium striatum, extra palpi, 524 Bettontjia, variation in molars, 258; cuniculus, lesueri, penicillata, 258 Bilateral asymmetry, Homceosis in cases of, 465 Bilateral Series, nature of. 88; Bieristic Variation of, 448 Bilateral Symmetry. 19 ; in variation of vertebra?, 128; in variation of Annelids, 167 ; in varia- tion of mamma, 183; in variation of teeth, 267; in cervical fistula. 175; in variation of ocelli, 292; in variation of digits, 402; in variation in antennae <>f /•'<•"> 1 Blatta, variation in number ><( tarsal joints, discussion of, 63; facts, 1 1 5 : regeneration of tarsus with 4 joint-. 116 Blue, as variation of i. .1. 1 1 Boar, Wild, extra digits, 38 Bombinator, vertebra . 127 37 578 INDEX OF SUBJECTS. Bomlms variabilis, antenna developed as foot, 147 Borribyx, extra wing, quercus, 284, rubi, 282 Box-turtle, digital variation, 396 Brachial plexus, birds, 129; Man, 113, 135 ; Bradypodidae, 141 Brachinus crepitans, double (?) leg, 546 Brachiopod, double monster, 566 Bradypodidae, vertebrae, 118; brachial plexus, 141 Brachy teles, teeth, 205 Branchiae, variations in number, 172 Branchiomma, double tail, 564 Branchipus, segmentation of abdomen, 97; relation to Artemia, 96 — 101 ; species dis- tinguished by sexual characters of male, 100 ferox, xpinosus, 97, 100; stagnalis, 100 Brill, pigmentation of blind side, 468, 470 Brimstone butterfly, variation in colour, 45 ; nature of pigment, 48 Broseus vulgaris, double (?) leg, 547 Buccinum, teeth, 262 ; double operculum, 457 Bucorvus, brachial plexus, 131, 132 Bulldog, teeth, 210, 221 Bulldog-headed races of Dogs, 57: of Fishes, 57 Buteo latissimus, extra digit, 393 ; vul- garis brachial plexus, 131 Buzzard, extra digit, 392, 393 Calathus fuscus, extra eye, 280; extra legs, cisteloides, 506, fulvipes, 507, grceeus, 505 Callidium variabile, double (?) antenna, 551; ciolaceum, extra antenna arising from head, 551 Call into rpha, colour-variation of species of this genus, 46 Callinectes hastatus, extra spines on lateral horn of carapace, 557 Callithrix, teeth, 208 Callorhinus ursinus, teeth, 343 Caloptenus «]>retus, colour-variation, 44 Calopteron reticulatum, extra antennae, 522 Calopus cisteloides, extra legs, 512 Calosoma investigator, extra antennae, 523; auropunctatum, double (?) leg, 548; double (?) antenna, sycophanta, triste, 550 Cancer pagurus, maxillipede developed as chela, 149, 150 ; extra parts of limbs, 527 ; variations in chelae, 530 — 536 Canidje, digits, 401; mammae, 189 teeth, 209—222; incisors, 210; canines, 210; premolars, 211; molars, 217 CaxidjE, teeth, Canis antarcticus, 215; azarce, 217; cancrivorus, 218; corsac, 214; dingo, 212, 215; javan- icns, 209; lacjopus, 220; later- alis, 212; lupus, 212,213,217, 220; magellanicus, 218; me- somelas, 212, 217 ; occidentalis, 214,219 ipennsylvanicus, 210 ; prinuevus, 209; procyonoides, 215,220; vetulus, 217 ; viver- rinus, 212; vulpes, 210, 212, 213, 214, 219, 220 ; zerda, 220 vertebras, 122; cervical rib, 122 Canines, supernumerary, Tiger, 225 ; Ass, 245; divided in Dor. 211 Capreolus, horns, 286; union of horns, 460; polydactylism, 371, 379 Caprimulgus, brachial plexus, 131 Carabus, antenna, supposed cases of double, auratus, cancellatus, catenulatus, emarginatus, ex- aratus, intricatus, italicus, sylvestris, 550 antennae, paired extra, arv en- sis, 523; auronitens, 522; monilis, 522; sacheri, 523 leg, supposed cases of double, creutzeri, 547; helluo, 547; intricatus, 545; melanckoli- cus, 548; nemoralis, 547; septemcarinatus, 547 legs, extra in Secondaiy Sym- metry, auratus, 511; auro- nitens, 511 ; cancellatus, 511; catenulatus, 512; grcecus, 486; granulatus,48£; irregu- laris, 497; italicus, 512; marginalis, 484; perforatus, 484; sche idler i, 4 V 3 palpi, supposed cases of double, auratus, purpurascens, splen- dens, 552 pronotum, division of, lothar- ingus, 456; scheidleri, 455 Carcinomata, multipolar cells in, 431 Garcinus nucnas, external segmentation of abdomen changed by parasites, 95 ; extra parts in limbs, 527, 531, 534 Carnivora, teeth, 209; vertebrae, 122 Carp, bulldog-headed, 57 Cassowary, feathers partially without barbules, 55 Castration, parasitic, of crabs, 95 Cat, variation in colours of, 48 digits, 312, 313; porydact3*lism in- herited, 323 spinal nerves, 138 teeth, 222 vertebrae, 122 Caterpillars, segmental Repetition of pattern in, 25 Catocala nupta, colour-variation in hind wings, 44, 46 INDEX OF SUBJECTS. 579 Caudal fin, division of, in Gold-fishes, 451 Cebida), teeth, 205 Cebus, teeth, 205 Cell-division, variations in, 430 Centrosomes, variations in number of, 480 Cephalotia, 458 Cerambyx, extra legs, 491; double (?) antenna, cerdo, scopolii, 551; extra antenna arising from head, cerdo, 551 Cercocebus, teeth, 204 Cercopithecus, teeth, 204; abnormality in, 204 Ceroglossus valdivice, extra legs, 500 Cervical vertebrae, assumption of dorsal characters, Man, 107 Cervus axis, molar, 246 rufus, premolar, 246 darna, extra digits, 379 Cestoda, variation in segmentation of, 168; bifurcation and other conditions allied to duplicity, 565 Cestracion, teeth, 261 Cetonia, extra legs, opaca, 488, morio, 512 Chalcides, digital variation in the genus, 395 Chamois, extra horns, 286 Charadrius, brachial plexus, 130, 132 Chela?, extra parts in Secondary Sym- metry, 528 ; amorphous cases, 538; duplicity of, 540 developed from third maxillipede in Cancer, 149 Chelonia, axial duplicity, 563 Gheraps preissii, apparent presence of female openings in males, 155 Chiasognathus grantil, double (?) anten- na, 551 •Chilognatha and Chilopoda, variation in segmentation of, 93 Chirocephalus, sujaernumerary horn to generative sac, 457 Chimpanzee, vertebrae, 116 spinal nerves, 139 teeth, 202 'Chionobas, eye-spots, 295 Chironomw, double head, 565 Chiropotes, 208 Chitons, repetition of eyes in, 26; vari- ation in colours of scutes, 307 ChUenius nigricornis, extra legs, 512; double (?) leg, holosericus, 546, dijli- nis, 548, vestitus, 548 Cheerocampa, colours of larva 3 , 304 Cholapus, vertebrae, 118, 120; brachial plexus, 141 Cholornis, hallux absent, 397 Chordata, segmentation of, 86 Chroicocephalus, brachial plexus, 130 dhrysemys, axial duplicity, 563 Chrysomela, division of pronotum,/HCt7f(i, 455 Chry8omela, extra legs, banksii, 194; graminis, 198 double (?) leg, hcemoptera, 517 double (?) antenna, eacalia , 550 Chub, bulldog-headed, 58 Cicindela sylvatica, double (?) antenna, 550 Cidarite8, 4-rayed specimen, 411 Clmbex axillaris", antenna developed as foot, 146 Cimoliasaurus, imperfect division of ver- tebra?, 103 Ciona intestinal is, variation in number of stigmata, 172 Cistudo, digital variation in, 396 Cladocera of salt lakes, 101 Clausilia bidens, extra eye, 280 Clavatella, variation in number of s< g ments, 425 ; in number of eyes in each segment, 425 Clupea pilchardus, scales, 274 Glythra quadripunctata, extra legs. 5os Clytus liciatus, extra legs, 508; extra antenna?, arcuatus, 522, tricolor, 522; double (?) antenna, arcuatus, 551 Coccinclla decempunctata, bipunctata and septeiupunctata, colour-variation, 49, 572 Cochin fowls, "silky" variety, 55 Cockroach, variation in number of tarsal joints, 63, 415 Coelenterata, imperfect division, 566 Colias, colour-variation, 44 ; interme- diates between ediua and helice, 14; varieties of hyale, 45 Colobns, teeth, 204 Colour and Colour-patterns, variations in, 42, 288, 572 Colour-variation, discontinuity of, per- haps chemical, 72; simultaneous, in segments, <\c, 303 Coluber, double monster, 561 Columba, brachial plexus, 131, 134 Colymbetes sturmii, extra legs, 512; ad- spersus, double (?) leg, 548; coriaceut, double (?) antenna, 550 Col y tubus, brachial plexus, 130 Conepatus chilensti and mapurito, teeth, 232 Continuity, use of term as applied to Variation. 15; of differences in En- vironment, 5 Copepoda, Of salt lakes, 101 Cordylophora lactutris, porystomatous specimens, 566 Correlation, between variations of nerves and vertebra, 145; between Keristic and Substantive Variation, L96 CorvtU, brachial plexus, 131 Corymbitet cupretu, colour-variation. 18 Counterparts, simultaneous variation of, 500 M7— 2 580 INDEX OF SUBJECTS. Cow, variation in number of teats, 188 Crab, extra parts of appendages, 527 — 536 ; variation in segmentation of ab- domen, 95 Crateronyx, extra wing, 285 Crayfish, variation in number of gene- rative openings, 152 ; repetition of parts of chelae, 529, 532, 537; extra parts in antennas, 538 Cribrella, abnormal branching of an arm, 440 Crinoids, radial joints, 421; variation in number of rays, 435 ; 4-rayed varieties, 436 ; 6-rayed varieties, 437 ; 3-rayed and 5-rayed varieties of a 4-rayed form, 437; variation in number of canals in stems, 438; abnormal branching, 438 Crista, division of embryos, 556 Crossarchus, teeth, 227—231 ; zebra, 230, 231 Crustacea, theory of descent of Yerte- brata from, 29 ; of salt lakes, 100 ; Secondary Symmetry in, 525; Homce- osis in, 149 Cryptohypnus riparivx, extra legs, 509 Cryptophagus scanicus, dentatus, double (?) antenna, 550 Ctenodrilus, double tail, 565 Cucumaria planei, with six radii, 433; double monster, 566 aciculi, double monster, 566 Cnon, one lower molar absent, 209 Cupressocrinus, imperfect variation to 4-rayed state, 437 ; variation in num- ber of canals in stalk, 438 Curve of Frequency of Variations, 37, 64 Cuvierian organs, variation in number of, 435 Cj'clopia, 458 Cygnus olor, cervical vertebras, 33 ; colour- variation of young, 44 ; atratus, brachial plexus, 130 Cyllo leda, variability of ocelli, 289 Cyncelurus, teeth, 222, 224 Cynocephalus jyorcarius, extra molar, 204 Cyprinus carpio, bulldog-headed varie- ties^?; hungaricus, ditto, 58; auratus, division of fins, 451 Cyprus, 4-horned sheep, 285 Cypselus, brachial plexus, 131 Cystophora cristata, premolars, 238; molars, 243 Dachshund, hallux in, 401 ; duplicity of hallux and pollex, 401 Dactylopodites. extra, 528 Dactylopsila, premolars, 255 Darwin's solution of problem of Species, 5; views on Reversion, 77; on sudden Variation in eye-spots, 289 Dasyuridas, incisors, 247 Daayurua, incisors, 247 ; premolars, 255 ; molars, 256 Dasyurus, viverrinus, variation in molars,. 256 maculatus, molars, 256 Deilephila euphorbia*, colours of larvae, 305; hippophaes, 305 Dendarus hybridus, extra antennas, 523 Descent, Doctrine of, assumed to be true, 4 Diaptomus, colour-variation of eggs, 44 Dicotyles torqaatus, incisors, 245 Didolphyidae, incisors, 246 Didelphys, teeth, 246, 258 Digits, Variation of Mammals. Capreolus, 374 ; Cat, 313; Cervus, 379; Dogs, 401; Erinaceus, 397; Elephas, 397; Goat, 377; Herpestidas, 346; Horse, 360; Hylobates, 346; Macacus, 340; Man, 324; Mule, 360, 370; Ox, 374, 383; Pig, 381, 387; Sheep, 373, 380 Birds. Anas, 392; Aquila, 393; Archibuteo, 392; Buteo, 393; Fowl,390;La/'us,393; Pheasant, 393; Rissa, 396; Turkey, 393 Reptiles. Chalcides, 395 ; Cis- tudo, 396 Reduction in number, Man, 355, 358 ; Artiodactyla, 383 Union of, Ox, 383; Pig, 387 ; Man, 355 Variation in, associated with other variations, 399 Inheritance of Variation in, 398 Recapitulation of evidence, 400 Dimorphic condition, its relation to the monomorphic condition, 37 Dimorphism in Spinal nerves, 138; in position of generative openings in Pachydrilus, 165, 168 ; in secondary sexual characters, 38 Diopatra, abnormal repetition, 159 Discoidea (Echinid), 4-rayed specimen, 442 Discontinuity of Species, 5 in Variation, a possibility, 17 ; suggestion as to its nature, 68, 568 in chemical processes, ] 6, 48, 72 in colour-variation, 43, 48, 72; in colour-patterns, 48 in states of matter, 16 of Meristic Variation per- haps mechanical, 70 of Substantive Variation perhaps in part chemi- cal, 71 in the Variation of spinal nerves, 145 in the Variation of the generative organs of Annelids, 168 INDEX OF SUBJECTS. 581 Discontinuity in the Variation of digits, •407 in Meristic Variation of Radial Series, 423 partly dependent upon Symmetry, 568 Discontinuous Variation, use of the term, 15 Disease, analogy with Variation, 74 Ditomus tricuspidatux, double (?) an- tenna, 550 Division of organs, a process of repro- duction, 193 of teeth, 268; of mamma?, 193; of digits, 349, 369; of ten- tacles, 280 ; of radius of Echinid, 446; median, 454 Dog, cervical rib, 122; hairless, 57; bull- dog, 210, 221; digits, 401; nipples, 189 teeth, 209—222; incisors, 210; canines, 211 ; premolars, 213, 215; molars, 220; deficiencies in Esquimaux, 215; in Inca, 216 Dog-whelk, colour-variation, 48 Domestication, variability falsely ascrib- ed to, 266, 401 Dunacia bidens, Variation in antennre, 413 Dorcadion rufipes, extra legs, 512 Dorking Fowl, digital variations, 390 — 395 Dorocidaris papillata, variation in pedi- cellaria?, 429 Double-foot, Artiodactyles, 378; Frog, 540; Macacus, 340; Man, 337, 338 Double-hand, 325, 331 Double Monsters, 559 Double-thumb, 349 Dromceolus barnabita, extra antennae, 523 Duck, no variation in number of digits recorded, 401 ; cases of absence of webs between toes, 401 Duplicity of single members of series not distinct from other modes of addition, 193, 407 of appendages, 406 ; in Arthro- poda, 539; in Vertebrata, 539 axial, 559 Dutch pug, 57 DyscJiirim globuloxus, extra legs, 512 Dytiscus marginalis, extra legs, 512 Eagle, extra digits, 393 Ears, repetitions of, known as cervical auricles, 180 Earthworms, variation of generative organs, 159 ; of segmentation, 157 ; asymmetrical arrangement of genera- tive organs, 160, 161 ; table of arrange- ment of ovaries, 162; duplicity of head, 565, of tail, 565 Earwig, variation of forceps, 40 ; of antennary joints, 413 Echinocomu, 4-rayed specimen, 441 ; alleged case of 3 rays, 411 Echinodermata, Meristic Variation in, 432; variations of pedicellaria-, 429; duplicity, Echinoidea, Meristic Variation of, 411 ; 4-rayed specimens, 441; partial dis- appearance of a ray, 413; partial duplicity of a ray, 446; 6-rayed speci- men, 445; pedicellariae, 429; variation in number of genital pores, 446 ; sym- metrical reduction of two rays, 4 13 Echinus melo, partial reduction of an ambulacrum, 443 EcJtinus sphcera, partial reduction of an interambulacrum, 445 Ectrodactylism, Man, 355, 358 Elater murinus, extra antennas, 522 ; variabilis^ extra leg, 547 ; hirtus, double (?) antenna, 551 Elcdone, supernumerary hectocotylus. 473 Eleodex pilosa, double (?) antenna, 551 Elephas, tusks, 244; hoofs, 397 Elytra, said to have been replaced by legs in Prionus, 148 Embryology, as a method of investigating problems of Descent, 7 Emperor moth, ocelli absent, 289, 301; colour- variations of larva, 306 Emu fowls, 55 Enchytr&'idae, generative openings, 165 Encrinus, variation in number of radial joints, 421 ; 4-rayed calyces. 436 ; radius bearing only one arm, 438 Enema pan, extra legs, 512 Entoniscians, alter segmentation of some crabs but not of all, !'"> Enhydris, incisors, 211 Epiglottis, division of, 451 Epipodites, variation of in Hippolyte, 151 Epistome (of Beetle), division of, 1">1 Erebia bland inn, ocelli, 289 Erinaceus, variation in hallux, 3'.i7 Eriphia spinifrom, extra chela . 528 Eros minutus, extra Legs, 487 Enox Indus, bulldog-headed, 58 Esquimaux Dog, absi ace of first pre- molars, 214, 215, •-'•-'}_ Euchloe, pigments of, 72 Eugeniacrinus, 4-rayed specimens, i Euprepia puipurea, extra palpi (alleged), 524 Eurycephahu maxillosus^ extra legs, 1^7 Euscnrpius, double tail, 565 Eve of Palinurtu developed as antenna, 160 Eye-colour of Man. 43 Eye-spots, 288; Variation as a whole. 291; outer /.one- first to appear, 291; analogy with chemical phenomena. 582 INDEX OF SUBJECTS. 292; in Linear Series, 288, 293; simultaneous Variation of, 293 ; corre- lated with variation of neuration, 293, 301 Arge, 295; Chionobas, 295; Hip- parchia, 294; Satyrus, 295; Morpho, 296 ; Vanessa, 299 ; Junonia, 299, 300; Pararge, 300; Saturnia, 301, 302; Raiidae, 302; Polyplectron, 450 Eyes of Clavatella, variation in number, 425 Eyes of Molluscs, 279; of Insects, 280; union of, 458, 461 Feathers, of "hairy" Moorhen, without barbules, 55 Felid.e, digits, 313 teeth, 223—226 Felis brachyurus, 224; cali- gata, 223 ; caracal, 224 catus, 224; chaus, 224; chi nensis, 224 ; concolor, 223 domestica, 223, 224, 225, 226 eyra, 223; fontanieri, 225 226 ; inconspicua, 223 ; ja guarondi, 224 ; javanensis 224; jubata, 224; leo, 226 /;//(.r, 226; manicirfata, 223 manul, 224; minuta, 223 nebulosa, 224; cwca, 224 pajeros, 224; pardalis, 226 pardus, 223, 226; tetraodon 223; tigrina, 22G; tigris, 224, 225 vertebrae, 122 Feronia muhlfeldii, extra legs, 485 Fins, division of, in Gold-fish, 451 Fishes, undifferentiated teeth in certain, 32 ; bulldog-headed, 57 division of caudal fins, 451 ; scales, 274 ; flat-fishes, 466 Fistulae, cervical, 174; morphology of, 176 ; aural, 177 in Man, 175; in Pig, 179; in Horse, 180; unknown in Sheep, Goats and Oxen, 180 Flat-fishes, reversed varieties, 54, 466 ; "double" varieties, 466 Fcenius tarsatorius, extra legs, 491 Foot, double, Artiodactyla, 378 ; Frog, 540; Macacus, 340; Man, 337, 338 Foraminifera, duplicity, 566 Forfieula auricularia, variation of for- ceps, 40; of antennary joints, 413 Fowls, silky variety of, 55 digital variation in, 390; ovary and oviduct, 465 Frog, vertebrae, 124; extra legs, 554; double foot, 540 ; Secondary Sym- metry, 554 Fusus antiquus, sinistral, 54 Galerita africana, extra legs, 495 Galerites albogalerus, 6-raved specimen, 445 subrotiuidus, 4-rayed specimen, 441 Galictis, teeth, barbara, vittata, 232 vertebrae, 123 GaUinula chloropus, hairy variety, 55 ; extra digits, 392 Gallus, brachial plexus, 130; digits, 390; oviduct, 465 Garganey Teal, division of digits, 392 Garrulus, brachial plexus and ribs, 135 Gasteroxteu*, scales, 276 Gavialis, change in number of vertebrae, 123 Gecinus, brachial plexus, 131 Generative openings, repetition of, in Astacus, 152; absence of, in Astacus, 152, 154; of Earthworms, 159; of Hirudo, 166 Generative organs of Earthworms, varia- tions in, 159; of Leeches, 165 Genital pores, variation in number in Echini, 446 Geophilus, variation in number of seg- ments, 94 Geotrupes mutator, extra legs, 500 : typhcvus, extra antennae, 515 Gill-slits, of Ascidians, 171; of Hyxine, 172; of Bdellostoma, 173; of Ammo- coctes, 174 ; of Notidanidae, 174 ; of Balanoglossus and Amphioxus, 174 Glaucium luteum, colour-variation, 47 Gmelin's test for bile-salts, 292 Goat, incisor, 245 ; horns, 286 ; digits, 377 ; cervical auricles, 180 Gold-fish, simultaneous variation in length of tail and fins, 309; division of anal and caudal fins, 451; "Tele- scope," 453 Gonepteryx rJiamni, similarity of fore and hind wings, 25 colour - variation, 45 ; nature of the yellow pig- ment, 48 extra wing, 283 Goose, brachial plexus, 133; pygomelian. 401 Gorilla, vertebrae, 117; spinal nerves, 139; teeth, 202 Goura, brachial plexus, 130 Grits, brachial plexus, 130 Guinea-hen, double-hallux, 392 Guinea-pig, inversion of layers in, 9 Gido, teeth, 231 Haemal spines, division of, in Gold- fishes, 453 Hair, absence of, in Mouse, Horse, Shrew, 56 ; silky in Mouse, 55 ; excessive length in mane and tail of a horse, 309 INDEX OF SUBJECTS. 583 "Hairy" Moorhen, 55 Halichoerus, vertebras, 123; molars, 242, 243 Haliotis, extra row of perforations, 287; perforations occluded, 287; perfora- tions confluent, 287 Halla, imperfect segmentation in, 156 Hallux, duplicity in Man, 349; Fowl, 390; variations in Kittiwake (Rissa), 396; Erinaceus, 397; Herpestidae, 397, normally absent in certain birds, 396 Hammaticherus hews, double (?) an- tenna, 551 Hand, digital variations in, 324; double, 325, 331 progressive series of Conditions, 324 Hapalida?, teeth, 208 Harpalus, rubripes, extra legs, 493; cal- ceatus, double (?) antenna, 550 Hawthorn, variation of, 569 Hectocotylus, supernumerary, in Ele- done, 473 Helictis orientalis, teeth, 233, 234 Helix kermovani, extra e3'e, 280 hispida, union of tentacles, 461 Heloderma, vertebrae, 123 Ilelops ceeruleus, extra antennae, 523 sulcipennis, extra palpi, 524 Hemiaster ; cases in which one ambula- crum wanting, 445 ; two ambulacra reduced, 443 ; duplicity of ambulacra, 446 Hepialus humuli, males like females in Shetland, 254 Heptanchus, seven gills, 174 Heredity, objection to use of term, 75 ; in digital variation, 398 Hermaphroditism, 67 ; in bees, 68 Hermodice carunculata , abnormal seg- mentation, 158 Herpestid.e, hallux, 397 teeth, 227-231 Herpestes galera, 229; gracilis, 227, 228, 229; griseus, 229; ichneu- mon, 229, 230, 231 ; microcephalus, 229; nipalcnsis, 227; nyula, 228; persicus, 227; pulverulentus, 228, 229; smithii, 228, 229 Herring, supposed hybrid with Pilchard, 275 Heterocephalus, a naked Eodent, 56 Heterogeneity, universal presence of in living things, 18 symmetrically distributed around centres or axes, 19 Heterorhina nigritarsis, division of pro- notum, 455 Hexanchus, six gills, 174 Hipparchia tithonus, eye-spots, 293, 294 Hippocampus compared with Pliyllo- pteryx, 309 Hippoglossus pinguis, 471 Hippolyte fabricii, variation in epipo- dites of legs, 151 Hirudinea, variation in generative organs, 165 in colours, 304 Hirudo medicinalis, variation in numbei of testes, 165, L66 officinalis, supernumerary penis, 166 HUter cadari rinus, extra legs, 512 Holopus rangi, 4-rayed specimen, 436 Holothurioidea, variation in number of radii, 433; variations in numbers of organs, 435; double monsters, 5C6 Homarus, repetition of parts in cheliped, 530; in chela , 531-538 ; colour varia- tion, 44; hermaphrodite, 155 "Homodynamy," 133 Hornceosis, use of the term, 85 between vertebra;, 106-127 : backward and forward, use of terms, 111; forward in vertebra?, 112; backward in vertebra, 111 ; in spinal nerves, 144 ; of appendages in Arthropoda, 146; in Beg- ments of Annelids with re- spect to genital organs, 162, 163, 167, eve; in teeth, 272; in bilateral asymmetry, 465; in parts of flowers, 111 Homology between members of Series of Repetitions, 30 individual, not attributed if series is undifferentiated, 32; attempt to trace in mammas, 191 ; discuss* J in the case of teeth, 269; in the case of digits, 351, 391, 371, 377; in the case of joints of tarsus of Blatta , 418 ; in the case of radii of Holothurioidea, 433 Horns, Sheep, 285 ; Goat, 286; Boebuok, 286, 460 ; Chamois, 286 ; of EU A ■ buck united in middle line, 4»ii» Horse, similarity of fore and hind L< 25, 26 naked variety, 56 ; teeth, 244, 2 !•"> cervical fistula?, 180 simultaneous variation of mane and tail, 309 extra digits, 360; by development of digit ii. ;stil 367 by development ofdigit iv,367 by development of digits n and iv, 368 by division of digit in, 369 by intermediate process, 371 584 INDEX OF SUBJECTS. Hyas, double chela, 540; double index, 541 Hybrids, supposed, between Herring and Pilchard, 274 ; supposed, between Tur- bot and Brill, 468 ; supposed, in genus Terias, 52, 53 Hydrobius fuscijjes, pronotum having three lobes, 454 Ilylobates, vertebrae, 118; teeth, 204; leuciscus, extra digit, 346 Hylotrupes bajulus, extra legs, 494 Hypsiprymnus, teeth, 258 Iceland, 4-horned sheep, 285 Ichneumon luctato^•ius, extra legs, 511 Ichueumonidae, extra legs, 491, 511 Icticyon venations, teeth, 220 Ictonyx, teeth, 233 Images, relation of, the basis of Symme- try, 19 between upper and lower jaws, 196, 267; between right and left sides, 88; in the case of the manus and pes, 404 division and union of parts re- lated as, 449 principles of, followed in the structure and position of parts in Minor Symmetry, 479 Inca Dogs, a bulldog found amongst, 57 ; variation of premolars and molars, 216, 222 Incisors, supernumerary, Gorilla, 203 ; Ateles, 207; Canidae, 210; Felidae,222; Herpestidas,227; Pecora, 245; Licotyles, 245; Horse, 244 division of, Canidse, 210; Ele- phas, 244 absence of, Canidse, 211 ; Feli- dae, 222; Herpestidae, 227; Phocida?, 235 ; Horse, 244 Index of crabs and lobsters, peculiarity in repetition of, 557 Individuality, attributed to members of Meristic Series, 31 ; such individuality not respected in Variation, 32; cases illustrating the absence of supposed individuality in Members of Meristic Series, 104, 115, 124, 191, 269, 407, 433; an unfortunate term, 556 Jacamaralcyon tridactyla, distinguished by absence of hallux, 396 Jackal, vertebrae, 122; teeth, 217 Japanese pug, probable independent origin of, 57 Jaws, relation of upper to lower, 196 Julodis cequinoctialis, extra legs, 503; clouei, double (?) antenna, 551 Julus tevrestris, mode of increase in number of segments, 93 Kallima inachys, colour- variation, 53 Karvokinesis, symmetry in, 20; varia- tions in, 430; bilaterally symmetrical variation of, in the segmentation of an egg, 464 Kidney, supernumerary, 277 ; horse- shoe, 278, 459 Kittiwake, variations in hallux, 396 Laciniation, simultaneous, of petals, 310 Lady-birds, colour-variation, 49 Lagorchestes, teeth, 258 Lagothrix, teeth, 208 Lamarck's solution of problem of Species, 4 Lamellibranchs, sinistral, 54 Lamia textor, double (?) antenna, 551 Larus leucopterus, digits, 393 Larvae of Lepidoptera, variations in colours of, 304 Leaf-butterfly, colour-variation, 53 Leeches, variation in generative organs of, 165 ; in colours, 304 Legs, extra, in Secondary Symmetry, general account, 475, cases in Insects, 483; in Position V, 483 ; in Position VAA, 485 ; in Position A, 487; in Position DA, 491; in Position D, 494; in Position DP, 496; Position P, 498 ; Position VP, 500. Uncon- formable cases, 503; miscel- laneous cases, 511 ; in Crus- tacea, 526 ; in vertebrates, 554 supposed double in Insects, 544 Leopard, two cases of dental variation in a Chinese, 225, 226 Lepidoptera, colour-variation of larvae, 304; ocellar markings, 288; nature of yellow pigments, 73 Leptura testacea, double (?) leg, 545 Leuciscus dobula, bulldog-headed variety, 58 Lichnanthe vulpina, extra antennae, 517 Ligula, absence of segmentation in, 168 Limax, union of tentacles, 460 Limenitis populi, extra wing, 283 Limulus, division of caudal spine, 450, 456 Linaria, many symmetrical variations of, 76 Linckia multijiora, fission, 433 Linear Series, Meristic Variation in, 63 ; simultaneity in colour-variations of, 303 Lissotriton, supposed double limb, 539 Lithobius, number of segments, 93 Lithodes arctica, extra legs, 527 Littorina rudis, colour- variation, 49 Littorina, sp. , extra eye, 280 Lixus angustatus, division of pronotum, 456 Lizards, digital variation in, 395, 396 Lobster, colour-variation, 44 ; herma- phrodite, 155; variations in chelae, 530—538 INDEX OF SUBJECTS. 585 Local Races, evidence as to, not a direct contribution to Study of Variation, 17 Locusts, variation in colour of tibia?, 44 Loligo, variations in segmentation of egg, 4(i3 Lucanus cervus, extra antennary branch, 2 cases, 549 ; extra branch on man- dible, 2 cases, 552 ; capreolus, ditto, 552 Luidia ciliaris, variation of pedicellariae, 429 Lumbo-sacral plexus, 138 Lumbriconercis, imperfect segmentation, 156 Lumbriculus, double tail, 565 Lumbricus, undifferentiated segments in, 82 ; imperfect segmenta- tion, 156 ; spiral segmen- tation, 157 ; repetition of ovaries, 160; asymmetrical arrangement of organs, 160, 161 ; variation of genital openings, 162 ; duplicity, 565 agricola, 162; herculeus, 160; pvrpurens, 160; terrestris, 156, 157 ; turgidus, 160 Lupa dicantha, extra index, 542 Lurcher, teeth, 221 Lutra, teeth, 228, 233, 234, 235 constancy of p l in L. vulgaris, 228 Lyccena icarus, extra wing, 284 Lycalopex group of Foxes, frecpuency of extra molars in, 217 Lychnis, repetition of fimbriation in petals, 26 Lycus, double (?) antenna, 551 Lynx, teeth, 224 Lysimaehia, Meristic variation in flower of, 61 Lysiphlebus, variation in number of an- tennary joints, 412 Macacus cynomologus, syndactylism, 356 inuus, spinal nerves, 137, 139 teeth, 204 radiatus, doubtful extra molars, 204 rhesus, extra molar, 204 Macroglossa, colours of larvae, 304, 305 Macrognathus nepalensis, double (?) an- tenna, 551 Macropodidae, teeth, 259 Macrorhinus leoninus, teeth, 243 Madreporites, repetition of, 440 Maia squinado, extra index, 542 Major Symmetry, 21, 87 Malachius marginellus, extra antenna, 522 Males, high and low, 39 Mallodon, double (?) leg, 547 Mammae, numerical Variation in, 181 ; along mammary lines, 181 ; in other positions, 186 ; in axilla, 185 ; below and inter- nal to normal mamma, 186; above and external, 185 Mammae, variation in Cow, 101 ; Dog. 189; Pig, 190; Man, 181; A]h -. L88 comment on facts, 191 development of, 191 Mammary extensions to axilla, 185 lines, 181 tumours. 185, 187 Man, cervical fistula;, 174; cervical auri- cles, 177 digits, increase in number, 324 : reduction in number, 355; poly- dactyliam in general, 344; double- hand, 331 ; symmetry of manna and pes, 403 kidneys, union of, 459; renal arte- ries, 277 ; ureter-. 27> mammae, 181 nerves, spinal, 135; brachial plexus. 135 ; notable variation in, 137, 113 ; lumbo-sacral plexus com- pared with that of Chimpanzee, etc., 138 teeth, 198 transposition of viscera, 559 uterus, double, Darwin's comment on, 77 vertebrae, Meristic and Homceotic variation in, 103, 106 — 116, 458 Mandibles, supposed duplicity of, in Lucanus, 552 Manns, variations in, compared with those of pes, 405 ; as a system of Minor Symmetry. 4(>:-i Marsupialia, teeth. 2 16 — 258 Mastiff, teeth, 210, 221 ; hallux per- mitted in, 401 Maternal impressions and extra Legs in a beetle, 512 Maxillipede developed as a chela, 149, 150 Median nerve, variations in composition of, 136 Medicago, repetition of brown Bpol in leaflets, 26 Medusas, Meristic Variation i>i\ [23 ; duplicity in, 666 Melanopliu packardit, colour-variation, 44 Meles, teeth, 2:52, 233, 236 Mellivora, teeth, 233, 235 Meloe coriaceus, double (?) I , 547 j pro8carabau8i extra 1. 188; viola- a us, extra antenna HJelolonthavulgarii, division ol pronotum i .". . . i ."> \ division of pygi- dium, : tra legs, 184, 512 extra antennas, 515, 520, 533, 550 586 INDEX OF SUBJECTS. Melolontha vulgaris, double (?) leg, 545 hippocastani, extra antennae, 510, 557 Mephitis, teeth, 232 Merism, 20; importance of, to Study of Variation, 23 indirect bearing of, on the magnitude of Variations, 25 Meristic Repetition, 20 ; kinship of parts so repeated, 26 ; similar Variation of parts in, 27, 310, 46-4; compared with asexual reproduction, 34 Meristic Variation, distinguished from Substantive Variation, 22 ; compared with Hoinceotic Variation, 84 Metacarpals, development of lateral, in Artiodactyla in correlation with syn- dactylism of metacarpals III and IV, 383 Metameric Segmentation, not distin- guishable from other forms of Repe- tition, 28 ; errors derived from such distinction, 30 Metasternal plates, division of, 456 Metazoa, comparison with Protozoa, 35 Metritis contractus, extra legs, 503 Middle Line, division by images in, 404, 450 ; union of images in, 383, 458 Minnow, bulldog-headed specimen, 58 Minor Symmetry, 21, 88 ; Meristic Varia- tion in, 311, 410 ; in manus and pes, 403 Molars, supernumerary, Simla, 200 ; Troglodytes, 202; Gorilla, 203; Cynocephalus, 204; Ma- cacus, 204 ; Cebus, 205 ; Ateles, 205 ; Mycetes, 207 ; Canidae, 217, 220 ; Felidae, 226 ; Her- pestidae, 230; Mustelidae, 234; Phocidse, 242; Ungulata, 245, 246; Dasyurus, 256; Bet- tongia, 258 special frequency in Anthro- poid Apes, 200; in Lycalopex group of Foxes, 217 absent, Sirnia, 200; Ateles, 207 ; Pithecia, 208; Canidae, 219, 221; Felidae, 226; Herpes- tidae, 231; Mustelidae, 235; Phocidse, 243; Bettongia, 258 division of, Canis cancrivorns, 219 ; Crossarchus, 230 Variation in form, Crossarchus, 231 ; Dasyurus, 256 in Icticyon and Otocyon, 220 Monkevs, Old World, teeth, 204; New World, 205 Monodon, development of right tusk, 465 Monomorphism, 33 Monotonia quadricollis, double (?) an- tenna, 550 Moorhen, hairy varietv, 55; extra digits, 392 Morpho, eye-spots, 296—299 achillcs, 297; menelaus, 298; montezuma, 297; psyche, 299 ; sulkoicskii, 299 Mouse, colour-variation, 44 ; with silky hair, 55 ; black variety, 55 ; naked, 56 Mugil capito, bulldog-headed, 58 Mule, rarity of digital variation in, 360 ; case of, 370 Mullet, bulldog-headed varietj-, 58 Multipolar cells, 430 Mustelidae, teeth, 231, 235; premolars in M. foina, martes, melanojnis, zibellina, 231 Mycetes, teeth, 207, 208 Mycomelic acid, relation to yellow colouring matters, 73 Mydaus, teeth, 232 Myriapoda, variation in number of seg- ments, 91, 93 Myrmecobius, incisors, 247, 248 Myxine, variations in number of gill- sacs, 172 Ncenia typica, extra wing, 284 Narcissus, Substantive and Meristic Variation in, 23 ; colour- variation, 40 Narwhal, development of tusks, 465 Nasalis, teeth, 204 Natural Selection, chief objection to theory of, 5 ; misrepresentations of the theory, 80 ; difficulty in connexion with regeneration, 420 Navosoma, extra antennae, 521 Nebria, double (?) antenna, 550; gyllen- halli, double (?) maxillary palp, 551 Nectarine, discontinuous variation in, 59 Nereis, double tail, 564 Nerves, spinal, Birds, 129 — 135; Man, 135; Apes, 138; Cat, 138; Dog, 140; Brady - podidae, 141; Pipa, 141 attempt to homologize, 32 variations, 129-145 correlation with verte- brae, 145 relation to limbs, 143 Neural canal, division of, 451 Neuration of wings varying with eye- spots, 293 Nigidius, extra branch on antenna, 549 Nipples, supernumerary, on normal breast, 184; on normal areola bifid, 184; on mammary lines, 186; in Pig, 190; in Dog, 189 Notidanidae, number of gills, 174 Nuclei, multipolar division, 430, 464; precocious division, 464 Nyctcreates procyonoides, teeth, 215 Nyctipithecus, teeth, 208 INDEX <)F sriUKcTs. .W Ocellar markings, 288, 449 Lepidoptera, 288 ; Raiida , 302 ; Birds, 449 Odontolabis stevensii, extra antennae, ">18, 557 Oligochseta, axial duplicity, 503 ; ge- nerative organs, 159; segmentation, 156 Ommatophoca rossii, premolars, 237 Onitis bison, division of pronotum, 455 Operculum, double in Buccinum, 457 Ophiacantha anomala, normally arms, not known to divide, 433 Opkiactis, fission, 433 Ophibolus, double monster, 561 Ophidia, vertebra, 103, 123 Ophidiaster cribrarius, fission, 433 (Jphiocoma pumila, young with 6 arms, adults witb 5 arms, 433 Ophiothela isidicola, fission, 433 Ophiuroidea, variation in number of arms, 447; fission, 433 Opisthocomus, brachial plexus, 130 Orang, vertebrae, 118; spinal nerves, 13'J ; teeth, 200 ; extra digit, 349 ; extra mamma, 188 Organic Stability, 36 OrtUosia Icevis, extra wing, 284 Oryctes nasicornis, division of pronotum, 455; extra legs, 512 Osmoderma eremita, double (?) leg, 547 Otaria cinerea, molars, 240 jubata, premolars, 240, 243 ursina, premolars, 239, 241 Otocyon, teeth, 220, 221 Ouaharia, teeth, 208 Ovaries, variations in number and posi- tion in Earthworms, 160, 162 not always correlated with variations in oviducts, 167 Ovary, right, developing in Fowl, 466 Oviduct, right, case of, in Fowl, 466 Oviducts of Astacu*, variation in number, 152; in Earthworms, 167 Ox, incisors, 245; molar, 246; poly- dactylism, 374-381 ; syndactylism, 384-387; syndactylism together with development of digits II or V, 385 ; with duplicity of II and V, 386; cer- vical auricles and fistula? unknown, 180 Pachydrilus sphagnetprum, dimorphic in respect of position of generative open- ings, 165, 168 Painted Lady butterflv, colour-variation, 49 Palaornis torquatus, colour-variation, li-i Palamnaus borneensis, division of poison- spine, 457 Palinurus penicillatus, eye developed as antenna, 150 vulgaris, extra legs, 527 ; extra antennae, 538 Palloptera ustulata, abnormal growth from thorax, 285 Palpi, paired extra, in Insects, 524 supposed doable, 551 Pangenesis, 75 " Panmixia," 573 Papaver nudicaule, colour-variation, 16; pigment of, 17, 72 Parakeet, colour- variation, 13 Pararge megara, eye-spots, 289, 800 " Parhomology," 133 Pariah dog. teeth, 221 Parnassius, ocelli. 292 Parra, feathers, 55 Pasimachus punctulatus, double (?) . 547 Patella, extra tentacle and eye, 279 Pattern, universal presence of, in organ- isms, 19-21; difficulties arising from, 21 Peach, discontinuous variation in. 59 Peacock, ocelli, 449 Peacock butterfly, repetition of i spots in, 26; variation of, 299 Pecora, polydactylism, 'M'> Pecten, double eye-, 280 Pedicellariae, Meristio Vaiiatiou of, 4 J '. * Pelamis bicolor, imperfect division of vertebrae, 105; axial duplicity, 561 Pelecanus, brachial plexus, I'M Pelobates fuscus, extra spiracle, 165 Penis, supernumerary, in Hirudo, 166; in Aulastoma, 167 Pentacrinus miilleri, increase in nun: of radial join 4-rayed >p< cim< dubius, dumorti- i r/, jurensis, tub- tulcatus, 436 6-rayed specimens, jurensis, I Penthina salicella, extra wing, 285 Peramelidee, digits of pes, 313 Perichata, variation in number of -i mathecse, 165 \forbesi, hilgendorfi, 165 PeHcrocotus Hammeus, oolour-vanati 16 Perionyx, generative organ watus, 163, 167, L68 griim waldi, 164 l\ ripatus, variation in nnmbei i ments, 84, 91, 94 l\ taurus, premolars, 26*5 Puai.ani.i Kin.v.. incisors, 248; premo Lars, 248 256 Phalanger maculatus, incisors, 248; | molars, 258; females Bpot- t. i in Waigiu, 2 orientalis, incisors, 248, 250; premolars, 250 ornatus, first pn molar two root* d as \;n tation, 25 i ursinus, first premolar nor- mallv two-root* d. 254 588 INDEX OF SUBJECTS. Phalanges, reduction in number, 355 Phascologale dorsal is, teeth, 257 Pheasant, digits, 393 Philonthus succicola, double (?) leg, 548 ventralis, extra legs, 507 Phoca barbata, incisors, 235, 236 cristata, premolars, 238 groenlandica, premolars, 238, 2-40, 242; molars, 243 vitulina, premolars, 238, 241, 242; molars, 242 PJuvnicopterus, brachial plexus, 130 Phoxinus Icevis, bulldog-headed, 58 Phratora vitellines, colour-variation, 43 Phreoryctes, generative organs, 162 Phyllopertha horticola, extra antenna?, 514 Phyllophorus, tentacles not in multiples of live, 435 Phyllopteryx, compared with Hippo- campus, 309 Physa acuta, tentacle bifid, 280 Picua uiridis, colour-variation, 43; me- dius, brachial plexus, 131 Pieridae, colours of, 73; eye-spots in, 292 Pig, digits, 381; syndactylism. 387; syndactylism with division of digit V, 389 ; cervical auricles, 179 ; cervical fistulas, 180 Pigeon, cervical vertebras, 33 ; brachial plexus, 134 Pigments, definite variations proper to certain, 43; nature of yellow, in Pie- ridae, 48. Pike, bulldog-headed, 58 Pilchard, variation in scales, 274 ; sup- posed hybrid with Herring, 275 Pilumnus, not altered by Entoniscians, 95 Pimelia inter stitialis, extra legs, 498 scabrosa, extra antennae, 523 Pinnipedia, Teeth, 235—243 Pipa, spinal nerves, 141 Pithecia, absent molar, 208 sa tanas, syndactylism in, 356 Pityophis, axial duplicity, 561 Plaice, symmetrical spotting of blind side, 467 Plant, compared to the body of Man, 29 Platycerus caraboides, extra legs, 507 Platyonychus, not altered by Entonis- cians, 95 Platysomatichthys, 471 Pleuronectes, pigmentation of blind side, 467, 471 Plume moths, repetition of pattern in wings, 26 Pluteus, double, 35 Podargus, brachial plexus, 131 Pcecilogale, 232 Pointer, teeth, 221 Polian vesicles, variation in number of, 434, 435 Pollex, duplicity in, Man, 349 ; Bogs, 401 Polyarthron, variation in number of an- tennary joints, 412 Polychaeta, axial duplicity in, 564 Polydactylism, Cat, 312; Man, 324; Macacus, 340; Hylobatcs, 346; Simia, 349; irregularcasesinMan,353 ; Horse, 360—371 ; Artiodactyla, 373 Polydesmus, mode of increase in number of segments, 93 Pohjodontophis, vertebrae, 123 Polyphylla decemlineata, extra antennae, 518 ' Polyplectron, eye-spots, 449, 450 Polyzoa, division of embryos, 556 Poppy, Iceland, colour- variation, 46; Horned, colour- variation, 47 Porania, 4-rayed specimen, 440; irregu- lar division of an arm, 440 Portunion, change in Carcinus produced by, 95 Portunus puber, extra parts on chela, 535; not altered by Entoniscians, 95 Potorous, teeth, 358 Premolars, nomenclature, 199 supernumerary, Brachy teles, 205; Ateles, 206; Mycetes, 208; Canidae, 212—214; Felidae, 225 ; Herpestidae, 229; Mustelidae, 231—234; Phocidae, 237—242; Cer- vus, 246; Phalangeridae, 248; Phascologale, 257 absence of, Canidae, 214 — 216 ; Felidae, 224 ; Herpes- tidae, 229; Mustelidae, 231 —234 ; Phocidae, 237—242 apparent division, Brachy- teles, 205; Canidae, 213; Dasyurus, 255; Phocidae, 237 displacement and other va- riations, Simia, 201 Pbionus, supposed development of elytra as legs, coriarius, 148 variation in number of anten- nary joints, imbricomis, 411, Jissicornis, 412 extra legs, coriarius, 488, 512, califomicus, 544, 557, cori- aceus, 548 double (?) antenna, 551 double (?) legs, califomicus, 544 Procercea, double tail, 564 Protozoa, sujjposed relation to Metazoa, 35 ; duplicity, 566 Pseudochirus, premolars, 250, 255; in- cisors, 248 Pterostichus, extra legs, lucublandus, 512; miihlfeldii, 485; prevostii, 512; dou- ble (?) antenna, planipennis, 550 Ptinus latro, extra legs, 512; extra an- tennae, 522 INDEX OF SUBJECTS. .>:> Pujinus, brachial plexus, 130 Pug, breeds of, 57; teeth, 221 Purpura lapillus, colour-variation, 48 Putorius, teeth, 231, 234 Pygara anastomosis, extra wing, 284 Pygidium, division of, in Melolontho, 456 Pygoinelian geese, 401 Pyrameis cardui, aberrations of, 49, 52 ; var. kershawi, 49, 52; var. <'l>/>ui, 50, -51 Pyrodes speeiosus, extra legs, 490 Python, imperfect division of vertebra?, 103, 105 Radial joints of Crinoids, 421 Radial Series, Meristic Variation in, 60 ; evidence, 422; in Echinodermata, 432 Radii, variations in number, Holo- thurioidea, 433 ; Crinoidea, 435 ; As- teroidea, 439; Echinoidea, 441; Ophi- uroidea, 433, 447 Radius, absence of, 360 Radula? of Buccinum, 262 Raiidre, eye-spots, 302: extra fin, 540; division of fin into lobes, 540; separa- tion of fin from head, 540 Rana, vertebrae, 124, 126; double foot, 540 ; spinal nerves, 142 ; extra limbs, 554 Ranzania bertolonii, extra legs, 510 Raspberry, yellow variet}', 47 Red, variations of, 44 — 48 ; as variation from blue, 44 Renal arteries, 277 Repetition of Parts, association of these phenomena, 21 Repetition, Linear, Bilateral or Radial, distinctions between, 88 Units of, 556 Reptilia, vertebra?, 103, 123 Reversion, hypothesis made in order to escape recognition of Discontinuity in Variation, 76 Rhagium mordax, double (?) leg, 548 Rhea, brachial plexus, 130 Rhinoptera, teeth, 259 — 261, javanica, 261, jussieui, 259 Rhizocrinus, 6-rayed specimen, 437 Rhizotrogus, extra legs, aestivalis, 510; castanius, 512 extra antennae, aquinoc- tialis, 517 division of metasternal plates, 456 Rhombus, pigmentation of blind side, 467—471 ; Usvis, 467, 468, 470; maximus, 467, 470 variations in scales, 468 RJupichites permanicus, double (?) an- tenna, 550 Rhyttirhinus, supposed case of extra eye, 281 Ribs, division of, in Man, 105 cervical, in Man, 108, 112, 115; in Dog, 122; Bradypodids, 119: on 6th vertebra in Man, 108 Ribs, variations in dorso-lumbar region, Man, 109—116; Anthropoid Ap< s, 116— lis; Bradypodide, Vi\ ; Felis, 122; Canis, 122; Galietis, 123; Halichams, 123; eleven in Siamese Twins. ."> t , « i Rissa, variations of hallux in the genus 396, 397 Roebuck, horns, 286 ; polydactylism, 374,379; union of horns, 160 Rubus idaus, colour-variation, 17 Rupicapra tnif>:i Salmacina, double tail. 564 Salt lakes, Crustacea of. 96, LOO Samia cecropia, extra wing, 28 Sand-canals, repetition of, in Aster 440 Saperda carcharias, extra antenna ariai from head, 551 SarcophiluS) teeth, 255 Sarsia, Meristic Variation in. 424; with six segments, 424 ; with five Begments, 425 Saturnia carpini, repetition ofeye-8] in wings, 26; extra wing. 282; varia- tion of eye-spots, 289, 301, 302; colours of Larva, 306 Satyrus hyperanthus, eye-spots, 294 Sawfiy, extra legs, 502, 546 Scales of Pilchard, 271; of GasUi 276; of Snakes, 276 Scarites pyraemon, extra legs, 500 « Scheme, shewing the relations ^i parts in Secondary Symmetry, 1M Scolopendra, numlx r of w jm< nts. 94 Scorpion, double poison-spine, r~ double tail, 565 Saraptia fusca, extra antenna?, 523 Is, variations in dentition. 235 Segmentation, metameric, not in 1. distinol from other foi i of Repetition, 28; two way- by which a full s. mentation mayhavi l>< . □ achieved in phyiogeny, of Axthropoda, variation in. 91 ; impi if. ct in An- nelids. L56 : spiral in Annelids, L57 : variation of in Cestoda, L68, 17" of mamma . I'M of ovum, variations in. , 590 IXDEX OF SUBJECTS. Selachians, teeth in, 259 Semnopithecus, teeth, 204 Sepidium tuberculatum, double (?) an- tenna, 551 Sex, analogy with Discontinuous Varia- tion, 66 Sexual characters, statistics as to, in Beetles, 38; Earwigs, 40 of Hepialus in Shetland, 254 of Phalanger in Waigiu, 254 Sheep, cervical auricles, 180; incisors, 245 ; change in form of canines, 245 ; molar, 246; extra horns, 285; poly- dactylism, 373, 380 Sheep-dog, teeth, 221 Shetland, variety of Hepialus in, 254 Shrew, naked variety, 56 Siamese Twins, 560 Siberia, Crustacea of salt lakes, 97, 100 Silis rvficollis, extra"legs, 498 Silky fowls, 56 Silpha nigrita, extra legs, 501 ; granu- lata, double (?) leg, 548 Silurus, extra fin, 540 Simia, vertebrae, 118; teeth, 200; extra digit, 349 ; extra mamma, 188 Simultaneity of Variation, possibilities of, 25, 26, 308 ; in fore and hind wings of Lepidoptera, 293; in counter- parts, 569; in colours of segments of Lepidopterous larvae, 303 ; in Chiton idffi, 307; in limbs, 402; in homo- logous twins, 559 ; in radial segments, 423; not clearly distinguishable from Symmetry, 569 Sinistral varieties, 54 Situs transversus, 465, 560 Sledge-dog, absence of first premolar, 215; division of premolar, 214 Smerinthus, colours of larvae, ocellatus, pojnili, tilice, 306, 307 Snakes, vertebrae, 103, 123; axial du- plicity, 561 Solea, pigmentation of blind side, 471 Solenophorus strepens, double (?) an- tenna, 551 Sore.r, naked variety, 56 Spaniel, teeth, 221 Species, the problem of, 2. Methods of attacking, 6 Discontinuity of, a fact, 2 Specific Differences, indefinite, 2 Spermathecae of Earthworms, variation in number, &c. of, 160, 165 Spharocrinus, imperfect variation to 6- rayed state, 437 Sphingida?, repetition of markings in larvae of, 26 ; variation in, 304 Sphinx Ugustri, division of proboscis, 456 Spinal nerves, 129; Birds, 130; Man, 135; Primates, 138; Bra- dypodidre, 141 ; Pipa, 141; Rana, 142 dimorphism in respect of, 138 ; distribution to limbs, 143 ; Homeeosis, 144; recapitulation, 144 Spinal nerves, principles of distribution, 143 Spiracle, extra in tadpole of Pelobate*, 465 Stability, Organic, 36 Starfishes, theory of origin of repetition in, 29; variations in number of rays, 439 ; multiplication by fission, 433 Stentor, duplicity, 566 Sticlioj)us, arrangement of tube-feet changes with age, 435 Stickleback, variation in number of bony plates, 276 Stomobrachium octocostatum, variety having tentacles in double series, 425 S trau galia, double (?) antenna, atra, 551, calcarata, 551 Strategns antceus, extra legs, 512 Struthio, brachial plexus, 130 Styela, variations in branchial sac, 172 Subemarg inula, extra eye, 279 Substantive Variation, distinguished from Meristic, 23; cor- related with Meristic in vertebra?, 125 in size, 38, 40; in colour, 43 — 48; in colour-pat- terns, 48 — 54 ; miscel- laneous, 54 — 60 Swan, cervical vertebrae, 33; colour- variation of young, 44 ; brachial plexus, 130 Symmelian "monster," 459 Symmetry, the conception of, 19, 569 a relation between optic- al images, 19 almost universal pre- sence of in living or- ganisms, 21 of mammae, 191 in dental Variation, 267 in digital Variation, Man, 324,402; Cat, 314; in manus and pes, 4U3 in nuclear division, 430; in variations in seg- mentation of ovum, 463 in variations of homo- logous twins, 559, 560 in double monstrosity, 559 Bilateral, characters of, 88; as appearing in variations of flat- fishes, 467 Major and Minor, 21, 86 Primary and Secondary, 90 Kadial, characters of, 89 INDEX OF SUBJECTS. 591 Symmetry, Secondary, preliminary ac- count, 475; principles, 479 Scheme of relations of parts in, 481; parts repeated in, geometri- cally peripheral to points of origin, 557; relation to Primary, 556, 557 in Insects, 475; Crus- tacea, 525 ; Verte- brates, 553 ; Batra- chia, 554; Triton, 555 Syndactylism, Man, 355, 356; Pithecia, 356; Macacus, 356; Ox, 384—387; Pig, 387—390 Tadpole, extra Bpiracle in, 465 Tcenia coznurus, transposition of genera- tive organs, 170 ; case of six suckers and segments pris- matic, 565 elliptica, asymmetrical arrange- ment of genital pores, 170 saginata, "intercalated seg- ments, 169; repetition of gene- rative organs in proglottides, 169 ; two genital pores at the same level, 170; consecutive genital pores on same side, 170; bifurcation of chain, 566 solium, changes in position and alternate arrangement of geni- tal pores, 170 tenuicollis, bifurcation of chain, 566 Tail-fin, division of, in Gold-fish, 451 Tail-spine, division of, Limulus, 456; Scorpion, 457 Tapeworms, variations, 168 — 170; du- plicity in, 565 Tarsus, in some beetles with only four joints appearing, 25 ; variation in number of joints, Blatta, 63, 415; various numbers of joints in families of Orthoptera, 415 Taurhina nireus, extra legs, 509 Taxidea, teeth, 233 Ta.vus baccata, colour-variation, 47 Teal, Garganey, division of digits, 392 Teeth, in undifferentiated series not credited with individuality, 32 numerical Variation, 195 ; di- vision of, 268 ; duplicate, 268 ; statistics of Variation, 200, 209, 222, 235 relation of upper to lower, 196 of Primates, 199—208; Canidae, 209—222; Felidae, 223—226; Viverridee, 227—231; Mus- telidae, 231—235 : Pinnipedia, 235—243 ; Ungulata, 243— 246; Marsupialia, 246—258; Selachians, 259—262; 7.v a a in, 262 Teeth, terminal, least size of, 270; pn - sence and absence of, 269; Homteotic Variation in, 272 Recapitulation, 265 Telephorus, colour-variation, lividus, 43 division of pronotum, nigri- cans, 455 double (?) antenna, lividus, rotundicollis, 551 double (?) leg, <.ff,ir,itii-. fuscus, 5 18 extra Legs, rusticus, 502 " Telescope " Gold-fish, 453 Tellina, sinistral variety. 54 Tenebrio granarius, double (?) leg, 548 Tentacles of Molluscs united, Helix hispida, 461 ; Limazagn -• tie, 460 repeated, Patella vulgata, 27$ bifid, Phy8a acuta, 280 of Holothurians, 4.;~< Tenthredo solitaria, extra legs, 502 ignobilis, extra leg, 546 Terias, colour-variation, 52, "»:5 ; am - mone, hecabe, mandarina, mariesii, 52 ; betheseba, constantia, jaegeri, 53 Terminal members of Series, variation of, 79, 269, 271. 272. 407 teeth, 269, 272; digits, 107 Terrier, absence of premolar, 21"< Testes, variation in number in Hirudo, 165, 166 Tetraceros, horns not as in 4-horned Sheep, 285 Tetracrintu, normally 4-rayed, 5-r;r and 3 -rayed varieties, 137 Tetrops prceusta, double (?) It-}.'. ">1"> Thoracopagous twins, transposition in. 560 Thumb, variation in number of phalan- ges, 324 double, 349 Thylacinus, teeth, 255 Thylacites pilosus, double (?) antenna, 550 Thyonidium, variation in number of 01 gans, 435 Tiaraps polydiademata, specific charad of, 426 Timarcha tenebricosa, extra anteni 522 Tomato, colour-variation. 47 Tonicia, variation in colour of BOUfc 308 Tongue, division ^i. L51 ToxotUS, extra « \. . 280 Transposition of viscera. 560 Triasters, symmetry of. ISO; found in bilaterally symmetrica] areas "t" a menting ovum, 164 Trichodet syriacus, double i?. 1 leg, 547 Trichosurus vulpecula, premolars, 254 592 INDEX OF SUBJECTS. TricenopJwrus, segmentation of, 168 Triopa clavigera, rhiuophore trifid, 280 Triton, legs repeated, 555 Troglodytes, vertebra?, 116; teeth, 202 Trupidonutus, vertebrae, 123 ; scales, 276 Trout, bulklog-headed, 58, 59; axial du- plicity, 563 Tulip, Meristic Variation in, 60 Turbot, pigmentation of lower side, 467, 470 Turdus, brachial plexus, 131 Turkey, digits, 31)3 Twins, homologous, 559 ; Simultaneous Variation of, as a case of Bi- lateral Symmetry, 559 Siamese, peculiarities of, 560 ; thoracopagous, 560 in Echinoderms and in Amphi- oxus, 35 Typosxjllis, double head, 564 Uca una, extra parts in chela, 530 Ulna, a second, 331 Ulnar nerve, variations in composition of, 136; a second, 333 Ungulata, teeth, 243 ; digits, 360—390, 397 Union, mediau, 458; of horns of Roe- buck, 460; of eyes of Bee, 461; of kidneys, 459; of tentacles of Umax, 460; of tentacles of Helix, 461; of posterior limbs of Vertebrates, 459 ; of digits in Ox, 383, 386; of digits in Pig, 387—390 Units, of Repetition, 556 I'metos, brachial plexus, 131 Ureters, supernumerary, 278 "Useless'' parts, supposed variability of, 78 Uterus, double, Darwin's comment on, 77; is a case of median division, 451 Utility, fallacies of reasoning from, 12 Uvula, division of, 451 Vanessa atalanta, colour-variation, 46 urticce, extra wing, 283 io, eye-spots, 299, 300 Variation, defined, 3 the Study of, as a method of attacking the problem of Species, 6 Continuous and Discontinu- ous, 15 Meristic and Substantive, distinguished, 23, 24 magnitude of integral steps affected by Merisrn, 25 about a Mean form, 37 perfection in, 60, 64 causes of, 78 Homoeotic, 85, in vertebras, 106; in Arthropoda, 146; in teeth, 272 Simultaneity of, in repeated parts, 303, 402, 425, 464 Variations, minimal, questionable uti- lity of, 16 Vertebras, Meristic Variation in, 102 imperfect division, 103, 458 Homceotic Variation, 106 reduction in numbers, Man, 111 numerical variation, 102 Man, 103, 106—116; Anthro- poid Apes, 116; Bradypodi- dae, 118; Carnivora, 122; Reptilia, 123 ; Batrachia, 124; features of Variation recapitulated, 127; correla- tion with spinal nerves, 113, 115. 139, 145 Vesper us luridus, extra eye, 280 Veronica buxbaumii, numerous symme- trical variations in, 76 ; illus- trating variations of Bila- teral Series, 448 Viverridae, teeth, 227 — 231 Waigiu, female Phalanger maculatus coloured like male in island of, 254 Wall butterfl}', variation in ocelli and neuration, 300 Water-pore, extra, in Bipinnaria, 466 Webs, between toes of Duck, absent, 401 Weevils, four visible joints in tarsus, 25 Wing, supposed to replace a leg in Zy- gcena, 148 Wings, supernumerary in Insects, 281 fore and hind, varying simul- taneously in Lepidoptera, 293 quills of, varying with quills of tail in Pigeons, 309 Woodpecker, Green, colour-variation, 43 Xantho punctulatus, duplicity of index, 542 Xiphopagous twins, transposition of viscera in, 560 Xylotrupes gideon, variation of horns in, 38 Yellow, variations of, 43-48, 73 Yew, yellow-berried, 47 Zalophus calif or nianus, molars, 243 lobatus, premolars, 238, 242; molars, 243 Zebra, repetition of stripes in, 26 Zeugopterus, white varieties, 467; varia- tion in dorsal fin, 471 Zonabris quadripunctata, double (?) an- tenna, 551 Zonites prausta, extra antenna?, 522 Zyyana filipenduUc, colour variation, 46 supernumerary wing, 148 minos, colours, 46; extra wing, 284 IXDKX OF PERSONS. Acton, 286 Adolphi, 124, 127, 142 Agassiz, A., 469 Agassiz, L., 396, 424 Ahlfeld, 840, 354, 451, 458 Albrecht, 105, 540 Aldrovandi, 344 Allen, J. A., 243 Alston, 286 Ammon, 348, 349 Anderson, 399 Andrews, 563, 564 Annandale, 327, 345, 346, 350-352, 355- 358 Appellor", 473 Arloing, 363, 370 Ascherson, 174 Ashmead, 413 Asmuss, 484, 500 Asper, 167 Assheton, 152 Audouin, 512 Auld, 390 Austin, 436 Auvard, 349 Auzoux, 203 Babington, 47 Bacon, 29, 146 Baird, 223, 232 Balbiani, 566 Balding, 305 Balk will, 566 Ballantyne, 334 Bancroft, 561 Barbour, 563 Bardeleben, 183 Barr, P., 46 Barrier, 384, 388 Bartels, 187 Barth, 187 Bartlett, 216 Bassi, 512, 548, 551 Baster, 453 Bateson, Miss A., 77, 468 Bather, 436 Baudi, 456, 512, 551 Baudon, 54 Baum, 401 Baumuller, 374 Baur, 103, 105, 123, 124 Beddard, 159, 162, 163, 165 B. Bedria^a, 127 Bell, P. J., 443, 564, 565 Bellamy, 113 Belt, 56, 57 Beneden, van, 531 Benham, 152, 15i>, 161, 565 Beranger, 347 Bergendal, 555 Bergh, 160 Bernhardus a Berniz. 5j - Betta, de, 43 Bibron, 563 Bicknell, 45 Billardon de Sauvigny, 454 Billott, 399 Birkett, 178 Birnbaum, 350 Blackinore, 523 Blainville, de, 118, 119, 205, 224 Blanchard, 187 Blanford, W. T., 398 Blasius, 354 Bles, 440 Bleuse, 482, 508 Boas. 369, 383, 385 Boettger, 5. 127 Boyd-Cainpbell, 399 Bramson, 52 Brandt, 466 Bredin, 31M Breese, 565 Brenner, 3ti0 Brindley, 38, 39, 63, 280, 416 Brisout de Barneville, 116 Brooks, 466 Broonir. 565 Bruce, 181, 185 Brulerie, de la, 280 Brum r, I * Brunette, 56 l Brunner von Wattenwyl, 11, 113, 116 Buchanan, Mi^s P., 156, 1 57 Buckler, 304, 305, 307 38 594 INDEX OF PERSONS. Buffon, 286, 398 Bull, 340 Biilow, von, 565 Buquet, 551 Bureau, 540 Burmeister, 123, 232 Busch, 198, 345 Butler, A. G., 52, 53 Cauierano, 127, 546, 555 Cameron. 1S5 Canestrini, 58 Cantoni, 537 Carlet 59 Carpenter, P. H., 421, 422, 436-438 Carre, 339 Cassebohm, 178 Cauroi, du, 344, 354 Cavanna, 539, 555 Cazeaux, 185 Champneys, 139, 185 Chapman, J., 244 Charcot, lsl Chavignerie, de la, 455, 547 Chworostansky, 165 Claparede, 425, 564 Clark, J. A., 51 Clark, J. W., 465 Clarke, E., 397 Claus, 80, 100 Cleland, 401 Coale, 393 Cobbold, 566 Cockerell, 44 Cocks, 55 Colin, 169 Collin, 563, 565 Cooke, A. H., 262, 263 Coquillet, 413 Cori, 156, 157, 158 Cornevin, 363 Cornish, 150 Cotteau, 446 Couch, 440, 470, 471 Coues, 232, 390 Cowper, 391, 393 Cramer, 346 Cuenot, 429, 433, 441 Cunningham, 320, 467 Curtis, 547 Cusset, 176 Daintree, 376 Dale, 482, 547 Dareste, 458 Darwin, C, 1, 5, 13, 56, 57, 59, 77, 121, 288, 449 DavidofT, 566 Dawson, 566 Day, 275, 276, 302, 467, 540 Delplanque, 354, 370, 377, 379 Demidoff, 468 Dendy, 438 Desmarest, 152 Devay, 399 Dimmock, 543 Dobson, 397 Dohrn, 86 Donceel, de, 51 Donitz, 212, 217, 220, 246, 445 Donovan, 302, 471 Dorner, 561 Doue, 456 Doumerc, 512, 550 Drechsel, 455 Drew, 381 Driesch, 35 Dubois, 330 Duhamel du Monceau, 470, 471 Dumeril, 554, 563 Dunn, 374 Duns, 528 Duponchel, 456 Dusseau, 352, 355 Duval, 184 Dwight, 325, 334 Ebrard, 166, 304 Eck, 437 Edward, T., 43, 174, 563 Ehrenberg, 425, 426, 428 Eichwald, 560 Ekstein, 339 Ek strom, 471 Elwes, 45 Engramelle, 46 Ercolani, 369, 377, 380, 381, 392, 393, 540, 554, 555 Eudes-Deslongchamps, 180 Fackenheim, 345, 351, 352, 399 Failla-Tedaldi, 295 Fairmaire, 454 Farge, 327, 399 Fauvel, 44, 494, 508, 523 Faxon, 152, 530, 532, 533, 536, 537, 541, 542, 557 Field, 466 Filippi, 425 Fischer, 41 Fischer, Or., 174 Fischer, P., 54, 279, 566 Fischer de Waldheim, 97 Fisher, W. K., 392 Fitch, 565 Fitch, E. A.,'44 Fitzinger, 200 Flemming, 430 Flemyng, 307 Fleutiaux, 548 Flower, W. H., 106, 119, 217, 220, 233 Forbes, E., 54, 425, 460 Forbes, W. A., 356 Forgue, 143 Forskal, 540 Forsyth, 398 Fort, 344, 356, 358 Foster, 565 INDEX OF PER80N8. Fotherby, 360, 399 Franck, 368 French, 451 Freund, 459 Freyer, 524 Fricken, von, 512 Friedlowsky, 244, 356 Friele. 262, 264 Friend, 563, 565 Fries, 471 Frivaldsky, 500 Froriep, 35 1 Fumagalli, 336 Fiirbringer, 131, 133, 135, 142 Fiirst, 399 Gadeau de Kerville, 415, 455, 4s2, 510, 548, 549 Gaillard, 346, 350 Galton, F., 36, 40. 43, 418, 419 Garrod, 390 Gaskell, 86 Gaskoin, 56 Gautbier, 443, 445—447 Gebhard, 459 Gegenbaur, 77 Geissendbrfer, 360 Gene, J., 127 Geoffroy St Hilaire, I., 57, 205, 330, 368, 377, 379, 383, 392, 451, 459, 563 Gercke, 285 Gervais, 203 Gherini, 337 Giard, 95, 440, 468, 482, 545 Gibbons, Sir J., 44 Gibson, 166 Giebel, 234 Gifford, 44 Giraldes, 336 Girard, 305 Godman, 53, 297 Godwin-Austen, 286 Goldfuss, 436, 437 Goodman, 376 Goossens, 300 Gordon, 56 Gorre, 187 Gosse, 566 Gosselin, Mrs, 44 Gotte, 127 Gottsche, 466, 471 Goubaux, 180, 244, 245 Grandelement, 355 Grandin, 340 Gray, J. E., 56, 242, 287, 396 Gredler, 286, 511, 512, 550, 551 Green, 515 Grobben, 169 Gruber, W., 108, 111, 119, 122, 330, 345, 346, 350, 352, 354, 359, 360 Guerdan, 45H Guermonprez, 327 Giinther, 173, 174, 260, 309, 468 Gurlt, 368 Gurney, .1. H.. 1 ( in\. i| 1 1 in .•-, B60 Baacke, 1 13, L46 Bagen, I L8 Bagenbaoh, B52 Hammond, 805 I I;, 111. v. 160 Bannams, 1 84 Bark( r, A., 119 Barker, .1., 354, B Barmer, i M), 556 Harrington, 182, 191, "00 Harrison, 211 Bartung, 1-7 Harvey, 178 Haworth, L5 Heincki n. 526 Hell.i-, 1*7 Heller, 170 Henne^ny, 430 Hennig, 349 Hensel, 203, 20n. 212 216, 220, 223, 226, ->w>. 244, 246, 269 Herdman, 171, 172, 139, 156 Herkluts. 527, 528, 529, 542 Heron, Sir R., 453 Heron-Rover, 465, 55.1. 56] HerrichSchiilY.]', 51 Herrin^hain, 137, 138 Hertwig, O., 431 Heuglin, von. 234. 235 Heusinger, 174, 179 Hewett. 55 Hevden, H. von. 4s*. 512. 5 1* Heyden, L. von. 484, 187—490, 194, 517, 523, 550, 551 Heynold, 355 Higgins, 471 Hill, 391 Hincks. 425 His, 177 Hodgson, 209, 398 Hoeven. van der, 21 s Hoffmeister, 162 Honratli. 284 Hopkins. 48, 73 Horn, 411 Horst. 565 Howes, 126, 153, 210, 891, 121, 515 Hubner,&05 Hudson, 56 Hiigel, Huron A. von, 89 Humphreys, 221 Humphreys, 11. N.. 801 Humphry, 200 Huxley, 217, 218, 219 Imhoff, -")47 .Tiiekrl. 393 Jackson, '-531 Jaequelin-Duval, 524 596 INDEX OF PERSONS. Jaeger, G., 536 Janson, 482, 491 Jayne, 503, 512, 518, 524, 544, 547, 548, 550, 551 Jeffreys, G., 54, 457 Jekyll, Miss, 46 Jentink, 248, 252, 253 Jhering, von, 140, 142, 300 Johnson, Atbol, 354 Jollv, 337 Joly, 370, 372 Joseph, 350 Karoli, 532 Kawall, 551 Kerckring, 344 Kiesen wetter, von, 281 Kingsley, 539, 554 Kirk, 565 Kitt, 363, 383, 384, 386, 390 Kleyn, 453 Klingelhofer, 547, 551 Klob, 187 Koenen, von, 436 Kolbe, 484, 503 Kolliker, 142 Kostanecki, von, 175 Kraatz, 146, 454, 456, 484, 485, 494, 498, 502, 506, 509—511, 515, 516, 523, 545, 547, 548, 550, 551, 552 Krause, 455, 548 Kriechbaumer, 147 Krohn, 425 Kroyer, 151 Kuchenmeister, 560 Kuhnt, 339 Laboulbene, 512 Lacaze-Dutbiers, 171 Lacepede, 540, 561 Lafosse, 244 Lamarck, 4 Lambert, 446 Lampert, 435 Landois, 58, 383, 387, 511, 555 Lane, 113 Lang, 566 Langalli, 336 Langerhans, 564 Lankester, 536 Lannegrace, 143 Lanzoni, 561 Lataste, 127 Laurent, 184 Lavocat, 354, 372 Le Clerc, 357 Leech, J. H., 46 Lefebvre, 500 Le Gendre, 184 Leger, 527, 538 Legge, 46 Leichtenstern, 181 — 185 Lereboullet, 515 Le Senechal, 530, 535, 542 Letzner, 280, 523, 550 Leuckart, 168—170, 566 Levacher, 566 Leveling, 458 Lidth de Jeude, van, 58 Linnams, 453 Lisfranc, 355 Lister, 218, 457 Loriol, P. de, 436, 437, 438 Loudon, 47 Lucas, 399 Lucas, H., 462, 536, 542, 550, 551 Ludwig, H., 433, 566 Lunel, 58, 554 Liitken, 433 Lydekker, 105, 217, 233 Macalister, A., 112, 278 MacAndrew, 54 MacBride, 440 McCoy, 52 Mcintosh, 470, 564 Maggi, 530 Magitot, 198, 203, 205, 210, 221, 244, 245, 270 Malm, 469 Manifold, 451 Mantell, 436 Marjolin, 355 Marsh, 349 Marsh, C. D., 565 Marsh, O. C, 364, 366, 368 Marshall, 86 Martens, von, 155 Martin, 430 Mason, 282, 488, 498, 509, 548, 550 Mason, F. , 355 Masters, 60, 84, 310 Mayer, 200 Mazza, 555 Meckel, 278, 346, 458, 459 Melde, 355 Meldola, 284 Meyer, A. B., 441, 445 Michaelsen, 162, 164, 165 Mielecki, von, 175 Milne-Edwards, 151, 202, 527 Mitchill, 561, 563 Mivart, 212, 217, 219 Mobius, 401 Mocquerys, 455, 487, 488, 494, 496, 498, 501, 503, 507, 508, 512, 515, 517, 522, 545—548, 550—552 Mojsisovics, 367 Moniez, 169, 566 Moquin-Tandon, 280, 304 Morand, 346, 348, 354, 399 Moreau, 540 Morgan, T. H., 157, 466 Morot, 245, 384 Morris, F. O., 44, 401 Mortillet, de, 186 Mosley, S. L., 45, 300 Muir, 352, 399 INDEX OF PERSONS. 597 Miiller, A., 512 Miiller, J., 17.5 Murray, 330 Nathusius, H. von, 285, 373, 374 Nehring, 57, 123, 210, 212, 216, 221, 2 242 Neill, 540 Neugebauer, 183, 186 Neubofer, 170 Newman, 51, 205, 300 Newport, 04 Newton, A., 44, 55 Nicbolls, 155 Nilsson, 471 Norman, 100, 457 Notta, 185 Oberteufer, 330 Oberthiif , 44 Ocbsenbeimer, 40, 284, 302 Odin, 450 Olliff, 51, 52 Otto, 58, 278, 340, 348, 350, 354, 350, 458 Otto, H., 547, 548 Owen, 119, 188, 211, 261 Packard, 100, 457 Paget, Sir J., 175, 177 Pallas, 180 Parry, 520 Partsch, 451 Paullinus, 184, 187 Pavesi, 565 Pelseneer, 280 Pennetier, 482 Percy, 184, 187 Perroud, 512 Perty, 512, 548, 550, 551 Peters, 200, 277 Pbilippi, 443 Pichancourt, 400 Pocock, 93, 457, 565 Pooley, 451 Popham, 355 Porritt, 295 Pott, 399 Potton, 399 Pouchet, 451 Poulton, 304—307, 320, 321, 323 Prackel, 184 Prevost, 457 Price, 500 Puecb, 181 Pusch, 436 Putnam, 174, 396 Piitz, 366 Quenstedt, 430 (juinquaud, 185 Rabl, 176 Ragusa, 548 Rambur, 50 Ramsay, l;. 7. 244 RuefE, 344 Riitimeyer, 246 Saage, 1 L8 Salvia, 53, 2:17 Sanderson, 398 Sandifort, 458 Sarasin, 433 Sartorius, 512, 550 Saunders, Howard, 897 Sauvage, 276 Schaff, 210 Scbleep. 470 Schlegel, 220 Schmankewitsch, 96 Bchmeltz, 566 Schmitz, 177 Schneider, "'17. 550 Schneider, A.. 17 1 Schultze, L., 138 Schnltze, 0., 194 Sdater, P. L., 396 Sclater, W. L., 37 1 Scndder, "»0 Seba, 566 Sedgwick, 84, 92, 93, 173. 197 Seerig, 3 18 Seidel, L76 Seringe, 523 Serville, 412, 413 598 INDEX OF PERSONS. Shannon, 185 Sharp, D., 43, 53, 149, 411, 482, 494, 499 Shaw, E., 413 Shaw, V., 401 Sherrington, 137, 138, 144, 168 Siebold, von, 148 Sinety, 184 Smit, 471 Smith, E. A., 287 Smith, F., 551 Smith, S. J., 151 Solger, 141 Soubeiran, 529 South, 300 Spengel, 466 Speyer, 283 Spinola. 512 Spronok, 329 Stamati, 538 Stannius, 142, 455, 461, 512, 522, 547 Staudinger, 44 Steenstrup, 466, 469 Steindachner, 58, 468 Steinthal, 359 Stevens, 41 Stewart, C, 180, 429, 440, 446 Storer, 471 Strahl, 154 Strauch, 123 Strecker, 51, 283, 295 Streng, 352 Strombeck, von, 436, 438 Struthers, 103, 105—119, 122, 140, 327, 329, 334, 346, 351, 356, 370, 389 Studer, 277 Sundevall, 471 Sutton, 105, 176, 179, 180, 188, 555 Tachard, 398 Tarnier, 185, 345 Taschenberg, 512 Tegetmeier, 57, 393 Testut, 187 Thielmann, 277 Thomas, O., 56, 120, 199, 228, 230, 246 —249, 254, 257, 258, 313, 322, 397 Thompson, W., 565 Thomson, 412 Thomson, Wyville, 466 Tiedemann, 184, 512, 536, 540 Tischbein, 511 Traquair, 469 Treitschke, 284 Trelat, 451 Treuge, 512 Trimen, 51, 300 Trinchese, 118 Tuckerman, 170, 555 Turner, Sir W., 465 Urbantschitsch, 177 Vaillant, 309, 471 Viborg, 180 Virchow, 74, 177, 178, 17 Voigt, 58 Vrolik, 58 Wagner, 421 Wagner, J., 451 Walsingham, Lord, 300 Ward, E., 379 Warpachowski, 540 Watase, 451, 463 Waterhouse, F. H., 45, 545 Webb, S., 301 Wehenkel, 366, 368 Weir, J. Jenner, 45, 51, 52, 254 Weismann, 76, 304—307 Welcker, 118, 120 Weldon, 172 Werner, 170 Wesmael, 521 Westwood, 283, 284, 508, 551 Weyenbergh, 565 White, 44 Wilde, 178 Wilder, 465 Williams, 181, 185, 191 Wilson, 304, 305, 307 Wilson, E. B., 35 Windle, 221, 326, 328, 392, 560 Wiskott, 285 Wolf, 399 Woodgate, 284 Wood-Mason, 367 Woodward, M. F., 160, 162 Woodward, Smith, 259 Wright, 566 Wright, L., 55, 393 Wyman, 57, 203, 226, 401, 465, 561 Yarrell, 59, 469, 471, 540 Yarrow, 561 Youatt, 285, 286 Zeppelin, 565 Zundel, 180 FWPCT7T UBtAItT CAMBRIDGE '. PRINTED BY C. J. CLAY, M.A. AND SONS, AT THE UNIVERSITY PRESS. EVOLUTION. A THEORY OF DEVELOPMENT AND BEREDITY. By Henry B. Orr, Ph.D., Professor at the Tulane dniveraity of Louisiana. Crown 8vo. 8s. net. SC01\SMAX. — 'Professor Orr does not profess to have proved, <>r worked <>ut in its detail, his new " Theory of Development and Heredity. 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