THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID (Sutbts to the fgtn&mm of tlu Boston Sorittg of |tatural Historg. GUIDE TO THE INVERTEBRATES OF THE SYNOPTIC COLLECTION IN THE MUSEUM OF THE BOSTON SOCIETY OF NATURAL HISTORY. BY J. M. ARMS SHELDON. BOSTON : PUBLISHED BY THE SOCIETY. 1905. ^-Y 1 - I I BIAS TABLE OF CONTENTS. Introduction . . . . . . < . . 3-8 Arrangement of Synoptic Collection .... 9-12 PROTOZOA . . '. . ..... 13-59 Sarcodina Monera . . . . . . 13-20 Rhizopoda . . . . . 21-38 Heliozoa . . . . . 39 Radiolaria ...... 40-44 Mastigophora 45-52 Infusoria . . . 53-58 " Tentaculifera ...... 59 MESOZOA ......... 60-62 METAZOA 63-494 PORIFERA . . . 63-88 Calcarea . . . .. . . . ... 68-73 Silicea . . . . . . . . . 74-83 " Hexactinellida . . . , . . 75-76 " Lithistidae . . . ... ". 77 " Tetractinellida . . ... 77 " Monaxonia . . . . ". . . 78-83 Keratosa . 84-86 Summary ........ 87-88 COELENTERA . . . . . . . 89-143 Hydrozoa . . ... . . . . 89112 Hvdrophora ........ 89-104 Hydrocorallinae ... . . 93~95 Narcomedusae . . . . . 96-97 Tracomedusae . . . . . 98 Anthomedusae . . . . 99-100 Hydroidea . . . . . 101-103 Campanulariae . . . . 104 Discophora . 105-108 Siphonophora . . . . . . . 109-110 Ctenophora 111-112 Aiithozoa .' . . . . . . . . 113-141 Alcyonaria . 113-125 Zoantharia ........ 126-130 Madreporaria ....... 131-141 Imperforata ..... 131-138 Fungidae ..... 139 Perforata ..... 140 Summary . . . . ". . . . . 141-143 ECHINODERMA ' . . . . . . . 145-195 Cystoidea 145-148 Blastoidea . . . - . . . . 149-150 Crinoidea . 151-160 Asteroidea . . 161-168 Ophiuroidea . . . . * . . . 169-170 Echinoidea . . . . . . . 171-189 Clypeastroids . ... . . . 182-186 Spatangoids . . . ... . . 187-189 Holothuroidea . . . . .*.'". . : 190-192 Summary 193-195 MOLLUSCA . . . . .... . 196-263 Pelecypoda . . . . . . \ . . 196-212 Gastropoda . . . . . . . . 213-232 Nudibranchs ........ 233-231; Scaphopoda 236 Heteropoda . . . . , ." . . 237 Pteropoda . . . . . . . ' ' ," . 238-242 Cephalopoda . ... . . . . . 243-261 Tetrabranchiata ....... 244-256 Nautiloidea . . .. . . . . 244-249 Ammonoidea . . . " * . . . 250-256 Dibranchiata . . . . ... . 257-261 Belemnitidae . 257-261 Summary '. 262-263 VERMES . . . . 265-324 Brachiopoda . 265-286 Atremata . . . . . . , . 265-269 Neotremata . , ... . . . 270-271 Protremata . . ... . . . 272-275 Telotremata . . . . . . . . 276-286 Polyzoa . . . ... . . . 287 Annelida . . . . . ... 288-308 Chaetoptera . . . . . . ",. . . 288-304 Oligochaeta 305-306 Hirudinia . . . . . ,. . . 307-308 Gephyrea . . . ..... . 309-310 Nematodes . . . . . . . 311-313 Acanthocephala .' 314 Nemertea 315-316 Turbellaria . 317-320 Trematodes .... ... 321-322 Cestodes .... . ... . 323-324 CRUSTACEA .... . . . . . . 325360 Entomostraca . 3 2 5~33o Cirripedia 33 I ~33 2 Malacostraca 333~34O Macroura . . . . . . . .. . 341-352 Brachyura . . . ... . . 353-360 ARACHNOZOA . . . . . . . . 361-377 Trilobita - ... . . 361-363 Merostomata . . . ..... . 364-365 Arachnida . . ... . . . 366-377 MALACOPODA . ... . . . . 378-381 MYRIAPODA . . . . . . . . . 382-385 SYMPHYLA . . . . . . . 386-387 LNSECTA . 389-494 Thysanura . , . . . . . 389-395 Ephemeroptera 396-399 Odonata ......... 400403 Plecoptera . 404 Platvptera 405-410 Euplexoptera 411-412 Orthoptera . . . . . . . . 413-417 Thysanoptera . . 418 Hemiptera . . . . . . . 419-431 Coleoptera . . . . . . . 432-441; Neuroptera . . . . . . . . 446-448 Mecoptera ... . . . . . 449-450 Trichoptera 451-453 Lepidoptera . . . . . . . . 454-474 Hymenoptera . . . . ... 475-486 Diptera 487-494 INTRODUCTION. IN many of our natural history museums one room is devoted to a Synoptic Collection of animals. The stu- dent who wishes to get a comprehensive view of the whole animal kingdom spends most of his time on such a collection, since it embraces representative forms of all the principal groups from the simplest protozoan to the most complex mammal; in other words, from the Pro- tamoeba to man inclusive. It may be truly said that mankind is seeking as never before for a rational explanation of the origin and the development of animal life upon our earth. The more strenuous this search, the more imperative is the demand made upon naturalists to present in their museums, so far as possible, the most advanced knowledge concerning these problems. At the present time, therefore, it is not enough that a Synoptic Collection consist merely of specimens of animals effectively or artistically arranged. Neither is it sufficient that such a collection consist of species placed together by some arbitrary and artificial method. The student of the New Zoology demands that rela- tionship shall be the basis of classification, and that not only the descendants living to day shall be represented, but also their primitive ancestors that existed in an early geologic age. Indeed, a genealogical classification of animals is the goal to be striven for constantly by the naturalist of the twentieth century. The recognition of the possibility of such a classification tends toward the unification of collections which have hitherto remained isolated. For instance, it has been customary to place 4 INTRODUCTION. together all ancient animals existing in the form of fossils. These have been arranged stratigraphically, beginning with the fossils in the oldest strata and ending with those in the newest, or vice versa. For the purpose of historic geological study or for strictly palaeontological research, such collections are helpful. This arrangement has been, indeed, the only one possible up to within a very recent period. Even now there are naturalists who seriously question whether any other method of arrangement -"is possible. These maintain that our knowledge is not ade- quate to warrant an attempt at a natural classification of animals based upon genetic relationship. It must be borne in mind, however, that a vast amount of material in the form of well proven facts has accumu- lated since 1859, when Darwin's Origin of Species gave a new directive impulse to biological research. This ma- terial is found largely, it is true, in an almost infinite number of papers in which isolated adult species are figured and described. But notwithstanding this fact, it is also true that of late years there has been a growing tendency toward considering the life history of the indi- vidual species described, and this study has led in turn to an investigation into the life history of the group to which the given species belonged. In this way the signi- ficant correlation sexisting between the development of the individual, known as ontogeny, and the development of its class, or phylogeny, have been discovered. When it is remembered that these correlations are proofs of relationship or of descent from a common ancestor, then one begins to realize how many trustworthy guides there are, all pointing toward the desired goal. Our artificial classifications of animals, therefore, are not due " so much to insufficient knowledge of their early stages as to insufficient attention to what is actually known and published regarding them," as Mr. Samuel H. Scudder 1 !The Butterflies of New England, I, 1889, p. viii. INTRODUCTION. O has already pointed out in the case of the arbitrary clas- sifications of the Lepidoptera. When all this knowledge is brought together, assorted, and systematically used, then the sequence of life upon our planet will be demon- strated as never before. Then the isolation method of arrangement to which I have alluded will be relegated to the past and students will no longer receive the lasting impression that fossil forms are distinct creations having no connection with living organisms, but each museum will be in itself a revelation of the essential unity of all animal life. It is true that many of our museums are so con- structed that they are ill adapted for the demonstration of the evolution of inorganic and organic nature. But where this demonstration cannot be given with complete- ness, minor collections like a Synoptic Collection of geo- logical or zoological specimens may point out the way to the desired end. The following principles of classification Professor Alpheus Hyatt wished to have carried out in the Synop- tic Collection of this Museum, of which he was Curator during the preparation of nearly all of this Guide. First : In the arrangement of the material proceed always from the simple to the complex. Second : So far as possible let each group be repre- sented first by its primitive ancestors that lived in the pre-Cambrian, Cambrian, or early Palaeozoic times. Third : From these primitive ancestors pass to the embryonic and larval stages of generalized members of the group existing to-day ; and from these early stages to the adult stages which are invariably more specialized. Fourth : From the generalized adult members in every group proceed to the specialized members which have reached their present condition through the law of spe- cialization by addition. Fifth : In some of the most impressive instances go still farther to those extremely specialized adults which have become so by the law of specialization by reduction. O INTRODUCTION. We have attempted to carry out these principles in the different groups of invertebrates. With the increase of knowledge certain animals which are here described as primitive will doubtless be found to be reduced forms, while certain reduced forms may in reality be primitive. Notwithstanding these changes in the position of species, the principles of this genealogical classification will remain essentially the same. In order to bring ou* these principles clearly and for- cibly in the descriptive text of the Guide, it has been neces- sary to abandon altogether the use of certain terms, while the meaning of other terms has been restricted. Among those given up are the words "high," "low," "highest," "lowest." Textbooks and manuals have usually consid- ered animals as either "high" or "low." Generally speaking, vertebrates have been studied first, as the "highest" representatives of animal life, and all other forms have been "low" in comparison. In other cases the study of a class has begun with the so called " lowest" forms ; for instance, the Crustacea with the barnacles. These classifications were the best that were possible at the time they were made, and they met the necessities of the period. But the time is now ripe, as we have already said, for a more natural system of classification which shall embody and set forth the history of animal life on our globe. In a genealogical classification that illustrates the broad natural relationships which bind animals together genetically there can be no " high " nor " low." There can be only simple, primary forms from which have been evolved in the process of the ages complex and secondary forms. This, in reality, is the fundamental principle of our classification. Granted that this is true, then the most profound knowledge is needed concerning the prob- lems of heredity and of variation. Immense strides have been made the past quarter of a century, and epoch-mak- ing monographs on the development of certain animals have thrown strong light on these difficult problems. INTRODUCTION. 7 We maintain that this new light should be reflected in our museums, especially in our Synoptic Collections ; that here the workings of the law of heredity by which ani- mals are bound together by blood relationship should be illustrated by specimens, drawings, models, by everything in brief, that can most strongly impress the student. This demonstration would be more effective had we a closer acquaintance with the ancestral fauna of pre-Cambrian and Cambrian times. The masterly researches of Walcott into the Cambrian and Lower Silurian rocks, and the invalu- able investigations of Matthews in the Cambrian forma- tions of New Brunswick prove how important are these sources for studies in evolution in a field hitherto almost unexplored. Other terms which do not appear in this Guide are "degraded," "degenerate," "retrogressive," and "worm" as applied to the caterpillar stage of the Lepidoptera. The first two, " degraded " and " degenerate," are not used for two reasons : first, because they are associated in the popular mind with moral considerations, and this association often leads to mental confusion ; secondly, because we cannot see why an animal that has developed a part or an organ to the immense advantage of itself and its race should be called "degraded," even though many other organs have fallen into disuse or wholly disappeared in the process. In the case of parasites the use of these terms might be more allowable, were it not for the first reason stated. The word " retrogressive" is not used because it is mis- leading, since animals do not in reality go back to a more primitive and generalized condition, however much they may appear to do so. This is proved by the position of the so called " retrogressive species " in a genealogical record which can never be among the ancestral trunk forms. It cannot be, because these species as a rule bear evidences of the evolutionary stages through which they have passed ; and where such evidences are not apparent 8 INTRODUCTION. to the eye, it is rational to infer that vestigial organs can- not be the same as rudimentary organs. The use of the word "worm" is restricted to members of the subkingdom of Vermes. It is obviously misleading to apply it to such a specialized animal as a young butterfly or moth. "Simple" and "rudimentary" are used only in describ- ing primitive and generalized forms or organs. "Direct development" applies, as we use it, to the mode of development of the more generalized members of a class. Some naturalists, on the contrary, use it in the sense in which we have used accelerated or abbreviated development; the latter we apply only to the mode of development of the forms specialized by addition or reduc- tion. Primitive forms are spoken of as primary, generalized, simple, fundamental ; they have a primitive or a direct development, and some of their organs may exist as rudi- ments, hence the adjective rudimentary. Specialized forms, on the other hand, are spoken of as secondary, differentiated, complex, adaptive ; their devel- opment is either indirect (with a metamorphosis), accel- erated (where the early stages are passed through quickly or skipped), or suppressed (where the advanced stages are omitted) ; some of their organs may exist as vestiges, hence the adjective vestigial. The invertebrates or animals without a vertebral column are divided primarily into three divisions, the Protozoa, Mesozoa, and Metazoa. The Protozoa are represented in the collection by many forms, the Mesozoa by one species. The Metazoa are subdivided into nine large groups, the Porifera, Coelentera, Echinoderma, Mollusca, Vermes, Crustacea, Arachnozoa, Myriopoda, and Insecta. Some of these groups are again divided, as, for instance, the Insecta, where typical forms of sixteen orders are figured and described. THE SYNOPTIC COLLECTION. A Synoptic Collection of animals possesses one advan- tage over special collections, since it may illustrate on broad and general lines the principles of a natural classification. Our knowledge of the vast number of genera and species which make up many of the classes of the animal king- dom is not sufficient, as a rule, to enable us to group all the organisms of a given class according to their natural affinities, but in a Synoptic Collection, properly chosen specimens may be so arranged as to place before the stu- dent a more or less satisfactory demonstration of the principles that are based upon the genetic relationships of animals. A natural classification of all the species of the whole animal kingdom is, indeed, the goal of the natural philosopher, but this goal can be reached only through the tireless efforts of generations of devoted truth seekers. It is a well known fact that certain animals are simpler in structure than others, and it is also most probable that the simplest forms living to-day are the nearest repre- sentatives of those primitive organisms which gave rise through countless ages and generations to animals of greater and greater complexity. For this reason these simplest forms are often spoken of as primitive or ances- tral forms. Many of them are also called synthetic or generalized forms, since they combine, in essentially sim- ple condition, certain structural characters that are found more developed in their descendants, and because this (9) 10 SYNOPTIC COLLECTION. further development was probably effected by a process of specialization. This process of specialization may have followed along many lines of development in the successive generations of a species. Thus, for example, not only the locomotive organs but also the mouth parts, sense organs, and skeletal structures may have become differentiated, while corresponding inter- nal changes may have taken place, the resulting species possessing manifold organs and functions. Such animals are broadly differentiated species, becoming so by the law of specialization by addition. Secondly, the process of specialization may have followed along a few lines, result- ing in the excessive development of a few organs and the partial or complete loss of others. These animals are specialists by the law of specialization by reduction acting under favorable conditions. Thirdly, the same process under the thwarting influence of an extremely unfavorable environment may have tended, not towards many sided development and the production of a broadly differentiated species ; not towards the excessive development of a few organs with the loss of others and the consequent pro- duction of a more specialized species ; but rather towards a gradual diminution in the size of the organisms, a loss of many organs and functions, and finally towards the gradual extinction of the species or group. Such a spe- cies we shall describe as reduced, since it is truly an extreme product of the law of specialization by reduction. In any one of these three cases mentioned above we have originally primitive forms giving rise to secondary forms, and in a collection based upon natural relationships the former should always precede the latter. We have adhered strictly to this principle in the Synoptic Col- lection of this Museum, so far as the present state of our knowledge would permit. In the groups of the Metazoa or animals that follow after the Protozoa, and Mesozoa, the development of the PROTOZOA. 1 1 f an y gi ven species has been considered a more or less trustworthy guide for determining the phylogeny, or historic evolution, of the phylon or tribe to which the animal that produced the egg belonged. This egg, or ovum, as generally described, is a cell made of protoplasm and containing a nucleus within which is a nucleolus. It is, however, reasonable to suppose that this nucleated and therefore differentiated condition of protoplasm arose from an unnucleated and undifferentiated condition, and, therefore, we seek for what may be called the ancestral stages of the nucleated egg. If these stages have become obliterated in the eggs of the more specialized animals by the action of the law of acceleration in development, it would seem probable that they might be represented by the unnucleated adults of the Protozoa, and that a study of these simplest, one celled organisms, and of the spe- cializations leading from an unnucleated to a nucleated condition of protoplasm, might throw light not only on the origin of the nucleated egg, but also upon the natural classification of the Protozoa. Thirty years ago it would not have been possible to attempt such a classification of this subkingdom. But the observations and experiments of many investigators during the past few years have thrown strong light upon the structure and development of many species and the possible phylogenetic history of several groups. The elaborate work of Biitschli, com- prising three volumes of Bronn's Thier-Reich, and the great work of Haeckel, the Challenger Report on the Radiolaria, have both been published since 1880. Besides these, a large number of original papers and sev- eral special works on different groups have appeared since 1874; notable among these are the writings of Gru- ber, Hertwigand Lesser, Cienkowski, Schultze, Grenacher, Brandt, Verworn, Maupas, Mereschkowsky, Plate, Hofer, and of Leidy, W. Saville Kent, Brady, Dallinger and Drysdale, Lang, E. Ray Lankester, Hyatt, Ryder, Archer, Bessels, Calkins, Wilson, and others. Although we have 12 SYNOPTIC COLLECTION. not followed any one author in the arrangement of the Protozoa of the Synoptic Collection, yet we are chiefly indebted to the above named investigators for the facts upon which the arrangement is based. The Synoptic Collection of this Museum, is contained in Room E of the Main Hall. The two central floor cases (A and B) exhibit the classes of invertebrates, while the wall cases are reserved for the vertebrates. The Protozoa are in the horizontal part of section i of case A. These are represented by drawings, models, and fossils, since the animals living to-day are mostly micro- scopic. Beginning with the simplest Protozoan organisms, as represented by Plates 1-6, we pass to more and more differentiated forms until we reach the groups represented by Vorticella and Podophyra. Beyond these and under the Sponges are the Mesozoa, represented by Volvox. All the specimens and plates of drawings in each group are numbered in a continuous series. As a rule we begin at the lower right hand corner of each section, and pass to the left 1 and backward in the horizontal part, and upward in the erect part, ending at the upper left hand corner. Deviations from this rule are owing to the pecul- iar shape or the large size of the specimens. The figures on the plates are also numbered consecutively beginning with the lower left hand corner and ending with the upper right hand corner. 1 This arrangement is necessary to accord with the arrangement adopted throughout the Museum. PROTOZOA. 13 PROTOZOA. Section i (horizontal part). SARCODINA. MONERA. Scepticism prevails in regard to the existence of Hae- ckel's Monera. Nevertheless, as Calkins 1 remarks, the claim of Haeckel "that there are organisms without nuclei .... although it rests upon negative evidence, can- not be rejected until all the forms considered have been shown to possess them." It is readily conceivable that non-nucleated forms were the first to exist in a remote past, and that these antedated the nucleated forms seem a reasonable supposition. Some of these non-nucleated organisms have persisted, it would seem, since ancient times, although it is probable that all modern Protozoa differ in some respects from their primi- tive ancestors. Since these earliest ancestors were made of protoplasm only, being wholly without hard parts, no record of their structure has been preserved in the rocks. For this reason we must begin with the simplest Protozoa living to-day. In PL i, figs. i-6a, is represented the salt and fresh water form, Protamoeba primitiva Hkl., and in PI. 2, figs. i-4a, a species of marine Protamoeba (P. schultzeana Hkl.). There are many and strong reasons for maintain- ing that the first animal life which existed was marine. The first Protamoeba described and figured by Haeckel (PL i, figs. i-6a) was found in fresh water, but since then Protamoeba primitiva Hkl., has been discovered in salt water. With our present knowledge of the properties 1 The Protozoa, 1901, p. 40. (Columbia University Biological Series, VI.) 14 SYNOPTIC COLLECTION. of the elements of inorganic nature it is possible to con- ceive of the origin of a mass of protoplasm like the young Protamoeba (PL i, fig. i). This is seen to be nearly as large as the adult (fig. 2) , owing probably to rapid growth ; in P. schultzeana HkL, however, the young form (PI. 2, fig. i) is smaller than the full grown organism (PL 2, fig. 2). The youthful form of Protamoeba primitiva, like the adult, is a homogeneous, structureless mass of protoplasm or sarcode, possessing no organs nor covering, and is known as a cytode. No nucleus x is present, and no non-con- tractile or contractile cavities called vacuoles. Protamoeba schultzeana differs from Protamoeba primi- tiva by having the protoplasm differentiated into an outer layer or ectosarc and an inner layer or endosarc, both of which are extended to form irregular, knobbed, spherical continuations, as seen in the drawings (PL 2, figs. i~4a). Notwithstanding the extreme simplicity of structure of Protamoeba prtmitiva, the organism has the power of lo- comotion, as is well shown by PL i, figs. 2, 3. A pro- longation of the body, or pseudopodium, is extended and the streaming of the protoplasm into it causes the animal to creep over surfaces. This is probably one of the sim- plest physiological modes of motion, and results in pro- ducing a crawling type. The power of taking food by means of the pseudopodia was not observed by Haeckel, who described this form, although he proved that small particles were absorbed into the protoplasm of the body. In other species of the same genus the pseudopodia and body have been seen to envelop the food and the function of digestion followed. 1 Biitschli considers that Protamoeba (as well as all of its group of Monera) has a nucleus, but that it was not detected at the time this organism was studied, on account of the imperfect means of in- vestigation which then existed. On the other hand, no nucleus has been found in Protamoeba vorax by Gruber (stated by Rolleston and Jackson, Forms of Animal Life, ed. 2, 1888, p. 916), or in Archerina by E. Ray Lankester (Quart. Journ. Micr. Sci., XXV, 1885, p. 61), and these investigators have carried on their researches with modern appliances and according to modern histological methods. PROTOZOA. 15 It may be that, in the earliest condition of living pro- toplasm, nourishment was simply taken into the mass by a process analogous to absorption, and that the additional strength acquired in this way, together with a subsequent deficiency in the food supply, gave rise to a desire to go in search of food and therefore originated the function of locomotion. In the development of the more specialized animals the. passive, absorbent stage is not represented, so that the function of locomotion precedes the function of taking and digesting food. The function of reproduction is shown in PL i, figs. 4-6a, also in PL 2, rigs. 3~4a. The body becomes con- stricted (PL i, fig. 4), and this constriction continues un- affected by the change in form which each of the halves undergoes until only a mere thread connects the two parts (PL i, fig. 5 ; PL 2, fig. 3) ; this finally separates and each half rounds itself off immediately and creeps away as an independent organism (PL i, figs. 6, 6a ; PL 2, figs. 4, 4a). This process of reproduction is known as division or fission. It will be noticed that the two youth- ful forms resemble the parent before constriction of its body has taken place. We cannot fail to recognize in Protamoeba an organism performing the important vital functions of the more spe- cialized animals. We shall presently see how this knowl- edge of its life history is a natural introduction to the more differentiated Amoeba (PL 9), which is regarded by all biologists as an animal; and for this reason we prefer to place the Protamoeba among animals rather than among plants or neutral organisms. Portions of the sea bottom at great depths are covered by a vast gelatinous mass known as the Bathybius slime. This slime is, in part, made up of an infinite number of protoplasmic cytodes of various sizes, and imbedded in these are calcareous bodies called coccoliths, which are now considered to be vegetable in origin and therefore foreign to the true Bathybius. 16 SYNOPTIC COLLECTION. PI. 3, fig. i, represents one of the smaller cytodes. showing the blunt pseudopodia, and PL 3, fig. 2, one of the larger cytodes in the form of an irregular network with the imbedded coccoliths, greatly magnified. The indefi- nite form of the cytodes, the absence of organs and outer covering, and the possession of blunt pseudopodia, to- gether with the fact that movements have been observed in the protoplasm, suggest the possibility that we have here a vast number of marine Protamoeba-like organisms; but more investigations on the Bathybius are needed be- fore its exact nature and relations can be determined with certainty. It was called a mineral deposit by Wyville Thomson, its discoverer, but was considered an organic form by Huxley and Haeckel. If now the crawling marine Protamoeba should adapt itself to the life of a free swimmer in the open sea, we might expect to have as a result a form not unlike Pro- togenes primordialis Hkl. (PI. 4, fig. i). The flattened body of the creeping Protamoeba would tend to become more or less spherical when suspended in the water and the simple, blunt, ever-changing pseudopodia might de- velop into the long, branching, and more constant pro- pelling organs which enable the animal to swim rapidly through the sea. Be this as it may, we certainly recog- nize in this unnucleated Protozoan specialization of structure and function, and we find a correlation existing between habit and structure. If we could find a young form (PI. 4, fig. 2 ) 1 similar to Protogenes, which after growing to adult size divided by fission, and if these zoons, 2 instead of separating, remained together for a time at least, connected by their branching and anasto- mosing pseudopodia, then we should have a colonial form like Myxodictyum sociale Hkl. (PI. 4, fig. 3). Here we 1 It is probable, although not proved, that Myxodictyum sociale Hkl. arises by the detachment of single animals like PI. 4, fig. 2. 2 Zoon is substituted for individual. For reasons, see Hyatt, " Larval Theory of the Origin of Cellular Tissues," Proc. Boston Soc. Nat. Hist., XXIII, 1884, p. 46. PROTOZOA. 17 have a Protozoan that is probably single when young and colonial when adult, which illustrates an extremely inter- esting phase of development in animal life. The Protamoeba, Bathybius, Protogenes, and Myxo- dictyum belong to the simplest Monera; other genera of this group illustrate further specialization in structure. Archerina boltoni Lankester is represented in PI. 5, figs. 1,2. Fig. i may be the form that issues from the hard- ened case or cyst. It consists of a spherical body with long, motionless pseudopodia radiating outward from the surface. A large vacuole is seen in the interior. This organism is especially interesting because it contains chlorophyl. The latter is confined to a single or bifid corpuscle. No nucleus exists, but the chlorophyl cor- puscle appears to take the place of the nucleus, perform- ing a similar function in the process of reproduction. The corpuscle usually divides into four parts followed by the division of the surrounding protoplasm, until a colony is formed (PI. 5, fig. 2, a small bit taken from a large colony). This colony was decolorized, and the small chlorophyl corpuscles appeared as in PI. 5, fig. 3, while the large ones were undergoing division (see PI. 5, fig. 4). The Haeckelina borealis (PI. 6), discovered by Meresch- kowsky, shows a fixed or stationary Moner. The long, solid stem by which it is attached is secreted by the pro- toplasm, this secretion taking place constantly on one part of the body which, when the stem is formed, becomes the lower surface. This organism is without nucleus or vacuoles, but several round, strongly refracting balls are present in the protoplasm which are probably drops of oil. The pseudopodia are short and delicate, and are scattered over the whole surface. 1 1 Biitschli places this form among the Heliozoa, although he says vacuoles are wanting and presumably a nucleus, while there is no differentiation of the protoplasm into an outer part, or ectosarc, and inner part, or endosarc. Its striking resemblance to the Heliozoan, Clathrulina, will be seen by comparing PI. 6 with PL 43, fig. 7, but if the observations already made are accurate, the two forms are not closely related genetically. 18 SYNOPTIC COLLECTION. An unfilled gap exists between these forms, which are among the more undifferentiated members of the Monera and the Protomyxa, which Haeckel considers a Moner and Biitschli a Rhizopod. No nucleus has been dis- covered in Protomyxa, and for this reason we do not feel justified in placing it with the Rhizopods. On the other hand, the habit of fusing or blending with other zoons of its own kind, of covering itself with a hardened case or cyst and passing into a resting state, and especially of producing flagellate young, makes it seem not improbable that flagellate unnucleated adults which have arisen through adaptation of structure to habit may have existed as the ancestors of Protomyxa. This may be the case or else a nucleus may be found, when the Protomyxa can be placed among the Rhizopods as Biitschli has already done. The experiments of Gruber on Dimorpha mtitans (PL 50, figs. 1-9) suggest still another view, namely, that the flagellate condition may be assumed quickly in response to the need for rapid motion. Therefore, the flagellum in many cases of these simpler Protozoans may often be an adaptive and not an inherited character. PL 7, fig. i, represents the younger stage of Protomyxa as it issues from the cyst. After the exit it adopts the more usual crawling motion, thereby assuming the Pro- tamoeba-like form (PL 7, fig. 2) and showing an interme- diate stage between the flagellate and the Protamoeboid condition. In PL 7, figs. 3, 4, the Protamoeboid state is more pronounced. PL 7, fig. 5, is a single zoon showing the function of nutrition, a Navicula being assimilated by the plasma of the body. After nourishment is taken, vacuoles or cavities filled with fluid and without distinct walls begin to appear which are not found in the young (PL 7, figs. 1-3). A form like PL 7, fig. 5, was seen to fuse with a similar zoon. PL 7, fig. 6, represents three or four zoons that have fused together. PL 7, fig. 7, is an adult formed by the fusion of several zoons, and PL 7, fig. 8, an adult after being well fed. The vacuoles are PROTOZOA. 19 present in considerable numbers; these, however, are non-contractile and inconstant in position. The pseudo- podia branch and anastomose. Food material diatoms and the like is found in the protoplasm of the body". The adult draws in the pseudopodia and covers itself with a cyst (PI. 7, fig. 9). A structureless, glassy membrane surrounds the orange-red contents. PI. 7, rig. 10, repre- sents another stage more advanced in which the interior mass has become divided into many orange-red balls. In PI. 7, fig. 1 1, the cyst has opened and the flagellate young are issuing. This completes the cycle of the life of the Protomyxa. PI. 7, fig. 12, is an under-fed adult. We describe it here as an illustration of the fact that unfavorable condi- tions produce changes in structure which may tend towards the reduction of the zoon. The vacuoles have decreased in number and the pseudopodia only slightly branch and anastomose. The structural changes induced by the small quantity of food taken may be transient, as in the case figured above where the under-fed zoon might become like the over -fed specimen (PI. 7, fig. 8) by giv- ing it a larger supply of food. If, however, the cause of structural change, be it an insufficient diet or any other cause unfavorable for the development of the zoon, were continued through successive generations, the result prob- ably would be the production of a smaller, weaker, per- haps distorted form, and finally the total extinction of the species. Such a species may be called a reduced or a suppressed species, since it has suffered diminution in organs and efficiency. It is also often called simple, but in order to avoid the mental confusion which arises when this word simple is applied both to primitive and to reduced forms, we prefer to restrict its use to the former which have comparatively few organs and these oftentimes in rudimentary or developing condition. There are other reasons for doing this. While it may be true that there are reduced animals which cannot be distinguished from the primitively simple forms, yet in the greaf majority of 20 SYNOPTIC COLLECTION. cases they bear, at some time of life and especially when young, indubitable proofs of their evolutionary history. These proofs or revelations of their past condition make the reduced forms more complicated in reality than at first appears, and it is these structural characters which should receive a clear descriptive term free from ambig- uity, since it is these characters which are of very great importance in tracing the phylogenetic history of animals. The habit of fusion which has been observed in Pro- tomyxa is probably one important cause of the origin and differentiation of the organ known as the nucleus. We cannot suppose, however, that this process of differentia- tion was rapid, so that a well developed nucleus was made at once, but there were doubtless transitional organisms in which the nucleus was in the process of forming. We had arrived at this conclusion before having seen the work of Gruber x on Pachymyxa hystrix. In this form, Pachymyxa hystrix (PI. 8, figs. 3-7 ; fig. 3, a living specimen containing brown food material, and fig. 6, the same probably in the process of division), Gruber was never able to observe a nucleus, but he saw scattered in the protoplasm a large number of dark colored granules which became red when treated with a reagent (PI. 8, fig. 5). Specimens were also seen where the colored granules were surrounded by a colored zone of protoplasm so that they looked like little swarm buds (PI. 8, fig. 4), but the exit of these small bodies was not observed. This form of Pachymyxa has an outer layer differentiated into thickly set rods, between which the pseudopodia are thrust out. This is seen in PI. 8, figs. 3-5 and 7; in the last figure, fig. 7, a small portion is magnified, showing the rods and one pseudopodium drawn while in the coloring fluid. iZeitschr. f. wiss. Zool., XL, 1884, p. 122. On this subject Gruber says we may suppose that a stage preceded the formation of the typical Rhizopod nucleus, when little grains of nuclear substance lay scattered through the whole protoplasm, and that these only came together later to form the real nucleus. PROTOZOA. 21 In the naked and more simple form (PI. 8, figs, i, 2 probably a variety of the same species) there is, however, no such differentiation of the outer part; fig. i shows the brown food material in the interior and the pseudo- podia, and fig. 2 is a specimen colored and showing probably one stage of division in which the organism is separating into two parts. The nuclear grains are seen in this figure, as also in fig. 5. It is reasonable to suppose that a transitional organism exists, or has existed, in which the young stage has nu- clear grains and the adult a well formed nucleus, but we' have seen no such species described or figured. SARCODINA. RHIZOPODA. The probable intermediate forms just mentioned lead naturally to the group, Amoebina, represented by the Amoeba protens Leidy (PI. 9, figs. i-n). Here we have a typical Rhizopod with the organs and functions peculiar to such an animal. PL 9, fig. i, is probably the young of this species and fig. 2 presumably an older stage. In both the young and the adult (fig. 3) the protoplasm has become more or less differentiated into a clear outer layer, the ectosarc, and an inner granular portion, the endosarc. When, however, one observes by the aid of a microscope the granular endosarc flowing into the clear ectosarc and, as it were, taking possession of it, one becomes convinced that there is no constant line of demarcation between the two. 1 1 According to Leidy (Fresh-water Rhizopods of North America, U. S. Geol. Surv. Terr., XII, 1879, p. 24}, Dr. Wallich states that the ectosarc is due to a temporary and partial coagulation of the en- dosarc coming in contact with the water in which the animal lives, and it again reverts to the mass of the endosarc within the body. The process reminds one of the cooling of a molten mass of metal at the sides of a crucible, and the melting away again of the crust as it is stirred from the sides into the remainder of the molten mass within. ' SYNOPTIC COLLECTION. From this point of view the Amoeba is interesting as offering an intermediate position between organisms that are absolutely unprotected, like Protamoeba and others, and those that are permanently covered with hardened protoplasm or with a chitinous or a calcareous shell. Within the endosarc is a nucleus (fig. 3, white; fig. 4, the same colored) which consists of a nuclear membrane, nuclear fluid, often called sap, and suspended in the latter a large number of grains which allow themselves to be colored and are therefore called chromatin grains. The non-contractile vacuoles are present, and also a contractile or pulsating vacuole, or vesicle, as it is often called (fig. 3, pink in color) which is more or less constant in posi- tion, and which may have arisen phylogenetically from the former, as suggested by Haeckel. 1 Besides the vacuoles, nucleus, and minute crystals that are often found in the protoplasm, there are grains of sand which the animal has taken up in crawling over sur- faces, but which it has not formed into an outer covering or shell. The pseudopodia are blunt, like those of Pro- tamoeba, and are extended in the act of performing the function of locomotion (fig. 5). This figure shows also the transient tendency to an anterior and posterior region of the body which is sometimes observable. The Amoeba is a crawling type, although now and then it floats and swims. At such times its body becomes rounded and its pseudopodia radiate in different directions, as seen in fig. 6, which illustrates clearly the correlation of structure and habit. The power of taking food is finely shown in figs. 3 and 7. In fig. 7 a pair of pseudopodia, acting like the finger and thumb of the human hand, have come together at their ends, entirely encircling an active Infusorian, Urocentrum. Another recently captured Urocentrum is seen within the body of the Amoeba. In fig. 3, a diatom !Jena. Zeitschr., IV, 1868. Engl. transl., Quart. Journ. Micr. Sci., IX, 1869, p. 114. PROTOZOA. 23 has been caught, and is probably taken into the body through the extension or flowing of the ectosarc over it. After the food is digested the excrement is sometimes ejected simply by the unfolding of the protoplasmic body, and at other times is discharged from the posterior part of the body, as seen in fig. 5b. As already stated, the contractile vacuole is a cavity which is filled with fluid and which contracts and dilates quite regularly. According to the experiments of Grif- fiths, 1 it performs at times an excretory function similar to that of the kidneys in the more specialized animals, but it is interesting to note that at other times no waste nitrogenous matter is found. in the vacuole, and it is most likely, as stated by Griffiths, that the organ in its primi- tive condition performs more than one kind of work, com- bining, it may be, a respiratory with an excretory function. Experiments on the more differentiated Protozoa, such as Paramoecium and Vorticella, proved that the contractile vacuole in these forms performed the function of a true kidney, the product excreted being the same as in the most specialized animals. Circulatory movements of the endosarc have already been spoken of under the head of structure, and are men- tioned here again since they belong with the physiological activities of the Amoeba. PI. 9, fig. 8, represents the granular endosarc flowing into the hyaline ectosarc, the direction of the current being indicated by arrows. The susceptibility of the organism to external forces is shown in different ways; whenever the glass slide on which the Amoeba is crawling is touched or jarred, its pseudopodia are partially or wholly drawn in and a more or less spher- ical form is assumed, as seen in fig. 9.^ This irritability 1 Proc. Roy. Soc. Edinburgh, XVI, iSSS-'Sg, p. 131. 2 Amoeba radiosa. According to C. Scheel, Amoeba radiosa is the young of A. proteus. See his Beitrage zur Fortpflanzung der Amoben, in C. von Kupffer's Festschrift zum siebenzigsten Geburts- tag, 1899, pp. 569-580. 24 SYNOPTIC COLLECTION. of protoplasm may give rise in time to nerve force which ultimately in the more specialized animals becomes local- ized in a nervous system, and which manifests itself in consciousness and will power. The Amoeba proteus usually has but one nucleus (fig. 3), but sometimes a specimen is found with two nuclei (fig. 5). Reproduction in this species probably takes place by fis- sion. PI. 9, fig. 10, is a supposed Amoeba proteus in the act of dividing. The separation of the thread connecting the two parts occurred in ten minutes after the stage represented in the figure. Gruber's important experiments on Amoeba proteus and other Protozoa, in order to determine the part played by the nucleus in reproduction, prove that by artificial divi- sion only the portion possessing the nucleus is capable of reproducing itself. The Amoeba was divided as shown in PI. 9, fig. n, and the portion marked a lived, while b drew in its pseudopodia and died. After many experiments Gruber concludes that it is an incontrover- tible fact that the nucleus is the species-preservative con- stituent of the cell, and that to it is justly ascribed the highest importance in the processes of fecundation and inheritance. 1 If it is true that the continuance of the life of the species depends upon the nucleus, then it follows that in passing from the Protamoeba to the Amoeba a change has taken place in the protoplasmic organism. The generative power manifested by the cytode is cer- tainly an indication of the existence of a generative sub- stance making up a part at least of the cytode, and it would seem as if this substance had become localized in the nucleus of the Amoeba to form a distinct and species- preservative organ. The remarkable differentiations of the nucleus which are found in succeeding and more 1 Ann. and Mag. Nat. Hist., (5), XVII, 1886, p. 473. Translated from the Berichte der naturforschenden Gesellschaft zu Freiburg i. B., i, 1886. See also Hofer, Jena. Zeitschr., XXIV (Neue Folge, XVII), Heft i, 1889, P- 1O 5; an d Morgan, Regeneration, 1901, p. 65 (Columbia University Biological Series, VII). % PROTOZOA. 25 specialized genera of Protozoa tend to strengthen this hypothesis. It is probable, although it is not yet proved, that Amoeba proteus forms swarm-buds in the shape of little Amoebae. PI. 9 is instructive since it places before the student a simple organism capable of performing in a simple way the vital functions of the most specialized animals. Many interesting differentiations of structure are shown in other species of Amoeba. The marine Amoeba (A. obtecta) crawls with extreme slowness. According lo Gruber these Rhizopods do not exhibit any tendency to undertake migrations, and therefore when the conditions are favorable they lie together in great numbers and thus form regular societies. 1 In Amoeba polypodia M. Schultze (PI. 10, figs. i-8a), which may have one or several nuclei, the pseudopodia are numerous, and are more equal throughout their length, approaching the thread-like organs of many Foraminifera. The process of fission is shown in figs, i 8a, which illus- trate more clearly the different stages of development than preceding figures. The specimen observed had one nucleus. The division of this organ took, place in one minute and a half, and that of the body in eight and a half minutes, so that ten minutes were required for the whole process. Figs. 2-8a are drawn in outline, showing the division of the nucleus and protoplasmic body and also the increase in the number of vacuoles. There are organisms closely related to these Amoebae which seem to throw light on the origin of the flagel- lum, and to point to the probability that certain Rhizo- pods have given rise to the Mastigophora ( Flagellata.) According to Calkins, 2 however, there is no conclusive 1 Zeitschr. f. wiss. Zool., XXXVIII, 1883, p. 56. Engl. transl., Ann. and Mag. Nat. Hist, (5), XI, 1883, p. 276. 2 The Protozoa, 1901, p. 105. (Columbia University Biological Series, VI.) 26 SYNOPTIC COLLECTION. evidence to support the view that Rhizopods are more primitive than Flagellata, or vice versa. He says : ; ' Their mutual affinities are very close, and together they stand as the most primitive forms of modern Protozoa." While this may be true, a much more consistent ar- rangement can be made if one begins with the Sarcodina, as Calkins has done, and passes to the Mastigophora ( = Flagellata) and then to the most specialized Infusoria (see p. 53). The whip-bearing Rhizopod (PI. n,figs. 1,2) repre- sents an adult which combines the flagellum with the Amoeboid pseudopodia. This flagellum is eight or ten times the length of the body. When the motion changes from creeping to swimming, the body lengthens as seen in fig. 2. Amoeba quinta l shows a marked specialization of the nucleus. PL 12, fig. i, is a young form with eight nuclei. Whether the youngest stage has one nucleus cannot be stated.' 2 PL 12, fig. 2, represents an adult with twenty- four nuclei (more existed but were omitted for the sake of clearness), and the species may have hundreds, this increase taking place, as the figures show, with the growth of the animal. PL 12, fig. 2a, represents the nucleus as it appears before staining, which shows a differentiation in structure from the nucleus of Amoeba proteus (PL 9, fig. 3). The outer membrane lies over a peripheral layer of granules, and the central portion is filled with a mass which appears granular. When colored, the nucleus has the appearance seen in PL 12, fig. 2, which is much more 1 This species was described by Gruber as Amoeba proteus (Zeit- schr. f. wiss. Zool., XXXVIII, 1883. p. 382), but afterward was found by him to be Amoeba quinta (ibid., XLI, 1885. p. 205). See his description of Amoeba proteus (ibid., XLI, 1885, p. 216, pi. XV, figs. 43-45-) 2 Gruber, Zeitschr. f. wiss. Zool., XLI, 1885. This author says that what Btitschli has shown as such appears to belong to another species of Amoeba. PROTOZOA. 27 specialized than the colored nucleus of A. proteus (PI. 9, fig. 4) . Inside of the dark colored outer layer is a zone of nuclear sap, while the central mass we may probably indicate as a nucleolus. 1 In PI. 12, fig. 2, four of the twenty-four nuclei are in the process of division, and the figure is very instructive as showing the origin of the many-nucleated forms. The process is probably rapid, and this may account for the fact that few naturalists have been fortunate enough to observe and draw it. In Pelomyxa palustris Greef we have an Amoeba-like form when young' 2 (PI. 13, figs. 1-4). Many of these Amoebae came from a dead Pelomyxa. After moving about, they became more quiet (PI. 14, fig. 5), some con- tracted themselves into a spherical or pear-shaped body (PI. 13, figs. 6, 7), after which a long vibrating thread was stretched out (PI. 13, fig. 8), and the Amoeba became transformed into a flagellate animal. After rapid rotat- ing movements this young flagellate organism passed out of sight, "rowing with the front, quickly swinging whip," so that unfortunately its further development was not observed. Whether the flagellate young remained a flag- ellate organism, or whether it passed into the unflagellate adult (PL 13, fig. 9) cannot be stated. In the adult, the tendency towards an anterior and a posterior region of the body is marked. The animal stretches itself out and moves in curves, turning the forward end, now to the right, now to the left (PI. 13, fig. 9). At the posterior end there is a glassy disc-like expansion. PI. 13, fig. 10, is a magnified portion of the body. Many nuclei are present which may be converted into the "shining bod- iGruber, Zeitschr. f. wiss. Zool., XXXVIII, 1883. According to Calkins, the Protozoan cell, with possibly one exception, has no true nucleolus comparable with the nucleolus of the Metazoan cell. What has been so called is, according to this author, either func- tional chromatin that has aggregated into a mass, or an intranuclear sphere or division center (see The Protozoa, 1901, p. 253). 2 Greef , Arch. f. mikr. Anat., X, Supplement, 1874, p. 51. 28 SYNOPTIC COLLECTION. ies" 1 that give rise to the Amoeba-like young (PI. 13, figs. 1-4). The little rods (PI. 13, fig. 10) are thought to be parasitic plants. The streaming of the endosarc with its vacuoles, rods, etc., into 'the hyaline ectosarc is well shown in the drawing. If the flagellate condition is a normal stage in the devel- opment of Pelomyxa and not a parasitic organism as main- tained by some naturalists, the species is an exceedingly interesting one. Observations on such forms as the whip- bearing Rhizopods, Pelomyxa, and also those of Gruber on Dimorpha mutans show that the amoeboid and flagel- late conditions are marked in these less specialized organ- isms by extreme variability, depending, it may be, upon the need for slow or rapid motion. The flagellum arising in this way as an adaptive character may become fixed in the organization and finally inherited as a permanent organ, which would seem to be the case in the Mastigo- phora (= Flagellata). The group of Amoebina represented by DifHugia (PI. 14, fig. i) not only possesses many nuclei, but these have become differentiated so that each contains one or more nucleoli (fig. la). In addition to this specialization in structure the protoplasm is not only capable of taking up sand grains, like that of the Amoeba proteus, but it is able to lay a part of these on the surface for a protective cover- ing or shell. PI. 14, fig. i, is a vertical section through the shell and body of Difflugia urceolata Carter. The hyaline ectosarc extends out into the pseudopodia which are stretched from the opening. In the protoplasm of the interior are seen the nuclei colored red (PI. 14, fig. la, nucleus, uncolored and magnified), besides sand and bits of nourishment. Figs. 2-5 illustrate the division and shell formation of the same species. In order to determine how the shell was *For views on this subject see Greef, Arch. f. mikr Anat., X, Sup- plement; also Gruber, Zeitschr. f. wiss. Zool., XLI, 1885. PROTOZOA. 29 formed, Verworn 1 isolated a specimen and gave it splinters of blue glass. He observed repeatedly that the Difflugia crept by the splinters, its pseudopodia pushing them away instead of taking them up. After a time a Cypris passed and irritated the pseudopodia, which caused a sticky secre- tion to form on their surface, so that pieces of glass were caught in it and were then taken into the body with the pseudopodia. Afterward Verworn irritated the pseudopodia with a needle; the surface became rough and took up glass which before it did not do. The splinters were really drawn into the protoplasm so that the interior contained a little heap of them. These observations tend to prove that the origin of the shell of Difflugia urceolata is mechanical and largely a matter of accident. Later experiments upon Difflugia lobostoma Verworn,' 2 tend to prove that the animal does not exhibit a conscious choice in the taking up of material for its shell, nor does there seem to be any calculation in regard to the quantity of sand grains or glass splinters needed. Sometimes a mass was taken and then thrown out in order apparently to take up more a desire to get, it would seem, rather than to use. Verworn saw two, three, and even five zoons of this species of Difflugia in conjugation. He proved by experi- ment that two zoons might touch each other for a long time without blending, while other zoons united with the fusion of the protoplasm. Experiments were made to cause zoons to blend by keeping two close together, but were unsuccessful, and the author considers that it is proved indubitably that every zoon cannot blend with every other. On the other hand, two zoons which were in conjugation were separated but these came together again, showing that one must exert a directive influence upon the other or the two upon each other. The cause may be of a chemical nature, as maintained by Verworn. 1 Zeitschr. f. wiss. Zool., XLVI, 1888, Heft IV, p. 455. 2 Zeitschr. f. wiss. Zool., L, Heft 3, 1890, p. 449. 30 SYNOPTIC COLLECTION. The process of division is illustrated by PL 14, figs. 2-5. First a swelling (fig. 2) is seen at the mouth of the shell which approaches the spherical form (fig. 3). The pro- toplasmic swelling reached in time the size of the parent form and a mass of glass splinters was seen entering the newly formed half (fig. 4) where the protoplasm with the splinters showed a slowly flowing movement. In the most advanced stage of division the protoplasm which had curved forward had taken the form of a Difflugia shell, and the glass splinters were placed in a layer upon its surface (fig. 5). The new half did not seem to have a firm shell, as the splinters of glass were still quite loosely joined to one another. The next day the zoon separated from the parent, its shell assumed the charac- teristic form, while the pieces of blue glass were united by means of a binding material which was still quite colorless, and which, after some days, began to assume a darker brownish shade. Verworn succeeded in taking off the shell and obtained the naked Difnugia. Several of these shell-less specimens he kept for three weeks, and no attempt was made on the part of the animal to make a new shell. He therefore concludes, after many experi- ments, that the species of Difnugia do not reconstruct an injured shell nor make another when one has been removed. The Foraminifera are Rhizopods in which the pro- toplasm is differentiated into ectosarc and endosarc, and the nucleus has a membrane, a distinct chromatin net- work with one or more nucleoli (Biitschli). In certain forms, like Trochammina (= Rotating) inflata, and in Ovulina, one half of the nucleus has been found to con- sist of chromatin, the other of a non-staining substance. The less differentiated Foraminifera possess a one cham- bered shell, and are single forms, while the most differ- entiated have a complex, many chambered shell; each chamber, it may be, representing a zoon, and if so the 1 Throughout this Guide synonyms are placed in parenthesis. PROTOZOA. 31 many chambered shell represents a colony. Many natur- alists, however, hold that this is not a colony, but is one zoon with a polythalamous shell. In the case of Difflugia just described, the bud represented another zoon that in this species separates from the parent form, but which in the complex Foraminifera remains attached and makes its own covering. In the arrangement of the Foraminif- era the single forms are given first when this is possible, and afterward the colonial forms which may have arisen from them phylogenetically. Saccammina is a simple, hollow, spherical Rhizopod which usually occurs single (PI. 15, fig. i, S. sphaerica M. Sars). Sometimes several shells adhere by their ex- ternal surfaces and the openings remain distinct, as shown in PI. 15, fig. 2, a form which has received the name of Saccammina socialis. This association of zoons where there is no organic connection reminds one of the " so- cieties " of the marine Amoeba obtecta (see p. 25) and of the association of the cytodes of Bathybius. In fig. 3 (S. sphaerica} we have such a rude attempt at a colony that it seems to be an initial effort. These zoons are connected by protoplasmic extensions, or stolons. The largest chamber was the primordial one, and was fastened between two stones ; the succeeding zoons then arose as buds which formed their shells in an irregular manner, and the terminal chamber was merely a mass of sand grains with large interstitial openings through which passed the pseudopodia. The specimen (No. 16) and PI. 17, figs, i 8, represent Astrorhiza liwicola Sandahl, 1 described by Bessels under 1 This name was given by Sandahl (Ofvers. Kongl. Vetenskaps- Akad. Forhandl., XIV, p. 299) in 1857, and is retained on account of priority. Brady places Astrorhiza among the Foraminifera. Ac- cording to Sandahl there are many nuclei, but these are figured by him as occurring among the grains of the pseudopodia. an unusual position for nuclei. Bessels, whose observations are more extended, neither figures nor describes a nucleus. Until positive knowledge is obtained we place it provisionally among the Foraminifera. 32 SYNOPTIC COLLECTION. the name of Haeckelina gigantea. PI. 17, fig. i, represents the young Astrorhiza which has arisen by a forcible sepa- ration of a piece of the arm, it being probable that new animals or zoons arise from the swollen ends of the arms. It is Amoeba-like, and is without a shell. The drawing represents it just after its separation ; PI. 17, fig. 2, is the same ten hours later ; fig. 3, the same somewhat con- tracted ; fig. 4, the same four days after separation (one projection sends out a number of delicate thread-like pseudopodia which branch slightly) ; fig. 5 is an older stage in which the dark brown protoplasm is not yet cov- ered with a shell ; fig. 6 represents one still further de- veloped which appears to be on the point of making a shell. The process of specialization continues until the full grown organism (.fig. 7) has the shell completed. The material of which it is made is usually sand or mud. It has a varying number of continuations from which ex- tend the pseudopodia. Fig. 8 is the drawing of a colony of seven adult zoons united by their arms which in this case serve as stolons. According to Neumayr 1 the irregular agglutinating Foraminifera, such as the Astrorhizidae, have given rise to the regular agglutinating forms, and these in turn to the imperf orated and the perforated calcareous Forami- nifera. Re.ophax bacillaris Brady (No. 18), and R. nodulosa Brady (No. 19), are more regular than Astrorhiza, though they are rough on the surface and are usually made of sand with a silicious cement. Cornnspira involvens Reuss. (PI. 20, fig. i), is one of the imperforate limy shells. It has a variable number of undivided convolutions making a circular flattened shell. Another species, C. striolata Brady (PI. 20, fig. 2), broadens out and passes over into a form resembling Peneroplis, soon to be described. !Die Stamme des Thierreiches, I, 1889, p. 198. PROTOZOA. 38 The Miliolidae are represented by the mounted speci- mens (No. 21). The term Miliola may be used very properly in a generic sense to comprehend a great variety of closely associated forms having the same general type of structure (Brady). It is reasonable to suppose that a single form, Uniloculina or Loculina, exists, or has existed in the past, although no such form has been described. The Biloculina (No. 21) has two chambers visible exter- nally, and each successive segment encloses the younger ones on the same side. The group of Foramjnifera is a very remarkable one for studying gradational forms. Here, to the inexpressi- ble delight of the student, all artificial systems break down. "It is only," says Brady, "as we learn to recognize the fact that among the Rhizopoda the so called ' species ' rep- resent no more than terms of a series of which very fre- quently every intermediate link can be supplied that we arrive at any just idea of their relationship." l Among the more specialized groups of animals many of the interme- diate forms are unfortunately wanting, but these doubtless either exist at the present time or have existed in the past, and if the lesson taught by the Foraminifera could be impressed upon the student at the beginning of his studies, he would be less inclined to draw sharp lines of demarca- tion, since these are arbitrary and unauthorized by nature. No. 22 and PI. 23, figs. 1-7, represent Peneroplis, of which Brady says there is no genus of Foraminifera embracing so great a variety of external form in which the morphological sequence is at once so simple and so com- plete. 2 PL 23, fig. i, is a young specimen of Peneroplis show- ing the spiral mode of growth. Fig. 2 is an adult of the 1 Challenger Report on the Foraminifera, IX, 1884, p. 49. 2 For other figures showing the variety in external form of this genus, see Brady, Challenger Report on the Foraminifera, IX, 1884, PI. XIII; also Carpenter, Introd. to Study of Foraminifera, PI. VII. 34 SYNOPTIC COLLECTION. Dendritine variety in which the last chamber is taking the rectilinear mode of growth. Fig. 3 is the Spiroline vari- ety of the same genus in which a considerable portion of the shell is rectilinear. Fig. 4 (Peneroplis arietinus Batsch.), fig. 5 (longitudinal section of the same), and fig. 6 (Peneroplis cylindraceus Lamarck) show the gradual diminution of the spiral portion and the increase of the rectilinear part. These figures illustrate the changes from a spiral to a rectilinear mode of growth in different species of one genus, while the slides No. 24 (specimens obtained from the sand of the Bahamas) and PI. 25, figs. 1-5, exhibit the changes from a spiral to an annular growth in one species. Orbiculina adimca F. u. M. PL 2 5, fig. 6, is a section giving the interior of the shell. It shows that the primordial chamber was globular and that subse- quently spiral growth took place followed by annular growth. Unusual interest attaches to the species Orbitolites ten- nis sima Carpentet (PI. 26). Beginning as a globular shell it passes into the undivided Cornuspira condition which is clearly marked in the young; the later convolu- tions are sometimes constricted at opposite points, thus indicating the Milioline stage. Next the spiral stretches, after the fashion of a Peneroplis. The chambers extend themselves extraordinarily in breadth, until by the meeting of the lateral ends a ring is formed around the spiral part of the' shell, as in Orbiculina. These annular rings or chambers are divided by cross walls into a great number of chamberlets. Finally the complex structure with many additional covering cells or chambers peculiar to Orbito- lites is developed. 1 Miliota, Peneroplis, Orbiculina, and Orbitolites belong to the calcareous group of Porcellanous Foraminifera. The calcareous group' with a hyaline or glassy appear- 1 For further information see Carpenter, Rep. Chall. Exped., Zool., VII, part XXI, 1883, pp. 1-49, pis. I-VIII. PROTOZOA. 35 ance is represented in the Collection both by fossils and by series of drawings. The simplest or most elemen- tary structure in this latter group is to be found in the shell of Lagena (PI. 27, figs. 1,2). Fig. i. Lagenaglobosa Montagu, shows the globular shell so common as the ground form of the Foraminifera, and fig. 2, Lagena laevis Montagu, represents a flask-shaped modification of the primitive form. The shell of Lagena is a single chamber with a terminal opening. The walls are calcareous and finely perforated for the exit of the pseudopodia. This genus like others exhibits great variation. Nodosavia (PI. 27, figs. 3-5, No. 28, N. soluta Reuss.) consists of chambers united in a straight or curved line, with the opening in the center of the terminal chamber. PI. 27, fig. 3. is Nodosaria simplex Silvestri, consisting of two chambers in a straight line, and fig. 4 is another spe- cies of the same genus (Nodosaria subtertenuata Schwager) composed of several chambers. Fig. 5, Nodosaria (= Dentalina) farcimen Soldani, has more chambers and the shell shows a tendency to curve. The group represented by Globigerina is one of great interest since the ooze of portions of the deep sea is largely made up of the shells of these Foraminifera. Although existing in such vast numbers to-day, both Globigerina and Orbulina (see p. 36) have been dis- covered recently in the ancient Cambrian formation of New Brunswick. 1 Here they occur well preserved in shales and in phosphate nodules. Sufficient investiga- tions, however, have not been made to prove beyond doubt that this ancient Orbulina is the primitive ancestral form of Globigerina. Cayeux's paper 2 is interesting in this connection. He 1 Matthews, Trans. N. Y. Acad. Sci., XII, 1893; also XIV, March, 1895. 2 Sur la presence de restes de Foraminiferes dans les terrains pre*- Cambriens de Bretagne. 1894. See also review of M. Cayeux's paper by G. F. Matthews, Amer. Geol., XV, 1895, p. 146. 36 SYNOPTIC COLLECTION. has found one-chambered shells in the pre-Cambrian rocks of Brittany, but is unable to -determine with cer- tainty whether they are primitive Foraminifera or Radio- laria ; he thinks they may be the latter and therefore does not figure them. They are doubtless older than those discovered in New Brunswick, as pointed out by Mat- thews, since they occur in an older series of rocks and are very much smaller in size. Associated with the unilocu- lar forms are Foraminifera consisting of from two to seven chambers (PL 29, figs. 1-6) and belonging to the Perfor- ata. Fig. i shows a two-chambered shell, figs. 2 and 3, three-chambered shells, figs. 4 and 5, two different forms of four-chambered shells; fig. 6 is the only shell possess- ing more than four chambers that M. Cayeux has found. The irregularity and imperfect attempts of these primitive Perforata to make a symmetrical shell remind one of the similar efforts and results among the I mperforata already figured and described. The microscopic slide No. 30 represents the Globige- rina ooze from the deep sea off Cape Hatteras obtained by the U. S. S. Albatross, in 1883. Although the Glo- bigerina shells predominate in it, yet a number of other genera are also represented. PI. 31 is a beautiful draw- ing taken from the Narrative of the Challenger Report (Vol. i, part 2, PI. N, fig. 10. p. 926) of Globigerina ooze seen by reflected light. This was dredged from a depth of 1900 fathoms in lat. 21 38' N.. long. 44 39' W. Slide No. 32 exhibits Globigerina shells dredged from the At- lantic. No. 33 is the rosy Globigerina rubra d'Orbigny. PI. 34, fig. i, is the young of a bottom specimen of Glo- bigerina bulliodes d'Orbigny, which does not possess spines; PL 34, fig. 2, the adult, showing more chambers, and fig. 3, a view of the same, showing the large opening of the last chamber. We have already pointed out that doubtless Globigerina arose from a single hollow sphere such as Orbulina (slide No. 35) appears to be when observed externally ; PROTOZOA. 37 but the internal structure of many species of this genus shows it to be more specialized than Globigerina. In slide No. 36 a number of Orbulina shells are seen with Globigerina-like shells inside. (The broken yellow speci- men on the slide is probably another genus.) PI. 37, fig. i, is Orbulina universa d'Orbigny, in which the Globige- rina-like shell in the interior is not wholly covered by the exterior spherical shell. Fig. 2, a surface specimen, shows the covering entire but thin, so that the inner shell can *be easily seen through it. Fig. 3 is the Globigerina- like shell from which the outer Orbuline sphere has been removed. The shell is provided with spines, like most surface specimens, and its chambers are partly or wholly filled with .protoplasm. In fig. 4, a bottom specimen, the inner shell is not seen, owing to the thickness of the wall. Fig. 5 is an old bottom specimen in which the inner shell does not exist but the wall is laminated, giving the appearance when seen under the microscope of spheres within spheres. This laminated appearance is observable in some of the specimens in the microscppic preparation No. 36. According to the observations of Shacko, 1 which were made on bottom specimens, only the young Orbu- linae have Globigerina-like shells, while in very large and old bottom specimens they do not occur. From the observations made on Globigerina and Orbu- lina it may be possible that we have here only one genus. In such a case, the youngest or nepionic stage would be represented by a single thin-walled hollow sphere ; the adolescent or neanic stage by several spheres fastened together ; the mature or ephebic stage by several united spheres completely enclosed in the last globular chamber ; and the old age or gerontic stage by a single hollow sphere, the thick wall of which is laminated. Either this is the case or else Globigerina is the more primitive, ancestral form, which in course of time was developed !Arch. f. Naturgeschichte, XLIX, I, 1883. 38 SYNOPTIC COLLECTION. into the Orbulina that possesses Globigerina characters in youth and loses them in age. In PI. 38, figs. 1,2, Hastigerina murrayi Wy. T., which belongs to the Globigerina group, is represented. The shell is thin and possesses spines (fig. i). The proto- plasm of the living animal envelops the shell, taking the peculiar form of bubble-like extensions, and thrown out- ward beyond these are the extremely long pseudopodia (fig- 2). The group of Nummulitidae is the most differentiated of the Foraminifera. The mounted specimen No. 39, Fusilina, is exclusively fossil. The shell is bilaterally symmetrical. The chambers extend from one end of the shell to the other, and each convolution encloses the pre- vious whorl. The walls of the chambers are usually single, and there are no interseptal canals. Nummulites is represented in the Collection by speci- mens (Nos. 40, 41). No. 40 shows two whole shells, and between these a horizontal and a vertical section ; back of these single specimens are two pieces of Nummulitic limestone ; one showing fresh surfaces, while the other has been weathered by the action of the carbon dioxide and moisture in the air so that the shells stand out more prominently. No. 41 is remarkable for its size, being a giant of its kind. The internal structure is shown in PI. 42. The figure at the left is a horizontal section of Nummulites granules a d'Arch., showing the double walls between the chambers and the canal system. The two central figures are Nummulites laevigata Lam.; one the whole shell and the other a vertical section showing chambers and walls. The figure at the right is Num- mulites mamillata d'Arch., with a portion of the outer shell removed. PROTOZOA. 39 SARCODINA. HELIOZOA. One of the most familiar examples of the Heliozoa is Actinophrys sol Ehr. (PL 43, figs. 1-3). Fig. i is the young stage observed by Kent, which possessed a flagel- lum. While swimming it projects blunt pseudopodia from all sides (fig. 2). Its motions then become slower, the flagellum is withdrawn, when suddenly thread-like organs are put out in every direction and the animal is transformed into the adult Actinophrys (fig. 3). If the naked spherical body of a typical Rhizopod should re- main constant in form, and the pseudopodia should radi- ate as long thread-like organs and preserve this character essentially unchanged, then we should have the Actino- phrys in outward appearance. In the Heliozoa there may be one or many nuclei. In Actinosphaerium, a Heliozoan closely related to Actinophrys, from one to two hundred nuclei are not uncommon, and this large number in the adult is reached from one nucleus or a few nuclei in the young (Biitschli). Actinophrys increases by fission, and this sometimes gives rise to a colony. 1 PI. 43, fig. 4, represents a young embryo of Clathrulina elegans Cienkowski 2 which soon develops into the form represented by fig. 5. Its striking resemblance at this stage to Actinophrys is at once apparent. Like that Heliozoan it is without a stem or a skeleton. In fig. 6 these have been developed, the stem being secreted first, but both are as yet nearly colorless. Fig. 7 is the sta- tionary adult with its stem (only part of which is shown in the drawing) and skeleton. The pseudopodia extend in all directions from the openings of the shell. After a time these are drawn in and fission takes place, each prod- 1 For views in regard to the process of conjugation of Actino- phrys and the Heliozoa in general, see Btitschli, Bronn's Thier- Reich, I, 1881, p. 317. 2 See Arch. f. mikr. Anat., Ill, 1867, p. 311. 40 SYNOPTIC COLLECTION. uct of the fission becoming encysted within the shell. Fig. 8 shows four cysts, which in time are ruptured, allowing the embryos to slip out. The process of development observed by Hertwig l differed somewhat from the above. He saw the division of the body with the formation of flagellate young (PI. 44, fig. i). Each swarmer possessed a nucleus and sev- eral contractile vacuoles, while in the forward end it was provided with two whips. About half an hour after leav- ing the parent, it settled perpendicularly upon an object, took on a spherical form and a naked Clathrulina re- sulted. The stem had its origin in a depression of the body which is visible on the surface as a sharply defined circle (seen in PI. 44, fig. 2, in the center of the draw- ing). It grows long, as represented in fig. 3, which is a naked Clathrulina before the shell is formed. SARCODINA. RADIOLARIA. We may turn with a feeling of assurance to the primi- tive forms of Radiolaria discovered by M. L. Cayeux 2 in pre-Cambrian rocks as the remote ancestral forms of Radiolaria living to-day. These minute, silicious shells remained practically unchanged during the metamorphism of the surrounding rock. The primitive Radiolaria were spherical, spineless, and some had an imperfectly trellised skeleton. Of those that were symmetrical Cenosphoera (PI. 45, fig. i, x 1350; fig. 2, section of the same) was one of the most generalized. The characteristic network is seen in these shells with perfect clearness. Though found in pre-Cambrian and Silurian rocks, this genus occurs at the present time both on the surface and at 1 See Arch. f. mikr. Anat., X, Supplement, 1874, p. 2. 2 Bull. Soc. Geol. de France, 36 Sen, XXII, 1894, p. 197. Compte Rendu Soc. Geol. de France, May, 1894, p. Ixxix. See also Amer. Geol., XV, 1895, p. 146. PROTOZOA. 41 great depths of the sea. The figures of Haeckel 1 show that this genus and several other genera of the Radiolaria have remained essentially unchanged since protozoic times. Some of the Radiolaria have spines, as seen in PI. 45, figs. 3-5. Fig. 3, Xiphosphoera, has two equal spines; fig. 4, Staurosphoera, has four; while fig. 5, Acanthosphoera, has numerous spines at the nodes of the lattice work, though only three have been preserved. The basket form is seen in Tripodiscium (PL 45, fig. 6), while in fig. 7 (which belongs to the section of the Dicyrtida, though the family is not determined) the shell is divided into three parts with numerous spines. It has been pointed out by Haeckel that the simple skeletonless Heliozoan, Actinophrys, might give rise to the simple shell-less Radiolarian, Actissa princeps Hkl. (PI. 46, fig. 2), the stem-form from which probably the whole group of Radiolaria has descended. The young Actissa (fig. i) possesses one nucleus and is a flagellate form. This passes probably into the Actinophrys stage which unfortunately has not been observed. Afterward a membrane, known as the central capsule, forms, which is wholly absent in the young. The possession of this organ separates the adult and more specialized Actissa from Actinophrys, and is the peculiar and marked charac- teristic of a Radiolarian. PI. 46, fig. 2, is the adult. The large round nucleus is seen in the center with its nucleolus. Around the nucleus is finely granulated pro- toplasm containing many clear spherical vacuoles. These parts are contained in the porous central capsule ; outside of the capsule is seen the jelly envelope or calymma which in the figure is yellow but colorless in the living Radiolarian. It is indeed seldom visible in the living, freshly taken animal when observed in sea water, but since it does not readily become colored, its size and form can be made out definitely by placing the specimen in 1 Challenger Report, Zool, XVIII. 42 SYNOPTIC COLLECTION. coloring matter. The calymma is pierced by the long radial pseudopodia, which arise outside of the central capsule. Late in the life of the adult the nucleus divides into a large number of nuclei, as seen in fig. 3a, which is a diagrammatic drawing of one half of a central capsule of an older specimen than fig. 2, the other half being like it, of course, at this stage of development. These nuclei together with a part of the surrounding protoplasm are transformed into the flagellate young (fig. 3b, a diagram- matic view of one half of a central capsule in a more advanced stage of development than fig. 3a). Actissa is a single form like most of the Radiolaria. As has been stated, it never secretes a skeleton, but many Radiolaria make silicious shells of rare beauty and great complexity. The microscopic preparation (No. 47), when seen under a high power, shows delicate lattice- work forms known under the familiar name of Polycys- tina, which was given by Khrenberg to that part of the Radiolaria described by Haeckel as the Spumellaria and Nasellaria. These shells were taken from the famous Polycystine marl of Barbadoes in the Antilles which belongs to the Miocene period, and which is the richest of all the Radiolarian deposits. Living Radiolaria are represented, greatly magnified, in PI. 48, figs. 1,2. In fig. i, Thalassophysa pelagica? the delicate pseudopodia radiate in all directions from the shell. Fig. 2, Theopilium cranoides? shows these and also the basket-like form and delicate lacework of the shell. The colonial Radiolaria are represented by Collozoum inerme Hkl. (PI. 49, figs. i-io). Figs. 1-3 represent the young. Here we find for the first time different kinds of zoons and this differentiation in structure is suggestive of 1 Thalassicolla pelagica in Haeckel's Monograph. 2 Eucyrtidium cranoides in the Monograph. PROTOZOA. 43 a differentiation in the processes which have produced the zoons. Fig. i is known as an isospore ; it is provided with a whip, a homogeneous nucleus of uniform constitu- tion, and a little rod-like crystal. Figs. 2 and 3 represent the anisospores (fig. 2 the large macrospore and fig. 3 the smaller microspore) which are never produced by the less specialized Actissa. These are provided with a whip, 1 a heterogeneous nucleus of two-fold constitution, and fat granules, but the crystal is often wanting. Unfortunately all attempts have failed to follow the development of the flagellate young to the typical Radiolarian condition represented by Actissa. It is probable, however, that the phenomenon of accidental fusion of different zoons observable in the simpler Rhizopods has given rise in the colonial Radiolaria to the phenomenon of genetic union or conjugation, and that the macrospore and microspore unite ; if this is true we may have here the simplest form of sexual reproduction. After this possible union it is probable that a single form arises like Actissa which becomes a colony by the division of the nucleus, the prod- ucts of the division remaining united as seen in fig. 4, which is a young, unarticulated colony. Fig. 5 is a piece of a young colony showing how the many central capsules (represented by red dots in fig. 4) have arisen. There are eight of these capsules, two of which are in the act of dividing. The nucleus is seen in different stages of divi- sion. Around the central capsules extends the jelly like calymma (blue in the figure) comparable with the jelly envelopes (yellow in the figure) of Actissa. Numerous vacuoles and yellow cells are seen in the calymma. The latter contain starch and are unicellular yellow algae which live with many Radiolaria. True to their plant nature, these yellow cells give out oxygen which is eagerly taken by the Radiolarian, while the latter, equally true to its ani- 1 Brandt says they possess most probably two whips (see Fauna und Flora des Golfes von Neapel, XIII, p. 167). 44 SYNOPTIC COLLECTION. mal nature, gives forth carbon dioxide. This supplemen- tary relation where there is a mutual dependence of the one upon the other, is known as symbiosis and will be found to- occur among other more specialized animals. The division of the nucleus takes place early in life and this is a fact of great significance. The law of accelera- tion in development which has been demonstrated in many groups of the Metazoa, may have acted in this case, caus- ing the characteristic late nuclear division peculiar to the single Radiolaria, like Actissa, to appear early in the life of the zoon. After the division the process of spe- cialization is carried on in a most interesting manner, as shown in figs. 6-9, and results finally in the formation of the asexual isospores and the probably sexual aniso- spores. Fig. 6 is a zoon in the act of forming isospores. The original central nucleus has divided into many nuclei, and its place has been taken by a large oil globule. The nuclei lie close together but do not press upon each other sufficiently to be flattened into polyhedrons. The crystals first appear like lengthened granules and one is laid close to a nucleus. Gradually they grow into the form shown in fig. 6. In fig. 7, a, b (a diagrammatic representation of later stages in the process), the nuclei and crystals have arranged themselves near the periphery, while the large oil globule remains in the center. Finally disintegration takes place and the isospores appear. Fig. 8 is a dia- grammatic representation of the process of forming aniso- spores drawn from balsam preparations. In early stages (fig. 8a, fig. 9) irregular groups of differentiated nuclei occur in spherical masses of plasma (fig. 9 shows a group' of three nuclei in such a spherical mass) , and in the inter- substance between these are found large, homogeneous nuclei, sometimes drawn out to a point at either end (fig. 9b). With the diminution of the central oil globule there appear the grape-like clusters of fat seen in figs. 8 a, b, c. In fig. 8b (a later stage than 8a) the groups of nuclei have increased in number and the homogeneous PROTOZOA. 45 nuclei with most of the intersubstance have disappeared. A difference in the size of the nuclei is apparent. This difference is still more plainly seen in the later stage (fig. 8c) in which scarcely a trace of the intersubstance remains. Finally the formation of anisospores takes place. The clusters of fat fall apart into granules and each spherical mass divides into as many wedge shaped pieces as there are nuclei (fig. 8d). These ultimately fall apart when the large macrospores (fig. 2) and small microspores (fig. 3) appear. Fig. 10 is a mature (usu- ally called "old vegetative") colony in which the flagel- late young are ready to be set free by the disintegration of the colony. It is distinguished from the young colony (fig. 4) by its plain articulations. According to Haeckel the same Polycyttaria or colonial Radiolaria which produce anisospores also produce, at other times, the asexuaf isospores, so that it would seem that these two forms of reproduction alternate with each other, and if so, we have here in the simplest subkingdom of animals the phenomenon of alternation of generations. This variability in function as well as variability in struc- ture is just what one would expect to find among organ- isms which have not yet learned the ways of their more specialized and therefore more stable descendants. MASTIGOPHORA. We now come to a group whose peculiar and more or less constant characteristic is the possession of a whip or flagellum, and which for this reason is known by some as the Mastigophora and by others as the Flagellata. We have found the flagellum among the Rhizopoda, Heliozoa, and Radiolaria ; wherever, in fact, there has been need for rapid motion it seems to have been developed as an adap- tive character. In the typical Mastigophora it seems to have become fixed in the organization and therefore an 46 SYNOPTIC COLLECTION. inherited character. The variability of this organ in the intermediate forms, and the close connection between the Heliozoa and Mastigophora are shown in the extremely interesting transitional organism, Dimorpha mutans Gru- ber, 1 to which we have already referred. When first observed the animal ajppeared to be an Amoeba radios a or a Heliozoan, but suddenly it fell into a trembling motion and a long whip was thrown out. PL 50, figs, i 8, show the changes undergone in about two hours. In fig. i the animal is leaving the Heliozoan stage, the body is still spherical, but the pseudopodia are short and one long whip begins to strike the water. The next moment the body is extended lengthwise and becomes egg-shaped. The pseudopodia shorten themselves still more, and the Dimorpha begins to swim propelled by two long whips. At times one of the whips beats the water while the other trails behind (fig. 2). Suddenly the animal stops swim- ming and turns the forward end of its body downward while the whips feel about on the bottom (fig. 3). All movements cease, the body becomes spherical and frcia every side fine ray-like pseudopodia are thrust out (fig. 4). But the Dimorpha seems not satisfied with the spot it has chosen, or it is disturbed in some other way, for the above described transformation occurs again (fig. 5), and the body becomes quite smooth during its rapid swimming (fig. 6) . The little sun-animal has transformed itself into such a perfect whipped creature that it is difficult to keep track of it among the other flagellate organisms in the water. After swimming about it comes to rest again (fig. 7), "thrusts out its pseudopodia, and transforms itself in a few moments into a Heliozoan (fig. 8). Fig. 9 repre- sents the Dimorpha in its usual condition. The body is pointed at the posterior end where the food elements are crowded closely together. Gruber. to whom we are indebted for the above description, tried various experi- iZeitschr. f. wiss. Zool., XXXVI, 1882, p. 445. PROTOZOA. 47 ments and found he was able to force the animal from a Heliozoan to a flagellate condition by striking the sides of the dish when, as if disturbed, the Dimorpha would develop whips and swim quickly about. The flagellate Mastigophora are well represented by the series of forms shown in PL 51. The body of Monas termo Ehr. ? (fig. i, x 950) is occasionally somewhat amoeboid, sending out short pseudopodia-like continua- tions. It is a free-swimming animal but may become fastened temporarily by a thread-like prolongation of the posterior end of the body (fig. 2, x 1200). At the for- ward end is the whip or flagellum, and on one side of its base is the beak-like prominence or lip. Between this lip and the base of the flagellum is the mouth, which, how- ever, does not extend into an oesophagus. The flagellum catches the food and it is thrown with a sudden jerk directly against the mouth. "If acceptable for food the flagellum presses its base down upon the morsel, and at the same time the lip is thrown back so as to disclose the mouth, and then bent over the particle as it sinks into the latter. When the lip has obtained a fair hold upon the food, the flagellum withdraws from its incumbent position, and returns to its former rigid, watchful cordi- tion. The process of deglutition is then carried on by the help of the lip alone, which expands laterally until it completely overlies the particle. All this is done- quite rapidly, in a few seconds; and then the food glides quickly into the depths of the body, and is enveloped in a digestive vacuole, whilst the lip assumes its usual coni- cal shape and proportions." We have quoted the above from Prof. H. James-Clark 1 to show the specialization in structure which characterizes this animnl. In none of the Protozoa already described have we found an appara- tus for forcing food into the body at one particular place. If this process were long continued, it is not difficult to 1 Mem. Boston Soc. Nat. Hist., I, 1866, p. 307. 48 SYNOPTIC COLLECTION. understand how the mouth, oesophagus, and the other tubes and sacs of the digestive system originated. After the food has been retained in the body for a time the excrement is thrown out at a place near the mouth or through the mouth itself, instead of being ejected from any part of the body, as is the rule with the Amoeba. Reproduction takes place in this .genus by longitudinal fission and by the breaking up of the body into flagellate young. The researches of Messrs. Dallinger and Drys- dale have shown that the phenomenon of fission in these minute forms " is not a mere division of undifferentiated sarcode into two parts." Before separation takes place there is always a germination of the anatomical elements which make the new monad complete, while in many instances the fission is preceded by a suddenly induced amoeboid condition. 1 The young Monosiga globulosa S. K. (PI. 51, fig. 3) is a free-swimming uniflagellate form which bears a resem- blance to Monas (PL 51, fig. i). In course of time it becomes stationary, as seen in fig. 4. Next, the stem and collar are developed (fig. 5 is the adult), the latter being the peculiar characteristic of many Flagellata but which is entirely wanting in the young Monosiga and in the adult Monas. It has been pointed out by Kent that this collar is a film of protoplasm which can be extended and withdrawn at will into the substance of the body in the same way as the pseudopodia of an Amoeba. Combined with the flagellum it serves as a most efficient trap for obtaining food. Fig. 6 is the adult of another species, Monosiga gracilis S. K., greatly magnified. The nucleus is seen near the central part of the body. The process of digestion is shown by the food particles colored blue which are circulating through the body. In this genus reproduction takes place both by longitudinal and by transverse fission and also by the breaking up of the body into flagellate young. 1 Monthly Micr. Journ., XI, 1874, p. 7. PROTOZOA. 49 We pass naturally from the solitary Monosiga to the colonial Codosiga pulcherrimus Jas.-Clk. PI. 51, fig. 7, is the single, comparatively young zoon which has broken away from its colonial home and is a free-moving animal. During its young life it swims at times rapidly with its basal end extending forward, and the flagellum following behind "and vibrating in rapid undulatory and gyratory curves as if it were the screw propeller of some sub- aqueous vessel." 1 Finding a favorable spot whereon to settle, the Codosiga secretes a stem and becomes a fixed animal (fig. 8). The "body is surmounted above by the high collar. The dotted lines irt the drawing indicate the degree of the lateral vibratile expansion of the collar. From the middle of the cone of the body extends the flagellum. Figs. 9-16 of PI. 51 illustrate the process of reproduction by fission, the stem not being drawn. At first the collar bulged as seen in fig. 9. Soon after this the flagellum grew shorter and finally disappeared, while a narrow furrow was seen in the anterior part of the body (fig. 10). This furrow extended downward, while the collar became more cone-like (fig. n). Soon after this the collar began to expand and the body was divided about half way to its base. At each free rounded end a flagellum began to be developed which kept up a trembling motion (fig. 12). The body divided mostly to the base and the collar broadened (fig. 13). The process of division next extended into the collar (fig. 14) and con- tinued, the collar growing broader and longer (fig. 15) until finally the self-division of the collar and body was complete and extended downward into the pedicel (fig. 16). A colony of two is often found; sometimes these increase to five (fig. 17), and occasionally as many as eight are produced. Fig. 18 is a free-swimming colony, Desmarella moniliformis S. K. The early stages of this species have not been observed, and therefore in the 1 James-Clark, Mem. Boston Soc. Nat. Hist., I, 1866, p. 315. 50 SYNOPTIC COLLECTION. absence of positive knowledge we can only reason from analogy in regard to the rightful position of the genus in a natural classification. In more specialized animals such as certain corals, Polyzoa, and others, the free- swimming colonies are derived from fixed colonial forms which have lost their organs of attachment. It is, there- fore, probable that when the life history of Desmarella is known it will be found that the earliest stages of the genus bear structural evidences of its descent from a stationary form. If such evidences are not obtained by accurate microscopical research, it might still be possible that they have become Vholly obliterated through the action of the law of acceleration in development. The colony of Desmarella is never large, numbering only from two to eight zoons. In the light of the Flagellata already described, the development of Proterospongia haeckeliS. K. is extremely interesting. The animal begins its existence as a single attached uniflagellate organism without a collar (PL 51, fig. 19). Afterward the collar develops, and in this stage the Proterospongia resembles a Monosiga. Next a muci- laginous film is extended around the body below the col- lar (fig* 20). By binary fission two zoons are produced (fig. 21). Figs. 22 and 23 represent small colonies and fig. 24 a large one of between forty and fifty zoons. Cells migrate from the surface to the interior and become reproductive in function. Some of the zoons in figs. 23 and 24 have drawn in their flagella and the body has assumed an amoeboid appearance. This is in prepara- tion for the encysted state (see fig. 24), after which the mass breaks up into a large number of flagellate young. All the Mastigophora or Flagellata so far described belong to the subclass Flagellidia. The following Dino- flagellidia are represented by Peridinium and the Cysto- flagellidia by Noctiluca. The species Peridinium tripos Ehr. (PI. 52, fig. i) is provided with a transverse groove. According to the PROTOZOA. 51 observations of Klebs and Biitschli a second flagellum lies horizontally in this groove which has hitherto been mistaken for a girdle of cilia. The body is covered with a cellulose (Bergh) carapace formerly supposed to be silicious or chitinous, and its shape is unique, having three horns, two of which are in front and one behind. Kent l has pointed out the isomorphic resemblance exist- ing between the bodies of the Peridinidae and the larvae of certain Echinoderms and Crustacea. The mechanical conditions for a floating existence have probably been the controlling cause of this peculiar shape of the body. PI. 52, fig. 2 (P. arcticum Ehr., dorsal view) has long arms and the serrations seen in fig. i have here become spines. According to Claparede and Lachmann these are two of a large number of varieties of the species of Cera- tium tripos. Although these two forms may occur in the same locality, the Peridinium arcticum Ehr. is found most abundantly in the colder, denser waters of the arctic seas, where its broader and stouter arms probably assist in preserving the equilibrium of the body. We come now to one of the members of the group of Mastigophora which has long been known on account of its remarkable property of brilliant phosphorescence. The Noctiluca miliaris Sur. is cosmopolitan, and to it are largely due the beautiful illuminations of the sea at night. The young Noctiluca (PI. 53, figs. 1-6) shows specializa- tion in structune by the possession of a whip and a tenta- cle-like organ near the mouth. The adult (PI. 53, fig. 7) has a transparent body in the form of a peach surrounded by a distinct membrane. The protoplasm radiates from the center of the body, and spreads itself in a layer over the inner surface of the membrane (Kent). The mouth is at the bottom of a depression where the flagellum originates (which is not clearly seen in the drawing 2 ) and 1 Manual of the Infusoria, I, 1880, p. 452. 2 See Huxley, Quart. Journ. Micr. Sci., Ill, 1855, PI. 5, fig. 3. 52 SYNOPTIC COLLECTION. near it is the "tooth" and the long tentacle-like organ which is transversely striated. The mouth leads into a tube and this to a digestive sac. 1 The reproduction of the Noctiluca has been described in detail by Cienkowski.' 2 This investigator maintains that we have here two identical histological cells blending and, therefore, that conjugation in the Noctiluca belongs in the rank of such phenomena of blending as aim at an accelerated assimilation, and that it stands in no relation with the more specialized sexual process of reproduction of the Metazoa. This view may certainly be questioned, since the act of conjugation, upon which, according to Cienkowski, the formation of swarmers seems to be in a high degree dependent, if not a sexual act, is most proba- bly the initiative process leading towards the more spe- cialized sexual process of the Metazoa. While it is true that most of the Mastigophora have only one nucleus, yet this one is not probably identical in constitution with the simple nucleus of the Amoeba or with the nuclei of a many nucleated Rhizopod, since con- jugation between the zoons of the Mastigophora is the rule rather than the exception, and this more constant differentiation in the process of reproduction is doubtless attended with a differentiation in the nature of the repro- ductive organ. Associated with this specialization of process and function there is also the structural differ- entiation of a primitive digestive system, and of a more or less stable body with its constant accompaniment, in youth as well as in adult life, of a locomotive and prehen- sile organ. For these reasons the Mastigophora ( Flagel- lata) may be considered as more specialized organisms than the Rhizopods. Although Bergh 3 has supported the opposite view considering that the Rhizopods have arisen from the Flagellata, nevertheless the burden of evidence 1 Packard, Zoology, 1886, pp. 33, 34. 2 Arch. f. mikr. Anat., IX, 1873. 3 Morph. Jahrb., VII, 1882, pp. 272, 273. PROTOZOA. 53 seems to be against this view if we maintain that the more elementary organisms came into existence first and gave rise to the secondary or more complicated forms. Surely one of the simplest representatives of the Flagel- lata, the Monas termo, already described, is much more specialized than the structureless, organless, ever-chang- ing mass of protoplasm, the Protamoeba. INFUSORIA. The cilia or short hairs that clothe the cell of an Infu- sorian, either partly or wholly, constitute one of the important characters of this most specialized group of Protozoa. We have seen that pseudopodia and flagella can be converted the one into the other, but this is not the case with pseudopodia and cilia. The latter have become permanent and unchanging locomotive organs. They move in unison after the fashion of paddles, while the flagellum may be likened to a whip. One of the commonest Infusorians to be found in stag- nant water and vegetable infusions is Paramoecium cauda- tum Ehr. (PI. 54). Although of comparatively large size, its rapid twisting motions make it difficult to observe its many interesting specializations of structure. The flagellum which we have seen so often in preceding forms has disappeared, and the body of the Paramoecium is provided with cilia which extend in longitudinal rows. Here is found greater differentiation in the digestive sys- tem, since the mouth which is at the bottom of the ciliated depression (near the lower of the two outer arrows in the left of the figure) leads into a tube that extends down- ward a short distance. Food was given the Paramoecium in the form of partly decomposed indigo obtained from maceration of the leaves of the indigo plant, also carmine from dried cochineal insects. The arrows on the left of the drawing indicate the course of the particles of indigo 54 SYNOPTIC COLLECTION. as they were whirled along by the cilia of the disc. Many of the particles are seen passing downward into the tube at the end of which they have formed a pellet that be- comes surrounded by a jelly-like substance. The arrows within the body show the definite course of the pellets in the body cavity. The nourishment having been separated from the food, the excrement is ejected at the swelling which rises temporarily on the ventral side of the poste- rior part of the body, as seen on the left of the drawing. The contractile vesicle according to Kent is normally spherical, as represented in the posterior part of the body, but under pressure it assumes the condition seen in the anterior portion of the body extending outward in the form of ray-like continuations. The nucleus, colored yellow in the drawing, is the long tubular organ with three enlargements just in front of the posterior spherical contractile vesicle. E. Ray Lankester 1 has shown in Paramoedum aurelia Mull. 2 a marked differentiation of the protoplasm into two well denned parts. The outer por- tion is bounded by a cuticle that is pierced by holes through which pass the cilia. Just under the cuticle are little sacs or tricocysts, each one containing a thread which can be thrown out, and which is helpful as a defen- sive and probably as an offensive organ. Attached to one side of the nucleus is the apparently small nucleus, the paranucleus,3 which probably arises from the nucleus. The investigations of Balbiani and others have shown that the reproductive phenomena of Paramoecium and the Infusoria generally are more complicated than those of the Rhizopods or the Flagellata. Temporary conjuga- tion takes place between the zoons of Paramoecium and 1 Encycl. Brit., ed. 9, XIX, 1885. 2 The Paramoecium caudatum of Ehrenberg is probably a variety of the P. aurelia of M tiller. 3 The paranuclei are sometimes called nucleoli. but objectionably, since the paranucleus > has nothing to do with the nucleolus of a typical cell (E. Ray Lankester, Encycl. Brit., ed. 9, XIX, 1885). PROTOZOA. 55 may last five or six days or even longer. This union brings about important changes, the nucleus is broken up, the paranuclei divide, and protoplasm may be inter- changed as wejl as paranuclei. The two zoons then sep- arate and a reconstruction of the parts takes place with rejuvenescence of the organs followed by fission. 1 While Paramoecium is a free-swimming single form in youth and adult life, Stentor polymorphus Mull. (PI. 55, figs. 1-3) is sometimes a single swimmer when young and often a stationary and colonial form when full grown. The little embryo of Stentor (fig. i) is nearly spherical in shape (the ground form of most Protozoa). Its cilia, even when within the body of the parent, are developed, but it possesses neither a mouth nor an esophageal tube. In time, however, these appear (fig. 2) ; the rounded body becomes trumpet-shaped and is often attached to some object. The Stentor then secretes a mucilaginous sheath about the posterior tubular portion of its graceful body (fig. 3). The upper anterior expansion of the trumpet has the delicate wreath of cilia and the large cilia near the mouth describe a spiral. The mouth ex- tends into a spiral tube. The protoplasm of Stentor has become differentiated to form a layer of thread-like fibrillae which extends from the anterior to the posterior end of the body and is extremely elastic. Another set of these fibrillae surrounds the ciliated disc and helps to close this region when the Stentor is contracted. This differentiated layer of elastic fibrillae is probably the initial form of the muscular sys- tem of the more specialized animals. The long beaded nucleus is seen at the right of PI. 55, fig. 3. Unlike most 1 According to Eigenmann (Bull. U. S. Fish Commission, XII, 1892), the ciliate Infusoria have two nuclei, the macronucleus and the micronucleus, the former of which is probably represented by the yolk nucleus of the Metazoa. This author gives a diagram showing the maturation, conjugation, and segmentation of Protozoa and Metazoa. 56 SYNOPTIC COLLECTION. Protozoa the Stentor divides obliquely instead of trans- versely or longitudinally. This is in accordance with the spiral structure of the Infusoria. Just above the mucilag- inous sheath the lateral line of cilia is seen to curve spi- rally ; this marks the spot where a future zoon is to arise by fission. The newly formed zoon sometimes remains with the parent, producing a small colony. Gruber l ascertained by experiment that division of Stentor took place in most cases at intervals of two days, that daughter zoons divided into granddaughters in the second day after their separation, and granddaughters in another two days into great granddaughters, and so on. In 42 out of 56 cases division took place on the second day after the preceding one. This mode of reproduction is not the only one peculiar to Stentor. A further differen- tiation in the process of fission is observable. The nucleus develops germs or embryos which, becoming detached from it, leave the body of the parent and swim freely about. Such embryos are represented by figs, i and 2 in PI. 55. We will now pass to a fixed colonial form of the Infu- soria. The student of nature may find keen enjoyment in the study of the beautiful bell Vorticellidae. These Pro- tozoa are characterized by marked specializations of struc- ture. The protoplasm of which the bell-shaped body is made has become differentiated into three parts, the cu- ticle, ectosarc, and endosarc. Furthermore, the ectosarc has undergone a change whereby the outer portion has become converted into a muscular layer which, according to some authors, extends into the stem, forming the highly contractile spiral axis. The digestive system has become developed so that there is not only a mouth opening but a distinct tube-esophagus leading downward into the body. At the mouth opening this tube flares, and the enlargement is often called the vestibule, while the con- fer, naturforsch. Gesellsch. Freiburg i. B., I, 1886, Heft 2. Engl. transl., Ann. and Mag. Nat. Hist., (5), XVII, 1886, p. 473. PROTOZOA. 57 tracted portion of the tube beyond is the esophagus proper. As yet the digestive system is not complete, there being no separate opening or anus on the surface for the exit of waste matter. If the Vorticella is given carmine or indigo, the way the food is caught by the cilia (which are borne on the thickened rim or peristome surrounding the disc of the bell) and its circulation through the ciliated vestibule and esophagus and through the endosarc of the body to its exit at the mouth, can all be observed with the microscope. With the differentia- tion of the muscular and digestive systems there is a greater specialization in the reproductive system and in the processes which lead to increase. PI. 56, figs. 1-29, taken from Everts, 1 illustrate the process of reproduction through longitudinal fission, and figs. 30-34, after Greef, 2 the process through the conjugative act. Beginning with the little ball (fig. i) which issues from the cyst, we find it a tiny mass of protoplasm showing no differentiation. It agrees structurally at this time with a cytode, since no cell wall is discovered, and it is not until the cilia are developed that it becomes a cell with a nucleus. A vac- uole appears (fig. 2), next a swelling (fig. 3), and a wreath of cilia (fig. 4). The form changes and an organism appears which is likened by Everts to the Trichodina grandinella described by Ehrenberg. This Trichodina (fig. 5) continues to grow (figs. 6-9) until transverse constriction takes place with a separation into two Trichodinas (fig. 10). Then the body lengthens (figs, n, 12) with the formation of the peristome (fig. 13), after which the stem is secreted (figs. 14-17). Fig. iya represents a stemmed Vorticella much enlarged. This form contracts (fig. 18), the body broadens (fig. 19), and the nucleus ta*kes a position at right angk s to the stem. A constriction takes place (fig. 20) which increases (fig. 21) until the. division is complete (fig. 22). A wreath of Zeitschr. f. wiss. Zool., XXIII, 1873. 2 Arch. f. Naturg., XXXVI, I, 1870. 58 SYNOPTIC COLLECTION. cilia next appears at the posterior end of the body of one of the zoons (fig. 23), the forward end contracts, the disc and cilia are drawn in (fig. 24), and finally by strong efforts the zoon frees itself (fig. 25). The remaining zoon afterward becomes free in a similar manner. The movements of the free Vorticella are lively for a time, then it becomes quiet, takes on a spherical form (figs. 26, 27), the wreath disappears and the nucleus divides (fig. 28). The shrunken cyst covering is seen in fig. 29 with seven balls within. This completes the life cycle. This species also increases through conjugation, as has been stated. A smaller zoon, the microgonidium, approaches a larger stemmed zoon, the macrogonidium (fig. 30). The basal part becomes drawn in to form the sucker by means of which the small zoon attaches itself to the side of the larger one (fig. 31). When this is done, the conical base is stretched out again, whereby a boring organ is pro- duced, and the body of the small Vorticella becomes a mere lump (fig. 32). Gradually the contents of the body pass wholly into the larger zoon, leaving only a sac-like skin (fig. 33). The bristles on this sac may be the wrin- kles of the ring-like cuticle. Finally the sac-like skin is thrown off (fig. 34), and the two animals are fused together indistinguishably. It would seem that here the whole body of the zoon corresponds to the ovum and the spermatozoon, and if so, We have as the result of their union a fertilized egg. Much difference of opinion exists, however, in regard to the real significance of the act of conjugation. But whether this act is a sexual or an asex- ual one, it can be said with certainty that the process is far more specialized than the apparently accidental fusion of the Rhizopods. Furthermore, it. is rational to suppose, as before stated, that this process is at least the initiatory leading to the complicated reproductive phenomena of the specialized Metazoa. l 1 For a discussion of this subject, see Calkins, The Protozoa, 1901, chapter VII. PROTOZOA. 59 It is interesting to note that in one species of this genus, Vorticella umbellaria C. & L., there are nemato- cysts or thread cells which are more effective weapons than the tricocysts. Each of these cells contains a spirally wound thread, like the thread cells of the more specialized Coelentera soon to be described. The compound colonial form, Zoothamnium alternans C. & L. (PI. 57), is, according to Kent, one of the most remarkable instances of polymorphism among the Infuso- ria. In this genus there are three differentiated forms of zoons. PI. 57 shows two of these forms. The large size of the macrogonidia in this species is unusual. INFUSORIA. TENTACULIFERA. The Tentaculifera are represented in the Collection by the Podophrya gemmipara Hertwig (PL 58, figs. 1-4, a-e). By the possession of cilia, the young form (fig. i) shows its probable relationship with the ciliate Infusoria. In the course of development the cilia disappear. Kent observed, however, in specimens obtained from North Wales in 1 88 1, that the embryos were provided with short tentacles either in addition to or in place of a more or less conspicuously developed ciliary covering. Fig. 2 is a young form showing the origin of the stem. The adult (fig. 3) is much more differentiated. The food- catching organs or tentacles have increased in number. Nutting 1 has given figures of another species of Podo- phrya (probably P. compressa) showing how the young embryo after becoming attached, develops a few tentacles at first, which increase in number with the growth of the animal. Besides the tentacles there are sucking tubes which broaden out at the end after the fashion of a sucker (see fig. 3). The prey is caught by the tentacles iAmer. Nat., XXII, 1888. 60 SYNOPTIC COLLECTION. and afterward sucked into the body of the Podophrya by means of the sucking tube, though the process is not well understood. Propagation takes place by the formation of buds or embryos from the oral surface. Eight of these buds are seen in PI. 58, fig. 4. The nucleus in the young forms is comparatively simple, but in the large, old specimens it has an extraordinarily complicated structure. This increase in complexity is finely shown in figs. a-e. Fig. a is a young Podophrya with a simple horseshoe nucleus ; in fig. b the nucleus has changed its form, and in fig. c it has become forked. Fig. d shows four embryos with the branches of the nucleus extending towards them, and in fig. e they have penetrated the embryos. In this sketch of the Protozoa we have attempted to point out some of the many differentiations whereby a structureless mass of protoplasm, like Protamoeba, may become a specialized organism like an Infusorian. MESOZOA. The division of animals known as the Mesozoa holds middle ground between the Protozoa and the Metazoa, and is of great importance from a phylogenetic point of view, as will be seen hereafter when the development of the egg of a Metazoan is traced. The Mesozoa are represented in the collection by Volvox globator L. No drawing can reproduce the beauty of the living Volvox. A tiny ball of vivid green, it revolves through the water with graceful and rapid mo- tions, offering a puzzle to both the botanist and the zoologist. Although claimed as a plant by a number of botanists, its morphological relations to animal forms and the history of its development lead many zoologists to place it among animals. It seems probable that Volvox has arisen from the MESOZOA. 61 Protozoa Flagellata, among which it is placed by Biitschli, who, nevertheless, says that strictly speaking the genus does not belong here, since the so-called colo- nies are in reality many-celled individuals. 1 We have in Volvox an organism of many cells which are arranged in one layer around a central cavity. This cavity is hollow in so far as it is destitute of cells, though it is filled with a gelatinous cellulose substance which is secreted by the cells and in the periphery of which they lie embedded, connected by delicate threads of proto- plasm. It has already been shown that many adult Protozoa represent the simple unfertilized egg, and that probably some of the most specialized members of this branch, such as Vorticella, reach in their development the condi- tion of the fertilized egg. If, now, this egg were to divide and the products of division remain together and arrange themselves in a layer around a central cavity, then we should have the next stage of development of the fertilized egg, known as the blastula, which is well represented by the adult Volvox. In Volvox the peripheral layer is made of flagellate motor and feeding cells called somatic cells (PL 59, fig. i). There may be 12,000 of these cells in an adult and each one has two long whips which pierce the outer wall surrounding the cells. A few of these somatic cells which migrate from the surface and are just inside of this peripheral layer have the power of dividing or of asexual reproduction, and are known as parthenogonidia (PL 59, fig. 2 a-e, illustrating the process of divisio'n) . These parthenogonidia give rise to asexual adults (fig. 3) that often contain eight smaller Volvoces which revolve within the parent, and each of these in turn contains eight more, so that three generations are represented as seen in fig. 3. When the parent capsule is ruptured, the eight smaller 1 Bronn's Thierreich, II, 1883, p. 775. 62 SYNOPTIC COLLECTION. spheres leave the parent one by one, rotating swiftly through the water. After asexual reproduction has continued for some time, cells which are apparently parthenogonidia at first become biflagellate male cells or microgonidia (fig. 4) . and large, unflagellate female cells or macrogonidia ; one of these macrogonidia (fig. 5) is being fertilized by the microgonidia. This process of fertilization is similar to that of specialized plants and animals ; after fertiliza- tion, cleavage takes place and both somatic cells and par- thenogonidia are formed before the embryo leaves the parent. After this, the young develops into a sexual adult (fig. 6). In this figure, a is a male cell seen from above ; a 2 the same from the side ; a 8 with the micro- gonidia separated ; a 4 with only a few microgonidia ; the others having escaped are moving about in the central cavity. Fig. 6 b, is a female cell ; b 2 the same with vacuoles in the inside ; in b 8 the microgonidia have fast- ened themselves on the gelatinous covering of the female cell ; sometimes three penetrate the covering and bore into the interior, when a fertilized egg results, which is the sexual method of reproduction in Volvox. The extremely interesting observation of Ryder 1 on Volvox minor shows, that, in spite of its nearly spherical form, there is a polar differentiation of the body with the specialization of possible sense organs at the anterior pole. According to this investigator the anterior pole of the blastula is always directed forward when the animal is in motion, and therefore it is this pole which is brought into the most dangerous position. Now, it is instructive to note that the peculiar organs known as " eye-spots " are developed much more at this pole than elsewhere, being r in fact, so slightly developed at the posterior pole, where there is little use for them, as to be nearly absent. There- 1 Amer. Nat., XXIII, 1889, p. 218-221 ; also Proc. Acad. Nat. Sci. Phila., May, 1889, p. 138-140. METAZOA - PORIFERA. fore it is plain, says Ryder, that if these organs are visual or sensitive to light or any other natural agent, they are best developed in just the position in which they are of the most service to the organism. METAZOA. PORIFERA. Section i (erect part). Great advances have been made in the direction of a natural classification of the Porifera since 1872, but nevertheless naturalists still differ not only in regard to the systematic position of these animals, but also in respect to their anatomical structure. 1 They are considered as members of the next more spe- cialized subkingdom, the Coelentera, by Haeckel, Leuck- art, Marshall, Polejaeff, Schulze, R. von Lendenfeld, 2 and Ganin. Marshall 3 even goes so far as to regard them as reduced members of this group, finding evidences, as he thinks, of the former existence of tentacles, thread 1 Dr. R. von Lendenfeld has given a clear and an extremely inter- esting history of our knowledge of sponges in the Introduction to his Monograph of the Australian Sponges, Proc. Linn. Soc. New South Wales, IX, part i, 1884. For the most complete bibliogra- phy on the subject, see Rauff's great work on Palaeospongiologie, Palaeontographica, XL, i893~'94. 2 According to this author the Metazoa are naturally divided into two groups or grades ; the Coelentera with a simple undivided body cavity, all the parts of which are in direct connection with one another ; and the Coelomata, which have two distinct and entirely separated body cavities, a gastral and a perigastric cavity. The sponges, according to this author, have a simple and continuous body cavity, so that they are regarded by him as Coelentera (Proc. Zool. Soc. London, 1886, p. 565). 3 Zeitschr. f. wiss. Zool., XXXVII, 1882, p. 246. Jena. Zeitschr., XVIII, 1885. See Ann. and Mag. Nat. Hist., (5), XVI, 1885. 64 SYNOPTIC COLLECTION. cells, and mesenteric pouches. This would place sponges after the Hydrozoa and Anthozoa in a natural classifica- tion, but the views of Marshall have not been established. 1 Biitschli and Sollas maintain that sponges belong to an independent phylum, and give it the name of Parazoa. 2 Owing to certain marked structural characters we have considered the group as belonging to the Metazoa, but as an independent and primitive group of this phylum having more or less remote ancestral forms among" the Protozoa. At the same time it must be borne in mind that the primitive characters are most plainly seen before the sponge becomes a sessile animal, and that after fixation takes place, certain adaptive characteristics and evidences of reduction appear. It would seem as if the Porifera and Coelentera, as descendants, speaking broadly, of the Protozoa and Mesozoa, traveled along similar roads for a short distance till the sedentary habits of the former and the free-swimming, active life of most of the latter caused a divergence of the roads. The processes by which the Metazoa have arisen from the Protozoa through the Mesozoa have not been deter- mined with certainty. The two leading views in regard to the subject are those of Haeckel and Metschnikoff. According to the gastraea theory of Haeckel the fertilized egg of a Metazoan, a sponge for example, arises from an unnucleated mass of protoplasm comparable with the Monera of the Protozoa. Becoming nucleated and fer- tilized, it may be compared with the adults of the most specialized Protozoa. This egg becomes segmented, thereby forming many similar but still united cells. These resemble remotely a mulberry, so that the egg at this stage is known as the morula. The cells arrange them- selves about a central cavity filled, with fluid, and this stage is the blastula. Next the cells at one pole of the 1 See " The Relationships of the Porifera," Vosmaer, Ann. and Mag. Nat. Hist., (5), XIX, 1887, p. 249. 2 Reasons for this classification are given in the Rep. Chall. Exp., Zool., XXV, 1888, p. xcii. METAZOA PORIFERA. 65 blastula become differentiated and turn inward or become invaginated, and the embryo possesses two layers (the outer layer or ectoderm and the inner layer or endoderm), a gastral cavity or archenteron, with an opening, the blas- topore. As the process of digestion was supposed to go on in the gastral cavity, the embryo at this stage was called the gastrula. It will be noticed, that, according to this theory, the invaginated gastrula represents a primitive stage in the development, arising directly from the blastula ; also that the archenteron and blastopore are primitive and not secondarily acquired characters. Furthermore, the proc- ess of invagination, by which these conditions have been brought about] must of course, according to this theory, be a primitive process. Haeckel maintains that the proc- ess of delamination or the cross division of cells, to be spoken of hereafter, is a modification of invagination, but does not show how the one is derived from the other. Extended observations on sponges and Coelentera proved that the occurrence of the invaginated gastrula was exceptional instead of normal, as would be expected in these, the simplest and most generalized groups. In Ascetta primordialis, one of the simplest calcareous sponges, and in the silicious and horny sponges, in the Hydrozoa and Anthozoa, the stage following the blastula is not, as a rule, an invaginated gastrula but something quite different. It is a solid, mouthless embryo, consist- ing of one layer of cells on the periphery and a mass of cells in the interior. The parenchymella theory of Metschnikoff throws light on the origin of this stage of development. The blastula, according to this author, is converted into the solid em- bryo or parenchymella 1 by the process of immigration of cells from the surface (such as was seen in Proterospongia 1 We use parenchymella (Metschnikoff) instead of planula (Lan- kester) because the theory of Metschnikoff is given the preference to that of Lankester. (See McMurrich, Biol. Lect. Mar. Biol. Lab.. Wood's Hole, 1891.) 66 SYNOPTIC COLLECTION. and Volvox) and also by the delamination of the inner ends of the ectoderm cells. The former process results from the longitudinal division of the cells, the latter from cross division. In Proterospongia and Volvox the migrat- ing cells become reproductive, but with this differentia- tion in function it is not difficult to conceive that other cells might become digestive and pass to the interior, leaving the Ipcomotor whipped cells on the surface. The fact now demonstrated, that digestion in many of the more generalized Metazoa is intra-cellular, or carried on within the cells, and not in a stomach or archenteron, strengthens the theory of Metschnikoff. In time the cells within the solid embryo arrange themselves in a layer to form the endoderm. Later an opening breaks through the two layers, endoderm and ectoderm. The resultant form is similar in appearance to the invaginated gastrula, but in this case it is clear that the endoderm is not formed as a bag-shaped invagination with a terminal opening. The parenchymella is in reality the primitive condition, arising from the blastula, and the gastrula-like stage is acquired later. It is not difficult to see how the process of immigration might apparently give rise to invagination in certain cases, since if the cells migrated en masse from one pole of the blastula instead of individually from all points of the sur- face, a form would appear resembling an invaginated gastrula. The formation of the parenchymella and the resultant gastrula-like embryo is the normal development of most of the Porifera and Coelentera, the invaginated gastrula occurring rarely, as for example in Sycandra 1 1 Dr. Otto Maas (Zoologische Jahrbiicher, Anat, VII, Heft 2, 1893) maintains that the invagination of the "ciliated" cells in Sycandra has nothing to do with the process of gastrulation, the two layered embryo being already formed, according to this author, before the occurrence of this invagination. A " fundamental simi- larity " Dr. Maas finds between the development of the calcareous and horny sponges, and he thinks that the apparent exceptions to the rule (Sycandra, Oscarella, etc.) will be found to conform to it on further study. METAZOA PORIFERA. 67 among the most specialized calcareous sponges and Ha- lisarca (=Oscarella) among the silicious group. Up to the time of the formation of the gastrula-like embryo the development of the sponge is parallel and similar to that of the Coelentera. After the gastrula-like stage, how- ever, the transformations that the young sponge goes through are peculiar to the Porifera. These stages end in the formation of an oval form with a girdle of larger cells and a circlet of cilia around what was the opening of the gastrula-like embryo, but which has been plugged up by the growth of cells in the interior. This larva is collared ; it is the typical Poriferan form and when one finds it he knows that he is looking at the young of a sponge. This little active creature is not guided by its intelligence in the search for food nor by any particular instinct. The tides and currents carry it (since its own power of swimming is not very effective), and where they flow there is always food of the right sort in abun- dance. If the little larva floats out of the proper region it would fasten itself probably to any sufficiently smooth, hard substance, and either lead a half-starved abbrevi- ated existence, or meet with an untimely death choked by muddy sediments or killed by some other equally effective agency. When about to settle, the collar spreads itself out by growth, forming the base, and by closely fitting itself to the surface excludes the water and air, thus fas- tening the body by the weight of these elements to "its selected spot as a boy fastens a sucking disk of wet leather to a stone. The cavity which appears in the body after this stage has no external opening ; the latter breaks through at the end opposite the plugged up opening of the gastrula- like embryo. The cells of its walls have flagella and collars. These organs appear at different times, and on different parts of the body, but they become perma- nent in the interior of the ampullae or little sacs after this stage and are not found, as a rule, on the membranes of other parts or on the exterior. 68 SYNOPTIC COLLECTION. The primitive and most generalized Porifera must be those sponges that in their adult form and characters most nearly approach the gastrula-like embryo. It will be seen that such sponges are the Calcarea or the group of calcareous sponges next to be described. CALCAREA. It cannot be doubted that a form existed in the past (if it is not living at the present time) which possessed the simple structure of the generalized Calcarea, but which was without a skeleton of any kind and also with- out the power of taking up foreign matter to make one. Such a sponge would be a primitive one, and its develop- ment would throw much light on the origin and classifi- cation of the Porifera. Until this gap is filled we must begin with Prophysema primordiale Hkl. (PI. 60). * Al- though this sponge never develops a skeleton, yet it pos- sesses the capacity, exhibited by a few other sponges and by some Protozoa, of taking up foreign substances (in this case both silicious and calcareous spicules) and of making a false skeleton sufficient for the support of its own body. Prophysema is a simple attached tube with one open- ing, and with the body cavity lined with flagellate cells. form was previously described by Haeckel as Haliphysema primordiale Hkl. (Jena. Zeitschr., XT, 1877). According to Kent, E. Ray Lankester, and Mobius, the type species of Haliphysema (H. tumanowiczi) is a Protozoan of the Rhizopod group. Haeckel now agrees with these authorities that the interior of this last named species is filled with protoplasm which extends from the single opening in the form of pseudopodia and that, therefore, this form is a Rhizopod, but he also maintains that in the species for- merly called Haliphysema primordiale but now named Prophysema primordiale there is a distinct body cavity lined with flagellate epi- thelium, so that this species is a true sponge. For further informa- tion see Rep. Chall. Exp., Zool., XXXII, part 82, 1889, p. 26. METAZOA PORIFERA. 69 It may be that even pores do not exist, and if so the water may be taken in and thrown out at the large open- ing, but in the absence of any special apparatus for sift- ing the water it is more reasonable to suppose that if this body is really a sponge, as claimed by Haeckel, it would when living and feeding in its native element have tem- porary pores of minute size capable of opening through the walls between the cells. These could furnish the internal cavity with food of sufficiently minute size to be handled by the flagella and to be swallowed by the micro- scopic cells of the walls. Ascetta primordialis Hkl., is the simplest form now known with certainty to be a sponge. If it were deprived of its skeleton it would represent the simplest sponge type, to which Haeckel 1 has given the name of Olynthus. The fertilized egg (PI. 61, figs. 1-3) of this species of Ascetta undergoes segmentation and a one layered bias- tula results. While still within the body of the parent cells migrate from the surface of the blastula to its interior central cavity and this process continues after the larva has passed into the water (PI. 61, fig. 4) until the cavity is filled (fig. 5). The adult Ascetta (PI. 62, fig. i ; fig. 2, the same with a portion of the external wall removed) is a simple bag which is capable of varying its form so that at times it resembles a vase, a cylinder, a pear, or even an egg. At one end it is attached, and at the other there is a large opening. The walls of the bag are thin and are pierced by numerous transient pores which are supposed to open anywhere through the walls of the body, not having any constant location. There are no persistent canals but the water passes through the shifting pores into the body cavity which is lined with flagellate and collared endodermal cells. The middle layer of cells known as the mesoderm is thin but gives rise to one, three, and four rayed spicules which are !Rep. Chall. Exp., Zool., XXXII, part 82, 1889. 70 SYNOPTIC COLLECTION. arranged in one layer. The ectoderm is colored blue in the figure, and is seen to invest the whole body and cover the projecting spicules. Ascetta represents the group of sponges known as Ascones. The " canal system " of other sponges scarcely exists in this group, since the body cavity is a sac or am- pulla without radiating canals. If we imagine a number of Ascetta-like forms budding from a common base and from each other's sides, so as to form a bushy colony, we have a sponge like Leucosolenia (No. 63), one of the commonest on our coast. This is a simple thin-walled, Calcareous sponge like Ascetta except that the young single tube gives rise to branches by budding, and these branches to others, until a colonial form is produced. PI. 63, figs. 1-3, show the structure of the adult Leucosolenia (species probably coriacea Montague). A character of this genus is the sieve which extends over the cloacal opening seen in fig. i, where a portion of the upper part of the tube has been cut away. Fig. 2 is a vertical sec- tion of one tube showing the flagellate cells of the endo- derm, the large central cavity, the ectoderm, and at the top the sieve. Rising above the sieve, the ectoderm by doubling upon itself forms a two layered ectodermal collar. In fig. 3 the sieve is separated from the tube. Its cells have a central portion containing a nucleus which is more clearly seen in one of the upper and cen- tral cells, where it is indicated by a black circle. The cells extend out into a number of processes and unite with those of other cells, thus forming a network with large openings. In this case the body of the cell forms the node, but sometimes the node is produced by the union of three cell processes. Fig. 4 is a spicule of this genus. Fig. 5 is another species of Leucosolenia (Z. dathrus O. S.) which has been described as without large openings. When seen in healthy living condition the cloaca is widely extended (fig. 6) ; when contracted the opening closes as in fig. 7. The sphincter by which the METAZOA PORIFERA. 7 1 work is accomplished is represented at the base of the collar by a black line. Several authors describe the endoderm in this genus as many layered, but Minchin proved that this appearance is wholly due to contraction. When fully expanded the endoderm has only one layer, but when contracted it is as shown in fig. 8 ; fig. 9 is a portion of the endoderm from fig. 8 more highly magnified. The genus Sycandra is one of the most differentiated of the calcareous sponges. Some of the species, like Sycandra (=Sycon) raphanus Hkl. (No. 65), are single, while other species, like Sycandra arborea Hkl., form col- onies. The egg and spermatozoon in Sycandra raphanus Hkl., are transformed cells of the mesoderm. The fertil- ized egg (PI. 64, fig. i) possesses a nucleus and is capable of creeping amoeboid movements. In fig. 2 the nucleus has divided. Fig. 3 shows the first cleavage or furrowing stage from above, and fig. 3 a the same from the side. Fig. 4 shows four cells, fig. 5 eight cells still lying in pairs ; fig. 5 a the same from the side; fig. 6 sixteen cells, fig. 6a the same from the side ; in fig. 7 a large number are rep- resented. This repeated division gives rise to a hollow sphere, the wall of which is formed by a single layer of celis. PI. 64, fig. 8, is the blastula with its eight dark granular cells surrounding a basal opening, and fig. 9 is a further developed, entirely closed blastula. In fig. 10 the embryo has become differentiated into halves unlike each other, for which reason it is known as an amphiblastula. This is probably a modification of the primitive blastula already described, and if so it is a secondary and more specialized form. The granular cells have increased in number, and are at the broader end, while flagellated cells are at the smaller end. In this condition the embryo leaves the parent. Fig. 1 1 is a more advanced stage in which the flagellated layer has become flattened ; in fig. 12, it is still more depressed, and in fig. 13 has disappeared within (see note p. 66). The larva settles mouth downward 72 SYNOPTIC COLLECTION. (fig, 14), which is filled up with granular cells. Between the two layers of cells there is a narrow bright zone which Schultze considers the first indication of the gelatinous inter-layer, mesoderm, that reaches such a great develop- ment in most sponges. The spicules appear in the mesoderm, first in the form of slender, straight little rods pointed at both ends (see fig. 15), which fact favors the view that the first formed spicules were one rayed and straight. They thicken as they grow and curve into a slightly S-shaped form. After- wards three rayed and four rayed spicules are formed, one of the arms of which extends inward, while the other three are on the surface and probably serve for protec- tion. The larva lengthens, pores form in the wall, and the large opening at the top breaks through the ectoderm. It is now clear that this opening is" not a mouth nor a primitive character, but a secondary feature, occurring in a past embryonic stage, and is in reality a cloacal open- ing for the ejection of the waste products of the body. The cells of the endoderm acquire collars and flagella. The body cavity of the young Sycandra is now a simple ampulla having as yet no branches. In this stage it is identical with an adult Ascon, like Ascetta, which it structurally represents. Later the mesoderm thickens, the pores grow into, tubes, the ampullaceous sacs are formed near the food supply, the cells of the body cavity lose their flagella, the cells of the ampullaceous sacs acquire collars and flagella, and from that time the work of taking food and digesting it for the use of the other cells is done by them. Thus the single primitive diges- tive cavity becomes a cloacal trunk, pores become tubes branching from this trunk, and the function of the cavity is transferred to the little sacs or ampullae formed in the canals as they are stretched out by the thickening of the mesoderm. This is a process of reduction resulting in transforming a normally formed, symmetric, vase- shaped, METAZOA PORIFERA. 7 single individual with one central trunk into a creature with overgrown walls to the body, with a radiating or branching cavity, and with the digestive function of the central trunk transferred to expanded portions of the branches or canals near the exterior. The whole process evidently hinges on the rapid growth of the mesoderm,. because when this is thin the food supply is close to the central cavity ; when this is thickened the pores must become tubes ; when it is still thicker, the tubes must lengthen. The food supply of the body is thus carried away from the central cavity, and it is but natural that the cells in the canals nearer the pores should get more, grow more and gradually make it unnecessary or impossi- ble for the cells farther inward to get food. These last must then necessarily suffer reduction and lose first the use and then the habit of growing out collars and flagella, and sink into the form of epithelial membrane cells. The function of the short canal leading into the ampulla from the exterior is obviously to bring food of microscopic size, and that of the continuation of the canal beyond the ampulla is to carry away the excrements of the ampullaceous cells. These cells are voracious feeders and throw out a large amount of waste matter which is carried into the great central cavity by the excurrent canals, and thence it is transported to be ejected at the cloacal opening above. We shall presently see how in other orders of sponges the law of specialization by reduction has destroyed all tendency to grow into symmetrical shapes, so that the Silicea and Keratosa well deserve the designation of amorphous or formless, so often bestowed upon them. This irregularity in form together with greater com- plexity of structure is found in Leuconia aspera (No. 66) which represents the group of Leucones, the most spe- cialized of the calcareous sponges. 74 SYNOPTIC COLLECTION. SlLICEA. We cannot pass to the silicious sponges without con- sidering briefly some of the embryological facts relating to their development. The egg of most silicious sponges in the earliest stages is solid 1 but becomes hollow subse- quently. Later a granular mass accumulates in the interior so that the egg is again solid. The endoderm is formed not by an invagination of a portion of the ecto- derm, but by delamination from the ectoderm, and it is this mass of cells cut off from the ectoderm which fills up the central portion of the young sponge. Both Hyatt and Barrois agree that no gastrula stage exists in either the silicious or the horny sponges. After the appear- ance of the ampullaceous sacs and the spicules, the larva becomes fixed by the collar at the oral end of its body. The canals and pores form and afterward, probably through the mechanical pressure of the water, the cloacal opening breaks through the ectoderm. It will be seen that here, as in the calcareous sponges, this opening is not comparable with the mouth of other animals, but is a secondary formation and in function a cloaca. Halisarca (= Oscarclla) lobularis O. Schmidt (If. dujar- dini Duj., PI. 67, encrusting a stone), may be one of the simplest of the silicious sponges. Its cells are less differ- entiated than those of most sponges. The ectodermal cells retain their fiagella throughout life, and the cells of the mes- oderm are not modified, as in the more specialized forms. 2 There is no skeleton, and in the absence of positive information it is possible that Halisarca is one of the primitive forms. Authorities differ with regard to the origin of this genus, and it is at present impracticable to determine whether it is a reduced form, a descendant of 1 Hyatt, Proc. Boston Soc. Nat. Hist., XIX, 1878, p. 12. 2 Sollas, Quart. Journ. Micr. Sci., XXIV, 1884, . 618. METAZOA PORIFERA. 75 genera with skeletal structures which has reached its present condition by reduction, or whether it is an existing representative of a primitive type which has never had any skeletal structures. Whatever way the result has been arrived at, the existing Halisarca is obviously a skeleton- less kind of silicious sponge, and can be used to show what such forms are like. It is' a fleshy animal with the typical characters of pores, canals, ampullaceous sacs, and cloa- cal opening. The genus is interesting because it increases not only by eggs but also by a process known as budding which is essentially the same as that of division so com- mon among the Protozoa. In this case, however, there is not an equal division of the body, but a part separates from the rest and becomes a new animal. SILICEA. HEXACTINELLIDA. This group is represented by fossils, and living mem- bers are mostly found in the deep seas. Although the oldest silicious sponges probably possessed separate spic- ules, yet on the death of the animal these would fall apart and be swept away and deposited along with other re- mains, so that no satisfactory inferences can be drawn in regard to the sponges possessing them. The predominating six rayed spicules of the group have been shown to be simply a modification of the three rayed form which we have found among the Calcarea. It has also been proved that the anatomical structure and the development of these sponges are in some ways like those of the calcareous sponges. For these reasons, and because the group is found in the oldest geological forma- tions, the Hexactinellida are considered as the more gen- eralized of the silicious sponges. Ventriculites (No. 68), often occurring in the chalk, is made up of six rayed spicules which are always fused together. It is more or less cup-shaped with a wide cen- 76 SYNOPTIC COLLECTION. tral hollow. In Hyalonema sieboldi Gray (No. 69), the cup-shaped body is supported on a long tuft of silicious spicules, by means of which the animal is anchored in the mud. These rooting spicules are sometimes two feet long, while the spicules of the body are varied and beau- tiful in design. The probable ancestor of Euplectella speciosa Q. & M., was one of the Dictyospongidae which were vase-shaped sponges composed of spicules that united to form a frame- work similar to that of Euplectella. This has disap- peared from the fossils but the tracery of the fibers may be seen on their surfaces. In the living Euplectella (No. 70) the delicate skeleton is covered by a grayish brown fleshy matter and skin. It is interesting to note that the young Euplectella has the spicules separated, but with the growth of the animal fusion takes place to form the deli- cate framework. The sponge skeleton consists of longi- tudinal and circular silicious strands intersecting in such a way as to form meshes. Besides these there are ridges of fibers which run spirally around the skeleton. The upper end is closed by a sieve-like plate, while at the lower end long silicious spicules extend downward to anchor the animal in the mud. In dried specimens of the skeleton these long, fiber-like spicules are usually bent upward around the base of the sponge, and they are also thus represented in drawings. Such specimens and fig- ures are misleading, since these spicules always extend downward and outward for the purpose of firmly anchor- ing the animal. An interesting case of commensalism is offered by Euplectella, since it often harbors within the hollow of its vase-like structure a little shrimp, Spongicola. In the Hexactinellida there is no drainage canal sys- tem, as the large ampullaceous sacs open directly into the great cloacal tube which is closed at the opening above by the sieve-like plate. The % members of this group resemble the Calcarea in METAZOA PORIFERA. 77 being more symmetrical and constant in form than the members of othef orders of Silicea. They also stand correspondingly near to the Calcarea in their organiza- tion, as has already been stated. The mesoderm is not so thin, but it approximates to the condition of that of the more primitive calcareous sponges, and in accord with this the excurrent canals are not found, and the ampullae open directly into the cloacal trunk in some forms. Thus the organization is just a grade more specialized than in the Ascones with their digestive cells in the central trunk, and less specialized than Sycones with their ampullae in the canals of the lateral branches of the water system. SILICEA. LITHISTIDAE. These forms have a thick stony wall and irregular spicules some of which are cleft into ragged branches. The fossil Tragos (No. 71) is a representative. It is shaped like a funnel and the exterior wall is often wrinkled concentrically. SILICEA. TETRACTINELLIDA. Tetilla sandalina Sollas (PL 72, fig. i) is a representa- tive of the simple Tetractinellida. It has a single open- ing at one end with papillae at the other. The outer portion of the sponge is soft, not differing essentially from the inner. The mesoderm is slightly developed. The ampullaceous sacs (fig. 2) with their flagellate cells are large, and open by a wide mouth into the excurrent canals. The spicules vary from a straight rod to an S-shaped form (fig. 3). They are seen in fig. 2, where the straight ones overlap, forming "spicular fibers." Tethya (No. 73; PL 74, figs, i, 2) has a spherical form with one or more small openings. The outer sur- fO SYNOPTIC COLLECTION. face of the ectoderm is differentiated into a hardened wall or cortex with a distinct fibrous layer. The skeleton in Tethya has a radiate arrangement. The spicules when typical have a long straight axis with three curved horns. Besides these there are straight spicules with both ends alike, and also star-like silicious forms. Fig. 2 is a vertical section of Tethya showing its system of tubes, the cloacal opening to one side, and the silicious threads extending from the base. The power of adapta- tion possessed by most animals in a greater or less degree is strikingly seen in Tethya. With a rounded form and a yellowish color which have given it the name of "the orange of the sea" (see fig. i), it has succeeded in secur- ing a firmer hold by means of long, tough, silicious threads (PI. 74) which act as anchors penetrating the mud and holding the growing sponge upright. The spe- cies shown has a peculiar adaptation of this habit, having a network of silicious threads like a mat of coarse wool on its base. These catch the fine gravel sifted out of the mud by the movements of the animal caused by the waves, and this gravel makes its lower side much the heavier. If now the animal is upset or swept away by the current or waves, the gravel acting as ballast will always serve to keep it right side up. One of the most complex forms of this group is Geodia (No. 75). Here the outer part is differentiated to form a cortex and the mesoderm is thick. The spicules are unusually large and can be seen with the naked eye. SlLICEA. MONAXONIA. There is no sharp line of division between the Tetrac- tinellida and the Monaxonia. Suberites (No. 76 ; No. 77, dried specimen) is instructive, since it has adapted itself to a free life on shifting sands. Its pores are so small and the structure so dense that the sand cannot pass METAZOA PORIFERA. 79 Hito the sponge, and its lightness keeps it from being buried (Hyatt, Stand. Nat. Hist, I, 1885, p. 66). The Suberitidae offer fine examples of spiral and radiate structure of the skeleton. This is seen in Stylocordyla stipitata var. globosa (PI. 78, figs. 1-3). Fig. i shows spiral arrangement of the bands of spicules in one speci- men ; fig. 2 is a longitudinal section of another speci- men, showing radiate structure; and fig. 3 is a cross section of the same, showing the longitudinal spicules of the stem by which the sponge is attached and the radiate arrangement of the spicules of the body part. The ends of the spicules of the stem which have been cut are seen near the center of the drawing. In most of the Monaxo- nia there is more or less horny cementing material called spongin. It is interesting to note that the chemical composition of this substance is similar to that of chitin, Krukenberg having given it the chemical for- mula C 30 H 46 N 9 O 13 , while that of chitin is C 15 H 26 N 2 O 10 . Another member of the Suberitidae is Raphiophora patera Gray (No. 79), which is on the top of Section i. This is one of the largest species of the Porifera and its size and shape have given it the name of Neptune's Cup. Cliona (No. 80) is a borer into the living and dead shells of mollusks, especially the oyster, and into lime- stone, etc. PI. 81, fig. i, represents the openings of the young Cliona enlarged, and fig. 2 shows the work of the sponge in the interior of the shell. Just beneath the outer surface is a series of excavations, and narrow passages connect these with another series of cavities below. When the shell is completely mined, the sponge swells out in a bulbous mass on the outside (fig. 3). Having destroyed the shell, it will takesr>nd into its body, as seen in fig. 4, which is a section of the sponge show- ing fine black sand in the tubes and cavities of the inte- rior. It also surrounds stones and takes them in, as seen in fig. 5. No. 82 is a specimen of Italian marble bored by 80 SYM OPTIC COLLECTION. Cliona. This marble lay in water seven years, during which time the borings from one and a half to two inches in depth were made. Dr. Leidy 1 states that the large and numerous shells of the dead oysters in an extensive bed planted by Beasley at Great Egg Harbor, were so completely riddled in two years by the Cliona that they were crushed with ease. The process of boring is both mechanical and chemi- cal, and the habit seems to be an acquired one which has been transmitted, Nassonow 2 stating that the young begin to bore before the formation of the spicular skeleton. The body puts forth fleshy outrunners and it is largely these that do the work. . It is also probable that an acid is secreted which aids in the work. Unlike most sponges the Cliona discharges its eggs into the water before the formation of the embryo has begun, so that the whole development goes on outside the parent. The skeleton is made up of one rayed spicules, many of which are pin-shaped. Ryder^ has shown that the protoplasm in sponges executes delicate fluctuating move- ments, so that in Cliona as in Stylocordyla and many other genera, the needles are drawn into bundles or rows extending in particular directions. In the fresh-water sponges (Spongilla, No. 83) the silicious spicules are numerous, while a small quantity of spongin is developed. These sponges, although probably derived from some marine form, yet develop a structure which is never found in the latter ; namely, the statoblasts or winter buds. These are internal buds which are enclosed in horny cases with peculiar spicules. When the sponge dies the winter buds survive ; these are so slightly affected by heat or cold that by them the perpet- uation of the species is rendered more sure. In addition iProc. Acad. Nat. Sci. Phila., VIII, 1857, p. 162. 2 Zeitschr. f. wiss. Zool., XXXIX, 1883, p. 300. 3 Amer. Nat., XIII, May, 1879. METAZOA PORIFERA. 81 to the peculiar spicules just named there are two other kinds of spicules forming the skeleton and strengthening the dermis. An interesting specimen allied to Spongilla lacustris has been described by Edward Potts. This sponge is found incrusting marine organisms such as bar- nacles and the calcareous tubes of Serpula, in the fresh water of a creek in the southwestern part of Florida. The presence of the barnacles can only be accounted for by the action of the strong southeast winds which back up the salt water into the rivers and creeks. The young barnacles, having followed the influx of salt water and attached themselves to the rocks on the bottom, may have attained a portion of their growth while immersed in fresh water after the subsidence of the salt water. If this be true it is suggestive of the possibility of the conversion of the marine barnacle into a fresh-water species. The sponges already spoken of as occurring on these animals have the peculiar habit of hiding away the winter buds within the barnacles or in the tubes of the Serpula. A sponge (Reniera), closely related to the Chalinula next to be described, is said to possess thread cells or nematocysts which were formerly supposed to be the exclusive possession of the next branch, the Coelentera, but which have already been found in the Protozoa. In this group the embryo has a pigmented spot on one end of its oval body which may perhaps be considered as an eye. 1 Chalinula oculata Pallas is of especial interest to New Englanders since it grows abundantly along the eastern coast. In this sponge the spicules are straight and exist as vestiges, while the horny matter has increased in quantity. Keller 2 has observed and figured the consecutive stages 1 Lendenf eld, Mon. Australian Sponges, Proc. Linn. Soc. New South Wales, IX, part 2, 1884, p. 324. 2 Zeitschr. f. wiss. Zool., XXXIII, 1880, p. 317. 82 SYNOPTIC COLLECTION. of development of another species, Chalinula fertilis Keller, and by so doing has thrown strong light on many important points. Besides the asexual mode of increase through budding, there occurs a sexual propagation, the latter probably taking place only in the spring. In this sponge the sexes are distinct, the females being two or three times larger than the males. As soon as the forma- tion of the egg begins the ordinary brown color of the female changes to red, becoming in very vigorous animals almost a cherry red. This color disappears after fertili- zation or at the beginning of the egg furrowing, and the female becomes ochre yellow at the time the larvae swarm out. The males do not change their color. PL 84, fig. i, is a young, unfertilized egg which possesses amoeboid movements. Fig. 2 represents a spermatozoon which reminds one of a flagellate Protozoan. Fig. 3 is a mature egg which has become spherical in form and sur- rounded by a capsule. Nutritive mesoderm cells are seen near it. The capsule is formed early and it must be assumed, therefore, that the spermatozoon pierces it in order to reach the egg within. After impregnation, the furrowing takes place quickly, and normally covers from twenty to thirty hours. It is total, but the cells are un- equal in size and there is no segmentation cavity. Fig. 4 shows the first two furrowing cells ; fig. 5, the stage with four cells lying in a plane. In fig. 6 (figs. 6-9 drawn without capsule) these cells have arranged themselves in a pyramidal form, the large cell being the parent cell of the endoderm. Fig. 7 has seven cells and fig. 8 fourteen . cells. Here the two large endoderm cells are partly surrounded by ectoderm cells. In fig. 9 the endoderm forms a central mass of cells and appears at the peri- phery as a plug. The other cells on the surface are ecto- dermic. 1 1 According to Wilson (see " Notes on the Development of some Sponges," Journ. of Morphology, V., no. 3, 1891, p. 516), it is probably not the endoderm that protrudes at this pole, but the ectoderm, which is greatly flattened over this region. METAZOA PORIFERA. 83 PI. 84, fig. 10, is a later stage still enclosed in the cap- sule ; the cylindrical ectoderm cells have already devel- oped whips ; the plug is strongly pigmented. In the mesoderm, flint needles (colored blue in the figure) have begun to form. They are at first irregular and scattered. It is a fact of great significance that the spicules appear before the formation of the cementing material, spongin. The latter is probably a secretion of the mesoderm, and is deposited according to need in layers around the spicules (see PI. 84, fig. 20). This furnishes a strong argument in favor of the view that a part at least of the horny sponges are descendants of the silicious sponges. PI. 84, fig. ii is the free-swimming larva which has escaped from the capsule and the body of the parent. As it swims the pointed end is directed forward. No inner cavity yet exists. Figs. 12 and 13 represent the larva just before becoming attached. It is now much flattened (fig. 12, peripheral view; fig. 13, broadside). About thirty-six hours after settlement, it looks as shown in fig. 14. The isolated spicule in the larva is seen in fig. 15, still lying within its cell. No cavity had appeared two and a half days after settlement. Fig. 16 is a view of the young sponge (natural size) five days after becom- ing attached. The ampullaceous sacs with whipped cells are now numerous and open into a wide cavity. The cloacal opening arises on this day (the fifth) by the body cavity breaking through the outside wall, and on the same day and by a similar process the pores are formed (see fig. 17, a vertical section of the sponge at this stage). When the canals and pores appear the stream of water acts effectively upon the position of the needles and fortns radial lines. Figs. 18 and 19 give us the external and internal structure of the adult. Fig. 20 shows the spicules of the adult bound together by spongin. Fig. 2 1 represents a small female colony. No. 85 is a larger adult. The following is a summary of the time required for the six stages of development, as given by Keller. 84 SYNOPTIC COLLECTION. First : Duration of the furrowing period, thirty hours. Second: Swarming out of the larvae, continuing to the end of the second day. Third : Free-living larva stage during third, fourth, and fifth days. Fourth : Settlement on fifth day. Fifth : Formation of the ampullaceous sacs and of the body cavity on the eighth day. Sixth : Break- ing through of the cloacal opening and the formation of the skin pores. According to Dendy l the West Indian Chalininae offer the strongest arguments in favor of the view that the Keratosa have descended polyphyletically from sev- eral distinct groups of silicious sponges. In different species of the same genus he has traced the gradual reduction and disappearance of the spicules until forms are reached like Spinosella maxima Dendy, and Spinosella plicifera D. & M., which sometimes still contain traces of the spicules imbedded in the horny fiber, and apparently on the verge of disappearance, while at other times they contain no spicules whatever, and yet the specimens with spicules and those without are specifically indistinguish- able. No. 86 Tuba (= Spinosella' 2 ) vaginalis Lam. var. sororia, and No. 87, Tuba scrobiculata D. & M., show the variation in form peculiar to this genus of sponges. KERATOSA. The Keratosa are not found in a fossil condition. They are probably the specialized descendants of silicious forms, some of which have already been described. This view finds additional confirmation in the researches of Maas 8 who states that the embryological development 1 Trans. Zool. Soc. London, XII, part 14, 1890. 2 Vosmaer in 1885 substituted the generic name of Spinosella for the familiar one of Tuba. 3 Zool. Jahrb., Anat., VII, Heft 2, 1893, p. 331. METAZOA PORIFERA. 85 of the horny sponges is so similar to that of the silicious sponges that a precise description would be mere repeti- tion. According to this author the horny sponges are more nearly related to the silicious than are the silicious sponges among themselves ; so that a separation of an independent order of fibrous sponges does not seem justi- fied from a morphological point of view but only as a matter of convenience. One of the simplest sponges belonging to this group is Ammolynthus prototypus Hkl. (PI. 88, fig. i). A cross section (partly diagrammatic) is seen in fig. 2 which exhibits the egg with its nucleus and nucleolus. The sponge that grows from this egg consists of a simple tube with one large opening (fig. i). The body cavity is sim- ple (fig. 2) and without branches, the canal system being similar to that of the Ascones among the Calcarea. The walls of the tubular body are pierced by many pores through which the water enters ; this flows into the large central cavity which is lined with endodermal flagellate cells. No skeleton is developed, but the animal takes up Radiolarian shells (see figs, i, 2) and in this way makes a false skeleton. This sponge and the other species of the group to which it belongs are remarkable examples of symbiosis already seen among the Protozoa (see p. 44) . In place of the horny fibers of other keratose sponges it has the tubes of a hydroid which serve the purpose of a support- ing framework. Ammosolenia (PL 88, fig. 3) is similar in structure to Ammolynthus but is a colonial sponge corresponding to the Leucosolenia in the calcareous group. An extremely interesting form is represented by PI. 89, fig. i. Here in Darwinella australiensis Carter, we have a sponge with spicules made of spongin instead of carbonate of lime or silica. No spicules are wholly min- eral, however, and this being the case, it is not difficult to understand, as pointed out by R. von Lendenfeld, how 86 SYNOPTIC COLLECTION. the inorganic silica may have been replaced by the organic horny material. The spicules vary but are built on the triaxon plan. Besides the horny spicules there are horny fibers which do not unite to form a network. We have here just those conditions which one might expect to find in a transitional form between the silicious and the horny sponges where the silica is replaced by spongin, and where the horny skeleton has not yet become the complex network seen in the more specialized genera. The canal system of Darwinella is simple and im- branched and the ampullaceous sacs are of large size. Another genus, Aplysilla, is placed near Darwinella which it resembles by having large ampullae, simple canals, and isolated erect horny fibers, but it differs from this genus by having no horny spicules. These have wholly disappeared and the skeleton, now entirely fibrous, is destined to develop in succeeding more specialized forms until a labyrinthian network of fibers is the result. Hircinia campana Hyatt (No. 90), is normally vase- shaped, but is subject to great variation, sometimes becoming tubular, as proved by specimen No. 91. It has been shown l that although this variation is great as compared with the more specialized invertebrates, never- theless a formula may be given which expresses the possible range of variation in every species. One of the simplest of the Hircinia (If. cactus) has a skeleton com- posed of simple main fibers which contain foreign sub- stance and slightly branched connecting fibers which are free from foreign particles. The spongin of which the fibers are composed is stratified and a granular axial thread is present. In Verotigia fistnlaris Bon. (Nos. 92, 93), the fibers are so large that their tubular form can be seen with the eye. They are loosely put together, but the main and 1 Hyatt, Mem. Boston Soc. Nat. Hist., II, pt IV, no. 5, 1877, p. 483- METAZOA PORIFERA. 87 connecting fibers are not easily determined. The two specimens show variation in form. Carteriospongia radiata Hyatt, var. dulcina (No. 94), is one of the most beautiful of horny sponges. It grows upward from a stem in the form of delicate fronds. The surface of the fronds is smooth and the fibers are so closely woven that they form a veil on the upper side, and sometimes on the lower, which bridges over the inequalities of the interior. Large specimens of Carterio- spongia may have as many as sixty branches. The most complex representatives of fhe group of horny sponges belong to the family Spongidae. Nos. 95 97 are Spongia tubulifera Lam., var. rotunda Hyatt. No. 95 is a vertical section through the body of the sponge, showing the flesh, the large central tubes with radiating tubes, and the openings of other tubes which run in all directions through the sponge body. No. 96 is a dried specimen of the flesh and skeleton, and No. 97 is the skeleton with the flesh removed. The fibers are fine and soft. No. 98 is another species of the same genus, S. molissima Schm., in which the fibers are dense and closely woven. This collection of sponges with the supplementary drawings illustrates the following points. The sponge animal arises from an egg which resem- bles many adult Protozoa. The egg in its further development passes through a blastula stage, thereby representing the adult Volvox of the Mesozoa. The blastula stage is succeeded in most sponges by a solid parenchymella stage. The endoderm arises by a process either of immigration or of delamination of cells, and a two layered organism is produced. Subsequently an internal cavity and an external mouth opening are formed. This stage is transient, since by the formation of a middle layer or mesoderm the adult always becomes a three layered organism. 88 SYNOPTIC COLLECTION. The flagellate and collared cells of the endoderm are unique, and may indicate genetic relationship with the Flagellata of the Protozoa or parallelism of development in two different groups. When fixation takes place, the sponge settles with its mouth downward, after which the cloaca breaks through the ectoderm, proving thereby that this opening is not a primitive but a secondary character. The primitive, adult, ancestral form of the group of sponges was a simple, skeletonless, tubular organism with a water system consisting of transient pores, and a central cavity with no canals and no ampullaceous sacs. This primitive form is inherited with certain modifica- tions by many of the simpler members of the different orders of sponges. By a differentiation of this primitive form the most specialized sponges with canals and sacs have arisen. The calcareous and silicious sponges are considered the most generalized and the keratose sponges the most specialized for the following reasons. The calcareous sponges, as a group, are most rudimen- tary in structure. The Silicea are found in ancient geo- logical formations and in the deep seas of to-day, while the Keratosa do not occur as fossils. - The history of the development of the transitional forms, the silica-and-keratose sponges, proves that the silica appears first and afterward the spongin is devel- oped. METAZOA COELENTERA. 89 \ COELENTERA. Section 2. HYDROZOA. HYDROPHORA. If we consider the Protozoa arid Mesozoa as constituting the trunk of our genealogical tree and the Porifera as the first short branch sent off from this trunk, then the Coelen- tera through comparative simplicity of structure represent the second branch. Although an unbroken line of descent from the many-celled, one layered Mesozoan to the Hydro- zoa (the most generalized class of the Coelentera) cannot be traced, yet it is not difficult to conceive of an animal like a primitive Hydroid arising from an ancestral form similar to that which produced in course of generations the simplest, tubular sponges. The two theories held by naturalists in regard to the origin of the Metazoa have already been stated (see p. 64). Briefly summarized it may be said that, according to one view, the one layered blastula gives rise to a two layered invaginate gastrula, the ancestral form of which, the Gastraea, has not been discovered. The gastrula in turn produces a form that is two layered in youth and three layered in the adult, like the sponge. According to the second theory, the blastula gives rise to a solid parenchymella which in time becomes two lay- ered and hollow and afterward is provided with an open- ing. In this case no primitive invaginate gastrula exists. The Hydrophora or Hydromedusae, now to be described, illustrate almost universally the second mode of develop- ment, and some naturalists l even maintain that not a single invaginate hydroid gastrula has been observed. 1 W. K. Brooks, Mem. Boston Soc. Nat. Hist., Ill, no. 12, 1886, p. 401. 90 SYNOPTIC COLLECTION. It is probable that the ancestor of the class of Hydroids, like that of the Porifera, was a fleshy animal without either a horny or a stony skeleton, but under ordinary conditions such a form would not be preserved. The skeleton of a primitive hydroid, Corynoides calicu- laris Nich. (No. 99 ; PI. 100, drawing of the same en- larged), is found as a fossil in the ancient geological formations. It was tubular in form, chitinous in structure, and striated on the outside as shown in the figure. The body of the aclult, one may infer from the skeleton, was tubular with an opening or mouth at one end raised, it may be, on an oral cone, the base of which may or may not have been surrounded by tentacles. This mouth probably led into a hollow body cavity. The basal portion of the tubular skeleton ended in two little spines, but there is no indication in the fossils that the animal was attached, and therefore the conclusion may be drawn that it was free- moving both in youth and in adult life. Nothing is known of the development of this ancient hydroid, but the simplicity of its structure as shown by its skeleton leads to the natural supposition that the develop- ment was primitive ; that is, without a metamorphosis of any kind. The descendants of this single marine form may have budded, and if the new zoons remained together a free- moving colony would arise similar in some respects to Graptolites (Nos. 101-104). According to Lapworth, 1 who has studied the develop- ment of the Graptolitidae, the colonies arise from a " small, pointed, triangular or rather dagger-like 'germ'," which he calls the sicula. It may be that this youthful stage is the representative of the single, ancestral Corynoides, al- though this is not proved. In time a solid axis or virgu- la develops in the outer wall of the sicula and often extends beyond it at either end. A small bud usually appears at . Mag., London, X, 1873. METAZOA COELENTERA. 91 the larger end and this forms a protecting cup or theca. While this is the rule, there are genera in which the bud arises from the middle portion of the sicula and from the smaller end. As a general thing the sicula is retained unchanged in form by the mature animal, but in a few species it is absorbed or becomes obsolete in old age. The group of Monograptidae is represented by Mono- graptus (No. 101), which has a single series of cups or thecae on one side and at their base a well developed virgula. Wiman l has made a study of the Diplograptidae which are represented in the Collection by Diplograptus (No. 102). He finds that these forms arise in the same way as the Monograptidae, and it seems probable that they are the specialized descendants of the last named group. The sicula of Diplograptus (PI. 103, fig. i, young, dorsal view; fig. 2, adult, front view) consists of two parts : the proximal portion marked diagonally ; the distal, longitudinally (seen in fig. i). The sicula is open at its base, and at one side is the rod or virgula. This sicula gives forth one bud only, which does not develop into a canal as heretofore supposed, but into a cup or theca. Fig. 3 is a front view of the first theca budded from the sicula, and fig. 4 is a dorsal view of the same. The circular perforation in fig. 3 marks its origin from the sicula. The theca grows downward, then outward. Fig. 5 is the first theca with three spines, two of which are united by a thin skin. The theca is seen to have grown outward and upward. In time this theca buds and the second theca grows around to the opposite side. This process is repeated, the second giving rise to the third, the third to the fourth, so that the statement can be made that each theca comes from the next more proximally situated theca of the opposite side and not from a canal. Fig. 6 1 Journ. of Geol., II, no. 3, Apr.-May, 1894, p. 267. See also Holm, Geol. Mag., London, Decade IV, II, 1895. 92 SYNOPTIC COLLECTION. is a front view showing especially the form and position of the second and third thecae, and fig. 7 shows four thecae and the partly imbedded sicula. In fig. 8 it is seen how the thecae extend more and more over the sicula until the latter becomes incorporated in the main mass or hydro- zoma. At this time the distal end of the virgula begins to grow, and it becomes stouter the farther it gets from the point of the sicula. In fig. 9 the distal end only of a hydrozoma is drawn, the proximal end with its imbedded sicula not being represented. It is interesting to note that Ruedemann J has shown that some species of Diplograptus occur in large compound colonies consisting of many branches or stipes united in the center as seen in PI. 104. These hydroids probably consisted of nutritive zoons possessing tentacles for catch- ing food and cavities for digesting it. Besides these there were doubtless other zoons which were reproductive in function. The latter in the more specialized forms may have freed themselves from the colony and swum away as independent organisms or medusae. That medusae lived as far back as the lower Cambrian has been proved by Walcott. 2 As we come down to the present time we find the probable representatives of the Graptolites in the Plumularian hydroids, Aglaophenia (No. 105) and Sertularia (No. 106; no. 107, dried specimen). The former has the thecae on one side of each branch, while Sertularia has them on both sides. These hydroids have reduced characters, since the reproductive buds or gono- phores, which in a progressive form swim away as free medusae, here never become detached. These are finely shown in Sertularia argentea Ellis and Sol. (No. 106). !Rep. State Geol. N. Y., 1894, p. 219. 2 U. S. Geol. Surv., Monograph, XXX, li METAZOA COELENTERA. 93 HYDROPHORA. HYDROCORALLINAE. The position of the Hydrocorallinae in a natural classi- fication has not been determined with certainty, l but they are placed here provisionally. Millepora is a colonial form which secretes a calcareous skeleton (No. 108). The zoons occur in groups (PI. 109, fig. i), each group consisting of a short central zoon and six or eight long ones about it ; in fig. i one of the latter is omitted for the sake of clearness. The central zoon, called the gastrozooid, possesses a mouth and four or more tentacles, while the surrounding dactylozooids are mouthless. The body cavities of these zoons are not di- vided by partitions, but are continuous into the canals which traverse the surrounding flesh or coenosarc in every direction. The dactylozooids apparently catch the food and carry it to the gastrozooid, and are therefore tentacular in func- tion while they bear numerous small tentacles on their sides. One of these is represented in fig. 2, much enlarged. Figs. 3 and 4 represent a nematocyst taken from the ten- tacles; these are like those of most hydroids. Fig. 3 repre- sents the thread within the cell and fig. 4 shows it thrown out. Besides this kind of thread cell there is another in Millepora found near the bases of the zoons and shown in figs. 5 and 6. Fig. 7 is a cross section of a gastrozooid showing on the outside the ectoderm nematocysts in dif- ferent stages of development. Inside are the large trans- parent cells which are called gastric because they occur only in the gastrozooid and therefore may be digestive in function. The muscles by which the zoons contract are shown in fig. 8 which is a diagram of the longitudinal 1 For a discussion of the different views on the subject, see Moseley, Chall. Rep., Zoo!., II, part 7, 1881, p. 98; also Hickson, Quart. Journ. Micr. Sci., XXXII, 1891^.375; Proc. Zool. Soc. London, 1898, p. 246. 94 SYNOPTIC COLLECTION. bundles of fibers that arise from the radiating vessels, the latter being the continuations of the body cavities of the zoons. Besides the longitudinal muscles the circular muscles are shown. Fig. 9 is a vertical section through the decalcified superficial fleshy lamina which was living before decalcification began ; the ectoderm is distinctly seen, also the retracted gastrozooids on the right (one of the four tentacles is not drawn) , and the retracted dactylozooid on the left. The network of fleshy tubes is finely seen and where these are cut the dark pigment cells of the endoderm are visible. The limy network of the skeleton is shown by the open spaces between the fleshy tubes. Figs. 10-15 represent the skeleton. Fig. 10 is a fragment magnified two diameters, showing the branch- ing form and the pores scattered over the surface. Fig. 1 1 is a drawing of a thin section of the skeleton showing its nbro-crystalline structure. Fig. 12 is a complete group of pores consisting of one central gastrozooid pore and eight dactylozooid pores, greatly enlarged. The structure is brought out clearly by figs. 13-15. Fig. 13 is a verti- cal section of the skeleton. The large gastrozooid pore is seen in the middle and the floor that separated the last formed living chamber from those below which are dead. The branches of the canal system are plainly shown. Fig. 14 is a horizontal section cut parallel to the outer surface, showing part of a group and the system of canals. In fig. 15 the pores and canals have become filled with black foreign matter making a cast of the canal system of the flesh or coenosarc. Nothing was known of the generative organs of Millepora till 1884, when Quelch l found among the young branchlets of the hard skeleton large ampulla- like cavities similar to those that had previously been observed in a related group, the Stylasteridae. These cavities contained gonophores and in the specimen exam- ined only the male elements, spermatozoa, were found. i Nature, XXX, 1884, p. 539. METAZOA COELENTERA. 95 In 1886, Hickson 1 observed that the generative prod- ucts of Millepora were formed in little capsules in the walls of the canals and that both male and female cap- sules were found in the same canals. This author has also described and figured 2 the medusae of Millepora. These are formed by a metamorphosis of an ordinary zoon, usually a dactylozooid but sometimes a gastrozooid. They occur in ampulla-like cavities of the coenosarc. When they leave the parent form they are without the radial or ring canals, veil (velum), and sensory organs common to the more specialized medusae. It may be that these develop later while the animal swims about in the water, or it may be the medusae remain in a primitive condition. PI. no, fig. i, is a section through a medusa of Mille- pora murrayi. It has a well developed manubrium (the part hanging down like a handle), containing a cavity continuous with a large canal of the parent stock; the rounded masses on either side of the manubrium repre- sent the sperm, and the outer encircling portion the um- brella. The ectodermal parts are shaded pink and the endodermal blue. Fig. 2 is a section of an older medusa that is not organically connected with the colony at any point and is probably ready to escape. Distichopora (No. in) has a beautiful pink skeleton. The openings are not in groups as in Millepora, but are either in rows along the edges of the branches or arranged in wavy lines over the surface. The rows of pores con- sist of a middle row of gastrozooids with dactylozooids on either side. The ampulla-like cavities in this genus are on one or both faces of the branch. The gonophores are not metamorphosed dactylozooids, becoming free-swim- ming medusae, but are modifications of the ova and sperm cells in the canals of the coenosarc which never become detached. !Proc. Roy. Soc. London, XL, 1886, p. 325. 2 Quart. Journ. Micr. Sci., XXXII, 1891, p. 375. SYNOPTIC COLLECTION. H YDROPHORA. NARCOMEDUSAE. The Narcomedusae are a group of living hydroids which throw considerable light on the evolutionary history of the Hydrozoa, as pointed out by Brooks. 1 PL 112, figs. 1-19, represents the development of Aeginopsis from the egg to the hydra stage. Fig. i is the fresh laid egg; fig. 2, the two celled stage; fig. 3, the beginning of the second furrowing stage ; fig. 4, the four celled stage ; fig. 5, the beginning of the third furrowing stage; fig. 6, the eight celled stage; and .fig. 7, the beginning of the fourth furrowing stage ; fig. 8 is the sixteen celled embryo in cross section; fig. 9, the embryo composed of about thirty-two cells. Figs. 10 and 1 1 show isolated cells of the same embryo; fig. 10 is the endoderm cell just formed, and fig. ii, the completed or finished endoderm cell. Fig. 12 is the embryo of fifty-nine cells ; fig. 13 is the two layered larva; fig. 14, the larva lengthened; fig. 15, the further developed larva; figs. 16 and 17, cells of the same (16, cell of ectoderm; 17, of endoderm) ; fig. 18 is the larva with two tentacles and no mouth; fig. 19, the larva of the fourth day. It is now a hydra witji a shortened body, a mouth at the end of a long oral cone, at the base of which are tentacles. Unfortunately Metschnikoff did not figure the further development of the hydra into the medusa. The tentacular zone, however, grows out into an umbrella which carries the tentacles with it; sense organs and a veil or velum are soon acquired, and the hydra becomes converted into a medusa. Its parts can be plainly traced in the medusa, and the difference in external appearance is due mainly to the great develop- ment of the middle layer or mesoderm which forms the umbrella. If now we could find a genus where the larva, while yet a hydra, should fasten itself to some object, iMem. Boston Soc. Nat. Hist., Ill, no. -12, 1886. METAZOA COELENTERA. 97 either an animal or a rock, and should bud, then a colony would arise. This is precisely the case with Cunocantha ( Cunoctantha^} octonaria Hkl., or Cunina octonaria McGrady, the latter name being the more familiar one. PI. 113 gives the development of this genus, and No. 114 is the medusa of Cunina campanulata Ed. PI. 113, fig. i, is the larva. (Figs, i and 3 are drawn in a position to show the hydra-like larva; fig. 5, to show the medusa-like adult.) The aboral end of the body is shortened; there are two opposite tentacles which have clusters of thread cells at their ends. The oral cone which extends above is very long and at its end is the small mouth. The internal cavity is lined with large endodermal cells seen in the figure. The ectoderm is thin excepting at the extremities of the tentacles and at the aboral end of the body. This larva now enters the bell cavity of Turritop- sis, another Hydrozoan, and fastens itself by its tentacles, as seen in fig. 2. The oral cone becomes extremely long, is inserted in the mouth of Turritopsis, and two more tentacles grow. This stage is more clearly seen in fig. 3. Either before or after the secondary tentacles appear, the hydra puts forth buds from the aboral end of the body and a colony is formed as seen in figs. 4 and 5. A rim grows out from the body in the tentacular zone and this rim becomes divided into eight lobes, each one of which contains a branch from the central digestive cavity. The bud, thus changed, escapes into the water and is a medusa (PI. 1 13, fig. 6) with a long oral cone. Later the umbrella enlarges while the oral cone remains about the same as seen in fig. 7, which is an aboral view of an adult medusa. Each member of the colony becomes converted into a medusa, so that here we have budding and a primitive kind of metamorphosis but no alternation of generations. The Cunina parasitica, however, which attaches itself 1 H. V. Wilson, Stud. Biol. Lab. Johns Hopkins Univ., IV, no. 2, 1887, p. 95. 98 SYNOPTIC COLLECTION. to one of the Geryonids, remains a hydra, while its buds develop into medusae and swim away. Here, then, we have the metamorphosis of Aeginopsis converted into the alternation of generations so peculiar to this class of ani- mals. The objection may here be urged that the genus Cunina is parasitic or semi-parasitic in habit and that therefore it is a specialized and reduced genus. The stock form Aeginopsis, which is the key to our classification, is not a parasite at any period of life. Cunina octonaria does not seem to be much more of a parasite than an animal that happens to settle upon something, it may be another animal or a rock, for a short time. It is free at first, then attaches itself to an animal for a brief period, and after- ward lives an independent life. The species Cunina par- asitica is a parasite, as its name implies, but it illustrates so admirably what seems to us the next step in the evolu- tionary development of this class of animals that we use it provisionally, until at least a non-parasitic form can be found which will illustrate the same type of life history. HYDROPHORA. TRACHOMEDUSAE. The Trachomedusae are represented in the Collection by Carmarina ( = Geryonia) hastatalAld. (No. 115), which corresponds to Aeginopsis among the Narcomedusae in passing through a metamorphosis without budding or alternation of generations. It is an interesting fact that the larval Geryonidae have solid tentacles, while in the adults these are replaced by hollow ones. The Tracho- medusae include Aglaura whose complete development has been worked out by Metschnikoff. PL 116, fig. i is the fresh laid egg drawn from life; fig. 2, the same treated with osmic acid ; fig. 3 shows the beginning of .segmenta- tion ; fig. 4. the egg divided into two cells; fig. 5, the four celled stage ; fig. 6 is the third furrowing stage from METAZOA COELENTERA. 99 above; fig. 7, the same in profile; fig. 8 is the beginning of the fourth furrowing stage ; fig. 9, the same a half hour afterward ; fig. 10, the same three quarters of an hour after fig. 8. The rotating movements of the embryo begin at tfns time. Figs, n and 12 are further developed stages; fig. 13 is the morula stage; fig. 14, the larva with two layers; figs. 15 and 16 are the free-swimming larvae; fig. 17 is the larva with nettle capsule ; fig. 18, a further developed larva; fig. 19, a larva with projecting tentacles ; fig. 20, larva with gastro-vascular cavity.; fig. 21 shows the beginnings of the wider tentacles; fig. 22 is a larva forty-five hours old, and fig. 23, one fifty-two hours old; fig. 24 is a larva with eight tentacles, and fig. 25, one with twelve tentacles; fig. 26 is the same in profile, and fig. 27, the disc of same from above. Fig. 28 is the adult Aglaura. In some of the most specialized genera of the Tracho- medusae there are various secondary modifications, and the adult characteristic of a peculiar bell-shaped body appears in the young. HYDROPHORA. ANTHOMEDUSAE. Acaulis (PI. 117, figs. 13) may be one of the primi- tive forms of the Anthomedusae, although as yet it is not positively known that the medusae become free. Fig. 1 represents a portion of a young Acaulis. The blunt posterior end is shown with both the temporary tentacles, which are short and swollen at their ends, and the perma- nent ones which are long and slender throughout. Figs. 2 and 3 probably represent the adult, one much enlarged, the other natural size. The mouth is at the smaller end with numerous papillae about it ; the temporary tentacles of the young have disappeared. Below the papillae are the clusters of gonophores which Stimpson observed "in an advanced stage of development, soon to become free- 100 SYNOPTIC COLLECTION. swimming individuals." The adult Acaulis (figs. 2, 3) is attached by its base. Among the Tubularians there are some species which develop free medusae, while others are more or less reduced. In this group the zoons are at the ends of long tubes, and those with the reproductive function are some- times in the form of clusters of grapes. Corymorpha nutans Sars (No. 118), is a solitary Tubu- larian. The natural size is represented at the left, while just back of it -is the same greatly enlarged. At its base are many thread-like organs for anchoring the animal in the sand. A number of short tentacles are seen around the mouth, and farther down there is another circlet of much longer feelers. Between these two sets of tentacles are the medusae buds. These have only one tentacle when young and attached and also when mature and free (No. 118, at the right). This model clearly shows the four radiating canals and the manubrium. In Turritopsis (No. 119) we have a greater complexity of the hydroid stage than that previously described. The free-swimming embryo does not grow into a hydra, but, spreading out more or less like a root, attaches itself and buds forth hydras. In .this way a colony arises. The hydras in their turn bud medusae which swim away. Here we have a modification of the phenomenon of alter- nation of generations and a root-like form existing between the parenchymella and the hydroid stage. The life history of Podocoryne is especially interesting. It begins its existence as a hydroid, then forms a colony by budding, and puts forth secondary buds in the form of medusae. These swim away, but after a time they take on reduced characters. The veil disappears, the bell is reversed, shrunken to a shapeless mass, and turned back with the tentacles (PI. 120). The eggs are seen in the walls of the manubrium which hangs down below the shrunken bell. This figure is instructive as showing the difference METAZOA COELENTERA. 101 between a reduced and a primitive form. While resem- bling each other in a general way, close examination reveals here, as in the great majority of cases, the evolu- tionary stages through which the hydroid has passed. Cladonema (No. 121) is another Tubularian which illustrates suppressed development. The model repre- sents the hydroid of natural size (a) and enlarged (b) ; c and d are the young and the adult medusae. When old, the medusa tends to lose its umbrella and takes on other reduced characters. Tubularia larynx E. & S. (No. 122), is one of our common hydroids and is a good example of suppressed development. The zoons rise from basal stolons which form a network and grow to the height of four or five inches. The network and ascending tubes are protected by a chitinous sheath, but this does not cover the main body of the zoon, often called the hydranth. Each hydranth has a double row of tentacles. Below these on the reproductive zoons are the grape-like clusters of medusae which never become detached. The scarlet colored masses of Clava (No. 123) are abundant on the New England coast. The larval hydra becomes attached and forms a colony like the parent. The model represents the nutritive zoons with many ten- tacles, and the reproductive zoons are in clusters beneath ; as these are medusae which never become free, we have here another illustration of suppressed development. HYDROPHORA. HYDROIDEA. The fresh-water Microhydra ryderi Potts, 1 is described here since it produces free-swimming medusae 2 , which, 1 Amer. Nat, XIX, 1885, p. 1232. Quart. Journ. Micr. Sci. XXX, 1890, p. 507." 2 Potts, Amer. Nat., XXXI, 1897, p. 1032. 102 SYNOPTIC COLLECTION. so far as our knowledge goes, is not true of Protohydra or Hydra. In the hydro id state Microhydra is greatly reduced, since it possesses neither chitinous coat nor ten- tacles, and is also without a pedal disc. According to Potts this species was found living as a messmate among colonies of Bryozoa " where its own disabilities as a food collector .... were supplemented by the life sustaining currents induced by its more active neighbors." This habit has doubtless brought about this reduced structural condition. The marine and fresh-water Protohydra of Greef is rep- resented by Pis. 124 and 125. It is less reduced than Microhydra, by possessing a chitinous coat and by living in both salt and fresh water, but, like this genus, it is with- out tentacles. PI. 124, fig. i represents Protohydra con- tracted into a spherical form. Its color is a fox brown. Fig. 2 shows the little animal in the act of stretching out, and in figs. 3 and 4 it is still more extended. In the lat- ter figure the mouth is seen at the top and the foot disc at the posterior end. Fig. 5 is a Protohydra that has swallowed a Copepod larger than its own body. The long bristles at the posterior end of the crustacean extend from the mouth. Inside the hydroid the outlines of the Cope- pod can be made out and also one of its red eyes. Fig. 6 is the forward end enlarged, showing the edges of the mouth without even the vestiges of tentacles. Fig. 7 is a portion of the body showing the network of cells. In these figures the nearly colorless ectoderm is seen and the underlying pigmented endoderm : no cuticle is repre- sented excepting in fig. 8 (which is the posterior part of a specimen that has been paralyzed in fresh water) where it is visible outside of the cellular ectoderm. According to Greef 1 this is most constant at the end of the body where it has separated from the epithelium and surrounds the body like a tube. Towards the forward end it lies 1 Zeitschr. f. wiss. Zool., XX, p. 1070. METAZOA COELENTERA. 103 so close to the surface that one may doubt its existence. Singularly enough Protohydra increases by cross division. PI. 125, fig. i shows the beginning of the process. The constriction goes on until the two are nearly ready to separate" (figs. 2,3) when the two break away and live independent lives. This process of reproduction may indicate affinities with the Protozoa, some of which, as we have seen, increase by transverse division, or it may be possible that Protohydra is a reduced form of the Discophora, a group which multiplies by cross division with alternation of gen- erations, and one which will be described farther on. We consider Hydra as a reduced form although most of the books place it as a primitive hydroid. Observa- tions 1 have shown that the ectoderm of the embryo of Hydra excretes a chitinous coat. This is probably the vestige of the horny covering or exoskeleton of the Tubu- larian hydroids. Later this sheath is thrown off. We have already seen that primitive forms are, as a rule, marine, and the Hydra has been found but once in brackish "water, 2 being preeminently a fresh-water animal. The middle layer which exists under varying forms in the Coelentera consists in the Hydra of many delicate fila- ments extending from the cells of the ectoderm. These may represent either rudiments or vestiges of cells and in the present state of our knowledge it is impossible to say which they are with absolute certainty. It would seem, however, from observations already made, that they are vestiges and that we are not dealing here with a prim- itive adult two layered* animal, whose proper taxonomic position would be before the sponges, but rather with a modified and reduced hydroid form. 1 See Kleinenberg, The Hydra, 1872. Huxley, Anatomy of Invertebrate Animals, 1878, p. 121. Korotneff, Embryology of the Hydra, Zeitschr. f. wiss. Zool., XXXVIII, 1883, pp. 314-321. Brauer, Zeitschr. f. wiss. Zool., LII, 1891 ; abstract, Journ. Roy. Micr. Soc., 1891, p. 609 ; also Amer. Nat., XXV, 1891, p. 1027. 2 Stand. Nat. Hist., I, 1885, p. 77. 104 SYNOPTIC COLLECTION. The adult Hydra (No. 126, natural size; PI. 127, fig. i) has a tubular body with a mouth at the end of an oral cone. At the base of the latter is a circle of tenta- cles. These never possess the primitive character of solidity but are from the first hollow prolongations of the body wall. This mature form buds into other hydras (No. 126) ; it also reproduces sexually. PI. 127, fig.. 2, represents the Hydra, enlarged, with a swelling which is an ovum or egg, and nearer the tentacles are two smaller swellings that are sacs containing the spermatozoa. This animal never buds a medusa; in fact, no medusoid char- acters have been observed in the embryo, and for this reason some naturalists maintain that the Hydra cannot be a reduced form. The difficulty of explaining the non- existence of medusoid characters in the young, however, is not so great as that which the advocates of the primi- tive character of Hydra find in explaining the existence of the chitinous sheath in the embryo. There are forms in other classes of the animal kingdom which have become so extremely reduced as to lose even in their embryo- logical development the .characters of their previously differentiated condition, and it seems probable that the Hydra can be numbered among these forms. HYDROPHORA. CAMPANULARIAE. The Campanulariae are represented by Obelia (No. 128), Tima (No. 129), Gonionemus (No. 130), and Gonothyraea (No. 131 ; PI. 132). * In Obelia we have a complicated structure and life history. Its egg develops into a parenchymella which becomes attached. It now forms a "star-shaped root" or hydrorhiza from which the first zoon is budded ; afterward other zoons bud out from it and a colony is produced. Here, as in Turritopsis of the Tubulariae, we have a precocious embryo and an alternation of generations between the parenchymella and hydra stages. METAZOA COELENTERA. 105 The hydras budded from the star-shaped root become differentiated into nutritive and reproductive zoons, the latter giving rise to medusa buds. These medusae are free in Obelia, Tima, and Gonionemus (No. 130, show- ing young stages), but in Gonothyraea (No. 131 ; PI. 132, enlarged) they are reduced and always remain attached. DISCOPHORA. We have shown that the complex larval colonies and specialized adults of the Hydrophora may have arisen from the comparatively simple Aeginopsis. It may be possible also that this same form, or one similar to it, produced along another line of development the Disco- phora. The egg of most Discophora, like that of Aegi- nopsis, develops into a free-swimming, ciliated, solid embryo or parenchymella. This attaches itself and in time becomes a hydra. By a remarkable growth the height increases greatly. The body then begins to divide horizontally, and the saucer-like divisions free themselves as medusae. Thus it is seen that one hydra gives rise by the process of division to several medusae. The latter produce eggs which develop into the hydra form, so that we have an asexual hydroid generation alternating with a sexual medusa generation. The Discophora are repre- sented in the Collection by Cyanea capillata Linn. (No. 133, greatly reduced), Aurelia flavidula Per. & Less. (PI. 134), and Aurelia aurita Lirwi. (No. 135, young medusa; No. 136, adult). It is interesting to note that the adult medusa of Cyanea sometimes attaches itself quite firmly to an object. One observed by Dr. Robert T. Jackson, at Eastport, Maine, in the summer of 1892, was settled so firmly that it required considerable force to separate it from the tub in which it was living. While attached, its resemblance to a hydra was striking. The segmentation of the egg of Cyanea is regular and 106 SYNOPTIC COLLECTION. results in the formation of a blastula. Cells then migrate into the interior and afterward arrange themselves as an incomplete layer on the inner side. Here, then, in Cyanea we have the stage following the blastula produced by the immigration of cells and not by the invagination of a layer. The parenchymella, after swimming about freely, settles down and forms a cyst. Soon after leaving the cyst a mouth opens and four tentacles are developed. 1 The development of Aurelia illustrates that of most Discophora. PI. 134, fig. i, represents one of the early stages of the egg, and fig. 2, the fully grown egg. Seg- mentation takes place and when the embryo leaves the parent it swims about by means of cilia (fig. 3). Grad- ually the two layers are formed (fig. 4) , then the digestive cavity (fig. 5). Afterward a depression in the outer sur- face of the inner wall marks the position of the future mouth (fig. 6) ; in time the outer wall is pierced and the mouth and passage leading to the digestive cavity appear. The embryo becomes elongated (fig. 7) . It now gives up its free life. According to Prof. Louis Agassiz, " it settles down upon its narrow end ; it wavers, and sways to and fro as if it were trying to force its way downward into the substance upon which it has fastened itself, and then, as if dissatisfied with the promise of a good basis for its foun- dation, it suddenly loosens its hold and swims away to another locality, there to repeat the same kind of examina- tion until finally, after perhaps half a dozen attempts .... it finds a suitable place to rest upon permanently." The changes which take place at this time are more clearly seen in figs. 8-n which are taken from the development of Cyanea already briefly described. Fig. 8 represents the embryo with a chitinous base which serves to strengthen its attachment. In fig. 9 the two tentacles are just beginning to grow. Fig. 10 has four tentacles (well provided with thread cells) and a wide opened 1 See Smith, Bull. Mus. Comp. Zool., XXII, 1891, p. 124. METAZOA COELENTER A. 107 mouth. Fig. 1 1 is a so called scyphostoma with four tentacles extended, surrounding a mouth at the end of an ora'l cone. It is interesting to note that the scyphostoma of Cyanea has a horny sheath similar to that possessed by the Tubu- lariae. No such sheath has been observed in Aurelia. One feature of the anatomy of the scyphostoma is of im- portance. Four ridges extend from the inner wall into the central cavity and divide its outer portion into four chambers. These are probably the beginnings of the mesenteries of the Anthozoa. The scyphostoma of Aurelia (fig. 12) normally develops sixteen tentacles. It is converted into the so called stro- bila in the following way. A horizontal constriction takes place just below the outer base of the tentacles (fig. 13) ; this is followed by another (fig. 14), and a third (fig. 15), and still others, until nearly the whole body is divided into saucer-like sections. At the base of these sections or discs (fig. 1 6) is developed a circle of tentacles similar to those at the top of the scyphostoma when it began to di- vide. Below this circle of secondary feelers is the rem- nant of the old scyphostoma. The strobila stage succeed- ing the scyphostoma is now completed. The uppermost and oldest disc which has become eight lobed, separates first, then the others follow in succession, fig. 17 rep- resenting the last disc about to drop off. This free stage of the Discophoran is known as the ephyra. After sepa- ration the ephyra turns over (fig. 18, enlarged ten diame- ters, with the lips of the mouth prominent) and is a well developed medusa (fig. 19, natural size). The parts are better seen in the larger species, A. aurita Linn. (Nos. 135, 136). The most important organ of the adult is the umbrella ; this is usually divided into eight lobes (No. 136). Hanging from the center of the lower side are four long oral appendages. A system of tubes extends from the central digestive cavity to the circumference, and alter- nates with another system which connects with the large genital organs on the dorsal side of the Aurelia. 108 SYNOPTIC COLLECTION. Aurelia generally develops with alternation of genera- tions, as above described, but in isolated cases the devel- opment is accelerated, the hydroid stage being omitted, and the medusa develops at once from the egg. In Pelagia noctiluca Pe'r. & Less. (No. 137), the sessile hydra stage is always omitted and the parenchymella de- velops without intermediate forms into the medusa. This process is not comparable with the simple, primitive de- velopment of ancestral forms, nor with the direct develop- ment of Aeginopsis; neither can it be compared with the indirect development peculiar to those forms which pass through an alternation of generations, nor with the sup- pressed development observed in Hydra. It is rather an illustration of accelerated development which character- izes not the primitive but the secondary and specialized members of a group. A more complicated condition is found in Rhizostnma pulmo Linn. (Nos. 138, 139) in which the margins of the lips have become united so that the food is taken in through a large number of minute openings in the tenta- cles. Haliclystus auricula Clark (No. 140), is our common Lucernarian. It is a beautiful green medusa about an inch in diameter and is fastened temporarily by a sucker on the smaller end of its bo^ly. The habit of creeping peculiar to the adult Haliclystus has become fixed in the young, so that the latter is not free-swimming but crawls over eel grass from an early age. This is also true of the young of Lucernaria, which is not provided with cilia but creeps over surfaces. The adult Lucernaria (No. 141) is divided into eight lobes. The cavity of the oral cone communicates with a central chamber whence four wide chambers pass into the lobes. METAZOA COELENTERA. 109 SlPHONOPHORA. There is a good reason for placing the Siphonophora as the most specialized group of the Hydrozoa, since the proc- ess of budding which we have found in the larval Hydra is carried back to a still earlier stage and exists in the embryo itself. This precocious germ develops into a com- plex colony of hydra-like and medusa-like zoons. Velella mutica Bosc (No. 142) in addition to a float has a triangular sail. According to A. Agassiz, Velella has much in common with the Tubularians, the young medusa resembling in a marked degree the medusae of that group. In the adult Velella a single feeding zoon extends downward from the lower side and around it are many small appendages in the form of delicate threads which bear tiny medusae buds ; these separate and swim away. The float above is surmounted by the sail (finely seen in the alcoholic specimen, No. 142) which, according to Agassiz, 1 is left handed ; that is, the sail runs northwest and southeast, the longitudinal axis of the float being placed north and south. In 2500 specimens thrown on the beaches at the Tortugas the position of the sail was the same, showing that this character has become so firmly fixed in the organization that it is not subject to variation. Porpita linnaeana Less. (No. 143; No. 144, preserved specimen; No. 145, model of P. umbrella Esch.), proba- bly possesses a sail in youth which is lost in maturity. It has a central disc, the upper side of which is corru- gated. The internal structure is somewhat complex. Long and short tentacles extend from the edge of the disc (No. 145), and these are provided with knobs which can be seen flattened in the preserved specimen (No. 144). Near the disc and at the base of the tentacles are the 1 Mem. Mus. Comp. Zool., VIII, 1883. 110 SYNOPTIC COLLECTION. feeding and reproductive zoons. The latter give rise to medusae buds which may be seen in different stages of development in the living animals until finally they become detached and swim away. Physalia, or the Portuguese Man-of-war (No. 146; No. 147, P. arethusa Till.; No. 148, model of P. pelagica Linn.), has a beautiful pear-shaped float surmounted by a crest or sail, well seen in No. 147. According to the observations of Huxley on young Physaliae it is probable that the float represents the primary Hydra. At the broader end of the lower side of the float are different kinds of zoons; these perform a different kind of work and are therefore unlike in structure. Prof. Agassiz observed that the largest zoons are on the windward side of the animal and are provided with tentacles which vary in length from 20 to 50 feet. The feeding zoons are of two kinds, and besides these there are medusa buds which do not break away as free medusae but are modified into swimming or propelling bells. Agalma rigidum Hkl, (No. 149), is a complex organ- ism. It has a flexible hollow stem which is divided into two parts and which bears all the appendages. At one end the stem enlarges to form the air-bladder or float which is reduced and apparently too small to be function- ally useful. The two parts of the stem are called the nectostem and polypstem. The nectostem carries bodies which resemble medusae but which are without a mouth or stomach. If originally medusae, they have become reduced into propelling organs or swimming bells. The polypstem has covering scales probably for protecting the bodies beneath them. These bodies are of three differ- ent kinds: nutritive zoons, small organs called tasters which, according to Haeckel, 1 have a sensory function acting as organs of taste or sight, and sexual bells or 1 Chall. Rep., Zool., XXVIII, part 77, 1888, Siphonophora, p. 16. METAZOA COELENTERA. Ill zoons. The first have long tentacles and supply nourish- ing fluids to the whole colony, pouring them into the cavity of the stem, the common reservoir from which the swimming bells and other zoons draw. The sexual bells are male and female and each female bell contains one egg. Apolemia (No. 150) is another float-bearing Siphono- phore in which the polypstem has the covering scales arranged in clusters with the tasters, feeding and repro- ductive zoons. Abyla pentagona Esch. (No. 151), undergoes an addi- tional process in the course of its development. Each segment of the Siphonophore becomes detached and lives an independent life. It is a feeding zoon with two loco- motive bells for swimming, in which are the reproductive organs. In this changed condition some of the parts may become greatly altered in form. CTENOPHORA. The Ctenophora are interesting since they possess characters in common with the Hydrozoa, the Worms, and the Echinoderms. It may be they have arisen from the Anthomedusan, Ctenaria ctenophora, and, if so, they are the most differentiated of Medusae. On the other hand, they have certain structures peculiar to the Turbel- larian worms, while the possession of a digestive and water vascular system in communication with each other points to a relationship with the Echinoderms. 1 Accord- ing to Chun, 2 the development of the egg of the Cteno- phora is similar in the different genera, but the varia- tions appear during the postembryonic development. The group is represented in the Collection by Pleuro- 1 A. Agassiz, Mem. Amer. Acad. Arts and Sci., X, no. 3, 1874, p. 379- 2 Fauna und Flora des Golfes von Neapel, I, Leipzig, 1880. 112 SYNOPTIC COLLECTION. brachia rhododactyla Ag. (No. 152), Cestum veneris Less. (No. 153). Idyia roseola Ag. (No. 154), and Beroe ovata Esch. (No. 155). Pleurobrachia rhododactyla Ag. (No. 152), is frequently seen off the New England coast. Its transparent body is spherical, with eight rows of comb-like structures or plates extending from pole to pole. These are, in reality, cilia which have become united, as shown by the development of the animal. They constitute the peculiar characteristic of this group, giving it the name Ctenophora. The ex- tremely long tentacles may extend from the body or else be tucked away out of sight in two lateral pockets. It has been found that another Ctenophoran, Bolina, is so similar to Pleurobrachia when it leaves the egg, that one cannot be distinguished from the other except that the compression of the body in Bolina is in a plane at right angles to that of Pleurobrachia. The postern bryonic de- velopment, however, produces marked changes of form, complex windings of . vessels, and the almost complete disappearance of tentacles which are at first developed like those of Pleurobraehia. Cestum veneris Less. (No. 153), is instructive on ac- count of its phylogenetic relations to other Ctenophora. There are few groups of the animal kingdom where the postembryonic metamorphosis so strikingly recapitulates, even in the details of organization, the adult forms of more simply organized groups, as do the larval stages of Cestum and the lobed Ctenophora recapitulate the adult stages of the generalized Ctenophora. 1 The adult Cestum has distinct bilateral symmetry. Its long, belt-like appearance has won for it the name of Venus's girdle. Eight rows of plates or combs extend longitudinally down the body, and these aid in locomotion. The mouth is near the middle of the belt-like body and possesses two tentacles which extend from a pocket. 1 Allman, On the Development of Ctenophora, Journ. Linn. Soc. London, Zool., XVI, 1882, p. 106. METAZOA COELENTERA. 113 Idyia roseola Ag. (No. 154) and Beroe ' ovata Esch. (No. 155) are elongated in form and both are without tentacles. Sections 3, 4. ANTHOZOA. ALCYONARIA. It is reasonable to suppose from what is already known that the ancestral form of the Anthozoa possessed a simple, tubular, fleshy body with a mouth at the end of an oral cone, at the base of which was a limited number of solid tentacles. Such a form would resemble closely the scy- phostoma of the Hydrozoa, and the majority of naturalists consider this as the ancestral form of the Anthozoa. If we imagine the oral cone of the scyphostoma turned inward, we have an internal bag hanging within the body cavity. Again,- if we suppose that the fleshy walls or mesenteries which are indicated in Cyanea (see p. 107) grow longer and join the central bag, then we have the hydroid plan of structure converted into the Actinian plan. This is a crude but graphic way of illustrating the hydroid and the Actinian type of structure and the possible conversion of the one into the other, although it must be remembered that there are no embryological facts to prove that these changes actually took place. 1 This early ancestral form probably followed essentially the same path of development as the hydroid, since the Actinian of to-day passes through the blastula, parenchy- mella, and secondary gastrula (not invaginated) stages. While, however, the parenchymellaof the hydroid is usually produced by the immigration of cells from the surface to the interior, that of the Anthozoa is generally made by delamination of the inner ends of the ectoderm cells. This process is brought about through differentiation of IE. B. Wilson, Phil. Trans., CLXXIV, 1883, p. 762. 114 SYNOPTIC COLLECTION. these parts of the cells, owing to the accumulation in them of food material. It is probable from the evidence now at hand that the ancestral form above described, developed four mesen- teries. The Hexactiniae, to be described farther on, pass through a stage with four mesenteries, which antedates the Edwardsia stage of eight mesenteries. This form may have given rise to a branch which through continued specialization reached the condition now shown in the Alcyonaria. It is customary to consider the Alcyonaria as more specialized than the Hexactiniae, and for this reason they are generally placed after this group; but set ting aside their variety of form and delicacy of structure, they seem in reality more simple, especially when the single, generalized Alcyonarians are considered. There is also another good reason for placing the Alcyo- naria as the more primitive group. Recent investiga- tions 1 upon Alcyonaria and the ancient tabulate corals tend to prove that the latter group (with the exception of a few species) are ancestral forms of the Alcyonaria. For this reason some of the tabulate corals have been taken from the Zoantharia where hitherto they have been placed, and are here considered as the primitive fore- runners of the Alcyonaria. Cladochonus ( = Pyrgia) michelini M.-Ed. & H., is a single, trumpet-shaped form when young (PI. 156, fig. i, natural size; fig. 2, enlarged), and though without pores, walls, or horizontal floors, called tabulae, it is probably related to Aulopora (No. 157) and the other tabulate corals. When mature it forms a simple colony and the zoons are attached by processes which extend from the lower surface. These are seen in PI. 156, figs, i, 2. 1 Sardeson, Ueber die Beziehungen der fossilen Tabulaten zu den Alcyonarien. Neues Jahrb. f. Min., Geol. u. Pal., Beilage Band X, Heft 3, 1896; see also Moseley, Chall. Rep., Zool., II, part 7, 1881, p. 102. METAZOA COELENTERA. 115 AuJopora serpens Goldf. (No. 157) begins as a single form, then by budding, a creeping, irregular colony is produced. The origin and structure of a compound coral is illustrated by Pleurodictyum lenticulare Hall (PL 158, figs. 1-9). The first coral animal that started the colony was single. Its skeleton was shaped like an inverted cone smooth in the earliest and ribbed in the later stage (figs. 1,2, 3). At first the interior is simply granulose. but above the middle portion the granules are arranged in rows which are probably the beginnings of walls. When limy walls exist in the Alcyonaria, they riiay be called pseudosepta, since the true septa of the Hexactiniae correspond in disposition and number to the fleshy mesenteries, which cannot be said of the walls of the Alcyonaria in general. These rudimentary walls are without pores and the whole skeleton is covered by an external limy layer, the epitheca. Thus it is seen that the primitive ancestral form of corals, as proved by this first stage of the compound coral, is extremely simple, imperforate, and without tabulae or well developed walls. In the next stage a bud appears which is in direct communication with the parent form, giving rise to an opening or pore in the wall of the latter (fig. 4). This is the Aulopora stage which is seen more clearly in fig. 5. Some doubt exists in regard to this figure, but in all respects excepting the position and direc- tion of the bud, this form agrees with Pleurodictyum lenti- culare and may therefore be regarded as one of its early stages. The buds appear alternately (figs. 6, 7, 8) until a circle surrounds the original form (fig. 9). The second stage is now completed. The colony increases twice in diameter until the mature condition is reached. The origin and growth of the colony of Michelinia con- vexa d'Orb., are shown diagrammatically in PL 159, figs. 1-7. In fig. i the first corallite is represented in the cen- ter with its circle of corallites which have arisen alter- nately, as in Pleurodictyum lenticulare. Michelinia, how- ever, advances farther than the last named coral and 116 SYNOPTIC COLLECTION. builds up a large colony by a process of intermural bud- ding. Fig. 2 shows how the buds are given off between the walls of the coral Utes, truncating three angles of the parent form. Next, three more buds appear, truncating the other three angles and pushing the original circle far- ther away (fig. 3). Fig. 4 shows the circle of intermural buds larger in size, while the buds between the walls of the original circle (three of which are seen in fig. 3) have been formed. These have increased in size in fig. 5. In fig. 6 all these buds have grown and the corallites of the original circle are separated not only from the parent form but also from one another. Fig. 7 gives a vertical view of the same, the numbers 1-6 corresponding with the numbers of the views seen from above. These figures illustrate finely how the shape of the corallites is due to pressure. Favosites (No. 160) is a compound colony like Miche- linia. Its development follows the same general law that governs the intermural budding of Michelinia, but is more complicated, owing probably to acceleration in de- velopment. Girty 1 has shown that the colony springs from a single animal which is similar in general aspect to the original zoon of Pleurodictyum. This zoon is pros- trate, slightly curved at first, and is attached by its dorsal side. When full grown the zoon is more erect and gives off four buds from its dorsal side. Each is connected with the parent form by means of a pore. Next, five buds appear in the peripheral spaces between those already existing. It is not until there are nineteen buds that the original one is surrounded. In this one-sided or unilateral budding Favosites differs from the last two colonies de- scribed. The generalized members of the living Alcyonaria the Proto- Alcyonaria are the three genera Monoxenia, Hartea, and Haimea; of these, Monoxenia is represented in the Collection by a drawing. It is unfortunate that 1 Amer. Geol., XV, Mar., 1895. METAZOA COELENTERA. 117 scarcely anything is known of the development of these primitive forms, since this knowledge would doubtless throw light on the phylogeny of the Anthozoa. , Monoxenia (PI. 161, greatly enlarged) never secretes a skeleton or any hard parts. Its tubular fleshy body has only eight tentacles (PI. 161) and these are hollow pro- longations of the internal cavity (PI. 162, fig. i, longi- tudinal section of the body) . The internal structure is simple, since there are only eight mesenteries (PI. 162, fig. 2). These bear clusters of eggs which are also seen in fig. i. The cross section is made near the central part of the body cavity which is marked by the dotted line. It cuts through a mesentery on one side and between two mesenteries on the other. Hartea is another simple form with eight tentacles and mesenteries, but in this case the base of the body and the tentacles are provided with star-shaped spicules. Haimea has variously shaped spicules and this gen us also possesses thread cells or nematocysts. In these three genera no ciliated groove (siphono- glyph) at one end of the mouth opening has been described, and probably none exists. The last two gen- era have a skeleton consisting of spicules. They are found only on the base or in the body walls and are never secreted in the body cavily ; there are therefore no false nor true septa. This can be said not only of these genera but also of all living Alcyonaria, and it is prob- able that this changed and reduced condition of the skeleton has been brought about since the tabulate ancestors of the Alcyonaria flourished in Palaeozoic times. From single forms we pass to simple colonies. Cornu- laria cornucopiae Lam., is a simple colony without spic- ules but with more or less horny matter. It is interesting to note that in this species the ectoderm secretes a horny sheath (PI. 163, fig. i) which reminds one of the external skeleton of the hydroids. 118 SYNOPTIC COLLECTION. A related genus, Clavularia crassa M. & K. (PI. 163, fig. 2), is a simple colony with retractile zoons. It has spicules but no horny sheath. In Clavularia viridis Q. & G., the first zoons spring from the basal stolon, but higher up they are united by simple tubes from which other zoons are budded (see PI. 164, fig. i, showing the skeleton of a zoon that has budded from the connecting tube). The grooves on the surface of the skeleton mark the position of the eight mesenteries within. The skel- eton consists of a coriaceous substance with a few scattered spicules, and is without openings, therefore imperforate. Clavularia glauca Hickson 1 ( = Anthelia glauca Savig.) (No. 165) puts out a fleshy membrane, the coenosarc, from the bases of the zoons ; this fleshy floor is provided with nutritive canals and secretes the limy coenenchyma. The organ-pipe coral, Tubipora hemprichi Ehr. (No. 1 66), when young has a long, tubular, fleshy body with the mouth in the middle of the oral disc surrounded by eight tentacles. The latter are fringed with small papil- lae, each one of which has a tiny opening at the end. The basal portion of the body sends out a fleshy layer which extends over the surface of the rock and from which other zoons are budded. As the colony increases in size this flat lamella ceases to grow and its work of giving origin to new zoons is at an end. Around the oral end of the body there spreads out a rim (No. 166). This may surround neighboring tubes or fuse with adjacent rims, thereby forming horizontal platforms from which other zoons arise. The spicules first appear singly in the mesoderm of the base and walls of the tubes and of the cross platforms, but during the growth of the animals they become united by the serrations of their edges to form a solid skeleton (N"o. 167). The sutures between the spicules can be 1 See Trans. Zool. Soc. London, XIII, 1892, p. 333. METAZOA COELENTERA. 119 plainly seen with the microscope ; they extend crosswise, as do also the long axes of the spicules. Occasionally, according to Hickson, they project into the cavity of the coral animal and look like the so called " septa " of Syringopora. No true septa are developed in Tubipora but within the tubes are found variously shaped tabulae, some flat and others funnel-shaped. It is an interesting fact that at the free end of the zoon the spicules are sep- arate as they were in the single form that started the colony. The danger of multiplying species that really do not exist in nature has recently been pointed out by Hickson, 1 who states that the principal character which has been used for distinguishing species of Tubipora is the diameter of the zoQn walls, "and this character in every specimen depends entirely upon the situation on the reef in which it happened to grow." "Our desire to make new species," says this author elsewhere, "seems to have blinded us to what is perhaps the most important feature of Zoophytes the infinite variety of growth they may exhibit to meet the varying conditions of their existence." 2 Parakyonium elegans M.-Ed. & H., (No. 168) is a colo- nial form with a spicular skeleton. The lower, stem-like portion is more dense than the upper part. and is without zoons, while the small branches which are given off from the upper portion are covered with zoons. Most of this part can be withdrawn to the stem. The zoons have very long tubes which can be seen in a vertical section extend- ing from the stem to the surface. Surrounding these is a thick coenenchyma which reaches up to the retractile por- tion. The body cavities communicate with one another by a system of nutritive canals. Alcyonium palmatum Pallas (No. 169, the remaining Alcyonaria are placed, on 1 A. Willey, Zoological Results, part 4, Apr., 1900, p. 493. 8 Trans, and Ann. Rep. Manchester Micr. Soc., Address of Presi- dent, 1899. 120 SYNOPTIC COLLECTION. account of their shape, in the erect portion of Section 3) resembles Paralcyonium. The colony is supported by a short stem which is often without zoons and broad- ens out into several lobed masses which are thickly covered with coral animals. This genus is sometimes imbedded in sand while other species attach themselves to the stems of plants. Ammothea nitida Verr. (No. 170), may have finger-like projections extending from a flat base. The zoons in this case are not retractile. Spongodes celosia^Less. (No. 171), is a colonial form in which the cortex of the stem and branches contains large spicules. The zoons are not retractile and their tops are protected by spindle-shaped spicules. Virgularia (No. 172) bears the zoons nearly.sessile on the central stem. This genus with the one that follows, is among the simpler forms of the Pennatulidae and they are both found in deep water. Kophobelemnon (No. 173,^. stelliferum O. F. Mull.) has the central stem thick and bears large retractile zoons. The more complex Pennatulidae are represented by Pen- natula aculeata Dan. & Rev. (No. 174), Pennatula phospho- rea Linn. (No. 175), and Pennatula rubra Ellis (No. 176). In this genus there is a long central stem with well developed zoons on more than a half of its length. The stem is deeply grooved on the dorsal side and the lower portion is sunk in sand and mud. These zoons are dimorphic, some being sexual and others without repro- ductive organs. In Renilla, (PI. 177 ; Nos. 178, 179), the sexes are dis- tinct and the eggs and spermatozoa are discharged at the same time, fertilization taking place in the water. It is interesting to note that the segmentation of the egg is so extremely variable "it is safe to say no two eggs ever develop in precisely the same way." The following life history illustrates the good results which may be obtained when naturalists cooperate for a METAZOA COELENTERA. 121 common object. Three investigators 1 worked together on the eggs of Renilla, keeping them under continuous observation, and "were thus enabled to determine with all possible certainty the fact that at least five or six well- marked modes of yolk cleavage with many minor varia- tions, may occur as normal phenomena of development, that the segmentation may be at first equal or unequal, complete or partial, regular or irregular, and that a great amount of variation exists in the duration of the various stages of activity and quiescence." PL 177, figs. 1-14, illustrates the consecutive stages of development in one individual, the time required being 115 minutes. The egg first divided into eight spheres (one third of the specimens examined divided in this way, but usually this stage is skipped and the egg cleaves at once into sixteen spheres). When the sixteen-sphere stage is reached the process of delamination begins. This process does not go on simultaneously in all the spheres but occurs later in some cells than in others. Fig. 15 is a section of the embryo in which the inner ends of the cells are separating or have just separated from the outer portion. The cavities seen in the figure are caused by shrinkage. Fig. 16 shows the process of delamination completed. At this time the egg consists of a solid mass of cells in which there is no trace of the segmentation cavity. The cells of the outside and of the central mass grow smaller in size as they increase in number. Fig. 17 gives in outline the shape of a larva twelve hours old. When the embryo is about twenty hours old a change begins to take place, and a few hours later the endoderm appears by a differentiation of those cells of the central mass lying just under the outer layer. This is well seen in figs. 18 and 19. Fig. 20 is a twenty-four hours old embryo. It is now covered with cilia which at first do not possess the power 1 See E. B. Wilson, Phil. Trans., London, 1883, p. 723. 122 SYNOPTIC COLLECTION. of motion, but afterwards become active, propelling the larva through the water. When the larva is twenty- eight hours old the ends of the ectoderm cells are swollen and bulbous, as seen in fig. 21, and the ball-like portion separates off to form the supporting lamella or mesoderm (fig. 22, m). At the end of forty-eight hours all the central cells not used in the formation of the endoderm have been absorbed as food by the endoderm cells and the central region is an empty cavity. In this case, as pointed out by Wilson, digestion in the young Renilla is intra-cellular or amoeboid. This is the most primitive mode of digestion and is probably inherited by the Pori- fera and Coelentera from the Protozoa. Usually between the fortieth and fiftieth hour the internal bag is formed and the central cavity is divided into chambers by mesenteries. The cells at the large end of the body increase rapidly and are pushed inward in a solid mass (fig. 23,^), forming a plug. In time a narrow cavity is seen in its center (fig. 24, c), This cavity has no communication with the exterior for twenty to twenty-five hours. At the end of this time the cavity breaks through and a mouth is formed ; afterward an opening occurs at the lower end, placing the internal bag in communication with the central cavity. As already stated, the mesenteries appear at the same time that the bag is formed. They consist of eight thick plates- of endoderm cells which extend down from the oral end of the body and are of different lengths. These are seen in fig. 25, which is a cross section of the anterior part of a forty-eight hours' larva, and in fig. 26, a cross section of the posterior portion of a four days' larva. In the living animal thes.e mesenteries arise as bilateral organs ; that is, they appear one on either side of the median plane of the body. (The figures 25 and 26 should be turned slightly to show the bilateral condition more plainly. The dotted line in fig. 26 indicates the median plane of the body.) For the reason that these partitions METAZOA COELENTERA. 123 are single and are arranged four on each side of the median line of the body they are called bilateral mesen- teries. They can be distinguished from the biradial mesenteries of the Hexactiniae s:nce these arise in pairs that radiate from the center to the circumference. When the animal is placed in accordance with this bilateral arrangement, there is a dorsal and a ventral side. The former differs from the latter by having the mesenteries much shorter, as shown in fig. 26. These walls may be seen on the outside in a three-and-a-half days' larva (fig. 27 ; fig. 28, the same contracted). It is at this early time or even a little earlier (seventy- two hours) that buds appear, as will be described farther on. Figures 29 and 30 show the larva when it has settled. The tentacles are at first quite simple but during growth become pinnate. The fact that, according to Wilson, the eight mesenteries and eight tentacles appear at one time and not in sequence, as is the case in the Hexactiniae, does not prove that the Alcyonaria are more specialized than the Hexactiniae. In order to demonstrate this view, evidences of the reduced character of the Hexac- tiniae, such as the reduction of biradial mesenteries, must be brought forward. The abbreviated record in the development of forms like Renilla tends to prove that these are more specialized members of the Alcyonaria, and we should predict that the primitive forms of the group would show a regular sequence in the appearance of the mesenteries. The spicules of Renilla are formed, according to Wilson, in both the endoderm and the ectoderm. Those of the endoderm appear first ; they are oval nodules and are not numerous. Fig. 31 represents a young stage; fig. 32, an old stage ; and fig. 33, the spicule taken from the cell. The spicules of the ectoderm appear soon after the attachment of the larva. They are at first rod-like and colorless, and not until a colony is formed, do they 124 SYNOPTIC COLLECTION. become purple. Figs. 34 and 35 are ectoderm cells con- taining young spicules ^ fig. 34 being not more than one eighth the length of a fully formed spicule. The calcare- ous matter first takes the form of elongated concretions and these like the endodermic spicules are formed by a process of crystallization, as shown by Prof. B. K. Emerson. It is an interesting fact that the development of the spicules in the Alcyonaria is similar to the forma- tion of these hard parts in the mesoderm of sponges, as observed by Schultze and Metschnikoff, and seems not unlike the formation of crystals in vegetable cells, as sug- gested by Wilson. It has already been stated that the larva begins to form a colony while it is free. It is probable, as pointed out by Wilson, that the necessity for motion is the cause for the early development of the buds. If the parent after becoming attached had no means of moving, it would doubtless be "smothered in the drifting sand." The position of the first two buds, as seen in fig. 27, is con- stant. The development differs from that of the parent zoon which has arisen from an egg, so that one ought not to compare egg development with bud development. The young colony takes in water and by means of strong internal currents is able to creep. It is instructive to note that an allied genus, Leptogor- gia, does not possess the power of creeping but fastens itself early in life to safe objects, and Dr. Wilson detected no buds at the end of two months. Fig. 36 is a young colony with five pairs of buds. In the adult (No. 178, with zoon expanded; No. 179, contracted) the young marginal zoons move the whole colony, and as they mature, become nutritive and reproductive. In time the zoons of this primary group become centers of multiplica- tion and many secondary groups are formed, while com- plexity marks the whole organization. The marked bilateral symmetry of Renilla is an evi- dence that the group to which it belongs is more primitive METAZOA COELENTERA. 125 than the Hexactiniae, since the latter are bilateral in early life and become radiate afterward, owing to attachment and the action of physical forces. Another colonial form is Veretillum (No. 180) which is related to Renilla. Briareum (No. 181, see upper shelf) of the Gorgon- acea is an upright, irregularly lobed colony. The zoons are without protecting cups and can be entirely withdrawn into the coenenchyma which is abundantly supplied with spicules. The central mass, which can hardly be called an axis, is supplied with nutritive canals. In Melitodes, (No. 182, M. ochracea Verr.), the axis is jointed and the sections consist of alternating portions of horny and calcareous matter. The horny sections are in reality made of a horny substance and loose spicules, while the calcareous parts are composed of consolidated spicules. All the joints are penetrated by canals. The spicules in Corallium rubrum Linn. (No. 183), unite to form a dense calcareous axis (No. 184), which is a beautiful red color and used for ornaments. The young coral animal has a mouth surrounded by eight white, pinnate tentacles (No. 183). The internal bag leads into the body cavity which is divided by eight mesenteries into eight chambers. The outer flesh is a bright red color and is stiffened by spicules. This single zoon buds and a colony arises. The body cavities of all the zoons connect with a series of water tubes ; these press upon the calcareous stem which is secreted by the bases of the zoons and while it is yet soft, indent its surface. Isis (No. 185) has a jointed axis consisting of horny and silicious sections. The zoons can be withdrawn into the thick coenenchyma. The spicules are club-shaped and stellate in form. An upright colony is formed by Xiphigorgia (No. 186). A related form, Plexaura (No. 187), has a horny axis, while the coenenchyma has variously shaped spicules. 126 SYNOPTIC COLLECTION. Small canals radiate from the cavities of the zoons and open into the longitudinal canals around the axis. The fan coral, Rhipidogorgia. (No. 188) is another upright coral, the branches of which unite to form a net- work. The zoons are arranged on either side of the intersecting branches. The yellow flesh is stiffened by spicules of different shapes and the axis (No. 189) is horny. ANTHOZOA. ZOANTHARIA. Coming to the present day we find among living Zoantharia the fleshy Actiniae which never make a skele- ton. The researches of Boveri, 1 McMurrich, 2 and others make it very probable that all the Actinian types have descended directly or indirectly from the Edwardsiae. Edwardsiae. Edwardsia claparedi Pane. (PI. 190, figs, i, 2) is a single form with eight simple tentacles. Its body cavity is divided into chambers by eight bilateral mesenteries (fig. 2). These Actiniae have the dorsal and ventral differentiation of the body well marked, so that a bilateral arrangement of the parts is the predomi- nating characteristic (fig. 2). When young, Edwardsia is free-swimming, but later it becomes stationary by burying the posterior part of its body in sand. A related form, Cerianthus membranaceus (No. 191) has a similar habit. Antipathes subpinnata (No. 192) represents the Anti- pathariae. -Nothing has been done as yet with the embryo- logical development of this group. The young Antipathes is a single, fleshy animal. At one end is the mouth with 'Zeitschr. f. wiss. Zool., XLIX, 1889, p. 492. 2 Journ. of Morph., IV, V, 1 890^9 1 ; Proc. U. S. Nat. Mus., XVI, 1893. METAZOA COELENTERA. 1 27 six simple tentacles. The mouth leads into an internal bag l which communicates with the body cavity. The latter is divided by six bilateral mesenteries. So far no trace of biradial mesenteries has been discovered in the young Antipathes, and these mesenteries we should expect to find . if the group were reduced descendants of the Hexactiniae as some naturalists maintain. The young Antipathes sends out fleshy prolongations from the basal portion of its body and these bud other zoons,. thus giving rise to a colony (No. 192). The bases of all the zoons secrete a black horny stem or axis (No. 193, A. dissecta D. & M.) , which gives rigidity to the stalk. This secretion is restricted to the "foot" of the zoons, the body walls never taking part. We have seen that this is also the case with some of the Alcyonaria, a group in which Antipathes is sometimes placed. The posses- sion, however, of six bilateral mesenteries seems to show relationship with the Hexactiniae. Zoanfhtos so lander i^ess. (No. 194), is a simple colony, the members of which are connected by stolons. The arrangement of the mesenteries is still essentially bi- lateral. In Mammillifera ? (No. 195). the zoons arise from a basal membrane and are of about the same height. Hexactiniae. The simple members of this group are illustrated by Halcampa chrys ant helium Gse. (No. 196), which is a free-swimming animal. In its development it passes through the Edwardsia stage of eight bilateral mesenteries, but when adult it possesses twelve biradia! mesenteries. The Actiniae next to be described are bilateral in the 1 This organ is called in text books and manuals "oesophagus," "stomach," "stomodaeum." According to Prof. E. B, Wilson it is an ectodermic structure and has nothing to do with the stomach structurally or functionally. It is homologous with a stomodaeum, or, what is more probable, with a fused stomodaeum and procto- daeum. We have called it simply a bag. 128 SYNOPTIC COLLECTION. early stages of development, but afterward develop a radial symmetry. 1 Actiniae. It is now pretty well established that the Actiniae are bisexual. The egg of our common sea anemone, Metridium marginatum Ag. (PI. 197, figs, i-io), leaves the parent form unfertilized. This is not the case with all Hexactiniae, the embryo of Rhodactis being so far developed when it passes into the water as to possess from two to four mesenteries, while that of Aulactinia possesses eight or twelve. Fig. i is an immature ovum taken from the ovary. The nucleus with its nucleolus and the process extending outward at one pole are clearly seen. Figs. 2-6 represent the segmentation of the egg ; fig. 7 is the young blastula ; fig. 8, an optical section of a free-swimming blastula. Some of the embryos at this stage are hollow and seem to be empty, while others (fig. 9) are filled with a liquid containing scattered cells. Fig. TO illustrates the formation of the endoderm by delamination of the inner ends of the ectoderm cells. After this stage ihe mouth breaks through, making an opening to the internal cavity. The young Actinian (PI. 198, figs. 1-3 ; the vertical line represents the height of the anemone when expanded) is a single, fleshy animal. The mouth is surrounded by a limited number of hollow tentacles. It leads into the in- ternal bag which communicates with the body cavity. The latter is divided first by four, then by eight mesen- teries which arise bilaterally. There is no indication of a skeleton in the young sea anemone, neither is there so great differentiation in the histological structure of the animal as in more specialized Anthozoa. For these reasons, and because the mesenteries arise on either side of the median plane of the body, producing bilateral symmetry, we regard the Actinia as a primitive rather than a reduced form. When the animal grows older the bilateral arrangement of parts gives way to a radial 1 Moseley, Quart. Journ. Micr. Sci., XXII, 1882, p. 395. METAZOA COELENTERA. 129 arrangement. Thus the base of the anemone (PI. 198, fig. 3) exhibits a small number of biradial partitions. Young and adult stages of the anemone are seen in the alcoholic specimens (No. 199). The cylindrical body is usually attached by its base (No. 199), although it has the power of gliding over surfaces. The mouth is surrounded by tentacles (Nos. 199, 200) which can be drawn in and entirely concealed. The mouth is open and more or less circular in the alcoholic specimens (Nos. 199, 200), but in life it is slit- like. It is provided with two siphono- glyphs. In the living animal these are seen to be lined with long cilia. When the mouth is closed the central parts come together, while the siphonoglyph at either end is open so that a current of water can be kept circulating through the body. The mouth of the adult opens into the flattened internal bag, and the latter into the body cavity, which is divided into chambers by biradial mesen- teries, seen in the preparation (No. 201). At each end of the flattened bag there is a pair of mesenteries called " directives." Four other pairs of long walls reach the central bag, making six pairs of primary mesenteries. Besides these there are cycles of shorter pairs, the num- ber depending upon the age of the anemone. When mature the mesenteries bear the long convoluted repro- ductive organs. The mesenteries are not arranged symmetrically and equally distant from one another, as might be inferred from figures often given in textbooks. In a collection of twenty-one anemones sent from Beverly bridge, not one showed a perfectly symmetrical arrangement. In nearly all, six or eight of the mesenteries which reached the central bag were bunched closely together, while the re- maining ones were separated from these by a greater or less distance. One specimen had four biradial pairs and an odd one ; two specimens had six pairs and an odd one ; another was found with seven pairs and an odd one, while still another had eight pairs. 130 SYNOPTIC COLLECTION. The shorter mesenteries bear long filaments which are provided with thread cells, and which can be thrown out of the mouth and through openings in the body wall. Actiniae generally reproduce in the manner already de- scribed, but occasionally they increase by budding and by fission. No. 202 is a rare specimen of Metridium which has two mouths in the oral disc. When a constric- tion takes place between these two and the oral disc divides, the method of fission is illustrated, and two ani- mals are produced which in No. 203 have not separated. There are a number of different genera of Actiniae in the Collection illustrating interesting features. Anemonia sulcata (No. 204), is remarkable for its short body and its numerous large, long tentacles which float in the water like hungry food catchers. The slit-like mouth with thickened lips peculiar to anemones is well seen in Adamsia rondeleti (No. 205). This anemone has the habit of fastening itself to the inner part of the opening of a Gastropod shell, as shown in No. 205 ; the bases of the different animals often touch one another, but there is no organic connection. One species of this genus (A. palliata) is found as a messmate on the back of the crab, Pagurus prideauxi. Anthea cereus Johnst. (No. 206), has little power of drawing in its tentacles, which are placed at the junction of the body wall and the oral disc. The exquisite color- ing of Actiniae is illustrated by all the glass models of these animals but especially by this species of Anthea. Bunodes crispa Ehr. (No. 207), is a rare anemone. The surface of the upper part of the body has many warts which are used as suckers for mooring the animal or for the attachment of foreign particles. 1 There is an indefi- nite number of retractile tentacles, some small and others so large and long that they look like grasping organs. Suctorial warts similar to those of Bunodes are also found in Tealia crassicornis Mull. (No. 208). 'Proc. Roy. Dublin Soc., VI, 1889, p. 315. METAZOA COELENTERA. 4 131 The body of Phymactis florida Drayton (No. 209), is much shorter than that of Metridium ; its mouth is ele- vated above the oral disc and surrounded by short tenta- cles. Phyllactis punctata Couthouy (No. 210), is a large Actinian in which the inner tentacles are similar to those of our common sea anemone, while the outer ones are like fluted lobes edged with green. These lobes sometimes adhere together nearly their whole length. This Actinian is found buried up to its disc in sand. According to Dana this creature crawled on glass by means of its outer lobed tentacles. Biddium parasiticum Ag. (PI. 211, figs, i, 2, natural size), is interesting since, unlike most Actiniae, it pos- sesses an anus at the posterior end of its body. It is found in the mouth-folds of the medusa, Cyanea arctica Per. & Less. The body is long and ribbed from one end to the other. Besides the longitudinal markings there are many transverse wrinkles. Fig. i shows the body con- tracted and the anus open. The terminal opening in five tentacles is seen, two are closed, and one is turned from the observer. In fig. 2 the body is expanded and the anus closed ; the twelve tentacles are visible. Fig. 3 is an enlarged drawing of the posterior portion of the body, showing the terminal anus and the rows of minute openings which radiate from it. ANTHOZOA. MADREPORARIA. The Madreporaria may be grouped into the Aporosa or Imperforata, the Fungidae, and the Perforata. It must be borne in mind, however, that there are no sharp divi- sion lines between these groups. The time will doubtless come when the ancient imperforate Madreporaria will be distributed as ancestral forms among the different families 132 SYNOPTIC COLLECTION. of corals living to-day, but at present so much uncertainty exists in regard to their true relationships that we consider them as ancestors of the whole group of Madreporaria. The skeleton of the Madreporaria is not spicular, like that of the Alcyonaria, but it is a hard, solid secretion of carbonate of lime. The theca in the Imperforata is not pierced by openings or pores, so that there is no system of canals connecting different corallites. In the Madreporaria Fungidae the young are imperforate and the adult perforate, while in the Perforata there are numerous pores both in the young and the adult stages, and the corallites are in communication with one another. The structure of these three groups is essentially similar to that of the sea anemones or Hexactiniae just described, with the exception that the Madreporaria possess a skele- ton. The formation of the skeleton has been studied by many, notably by von Koch 1 and Ogilvie.' 2 The larva begins to form a skeleton after it is attached. The first rudiment is a disc perforated in the center which after- ward becomes entire. This disc is between the ectoderm of the larva and the rock to which the latter is attached, and is a secretion of the ectoderm. It cannot be formed by either the endoderm or the mesoderm, since it is sepa- rated from these layers by the ectoderm. In time there appear radial ridges or upward foldings of the basal disc. The ectoderm in these foldings secretes carbonate of lime and thus limy septa are formed. In one genus observed 3 there were twelve mesenteries and twelve septa, six in the chambers between each biradial pair of mesenteries (entosepta) and six others in the chambers between two adjoining biradial pairs (exosepta). In the younger zoons there were twelve mesenteries and only six septa, and 1 Mitth. d. Zool. Stat. Neapel, III, 1882. Morph. Jahrb., V, VI, VIII. See also Fowler, Quart. Journ. Micr. Sci., XXV, 1885. 2 Proc. Roy. Soc. London, LIX, 1895; Phil. Trans. Roy. Soc. London, B, CLXXXVII, 1896. 3 Madreporia variabilis. METAZOA COELENTEPA. 133 these were the entosepta. In time, according to von Koch, the septa fork at their ends and later these ends fuse to form the cups or thecae. According to Lacaze- Duthiers the theca arises as a ring-like thickening of the base entirely independent of the septa. 1 Sometimes the central ends of the septa fuse and form the columella. While these changes are taking place, the ectoderm at the free margin of the young coral animal secretes lime whereby the epitheca is formed. This is a thin imperfo- rate layer which is originally free from the theca but which secondarily fuses with it. Many of the imperforate Madreporaria occur in the early geologic formations. The structure of the skeleton of these ancient corals also called Rugosa and Tetraco- ralla does not differ from that of recent corals. The tetrameral symmetry (or having the parts in multiplies of four) peculiar to- many of them is not a constant charac- ter, and a hexameral symmetry is not by any means char- acteristic of recent corals. 2 The relationship between these ancient and modern forms causes them to be placed together under the head of the Madreporaria Aporosa. It is probable that the earliest ancestors of our coral animals were disc-like in form, for the reason that this is the first condition of the skeleton of existing species. In time this disc-shaped coral probably became cup- or horn- shaped, a very common form among ancient species. The primitive disc-shaped ancestors are not known with certainty, so that we must pass to the cup-shaped forms; of these there are a number in the Collection. Cystiphyllum americanum E. & H. (No. 212), has septa that are only slightly developed, being indicated by mere ridges. The coral is vesicular throughout but towards 1 For a discussion of these views, see Fowler, Quart. Journ. Micr. Sci., XXV, 1885. 2 Treatise on Zoology, ed. by E. Ray Lankester, Part 2, 1900, p. 70. 134 SYNOPTIC COLLECTION. the base the vesicles are larger and there is a tendency towards forming tabulae. During periods of rest or com- parative inactivity the vesicular mass becomes more or less dense and apparently a cup is formed. For this reason there is a succession of cups, representing not differ- ent zoons that have budded but different degrees of activ- ity in forming the skeleton. If each were a bud, one ought to find the epitheca extending down into the cup, which is not the case. Still there are some specimens which appear to be made of the skeletons of two zoons, and as the epitheca is continued on the outside it is diffi- cult to give an explanation. In most specimens the epi- theca is worn off, but when preserved it shows distinct concentric ridges. The operculated corals seem to be related to the Cysti- phyllidae although they are more specialized in structure. One of the forms whose affinities have so far baffied naturalists is the Cretaceous Barrettia monilifera Wood- ward (PI. 213, fig. i, greatly reduced). Its shape and general appearance would place it with Calceola and the other operculated corals, but in structure it is different from any fossil so far discovered. According to Wood- ward, who first described the specimen (1862), it belongs to the Rudistae, a group of molluscs to which also Hip- purites and Radiolites (PI. 428, figs, i, 2) belong. This view was based upon the fact that in Woodward's speci- mens Barrettia possessed a bivalve shell. According to Whitfield (1897) Barrettia is more nearly related to corals than to molluscs. The visceral cavity occupied the center (PI. 213, fig. 2, longitudinal section ; fig. 3, cross section). Below, it was divided by transverse partitions (fig. 4). Radiating from the central cavity were lines of vertical tubes or monili- form rays (figs. 3, 4), and close by it was a larger tube divided by transverse walls (fig. 4 a). The spaces between the radiating rows of tubes were filled with four-walled tubes which were also divided .METAZOA COELENTERA. 135 horizontally by walls (fig. 5, summit view; fig. 6, vertical section). The moniliform rays may be seen in fig. 5, in the ridges between the rows of four-walled cells. The specimens described by Whitfield (figs. 4-6) showed no upper valve ; in fact, there was nothing to indicate a molluscan character in the genus, such as is plainly seen among the Rudistae. At the same time the genus is different from any of the operculated corals, although it is placed in this group provisionally until more perfect specimens can be obtained. The single form Zaphrentis (No. 214) of the family Zaphrentidae has a bilateral arrangement of the septa. The "pit" .or fossula usually contains a shorter septum. Here were probably the mesenteries that bore the repro- ductive organs. The septa are contorted at the center and the tabulae are not clearly defined, while there is scarcely any vesicular structure. Cyathaxonia prolifera McChes. (No. 215), is a single form with septa arranged radially and a central projecting columella. The young Cyathaxonia has an epitheca on the end, which is very delicate, so that it is usually worn off and is seldom seen in fossils. Heliophyllum halliY,. & H. (No. 216), is an illustration of a single Cyathophylloid coral. It has the form of a flaring shallow cup. The epitheca is seen on the outside, while the vertical septa are distinctly seen within the cup and are radially arranged. Between the septa on the outer side there is more or less vesicular structure ; the tabulae cannot be made out in the specimens but the ridges on the septa are plainly seen and appear like cross bars between the septa. Acervularia ananas Linn. (No. 217), is a colonial form consisting of many coral animals that lived closely to- gether. Here there is an external epitheca. The septa extended to the central bag, and below this organ to the center. They are indicated on the surface of the coral by radiating lines. The vesicular structure has largely 136 SYNOPTIC COLLECTION. disappeared. Budding takes place from the edge of the cup and a spreading form results. Lithostrotion canadense Castelnau (No. 218), is another colonial form in which the vertical septa and columella are clearly shown ; the tabulae are seen on a broken sur- face. Turbinolia sessilis Blainv. (No. 219), of the family Turbinolidae is a single coral of more recent date. It has a columella projecting in the center (although not shown in the specimen) and the septa are arranged radially. A single, deep-sea form is Caryophyllia (No. 220, C. smithi var. castanea). This is a most instructive speci- men, for it exhibits the striking similarity between a sea anemone and a coral animal. The epitheca is formed around the lower part of the body. The septa of the skeleton are numerous and the larger ones predominate. In the center is a twisted columella. Oculina (No. 221), is one of the irregular branching corals with rounded tips. The corallites are distinct, with the coenenchyma showing plainly near the base but almost wholly disappearing at the ends of the branches. The colonial Pocillopora, represented by the large, handsome specimen on the lowest shelf of the erect por- tion of Section 4 (No. 222, P. nobilis Verr.), has stout obtuse branches. As in Oculina, the corallites on the sides of the branches are separated by the coenenchyma, but at the ends they are crowded closely together. The tabulae show finely in a side view. The columella is sometimes well developed but in other specimens poorly. This coral increases by budding and rarely by fission. The thecae in Pocillopora are divided by a long median septum ; the other septa in this genus and in the beauti- ful Seriatopora (No. 223, see lowest shelf), are minute, and in the latter genus the tabulae are scarcely visible. The family Astraeidae is a large one, including many genera. Antill/a explanata Pourtales ( = Lithophyllia METAZOA COELENTERA. 1 37 cubensis^ M.-Ed. & H.) (PI. 224), is one of the more generalized members of the family. It is disc-shaped (PI. 224, fig. i) like the original basal plate of the Madreporian skeleton. Antillia offers an illustration of the co-existence of the epitheca and theca in one zoon. The epitheca, which is well developed in this species, is shown in fig. 2, and also the central small area of attach- ment. Cladocora caespitosa Lam. is seen in the glass model (No. 225). At the left is a single zoon much enlarged^ and just back of it is the colony. The theca is present and the ridges on the outside correspond to the septa. Vesicular structure exists though in small quantities, and the epitheca is only slightly developed. The little Astrangia danae Ag. (No. 226 ; No. 227,. skeletons attached to a stone), is the only coral living in our New England waters. It is a colonial form and the corallites are connected by the coenenchyma. The septa unite at the center in a columella and there is no epitheca. There are many corals, like Mussa, Manicina, and the like, that increase by a process of incomplete fission which results in winding furrows with such indistinct thecae that often the limits of the different skeletons cannot be made out with certainty. The septa in Mussa tenuidentata M.-Ed. & H. (No. 228), are large and toothed and the columella is spongy. In some specimens the epitheca is slightly developed and in others it does not exist. According to Martin Duncan 2 the young of this genus cannot be distinguished from simple Astraeidae of the Antillia type. Mussa increases by fission, as we have said, and the process is often illustrated in one specimen where the original circular corallite may be found, and also more advanced corallites that are elongated, constricted, and nearly or wholly divided. 1 Quart. Journ. Geol. Soc. London, LI, 1895, p. 259. 2 Journ. Linn. Soc. London, Zool., XVIII, 1884, p. 83. 138 SYNOPTIC COLLECTION. Manicina is interesting for the reason that it is a rapid swimmer when young, fixed by a pedicel when mature, and free again when old. In developing, the stage with eight mesenteries is followed in a day or two by the stage with twelve. 1 The skeletons (No. 229) show different stages of growth, the colony never becoming much larger than the largest specimen. Euphyllia gracilis Dana (No. 230), forms small colo- nies. The thecae in this genus are circular, compressed, and sometimes meandering. The same method of reproduction is illustrated by the massive brain coral, Diploria cerebriformis M.-Ed. & H. (No. 231), which grows to a great size and which repre- sents the skeletons of a vast number of coral animals. Favia (No. 232) is a hemispherical colonial form in which the corallites are united and the septa are toothed. The columella is spongy and an epitheca sometimes ex- ists. Orbicella annularis Dana (No. 233), is also hemispheri- cal in shape and the new buds arise in the spaces between the corallites. The corallites in Galaxea fascicularis Oken (No. 234), project from the surrounding coenenchyma. Each is marked by striae which indicate the septa. The latter are distinct and the longer ones reach to the columella which does not project upward. This genus increases by budding from the walls of the corallites and also from the basal coenosarc that extends between the corallites. The coral takes on a foliaceous shape in Agaricia agaricitcs E. & H. (No. 235). The columella is present but the septa are not numerous. Pachyseris luevicollis E. & H. (No. 236), is a related form. IH. V. Wilson, Journ. of Morph., II, No. 2, 1888, p. 191. METAZOA COELENTERA. 139 MADREPORAKIA FUNGIDAE. Palaeocyclus (No. 237) and Cyclolites (No. 237) are mushroom-corals which antedate our present Fungia. From a study of the early stages of the latter, however, it is probable that all these coral animals arose from a cup-shaped rather than a mushroom-shaped ancestor. It may be that a still more remote ancestor was disc-shaped, as we have already said, and that the Madreporaria Fungidae, which possess a similar plate-like form, are its specialized and reduced descendants. Nothing is known of the young stages of Palaeocyclus and Cyclolites. The adult is disc-shaped and the epitheca is confined to the base. The septa rise as so many walls of varying length from the basal plates. Turning to the development of Fungia we find that the parent stock is attached (PI. 239, fig. i). It is cup-shaped with a distinct theca, while the cavity of the cup is divided into chambers by septa. In this stage it resembles Caryo- phyllia. In time the oral disc increases in size at the expense apparently of the thecal portion (fig. 2). The growth is lateral, until at last the young Fungia separates from the parent stock a short distance below the disc where the dark line is seen in fig. 3. When set free the Fungia has an opening beneath, where it was fastened, but this quickly fills up by a secretion of carbonate of lime. The scar is seen in young specimens (No. 240). The Fungia is henceforth free (PI. 239, figs. 4, 5) with only slight evidences on the lower side of its attachment, and these finally disappear (fig. 6) . The parent stock continues to bud forth other animals which likewise become detached. According to Semper 1 the parent stock is comparable to the strobila of the Discophora and exhibits a true alternation of generations. 1 Zeitschr. f. wiss. Zool., XXII, 1872, p. 267. 140 SYNOPTIC COLLECTION; Bourne 1 objects to the use of the word strobila which was originally applied to the dividing parent stock of Aurelia. This is essentially different from the bud-pro- ducing parent stock of Fungia, and since it is objection- able to use the same name for two very different phe- nomena Bourne uses nurse stock for the fixed parent of Fungia. Rarely a specimen is found with the parent stock attached to it, as seen in No. 240. This stock was cov- ered over with limy deposits by the growing animal, and these had to be removed by acid when the original stock form was exposed with its cup like shape and internal walls. The central or younger portions of the adult Fungia (No. 241) are imperforate but the older portions are perforated. The septa increase in number from the cen- ter outwards, as is well shown in No. 241. MADREPORARIA PERFORATA. The simpler members of the Madreporaria Perforata are Dendrophyllia (No. 242) and Coenopsammia. (No. 243, C. tenuilamillosa Verr.) . The former is a branching coral and the latter a low, spreading form. The corallites in both are large and the septa are distinct. Buds grow from the sides of the corallites but a massive colony never results. Astroides calycularis Pallas (No. 244), is a simple col- ony in which the corallites are packed closely together and rise to about the same height. This was one of the species on which von Koch made his valuable investiga- tions upon the formation of the coral skeleton. The Madrepore coral (Nos. 245-248), is a typical example of the Perforata. The pores may be finely seen 1 Quart. Journ. Micr. Sci., XXVII, 1887, p. 294. METAZOA COELENTERA. 141 when a specimen is held to the light. No. 247 is a verti- cal section of this coral that exhibits these characteristic openings by means of which the zoons communicate with one another. This coral assumes different shapes ; it is branching (No. 245, in more natural condition than No. 248, which has been bleached), and it is flat and encrust- ing (No. 246, Madrepora convexa Dana). The long septa reach the center, where there is a more or less spongy columella. The walls of the corallites are not distinct from the coenenchyma, which is largely developed ; and the epitheca is wanting. Budding takes place from the central and parent form which has remarkable vitality, and also from the sides of other corallites which are larger and longer than most of their neighbors. The skeleton of the central parent zoon is seen cut in two in No. 247. In healthy condition the ends of the branches of Madrepore are always pointed, but in No. 248 there are a number of diseased tips with a puffed out, swollen appearance. The corallites in Porites (No. 249, P. claviaria Lam., a branching form; No. 250, vertical section of P. astrae- oides Lam., a rounded form) are crowded thickly together on a level, with no intervening coenenchyma. The septa are imperfect and spinous ; there are no tabulae and the columella is small. The coral is more dense than in Madrepore (compare No. 247 with No. 250), and there is no large parent zoon. We have attempted to show that the Coelentera as represented by the Hydrozoa and Anthozoa have a defi- nite form and a body cavity all the parts of which are in communication with one another. Beginning with a primi- tive Palaeozoic ancestor we pass to living free-swimming hydroids that have a direct development, the hydroid growing into a medusa. Again, free swimming hydroids become attached and colonies arise by budding. These produce free medusae 142 SYNOPTIC COLLECTION. whose eggs develop into fixed or stationary hydroids, there- by illustrating the process of indirect development and the alternation of generations. The eggs of other medusae develop into medusae, skip- ping altogether the hydroid stage and illustrating the proc- ess of accelerated development. Lastly, certain hydroids whose ancestors, we have reason to believe, produced free medusae have taken on such reduced characters it seems probable that the me- dusa stage is omitted in their ontogeny, and, if so, they illustrate suppressed development. Acceleration in development is shown by the Disco- phora, while specialization of structure and function, re- sulting in complex colonial life, is characteristic of the Si- phonophora. The Ctenophora constitute one of those interesting syn- thetic types whose relationships reach out beyond the limits of the Hydrozoa, beyond even the boundaries of the Coelentera, to the subkingdom of the Echinoderms. The ancestors of the Alcyonarian branch of the Antho- zoa are illustrated by a series of forms which show most admirably the gradual transition from the primitive and simple to the secondary and complex. The living Alcyonaria have in addition to what the Hy- drozoan possesses, an internal bag and a body cavity divided into chambers by eight bilateral mesenteries. Their skeleton is made of spicules and is chiefly a secre- tion of the ectoderm of the basal membrane of the zoons. The Zoantharia likewise have an internal bag and in youth a body cavity divided by eight bilateral mesenteries, but in maturity this cavity is divided by numerous bira- dial mesenteries. The skeleton of the Madreporaria is a solid secretion of the ectoderm and consists, speaking generally, of a basal disc and a theca with true septa. The processes of reproduction budding and fission and the influence of physical forces have brought about METAZOA COELENTERA. 143 a great variety in form, but through this extreme diversity the fundamental type of structure remains the same. The subkingdom of Vermes or Worms is placed next the Coelentera by many authorities, and the larvae of cer- tain worms are considered as the nearest approach to the ancestral forms from which all the remaining invertebrates and also the vertebrates have descended. There is a resemblance, speaking broadly, between the larvae of echinoderms, molluscs, and worms, but this sim- ilarity may be due to inheritance from some pre-Cam- brian ancestor from which the three branches have devel- oped along different lines. When one considers the varied and extreme specializations of worms ; the articu- late plan of structure differing so essentially from the ra- diate plan ; the greatly developed muscular system and the complex excretory and reproductive organs ; the large number of extremely reduced forms, one finds it easier to place the worms among the more specialized and the ar- ticulated animals than next to the comparatively simple Coelentera. The Echinoderms, on the other hand, are pre-eminently radiate organisms, and in many ways they possess char- acters in common with the Coelentera. METAZOA ECHINODERMA. 145 ECHINODERMA. Sections 5, 6. CYSTOIDEA. Most palaeontologists consider the Cystoidea as the Palaeozoic ancestors of the Echinoderms, while embryolo- gists hold that this view is not supported by facts. Ac- cording to Bury 1 there is not the slightest embryological evidence that the Echinoderms have passed through a stage in which they are fixed by the aboral pole, like the Cystoids. He goes on to say, " Nevertheless, almost all embryologists, apparently out of deference to palaeonto- logical conclusions, have thought it necessary to assume that ontogeny is misleading, and that a period of fixation really did take place of which all traces have since disap- peared. Now this involves us in a question of fundamen- tal importance. If palaeontologists have really proved beyond any reasonable doubt that the Echinozoa are de- rived from fixed ancestors, then ontogeny is misleading; but if it is misleading to such an extent as to obliterate all traces of a process of such immense importance, I for my part do not see how we can trust it in other particu- lars, and those who rely upon it for indications of phylo- genetic history had better reconsider their position." Professor Bury then takes up the question at length from the embryological point of view and deduces reasons for considering that the ancestors of Echinoderms were unat- tached forms. It has been shown by Hyatt and other investigators that it may be possible for all traces of an ancestral structure to be lost, and still the ontogeny of the individual be abso- 1 Metamorphosis of Echinoderms. Quart. Journ. Micr. Sci., n. s., XXXVIII, 1895, p. 93. 146 SYNOPTIC COLLECTION. lutely luminous with the light it throws upon the phylo- genetic history of its group. So far from being mislead- ing, such an ontogeny is the normal and inevitable result of the operation of the law of acceleration in development by which adult characters are inherited earlier and earlier in the life of the individual, until it may be they appear in the embryo only, and finally disappear altogether. According to A. Agassiz 1 the Cystoids and Blastoids represent among fossil Echinoderms the nearest approach we have yet discovered to the imaginary prototype of the subkingdom of spiny-skinned animals. The characters possessed by the living Echinoderma are such that they can be explained satisfactorily only by supposing that these animals are the descendants of attached forms. It may be possible, as already suggested, that the ancestors of the attached forms, living in some remote pre-Cambrian age, were free-swimming, and that these free-swimming adults are represented, with few or many modifications, by the larvae of existing Echino- derms, molluscs, and worms. Be this as it may, the fact is pretty well established that our present free-moving Echinoderms are directly descended from fixed or sta- tionary ancestors. One of the simplest Cystoids is Aristocystis (PI. 251, figs, i, 2, A. bohemicus Hkl.). Here we have a body pro- tected by many calcareous plates placed together irregu- larly. It was attached by its base (fig. 2), which was surrounded by more regular plates ; as yet no stem had developed. The slit-like mouth was on the upper side (fig. 3, m), and at one side was the anus (fig. 3, a) closed by a pyramid of plates. Between these two open- ings there was a pore, now thought to be the genital pore (fig. 3, g). Near the mouth there was still another open- ing supposed to be for respiration and called a hydropore (fig. 3, h). In this genus there were no specialized areas 1 Proc. Amer. Assoc. Adv. Sci., XXIX, 1880, p. 411. METAZOA ECHINODERMA. 147 of plates known as food grooves or ambulacra, and no arms extended from the body. Another primitive form was Lichenocrinus dyeri Hall (PI. 252, figs. 1-4). Little is positively known in regard to this genus, and it is only on account of the structure of the stem that a figure of it is placed on exhibition. The portion preserved (figs, i, 2) was probably the basal part which was attached to shells, etc., as seen in fig. i. It was covered by irregular and imperforate plates (fig. 2), which rested upon many radiating parti- tions, seen in fig. 3, where the outer plates have been weathered and have disappeared. They are also seen in fig. 4, which is the lower or attached side. There is no indication of arms or of areas of plates, the ambulacra, but in the center a stem is visible, which probably sup- ported the body. The genus is chiefly valuable in show- ing the structure of a primitive stem. The five parts making up the column can be distinctly seen (fig. 2), whereas in the more specialized members of the group they are consolidated so that their boundaries cannot be made out. In the Cystoid Amygdalocystis (PI. 253, A. florcahs Billings), the ambulacra consist of a double row of imper- forate plates and are concealed by covering plates. This double row extended over the summit. The figure shows several joints of the ambulacrum, each one of which bears a pinnule ; also the body with many plates indefinitely arranged, and the round stem. The mouth (m) and the anus (a) are seen on the upper side. In Mesocystis ( = Mesites) (PI. 254, M. pusirefski}, the five ambulacra are present and are built on top of the body plates. While the ambulacra are imperforate and there are no holes between the plates, the body plates are perforated. The position of the ambulacra in this genus suggests their possible origin (see p. 149). The mouth (PI. 254, m) is at the summit and the anus (a) farther down ; h is supposed to be a hydropore, though Lankester thinks it is due to a boring parasite. 148 SYNOPTIC COLLECTION. We reach a condition in Glyptosphaera (PI. 255, G. leuchtenbergi} in which the body plates are perforated, the pores being in pairs. The ambulacra are on top of the body plates, as in Mesocystis. They are long, nar- row, and branching, and are apparently without pores. They lead to the mouth which is covered by plates. The body of Echinosphaerites is globular, as shown by PI. 257 (E. aurantium Rising); the specimen (No. 256) is somewhat distorted by pressure, though with this exception it shows the characteristic features well. The body is protected by irregular plates (No. 256; PL 257) and provided with two or three small imperfect arms which are broken off in most specimens. Just under a thin limy film covering the outer plates of the body there are ducts (No. 256), the openings to which are arranged in the form of rhombs, and they are therefore called "pore-rhombs" (see No. 256 and PI. 257). These ducts pass horizontally from one plate to the other, but the pores of the rhombs communicate with short canals that pass vertically through the plates. Probably these canals and pores aided in respiration. The mouth in Echino- sphaerites is at the apex, while the anus is on one side (No. 256) protected by a pyramid of plates, as shown in both specimen and figure. Between the mouth and anus, a little to the right of the former, is the genital pore (No. 256; PI. 257). One of the more specialized Cystoids is Caryocrinus ornatus Say (Nos. 258, 259). The stem by which it was fastened (not seen in the specimen) was composed of many discs. Above the stem was the body, protected by circles of regular plates, finely seen in No. 258. The basal plates compose the first circle and above these is the circle of radials (No. 259). In this genus the plates at the base of the arms, often called interradials, perform the work of true body plates. The arms were perhaps little appendages like pinnules, but are usually broken off, as in the specimens. The ambulacra in the middle METAZOA ECHINODERMA. 149 of the arms were covered and led to the mouth which was also covered over by a series of plates. The anus is in the body plates and outside of the arms. The possession of a complete digestive system ending in an anus and entirely separate from the body cavity is a distinctive feature of the Echinoderma, separating this subkingdom from the Coelentera. The body plates in Caryocrinus were pierced by holes which were the openings of the tubes that ran along the inner side of the plates, and which connected with the respiratory organs or hydrospires. In the Cystoidea the ambulacra constitute the feeding and not the locomotive system, so that, were we consider- ing function rather than homology, food grooves would be a good name for ambulacra and tentacles an appropriate name for the organs which came out of the openings of the food, grooves. It is probable, as we have already said, that the first forms were without food grooves or ambula- cra ; these may have appeared later as hollows scooped out of the surface of the body, so that the ambulacral plates were set in between the body plates. The next step might be to set these on top of the body plates, as in Meso- cystis. Finally, they might be pushed upward still more, until they were off of the body altogether, as in Caryocri- nus, forming the ambulacra of the arms. BLASTOIDEA. The Blastoids probably sprang from the Cystoids. One of the most generalized Blastoids is Codaster (PI. 260). Here the body is attached by a stem and it is made of reg- ular plates consisting of basals, forked radials, and inter- radials. Its ventral side (PI. 260) is wide and nearly flat, and on this flattened area the five imperforate ambulacra (PI. 260, am) are spread out. The many slits (PI. 260, s) of the hydrospires are exposed between the ambulacral areas. The anus (PI. 260, a) is flush with the surface. 150 SYNOPTIC COLLECTION. The central mouth was concealed by oral plates in the living animal, and the ambulacra were also covered. Co- daster like all Blastoids is without arms, but short pinnules are attached to the ambulacra. In another genus, Orophocrinus (PI. 261), the numerous hydrospiral slits are reduced to ten slits, two on each side of an ambulacrum (PI. 261, s). In this figure the cover- ing plates are seen over the ambulacra. If we suppose the hydrospires crowded under the ambu- lacral areas and these slits shortened till only an opening is left at the top, we have the condition found in the fol- lowing more specialized Blastoids. Pentremites godoni Shum. (No. 262), is a stalked Blas- toid, but the stem is so short and small that it is rarely preserved. The body in this genus, as in all Blastoids of its group (Pentremitidae), becomes constricted and the inner portion of the basal plates helps to form the upper- most disc of the stem. The bas.ils and radials are well seen in No. 262, especially in the middle specimen .(b) in the lower row, and the upper right hand specimen (e). Each of the five ambulacra consists of two parts, the lancet-shaped portion in the middle which is made of many small plates, and the side pieces or plates. Near the outer edge of the lancet plate there is a row of sock- ets where the long delicate pinnules were attached. The food was caught by these pinnules and carried by cilia in the transverse channels to the median channel and thence to the mouth which was in the center of the oral disc. The ambulacral groove is said to have been covered by plates, but these are not seen in any of the specimens in the Society's collection. On the outer edges of each ambulacrum is a row of holes (No. 262, a, b, d, e) for admitting water to the tubes or hydrospires inside. The latter open at the top in the five holes or spiracles around the mouth (No. 262, c, d). In reality four of the spiracles are divided by a partition, while the largest one is divided twice. Of the eleven METAZOA ECHINODERMA. 151 openings thus formed ten are spiracles and one is the anus. We have seen that the hydrospiral or respiratory system is not found in the primitive forms of Cystoids. Where it first occurs, it is independent of the feeding system and is on the surface, as in Echinosphaerites. Later, among the Blastoids especially, it is sunk under and crowded closely against the feeding system. Various interesting modifications take place in the structure of Blastoids. The body may become elongated and the ambulacra narrow, as seen in Tricoelocrinus obli- quatus Worthen (No. 263), where the lancet plate is cov- ered by the side plates. In Nucleocrinus vernueilli Troost (No. 264), the basal plates are very small and sunken; the radials are also reduced in size, while the broad interradials and the nar- row ambulacra make up most of the body. The latter extend from the top or ventral side downward to the lower side. One genus of Blastoids, Eleutherocrinus (E. cassedayi Shum., No. 265), shows a peculiar specialization of structure. One ambulacrum has become modified and is found at the top, leaving only four long ambulacra. It is interesting to note that this specialization of the ambu- lacra appears in a stemless and, therefore, a reduced blas- toid. CRINOIDEA. The Crinoidea may be divided into two series, each one of which begins with stemmed species and ends in a stemless form. The more generalized series is represented in the Collection by Haplocrinus, Cupressocrinus, Cyathocrinus, Encrinus, and Marsupites. Haplocrinus (No. 266) has the body made up of two circles of plates ; the circle at the base of the body and 152 SYNOPTIC COLLECTION. just above the stem is composed of basals and the circle above of radials. The other genera have three circles of plates; the one at the base of the body and above the stern is the circle of underbasals and above this are the basals and radials. Those forms which have basals and no underbasals are known as monocyclic Crinoids and those with both basals and underbasals as dicyclic forms. According to some investigators the monocyclic Cri- noids of recent geologic epochs and those living to-day have descended from the ancient dicyclic forms. If this is the case, they have become specialized by reduction. While this is probably true, it must be borne in mind that the ancient dicyclic forms may have arisen from prim- itive monocyclic Crinoids, which one would expect to find in pre-Cambrian formations. According to Bather and Lankester, 1 there is evidence that the monocyclic forms have descended from Cambrian or pre-Cambrian monocyclic ancestors, and the dicyclic species from dicyclic ancestors, though it is not known in what forms these two independent lines converge. We will consider Haplocrinus as an example of the ancient monocyclic group. Its body (PI. 266, figs. 1-3, H. mespi- liformis) is small and attached by a round stem not seen in the drawings. It is composed of basals and radials, as we have already said, and these plates are fastened together by close sutures, so that they are immovable (fig. i, side view). The radials are perforated. The ventral pyramid consists of oral plates only, 2 which rest upon the radials. Fig. 2 is the ventral surface with the pyramid of five oral plates; the posterior plate which contains the anus is seen to be larger and is carried forward between the lateral-anterior plates covering the mouth. Some- 1 Treat. Zool., Part III, 1900, p. 138. 2 Wachsmuth and Springer, Proc. Acad. Nat. Sci. Phila., 1888; also ibid., 1890. METAZOA ECHINODERMA. 153 times this tongue-like projection has a node on top, as in fig. 3. The presence of the anus causes more or less irregularity in the plates of the body (see fig. i). The ambulacra run out from the mouth across the ventral disc and under the oral plates to the arms. The arms in Haplocrinus are only slightly developed, and are usually broken off in specimens, but their points of attachment are seen (figs. 1-3). They consist of one series of sections divided by joints, and they lie in grooves which run along the sides of the orals ; in two of the grooves the first section of the arms is seen (fig. 3). Haplocrinus retains its simplicity of structure through- out life, -remaining "permanently in the condition of a very young larva." l Certain peculiar specializations of structure are found in Cupressocrinus abbreviates Goldf. (No. 267), which, though a primitive form, has developed, it would seem, along a different line from Haplocrinus. This genus has a stout, round stem (PI. 268, fig. 2), but according to Bather, 2 it "endeavours at times to break with old traditions, and appears with a triradiate or quinqueradiate stem " (see PI. 268, figs. 3,4). The body is composed of a centro-dorsal plate (fig. i), made of a ring of united underbasal plates. Above this plate are five large basals and five radials (No. 267; also PI. 268, figs. 1,2). In this genus the regularity of the plates is slightly disturbed by the anal plates. The ventral disc is concealed in No. 267 by the five short, simple arms which are as broad at their point of attachment as the radial plates (PI. 268, fig. i). These arms bore pinnules which, according to Wachsrnuth and Springer, were arranged like those of Blastoids, there being four or m ;>re to each arm joint.3 1 Carpenter, Chall. Rep., Zool., XI, part 32, 1884, p. 157. 2 Quart. Journ. Geol. Soc. London, Feb., 1889, p. 167. 3 Proc. Acad. Nat. Sci. Phila., 1886, p. 180. 154 SYNOPTIC COLLECTION. The most complex Cyathocrinoid must have passed through a stage in early life when it closely resembled Haplocrinus. Cyathocrinus (PI. 269, figs, i-io; No. 270), is attached by a round stem (No. 270, C. multibrachiatus L. & C.; PI. 269, fig. 2) which never developed branches or cirri (see figs. 1,4). Small underbasal plates, five in number, are found (not seen in No. 270, but figured in PI. 269, fig. i, young stage, and fig. 3, plates of body sepa- rated). The underbasals are characteristic of Palaeozoic Crinoids, as we have already said, but do not occur among recent adult forms. 1 Fig. 4 represents the adult in which the plates of the body are not so distinctly seen as in the young (fig. i). Above the underbasals are five brasals and five radials with a small anal plate. These are not seen in No. 270, but are shown in figs. 1.3. The basals de- velop very early in the young and have nearly reached their full size when the radials are still small. 2 An anal tube (ventral sac, Wachsmuth and Springer) rose from the ventral surface, which was short and covered by plates (figs, i, 4, 5). The ambulacral grooves run out from the mouth, across the ventral surface, and are concealed by small, irregular covering plates (fig. 6 ; fig. 7, ventral surface with ambu- lacrals and covering plates removed). When the Crinoid was alive, these covering plates could open (fig. 8) , and thus food could pass through the grooves (figs. 7, 9) to the mouth, after which the covering plates were again closed, as seen in fig. 10. A few long, slender arms are sent off from the radials, which in some species fork many times forming armlets, but which are without pinnules (figs. 1,4). The interesting discovery was made by Wachsmuth and Springer 3 that what had been considered hitherto as i Chall. Rep., Zool., XI, part 32, 1884, p. 152. 2 Chall. Rep., loc. cit., p. 169. 3 Transition forms in Crinoids and description of five new species, Proc. Acad. Nat. Sci. Phila., 1878, p. 256. METAZOA ECHINODERMA. 155 four species l of this genus were in reality different stages of growth of one species, for which the older name of Cyathocrinus iowensis is retained. After an examination of a great number of specimens, it was found that the young was represented by the species C. divaricatus Hall which possessed good-sized basal plates. As the animal grew older, these plates became smaller, while at the sa/ne time the radials (subradials of Wachsmuth and Springer) increased in size. This is seen in C. iowensis, which these authorities have proved, is identical with C. rimi- nalis Hall. The mature form, having the smallest basals and largest radials, is C, malvaceus Hall. Poteriocrinus zeaeformis Schultze (No. 271; PI. 272, figs, i, 2, P. circumtextus M. & G.), has a long slender stem which is not seen in the figures. Its body is made up of underbasal, basal, and radial plates with the first arm sections or brachials fastened by suture to the radials. The anal tube rises from the ventral disc, and is seen in both the specimens (No. 271) and figures (PI. 272). The long, delicate arms are forked and their pinnules can be distinctly made out in the specimen (No. 271). Encrinus liliiformis Lam. (No. 273), is one of the best known Crinoids. The body is so large that it needs firmer support than the stem alone can furnish, and therefore root-like extensions or cirri are thrown out which help to fasten the animal securely in the mud. The plates of the body are regular, consisting normally of five underbasals, covered by the top stem joint, five basals, and five radials. The oral plates are present in the young but usually disappear in the adult, while the anal plates are found only in the young. The anus per- forates the oral disc within the circle of arms instead of being outside the arms as in some Cystoids. 1 Cyathocrinus iowensis O. & Sh., C. divaricatus Hall, C. malva- ceus Hall, and C. viminalis Hall. 156 SYNOPTIC COLLECTION. The mouth and five ambulacra are without covering plates. The arms of the very young Encrinus are at first made of single sections, that is, they are uniserial, but afterwards they become biserial 1 a proof that the uni- serial condition is the more primitive. In the Crinoids there were no tubes or hydrospires, but respiration took place through pores between the plates of the oral surface. Marsupites (No. 274) is an instructive form. In youth it is attached by a stem, but later it breaks away, and the rounded posterior part of the body usually shows no scar. Underbasals, basals, and radials are all present ; these are thin and flexible. 2 The ventral disc is not preserved in any of the specimens. The arms are uniserial, but are usually broken off. The second series of Crinoids is more specialized, speaking generally, than the first. Platycrinus (No. 275, P. hemisphericus\ PI. 276, P. tri- gintidactylus Aus.) has a body made of basals and radinls, the former of which are unequal. From the ventral side rises a large anal tube (see PI. 276). The arms are free, they fork a few times, and are well supplied with pinnules. The ambulacra are concealed by covering plates. Actinocrinus (No. 277) has a small body without underbasals, and the arms are attached near its middle. The basals are reduced to three in this genus. The specimen (No. 277 a) has eight arms, and the pinnules of one are fairly well preserved. The food was caught by the pinnules and carried down to the base of the arms where it passed through the covered tunnels of the ambu- lacra to the mouth. The convergence of these ambula- cral grooves a little to one side of the center is seen in the internal casts of Actinocrinus (No. 277 b-d) . Here 1 Wachsmuth and Springer, Proc. Acad. Nat. Sci. Phila., 1886, p. 230. 2 Bather, Proc. Zool. Soc. London, 1895, p. 996. METAZOA ECHINODERMA. 157 the grooves have become filled with solid matter, but the position of the parts is well shown. The branching of the arms on leaving the body is seen in another cast, No. 277 e, where the aboral side is uppermost. From the oral disc extended a long anal tube. This is seen in No. 277 a, while its position is indicated in the casts. Respiration was probably effected in Actinocrinus by tentacles on the edges of the ambulacra. Marsupiocrinus (No. 278, M. caelatus Phil.) has a lower oral vault than Actinocrinus, and it is composed of a larger number of plates than usually is found. The arms are provided with pinnules (No. 278) but are unbranched. Similar in general structure to Marsupiocrinus is Eucalyp- tocrinus caelatus Hall (No. 279). This Crinoid when full grown had a large, plump, complex body, which was con- cave at the bottom, the basals and in some cases the radi- als extending upward and forming a cone. The arms are comparatively small, set in deep recesses (No. 279), and the ambulacra have the same structure as in Actinocrinus. Here the anal tube was very long and large. Apiocrinus (No. 280) differs from the preceding in that the stem forms a portion of the body. These two parts can always be distinguished from each other, as the por- tion corresponding to the body of other Crinoids has vertical and oblique lines, while the stem portion has only circular lines, dividing it into horizontal discs. The ambulacra are uncovered, and there is no vault or anal tube. Millericrinus mespiliformis d 'Orb. (No. 281), is similar to Apiocrinus in some respects. As a general thing both have the stem enlarged, but that of Millericrinus widens more gradually, and the upper joint is not much larger than those below it. Recently, vestiges of underbasals have been found in two species of this genus, and in both cases these plates had separated from the basal and be- come attached to the top stem joint (No. 281). Most of the forms of Crinoids already described have 158 SYNOPTIC COLLECTION. had a body composed of five basals and five radials. This, however, is not the case with Trigonocrinus. Its peculiar structure tends to prove that it is a form special- ized by reduction. PL 282, figs. 1-5, illustrate the prob- able evolution of this genus. Starting as a normal Crinoid with five basals and five radials (fig. i) it loses in time one basal and one radial and is like fig. 2. Three basals then become larger at the expense of one, while two radials increase in size (fig. 3). Trigonocrinus has reached the stage represented by fig. 4, in which the three basals are fused into one ring with only a vestige of the fourth plate, while two of the radials are usually fused. If this process of specialization by reduction is carried still farther, the vestige of a fourth basal would disappear and the two radial plates would become united, leaving no suture, so that one could see only three basals and three radials (fig. 5). An illustration of a Crinoid specialized by reduction is found in Cheirocrinus (No. 283, model of C. r&rttrHaH). For some reason the body with its drooping arms hung downward from the top of the stem (No. 283). This peculiar and unfavorable position has doubtless caused the irregularity in the body plates, and a reduction in the number of basals from five to three. The radials vary in form and bear only three arms. The living Crinoids are represented in this Collection by Metacrinus, Pentacrinus, Antedon, and Thauma- tocrinus. The magnificent specimen of the living Crinoid, Meta- crinus interruptus Carp. (No. 284), shows some of the parts on a large scale. The long stem is nearly round at its base, though it becomes pentagonal higher up. Many jointed cirri are given off in whorls along the whole length of the stem and the latter are closer together near the body. The body itself is surprisingly small. It consists of little basal and radial plates, while the lower plates of the five arms help to make up a portion of its upper part. METAZOA ECHINODERMA. 1 59 The large branching arms with their many pinnules are extremely graceful organs. The disc is small and the ambulacra extend from the mouth to the ends of the arms. The body is also small in Pentacrinus (No. 285), con- sisting chiefly of five basals and five radials. There are vestiges of underbasals, but these are sometimes wholly resorbed in the adult. Pentacrinus is attached by a long pentagonal stem (No. 286), the joints of which bear cirri. The ventral surface is flexible and has many irregular plates. The mouth is exposed and from it extend the five uncovered ambulacra. The uniserial arms are greatly developed, having a large number of branches which are well supplied with pinnules. Antedon ( = Comatuld) rosacea Linck (PL 287 ; No. 288) is a living Crinoid of great interest, inasmuch as its devel- opment recapitulates in a marked degree the history of the group to which it belongs. After escaping from the egg, the embryo is free and moves by means of bands of cilia (PI. 287, fig. i). Early on the eighth day (Bury) after development began, the larva became attached. On the tenth day the larva had developed a stem (fig. 2). In this stage the underbasals are found (fig. 2. ub} and above these the basals (fig. 2, b) . Although the sutures indicate only three under- basal plates, one small and two large, nevertheless it is probable that each large plate is formed by the coales- cence of two plates, so that originally there were five underbasals. 1 The resemblance of Antedon to a Cystoid is now strik- ing, and the existence of underbasals in the young is evi- dence of descent from the Palaeozoic Crinoids in which we have already seen underbasals well developed. As Antedon grows older, the underbasals and the top stem joint fuse into a single plate, the centro-dorsal, so that 'Phil. Trans. Roy. Soc. London, CLXXIX, 1888, p. 288. 160 SYNOPTIC COLLECTION. Antedon passes through the condition already shown by Millericrinus (No. 281). The armless Cystoid stage passes into the Penta- crinoid stage, in which uniserial arms grow out (fig. 3). These continue to increase in number. The centro-dorsal plate develops cirri, and by this time all trace of the underbasals is lost. 1 When ten cirri are developed, a separation takes place between the centro-dorsal plate and the stem ; the latter is left attached, while the animal breaks away and is henceforth free. A tiny opening is left in the middle of the aboral side, but later this is filled, though traces of the scar may be seen internally. After the animal liberates itself from its stem, it swims freely in the water. The cirri are used occasionally for crawling about on marine plants, or at other times for anchoring itself to rocks. According to Carpenter, 2 the adult Antedon has the habit of fixing itself to a rock and remaining for long periods. In this stage the body is extremely small and the basals have become metamor- phosed into the so called rosette, which is wholly con- cealed in the cavity of the ring formed by the radials. The mouth is in the middle of the oral disc and at one side of this opening is the anal tube. The fiye arms divide almost immediately to form ten organs which are disproportionately large for the size of the body and are well provided with pinnules. The floor of each ambulacral groove is ciliated, and the five ciliated grooves extend from the mouth over the oral disc to the ends of the arms. Actinometra (No. 289) is similar to Antedon but differs from it by having the mouth at one side of the oral disc and the anal tube near the center. 1 Carpenter, stated by Wachsmuth and Springer, Proc. Acad. Nat. Sci. Phila., 1888, p. 352. 2 Phil. Trans. Roy. Soc. London, CLVI, 1866, p. 698. METAZOA ECHINODERMA. 161 ASTEROIDEA. It is probable that Agelacrinus, belonging to the Agel acrinidae, was a descendant of an ancestral form from which the Asteroidea or starfishes of to-day arose. Using a simple but clear illustration we may say that if the hand should represent this trunk form, then the first fin- ger would stand for the Agelacrinidae. Another finger would represent the Asteroidea which began with the same trunk but developed along another and quite inde- pendent line. Since Agelacrinus comes nearer the probable ancestral form than any other fossil or any living species, we begin the study of the Asteroidea with this genus. Agelacrinus (No. 290, A. rhenanus} was without a stem, but it was attached by its dorsal or aboral side. The circular flat- tened . body was covered by a great number of small irregular plates which were imbricated or arranged like shingles on a roof. These plates were perforated, and usually the pores were in pairs. The mouth was in the middle of the upper side and was covered by plates. Radiating from the mouth were five ambulacra (No. 290) also protected by covering plates. At the tip of each ambulacrum there was a hole for the admission of water. Each ambulacrum consisted of two rows of plates and between these plates there were holes. The anus was situated in one of the areas outside of the oral disc, and between two of the ambulacra ; it was also covered by plates which were set into the body plates. The irregularity of the body plates, the absence of- arms, and the fact that the mouth, ambulacra, and anus were concealed by plates, all remind one of both- the Cystoids and the Blastoids. Zittel places this genus with the Cystoidea, though it seems to have more points of resemblance with the Asteroidea. 162 SYNOPTIC COLLECTION. Since specialized Asteroidea occur with the Cystoidea in the Cambrian formations, it is impossible for the former to have descended from the latter. We must, therefore, look for the ancestors of both groups in the pre-Cambrian rocks, and it seems most likely that such a form will combine the characters of both Cystoidea and Asteroidea. Most of the Palaeozoic starfishes, like those of to-day, were free -moving and crawled with the oral or actinal side downward. If we suppose an ancient star- fish to be attached by a stem extending downward from the middle of the aboral or abactinal surface, we have a striking resemblance to a stalked Crinoid. In such a case the mouth is in the middle of the upper side and the ambulacra run out from it into the arms. When, however, the starfish became free-moving, it turned upon the ventral side and the tentacles which had been use- ful in catching food became modified in time into loco- motor organs. It seems probable that the ancestral starfishes had a pentagonal body with spines slightly developed, and two rows of plates in each ambulacrum, the plates of one row alternating with those of the other. One of the descendants of such a form may be the living Ctenodiscus (No. 291, C. crispalus D. Kor.). When young (No. 291 a), it has a dome-like body which becomes flatter with age (No. 291 b, c). The adult has a large disc and short arms, giving it a pentagonal outline. The plates of the aboral side (No. 291 b) are small and leathery, the spines being slightly developed. Near the center is the anal tubercle. Each ambulacrum on the ventral side (No. 291 c) consists of two rows of alternating plates which are broad and not crowded closely together. There are two rows of holes for the tentacles which are without sucking discs. Every ambulacrum is flanked on each side by a row of good-sized interambulacral plates, and outside of these are well developed marginal plates (No. 291 c). METAZOA ECHINODERMA. 168 Gradually the pentagonal form tended to give way in Palaeozoic time to the stellate form illustrated by the ancient starfish Palaeaster (No. 292, model). The plates of the aboral side of the central disc are small and indefi- nite, but those of the arms are more or less regular (No. 292, specimen on the left). The anus is found on the aboral side, though the model does not show its posi- tion. The mouth is uncovered, but is surrounded by five plates. The ambulacra are also uncovered and con- sist of two rows of alternating plates (No. 292, specimen on the right) ; on the outer edge of each plate there is an opening for a tentacle (No. 292). Thus there are two straight rows of holes extending through each ambulacral groove. On either side of the ambulacral plates there is a row of prominent interambulacral (adambulacral, Zittel) plates (No. 292 b), and outside of these are large margi- nal plates. Respiration was effected in these early forms as in modern species by means of a water system consisting of a sieve or madreporic body, which in ancient forms was on the ventral side (Zittel), and of radiating tubes. The primitive forms are also represented by A stropecten variabilis Liitk. (No. 293), in which the marginal plates are conspicuous. Here the arms are more tapering than in Ctenodiscus, but the tentacles are still pointed and remain in two rows. In Hippasteria phrygiana Ag. (No. 294), the ambu- lacral plates are opposite and not alternating ; the tenta- cles are in two rows, but instead of being pointed they are provided with sucking discs and are, therefore, no longer true tentacles but rather locomotive organs or " tube feet." These organs are seen in the preparation (No. 295) which is a dissection to show the water-vascu- lar system after injection with blue coloring fluid. This system will be described more at length under the com- mon starfish, Asterias (see pp. 165-169). The ovaries 164 SYNOPTIC COLLECTION. and their openings are also seen in this preparation. No. 296 shows the stomach and its coecal appendages. The marginal plates in these forms are large, but those on the upper side have become small in Pentaceros modestus Gray (No. 297). The interambulacral plates are of good size and the tube feet have large suckers. The aboral disc and the sides of the arms are provided with stout conical spines. This tendency for the large marginal plates of the primitive forms to become reduced in size is seen in Paulia horrida Gray (No. 298). The spines in this genus are large and strong, and are found on the most exposed points. In the starfishes so far described the development of the ambulacral system and of the test or skeleton goes on together, but in the more specialized forms which follow, the development of the ambulacral system is accelerated. 1 In Linckia unifascialis Gray (No. 299) the disc is small and the arms long and six in number. Like the earlier forms it is spineless. The marginal plates are reduced in size. The ambulacra are narrow and some- what crowded, while they carry two rows of tube feet provided with suckers. The tendency to multiply the number of arms is seen in Solaster endeca Forbes (No. 300). Here there are nine rays radiating from a disc of considerable size. There are few spines, and the surface is granular. The two rows of ambulacral feet are pro- vided with sucking discs. The deep-sea species, Zoroaster fulgens Wyv. Thorn. (PI. 301, figs. 1-3), is of especial interest. The young (fig. i) has a much higher disc than the adult. The plates of the aboral side are distinctly seen, and for this reason the genus is an admirable one for comparison with Crinoids. The central plate is surrounded by five 1 Sladen, Chall. Rep., Zool., XXX, part 51, 1889, p. xxxv. METAZOA ECHINODERMA. 165 small underbasals (fig. i) and five basals (shaded in fig. i). Outside of these are five radials. Regular plates extend outward to t-he tip of the arms, where are found the terminal or ocular plates. This definite ar- rangement of plates so finely illustrated by both the larval and adult Zoroaster, occurs in some of the larvae of the more specialized Asteroidea, but is soon lost in, the process of development. While these characters are all of a primitive nature, Zoroaster possesses other peculiarities which place it near the more specialized genus Asterias. The disc is small and the arms long and tapering (fig. 2, showing spines but not plates). The tube feet have sucking discs, and, unlike the genera already described, there are four rows of these locomotive organs (fig. 3). One of the commonest starfishes on the New England coast is Asterias forbesi Verr. (Nos. 302-308). This ani- mal passes through an indirect development with a marked and peculiar metamorphosis. Like most starfishes when young, the larva or brachio- laria, as it is called, is bilateral with four arms on either side, so that the marked radial symmetry which appears later is a secondary and not a primitive character. The aboral side is raised and more or less dome- shaped. The spines are in regular rows, according to A. Agassiz, and the plates remind one of those of Crinoids. Underbasal plates have been found in two species of Asterias (A. rtibens and A, glarialis 1 ). The basals and radials appear in the very young larva and are homolo- gous with the same plates in the Crinoid ; but as develop- ment goes on, it becomes impossible to trace them. By many authors the terminals or ocular plates of starfishes, Ophiurans, and sea urchins have been considered as homologous with the radials of Crinoids ; but it has been shown 2 that the radials in starfishes are developed be- 'Sladen, Quart. Journ. Micr. Sci., XXIV, 1884, p. 34. 2 Sladen, ibid., p. 29. 166 SYNOPTIC COLLECTION. tween the basals and terminals, and that the latter are pushed outward with the growing arms. These are addi- tional plates and are not horaologous with any plates of the Crinoids. The anus in the young is near the edge of the oral or actinal side. The arms at this time are broad, short, and unequal in length. The ambulacra running out from the mouth have two rows of organs which are like tentacles, being pointed at the end. The madreporic body is near the edge of the actinal side. As the starfish grows older, radial symmetry predominates, and the five equal arms radiate from the small central disc. The body becomes flat- tened, and the spines and plates more or less irregular. The monotony of the spiny upper surface is broken by the little radiately-grooved madreporic body (No. 302) which has moved from the actinal area and is at the junc- tion of two arms on the abactinal side. The anus has also moved and is near the center of the abactinal side. The ambulacra carry four rows of organs which have devel- oped suckers at the ends and become thereby efficient locomotive organs. In the center of the ventral side is the mouth sur- rounded by a membrane and guarded by five sets of spines. Although the normal number of arms is five, it some- times happens that only four are developed. On the other hand in a collection of about eight hundred star- fishes from Salem Harbor, there were, according to Mr. N. L. Wilson, two six-rayed specimens and one seven- rayed specimen. The power of the animal to reproduce lost arms is shown in No. 303 where four arms have been lost, but one has grown out to half the size of the fully grown arms. No. 304 is probably a starfish that has been wounded in some way. In trying to repair the injury it produced the semblance of an arm. A specimen of this kind is met with occasionally on our coast. METAZOA ECHINODERMA. 167 The skeleton of the adult is composed of an irregular network of beams and spines which are covered by a thin layer often called the epidermis. This layer can be scraped off with a knife, proving that the skeleton is internal. The majority of the spines are immovably fast- ened to the beams of the skeleton, but on the lower side along each ambulacrum there are spines of quite a differ- ent character from those above. These are more slender and tapering, and are connected with the skeleton either by cushions or by ball-and-socket joints, allowing of con- siderable freedom of motion. Among the spines of the starfish are little characteristic forked organs called pedi- cellariae, which are spines modified for a special purpose not yet known with certainty, though it is evident that they are used for taking hold of objects. They are found at the bases of the spines, on the soft membrane between the spines, and also on the movable spines of the lower side. In those Asteroidea that have four rows of tube feet there are two kinds of pedicellariae ; in one the blades are opposite and in the other they cross like scis- sors. The plates of the skeleton are finely seen in the prepara- tion. No. 305 (specimen on the left) shows the irregular network of plates in the upper side or back, and the speci- men on the right the two rows of ambulacral and interam- bulacral plates in the lower side. The ambulacral plates are movably articulated at the inner end. Between the am- bulacral plates can be seen the four rows of holeb through which pass the tube feet with sucking discs at their ends. On each side of the groove formed by the ambulacral plates is the row of rounded, imperforate interambulacral plates which bear the movable spines already described. Nos. 306-308 are preparations of the starfish, showing the internal structure. The mouth leads into a stomach which can be thrown over a mussel or other animal. By the power of suction the food is taken in and the hard parts thrown out of the mouth. A coecal prolongation is con- 168 SYNOPTIC COLLECTION. tinued from the stomach into each arm (No. 306). The stomach is extended above into a short, indefinite intestine which opens near the center of the aboral area. It does not seem to be functionally useful and may be the remain- ing vestige of the well defined anus of the Crinoids (Pack- ard). Opening into the intestine is the liver which consists of two long branches that extend into each arm (see No. 306). According to Griffith and Johnstone 1 the "saccu- lar diverticula " of the starfish are not hepatic but pancre- atic in function. On chemical analysis they find the secre- tion is similar to that of the vertebrate pancreas. The reproductive organs ovaries or testes are on either side of each arm (No. 308) and open by slits at the base of the arms near their junction with the central disc. No. 306 and also No. 307 are specimens injected with blue colored fluid to show the water-vascular system, which arises as an outgrowth from the digestive system as is the case with the Ctenophora. It consists of the madreporic body, a short canal called the stone canal which extends to a circular ring around the mouth (cir- cumoral ring) from which five radial vessels are given off, one into each arm ; these in turn connect with the water sacs or ampullae of the tube feet which are seen in No. 307 extending in rows to the tip of each arm. The true vascular blood system is difficult to observe. The heart or pulsating vessel runs parallel with the stone canal. The body cavity is filled with a watery fluid containing corpuscles evidently representing the blood of more spe- cialized animals. There are also delicate, tubular organs, described as dermal branchiae, extending from the dorsal surface, which probably have a respiratory function; sometimes these may be seen swollen with water. On the dorsal side there are many minute pores through which water may enter or leave the body cavity. 1 Proc. Roy. Soc. Edinburgh, XV, 1888 ; quoted in Amer. Nat., XXIII, 1889, p. 1101. METAZOA ECHINODERMA. 169 The preparation (No. 308) shows the nervous system in part. This consists of a ring encircling the esopha- gus, and radial nerves which are the white cords seen in No. 308 running to the end of the arms. OPHIUROIDEA. The evidence seems to point to the view that the Ophiu- rans have descended from some one of the more specialized Crinoids - 1 Notwithstanding that many genera retain throughout life the underbasals, basals, and radials of the abactinal area possessed by some Crinoids and by larval Asteroidea, nevertheless peculiar modifications have arisen which place the adult Ophiurans farther from the primi- tive, pentagonal, larval form than the adult Asteroids. Generally speaking the radials are developed before the basals and underbasals, and are of large size. We have seen in the specialized Crinoids the tendency toward the increasing development of the radials and the reduction of the basals. It has been shown by Fewkes 2 and others that the young Ophiuran, like Asterias, is at first bilaterally sym- metrical and that later it takes on the pentagonal form which gradually, with the development of the arms, changes to the modified stellate condition of the adult. The bilateral larva possesses an intestine and anus, but later both disappear, so that the adult is more reduced in this particular than the starfish. Ophiopholis aculeata Gray (No. 309), has a circular, sharply defined disc which bears minute spines. The long r rounded, un branched arms run out directly from the disc and are of about the same size throughout. They are pro- tected by haj-d plates, dorsal, lateral, and ventral shields,. 1 Sladen, Quart. Journ. Micr. Sci., XXIV, 1884. 2 Bull. Mus. Comp. Zool., XIII, no. 4, 1887, p. 107. 170 SYNOPTIC COLLECTION. the homologies of which are a subject of much discus- sion. It is generally considered that the ambulacral plates are inside the arms in the form of an axis of jointed sections or arm-bones. If this is the case, then the ventral plates are additional ones and are not homologous with any other plates of the Asteroids. 1 They may be developed for the purpose of protecting the delicate water-tube, blood-tube, and nerves which run through the arms and which are ex- posed in Asterias. The lateral plates bear lateral spines which are probably helpful in locomotion. Each arm-bone is pierced by a water-tube or tube foot which is without ampulla or sucking disc, and therefore of no use as a lo- comotive organ. These tube feet come out between the ventral and lateral shields. Above, the base of each arm is protected on either side by the so called radial shields, while below near the mouth are the oral shields. The internal organs are all concentrated within the disc. The genital organs open by slits on the lower side at the base of the arms. The madreporic body is also on the lower side in one of the mouth plates. Ophiopholis de- velops without a metamorphosis. The disc of Ophiura (No. 3'io, O. panamteri Liitk.) is granulated, and the arms are well protected by the numerous short flattened spines. Ophioplocus (No. 311) resembles Ophiura in having a granulated disc. The radial shields are small. Ophio- coma cethiops Liitk. (No. 312) has wide upper arm-plates and large spines. The young Astrophyton resembles the typical Ophiuran in having a flat disc covered by plates. In the process of growth, these become covered by a granulation and later both granulation and plates, except those at the mar- gin, disappear. 2 1 Bull. Mus. Comp. Zool., loc. cit., p. 144. 2 Chall. Rep., Zool., V, part 14, 1882, p. 253. METAZOA ECHINODERMA. 171 The radial shields increase in size. The arms divide many times and the great number of flexible branches intertwine with one another, giving a basket-like appear- ance, and the name of Basket-fish, to the animal (No. 313). These arms are without the dorsal or ventral plates pecul- iar to most Ophiurans, though there are irregular plates which may be vestiges under a thick skin. The arms are without spines. In some species of Astrophyton there are no oral shields, while there may be one madreporic body or five. ECHINOIDEA. The primitive rocks of the Lower Silurian formation have yielded a primitive sea urchin whose marked sim- plicity of structure offers a sufficient reason for consider- ing it as an ancestral form. This urchin, Bdthriocidaris pahle?ii Schmidt, by name (PI. 314, fig. i, enlarged twice), has a globular corona (popularly called shell) with the mouth in the middle of the lower or abactinal side and the anus opposite. It has a small number of simple spines, a few of which are seen attached in the figure. The spines are only 4 mm. long and are therefore not of disproportionate length. The ambulacra are the first areas to be developed, around the oral disc or peristome (fig. 2) ; they are, therefore, of primary importance, while the interambulacra arise secondarily in the spaces between the ambulacra. Beginning at the center of the actinal area it is seen that there are two complete circles of ambulacral plates extending around the mouth, then comes a circle of ten ambulacral plates and five interam- bulacra 1 plates not wholly seen in fig. 2, i' . The ambu- lacral plates are pierced by two holes which are separated by a partition. It is seen that each ambulacrum origi- nates in two plates, while each interambulacrum arises from one plate. This stage is permanent throughout the 172 SYNOPTIC COLLECTION. life of Bothriocidaris. It is a primitive and an extremely important stage, illuminating the otherwise obscurely complex structure of the specialized Echinoidea. For this reason it is called by Dr. Robert T. Jackson the protechinus stage. 1 As we have already said, the anus is opposite the mouth. It is surrounded by plates, outside of which are ten terminal plates of the ambulacral and interambulacral areas. Each ambulacrum and interambulacrum ends in one plate but none of these plates have pores. Thus it is seen that there is little differentiation of the abactinal area from the corona proper. Summing up the distinguishing characters of this ancient Echinoid we have the following: A small number of plates in the globular corona ; slight differen- tiation of the actinal and abactinal areas from the corona proper ; a small number of simple spines. If now we come to the present time and examine Goni- oridaris canaliculata A. Ag., we find in the young (PI. 315, fig. i ; fig. 2, side view of same) some instructive structural features. Around the mouth is a circle of ambulacral plates, while the circle next to this one has ten ambulacral plates (fig. i) and five interambulacral plates (fig. i, /) as in Bothriocidaris. Therefore it is true that each ambulacrum in Goniocidaris arises from two plates, and each interam- bulacrum from one as in the ancient genus. The individual plates of the ambulacra are hexagonal and nearly on a level with the hexagonal interambulacral plates as in Bothriocidaris, but unlike this genus each plate has only one pore. The similarity in structure between the young Goniocid- aris and the adult Bothriocidaris is striking and of value 1 We are indebted to Dr. Jackson for many of our figures and facts concerning fossil Echinoidea. See Bull. Geol. Soc. Amer., VII, 1896, pp. 135-170; also pp. 171-254. METAZOA ECHINODERMA. 173 from a phylogenetic point of view. As Goniocidaris grows older, two rows of interambulacral plates arise from the single plate (fig. i, i, 2 ; also fig. 2) so that there are two rows of ambulacral plates alternating with two rows of interambulacral plates. The ambulacral plates become differentiated and are lower than the pentagonal interam- bulacral plates, while each plate has two pores. The adult Goniocidaris never goes beyond the stage rep- resented by the two rowed ambulacra and interambulacra. Correlated with this simplicity of external structure we have a primitive mode of development. In other words, Goniocidaris develops from the egg without passing through a metamorphosis. We have already seen that while a few starfishes develop in a primitive way, most of them pass through a complex metamorphosis. The early stages "of Echinoids that under- go such a transformation are similar to those of starfishes. The embryo or pluteus has eight arms and is bilaterally symmetrical. The metamorphosis of the Echinoid, how- ever, is accomplished very rapidly. "In less than an hour," according to Bury, 1 "a perfect Pluteus is trans- formed into a small, rounded Echinoid in which radiate symmetry entirely replaces the bilateral symmetry of the larva." The internal structure of the young Goniocidaris is primitive. For a time the intestine is a closed tube, there being no mouth nor anus. During this period the animal takes no food, and moves about by five provisional tube feet. It is later that the eating apparatus is developed which causes a modification of the oral area and a resorp- tion of some of the plates of the corona ; finally the intes- tine breaks through the anal disc. The genus Cidaris (No. 316, C. thouarsi Val., with spines; No. 317, without spines) when young possesses the circle of ventral plates entire, and also the primitive 1 Quart. Journ. Micr. Soc., XXXVIII, 1895, p. 77. 174 SYNOPTIC COLLECTION. condition of the two rowed ambulacra and the one rowed interambulacra. Later some of the ventral plates are resorbed causing more or less irregularity in the shape of those that are left, while the tv\o rowed interambulacra arise and remain essentially unchanged. The ambulacra of the adult' are narrow with a single nearly vertical row of paired pores. The interambulacra on the other hand are broad and carry the primary spines which are large and few in number. The anus is somewhat raised above the anal disc. Surrounding the latter is the ring of genital and ocular plates, the genitals pointing outward and the triangular ocular plates inward. The spines of this species are cylindrical. Some are young and short with distinct vertical ridges on the sur- face, while the older ones are long and are entirely cov- ered with a growth of algae, etc. Very different from these are the modified spines which are found on the abactinal surface of the corona and which also crowd the actirial area. These are like short, stout, flattened clubs. It has been seen that the Cidaridae of the present era retain in their youth many of the primitive characters of the ancestral Bothriocidaris. The changes that convert the young into the adult are an increase in the number of coronal plates, the differentiation of the actinal and abac- tinal areas from the rest of the corona and the modifica- tion of the spines. While the Cidaridae represent one division of ancient Echinoids, another and more specialized division includes the Melonitidae. The generalized members of this family are Rhoechinus and Palaeechinus, and the specialized are Oligoporus and Melonites. Although there is a slight overlapping of the ambu- lacral plates in Rhoechinus, as seen in PI. 318, fig. i, owing to the fact that these plates are not united along their edges, still they may be said to extend across one half of the ambulacral area as in the ancestral form so that only two rows of ambulacral plates exist. METAZOA ECHINODERMA. 175 The number of rows of plates in the interambulacral areas of the simplest species of .this genus is four, and of the most specialized eight. The adult Palaeechinus gigas McCoy, has the primitive ambulacral plates, , <, on the margin of the ambulacral area (PL 318, fig. 2, shows a portion of one ambulacrum ; b, primitive plate; a not drawn), while two other plates have arisen (a 1 , b 1 ). The interambulacrum has from five to six or seven rows of plates ; six are clearly shown by the red dotted lines in fig. 3. This drawing begins at the point of origination of the fifth row of plates, those below this point not being preserved in the specimen. The fig- ure shows that the columns 5 and 6 originate in a single plate as we have already seen is the case with the inter- ambulacral rows of Bothriocidaris. The initial plate is always near a seven-sided or heptagon plate (fig. 3, JT). In Palaeechinus the anal disc is surrounded by the ring of alternating genital and ocular plates ; the former are pierced by three holes while the latter have two. When we pass to the genus Oligoporus we find in the young as represented at the ventral border two rows of ambulacral plates (PI. 319, fig. i, a, b) , while farther up the corona the adult condition of four plates (fig. i, 0, b, a', '; fig. 2) is seen, and still farther up new plates arise (fig- 2). The number of rows of interambulacral plates has in- creased to nine (fig. 3) in the most specialized species of this genus (^Oligoporus danae M. & W.). The forms we have already described lead the way to a better understanding of the complex structure of Melo- nites (No. 320, a-d, M. multiporus Norw. & Owen). These fossils are occasionally preserved with some of the spines attached. The latter are small (PI. 321, fig. i, magnified 6+ diameters) and when not fastened are some- times found in the hollows of the corona. The ventral border of the shell (see No. 320, a, b\ PI. 321, fig. 2) shows the ambulacra and interambulacra. 176 SYNOPTIC COLLECTION. The .ambulacra arise from four plates (PI. 321, fig. 2, a, b, a\ b 1 ; fig. 3, ambulacrum enlarged, a, b, a', b 1 ). This would indicate that in the development of Melonites the adult condition of Bothriocidaris, in which the ambulacra consist of two rows of plates, has been skipped by the law of acceleration in development, and that the four-plate stage is homologous with the adult of Oligoporus, as pointed out by Jackson, or it may be, as suggested by this investigator, that the ambulacrum of Melonites starts with two plates which might be seen in the young could such specimens be obtained. If this is the case these plates have been resorbed during the growth of the animal. New rows of plates are added between those already formed (PI. 321, fig. 3, c, d, and e,f) , so that each ambu- lacrum becomes more complex than any so far described. A cross section of an ambulacrum (fig. 4, magnified 2 diameters) shows the relative thickness of the four ambu- lacral plates, and also proves the fact that the holes pass diagonally and not straight through the shell. The dotted portions of the pores are reconstructions, these parts not being clearly shown in the section. The interambulacrum (No. 320; also PI. 321, figs. 2, 5) apparently arises from two plates as seen in the speci- mens (No. 320, the dotted lines beginning in two plates; also seen in PI. 321, figs. 2, 5). According to Jackson it is most probable that this area originates in one plate, which later was resorbed. With the growth of the animal the interambulacrum becomes complicated by the addi- tion of a number of rows (fig. 5). This diagram repre- sents the ideal arrangement of plates in one interambula- crum as determined by prolonged and critical observation of a large number of specimens. The theoretical plate /' is included in the figure to indicate all the possible plates the interambulacrum had at any period of growth. This plate is resorbed in the adult, as already stated. Eight rows are found most commonly. As these rows approach the anal area the mechanical necessity of the case com- METAZOA ECHINODERMA. 177 pels them to be drawn out and to diminish in number while at the same time the plates themselves become more or less rhombic in form. The lines x, y, z in PI. 321, fig. 5, bisect eight rows, and indicate by their narrowing angle the stringing-out arrangement of the plates in this area (Jackson) . This reduction does not seem to be comparable to the dying out of parts or organs so characteristic of gerontic forms. As Dr. Jackson aptly says, it may be compared to a flock of sheep coming through a narrow pass. The small number in the pass does not mean that the flock is les- sening, but that no more can get through at once. If this were a gerontic condition we should expect to find the middle or latest formed rows disappearing first and not the lateral or primary rows. This is the case in the few gerontic specimens observed (see below). If now a graphic summary of our knowledge of the development of the ambulacra of the Palaeozoic Echini be given (PI. 322, A-G) it will show at a glance that the primitive and fundamental simplicity of Bothriocidaris (A) has given rise through progressive steps represented by Rhoechinus (B), Palaeechinus (C), and Oligoporus (D at ventral border, E at ambitus) to the complexity of Melonites (F at ventral border, G at ambitus). Dotted lines are drawn through the primary plates a, b in each, and also through the secondary plates a\ tf. New plates begin to appear between these in Oligoporus (E) and probably constitute the rows c, d in Melonites near the ventral border (PI. 321, fig. 3), while at the ambitus ten rows are found. The remarkably large #nd fine speci- men of Melonites gigantcus Jackson (Pi. 323, photo- graph) shows still greater specialization than Melonites multiporus. There are twelve rows of ambulacral and eleven of interambulacral plates. The interambulacral area (PI. 323, fig. 2, at the right) is especially interesting, since it shows a tendency toward specialization by reduc- tion. The last formed row of plates (n) has died out 178 SYNOPTIC COLLECTION. completely before reaching the anal area. Only a few specimens with this specialized character have been observed. In this species the new rows are introduced early in life, showing that the law of acceleration in development is in operation. The Melonite form is also much more pronounced than in Melonites multiporus. The anal disc of Melonites is surrounded by the ring of alternating genital and ocular plates. The five genital plates can seldom be seen in specimens although well preserved in No. 320. These plates are pierced by holes, while the ocular plates, according to Jackson, are without perforations. 1 It is seldom that the history of a group can be made out by the study of a portion of the adult of a single genus, but we have already seen that such is the case with Melonites. The primitive condition of Bothrioci- daris, the successive progressive stages of Rhoechinus, Palaeechinus, and Oligoporus are all represented in the ventral border and in one ambulacral and one interambu- lacral area of Melonites. Nor is this all; the greater specialization by the process of reduction is illustrated by a few specimens of this genus. We have seen that Goniocidaris and Cidaris are among the most primitive of living Echinoids. Alexander 1 Meek and Worthen (Geological Survey of Illinois, II, 1866, p. 228) state that the ocular plates of Melonites multiporus M. & W., are without any traces of pores, and the figures are drawn without them. In a footnote, however, they add, since the above was written, we have^ examined "another fine specimen showing the disc. In this there are four ovarian pores in three plates, and three in each of the other two, while in two of the ocular pieces there is apparently a single pore near one side." Roemer figures the oculars with two pores (see Arch. f. Naturg., I, 1855, pl..xii, fig. 4). In the text he says, p. 322, "The number and position of the pores in these [ocular plates] cannot be recognized with complete certainty, yet, there are apparently two of them in each plate and at the same height as those in the larger plates" [geni- tal plates]. METAZOA ECHINODERMA. 179 Agassiz l has shown that the young of all other Echini have the general characteristics of these primitive forms. They all agree in having a small number of plates in the corona, slight separation of the actinal and abactinal areas from the corona proper, nearly vertical rows of paired pores, and a few spines of disproportionate length. Having this common origin we shall see what variations arise in the adults of a number of species. In Arbacia pustulosa Gray (No. 324), the actinal area is large and the ambulacra are broad at the starting point, growing narrower as they reach the edge or ambi- tus. The interambulacra, on the other hand, are narrow at the ventral border and broader towards the ambitus. The pores preserve their primitive character, being in sim- ple vertical rows. The anal disc in this species consists of five plates ; around these is the ring of five genital plates which are developed after the anal disc. The ocu- lars are crowded outside of this ring and fit into the places left by the outer angles of the genitals. This genus is interesting for the fact that its spines never become artic- ulated but remain in the more primitive condition of the unjointed spines of the starfish. In Diadema setosum Gray (Nos. 325, 326), the nearly vertical row of pores in the narrow ambulacra becomes changed during the growth of the animal into nearly ver- tical arcs of three or four pairs of pores. The corona is thin with broad interambulacra. The actinal area is membranous with well developed teeth. The anal disc (No. 326) is also membranous and flexible, with the anus raised on a tube near the center. According to A. Agassiz 2 this anal tube is as prominent in the young as the anal tube of some species of Comatulae. Three of 1 Palaeontological and Embryological Development, Proc. Amer. Assoc. Adv. Sci., XXIX, 1880, p. 389; also consult review of the same by E. D. Cope, Amer. Nat., Oct., r88o, p. 725. 2 Rev. of Echin., Mem. Mus. Comp. Zool., Ill, 1872, p. 276. 180 SYNOPTIC COLLECTION. the ocular plates join the membranous disc, and separate the genital plates, while the other two which are each side of the madreporic plate are crowded outside of the ring so that they do not touch the anal membrane. The slender spines of the adult (No. 325) are usually more or less solid though in youth they are hollow. They vary in size, the smaller ones being light colored and the large ones dark with longitudinal ridges. These ridges are provided with short pointed teeth, so that one cannot pass the finger downward from the tip end of the spine to its base without being pricked by the sharp points. Echinothrix turcarum Ret. (No. 327), has the pores in arcs of three pairs similar to those of Diadema, but unlike this genus the arcs are independent of each other. The ambulacra broaden out slightly on the abactinal sur- face, suggesting the petaloid condition of the more special- ized Clypeastroids. The ambulacral areas are crowded with many small spines, while the longer and more delicate ones are on the interambulacra. Colobocentrotus atratus Br. (No. 328), is peculiarly modified in the shape of its corona and spines. The ven- tral side of the former is very flat and the dorsal part rises like a low dome. The closely set, dark colored spines, like tiles in a pavement, cover this dome, completely con- cealing everything beneath. If these spines are removed the low rounded tubercles are seen (No. 328). The ven- tral surface is covered with short cylindrical spines crowded closely together. From the ambitus the long spines resembling clubs extend downward causing the sea urchin to look as though it were mounted on many stilts. It is these spines that mask the real shape of the corona, making the dome appear much higher than it really is. In spite of the close pavement of spines there are many tube feet in the ambulacral areas ; these are arranged in arcs of six or seven pairs. The young Heterocentrotus mammillatus Br. (No. 329), METAZOA ECHINODERMA. 181 shows the dark pavement spines finely, especially on the dorsal side. Among these, on the ventral side, are spines similar to those on which Colobocentrotus stands. The longest club-shaped spines extend outward from the sides of the corona, while young ones are seen just growing from the upper surface. In the adult (Nos. 330, 331) the pavement spines have longer cylindrical stems by which they are attached, while the great club-shaped spines have become formidable organs of defence. The size of these organs is correlated with the increased thickness of the corona. The oral area is large, having encroached upon the corona. The ambulacra are broader on the lower side than the interambulacra, while above the ambitus they are narrow, and the pores are in narrow arcs of num- erous pairs. Our common sea urchin, Strongylocentrotus drobachi- ensis A. Ag. (PI. 332 ; No. 333, two spiny specimens and a preparation of the shell), has the corona made of two rowed ambulacra and interambulacra. Each ambulacrum begins in the young with two plates, as shown in PI. 332, fig. i, and each interambulacrum in one plate (fig. i, i'). As the urchin grows older a portion of the ventral border is resorbed, as shown in fig. 2, and the oral area is mem- branous and spineless. No new rows of plates are added in either the ambulacra or interambulacra, so that there are only twenty rows of plates in all. These are shown in the admirable preparation (No. 333), where each indi- vidual plate has been separated and mounted. The ambulacral plates show the arcs of pores which vary but usually consist, of four or five pairs. These have arisen from the unbroken vertical rows of pores of the young. The anal disc is seen to the right, made of tiny plates which are placed together with considerable irregularity; a little to one side of the center is the anus. The last plate terminating each interambulacrum is a genital, the largest of which is the madreporic body ; an ocular plate is at the tip end of each ambulacral area. The five geni- 182 SYNOPTIC COLLECTION. tals and the two oculars form the ring around the anal disc, the other three oculars being crowded outside the ring. The globular form and melon-like aspect of Echinus melo Lam. (No. 334), are striking. These melon-like sec- tions mark off distinctly the five ambulacral and five inter- ambulacra] areas. The plates of the anal area are numerous, small, and irregular, while the five ocular plates are all crowded out- side of the ring. The spines of Echinus acutus Lam. (No. 335), are far removed from those of primitive and embryonic forms, being small, short, and similar on both ambulacra and in- terambulacra. In this specimen the tube feet are seen extending from the shell. IRREGULAR SEA URCHINS. CLYPEASTROIDS. Pygaster patelliformis Ag. (No. 336), is one of the primitive Clypeastroids. The corona is dome-shaped above and flattened below, resembling the regular sea urchins. The mouth is placed near the center of the oral area, but the anus is not directly opposite as in the sea urchins so far examined. It extends from near the apical disc to the margin and is large in size. The ambu- lacral areas are narrow with simple vertical rows of paired pores, while the interambulacra are broad. Young Clypeastroids in general possess a small number of plates in the globular corona, a few large spines and tubercles, simple vertical rows of pores with no petal-like pattern on the dorsal side. Internally there are no parti- tions. With age the corona becomes more flattened, the number of plates increases, the spines grow smaller, and the pores form into petals, proving that the petaloid con- dition is a specialized one ; and that the sea urchins pos- sessing it should be placed after those whose pores are in METAZOA ECHINODERMA. 183 vertical rows or in arcs. The internal partitions so char- acteristic of the irregular sea urchins are found in the adult, sometimes, however, in a rudimentary condition. The typical characteristics of the first division of the irregular sea urchins are well shown in Clypeaster sub- depressus Ag. (No. 337), and for this reason, it would seem, the name of Clypeastroids is given to the division. There is, however, no well defined line between this group and the next, the Spatangoids, so that it seems better to place both under the head of the irregular sea urchins. The corona of Clypeaster is flattened and longer than it is broad. It can be so placed as to bring the odd am- bulacral petal in the median line, and the remaining two pairs of petals on either side, thus dividing the test into two nearly equal parts. The mouth is near the middle of the lower side and the simple ambulacral grooves extend outward from it. There are delicate spines in the grooves, and stronger ones on top of the conspicuous petals when these are formed. The anal system has moved from the upper to the lower side, near the margin, and the anus is seen in No. 337, so that the Clypeastroid has an anterior and a pos- terior end. The abactinal area is far more indefinite than in the regular urchins. It is made up partly of the madreporic body which is in the center. Four or five genital open- ings are seen, but the plates themselves do not appear. If the upper portion of the test is removed (No. 337), the immense jaws with two teeth are exposed. These jaws consist of five strong parts which taken together con- stitute a powerful eating apparatus. The upper and lower parts of the shell are connected by slender pillars (No. 337) which are an important characteristic of the Clype- astroids, the regular sea urchins having nothing of the kind. Around the outer edge these pillars unite, forming more or less open walls, as seen in No. 337 where a por- tion of the edge has been removed. 184 SYNOPTIC COLLECTION. Sometimes the ambulacral petals take up the greater part of the upper surface of the corona, as is the case with Echinanthus rosaceus Gray (Nos. 338-340). The central portion of each petal is raised while the furrows of the pore-bearing zones are sunken, making the rosette most conspicuous. Here, as in Clypeaster, the madreporic body is in the center. Joined to it are the ocular plates perforated for the ocular pores (not seen in No. 339), while beyond it are the genital plates with their openings (No. 339). The spines of this genus are small as are most of the Clypeastroids. When removed as in No. 339 the tubercles are seen to be much reduced in size from the regular urchins. The vertical section (No. 340) ex- hibits the powerful jaws and the massive pillars of the interior. Not only are the upper and lower portions of the test united by pillars but in Laganum depressum Less. (No. 341), there are walls running parallel with the margin, as seen in the cross section (No. 342). In this genus the edge is much thickened, and the anus is on the lower side quite near the mouth. The young Echinarachnius parma Gray, varies in form, but in No. 343 it is circular and somewhat dome-shaped, while in other specimens it is elliptical. No. 343, a-e, has light colored spines attached. There are two rows of these on both the ambulacra and interambulacra. They are short and delicate, very different from the long spines of the primitive and embryonic regular sea urchins. The youngest specimen (No. 343, a) is without a distinct am- bula'cral pattern, and the ambulacral grooves of the lower surface are scarcely visible. In an older specimen meas- uring 5.1 mm. these grooves have been seen, and accord- ing to A. Agassiz minute pores were formed in them. The mouth is near the middle of the lower side pro- tected by spines above (No. 343, c) and sunken within the corona are the five horizontal teeth. The anus at this stage is on the upper side a short distance from the METAZOA ECHINODERMA. 185 margin (No. 343, b), while the madreporic body occupies the usual central position of the anal area as seen in the regular sea urchins. No. 343, g, has been bleached by nature and through the microscope the openings of the madreporic body are clearly seen. As the sand-dollar grows older it becomes flattened and more or less heart-shaped (No. 343, h-1). The petals become distinct, the outer ends are open, and the pores extend towards the ambitus, but do not reach the edge. At this time the internal partitions radiate in five pairs from the edge toward the center and there are few pillars. The ambulacra and interambulacra are often distinctly seen in these younger stages, as in No. 343, m and n, where the limits of the individual plates can be easily traced ; those on the lower surface are much more irregular than those above. The ambulacral furrows are simple but branch at their outer extremities. Sometimes, as in No. 343, p. there is no indication whatever of these furrows. The ocular openings at the ends of the ambulacra are large, but the genital plates and pores cannot be detected. The adult (No. 343, r, s) is more flattened than any of the Clypeastroids and is covered by tiny, dark colored spines (No. 343, r). It is usually difficult to make out the ambulacral and interambulacral plates, but if the specimen is bleached by nature, or treated with acid as is the case with No. 343, s, they come out more clearly. They are also finely seen from the inside when the dorsal side is removed. The ambulacral furrows are well defined and branch a few times. The petals above are large with furrows between the holes ; they open at their outer ends in very flat sand-dollars while in more convex specimens they nearly converge. A few pairs of pores extend downward from the petals towards the edge (No. 343, s). The anus has moved downward to the edge (No. 343, 186 SYNOPTIC COLLECTION. r, s). Around the madreporic body are five ocular openings at the ends of the ambulacra, and four genital openings at the ends of the interambulacra. The inter- ambulacrum opposite the odd petal is without a pore. The preparation (No. 344) shows the five pairs of parti- tions which radiate from the edge towards the center with space between each pair of partitions. There are other pairs that occupy the interambulacral areas while many pillars are crowded together on the ambulacra. Greater specialization of structure marks the species Echinarachnius excentricus Val. (No. 345). Here the lower side is marked by radiating furrows that divide close to the mouth and afterward subdivide and send their branches over to the upper surface. Three of the petals are larger than the other two, and the mound bearing the rosette is not in the center but nearer the posterior end. The anus has moved from the edge to the lower side. Encope grandis Ag., when young is circular in outline and is without the rosette or lunules. The adult (No. 346) has five large openings into the margin besides the completed lunule in the median interambulacrum. The petals of the rosette differ in size and shape, the pos- terior pair being longer than the others and extending nearly to the lunules. The madreporic body is star-shaped and four genital openings are at the tips of the rays, while the fifth opening is nearer the center. The five ocular pores are at the angles of the rays. In conclusion it may be said that the young of all the Clypeastroids are much more like Echinometra and the regular sea urchins than they are like the adults of their own group. This is sufficient reason for placing the Clypeastroids next the regular sea urchins and before the Spatangoids. METAZOA ECHINODERMA. 187 IRREGULAR SEA URCHINS. SPATANGOIDS. One of the ancestral forms of the more specialized division of the irregular sea urchins commonly called Spatangoids is Pyri?ia subsphaeroidalis d'Orb. (No. 347), in which the test is high and dome-shaped and the ambu- lacra are arranged in the primitive fashion of vertical rows from mouth to apex. The mouth is nearly central in this genus, while the anus is on the dorsal side of the posterior part. The young forms of this group which are living to-day are similar to the young of the regular urchins and of the Clypeastroids. In fact the starting point of these groups is the same, as shown by A. Agassiz. 1 The Spatangoids have at first the vertical row of pores running from mouth to apex, few tubercles of large size, spines of disproportionate length and size, and a simple lipless mouth. The adults, however, carry specialization much farther than any other members of the class. Beginning with the more generalized forms we find Echinoneus semihmaris Lam. (No. 348), is dome-shaped with the ambulacra in vertical rows and no petals formed throughout life. The mouth is near the center and as in many Spatangoids is without teeth, while the anus in this genus is between the mouth and posterior end. Four genital and five ocular pores are seen in the abactinal area. In addition to the ordinary tubercles Echinoneus has others that have the appearance of glass and carry no spines. Hybodypus caudatus Wright (No. 349), is a small somewhat flattened urchin with the three anterior ambu- lacra separated from the two posterior ones. Here the mouth has moved a little towards the anterior side while the anus is in a depression on the dorsal side. 1 Proc. Amer. Assoc. Adv. Sci., XXIX, 1880, p. 397. 188 SYNOPTIC COLLECTION. Toxaster oblongus Deluc. (No. 350), is longer than broad with a groove at the anterior end, the posterior end being high with the anus visible. Holaster striato-radiatus d'Orb. (No. 351), is a high dome-shaped Spatangoid with simple narrow ambulacra and broad interambulacra. The mouth is at the anterior end of the ventral side and the anus at the posterior end. The abactinal area cannot be made out in the specimen but the boundary lines of some of the plates can be traced. Colly rites dorsalis Ag. (No. 352), shows more plainly the specialization in the position of the ambulacra, three of which are in front while the other two are widely sep- arated from them. This drawing out of the abactinal area in an antero-posterior direction has caused a sep- aration in the genital and ocular plates. No. 353 is an interesting specimen of Micraster from the Lower Greensand. It is a jasper cast in which the posterior end is preserved. The partition between the paired pores is clearly shown and three of the ambulacra, while the ornamentation is well preserved. This genus is usually distinctly heart-shaped with the bilabiate mouth placed far forward and the odd anterior ambulacrum in a groove. Hemiaster minimus Desor (No. 354), when young has the anus nearly central and the test has much the appearance of that of the regular urchins. Marked changes take place, however, in the course of develop- ment. The outline of the urchin becomes more irregular and flattened, and some of the ambulacral plates become modified into four deep cups or pouches for the purpose of holding and protecting the eggs. Within these pouches the embryos develop; by the law of acceleration the meta- morphosis is skipped, and the embryos are retained by the parent until the plates of the test are formed. The adult has a band of microscopic tubercles called fascicles encircling the petals. METAZOA ECHINODERMA. 189 A giant among its kindred is Metalia pectoralis A. Ag. (No. 355). Some of its spines are peculiarly modi- fied, being so extremely long and delicate that they are rarely preserved. These are attached to small areas on each side of the dorsal median line and within the fasci- ole. They are capable of lying flat upon the corona, as seen in No. 355. On other parts of the body the spines vary in length and in some places they are distinctly curved. The mouth is near the forward end and the anus in the large blunt posterior extremity. The marked sexual difference in size is shown by No. 355 ; the female is much larger than the male, while the latter is rarely found. The corona denuded of spines is a beautiful object (No. 356). Another large, robust urchin is Meoma ventricosa Liitk. (No. 357, ventral side). Here similar spines cover the whole surface. The mouth (No. 357) has a large lip and the anus is at the posterior end of the body. The sunken petaloid ambulacra above are conspicuous. Among the most specialized of the irregular urchins is Moira atropos Ag. (No. 358). Here different parts of the test are made of variously shaped plates. The mouth is far forward, and the anus is at the upper side of the blunt posterior end. There appear to be deep slits on the upper side and on looking more closely the ambu- lacral pores are seen at the bottom of four slits. The fifth one, which is more like a groove than a slit, extends forward and turning downward reaches the mouth. The young are carried in these sunken ambulacra after much the same fashion as in Hemiaster. The variation in the shape and size of the interambulacral plates is great. An extreme of specialization is reached when one examines A mphidetus cordatus Ag. (No. 359). The short silky spines (No. 359, c) conceal the ambulacra and interambulacra which are most curiously modified. In- stead of simple vertical rows or the usual rosette of petals there is here a star-like arrangement of the ambulacra 190 SYNOPTIC COLLECTION. (No. 359, b, d), the narrow points of the star radiating downward toward the ambitus when they become some- what obscure only to reappear on the ventral side (No. 359, b) in the form of perforated bands which reach to the mouth. Between these bands the interambulacra are set in, the different areas and the individual plates composing them varying greatly in shape and size. The mouth (No. 359, b) is at the anterior end with its lip, while the anal disc at the posterior end (No. 359, a, test of a younger specimen than the others) is perfectly preserved. Below this anal plate there is another with three openings on either side. In the sunken area at the top are four openings. H OLOTHUROIDEA . We know nothing of the ancient ancestral Holothuroids excepting by the minute hard parts, spicules, wheels, anchors, etc., which are preserved in the rocks. These occur no farther back than the Carbonic age (Zittel). They throw little light upon the phylogenetic history of the group, and therefore we must turn to the primitive forms living to-day. Among the deep-sea Holothuroids are the Elasipoda which retain the characters of the larva in the adult stage more than any other members of the class. Accordingly in describing the adult we are giving the more essential larval characteristics. Generally speaking, the body is distinctly bilateral (PI. 360, figs. 1-4, Elpidia verrucosa Theel. and Scotoph- anes murrayi Theel), while its walls are provided with simple spicules of few rays. The dorsal part of the body extends in front, causing the mouth to turn towards the ventral side (see figs. 2, 4) instead of being terminal. The anus is dorsal in position (fig. i) or terminal as in Scotophanes (fig. 4). The ventral surface is flattened, METAZO A - ECH INODERMA . 191 consisting of two ambulacra (figs. 2, 4), and the ambu- lacral feet with sucking discs are restricted to this side and extend in pairs towards the posterior end of the body (rigs, i, 2, 4). On the dorsal side there are tubu- lar organs which, as they perform a different function from the ambulacral feet, are without sucking discs (fig! 3 ; in fig. i these organs are broken off, but the four openings on the anterior part of the body show their position). In many Elasipoda the water-vascular system com- municates with the exterior by means of the madreporic body. Moreover, the circular ring around the mouth is made up of simple spicules which are separated from one another. The internal respiratory organs lack the usual tree-like form, and the tentacles are few in number, usually not more than ten in the Elpidiidae, the most generalized family. While the Elasipoda have retained the larval characters more than the other members of the class, still we cannot fail to see'what The'el l has already pointed out, that these Echinoderms are more like the specialized forms of most invertebrates in several important particulars. They are bilaterally symmetrical. They have a distinct antero- posterior axis and a ventral side differentiated from the dorsal. They have a small number of locomotive organs and these have a definite position. The remaining families of Holothuroids the Pedata and Apoda when young resemble the Elasipoda. Most of these forms belong to the shallow waters and they have become greatly modified to meet widely dif- ferent conditions. At first the madreporic body opens on the exterior, but later the connection is lost and the canal ends blindly in the interior. Rep., Zool., IV, part 13, 1882, p. 147. 192 SYNOPTIC COLLECTION. Pedata. One of the more generalized members of the Pedata is Holothiiria tubulosa Tied. (No. 361, model), in which the body exhibits a distinct antero-posterior axis. This genus has the feet scattered over the surface instead of being arranged in rows. Another representative of this group is Pentacta fron- dosa Jaeger (No. 362), in which the division of the body into five distinct areas is finely shown. Two double rows of ambulacral feet extend down the dorsal side and three on the ventral side. There are also dorsal feet in the interambulacral areas. The terminal mouth is surrounded by numerous organs resembling tentacles but which serve as branchiae or external gills. The madreporic body is internal. The anus is at the posterior end, and the respiratory tree is given off from the cloaca near the vent. This is seen in No. 363 which is a dissection showing chiefly the digestive and reproductive systems. A peculiar modification of structure is seen in Psolus fabrici Semper (=.Lophothuria fabrici Verr.) (No. 364), where the lower surface is converted into a creeping-disc resembling the foot of a gastropod. It has three rows of ambulacral feet and there are none on the scaly dorsal side. Cucumaria crocea Less., in its development skips alto- gether the larval stage and enters upon the adoles- cent or neanic period. The young of Cucumaria crocea Less. (PI. 365, fig. i, dorsal side; fig. 2, ventral side), were found by Sir Wyville Thomson 1 attached to the two rows of ambulacral feet on the back of the mother. They were all "miniatures of their parents," excepting that their dorsal ambulacral feet were in an undeveloped condition, while their ventral feet were early and well developed and used for clinging to the parent. The adult like the larva is elongated with distinct rows of feet iQtioted by Th^el in Chall. Rep., Zoo!., XIV, part 32, 1886, p. 60. METAZOA ECHINODERMA. 193 extending from one end to the other. The mouth and anus are both terminal. Apoda. The reduction of parts is going on in the group to which Caudina arenata Stimp. (No. 366), belongs. The young and adult, both seen in No. 366, are similar in external appearance. The rows of feet have disappeared, and the water-vascular system is, there- fore, much reduced. Ludwig has shown that an allied form, Chirodota rotifera Pourtales, has a stage in which it loses its madreporic body and the stone canal detaches itself from the dorsal wall, becoming enclosed within the perisoma. The most specialized of all the Holothuria is Synapta (No. 367, S. glabra Semper), found in the shallower waters of the shore region. The body has become modified and is extremely elon- gated. It contains spicules in the shape of anchors and plates. The feet have disappeared and the radial ambu- lacral vessels are also wanting, so that the water-vascular system is reduced to a ring around the mouth. There is no respiratory tree and altogether the genus is a good illustration of specialization by reduction. To recapitulate briefly : The pre-Cambrian ancestor of the Echinoderms was probably free swimming and may be represented by certain larvae of existing Echinoderms. The Palaeozoic ancestors, however, were with little doubt attached forms. Of these the Cystoids and Blastoids had a more or less globular body which was either sessile or fastened by a stem. The body was covered with plates which at first were placed together irregularly but in later forms were arranged in regular circles. The oral surface was above and the aboral below. By the differentiation of areas of plates, called ambulacra, and of feathery pinnules, the apparatus for catching food and carrying it to the mouth became more efficient. .Pores through the body wall admitted water to the respiratory organs or hydrospires. 194 SYNOPTIC COLLECTION. In the case of the Crinoids specialization not only brought about greater regularity in the body plates but arms were developed ; the ambulacra still served as food grooves, through the holes of which numerous pointed tentacles were put out. The digestive system in these ancient Echinoderms was distinct from the body cavity and its two openings mouth and anus were usually on the upper side. The Asteroidea, living to-day, pass through a transient stage in their development when they are attached. In becoming free they turn over so that the oral side is below and the aboral above. In this favorable position for obtaining food from the sea bottom by means of the mouth, the pointed tentacles of the ambulacra develop suckers and become locomotive organs or tube feet. It is probable that further specialization causes the almost useless ambulacra of the Ophiuroidea to become internal, and the equally useless tube feet to take on reduced characters. Besides the ambulacral plates of the typical Asteroidea there are rows of interambulacral plates on the ventral side, while the dorsal side is made of irregular plates. The digestive system is complete, but in most cases the anus opens opposite the mouth on the dorsal side. Water is admitted to the body cavity of the Asteroidea through a sieve-like organ which connects with a series of tubes that serve the double function of respiration and locomotion. Greater concentration marked the organiza- tion of the Echinoidea. The ambulacral and interambu- lacral plates of the typical Asteroidea here reach an extreme development, while the irregular plates have almost wholly disappeared. All trace of a fixed stage is lost in the ontogeny of the Echinoidea, so that the larvae are free from the start. The digestive and water-vascular systems are similar to those of the typical Asteroidea, with the exception of certain specializations such as the eating apparatus or "teeth" and the reduced tube feet of many sea urchins. METAZOA ECHINODERMA. 1 95 The Holothuroidea like the Echinoidea have no fixed stage in their development. As has been said, they resemble the more specialized invertebrates in being bilaterally symmetrical and in having an antero-posterior axis of the body. They possess many reduced characters ; the number of feet is limited, and the water-vascular system in some forms is a mere ring around the mouth. This reduction is indicative of specialization and it offers a reason for placing this group farthest from the primitive ancestral form of Echinoderms. 196 SYNOPTIC COLLECTION. MOLLUSCA. Section 7. PELECYPODA. The arrangement of the molluscs in the Synoptic Col- lection is governed by the same principle that controls the classification of the preceding subkingdoms. We con- sider first, primitive ancestral Pelecypods and the early stages of living forms; secondly, the specialization of adults. Since a fleshy animal antedates, as a rule, a skel- eton-bearing animal, as we have seen in the Protozoa, Porifera, and Coelentera, and since, also, fleshy parts are not usually preserved in the geologic formations, we turn to the embryonic and larval stages of existing species to determine so far as possible the characters of the ances- tral fleshy forms. On the other hand, since the skeleton or shell when made, is a comparatively sure guide to the structure of the soft parts, we regard with special interest the remains of the primitive Mollusca in the Protozoic and the Palaeozoic strata. An early stage of the pres- ent Pelecypod larva is the trochophore (PI. 368). It is a little fleshy creature whose distinctive features are a cil- iated locomotive ring (the velum) in front of the mouth, and a tiny sac or shell gland on the dorsal surface. This sac is simply a portion of the outer wall turned inward, but it plays an important part since it is soon everted and at once the shell begins to form on its surface. The latter is secreted extremely early in the life of the embryo, therefore it is inherited, and of value phylogenetically. At first it is shaped like a tiny plate or cap. and therefore the ancestor from which the Mollusca descended prob- ably possessed such a shaped shell. In the case of the developing Pelecypod the tiny plate forms into two parts or valves, while in the Gastropod the cap becomes a cone and later a new shell is formed which in most cases becomes a spiral. METAZOA MOLLUSCA. 197 The name Pelecypoda is given to the most generalized class of molluscs in preference to Lamellibranchiata for three reasons, viz., it has priority over the latter name ; it is in uniformity with the names of the other classes of Mollusca (Gastropoda, Pteropoda, Cephalopoda) ; the word Lamellibranchiata refers to the gill which is one of the most variable organs of a mollusc, while Pelecypoda, Gastropoda, etc., refer to the foot, one of the most stable molluscan organs. 1 The classification adopted in this guide is, with certain modifications, that of W. H. Ball 2 and of Dr. Robert T. Jackson. Dall considers the structure and development of the hinge first, and secondly, the sum total of organic characters. As a result of these studies he divides the class into three orders. The first possesses the simplest possible hinge, having the two toothless edges of the shell in contact and united by a ligament. The second has the hinge provided with transverse or cardinal teeth and the third has teeth parallel with the margin and known as lateral teeth. 3 There is no sharp line of divi- sion between the last two orders, as many shells have both the cardinal and the lateral teeth. In these cases the general characters usually enable one to decide to which order a shell belongs. There is here as in every class the difficulty of determining the primitive and the reduced forms. Some shells that do not possess teeth to-day are really the descendants of toothed shell-bearing Mollusca. On the other hand the most primitive Pelecypods were doubtless toothless. Whether these truly primitive forms exist at the present time is a question. Many of the members of Ball's first order have become extremely 1 Ball, Amer. Journ. Sci., ser. 3, XXXVIII, 1889, p. 446. 2 Rep. on Mollusca, Bull. Mus. Comp. Zool., XII, 1886; Amer. Journ. Sci., ser. 3, XXXVIII, 1889, p. 445 ; Trans. Wagner Free Inst. Sci., Phila., Ill, part 3, 1895. 3 See Bernard, Bull. Soc. Ge"ol. de France, ser. 3, XXIII, 1895 ; XXIV, 1896. 198 SYNOPTIC COLLECTION. specialized through the habit of boring, etc., so that it would seem as if these were reduced rather than primi- tive forms of the class. It is probable, however, that they are simply reduced members of the order which has Sol- enomya and Anatina for its primitive representatives. The weak, toothless condition of the ancestors could hardly be preserved in the descendants, as pointed out by Dall, unless the animals became borers or burrowers. If the shell-bearing ancestral form of the Mollusca is sought in the Cambrian formations, one finds that nearly four hundred species of molluscs then existed which include representatives of nearly all the great orders exist- ing 'to-day, and which, according to Cooke, 1 are without the slightest sign of approximation to one another. If this is true, the point of convergence of these divergent lines lies far back in pre-Cambrian times. Until more investigations have been made on these ancient rocks, one can judge of the ancestral forms of Pelecypods suc- ceeding the plate or cap-like condition by inference only. It seems probable, however, that such a form possessed a small, smooth, more or less circular shell ; that the two valves were equal in size and were connected at the tooth- less hinge area by a flexible membrane, the ligament. This is the character of the young shell or prodissoconch (Jackson) of many larval bivalves existing to-day. Such a form may be represented by Modioloides prisca Walcott (No. 369, fig. i, enlarged), found as an internal cast in the Cambrian formation. Another genus, Cardiola (No. 369, fig. 2, C. cornucopiae Goldf.), possesses most of the archetypal characters. The descendants of such a form may be Solenomya, Anatina, and the like. Soknomya velum Say (No. 370 ; No. 371, shells), has a small, thin, delicate shell, having, contrary to rule, the posterior end shorter than the ante- 1 Cambridge Natural History, Til, 1895, p. 2. METAZOA MOLLUSCA. 199 rior. 1 A glossy horny layer covers the opening between the valves; when the animal is young (No. 371 a), this horny layer is entire or simply pinked at the anterior and posterior ends, but as the animal grows older it is slit into strips (No. 371). The hinge is without teeth. The internal portion of the ligament is back of the beaks in a triangular receptacle and is strengthened by limy, arched supports. Just in front of the latter are the distinct ante- rior muscle marks. The shell of most primitive forms is nacreous, that is, pearly, but Solenomya is only slightly so. The gills of this genus are in a primitive condition, similar to those of Nucula (see p. 202). The foot (No. 370) does much hard work enabling the animal to swim and to bore, so that it is large in proportion to the size of the animal. The mantle is not drawn out into tubes or siphons. Anatina truncata Lam. (No. 372), is a delicate, trans- lucent, and pearly shell with the posterior end truncated and the anterior rounded. The two valves are open nearly all the way round, so that, as compared with many bivalves, they afford slight protection to the soft body within. According to Smith 2 one species of this genus, Anatina elliptica, shows the two ends nearly alike, while others have the anterior portion longer than the posterior, the reverse being the case with the young. The hinge has a socket for the internal ligament called a fossette, which is strengthened in its position by two limy supports that radiate downward towards the center of the shell (No. 372, specimen at right). This genus has only two gills, one on each side of the so 1 When we speak of the anterior and posterior end of a shell, the latter is mounted with the anterior end away from the observer a favorable position for comparison with one's own body. In other cases the shells are mounted to show certain important features. In a few cases delicate shells have been left as first mounted, owing to the danger incurred in remounting. 2 Chall. Rep., Zool., XHI, part 35, 1885, p. 77. 200 SYNOPTIC COLLECTION. called body. 1 It has tubes or siphons which are separate throughout their whole extent, and a foot with a cleft. A peculiar bivalve with a body larger than its shell is illustrated by Cyrtodaria siliqua Daudin (No. 373). One preparation shows the remarkably large muscular siphon extended at the posterior end and the comparatively small foot at the anterior end. The other preparation is the fleshy animal taken from its shell. The plump, rounded body contains most of the internal organs. There are two gills, one on either side of the body, and each gill consists of two leaves. Mya arenctria Linn. (Pis. 374, 376; No. 375), is one of our commonest shells. Ryder 2 has shown that the young clam is attached by a mass of threads called a byssus, but probably only for a short time. The two valves in youth and maturity are equal, therefore the shell is equivalved (PI. 374; No. 375), but the anterior end is broader than the posterior (PL 374). The light brown external horny layer is thin and usually worn off, showing the lines of growth which are the edges of the layers that make up the shell. The left valve (PI. 374, valve on the left) is provided with one tooth (instead of three as is usually the c'ase), and the right valve (PI. 374, valve on the right) with a cavity which contains the inter- nal ligament. The impressions of the two muscles, the mantle, and the siphon, are more distinctly seen in shells of Mactra (see Nos. 411-413). The clam is a differentiated member of its order. Since the internal organs are also better seen in the larger genus, Mactra, we will speak briefly of them here. The mantle has become a sac-like organ with three openings, two at the end of the siphon and one at the anterior end through which the foot passes. The mantle is thickened on the edge and supplied with pigment cells which produce many of the colors of the shell. 1 Bull. Mus. Comp. Zool., XII, 1886, p. 306. 8 Amer. Nat., XXIII, 1889, p. 65. METAZOA MOLLUSCA. 201 The gills have become more complex, consisting of many longitudinal tubes connected by cross tubes. The mouth is provided with two pairs of palpi and leads into the so called "body" containing the stomach, liver, most of the intestines, and the reproductive organs. The long, cartilaginous rod called the crystalline style may give rigidity to this part of the animal. The intestine leaves the body, passes dorsally under the beak and through the heart. It terminates a short distance from the upper tube of the siphon lying in the path of the out- going current of water. The more specialized members of the group are Pholas, Aspergillum, and Teredo. Pholas dactylus (Nos. 377, 378) has a large opening in the anterior end filled by the foot. This genus has the habit of boring. The valves are united by an external ligament, and the hinge has two plates to strengthen the union but no teeth. Aspergillum when young has a bivalve shell. As the animal grows older the siphon grows to a large size, and is covered by a limy tube in which the tiny reduced bivalve shell becomes imbedded, as seen in No. 379, specimen at the right. At the end of the tube is a sieve surrounded by a frill. At the other end are one or more frills which are broken off in the specimen. In Asper- gillum the mantle is bag-like, having the two si phonal openings and one at the anterior end. Teredo has a long body ; at the larger end is a little bivalve shell which is without teeth or ligament. The mantle is drawn out into a long siphon near the end of which are organs probably used for boring into wood. It is a strange freak that causes the animal to live in wood, since it never uses it for food. Early in life, however, it begins to bore, and lines its tunnel with a calcareous secretion as seen in No. 380. It never leaves its tunnel and depends for food upon the microscopic plants and animals which are brought in the water. Many Teredos 202 SYNOPTIC COLLECTION. may bore into the same piece of wood, but these tunnels do not, as a rule, come in contact. The second group of Pelecypods, or those possessing transverse teeth on the hinge area, may have descended from forms like Nucula or even from some simpler spe- cies. 1 Nucula occurs in the ancient formations (No. 381, JV. ventricosa Hall) and has continued slightly modified to the present day (No. 382, N. tenuis ; No. 383, N. mar- garitacea Lam.). It is a smooth, symmetrical shell with equal valves. Contrary to the usual rule the umbos are directed towards the posterior end of the body which is short and rounded, while the forward end is longer and more pointed. The primitive hinge area is curved and bears a few teeth which are at right angles to the antero- posterior axis of the body. This primitive hinge area or cardo is better seen in the larger shell, Area Occident alts Phil. (No. 384). Here it is long and straight, and the many transverse teeth are well developed. In this genus the umbos are widely separated and the ligament lies between them. In Nucula the hinge area has a triangular pit for the internal portion of the ligament, called by Dall the "resilium," which aids the external ligament in uniting and opening the valves. The whole shell is made of a pearly or nacreous substance, and in its young and adult stages no prismatic structure is ever developed. The fleshy animal is primitive in structure like its shell. The edges of the mantle are free, without tentacles, and are not drawn out to form a tube or siphon. Two adduc- tor muscles are present, one at either end of the body. The gills are in two pairs in the form of simple, straight, and separate filaments. The young Nucula is active and throughout life it never becomes attached. The foot has a cleft and can be flattened into a disc and used in crawling. 1 For a discussion of the subject see Verrill, Trans. Conn. Acad. Arts and Sci., X, part i, 1899, p. 45. METAZOA MOLLUSCA. 203 Rhombopteria (PI. 385) represents a branch from the primitive Nuculoid ancestral form, and is the probable ancestor of the Aviculidae to which Pecten belongs. Its shell was oblique, and it had a straight hinge line which extended on either side of the umbos. The young of another genus, Pterinopecten, resembles the adult Rhombopteria, while the hinge line of the adult is long and the ears slightly developed. The young Aviculopecten resembles the adult Pterinopecten but the adult has a shortened hinge line and a much greater development of the ears. The shell of the young Pecten (PI. 386, fig. i, viewed from the left side; fig. 2, the same from the right side; x 50 diameters) has the embryonic sheH or prodisso- conch which represents the ancestral Nucula while the succeeding stages resemble Rhombopteria, Pterinopecten, and Aviculopecten. At first there are no plications and the prodissoconch is without ears. According to Dall l the very young valves of many species of Pecten have the transverse groovings of the hinge, representing the teeth of Nucula and Area. Fig. 3 is an older stage, x 40 diameters, and fig. 4 shows the fleshy animal at the same stage. The two mantle borders are free and each posses- ses a single row of eyes which alternate with single ten- tacles. In a later stage two tentacles alternate with one eye. The animal uses its long narrow foot actively so that it is finely developed. Fig. 5 is the same shell viewed from the right side, while fig. 6 is an older shell, x 16 diameters. The plications and ears are now well devel- oped. The two borders of the mantle are extended to form a tube just under the dorsal ear. Here the effete matter is carried away in the outgoing current of water, the direction of the current being indicated by an arrow (fig. 6) . The gills of the very young Pecten are probably four sets or two pairs of straight filaments, but when the 1 Amer. Journ. Sci., ser. 3, XXXVIII, 1889, p. 459. 204 SYNOPTIC COLLECTION. young animal has reached the stage represented by fig. 6 the ends of the inner pair are turned inward while those of the outer pair are reflected outward, as seen in fig. 7 which represents the gills of the adult. When young the Pecten attaches itself by a byssus and always lies on the right valve. After becoming attached it may detach itself but soon becomes fastened again. When it reaches adult life it is free, but keeps the same position with the right valve below, and swims by clapping its valves together. At this stage the hinge is toothless. No. 387 is a species of Pecten showing the mantle, large muscle, and gills. Pecten varius Linn. (No. 388), illustrates the unequal development of the ears and the variation in color in one species. No. "389 is a remarkably fine specimen of the adult Pecten maximus,and PI. 390, figs, i, 2, are drawings of the same. Here we have in one shell an epitome of a great part of the life history of the group to which Pecten belongs. The prodissoconch has disappeared, the peduncle hav- ing usurped its place, but the tiny cavity (No. 389 ; PL 390, fig. 2) at the beak remains, telling of the rounded outline and long hinge line of the embryonic shell. The larval or nepionic stage is convex at first and smooth with concentric markings. The hinge is long, while ears and ribs are not developed. In the later nepionic stage the beginnings of ribs are seen. At this time the shell is light yellow in color. In the adolescent or neanic stage the shell becomes concave and ribs are more developed. The mature or ephebic stage is convex at first and the ribs are prominent, while the color has changed to red- dish. The later ephebic stage shows a tendency to return to the concave condition which increases in the gerontic stage. This is seen in the specimen and in fig. 2, but still better in fig. i, which is a section through the middle of the two valves, the lower valve being on the right. The ribs tend to flatten out in the gerontic stage, while the concentric markings become prominent and are nearer together. METAZOA MOLLUSCA. 205 In passing through these stages the shell illustrates Minot's law of growth ; /'. ^., growth decreases as the size of the animal increases. In the younger stages growth was rapid, the hinge extended in length and the shell doubled its size in a brief time, but in the gerontic stage, growth is limited and the hinge area is narrow, as seen by tracing the edges of the layers from the broad, rounded, posterior part to the comparatively short hinge line. Anomia (PI. 391, A. simplex, No. 392), is related to Pecten though it is a much more specialized form. When young it is found free and crawls by means of its large foot which is seen extended in PI. 391, fig. 2. The very young shell (fig. i, left or upper valve) has the prodisso- conch on the edge. Fig. 2 is a somewhat older stage seen from the left or upper side. The later dissoconch layers of shell are beginning to encircle the prodissoconch. Fig. 3 is the same shell as Fig. 2 viewed from the right or lower side. The byssal notch is indicated on the edge of the prodissoconch in which particular, Anomia differs from Pecten, the latter having an entire prodissoconch. The byssal notch was originally on the edge, but has extended nearly to the center and is partly encircled by the layers. The prodissoconch becomes entirely enclosed by layers. Fig. 4 is an older stage which shows how the encircling layers have pushed the prodissoconch inward some distance from its original position on the margin. The byssal notch of the lower valve is finally com- pletely enclosed by shell layers, as seen in fig. 5 (adult Anomia, lower side ; fig. 6, side view of the same). At first, when the byssus is surrounded, the opening or foramen is small, but it becomes larger by the resorp- tion of the shell. Specimens of the adult are seen in No. 392 ; (a) is the whole shell; (b) the upper valve showing the scaly appearance due to the irregular layers of shell ; (c) is the lower valve. The same trunk forms, Nucula and Rhombopteria, 206 SYNOPTIC COLLECTION. probably gave rise to Leptodesma (PI. 393) which has an oblique body with the posterior wing extended, while the anterior border is acute and there is a byssal sinus. These forms may in time have produced another series represented by Aviculopinna and Pinna. Aviculopinna (PI. 394) is wedge-shaped and without ears. The two valves are equal and marked by concen- tric lines. The beaks are a little behind the anterior end of the shell. Pinna (No. 395, P. rudis Linn.), the probable descend- ant of Aviculopinna, has the same wedge-shaped, equi- valved, and earless shell. The concentric and longitudinal markings are about equally developed. The beaks in Pinna are placed at the anterior end of the shell. The hinge is in a reduced condition, having no teeth, and the substance of the shell is mostly prismatic, very little nacreous matter being found. In this form the anterior muscle is four or five times smaller than the posterior, being on the way to a reduced condition. 1 Other descendants of Nucula, Rhombopteria, and Leptodesma were probably Melina, Avicula, (= Pteria) Malleus, and Ostrea. The shell of Melina (No. 396; PL 397, figs, i, 2) is extremely flat, and the posterior part is prolonged to one side making .the shell appear as if deformed. The hinge area (PL 397, fig. 2) has little pits for the ligament which holds the two valves together. Avicula^ (PL 398, fig. i, young), has the Nucula-like prodissoconch and the subsequent nepionic stage repre- senting Rhombopteria. It has a straight hinge line, but its posterior wing is extended and there is a deep byssal sinus in the right valve (fig. 2). The triangular pit exists in all Aviculas. The later stage represented by fig. 3 is the Leptodesma stage. The adult has the shell oblique 1 Sharp, Proc. Acad. Nat. Sci., Phila., 1888, pp. 122, 123. METAZOA MOLLUSCA. 207 and the right valve is smaller and flatter than the left. The hinge has one or two transverse or cardinal teeth. Malleus when young (No. 399 a) somewhat resembles the adult Avicula. The hinge line is long with the beak at one end. Only one wing is developed. Later growth takes place on the other side of the beak (No. ^gb) and the result is a wing in masquerade. The adult (No. 400) for obvious reasons is familiarly known as the "hammer- oyster." One of the ancestral forms of the oyster was Gryphaea arcuata Lam. (No. 401). The large deep lower valve and the small lid-like upper valve, the curved beak and the lines of growth are all well preserved in the fossil. The development of the oyster from the embryo to the adult is given in PI. 402, figs. 1-19 ; figs. 1-3, Ostrea edu Us \Jx\n.\ figs. 4-19, our common species, O. virgin- tana Listner (=O. virginica Gmel.). The segmentation and earliest embryonic stages are omitted, although like the later stages, they illustrate accelerated development. In the embryonic stage (figs. 1-3) the shell is symmet rical with a straight hinge line (fig. i) situated on the dorsal side. The valves are equal (fig. 2) with only slightly developed umbos. In this condition the shell bears a striking resemblance to the equivalved bivalves already described. At this time both the mouth (fig. 3, m) and anus (fig. 3, a) are situated ventrally, while there is but a single muscle, the anterior adductor (fig. 3, a, a) . A ciliated velum (fig. 3, v) still persists as the little oyster swims about freely in the sea. The stages of development between the one repre- sented by figs. 1-3 and that shown by figs. 4, 5, have never been figured or described. The latter (figs. 4, 5) represents our common species, when it has completed the embryonic or prodissoconch stage, and has fastened itself by the edge of the left valve (fig. 5), using the reflected margin of the mantle (fig. 5, m) to accomplish the work. 208 SYNOPTIC COLLECTION. This early fixation of the oyster has doubtless caused the reduction of the foot, which exists as a mere vestige in an early embryonic stage and is lost altogether before the embryonic stages figured in PL 402. The straight hinge line of the embryonic shell has given way to a curved line with high umbos (figs. 4, 5 ; also fig. 6, which shows the shell attached by the left valve in an almost vertical position). An important change has taken place in the structure of the oyster, for instead of having one muscle it now possesses two, a posterior adductor (figs. 4, 5,/tf) having been developed. The gills (figs. 4, 5, g) are still in a primitive condition, consisting of straight simple filaments (fig. 7). The sit- uation of the mouth can be judged by the position of the palpi (figs. 4, 5,//), but the anus has changed its place, having moved dorsally before the development of the posterior adductor muscle which took place on its ventral side. The beginning of the nepionic stage is represented in fig. 8. Here the left valve is below and the right above, and on the edges of these valves the new growth of the nepionic shell is being added to the prodissoconch. The internal organs in the early nepionic stage are shown in fig. 9. The single adductor muscle (fig. 9, ad) is in a similar position to that of the adult. The gills have passed througn the stage represented by fig. 10 and are now in the condition illustrated by fig. n, in which the filaments are connected by cross bars. The substages of the nepionic stage are so well shown in the shell of the oyster, that contrary to our usual rule, we illustrate them by figures. Fig. 12, /, represents the prodissoconch succeeded by the first nepionic growth. In figs. 13 and 14 two and a half of the third nepionic substages are figured. At this time the right or upper valve is convex (fig. 13) and the left or lower valve (fig. 14) is flat. The tip of the left valve (fig. 15, x 87 diameters, view of interior) shows the prodissoconch (fig. 15, /) METAZOA MOLLUSCA. 209 and the nepionic growth with the cartilage pit or furrow running through the middle. On either side of the true nepionic shell there is a flange-like extension (fig. i5,/) of the margin which passes over the object of support. The shell, as it appears at the end of the four nepionic substages and the neanic stage, is represented in fig. 16, right valve, and fig. 17, left valve. The sinus (figs. 16, 17, s) is clearly indicated, and it marks the position of the outgoing current of water. Changes take place in the shape of the shell during the ephebic stage, the variations depending largely upon the surroundings. As a rule the lower or left valve becomes deep and cup-shaped, while the right valve flattens. This is seen in fig. 18, which represents two adults. The upper specimen is growing with the left, deep valve below, and the right, flat valve above. The right hand specimen, however, reverses this condition, so that the left, deep, attached valve is above and the flat valve below. In both cases the same relative form of the valves is maintained. The adult oyster (No. 403, alcoholic specimen ; 404, model; 405, shells, young and adult) has but one muscle, the anterior adductor having disappeared. The posterior adductor holds a more central position (Nos. 403, 404) and the dark purple scar is seen in No. 405. The palpi have moved dorsally and are nearer the hinge line. The model shows the two leaves of the mantle, one of which is thrown back exposing the gills. These organs have become more complicated in structure, as shown by PI. 402, fig. 19. Unionidae. It is very rare to find parasites at any period of life among molluscs. The fresh-water Lamp- silis (= Unio) (No. 406, Z. nasutus Say; Nos. 407, 408, L. radiata Gmel.) and Anodonta (No. 409) however, pass the young stage attached to fishes. Their develop- ment is, therefore, more complicated than that of most molluscs. The eggs are carried in little pouches in the gill cavities of the parents. No. 407 is the female of 210 SYNOPTIC COLLECTION. Lampsilis radiata with the broad sacs of the outer gills filled with embryos. The peculiar characters which separate the larvae of the Unionidae from those of other Pelecypods appear very early in the embryo and are found in both the inter- nal and the external parts. A shell is formed with a straight hinge line. It is provided with hooks which later become a necessity to the larvae. The byssus and spiny beaks form, and peculiar sense organs are developed on the inner surface of the mantle. All this takes place before the animal leaves its parent. This stage is known as the glochidium. Becoming free, the glochidium attaches itself by the byssus, or if fish are near it, fastens itself to the gills, fins, or other parts of the fish by the hooks of its shell and lives the life of a parasite, its host providing the necessary nourishment. All this time the intestine is a closed internal sac and of little use. Later the sac elongates and an opening breaks through. A metamorphosis takes place, two adductors appear in place of one, gills develop, and the peculiar sense organs disap- pear. When fully developed, with the exception of the reproductive organs, it leaves the fish and becomes extremely lively while its further development goes on. The adult shell (No. 406, Lampsilis nasutus Say ; No. 407, L. radiata Gmel.) , has the transverse teeth which prove the origin of the Unionida'e, while the peculiar marginal teeth of the third group are developed later. The hinge of Anodonta (No. 409), however, is so much reduced that it is toothless. The third order, in which there are teeth parallel to the margin, is represented by a number of genera. It is important to bear in mind that transverse teeth also usually occur, so that in the differentiated forms the hinge is remarkable for its perfection of mechanism for efficient work. Petricola is both a free and a boring mollusc. It is found in soft marshy earth as at Revere Beach and also - METAZOA MOLLUSCA. 211 in limestone rocks (No. 410, P. corditoides). The teeth of the hinge are usually broken off, but when preserved there are two in each valve. The mantle lobes are united. The anterior end is short and the posterior gaping. Mactra (= Spisula) solidissima Dillw. (No. 411), is one of our largest New England bivalves. The animal is free-moving and is therefore symmetrical. The horny layer is light brown in color (Nos. 411, 412). The umbos are directed anteriorly. The pit, with its internal liga- ment, and the external ligament are sometimes developed. The cardinal tooth is nearly vertical while the marginal teeth are long. The dissection (No. 413) and model (No. 412) show the principal internal organs and give their names. The mantle is seen extending along the edge of the shell (Nos. 412, 413) ; it has three openings; one at the anterior end through which the foot passes out, and two at the end of the siphon. This siphon is really a double tube; one, "the branchial siphon," is for the ingoing current of water, and the other, "the cloacal siphon," for the outgoing current. The anterior and posterior adductor muscles, the gills injected with red coloring fluid, the mouth organs called palpi, and the strong muscular foot are all shown in the preparation. Psammobia vespertina Gmel. (No. 414), has two long delicate siphonal tubes separate throughout their whole length. The siphonal tubes are separate only a short distance in Psammosolen strigillatus Linn. (No. 415). The foot in this genus is of great size and strength. Ensis directus Con. {Ensis americana Verr.) (Nos. 416 418), and the European species, Ensis ensis Linn. (No. 419) have a long razor-like shell covered when young (No. 416) with a glossy horny layer, but which is often partly worn off in the adult (No. 417). This animal travels rapidly through the sand as can be proved by any one who attempts to dig it up. Notwithstanding this fact, the horny layer is seldom found entirely worn off. The model (No. 418) shows the adult animal with the mantle 212 SYNOPTIC COLLECTION. extended from the shell; at one end is the siphon and at the other the foot (Nos. 417, 418). Donax scortum Linn. (No. 420), is triangular in shape. The hinge area has two cardinal teeth on one valve and one on the other that fits between the two. The two marginal teeth fit into depressions. A rounded ligament is external. Cardium edule Linn. (No. 421), is represented by shells of different ages. At first the shell has shallow grooves or plications, but these grow deeper and cause the shell to be thicker and stronger. The hinge has both tranverse and parallel teeth. The umbos are close together and the ligament is external. The muscle impressions are distinct, but the mantle mark is often obscure, while there is no siphon impression, although the animal has a short siphon. In Cardium the foot (No. 422, C. aculeatuni) can be suddenly bent so that the animal leaps through the water. The changes in color of the external horny layer are finely illustrated by Cyprina islandica Lam. The young (Nos. 423, 424) is light brown in color. This becomes a rich shade of brown in the adult, while in the old shell (No. 424, specimen at the right) it is nearly black, and so brittle that it can be easily scraped off (No. 424). The ligament is partly internal and the hinge has three cardi- nal teeth besides the marginal teeth. The two muscle impressions and the mantle impression in this shell are often distinct but the short siphon makes no mark. Cytherea (= Venus) verrucosa Linn. (No. 425), is a large plump shell when full grown with prominent beaks, be- hind which is a large external ligament. The well devel- oped hinge area has three cardinal teeth. The shell is porcellanous like most of the more specialized shells, with both muscle, mantle, and siphon marks well shown. Smith says 1 that one species of this genus (C. torresiand] has the posterior end broader in the early stages than 1 Chall. Rep., Zool , XIII, part 35, 1885, p. 119. METAZOA MOLLUSCA. 213 the anterior end, while in the adult it is narrower. This indicates a development of the forward or head end of the body. Hysteroconcha lupanaria Less. (No. 426), is instructive as showing how age affects the development and increase of spines, ridges, and projecting shelves. The young shell is smooth. In the nepionic stage the spines are short. They appear to be formed by the shell layers meeting along two ridges on the posterior end and being prolonged in such a way as to leave a groove on the upper side of the long tapering spine ; in these grooves foreign particles are often caught. A unique specialization of the Pelecypods is found in the Cretaceous Coralliochama (No. 427, C. orcutti White), and Radiolites (PL 428). In Coralliochama one valve is deep and more or less distorted, while the upper valve is convex (see No. 427). In Radiolites the upper valve is flat and serves as a lid or cover. These Pelecypods may be related to the Chamidae. Specialization has gone on in Tridacna crocea Lam. (No. 429). As the circular young shell grows older, the wavy lines become ridges and the shell lengthens in an antero-posterior direction. This species in the adult stage is colossal in size and all traces of the young shell are lost. The same tendency is observed in Chama laza- rus Linn. (No. 430) where the originally smooth shell quickly becomes ornamented, the edges of the layers of shell extending into short, broad, flat spines. Sections. GASTROPODA. The earliest larval stage of existing Gastropods is the trochophore which is so strikingly like the trochophqre of Pelecypods already described that the two probably arose from a common ancestor. As a rule the tiny cap- like shell of the Gastropod becomes a cone, as seen in 214 SYNOPTIC COLLECTION. PI. 431. This stage succeeds the trochophore, and is known as the veliger a characteristic stage in the devel- opment of Gastropods. The ciliated velum still exists and the foot is also formed. In most Gastropods this cone-like shell becomes a spiral, but in Chitons (No. 432, C. magnificus Desh.), which may be primitive Gastropods, 1 the one-valved shell is made of eight pieces. In No. 433 these pieces are separated and are seen to be essentially alike. Chiton existed in the Silurian age and has undergone comparatively little change since that time. The animal agrees with many Pelecypods in being bilaterally symmet- rical. On the other hand, the head is indistinctly marked off from the rest of the body and there is a well developed lingual ribbon (an apparatus for eating) which is possessed by Gastropods. The cone-like shell may be represented by Tryblidium (PI. 434, T. nycteis Billings) from the Cambrian, which had a smooth cap-like shell when young with an entire margin, becoming in the adult like a shallow cone (PI. 434, fig. i) with the apex placed near the forward end (% 2)- As we have just said, the cone of most young Gastro- pods becomes a spiral and this youngest spiral shell or protoconch (PI. 43 5 ) 2 is smooth, rounded, and light col- ored. It is formed at the apex of the shell but is usu- ally broken off and lost. In the Ordovician fauna, Pleurotomaria (No. 436, P. 1 Conflicting views are held in regard to the position of the Chi- tons. Some naturalists place them before the Pelecypods, while others assign them a position between the Pelecypods and Gastro- pods. They are here placed provisionally among the more primi- tive Gastropods. 2 Although this is the protoconch of Fulgur, (see p. 223 and Nos. 462-465), a more specialized species than those we are now describ- ing, yet it is placed here for the purpose of showing the general characters of the Gastropod protoconch. METAZOA MOLLUSCA. 215 sulcomarginata) occurs, which was a coiled shell consist- ing of a few whorls with a slit in the margin of the aperture, that was either filled as the animal grew older, making a continuous band, or partly filled giving rise to openings. In the Silurian and Devonian ages, Platyceras (No. 437, P. erectum Hall) existed, the apex of which was twisted so as to form a spiral while the later whorl was flaring, showing a tendency to uncoil. an old age or gerontic character. In the group of Gastropods represented by Tryblidium, Pleurotomaria, and their descendants Patella, Haliotis, etc., there seems not to be any primitive genus with a cap-like shell in the adult stage. Neither is there a genus with the loosely-coiled shell, the transitional form between the cap and the close spiral, such as is found in the class of Cephalopoda. Both Patella and Fissurella were formerly supposed to be primitive members of the group to which they belong; but in reality they are found to be specialized forms. This is proved by their development, which in the case of Fissurella has been figured and described from the egg to the adult stage. 1 Since the adult Patella is less modified than the adult Fissurella, it will be briefly described. We pass over the development of the egg and the for- mation of the embryonic nautiloid shell figured by Patten, 2 and come to the patelliform stages of the shell. In one of the simplest Patellidae, Acmaea, the shell is without ribs, spines, or ornaments of any kind, and one species, A. punctulata Gmel., is conical when young though it is depressed like most of its group when full grown. In Helcioniscus exaratus Nutt., often called Patella (No. 438), the perfect shell is smooth at the apex, but 1 Boutan, Arch, de Zool. Exper. et Gdn., ser. 2, III, suppl., 1885. 2 Arbeit, zool. Inst. Univ. Wien, VI, 1886. 216 SYNOPTIC COLLECTION. later becomes ribbed or crenulated. In all the shells the margin is entire. The adult of Helcioniscus has a circu- lar foot, and the functional lamellar gills which are called pallial gills lie in a groove between the foot and the man- tle. These are really secondary gills, as the original breathing organs exist as mere remnants on each side of the neck. The heart of Helcioniscus consists of a single auricle and ventricle. The eggs of Fissurella (PL 439, figs. 1-12) are joined together by an albuminous substance which swells in water to a large size, like that in which frogs' eggs are embedded. These eggs (fig. i) are not laid through the apical hole, as has been supposed, but through the ante- rior opening of the branchial chamber. The egg passes through the usual stages of segmentation until the embryo (fig. 2) with velum, beginning of foot, primitive mouth, and invaginated shell gland is attained. While the embryo is still within the egg, the shell is formed (fig. 2). At first it is made of particles of lime separated from each other; afterwards these become con- solidated, and the shell exhibits a lace-like pattern. Since the characteristic twisting of the embryo has already begun, the shell is asymmetrical, and the little embryo has the characters of a young Gastropod, i. e., a coiled shell, a ciliated velum, and a foot (figs. 3, 4). When still older, the shell possesses an operculum (fig. 5). When the embryo leaves the egg, the last vestiges of the velum remain and aid the foot in locomotion. The embryonic shell is not replaced by another but is persis- tent. Its margin begins to spread out, and the new layers take on markings very different from the plain embryonic shell (fig. 6, dorsal view; fig. 7, ventral side). At this time the foot is long and narrow, and the long tentacles have eyes at their bases. Up to this time the margin has been entire, like the margin of Patella, but soon a slit appears (fig. 8). Gradually this slit is sur- rounded by shell layers whereby it is converted into a METAZO A MOLLUSCA. 217 hole, while the coil portion of the shell becomes reduced in size and is carried towards the posterior end (fig. 9). This is seen on the edge of fig. 10, which is a ventral view showing the foot, eyes, radula, and mantle. With the growth of the shell the hole approaches the summit (fig. u), until finally it occupies a nearly central position with the vestige of the coiled shell behind it (fig. 12). Thus it is seen that the symmetry of the adult (fig. 12 ; see also No. 440) is not primitive but is secondarily acquired. A fold of the mantle lies in the slit, and later occupies the hole. It is thought to have an excretory function, and if so, it serves as an anal siphon. Fissurella has the original gills fully developed, one on each side of the neck. The nephridia are also present. The heart has two auricles and a ventricle. Some specimens of the Stomatellidae are limpet-like, while others (No. 441, Stomatella imbricata Lam.), have a spiral shell without perforations and with a large aperture. The young Haliotis has an imperforate shell, but in the course of development a slit occurs in the margin of the aperture through which the siphon is extended. With the growth of the shell this slit is not continuous but a series of holes is formed (see Nos. 442, 443) some of which, according to Cooke, admit water to the gills, while others are anal in function. With the growth of the animal the first formed holes tend to become filled with a limy deposit. The primitive gills and excretory organs or nephridia are in pairs although the beginning of the spiral has brought the anus from the posterior end of the body towards the anterior median line. The specimen of Crucibulum (No. 444, C. striatnm Say), exhibits the fleshy body in the shell with its mantle and muscular foot. The anterior part of the body has become differentiated to form a head (see No. 444) which be.ars sense organs. This specialization of the Gastro- pods in general shows a marked advance over all the classes of animals so far described. 218 SYNOPTIC COLLECTION. The shell of Crepidula (No. 445, C. nivea C. B. Adams), is slightly coiled and the last whorl is large and flaring like that of Haliotis. In the inside a projecting horizon- tal wall covers the posterior half of the shell. No. 446 shows the peculiar habit these animals possess of growing on top of one another. Sometimes one species of Cre- pidula (C. plana Say) takes possession of the inner side of a univalve shell, often Lunatia heros (No. 446). Five or six different stages are seen in this specimen. The young shells are round and smooth, as compared with the adults, which are long, narrow, and extremely flat. Owing probably to the hidden situation in which they live, they are nearly colorless. The gills in the family Calyptraeidae, to which Crepi- dula belongs, are much more like Pelecypod gills than are those of most Gastropods. The lamellae are long and much like filaments and are strengthened by chitinous rods. 1 Since the primitive or embryonic shell is uncoiled and imperforate, and in shape like a cap or the beginning of a cone, we know that the spiral condition is a secondary one. It would seem most probable that before the perfect spiral form was attained the cone would be loosely coiled, arid that only after many generations and a long period of time could we have the complete amalgamation of the inner wall of a whorl to the preceding whorl which marks the tightly coiled spirals of many existing species. Since, also, the primitive shell is usually both smooth and color- less or nearly so, it follows that the highly ornamented and brilliantly colored shells are far removed from the primitive form. The ontogeny of many Gastropods has not been worked out, so that it is impossible to give a classification which shall show the genetic relationships of all the different species. It is most probable that the ancestral form, represented by the embryonic shell of 1 Dall, Bull. Mus. Comp. Zool., XVIII, 1889, p. 285. METAZOA MOLLUSCA. 219 many existing species, gave rise to different branches, each one of which has passed or is passing through a straight, a loosely coiled, and a tightly coiled stage. In such a case we should have many similar forms which are not closely related genetically but which are examples of parallelism. In a natural classification these hold their rightful position between the primitive and the more specialized members of their respective groups. Such a classification is not based upon the structure of the shell exclusively, inasmuch as the shell is a tell-tale part of the organism ; generally speaking, a straight shell has a straight body within it, and a coiled shell a coiled body. The straight body has the bilateral symmetry character- istic of early stages of animals, while the coiled body has succeeded in making such a twist in its organs as to bring the opening of the alimentary canal at the anterior instead of the posterior end. This twisting is indicative of com- plexity, and removes the form possessing it from its primi- tive ancestor. We shall illustrate the possible evolution of the Gastropod organism from straight through loosely to tightly coiled and involute forms. Future research will not probably change the principle of classification, though it will doubtless bring the special forms selected into genetic relations, so that each will hold its proper place in its own particular series. We can readily conceive of a straight tube becoming coiled so that the whorls would barely touch one another. In this case the resultant form would be a smooth unornamented spiral. In the loosely coiled shell of to-day (he margin of the aperture has a reflected lip as in Scala (No. 447, S. pretiosa Linn.). This shell shows how a tube may be twisted so that the whorls scarcely come in contact. The first whorl (No. 447) is nearly smooth, but each successive whorl shows an increase in the size of the ridges till they look like pro- jecting shelves extending entirely around the tube. By examining the opening, it is seen that a shelf is in reality the lip of the aperture which is made by the mantle during a period of rest. SYNOPTIC COLLECTION. Solarium modestum Phil. (No. 448), exhibits a much closer coiling of the tube. The youngest portion of the shell which is always at the apex is smooth and polished (No. 448). Each succeeding whorl becomes consolidated with the preceding one on the inner side, but in turning round, the tube leaves so large a space in the middle (called the umbilicus) that one can see nearly to the apex of the shell (No. 449, S. perspectivum Lam.). Surcula australis Roissy (No. 450), looks like an inef- fectual attempt to make a perfect spiral. The revolving bands and lines are often broken where additions have been put on at the margin. In this way the apertures of the younger shells can be easily traced and the length of the successive canals ascertained. This irregularity is chiefly due to the anal slit in the posterior end of the aperture which reminds one of the slit in Pleurotomaria, Haliotis, and the like. Most of the members of the family Pleurotomidae to which Surcula belongs, are with- out a horny or calcareous operculum for closing the aper- ture, and this is a characteristic of the deep-sea forms where the struggle for existence is reduced to a minimum and where therefore there is little need of protection from other animals. 1 The shell of Lunatia heros Adams (No. 451 ; see the lowest shelf of the erect portion of Section 8) is a simple spiral of a few turns, and is open nearly to the apex. The shell is thin and covered by a yellowish brown layer which is usually more or less worn off. As the shell increases in size it becomes thicker. Those living on the outer beaches where the waves break with force are much larger and stronger than those in quiet waters. The specimen (No. 451) shows the large size of the foot and the mantle extending over the edge of the shell. This foot can be completely withdrawn into the shell and the aperture closed by a horny operculum. 1 Uall, Bull. Mus. Comp. Zool., XVIII, 1889, p. 455. METAZOA MOLLUSCA. 221 One of the distinctive organs of the Gastropods is the lingual ribbon or odontophore (No. 452, odontophore of Lunatia heros}. It is a band armed on the upper side with chitinous teeth and attached at the back of the mouth ; the forward end is free. It is used as a rasping and scraping organ in obtaining food. One of the many classifications of the Gastropods is based on the struc- ture and variations of the odontophore. Like Lunatia, Natica hebraea Mart. (No. 453), is a simple spiral but the umbilicus contains a solid pillar or columella round which the whorls of the shell turn. No. 454 (Neverita duplicata Stimp., see lowest shelf of erect part of Section) shows still better than Lunatia the greatly distended muscular foot. It seems incredible that so large an organ can be contained in so small a shell. An instructive series is furnished by Polinices (No. 455, P. mantilla Linn.) : (a) is the young shell showing the open umbilicus ; a wire thrust into this opening^reaches upward nearly to the apex ; (b) has the umbilicus still visible though the wire does not penetrate so near the apex, showing that the umbilicus is becoming filled by the columella which adheres to it and is spirally twisted ; at this stage the inner lip has a sharp edge. In (c) the umbilicus is entirely concealed by the thickened inner lip ; in this specimen the horny operculum is in place ; the lines of growth near the margin are fine and close together while in (d) which likewise has the umbilicus concealed, the lines of growth are coarser. No. 455 e, is probably a reduced form ; although about a third smaller than (d), its weight is essentially the same, and a thick heavy deposit is laid on over the umbilicus. This series shows that the open umbilicus is a primary con- dition and the concealed umbilicus is secondary. This furnishes a good phylogenetic reason for placing those shells with the open umbilicus as more generalized in a system of classification. The next group of plain but tightly coiled shells with- 222 SYNOPTIC COLLECTION. out umbilicus is represented in the Collection by a number of specimens which may belong, as we have already pointed out, to as many different series. lanthina has a spiral shell resembling Lunatia in shape. It is translucent with violet colored areas. This mollusc makes a swimming float of cartilaginous air sacs which serves to keep it at the surface. To the under surface of this float are attached the egg capsules (see No. 456). The egg cases (No. 457 ; see erect part of Section) of Buccinum undatum Linn., are in masses. The shell is closely coiled and ribbed at right angles to the lines of growth (see No. 458). Turbo setosus Gmel. (No. 459) begins as a smooth, col- orless or yellow shell, then becomes ridged and is of a vivid green color, while the older whorls are dark green, marked by reddish brown spots. The aperture is entire. Litorina littorea Linn., has been imported from Europe, and in 1872 appeared in Massachusetts; since then it has spread with remarkable rapidity. The British form (No. 460, L. obtusata Linn.), is a smooth spiral without an um- bilicus. The shape varies like that of most littoral species, some specimens having a spire of three or four whorls, while in others the spire is depressed so that all the whorls excepting the last or body whorl are on a horizontal plane. Our New England species generally has a sharp spire and revolving lines on the whorls, while the color is a dingy brown or red. The external horny layer when fresh is a chestnut brown. Cydostoma elegans Drap. (No. 461 model), is similar to Litorina in many structural points but it has become more specialized by losing gills and breathing air by means of lungs. In a classification based strictly upon the struc- ture of the breathing organs the Cyclostoma would be placed with the Pulmonifera, but it is not probable that this would indicate its relationships. The model repre- sents the animal with the foot expanded ; at the anterior end is the head with two tentacles extended, at the base of which are the eyes. METAZOA MOLLUSCA. 223 Fulgur (Nos. 462-465, F. canaliculatum Say), places its eggs in horny sacs or capsules which it fastens together in a long string (No. 463; see lowest shelf). These maybe opened and the young (No. 462) observed in different stages of development. The specimens possess a smooth rounded protoconch, so thin and translucent as to show the yellow body within. The succeeding whorl is ribbed, and extends into a long canal giving the shell a pear-like shape which remains essentially the same in older stages (Nos. 464, 465). The model (No. 465, placed on account of size at the back of the Section on the right) shows the large foot extended as in the act of crawling ; the head with its tentacles ; the mantle on the edge of the shell ; and the siphon in the long canal. Fasciolaria is nearly related to Fulgur and its exquisite egg cases are seen in No. 466 (see erect portion of Sec- tion) . This species (F. tulipa Linn.) fastens these flower- like cases to some foreign object, coral in this instance. Across the free end of the tube, stretches a membrane which opens when the young are ready to escape. Magilus antiquus Mont, is a reduced form, the reduc- tion being due most probably to the habit of living in coral. The young shell (PL 467) is a thin spiral of three or four whorls, proving that its more immediate ancestors had a spiral shell. The latter is similar to that of Natica, Buccinum, and the like, and for this reason it is placed near them. In order to keep on a level with the surface of the growing coral, Magilus ceases to revolve, and puts out a long, nearly straight tube (No. 468). As it advances with the new growth it fills up the spiral and tube behind it. The veliger stage of Astyris (Pis. 469, 470, x 100 diameters ; the colors are schematic), shows the large lobed, ciliated velum, so characteristic of this stage of Gastropods, and the spiral shell. The adult (No. 471) has a shell with few whorls. The model represents the animal as walking on the sand with extended foot, ten- tacles, and siphon. 224 SYNOPTIC COLLECTION. In Terebra and Turritella we have illustrations of a perfect spiral of many whorls without projecting orna- mentation in the form of spikes or flutings. In Terebra subulata Lam. (No. 472), the early whorls are nearly colorless but those succeeding are marked by deep red spots. Both the young and adult shells are smooth, not having even the revolving lines and ridges seen in Turri- tella (No. 473 ; in this shell the youngest specimen has nineteen whorls and the one with the largest body whorl only sixteen, showing that the youngest whorls are broken off). The margin is entire in both genera. Cerithium tuberosum Fabr. (No. 474), has the revolving lines of Turritella and in addition the vertical ridges. The mar- gin has a short, slightly recurved canal. Vermicularia begins its life with a tightly coiled shell (see No. 475, V. spirata Phil.) that is similar to Turritella. Living in the cavities of a sponge it needs to keep at the surface of the growing animal in order to obtain food. It succeeds in doing this by forming a loosely coiled shell (No. 475) or in growing straight. We have here and in Magilus similar conditions producing similar results, and both are good illustrations of adaptation of structure to habit. On the west coast of Florida, Vermetus lumbricalis, var. nigricans Dall, forms rock-like masses, as shown in No. 476 (which, on account of its size, is placed at the back of Section 8) . When in the water the tubes are erect. The greater part of each tube is straight though some of the tubes show a spiral structure at the smaller end. Gyrineum spinosum Lam. (No. 477), has a colorless, smooth, snail-like spiral at the apex, the general appear- ance of which is distinctively unlike the succeeding whorls. The latter are somewhat flattened and have vertical ridges or varices with intervening short knobs and spikes. Ac- cording to Adams the shells that are armed with these knobs are found in rocky places, while the smoother spec- imens come from deep waters. METAZOA MOLLUSCA. Murex (No. 478, M. tenuispina Lam.), is an illustration of a specialized shell of this group. In this species the protoconch is preserved as a tiny white pearly shell. Extending below this are two or three whorls with ridges but without the long slender projections which ornament the succeeding whorls to an extreme degree. Conus bandanus Brug. (No. 479), is like an inverted cone, the last whorl being large and making most of the cone. The number of whorls can be indistinctly traced, encircling the apex at the broad posterior end. The aper- ture is neither notched nor drawn into a long canal. Trochus (=. Tectus) fenestratus Gmel. (No. 480), is a tightly coiled tube, the whorls increasing in number and being uniform in ornamentation. Aulica deshayesi Reeve (No. 481), is a : n instructive species since the protoconch is so large that its distinctive characters can be seen and thereby the ancestral form of the genus determined. This embryonic shell is a plump, globular spiral, light colored and smooth, and revolves in a different plane from the rest of the shell. One can dis- tinctly make out where the nepionic stage begins by not- ing the origin of the revolving lines and vertical ridges. The ephebic stage lasts until ' the ridges begin to dis- appear, as seen in No. 481. The vertical markings become coarser, which are characters of the gerontic stage. Oliva erythrostoma Lam. (No. 482), is similar in the different stages, as shown in the specimens, but by examining the apex, a colorless translucent spiral is seen which represents the ancestral form. The last whorl con- stitutes most of the visible shell, but the number of whorls encircling the apex can be easily counted. The specimens show considerable variation in color. The resemblance of Oliva, Aulica, and the like to the young Cypraea argues for a close relationship between these forms. In Cymbium cymbium Linn. (No. 483), the apex is smooth and flattened, and only two whorls are visible. 226 SYNOPTIC COLLECTION. The shell is notched and the animal has a short siphon. According to Adanson l many living Cymbia were found with living young in their bodies, thus proving them to be viviparous. The young (there are only four or five in each Cymbium) leave the mother when the shell is an inch long. Strombus costatus Gmel. is a plain spiral in which the whorls can be readily counted. The aperture of the adult extends upward on the preceding whorl and be- comes flaring with a recurved canal. No. 484 is an antero-posterior section through the middle of the shell, showing the internal structure, and No. 485 is a cross section of another species, S. gigas. Pteroceras lambis Linn, carries this mode of develop- ment farther than Strombus. It is illustrated by a fine series (No. 486) showing marked changes between the young and adult stages: (a) is a plain spiral having a long, narrow, notched aperture with a thin, sharp, unorna- mented margin ; (b) is the dorsal side, showing yellowish color banded with red ; (c-f) all exhibit the plainness of slightly older shells. In (g) the margin of the aperture extends toward the apex as in Strombus, and in (h) and (i) it goes beyond it, changing essentially the shape of the shell and giving a wide, flaring aperture with a canal at either end. The margin becomes fluted at first and afterward extends outward in long, half open canals which finally become closed solid spines 2 (see j and k). Phalium inflata Shaw (No. 487), has the first whorls light colored and plain ; those succeeding may have the marks of the lip or not, one being without them and two having them. The canal is short and instead of being prolonged as in Murex, it is sharply recurved. No. 488 is a section of a small specimen of Cassis cameo Stimp. Cassis grows to a large size and is much used in making cameos. 1 See Adams, Genera of Moll., I, 1858, p. 158. 2 Adams, loc. cit., I, p. 260. METAZOA MOLLUSCA. 227 The series of Cypraea cervus Linn. (No. 489 a-c) is extremely instructive. The young shell (a) is a spiral in which the number of whorls can be easily counted. A still earlier stage, of which there is no specimen, is a simple, thin, snail-like spiral (Adams). The shape of (a) is similar to Oliva, Cymbium, and the like. The aperture is also long with a thin, sharp, untoothed, and unorna- mented margin, and a slight notch at the anterior end. In (b) the shape has changed, the margin of the aperture has thickened and turned inward, while both sides of the opening are toothed and both ends notched. In (c) only vestiges of the spiral remain, which no one would recog- nize who had not seen the younger stages; thus the shell has taken on a character that separates it from those pre- viously described and which places it with the more spe- cialized forms. If a vertical section of the shell is made, the whorls are seen inside (No. 490, C. exanthema Linn.) concealed by the last body whorl. No. 489 c is of re- markable size and is lighter in weight than some of smaller size. It is thus seen that the development of Cypraea is an epitome of the life history of those Gastropods which have a simple, snail-like spiral in adult life, and of those with the modified spiral of Oliva and Cymbium. A still more specialized form is Cypraea mauritiana Linn. Its development is shown in the series No. 491. The first six specimens would hardly be called the young of the last six, so unlike are they in shape and coloring. In the youngest specimen in the series, the spire with its small whorls and large body whorl is seen. The shell is now strikingly like Oliva. The long aperture has a sharp margin which as yet has not turned inward. In the older stages the shape changes ; the early spiral is concealed by the enamel which the mantle has laid on. There are two broad, thick, flat, toothed lips with a nar- row aperture and a canal at either end. The two largest specimens have grown high vertically, and this peculiar 2*28 SYNOPTIC COLLECTION. shape with the flattened lips makes the shell more spe- cialized than those of the other species of Cypraea already described. Cypraea is a transitional form between those shells that have the external spiral represented by the young and those which have the spiral partly or wholly internal, being covered by the growth of the later whorls. Ultimus gibbosa Linn. (No. 492), does not show even in youth any embryonic shell or spiral. The shell re- volves so that each whorl covers the preceding. The margin of the aperture is thin and easily broken. In course of growth the margin thickens and turns inward, so that the adult has a strong incurving lip. A related species, Simnia acicularis Lam. (No. 493), offers a striking example of mimicry. In the present instance it has taken on the uniform deep purple color of the coral on which it lives. When it chooses the yellow coral, Rhipidogorgia, for its home, it assumes the yellow color, and on white coral it is nearly white. Its foot is narrow and well adapted for clinging to the coral. Transitional forms between marine Gastropods and fresh-water or land species are found in Nerita, Neritina, and the like. The transition from the one to the other is governed by natural causes which we have already found are not difficult to explain. The youngest portion of the shell of Nerita versicolor Gmel. is yellow, smooth, and unmarked by color spots, as seen in the first whorl of No. 494. In the next whorl the surface is ridged, and the color is nearly white marked by dark irregular spots. The teeth on the left of the aperture are barely indicated and none are seen on the right side. In (b) the ridges are more pronounced and there are suggestions of teeth on the right side. In (c) the youngest portion is colorless, as is the case with a number of the older forms ; (e) has a predominance of red color over the .darker shade of the youngest shell, and the teeth on both sides are well developed; (g) and (h) illustrate the variation in color from a light to a dark METAZOA MOLLUSCA. 229 shell. This subject of color variation in a single species is shown still better by Nerita peloronta Linn. (No. 495). Here we have nineteen shells varying from a nearly white shell spotted here and there with pink to a dark purplish shell apparently banded and spotted with lighter shades. The youngest stage in all the specimens is either white or yellow, without spots or bands, and is smooth ; (y) and (z) are in their natural state, while the others have been boiled in caustic potash for about ten minutes, so that these bright colors are not seen in the living ani- mals ; (z) is an adult which is mounted to show the bright red spot near the large tooth that has given the 'name of Bleeding Tooth to this species, and also the operculum which is in place and is deeply colored, (q) is an illus- tration of albinism', the spot that is usually blood red being nearly colorless. Neritina (No. 496, N. canalis Sowb.), is a genus of especial interest since some of the species live in the saltest of sea water, that of a lagoon, while most are either brackish or fresh-water or land animals. Certain marine species are practically land animals, since they live where they cannot be immersed in water excepting at extremely high tides, and even then they would not be covered unless the waves dash upon the rocks where they live. Adams 1 speaks of some species living in trees over- hanging water. The shell of Neritina canalis Sowb. (No. 496), is cov- ered by a thick, dark brown horny layer which, when broken off, reveals a shell of peculiar whiteness. Pulmonifera. Many Gastropods that were originally marine animals have doubtless become in the course of many generations, and a longer or shorter period of time, fresh-water or land animals. Most of these now bear the name of Pulmonifera, since they no longer breathe air dissolved in water, but are equipped with 1 Genera of Moll, I, 1858, p. 381. 230 SYNOPTIC COLLECTION. primitive lungs in the form of a pulmonary sac or cavity. As a proof that the Pulmonifera are more specialized than the groups already described, it may be stated that many Pulmonates fill their lung sac with fresh water in the younger stages and only later in life dispense with the water. There are objections to the use of the term Pulmonifera, since some of the air-breathing Gastropods (Cyclostoma, for instance; -see No. 461) are so different in structure from the typical Pulmonifera that they can- not be placed in this group but are specialized air-breath- ing members of more generalized groups. As a rule the shells of the Pulmonifera do not attain that brilliancy of coloring and that extreme ornamenta- tion which may be observed in their marine ancestors. Among the fresh-water and land Gastropods there are no forms possessing the straight cone-like shell, but the shallow cup of Patella and the spiral of Crepidula are represented by Ancylus and Gundlachia. These Gastro- pods have habits similar to those of their marine relatives and the structure is similar. We have not found a spiral so loosely coiled as Scala ; the majority represent the group of tightly coiled plain spirals, the chief difference between the genera being in the plane of the coiling. Ampularia globosa Swains. (No. 497), is a simple spiral with a small umbilicus, holding a similar place among fresh-water univalves that Lunatia holds among the ma- rine. The glossy, horny layer of this genus is striking, reminding one of this finely developed layer on fresh- water bivalves. The operculum of the young and the adult shell is not spiral, but the additions are made con- centrically (see No. 497). In this genus the left gill is vestigial, the mantle cavity having a large pulmonary sac on each side. These mol- luscs are amphibious, being able to live a long time out of water. Another fresh-water form is the pond snail, Limnaeus stagnalis O. F. Mull. (No. 498) . It comes to the sur- METAZOA MOLLUSCA. 231 face for air, but whether this is a necessity for maintain- ing life is not yet settled. The model shows the long respiratory tube containing bubbles of air which the snail extends from the respiratory opening to the surface of the water. The tentacles are flattened, as seen in No. 498. When ponds dry up, these snails bury themselves in the mud and in this situation can live for a considerable time. Planorbis corneus Linn. (No. 499), is a good example of a shell coiled on a horizontal plane. The whorls are few in number and the aperture is entire and flaring. Polygyratia polygyrata Bonn. (No. 500), is a still better example of a horizontal spiral consisting of eight closely coiled whorls with the ninth unfinished. The aperture like that of Planorbis is entire. Campeloma (No. 501, C. decisa Say) and Melania (No. 502, M. hastata Lea), are exceptional Gastropods, inas- much as both are viviparous. Vivipara (= Paludina) carries its young about with it for three or four weeks after birth. The land Gastropods are represented by a number of species. Helicostyla leai Pfr. (No. 503), is a smooth beautiful white spiral of three or four whorls. The aper- ture is entire, and there is no umbilicus. The eggs of this genus are protected by a limy shell so that they re- semble those of birds. Helix (No. 504) is one of the commonest land snails. The youngest shells (see No. 504) are so thin and fragile that they can be easily crushed between the fingers. The margin is sharp and lipless. When older the shell is stouter with a thick white lip (No. 504). The last speci- men in the upper right hand corner is reduced, being small in size but provided with the thickened lip. The adult animal (No. 505, H. hortensis O. F. Mull. ; No. 506, H. pomatia Linn., see topmost shelf), is represented with foot extended, and with the shell containing the spiral portion of the body in normal position when the snail is crawling. The head has two pairs of tentacles, and the 232 SYNOPTIC COLLECTION. black eyes are distinctly seen at the ends of the longer pair. No. 507 is a model showing the internal organs of Helix pomatia Linn. The various parts are marked ; those on the left are the buccal body, esophagus, salivary glands, stomach, liver, intestine, and the pulmonary cham- ber ; and those on the right the reproductive organs and slime glands. The land Gastropods most specialized by reduction are the slugs, represented by Limax (Nos. 508-511). Here the shell is reduced to a thin, flat plate on the back (see model of Limax maximus Linn., No. 508), and this has become internal. The spiral body of most Gastropods no longer exists, but the body of the slug is long with the foot on the ventral side (No. 509, L. flavis Linn.). The preparation (No. 510) shows the general anatomy of Limax rufus, while the genital organs are seen in No. 5"- Section 9 of Case B is taken up with the Tectibranchs, Nudibranchs, Scaphopoda, Heteropoda, and Pteropoda. These are considered as so many groups of molluscs which have become modified, each in its own special and dis- tinctive way, to meet the requirements of existence. The Pteropods are probably the most specialized, and the most closely related to the Cephalopods; but on account of their minute size, they are placed in the horizontal part of Section 9. Here they can be seen and studied more easily than in the erect portion, where, according to our system, they properly belong. Some of the Tectibranchs have well developed shells, like Tornatella (No. 512, T. solidula Lam.) and Bullus (No. 513, B. oblongus A. Adams), while in others (Aplysia, No. 514, see erect part of Section, No. 515, and Pleurobranchus, No. 516) the shell exists only as a vestige. Tornatella (No. 512), reminds one of Oliva (No. 482) with its short spire and large body whorl. Bullus (No. 513) even when young shows no spiral form, but if a cross section of the shell is made near the posterior end the METAZOA MOLLUSCA. 233 spiral is seen within. Every whorl entirely conceals the preceding, as we have seen it in Ultimus (No. 492). The "sea-hare," Aplysia (No. 514, A. limacina; No. 515, A. inca d'Orb.) has only the remnant of a shell on its back in the form of a concave plate, and this is concealed by a fold of the mantle. On the dorsal side the mantle grows out into two large folds, called epipodia (see Nos. 514, 515) which are used in swimming. The single branchia is on the back protected by the mantle. The model (No. 515) represents the animal as crawling on its long ventral foot. Garstang 1 has pointed out the interest- ing fact that young Aplysiae in migrating during growth from deep water to the shore pass through algae colored first red, then brown, and finally olive green, and that these animals change their colors from red to green in accordance with their surroundings. The shell is reduced and concealed by the mantle in Pleurobranchus (No. 516, P. grandis Pease). Lobiger (No. 517, L. picta Pease), has a small shell on its back and two pairs of wing-like swimming organs extending from the sides of the body. NUDIBRANCHS. The Nudibranchs pass through a trochophore and veli- ger stage in their development. They possess a spiral or nautiloid shell before they leave the egg, and the body at this time is more or less spiral in form. During the growth of the larva the shell disappears and the animal extends lengthwise. The possession of a shell in the embryo is evidence that the Nudibranchs have descended from Gastropods with spirally coiled shells. According to Kingsley 2 the twisting or torsion of the body has not been carried to its full extent, which would indicate a primitive 1 Journ. Mar. Biol. Assoc., n. s., I, 1889-90, p. 411. 2 Stand. Nat. Hist., I, 1885, p. 295. 234 SYNOPTIC COLLECTION. condition. But inasmuch as this torsion is greater in the embryo than in the adult, the less degree of twisting is a reduced rather than a primitive characteristic. The asym- metrical condition of the heart and the nephridium prove that the bilateral symmetry of the adult is also a second- arily acquired and not a primitive condition. Gilchrist 1 has shown that, while the original bilateral symmetry is apparently assumed, the organs which were lost on one side in the twisting of the straight body into a spiral are never again developed. Not only has the Nudibranch lost its shell, but in some species the mantle has disappeared. In other ways this group has become peculiarly special- ized. Many Nudibranchs are without true tentacles, while most have organs called dorsal tentacles or rhinophores which are supposed to be organs of smell. The branchiae are not like the gills of most molluscs, but are secondarily acquired, respiratory organs, and are often called cerata to distinguish them from the primitive gill. These bran- chiae vary greatly both in shape and position and are often extremely beautiful organs. Eolis ( = Aeolis) coronata Forbes lays its eggs in a close-set spiral coil of four volutions (PI. 518, fig. i ; fig. 2, a portion of the same magnified, showing the eggs imbedded in a gelatinous thread). The larva (fig. 3) is provided with a spiral shell (fig. 4), which is closed by an operculum. At this stage the larva has the two ciliated oral lobes which aid in locomotion. With the growth of the animal the shell and operculum disappear and the oral lobes are either modified or wholly absorbed. The mature Eolis (fig. 5, upper side; fig. 6, lower side; No. 519, E. papillosa Loven), has a long slug-like body wholly unprotected by a calcareous or horny shell. The forward part bears a pair of tentacles, and also a pair of rhinophores or dorsal tentacles. Along the back the brilliantly col- 1 Proc. Roy. Soc. Edinburgh, XX, 1895, p. 368. METAZOA MOLLUSCA. "235 ored branchiae are arranged in six clusters, each cluster consisting of many papillae. These branchiae are liable to fall off, and sometimes a whole cluster is wanting, In Flabellina (No. 520, F. janthina Angas), a related form, the branchiae are ^numerous and tube-like, as they are also in Spnrilla neapolitana (No. 521). The branchiae in Gtaucus longicornis Reinh. (No. 522), are in the form of clusters of long slender filaments on either side of the tapering body. These branchiae are not only respiratory organs but are used for swimming when the little creature with ventral side uppermost darts through the water. Tethys leporina Linn. (No. 523), is a Nudibranch of rare beauty. It is nearly transparent, with light and dark red spots. The forward part is broad and has a delicate fringe. The dorsal tentacles are leaf-like and the bran- chiae extend down the body on either side. At the pos- terior end the mantle is extended into an excurrent siphon. Melibe (No. 524, M. fimbriata Aid. & Hanc.) has the head differentiated from the body ; it bears two prominent dorsal tentacles enlarged at the end. The body is cov- ered with papillae, and along each side are large club- shaped branchiae, which after the first pair are placed alternately. . Dendronotus arborescens Mull. (No. 525), is similar in many respects to Eolis. When young it is nearly color- less, but the adult is subject to much variation in color ; usually, however, it is reddish, as seen in No. 525. The head is provided in front with branched append- ages. Above are the dorsal tentacles which can be withdrawn into sheaths. Along each side of the body are the arborescent branchiae.- The long tapering foot is well adapted for clasping seaweed and is used in this way as well as in crawling. Scyllaea marmnrata Aid. & Hanc. (No. 526), is a small Nudibranch with two pairs of gills. The animal resembles the Sargassum sea-weed in which it lives, and 236 SYNOPTIC COLLECTION. its long narrow foot with thin and flexible sides is well adapted for clasping the stems of algae. The branchiae in Pleurophyllidia (No. 527, P. setnperi Bergh), consist of leaf-like organs on each side of the body between the foot and the doreal portion of the mantle. In Doris (No. 528, D. nubilosa Pease) they form a circle around the anus and are retractile, while in Trevelyana (No. 529, T. cristata Bergh) and Plocamo- phorus (No. 530, P. imperialis Angas) they are not so completely retractile, although according to Eliot, 1 they retract when touched in the living animal, but remain out- side in alcoholic specimens. Among the Nudibranchs that have lost both shell and branchiae are Phyllobranchus (No. 531, P. orientalis Kol.) and Elysia (No. 532, E. chlorotica Gould) ; while in Pontolimax ( = Limapontia) (No. 533, P. capitatus O. F. Mull.) no shell, branchiae, nor appendages exist. It is interesting to note that the law of acceleration in development has brought about a condensation of embry- onic stages in two Nudibranchs, Cenia cocksi and PeJta coronata? so that the veliger stage with the ciliated velum and the shell is omitted from the ontogeny. SCAPHOPODA. The Scaphopoda are a small group represented by Den- talium (Nos. 534-536). The tube like shell of this genus is not made by the addition of successive layers to the margin of a cone-like embryonic shell, as a primitive Gastropod shell would be formed. On the contrary, the mantle at first consists of two folds which in the process of development come together on the ventral side and 1 Proc. Acad. Nat. Sci. Phila., 1899, P- 5 2 - 2 Zool. Anz., XXIII, 1900; quoted in Science, n. s., XII, 1900, p. 824. METAZOA MOLLUSCA. 237 make a tube with an opening at each end. The shell formed by the mantle grows in the same way, and is a tube open at either end. No. 534 (D. entalis Linn.), shows the animal within the tube. From the larger or anterior end the foot projects. The mouth with the odontophore is at the base of the foot. Plate 535 represents the fleshy animal as taken from the shell; fig. i, dorsal view, fig. 2, ventral, and fig 3, lat- eral view. The organ colored dark green in the model (No. 536) is the liver; the kidney is at the forward end of the liver, while the generative organs are on one side and are colored yellow. . HETEROPODA. In the Heteropoda the foot is modified in different ways, sometimes being in the form of a vertical fin extending from the ventral side. The variability of the gills is shown by the fact that in this group they are present or absent in species of the same genus and even in speci- mens of the same species. 1 Atlanta peroni Les. (No. 537), has a glassy shell which is a vertical spiral in the young animal, but which later be- comes flattened in one plane. The last whorl increases rapidly in size, and the aperture is flaring. The fleshy body takes the coiled spiral form of the shell and can be wholly drawn into it and protected by the operculum. Around the outside of the shell there is a thin sharp keel which looks at first glance like a delicate membrane. Carinaria cristata has a smooth coiled shell when young (PI. 538, fig. i, left side; fig. 2, right side; en- larged). When older the shell takes the form of a coni- cal cap, seen in fig. 3, with flutings on the outer surface. No. 539 is the shell of the adult of another species, C. 1 Tryon, Structural and Systematic Conchology, II, 1883, p-348. 238 SYNOPTIC COLLECTION. lamarcki P. & L., in which the early tendency to coiling is seen at the apex, while No. 540, C. cithara Bens., is suggestive only of the cap-like form. No. 541 is the fleshy animal (C. mediterranea), and PI. 542, a drawing of C.fragilis Bory. It is drawn with the ventral side upper- most, the position it often takes in swimming. The body is long and the leaf-like fin (see No. 541) which is a modi- fied foot is seen above, while below, the visceral mass con- sisting of liver, kidney, heart, reproductive organs, etc., is reduced in size and covered by the small shell (No. 540- The more specialized Heteropods are represented by Pterotrachea (No. 543, P. mutica-, No. 544, P. coronata\ see lowest shelf) in which the body has lost its spiral form and become cylindrical, while the shell has wholly disappeared. The tentacles are also lost and the gills exist only as vestiges. PTEROPODA. Recent researches point to the conclusion that the ancestors of our present Pteropods existed in the early Palaeozoic times. A near ally of Tentaculites, Orygoceras (PL 545, fig. i, O. dentaliforme ?), had a plain unornamented shell. The protoconch is not represented in the figures of this spe- cies, but is finely shown in O. cornucopia* (PL 545, fig. 2). Succeeding the protoconch the young shell of this species is seen to be unornamented like the adult (fig. i). As the animal grows older the shell becomes ridged by many circular rings (fig. 2). Tentaculites (No. 546, T. gyr acanthus Eaton; PL 547, T. acuarius Richt.), has a straight, cone-shaped shell like that of Orygoceras, with a simple circular aperture, and with concentric ridges of rings extending around the out- side. These ridges are carried back nearly to the proto- METAZOA MOLLUSCA. 239 conch by the law of acceleration in development, so that Tentaculites comes naturally after Orygoceras in our classification. Hyolithes (No. 548, H. primordialis Hall), is usually straight, but sometimes curved. Its aperture is triangular and is provided with an operculum. The shell is divided off in the interior by horizontal partitions. Conularia (No. 549, C. congregata Hall), has a very thin straight shell with a four-sided aperture. According to Ruedemann 1 Conularia is at times a sessile form and is found attached to older individuals (PI. 550, fig. i, C. gracilis Hall, x 2) or sometimes to foreign objects. PI. 550, fig. 2, exhibits the young of different ages attached. The full and beautiful researches of Fol 2 upon Ptero- pods have given us much knowledge concerning the life histories of these interesting animals as well as their habits and structure. The eggs of most species are laid at the going down of the sun, and the number produced by one individual is enormous. When the Pteropod embryo of to-day leaves the egg it possesses a shell and a velum. In some genera the shell is present throughout life, while in others it is possessed by the larva only. The velum disappears, and the foot changes from a creeping to a swimming organ by devel- oping two broad lateral expansions usually called wings, but which are really oar-like fins. According to Pelsen- eer these little creatures swim in a nearly vertical posi- tion with the head uppermost or slightly sloping, so that the foot is turned upward, while the fins move backward and forward. The division of the group into Thecosomata and Gym- nosomata is in accordance with the principle of a natural classification. 1 Amer. Geol., XVII, XVIII, 1896. 2 Arch. d. Zooi. Exper. et Gen., IV, 1875. 240 SYNOPTIC COLLECTION. Pelseneer, who has made a special study of the anat- omy of these forms, admits that "the division established on the very empirical character of the presence or the absence of a shell, is quite justified by the anatomical differences." 1 Thecosomata. The Thecosomata are among the more primitive forms. They possess a shell, and the animal adds new layers to it as it grows. The head is indistinct and the wing-like organs extend from it on either side and are joined at the anterior edge above the mouth. The anus is on the left side. It may be that there are primitive forms among the straight, cone-shaped Pteropods living to-day, but judging from our present knowledge of the anatomy of these straight forms, one must consider them as secondary and specialized members of the Pteropod group, and the spiral forms living to-day as the more generalized. The spiral condition is represented by Spirialis aus- tralis Soul. (No. 551; PL 552). Its tiny spiral shell protects a spirally twisted body and the aperture is closed by an operculum. Spirialis rostralis Soul. (No. 553 ; PI. 554), has a nauti- loid shell with an umbilicus. The figures exhibit the forward part of the body with its appendages, the ex- panded wings, and the viscera enclosed by the mantle. Creseis aticula Rang (No. 555, alcoholic specimen ; Nos. 556, 557, shells; PI. 558, figure of animal in shell), is provided when young like all Pteropods with a shell formed by the everted shell gland. In most members of the group this shell disappears and a secondary shell is formed. In Creseis, however, the primitive and second- ary shells are both retained throughout life. The adult shell is smooth, cone-shaped, and bilaterally symmetrical, with a simple aperture. It would seem that this bilateral symmetry was evi-. 1 Chall. Rep., Zoo!., XIX, part I, 1887, p. i. METAZOA MOLLUSCA. 241 dence of a primitive condition, but the asymmetry of the internal organs proves, as already pointed out, that these forms have descended from spiral, asymmetrical Ptero- pods. The shell has become adapted for swimming, while the internal organs have not been so modified. To strengthen these views there are species of these usually straight forms which have the protoconch coiled dorsally, indicating a former coiled condition. 1 This genus exhibits the cone-in-cone structure plainly seen in Creseis striata Rang (No. 559 ; PI. 560), which is large and finely striated on the outside. This straight cone may sometimes in the same species become horn-shaped, as seen in PL 560. Cuvieria columnella Rang is like Creseis when a larva. No. 561 is a very rare specimen in which the small cone- shaped young is seen preserved. When older the animal builds a transverse partition across the slender tube, then advances and makes a much larger tube (No. 562). The young shell is usually broken off, so that only the part built by the adult is seen (PI. 563).' Cymbulia peroni Cuv. (No. 564, animal; No. 565, model ; PL 566), is a recent form, and has an external, spiral, operculated shell when a larva. This is thrown off and a secondary shell forms which is also cast aside. Finally in some species an internal cartilaginous shell is produced which is retained throughout life. The figure on the left in PL 566 is a view of the shell of Cymbulia from above with the wings expanded, and the figure on the right a side view showing the slipper-like form of the shell and the position of the animal within it. The model (No. 565) represents the adult with its delicate wings spread. Tiedemannia neapolitana (No. 567) is a nearly related genus with an internal shell. The shell of Hyalea is essentially a hollow cone. The 1 Chall. Rep., ZooL, XXIII, Rep. on Pteropods, part 3, 1888, p. 36. 242 SYNOPTIC COLLECTION. illustration shows the exquisite delicacy of Hyalea globu- losa Rang with its blue shell and softly tinted wings. In this species the shell (No. 568) is nearly globular with the dorsal part projecting in front (PI. 569) and the ven- tral part convex. Hyalea tridentata Lam. (No. 570), is a much larger species with a golden shell (No. 571) and purple and golden wings (PL 572). The upper and lower parts of the shell, and the open spaces between the two are seen in the side view (PI. 572, figure on the right). Cleodora cuspidata Bosc. is protected by a glassy, nearly transparent shell (No. 573) with three projecting spikes. The visceral mass is colored in the figure (PI. 574), while the other parts are nearly colorless. The alcoholic speci- mens (No. 575) show different ages of another species, Cleodora pyramidata. Balantium recurvum Child (No. 576), is one of the larger Pteropods. Its shell is triangular in shape and terminates in a sharp point. Its delicate coloring and symmetrical transverse markings make it a beautiful object. Gymnosomata. The larva of Clio, a member of the Gymnosomata, loses its primitive and secondary shell and its velum after which a second larval form appears with three bands of cilia encircling its body. This second larva is without a mantle and secretes no shell. The adult (No. 577, alcoholic specimen ; PL 578, Clio ( = Clione) borealis Pe'ron) has a long body with a distinct head. The latter bears two pairs of tentacles which are provided with a vast number of tiny suckers. The wings are distinct from the head and do not join in front, in which particulars the Gymnosomata differ from the The- cosomata. The foot is also distinct from the wings and consists of a posterior lobe with two smaller anterior ones. In all these forms the anus is on the right instead of the left side of the body. Pneumodermon peroni Q. & G. loses its mantle and shell METAZOA MOLLUSCA. 243 like Clio (No. 577) and moves by means of bands of cilia. The adult (No. 579, No. 580, P. violaceum d'Orb.), pos- sesses a distinct head which carries specialized tentacles having suckers similar to those of cuttlefishes. At the posterior end of the body there are external gills (No. 58o). Clionopsis krohni (No. 581; No. 582, C. flavescens Gegenbaur) has a barrel-shaped, shell-less body which is nearly transparent, and the visceral mass extends to the posterior end. The head is small with no mouth appendages. Section 10. CEPHALOPODA. The Cephalopoda and Brachiopoda are perhaps the best groups that can be chosen at the present time to illustrate a natural classification based upon the stages of growth and decline. It is obviously impossible to follow out this classification in detail, to trace the numerous branches of the Cephalopod trunk to say nothing of the minute twig- like divisions and subdivisions of these branches. It is hoped , however, that such a series of specimens and draw- ings has been selected, and such an arrangement of these made, as will give the student a clear general view of the subject. It is well to impress upon one's mind at the very out- set the truth of the words: "A single shell, either from a living or fossil form, may present, accurately, the general history of the development of the young, the stages of the adult and of old age." 1 1 Hyatt, Fossil Cephalopods in the Museum of Comparative Zoology, Proc. Amer. Assoc. Adv. Sci., XXXII, 1883, p. 323. 244 SYNOPTIC COLLECTION. TETRABRANCHIATA. NAUTILOIDEA. When the Nautiloidea first appear in the Palaeozoic strata they are specialized in so many ways, the inference may be drawn that we are ignorant of the radical stock from which all the Cephalopods have descended. A study of the embryological and larval structure of living Nauti- loids, however, leads to the conclusion that Diphragmo- ceras, Piloceras (PI. 583), and Endoceras (No. 584) are among the generalized ancestors of the group. A knowl- edge of these genera and of the Orthoceratites, soon to be described, enables one to give an hypothetical ancestral form with a great degree of certainty. Diphragmoceras is a nearly straight tube divided into a few chambers by simple plain partitions or septa. Through these septa runs a large tube or siphuncle which is divided by septa similar to those in the surrounding shell. The structure of the siphuncle is an important character in the classification of the Nautiloids, primitive forms and the young of specialized genera having large siphuncles, while those of adult specialized forms are small and contracted. 1 Unfortunately the young Piloceras has not been de- scribed. The adult is both straight (PL 583) and curved. It is divided by septa and has a large siphuncle. Near the apex the siphuncle exhibits a cone-in-cone structure which is more developed in Endoceras. The latter genus, when young, may represent the full grown Piloceras. The adult Endoceras (No. 584; PI. 585, vertical section of E. proteiforme Hall, greatly reduced), is a straight form with a shell divided into chambers by septa. Each septum extends downward beyond the one next below, forming funnels which taken together make a complete siphun- cle (see PI. 585). This tube is large, being sometimes 1 See Hyatt, Proc. Amer. Assoc. Adv. Sci., XLVII, 1898, p. 363. METAZOA MOLLUSCA. 245 more than one half the diameter of the shell. Within the siphuncle are cones, one within another, which are much more plainly seen than in Piloceras. To understand this structure, one must consider the fleshy body of the animal. This occupied the outermost chamber of the shell. Extending backward a considerable distance from its pos- terior part was a bag-like prolongation which secreted shell in the form of a cone. At certain periods the body advanced and while resting built another cone, thus giving rise to the cone-in-cone structure seen in PI. 585. Extending from the spire of the cones backward to the apex of the shell was a hollow tube, the endosiphuncle, also plainly seen in PI. 585. Diphragmoceras, Piloceras, and Endoceras represent generalized forms having huge siphuncles. These be- come only slightly contracted in later stages of growth. In fact the generalized members of this class do not pass through marked changes in external form and ornamenta- tion or in internal structure ; one genus, Cyrtocerina, proba- bly preserving its large siphuncle unchanged throughout life. 1 Much more is known of the young of the genus Ortho- ceras than of the preceding genera. Its protoconch has been observed. Figs. 1-3 of PI. 586 represent the proto- conch of Orthoceras elegans Munst, from the front, side, and above ; (a) protoconch, (b) shell ; figs. 4-6, the proto- conch of Spyroceras (= Orthoceras) crotalum Hall. This protoconch is a chamberless, septa-less shell, usually very much shrunken owing to the delicate substance conchi- olin of which it was made. Here we have a clew to the radical form that gave rise to the Cephalopods, and proba- bly to the Gastropods and Pteropods as well. In figs. 4-6 not only is the protoconch distinctly seen but also the different substages of the nepionic stage. 1 Hyatt, Genesis of the Arietidae, Smithsonian Contrib. to Knowl- edge, XXVI, 1889, p. 39. 246 SYNOPTIC COLLECTION. The markings of the protoconch are carried over contin- uously to the beginning of the nepionic stage, proving conclusively that the shell or conch was formed on the edges of the protoconch. Usually the protoconch is broken off and in these cases a scar is left. Fig. 7 (O. unguis) shows the scar and the conch of the apex. Fig. 8 is a view of the apex of the same species after the proto- conch has been accidentally broken off, fracturing the outer shell and exposing the scar. The young has a large siphuncle which afterwards in the process of growth becomes contracted, but never develops the cone-in-cone structure, or an endosiphuncle. This tends to prove that Orthoceras descended from forms with a large siphuncle and that the small siphuncle is a secondary condition. The position of the siphuncle is usually near the center of the septa, as seen in No. 587, which represents a portion of the adult shell. The septa are plain and concave towards the living chamber. The shell is straight and unornamented, with a simple aperture. It is marked by that genuine simplicity which characterizes primitive forms. The tendency of the primitive straight shell to become coiled is shown in Cyrtoceras and Gyroceras. Cyrtoceras (PI. 588) is more or less curved, but is never coiled. The septa are concave towards the forward part, the aperture is large, and the ventral sinus is distinct. In Gyroceras (PI. 589) the process of coiling begins, but the whorls are not in contact, so that the result is a loose spiral. The aperture is simple and the septa are plain and concave. There are fossil forms among the Nautiloids in which the whorls are closely coiled, as in Nautilus dekayi Mor- ten (No. 590, showing septa and siphuncle) and Nautilus intermedius Sow. (No. 591). In some species these whorls are visible (No. 591 ; No. 592, Nautilus umbilicatus Lis- ter; section of shell), and in consequence of this mode of growth the species has a deep umbilicus on either side. METAZOA MOLLUSCA. 247 The tendency .towards becoming an involute shell is seen in Nautilus stenomphalus Sow. (Nos. 593, 594). The involute shell in which the earlier whorls are entirely concealed by the latest whorl is seen in Nautilus pompi- lius Linn. (PI. 595 ; Nos. 596, 597). The development of this species is extremely interesting from a phylo- genetic point of view. The first chamber of the shell of the young Nautilus has a linear scar (PI. 595, fig. 2) which probably marks the spot where the protoconch was broken off. The protoconch itself has never been found in perfect condition in this group, though the scar bears strong evidence of its former existence. There are good reasons why the protoconch of Nautilus should be lost. It was probably made of frail material which would easily be broken while the animal was swimming about in the sea. Then again, when the young, nearly straight shell began to coil, the hard calcareous first whorl would come so close to the delicate protoconch that the latter could hardly fail to be destroyed. The protoconch was doubt- less connected with the first chamber by an 'opening which is plugged up in the present Nautili, the scar mark- ing its position. In a section through a young shell of Nautilus pompi- lius Linn. (PI. 595, fig. i), the first living chamber is almost straight, while the rest is slightly curved. This chamber was occupied by the young animal after the pro- toconch stage. It was septa-less like the protoconch and without a siphuncle. In course of time the animal ad- vanced and made a wall or septum behind it. This sep- tum bent downward into the first chamber forming a coecum or the beginning of the siphuncle as seen in the figure. The second septum likewise is prolonged, and its coecum extends downward into the first coecum. the bot- tom of the coecum forming a septum across the siphuncle. This early condition of Nautilus represents the adult Di- phragmoceras with its large septate siphuncle. The third septum in Nautilus extends only to the sec- 248 SYNOPTIC COLLECTION. ond septum, forming a long funnel with no septum at the bottom. The siphuncle begins to contract and from this time on is without septa, resembling the contracted septa- less siphuncle of Orthoceras which arises in the same way ; i. e., by the formation of long funnels. Fig. 2 represents the nepionic stage of Nautilus as seen from the front. The specimen has been obtained by breaking down a full grown shell. The vertical scar marking the position of the protoconch is distinct, while the circular siphuncle is of large size. Fig. 3 is the same seen from the side. It shows the increase in ornamenta- tion from a comparatively smooth shell. The lines of growth do not bend backward in the middle of the ven- tral side but run nearly straight. Fig. 4 shows finely the scar and the area of attachment of the protoconch ; the siphuncle and first few septa are also plainly visible. The adult Nautilus is represented by No. 596, the shell ; and No. 597, a section showing an alcoholic specimen of the fleshy animal within its shell. The involute spiral form has been attained and the coiling has taken place in such a way that the ventral convex side is outermost and the concave dorsal side innermost. As the shell coiled, the newly formed, more or less plastic whorl came in contact with, and was pressed by the harder and older preceding whorl. The tighter the coiling the deeper we should say would be the impres- sion. This impressed area in the dorsal side of the shell is known as the impressed zone, and is an important character in both Nautiloids and Ammonoids. In the adult Nautilus the septa extend backward only a short distance, giving rise to short funnels in place of the long ones of more generalized forms. These funnels are connected by a porous tube secreted by the siphon, and the two taken together form the siphuncle. This is well seen in the section of the shell (Nos. 592, 597) run- ning from the outermost chamber to the innermost. Its position is near the center of the concave septa. It will METAZOA MOLLUSCA. 249 be observed that the septa are much nearer together in the adult than in the young (PI. 595, fig. i). If a sec- tion of an old shell is examined the septa are sometimes found even nearer together than in the ephebic stage. This is especially interesting and exceptional, since just the opposite condition of things exists in the old age or gerontic stage from what has been described in the young stage. A study of the young and the adult shell leads to a study of the fleshy parts of the animal. No. 597 is an alcoholic specimen of the Nautilus. It is placed in its natural position with the ventral side below. The large head and body of the animal occupy the outer chamber of the shell, and the long fleshy tube or siphon extends from the posterior part of the body backward to the inner- most chamber. It is supposed by some that the cham- bers of the shell are supplied with gas and by others with liquid. On the ventral side the two flaps of the mantle have united, forming an ambulatory pipe or hyponome by means of which the animal is propelled through the water. The motions of this organ have caused a sinus in the aperture of the shell (see Nos. 592-594, 596), and the additional layers made to the shell, indicated by the lines of growth, bend backward running parallel with this sinus. As we have already said, no sinus occurs in the young Nautilus, so that probably at this stage it is not a swimming animal. The mouth of the creature is sur- rounded by arms for obtaining food, but these are with- out sucking cups. The edges of the mantle make the shell already de- scribed, while the mantle on the posterior part of the body builds the septa during periods of rest. The short funnels of the siphuncle are made by the mantle, while the siphon secretes the porous wall which connects the funnels together. In the group of Nautiloids there is no straight old age form, the involute form existing at the present time. 250 SYNOPTIC COLLECTION. AMMONOIDEA. There are sufficient remnants of the early transitional forms left in the Silurian rocks to demonstrate the former connection of the Nautiloids and the Ammonoids. 1 The common ancestor for the two groups probably existed in pre-Cambrian times, but this form has not been discov- ered. Clarke 2 has described an Orthoceras-like form from the Devonian. It has a large, plump protoconch (PI. 598, fig. i) like that of Ammonoids, but the central position of the siphuncle (fig. 2) is like that of Orthoceras. According to Clarke this protoconch was probably de- rived from so young a shell that atrophy and wrinkling had not taken place, as is the case with the mature Ortho- ceran shells, all of which have been found in a later geo- logic formation. The connection of the protoconch with the conch is seen to be large, which is the case with the generalized Ammonoids, while it is narrow in the Nauti- loids, as seen in PI. 586. Bactrites is probably the primitive straight form from which the Ammonoidea arose. The protoconch is seen in PI. 599, fig. i, while in fig. 2 it occurs with a few chambers. When this protoconch is not present, the apex (fig. 3 ) is marked by a scar (figs. 3, 4). When the protoconch is broken off the opening of the siphuncle in the first sep- tum (PI. 599, fig. 5, somewhat broken), is seen to be intra- marginal instead of being central as in Orthoceras, or marginal as in typical Ammonoids. PI. 599, fig. 6, shows the protoconch and the enlargement of the shell which goes on until two chambers have been formed, after which the tube contracts. An older specimen is figured in PI. 599, fig. 7 (a dorsal 1 Hyatt, Proc. Amer. Assoc. Adv. Sci., XXXII, 1883. 2 Amer. Geol., XII, 1893, p. 112. METAZOA MOLLUSC A. 251 view of an internal cast), showing the long tube, the slightly oblique sutures, and the flaring aperture. As specimens are usually preserved the siphuncle appears to be distinctly marginal, but Clarke has shown that this is not the case, but that a narrow portion of the septum lies between the siphonal funnel and the shell wall. This is shown in fig. 8, which is the interior of a portion of the shell showing the intra-marginal position of the siphonal funnel. Mimoceras ( = Goniatites) compressum (PI. 600), has a protoconch which is permanent throughout life. This is well seen in figs. 1-3. These figures show that the shell is nearly straight at first, and that the septa, and therefore the sutures, are primitive and similar to those of the Nau- tiloidea. The septa are, in fact, concave both in the young and in the adult. The siphuncle is nearer the center at first and later approaches the ventral side. The adolescent shell is loosely coiled (fig. 3), the whorls not being in contact. Later, however, the shell becomes closely coiled, as seen in figs. 4, 5 ; also figs. 6, 7 (M. ambigena). Fig. 5 shows the older septa with the siphonal lobe. The outline of the aperture of the shell is rounded on the dorsal as well as the ventral side (fig. 7 ). This is an important character showing the absence of an impressed zone at a late stage. In these generalized forms of the Ammonoidea, signifi- cantly called the Nautilinidae, the Nautiloid characters are retained for a considerable length of time, but later new structural features appear which are distinctly Am- monoidai. Adult Goniatites in general have the septa concave as in the Nautiloids, but the sutures though simple (No. 60 1, Brancoceras ixion Hyatt), have a few lobes (backward bendings of the septa) and saddles (forward bendings of the same parts). The aperture is simple with ventral sinus like that of Nautilus. The siphuncle is at first cen- tral in position and later reaches the ventral margin where 252 SYNOPTIC COLLECTION. it makes a siphuncle lobe (No. 601, specimen on the right), which later in life in some species becomes divided, giving rise to the siphuncle saddle. The Goniatites cease to exist in the Carboniferous age and the Ceratites appear. The specimen of Ceratites (No. 602, C. nodosus De H.), does not show the younger whorls but the sutures of the last whorl are finely seen. The number of saddles and lobes has increased but still can be easily counted. The bottom of the lobes is ser- rated, which may be seen in several places in the speci- men. The more primitive Ammonitidae are represented by Deroceras (= Ammonites) planicosta Hyatt. Here the pro- toconch is large and globular (PI. 603, fig. i). In this figure the shell is seen on the right with a few septa, and on the left it is broken exposing the cast of the proto- conch. Fig. 2 is a section of the same. The contraction of the siphuncle is well seen. Fig. 3 is a section through the shell with the protoconch broken off. The coecum formed by the first septum is finely shown ; three other septa are drawn. An organic deposit fills the siphuncle. Fig. 4 is a section through the shell of a related genus, Plenroceras spinatum Branco, showing the protoconch in the center, the coecum and siphuncle, the first concave Nautiloid septum, and the remaining convex Atnmonoidal septa. It is interesting to know that the septa of the first formed chambers are simply curved, while in the adoles- cent stage they resemble those of Goniatites, having few lobes and saddles (see fig. 5). In the whorls of the adult they are always folded (see outer whorl in fig. 5). In this adult shell the ventral sinus of the aperture, so conspicuous in the Nautiloids, has disappeared and the lines of growth are continued straight across the ventral portion. This being the case we must infer that the organ which caused the sinus has disappeared. Hyatt 1 1 Genesis of the Arietidae, Smithsonian Contrib. to Knowledge, XXVI, 1889. M ETAZOA MOLLUSCA . 253 has pointed out that this change in structure indicates a change in habits whereby a swimming type of Cepha- lopod has been converted into a crawling type. In Dactylioceras (No. 604, D. commune Hyatt), the whorls are closely coiled and in the same plane ; all are visible and the ornamentation is similar. These characters are seen on a large scale in Ammo- nites parkinsoni which, on account of its size, is placed at the back of the Section (see No. 605 ; No. 606, horizon- tal section of the same). A portion of the shell has been removed in No. 605, and the surface polished, thereby bringing out the sutures finely. In No. 606 the cham- bers and their walls are well shown. Asteroceras ( = Ammonites, also = Arietites) obtusum Hyatt (No. 607) has the whorls in one plane and all can be counted. The shell is tightly coiled and even the youngest whorls are ornamented with ribs. This speci- men has most of the shell well preserved. The sutures are hidden, but where the shell is broken off the serrated or fluted edges of the septa are visible though more clearly seen in No. 608 where the outer shell is entirely gone. These sutures are complex as compared with those of Goniatites, Ceratites, or the primitive Ammonites. The siphuncle is seen on the edge and the specimen also shows how the dorsal side of the shell has become im- pressed by close coiling. The living chamber extends backward a considerable distance (No. 608), the last formed septum marking its posterior limit. The complexity of the septa is seen in Lytocera s jurense Sitt. (No. 609), where the edges of the septa have been painted red to bring out their structure more plainly. No. 6 10, Stephanoceras tarA^&xr/d'Orb., shows the tend- ency of a closely coiled shell to become involute. The last whorl spreads out laterally and partially covers the preceding whorls, leaving a deep umbilicus on either side. The dorsum is deeply impressed in this genus. Several of the specimens in No. 608 have a portion of the exter- 254 SYNOPTIC COLLECTION. nal shell preserved which exhibits a brilliant iridescence. Where the shell is broken the septa and chambers are visible. The middle portion of the septum in the upper left hand specimen is seen to be nearly flat but the edges are deeply fluted. In the largest specimen on the right, the shell is mostly worn away, revealing the complex character of the sutures. No. 611, Perisphinctes, belongs to another series in which the shell is compressed, but the younger whorls are not covered. The marginal siphuncle and the fluted sutures are remarkably well seen in this specimen. An- other species of this genus, No. 612, P. comptoni Pratt, has long lateral processes or ears extending from the liv- ing chamber. Phylloceras heterophyllum Suss. (No. 613). is not only compressed but involute. The shell has mostly disap- peared, revealing the extremely complex character of the sutures. The section shows the protoconch in the cen- ter, the closely coiled young shell, the septa, and the chambers filled with mineral matter. As might be ex- pected these extremely specialized Ammonites are not found in the ancient Palaeozoic strata but occur in the Mesozoic formations. Aturia zizac Sow. is found in the recent Tertiary rocks, and is a compressed, involute form with specialized sutures, and differentiated, nearly dorsal siphuncle (No. 614; also PI. 615, figs. 1-3). Growth in this genus is very rapid during the nepionic stage, the coiling is close, and the funnels of the siphuncle are flaring (see fig. i). Fig. 2 is a front view, and fig. 3 a side view of the nepi- onic and half of the neanic stages. Fig. 2 shows the nearly dorsal position of the siphuncle, and fig. 3 the lobes of the first four sutures. No. 616, Aturia aturi Bast, is a valuable specimen obtained by breaking down the shell so that the funnels of the siphuncle are exposed. It has been shown that the Nautiloids and Ammonoids both arose from straight Orthoceras-like shells, and in METAZOA MOLLUSCA. 255 their development passed through the loosely coiled, tightly coiled, and involute stages. The Nautilus was seen to be an involute form, but no reduced stage with a more or less uncoiled spire was described since no such form has been discovered. Among the Ammonoids, however, a number of series have been traced from the straight primitive form through the involute stages to the straight reduced condition. The Ammonites culminated in the Jurassic period. At the close of this period in all probability there was some great climatic change which caused reduction. The Nautiloids were somewhat affected, but not enough to cause them to become extinct. Those that died, did so slowly. The Ammonites, on the contrary, developed extraordinary reduced forms and afterwards became ex- tinct. The first indications of reduction are a lateral contrac- tion in the whorl (see No. 617, Sphaeroceras brochi Sow.), attended with a diminution in the size and a decrease in the vertical height (No. 618, Sphaeroceras wrighti}. In some cases the process is carried so far that the terminal portion of the last whorl separates from the preceding whorls and grows out straight, as seen in Scaphites nodo- sus Meek. The young Scaphites (No. 619, specimen on the left, and the section, No. 620) are closely coiled, but the older stage (No. 619, specimen on the right) has begun to uncoil. This is still better seen in No. 621, which is a cast of an aged specimen of Eurystomites kel- loggi showing the free volution or whorl. Another old age form is seen in No. 622, Helicoceras stevensoni Whitfield, where the asymmetrical spiral has partly uncoiled, and the last whorl has a secondary back- ward crook bringing the aperture of the shell near the base of the spire. The uncoiled condition is carried still farther in Crio- ceras bifurcatus Quenst. (No. 623), in which the shape is more like a hook than a spiral. 256 SYNOPTIC COLLECTION. Finally, the straight form is very nearly attained in Baculites (PI. 624, figs, i-io ; No. 625), but this straight adult Ammonite has a tiny coiled shell when young. It is interesting to note that the protoconch has become modified, so that its shape is suggestive of a spiral when seen from the side (PI. 624, fig. i). The typical globu- lar form has become broadly elliptical (fig. 2, front view) with a projection extending forward (fig. i). . The earliest stage of the larval nepionic shell is seen in fig. 3. An older shell having four septa shows the siphuncle near the center (fig. 4). The aperture at this stage is broad, and the area of contact of the revolving whorl upon the preceding whorl is also broad, as shown by the dotted lines. The septa at first are simple. Fig. 5 represents a side view of the shell with six septa, and fig. 6 the first six sutures. Three of these sutures are simple, while the remaining three are similar to the sutures of Goniatites. A front view of a stage with thir- teen septa (fig. 7) shows the siphuncle near the margin, the aperture and area of contact narrower so that the growing whorl envelops less of the shell. In a still older stage with seventeen septa (fig. 8) the siphuncle is close to the edge, the aperture is almost circular, while the area of contact is much narrower, as indicated by the dotted lines. When the shell has the diameter of one millimeter and consists of two or two and a half whorls with from twenty to twenty-five septa it begins to grow out in a straight line. Fig. 9 represents the adolescent (neanic) shell at this stage with the lines of growth and the ros- trum at the opening. The sutures, which are concealed in fig. 9, become more complex, passing from the Goniatite condition to the Ceratite (see lower suture in fig. 10) at about the thirtieth septum or after the shell has become straight. After this the lobes and saddles increase in number until the extremely complex sutures of the adult Ammonite are produced (upper sutures in fig. 10; see also No. 625). METAZOA MOLLUSCA. 257 In the history of the development of Baculites we have positive proof of the reduced character of the genus. In- stead of being a relative of the primitive straight Ortho- ceras or of Bactrites, it is an extremely specialized form whose ancestors in their evolutionary history passed through the various stages of shell development. Of these stages the straight and loosely coiled stages are omitted in Baculites, so that the animal begins life with a tightly coiled shell, which, however, ceases to coil in the neanic stage, forming thereafter a straight cone. DlBRANCHIATA. BfiLEMNITIDAE. The Belemnitidae begin in the Triassic period and are therefore more recent than the Nautiloids or the Am mo- noids. We should expect to find them more specialized though still retaining certain characters of their ancestors. We have seen in Nautilus the dorsal fold of the mantle which secretes the black pigment layer. In Aulacoceras (PL 626, figs. 1-3, A. reticulatum Hauer), the dorsal fold was nearly closed and secreted a shell with three princi- pal parts: the chambered shell or phragmacone (fig i, ph) ; the guard (fig. i,,^; fig. 3), and a prolongation of the phragmacone, the pro-ostracum (see upper part of fig. i), often called the pen, which is seldom preserved. The phragmacone has chambers, septa, and siphuncle (fig. 2, section). It corresponds with the shell of the Tetra- branchiata, but differs from the latter by being internal. The more specialized form, Belemnites (No. 627), has a conical, chambered shell, at the anterior end of which on the dorsal side there was the shovel-like projection or pro-ostracum. The septa of the shell were plain (No. 627), concave, and were pierced by a siphuncle which does not show in the specimen. This shell is external in the young Belemnite. In time the dorsal flap of the mantle grows out and around the shell, its two edges not 258 SYNOPTIC COLLECTION. meeting ventrally at first, but eventually coming together and joining. When this has happened, the mantle makes the first layer of the guard (No. 627). Successive layers are put on from without, thereby illustrating exogenous growth. In many genera the guard extends a consider- able distance below the chambered shell and is the part most frequently preserved (see No. 628, B. subquadratus Roem.). Thus it is seen that Belemnites carries specialization so far that the shell is enclosed and a secondary struc- ture, the guard, is formed. One of the descendants of the Belemnites is the beauti- ful living Spirula (Nos. 629, 630) which has lost both the pen and the guard. A perfect specimen of this animal is extremely rare, 1 but the alcoholic specimen (No. 629), though mutilated, shows that the shell is partly internal. It also exhibits a portion of the mantle and what some naturalists consider the disc of attachment. The shell has a large, globular protoconch finely seen in No. 630. The plain concave septa are pierced by the marginal siphuncle which is made up of funnels that extend from one septum to another. Belosepia, according to Zittel, connects the Phragma- phora (Belemnites, Spirula, etc.) with the Sepiophora (cuttlefishes and squids). It has a guard and the chambered shell is represented indistinctly. The young cuttlefish of to-day, Sepia officinalis Linn. (PL 631, figs, i, 2), has the interesting habit of fas- tening itself, for a day or two after hatching, by a portion of the lower side of the body and of the ventral arms. This sucker-like area is flat and nearly colorless, and reminds one forcibly of the foot of a Gastropod. Fig. i is a view of the animal drawn from below when attached to a glass plate ; the arms are retracted. Fig. 2 is from 1 According to Pelseneer (Nat. Sci., VII, 1895, p. 63) only five complete specimens are known. METAZOA MOLLUSCA. '259 above while in the same position. The line between the two figures represents the actual length of the animals. After detaching itself, the young Sepia swims by means of the thin border of the mantle, and only when irritated uses the ambulatory pipe for darting backwards. The outer skin or integument of the disc of attachment is so thin that the ink bag can be clearly seen near the center of it. .According to Bather, 1 one larval Sepia, when irritated, ejected ink twice within one minute of being taken from the egg-capsule. The ink, however, was not sufficiently dense to obscure the motions of the animal. The adult (No. 632 ; No. 633, model of the same) loses the habit of attaching itself and of swimming by its mantle, while the ambulatory pipe becomes the chief means of rapid locomotion. The ink bag is large and an efficient means of protection. The pro-ostracum or pen is developed, being the calcareous portion familiarly known as cuttle bone. At its base there is a vestige of the chambered shell, while the guard has become nearly obsolete. These animals have short, stout, bag-like bodies with eight short arms and two longer ones. The alcoholic specimen, No. 632, exhibits the open mouth with its horny, beak-like teeth. There are two of these and the lower one is the larger. The ambulatory pipe is conspicuous. The cuttlefish possesses an ink bag which contains the sepia used as the basis of the pig- ment. The squid is another living representative of the more specialized Cephalopods, which has lost both external and internal chambered shell and has nothing but a horny pen. This pen is situated in the dorsal part of the mantle and can be of little use to the animal. The eggs of the squid are in long, pod-like cases (No. 634), which are fastened together in large clusters. In its development, and in that of all Cephalopods, definite Journ. of Malacology, IV, No. 2, 1895. 260 SYNOPTIC COLLECTION. traces of the veliger stage (which has been described in the Pelecypods and Gastropods) are entirely lost by the law of acceleration in development. The squid (No. 635, Loligo vulgaris Lam.), has a long body covered with a leathery mantle with a fin on either side of the posterior end. At the forward end the mantle is free, so that the water passes into the cavity of the body, and bathes the two gills which are placed one on either side (see preparation, No. 636). After the water has flowed in, the mantle is applied closely to the neck so that the body cavity is a tight bag with only one opening, and that is the ambulatory pipe or hyponome which we found in the Nautilus. The forcible ejection of the water through this pipe sends the animal swiftly backwards. The waste products of the body and the inky fluid for protection are also discharged through this pipe. The head of the squid is provided with two eyes which are more highly organized than any other invertebrate eye, but have only a superficial resemblance to the vertebrate eye. The mouth- has a horny beak and a lingual ribbon. It is surrounded by eight short arms and two long ones which have suckers. In the preparation (No. 636) an incision has been made along the middle of the ventral side, and the mantle laid back exposing the internal organs. A slender tube, the esophagus, extends from the mouth to the long, sac-like stomach which has a bag- like coecum near the pyloric or forward end. The intes- tine, another slender tube, is seen running forward from the stomach under the liver, and by the side of the duct of the ink bag. The anus and the outlet of the duct are near the base of the ambulatory pipe and directly in the path of the outgoing current of water which, as we have already said, carries away the products of both intestine and ink bag. The heart is situated near the base of the gills ; back of it and occupying the greater part of the body cavity is the mass of eggs. The embryo of Octopus has a shell sac on the forward METAZOA MOLLUSCA. 201 part of the dorsal side of the body, but as it develops this shell sac becomes aborted and neither the young (No. 637) nor the adult Octopus (No. 638) have a vestige of a shell. The animal is built upon the same plan of structure as the squid. The model shows the natural position of the Octopus with the mouth downward and long arms extending out on all sides, provided with the sucking discs that make this animal a formidable one. Above is the great rounded head with its prom- inent eyes. The alcoholic specimen (No. 639) shows the large open hyponome, the arms surrounding the mouth, and the round plump body. The membrane that connects the base of the long tapering arms and the suckers are well seen in No. 640. The hyponome in this specimen is small. In Elcdone aldrovandi Delle Chiaje (No. 641), there is but one row of suckers on the arms. Loligopsis verani Fer. (No. 642), has a more slender body and two very long delicate arms. Argonauta argo Linn., or the Paper Nautilus (No. 643, eggs, 2 females, i male) is related to the Octopus, the structure of the two animals being similar. Here we have no shell comparable with that of other Cephalopods. The male (No. 643, alcoholic specimen ; No. 644, model) is without any protective covering, but the female (No. 643, alcoholic specimen ; No. 645, model) has an egg case (No. 646) of exquisite beauty. This case is in the form of a spiral shell, and is developed late in a post- embryonic stage. It is composed of three layers, one made by the edge of the mantle, another by the whole mantle, and the outer layer by the two large arms (see No. 645). The last named layer does not occur in the shells of other Cephalopods. The male is very much smaller than the female. One of the arms becomes modified and enclosed in a sac, as seen in No. 644. Later this sac splits and the arm is 262 SYNOPTIC COLLECTION. free (No. 644). The two halves of the sac then reunite and the sac thereby formed becomes filled with spermato- zoa. The arm with the sperm is detached and finds its way to the mantle cavity of the female. No. 645 shows the two large arms of the female that have become greatly modified in structure. In the alcoholic specimen these are much contracted. They are usually applied closely to the outer surface of the shell and are not carried as sails though often so figured in the books. The Argonaut propels itself through the water in pre- cisely the same way as the squid, having the same hydraulic apparatus. The Mollusca constitute a subkingdom of immense size and unnumbered variations. Underlying these variations, however, there is a fundamental unity. Most Mollusca pass through a trochophore and a veliger stage in their development ; most possess a shell gland the first product of which is a simple, unornamented, colorless or slightly colored, plate-like shell. If this plate-like shell divides into two parts the result is a bivalve shell, the distinctive character of the class of Pelecypods. If it becomes a spiral cone, the univalve shell and the class of Gastropods results. If the spiral cone becomes chambered, the product is the shell peculiar to the Cephalopods. Free-moving, sedentary, and boring habits produce modifications in the shell. Among Pelecypods the free- moving species, as a rule, have equivalved. symmetrical shells, while the sedentary forms are unequivalved and asymmetrical. The boring habit in both Pelecypods and Gastropods tends towards the reduction of the shell, until only a vestige of it remains. Other causes have produced a similar reduction. The free-swimming habits of the Heteropods have resulted in the development of a fin-like organ, while the shell, being of little use, has become small and inconspicuous. The Nudibranchs carry the process still farther, since they possess a shell in the METAZOA MOLLUSCA. 263 embryonic stage only, which is quickly lost, so that the adult is without even a vestige of a protective covering. The marine Gastropods probably gave rise to the specialized fresh-water and terrestrial species, transi- tional forms existing at the present time. The Cephalopoda illustrate acceleration in development and specialization in structure. The external, chambered shell becomes internal and extremely modified ; it may also exist as a vestige or be wanting altogether. METAZOA VERMES. 265 VERMES. Section n and 12 (in part). BRACHIOPODA. ATREMATA. The class of Brachiopoda, as already stated, is one of the best for illustrating a classification based on the -stages of growth and decline. The ancestral form, Paterina, which Beecher described and figured, 1 is now considered by Walcott 2 to be identi- cal with the genus Iphidea ; and in the Iphidea, Walcott has found a rudimentary cardinal or hinge area. This fact prevents the Iphidea and the Paterina, if they be the same, from representing the most primitive form conceiva- ble; that is, a shell without even the rudiment of a cardi- nal area. There is little doubt, however, that such a primitive form existed and in time will be discovered. To such a genus, when found, the name of Paterina should surely be given in consideration of Beecher's classic researches on the class of Brachiopoda. Until this new, theoretical form is brought to light, we will bear in mind that the Iphidea is the simplest form yet discovered and described, while at the same time we shall accept the shell as described by Beecher under the name of Paterina as representing the still more primitive form that is to be discovered. This Paterina shell is simple in youth (PI. 647, fig. i, P. labradorica Billings, pedicle valve) and also in maturity (fig. 2, brachial valve), having two nearly equal valves which are semi-elliptical in shape. The hinge line is straight and nearly equal in length to the width of the 1 Amer. Journ. Sci., (3), XLI, 1891 ; (3), XLIV, 1892. 2 Proc. U. S. Nat. Mus., XIX, 1897, pp. 707-718. 266 SYNOPTIC COLLECTION. shell. The lines of growth run parallel with one another and there is no ornamentation of any kind. The new layers of shell are added at the anterior 1 and lateral margins, so that the pedicle at the posterior end is always free. The embryonic shell (uncolored in PL 647, figs, i, 2) or protegulum (meaning early covering) is similar in form to the mature shell. As we have already said, the youth- ful (nepionic), adolescent (neanic), and mature (ephebic) stages are all alike (see PI. 647, figs. i. 2), so that it is impossible to tell where one stage ends or another begins. The valves of the shell are not articulated together by teeth and sockets, but are held in place by muscles. The pedicle valve is slightly more convex than the brachial valve, so that an opening is produced through which passes the short pedicle. This opening, according to Beecher's figures, is shared alike by both valves, so that the pedicle is free. As already stated, Walcott has found the region between the two valves more or less closed by rudimentary cardinal areas. Plate 648, figs. 1-4, represents Walcott's figures of Iphidea. The brachial valve is seen in fig. i ; fig. 2 is a summit view of the pedicle valve ; while a side view of the same is shown in fig. 3. The imperfectly defined, rather narrow cardinal area is shown in fig. 4 with a broad plate, called the prodeltidium, just under the beak. The latter is formed by the pedicle and not by the mantle as is the case with the deltaria (see p. 277). The ancestral species from the Cambrian and Lower Silurian, Obolella polita Hall (No. 649 ; PL 650, fig. i), had a more or less circular form. This shape of the adult shell is peculiar to many young Brachiopoda, so that when 1 In order to see the characteristic parts plainly, the specimens are mounted, and the figures are drawn, with the anterior end towards the observer. This is contrary to the usual rule which places the animal with the forward end away from the observer the most favorable position when comparison with his own body is desired. METAZOA VERMES. 267 they attain this form they are said to be in the Obolella stage of development. Each valve of Obolella had a rudimentary cardinal or hinge area in which a groove was scooped out for the pedi- cle. This groove is seen in an interior view of the bra- chial valve (fig. 2) and still more clearly in the pedicle valve (fig. 3). The markings in the interior of the valves (figs. 2, 3) are the scars left by the muscles. One of the more progressive species closely related to Paterina and Obolella, is Trimerella (PI. 651, fig. i, T. ohioensis Meek, external view of pedicle valve ; fig. 2, inter- nal view) which has a large hinge area, finely seen in fig. 2, and a furrow bounded by ridges, the inner edges of which serve as teeth. This primitive mechanism is sug- gestive of the more perfect articulation by teeth and sockets of the more specialized Brachiopoda. Paterina, Obolella, and Trimerella represent the Atre- mata, to which group of Brachiopoda Lingulepis (No. 652) and Lingula (No. 654) also belong. In Lingulepis (No. 652, L. pinniformis Owen, = Lingula antiqua Hall) the shape is rounded and similar to Obolella. The valves are also unequal, and in other structural characters this genus is intermediate between the Obolellidae and the more specialized Lingulidae represented by Lingula. The power of resisting adverse conditions is so great in Lingula that it has come down to us essentially unchanged in structure from the early geologic period known as the Ordovician, which followed the Cambrian. Its persist- ence in time, according to Hall, 1 is "unequaled by that of any other known genus of organisms." The embryonic shell of the Lingula living to-day is similar to that of Paterina. PI. 653, figs. 1-3, represents a closely allied genus, Glottidia albida Hinds. Fig. i shows the Paterina-like shell (left unshaded in the draw- ing) and the long hinge line ; also the youthful (nepkmic) 1 Pal. N. Y., VIII, part i, 1892, p. 7. 208 SYNOPTIC COLLECTION. stage when the shell has assumed the more rounded out- line of Obolella. That this stage is more specialized than the Paterina-stage ,is proved by the fact, that, whenever the two stages occur in the development of a species, the Obolella-stage always follows the Paterina-stage. The hinge line grows narrower in the neanic (fig. 2) and the ephebic stage (fig. 3), while the shell becomes tongue- shaped in form. The larva of the living Lingula is free swimming, but soon a pedicle is developed which becomes a long flexible organ in the adult (No. 654). This pedicle is not attached, but the end is buried in the sand and protected by a tube made of sand grains, after the fashion of the protective coverings of worms. According to Morse 1 the Lingula partially recedes into its sand tube after the manner of worms. The shell is in a line with the pedicle, and the length and flexibility of the latter organ allow the shell freedom of motion in any direction. Beecher' 2 has shown that physical forces acting simi- larly on all sides of a shell, which in this case is made possible by the long pedicle, tend to produce equal valves, such as are seen in Lingula. Comparative simplicity of structure marks the internal organs as well as the external characters of the Atremata. The fleshy body takes up the greater part of the shell, while the arms or brachia (the characteristic organs which have given the name of Brachiopoda or arm-footed animals to the group) are without limy supports of any kind. Since these organs are of importance in determining the phylogenetic relations of genera, we will give figures to illustrate their stages of development. Their mode of growth "is alike in the larval stages of all Brachiopods." They first develop tentacles in pairs on each side of the median line in front of the mouth. This stage is repre- 1 Proc. Boston Soc. Nat. Hist., XV, 1873, p. 372. 2 Amer. Journ. Sci., (3), XLI, April, 1891. METAZOA VERMES. 269 sented in Glottidia and Lingula in PI. 655, figs. 1-4. New tentacles are continually added at the same points, until by pushing back the older ones a complete circle is formed about the mouth (fig. 2), which later becomes introverted in front (fig. 3). From this common and simple struc- ture are developed all the complicated brachia of the more specialized orders (Beecher). In the case of Lingula the growing points at which new tentacles arise, separate and the adult possesses two coiled arms one on each side of the median line (fig. 4). We have already seen that members of the Atremata, Trimerella for instance, exhibit specializations of struc- ture illustrating progressive tendencies, but the group contains no old age forms. According to Beecher's classification, the Atremata are followed by the Neotremata, Protremata, and Telotre- mata, the first two being the more primitive orders and the last two the more specialized. This arrangement is in accordance with the geological history of the four orders, since the Atremata were the first to appear and the Telo- tremata the last. Schuchert's classification 1 gives the following arrange- ment : Atremata, Telotremata, Neotremata, Protremata. This investigator makes a fundamental division of the class into two groups, the Homocaulia or those Brachio- pods in which the pedicle is common to both valves, and the Idiocaulia in which the pedicle is restricted to one valve. The Atremata and Telotremata belong to the first division, according to Schuchert, and the Neotremata and Protremata to the second. The fact that the Atremata and Neotremata are the most primitive of the four orders and are consecutive, is not considered a reason by Schuchert for placing the one after the other in a classification. Inasmuch as the line of descent is direct from Atremata to Telotremata and 1 Bull. U. S. Geol. Surv. , no. 87, 1897, pp. 118-135. 270 SYNOPTIC COLLECTION. not by the way of the Neotremata or Protremata, he places the Telotremata next the Atremata. The Neotremata and Protremata branch off from the Atremata at a much lower geological horizon than the Telotremata. According to Beecher the Neotremata have a protegulum like that of the Atremata and a Paterina stage when the pedicle passes out freely between the valves. According to Schuchert the pedicle opening in this order is restricted throughout life to the pedicle valve. Even if this be true with the forms so far described, we predict that other forms will be discovered which have the pedicle opening common to both valves in the nepi- onic stage. For this reason we shall take up the Neotremata next, bearing in mind that more investigations are needed on the fossil forms belonging to this order, as well as on the early stages of development of existing species. BRACHIOPODA. NEOTREMATA. One of the more primitive members of the Neotremata is Paterula (PI. 656, figs, i, 2. P. bohemica Barr.). It has a horny shell and when young is similar to Paterina, but later, layers are put on the brachial valve (fig. i) posteriorly to the beak which cause the beak to become internal and the shell circular in outline. The pedicle valve (fig. 2) is differentiated from the brachial by having a notch in the margin which remains open in the adult (fig. 2). The arms or brachia in Paterula are two single spirals without limy supports. Another genus, Discinisca (No. 657, D. laevis Sow.), has the protegulum of the brachial valve at the margin in the youngest stage and later near the margin, but with growth the protegulum becomes surrounded by more layers, as seen in No. 657. The edge of the pedicle valve (No. 657) is notched on the margin for the passage of the METAZOA VERMES. 271 pedicle, but this notch becomes surrounded by shell lay- ers in the adult. This mode of growth is also peculiar to Discina, another member of the Neotremata, and when it occurs in the more specialized groups of Brachiopods it is usually called the Discinoid stage of development. One of the most instructive forms is Orbiculoidea (No. 658, O. lamellosa Hall ; No. 659, O. mimita Hall; PI. 660, figs. 1-4, the same species; No. 661, O. nitida Phillips). Beginning with the protegulum, it passes through the Pa- terina stage (No. 659; PI. 660, fig. i) with its nearly equal valves, straight external or marginal hinge line, and its concentric parallel growth lines. The pedicle passes out freely between the two valves. This is the early nepionic stage. In the later stage, layers of shell have encircled the protegulum (No. 659 ; PI. 660, fig. 2)> causing the shell to become circular in outline, like Obo- lella, with no hinge line, and with the beaks internal though still near the margin. In the neanic stage the beak is still farther from the margin (No. 659) while in the ephebic stage (No. 659) it is slightly less eccentric and would seem to be passing into the gerontic stage. The condition of the adult bra- chial valve as compared with that of the young is shown in PL 660, fig. 4. The pedicle valve (No. 658, a, b; PI. 660, fig. 3), has the protegulum at the center and an open pedicle notch as in the adult Paterula, but later the formation of circu- lar layers of shell converts this notch into a hole through which the pedicle passes (No. 658, a, b). This hole be- comes partly filled with a plate called the listrium (see No. 658, a, b). It is probable that Crania (No. 662, C. anomala-, No. 663, C. tubinata Poli) represents a reduced and specialized condition of the Neotremata. The complete life history of this genus has never been figured and described. It is known that, when young, the pedicle valve has an open notch like that of the adult Paterula. It is probable that 272 SYNOPTIC COLLECTION. very early this notch is surrounded by shell layers, although no specimen showing this holoperipheral growth has been found. This is probably due to the fact ' that when very young the animal becomes attached to a rock (No. 663) by its pedicle valve which causes the pedicle to disappear and with it the notch and the circular layers if any such exist. BRACHIOPODA. PROTREMATA. The Protremata may have arisen from some Paterina- like ancestor which lived in pre-Cambrian times, or may have branched off from the Neotremata at a later period. The forms known to us illustrate specialization of struc- ture brought about through acceleration in development. One of the more generalized forms is Kutorgina cingu- lata Billings (PL 664, figs. 1-3). Here the hinge line is straight (fig. i), and there is a narrow rudimentary cardinal area on the pedicle valve (figs, i, 2,/z'). This valve (fig. 3) rises above the brachial (figs. 1,2, bv) and a large open- ing is left for the passage of the pedicle (fig. 2) which is only slightly restricted by the deltidium. This plate in the Protremata is formed in the embryo and is a shell growth from the brachial side of the body which later becomes attached to the pedicle valve. 1 The teeth in Kutorgina are primitive and are situated at the outer ends of the cardinal area. Figures illustrating the stages of development are given under Thecidium (see p. 273). The brachial valve in the Protremata, as in the other orders, is less differentiated than the pedicle valve, and shows the protegulum as in the Atremata. When ex- tremely young, the shell probably passes through a long- hinged or Paterina stage, but in the early nepionic stage of most genera the pedicle is surrounded by shell layers 1 See Beecher, Amer. Journ. Sci., (3), XLIV, 1892, pp. 142-147. METAZOA VERMES. 273 and the pedicle valve becomes circular in form, the shell passing through a stage similar to that which we have already described as the Discinoid stage of the Neotrem- ata. This is shown in Leptaena rhomboidalis Wilck. (PI. 665, fig. i). As growth continues, the neanic stage (fig. 2) is marked by radiating lines. The peripheral layers are resorbed, so that the pedicle opening approaches the edge (fig. 2) and in the ephebic stage reaches it (fig. 3; see also No. 666). In this stage the cardinal areas of both the convex pedicle valve (No. 666) and the concave brachial valve are long, flat, and narrow with a triangular fissure for the pedicle which is partly filled by a deltidium. Finally the pedicle disappears altogether, and Leptaena is free as in its young condition. In old age the anterior and lateral portions of the valves bend at nearly right angles (No. 666) to the plane of the younger shell, and the layers of growth are crowded closely together (No. 667). The arms or brachia in Leptaena and in the Protremata generally are not supported by a limy skeleton. The only living representative of the Protremata is the genus Thecidium ( = Lacazella). The cephalula stage (as it is called) is represented in PI. 668, fig. i, a dorso- ventral longitudinal section of T. mediterraneum Risso. The mantle lobes (fig. i, d and v) are unequal. The limy dorsal valve (ds) and the shell-plate (del) begin to form ; the latter on the dorsal side of the body. The larva transforms by the mantle lobes bending upward, which causes the shell-secreting surfaces (indicated by the heavy black lines) to come on the exterior (fig. 2). The shell-plate (del) is below the hinge line (fig. 2, hi). The adult (fig. 3) shows one valve and the deltidium (del), and the side view (fig. 4) gives both valves marked by concentric lines, the hinge line (hi) and the deltidium (del). These figures show that the deltidium is formed on the brachial side of the body, as already stated, and on that 274 SYNOPTIC COLLECTION. segment which subsequently becomes the pedicle ; after- wards it is fastened to the pedicle valve. Thecidium is especially interesting as it is the only Brachiopod which retains a true deltidium at maturity. 1 It is instructive to note that after the pedicle is lost, in several genera of this order, spines are developed for the purpose of anchoring the animal. In Chonetes granu- lifera Owen (No.- 669), these spines are found only on the cardinal margin of the pedicle valve. Productus nebras- kensis Owen (No. 670), however, inherits such a weak pedicle that this organ soon disappears, and spines are developed over the entire surface of the pedicle valve and sometimes are also found on the brachial valve. The animal lies on the pedicle valve fastened by its spines. Vestiges of the cardinal areas and teeth are sometimes present in this genus, but are often wanting. The beak is high and curved, and no trace of a pedicle opening remains. Many of these characters are intensified in the old age stage (No. 671). The shell extends ante- riorly and broadens outward at the same time. The beak of the pedicle valve is bent far inward and the ped- icle opening has wholly disappeared. The ribs which are prominent and regular in the adult stage, partially die out and become more or less irregular (see No. 671). Interesting specializations of structure are illustrated by Orthis (= Platystrophia 2 ) (No. 672). We have here large cardinal areas and perfect articulation by teeth and sockets. The area of the pedicle valve has a large pedicle opening or delthyrium, and that of the brachial valve has a similar opening, the chelyrium. When young, these openings are partially closed by plates, the deltidium and chilidium. In the course of development, however, the plates are resorbed so that open passages remain in the adult (see No. 672). 1 Hail and Clark, Nat. Hist. N. Y., Pal., VIII, part 2, 1894, p. 283. 2 See Cumings, Amer. Journ. Sci., (4), XV, nos. 85, 86, 1903. METAZOA VERMES. 275 The changes which take place in the development of a Protrematous shell are well shown by Bilobites varicus Conrad (PI. 673, figs. 1-12). It begins as a smooth, straight-hinged form with the hinge as broad as the shell and with a rounded front margin (figs, i, 2). Occasion- ally while the shell is in the nepionic stage the deltidium of the pedicle valve is retained, as seen in fig. 3, which also shows the cardinal area and pedicle opening. The deltidium is lost in the neanic or the ephebic stage and the pedicle passes out of the large opening. Gradually the rounded front margin, seen in figs. 1,2, becomes straight (fig. 4), and later a sinus is developed (fig. 5) which afterward becomes more pronounced (figs. 6-n). The pedicle valve is at first shorter than the brachial, and for this reason is not seen in figs. 1,2, 4-6 ; soon, however, it grows longer (fig. 7) and the cardinal area with its pedicle opening is distinctly seen (figs. 8-10). The adult shell (fig. u) has a narrow hinge line, while the anterior portion of the shell is broad and strongly bilobed. In the old age or gerontic stage the sinus becomes nearly obliterated (fig. 12). and the anterior portion of the shell resembles that of the young stage represented in fig. 5. One of the most differentiated members of the Protre- mata is the genus Pentamerus (No. 674, P. oblongus Sow.). The variation in form of this genus is shown by the specimens (No. 674, e, f) which are casts of the interior. The beaks even in the young stages (No. 673, a-d) are incurved, and so strongly is this the case in the adult (e, f) that the small pedicle opening is concealed. The deltidium when present (which is rarely the case) is concave. This genus is an exception among the Protremata, inas- much as the arms are supported by two limy processes called crura. These crura unite to form a plate, the cru- rulium, which is used for the attachment of muscles. The pedicle valve also has a large, strong, internal plate, 276 SYNOPTIC COLLECTION. the " shoe-lifter " or spondylium, which serves the same purpose. BRACHIOPODA. TELOTREMATA. One of the most primitive members of the Telotremata is Protorhyncha aequiradiata Hall (PL 675, figs. 1-3). We know nothing of the early development of this spe- cies, but the adult is primitive in its characteristics, so that it is reasonable to assume that the young stages must have been still more primitive. It has been ascer- tained in living genera of this order (Telotremata) that in the nepionic and early neanic stages the pedicle passes out freely between the two valves, the opening being shared by both as in the Atremata. In the later neanic period the shell layers extend entirely round the pedicle, so that this organ becomes restricted to the pedicle valve. In the adult or ephebic stage of Protorhyncha (figs. 1-3) the pedicle opening is triangular, and is rarely closed by plates of any kind. There is no cardinal area in Protorhyncha, according to Schuchert, 1 while Hall and Clarke 2 figure a small rudi- mentary area (fig. 2). The adult shell is narrow at the beak or rostrate in form (PL 675, fig. i, internal cast of the brachial valve; fig. 3, internal cast of the pedicle valve). The arms of Protorhyncha are fleshy and not strength- ened by limy supports ; even crura, the parts to which the brachial supports are fastened, are not developed. According to Schuchert 3 the oldest Rhynchonelloids are rostrate in form, like Protorhyncha, and the ontogeny of several living species of the genus has not revealed a long-hinged stage. 1 Bull. U. S. Geol. Surv., no. 87, 1897, p. 87. 2 i3th Ann. Rep. State Geol. N. Y., 1893. 3 Loc. cit., p. 83. METAZOA VERMES. 277 Rhynchonella peregrina (No. 676) from the Cretaceous, Rhynchonella octoplicata (No. 677), and Rhynchonella psittacea Dvds. (= Ffemithyris psittacea Chemnitz) (No. 678 ; No. 679, shells of the same), living to-day, show no marked difference in form from the primitive Pro- torhyncha of the Silurian formation, although the size varies, Rhynchonella peregrina being the giant of the genus. This species exhibits the curved hinge line (No. 676), the prominent beak, and the pedicle opening which is partly closed by two plates called by Hall and Clarke deltaria. The origin of these plates is entirely different from that of the single plate, the deltidium. As we have already seen in the Protremata (see p. 272), the deltidium is a primitive character arising in the embryo or early nepionic stage of development, while the deltaria are formed in the neanic or the ephebic stage and are made by extensions of the mantle. Owing to this difference in origin and structure, and in order to save confusion, we prefer the name of deltaria to deltidial plates given by many naturalists. The smooth, unornamented condition of the young Rhynchonella shell is seen in No. 677, while the later stages are marked by ribs and flirtings. Along the mar- gin, the layers are crowded closely together, an indication of the gerontic stage. The specimen of Rhynchonella psittacea Dvds. (No. 678) is attached to a pebble. Unlike Protorhyncha, this genus has the arms supported by two short, simply curved processes, the crura (see No. 679, f; PI. 680), which are attached to the brachial valve (see No. 678 specimen with arms extended). Specialization of parts is finely illustrated in this order by the structure of the brachia and their internal limy supports or brachidia. Beginning with the simple, curved crura of the Rhynchonellae (PL 680, crura with the fleshy arms coiled), we pass to Centronella (C. glansfagea Bill- ings; PI. 681, fig. i, dorsal view; fig. 2, ventral view; 278 SYNOPTIC COLLECTION. fig. 3, side view), in which a primitive loop (fig. 4; fig. 5, side view of same) descends from the brachial valve. This is made by two leaf-like parts or lamellae which are attached to the crura and which unite in the median line to form the broad loop. The hinge area with its ridges and the muscular scars are seen in fig. 6. Stringocephalns burtini Defr. (PL 682 ; No. 683) is a Devonian representative of a more specialized family. In the young shell (PI. 682, fig. i) the triangular pedicle passage or delthyrium is open or sometimes partly closed by partially developed deltaria ; in the adult (PL 682, figs. 2-4 ; No. 683) it is wholly closed excepting the pedicle opening (fig. 2), while in the old age stage (fig. 5 ; No. 683, specimen on the right) the coalescence of the plates into one plate (called the deltarium and the pseudodel- tidium) is almost complete, and the pedicle opening is greatly reduced in size. The arm supports consist of a long loop which extends around the margin of the brachial valve. Its form and the radial filaments extending from it are seen on the left of PL 682, fig. 3. The strong cardinal process extending from the brachial valve towards the large median septum of the pedicle valve on the right is also well seen in fig. 3. The changes which a Centronella-like loop often under- goes are well illustrated in the Palaeozoic Brachiopod, Dielasma turgidum (PL 684, figs. 1-5). Fig. i is the Centronella-like loop of the young. The pointed ante- rior portion is resorbed and two points extend forward (fig. 2). The process of resorption continues till the loop has the form of fig. 3. In the loop of the adult the two branches or lamellae diverge, as seen in fig. 4, x 6; fig. 5 is a side view showing the crus and loop on the right and the median septum on the left. Among the instructive forms of the Telotremata living to-day are Terebratula and Terebratulina. One of the forms of Terebratula (T. insignis d'Orb.; METAZOA VERMES. 279 No. 685) belonging to the Jurassic, was of remarkably large size. The pedicle opening and the deltaria are well shown in the specimen. The anterior margin exhibits the gerontic character of layers crowded closely together. The position of a living Terebratula is well shown in No. 686, T. vitrea Born.; also No. 687, where the Brachi- opod is attached to coral. The pedicle is tiny for the size of the valves, which are nearly erect. The brachial valve (No. 688, b) has the loop attached to it. This loop began as a primitive Centronella loop and passed through changes similar to those which will be described farther on in the closely related genus Terebratulina. The pedicle valve (No. 688, c) has a circular pedicle opening ; the del- taria are small and concave, so that the brachial valve moves upon the pedicle, though the motion is limited, especially in the older, more rotund specimens. The development of Terebratulina septentrionalis Couth. (PI. 689, figs. 1-7; No. 690), throws light on several important points. The earliest stage observed after the egg-stage is represented in fig. i, where the animal is extremely minute, the length of its shell being indicated by the line enclosed in the circle. It is attached to a rock, and rests upon its broad hinge area with the anterior margin uppermost, as seen in the drawing. The shell is comparatively broad and short, and there is a wide pedi- cle opening. Its form, however, changes rapidly, becom- ing like Lingula (fig. 2), though still retaining the wide anterior margin. The pedicle is long, allowing freedom of motion to the valves which are seen in fig. 3 in a partial lateral view. The animal is able to " whirl quickly " on its pivot-like pedicle, and is represented in motion and at rest in fig. 4, When in motion, it is nearly erect with the valves open, and the cilia of the tentacles are active in catching food ; while at rest, the valves are closed and the brachial valve often lies on the rock or other object of support. Further development causes the shell to broaden out anteriorly and to become ornamented by ribs (fig. 6). 280 SYNOPTIC COLLECTION. A distinct line is seen in this figure marking off the nepionic, Lingula-like stage from the succeeding neanic stage. When the brachial valve is thrown open (fig. 5), the crura (cr), which have already begun to form, are seen supporting the crown of tentacles. The changes which take place in the external shell between the stage repre- sented in figs. 5, 6, and the completed shell, fig. 7, were not figured by Morse. The development of the cardinal region of the pedicle valve, however, was given (PL 691, figs. 1-4). The pedicle opening becomes more circular in outline and truncates the beak of the pedicle valve (compare figs. 1-4 in PI. 691 ; see also No. 692, T. crassei Dvds.). The deltaria are small and concave, while the teeth, which are prominent in the earlier stages (PI. 691, figs. 1-3, t), are reduced in size in the adult (fig. 4, /). The development of the brachial loop is shown in PI. 691, figs. 5-8. Beginning as little swellings or processes (fig. 5,