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A TREATISE ON 
 
 THE COMMON SOLE 
 
 (SOLEA VULGARIS), 
 
 CONSIDERED BOTH AS AH ORGANISM AND AS A COMMODITY. 
 
 PREPARED FOR THE 
 
 MAPJNE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM 
 
 J. T. CUNNINGHAM, M.A., F.R.S.E. 
 
 Late Fellow of University College, Oxford; Naturalist to the Association. 
 
 PLYMOUTH : 
 PUBLISHED BY THE ASSOCIATION, 
 
 1890. 
 
J*. 
 
 LONDON : 
 HARRISON AND SONS, PRINTERS IN ORDINARY TO HER MAJESTY, 
 
 ST. MARTIN'S LANE. 
 
5? 
 
 C&t 
 
 CONTENTS. 
 
 Page 
 Preface .... v 
 
 PART I. 
 TAXONOMICAL. 
 
 CHAPTER 1. Classification of the Flat-fishes 3 
 
 CHAPTER 2. History of the Genus Solea 11 
 
 CHAPTER 3, Solea vulgaris, Quensel 15 
 
 CHAPTER 4. Solea lascaris, Bonaparte 20 
 
 CHAPTER 5. Solea variegata, Fleming (Donovan) 25 
 
 CHAPTER 6. Solea lutea, Bonaparte 29 
 
 CHAPTER 7. Solea G-rcenii, Giinther . 32 
 
 PART II. 
 MORPHOLOGICAL. 
 
 CHAPTER 1. The Osseous Skeleton 35 
 
 The Skull 35 
 
 The Vertebral Column 38 
 
 The Jaws and Branchial Arches 41 
 
 CHAPTER 2. The Fibrous Membranes and Musculature 45 
 
 The Fibrous Membranes 45 
 
 The Musculature 46 
 
 CHAPTER 3. The Viscera, and Vascular System 54 
 
 The Viscera, female 54 
 
 Ditto, male 56 
 
 Minute Structure of the Reproductive Organs, and Development of the 
 
 Reproductive Elements 9 
 
 The Vascular System 64 
 
 A 2 
 
IV 
 
 Page 
 
 CHAPTER 4. The Nervous System 66 
 
 The Brain 66 
 
 The Cranial Nerves. 68 
 
 CHAPTER 5. The Skin 73 
 
 Dermal Canals and Sense Organs 74 
 
 Minute Structure of the Skin, Dermal Tubes, and Sense Organs .... 79 
 
 CHAPTER 6. Embryology 84 
 
 CHAPTER 7. Structure of Phyllonella solece 93 
 
 PART III. 
 
 BlONOMICAL. 
 
 CHAPTER 1. Geographical Distribution 99 
 
 CHAPTER 2. Habits, Food, &c 101 
 
 Food 105 
 
 Parasites. . . 108 
 
 Enemies : 109 
 
 CHAPTER 3. Colour 110 
 
 CHAPTER 4. Breeding 114 
 
 CHAPTER 5. Development and Growth 119 
 
 PART IV. 
 
 ECONOMICAL. 
 
 CHAPTER 1. Artificial Propagation 129 
 
 CHAPTER 2. The Sole Fishery .137 
 
 CHAPTER 3. Practical Measures 142 
 
PREFACE. 
 
 THE distinction between theory and practice is one that is generally recognised in all 
 departments of human affairs. By theory in this context is meant pure knowledge 
 the knowledge of things as they are apart from any use which may be made of the 
 knowledge. This kind of knowledge the result of the most careful investigation, 
 continually corrected by improved experiments and more widely extended observation, 
 and subjected to the most rigid criticism by successive generations of enquirers is 
 pure science. Practice, on the other hand, or practical knowledge, is the knowledge 
 of the methods by which the material and the forces of nature can be made to 
 satisfy human needs and desires. Practice necessarily depends on some knowledge 
 of the properties and relations of natural objects and forces, though in many cases 
 it may simply consist in knowing that a certain desired result will generally be 
 produced by particular operations. This is the kind of knowledge possessed by 
 men trained and experienced in particular " trades " or crafts. 
 
 The distinction has existed since the very commencement of human civilisation. 
 The earliest representatives of humanity, like the most primitive savages now existing, 
 had some knowledge of their surroundings which was not directly useful to them, while 
 they understood very little the arts which they practised. To some extent the develop- 
 ment of pure science and that of practical science have proceeded independently, but to 
 a large extent they have influenced one another. Practical science has often received a. 
 great impetus from the discoveries of abstract inquiry, and pure science has often made 
 enormous strides by the study of the results exhibited by industrial processes. On the 
 whole the tendency of the development of the two is towards a perfect harmony in 
 which the knowledge of the universal interaction of natural forces would completely 
 
VI 
 
 explain all that takes place in industrial processes, and on the other hand industrial 
 processes would be perfected by the application of a complete knowledge of the 
 mechanism of nature. 
 
 Thus, although there is a great distinction between science and practice, each is to a 
 large extent dependent on the aid of the other. Their influence upon each other 
 could be illustrated by the history of any branch of science : it is illustrated by the 
 history of biological arts and sciences. The discovery that the great depths of the 
 ocean were inhabited by living animals was directly due to the laying of the telegraph 
 cable from Europe to America. The medical sciences, anatomy and physiology, sprang 
 not solely from the desire for knowledge, but from the practice of the healing art, 
 and the desire to improve that art. Botany took its rise from the knowledge of 
 simples, the use of plants as remedies for diseases and disorders of the human body. 
 Zoology and comparative anatomy and physiology have been largely aided in their 
 development by the medical sciences. Marine zoology has ever been to a great degree 
 dependent on the assistance of fishermen and fishing engines. Science has received 
 definite additions from investigations carried out with the object of cultivating oysters. 
 The explanation of evolution is sought in the study of the variations of domesticated 
 animals and plants. Are there, on the other hand, any cases in which human arts and 
 industries have directly benefited by the biological sciences ? To answer this question 
 by even briefly enumerating the recent discoveries concerning animal and vegetable, 
 parasites which have revolutionised the practice of agriculture would require a 
 volume. But it must be confessed that the fishing industry has hitherto, in this 
 country at least, not been greatly benefited by the scientific knowledge of fishes hitherto 
 available. Yet zoological science and the methods of that science have not been 
 entirely without effect upon the supply of aquatic animals for the wants of man. 
 Oyster-culture based upon scientific knowledge has been very successful in Holland 
 and France. Knowledge of the conditions of life of the salmon has been applied to 
 maintain and increase the abundance of that fish in this country, and of allied fishes 
 in America. The shad has been propagated with great success on the Atlantic coast 
 of the United States. It remains true that there exists a great deal of scientific 
 knowledge of marine fishes which has hitherto not at all affected the sea-fishing 
 industry. But it is also true that no great endeavours have yet been made to 
 bring science and practice in this direction into relation with one another, and also 
 that our knowledge of the life of marine fishes is in many respects still extremely 
 
Yll 
 
 limited. The structure of these fishes and their place in the general classification of 
 thtt animal kingdom has been to some extent ascertained, but of their conditions of life, 
 their food, rate of growth, the causes which favour or limit their abundance, we still 
 know very little. It was only in 1864, when Professor Sars identified the floating eggs 
 of the cod, that it was first discovered that the eggs of any marine fish passed through 
 their development while suspended in the surface waters of the sea. The know- 
 ledge of structure and classification is not entirely useless from the practical point 
 of view, for it is absolutely necessary as a basis from which to investigate the different 
 conditions of life of the different species. The species must be considered separately, 
 for their mutual relations are so complicated that it is impossible to deal with, them 
 together. 
 
 The object of the present work is to place side by side the results of a scientific 
 study of the common sole and an account of the present condition of the sole fishery, 
 and then to consider what are the possible practical applications of the former to the 
 purpose of maintaining or increasing the supply of soles available for the market. 
 
 The work was undertaken under instructions from the Council of the Marine 
 Biological Association, and the investigations described were carried out at the 
 Association's Laboratory at Plymouth. Nearly the whole of my time and energy since 
 November, 1888, have been devoted to the subject. The instructions of the Council 
 
 
 
 were quite general, but from Professor Lankester I have received much guidance 
 as to the scope of the investigations and the plan of the book. The responsibility, 
 however, for all the views and statements rests entirely upon myself. When studying 
 the taxonomical part of the subject in November, 1889, I visited the British Museum 
 of Natural History, and examined all the type specimens of European species of sole. 
 I have to thank Dr. Giinther for the courtesy and assistance I then received from 
 him. At that time I gathered from conversations with him that he still believed 
 in an English species, Solea aurantiaca, distinct from the Solea lascaris of either Eisso 
 or Bonaparte. I was therefore surprised to see that in a communication to the 
 Zoological Society in January last he abandoned this opinion, and adopted the 
 conclusion of most recent writers on the subject that the English and the Mediter- 
 ranean form belong to the same species. My discussion of the question in the 
 present work was written in November, 1889, immediately after my visit to the 
 national collection. 
 
 I have much pleasure in thanking Mr. Dunn, of Mevagissey, and my friend Eupert 
 
VI 11 
 
 Vallentin, Esq., of Falmouth, for the most important assistance they rendered me in 
 procuring specimens of the sole in the younger stages of growth. I am still more 
 deeply indebted to Miss Annie Willis for the skill and care which she devoted to the 
 water-colour drawings reproduced in Plates I to IX. The beauty, minuteness of detail, 
 and artistic finish of her work are evident enough in the lithographic copies, and I need 
 only add that the drawings were executed from the actual objects under my direct 
 supervision, and that I can answer for their perfect faithfulness. 
 
 J. T. C. 
 
 PLYMOUTH, 
 
 March 13, 1890. 
 
PART I. 
 
 TAXONOMICAL 
 
CHAPTER I. 
 
 CLASSIFICATION OF THE FLAT-FISHES. 
 
 IT is a matter of general knowledge and experience that the various kinds of flat- 
 fishes resemble one another and differ from all other fishes in these conspicuous 
 features : that their form is very flat, that one side is coloured and the other of a pure 
 opaque white, and that there are two eyes on the coloured side and none on the white 
 side. It is further generally known, from the observation of such fishes in the living 
 state in aquaria, that when alive they are usually resting on the white side at the 
 bottom of the water, sometimes gliding gently over the ground, sometimes burying 
 themselves in the sand, which is the material on which they are accustomed to live, 
 and only occasionally rising up from the bottom and swimming in a horizontal position 
 through the water. The common sole is also as a rule recognised by everybody as a 
 particular kind of flat-fish, being readily distinguished by its gently curved outline, 
 especially by the regular, almost semicircular, shape of the snout, and by the dull 
 brown colour of its upper side after death. 
 
 But this is only true of the sole as it is usually seen by the majority of people, that 
 is in its adult condition. Ordinary habits of observation are not sufficient to dis- 
 tinguish the sole in its very young condition from other kinds of flat-fishes : only 
 naturalists are able to separate the kinds from one another among individuals from 
 one to three inches in length. Even fishermen, who might be supposed to have 
 unusual opportunities of comparing different kinds of fishes, but who, as a matter of 
 fact, have usually no leisure and no superfluous energy to devote to accurate and 
 minute observation, constantly mistake various kinds of flat-fishes in their young stages 
 for young soles. The reason of this is not that the young fishes between one and 
 three inches long differ in their characters from full-grown specimens, but simply that 
 the characteristic features are on a much smaller scale, and therefore are not seen 
 without attentive observation. 
 
 Untrained powers of observation are also unable to compare the degree of difference 
 between one kind of flat-fish and another. The plaice and flounder are named 
 independently ; but a fish which resembles the plaice and flounder far more closely 
 than it does the sole is sold under the name of merry-sole in Devonshire and lemon- 
 sole in London. This may be partly due to an inclination to enhance its value in the 
 
 B 2 
 
eyes of the consumer. Again, more than one kind of sole is sometimes sold under 
 that name. 
 
 It is evident, then, that before we commence the study of the common sole we must 
 make ourselves accurately acquainted with its special features, so that we may not 
 mistake other kinds for it, and may identify it with certainty at all stages of its 
 existence. In order to discover these special features we must compare all the kinds 
 of flat-fishes with other fishes and with one another and thus ascertain 1st, what 
 features are common to all of them ; 2nd, what features are common to certain divi- 
 sions of them and especially to the division which includes the sole ; 3rd, what are the 
 differences between the several kinds or species included in this particular division. 
 
 In order to study the characters of the flat-fishes we must of course give names to 
 their various organs ; but all the bony fishes are made up of the same organs in 
 different shapes and sizes and in various proportions to one another. Thus we have 
 only to examine the sole and compare it with a fish of the more usual structure in 
 order to recognise the various organs which have long borne appropriate names. 
 
 In any fish of the ordinary type, for example, a salmon, herring, cod, perch, 
 mackerel, &c., the two sides resemble one another in form, structure, and colour, and 
 correspond to one another in the position and direction of their component organs. 
 In other words, all the organs, with the exception of some of the internal, are in pairs, 
 the two members of each pair being situated on opposite sides of the middle plane of 
 the body, at the same level, and at equal distances from it. This plan of structure 
 occurs in the majority of fishes and nearly all the other vertebrates, and also in the 
 greater number of the lower animals, for instance in Crustacea and insects. To 
 obtain a distinct idea of it we may reflect that the body of any animal in which it 
 occurs, say a normal fish, a dog, or a man, has length, thickness, and breadth. The 
 length is measured from the head to the posterior end of the body, the thickness from 
 the back to the ventral surface, the breadth from side to side. Now the organs at 
 opposite ends of the line which measures length are utterly different jp form and 
 structure, and those at the back are equally different from those opposite to them at 
 the ventral surface. But, wherever we measure the breadth, the parts at one end of 
 the line along which we measure will be exactly similar in form and structure to 
 those at the other, but exactly reversed in horizontal direction. This structural 
 feature is called bilateral symmetry. 
 
 The greater number of fishes are bilaterally symmetrical, and the line along the 
 surface which separates the two similar halves passes between the eyes at an equal 
 distance from each. If we look for the line which divides two similar halves in the 
 sole we shall not be able to find it. It is obvious that a line drawn between the eyes 
 does not divide the head into two equal and similar parts ; but if we look for the 
 paired organs of the ordinary fish in the sole we shall find in most cases that one of 
 each pair is on the coloured or upper side of the sole, and the other on the white or 
 lower side, but that in many cases the two members of each pair are not so exactly 
 
similar as they are in the ordinary fish. Thus in the sole there is a gill-cover or 
 operculum on the upper side and another on the lower, and beneath each is a similar 
 gill-apparatus ; half the mouth is on the upper side and half on the lower ; there are 
 two nostrils on the upper side and two on the lower ; a pectoral fin and a pelvic fin on 
 the upper side and two corresponding fins on the lower ; scales on the upper side and 
 similar scales with a corresponding arrangement on the lower; and finally a line of 
 peculiar scales, a lateral line, along the middle of the upper side and a similar line on 
 the lower. It follows, therefore, that the long continuous fins along the two edges of 
 the sole correspond to the median fins of the ordinary fish, and as we find the anus and 
 the junction of the gill arches on one edge of the sole, this edge corresponds to the 
 ventral median line of the ordinary fish, so that the elongated fringing fins of the 
 sole are the dorsal and ventral median fins respectively ; the ventral median fin is 
 generally called the anal fin. We thus find that the upper side of the sole is the right 
 side and the lower the left, and the edge on which the anus opens is the ventral edge, 
 the other the dorsal. But the two eyes, though in other respects similar to the two 
 eyes of an ordinary fish, are both on the right side, one nearer to the dorsal edge, the 
 other nearer to the ventral. We may distinguish these eyes as the dorsal and ventral 
 respectively, and even without further knowledge we might consider it probable that 
 the dorsal eye corresponds to the left eye of an ordinary fish and the ventral to the 
 right, and the idea would naturally occur to us that the left eye in the sole had been 
 somehow drawn out of its original position on the left side and carried round to the 
 right side. 
 
 The fins of the sole are all supported by flexible or soft rays ; none of the rays are 
 rigid pointed spines ; but this is a character which occurs in certain symmetrical 
 fishes, for example, the cod and whiting. The possession of a single elongated 
 median dorsal fin and a single similar ventral fin is also not peculiar to the sole : some 
 members of the cod family have but a singLe dorsal and ventral fin. But no 
 symmetrical fish has a dorsal fin extending so far forwards as the sole : in the latter 
 this fin is continued to a point on the edge of the body anterior to the eyes, and in 
 every flat-fish, except one species, it extends at least as far as a point above the dorsal 
 eye, while in all symmetrical fishes the limit is somewhat behind the eyes. 
 
 The lower or left side of the sole differs from the right side not only in being white 
 instead of coloured, but also in being flatter, and the fin- rays of the median fins are 
 also more prominent on this side. 
 
 The examination of other flat fishes will show that they resemble the sole and differ 
 from symmetrical fishes in the features just mentioned, if we except the fact that in 
 some kinds it is the left side and not the right which is coloured and which bears the 
 eyes. Thus the turbot and brill have the eyes on the left side, while the plaice 
 flounder, dab, and halibut, like the sole, have them on the right side. 
 
 All the various kinds of flat fishes thus resemble one another and differ from 
 symmetrical fishes in the particulars now described, which may be thus summarised : 
 
Body much compressed bilaterally and extended dorso-ventrally : one side, on which 
 the fish rests during life, opaque white, natter than the other, which is more convex 
 and exhibits colour and markings : both eyes on the coloured side of the head. 
 Pectoral and pelivc fins small, the former sometimes absent ; a single elongated dorsal 
 fin which extends forwards as far as or beyond the level of the dorsal eye, except in 
 one instance where it ends a little behind the eye; a single elongated anal fin 
 extending from the base of the tail to the anus, which is a short distance behind the 
 opercular apertures. 
 
 The fishes thus characterised form a single family the Pleuronectidce ( = side- 
 swimmers, from Greek 7r\ev/>a, the side ; irfx ** ^ swim). The large number of kinds 
 or species which can be distinguished among them are divided into a number of groups 
 according to the degree of difference between them, any two species of the same group 
 being much more closely similar to one another than to the members of any other 
 group. These groups are the genera. Thus the difference between a plaice and a 
 sole is much greater than the difference between a plaice and a flounder. The plaice 
 and the flounder resemble each other in the shape of the body, in the large prominent 
 eyes, and the small terminal mouth and pointed snout. Again, if we compare a turbot 
 and a brill we find that they resemble one another very closely : they both have a deep 
 straight mouth cleft, the anterior end of which is at the extreme apex of the snout, and 
 both have a more or less rhomboidal shape. 
 
 The various kinds of sole are all distinguished from other flat fishes by the gradual 
 and regular curve formed by the outline of the body, which, excepting the tail, is 
 almost a perfect oval, the semicircular form of the snout being specially characteristic. 
 The dorsal fin commences on the snout, and is not continuous with the caudal fin ; the 
 cleft of the mouth on each side is curved downwards. The mouth is asymmetrical, the 
 jaws being stronger on the lower side, and only on this side containing teeth, which 
 are small and slender. The eyes are on the right side and small, the dorsal being in 
 advance of the ventral. The scales are small and fringed with small projecting spines, 
 that is, are of the kind called ctenoid. The lateral line is straight from the head to the 
 tail, and runs along the middle of each side, but it also sends a curved branch forwards 
 on the head which runs parallel to the base of the dorsal fin towards the snout. 
 
 All the Pleuronectidce exhibiting the above features are called Solea, with a 
 distinguishing adjective to indicate the particular kind or species referred to. In 
 other words, the species which resemble one another in these particulars and differ 
 only in more, minute details are classed together in a genus which bears the Latin 
 name Solea in the universal language of Zoology. 
 
 There are other kinds of sole besides the common sole, that is to say, there are other 
 kinds of flatfishes which resemble the sole in all the features in which the sole differs 
 from the turbot or the flounder, but differ from it in more minute details. One kind 
 is sometimes sold together with the common sole without being distinguished, and 
 sometimes is distinguished as the sand sole. It differs from the common sole chiefly 
 
in two characters : (1) it is somewhat lighter in colour after death, and instead of large 
 black blotches on the coloured side it has small black specks scattered almost 
 uniformly over the surface ; (2) the anterior nostril of the lower side is very large and 
 conspicuous, it is dilated and has folds radiating from its wall into its cavity. At 
 Plymouth and other places on the south coast of Devon and Cornwall another flat- 
 fish is commonly sold which is called the thick-back. This is evidently a kind, of sole, 
 but is distinguished by its smaller size, and by its colour and marking, which consists 
 of black transverse stripes on a red ground. 
 
 Several kinds of flat-fishes are obtained from British seas, which are too small and 
 too scarce to be of any value as food, but which of course have been studied by 
 zoologists equally with the edible species. 
 
 After studying all the species of flat-fishes brought together in the British Museum 
 from all parts of the world, Dr. Giinther has classified them in thirty-four genera, 
 including Solea. But of these only seven include species which occur on the British 
 coasts. Zoologists often differ as to the limitations of genera, because it is in many 
 cases difficult to decide whether several species differ from one another to an equal 
 degree and ought therefore to be classed in a single genus, or whether they differ in 
 different degrees and ought to be separated into two or more genera. Eecent 
 authorities also recognise seven genera among British forms namely, Hippoglossus, 
 Hippoglossoides, Rhombus, Zeugopterus, Arnoglossus, Pleuronectes, and Solea. The 
 external differences which distinguish the genera and species of British forms may be 
 presented analytically thus : 
 
 A. Eyes on the left side ; mouth terminal ; teeth on both sides ; ventral eye anterior 
 to the dorsal. 
 
 1 . Rhombus. Shape rhomboidal, middle of the body being very broad ; 
 
 mouth large ; lateral line with a semicircular curve anteriorly. 
 
 Rhombus maximus, the Turbot. No ordinary scales, but pointed 
 tubercles uniformly scattered over skin. 
 
 Rhombus Icevis, the Brill. Small scales ; no tubercles. 
 
 2. Zeugopterus. Shape almost rectangular, anterior end obtuse ; lateral line 
 
 with a semicircular curve anteriorly ; scales ctenoid. 
 
 Zeugopterus unimaculatus, first dorsal ray elongated and undivided, 
 median fins not prolonged under the base of the tail ; a conspicuous 
 large dark spot towards the posterior end of the lateral line. 
 
 Zeugopterus punctatus, first dorsal ray not elongated, median fins 
 prolonged under the base of the tail. 
 
 3. Arnoglossus. Shape oval, rather narrow, with sharp snout; eyes large, 
 
 almost level, ventral slightly more advanced. Cleft of mouth deep. 
 Teeth small, one or two rows in both jaws ; present or absent from the 
 vomer ; none on the palatines. Gill-membranes somewhat broadly united 
 
8 
 
 at the throat. Dorsal fin commencing on the snout in front of the eyes, 
 and not continuous with caudal. Nearly all the rays of the dorsal and 
 anal simple and undivided. Scales somewhat large, easily detached, 
 ctenoid. Lateral line with a rectangular bight above the pectoral. 
 
 Arnoglossus megastoma (Megrim at Plymouth). Teeth on the vomer. 
 Anterior dorsal rays united by membrane for half of their length. The 
 base of the dorsal fin not passing on to the lower side of the head 
 anteriorly. Anterior nostril of the lower side protected by a broad flap 
 of flexible membrane. Eyes very large. Scales not so deciduous as in 
 the following species. Snout pointed. 
 
 Arnoglossus laterna (Scald-fish or Scald-back at Plymouth). No teeth 
 on the vomer. Anterior dorsal rays free and separate ; the membrane 
 of the rest of the fin very slight, the rays easily becoming separate. 
 The anterior rays of the dorsal fin arise from the lower surface of 
 the head. Eyes not very large. Snout somewhat blunt. The base of 
 the left pelvic fin extends from the throat to the anus, and behind it 
 are one or two prominent spines. The four anterior rays of the dorsal 
 fin are very thick and much elongated in the male, not in the female. 
 Arnoglossus lophotes, Giinther, is the male. 
 
 B. Eyes on the right side. 
 
 I. Mouth terminal and large, teeth on both sides. 
 
 1. Hippoglossus. Shape lanceolate ; dorsal fin commencing above the dorsal 
 
 eye ; scales cycloid. Lateral line with a slight curve anteriorly. 
 Hippoglossus vulgaris, the Halibut. 
 
 2. Hippoglossoides. Anterior end not much narrowed ; dorsal and ventral 
 
 edges rather straight ; scales ctenoid. Lateral line straight. 
 Hippoglossoides limandoides, the Long Eough Dab. 
 
 n. Mouth terminal and extremely small ; teeth most developed on the lower 
 side. 
 
 1. Pleuronectes. Dorsal fin commencing above the dorsal eye ; eyes large 
 and prominent ; scales small or rudimentary. 
 
 Pleuronectes platessa, the Plaice. Bony tubercles on the interorbital 
 ridge. Bright red spots ; scales uniform. Lateral line nearly straight. 
 
 Pleuronectes microcephalus, the Merry- sole or Lemon-sole. Skin slimy. 
 Lateral line with a very small anterior curve. Colours mottled with a 
 good deal of yellow ; scales cycloid. Shape somewhat rectangular. 
 
 Pleuronectes cynoglossus, the Pole-flounder or Witch. Shape elongated; 
 dorsal and ventral edges very gradually curved. Lateral line straight. 
 
Pleuronectes flesus, the Common Flounder. Ossicles at base of dorsal 
 and anal fins. Scales rough along lateral line, elsewhere rudimentary. 
 
 Pleuronectes limanda. Shape rhomboidal; snout pointed. Lateral 
 line with a small semicircular curve anteriorly. 
 
 III. Mouth rather small, and not terminal, but curved down to the ventral 
 edge ; teeth present only on the lower side. 
 
 1. Solea. The shape oval, outline of the snout regularly semicircular. Scales 
 ctenoid. Lateral line straight, but with an anterior dorsal curve on 
 the head. Tactile filaments on the lower side of the snout. Paired 
 fins may be rudimentary or absent. The dorsal eye anterior to the 
 lower. 
 
 Solea vulgarly the Common Sole. Pectorals on both sides of con- 
 siderable size ; nostrils on the two sides similar ; filaments of the under 
 side of the snout closely crowded together not forming any pattern. 
 Markings of the upper side consisting of longitudinal series of black 
 blotches on a yellowish-brown ground. 
 
 Solea lascaris, the French Sole or Sand Sole. Differs from the 
 preceding in two characters viz., the anterior nostril on the lower side 
 is dilated and fringed internally ; each of the black blotches of the 
 preceding species is represented by a number of small black specks. 
 
 Solea variegata, the Thick-back. Nostrils on both sides similar ; 
 pectoral and pelvic fins rudimentary ; filaments of the lower side of the 
 snout connected at their bases by membranes which surround square 
 depressions. Mouth more terminal and less curved than in the other 
 species. Markings consist of five transverse dark bands. 
 
 Solea lutea. Resembles the preceding in other respects, but has the 
 mouth much curved, the dorsal fin commencing on the extreme 
 anterior end of the snout. The markings consist of dark blotches 
 arranged as in . rulgaris, but there is in addition a thin black line 
 along every fifth or sixth ray in the dorsal and anal fins. 
 
 Solea Greenii, a new species just defined by Dr. Gunther, has the 
 scales, fin -rays, and filaments of the left side of the head as in vulgaris, 
 but rudimentary pectorals. 
 
 Plates I to VII, which exhibit with great accuracy the natural appearance of the 
 fish, will illustrate the distinguishing external features of the four commoner British 
 species of sole. But although the above-mentioned characters are those which 
 principally distinguish the species from one another, they do not exactly resemble one 
 another in every other respect. We may proceed to study their characters in greater 
 
 c 
 
10 
 
 detail, in order to obtain a complete knowledge of their specific peculiarities. In 
 describing the characters of a fish, it is usual to commence by counting the fin-rays in 
 each fin," the number of scales in the lateral line, wherever this is possible, the number 
 of vertebrae, and the number of rays which support the membrane covering the gills 
 beneath the operculum ; these are called the branchiostegal rays. These numbers 
 are all put down in succession with initial letters to indicate the organs they refer to, 
 so as to form a numerical formula. Thus : 
 
 B. = Branchiostegal. 
 D. = Dorsal fin. 
 A. = Anal fin. 
 L.I. = Lateral line. 
 
 Pt. = Pectoral fin. 
 Pv. = Pelvic fin. 
 C. = Caudal fin. 
 Vert. = Vertebras. 
 
 The proportions of the fish are expressed numerically by stating the number of 
 times a given length is contained in the total length : the reason of this is that the 
 measurements are made with a pair of compasses, which are first adjusted to the length 
 of a certain organ, and then used to mark off successive lengths equal to this along the 
 body-length. 
 
11 
 
 CHAPTER II. 
 
 HISTOKY OF THE GENUS SOLE A. 
 
 THE flat-fishes have been always placed together in one group in all attempts to classify 
 fishes from the time of the ancient Greeks and Eomans up to the present. Thus 
 Aristotle called them i/^TraJSeig. But in ancient times other fishes of a flat shape, 
 but symmetrical, like the dorey and the skate, have often been united with them. Thus 
 Eondelet includes among the " poissons plats " the dorey and two other symmetrical 
 fishes and all the skates and rays. In the ancient and pre-Linnaean times ideas 
 of classification were somewhat vague ; the idea of genus and species existed, though 
 it was not accurately defined, but degrees of classification regularly subordinated to 
 one another could not be established by men who had little real knowledge of the 
 structure and physiology of animals. Eondelet includes all marine animals among his 
 " Poissons," yet his arrangement of the true Pleuronectidse in genera and species is 
 more similar to that which is now accepted than the classification adopted by Artedi 
 and Linnaeus. Eondelet describes the genus Rhombus with two species, one with 
 spines and the other without, the turbot and the brill ; the genus Rhomboides ; 
 Citharus with two species ; Passer with four species, Passer, the plaice, Passer quad- 
 ratulus, Passer liinanda, and Passer flesus (the flounder) ; the genus Solea, with six 
 species, Solea, the common sole, Solea oculata (la Pegouse), la Pole, Arnoglossus, Solea 
 linguki, and Hippoglossus. 
 
 Artedi arranged all the flat fishes into one genus Pleuronectes, a name which he 
 introduced into zoology for the first time, and Linnaeus followed his example. The 
 12th edition of the " Systenia Nature " was published in 1766. The successors of 
 Linnaeus for some time continued to follow him and Artedi, merely dividing the genus 
 in an arbitrary way into subgenera. Lacepede, in his " Histoire Nat. des Poissons," 
 published in 1798, defines four subgenera of Pleuronectes, but without giving them 
 distinguishing names : the first of them comprises only the halibut and the flounder, 
 united because their eyes are on the right side and they have a curve in the lateral 
 line. Similarly, Eisso, in his " Ichthyologie de Nice," 1810, arranges the species under 
 two subgenera, according to the side on which the eyes are situated. 
 
 Quensel in 1806 divided the genus into two, with the following definitions: 
 Plearonecte-s, having complete jaws not covered with scales ; the maxillary dilated 
 
 c 2 
 
and free at its extremity ; the mandible with cutaneous folds between its limbs at the 
 chin. Gill-opening extending above the opercular angle or at least above the pectoral. 
 The lower eye more anterior than the upper one, and the nostrils distant from the 
 jaws, that of the blind side being near the dorsal edge. 
 
 Solea, in which the jaws are covered with scales, the superior one not fully 
 developed, and the scaly mandible not showing the usual folds at the chin. Gill- 
 openings wholly below the pectorals. The inferior eye farther back than the superior 
 one. Nostrils on both sides near the jaws. All the fin-rays divided, no spine in the 
 anal. (Richardson's Yarrell, Vol. I., p. 608.) 
 
 In the "Regne Animal," first edition, 1817, Cuvier makes the Linnasan genus into 
 a family, which he calls simply " poissons plats," and divides it into genera and species 
 as follows : 
 
 Platessa, including the plaice, Platessa platessa ; the flounder, Plaiessa flesus ; the 
 dab, Platessa limanda. 
 
 Hippoglossus. including the PI. hippoglossus of Linnseus, and several species of the 
 Mediterranean described by other authors. 
 
 Rhombus, including Rhombus maximus, the turbot and the brill, the PL nudus of 
 "Risso (apparently an Arnoglossus), and other species in which the upper eye 
 is at a great distance above and behind the lower. 
 
 Solea, including the common sole, PL solea, Lin., the Pole of Belon, the Solea 
 oculata of Hondelet, the Pegouse of Eisso, and the lascaris and theophilus of 
 the same author. Also certain foreign species in which the vertical fins are 
 continuous, PL zebra, Bloch, PL plagusia, Lin. (These species now form the 
 genus Plagusia.} 
 
 The Monochires, in which the right pectoral is very small, and the left minute 
 or altogether wanting, e.g., Linguatula, Eondelet, and the Achires, which have 
 no pectorals at all, are mentioned apparently as subgenera. Those Achires in 
 which the vertical fins are continuous with the caudal are distinguished as 
 Plagusia. 
 
 The definition of Solea given by Cuvier is as follows : 
 
 " Their peculiar character is that the mouth is twisted and as it were monstrous on 
 the side opposite to the eyes, and furnished on that side only with slender teeth closely 
 crowded together like the pile of velvet, while the side where the eyes are has no teeth. 
 Their form is oblong, their snout round and always projecting beyond the mouth ; the 
 dorsal fin commencing over the mouth, and extending like the anal up to the caudal. 
 Their lateral line is straight ; the side of the head opposite to the eyes is generally 
 furnished with a sort of villosity. Their intestine is long, with several convolutions, 
 and without caeca." 
 
 It is evident that this definition of the genus admits of but little improvement. 
 Cuvier obviously meant the Monochires, Achires, and Plagusia to be mere subgenera 
 
13 
 
 indicating the grouping of the various species. But subsequent authors frequently 
 raised these divisions to the rank of distinct genera. Bonaparte, 1841, separated the 
 last subdivision of Cuvier only as a distinct genus, namely, Plagusia. 
 
 Dr. Gimther, in his important work, " The British Museum Catalogue of Fishes," 
 gives a comprehensive classification of the Pleuronectidae, which includes all the 
 forms up to that time described in the literature or represented in the great national 
 collection. He distinguishes in all thirty-four genera, many of which are entirely 
 new, while the limits and definitions of the rest are revised. His definition of Solea 
 is as follows : 
 
 Eyes on the right side, the upper being more or less in advance of the lower. Cleft 
 of the mouth narrow, twisted round to the left side. Teeth on the blind side only, 
 where they are villiform, forming bands : no vomerine or palatine teeth. The dorsal 
 fin commences on the snout, and is not confluent with the caudal. Scales very small ; 
 ctenoid. Lateral line straight. 
 
 Thus the chief difference between this definition and Cuvier's is that it excludes all 
 the forms in which the longitudinal fins are continuous with the caudal. All the British 
 forms of sole described in the present work are included by Giiiither in the genus Solea. 
 But almost every author defines the genera of Pleuronectidae, even at the present day, 
 in some degree after his own fashion. There is a general agreement, together with 
 differences of opinion on certain points. In the Pleuronectidae, as in nearly all families 
 of animals, there are certain well-marked species which are recognised by all naturalists. 
 There are others, especially those founded upon a small number of specimens, which 
 are more difficult to separate, and concerning which differences of opinion exist. But 
 the question of the arrangement of the species into genera gives rise to much greater 
 differences of opinion. The arrangement of course depends on which of the characters 
 possessed by several species in common, are taken as characterising a genus. If one 
 character is taken, a certain number of species are united by it ; if another is taken 
 the same species are scattered among other genera. Thus the fish called in this work 
 Arnoglossiis mtgastoma is variously placed. By Giinther it is placed in the genus 
 Rho?nbu$, because it possesses teeth on the vomer. By Moreau, whose arrangement 
 seems to me more original than natural, it is placed in the genus Pleuronectes. The 
 characters in which the species agrees with Ai*noglossus laterna s'eem to me to be more 
 numerous and important than the presence or absence of vomerine teeth, and I have 
 therefore followed those authors who include it in the genus Arnoglossus. 
 
 In describing the British species I shall give not merely the range of variation 
 of each numerical character, but the actual numbers observed in several individuals. 
 It must be pointed out that the number of scales in the lateral line is always 
 obtained not by counting the scales in the line itself, but the series of oblique trans- 
 verse rows of scales which cross the lateral line ; the scales are so arranged as to 
 form rows which run obliquely downwards somewhat from before backwards, other 
 rows which run more obliquely downwards and from behind forwards, and others, 
 
14 
 
 which are not so distinct, which run straight from before backwards ; it is the rows of 
 the first kind which are counted. The number of these rows indicated by the letters 
 L.I. is not so absolutely certain as the number of fin-rays in a fin, for the rows of scales 
 are counted from the commencement of the lateral line to the base of the tail, and as 
 the lateral line is actually continued to the very extremity of the tail, while the scales 
 diminish in size gradually at the base of the tail until they get so small that the rows 
 cannot be counted, there is, of course, no definite point where the counting ceases. 
 
15 
 
 CHAPTER III. 
 
 SOLEA VULGARIS, QCESSBL. 
 [PLATES I to V.] 
 
 Synonymy. 
 
 ftoi--/\u.'affoi, A then, vii, p. 288. 
 
 " Lingulaca," Varro and Plautus. 
 
 " Solea," Ovid, v. 124 ; Plin., ix, c. 16. 
 
 ''Bnglossns sive Solea," Kondeletius, xi, c. 11, p. 320, and other mediaeval authors. 
 
 " La Sole," Rondelet, 1558, French edition, Lyons, p. 256. 
 
 ' Plenronectes, sp.," Artedi, 1734, Genera, p. 18, No. 6 ; Species, p. 60, No. 5 ; Synonymia, 
 
 p. 32, No. 8. 
 %i Pleuronectes solea," Lin., Sytf. Nat., 1, p. -157 ; Bloch, 1784, Fi*che Deiitschl., ii, p. 42, 
 
 taf. 45 ; Lacepede, iv, p. G23 ; Donovan, 1808, Brit. Fish., Hi. pi. 52; Risso, 1810, 
 
 IcJith. Nice, p. 307. 
 
 " Sole," Pennant, Brit. Zool., iii, p. 203. 
 ' La Sole," Dnhamel, iii, sec. 9, p. 257, pi. 1. 
 ''Solea vnlgaris," Quensel, 1806, Vet. Akad. Handl., p. 230; Risso, 1826, Nat. 
 
 Hist. Eur. Mer., iii, p. 247 ; Bonaparte, Fauna Ital., iii, 26 ; Gunther, 1862, 
 
 Brit. Mus. Catal., iv, p. 463; Moreau, 1881, Poissons de la France, p. 304; 
 
 Francis Day, 1884, Fish. Gt. Brit, awl Ire., p. 39, pi. cvi. 
 
 Males. 
 
 Females. 
 
 Total length j 
 
 16-9 cm. 
 = 6g in. 
 
 26-4 cm. 
 
 = 10| in. 
 
 33-2 cm. 
 
 17-6 cm. 
 
 19-4 cm. 
 
 35-6 cm. 
 = 14 in. 
 
 38 cm. 
 i = 15 in. 
 
 Length ^ 
 
 3f 
 
 3rV 
 
 3^ 
 
 I 
 
 3 
 
 a* 
 
 *T\ 
 
 height J 
 
 Length 1 
 
 Kl 
 
 
 
 C3 K3 
 
 ! 
 
 
 head / 
 
 t 
 
 6 
 
 6 4 
 
 5 4 5 4 
 
 b 12 
 
 
 D 
 
 90 
 
 83 
 
 86 
 
 86 83 
 
 81 
 
 87 
 
 A 
 
 74 
 
 69 
 
 74 
 
 69 66 
 
 73 
 
 70 
 
 C 
 
 21 
 
 20 
 
 21 
 
 20 21 
 
 22 
 
 20 
 
 Pt 
 
 7 
 
 8 
 
 8 
 
 8 
 
 ft 
 
 7 r. 81. 
 
 9 
 
 Pv 
 
 5 
 
 5 
 
 5 
 
 5 5 
 
 5 
 
 5 
 
 L.I 
 
 159 
 
 155 
 
 160 
 
 153 149 
 
 166 
 
 166 
 
 Yert 
 
 " 
 
 50 
 
 48 
 
 
 
 
 
 50 
 
 48 
 
 A COMPAKISON of the above figures gives the following results. There are no 
 constant sexual differences in any of the ten characters given in the table, except 
 
16 
 
 that the females reach the larger size, nor any constant differences depending on size, 
 although it is possible that a slight increase in the number of rows of scales takes 
 place in individuals which grow very large. The largest individuals in the above 
 table have the largest number of rows of scales. The number of pelvic fin-rays is 
 constant, that of the pectoral rays, and of the caudal, nearly so. The number of 
 vertebrae varies very slightly. The range of the numbers of the dorsal and anal 
 fin-rays is considerable, in the above specimens 83 to 90, and 66 to 74, respectively 
 The range for the lateral line scales is greater, namely, 149 to 166. In all these cases 
 examination of a greater number of specimens would doubtless have extended the 
 range. 
 
 Fins. The dorsal fin commences a little in front of the dorsal eye, but behind the 
 apex of the snout. The right pectoral is scarcely longer than the left and is contained 
 two and a half times in the length of the head. 
 
 Eyes. Longitudinal diameter of eye one-sixth the length of the head ; scaled skin 
 between the eyes equal in breadth to the longitudinal diameter of the eye ; distance of 
 dorsal eye from edge of the snout equal to the longitudinal diameter of the eye. 
 Posterior edge of dorsal eye on a level with the middle of the ventral. 
 
 Nostrils. On the right side both nostrils are close together immediately in front 
 of the ventral eye and close to the edge of the upper lip. Both are tubular, the 
 posterior a little the wider, the anterior the longer. On the left side the two nostrils 
 are also thin walled tubes, the anterior being prominent and larger, the posterior quite 
 obscure ; the latter is about half an inch (in adult) above and behind the former. 
 
 Mouth. Extends backwards to beneath the middle of the ventral eye : the teeth 
 on the lower side are slender rods set close together in a broad curved patch in each 
 jaw. The villi on the under side of the snout are really connected at the base by 
 slight membranes which enclose depressions of the surface, but the latter are very 
 small and the villi are therefore closely crowded together. 
 
 Scales. On the right side extend over the whole surface of the head up to its very 
 edges, on the lower side they decrease in size in the neighbourhood of the villi and 
 disappear where these are fully developed. The villous area is bounded posteriorly 
 by a straight transverse line running a short distance behind the angle of the mouth. 
 One of the largest scales from the middle region of the right side of the body (PI. XIV, 1) 
 has sixteen radiating rows of spines, five spines in each of the middle rows. 
 
 The curved anterior portion of the lateral line is very distinct on the right side, 
 and can be traced running parallel to the edge of the body right to the apex of the 
 snout. On the lower side a similar curve exists, and in addition a line belonging to 
 the same system which runs straight forwards from the origin of the former above the 
 mouth, giving off transverse branches. 
 
 Colour. The dead sole in the market generally appears to be of a uniform dull 
 dark brown on the upper side, but closer examination show r s that there are black 
 blotches as well on the brown ground. During life the colours are much brighter, 
 
17 
 
 and the markings much more conspicuous. Although the colours vary with the 
 ground on which the animal rests, this variation is only in depth of tint ; the 
 markings are constant for the same individual, and vary but little in different 
 individuals, they have therefore quite as much importance as a specific character as 
 any other feature in the aniniaL 
 
 The markings, then, in the living fish consist of large dark blotches and small white 
 spots on a yellowish-grey ground. The dark blotches, brown or black according 
 to their intensity, are arranged symmetrically so as to form a definite pattern: the 
 largest blotches are in three rows, one along the lateral line, one near the base of 
 the dorsal, and one near that of the anal fin. Usually there are five or six of these 
 blotches in each row, but in some specimens there may be as many as eight in one or 
 more of the rows. The first blotch of the dorsal row is close behind the anterior 
 curve of the lateral line, and the last near the base of the tail ; the first of the central 
 row is just above the end of the pectoral fin, and the first of the ventral series is at 
 the base of the pelvic fin. The first and last in each series are always fainter and 
 smaller, while those in the centre of the series are larger and more conspicuous. In 
 each of the intervals between the blotches in each series is a lighter white spot, 
 smaller and with a more definite outline than the dark blotches. Other white spots 
 frequently appear around the dark blotches. Between the central row of blotches, 
 and each of the external rows is another row of similar blotches of smaller size ; 
 these are closer together, nine or ten of them can be usually counted in each series, 
 and in the intervals between them there are small white spots. These are the 
 principal markings, but there are in addition narrow irregular branching streaks of a 
 lighter brown extending from the edges of the dark blotches over the spaces between 
 them ; these streaks usually contain dark or black specks, but under certain conditions 
 they are everywhere almost as dark as the blotches, and then the latter are connected 
 together by an irregular network of black streaks. Outside the external series of 
 blotches, between them and the bases of the dorsal and anal fins respectively, is a 
 band free from markings where the ground colour is uniform and lighter than 
 elsewhere. The dorsal and anal fins themselves exhibit three distinct longitudinal 
 bands of colour ; the basal third is dark, being densely sprinkled with minute black 
 specks on a yellow ground, the middle portion is yellow without the black specks, 
 while the extreme edge is colourless, the membrane between the rays being here 
 transparent, while the skin over the extremities of the rays themselves is opaque white. 
 The extreme dorsal and ventral edge of the tail fin are opaque white, the external 
 portion of the tail, including the terminal half, is yellow, this portion being continuous 
 with the light band which lies within the bases of the dorsal and anal fins ; the 
 internal and basal part of the tail is sprinkled with black like the basal part of the 
 dorsal and anal fins. The right side of the head is coloured like the parts of the 
 body-surface between the blotches, that is, with blacks specks connected by faint 
 brown lines on a yellowish ground. 
 
 D 
 
18 
 
 The pectoral fin has usually a black spot on its outer half, but very often this spot is 
 only light brown, its intensity varying according to the action of light upon the 
 animal. 
 
 When we examine still more minutely the elements of the coloration now described, 
 we find that each of them is compound, made up of still smaller markings which 
 have a definite relation to the scales. The scales are imbricated like the tiles on a 
 roof, and the exposed portion of each, which projects backwards, has the shape 
 of the sector of a circle. Except in the white spots, where the whole sector is 
 opaque white, the basal angle of the sector is lightest in colour, and the colour 
 deepens in intensity to the extreme border which is darkest. Even in the lightest 
 part of the ground colour the border of each scale is distinctly defined by its 
 brownish colour, while in the darkest part of the blotches and black specks the curved 
 edge and the posterior half of the scale is black, while the anterior angle is light 
 brown or even yellow. 
 
 The scales do not extend right up to the edge of the transparent cornea of the eyes, 
 the skin bordering the cornea is smooth, and coloured green with brown specks, the 
 iris is yellowish-grey marked with radiating brown lines. The pupil is black at its 
 edges, but in the centre of it is a beautiful iridescent spot which dissection shows to 
 belong not to the surface of the cornea, but to that of the crystalline lens. 
 
 This species, being abundant on both the shores of the Mediterranean and the 
 Atlantic coasts of Europe, has been generally known since the earliest historical times. 
 It is mentioned by some of the ancient historical writers as /3ovyXwo-<rog by the 
 Greeks, and lingulaca or solea by the Eomans. The former two names are taken from 
 its resemblance in shape to the tongue, the latter from its resemblance to the sole of 
 a shoe. Similar names are still in use in the various European languages : the 
 Germans call it zunge, the tongue, and we call it the sole. In Italy it is called in 
 some places lingua or liriguattola, in others sogliola. The name tongue is also used 
 sometimes for small soles at Billingsgate. 
 
 After the revival of learning in the sixteenth century, when the study of systematic 
 natural history began to develop, the name Buglossus or Solea, borrowed from the 
 ancients, was used for this fish by all naturalists up to the time of Artedi, that is up 
 to the commencement of the eighteenth century. 
 
 Artedi, who died in 1734, placed all the flat fishes which had previously been 
 usually grouped together by the mediaeval ichthyologists, in one genus, Pleuronectes, 
 a name first introduced by himself. 
 
 Linnaeus, who edited Artedi's works, added little to the knowledge of fishes beyond 
 applying binomial terms to the species defined by the latter. He named the sole 
 Pleuronecles solea, in which he was followed by a number of his successors. 
 
 But it was soon found necessary to make the flat' fishes not a single genus, but a 
 family, classifying the diverse forms under various genera. This was in reality a 
 return to the practice of the pre-Linnaean naturalists, the results of Artedi's accurate 
 
J9 
 
 distinctions and Linnaeus' system of nomenclature being retained. The name Solea 
 rul'/aris was first used by Quensel, a Swedish zoologist, in 1806, and it has been 
 generally employed since that time. The species has since then always formed the 
 type of the genus, the number of species included with it varying in the systems of 
 classification adopted by different ichthyologists. 
 
 D 
 
20 
 
 CHAPTER IV. 
 
 [PLATE VI.] 
 
 Synonymy. 
 
 " Pleuronectes lascaris," Risso, 1810, IchtTiyologie de Nice, p. 311. 
 
 " Solea lascaris," Risso, 1826, Hist. Nat. de VEur. Her., t. iii, p. 249. 
 
 "Solea nasuta," Nordm, in Demid. Voy. Russ. Merid. Zool., iii, Poissons, Tab. 31. 
 
 " Solea lascaris," Bonaparte, 1841, Fauna Italica, t. iii, 27*, with 2 figures. 
 
 " Solea pegusa," Yarrell, 1829, Zool. Journal, vol. iv, p. 467, pi. 16. 
 
 " Lemon Sole," Yarrell, 1836. Brit. Fishes, first edition, vol. ii, p. 260. 
 
 " Solea anrantiaca," Giinther, 1862, Cat. Brit. Mus., vol. iv, p. 467. 
 
 " Solea lascaris," Moreau, 1881, Poissons de la France, t. iii, p. 307. 
 
 "Solea lascaris," Francis Day, 1884, Fishes, Gt. Brit, and Ire., vol. ii, p. 42, pi. 107 
 
 
 Male. 
 
 
 Females. 
 
 
 Total length j 
 Lengih "^ 
 
 17-2 cm. 
 6Hin. 
 
 05 
 
 18-9 cm. 
 7-^ in. 
 
 914 
 
 19-2 cm. 
 7in. 
 
 9-2 
 
 26-1 cm. 
 10 T <V in. 
 
 01 7 
 
 height / 
 Length 1 
 
 ^6 
 54 
 
 ^1 7 
 
 5s 
 
 KL2 
 
 ^2 1 
 62 
 
 head / 
 D 
 
 1 
 
 79 
 
 s 
 
 81 
 
 b i 
 
 89 
 
 i 
 
 82 
 
 A 
 
 67 
 
 67 
 
 70 
 
 70 
 
 C 
 
 20 
 
 20 
 
 20 
 
 20 
 
 Pt. ... 
 
 9 
 
 9 
 
 8 
 
 9 
 
 Pv 
 
 5 
 
 5 
 
 5 
 
 5 
 
 L.I 
 
 125 
 
 125 
 
 123 
 
 119 
 
 Vert 
 
 
 
 46 
 
 46 
 
 OF this species I have only been able to make a detailed examination of the four 
 specimens whose numerical peculiarities are given in the above table. 
 
 Comparison of the above characters with those of Solea vulgaris shows that the 
 present species is much broader in proportion to its length than the former, that the 
 proportion of the length of the head to the total length is about the same, that the 
 vertebrae are fewer in number, and the scales larger in proportion to the length of 
 the body. 
 
21 
 
 Fins. The dorsal commences just a trifle farther forwards than in S. vulgaris, the 
 base of the first ray being in line with the longitudinal diameter of the upper eye. 
 The two pectorals are equal in length, and the length is contained two and a half 
 times in the length of the head. 
 
 cs. Dorsal eye half of its longitudinal diameter in front of the ventral, and 
 more than its long diameter from the end of the snout ; therefore not so near the edge 
 as in vulgar is. 
 
 Xostrils. Both nostrils on the right side close together immediately in front of 
 the ventral eye, both tubular, but the anterior considerably the longer. On the 
 left side the anterior nostril is very broad and dilated, its edges being reflected 
 outwards. These edges are covered externally with the slender papillae of the under 
 surface of the snout. Internally there are a number of folds projecting from the 
 inner surface of the nostril radially towards its centre, the ventral of these folds being 
 thicker than the rest : the posterior nostril is tubular, narrow, and flaccid, and situated 
 a short distance behind the upper part of the rim of the anterior. 
 
 Mouth and Teeth as in vulgaris. The villi of the under side of the snout are finer 
 and even more closely crowded than in vulgarise they are especially long and 
 numerous round the edge of the dilated nostril. The villous area does not extend so 
 far backwards as in vulgaris. The scales cover the whole right side of the head, as in 
 vulgaris, but on the lower side they extend farther forwards above the nostrils, though 
 lines of villi are developed along the transverse branches of the cephalic portion of the 
 lateral line system. One of the scales from the middle region of the right side of the 
 body has seventeen radiating rows of spines, six spines in each of the middle rows. 
 (PI/ XIV, 4.) 
 
 The curved portion of the lateral line on the head on the right side is almost as dis- 
 tinct as in vulgaris\ on the lower side the arrangement is the same as in that species. 
 lour. After death the colour is much lighter than that of vulgaris, being yellow- 
 brown instead of dull brown ; hence the name lemon sole by which the species is some- 
 times called. In life the ground colour is a brownish-yellow, and the markings consist 
 of numerous small black specks scattered pretty uniformly over the whole surface. 
 Careful examination shows that among these black specks, groups can be recognised 
 which correspond in position with the black blotches of the common sole. In these 
 groups the specks are somewhat larger and closer together than elsewhere. Thus the 
 markings of the present species could be derived from those of vulgaris by taking 
 away so much of the black of the blotches in the latter as to leave only a group of 
 distinct specks. Among the specks are scattered other small spots of a light blue 
 colour ; these correspond to the white spots of vulgaris, but I have never seen them 
 white. What was said of the relation of the colour to the scales in vulgaris applies 
 here also ; many of the scales are bright yellow at their bases. The colour of the fins 
 resembles that in vulgaris ; there is a black spot on the outer half of the pectoral. 
 The eyes are coloured as in vulgaris. 
 
22 
 
 The British form of Solea, which is distinguished from the others by the dilatation of 
 the left nostril, was first observed by Yarrell, who described and figured it in the 
 " Zoological Journal," Vol. IV, in 1829, under the name Solea pegusa. His description is 
 so bad that it would be impossible to identify the species by its means with certainty, 
 but his plate shows the distinguishing characters quite clearly. Yarrell considered 
 his specimens to belong to the species Pleuronectes pegusa of Lacepede's " Histoire 
 Naturelle des Poissons," Vol, IV, 1803, and with the Pleuronectes pegusa of Eisso's 
 " Ichthyologie de Nice," 1810, which is called Monochirus pegusa in the same author's 
 " Hist. Nat. de 1'Europe Meridionale." In the third edition of Yarrell's " British Fishes," 
 Sir John Eichardson identified this species as the Pleuronectes nasutus of Pallas' 
 " Zoographia Eosso-Asiatica," 1811. But the PL pegusa of Lacepede is the Solea 
 ocellata of Giinther's Catalogue, the Pleuronectes ocellatus of Linnaeus, the Solea 
 oculata of Eondelet, a well-marked species in which the nostril is not dilated ; and the 
 Monochirus pegusa of Eisso is another species of the Mediterranean which has no 
 pectoral fin on the blind side, and in which also the left nostril is not dilated : it is the 
 Solea monochir of Giinther's Catalogue. 
 
 Yarrell's identification was therefore entirely incorrect, and Pallas' description of 
 PL nasutus is so extremely vague that it is difficult to ascertain to what species it 
 referred. The specimens described by Pallas by the name nasutus were taken in the 
 Theodosian Gulf in the Black Sea. The Solea ocellata and Solea monochir both occur 
 at Nice. 
 
 Dr. Giinther, in his "Catalogue of the Fishes in the British Museum," Vol. IV, 1862, 
 distinguishes four species of Solea in which the left nostril is dilated and flattened. 
 The British form, called by Yarrell Solea pegusa, the lemon sole, or French sole, is 
 described as distinct from, any other known species, and is named by Dr. Giinther, 
 Solea aurantiaca. The second of the four species is the Solea lascaris of Eisso, the 
 thiid Solea impar of Bennett, and the fourth Solea margaritifera of Giinther, another 
 new species. I have examined myself the specimens in the collections of the British 
 Museum, which Dr. Giinther thus described in his Catalogue, and in many respects I 
 cannot agree with him in his arrangement and identification of them. 
 
 Eisso's original description of Solea lascaris is not very exact, and the small figure 
 he gives is quite worthless ; it would be impossible to identify the species from the 
 figure. The numbers of fin-rays he gives are as follows : 
 
 D. 85, A. 68, P. 7, V. 5, C. 15. 
 
 He says that the colour is " fauve tigre de noir, avec des reflets violets, parsemes de 
 points grisatres sur la surface droite." He says that the upper jaw covers the inferior 
 in such a manner as to imitate the beak of a parroquet, and then continues : " Le 
 dessous de la t&te est orne de petits cils soyeux, blanchatres, entourant un long tube 
 qui re"pand une humeur glaireuse." Now it is difficult to understand how a naturalist 
 could describe the dilated nostril of Yarrell's lemon sole as " un long tube," but as 
 
23 
 
 Eisso makes no mention of any nostril on the under side of the head of any other 
 species of Pleuronectes, it is pretty evident that he was struck with a peculiar 
 conspicuous nostril, such as exists in the English form we are considering. 
 
 Bonaparte oives a good description and two excellent coloured figures in his ".Fauna 
 Italica," 1832-41, of a species which he calls Solea lascaris, and which he identifies 
 with the Solea lascaris of Eisso's " Hist. Xatur. de 1'Europe Mer.," the Pleuronectes 
 lascaris of the same author's " Ichthyologie de Xice." The fin formula given by 
 Bonaparte is 
 
 D. 78, A. 60, P. 8,Y. 5, C. 19. 
 
 It will be seen that the formula given by Eisso agrees perfectly with the numbers 
 observed by myself in British specimens, and that Bonaparte's differs so little from the 
 lowest numbers found by me that, considering the rest of his description and his figures, 
 there can be no doubt that the British specimens are of the same species as those 
 observed by him. I conclude, therefore, that Bonaparte was correct in his identifi- 
 cation, and that the British species of sole, described above, is the Solea lascaris of 
 Eisso, more completely described by Bonaparte under the same name. 
 
 Dr. Giiuther identified the Solea irnpar of Bennett, of which he possessed only the 
 original type specimen described by Bennett himself, with the Solea lascaris of 
 Bonaparte. But, after carefully examining the specimen and the descriptions myself, 
 I am unable to accept Dr. Giinther's conclusion. 
 
 In the British Museum Catalogue a single specimen is identified as the Solea lascaris 
 of Eisso. The chief peculiarities in Dr. Giinther's definition of this species are : the 
 small size of the scales, the formula being LI. 150; the narrowness of the body, the 
 height being one-third of the total length; and the prolongation of the upper jaw, 
 which is described as " produced into a longish lobe overhanging the lower." Of 
 these characters only the last corresponds to anything in Eisso's description ; but I 
 find that in my English specimens of the lemon sole, the upper jaw embraces the 
 apex of the lower somewhat more than in the common sole, and that in the 
 British Museum specimen the jaws do not differ to any appreciable extent in this 
 respect from the English form. What Eisso says on this point applies to the English 
 specimens. Eisso says nothing concerning the number of the scales nor of the 
 proportion of breadth to length in his lascaris. 
 
 The specimen which Giinther calls Solea lascaris came from Madeira ; the specimen 
 called Solea impar by Bennett came from the Atlantic coast of North Africa. Eisso's 
 Solea lascaris on the other hand, occurred at Xice, and Bonaparte's species is described 
 as common at Venice, at Nice, and on the Eoman shores. In the collections under 
 Dr. Giinther's charge there are specimens identified as Solea aurantiaca from Lisbon 
 and from Xice. Thus specimens of the same species as the English specimens have 
 been found at Xice, while the British Museum possesses no specimen identified with 
 Eisso's lascaris, or with Bonaparte's lascaris from any part of the Mediterranean. 
 
24 
 
 I will now shortly consider the question of the identification of the actual, specimens 
 catalogued by Giinther. In the single specimen he calls lascaris I could count only 
 133 rows of scales, a number not much larger than the maximum 125 found by 
 me in the English form. As for its narrowness, it had been forced into a bottle much 
 too narrow for it, and had in consequence been much compressed in breadth, so that 
 I think it is scarcely possible to be certain about its proportions. I do not consider 
 it to be specifically distinct from the Solea lascaris of Bonaparte. 
 
 Solea impar, Bennett, and Solea mar^aritifera, Giinther, must for the present be 
 considered distinct. They differ from English specimens of Solea lascaris in numerical 
 characters and also in colour. Both of them possess the marking characteristic of 
 vulgaris, that is to say, there are dark spots arranged as in vulgaris, not divided up 
 into small specks as in lascaris. Margaritifera is further distinguished by the con- 
 spicuousness of the small white spots in the type specimen in spirit. It may be found 
 in the future that English specimens of S. lascaris exhibit a range of variation which 
 would include both these species. 
 
 Moreau, in his "Poissons de la France," 1881, also identifies the Solea aurantiaca of 
 Giinther with the Solea lascaris of Eisso and Bonaparte, but he further includes the Solea 
 impar. Bennett, in the same species, although it is not clear from his description 
 whether he actually discovered by his own observation that the range of variation of 
 lascaris included the characters of impar. Francis Day, in his "Fishes of Great Britain 
 and Ireland," 1880-84, gives the same synonymy as Moreau. 
 
25 
 
 CHAFfEK V. 
 
 SOLE A VARIEGATA, FLEMING (DONOVAN). 
 [PLATE YH, FIGS, 1 AND 2.] 
 
 Synonymy. 
 
 ' Pleuronectes variegatus," Donovan, 1808, Xat. Hist. Brit. Fishes, pi. 117 
 1 Pleuronectes mangilli," Risso, 1810, Ichth. Nice, p. 310. 
 1 Rhombus mangili," Risso, 1826, Hist. Nat. Eur. Her., p. 255. 
 Variegated Sole," Yarrell, 1836, Brit. Fishes, first edition, p. 262, 
 
 Monoebirus variegatus," Thompson, 1839, Ann. Nat. Hist,, vol. ii, p. 404, 
 
 Solea mangilii," Bonaparte, 1841, Fauna Italica, t. iii, 27**. 
 
 Solea variegata," Fleming, Brit. Animals, p. 197 ; Giinther, Catal., iv, p. 469. 
 Variegated Sole," Couch, Fish. Brit. Isles, iii, p. 203, pi. 177. 
 Solea variegata," Giinther, 1862, Brit. 3/ks. Catal., vol. iv, p. 469. 
 Microchirns variegatus," Moreau, 1821, Puissons de la France, t. iii, p. 317. 
 Solea variegata," Francis Day, 1884, Fislies Gt. Brit, and Ire,, vol. ii, p. 43, pi. 108, 
 fig.l. 
 
 
 Males. 
 
 
 Females. 
 
 Total length j 
 
 17'2 cm. 17-9 cm. 
 6| in. 7 in. 
 
 18-3 cm. 
 
 7in. 
 
 19-1 cm. 19-7 cm. 
 7i in. 7| in. 
 
 19-9 cm. 
 7H- 
 
 20 cm. 
 7* in. 
 
 21 cm. 21 cm. 
 8 in. 8^ in. 
 
 Length "1 
 height J 
 
 3* 31 
 
 3i 3^ 3^ 
 
 3i 
 
 3J 
 
 3f 
 
 3i 
 
 Length "J 
 
 6* 6 
 
 6^ i 6 6 
 
 61 
 
 61 
 
 ^ 
 
 6i 
 
 head / 
 
 D 68 74 
 
 68 
 
 74 73 
 
 69 
 
 72 
 
 72 
 
 71 
 
 A 53 54 52 
 
 58 
 
 55 
 
 55 
 
 57 
 
 56 
 
 54 
 
 C 18 18 18 
 
 16 
 
 18 
 
 18 
 
 18 
 
 18 
 
 18 
 
 Pt 4r. 11. 5r. 11. 4r. 21. 
 
 4r. 11. 
 
 4r. 21. 
 
 4r. 11. 
 
 4r. 11. 
 
 5 r. 3 1. 
 
 4r. 11. 
 
 Pv 5 5 
 
 5 
 
 5 5 
 
 5 
 
 5 
 
 t) 
 
 5 
 
 L.I 89 93 
 
 90 
 
 92 88 
 
 89 
 
 89 
 
 104 
 
 87 
 
 Vert. ... 40 
 
 . 
 
 
 4L 
 
 40 
 
 THE above figures show that while the two preceding species cannot be separated 
 by the range of variation of the numbers of fin-rays in the dorsal and anal fins, the 
 
 E 
 
present species can be so separated from those two. The range for the dorsal fin-rays 
 in the above specimens is 68-74. Dr. Giintlier in his Catalogue gives 63-73, Day's 
 "British Fishes" gives 65-74: the total range recorded therefore is 63 to 74. Similarly 
 for the anal fin-ravs the ram?e in the above table is 52-58; Gttuther gives 53-57; Day 
 
 / 
 
 55-58, therefore the range in my table is the greatest recorded. Day gives the number 
 of caudal fin-rays as 15, evidently not counting the smaller external rays. Giinther 
 gives the scales of the lateral line as 85, Day as 85 to 90 ; the range in my specimens 
 is 87-104. The number of vertebrae is here again very constant, and forms a good 
 specific character, though it must be remembered that it is doubtful if it would serve 
 to distinguish this species from all other known species of Solea. The proportion of 
 breadth to length resembles that in vulgaris, and is therefore less than in lascaris, 
 while the proportion of head to length is usually less than in the other two species, but 
 does not form a marked specific character. 
 
 Fins. The dorsal commences slightly farther forwards than in the two preceding 
 species, the base of the first ray being actually nearer to the mouth than is the con- 
 tinuation of the longitudinal diameter of the dorsal eye. The right pectoral is much 
 larger than the left, but much smaller than the pectoral of the preceding species : its 
 length is contained 3 J to 4| times in the length of the head. The left pectoral is a 
 mere insignificant filament, never more than J in. long, sometimes much smaller : it 
 may contain one, two, or even three rudimentary fin-rays. 
 
 Eyes. The dorsal is only Jrd its own longitudinal diameter in front of the ventral, 
 and f rds of the same length from the edge of the snout. 
 
 Nostrils. The two on the right side are in the same position as in the preceding 
 species, but the posterior is smaller, and the anterior a more elongated tube than in 
 them. The two on the left side are situated as in S. vulyaris, but are smaller and less 
 conspicuous. 
 
 Mouth is much less curved downwards than in the two preceding species, the anterior 
 end of the cleft being slightly more dorsal than the angle of the cleft, while in the two 
 previous species it is considerably more ventral : the anterior end of the cleft is in fact 
 on the same longitudinal level as the lower border of the ventral eye, while in the 
 other two species it is considerably ventral to that level. The snout is more truncated 
 than in the other two species, the apex scarcely projecting beyond the anterior end of 
 the mouth-cleft. Two patches of rod-like teeth, as in the other species, on the left side. 
 The villi of the under side of the snout form short fringes at the edge of somewhat 
 broad membranous folds of the skin, which have a reticulate arrangement enclosing 
 quadrangular depressions of considerable size. This conspicuous reticulate arrange- 
 ment of fringed membranes forms a distinct contrast to the closely crowded filaments 
 in the two previous species (PI. VII, 2). 
 
 The scales are absolutely broader than in any of the other British species, the 
 breadth being almost equal to the length : they are also much larger in proportion to 
 the size of the body than in either of the two preceding species, as is evident from 
 
27 
 
 the number of lateral line scales given in the numerical table. A scale from the 
 middle of the body (PI. XIV, 3) has 26 rows of spines, the middle rows having 8 spines 
 each. 
 
 The posterior vertical portion of the curve of the lateral line on the right side of the 
 head can be detected with difficulty, but the anterior part parallel to the base of the 
 dorsal fin is wanting altogether. The branches of the lateral line system on the left 
 side of the head in the previous species are also invisible in variegata. 
 
 Colour. The general colour is much brighter than that of either of the preceding 
 species, being a distinctly reddish-brown with markings deepening to black. Of these 
 markings the principal are five broad dark transverse bands, each of which terminates 
 at either end in a large intensely black blotch situated partly on the side of the body, 
 partly on the longitudinal fin. The first of these bands passes across just behind the 
 pectoral fin, the others are at about equal distances, the last covering the ends of the 
 dorsal and anal fins and the base of the tail. The central part of each band is only slightly 
 darker than the neighbouring surface, but its anterior and posterior edges are usually 
 very sharply defined. The darkening of the bands is produced by the presence of a thin 
 black border at the edge of the scales, and the sudden extension of this black border 
 over the whole scale produces the black blotch at each end of the band. Between the 
 principal bands there are lighter areas which are again marked by one broad or two 
 narrow secondary bands : these also terminate in black patches, which in this case are 
 usually situated on the outer part of the fin and extend to its edge : these patches are 
 smaller and less regular than those belonging to the principal bands. There is a 
 single secondary band not very well defined passing over the operculum : the rest of 
 the head is almost uniform in colour. 
 
 The anterior part of the tail, behind the last of the principal dark bands, is lighter 
 than any other part of the body, its tint being yellow, while the rest of the tail is dark 
 brown, the colour being here chiefly situated in the membrane between the rays. The 
 tips of the dorsal and anal fin-rays are, as in the preceding species, opaque white. The 
 brightness of the red tint in the coloration fades considerably after death, approximating 
 more to grey. 
 
 What was said of the relation of the colour to the scales in the preceding species 
 applies to this species also, but to a less degree ; the extreme edge of every scale in the 
 lighter parts is brown, but each scale is everywhere more uniform in colour than in 
 mil gar is or lascaris. 
 
 This species is well marked, and has generally been recognised by ichthyologists 
 since its first discovery. It was first distinguished in England by Donovan, who 
 obtained a single specimen from the London market in 1807. He described and 
 figured it in his "British Fishes" under the name Pleuronectes variegatus as a nondescript 
 (new) species, although it has since been found that Duhamel had previously described 
 it in his " Poissons de la France " under the name Pole panachee. Donovan's coloured 
 figure is fairly good, but it represents the markings across the body as somewhat 
 
 E 2 
 
28 
 
 irregular interrupted stripes, instead of regular dark bands. It is possible that in 
 Donovan's specimen the markings were as he figured them, but I have never seen such 
 a variety of colouring, and it is more probable that in the single dead specimen from 
 the market he did not perceive the markings accurately. 
 
 The species was independently described as new by Eisso in his "Ichth. de Nice": that 
 his species is the same is evident from his accurate description of the colour and 
 markings and some other characters. He gave it the name Pleuronectes mangilii^ after 
 the surname of one of his contemporaries. In his later work, the " Hist. Nat. de 1'Europe 
 Meridionale," he calls the species Rhombus mangili. He gives no figure. 
 
 Yarrell, in his first edition, gives a description and a woodcut from a specimen from 
 Cornwall, but his figure looks as if it had been copied from Donovan's plate. Yarrell 
 incorrectly identified the species with the Solea lingula of Eondelet, the Linguatula of 
 Cuvier, a mistake which he afterwards corrected in his supplement. 
 
 Bonaparte gives an excellent description and a coloured figure of the species under 
 the name Solea mangilii, identifying it with Eisso's species. His figure beautifully 
 shows the dark transverse bands terminating at either end in black blotches which 
 extend on to the fins. 
 
 Gtinther in his Catalogue gave a complete and correct account of the synonymy 
 of the species ; his list of synonyms shows that the species has been described 
 independently at least four times, first as the Pole panachee by Duhamel, then as 
 PI. variegatus by Donovan, as PL microchirus by Delaroche, and as PL mangilii 
 by Eisso. 
 
 Moreau and Day give good descriptions of the species. The former gives no figure; 
 the figure of the latter is not good, it gives the markings very incorrectly. 
 
29 
 
 CHAPTER VI. 
 
 SO LEA LUTE A, BONAPARTE. 
 
 [PLATE VII, FIGS. 3 AND 4J 
 
 Synonymy. 
 
 " Solea parva sive lingula," Rondeletius, 1554, De Piscibus Marinis, xi, c. 15, p. 32, 
 
 with fig. 
 
 "La petite Sole," Rondelet, 1558, French edition. 
 " Pleuronectes luteus," Risso, 1810, Iclitli. de Nice, p. 312. 
 " Rhombus luteus," Risso, 1826, Hist. Nat. Eur. Mer., t. iii, p. 257. 
 " Solea lutea," Bonaparte, 1841, Fauna Italica, t. iii, p. 28. 
 
 " Monochirus minutus," Parnell, 1837, Mag. Zool. and Hot., vol. i, p. 527, pi. 16, No. 2. 
 " The Solenette," Yarrell, 1839, Brit. Fishes, first edit. Suppl., p. 36. 
 " Monochirus linguatulus," Thompson, 1839, Ann. Nat. Hist., vol. ii, p. 405. 
 " Solea lutea," Giinther, 1862, Cat. Brit. Mus., vol. iv, p. 469. 
 " Solea minuta," Giinther, 1862, ibid., p. 470. 
 
 
 
 Total length . 
 Length ~[ 
 
 Sex? 
 
 Male. 
 
 Female. 
 
 5'2 cm. 
 2^ in. 
 
 8i 
 
 4| 
 
 73 
 59 
 16 
 2 r. 11. 
 5 
 
 1V6 cm. 
 
 4^ in. 
 
 Q2 
 
 7'3 cm. 
 
 2|in. 
 
 3 
 
 5 
 
 73 
 53 
 16 
 4 r. 1 1. 
 5 r. 3 1. 
 62 
 
 ll'l cm. 
 
 4f in. 
 
 3 T * 
 
 5^ 
 
 69 
 55 
 18 
 4 r. 11. 
 5 
 66 
 37 
 
 height \ 
 Length I 
 head j ' ' 
 D 
 A 
 
 5 
 
 Cl 
 
 4 
 
 77 
 63 
 18 
 3 r. 11. 
 
 5 
 68 
 
 C. . . 
 
 Pt 
 Pv 
 
 L.I. . . . 
 
 Vert 
 
 
 THE above table includes the characters of only a very small number of specimens, as 
 I have not had an opportunity of examining more. The measurements of the total 
 length show that this is the smallest species of the five. The head is longer in 
 
30 
 
 proportion to the total length than in any of the other species; the proportion of 
 greatest breadth to length is about the same as in vulgaris and variegata. But the body 
 is considerably narrower towards the tail than in either of the other species. The range 
 for the dorsal fin-rays in the above specimens is 69-77 ; Day gives 65-72. The range 
 of number for the anal fin-rays in the above table is 53-63 ; Day gives 50 to 56. 
 Day gives the lateral line scales as 72 ; the range in my specimens was 62 to 68. 
 
 Fins. The dorsal fin commences nearer to the mouth than in any of the other 
 species ; the base of the first ray being on the very apex of the snout, on a level 
 longitudinally with the upper border of the ventral eye. The pectorals are as in 
 variegata rudimentary ; the right is contained about 4| times in the length of the head ; 
 the left is extremely minute. 
 
 Eyes. The dorsal is one-half its longitudinal diameter in front of the ventral and 
 less than its diameter from the edge of the snout ; they are very close together, the 
 distance between them equal to half the longitudinal diameter of either. 
 
 Nostrils on the right side in their usual position, the posterior short and small, the 
 anterior tubular and long ; on the left side similar to those of variegata. 
 
 Mouth strongly curved downwards as in vulgaris ; snout rounded as in that 
 species. 
 
 The villi on the lower side the snout are arranged in the same manner as in 
 variegata. 
 
 The scales absolutely are smaller than in either of the other species, though, as shown 
 by the number of scales in the lateral line, they are in proportion to the length of the 
 body larger than in the other species ; and they are not so broad in proportion to their 
 length as in variegata. One of the scales from the middle of the body has 2 1 rows of 
 spines, 4 spines in each of the middle rows (PI. XIV, 5). 
 
 No branches of the lateral line are visible externally on either side of the head. 
 
 Colour. It is curious that, although in the character of its pectoral fins and of the 
 villi of the lower side of the snout, this species closely resembles variegata, its markings 
 are almost the same as those of vulgaris. In other words, there is here no correlation 
 between the marking and other characters. 
 
 The ground colour of the right side during life is a dull reddish-brown. On this 
 ground there are dark brown spots arranged as in vulgaris ; there are three principal 
 longitudinal rows of these, of which the central row contains usually five spots, the 
 dorsal and ventral rows seven or eight. Alternating with the brown spots are light 
 blue ones representing the white spots of vulgaris. There are also two intermediate 
 longitudinal rows of dark spots. But the markings of the dorsal and anal fins differ 
 considerably from those of vulgaris ; these fins show no longitudinal bands of colour, 
 but numerous narrow transverse stripes, each sixth or seventh ray being coloured a 
 deep black ; the rest of these fins has a yellowish colour which is deepest towards the 
 base of the fins. The anterior part of the head is free from spots, the tail has a little 
 black at its middle third. 
 
31 
 
 This species was first recognised as distinct in Britain by Parnell, who described it in 
 the "Magazine of Zoology and Botany," Vol. I, 1837, under the name Monochirus 
 minutus. He believed that it had never been described before, and therefore gave it 
 the name minutus. placing it in Cuvier's sub-genus Monochirus. He gives a figure of 
 it, and mentions as its specific character that every sixth or seventh ray of the dorsal 
 and ventral fin is black ; he obtained his specimens at Brixhain from the trawlers. 
 W. Thompson in the " Annals of Natural History," Vol. II, 1839, identified ParnelTs 
 species minutus with that mentioned by Cuvier in the " Eegne Animal," under the name 
 Linguatula, which is the Solea parva slve lingula of Eondelet, Cuvier defines the 
 Monochires as those specimens of Solea in which the pectorals are minute, the left 
 being either very minute or altogether wanting. 
 
 I have consulted a French translation of Eondelet's original Latin work ; this trans- 
 lation is dated "Lion " (Lyons), 1558. The names here given are La petite Sole, and 
 Solea lingula, and though no characteristic specific features are mentioned in the 
 description, the figure given agrees very well in shape with specimens of the present 
 species ; this figure shows the left side of the fish, 
 
 Yarrell introduced a figure and description of Parnell's Monochirus minutus into his 
 supplement to the first edition of his " British Fishes," not having been acquainted with 
 the species when he published the book, 
 
 Parnell's species was described as distinct by Dr, Giinther in the British Museum 
 Catalogue, under the name Solea minuta from two specimens, one, a dried skin, from 
 Yarrell's collection, the other, stuffed and dried, from Brixham, 
 
 Moreau, in his "Poissons de la France," 1881, in describing Microchirus luteus, the 
 Solea lutea of Bonaparte, suggests by means of a note of interrogation that Solea minuta 
 is a synonym of that species, and Francis Day, in his '* Fishes of Great Britain and 
 Ireland," states without reservation that the two species are identical. 
 
 Dr. Giinther in his Catalogue describes one specimen of Bonaparte's Solea lutea. He 
 has informed me that he now considers the two species to be identical, and after 
 examination of English specimens and Mediterranean specimens of lutea at the British 
 Museum, and comparing them with the various descriptions, I have no doubt myself 
 that lutea and minuta are the same species. 
 
 This species was first described by Eisso, in his "Ichthyologie de Nice," under the name 
 Pkuronectes luteus, and his description is sufficiently accurate for its identification. 
 The same author, in his " Histoire Naturel de 1'Europe Meridionale," placed the species in 
 the genus Rhombus, calling it Hhombus luteus. Bonaparte, in his " Fauna Italica," gives 
 an excellent description, and two very good coloured figures. He describes the colour 
 of the body, apart from the fins, as a uniform golden yellow without spots, but in 
 Mediterranean specimens in the British Museum I found the markings which I have 
 described above in English specimens. 
 
32 
 
 CHAPTER VII. 
 
 SOLEA GREENII, GUNTHER. 
 
 " Solea Greenii," Giinther, 1889, Ann. Mag. Nat. Hist., vol. iv, No. 24. 
 
 Length Length 
 
 Sex, female. Total length, 19 cm. (7^ in.). hej g ht = over 3. hea( ^ = 6$. 
 
 D. 81. A. 67. C. 19. Pt. 4r. 21. Pv. 5. LI. 138. 
 
 THE above are the characters of a single specimen obtained by Mr. Bourne, Director of 
 the Plymouth Laboratory, by the trawl on board H.M.S. "Kesearch," on July 13, 1889, 
 in long. 49 5' N., lat. 11 14' W., at a depth of 217 fathoms. 
 
 The characters of the species are, as Dr. Giinther points out, intermediate between 
 those of vulgaris and variegata. The filaments on the under side of the head are 
 uniformly distributed as in vulgaris, but there is a series of transverse rows of such 
 filaments along the whole length of the lateral line on the lower side, a character I 
 have not seen in any other species. The pectorals are rudimentary as in variegata. 
 The cephalic curve of the lateral line runs backwards before turning forwards. In 
 colour the upper side is an almost uniform brownish-grey in spirit ; but there are 
 also dark blotches or large spots ; there are six of these along the dorsal edge of the 
 body and five along the ventral ; also two along the lateral line posteriorly ; these two 
 with two dorsal and two ventral spots form two almost continuous transverse bands ; 
 another interesting transition from vulgaris to variegata. The outer half of the 
 longitudinal fins has also a good deal of black pigment. 
 
 The ground where Mr. Bourne's specimen was taken was a fine grey sand containing 
 Foraminifera. Mr. Green also obtained only a single specimen from a depth of 
 150 fms. 47 miles west of Bull Eock off Balinskellys Bay. 
 
 Thus this species lives just beyond the 100-fathom line in that part of the Atlantic 
 which lies S.W. of Ireland. 
 
PART II. 
 
 MORPHOLOGICAL. 
 
CHAPTER I. 
 
 THE OSSEOUS SKELETON. 
 
 THE whole body of the sole is covered by the skin, which as everyone knows is so slightly 
 attached to the parts beneath it that it can be stripped off as a definite continuous 
 membrane. Beneath it is found the flesh, which consists of the muscles, by the 
 contraction of which all the movements of the fish are produced. The muscles are 
 attached to the bones which together form the skeleton. In the middle region of 
 the body on the ventral side is a cavity with smooth walls, within which are contained 
 the entrails, or viscera, consisting of the organs of digestion, excretion, and 
 reproduction. The principal organ of digestion is the digestive tube which leads from 
 the mouth and after various convolutions opens to the exterior again at the vent or 
 anus. The organs of respiration or gills are fringes supported on rods between which 
 are slits or clefts by which the cavity of the throat opens on each side into a gill 
 chamber. Each gill chamber again opens by a single aperture to the exterior. The 
 blood vessels ramify in the substance of all the organs now mentioned, but the heart 
 which keeps the blood moving in circulation is contained in a special cavity which is 
 separate from that containing the viscera. The skin and the membrane lining the 
 digestive tube become continuous with one another at the mouth and anus, and at the 
 gill-clefts. The nerves also ramify in the substance of the muscles and other organs, 
 but, excepting the sympathetic system, they all radiate from the brain and spinal cord 
 which are contained in a chamber on the dorsal side of the skeleton, the brain being 
 contained in the cavity of the skull, the spinal cord being enclosed by a series of 
 arches formed by processes of the spine. Some of the nerves convey the impressions 
 received by the senses to the brain, and may be regarded as proceeding from the sense 
 organs to the brain ; the principal sense organs are the skin, the eyes, the ears, and 
 the olfactory organs. The other nerves conduct impulses from the brain and spinal 
 cord to the muscles and other organs causing the former to contract and regulating 
 the functions of the latter. 
 
 The structure and relations of these various organs can be made most easily 
 intelligible by describing the skeleton first. 
 
 The Skull. The central part of the skeleton consists of the skull and the vertebral 
 column, the latter being composed of a longitudinal series of distinct bones, the 
 
 F 2 
 
36 
 
 vertebras : the skull here means the bony structure which contains the brain, and 
 supports the eyes, ears, and olfactory organs, and which remains as a united whole 
 when the soft parts of the head of the fish are removed by boiling or otherwise. The 
 form of the skull is shown by four drawings of it on Plate XI (Figs. 5-8). It consists of 
 two main portions. The posterior and larger portion has a somewhat cylindrical shape, 
 and encloses a cavity in which the brain lies in the entire fish, this is the cranial 
 portion ; the anterior or facial portion does not enclose a cavity, but may be said to 
 consist of three separate processes from the brain-case which unite together at their 
 anterior ends. One of these processes is (apparently) on the right side of the head of the 
 fish and separates the eyes from one another ; it may be called the interorbital septum, 
 the not very definite concavities on either side of it in which the eyes lie being the 
 orbits. 
 
 If the skull is placed in the position it occupies when the entire fish is held vertically 
 upright on its ventral edge, that is in the same position in which a symmetrical fish 
 swims, the cranial portion of the skull will be seen to be almost perfectly symmetrical 
 while no symmetry is visible in the facial portion. Comparing the cranial portion 
 with the corresponding part of the skull of a symmetrical fish, we can recognise in its 
 walls the same bones as in the latter, the walls being made up of these bones firmly 
 united at their edges. These edges are usually irregularly toothed so as to fit into 
 each other, and the lines of junction are called sutures. The sutures can be traced out 
 with care in the entire cranium, but where they are obscure the exact limits of the 
 component bones can be found by boiling the skull and pulling the separate bones away 
 from one another. The outlines of these bones are indicated on the figures of the 
 skull. The auditory organs in the entire fish are situated within the convex side walls 
 of the cranial portion, and the bones of this part have names with the suffix " otic," 
 implying their relation to the ear. 
 
 The back of the cranial portion is called in all vertebrates the occiput and the bones 
 of this part occipital bones. In this wall of the cranium is a large circular aperture, 
 the occipital foramen, through which the spinal cord is continued forwards into the 
 brain. Below the occipital foramen is a solid bone with a conical depression in its 
 posterior surface, this is the basi-occipital, and the depression marks the place where 
 the first vertebra is attached to the skull. At the sides of the occipital foramen 
 inferiorly are the two ex-occipital bones, ex.o., one on each side. Above these, reaching 
 to the upper edge of the foramen, are two large somewhat convex bones, the epiotics, ep.o. 
 On the dorsal surface of the skull there is in the centre a large median flat bone, the 
 supra-occipital, s.o., which in many vertebrate skulls extends to the edge of the occipital 
 foramen, but is here separated from it by the epiotics. On either side of the 
 supra-occipital is & parietal bone, pa. In either lateral wall of the cranium, adjoining 
 the edges of the ex-occipital, epiotic, and parietal, there is a somewhat large bone 
 having a rugged process projecting outwards ; this is the pier otic bone, pt.o. In front 
 of this is a slightly smaller square bone, the sphenotic, sp.o. Between the pterotic 
 
37 
 
 and the basi-occipital is a small square bone, the opisthotic^ op.o., and in front of this 
 below the sphenotic is the prootic, pr.o. 
 
 Adjoining the edges of both prootics and sphenotics, and attached behind to the 
 basi-occipital, is an elongated keeled bone which projects forwards to form the ventral 
 process of the facial portion of the skull : this is the parasphenoid, pa.s ; its posterior 
 portion forms the anterior part of the floor of the cranium. Attached to the ventral 
 surface of the parasphenoid is a bone which is elongated dorsally and projects 
 ventrally into a cylindrical knob ; this is the vomer, vo. The interorbital septum is 
 formed by the anterior processes of two bones whose flat posterior portions are nearly 
 symmetrical and form the anterior part of the roof of the cranium, attached behind to 
 the edges of the supra-occipital and parietals. These are the frontal bones, r.f., l.f. 
 These bones are, as compared with the corresponding bones of the skull of a 
 symmetrical fish, the most distorted of all the bones in the skull of the sole. In a 
 symmetrical fish the frontal bones are perfectly symmetrical, and their anterior parts 
 lie above and between the symmetrically placed eyes. In the sole also their anterior 
 processes are between the orbits, but have been twisted round through an angle of 
 90, so that the middle line of the dorsal surface of the cranium when produced 
 forwards does not pass between the frontal bones, but a line drawn in a longitudinal 
 direction over the right surface of the cranium, across the pteroic and sphenotic bones 
 does pass between their anterior processes. This shows that the dorsal eye of the sole 
 is really the left eye, and that the eyes and orbits with the interorbital septum have, 
 as compared with those of a symmetrical fish, been twisted round through an angle of 
 90 while the cranial portion of the skull remained stationary. Connecting the 
 inferior process formed by the parasphenoid and vomer with the interorbital septum 
 anteriorly is a single bone having a somewhat hooked process in front the mesethmoid^ 
 mes.e. Attached to the mesethmoid posteriorly on the left side, and joined also to the 
 parasphenoid, is a large flat bone concave towards the right, the left ectethmoid^ ect.e. 
 A posterior process of this bone unites with an anterior process of the left sphenotic to 
 form the third process of the facial region of the skull. The right ectethmoid is a small 
 ring-shaped bone attached ventrally to the anterior end of the frontals and to the 
 mesethmoid. 
 
 Between the origins of the three facial processes the cranial cavity opens anteriorly 
 by a wide aperture. There is a large round foramen in the left ectethmoid, leading 
 from the left orbit to the external surface of the facial part of the skull. On the upper 
 surface of the cranial portion there is a small foramen in the flat posterior portion of 
 each frontal bone, the left foramen being larger than the right. At the anterior and 
 inferior edge of each sphenotic bone there is a considerable indentation, which, with a 
 corresponding indentation in the edge of the parasphenoid, forms a large foramen, the 
 sphenotic foramen. That of the left side is twice as large as that of the right, and in 
 front of the former are two small foramina which are absent on the right side. 
 Through each prootic bone is a smaller foramen, the prootic foramen ; the left of these 
 
38 
 
 is a little larger than the right. In the posterior part of each opisthotic bone is a 
 minute opisthotic foramen. In each ex-occipital there is a considerable foramen 
 directed downwards, and behind this a minute foramen directed outwards. 
 
 It now remains to call attention to the form of the outer surface of the skull. The 
 pterotic process projecting outwards from the pterotic bone has already been 
 mentioned. A similar but longer and natter process projects from the sphenotic 
 bone above the sphenotic foramen ; these processes serve for the attachment of muscles. 
 Below these two processes are two smooth depressions in which are articulated the two 
 heads of the hyomandibular, a bone which is connected with the jaws and branchial 
 apparatus. In the centre of the supra-occipital bone is a somewhat elongated crest. 
 At each side of the dorsal surface of the skull posteriorly is another crest longitudinally 
 directed, formed partly from the pterotic, partly from the parietal bone : this may be 
 called the parietal crest ; the one on the right is larger than that on the left. These 
 crests also serve for the attachment of muscles. At the anterior part of the basi- 
 occipital bone are a pair of conical prominences with their broad bases downwards : 
 these are continuous with one another in the median plane. The left ectethmoid bone 
 sends off a curved process towards the right side. 
 
 The Vertebral Column. Any one of the vertebrae from the middle third of the spine 
 consists of a somewhat cylindrical central mass, the centrum, and two elongated 
 processes or spines, a dorsal and a ventral. The centrum has the form of two truncated 
 hollow cones placed with their narrower ends towards each other and united together 
 by a solid disc. The conical hollow at the anterior and posterior surfaces of each 
 centrum with the corresponding hollows of the adjacent vertebrae, enclose cavities 
 which are filled by an elastic gelatinous tissue. The lateral depressions at the right 
 and left sides of the centrum are each divided by a longitudinal ridge of bone. The 
 dorsal spine really consists of two hollow bony tubes which diverge at their bases, 
 where they are united with the centrum towards the anterior edge of its dorsal surface, 
 and which are united firmly together in the median plane of the fish's body for the 
 greater part of their length. The diverging legs of the spine form a pointed 
 arch, and through the series of these arches runs the spinal cord, which is thus 
 protected from pressure by the bony arches. The leg of the spine on each side of the 
 vertebra is expanded longitudinally where it joins the centrum, and in this expanded 
 part are two foramina, through which the ventral and dorsal roots of a spinal nerve 
 pass. The ventral spine of the vertebra has a similar structure, but the arch between 
 its legs is larger, and through the series of these arches run blood vessels. There are 
 50 vertebrae altogether, and the llth to the 50th have the structure now described. 
 The dorsal and ventral processes in all these are very long, four to five times as long as 
 the centrum. In the first of these vertebrae the spines are almost at right angles to 
 the centrum, but towards the posterior end they slope more and more backwards. 
 The spines increase in length slightly towards the centre of this region, and again 
 decrease slightly at the posterior end. The centra become longer and narrower 
 
39 
 
 towards the posterior end. Behind the last of these vertebras are bones which 
 terminate the vertebral column : these consist of a central fan-shaped bone, the anterior 
 end of which is shaped like the anterior part of a vertebra, and is connected with the 
 posterior face of the last vertebra by membrane, and two other flat bones, dorsal and 
 ventral to the central one. The central bone expands posteriorly in the median plane 
 of the body into a triangular plate, which is partially divided by radiating furrows into 
 a number of rods. These rods are known from their development to represent the 
 ventral spines of a number of vertebras fused together into the fan-shaped bone. The 
 flat bones dorsal and ventral to the fan-shaped bone are similarly divided, but are much 
 narrower : these are obviously also dorsal and ventral spines of the more anterior of 
 the vertebras represented by the fan -shaped bone. The rays of the caudal fin articulate 
 with the ends of these rods (PI. X). 
 
 The ten anterior vertebras differ considerably from the posterior 40. All of them 
 have dorsal spines except the first : these spines resemble those of the vertebras already 
 described, except that they become thicker and shorter and more inclined forwards 
 towards the anterior end. The dorsal spine of the second vertebra leans forward so 
 much that it is in contact with the posterior face of the skull. The fifth to the tenth 
 vertebras have ventral spines also, but these are of rapidly decreasing length from the 
 tenth to the fifth, and are also much inclined backwards. The first four vertebras 
 have no ventral spines. The second to the eighth vertebras, seven in all, bear very 
 slender short ribs which are not processes of the vertebrae, but separate bones which 
 articulate with the centra at the upper side of their lateral ridges. The first vertebra 
 is rudimentary : its centrum is very narrow antero-posteriorly, and it has two small 
 dorsal processes which lie along the front edge of the base of the dorsal processes of 
 the second vertebra, but do not unite to form a spine. 
 
 The centra of all these vertebras are united together in the following way. The 
 posterior face of each vertebra has, as we have seen, a conical depression or cavity : the 
 rim of this cavity is united firmly to the corresponding rim on the anterior face of the 
 succeeding vertebra by strong tough membrane, which is continued over the surface of 
 the vertebras, which is in fact part of the periosteal membrane. The closed cavities 
 formed by the juxtaposition of the conical depressions are filled by a firm elastic 
 gelatinous tissue which forms so many elastic pads between the centra. The connection 
 of the ex-occipital bone of the skull with the first vertebra is of the same kind as that 
 between adjacent vertebras. 
 
 Closely connected with the vertebral column is the system of bones which forms the 
 framework and support of the median fins. Placed like the vertebral spines in the 
 median plane of the body and extending outwards from the ends of those spines are a 
 great number of bones shaped somewhat like paddles. These are the interspinous bones. 
 Each consists of a long slender shaft and a broad head expanded in the median plane 
 They are placed with their shafts towards the vertebras, their heads projecting 
 outwards. The ends of the shafts lie alongside the ends of the spines of the vertebras 
 
40 
 
 in the intervals between the spines, hence the name of these bones. There are usually 
 two interspinous bones between two adjacent vertebral spines, never more than two, 
 but in many cases only one : one interspinous bone, in Fig. 1 on PI. X, has two shafts 
 to a single head, the end of a vertebral spine lying between the two shafts. In the 
 middle region of the body each interspinous bone has a small wing-like expansion on 
 each side of the shaft just below the head. On the dorsal side the interspinous bones 
 are perpendicular to the vertebral column at about one-fourth of the whole length 
 from the anterior end of the body : from this region to the tail they slope more and 
 more backwards ; from this region forwards they slope more and more forwards. In 
 front of the dorsal spine of the second vertebra there are three short stout interspinous 
 bones whose inner ends lie close to the middle dorsal line of the cranial portion of the 
 skull. In front of these is a large curved spine-shaped bone pointed at its outer end, 
 stout and blunt at its inner, which curves forwards almost parallel to the axis of the 
 skull. To the dorsal side of this bone are attached two short interspinous bones. 
 
 On the ventral side the interspinous bone in front of the ventral spine of the eleventh 
 vertebra is almost perpendicular to the vertebral column : from this point to the tail 
 region the interspinous bones slope more and more towards the posterior end. In 
 front of the same interspinous bone there is one other free interspinous bone slightly 
 inclined forwards, and in front of this is a stout curved cylindrical bone, which 
 terminates the series anteriorly and forms the posterior boundary in the median plane 
 of the main body-cavity of the fish. This cylindrical bone bears four shortened 
 interspinous bones which are inclined forwards and are successively shorter arid shorter, 
 the most anterior being merely a small head without a shaft. 
 
 The fin-rays of the dorsal and ventral median fins, of the dorsal fin and anal fin as 
 they are usually termed, are not articulated directly with the outer ends or " heads " 
 of the interspinous bones : to these heads are attached a series of nodules of cartilage, 
 elongated from before backwards, and somewhat cylindrical in shape. Except in a 
 certain region each of these nodules is situated between two adjacent heads of 
 interspinous bones, attached to both of them. The region excepted is the anterior 
 part of the dorsal series, where one nodule is attached separately to each head. 
 
 The fin-rays have the following structure. Each ray is compound and constructed 
 somewhat in the same fashion as a vertebral spine. It consists of a right and left half, 
 which are separate and divergent at their inner ends, attached together in the median 
 plane of the fish for the outer seven-eighths of their length. The divergent ends embrace 
 one of the cartilaginous nodules previously described, bestriding it as a man bestrides a 
 saddle, and are attached to it by fibrous membrane in this position. One of the halves 
 of the fin-ray thus belongs to the right or coloured side of the fin, the other to the left 
 or white side. In consequence of the mode of attachment described, the fin-ray can 
 only move on the cartilaginous nodule backwards and forwards : as a matter of fact 
 its motion is limited between a position in which it is perpendicular to the longitudinal 
 axis of the fish, and a position in which it lies inclined backwards from its attached 
 
41 
 
 base, and almost parallel to the axis of the fish. The outer part of the fin-ray formed 
 of the two united lateral halves bifurcates in an ant ero- posterior direction into two 
 divergent branches. Thus the outer half of the fin-ray consists of two diverging 
 branches both in the plane of the fin, cne anterior and one posterior, but each of these 
 is made up of two lateral halves glued as it were together lengthwise. Thus if a fin- 
 ray is separated, and a knife passed between the diverging right and left legs of the ray, 
 the whole ray can be easily divided into a right half ray and a left half ray, and each 
 of these is forked at its outer half length into two branches. The basal portion of the 
 fin ray is solid, but the outer five-sixths, including the two forked branches, consist of 
 a series of short cylindrical bony pieces united by flexible membrane. Thus the outer 
 part of the fin-ray resembles somewhat the series of vertebral centra on a small scale 
 and without the spines, if we suppose the series of centra after being single for a 
 certain length to branch into two series having the same structure. 
 
 The tail fin-rays resemble those of the dorsal and anal fins in general structure, but 
 are more branched : in them each of the two original branches divides again into two, 
 and some of these again into two : the branching of the ray is always dichotomous, 
 that is. a branch when it divides splits only into two smaller branches, but of the four 
 secondary branches all do not always divide : thus the fin-ray terminates in seven or 
 eight branches spread out like a fan. The caudal fin-rays are not in connection with 
 either interspinous bones or cartilaginous nodules, but are articulated directly to the 
 terminal bones of the vertebral column, and to the spines of the last vertebra. 
 
 The skeleton of the paired fins is closely related to that of the branchial region and 
 will be described in connection with it. 
 
 The Jaws and Branchial Arches. 
 
 We have now to consider the bones of the jaws and branchial arches, and other 
 bones connected with the skull. The more superficial of these bones are shown in 
 Figs. 1 and 2, PI. XI. The bones of the right side, Fig. 1, differ considerably in size 
 from those on the left, although in their relations the bones of the two sides correspond 
 to one another. The bones of the right side are as follows. The two sockets in the 
 side of the cranial portion of the skull, in the pterotic and sphenotic bones, contain 
 the two rounded heads of a flat elongated bone which extends downwards and 
 somewhat forwards. This is the hyomandibular , hm. To the lower end of this bone is 
 attached a system of flat bones which projects horizontally forwards into a smooth 
 knob with which the lower jaw is articulated, and sends off upwards and forwards a 
 flat band of bone, the end of which is acrain attached to the skull at the side of the 
 
 c 
 
 vomerine projection. At the posterior border of the hyomandibular and the system 
 of bones just mentioned is a crescent-shaped bone, which is firmly attached to the 
 others and acts like a splint, binding them rigidly together. This is the preopercular, po. 
 The separate bones of the system connected with the lower end of the hyomandibular 
 
 G 
 
42 
 
 are as follows. Directly attached to the end of the hyomandibular is seen the end of 
 a bone which passes downwards beneath the preoperculum out of sight, and is 
 connected with the system of branchial arches which occupy a deeper position. This 
 is the stylohyal. Anterior to this is a flat bone which projects into the quadrate in its 
 under surface, this is the symplectic, s. Dorsal to this is a flat somewhat concave bone 
 with a triangular outline, the metapterygoid, mt. The triangular bone, which is at the 
 anterior end of the series, and which supplies the rounded head to which the lower 
 jaw or mandible, m., is articulated, is the quadrate, q. Eunning upwards from the 
 quadrate dorsally are a pair of splinter-like bones, the anterior of which is the 
 pterygoid, pt., and the posterior the mesopterygoid, ms. Connecting these with the 
 skull at the side of the vomerine process is the palatine, pa. It will be seen that all 
 these bones are somewhat larger on the left side, Fig. 2, than on the right, Fig. 1. 
 The superiority is especially well marked in the pterygo-palatine bar, which is broad 
 and strong on the right, narrow and delicate on the left. 
 
 Attached to the posterior edge of the hyomandibular and preopercular is the oper- 
 culum, which is chiefly composed of the three bones,o.,io., so. : these are the opercidar, o., 
 which is articulated to a knob projecting downwards on the posterior side of the 
 head of the hyomandibular, the inter opercular, i.o., and the sub-opercidar, s.o., which 
 are only held in their places by the fibrous tissue of the operculum. The lower jaw 
 is called the mandible, which consists of three bones, the articular, angular, and dentary, 
 fitted and firmly united together : the upper jaw consists of two bones, the maxilla, x, 
 and the premaxilla, p x. All these bones are much smaller on the right or upper side 
 of the head than on the left or lower ; this is especially true of the maxilla and 
 premaxilla which, as the figures show, are almost rudimentary on the right side, and 
 very large on the left. On the left side the maxilla is entirely excluded from the edge 
 of the lip ; on the right side its posterior process forms part of that edge. The 
 mandible on the right side has the form of an elongated bar, on the left side it is a 
 broad triangular stout plate, the dorsal edge of which is strongly convex and bears a 
 patch of rod-like teeth, biting against a concave larger patch of similar teeth in the 
 premaxiila. On the left side the end of the premaxilla articulates with a knob on the 
 mandible, an arrangement which makes the bite much more effective ; on the rio-ht side 
 there is no such articulation. The two mandibles are firmly united together anteriorly 
 in what is called the symphysis of the mandibles. The anterior ends of the maxillse 
 and premaxillae are all firmly united together and to the lower side of the mesethmoid 
 bone by fibrous membrane. 
 
 If we now dissect away all the bones above described except the Iryomandibular, 
 we find the bones of the branchial apparatus lying beneath them as shown in Plate XI, 
 Fig. 3, from the right side. The gills themselves are vascular fringes which project 
 outwards and backwards from a series of bars ; between these are the clefts by which 
 the water passes from the cavity of the throat to the gill chamber and so to the exterior. 
 These bars are called the branchial arches, from their curved shape, and each bar is 
 
43 
 
 supported by a series of bones called a (bony) branchial arch. The first of these arches 
 is different from the rest, and is called the hyoid arch. It is attached to the end of the 
 hyomandibular, and consists of, 1st, the small cylindrical bone, marked 2 in the figure, 
 and called stylo-hyal ; next, two broad stout bones placed end to end, 3 and c.h. in the 
 figure, the epi-hyal and cerato-hyal; and finally, two cubical bones placed side by side, 
 the hypo-hyals, h.h. Between the hypo-hyals of the opposite sides is inserted a bone 
 which is flattened in the median plane of the fish's body : this is usually called the 1st 
 basi-braitcJilal, although in the sole it is connected only with the bones of the hyoid 
 arch. Above it is a cylindrical bone called the basi-hyal or entoglossal, b.h. 
 
 Attached to the lower edge of the epi- and cerato-hyals are a series of long bones like 
 curved spines, 3 to thje epi-hyal, and 4 to the cerato-hyal. These are the branchiostegal 
 rays, and they support a curved membrane which extends inwards from the inside of 
 the lower edge of the operculum, and in ordinary respiration closes the lower part of 
 the opercular aperture. 
 
 The 1st branchial arch is composed of a chain of bones of which the most dorsal 
 attached to the side of the keel of the parasphenoid bone is the pharyngo-branchial, 8, 
 next to this is the epi- branchial, 9 : these two are directed downwards and outwards, but 
 the cerato-branchial, c.b. 1, which succeeds, passes inwards and forwards; it is followed by 
 the hypo-branchial, which is joined to the median 2nd basi-branchial, b.b. 2. The other 
 arches, four in number, exhibit a similar plan of structure, but the last is much reduced. 
 The pharyngo-branchials of the 2nd, 3rd, and 4th arches are not styliform, like that of 
 the first, but are broad and flat ; the 3rd and 4th are fused together, the 2nd is united 
 to them, and all three bear teeth on their lower surfaces and form together the upper 
 pharyngeal bone. The second hypo-branchial is articulated with the third basi- 
 branchial, and the third hypo-branchial conies into slight connection with the posterior 
 end of the same median bone. The two hypo-branchials of the fourth pair of arches 
 are fused together to form a rhouiboidal cartilage in the middle line behind the third 
 basi-branchial. The fifth arch is represented only by a cerato-branchial on each side, 
 which meets its fellow in the middle line ; these two bones bear teeth on their upper 
 surface, and being situated in the ventral wall of the throat they bite against the upper 
 pharyngeal teeth, forming a second masticatory apparatus; these bones of the fifth 
 arch are usually called the lower pharyngeals. The relations of the hyoid and branchial 
 arches of the opposite sides are shown in Plate XI, Fig. 4 where they are seen spread 
 out with their internal surfaces upwards. 
 
 The pectoral and pelvic fins on each side are attached to the posterior border of a 
 bony arch which extends froni the back of the skull downwards, curving first back- 
 wards and then forwards, and meeting its fellow of the opposite side at the ventral 
 edge of the body. This bony arch forms the posterior border of the opercular cleft. It 
 consists of the following bones : & post-temporal, 25, Fig. 3, which is forked anteriorly and 
 attached by membrane to the posterior wall of the skull, the upper branch of the fork 
 being connected with the epiotic, the lower with the opisthotic ; a supra-clavicle, 26, an 
 
 G 2 
 
44 
 
 elongated bone joined on to the lower end of the post-temporal, a clavicle, 27, which curves 
 forwards, and is shaped like a trough the cavity of which is posterior, the trough being 
 V-shaped in section. The clavicle is connected at its lower end, in the median ventral 
 line, with its fellow of the opposite side. 
 
 The pectoral fin is supported by a flat basal plate attached within the upper part of 
 the trough of the clavicle ; this plate consists of two bones united by cartilage ; the 
 upper of these, 29, is the scapula; the lower, 30, the coracoid. The pectoral fin-rays 
 are articulated to the posterior cartilaginous edge of this basal plate directly as the 
 caudal fin-rays to the fan-shaped terminal bone of the vertebral column. 
 
 The pelvic fin is similarly supported by a triangular single bone, 31, which is attached 
 to the lower end of the clavicle. It is usually called the pubic bone, though it is 
 probably homologous, not with any part of the pelvic arch of Elasmobranchs, but 
 with the basal cartilages of the pelvic fin in those forms. 
 
 A flat bone in the median plane extends forwards from the junction of the clavicles 
 to the lower edge of the first basi-branchial. This bone, marked 28 in Fig. 3, has been 
 called the urohyal by Huxley, basi-branchiostegal by Parker, but has really nothing 
 to do either with the hyoid arch or the branchiostegal membrane ; it is better to call 
 it simply the jugular bone. Posteriorly it sends off a pointed ventral process, while 
 the anterior three-fourths of it form a band of uniform width. 
 
45 
 
 CHAPTER II. 
 
 THE FIBROUS MEMBRANES AND MUSCULATURE. 
 
 The Fibrous Membranes. 
 
 ALL the bones of the skeleton now described are bound together by strong fibrous 
 membranes. In the median plane a tough membrane of this kind extends from bone to 
 bone everywhere except in the median visceral cavity, so that the whole body of the fish, 
 excluding the region of this cavity and the ventral region of the head, is divided into 
 two lateral similar halves by a continuous partition consisting of a tough membrane 
 supported by the bony framework. The structure of this partition in fact resembles 
 that of one of the screens often used in our rooms to keep off draughts, the bones 
 corresponding to the wooden framework, the membrane to the canvas stretched over 
 it. But there is in the organic structure a more intimate connection between the 
 fibrous membrane and the bony framework. Every bone is clothed externally by a 
 tough fibrous membrane, the periosteum, and this is actually continuous with the 
 membrane which connects the bones together. The whole structure is as it were a 
 continuous deposit in which certain parts have been differentiated by the deposition 
 of calcareous compounds and structural modification to form bone. Yet, tough and 
 strong as the fibrous membrane is in its natural state, firm as it is found to be when 
 the muscles are dissected away in the dead fish, if the fish is boiled for a short time it 
 dissolves, and the bones all fall asunder. The reason of this is that the basis of the 
 material of which the fibres consist is gelatine, and therefore though they retain their 
 strength and structure during life, or in cold water, when subjected to the action of 
 boiling water their structure is destroyed and they become simply a mass of soft liquid 
 jelly. 
 
 The median fibrous membrane is continuous laterally with other membranes which 
 are placed at right angles to it and connected with the vertebrse and interspinous 
 bones. These lateral membranes run between the various muscles, which are attached 
 to them, and externally become continuous with the derma, or deeper fibrous layer of 
 the skin. The principal of the lateral membranes on each side runs longitudinally 
 along the centre of the vertebrae from the skull to the tail, and extends outwards to 
 the skin, thus dividing the muscles of each side of the body into a dorsal and a ventral 
 
46 
 
 half. Shorter membranes transverse to this divide the muscles again into a series of 
 oblique flakes which are seen separating from one another in a boiled fish brought to 
 
 table. 
 
 In a symmetrical fish the median skeletal partition formed by the vertebras and 
 their spines and the interspinous bones terminates at the back of the skull, but in the 
 sole it is extended still further anteriorly over the dorsal side of the skull to the 
 extremity of the snout. The attachment of the membrane to the skull runs at first 
 along the median dorsal line of the skull, that is, the morphological median line, but 
 anteriorly it runs to the left of this line. It crosses the base of the left frontal bone 
 and is continued along the edge of the large left ectethmoid and finally to the left edge 
 of the mesethmoid. Thus, morphologically, the median skeletal partition is continued 
 forwards on the left side of the facial region ventral to the left eye, though actually 
 the anterior continuation is in the same plane as the main part of the partition. This 
 anterior continuation is of course due to the anterior development of the dorsal fin 
 which is supported by it. 
 
 Musculature. 
 
 A general view oi the muscles of the right side of the sole is given on Plate XII. 
 The white parts in that drawing represent the white tendinous membranes, excepting 
 some of the bones of the head which are smoothly shaded, and the fin-rays : the 
 shading of fine lines indicates the muscles, the lines being drawn in the direction of 
 the muscle-fibres. The principal muscles of the body are the great lateral muscles, 
 one dorsal and one ventral, separated from one another by the longitudinal fibrous 
 membrane already described as projecting from the centra of the vertebrae outwards 
 to the skin. Each lateral muscle consists of a longitudinal series of folded plates or 
 segments, separated from one another by the transverse membranes previously 
 mentioned. The fibres in the muscle-segments run in an antero-posterior direction 
 parallel to one another, and are attached at each end to the transverse membranes, or 
 to the bones and membrane in the median plane of the body. The transverse fibrous 
 membranes have a curious folded and twisted arrangement. The outer edge of each, 
 as can be seen from the illustration, has the form of the letter S. Starting from the 
 longitudinal lateral membrane it curves first anteriorly, then posteriorly, and finally 
 runs anteriorly again, thus forming two curves in opposite directions and a larger outer 
 portion running obliquely forwards. The membrane itself is deeply hollowed 
 forwards in the region of the first curve, backwards in that of the second, so 
 t* .at the inner edge of the membrane instead of being S shaped is Z-shaped. This 
 inner edge of the transverse membrane is attached to the median bones and membrane 
 in the following way : it runs first along a vertebral spine for a short distance, then 
 suddenly turns off at an angle and runs directly backwards till it reaches the next 
 spine behind, along which it runs outwards (dorsally or ventrally) for some distance, 
 
47 
 
 and then again leaves that spine and runs obliquely forwards. Thus each transverse 
 membrane is attached by its inner edge to two adjacent vertebral spines at different 
 parts of its length, and along the rest of its length is continuous with the median fibrous 
 membrane which extends between the spines and the interspinous bones. 
 
 The anterior segments of the dorsal lateral muscle are much elongated and bent 
 forwards, so that their separating membranes are attached to the dorsal surface of the 
 skull, the anterior interspinous bones and the membrane connecting the latter. 
 
 The anterior segments of the ventral muscle covering the visceral region are straighter 
 than the posterior, and the inner edges of the dividing membranes are not attached to 
 any firm skeletal structure, but simply to the fibrous membrane which encloses the body- 
 cavity, the peritoneal membrane. The ventral part of the ventral lateral muscle on 
 each side is also separated from the median skeletal partition by the posterior prolonga- 
 tion of the body-cavity. 
 
 The posterior muscle-segments, in correspondence with the greater backward slope 
 of the vertebral spines, are folded to a much greater extent than the anterior. The 
 terminal segments form a system of muscles which are attached to the bases of the 
 caudal fin-rays. 
 
 It follows from the description that in each lateral muscle there are as many muscle 
 segments as there are vertebrae, and that each dividing membrane corresponds to a 
 vertebra Thus the muscle segments themselves correspond to the junctions between the 
 vertebral centra, an arrangement which allows the vertebral column to be bent in all 
 directions by the action of the lateral muscles. It is clear that, although it is difficult to 
 understand in detail the effect of the complicated attachments above described in the 
 contraction of the muscles, the general effect of the contraction of the lateral muscles of 
 one side is to bend the body powerfully towards that side, and it is by this alternate 
 bending of the body first to one side then to the other that the sole swims through the 
 water when it rises from the bottom, or swims along the bottom. The lateral muscles 
 form the bulk of the edible portion of the fish. The lateral muscles of the left or lower 
 side do not differ in any important respect from those of the right. 
 
 The other muscles of the sole are the muscles of the fins and the muscles of the 
 ventral region of the head, and the eye muscles. 
 
 The muscles of the longitudinal fins are well developed and important. The caudal 
 fin-rays are, as has been mentioned, moved by muscles which represent the terminal 
 muscle segments of the lateral muscles. The dorsal and anal fin-rays are moved by two 
 distinct systems of muscles. One system serves to erect the rays and to depress them 
 by causing them to slope backwards till they are almost parallel to the edge of the 
 body. The other system moves the rays away from the median plane, either to the right 
 side or to the left (upwards or downwards in the natural position of the sole). The 
 muscles of the former system may be called the elevators and depressors of the fin-rays, 
 those of the other the right and left abductors. The abductors of the fin-rays are 
 superficial, lying immediately beneath the skin ; there is a single muscle on each side 
 
48 
 
 to each ray. These muscles take their origin from the fibrous tissue which covers the 
 lateral muscles and which is continuous with the fibrous layer of the skin. Each 
 muscle is inserted into the side of a fin-ray outside its articulation, but the end of 
 the muscle also has connections by means of fibrous tissue with the ends of the 
 interspinous bones. 
 
 The elevators and depressors lie beneath the abductors : there is one elevator and one 
 depressor on each side of the body to each fin-ray. In the greater part of the fins the 
 heads of the interspinous bones are between the bases of the fin-rays, and each 
 elevator lies along the posterior half of the side of an interspinous bone, while each 
 depressor lies along the anterior half. These muscles are considerably smaller than 
 the abductors. They are inserted into the bases of the fin-rays in front and behind and 
 take their origins from the surface of the interspinous bones and intermediate fibrous 
 membrane. Their inner ends extend beneath the outer edges of the lateral muscles, 
 which are free. The elevators and depressors of the fin-rays are shown in Plate XII. 
 along the whole of the ventral side of the body and the anterior part of the dorsal 
 side, while the abductors are shown along the posterior three-fourths of the dorsal side. 
 
 The muscles of the rays of the pectoral and pelvic fins are closely similar and require 
 no special description. 
 
 The muscles of the ventral region of the head may be classified according to their 
 functions into two divisions the masticatory and the respiratory, the former moving 
 the jaws, the latter the branchial arches. 
 
 The most powerful of the masticatory muscles is the common jaw muscle, which 
 partly corresponds to the temporal and masseter muscles in man. Its origin occupies 
 the outer surface of the " suspensorium," i.e., the system of bones to which the 
 mandible is articulated, and part of the surface of the skull. It consists of two portions, 
 a superficial and a deeper, the former arises from the hyomandibular and the anterior 
 edge of the preoperculum, and from the anterior part of the sphenotic, and from the 
 basal portion of the right frontal ; the deeper portion is smaller and arises from the 
 metapterygoid, symplectic, and quadrate. Between the two portions runs a large nerve, 
 the mandibular branch of the fifth cranial nerve. Both portions of the muscle on the 
 right side of the head terminate in a tendinous structure which divides into two 
 tendons, the upper is longer and thinner and is inserted into the middle of the posterior 
 edge of the maxilla, the lower is shorter and broader and is inserted into the upper edge 
 of the mandible, chiefly into the articular bone, a little in front of the articulation of 
 the mandible with the quadrate. It is evident that the chief function of this muscle is to 
 bring the jaws together, which it does principally by powerfully pulling the mandible 
 upwards, while its upper tendon draws the upper jaw downwards and backwards. The 
 muscle on the left side of the head is somewhat larger than on the right, and is inserted 
 only into the mandible, the tendon passing to the maxilla being entirely absent. 
 
 The levator suspensorii is a muscle which arises from the sphenotic, especially from 
 the lateral process of that bone, and is inserted into the head of the hyomandibular. 
 
49 
 
 The depression of the lower jaw is effected by the paired geniohyoid muscles, each 
 of which arises from the external surface of the hypohyal and ceratohyal, and is 
 inserted into the inner surface of the symphysis of the lower jaw, that is to say, of the 
 junction between the two mandibles of opposite sides. 
 
 From the lateral surface of the parasphenoid passes on each side a broad band of 
 muscle outwards to the hyomandibular and pterygoid bones : these are the palatal 
 muscles which constrict the cavity of the mouth in swallowing. 
 
 Behind the last there are other transverse muscles passing from the side of the skull 
 to the inner surface of the hyomandibular and operculum. 
 
 A strong broad transverse muscle passes from the inner surface of one mandible 
 anteriorly to the inner surface of the other ; this is the musculus transversus inandibulce. 
 It lies immediately beneath the skin of the floor of the mouth, and assists considerably 
 in the biting action of the mandible of the left side. 
 
 Most of these muscles, although chiefly concerned in seizing and swallowing food, are 
 also used in inhaling water through the mouth for respiration. The following muscles 
 connected with the branchial arches are almost entirely respiratory. 
 
 The most superficial of them is the levator opercuU, which rises from the ridge and 
 process of the pterotic and is inserted into the head and upper edge of the operculum : 
 it raises the gill- cover. 
 
 The gill-arches are raised in inspiration by the levatores arcuum branchialium, which 
 arise from the inner side of the articulation of the hyomandibular bone with the prootic 
 and opisthotic, and are inserted into the outer surfaces of the bony branchial arches, 
 into the epi -branchial bones. 
 
 Internal to the last are other muscles which pass from the inferior conical process of 
 the basi-occipital to the pharyngobranchials of the 2nd, 3rd, and 4th branchial 
 arches, that is, to the superior pharyngeal bones. The first pharyngobranchial bone, 
 which is small and slender, lies along the side of the posterior end of the parasphenoid, 
 to which it is connected only by connective tissue. 
 
 A powerful muscle posterior to the last passes from the lower surface of the anterior 
 vertebrae forwards to the dorsal surface of the superior pharyngeal bones : this muscle 
 retracts those bones, and is therefore inspiratory. 
 
 On each side two muscles arise from the anterior surface of the clavicle and pass 
 upwards and forwards to the posterior surface of the inferior pharyngeal bone. As 
 this latter bone is destitute of gills, and all the gill clefts lie in front of it, its retraction 
 assists to open these clefts : these muscles are therefore inspiratory. 
 
 Expiration is effected by all the muscles which constrict the cavity of the mouth and 
 throat, the jaws being shut first. In addition to some of those already mentioned the 
 following, which bring the branchial arches into contact with one another, are expiratory. 
 
 Transverse muscles between the two inferior pharyngeal bones, and betwe-en the 
 cerato-branchials of the 4th branchial arch. 
 
 Transverse muscles between the superior pharyngeal bones. 
 
 H 
 
50 
 
 A strong flat muscle on each side which arises from the lower end oi the clavicle 
 and is inserted into the sides of the jugular bone. 
 
 Small muscles between the upper and lower extremities of the branchial arches. 
 
 The eye muscles in the flat fishes are of special interest on account of the peculiar 
 distortion of the eyes which these fishes exhibit. 
 
 The eye muscles in the sole consist, as in symmetrical fishes, of four recti muscles 
 and two oblique. The recti pass obliquely forwards from the back of the orbit to the 
 outer surface of the eyeball, to which they are attached at equal distances ; in a 
 symmetrical fish, as in every other vertebrate, one is attached at the dorsal side, one at 
 the ventral, one to the anterior, and one to the posterior : these are respectively 
 named the superior and inferior, internal and external, recti. In the sole the superior 
 rectus is uppermost in the natural position of the fish, having followed the torsion of 
 the orbits without altering its position in relation to the interorbital processes of 
 the frontal bones. Similarly the internal rectus of each eye is next to the interorbital 
 septum. The superior and inferior recti of each e} 7 e are much thicker than the 
 internal and external. All the recti of both eyes take their origin from the internal 
 surface of the parasphenoid bone, within the cavity of the skull, but below the anterior 
 part of the brain. 
 
 Of the two oblique muscles of each eye that which is nearest to the interorbital 
 septum is the superior, the other the inferior. Their direction is transverse to that of 
 the recti muscles. The superior passes outside the end of the internal rectus, and is 
 inserted into the eyeball between the insertion of that muscle and that of the superior 
 rectus. The inferior oblique passes outside the end of the inferior rectus, and is 
 inserted between the insertion of that muscle and that of the external rectus. The 
 origins of the oblique muscles in the sole and their direction are extremely peculiar and 
 interesting. In a symmetrical fish the origins of these muscles are on the inner sides 
 of the orbits, that is, on the side towards the median plane of the head. The median 
 plane of the head in the sole is morphologically represented by the bony interorbital 
 septum ; the oblique muscles of the ventral eye in the sole do arise from the interorbital 
 septum, those of the dorsal or right eye do not. The superior oblique of the ventral 
 eye arises from the small left ectethmoid which is on the right edge of the interorbital 
 septum ; the inferior oblique arises from the external surface of the parasphenoid 
 below the right ectethmoid. But both oblique muscles of the left or dorsal eye arise 
 from the inner surface of the left ectethmoid, which is not part of the interorbital 
 septum. The origin of the muscles is just outside the olfactory foramen. The surface 
 from which the muscles spring looks to the right side of the sole, or, in the natural 
 position of the sole, directly upwards. Thus the direction of the oblique muscles of 
 the dorsal (left) eye of the sole "is at right angles to the direction of those of the ventral 
 (right). In fact, though the right ectethmoid bone has been shifted from its original 
 position in the symmetrical fish to a very remarkable degree, the left ectethmoid is in 
 tho fame position : it has been rotated but not shifted in position. The surface of the 
 
51 
 
 left ectethmoid. to which the oblique eye muscles are attached, originally looked 
 outwards to the left ; now it looks upward, and it has become increased in size. 
 Moreover, the left ectethmoid is still on the left side of the head, where it was 
 originally before the distortion commenced. Another important fact is that the 
 oblique muscles of ihe left eye are somewhat larger and stronger than those of the 
 right. 
 
 These facts seem to me to have an important bearing on the question of the evolution 
 of the sole and other flat fishes, of the process by which the peculiar asymmetry which 
 characterises them was produced. All zoologists are evolutionists now, and it is 
 generally admitted that the flat fishes are descended from remote ancestors which 
 were symmetrical throughout their lives. This is sufficiently evident from the fact 
 that all flat fishes when first hatched, and for some time afterwards, are at the 
 present day perfectly symmetrical. But two entirely opposite views are at present 
 held by different zoologists as to the process of evolution. One school of evolutionists 
 goes bevond Darwin in one direction, the other in another. The former school believe 
 
 / ' 
 
 that although the conditions of life and the habits of an individual animal do affect 
 its structure, modify it in various ways, these modifications are never inherited and 
 cannot therefore have anything to do with the process of evolution. All evolution 
 according to this view is due to the natural selection of variations which are an 
 advantage to the individuals in which thev occur, and these variations are all due to 
 
 / 
 
 causes existing before the development of the individual. Such variations are called 
 congenital, and are inherited usually by the offspring of the individuals which 
 possess them, and usually develop to a still greater degree in the offspring of two 
 parents who both possessed them. These variations are entirely independent of 
 the habits or conditions or the use and disuse of organs. Such evolutionists explain 
 the distortion of the eyes in flat fishes in this way. A certain species of fish in remote 
 ages found it necessary to lie on the bottom ; among the individuals of this species 
 some had eyes which were very slightly asymmetrical, the lower eye being slightly 
 nearer the edge of the body than in the other individuals. Consequently these 
 individuals being able to see more than the others lived longest, escaped their 
 enemies^ and left most offspring. As they bred together, and as variations again 
 occurred, some of these offspring had the lower eye still nearer to the edge of the 
 head, and these survived while the others perished, and so on, until in course of long 
 ages the present flat-fishes were produced. 
 
 The other school of evolutionists believe that acquired characters are inherited to some 
 degree. It is admitted that the use of an organ enlarges it and improves it, and they 
 believe there is plenty of evidence that when the use of an organ in a particular manner 
 is continued generation after generation the modification is partly inherited in each 
 generation, and at last is wholly inherited. They hold therefore that the adaptations 
 of organs to particular purposes, which are so conspicuous in animals and in plants, 
 are due to the use of the organs for those purposes, and, though the modification 
 
 H2 
 
52 
 
 may be favoured and hastened by selection, it would take place without selection, 
 while selection could not produce adaptations without the inheritance of acquired 
 characters. They maintain, in fact, that there is no evidence of the occurrence of 
 such variations as would give rise to adaptations except under the influence of 
 stimuli and functional exercise. 
 
 Thus these evolutionists would explain the distortion of the eyes in flat fishes in 
 this way. A species of fish took to crouching flat on the ground on one side of the 
 body. But at first they did not lie perfectly flat, but slanting, lifting up their heads 
 so as to use the lower eye, and using the muscles of this eye so as to turn the pupil 
 into a horizontal direction, and look along the edge of the head. In consequence of 
 this, the lower eye pressed on the interorbital septum, and caused it to be flattened. 
 This pressure being continued for millions of generations the flattening and distortion 
 of the interorbital septum came to be inherited until at last the two eyes were on one 
 side of the head. 
 
 Now it is clear that no action of a given muscle of the eye could transport 
 that muscle from one part of the head to another, and evolutionists who had not 
 studied the anatomy of the head of flat fishes have made that objection to the above 
 explanation. But no such transportation has occurred as was shown in the description 
 given above. The attachment of the recti muscles of both eyes remains in the flat 
 fish exactly where it is in the symmetrical fish. The cranial region and branchial 
 region are unaltered. But the fishes which were the ancestors of the existing flat 
 fishes, in order to twist the lower eye till its optical axis was almost parallel to the 
 surface of the head, must have used the oblique muscles belonging to that eye. It is 
 a physiological necessity that such a constant and extreme exertion of those muscles 
 must in the individual have produced structural modifications, especially if it was 
 commenced at an early age. The eye must have pressed on the interorbital septum 
 in the sole on the left side, and this pressure would not have been counteracted by 
 any pressure on the other side, for the right eye was required to look upwards and 
 ventrally. Such pressure must have caused absorption and distortion of the inter- 
 orbital septum, that is to say, the septum would by that alone have become thin and 
 flat and bent to the right side. The increased exercise of the left oblique muscles 
 must also have caused them to become larger and stronger, and also have resulted in 
 the enlargement of the bone to which they were attached ; for it is an established and 
 certain fact that the exercise of a muscle causes it to increase in size and causes an 
 increased development of bone at its attachment. But the direction of the strain of 
 the muscles must have caused a torsion of the bone to which they were attached, 
 so that the surface of attachment which originally looked outwards to the left came 
 to look upwards. These are exactly the changes which we find to have taken place 
 in the head of the sole. If the change had been due to the selection of variations 
 which were independent of the effects of function, then we should expect that the 
 left ectethmoid would have remained symmetrical with the right, for the left eye could 
 
53 
 
 have been worked in its present position just as well if the oblique muscles had been 
 attached to the side of the interorbital septum, as the right muscles are. But, on the 
 theory for which I contend, there must have been some fixed point or fulcrum which 
 remained fixed while the action of the muscles altered the position of neighbouring 
 parts in relation to this fixed structure. The left ectetmoid of the sole fulfils the 
 precise conditions required of such a fulcrum. A man cannot lift himself up in a 
 basket, and the eye muscles could not b} T physiological effects have removed themselves 
 bodily by their own action to a new position. But two muscles by straining on their 
 own attachment, when unresisted by other muscles could twist neighbouring structures 
 round that attachment, must in fact do so, the bone to which they were attached 
 remaining in the same position and becoming enlarged. This is exactly what we find 
 to have taken place in the sole. Thus the change which has taken place in evolution 
 in the eyes and orbits of the sole is exactly of the same kind and in the same direction 
 as, but much greater in degree than, the change which must have taken place in the 
 individual fish which lay on its side and looked out witli its lower eye beyond the 
 e:lge of its head. Why, then, should we hesitate to conclude that the evolution has 
 been due to the accumulation, by inheritance, of the modifications due to known 
 physiological effects of functional activity? The only reason for hesitation is that 
 some zoologists say that acquired characters are not inherited, an assertion which 
 seems to me to be contrary to the evidence on the subject. However, this is not the 
 place to enter upon a discussion of the question of the heredity of acquired characters. 
 My purpose has been merely to describe the relations of the eye muscles to the orbits 
 in the sole, relations which I believe are not accurately described in any existing 
 anatomical treatise, and to point out that these relations are such as would necessarily 
 have resulted if the distortion of the orbits and the migration of the left eye hid been 
 due in the course of evolution to the constant action of the oblique muscles of the 
 left eye. It must be remembered that the other peculiarities in the structure of the 
 sole, namely, the extension of the dorsal fin to the snout and the asymmetrical 
 development of the jaws, are not in any sense consequences of the distortion of the 
 orbits. In many flat fishes both eyes are on one side, as in the sole, while the jaws of 
 the two sides are almost perfect!) 7 symmetrical, and the dorsal fin terminates behind 
 the eyes. I believe that both these peculiarities in the sole are modifications due to 
 physiological causes connected with the habit of lying on the left side ; but it is certain, 
 I think, that these physiological causes have nothing to do with the action of the 
 oblique muscles of the left eye. In endeavouring to trace the evolution of the sole 
 from a symmetrical ancestor each modification must be explained separately ; the 
 distortion of the eyes and orbits may be explained by the action of the oblique 
 muscles of the eyes, but this cause does not in the least explain the absence of colour 
 on the under side, nor the greater size of the jaws on the lower side, nor the anterior 
 extension of the dorsal fin. 
 
54 
 
 CHAPTER III. 
 
 THE VISCEKA, AND VASCULAR SYSTEM. 
 
 The Viscera. 
 
 IN the female the body cavity consists of three parts : a main central cavity, and 
 two extensions or diverticula opening out of it. The central cavity is situated 
 immediately behind the gill region and beneath the ten anterior vertebras, and extends 
 back to the anterior ventral interspinous bone. The two diverticula extend backwards 
 from the main cavity, one on each side of the median skeletal partition of the body 
 along the ventral edge. These lateral cavities extend from a little behind the anus 
 to jth the length of the body from the tail, getting narrower dorso-ventrally towards 
 the posterior end. The median anterior cavity contains the stomach and part of the 
 intestine, the liver, and the spleen (see Plate VIII, \ ). The right lateral cavity is the 
 larger, and contains four parallel sections of the alimentary canal, also the right ovary. 
 The left cavity contains only the left ovary and a part of the left kidney, which projects 
 into it. 
 
 The liver is shaped like a flat cake with one surface smooth and the other made 
 irregular by the entrance of blood vessels, &c. The greater part of this smooth 
 surface is turned to the left, and occupies nearly the whole dorso-ventral extent of 
 the main body cavity ; it is the only thing seen in that body cavity on removing the 
 left body wall. But the liver is doubled on itself anteriorly so that a smaller portion 
 of the smooth surface lies beneath the body wall of the right side in the anterior 
 part of the body cavity. 
 
 Projecting from beyond this surface towards the dorsal boundary of the body cavity 
 on the right side is seen the gall bladder, which is spherical. The liver is attached to 
 the anterior wall of the body cavity by a short ligament, situated in the median line 
 towards the dorsal limit of the anterior wall, about 1 cm. long at its peritoneal 
 attachment, and 3 mm. at its hepatic. 
 
 The oesophagus passes into the main body cavity at its dorso-anterior angle, dorsal 
 to the liver, then with a very slight dilatation to form the stomach it passes backwards 
 enveloped between the two parts of the liver, then following the boundary of the 
 
55 
 
 main body cavity in the median plane the stomach curves downwards, ending at 
 the pylorus at the ventro-posterior angle of the body cavity. Then commences the 
 intestine, the first part of which may, as usual, be called the duodenum. At its 
 commencement this is but little narrower than the stomach, but it rapidly narrows, 
 and, passing forwards to the antero-ventral angle of the body cavity, bends at an acute 
 angle and runs backwards and upwards along the border of the right fold of the liver, 
 crossing the stomach on the right side to enter the right lateral body cavity along the 
 dorsal part of which it runs to a little distance from its posterior end. The duodenum, 
 like the stomach, is white, and has thick muscular walls, but towards the posterior 
 end of the right lateral cavity it commences to get thinner walled and wider, and also 
 darker from the contents seen through the walls. It now bends completely on itself, 
 becoming considerably wider, and so passes into what may be called the ileum, which has 
 extremely thin walls. This passes forwards along the ventral side of the right cavity 
 in contact ventrally with the right ovary till it reaches to about the middle of the 
 main body cavity where, lying on the right side of the duodenum, it again bends on 
 itself and passes into the next length, which may be called the colon. At the bend, 
 and about a centimetre on either side of it, the walls are again white, thick, and 
 muscular, and the diameter of the tube is much reduced at this portion, which forms 
 a kind of ileo-colonic valve, but internally there are no transverse folds of the wall, 
 only longitudinal folds. After the bend the tube again dilates, this time suddenly, 
 and the colon, with thin flaccid walls, passes back again into the right lateral 
 cavity dorsal to the ileum, to a point about 2 cm. anterior to the end of the 
 duodenum. At this point the colon, without any change of character, passes into the 
 rectum, which passes forwards again on the dorsal side of and partially covering 
 the colon, to the antero-ventral angle of the main body cavity, where it opens at the 
 anus. 
 
 The spleen lies anterior to the stomach, between it and the liver, and a portion of it 
 is sometimes visible on removing the right body wall, between the duodenum and the 
 rectum. There is no pancreas, and no pyloric casca. All the parts of the intestine 
 and the liver and spleen are connected together by the branches of the splanchnic 
 artery and portal vein : these are especially conspicuous between the duodenum and 
 the liver, where they run from one to the other across the spleen. 
 
 The gall duct runs downwards from the gall bladder and opens into the duodenum 
 a little behind the pylorus on the anterior side. The hepatic duct leaves the liver in 
 the angle between the two folds and joins the gall duct about 1 cm. from the gall 
 bladder. 
 
 Cutting through the oesophagus and the terminal part of the rectum we now 
 remove the whole of the intestine, liver, and spleen, and examine the kidneys anc? 
 ovaries. 
 
 The two ovaries extend, as has been said, along the ventral border of the right 
 and left body cavities respectively. They are both about the same length, but the 
 
56 
 
 right is thicker. The ovaries are not suspended by membranes (mesoaria) as in 
 symmetrical fishes, but lie like kidneys beneath the peritoneum which passes over 
 them. Morphologically the mesoarium may be considered to have fused with the 
 surface of the median partition which separates the lateral body cavities from one 
 another. Or, to regard the evolution in a different way, it may be that the ovaries 
 have grown back post-anally beneath the peritoneum. Each ovary has a containing 
 wall which is independent of the peritoneum, though attached to it : the latter can be 
 separated from the former with facility. The ovarian artery and vein pass down together 
 on each side from the posterior end of the main body cavity, and run along the dorsal 
 side of each ovary. The walls of the two ovaries unite anteriorly on the ventral side 
 of the main body cavity to form a single wide tube which opens to the exterior behind 
 the anus and conducts the ova to the exterior. When the ovary is cut open the 
 germinal surface covered with projecting ovigerous lamellas having a general 
 longitudinal direction, is seen to extend all round the internal surface except along 
 the median ventral line, where the surface of the ovarian wall is quite smooth and 
 destitute of ovigerous lamellae : this probably represents the suture along which in 
 development the edges of the ovarian lamina joined together to form a tube. 
 
 On the dorsal wall of the main body cavity the renal organs form a broad reddish band, 
 placed in the centre and symmetrically, the two kidneys seem to be fused together in 
 the middle line. No part of the renal mass is continued into the right lateral body 
 cavity, but it is continued as a bulging thick mass into the dorsal part of the left 
 lateral cavity, where it is in contact ventrally with the left ovary. From the ventral 
 anterior corner of this mass there comes off a single short renal duct which opens out 
 into a large urinary vesicle. This vesicle sends a prolongation backwards between 
 the left ovary and the wall of the left lateral cavity, and it extends downwards behind 
 the common oviduct, between this and the wall of the main body cavity, to open to 
 the exterior on a small papilla on the right side. The opening of the oviduct, 
 although in the same depression of the skin as the anus, is separated from the 
 latter by a fold of membrane. Anteriorly the kidneys extend beyond the main body 
 cavity between the ossophagus and the muscles dorsal to it, as far as the posterior 
 surface of the skull. 
 
 Description of the Viscera of the male from a specimen I foot long (31 cm.). 
 
 Plate IX. 
 
 The intestines are arranged as in the female except that they do not reach quite so 
 far back in the right lateral body cavity, that is, they are slightly shorter. In front 
 of the bend which divides the colon from the ileum, is seen the urinary bladder, 
 distended. No part of the testes is seen without disturbing the organs in the body 
 
57 
 
 cavity. When the intestines are lifted up or removed, the right testis is seen, a 
 triangular Hat solid mass about 8 mm. broad at its posterior end, and 1 3 mm. long, 
 lying at the anterior end of the right lateral body cavity, close to the front edge of the 
 skeletal partition to which its inner surface is attached. 
 
 On the left side there is no left lateral body cavity, but the posterior portion of the 
 fused renal organs extends backwards between the lateral muscle and the skeletal 
 partition : this part of the kidney is as large in proportion as in the female, and has the 
 same relations to the urinary bladder. 
 
 The left testis is only about half the size of the right. In this specimen it was 4 mm. 
 broad above, and 10 mm. in length. The right testis is somewhat flat, and its greatest 
 length is nearly antero-posterior in direction ; the left has the form of a triangular 
 pyramid with its point downwards, and its greatest length is dorso-ventral in direction. 
 The left testis is situated in the main body cavity attached to the peritoneum over the 
 surface of the kidney by a membrane, the mesorchium. 
 
 From the apex of each testis passes off the vas deferens or duct by which the milt 
 or semen is conveyed to the exterior. Each vas deferens contains not a single cavity 
 but several, and it is attached to the anterior surface of the urinary bladder. The 
 vasa deferentia being translucent are not conspicuous ; their external aperture is at 
 the end of a small papilla on the right side, which is pierced also by the terminal 
 part of the urinary duct. Thus in both sexes there is a papilla on the right side ; in 
 the female it is a urinary papilla, in the male it is urinogenital. In the figure the 
 wooden rod is inserted through the anus into the end of the rectum, while the black 
 bristle passes into the urinary bladder the walls of which are exceedingly transparent 
 and indistinct, especially when the bladder is empty and collapsed. 
 
 Thus the male organs of reproduction in the sole are extraordinarily small in 
 proportion to the size of the body. In other 'flat fishes, e.g., the plaice, PL platessa, or 
 merry -sole, PL microcephalus, they are smaller than the ovaries, it is true, but many 
 times larger than those of the sole, and in the breeding season they become enlarged 
 and soft, and of a milk- white colour. In this condition they at once attract notice 
 when a male fish is cut open. In the sole, on the contrary, although the testes become 
 slightly enlarged during the spawning period, they become neither white, nor soft, 
 nor conspicuous. In fact they are not known to the fishermen, who are unable to 
 recognise in the small yellow organs of the sole the mala reproductive organs 
 which they usually find in other fishes as large, white, soft, and conspicuous 
 masses. The testes of the sole are, moreover, completely concealed beneath the 
 intestine. Until recently even ichthyologists were for the most part unacquainted 
 with the structure and relations of the male organs of the sole. In the 
 Fifth Annual Eeport of the Fishery Board for Scotland, p. 233, it is stated that " the 
 hatching of the sole, e.g., presents this one great difficulty, that males are rarely ever 
 captured, or, at least if captured, are seldom identified." As a matter of fact males 
 
58 
 
 are captured in greater numbers than females, but fishermen are unable to distinguish 
 the males from unripe or immature females. 
 
 One part of the viscera, which has the same relations in both sexes, still remains 
 undescribed, namely, the anterior part of the intestine, and the gills which are con- 
 nected with it. The anterior part of the intestine itself needs no very elaborate 
 description : it consists simply of the mouth and throat, the walls of which differ only 
 from the stomach in the fact that they are almost everywhere continuous with the 
 surrounding muscles and other tissues, instead of being separated from them by part 
 of the body cavity. Beneath the throat there is a part of the body cavity entirely 
 separated from the rest, namely, the pericardium, which contains the heart, and which 
 will be described below. The teeth previously mentioned as connected with or 
 embedded in the superior and inferior pharyngeal bones of course project through the 
 walls of the throat, and help to masticate or grasp the food. The series of basihyal 
 and basibranchial bones, clothed with mucous membrane, form a pointed conical tongue 
 in the floor of the mouth, which is used in swallowing. 
 
 At the sides of the throat is the important respiratory apparatus. Between the 
 branchial arches are a number of clefts by which the cavity of the throat opens to 
 the exterior. The bony arch is clothed with connective tissue, muscle, and mucous 
 membrane, and this mucous membrane becomes continuous through the cleft with the 
 outermost layer of the skin on the external surface of the body. The most anterior 
 cleft is between the hyomandibular bone and the first branchial arch : the cleft extends 
 upwards to the middle of the epibranchial bone, downwards to the end of the cerato- 
 branchial. The 2nd, 3rd, and 4th clefts become gradually shorter, scarcely extending 
 upwards beyond the cerato-branchials. The 5th cleft is very short, it is situated 
 between the 4th cerato -branchial bone and the 5th cerato-branchial or lower pharyn- 
 geal bone. The latter is continuously connected by muscle and connective tissue with 
 the pectoral arch ; there is no cleft behind it. On the outer face of each arch there is 
 a double series of long straight filaments, the branchial filaments. Each of these is 
 supported by a rod of fibrous skeletal tissue which runs up its centre, and between 
 this rod and the epithelium, or layer of delicate cells which covers the surface of the 
 filament, there is a rich plexus of capillary blood vessels. The blood coursing throuoh 
 these gives out its carbonic acid to the sea water which passes through the gill clefts 
 and absorbs oxygen from the sea water, which oxygen is necessary for the oxidization 
 of the tissues that goes on throughout life. 
 
 In front of the first branchial cleft, running in an antero-posterior direction beneath 
 the dorsal part of the hyomandibular bone, is a rudimentary branchia, composed not 
 of long branchial filaments, but a few vascular folds of the mucous membrane : this 
 is called the pseudo-branchia and is found in the majority of bony fishes. The pseudo- 
 branchia represents part of the branchia of the hyoid arch. On the inner surface of 
 the branchial arches there are email fleshy projections ; in many fish these are lon<? 
 projecting rods called the gill rakers. In the sole they are rudimentary. 
 
59 
 
 The branchiostegal rays support a membrane which is externally for the greater part 
 of its length continuous with the opercular flap, but is free at its edge, and extends 
 somewhat beyond the flap ; it forms a concavity which directs the water pressed out 
 in expiration upwards towards the base of the pectoral fin. The edge of the branchi- 
 ostegal membrane is, in ordinary respiration, kept pressed against the posterior wall 
 of the branchial cavity except opposite the base of the pectoral fin, where the membrane 
 forms a small aperture by which the water that has passed over the gills escapes. The 
 opercular flap supported by the opercular bones forms the external wall of the 
 branchial chamber, in which the branchiae are contained and concealed, but the oper- 
 cular flap is morphologically nothing but a fold of skin projecting backwards from the 
 hyoid arch and supported by dermal bones. The branchiostegal rays represent the 
 branchial skeletal rods of the lower part of the hyoid arch : they have been much 
 enlarged, and the filaments they supported have lost their branchial function, and 
 coalesced to form the branchiostegal membrane. 
 
 Minute Structure of the Reproductive Organs and Development of the Reproductive 
 
 Elements. 
 
 It has already been mentioned that the ovary consists of a hollow tube from the inner 
 surface of the walls of which project a number of longitudinal lamellae containing the 
 ova. A section of a young ovary of the right side is represented in PI. XIII, 1, as 
 seen under a low magnifying power, namely Zeiss' objective A, ocular 2, The specimen 
 from which this ovary was taken was 7^ in. long, and was immature. But the 
 structure of a mature ovary is similar in all respects except the size of the ova. 
 The wall of the ovary consists of laminated fibrous tissue, and the ovigerous lamellae 
 are supported by projections of this tissue into the interior of the ovary. On the 
 dorsal side of the transverse section are seen two blood vessels, the ovarian artery and 
 vein. The ovigerous lamellae are absent from, a small portion of the ventral wall of 
 the ovary, where the internal surface of the wall is smooth and barren. The surface 
 of the ovigerous lamellae is covered by a thin epithelium of cells too minute to be 
 distinguished separately under a low power. Here and there in this epithelium young 
 ova are seen developing. The epithelium is called the germinal epithelium, and 
 from its cells all the ova are originally derived. The older ova are seen below the 
 epithelium in the substance of the ovigerous lamellae. The lamellae contain in their 
 centre a plate of somewhat dense fibrous tissue, from which a loose reticulum of 
 fibrous strands and bands extends to the germinal epithelium. The older ova sink 
 into this loose fibrous layer, and each ovum is surrounded and enveloped by strands 
 of the fibrous tissue. The spaces in the fibrous reticulum are doubtless in life filled 
 with lymph, while the tissue itself is richly supplied with capillary blood vessels. The 
 
 i 2 
 
60 
 
 largest ova in the ovary at this stage are still very young, and each consists of a 
 protoplasmic mass containing a nucleus. The nucleus is a spherical vesicle bounded 
 by a membrane and containing protoplasmic strands and a number of nucleoli 
 which are all situated at the periphery of the nucleus. In a stained preparation the 
 nucleoli and the protoplasm of the ovum surrounding the nucleus are deeply stained, 
 but the rest of the nucleus, consisting chiefly of liquid contents, is scarcely stained at 
 all. Thus in each ovum the nucleus is seen as a clear central space containing several 
 deeply stained globules arranged withiu its external border. There is little doubt 
 that the fibrous connective tissue in the living state is more compact than I have 
 represented it to be. The ova contract in the process of preparation and leave open 
 spaces between them across which fibres are seen passing. But nevertheless it is 
 certain that the fibrous tissue is reticular, and that it is traversed by spaces containing 
 lymph. 
 
 When a portion of an ovigerous lamella from a young ovary is examined with a 
 high power it presents the appearance shown in PL XIII, 2. The preparation from 
 which this figure is taken was made from the ovary of a sole 10^ inches long, killed 
 in January. This also was an ovary which had never produced ripe ova, an im- 
 mature ovary. It will be seen that the cells of the germinal epithelium are extremely 
 minute and their outlines undefined. The ova are evidently produced by the 
 enlargement of single cells of this epithelium, and as they increase in size they pass 
 downwards into the fibrous " stroma." Even round the largest ova in an ovary at 
 this stage no envelope can be detected except a fibrous membrane belonging to the 
 " stroma " of the ovary. The protoplasm of the ovum, although it has grown in 
 quantity, still exhibits no differentiation. The largest ovum represented in Fig. 2 is 
 12 mm. in diameter. 
 
 But ova which are approaching maturity show a much more complicated structure. 
 Fig. 3 is drawn from a section prepared from an ovary in the spawning condition ; 
 in fact the ovary was almost spent, but a few immature ova remained in it, and a 
 section of one of these is represented in the figure. This ovum is seen to be enclosed 
 by a thick envelope, exhibiting in section close set radiating lines. This envelope is 
 not stained in the preparation. The radiating lines are really exceedingly fine tubules 
 passing through the substance of the envelope and through these the protoplasm of the 
 ovum communicates with the nutritive fluids outside. This envelope is the immature 
 stage of the membrane surrounding the ripe ovum when it is shed, but at this stage it 
 ia much thicker in proportion to the size of the ovum than in the state of maturity. 
 This envelope may be called the vitelline membrane ; in the eggs of some fishes it i& 
 differentiated into two layers, but in the sole I can find no distinction except that the 
 exterior surface of the membrane forms a kind of thin cuticle. The ovum within the 
 membrane presents an appearance very different from that of the younger ovum 
 previously described. Instead of a mass of granular protoplasm there are here a great 
 number of spherical vesicles crowded together. These vesicles contain a number of 
 
61 
 
 granules scattered through a transparent substance. They are the yolk vesicles. 
 Attentive examination shows that the yolk vesicles are contained in the original 
 protoplasm of the ovum, which everywhere extends among them, forming a network. 
 In fact the yolk vesicles are developed by the protoplasm within itself. The protoplasm 
 takes up the nutritive liquid materials derived from the blood and alters these by its 
 living chemistry so as to form these yolk vesicles which grow as it were at all points 
 throughout the substance of the protoplasm. Tn the mature ovum these yolk vesicles 
 become homogeneous and transparent, and flow together, with the exception of a few 
 of them, which remain separate but transparent near the outer surface of the ovum. 
 In the ovum now under consideration the nucleus retains the structure described in 
 the younger stage, and is still near the centre of the ovum. When the yolk vesicles 
 fuse the nucleus passes to the exterior with the protoplasm, the whole of which forms 
 a superficial layer enclosing the central semifluid yolk as in a bladder. 
 
 We have now to consider the ovarian structures surrounding the egg at the stage 
 represented in Fig. 3. It is easy to recognise outside of all the thin membrane of 
 fibrous tissue connected with and belonging to the stroma of the ovary. This may be 
 called the follicular membrane, the ovarian capsule enclosing the ovum being usually 
 known as the follicle. The follicular membrane exhibits nuclei along the course of the 
 fibres composing it, and it contains a number of capillary blood vessels, communicating 
 with larger vessels in the stroma (b.v. in Fig. 3). But within the follicular membrane 
 is a regular epithelium which was not seen in the younger stage of the ovum. This is 
 composed of a single layer of cells possessing large distinct nuclei. These cells in the 
 preparation are separated from one another at their internal ends, but this is probably 
 due to the contraction caused by reagents. Such a follicular epithelium is found round 
 the ripening ova of all vertebrates. But it is still an open question whence it is 
 derived. It has been maintained by many great authorities that the follicular cells 
 are derived from the germinal epithelium ; that when on ovum separates from the 
 epithelium and sinks into the stroma it takes with it a few other cells of the epithelium, 
 which multiply by division and form the follicular epithelium. This conclusion 
 has been drawn mainly from the study of the ovary in embryos, not from that of 
 developing ova in adult animals. As I have shown I have failed to trace any 
 connection between the follicular epithelium and the germinal epithelium. The former 
 seems to me to be entirely wanting for a considerable period after the young ovum has 
 separated from the germinal epithelium. The cells of the follicular epithelium become 
 visible about the same time as the commencement of the vitelline membrane. If these 
 cells are not derived from the germinal epithelium they must be derived either from 
 the egg itself or from the stroma of the ovary. There is no evidence of their derivation 
 from the e^cr itself at least in bonv fishes, and it is inconsistent with what we know of 
 
 CO * 
 
 fibrous tissue to suppose that the nucleated fibres can produce cubical cells. The 
 follicular cells cannot be developed independently from nutritive material derived from 
 the blood, they must be descendants of previously existing cells, for we know of no 
 
case in which nucleated cells arise, except as the progeny of other cells. There is 
 thus only one source left to which we can attribute the origin of the follicular cells, 
 namely, the colourless amoeboid wandering lymph cells, which occur in the interstitial 
 lymph spaces of all connective tissue. These cells are usually small, and it is possible 
 that they might intrude themselves through the spaces between the fibres of the 
 follicular membrane and so take up a position between that membrane and the surface 
 of the vitelline membrane, and then growing in size form the follicular epithelium. 
 The question of the origin of the follicular cells cannot however be considered as 
 decided ; Professor Emery in his monograph on Fierasfer, like myself, considers it 
 improbable that they are derived from the germinal epithelium, but expresses no 
 positive opinion as to their real origin. 
 
 As the egg in the ovary increases in size and approaches maturity its circumference 
 reaches again the surface of the ovigerous lamella, and ultimately when it is quite ripe 
 the germinal epithelium, the follicular membrane, and the follicular epithelium burst and 
 the ripe egg enveloped only by the vitelline membrane escapes into the cavity of the 
 ovary, whence it passes out through the external genital aperture to the exterior, where 
 it is fertilised, 
 
 The structure of the testis of the sole is very different from that of the ovary, and 
 closely resembles that of the testis in other bony fishes. PI. XIII, 4, shows the structure 
 of the testis of a young male sole 9 in. long, killed February 4th, 1889. The testis of 
 a full-grown male sole is similar, but I have represented the transverse section of 
 a small testis in order to include the whole of the section without making the 
 figure inconveniently large. The substance of the organ consists principally of 
 cylindrical tubes having walls of fibrous membrane and containing the spermatic cells. 
 These tubes are closed at the end which is most remote from the testicular duct leading 
 to the exterior, and these closed ends are all situated immediately beneath the surface 
 of the organ. From the closed ends the tubes pass radially inwards towards the 
 central region of the organ, except at the sides where their course is more longitudinal, 
 The tubes are so numerous as to be in contact with one another along their sides. As 
 in the case of the ovary the " stroma " of the organ consists of fibrous connective tissue 
 which fills up the interstices between the testicular tubes and forms a thin layer round 
 the organ externally. In the central region of the organ the testicular tubes 
 communicate with a number of longitudinal tubes much smaller in number than the 
 tubes themselves and of various sizes, some smaller, some larger, than the testicular 
 tubes. These longitudinal tubes convey the spermatozoa towards the efferent ducts, 
 and do not themselves produce spermatic cells : they are scattered with no regular 
 arrangement through the dense fibrous stroma. Inferiorly the fibrous stroma of the 
 testis is looser in texture and becomes continuous with the fibrous connective tissue of 
 the wall of the body cavity to which the testis is attached. Thus, to use the terms 
 frequently employed in human anatomy, the testis of the sole consists of a cortical 
 portion and a central medulla, the cortical portion consisting of tubes placed 
 
63 
 
 perpendicular to the surface, their outer ends being closed, and the medulla of 
 longitudinal tubes separated from one another by fibrous connective tissue. This 
 medullary portion is prolonged beyond the organ itself in the form of a band which 
 passes down the surface of the urinary bladder to the genital opening. Sections of 
 this band show that the longitudinal efferent tubes do not unite into a single duct or 
 i' as deferens, but are only slightly reduced in number by coalescence, so that a large 
 number of tubes remain separate even to the external opening. Fig. 6 exhibits a 
 section of the cord or band connecting the testis with the exterior and containing the 
 separate efferent tubes. This section is more highly magnified than that shown in 
 Fig. 4, and is taken from the testis of a full-grown male preserved while in full genera- 
 tive activity, in March, 1889. The spermatozoa are seen within the efferent tubes, 
 completely filling the cavity of some of them, and appearing under a low magnifying 
 power as deeply stained granules : these granules are. the heads of the spermatozoa, 
 the tails or vibratile appendages not being visible. 
 
 If the cortical tubes in the section shown in Fig. 4 are examined under a more 
 powerful objective, each of them presents the structure shown in Fig. 5. At the closed 
 end of the tube are a number of large polygonal cells forming an epithelium. Each 
 of these cells has a large nucleus with many nucleoli ; lower down the tube is filled 
 with smaller and smaller cells produced by the division of the large cells. The large 
 cells are evidently constantly being multiplied by division* and after reaching a certain 
 size each is pushed down into the cavity of the tube where it divides and subdivides, 
 forming a cluster of smaller cells. In some parts of the tube such clusters of small cells 
 produced from a single original cell can be distinguished j but they easily break up and 
 the cells of various clusters are confused together. In some of the young clusters 
 near the closed end of the tube all the nuclei are seen in a state of division showing 
 that each cell is dividing into two. 
 
 The large cells at the closed end of the tube correspond to the germinal epithelium 
 of the ovary ; they do not extend down the sides of the tube, but are confined to its 
 end : they are the male germinal cells and from them all the spermatozoa are 
 produced. 
 
 As the cells pass down the testicular tube they get smaller and smaller, and in the 
 lower ends and in sections of the deeper portions cut transversely they are seen to have 
 reached their limit of subdivision, for amongst them are seen deeply stained minute 
 spherical bodies which are the heads of spermatozoa. The minute cells produced 
 by continued subdivision are converted into spermatozoa and are called the 
 spermatoblasts. The details of the development of a spermatozoon from one of 
 these spermatoblasts can only be followed out by teasing up a portion of the testis on 
 a glass slide and examining it microscopically with the aid of reagents. The process 
 cannot be followed satisfactorily in sections because in these the elements are cut up 
 into pieces. I have not followed the process of development in the sole ; I will 
 therefore merely explain here that the protoplasm of the spermatoblast elongates 
 
64 
 
 into a slender filament, while the nucleus alters in properties, imbibing stains such as 
 carmine more intensely, and forms what is called the head of the spermatozoon. 
 During the spawning period all the testicular cells, except the large cells of the 
 male germinal epithelium at the closed ends of the testicular tubes, are converted into 
 spermatozoa, which are conveyed to the exterior suspended in a liquid similar to 
 lymph. This liquid is produced within the testis, being probably exuded from 
 the blood vessels and lymph of the testicular stroma into the testicular tubes. The 
 liquid containing the spermatozoa is usually called the milt. When the spermatozoa 
 reach the sea water they swim about actively, and when one meets a ripe ovum it 
 enters its substance and fertilises it. 
 
 The Vascular System. 
 
 The blood vessels ramify through all the tissues, including the skin and nervous 
 system, which have not yet been particularly described. But as the heart, which is the 
 central organ of the vascular system, is closely related to the body cavity and to the 
 branchiae, the system may be conveniently described here. 
 
 The heart, as was before mentioned, is enclosed in a special chamber of its own, 
 which is really a part of the body cavity, though it is entirely shut off from the visceral 
 cavity in which the organs of digestion, &c., are contained. This cavity containing the 
 heart, the pericardium, is situated between the posterior and internal walls of the two 
 branchial chambers ; the cavity is wedge-shaped, the edge of the wedge being anterior, 
 the base posterior. Posteriorly the pericardium is separated from the visceral 
 cavity by a thin membrane which lies in front of the liver and below the gullet or 
 oesphagus. Outside the pericardium on either side is the bone called the clavicle. 
 The heart itself is conical in shape, the point being ventral and directed downwards 
 and slightly forwards, the broad base being dorsal. -It is hollow and divided into two 
 portions connected by a valve. The dorsal portion has very thin walls, and is called 
 the auricle ; the ventral portion has thick muscular walls, and is called the ventricle. 
 Into the dorsal end of the auricle open three large veins by which the blood which has 
 passed through the various parts of the body is conducted into the cavity of the 
 auricle. These veins are the ductus Cuvieri which pass one on either side of the 
 oesophagus from the kidneys, and the hepatic vein which passes forwards from the liver 
 below the (esophagus. The ductus Cuvieri of each side is formed by the union of two 
 veins, one running forwards in the substance of the kidney and conveying the blood 
 from the trunk, the other running backwards from the head and conveying the blood 
 from the brain, skull, &c. ; these are called the anterior and posterior cardinal 
 veins. 
 
 The ventricle sends off a single main blood vessel, the ventral aorta. At the opening 
 of this vessel from the ventricle, there are three internal folds or valves which prevent 
 
65 
 
 the blood returning to the ventricle. This vessel passes forwards along the dorsal 
 edge of the jugular bone, and beneath the basi-branchials it divides, giving off on each 
 side an artery to each of the first four branchial arches ; from the artery of the first 
 arch a branch passes to the pseudobranchia. The fifth arch, bearing no branchial 
 filament, does not receive a special branchial artery. The branchial arteries run along 
 the branchial arches giving off smaller vessels which break up into the capillaries of 
 the branchial filaments. These capillaries unite again into the efferent branchial 
 vessels which run in the branchial arches towards the dorsal side of the pharynx or 
 throat, where they unite together into a single median dorsal aorta. From the efferent 
 branchial vessels are given off arteries which supply the brain, skull, and other parts 
 of the head. From the dorsal aorta is given off at the anterior end of the body cavity 
 the coeliac artery which supplies the intestine spleen, and liver with arterial blood. 
 The dorsal aorta runs backwards in the canal formed by the series of divergent bases 
 of the ventral spines of the vertebras, and is therefore in its anterior part dorsal to the 
 kidneys. It gives off special arteries which descend to supply the generative organs. 
 It also throughout its course gives off a pair of arteries to each segment of the lateral 
 muscles, from which branches supply the skin, bones, and all parts of the body. 
 
 The return of the exhausted venous blood from the tissues to the heart takes place 
 by a somewhat curious route. The veins of the head unite into the two anterior 
 cardinals, already mentioned, one on each side. But nearly all the veins of the trunk 
 fall ultimately into the caudal vein which runs forwards in the same bone-protected 
 canal as the aorta, as far as the interval between the ventral spines of the ninth and 
 tenth vertebras, where it bends suddenly towards the ventral edge of the body and 
 enters the dorsal side of the renal mass. The veins of the trunk in front of the caudal 
 vein fall into the kidney by separate collecting veins. A number of the veins of the 
 ventral side of the trunk, behind the kidney, unite into a longitudinal vein, which runs 
 forwards along the left side of the median skeletal partition and enters the posterior 
 apex of the part of the kidney which extends backwards on the left side behind the 
 main body cavity. Thus nearly all the venous blood in the trunk is conveyed into the 
 renal mass, where the urinary excretion is extracted from it, and whence it is passed 
 on by the posterior cardinal veins to the heart. The veins of the spleen and intestines on 
 the other hand unite into a single vein which enters the liver where it breaks up into 
 capillaries, and these unite again to form the hepatic vein which opens into the auricle. 
 
 K 
 
66 
 
 CHAPTER IV. 
 THE NEBVOUS SYSTEM 
 
 The Brain. The brain of the sole has no very special features which distinguish it 
 among those of other bony fishes. The position of the brain is almost entirely 
 unaffected by the change which has taken place in the normal position of the fish ; the 
 posterior part of the skull, as was previously pointed out, has neither twisted nor 
 become asymmetrical, and the corresponding part of the brain also retains its original 
 position and symmetry. But it seems still more remarkable that the anterior part of the 
 brain has not to any great degree followed the anterior part of the skull in the rotation 
 which the latter has performed. When the brain is exposed from the upper (right) 
 side of the fish, the right side of the organ is seen, .the extreme anterior end being 
 alone very slightly turned round towards this side. This absence of change in the 
 position of the brain is not so paradoxical when we compare carefully the relation of 
 the organ to the skull. The anterior end of the brain lies beneath the posterior 
 portions of the frontal bones, and these retain their original position. 
 
 It might have been expected that the change in the position of the anterior cranial 
 nerves would have caused a greater twisting of the brain ; but we find that the trunks 
 of the nerves have moved while their roots have been very slightly affected. 
 
 Viewed from the dorsal side the brain exhibits the same series of ganglionic masses 
 which are seen in other bony fishes. At the posterior end is the single median globular 
 cerebellum which projects backwards above the anterior thickened continuation of the 
 spinal cord, called the medulla oblongata. In front of the cerebellum is the pair of 
 masses whence the optic nerves arise, the optic lobes, each of which is almost as large 
 as the cerebellum ; in front of thess again is the pair of cerebral hemispheres which 
 are slightly smaller than the optic lobes, and immediately in front of the .cerebral 
 hemispheres are the olfactory lobes. In some bony fishes the olfactory lobes are 
 removed to some distance from the brain and placed in proximity to the olfactory 
 capsules, being connected with the brain by long nervous peduncles or crura ; e.g., in 
 the cod and carp. But in the sole as in other flat-fishes, and in the perch, mackerel, 
 pike, gurnard, and others, the olfactory lobes form part of the brain and are at a 
 distance from the olfactory capsules ; with which they are connected by the olfactory 
 nerves. 
 
67 
 
 The under surface of the brain exhibits beneath the cerebellum the continuation 
 forwards of the medulla oblongata which forms as it were the stalk supporting the 
 dorsal lobes. Beneath the front part of the optic lobes, however, an inferior outgrowth 
 is seen ; this consists of a pair of lobes called the lobi inferiores between which is a 
 vascular organ called the pituitary body, or hypophysis cerebri, supported on a hollow 
 conical outgrowth called the infundibulum. 
 
 The brain contains a central cavity which is the continuation of the central canal of 
 the spinal cord. This cavity terminates in the middle line between the cerebral 
 hemispheres, but laterally it sends off two diverging prolongations into the interior of 
 these hemispheres. The medulla oblongata and its continuation, the crura cerebri, are 
 situated below the central cavity, while the cerebellum, the optic lobes, and the upper 
 part of the cerebral lobes are enlargements of the roof of the cavity. The infundibulum 
 and pituitary body form a downward diverticulum of the cavity beneath the point 
 where it bifurcates into the cavities of the cerebral lobes ; and a corresponding diver- 
 ticulum towards the dorsal side exists between the anterior part of the optic lobes, and 
 is called the pineal gland. The pineal gland, like the pituitary body, is a vascular 
 structure in fishes. In some reptiles it has been found to have a structure resembling 
 that of the vertebrate eye. 
 
 The olfactory lobes are continuous with the inferior portion of the cerebral hemi- 
 spheres. In the sole the left olfactory lobe is somewhat larger than the right, a difference 
 which is related to the great development of the left olfactory capsule. But there is no 
 inequality in the size of the optic lobes or optic nerves, such as that which according 
 to Owen occurs in the halibut and some other Pleuronectidce. In Owen's figure of 
 the halibut the right optic lobe and left optic nerve are the larger ; the eyes of this 
 species, as of the sole, are on the right side, so that the larger structures are those 
 belonging to the eye which has migrated. 
 
 It would naturally be inferred that the left eye was larger than the right in the 
 halibut, but I have not been able to find any allusion to an inequality in the size of the 
 eyes themselves. 
 
 As in all bony fishes the brain of the sole is much smaller than the cavity in which 
 it lies. The widest part of the cavity within the skull is the posterior part : here the 
 brain passes forwards from the foramen magnum as an axis in the centre of the cavity, 
 the surrounding space being occupied by the auditory organs. The sacculi meeting 
 in the middle line below, occupy the space below the brain, while the semicircular 
 canals intervene between the latter and the skull-walls dorsally and laterally. A 
 transverse ridge on the inner surface of the skull-wall, forming part of the sphenotic 
 and prootic bones, limits anteriorly the cavity occupied by the sacculi. In front of 
 this ridge is another ventral depression occupied by the optic thalami and pituitary 
 body, while above the optic lobes and cerebral hemispheres there is a considerable 
 space occupied only by spongy connective tissue containing fluid the arachnoid 
 membrane. The internal hollow of the parasphenoid bone in front of the pituitary 
 
 K 2 
 
68 
 
 body is occupied by the insertion of the muscles of the two eyes, these muscles being 
 separated from the interior cavity of the skull by a tough membrane, continuous with 
 the dura mater posteriorly, and anteriorly with the membrane which completes the 
 septum between the orbits. This membrane is pierced /or the exit of the optic, 
 olfactory, and other nerves, and on it rest the olfactory lobes. 
 
 The Cranial Nerves. 
 
 The olfactory nerves pass from the olfactory lobes to the olfactory capsules, termi- 
 nating in the olfactory epithelium of these organs. Owing to the rotation of the left 
 eye and orbit the position of these nerves in the sole is peculiar. Each olfactory nerve 
 in all fishes passes over the dorsal side of the recti muscles of the eye. The relations 
 of the nerves to surrounding structures are not altered in the sole, but the rotation of 
 the eyes has brought the- olfactory nerves into asymmetrical positions. Thus both of 
 these nerves are apparently on the upper (right) side of the head, though morphologi- 
 cally they are on opposite sides. Both of them, like other structures connected with 
 the orbits, are on the coloured side of the head, .to the right of the anterior part of the 
 dorsal fin. The left nerve passes above the recti muscles of the left eye close to the 
 interorbital septum, and in front of these muscles bends downwards and passes through 
 the large foramen in the left ectethmoid bone (PL XI, 6, I) to reach the left olfactory 
 capsule on the lower side of the head. 
 
 The right nerve has a perfectly straight course along the ventral (right) side of the 
 interorbital septum, dorsal to the recti muscles of the ventral (right) eye. It passes 
 through the foramen in the right ectethmoid without any bending, and then bends 
 slightly downwards to the olfactory capsule of the upper (right) side. 
 
 Each of these nerves, though spoken of in the singular, consists of a bundle of 
 separate nerves, which are separate throughout their course, and not united into a 
 single cord. 
 
 The optic nerves, as usual in bony fishes, cross one another at their origin without 
 mingling. The dorsal (left) nerve is very slightly longer than the ventral (right). The 
 left arises from the lower side of the right optic lobe in front of the lobus inferior or 
 optic thalamus, the right from a corresponding position on the left side. The optic 
 nerve passes between the internal and superior rectus close to their origin into the 
 space enclosed by the recti muscles, and so reaches the eye-ball, 
 
 The third, fourth, and sixth pairs of cranial nerves are motor nerves all distributed to 
 the muscles of the eyes. The third pair are called the motores oculorum and split up 
 into branches which enter the superior, inferior, and internal recti, and the inferior 
 oblique muscles. The fourth pair of nerves are called trochleares and supply the 
 superior oblique muscles exclusively. The sixth pair are called abducentes, and enter 
 only the external recti muscles. These nerves arise from the sides of the lower part of 
 
69 
 
 the brain behind the origins of the optic nerves, and pass from the skull by apertures 
 in the membrane which closes its anterior opening. 
 
 The fifth nerve or trigeminal arises by several roots from the side of the medulla 
 oblongata below the cerebellum : in its origin it is closely connected with the seventh 
 or facial nerve. In fact the two nerves arise from a number of roots common to both, 
 of which the dorsal are sensory, the ventral motor ; the fifth nerve is chiefly composed 
 of fibres from the sensory roots, with the addition of some from the motor, while the 
 facial consists chiefly of fibres from the motor roots, with the addition of some from 
 the sensory. 
 
 The fifth nerve consists of a large number of branches. It does not leave the skull 
 by a single trunk, but divides on the inner wall of the skull into several, the largest 
 and most important of which leaves the skull after a very short course by the large 
 trigeminal foramen in the lower part of the sphenotic bone. The other two branches 
 run for some distance on the inner wall of the skull before emerging : one of them runs 
 directly forwards and emerges through the anterior membrane which separates the 
 skull from the orbits ; this forms the orbito-nasal nerve ; the other curves upwards and 
 forwards and emerges by a small foramen in the frontal bone. As the corresponding 
 nerves differ on the two sides it will be necessary to describe them separately. 
 
 The course of both orbito-nasal nerves, like that of the two olfactory, is to be followed 
 by dissection of the upper side of the head ; for each orbito-nasal nerve lies in close 
 relation to the olfactory, lying in the ordinary fish dorsal to the olfactory and between 
 the eye muscles and the interorbital septum. Accordingly in the sole the orbito-nasal 
 nerves are found on the upper side of the head, one on either side of the interorbital 
 septum. But the dorsal (left) is much larger, and longer than the ventral (right). The 
 left nerve passes over the surface of the mesethmoid bone at the bottom of the rounded 
 notch between the left ectethmoid and the mesethmoid, and then enters the gelatinous 
 tissue of the end of the snout, sends branches to the skin of the upper side at this part 
 of the snout, but is chiefly distributed to the tactile filaments of the skin on the lower 
 side between the olfactory capsule and the edge of the snout. The right nerve just 
 behind the right ectethmoid passes into a canal between the right frontal bone and the 
 right ectethmoid, and thence emerges again on the right upper surface of the meseth- 
 moid, enters the gelatinous tissue of the snout, and supplies the small area of skin on 
 the upper side between the mouth and the apex of the snout. 
 
 The right dorsal branch of the fifth, after its upward course on the internal surface 
 of the skull, emerges by a small foramen in the flat proximal portion of the right frontal 
 bone, and thence passes forwards, at some depth from the surface, between the cephalic 
 portion of the lateral muscle and the membrane which forms the dorsal boundary 
 of the dorsal (left) orbit. It supplies the skin of the extreme anterior end of the 
 dorsal fin on the upper side. It seems at first sight that this nerve has changed its 
 morphological relations ; for since it belongs to the right side of the head we might 
 expect to find its anterior part on the ventral or right side of the interorbital septum, 
 
70 
 
 with the right orbito-nasal ; whereas it actually runs on what is morphologically the 
 ventral side of the left eye, crossing in its course the left olfactory and orbito-nasal 
 nerves. But the explanation of this apparent anomaly is not difficult. The dorsal 
 branch of the fifth is a sensory nerve and was connected in the original symmetrical 
 fish with the skin of the extremity of the dorsal fin which was originally posterior to 
 the eyes. The fin remained behind the eyes during the rotation of the latter, and 
 after the left eye had travelled round to the right side, the dorsal fin with the neigh- 
 bouring muscles began to extend forwards. But instead of extending forwards along 
 the now distorted median dorsal line, the fin grew forward along the edge of the left 
 ectethmoid bone, which supports the left eye in its new position, and which is mor- 
 phologically ventral to the left eye. The nerve connected with the fin necessarily 
 accompanied the latter in its growth, and thus this nerve comes to be actually dorsal 
 and morphologically ventral to the left eye. The origin of the nerve remains in its 
 original position posterior to the eyes on the right side of the skull. 
 
 The corresponding nerve of the left side makes its exit from the skull from a corres- 
 ponding foramen in the flat proximal portion of the left frontal bone, on the lower (left) 
 side of the dorsal fin ; it passes forwards on the left side of the fin to its apex. 
 
 On the right side the trunk of the fifth nerve, which emerges from the skull through 
 the sphenotic foramen, divides immediately after its exit into two large branches, the 
 maxillary and mandibular nerves. The maxillary branch supplies with sensory fibres 
 the skin of the upper jaw and also sends motor fibres to the palatal muscle. The 
 mandibular branch supplies with sensory fibres the skin of the lower jaw; the largest 
 division of it enters a canal in the mandibular bone, whence it supplies the mucous 
 membrane of the floor of the mouth. The main trunk of these two branches, the 
 maxillary and mandibular, while still within the skull, gives off a small nerve which 
 leaves the skull by the great anterior opening, and passes forwards below the recti 
 muscles of the eye ; it supplies the anterior part of the palate and is called the palato- 
 nasal. 
 
 On the left side these branches of the fifth are much enlarged, their sensory fibres 
 being multiplied in proportion to the great development of tactile filaments and 
 epidermic sense-organs on this side. The palato-nasal branch reaches this side of the 
 head partly through the gap between the ectethmoid and parasphenoid, partly through 
 a foramen in the sphenotic in front of the large sphenotic foramen. The latter foramen 
 is much larger than that on the right side, and the common trunk of the maxillary and 
 mandibular nerves which passes through it is proportionally large. These branches of 
 the fifth on the left side are represented in PI. XV, 2, where the maxillary is indicated 
 by Y 2, the palato-nasal by V 2a, and the mandibular by V 3. The dorsal branch 
 of the fifth, which accompanies the dorsal fin, is seen passing forwards just above the 
 palato-nasal. 
 
 The seventh cranial nerve is called the facial ; its distribution is the same on both 
 sides, as it belongs to a region of which the symmetry has not been disturbed. The 
 
71 
 
 principal trunk of the facial leaves the skull by a circular foramen in the prootic bone, 
 and then passes through a foramen in the head of the hyomandibular. But after this 
 it is still covered by the preoperculum, which must be removed before the distribution 
 of the nerve can be observed: the facial runs for some distance between the 
 hyomandibular and the preoperculum. Soon after its exit from the hyomandibular 
 foramen the nerve trunk divides into two branches, the posterior of which is the 
 ramus opercularis, the anterior the ramus hyoideo-mandibularis. The ramus opercidaris 
 (VII 2a, PI. XV, 2) divides into branches which are distributed to the skin of the 
 operculum. The ramus hyoideo-mandibularis divides into two branches, one of which, 
 the ramus mandibularis, VII 1, runs along the anterior part of the surface of the 
 quadrate. It gives off branches to the jaw-muscle, and into the substance of the 
 quadrate, and passes through a foramen in the head of the quadrate to the inner side 
 of the niandibular bone, where it supplies the transverse mandibular muscle, the genio- 
 hyoid muscle, and the mucous membrane of the floor of the mouth. The other branch, 
 the ramus hyoideus, VII 2, bends inwards to reach the inner side of the stylohyal 
 bone, and is distributed to the inner surface of the hyoid arch. 
 
 The eighth cranial nerve is the auditory, which never leaves the interior of the skull, 
 but is exclusively distributed to the auditory organ : it is the auditory nerve. 
 
 The ninth cranial nerve is called the glosso-pharyngeal, a name taken from human 
 anatomy, but not at all appropriate to the anatomy of fishes. This nerve, like the 
 seventh, is distributed in the same way on each side. It makes its exit from the skull 
 by a special small foramen in the opisthotic bone, arising from the medulla oblongata 
 by an independent root. On the trunk of the nerve, a little beyond its exit from the 
 skull, there is a ganglion of considerable size, below which the nerve bifurcates into 
 two branches. The anterior branch goes to the posterior surface of the operculum 
 and hyoid arch, the posterior to the anterior surface of the first branchial arch. 
 
 The tenth cranial nerve, called nervus vagus, is more widely distributed than any 
 of the others, and represents a series of nerves united into a common trunk at their 
 origin. The single trunk passes out of the skull through a circular foramen in the 
 exoccipital bone, and then divides into several branches. The first branch, the most 
 anterior, bifurcates into two, and has a large ganglion at the point of bifurcation ; 
 it forks over the second branchial cleft, the front branch going to the posterior face of 
 the first branchial arch, the posterior branch to the anterior face of the second 
 branchial arch. Similarly the second branch of the vagus bifurcates over the third 
 branchial cleft, and has a ganglion at its point of bifurcation. The third branch has 
 no ganglion, but bifurcates in the same way over the fourth branchial cleft. The 
 fourth branch bifurcates over the fifth branchial cleft, its anterior branch going to the 
 posterior face of the fourth branchial arch, its posterior branch to the posterior wall of 
 the branchial chamber and the fifth branchial arch. A nerve from this branch goes 
 to the heart. The fifth branch of the vagus runs down the oesophagus to the stomach. 
 The sixth branch is the lateral nerve or nerve of the lateral line : it runs close above 
 
72 
 
 the vertebral centra on the ventral side of the band of connective tissue which 
 separates the dorsal and ventral lateral muscles. From this position it sends off nerves 
 which supply the sense-organs of the dermal canal of the lateral line. At its origin 
 this nerve gives off on each side a branch which curves upwards and forwards and runs 
 immediately beneath the skin along the course of the supra-temporal dermal canal on 
 the right side, the series of supra-temporal superficial sense-organs' on the left side. 
 On the left side there is another nerve given off from the lateral nerve at its origin : this 
 nerve runs immediately beneath the skin straight forwards across the side of the lateral 
 ridge of the skull : it supplies the superficial sense organs of the epidermis which lie 
 along this direction. The two nerves last mentioned are shown in PL XV, 2, indicated 
 as X 6a and X 6b. 
 
 PI. XV, 2, exhibits the cutaneous branches of the cranial nerves on the left side, and 
 is intended to show the great development of these branches which has taken place in 
 connection with the numerous tactile filaments and epidermic sense-organs which have 
 been developed on the skin of the left side of the head. 
 
CHAPTER V. 
 
 THE SKIN. 
 
 THE skin everywhere consists of two layers very different from one another in structure. 
 The lower layer, which is much the thicker, consists of fibrous connective tissue, 
 forming a dense tough membrane. This layer is about -^-th of an inch thick (1 mm.). 
 It is clothed externally by a thin layer of cells, the longer axis of which is perpen- 
 dicular to the surface of the body : this is the epidermis. The lower layer or derma 
 contains the scales, the ends of which project backwards through the epidermis, and 
 the pigment cells or chromatophores. On the lower side of the head anteriorly the 
 skin forms a number of flexible papilke, or filaments, which are delicate tactile organs. 
 The skin is continued over the eyes, but the part which covers the eye is thin and 
 perfectly transparent. Scales are present in the skin everywhere, except over the eyes 
 and in the region of the tactile filaments. The scales can be detached from the skin 
 without difficulty, and when separated and examined with a low power of the 
 microscope present the appearance shown in Fig. 1, PI. XIV. The largest scales are 
 in the central region of the surface of either side. The scales consist of plates of 
 fibrous tissue hardened by the deposition of lime-salts. Each has the form of a 
 rectangle at the posterior end of which is a portion bounded internally by two straight 
 lines meeting at an obtuse angle, outwardly by a semicircular curve, and covered with 
 sixteen rows of spines. In each row the outermost spine is the largest, the others 
 becoming gradually shorter : there are five spines in each row, and the rows radiate 
 from the angle at which the internal bounding lines of the spinous area meet. This 
 spinous area is the only portion of the scale which is exposed at the surface of the skin, 
 the remainder being imbedded in a socket and overlapped by adjacent scales ; they 
 are placed with their longer axes directed backwards, and each overlaps the one 
 behind it. They are arranged quincuncially, that is, each scale in any transverse row 
 lies over the line where the edges of two adjacent scales of the row behind meet one 
 another. In consequence of this quincuncial arrangement the transverse rows, which 
 are perpendicular to the longitudinal axis of the fish, are not easily recognised ; but two 
 series of oblique rows are visible, one series running downwards from right to left, the 
 other downwards from left to right. In the same way in the pattern of a wall paper 
 when there is a figure repeated at equal distances in lines crossing one another at right 
 
 L 
 
74 
 
 angles, but arranged quincuncially, the rectangular lines cannot easily be followed, 
 but two oblique or diagonal series become conspicuous. It is the oblique rows of 
 scales, either those from right to left or from left to right, which are counted in 
 describing the specific characters of a fish. 
 
 The imbedded portion of a scale exhibits a number of parallel curved lines, the 
 edges of the laminee of which it is composed. The directions of these lines divide this 
 portion of the scale into three areas : a triangular area bounded by the anterior edge 
 of the scale and two lines which meet at an acute angle near the anterior apex of the 
 spinous portion, and two similar areas on either side of this. The anterior portion is 
 divided up by a number of radiating straight lines, into radiating strips, each of which 
 is occupied by a series of short curved parallel lines. The two other areas are 
 occupied by lines parallel to the dorsal and ventral edges of the scale. 
 
 The scales of Solea lascaris, variegata, and lutea resemble those of S. vulgaris in 
 Structure. The scale of lascaris, Fig. 4, PI. XIV, is the largest : it has the same 
 general shape as that of vulgaris, but the spines are more pointed, and there are 
 seventeen rows of them, and six spines in each of the central rows. The scale of 
 variegata. Fig. 3, is shorter in proportion to its bread th than that of lascaris, it has 26 
 rows of spines, with eight spines in each central row : the spines, except the most 
 external, are short and blunt. The scale of lutea, Fig. 5, is the smallest of the four : 
 in shape it resembles that of vulgaris ; it has 21 rows of spines, four spines in each of 
 the central rows ; the spines are rather short and pointed. 
 
 The " lateril line " which runs down the centre of each side of the sole is formed by 
 a series of scales which are very different from the ordinary scales of the body. They 
 have no spines, and no portion of them projects beyond the surface of the skin. One 
 of theSe scales from Solea vulgaris is represented in Fig. 2, PI. XIV. Anteriorly its 
 structure resembles one of the ordinary scales, but posteriorly it is narrowed to a blunt 
 apex and the spinous portion is wanting. On its external surface, for a little more 
 than half its length posteriorly, there runs a kind of tunnel with rounded roof which, 
 with the scale below, forms a tube open at both ends : this tube or tunnel is broader in 
 front than behind. In the floor of the tunnel, not far from the posterior end of the 
 scale, is a large oval aperture. These scales of the lateral line overlap one another in 
 such a way that the aperture in the floor of the tunnel of one is just in front of the 
 anterior aperture of the tunnel of the scale behind it. 
 
 Dermal Canals and Sense-organs. 
 
 This system consists of a number of connected tubular channels running in the 
 derma or in bones originally derived from the derma. The longest and most easily 
 observed of these tubes runs beneath the lateral line. It is lined by a cellular layer 
 somewhat similar to the superficial epidermis, and it runs through the series of bony 
 tubes just described as belonging to the scales of the lateral line. Tracing the tube 
 
from before backwards we find that the tube enters the anterior end of the tunnel on 
 each scale and passes through the aperture in the floor of the tunnel to enter the 
 tunnel of the next scale, and so on. But before passing through the aperture in the 
 floor of the tunnel the tube gives off a branch which continues to run through the 
 tunnel to its posterior aperture, and passes beyond the scale to open by a pore on the 
 surface of the skin. Thus corresponding to each scale of the lateral line there is a 
 pore in the skin which leads into the dermal tube of the lateral line. The course of 
 i-he tube and its relation to the scales are exhibited in Fig. 6, PI. XIV, which 
 represents an ideal longitudinal section of the skin along the lateral line : sc. indicates 
 the scales in section, d.t., the tube, p, the external pores. The left end of the section 
 is the anterior. On the inner wall of this lateral dermal tube are a number of sense- 
 organs supplied with branches of the nervus lateralis, which in the sole as in the 
 majority of fishes is a branch of the vagus. If we follow the lateral dermal tube 
 forwards we find that at the side of the back part of the skull, over the parietal crest, 
 it becomes separate from the skin and enters the hinder branch of a triradiate bony 
 tube : one branch of this bone passes straight forwards for a short distance and then 
 terminates, and the lateral tube then enters a tube in the pterotic bone. This tube 
 excavated beneath the surface of the bones of the skull is continued forwards, sometimes 
 opening into a groove on the lateral ridge of the skull : it passes just above the 
 posterior corner of the sphenotic bone, and then enters the outer edge of the posterior 
 half of the frontal ; then it is continued as an enclosed tube through the interorbital 
 process of the frontal, and emerging from this enters a separate tubular bone similar 
 to that which lies on the outer surface of the parietal crest. This bone bifurcates each 
 branch ending in the skin, probably by an opening to the exterior. This last bone is 
 the nasal : the former may be called the supra-temporal bone. (See Fig. A on the 
 following page.) 
 
 It follows of course from the peculiar modification of the frontal bones that the 
 cephalic portion of the lateral tube on the left side, following the course of the left 
 frontal bone, passes from the apparent left side of the head to the right : morpho- 
 logically of course it retains its proper relations, but as it passed originally dorsal to 
 the left eye, it has been pushed over by the movement of that eye to the right side, 
 and so comes to lie to the right of the anterior part of the dorsal fin. But the left 
 nasal bone is on the left side, for the tube after leaving the left frontal bone bends 
 beneath the anterior dorsal interspinous bone, to the left side of the snout : thus the 
 left nasal bone is attached to the skin in front of the nasal capsule of the left side. 
 The right nasal bone lies in front of the nasal capsule of the right side. 
 
 The supra-temporal bone, besides its posterior and anterior openings, has two others, 
 a dorsal and a ventral. The dorsal opening is at the end of a short branch, and leads 
 into a tube in the derma surrounded by modified scales, and in all respects resembling 
 the tube of the lateral line : this supra-temporal dermal tube in fact lies under and is 
 the cause of the supra-temporal branch of the lateral line described with the external. 
 
 L 2 
 
76 
 
 leatures of the sole. The ventral opening of the supra-temporal bone leads into a 
 membranous separate tube, which passes beneath the skin in a ventral direction, runs 
 through a tube which pierces the preopercular bone, and is continued forwards to the 
 
 mandible. 
 
 Now the supra-temporal tubes are, as we have seen, dermal, and pass through 
 apertures in a series of scales similar to those of other parts of the skin in structure. 
 On the right side the supra-temporal tube retains this structure throughout up to its 
 termination at the extreme apex of the snout. But on the left side anteriorly the 
 scales disappear, and the supra-temporal tube opens out on to the surface, its sense 
 organs becoming quite superficial : they are situated between the bases of the tactile 
 filaments of the lower surface of the snout. 
 
 In the cod (Gadus morrhua) the lateral cephalic tube gives off another branch 
 
 l.n. 
 
 Fig. A. A diagram to illustrate the distribution of the epidermic sense-organs and dermal tubes on 
 the head of the sole, a, the anterior continuation of the lateral tube ; &, the supra-temporal tube ; 
 c, the preopercular tube ; cZ', the sub-ocular organs of the left side ; Z, the lateral line tube ; 
 r.?&., right nasal bone ; l.n., left nasal bone ; t, the supra- temporal bone. 
 
 besides those already mentioned, namely a sub-ocular tube, which is enclosed by a 
 series of scale-like bones, the sub-orbital bones. This sub-ocular branch is found in 
 the plaice (Pleuronectes platessd] on the right side as a canal in the derma beneath 
 the ventral eye ; while on the left side it exists as a dermal tube between the mouth 
 and the supra-temporal tube. In the sole I have been unable to find a trace of the 
 sub-ocular tube on the right side, but on the left side it is represented by superficial 
 epidermic sense-organs distributed all over the skin between the cleft of the mouth 
 and the sense-organs of the supra-temporal line. In the sole there are in addition a 
 number of superficial sense-organs along the line of the pre-opercular tube, forming a 
 single series along the upper part of that tube, and spreading out over the whole area 
 behind the mouth- cleft below. 
 
 The lateral cephalic tube and the pre-opercular tube, which are to a large extent 
 enclosed in solid bone, nevertheless communicate at intervals with the exterior by 
 
77 
 
 means of short tubes which open on the surface of the skin ; the supra-temporal and 
 sub-ocular dermal tubes where they exist, are also connected by short tubes with 
 superficial pores, so that all the tubes of the system are related to the skin in almost 
 the same way as the tube of the lateral line. The cephalic tubes also in all probability 
 contain sense-organs similar to those of the lateral tube. The tubes of the head are 
 innervated by branches of the cranial nerves. The supra-ocular part of the lateral 
 cephalic tube receives branches from the orbito-nasal nerve, the sub-ocular tube is 
 innervated by branches from the maxillary and palato-nasal nerves, the pre-opercular 
 tube is supplied from the seventh or facial nerve. There is little doubt that the 
 lateral and pre-opercular cephalic tubes, now enclosed in solid bone, were, like the rest, 
 originally dermal tubes enclosed by tubular scales. In fact, the bones through which 
 they pass represent dermal scales fused together. The tubes and the bones thus 
 produced have sunk beneath the skin, and the bones have become part of the skull. 
 
 Fig. B. A diagram to illustrate the distribution of the dermal tabes in the head of the cod. Letters 
 as in the diagram of the sole. 
 
 But all these dermal tubes at a still earlier period were part of the external surface of 
 the skin. The sense-organs of the tubes and their epithelium are really derived from 
 the epidermis. In some cases the organs of the lateral line are superficial throughout 
 life, for example, in the gobies and the mullet, and in all cases they are developed in 
 the embryo or young fish in the external epidermis. The tubes are formed both in 
 evolution and development by the deepening and ultimate enclosure of grooves on the 
 
 surface which include the sense-organs. 
 
 e> 
 
 In the cod, which may be taken as exhibiting pretty nearly the original condition 
 of the cephalic tubes of the sole and other flat-fishes, there are no superficial sense- 
 organs on the head, and the tubes of the two sides are symmetrically arranged. 
 
78 
 
 The diagram, Fig. B, shows the position and the relations of the cephalic tubes In 
 that species. The supra-temporal tubes are short, and are surrounded by thin tubular 
 scale-like bones. The sub-ocular tube is also enclosed in a series of tubular bony 
 scales, the sub-orbital bones. Both these and the supra-temporal bones, though 
 homologous with the ordinary dermal scales, are not similar to them, having a much 
 larger size and deeper position. 
 
 In the sole the changes which have taken place in the course of evolution are as 
 follows : The supra-temporal tubes have become much elongated, having grown 
 forwards with the anterior extension of the dorsal fin till they reach the extremity of 
 the snout. On the right side the tube is no longer enclosed by peculiar scale-like 
 bones, but by tubular dermal scales, closely resembling the ordinary scales of the skin. 
 On the left side of the head, the scales having disappeared anteriorly, the supra- 
 temporal tube has opened out on to the surface, and the sense-organs which belong to 
 it have become superficial. The two supra-temporal tubes are symmetrical in relation 
 to the two sides of the dorsal fin, but entirely asymmetrical in relation to other parts 
 of the head ; for in consequence of their relation to the fin they both lie morpho- 
 logically ventral to the left eye, between the left eye and the mouth. 
 
 The lateral cephalic tube of the left side has been distorted by the change of 
 position of the left orbit. Its posterior part retains its original position, but its 
 anterior or supra-ocular part lying in the inter-orbital process of the left frontal bone, 
 bends round towards the right side and runs close beside the right supra-ocular tube 
 between the two eyes. 
 
 The sub-ocular tube of the right side has disappeared ; that of the left side is 
 represented by the numerous superficial sense-organs which lie above the mouth on 
 the lower side of the head. 
 
 The two pre-opercular tubes remain in their original position, but on the left side a 
 number of superficial sense-organs have been developed over the region of the 
 pre-opercular tube. This is, in some respects, one of the most remarkable of the 
 peculiar developments in the head of the sole. It is intelligible that a dermal tube 
 originally derived from a superficial groove should again become superficial ; but it is 
 surprising to find surperficial organs developing anew, outside a tube which contains 
 similar organs originally derived from the surface. 
 
 The supra-temporal tubes are innervated by a long branch from the lateral nerve 
 belonging to the vagus. On the left side a similar branch of the vagus passes 
 forwards towards the sub-ocular sense-organs. Along the proximal part of the course 
 of this nerve is a single series of superficial sense-organs, which lies over the proximal 
 part of the lateral cephalic tubes. I have not been able to decide whether this series 
 really belongs to the sub-ocular series of the left side, or bears the same relation to the 
 proximal part of the lateral cephalic tube as the pre-opercular superficial organs to 
 the pre-opercular tube. In studying the relations of the mucous tubes and epidermic 
 sense-organs in the head of the sole, I have been very greatly assisted by a paper by 
 
79 
 
 Dr. Eamsay H. Traqnair, published in 1865.*" The sole is not considered in this 
 paper, but the interpretation of the distribution of the organs and canals in this 
 species is comparatively easy after Dr. Traquair's lucid explanation of the derivation 
 of the arrangements found in other flat-fishes from the original symmetrical condition. 
 The diagram of the arrangement in the cod which I have given is copied, with 
 slight modifications, from Dr. Traquair's ; and my diagram of the arrangement in the 
 sole is constructed on the same plan as his diagrams of the arrangements in the plaice 
 and other species. 
 
 Minute Structure of the Skin, Dermal Tubes, and Sense-organs. 
 
 Wlien thin sections of the skin are prepared and examined under the microscope, 
 the derma is seen to be composed of a number of sheets and bands of felted fibres, as in 
 PI. XIV, 6. In my preparations no nuclei are visible in this tissue, but the pieces of 
 skin were decalcified in weak nitric acid before they were cut, in order to remove the 
 lime from the scales, and the action of the acid may have somewhat altered the 
 condition of the fibrils. The scales, as seen in section, consist of thin laminae lying one 
 upon another ; the laminae are entirely homogeneous in structure, and seem to be 
 simply sheets of the fibrous tissue which have been consolidated and then impregnated 
 with calcareous salts. The scales are contained in cavities of the fibrous tissue. In the 
 preparations the fibrous tissue is separated slightly from the surface of the scales, but 
 this is doubtless due to the shrinking produced by the process of preparation, and in 
 life the fibrous tissue is in contact with the surface of the scale. Above the scales 
 there is a layer of delicate spongy fibrous tissue in which the fibres are short, and run 
 in a vertical as well as a longitudinal direction; this reticular tissue contains 
 numerous nuclei. This tissue separates the external surface of the scale from the 
 dense fibrous laminated tissue, while the internal surface of the scale is in immediate 
 contact with the latter. The epidermis consists of several, six or seven, layers of cells. 
 At the base of the epidermis the cells are polygonal and as broad as they are high : 
 each cell contains a large nucleus, which becomes deeply stained under the action of 
 staining liquids. Towards the outer surface most of the cells become thin and flat, 
 as in the human epidermis, but in preparations a certain number of them are large 
 spherical vesicles. These are mucous cells. The surface of the sole as of most other 
 fishes is. during life, always covered with a certain amount of slimy mucus which ia 
 derived from the epidermis. This mucus is produced by the discharge of the contents 
 of the globular mucous cells just mentioned. The cells at the base of Ihe epidermis 
 are constantly multiplying and growing, and in consequence the outermost of them 
 are gradually pushed to the surface. The superficial layers are as constantly broken 
 down and, as it were, dissolved away, some of the cells becoming, before they reach 
 the surface, converted into capsules of mucus, and this mucus, together with the 
 
 * "On the Asymmetry of the Pleuronectidae, as elucidated by an Examination of the Skeleton in 
 the Tarbot. Halibat, and Plaice." (" Trans." Lin. Soc., vol. xxv.) 
 
SO 
 
 debris of the other superficial cells, forms the slimy coating of the fish's skin. There 
 are no special glands connected with the skin of the sole. 
 
 In the outermost layers of the fibrous derma, immediately beneath the epidermis, 
 are situated the pigment cells or chromatophores. Some chromatophores are also 
 found in a deeper position, in the fibrous tissue which lies between the deeper parts of 
 the scales, but no pigment is found below the level of the skin to which the anterior 
 edges of the scales reach. The epidermis and the thin subjacent layer of the derma, 
 which contains the chromatophores, are continued over the exposed portions of the 
 scales, with the exception of the longest most posterior spines of the scales : these pierce 
 through the skin and epidermis and project beyond the latter. 
 
 The appearance of a longitudinal section through the dermal tube of the lateral line, 
 magnified 40 times, is shown in Fig. 6, Plate XIV. In other parts of the skin muscles 
 are of course found below the derma, but the dermal tube of the lateral line lies 
 directly above the connective tissue partition between the dorsal and ventral lateral 
 muscles, and the connective tissue of this partition passes directly into the skin. 
 The fibrous tissue of this partition contains large spaces occupied by loose 
 reticular tissue the meshes of which are large and filled during life with lymph ; 
 this tissue is seen in the lowest part of the figure. The figure includes one whole scale 
 of the lateral line and parts of two others ; the three pores, p,p,p, corresponding to 
 these scales are seen leading into the dermal tube. The section passes longitudinally 
 through the centre of the dermal tube and therefore the roof of the tunnel formed by 
 each scale is seen above the dermal tube, and the floor below it. The dermal tube is 
 seen bending down to pass through the hole in one scale to enter the tunnel of the 
 scale behind it ; beyond the hole in the floor of the scale a branch of the dermal tube 
 passes backwards to open on the surface at the external pore. The dermal tube is 
 lined by an epithelium which is only separated from the surface of the scales by 
 a very thin fibrous membrane. This epithelium is continuous with the epidermis at 
 the external pores, but differs much from the epidermis in character. It is of very 
 slight thickness, consisting only of two or three layers of cells. The lowest layer 
 consists of small undifferentiated cells which grow and multiply, continually 
 replenishing the outer layers. Nearly all these outer cells are globular and vesicular ; 
 that is they form hollow capsules, doubtless containing mucus. During life the dermal 
 tube contains mucus, which is the product of this epithelium. But at certain places 
 this epithelium contains sense-organs, consisting of portions of the epithelium which 
 have an entirely different structure and function. The cells of the sense-organs are not 
 secretory but sensory, and they are connected with nerve fibrils. One of these sense- 
 organs, as seen in longitudinal section, is shown at s.o, in PI. XIV, 6. It is situated on 
 the inner wall of the dermal tube, and lies on the floor of the tunnel of a scale a little 
 in front of the hole through which the dermal tube passes to the next scale. At a point 
 near the anterior and deep border of the scale containing the sense-organ there is a 
 small aperture in the scale through which a nerve passes from the skin below the scale. 
 
81 
 
 This nerve (n, Fig 6) runs posteriorly along the surface of the scale, beneath the 
 epithelium of the dermal tube, to the sense-organ. The sense-organ consists of a 
 number of thin elongated cells placed so that their length is almost perpendicular to the 
 wall of the dermal tube. Each of these cells contains in its lower portion a spindle- 
 shaped swelling which contains a nucleus. One end of each cell reaches the surface of the 
 sense-organ, and the other reaches its basement membrane : the cells are all in contact, 
 the nuclear swellings being so arranged that the cells are packed in the least possible 
 compass. Thus the nuclear swelling of one cell is at its base, that of the next some- 
 what higher up, so that the nuclei form two rows, and the nuclei of some of the cells 
 are even higher still, forming a third row. But it is only the nuclei which are in two 
 or three layers, the cells are all in a single layer side by side. The nuclei, in spite of 
 the arrangement described, occupy more space than the cells, and consequently the 
 base of the sense-organ is broader than its surface, so that only the central cells are 
 straight, the external cells curving at their upper ends towards the centre of the sense- 
 orcran. The upper end of each cell ends in a delicate protoplasmic hair which projects 
 into the cavity of the dermal tube. The lower end of each cell is continuous with one 
 of the ultimate fibrils of the nerve previously mentioned. I have not made out this 
 connection in all the cells, but I have traced it in some, and believe that it exists in all. 
 In some preparations a kind of clot is seen on the surface of the sense organ, and 
 sometimes this seems to have separated from the surface of the organ, breaking off the 
 sensory hairs and taking them with it. This clot often present a laminated appearance, 
 as if formed of thin layers one over another. It has been seen in some fishes in an 
 organ examined in a perfectly fresh condition. Prof. Emery* concludes that the laminse 
 of the clot, which is generally called the cupula, are successive cuticles secreted by 
 the peripheral cells of the sense organ. I think it is difficult to accept this conclusion, 
 and am inclined to think the cupula is, during life, of a mucous nature, and therefore 
 semi-liquid. It seems certain that the sensory hairs are imbedded in the cupula. It 
 is difficult to understand how such cells as those of the sense-organ should secrete 
 mucus or form a cuticle : perhaps the cupula is nothing more than the ordinary mucus 
 of the dermal tube which keeps a constant position in preparations because it is retained 
 by the numerous sensory hairs. 
 
 There is not a sense-organ to every scale of the lateral line ; in the middle of the 
 body there is a sense organ on every third scale, that is to say, there are two scales 
 bearing no sense-organs between two scales which bear them. The position of the 
 sense-organ in relation to the scale on which it is situated is always the same. 
 
 The function of these sense organs is still entirely unknown. It has been suggested 
 that they convey to the fish a sense of its position in the water, and so enable it to 
 retain its vertical position, but the evidence for this is not very conclusive : if it were 
 true we should expect to find the organs atrophied in the flat fishes which have 
 
 * " Fauna and Flora des Golfes von Neapel," "Fierasfer." 
 
 II 
 
82 
 
 abandoned the vertical position altogether. What stimulus affects the organs it is 
 difficult to imagine : and it is also difficult to understand how the sensory hairs act 
 immersed as they are in the substance, whether it be mucus or not, which forms the 
 so-called cupula. But that these organs are of great importance to aquatic vertebrates 
 there can be no doubt, since they occur not only in all kinds of fishes but in aquatic 
 Amphibia : they are even present in the tadpole and other larval batrachians so long 
 as they retain their aquatic respiration. 
 
 These sense-organs are in all cases first developed in the superficial epidermis ; the 
 development of the dermal tube in which they are enclosed takes place subsequently. 
 The dermal tube is formed from a superficial groove which appears on the surface of 
 the skin along the line where the sense-organs are situated. The groove becomes 
 deeper and its edges meet over it and coalesce everywhere except where the pores are 
 left by which the tube communicates with the exterior. In some fishes, e.g., Gobius, 
 the sense-organs remain superficial throughout life, no lateral dermal tube being 
 developed. 
 
 As I have already mentioned (p. 76) there are also a number of superficial sense-organs 
 on the under side of the head of the sole. These organs are situated in the depressions 
 between the villi or tactile filaments with which the skin in this region is provided. 
 The minute structure of this part of the skin is illustrated by Fig. I, Plate XV, 
 which is drawn from a section of the part of the skin above the posterior half of the 
 mouth cleft on the lower side of the body. Some of the filaments are long and slender, 
 others short and blunt. Eunning up the centre of each filament is a sausage- shaped 
 supporting rod which is composed of a tissue having the structure of fibro-cartilage. 
 In section this body exhibits fibres anastomosing with one another and running in a 
 direction transverse to the longer axis of the rod. These fibres contain nuclei, and 
 the interspaces between them are filled by a homogeneous solid substance of the 
 nature of cartilage. These supporting rods belong to the derma. The epidermis is 
 continued over the filament, becoming thinner at the apex, and between the supporting 
 rod or core and the epidermis is a continuation of the fibrous tissue of the derma. 
 Running up the sides of the supporting rod are several fine nerves. These nerves send 
 off fibrils which branch, and their ultimate ramifications enter the epidermis. There 
 are no special sense-organs of any kind in connection with these nerve fibrils : the 
 ultimate termination of the fibrils I have not been able to trace : they penetrate between 
 the cells of the epidermis, and doubtless ultimately come into connection with some of 
 the epidermic cells. Nerve-fibrils are known to enter the epidermis in the same way in 
 the skin of the tip of the human finger, and in all probability help to give that skin its 
 delicate sense of touch. I have indicated the connection of the ultimate nerve-fibrils 
 with the epidermis on the right side of the figure. On the left side of the figure 
 are sections of four short blunt filaments which do not project far beyond the surface 
 of the skin. Around the cores of these, besides the black lines indicating parts of 
 nerves, is a coarse stippling which represents the appearance of a curious granular 
 
83 
 
 tissue occurring in lliis position in all the filaments. This tissue obscures the nerve 
 fibres and makes it somewhat difficult to follow out their course in the sections. The 
 sections from which the present description is taken, and one of which is represented 
 slightly diagrammatic-ally by the figure, were prepared from pieces of skin treated when 
 fresh with chloride of gold. This reagent stains the nerves black or violet, and affects 
 the remaining tissues slightly or not at all. Thus the nerves can be traced through the 
 granular tissue just mentioned. The granular tissue is somewhat opaque, consisting of 
 irregularly branched cells the contents of which are coarsely granular. These cells 
 exactly resemble in structure the chromatophores of the right or coloured side of the 
 body, but they are not coloured. In fact, to use a seeming paradox, these cells are 
 colourless chromatophores ; that is to say, they are chromatophores of which the granules 
 instead of being black or orange are white and opaque. Thus the white colour of the 
 under side of the sole is not due to the absence of chromatophores, but merely to the 
 absence of what is usually called colour in the chromatophores ; the pigment cells are 
 not absent from the skin of the lower side, but are bleached. It is a very common 
 thing to find coloured blotches on the lower side of a sole, and from the above it is 
 evident that these coloured blotches are not due to the development of chromatophores 
 in certain areas while they are absent elsewhere, but are due to the fact that the 
 chromatophores in these areas are coloured, while in the rest of the skin of the lower 
 surface they are white. 
 
 One of the superficial epidermic sense-organs of the under side of the head is 
 represented in section in the figure. It will be seen that they do not differ in structure 
 from the sense-organs of the dermal tube of the lateral line. The sensory hairs are 
 present in these organs, though not shown in the figure, as they are not well preserved 
 by the chloride of gold method of preparation. 
 
 M 2 
 
84 
 
 CHAPTER VI. 
 EMBEYOLOGY. 
 
 THE ripe ovum of Solea vulgaris after it has been removed from the body of the fish 
 and is floating in sea water, and when it has not been fertilised, has the following 
 structure: The whole ovum is a spherical transparent body measuring 1'47 to 1-51 
 mm. ('05 to '06 inch) in diameter, the size of different eggs varying within these 
 limits. The ovum consists of a definite thin transparent membrane surrounding a 
 solid mass ; the former may be called the vitelline membrane, the latter the ovum in a 
 stricter sense of the word. The whole of the egg with its envelope corresponds only 
 to the yolk of a hen's egg, there is nothing about it which represents the " white " or 
 the shell of the latter. The yolk of a hen's egg is surrounded by a thin membrane of 
 its own which corresponds to the vitelline membrane of the sole's egg. The ovum 
 proper within the vitelline membrane consists of two different parts : a smaller 
 somewhat protuberant portion which is more granular and less transparent, and a 
 more transparent larger portion. The former is the germ (blastodisc), and consists of 
 living organic matter known as protoplasm. This germ is actually alive, and it 
 exhibits spontaneous movements and changes which gradually lead to the formation of 
 the young fish, while the larger portion is the yolk, and is simply a supply of very 
 nutritious food on which the germ lives and by means of which it grows. The yolk is 
 in fact gradually absorbed by the embryo during its development. In consequence of 
 the protuberance of the germ, the vitelline membrane being stiff and spherical, there is 
 a space between the membrane and the surface of the ovum all round the junction of 
 the germ with the yolk : this is the perivitelline space. Immediately beneath the germ 
 the yolk is divided up into large separate masses of a cubical shape : these masses 
 form a single layer, the rest of the yolk being undivided. The yolk is more or less 
 liquid, and it is confined within a delicate pellicle of protoplasm which extends from 
 the edge of the germ all round the yolk. Thus the yolk is really contained within the 
 protoplasmic germ. In fact the germ is the essential part of the ovum ; some animals 
 produce ova without either membrane or yolk : the yolk is to be regarded as an 
 accumulation of food material within the protoplasm of a reproductive "cell" or plastid. 
 On the surface of the yolk, immediately beneath its protoplasmic pellicle, are several 
 groups of minute oil globules. On account of their refracting power these appear 
 
opaque white by reflected light and dark by transmitted light. They represent an 
 excess of fatty matter belonging to the yolk. 
 
 I have not seen the ripe ovum of the sole immediately after its escape from the ovary. 
 But the ova of other flat-fishes have been studied by myself and others immediately 
 after extrusion, and it has been found, e.g., in the cod and the flounder, that at first 
 the germinal protoplasm is not aggregated into a protuberant mass, but is more 
 extended over the surface of the yolk, and that the vitelline membrane is everywhere 
 in direct contact with the ovum. The aggregation of the protoplasm into a distinct 
 germinal mass and the consequent formation of the perivitelline space take place after 
 the extrusion of the ovum, and take place in the same way whether the ovum is 
 fertilised or not. 
 
 I have not particularly studied the spermatozoon of the sole, but have observed it 
 sufficiently to state that it does not differ in structure in any important respect from 
 that of other flat-fishes. The milt is very scanty in quantity and thin and transparent 
 in appearance, but its peculiarities will be considered in connection with the subject of 
 the artificial propagation of the species. I have given a figure of the spermatozoon of 
 the dab, Pleuronectes limanda, PL XIII, 7, having accidently omitted to make a drawing 
 of that of the sole. In all bony fishes (Teleostei) the head of the spermatozoon is pear- 
 shaped, the pointed end being directed forwards in motion. The long slender vibratile 
 filament or " tail " is attached to the broader end of the head. The spermatozoa are 
 exceedingly small, quite indistinguishable to the unaided eye, but when the fresh 
 milt is placed under the microscope multitudes of them are seen actively lashing 
 themselves about in all directions. The total length of a spermatozoon of the sole is 
 about youths of an inch ("07 mm.). 
 
 Fertilisation of the ovum usually takes place immediately after extrusion, and 
 consists in the entrance of a single spermatozoon into the germinal protoplasm. I 
 have not studied the details of the process in the sole's ovum, but have done so in the 
 ova of the dab (Pleuronectes limanda) and another species (PL cynoglossus). The 
 process in the sole is doubtless the same as in these species, and is as follows : Over 
 the centre of the germinal protoplasm there is a minute aperture in the vitelline 
 membrane which is called the micropyle. Through this aperture a spermatozoon passes, 
 and penetrates into the germinal protoplasm. In the latter is the nucleus which, as 
 the ovum matures, becomes indistinct, and can only be made visible by coagulating 
 the protoplasm with acetic acid or some other chemical reagent. This nucleus can 
 also be stained, as it absorbs colouring fluids, such as solutions of carmine, to a greater 
 extent than the surrounding protoplasm. The nucleus before fertilisation is complete 
 passes to the surface of the germ and gives off in succession two small portions of itself, 
 the polar bodies, which are expelled from the ovum. The nucleus after this forms the 
 female pronucleus, and the head of the spermatozoon which has entered the germ 
 forms a similar minute body, the male pronucleus : these two unite into a single 
 nucleus, the segmentation nucleus 
 
86 
 
 The fertilised ovum of the sole, then, possesses the same structure as was above 
 described in the unfertilised, and also something not mentioned in the previous 
 description, namely, a nucleus in the germ formed by the coalescence of two pronuclei, 
 one derived from the nucleus of the unfertilised egg, the other from the head of a 
 spermatozoon. 
 
 The first visible change which takes place after fertilisation is the division of the 
 germinal mass into a number of small segments. The mass first divides into two 
 halves separated by a superficial furrow extending across its middle. Another furrow 
 then appears crossing the first, so that the mass is divided into four portions. Each of 
 these divides again into two and then into four, so that there are now sixteen segments. 
 Then divisions take place in a direction parallel to the surface of the mass, so that it 
 comes to consist not of one layer of segments, but of several layers. As this process 
 of segmentation continues the segments continually become smaller, so that the 
 condition is reached which is seen in Plate XV, Fig. 3. During this time movement of 
 the protoplasm on the surface of the yolk and between the yolk segments has caused the 
 latter to extend somewhat beyond the edges of the germinal mass. 
 
 The mass of protoplasmic segments into which the original single large mass has 
 thus been converted now begins to become thinner and broader, extending itself 
 so as to envelop the yolk, as in Plate XV, Fig. 4. When this process begins a cavity 
 is formed between the yolk and the central part of the germinal mass. The germinal 
 mass as it extends over the surface of the yolk soon becomes so thin that it must now 
 be called the germinal membrane (blastoderm). Fig. 5 shows the stage at which the 
 germinal membrane has enveloped more than half the yolk. The external part of the 
 germinal membrane for some distance from the edge is thicker than the central 
 portion : this thicker portion rests upon the yolk, while the central part is separated 
 from the yolk by the flat cavity already mentioned. This cavity is not exactly in the 
 centre of the membrane, the thicker external ring extending farther inwards (on the 
 right of Fig. 5) at one point than elsewhere : this broadest part of the germinal ring is 
 also the thickest part, and it forms the rudiment which will give rise to the upper or 
 dorsal part of the body of the young fish. It must be observed that the layer of yolk 
 segments extends pari passu with the germinal membrane, and that the patches of oil 
 globules are always at the edge of the extending membrane. 
 
 As the germinal membrane continues to extend the circumference of the germinal 
 ring of course gets smaller ; the rudiment of the young fish above mentioned remains 
 with its internal extremity in the same position, continually increasing in length as the 
 edge of the membrane extends over the yolk, until when the yolk is completely 
 enclosed, the whole of the germinal ring has been taken up into this rudiment. The 
 dorsal rudiment by this time has become much thicker and forms an almost cylindrical 
 rod, from the sides of which the germinal membrane extends over the yolk. The oil 
 globules are now arranged beneath the sides of the dorsal rudiment, while the yolk 
 
87 
 
 segments form a layer extending over the whole surface of the yolk. The end of the 
 rudiment which was originally turned towards the centre of the germinal membrane 
 becomes enlarged and forms the head of the fish ; the point where the edges of the 
 membrane closed together forms the posterior end. After a short time two spherical 
 masses are seen defined in the head of the embryo : these are the first rudiments of the 
 eyes. The centre of the dorsal rudiment begins to be divided by transverse divisions 
 into segments : these segments are blocks of tissue which will afterwards form the large 
 lateral muscles of the fish. At the tail end a small round cavity appears, which 
 afterwards becomes part of the cavity of the intestine. These various structures are 
 seen in Plate XV, Fig. 6, and Plate XVI, Fig. 1, one of which shows a profile, the other 
 a ventral, view of the embryo at the stage now described. 
 
 At this stage scattered black dots have appeared on the external surface of the dorsal 
 rudiment, extending out over the surface of the yolk some distance from the sides of 
 the latter. These are pigment cells, and are situated in the skin : they are usually 
 called chromatophores. 
 
 What I have called the dorsal rudiment is the solid dorsal portion of the young fish 
 containing the rudiments of the brain and spinal cord, of the backbone below these, 
 and of the lateral muscles at the sides. The yolk sac represents the abdomen of the 
 young fish. The intestine is formed as a simple tube beneath the dorsal rudiment 
 resting on the surface of the yolk. It is at first closed at each end, neither mouth nor 
 anus being yet formed 
 
 After this stage a cavity appears at the anterior end of the embryo between the 
 germinal membrane and the yolk. The segmentation cavity previously described 
 ceased to be visible after the envelopment of the yolk by the germinal membrane, the 
 latter having come into contact with the former. The cavity which now appears has 
 exactly the same position as the segmentation cavity. The embryo grows out 
 posteriorly, forming a tail which is independent of the yolk sac. The black chromato- 
 phores increase in number and extend over the whole surface of the yolk sac, at the 
 same time they become branched, sending out short branches in all directions so as to 
 assume a stellate form. Other chromatophores also appear in addition which are of a 
 yellow colour, appearing darker when seen by reflected light. These changes are seen 
 in Plate XVI, Fig. 2. 
 
 As the tail increases in length a fold of the skin is formed in the middle line along 
 its dorsal and ventral edge ; the dorsal fold extending to the head of the embryo. The 
 other changes which have taken place by the time the young fish is hatched will be 
 understood by reference to Plate XVI, Fig. 3, which shows the fish immediately after 
 hatching. The yolk is now considerably diminished and the intestinal tube opens 
 behind it by the anus. The tail measured from the anus is as long as the distance 
 from the anus to the front of the head. The wide membranous fold is seen extending 
 along the middle ventral line of the tail and along the median dorsal line of the fish to 
 the back of the head : this is the primordial median fin. There is still no mouth. 
 
'88 
 
 Behind the eye is a small oval cavity containing two specks. This is the primitive ear, 
 the black specks being small particles of carbonate of lime formed within the auditory 
 cavity. Beneath the throat is seen a small tubular structure, which in the living young 
 fish pulsates regularly : this is the heart. From the line where the wall of the yolk sac, 
 or abdomen, joins the body there projects a semicircular membranous fold, which is 
 the beginning of the pectoral fin. No indication of the pelvic fins is yet present. The 
 trunk of the young fish is seen to be divided by a series of curved transverse lines : 
 these are the divisions between the muscular masses of which the trunk muscles are 
 composed. A kind of tube runs down the centre of the body, the contents of which 
 show a recticulate structure. This tube is the notochord, which contains gelatinous 
 material in a number of cavities divided from one another by thin partitions like the 
 cavities of a sponge. No bone is yet formed, but the vertebrae when they develop 
 arise as a series of bony rings formed round the notochord. The chromatophores are 
 now much more abundant than in the embryo before hatching ; there are still only 
 two kinds, the black and yellow, and both are much branched ; the two kinds are 
 everywhere mingled together. The pigment is abundant in the primordial median fin, 
 except at its posterior extremity. 
 
 Fig. 4 is a drawing from another recently-hatched sole, a few hours older than that 
 shown in Fig. 3. It will be observed that this figure shows the left side of the fish, 
 while Fig. 3 shows the right side, and that the two sides correspond in all respects. 
 The newly-hatched sole, or larva of the sole as it may be called, exhibits perfect 
 bilateral symmetry and therein resembles the adults of the greater number of marine 
 fishes. In Fig. 4 the olfactory organ is seen in front of the eye : it is on each side a 
 simple rounded cavity opening by a small aperture to the exterior. 
 
 It may be explained here, though it is not evident in the figures, that the cavity 
 surrounding the yolk in the larval sole contains primitive blood ; this primitive blood 
 contains minute colourless corpuscles, but no red corpuscles, which are not formed till a 
 later stage. The posterior end of the heart is open to this cavity, and the blood is 
 propelled from the cavity along the vessels at the side of the throat into the aorta 
 which runs beneath the notochord, and from the aorta to the cavity again. 
 
 The newly-hatched larva is from 3'55 to 3*75 mm. in length ('142 to '15 inches), or 
 between one-seventh and one-sixth of an inch, and about two and-a-half times as long 
 as the diameter of the ovum. 
 
 Up to this point the stages of development have been described as they are seen in 
 the living egg or newly-hatched fish, and all the figures referred to are from drawings 
 made by the aid of the camera lucida with a low power of the microscope. But, 
 although I have not studied the subject especially in the egg of the sole, it will be con- 
 venient here to give a brief description of the internal processes of development so far 
 as they are known to occur in the eggs of fishes. 
 
 The germinal ring when examined by means of prepared thin sections is found to 
 consist of three layers of cells. The outermost, which is two cells thick, is called the 
 
89 
 
 epiblast, and gives rise to the epidermis and other organs, the innermost, which is only 
 one cell thick, is called the hypoblast, and gives rise to the intestine, the middle layer is 
 called the niesoblast, and gives rise to the bones, muscles, and blood vessels. In the 
 dorsal rudiment the same three layers are found, but the epiblast is here thickened into 
 a great keel which extends inwards and causes the projection of the rudiment ; the 
 greater part of this keel ultimately separates from the extreme outer layer and forms 
 the brain and spinal cord. In the centre of the rudiment beneath the keel is a 
 cylindrical rod of cells which become converted into an elastic supporting structure, 
 the notochord. Bound the yolk, when it has been completely enveloped, there is a 
 layer of protoplasm containing nuclei, but not divided up into cells. The hypoblast 
 rests on this layer which is called the periblast. In the ventral region of the developing 
 embryo there is nothing but epiblast separated from the periblast by the flattened 
 cavity previously mentioned and called the segmentation cavity. The hypoblast bends 
 round and forms a straight tube which lies in a depression in the periblast. This tube 
 is the intestine, and when first formed has neither anterior nor posterior opening, 
 neither mouth nor anus. The swelling of the anterior part of the epiblastic keel forms 
 the brain and causes the protuberance of the head. The sense organs are formed by 
 thickenings of the epiblast: these thickenings become hollow and globular and, sinking 
 into the interior part of the head (except the nasal organs), become connected with the 
 brain by the sensory nerves. The nasal organs become cup-shaped, their cavities 
 being open to the exterior by a single aperture each, which is ultimately divided 
 into two, the two nostrils of each organ. The heart is formed from mesoblast which 
 extends below the front part of the intestinal tube ; it opens posteriorly at first from 
 the segmentation cavity, but when the yolk is absorbed becomes connected with 
 veins. The inner part of the mesoblast forms the muscles and skeleton, the outer part 
 forms the fibrous layer of the skin in which the scales are produced. Eings of bone 
 formed round the notochord give rise to the vertebrae, while the bones of the skull 
 are formed from the mesoblast round the brain. The formation of the mouth and gills 
 takes place after hatching by the development of rods of cartilage between which clefts 
 appear placing the anterior part of the intestine in communication with the exterior. 
 The mesoblast on each side splits horizontally, its inner thinner layer remaining 
 attached to the intestine to form the muscles and fibrous tissue of the gut, while the 
 outer part forms the body muscles. The cavity thus formed is the body cavity, and at 
 the dorsal part of it are formed the kidneys and reproductive organs. The liver is 
 formed as an outgrowth from the intestine. The fins are merely folds of the skin, the 
 mesoblast of which gives rise to their muscles and bony rays. 
 
 I have not succeeded in obtaining any specimens of the young sole in process of 
 metamorphosis ; the next stage in which I have met with it is that of a small fish 
 having in almost all respects the same structure as the adult. The smallest specimens 
 of this kind which I obtained were from J in. to in. in length (12 to 15 mm.). 
 One of them is represented in Plate XVI, Fig. 5, magnified 8J times. The great 
 
 N 
 
90 
 
 similarity of the young sole at this minute size to the full-grown adult is evident from 
 the figure. The chief difference is in the relations of the intestine. The right lateral 
 diverticulum of the body cavity is scarcely at all developed, and the four lengths of 
 intestine which occupy that diverticulum in the adult are absent. The intestine 
 extends backwards only very slightly beyond the anterior ventral interspinous bone. 
 The dorsal eye is slightly nearer to the edge of the head than in the adult, otherwise 
 the metamorphosis is complete. The colour has disappeared from the lower side, the 
 markings of the species are completely developed on the upper side. The pigmentation 
 of the upper side is not nearly so dense as in the adult, and the whole body is some- 
 what translucent, but nevertheless when the young fish is seen in the living state by 
 reflected light, whether resting on the bottom or swimming horizontally in the water, 
 its upper side shows the same colour as the adult, and undergoes the same changes of 
 colour on different materials in consequence of the action of light. The identification of 
 the young sole, Solea vulgaris, at this stage is neither doubtful nor difficult, for, although 
 some of the characters of the adult are not discernible, others can be perceived easily 
 enough. The large number of anal fin rays distinguishes it from either S. variegata 
 or minuta, while the tubular form of the anterior left nostril distinguishes it from 
 lascaris. I obtained specimens of this stage on three occasions within a short time, in 
 1889, from the shore at low water at spring tides. On the third occasion I received 
 only one specimen which was nearly three-quarters of an inch long (18 mm.). 
 
 I could not trace the further development of these young soles, for they disappeared 
 from the shore. But no important changes of structure were required to produce the 
 adult, further development consisted almost entirely in the increase of size. For the 
 discussion of the later growth reference must be made to the next part of this 
 memoir. 
 
 The only other species of Solea whose development I have been able to study is 
 S. variegata. The eggs of this species are smaller than those of vulgaris, measuring 
 1'28 to 1-36 mm. in diameter. The egg, Plate XVI, Fig. 6, is easily recognised and 
 distinguished from that of S. vulgaris by the peculiarity of its oil globules, which, instead 
 of being very minute and numerous and aggregated in a number of distinct groups. 
 are of considerable size and scattered singly and separately all over the surface of the 
 yolk. The external layer of segmented yolk is present as in S. vulgaris. The develop- 
 ment of course takes place in the same way as in the latter. When the chromatophores 
 appear they form another distinguishing feature ; there are both yellow and black 
 chromatophores as in vulgaris, but the former are much lighter in this species, inclining 
 to lemon colour, while those of vulgaris are darker. 
 
 Figs. 1 and 2 on Plate XVII show two stages of the hatched larva of the " thick- 
 back." The younger, Fig. 1, immediately after hatching, has of course the largest 
 yolk-sac and the shortest length of body; it is 2 '42 mm. in length. The heart 
 is just visible, but is compressed between the yolk and the under side of the throat, 
 the pericardium being but slightly developed and scarcely visible. The stage shown 
 
91 
 
 in Fig. 2 is that of a larva two days after hatching ; the larva from which the figure 
 was taken was 2*52 mm. in length. 
 
 The eggs of the other species of Solea I have not yet seen, but for the sake of 
 comparison I have illustrated the development of several species of flat-fish. Figs. 
 3, 4, 5, Plate XVII, and Fig. 1, Plate XVIII, represent a series of stages in the 
 development of the common flounder, Pleuronectes flesus, from the time of hatching 
 till the completion of the metamorphosis. Fig. 3, Plate XVII, is from a larva hatched 
 under artificial conditions on February 18, 1889, and drawn two days afterwards : 
 its length was 3'56 mm. The chromatophores are arranged in such a way as to form 
 two transverse bands, one at the level of the anus, the other some distance behind it ; 
 two dark bands in these positions are more or less conspicuous in several species of 
 Pleuronectes in the adult condition. Fig. 4 shows the same larva when the yolk has 
 been entirely absorbed and the mouth and gill-slits have been developed : its length was 
 3' 94 mm. The pectoral fin is relatively very large at this stage. This condition was 
 reached in confinement on February 24, by larvae hatched on February 18. The next 
 stage was observed in young fish found in the harbour at Mevagissey at low tide on 
 April 2, and is represented in Fig. 5. The length of the fish from which this 
 figure was drawn was 10*5 mm., or a little over three-eighths of an inch. This stage 
 
 O 7 O O 
 
 is the beginning of the metamorphosis. The left eye has travelled upwards so as to 
 project above the edge of the head, but it is still on the left side. The little fish in 
 this condition swims on its edge, but slightly inclined to the left side. It is still 
 extremely transparent, so that when alive it is only rendered visible by the metallic 
 brilliancy of the choroid coat of the eyes, which shine through the transparent tissues 
 in the sun like two metal beads. The yellow spot in the visceral cavity in the figure 
 is the gall bladder. Fig. 1, Plate XVIII, shows a later stage in which the left eye 
 has reached the edge of the head, so that its lens and cornea are visible on the right 
 side. The fish from which this figure was taken was actually smaller than that 
 represented in Fig-. 5, Plate XVII, probably because its metamorphosis had begun 
 somewhat earlier. It seems that in some individuals the metamorphosis is completed 
 while they are smaller in size than others at an earlier stage of development. The 
 fish represented in Fig. 1, Plate XVIII, was exactly 1 cm. in length. It was much 
 more opaque and more pigmented than the stage previously described ; in fact, though 
 slightly translucent when seen under the microscope by transmitted light, to the 
 unaided eye it appeared quite opaque. It will be noticed that the interval of time 
 between the stage of Fig. 4, and that of Fig. 5, Plate XVII, was about five weeks, and 
 that in that time nearly all the organs had reached their final form. The muscles 
 and skeleton have developed very greatly. The part of the body behind the anus 
 has increased very much in dorso-ventral breadth, and in it the vertebrae with their 
 spines, the interspinous bones, and the fin rays have been completely formed. 
 
 Fig. 2, Plate XVIII, represents the larva of the dab (Pleuronectes limandd] imme- 
 diately after hatching. The larva from which this figure was taken was hatched in 
 
 x 2 
 
92 
 
 the Laboratory from an egg artificially fertilised on March 1, 1889. The length 
 of the larva was 2 '87 mm. The development of chromatophores in the median 
 fin fold does not take place in this species at so early a stage as in P. flesus. 
 
 Fig. 3 of the same Plate represents a stage in the development of P. microceplialus, 
 the merry sole of the Plymouth fishermen, the lemon sole of Scotland and most parts 
 of England. The larva from which this figure was drawn was also hatched in the 
 Laboratory, and was four days old ; a small quantity of yolk still remained in the 
 body cavity. The chromatophores at this stage form five well-marked interrupted 
 transverse bands. 
 
 Fig. 4 of the same Plate represents a larva of the plaice (P. platessd], just after the 
 complete absorption of the yolk, This larva was also hatched in confinement : it was 
 drawn on February 27, five days after hatching. The larva of the plaice is much 
 larger than that of any of the other species here mentioned : at the stage figured it was 
 6 '5 mm. in length. 
 
 Fig. 5 represents the appearance and natural size of a living larva of the brill 
 (Rhombus Icevis). The young of the turbot and brill remain pelagic until after the 
 completion of the metamorphosis, that is, they swim about near the surface of the 
 water, and are commonly met with in the still waters of inlets and harbours at the 
 proper time of year, namely, in June and July. The one here represented was taken 
 in Sutton Pool, Plymouth, on June 1. Their pelagic habit is correlated with the 
 development of a relatively large air bladder, an Organ which is entirely wanting 
 in the adult. Although they swim freely in the surface waters they do not swim 
 vertically when the right eye has migrated to the left side, but horizontally ; during 
 metamorphosis their inclination from the vertical in swimming is proportional to the 
 degree of asymmetry of their eyes. 
 
CHAPTER VII. 
 
 STRUCTURE OF PHYLLONELLA SOLE^E, VAN BENEDEN AND HESSE, 
 A PAEASITE OF THE COMMON SOLE. 
 
 ON the lower side of the sole are usually found specimens of a small parasitic flat 
 worm which lives on the surface "of the skin. This creature was first named and 
 described by two Belgian zoologists, Van Beneden and Hesse, who called it Phyllonella 
 solece. It is of flattened shape, the dorsal surface being slightly more convex than 
 
 ay. 
 
 /P 
 
 ERRATA. 
 
 For Figs. 6 and 6, see page 93 of the text. 
 For Fio-. 7, read Fig. 6 (marked Fig. 6 in plate). 
 
 rig. U. 
 
 Fig. C. Egg of PJiyllonella solece^ seen under microscope in the fresh condition. Magnified 100 times. 
 Fig, D. Phyllonella solece, the ventral side uppermost, magnified 17 times; p.s., posterior sucker; 
 a.jji, anterior glandular patches; p., aperture of penis-sheath ; ., aperture of .the uterus. 
 
92 
 
 the Laboratory from an egg artificially fertilised on March 1, 1889. The length 
 of the larva was 2'87 mm. The development of chromatophores in the median 
 fin fold does not take place in this species at so early a stage as in P. flesus. 
 
 Fig. 3 of the same Plate represents a stage in the development of P. microcephalies, 
 the merry sole of the Plymouth fishermen, the lemon sole of Scotland and most parts 
 of England. The larva from which this figure was drawn was also hatched in the 
 Laboratory, and was four days old ; a small quantity of yolk still remained in the 
 body cavity. The chromatophores at this stage form five well-marked interrupted 
 transverse bands. 
 
 Fig. 4 of the same Plate represents a larva of the plaice (P. platessa), just after the 
 complete absorption of the yolk, This larva was also hatched in confinement : it was 
 drawn on February 27, five days after hatching. The larva of the plaice is much 
 larger than that of any of the other species here mentioned : at the stage figured it was 
 6 - 5 mm. in length. 
 
 Fig. 5 represents the appearance and natural size of a living larva of the brill 
 (Rhombus Icevis). The young of the turbot and brill remain pelagic until after the 
 completion of the metamorphosis, that is, they swim about near the surface of the 
 water, and are commonly met with in the still waters of inlets and harbours at the 
 proper time of year, namely, in June and July. The one here represented was taken 
 in Button Pool, Plymouth, on June 1. Their pelagic habit is correlated with the 
 development of a relatively large air bladder, an organ which is entirely wanting 
 -i_^w_oilij Althmmh they. swim. freely in the surface waters they do not swim 
 
CHAPTER VII. 
 
 STKUCTUKE OF PHYLLONELLA SOLE^E, VAN BENEDEN AND HESSE, 
 A PAEASITE OF THE COMMON SOLE. 
 
 ON the lower side of the sole are usually found specimens of a small parasitic flat 
 worm which lives on the surface "of the skin. This creature was first named and 
 described by two Belgian zoologists, Van Beneden and Hesse, who called it Phyllonella 
 solece. It is of flattened shape, the dorsal surface being slightly more convex than 
 
 Fig. C. 
 
 Fig. D. 
 
 Fig. C. Egg of Pfiyllonella solece, seen under microscope in the fresh condition. Magnified 100 times. 
 Fig. D. Phyllonella solece, the ventral side uppermost, magnified 17 times; p.s., posterior sucker \ 
 a.g>, anterior glandular patches ; p., aperture of penis-sheath ; u., aperture of the uterua, 
 
94 
 
 the ventral, and the outline of the body is an oval with projecting ends, so that its 
 shape resembles that of a small leaf. The animal, when adult, is usually about one- 
 fourth of an inch in length (6 or 7 mm.), and one-eighth of an inch (3 mm.), in 
 greatest breadth, but young individuals are smaller, and larger specimens are often 
 seen. The structure of this parasite is shown in the accompanying woodcut, Fig. D, 
 which represents the appearance of a living specimen under the microscope. At the 
 posterior end of the body is a large muscular sucker, p. s., almost circular in shape : 
 the concavity of this sucker is ventral, and it is attached to the body by a peduncle 
 at about the middle of its dorsal surface. On the ventral side of the sucker are two 
 pairs of hooks imbedded in the skin, with their recurved points protruding. One 
 pair of these hooks are long and directed backwards, their points being near the 
 posterior edge of the sucker, the other pair are short, and their points near the centre 
 of the sucker. At the anterior end of the body there is a semicircular projection, the 
 ventral edges of which are provided with a pair of glands, a.g., for adhesion Behind 
 this projection is the small mouth, and at the left hand side of the projection are the 
 two genital apertures, p., u., close together. The worm crawls about on the skin of 
 the lower side of the sole, anchoring itself to the spines of the fish's scales by means 
 of its sucker and its hooks, and using the anterior glands for adhering by that end 
 when it moves its posterior sucker from one position to another. 
 
 The most extensive and conspicuous organs are the generative, male and female, 
 for the animal is hermaphrodite, arid each individual produces both spermatozoa and 
 ova. The digestive organs are small, consisting only of a sac-like organ into which 
 the mouth opens, and which is lined by very large cells with enormous nuclei. This 
 organ may be called the alimentary sac, since it presents no distinction of parts. In 
 front of the alimentary sac dorsally are two simple nerve ganglia, giving off a main 
 lateral nerve cord on each side, which passes backwards. In the skin above these 
 ganglia, the cerebral ganglia, are two pairs of eyes, or rather pigment spots which 
 are doubtless organs sensitive to light. The renal organs consist of a system of minute 
 ramified ciliated tubes communicating with two main lateral tubes, which probably 
 open by a single dorsal opening at the posterior end. The rest of the body consists 
 of the generative organs, and a dense parenchyma of cells filling up the interspaces 
 between the various organs. 
 
 Uniformly scattered throughout the parenchyma of the body are a large number of 
 globular organs consisting of aggregations of peculiar cells : these are the yolk-glands. 
 They are situated at the ends of the ultimate ramifications of a ramified system of tubes 
 which are the yolk-ducts, and which are completely filled with granular gtobules similar 
 to the contents of the cells of the yolk-glands. The yolk-ducts on each side of the body 
 ultimately unite into a single large duct which opens into a sac situated a little to the 
 left of the middle line, about one-third of the length of the body from the anterior 
 end. This is the yolk-reservoir : it is elliptical in shape and transversely placed. The 
 yolk-reservoir is filled with the same material as the yolk-ducts ; the terminal yolk-ducts 
 
95 
 
 which open into it on each side are ventral in position. The ovary is a flattened sac 
 with a circular outline situated immediately behind the yolk-reservoir. It is filled with 
 small spherical ova, each containing a large nucleus or germinal vesicle. In front of 
 the ovary, dorsal to the right main yolk-duct, is a sac with the shape of a pyramid. 
 Into this sac or vestibule open a short oviduct from the ovary, a short duct from the 
 volk-reservoir, and two minute short ducts from two spherical capsules containing 
 spermatozoa. Here the egg is fertilised. From the vestibule the oviduct is continued 
 for some distance as a narrow convoluted tube, which then suddenly expands into a 
 thick-walled sac shaped like a club, the thick end being internal, and the thin end 
 opening to the exterior on the edge of the body to the left of the anterior apex. This 
 thick-walled sac may be called the uterus. The fertilised ovum in the vestibule is 
 surrounded by a quantity of yolk, and the compound mass thus formed passes down the 
 oviduct to the uterus, where it is surrounded by a chitinous hard shell produced from 
 the wall of the uterus. The shell has the shape of a triangular pyramid, and its apex 
 is prolonged into a long thin filament, swelling at intervals into bead-like globules. 
 This filament is doubtless adhesive, and by it the egg when laid, Fig. C, is attached to 
 the skin of the sole, there to develop into a young Phyllonella. 
 
 The primary male organs are a pair of globular testes situated a short distance 
 behind the ovary, one on each side of the middle line. These testes are simple sacs, 
 the walls of which are lined by cells which give rise to the spermatozoa. Some of 
 these cells become free in the cavity of the testis, and undergo subdivision, each of 
 them forming a spherical cluster of small cells, the spermatoblasts, each of which is 
 converted into a spermatozoon. From the anterior surface of each testis passes off a 
 tube or duct, the vas deferens ; the two ducts unite just behind the ovary, and the 
 single vas deferens passes round the left side of the ovary, and the left side of the yolk- 
 reservoir, dorsal to the left main yolk-duct. In the part of its course which lies in 
 contact with the yolk-reservoir the vas deferens is connected with a coiled sac closed 
 at its farther end. This is a reservoir for the ripe spermatozoa, and must be called the 
 vesicula seminalis. After a tortuous course the vas deferens opens into an intromittent 
 organ, the penis. The mechanism of this organ I have not been able completely 
 to elucidate. It consists principally of a club-shaped structure lying between the 
 uterus and the alimentary sac. Along its outer half this structure contains a canal, 
 which is at the side of it, not in the centre : into this canal the vas deferens opens, 
 and by it the spermatic fluid is conveyed to the exterior. The inner half of the 
 structure contains granular matter, but, as far as I can make it out, is not a gland. 
 At the base of the penis is a pear-shaped structure with radiating bands in its interior, 
 which converge into a band apparently of muscle, which seems to run into and become 
 merged in the substance of the penis. I am inclined to think that these structures 
 have something to do with the protrusion and retraction of the penis, but I am unable 
 to understand how they act. 
 
 In the chief features of its structure Phyllonella solece resembles a number of other 
 
96 
 
 external parasites of fishes which are classed in a family called the Tristomidse. 
 Most of these forms possess a small sucker on either side of the anterior end of the 
 body as well as one large posterior sucker, hence the name of the family. The 
 glandular areas described on the anterior end of Phyllonella represent the anterior 
 suckers. The Tristoniidas belong to the order Trematoda. 
 
PART III. 
 
 BIONOMICAL. 
 
 O 
 
99 
 
 CHAPTER I. 
 
 GEOGRAPHICAL DISTRIBUTION. 
 
 THE common sole is a somewhat southern species. In the neighbourhood of the 
 British Islands it is found in considerable abundance all over the southern part of 
 the North Sea, south of a line drawn from Flamborough Head in Yorkshire to the 
 north-west coast of Denmark. North of this line it is scarce. It is occasionally taken 
 off the mouth of the Firth of Forth, but very rarely. It is said to have been taken in 
 the Moray Firth, and off the Orkney and Shetland Islands. On the east side of the 
 North Sea it enters the Baltic, being occasionally taken on the north and east coasts of 
 Denmark and the coasts of Schleswig-Holstein and Mecklenburg. Further east in the 
 Baltic it has not been observed. Occasional examples have been taken on the west 
 coast of Norway up to the sixty-fourth degree of north latitude the neighbourhood of 
 Trondhjem. It occurs in some abundance all round the shores of Ireland, and on the 
 west coast of Britain from the mouth of the Firth of Clyde southwards, becoming 
 more abundant towards the south. It is abundant in the Bristol Channel and 
 throughout the English Channel, in the Bay of Biscay and southward along the west 
 coast of Portugal. It extends throughout the Mediterranean and probably into the 
 Black Sea. How far south the species extends along the coast of Africa I have not been 
 able to ascertain : it is not mentioned in Lowe's " Synopsis of the Fishes of Madeira," 
 1837. 
 
 The other three species, lascaris, variegata, and lutea, are common to the south-west 
 coast of England and the shores of Italy. In all probability they occur also along all 
 the intermediate coast-line. Lascaris occurs also at Madeira, if the specimen called 
 lascaris by Gimther is to be considered as of the same species as the English form. 
 Solea impar, Bennett, and probably S. margaritifera, Giinther, both closely allied to 
 lascaris^ come from the Atlantic coast of northern Africa. 
 
 There are a large number of other species of Solea as here denned besides those 
 which occur in Britain. There are several which exist in the Mediterranean, namely, 
 Solea Kleinii, Solea ocellata, Solea monochir. One species is known from the west 
 coast of Africa, viz., Solea senegalensis. On the west side of the Atlantic the genus 
 is but slightly represented. One of the few things in which the citizens of the United 
 
 o 2 
 
100 
 
 States of America confess that their country is inferior to Europe is that they have 
 
 neither the sole nor the turbot in their seas. The only species of Solea on the 
 
 northern part of the Atlantic coast of the United States is Solea achirus, Linngeus, a 
 
 species with no pectoral fins, which grows to the length of only six inches, and is 
 
 quite useless as food. Solea inscripta, Gosse, occurs at Jamaica. Other similar species, 
 
 with pectorals rudimentary or absent, occur at the Keys of Florida. Solea reticulata, 
 
 Gronovii, maculipinnis, mentalis, Jenynsii, in Dr. Gunther's catalogue, are all forms 
 
 with rudimentary pectorals occurring on the Atlantic coasts of the West Indies 
 
 and South America. In the Indian Ocean, according to Dr. Gtinther, there is one 
 
 species, Solea Indica, from Madras, also belonging to the subgenus Achirus, In the 
 
 East Indian seas there are several species known: Solea heterorhina, from Celebes 
 
 and Amboyna, and Solea humilis, from the Malacca Straits and Java, with well 
 
 developed pectorals; Solea trichodactylus and S. Thepassii, with rudimentary 
 
 pectorals. Solea microcephala lives on the coast of New South Wales in Australia; 
 
 further north on the west side of the Pacific we have S. Japonica, from Japan, 
 
 S. ovata, from Chinese seas. On the east side of the Pacific, on the coast of Central 
 
 America, there are Solea scutum, S. Fonsecensis and S. fimbriata. Thus the genus is 
 
 well represented in all the tropical seas, extending into the temperate zones both to 
 
 the north and south. But no species is of any importance as human food except the 
 
 Solea vulgaris of Europe. 
 
101 
 
 CHAPTER II. 
 
 HABITS, FOOD, ETC. 
 
 THE habits of the adult sole in its natural state cannot be directly observed : we can 
 only ascertain the means by which it is captured, the character of the sea-bottom 
 whence it is taken, the animals which are taken with it, and the food which is found 
 in its stomach. By supplementing the knowledge thus gained with observations on 
 the living fish kept in large aquarium tanks we can obtain a tolerably complete 
 knowledge of the sole's mode of life. 
 
 The sole is rarely, if ever, captured by any other instrument than the trawl. The 
 great majority of the soles brought to market are obtained by the large beam trawl, 
 worked by the large deep-sea trawlers, but it is also frequently captured by the 
 otter- trawl used chiefly by amateurs, and also by the small trawls used for catching 
 shrimps and prawns. The usual depth at which soles are found is from 20 to 
 40 fathoms, but it may exist at greater depths ; it probably does not extend beyond 
 100 fathoms. 
 
 Adult soles may occur at any depth less than 20 fathoms, but usually in shallow 
 water, less than ten fathoms deep, only young individuals are found. However, 
 exceptions to this rule occur not infrequently ; the fisherman of the Plymouth 
 Laboratory has several times caught an adult sole in Plymouth Sound within the 
 Breakwater. Once he caught a full-grown specimen of large size in the Catwater, 
 which is the estuary of the Eiver Plym, opening into the north-east corner of the 
 Sound. On May 9, 1889, he took a specimen 13f in. (35 cm.) long, a short distance 
 from the mouth of the same estuary, and a third specimen he captured a little later 
 in another part of the Sound. Small specimens six and a half to nine and a half 
 inches (17 to 23 cm.) in length are not uncommon in the Sound, half a dozen being 
 frequently taken in two or three hours' work with the shrimp trawl. These immature 
 soles in fact, according to my experience, are more abundant within the Sound than on 
 the neighbouring open shores outside it. 
 
 Off Plymouth soles are comparatively scarce at the present time : it is rare to take 
 more than four or five in a single haul of the trawl, and sometimes only one or none 
 at all are obtained. At a considerable distance south of the Eddystone they become 
 
102 
 
 somewhat more plentiful. They are much more abundant on a rough area of ground 
 to the west of the Eddystone, off Dodman Point in Cornwall. In this neighbourhood 
 I saw about fifteen soles in a single haul of the trawl in April, 1889. This ground 
 is often called the " California " ground, a name which was given to it when it was 
 first worked at the time of the rush to the gold-diggings in California. On the area 
 called by the Plymouth fishermen the Mount's Bay ground, soles are fairly abundant. 
 This ground lies off the entrance of Mount's Bay to the south of the Wolf Eock. 
 When I was on a trawler working there in April, 1889, the catches of soles numbered 
 six, seventeen, and fifty-seven, in three different hauls. The species is still more 
 abundant on the fishing grounds off the north coast of Cornwall, and in 1889 large 
 numbers of trawlers from Lowestoft, Grimsby, and other ports on the east coast 
 worked over these grounds for several months in the earlier part of the year ; but 
 I have never been there myself. In 1889 the Newly n fishermen, who are usually 
 exclusively engaged in drift-net fishing, found that large soles were abundant inside 
 Mount's Bay on the west of the Land's End promontory. They obtained small 
 trawls about twenty feet long which they worked over this area from their small 
 luggers in the month of March, when no mackerel or other surface fish were to be 
 caught. One boat in which I went out obtained eleven, seventeen, and eleven soles 
 in three separate hauls, many of the fish being very fine specimens. 
 
 None of the grounds mentioned are at a much greater depth than forty fathoms ; 
 over the ground last mentioned the ground varies from twenty to thirty-five fathoms. 
 All these areas are more or less sandy, the sand being in all cases of a very fine 
 texture and of dull grey colour. Trawls cannot be worked over a hard and rugged 
 bottom formed of rocks, but some of the grounds above mentioned where trawling is 
 carried on are by no means smooth. From the California ground the trawl brings 
 up numbers of the large mussel-like bivalve, Pinna nobilis, called caperlonga at 
 Plymouth, numbers of Pectens, called at Plymouth queens, at other places scallops or 
 clams, and large rugged stones. But we may conclude from the habits of the sole in 
 the aquarium that such ground contains patches of loose sand or gravel, and that 
 the soles live on these ; for in the aquarium the sole invariably when alarmed, like 
 all other flat-fish, buries itself in sand or gravel by rapidly shaking its longitudinal 
 fins. If a live sole in captivity is placed in sea water on a smooth solid surface, such 
 as the bottom of a flat porcelain dish, or the bare wooden or slate bottom of a tub 
 or tank it instinctively shakes its fin in the peculiar way by which it shakes the sand 
 or gravel over its " back." when there is any sand or gravel beneath it. This rapid 
 movement of the fins is therefore a characteristic of its habits of life, and it is extremely 
 effective. The fish on a layer of sand, when alarmed, disappears in an instant, the 
 agitation of the sand renders the water around it turbid so that it is difficult to 
 locate the exact spot where the fish has buried itself. Usually when resting undisturbed 
 beneath the sand or gravel it leaves its eyes uncovered, and these can be detected by 
 careful search : but not easily for they do not differ greatly in appearance from small 
 
103 
 
 bright pebbles or fragments of fctone. When the material the fish rests on is fine, like 
 sand, or contains an admixture of fine particles, a thin layer of the finer material 
 remains on the back of the fish when it emerges and moves about ; the fine particle 
 are retained on the skin partly by the adhesive property of the viscid mucus which 
 exists on the skin of all fishes, and partly by the minute spines of the scales The 
 sole thus moving gently about with its upper side covered with sand is partially 
 concealed, often only its actual movement betrays its existence. 
 
 Solea lascaris is a rare fish in the neighbourhood of Plymouth. For a long time I 
 never met with a single specimen. The fishermen did not seem to know it by any of 
 the vernacular names given in books. The first specimen I obtained was discovered 
 by the Laboratory fisherman among a number of common soles exposed on the fish 
 quay for auction. He selected it on account of its peculiar appearance, after I had 
 described the species to him and requested him to search for specimens. The 
 fisherman to whom it belonged when asked its name said it was a " sand-sole." I 
 could not ascertain accurately where this specimen was taken, but it probably was 
 caught a long distance from land towards the central region of the channel. On 
 June 17, 1889, 1 trawled at night in Whitsand Bay for the purpose of obtaining if 
 possible young specimens of the common sole. In the products of this trawling I 
 discovered on my return three small specimens of Solea lascaris measuring 7|, 7^, 
 6f inches (19 cm., 19 cm., 17 cm.), respectively. The depth of water where these 
 were taken was three to five fathoms, the bottom a fine clean sand of light yellow, 
 almost silvery, colour. 
 
 Solea varieyata, the thickback, is very common off Plymouth, but only in deep 
 water. I have never met with a specimen in or near the Sound, either young or 
 adult. On April 19, 1889, when I was on board a trawler fifteen or sixteen miles 
 S.~W. of the Eddystone, 213 thickbacks were taken in a single haul of the trawl. On 
 the Mount's Bay ground they are much less plentiful. 
 
 Half-grown specimens of Solea lutea are fairly common in Plymouth Sound, but I have 
 never found adults there. The only adults I have seen were obtained from deep 
 water by a larger trawl, and the exact locality was not recorded. In the Sound the 
 young specimens, one to two inches in length, are especially abundant in Cawsand Bay, 
 in three to five fathoms of water on a bottom of fine sand of a dull grey colour. I have 
 frequently taken half a dozen there in a single haul of the shrimp trawl, together with 
 young scald-backs (Arnoglossus laterna). The shrimp trawlers believe both these fish to 
 be the young of the common sole. 
 
 I have not been able to keep thickbacks alive in the aquarium, but there are living 
 specimens of the lascaris and lutea in our tanks, and they do not differ in their habits 
 from the common sole. 
 
 There is no doubt, then, that the common sole lives naturally on ground consisting of 
 sand or gravel or other loose material, and that it has the instinct of seeking 
 concealment by burying itself beneath the surface of the ground by a rapid shaking of 
 
104 
 
 its fins, an instinct which is exercised at the least cause of alarm, as the fish is 
 exceedingly shy and timid. All the other flat-fishes have the same habit, but of those 
 observed in our aquaria, namely, the plaice, dab, flounder, and turbot, none remain 
 concealed so persistently as the sole, at least in the daytime. In the night soles 
 behave quite differently, they then emerge from beneath the ground and move actively 
 about in search of food. In the daytime it is extremely difficult to discover how 
 many soles there are in a given tank even by driving them out of the gravel with a 
 stick : but on going to the same tank in the dark with a lighted taper one may count 
 twenty or thirty where only five or six were expected. But they soon disappear if the 
 light is held over the surface of the water. 
 
 The sole then is a nocturnal fish in the aquarium, and therefore doubtless also at the 
 bottom of the sea. This agrees with the belief of the majority of trawlermen that 
 more soles are caught in the trawl by night than by day. I have met one or two 
 fishermen who deny this and assert that they have sometimes taken a good number of 
 soles in a daylight haul and scarcely any in the following night. But of course 
 exceptional cases may well occur, and are probably to be explained by the fact that 
 soles were abundant in the track passed over by the trawl in the daytime, and very 
 scarce in the ground swept at night. Of course some soles are taken in daylight, and 
 it will be easily understood when the mode in which the trawl works is considered, 
 that it depends on the position and behaviour of each individual sole whether it passes 
 over the foot-rope into the net or not. If the foot -rope is heavy and the trawl going 
 at a moderate speed it may disturb the ground deep enough to cause most of the soles 
 in its path to rise from the bottom, in which case they will most likely pass over the 
 foot-rope and be swept into the net : if on the other hand the foot-rope passes more 
 lightly over the surface, or if the soles bury themselves more deeply instead of rising 
 in alarm the rope will pass above them and they will escape capture. 
 
 There can be no doubt that at 30 to 40 fathoms depth beneath the surface of the 
 sea there is in the daytime a good deal of light, but still much less than at the surface 
 or in an aquarium tank. It has been ascertained that light disappears altogether at 
 200 fathoms, and if we assume that the absorption is proportional to the depth there 
 must be at 50 fathoms three-quarters of the quantity of light that exists at the surface. 
 Now the quantity of light in our aquarium is a great deal less than the quantity 
 outside, as a great part of the windows are obscured. It follows, therefore, that the 
 tanks in the aquarium are not very much more illuminated than the sea bottom at a 
 depth of thirty fathoms, and it may justly be concluded that soles in their natural 
 condition at that depth will for the most part remain buried during the day and emerge 
 from the sand to seek food at night : the sole therefore is a nocturnal fish in its natural 
 state. 
 
105 
 
 The Food of the Sole, and its Method of Feeding. 
 
 Although the sole is more active by night than by day, it can often be seen feeding 
 in our tanks in the daytime : there is not a constant supply of food in the tanks, and 
 when food is thrown in the fishes are usually so hungry that they begin to feed at 
 once. The food supplied to the soles and other flat-fishes consists principally of marine 
 worms (chiefly Nereis Dumerilii}, shrimps, and fish cut up into small pieces, usually 
 pilchard, mackerel, or gurnard. Of these the soles prefer the worms. In seeking their 
 food the soles are guided first of all by the sense of smell : by this they perceive the 
 presence of food in their neighbourhood, and the sense of sight is not employed 
 for this purpose. But in hunting for their food, and in localising its position before 
 biting at it, they rely entirely on the specialised tactile filaments of the skin on the 
 under side of the head. A sole when searching for food moves slowly about gently 
 tapping every part of the sandy bottom with the lower surface of its head. While 
 the sole is thus engaged its back is very frequently covered with a thin layer of 
 sand, so that scarcely any part of it is visible except the eyes and mouth and some 
 of the filaments below the snout when the latter is raised : it is only noticeable on 
 account of its movements, and because its form can be traced out and distinguished 
 from the flat surface of the sand around it. When in the course of this deliberate 
 exploration the lower side of the head feels a worm or other morsel of food, the sole 
 immediately seizes it with a vigorous and sudden snap of the lower half of the jaws 
 where the teeth are situated, and then swallows it with the sand which adheres to it. 
 I have often placed a worm on the upper side of a sole thus engaged in hunting its 
 prey. When this is done it makes not the slightest difference to the sole's behaviour : 
 the fish goes on tapping as before, evidently unconscious that it is carrying a palatable 
 morsel about with it. When the sole feels a worm or other piece of food with its 
 tactile filaments it cannot see it, and it never snaps at any food which it has not first 
 felt in this way. It is in fact unable to localise the position of its food and so to 
 direct the motion of its jaws to the object to be seized unless it has felt this object with 
 these tactile filaments. In other words the afferent sensory impulse produced by the 
 contact of the food with the sensitive filaments is necessary for the co-ordination of the 
 movements of the head and jaws by which the food is seized. 
 
 I have examined the intestines of a large number of soles in order to discover what 
 they had been feeding on before they were caught. It is the custom of trawlers to gut 
 their soles on board before they put them away in the hold of the vessel. They also 
 gut turbot, brill, dorey, and haddock, though of the latter they do not usually catch 
 many off Plymouth ; sometimes they take a considerable number off Mount's Bay and 
 the north coast of Cornwall. I obtained the intestines of soles sometimes by putting 
 them into a jar of spirit when I was out with a trawler myself, more frequently by 
 sending jars of spirit on board a boat and paying the men to bring back in them the 
 
 p 
 
106 
 
 intestines of all the soles they caught. It is very seldom that anything is found in the 
 stomach or intestine of a sole which can be satisfactorily identified. The stomach is 
 very slightly differentiated, it is only distinguished by the somewhat greater thickness 
 of its walls from the intestine, and is only marked off from the latter by a slight 
 pyloric constriction situated beneath the middle of the liver. The stomach after death 
 is almost invariably found empty. In the course of the intestine in a small percentage 
 of specimens small masses of the indigestible remnants of food occur. These masses 
 are usually black and enveloped in mucus. Usually they contain fragments of shells 
 with bristles of marine (Cheetopod) worms and other debris, and rarely something is 
 found in them whose specific origin can be recognised. The following is the record of 
 the intestines I have examined : 
 
 December 22 and 23, 1887, 9 miles W. by S. of Eddystone, 40 fms. A number of 
 
 specimens : six contained food. 
 
 (1.) Proboscis of Gasteropod, one small Ophiurid, pieces of Lamellibranch shells. 
 (2.) Pieces of Lamellibranch shells, and remains of the contained animals. 
 (3.) Fragments of Lamellibranch shells. 
 (4.) Ditto. 
 (5.) Ditto, and a long specimen of errant Poly chaste worm, genus and species 
 
 unrecognizable. 
 (6.) Fragments of Lamellibranch shells. 
 
 January 23, 1888. Nine miles S.W. of Eddystone, nine specimens, two containing 
 food. 
 
 (1.) Nika edulis, Eisso (a Decapod Crustacean) a single specimen; also a Holo- 
 
 thurian, sp. ? 
 (2.) Kernains of Chastopoda. 
 
 Same date. Six miles S. of Eddystone, sixteen specimens, all empty except one. 
 (1.) A piece of Sertularella (Hydroid). 
 
 January 30, 1888. Nine miles S.E. of Eddystone ; bottom sand. Fourteen 
 
 specimens, three containing food : 
 (1.) Two Synapta digitata. 
 (2.) Several Ophioglypka albida. 
 (3.) Two Ophioglypha albida. 
 
 February 7, 1888. Seven or eight miles W. by S. of Eddystone ; queen ground," 
 i.e., Pecten opercularis abundant on the bottom; nine specimens, four con- 
 taining food. 
 
 (1.) Nine Ophioglypha albida ; one Chajtopod unrecognizable. 
 
 (2.) One Chastopod. 
 
 (3.) Two Ophioglypha albida, one Amphipod. 
 
 (4.) Four Ophioglypha albida, one Amphipod. 
 
107 
 
 February 17, 1888. Twenty-five miles off the Lizard, 40 fms., sand. A great 
 
 number of specimens, eight containing food. 
 
 (1.) Eemains of Ophioglypha albida, and fragments of Lamellibranch shells. 
 (2.) Fragments of Lamellibranch shells. 
 (3.) A few fragments of shells, small pieces of membrane, and a large number of 
 
 large Chaetopod bristles, Aphrodite or Hermione. 
 (4.) Small Lamellibranch shells and fragments. One of these close to the anus 
 
 was entire, the colour unaltered and the animal undigested. 
 (5.) Small Lamellibranch shells and bristles of Aphrodite or Hermione. 
 (6.) Fragments of shells ; one small Lamellibranch Donax shell entire near 
 
 anus, animal absent. 
 (7.) Chaetopod bristles. 
 
 March 24. Off Mount's Bay. Thirty-seven specimens, ten containing food. 
 (1.) Pieces of Sertularian Hydroid, and remains of Chaetopod tube. 
 (2.) Anterior part of large Chsetopod of fam. Terebellidae. Fragments of shells. 
 
 Piece of Cellaria fistulosa. 
 
 (3.) Fragments of shells. Piece of Chaetopod tube. 
 (4.) Large Chaetopod bristles, probably of Hermione. 
 (5.) Piece of Chaetopod tube. Fragments of shells 
 (6.) Large bristles, probably of Hermione. 
 (7.) Piece of Chaetopod tube. Fragments of shells. 
 (8.) Fragments of shells. 
 (9.) Large bristles, probably of Hermione. 
 (10.) Tail of Decapod Crustacean, probably shrimp. 
 
 April, 1889. Off Mount's Bay. A large number of specimens. 
 (1.) Brfstles of Chaetopoda. 
 (2.) Bristles of Chaetopoda, among them the dorsal hook of Melinna cristata, 
 
 Malmgren. 
 
 (3.) Cuticle of a long specimen of Lumbrinereis sp. 
 (4.) A long, much-digested specimen of a Gephyrean, Sipv.nculus (?) 
 
 Also in several the aciculi of Hermione or Aphrodite and, in several, 
 cylindrical masses of debris containing small shells, e.g., Pecten tigrinus and 
 fragments of shells, entangled fibres, and pieces of membrane from the tubes 
 of tubicolous Chaetopoda ; also fragment of calcareous Polyzoon. 
 
 I believe that the fragments of shells and pieces of tough membrane which occur so 
 frequently in the sole's intestines are the remains of the tubes of Thelepus circinncita, 
 Malmgren, a Chaetopod belonging to the family Terebellidae, which inhabits a mem- 
 branous tube attached by its whole length to stones or shells, and covered externally 
 with calcareous fragments of all kinds, such as fragments of shells, or entire small 
 
 p 2 
 
108 
 
 shells, small stones, pieces of calcareous Polyzoa, &c. If this is so, this species and 
 others possessing a similar tube must form a large portion of the sole's food. The 
 total number of specimens the contents of whose stomachs are recorded in the above 
 list is thirty-six. Of these eighteen, or 50 per cent., contained remains of marine 
 annelids (Chtopods). If we add to these the number of specimens which contained 
 no remains of ChaJtopods but fragments of shells, probably derived from the tubes 
 of annelids, the number becomes twenty-eight or 77 per cent. Seven specimens 
 contained OpUoglypha alUda or other Ophiurid, or 19 per cent. One specimen 
 contained Synapta digitata, and one another Holothurian. Crustacea were present in 
 four specimens, or 11 per cent. In three specimens there were Mollusca probably 
 not derived from the tubes of Chsetopods, or over 8 per cent. Thus it is evident 
 that soles in their natural state feed chiefly on Chastopods, and it is probable that the 
 bodies of these are rapidly digested, so that it is very difficult to identify the species to 
 which their remains belonged. 
 
 Parasites. 
 
 The common sole is remarkably free from parasites, which in many fishes occur 
 constantly in great number and variety. I have seen no internal parasites in the sole 
 except an occasional Nematode, or small thread-worm. Of external parasites the only 
 form I have observed is the Trematode, Phyllonella solece, whose structure has been 
 described at length in the preceding Section. This creature appears to do no harm to 
 the fish. I have never seen any signs of irritation or inflammation of the skin on which 
 numbers of the parasite were living. Sometimes as many as twenty or thirty specimens 
 of the parasite occur on a single sole. Phyllonella is, as I have described it previously, 
 hermaphrodite, but it does not fertilise its own eggs. I have not seen it in copula- 
 tion, but it may be inferred from the structure of the generative organs that two indi- 
 viduals copulate reciprocally, the penis of each being inserted into the uterus of the 
 other, and the seminal fluid received by each uterus passing up the oviduct to be 
 stored up in the spermathecae. Fertilisation of the ova then takes place after copu- 
 lation, and is effected by the spermatozoa which are expelled from the spermathecse 
 into the vestibule into which the ova pass from the ovary. The fertilised ovum, 
 together with a quantity of yolk, is surrounded by its peculiar shell in the uterus and 
 then the deposited ovum adheres by its filament to the skin of the sole. I have not 
 traced the development of the parasite, but have no doubt that it is direct, that the 
 young is hatched in a form closely resembling the adult, and immediately adheres by 
 its posterior sucker to the sole's skin. The parasite doubtless is nourished by the 
 mucus of the skin on which it lives, but how far its nutrition is effected by digestion of 
 the mucus within the small alimentary sac, and how far by direct absorption through 
 the surface of the body, it is impossible to say. The parasites spread from one sole to 
 another in all probability when the fish accidentally come into contact with one 
 another. 
 
109 
 
 Enemies. 
 
 I am inclined to think that the principal and most deadly enemy of the sole is man. 
 But my evidence on this subject is by no means extensive. I have never seen an adult 
 sole in the stomach of any fish except the angler, but on the other hand, I have not 
 devoted much time to recording the contents of the stomachs of the larger predatory 
 fishes. Considering the great timidity of the sole it is difficult to avoid the inference 
 that it has many enemies to fear. Probably young soles and other flat-fishes living in 
 the conditions in which I found them in Mevagissey harbour are largely devoured by 
 gulls and shore birds when left by the receding tide in the shallow pools of the shore, 
 but I cannot assert this from direct observation. I have once or twice seen large 
 conger seize and devour flounders in a large tank of our aquarium ; there were no 
 soles in the same tank, but it may be inferred that conger would devour soles when 
 they had the opportunity, and that they do devour them in the open sea. But it 
 must be mentioned that our captive conger have by no means eaten all the flounders 
 in their tank ; probably they are never so hungry when fed regularly in captivity as 
 when they have to seek their own living in the wild state, and therefore conger may 
 reasonably be reckoned, on the south coast, among the enemies of the sole. I have 
 never eeea the common spotted dog-fish (Scyllium canicula and Sc. catulus) eat flat- 
 fishes in the tanks, though they are kept together in the same tank, but I think 
 cod and hake probably eat soles and other flat-fishes sometimes. One of the 
 commonest and most destructive enemies of ground fishes is the angler (Lophius 
 piscatorius] which grows to an enormous size and consists almost entirely of a huge 
 mouth and a small conical tail. I have frequently seen several large specimens of 
 this fish in a single haul of the trawl, and it constantly swallows other fish, including 
 flat-fish, even after it is in the trawl, its voracity being so great that it devours its 
 fellow captives. I have often seen soles taken from its stomach on the deck of a 
 trawler, and when extracted they are usually quite uninjured and are packed away 
 with the rest for market ; so that when we eat a sole we cannot be certain that it has 
 not been swallowed before. The angler is very inactive, its powers of locomotion 
 being limited. It partly buries itself in the sand on which it lives, and its colour and 
 appendages are such that in this condition its true character is perfectly concealed. 
 Over the head are long flexible filaments which are supposed to serve as a lure to 
 attract other fishes, but which probably have lit t tle effect on soles because they do 
 not hunt by sight. The angler thus forms a living and deadly pitfall. Any fish 
 coming unconsciously near its terrible gape is seized and engulphed in the great 
 cavity of its mouth, and soles of the largest size are swallowed by it with ease. 
 
110 
 
 CHAPTER, III. 
 
 COLOUR. 
 
 THE colour and markings of the upper side of the common sole, so far as they are 
 permanent.and characteristic of the species, have already been described. But, as was 
 mentioned in connection with that description, the skin of the fish is capable during life of 
 exhibiting considerable changes in the intensity and to some extent in the quality of its 
 colours. It is- exceedingly difficult to study these changes of colour in a living fish if the 
 material on which it is placed consists of fine particles, like sand or mud. For the fish 
 will persist in burying itself, and it is impossible to keep the skin free from particles of 
 the material, so that an accurate estimation of the colour under particular conditions 
 can scarcely be made. It is not difficult to keep a sole alive and in a healthy condition 
 for several days or even weeks in a shallow vessel supplied with a current of sea water. 
 In order to study the colour-changes carefully I kept specimens in this way, allowing 
 them to rest either on a solid surface or on a material of coarse texture without fine 
 particles, namely, coarse gravel or broken coal thoroughly washed in running water. 
 
 It is generally believed that the colour and marking of the sole's skin assimilates 
 itself to the colour and texture of the ground on which it rests. The following 
 observations were made in order to obtain definite results as to the extent and 
 character of this assimilation : I found that the contrast between the markings and 
 the ground-colour of the skin was most conspicuous when the fish was lying on a coarse 
 bright clean gravel. The gravel which I used had a general orange tint, but it 
 contained, besides yellow and orange coloured pebbles, a considerable number of black 
 and white. The appearance of the fish when resting on this gravel is shown in Plate I. 
 The ground colour is a greenish grey, and on this ground all the spots and markings 
 ever present in a sole are well marked. The principal dark blotches are very 
 conspicuous and well defined ; the irregular lighter bands which connect them ramify 
 in the spaces between them. The blotches are in places quite black, the black being 
 always confined to the outer part of the scales, the anterior part of these being always 
 somewhat lighter. The small white spots alternating with the blotches are also fully 
 expressed. The dark spot at the outer end of the pectoral is pronounced. It is 
 evident from the drawing that there is no exact similarity between the colour and 
 markings of the fish and the appearance of the surrounding gravel ; but it is also 
 
Ill 
 
 evident that the sole in this condition has, like the gravel, a variegated colouring 
 which at some distance from the eye renders it less conspicuous. The black spots and 
 the small white spots resemble the black and white pebbles of the gravel ; but on the 
 other hand, the continuous streak of opaque white along the edge of the fins is 
 distinctly conspicuous. A sole on gravel of this kind in a tank of some size is usually 
 either completely or partially buried under the gravel, and when the fins are thus 
 concealed and only part of the body exposed the sole may easily escape notice from a 
 human observer. On the other hand, it is also very easy to discover a sole in such a 
 condition when one looks for it. I believe that soles are seldom on gravel in their 
 natural state ; for I have found that on gravel or sharp sand they nearly always sooner 
 or later injure their fins or skin, and that abrasions so produced usually lead to 
 inflammation which causes death. 
 
 I placed another sole in a large shallow dish of white porcelain of the kind .used in 
 photographic manipulation. No material of any kind was placed in the dish, the fish 
 rested on the smooth white surface of the porcelain, and it was exposed to the full 
 daylight of the south windows of the Laboratory. Plate III is a reproduction of the 
 water colour drawing made from the sole in this condition. The paleness of the 
 colouring is extraordinary. The darkest tint in the blotches is a straw colour, 
 scarcely darker than the yellow of the fin-membranes. The ground-colour is a pale 
 grey with a slight tinge of blue in places. The white spots have disappeared entirely, 
 a result which would not have been expected : the spots where they existed are 
 somewhat blue. The dark spot on the fin is the darkest colour in the whole surface, 
 and has still streaks of dark brown between the fin rays. The sole used in this 
 experiment was a male 10^ inches (26'7 cm.) long ; but I found that the sole from 
 which Plate I was drawn became as pale as this when placed under the same 
 conditions. 
 
 The drawing of the sole just described was finished on June 8, 1889. This sole 
 died shortly afterwards and its appearance the day after death is represented on PL IV. 
 Another sole was taken for the drawing given in PI. I. I found when this latter 
 specimen was placed on the white porcelain that it became in a few minutes as light 
 as the figure on PI. Ill, but after it had been left all night in the same condition, on 
 the following morning the small spots which on gravel were opaque white had become 
 quite a dark grey and formed a marked contrast to the surrounding yellow. 
 
 To ascertain the maximum darkening of colour possible I used the same sole from 
 which PL I was taken. At first I found it difficult to produce any colouring much 
 darker than that of PL I. I lined the porcelain dish with black paper and placed the 
 fish on that, but it showed much the same colours. Then I varnished the dish with 
 black varnish of a deeper black than the paper, but got no better result. It then 
 occurred to me that the maximum of darkness could not be obtained until the quantity 
 of light was reduced ; accordingly 1 placed some washed coal at the bottom of a tub 
 about nine inches deep, and placed the sole on this ; then I placed the tub on the 
 
112 
 
 north side of the Laboratory at some distance from the windows in a position where it 
 was partly shaded. Then the result shown in Plate II was produced. But the 
 drawing for this plate had to be finished from the sole in the position I have described. 
 When the sole in the tub at its maximum darkness was carried to a table in front of 
 the window, the colours immediately began to get lighter. I found that the white 
 spots were exceedingly curious in their behaviour. As I have mentioned, on white 
 porcelain with plenty of light the white spots disappear as such and are changed into 
 bluish spots which sometimes become quite dark and conspicuous. The white spots 
 also disappeared in the sole which was kept on coal with very little light, reappearing 
 in a few seconds when more light was admitted. Thus the white spots are generally 
 visible except on white ground with a great deal of light, or black ground with very 
 
 little. 
 
 As to the rate of change it is usually quite rapid. A sole placed on the white dish 
 begins to get lighter almost immediately ; when it is disturbed with the hand the colours 
 become darker again, but when left alone it continues to grow paler. However, the 
 full effect is not seen till the fish has been some hours on the white ground. 
 
 A sole kept on coarse yellow gravel in front of a window is very inconstant in its 
 colouring : it sometimes exhibits its markings quite distinctly for some hours, and then 
 begins to grow pale, its black blotches almost vanishing. 
 
 On May ^2, I took a sole in which the markings were well expressed and the 
 colour moderately dark, and placed it on the white porcelain dish ; in a short time the 
 colours had become pale, and the dark blotches had become yellow. Then I placed 
 some fine shingle in the dish, intending to bring the markings out again, but to my 
 surprise the black blotches had not returned when I examined the fish the next 
 morning, and did not return completely when I placed it in an oaken tub nine inches 
 high, although the ground colour became somewhat darker. 
 
 All the changes are evidently due to the action of light and depend on the quantity 
 of light acting on the sole, not on the tint or texture of the ground on which it' rests. 
 The behaviour of the white spots I cannot yet explain, but all the rest seems to me 
 easily intelligible when regarded in this way. The colour and markings of the skin are 
 due to a vast number of chromatophores situated in the skin beneath the epidermis : 
 these are of two colours, the black and the yellow, and in some places there are others 
 containing a somewhat iridescent pigment. The last are particularly abundant in the 
 white spots, the black especially abundant in the dark markings. Light causes these 
 chromatophores to contract. When expanded the chromatophores or pigment-cells 
 are stellate, giving out ramified processes on all sides. When they are contracted all 
 these processes are withdrawn and each cell becomes a mere minute speck of pigment. 
 The position of these chromatophores is fixed, and therefore when they are expanded, 
 in the absence of light, the markings always reappear 'in exactly the same positions, in 
 fact the markings never entirely disappear. When a very strong light falls upon the 
 sole all the chromatophores are contracted, and all the parts become proportionally 
 
113 
 
 lighter; when the light is diminished the chromatophores expand and the colours 
 become darker. It is evident that with the same amount of illumination the alteration 
 of the colour and composition of the ground on which the sole rests alters the quantity 
 of light acting on the fish. For if the ground is black all the light which falls upon 
 that ground is absorbed, and the sole is only affected by the rays which fall directly 
 upon it, while if the ground is light-coloured nearly all the light which falls upon it is 
 reflected, and the diffused light which falls upon the sole is therefore greatly increased. 
 Just as a room is much lighter with the same windows if its walls are white than if 
 they are black. 
 
 The sole does not become uniformly coloured on a uniformly coloured ground. In 
 some of the laboratory tanks we have at the bottom a dark grey fine sand brought 
 from a part of the sea shore. This sand is extremely uniform in colour, and is exactly 
 of the same kind as the sand brought up by the trawl from the trawling grounds off 
 Plymouth and off Mount's Bay. In the tanks the soles usually have some of this sand 
 on their skins, and are therefore by no means conspicuous, but whenever their skins 
 are visible it is seen that the black markings are pronounced. The ground colour of 
 the soles in this condition approximates closely to that of the sand, but the presence of 
 the black spots does not seem to me to aid in the resemblance at all. I placed a large 
 sole in a shallow tub on some of this sand in order to make a careful observation. 
 After three days the colouring of this sole was as follows : The intermediate black spots 
 were almost invisible ; of the dorsal series the second was faint, the third, fourth, and 
 fifth well marked and black ; of the median series only the third and fourth were 
 well marked', but not black. The ventral spots were all visible but faint ; termination 
 of the pectoral reddish-brown, white spots alternating with black quite distinct. 
 
 
 
114 
 
 CHAPTER IV. 
 
 BREEDING. 
 
 THE egg of any particular species of fish is derived from a female individual of that 
 species, and after a process of development becomes another individual of that species, 
 presenting the characteristic specific characters. As the eggs of nearly all marine fishes 
 are left to themselves after being shed from the body of the female, the parents taking 
 no care of them, there are only two possible methods of ascertaining the species to 
 which a particular kind of egg belongs, or of tracing the development of any particular 
 species of fish. One method is to observe the deposition of the eggs by the female, or 
 to detain them by artificial fertilisation, then to examine these eggs and study their 
 development. The other is to examine all kinds of eggs that can be obtained, and to 
 trace their development up to the stage when the young fish presents specific charac- 
 ters by which it can be identified. The latter method presents more difficulties and 
 uncertainties than the former. 
 
 The greater number of marine fishes shed eggs or spawn at one particular period of 
 the year, a period extending over one or a few months. During the rest of the year 
 the development of ova in the ovaries proceeds gradually until the next annual breeding 
 season, when the annual crop of mature ova is again shed. As the ova develop in the 
 ovary they increase greatly in size and number, and thus the ovary itself becomes 
 much enlarged, and finally attains a very considerable size in proportion to the rest of 
 the body of the female. This enlargement of the ovary produces a corresponding 
 enlargement of the visceral region of the female. The small testes do not exhibit any 
 corresponding increase in size in the sole. In most fishes the testes in the male enlarge 
 at the breeding season in some degree, and in some they become very nearly as large 
 as the ovaries in the female. In the herring, for instance, it is not possible to distinguish 
 the males from the females among ripe specimens taken from the net when captured, 
 except by squeezing them and observing whether eggs or milt escape from the genital 
 aperture. But in the sole the ripe females can be easily distinguished by the enlarge- 
 ment of the ovarian region. It is not so easy to distinguish the smaller males from 
 small immature females, but among larger specimens the males can usually be identi- 
 fied by holding the fish up against the light, when in the male the posterior part of the 
 ventral region behind the intestines is seen to be translucent ; while in the female even 
 
115 
 
 if the ovary be not much enlarged it usually produces an opacity extending back far 
 behind the intestines near to the base of the tail. 
 
 The enlargement of the ovaries in the female sole becomes noticeable in January and 
 February, and ripe actively moving spermatozoa are found at this season by examining 
 under the microscope a portion of the testis of the male. I have not succeeded in 
 observing the natural deposition of the ova by living soles in captivity. I attempted 
 to do this in the spring of the present year (1889). At my request living soles were 
 brought to the aquarium during the previous winter months from the deep sea 
 trawlers and from the shrimp trawls worked in Plymouth Sound. But the specimens 
 obtained from the latter were all small, and although they lived well were too young 
 to breed ; while the larger ones from the large trawlers although living when brought 
 in invariably died after a few days in the tanks. The reason of this was that the large 
 soles were always more or less injured by the trawl or by subsequent handling. The 
 large trawls are towed usually for a long time, six to twelve hours or more, and the 
 captured soles and other fish during this time are injured by their struggles and by the 
 pressure and weight of the whole contents of the trawl. After the soles are placed in 
 tubs of water on board the vessel the voyage back to harbour occupies a long time 
 during which they are knocked about by the motion of the vessel. In consequence of 
 this mechanical violence the skins of soles brought to me from the deep sea were 
 always more or less abraded, and the scales torn off at one or more places. The 
 injured parts of the skin in a few days always underwent inflammation and sloughing, 
 and the diseased condition spread over the surface till the fish died. I have found 
 that the sole is tenacious of life and will bear a great deal of handling so long as the 
 skin is uninjured and the scales not removed, but that very slight injury to the skin 
 and scales leads to inflammation and death. In other fish, for instance, the conger and 
 grey mullet (Mugil chelo], considerable wounds on the skin are healed up in a very 
 short time without any inflammation ; the mullet will reproduce nearly all its scales in 
 a week or two. 
 
 I was unable therefore to study the breeding of the sole in specimens living in 
 captivity, and my investigations of the reproduction of this species, as of many others, 
 have been carried on at sea on board of trawling smacks by examination of the fish 
 when brought up by the trawl. 
 
 With very few exceptions the eggs of all deep sea food-fishes have been found to be 
 small in size, spherical in shape, transparent, and buoyant in sea water, and after being 
 extruded by the parent fish to undergo development while suspended, separate and 
 independent of one another, in the surface waters of the sea. All the flat-fishes 
 investigated have been found to shed eggs of this kind, and the sole proves to agree in 
 this respect with its allies, the plaice, flounder, turbot, &c. As in other fishes, gentle 
 pressure by the fingers and thumb applied to the ovarian region of the ripe female 
 sole causes the ripe ova to escape from the aperture by which the ovaries open to the 
 exterior. The ovaries lie entirely behind the aperture, and therefore the pressure must 
 
 Q 2 
 
116 
 
 be exerted from behind forwards. To examine the eggs and keep them alive they must 
 be received when pressed from the fish into a bottle of clean sea water. By squeezing 
 a number of captured soles in this way in March, when the ovaries are found to be 
 much enlarged and soft to the touch, some are found from which transparent eggs can 
 be pressed out. When a considerable pressure is exerted part of the contents of the 
 ovary can be squeezed out of any sole in which the ovaries are large, but when the 
 ripe transparent ova have once been obtained it is easy to distinguish them from the 
 .smaller unripe ova which escape when too much pressure is applied. These unripe ova 
 are yellowish-white and quite opaque : they do not separate from one another when 
 they fall into sea water, and membranes containing blood, derived from the tissues of 
 the ovary, are usually seen connected with them. In March a number of soles taken 
 at one haul of the trawl include, besides somewhat small immature specimens and males, 
 some large females which yield no ripe eggs, whose eggs have not yet reached maturity, 
 and only one or two from which ripe eggs can be obtained. Very often only a small 
 number of ripe eggs can be obtained when the fish is first squeezed, afterwards unripe 
 e^crs escaping. This proves that the eggs in the ovary are not matured all at once, 
 but in gradual succession. But the process of ripening seems to become more rapid 
 towards the end of the spawning period in a given fish than at the beginning, and the 
 eggs are evidently extruded immediately after they are ripe ; for although I have 
 examined large numbers of female soles which yielded a few dozen ripe ova. and whose 
 ovaries after the extrusion of these remained distended with unripe ova, I have only 
 once found a specimen whose ovaries contained ripe ova only. This specimen was 
 captured in a small-sized trawl worked from a Newlyn drift-net boat, on the morning 
 of March 23, 1889. I squeezed several thousand ripe ova from it, and the ovaries 
 were then completely empty. When all the ova of one season are shed the ovaries 
 are left as flaccid sacs which soon shrink considerably in size. Fish in this condition are 
 usually said to be "spent" or "shotten": the latter is the Scottish expression. The 
 specimen just referred to was of very large size. It measured 20tjr inches in length, 9^ in 
 breadth. The boat by which it was taken was trawling at a depth of about 30 fathoms 
 on the north-west side of Mount's Bay, off the coast of the Land's End promontory. 
 At the same haul, and in others previously made, shotten females, partially ripe and 
 unripe females were taken. The only conclusion to be drawn from these facts is that 
 only a few ova are ripened at a time in a given female at the earlier stages of the 
 spawning process; while at the later stages though a large number of ova are ripened 
 at one time they are very soon shed, and therefore the capture of a female at the par- 
 ticular moment when she contains a large number of ripe ova is a rare occurrence. 
 
 As stated above the spent condition of the female is easily recognised, and when 
 only spent females are captured the end of the spawning period for the species is 
 determined. I investigated the duration of the period during the two successive 
 seasons of 1888 and 1889, and found that it ended some weeks earlier in the latter 
 year than in the former, a fact which can only be explained by the warmer weather 
 
117 
 
 and consequently higher temperature of the sea in the spring of 1889. In the latter 
 year, when on board a trawler south of the Wolf Eock which lies to the west of the 
 Land's End, on April 11 and 12 I found nearly all the female soles completely 
 spent, a few containing nothing but a small number of ripe ova. The surface tempera- 
 ture of the sea at that time and place was 48'5 F. (9 0- 2 C.). In 1888 the fisherman in 
 the service of the Plymouth Laboratory obtained ripe soles on April 26 and 27 at a 
 distance of 40 miles north of the Land's End where the surface temperature was 46 0> F. 
 (7-7 C.) and the bottom temperature at 50 fins, was 45'0 F. (7-2 C.). The temperature 
 on April 6, 1888, to the south of the Wolf Eock was 46'0 F. (7-7 C.). The following 
 temperatures of the surface of the sea will show the difference of the two seasons : 
 
 1888. 
 
 1889. 
 
 March 6. S. of Wolf Rock .... 
 
 F. 
 
 C. 
 
 March 1. S. of Wolf Rock .... 
 
 F. 
 
 C. 
 
 45 -8 
 
 7 -6 
 
 48 -0 
 
 8 -8 
 
 April 4. .... 
 May 10. .... 
 
 45 -5 
 50 -1 
 
 7 -5 
 10 -0 
 
 April 9. 
 
 48 -5 
 
 9 '2 
 
 March 26. S. of Plymouth Breakwater 
 
 9Q 
 
 ** 
 
 April 9. Plymouth Sound .... 
 May 31. S. of Plymouth Breakwater 
 
 43 -0 
 43 -5 
 44 -0 
 49 -0 
 
 6-l 
 6'3 
 6 -6 
 9 -4 
 
 April 3. S. of Plymouth Breakwater 
 May 15. 
 
 ,, 21. 
 
 46 -0 
 54 -0 
 56 -5 
 
 7 -7 
 12 -2 
 13 -6 
 
 I have not determined so exactly the commencement of the spawning period in the 
 two seasons. In 1888 I examined several soles taken nine or ten miles W. by S. 
 of the Eddystone, on February 6. Only one yielded a few ripe ova, about a dozen ; 
 the rest were all unripe. 
 
 It is thus evident that the spawning period of the sole extends from the middle of 
 February to the end of April ; but that the greater number of individuals shed their 
 spawn in March, and the early part of April ; and that in warm seasons the spawning 
 is completed by the end of the second week in April ; while in colder seasons some 
 individuals are found still spawning up till the end of April, and a few eggs may not 
 be shed till the middle of May. 
 
 Little has yet been said about the males. Necessarily the male reproductive 
 elements consisting of the fluid milt, which contains the innumerable spermatozoa, 
 are discharged at the same period as the ova. But the testes and the milt of the sole 
 differ remarkably from those of any other marine fish I have examined. In other 
 fishes the testes in the spawning season are much enlarged, and very soft, so that 
 when the fish is opened very slight handling tears or ruptures the testes, causing the 
 escape of a thick viscous opaque white fluid, the milt. When the ripe male fish is 
 gently squeezed the milt escapes from the genital aperture in large white drops 
 having the appearance of milk, which when allowed to fall in sea water mix with it 
 and render it turbid. But when a male sole is opened in the breeding season the testes 
 
118 
 
 are neither much enlarged nor soft : they present much the same appearance as at any 
 other time of the year, though spermatozoa may be seen in a portion examined 
 under the microscope. And when the male is squeezed in the region of the testes, no 
 milk-white fluid is seen to escape ; some fluid may, and does, escape, but it is small 
 in quantity and thin and transparent, so that it is almost impossible when handling 
 soles on board a trawler to distinguish milt thus squeezed out from the sea water, 
 urinary fluid, or mucus from the skin, which also drip from the fish. 
 
119 
 
 CHAPTER V 
 
 DEVELOPMENT AND GROWTH. 
 
 THE eggs of fishes do not develop unless acted upon by the milt of the male. In all 
 species of marine bony fishes, with very few exceptions, the eggs do not come [into 
 contact with the milt until after they have been discharged from the body of the 
 female ; the whole process of development takes place outside the body of the parent in 
 the water of the sea. When the egg of a bird is laid it requires only to be kept at a 
 certain constant temperature to develop into a chick. When the egg of a snake or lizard 
 is laid it develops at the natural temperature of the air without any additional warmth 
 derived from the mother's body, and after a certain time a young snake or lizard is 
 hatched from it. When the egg, or " purse," of the skate is laid, or taken from the 
 body of the mother, it develops into a young skate as it lies at the bottom of the sea, 
 or in an aquarium tank. In the spiny dog-fish (Acanthias vulgaris), the eggs develop 
 within the oviducts of the female, and do not escape till they have reached the 
 condition of actively moving young dog-fish, in all respects except size resembling 
 their parents. But in all these cases the egg has been acted upon by the milt of the 
 male while still within the body of the female. When ripe eggs are pressed 
 from the ovary of the female sole into clean sea water they do not develop into 
 young fishes, but after floating for a few days in the condition previously described as 
 that of the unfertilised ovum they die, sink to the bottom, and decompose. This 
 proves that the eggs of the sole are not fertilised or acted upon by the male repro- 
 ductive elements within the body of the mother, but only after extrusion. 
 
 I have not been able hitherto to observe the natural process of shedding and 
 fertilising the eggs of the sole in living specimens in our tanks, and it is of course 
 impossible to observe the process in living soles in the sea. It is known that in 
 pelagic fish, like the herring, the fish spawn while collected in crowded shoals, 
 males and females being mingled together, and that the females simply shed their eggs, 
 and the males their milt into the water near the bottom simultaneously. The water 
 into which the eggs pass is thus teeming with spermatozoa, and none of them 
 can escape fertilisation. But in the herring the testes are as large as the ovaries, 
 and the quantity of milt produced by a single fish is very large. In most flat-fishes 
 
120 
 
 the testes are smaller than the ovaries, but still they are of considerable size, 
 and a considerable quantity of milt is produced. When we consider the small size of 
 the testes in the sole, and the small quantity of milt produced by a single male, it 
 seems difficult to understand how the large number of eggs produced by a single 
 female get fertilised at all. It seems to me that the only way to explain the facts is 
 to suppose that soles pair together like birds, or at least that the males do not like 
 some other fish shed their milt into the water at random, but shed it in the immediate 
 neighbourhood of a female at the moment when she discharges some ova. Some of 
 the wrasses pair and shed their milt in this way : I remember watching the process 
 once in one of the tanks of the Naples aquarium, but I do not remember to what 
 species the fish I saw belonged. 
 
 After I had drawn the inference that some kind of direct fertilisation took place in 
 soles, I found my opinion supported in a curious way by a statement of JSTordman in 
 his description of the fishes of the Black Sea, published in 1840 (see DemidofTs " Voy. 
 Euss. Merid. Zool., Ill, Poissons," Solea nasuta). The statement I refer to is that the 
 male and female of the species called by Nordman Solea nasuta, which is, as far as I 
 can see, the same as the Solea lascaris of the English coast, during copulation 
 adhere together by means of a glutinous liquid, and are sometimes taken in the nets 
 in this condition. 
 
 The ripe ova pressed from female soles during the spawning period, when placed in 
 a bottle containing sea water taken from the surface of the sea at the place where the 
 fish are caught, float at the surface of this water. That ova so obtained are perfectly 
 ripe and uninjured by the artificial method by which they are taken from the fish is 
 proved by the fact that when milt is added to the water the eggs are fertilised, and 
 when taken on shore and kept in proper conditions will go on developing until they 
 hatch into normal young fish. This is the process of artificial fertilisation which will 
 be more fully considered in the next section. The observation of artificially fertilised 
 ova kept in aquaria shows the rate at which the development proceeds at a given 
 temperature, for it must be noted that the rate of development of all fishes' ova varies 
 considerably according to the temperature of the water in which they are contained. 
 The following are the details of my observations on artificially fertilised ova kept in 
 aquaria : 
 
 May 16, 1888. Two or three soles' ova fertilised south of the Wolf Eock at 
 4 p.m. Temperature of surface of the sea, 50 F. (10 C.). 
 
 May 19. One of the above ova still alive: the blastoderm had completely 
 enveloped the yolk, and the dorsal rudiment with Kupher's vesicle was 
 completely formed. Temperature in hatching jar, 53'0 F. (ll-7 C,). 
 
 March 23, 1889. Several thousand soles' ova fertilised off the Land's End promon- 
 tory at 7 a.m. Temperature of the sea water at surface, 48'2 F. (9'0 C.). 
 Eggs placed in hatching jar at the Laboratory the same evening. 
 
121 
 
 March 24. Examined the eggs ; found segmentation completed, the blastoderm 
 commencing to spread over the yolk. Temperature of water in the hatching 
 jar, 50-1 F. (10'l C.). 
 
 March 25. Blastoderm covering three-fourths of the yolk. Temperature the 
 same. 
 
 March 26. The yolk completely enveloped by the blastoderm, stage shown in 
 PI. XV, Fig. 4. 
 
 March 27. Eggs all dead. 
 
 00" 
 
 March 29. Six soles' ova obtained from surface of the sea in stage just after the 
 closing of the blastopore, that is, after ' the envelopment of the yolk by the 
 blastoderm. Placed in a small jar with water at 50'3 F. to 53*6 F. (10*2 to 
 12 C.). 
 
 April 5 and 6. Three of the above eggs hatched. 
 
 The eggs last mentioned were at about the same stage when first obtained as the 
 previous lot when they died. It may be inferred therefore that at the temperature 
 above given, about 50 to 53 F. (10 to 12 C.), soles' eggs would hatch ten or 
 eleven days after fertilisation. The following experiment is more complete : 
 
 April 11. 12.5 a.m. Several hundred ripe eggs obtained from soles trawled 
 south of the Wolf Rock : artificial fertilisation attempted with testes taken from 
 the males and crushed in the water. Temperature of surface water of the sea, 
 48-5 F. (9-2 C.). 
 
 April 13. Eight of the above eggs found to be fertilised and developing; 
 temperature of the water in the bottle in which they were carried, 9*5 C. 
 These were transferred to a small jar in the Laboratory ; temperature, 10'0 C. 
 Density of the water brought from south of Wolf Bock, r0271. Density of 
 aquarium water, 1'028. 
 
 April 16. Two of the eggs killed for investigation; one died. Temperature in 
 aquarium, 9'0 C. 
 
 April 17. Temperature in aquarium, 9*2 C. 
 April 18. Temperature in aquarium, 9'7 C. 
 April 20. Two of the eggs hatched out. 
 
 Thus two of these eggs hatched on the tenth day after fertilisation in water at a 
 temperature of 48'0 F. to 50'0 F. (9 to 10 C.). Now, as I have shown, the spawning 
 period of the sole terminates sooner or later according to the temperature of the sea, 
 and scarcely any ova are shed after the temperature has risen to 50'0 F. At the 
 beginning of the spawning period, in the latter half of February, the temperature is 
 
 B 
 
122 
 
 from 43 to 45 F. (6'l C. to 7'2 C.), and at this temperature the ova would probably 
 take between two and three weeks to hatch. 
 
 It is certain that the eggs of the sole do undergo the same development at about 
 the same rate in their natural condition as they do in experimental conditions. For 
 the characteristics of the sole's ovum having been observed, namely, the size, the layer 
 of segments in the yolk, and the groups of minute oil globules, it is possible to identify 
 ova found in the sea possessing these characteristics as those of the sole. The surface 
 waters of the sea off the coasts of Devon and Cornwall contain nearly all the year round 
 vast numbers of buoyant fishes' eggs. These can very easily be collected by slowly 
 towing through the water from a boat a conical net made of muslin or silk bolting 
 cloth. Among the eggs so collected those of the sole are found in small numbers in 
 March and April, sometimes at the end of February or beginning of May, but at no 
 other time of the year. 
 
 The development of the sole within the egg is rather slow compared to that of 
 some other flat-fishes. The eggs of Pleuronectes flesus, the flounder, hatched in my 
 hatching jars in six days at a temperature of 50 F. (10'0 0.) ; the eggs of the plaice 
 (Pleuronectes platessa) hatched in 10 days at the same temperature; those of 
 Pleuronectes microcephalus, the merry-sole, hatched in eight days at a temperature of 
 about 49-l F. (9-5 C.). 
 
 I have never found the ova of the common sole very numerous among the pelagic 
 ova collected by means of the tow net. The largest number I have obtained at one 
 time is six : these were taken a little to the south-west of the Mewstone. 
 
 The density of the water in which soles' ova are found suspended at sea varies 
 slightly in different places. Examples of water from the sea to the south of the Wolf 
 Eock I have found to be 1*027 (distilled water being 1 ? 0), while samples from the sea 
 off Plymouth, inside the Eddystone, have a density of 1-0267 or 1'0268. I found in 
 my experiments that the sole's ova frequently sank in the aquarium water towards the 
 close of their development, that is shortly before they hatched, and that the larvse 
 lay on the bottom of the jar after hatching : yet the density of this water was 1'027. 
 This shows that the eggs become heavier as development advances, though the 
 sinking of the eggs is probably hastened in the hatching apparatus by the accumu- 
 lation of particles of sediment upon them. The eggs themselves certainly float in the 
 sea until they are hatched, for they are frequently taken in the tow net when just 
 ready to hatch. 
 
 I have not been able to keep the larvse alive mo-re than a day or two after hatching. 
 In fact, owing to the difficulties of artificial fertilisation I have never had a sufficient 
 number to experiment with. I have been equally unsuccessful in procuring the larvae 
 from the sea: it is probable that soon after hatching the larvse sink towards the 
 bottom. Some of the stages given in the illustrations to this book of the larvae of 
 other species of flat-fishes show that at first one of the most obvious changes which 
 takes place after hatching is the absorption of the yolk. Nourished by the yolk thus 
 
123 
 
 absorbed the larva developes in all its organs. The pectoral fin grows into a large 
 semicircular paddle, the length increases, the black pigment of the eyes (in the 
 choroid) is developed, and the jaws acquire their definite structure. When the sole is 
 first hatched it has no mouth, and takes no food : the mouth is developed before the 
 yolk is absorbed, but not until the absorption is completed does the young fish begin 
 to feed. The newly -hatched sole is 3*55 to 3*75 mm. long, between jth and i-gths of 
 an inch. It is perfectly symmetrical, having an eye on each side of its head, and 
 swimming vertically in the water, but it swims with its ventral edge uppermost, 
 because the yolk is lighter than the back of the fish. 
 
 The next stage in which I have discovered the young sole is immediately after the 
 completion of its metamorphosis, that is, after it has ceased to be symmetrical and to 
 swim vertically in the water, and has taken to lying flat on the sand, and has both 
 eyes on the right side of its head. I had searched everywhere for larval soles at the 
 bottom of the sea, after the eggs had disappeared from the surface, and had had a 
 special trawl with very small meshes made to capture them with, but could not 
 discover any. At last I obtained some through the assistance of Mr. Matthias Dunn, 
 of Mevagissey, who has been for years the friend and counsellor of all naturalists 
 engaged in the study of British fishes. On April 3, Mr. Dunn sent up to the Plymouth 
 Laboratory a number of young living flat-fishes-. I found on examination that these 
 were all Pleuronectes flesus, the flounder. Some of these were very transparent and 
 only partially metamorphosed, the left eye being still on the lower side, but near the 
 edge of the head ; in others the eye was actually in the edge of the head, looking 
 horizontally outwards. Mr. Dunn said nothing about soles, in fact at this time there 
 were no young soles in process of metamorphosis. Having failed to obtain young 
 soles by trawling, I wrote to Mr. Dunn, and arranged with him to meet him at 
 Mevagissey and examine the place where he caught his young flounders. I went to 
 Mevagissey on May 15, and found that the young flounders were found in thousands, 
 if not millions, in the pools and runlets left at low water during spring tides on the 
 bottom of the harbour. The old harbour at Mevagissey (a new additional outer 
 harbour was then being built) is completely emptied of water at the ebb during 
 springs, and the bottom consists of sandy mud. I went over the harbour with Mr. 
 Dunn, and caught numbers of the young flounders with an ordinary cup. The little 
 fish are in constant motion, some of them continually rising to the surface of the 
 shallow pools in the sand and then sinking again to the bottom. We found a few 
 soles along with the innumerable flounders. Many of the flounders were still 
 transparent and only partially or scarcely at all metamorphosed, but in all the soles 
 the metamorphosis was complete. On this day I only caught three young soles, but 
 the following day Mr. Dunn sent to me at Plymouth fifteen more. These young soles 
 were from 12 to 15 mm. long: their characters are represented in PI. XVI, 3, 
 which is 8j times the natural size. They possess nearly all the characters of the 
 adult, the chief exception being that the intestine is simpler and shorter, its coils only 
 
 R 2 
 
124 
 
 extending back a little behind the anterior end of the ventral fin. The eyes are both 
 on the right side as in the adult. The skin and body are more transparent than in 
 full-grown soles, but the pigment of the upper side exhibits perfectly the arrangement 
 of spots which characterises Solea vulgaris. 
 
 On May 17, I examined at low water the shores of Sutton Pool and the mouth of 
 the Catte water in order to find out whether young flounders or soles were to be seen 
 in the tidal pools there, as in the harbour at Mevagissey. I could not find a single 
 specimen, but the next day some boys brought me two specimens of young flounders 
 (PL flesus) taken at low tide on the shore of Sutton Pool. 
 
 These young soles, 12 mm. long, from Mevagissey could not have been more than 
 two months and a half to three months old, if the eggs from which they grew were 
 shed at the middle of February or the beginning of March, that is at the commence- 
 ment of the spawning period of the sole ; and it is very probable that they were only two 
 months old or even less. As the larvie are not hatched until a fortnight after 
 fertilisation, we may conclude that the metamorphosis occurs within about six weeks 
 after hatching. 
 
 At the next spring tides, namely, on May 31, Mr. Dunn sent me up some more 
 young flat-fishes from Mevagissey harbour: among these was one young sole, the only 
 one he could find, it measured j in. (18 mm.) in length. After this he could find no 
 more young soles in the tidal pools : they all disappeared, having either left the shore 
 for deeper water, or having become strong enough and active enough to swim away 
 with the retreating tide and avoid being left between tide marks. Durin^ the 
 following months I perseveringly endeavoured to capture young soles in their later 
 stages. I trawled with my specially constructed trawl in Whitsand Bay frequently 
 both by night and day, and also in Cawsand Bay and other sandy parts of Plymouth 
 Sound, but I never got any young soles. In Whitsand Bay at night I got a large 
 number of young plaice, pouting (Gadus luscus), and other young fishes, but not a 
 single sole. 
 
 Mr. Dunn having told me that he believed there were large numbers of young soles 
 in the estuaries of the Fal and Helford rivers, I asked my friend Mr. Eupert Vallentin, 
 of Falmouth, to make investigations and see if he could find any specimens. Mr. 
 Vallentin accordingly made a most careful and complete examination of the two 
 estuaries with the following results. He went to Malpas, a place about two miles 
 below Truro, and there found one man, the innkeeper, who possessed a seine which 
 he used for taking flat-fish. On the 27th July Mr. Vallentin had a series of hauls 
 made with this seine, the meshes of which were so small as only to admit the tip of 
 the little finger. After several hauls the total catch of flat fishes was: 
 Four Flounders from 8 to 12 inches long, 
 Four Soles, 5| inches, 5| inches, 6 inches, 7| inches in length. 
 
 The two smallest of the soles were sent to me, and I was able therefore to make 
 certain that they were really Solea vulgaris. 
 
125 
 
 Mr. Vallentin next on July 29, had a large seine sixty fathoms long and two 
 fathoms deep hauled in the Helford Eiver ; two hauls were taken, and a number of red 
 mullet and flounders were taken, but only one sole, which was sent to me. It was 
 4-fg inches in length. 
 
 Now it is obviously impossible to believe that young soles which were inch in 
 length on May 31, could have grown to 5 inches in length by the end of July. The 
 growth of flat-fishes is not so rapid as that. The spawning of the plaice at Plymouth 
 takes place in February, and is completed early in March. On June 17, 1889, I 
 obtained a large number of young plaice by trawling at night in Whitsand Bay : these 
 measured If to 2-^ inches (3'4 to 5'9 cm.) in length; another specimen which I got 
 from Sutton Pool on September 28, measured 2-^ inches (6 '2 cm.). On May 16, 
 1889, I obtained a large number of small plaice from the Cattewater, where I saw 
 them caught in a small seine : these measured 4f to nearly 7 inches in length. It is 
 evident therefore that these last specimens were more than a year old, namely, fifteen 
 months, and it is obvious that the soles caught by Mr. Vallentin were sixteen months 
 old, reckoning from the end of March as the spawning time. They were soles in the 
 second year of their growth. I have in my collection another small sole, measuring 
 4| inches (12'5 cm.) which was caught either in Plymouth Sound or on the trawling 
 ground off Plymouth, at the end of February, 1888. This must have been just a year old. 
 
 Why I have failed to obtain soles in the first year of their growth, after the stage 
 of those found at Mevagissey in May, I cannot understand. It may be owing to some 
 peculiarity of habit, that though I obtained young plaice and other species of flat- 
 fishes by trawling in shallow water in Whitsand Bay, I caught no soles. Of course 
 soles in the neighbourhood of Plymouth are much less numerous than plaice, flounders, 
 dabs, or merry-soles (PI. 'microcephalus), and this doubtless adds to the difficulty of 
 finding them. However, the problem will, I hope, be solved next year. 
 
 It has been shown that the young soles spawned in March have completed their 
 metamorphosis by the middle of May, when they are ^ to ^ inch in length (12 to 
 15 mm.); that on May 31 they are about inch long (18 mm.); and that in one 
 year they grow to about 5 inches in length. We have now to consider their subsequent 
 growth. 
 
 Soles of small size but larger than any of those just mentioned are taken in 
 Plymouth Sound in considerable numbers by the small shrimps trawls, which have a 
 beam of 12 to 15 feet in length. Such trawls are regularly worked in the Sound for 
 shrimps and prawns, and one of them is regularly used for the collecting work of our 
 Laboratory. On May 10, 1889, the Laboratory fisherman took with the shrimp 
 trawl in the Cattewater, six soles measuring 6f to 7 inches in length (17'1 cm. to 
 19'6 cm.). Another caught on May 6, measured 9^ inches (23 - 3 cm.). I consider 
 these soles to be just over two years old. Soles from this size upwards are almost 
 always to be caught in the Sound, but the larger are less plentiful. They are never 
 very abundant, but usually about half-a-dozen can be caught in a day's work. 
 
126 
 
 Adult soles, as sold in the market, vary from about 12 to 16 inches in length (30 
 to 40 cm.). If we take the medium size, 14 inches (or 35 cm.), it is evident that this 
 size cannot be reached in one year more by soles which at two years are only 6| to 
 9 inches in length. In all probability the length of 14 inches is not reached until 
 after the fish is four years old, and at three years it is only about 11 inches long. 
 
 The difficulty of distinguishing the ages of soles after the first year is due to the 
 fact that at a given time a series of sizes may be found from those which are probably 
 two years old to those which are three. The explanation of this is, first, that the 
 spawning time lasts altogether at least two months, and that the rate of growth 
 doubtless varies in different individuals according to the amount of food they have 
 been able to obtain. 
 
 The largest sole I have ever seen was one I obtained when trawling off the Land's 
 End in March, 1889. It was a ripe female, and measured 20 J inches in length, 9J 
 in breadth (52 cm. by 24 cm.). But still larger specimens have been recorded. 
 According to Day a Mr. Grove, of Charing Cross, received one from Torbay in 1882, 
 which was 24 inches (61 cm.) long, and weighed 6J Ibs. Yarrell mentions one taken 
 to the Totness market in 1826 which was 26 inches (66 cm.) long, 11 J inches 
 (29-2 cm.) broad, and weighed 9 Ibs. Probably the sole, like most fishes, goes on 
 growing as long as it lives, and taking the growth as 3 inches a year after the first 
 year, when it grows 5 inches, the fish I saw. which was 20^ inches long, must have 
 been six years old. 
 
PART IV. 
 
 ECONOMICAL. 
 
 
129 
 
 CHAPTER I. 
 
 ARTIFICIAL PEOPAGATION. 
 
 THE commonest and most obvious method of attempting to increase the supply of a 
 valuable fish is to hatch its eggs. The young when hatched may be disposed of in one 
 of two ways. They may be kept in captivity and regularly supplied with food until 
 large enough to be valuable, or they may be set free in the natural haunts of the 
 species so as to replenish its numbers. The question of the best way to increase the 
 supply of soles will be fully discussed subsequently. At present I shall describe my 
 own experiments on the artificial propagation of the species. 
 
 In the case of a number of species of valuable marine food-fishes there is no great 
 difficulty in obtaining large numbers of eggs from the fish, fertilising and hatching 
 them. The eggs become ripe at the spawning period, and it is perfectly easy to tell 
 whether the eggs of a given species are ripe or not. The number of eggs which ripen 
 at one- time varies in different species. In some, as the herring, nearly all the eggs 
 become ripe simultaneously. When the eggs are ripe they can be squeezed out of the 
 ovary by gently squeezing the abdomen of the fish with the fingers and thumb. They 
 run out in a continuous stream, and no blood or membranes escape with them : if the 
 eggs are not ripe no eggs escape unless considerable pressure is applied, and when they 
 are forced out they are accompanied by blood and by membranes containing blood' 
 vessels. When the eggs in the ovary all ripen simultaneously, or nearly so, as in the 
 herring, the ovaries can be entirely emptied by gentle pressure. In all fishes that I 
 have examined, the number of eggs ripe at the same time increases after the .spawning 
 has commenced, so that the ovaries after a certain number of eggs have been shed 
 contain ripe eggs only and can be entirely emptied. In the cod family the ripening of 
 the eggs goes 011 very gradually, so that only a portion of the eggs in the ovaries of a 
 female can be pressed out at one time. The eggs of the sole ripen gradually at first, 
 but after spawning has commenced and some of the eggs have been shed the rest all 
 ripen simultaneously. The eggs also seem to be shed as soon as they are ripe. These 
 are the conclusions I form from my experience, which is that I have usually met with 
 soles whose ovaries were either full of unripe eggs and yielded very few which were 
 ripe, or else were quite empty, all the eggs having been shed. 
 
 I commenced my experiments on the sole in 1888. At my first attempt, which wa,s 
 
130 
 
 on a trawler to the west of the Eddystone on February 6, I got a few, very few, 
 ripe ova, and could get no milt by squeezing any of the fish. I did not then know that 
 the testes were small and the milt small in quantity in die sole. Only two or three of 
 the ova then obtained were found to be floating in my bottles when I returned to shore, 
 and none of these were fertilised. My next attempt was on March 6 and 7, when 
 I was on a trawler to the S.E. of the Wolf Eock. Only two or three females out of 
 nearly a hundred were then found to yield ripe ova, and as I could squeeze no milt 
 from the males, I cut out the testes, cut them into two or three pieces and placed them 
 in the bottles with the ova. On my return to Plymouth on March 8, I found only 
 about a dozen ova floating, and of these only two or three were fertilised and showing 
 the commencement of development. I made another attempt on the same fishing 
 ground between April 3 and 7, but on my return found that not a single ovum 
 was fertilised. On this occasion I got a considerable number of ripe eggs altogether, 
 but only a few from each fish. From May 15 to 18, when I was in a trawler on 
 the same ground, we had very bad weather : nearly all the soles were spent, but some 
 ripe ova were obtained from one specimen, and three or four of these were found to 
 be fertilised by the pieces of testis. 
 
 It seemed therefore from these experiments made in 1 888 that the artificial fertilisa- 
 tion of soles' ova was a matter of the greatest difficulty. T had succeeded in ascertaining 
 the characters of healthy fertilised ova from the few I had been able to procure, and 
 was therefore able to identify the sole's ovum when it occurred in the produce of the 
 tow-net, and I had also observed and made drawings of some stages of the development, 
 but this, though valuable knowledge, brought me very little nearer to the practical 
 object of my experiments. 
 
 In the season of 1889 I continued the experiments. I had found that soles were 
 
 scarce on the Plymouth trawling ground, which extends from the Dodman Point in 
 
 Cornwall, to the neighbourhood of Bolt Head in Devon, both inside and outside the 
 
 Eddystone. On this ground very often no soles at all are found in a haul of the trawl, 
 
 and when there are some very often all are immature, or when a ripe female is taken 
 
 there are no males. On February 12, 1889, I was on a trawler which towed her trawl 
 
 from off Looe to a point south of the Plymouth Breakwater lighthouse : four soles 
 
 were taken in this haul of which only one was adult, and that not ripe. On March 14, 
 
 I went out again, and this time the trawl was worked about 10 miles south of the 
 
 Eddystone. Two hauls were made : in the first there was one sole, in the second none, 
 
 although the first haul was made in the night. After this I heard that some of the 
 
 Newlyn mackerel boats were working small trawls in Mount's Bay in order to earn 
 
 something while waiting for the commencement of the mackerel season. I therefore 
 
 went down to Penzance by rail, taking with me a number of collecting bottles to bring 
 
 back soles' ova. I went out in one of the boats on March 22. On this occasion I 
 
 examined the testes very carefully. I tried a large number of males, and could not 
 
 squeeze from any of them the thick milk-white milt which is so characteristic of the 
 
131 
 
 ripe males of other fishes I have examined. Liquid came from them of course, and in 
 some cases it had a slightly milky appearance, but it was never possible to distinguish 
 the milt derived from the testes from the urine coming from the urinary bladder. It 
 was therefore useless to squeeze a male sole over a bottle containing ova in order to 
 fertilise them, for it was impossible to know whether any milt entered the bottle or 
 not. I dissected out the testes themselves from several specimens, and cut them in 
 half and crushed them between my fingers, and .found that all the liquid that came 
 from them was thin and almost clear, only very slightly turbid. It is evident, therefore, 
 seeing that these testes came from ripe males, that the sole does not produce any milk- 
 white thick secretion such as constitutes the milt of other fishes. The milt of the sole 
 is not only very limited in quantity, but is a thin liquid only slightly turbid, which is 
 difficult to distinguish when the male is squeezed. A considerable number of soles 
 were taken on this excursion. Some of the females were spent, some unripe, some 
 yielded only about a dozen ripe ova. But one female, the largest specimen I ever saw 
 (see page 126) yielded several thousand ripe ova. The ovaries of this specimen con- 
 tained ripe ova only : she was at the last stage of spawning, and probably these ripe 
 eggs were nearly half the entire number produced that season, the rest having already 
 been shed. Having fully investigated the males I concluded that the only method 
 likelv to ensure fertilisation was to extract testes from the male soles, and crush these 
 
 
 
 up into a pulp between my fingers in the water into which the ova were to be allowed 
 to fall. In this way the whole of the milt contained in the male organs was sure to be 
 set free in the water containing the ova. I found this method perfectly successful. 
 
 At the Laboratory there was now a constant circulation of sea-water, and apparatus 
 for hatching floating ova which had been found to work admirably. The year before 
 the Aquarium was unfinished and there was no constant supply of sea-water. I landed 
 at Penzance with fertilised soles' eggs on the morning of March 23. The eggs were 
 contained in short wide glass jars such as are used for conveying sweets: over the 
 mouth of each was tied silk bolting cloth to prevent the eggs escaping, and this, to 
 some extent, prevented the water splashing over. I placed the bottles, held in a 
 divided basket, in the break-van of a train, and took them to Plymouth, where I arrived 
 the same evening. The eggs were at once placed in the hatching jars ; they seemed 
 quite healthy, and microscopic examination showed that they were all fertilised. 
 
 The apparatus and method I adopted last spring for hatching floating eggs were as 
 follows : The apparatus is a modification of that recommended by H. C. Chester, of the 
 United States Fish Commission.* The arrangement of Chester's apparatus is represented 
 in Fig. E (p. 132) : it consists of a tall glass jar, j, which has an open narrow neck 
 above and is widely open below. This is placed in a tank having a constant supply of 
 sea-water, the overflow of which takes place through a siphon tube, s, having a diameter 
 greater than that of the inflow. The water in the jar is of course always at the same 
 
 Vide "Devel. Osseous Fishes," by J. A. Ryder, Rep. U. S. Fish Commission for 1885, p. 499. 
 
132 
 
 level as the water in the tank. When the siphon of the outflow tube is empty the 
 water in the tank and jar rises until the level of its surface reaches the bend of the 
 siphon. Then the siphon fills and commences to act and the level of the water sinks 
 gradually until it falls below the short leg of the siphon, when the latter empties and the 
 outflow stops. The wide opening at the bottom of the jar is covered with a single 
 thickness of coarse cheese cloth to prevent the escape of the eggs which are introduced 
 into the jars through the narrow opening of the neck above. The rise and fall of the 
 water is only five inches vertically. Eyder says that cod eggs were hatched in this way 
 with a loss of only five per cent. I tried this apparatus with a large number of eggs 
 of the flounder and plaice (Pleuronectes flesus and P. platessa). 
 
 /\ 
 
 Fig. E. Fig. F. 
 
 Fig. E. Diagram of a transverse section of an apparatus for hatching buoyant fish eggs, arranged 
 according to the method devised by Captain Chester, of the United States Fish Commission. 
 
 Fig. F exhibits the modification of the apparatus adopted in the Laboratory of the Marine Biological 
 
 Association. 
 
 j, The glass hatching jar, resting on two bricks in a small tank containing sea-water ; o, the overflow 
 tube ; s, siphon in the overflow tube ; t, an indiarubber tube conducting the inflowing water 
 into the interior of the hatching jar. The dots represent the eggs. 
 
 On February 12 I placed a large number of ova of the flounder, artificially 
 fertilised the same day, in two glass jars of the form described. The jars were 8 inches 
 wide and 17 inches high. The bottom of each jar was covered with silk bolting cloth. 
 Each jar was supported on two bricks resting on the bottom of a shallow aquarium tank 
 made of slate and glass. The water escaped from the tank by a stand pipe into which 
 I fitted a glass siphon so that the level of the water in the tank oscillated between limits 
 about 4 inches apart. The water inside the jar was of course perfectly still : its 
 gradual rising and sinking caused no disturbance in it, in fact I found that the upper 
 part of the water in the jar was scarcely changed or affected by the rise and fall. 
 This will readily be understood. The total height of water in the jar was about 10 
 inches : at the top of this floated the eggs which formed a layer about J inch thick. 
 As the level of the water in the tank sank, the water at the bottom of the jar escaped 
 through the bolting cloth. When the tank was at its lowest level the height of the 
 water within the jar was still 6 inches. When the water rose again all this water 
 was bodily lifted up with the layer of eggs at its surface, while 4 inches of new water 
 
133 
 
 entered the bottom of the jar. Thus the 6 inches of water simply rose and fell 
 gradually without being renewed or circulated : the only change effected in it was that 
 which took place at the bottom layers by contact with the new water which entered 
 the jar every time the level of the water rose. The upper layer of water containing 
 the ova was practically stagnant. . The fall and rise of the water occupied each three 
 quarters of an hour. 
 
 On February 161 found that about half the ova in each jar were dead, lying on the 
 bolting cloth at the bottom and contaminating all the water that entered the jar. I 
 therefore removed these dead ova by means of a siphon, and changed the arrangement 
 in one jar. I left the jars in the same position, but removed the siphon from the 
 overflow pipe of one tank and introduced into the jar (Fig. F) an indiarubber 
 tube, t, leading from a jet supplying clean sea-water. I regulated the force of the water 
 discharged by the indiarubber tube. The tube reached just below the lowest level to 
 which the water in the jar sank, and the force of the water escaping from it kept the 
 ova in constant but very gentle motion. Thus clean water was constantly entering the 
 jar and escaping through the bolting cloth at the bottom, and the eggs were separate 
 in the water, not in contact with one another in a dense layer. 
 
 On February 17, I found that all the ova in the unaltered jar, except a dozen or 
 two, were dead, while in the jar provided with the new arrangement, only a dozen 
 or two out of several thousand had died. But I found that the new arrangement was 
 not perfect. The water when its surface fell in the jar left a number of ova adhering 
 to the sides of the jar, which were thus for a considerable time out of water. These 
 eggs so stranded died. I therefore placed the jar in another tank in which there was 
 no siphon in the overflow pipe, so that the water in the tank and jar was at a constant 
 level. I made the indiarubber tube delivering inside the jar longer so that the 
 water escaping at its end threw it into a regular gentle rhythmical motion which 
 served to keep the ova uniformly distributed throughout the water in the jar. I found 
 this method answered perfectly. The water in the jar was constantly renewed, and, 
 a very important point, no sediment settled on the ova. In. fact, the eggs thus treated 
 were as clean and transparent as eggs taken by the tow-net from the sea, a result I 
 never before obtained with ecrgs artificially treated. 
 
 On February 18, I found all the ova in the new apparatus had hatched ; in the 
 jar left with the original arrangement a few eggs were still alive and some of these 
 were hatched, but not all. It seems therefore that the motion of the eggs facilitates 
 hatching, as it enables the larva to get rid of its egg shell more easily than it can in 
 still water. The number of larvae hatched in the unaltered jar was quite insignificant, 
 not more than a dozen altogether, while in the altered arrangement I had between 
 one and two thousand healthy la.rvas. The two jars originally contained about the 
 same number of eggs. In a third jar I had placed, on February 12, a large 
 number of fertilised ova of the plaice. This jar was arranged on the American plan, 
 and was left in this condition without change. On February 19, only about twenty 
 
of these e< s remained ; the rest had all died, notwithstanding that I took care to 
 remove all dead eggs every day. 
 
 The arrangement which I adopted and found perfectly satisfactory is shown in the 
 diagram, Fig. F. It may of course be carried out on any scale, and does not require 
 a great deal of space. It is better to increase .the capacity of the apparatus by 
 increasing the number of the jars rather than by increasing the size. Jars larger than 
 those I have described become unwieldy. 
 
 I found the method suited the hatched flounder larvae extremely well : they lived 
 in the jars in perfect health until the yolk was entirely absorbed. I did not succeed 
 in feeding them after that period. It would probably be necessary when the yolk 
 was absorbed to turn then out into a larger tank, as feeding in a confined space 
 contaminates the water. A few of the plaice eggs hatched on February 22, and 
 one or two of them lived till the yolk was absorbed in the apparatus arranged on the 
 American method ; but this was the total result out of several thousand ova. 
 
 To return to the eggs of the sole which I obtained in Mount's Bay on March 23. 
 I placed them in two hatching jars arranged in the way I have described. There 
 were several thousand of the eggs, but I did not count them. As I have said, they 
 were all fertilised and had commenced to develop when placed in the hatching jars. 
 On March 24, when I examined them, I found to my surprise that nearly half in 
 each jar were dead. The blastoderm in the dead ones was formed, but some abnormal 
 appearances were seen round its edge. I removed the dead eggs, and hoped the 
 mortality was over arid that the rest would live. But the next day I found again 
 half of those left had died. In the living ones the germinal membrane had enveloped 
 more than half the yolk : many of them seemed unhealthy. On March 26, only about 
 six eggs- in each jar were left alive, and these were dying, although in them the 
 embryo was already formed. As I had succeeded in keeping eggs of the sole, 
 artificially fertilised, alive for a considerable time with only the roughest apparatus, 
 and as I afterwards hatched eggs taken by the tow-net from the sea, the cause of 
 death in the above experiment clearly could not be attributed to the water of the 
 aquarium or any of the conditions under which the eggs were kept after they were 
 brought to the Laboratory. I could only attribute it to the railway journey which 
 had shaken and jolted the eggs and so injured them mechanically. It might be 
 suggested that there was too great a difference of temperature between the water in 
 which the eggs were carried from Penzance and the water of the hatching jars, but 
 other experiments showed that eggs taken from the sea lived well in the sea water of 
 the Laboratory, and the weather during the railway journey was neither hot 
 enough to heat the water in the jars containing the eggs nor cold enough to cool it 
 to any extent. 
 
 Believing it useless to carry fertilised eggs by rail, I went out on April the 8th, on 
 board a trawler which was going to fish on the Mount's Bay ground. On April 11, 
 12.5 a.m., the trawl was hauled with seventeen soles in it. Of these I examined 
 
]35 
 
 eleven, the rest were not found till afterwards when the decks were cleared np. Of 
 these eleven, three were females almost spent but still containing some ripe ova : one 
 was a female still unripe, four were spent females, and three were males. I got 300 
 or 400 ecro-s altogether which I tried to fertilise as before by crushing testes in the 
 
 GO O O 
 
 water. At 4.30 p.m. the same day from six soles taken I got about a dozen more ova. 
 On April 12, at 8 a.m., after a good night's haul, fifty-seven soles were brought on 
 deck. Of these fifteen were small, under nine inches in length, and not sexually 
 mature ; eighteen were males ; nineteen large females entirely spent ; five large females, 
 which yielded a few ripe ova. 
 
 I may conveniently refer to the eggs obtained from the different hauls of this cruise 
 as lot ], lot 2, and lot 3. On April 12, while still at sea, I observed that a large 
 proportion of the eggs of lot 1, fertilised the previous day, had died and sunk. These 
 were probably not fertilised, but I do not know why the . fertilisation had failed ; it 
 may have been because the males were either immature or spent. I found when I 
 returned to the Laboratory, on April 13, that only eight eggs in lot 1 were alive and 
 developing ; in lot 2 some were floating but none fertilised ; in lot 3 two or three ova 
 were alive and developing. 
 
 On April 15, there were altogether nine eggs left alive : of these I preserved two 
 for microscopic examination and left the other seven in a small glass jar provided 
 with a circulation, not in one of the hatching jars above described, but an ordinary 
 jar, the only difference in the arrangement being that the overflow of the water took 
 place through a protected siphon, the jar standing in the air, not in the water of a 
 tank. On April 16, I again went to sea, and returned on April 20, when I found 
 of the seven eggs I left in the Laboratory two were hatched, two alive but unhatched, 
 and the rest dead. The circulation had almost stopped, the supply tube having got 
 choked. On April 21 the two larvae were dead, and one of the eggs: the last egg 
 hatched on April 22, but died the same day. 
 
 The above results prove that it is possible to artificially fertilise the eggs of the 
 sole and to hatch the eggs so fertilised in a hatching jar provided with a circulation. 
 They prove also that the cause of the death of the large number of eggs brought from 
 Penzance was not in any of the conditions to which they were exposed in the 
 Laboratory. The reason that I did not place the seven eggs just mentioned in a large 
 hatching jar was that it is difficult to find such a small number in such a jar, or 
 extract them for closer examination. 
 
 POSTSCRIPT (May 3, 1890). While these pages have been passing through the 
 press the spawning period of the sole has again arrived, and I have renewed my 
 endeavours to perfect a method of artificial propagation. In consequence of 
 previous experience my success has been greater than in former seasons. During 
 a week I spent on a Lowestoft trawler in the Bristol Channel from April 9 to 
 April 16, I obtained a large number hundreds of thousands of ripe soles' 
 
I tried to fertilise these in the usual manner by extracting the male organs and 
 crushing them in the water containing the eggs. On my return. I found less than 
 half the eggs taken were floating, but only about half of these last proved to be 
 fertilised. However, those which were fertilised were hatched in the hatching jars 
 without difficulty, and I obtained thousands of larvae. Some of the eggs were lost 
 before hatching because they ceased to float, and many larvse were lost for a similar 
 reason, as they began to sink two or three days after hatching. However, a large 
 number of the larvas were successfully kept alive until the mouth had developed, 
 the yolk was almost entirely absorbed, and feeding had commenced. Then they 
 all died. Thus when the eggs are once fertilised they can be hatched without 
 difficulty. 
 
137 
 
 CHAPTER II. 
 
 THE SOLE FISHEKY. 
 
 WE have next to consider the present condition of the sole fishery and to ascertain 
 whether the supply of soles in British waters has decreased in recent times. The 
 materials available for this enquiry are extremely scanty. Fishery statistics have been 
 systematically recorded for many years past in Scotland, but as there are no soles, 
 except as occasional rarities, in Scottish waters, these statistics are of no use for our 
 present purpose. The statistics of Irish fisheries on the other hand have only been 
 collected at all comprehensively since 1887, and the quantity of soles and other fish 
 landed at a certain number of Irish ports is recorded for only two years up to the 
 present time, namely, 1888 and 1889. For England and Wales analytical statistics 
 have been published in the " Statistical Tables and Memorandum relating to the Sea 
 Fisheries, &c." compiled by the Fisheries Sub-department of the Board of Trade, since 
 .the year 1886. The figures in these tables of the total quantities of soles and other 
 prime fish landed on the English and Welsh coasts in successive years are given in the 
 following table : 
 
 
 Soles. 
 
 Turbot. 
 
 Prime Fish not separated. 
 
 Quantity. 
 
 Cwts. 
 
 Value, 
 jp 
 
 Average 
 price 
 per cwt. 
 
 Quantity. 
 Cwts. 
 
 Value. 
 
 
 Average 
 price 
 per cwt. 
 
 Q.uantity. 
 Cwts. 
 
 Value. 
 
 
 Average 
 price 
 per cwt. 
 
 1886 . . 98,078 
 
 427,452 
 
 s. d. 
 472 
 
 59,850 
 
 182,665 
 
 s. d. 
 3 1 0* 
 
 370,014 
 
 369,089 
 
 *. d. 
 19 11J- 
 
 1887 . . 85,316 
 
 389,414 
 
 4 11 3| 
 
 63,166 
 
 184,662 
 
 2 18 5f | 115,850 
 
 368,674 3 3 7J 
 
 1888 . . 72,522 
 
 379,382 
 
 5 4 7t 
 
 55,041 
 
 171,967 
 
 3 2 5f 113,415 
 
 316,966 2 15 10J 
 
 1889 . . 
 
 74,143 
 
 431,269 
 
 5 16 4 
 
 53,576 
 
 180,841 
 
 376 
 
 35,982 
 
 126,924 
 
 3 10 6i 
 
 
 Totals of Prime Fish. 
 
 Totals of all Fish except 
 Shell-fish. 
 
 Quantity. 
 Cwts. 
 
 Value. 
 
 
 Average 
 price 
 per cwt. 
 
 Quantity. 
 Cwts. 
 
 Value. Avera S e 
 price 
 
 per. cwt. 
 
 1886 .... 
 
 527,942 
 
 979,206 
 
 s. d. 
 1 17 1 
 
 6,412,433 
 
 s. d. 
 3,688,079 11 6 
 
 18S7 .... 
 
 264,332 
 
 942,750 
 
 3 11 4 
 
 6,029,481 
 
 3,778,958 12 6 
 
 1888 .... 
 
 240,978 
 
 868,315 
 
 3 12 Of 
 
 6,348,072 
 
 3,948,013 12 5i 
 
 1889 .... 
 
 163,701 
 
 739,034 
 
 4 10 3 
 
 6,464,564 
 
 3,862,389 11 1H 
 
138 
 
 All the above figures, according to the explanation given by the officials who 
 publish the statistics, refer to the fish as landed ; the prices are the " wholesale values 
 at the places of landing," by which I believe is meant the prices actually paid to the 
 auctioneers who sell the fish for the fishermen and smackowners. The classification 
 is made according to the way in which the fish are packed when brought ashore. 
 The best and the largest quantity of the soles and turbots are placed in boxes by 
 themselves not mixed with any other fish, while if there are not sufficient soles or 
 turbots in a catch to make it worth while to pack them separately they are put 
 together with other kinds of " best " or " prime " fish. Therefore the figures under 
 the heading " soles " do not represent the total quantity of soles landed. There are tons 
 of soles and turbot included under the heading of " prime fish not separated." Now, 
 if we look at the figures referring to soles only, we find that in the three years 1886, 
 1887, 1888, there was an annual decrease of 13,000 cwt., a very startling result. But 
 in 1885) there was an increase of nearly 2,000 over 1888. But this latter increase 
 is much more than balanced by the enormous decrease in the quantity of miscellaneous 
 prime fish in 1889, a decrease of 77,433 cwt. In no year was the decrease in 
 the quantity of separated soles balanced by an increase in the quantity of mis- 
 cellaneous prime fish ; on the contrary, there was a steady decrease in the latter 
 in 1887, 1888, and 1889. The figure of this item in 1886 must be kept apart, for 
 in five months of that year haddock were included under it at Billingsgate when 
 packed with prime fish, while since then haddock have been ostimated separately. 
 This alteration also affects the totals of prime fish; but neglecting 1886 there was a 
 great annual decrease in the total quantity of prirne fish landed. There is no doubt 
 therefore on the whole that since statistics have been kept, since the year 1886, there 
 has been a steady decrease in the quantity of soles landed on the coast of England 
 and Wales. I think it is very probable that the slight increase in the quantity of soles 
 landed separately in 1889 is due to the fact that in the earlier half of this year a large 
 number of North Sea trawling smacks left their own grounds and went to work off the 
 north coast of Cornwall, on a trawling ground which had previously been almost 
 entirely neglected, and on which soles were found in great abundance. This ground 
 was first tried by some Brixham trawlers in 1887. 
 
 Another sure indication of the increasing scarcity of soles is the steady rise in price. 
 The price of soles sold separately has risen 4s. to 13s. per cwt. every year. The 
 price of turbot has not increased so steadily, though there is indication of increasing 
 scarcity of this fish also. The price of mixed prime fish is somewhat irregular : that 
 of the year 1886 is of no value to our inquiry for the reason before mentioned, and 
 the prices in other years may and probably do vary with the proportion of soles in the 
 boxes. The average price of prime fish taken altogether has increased steadily. In 
 1889 it was 18s. 3d. per cwt. greater than in 1888. The Board of Trade tables give 
 the average price of soles per Ib. for each year, and it is interesting to compare these 
 with the prices for the ten years 1856 to 1865. In the report of the Sea Fisheries 
 
139 
 
 Commission of 1866 1 find a table giving the price of various kinds of fish during those 
 years both in the Manchester Fish Market and that of Newcastle-on-Tyne. The figures 
 are as follows : 
 
 MANCHESTER. 
 
 r 
 
 1856. 
 
 1857. 
 
 1858. 
 
 1859. 
 
 1860. 
 
 1861. 
 
 j 3d. to 4-d. 
 
 Qd. to 8d. 
 
 5rf. to 8<i. 
 
 6d. to lOd. 
 
 4d. to Qd. 
 
 Qd. to 8d. 
 
 Soles per Ib. 
 
 .j 
 
 
 
 
 
 
 
 
 
 
 1862. 
 
 1863. 1865. 
 
 
 
 Qd. to 8d. 8d. to 
 
 lOd. 6cZ. 
 
 to 8d. 
 
 
 NEWCASTLE. 
 
 r 
 
 1856. 
 
 1857. 
 
 1858. 
 
 1859. 
 
 1860. 
 
 1861. 
 
 
 
 i. to 1/3. 
 
 I/- to 1/6. 
 
 I/- to 1/6. 
 
 1/3 to 1/9. 
 
 1/3 to 1/9. 
 
 1/3 to 1/9. 
 
 Soles per pair 
 
 .4 
 
 
 
 
 
 
 
 
 
 
 1862. 
 
 1863. 
 
 1864. 
 
 1865. 
 
 
 
 I 
 
 
 1/6 to 2/-. 
 
 1/6 to 2/-. 
 
 1/9 to 2/- 
 
 1/9 to 2 
 
 / 
 
 Thus the price in both places was about doubled in the ten years. The average 
 prices of soles per Ib. in the past four years according to the Board of Trade returns 
 are : 
 
 1886. 1887. 1888. 1889. 
 
 12-46d. 
 
 To compare these with the Manchester prices given above it must be remembered 
 that the latter prices are retail, or very nearly so : that is, they are the prices of the 
 fish after they had been carried from the landing place to Manchester, and therefore 
 include the cost of carriage and the profits of the merchants and salesmen. Thus* the 
 rise in the price of soles since 1856 is at least from 3d. to Is. per Ib., or fourfold : and 
 this is not due to any decrease in the value of money, for almost everything else has 
 become cheaper. 
 
 It may be urged that the total quantity of all fish landed has not decreased but 
 only slightly fluctuated. But this is no compensation for the scarcity and dearness of 
 soles. It may be partly due to the greater value of second rate fish caused by the 
 diminution in the supply of prime fish, and it may be partly due to the fact that many 
 kinds of fish such as herrings, mackerel, and pilchard vary considerably in abundance 
 in different years from causes which are apparently not connected with fishing 
 operations. But soles are stationary fish : they do not move in shoals, nor as far as we 
 know move about at all to any great distance, and the only cause to which we can 
 attribute the decrease in the supply is constant fishing. The decrease is certainly not 
 due to any decrease in the numbers of trawlers, for the trawling fleets grow larger 
 almost every year. 
 
 The statistics I have discussed are as far as I can discover all that are available. As 
 a nation we ought to be thoroughly ashamed that no statistics worth the name were 
 kept either in England or Ireland before the year 1886. Before that time there were 
 periodical agitations about some particular kind of fishing which was said by those not 
 engaged in it to be injuring the fisheries. These agitations usually arose out of jealousies 
 
 between different classes of fishermen, and were founded chiefly on prejudice and 
 
 T 2 
 
140 
 
 ignorance. The Government of the day appointed Eoyal Commissions to inquire into 
 the questions in dispute. These Commissions proceeded to investigate the matter not 
 by considering the facts, for there were usually none established either of a statistical 
 or biological character, but by taking down carefully and printing the statements of 
 the disputing fishermen themselves and weighing the assertions of one set against those 
 of the other. Of course the Cc mmissions collected together those facts bearing on the 
 matter which were known, and their reports contain a certain amount of grain 
 amongst a great deal of chaff. They also constantly reported that the only satisfactory 
 method of investigating problems concerning the fisheries was to study the natural 
 history of the fishes and to record fishery statistics. Probably the various Commissions 
 cost quite as much as a proper fisheries department, including a scientific as well as a 
 statistical staff, would have cost, but it was the traditional British method to appoint 
 Commissions. The public authorities have now commenced to collect and record 
 statistics, but they are yet far from the organisation of a satisfactory and convenient 
 system. In order to find information about the English sea-fisheries now we have to 
 search three distinct publications ; the statistics of fish landed are given in the 
 " Statistical Tables and Memorandum," the number of boata and men are to be found in 
 the Annual Statement of Navigation and Shipping, the preparation of which is entirely 
 out of the control of the Fisheries Sub-department, and finally a certain amount of 
 miscellaneous information is given in the Annual Eeports of the Inspector of Sea 
 Fisheries. 
 
 But apart from this inconvenience a great deal of improvement might be effected in 
 the system of recording the statistics. The difficulty of finding the total quantity of 
 soles landed has been sufficiently obvious from the above discussion. It might at first 
 be supposed that all the soles landed were included under the heading " soles," but we 
 find on careful examination that some soles are also included in the item of "prime 
 fish not separately distinguished." Of course this inconvenience is due to the customs 
 of the trade : sometimes soles are sold in trunks unmixed with other fish, while boxes 
 of mixed fish, including soles and small turbot, are also sold entire. But at least some 
 effort might be made to ascertain and inform the public what proportion the soles sold 
 separately bear to the total amount, whether the proportion is approximately constant 
 or not. If it has been found possible to separate the haddocks which are sent to 
 Billingsgate packed with prime fish, it ought to be possible to separate the soles. 
 Another peculiarity in the tables which must shock the mind of anyone engaged in the 
 fish trade on the east coast or in London, is that beside the item soles in the figures for 
 England and Wales is placed an item in the figures for Scotland which a foot-note 
 explains to refer to lemon-soles. Now lemon-soles are no more soles than plaice are, 
 and their value is scarcely greater than that of plaice. Besides, quantities of lemon-soles 
 are sold in the London market and other English markets, but we are not told where 
 they are placed in the English statistics. We do not even know whether they are classed 
 as " prime fish not separately distinguished " or not. However, it is very satisfactory 
 
141 
 
 that complete statistics are now annually recorded, and it ought to be possible in future 
 to find at once whether the supply of a given fish has decreased or increased : the 
 importance of this possibility in relation to the trial of any measures, legislative or 
 otherwise, intended to maintain or increase the abundance of particular kinds of fish, 
 cannot be over estimated. 
 
142 
 
 CHAPTER TIL 
 
 PEACTICAL MEASURES. 
 
 THE question we have here to consider is : Can soles be made more plentiful by measures 
 which are not only possible but practicable, that is, which are sufficiently easy to be 
 carried out, when they are understood and have become familiar,, without a degree 
 of exertion and expense too great in comparison with the results gained? In 
 examining into this problem we must distinguish the two ways in which human action 
 can be applied to a valuable wild animal. One way is to keep the animal under entire 
 control by taking it into captivity : this may be called domesticating the animal, the 
 word domestication being used with a wide signification, and not necessarily implying 
 the taming of the animal. The other way is to leave the animal in perfect freedom, and 
 to increase its numbers by protecting it and promoting its reproduction. With regard 
 to the sole we will consider the latter method first. 
 
 At present our knowledge is much too scanty to allow us at once to reach definite 
 conclusions and calculate with certainty the effects of measures which suggest them- 
 selves. We do not know exactly what proportion of soles are usually destroyed in 
 nature at different stages of their existence : the proportion which reach adult age 
 from a given number of eggs must, we know, be very small. 
 
 We know that the " prosperity," if I may use the word, of a species depends on a 
 chain of extremely delicate relations between it and the other species of the fauna and 
 flora of its habitat : and we have reason to infer that in some cases these relations and 
 the species themselves are affected to an enormous extent by physical, i.e., meteoro- 
 logical conditions over which man has no control. In order to know how man's action 
 can increase or maintain the abundance of a species we require to know how his 
 action in the past has decreased its numbers. Professor Huxley, in the case of the 
 herring, for instance, has argued that enormous as is the number of herrings captured 
 annually on the coasts of Britain, the evidence leads to the conclusion that the 
 number destroyed by man is quite insignificant in comparison with the numbers 
 destroyed by the natural enemies of the herring by the cod and sea-birds and other 
 animals which prey upon it. And this conclusion seems to be supported by a 
 comparison of the abundance of herrings in different years. The number of herring 
 fishermen, the efficiency of their boats and nets, and the extent of their operations has 
 
143 
 
 increased steadily and largely during the past twenty years. But although herrings 
 have been somewhat scarcer in some years than others, there is absolutely no evidence 
 that the supply has gradually decreased. On the contrary, the following figures will 
 show that the supply has on the whole increased as the number, efficiency, and size 
 of boats and nets increased, but has not increased continuously in proportion to the 
 increase in the apparatus of capture, nor decreased after a certain maximum in 
 consequence of the great number annually captured. In fact as far as we can see at 
 present the abundance of herrings in different years fluctuates in consequence of 
 conditions not only beyond human control, but at present unknown. The number of 
 barrels of herrings cured in Scotland was : 
 
 In the year 1870 833,1 60 
 
 1874 1,000,561 
 
 1879 841,796 
 
 1880 ? . 1,473,600 
 
 1881 1,111,155 
 
 1884 1,697,952 
 
 1888 .. ,. ,, ., 1,118,872 
 
 But, on the other hand, we know that human rapacity and recklessness have entirely 
 or nearly exterminated certain species of animals which were at one time very 
 abundant in certain regions. The Dodo and the Ehytina were exterminated by man, 
 and the Greenland whale and the American bison seem to be rapidly approaching the 
 same end. The Dodo was confined to the island of Mauritius, and seems to have 
 been more persecuted by the domestic animals introduced by the Dutch discoverers of 
 the island than by the Dutch themselves : it could only have been saved by being 
 domesticated, and apparently it was not sufficiently valuable to be worth keeping. 
 The Rhytina was a kind of Manatee which lived on Behring's Island and Copper 
 Island in the North Pacific, and was extremely numerous on the former in 1741, when 
 the island was first discovered. It- was exterminated in less than, fifty years by Russian 
 hunters and traders who lived upon its flesh. The Rhytina was of enormous size, and 
 quite harmless, and its extinction was doubtless largely due to these circumstances, 
 which made its slaughter easy, and to its slow rate of multiplication. 
 
 The history of the northern fur seal of the Behring Sea is Jess mournful, and at the 
 same time most interesting and instructive. This species, Callorhinus ursinus, breeds 
 only on two islands of the Pribylov group off the coast of Alaska, on the Commander 
 Islands in Behring Sea, and one other in the same region. The seals arrive at these islands 
 late in spring, and remain on shore until the beginning of November, The females bring 
 forth their pups soon after landing, and before the mothers leave the islands these pups 
 are weaned, and able to travel with them. During the winter months the seals seem to 
 disperse and live in the sea, but I have found no account of their mode of life during this 
 period. In 1870 the Alaska Commercial Company of San Francisco received a lease 
 
144 
 
 of the Pribylov Islands from the United States Government at a rent of $55,000 or 
 11,000 a year, and afterwards rented the other seal islands from the Eussian 
 Government. This company since that time has slaughtered 100,000 seals annually 
 on the Pribylov Islands alone, for the sake of their skins, and yet has not diminished 
 in the least the abundance of the animals, but rather increased it. Yet it is practically 
 certain that if the seal islands had been open to hunters of all nations, considering 
 the great value of the skins, the numbers of the species would by this time have 
 been seriously diminished, and probably the species would ultimately have been exter- 
 minated. What is the reason of the different results obtained by the Company ? It 
 is the story of the goose with the golden eggs. The old male seals are polygamous 
 and very pugnacious, and do not allow the young males to possess any wives at all. 
 The young bachelors live in a herd by themselves, and only these are killed ; no 
 females are destroyed. The check on the number of males is an advantage to the 
 species, for when there are too many, the amount" of fighting that goes on in the 
 " rookeries " destroys a number of cubs. 
 
 In the case of this fur seal a whole species has been practically made private 
 property without being in any sense of the w r ord domesticated. It is evidently 
 impossible for a company to acquire exclusive possession of the whole of any species 
 of marine fish. But our marine fisheries are the property of the nation, and the 
 fishermen can be controlled by legislation, if measures can be found which have such 
 a relation to the conditions of life and reproduction of the various species as to result 
 in benefits both to the fishermen and the whole nation. 
 
 Legal measures have from time to time been taken to prevent the reduction of the 
 numbers of valuable marine animals by prohibiting the capture of the young individuals 
 below a certain size. Such measures doubtless have a good effect when carried out, 
 for, in the first place, small individuals have generally a very small value, while the same 
 individuals when full grown are worth many times as much ; and, in the second place, 
 if the young individuals are destroyed there will be no parents to succeed those from 
 which they were derived. But these measures, however effectively carried out, will not 
 prevent the scarcity of a species if the adults are constantly destroyed in such 
 numbers that there are not enough left to produce sufficient eggs to give rise to the 
 next generation. The latter has been the case with species of fish which ascend rivers 
 and estuaries in order to breed. A measure applied to prevent the too great 
 destruction of adults in this case is that of prohibiting the capture of any individuals 
 whether young or adult during the breeding period, the institution of " close seasons." 
 Now if the regulations concerning close seasons were carried out in regard to the 
 salmon in such a way that no adult salmon in a river in a given winter were killed 
 until after it had spawned, and all were killed after spawning, and at the same 
 time no immature fish were killed, it is clear that the result would be that each 
 fish that arrived at maturity would certainly breed once, and only once. And 
 there seems no reason why this should not be sufficient to maintain the abundance 
 
145 
 
 of the species ; for the number of eggs produced by a female salmon at one spawning 
 season is very large. But as a matter of fact the regulations are not enforced 
 in this way : the salmon ascend rivers throughout the summer, and do not spawn 
 till autumn, and the fish that have recently spawned are of no value. Those that 
 are sought are those that have just entered the river. The annual close season 
 is limited to the actual spawning period. In consequence it is only those adults 
 which escape the net, the hook, and the trap which survive to deposit their eggs and 
 milt. However, even thus the close season has a good effect, for it ensures that the 
 adults who do escape shall shed their reproductive products in peace and security, and 
 the eggs are therefore all fertilised and placed in conditions proper for development, 
 while if the fish were disturbed, a greater number would be destroyed,- and the eggs 
 of those that were left would not be so properly deposited. 
 
 But another method which has been applied to anadromous fish is that of artificial 
 propagation. This has been successful chiefly in the case of Salmonidse and of the 
 American shad, Alosa sapidissima. It seems to me that the application of this measure 
 deserves to be considered carefully. Let us suppose a river visited regularly by salmon 
 for the purpose of spawning. If during the close season pisciculturists are permitted 
 to catch a number of the spawning salmon in the river, strip them of their eggs and 
 milt and hatch them in the most perfectly arranged hatchery, and then turn the fry at 
 a certain stage again into the river, what will be the result ? If a greater percentage 
 of eggs can be hatched under artificial conditions than under the natural, then of 
 course the result will be to increase the number of fry produced in the river. 
 
 This may be the case supposing that the eggs are preyed upon by other fishes or 
 animals in the natural state, from which they are of course protected in the hatchery. 
 But it would be equally effective to leave the eggs in the natural state and destroy 
 their enemies. The artificially hatched fry are returned to the river soon after 
 hatching, so that they are protected for a very short time, which, however, may be an 
 advantage if in the natural state they are devoured in numbers when first hatched. Of 
 course all this only applies to the case supposed. When artificially fertilised eggs or 
 hatched fry, derived from other places, are put into a river, they will of course add to 
 the salmon population of the river if the conditions necessary for their life prevail in 
 that river. 
 
 Considering now the case of the American shad, we find the problem different. The 
 estuaries, when the American Fish Commission commenced operations, were over fished, 
 and some had been entirely depopulated. There was no close season for shad, in fact it 
 was scarcely possible to institute one, for the shad unlike the salmon enters the river 
 only a very short time before it actually spawns, and the immense majority of 
 individuals captured are, like the herrings taken in Britain, either actually ripe or 
 very nearly so. Hence a close season would have meant prohibiting the fishing- 
 altogether. Such numbers of shad were taken for many years, that the number of 
 eggs deposited was not nearly sufficient to keep up the numbers of the species. Nearly 
 
 u 
 
146 
 
 all tli e ripe eggs and milt which ought to have developed into the next generation were 
 actually devoured by the people who ate the shad. The pisciculturists, under the 
 direction of the Fish Commissioner, therefore first invented methods and apparatus by 
 which the eggs of the shad could be artificially fertilised and hatched, and then they 
 organised a system under which every year a large number of the ripe fish captured 
 were stripped of their eggs and milt which were returned either to the same river or 
 others in the form of healthy fry. The consequence is that now the estuaries on the 
 Atlantic side of the United States yield annually a rich harvest of adult shad, and this 
 valuable fishery is absolutely dependent on the piscicultural operations of the National 
 Fish Commission. 
 
 Let us now consider the case of the sole. Soles are captured without intermission 
 the whole year round, and their habitat is practically only coextensive with the 
 trawling grounds. Soles do not, our knowledge enables us to infer with some 
 certainty, migrate or travel about to any great extent. There may be of course 
 distant areas where soles are abundant, but the existence of these is not sufficient to 
 maintain the sole population of the extensive areas where they are constantly captured. 
 Now I have shown that the artificial fertilisation and hatching of soles' eggs, though 
 presenting unusual difficulties, is by no means impossible. It is almost impossible to 
 interfere with trawling. Suppose that by further experiments it were shown that 
 millions of soles' eggs could be artificially fertilised, hatched, and returned to the sea. 
 It is evident that this would necessarily have the effect of increasing the supply of 
 soles. For all these eggs would be procured from soles captured for the market, and 
 would, if not artificially hatched, be devoured along with the soles themselves. Of 
 course the expense of providing properly equipped hatcheries and maintaining a staff 
 of men who would collect the eggs and take care of them during development would 
 be very large. But if this expense were provided from the public funds, some return 
 for it would be received by the public in the form of more abundant and cheaper soles. 
 Whether the national account on this item would result in an annual profit or an 
 annual loss I am not yet prepared to say. 
 
 On the other hand, it seems to me at least possible that the artificial fertilisation 
 of the eggs would alone be sufficient, and that the artificial hatching in expensive 
 hatcheries would be unnecessary. We have at present little reason to assume that, 
 given a certain number of fertilised eggs more fry would be produced from them by 
 hatching them in artificial apparatus than by placing them in the sea to develop under 
 natural conditions. It is conceivable that the ripe females and males captured by the 
 trawl during the spawning season should be stripped by a man on board a trawler, 
 and the fertilised eggs so obtained should be simply thrown overboard. This would 
 be a direct gain to the sole population of our seas, for every one of those eggs would, 
 f not Artificially fertilised, be sent to market inside the female soles and cooked. In 
 fact ripe eggs are now cooked in the ovaries of soles in enormous numbers every 
 spawning season. 
 
147 
 
 Of course much greater results would be effected by simply prohibiting the capture 
 of soles at all from the middle of February to the end of April ; but this could only be 
 done by prohibiting trawling during those months, for in my opinion soles once 
 captured in the trawl are usually too much injured to survive if again returned to the 
 sea. I have shown that they do not survive when placed in our aquarium tanks (see 
 p. 11 5). If trawling were prohibited who would compensate the fishermen and capitalists 
 engaged in the business ? That would be more expensive than maintaining a national 
 staff of pisciculturists to hatch soles' eggs. On the other hand, we must consider if it 
 is possible under any imaginary system that there should be a man on board every 
 trawler capable of artificially fertilising the eggs of soles during the spawning period. 
 It would scarcely be practicable to send out a trained pisciculturist in every trawler. 
 It is possible, however, in imagination at least, that the skipper of every trawler should 
 carry out the necessary operations, though it would probably be a long time before 
 trawling skippers would possess the necessary knowledge or care sufficiently for the 
 future. If such operations were expected of them they would have to be trained in 
 practical pisciculture, and pass an examination in that subject as they are now 
 required to pass in seamanship. 
 
 I make no claim to originality in this idea. Years ago Professor Ewart, of the 
 University of Edinburgh, who has identified himself with the piscicultural work of the 
 Scottish Fishery Board, published the suggestion of a similar scheme to be applied to 
 herrings. I believe it has never been carried out, and I doubt at present if such 
 measures for maintaining the supply of herrings are required. It has occurred to me to 
 consider whether the same scheme might be applied to soles, and I think it quite pos- 
 sible that Professor Ewart's suggestion may hi the future lead to very important results. 
 
 The only other possible methods of increasing the numbers of soles are to increase 
 the supply of food or to diminish the numbers of the natural enemies of the sole. No 
 practical means can be suggested by which the supply of food could be increased, but 
 it might well be worth while to rigorously destroy useless predatory fish which have no 
 value themselves and which live entirely on valuable food fishes. At present trawlers 
 constantly throw back anglers and dog-fishes into the sea alive after they have brought 
 them on deck. I think it would be advisable that these fishes should be systematically 
 killed before being returned to the sea, for if valuable fishes can be diminished in 
 numbers the abundance of their enemies could be reduced also. 
 
 There is not much to be said about the domestication of soles. It is certain that 
 soles will live in captivity and grow to a large size. The Association is now making 
 arrangements to keep young soles in a large piece of enclosed sea-water at Sheerness. 
 But it is evident that the capture of young soles to be merely retained in captivity and 
 killed when mature will not prevent the diminution of the numbers in the sea. If the 
 adults were kept in captivity and their eggs taken and reared a new industry of sole- 
 raising might be started, but it is doubtful whether this would compensate for the 
 extermination of soles from the great trawling grounds. 
 
PLATES. 
 
PLATE I. 
 
 Drawing of a living Sole, lying on coarse bright-coloured gravel, in a shallow porcelain 
 dish full of sea-water, and exposed to daylight from a south window. 
 
PLATE II. 
 
 
 
 Drawing of the same specimen as that represented in Plate I lying on washed coal in 
 a deep wooden tub and shaded from the light. 
 
PLATE III. 
 
 Drawing of a living Sole, not the same specimen as represented in Plate I, lying in a 
 shallow dish of white porcelain full of sea-water and exposed to strong day- 
 light from a south window. 
 

 : 
 
PLATE IV. 
 
 Drawing of the specimen represented in Plate III on the day after its death. 
 
o 
 
 CL 
 
PLATE V. 
 
 The lower (left) side of the Common Sole. Two specimens, of the parasite Phyllonella 
 solece are shown on the skin behind the head just below the lateral line. 
 

 CL 
 
 I 
 
 rf >& 
 
 r 
 
 fT~~7 
 
 ' 
 
PLATE VI. 
 
 Fig. 1. The Lemon or Sand Sole (Solea lascaris\ natural size. 
 
 Fig. 2. Lower side of the head of the same, showing the dilated anterior nostril. 
 

PLATE VII. 
 
 Fig. 1. The Thickback (Solea variegata), natural size. 
 Fig. 2. Lower side of the head of the same. 
 Fig. 3. The Solenette (Solea lutea\ natural size. 
 Fig. 4. Lower side of the same. 
 
f 
 
 
PLATE VIII. 
 
 Fig. 1. The viscera of the female Common Sole in situ, natural size. 
 
 Fig. 2. The body cavity of the female Common Sole after all the viscera have been 
 removed except the ovary and kidneys, which are left in situ. The wooden 
 rod passes through the anus, the blue probe passes through the external 
 aperture of the common oviduct up into the left ovary, the black bristle 
 passes into the urinary bladder which lies beneath the oviduct. 
 
PLATE IX. 
 
 Fig. 1. The viscera of the male Common Sole in situ, natural size. 
 
 Fig. 2. The body cavity of the male Common Sole after all the viscera have been 
 removed except the testes and kidneys, which are left in situ, natural size. 
 The wooden rod passes through the anus, the black bristle passes into the 
 urinary bladder, which lies beneath the cords containing the testicular 
 ducts. 
 

 I 
 
PLATE X. 
 
 Fig. 1. The skeleton of the Common Sole; the branchial arches, jaws, and bones of 
 the paired fins have been removed, all the other bones are in their natural 
 position in relation to one another. 
 
 Fig. 2. One of the dorsal fin-rays : a. from the side ; b. from the front. 
 
PLATE X 
 
 Fig. 1. The superficial bones of the right or upper side of the head of the Common 
 Sole. 
 
 Fig. 2. The superficial bones of the left or lower side. 
 Eefereiice letters : 
 
 Jim, hyomandibular. 
 
 ms, mesopterygoid. 
 
 mt, metapterygoid. 
 
 m, mandible. 
 
 pt, pterygoid. 
 
 pa, palatine. 
 
 s, symplectic. 
 
 q, quadrate. 
 
 x, maxilla. 
 
 px, pre maxilla. 
 
 o, opercular. 
 
 po, preopercular. 
 
 io, iiiteropercular. 
 
 so, subopercular. 
 
 Fig. 3. The bones of the branchial arches and paired fins, lateral view. 
 Fig. 4. The bony branchial arches spread out and seen from the dorsal side. 
 Eeference letters and numbers : 
 
 66 1, 1st basibranchial. 
 
 66 2, 2nd ditto. 
 
 663, 3rd ditto. 
 
 6A, basihyal. 
 
 Tih, hypohyals. 
 
 ch. ceratohyal. 
 
 c6 1, 1st cerate-branchial. 
 
 c6 2, 2nd ditto. 
 
 Ip, lower pharyngeal. 
 
 up, upper pharyngeal. 
 
 2, stylohyal. 
 
 3, epihyal. 
 
 8, 1st pharyngobranchial. 
 
 9, 1st epibranchial. 
 11, 1st hypobrancbial. 
 
 14, 2nd epibranchial. 
 
 16, 2nd hypobrauchial. 
 
 17, 3rd pharyngobrauchial. 
 
 18, 3rd epibranchial. 
 
 19, 3rd eeratobranchial. 
 
 20, 3rd hypobranchial. 
 
 21, 4th epibranchial. 
 
 25, post-temporal. 
 
 26, supra-clavicular. 
 
 27, clavicle. 
 
 28, jugular. 
 
 29, scapulfi. 
 
 30, coracoid. 
 
 31, pubic. 
 
 Fig. 5. The skull, showing the separate bones and their sutures, from the right side. 
 Fig. 6. The same from the left side. 
 Fig. 7. The same from the dorsal side. 
 Fig. 8. The posterior surface. 
 Eeference letters : 
 
 6.0. 
 
 s.o. 
 
 ex.o. 
 
 ep.o. 
 
 pt.o. 
 
 op.o. 
 
 pr.o. 
 
 sp'.o. 
 
 basioccipital. 
 
 supraoccipital. 
 
 exoccipital. 
 
 epiotic. 
 
 pterotic. 
 
 opisthotic. 
 
 prootic. 
 
 sphenotic. 
 
 pa. parietal. 
 
 l.f. left frontal. 
 
 r.f. right frontrJ. 
 
 pa.s. parasphenoid. 
 
 vo. vomer. 
 
 tries, e. mesethmoid. 
 
 r.ect.e. right ectethmoid. 
 
 l.ect.e. left ditto. 
 
.-.ep.o 
 
 1 
 
 ' 
 
 PT.O. 
 
 
 Solea vulgaris 
 
 Imp Camb. Sci.h 
 
PLATE XII. 
 
 General view of the musculature of the Common Sole seen from the right side, after 
 removal of the skin. The superficial abductors of the ventral fin have been 
 removed, to expose the elevators and depressors of the ventral fin-rays which 
 lie beneath them : the same dissection has been made along the anterior 
 fourth of the dorsal fin. 
 

 
 
 
 t 
 
 I 
 
 '/ 
 
 f 
 
 ^ 
 vf 
 
 
 
 xV 
 
PLATE XIII. 
 
 Fig. 1. Transverse section of the right ovary of a young Common Sole, 7^ inches long, 
 killed May 2, 1889 ; magnified 45 times, linear. 
 
 f.e. fibrous tissues forming the wall of the ovary. 
 o.g. ovigerous lamellae. 
 b.v. blood-vessels, ovarian artery and vein. 
 
 Fig. 2. Portion of an ovigerous lamella from transverse section of an ovary of a Sole 
 10J inches long, killed January 28, 1889 ; magnified 450 times. 
 
 g.e. germinal epithelium. 
 o. ova. 
 
 Fig. 3. Section of an ovum approaching maturity, from the ovary of a Sole killed 
 when spawning was almost finished, on April 11, 1889 ; magnified 70 times. 
 
 b.v. blood-vessels. 
 f.e. follicular epithelium. 
 f.m. follicular membrane. 
 v.m. vitelline membrane. 
 
 Fig. 4. Transverse section of the right testis of a Sole 9 inches long, immature ; 
 
 magnified 45 times. 
 
 f.e. fibrous envelope. 
 
 r.t. radial testicular tubes. 
 
 l.t. longitudinal testicular tubes. 
 
 Fig. 5. Closed end of one of the radial testicular tubes shown in Fig. 4 ; magnified 450 
 
 times. 
 
 f.e. fibrous envelope. 
 
 g.e. male germinal epithelium. 
 
 Fig. 5a. Longitudinal portion of a testicular tube from the same section cut 
 transversely, containing spermatoblasts and ripe spermatozoa ; magnified 
 450 times. 
 
 Fig. 6. Transverse section of the cord containing the testicular ducts from an adult 
 male Sole killed in the breeding season, March 23, 1889; magnified 70 
 times. 
 
 f.t. fibrous tissue. 
 
 l.t. the testicular ducts. 
 
 u.l). urinary bladder lined by an epithelium. 
 
 Fig. 7. Spermatozoon of Dab (Pleuronectes limanJa) ; magnified 500 times. 
 

 
 : 
 
 
 OQ 
 
 
 
 
 
 
 , 
 
 
 Solea vuljaris 
 
 imp Csonb i 
 
PLATE XIV. 
 
 Fig. 1. Scale of Common Sole from middle of body ; magnified. 
 
 Fig. 2. One of the lateral line scales of the same. 
 
 Fig. 3. Scale of Thickback. 
 
 Fig. 4. Scale of Lemon or Sand Sole. 
 
 Fig. 5. Scale of Solenette. 
 
 Fig. 6. Phyllonella solece, the parasite from the skin of the Common Sole ; magnified. 
 
 p.s. posterior sucker. 
 
 p. aperture for the penis. 
 
 u. aperture of the uterus. 
 a.g. anterior glandular areas. 
 
 Fig 6a. Egg of same, magnified 100 times. 
 
 Fig. 7. Ideal longitudinal section of the skin along the lateral line of the Common Sole ; 
 magnified 70 times. 
 
 ep. epidermis. 
 
 c. chromatophores. 
 d.t. dermal tube. 
 s.c. scale in section. 
 
 /. fibrous tissue of the derma with areolar tissue in spaces. 
 
 p. external pores. 
 s.o. sense organ. 
 
 n. nerve. 
 

 ,J> 
 
 -.n.del 
 
 Solea vulgar is 
 
 -."ib Sc: 
 
PLATE XV. 
 
 i<*. 1 . Section of a portion of the skin of the lower side of head of the Common 
 Sole; magnified 70 times. Reference letters as in Fig. 7, PI. XIV, with 
 the addition of//, tactile filaments. 
 
 Fig. 2. Lower side of the head of the Sole dissected to show the cutaneous nerves : 
 natural size. 
 
 V 2. Maxillary branch of the 5th. 
 
 V 2 a. palato-nasal branch of 5th. 
 
 V 2. mandibular branch of 5th. 
 
 VII 1. mandibular branch of 7th. 
 
 VII 2. hyoidean branch of 7th. 
 
 VII 2 a. opercular branch of 7th. 
 
 X 6 a. supra- temporal branch of vagus. 
 X 6 b. another anterior branch of the vagus. 
 
 Fig, 3. Egg of Common Sole taken in tow-net in Mount's Bay, March 1, 1889. 
 Magnified 45 times, bl. blastoderm, y.s. yolk segments, o.g. oil globules. 
 
 Fig. 4. An egg of the same, artificially fertilised, March 23, 7 a.m. ; drawn March 24, 
 5 p.m.; same magnification. 
 
 Fig. 5. An egg of the same, artificially fertilised, March 23, 7 a.m. ; drawn March 25, 
 12 noon ; same magnification. 
 
 Fig. 6. An egg, fertilised artificially, April 12, 1889 ; dranw April 15, 4 p.m. 
 Both black and coloured pigment cells present, the latter green by reflected 
 light ; e. eye, m.s. mesoblastic somites. 
 

 :. 
 
 
 
 Solea vuljaris 
 
 
PLATE XVI. 
 
 Fig. 1. Egg of Common Sole, artificially fertilised, April 12, 1889, 10 a.m.; drawn 
 April 15, 4 p.m. Magnified 45 times ; same stage as that shown in PL XV, 
 Fig 6, in profile, o.g. oil globules. 
 
 Fig. 2. An egg of same taken in tow-net off Plymouth (near the Mewstone), March 29, 
 1889 ; drawn March 30 ; same magnification, e. eye. yk. yolk. 
 
 Fig. 3. Larva of same taken 4 m. south of the Mewstone, March 30, 1889 ; right 
 side ; magnified 35 times, yk. yolk. au. auditory organ, na. nasal capsule. 
 
 Fig. 4. Larva of same, hatched March 28, from egg taken off Penlee Point, March 27, 
 left side ; magnified 35 times, ht. heart, pt. pectoral fin. int. intestine. 
 
 Fig. 5. Young Common Sole f inch long, taken in Mevagissey Harbour, May 15, 
 1889 ; magnified 8J times. 
 
 Fig. 6. Egg of the Thickback (Solea variegata), taken in tow- net S. of the Eddystone ; 
 drawn April 21, 1889; magnified 45 times. 
 
Plate X\7. 
 
 
 
 v-.-.*"; :; *-'-;' :-*:/*. ;' 
 
 ' 3*$+*'$^: '* l " ,'*- 
 
 SOLL'A VAR:: 
 
 Fig. 1-'5. SOLEA VULGARIS. Fig. 6. SOLEA VARIECATA. 
 
PLATE XVII. 
 
 Fig. 1. Larva of Thickback newly hatched, April 24, 1889 ; magnified 35 times. 
 Pigment as seen by reflected light, yk. yolk. 
 
 Fig. 2, Larva of same two days after hatching, April 23, 1889. Same magnification 
 pt. pectoral fin. ht. heart. 
 
 Fig. 3. Larva of Flounder (Pleuronectes Jlesus), two days after hatching, February 20, 
 1889, from egg artificially fertilised ; magnified 35 times. 
 
 Fig. 4. Larva of same six days after hatching, February 24, 1889, from the same 
 lot as the preceding ; same magnification. 
 
 Fig. 5. Young Flounder taken in Mevagissey Harbour, April 2, 1889 ; drawn April 5 ; 
 magnified about 18 times. 
 
Plate X\ 
 
 + <> 
 
 
 PLEURONECTES FLESUS. 
 
 ;;ze 
 
 I 
 
 PLEURONECTES FLESUS 
 
 
 F&1.2. SOLEA VARIEGATA. Fig 3 5 PLEURONECTES FLESUS. 
 
PLATE XVIIL 
 
 Fig. 1. Young Flounder (Pleuronectes flesus] taken in Mevagissey Harbour, April 2, 
 1889 ; magnified about 14J times, pv. pelvic fin. 
 
 Fig. 2. Larva of Dab (Pleuronectes limanda) newly hatched, from artificially fertilised 
 egg, March 11, 1889; magnified 35 times, pt. pectoral fin. yk. yolk. 
 
 Fig. 3. Larva of Merry Sole (Pleuronectes microcephalus\ March 25, 1889, four days 
 after hatching, from artificially fertilised egg ; same magnification. I. liver. 
 Jit. heart. 
 
 Fig. 4. Larva of Plaice (Pleuronectes platessa\ February 27, 1889, five days after 
 hatching, from artificially fertilised egg; same magnification, a. anus. 
 nch. notochord. 
 
 Fig. 5. Young Brill (Rhombus Icevis) taken at surface of water in Button Pool, June 1, 
 1889 ; natural size. 
 

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