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F ‘ E44 Paranal osha Mfg At (Mey ta tale ‘ Or parr \ beh teas Soar earn f ih? ‘ j ben phi A ype gt i Lawl shyagle », m {4 be gt Na ¢ RTOS eta eae ee sit vee by a un a3 bates eit foul Rens (9 o) a fet Per rny on «3 pes ravitt a’¢s ut oh vata feig hoes ag ‘penne we aM g Huth Akin te ihe: Ue) Shee hares be rey babe Poel ob Yeeke gereet Shad eee op etd ed TP io kite Poin Cr at py et Arg? u Kite hg Ie are conn we dee Peete: Maren a ar cut rang yee epg age sy? aa t teens ut a ee | . ’ 4 Cd Se kes 4 : ‘ neon ‘ é et: a Lard eee vi dattegrees 4 bie oh PPI wathura: pte te berry tard rs teat he De Breet rec a ’ “Bibra te gehtetys ete boda Dat bay re + te dishae uy a eee 7 Wacky hb glen pags a bor etesd > Hg ane oy CO Pe rs " whine aa aN au A ft Pre Pe "| , ? $ A piel “ os sate ee t ; a atin he Fem Sait AL att eats ah ee Roe | sa baae 1 ! Hiiatety'p third he dew : . rl ieedeit cat ba tar \ AN oath aas aMiPese, Pars Bey ! yes en at ewe 2 a “3 i bigcare tes a Radeegealdy tiie i, : ‘ She 4 ge *y ‘ oh Us ahi gy iy rhe acae hid F 4 a | Bhi! eg? 4 rh Pah aware ct a <4 Re eu WR eee ties She ptereee ag t ee oe wae ' ‘ei eetaru Y Reasnt tit ae ot Aa ‘ s ¢ PT een ena Hehehe pi ay! 7 aC cP +9 ° | 95 aed if? + ; bias 4 e] iy < ' as Mors ot ty it ‘ hard ay RMSE ee 4 i DUE Paty , "i Pury fants! I ebend ihe Mantel Pore ge 0 rat aie wetlee Aesth, ? - Ja tye) My ay Baie Tipe ges See! i it eee LPL Return this book on or before the Latest Date stamped below. University of Illinois Library L161—H41 Digitized by the Internet Archive , in 2014 https://archive.org/details/quarterlyjournal4419unse Wy) j Wi een Day ha 8) QUARTERLY JOURNAL MICKOSCOPICAL SCIENCE. H. RAY LANKESTER, M.A., LL.D., F.R.S., HONORARY FELLOW OF EXETER COLLEGE, OXFORD} CORRESPONDENT OF THE INSTITUTE OF FRANCE AND OF THE IMPERIAL ACADEMY OF SCIENCES OF ST. PETERSBURG, AND OF THE ACADEMY OF SCIENCES OF PHILADELPHIA} FOREIGN MEMBER OF THE ROYAL BOHEMIAN SOCIETY OF SCIENCES, AND OF THE ACADEMY OF THE LINCEI OF ROME; ASSOCIATE OF THE ROYAL ACADEMY OF BELGIUM; HONORARY MEMBER OF THE NEW YORK ACADEMY OF SCIENCES, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY, AND OF THE ROYAL PHYSICAL SOCIETY OF EDINBURGH 3} HONORARY MEMBER OF THE BIOLOGICAL SOCIETY OF PARIS; DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS OF THE BRITISH MUSEUM; LATE FULLERIAN PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN. WITH THE CO-OPERATION OF ADAM SEDGWICK, M.A., F.R.S., FELLOW AND TUTOR OF TRINITY COLLEGE, CAMBRIDGE 3 W. F. KR. WELDON, MA., F.RS., LINACKE PROFESSOR OF COMPARATIVE ANATOMY AND FELLOW OF MERTON COLLEGE, OXFORD; LATE FELLOW OF 8T. JOHN’S COLLEGE, CAMBRIDGE ; AND SYDNEY J. HICKSON, M.A., F.R.S., BEYER PROFESSOR OF ZOOLOGY IN THE OWENS COLLEGE, MANCHESTER. VOLUME 44,.—New Sprtgs, With Aithographic Plates and Engrabings on lod [Oz 94¢\ o) mds Hyer BNW NN | { N Hayy Wornabsyan pred LONDON: J. & A. CHURCHILL, 7, GREAT MARLBOROUGH STREET. 1901. ~~ a i ae : i PT er row e@-> ee ot hel ig CONTENTS. CONTENTS OF No. 173, N.S., NOVEMBER, 1900. MEMOIRS: PAGE The * Sexual Season”? of Mammals and the Relation of the ‘‘ Pro- cestrum” to Menstruation, By Water Hears, M.A., Trinity College, Cambridge . ; : ; ‘ : 1 A Description of Ephydatia blembingia, with an Account of the Formation and Structure of the Gemmule. By RicHarp vans, B.A. (With Plates 1—4) . = Heh! On a Collection of Nemerteans from Singapore. By KR. C. ’ Punnett, B.A. (With Plates 5—8) : at On the Protostigmata of Molgula manhattensis (De Kay). By ArtHuR Witury. (With Plate 9) . ; : . 14d CONTENTS OF No. 174, N.S., MARCH, 1901. MEMOIRS: The Development and Succession of Teeth in Hatteria puuc- tata. By H. Spencer Harrison, B.Sce.(Lond.), A.R.C.Sc., Demonstrator and Assistant Lecturer in Biology, University College, Cardiff. (From the Zoological Laboratory, Royal Col- lege of Science, London, and University College, Cardiff.) (With Plates 10O—12) . F : se ol The Anatomy of Pleurotomaria Beyrichii, Hilg. By Martin F. Woopwarp, Demonstrator of Zoology, Royal College of Science, London. (With Plates 13—16) ‘ 2 o= eee Dolichorhynehus indicus, n. g., n. sp., a New Acraniate. By ARTHUR WILLEY : : : : . 269 Heteropleuron Hectori, the New Zealand Lancelet. By W. BiaxianD Benuam, D.Sc., M.A., F.Z.S., Professor of Biology in the University of Otago. (With Plate 17). : : 203 lV CONTENTS. On some Parasites found in Echinus esculentus, L. By ARTHUR KE. Suiptey, M.A., Fellow and Tutor of Christ’s Col- lege, Cambridge, and Lecturer in the Advanced Morphology of the Invertebrata in the University. (With Plate 18) The Scottish Silurian Scorpion. By R. I. Pococx. (With Plate 19) 5 2 ; , : : CONTENTS OF (No. 175, N.S] DEA 20 MEMOIRS: The Life-History of Nucula delphinodonta (Mighels). By Gitman A. Drew, Professor of Biology, University of Maine, Orono, Me. (With Plates 20-—25) On the Structure of the Hairs of Mylodon Listai and other South American Edentata. By W.G. Ripgwoop, D.Sc., F.L.S., Lecturer on Biology at the Medical School of St. Mary’s Hos- pital, London. (With Plate 26) On the Structure and Affinities of Saccocirrus. By Epwin S. GoopricH, M.A., Fellow of Merton College, Oxford. (With Plates 27—29) : : On the Question of Priority with regard to certain Discoveries upon the Adtiology of Malarial Diseases. By Grorex H. F. Nurratt, M.A., M.D., Ph.D., University Lecturer in Bacteri- ology and Preventive Medicine, Cambridge Studies in the Retina: Rods and Cones in the Frog and in some other Amphibia. By H. M. Bernarp, M.A.Cantab. (from the Biological Laboratories, Royal College of Science, London). Part LI. (With Plates 30 and 31) Staining with Brazilin. By Sypney J. Hickson, Beyer Professor of Zoology in the Owens College, Manchester CONTENTS OF No. 176, N.S., AUGUST, 1901. MEMOIRS : On Two New Species of Onychophora from the Siamese Malay States. By Ricuarp Evans, M.A., B.Se., of Jesus College, Oxford. (With Plates 82—37) . ' : PAGE 281 291 313 393 413 429 443 469 473 CONTENTS. Vv PAGE Koperipatus Butleri (nov. sp.). By Ricuarp Evans, M.A., B.Sce., of Jesus College, Oxford. (With Plate 38) + 539 On Two New British Nemerteans. By R. C. Punnett, B.A. (With Plates 39 and 40) ; : ; . 547 The Celomic Fluid in Acanthodrilids. By W. Braxtanpn Benuam, D.Sc., M.A., F.Z.S., Professor of Biology in the University of Otago, New Zealand. (With Plate 41) . : . 565 The Crystalline Style of Lamellibranchia. By S. B. Mirra, of Calcutta, late of University College, London. (With Plate 42) 591 Tire, INDEX, AND CoNTENTs. VoL. 44.—NEW SERIES. bh The ‘Sexual Season’? of Mammals and the Relation of the “ Pro-cstrum” to Menstruation. By Walter Heape, M.A., Trinity College, Cambridge. ContTENTS. Introduction The sexual season of ‘ale raarnitivals The breeding season of female mammals The sexual season of female mammals The periodicity of the sexual season in monestrous manent in fhe absence of the male The duration of the sexual season in a ireatnane ANNE in ie ale sence of the male . . - ; The duration of the estrus in menmeattaus aid polycestrous anal in the absence of the male The effect of maternal influences on the esa season mw on date The pro-cestrum The period of cestrus Summary and conclusion Literature : : : : INTRODUCTION. Tue following paper is concerned with certain phenomena which affect reproduction and which occur in female mammals prior to the fertilisation of the ovum. The times of propagation of the species and the behaviour of many female mammals during certain portions of vou. 44, pART 1.—NEW SERLES. | A the 2 WALTER HEAP, breeding season have been noted by zoologists, but the changes which take place in the female generative system prior to gestation require examination which it is impossible to extend, with few exceptions, to mammals in the wild state, and almost all that is known on this matter is derived from a study of domesticated mammals and of some few wild animals kept in captivity. But little attention, however, has been paid to the subject at all by scientific students, while the only attempt, so far as | am aware, which has been made to treat it from a comparative point of view is that of Wiltshire, whose “ Lectures on the Comparative Physiology of Menstrua- tion” were published in the ‘British Medical Journal’ (1883), The subject is of importance in proportion to the light it may throw upon the evolution of the functional phenomena of breeding. To attack such a subject by means of data obtained from the highest groups of animals may seem to many to be beginning at the wrong end of the story, and there is, of course, much truth in that view ; but knowledge of the physiology of the lower animals is at present very limited, and information regarding the habits of most of them at times of reproduction extremely scanty ;! on the other hand, we have available some knowledge of the habits of many classes of mammals and of the variety of sexual phenomena exhibited by them. The data for a comprehensive comparative account even in mammals does not exist; at the same time there is sufficient material at hand, in my opinion, to permit of a foundation being laid, upon which it will be more easy to arrange facts in the future. It is, therefore, not with any idea of finality, but with the purpose of suggesting a wide field of inquiry, and with the hope of assisting therein, that this chapter on the comparative physiology of breeding has been written. In the first place, with regard to the terms to be used ; at present there is great confusion regarding those used by breeders ; the same terms are used for both male and female ' In this relation Dr. Lo Bianco’s papers in the ‘ Mitth. Zool. Stat. Neapel,’ vol. vill, 1888, and vol. xui, 1899, are of great value. HK, © SEXUAL SEASON’? OF MAMMALS. 3 animals when they should not be so used, the same terms are used for different processes and conditions in female mam- mals, and it is necessary for a clear understanding of the subject that the limits of their use should be defined, and where needful new terms adopted. One of the most fertile sources of confusion is, disregard of the fact that the history of the generative phenomena exhibited by female mammals is different when reproduc- tion takes place and when it does not take place; it is essential that this fact should be kept in mind. The remainder of this Introduction I have devoted to a definition of the terms used in the following pages, and to an endeavour to show wherein they differ or are in accord with those now in use. Reproductive Period.—lI have used this expression to denote the whole of that period in the hfe of a mammal, whether male or female, during which its generative organs are capable of the reproductive function ; and in contrast to the Pre-reproductive and Post-reproductive periods which severally precede and follow it, during which the gene- rative organs are either not fully developed or are degenerate. The bearing of young, however, is not possible at all times during the reproductive period. In the course of that period there are intervals during which the generative organs of all mammals exhibit, on the one hand special activity, and on the other hand a fallow condition. This variation is periodic, and is due, not to a periodic degeneration from a stable con- dition, but to the periodic accession of a special stimulus, culminating in sexual desire, and resulting in coition and in gestation in the female when conception takes place. The periodicity of this stimulus is very variable, and is influenced by many factors of both extraneous and internal origin. Breeding Season is adopted to denote the whole of that consecutive period during which any male or female mammal is concerned in the production of young, and it is not appli- cable to any isolated portion of that period. A WALTER HEAPE. Although the part which the male takes in breeding is confined to the insemination of the female, while the whole of the rest of the process is carried on by the female, and in spite of the fact that the word “breed ” carries with it, in its original sense, as I understand it, the giving of nourish- ment, and might perhaps in that sense be confined to the female, it is impossible to avoid including the male. The extent of the breeding season of a male depends upon the length of time during which he is preparing for, and is capable of, inseminating a female; while the extent of the breeding season of a female mammal depends upon the extent of the sexual season, during which her generative organs are pre- paring for conception, plus the time occupied by gestation, or the gestation period. The term has been used to describe specially the season when mammals copulate, or, again, it has been used to specially designate the period of gestation in the female; but it is not applicable as a definitive of either of these periods separately, and must be used for the whole consecutive breeding period experienced, and in this sense is applicable to both male and female mammals. The term “ breeding” is also frequently used in connection with the rearing of the young after birth, and this has given rise to confusion, inasmuch as while the mother is providing nutriment for young already born, she may or may not be bearing others. It is obviously inconvenient to include the period of suckling in the “ breeding season,” for which reason I have called it the Nursing Period. Sexual Season isa term I have used to designate, for both male and female mammals, the particular time or times of the year during which their sexual organs exhibit special activity. Some mammals experience only one sexual season each year, some experience more than one; in some it is a brief period, in others it occupies a much longer time ; in some the sexual season of the female may be interfered with by gestation, in others it 1s not. THE ‘* SEXUAL SEASON’? OF MAMMALS. 5 It is a convenience to be able to use one term for this phenomena in both sexes, but it is to be noted in the first place, that the sexual season of an individual male and indi- vidual female of the same species is not necessarily coincident, either with regard to time or with regard to extent; and in the second place, that the phenomena exhibited are different in the two sexes. [or this reason special terms are used for each sex. The Male Sexual Season. Rutting Season.—This term is used to describe all seasons of special activity of the generative organs of the male, during which he is desirous of coition and normally capable of inseminating the female. In some animals these seasons are of short duration and at long intervals ; in others the intervals may be shorter or the duration of the season longer ; while in others, again, there would appear to be little or no cessation of the generative power. It is necessary here to remark that the term “rut” (German “ Brunst,’’ French “rut’’) is used by German and French authors frequently, and by some English writers, to designate the conditions obtaining in both male and female mammals during the sexual season. ‘This is an error; it is essentially a word which should be confined to the phenomena exhibited by the male; it has its origin in the Latin word “yrugire,”’ to roar or bellow, and is, I believe, strictly appli- cable only to such animals as stags and boars. There are, however, other male animals to which the term may be applied in its original sense, as, for instance, the bull elephant in a condition of *‘ must,” and it will be convenient to extend the use of the term “rut” to the males of all animals which exhibit seasons of special generative activity ; to those, on the other hand, who are capable of inseminating the female at all times of the year, the term is not applicable. The Female Sexual Season. In the case of the female the activity of her generative 6 WALTER HEAPE. organs and the form which that activity takes is modified by conception, and it is necessary to consider the subject under two heads: (1) when reproduction does not take place, that is in the absence of the male, or when coition does not result in conception; and (2) when reproduction does take place. Under either of these circumstances the changes which take place in the generative system are both complex and variable, and for purposes of comparative study must be identified. (1) When Reproduction does not take place.—In the first place we will consider the changes which take place in the simplest form of the female sexual season, and after- wards indicate the nature of the more complicated processes. Pro-cstrum, or the Pro-cstrous Period, is the term I have adopted to describe the first phases of generative activity in the female mammal at the beginning of a sexual season ; it 1s identical with the period spoken of by the more accurate breeders as the time during which an animal is ‘““coming on heat,” or “coming in season.” During this period certain changes take place in the generative organs which, while in some animals they are more drastic, in some more complete than in others, are based on the same plan, - have the same object, and the same effect in all. They result in a condition which I have called— Gistrus.—This is the climax of the process ; it is the special period of sexual desire of the female; it is during cestrus, and only at that time, the female is willing to receive the male and fruitful coition rendered possible in most, if not in all, mammals. (Hstrus may be a brief period and exist for only a few hours, or it may extend for days, or apparently even for weeks; it is possible, however, normally, only as a result of the active changes which take place in the generative organs during pro-cestrum. The period of cestrus is referred to by various writers as’ “ Brunst,’ “rut,” “heat.” = “seacam: ae Ori, eer THE ** SEXUAL SEASON” OF MAMMALS. 7 “costrum;”? as I have before remarked, some of these terms are used also to designate the rutting season of the male, and most of them are used indiscriminately for both the periods of pro-cestrum and cestrus, which I seek now to establish for the female. In comparing, therefore, the writings of former investigators with the statements made in the follow- ing paper, it must be recollected that the various terms hitherto used are not necessarily homologous with those used by me, and are not necessarily descriptive of the sexual season or of the breeding season of female mammals, as I understand these processes. Much of the confusion and misunderstanding which exists, regarding breeding phe- nomena, is due to the indiscriminate use of the terms above noted, and it is essential that their use should be reso icted, or given up altogether. There is one point which I should briefly refer to here. I have said above that cestrus, the period of desire, normally follows pro-cestrum ; but there are times when the females of certain, probably of many, mammals are anxious to receive the male without the pro-cestrum having taken place. This condition may occur in various mammals during pregnancy, and has frequently been noticed in most species of domestic mammals during that period, while it is evident -ina considerable number of animals also at other times. This may be called abnormal cestrus. Normal cestrus, as we shall see below, occurs in conjunction with certain changes in the uterine tissue, and this is accompanied by congestion and stimulation or irritation of the copulatory organs; whether the congested condition of the latter organs is in itself sufficient to induce cestrus, or whether the presence of some peculiar substance in the blood, or other influences, are essential for that purpose, is not known ; however that may be, congestion is invariably present, and is an essential condition. So also in abnormal cestrus, congestion of the copulatory organs takes place, but the changes in the uterus which are evident in normal cestrus are apparently absent. When 8 WALTER HEAPR. cestrus occurs during pregnancy it is probably due to a temporary diversion of a superabundant supply of placental blood ; when it occurs at other times, the highly nutritious food, with which the animals which experience it appear to be generally supplied, or the condition resulting therefrom, is possibly largely responsible for it. Metcestrum, or the Metestrous Period.—If concep- tion does not take place during estrus the activity of the generative organs gradually subsides during a definite period, which I have called the metcestrum ; and this is followed, in the simple form which we are now considering, by a long period of rest. Anestrum, or the Ancestrous Period, is the name I have given to this period of rest. It may last two or three or eleven or possibly more months, and during that time the generative organs lie fallow in the non-pregnant female. It is eventually succeeded by a new pro-cestrum, and the four periods, pro-cestrum, cestrus, metcestrum, and ancestrum, con- stitute what I have designated as the ancestrous cycle. By some this period of ancestrum is called the non-breed- ing season, but this is not correct, for although conception cannot take place during this period it may be occupied partially or wholly by the period of gestation, and inasmuch as gestation is included in the breeding season, the ancestrum cannot be considered as a non-breeding season. We now have to consider a more complicated form of sexual season. In this case the sexual season is ushered in as before, with the pro-cestrum, cestrus follows, and is succeeded by metcestrum, but instead of the ancestrum, a short quiescent period now occurs which I have called the— Dicestrum, or the Dicwstrous Period.—This is a brief period lasting only a few days, at the most probably not more than twelve or fourteen days, while in some animals four to six days may be its duration. It is followed at once by a new pro-cestrum, and the four periods, pro-cestrum, cestrus, metoestrum, and dicestrum, I have designated the dicestrous cycle. THE °“*SBXUAL SEASON’’ OF MAMMATS. 9 In those animals which experience the dicestrous cycle the sexual season (when conception does not take place) consists of a series of such cycles, two or more; and may occupy any length of time from one month to the whole year. In the former case it is limited to a definite portion of the year only, while in the latter case it may be coincident with the whole reproductive period [human female, under certain conditions]. But when the recurrence of the dicestrous cycle is limited to a definite portion of the year, the sexual season is, of course, also limited to that period, and there is consequently a period of rest, which is the ancestrum. In such cases the non-pregnant female experiences a series of dicestrous cycles during the sexual season, at the end of which, instead of dicestrum following metcestrum, the latter is succeeded by ancestrum, which persists until the next sexual season occurs. In order to distinguish between the two classes of female mammals into which the occurrence or absence of dicestrum divides them, I have called those which experience a single cestrus during each sexual season, or in other words those in which the ancestrous cycle only occurs, monestrous mammals; while those whose sexual season is occupied by a series of dicestrous cycles, or in other words those who experience a series of recurrent cestri, I have called poly- cestrous mammals. The complication into which an otherwise simple story is thrown is due, therefore, to variation in the quiescent period. In some animals this may bea very brief period, never lasting more than a few days; in others it may occupy from two to eleven months each time it occurs; while in others again both these conditions are experienced at different times of the year. Functionally, no doubt, these two varieties of the quiescent period are homologous, the one is a modification of the other ; and the modification is probably due, as will be shown below, to an increased or decreased power of reproduction. At the same time, for the purposes of the present paper, the difference between them is essential, and their relation to the sexual] 10 WALTER HBEAPE, season renders it necessary to discriminate clearly between them. The result of the foregoing may be summarised thus: when the male has not access to the female during the sexual season, or when insemination at that time does not result in the fertilisation of an ovum, pro-cestrum and cestrus are followed by metcestrum and, if the animal be polycestrous, dicestrum is followed by another pro-cestrum, and such di- cestrous cycles continue so long as the sexual season lasts ; whereas if the animal be moncestrous, or if the dicestrous cycles of the polycestrous animal be ended, ancestrum follows, and persists until a new sexual season occurs. A few examples will render the foregoing somewhat more clear. Among moncestrous mammals is the wolf, which, in the wild state, experiences only one sexual season at a particular time each year; in her case pro-cestrum and cestrus are followed, when conception does not take place, by met- cestrum, and the whole of the remainder of the year is occupied by ancestrum. She therefore experiences a single anoestrous cycle each year. Another moncestrous animal is the domestic bitch; but in her case, in the absence of gestation, the ancestrous cycle may recur two, three, or even four times each year. Among polycestrous mammals the mare may be taken as an example; durmg a certain portion of the year, of variable extent, she undergoes a series of dicestrous cycles when she is not pregnant; this portion of the year is her sexual season; when it is over ancestrum occurs and lasts until the commencement of the same time the following year. ‘he human female, who is also a polycestrous mammal, under certain circumstances has a continuous series of dicestrous cycles throughout the year when she is not preg- nant, and is thus subject to a sexual season during the whole of her reproductive period. (2) When Reproduction does take place.—In this case the pro-cestrum is followed by cestrus, during which period insemination occurs and the ovum or ova are fer- THE *“* SEXUAL SEASON’? OF MAMMALS. 1] tilised; gestation results and persists until parturition takes place. After parturition there may be a considerable interval of rest ; this interval may occupy only what remains of the ancestrous period which the same animal would experience in case it had not borne young, or it may persist during a nursing period which extends beyond the normal limits of such ancestrous period, or it may be even still further pro- longed. On the other hand, parturition may be followed almost immediately, and in spite of the nursing period, by pro-cestrum, cestrus, insemination, and renewed gestation. While finally, the same animal may at one time of the year exhibit a recurrent gestation, while at another time of the year its generative organs may continue fallow for the re- mainder of that interval which represents the ancestrous period. Such briefly are the different types of breeding phenomena exhibited by female mammals during their reproductive period; the following account will show that they all con- form to one plan, and that the variability, which altered conditions of life induce therein, clearly indicates the origin of these types. On this account the subject is likely to be of considerable interest to students of variation, and the collection of facts which bear thereon is urgently needed. The Sexual Season of Male Mammals. It is unnecessary to do more than mention here that males may be divided into two classes: those which rut (stag), and those which do not rut (dog). Rutting males have a special sexual season; those which do not rut experience sexual capability all the year round. The sexual season of some males in captivity! is capable 1 Information regarding wild animals in captivity, unless otherwise stated, has been obtained from certain keepers in the Zoological Gardens of London, whose statements appear to me to be reliable. The reference given in the text is (Zoo,), 12 WALTER HEAPE. of modification similar to that of certain females under the same conditions; for instance, wapiti stags under natural conditions have a special lhmited rutting season, but in captivity (Zoo.) they rut all the year round except during the season when they cast their antlers and until those structures grow again. When rutting exists it is probably excited by similar influences to those which induce the advent of cestrus in the female ; on the other hand, when the sexual season of a male is a permanent characteristic, either all the females of that species have a sexual season all the year round or individual females have different times for their sexual season. As examples of these two conditions it may be pointed out that the camel in the Zoological Gardens of London ruts at much the same time as the female camels experience cestrus in Mongolia, namely, early in spring (Prejevalsky, 1876), although in the Gardens there are no female camels ; while the sexual passions of the dog, on the other hand, are excited by oestrus of the bitch and may be called forth at any time of the year. At the same time the proximity of the two sexes may stimulate both cestrus and rutting. The stimulation of cestrus is noticed in some of the larger carnivora in the Zoological Gardens by the presence of the male, while I have noticed rut in Semnopithecus entellus, in the Calcutta Zoological Gardens, stimulated by the female; and rut in the domestic rabbit stimulated by a doe under the influence of cestrus. | It is interesting to observe that while the sexual activity of domestic mammals (Miiller, 1838) and of wild animals in captivity (Heck, 1899) may be more frequently exhibited, it is not so violent as is shown by animals in the wild state. For the purposes of this paper, this is all that need be said specially, regarding the generative phenomena exhibited by the male ; although the activity of his generative organs may be to some extent influenced by the presence or absence of the THE ** SEXUAL SEASON’”’ OF MAMMALS. 13 female, the general scheme of his reproductive period, and breeding, sexual or rutting season, remains the same. The Breeding Season of Female Mammals. The breeding season of mammals should rightly be con- sidered after the sexual season has been discussed, but, owing to the fact that the term “ breeding season ”’ has been so universally used to designate the sexual season as well as the gestation period of breeding mammals, it is necessary to say a few words here in order to make the following account clear. The occurrence of a breeding season depends upon the occurrence of a sexual season, and those factors which influence the former, influence also the latter, and will be treated under that head. The same is true for the recurrence of both the breeding and the sexual seasons. The recurrence of the sexual season may be interfered with by the bearing of young, both gestation and nursing may so interfere, but that does not remove a consideration of the question, under such circumstances, out of the realm of the sexual season; the effect of these processes, of bearing young and of nursing young, on the sexual season, must be con- sidered in relation to that period, and must not be supposed to have relation only to the remainder of the breeding season. Questions regarding the breeding season of mammals con- cern what happens during both the sexual and the gestation periods jointly, and, as I have before stated, the expression is a term used to define the period passed through by an animal which experiences both these processes ; it is not applicable as an expression or term which may be used for the occurrence of either of them separately, nor for the effect one of these processes may have upon the other. A. breeding season may include only one sexual season and one gestation period; this is true for all moncestrous mam- ~ mals, of which the bitch will serve as an example, and it may 14 WALTER HEAPE. be also true for certain polycestrous mammals, as, for in- stance, the mare, under certain circumstances. On the other hand it may include several sexual seasons and several gesta- tion periods, a condition to which only certain polycestrous mammals can attain, of which the rat is an example. The time occupied by a breeding season is very variable, from a few weeks (bitch) to several months (mare), and even more than a year (elephant). There may be only one breeding season in the course of several years, as shown by the walrus (Bell, 1874), elephant, and probably rhinoceros (Willoughby, 1889). There may be one breeding season each year (mare) or more than one (domestic bitch and cat). The result of a breeding season may be the birth of one young one (mare usually), one litter of young ones (bitch), or many litters (rat). There may be great variation in the period of gestation of different species of the same order of mammals. For in- stance, among Rodents, the rat goes twenty-one days in young, the rabbit thirty-two days, the guinea-pig sixty-three days. Among HEquide, mares carry their foals eleven months, asses from three hundred and fifty-eight to three hundred and eighty-five days, and Burchell’s zebra over thirteen months (Tegetmeier and Sutherland, 1895). Among Ovide the Barbary wild sheep goes from twelve to fifteen weeks in young (Zoo.), while the domestic sheep in this country averages about twenty-one weeks. There may even be variation in the period of gestation ir varieties of one species ; for instance, Merino sheep average 150°3 days’ gestation, while Southdowns average 144-2 days (Darwin, 1875), and different breeds of cows apparently vary from 277 to 288°75 days’ gestation (Varigny, 1892). The supply of food available may influence the length of time occupied by gestation. A correspondent who is a sheep breeder informed me that his ewes, when run on poor land, experience an appreciably longer gestation period than those run on rich land; and I am strongly inclined to think investigation will show that the supply of food, and the THE °° SEXUAL SEASON’? OF MAMMALS. 15 quality of that food, have very marked effects not only upon breeding seasons and gestation periods, but upon fertility generally, upon the mother and upon the foetus (Latarte, 1891). It is with such questions as these that the consideration of the breeding season as a whole 1s concerned; with them the following paper does not deal, and it is obvious that before they can be profitably discussed, not only the sexual season, but the gestation period must be examined separately. The Sexual Season of Female Mammals. In dealing with this subject we have to discriminate be- tween mammals under three different conditions: namely, wild animals in a state of nature, wild animals in captivity, and domesticated animals ; and this is necessary, because the generative system of wild animals is affected by the condi- tions attending captivity, because the effect of captivity is not necessarily the same as the effect of domestication, and because wild animals cannot be examined so closely as the others and less is known about them. In dealing with wild animals in captivity it 1s necessary to -- bear in mind the fact that good food, warmth, and shelter have a very great effect on the increase of the generative powers of some animals, while on others a strange climate, confinement, want of violent exercise, and probably the absence of opportunity for periodic gorging of freshly killed food, or of a sufficient variety of food, have the opposite effect. As an example of the former the deer and cattle in the Zoological Gardens may be quoted, as an example of the latter some of the larger carnivora will stand. In dealing with domesticated animals we do not know what the original conditions were, and we have to take the facts as they stand. At the same time we may assume that animals which do not show themselves to be prolific under domestication are rarely domesticated, and that a very long 16 WALTER HEAPE, course of artificial selection, added to the plentiful supply of food, with warmth and shelter inseparable from domestica- tion, has no doubt greatly increased their power of repro- duction. As has been already stated, there are two forms of sexual season evident in female mammals; the moncestrous, in which there is only a single cestrus at one or more particular times of the year (bitch), and the polycestrous, in which there are two or more concurrent dicestrous cycles at a particular time of the year (mare). The sexual season may be influenced by the climate of the region in which the animal lives, by the seasons of the year when these are of marked variation, and by the supply of food, or possibly by the nature of the food, obtainable. ‘These may be called climatic influences. It may also be influenced by special nervous, vascular, and secretory peculiarities of the individual and by its habits of life. These may be called individual influences. It may also be influenced by the length of gestation, the claims of the newly-born offspring on the mother (i.e. nursing), and by her powers of recuperation. ‘These may be called maternal influences. Such influences may affect the time of year when the sexual season occurs, its recurrence, and its duration. The influences which affect the time of year when the sexual season occurs, concern both moncestrous and polycestrous mammals, and are essentially governed by climatic considera- tions, including the supply of food. The recurrence and duration of the sexual season on the other hand are affected either by climatic, individual, or maternal influences, and are also experienced both by moncestrous and polycestrous mammals, though in a somewhat different way by each. In order to understand this difference it is necessary to examine briefly what occurs in these two classes of animals. Among moneestrous animals there are a variable number of sexual seasons each year, one or more, each composed of a single oestrous of variable duration. So that the result of the a THE °° SEXUAL SEASON’? OF MAMMALS. 17 different influences which affect the sexual season may be either to increase or decrease the periodicity of that season, or to increase or decrease the duration of each one. Among polycestrous animals there is usually one sexual season per annum, which is composed of two or more dices- trous cycles, and the result of these influences on such animals may be, either to increase or decrease the number of con- secutive dicestrous cycles in any one sexual season, or to increase or decrease the duration of each cycle. The effect of these influences in both cases 1s to increase or decrease the reproductive power of the animals, and they act in moncestrous animals by affecting both the periodicity and duration of the sexual season, in polycestrous animals chiefly by affecting the duration, but in two different ways, namely by increasing or decreasing both the number of consecutive dicestrous cycles and the duration of the cestri which occur therein. Modification of the periodicity of the sexual season, there- fore, is chiefly found among monecestrous animals ; while modi- fication of its duration is common to both moncestrous and polycestrous animals. It would seem possible to simplify these conditions if it were assumed that the polycestrous arose from the moncestrous condition ; if if were assumed, in point of fact, that polycestrum is simply a condition arrived at by the concentration of several moncestrous sexual seasons. There might seem to be some reason for this when such animals as the red deer, for instance, are considered ; in the wild state this animal is apparently moncestrous, while in captivity it is polycestrous, at any rate in this country. But it may equally plausibly be argued that moncestrum is simply decentralised polycestrum. There are instances among domesticated animals of monoestrous animals with a tendency to polycestrum (bitch), and of polycestrous animals with a tendency to moneestrum (mare). Soalso among wild animals there are instances of animals which are moncestrous in one chmate and apparently polycestrous in another (Sciurus vulgaris) (compare Bell, 1874, and Lataste, 1887). vot, 44, part 1.—NkEW SERIES, B 18 WALTER HEAPE. I doubt if, in the present state of our knowledge of the subject, it is possible to determine which is the original of these two conditions. The behaviour of animals in captivity and under domestication inclines one to believe that monces- trum is the original form ; then, again, it is the simplest form, and on that ground may be thought the more archaic. But, on the other hand, it is the lower animals which are the most prolific breeders, and, for many reasons, we may perhaps expect the ancestral mammal to have been more prolific than wild animals are now. If this should be true, the increased capacity for reproduc- tion, shown by domesticated animals, would indicate rever- sion to ancestral powers, due to the removal of such obstruc- tions as must be inseparable from the strugele for existence. Thus all we can be certain of is the close similarity between these two forms of sexual season. A further complication is introduced by certain breeds of domesticated sheep and by pigs; these are polycestrous ani- mals when domesticated, and they may also exhibit more than one sexual season each year. Such a condition appears to be exceptional, and I have not included this form of variation in the foregoing account for that reason; but I am quite prepared to believe a more exact knowledge of what takes place among domesticated animals will show a similar varia- tion among individuals of other classes of animals. Variation in the periodicity of sexual seasons is brought about by an increase or decrease in the persistence of the anoestrum, and has nothing to do, necessarily, with variation in the cestrus cycle itself; while, on the other hand, variation in the duration of a sexual season is brought about by an increase or decrease in the number of consecutive dicestrous cycles (polycestrous mammals), or by an increase or decrease in the persistence of the cestrus (moncestrous and polycestrous mammals), the ancestrum being only secondarily affected in consequence thereof. ; The effect of an increase in the periodicity of sexual seasons may be twofold; it permits of reproduction at differ- "HE ** SBXUAL SEASON’? OF MAMMALS, 19 ent times of the year, and, when gestation is of sufficiently short duration, of reproduction more than once a year. An increase in the duration of the sexual season may also have two effects; it gives increased opportunity for successful coition, highly advantageous to those animals which live an isolated life, while, among animals which experience a suffi- ciently short period of gestation, it gives them opportunity for reproducing several times in each season. On the other hand, a decrease in the periodicity or duration of the sexual season has an opposite effect. It would seem highly probable that the method of increas- ing or decreasing the opportunities of reproduction varies with the habits of animals, the claims of maternity, and the climate in which they live. The different methods are not necessarily peculiar to particular groups or classes of animals, and they may vary, within limits, in the same species in different localities and in the same individual under different circumstances. Climatic and maternal influences may be observed in wild, captive, and domesticated animals; but individual influences can only be noted in the two latter classes, and especially in domestic mammals. It has been freely stated, originally by Aristotle and sub- sequently by numerous biologists, that the sexual seasons are governed by the requirements of the newly born young ; in other words that the season for conception is regulated by the length of gestation and the time of year which is most favourable for the birth of the young; and it is argued, that the different times of the year during which the sexual seasons of similar animals occur is sufficient ground for that view. I cannot agree with this opinion ; if it were so, why should some bats experience a sexual season in the autumn and not produce young until about June (Beneden, 1880, and others, see below), although not more that two months are required for gestation and these animals are active for that length of time in the spring, before parturition takes place? Again, why should roe deer, in Germany, have their sexual season 20 WALTER HEAPRE. in early autumn, when the embryo does not develop beyond the segmentation stage until the following spring? (Bischoff, 1854). Why should the seal take eleven to twelve months for gestation, while a large dog only requires three months? If there was a great difference in the size of these animals the variation might to some extent be accounted for, but it is not so. ltis true that the newly born seal is a far more perfect animal than the newly born puppy, but it cannot be that the whole of the difference in the time of gestation, namely, eight to nine months, is required for the extra development of the more perfect seal embryo, other factors being equal. Again, how is it that an unusual change of climate will affect the sexual season of an animal? This is constantly observed among domesticated animals, and a very marked case is recorded of cows, in Skye, after an exceptionally severe winter (Youatt, 1834). And how is it that the sexual season, for instance, of the fox (Bischoff, 1863) and red deer (Cameron, 1900), is modified in accordance with the nature of the country in which 1¢ lives, whether high or low ground, in accordance with the age of the animal, and probably also in accordance with its bodily condition ? There seems to me ample reason for the belief that the sexual - season 1s governed directly by the influences detailed above— climatic, individual, and maternal; and that variation in the rate of development of the embryo, in the length of gestation, and in the powers of nursing, are quite sufficient to provide for the launching of the young at a favourable time of the year. The origin of the sexual season is another matter; for a solution of this question a comparative study of the phe- nomena in the lower animals is necessary. That it is the result of a stimulus which may be effected through the alimentary canal is demonstrated by the effect upon ewes of certain stimulating foods; the sexual season of ewes may be thus forced by “flushing” them, as it is called by flockmasters. In the same way it is stated that a quart of milk, drawn THE ‘‘ SEXUAL SEASON’’ OF MAMMALS. 21 from a cow “in season”’ (i. e. during cestrus), but which has not had the bull, will, if drunk by another cow, bring on the sexual season of the latter (Youatt, 1834). ‘hat it is associated with a stimulus which is manifested by exceptional vigour and exceptional bodily ‘condition ” is demonstrated by the pugnacity of the males at such times, by the restless activity of the females, by the brilliant colouring of such widely divergent animals as, for instance, annelids, amphibia, birds, and mammals, by the condition of the plumage of birds, and of the pelage or skin of mammals. That itis associated with nutrition, and thatitis a stimulus which is gradually collected, is indicated by the increased frequency of the sexual season among domesticated mammals as compared with nearly allied species in the wild state. That it is manifested by hypertrophy aud by congestion of the mucous tissue of the generative organs, and of various other organs, such as the wattles and combs of birds, the crest of the newt; and by the activity of special glands, the affection of all of which may be exceedingly severe, is true. These,and many other similar facts,are well known, but they do not assist in the elucidation of the origin of the function. The most that they do is to show thut the sexual instinct is seasonal, and that nutrition, whether affected by external or internal factors, plays an important part in its manifestation. The Periodicity of the Sexual Season in Moncestrous Mammals in the Absence of the Male. In the absence of gestation most mammals would appear to experience at least one sexual season per annum, under natural conditions, but there is great variation in the periodicity of the sexual season in captive and domesticated mammals, the variation being extended not only to varieties of a species, but also to individuals of that species under domestication. Among certain wild animals which are known to undergo parturition only during a very circumscribed time, the moncestrous condition may be assumed as probable, and the periodicity of the sexual season calculated ; but it must be 22 WALTER HAPE, recollected that without accurate observation, during the ab- sence of the male, it cannot positively be asserted that such animals are moncestrous. In the case of the bitch, in Danish Greenland the bitch generally experiences only one sexual season per annum, though sometimes she may have two (Rink, 1877). In this country, as a rule, the bitch has two sexual seasons each year, one in the spring and one in the autumn, but there are wide variations to this rule. She may have only one sexual season per annum, or it may occur every eleven, ten, nine, elght, seven, six, five, or four months (Stonehenge, 1887). It seems probable the sexual season recurs less frequently in breeds of large dogs as a rule; a correspondent: (Dr. Inmann), who breeds St. Bernard dogs, informs me this is his experience, and I have had information from other breeders of large dogs, mastiffs and bloodhounds, which shows there is an obvious tendency in this direction; at the same time it does not appear to be by any means a universal rule. Again, while the spring and autumn are the usual times when the sexual seasons of dogs occur, the sexual seasons of each bitch have a more or less exact periodicity peculiar to herself. Finally, the sexual seasons of any bitch may be interfered with to the extent even of complete cessation, if she is sys- tematically prevented from breeding. The bitch may be considered a case of extreme variation in the periodicity of the sexual seasons of a moncestrous domes- ticated mammal. The normal two sexual seasons experienced in this country are reduced usually to one in Danish Greenland, probably owing to the effect of climatic influences, while the variations which exist in this country indicate the effect of individual influences, which are largely stimulated by artificial selection and domestication. The wolf, jackal, and fox are moncestrous like the dog, and. in captivity in the Zoological Gardens they show two sexual seasons per annum, lke the normal dog in this country. Bears are also moncestrous, but they have only one sexual season per annum in the Zoological Gardens. THE ‘* SEXUAL SEASON’? OF MAMMALS, 23 Badgers also are probably moncestrous, but there is great uncertainty regarding their breeding (Harting, 1888; Den- wood, 1894). The same is true for the Barbary wild sheep ; they are said to be moncestrous and to have one sexual season per annum in captivity in this country (Zoo.). The red deer, fallow deer, and roe deer are probably monoestrous in the wild state; they have only one sexual season of very limited duration (Bell, 1874). The same may be said for the ibex, Markhor, Barasingh, and Hemitragus jemlaicus in Cashmir (Laurence, 1895), possibly also the American bison (Allen, 1876), and various other species of Bos, Ovis, and Capra (Lydekker, 1898) ; also the black-tailed deer in Montana (Roosevelt, 1893), and several antelopes (Sclater and ‘Thomas, 1900). The truth regarding these animals is not, however, known ; their moncestrous condition is rendered probable from the known very limited sexual and calving seasons, but it is by no means certain. The genus Sorex, some of the Mustela, Myoxus avel- lanarius, Arvicola amphibius, and Sciurus vulgaris, in this country (Bell, 1874) are probably monestrous in the wild state, as are also the wild cat and the fox, and they have only one sexual season. Phoca vitulina, P. hispida, P. groenlandica, Cysto- phora cristata, and Halichcrus gryphus have all a very limited sexual season, occurring once only in the year, and it is highly probable they also are moncestrous (Bell, 1874, and Turner, 1875). Variation in the periodicity of the sexual season of various domesticated animals, in comparison with nearly allied species in the wild state, has been observed in a few cases. The cat in the wild state has one (Hamilton, 1896)—some say two (Mivart, 1881), though this seems doubtful—sexual season per annum, while the domestic cat may have three or four sexual seasons each year. The sow has only one sexual season in the wild state in 24, WALTER HEAPE., France (Beever, 1870), but it 1s not clear whether she 1s monecestrous or polycestrous; when domesticated, however, she is polycestrous (leming, 1878; see also Aristotle). Certain wild sheep, O. argali, O. burrhel, O. pol, have only one sexual season per annum, and are probably moncestrous (Prejevalsky, 1876) ; whereas domesticated sheep are polycestrous, and may have such an extended series of dicestrous cycles that they are capable of producing young almost at any time of the year; such, for instance, are Dorset Horns in the south of England and Hampshire Downs in some parts of Ireland (compare also Aristotle). As a rule, however, sheep in this country have a much more limited polycestrous season,—as, for instance, the Scotch black-faced sheep, which has only two recurrent periods of cestrus (Cameron, 1900). Variation in the periodicity of the sexual season of wild animals, as compared with individuals of the same species in captivity, has been noted in but few cases. Some of the large carnivora in the Zoological Gardens exhibit great irre- gularity in their sexual seasons, but too little attention has been paid to the subject in these animals to allow of more being said than that, in some cases, their generative activity appears to have been stimulated, in others checked. The wolves in the Zoological Gardens have two sexual seasons, while the Tibet wolf (L. chanco) has only one (Pre- jevalsky, 1876) in a wild state; in New Mexico also, I am told by a keen sportsman familiar with the country, wolves bear young only once each year (W. Ruston). The same is true for the foxes in the Zoological Gardens; they have two sexual seasons, while the Tibet fox (Prejevalsky, 1876) and the English fox (Bell, 1874) have only one in the wild condition. The wild cat, on the other hand, in captivity does not experience more sexual seasons than when in a feral state, namely one (Hamilton, 1896); and the tame cat, when it becomes wild, has apparently only one sexual season, whereas the same animal under domestication has from two to four sexual seasons per annum. THE °° SEXUAL SEASON’? OF MAMMALS. 25 Among the deer in the Zoological Gardens their generative activity appears to have been universally stimulated—they will be referred to under the heading of “ Duration of the Sexual Seasonin Polycestrous Mammals,”—for it would seem that their normal (as I have considered it) moncestrous sexual season 1s increased by the conditions of captivity until it may become a continuous polycestrous sexual season. The Barbary wild sheep, on the other hand, does not appear to be affected by captivity ; it exhibits a single moncestrous sexual season only, each year (Zoo.), and that is probably its condition in the wild state if we may judge from what is known of O. argali, and O. burrhel in Tibet (Prejevalsky, 1876). It is with some hesitation I have included among monces- trous mammals deer, sheep, and pigs in the wild state; their retention in this class is doubtful; but if these animals were omitted there remains a remarkable series of examples of the variability of the sexual season of moncestrous mammals under various conditions. The Duration of the Sexual Seasonin Polyestrous Mammals in the Absence of the Male. ‘he duration of the sexual season in these animals depends upon two factors, the length of the dicestrous cycle and the number of times it recurs. Both factors may be different in different species of animals, and either may be different in different individuals of some species, or variable in the same individual at different times. Knowledge of polycestrum in animals in a wild state in this country is limited to certain rodents. The rat (M. decumanus), mouse (M. musculus), and the rabbit in this country are known to experience a recurrence of the dices- trous cycle. It is probably recurrent also in M. minutus, M. sylvaticus, M. rattus, Arvicolaagrestis, A. glare- olus, and Lepus timidus; while possibly Mustela vul- garisand Lepus variabilis, under favourablecircumstances, may also experience a recurrence of the dicestrous cycle, judging from the account given of them by Bell (1874). 26 WALTER HBAPE. In Southern Kurope and Algiers polyoestrum is apparently usual amongst rodents (Lataste, 1887). It appears to be ascertained for Sciurus vulgaris living in that part of the world—though the same animal is probably moncestrous in thiscountry—for Hliomys quercinus, Gerbillus hirtipes, Dipodillus campestris, D. simoni, Meriones shawi, M. longifrons, Mus musculus, M. rattus, M. decu- manus, and to be probably true also for several other species. The animals on which these observations were made by Lataste were kept in captivity, but there is good reason to think that the conditions under which they were kept did not interfere with their habits in this respect. Among domesticated animals polycestrum occurs in horses, cattle, sheep, and pigs. While for wild animals in captivity it has been observed (Zoo.) in the gayal and bison; in wapiti, axis and red deer; in the gnu, eland, nilghau, and waterbuck ; in Gazelle dorcas, in giraffes, in elephants, and probably in kangaroos. In its most complete form polycestrum occurs in certain monkeys and in the human female; probably most monkeys are similarly affected, and possibly also lemurs; in these animals there is a regularly recurrent series of dicestrous cycles throughout the year. The Duration of the Dicstrous Cycle varies from five days (exceptional in rodents, Lataste, 1887) to as much as two months (exceptional in mares, and in various wild animals in captivity from time to time, Zoo.). The usual length of the dicestrous cycle for rodents is ten to twenty days, and in other animals in which the phenomena has been observed from three to four weeks. In the rodents observed by Lataste (1887) the dicestrous cycle was usually ten days, and in the rat and mouse in this country the same may be said to be approximately true. In the domestic rabbit, however, I find great variability ; while some indivi- duals exhibit cestrus every three weeks fairly regularly, others do so every ten days; on the whole I think ten to fifteen days is the usual length of their dicestrous cycle. THE ‘SEXUAL SEASON’? OF MAMMALS. 97 In the domestic mare and cow three to four weeks, and in the domestic sheep and pig two to four weeks is said (Fleming, 1878) to be the length of the dicestrous cycle, while another authority (Hllenberger, 1892) regards three to four weeks as the usual time for all these animals. In wild cattle, deer, and antelopes in captivity (Zoo.) three weeks is the usual time. In monkeys it appears to be about one month in duration (Heape, 1894, 1897, Keith, 1899). In the human female, while twenty-eight days is the normal length of time occupied by the dicestrous cycle, it is fre- quently experienced every three weeks or every five weeks, while occasionally even shorter or longer periods are known. Aristotle is represented to have made the extraordinary state- ment that few women menstruate every month, while most menstruate every three months. It would seem possible that the opposite is what he meant; at the same time it should be remarked that various observers (Wiltshire, 1883) have re- corded their opinion that the women of certain tribes in different parts of the world menstruate only at long intervals (see also Ellis). The recurrence of the Dicstrous Cycle is also very variable; exact knowledge on this point is not possible for wild animals; only those under observation, captive or domestic, can supply the requisite information. The known limitations of the sexual season among certain wild animals, however, admit of a fairly accurate idea being gained of the recurrence of their dicestrous cycles, although not accurately enough to enable one to determine with cer- tainty whether an animal is moncestrous or polycestrous. For instance, the American bison (Allen, 1876) experiences a sexual season from some time in July until some time in August. In the Cashmir ibex it persists during parts of November and December. In the Markhor and Hemitra- gus jemlaicus in Cashmir it occurs in December, while in the “Barasingh” in that country from September 20th to November 20th it has been observed (Laurence, 1895), In Scotland the red deer’s sexual season lasts three weeks, 28 WALTER HEBAPE, during September and October, according to Cameron (1900) six weeks, while in this country September is the sexual month for the fallow deer, and July and August the time when the roe deer will receive the male. In all these cases there can be little over three weeks during which copulation takes place, and the extremely limited period during which parturition occurs strongly corroborates the view that this is the extent of the usual time during which sexual intercourse is possible. The fact that im captivity three weeks is the usual period which intervenes between two cestri in such animals, and the extreme probability that individual females do not all ex- perience cestrus at exactly the same time (Cameron, 1900), predispose one to believe that they are moncestrous in the wild state ; but, if the limit of time for coition 1s three weeks, there is still just time for the females to undergo two dices- trous cycles, and it is this possibility which prevents positive assertion on the matter. Among captive animals (Zoo.) not more than two dicestrous cycles have been observed in the gnu during one sexual season. Gazelle dorcas has two or three; the giraffe about three; while the eland, nylghau, and waterbuck have a series of dicestrous cycles, each lasting three weeks, during May, June, and July each year. The gayal and bison, the axis and wapiti deer, on the other hand, experience a continuous series of dicestrous cycles all the year round, at intervals of about three weeks. ‘The hippopotamus at present in the Gardens is an old animal ; for long she showed no signs of asexual season, but lately she has done so at irregular intervals; no doubt in her case captivity has checked the generative function, for a former specimen which bore three young while there is said to have exhibited monthly sexual excitement (Wiltshire, 1883). Among wild rodents in this country, recurrent dicestrous cycles last about two months, probably,in Lepus variabilis; about three months, probably, in Arvicola agrestis; from four to six months, probably, in Mus minutus; about nine THE ** SEXUAL SEASON’? OF MAMMALS. 29 months in Mus rattus; and even longer, perhaps, n Mus musculus and M. decumanus. _ Bell (1874) appears to think that, under favourable cireum- stances, the dicestrous cycles may continue all the year round in these latter animals and in the rabbit, but I am inclined to think such a condition is unusual in this country among wild rodents, since it is exceptional to find any of them pregnant during the winter months. Among domesticated animals the period during which the dicestrous cycles recur, in the absence of the male, lasts from one month to as many as eight months for the mare, about five to six months for the rabbit, from one to three months for the sheep (with certain exceptions), and about two months for the pig. So far as the domestic rabbit is concerned, no doubt, if they are kept warm, carefully fed, and their breed- ing carefully regulated throughout the spring and summer, they may exhibit cestrus also in winter, but it must be recol- lected that here we are treating of cestrus independent of pregnancy, which is a very different matter. Among certain monkeys, probably in most of them, the dicestrous cycle recurs all the year round (Geoffroy, St. Hilaire _and Cuvier, Ehrenberg, 1833, Numan, 1838, Heape, 1894, 1897, Keith, 1899 ; compare also Rengger, 1830, Sutton, 1880, and Hillis). In the human female, as a rule, this is also the case; there appear, however, to be exceptions to this rule, for instance, the women of the Hsquimaux peoples living between the seventy-sixth and seventy-ninth parallel do not always menstruate during the winter months. It is said (Cook, 1894) that not more than 10 per cent. of these women menstruate during the long dark winter months, and itis possibletoimagine that the peculiar conditions of life they experience during that time may well be responsible for their peculiarity. If this be so, a true ancestrous period may be experienced by women. Rink’s (1877) account of the origin of these people, if correct, precludes the probability that the occurrence of an ancestrous period is a racial characteristic, and emphasises the view that it is a variation due to climatic conditions. 30 WALTER HEAPE, It is held by some writers, several of which are quoted by Wiltshire (1883), that the women of various savage tribes exhibit the menstrual flow only at intervals of several months; and the same author remarks on the fact that girls at puberty in this country menstruate only at intervals of three, four, or six months ; and that it may be this condition is an indication of an ancestral habit. LHllis also quotes various authors who state that menstruation takes place at long intervals in women of Lapland, Greenland, the Faroe Islands, Tierra del Fuego, and among the Guaranis of Paraguay. The effect of captivity or domestication on the duration of the sexual season in mammals is very re- markable. As has been already pointed out, wild sheep have only a very limited sexual season per annum (O. argali, burrhel and poli, in Tibet, Prejevalsky, 1876), a condition which is maintained by the Barbary wild sheep in captivity in this country (Zoo.); whereas the domestic sheep has a much longer sexual season, and im addition has for many centuries (Aristotle) been capable of reproducing twice in each year under favourable circumstances. Again, the wild goat has a very limited sexual season (Lydekker, 1898), whereas the domesticated goat will receive the male at almost any time (Low, 1845). A more remark- able example 1s that of certain deer in captivity (Zoo.). Wild red deer have a special sexual season, extending little over three weeks (Bell, 1874), and including certainly not more than two dicestrous cycles; whereas in captivity (Zoo.) the sexual season of these animals extends over most of the year, and consists of an extensive series of dicestrous cycles. A similar condition prevails with the wapiti deer in the wild state (Roosevelt, 1893), while in captivity (Zoo.) the possibility of pregnancy at any time of the year is only pre- vented by the fact that the male does not rut during the casting and growth of his antlers; and it is asserted that park-fed wapiti stags in America are able to beget offspring even after their horns are shed (Caton, 1881), THE ‘* SEXUAL SEASON’? OF MAMMALS. 31 Wild cattle in captivity (Zoo.) are also capable of repro- duction at any time of the year, and they also experience a remarkable increase in the recurrence of their dicestrous cycles, from what we are led to infer, by the limited calving season, is the case among similar animals in the wild state. Among domesticated mammals similar modifications are evident, not only in animals of different species, but in indi- viduals of the same species, as, for instance, in cattle and horses. Mares may have only one period of cestrus in the year, in which case they are purely moncestrous animals, but this is a rare condition; rarely, also, they may have two dicestrous cycles, but usually they have many. In the latter case cestrus may recur every three weeks, or the interval may be longer. As a rule among thoroughbred mares the history of the sexual season shows a series of dicestrous cycles, each occupy- ing about three weeks and recurring throughout the spring and often until the early autumn, as many as seven or eight months being in some cases thus occupied. Although these animals—horses, cattle, and deer—either in captivity or under domestication, experience such an ex- tensive increase in the consecutive recurrence of the dicestrous cycle, it is not a condition natural to them; it is due, in all probability, to the care and attention paid to them by man; in the same way, it may be argued, that the stimulated power of reproduction evinced by certain rodents is also due to the advantages derived from their intimate relations with the luxuries of civilisation (rat and mouse). The only animals, so far as is at present known, which experience a continuous series of dicestrous cycles in a state of nature are certain monkeys. The fact that it is possible to induce such an enormously increased capacity for cestrus in any animals, prepares one to consider the regular recurrence of the dicestrous cycle in monkeys, and in the human female also, as a very slight step inadvance ; and when the whole of the evidence is considered, 32 WALTER HBAPE. it will, I believe, be found that the regularly recurrent dicestrous cycles of the Primates are strictly homologous with the more or less regular dicestrous and ancestrous cycles of the lower animals. The Sexual Season-in Monkeys.—The consideration of this subject introduces a further complication, and that is, while monkeys may have a continuous series of dicestrous cycles, they are not all of them fitted for reproduction at all times of the year. Some monkeys in tropical countries may be in a condition to become pregnant at all times of the year; though thisis by no means certain it is not an impossible fact, but others are certainly not so. For instance the chimpanzee and gorilla are said to have a special sexual season in West Africa (Garner, 1896). Semnopithecus entellus, from the jungles on the south bank of the Hugl, has a definite time for reproduction (Heape, 1894); and Macacus rhesus, the area of whose geographical distribution is very large, apparently produces young at different and definite times in different districts (Heape, 1897). There is every reason to believe, however, that these ani- mals experience regular recurrent dicestrous cycles through- out the whole year. If the dicestrous cycle of a monkey is homologous with the anoestrous cycle of a dog—and that this homology exists will be apparent when the question is considered from a histo- logical point of view—it is obvious that we are naturally led to suppose that an increased number of cestri should result in an increased number of opportunities for pregnancy, pre- cisely as in the case of the mare, deer, etc. But this is not so, and the result 1s that there exist certain mammals which, while they exhibit a continuous recurrence of the dicestrous cycle, have a circumscribed season for conception. As I have shown elsewhere (Heape, 1894, 1897), this result is due to the fact that, although menstruation recurs reou- larly, ovulation does not; or, in other words, that oyula- THE ** SEXUAL SEASON’? OF MAMMALS. 33 tion is not necessarily coincident with the cestrus in these animals. This opens up a wide question, which I hope to treat of in a separate paper, but it is necessary to refer to it here in order to point out, that the limited season for conception in some monkeys is no reason for regarding their dicestrous cycle as in any way different from that of other animals. Briefly, we may say that both ovulation and cestrus are due to stimulating influences. But they are not necessarily co- incident in the lower animals, and they are not necessarily both induced by the same means, nor at the same time. In the virgin domesticated rabbit I find that ovulation does not occur in consequence of cestrus alone; while various observers have shown that in the bat ovulation may occur at quite a different time of year from cestrus, in some cases probably as much as six months may intervene between the two functions in this animal (Benecke, 1879; Himer, 1879 ; Fries, 1879; Beneden and Julin, 1880). Again, as I have already noted, there may be abnormal cestrus In many animals, it may occur during gestation and be independent of ovulation ; while finally, it is quite certain that. many animals which usually experience ovulation during cestrus, sometimes fail to become pregnant at that time in consequence of the failure of the function of ovulation. Such being the case, it may truly be said the period of cestrus is not invariably identical with the period of ovula- tion; the two are separate functions, possibly closely asso- ciated, but also possibly widely divergent. In monkeys we have an instance of animals in which the rhythm of ovulation may be different from the rhythm of cestrus, but it must not be supposed, on this account, that either of these processes is nob homologous with the same process in other animals in which the rhythm may be identical, It would seem as if the sexual activity of these animals had been developed more than, and out of propor- tion to, the ovarian activity; or, in other words, that their sexual powers were greater than their powers of reproduction. VOL. 44, PAR’ 1.—NEW SERIES. Cc 34 WALTER HEAPE. The ideas on this subject which have for so long prevailed and which even now are taught, namely, the identity of “menstruation”?! and of cestrus with ovulation, would make this view impossible; but since it is known that, in various animals, either ‘‘menstruation”’ or cestrus may take place without ovulation, and that ovulation may occur without the coincidence of “ menstruation”? (Leopold and Mironoff, 1894) or of cestrus (bat), the possibility of isolating these func- tions is demonstrated. Thus it is no longer impossible to suppose that, while they are both due to similar stimulating influences, one of them may be developed in excess of the other. In this respect monkeys stand in an intermediate position between the lower mammals and man. The Sexual Season in Man.—In the human female this question of the simultaneity of ovulation and cstrus (“ menstruation,” as it has been wrongly called) has given rise to wide discussion. I have referred to the question somewhat fully elsewhere (Heape, 1894, 1897, 1898), and have shown that the majority of modern writers on the sub- ject are in favour of the view that the two functions are not necessarily coincident in the human female, the correctness of which conclusion it seems to me impossible to doubt. With regard to the existence of a special limited sexual season or seasons, it is interesting to note that there is some evidence of such in the human female; evidence both of a time in the past when such special seasons were common to all, and of a time in the present day to which certain peoples confine such matters and during which most peoples exhibit special generative activity. Here again we are upon the edge of a very wide field of research which it is impossible to do more than touch. I may, however, briefly draw attention to certain facts which in my opinion throw some light upon the matter. Feasts, similar to the erotic feasts which were indulged in by the ancients—Babylonians, Phoenicians, Egyptians, Greeks, and Romans (Ploss, 1887),—were still practised to 1 « Menstruation ” is used here in its original sense, THE ‘‘ SEXUAL SEASON’? OF MAMMALS. 35 some extent in the sixteenth century in Russia (Kowalewsky, 1890 and 1891), and in some parts of India at a much more recent date (Rousselet, 1876), while such customs as ‘‘ swneyd Bragod”’ (Owen, 1886) and possibly our own “bean feasts” may not improbably be the modern representatives of these ancient customs in our own country. Again, it is worthy of note that the erotic feasts of more civilised peoples are not greatly dissimilar to the sexual feasts and dances of the savage peoples of Australia, Polynesia, West Africa, South America, New Britain, and West Asia (Ploss, 1887). Apart from the fact that many of them surely have some reference to phallic worship, as in the case of the maypole, the origin of these feasts—shrouded as they are in the mists of ancient customs now but little understood, and of laws long since forgotten, complicated as they are by customs, religions, and laws of a later growth—is not de- finitely known. It is indeed a matter of the greatest difficulty to trace, justly, the true relation and likeness of any one of these customs to another, however similar they apparently may be. At the same time the universality of such customs is very remarkable, and may, I think with some justice, prepare one to believe that in prehistoric times man was impelled to indulge, if not wholly, at least more freely, in sexual inter- course at certain seasons rather than at other times of the year. Hill (1888) attempts to trace the apparent survival of a human pairing season, by the customs of the Hindus and the proportions of births in each month of the year; while Westermarck (1891) records customs and statistics which certainly point even more strongly in the same direction. Ploss (1887) also gives many valuable statistics for Russia, Germany, Italy, and France; and Haycraft (1880) does the same for Scotland. It is remarkable that the statistics brought forward by these authors in all cases show a con- siderable rise in the birth rate at certain seasons. In Scot- land, Haycraft oints out that from 1866 to 1875 a marked 36 WALTER HEAPE. increase of births occurred with striking regularity in April, showing that a maximum of conceptions takes place in July. Hill says that ten years’ statistics of the district in which he lived in India show that the maximum of conceptions occurs in December, when food is cheapest and the salubrity of the country at its best; while the minimum of conceptions occurs in September, towards the end of the hot season, when food is most scarce and malaria rife. Ploss shows that in Russia the maximum of conceptions takes place in autumn, in Germany during May and December, while in Italy and France May is the month responsible for most conceptions. This author also points out that in Russia religion affects the birth-curve, and he traces the cause to fasting seasons. Westermarck goes very fully into this matter, and has collected a great many facts bearing upon it which are of great interest. The sexual instinct in civilised man, he concludes, has two special seasons of activity—spring and autumn, but it is most active towards the end of spring as a rule, in the south of Europe this activity being most marked somewhat earlier than it is in the more northern countries. Illegitimate births, it is remarked, are comparatively more numerous in early spring, and this, it is suggested, is due to an increase of sexual instinct during May and June. ‘These conclusions are interesting inasmuch as they indicate a season or seasons which may be the original sexual seasons ; but it is the evidence he produces of the sexual seasons of more savage peoples which is of special interest here. Some of the Indians of California are stated to have a regular sexual season, spring being a literal St. Valentine’s Day with them. The Watch-and-dies of West Australia and the Tasmanians have sexual feasts in the middle of spring-time. The Hos, an Indian hill tribe, have a similar feast, which becomes a saturnalia during which absolute sexual freedom is indulged in, in the month of January; while among the Santals, another hill tribe, marriages mostly take place in THE ** SEXUAL SEASON’? OF MAMMALS. 37 January. Among the lower castes of the Panjas in Jeypore a festival in January is kept up for a month, during which promiscuous sexual intercourse is allowed. The Kotars, a tribe in the Neilgherries, have a similar feast marked by similar licence and debauchery; and the same may be said for the Keres in New Mexico, the Hottentots, and some tribes near Nyassa. In New Caledonia November (that is late spring) used to be the time when marriage engagements were made, and among the Rajputs of Mewar the last days of spring are dedicated to the god of love. . Among the Kaffirs of Cis-Natalan Kafirland more children are born in August and September than in any other month, and it seems probable this is due to certain feasts during which there is unrestricted intercourse between the un- married people of both sexes. Among the Bateke—Stanley Pool—most children are born in September and October—the season of the early rains,— and it is said the same is the case among the Bakongo. In Chili the maximum of births occurs in September. Dalton (1872) gives an account of the Miris, an Indian hill tribe, which shows that at one season of the year sexual relations between the unmarried are specially counte- nanced and indulged in. My friend Mr. Caldwell tells me that the Queensland natives with which he was brought in contact have a distinct sexual season in September (that is spring), and that they cannot be prevailed upon to do any work for some weeks at that time of the year. Cook (1894) records that the Esquimaux which inhabit the country lying between the seventy-sixth and seventy-ninth parallels, exhibit a distinct sexual season, which recurs with great intensity at the first appearance of the sun, and that little else is thought of for some time afterwards: an account which is in agreement with statements made by Bosquet (1885) regarding other Hsquimaux. Finally Man (1882) notes that the children of the natives 38 WALTER HEAPE. of the Andaman Islands are said to be born mostly at a particular time of the year—during the rains. I have not done more here than simply to indicate the bearing of a very considerable literature which deals specially or incidentally with this subject ; one section of this literature demonstrates by means of statistics, for countries where such are available, an excessive birth rate in special seasons; the other shows that the habits and customs of the less civilised peoples indicate that their sexual and reproductive functions are specially stimulated at definite times of the year. While there is some variation in the season for special sexual activity indicated by the above statements, spring is obviously the most usual time. Hutchinson (1897) seeks to show that the time of marriage among certain widely diver- gent people is largely governed by times of agricultural plenty; for economic reasons this might reasonably be expected, though the evidence he brings forward is not at all conclusive. But it does not seem to me to bean important point. Many reasons, religious or otherwise social, may have arisen to interfere with such a rule, supposing it ever was a rule. The importance of the evidence consists in the proof that any time is or was specially conducive to sexual dis- turbance, and this, I think, has been proved. (See also Laycock [1840] and Ellis’s very interesting résumé of this question.) The wide variation in the time of the year during which the sexual season of the lower mammals occurs in different parts of the world, renders it not surprising that there should be wide variation in man also in this respect, in different geographical areas. However that may be, the fact remains that there is much evidence in favour of the view that special sexual seasons were, at one time, universally experienced by the various races of man, a fact of great importance from a comparative | point of view. But not only is there evidence of a circumscribed period for reproduction in the ancestral human being, and in those a] ** SEXUAL SEASON”? OF MAMMALS. 39 peoples who ccupy a low position in the scale of civilisation, but there is Iso evidence that the latter produce smaller families. In some cses this is ascribed to the practice of infant marriage, to she strain of child-bearing on a mother who requires for ‘erself all the nourishment she is capable of assimilating ; but comparatively small families are usual in many savage \eoples whose women do not become mothers at a very earlyage (Westermarck, 1891). In these cages the result is probably due not only to pro- longed lactatim, or to infant mortality, but to inability to produce more Children; -for, as the practice of polygamy shows, the adwntage of large families is fully recognised, and each indiyicual woman will be required to Pee ei as frequently as possible. ny It would seem highly probable, therefore, that the repro- ductive powerof man has increased with civilisation, precisely as it may be iicreased in the lower animals by domestication ; that the -tect of a regular supply of good food, together with all the other stimulating factors available and exercised ia modern civilised communities, has resulted in such great activity of the generative organs, and so great an increase in the supply of the reproductive elements, that conception in the healthy human female may be said to be possible almost at any time during the reproductive period. We have come to believe that it is to the regular monthly menstrual periods, which the human female generally ex- periences, that this great reproductive power is due. But the evidence of a regular menstruation with a limited con- ception period in monkeys, shows that this is certainly not so. As in monkeys, so in man, these two functions are not necessarily equally developed. I think it may fairly be stated that an increase in the frequency of menstruation is not necessarily a sign of an increased power of reproduction among women, and that there is no indication that women who menstruate every two or.three weeks are more prolific than those who menstruate 40 WALTER HEAPE. every month; in fact, the reverse is probab] true, and the excessive activity of the menstrual organ, if it ; not developed at the expense of the reproductive power, yn many cases results in lessened fertility. We are here doubtless in the region of pathlogical condi- tions, since when there is a considerably incraged menstrua- tion, either by increase of the amount of the menstrual flow or by decrease of the intra-menstrual peric], it is accom- panied by exhaustion and the evils which res ]+ therefrom. If the above be true, it would appear that jyvilised woman has reached the limits of reproduction comp,tible with her mode of life, and it may be concluded that »ereased repro- ductive power will not arise until her power, of assimilation are increased to a sufficient extent, and unti the products of that assimilation are devoted more exclusi'ely to the repro- ductive function. The Duration of the @strus in Monwstrous and Polyestrous Mammals in the Absenco of the Male. There is very little known regarding this point except in certain domesticated animals. ‘The cestrus of moneestrous mammals may last a short or a long time. In the Barbary wild sheep in captivity (Zoo.) it only lasts a few hours. In the bitch it lasts a variable time, variable both in different individuals of the same species and in the same individual at different times. ‘The winter cestrus of the bitch does not last so long as the summer cestrus in certain breeds ; a well-known breeder (Dr. Inman) has assured me this is the case with his bitches. The usual time is probably from seven to nine days. A most careful observer, however, tells me that a bitch which he had for many years usually remained in a condition of cstrus for nine days, but sometimes it persisted in her for fourteen days. Other breeders have informed me they have had bitches undergoing cestrus for even a longer period than this, but it is undoubtedly an exceptional experience. ) THE “SEXUAL SEASON’? OF MAMMALS. | In certain bloodhounds a well-known breeder (Mr. Brough) has observed cestrus to last twenty-one days, but only very ex- ceptionally,and not as a characteristic of any particular bitch. There can be little doubt the persistence of cestrus in bitches may be influenced by their temperament, by their food, and by the particular conditions of existence expe- rienced by each bitch. Wolves, jackals, and foxes in the Zoological Gardens have about the same duration for cestrus as the average bitch, from seven to nine days. In the cat cestrus lasts nine to ten days (Hamilton, 1896); in tigers in captivity (Zoo.) for eight days at the longest. In bears, on the other hand (Zoo.), cestrus appears to last continuously for two to three months ; it must be recollected, however, that this occurs with females kept together with males under conditions which, while they may very probably excite sexual feelings, do not result in gestation. Among wild animals the duration of the cestrus can only be assumed by comparison with other individuals of the Same species in captivity; although the duration of the sexual season may be inferred from the known season during which parturition takes place, the duration of the oestrus cannot be so determined. Among polycestrous mammals there is not such great varia- tion in the duration of cestrus, since, instead of a long period of cestrus, these animals exhibit a recurrence thereof ; still there is some difference apparent: the domestic sheep has oestrus for only a few hours, say twelve hours; the cow for not more than twenty-four hours as a rule; while antelope, deer, and wild cattle in captivity (Zoo.) closely imitate domestic cattle and sheep in this respect. The mare endures cestrus probably for a slightly longer period as a rule, but this depends very much on the tempera- ment of the individual mare, and the conditions under which she is kept. The elephant in the Zoological Gardens has persistent cestrus for probably three to four days. 42 WALTER HEAPK. In monkeys the cestrus has not usually been carefully noticed, but | am assured that the Moor macac in confinement (Zoo.) has a definite cestrus which lasts two or three days ; and inafew other monkeys a similar condition has been from time to time noticed (Hills). In the human female there is not wanting evidence of a similar condition (Aristotle; Martin, 1888; Haycraft, 1880), and on this point information has been supplied to me by various experts, which leads me to think it will probably be found that those women who are most robust, and who suffer least from the enervating effects of civilised hfe, experience a condition comparable to that of cestrus in the lower mam- mals (confer also Hillis). The Effect of Maternal Influences on the Sexual Season and on CUstrus. Maternal influences may or may not completely disorganise the sexual season; this depends upon whether or not they interfere with its recurrence or with that of cestrus. Gestation.—Gestation may or may not interfere with ihe recurrence of one or other of these factors. In the dog it does not do so, because the dog has only one cestrus during each sexual season, and the period between two sexual seasons, i.e. the ancestrum, is longer than the period of gestation. In the elephant it does do so, because the gestation period is longer than the ancestrous period. So also with badgers this appears probable (Denwood, 1894). In camels, whose gestation occupies thirteen months, the sexual season is inter- fered with by gestation, and is on that account put off for another year. ‘lhe camel conceives every two years (Swayne, 1895). Inthe rat, on the other hand, gestation does not interfere with the recurrence of the sexual season, but does interfere with that of cestrus, because the rat has a series of dicestrous cycles in each sexual season, and she may also undergo a series of gestation periods during that time, and because the maternal generative cycle (twenty-one days) is longer than the dicestrous cycle (ten days). THE “ SEXUAL SEASON” OF MAMMALS. 43 But whenever gestation occurs it encroaches upon, if it does not entirely absorb, the ancestrum ; that is to say, it re- duces the period during which the generative organs would lie fallow if the sexual season were a barren one. Thus in the case of the mare, a barren sexual season may consist of a series of dicestrous cycles lasting for as long as six months, in which case the ancestrum lasts six months also, after which another sexual season again begins. A reproductive sexual season, however, results in a period of eleven months’ gestation; interfering not only with the dicestrous cycles which would have recurred if conception had not taken place, but also absorbing practically the whole of the ancestrum ; for, nine days after parturition, the ma- jority of mares again experience cestrus. Nursing.—Nursing also may or may not interfere with the recurrence of the sexual season and of cestrus. ‘lhe rat suckles her new-born litter of young while pregnant with another litter; so also does the domestic rabbit and guinea-pig, and probably many rodents. ‘lhe mare also, as a rule, readily becomes pregnant while suckling her newly born foal. Here, however, there is some evidence of variation, for I am informed, by a breeder of large shire horses in the west of England, that many of the mares in his stud become pregnant only once every two years; the drain on the system, in consequence of gestation and nursing, in these large animals being, apparently, too great to admit of the immediate recurrence of another sexualseason. Another breeder of shire horses, however, assures me that he gets a foal each year from his mares. On the whole there is some reason to believe that, unless these large mares are exceptionally carefully tended, they are lable to miss bearing annually, from time to time. A few instances may be given here of animals in the wild state which do not bear young every year. ‘The grizzly bear in British Columbia bears young only every second year (Somerset, 1895). The wild yak in the Tibetan desert only produces a calf every second year (Prejevalsky, 1876), and 44, WALTER HEAPBE. the same is probably true for the Greenland musk ox (Lydekker, 1898); while the walrus, which goes nearly twelve months with young, nurses her calf or provides it with food for two years (Bell, 1874), and during that time anoestrum appears to persist. Similar evidence of variation is to be found in the human female. Among the Esquimaux in high latitudes children are nursed from four to six years, and women bear children about every four years (Cook, 1894). It 1s not uncommon to hear of women of various tribes purposely prolonging the nursing period in order to avoid too frequent breeding. The Waganda women nurse their children until two years of age, and live apart from their husbands from the time of con- ception until the child is weaned (Felkin, 1885). ‘The Andaman Island native women nurse their children as long as they can (Man, 1882). On the other hand, it is recorded that among the North-west Central Queensland natives nursing may go on for three, four, or five years, and a mother is frequently seen with two children of different ages at the breast (Roth, 1897). Among more civilised women menstrua- tion is frequently in abeyance during the nursing period, nevertheless many women menstruate while lactation is still possible. Such a possibility is not confined to women among menstruating animals. I have seen a monkey, Macacus cynomolgus, in the gardens of the Zoological Society at Calcutta, which menstruated regularly while still suckling a young one. The whole question of lactation and its relation to sexual phenomena, more especially gestation, is of great interest, all the more perhaps when it is remembered that virgin bitches frequently secrete milk in sufficient quantities to interfere with their work (foxhounds), while mules have been known to nurse successfully the foal of a mare; but for our present purpose sufficient has been said, and in conclusion it may be argued that when nursing encroaches upon the sexual season, the recurrence of the latter depends upon the vigour of the mother and her powers of recuperation. THE ‘* SEXUAL SHASON’’ OF MAMMALS. AD The Pro-cstrum. The pro-cestrum, as I have already stated, is the forerunner of estrus. Evidence of it is to be seen in each of the large eroups of the Vertebrata, fishes, amphibia, reptiles, birds, and mammals (Wiltshire, 1883), and it must be regarded in all of them as a sign of the preparation of the generative system for the sexual act. Pro-cestrum is usually associated, in the minds of breeders, with reproduction, to an extent which entails the supposition that the same stimulus which incites the former also causes the latter ; but the fact that pro-cestrum may occur normally without the concurrent production of ova shows that the two functions are not always interdependent, and that what serves as sufficient stimulus for sexual desire is not necessarily sufficient for reproduction. A consideration of these relationships belongs rather to the study of ovulation than to the subject-matter of the present paper. I would merely remark here that while the ovary probably does participate to some extent in the excitement evidenced by pro-cestrum, this function in mammals must be considered as evidence mainly of sexual rather than of repro- ductive power. Pro-cestrum is first evident in the tissue of the external generative organs and the surrounding parts, and while it increases in intensity there, it extends to the uterus; during this time certain changes (to be mentioned below) take place in the uterine tissue, and they are followed by the subsidence of the disturbance, first in the uterus and finally in the external generative organs. The length of time during which pro-cestrum lasts is ex- tremely difficult to determine ; there seems to be considerable variation in different animals, and in the same animal at different times; but that may be due to variation in the intensity of the external evidence rather than to variation in the duration of the pro-cestrum itself. In the rabbit I have observed this period lasts, probably, A6 WALTER HEAPE. one to four days; in the bitch seven to twelve days (Stone- henge, 1887); in the chimpanzee six to eight days (Keith, 1899). In cattle and sheep the external evidence of pro- cestrum is difficult to determine, and cestrus appears to follow very quickly upon the former, about one day after or less. Pigs, on the other hand, exhibit external signs of pro-cestrum somewhat longer, while mares are very variable in this respect. A. further consideration of the subject is divided into the external and internal evidence of pro-cestrum. The External Evidence of Pro-cstrum in Mam- mals.—The first sign of pro-cestrum noticed, in the lower mammals, is a swollen and congested vulva, and a general restlessness, excitement, or uneasiness. There are other signs familiar to breeders of various mammals, such as the congested conjunctiva of the rabbit’s eye, and the droop- ing ear of the pig, which are considered by some as even more reliable indications of the probability or capability of conception than is afforded by the vulva alone. Many monkeys (Heape, 1894, 1897, Keith, 1899) exhibit conges- tion of the face and nipples, as wellas of the buttocks, thighs, and neighbouring parts; sometimes they are congested to a very marked extent, and in some species a swelling, occa- sionally prodigious, of the soft tissues round the anal and generative openings, which is also at the time brilliantly congested, indicates the progress of the pro-cestrum. The Pro-cestrous Discharge and Menstrual Flow. —Following the swelling and congestion of the external generative organs, there is, in most animals, a discharge from the generative canal. The discharge may consist merely of mucus from the uterine glands and from the glands of the cervix and from those in the neighbourhood of the vaginal orifice, of the products derived from the breaking down of epithelial tissue, and of fragments or small masses of pave- ment epithelium from the vagina; such a discharge is usually to be seen in the rat and mole. : In addition, fragments. or small masses of columnar uterine epithelium may be observed in various animals. Again, to THE ‘*‘ SEXUAL SEASON’? OF MAMMALS. 47 the above, blood may be added for a large number of animals, some of which rarely, some frequently, and some always suffer from a loss of blood. While, finally, more or less com- pact masses of uterine stroma tissue are included in the discharge of the Primates and some of the lower mammals. Blood has been observed in the discharge during pro-cestrum in the mare, ass, cow, sheep, goat, pig, cat, rabbit (Aristotle ; Ellenberger, 1892; Fleming, 1878; Wiltshire, 1883), and rat (Lataste, 1887) ; it is also recorded as having been observed in marsupials (Wiltshire, 1883); in the bitch it is almost invariably present, and so also it would appear to be in Pachyuromys duprasi, Dipodillus simoni, Meriones shawi (Lataste, 1887), and in Tupaja javanica and Tarsius spectrum (Stratz, 1898). In mostof these animals there is only enough blood to tinge the discharge more or less, but in the bitch, and probably T. javanica and T. spectrum, there is a flow of blood almost as concentrated as that recorded for monkeys (Heape, 1894, 1897). It has been recorded for a large herd of highly bred Alderney or Jersey cattle in the south of England, that a discharge of blood is of regular recurrence among them (Wiltshire, 1883) ; but so far as I can learn this is excep- tional, although its occurrence in individuals is by no means rare. It has been suggested that bleeding in the lower mammals during pro-cestrum is confined to domesticated species, but this is not true (Lataste, 1887; Stratz, 1898; Wiltshire, 1883) ; at the same time it is not improbable that the circumstances attending domestication tend to increase the flow of blood from the uterus, and that highly bred domesticated animals are more liable to experience it than those which are hardier, less carefully attended to, and less luxuriously fed. The pro-cestrous discharge, then, varies in quality in dif- ferent animals, and not only is this true, but it varies at different times in the same animal, both as to quantity and quality. There is ample evidence of this in various human tribes (Holder, 1892, Ellis) and in individuals. Among 48 WALTER HBEAPE., domesticated animals, mares, cows, sheep, and rabbits do not always experience a loss of blood ; further, individual animals of these species sometimes experience a much more profuse flow than at other times, or they may experience a profuse flow only rarely or not at all. | The Internal Phenomena of Pro-wstrum.—It will be convenient first to abstract the account I have given else- where (Heape, 1894) of the changes which take place in the uterus of the monkey during pro-cestrum, and then to com- pare these changes with those which occur at that time in the human female on the one hand, and in the lower animals on the other. A. Period of Rest.—Stage I. The resting stage. This is the period before pro-cestrum occurs, and at that time the uterine mucosa is a shallow bed, opaque, white, and anemic. sp. Period of Growth.—Stage II. The growth of stroma. It is now that pro-cestrum first becomes apparent ; the uterine stroma thickens, hypertrophy takes place, and it becomes semi-transparent, soft, and flabby. Stage III. The increase of vessels. The growth of the stroma tissue is rapidly followed by an increase in the number and size of the vessels of the stroma, the whole becomes richly supplied with blood, and the surface is flushed and highly vascular. This process goes on until the whole of the uterine stroma becomes tense and brilliantly injected with blood. c. Period of Degeneration.—Stage 4. The breaking down of vessels. ‘The walls of the superficial vessels now break down, and the blood contained therein is extravasated throughout the superficial portion of the mucosa. Stage V. The formation of lacune. The extravasated blood becomes gradually collected in lacune, which at first lie within the stroma, but gradually become enlarged and project as rounded hillocks, bounded superficially by the uterine epithelium, into the cavity of the uterus. Stage VI. The rupture of lacunz. The superficial mucosa cells, isolated or in patches, now begin to degenerate ; they THe ‘SEXUAL SEASON’? OF MAMMALS. 49 are cut off, as it were, by the extravasated blood, from the deeper mucosa cells, and they shrivel up and die. Soon the uterine epithelium follows suit and, with the degeneration of its cells, loses its continuity and ruptures, thus allowing the blood hitherto contained to pour into the uterine cavity. Stage VII. The formation of the menstrual clot. With the blood which is poured out from the ruptured lacunz is mixed also degenerated epithelium cells, isolated or in strings ; and as the tissue below is laid bare, the extravasated blood in the deeper parts of the mucosa, together with stroma tissue and the superficial portion of uterine glands, also collects in the uterine cavity, and the whole forms therein a more or less dense clot. Some of the blood and degenerate uterine tissue oozes out through the os uteri to the vagina and thence to the exterior while the process is in progress, but there is fre- quently left behind until a later stage a clot, which in some cases entirely fills the uterine cavity. D. Periodof Recuperation.—Stage VIII. The recupera- tive stage. While the clot is still within the uterus, a new epi- thelium begins to grow over the, now much reduced, uterine stroma. Atthe same time new capillary vessels are formed, the extravasated blood which stillremains in the tissues is collected therein, and brought back into the circulatory system. During this period the clot is expelled, and subsequently the uterus assumes again the appearance first described, and eventually becomes again at rest. It is at or towards the close of this period that cestrus normally occurs. For the human female the histology of pro-cestrum (men- struation) has never been so fully worked out in healthy normal uteri. Many observers have described isolated specimens, and most of them have had recourse to material which has either been obtained some time after death, or from indi- viduals suffering from diseases which may well have produced pathological changes in the uterine tissue. Then, again, the extent of menstruation varies in different peoples and indi- viduals, and in the same individual at different times. The amount of the menstrual flow and the quality of that flow also VoL. 44, PART [.—NEW SERIES. D 50 WALTER HEAPE. varies, to such an extent, indeed, that, while some women lose a large amount of blood at each pro-cestrum, others sometimes and some never lose any at all. It is not surprising, there- fore, to find that while some observers hold that no change takes place in the uterine tissue during pro-cestrum, others state that highly specialised decidual tissue is formed at that time; while some deny that even a portion of the uterine epi- thelium is lost by denudation during pro-cestrum, others maintain that the whole of the mucosa layer is discarded during that process. The question has been somewhat fully discussed by me in a former paper (Heape, 1894), where an account is also given of the more important literature of the subject. Here it is only necessary to add the conclusions arrived at, which are that in all essential points the menstruation or pro-cestrum of the human female is identical with that of monkeys. More recently I have described (Heape, 1898) two menstruating human uteri, the first of which shows congestion and is closely comparable to Stage IV of the monkey, while the second shows denudation, and appears to be practically identical with Stage VII of the monkey. A. slightly earher condition of denudation in the human uterus has been described and figured by Minot (1892), and again supports the view above expressed. Among lemurs, Stratz (1898) has described what he calls bloody ‘ menstruation” for Tarsius spectrum. I gather that, in this animal, denudation of the epithelium of the uterus takes place and that Stage VII exists; but there is no proof that denudation extends to the stroma tissue, and therein possi- bly les the difference between lemurs and monkeys, otherwise there can be little doubt of the homology of the process in these two animals. Stratz has also described the existence of a blood-clot and a “menstrual”! flow in Tupaja javanica, and here again the 1 The use of the term “ menstrual” flow, as it is here used, to denote a flow of blood from the uterus, without regard to the periodicity of that flow, is to be deprecated. > THE ‘* SEXUAL SEASON’? OF MAMMALS. 51 tissue contained in the clot apparently consists only of desquamated epithelium. Retterer (1892) has given a more detailed account of what happens during the pro-cestrum of the bitch. During period A, of rest, Stage I, the mucosa of the uterine horns is firm, pale, and of a thickness of °3 to*°5 mm.; but with the com- mencement of pro-cestrum, period B, there is a well-marked Stage, II, in which the mucosa grows rapidly to three or four times its original thickness, and becomes soft and spongy. Stage III is also well marked, and the mucosa becomes injected with numerous vessels distended with blood. Then period ¢ occurs, and Stage IV is marked by the breaking down of the vessels and extravasation of the blood in the mucosa tissue. Lacune are formed, Stage V, which, during Stage VI, rupture, and pour the contained blood into the uterine cavity. So far the similarity of the progress of the pro-cestrum in the bitch is practically identical with that of monkeys, but there is no blood-clot formed, and Retterer’s account renders it doubtful whether any denudation, even of epithelium, takes place. He himself thinks not. I have myself worked out the history of the pro-cstrum of the bitch to some extent, and have satisfied myself that Retterer’s account is true in all essential details. I have also failed to find any area of the uterine mucosa which has been denuded of epithelium, and do not believe that this process occurs to any extent; at the same time, where lacune rupture there must be loss of epithelium, though I think denudation is confined to these spots. The pigmentation of the uterus, described by Altmann (1878), is further evidence of the probability that much of the extravasated blood is not discharged into the uterine cavity, but is retained in the uterine tissue and absorbed from thence. ‘The homology of this process in the bitch with that-already described for monkeys is absolutely certain, and if nothing more were known, would establish the identity of the pro- D2 WALTER HEAPE. cestrum in these animals; or, in other words, the homology between the pro-cestrum (so-called ‘‘heat”’) of the lower mammals and the menstruation of the Primates. The absence of Stage VII, the menstrual clot, is not to be wondered at in a large bifid uterus ; the denudation of tissue in sufficient quantity to form a clot would be a very severe operation in such a comparatively large organ. The only other paper dealing with this subject, for the bitch, with which I am acquainted (Johnstone, 1888), treats of what the author calls the “ corpuscular development ” of the mucosa of the bitch during the pro-cestrum, but I do not gather the author has satisfactorily demonstrated the truth of the view he advocates (see also Johnstone, 1895). Pouchet’s description of the changes in the uterus of the sow during pro-cestrum shows the existence of Stages II and III (Wiltshire, 1883) ; he does not describe the breaking down of vessels or the formation of lacunze, but his description of the histology of the uterine discharge shows that it contains, besides mucus, both blood and uterine epithehum. Stage IV, therefore, is assuredly represented, and there can be little doubt that Stages V and VI are also passed through, since there must have been rupture of the uterine tissue in order that pieces of it should be contained in the discharge. Hilenberger’s (1892) account of the changes which take place during pro-cestrum in domestic mammals includes Stages II and III; he also does not describe Stages IV, V, and VI, but he records the presence of both blood and epi- thelial cells in the discharge, and these stages must therefore have been passed through, although denudation is in all probability very slight. Fleming (1878) adopts the view that, among ruminants, the blood which finds its way to the exterior exudes from the cotyledons; while Hllenberger describes pigmentation there, and states it is caused by the blood left behind in that tissue after pro-cestrum has occurred. Bonnet (1892) also describes Stages II and III in various domestic mammals during pro-cestrum, but he also adds THE ‘* SEXUAL SEASON’? OF MAMMALS. 53 Stage IV for ruminants, horse and pig, and where external bleeding is seen in these animals the occurrence of the equivalent of Stages V and VI is essential. Kazzander (1890) notes the existence of extravasated blood (Stage IV) in the sheep’s uterus during pro-cestrum, at a period before external bleeding is noted; so that when the latter occurs, a condition equivalent to Stage VI is passed through by this animal. Both this author and Bonnet (1880, 1882), whom he quotes, describe pigmentation in the uterine mucosa of the sheep, and consider it is due to the extrava- sated blood which is not discharged during the pro-cestrum. Lataste (1887) describes desquamation of uterine epithelium in several Muride, and states that it takes place independently of pro-cestrum (or, as he calls it, “ rut”), during which Stages II and III are noted, and at the close of which a bloody dis- charge (which he calls “menstruation”’) is evident. Stages IV, V, and VI are therefore probably also passed through in the case of these animals. I find it dificult to determine exactly what this author means, but I gather it is his opinion that in these animals there is a periodic shedding of uterine and superficial vaginal epithelium, and that this precedes and is independent of the pro-cstrous discharge (p. 163) ; if this be so it is quite dif- ferent from anything which has been already described for any other of the lower mammalia, and is comparable only to that somewhat rare phenomenon, exfoliation of the vagina, in the humanfemale. The same author declares (1898) there is a rhythmical transformation of the epithelium of the vagina in certain of the lower mammalia, which is in connection with rhythmical generative changes; he describes the denudation of this epithelium, and its recuperation from the lower layers. The subject has been very rarely investigated in the lower mammals, and still more rarely has it been attacked from a histological point of view; isolated specimens have been described with more or less detail, but no attempt has been made to work out the history of the process by any one, so far as I know, but Retterer. 04 WALTER HEAPE. For this reason the evidence available is fragmentary, but it is remarkably consistent ; and although further researches may, and probably will, show variations in detail, the broad fact of the homology of the internal process of pro-cestrum in all mammals is sufficiently demonstrated. This we may summarise as follows: the uterus of all mammals during the quiescent period is comparatively aneemic, and its mucosa is a thin layer; it has at that period the appearance of lying fallow. During pro-cestrum hypertrophy of the mucosa first takes place, and is followed by congestion, which results usually in the rupture of the superficial vessels and consequent ex- travasation of the blood into the surrounding tissue ; in some cases this extravasated blood finds its way into the cavity of the uterus and thence to the exterior, with either more or less denudation of the superficial mucosa, while in other cases there is no external hemorrhage, and the extravasated blood is absorbed in situ. While, therefore, neither the discharge of blood nor the extravasation of blood is an essential feature of the pro-cestrum, the hypertrophy and con- gestion of the mucosa is invariably present in all mammals, a condition which we may confidently expect to find also in the lower Vertebrata. The Period of Gstrus. The period of normal cestrus, as I have stated in the intro- duction to this paper, occurs as a result of pro-cestrum. As arule breeders regard cestrus (the period of desire) as an attendant condition of pro-cestrum rather than as a result thereof; where there is no discharge evident there is some excuse for this view, especially as, even when a discharge does occur, cestrus may happen before the discharge com- pletely ceases. Cistrus, however, is possible only after the changes due to pro-cestrum have taken place in the uterus. A wave of disturbance, at first evident in the external generative organs, extends to the uterus, and after the various phases of pro-cestrum have been gone through in that organ, THR ““ SEXUAL SEASON’? OF MAMMALS. 55 and the excitement there is subsiding, it would seem as if the external organs gain renewed stimulus, and it is then that cestrus takes place. If the uterine changes are confined to Stages II and ITI, that is simply hypertrophy and conges- tion of the mucosa, cestrus rapidly follows the first external signs of pro-cestrum ; but if more elaborate disturbance takes place in the uterus, the period of cestrus is delayed. Thus it is during the subsidence of the uterine disturbance that oestrus takes place. The period during which the dis- charge continues is not, however, a true indication of the permanence of the uterine disturbance. In comparatively large uteri, especially in those which extend as long horns from the corpus uteri, the area of denudation or hemorrhage may be situated far from the vagina; and the products of that hemorrhage and of denudation may take a considerable time to find their way to the exterior; this is especially the case where there is little blood and much mucous discharge. We have seen above that in the monkey, Stage VIII, a new epithelium is formed over the surface of the newly denuded uterus before the blood-clot is evacuated; and in the same way, before the discharge from long-horned uteri reaches the exterior, the uterine disturbance is largely allayed, and renewed stimulus may be supplied to the ex- ternal generative organs. In all animals which have been investigated, coition is not allowed by the female until some time after the swelling and congestion of the vulva and surrounding tissue is first demonstrated, and in those animals which suffer from a considerable discharge of blood, the main portion of that discharge, if not the whole of it, will be evacuated before sexual intercourse is allowed. Thus in Pachyaromys duprasi, which experiences hemorrhage, coition is not allowed during the flow (Lataste, 1887). Bitches, except rarely, receive the dog only after bleeding is over (Stonehenge, 1887), although a mucous discharge, which frequently continues after the discharge of blood 56 WALTER HEAPE., ceases, may be still in progress at the time coition is per- mitted by the bitch (Millais). The Moor mace in the Zoological Gardens has a definite cestrus, which always occurs shortly after the menstrual discharge ceases, and which lasts for two or three days; and there is strong reason for believing this is also the case with various other monkeys, as, for instance, the orang-utang (Hillis). The human female frequently experiences cestrus with marked strength after menstruation is over (Martin, 1888), more especially, it would appear, in those individuals who do not suffer from excessive menstruation,—in other words, in those whose generative system is least disturbed by the consequences of civilisation and social life. This special time for cestrus, in the human female, has very frequently been denied, and no doubt civilisation and modern social life do much to check the natural sexual instinct where there is undue strain on the constitution, or to stimulate it at other times, where extreme vigour is the result. For these reasons a definite period of cestrus may readily be interfered with, but the instinct is, | am convinced, still marked. lls quotes various authors who hold a similar view, but they do not all agree as to the time when cestrus occurs; if, therefore, the views which I have advocated here are correct, it would seem probable that abnormal cestrus has been mistaken for true cestrus in many of these cases. Summary and Conclusion. Introduction.—After criticising the terms commonly used to denote the various stages of the “‘ sexual season” of mammals, I have defined the terms used in the present paper. Female mammals are divided into two classes, ‘ monces- trous”’ and “ polycestrous”” mammals, and I have explained that, in the absence of the male, “ pro-cestrum,”’ “ cestrus,” and ‘‘metcestrum”’ are followed by ‘‘ dicestrum” in polycs- trous mammals, during the recurrence of the “ dicestrous THE ** SEXUAL SEASON’? OF MAMMALS. cycles,’ and by “ancstrum” in moncestrous mamma s always, and in polycestrous mammals at the close of the sexual season. The difference between the dicestrous or ancestrous cycles in the absence of the male, and the “maternal generative cycle” when cestrus is followed by insemination, fertilisation of the ovum, and gestation, is drawn attention to. The occurrence of abnormal cestrus is noted. The Breeding Season of Mammals is merely touched upon; inasmuch as it concerns what happens during both the sexual season and the gestation period jointly, its full con- sideration is not possible in this paper. The Sexual Season of Male Mammals.—Males are divided into two classes, those which have a special sexual season, “rut,” and those which are sexually capable all the year round. ‘The influence of captivity is touched upon, and it is shown that, while sexual activity is not so violent in captive animals as in those in the wild state, it may be much more frequently or continuously exhibited. The Sexual Season of Female Mammals.—tThis is considered in wild mammals in a state of nature, in those which are captive, and in domestic mammals ; and the effects of climatic, individual, and maternal influences are drawn attention to. Among moncestrous mammals the effect of these influences may be to increase or decrease the periodicity or the duration of the sexual season, while among polyce '~ *.’ nammals the effect may be to increase or decrease the numoper of dicestrous cycles in each sexual season or the duration of each cycle; the effect in both classes of animals being to increase or decrease their reproductive power. It is pointed out that the knowledge at present available throws no light on the origin of the sexual season; but that it is due to astimulus which appears to be gradually collected, that itis associated with nutrition, and is manifested by excep- tional vigour and bodily ‘ condition ” seems assured. The Periodicity of the Sexual Season in Mones- 58 WALTER HEAPE. trous Mammals in the Absence of the Male.—This is shown to be affected by climatic and by individual influ- ences, to be more frequent in domesticated than in wild animals of the same species, and to be variously affected by captivity. The Duration of the Sexual Season in Polyestrous Mammals in the Absence of the Male.—The sexual season in these animals is affected by the duration and the recurrence of the dicestrous cycle; as in monestrous mam- mals, it is shown to be affected by climatic and individual influences, by domestication and captivity. It is here that we are first brought into contact with monkeys and man, and I have endeavoured to show that the sexual season which undoubtedly exists in monkeys, exists also in certain human peoples in the present day, while there is some evidence that, in the past, all peoples were similarly affected, and that a definite sexual season was the rule. The fact that, in spite of the regular recurrence of the cestrus, monkeys have only a limited season during which conception is possible, is drawn attention to. It is pointed out that this is due to the fact that the ovary is not active all the year round, and evidence is brought to show that the function of ovula- tion is also not necessarily coincident with cestrus in various other mammals. This condition is apparently due to the want of sufficient energy for both cestrus and ovulation. The Duration of the Gistrus in Monestrous and Polycstrous Mammals inthe Absence of the Male. — Knowledge of this point is practically confined to domesti- cated mammals and to certain animals in captivity, and the evidence, which a study of these animals renders available, shows that the duration of cestrus is very variable, not only in different species, but also in different individuals of the same species, and in the same individuals at different times. There is greater variation in this respect among moneestrous than among polycestrous mammals, as a rule. The Effect of Maternal Influences on the Sexual Season and (istrus.—These may or may not completely THE °° SEXUAL SEASON’”’ OF MAMMALS. 59 disorganise the sexual season, and this depends on whether or not they interfere with its recurrence or with that of cestrus. The above is true for both moncestrous and polycestrous mammals, for both gestation and nursing; but whereas gestation interferes with the recurrence of the cestrus, only if it extends over the time which would otherwise be a sexual season, the interference of nursing depends upon the vigour of the mother and her powers of recuperation. The Pro-cestrum.—LHvidence of pro-cestrum is to be seen in all Vertebrata, and is the forerunner of cestrus. It is first noticeable in mammals in the external generative organs, and extends thence to the uterus. The essential manifestations thereof are first hypertrophy, and secondly congestion of the tissues affected, and this is very usually, indeed probably always, followed by a discharge. The discharge always consists partly of mucus from the uterus, and partly of desquamated vaginal epithelium and the products of broken-down epithelial tissue. In some animals always, and in others sometimes, blood is also evacuated, which has its origin from the uterine mucosa, in which case there is always more or less of uterine tissue also contained in the discharge. There is very considerable variation in the extent of both hypertrophy and congestion of the tissue in various mammals, but it is essential to note that these phenomena are to some extent always present, and are frequently combined with the rupture of the congested vessels in the mucosa, and also, more rarely, with a discharge of blood from, and still more rarely a denudation of, the superficial uterine mucosa. The evolution of the pro-cestrum in its most advanced form, that is to say the menstruation of the Primates, from the simplest form, as it appears in such animals as the mole, is traced, and menstruation is shown to be identical with “heat.” The Period of G@strus.—This is possible only after 60 WALTER HEAPE, the active changes due to pro-cestrum have taken place in the uterus ; it is always present, under normal conditions, in the lower mammals at that time, and is much more frequent then in the Primates than is generally supposed. Conclusion. The conclusions I draw from the evidence detailed above are then, very briefly, as follows : A sexual season is common to all female mammals; its recurrence may be interfered with in consequence of climatic, individual, or maternal influences, and it may be modified by the influences attending captivity, domestication, or civilisa- tion. The modification brought about by one or other of these various influences is not necessarily the same in different species of the same genus, nor in different individuals of the same species, nor even in the same individual at all times ; but whatever differences there may be, they are merely modifications of the same plan. The sexual season of all mammals is evidenced by a series of phenomena which constitute, in the absence of the male, one oestrous cycle (moncestrous mammals) or a series of cestrous cycles (polycestrous mammals); animals usually moncestrous may, under certain circumstances, show a tendency to polycestrum ; in the same way animals usually polycestrous may show a tendency to moncestrum. These two conditions are very closely related, and the main difference between them is the method by which the reproductive power is increased. The various constituent parts of an cestrous cycle are in- variably demonstrated in all mammals ; there is in all of them a period during which the generative organs are hypertro- phied and congested (pro-cestrum), followed by a period of desire for coition (cestrus), which, in the absence of the male, gradually dies away (metcestrum), and results in a period of rest (dicestrum or ancestrum). When this period of rest merely separates two recurrent dicestrous cycles it is brief, THE ‘* SEXUAL SEASON’? OF MAMMALS. 61 and I have called it the dicestrum; but where it serves to separate two sexual seasons it persists for a considerable length of time, and I have called it the ancestrum. The pro-cestrum is always associated with hypertrophy and congestion of both external and internal sexual organs and the uterus, and with a discharge from the generative orifice. These phenomena are common to all mammals; they may, however, be further complicated. These complications may include rupture of the congested vessels of the hypertrophied superficial uterine mucosa, and extravasation of the blood contained therein ; they may include a discharge of this blood into the uterine cavity, and from thence to the exterior; and even more or less denudation of the mucosa may take place, leading to the formation of a menstrual clot. The rupture of the vessels of the mucosa and the subse- quent phenomena are not experienced by all mammals; they are supplementary to the essential factors of pro-cestrum, and occur in part rarely in some animals, in part always in some animals, and in a complete sequence only, so far as is known, in Primates. That the pro-cestrum of Primates is identical with the pro- cestrum of other mammals does not, however, admit of any doubt ; there is ample evidence of this in the various inter- mediate conditions of other mammals, by means of which, and bearing in mind the influence of domestication and civilisation on polycestrum, the evolution of the menstruation of monkeys and of the human female from the pro-cestrum of the lower mammals can be surely traced. A further evidence of this is the time of the occurrence of cestrus. It is mani- fested at a certain period after pro-cestrum, and has a certain relation to it—that is, itfollows and is not coincident with pro-cestrum in the lower mammals, as is usually supposed. In some monkeys the same relation of cestrus to pro-cestrum obtains, and in others it is probably so, while in the human female there is evidence of a similar condition, especially, probably, among normally strong individuals who lead a healthy life. | 62 WALTER HEAPE., Thus the human female may exhibit a sexual season, a pro-cestrum, and a period of cestrus, precisely like any other mammal, and the homology of these processes in all mammals is, in my opinion, established. A review of the literature which treats of the relation be- tween ‘‘heat” or “rut,” as it is usually called, and men- struation, resolves itself practically into an enumeration of those who deny there is any ground for comparison, and those who assert they are identical processes. I do not propose to enter into a detailed criticism of the voluminous literature which bears upon the subject, but will content myself with quoting the essence of the most frequent assertions which are made for and against the homology of these processes, and with briefly replying to them. ‘Those who uphold the homology do so because— I, There is congestion of the generative organs during both “ heat” and menstruation. II. There may be a recurrence of ‘‘ heat” as there is a re- currence of menstruation. III. The discharge during “heat” may be of a menstrual character. IV. From a phylogenetic point of view the homology is to be expected. These statements may be disposed of together ; so far as they go they are true enough, but they are not in themselves, separately nor collectively, conclusive evidence. ‘hose who deny the homology do so because— 1. The discharge during “heat” in the lower animals is said to be mucus, while in the human female it is mostly blood. 2. The time of “heat” is said to be the only time the lower animals will permit of coition, while sexual union during menstruation is a very rare occurrence. 3. “Heat” or “rut” is said to occur in both males and females in the lower animals and to depend upon the seasons, whereas in the human species it is said to be not so. 4, After “heat” the female of the lower animals is said THE °* SEXUAL SEASON? OF MAMMALS. 638 to refuse the male, whereas in the human female sexual desire is not confined to the time of menstruation. 5. “ Heat” is necessary to the production of the species in the lower animals, while in woman “desire” is said to be not essential to conception. 6. In the lower animals the ovaries are said to contain ripe ova only during the time of “heat,” whereas ripe ova are said to be found in the human ovary at all times with- out reference to menstruation. 7. There is said to be no proof of the identity of the two conditions. I think these propositions fairly cover the ground over which those who deny the relationship of what they call “heat” to menstruation have hitherto travelled. It will be seen at a glance that the denials originate, in most instances, in misconception of the facts, and that many of the errors are due to the misuse of terms. It will be worth while, however, to answer each of them separately, and the following replies are numbered to corre- spond with the numbers of the above objections. 1. The discharge in many animals during the pro-cestrum contains blood and sometimes uterine tissue ; it is not always solely mucus, and when blood is absent it has been shown that its absence is due to a modification of, and not to any radical difference in, the process. 2. The term “heat” is here wrongly used; it is made to include both the pro-cestrum and the cestrus in the lower mam- mals, and is compared in that extended sense with the term menstruation, which is an error. The time the lower animals will permit of coition is not during pro-cestrum, which is synonymous with menstruation, but during cestrus, which immediately follows the pro-cestrum. I have shown above that there is not wanting evidence that the same may be true for the human female. 3. Although the time for sexual intercourse among human beings is not universally confined to particular seasons, I have shown that in some cases this is so, and that in all 64 WALTER HEAPE. peoples there is a marked disposition to indulge in sexual intercourse at particular times of the year, which are un- doubtedly comparable to the so-called “ breeding seasons ”’ of the lower mammals. Further, in certain domesticated animals and certain wild animals kept in captivity the males do not “rut” only at certain times of the year, but are prepared to propagate at all times (dog) or almost at all times (captive cattle or deer) throughout the year. 4, There is some truth in this objection; but it must not be forgotten that, among the lower mammals, while captivity and domestication reduce the violence of the sexual passion, they increase its frequency; and that in civilised woman, in all probability, it is this variation of the function still further exaggerated which is responsible for the difference (see also 2). 5. Here again the objection is largely due to a mistaken use of the term “heat,” which in this case is used to denote cestrus. Menstruation, that is pro-cestrum,in women is as necessary to the production of the species as pro-cestrum in the lower animals can be; the fact that cestrus is less pronounced in the former is true, but it is not altogether absent, and has already been referred to in the replies to propositions num- bered 2 and 4. 6. This objection has reference to the question of ovulation, which has not been treated of in this paper; with regard to it I would merely say, that ovulation in certain of the lower mammals is not necessarily coincident with cestrus, while in some of them cestrus and ovulation are quite separate functions. Ripe ova are not found at all times in each human female, and the fact that they may be found at times which are not coincident with menstruation, is merely further evidence that these functions are independent also in women. Further, the degree of independence which these two functions assume is apparently variable in the human female. 7. The answer to this objection is contained in the foregoing paper. He °* SEXUAL SHASON’” OF MAMMALS. 65 In spite of the fact that the evidence I have brought forward is fragmentary, and notwithstanding that only the fringe of a vast subject has been touched upon, I venture to hope enough has been said to show that the wide variations in the sexual functions exhibited by various mammals are variations in degree, not variations in kind; and I venture to think that the evidence of the homology, not only of pro- cestrum and menstruation, but of each of the various sexual phenomena dealt with in the various types, is incontrovertible. One word with regard to the future development of the subject. It is the cause of the sexual season which requires determination. Much stress has been laid upon the rhythmical nature of all breeding processes; this has been carried furthest by Lataste (1887 and 1891), and by Beard in a very suggestive paper on eestation (1897). So far as the sexual season is concerned, its rhythm is no explanation of its origin. It may, I suppose, be asserted that all forces are exerted rhythmically, that is a condition ; whereas what is required here is knowledge of the nature of the force itself, and the causes which govern or limit its rhythm. These are questions for the comparative physiologist, in whose hands, as it seems to me, lie so many of the great bio- logical problems of the day. Speaking generally, the rhythm of the sexual season and the power of breeding is seasonal, it is governed by external forces which are exerted in consequence of seasonal change, and by internal forces which are dependent upon individual powers; further there is abundant evidence that nutriment, and the capacity for storing nutriment, and the energy result- ing therefrom are essential factors. I differ from those who, like Beard, consider the ovary the seat of the governing power of the breeding function ; ovula- tion and the cestrus cycle are not necessarily coincident, the stimulus sufficient to induce the one is apparently not suffi- cient in all cases to induce the other, and it would appear that the requisite initiative is independently produced. vol. 44, pakr 1.—NEW SERIES. E 66 WALTER HEAPE. I am tempted to suggest the probability that there 1s present in the blood from time to time what may be called an oestrus toxin, to suggest that its presence 1s due to the external and internal forces mentioned above, and to relegate - to it the power which stimulates the activity of the sexual season, and brings about the actual production of those generative elements which nutrition has enabled the animal to elaborate. It appears to me that research in this direction would be likely to be rewarded; it would not only be of great theo- retical interest, but might well lead to increase of knowledge regarding some of the causes of sterility, and prove of enor- mous practical value. LITERATURE. AtLen.—‘‘ The American Bisons, Living and Extinct,’ ‘Mems. of Museum of Comp. Zool. at Harvard Coll., Cambridge, Mass.,’ 1876. Attmann.—Article in ‘Jahresbericht tber die LFortsch. der Anat. und Physiologie,’ Hoffmann and Schwalbe, vol. vi, 1878. ARIstoTLE.—‘ History of Animals,’ Bohn’s Library, 1883. Brarp.—‘ The Space of Gestation and the Cause of Birth,’ Jena, 1897. BrEver.—‘ Notes on Fields and Cattle,’ 1870. Betit.—‘ A History of British Quadrupeds,’ 2nd edit., 1874. Benecke.—“ Ueber Reifung und Befruchtung der Kies bei den Fledermausen,” ‘Zoologischer Auzeiger,’ vol. 11, 1879. 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Grorrroy Sarnt-HILArIRE and Cuvier.—‘ Hist. natur. des Mammileres.’ GraBHam.—“On the Breeding of Sorex araneus,” ‘ Zoologist, vol. xx, 1896. Guisr.—‘ On the Tribes inhabiting the Mouth of the Wanegela River, New Guinea,” ‘Journ. Anthropological Instit.,’ vol. 1, 1899. Hamitton.—‘ The Wild Cat of Europe,’ 1896. Hartinc.—‘ The Badger,” ‘ Zoologist,’ vol. xii, 1888. Haycrarr.—‘* On some Physiological Results of Temperature Variations,” ‘Trans. Royal Society Kdinburgh,’ vol. xxix, 1880. Hearp.—< The Menstruation of Semnopithecus entellus,” ‘Trans. Royal Society,’ 1894. Heare.—‘‘ The Menstruation and Ovulation of Macacus rhesus,” ‘Trans. Royal Society,’ 1897. 68 WALTER HEAPE. Heargn.—“ The Menstruation of Monkeys and the Human Female,” ‘Trans. Obstetrical Society,’ vol. xl, 1898. Hinck.—Zoologischen Gartens, Berlin, private leiter, 1899. Hiti.—“ Life Statistics of an Indian Province,” ‘Nature,’ July 12th, 1888. Hoiprr.—“ Gynecological Notes among American Indians,” ‘ Amer. Journ. of Obstetrics, 1892. Hurcurnson.—* Marriage Customs in Many Lands,’ 1897. JOHNSTON.—‘ British Central Africa,” 1897. Jounstene.—‘‘ The Endometrium in the Cycle of the Rat,” ‘ British Gyne- cological Journal,’ vol. in, 1888. Jounstonn.— Relation of Menstruation to other Reproductive Functions,” ‘Amer. Journ. of Obstetrics,’ vol. xxxu, 1895. KAzzZANDER.—‘‘ Ueber die Pigmentation der Uterinschleimhaut des Schafes,” ‘ Archiv ftir mikroskop. Anat.,’ vol. xxxvi, 1890. Keiry.—‘‘ The Relationship of the Chimpanzees to the Gorilla,” ‘ Proc. Zool. Soc.,- 1699. KovaLrEvsky.—‘ Modern Customs and Ancient Laws of Russia,’ 1891. KowaLewsky.—‘ Marriage among the Karly Slavs,’ ‘ Folklore,’ vol. i, 1890. Latastr.—‘ Recherches de Zooéthique sur les Mammiféres de l’ordre des Rongeurs,’ Bordeaux, 1887. Lataste.— Des variations de durée de Ja gestation chez les Mammiferes,” ‘Comp. Rend. et Mém. de la Soc. de Biologie,’ Ser. 9, vol. iii, 1891. 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THE ‘* SEXUAL SEASON’’ OF MAMMALS. 69 Mituais, the late Sir Evrrett.—‘ Letters.’ Minot.— Human Embryology,’ 1892. Mivart.— The Cat,’ 1881. Mittpr.—‘ Elements of Physiology,’ translated by W. Baly, London, 1838. Numan.—“ Over de periodische ontlasting van bloed, ete., de menstruatie der vrouw,” ‘ Froriep’s Notizen,’ No. 150, 1838. Owxn.—‘ Old Stone Crosses of the Vale of Clwyd and Neighbouring Parishes,’ 1886. Pioss.— Das Weib,’ 1887. PrevEvatsky.—‘ Mongolia, the Tangut Country, and the Solitudes of Northern Tibet,’ translated by Morgan, London, 1876. RenecEer.— Naturgeschichte d. Saugethiere von Paraguay,’ Basel, 1830. RetrererR.— Sur les modifications de la muqueuse utérine a l’époque du rut,” Société de Biologie, July 15th, 1892. Rinx.—‘ Danish Greenland, its People and Products,’ 1877. Rink.—‘ The Eskimo Tribes,’ 1887. RoosEVELT.—‘ The Wilderness Hunter,’ 1893. Rotu.— Ethnological Studies among the North-west Central Queensland Aborigines,’ 1897. | RovussELET.—‘ India and its Native Princes,’ 1876. SciaTER and ''Homas.—‘ The Book of Antelopes,’ 1900. SomERSET.—‘ The Land of the Muskeg,’ 1895. SOUTHWELL. —“ On the Winter Breeding of the Otter,” ‘ Zoologist,’ 1888. STONEHENGE.—‘ The Horse in the Stable and the Field,’ 1877. SToNEHENGE.—‘ The Dog in Health and Disease,’ 4th edit., 1887. StRaTZ.-—“ Die Geschlechtsreife Siugethiereierstock,” ‘ Haag. Mart. Nijhoff,’ 1898. Surron.—* Menstruation in Monkeys,” ‘ Brit. Gynaecological Journal,’ vol. ii, 1880. Swayne.— Seventeen Trips through Somaliland,’ 1895. TEGETMEIER and SuTHERLAND.—‘ Horses, Asses, Zebras, Mules, and Mule Breeding,’ 1895. Turner.—‘‘ On the Placentation of Seals,” ‘Trans. Royal Society Edinburgh,’ vol. xxvii, 1875. Varieny.—‘ Experimental Evolution,’ 1892. Wavr.— Ingleby Lectures,” ‘ Lancet,’ June, 1886. WesTERMARCK.—‘ The History of Human Marriage,’ 1891. Wittovcury,—‘ Wast Africa and its Big Game,’ 1889. 70 WALTER HEAPE. b Wittsnirre.—“ Lectures on the Comparative Physiology of Menstruation,’ ‘ British Medical Journal,’ 1883. Youatr.— Cattle,” ‘ Library of Useful Knowledge,’ 1834. Youatt.—‘ The Sheep,” ‘ Library of Useful Knowledge,’ 1837. Youatr.—‘ The Pig,’ 1860. DESCRIPTION OF EPHYDATIA BLEMBINGIA. fl A Description of Ephydatia blembingia, with an Account of the Formation and Structure of the Gemmule. By Richard Evans, ™.A., B.Sc. With Plates 1-—4. CONTENTS. PAGE Part I.—TueE Morpnonoey, BTc., of HPHYDATIA BLEMBINGIA. J. Introduction . : : une II. Description Seb plindatia bl Shee : P - te (1) Colour, habits of growth, and external form : moe ee (2) Skeleton : é ; F elo A. Spicules : : : Rene) B. Arrangement of apicailes to fen fibres ‘ = 2246 c. Spongin : : ; mee ile (3) Canal system 3 fen ee Bap ai (4) The structure of the mature Pemil a aie: III. Affinities of Ephydatia blembingia . ‘ ee IV. Summary . : : : : : sar Sil Part IJ.—THe Formation oF THE GEMMULE oF HPHYDATIA BLEMBINGIA. I. Introduction : ; : ‘ : rod II. Historical review . 89 III. Descriptive account of the development of ‘ie patna of phase datia blembingia 4 A es9 (1) Origin, ete., of the reproductive ae of the ermnnle weed (2) Origin, ete., of the cells which form the chitinous layers, ete. 91 (3) Origin, ete., of the scleroblasts and amphidiscs ne (4) Structure, etc., of the “ trophocytes ” ; . 94 (5) General conclusions . : fe 2 es IV. Critical review of previous accounts ; 96 V. Bibliography ; yells: Description of Plates. ‘ ; 105 72, RICHARD EVANS, Part I.—The Morphology, etc., of Ephydatia blembingia. I. IntTrRopvucttion. Ephydatia blembingia is a fresh-water sponge which Mr. Annandale came across in a small pool of water while in search of snails. It was collected and preserved by me on the 23rd of July last year. The specific name blembingia has been applied to it on account of its locality. Blembing is a small Malay village which was visited by the members of an expedition sent out by Cambridge University to the Siamese Malay States, and which is situated on a small river of the same name. The river Blembing 1s a tributary of the Pergau, which in its turn empties itself into the Kelantan River. The pool of water in which the sponge, now described for the first time, was found, was situated in a comparatively dense jungle at a distance of a few yards from the bank of the river. The trees growing around it were so big, and their foliage so thick, as to admit of only a small amount of light ever passing through them. Consequently the pool of water in which Ephydatia blembingia was found was always in a deep shade. The material which I collected was preserved in the following reagents : (1) Flemming’s solution (weak fluid). (2) Saturated solution of corrosive sublimate (92 volumes) and glacial acetic acid (8 volumes). (3) Absolute alcohol. (4) Rectified 70 per cent. spirits. II. Drescriretion oF EPHYDATIA BLEMBINGIA. (1) Colour, Habits of Growth,and External Form.— Ephydatia blembingia is almost colourless, or to use a term which was used many years ago by Professor Lankester (11) to describe the colour of Spongilla from the Thames, it is “pale flesh-coloured.” Knowing as we do that Spongilla DESCRIPTION OF EPHYDATIA BLEMBINGIA. 73 lacustris and Ephydatia fluviatilis, denizens of our own rivers, are green in colour only when they grow in bright sunlight, this is what we would have expected in the case of a sponge which grew in a pool of water scarcely ever brightened by direct sunlight. The habits of growth of Ephydatia blembingia are peculiar. In reality it is an encrusting sponge, though some specimens have a massive appearance. But this is due to the habit of growing on such supports as blades of grass and branching weeds of various kinds which inhabit the same pool of water as the sponge. It never seems to produce independent branches, which, when present, give a sponge a kind of bush-hke appearance, as Spongilla lacustris does. If, at first, a specimen appears to branch, on closer examina- tion the apparent branching reveals itself as the result of creeping over a branched support. Consequently, in spite of its massive appearance, Ephydatia blembingia is an encrusting sponge. The biggest specimens measure no more than about an inch across (PI. I, fig. 1). The surface texture of the preserved sponge is somewhat woolly, an appearance caused by the spicule fibres which sup- port the otherwise smooth dermal membrane. The fibres often penetrate the membrane, owing undoubtedly to its being rubbed off their extreme points. To sum up, Ephydatia blembingia may be described as a pale flesh-coloured sponge, with encrusting habits, creeping over branched vegetable supports, and consequently irregular in shape and woolly in texture. The oscula, not to speak of the dermal ostia, are so small as to be invisible without the aid of the microscope. The openings represented in fig. 1 are those of the inhalant canals seen through the dermal membrane. (2) Skeleton.—The skeleton consists almost entirely of spicules, which I shall now proceed to describe. | A. Spicules.—In order to facilitate the description of this most important element of the skeleton, I shall arrange the spicules under three heads, 74 RICHARD EVANS. (a) The first group of spicules consist of diactinal monaxons or amphioxea, which are usually curved, though straight specimens are occasionally seen (PI. 1, fig. 3, a—e). (b) The second group also consists of curved amphioxea, but for reasons which will be stated further on they are sepa- rated from the first group (PI. 1, fig. 3, f). (c) The third group consists of amphidiscs, which may be present in a fully developed or in an immature form (PI. 1, figs. 3, g—m, 4, a—c). (a) The amphioxea belonging to the first group taper eradually to a sharp point. They are never provided with a swelling at the middle point of the shaft, and scarcely ever are they malformed or modified inany way. In both respects, therefore, they differ most strikingly from the spicules of Spongilla moorei, a description of which was published in this journal a year and a half ago. They appear to be in- variably covered with small spines. (b) The amphioxea belonging to the second group are invariably curved and covered with small spines. In fact, they present the same characters as the spicules of the first group, but differ from them in being only half as long and less than half as thick. They are not found in the general tissues of the sponge or in its membranes, but are erouped together round small bodies’ which are embedded in 1 The bodies above mentioned seem to possess a definite outline, and to lie in cavities of their own, much in the same way as the gemmules (PI. 4, fig. 17). Ihave no conception what these bodies are, but several solutions have suggested themselves. Unfortunately I have been unable to find them in thin sections, and consequently cannot speak of their internal structure. The first suggestion, with regard to their nature, to present itself was that they were a second kind of gemmule. The arrangement of the spicules round them reminds us of that of the spicules round the gemmules of Spongilla lacustris, and is, so far, in favour of the supposition that these bodies are some kind of gemmules. But apart from the fact that Ephydatia blem- bingia possesses another kind of gemmule, these structures are much more transparent than ordinary gemmules are at any stage in their development or when they are mature. If they were gemmules their basket-like shape could be easily explained as the result of contraction under the action of preserving reagents, owing to the cuticular coat being extremely thin. Apart from the DESCRIPTION OF EPHYDATIA BLEMBINGIA. 70 the deeper tissues, and which present a kind of basket- shaped form. (c) The last class of spicules to be considered consists of the amphidiscs (Pl. 1, fig. 4, b). The diameter of the hat- shaped disc is about three times that of the shaft. The two discs are exactly similar in size and shape. ‘The surface situated away from the shaft is smooth and convex, while the other surface is concave. Their margins are very finely serrated. The shaft is covered with spines which are conical in shape and placed at right angles to the axis of the amphi- discs. In addition to the fully mature forms, all the stages of development are represented, from the simple rod slightly fact that, if the supposition here made were true, it would cut at the very root of the system of division into sub-families, now adopted, of the so-called Spongillidz, the reasons given above seem to be sufficiently weighty to compel us to lay aside this possible view of the nature of these enigmatical bodies. The second supposition that suggests itself as a solution of the problem is that these structures are a kind of symbiotic or parasitic sponge. ‘This supposition is not so unreasonable as it would at first appear, for we already know that Spongilla bohmii is parasitic on Spongilla nitens (17). Be- sides, it must be remembered that all the spicules in connection with these bodies are quite different from those which form the sponge skeleton, being, as has been stated already, only half as long and less than half as thick. It is no argument to say that they are incompletely developed, for they are all of equal size, which would not be the case if they were merely young spicules. However, if these bodies are of the nature of a parasitic sponge, there are, at present, no data by which its position among the Spongillide can be determined. There is still left another possible solution of the problem, namely, that the bodies here discussed are the result of parasitism on the part of some animal other than a parasitic sponge. If this supposition were true, these bodies would have to be considered as a kind of gall, by means of which the sponge endeavoured to protect itself from the action of an unwelcome intruder. But there are two facts which go against this view. In the first place, though I have examined several of these bodies, I have so far failed to find any animal inside them. In the second place, though there are many parasites in the sponge, not one of them has as yet been found to possess such a coat as these bodies would provide. Though it must be left an open question what the nature of these bodies are, for the reasons given above I am inclined to adopt the view that they are parasitic sponges, 76 RICHARD EVANS. swollen at both ends to the fully-formed amphidiscs. Their development, however, will be considered along with that of the gemmule. B. The Arrangement of the Spicules to form Fibres, etc. (Pl. 1, fig. 2).—The spicule fibres are poorly developed, and consequently stand in a most marked contrast with those of some other fresh-water sponges. I have never seen more than three spicules situated side by side in a spicule fibre, and scarcely ever saw more than two. As often as not, the spicules seem to be arranged end on in a single file. In the deeper parts of the sponge, fibres are almost non-existent, the spicules lying about freely and presenting no particular arrangement. Nearer the surface, however, the fibres are better developed, and traverse the strands of tissue which separate the various compartments of the sub-dermal cavity from one another. On the outer ends of the fibres is situated the dermal membrane, which is often pierced owing merely to the wear and tear of the life which the sponge lives. Owing to the absence of flesh spicules or microscleres, the skeletal fibres formed of megascleres present an evident tendency to run in the vicinity of the membranes which line the canals and cavities of the sponge. As has been stated above, spicules of the class b take no part in the formation of the skeleton, but this is not true of those belonging to class ¢, i.e. the amphidises. The latter are found in all stages of development scattered about in the oeneral tissues of the sponge, while the former are limited to the walls of the enigmatic bodies described above. Special stress must be put on the fact that the developing stages of the amphidiscs have been seen in the sponge tissues, and not in the gemiule wall. c. Spongin.—lIt is scarcely necessary to mention spongin in connection with Kphydatia blembingia, for it is almost completely absent. In this respect the sponge here described strongly contrasts with some fresh-water sponges. In Spongilla moorei the spicule fibres and the dermal mem- brane are covered with this substance (7), but in Ephy- DESCRIPTION OF EPHYDATIA BLEMBINGITA, LG datia blembingia there is no spongin on the surface, and the spicule fibres are, at most, provided with a very small amount at the junction of the spicules. This difference is explained by the dissumilarity im the con- ditions of life. On the one hand, Ephydatia blembingia lives in a small pool of water which probably dries up for the ereater part of the year; while Spongilla moorei, on the other hand, lives at the bottom of Lake Tanganyika. There- fore, the former may be described as an annual, while the latter—so to speak—is a perennial spongilla. If this differ- ence in the conditions of life under which these two sponges live were to have any effect at all, we would naturally expect the spongin part of the skeleton to suffer most. (3) The Canal System.—Owing to the presence of gem- mules in all stages of development, the canal system could hardly be in such a condition as to be capable of minute description, for the formation of gemmules is accompanied by the breaking down of the sponge tissue. Besides, we know of no preserving fluid that does not admit of a considerable amount of disassociation of the tissue cells of the Monaxo- nida. Though they be preserved with the greatest care, and with the best reagents known, free cells are found in great abundance in the interior of the sponge tissues. The presence of so many amoeboid cells is conducive to this state of things. Consequently our remarks on the canal system must be meagre at best. As has been stated above, the dermal ostia are micro- scopically small but comparatively numerous. ‘They open as usual into the subdermal cavities, which are large and ex- tensive (fig. 2), and which are lined by cells which possess granular nuclei. These in their turn open into the inhalant canals, which are also well developed, but decrease in size towards the surface of fixation of the sponge. The flagellated chambers are small and numerous, lying about in the extremely loose tissues of the sponge. The exhalant canals, though at first of fine calibre, assume comparatively huge proportions. The oscula, however, by which they open to the exterior are 78 RICHARD EVANS. small. The membranes which line the canals are not pro- vided with special spicules, but are supported by the spicule fibres, which are situated close to the lining membranes. 4. The Structure of the Gemmule.—The gemmules are scattered about singly throughout the whole tissue of the sponge. They are found, on the one hand, near the surface, and on the other hand, quite close to the vegetable supports of the sponge. They are never found in groups. Hach gem- mule occupies its own cavity (Pl. 1, fig. 2, gem.). I shall here describe only the structure of the mature gem- mule, the development of which will be described in Part II. Nevertheless, it must be remembered that the sponge con- tained gemmules in all stages of development at the time it was collected. The gemmule is oval in shape, being, as a rule, slightly flattened on the side on which the opening is situated. The external opening or pore is placed at the bottom of a small depression surrounded by a rosette-like structure, which is raised up, and into the composition of which all the layers of the gemmule coat enter (Pl. 1, fig. 7). The contents of the gemmule consist of a number a glo- bular cells which are full of oval-shaped food granules. The cells are all alike, and the whole mass possesses no membrane of any kind save the gemmule coat, which I shall now proceed to describe. The gemmule coat consists of three layers which differ from one another, to a considerable degree, both in structure and extent of development. The inner layer of the gemmule coat completely surrounds the cells which are situated in the interior. It presents the general shape of the gemmule and is prolonged round the aperture to form a kind of a tube, the passage through which is interrupted by a chitinous membrane situated about the middle. The cellular contents of the gemmule extend into the inner half, and the second layer of the gemmule coat to the outer half of thistube. Instructure this layer is chitinous, and resists the action of all ordinary reagents, save the mineral DESCRIPTION OF EPHYDATIA BLEMBINGIA. 79 acids. It often happens, that, in sections, it splits im two, a result brought about by the weakening produced through the inner ends of the amphidiscs being embedded in it, and not lying upon it as is usually described in the gemmules of EKphydatia. The line along which the splitting takes place is that in which the discs are situated (Pl. 4, fig. 17, a). The middle layer of the gemmule coat is by far the thickest and approximately extends over the whole length of the shafts of the amphidiscs. It is clear in structure, and presents in section the appearance of ordinary parenchyma with very small granules at the nodes. In the fully developed gemmule there are no lines of division indicative of the different cells out of which it was originally formed (Pl. 4, fig. 17, a). The outer layer of the gemmule coat is thinner than either of the other two, and in it are embedded the outer ends of the amphidiscs. It consists of the same substance as the inner layer but is much more granular. In the mature gem- mule it 1s often rubbed off, and consequently the outer discs of the spicules protrude from the gemmule coat (PI. 4, fig. eZ 0) The amphidiscs he partly in the three layers. The inner disc hes in the corresponding layer, the shaft in the middle layer, and the outer disc in the thin outer layer. They are so closely packed that the discs overlap one another and consequently are not on the same level. Their shafts never seem to cross one another, but le approximately parallel. Ill. Tar Arrinitiges oF HPHYDATIA BLEMBINGIA. The presence of gemmules in the material at my disposal made the task of determining the systematic position of the fresh-water sponge here described a comparatively easy one. The possession of gemmules excludes it from the sub-family Lubomirskine, which is a sub-family created for the pur- pose of grouping together a number of fresh-water sponges in which the gemmule, if 1t does exist, has not yet been discovered. Further, the existence of the thick coat which surrounds the gemmule cells and which contains, embedded 8O RICHARD EVANS. in it, a thickly-set layer of amphidiscs separates it, on the one hand, from the sub-family Spongilline, and on the other hand places it among the Meyenine. Again, its generic position is not difficult to determine. The equality of size of the amphidisc rotules separates it from both Tubella and Parmula, the serrated edge of the rotules from Trochospongilla, the equality in length of all the amphi- discs from Heteromeyenza, and the absence of any kind of filament or appendage, attached to the chitinous tube, from Carterius. Consequently the sponge, which is described in this paper, belongs to the genus Ephydatia. Of the species contained in this genus, the sponge to which the name Hphy- datia blembingia has been given seems to approach Ephydatia plumosa (Carter, 2) more closely than it does any other well-marked species. Several species of the genus Ephydatia are provided with amphioxea, which are covered with small spines, and are the constituent elements of the skeletal fibres. In Ephydatia fluviatilis (17) both smooth and spined spicules occur together. It follows, therefore, that the presence or absence of small spines on the skeletal spicules is not distinctive as a specific character. Potts (17) seems to consider this difference so unimportant that he describes an American sponge, to which he has given the name palmeri, as a mere variety of the Indian sponge plumosa; though the skeletal spicules in the former are covered with small spines, while in the latter they are smooth. The skeletal spicules of Hphydatia blembingia agree with those of palmeri, and not with those of plumosa. The amphidiscs seem to be closely sumlar in plumosa, palmeri, and blembingia, though the rotules appear to be more deeply notched in the two sponges mentioned first than they are in blembingia. If these were all the differences that could be enumerated the sponge now discussed would have to be considered a slight variety of the species plumosa, if, indeed, not actually identical with the variety palmerti. However, there still remains to be mentioned another most important difference, namely, the absence from blembingia DESCRIPTION OF EPHYDATIA BLEMBINGTA. 8] of the flesh spicules so characteristic of both plumosa and palmeri. Though this 1s a negative character, combined with the other differences it seems to be a sufficient reason for the formation of a new species, to which I have given the name blembingia. IV. Summary. Ephydatia blembingia is an encrusting sponge which orows on vegetable supports. It is pale flesh in colour, and loose in texture. The skeletal spicules are covered with small spines. Flesh spicules are absent unless the small amphioxea (b) be considered to belong to such a category. The spicule fibres are poorly developed, and in the deeper parts of the sponge the spicules, as a rule, he about irregularly arranged in the tissues. Spongin is present only in very small quan- tities. The gemmules are numerous, but not aggregated in eroups. They are situated—each one occupying a cavity of its own—near the surface as well as deeper down in the tissues of the sponge. They are oval in shape, and possess an opening resembling that of a bottle, which is obstructed by a chitinous septum. They are provided with a thick and well-developed coat, in which amphidises of equal lengths are arranged in a single layer. The shaft of the amphidiscs is furnished with conical spines, large in size and situated at right angles to the longitudinal axis. The outer surface of the discs is convex, and the margin is slightly serrated. Amphi- discs, in all stages of development, are scattered about in the sponge tissue where they are formed. Part II.—The Formation of the Gemmule of Ephydatia blembingia. I. Invrropvucttion. When I took the description of Hphydatia blembingia in hand I had no intention of describing the development of von. 44, PART 1.—NEW SERIES, P 82 RICHARD EVANS. the gemmule ; but when I saw that the material at my disposal contained gemmules in all stages of development I thought it would be a mistake not to describe it. Further, I was en- couraged to do so by Professor Weldon, to whom I am greatly indebted both for the free use of his laboratory and all its resources, and for much invaluable assistance, especially in connection with the literature on the subject. I shall first give a summary of what is already known of the gemmule. I shall then proceed to describe my own observations, the method followed being that of tracing the origin and subse- quent changes of the various cells which take part in the process, this method being considered simpler and more intel- ligible than that of giving a complete description of the differ- ent stages of development. The reader can easily make out for himself, by examining the figures 8,9, ... . 17, the true relation of the changes in the different parts of the developing eemmule much better than by reading the best possible description. Finally, I shall review previous accounts and compare my own conclusions with them. IJ. Historica, Review. Carter (2), who was the first to attempt an explanation of the origin of the gemmule, which he terms the seed-like body, writes as follows :—“ At the earliest period of development in which I have recognised the seed-like body it has been com- posed of a number of cells, united together in a globular or ovoid mass (according to the species) by an intercellular substance. In this stage, apparently without any capsule, and about half the size of the full-developed seed-like body, it seems to lie in a cavity formed by a condensation of the common structure of the sponge immediately surrounding it. It passes from the state just mentioned into a more circum- scribed form, then becomes surrounded by a soft, white, compressible capsule ; and finally thickens, turns yellow, and develops upon its exterior a firm crust of siliceous spicules.” He says with regard to the origin of the gemmule, “I do not DESCRIPTION OF EPHYDATIA BLEMBINGIA. 5) wish it to be inferred that I am of opinion that the seed-like body is but an ageregate of separate sponge-cells;” and further, after describing certain cells of the sponge, he says: “It may, perhaps, be one of these cell-bearing cells which becomes the seed-like body.” Iieberkiihn (12), in the year 1856, published an account of the origin and structure of the gemmule. He found in the deeper parts of the sponge shiny white gemmules, which on the whole appeared like ordinary brown gemmules, and which possessed exceedingly plain amphidiscs. He also found other gemmules, distinguished by their very delicate trans- parent shells, also possessing very obvious amphidiscs. These, he said, had a superficial layer of a substance feebly refrac- tile, and a central mass brilliantly refractile. The feebly refrac- tile cells separated easily, while the others only did so with difficulty. In these bodies he was not able to find the delicate transparent encrusting layer, which he had seen round the white gemmule; but found a layer of cell-like spherules which resembled the ordinary sponge-cells in the arrangement of their granules and of their nucleolus; while others contained the amphidises. Some of the enclosed amphidiscs had exactly the shape of those found surrounding the ordinary gemmule. Others, he said, did not possess the two discs, but in the interior of each cell-like structure there was a delicate rod with a shght knob-like swelling at each end. In others a series of very fine spicules radiate from the terminal swelling. He derived the amphidiscs by imagining these spicules to become broader, and the axial rod to become thicker. The contours of the cells containing the spicules were described as being as sharp as those of ordinary sponge-cells. He could find no nuclei in these cells. He finally concluded that these bodies were incompletely developed gemmules. He also found certain bodies which he described as white aggregations of sponge-cells, possessed of the same size and shape as ordinary gemmules. In the same year he published a second paper, in which he summed up as follows (18) :—‘ That the gemmules are derived from a heap of ordinary sponge-cells 84, RICHARD EVANS. we can very plainly see in that branched sponge which has gvemmules with smooth shells. In a longitudinal section of a suitable piece we find—(1) Gemmules which are completely developed, and possess a smooth shell containing a large number of the rounded masses accurately described by Meyen. Rach of these masses is spherical, and contains in its interior an albuminous fluid and many strongly refractive spherules. It is about as large as a sponge-cell, and quickly disintegrates in water. (2) Gemmules with an obvious shell, which con- tains Meyen’s spherical masses and also contains bodies which have Meyen’s masses, but are distinguished from these by sending pseudopodia like the ordinary sponge-cells. (3) Gemmules in which the shell and the pore are obvious, con- taining only cellular bodies which send out pseudopodia. Some of these contain a nucleus and a nucleolus like sponge- cells, and are distinguished from these only by the fact that they contain in their interior the refracting spherules already alluded to. (4) Spherical heaps corresponding in size to the gemmules which consist of the above-mentioned bodies, sending out pseudopodia, and of undoubted sponge-cells. The sponge-cells have an obvious nucleus and nucleolus, and they contain besides a mass of very fine granules, which may be scattered through the whole cell-body or may be collected in smal] spherical masses. These spherical masses are of the same size as the refracting spherules already described, and one or two such spherules are often found in the sponge-cells. Round some of these spherical heaps of cells a very fine structureless membrane can be recognised. The spherical masses of Meyen which are commonly found in gemmules are nothing else than altered sponge-cells ; by compressing the contents of the gemmule under the cover-slp we can find a nucleus and a neucleolus in every such mass; but nucleus and nucleolus are so hidden by the strongly refractile contents of the Meyen’s masses that they can only be demonstrated by a process of pressure. These nuclei and nucleoli do not espe- cially differ from those of ordinary sponge-cells.” Lieberkiihn again, in a third paper (14), speaks as follows DESCRIPTION OF EPHYDA'TIA BLEMBINGIA. 85 of the gemmule :—“ The gemmules are not eggs, but a sort of cyst or capsule, out of which the same individual which built them ultimately creeps through the pore.” In a later publication (8) Carter describes the seed-like bodies as being globular in shape, and consisting of a cori- aceous membrane enclosing a number of delicate, transparent, spherical cells, more or less filled with ovules and granular matter, while an incrustation of gelatinous matter charged with small spicules peculiar to the species surrounds the ex- terior of the coriaceous membrane. “It has also been shown,” he adds, “that at an early period of development the spherical masses, which we shall henceforth call ovi-bearing cells, are polymorphic—identical, but for the ovules, with the ordinary sponge-cells—and surrounded by a layer of peculiar cells equally polymorphic, which I have conjectured to be the chief agents engaged in constructing the capsule.” Again, in a later publication (4), he speaks of the “ova”— preferring the term “ovum” to “seed-like body”—of Spon- gilla as follows:—“ At an early period of the ovum the spherical cells, though already filled with the refractive granules, are few in number and sub-polymorphic; hence it may be reasonably inferred that their multiplication as the ovum increases in size 1s produced by fission; the younger the ovum the more polymorphic and resistent are these cells, while the older it becomes the more they are attenuated, and the more rapidly they burst by endosmose after liberation.” In the year 1874 he further writes of the gemmules as follows (5) :—“It may be a question whether the entire body may not be the ovarium of a Spongozoon in the first place; while, as in hundreds of instances of the same kind in the animal kingdom, all the other parts have perished, their function having ended when sufficient nutriment had been gathered and assimilated to support the reproductive elements until they could do this for themselves.” Further on he adds, “Tt is an assemblage of ova which are at once developed to- gether into a young Spongilla.” Tn his final communication (6) on the gemmule, he views it 86 RICHARD EVANS. “as a simple ovum with modified form to meet the require- ments of the case.” It seems Carter was always uncertain as to the origin of the gemmule, and at one time or another he appears to have had four views. First, that the gemmule was a mere aggre- gation of sponge-cells; secondly, that it was an aggregation of cells produced from one cell, the “ovi-bearing” cell ; thirdly, that it was a single ovum, which was his final view ; and fourthly, that it was a single “ovarium” of a dead “ spongozoon.” In the year 1884 Marshall published an account of the de- velopment of the gemmule of Spongilla-lacustris (15). He says that the first sign of the gemmule consists of a number of amceboid cells, which are found in the neighbour- hood of the inhalant canals and the ciliated chambers, and which he terms the “trophophores.” ‘They fill themselves with reserve material, and wander together in groups. They become round and give up water, so that they look like masses of reserved food material. Very early round the pseudomorula formed in this way there appears a delicate structureless membrane, a cuticle, the matrix of which should be probably looked for on the surface of the pseudomorula itself. The “mesoderm” outside this cuticle builds at first an endothelium which deposits on the cuticle further layers of horny substance and delicate siliceous structures, in this case spiny tangential needles. In the year 1886 appeared Goette’s account of the develop- ment of the gemmule of Spongilla fluviatilis (10). He says that the first rudiment of the gemmule is formed by an ageregation of ordinary parenchyma cells in a nearly spheri- cal area of 36—44 4 in diameter; really, the flagellated chambers and canals of this region become enclosed in the ageregation, which is produced through hypertrophy of the cells. In this aggregation of cells the formation of two layers quickly takes place; a central mass of cells, con- taining a great number of yolk-granules, and an outer shect of cells, which become club-shaped and form a kind of DESCRIPTION OF EPHYDATIA BLEMBINGIA. - 87 columnar epithelium round the central mass. This sheet secretes a cuticle round the central mass, and its cells form the amphidiscs. Subsequently the club-shaped cells migrate outwards, and secrete a second cuticle outside the amphi- discs. | | In the same year as Goette, and independently of him, Wierzejski described the development of the gemmule (19). He describes the first rudiment of the gemmule as a group of naked amoeboid cells. He says that the cells of the mother- sponge can migrate to the body of the gemmule and thus increase its volume. The heap of cells brought together through migration from the sponge tissue become differen- tiated into a central mass and a peripheral layer. Shining spherules and granules are deposited in the cells of the central mass, those of the peripheral layer becoming co- lumnar. The amphidiscs are not developed in the peripheral cells, but in the surrounding tissues, and only subsequently migrate to the columnar layer. In the year 1892 Zykoff published an account of the de velopment of the gemmule (21). This account adds little, if anything, to what was known before of the formation of the gemmule. He found, among the ordinary ameceboid cells of the parenchyma, cells which contained a number of refractive granules of a very definite form, which he describes as boat- shaped. He considers the appearance of refractive yolk- substance in a few amoeboid cells of the mesenchyme as the first step in the development of the gemmule. ‘These amceboid cells have the protoplasmic structure of Fiedler’s amoeboid “ Mresszellen,” but the nuclear structure of his “ Nahrzellen.” He disagrees with Goette and supports Wierzejski on the question of the origin of the first rudiment of the gemmule. He denies Goette’s statement that the flagellated chambers and the epithelial lining of the canals participate in the formation of the gemmule. The rudiment of the gemmule soon becomes differentiated to a central mass of yolk-cells, among which amceboid cells of the mesenchyme occur, and a peripheral stage which consists of one or two concentric layers 88 RICHARD EVANS, of mesenchyme cells of the sponge. The peripheral cells be- come club-shaped and not columnar. This change takes place gradually, not all at once. The club-shaped cells secrete the inner cuticle, and the amphidiscs migrate from the sponge and take up their position among the club-shaped cells, which subsequently migrate outwards, secrete the outer cuticle, and, finally losmg their club-shaped form, gradually become re- sorbed. In the year 1893 Weltner published a short paper (18), in which he brings together the different views expressed as to several important points in connection with the structure and development of the gemmule, and from his own observations draws his own conclusions. Having discussed the use of the protective coat; the presence of a thin membrane, which he does not believe to exist, round the reproductive portion of the gemmule; the number of nuclei in each cell, of which he has seen more than one in several cases, he finally deals with the question of the origin of the cells of the gemmule, in the first rudiment of which he finds three kinds of cells, namely cells which have yolk-bodies alone, cells which display fine granules of equal size and a distinct nucleolus, and cells which have large granules of unequal size. The third class of cells are different from the cells with granules of unequal size found in the parenchyme. He comes to the conclusion that the development of the eeimmule is not yet sufficiently known, and that a fresh inquiry should be instituted as to two main points: first, the origin and nature of the cells which form the first rudi- ment of the gemmule; secondly, to ascertain the fate of these cells. He suggests that their origin and nature should be exa- mined with a view to the following possibilities : Is the first rudiment of the gemmule formed from a single cell which has the value of an egg? Then the gemmule should be a group of segmenting cells. Or, does the inner mass of the gemmule arise from one class of cells derived from the previous mesoderm DESCRIPTION OF EPHYDATIA BLEMBINGIA. 89 Or does it arise from more than one class of mesoderm cells ? Or, finally, is it built from different germ layers (two or three) ? The gemmule should then be considered a bud. In Section III of the second part of this paper I shall give an account of the development of the gemmule in Ephy- datia blembingia, reserving criticism of whatever kind to Section IV. In Section III I shall include nothing but a simple description, followed by a few conclusions. This course will be pursued in order to make the account more available and more intelligible to the reader than it would be if it were mixed up with critical remarks and conclusions scattered about throughout the paper. Ill. Descriptive Account oF THE DEVELOPMENT OF THE GEMMULE OF HPHYDATIA BLEMBINGIA. (1) Origin and Further Development of the Repro- ductive Part of the Gemmule.—the first sign of prepara- tion for the formation of the gemmule consists in the presence of single cells or small groups of cells scattered about chiefly in the dermal membrane ; the strands of tissues which support the dermal membrane ; and in the tissues situated immediately below the subdermal cavity. The protoplasm of the cells in question is uniformly clear, and the nucleus 1s granular and not vesicular (Pl. 2, fig. 8). I have been unable to detect a karyokinetic figure in any of these cells. Consequently I am of opinion that the constituent cells of these groups seldom divide during the early stages of formation of the gemmule, which is contrary to what must have been the case if the cells of the repro- ductive part of the gemmule were derived from one mother- cell, The cells in virtue of their power of wandering travel through the dermal membrane, and strands of tissue which support the membrane, and become aggregated in groups situated either deep in the tissues of the sponge or even in the strands of tissue above mentioned (PI. 2, fig. 8). 90 RICHARD EVANS. The protoplasm soon loses its uniformly clear appearance and becomes unevenly granular (PI. 2, fig. 9), a feature which rapidly becomes more accentuated (PI. 2, fig. 10). The con- tained granules or irregular blotches at this stage he in round, clear spaces in the protoplasm, but they soon increase in size to such an extent as to fill the spaces above mentioned. At the same time they acquire an oval or spherical form and exhibit a certain amount of internal structure, in the form of unevenly distributed granules of very small size (PI. 2, fig. 11a). The subsequent change in the interior of the spherical granules or yolk bodies, as they may be termed henceforth, consists in the differentiation of a peripheral layer or coat which sometimes, though not always, contains fine granules, from a centre which invariably seems to possess a finely granular structure (Pl. 3, fig. 13d). The yolk bodies have at this stage attained their ultimate structure, and fill the cell in which they have been formed. While these changes are going on a curious change takes place in the character of the nucleus. At first granular, it now becomes vesicular, or perhaps more correctly it presents an appearance intermediate between the typical vesicular nucleus with a solid nucleolus and a granular nucleus (Pl. 3, fig. 13d, nu.). The cells seem never to possess more than one nucleus. The yolk cells, as they may be termed henceforth, have increased slightly in size during the changes above described. However, they retain their individuality, though owing to the pressure which they exert on one another they are often polygonal in shape. In the fully developed gemmule they are so pressed against one another that their individual outline can be seen only with difficulty, which is in no way a remark- able thing seeing that at no stage do they possess a definite cell wall though having a well-defined cell limit. The yolk cells collectively, or the reproductive part of the vemmule, as they may be termed, at no stage possess a membrane, though in the fully mature gemmule they are so pressed against the inner chitinous layer of the protective DESCRIPTION OF EPHYDATIA BLEMBINGIA. 91 coat as to present a perfectly smooth and membrane-like appearance. (2) The Origin and Subsequent Changes of the Cells which produce the Ground Substance of the Protective Coat of the Gemmule.—These cells, after having wandered from the general sponge tissues, appear in the neighbourhood of the gemmule as a loosely arranged layer situated outside the future yolk cells. Fig. lla (PI. 2) shows how they travel towards the developing gemmule and how they become concentrated to form a layer. Their general protoplasm is clear, but they contain a number of granules or yolk bodies which resemble those of the yolk cells. In addition, they often contain a much bigger spherical body which seems to be of the same nature as what I have described in my account of the structure of the larva of Spongilla lacustris as nutritive vacuoles. The cells which develop to yolk cells seem never to contain either of the above bodies at their first appearance. At first they are spherical in shape, but soon become columnar, though never club-shaped. However, their outer end may be round and not flat during certain stages (PI. 3, fig. 13, and PI. 4, fig. 15a). They assume the columnar form, at first, only on one side of the reproductive mass of cells, the columnar layer so formed gradually increasing in extent until it completely surrounds the yolk cells. The poimt at which the columnar layer is finally completed marks the position of the future pore of the gemmule. Subsequent to the assumption of the columnar form, these cells begin to secrete the inner chitinous layer, which in its formation follows the same course as the columnar layer did, which is a proof that the layer in question is secreted by the columnar cells and not by yolk cells (Pl. 3, fig. 18; Pl. 4, figs. 14 and 15). Soon after the amphidiscs have taken up their position among the columnar cells—a phenomenon which takes place soon after the formation of the. columnar layer—the latter grow out and before long appear outside the outer ends of 92 RICHARD EVANS. the amphidiscs (Pl. 4, fig. 16). While this is going on their inner ends situated between the amphidiscs become trans- formed to the parenchyma-lhke substance situated in the mature gemmule between the inner and outer chitinous coats. During the elongation of the columnar cells outwardly the nucleus is carried along. After their inner moiety has been modified and the nucleus has passed to the outer portion they secrete the outer chitinous layer and ultimately break off, and so becoming liberated they pass back again to the sponge tissue (Pl. 4, fig. 16a). The nucleus at the close of these changes, as at the beginning, 1s vesicular. The outer chitinous coat 1s much thinner and less homo- geneous than the inner. In the fully mature gemmule the greater part of it is lost, so that the outer ends of the amphidises are uncovered. (3) The Origin, Migration, and Final Modification of the Scleroblasts, inside which the Amphidiscs are developed, and their Migration from the Sponge Tissue into the Columnar Layer.—At the outset special emphasis must be laid on the point that imcompletely deve- loped amphidiscs were never seen in the protective coat of the gemmule, whether during the early or later stages. The amphidises situated in the gemmule coat are always fully developed, while in the sponge tissues incompletely developed stages as well as fully developed ones are plentiful. The first stage observed in the formation of the amphidiscs consists of a rod-like structure swollen at both ends (PI. 1, fig. 3, m,and fig. 6,a), in which respect they differ essentially from the young stages of the amphioxea, which are always pointed (Pl. 1, fig. 5). Both kinds make their first appear- ance in cells with vesicular nuclei, which soon become trans- formed and become granular, especially in the mother-cells of the amphidiscs. The next change consists in the deve- lopment of a more or less conical form by the ends of the above-mentioned rods, the cone-shaped end at the same time becoming surrounded by a rim (Pl. 1, fig. 6, 6). The cone- shaped end, together with its shghtly developed rim, ulti- DESCRIPTION OF EPHYDATIA BLEMBINGIA. 93 mately grows to the hat-shaped dise. Throughout the pro- cess of formation of the amphidisc both ends are of the same shape. If one end is incompletely developed, the other is equally so. The spicules retain their position inside the scleroblast until they have reached their definitive form, and there seems to be no reason for supposing that, were the scleroblast in any way injured, the spicule could ever attain full development. The amphidises thus described assume their ultimate form while yet in the general tissues of the sponge. It is important to remember that they are developed in cells which are essentially amoeboid. When gemmules are being developed, the scleroblasts in virtue of their inherent power of locomotion move towards them. They travel along the strands of tissue which have been described above as passing from the general sponge tissue to the somewhat loose membrane which surrounds the gemmule. Ultimately they make their way among the columnar cells which surround the gemmule (Pl. 4, figs. 14 and 156). Fig. 156 (Pl. 4) is particularly interesting in that it shows the last spicule that has entered the columnar layer as well as one situated in a strand of tissue close by. The latter is on its way to take up its position alongside the former spicule among the columnar cells. When the amphidiscs, still situated inside the sclero- blasts, have reached their final position, at first they are longer than the columnar cells, which he completely inside their outer ends. At this stage the scleroblasts, though already considerably modified, can be distinctly seen. In the fully grown gemmule, however, they are indistinguishable from the parenchyma-like substance produced from the modi- fied inner ends of the columnar cells. The scleroblasts with their contained amphidiscs first push their way in among the columnar cells at that point where the columnar layer and the inner chitinous coat made their first appearance. ‘They become more numerous and gradually increase in number until finally they envelop the whole eemmule (Pl. 4, figs. 15 and 16). There are, therefore, three distinct structures at least which first appear on the same 94, RICHARD EVANS. side of the central cells, i.e. on the side opposite the point which later on will be occupied by the pore, and all three increase in extent in a similar way. They ultimately form complete layers, though one of them, viz. the columnar layer, is no longer found in the mature gemmule. The migration of scleroblasts, or cells that would become scleroblasts, is not a new idea to zoological literature. Mr. Bourne described such migration of the calicoblasts in Helio- pora coerulea (1), and Professor Minchin has given a full account of the migration of the epithelial cells in the Ascons to the interior, and the subsequent formation of spicules inside them (16). It is true that in both these cases the migration to the interior is previous to the formation of spicules, while in Ephydatia blembingia the amphidiscs are fully formed before the change of position takes place. This difference does not in any way tend to minimise the importance of the facts described above. The amphidiscs are so small as com- pared with ordinary spicules, and their ends are rounded, con- sequently there is no inherent improbability in the view that they are carried from one place to another by the scleroblasts. (4) The Origin, Structure, and History of the Trophocytes.—The trophocytes are large round cells with vesicular nuclei, the chromatin of which is for the most part aggregated in small granules either round the spherical central corpuscle or against the nuclear membrane, the inter- vening space being, as a rule, occupied by only a few small granules. In the immediate neighbourhood of the nucleus there are innumerable small and irregularly shaped granules which give the cell a dirty-looking appearance, the peripheral portion being exceptionally clear and devoid of granules of any kind. A negative feature of these cells is seen in the absence of both yolk bodies and nutritive vacuoles. The trophocytes originate from the sponge as a separate class of cells, ike the three other classes which have been already considered. ‘They migrate from the sponge tissue at the same time as, and along with, the cells which become columnar. While the columnar cells always remain outside DESCRIPTION OF EPHYDATIA BLEMBINGIA. 95 the yolk-cells, the trophocytes pass in among them. They are incapable of passing through the columnar layer after it has been completely formed, but seem to be able to push their way through when the cells in question are arranging themselves and becoming elongated. Not all of them pass among the yolk-cells, some, as it appears, only entering among the developing columnar cells and turning back. The majority of them, however, seem to pass among the yolk-cells. Asa rule, they pass through the developing columnar layer singly, but occasionally groups of several cells are witnessed making their way in. After the trophocytes have entered among the yolk-cells they distribute nutritive material to them, pro- bably in solution. They take no part in the formation of the reproductive portion of the gemmule further than to supply it with nutritive material which the yolk-cells store up in the yolk-bodies. When the inner chitinous layer is about half formed (Pl. 3, fig. 131), the few remaining trophophores are seen travelling towards that part of the gemmule where the pore will appear. They pass out and become scattered about round the gemmule (Pl. 3, fig. 13c). It is not difficult to understand why the trophocytes travel all in the same direc- tion, 1. e. away from the portion that is already formed of the inner chitinous layer, for it is undoubtedly the direction of least resistance. 5. Summary of Conclusions.—(1) Four classes of cells, each of which is derived independently from the sponge, take part in the formation of the gemmule ; first, the mother- cells of the yolk-cells which, alone, constitute the reproduc- tive portion of the gemmule; secondly, the mother-cells of the columnar cells which pass back to the sponge; thirdly, the mother-cells of the amphidiscs, “ scleroblasts,’ which ' The sections represented in figs. 13—13d (Pl. 3) were cut from material preserved in Flemming’s weak solution, while those represented in ail the other figures were from material preserved either in absolute alcohol or in a mixture of 92 parts of saturated solution of corrosive sublimate and 8 parts of glacial acetic. This explains the absence of the dirty-looking granules from all the trophocytes except those represented in figs. 13—13d (PI. 3). 96 RICHARD EVANS. become modified and form a part of the intermediate layer of the protective coat of the gemmule ; and fourthly, the tropho- cytes, whose function is to supply both the columnar and the yolk cells with food material, and which, like the columnar cells, pass back to the sponge. (2) The yolk-cells and the columnar cells draw their food material in solution from the trophocytes; the yolk-cells storing it up as a reserve in the yolk bodies; the columnar cells using it in such a way as to enable them to secrete the inner chitinous layer, to grow and pass out between the outer ends of the amphidisces, their inner ends being’ modified to form the greater part of the ground substance of the pro- tective coat of the gemmule, and finally to secrete the outer chitinous layer ; processes which mean that there is an enor- mous amount of metabolism gome on. (3) The amphidises are developed in cells, the scleroblasts, which carry them through strands of the sponge tissue to their ultimate position in the protective coat of the gemmule., TV. CriticAL Review or Previous Accounts. On perusal of the historical section of this paper it will be seen that the views which have been expressed as to the first appearance of the gemmule are numerous and conflicting. The only thing certain is that a group or aggregation of cells is formed. How it is formed and whence it is derived no one seems to know, though every one has a theory to put forward. Again, it is equally uncertain whether the gemmule is formed from the group which first appears, or whether this group in order to build up the gemmule structure acquires recruits from among the sponge cells and tissues. Probably the first question that should be discussed is whether the group of cells above mentioned is the product of cell migration to one spot, or of cell division either of a single cell or of a group of cells. In his first attempt to explain the origin and structure of the gemmule in the year 1849 (2), Carter expressed himself DESCRIPTION OF EPHYDATIA BLEMBINGIA. 97 in favour of the view that the gemmule is derived from what he calls an “ovi-bearing cell.” In the year 1886 Goette supports the view that this group of cells is the product of cell proliferation (hypertrophy) (10). In reply to both of these views it will suffice to point out that at no stage during the early development of the gem- mule are there any signs of cell division. Though during the very earliest stages the cells are absolutely clear (Pl. 2, fie. 8) I am totally unable to find the least sign of nuclear division, not to speak of fragmentation. In all cases the nuclei seem to be well formed, and in no way modified. Carter had not the facts required to support his view, while Goette seems to have merely figured a piece of ordinary sponge, indifferently preserved, as the first rudiment of the gemmule. For fig. 31 (10). can hardly be explained in any other way. It must be admitted as certain that he saw flagellated chambers and canals in the specimen represented in the above-mentioned figure, but it seems almost equally certain that what he saw was not the rudiment of a gemmule, for the gemmule at its first appearance offers no points of comparison with Goette’s representation. From the con- sideration of the absence of cell division, the view that the vemmule rudiment is formed by that means may be set aside— to say the least—as a most highly improbable one. The second view of the origin of the gemmule rudiment to be considered is the one according to which it contains collar cells and flat epithelium cells, or, as Weltner expresses it, that it consists of cells from two or three germ layers. This view has its most influential advocate in Goette. It was held by Carter also at one time, and probably by Lieberkiihn, who says of the spherical heaps of cells he found in the sponge tissue, that, besides containing Meyen’s masses, they also contain undoubted sponge cells. If the explanation given above of Goette’s fig. 31 (10) is correct—and it seems that it must be—it easily explains how he arrived at the conclusion that all the sponge layers parti- cipate in the formation of the gemmule. Besides, it is quite von. 44, part 1.—NEW SERIES. G 98 RICHARD EVANS. possible that those who hold this view of the origin of the gemmule are mentally dominated by the principles of the “Germ Layer Theory.” If so, this would be a splendid example of an otherwise good theory leading to false conclu- sions. Further, it is more than probable that Carter, Lieber- ktthn, and Goette never saw the first signs of the formation of the gemmule. This is undoubtedly the most charitable view to take of the conclusions they arrived at. Now that the above-mentioned views have been disposed of, there remain for consideration two more views, one of which can be set aside after only a few remarks. The view in question is the one according to which the gemmule is derived from a group of cells, all of which are alike. This view has not found favour with those who have investigated the structure and formation of the gemmule. Carter at one time held it (5), thinking that the gemmule was an ovarium of a “Spongozoon,” a name which he gave to his imaginary sponge-animal. However, in a later publication he gave his support to another view. In fact, a single glance at a good section of the gemmule during some of the early stages is enough to cause one to recoil from the idea that only one class of cells take part in its formation. Consequently there remains only one view, namely, that the gemmule originates from a number of cells belonging to various classes. This view, in one form or another, 1s supported by Marshall (15), Wierzejski (19), Zykoff (21), and Weltner (18). Marshall’s account does not concern us as much as those of the other authors above mentioned do, for the reason that he worked on the gemmule of a species belonging to a different venus. There is, however, one pomt which must be men- tioned. The point in question is that he derives the gem- mules from two classes of cells at least; namely, the cells which he terms “ trophophores,’ and which give rise to the contents of the gemmule, that is the reproductive part, as well as to the delicate structureless membrane surrounding it; and the “ mesoderm” cells, which give rise to the outer shell as well as to the spicules. The importance of this dis- DESCRIPTION OF EPHYDATIA BLEMBINGIA. 99 covery lies in the fact that the reproductive part of the gemmule and its protective coat are respectively formed from classes of cells which are absolutely different, a conclusion which is endorsed in the present paper, though the existence of Marshall’s “ delicate membrane” round the central mass is here denied. Wierzejski, evidently, has observed some phenomena which he did not understand. According to this author a first heap of naked amoeboid cells becomes differentiated to a central mass of yolk containing cells, and a peripheral layer of columnar cells. But he also states that the cells of the mother sponge can even migrate to the body of the gemmule, and thus increase its size. In the hght of the facts which have been described in the foregoing section of this paper, it seems certain that Wierzejski discovered the migration of cells, on the one hand, to form the columnar layer, and on the other hand to feed the mother-cells of the reproductive cells of the gemmule. Wierzejski in describing the first group of cells uses the term “ pseudomorula,” and, probably knowing that a true morula always becomes differentiated to two classes of cells, he comes to the conclusion, as it appears, that his “pseudomorula” must do the same. Consequently he commits the mistake of describing the columnar layer of cells as originating by differentiation from his pseudomorula instead of by further migration from the sponge tissue. Not only this, he was also unfortunate in not being able to discover the true nature of the cells which migrated to the interior of the gemmule, as he says, to increase its size. His failure was probably due to the method of preservation he used. Before proceeding any further, it is necessary to refer to Fiedler’s account of the cells which he found during his in- vestigations of Ephydatia fluviatilis (9). Fiedler de- scribes and figures two kinds of cells (9, pl. x1, figs. 3 and 4, and pl. xu, figs. 86 and 37). One kind, which he terms “amoeboid Fresszellen,’ has granules of equal size in its protoplasm, and a nucleus the chromatin of which is arranged in a network. The other kind, which he terms “amoeboid 100 RICHARD EVANS. Nahrzellen,’” has granules of unequal size in its protoplasm, and a nucleus with a distinct nucleolus. Zykoff, who writes in the light of Fiedler’s discoveries, considers the appearance of refractive yolk substance in a few amoeboid cells of the mesenchyme as the first development of the gemmule. He finds these cells belong to neither of Fiedler’s classes of cells, for they have the protoplasm of the “amoeboid Fresszellen” and the nucleus of the “amece- boid Nahrzellen.” These cells, together with others like them, but without yolk substance, are described as creeping together to form a spherical heap of cells, which differen- tiates to a central mass which consists of yolk-cells, amongst which here and there are scattered amoeboid cells of the mesenchyme, and to a peripheral sheet of mesenchyme cells without yolk, which pass to the general mesenchyme of the sponge. Aykoff has described Wierzejski’s figures as being diagrammatic and far from the truth. His figures, however, might with a certain amount of propriety be described in the same terms, and Weltner’s criticism that they are not natural is quite true. Zykoff, however, isin error when he says the cells of the peripheral sheet above mentioned do not contain yolk. It is true that there are cells among them without spherical bodies in them, the trophocytes of the present paper; but it is equally true that the greater number of them contain bodies which are in all respects similar to the “re- fractive yolk substance” which Zykoff professes to have seen “in a few amceboid cells of the mesenchyme,” which he de- scribes as the appearance of the first development of the oemmule. Zykoff has here failed to distinguish between two classes of cells, and consequently the description he has given of them is not true of either. The cells which he found to contain yolk-bodies in the sponge tissue, and which, he assumes, become the yolk-cells, develop, as it appears, to the columnar cells, and do not fall under the category of “ amce- boid Fresszellen,” or that of “amoeboid Nahrzellen.’ They form a separate class, while the other cells found among them as well as among the yolk-cells must be placed in a class by DESCRIPTION OF EPHYDATIA BLEMBINGIA. 101 themselves. In the present account they have been termed “trophocytes,’ and seem to be identical with Fuiedler’s “Nahrzellen.” Zykoff found the cells in question among the yolk-cells, but does not properly account for their absence from that position in later stages. It seems certain that Zykoff never saw the first stages in the development of the eemmule. His first figure has not the remotest resemblance to the first rudiment of the gemmule. If he never saw the first stages, this explains how he missed the cells with nuclei the chromatin of which is arranged in a network at first, but later on presents the appearance of a modified vesicular nucleus. However, there seems to be little doubt but that these cells form a different class from the above-mentioned classes, and correspond when they are coming together in all respects to Fiedler’s “Fresszellen.” Consequently, at the time the peripheral layer of cells appears the whole group consists of three classes of cells: first, the mother-cells of the yolk-cells ; secondly, the mother-cells of the columnar cells ; and thirdly, the “trophocytes.” ‘The first class consists of Fiedler’s ‘amoeboid Fresszellen,’ the third class of his “amoeboid Nahrzellen,’ while the second class consists of those cells which, according to Weltner, belong to neither of Fiedler’s classes, and, according to Zykoff, occupy a position between the two. | Now that the somewhat difficult questions of the origin and fate of the cells above discussed seems to have been solved, there remain but few points to be considered in connection with the formation of the protective coat of the gemmule. At no stage in the formation of the gemmule was a delicate coat or membrane, situated internally to the mner chitinous layer, found to exist. It often happens, however, that the outer limit of the reproductive portion of the gemmule is sharp, smooth, and well defined. But there is no membrane, the sharpness of contour being merely the result of the pres- sure exerted by the mass of cells on the inner chitinous layer. The cells of the outer layer are columnar in form, and not club-shaped. This, however, is a small point hardly worthy 102 RICHARD EVANS. of all the importance attached to it by Zykoff. ‘The columnar cells during their transference from the inner to the outer side of the external ends of the amphidiscs grow out rather than migrate out. The result is that the spaces between the amphidises are partly occupied by the inner moiety of the cells, which moiety, beimg more or less cut off by the outer ends of the amphidiscs, becomes transformed to the paren- chyma-lke substance which occupies that position im the mature gemmule. That this is true can be easily seen on examination of fig. 15d (Pl. 4), where the inner ends of the columnar cells are already undergoing the above-mentioned transformation, though the amphidiscs are not yet in position. Consequently the origin of this layer need no longer be con- sidered unknown, as has been done by Goette and Zykoff. The next question to be considered is the origin of the amphidises. Lieberkiihn describes the amphidiscs as being developed in some of the cells of the peripheral Jayer (see p. 83). Goette figures a developing amphidisec in one of these cells, and describes these spicules as being formed from within outwards. As has already been pointed out, incom- pletely developed amphidises are never seen in the gemmule coat (p. 92), but are abundant in the sponge tissue. They seem to be invariably symmetrical in form, one end being the exact counterpart of the other. Goette seems to have been in error on both these points. Zykoff merely confirms Wierzejski’s view that the amphi- discs are formed outside the gemmule, but neither of them was able to find the scleroblast, which is most surprising, seeing that Lieberkithn says that the outlines of the cellular structures containing the amphidiscs are as sharp as those of ordinary sponge cells. Zykoff discusses at considerable length the mode of migration of the amphidiscs from the sponge tissue to the gemmule coat, and arrives at the somewhat amusing conclusion that they are pushed from one position to the other by the sponge cells, much in the same way, I should imagine, as a colony of ants carries away bits of food which are too heavy a bundle for one. The presence of amphidises DESCRIPTION OF EPHYDATIA BLEMBINGIA. 103 in the scleroblasts, both in the sponge tissue and in the gem- mule coat, disposes of the necessity of such a supposition. It seems that it may be considered as finally established that the amphidises are carried to their ultimate position by the sclero- blasts which secrete them. | In conclusion | wish to offer my sincerest thanks to Pro- fessor Weldon for the free use of his laboratory and all its resources, as well as for much invaluable assistance in relation to the hterature of the subject; to Professor Minchin for reading the proof sheets; to the Government Grant Com- mittee of the Royal Society for their kind and timely assist- ance; and to the Principal and Fellows of Jesus College, Oxford, for further help. THE DEPARTMENT OF COMPARATIVE ANATOMY, THE MusrEuM, OXFORD. V. BrsLioGRAPHY. 1. Bournz, G. C.—‘‘On the Structure and Affinities of Heliopora coerulea, Pallas, with some Observations on the Structure of Xenia and Heteroxenia,” ‘ Phil. Trans. Roy. Soc. Lond.,’ vol. clxxxvi (1895), B, pp. 455—483, Plates 10O—13. 2. Carter, H. J.—“‘A Descriptive Account of the Fresh-water Sponges (genus Spongilla) in the Island of Bombay, with Observations on the Structure and Development,” ‘Ann. Mag. Nat. Hist.’ (2), vol. iv, pp. 81—100, Plates 3—5. 3. Carrer, H. J.—‘On the Ultimate Structure of Spongilla and Additional Notes on Fresh-water Infusoria,”’ ‘Ann. Mag. Nat. Hist.’ (2), vol. xx, pp. 21—41, Plate 1. 4. Carter, H. J—‘On the Identity in Structure and Composition of the So-called Seed-like Body of Spongilla with the Winter Ege of the Bryozoa, and the Presence of Starch Granules in each,” ‘Ann. Mag. Nat. Hist.’ (3), vol. ii, pp. 331—348, Plate 8. 5. Carter, H. J—“ Development of the Marine Sponges from the Earliest Recognisable Appearance of the Ovum to the Perfected Individual,” ‘Ann. Mag. Nat. Hist.’ (4), vol. xiv, pp. 388—406. 6. Carter, H. J.—“On the Nature of the Seed-like body of Spongilla, on the Origin of the Mother Cell of the Spicule, and on the Presence of Spermatozoa in Spongida,” ‘Ann. Mag. Nat. Hist.’ (4), vol. xiv, pp. 97—111, Plate 10. 104. RICHARD EVANS, 7. Evans, R.—‘ A Description of Two New Species of Spongilla from Lake Tanganyika,” ‘Quart. Journ. Mier. Sci.,’ N.S., vol. xli, pp. 471—488, Plates 37 and 38, 8. Evans, R—‘‘The Structure and Metamorphosis of the Larvaof Spongilla lacustris,” ‘Quart. Journ. Micr. Sci.,’ N.S., vol. xlii, pp. 363—476, Plates 35—41. / 9, Virepiter, K. A.—‘* Ueber Hi- und Spermabildung bei Spongilla fluviatilis,” ‘ Zeits. f. wissen. Zool.,’ Bd. xlvii. 10. Gortte, A.—‘* Untersuchungen zur Entwicklungsgeschichte von Spon- villa fluviatilis,’ Hamburg and Leipzig, 1886. 11. Lanxester, EH. R.— On the Chorophyll Corpuscles and Amyloid Deposits of Spongilla and Hydra,” ‘Quart. Journ. Mier. Sci.,’ N.S., vol. xxui, pp. 229—254, Plate 20. 12. Lizperktun, N.—‘ Beitrage zur Entwicklungsgeschichte der Spon- villen,”’ ‘Arch. Anat. Phys.,’ J. Muller, 1856, pp. 1—19. 13. Linperxtun, N.—“ Zur Entwicklungsgeschichte der Spongillen,” ‘ Arch. Anat. Phys.,’ J. Muller, 1856, pp. 899—414, Taf. xv. 14. Lirperktun, N.—“Zusatze zur Entwicklungsgeschichte der Spongillen,”’ ‘Arch. Anat. Phys.,’ pp. 496—514, Taf. xviil, figs. 8—18. 15. Marsuatt, W.— Vorl. Bemerkungen tber die Fortpflanzungs-Ver- haltinisse von Spongilla lacustris,’ ‘Sitzungsb. Naturf. Ges.,’ Leipzig, Jahre. xi, 1884. 16. Mincury, HK. A.—‘ Materials fora Monograph of the Ascons. I. On the Origin and Growth of the Triradiate and Quadrirate Spicules in the Family Clathrinide,’ ‘Quart. Journ. Mier. Sci.,’ N.S., vol. xl, pp. 469—587, Plates 388—42. 17. Ports, .— Contributions towards a Synopsis of American Freshwater Sponges, &c.” ‘ Proc. Acad. Nat. Sci.,’ Philadelphia, 1887, p. 158. 18. Wr._tner, W.—* Bemerkungen uber den Bau und die Entwicklung der Gemmula der Spongilliden,” ‘Biol. Centralbl.,’ vol. xi, pp. 119 —126. Abstract in ‘Zool. Record,’ 1892, also in ‘Journ. Roy. Mier. Soc.’ (18938), p. 492. 19. Wixrzessk1, A.—“‘ Le developpement des gemmules des Eponges déau douce d’Europe,” ‘ Archives slaves de Biologie’? (1886), p. 26, Taf. I. 20. Zyxorr, W.— gw 3% -_ - “ - nL ne : . % ' A Lene " ’ < ae led 2 - > \ 1 aM €3 + nl 7 if. we a) ey dhe ‘ 4 ‘wihvem@a, 4.’ uy yy Dy ta i ar. : - ‘ea! : ioe mire: v . y= (or 2 Ww ' * 2 een t ,* . n . . i 4 i ; . co 4 y 2 a - " 3 han j s a 7 ae : - Pat 4 * . , ad 4 ’ 4 a ‘ i { I A 24 A 7 : 2 ‘ Fy 4 F : : ’ ad be ‘ F ~ oN . 4 : ‘ i ’ 4 ’ a & . { cs "his ? : vi ‘ 7 4 " € . e ! « + ae f j i ' r : 5 : 4 = \ ° ‘ , 2 i ' 7 + w & t - > p ; i ey aR e 2 cy ic Ff ‘ Ga i \ ¥ i 1% ~ ' . ' " v YY & F é ; ’ 4 7 - eal - v7 7 a ‘S 1 i i - a = , ’ f yr. a, = = ‘ we f, i ’ - , $ ‘ ¥ x - ae i WN ST , PEI ag ey) torn te i ravahivend a@anai Uy Liss sit) ONAL} ay aN F i “Ahad bays. Sd Pay A.5.Huth Lith’ London = ee np eee SSeS Sy, ‘ Cee nr ST x x “i ay 7 S Al, St mi -- aor PA, ' Ay " oP rt ’ 7 « _. CH NS ICG e / ~ J Y al —= | oc a = —=4 Eyes ore! =| ial 6 wr SU. Lari. Foun, Moor Sa, 0 Oe. s! yeaa tn amen en tana Ra mane maa mip Nae ran Ry DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 161 The Development and Succession of Teeth in Hatteria punctata. By H. Spencer Harrison, B.Sc.(Lond.), A.R.C.S8c., Demonstrator and Assistant Lecturer in Biology, University College, Cardiff. (From the Zoological Laboratory, Royal College of Science, London, and University College, Cardiff.) With Plates 10—12. INTRODUCTION. Tue dentition of Hatteria presents certain peculiar and characteristic features, which have always attracted atten- tion, and many of which have not yet received adequate ex- planation. JI need only mention here such points as the structure of the premaxillary and anterior mandibular teeth, the irregularity in occurrence and number of vomerine teeth, and the part taken by the edges of the jaws when the teeth have become worn down. Other matters on which uncer- tainty exists are the presence or absence of enamel, and the extent of the tooth change, which is usually stated not to occur at all. Owing to the great difficulty of obtaining embryos and young, our knowledge on these points is in- complete. However, Professor Dendy has recently to a large extent overcome this difficulty, and most of the ma- terial on which this investigation is based was sent to Eng- land by him. In my endeavours to clear up the points at issue, | have been greatly indebted to Professor Howes and VOL, 44, PART 2,—NEW SERIES. L 162 H. SPENCER HARRISON. Mr. Swinnerton, who have generously placed at my disposal all the slides and preparations made for their research on the development of the skeleton, and who have also granted me the privilege of examining their manuscript and figures. My thanks are also due to Professor Howes for suggesting this research and for the use of a table in his laboratory, and to Mr. M. F. Woodward for much friendly criticism and advice. Historical. The first account of the adult dentition of Hatteria is that given in 1867 by Giinther (1), where he emphasises the acro- dont character, and points out the important part played by the edges of the dentigerous bones when the teeth have be- come worn down. He gives a full account of the macro- scopic features of the dentition of the adult, but appears to have examined no individuals with vomerine teeth. He also describes a young specimen (seven inches long) in which each of the premaxillary teeth of the adult was repre- sented by two, and each of the large anterior mandibular teeth by three separate teeth. In this young specimen he could distinguish no polished surface on the “alveolar” edges, but does not speak positively on this point. The discovery of the occurrence of vomerine teeth was made by Baur (2) in 1886. His specimen was 210 mm. in length, and had a tooth on each vomer. In 1890 Professor Howes (3) examined nine specimens for vomerine teeth. In five of these no such teeth were to be found; in one they were bilaterally symmetrical, in one the last traces could be detected, in one there was a tooth on the right side only, and in another the right tooth was larger than the left. In no case did they project into the cavity of the mouth. Even when teeth were wanting he found a ridge of the mucous membrane in the proper position on the vomer. He suggested finally that the vomerine teeth are vestigial structures, and are undergoing suppression from left to night, DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 163 Siebenrock (4) in 1893 described a specimen having two vomerine teeth on the right side and one on the left. This was the only instance of teeth occurring on the vomer out of nine specimens examined. He states that the tips were covered with enamel. In the same year Rose (5) stated that he could find no tooth replacement in Hatteria, although he apparently found an ‘“Hrsatzleiste.’ He says “ .. . trotzdem findet sich, besonders im Oberkiefer, hinter den functionirenden Zihnen eine wohl entwickelte Zahn- oder Hrsatzleiste. Am hinteren Ende derselben findet zeitlebens eine fortwahrende Neubil- dung von Zahnen statt.” It is, however, difficult to say from the context whether he is referring to Hatteria, or Chameleo, or both. Later, also, he says that in Chameeleo, “und ver- mutlich auch bei Hatteria,”’ there is behind the functional teeth “eine giinzlich functionlose! aber wohl entwickelte Zahn- oder Ersatzleiste.” Burckhardt (6) in 1896, ina review of our knowledge of the dentition of the Sauropsida, expresses his belief that the form of the anterior teeth of Hatteria is due to concrescence. About the same time Baur (7) examined the skull of a young Hatteria (25 mm. from premaxilla to occipital con- dyle), and found two separate teeth in each premaxilla, an outer larger and an inner smaller one, the latter having at its base a replacing tooth, which, however, he says does not become functional. In speaking of the maxilla also, he says, “Der fiinfte Zahn besitzt wie der Innere des Premaxillare einen Hrsatzzahn, und der letzte steht frei in einer Alveole.” He found a well-developed tooth on each vomer, and in addition an anterior small one on the left side. He states that the second tooth in the mandible has an “ Hrsatzzaln,” and concludes that Hatteria has an incomplete set of succes- sional teeth, which, however, are never functional. He does not give his reasons for the latter part of his conclusion. Osawa (8), in 1897, stated that the teeth of Hatteria con- sist chiefly of dentine. He could find no enamel, and to its 1 The spacing is mipe.—H, 8, H, LOA. H. SPENCER HARRISON. presumed absence he attributes the early wearing down of the teeth. He found no true cement; but bone corpuscles and dentine tubules occur side by side, so that at this point he considers we have to do with osteodentine. In 1899, in his paper on the “ Outlines of the Development of Hatteria,’ Dendy (9) first described the presence of three separate teeth in each premaxilla and on each side of the mandibular symphysis, at 4 period just before hatching. He suggests that fusion takes place later, the result being the formation of the four anterior teeth of the adult. Howes and Swinnerton (10), in a paper at present in the press, point out that the middle premaxillary tooth on each side ceases to grow after a certain stage (Stage S), and is in all probability shed. They also figure the replacing tooth lying lingually to it, but owing to lack of material they do not venture to decide whether this does or does not be- come functional. ‘They discuss Baur’s observations, and draw attention to the alternation in size of the teeth in the embryos and young. ‘They found no calcified vomerine teeth in any of the embryonic stages investigated. As regards the substance on the exposed surfaces of the denti- gerous bones, they accept T’omes’s (11) view that it consists of true bone, and they have therefore introduced a new term —‘‘hyperacrodont”—for describing the secondarily theco- dont condition produced in some of the teeth by the dis- position of this bone round their bases. Material and Observations. I have examined complete series of sections taken in various planes, through embryos and young of several stages, ranging from about the third month of incubation (Q) to a period some months after hatching. I have also examined preparations, dissections, and specimens of young and adult animals. In describing the stages I shall make use of letters and numbers in the same sense as Dendy, and as Howes and Swinnerton, adding such other data as may be desirable. DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 165 Stage Q. Embryo Q, 524, in about the third month of incubation. The skeleton is mainly cartilaginous, but along the upper border of Meckel’s cartilage, and in several other regions, a considerable amount of ossification has taken place. Length of head as measured from sections 5 mm. ~The epithelium along the upper and lower jaws has grown down into the mesoderm in the form of a well-marked dental lamina, consisting of an outer limiting layer of columnar cells, and a central core of more irregular ones (fig. 1, d.l.). The line of ingrowth is marked on the surface of the epithelium by a shallow groove, the dental furrow (fig. 1, d.f.), such as has been described in many other vertebrates. The dental lamina is on the whole less developed in the lower than the upper jaw, and in the former is quite indistinguishable for some little distance in the middle line anteriorly ; in the latter, also, it is not con- spicuous in this region. The most interesting feature of this stage is the presence of minute teeth, which are perhaps homologous with the early (embryonic) dentition described by Rose (12, 13) in the Crocodile, by Leche (14) in Iguana tuberculata, and by others in various fishes and Amphibians. The best developed tooth of this first series is shown in fig. 2. Here we see that the tooth is formed just below the epidermis, and has a well-defined enamel organ, although I have been unable to detect any enamel. ‘The presence of the tooth produces a prominent papilla. The dentine is formed by the activity of odontoblasts, which do not be- come so elongated as do those of the next set of teeth, but the process of dentine formation is apparently the same in the two cases. In fact, except for the minute size and the position immediately below the epidermis, the members of the first series of teeth are very similar to those of the functional set. Referring to fig. 1, we see that at the labial attachment of the dental lamina to the epithelium there is 166 H. SPENCER HARRISON. an enamel organ, in which the deepest layer of cells is beginning to assume the character of an enamel epithelium, part of the cells belonging to the epithelium of the jaw at this point, while the others belong to the labial side of the dental lamina. There is as usual a great accumulation of mesodermal cells below the epidermal cap, and also in the region towards which the dental lamina is growing. ‘This enamel organ belongs to the first series, and its position is obviously labial to the dental lamina; with the exception of the palatine teeth of this series the dental lamina always occupies this relative position. As Rose (12) says of the Crocodile, “‘ hegen die verkalkten Zahnchen der ersten Serie nach aussen von der Zahnleiste.” Leche also (14) says of the embryonic teeth of Iguana tuberculata, “ Es ist besonders hervorzuheben dass die fraglichen Zaihne nur im Bereiche der Schmeltzleiste entstehen.”’ In this specimen of Hatteria I found a pair of calcified teeth of the first series in both upper and lower jaw; in each case these were the second in order, the anterior pair above and below being represented by enamel organs. Of the latter, I found on each side eight above and seven below, a number which corresponds fairly well with the number of calcified teeth occurring at a later stage. This is considerably more than have been found in Iguana or Crocodilus. The presence of an enamel organ usually produces an epidermal papilla, which is probably what Rose (18) found in the Crocodile and described as follows:—‘“ Die ersten Zahnanlagen der Krokodile zeigen sich ganz ahnlich wie die Placoid-schuppen und ersten Zahne der Selachier in Form von frei tiber die Kiefersehleimhaut hervorstehenden Papillen.” He says also, ‘ Die ersten Zahnchen entstehen ganz ahnlich wie bei Selachiern durch Verkalkung von frei iiber die Schleimhautoberflache hervorragenden Schleim- hautpapillen.” Although I should scarcely describe the pro- cess of formation of the first teeth in Hatteria in these terms, I am inclined to think there is no fundamental point of difference between this and Crocodilus. Rose in the same DEVELOPMENT OF THHKTH IN HATTERIA PUNCTATA. 167 paper refers to “ Hpithelwucherungen,” which are formed before the ingrowth of the dental lamina and which pro- ject above the surface of the mucous membrane; it is not easy to be sure when he is speaking of these, and when of the papilles produced by the presence of an enamel organ of the first series! In a recent paper, Laaser (15), in de- scribing the development of the dental lamina in Spinax niger, says: ‘ Die ersten Gahne liegen also meist am Uebergang vom ausseren Zahnepithel zur Zahnleiste ;”’ and his fig. 4, showing the enamel organ of such a tooth, is almost a fac-simile of my fig. 1. Here, then, we have a Selachian whose first teeth originate in the same way as do those of Hatteria, and in neither case can we accurately speak of development “durch Verkalkung von frei iiber die Schleimhautoberflache hervorragenden Schleimhautpapillen.” In addition to the marginal teeth of the upper and lower jaws, there are present in a position slightly posterior and external to the choane, two calcified teeth of the first series, one on each side. As is seen from an examination of later stages, this situation corresponds to the anterior extremity of the line along which the palatine dental lamina is subse- quently formed. It is interesting that each of these teeth is situated within a prominent papilla, but owing to the lack of sections showing their development I am unable to say what is the time of origin of the papilla, i.e. whether before or after the tooth is formed. Taking all points into consideration, the teeth of this series seem to resemble more closely those of Iguana tuber- culata than those of the Crocodile. The latter in particular, according to Rose, form a “‘Cementsockel,” and are eventually removed by absorption within the mesoderm. In Hatteria, on the contrary, no such substance is produced, and instead of passing deeper into the mesoderm the teeth are moved ' In Hatteria the apex of most of these papillae is certainly in the form of a small group of cells (not shown in my fig. 1), which suggest ‘“ Epithel- wucherungen.” These may correspond to what Rose describes, but my specimens do not enable me to say whether they arise before the enamel organs are formed. 168 H. SPENCER HARRISON. into the epidermis, and are finally shed about the time of hatching (see later stages and fig. 12). In these features Iguana appears to agree with Hatteria. The general resemblance to the functional teeth which is exhibited by these embryonic teeth in their development and structure, causes me to doubt their special homology with the placoid scale, and I prefer to describe them as simply belonging to the first or embryonic dentition, which is no longer functional, but which, no doubt, was so when the incubation period of Hatteria was shorter than it is at present. At Stage Q the teeth of the future functional series have not yet begun their development. Stage R. Embryo R, 142, in about the fifth month of incubation. Length of head from occipital condyle to premaxilla 6°5 mm. This embryo shows a very considerable advance on the last. The teeth of the first series are now all calcified, and show some degree of degeneration, inasmuch as many of them have become solid nodules of dentine, lying immediately below the epidermis, and having lost their pulp. The enamel epi- thelium in some cases is still distinct, and an unmistakable tendency to the formation of stellate tissue is occasionally to be seen. The teeth number about fourteen above and fourteen below, in addition to the palatine pair. We found in Stage Q that there were only six of these teeth in a calcified con- dition, the others being represented by a slightly greater number of enamel organs than there are teeth at this stage. In dealing with vestigial structures of this kind, little morphological importance can probably be attached to such differences in time of development, but it 1s interesting to note that the first marginal teeth to calcify are those four which lie near the anterior angles of the jaws, and which, in a young animal, would be most useful in catching small prey. The teeth and enamel organs belonging to the future functional series of the young animal are at this stage con- DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 169 spicuous structures. Many of them are well advanced in calcification, and a deposit of enamel has commenced. In fig. 3 is shown the enamel organ of the first premaxillary tooth of the right side. The mesodermal papilla indents the deepest portion of the dental lamina at this point, and there is no indication of a lingual continuation of the latter. The enamel epithelium is conspicuous, and evidences of the stel- late tissue are seen, while the mesoderm shows a tendency to form a capsule. In this tooth no calcification has yet occurred, and the odontoblasts are still undifferentiated meso- derm cells. In the second premaxillary tooth, however, there is a considerable degree of calcification, and an indication of a prolongation of the dental lamina on the lingual side can be detected. In both these points the third premaxillary resembles the first. Comparing these three teeth with the corresponding anterior three on each side in the lower jaw, we find that similar relations obtain, i.e. that the second is more advanced than the other two, and shows indications of a lingual prolongation of the dental lamina. I shall have more to say on these points in the sequel. Hach maxilla has ten teeth, most of which are more or less calcified; but here, again, there is a well-marked alternation in the degree of calcification. As sagittal sections only of this embryo were at my disposal, | am unable to give the precise relations of the dental lamina in the lateral regions of the jaws. The mandibular teeth posterior to the first three (eight in number on each side) are, as regards the first six, well calcified, the two posterior only slightly so. The anterior end of the palatine tooth-bearing regions is indicated by the presence, on each side, of the tooth of the first series, mentioned in the last section. The dental lamina bears three enamel organs, which show no calcification. Kmbryo R, 162, in about the eighth month of incubation. Although this is apparently so much older than the last embryo, the stage in development is actually not much more advanced, for Dendy (loc. cit.) has pointed out that, for a long period during the winter months, very little progress 170 H. SPENCER HARRISON. made, and embryos from the fifth to the ninth or tenth month of incubation may all be included in his Stage R. The teeth of the first series have become less tooth-lke in ' form, and some of them are enclosed in the epidermis (fig. 4, pal. 1). They are not so numerous as in the last embryo described, and perhaps some of them have already been shed. They occur as far back in the jaw as the ninth maxillary teeth of the future functional series. As regards the future functional teeth, there are in each premaxilla three teeth, the first being smaller and _ less developed than the other two, and the second being the most advanced. Hach maxilla has ten teeth, and, as in the last embryo, these exhibit an alternation similar to that already described, but in this case I am able to give amore detailed description. Before doing so I wish to refer to fig. 11, where the alternating series of the maxilla at Stage S is shown. Here a large tooth alternates with a small one, and the larger differ somewhat in shape from the smaller. A comparison of figs. 6 and 7 will illustrate the condition found in frontal sections at Stage R. Fig. 6 shows a tooth having a consider- able development of dentine, a lingual prolongation of the dental lamina (7. d. l.), stellate tissue much broken down and only separated from the exterior by two or three layers of flattened cells. Fig. 7, on the other hand, shows a tooth in which the amount of dentine is much less, though the enamel organ as a whole is larger; there is no lingual prolongation of the dental lamina; the stellate tissue is more intact, and is separated from the exterior by several layers of cells; the whole structure is obviously in an earlier stage of deve- lopment. Fig. 6 is the eighth maxillary tooth of the right side, and fig. 7 is the tooth immediately anterior to it; the former represents one of the smaller teeth of the alternating series shown in fig. 11, the latter one of the larger. This alternation of character, as seen in sections, prevails through- out the maxillary series, and it is difficult to avoid coming to the conclusion that we are here dealing DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 171 with two dentitions, the smaller tooth representing an earlier set, and the largeralater one. The same is true of the premaxillary teeth, where only the second belongs to the earlier set. The interpretation of the epithelial strand lingual to the smaller teeth (fig. 6, 7.d.1.; fig. 4, 7. d. 1.) as a residual dental lamina seems to me to be justifiable, although at later stages, and at this stage in the lower jaw (fig. 9, man. lin.), epithelial ingrowths of a different nature arise, which produce some uncertainty. The fifth pair of maxillary teeth form an exception to the regular alternation, inasmuch as though they resemble the larger teeth in most respects, they have an apparent residual dental lamina. This fact has an interest in view of the development of a successional tooth at this point at a much later stage. Labially to the enamel organs the epidermis is beginning to grow down into the mesoderm in the form of a band of cells more or less closely connected with the enamel organs or with the dental lamina in the intermediate regions (figs. 4, 5, 6, 7, m. lab.). This is the labio-dental strand, and its further development will be seen in later stages. The most anterior indication of the palatine dental lamina occurs at the level of the sixth pair of maxillary teeth. The epidermal ingrowth is anteriorly a solid roundish mass of cells, which, traced backwards, is found to assume in section a crescentic form, the attachment to the epithelium being by the convex side of the crescent. The inner limb is the one more closely related to the enamel organs, and represents the dental lamina. ‘The outer limb, on the other hand, is more independent (figs. 4 and 5, p. lab.), and repre- sents a glandular ingrowth, the relations of which will be presently described. The most anterior tooth of the palatine belongs to the first (embryonic) dentition, and is situated lingually to the dental lamina (fig. 4, pal. 1). It is a more or less triangular fragment of dentine, completely enclosed in epidermis, and on the point of being shed. Its position is exceptional, as the teeth of this series are usually labial to the dental lamina; but I do not attach much importance to 172 H. SPENCER HARRISON. this divergence from the rule, as this particular tooth is formed before the dental lamina, and may easily have reached its present relative position through the growth of the epidermis. ‘The palatine dental lamina of each side has four enamel organs, of which the first two only have partially calcified teeth (fig. 4, p. e. o.; this section passes through the anterior portion of the first enamel organ). The second is the only one having an epidermal strand lingual to the enamel organ. Between the teeth the dental lamina is con- tinued as a well-marked strand of cells (fig. 5, d. l.) in both palatine and maxilla: in the maxilla it terminates without becoming separated from the epidermis; in the palatine the dental lamina and the lingual epidermal ingrowth run together behind (as they arise together in front), and form a roundish knob of cells attached to the epidermis, which, again, is continuous posteriorly with a groove in the roof of the mouth. In the mandible of the last embryo described we saw that of the first three teeth on each side the second was more advanced than the other two, and this is the case in the present specimen. It has the same claim to be considered a member of an earlier series than the others as has. the second premaxillary. There are now ten pairs of calcified cheek teeth, and a pair of enamel organs without calcification on the posterior free prolongations of the dental lamine. 210 H. SPENCER HARRISON, 11. C. S. Tomzus.—‘ Manual of Dental Anatomy,’ 1894, 4th edition, p. 258. 12. C. Résu.—‘‘ Ueber die Zahnentwickelung der Krokodile,” ‘ Morpholog. Arbeit.,’ Bd. 11, 1894. 18. C. Rész.— Die Zahnentwickelung der Krokodile,” ‘Anat. Anz.,’ Bd. vil, 1892. 14. Lecuy.—‘ Ueber die Zahnentwickelung von Iguana tuberculata,” ‘Anat. Anz.,’ Bd. viii, 1893. 15. LAAsER.—“ Die Entwickelung der Zahnleiste bei den Selachiern,” ‘ Anat. Anz.,’ Bd. xvii, Nos. 24, 25, 1900. 16. A. Cartssen.—‘ Ueber den Zahmnersatz bei Agama colonorum,” ‘Anat. Anz.,’ Bd. xi, 1896. 17. C. S. Tomrs.—‘‘ The Development of the Teeth of the Newt, Frog, Slowworm, and Green Lizard,” ‘ Phil. Trans.,’ part i, 1875. 18. C. 8. Tomes.—“‘ On the Structure and Development of the Teeth of Ophidia,”’ ibid. 19. Santa Srrena.— Ueber den Bau und die Entwickelung der Zahne bei den Amphibien und Reptilien,” ‘ Verhand. d. Phys.-med. Gesellsch. in Wiirzburg,’ Bd. 11, 1872. 20. Bronn’s ‘Klassen u. Ordnungen des Thierreichs,’ Bd. vi, Abth. iii (Reptilien). 21. Knox.—‘‘ On the Tuatara,”’ ‘ Trans. New Zealand Inst.,’ vol. ii, 1869. 22. Newman.—“ Notes on the Physiology and Anatomy of the Tuatara,” ‘Trans. New Zealand Inst.,’ vol. x, 1877. 23. ZirtEL.—‘ Handbuch der Palaeontologie,’ vol. iii, Vertebrata, 1887, 1890. DESCRIPTION OF PLATES 10—12, Illustrating Mr. H. Spencer Harrison’s paper on “The De- velopment and Succession of Teeth in Hatteria punctata.” List oF REFERENCE LETTERS. Ant. Anterior. ad. Adamautoblasts. 6.v. Blood-vessel. cav. Artificial space. c.g. Crista gingivalis inferior. d. Dentine. dex. Dentary. d./. Dental lamina. ex. Enamel. e.o.1. Enamel organ of tooth of first (embry- onic) series. ep. Epithelium of buccal cavity. g/. Gland. Zaé. Labial side of section. Lz. Lingual side of section. J/.d.gr. Labio-dentai groove. DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 211 lin. gr. Mandibular (internal) dental fossa. man. Mandible. maz. lab. Hpi- thelial ingrowth labial to mandibular teeth (labio-dental strand). maz. lin. Epithelial ingrowth lingual to mandibular teeth. maz.f. Maxillary tooth of functional series. mes. Mesoderm. mk. Meckel’s cartilage. m./ab. Epi- thelial ingrowth labial to maxillary teeth (labio-dental strand). m. lin. Hpi- thelial ingrowth lingual to maxillary tooth. m.p. Mesodermal dental papilla. p.lab. Epithelial ingrowth labial to palatine teeth. yp. diz. Epithelial in- erowth lingual to palatine teeth. pm. Premaxilla. pos¢. Posterior. r. 4. J. Residual dental lamina. s¢. Stellate tissue of enamel organ. ¢. s. Successional tooth. ~ ‘lines of all sections drawn with camera lucida.) Fic. 1.—Section of the enamel organ of a tooth of the first series (first, left, upper), with dental lamina on the lingual side. d.f Dental furrow. (Embryo Q, 52a. Sagittal section. x 240.) Fie. 2.—Section of the second tooth of the first series, which is already well calcified. (From same series of sections as fig. 1. x 240.) Fie. 3.—Section through the enamel organ of the first premaxillary tooth (right), belonging to the future functional series. (Embryo R, 142. Sagittal section. xX 240.) Fic. 4.—Section through enamel organ of the right anterior palatine tooth, and the sixth maxillary, of the functional series. The small palatine tooth of the first series is seen lying lingually to the palatine, enclosed in epidermis. The epidermal ingrowth labial to maxillary (labio-dental strand) is just becoming evident. p.e.o. Enamel organ of palatine tooth of functional series. pal.\. Palatine tooth of first series. (R, 162. Frontal section. x 60.) Fie. 5.—Section through left maxillary, palatine, and mandibular dental regions, immediately posterior to first palatine tooth, and through the seventh mandibular. (From same series as fig. 4. x 60.) Tic. 6.—Section through eighth maxillary tooth of right side. This is one of the smaller teeth of the alternating series (cf. fig. 11), and is more advanced than the seventh (cf. fig. 7). (R, 162. Frontal section. x 240.) Fie. 7.—Section through seventh maxillary tooth of right side, for com- parison with fig. 6. (R, 162. Frontal section. x 240.) Fie. 8.—Section through the eighth mandibular (left). (R—S. Frontal section. x 60.) Fie. 9.—Section through right palatine and maxillary teeth to show the relations of the epidermal ingrowths at this stage. pad. f. Palatine tooth of functional series. maz. Maxilla. (Embryo R—S. Frontal. x 60.) Fie. 10.—View of premaxillary and anterior mandibular teeth at Stage S, from a prepared skull. x 5. Vie. 11.—Lateral view of teeth at Stage S, to show the conspicuous alter- DALY H. SPENCER HARRISON. nation in the maxillary and the less marked one in the mandibular teeth. Palatine teeth not shown. xX 5. Fie. 12.—Section of a lower tooth of the first series at Stage S. 7.1. Tooth of first series. ep.s. Capsule of flattened cells. (S.2. x 240.) Fig. 13.—Section of palate passing through the enamel organ of the vomerine tooth of left side. Vo. Vomer. V.¢.0. Enamel organ. (S. Sagital. x 240.) Fie. 14.—Section of mandibular tooth, with bone of jaw. In this section are also figured the labio-dental groove (/.d.gr.), formed from the corre- sponding strand of cells by splitting ; also the mandibular dental fossa, formed in the same way from the lingual ingrowth, cutting off a ridge of mucous membrane (with a core of mesoderm), which runs between the inner face of the jaw and teeth and the tongue (ef. also figs. 5, 8,19). The glands on the sides of the grooves and on the lower lip (Z. /.), together with the shelf of the latter, are shown. The enamel of the tooth has been removed in the process of preparation. At the base of the internal dental fossa a solid ridge of epithelial cells (7.d.¢.) remains non-glandular, and no doubt represents the dental lamina, which has been carried down by the glandular ingrowth (cf. figs. 19, r.d./., and 18, ¢.s.'). (Embryo 8, 19a. Frontal section. x 60.) Fie. 15.—Section of junction of tooth and bone at Stage 8. On its internal surface the dentine has a more recently formed layer (unshaded). On the labial side the close attachment of the epithelium to the tooth and bone is shown. 6.c¢. Bone-corpuscles. ep. gr. Epithelium of inner limb of Jabio-dental groove. (S, 19a. Frontal section. x 240.) Fig. 16.—Sagittal section through posterior part of right upper and lower jaws at Stage 8, to show the posterior continuation of the dental lamine of maxilla and dentary. Three large teeth have been cut through, and one small one on the upper dental jamina. e. 0. f. Enamel organ of tooth of alternating series. (S2. Sagittal. x 60.) Fic. 17.—Anterior view of premaxillary and anterior mandibular teeth at Stage T, to show the relative reduction in size of the second premaxillary on each side. x 5, Fie. 18.—Sagittal section through the second premaxillary tooth of one side, to show the development of a successional tooth, which arises from the epithelium near the deepest part of the internal dental fossa (cz. gr’.). The glandular portion of the latter is not evident, and the labial side of the section is damaged. The functional tooth is seen to be attached to the bone on the labial side only. pme.¢. Second premaxillary tooth. ¢.s. 1. First successional tooth. (Stage T. Sagittal section. x 60.) Fig. 19.—Section through third mandibular tooth of one side, showing a well-defined mass of epithelial cells at the base of the internal dental fossa, The interpretation of this as a dental lamina is justified by the formation of DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 213 successional teeth on its lingual side at a later stage (see also fig. 18). (Stage T. x 60.) Fires. 20, 21, 22.—Three stages in the development and succession of teeth in the premaxilla (right) of specimens 17 cm., 17°8 cm., and 21'2 em. in leneth. 1, 2,3 are the teeth of the newly-hatched animal; 7. s. 1, 2, and 3, are the successional teeth in the order of their formation. (¢. s. 1 in fig. 20 was missing in the preparation figured, but was inserted from sections). x 10: Fic. 28.—Inner view of the anterior maxillary teeth of left side, from a specimen 17°8 cm. in length. ¢.s. 1 is the first successional tooth of the maxilla, which has cut the gum but is not yet fused with the bone. x 14. Fig. 24.—Transverse section across the vomers (vo.), cutting the two vomerine teeth (/.v. ¢., 7. v. ¢.) more or less longitudinally. The left tooth had a considerable backward curve, which partly accounts for its division into a free and an attached portion. From the same specimen as the last figure. < 50. Fie. 25.—Inner view of anterior maxillary teeth of left side, from speci- men 21'2cm. in length. 7.5.1, 2, and 3 are the successional teeth, the last being still deeply seated. x 14. Fic. 26.—Inner view of anterior mandibular teeth of left side, showing two successional teeth. ¢. s, 1 no doubt replaced two of the earlier set (from same specimen as last figure). x 14. Fic. 27.—Outline of marginal teeth of 21:2 cm. specimen. The uniform series in the lower jaw already occupies considerable space, whereas all the maxillary teeth are of the alternating series or their vertical successors (the same may be said of the palatines at this stage). x 5. Fic. 28.—Portion of ground longitudinal section through the base of a young tooth, to show the branching dentinal tubules (d. ¢.) with their pro- longations into the enamel (d. /’.). x 800. Fie. 29.—Portion of a ground section through the specialised outer layer of bone, on the lingual side of the adult lower jaw, to show the close resemblance to enamel. 4. c. Bone-corpuscles. x 300. 20s ~ 7 ‘ i> , < — tu — ’ ‘ a -) = 5 ' . F ' = iw 2 ‘ 4 7 ." J =. i. } i a r ee ne fs 29 * @ 7 ~ - wipes te. NG u ok. Z Aphprbiohala 7 Tas Luar. Soupn. Mor See Ub WN S PF y Ld ab L, A =. ¥ 2 ww. ° é a a? feng? ~ - eal . / . +f) * .¥ Pe = ‘ London. AS Huth, Lith? LL] Cc O74 Lo AW url Sour Aor Sw Dod Ze a) ¥ / AA eOTRLEN Re a eee th” London J 7 rH cs 2 aa — ta ta PN SP Cle if 4 AL StL 4 uf a vb. wan, For L, Tova a te oP Ne ae Ze L\/\y VAVAAUAY a ua a = xt f\ j ov \f\ \ \ H.S.H. del. ry hana Dery ‘ THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 215 The Anatomy of Pleurotomaria Beyrichii, Hilg. By Martin F. Woodward, Demonstrator of Zoology, Royal College of Science, London. With Plates 13—16. THE vast antiquity which characterises the genus Pleuro- tomaria—for no one can doubt the identity of the living and fossil shells which are customarily grouped together under this name—has justly endowed this mollusc with great interest for those studying the ancestry of the Prosobran- chia. When, therefore, a living example was obtained by Agassiz in 1871, and later in 1879 several specimens of both P. Quoyana and P. Adansoniana were dredged by the United States steamer “ Blake,” the result of an investiga- tion of the anatomy of these forms was awaited with great interest. Unfortunately, however, the specimens all turned out to be in a bad state of preservation, and although falling into such skilled hands as those of Dr. Dall, it was found impossible to make out much of their anatomy. Dall, how- ever, published ! figures and descriptions of the external cha- racters of the animals, of the radulz and of some few points in connection with the pallial complex, the rest of the body being too much decomposed for investigation. During the last few years a further examination of one of 1 “ Report on the Mollusca dredged by the United States steamer ‘ Blake,’ ” ‘Bull. Mus. Comp. Zool., Harvard,’ vol. xviii, 1889. 216 MARTIN F. WOODWARD. the specimens of P. Quoyana obtained by the “ Blake ” has been made by Fischer and Bouvier,! and these authors have made a still more detailed examination of the radula of this form, and also of the nervous system, which had not previ- ously been examined. These investigators have published a most exhaustive history of the genus, giving in addition a complete list of the recent specimens obtained up to the year 1898, and they further append a full literature relating to this mollusc. Since it is not my intention to enter into these branches of the subject, I must refer the reader to Messrs. Bouvier and Fischer’s paper.’ Through the kindness of the Director of the Natural History Museum I had placed at my disposal an example of the animal of P. Beyrichii obtained off Boshu, in Japan. The animal was beautifully preserved, but unfortunately it declined to part company with its shell save in pieces, so that my first investigation was much retarded by having to build up the anatomy of the animal from these fragments. TF ortu- nately, however, two more specimens were obtained by the Museum and handed over to me by Professor EH. Ray Lan- kester, whom I have to thank for entrusting their examina- tion to me. Without these additional specimens my results would have been very incomplete, since the first specimen, though in much the best state of preservation, was in so many fraginents that 1b was extremely difficult if not impos- sible to make out the exact relations of some of the organs. Although my investigations are largely based on an examina- 1 «Etude monographique des Pleurotomaries actuel,” ‘Archiv. Zool. éxp.’ (3), vol. vi, 1898. Reprinted in ‘ Bull. Mus. Comp. Zool.; Harvard,’ vol. XK 2 Since the publication of Bouvier and Fischer’s monograph at least five new specimens of P. Beyrichii have been obtained. These all came from the Boshu, Japan, being captured alive in nets set at the bottom at a depth of seventy to eighty fathoms; they were preserved in spirit with the animal. One of these specimens has been described by Rolle (‘ Nachrbl. Deutsch. Malak. Ges.,’ 1899) as a new species under the name of P.salmiana. I think, myself, that is only a variety of P. Beyrichii. An additional shell of P, Adansoniana has also been obtained, THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 217 tion of the fragmentary specimen, they have in every case been verified by a comparison with the two complete speci- mens. The External Characters.—The first example which came into my hands was the identical specimen whose ex- ternal characters were described by Professor Mitsukuri in the ‘Annotat. Zool.,’ Japan, vol.i, p. 67; consequently I cannot do better than quote his description in extenso. “The animal was not very lively and could not be per- suaded to extend itself fully. At the utmost we were able to see the foot and a part of the head. The sole of the foot was straw-yellow. The side of the foot and the throat were mottled with large and small patches, and streaks of deep carmine-red on the ground colour of reddish yellow. The proboscis was uniformly deep carmine-red. The left tentacle had a small branch near the tip. On the sides and the posterior aspect of the foot we were able to make out two lobes, one standing up from each side of the foot and applied to the shell. It seemed probable to me that when fully extended these lobes enveloped the shell to a greater extent, a supposition which is strengthened, as was first pointed out by Mr. Namiye, by the fact that the shells of Pleuroto- maria hitherto found are all extremely clean, and have never barnacles, worm-tubes, etc., attached to them. ‘The mantle was not at all visible, and we were thus not able to see how it is related to the slit on the outer lip.” It will be seen from the above account that Mitsukuri makes no mention either of the presence or absence of an operculum—a strange omission when we remember that an operculum had been described by Dall as present in both P. Quoyana and P. Adansoniana. When I received the specimen I found that it had no operculum, nor could: I find, after a careful examination, any suggestion that the operculum had been torn away. ‘The only indication of the possible presence of this organ was a minute lobe (fie. 2, op. l.) situated on the dorsal side of the foot in the position of the opercular lobe of Trochus. The arrival of the 218 MARTIN F. WOODWARD. second specimen, however, showed that P. Beyrichii, like the two other species mentioned above, possessed a fairly stout though somewhat small operculum attached to the foot by a large circular lobe (figs. 3 and 4). We are, however, still unable to determine whether the first specimen had lost its operculum during its free life, or if it had been born without one. Judging from the presence of the opercular lobe, I should be inclined, in spite of its small size, to suggest that the operculum had been present, but accidentally lost either through disease, or mishap, early in life. The operculum (fig. 4) is nearly circular in outline, measuring, in the largest specimen, 14°5 mm. in diameter ; in character it is trochiform, consisting of about twenty closely coiled whorls, strongly marked with line of growth. It is apparently composed solely of dark brown horny (chitinous) matter, and for its size is very thick and strong, retaining its thickness quite to the margin. The mouth of the shell from which the operculum was taken measured 40 mm. in transverse and 30 mm. in vertical dia- meter. Hence it will be seen that the operculum can be of very little use in closing the aperture, and thus protecting the retracted animal; it may, however, be of some service in protecting the upper surface of the foot from mechanical injury which might be caused by the rubbing of the shell when the animal was fully extended, since under these con- ditions the shell rests, as in the Trochide and Turbinide, directly upon the operculum. Compared with the opercula of P. Quoyana and P. Adan- soniana, the operculum of P. Beyrichii appears to most nearly resemble that of the first-named species, although Dall in his description does not mention what is such a striking feature in P. Beyrichii, the thickness of the oper- culum. In P. Adansoniana the operculum is very much larger and thinner, and still more closely resembles the opercula of the Trochide. The small size of the operculum in two of the three speci- mens, and its absence in the third, suggests that this organ THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 219 is of very little importance to P. Beyrichii, and that pos- sibly it will disappear in the near future. The Foot.—The foot, although contracted in my speci- mens, is still very large, and is evidently capable of great extension. As is the case with many Prosobranchs its ante- rior margin is double (figs. 1, 2, and 7), the upper surface of the foot being separated from the sole by a well-marked transverse groove. We are quite at a loss to account for this structure, which is evidently of great importance since it is present in so many Gastropoda. The lateral surfaces of the foot are finely rugose, being closely beset with minute papille (figs. 1 and 2). These papille are wanting on the dorsal surface, which is separated from the lateral surfaces by the paired epipodial folds (ep.). At the anterior extremity of the dorsal surface is situated the opercular lobe (figs. 2 and 3, op.l.); this in its func- tional condition is circular and nearly as large as the oper- culum. On the right side it is produced out into a little lobe, which is in turn attached to the upper surface of the foot, and marks the growing point of the multispiral operculum. Behind the opercular lobe a median longitudinal groove leads to the posterior end of the foot; on either side of this is a modified area due to the presence of numerous transverse grooves originating from the median one; some of these are symmetrically arranged, but others are unpaired (fig. 2). This somewhat y-shaped modified area is bounded in front by a couple of longitudinally-placed bands running back from under the opercular lobe; these, however, only extend for about one third of the length of this area, which is else- where bounded by a groove marking the commencement of the epipodium. A similar modified area was found by Dall in P. Adansoniana, but strangely enough this appears to be quite wanting in P. Quoyana, a point upon which Dall lays some stress. This is a very curious fact, for in other respects, notably in the operculum and in the radula, as we shall see later, P. Beyrichii is more closely related to P. Quoyana than to P. Adansoniana, a relationship which 220 MARTIN F. WOODWARD. had already been noted by Crosse and Fischer from a study of the shells, and expressed by the institution of the section Perotrochus for the first two species. This peculiar specialised area is also to be met with in the Trochide (notably in T. [Gibbula] magus and T. [Callio- stoma] zizyphinus); but though so commonly present, I am unable to offer any suggestion as ‘to its function. The Epipodium.—This structure, which is so charac- teristic of the majority of the Diotocardia, or of that sub- division for which Fischer proposed the name 'Thysanopoda, is not conspicuously developed in P. Beyrichii. It takes the form of a couple of folds, one on either side of the body. They start a short distance behind the head and attain their maximum development in the region of the operculum ; whence they extend back in the posterior extremity of the foot, practically meeting in the middle line behind the median dorsal groove. ‘These folds, which are evidently somewhat contracted in the spirit specimen, are like the rest of the body covered with minute papille, and are entirely devoid of those accessory lapets and tentacles so characteristic of the epipodia of the Trochidz, Haliotidz, and other Thysanopoda. Judging by the figures given by Dall (op. cit., pl. xxx, figs. 1, 4, and 5) of the hving animal of P. Adansoniana, the epipodium would be more conspicuous in the living animal in P. Quoyana; Fischer and Bouvier even speak of it as being largely developed. In comparison with the Trochide and Haliotide, however, I should rather conclude that the epipodium was feebly developed in Pleurotomaria. I do not think there is any evidence to support the view advanced by Mitsukuri that these lobes partly envelop the shell, although they are apparently closely appled to its base, and I would rather account for the clean nature of the shell by the habitat of the animal being in deep water— seventy to eighty fathoms,—where life, both animal and vegetable, is not so abundant asin the littoral zone inhabited by the Trochidz, whose shells are so generally encrusted with foreign matter. THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 221 The Head.—The head is large and produced into a somewhat cylindrical snout, bent downwards as in the T'ro- chide. On the under surface, which is abruptly truncated, is situated the mouth, surrounded by a horseshoe-shaped lp, the gap in the lip being placed ventrally. The head and anterior part of the body are much smoother than the foot, being practically devoid of papille. The tentacles are situated low down on either side of the head. In form they are cylin- drical, with roughly pointed extremities ; they are highly mus- cular and evidently much contracted. ‘The only peculiar feature about them is the tendency which they show to be- come branched at their free ends; this is most marked in the left tentacle of the first specimen examined (fig. 1), but the second specimen also showed indications of a similar condi- tion in both tentacles, although to a lesser degree, while the right tentacle of the third specimen shows no less than two accessory branches. The Eyes.—The eyes, which are small and inconspicuous, are situated, each on a slight elevation, at the posterior side of the base of the tentacle. Examination with a lens shows the cornea to be perforated, as in Trochus and most Dioto- cardia. An examination of sections (fig. 20), however, shows that they are simple in constitution; like those of Trochus the central cavity is only partially filled by a vitreous body, the rest of the space being occupied by sea-water. The eyes, as may be supposed, are not specially well pre- served, but one can see that the retina consists of a series of pigmented rods, turned towards the optic cup, and an external layer of ganglionic cells. I was unable to make out the clear distal segments of the rods, such as are figured for other Diotocardia. The retina is bounded by a delicate capsule, outside which we see the optic nerve and a few mesodermal pigment cells. ‘The retinal pigments extend out through the perforation in the optic cup into the adjacent epidermis. The structure of the vitreous body suggests that is secreted by the individual rod-cells. Paya MARTIN F. WOODWARD. The Mantle.—In the contracted state of the dead animal the mantle-slit, so characteristic of this genus, is inconspi- cuous, and appears more like a broad, shallow sinus than a deep narrow slit; even in the living animal Mitsukuri was un- able to observe its relation to the shell-slit. Its true relation is, however, well seen in Dall’s figures of P. Quoyana and P. Adansoniana taken from the living animal. In these forms we see that the margins of the mantle-cleft are closely applied to the margins of the shell-slit, through which they may slightly protrude. The free edge of the mantle is thick- ened and closely beset with numerous small papille, which are evidently slightly protrusible, although not to the extent seen in Haliotis. The mantle-fold completely encircles the body, but is only feebly developed behind, and in this region its margin is quite smooth. The Pallial Complex.—Owing to the bad state of preservation of the specimens collected by the “ Blake,” Dall was unable to give us much information concerning the organs falling under this category ; he was further unfortunate in his attempts to identify these badly preserved parts, and consequently, beyond a slight knowledge of the gills, we were quite in the dark as to the relations of the kidneys and the genitalia, since the structures to which Dall, and after him Fischer and Bouvier, applied these names, have quite different significances. The Ctenidia.—The gills are very large and conspicuous, and possess the form characteristic of the Scutibranchia (figs. 5,6, 7 and 14). The two gills, though symmetrically placed, are not equally developed, that on the left side being very much larger than that on the right (cf. figs. 5 and 7). This is a very interesting feature, which is obviously con- nected with the dextral coiling of the shell, and one which is of great significance when studying the phylogeny of the Azygobranchia. Hach gill is characteristically bipectinate, consisting of an axis which takes the form of a long and some- what stout septum, containing the efferent and afferent bran- chial vessels, and two sets of gill-filaments, which have the THE ANATOMY OF PLEUROTOMARIA BEYRICHIT. 228 form of triangular plates, whose surfaces bear a number of fine plications (fig. 14). In each gill the inner or under set of plates are somewhat smaller than the outer set, a con- dition leading towards the more specialised one seen in the Trochide. As in other Scutibranchs, the anterior end of each gill is not attached to the mantle, but projects freely into the mantle-cavity, and, in the contracted state of the mantle, almost beyond the anterior margin of that fold. Structure of the Gill-plates.—A careful study of sections of the gill taken through the three principal planes, i.e. transverse to the long axis, longitudinal sections parallel to the gill-septum, and horizontal sections, enables us to construct a diagram (fig. 15) showing the circulation of the blood in the gill-plates. ‘Theafferent branchial vessel (a. b.), as we have already seen, is situated at the ventral edge of the gill-septum under a thickened ridge of glandular epi- dermis; this vessel gives off on either side small branches, which enter one into each of the very thin gill-plates. The vessel then spreads out as a delicate film between the two laminze which together constitute the plate. After the blood is aerated by being brought into such close proximity to the sea-water it leaves the plate near its dorsal attachment, this efferent channel joins across the septum with the corre- sponding vein from the opposite plate, the conjoint vessel runs up the septum and enters the efferent branchial vessel (e. b.), which lies at the junction of the septum and mantle. It must not, however, be supposed that the space between the two lamine of a gill-plate is as simple as represented diagrammati- cally on the left of fig. 15; such is not the case, the space being broken up into numerous small channels by the pre- sence of great numbers of interlaminar connections (0. l. c., figs. 15, 16, and 18), extending across the space and joining the two laminz which compose the gill-plate. The blood thus takes a very sinuous course among these connections. A somewhat larger channel is, however, present all round the margin of the gill-plate. The extremely delicate nature of the gill-plates is well seen — Q24 MARTIN F. WOODWARD. in fig. 16, which represents vertical sections across two gill- plates. The ventral and dorsal margins are seen to be dilated, as also are the blood-spaces nearer the dorsal margin, in which region also the interlaminar connections are larger and fewer, whence the dotted appearance seen in fig. 14. The curious crumpling shown in the ventral part of these plates (fig. 16) represents transverse sections through the folds seen in the surface view of gill-plate (fig. 14); this appearance suggests that the margin of the gill-plate is too short to surround the central area without the latter becoming puck- ered. The gill-plates present another interesting feature in the presence along their outer margins of a couple of sup- porting rods (s. 7.), the relations of which are well shown in figs. 15 and 18. Froman examination of a transverse section of these rods (fig. 18) it will be seen that they are flattened structures, closely applied to the base of the epidermal cells, and enclosing between them portions of the blood-space of the gill-plate. A section taken parallel to the gill septum and passing through the dorsal junctions of the gill-plates with the septum (fig. 17) shows that the two rods in each plate are perfectly independent of one another, and that each rod is related to two gill-plates. In other words, each rod is a U-shaped structure which embraces the space between two gill-plates, one limb extending into each of these plates, a condition which at first sight reminds one of the relation of the gill-skeleton in the Lamellibranchia. ‘lhe epithelium covering the margin of the gill-plates is thickened and special- ised ; that covering the ventral margin 1s ciliated (fig. 16), so, too, is that covering the outer border of the plate (fig. 18). Specially long cilia are present near the outer margin in two bands, one on either side of the plate a short distance from the free margin (figs. 16 and 18); the cells bearing these cilia are particularly large, and are closely related to the supporting rods. Comparison with the Lamellibranch Gill.—tThe general structure and relation of the gill as seen in the zygobranchiate Diotocardia is highly suggestive of that 7 THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 225 met with in the more lowly Lamellibranchs, viz. the Proto- branchia (Mitsukuri!), Consequently one might naturally expect to find a similar resemblance in the finer structure of these two organs. In this, however, one is doomed to disap- pointment, for although at first sight there appears to be a great resemblance (cf. Mitsukuri, op. cit., pl. xxxiv, figs. 6 and 8, and my figs. 17 and 18), yet when we examine this more carefully we find that instead of a resemblance, there is in reality a very marked difference. Thus in Nucula the supporting rods lie along the ventral border of the gill-plates and meet along the ventral edge of the gill-septum, whereas in Pleurotomaria, as we have seen, the gill-skeleton is situated along the outer or dorso-lateral margin of the plates, and the connections between the adjacent rods take place at the dorsal attachment of the plates to the septum. Simi- larly, the modified ciliated epithelium, which is closely related to these rods, is dorso- lateral in the Gastropod, and ventral in the Lamellibranch. We thus see that there is a very strik- ing and fundamental difference in the relation of the gill- skeleton in the two groups, and one which must tend to throw back the common ancestor of the two to a still earlier period than that generally assigned to it. ‘The dorso-lateral position of the supporting rods is, how- ever, found in another great Molluscan order, the Cephalopoda. Thus in Sepia Burne ? has described cartilaginous rods, one to each guill-plate, strengthening the supporting lamella, in a position corresponding to the outer and dorsal margin of the gill-plate of Pleurotomaria. ‘This is an interesting point, for, as we shall see later, the Diotocardia appear to approach the Cephalopoda further in the relation of the spiral stomach- cecum. ‘I'he skeletal difference between the gills of the Diotocardia and the Protobranchia is, however, far more surprising than the resemblance of the former to the Cepha- lopoda, for, in addition to the general form and relation of 1 “On the Structure and Significance of some Aberrant Forms of Lamelli- branchiate Gills,” ‘ Quart. Journ. Mier. Sci.,’ vol. xxi, 1881. 2 “Proc. Mal. Soc.,’ vol. iii, p. 53. VOL. 44, PART 2,—NEW SERIES, P 226 ' + MARTIN F. WOODWARD. the gill, Nucula approaches the Diotocardia in so many other respects that one would naturally have expected a very close agreement on this point. In the face of the unexpected difference one feels some doubt as to the full value of generally accepted views on the relations of these forms. The Branchial Ganglia.—On the outer side of each oill and close to its anterior point of attachment is situated avery conspicuous hemispherical swelling (figs. 5, 6, and 7, bn. g.). These protuberances, which were described by Dall as blood-sinuses, are caused by the presence of a large ganglion, situated on the branchial nerve. The branchial ganglia are the most conspicuous ganglionic swellings on the nervous system. In section (fig. 19) they exhibit a great accumulation of nerve-cells, arranged in two layers round the periphery of the ganglion, a narrower outer and a broader inner layer, the two being separated by a very narrow band of fibrous tissue. The centre of the ganglion is occupied by a great mass of fibrous tissue, the bundles of which run in various directions. Near the periphery of the central mass are some curious dim bodies, which at first sight suggest large ganglionic cells; but the entire absence of nuclei and the want of sharpness of outline lead me to conclude that they are in reality bundles of fibre, rather more closely packed than usual. A very large nerve is given off from the ganglion to the gill, and from this is derived that very conspicuous layer of nerves (fig. 15, ». J.) following the course of the efferent branchial vessel. The Osphradium.—Dall has figured a small hemispheri- cal structure, situated somewhat nearer the middle line than is the branchial ganglion (blood-sinus of Dall), which he thinks may represent the osphradium. His description of the position of this organ is, however, not very clear; and a comparison of his figure (op. cit., pl. xxx, fig. 2) with my fig. 6 suggests that the gill he represents is the right gill seen from below, in which case his osphradium would in reality be situated externally to the branchial ganglion, its THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 927 more median position being only an apparent one due to the displacement of the mantle in the dissection. However this may be, I have utterly failed to find any such structure, either internally or externally to the branchial ganglion ; and if I am correct in my identification of the osphradium I cannot help doubting the osphradial nature of the structure to which Dall assigns this significance in P. Adansoniana. While examining a series of transverse sections through the free end of the gill I noticed a thickened patch of epithe- lium situated on the ventral or external border of the gill, and extending from near the point of attachment to the free end (figs. 5—7, os.). An examination of these sections shows that this thickened patch of epithelium overlies the great branchial nerve, and receives numerous branches from it. The epithelium itself has all the character of a sensory one, consisting as it does of delicate fusiform cells supported by more columnar ones, and also exhibiting a few pigment cells. Although a few gland cells are to be seen they are much less numerous here than in the adjacent epithelium. At times there is even a suggestion of the bunching together of these cells into oval masses, not unlike the taste bulbs of the Vertebrata and the sensory organs of Acavus Waltoni, as described by the Sarasins. The identity of this strip of sensory epithelium with the osphradium is confirmed by a comparison with the latter organ, as seen in Haliotis. In this genus the osphradium, as described by Spengel, has precisely the same relationship and form as the strip of sensory epithelium found in Pleuro- tomaria Beyrichii, which last we may, I think, safely identify as the osphradium. At the posterior end of each gill the afferent and effer- ent branchial vessels may be seen (figs. 5 and 7, a. b. and e. b.). The former, springing from a sinus (figs. 7 and 23, v. s.) situated ventrally to the rectum and ureter, run forward near the former structure and diverge outward to the gills; while the latter, passing on either side of the mantle-cavity, converge on the heart. As we have already seen, the afferent 228 MARTIN F. WOODWARD. vessel lies near the free margin of the gill-septum, while the efferent vessel is situated at its base. The Hypobranchial Mucous Glands.—One of the most striking features in the mantle-cavity is a large oval glandular structure, which, occupying a median position, extends from the posterior limit of the mantle-sht along the roof of the mantle-cavity to about the level of the posterior end of the right gill (figs. 5, 6, and 7, m. g.). In one specimen this gland still retained a pinkish colora- tion. This gland is partially divided by a median longitudinal furrow into two halves, each of which is marked by a number of more or less interrupted grooves which converge on the median one. ‘The whole structure presents an appearance not unlike the venation of a leaf. Anteriorly, however, the two halves of the gland slightly separate from one another, and end in a couple of pointed structures, in which Dall thought he could perceive openings which he took to be the renal apertures. In this supposition he was mistaken, for the renal organs have a perfectly normal position, and the gland, as may be seen from a microscopic examination, is a true mucous gland: further, if we examine Haliotis we shall find a gland, the hypobranchial mucous gland, occu- pying a precisely similar position; and I think there can be no question as to the homology of these two structures and of the similarly named gland of the Monotocardia. Two additional mucous glands are found in the roof of the mantle-cavity behind the large hypobranchial gland (figs. 5 and 7, mg’. and mg’’.) ; these are situated one at the base of each gill, that on the left being much the largest, a further example of the asymmetry which we have already seen fore- shadowed in the gills, and which affects the whole pallial complex. The rectum is situated somewhat to the right side, and extends forward over the hypobranchial gland in a variable manner (cf. figs. 5 and 7); but in neither of my specimens does it extend so far forward as in the P. Adansoniana figured by Dall. THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 229 The Kidneys.—As in the majority of the Diotocardia, there are two kidneys, a right and a left one, which exhibit very different structure and perform different functions. The left kidney or papillary sac is situated in the left-hand upper corner of the mantle-cavity. In form it is somewhat oval, and it opens by a wide slit-like aperture into the mantle- cavity near the rectum (figs. 7, 23, and 26, J. k.a.).. On cutting open this sac it is found to have a large central cavity bounded by thick walls, whose epithelium is thickened and forms numerous rounded papille ; the outer wall is, moreover, folded. As in Trochus and Haliotis, this left kidney alone communicates with the pericardium, the reno-peri- cardial pore taking the form of a long canal, which runs along the floor of the papillary sac and opens into it near its external aperture by a ciliated slit (figs. 24—26, 1. p.c.). The structure of this kidney and the relation of the reno- pericardial pore closely resemble that seen in Trochus, the only difference being that in the latter the reno-pericardial canal is distinctly shorter, about half as long, but otherwise it has the same relation. Unlike the condition seen in Patella (Goodrich!), it is the aperture leading into the kidney which is ciliated in Trochus, and not that leading into the pericardium. A microscopic investigation of the papillary sac shows that this organ is highly vascular, but I have been unable to ascertain whence this blood-supply is derived. According to Perrier? the vascular system of the left kidney of the Dioto- cardia is directly connected with the auricle or auricles, is, we may fairly assume, a similar condition for Pleurotomaria. The folds and papille which project into the central cavity are invariably supplied with conspicuous blood-lacune, which break up into a rich capillary system ; this lies embedded in a connective-tissue framework containing large quantities of * “On the Reno-pericardial Canals in Patella,” ‘Quart. Journ. Micro. Sci.,’ vol. xli, 1899. 9 2 « Recherches sur l’Anatomie et PHistologie du rein des Gastéropodes prosobranches,” ‘ Ann. Sci. Nat.,’ (7) Zool., tom. vili, 1889. 230 MARTIN F. WOODWARD. leucocytes. The whole papilla is covered by an epithelium whose cells are somewhat conical; the free expanded bases of these cells are crowded with yellowish granules, which, since they are also seen in some of the leucocytes, are probably waste matter taken up by phagocytes in different parts of the body, and carried to the papillary sac to be discharged. The right kidney is very large and complicated, and probably forms the more important excretory organ, beside serving to transmit the genital products. ‘This kidney opens into the mantle-cavity through a glandular tube, which, from a situation to the right of, has now come to lie almost ven- trally to the rectum. This thick-walled glandular tube passes behind into a thin-walled funnel-shaped structure, which may be termed the ureter (w.), but is really the commence- ment of the kidney-chamber (k. c.) ; this passes back beneath the pericardium, and enlarges behind this structure to form a wide chamber with thick walls, the posterior portion of the right kidney (p. 7. k.). The walls of this chamber project into the cavity in the form of a series of deep semilunar folds, covered with glandular epithelium and richly supplied by a plexus of blood-vessels containing venous blood. This, however, only forms a part of the right kidney, a very large portion running forward below the floor of the mantle-cavity between the crop and the intestine as far forward as the point where the brown tint stops, and marked a.r. k., fig. 7. We may speak of this portion as the anterior lobe of the right kidney (figs. 23, 25, and 26, a.7.k.) ; its cavity communicates with the kidney-chamber near the anterior boundary of the pericardium. Like the posterior lobe it is richly supplied with venous blood, since it receives all the blood coming from the anterior part of the body and from the foot on its way to the gills. The right kidney has thus a very complicated form, and one that will be best understood by an examination of the diagrams given in figs. 25 and 26. The Genital Organs.—Of the three specimens examined two were females and the third a male. The genital gland, which presents a similar appearance in both sexes, forms as THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 231 in other Prosobranchia a fairly thick investment to the dorsal surface of the liver (fig. 7, g. g.), extending to the top of the spire. The origin of the efferent duct from the gland was not to be made out owing to the upper part of the body being slightly damaged in removal from the shell, but I think there can be no doukt that the genital products are shed into a series of thin-walled remnants of the true ccelom, which in turn unite to form the somewhat thickened duct (g.d.) shown in figs. 23—26. This duct, which is present in both sexes, runs on the inner side of the spire, and communicates by a slit-like opening (g.a.) with that portion of the right kidney-chamber which we termed the ureter (w.). The conclusion that this is the genital duct is supported by a comparison with Trochus, where the undoubted genital duct has precisely the same relationships. In the male this constitutes the whole of the genital system, there being no accessory organs, the genital products passing out directly through the unmodified right ureter. In the female, however, the distal portion of the ureter which serves to transmit both the excretory and genital products becomes much modified, owing to the enormous development of glan- dular tissue in its walls; the latter become so much thickened that it is by no means easy to tind the lumen of this tube, which may now be called the oviduct (ov. d.). The presence of this modified oviduct places Pleuroto- maria about on the level with the T'rochide, and indicates a somewhat more specialised condition than that met with in many Diotocardia, for in these latter the genital products are discharged into the mantle-cavity through the unmodified right kidney duct,—in some cases, it is thought, without the intervention even of the simple genital] duct seen above. The Alimentary Canal.—The mouth communicates with a thick-walled buccal cavity situated in the free portion of the head. This buccal mass, which is slightly constricted by the nerve-ring, is closely attached to the body-wall by nu- merous short radiating muscle-fibres (figs. 6, 7, and 8), which 232 MARTIN F. WOODWARD. are, however, less developed posteriorly where the salivary gland (fig. 8, sl. g.) occupies the roof of this structure. On opening the buccal cavity a couple of laterally placed folds, covered with horny matter, will be seen (fig. 9,7.). These folds, which undoubtedly correspond to the jaws of other Gastropods, are but feebly developed in Pleuroto- maria, and probably serve, as Dall suggested, to protect the soft wall of the buccal cavity from the scraping action of the radula. The structure of one of these is shown in fig. 54. In front of the horny jaws a number of small flattened papille, also covered with horny matter, are to be seen (fig. 9, k. ».). Between and behind the jaws the ventrally placed odontophore may be seen bearing the chitinous radula (rd.), the functional portion of which when at rest appears some- what V-shaped when viewed from above, and thus only covers the central portion of the odontophore, the sides of which are covered by the lateral extension of the radular membrane. Thus the whole of the buccai cavity is more or less protected by a lining of chitin. The Salivary Glands form a compact mass in the roof of the alimentary canal, at the junction of the buccal mass and the crop (figs. 6—8, s.g.); their ducts (sl.d.), which are closely related to the buccal nerves, run forward within the thickness of the wall of the buccal mass, and open into the buccal cavity just above the odontophore (fig. 10). The gland, which is a much branched one (fig. 8), was not well enough preserved to enable me to study its histology. The odontophore is enormously developed, being highly muscular, and further strengthened by the odontophoral car- tilages. When at rest it forms a comparatively slight projec- tion into the buccal cavity, but, on the other hand, it projects as a great muscular mass into the hemoceele (fig. 7, od.). Between it and the crop the enormous radular sac (r. s.) will be seen extending back for two or more inches, and becoming involved in the anterior lobe of the right kidney. ~The Musculature of the Buccal Mass.—As in other Odontophora, the muscles of the buccal mass can be divided THER ANATOMY OF PLEUROTOMARIA BEYRICHII. 283 into the extrinsic and the intrinsic muscles; the former being concerned more in the movement of the mass as a whole, while the latter are specially related to the movements of the odontophore. Extrinsic Muscles.—Curiously enough, these seem to be mainly protractor muscles, the retractors being but feebly developed. (1) The lateral protractors. Three laterally placed vertical sheets of muscle arising from the side wall of the head, and inserted towards the posterior end of the buccal mass (fig. 30 A, J. pr.). (2) The ventral protractors. A large paired muscle arising from the region of the jower lip, and inserted upon the basal cartilages (fig. 380 H, v. pr.). (3) The lateral retractors (? divaricators of the carti- lages). Five or six small strands of muscles arising from the side wall of the head, and inserted upon the main odonto- phoral cartilage just below the edge of the radular membrane (figs. 9 and 380 A, l.r.). (4) The ventral retractors (?). A pair of short longi- tudinal sheets of muscle arising from the body-wall just above the pleuro-pedal cords, and inserted upon the radular sac as 1t emerges from the odontophoral mass (figs. 29 and on) TAS 7.) (5) The depressor muscle (figs. 30 Band D,d.m.). A small muscle inserted upon the main cartilage, just in front of the insertion of No. 3, and passing down to the ventral side of the head. I have called Nos. 3 and 4 retractors because when the buccal mass is protruded their fibres would be on a stretch, but I think that this is probably only part of their function. Thus if the right and left portion of No. 3 contracted to- gether they would separate the main odontophoral cartilages, and No. 4 may also function to prevent too great a displace- ment of the growing part of the radula. Intrinsic Muscles.—These, again, fall under two heads: those concerned in the movements of the radula itself by 234 MARTIN F. WOODWARD. acting directly upon it, or upon the infra-radular membrane ; and those concerned in the movements of the odontophoral cartilages. On examination of the odontophore from the side, after removal of the extrinsic muscles, three muscles will be seen (fig. 30 B). One of these (d.J.m.) runs from the outer edge of the infra-radular membrane to the upper border of the main odontophoral cartilage, the fibres being arranged some- what obliquely to the length of the cartilage. This muscle must by its contraction serve to flatten, 7.e. expand, the radula, and at the same time slightly pulls it back over the odontophoral cartilages. It is the largest and most powerful of the intrinsic muscles, and may be termed the dorsal or postero-dorsal longitudinal muscle. Three muscles are an- tagonistic to this; one of these (v.l.m.) is a small ventro- lateral band attached in front to the antero-ventral edge of the infra-radular membrane, and behind to the accessory basal odontophoral cartilage. This muscle, which we may term the ventral or antero- ventral longitudinal muscle, serves to pull the radula over the odontophoral cartilage, and also to flatten the anterior part of the radula. The second of these muscles is not seen in this dissection, since it lies on the inner side of the main cartilage ; it is, however, shown in the median, the ventral and dorsal aspects (fig. 30 H, #, G,2.1.m.). This muscle is attached to the under side of the radula and to the infra-radular membrane, where it underlies the middle functional part of the radula, its insertion forming an oblique line, starting near the median ventral line, and passing up- wards and outward until it ends on the edge of the basal - membrane of the radula; posteriorly this muscle is attached behind to the accessory basal cartilage. The contraction of this muscle causes the radula to assume once more its V-shaped grooved character, and in addition it acts as a powerful retractor. It may be termed the internal longi- tudinal muscle. The third muscle is a very small one (fig. 30 D, x.) attached to the infra-radular membrane laterally, and running forwards it is inserted up the anterior portion THE ANATOMY OF PLEUROTOMARIA BUEYRICHIL. 250 of the odontophoral cartilage; it pulls the radula forwards and inwards. The remaining muscles only act indirectly upon the radula through the movements of the odontophoral cartilages. One of these lies at the side of the main cartilage, to which it is attached by a long fleshy insertion (fig. 30 C, l.l.m.) ; it then runs back as a flat muscular band, and takes its origin from the outer border of the basal cartilage. ‘The contracture of this pair of muscles causes the anterior ends of two main cartilages to diverge, and so tends to flatten the anterior part of the radula. The second of these two muscles is situated ventrally, and is the only unpaired muscle in the buccal mass ; it consists of a transverse band of fibres running from the outer border of one main cartilage to the corre- sponding surface of the other, and thus by its contraction approximates the cartilages (fig. 30 G and H, v. t.m.). The odontophoral cartilages are four in number. Of these two are very large and laterally compressed, constituting the main cartilages which support the radula. The remaining two are the small basal plates presenting concave surfaces for articulation with the former. In spite of the small size of the basal plates, they appear to be the relatively fixed points for insertion of the majority of the muscles of the buccal mass. The radula itself will be considered later. Owing to the complicated nature of the movements of the radula we commonly find that the muscles of the odontophore are similarly complicated. Unfortunately it is not easy to ascertain with any degree of precision the exact nature of the movements produced by the contraction of a given muscle, and consequently it is inadvisable in the present state of our knowledge to give them very precise names. It is interesting to find that the arrangement of the odonto- phoral muscles of Pleurotomaria compares very closely with that described as occurring in Patella by Geddes.! 1 Qn the Mechanism of the Odoutophore of certain Mollusca,” ‘Trans. Zool. Soc.,’ vol. x, 1879. 236 MARTIN F. WOODWARD. Thus we find in both forms similarly placed lateral and ventral protractors among the extrinsic muscles, while among the intrinsic the dorsal, ventral longitudinal muscles connected with the infra-radular membrane are similar, as also is the transverse ventral muscle. The remaining muscles, however, differ, as, moreover, do the cartilages, since there are three pairs of cartilages in Patella and only two pairs in Pleurotomaria. The Crop.—As in most Diotocardia, the first portion of the cesophagus is much dilated and saccular, and may be thus spokenof asacrop. Itis closely connected with the body-wall by fine bundles of muscle-fibres, making the removal of the latter very difficult, and giving the crop a villous appearance. Its internal structure also is very characteristic, its walls, as in Haliotis, being thickly covered by numerous papille (figs. 9 and 10). ‘hese papille are, however, wanting in front where the crop and buccal cavity join; and in the morphological dorsal and ventral middle line. The epithelium covering these papille is highly glandular, and the centre of each papilla is a blood-lacuna. The presence of the papille thus causes an increase of the secretory epithelium. Situated immediately behind the odontophore is a somewhat oval thickening. At a little distance from this structure we find on either side a slit-like depression (fig. 10, Ip. lp'.), which we may term the lateral cesophageal pouch. Hach of these depressions is bounded by a couple of folds (lettered in fic. 10, 1 and 2 on the left side, and 3 and 4 on the right). Tracing these structures back, we find that by their enlarge- ment and rotation they cause the crop to assume a very complicated form. ‘Thus the two ventral folds 2 and 3, enclosing between them the ventral median area, pass first to the right side and then gradually ascend until they assume a dorsal position; this causes a corresponding displacement of the two dorsal folds (1 and 4), which pass down the left side until they attain a ventral position. At the same time the lateral pouches become enlarged, and undergo a corresponding displacement; thus the original left pouch (/p.) now constitutes THE ANATOMY OF PLEUROTOMARIA BEYRICHII. Day, the ventral and right half of the crop, while the right pouch (lp 1.), which is somewhat smaller, forms the dorsal and left portion of the same. The non-papillate median dorsal and ventral areas remain small, and are practically reversed in position. ‘he position of these folds and pouches is shown in figs. 10 and 11, the latter being a diagrammatic transverse section of the crop, from which it will be seen that the enlargement of the crop is practically confined to the lateral pouches. Tracing the crop still further back it is found to gradually diminish in size and complication, until it assumes the form of a simple tube with rather thick walls, which we may speak of as the cesophagus (fig. 7, 0. e.). The Stomach.—The cesophagus extends back a little behind the heart, and then suddenly debouches into the stomach, which, as a large U-shaped cavity, lies below and behind the right kidney (figs. 7 and 12, st.). The cavity of the stomach is large and divided by a marked constriction into a right and left portion, the former receiving the cesophagus, while the latter receives the bile-duct (6. d.), and gives origin to the intestine and the spiral cecum (sp. c.). The cesophageal aperture is very narrow and guarded by a sphincter, while the intestinal orifice is large (fig. 12). ‘The bile-duct (b. d.) opens by a wide slit situated immediately to the left of the semilunar fold which grows in from the floor of the stomach and separates the two chambers. The spiral czecum (sp. c.) opens on the dorsal wall imme- diately above the bile-duct, but the structure which may be described as the columella of the spiral czecum is prolonged down to the floor of the stomach, and forms the anterior lip of the constriction between the two stomach-chambers. The ceecum itself forms a perfect helicoid spiral situated dorsally, and overlying the two halves of the stomach. A spiral stomach-cecum is a very characteristic feature of those Diotocardia possessed of a spiral shell, being specially well marked in Trochus (fig. 18), Turbo, and Phasianella; it is also developed in Haliotis, and in a very much modified JOS MARTIN F. WOODWARD. form in Scutum and Fissurella. Traces of this organ are also found in that primitive teenioglossan, Nassopsis. The almost universal occurrence of this organ in the Dioto- cardia suggests that it is a structure of great antiquity and functional importance, although we are unable to ascribe any special physiological function to it. This caecum is in most cases connected with the postero- dorsal wall of the stomach (postero-ventral in Phasianella), and its lips are invariably related to the opening of the bile- duct. Regarding the stomach as a U-shaped structure composed of an cesophageal and an intestinal chamber, the czecum invariably arises close to the junction of the two, but essentially belonging to the intestinal chamber, and is closely associated with the bile-ducts. This structure has no homology with the crystalline style sac of other Gastropoda or of the Lamellibranchia ; the two struc- tures are undoubtedly co-existent in Nassopsis (Moore }), and possibly in some Diotocardia. It is, however, extremely suggestive of the spiral czecum present in the Cephalopoda, which, like the ceecum described above, is a postero-dorsal outgrowth from the stomach, closely related to the bile-ducts and to the point of origin of the intestine. An attempt to homologise the spiral czecum found in two such distinct orders of Mollusca as the Gastropoda and the Cephalopoda may at first sight seem unjustifiable, but the rela- tions of the two organs to the alimentary canal are so precisely alike that one cannot help being struck with their similitude. It is, moreover, generally accepted that the Cephalopoda and Gastropoda are descended from a common ancestor, so that presence in the two groups of a spiral stomach-cecum is not so surprising, and would only suggest that this struc- ture was present in that ancestral form. Unfortunately we know nothing of the connecting type, which is not astonishing when we remember that both the Cephalopoda and the Dioto- cardia extend back to the Cambrian epoch. The only group 1 «The Molluses of the Great African Lakes. IV. Nassopsis and Bytho- ceras,” ‘Quart. Journ, Micro, Sci.,’ vol, xlii, 1899, THE ANATOMY OF PLEUROTOMARIA BEYRICHIT. 239 which is sometimes regarded as representing the primitive molluscan stock, viz. the Amphineura, does not exhibit this organ; but, on the other hand, they do not extend back so far in time, the earliest. chiton being only found in the Ordovician ; and further, the components of this group, while retaining many primitive features, are obviously specialised along a particular line, so that I do not think the absence of this spiral caecum in the Amphineura can be regarded as disprov- ing the homology of the two ceca seen respectively in the Cephalopoda and Diotocardia. From a consideration, therefore, of the similar structural relations of the spiral czecum in these two groups, I conclude that the two structures are homologous. The intestine (figs. 7 and 12, int.) is very simple. It runs forward until within about half an inch of the salivary glands, and then forming a U-shaped bend, it passes back towards the stomach, whence it curves dorsally, perforating the pericardium and the ventricle, and bending once more on itself, it enters the mantle-cavity, to the roof of which it is attached, at first slightly to the right of the middle line, but gradually assuming a more median position (figs. 5 and 7,7.). It is attached below the hypobranchial gland, and opens into the mantle-cavity by the anal orifice situated some considerable distance from the posterior limit of the mantle-slit, and there- fore very differently from the condition observed by Dall in P. Adansoniana. The Vascular System.—The heart, which is enclosed in a spacious pericardium (figs. 7 and 23—26), is that of a typical Zygobranch, consisting of a muscular ventricle (v.) surrounding the rectum, and a pair of thin-walled auricles (1. aw. and 7. au.), which receive the blood from the long efferent branchial vessels. A common aorta springs from the posterior portion of the ventricle, and soon divides into an anterior and a posterior artery ; the former (figs. 6, 7, and 28, a. a.) is distributed to the anterior and ventral parts of the body, while the latter supplies the stomach, liver, and genital gland, 24.0 MARTIN F. WOODWARD. a The venous system takes the form of series of more or less well-marked canals and sinuses, which are specially conspicu- ous in the region of the right kidney. The blood from the foot and anterior parts of the body is apparently collected into a series of channels, which run in close connection with the excretory epithelium of the anterior lobe of the kidney, while that from the liver and stomach passes through the posterior lobe. These various renal veins eventually open into a large sinus situated ventrally to the ureter, genital duct, pericardium, and rectum (figs. 7 and 23, v. s.), from which the afferent branchial vessels arise. The body-cavity of the adult is very inconspicuous, owing to the great development of the crop with its radiating muscle-fibres. This cavity represents part of the venous system, and is of the nature of a hzmoccele. The true ccelom is only represented in the pericardial, renal, and genital cavities. The Nervous System.—An examination of fig. 27 will show at a glance that the nervous system of P. Beyrichii presents all the essential features of that of a typical Dioto- cardian, this being especially noticeable in the practical absence of distinct ganglia; for although on the removal of the dense connective-tissue sheath a certain amount of orange colour is noticeable in the cerebral and pedal centres, thus indicating an accumulation of nerve-cells, yet an examination of a series of sections through these regions and the inter- vening connectives shows (fig. 22) that while the nerve-cells are more abundant in these coloured areas, yet they are not confined to these regions, but are distributed, though in smaller numbers, throughout the whole length of the connec- tives, commissures, and even many of the nerves. The orange-coloured areas where the nerve-cells are more abun- dant correspond with the cerebral centres (cb. g.), the points of origin of the visceral loop (pl. ¢.), and the anterior portion of the pleuro-pedal cords. ‘This distribution of the nerve- cells along the connectives makes it extremely difficult to localise the individual ganglia, and forces us to rely rather upon the points of origin of certain nerves than upon the THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 241 definite accumulation of nerve-cells met with in other Proso- branchs. Fischer and Bouvier seem to have been misled, either by this coloration or by the slight swelling of the cords in certain of these regions, into the belief of the existence of definite ganglionic areas, and they indicate such regions by means of dots in their figures; they appear to have over- looked the presence of nerve-cells along the connectives, and the still more important, though shght, accumulation and coloration at the point of origin of the visceral nerve. The Cerebral Ganglia.—The circum-cesophageal nerve- ring 1s much enlarged on either side of the anterior part of the buccal cavity, and since the tentacular and certain other nerves which are characteristic of the cerebral ganglion of other Prosobranchs arise from this region, we may. regard it as representing that ganglion. The cerebral ganglia are, then, a pair of elongate band-lke structures widening out below ; they are connected together above the buccal mass by a slightly narrow region (cb. c.), which represents the cerebral commissure of more specialised forms, but which here is indistinguishable from the ganglia themselves, since both in its size and in the number of its ganghonie cells it passes imperceptibly into the laterally placed ganglionic areas. The cerebral ganglia give origin to five pairs of nerves supplying the lips (figs. 21, 22, and 29), and to a pair of laterally placed tentacular nerves (¢. 1.), from which in turn the optic nerve arises. Arising with the most ventral of these labial nerves is a broad nerve which runs downwards and below the buccal mass (figs. 21 and 29); this nerve gives off a sixth lip-nerve, and is then continued ven- trally to the mouth and close to the lips, to meet and fuse with a similar nerve from the opposite side of the body, thus constituting the labial commissure (J. c.) so characteristic of the Diotocardia and archi-Teenioglossa. Yet another nerve arises from the ventral continuation of the cerebral ganglion, but in order to see this properly the mesial aspect of the ganglion must be examined. Such a VOL. 44, parr 2.—NEW SERIKS. Q 94.2 MARTIN F. WOODWARD. view (fig. 21) shows a nerve arising just between the fourth and fifth lip-nerves; this nerve, the buccal nerve (b. n.), curves sharply up over the muscular odontophore, giving off branches on its course. After ascending for some distance it bends sharply back and becomes greatly enlarged, and may now be spoken of as the buccal ganglion (figs. 8 and 29, b.g.). This ganglion is a curiously elongate structure, and gives off branches anteriorly and ventrally ; while the main mass is continued back under the radular sac, where it unites with its fellow from the opposite side (fig. 27). A very con- spicuous branch arises from the middle of the dorsal border of the ganglion, which curving upwards and backwards runsalong the salivary duct and supplies the salivary gland (figs. 8and 29). From the posterior border of the cerebral ganglia two very large cords arise, these represent the cerebro-pleural and cerebro-pedal connectives ; of these the former and more posterior cord is as usual much the larger. As with the other parts of the nervous system, ganglionic cells are scattered along the length of these cords, more especially at the periphery, and more abundantly in the cerebro-pleural ‘than in the cerebro-pedal connective (fig. 22). The cerebro-pedal connective passes back, taking at first a somewhat horizontal position, but eventually curving down- ward to join the great scalariform pleuro-pedal cords. It is closely followed by the cerebro-pleural connective, and the two become reunited near the posterior border of the great odontophoral muscular mass. The combined pleuro-pedal mass then enters the foot, where it becomes connected by a transverse commissure with the corresponding structure from the opposite side (figs. 21 and 27). This transverse commissure contains elements derived from both the pleural and pedal systems (fig. 21). The Pleuro-pedal Cords.—Although the pleural and pedal cords are now closely connected, they can still be dis- tinguished from one another by the presence of a groove which runs along the whole length of the combined pleuro- pedal cord (figs. 28 and 29). THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 243 This separation is probably only an external one, since sections through the cords fail to reveal any continuous layer of connective tissue separating the two, and bundles of nerve-fibres apparently pass from the ventral to‘the dorsal moieties of the cord, and vice versa. The right an left pleuro-pedal cords now diverge slightly from one another and run back within the substance of the foot, each cord lying in a slight blood-sinus situated below and on either side of the main pedal sinus. The cords extend to the posterior extremity of the foot, and are furthest apart near the middle of the foot ; toward the posterior end they become somewhat approximated (fig. 27). These cords, along which ganglionic cells are fairly evenly distributed, are, as we have seen, equally derived from the pedal and pleural systems: in width each cord at its anterior extremity is but very slightly if at all larger than the cerebro-pleural and cerebro-pedal connectives when closely approximated, i.e. there is no marked swelling indicative of a great accumulation of ganglionic cells (fig. 22).. In fact, there is but a slight increase in number of these cells in - this region, and that mainly in the ventral or pedal portion. It becomes then very difficult if not impossible to speak of a’ pedal, and, as I shall endeavour to show later, inadvisable to attempt to identify a pleural ganglion in this pleuro-pedal cord. These ganglionic pleuro-pedal cords are connected at inter- vals by transverse commissures: the first of these, as already mentioned, is derived from both the pleural and pedal moieties ; but the posterior ones, of which there are at least twelve, at first sight would be considered as derived ex- clusively from the pedal portion of the cord. An examina- tion of sections, however, reveals the fact that a bundle of nerve-fibres comes down from the dorsal portion of the pleuro-pedal cords and enters the commissure, which is there- fore derived equally from both portions of the cord. The laterally placed. pedal nerves arise like the above from both portions of the cord. ‘The double root of these nerves is often very conspicuous (fig. 21, p?.); somewhat resembling 244. MARTIN F. WOODWARD. the dorsal and ventral roots of a vertebrate spinal nerve. In addition to these large latero-ventral nerves there are present certain small nerves, which apparently arise from the pleural portion of the cord and pass to the dorsal pedal muscles. When, however, we remember that the distinction between these two portions of the cord is practically only an external one we shall probably be right in concluding that all the nerves derived from these cords are connected with both subdivisions. In connection with the apparent separation of the pleuro- pedal cords into two distinct portions by means of a longi- tudinal groove it is interesting to note that Haller! had already come to the conclusion that this grooee has no mor- phological significance; thus he found in other Rhipidoglossa, as | have found in Pleurotomaria, that transverse sections of this cord failed to reveal any line of separation between the pleural and pedal portions of nerve tracts running from one into the other. Visceral Commissure.—As suggested by Bouvier and Fischer from the study of an imperfect specimen, Pleuro- tomaria exhibits a typical streptoneurous condition in its visceral loop (figs. 6, 27, and 28); but at the same time this mollusc is most peculiar among the Diotocardia in the point of origin of its visceral nerves. If the cerebro-pleural connective on either side of the body be examined, it will be seen that between its origin from the cerebral ganglion and its fusion with the pedal system it gives rise to a very large nerve, whose relations at once identify it with the visceral nerve, that on the right side being the supra- and that on the left the sub-intestinal nerve. As already mentioned, the points of origin of these nerves appear, after the removal of the thick nerve-sheath, shghtly orange-coloured, owing to the presence of a considerable number of nerve-cells which are continued, though in smaller numbers, from this point up to the branchial ganglion. The 1 « Untersuchungen tiber marine Rhipidoglossen. II. Textus des Central- nervensystem und seiner Hillen,’”’ ‘ Morph. Jahrb.,’ Bd. xi, 1886. THE ANATOMY OF PLEUROTOMARIA BEYRICHII. Q45 origin of the visceral nerves alone would suggest that we were here dealing with the pleural centres—a view which is greatly strengthened by the presence of an accumulation of nerve-cells, and to which we shall refer again. The right half of the visceral loop arises fairly close to the cerebral ganglion, whereas the left half originates very much closer to the pedal ganglion (cf. figs. 21, 22, and 27), thus producing a marked asymmetry. The supra-intestinal nerve passes over the alimentary canal immediately behind the salivary gland (figs. 6, 10, and 29), whereas the subintestinal passes below the crop and radular sac. Both of these nerves perforate the muscular body-wall, and come to lie in the mantle close to its junction with the former (figs. 6 and 28). Hach nerve then bifurcates, one portion running back parallel with the gill to complete the visceral loop by uniting with its fellow in a blood-sinus just below the right kidney duct (figs. 23 and 27), while the other portion runs out and gives rise to the immense bran- chial ganglion, which forms a large round swelling close to the point of attachment of the gill, which it innervates. There is no distinct abdominal ganglion such as was surmised by Fischer and Bouvier. In addition to the great visceral nerves a number of smaller nerves arise from the pleural connectives, the presence of which strengthens the view that the pleural ganglia are not yet condensed in Pleurotomaria, and that this mollusc is a fairly primitive one, for in most other Gastropods there is a tendency for these nerves supplying the muscles of the side wall of the head and posterior parts of the mantle to take the form of one large nerve arising in fairly close connection with the pleural ganglion. So far as I can ascertain about four moderately conspicuous nerves arise from the two cerebro-pleural connectives to be distributed to the side walls of the head (fig. 21). From the connective behind the origin of the visceral loop, to which I apply the term pleuro-pedal connective, and before it fuses with the cerebro-pedal connective, there arise two 2.46 MARTIN F. WOODWARD. fairly large nerves (figs. 21, 22, 28, 29); one of these runs forwards between the cerebro-pleural and cerebro-pedal con- nectives (fig. 22) to the muscles of the side of the neck, while the other runs up to the body-wall above the crop to the floor of the mantle cavity; this last may be Bouvier and Fischer’s pallial nerve, although it does not arise at the same spot. I do not feel at all certain about the identity of these nerves, since I have not been able to trace any of them to the free mantle-fold, and consequently am not inclined to call any of them pallial nerves. Still less am I satisfied concern- ing the presence of the primary pallial nerves of these authors, and I take it that they rather assume that such nerves must be present. An examination of their fig. C, op. cit., p. 170, will show two large nerves arising from the upper part of the pleuro-pedal cords, the anterior of these corre- sponding with the nerve marked with an asterisk in my figs. 21 and 22; the nerve runs up parallel to my pleuro-pedal connective, branching repeatedly, and is eventually lost in the muscle of this portion of the body: it is possible that some of its finer fibres may penetrate into the mantle. With regard to the second, which they represent as co-extensive with the pleuro-pedal cords, I can only say that it does not exist in P. Beyrichii. Behind the last-mentioned nerve a series of four small nerves are seen to arise from the pleural portion of the pleuro-pedal cords, between the point of origin of the first and second pedal nerves (figs. 21 and 22, p.1 and .2). These nerves, which are distributed to the muscles on the dorsal surface of the foot where the latter joins the body, —i.e. to the commencement of the columella muscle (fig. 28) —are the only nerves which occur in the region corre- sponding to that whence Bouvier and Fischer’s great hypo- thetical pallial nerve springs; they are, however, quite small, and I have not been able to trace them beyond the columella muscle. Since I cannot think that there is hkely to be any great difference between the different species of Pleuroto- maria in this respect, I can only conclude that the great primary pallial nerve of Bouvier and Fischer does not exist THE ANATOMY OF PLEUROTOMARIA BEYRICHII. Q47 in Pleurotomaria. Even in Trochus I think they greatly overrate the size and importance of this nerve, which so far as I can find is a small nerve distributed to the posterior portion of the mantle, and probably to the secretory epithe- lium of that region. A few small nerves arise from the cerebro-pedal commis- sure, these being distributed to the muscles between the under lip and the foot. The Sense-organs.—The eyes and osphradia having been already described, it only remains to draw attention to the otocysts. These latter take the form of a pair of large vesicles, situated just above and in front of the pleuro- pedal cords (fig. 27). The actual otocyst is not very large, but it 1s surrounded by a very tough, thick, concentric ar- ranged sheath of connective tissue (fig. 31 4). The otoconia are small and numerous; typically they are spherical bodies, varying much in size and often fusing together to form reniform structures (fig. 31 B). The Radula (figs. 32—52).—The radula of Pleuroto maria Beyrichii is extremely complex, and exhibits the same type as that described for P. Adansoniana by Dall, and P. Quoyana by Fischer and Bouvier. In the nuraber and character of its teeth it more closely approximates to the latter species—a fact which strongly supports the view ad- vanced by Crosse in 1882, from the study of the shells, that these two species should be grouped together as a section or sub-genus of Pleurotomaria, for which group P. Fischer proposed the name Perotrochus. The radula is very large, one example measuring 62 mm. long by 5mm. wide. The greater portion of the radula is of course not functional, but lies buried in the radular sac, which extends up to the anterior lobe of the right kidney. In fig. 32 I have given a view of half a transverse row, which, as mentioned by Fischer and Bouvier, does not run straight across the radula, but has a somewhat V-shaped course. The number of teeth in a transverse row is 228; one of 248 MARTIN F. WOODWARD. these being unpaired occupies the centre of the row, and on either side of this are situated 111 teeth. So far as I can see from the examination of many rows this number is quite con- stant. ‘The lateral teeth exhibit a number of different types, at least five, which, however, merge imperceptibly into one another. For convenience’ sake we may, however, follow Fischer and Bouvier, and divide them into the following groups:—(1) The central teeth, (2) the lamellate teeth, (3) the hooked teeth or uncini, (4) the brush or tufted teeth, (5) flabelliform teeth. The Rhachian or Unpaired Tooth.—This tooth (figs. 32 and 33) hasa very curious form. Viewed from above (fig. 32), it appears to consist of a somewhat pointed oval or lanceolate lamella, which overlaps the adjacent central teeth. When, however, the rhachian tooth is isolated and viewed from the side (fig. 33), 1t is seen that this more or less horizontally placed lamella is attached to a longitudinally placed vertical plate, the posterior half of which is thickened, and forms the base of attachment of the tooth to the basal membrane. The tooth thus consists of two pieces—a flat horizontal lamella, and a vertical plate strengthening and attaching the former to the radular membrane. The Central Pairs.—On either side of the rhachian are situated three large teeth (fig. 32), which, while asymmetrical in form, nevertheless approximate somewhat in structure to the symmetrical rhachian tooth, forming a gradation between this tooth and the more laterally placed lamellate teeth. It is very difficult, if not impossible, to draw a lne between these central pairs and the lamellate teeth, and we only separate them for the convenience of description. In the central teeth (figs. 34—86) the vertical plate has greatly increased in size, while the horizontal lamella, so characteristic of the rhachidian, is much reduced, and only present on the outer side of the vertical plate near the base of attachment ; it still, however, overlaps the tooth immediately external to it (fig. 32). The portion corresponding to the vertical plate of the rhachian is now no longer placed vertically, but has become THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 249 inclined to the basal membrane, and its anterior extremity is much widened. The form of these teeth may be best under- stood by an examination of figs. 32—36. The Lamellate Teeth.—lIt will be seen from figs. 32 and 36 that the central teeth are not sharply marked off from the more laterally placed lamellate teeth, but pass imperceptibly into them. Thus, owing to its size, the first lamellate tooth might be almost equally well classified with the central teeth. There are twenty-one teeth which may be grouped under this head. Though varying in size, they are, on the whole, the smallest teeth in the radula, and present very uniform characters. ‘The free end of each of these teeth is abruptly truncated, and the upper border is generally straight, while the under margin is either convex or angulated, and the base of attachment is small (figs. 32, and 37 A, B,C, D). The lamellate teeth are far more complicated than would appear at first sight, so much so that it is very difficult indeed to gain any idea of their form from a written description. I have therefore thought it better to give several drawings of one of these teeth in different positions (see ne ora, B.C, D), and to these I must refer the reader who desires to obtain an idea of the form of these very characteristic teeth. The first five or six of these teeth presenta slightly concave free border, and thus approach the central pairs, which they further resemble in the greater development of the outwardly flexed free margin, which evidently represents the last trace of the overlapping lamella of the central teeth. As we pass outward the lamellate teeth increase in size, and thus approximate to the hooked teeth (figs. 52 and 38). The Hooked Teeth or Uncini.—The gradation between the lamellate and the hooked teeth is completed by the twenty-fifth tooth (fig. 88), which, though only slightly larger than the preceding tooth, approximates in form to the more lateral hooked teeth. It will be seen to present a double curvature in its free margin, and a slightly hooked free extremity. The twenty- -sixth tooth (fig. 39) is much larger 250 MARTIN F. WOODWARD. than the above, and shows a well-marked hook at its extremity, and a small cusp a little below this; this cusp is still visible on the twenty-seventh (fig. 40) but completely disappears on the succeeding teeth, which have the form of long massive hooks (figs. 41 and 42), and constitute the largest teeth on the radula. After the thirtieth, the teeth, while still remaining long, become much slighter (fig. 42), and soon (about the thirty-seventh) begin to show signs of the development of two additional cusps (fig. 43), which attain their full development on the forty-ninth tooth (fig. 44). The teeth have now the form of long delicate sickles, the free end of which exhibits two deep notches. The last one or two hooked teeth are somewhat shorter than the earlier ones, and thus lead to the distinctly shorter brush teeth. I have somewhat arbitrarily drawn the line separating the hooked and the brush teeth between the forty-first and forty- second tooth, thus making seventeen hooked teeth. The Brush Teeth.—The forty-second tooth at first sight does not appear to differ materially from the forty-first, but a more careful examination shows that it possesses on either side on a level with the lowest cusp two minute bristles (fig. 45). On the next tooth these bristles are longer, and one or two more are appearing (fig. 45); and if we examine the feature as we pass outward in the row of teeth (figs. 47— 52) we find that the bristles steadily increase in number and length, until by the forty-ninth tooth they form a consider- able brush reaching to the free end of the tooth. Thus it will be seen that it is impossible to separate the forty-second tooth from the true brush teeth; and although it is more closely approximate in general appearance to the hooked teeth, yet, in the presence of the two minute hairs on either side, it already shows the essential feature of the brush teeth. The brush teeth are sixty-three in number, and they form the most characteristic feature of the radula of Pleuroto- maria. A tooth taken from the middle of this series (fig. 50) shows THRE ANATOMY OF PLEUROTOMARIA BEYRICHII. 251 a decided reduction in the length of the hooked portion of the tooth, the three cusps being now somewhat closely crowded near the free end of the tooth. The tuft of bristles now appears to be inserted lower down on a ridge placed transversely to the axis of the tooth, and the bristles them- selves, forming a compact brush, extend considerably beyond the free end of the tooth (figs. 50—52). With the reduction of the hooked portion of the tooth the two sets of bristles meet behind, and now form a horseshoe-shaped brush embracing the end of the tooth. Passing outward the teeth become still more delicate, and the cusps smaller and smaller, until they completely disappear. Traces of the cusp-bearing lobe are, however, still distinctly visible on the 101st tooth, although it is now only a narrow slightly notched process. ‘The same structure, but still smaller and devoid of notches, may be seen on the 102nd and 103rd teeth, and I think on all the remaining teeth, in the form of a slight process on upper border of the teeth. As the upper tooth-bearing lobe becomes reduced, the two sets of bristles run together and form a single clump, and gradually approach the free upper border of the tooth. This latter condition is accelerated by the development on 101st— 104th of a lamina springing from the back of the tooth, and foreshadowing the flabelliform tooth (fig. 53). The bristles remain well developed after the disappearance of the cusps, and even the 103rd tooth possesses a good brush. The 104th, however, shows a marked reduction in its bristles, and this is the last of the brush teeth, since the 105th tooth is entirely devoid of these structures. In other respects the difference between these two teeth is slight, their general form being very similar. The Flabelliform Teeth.—There are seven of these teeth (the 105th to the 111th inclusive), which have the form of delicate narrow lamelle, arranged like the rays of a fan; they all bear a slight notch at their free end, corresponding to the point of attachment of the bristles in the brush teeth, and possibly representing the tooth-bearing lobe, 252 MARTIN F. WOODWARD. The Radula as a Whole—If we recognise the five divisions described above, we may express the arrangement and number of teeth on the radula by the following numerals : 7, 68, 17, 20,3; R. 3, 20, 17, 63, 7; there beme,as we have seen, a single rhachian, 3 central pairs, 20 lamellate, 17 hooked, 63 brush, and 7 flabelliform teeth. One of the most noticeable features in this radula, how- ever, is the great difficulty which its teeth offer to our attempts to arrange them in groups, this being due to the presence of intermediate forms between each two adjacent groups of teeth, thus causing them to merge into one ano- ther, and making it almost impossible to draw any sharp line between them. Nevertheless there are a number of very marked types of teeth in this radula, notably the lamellate, the hooked, the brush, and the flabelliform teeth; of these the lamellate and the brush teeth are very striking and peculiar, and not apparently met with in any other mollusc. It is somewhat difficult to understand the function of the lamellate and brush teeth, especially the former, and in order to do so we require to know more about the habits and the nature of the food of Pleurotomaria, An examination of the contents of the stomach of two specimens revealed a large quantity of sponge spicules, both megascleres and micro- scleres, belonging to one of the Halichondrina (? a species of Amphilectus). From the fact that many of these spicules appeared to be bound together by tissue, I conclude that Pleurotomaria feeds on the living sponge. For this pur- pose the hooked teeth would be useful in tearing away great pieces of the sponge, and the brush teeth might at the same time rasp away some of the flesh from the spicules ; but one is still at a loss to understand the action of the lamellate teeth. Another peculiar feature in this radula is the presence of what Bouvier and Fischer term the accessory basal plates. These structures take the form of little chitinous plates, somewhat of the same shape as the basal plates of the teeth themselves, which are attached to the radular mem- THE ANATOMY OF PLEUROTOMARIA BEYRICHII. Daye brane. These accessory plates, of which there are about thirty-seven on each side of the middle line in each row of teeth, are situated about in the middle of each half-row of teeth, commencing with the twenty-seventh and extending out as far as about the sixty-fourth tooth. They appear to alternate with the true bases of the teeth in front, whereas posteriorly they underlie them. ‘The row represented in fig. 32 would underlie the next posterior row of teeth. Comparison with the Radula of P. Quoyana and P. Adansoniana. The radulze of the three species of Pleurotomaria, of which the animals have been examined, stand apart from those of all other Diotocardia in the absence of that sharp division into regions which is so characteristic of the ma- jority of this group. They are further to be distinguished by the character of their central teeth, and in the possession of brush teeth. Of the two species, P. Quoyana much more nearly ap- proaches P. Beyrichii in the character of its radula than does P. Adansoniana. ‘The radula of the former, accord- ing to Bouvier and Fischer, may be expressed as follows :-— R. 8, 24, 13, 63, 6, there being 109 teeth on either side of the rhachian. Except in the number of the teeth in the different groups there is very little difference indeed between the two species, the resemblance being so close that one might almost match the individual teeth in the two radule ; thus the rhachi- dian, the central pairs, and the lamellate are very similar, the only difference being in the greater number of lamellate teeth (twenty-four) in P. Quoyana. The thirtieth tooth of the latter species forms an exact match with the twenty- sixth of P. Beyrichii, and the fiftieth with the forty-third. This close resemblance between the raduleze of these two species is strong argument in favour of the retention of these two forms in a sub-section of the genus Pleuroto- maria (section Perotrochus, Fischer). Since P. Bey- 254, MARTIN F. WOODWARD. richii so ciosely resembles P. Quoyana in its radula, it differs equally with the latter species from P. Adanso- niana, the radula of which, according to Dall, shows a rhachian, 15 laterals, 6 tufted uncini, 4 denticulate uncini, and 45 simple uncini, or 69 teeth on either side of the rhachian. An examination of his figure would lead us to interpret the teeth somewhat differently, but since the num- bering of the teeth in the plate and account given in the text are at variance a detailed comparison becomes difficult. It is obvious, however, that this form differs considerably in its radula from the section Perotrochus, and thus justifies Fischer’s creation of the section Entemnotrochus. A comparison of the Pleurotomarian radula with that of other Diotocardia is almost impossible, for while the former is a typical rhipidoglossate radula, yet it 1s so peculiar that we can find no other living form which at all approximates to it. This is, perhaps, not so surprising when we consider the great antiquity of this form, on which account we might expect that Pleurotomaria would show either a very primitive type, or if, on the other hand, the radula had undergone much change, that it would show a very spe- cialised one. When we attempt to decide the question as to the primi- tive or specialised nature of this radula, we are at once at fault, for we have not one particle of evidence to show us what the nature of the pro-rhipidoglossate radula was. All the evidence we possess tells us that the Diotocardia are un- doubtedly the most primitive of living Prosobranchia, and that they all possess the highly developed rhipidoglossate type of radula. Of the early Diotocardia, Pleurotomaria is the only form of which we have any knowledge, all the other living zygobranchiate Diotocardia being comparatively modern forms, and this genus also shows us a rhipidoglos- sate radula. It is true that the radula of Pleurotomaria differs from that of all other Diotocardia in the absence of those sharply marked regions which are so characteristic of the majority of the rhipidoglossate radule. The question THE ANATOMY OF PLEUROTOMARIA BHYRICHII. 255 then arises as to whether, taking into consideration the anti- quity of Pleurotomaria, we are justified in regarding this feature as a primitive one. Considerable stress has been laid by Troschel, Moore, and others upon the breaking up of the rhipidoglossate radula into zones, three on either side of the rhachian tooth, and on the occasional replacement of the great group of marginal laterals by one large tooth, which, however, generally re- tains sufficient traces of the individuals which it replaces to suggest that it represents a fusion of teeth, a view which is supported when we find that this takes place in undoubtedly specialised forms (notably in Addisonia and Cocculina among the Rhipidoglossa, and certain Cyclophoride among the archi-Teenioglossa). Such a condition has led some to suppose that the tooth arrangement met with in the Tenio- glossa might be derived from the Rhipidoglossate radula by a fusion of the elements of the three zones, thus giving a formula of 1.1.1.1.1.1.1, a view which the condition of the archi-Teenioglossate Cyclophoride seems to support. If, then, this subdivision of the row of teeth into sharply marked zones is a foreshadowing or a tendency in the direc- tion of the condition met with in the Tznioglossa, it seems only natural to conclude that this in turn was derived from a radula in which all the teeth in a transverse row were sunilar. Such a stage has not been preserved to us, but in Pleurotomaria we have an approximation to this condition, inasmuch as all the various specialised tooth areas merge imperceptibly into one another, and this in my opinion is a very primitive character. I therefore conclude that, in spite of its very specialised brush teeth, the radula of Pleurotomaria exhibits the most primitive type among all existing Gastropods. Considerations regarding the Primitive Nature of Pleurotomaria.—lIf we are justified in concluding, as I have done above, that in its radula Pleurotomaria is a most primitive form, then we might naturally expect to find indications of this primitive character in other of its organs. 956 MARTIN F. WOODWARD. We have already in dealing with the different organs suggested that certain of them presented primitive characters, —for example, the eye, the spiral cecum in the stomach, and still more notably the characters of the nervous system. The morphology of the nervous system has already been dealt with at length by Bouvier and Fischer, especially with reference to the relation of the pleuro-pedal cords to the origin of the visceral connectives from the conditions seen in Chiton. Personally, however, Ido not think Pleurotomaria throws any fresh light on this branch of inquiry. ‘This, nevertheless, does not rob the nervous system of the mollusc of all interest, for, as we have already seen, in the very uniform distribution of the nerve-cells through the connec- tives and commissures, and the consequent practical absence of distinct gangha, we have retained in Pleurotomaria, no matter what view we take of the origin of the molluscan nervous system, a very primitive feature. The second point of interest, which taken in connection with the above yields to no other feature in the anatomy of Pleurotomaria in its importance, concerns the position of the pleural centres. In the Gastropoda the pleural ganglia may be defined as the accumulations of nerve-cells related to both the cerebral and pedal ganglia, and giving origin to the visceral connectives, these being the only constant features presented by the pleural centres. In position the pleural centres may vary from one close to the cerebral ganglia, as exemplified by the majority of the Monotocardia, to one close to the pedals as in Haliotis-and Trochus, but in each case the visceral nerves arise direct from these ganglia. In Pleurotomaria, however, these nerves arise as we have seen from the connective joining the cerebral with the pleuro-pedal cords, so that if Bouvier and Fischer are correct in their localisation of the pleural centres at the anterior end and on the upper surface of the pleuro-pedal cords, we should have the very peculiar and absolutely unique condition of the visceral nerve arising from the cerebro- pleural connective quite independent of the pleural centre ; THE ANATOMY OF PLEUROTOMARIA BEYRICHII. ra but, as I have pointed out above, although there is a certain amount of concentration of nerve-cells in this region, yet it is mainly in the ventral half of the pleuro-pedal cords, i. e. in the region of the pedal ganglion. Moreover, while the nerve- cells are distributed along the whole pleural connective, yet they are distinctly concentrated to a small extent round the origin of the visceral nerve sufficient to give it a slightly orange colour, an appearance which distinctly suggests the localisation of the pleural centre at this point, a condition which would be in harmony with what we find in many other Gastropoda. From these considerations I am forced to the conclusion that the pleural ganglion, such as figured by Fischer and Bouvier, does not exist, and that a distinct pleural ganglion has not yet evolved in Pleurotomaria. Never- theless we can distinguish a pleural centre in the point of origin of the visceral nerves, and it is here that a pleural ganglion would form by an aggregation of nerve-cells, sup- posing a form were to arise from Pleurotomaria possessed of distinct ganglia. The above conclusion is of great importance in considering the phylogeny of the Tenioglossa, for with the exception of Cyclophorus and Ampullaria—two very aberrant archi- Teenioglossa, all the remaining members of the great tzenio- elossate group exhibit a condition in which the pleural ganglia are more nearly approximated to the cerebral ganglia than to the pleuro-pedal cords. The connection of these forms with the typical nervous system of the Diotocardia has been sought in the Cyclophoride and in the Trochide, but a careful consideration of both these well-known types of nervous system will show that they are both specialised along a different line from that characteristic of the Tenio- olossa, by a tendency of the pleural ganglion to mount up the visceral nerve (see Bouvier and Fischer’s diagram, figs. p and gE). On the other hand, in Paludina, the form which, so far as its nervous system is concerned, appears to me to be the only true archi-tenioglossan, the pleural ganglion giving origin to the visceral nerve is little more than a swelling VOL, 44, PART 2,—NEW SERIES, R 258 ; MARTIN F. WOODWARD. along the course of the posterior connective joining the cere- bral to the pleuro-pedal cords. This condition is practically the. same as that seen in Pleurotomaria if we imagine a crowding together of the ganglionic cells at the point of origin of the visceral_nerve, and is the natural outcome of that tendency towards a shortening of the nerve-tracts and concentration of the nerve-cells into ganglia which is so characteristic of the Gastropoda. From the condition seen in Paludina it would be very easy to derive, by a shortening of the cerebro-pleural con- nective, the condition of all other Teenioglossa, with the possible exception of the Cyclophoride and Ampullaria, which are probably special and independent derivatives of more specialised Diotocardia. From the above consideration I conclude that Pleuro- tomaria in its nervous system, as in some other points in its anatomy, is the most primitive of existing Diotocardia, and presents a condition from which that of the majority of the Tzenioglossa may be derived,—possibly also that of the other Diotocardia, the form in the latter being attained by a shortening of the pleuro-pedal connective, thus causing the pleural centres to be approximate to the pedal ganglia; thus the condition seen in Haliotis, Trochus, Fissurella, and Patella would be a derived and not a primitive one. While it is fairly easy to derive the Monotocardian type of nervous system, radula, gill, and reproductive system from the corresponding organs of existing Diotocardia, yet in the conformation of the kidneys we meet one of the greatest stumblingblocks in our attempt to derive the former group from the latter. All the Diotocardia with the exception of the aberrant Neritinoid group possess two kidneys, and in the majority these two organs differ markedly in structure and function.! 1 In Fissurella and Patella, both of which, however, are specialised forms, the two kidneys, though differing in size and relationship, are both excretory in function; but the left kidney, as in other Diotocardia, derives its blood-supply from the auricles. . THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 259 The left characteristically forms the papillary sac, and alone (save in Patella) communicates with the pericardium: this organ is not truly excretory, but serves as a reserve organ, and only removes foreign matter by phagocytosis ; thus if in- soluble powder-like carmine be injected into the body it is removed by phagocytes which discharge through the papil- lary sac (Pelseneer!). This left kidney has also a peculiar and characteristic blood-supply, being directly connected with the auricle or auricles (Perrier, op. cit.), and thus receives arterial blood. The right kidney, on the other hand, is very large, and characteristically situated between the pericardium and stomach, being also at times extended below the former into the anterior part of the hemoccele. This kidney, which receives the venous blood on its way to the gills, is the true excretory organ, since it alone removes the soluble waste products. The right kidney further serves to transmit the genital products, its duct being frequently modified and olandular in this connection. In the adult Monotocardian a single kidney alone is present. The position occupied by this gland is somewhat intermediate between that of the two seen in the Diotocardia, being placed in the majority between the pericardium and stomach. It opens normally (where no secondary ureter is developed) by a slit-like orifice between the rectum and gill near the posterior limit of the mantle-cavity, much as does the left kidney of the Diotocardia, and it further resembles that organ in the fact that its cavity communicates with the peri- cardium ; but at the same time it is a true kidney, and func- tions like the right kidney of the Diotocardia. Closely pressed between this organ and the pericardium is a glandular mass, often spoken of as the renal gland; the last organ has the peculiar blood-supply found in the papillary sac of the Diotocardia, which it further resembles in function (Perrier). We see, then, that the kidneys of these two great sub- 1 “ Tes reins, les glandes genitales, et leurs conduits dans les Mollusques,” ‘Zool. Anz.,’ Bd. xix, 1896, 260) MARTIN F. WOODWARD. divisions of the Streptoneura are very differently developed, and it is consequently not surprising that a considerable diversity of opinion has been expressed concerning the homology of the single kidney of the Monotocardia. A consideration of the position of the orifice of this organ in the Monotocardia and its possession of a reno-pericardial pore at once suggests a comparison with the left kidney or papillary sac; but on the other hand in the position of the gland itself, in the nature of its activity, and in the actual presence of the peculiar renal gland, it more nearly approxi- mates to the corresponding right organ of the Diotocardia. Ray Lankester appears to have been the first to seriously attempt to seek for the homology of the single kidney of the Monotocardia in the left kidney of the Diotocardia, and this view, which is now practically universally accepted, has been further supported by the embryological works of v. Erlanger on Paludina,! and on comparative grounds by Pelseneer. Practically the only opponents of this view in recent years have been Haller? and Perrier. The first view, which is based mainly upon the considera- tion of the relation of the kidney to the rectum and the pre- sence of a reno-pericardial pore, receives additional support from v. Hrlanger’s ontogenetic observations. An examina- tion of these latter shows them to be much less satisfactory than one would gather from the account given in the average text-book, since the only trace of the supposed missing kidney, the adult right, is an angulation and faintest indi- cation of an outgrowth from the pericardium (ccelom) on the opposite side to that at which the functional kidney is deve- loping. This vestigial structure disappears very speedily without ever attaining any characters which would stamp it as a kidney, so that the support afforded to this theory by v. Hrlanger’s ontogenetic researches is very meagre. A similar unsatisfactory condition is attached to his surmise— 1 «< Zur Entwicklung von Paludina vivipara,” ‘ Morph. Jahrb.,’ Bd. xvii, 1891. 2 «* Beitrage zur Kenntniss der Niere der Prosobranchia,” ‘ Morph. Jahrb.,’ Bd. xi, 1886. THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 261 for it is no more—that the genital duct of Paludina arises from the right secondary ureter, a structure which is not known to be present in any living mollusc, and whose existence we have no reason to presuppose. If, however, we may rely upon these ontogenetic researches, then the single kidney of the adult Monotocardia would be the left kidney or papillary sac of the Diotocardia, a view which is supported by the presence of a reno-pericardial pore. Against this view we have the position of the kidney in relation to the stomach and pericardium in the majority of the Monotocardia (Paludina being an exception), and the necessity, if we accept it, to seek our ancestral Monoto- cardian in some very archaic Diotocardian, one in which the left kidney has not attained the specialised character of a papillary sac.1. Moreover the acceptance of this view does not explain the presence of the peculiar renal gland in the Monotocardia, which has much the character of, and which possesses the peculiar vascular relation of the papillary sac. Perrier, who made a very exhaustive investigation on the molluscan kidney, believes that the single kidney of the Monocardia contains representatives of both the kidneys of the Diotocardia, and he sees in the renal gland of the former group the representative of the papillary sac of the latter group. This view, which is an extremely suggestive one, has not met the consideration which it deserves, most zoo- logists apparently accepting Hrlanger’s statements on the development of these organs in Paludina as conclusively proving that the monotocardian kidney is the papillary sac. It is, however, possible to approach this subject from ano- ther standpoint, and to endeavour to reconstruct the stages which must have occurred in the displacement of the kidney following upon the disappearance of the right gill and the consequent displacement of the heart and pericardium, and 1 It might be thought that Fissurella or Patella among living Dioto- cardians presented us with the condition we want, but these forms are too obviously specialised in other respects to serve as the ancestors of the Mono- tocardia. 262 MARTIN F, WOODWARD. it appears to me if this view be carefully followed out that it is possible to derive the Monotocardia from such an existing Diotocardian as Pleurotomaria. If we examine the condition of these organs in one of the Azygobranchia we shall find that with the loss of the nght auricle and gill the pericardium becomes displaced to the left, and consequently the two kidneys approach one another very nearly, so much so that Haller thought he found a com- munication between the two. It appears, however, doubtful if such a connection was present in the forms he examined, but at the same time it seems extremely probable to me that such a condition was attained in the early Monotocardia, as the pericardium shifted further to the left to take up a posi- tion at the end of the left gill, and the two kidneys conse- quently came into close contact. Supposing a perforation to occur in the wall intervening between the two kidneys, a condition would be attained that would be of the greatest advantage to the mollusc, as it would enable it to discharge the secretion of the right kidney through the cavity of the left, while the old right kidney-duct would now serve to transmit the genital products unmixed with excreta. By a diminution in size of the glandular portion of the papillary sac, and a complete severance of the right kidney duct as a genital duct, we arrive at the condition of the Monotocardia, in which we find a kidney situated in the position of the right kidney, but whose cavity communicates with the pericardium, and whose aperture suggests that of the papillary sac; while packed in between this kidney and the pericardium is the degenerate glandular portion of the papillary sac forming the renal gland. I would thus regard with Perrier the single kidney of the Monotocardia as representing the excretory part of the right kidney of the Diotocardia plus the cavity, external aperture, and reno-pericardial pore of the papillary sac; while the glandular part of the latter structure persists as the renal . gland, and the duct of the right kidney becomes the genital duct. THE ANATOMY OF PLEUBOTOMARIA BEYRICHII. 2638 If these conclusions regarding the homology of the kidney of the Monotocardia have any truth in them, then it would be quite possible to derive the Monotocardia from a Dioto- cardian having the type of kidney seen in Pleurotomaria, Trochus, or Haliotis. As I have already pointed out, the nervous system of Pleurotomaria would serve as an excellent starting-point from which to derive that characteristic of the Tzenioglossa, better by far than that of Trochus, which in the character of its gills more nearly approaches the Monotocardia. ‘The general lowly character of Pleurotomaria, especially of its nervous system and radula, and slight reduction of the right gill, taken together with its great antiquity, justifies us, I think, in regarding it as a very primitive form, and one from which the great monotocardian group may very possibly have arisen, and possibly also some of the subdivisions of the Diotocardia. | The following is a brief summary of some of the conclu- sions at which I have arrived. SUMMARY. 1, Pleurotomaria is a typical example of a zygobran- chiate Diotocardian. 2. In the absence of sharply marked specialised regions in the radula Pleurotomaria Beyrichii and P. Quoyana are distinctly primitive among the Rhipidoglossa. 3. Inthe reduction of the right gill Pleurotomaria tends to approach the azygobranchiate Diotocardia. 4, In the uniform distribution of the ganglionic cells through the connectives, the commissure, and even the large nerves, and the consequent absence of distinct ganglia, Pleurotomaria is extremely primitive. 5. In the position of the point of origin of the visceral loop (roughly halfway between the cerebral and pedal regions) Pleurotomaria approaches the archi-tenioglossate Paludina and Nassopsis. 6. The pleural ganglion probably arises at the point of 264 MARTIN F. WOODWARD. origin of the visceral loop by a further concentration of the ganglionic cells. 7. There is no special concentration of the ganglonic cells just above the future pedal ganglion, such as Bouvier and Fischer identify as the pleural ganghon. ~ | 8. That in the position of the supporting skeleton of the gills and the possession of a spiral stomach-cecum Pleuro- tomaria shows signs of a common ancestry with the Cephalopoda. 9. That Perrier is correct in regarding the single kidney (including the renal gland) of the Monotocardia as represent- ing both the right and left kidney of the Diotocardia. 10. That Pleurotomaria may be regarded as a form very closely related to the stock from which the Monotocardia originated. July, 1900. DESCRIPTION OF PLATHS 13-16; [llustrating Mr. Martin F. Woodward’s paper on “The Anatomy of Pleurotomaria Beyrichiu, Hilg.” List of Reference Letters. a. a. Anterior aorta. a. 5. Afferent branchial vessel. a. p. Pedal artery, a.7.k. Anterior lobe of right kidney. 4. d. Bile-duct. 4. g. Buccal eanglion. 0d. x. Buccal nerve. 6. g. Branchial ganglion. cb. c. Cerebral commissure. cd. g. Cerebral ganglion. cd. p. Cerebro-pedal connective. cd. pl. Cerebro-pleural connective. cr. Crop. d.d. m. Dorsal longitudinal muscle. d. m. Depressor muscle. e. 4. Efferent branchial vessel. ep. Epipodium. g'5g' Right and left gills. g. a. Genital aperture. g. d. Genital duct. g. 7. Genital gland. 4. p. Horny buccal papilla. 7. 7. c. Interlaminar connections. i. 2. m. Internal longitudinal muscle. i¢. Intestine. 7. 7. m. Infra-radular membrane. j. Jaw. &. ¢. Kidney chamber (right). /. Liver. /. au. Left auricle. J. c. Labial commissure. 7. &. Left kidney (papillary sac). 7. &. a. Left renal aperiure. /. . m. Lateral longitudinal muscle, /. m, Longitu- THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 265 dinal muscle of gill-septum. 7. p., /. p.1 Lateral esophageal pouches. 7. pr. Lateral protractor. /. 7. Lateral retractor. #. Mouth. ma. Mantle. m.c. Mantle cavity. m.g. Mucous (hypobranchial) gland. . m.g!., m.g''. Accessory mucous glands. m, s. Mantle-slit. . /. Nerve-layer in gill-septum. od. Odoutophore. od. e’., od. c’. Odontophoral cartilages. @.Cisophagus. 0. 2. Optic nerve. op. /. Opercular lobe. os. Osphradium. of. ~. Otocyst nerve. ovd. Oviduct. p’., p!’. First and second pedal nerves. p.7. &. Posterior lobe of right kiduey. pe. Pericardium. pi. c. Pleural centre. p/. p. Pleuro-pedal connective. rd. Radula. r. Rectum. 7. av. Right auricle. 7. 4. a. Right kidney aperture. 7. 4. d. Right kidney duct. 7. p. c. Reno-pericardial canal. r,s Radular sac. s.7. Supporting rods. 8d. ix¢. Subintestinal nerve. — s/. d. Salivary duct. s/. g. Salivary gland. sp. a. Supra-neural artery. sp. ¢. Spiral cecum. sp. iv¢. Supra-intestinal nerve. s¢. Stomach. 7. ”. Tentacular nerve. w. Ureter (right kidney duct). v. Ventricle. v. 4. Vitreous body. v. 7. m. Ventral longitudinal muscle. v. pr. Ventral protractor. v. 7. Ventral retractor. v.s. Venous sinuses. v. ¢. m. Ventral transverse muscle. The figures, unless otherwise stated, are of the natural size. PLATE 13. Figs. 1—12. Pleurotomaria Beyrichii. Fre, 1.—Anterior part of the body viewed from the left side, showing the bifid left tentacle. Fic. 2.—Anterior part of the body viewed from above, to show dorsal surface of foot. This specimen had lost its operculum. Fic. 3.—Opercular lobe of normal specimen. Fie. 4.—Operculum. Fic. 5.—Dorsal wall of mantle cavity, with gills, mucous glands, and rectum ; viewed from below. Fic. 6.—Dissection of the anterior part of the body; mantle divided and reflected, floor of mantle cavity and dorsal surface of head removed, to show the relations of the anterior viscera. Fic. 7.—General dissection from the right side, showing the mutual relations of the alimentary canal, nervous system, heart, and pallial complex. The forward extension of the right kidney is indicated by a brown shade. Fie. 8.—Side view of the buccal mass, showing the salivary gland with its duct, the cerebral ganglia, and the buccal nerves. Enlarged. Fig. 9.—Dissection of the buccal cavity, showing the radula, jaws, and horny papille. Fie. 10.—Dissection of the buccal mass and crop: 1 and 2 the left, 3 and 4. the right cesophageal folds. Fie. 11.—Diagrammatic transverse section across the crop. 266 MARTIN F. WOODWARD. Fig. 12.—Dissection of the stomach with its spiral cecum, from above. Fig. 13.—Dissection of the stomach of Trochus zizyphinus, from above. Enlarged. PLATE 14. £. Beyrichir. Fre, 14.—Transverse section of the gill and branchial ganglion, showing the gill-plates in surface view. Somewhat diagrammatic. x about 12. Fie. 15.—Transverse section of the gill, showing the circulation of the blood in the gill-plates. Diagram constructed from sections. x about 13. Fie. 16.—Section across two gill-plates, taken along the line a 4, Vig. 14. x about 36. Fic. 17.—Section parallel to the last, but passing through the dorsal junction of the gill-plates with the septum. x 170. Fie. 18.—Horizontal section across the outer margin of a gill-plate. x 500. Fre. 19.—Section through the branchial ganglion at the origin of the branchial nerve. ‘The ganglion is slightly contracted away from the connec. tive tissue of the mantle. x 50. Fic. 20.—Section through the eye. x 60. Fie. 21.—Anterior portion of the nervous system from the left side of the body viewed from within, showing the cerebral ganglion and its connections with the pleuro-pedal cords, together with the origin of the subintestinal nerve and the principal nerves to the head and side-walls of the anterior part of the body. ‘The first transverse pedal commissure is seen to be formed from both the pleural and pedal cords, as also is the second pedal nerve. X 23. Vic. 22.—The corresponding portion of the nervous system from the right side of the body, viewed from without. Drawn from a dissection with the portion of the nerve-cells indicated diagrammatically from microtome sections. X 6. PLATE 15. Fic. 23.—Dissection of the kidneys and pericardium, showing the extent of the right kidney and its relation to the genital duct; also the great venous sinus. Fie. 24.—Dissection showing the relation of the left kidney to the peri cardium. Fie. 25.—Semi-diagrammatic representation of the two kidneys, the peri- cardium, reno-pericardial canal, and genital duct. Fic. 26.—Schematic representation of the same. THE ANATOMY OF PLEUROTOMARIA BEYRICHII. 267 Fic. 27.—Diagram of the nervous system viewed from above. Fie. 28.—Dissection of the head, foot, and mantle, showing the rejations of the nervous system on the right side of the body; also the anterior aorta and supra-neural and pedal artery. Fic. 29.—Enlarged view of the brain, cerebro-pleural, and cerebro-pedal connectives, and the relation of the nerves to the lips and buccal mass. Fie. 80,—A—H. Hight views of the musculature of the buccal mass. 4. Dorsal view. &. Side view, with the lateral protractor (2. pr.) reflected. C. Ditto, with the ventral longitudinal muscle (v. /. m.) reflected. D. Ditto, after the removal of the lateral longitudinal, the radula, and greater part of the infra-radular membrane (t.7.m.). #. Ditto, after the removal of the main odontophoral cartilage, exposing the internal longitudinal muscle (¢. 7. m.). F. Dorsal dissection, showing the cartilages on the left, and the muscles and infra-radular membrane on the right. G@. Viewed from below, showing the transverse muscle (v.é.m.). H. Diagrammatic transverse section. Fie. 31.—A. Entire otocysts. x 50. B. Isolated otoconia. x 400. PLATE 16. Fite, 32.—Half a transverse row of teeth, including the rhachidian. x 50. Fic. 83.—Rhachian tooth, side view. x 66. Fic. 34.—First central tooth, side view. x 66. Fig. 35.—Second central tooth, side view. x 66. Fie. 36.—Third central, with first and second lamellate tooth. x 66. Fie. 37.—Four views of a typical lamellate tooth, from the left side of the radula. 4. Viewed from the outer side. £&. Normal view. C. Edge on. D. Viewed from below. x 140. Fic. 38.—Twenty-fifth tooth. x 60. Fie. 389.—Twenty-sixth tooth. x 60. Fic. 40.—Twenty-seventh tooth. x 60. Fie. 41.—Thirtieth tooth. x 60. Fic. 42.—Thirty-fourth tooth. x 60. Fic. 43.—Thirty-seventh tooth. x 60. Fic. 44.—Thirty-ninth tooth. x 60. Fic. 45.—Forty-second tooth. x 120. Fie. 46.—Forty-third tooth. x 120. Fie. 47.—Forty-fourth tooth. x 120. Vie. 48.—Forty-seventh tooth. x 120. Fic. 49.—Forty-ninth tooth. x 120. Vie. 50.—Type of tooth between the fiftieth and the sixtieth. x 120. 268 MARTIN F. WOODWARD. Fie. 51.—Seventy-fourth tooth. x 120. Fie. 52.—Ninety-seventh tooth. x 120. Fic. 53.—Last four brush teeth and the seven flabelliform teeth, i. e. the 101st to the 111th tooth, from the left side.of the radula. x 120. Vic. 54.—Left jaw, from its inner side. x 9. i a ee re aa play | ow ia a @ eo oe f4 : os ro) oO — 4 ~~ uw a Si oO a LS, ondon xr thy Auli, 1 n Ad iu NSL Vot Ld, od. AS. Hut sae tere Luart. Fourn. Murr Seu. NS mm PS 1600 Eg x 4 furtin Woodward del. sein DCCCCCOOER eemnaucvnonN, ~ 1 & & Wy, CGR mM y, ea SH] | Ay iY 7 4 4 Rong 2 8 ~ Ss \ \ \ \ rT 106) \ hy) Hal Be cy * a , ¥ . *e i S — » -_ « * . aul 7 = a - 1 oo ire a i) -. s as ae, rine Tt) ee ee AS S Oy. n J uth, Lith if Seu Le. 44 NS F415 Rcicr ALO g | Martin Woodward del, Quart Sourn Mur Se, Ud £ LN SIV IE AR Lith-A S.Huth London. > an Se y. 6 > aes all - Aen os ee = r . i t ; q 7 1 e - ne i vA * \ ni DOLICHORHYNCHUS INDICUS, A NEW ACRANIATE. 269 Dolichorhynchus indicus, n. g., n. sp. A New Acraniate. By Arthur Willey. In the collection of Polycheeta made during the voyages of H.M.S. “Investigator,” in the Indian Ocean, under the direction of Dr. Alcock, there is a tube containing several specimens of an Amphioxus, which on inspection has proved to be the type of a new sub-genus of the genus Bran- chiostoma. Not one of the specimens appears to be in a condition of sexual maturity, in spite of the fact that the largest attains a length of 25°75 mm. The body is elongated, slender, late- rally compressed, and tapering gradually towards the posterior end, There are seventy-one myotomes, and the formula is 42—14—15. The feature which at once differentiates it from all other known forms of Amphioxus is the great length of the pre- oral lobe, close upon 2 mm. measured from the anterior termination of the neurochord, or equal in length to the first six myotomes (Fig. 1). The metapleural folds terminate sym- metrically some distance behind the atriopore on either side of the ventral fin, a fact which denotes the systematic posi- tion of the species in the absence of data afforded by the gonads (Fig. 2). There are about forty-five ventral fin cham- bers behind the termination of the metapleural folds, and four or five in front of this point.. In the specimen figured the tentacular cirri (buccal cirri) are mostly concealed within the vestibule of the mouth, but the ends of several are pro- jecting from beneath the oral hood in front. The dorsal fin is well marked, being about one fifth the 270 ARTHUR WILLEY. total height of the body. In the single specimen cut for the examination of the ventral fin rays they do not appear as paired structures, but as massive median expansions of the hyaline laminar tissue. It will be noticed that the modification which characterises this species, namely, the prolongation of the notochord and cephalic fin in front, is of an exactly opposite nature to that Ta Anterior region of D. indicus, comprising the oral hood and pre-oral lobe from the left side. The anterior end of the neurochord with the eye-spot projects in front of the first myotome. hies2: Region of the atriopore of D. indicus in ventral view, to show the symmetrical termination of the metapleural folds on either side of the ventral fin behind the V-shaped atriopore. which distinguishes Asymmetron, where the notochord and caudal fin extend far behind the posterior limit of the myotomes. Locality.—Off Black Pagoda, Orissa Coast ; 11 fathoms; - January 15th, 1889. DOLICHORHYNCHUS INDICUS, A NEW ACRANIATE. 271 The following tabulation of the genera and sub-genera of Amphioxus will serve to show the systematic position of the new form. Genus I.—Branchiostoma, Costa, 1834. With biserial gonads. Sub-genus 1.—Amphioxus, Yarrell, 1836. Type, A. lanceolatus (Pallas). Sub-genus 2.—Dolichorhynchus, n. g. Type, D. indicus, n. sp. Genus I].—Heteropleuron, Kirkaldy, 1895. With uniserial gonads. Sub-genus 1.—Paramphioxus, Haeckel, 1893 [in Semon’s ‘ Forschungsreise,’ Bd. i, p. xii]. Type, P. bassanus (Giinther). Sub-genus 2.—Hpigonichthys, W. Peters, 1876. Type, H. cultellus, Peters. Sub-genus 3.—Asymmetron, H. A. Andrews, 1893. Type, A. lucayanum, Andrews. Of the above sub-genera the three which are most peculiar in external form, namely, Dolichorhynchus, Hpigonich- thys, and Asymmetron, are monotypic if we consider Asymmetron caudatum, Willey, 1896, to be merely of subspecific rank, as would seem to be the case. HETEROPLEURON HECTORI, NEW ZEALAND LANCELET. 278 Heteropleuron hectori, the New Zealand Lancelet. By W. Blaxiand Benham, D.Sc., ¥I.A., F.Z.S8., Professor of Biology in the University of Otago. With Plate 17. By the kindness of Sir James Hector I have been able to examine a couple of specimens of an “ Amphioxus”’ that have been for some years past in the Colonial Museum at Wellington, N.Z. The specimens are referred to by Captain Hutton in his ‘Catalogue of the Fishes of New Zealand,’ published by the Colonial Museum and Geological Survey Department in 1872. On p. 88 of this catalogue, under the title of “ Bran- chiostoma lanceolatum,” a brief series of measurements are given, but- without any details to enable one to judge that they are different from the type of the family. At that period, and for some years later, indeed, even Dr. Giinther believed that the various specimens from extra-Huropean seas belonged to this same species, as is evident from the account of the lancelet in his ‘Study of Fishes’ (1880). Since Hutton’s reference to them they seem to have been entirely overlooked by recent writers, for no mention is made of any New Zealand representative of the family either by Andrews, by Willey, or by Kirkaldy, in their respective accounts of this animal. . This New Zealand Lancelet is the type of a new species of VoL, 44, pART 2,—NEW SERIES. S 274 W. BLAXLAND BENHAM. the genus Heteropleuron, for which I propose the name H. hector. ‘The specimens had apparently been preserved in osmic acid, for they are dark grey ; and though they had received various slight injuries to the side of the body and to the fins, they are in sufficiently good condition to enable me to make out all the important specific characters. One of the specimens | was permitted to open, doing as little damage to it as possible ; and afterwards I cleared it in oil of cloves for more detailed examination of certain parts. The extreme tips at both ends of the body in each specimen were more or less injured, but by comparing the two I have been able to reconstruct, with some confidence, these ends. The injury affects the tip of the caudal fin, and part of the rostral, which was folded round the side: in the case of the latter the outlines are in the drawings represented by dotted lines, as there is some doubt as to the exact form of the fin; while the general curvature of the upper and lower margins of the caudal fin, preceding the injury, suffices to show that probably the fin is naturally of the form shown in the drawing. Heteropleuron hectori, n.sp., has a length of about two . inches, the actual measurements being 48 mm. and 49 mm. respectively. The myotomes number 84 or 85, and the myotome formula is 53 + 19 (20) + 12,1.e. there are 53 myotomes from the anterior end to the hinder margin of the atriopore, 19 or 20 thence to the posterior margin of the anus, and the remaining 12 are post-anal. The last two or three are very small, and the usual difficulties in deciding as to the exact number of myotomes between atriopore and anus were en- countered. But from careful examination of the two speci- mens, I believe that the above formula (which, as Kirkaldy’s paper! shows, is subject to individual variation in all species) is correct. The dorsal fin is very shallow over the greater part of its ’ « Revision of the Branchiostomide,” ‘Quart. Journ. Micr. Sci.,’ xxxvii. HETEROPLEURON HECTORI, NEW ZEALAND LANCELET. 27 extent, though rather higher over its anterior quarter ; while shortly before the level of the atriopore it again gradually rises to form the caudal fin. ‘The fin rays cease at the level of the anus. The rostral fin—as I have remarked—is only indicated in the drawing with some hesitation ; but it appears to be rhomboidal in outline, rising suddenly from the dorsal. The ventral fin, or pre-anal region of the median fin, is short and low; it contains about a dozen unpaired fin-ray boxes, which are, however, without fin rays, as is the case, too, in H. cultellum. At first these boxes are quite distinct, but after twelve or fourteen complete ones the outlines become less and less distinct, and soon disappear altogether. The caudal fin rises quite gradually from the dorsal, at about the level of the atriopore, without any abrupt angle, such as is seen in H. bassanum and H. cingalense; but in this respect it resembles H. cultellum. Its lower moiety is, however, deeper than the upper, and rises rela- tively far forwards—about the seventh myotome behind the atriopore. It attains its greatest height at about the fourteenth post-atrioporal myotome, that is some distance anterior to the anus. Posteriorly the upper and lower margins slope gradually, and equally and regularly backwards, and appear to pass in the same curve to a point a short distance behind the notochord. On examining the transparent specimen I noted a series of short brownish chitinoid rods along the ventral base of the caudal fin, extending outwards from the lower ends of the muscles for a distance equal to about one fourth the depth of the fin (fig. 5). Hach rod spreads out slightly near its distal end, and becomes thinner and more transparent— losing itself in the tissue of the fin. These rods I traced backwards to the end of the body, whilst forwards there is a great gap between them and the ventral fin-ray boxes, the walls of which have quite a different aspect from the rods, which do not appear to be optical sections of transverse walls, but appear to be definite, solid, rod-like structures. 276 W. BLAXLAND BENHAM. Along the upper base of the caudal are also a few shorter and less distinct rod-like structures, but I do not feel sure that in this case they are not the transverse walls of empty fin-ray boxes ; the animal was lying in an awkward position, and though there was_a gap between the dorsal rod-like structures and the hindermost distinct fin-ray boxes, yet the higher surface of the body was here slightly injured and torn, so that it was not possible to trace the continuity of the two series. At first I imagined that we had in this species an interest- ing vestige of the peculiar caudal fin rays of the early larva, as figured in Lankester and Willey’s memoir! (pl. xxix, fig. 1). But on examining the tail of a’specimen of H. bassanum I found that it was unnecessary to explain the appearance in this temptingly interesting manner; for in H. bassanum I find that the fin rays of the ventral fin are continued past the anus along the under surface of the body to the antepenultimate myotome (fig. 6) : it is true they and their ‘ boxes” are smaller here than in the true ventral fin, anterior to the anus, but they are perfectly distinct right along the base of the caudal fin. These ventral rays extend further backwards than do the dorsal fin rays, which are here only represented by a series of empty boxes and irregular ‘“lymph-spaces ;’”’ in fact, the “rods” in H. hectori are the shallow transverse walls of the empty fin-ray boxes. ‘This post-anal extension of the fin rays does not appear to have been noted? in any other member of the group; and in A. lanceolatus Lankester states definitely that they cease in front of the anus, and [ have examined mounted specimens myself and can confirm this statement. In connection with H. bassanum I have to correct what appears to be an error in Kirkaldy’s diagnosis of this species, where it is stated (p. 314) that the ventral fin-ray 1 Lankester and Willey, ‘‘ Development of the Atrial Chamber in Amphi- oxus,” ‘Quart. Journ. Mier. Sci.,’ xxxi. 2 “Contributions to the Knowledge of A. lanceolatus,” ‘Quart. Journ. Mier. Sci.,’ xxix, p. 373. HETEROPLEURON HECTORI, NEW ZEALAND LANCELET., 277 chambers contain “ paired fin rays.” In specimens collected in Port Phillip, and presented to me by Prof. Dendy, I find, on the contrary, most definitely only a single series of fin rays in the ventral fin in this species. This continuity of the fin rays post-anally seems to show the probability that the “ventral fin” is a part of the ‘‘ median fin,’ as is suggested by Lankester and Willey (p. 456), in opposition to the earlier view by the former author that the ventral fin is the result of fusion of a paired structure (3, p.373). It becomes more evident that the double fin rays of A. lanceolatus are secondary, arising perhaps as a result of splitting of single rays. The pre-oral hood is much deeper on the right than on the left side, so that when viewed from the latter aspect both margins and their cirri are visible (fig. 2), and the vestibule opens distinctly on the left side of the animal. ‘This is even better seen in a ventral view (fig. 4), where the right hood is seen passing obliquely forwards to be continued into the ventral fin, while the left margin disappears from view as it curves dorsally upwards. In the drawings of Heteropleuron and Asymmetron given by Kirkaldy and Andrews! the vestibule and its opening are represented as being quite symmetrical. It is of interest that in this new species a condition is retained which isa distinct reminiscence of the larval state of affairs. Further, the cirri on the right side are somewhat shorter than those on the left. These cirri number nineteen on each side, with one median ventral, which is shorter than the lowest of the lateral series ; these commence as long filiform structures, and gradually diminish in length as the series approaches the dorsal termination. The gonads, present only on the right side, appear to be about eighteen in number, but as they dropped away from the body-wall as it was turned aside there may have been a few more. 1 «An Undescribed Acraniate—Assymmetron lucayanum,” ‘Stud, Biol. Lab, J. Hi. Univ.,’ v, 278 W. BLAXLAND BENHAM. It is scarcely necessary to state that the right metapleur is continuous with the ventral fin, as that is one of the characters of the genus. Locality.—EHast coast of the North Island of New Zealand.! From this brief but sufficient survey of the external characters of the New Zealand species, it will be seen that it differs from each of the previously known species of Hetero- pleuron. In form this new species seems, from the drawings avail- able, to be somewhat stouter than other species, while the tapering anteriorly is comparatively sudden (fig. 1). The greatest height, measured from the upper edge of the dorsal fin to the lower margin of the metapleure, is 5 mm., which is about one tenth of the total length. These measurements are, of course, liable to variation according to the condition of preservation ; my specimens, however, are not shrunk in the way that occurs when living specimens are plunged into strong alcohol, but have retained a form similar to that of A. lanceolatus preserved in picric acid, and though some- what soft are not in any way “rotten.” Therefore I think the form given in the plate, which is drawn to scale, is as nearly as possible true to life. It must be borne in mind, however, that the pre-oral hood is retracted, while in the most reliable drawing of Amphioxus, viz. that given by Pro- fessor Lankester, this hood hangs down as a nearly semi- circular membrane. The left metapleural ridge can be traced in my specimens right forwards above the hood, which has shrunk upwards below it (see fig. 2). The distance between the atriopore and the anus is one sixth of the total length, and the distance of the anus from the end of the body is one sixteenth of the total. In size it exceeds the largest, which is H. bassanum, 1 According to a verbal communication by Sir James Hector, these two specimens were collected at Awanui, just south of the East Cape; whilst Hutton in the ‘ Catalogue’ gives as the cay “Poverty Bay,” which is a little further south, HETEROPLEURON HECTORI, NEW ZEALAND LANCELET, 279 with a length of 43 mm.; in total number of myotomes, too, it exceeds any Amphioxid hitherto described—the nearest approach being seventy-nine in “ A. elongatum” of San- deval, and seventy-eight in H. bassanum. It is perhaps worth noting that this excess is chiefly due to an increase in the number of pre-atrioporal segments; for the post-anal segments in other species are from eight in H. cingalense to fourteen or even seventeen in H. bassanum, with an interporal number of ten to seventeen in the various species. In regard to the caudal fin, there is equally sufficient evi- dence of distinctness, for whereas in H. bassanum it com- mences behind the anus, in H. cingalense it arises immediately in front of it, and is very short; while in H. cultellum, though it begins at a point further forward, yet this point is some distance relatively behind its point of origin in H. hectori, while the position of the greatest depth is behind the anus in all three, instead of being ante- rior to it, as in the present species. The sea surrounding Australia and the neighbouring islands is evidently rich in species of Branchiostomide, for already four species belonging to each of the three known genera have been recorded,—viz. Amphioxus belcheri, Gray, from Torres Straits, as well as from the coast of Borneo; Heteropleuron cultellum, Peters, from Torres Straits and further east coast of Australia; Asymmetron caudatum, Willey, from the Louisiade Archipelago,! due east of the Torres Straits; and H. bassanum, Giinther, from the south of Australia, from Bass’s Straits. The present species thus makes the fifth in these southern seas ; its habitat is two thousand miles or more distant from each of these localities. These seas appear to be the home of the asymmetrical species, and one is tempted to think that these may be the more primitive of the family, especially as my species presents one, perhaps two survivals apparently of a larval condition. 1 ‘Quart. Journ. Mier. Sei.,’ vol. xxxix, p, 210, 280 W. BLAXLAND BENHAM. I regret that I have been unable to make a fuller exami- nation of this interesting species, and look forward to obtain- ing living specimens; but it appeared worth while to rescue these individuals from their obscurity when it was found that they differed from those of the neighbouring seas, DUNEDIN; August 25th, 1900. EXPLANATION (OR Praia: Illustrating Professor Blaxland Benham’s paper on “Heteropleuron hectori, the New Zealand Lancelet.” Fic. 1.—Heteropleuron hectori, n. sp. (x 2). a. Metapleur. 3. Floor of atrium. c. Atriopore. d. Anus. Fic. 2.—Heteropleuron hectori. Side view of the anterior end (xX 8). a. Left metapleur. J&. Floor of the atrium. e¢. Right metapleur. The outline of the rostral fin is dotted, as there is some doubt, as to its true shape and size. Fic. 3.—Hinder end of the same (X 8). a@. Left metapleur. 4. Atriopore. e. Ventral fin. d. Anus. Fig. 4.—Ventral view of the anterior end of the same, showing the vesti- bule opening distinctly on the left side of the animal. @. Left metapleur. 4. Floor of atrium. c¢. Right metapleur. d. Ventral fin. Fie. 5.—A portion of the ventral base of the caudal fin of a transparent specimen, seen under a low power. a. Muscles. 4. Fin. ec. Rod-like structures, the walls of empty fin-ray boxes. Fie. 6.—View of the tail of H. bassanum, cleared in clove oil, showing the post-anal continuation of the ventral finrays. The myotome marked 3 is the antepenultimate segment, beyond which the fin rays are absent. a. Ventral caudal expansion of median fin, the edge of which is folded. 4, Fin rays. ¢. Dorsal portion of the caudal fin, along the base of which empty “boxes ” and lymph-spaces are seen. Fie. 7.—A view of a portion of the per-anal part of the ventral fin of H. bassanum. The lower part of the body was cut off, cleared and mounted ; it is seen from below, and shows a single series of fin rays. Wen ADL fh pond nape An NS ELIT ? J AS Huth Lith’ London. Se roe ey Vol. 4 ADO ag Quant, Pun \ q \ 3 J Lonio pe ones BS Se aa PARASITES FOUND IN ECHINUS ESCULENTUS, L. 281 On some Parasites found in Echinus esculentus, L. By Arthur E. Shipley, M.A., Fellow and Tutor of Christ’s College, Cambridge, and Lecturer in the Advanced Morphology of the Invertebrata in the University. With Plate 18. I. TURBELLARIA. THE interesting parasite, Syndesmus, was first observed by Patrick Geddes,! who, however, beyond drawing attention to its partly Turbellarian, partly Trematode characters, made no attempt to describe it. He found it in the perivisceral cavity of Echinus esculentus, L. W. A. Silliman? in the following year gave a description of the external features of the parasite, and suggested the generic name Syndesmus. He found it living on a large green nematode, which seemed to him to bea parasite of KE. esculentus taken at Roscoff. Five years later Ph. Francois? in the same Proceedings records the occurrence of this animal in the intestine of Strongylocentrotus lividus, Lam., and of KH. acutus, Lam., at Banyuls. His description, however, differs mate- rially from that of Silliman,—so much so, indeed, that Braun# 1“ Arch. Zool.,’ exp. 1, ser. viii, 1879-80, p. 488. WC uiecNG: oCk. xCiM,, Lood, ps LOST. 3" Ibid. ci, 1886; ps 722: 4 “Central. Bakter.,’ v, 1889; p. 41. 282 ARTHUR FE. SHIPLEY. remarks that one might think that the two authors were observing different species. Frangois suggests the specific name echinorum. The animal is again recorded in 1892-3 by L. Cuénot,} who draws attention to the fact that it corresponds well with the character of the family Vorricipa of von Graff, and indeed to his sub-family Vorricina Parastrica, which includesanother parasitic genus of Turbellaria, Anoplodium, also found in echinoderms. Silliman, Francois, and Cuénot all promise full accounts with figures of the anatomy, but as far as I can find out these have not yet appeared. Last autumn my friend Mr. W. F. Cooper brought me eleven specimens of this parasite which he had found, ten in the alimentary canal, and one lying on the genital gland in the perivisceral cavity of a specimen of Hchinus escu- lentus, L., that he was dissecting at the Marine Biological Laboratory at Plymouth. This winter I have worked out the anatomy of the form and made numerous drawings. After I had completed the work I discovered that Professor Russo 2 had been over very much the same ground; he has, I believe, anticipated me in many details, but as the parasite is very interesting, and is now recorded from the British area, and as the periodical in which Professor Rosso’s full paper appears is very inaccessible—I have not been able to find a copy in any of our libraries—I have thought it not useless to publish the following general account of the anatomy of Syndesmus echinorum, Frang. Anatomy: External Features.—The eleven specimens vary from 1 mm. to 2 mm. in length, and their greatest breadth is one half of their length. ‘These dimensions are considerably less than those recorded by Frangois. His specimens were nearly twice this size. In shape the animals are leaf-like, and have a tendency to be hollowed out ventrally. The anterior end is more rounded than the posterior, but in 1 «Rev. biol. Nord France,’ v, 1892-3, p. 1. 2 € Rie, Labor. anat. Roma,’ v, 1895, abstracted in ‘ Monit, Zool. ital.,’ vii, 1896, p. 6. PARASITES FOUND IN ECHINUS ESCULENTUS, L. 283 some cases the latter is produced into a small papilla caused by the evagination of the penis. The mouth leads into a well-marked sucker-lke pharynx. It is situated on the ventral surface in the middle line, about one eighth of the body-length from the anterior end of the animal. The opening of the vas deferens, the vagina, and the uterus are all at the posterior end of the body, and open by a common pore (figs. 4 and 5). There are no tentacles, or papillae, or hooks, or spines, and as far as I could observe no skin-glands. Histology.—The whole body is covered with a thin but distinct cuticle of uniform thickness (fig. 6). This is continued into the mouth and genital openings, but soon disappears. Externally this cuticle bears numerous small processes, very minute, but sufficient to give a rough appearance to the out- side surface under a high power of the microscope. These are almost certainly the cilia described by all authors who have observed the animal alive. The cuticle is secreted by a single layer of ectoderm cells with large, clear, spherical nuclei (fig. 6). In some sections these ectoderm cells showed fairly definite cell limits, and in that case each cell was about as broad as it was long; in other cases the limits of the cell could only be guessed by observing the nuclei placed at regular intervals. In all the specimens I cut the ectoderm of the dorsal and _ ventral surfaces had separated from the subjacent tissues, leaving a considerable space, but it had retained its normal position along the edges of the animal. Beneath the layer of ectoderm cells is a basement mem- brane, which seems, however, to belong rather to the under- lying parenchymatous cells than to the ectoderm ; it gives a smooth and clearly defined outline to the body where the ectoderm has broken loose from it. The muscular system described by some authors was not visible in my sections. The parenchyma of the body presented different appearances in accordance with the different state of preservation of the 284, ARTHUR E. SHIPLEY. specimens. It consists in the more typical form of a number of large, more or less cubical ceils, full of a densely granular protoplasm. ‘The celis take every variety of shape, owing to mutual pressure and the various strains and stresses which affect them. In hte their outline cannot remain constant for any length of time. In the more poorly pre- served specimens the granular protoplasm had shrunk away from the firmer exterior of all but one surface of the cell, leaving a large but irregular vacuole. The firm external part of the cell, with from time to time patches of contracted protoplasm adhering to it, gives the parenchyma the appear- ance of a network with considerable vacuoles. When this firmer exterior is a little more emphasised it forms the base- ment membrane, which underlies the ectoderm and surrounds the various parts of the reproductive system ; it is, however, very noteworthy that no such basement membrane surrounds the alimentary canal or intestine. The Digestive System.—The mouth is ventral, in the middle line and situated about the distance of one eighth or one tenth of the body-length from the anterior end of the body (fig. 4). It leads by a very short passage, lined by cuticle, and bearing as far as I could make out no glands of any sort, into a spherical pharynx. ‘his organ is of the type found in Vortex or Plagiostoma. The minute lumen is lmed by a uniform cuticle, and the bulk of the thick wall is built up of radial muscle-fibres, among which a few large nuclei stand out in stained sections (fig. 7). From the inner end of the pharynx a very short cesophagus provided with numerous glands—the so-called salivary glands—leads to the digestive sac. The stomach or intestine, or, as I prefer to call it, the digestive sac, is a rod-like organ extending along the middle line of the animal, and so close to the dorsal surface that there is practically none of the parenchymatous tissue which serves as a packing for the various organs of the body be- tween it and the epidermis (fig. 2). The axis of the lumen of the mouth, pharynx, and cesophagus is a dorso-ventral one, but PARASITES FOUND IN KCHINUS ESCULENTUS, L. 280 where the last-named passage joins the digestive sac it forms a right angle with the lumen of the alimentary canal. Ante- riorly the digestive sac extends a little way in front of the level of the entrance of the cesophagus, and when looking through a series of transverse sections 1t comes into view before any trace of the pharynx makes its appearance. Posteriorly the digestive sac extends to near the end of the body, coming to an end at a distance of perhaps one tenth or one twelfth of the total body-length from the end. The digestive sac is lined by a very definite layer which is in the main a plasmodium, though it shows here and there traces of division into cell areas (fig. 6). The limit of the tube is clearly defined, but the basement membrane is very thin, and in places the outer edges of the endoderm plas- modium rests against the packing cells of the body. Inter- nally the lning is produced into many apparently amoeboid processes or pseudopodia, which project loosely into the cavity, and the free ends of which often are cut off and lie as isolated pieces of stained protoplasm in the sections. It is along the inner boundary from which these processes arise that evidence of cell structure 1s most evident, since the chinks between the bases of the pseudopodia are continued by fine lines, which pass a little way into plasmodium, dividing it as it were into cell areas. Throughout the plasmodium deeply staming nuclei are distributed, and numerous vacuoles are scattered; some apparently contain drops of fluid, probably oil or fat; others contain uniformly staining spheres of unknown nature. I have not been able to find any trace of a secretory apparatus; neither canals nor pore could be made out in any of my sections. Nervous System.—The nervous system consists of a well-marked ganglion, situated just anterior to the mouth ; it is somewhat rectangular in outline, and a nerve is given off from each angle. The anterior pair of nerves soon disappear ; the posterior, which bend backwards, are stained, but I failed to follow them very far down the body. In one stained 286 ARTHUR EH. SHIPLEY. specimen a median nerve seemed to leave the ganglion between the anterior two nerves. It is probable that this nerve divides into two branches. Reproductive System.—The external opening of the vas deferens and of the-uterus he side by side, close to one another, at the posterior end of the body. The male reproductive organs consist of paired branching testes. Hach half-presents some ten or twelve twigs lying on either side of the anterior end of the digestive sac, and ex- tending in front of the mouth (fig. 5). These twigs fill up most of the sides of the body, from in front of the mouth to the region of the yolk-glands. The several branches of each half of the testis unite and open intoa pair of tubes, which may be termed the vasa efferentia. These soon fall into one another, and form a long median and anteriorly much-coiled tube. This vas deferens makes a well-marked loop forward to the left of the mouth (fig. 4). In its hindermost part, however, the tube is straight, and is provided with thick muscular walls lined with a cuticle. Russo describes a complicated penis. I have not been able to follow all his details, but there is undoubtedly a protrusible intromittent organ present. The histology of the male reproductive organs presents little worthy of notice. The branches of the testis were outlined by a very thin basement membrane, but beyond this they presented no special investiture. ‘Their contents were cells of some size with large nuclei and conspicuous chromatin. Near the end next the ducts, bundles of tailed spermatozoa are to be seen. ‘he vas deferens is a long and much-coiled duct, so that, as a rule, portions of it are seen several times in any one section. It has a smooth internal wall or cuticle, and apparently a thin muscular lining; at the posterior end the wall of the tube is very much thickened by a stout muscular sheath, and this portion is protrusible, and indeed in one specimen is protruded as a penis. The ovary, like the testis, is double and branched ; each half is compared by Francois to a hand with the fingers extended. PARASITES FOUND IN ECHINUS ESCULENTUS, L. 287 Each branch of the ovary contains, as a rule, a single row of large angular ova, with very large spherical nuclei. The ova are mostly bounded by flat sides. They show some tendency to squeeze one another out of the single row, and when this is the case the row appears double. The ova at the end of each branch next the outlet are markedly bigger and more rounded than those near the top, where they are very small, and apparently it is here that they arise. The coating of the ovary is thin, and it is continued in each side into a short duct which unites with its fellow, and at or near the point of union the ducts of the yolk-glands open. The yolk-glands are large and branching; they he on each side of the body between the testes and the ovary,—on the whole, more dorsal than the ovaries (fig. 2). The tissue of the yolk-glands is dense, and stains deeply near the tips of the branches; but it becomes much vacuolated and stains less deeply near its opening, which leads into the duct of the yolk- olands. The two oviducts of each side and the two ducts of the yolk-glands open into acommon chamber of somewhat angular shape. The shell-glands are paired, and occupy much of the posterior end of the body. The numerous little glands which constitute the organ are unicellular and generally somewhat angular in shape, packed away as they are amongst the interstices of the parenchyma. Hach is crowded with fine granules, and leads by a very delicate duct, which, converging towards each side of the uterus, does not open into the yolk- gland ovary complex, but as far as I can make out into the uterus. In each specimen the uterus contained a beautiful golden egg, oval in outline and continued posteriorly into a long filament. This filament is bent and curved so as to forma tangled skein in the centre of the body; gradually it becomes finer, and its end, which is of extreme tenuity, lies in the neighbourhood of the external opening of the uterus. ‘lhe 288 ARTHUR E. SHIPLEY. contents of the golden egg-shell stained uniformly and deeply, so that no nucleus could be detected. In bulk the egg in the egg-shell surpassed the ripe ova in the yolk-gland ovary complex by some five or six times; this is almost certainly due to the addition of the yolk. On the other hand, the golden case may have been an egg capsule, and contained more than one egg. I rather gather that Russo takes this view. II. NemATopA. In 1854 Dr. Leydig! described some nematodes belonging to the genus Oncholaimus which he had found in the alimentary canal of Echinus esculentus. The parasites were 4 mm. long, thread-like and pointed at both extremities. The oral cavity was provided with a certain toothed and ridged armature in the shape of thickenings of the cuticle prolonged from the firm cuticle covering the body. The cesophagus was long, and posteriorly enlarged, but nowhere did it form a bulb. ‘The intestine ran in a straight line to the anus at the base of the tail, and had a brown colour due to pigmented granules which crowded the cells. ‘The ovary had an anterior and a posterior branch, and each branch terminated in a line which doubles back and ends near the genital opening about the middle of the body. The ripe egg was of considerable size and of oval shape. ‘The oviducts united to form a sharply defined vagina. The cuticle had longitudinal striations. Dr. Leydig suggested the name Oncholaimus echini for this parasite. The only other nematode that I find mentioned as coming from within the body of Hchinus esculentus is the large green nematode of Silliman, which presumably—it is not quite certain—came out of one of these creatures taken at Roscoff. A year or two ago Mr. A. J. Smith, assistant at the Marine Biological Laboratory at Plymouth, found two or three very long nematodes in the perivisceral cavity of an H. esculentus at Plymouth, which he sent to me for investiga- 1 ¢Muller’s Archiv,’ Jahrgang 1854, p. 291. PARASITES FOUND IN ECHINUS ESCULENTUS, L. 289 tion. Unfortunately I did not undertake this at once, and when I came to look at the specimens a short time ago I found that, owing to a piece of iron being in the bottle in which they were preserved, the nematodes had become coated with rust, and in freeing it from rust their structure was so injured that nothing of their histology could be made out. The larger worm had further been injured in extracting it from the shell of the host. Beyond the facts that the longest ametode i is some 46 cm. in length, a little under 1 mm. in average diameter, and the smaller specimens were some 6 cm. in length; that both ends of the animals taper, but more particularly the anterior ; that the posterior end is recurved, as is so usual amongst male nematodes ; and that the alimentary canal was visible through the skin in the line specimens as an opaque strand, I can say nothing. HKnonugh is not known to warrant the suggestion of any specific characters, and I mention the parasite only in the hope that it may attract attention to it and lead to its being found again, carefully preserved, and investigated. ZOOLOGICAL LABORATORY, CAMBRIDGE; Apri) L900: EXPLANATION OF PLATE 18, Illustrating Mr. Arthur HE. Shipley’s paper ‘“‘ On some Parasites found in Echinus esculentus, L.” List or ABBREVIATIONS. e. Cuticle. e.g. Cerebral ganglion. egg. Egg in uterus. ep. Hpidermis. g.d@. Genital duct. g.p. Genital pore. hyp. Amceboid plasmodium lining intestine, @. Intestine. m, Mouth. ov. Ovary. par. Parenchyma. se. Sucker. s.g/. Salivary gland. sh. gl. Shell-gland. ¢. Testis. v. Vagina. v.d, Vas deferens. y.g. Yolk-gland. x Tsar ; Fie. 1.—A longitudinal horizontal section through Syndesmus echi- norum near the ventral surface. VoL. 44, PART 2.—NEW SERIES. 2 290 ARTHUR E. SHIPLEY. Fig. 2.—A transverse section through about the centre of the body of Syndesmus echinorum. Fig. 3.—A longitudinal horizontal section through Syndesmus echino- rum. This section is cut in a somewhat oblique plane, the anterior end being nearer the dorsal surface, the posterior nearer the ventral surface. Vie. 4.—A sketch of a stained and mounted specimen of Syndesmus echinorum. ‘The parts shown can be identified by a reference to Vig. 5. Fic. 5.—A diagram to explain the anatomy of Syndesmus echinorum. Fic. 6.—A small portion of the epidermis and intestinal wall of Syn- desmus echinorum, very highly magnified to show the nature of the plasmodium lining the alimentary canal. Fie. 7.—A transverse section of Syndesmus echinorum through the region of the mouth and pharynx. To the left the anterior loop of the vas deferens is shown. Fie. 8.—Large nematode extracted from the celom of Echinus escu- lentusss 3x de pommmneerer acari a a ee Soety s —e ; ‘ Sanave Nt rea man rennin ent hie LS ? f yas hy ieee | Ny aoe Hl THE SCOTTISH SILURIAN SCORPION. 291 The Scottish Silurian Scorpion. By R. I. Pocock. With Plate 19. 1. InrrRopucrory REMARKS. Our knowledge of the existence of scorpions in marine beds of Upper Silurian age dates from the publication of an an- nouncement to this effect in the ‘Comptes rendus de Académie des Sciences,’ Paris, in December, 1884, wherein Professor Lindstr6m and Dr. Thorell gave an account of the discovery of the well-preserved remains of a fossil scorpion at Gotland in Sweden, proposing for the new form the name Paleophonus nuncius. This important find in paleon- tology attracted wide-spread interest, and was discussed in various journals, scientific and popular. In 1885 it was fol- lowed by an exhaustive memoir on the fossil by Lindstrém and Thorell (‘Kongl. Sv. Vet.-Akad. Handl.,’ xxi, No. 9, 1885). Prior to the appearance of this memoir an article entitled “Ancient Air Breathers,” by Mr. B. N. Peach, was printed in ‘Nature’ (vol. xxxi, pp. 295—298, 1885). In this a preliminary description was given of a second Upper Silurian scorpion, which had been unearthed in the summer of 1883 at Lesmahago, in Lanarkshire, and formed part of the rich collection of fossils belonging to Dr. Hunter. ‘The value of this second specimen was enhanced by the circumstance that it fortunately lies with its ventral surface exposed, and is thus the complement, as it were, of the Gotland fossil, of which 992 R. I. POCOCK. the dorsal surface, at all events, of the anterior half of the body is uppermost. For those who hold that the terrestrial Arachnids are descended from marine ancestors allied to Limulus and the Kurypterida, and recognise genetic affinity instead of “ for- tuitous coincidence” and “convergence” in the many deep- seated structural resemblances between the two groups, these archaic scorpions have, since their discovery, been vested with a peculiar interest, largely in view of the possibility of their supplying fresh evidence in support of this relationship. Little in this direction was yielded by the memoir on the Gotland scorpion; and Peach’s description of the Scotch specimen, although containing many important anatomical observations, was by no means exhaustive, and the figure that accompanied it not all that could be desired. Hence it has for many years been felt that a complete and properly illus- trated account of this unique fossil would make a valuable addition to zoological literature. In July of last year Prof. Ray Lankester wrote for the loan of the specimen to the authorities of the Kilmarnock Museum, where it has been preserved since the death of Dr. Hunter. The authorities not only kindly and promptly acceded to the request, but most generously permitted the specimen to be kept for three months at the Natural History Museum. | oladly avail myself of this opportunity to express my sincere thanks to Professor Lankester for placing the specimen in ny hands for investigation. Iam also indebted to Miss G,. M. Woodward for the trouble and time she devoted to the lithograph, her skill and experience in interpreting fossils being most helpful in the present instance. 2. DESCRIPTION OF THE SPECIMEN. So far as the disposition of the various members is con- — cerned, my restoration agrees with that of Mr. Peach in most particulars. I think, however, that the second leg on the right side lies distally across the anterior portion of the THE SCOTTISH SILURIAN SCORPION. 293 “hand” of the chela, and not across its posterior portion as shown in the figure in ‘Nature.’ One or two other particu- lars in which I differ from him are referred to in the following pages. The specimen gives the following measurements in milli- metres :—Total length on stone 32°5, actual total length when extended 35°5, trunk 16°5, tail 19. The Gotland specimen is considerably larger, measuring 62 mm. in total length, the tail being at least 26 mm. Prosoma.—Owing to the outward displacement of the chele the anterior portion of the carapace is visible between the basal segments of these appendages, and in front of those of the first pair of legs. Its surface is thickly granular, its anterior border hghtly concave, as is the Gotland specimen, and its antero-lateral angles subquadrate. Hyes.—In the Gotland specimen no trace of eyes, either median or lateral, is discernible, though the median ocular tubercle of recent scorpions is represented by a relatively large and longitudinally oval elevation, situated in the ante- rior third of the carapace, and separated from its anterior edge by a space equalling about one half the length of the elevation. Judging from the figure, this tubercle is pre- served in its entirety; hence there is no reason to doubt that if eyes had been borne upon it, some trace of them at least would have been preserved. In the Scotch specimen also there is no sign of the lateral eyes. If, however, as is possible, these organs existed, and were placed behind the level of the median eyes, as is the case in the normal Pedipalpi, and, as is alleged, in the Car- boniferous Anthracoscorpu, they would be concealed from view beneath the basal segments of the anterior legs, which on each side overlie that portion of the carapace immediately behind the median eyes. The median eyes are very distinctly represented by a pair of elliptical impressions situated close together, one on each side of the middle line, and scarcely more than their own long diameter from the anterior border of the carapace. ‘There is no evidence that these eyes were 294, R. I. POCOCK. elevated upon a tubercle. If, indeed, such a tubercle existed as is exhibited in the Gotland specimen, the eyes must have been situated on its extreme anterior border. The presence of these median eyes, and the probable absence of the tubercle, are two important structural differences to distinguish the Scotch specimen from the Swedish. Appendages.—The six pairs of prosomatic appendages (i—vi, Pl. 19) are preserved in a state of greater or less com- pleteness, those on the left side being on the whole more clearly defined than those on the right. The chelicerw or mandibles are, as in the Gotland specimen, very large as compared with those of recent scor- pions. The left chelicera, crushed out of shape and position, shows no recognisable feature but a portion of the immove- able digit. The right, on the contrary, is well preserved and occupies its normal position, projecting straight for- wards from the fore-part of the prosoma. The immoveable digit is slender, pointed, and nearly straight; the moveable is equally slender and pointed, but is lightly curved and armed in the middle of its lower edge with a single tubercular tooth. It is noticeable that the digits of the chelicera are thinner, and overlap at the apex to a much greater extent than in the Gotland fossil. Owing to the distortion and displacement of the left che- licera a portion of the matrix is displayed between the bases of the two appendages just in front of the middle line of the anterior border of the carapace. Presumably it is this por- tion of matrix which Mr. Peach describes—I think errone- ously—as ‘a fleshy labrum (camerostome) between the bases of the cheliceree.” Chele.—As in the Gotland specimen, these appendages do not appear to differ in any essential respects from those of recent scorpions. Their basal segments are too badly preserved for delineation—a particularly regrettable circum- stance in view of the fact that in the Gotland specimen they are concealed from view. Hence it is impossible to surmise whether they took a greater, less, or an equal share in masti- THE SCOTTISH SILURIAN SCORPION. 295 cation as compared with those of existing forms. The second segments project on each side of the antero-lateral angles of the carapace, and are granularly sculptured. ‘The anterior surface of the third segment is apparently normally crested above and below, and the fourth segment of the left side shows traces of the basal prominence so noticeable in living species. Granules are observable along the anterior side of both these segments. The fifth segment (hand) of the left side differs in shape from that of the mght, being more oval in form, with its posterior border in approximately the same straight line as that of the distal segment, the bulge being confined to the anterior surface as in the Got- land specimen and recent species. On the right side the hand is unusually globular, its posterior surface, probably owing to crushing, being abnormally swollen. The fingers are thinner, more taper, and straighter than in the Gotland specimen and recent scorpions. No distinct joint between the finger and hand is discernible, although presumably it is the under side of the hand and of the moveable finger that 1s exposed to view, both on the right and left sides. It is possible that the shallow median longitudinal groove observable on the finger of the right chela represents the line along which the two fingers meet when closed. The finger of the opposite side is similarly marked with a fine sculptured ridge. Legs.—So far as can be ascertained the legs resemble those of the Gotland specimen in length, strength, and seg- mentation. As in other scorpions, and typically in all orders of Arachnida, they increase in length from before back- wards, the fourth pair being nearly half as long again as the first. ‘They consist, moreover, of what is doubtless the primi- tive number of segments—namely, seven. Primitiveness of segmentation is also shown by the subequality in length of the individual segments—a character which, in conjunction with the sharply pointed, practically clawless terminal segment, serves to distinguish the legs of Paleophonus from those of all other scorpions, living or fossil. I say 296 R. I. POCOCK., practically clawless because Thorell detected a minute claw- like structure at the tip of the seventh (tarsal) seament in Fre. 1.—Restoration of Paleophonus nuncius. Dorsal view (after Thorell). the Gotland specimen. Although no trace of such a struc- ture was found in the Scotch fossil, no great value must be Ly] THE SCOTTISH SILURIAN SCORPION. 297 attached to its apparent absence, in view of the chances against the preservation of an organ so delicate. Nor was I able to detect a sign of the presence on the fifth segment of any of the legs of that spur so clearly shown on the first, second, and third pairs in the Gotland fossil, and described and figured by Thorell (see cut, p. 296). The interest invested in this spur depends upon the probability of its direct homology with the so-called “ tibial spur” found upon the arthrodial membrane at the distal end of the fifth segment in some recent Buthoid scorpions. Certain genera of this family (e.g. Buthus, Lychas) possess it upon the third and fourth legs, one alone (Babycurus) retaining it only on the fourth leg. Assuming that the spurs in the genera just mentioned are homologous to those found in the Swedish Paleophonus, their presence upon the third and fourth, or upon the fourth leg in the former, and upon the first, second, and third legs in the latter, suggests that scorpions primitively possessed them upon all four legs. In that case the absence of the spur from the fourth leg in the type of Paleophonus nuncius may be a natural characteristic of the species, or may be due to a mere accident of preservation. The same may be said of the apparent total absence of this spur from the legs of the Scotch specimen. There is, however, a still deeper interest attached to this spur, on account of its apparent presence upon the fourth lege (sixth prosomatic appendage) of Limulus. The first and second appendages of this animal agree in structure and in the number of segments with those of scorpions, the former consisting of three and the latter of six segments. But the third, fourth, and fifth appendages of Limulus also consist apparently of six segments, resembling in all particulars those of the second pair. In the scorpions, on the contrary, these appendages, as well as the sixth pair, consist of seven seg- ments, the distal being furnished with a pair of moveable claws. Careful examination of these appendages in Limulus, how- ever, shows that the fourth segment is encircled in its basal 298 R. 1. POCOCK. half with a sutural impression, which represents, I believe, the line of union between two segments, the portion on the proximal side of the line being the fourth, that on the distal side the fifth segment of the appendage. If this interpre- tation be correct there is the same number of segments in these appendages in both Limulus and the scorpions. Now in the fourth leg of Limulus (exceptin L. rotundicauda) the fifth segment, according to this new method of enumera- tion, 1s furnished beneath distally with a spur like those described above in the scorpions. Again, at the extremity of the sixth segment in Limulus there are four moveable lobate sclerites, which spread out like the fingers of a hand when the leg is plunged into the mud. At the extremity of the sixth segment in the scorpion’s leg, or rather on the arthrodial membrane between it and the seventh, there are either one or two “ pedal” spurs, which represent, I suggest, the lobate sclerites in the same position on the leg of Limulus. Lastly, there is attached to the distal extremity of the seventh segment in Limulus a pair of short moveable sclerites, forming a small nipper. Similarly there is a pair of moveable sclerites or claws articulated to the distal extremity of the seventh segment in the scorpion’s leg. The annexed figure (ig. 2) will make these suggested homologies clear. Whether Paleophonus possessed any structures com- parable to the pedal spurs of recent scorpions and to the lobate sclerites of Limulus is doubtful. I can detect nothing comparable to them in the Scottish specimen, but the figure of the Gotland specimen suggests the possibility of the presence of one or more spurs at the distal end of the sixth segment. It is a matter for regret that the exact structure of the basal segments of the legs, and the relation of these segments to one another, are not with certainty interpretable, owing to the crushing and displacement of the parts composing the ventral area of the prosoma, and of the anterior somites of the mesosoma. Hence too much reliance must not be placed THE SCOTTISH SILURIAN SCORPION. 299 upon the accuracy of the attempted restoration of these structures, Fie. 2.—a. Fourth leg of Limulus moluccanus. B. Fourth leg of a recent scorpion (Buthus australis). c. Third leg of Silurian scorpion, Paleophonus nuncius, after Thorell. 1—7. Segments. s. Suture between fourth and fifth segments of the leg in Limulus. sp. Spurs and lobate sclerites. ? sy. Processes possibly re- presenting the point of attachment of spurs in Paleophonus. c/, Claws in the scorpion, and pair of sclerites forming a nipper in Limulus. In existing scorpions the basal segments (coxee) of the legs of the first and second pairs are furnished with a for- 300 Rey SeOCOgK, wardly directed sterno-coxal or maxillary process, the coxe of the second lee meeting each other in the middle line in front of the prosomatic sternum, and sending forwards these processes, which are in contact throughout their length, to YO Fre. 3.—Restoration of Paleophonus ILunteri (ventral view). underlie the mouth. The coxe of the third and fourth legs, on the contrary, are devoid of sterno-coxal processes, and are separated from each other in the middle line by the sternal plate, against the sides of which they abut. THE SCOTTISH SILURIAN SCORPION. 301 A very different state of things appears to obtain in Paleophonus. No trace of a sterno-coxal process is dis- coverable upon the first leg. On the second, however, a small one seems to be present. ‘his lies transversely, and meets its fellow of the opposite side in the middle line. On the third leg a process similar in its form and relations is also indicated, and the segment that bears it, imstead of abutting against the sternum, is mesially in contact with its fellow. The probability of the correctness of this conclusion is enhanced by its tallying with Peach’s opinion. I cannot, however, quite agree with this author in believing that the legs of the fourth pair are basally separated by the sternum as in recent scorpions. On the left side of the specimen, where the leg is well preserved, the segments seem to be traceable right up to the middle line, the basal segment being sharply defined. On the right side, however, this is not so clearly indicated, on account of a displacement which has resulted in the overlap of the proximal end of the fourth leg by that of the third. The sternum (st., P]. 19) does not stand out as a sharply defined plate with clean-cut edges, bunt is merely represented by the subpentagonal area that lies between and behind the two proximal segments of the fourth leg of the left side, and those of the third and fourth legs of the right side. It shows a famt central circular depression answering presumably to the similarly shaped sternal depression in Cherilus, and to the median groove in other recent scorpions. The above-described arrangement of the skeletal pieces, forming the ventral surface of the prosoma, offers many points of morphological importance in view of the differences that obtain in this particular between the recent scorpions and Limulus or one of the Hurypterida. The relations of the sternum to the coxee and the cox to each other in the scorpions have already been described. Those of Limulus and the Hurypterida may be stated in a very few words. In the latter the basal segments of all the appendages, ex- 302 R. I. POCOCK. cepting those of the first pair, acted as jaws, and were frequently armed with teeth, the greatest share in crushing and masticating food falling to the cox of the fourth pair, which were especially enlarged for the purpose. Behind, and partially concealing them from the ventral side, lay a large plate, the so-called ‘ metastoma,”’ the homologue of the scorpion’s sternum. To all intents and purposes the same arrangement is found in Limulus, except that the coxe of the fourth are less masticatory in function, and the “ meta- stoma’? is represented by a pair of moveable sclerites, the “chilaria,” set immediately behind and between the bases of the legs of the fourth pair. In Paleophonus the sternal plate of the prosoma lies apparently behind the basal segments of the fourth legs as in Limulus, and, as in the latter and in the Eurypterida, the basal segments of all the appendages were in contact or capable of meeting in the middle line. On the other hand, the coxee of the fourth were small and functionless so far as the mouth was concerned, and food was probably crushed by those of the chelee as in recent scorpions, the sterno-coxal sclerites of the second and third pairs assisting in this process, and preventing the escape of nutritive juices. Thus, so far as the parts now under discussion are concerned, this archaic scorpion presents a condition of things intermediate in many particulars between that of the typical scorpions and of Limulus or Hurypterus. Mesosoma.—The ventral portion of the first somite of the mesosoma is represented by a relatively short but wide area lying behind the sternal region of the prosoma. ‘This area is marked in the middle line with a short longitudinal groove (gen., Pl. 19), representing in all probability the divi- sional line between the right and left halves of the genital operculum. On each side this area is impressed with a shallow but conspicuous indentation, which from its position seems hollowed out for the reception of the third segment of the fourth leg, perhaps in order that this portion of the appendage might be insunk to the level of the generative THE SCOTTISH SILURIAN SCORPION. 3038 orifice, so that its prominence should offer no obstacle to the act of copulation. A short distance behind the genital cleft a similar but larger and more conspicuous median cleft is visible. ‘This is flanked on each side by a narrow longitudinally elongate plate or lobe (end., Pl. 19), somewhat resembling one half of the genital operculum of recent scorpions. On the outer side of the right-hand lobe lies a bisegmented appendage (pect., Pl. 19), which may be regarded as the homologue of a recent scorpion’s pecten or comb. Along the posterior border of this appendage are traceable a number of fine striz occupying the position of the pectinal teeth. Similar striz are traceable upon the left-hand side, although the pecten itself is obliterated. Peach regarded the cleft between the two above-described lobes as the generative aperture, a conclusion it is impossible to accept in view of the improbability of the backward move- ment of this aperture on to the somite that bears the pec- tines. The opinion, which I here put forward, that the generative aperture is represented by the slit which, although not mentioned by Peach, appears on his published figure immediately behind the pentagonal prosomatic sternite, seems on morphological grounds far more likely to be correct. Thorell, moreover, suggested that the pair of lobes lying between the pectines correspond to the small, sometimes longitudinally grooved pectinal sternite of recent scorpions. This may be the true interpretation; but the shape of the lobes, the length and depth of the groove that separates them, and their relations to the pecten, suggest that they have another significance, and are probably to be regarded as the inner branches of an appendage of which the pecten is the outer branch. From this standpoint the appendage may be compared with the mesosomatic appendages of Limulus, and of the archaic spider Liphistius. In the former the appendages (except in the case of the genital operculum of the Kastern species) consist of a broad foliaceous trisegmented external branch, and of a slender trisegmented internal 304 R. I. POCOCK. branch. In Liphistius also there are two branches, the inner slender and unsegmented, the outer stout and composed of two principal segments. Although in general form the inner lobes (end., Pl. 19) of Paleophonus resemble those of Limulus, they differ from the latter, and approach those of Liphistius in being unsegmented. The outer branch is broad and flattened, and is somewhat like that of Limulus, except that it 1s relatively smaller, and hes with its axial line directed, not longitudinally, but obliquely outwards and backwards like the comb of a typical scorpion. It shows, however, no signs of segmentation into so-called “ fulcra ” and ‘intermediate lamelle,’ such as are found in the combs in the majority of species. Structurally, in short, it is inter- mediate between a typical comb and the outer branch of one of the mesosomatic appendages of Limulus. Furthermore, the fine strize which fringe its posterior edge are, in my opinion, too delicate to be the remains of teeth comparable in shape and size to those of recent scorpions. Rather would I suggest that they are portions of the edges of branchial lamellee which were affixed hke those of Limulus to the posterior side of the appendage, with their lines of attach- ment lying at right angles to its longitudinal axis. These appendages overlie and almost completely conceal the sternite of the third mesosomatic somite. The stern- ites of the fourth, fifth, and sixth somites, however, are fully exposed and well preserved. They are granular, and resemble the corresponding plates in recent scorpions but for the absence of the muscular impressions and, so far as my observations go, of the stigmata. Peach, however, declares most emphatically that “all four sterna exhibit on the right side undoubted slit-hke stigmata at the usual places.” It is true that the sternites are somewhat wrinkled laterally, and, as shown on PI]. 19, exhibit certain shallow impressions, which, especially in the case of the fourth and fifth sternites, might be mistaken for stigmata; but it is hard to believe that slits as conspicuous as the stigmata of recent scorpions should be so indistinctly preserved on sternites in such an THE SCOTTISH SILURIAN SCORPION. 305 admirable state of conservation that even their granulation is still apparent. Nevertheless it must be borne in mind that Peach’s opinion on this point is in complete agreement with Thorell’s regarding the Gotland specimen. According to Thorell this specimen exhibits on its right side a portion of a displaced sternal plate, upon which a distinct stigma is visible. This sternal plate he assigns to the third somite of the mesosoma; but a glance at his draw- ing shows that the greater part of it les at the sides of and beneath the tergite of the second somite, and that at all events a large part of the third sternite is situated on the left-hand side beneath its corresponding tergite. To hold that this third sternite has been fractured and displaced to the exsent that Thorell’s interpretation demands appears to me to be an opinion based on an improbability. From the position of the fragment that protrudes on the right-hand side, I judge that it belongs to the second mesosomatic somite— a somite which in all known scorpions bears the pectines but is without stigmata,—and that it is part of its pleural mem- brane. ‘This interpretation, if correct, involves the conclusion that the “spiraculum” described by Thorell is a fortuitous crack 11 the integument. There is one other point, too, bear- ing incirectly upon the question of the presence or absence of stigmata, in which, without further evidence, I find it im- possible to accept Thorell’s decision. The Swedish specimen is broken in two by a transverse fracture, crossing the fourth somite of the mesosoma. The posterior half thus contains the fifth and sixth mesosomatic somites and the metasoma. It is admitted—and there is no reason to doubt—that the ventral surface of the metasoma is exposed. According to Thorell, however, the two mesosomatic somites which go to make up the severed portion of the body he back uppermost. This supposition implies the belief that the severed portion of the specimen was itself completely divided into two at the junction of the mesosoma and metasoma, that the latter was overturned, and was so accurately fitted into place that perfect continuity between it and the mesosoma was restored. That vou. 44, PART 2.—NEW SERIES. U 306 R. I. POCOCK. the uninterrupted outline presented by the somites in question, which imparts so natural an appearance to this region, is thus the result of pure accident I find hardly credible. In fact, there is, I think, no reason to doubt that the fifth and sixth mesosomatic somites were united to the metasoma, and shared its unmistakable inversion. Hence the plates in question are sternites. ‘lhe important point attached to this conclusion is the absence of stigmata on these sternites. Perhaps it was this fact which led Thorell to his decision as to their tergal character. The above-given reasons justify a sceptical attitude towards the alleged existence of stigmata in the Gotland Paleopho- nus, at all events until a further examination of the specimen settles the points now under dispute. And since I found no distinct traces of stigmata in the Scotch specimen, I am in- clined to belheve that Peach fell into error on this point perhaps influenced in part by the alleged presence of stigmata in the Gotland example, perhaps in part by the assumption that a form so closely resembling recent scorpions in other structural details must also resemble them in the nature of its respiratory organs. To the belief in the presence of stigmata, implying the existence of organs fitted for aérial respiration, coupled with the knowledge of the terrestrial habits of all living scorpions, is traceable the conviction evinced by most previous writers that these Silurian scorpions lived on the land. This belief is less easy to reconcile with the facts that both the known specimens are relatively inanadmirable state of preservation, and were met with in strata of undoubted marine origin, containing abundance of admittedly marine organisms, than the behef, which I hold, that Paleeophonus lived in the sea, probably in shallow water, its strong, sharply pointed legs being admirably fitted, like those of a crab, for maintaining a secure hold amongst the seaweed or on the jagged surface of rocks, and for resisting the force of the rising and falling waves. Respiration, as already suggested, may have been effected THE SCOTTISH SILURIAN SCORPION. 307 by means of the appendages of the second mesosomatic somite, although it must be admitted they appear too small to have performed this office for the whole organism without help from other organs. It is possible that there were such organs in the form of small appendages bearing branchial lamella attached to the mesosomatic sterna. But if so, no definite trace of such has been preserved. Or, indeed, it is possible that the ventral plates, above regarded as meso- somatic sternites, may have been broadly laminate mesosomatic appendages, closely pressed down against the ventral surface of this region, and bearing branchial lamelle on their pos- terior surfaces. This suggestion gains some support from the fact that the laminate mesosomatic appendages of the Hurypterida are generally indistinguishable from sternal plates. Metasoma.—This region of the body in the Scotch speci- men closely resembles that of the Swedish specimen, the same surface, namely the ventral, being in each case uppermost. Peach, however, states that the dorsal surface of the posterior caudal segments is in part exposed. According to my inter- pretation, on the contrary, in all the segments it is the area lying between the inferior lateral keel on the left side (in/. lat. and sup. lat., Pl. 19) and the superior lateral keel on the right that is exposed. Both of these keels are granular. As in most recent scorpions, a pair of median keels (inf. med., Pl. 19) lie along the lower surface of the tail, between the inferior lateral keels on the first four segments of the tail. Keels corresponding to these four inferior medians and inferior laterals are traceable upon the first metasomatic sternite, and also, I think, upon the sixth (fifth caudal segment). ‘This last fact, if true, is of some interest, inas- much as it shows a more primitive arrangement than is found in recent scorpions, where the two median keels have invariably coalesced into one. The inferior median keels on the pos- terior caudal segments appear to be smooth. In the Swedish specimen they are granular. ‘I'he lower side of the vesicle is granular in both, but the aculeus in the Scotch example is 308 R. 1.. POCOCK. apparently less curved, less circular in section, and more tri- angular than in recent scorpions and the Swedish specimen. 5. DESCRIPTION OF THE SPECIES, WITH NOTES ON THE OTHER KNOWN: SILURIAN SCORPIONS. The preceding description of the Scottish fossil, and the comparisons that have been made between it and the Swedish specimen, have revealed some noticeable structural differ- ences between the two, which leave no other course open than to regard the former as the representative of a distinct and undescribed species. This I propose to dedicate to Dr. Hunter, and to diagnose as follows : Paleophonus Hunter, sp. n. Differing from P. nuncius in its much smaller size, being 35°5 mm. as compared with 62 mm. in total length, in possessing a pair of median eyes set close to the anterior border of the carapace, in having the digits of the chelicere longer and thinner, and the moveable more curved, and the cheleas very much lighter in build, with the digits nearly straight; in the absence of a spur from the fifth segment of the first, second, and third pairs of legs, and in the smooth- ness of the inferior median keels on the posterior segments of the tail. In addition to the specimens discussed in the preceding pages, two other scorpions have been recorded from Silurian strata, namely, Proscorpius Osborni and Paleophonus loudonensis. The first was described by Whitfield (‘Science,’ vi, p. 88, 1885; ‘Bull. Amer. Mus. Nat. Hist.,” 1, No. 6, pp. 181 to 190, 1885), and was based upon a fairly well preserved specimen, with the dorsal surface exposed, from rocks referred to the middle of the Upper Silurian. Like the Swedish and Scotch specimens, it was associated with fossil remains of Pterygotus, Hurypterus, and other marine organisms. The specimen was examined by both Whitfield and THE SCOTTISH SILURIAN SCORPION. 309 “Scudder. The latter (Zittel’s ‘ Handbuch der Palaontologie,’ 11, p. 739, 1885) classified it with the Carboniferous scorpions on account of the alleged presence of a pair of claws at the extremity of the anterior leg of the left side. ‘This classifi- cation was endorsed by Whitfield, who based the genus Proscorpius mainly upon these claws, declaring them to be very similar to those of living forms. His figure shows no such similarity. The apical segment of the leg is simply bifid at the tip, a feature which may be due to fracture, or may represent a pair of sclerites like those borne at the tip of the distal segment of the fourth leg of Limulus; or may be explained on the supposition that the end segment ter- minated in a sharp point as in Paleophonus, and was furnished near the tip with a moveable spine or spur. Since, however, there is no agreement between Scudder and Whit- field as to whether the segment stated to possess these claws is numerically the third or sixth from the base, it seems idle to discuss the matter further. If Scudder’s interpretation of the numbers of the segments is correct, these “ claws”’ are situated at the end of the third or fourth segment, and cannot be compared with the tarsal claws of other scorpions. Apart from the leg, the chief points of interest connected with Proscorpius Osborni are the presence of a pair of eyes on a median ocular tubercle, and of a row of lateral eyes (not shown in the figures, by the way) on each side of the carapace. ‘lhe rounded median tubercle projects in the middle line of the fore border of the carapace, the lateral angles of which are also rounded. Hence the trilobate appearance of the anterior border of this plate, which forms such a contrast to the even emargination seen in the Swedish and Scotch Palewophonus. It is further to be noticed that the dorsal integument is smooth, and not granular as in Paleophonus nuncius. Along the right-hand side of the specimen, both Scudder and Whitfield agree that six (five mesosomatic and one metasomatic) abdominal sternites are exposed. The first of these belongs to the second mesosomatic somite, which in 310 R. I. POCOCK. recent scorpions bears the pectines and has no appreciable sternal area. But there appears to me to be no reason for regarding this so-called sternal area other than as the pleural membrane of the second somite of the mesosoma. Mr. Whitfield could find no satisfactory evidence for the existence of stigmata, and infers from this fact, and from the nature of the strata in which the specimen was preserved, that the species was ‘ aquatic in habits,” and furnishes a “link between the true aquatic forms hke Hurypterus and Pterygotus and the true air-breathing scorpions of recent periods.” Of Paleophonus loudonensis, described by Laurie, from the Upper Silurians of the Pentland Hills (‘Tr. Royal Soc. Edinb.,’ xxxix, p. 076, pl. 1, fig. 1, 1839), little: need be said, the specimen being too imperfectly preserved to yield satisfactory data for discussion. That the specimen was specifically distinct both from P. nuncius and P. Hunteri cannot be doubted if the great length of the carapace and the slenderness of the tail in the fossil are not attributable to imperfection of preservation. Asin P. Hunter, there are a pair of median eyes close behind the fore border of the cara- pace, which is emarginate. No genuine stigmata were discovered, but on some of the mesosomatic somites a curved ridge running obliquely out- wards and backwards on the sides of the segments was traceable. ‘The ridge on the second somite Laurie inter- prets as the impression of the outiine of the pecten, those on the others as the outline of a plate-like guill-bearing appendage. 4, RECAPITULATION. From a morphological point of view, perhaps the most important results obtaied by the examination of this fossil are those connected with the structures of the basal segments of the prosomatic appendages, and their relation to the sternal area of this region, and those connected with the THE SCOTTISH SILURIAN SCORPION. Sal id! structure of the appendage of the second somite of the mesosoma. If the above-given interpretation of the arrangement of the parts constituting the ventral side of the prosoma is correct—and I do not think it is likely to be very far wrong —Paleophonus occupies an intermediate position between Limulus and the Kurypterida on the one hand, and recent scorpions on the other, standing, if anything, rather nearer to the former than to the latter. The same may be said of the structure of the second mesosomatic appendage, which with its outer and inner branch is hke the corresponding appendage in Limulus; while the outer branch itself, although in general form and size resembling the pecten of a scorpion, offers some inte- resting structural features in which it differs from that organ, and resembles the outer branch of a mesosomatic limb of Limulus. On the whole, it must be admitted that Paleophonus Hunteri supplies a few more links to the chain of evidence pointing to the descent of the scorpions from marine Limu- loid ancestors. EXPLANATION OF PLATE 19, Illustrating Mr. Pocock’s paper on “The Scottish Silurian Scorpion”? (Paleophonus Hunteri). The figure gives a magnified view of the specimen of Paleophonus Hunteri, Pocock, from the Upper Silurian of Lesmahago, Lanarkshire. It was formerly in the collection of Dr. Hunter, and is now in the Kilmarnock Museum, ‘This lithograph was executed from the specimen itself by Miss G. M. Woodward, under the supervision of Mr. R. I. Pocock, in October, 1900. I—VvI. Prosomatic appendages. sf. Sternal area of prosoma. gev. Genital cleft. pect. Pecten, or external branch of appendage of second somite of mesosoma. end. Internal branch of appendage of second somite of meso- soma, sup. lat., inf. lat., inf. med. Superior lateral, inferior lateral, and in- ferior median crests of fourth somite of metasoma. -* 9 Quant, Foun Mor Sa Vol bL NS PLT9 LV. > Z yea P= = f L722 FIVER. (4 GM.W ). Ht oodward del. et lith. A.S. Huth imp. THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 318 The Life-History of Nucula delphinodonta (Mighels). By Gilman A. Drew, Professor of Biology, University of Maine, Orono, Me. With Plates 20—25. THE material upon which these observations were made was secured at Casco Bay, Maine, during the summers of 1897 and 1898. Nucula delphinodonta is a small form, seldom growing to be more than 4 mm. in length, and as it lives below low-tide mark it is not very well known by col- lectors. By using a sufficiently fine dredge, however, un- limited numbers of adult and young specimens may be procured. Individuals may be found living under very different conditions; in inlets and protected places, and ex- posed to the open sea, and from near low-tide mark to a depth of several fathoms. ‘The principal habitat, however, is in the shallow inlets and near the heads of sounds, where the bottom is composed of fine mud, mixed with some sand, broken shells, and decaying vegetable matter. Individuals are most numerous just outside of the eel grass which skirts the shore where the bottom is of this character, in water which at low tide is from one to three fathoms deep. The mud in which they live is much like that inhabited by y - Yoldia limatula, except that it is not so free from shore _ _ débris. Although some specimens may be obtained where Ea Yoldia i is most abundant, they are generally more numerous Piss VOL. 44, PART 3.—NEW SERIES. x 314 GILMAN A. DREW. somewhat nearer the shore, and they may be very numerous at considerable distances from places where Yoldia is known to thrive. In picturing the conditions under which these animals live along the coast of Maine, the reader should not fail to take into account the average tide of about ten feet, which keeps the water very pure over a comparatively foul bottom. The fauna and flora of these bottoms are very abundant and di- versified, but have not been carefully catalogued. Diatoms of several species abound, and form a large part of the food of Nucula. Other Algz, Ostracods, Foraminifers, small Lamellibranchs, and Gastropods are also very abundant, and small individuals of most of these forms are occasionally found in the stomachs of preserved specimens. While I have never succeeded in getting individuals to form brood-sacs in captivity, they live well in aquaria, and may be kept for several weeks either in vessels containing the mud in which they normally live, or in vessels without this mud. It is not even essential that the water be changed very frequently. When placed in vessels containing mud they bury them- selves, and seem never to come to the surface to stay for any considerable time. ‘They are at all times comparatively sluggish, and seem to wander around in the mud by slow thrusts and retractions of the foot, which is a very perfect burrowing organ. When placed in mud that is just suffi- ciently deep to cover them, their movements can be followed fairly well by the movements of the mud. ‘To see them feeding it is necessary to use only a very thin layer of mud. The action of the palp appendages can then be observed. They perform the same function that 1s performed by similar appendages on the palps of Yoldia (1), that is, they are food collectors. Nucula delphinodonta seems normally to feed beneath the surface of the mud, so feeding cannot be observed as easily as it can be in the case of Yoldia (Text- fic. T). The movements of the foot are best observed by placing HE LIFE-HISTORY OF NUCULA DELPHINODONTA. 815 specimens in shallow dishes of sea water. When specimens are placed on mud they bury themselves so promptly that the movements of the foot cannot be carefully followed. The movements are all such as would be of service in bur- rowing in mud. Although specimens have been kept under observation under different conditions for long periods of time, I have never known one to execute movements that could be interpreted as creeping. In 1853 Forbes and Hanley, in describing Nucula nucleus (4), made the fol- lowing statement :—“ The foot is white, and as if peduncu- lated and deeply grooved, so as to expand into a broad leaf- shaped disc with serrated margins; by means of this organ it can creep like a Gasteropod, and we have seen it walk up the sides of a glass of sea water.” This seems to be the only observation of this kind on record, although many students have worked on this and related forms. ‘The authors who have adopted the view that the foot functions as a creeping organ in members of this group have, in nearly every case, had only preserved material to work upon, and perhaps have been influenced by finding so many characters that seem to them to denote generalised structure. Some Lamellibranchs are able to pull themselves over smooth surfaces, but my observations lead me to believe that the form and structure of foot found in this group is especially poorly adapted for such a purpose (3). ‘The expanded foot of Nucula delphinodonta is relatively very large, and the almost spherical shell is frequently turned from one side to the other, but nothing comparable to creeping has been observed. Although many Lamellibranchs carry their eggs and de- veloping embryos, I think this is the first case reported where a special external sac is formed for the purpose. ‘This sac (fig. 1) is composed of a mucus-like material, mixed with foreign bodies, and is attached to the posterior ends of the valves of the shell. Although the process of making the sac has never been observed, it seems probable that the mucus-like material is secreted by the hypobranchial glands, 316 GILMAN A. DREW. This material is probably passed posteriorly by the action of the cilia on the mantle, and very likely the respiratory cur- rents of water swell it into a sort of bubble that remains attached to the posterior ends of the shell-valves, and, while still soft, adheres to the foreign particles with which it comes in contact. That the hypobranchial glands are concerned in the forma- tion of the material from which the brood-sac is formed is indicated by their appearance before and after the sacs have been formed. In females in which the ovaries are still full of eggs, the cells of the hypobranchial glands are large and gorged with secretions, while in females that have formed the brood-sacs the cells are shrivelled and almost devoid of secretions. The eggs are deposited in the brood-sac (fig. 1), and in it the embryos are carried until they reach an advanced stage in development, probably for a period of three or four weeks. The eggs of this species are brown, opaque, few in number, and correspondingly large. From about twenty to seventy may be found in a sac, and they average about ‘21 mm. in diameter. Hach egg is enclosed in a membrane that is pro- bably secreted by the egg, but its formation has not been observed. Fertilisation is probably accomplished in the brood-sac. Eggs and young embryos do not live well after they are removed from the brood-sacs, so the ages of the various stages have not been determined. Processes of maturation and cleavage proceed slowly. ‘he time between the appearance of the first and the second polar body is frequently as much as two hours, and the time between cleavages seems to be nearly or quite as long. It is not beyond doubt, however, that the removal of the eggs from the brood-sacs influenced the length of time. That develop- ment is slow is not to be doubted. Embryos taken from the brood-sacs of specimens kept under as nearly natural condi- tions as possible for a month, had only reached the stage where two gill-lobes were formed. It seems probable that the polar bodies may be formed by THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 317 egos that have not been fertilised. Eggs were sometimes obtained that formed polar bodies and developed no further.’ Just before each polar body is formed, a more or less distinct, and frequently a very pronounced swelling, makes OW FIG A ate fit OD Trxt-Fics. A, B, C, and D.—Karly stages in the development of Nucula delphinodonta. its appearance on the side of the egg opposite the point 1 Most of the eggs of an isolated specimen of Nucula proxima, a form that throws its eggs free into the water, formed the polar bodies, and a few eggs cleft the first time. It is possible that some sperm were in the water, but the water had not been changed for nearly twenty-four hours before the eggs were laid, and sperm of this species do not seem to retain their vitality for nearly so long a time. 318 GILMAN A. DREW. where the polar body will appear. In the preparation for the first cleavage a similar swelling is formed on the side opposite the polar bodies. When the egg divides, the divid- ing wall passes to one side of this swelling. The two blasto- meres are accordingly rather unequal in size. The difference in the size of the two blastomeres seems to depend upon the size of the swelling that precedes their formation. Cleavage into four and eight cells (Text-figs. C and D) are typical. The polar bodies retain their position on the animal pole until the embryo acquires cilia, when they are rolled around on the inside of the membrane. No attempt has been made to follow out the fate of the individual cells. In the sixteen-celled stage, figs. 2 and 3, a small cleavage cavity is present. Later this becomes slightly more pro- nounced. ‘The cells on one side of the blastula divide more rapidly than those on the other side, and push over them in ~ the form of a cap (fig. 4). A pocket appears between the large cells at such a point as is indicated by the asterisk in fig. 4. Just how this pocket is formed is still a matter of some doubt, but it seems to be formed by the separation and division of some of the larger cells. This pocket (fig. 8) can now be compared with the invaginate portion of a gastrula. It represents the first appearance of the gut. About the time that the pocket is formed most of the smaller surface cells acquire cilia (fig. 6), and the embryo begins to roll around in the membrane. ‘The cilia are all short, similar in appearance, and seem to be evenly scattered over the surfaces of the cells. In whole mounts the boundaries of the surface cells are not very distinct, but the cells do not seem to have a very definite arrangement. From these small surface cells, that at this stage appear very much alike, the test,! the apical plate, and the cerebral ganglia are formed. The large cells near the blastopore do not bear cilia, at 1 T use the term “test” here, as in former publications, to designate the surface cells that bear cilia and may be homologised with the velum of other forms. THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 319 least none could be found on preserved specimens. They are concerned in the formation of the shell-gland. The embryo is still nearly spherical, and so opaque that, while alive, internal changes cannot be followed. A few cells, probably the beginning of the mesoderm, lie above and by the sides of the gut. About this time some of the surface cells around the blastopore divide, and push in to form a stomodeum. Other cells near the blastopore become enclosed by the surface cells, and together with cells probably derived from those forming the stomodzeum, finally form a portion of the new ectoderm, that soon covers the body of the embryo inside of the test. When the ectodermal layer is complete it joins, but does not enclose, the stomodzeum. In position as well as origin the stomodzeum is ectodermal. Before the ectodermal layer is complete the embryo begins to elongate, and the surface cells close in over the shell- gland from the sides and anterior end. At the same time the surface cells become arranged in rather definite rows. It is very difficult to get satisfactory views of these cells in whole mounts, but there seem to be five rows, beside a group at the anterior end that forms the apical plate. ‘T'wo or three of the posterior rows are interrupted in the region of the shell-gland, but this interruption disappears as the shell- gland becomes closed in. Closing is never complete. A small opening is left dorsal to the blastopore, separated from it by the width of one test cell (fig. 15). The anus comes to lie near this opening at a later stage (fig. 24). Before the shell-gland is covered the gut turns towards the dorsal side (fig. 11, mg.), and the mesoderm cells take up a position near the posterior end of the embryo. Two of the mesoderm cells are large, and have very large and conspicuous nuclei. These cells are far posterior, and lie side by side. Soon after the shell-gland is covered, the gut begins to grow posteriorly, almost, if not quite, in contact with the shell-gland dorsally, and separated from the stomodzum ventrally by a few mesoderm cells (fig. 15). A small space appears among these mesoderm cells that later becomes con- 320 GILMAN A. DREW. nected with a space that is formed between the gut and the shell-gland. At no stage in its development is the shell-gland invagi- nated. From the time of its formation it arches dorsally to some extent (figs. 7 and 9, sg.). Just before it becomes covered by the test it flattens somewhat (figs. 11 and 12), but it soon arches dorsally again and becomes quite convex (fig. 17, sg.). The cells that give rise to the cerebral ganglia are few in number (fig. 15, cg.), and lie ventral to the anterior end of the stomodeum. They frequently come to the surface, but Text-Fic. E.—Surface view of a young embryo of Nucula delphinodonta. they may be entirely covered by test cells. A more or less distinctly recognisable test cell lies between the cerebral ganglia and the apical plate, but beneath this test cell the cerebral ganglia and the apical plate are in contact. ‘The two cerebral ganglia seem to originate from a single mass of cells. There is no indication of the formation of cerebral pouches, as in Yoldia (Text-fig. V). The position occupied by the developing body of Nucula does not make it necessary for the cerebral ganglia to shift their position from the point of their formation until the test is shed. ‘The apical plate is composed of a number of cells, the walls THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 321 of which are rather indistinct (fig. 15, ap.). They bear cilia that in size and distribution resemble those that cover the test cells. Under favourable conditions the test cells can be seen to be arranged in five rows; occasionally part of a sixth row is present. As in other stages, the boundaries between the test cells are poorly marked, and it is quite impossible to sketch them accurately. Text-fig. E shows their general arrangement, but it must be understood that this is quite diagrammatic. The cilia on the test cells of this species are not collected into bands as they are in Yoldia (Text-fig. F), TExt-Fic. F.—Surface view of a forty-five hour embryo of Y oldia limatula. ac. Apical cilia. 4/. Blastopore. «. Depression where the cells that form the cerebral ganglia come to the surface. but are evenly scattered over their surfaces. The embryo becomes free from the egg membrane about the time that the shell-gland becomes covered by the test, but the cilia are barely powerful enough to slowly move the embryo on the bottom of a dish. The absence of the bands of cilia, and of the long tuft of apical cilia, is probably due to the protected life of the embryo. Nucula proxima lays its eggs free in the water, where they are fertilised and develop. These embryos have to shift for themselves, and are very active. Here, as in Yoldia, the cilia on each of the three intermediate rows of test cells are long and collected into a band (Text- A. DREW. GILMAN O22 CS “purls-yjoyg °48 -ayeid jeoidy ‘dp Iqua "\say, “2 “uMapowloyg “775 qnS-pryy “Fu ‘pawisoy oie vlpsues [eaqasoo oy} YoIya Wor S|[PD ‘Hy -axodoyselg “79 ‘B[N4BUI] VIP[OR JO oA ano xis-£,ATY4 B JO WOryoas [By4yLOVs WeIpa|{—'H “9-LXAT, THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 9323 fig. H). Sometimes part of a fourth band is present. The end rows of test cells have the cilia evenly scattered over their surfaces. The apical cilia are long and bunched into a sort of whip that precedes the embryo when it swims. In fact, the embryo resembles that of Yoldia so closely that, except fora difference in size and a slight difference in shape, a description of the surface appearance and movements of one will do very well for the other also. The cilia on the embryos of Nucula delphinodonta may then be regarded as arrested in their development. Life in the protecting brood-sac makes active locomotion unnecessary and even dangerous, inasmuch as active embryos would be likely to find their way out of the brood-sac, and so be exposed to outside dangers. The embryos continue to elongate and begin to flatten slightly laterally (fig. 23). In the living embryo, viewed by transmitted light, this stage is marked by the appearance of a light spot near the dorsal margin. A smaller, much less distinct light spot has been present near the ventral margin for some time, and corresponds in position to the cavity that was mentioned as appearing in the mesoderm, ventral to the gut. This space has enlarged considerably (fig. 24), but is covered laterally by rather thick walls of ectoderm and by some mesoderm, so it is not very distinct. ‘lhe dorsal space is formed by the arching up and flattening out of the cells of the shell-gland, which are now beginning to form the mantle lobes (fig. 20). It is bounded dorsally, laterally, and poste- riorly by the mantle, anteriorly by the mantle and the apical plate, and ventrally by the gut and by the body-wall. A few cells, apparently mesodermal, lie in this space, generally attached to the mantle or to the gut. At a little later stage (fig. 25) two fibre-like cells stretch from the anterior end of the gut posteriorly and dorsally to the mantle. They are quite conspicuous in living embryos, and they retain their position until after the test is thrown away. About this stage the gut, which has grown posteriorly, DREW, GILMAN A, 324 “\soy, "2 ‘lunepowoyg ‘ps “puels-ljoyg “6s “yns-piyy “Fu -ayeld jeotdy ‘dv ‘ewrxoid eynonyy jo ofiquia anogq aay-AyU9M4 & JO MOTOS [eqIL¥s ULIPO|Y—'F{ “9M-LXTY, THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 325 acquires an anus (fig. 24). The anus is not directly applied to the pore that opens between the test cells, but it opens into a cavity that is continuous laterally with that portion of the embryo that, as the mantle continues to grow, becomes the mantle chamber, ‘This communication will be described in a later stage. The embryo flattens laterally until its thickness equals about two thirds of its dorso-ventral width, and the dorsal space becomes considerably enlarged (fig. 25). Near the anterior end ot this space the anterior adductor muscle (aa.) makes its appearance. At first it consists of a very few fibres, and is not conspicuous. The anterior enlarged portion of the gut takes on the distinctive characters of the stomach (sto.), and the liver grows out as paired right and left pouches (/.). The anterior end of the stomach is carried dorsally, and a more or less distinct bend is made where it joins the intestine. The relationship of the various cavities in the embryo to each other, and of the anal pore in the test to the mantle chamber, can be best understood by comparing the sagittal, horizontal, and transverse sections of embryos, represented on Plate 22, with the reconstruction of an embryo at the same stages of development (Plate 21, fig. 25). The position of the horizontal and transverse sections are indicated on fig. 25 by numbers that correspond to the numbers of the figures. The dorsal cavity is separated from the ventral cavity by the gut (fig. 28). Insome sections the two cavities communi- cate around the sides of the gut. ‘This may be due to shrinkage, but it seems more likely that the two portions are parts of a single cavity. Itis just possible that the cleavage cavity never entirely disappears, and that this cavity can be traced back to the blastoccele, but I am of the opinion that it is a later formation, and represents a schizoceele. Its fate is of interest, and will be referred to in later stages. The lobes of the mantle are now well formed, a distinct shell-cuticle has been secreted, and some lime salts have been deposited. ‘he stomodzum for most of its length is joined, DREW. GILMAN A. 326 “UOIPSULS [BIOS A ‘6a “yay, 7 “UNBpoWoyg “p7s “]JAYG *S “BIHUVS [esqa1ad at]} OF BdvjANS ot]} WO} Surpes, yonog “4 ‘uorsues jepag “4d ‘ajosnut soyonppe soliaysog “vd *4sho0\Q *70 "pues aAlysaorp af} JO 9qoy 4J9'T *77 ‘qmiysoyuy “ze “goog ff “wuosued perqaisg “40 ‘arodoyseig 79 “ello wordy ‘97 = “ajosnut 10joNppe LOWayWY “v7 ‘eIplo Jeaide oy} ynoyyIM Suoy ‘wut Z. aie suousedg “opis 4Jo] ay} Wo1y U9ds ST ofiquia ayy, "JO 4sBO ST 480} ot} o10Joq qsnf oSvys v ye V[NyeWI] eIp[OX jo OkAqua Uv jo UOLoNAysUOdOYy—'] “OIA-LXI, Bas \ ‘HE LIFE-HISTORY OF NUGULA DELPHINODONTA. 327 but is not enclosed by the body ectoderm (fig. 28), which in this region forms the walls of the foot (f.). Near its external opening the stomodeum has become free, and is more or less closely jointed to the test cells. The relation of the anal test pore to the mantle chamber can now be understood. As shown by a sagittal section (fig. 26), this pore opens into a small cavity that receives the anus. This cavity is bounded anteriorly by the posterior wall of the foot, and ventrally either by the stomodeum or by cells covering the dorsal portion of the stomodeum. Transverse (fig. 27) and horizontal (fig. 31) sections show that this cavity spreads out laterally, and becomes continuous with that portion of the mantle chamber posterior to the foot. At this stage the foot is very imperfectly formed, and contains the cavity that has been referred to as the ventral cavity. The cavity soon disappears, and the ectoderm on the two sides of the foot fuse ventrally, dorsal to the stomodeum. The foot is still very small, and shows no sign of its future activity. At a corresponding stage the foot of Yoldia is quite well developed (Text-fig. I). This is about the condition of the embryo when the test is thrown away. It takes several hours for embryos of this species to cast the test, a process that with Yoldia limatula and Nucula proxima is completed within a very few minutes after it is begun. ‘The test cells in the region of the anal pore break apart, and the whole mass is frequently pushed forward to the region of the apical plate. This stripping forward carries the outer end of the stomodzum forward to some such position as is shown by fig. 34. The cilia on the test cells remain feebly active for a considerable time. While the test cells, stomodeum, and apical plate still adhere to the embryo, the stomach and liver pouches are drawn some distance dorsally into the schizoccele (fig. 34, sto. and 1.). Whether the fibres extending from the stomach to the mantle are important in effecting this movement is not known. Their position is suggestive, but I have no direct evidence that they contract. The position now occupied by the stomach 328 GILMAN A. DREW. causes the bend where the intestine joins the stomach to become quite abrupt. At the same time that the stomach moves dorsally, the cerebral ganglia (fig. 34, cg.), which are stilla mass of rather undifferentiated cells, are carried up, and come to lie poste- rior and a little ventral to the anterior adductor muscle (aa.). The foot (f.) retains its position beneath the intestine and / eee | ee E. £ Spee Mie = \ &.. : Ms. pg ! ot '¢ Trext-ric. J.—Reconstruction of an embryo of Yoldia limatula at a stage during casting. Represented as seen from the right side, with the right shell-valve and mantle lobe removed. aa. Anterior adductor muscle. cg. cerebral ganglion. f Foot. g. Rudiment of gill. cz¢. Intestine. ot. Otocyst. pa. Posterior adductor muscle. pg. Pedal ganglion. +. Pouch that leads to the cerebral ganglia. 7/. Right lobe of the digestive gland. s¢d.Stomodeum. f¢. Adhering test cells. vg. Visceral ganglion. stomach, and in the general dorsal movement is carried a little further from the margin of the shell. A similar stage for Yoldia is represented by Text-fig. J. At the end of several hours the stomodeeum (fig. 34, std.) breaks across near the tip of the foot, and together with the apical plate and the remnants of the test cells is thrown away. From appear- ances I am inclined to believe that the whole of the apical THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 9829 plate is thrown away, but this may not be the case. The test cells may or may not remain attached to the apical plate and stomodzum until these are thrown away. Generally many of them break loose or go to pieces before this change occurs, but some of them nearly always remain. After casting is completed (fig. 35) the stomach (sto.) and the liver lobes (/.) are drawn further into the schizoccele, and the liver lobes begin to be flattened out against the mantle. The cerebral ganglia (cg.) lie almost directly posterior to the anterior adductor muscle (aa.), and the ectodermal thickenings that result in the formation of the pedal and visceral ganglia soon begin to form (fig. 36). Thus far in the development of the animal the shell-valves have remained gaping, but after the removal of the apical plate and the stomodzeum they are free to close. ‘This is effected by the contraction of the anterior adductor muscle, and materially diminishes the space between the shell-valves. The closing of the shell is accompanied by important changes in the liver pouches, changes similar to those that have been described for Yoldia (1). Apparently as the result of the mechanical pressure the liver pouches go to pieces, and the large cells of which they were composed become rounded and scattered through most of the schizoccele (fig. 36, z.). The posterior portion of the schizoccele is not filled by the scattered liver-cells. This persists and finally becomes the pericardium. The foot (fig. 39, f.) grows and soon executes feeble move- ments. The pedal ganglia (pg.) and visceral gangha (vg.) take on definite form; the posterior adductor muscle (pa.) appears ; and the imvaginations that result in the formation of the otocysts are formed. Very possibly commissures connect the ganglia at this time, but I have not been able tu distinguish them from the surrounding tissue until a some- what later stage. A thickening on the inner surface of the posterior end of each lobe of the mantle indicates the begin- ning of the formation of the gill (fig. 39, g.). About this time a little invagination on the mid-line of the VOL, 44, PARTY 3,—NEW SERIES, Y¥ 330 GILMAN A. DREW. ventral portion of the foot, just anterior to the heel-like projection, makes its appearance (fig. 39, bg.). This develops into the byssal gland. It grows rapidly until it becomes proportionately very large (fig. 45, bg.), then ceases to grow, and possibly shrinks somewhat. In the adult it is compara- tively insignificant (fig. 48). No signs of byssal threads have ever been observed, nor have the secretions ever been seen to protrude from the duct of the gland. The foot grows rapidly, and the projection that looks like a heel becomes more marked (fig. 40, f.). Anterior to this Text-Fia. K.—Reconstruction of a ten-day embryo of Yoldia limatula. Represented as seen from the right side with the right shell-valve and mantle lobe removed. aa. Anterior adductor muscle. cg. Cerebral ganglion. f£ Foot. g. Gill. iz¢. Intestine. 7/. Left lobe of the di- gestive gland. of. Otocyst. ja. Posterior adductor muscle. py. Pedal ganglion. 7l. Right lobe of the digestive gland. sto. Stomach. vg. Visceral ganglion. projection the sides grow ventrally faster than the interme- diate portion, and finally from the side flaps that are so characteristic of the foot of the adult. Movements of the foot now become energetic. The gill (fig. 40, g.) becomes more pronounced, and soon THE LIFE-HISTORY OF NUOCULA DELPHINODONTA. 331 unequal growth causes it to be divided into two lobes. The dorsal wall of the stomach re-forms, and the liver-cells begin to be rearranged. ‘I'he commissures between the ganglia are distinctly visible. The otocysts (ot.) are quite large, and contain granules. Although adults have canals leading from the otocysts to the exterior, I have not been able to demon- strate their existence in this or somewhat older stages. The presence of the otocystic canal had been explained (18) as the persistent opening of the otocyst, which was formed as an invagination from the surface of the body. This seems to be the natural explanation, but if canalsare present at this stage they are certainly very small. I am inclined to regard the exceedingly small size or absence of these canals as evidence against the view that the otoliths are foreign particles. Thus far most of the embryos have been carried in the brood-sacs, but many of them now become free. They are not set free by any act of the mother, but they individually find their way into the mantle chamber of the mother and so to the exterior. Frequently younger embryos become free, but they generally do not live long. Many embryos remain in the brood-sacs until a much later period, but they do not seem to be in need of its protection after the stage that has just been described. The brood-sacs frequently remain intact after all of the embryos have left them. The more dorsal of the gill lobes elongates into a finger- like process, and the ventral lobe broadens and becomes divided into two lobes (fig. 41, g.). New lobes are thus formed as the result of unequal growth of the most ventral lobe. About the time that the third lobe of the gill begins to form a few papille appear along the margins of the side flaps of the foot (fig. 41, f.). The liver lobes also become hollowed out and lose most of the rounded cells. Part of these cells seem to go to pieces much as if digested (fig. 43), and it seeims quite possible that this is the case, O32 GILMAN A. DREW. The heart (fig. 41, i.) is apparently formed from meso- dermal tissue that collects to form a strand, that runs across the pericardium from one side to the other. I have found no indication of its being formed as paired pouches, as described by Ziegler (20) for Cyclas cornea, nor have I found any evidence that it originates as two masses that grow toward each other. Its first appearance seems to be in the form of a mesodermal strand of tissue that soon hollows out and encloses the intestine. ‘The fact that the heart forms around the intestine, and not dorsal to it, is of interest, and will be discussed under the head of the Circulatory System. The growth of the kidneys, which are now present as small tubes, seems later to force the sides of the heart up around the intestine (fig. 68), so that the ventral portion of the ventricle becomes drawn out into a trough in which the intestine lies. As the kidneys grow the trough becomes deeper. By gradually closing in dorsal to the intestine at the anterior and posterior ends, the trough is shortened, and the intestine finally becomes free from the heart and lies ventral to it (fig. 69). This is accomplished by a very slow process, and is not completed until after the animal has become sexually mature. I am inclined toward the opinion that the kidneys are formed by the differentiation of mesodermal tissue. When they first appear each is a very narrow tube, and extends from its external opening in the mantle chamber to the mid- line of the body. I have not succeeded in demonstrating the inner pericardial openings of the kidneys in this or in later stages. The cells soon become large and vacuolated, and the kidneys grow rapidly and crowd anteriorly ventral to the pericardium, where they become coiled and _ sac- culated. With the formation of the fourth lobe of the gill (fig. 45) processes make their appearance on the bases of the lobes, between them and the mantle lobe to which the gill is attached. ‘hese processes grow to form what have been called the outer gill plates, but in this species their position THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 38388 is better described as posterior than outer. The lobes, at the bases of which the outer plates are formed, develop into the inner plates. Viewed from the side, both sets of plates are visible. The gills of Yoldia hang so that in a side view the outer plates hide the inner plates, which lie directly behind them (Text-fig. L). When viewing Nucula from the side we see that portion of the gill that corresponds to the ventral portion in Yoldia. The labial palps appear as patches of ciliaon embryos with three gill lobes (fig. 41). The outer palps soon begin to grow - sto’ ot’ pe | Text-Fig. L.—Adult specimen of Yoldia limatula. Represented as seen from the right side. Reconstructed to show internal organs. Fully grown specimens may be 6 cm. long. aa. Anterior adductor muscle. afm. Anterior foot muscles, dg. Byssal gland. cg. Cerebral ganglion. es. Wxhalant siphon. f. Foot. g. Gill. 2%. Heart. iz¢. Intestine. is. Inhalant siphon. Zp. Labial palp. of. Otocyst. pa. Posterior adductor muscle. pap. Palp appendage. pe. Posterior expansion of the margin of the mantle. p/fm. Posterior foot muscle. py. Pedal ganglion. sf. Siphonal tentacle. s¢o. Stomach. vg. Visceral ganglion. out as flaps (fig. 45, Ip.), and by the time that the fifth pair of gill plates are formed the inner palps are present as folds. The formation of the ridges on the ciliated surfaces of the outer palps begins with embryos having six pairs of gill plates, and the palp appendages are formed goon after 334 GILMAN A. DREW. (figs. 55 and 56). The development indicates that each palp appendage (fig. 56, pap.) is to be regarded as a pair of ridges with an enclosed groove, developed and modified so that it may be extended beyond the edges of the shell. Little remains to be described in this general sketch of the development, further than to call attention to the formation of the loops of the intestine, that are indicated in different stages of development by Text-figs. M to 8; to the forma- tion of the cartilage pit and teeth on the valves of the shell; to the formation of more gill plates and foot papille as these organs continue to grow ; to the appearance of the otocystic canals about the time that the sixth pair of gill plates are formed ; and to the formation of the genital organs. Mention should be made of a peculiar closed pouch (figs. 40, 48, and 63, v.), of unknown function, that lies just anterior to the anterior adductor muscle. It makes its appearance in embryos that are just getting the second gill lobes, and is fairly conspicuous in adult animals. Germ Layers. An almost spherical embryo is formed as the result of the first few cleavages (fig. 5), the cells on one side of which are much larger than those on the other side. The large cells extend far into the interior of the embryo, and the smaller cells form a cap over the larger ones (fig. 4). In reaching this stage of development the embryo has passed through a blastula stage, in which the cleavage cavity was very small (fig. 3). As the cells become arranged in the manner described, the greater part of the cleavage cavity disappears. It has not been determined whether any of it remains or not. A depression appears near one side of the group of larger cells at a point corresponding to the asterisk in fig. 4. This depression seems to be formed by the separa- tion and further division of some of the large cells, and results in the formation of the gut (fig. 8, mg.). The surface cells may now be regarded as ectoderm, and at least two kinds may be distinguished: small ones, which THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 335 finally form the test, the apical plate, the cerebral ganglia, the stomodzum, and a considerable portion of the future ecto- derm of the embryo; and large ones that form the shell-gland. The endodermal pouch is carried further into the interior by the division and pushing in of ectodermal cells in the region of the blastopore (figs. 9 and 11, mg.). In this way a long stomodzeum is formed on the ventral side of the de- veloping embryo. ‘The ectodermal covering of the later embryo, exclusive of that derived from the shell-gland, seems to be formed in connection with the formation of the stomo- deeum, by cells that wander in from the region of the blasto- pore, and perhaps from cells derived from the stomodeum itself. About the time that the stomodzeum begins to form, a few cells, two of which are quite large and conspicuous, make their appearance by the sides of the endodermal pouch, and extend between it and the shell-gland. These are meso- dermal cells. Their exact origin has not been traced. As the embryo elongates, the two large cells come to lie near the posterior end of the embryo (fig. 19). They probably correspond to similar cells that have frequently been de- scribed for other forms. Similar cells are found in Yoldia in a corresponding position. Test. As the result of the first few cleavages a number of large cells become covered on one side by a cap of smaller cells (fig.4). A part of the smaller cells become covered with cilia, about the time that the gut is formed (fig. 8) ; others near the blastopore divide rapidly and form the stomodeum (figs. 9 and 11) ; still others form the cerebral ganglia ; while others in the region of the blastopore wander in and form a part of the future ectoderm. The cells that bear cilia are concerned in the formation of the test and apical plate. These cells soon cover the surface that is not occupied by the shell-gland and the cerebral ganglia. Both the apical plate and the cerebral ganglia are 336 GILMAN A, DREW. small at this stage, consist of a very few cells, and can hardly be distinguished from the surrounding cells. ‘he apical cells acquire cilia about the time that the test cells do (figs. 9 and 11), and for some time they cannot be distinguished from them. Later the apical plate may be told by its shape and position (figs. 1d and 24, ap.). As development proceeds the test begins to close in over the shell-gland from the sides and anterior end (figs. L1O—13). Five rows of test cells can now be seen under favourable conditions, but their outlines are very hard to determine. Until the shell-gland is covered, two or three of the posterior rows are incomplete dorsally. A small pore is left near the posterior end, separated from the blastopore by the width of one test cell (fig. 1d). The anus comes to lie near this open- ing (fig. 24). The five rows of cells are now arranged much as shown in Text-fig. li. From the formation of the test until its ultimate disappearance its cells are evenly ciliated with short cilia. In this respect the embryos differ from those of Yoldia limatula (Text-fig. F) and Nucula proxima (Text-fig. H). Both of these forms have the cilia on each of the three inter- mediate rows of test cells collected into a band. Sometimes a fourth more or less complete band is present. ‘The cilia on the end rows of the test cells of all of the forms are short and evenly scattered over the surfaces of the cells. In this connection it is of interest to observe that the cilia on the apical plate of Nucula delphinodonta are short and independent, while those on the apical plates of Yoldia limatula and Nucula proxima are long and bunched together. They all seem to have a rather scattering origin, and when animals are killed the cilia become separated from one another. In both species of Nucula the embryo differs from that of Yoldia limatula in having a posterior opening in the test, dorsal to the blastopore (fig. 15, and Text-figs. G and H). This difference might easily be accounted for by a slight dif- ference in the closing in of the test over the shell-gland. THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 337 The ciliated embryos of Nucula delphinodonta, unlike those of the other two forms, are not able to swim freely in the water. At the most they are barely able to move on the surface of a glass dish. This is probably the result of their being carried in a protecting brood-sac. It seems but natural that the bands of strong cilia and the apical tuft of cilia would not be developed by embryos such as these, were there no need for active locomotion, and where active locomotion would be dangerous. It is for the best interest of embryos that they remain in the brood-sacs, where they are protected from many enemies. Were they capable of active movement, many would probably escape and perish. In the two related forms, Nucula proxima and Yoldia hmatula, the embryos have to depend on their own activities for their existence. It is highly probable that the embryos of the ancestors of Nucula delphinodonta led an active, free-swimming existence. ‘The rearing of embryos in protecting brood-sacs is very possibly connected with the present life of the animal beneath the surface of the mud, and, in any case, has prob- ably been acquired at a comparatively recent day. Again, the test in its present condition is of no appreciable value to the embryo, and no doubt is to be regarded as a vestige of a once functional organ. Young embryos of Nucula delphinodonta when taken from the brood-sacs do not live well, and it is accordingly difficult to determine how long the test is retained. As near as could be judged, it seems to be retained about two weeks. Its cells then begin to break apart near the posterior end of the embryo, and many of them move toward the anterior end, where they remain attached to the apical] plate and the stomodeum (fig. 34). Sometimes most of the cells of the test seem to thus accumulate at the anterior end, but they fre- quently become detached and go to pieces before reaching this position. In any case they, together with the apical plate, and the stomodzum, to the position of the future mouth, are finally thrown away (fig. 35). In many cases the 338 GILMAN A. DREW. process of casting occupies several and sometimes as many as fifteen hours. The process is much more rapid for both Yoldia limatula and Nucula proxima (2). It is quite possible that the difference in the length of the time occu- pied by the different embryos is connected with the differ- ence in the conditions under which they develop. Further study has tended to confirm my view that the test should be regarded as the homologue of the velum of other forms. In a former publication (1) I made the statement that “in either Dentalium or Patella, if we imagine the velum to be stretched posteriorly over the shell-gland dor- sally, and the foot ventrally, so as to enclose the body, the cesophagus will be pulled out into a narrow tube ventral to the foot, and the position of the blastopore will correspond to its position in Yoldia. Furthermore the position of the foot and shell-gland will correspond, and the alimentary canal will be bent in the same way.” ‘This states the case backward, and may be a little confusing. If we begin with the condition found in Yoldia and Nucula, and imagine the test to shrink until it consists of a band of ciliated cells sur- rounding the embryo anterior to the mouth, the condition would be comparable to that shown by embryos of Den- talium and Patella. As in the case of Yoldia, the closest resemblance to the test, outside of the group,is shown by Dondersia. Although Pruvot’s (15) account of these embryos is very short, and only three figures are given, there is quite a striking external resemblance. In both cases the surface cells are arranged in five rows, all of which bear cilia. They are both provided with apical plates, and with both the test is finally thrown away. The bodies of the embryos of Dondersia protrude posteriorly during development. A slight posterior protru- sion of the body of Nucula sometimes takes place through the opening dorsal to the blastopore. The resemblances shown by embryos of Dentalium (8 and 9) and Patella (12) are not so striking, but they are somewhat similar. The apparent posterior protrusion of the THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 339 body in each of these forms is such as might be produced if the body of Nucula were to grow and protrude to a corre- sponding extent. In such a case the test of Nucula would occupy a corresponding position to that occupied by the velum in the other forms. Apical Plate. At an early period the cells of the apical plate cannot be distinguished from those that form the test, but as develop- ment proceeds they become marked off as a rather definite plate at the anterior end of the embryo (figs. 11, 15, and 24, ap.). This plate is relatively large and thick, and extends posteriorly as far as the stomach. The cells from which the cerebral ganglia are formed lie ventral to it (figs. 15 and 24, cg.). Beneath the test the cerebral ganglia and the apical plate are in contact. The cells of the apical plate are evenly ciliated with short cilia, like those borne by the test cells (fig. 15). In this respect this species differs from both Nucula proxima and Yoldia limatula. Both of these forms have long apical cilia (Text-figs. G and H) that during life are bunched together (Text-fig. F). Nucula proxima has an apical plate that in extent may be compared to that of Nucula del- phinodonta, but the apical plate of Yoldia is comparatively very small. The short, diffuse cilia on the apical plate of Nucula delphinodonta are probably the result of the conditions that make active locomotion at this stage both unnecessary and dangerous. (See what is said regarding this under the head of Test.) Certainly most of the apical plate, and probably all of it, is cast away when the test is shed (figs. 34 and 35). Shell. Some lime salts are deposited soon after the cuticle of the shell begins to be secreted, which takes place about the time that the lobes of the mantle begin to form (fig. 20). When the test is shed (figs. 834 and 35), the shell-valves are white, 340 GILMAN A. DREW. glossy, and quite transparent. They do not correspond to the adult valves in shape (fig. 50), and they do not have the long, straight hinge-line of the prodissoconch of Yoldia (Text-fig. K). The hinge-line is not very definitely marked off from the rest of the shell, but it can be distinguished as a nearly straight or shightly curved portion on the dorsal margin (fig. 36). The difference in the shape of the prodissoconches of Nucula and Yoldia is quite marked, more marked than might have been expected for forms so closely related, when there is so much resemblance between the prodissoconches of many Lamelli- branchs (6). They both conform to the same type, how- ever. At first the valves are thin and have neither cartilage pit nor teeth. Soon after casting, a little knob of cartilage (fig. 36, ca.) makes its appearance near the middle of the hinge- line. The teeth do not form until a much later stage (fig. 46). About the time that the fifth pair of gill plates are formed, a tooth appears on each valve in front of the cartilage pit. This 1s soon followed by another, which is added anteriorly. The teeth posterior to the cartilage pit begin to appear about the time that the third tooth anterior to the cartilage pit is formed. New teeth in the posterior series are added pos- teriorly. Only about half as many teeth are formed posterior to the cartilage pit as anterior to it. Apparently as long as the shell continues to grow in size new teeth are added. Shells of fully grown specimens are about 4 mm. long, but they sometimes occur nearly 5 mm. long. Hach shell-valve is very convex (figs. 50 and 51), slightly oblong, and moderately thick. The beaks are directed pos- teriorly and placed far back on the shell. This gives an appearance quite the reverse of most Lamellibranch shells, which have the beaks nearer the anterior than the posterior ends, and directed forward. ‘he cuticle of the shell differs in different specimens from horn colour to dark brown or nearly black. It may be considerably broken near the beaks, but it is generally quite perfect and smooth. Unlike most Lamellibranchs, the shells of this species contain so much HE LIFE-HISTORY OF NUCULA DELPHINODONTA. 341 animal matter that they retain their forms after the lime salts have been dissolved away. ‘The material is quite tough, and frequently causes much trouble in cutting series of sections. Kach valve of the shell of fully adult animals has from ten to twelve teeth in the series anterior to the cartilage pit and five or six posterior to it (figs. 50 and 51). All of the teeth are more or less conical, pointed, curved toward the dorsal margin of the shell, and distinctly grooved on the side away from the cartilage pit. Mach series of teeth forms a ridge some distance from the dorsal margin of the shell, which disappears dorsal to the adductor muscle-scar. The teeth of the two valves interlock so completely that it is frequently quite impossible to separate the valves without breaking some of them. The cartilage pit is large and deep. The adductor muscle-scars and pallial lines are faintly marked. Mantle. The shell-gland is formed early. About the time that the eut is formed it consists of a number of large cells that lie near the blastopore, on what may be distinguished as the dorsal side of the embryo. Its cells do not seem to bear cilia, but only preserved material was at hand for the deter- mination of this point. The surrounding ciliated cells, those that form the test, begin to grow over the shell-gland from the sides and anterior end (figs. 10, 11, 12, and 13, sg.). At the same time the shell-gland flattens shghtly, and the cells along its margins push up and form a slight ridge, that keeps the surface of the shell-gland separated from the overgrowing test. Soon after the shell-gland is covered by the test, it arches dorsally, and the two come to he close together (figs. 17 and 18, sg.). As the embryo flattens laterally the shell- eland arches dorsally still more (fig. 20), and a space appears between it and the intestine. This space seems to be formed by the multiplication and flattening of the cells of the shell- oland, which arches dorsally and becomes separated from the intestine. Lateral folds (fig. 20, m.), the beginnings of the 342 “GILMAN A. DREW. mantle lobes, are soon formed. About this time the shell cuticle is secreted and some lime salts are deposited. Soon after casting has been completed, swellings, the beginnings of the gills (fig. 39, g.), are formed near the posterior margin of each lobe of the mantle. The gills are thus formed as appendages of the mantle. The mantle now has the adult structure and appearance, except that at a later stage a portion of its inner epithelium, and of the epithelium covering the suspensory membranes of the gills, becomes converted into the hypobranchial glands. These glands are present in both sexes, but just before the breeding season they are much better developed in the females than in the males, and there is considerable evidence that they furnish most, if not all, of the material from which the brood-sacs are formed. The margins of the mantle lobes remain thickened and contain the glands that secrete the cuticle of the shell. Some cells along the ventral and pos- terior borders of the mantle lobes bear cilia. Pallial muscles are attached to the shell-valves, and extend out to the margins of the mantle. These serve to retract the margins of the mantle when the shell is tightly closed. Foot. At a stage such as is represented by figs. 14 and 15, a group of cells lie between the gut and the stomodzum. These cells, together with the ectodermal side walls, are concerned in the formation of the foot. The side walls of the foot are continuous with the general ectodermal covering of the body beneath the test. The cells lying between the gut and the stomodeum are apparently mesodermal, and en- close a small space (figs. 15 and 24). The shell-gland spreads out, arches dorsally, and folds laterally to form the mantle, and a large space is left between it and the stomach and in- testine (figs. 20, 24, and 26). In some transverse sections the space between the stomodzeum and the intestine, and the space dorsal to the intestine, are more or less connected. ‘This connection may be due to shrinkage caused by pre- TH LIFE-HISTORY OF NUCULA DELPHINODONTA. 349 servatives, but it seems probable that the two spaces are naturally more or less definitely connected around the sides of the stomach and intestine, and that they may be regarded as a single cavity-—a schizoccele. The side walls of the foot join the stomodzeum, and are not continuous with each other ventrally (figs. 20 and 28). Just before the test is cast away they begin to unite dorsal to the stomodeeum, and the stomodzeum becomes comparatively free. This change begins at the posterior end of the foot and works forward. The process of casting is slow, and includes a large part of the stomodeum. When it is completed, the foot consists of a small mass of tissue, lying ventral to the stomach and intestine (figs. 34 and 35, f.). It is not capable of executing movements, and for a period of about a day, or even longer, the embryo lies perfectly quiet with the shell-valves tightly closed. At first I supposed that this comparatively im- mature condition of the foot at the time of casting was con- nected with the protected life of the embryo. The foot of Yoldia executes movements before the test is shed, and bur- rowing is begun almost as soon as the process is completed. It seemed natural to conclude that the greater development of Yoldia at this time depended upon the necessity for self- preservation. It was surprising, then, to find that at a cor- responding time the foot of Nucula proxima is no better developed than is the foot of Nucula delphinodonta. This seems very remarkable to me, for Nucula proxima inhabits muddy and shelly bottoms over which flow quite strong tidal currents. Under these conditions it would seem that such perfectly helpless embryos would surely perish. The foot of Nucula delphinodonta grows rapidly, and by the second day (fig. 36) performs feeble movements, but it is not thrust out of the shell for some time. It becomes provided with cilia (figs. 39 and 40), but they are not as powerful as those on the foot of Yoldia (Text-fig. K), and they are of but little service in locomotion. The first movements of the foot are feeble twitches. These 344. GILMAN A. DREW. in time become more frequent and powerful. Finally the foot is thrust out of the shell, stretched ventrally and anteriorly, swelled up at the end, and held more or less rigid while the cilia vibrate. After being held in this position for a few seconds it is withdrawn, either to remain quiet for some time, or to be immediately thrust out again. The earlier move- ments are not very energetic, and as the side flaps have not been formed, they are not like the movements of the adult. The first indication of the side flaps consists of a slight longitudinal groove on the mid-line of the ventral surface of the foot. On each side of this groove the foot grows to form flaps (figs. 40 and 61) that he side by side. Soon after the test is shed, a rounded knob develops on the postero-ventral portion of the foot (fig. 36). This grows quite rapidly, and forms the prominence that appears like a heel (figs. 40 and 41). It soon stops its rapid growth, and in the adult is comparatively small (figs. 48 and 49). In this species it is comparatively much larger in the adult animal than in any of the otber species that I have studied. The side flaps at first have smooth margins (fig. 40), but papillee soon begin to be formed (fig. 41). The anterior papille are formed first, and new ones are added posteriorly as the foot grows, until as many as thirteen pairs have been formed (fig. 48). The number differs with the size of the individual. Sexually mature specimens may be found with no more than eight pairs. The papillae are large, conical, more or less pointed, and very sensitive to mechanical stimu- lation. The movements of the foot of this species when compared with the movement of the foot of Yoldia are very deliberate, but the foot is so large, and the muscles so powerful, that burrowing is quite rapid. Individuals of this species seem normally to live entirely covered by mud, in which they wander around by slow thrusts and retractions of the foot. Specimens do not seem to come to the surface of the mud to remain for any considerable time, and it seems probable that the greater part of the lives of individuals are passed beneath THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 93495 the surface of the mud. Observations made on specimens kept in dishes of sea water in which there was no mud show that individuals of this species execute movements very similar to those executed by Yoldia (1), but that in all cases they are much more deliberate (8). Leaping movements are absent, but slow thrusts with the flaps extended may fre- quently be observed. In former publications attention has been called to the characteristic movements of the foot, and they need not here be redescribed (1 and 3). Asin the case of other members of this group, the movements of burrowing are very effective. The somewhat spherical shape of the shell, and the relatively large size of the foot, make it possible to raise the shell from the bottom of a dish, and occasionally to keep it balanced for a few seconds over the expanded foot. My observations lead me to believe that the animals never creep. As in Yoldia, the foot is supplied with complicated and powerful muscles (1 and 8). It is attached to the shell by three pairs of muscles, and by a few fibres that lie ventral to the genital mass and liver. ‘The posterior pair of foot muscles is very powerful. ‘These muscles are attached to the shell at the bases of the teeth, just anterior to the pos- terior adductor muscle, and extend along the sides of the foot in an anterior and ventral direction. They are the powerful retractor muscles of the foot. Fibres from them are extended into the muscular flaps, and are important in spreading them apart. The two anterior pairs of foot muscles correspond to the three anterior pairs of foot muscles in Yoldia. They are in- serted on the shell close together along the bases of the teeth, just posterior to the anterior adductor muscle. ‘The most anterior pair has much the same distribution as the two anterior pairs in Yoldia, and in some cases each muscle seems to be shghtly separated into two near its origin. They spread out along the sides of the foot, and are distributed to its posterior and ventral portions. These muscles seem to be closely connected with the muscle-fibres that are attached voL. 44, PART 3.—NEW SERIES. Z 346 GILMAN A. DREW. along the sides of the shell ventral to the genital mass and liver. The more posterior of the two anterior pairs of foot muscles passes between the pair just mentioned, and is dis- tributed to the anterior and ventral portions of the foot. In the foot all of the muscles are closely bound together by their own fibres and by interlacing fibres, so that many movements occur that cannot be explained by direct pulls of one or more muscles. It should constantly be borne in mind that the attachments of the fibres are all along the sides of the foot, and that many, if not most of the muscle-fibres pull from one portion of the body-wall to another, without chang- ing the relation of the body to the shell. Thus the flaps can be spread apart after the shell has been removed. By com- pressing the blood contained in the large spaces of the foot, many movements, especially those connected with protruding the foot, may be performed. As in the case of Yoldia, the foot muscles are so large that they are attached along a considerable portion of the dorsal surface of the shell. I regard this as the result of the size of specialised muscles, and do not agree with Pelseneer (18) that it should be regarded as a primitive character. Byssal Gland. The byssal gland is formed as an invagination, just ante- rior to the posterior projection of the foot, about the time that the side flaps of the foot begin to form (fig. 39). Although there is but a single external opening, the gland at first con- sists of right and left pouches that extend into the foot near its posterior side. The cells forming the upper portion of the gland soon become somewhat swollen, and do not stain very well with hematoxylin. The lumen of the gland soon shows traces of a secretion, but the secretion has never been seen protruding from the duct. The gland soon enlarges to a remarkable extent, becomes quite irregular, and the paired appearance disappears. At this stage, which extends from about the time that the gill acquires its third lobe (fig. 41) until about the time that it HE LIFE-HISTORY OF NUCULA DELPHINODONTA. 9347 acquires its fifth pair of plates (fig. 45), the byssal gland extends through a considerable portion of the foot, and in the posterior side of the foot it may extend to a position somewhat dorsal to the pedal ganglia. The cells of the gland during this stage are greatly swollen and vacuolated, and have thin, almost indistinguishable walls. They are crowded together so as to almost obliterate the lumen of the gland. The result is that stained sections of the gland have the appearance of a fibrous or reticular mass that is so mixed up as to be hardly intelligible. As the embryo gill begins to acquire its fifth pair of plates the byssal gland generally becomes less extensive. In the adult it is reduced to a small pouch (fig. 48, bg.) that opens in the median groove of the foot, just anterior to the heel- hike projection. ‘The dorsal, blind end of the pouch consists of comparatively large cells with small nuclei, and seems to contain some secretions. ‘They are not generally distended with secretion, and the duct is generally quite empty. Nothing comparable to byssal threads have been observed. ‘Towards the opening of the gland the cells become smaller and bear cilia. I have described the adult condition that seems most fre- quently to prevail. In a few specimens the gland cells are much shrunken, and seem to contain little or no secretion. In some specimens of Nucula proxima the gland is more extensive and the cells are greatly distended. ‘This would seem to indicate that the gland is functional, but not as an organ for the formation of threads. The present use of such a secretion is problematical. It is very natural to compare this gland to the mucus- secreting glands of Gastropoda, but there seems to be little direct evidence that they are homologous. Alimentary Canal. There is a stage when the embryo resembles an evibolic gastrula (fig. 4). A pouch appears between the large cells, at a point corresponding to the asterisk, that seems to be formed 348 GILMAN A. DREW. by the separation of some of the larger cells, accompanied by their division into smaller cells. This pouch is the first indication of the alimentary canal (fig. 8, mg.). Partly by the division of cells forming it, and partly by the addition of ectodermal cells around the blastopore, the gut is carried further into the interior (figs. 9 and 11), and comes to lie at the end of a narrow tube, the stomodzum (fig. 15, std.). The blastopore never closes, so from its first appearance the stomodzeum is connected with the gut. The blind end of the gut turns dorsally beneath the shell- gland (fig. 11, mg.), and soon begins to grow posteriorly (fig. 15,7nt.). It finally comes to the surface at the posterior end of the embryo at a point ventral to the shell-gland and dorsal to the blastopore (fig. 24), where the anus is formed. The anus does not open directly to the exterior, but opens into the mantle chamber near an external opening in the test. The alimentary canal at this stage consists of three distinct parts (fig. 24) : aslender tube, the stomodzeum (std.), opening through the blastopore and extending forward nearly to the apical plate that is formed from the ectoderm ; a rather thick- walled stomach (sto.) that hes dorsal to the anterior end of the stomodewum, and ventral to the shell-gland; and the intestine (int.), which joins the posterior end of the stomach, and at first has rather thick walls. Dorsal to the stomach and intestine, between them and the shell-gland, a cavity makes its appearance that communicates by lateral passages with another cavity that les ventral to the stomach and intestine, between them and the stomodzum. The ultimate fate of these cavities has been referred to in the sketch of the lfe-history, and in connection with the foot, and will again be referred to in connection with the peri- cardium. For some time they are rather large, and a portion of the alimentary canal is left quite free from surrounding tissue, except where it seems to rest on the walls of the developing foot (fig. 28). A short time before the test is shed the liver pouches make their appearance (fig. 25, 1.). These are formed from the sides of the anterior end of the stomach. THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 349 The cells of the epithelial walls of the stomach are of two kinds. Those at the anterior end of the stomach carry com- paratively few cilia, and those at the posterior end carry many cilia. At this stage some of the cells on the dorsal side of the stomach, near its anterior end, begin to secrete a mucus-like material that extends posteriorly in the lumen of the stomach as a small rod that probably represents the crystalline style (fig. 26). Later the posterior portion of the whole dorsal division of the stomach (the part that at this stage is the dorsal part of the anterior portion) is given over to secreting this material, but a definite rod may not be present. About the time that the embryo casts its test the stomach grows dorsally into the space above it, so that a ventral bend is formed where the stomach joins the intestine (fig. 26). This is the beginning of the abrupt bend that marks this portion of the alimentary canal in later hfe. Two fibre-like cells stretch across the dorsal space from the anterior end of the stomach to the mantle (fig. 25). Their position suggests that they may aid in moving the stomach into the more dorsal position, but there is no direct evidence that this is the case. When the test is cast away and the adductor muscle pulls the shell-valves together, the stomach is crowded further into the dorsal space, and the bend in the intestine becomes more pronounced (figs. 84and385). The same pressure appa- rently causes the liver pouches to go to pieces. Their cells become more or less separated, and fill the larger part of the cavity dorsal to the stomach (figs. 86—39, z.). The same changes have been noticed in embryos of Yoldia limatula and Nucula proxima. In all of these forms the changes occur in connection with the closing of the shell. Until the test is shed, tissue hes between the valves of the shell so that they cannot be shut together. When the tissue is removed, and the shell is closed, there is no longer room for the liver pouches to lie on the sides of the stomach and retain their original shape. ‘They are accordingly flattened and pressed 350 GILMAN A. DREW. into the unoccupied space dorsal to the stomach. The cells are no longer arranged to form definite walls (figs. 836—39, z.), but later some of them seem to form liver pouches again (figs. 42—44). A small portion of the space into which the stomach and liver are crowded is not filled, and finally forms the pericardium (figs. 39—41), The rupture of the lver pouches leaves the dorsal part of the stomach without side walls, and the dorsal wall is commonly broken (figs. 37 and 39). The dorsal wall is formed again before the liver pouches regain their cavities (fig. 40). Some of the separated liver cells find their ways into the open stomach (figs. 87 and 38), and together with mucus practically fill it. For a period of two or three days after casting, the animal is not active, and it is doubtful if it feeds. At the end of this time the walls of the stomach begin to re-form, and the mass of material that has filled the stomach has largely disappeared. For a number of days the liver does not form definite pouches. The rounded and scattered cells are finally collected into two masses (figs. 40 and 42) that finally form new liverlobes. The left is slightly larger than the right mass, but the masses are more nearly equal in size than is the case with Yoldia. In both cases it seems that the difference in the size of the two liver lobes causes the developing loops of the intestine to take up a posi- tion on the right side. Cavities gradually extend out into the liver pouches from the stomach (figs. 43 and 44). In the formation of the cavities some of the rounded cells seem to oo to pieces in much the same way as they would if digested. The elongation of the intestine that results in the forma- tion of the loops begins about the time that the embryo acquires its fourth pair of gill plates (fig.45). ‘This elonga- tion carries the portion of the intestine that lies dorsal to the posterior adductor muscle toward the posterior wall of the stomach and nearer the dorsal margin of the shell. The end of the loop is forced over to the right side, and is extended anteriorly nearly to the anterior wall of the stomach. At this stage (Text-fig. O) the loop of the intestine is much like THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 351 the loop that occursin adult Yoldia limatula (Text-fig. L). The dorsal bend now begins to elongate and project ante- riorly (Text-fig. P). This continues until the loop is ex- tended between the limbs of the loop that was made first (Text-fig. Q). The lower limb of the loop begins to elongate (Text-fig. R), and the adult condition is soon reached (Text- fig. S and fig. 48). ‘The heart makes its appearance some time before the loops i Ol AS fio NW fi¢O FIG g (GO), . Text-rics. M, N, O, P, Q, R, anv S.—Stages in the development of the loops of the intestine in Nucula delphinodonta. of the intestine begin to be formed (fig. 41). From the first appearance of its cavity the heart surrounds the intestine. This condition continues for a long time, until the loops of the intestine have been formed, and, in fact, until after the Bay GILMAN A. DREW. animal has reached sexual maturity. At first the intestine passes through the middle of the heart (fig. 67). The sides of the heart seem later to be forced dorsally by the growth of the kidneys, and the intestine becomes applied to the ventral wall of the heart. By the continued growth of the kidneys the ventral portion of the ventricle is drawn out into a trough, in which the intestine lies (fig. 68). The growth is continued until the trough is considerably deeper than the width of the intestine. By gradually closing in dorsal to the intestine at the anterior and posterior ends the trough is shortened, and the intestine finally becomes free from the heart and lies ventral to it (fig. 69). In the adult animal (fig. 48) the cesophagus is a rather broad and long, nearly cylindrical tube, that opens between the palps just posterior to the anterior adductor muscle. I find no indication of anything that can be interpreted as salivary glands at any stage in the development (18). Throughout its length it is evenly cilated and quite devoid of ridges. The corners of the mouth are continuous with the groove between the two labial palps. The stomach is large, somewhat spindle-shaped, and extends from near the dorsal margin of the shell to the level of the pedal gangha. Near its middle there is a nearly complete ridge of elongated epithelial cells, and frequently a more or less well-marked external groove that divides it into a dorsal and a ventral portion. The posterior and part of the lateral walls of the dorsal portion of the stomach are formed by long and slender epithelial cells that stain but slightly. ‘They secrete a mucus-like material that stains deeply, and probably corre- sponds to the crystalline style. In adults this secretion seldom takes the form of a rod, but in embryos a rod is commonly present (figs. 26, 28, 30, and 64). The remaining cells in the dorsal portion of the stomach are short, stain deeply, and are evenly ciliated. The ducts from the liver open in the dorsal end of this portion of the stomach. The epithelial cells of the ventral portion of the stomach are short, stain deeply, and carry a quantity of short cilia. THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 353 Leaving the ventral end of the stomach, the intestine bends dorsally, and follows the posterior walls of the stomach nearly to its dorsal end. Here the loops already described are formed. From the loops the intestine passes posteriorly ventral to the heart, bends around the posterior side of the posterior adductor muscle, and opens in the mantle chamber. It is composed of short ciliated cells that stain deeply. Its lumen varies greatly in size, according to the amount of matter it contains. Labial Palps. Soon after the embryo acquires its second gill lobe the epithelium around the mouth, and for a short distance along the sides of the body, becomes ciliated (fig. 41). This cilia- tion precedes the formation of the palps, and, to a certain extent, marks out the region where they will form. The cilia are more numerous immediately anterior to the mouth than they are immediately posterior toit, and they soon extend along the sides of the body for about half the width of the foot. The position of the ciliated patches on the body-wall is such that the dorsal portion of each tends to lie horizon- tally, and the ventral portion tends to the vertical position (fig. 62, Jp.). The groove thus formed becomes the groove between the outer and the inner palps. The portion above the groove forms the outer palp, and that below the groove the inner palp. This is accomplished by the growth and folding of the body-wall. The outer palp begins to grow first, and in such a way that the line marking the dorsal limit of the cilia becomes the free margin of the palp. This leaves the inner surface of each outer palp covered with cilia, and the outer surface unciliated. The two outer palps are continuous anterior to the mouth, where they form a slight ridge (figs. 54 and 63). For some time after the outer palps form folds, the inner palps are represented by ciliated ridges (fig. 54), that reach some distance beyond the posterior ends of the outer palps. These ridges grow so that the lines marking the ventral limit 3504 GILMAN A. DREW. of the cilia become the free margins of the inner palps. The two inner palps are continuous posterior to the mouth, where they form a slight ridge (figs. 55 and 63). Like the elevation anterior to the mouth, this never becomes prominent. The inner surface of each outer palp becomes folded near its anterior end to form ridges and grooves (fig. 55), and the postero-ventral portion protrudes to forma lobe. This lobe is the beginning of the formation of the palp appendage. The edges of this lobe soon begin to thicken, and a groove is left between the ridges thus formed. ‘This is accompanied by a considerable growth in length (fig. 56, pap.). At this stage of development the palp appendage is seen to corre- spond to two of the ridges on the general surface of the palp, with a groove enclosed between them. Posterior and dorsal to this appendage another smaller appendage is formed (fig. 56). This is also on the outer palp, and consists of two ridges with a groove between them. It never grows to be very long, but resembles the large appen- dage that lies ventral to it in its formation. As development proceeds the larger appendage (fig. 56, pap.) twists, so that its groove opens dorsally and posteriorly (fig. 57, pap.), and the smaller appendage twists so that its groove opens ventrally. This double twisting brings that portion of the small appendage that was dorsal nearly or quite in contact with that portion of the large appendage that was ventral, so that for a short distance the two grooves together form a tube that opens anteriorly between the two palps (fig. 57). During the development of the palp appen- dages both outer and inner palps have grown to be quite large, and their ciliated surfaces have been thrown into series of ridges and grooves. The palps on each side of an adult animal consist of two large, somewhat triangular folds of tissue (fig. 48, /p.), united to each other along their dorsal margins, and suspended from the body-wall by a thin membrane. The onter palps on the two sides of the body are connected in front of the THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 309 mouth by a small ridge that occupies the position of an upper lip. In the same way the inner palps are connected by a ridge posterior to the mouth that is comparable to a lower lip. The corners of the mouth are continuous with the space between the two palps of each side. The opposed surfaces of the palps are densely ciliated, and thrown into a series of ridges and grooves that tend to he opposite each other on the two palps. Near the free margins this arrange- ment may be considerably broken. Large blood-spaces follow along these ridges. Hach outer palp is supplied with two grooved appendages that originate near its dorsal margin. The most ventral of these appendages (fig. 48, pap.) can be extended far beyond the margin of the shell, and is used to elevate mud with the contained food. The dorsal appendage sets over the anterior end of the groove of the ventral appendage, and with it forms a short tube that opens between the palps. Hach ventral palp appendage is supplied with longitudinal muscles (fig. 66, /m.), that are continued in from the body-wall; with a large nerve (pn.) that originates in a cerebral ganglion, and runs posteriorly along the united dorsal margins of the outer and inner palps; and with a continuous blood-space (bs.). The epithelium lining the groove of the appendage is very thick, and is densely covered with cilia. The nuclei of these epithelial cells are very long and slender. The muscles in the palp appendages are so placed that their contraction causes the appendages to curl, as shown in fig. 48, pap. _ It is not easy to observe individuals of this species while they are feeding, as they normally live entirely covered by the mud. If specimens are placed in a dish of sea water, in which there is only a thin layer of mud, the action of the palp appendages may be observed. It is well to use as much mud as_ possible without affording the animals an opportunity to bury themselves, and to use specimens that have not been in mud for several days and are accordingly hungry. The mud is passed along the grooves of the palp appendages by the action of the cilia, and finally conducted 356 GILMAN A. DREW. between the palps, where the cilia carry it to the mouth. Very few specimens have shells that are transparent enough to allow observation of processes carried on inside of the shell, but there can be no doubt as to the path taken by the mud after it has started up the grooves in the palp appen- dages. Feeding is much more easily observed in the case of Yoldia limatula. In this species the animal has fre- CUE, ccs Trext-ricg. T.—An adult specimen of Yoldia limatula as it appears while feeding. es. Exhalant siphon. ds. Inhalant siphon. pap. Palp appen- dages. st. Siphonal tentacle. quently as much as one third of the posterior end of the shell above the mud while feeding (Text-fig. T). The palp appen- dages are protruded, and one at least bends over and inserts its tip in the mud. By the action of the cilia in the longi- tudinal groove, large quantities of mud and food are elevated. There is no reason to suppose that the palp appendages of THE LIFE-HISTORY OF NUCULA DELPHINODONTA. Bat Nucula are not as effective as those of Yoldia, but the method of life makes observation more difficult. As suggested by Mitsukuri (11), it seems probable that the large palps with their numerous large blood-spaces may be important respira- tory organs. Gills. A short time after the embryo sheds its test, a portion of each lobe of the mantle near its posterior border begins to thicken (fig. 39, g.) and then to project anteriorly. These thickenings are the beginnings of the gills. They grow rapidly, acquire cilia, broaden dorso-ventrally, and each begins to divide into two lobes (fig. 40, g.). The formation of the lobes is due to unequal growth more than to constriction. Hach lobe is at first a little knob that is flattened slightly laterally. As growth proceeds the ventral lobe broadens and flattens along its anterior border preparatory to the formation of another lobe. Coincident with these changes in the ventral lobe, the dorsal lobe grows anteriorly, and forms a rather long finger-like process or filament, that closely resembles the filaments of the developing gills of other Lamellibranchs (fig. 41, g.). New lobes are added to the gill by the unequal growth and division of each ventral lobe in its turn, and as the new lobes are formed the more dorsal lobes lengthen. Throughout life the gill occupies a decidedly dorso-ventral position, but growth carries the ventral end some distance toward the posterior end of the animal, so that the adult gill lies somewhat diagonally (fig. 48, .). In Yoldia (Text-fig. L) the gills lie more nearly parallel to the long axis of the body. The chitinous support of the gill makes its appearance when the gill is still in the two-lobed condition. At first it consists of a thin plate lying just beneath the epithelium on the anterior border of the gill, and is continued from one lobe into the other. Its ends he near the anterior extremity of each lobe. As the ventral lobe flattens the chitinous plate is extended along its anterior border, so that with the 358 GILMAN A. DREW. formation of the third lobe the plate is extended into it. In this way, as new lobes are formed, the chitinous plate is extended into each, and continues to be connected throughout the length of the gill. As the lobes grow to form filaments, the chitinous plates extend with them, and each becomes trough-shaped with the open side of the trough directed away from the corresponding lobe of the mantle. Later the free edges of the trough are brought near to- gether, and the support in each filament practically assumes the form of a tube that extends out nearly to the tip of each filament. The tubes that support the different filaments are united at their bases, so the chitinous support is continuous throughout the gill. As the lobes elongate to form filaments, the cilia on each becomes restricted, so that the side that is turned away from the lobe of the mantle to which it is attached becomes quite free from them. On the remaining sides the cilia are long and powerful. About the time that the fourth division of the gill is formed the mantle begins to thicken at the bases of the fila- ments, between them and the shell (fig. 45). These thicken- ings are generally opposite the bases of the filaments, and connected with them, but as there are sometimes more plates on one side of the gill’ of the adult animal than on the other, the thickenings are probably not always formed in this position. They represent the beginnings of the outer plates of the gill. The filaments, at the bases of which these thickenings are formed, form the inner plates of the gill. For a considerable time the outer plates remain much smaller than the inner plates, and they never quite equal them in size (fig. 53). As the outer plates of the gill are formed, the chitinous support is carried out into them as branches from the portion that runs lengthwise of the gill. 1 The term gill is for convenience applied to the respiratory organ on one side of the animal, although writers agree that it probably corresponds to tne two gills found on each side of most Lamellibranchs. HE LIFE-HISTORY OF NUCULA DELPHINODONTA. 359 These branches become trough-shaped, with the open part of the trough directed away from the inner plates. Finally, the free edges of the troughs come close together, as described in connection with the other set of filaments or plates. The chitinous material at the bases of the two sets of plates also becomes trough-shaped, and has the open portion of the trough directed away from the plates. Thus the chitinous support of the gill consists of two series of troughs, bent so as to form tubes, each of which is connected by one end to the side of a larger trough that runs lengthwise of the gill. The whole might be compared to a large trough with a series of spouts leaving each side, the individual spouts of the two series being placed opposite each other. Later, bridges are built across the main trough in the intervals between the side spouts. The whole system is in direct communication with the blood-spaces of the gill, but probably is not concerned with the circulation of the blood. The two sets of plates do not lie parallel to each other, but they grow away from each other at an obtuse angle. The inner plates grow almost in an anterior direction, and the outer plates grow laterally and a little posteriorly, so that the angle formed by the two sets of plates on the two sides of the gill is visible when the animal is viewed from the side. The suspensory membrane, formed by the growth of the mantle at the base of each gill, makes it possible for the gill to take up this position. The filaments begin to grow into flattened triangular plates about the time that the fourth division of the gill is formed. This is accomplished by slow, unequal growth, and throws no light on the phylogeny of the gill. It seems to be a matter of individual opinion whether each of the plates should be considered to be homologous with a descending filament of an ordinary Lamellibranch gill, or whether it should be con- sidered to be homologous with both a descending and an ascending filament. The adult structure of the gill of Nucula has been so care- fully and accurately described by others, that were it not for 360 GILMAN A. DREW. the sake of completeness, 1 would not be necessary to describe it here. Mitsukuri’s (11) description of the gill of Nucula proxima holds good in all essentials for the gill of this species, and since his description was published others have verified and supplemented his results (7, 13, and 16) until our knowledge of the structure is comparatively com- plete. The adult gill of Nucula delphinodonta is suspended from the body-wall by a fold of tissue, the suspensory mem- Vm Text-Fic. U.—A pair of plates from a gill of Yoldialimatula. 4s. Blood- space. cr. Chitinous rod. //m. Lower longitudinal muscle. sz. Sus- pensory membrane. wim. Upper longitudinal muscle. v. Cut surface of achitinous rod. y. Cut wall of the gill plate where it bends to join the plate anterior to it. brane (fig. 53, gs.), that was originally a fold on the inner surface of the mantle lobe. The suspensory membrane contains between its walls a large blood-space that communi- cates near its anterior end with the auricles of the heart, and throughout its length communicates with blood-spaces in the mantle. At intervals it communicates with similar spaces in the body proper. Unlike the suspensory membrane of Yoldia (Text-fig. U), this membrane is not very muscular, but some THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 3861 muscle-fibres are always present. The epithelium covering the outer surfaces of the suspensory membranes, those surfaces that are turned away from the mid-line of the body, is modified to form a portion of the hypobranchial glands. Each suspensory membrane bears two series of gill plates that generally lie opposite to each other. Occasionally a gill occurs in which there are more plates on one side than on the other, but even in these cases the order is interrupted only for a short distance. The number of plates differs with the size of the individual, but about twenty pairs seems to be common for well-grown specimens. Hach plate is thin and triangular, and is composed of epithelial walls, between which there are loose connective tissue, large blood-spaces, and the chitinous framework. The epithelial walls on the edges of the plates that are directed away from the suspensory membranes are thickened and covered with strong cilia. This thickened ciliated epithelium extends between the plates for a short distance, but most of the epithelium is quite thin and destitute of cilia. The wall of each plate is continuous with the wall of the plate that lies in front of it, with the wall of the plate that lies behind it, and with the plate on the other side of the gill that lies opposite to it. Near the border furthest from the suspensory membrane, the opposing walls of the two series of gill plates are separated so as to form a large blood-space (fig. 53, bs.), that runs the whole length of the gill. This space is continued as a narrow slit to the base of the suspensory membrane. Thus the blood-space in the suspensory membrane is in direct communication with the blood-space of each plate, and in the gill the blood is free to flow from one part to another. The chitinous framework consists of a bridged trough that occupies the bottom and part of the sides of the blood-space that hes between the two series of plates, and of two series of side spouts that project into the plates on the two sides, and le in contact with the thickened epithelium. Although the chitinous framework is arranged as a system of troughs and spouts that, from their position, must be filled with VOL. 44, pany 3,—NEW SERIES. AA 362 GILMAN A. DREW. blood, they are probably not directly concerned in the circu- lation of the blood. Between the chitinous trough and the suspensory mem- brane there is a small bundle of muscle-fibres that are con- tinued the whole length of the gill (fig. 53, Im.). This bundle lies in the open part of the chitinous trough, and probably corresponds to the large bundle that occupies a similar position in the gill of Yoldia (Text-fig. U, llm.). > / LEO gt, iG) Fig Ft Toe one a ‘ / ’ , al ~ . . . ® th : iy, =a ¢( F . x ’ j . / 4 \ ‘ i ' aaatons te pee ee i Bite ti ‘ a ey del A Drew GC! Yur. Jon Neor Sa Vot.44.NS PA.28. soe ee oe eee. “¥ : Ci S ae ; - ; : a oe Be Patt: ly Guy & , ts Nae ay VS : CYL ) 3 : ie 6) : bt te “FS Y SD tere RI sae every termeennony reerr earning ail —— \ = ham moe Siete Dor hon Aen rarer geile } | . E reir A'S Huth [it? London - BS aes e WES; fs ha ay a } wee Furr Mor Sv WSC ORS Re SL, hin er ae pemeee NT ta ds - ¥ ve S me 3 tv PN ES eS at cle ee A a a) GA Drew del, Quart. Sourn, Mion See Dt. EES IRE Do) Pe ati , Rt PRPS OREN Liq. 60. AS Huth Lith? London me ees pee a co aa WO. CW ae eA “alll Nets ‘i bi a STRUCTURE OF THE HAIRS OF MYLODON LISTAI. 393 On the Structure of the Hairs of Mylodon Listai and other South American Edentata. By W. G. Ridewood, D.Sc., F.L.S., Lecturer on Biology at the Medical School of St. Mary’s Hospital, London. With Plate 26. ‘THE interest attaching to the discovery of portions of well- preserved skin of a great Ground Sloth, very closely allied to if not identical with Mylodon, was considerably increased when it was found that the hairs do not agree in their minute structure with those of the Tree Sloths, Bradypus and Choleepus. While agreeing with the latter in the absence of a definite medulla, they are destitute of the extra-cortical layer which characterises the hairs of Bradypus, and have not the fluted surface which is such a distinctive feature of the hairs of Cholcepus. The characters of the hairs have been commented upon by several authors in the course of their remarks upon the remains of this ground sloth, but the subject has never been treated exhaustively ; and Professor Ray Lankester suggested to me that the matter was worthy of further inquiry, and that it was desirable to compare the newly discovered hairs not only with those of Bradypus and Cholcepus, but also with those of the ant-eaters and armadillos. The order Edentata, as at present constituted, will proba- bly prove to be an unnatural assemblage of animals, and it may become necessary, when our knowledge is more complete, vou, 44, PART 3,—NEW SERIES. CC 394. W. G. RIDEWOOD. to remove the Old World forms Manis and Orycteropus, to constitute two new orders by themselves. For the present purpose, however, the relationships are not material, except for the fact that the late traveller Ramon Lista saw and shot at a curious animal in South America, which he likened to a hairy and scaleless Pangolin. It is generally denied (Ameghino [1], Lonnberg [7, p. 168]) that this “ pangolin ” was the Mylodon of which the skin and bones have more recently been found. Accounts of the various pieces of skin fiacaver ed have been published by Ameghino (1), Lonnberg (7), Roth (14), Smith Woodward and Moreno (18), and Smith Woodward (19). The locality from which Dr. Ameghino obtained his specimen is not stated, but the other pieces of skin were found on different occasions in the loose earth of a cavern near Consuelo Cove, Last Hope Inlet, Patagonia. The deposit in which they were found is regarded as of Pampean age, and there can be no doubt that these ground sloths were con- temporaneous with man, if not actually living in the cavern in a state of domestication. Concerning the generic name, there appears to be no valid reason why Mylodon should not be used. The genus was first established by Owen in 1840 (11, p. 68), the type species being Mylodon Darwinii. ‘Two years later Owen (12) de- scribed a nearly complete skeleton of a ground sloth which he called robustus, and referred to thesame genus. Reinhardt (13), writing in 1879, showed that the two species were generically distinct, and renamed the earlier specimen Grypotherium. If, however, the rules of priority are to be observed at all, the term Mylodon should be retained for the species Darwinii, and the robustus should be accorded a new generic name. ‘lhe argument that the species robustus was fully described, whereas Darwinii was represented only by a fragment of jaw, is obviously inadmissible, for if the fragment is sufficiently perfect to enable Reinhardt’s specimen and those recently discovered to be regarded as generically identical with it, it is sufficiently perfect and important to STRUCTURE OF THE HAIRS OF MYLODON LISTAI. 399 act as the type of the genus. Glossotherium, a genus founded by Owen in 1840 (11, p. 57), is admitted by himselt (12, p. 154) to be identical with Mylodon Darwinii, and this genus may thus be dismissed as asynonym of Mylodon. The same fate befalls Neomylodon, since the newly dis- covered specimens to which the name was applied are widely regarded as generically, if not specifically (Nordenskj6ld [10]), identical with Owen’s MylodonDarwinii. Until, however, the specific identity has been more fully established it is preferable to retain Ameghino’s specific name of Listai for these remains. The hairs of Mylodon Listai have been described by Lonnberg (7), Jacob (4), and Smith Woodward (18 and 19), and transverse sections have been figured by the first two authors. The descriptions presuppose a knowledge of the hair structure in Bradypus, the ant-eaters and armadillos, and so in the present communication the consideration of the Mylodon hairs and the criticism of the views of these three authors are left till the last. The method adopted for the examination of the hairs was in all cases the same. The hairs were arranged with the roots pointing one way and the free ends the other; they were tied up in bundles, stained with a weak alcoholic solution of magenta, washed and dehydrated. The bundles were then soaked in xylol, and transferred to hard paraffin. After cooling the paraffin was cut into convenient blocks, and the sections were made by hand with a sliding motion of the razor. It was found that better results were obtained in this way than by the employment of any form of microtome. Some of the sections were mounted in glycerine jelly, but the majority in Canada balsam, since the former medium has the disadvantage of dissolving out the stam. A few hairs of each of the species studied were stained and mounted whole. For the Mylodon hairs I am indebted to the kindness of Dr. F. P. Moreno; the hairs of the other Kdentata were obtained from dried specimens in the Natural History Museum, London, 396 W. G. RIDEWOOD. Bradypus tridactylus. The hairs of Brady pus are oval in section, and exhibit a central clear area and a darker marginal area (fig. 3). The central area stains very-faintly if at all with magenta, and being brittle is apt to crack in the cutting. It is marked by a small number of minute air spaces, the true shape of which is fusiform. ‘The long axis of each spindle is parallel to the length of the hair, and consequently the transverse sections of the spaces are larger or smaller according as they are cut through the middle or near the ends of the spindles. ‘The outer substance stains deeply, and is thickly marked with dark granules, and exhibits at the same time two sets of radiating lines—a set of very fine and closely set lines around the outer edge, and a set of coarser and more irregular lines branching out from the central mass. The average size of the transverse section 1s 2404 x 145m. The outer substance is a layer not represented, or at least not in this form, in the hair of any other mammal. It does not extend the full length of the hair, but stops short near the free end, and is absent from the basal third of the hair. In optical section (fig. 4, upper part) 1t exhibits an oblique striation. ‘The terminal portion of the hair (the “‘ Endfaden ” of Welcker [17]) has the normal structure of a non-medullate hair with a scaly cuticle, but at a certain distance from the point the diameter increases quite suddenly by the addition of this new layer (fig. 2). The diminution in the width of the central core at this point is probably not real, but an optical effect due to the refrangibility of the external layer. The figure represents an optical section, not an actual slice taken from the middle of the hair. The basal third of the hair is thin as compared with the distal part, and measures only 64 across (fig. 6) ; it appears transparent when the hair has been clarified and mounted whole. In addition to the minute fusiform air spaces it frequently has larger air-filled cavities, blunt ended, and about 60, long and 6 u broad. The transverse section of this part of the hair is nearly STRUCTURE OF THE HAIRS OF MYLODON LISTAI. 397 circular (fig. 5). In all parts of the hair of Bradypus the cuticular scaling can be seen by suitable staiming and accu- rate focussing. That the central part of the hair of Bradypus is a cortex, and not medulla, as Eble supposed (2, Bd. 1, p. 440, and Taf. x, fig. 111), and that the peripheral part is extra-cortical, has been ably shown by Welcker (17), who applied the name ‘* Belegschicht ” to it. The relation which the extra-cortical layer bears to the normal cuticle is very difficult to determine. A careful examination of the part of the hair where the transition occurs between the normal terminal portion and the part provided with the extra-cortex (fig. 2) shows that the arrangement of the imbricate scales of the cuticle is con- tinued without interruption upon the exterior of the extra- cortical layer, thus seeming to show that the cuticle is con- tinued over the outer surface of this layer. The extra-cortex, however, is very friable in old hairs, and comes away readily, leaving the central column of cortical substance bare; and it is then seen that the surface of the column is marked by lines taking a more or less transverse course, and suggesting forcibly that the cuticular scaling is continued on the surface of the cortex beneath the extra-cortical layer. There is yet a third possibility, which may eventually prove to be the correct interpretation, since it accounts for both sets of appearances. It is that the extra-cortical layer is the cuticle itself, enormously thickened and distinctly cellular, instead of more or less homogeneous and structureless. ‘The arrangement of the cells would account for the markings on the external surface of the hair, and the scaly appearance of the cortical rod when laid bare would be due to the impress left by the extra-cortical cells. ‘The appearances presented by that basal part of the hair where the extra-cortex is just dwindling away certainly favours the third supposition. The cells of the extra-cortex get thinner and thinner, and come to resemble the scales of the cuticle. They become more firmly adherent to one another and to the cortex, they appear more homogeneous, and they stain less deeply. The figure given 398 Ww. G. RIDEWOOD. by Welcker (17, Taf. 1, fig. 11) of the young hair in its follicie at a time when the extra-cortex is forming would appear to allow of no alternative proposition. Yet Welcker was disposed to regard the Belegschicht as a new tissue inter- calated between the cuticle and the cortical rod (17, p. 44) ; and the effect obtained by macerating the hair in water, and thus causing a thin cuticular layer to peel off (17, Taf. i, fig. 14), lends support to his view. But this effect is very possi- bly due to the excessive cuticularisation of the outer parts of the external cells, and not to any morphological distinction of layers. Leydig (6, p. 687) took the extra-cortex, or at least a part of it, to be the cuticle, for he observed that, contrary to the generalisation made by Reissner and Reichert, the hair cuticle does contain pigment granules in one mammal, namely, Bradypus. Waldeyer (16, p. 186) supported, in the main, Welcker’s contention, and regarded the “ Rindenmantel ” as a layer peculiar to the sloths, and lying below the cuticula ; and Leche (8, p. 934) is probably only adopting Welcker’s suggestion when he remarks of the “ Umkleidungsschicht ” that ‘sie besteht aus einer zwischen Cuticula und Rinden- substanz gelegenen pulpdsen, lufthaltigen Zellenschicht.” Maurer (8, p. 278), on the other hand, holds that the thicken- ing of the distal part of the hair of Bradypus is mainly effected by the cuticle (Oberhautchen). His account, how- ever, is very confusing, since he speaks of a medulla extend- ing two thirds of the length of the hair, and of the cortical cells being pigmented; and although he gives the title of Welcker’s classical paper in his bibliography, he fails to contrast his own observations with those which this author had already placed on record. The biological significance of the extra-cortical layer is full of interest, and has been made known by the writings of Welcker (17) and Sorby (15). The layer has a tendency to crack in a transverse direction, and in the cracks there come to lodge unicellular alge, to which Kihn (17, p. 66) has given the name Pleurococcus Bradypi. The moisture of STRUCTURE OF THE HAIRS OF MYLODON LISTAI. 399 the climate in which Brady pus lives enables the alga to live and propagate in this curious position, and the sloth acquires a general green tint, which must render it very difficult to distinguish as it hangs among the green foliage. In thick transverse sections of the hair these algal bodies show up very clearly, since they stain deeply, and have a sharply defined, circular or slightly oval outline. Unless the hair is much broken they are confined to the outer parts of the extra- cortical layer. In addition to the larger hairs just described, Bradypus has a set of shorter and much finer hairs, constituting the under-fur. These hairs have a diameter of 24, and consist of a column of cortical substance traversed by fine fusiform air spaces, and covered by an imbricated cuticle (fig. 7). Like the larger hairs of the body, they have no medulla. Cholcepus didactylus. The hairs of Cholepus are no less remarkable than those of Bradypus, but in a totally different way. The bulk of the hair is composed of cortex, the surface of which is fluted orchannelled. The grooves, as is well known, are occupied by strands of extra-cortex, in which lives an alga—the Pleuro- coccus Cholepi of Kithn (17, p. 66). Even from the hairs of dried museum specimens a green solution, giving the absorption bands of chlorophyll, can be obtained by boiling first in water and then in alcohol. When seen in transverse section (fig. 8) the outline is oval, and measures about 150 x 904. The cortical substance is in some cases quite clear and hyaline, but in others it is marked by brown spots—differences presumably related to the age of the hairs. In both cases this cortical substance does not stain with magenta. But running throughout, except towards the summits of the superficial ridges of the hair, are irregular branching lines, which stain deeply, and are discernible in unstained sections by reason of their different refrangibility. In very thin sections these lines are 4.00 WwW. G. RIDEWOOD. seen to be empty tubes, with a deeply staining lining. These conditions do not appear to be paralleled in the hair of any other animal. ‘The branching tubes may possibly represent a diffused medulla, for in most hairs the medulla stains deeply and becomes largely infiltrated with air. This is the view taken by Waldeyer (16, p. 187), who writes that the hair shows “einen grossen centralen Markstrang, der aber durch Balken von Rindenschicht vielfach durchsetzt ist,’ and by Welcker (17, p. 55), according to whom ‘diese Markrohre ist, wie bereits Erdl[8] erwahnt, innerhalb des dickeren Thiels des Haars nicht circumscript, sondern in eigenthiimlicher Weise mit Rindenschicht untermischt.” Maurer’s account of the hair structure in Cholcepus (8, p. 278) is as unintelligible as his description of that of Bradypus. He speaks of the cortex being thin in the broad part of the hair, thereby implying that a compact central medulla is present. The cuticle is present, and it 1s imbricate, as can be seen by the serrated appearance of the edge of the hair when viewed in optical section. By staining rapidly, and washing before the deeper parts of the hair have become affected, the edges of the scales can be seen when the surface of the hair is infocus. This is particularly the case with the hairs of the under parts of the body, which have fewer longitudinal grooves than those on the back. On the summit of the ridges the cuticle is thick and highly refractive, but how the cuticle is continued from one ridge to the next it is difficult to determine. In very thin sections the cuticle can be traced down the sides of the groove, becoming thinner and thinner, and disappearing at the bottom. The grooves would thus seem to be morphologically outside the hair. Yet it can be seen in many places that the grooves are not perfect, as if made with a plough, but are discontinuous ; and each portion is canoe-shaped, open to the exterior at its middle, but covered in at the two ends. Sections taken across the end of such a segment of the groove show a continuous cover of cuticle (see a, fig. 8), and in surface view, with carefully stained specimens, the edges of the cuticular scales can be traced STRUCTURE OF THE HAIRS OF MYLODON LISTAL 401 across. It is no uncommon thing to find a ragged flap of cuticle overhanging the groove, as at 6 in fig. 8. ‘These facts tend to show that the grooves are subcuticular ; Welcker, in fact, goes so far as to state (17, p. 56) that the cuticle bridges over the grooves except in certain places, and his fig. 21 lends support to this view. And yet there is no denying the fact stated above, that the cuticle can be traced down the side of the groove. The logical conclusion, therefore, to which these facts point is that the grooves are morpho- logically intra-cuticular, a view which is in complete accord with the third suggestion offered in the case of the extra- cortex of Brad ypus—that the cells are those of the cuticular layer, more numerous and less cuticularised than usual. The hairs of Cholewpus are as a rule coarse, and with a single curve extending over the greater part of the length, while the basal fourth or so is wavy ; but in young specimens, and in some apparently adult specimens from Costa Rica, the hair is very delicate and soft, and sinuous from base to point. The differences may be specific,! or due to age, season, or sex. However, in these forms the hairs are only about 42 u across, and have only two or three furrows instead of the more usual nine, ten, or eleven. The alge, also, are quite absent from many of the grooves. When such an empty groove is examined in optical section (fig. 12) it exhibits the outlines of obsolete extra-cortical cells, the edges of which are conterminous with those serrations of the margin which indicate the edges of the cuticular scales. In baby specimens more than half of the hairs are slender, non-medullate cylin- ders, with very distinct scaly cuticle, and no grooves on the surface. They are only slightly shorter than the two- or three-grooved hairs just referred to, and constitute the nearest approach to an under-fur found in Choleepus. 1 The species didactylus and Hoffmanni were supposed to differ in the number of cervical vertebre. Although this distinction has broken down, Cholepus Hoffmanni may still prove to be a good species. Until more aceurate knowledge is available concerning the geographical range and internal anatomy of the so-called species of Cholepus the point must remain open. 402 W. G. RIDEWOOD. In Cholepus, as in Bradypus, the hairs are very thin at their basal ends (60 »). The flutings of the surface die away on the basal sixth of the hair, and here the structure is that of a normal non-medullate hair (figs. 10 and 11). The cortex 1s not marked by the deeply staining branched tubes, but is rendered slightly granular by the presence of a number of fine air spaces, some spherical and scattered, some sphe- rical and arranged in series of five or six, lke strings of beads, and some fusiform, as though formed by the coales- cence of such series of smaller cavities. ‘The cuticle is thin and distinctly imbricate. There are in Cholcpus no fine hairs to constitute a proper under-fur, and Welcker has remarked (17, p. 70), “ Der Gegensatz von Stichelhaaren und Wollhaaren fehlt bei Cholepus;” but de Meijere (9, p. 361) has described some flattened, stiff, and slightly curved hairs, much shorter than the ordinary hairs, and possessed of large medullary cells, surrounded by avery thin cortical layer. ‘These hairs I have searched for in vain. Myrmecophaga jubata. ‘he hairs of the great ant-eater are much flattened, and resemble a ribbon which is thinner in the middle than toward its edges. ‘lhe actual measurements are—breadth 400 uy, thickness in the middle 110, thickness near the edge 170 np. The cuticle is thin for the size of the hair, and exhibits, rather indistinctly, the usual imbricate or serrate appearance, according as a surface view or an optical section is taken. The cortex is full of air spaces (fig. 14), which are provided with a deeply staining lining after the manner of the branch- ing tubes which permeate the cortex of the Cholcpus hair. These spaces, however, can hardly be regarded as a diffused medulla, since a true medullary region is here differentiated ; and the suggestion made to this effect in the case of Cho- loepus thus receives by analogy a partial refutation. When the hair is examined from the side the cortical vacuoles are STRUCTURE OF THE HAIRS OF MYLODON LISTAI. 403 seen to consist of rows of six or seven spherical spaces arranged in the direction of the length of the hair. he middle spaces of each series are the largest, and the terminal ones the smallest, so that the general effect is that of a seg- mented spindle. In the pigmented parts of the hairs the pigment granules are disposed mainly around the smallest air spaces at the ends of the spindles. The central part of the hair is occupied by a slit-like air space partially filled with a highly refractive substance, which shows no traces of its cellular origin as the medulla so frequently does. The basal part of the hair is more cylindrical in shape than the middle part; and the medullary cavity dwindles gradually away, to disappear altogether in the part of the hair within the follicle, or just outside it. The basal parts are trans- parent, owing to the reduction in the number and size of the air vacuoles. A section of the hair taken about 3 mm. out- side the follicle is shown in fig. 15. Tamandua tetradacty la. In this ant-eater the hairs are less coarse than in Myr- mecophaga, and have the form of slightly compressed cylinders. The transverse section is oval in form, measures 140 w x 90 mw, and exhibits a solid, non-medullate area of cortex, marked with numerous brown spots arranged in groups (fig. 16). The cortex is enclosed within a thick and tangentially stratified cuticle of clear, highly refractive aspect. Hxamined from the side the cuticle shows the usual imbricate markings. The basal part of the hair is more circular in section; it is free from the brown granules, and contains only a few scattered air spaces of minute size. Cyclothurus didactylus. The two-toed ant-eater has in addition to the principal hairs of the body a well-developed under-fur of much finer hairs. The whole pelage is soft and fluffy. ‘The principal hairs, although much smaller than those of Tamandua, do AOA W. G. RIDEWOOD. not differ from these in any essential respect. ‘They have a fairly thick cuticle, but no medulla. They are broadest at about one sixth of their length from the free end, and in this part the cortex is coloured brown by numerous granules ; whereas in the basal half or more these are wanting, and the hair appears quite clear, with just an odd air vacuole here and there. The scaling of the cuticle is very strongly marked on the basal part of the hair, but in the pigmented portion it is less easy to distinguish. In the fine hairs of the under-fur the cuticular scaling is the most obvious feature. The greatest width of the larger hairs is 70 «4; that of the supplementary hairs 20 p. ‘There is, however, no rigid distinction between the two kinds of hair, and transitional forms are fairly common. Chlamydophorus truncatus. The soft fur of Chlamydophorus is made up of fine non-medullate hairs, the average breadth of which is 17 pu. The cortex 1s transparent and unpigmented, and contains only a few scattered granular markings. ‘The scales of the cuticle project considerably, and give a ragged appearance to the surface of the hair (fig. 17). Dasypus sexcinctus and villosus. In both species the hairs are coarse, brown, and oval in section. When examined from the side they show a fine and close longitudinal striation, due to the arrangement of highly refracting granules in fusiform series. The cuticular scaling is close, and can be made out only with difficulty. In Dasypus villosus (fig. 19) the section is less perfectly oval than in Dasypus sexcinctus (fig. 18), since it tends rather towards the rectangle in shape. ‘There is a distinct slit-like medullary cavity in D. villosus, but this is wanting STRUCTURE OF THE HAIRS OF MYLODON IISTAI. 405 in D. sexcinctus ;! the cuticle, also, is considerably thicker. In both species the granules in the cortex are most thickly set at some little distance from the margin, thus leaving a central part and a peripheral part of the cortex relatively clear. The long diameter of the oval measures about 230 u in both species. Tolypeutes conurus. Tolypeutes has solid hairs provided with a thin, finely scaled cuticle. The minute structure very closely resembles that of the Dasypus hairs; in fact, except for their lighter colour, these hairs might be considered as of intermediate character between those of the two species of Dasypus examined. The sections are oval in shape (fig. 20), and there is a central clear area suggesting a medulla such as occurs in Dasypus villosus, but it has no cavity, and does not stain differently from the cortex. The cortex contains bright granules, not of a brown colour, disposed most thickly around the central clearspace. Nearer the base of the hair the section is circular (fig. 22), and has no central clear area. The width of an average hair at its broadest part is 200 p. Tatusia novemcincta and pilosa. The hairs of T'atusia are clear, solid, and non-medullate, with a sharply marked cuticular scaling and a very faint longitudinal striation. In transverse section the cortex appears very clear, and contains only a few highly refractive colourless granules (fig. 23). These are uniformly distributed, and are particularly scarce in Tatusia novemcincta. The sections of the hairs of T. pilosa are oval, and measure 115 x 95 uw; while those of T. novemcincta are circular in shape, and measure 130 across. Mylodon Listai. The hairs of Mylodon Listai are solid, and without any 1 Lénnberg (7, p. 162) speaks of D. sexcinctus as though its hairs possessed a central pith. 4.06 W. G. RIDEWOOD. trace of medulla. The width is very uniform, and measures 170 » throughout the middle six eighths of the hair. The basal eighth is shghtly narrower, and the free end tapers gradually to a blunt point, which is missing from most of the hairs. : _ Sa Ne i RF oblique — -—- muscles rophiidia \ spermatheca’ \ epidermis intestie utestuve F Quart. Journ. of Microsc. Sctenee N.S VOLAALL, 28. intestine nephiridium ~~~ ; ~7>~ sperm - SAC See SSI pa aa eee 4 { . er ath CC a = ~~ septam * / % i em . N ‘ 5 5. : ‘ . a s ‘ : Me - ; 4 P . - ) 4 a - - Hs ie 2 re a - . a ' } : * E ee ae ‘ p io, ot ” - ey, 7 LSP - er ray et : = : & Be id ~ — a - ei - ’ x ‘ > « a 4 rer Sy x . . 5 - u i aa a od . J 7 7 . : ’ * ~ = . S a , A 7 all rs 7 j a ‘ e 7 ay rn 4 a a ut J : nage ine » arta we. + j 3 - » - % be tS - ws » a y ’ . i 7 7 7 : « q e ie = ol ow | > ms . d Te” 7 BA B Loe ae Rat ae ee ; : : Es a ; : 7 a as .* * le - . é s ak = 7 . eed ie we Ths ae: > um transverse carnal epidermis muscle ! ' t \ oesophageal stomatogasttc COMUNISSUTE TLET DE dorsal vessel vessel oesphageal -t COMMISSIILE stomiatogastrtc TLET DE Quart. Journ. of Microse. Scienee N.S.Vot. 44PL,29. Fig. flor dorsal longi © MALS CLES =3 - ee ge ee ee i ' 1 1 i | 1 1 / ventrTro lateral long wl ff MILES ACS / COMONL intestine longitl muscles \, NS \N : ND al duct Lith. Anst.v.A Funke Leipzig. THE ATIOLOGY OF MALARIAL DISEASES. 429 On the Question of Priority with Regard to certain Discoveries upon the Attiology of Malarial Diseases. By George H. F. Nuttall, W.A., M.D., Ph.D., University Lecturer in Bacteriology and Preventive Medicine, Cambridge. THouas it has long been a popular belief in certain countries that malaria is communicated to man by means of mosquitoes, experimental proof was lacking until a recent date. The history of the mosquito-malaria theory has been amply dis- cussed elsewhere by the writer, to whose papers the reader is also referred for a detailed description of the experimental work on the part played by mosquitoes in the propagation of malarial diseases.! It is not the object of this paper to discuss these matters in detail. Persons who read the medical literature of but one country will naturally become biassed in their judgment. This ac- counts for the fact that at present different investigators receive the credit of having definitely established the part played by mosquitoes in malarial diseases. In view of the confusion which will naturally result from the claims made 1 Nuttall, G. H. F. (1899-1900). I. “Onthe Role of Insects, Arachnids, and Myriapods as Carriers in the Spread of Bacterial and Parasitic Diseases of Man and Animals: a critical and historical Study ;” ‘Johns Hopkins Hospital Reports,’ vol. vill, pp. 1—154, 3 plates (Bibliography). II. ‘* Die Mosquito-Malaria-Theorie,” ‘ Centralbl. f. Bakteriologie,’ vol. xxv, pp. 162— 170, 209—216, 245—247, 285—296, 337—346 (Bibliography). III. “* Neuere Forschungen iiber die Rolle der Mosquitos bei der Verbreitung der Malaria : Zusammenfassendes Referat ;” ‘ Centralbl. f. Bakteriologie,’ vol. xxvi, pp. 140—147, and vol. xxvii, pp. 193—196, 218—225, 260—264, 328 —-340 (exhaustive Bibliography). 430 GEORGE H. F. NUTTALL. in various quarters, it seems eminently desirable to give a brief impartial summary of the experimental work which has been done, relying solely upon published researches, these being cited in their chronological order. With the facts thus marshalled before him every reader is at liberty to draw his own conclusions. The study of the hemocytozoa begins with the discovery by Ray Lankester in 1871 of Drepanidium ranarum. Human malarial parasites were seen, but their significance not comprehended until Laveran published his investigations in November, 1880. Following upon the fundamental work of Laveran, the most important discovery was that of Golgi (November, 1885), who demonstrated the relationship exist- ing between the life-cycle of the parasites within the human body and the occurrence of the febrile attack. With regard to these investigations there has never been any dispute on the question of priority, but this is far from being the case with the discoveries which followed. Any further disputes regarding the priority of subsequent discoveries should be disposed of by such a chronological record as that which follows, in which not only the year, but also the month and even day of publication are given. Chronology relating to certain of the more Im- portant Recent Researches on Malaria. 1893 and 1895, Sacharoff demonstrated the presence of chromatic substance within the “flagella” of certain avian parasites by means of the Romanowsky stain. | December 17th, 1895, Ross observed the process of “flagellation ” of crescentic parasites to occur in the stomach of mosquitoes (species not determined) fed on the blood of a malarial patient. 1896, Bignami and Dionisi report the negative results of two experi- ments made in 1893-4 with mosquitoes (species uncertain) collected in malarious localities, the insects being permitted to bite healthy per- sons. ‘They attribute the failure of the experiment to the dispersion of THE ATIOLOGY OF MALARIAL DISEASES. 43] the insects in the room where they were liberated, and to the experiment not having been continued long enough. They cite Calandruccio as having observed the degeneration of malarial parasites in the stomach of mosquitoes (species not stated). November 13th, 1897, MacCallum, in Baltimore, found that the “flagella” of Halteridium and of estivo-autumnal parasites constitute the male element, and serve to impregnate the “pig- mented spheres” or female element. In the case of Halteridium the impregnated spheres became con- verted into motile “vermicules.” ‘This transforma- tion was, however, not observed in the human parasites. December 18th, 1897, Ross fed mosquitoes upon human blood containing crescentic parasites. The ex- periments were made at Secunderabad, and were reported upon at the time as follows : After examining hundreds of mosquitoes fed on malarial blood, always with negative results, he obtained a few which belonged to a species with spotted wings, which he had hitherto not used. As Ross distinctly describes the egg of this species, there is no donbt whatever but that he was dealing with a species of Ano- pheles. The insects were bred from larve, and fed with blood containing crescentic parasites. Four to five days later peculiar pigmented cells were observed lying within the walls of their stomachs. These cells were round or oval; they measured 12—16 yw on the fourth, and 20» on the fifth day after feeding, and the pigment they contained was similar to that within the malarial para- sites in the blood upon which the insects had been fed. Such bodies could not be found in control mosquitoes. Ross concluded that he had found the mosquito which servedasa host for the parasite. February 26th, 1898, Ross refers again to his experiments with crescentic parasites. After examining some scores of “ dapple-winged”’ mosquitoes unfed or fed with healthy blood, all the results were negative until 432 GHORGE H. F. NUTTALL. “at last two of this species were persuaded to feed on a patient with crescents. One of them was killed next day; no pigmented cells could be found. The second was killed forty-eight hours after feeding ; numerous pigmented cells were present. They were all small, much smaller than epithelial cells, ovoid, about 7 win the major axis, and each contained about twenty granules of typical pigment, which were often arranged circumferentially, just as in the malarial parasite.” Though it is not stated in this publication that he raised these mosquitoes from larvee, reference to Ross’s previous paper (p. 1786) will show this to have been a part of the method he employed. Experiments with Tertian Parasites.—“ A hundred or more grey or May 21st, 1898, Experiments on Proteosoma. ‘barred-back” mosquitoes, unfed or fed on healthy or crescent blood, have been dissected without finding the pigment cells. At last one was observed feeding on a patient whose blood that morning had been seen to contain numerous mild tertian parasites.” Killed on the third day, the insect contained many pigmented cells measuring 8—25 p. (Ross subsequently discarded this experiment, as it was possible that the insect which was not raised from the larva had become infected with some other parasite.) Work- ing in Calcutta, Ross observed the development of Proteosoma in a species of Culex (subsequently determined as C. fatigans, Wied.), the insects being fed on the blood of infected crows, larks, and sparrows. The parasites found in the external coat of the insects’ stomachs measured 6 yw after thirty hours, 60 « after six days. ‘“‘Successive feeds by the same mosquito on the same bird are followed by fresh crops of young coccidia. Similar pigmented cells”? had been previously observed in mosquitoes fed on human parasites. Ninety- four per cent. of the mosquitoes fed on blood containing mature Proteosoma became infected. September 24th, 1898.—Manson reported to the British THE MTIOLOGY OF MALARIAL DISEASES. 433 Medical Association Meeting at Edinburgh (July) on behalf of Ross regarding further experiments with Proteosoma. These observations showed that the encapsulated parasites, on reaching a certain size, rup- tured and emptied their contents into the ccelom of the insect. The contents of the ruptured capsules consisted of minute spindle-shaped bodies, and these bodies sub- sequently accumulated in the salivary gland of the insect. When this had occurred the insects were capable of communicating the proteosomal infection to healthy birds. Of twenty-four sparrows exposed to the bites of insects fed on mature parasites, twenty-two became infected. October Ist, 1898, Grassi reported that he had reason for suspecting three species of Culicide as being carriers of malarial infection, claiming that they were confined in their geographical distribution to those regions where malaria was prevalent in Italy. The three species were Culex penicillaris, Anopheles claviger (syn. A. maculipennis), and a purported new species, Culex malarie.’ It has since been proved that only 1 In his paper in the ‘ Policlinico’ (October Ist, 1898), Grassi writes: ‘In conclusione, io sono @’ avviso che il Culex penicillaris e l’ Anopheles claviger o per lo meno il Culex penicillaris, fors’ anche il Culex malarie, nella malaria si comportano come le zecca nella febbre del Texas.” Grassi therefore makes a misstatement in a later paper (December Ist, 1900) when he writes, ‘ Proclamai come indiziati due specie di culex, ma sopratutto ? Anopheles claviger.”’ It is curious that Grassi should subsequently have continued to lay stress upon the geographical coincidence having led him to the discovery of Anopheles claviger being a host of malarial parasites, for two out of three species which he for this reason supposed must be hosts were afterwards proved not to be such. He certainly considered A. claviger at first to be of quite secondary importance; we have his own words for it : ‘ Certi casi di malaria sviluppatisi in Settembre a Locate Triulzi, nei quali gli Anopheles di certo o non punsero o soltanto rarissime volte, denunciano decisamente come trasmissore il Culex penicillaris, enorma- mente comune in tutti i luoghi malarici.’’ (The italics are Grassi’s.) It is bnt fair to Ross to state here that Grassi in his paper of the Ist of October refers to the experiments made by Smith and Kilborne upon Texas fever, and by Ross upon avian malaria as having been a “ forte argumento ” 434 GEORGE H. F. NUTTALL. the second of the three species named can serve as a host for human malarial parasites. ‘The coincidence in the geographical distribution of ague and malaria-bear- ing mosquitoes in Italy, as claimed repeatedly by Grassi, has been disproved by Celli. The claim that this geo- graphical agreement would probably be found to hold in other parts of the world has been disproved by Nut- tall, Cobbett, and Strangeways- Pigg (1901) in England. We cannot, therefore, accept Grassi’s statement that he discovered the malarial mosquito because of its geo- graphical distribution, pretty and ingenious as_ the hypothesis seemed in the beginning. It seems certain that Grassi was after all entirely guided by Ross’s pub- lication of December 18th, 1897, in which he describes an insect with spotted wings and eggs like those which characterise Anopheles. November 6th, 1898, Infection Experiment on Man.— Grassi mentions that Bignami had made an infection experiment by means of mosquitoes (the three species above named were employed) collected at Maccarese, a malarious locality. The result was positive in this case, the person acquiring estivo-autumnal fever. (Several infection experiments were subsequently car- ried out by Bignami, Bastianelh, and Grassi in colla- boration, these being reported in various papers of later date. The first experiment did not prove which species harboured the parasites, and of itself was insuf- ficient to establish the theory on a firm basis.) December 4th, 1898, Bastianelli, Bignami, and Grassi observed the development of crescentic parasites in Anopheles claviger, the appearances correspond- ing to those described by Ross for Proteosoma on the in favour of the mosquito-malaria hypothesis. In the paper read on the next day at the Accademia dei Lincei, under the same title as that which appeared in the ‘ Policlinico,’ Grassi omits to mention Ross, though he refers to what was known regarding Texas fever. The paper, published in the ‘ Transac- tions’ of the Accademia, differs in several respects from that which appeared in the ‘ Policlinico,’ THE ATIOLOGY OF MALARIAL DISEASES. 435 fourth day in Culex. Referring to his experiments with human parasites, they write, “ Verisimilmente i due mosquitos coli ali macchiate nei quali il Ross in India trovo stadi di sviluppo simili a quelli del proteosoma (3° giorno circa) appartenevano pure alla specie Anopheles claviger, Fabr.” (This statement is of interest in view of Grassi’s subsequent claim that Ross might very well have been working with insects belonging to the genus Culex, and not with Anopheles at all.) They, more- over, consider that Ross had not certainly determined the development of the crescents in his mosquitoes, for his observations had been broken off at too early a date ; besides which the insects might have infected themselves with hematozoa from some other animal. We have seen that the latter supposition is unwarranted, because Ross’s Anopheles were raised from larve. Moreover they themselves neglect to state that they raised their Ano- pheles from larve, so we must presume that they did not. Infection Experiment on Man.—In a foot-note to the above publication it is reported that the authors had successfully infected a person with tertian fever by means of infected A. claviger, collected at Maccarese. December 22nd, 1898, Grassi, Bignami, and Bastianelli follow the development of crescentic parasites in Anopheles claviger to the formation of ‘“ sporo- zoites,’’ the escape of the latter into the ccelom of the insect, and their accumulation in the salivary gland. The development was found to be slower at 20° to 22° than at 30° C. The fully developed capsules measured 70 w, the sporozoites measured 144. The process of development, the size of the fully developed capsules, and of the sporozoites, were the same as Ross had observed in Proteosoma. The development of tertian parasites was observed to take place in A. claviger up to the fifth day. February 2nd, 1899, Koch published a preliminary note 436 GEORGE H. F. NUTTALL. upon the results of the investigations conducted by the German Malaria Commission, consisting of himself, R. Pfeiffer, and H. Kossel. Further details will be found in a publication which appeared September 8th, 1899. The Commission observed the development of Pro- teosoma in Culex nemorosus, from the formation of the “ vermiculi” described by MacCallum for Halteri- dium to their appearance in the salivary gland of the insect. The process of fertilisation was found to occur in Proteosoma, as MacCallum had found for Halteri- dium and human crescentic parasites. Healthy birds were successfully infected by means of infected insects. The later publication, which is illustrated by excellent microphotographs, completely confirms the observations of Ross and others. February 5th, 1899, Grassi, Bignami, and Bastianelli observe the development of quartan parasites in A. claviger. Ross (September. 2nd, 1899) observed the development of quartan parasites in a species of Anopheles in Sierra Leone. January 23rd, 1899, Daniels reported to the Royal Society that he had been able to confirm Ross’s observations with Proteosoma. He followed their development in a species of Culex, and successfully infected healthy birds by means of infected insects. He added nothing to what Ross had already found. April 19th, 1899, Bastianelli and Bignami reported further studies upon the development of tertian parasites in Anopheles claviger, and describe three successful infection experiments on man by means of A. claviger previously fed on tertian parasites. May 7th, 1899, Grassi, Bignami, and Bastianelli report to the Accademia dei Lincei that they had observed the development of tertian and crescentic parasites in Anopheles bifurcatus. June 18th, 1899, Grassi observed the development of tertian and crescentic parasites in Anopheles THE #HTIOLOGY OF MALARIAL DISEASES. 437 pseudopictus, but not in various species of Culex. ‘The latter result again obtained later (October 4th, 1899). June 28th, 1899, Ross stated that Proteosoma scarcely developed in Culex at 21°, and that the growth of the parasites was already slowed at 27° C. in Calcutta. The development of tertian parasites in spotted-winged mosquitoes raised from larve was also observed (letter dated February 22nd, 1899, to Nuttall; see ‘ Centralbl. f. Bakteriologie,’ vol. xxv, p. 908). September, 1899, Bastianelli and Bignami give a de- tailed description of tertian and crescentic parasites, the publication being accompanied by the best coloured plates hitherto published, illustrating their development. They prove that a single infected Anopheles claviger may communicate malaria (tertian) to man. May 4th, 1900, Ziemann, working in Cameroon, observes the development of the parasites of tropical malaria in two species of Anopheles, as also the development of tertian parasites in one species of Anopheles. He followed the development to the appearance of sporozo- ites in the salivary glands of the insects. He subse- quently (November 22nd, 1900) found that the parasites would not develop in Cimex lectularius nor in sand- flies. September, 1900, van der Scheer and van Berlekom, in Holland, observe the development of tertian parasites in A. claviger. September 29th, 1900, Manson reported a positive infection experiment with tertian-infected Anopheles (spec. ?) imported from Rome, the insects being permitted to bite his son in London. October 6th, 1900, Rees reports a similar experiment to the former. | After perusing the above chronology, and remembering the question most disputed—the discovery of the develop- 438 GEORGE H. F. NUTTALL. ment of human parasites in Anopheles, we must conclude that the pigmented encapsulated bodies observed by Ross in “spotted-winged mosquitoes ” at Secunderabad were cres- centic parasites in early stages of development. In his first paper Ross definitely states that he raised the imagos from larve kept in bottles; that the parasites which subsequently developed within them contained a pigment similar to that of the parasites in man; and his description of the insects’ eggs leaves no room for doubt but that they were Ano- pheles. (In their paper of December 4th, 1898, Bastianelli, Bignami, and Grassi even made the statement that it is extremely likely that Ross’s spotted-winged mosquito was A. claviger!) The work done subsequently on Proteo- soma quite rightly confirmed Ross in his belief. We are, however, indebted to the Italian investigators named for completing the study of the further development of human parasites in various species of Anopheles, these studies being subsequently pursued by still other investigators in other countries.!_ Ross is perfectly justified in laying stress upon the fundamental importance of his discoveries in the development of Proteosoma, and there can be no doubt whatever about his work having served as a guide to sub- sequent investigators. There is no denying that both the human and avian parasites referred to offer great points of similarity throughout. The assumption was, therefore, per- fectly justified that the further stages in the development of crescentic parasites such as Ross had observed at Secunder- abad would be identical with what he saw in the case of Proteosoma afterwards in Calcutta. In conclusion we must not forget to mention the name of Patrick Manson, who until recently took no part in the experimental solution of the problem, but who throughout Ross’s investigations, which he stimulated, did much to further the studies which in one direction at least have reached such a satisfactory conclusion. ' Tt has not been deemed necessary to refer to all of these. THE ATLIOLOGY OF MALARIAL DISEASES. 439 PUBLICATIONS CITED. DASTIANELLI, G., and Bienami, A. (dated April 19th, 1899).—‘‘Sullo sviluppo dei parassiti della terzana nell?’ Anopheles claviger,” ‘Bullettino della R. Accad. Med. di Roma,’ anno xxv, 1898-9, fasc. 3 (reprint 28 pp.). BastIaANELLI, G., and Brenami, A. (published end of September, 1899).— I. “Sullo sviluppo dei parassiti della terzana nell’ Anopheles claviger.” II. ‘Sulla struttura dei parassiti malarici e in specie dei gameti dei parassiti estivo-autunnali,’ ‘Annali d’ Igiene speri- mentale,’ N.S., vol. ix, fase. 3, pp. 272—293 (1 col. plate), pp. 245 —257 (2 col. plates). BasTIANELLI, G., Bignami, A., and Grassi, B. (meeting of December 4th, 1898).—‘‘ Coltivazione delle semilune malariche dell’ uomo_ nell’ Anopheles claviger, Fabr. (Sinonimo, Anopheles maculi- pennis, Meig.); Nota preliminare,” ‘R. Accad. dei Lincei,’ vol. vil, 2 sem., ser. 5a, fasc. 11 (reprint 1 page). Bienamt, A. (1896).—** La ipotesi dei parassiti malarici fuori dell’ uomo,” ‘Policlinico, No. 14. Also transl., ‘ Hypothesis as to the Lite- History of the Malarial Parasite. outside the Human Body (apropos of an article by Dr. Patrick Manson),” ‘ Lancet,’ vol. ii, pp. 1363— 1867, 1441—1444. Crtui, A. (November 5th, 1900).—“ Beitrag zur Erkenntniss der Malaria- eptdemiologie vom neuesten aetiologischen Standpunkte aus,” ‘Centralbl. f. Bakteriol.,’ vol. xxviii, pp. 530—535. DanieE:s, C. W. (read March 16th, 1899).—*‘On Transmission of Proteo - soma to Birds by the Mosquito: a Report to the Malarial Committee of the Royal Society,” ‘ Proc. of the Royal Soc.,’ vol. Ixiv, pp. 443— 454. -Goxer (1886).-—‘‘ Sull’ infezione malarica,” ‘Arch. per le Scienz. med.,’ vol. x, pp. LO9—135. See also ‘ Arch. Ital. de Biol.,” vol. viii (1887). Grassi, B. (published October Ist and 2nd, 1898).—*‘ Rapporti tra la malaria e peculiari insetti (Zanzaroni e Zanzare palustri); Note preliminare,” ‘ Policlinico,’ vol. V—M (reprint 10 pp.). Also (under the same title though altered) ‘ Rendiconti della R. Accad. dei Lincei ’ (meeting of, October 2nd), vol. vii, 2 sem., pp. 163—172. Grassi, B. (June 22nd, 1899).—‘ Ancora sulla malaria,’ ‘R. Accad. dei Lincei,’ ser. 5a, vol. vill, 1 sem., fase. 12 (reprint 3 pp.). Grassi, B. (October 4th, 1899).—*‘ Osservazioni sul rapporto della seconda spedizione malarica in Italia presieduta dal Prof. Koch, etc.,” ‘ Rendi- conti della Kk. Accad. dei Lincei,’ Cl. di sc. fis., mat., e uat. 440 GEORGE H. F. NUTTALL. Grassi, b. (December Ist, 1900).—“‘ Per la storia delle recenti scoperte sulla malaria,” ‘ I] Policlinico,’ anno vii, No. 23, pp. 593—600. Grassi, B., Bienamt, A., and BASTIANELLI, G. (dated December 22nd, 1898). —‘* Ulteriori ricerche sul ciclo dei parassiti malarici umani nel corpo del zanzarone,” ‘ Rendiconti della R. Accad. dei Lincei.’ Grassi, B., Bienami, A., and BastiIaNELLI, G. (meeting of February 5th, 1899).—** Resoconto degli studi fatta sulla malaria durante il mese di gennailo,’”’ ‘ Rendiconti della R. Accad. dei Lincei,’ vol. viii, 1 sem., ser. 5a, fase. 3 (reprint 4 pp.). Grass!, B., Brenami, A., and BasTIANELLI, G. (meeting of May 7th, 1899).— *‘Ulteriori ricerche sulla malaria,’ ‘ Rendiconti della R. Accad. dei Lincei,’ Classe di sc. fis., mat., e nat., vol. vill, 1 sem., ser. 5a, fasc. 9 (reprint 5 pp.). Kocu, R. (February 2nd, 1899).—‘* Ergebnisse der wissenschiaftlichen Expe- dition des Geheimen Medicinalraths Professor Dr. Koch nach Italien zur Erforschung der Malaria,” * Deutsche med. Wochenschr.,’ Jahrg. 25, pp. 69, 70. (Preliminary Report ; see following.) Kocu, R. (September 8th, 1899).—‘* Ueber die Entwickelung der Malaria- parasiten,” ‘ Zeitschr. f. Hygiene u. Infektionskr.,’ vol. xxxu, pp. 1— 24 (4 Tafeln). Lanxester, Ray (1871).—‘‘Observations and Experiments on the Red Blood-corpuscle,” ‘ Quart. Journ. Mier. Sci.,’ vol. xi, p. 389. LANKESTER, Ray (1882).— On Drepanidium ranarum,” ‘Quart. Journ. Mier. Sci.,’ vol. xxii, p. 53. LAveERAN, A. (November 23rd, 1800).—‘* Note sur un nouveau parasite, etc.,” ‘Bull. de l’Acad. de Méd. de Paris.’ Laveran, A. (December 24th, 1880).—‘* Un nouveau parasite trouvé dans le sang des malades atteints de fiévre palustre ;”’ “Origine parasitaire des accidents de l’impaludisme,”’ ‘ Bull. et Mém. de la Soc. Méd. des Hopit. de Paris.’ MacCauuum, W. G. (November, 1897).—*‘ On the Hematozoan Infections of Birds,” ‘Johns Hopkins Hospital Bulletin,’ No. 80; also ‘ Lancet,’ 1897 (Preliminary Note). MacCat.um, W. G. (January, 1898).—‘‘On the Hamatozoan Infections of Birds,’ ‘Journ. of Experimental Medicine,’ vol. iu, No. 1, pp. 117— 136 (one coloured plate). Manson, P. (September 24th, 1898).—‘* The Mosquito and the Malaria Para- site,” ‘ Brit. Med. Journ.,’ vol. i, pp. 849—853, illustrated by figures obtained from Dr. Ronald Ross. (Reported at the meeting of the Brit. Med. Assoc., Edinburgh, in July.) Mawson, P. (September 29th, 1900).—‘‘ Experimental Proof of the Mosquito- . , 2 ws, THE ATIOLOGY OF MALARIAL DISEASES. 44] Malaria Theory,’ ‘Brit. Med. Journ.,’ vol. ii, pp. 949—951 (two fizures and one chart); also ‘ Lancet,’ vol. ii, pp. 923—925. Nutra, G. H. F., Copsett, L., and Stranceways Piece (January, 1901).— “Studies in Relation to Malaria. I. The Geographical Distribution of Anopheles in Relation to the Former Distribution of Ague in England ” (two maps), ‘Journ. of Hygiene,’ vol. i, pp. 4—44. Regs, D. C. (October 6th, 1900).—“ Experimental Proof of the Malaria- Mosquito Theory,” ‘ Brit. Med. Journ.,’ vol. ii, p. 1054. Ross, R. (December 17th, 1895).—‘ Proc. of the South Indian Branch of the Brit. Med. Assoc.;’ see also abstracts of Ross’s letters in Manson’s article, ‘ Lancet,’ 1896. Ross, R. (Report to the Director-General of the Indian Med. Service, dated September 19th, 1897, published 18th December, 1897, in England).— “‘On some Peculiar Pigmented Cells found in Two Mosquitoes fed on Malarial Blood” (with a note by Surgeon-Major Smyth), ‘ Brit. Med. Journ.,’ vol. 11, pp. 1786—1788. Ross, R. (February 26th, 1898).—‘‘ Pigmented Cells in Mosquitoes,” ‘ Brit. Med. Journ.,’ vol. i, pp. 550, 551. Ross, R. (May 21st, 1898).—‘ Report on the Cultivation of Proteosoma, Labbé, in Grey Mosquitoes ’ (Office of the Superintendent of Govern- ment Printing, Calcutta, India), 4to, 21 pages, 9 plates. Ross, R. (September 2nd, 1899).—‘*‘ The Cultivation of the Malarial Quartan Parasite in Anopheles,” ‘ Brit. Med. Journ.,’ vol. ii, p. 608. Sacuarorr, N. (December, 1893).—“ Recherches sur les hématozoaires des oiseaux,’ ‘ Annales de |’Inst. Pasteur,’ vol. vil, pp. 801—811 (une planche colorée). Sacuarorr, N. (1895).—‘‘ Ueber die selbstandiche Bewegung der Chromo- somen bei Malariaparasiten,” ‘Centralbl. f. Bakteriologie, vol. xvii, pp. 874—380 (2 ‘Tafeln). Van DER Scurrr, A., and BERDENIS vAN BeruExkom, J. J. (reprint re- ceived October, 1900).—‘ Malaria en Muskieten in Zeeland,” ‘ Ned. Tijdschrift voor Geneeskunde,’ vol. 11, No. 14 (reprint 16 pp., 1 plate). ZIEMANN, H. (June 21st, 1900).—‘* Ueber die Beziehungen der Mosquitos zu den Malariaparasiten in Kamerun,” ‘ Deutsche med. Wochenscehr.,’ Jahrg. xxvi, No. 25, p. 399. ZinMann, H. (November 22nd, 1900).—‘ Zweiter Bericht iiber Malaria und Moskitos an der afrikanischen Westkiiste,” ‘ Deutsche med. Wochen- schr.,’ Jahrg. xxvi, Nos. 47 and 48, pp. 753—756, 769—772. VoL, 44, PART 3.—NEW SERIES, FF STUDIES IN THE RETINA. 443 Studies in the Retina: Rods and Cones in the Frog and in some other Amphibia. By H. M. Bernard, M.A.Cantab. (From the Biological Laboratories, Royal College of Science, London.) With Plates 30 and 31. Part IT. Tue first part of this paper was devoted to showing that the structures called “‘ cones” in the amphibian retina were the earlier stages in the development of the new rods required by growth, and that they force their way in wherever there is room for them between already existing rods. The forms of these elements with the positions of their nuclei” were alone dealt with. In this paper it is proposed to give some account of the intimate structure of the amphibian rod. The minute details to be described will necessitate some discussion of the physiological processes which, so far as I have been able to interpret them, underlie their forms. Little success has so far attended the attempts of naturalists to unravel the finer structure of the rods. Indeed, the sub- ject seems to have been temporarily closed by the classical researches of Max Schultze in the sixties, for since that -time little or no advance has been made. The earlier 1 The final revision of this MS. was kindly undertaken by my friend Mr. Martin Woodward, during my temporary absence from England. ? On page 44 I inadvertently attributed to Borysiekiewitz an observation of my own. This will be fully dealt with in Part IIT. 4.44, H. M. BERNARD. literature is, however, full of scattered observations, and it is possible that some of them may have been overlooked by me or far too briefly noticed. I do not pretend to have mastered the whole of the literature on the retina. I do not wish, therefore, to make any claims to priority, but simply to describe my observations, referring briefly to those of former students, so far as I know of any covering the same ground. And here I should add that, while confining myself in this paper solely to the Amphibia,! these researches have extended over other Vertebrates, and that the general conclusions arrived at are not drawn solely from the facts here described. Knveloping Membranes.—While the existence of the membrane investing the inner limb of the rod requires no demonstration, it has been much disputed whether the outer limbs possess any such envelope or not. Apart from the fact that such a covering is difficult to demonstrate, it is possible that the conception of the rod as a cuticular structure may have strengthened the doubt. It has long been known that the outer limbs of the rods can be made to divide up trans- versely into discs, and that on such a dissolution no investing membrane can be seen (cf. Max Schultze’s figures, ‘ Arch. mikr. Anat.,’? Bd. i, pl. xin, figs. 11 c¢, etc.). Merkel? found membranes wherever he looked for them except in the Amphibia, while Landolt* figured very thick homogeneous membranes covering the rods (frog and newt) and the cones (newt). Iam not aware that these have ever been confirmed, and I doubt their existence. He figures them even passing in between outer lmb and ellipsoid. Something like what he figures may be seen in my fig. 13, c—i, the significance of which will be discussed later on. In the meantime I may state that I do not regard the thick rind there shown as an outer covering. 1 The following forms have been examined:—Rana temporaria, Bufo vulgaris, Molge cristata and M. vulgaris, Salamandra maculosa, and Siredon pisciformis. 2 «Arch, Anat. u. Phys.,’ 1870, pl. xiv. 3 «Arch, mikr, Anat.,’ Bd. vii, 1871, p. 81, pl. ix. STUDIES IN THE RETINA. 445 That enveloping membranes occur in the outer limbs of Amphibian rods is certain, both on theoretical grounds and because they can be demonstrated. As we saw in Part I of this paper (this Journal, p. 29), the rods are primarily protoplasmic vesicles protruded from the retina. The walls of the vesicles are of extraordinary delicacy and transparency, and it will be a triumph of microscopic technique when retinas can be fixed so as to show them intact. They are best seen in their very earliest stages of protrusion, before any rods are formed and the pigment is only just being forced away from the retina by their increase in number and size. From this early stage we traced them through their principal form-phases till they became normal rods, and all these phases were not only consistent with their being long, membranous sacs, but even confirmatory of this conception of their essential structure. Lastly, the persist- ence of the membrane covering the inner limbs has, as we have seen, long been an established fact. But granted that in all the earlier stages of the rods we have a wall to the vesicle—a wall which persists in the inner limb,—we have still to ask whether that is the case with the outer limb when the rod is complete. May not the proto- plasmic wall merge in the substance which fills up the interior of the outer limb and lose its individuality, so that it would be impossible to speak of any investing membrane? This is, of course, quite possible ; and, moreover, it is certain that even if it preserved its individuality one would rarely expect to demonstrate the existence of such a delicate film of transparent protoplasm round the outer limb of the amphibian rod, with its usually refractive contents. Actual observa- tions, however, show clearly that the protoplasmic wall does retain its individuality, and that to the last the rod is a thin protoplasmic vesicle filled up with matter, the origin and nature of which will be discussed in the following pages. As demonstration of this persistence of the protoplasmic wall of the vesicle, I will call attention to Pl. 30, fig. 2, which is taken from the retina of a toad. All the rods in this 446 H. M. BERNARD. retina are obviously bags which have, under pressures and strains, lost their normal cylindrical shapes, and are now pulled out or crushed together mto every variety of form, from short, rounded sacs to long, thin clubs with round knobs at the tips.’ Hndless, too, are the instances in which the inner and outer limbs have been pulled somewhat apart, and the stretched or torn membrane becomes visible under good microscopic powers. Important, also, in this connection is P]. 30, fig. 1, from a newt, in which in one spot all the rods were broken away, but their basal portions persisted emptied of all contents except the remains of the ellipsoids. This last is a fortunate observation, because it shows that, in essence, the inner and outer limbs are simply two sacs separated by a thin wall, and that the great differences seen between them must be referred entirely to their contents. To this we shall return later. Lastly, I have sections of a newt’s retina in which the thin coverings of the rods have taken stain, and are quite demon- strable in optical sections. External Markings.—The longitudinal striation of the outer limbs of the rods has long been seen, but its nature has never been satisfactorily settled. Max Schultze regarded it as a furrowing of the surface, and figured the cross-sections of the rod as having an outline like that shown in PI. 30, fig. 8. With regard to the inner limbs of the rods in Amphibia, exact records of striation are few. ‘The well-known “ Faser- korb” of Max Schultze was found by him, “ essentially the same,” in all the classes of Vertebrates, including the Am- phibia. He records finding it in the axolotl, and he figures it in the newt.” Hoffmann also figures the upper ends of these or similar threads round the bases of the inner limbs of amphibian rods, and forming a ring of needle-like points similar to those figured by Max Schultze as projecting from 1 Max Schultze gives a somewhat similar figure, viz. the sac-like rod of a pike, produced artificially (‘ Arch. mikr. Anat.,’ Bd. iii, pl. xiii, fig. 18 @). 2 ¢Arch. mikr. Anat.,’ Bd. v, p. 379, pl. xxii, fig. 2 a. STUDIES IN THE RETINA. 44.7 the membrana lim. externa when the rods and cones are broken away (cf. Hoffmann’s figures [Bronn’s ‘ Thierreich ; Amphibien,’ pl. xxii, 11—18, and pl. xxiv, 2—8] with Max Schultze’s [‘ Arch. mikr. Anat.,’ Bd. v, pl. xxii]). The latter author traced the threads of his ‘‘ Faserkorb ” proxi- mally into the connective tissue of the outer nuclear layer, but inasmuch as distally they ran on to the outer limbs of the rods, he clearly wished to see in them the ends of the nerves (cf. Stricker’s ‘ Handbuch’). Hoffmann, who figures the basal threads as running only a short way down the inner limbs of the Amphibia, and then only loosely applied, appa- rently regarded them as nothing more than hair-like prolon- gations of the membrana lim. externa. Further, as stated, Max Schultze described a continuation of his “ Faserkorb ” a short way down the outer limbs. Hoffmann (loc. cit.) also figures somewhat similar threads running on to the outer limbs of amphibian rods; these he could not explain because his basal threads were not supposed to run the whole length of the inner limbs. There seems, then, to have been a distinct tendency to attribute to the inner limbs in the Amphibia a system of longitudinal fibres, though apparently not so pronounced or complete as the “ Faserkorb”’ of the inner limbs of the human rods and cones. We may say, then, that the rods are thought to be longi- tudinally striated, but while the inner limbs are externally striated with fibrils the outer limbs are marked by furrows. My own observations entirely confirm the existence of longi- tudinal striz; but those on the inner limb and those on the outer limb are not distinct in kind from one another, but are parts of one system. Long before I had succeeded in discovering the true rela- tions of these striations to one another, I had noticed that the markings on the outer limbs consisted far more of longi- tudinal rows of dots than of furrows. The rows, though mostly continuous, are not always strictly parallel ; and the dots only occasionally fall into circular series running nearly 448 H. M. BERNARD. evenly round the rod. I find in my notes that at times two series of dots at right angles to one another are recorded as marking the exterior of the rods. The dots were usually shghtly drawn out longitudinally. Fig. 3, a, b,) are from my earlier drawings. It was noticed that the dots appeared almost as if they raised the surface of the rod, and that, hence, between the rows there were shght furrows, but on this point I have never satisfied myself; if any furrowing exists, it must be very slight. While these longitudinal rows of dots on the outer limbs were clear with any well-preserved retinas stained in Khrlich’s hematoxylin, it was not till I employed the iron-alum hematoxylin method of staining that I saw any striation of the inner limbs, and then, while that on the outer limbs was very strong and regular, that on the inner limbs was hardly ever regular, often indeed not recognisable as a system of striz at all. Further, I then found, as stated, that the two are not distinct phenomena, but that the fine staining threads which run down in the walls of the inner limbs are continued on to the outer limbs, as Max Schultze observed: but they do not stop short, as he supposed ; on the contrary, they run down the whole way, swelling into small clumps of staining matter at short dis- tances from one another, these clumps being the rows of dots I had seen all along. Fig. 11 shows diagrammatically the arrangements of this system of threads, while figs. 13, a—d, and 29, a, b, e—j, are from actual preparations of retinas from different Amphibia. Beginning usually faint near the nucleus, and seldom as a dis- tinct system, the arrangement gets more pronounced distally. It may be very pronounced indeed near the ellipsoid (e. g. in the toad, fig. 13, a, b). Here it passes on to the outer limbs, and, where inner and outer limbs are stretched a little apart, may be seen as a nearly regular ring of smooth, thin threads, 1 Cf, Max Schultze, ‘Arch. mikr. Anat.,’? Bd. iii, pl. xiii, fig. 11, where he shows a rod covered with ‘‘ pigment granules ;”’ another figure occurs in Bd. v, pl. xxii, fig. 17 @. The dots above referred to are quite distinct from pigment granules, one of which I have drawn in fig. 3, d. STUDIES IN THE RETINA. 4.4.9 not free, like Max Schultze’s needle-like prolongations of his “Faserkorb,” but rather as thickenings of the stretched membrane. On these threads clumps of staining matter soon appear (fig. 13, c). In the diagram, fig. 11, the system is drawn very symmetrically from the nucleus outward, but this is not by any means usually the case. The nearest approach to it has been found in the axolotl, preparations of which inspired this diagram. Fig. 29, 6, represents more truly the ordinary conditions. We have a gradual formation of the symmetrical system of striz towards the distal ends of the inner limbs (though usually quite irregularly), and when formed it passes on to the outer limbs. ‘There is some evi- dence that this is also what takes place in the human rods and cones, for the “ fibrillation” 1s said to be limited to the outer portions of the inner limbs (cf. ‘Quain’s Anatomy,’ 1894, vol. 1, part 3, p. 49, fig. 52, after Schwalbe). Some variation seems to occur in the numbers of the longi- tudinal threads on the outer limbs; they are sometimes very numerous (e. g. newt, fig. 30), at others very sparse ; and this is not only the case in different Amphibia, but in different specimens of the same. Figs. 3 and 6 are from different frogs; in one case the threads are crowded, and in the other quite far apart: the rods in this latter case have been greatly stretched, but one does not see why that should lessen the number of striz. The significance of some of the irregularities of this system of striz! will be better understood when we have described the connection between these threads and the contents of the vesicles in whose walls they occur. The rods, then, are delicate protoplasmic vesicles, in the thin walls of which staining threads occur. In the walls of the outer limbs these threads are usually more or less beaded with clumps of staining matter. The claim made by Max Schultze and Hoffmann (see the figures and plates re- 1 The spiral twist of the strize oa the outer limbs has been rightly attributed to torsion. Ihave only seen it, and then very marked, on rods broken off like that shown in fig, 13, c. 450 H. M. BERNARD. ferred to above) that the outer limbs of the cones are also striated will be discussed later. The Contents of the Rods.— According to Max Schultze the outer limbs of the rods are built up of discs joined together by some cementing substance. This descrip- tion, propounded by so great an observer, seems to have had the effect of turning away attention from Hensen’s figures of cross-sections of rods of the frog,’ which clearly showed some definite internal structure. It must, however, be admitted that Hensen’s cross-sections differed among themselves ; there were two kinds (see PI. 30, figs. 7, a, b, which reproduce them), and they were not easy to reconcile with one another. Nevertheless I think it cannot be doubted that the discs of Max Schultze, which are, I believe, artificial phenomena, helped to consign them to temporary oblivion. As a matter of fact, Hensen’s figures, which were optical sections and hence hazy, come near the truth, and are, as we shall see presently, reconcilable with my own observations. It seems fairly clear, for instance, that his two sections may compare with my own figs. 9, b, 18, g, and 12, 13, k, respectively. Hensen, however, was too anxious to discover nerve-endings, and was therefore prepared to see fibrils in any clear space or small refractive portion of the section. In the case of fig. 7, a, he thought the meshes of the reticulum round the periphery of the sections were fibrils of doubtful significance, but in fig. 7, b, those in the centre were regarded as nerves,— three, he thought, in the centre of each rod. With regard to the contents of the inner limb of the rod, its most conspicuous element, the “ ellipsoid,” has long been known; it has been regarded as the organ in which the nerves end (cf. fig. 28, on the right), and deserves a separate section. This is readily accorded, inasmuch as it admits of being described separately, and what follows will be clearer if we temporarily ignore it. At the same time we shall find it necessary to discuss the contents of both outer and inner limbs together, passing by for the present this particular body. 1 Virchow’s ‘ Arch. path. Anat.,’ Bd. xxxix, 1867, pl. xii, figs. 7 and 8. STUDIES IN THE RETINA. 451 For a ciear understanding of the description and figures relating to the contents of the rods to be here given, it is worth while turning once more to their development, and noting that, in essence, they are protoplasmic vesicles ex- truded from the retina. As seen in the first part of this paper, the early stages of these vesicles are seldom found intact, but when they are they usually appear clear, and apparently with only fluid contents. Faint traces of delicate proto- plasmic networks may occasionally be seen (see Part I, Pl. 3, fig. 16). Networks are, again, found in well-preserved and properly stained preparations in the large basal vacuoles of the cones (see Pl. 31, figs. 28, 27, 28). Later we find dis- tinct networks in the inner limbs of cones and rods, with usually a certain number of very pronounced threads running down in their delicate walls (see above and figs. 29, a, h, 2,); so also in the outer limbs—which, as we saw in Part I of this paper, began as fluid vesicles at the tips of the cones— a protoplasmic reticulum ultimately appears. The staining reticulum in the outer limbs is not often found as a simple meshwork, but this is sometimes the case, and we may assume that it first appears as such. ‘Two instances are shown in the figures (4, b, and 6). We gather from these cross-sections that the clumps on the longitudinal threads running down the rods are the points of attachment of this internal reti- culum to the walls of the vesicle. As a rule this reticulum is not evenly distributed ; we find a tendency for it to be compressed into the axis of the rod, always, however, remaining attached by its threads to the wall fibrils. As this compression increases the threads of the internal axial portion get very thick, coarse, and matted together. The compression may go so far that the reticulum merely consists of an axial strand with a few meshes in it, while the attaching threads are lengthened so as, in cross- section, to look like the spokes of a wheel (see figs. 12 and 13, k, and also cf. Hensen’s optical section reproduced in my fig. 7; 5). So far, then, the rods are protoplasmic vesicles, each 452 H. Ms BERNARD. divided into two compartments by a cross-membrane ;! and as they assume their definitive shapes they become gradually filled with a staining reticulum, which, omitting the ellipsoid, develops especially strongly in the outer and, in the adult Amphibian rod, more important of the compartments. This account seems to justify the description of the rods as prolongations of the ‘‘ visual cells.” It is obvious that each may be regarded as a prolongation of the cytoplasm belong- ing to each rod nucleus, a prolongation at first filled with fluid, but sooner or later containing also the usual reticulum which ramifies through the cytoplasm of ordinary cells. My only objection to this description is to the term ‘“ visual cells.” My researches long ago compelled me to abandon the usual conception of the retina as composed of cells, and I now regard it as a syncytium, in which the nuclei are arranged in layers, not as fixed morphological units, but solely as centres of physiological acti- vities which may at times require them to migrate outwards, ultimately, if life lasts long enough, to become rod nuclei. The evidence for this is, to my mind, so convincing that I have no hesitation in making the state- ment, even though it stands in such startling contrast to the conclusions of nearly all the most recent workers on the retina, such as Ramon y Cajal, Dogiel, and others, and though a criticism of the method and results of these authors is here out of the question. In the first part of this paper, p. 43, I referred to the migration of nuclei from the middle nuclear layer to the onter nuclear layer, and showed that, even if we could not see evidence of it in our sections, it would be necessary to assume it; and I here add figures of nuclei passing through the outer reticular layer in different Am- phibia (figs. 21—28, 25, 26); while, again, in fig. 24 one or perhaps two nuclei have moved outwards together, leaving a space vacant in the middle nuclear layer, and apparently 1 T have not yet been able to ascertain for certain the time of appearance of this membrane. As we shall see below, it probably appears before the ellipsoid, STUDIES IN THE RETINA. 453 dragging the cytoplasmic reticulum after them. Such figures might be multiplied indefinitely, and, moreover, taken from nearly every retina that is closely enough exa- mined. I reserve full discussion of this somewhat revolu- tionary conception of the retina as a syncytium for another communication. But in the meantime I feel compelled to state my conviction that the rods are not the prolon- gations of “visual cells,” but protrusions of the cytoplasm of the retinal syncytium, each, at least in the Amphibia, dominated by a nucleus. Passing on from this digression, and regarding it for the moment as indifferent how we describe the rods in their relations to the nuclei, the evidence is abundant, as I shall now endeavour to show, that these nuclei are the centres of the physiological activity which gives rise to the rods. In the first place, a great part, if not all of the fluid or hyaline matter, here always spoken of as fluid, which first causes the vesicle to protrude, comes from the associated nuclei. Fig. 17 can hardly admit of any other interpretation than that fluid is extruded by the nuclei into the inner limbs of rods. If it is objected that these figures might as easily be inter- preted as representing phenomena due to the stimulation of fixing agents, this argument will not apply to fig. 28, where we see a ‘‘ double cone,”! in which one nucleus is still large and vesicular, while the other is collapsed, because its fluid contents have been discharged into the base of the cone belonging to it. Indeed, a study of cones with their basal vacuoles makes it very evident that the fluid of these vacuoles has been derived from their nuclei. Large vesicular nuclei in the position of cone-nuclei, i.e. well within the membrana limitans externa, are very common and in striking contrast to the more condensed rod-nuclei (figs. 16, a, b, and 18). The same contrasts may also be found in the other nuclear layers, but here, again, it is impossible to give in this paper 1 For the correct interpretation of “double cones” in the Amphibia see Part I, p. 33. 454 H. M. BERNARD. an extended account of the observations made relating to this subject. Selecting one more instance, I would refer to fix. 20, in which a large fluid vesicle has been discharged from its associated nucleus, and apparently has not found a way down as a young cone between the adjoining rod-nuclei, or, if part of it has succeeded in doing so, that part did not come into the optical field. Lastly, fig. 19 shows a rod thrust outwards by an increase in size of its basal vacuole. In the second place, the staining reticulum of each rod is also certainly derived from its associated nucleus. Not only can the reticulum of the inner limbs be seen in direct con- nection with the linin network of the nucleus (see figs. 29, a, i,j), but a thick stream can be seen descending from the nucleus on to the ellipsoid (figs. 10,28, 27), a phenomenon to which we shall refer more fully later on. Indeed, if the form of the cone or young rod (figs. 13, d, 15, b, 23, 29, a+) with its nucleus surmounting its narrow basal neck be kept in mind, it is difficult to conceive of any other origin than the nucleus for the large amount of staining material which finds its way outwards into what was certainly originally a fluid vesicle, with, at the most, a few delicate reticular strands. The longitudinal fibrils running down the outer limbs are, in their shape and arrangement, evidence for this outward movement, while the clumps of staining matter along the whole length of their threads, and the density of the reticulum in the interiors of the rods, are witnesses of the immense quantity of this staining matter required. | Actual demonstration of the derivation of this reticulum of the outer limb from that of the inner limb, and both from the nuclear reticulum, can be seen in the figures. For in- stance, there occur, in different parts of the inner limb, often in the wall low down and partly apparently embedded in the ellipsoid, deeply staining refractive bodies, usually globular, and, what is more important to note, always sur- rounded by clear zones as if they were the centres of small fluid vacuoles (figs. 15, a, and 29,c—g). These are certainly 1 Many more are figured in Part I, Pl, 3. STUDIES IN THE RETINA. 455 chromatin globules, and are usually found in young rapidly growing retinas.’ In well-stained preparations it 1s common to find that, from these bodies, fine threads run down the walls of the outer limb. In one figure of a developed rod this thread was the only one which took the stain (fig. 29, c). In another figure, two staining and rather straggling threads came from one of these bodies, which had apparently been flattened out against the membranous partition between inner and outer limb (fig. 15, a). To this phenomenon, i.e. this membrane acting as a barrier between inner and outer limb, we shall return. Even where there are no such bright globules of chroma- tin, the derivation of the reticulum of the outer limb from that of the inner can be at once seen if we study the figures of the developing cones shown in fig. 29,e—j. These figures are merely a selection, and might be multiplied indefinitely. They show quite clearly that the staining material within the outer limb appears where the thin threads from the inner limb come down on its wall. This fact shows that the striation of the outer limbs of the cones figured by Max Schultze and Hoffmann may exist, not as a complete system as they repre- sented it, but as the first beginnings of the subsequent stria- tion of the rods. Unfortunately none of these figures (29) seem to show the true tips of the cones; still, enough is here seen to demon- strate the point we have immediately in hand. Lastly I would refer to fig. 26, which is by no means an uncommon phenomenon. A nucleus is seen passing through the outer reticular layer and about to join the outer nuclear layer (that of the rods and cones). It is preceded by a fluid space, while from it a very delicate reticulum streams out- wards. ‘This I interpret as representing a very early stage in the formation of a rod, being still entirely within the 1 The only other figure I know of which shows such a body is one by Hensen (I. c., fig. 7, c), who, as we have seen, came so near discovering the structure of the rods, having failed apparently for the want of better micro- scopic technique. 456 H. M. BERNARD. retina. The fluid vesicle in the ordinary course of things would, on approaching the mem. lim. externa, form the usual conical protrusion, and into it the staining reticulum would follow. On the other hand, it is only fair to note that streams of very delicate staining reticulum occur elsewhere ; one other, for instance, is shown running up from the left- hand rod-nucleus in fig. 27. The explanation of this must be deferred until I can at the same time give the evidence in full on which it rests, and this I hope to be able to do in the near future. Further Contents of the Rod.—So far, then, we have described the origin and structure of the rod as a protoplas- mic protrusion from the retina, containing the usual staining network very strongly developed in the outer limb, and with some Clear fluid in the meshes or interstices. This network and this fluid are not, however, the sole contents of the normal rod, and the striking difference between inner and outer limbs, apart from the difference in shape and density of the reticulum, is found in the fact that while the former remain protoplasmic vesicles, with apparently soft, flexible walls filled with these elementary constituents which we have described (passing over for the moment the ellipsoid), the outer limbs become filled with some highly refractive substance, which renders them turgid. The change from the loose, long terminal bag found at the tip of the advanced cone (c,) to the outer limb of the rod (7r,) (see Part I, Pl. 3, fig. 4) 1s seen to consist not only in the squeezing outwards of the staining matter to the distal end of the inner limb, but also in the filling up of the outer limb. Now while we have traced to its source some of the matter which helps to fill the outer limb, viz. the staining reticulum, this will not account for the refractive contents which now seem to make them turgid and cylindrical. Further, we saw that the outer limbs of the rods lengthened (from 7, to7;),and hence apparently continued to take in more of this refractive constituent of their contents ; and not only lengthened, but as a rule became also much thicker, I have STUDIES IN THE RETINA. 457 noticed also that the outer limbs of Schwalbe’s rods (r, and 74) were in most cases rather more deeply stained than the longer, thicker definitive rods, although I lay no great stress on this. The accidents which can never be eliminated from our technical methods are too numerous to allow conclusions to be based upon mere variations in diffuse staining. I mention the point, however, just because it is possible that the proportion of the refractive matter to the staining reticulum might be expected to be less in an outer limb, just beginning to fill up, than in a large swollen rod. Itis this refractive matter which gives the rods their characteristic appearances, and which has led to their being classed among cuticular structures. The source of this refractive matter is to be seen in the pigment epithelium into which the tips of the rods are plunged, and it is largely composed of pigment granules, probably with some portion of the protoplasm of the epithelial cells. At least the absorption of cytoplasm as well as pigment by the rods can actually be shown to take place under special cir- cumstances, as we shall presently see. In the first place, dealing for the moment with general considerations, I again refer to the development of the rod; a fluid vesicle is thrust into the pigment layer, and slowly becomes filled with refractive matter. Both the vesicle and the epithelial cells are, so far as we can see, naked proto- plasm in the very closest contact with one another,—indeed, tightly interlocked, the pigment cells constantly forcing a passage up between the packed rods.’ Between these some interaction is almost certain to take place. This interaction is, I contend, in part at least an absorption of pigment by the rods. The pigment of the epithelial cells is constantly recruited by an outward streaming of granules from the choroidal layer adjacent to it, a streaming which can be seen in every successful preparation. So that we may conclude that pigment is being used up and as constantly replaced. The only other alternatives to this view are either that the refractive matter in the outer limbs of the rods comes from 1 For the evidence that the rod layer is normally compact see Part I. VoL. 44, PART 3.—NEW SERIES, (cle 458 H. M. BERNARD. the retina, or that it is manufactured in situ within the rods. That it does not come from the retina, from which we can easily trace the fluid and the staining network, we gather from the total absence of any refractive matter in the inner limb except in the ellipsoid; and, as we shall presently see, the position of this body forms additional evidence that the source of the refractive matter is from without inwards to- wards the retina, and not from the retina outwards. That the matter is not manufactured in situ we gather from the microscopic appearances, which show very clearly that it is forced in through the walls. The evidence for this is to be seen in the changes already described, which take place in the character of the reticulum within the outer limb of the rod. Figs. 4, 6, and 6, b, show this reticulum simply diffused equally across the section; figs. 13, c—k, and 12 show different stages in its compression towards the axis of the rod. Now it is difficult to explain this compression except on the assumption of some matter passing in through the walls and crushing it inwards, stretching, or perhaps merely lengthening the threads which attach it to the walls. Fig. 18, 7, shows the process as being irregular, while fig. 14 shows that it may take place locally, i.e. along one side of a rod and not on the opposite side. This observation is im- portant, because it is in keeping with the fact that the tongues of the pigment cells run up lengthwise between the rods. Fig. 13, 7, shows that at times the reticulum, though compressed towards the axis, may retain some of its concentric threads, the refractive matter passing them by. ‘The refrac- tive layer was here 1°5 uw thick, the whole rod being 9 w.! Again, in eyes in which, after exposure to light, the pig- ment has been forced up to the membrana limitans externa, individual granules can be seen remaining behind after the general retreat of the pigment, and sticking to the clear protoplasmic walls of the inner limbs. Many of them can 1 Zenker (‘ Arch. mikr, Anat.,’ ii, 1867, p. 259) discovered that the outer layer of the rod is more highly refractive than the axial portion. STUDIES IN THE RETINA. 459 then be seen obviously fading away, the shape being re- tained, but the bright colour and sharpness of contour have disappeared, and the whole appearance suggests their being slowly absorbed. Although, as above stated, with the excep- tionof the ellipsoid (and the oil globule in thecones of the frog), I have never found refractive matter in the inner limbs in Amphibia, cases occur elsewhere in the animal kingdom in which large inner limbs become filled with it, but ina manner entirely confirmatory of my argument that its source is the pigment epithelium. ‘The clinging of pigment granules to the protoplasmic walls of cones was noted in Part I. Again, in a series of sections of retinas of animals which had been exposed for three hours to the ight of an arc lamp,! the heat rays being screened off as far as possible, one interesting result is conspicuous. The pigment epithelium is here and there disorganised, and isolated pigment cells have forced their way up to various heights among the rods. These can be found in all stages of losing their pigment ; some appear as nuclei still thickly enveloped in pigment, others with only a trace of pigment, while here and there nuclei alone persist from which all the pigment and the protoplasm have disappeared. Fig. 12 shows in a tangential section, selected because of the cross-sections of the rods, such a nucleus, bereft of all its pigment, embedded among rods, and in these latter the reticulum has been compressed into the axis, which, as above suggested, indicates the absorp- tion of extraneous matter through the walls. Other effects of this exposure to such a fierce light have still to be studied. For instance, the contents of the rods have a singularly blotchy appearance, but I cannot satisfy myself whether this lies in the object or in the accidents of staining. While these arguments are, I think, sufficient for the 1 T am indebted to my friend Mr. George Newth, of the Royal College of Science, not only for the use of the necessary apparatus, but also for indis- pensable advice and assistance in making a series of experiments with pure monochromatic light, the results of which are still being worked out. 460 H. M. BERNARD. present demonstration that the refractive matter within the outer limbs is absorbed by the rods from the pigment, I should like to mention two points on which I am in great uncertainty. It has appeared to me more than once as if the pigment granules could pass bodily into the rods, and, at least for a time, maintain their individuality. I do not see why this should not occasionally happen ; indeed, I cannot explain some of the phenomena on any other hypothesis. Still, the evidence shows conclusively that this is not the normal method, but that the pigment granules are absorbed as a colourless or nearly colourless refractive and amorphous matter. The occasional finding of retinas in which the colour of this refractive matter within the rod is the same as that of the pigment granules without (I have seen this in sections of the retinas of the pigeon and of frog tadpoles, etc.) may be mentioned, in passing, as additional evidence of the origin of the former from the latter. One appearance suggestive of pigment granules within the rod seen in osmic acid preparations must be familiar to all students of the retina. Itis the “ disc” formation on which Max Schultze laid so much stress. I now, however, refer this to a transverse flaking of the internal reticulum, perhaps a kind of coagulation of the same, as Max Schultze himself suggested. ‘The transverse flakes are usually deeply coloured by osmic acid, and often appear exactly like layers of intruded pigment granules. In preparations not treated with osmic acid the appearance is not to be found. The second point is the relation of the phenomena here detailed to the visual purple. This is said to be produced in the dark through the interaction of the rods and the pigment epithelium, i.e. when the epithelium is only in contact with the tips of the rods, and, further, it is said to be bleached by the light, i.e. when the rods should, according to my own observations, be absorbing clear refractive matter from the epithelial cells, which are then in intimate association with the rods, inasmuch as tongues of the cells then travel up between the rods. Iam of course aware that it is frequently STUDIES IN THE RETINA. A6 | maintained that fine protoplasmic processes of the pigment cells are permanently advanced as far forward as the mem- brana limitans externa, and are thus always in contact with the rods. Not in any single one of the retinas of some twenty-five vertebrates I have yet examined, and their number must, I think, now amount to fully one hundred, fixed and stained by all the latest methods, and examined with the best available microscopic lenses, have I been able to find a trace of these processes of the epithelial cells permanently interlocking with the rods. On the contrary, when the pig- ment is retracted the contour of the pigment cells is per- fectly straight or rounded as the case may be. Had such processes existed, I am convinced that at least some evidence of their presence would have forced itself on my attention long ago. I have, therefore, so far no point of connection to offer between the physiological details here described and the visual purple, which appears when, according to my own observations, the rods should be getting rid of the matter absorbed when last the light forced the pigment cells into close contact with them, and is bleached when they ought to be absorbing, and at the same time clarifying, the warm colouring matter of the pigment. A reconciliation of these observations will doubtless some day be forthcoming, and there the matter must be left for the present. The Hllipsoid.—This somewhat inappropriate name is usually applied to the body found in the inner limbs of the Amphibia where these limbs abut against the outer limbs. Max Schultze regarded it as a plano-convex lens; the name here adopted was suggested by Krause (“Opticus Ellip- soid’’). Itis here preferred robbed of its prefix ‘‘ opticus,” so as not necessarily to suggest special functions.! So far as the terms describe form alone, “ plano-convex ” is prefer- able to ellipsoid for the Amphibia, for that is the most usual definitive form assumed in the adult rod, i.e. when the rod is not very large and thick, as it is in the axolotl, in 1 Krause thought it was the nerve-end organ (‘ Anat. Untersuch.,’ 1860) 462 H. M. BERNARD. which case the body is usually an irregular flattened disc (fig. 23). As a matter of fact, the body is of very various shapes. Fig. 15 shows a series of cones and rods (salamander) in which only in a young cone is the body egg-shaped, in others it takes the shape of the tip of the swollen inner limb of the cone: if the latter is large, the body is large; if narrow, the body is narrow, while in the definitive rod it is uniformly plano-convex. It thus seems quite plastic in its earlier (cone) stage, and only assumes a definite form in the full-grown rod. Dealing, then, with this body as we have with the other contents of the rod, we must regard it as an aggregation of these contents which, for some reason or other, rests perma- nently against the transverse membrane separating the inner and outer limbs. It varies greatly in its staining. It is sometimes intensely stained, at others it 1s comparatively clear and refractive. In this latter case a dense stream of staining matter is very frequently seen descending upon it from the nucleus (see figs. 10, 238, 27). We cannot be far wrong, then, if we refer the variation in the intensity with which the body takes stain to the relative proportions of staining matter and refractive matter which compose it. For out of these two substances, which, as we have seen, together constitute the visible contents of the rods, it must surely consist. Regarding it for the moment in its definitive plano-convex form, it seems to me that we have, both in its shape and in its position, striking confirmation of our conclusion as to the origins of the contents of the rod. On the one hand, we have an outwardly streaming reticulum of staining matter which, so far as we can see, only manages to get further, 1. e. into the outer limb by way of the outer walls. There cer- tainly seems to be some condensation of the reticulum against the blind end of the inner limb (see fig. 27, left-hand figure). On the other hand, coming into the rods from the opposite direction, viz. from the pigment epithelium, we have the re- STUDIES IN THE RETINA, 463 fractive matter. "his, as we have seen, is absorbed by the walls of the rods filling them up till they are turgid. This matter would thus find its way inevitably up against the transverse membrane separating inner from outer limb, and, seeing that it passed through the outer wall into the rod, there is no apparent reason why it should not pass through this transverse membrane from the outer limb into the inner limb. ‘This, then, I believe, is what takes place, the very form of the ellipsoid being suggestive of its having been forced through to form a kind of drop on the proximal side of the transverse membrane. Confirmatory evidence will later be adduced from other retinas, but sufficient to establish the point will be found in what follows. When we come to the ellipsoid in the cones (see figs. 15, c—e) it would seem that the explanation we have given of it in the rod could hardly apply. There appears to be a transverse membrane (fig. 29, f, 7), but there is no swollen outer limb filling up with refractive matter. Nevertheless the explanation of the ellipsoid is practically the same, as we can gather from the conditions seen in the frog. In the cones of the frog there is invariably a round refractive globule at the junction of the basal and the conical portion. In well-stained specimens a mass of staining matter is generally seen abutting against this globule, as if they mutually blocked the way for one another. We thus get practically the same condition as in the rod, though in this case we do not know exactly where the transverse membrane is, 1.e. whether the refractive globule is on its inner or outer side. This parallel assumes (1) that the refractive globule of the cones of the frog is of the same substance and has the same source as the refractive matter in the rod, and (2) that this refractive globule and the adjacent staining matter will later fuse together to form the definitive ellipsoid. The former of these assumptions is, I think, fully justi- fiable. We have seen how readily pigment granules cling to the thin protoplasmic walls of the cones, and can be seen fading away on the fine membranous walls of the inner limbs 464 H. M. BERNARD. of the rods, as if in the act of being absorbed. Hence it is but natural to assume that some of the refractive matter which later fills these vesicles to overflowing should early find its way into the tips of the cones and be squeezed out by the lateral pressure described in Part I as existing in the rod layer, so as to appear as refractive globules just above the line where the pressure of the rods ceases, i.e. on a line between the junctions of the inner and outer limbs. The secondary thrusting back again of these globules in cones (c3), described in Part I of this paper, needs no comment. Then, again, I mentioned in Part I that in young tadpoles it was possible at times to see these globules actually dis- appearing in the ellipsoids of young rods (see Pl. 3, fig. 15), showing clearly that, in this refractive globule of the cone with its adjoining staining matter, we really have the ele- ments of the future ellipsoid, though not blended together. Further, in one of my slides of a young frog tadpole the refractive matter absorbed by the rod is not always dis- coloured; globules of bright reddish-brown matter exactly resembling the pigment in colour occur high up in the rod, near the transverse membrane, while as a complete confirma- tion of the argument, globules of exactly the same colour can here and there be found in the ellipsoids of the same rods. The condition found in the cones of the frog thus helps us to understand the ellipsoid in the cones of the other Am- phibia here dealt with. It has long been known that the refractive globule was absent from the cones of the toad, an absence which was disconcerting to the earlier investigators, who would attribute to it an important dioptric function. It is also absent from the cones of the salamander and the axolotl. In these cases, from our point of view, it is not so much that the refractive matter is absent, but that it never really forms as a distinct globule ; it is mixed with the staining matter to become the ellipsoid as fast as it collects. In the case of the newt, all students will remember that STUDIES IN THE RETINA. 465 Max Schultze, and others after him,! described and figured a combination of two “lenses,” a biconvex and a plano-convex, as a higher specialisation than the simple plano-convex “lens” (the ellipsoid) of the frog, toad, salamander, etc. Max Schultze even claimed that this lens could be isolated. The body which he figured can be seen frequently enough, but not by any means always in the shape of a biconvex lens. It is nothing but a fluid vacuole, more sharply defined than usual. Fig. 30 shows two rods of a newt side by side; in one there is a well-defined vacuole resting on the ellipsoid, and in the other a quite undefined vacuole lke that usually found in other Amphibia. The former is interesting because its origin from the nucleus can be seen, a second one appear- ing ready to escape. Most of the nuclei in this preparation have vacuoles about the same size as shown in fig. 30. Further, in very many of the outer limbs of the rods rows of fluid globules of different sizes can be seen. Compare the views as to the origin of the fluid on p. 453. Let us sum up the conclusions so far arrived at, forbearing to enter more fully into the physiological results obtained till the corroborative evidence yielded by the eyes of verte- brates other than Amphibia can be prepared for publi- cation. The rods in the Amphibia are specialised protrusions of the retina, consisting of extremely delicate protoplasmic vesi- cles, each divided by a transverse membrane into an inner and an outer compartment. The staining reticulum which traverses these vesicles is especially developed in the outer- most, into which it finds its way in threads down the walls. These threads, at short distances, give off other threads from small nodes into the interiors of these outer vesicles. These latter further become filled with refractive matter absorbed from the pigment epithelium, and certainly largely obtained from the pigment granules. This matter absorbed through the walls condenses the mass of the reticulum into the axes 1 Cf. ‘Arch. mikr. Anat.,’ Bd. v, 1869, pl. xxii, fig. 2@. See also‘ Bronn’s Thierreich ’ (Amphibia). A6 H. M. BERNARD. of the rods.