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FLOWER for the use of the N. Y. STATE VETERINARY COLLEGE 1897 The physiology of reproduction, DATE DUE aw bY, =, ; 6 DARL Ve . 3 NEF BE cn auc 1 20051 GAYLORD Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924000889661 THE PHYSIOLOGY OF REPRODUCTION THE PHYSIOLOGY OF REPRODUCTION BY FRANCIS H. A. MARSHALL M.A. (Canras.), D.Sc. (Epi. ) FELLOW OF CHRIST’S COLLEGE, CAMBRIDGE, AND UNIVERSITY LECTURER IN AGRICULTURAL PHYSIOLOGY WITH A PREFACE BY Prorrssor E. A. SCHAFER, Sc.D., LL.D., F.R.S. AND CONTRIBUTIONS BY WILLIAM CRAMER, Pu.D., D.Sc. AND JAMES LOCHHEAD, M.A., M.D., B.Sc., F.R.C.S.E. + WITH ILLUSTRATIONS LONGMANS, GREEN AND CoO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTYA 1910 All rights reserved Ve TO WALTER HEAPE, Esea., M.A., F.R.S. PREFACE THIs is the first time that the Physiology of the Organs of Reproduction has been presented in a complete form, and many who desire to obtain more precise knowledge regarding the problems with which it deals, than is to be found in text-books of Physiology, will welcome the appearance of Dr. Marshall’s book. The importance of such knowledge to the community in general is now becoming recognised, and the interest which the subject awakens is no longer confined to members of the medical profession and to breeders of animals. Especially will the work furnish a much needed introduction to the science of Eugenics, whilst the multiplicity of facts which are set forth, and the manner in which questions of difficulty are discussed, will have the effect at once of satisfying and of stimulating inquiry in a most important, if hitherto somewhat neglected, branch of Physiology. E, A. SCHAFER. UNIVERSITY, EDINBURGH, June 1910, CONTENTS PAGE INTRODUCTION . 1 CHAPTER I THE BREEDING SEASON . . . . . . . . . 4 Protozoa—Ccelenterata—Nemertea, &c.—Annelida—Arthropoda — Mollusca — Echinodermata — Cephalochordata — Pisces— Amphibia — Reptilia — Aves — Mammalia—Periodicity of Breeding, &c. CHAPTER II THE GsSTROUS CYCLE IN THE MAMMALIA Fi r i 5 » 385 Monotremata—Marsupialia—Rodentia— Ungulata—Cetacea— Carnivora—lInsectivora—Cheiroptera—Primates. CHAPTER III THE CHANGES THAT OCCUR IN THE NON-PREGNANT UTERUS DURING THE GSTR*>US CYCLE . . . . . . . . 75 The Cycle in Man—Monkeys—Lemurs—Insectivora—Carnivores —Ungulates. CHAPTER IV CHANGES IN THE OVARY—OOGENESIS—GROWTH OF FOLLICLES—- OVULATION—-FORMATION OF CORP°RA LUTEA AND ATRETIC FOLLICLES—-THE SIGNIFICANCE OF THE PROGSTROUS CHANGES IN THE UTERUS i : fi ‘ F i 113 Dev lopment of Ovary and Oédgenesis—Maturation and Ovulation —The Formation of the Corpus Luteum—tThe Atretic Follicle —Superfcetation—Formation of Ova—The Significance of the Procestrous Changes. CHAPTER V SPERMATOGENESIS—INSEMINATION . é ; ‘ ‘ ~ 46S Structure of Spermatozoa—Seminal Fluid—Movements of Sper- matozoa—lInsemination. ix x CONTENTS CHAPTER VI FERTILISATION . . . . . The Hereditary Effects of Fertilisation—Telegony—On Gametic Selection and the Conditions Favourable for the Occurrence of Fertilisation—Conjugation in the Protozoa—The Supposed Chemotactic Properties of Spermatozoa and their Relation to the Phenomena of Fertilisation—Artificial Aids to Fertilisa- tion—Artificial Parthenogenesis. CHAPTER VII THE ACCESSORY REPRODUCTIVE ORGANS OF THE MALE AND THE MECHANISMS CONCERNED IN INSEMINATION . . . . The Vesicule Seminales—The Prostate Gland—Cowper’s Glands —The Copulatory Organ—The Mechanisms of Erection, Ejaculation, and Retraction. CHAPTER VIII THE BIOCHEMISTRY OF THE SEXUAL ORGANS The Female Generative Organs: Mammals, Birds, Invertebrates —The Male Generative Organs: The Semen—The Chemistry of the Spermatozoon. CHAPTER IX THE TESTICLE AND THE OVARY AS ORGANS OF INTERNAL SECRETION . The Correlation between the Testis and the other Male Organs and Characters—The Correlation between the Ovary and the other Female Organs and Characters—The Factors which determine the Occurrence of Heat and Menstruation—The Function of the Corpus Luteum—The Supposed Internal Secretion of the Uterus—The Correlation between the Generative Organs and the Ductless Glands—General Conclusions regarding the Internal Secretions of the Ovary and the Testis—The Effects of Castration upon the General Metabolism. : CHAPTER X F@TAL NUTRITION: THE PLACENTA . Part I. The Placenta as an Organ of Nutrition—i. Historical Survey—ii. Structure and Functions of the Epithelial In- vestment of the Villi—iii. The Decidua. Part Il. The First Stages of Pregnancy : Placental Classification —i. The Ovarian Ovum.—ii. The Fertilised Ovum and its Coverings.—iii. The Uterine Mucosa.—iv. Placental Classi- fication. Part ILI. The Fetal Membranes, the Yolk-sac, and the Placenta --i. General Anatomy of the Fcetal Membranes. —ii. The Nutri- tive Importance of the Yolk-sac (Marsupialia, Ungulata, Carnivora, Proboscidea and Hyrax, Rodentia, Insectivora, 227 263 303 357 CONTENTS xi PAGE Primates).—iii. The Placenta in Indeciduata (Ungulata, Lemuroidea, Cetacea, Edentata, and Sirenia)._iv. The Placenta in Deciduata (Carnivora, Proboscidea, Hyrax, Rodentia, Insectivora, Cheiroptera, Primates).—v. General Considerations of Fetal Nutrition and the Placenta: A. The Plan of Placental Formation. 2. The Nature of the Tropho- blastic Activity. CHAPTER XI THE CHANGES IN THE MATERNAL ORGANISM DURING PREGNANCY . 490 I. The Stimulus for the Maternal Changes during Pregnancy.— II. Change in the Metabolism of the Mother during Pregnancy : A. The Sovrce of the Materials transferred to the New Or- ganism. 8B. The Body-Weight during Pregnancy. C. The Protein Metabolism in Pregnancy. D. The Carbohydrate Metabolism in Pregnancy. #. The Metabolism of Fats in Pregnancy. F. The Metabolism of Metals and Salts in Pregnancy. G. Respiratory Exchange during Pregnancy. — “III. The Changes in the Maternal Tissues during Pregnancy. CHAPTER XII THE INNERVATION OF THE FEMALE GENERATIVE ORGANS—-UTERINE CONTRACTION—PARTURITION—THE PUERPERAL STATE. . 526 The Innervation of the External Generative Organs—The Inner- vation of the Ovaries—The Innervation of the Uterus and Vagina and the Mechanism of Uterine Contraction—The Normal Course of Parturition in the Human Female— Parturition in other Mammalia—The Nervous Mechanism of Parturition—Changes in the Maternal Organism—The Cause of Birth—Prolonged Gestation—The Puerperium. CHAPTER XIII LACTATION . . Structure of the Mammary Glands—The Composition and Pro- perties of Milk—The Influence of Diet and other Factors on the Composition and Yield of Milk—The Duration of Lacta- tion—The Discharge of Milk—The Formation of the Organic Constituents of Milk—The Normal Growth of the Mammary Glands—The Factors which are concerned in the Process of Mammary Growth—The Factors which are concerned in the Commencement of Mammary Secretion—Criticisms. 553 CHAPTER XIV FERTILITY 586 Effect of Age—Effects of Environment and Nutrition—Effect of Prolonged Lactation—Effect of Drugs—Effects of In-Breed- ing and. Cross-Breeding—Inheritance of Fertility—Certain Causes of Sterility—Artificial Insemination as a Means of overcoming Sterility—Abortion—The Increase of Fertility, w Problem of Practical Breeding—The Birth-Rate in Man. xii CONTENTS CHAPTER XV PAGE THE FACTORS WHICH DETERMINE SEX . . . . . . 623 i. Theories which assume that Sex-determination takes place subsequently to Fertilisation.—ii. Theories which assume that Sex-determination takes place at the time of Fertilisation or previously to Fertilisation.—iii. Theories which limit Sex- determination to no particular period of development, or which assert that Sex may be established at different periods— Hermaphroditism and Sexual Latency—General Conclusions. CHAPTER XVI PHASES IN THE LIFE OF THE INDIVIDUAL—THE DURATION OF LIFE AND THE CAUSE OF DEATH . ‘ i 3 ‘ . 659 Growth of the Body before Birth—Growth of the Body after Birth—Puberty—The Menopause—Senescence—The Duration of Life and the Cause of Death. INDEX f 3 ; : . ‘ P ‘ - 689 10. 11. 12, 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. ILLUSTRATIONS xiii 5 Diagram illustrating the ‘“ Wellenbewegung ” hypothesis eT . Transverse section through Fallopian tube showing folded epithelium and muscular coat 76 . Se:tion of a cornu of a rabbit’s uterus 77 . Cross-section through cervical canal of human uterus 78 . Section through wall of vagina of monkey (upper part) 79 . Section through wall of vagina of monkey (lower part) 81 . Se.tion through mucosa of human uterus showing pre-menstrual congestion = ‘ . 82 . Section through mucosa of ee uterus sity extravasation of blood 84 . Section through mucosa of feces uterus Sewiig eb epithelial hematomata . 86 Section through mucosa of human uterus showing (desing into the cavity during menstruation : ; ‘ . 87 Section through mucosa of human uterus es the recupera- tion stage . : 4 5 : . 88 13. Sections through pcbeeaivaie uterine mucosa of Hog - 100-101 Section through edge of mucosa of dog during an early stage of recuperation . 4 : 103 Section through portion of mucosa of oe alate recuperation period 5 104 Section through portion of mucosa of iow dhitvfag isis as of recuperation . . . 105 Section through portion of procestrous uterine mucosa of patibie showing glandular activity 106 Section through portion of uterine mucosa of stlee Spence black pigment formed from extravasated blood 109 Section through ovary of cat 114 Section through ovary of adult dog . 115 Section through ovary of pig embryo 116 Cortex of pig embryo showing germinal acitheliura, & de. 117 Various stages in the development of the Graafian follicle (rabbit) . i é . 119 X1v ILLUSTRATIONS Fie. PAGE 24 to 27. Developing ova from ovary. : . . 120-121 28. Ovary at birth, showing primordial follicles 5 3 Z - 123 29. Young odcyte . . . . : . . 126 30. Young human Graafian follicle ; 4 - ; . 127 31. Human ovum at termination of growth period F : . 128 32. Human ovum examined fresh in the liquor folliculi . , 129 33. Recently ruptured follicle of mouse . 5 : é . . 144 34. Early stage in formation of corpus luteum of mouse ‘ . 145 35. Late stage in formation of corpus luteum of mouse . 4 . 146 36. Corpus luteum of mouse fully formed 147 37. Section through old corpus luteum . : : 5 . 153 38. Section through follicle in early stage of dednstetiod s . 155 39. Section through follicle in late stage F . : : . 157 40. Section through human testis and epididymis . ais . 166 41. Section through testis of monkey. . . 167 42. Section through portion of two seminiferous tiibules in testis of rat - 169 43. A cell of Sertoli with a) ae spermatid are Gane: to bs connected (human) . ‘ ‘ . : : . 170 44. Diagram illustrating the cycle of phases in spermatogenesis . 1b. 45. Scheme of spermatogenesis and odgenesis . : sho Ge . 171 46. Human spermatozoa on the flat and in profile . : : . 173 47. Human Spermatozoa ‘ . 5 fj 5 . (174 48. Different forms of spermatozoa on ‘different species of animals. : ‘ ‘ : : . 175 49. Diagram illustrating wave-like wae ai swimming sperma- _tozo6n é : 2 3 ; . . 177 50. Successive stages in ike Sertilineiions of an ovum of Bids esculentus, showing the entrance of the spermatozo6n 188 51. Three stages in the conjugation of male and female nucleus (Echinus) . é { Es : , é . - . 189 52. Fertilisation process in bat’s ovum . : A . . 190 53. Passage of convoluted seminiferous tubules into straight tubules, &e. ‘ : . 228 54. Transverse section through the Gabe of ins epidtaiemis : . 229 55. Transverse section through commencement of vas deferens . 230 56. Section through part of human prostate . : 5 3 235 57. Section through prostate gland of monkey : 4 . 237 58. Transverse section through adult human penis ‘ 243 59. Section through erectile tissue . ; 244 60. Part of transverse section through penis of tankay : . 245 61. Distal end of ram’s penis, showing glans and filiform appendage 247 62. Transverse section through filiform appendage of ram. . 248 FIG. ILLUSTRATIONS . Transverse section through middle of glans penis of ram . . Distal end of bull’s penis showing glans, &c. . End-bulb in prostate . Diagram illustrating innervation 1 of genital organs of male . at . Transverse section through rabbit’s uterus after ovariotomy . Transverse section through bitch’s uterus 94 months after ovariotomy . Section through ovary of rat after (eshenlentaion on to peri- toneum . Section through ovary of rat after tonsplantat on on to peri- toneum . Transverse section duaiat normal uterus of rat . Transverse section through uterus of rat after ovariotomy . Transverse section through uterus after ovarian transplantation . Section through rat’s kidney into the tissue of which an ovary had been transplanted . Part of an early human chorionic villus . Early blastocyst of rabbit . Diagram to illustrate the three parts of the sell of iis yolk- sac (rabbit) . . Diagram of an opossum Skies cea its sopendaes ; . Diagram showing the arrangement of foetal membranes in Dasyurus . Diagram showing the isenbene: of fcotal doutvanes in Perameles . Elongated blastocyst of sieeee at dinteenth dies of pregnancy . Transverse section through blastocyst of sheep at twenty- fifth day . Blastodermic vesicle of rabbit . Diagram of blastodermic vesicle of rabbit in longitudinal section . Diagram to illustrate foetal membranes of Erinaceus . Hypothetical section of human ovum imbedded in decidua . Portion of injected chorion of pig . Section through wall of uterus and blastocyst of pig at twentieth day of pregnancy . Diagram representing a stage in the formation of the placenta (pig) . Section through uterine and embryonic Baits of a cotyledon of sheep at twentieth day of pregnancy . Section through base of fcetal villus, &c. (sheep) & . Columnar trophoblast-cells from the base of fcetal villus at third month of pregnancy (cow) to show phagocytosis Xv PAGE 249 250 259 261 318 319 321 322 323 324 325 327 362 372 381 382 383 385 386 387 388 389 391 393 394 395 396 398 399 401 100. 101. 102. 108. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. 116. 117. 118. 119. 120. 121. 122. 123. ILLUSTRATIONS . First stage of cellular secretion in placenta of cow . . Ingestion and disintegration of red blood corpuscles by bets blast of sheep . Absorption of ‘‘ Stabchen ”’ by eaphobings of shes . The uterine mucosa of dog at about twenty-third day of pregnancy Ovum with zonary band of villi . The angioplasmode of dog at thirtieth day of pregnancy F . The labyrinth and green border of placenta of dog at fortieth day of pregnancy . Transverse section of a four days’ aaisiod sac at rabbit Transverse section of a seven days’ gestation sac of rabbit Thickened ectoderm in rabbit, attached to placental lobe Iron granules in placenta of rabbit at eighteenth day of pregnancy Glycogenic areas of rabbit? s ‘Gis. at twelfth ties of pregnancy : . , Inversion of germinal nee in Bisbedenmte vesicle of mouse . Longitudinal sections of implantation cavity of field-mouse about eighth day of pregnancy . : : : : Longitudinal section of uterus and implantation cavity of guinea-pig : é : 7 Blastodermic vesicle of prneee showing inversion of ger- minal layers Implantation cavity of guinea-pig Implantation cavity of guinea-pig Allantoidean diplo-trophoblast of Erinaceus Section in situ of ovum of Hrinaceus : : The extension of yolk-sac against lacunar ecephoblagt in Erinaceus : é Transverse section through uterus of Sorex a a age oe the blastocysts are still in the oviducts : Part of the anto-mesometrial wall of the uterus of Sorex . Uterus and embryo of Sorex Orifice of uterine gland of mole with cashubladia aon Replacement of omphaloidean by allantoidean placenta . Placenta of bat P : . t Median longitudinal section of an early penis, ovum, 0:4 mm. in length F é , r Diagram of the earliest ere ovum ties ae . Section through the wall of the uterus in the early part of pregnancy . Section of a portion of the wall of tthe Hemeg Bledtoayet . PAGE” 405 408 409 412 413 415 417 421 422 “eA 429 432 438 440 443 444 445 446 448 450 451 452 453 455 457 459 461 464 468 469 470 Fic. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134, 135. 136. 137. 13%. 139. 140. ILLUSTRATIONS Section of a portion of the necrotic zone of the decidua, &c. Section through embryonic region of ovum Condition of the glands at the beginning of pregnancy in ten Median longitudinal section of embryo of 2 mm. Diagram of stage in development of human placenta Fat in a villus of human placenta ‘é Tron granules in a villus of the placenta in Man The first stage in the revolution of the equine foetus The foal in the normal position for delivery Virgina] external os (human) Parous external os (human) 2 Section of mammary gland of woman 3 Section of mammary gland (human) during issialion Section of mammary gland (human) in full activity . Section through an alveolus with fat drops in cells Section of developing mammary gland of horse Section of mammary gland (human) showing aseelnane alveoli 141 to 147. Diagrams from Minot’s Problem of Age, Growth, 148. 149, 150. 151. 152. 153. 164, and Death Section through ovary of woman of fifty-s Six conne degenera- tion of follicles, &c. r ‘ Section through uterine mucous membrane of woman nad ee Section through vaginal mucous membrane of woman of sixty-one . 7 Group of nerve cells from the first cervical eomten of a child at birth . . . : Group of nerve cells from the aie devia gangion of a man of ninety-two ‘i Land tortoise aged at least sights belonging to M. Elie Metchnikoft . “ Lonk sheep aged eighteen years, with her = jai. xvii PAGE 471 472 473 475 476 479 480 535 536 550 ib. 556 557 558 559 574 575 663-9 673 674 675 677 678 680 681 ERRATA ” yg . 51, footnote}, instead of “ prjiewalsky” read “ prjewalskit.” a] . 806, 1. 12, instead of ‘‘castration.2”” read ‘‘castration.1” (that is, see footnote 1 instead of footnote ?). P. 306, 1. 13, instead of ‘‘about horned cattle” read ‘ about many horned cattle.’’ P. 306, 1. 9 from bottom, tnstead of ‘‘ males.1”’ read ‘ males.?”’ (that is, see footnote ? instead of footnote +), tg . 316, 1. 16, before “ Ruticilla” read “a specimen of,” as] . 855, 1, 3 from bottom, tnstead of “ Priestley’ read ‘‘ Pembrey.”’ THE PHYSIOLOGY OF REPRODUCTION INTRODUCTION SINCE the time when physiology first became an organised science many volumes have been written on the digestive, excretory, nervous, and other systems of the body, but no attempt has yet been made to supply those interested in the reproductive processes with a comprehensive treatise dealing with this branch of knowledge. Indeed, in most text-books on physiology now commonly in use either the section devoted to the reproductive organs is restricted to a few final pages seldom free from error, or else the subject is entirely omitted. Yet generative physiology forms the basis of gynecological science, and must ever bear a close relation to the study of animal breeding. In writing the present volume, therefore, I have been actuated by the desire to supply what appears to me to be a real deficiency ; and in doing so I have attempted, however inadequately, to co-ordinate or give a connected account of various groups of ascertained facts which hitherto have not been brought into relation. For this purpose I have had occasion to refer to many books and memoirs dealing with subjects that at first sight might have been supposed to differ considerably. Thus, works on zoology and anatomy, obstetrics and gynecology, physiology and agriculture, anthropology and statistics, have been consulted for such observations and records as seemed to have a bearing on the problems of reproduction. My sources of information are duly acknowledged in the footnotes, but I am glad to take this opportunity of mentioning the following works from which I have obtained special help : “The Evolution of Sex,” by Professors Geddes and Thomson, “ Obstetrics,” by Professor Whitridge Williams, the sections on A 2 THE PHYSIOLOGY OF REPRODUCTION the male and female reproductive organs, by Professor Nagel and Dr. Sellheim, in Professor Nagel’s “ Handbuch der Physi- ologie des Menchen,” “ Experimental Zoology,” by Professor T. H. Morgan, and the writings of Mr. Walter Heape. The present volume is addressed primarily to the trained biologist, but it is hoped that it may be of interest also to medical men engaged in gynecological practice, as well as to veterinarians and breeders of animals. As a general rule, I have confined myself to the physiology of generation among the higher forms, and more particularly the Mammalia, but I have not hesitated to discuss the reproductive processes in the Invertebrata in cases where they seemed likely to elucidate the more complex phenomena displayed by the higher animals. The all-important questions of heredity and variation, although intimately connected with the study of re- production, are not here touched upon, excepting for the merest reference, since these subjects have been dealt with in various recent works, and any attempt to include them would have involved the writing of a far larger book. Similarly, the sub- ject matter of cytology, as treated in such works as Professor Wilson’s volume on the cell, is also for the most part excluded. It may be objected that, for a book on physiology, too much space is devoted to the morphological side of the subject. This has been done purposely, since it seemed impossible to deal adequately with the physiological significance of the various sexual processes without describing the anatomical changes which these processes involve. In preparing this work I have been assisted by many friends. I have been fortunate in securing the co-operation of Dr. William Cramer and Dr. James Lochhead, of the University of Edinburgh. Dr. Cramer has contributed the section on the biochemistry of the sexual organs, while Dr. Lochhead has written the chapters on foetal nutrition and the metabolism of pregnancy, a labour of no inconsiderable magni- tude in view of the complexity of the subject. I take this opportunity of recording my indebtedness to Mr. Walter Heape, through whose influence I was first led to realise the importance of generative physiology both in its purely scientific and in its practical aspects. I am under no light obligation to Professor INTRODUCTION 3 Schafer for valuable and ready help at all stages in the prepara- tion of this volume. Professor Schafer has kindly looked through the manuscript of the chapter on “The Testicle and Ovary as Organs of Internal Secretion,” besides giving helpful advice and criticism on various points connected with publication. Indeed, it is not too much to say that had it not been for him, the book would scarcely have been written. Dr. H. K. Anderson and Professor Sutherland Simpson have read the manuscript or proofs of the chapter dealing with “The Accessory Male Organs.” Mr. E. 8. Carmichael, of the Royal Infirmary, Edin- burgh, has read the section dealing with parturition. Dr. J. H. Ashworth has looked through the chapter on “ Fertilisation ” ; and Dr. F. G. Hopkins has done’ the same for Dr. Cramer’s. biochemical chapter. Dr. Anderson and Dr. Ashworth have also given me the benefit of their special knowledge in other parts of the work. To all these I am under obligations. I wish also to tender my thanks to those authors and publishers who have kindly allowed me to reproduce illustrations from their respective works, as well as to record my indebtedness to the- following, who have been of service by giving me information, important references, or assistance in other ways :—Dr. Nelson Annandale, Superintendent of the Indian Museum, Calcutta, Dr. W. Blair Bell, of Liverpool, Mr. Eagle Clarke, Super- intendent of the Scottish National Museum, Professor J. C. Ewart, of the University of Edinburgh, Professor J. P. Hill, of University College, London, Dr. A. C. Haddon, of Christ’s College, Dr. W. A. Jolly, of the University of Edinburgh, Dr. Janet E. Lane-Claypon, of London, Mr. D. G. Lillie, of St. John’s College, Mr. K. J. J. Mackenzie, of Christ’s College, Mr. F, A. Potts, of Trinity Hall, Dr. C. G. Seligmann, of London, and Mr. A. E. Shipley, of Christ’s College. Lastly, I wish to acknowledge the assistance of Mr. C. H. Crawshaw, of Christ’s College, in the correction of the proofs, as well as to express my obligations to Mrs. Hingston Quiggin for the willing labour she has expended in preparing the index and finally revising the text, and to Mr. Richard Muir for the skilful manner in which he has executed those drawings which are new. CHAPTER I THE BREEDING SEASON « To everything there is a season, and a time to every purpose under the heaven.” —Eeclesiastes iii. 1. “|r is well known that almost all animals, except Man, have a stated season for the propagation of their species. Thus the female cat receives the male in September, January, and May. The she-wolf and fox in January; the doe in September and October. The spring and summer are the seasons appointed .for the amours of birds, and many species of fishes. The immense tribe of insects have likewise a determinate time for perpetuating their kind; this is the fine part of the year, and particularly in autumn and spring. The last-mentioned class of beings is subject to a variation that is not observed in the others. Unusual warmth or cold does not retard or forward the conjunction of birds or quadrupeds; but a late spring delays the amours of insects, and an early one forwards them. Thus it is observed that, in the same country, the insects on the mountains are later than in the plains.” The foregoing quotation from Spallanzani’s ‘‘Dissertations,” } although not strictly accurate in all its statements, contains a clear recognition of two fundamental facts which indeed have been realised from the earliest times; firstly, that the periods of reproductive activity among the great majority of animals (not to mention plants) occur rhythmically, the rhythm having a close connection with the changes of the seasons ; and secondly, that the reproductive rhythm is liable, to a greater or less extent, to be disturbed or altered by climatic or other environ- mental influences. And while there may be a basis of truth for the statement that the periodicity of the breeding season 1 Spallanzani, Dissertations relative to the Natural History of Animals and Vegetables. Translated from the Italian, vol. ii., London, 1784. 4 THE BREEDING SEASON 5 in the higher animals is less liable to modification than is the case with certain of the lower forms of life, there is abundant evidence that among the former no less than among insects the sexual functions are affected by external conditions and food supply. Darwin remarks that any sort of change in the habits of life of an animal, provided it be great enough, tends in some way to affect the powers of reproduction. ‘“ The result depends more on the constitution of the species than on the nature of the change ; for certain whole groups are affected more than others ; but exceptions always occur, for some species in the most fertile groups refuse to breed, and some in the most sterile groups breed freely.” ‘Sufficient evidence has now been advanced to prove that animals when first confined are eminently liable to suffer in their reproductive systems. We feel at first naturally inclined to attribute the result to loss of health, or at least to loss of vigour; but this view can hardly be admitted when we reflect how healthy, long-lived, and vigorous many animals are under captivity, such as parrots and hawks when used for hunting, chetahs when used for hunting, and elephants. The reproductive organs themselves are not diseased; and the diseases, from which animals in menageries usually perish, are not those which in any way affect their fertility.” It would seem probable that failure to breed among animals in a strange environment is due not, as has been suggested, to any toxic influence on the organs of generation, but to the same causes as those which restrict breeding in a state of nature to certain particular seasons, and that the sexual instinct can only be called into play in response to definite stimuli, the existence of which depends to a large extent upon appropriate seasonal and climatic changes.” There are at present no sufficient data for a comparative account of the physiology of breeding among the lower animals ; and in the present chapter, which is preliminary in character, I shall content myself with stating a few general facts about 1 Darwin, Variation of Animals and Plants, Popular Edition, vol. ii., London, 1905. 2 See especially page 20, where Bles’s observations on the breeding habits of Amphibia are referred to. 6 THE PHYSIOLOGY OF REPRODUCTION the breeding season, giving illustrations, taken from various groups of Vertebrates and Invertebrates, of its seasonal re- currence, and the manner in which this varies under altered conditions of life. PROTOZOA Among the Protozoa the organisms pass through successive phases of vitality, which are comparable to the different age- periods of the Metazoa. In such simple forms of life, fission or division into two parts is the usual method of reproduction,! and the frequency of its occurrence appears to depend more upon the phase which has been reached in the life-cycle, than upon the influences of the environment. Thus, there is a period of extreme vigour of cell-multiplication, corresponding to the youth of a metazoén; secondly, there is a period of maturity, characterised by changes in the chemical and physical properties of the cell, and leading to the formation of con- jugating individuals; and finally, in forms which do not con- jugate, there is a period of senescence which ends in death. It is interesting to note, however, that the rapidity of fission is affected by the temperature and the food; for example, an individual of the Ciliate Infusiorian, Stylonychia pustulata, if well supplied with food, divides once in twenty-four hours in a temperature of from 5° to 10° C., and once in twelve hours in a temperature of from 10° to 15° C2 Again, Flagellate Infusoria of different kinds have been induced to conjugate by changing the temperature or increasing the density in the surrounding medium.’ Furthermore, the life-cycle of Para- mecium may be renewed without the occurrence of conjuga- tion, that is to say, fission can be made to continue and senescence can be avoided, by introducing a change in the * In this process no material is lost, and two simple nucleated organisms result. During the period of maturity referred to in the text, multiplication is often preceded by union (either temporary or complete) of two individuals, and this process is called conjugation (see p. 211, Chap. VI.). * Sedgwick, Student’s Teat-Book of Zoology, vol. i., London, 1898. * Calkins points out that the same experiment is performed by mosquitoes and other insects on certain parasitic Protozoa, as when a parasite is with- drawn from the hot environment of the Mammalian blood into the compara- tively cold region of the mosquito’s alimentary tract, (“The Protozoan Life-Cycle,” Biol. Bull., vol. xi., 1906.) THE BREEDING SEASON 7 composition of the medium surrounding the culture.1 (See p. 213.) Moreover, there is evidence that in the case of Colpoda stent at least the occurrence of conjugation is determined entirely by the conditions of the surrounding medium. C@LENTERATA With the majority of the Metazoa, as already indicated, there is a more or less definitely restricted season to which the occurrence of the chief reproductive processes is confined. Thus in the common hydra of Bengal (Hydra orientalis, Annandale), which, like most other Ccelenterates, reproduces by budding as well as by the sexual method,? the former process occurs chiefly during winter, the buds developing into new individuals. Towards the beginning of the hot weather budding becomes less active, and in some individuals ceases altogether, while the same thing happens during periods of temporary warmth in winter. A rise in temperature induces a proportion of the individuals present in an aquarium or pond to develop testes or male reproductive glands; if the rise is considerable it may cause a few of the remaining individuals to produce ova. On the other hand, no individual living in its natural environ- ment has been known to exhibit any sign of sex after the rise in temperature had become steady. The conditions most favourable to the production of ova appear to be a period of comparatively low temperature and abundant nutrition fol- lowed by a sudden but not excessive rise of temperature.* 1 Calkins, loc. cit. 2 Asexual reproduction is of very common occurrence among the majority of the lower animals and plants. It may take the form of simple binary fission (in unicellular organisms), of spore formation, or of germination or budding. Sexual reproduction consists essentially of the union of two cells and their subsequent division to give rise to the new individual. In the multicellular organisms (Metazoa and Metaphyta) there are two kinds of con- jugating cells, or gametes, which are specialised for the purpose. These are produced by the male and female respectively, and are known as spermatozoa and ova. Thus, sexual reproduction in the Metazoa is a modification of con- jugation in the Protozoa, (See Chap. VI.) 3 Annandale, ‘‘The Common Hydra of Bengal,” Memoirs of the Asiatic Society of Bengal, vol. i., 1906. Cf Whitney, ‘‘The Influence of External Factors in causing the Development of the Sexual Organs in Hydra viridis,” 8 THE PHYSIOLOGY OF REPRODUCTION Some of the marine hydroids show an alternation of genera- tions which does not appear at first sight to be in any way related to change in the environment. In such cases the fertilised ovum develops into a polyp which gives nse to a colony of polyps by a process of sexual reproduction. After the colony has reached a certain size, a new kind of bud is formed, and this becomes a jelly-fish. The latter, after leading an independent existence, produces eggs, and these in turn become fertilised, giving rise to a new generation of polyps. Morgan points out that as the polyp colony goes on increasing in size, its relation to its surroundings must undergo change, and that, very possibly, it is this change which determines the development of jelly-fish in place of polyps. If this inter- pretation is correct the breeding season among marine hydroids is controlled by environmental conditions, just as it is among most other animals.1 Some interesting observations have been recorded by Ashworth and Annandale? about the breeding habits of sea- anemones. The species Sagartia troglodytes and Actinia mesem- bryanthemum, which are very prolific in captivity, have been noticed to breed regularly in the early spring. Actinia com- mences to produce young in the beginning of February, and Sagartia about a month later. As a rule the young are ex- truded in the early morning, and one individual may repeat Arch. f. Entwick.-Mechanik, vol. xxiv., 1907. Whitney says that in Hydra viridis an abundance of food following a low temperature causes a suppression of the formation of testes and ova. 1 Morgan, Experimental Zoology, New York, 1907. Morgan shows that the same point is illustrated by certain recent experiments of Klebs on flowering plants. These at first produce only leaves and branches. When they reach a certain size they produce flowers. Klebs regards the develop- ment of the flowers as beiug due to a relation that becomes established between the plant (when it has reached « certain stage of growth) and the environment. He shows also that by altering the environment a shoot may be induced to go on growing vegetatively, when it would ordinarily develop into a flowering branch. The flowering of the plant, therefore, is not merely the culmination of its form, as most botanists regard it. For much valuable and suggestive information on the factors which control breeding in plants G. Klebs’ work should be consulted. (Willkirliche Entwickelungsdnderungen bei Pflanzen, 1903.) ® Ashworth and Annandale, ‘‘ Observations on some Aged Specimens of Sagartia troglodytes, and on the Duration of Life in Ccelenterates,” Proc. Roy. Soc. Edin., vol. xxv., 1904. THE BREEDING SEASON 9 the process every morning for a number of weeks, when the breeding season comes to an end. In one season, when the aquaria were somewhat neglected, the specimens of Sagartia produced fewer young than usual, and these were not extruded until the beginning of April. Specimens of Actinza living in the same aquaria were more prolific, but their breeding season was also somewhat retarded. In the month of August two anemones of the species Sagartia troglodytes were brought from Thorshavn in the Feroés, and placed in the aquaria. In the following October both of these produced several young; while in April of the next year one of them again gave birth, but only to a single anemone. It seems probable that in this case the change of temperature or environment had induced the anemones to breed at an unusual season ; for it is unlikely that October is the normal period for reproduction in the Feroés, as by this time the sea has already begun to run high, and there would be a great risk of the young anemones becoming destroyed, being unable to attach themselves. Ashworth has pointed out} that in the coral Xenia hick- sont, which lives in the tropics, there is every evidence that spermatozoa are discharged over a very considerable period, if not practically throughout the whole year, whereas in the related form Alcyonium digitatum, of Northern Europe, the period during which the spermatozoa are discharged is limited to about a month in the winter. Ashworth remarks that the difference is probably due to the fact that Xenia, living on reefs in the shallow waters of tropical seas, is not subject to great variations in temperature and food-supply, while with Alcyonium, such variations are no doubt considerable. In a similar way Miss Pratt,” who has studied the process of odgenesis in Sarcophytum, Holophytum, and Sclerophytum, concludes that the sexually mature condition in these tropical genera extends over a considerably longer period than in the case of corals inhabiting temperate waters. It may also be noted that, whereas in the Ctenophora of the Mediterranean the breeding season extends throughout the 1 Ashworth, “ Structure of Xenia hicksoni,” Quar. Jour. Micr. Science, vol. xlii. 2 Pratt, “On Some Alcyonide,”” Herdman’s Ceylon Reports, vol. iii. 10 THE PHYSIOLOGY OF REPRODUCTION year, in members of the same class in northern seas it only lasts through the summer.* Nemertea, &c. The breeding season and its relation to the environment have formed the subject of a careful investigation by Child? in the case of a small Nemertean, Stychostemma asensoriatum, which is found very abundantly in one of the park lagoons of Chicago. The season extends from May to November or December, according to the temperature of the water. Hgg- laying can occur freely in the laboratory, the eggs being de- posited always during the night, or in darkness, when the animals move about freely. Although breeding in the natural state is restricted to the warmer part of the year, eggs can be obtained in the laboratory at practically any time, by simply regulating: the temperature. Thus egg-laying can be induced in the winter at ordinary room-temperature, even though the worms are kept without food. “In animals which contained only a few small odcytes when taken, and which are kept in clean water without food, the growth of the odcytes will continue, and within a week or two eggs may be laid.” “The body of the animal may even decrease somewhat in size during the growth of the odcytes.” It is clear, therefore, that in Stychostemma the limits of the breeding season are determined chiefly by the temperature of the water, and that food is a factor of secondary importance. Similarly, in the case of the parasitic Trematode, Diplozoin ; paradozum, which ordinarily produces eggs only in the summer, it has been found that the formation of eggs could be artificially prolonged throughout the winter, if the fishes on whose gills the animal lives are kept in an aquarium at summer heat.? ANNELIDA Certain species of Polychet Annelids, known as the Palolo worms, exhibit a quite remarkable regularity in the periodicity of their breeding habits. During their immaturity all the Palolos — >» Bourne, ‘‘ The Ctenophora,” Treatise on Zoology, vol. ii., London, 1900. * Child, ‘‘ The Habits and Natural History of Stychostemma,” American Naturalist, vol. xxxv., 1901. 5 Semper, Animal Life, London, 1881. THE BREEDING SEASON 11 live in burrows at the bottom of the water. With the attain- ment of sexual maturity, and under certain peculiar conditions, they swarm out for purposes of breeding. In the Atlantic Palolo (Eunice fucata) and the South Pacific Palolo (Hunice viridis) the process invariably takes place twice, upon or near the day of the last quarter of the moon; but with the former species it occurs in June and July, and with the latter in October and November. In the Japanese Palolo (Ceratocephale osawat) the swarming takes place on nights closely following the new and full moons (i.e. when the spring tides occur), in October and November, the worms swimming out regularly four times a year. Each swarming-period lasts from one to four days. It has been noted further that the swarm is greater after the new moon (when the spring tide is highest) than after the full moon (when the tide is not so high), that each swarming takes place invariably just after the flood in the evening, that it continues for from one to two hours, and is generally larger on warm, cloudy nights than on clear, chilly nights. It would appear also that no individual worm takes part in more than one swarming in the year.! ARTHROPODA Innumerable instances of the periodicity of breeding and its relation to seasonal and environmental changes might be ad- duced from the great group of Arthropods, but the reason for the variations which occur is not always obvious. Thus, in the common crayfish (Astacus fluviatilis), in France the males are said to approach the females in November, December, and January, whereas in England they begin to breed as early as the commencement of October, if not earlier.? Also, in the Cape species of Pertpatus (P. capensis) birth takes place in a fixed season (during April and May), whereas, in the South American species, births are said to occur probably throughout the entire year.* In the case of the hemipterous insect known as the plant- louse (Aphis), we have evidence that the mode of reproduction 1 Tzuka, ‘‘ Observations on the Japanese Palolo,” Jour. of the College of Science, University of Tokyo, vol. xvii., 1903. 2 Huxley, The Crayfish, London, 1880. % Sedgwick, ‘“‘ Peripatus,” Camb. Nat. Hist., vol. xii., London, 1901. 12 THE PHYSIOLOGY OF REPRODUCTION is dependent upon temperature. In a favourable summer the females of this animal may produce as many as fourteen con- secutive generations of young by parthenogenesis, the ova undergoing development without being fertilised by the male. At the beginning of the winter male plant-lice make their appearance and fertilise the eggs, which develop in the succeeding spring. Réaumur, however, by artificially maintaining a con- stant summer temperature, succeeded in producing more than fifty parthenogenetic generations of plant-lice, all descended from a single mother.? Morgan, however, describes some observations which seem to indicate that the change is not merely due to temperature. He shows, for example, that the sexual forms of Aphis may appear in the autumn before the onset of the cold weather, and conversely that many individuals may continue to reproduce parthenogenetically, until finally they perish from the cold. Morgan suggests that the alternation in the mode of reproduction may depend upon changes which take place in the food-plant in the autumn, instead of being solely a temperature effect. He shows also that there is evidence for the conclusion that in the genus Chermes, in which the alternation of generations occurs between the fir-tree and the larch, the conditions existing on the larch are those that call forth the sexual forms.? It has been supposed that the change in the environment is also responsible for determining the sexes in aphids. Miss Stevens, however, has recently shown that what appears to be a change in sex should rather be regarded as a change from the parthenogenetic to the sexual mode of reproduction.* According to this view the sex of each individual is determined by the character of the gamete or gametes by which it is developed. The supposed influence of food and external conditions upon sex-determination in various kinds of insects, and other animals, is discussed at some length in a future chapter of this work (Chapter XV.). Semper pointed out long ago that the occurrence of Tepro- duction (or of the particular mode of reproduction), with 1 Semper, loc. cit. ? Morgan, loc. cit. * Stevens, “Studies in the Germ-Cells of Aphids,” Carnegie Institution Report, Washington, 1906. THE BREEDING SEASON 13 insects as with other animals, depends, among other things, upon the nature of the diet, upon the chemical conditions of the surrounding medium, upon the moisture of the air, or upon other circumstances which are often unknown. Thus, failure to breed in a new environment is experienced by many Lepidoptera. For example, Death’s-Head hawk moths, which are commonly blown over to this country from the Continent, but do not breed here, deposit their eggs on young potato plants, and these develop into moths which emerge in the autumn. The eggs, however, are quite infertile, so that, as a result, the Death’s-Head has never established a footing in Britain, though stray specimens are often captured.1 In the case of other insects, such as the mosquito (Anopheles), there is direct evidence that food is an important factor in egg-formation. Thus it was found that mosquitoes fed on bananas refused to breed, but when fed on human blood they invariably laid eggs after two or three days.’ It is interesting to note also that in the mos- quitoes and other Culicide, the males are generally unable to suck blood, this habit being apparently correlated with the function of oviposition. Dr. Gordon Hewitt informs me that among the Empide, which are carnivorous, the females, during the nuptial flights, are always fed by the males on small insects, and that they seem incapable of discharging their sexual func- tions unless they are fed in this way.® In some insects oviposition takes place long after the death of the males. Thus, Lefroy and Howlett state that in the mango weevil (Cryptorhynchus gravis) the males die in August while the females live until the following March to lay eggs.* MoLiusca Among the marine Mollusca, in curious contrast to so many forms of life, winter is the usual time for the deposition of the 1 Country Side, October 27, 1906. Z 2 “Report of Malaria Expedition to Nigeria,” Liverpool, Trop. Med. Memoir, IV. See also Ross (Nature, vol. 1xxx., 1909), who says that females of Culex and Stegomya apparently only desire to suck blood after fertili- sation. 3 Howlett, ‘Coupling of Empis,” Ent. Mag., vol. xliii., 1907. 4 Lefroy and Howlett, Indian Insect Life, Calcutta, 1909. 14 THE PHYSIOLOGY OF REPRODUCTION eggs.. On our own coasts Nudibranchs come to shore to lay their eggs from January to April. Patella spawns from October until the end of the year. Purpura lapillus is said to be most active during the same season, but it breeds to some extent throughout the year. Buccinum undatum breeds from October until May, whereas Lettorina breeds all the year round. Among the land-Mollusca there is a more marked periodicity in the breeding season than among the marine forms. In temperate climates breeding is restricted to the summer. In the tropics the occurrence of the breeding season is generally determined by the alternations of wet and dry seasons. In other cases, where there are no great seasonal changes, the land-Mollusca may breed all the year round. The snails of the Mediterranean area, according to Semper, arrive at sexual maturity when they are six months old, and before they are fully grown. Those individuals which reach this age in the spring deposit eggs a second time after the heat of the summer is over, and so experience two breeding seasons in the year, with an interval of a few months between them during the hot weather. Semper shows, further, that individuals of the same genera, or perhaps even of the very same species, in the damper and colder climates of the north, do not lay eggs till development is complete ; while in the dry, warm region of the Mediterranean, they have produced two lots of eggs before they are fully grown. This is because completion of growth and sexual maturity do not necessarily coincide. In a similar way, in the pond-snail (Limnea) the minimum of temperature which admits of the assimilation of food, and so of growth, is much above the winter temperature of egg-deposition. . In tropical climates, where the variation in temperature throughout the vear is reduced to a minimum, the periodicity in the breeding habits of animals is to a considerable extent obliterated, at least in so far as it is dependent upon tempera- 1 Lo Bianco, ‘‘ Notizie biologische riguardanti specialmente il periodo di maturitd sessuale degli animali del golfo di Napoli.” Mitth. Zool. Stat. Neapol., vols, viii. and xiii. Much valuable information concerning the breeding habits of Mollusca and other animals, inhabiting the Bay of Naples, is given in these papers. * Cook, ‘‘ Mollusca,” Camb. Nat. Hist., vol. iii, London, 1895. 3 Semper, loc. cit. THE BREEDING SEASON 15 ture. Semper! says that few things impressed him more in the Philippine Islands than the absence of all true periodicity in the breeding habits not only of the land-molluscs, but also of the insects and other land-animals. “I could at all times find egos, larvee, and propagating individuals, in winter as well as in summer. It is true that drought occasions a certain periodicity, which is chiefly perceptible by the reduced number of in- dividuals in the dry months, and the greater number in the wet ones; it would seem that a much smaller number of eggs are hatched under great drought than when the air is very moist. Even in January, the coldest and driest month, I found land-snails which require much moisture, and at every stage of their development, but only in shady spots, in woods, or by the banks of streams. But what was far more striking in these islands was the total absence of all periodicity in the life of the sea-animals, particularly the invertebrata; and among these I could not detect a single species of which I could not at all seasons find fully grown specimens, young ones, and freshly deposited eggs.” Semper goes on to remark that even in some cold seas periodicity is far more often eliminated than is commonly supposed, and mentions that the eggs of the sea- mollusc, Tergipes, have been found at all seasons, like those of [ittorina on our own coasts. ECcHINODERMATA Sea-urchins and starfish, and other Echinodermata, appear generally to have a regularly recurrent breeding season, at which the genital organs swell up to an enormous size. In the sea-urchin, Echinus esculentus, these organs grow into huge tree-like structures with branched tubes, lined by the sexual cells. These are sold for food by the fishermen in Naples, who call them “frutta di mare.” It is said that a single female E. esculentus will produce as many as 20,000,000 eggs in a breeding season. At other times of the year the generative organs are so reduced as to be scarcely recognisable. E. esculentus at Port Erin, in the Isle of Man, spawns in June.” At Dunbar, in 1 Semper, loc. cit. 2 Chadwick, Liverpool Marine Biological Committee Memoirs, vol. iii., Echinus, Liverpool, 1900. 16 THE PHYSIOLOGY.OF REPRODUCTION Scotland, it has been observed to spawn at the same time. The sea-urchins at Naples spawn at the end of the year (H. acutus being mature in November and December, and H. macrotuberculatus,° from September onwards).? CEPHALOCHORDATA In the lancelet (Amphioxus lanceolatus) of the Mediterranean the breeding season extends from spring until autumn, the glands becoming so large by the ripening of ova and spermatozoa that the atrium is used up to its utmost capacity. Spawning, when it occurs, invariably takes place about sun-down (ze. between 5 and 7 P.m.), and never, so far as known, at any other time? Pisces Among fishes the duration of the breeding season varies considerably according to the group to which they belong. The ova of Elasmobranchs are deposited singly or in pairs at varying intervals throughout a great part of the year. In Teleosts, on the other hand, the breeding season is limited as a tule to the spring and summer in temperate climates. In a single individual spawning may last no longer than a few weeks or even days.* The enormous number of eggs produced by most Teleosts must be connected with the absence of internal fertilisation, involving a large wastage of ova which never come in contact with male cells or spermatozoa. The cod, off our own coasts, has a spawning season ex- tending from January to June, but the majority of individuals spawn in March. It has been found, however, that in some parts of the North Sea the cod may spawn in the autumn. In the whiting the spawning period lasts from early March until the third week in August.’ The investigations of the Marine 1 Lo Bianco, loc. cit. The spawning times of most of the Naples Echinoderms are given in these memoirs. * Willey, Amphiowus and the Ancestry of the Vertebrates, New York, 1894, 5 Bridge, ‘ Fishes,” Camb. Nat. Hist., vol. vii., London, 1905. * Masterman, “A Contribution to the Life-Histories of the Cod and Whiting,” Trans. Roy. Soc, Edin., vol. xl., 1900. THE BREEDING SEASON 17 Biological Association have shown that in the plaice of the South Devon bays the maximum spawning period is between the third week of January and the second week of February. This period in the North Sea and Irish Sea would appear to be slightly later. Herdman! records that, in the year 1904, the plaice in the open-air ponds at the Port Erin Biological Station started spawning on March 3, and those at the Peel (Lancashire) Sea Fish Hatchery (under cover) on March 1. In the Holostean fish, Lepidosteus, which lives in the fresh waters of North America, the breeding season recurs with a wonderful regularity about May. At this time the fish resort in large numbers to shallower water, where the temperature is higher. Here the ova and spermatozoa are emitted during recurrent periods of sexual excitement.” The related fish, Amia, of Central and Southern North America, spawns usually in May, the exact season depending somewhat upon the temperature of the water. The fish make their way from deep water to the shallow spawning place, which is generally at the end of a swampy lake.* In the Crossopterygian fish, Polypterus bichea, the ova ripen in the summer months from June to September, the breeding season depending upon the period of inundation, as in most of the Nile fishes. The other species of Polypterus (P. senegalis and P. laprodei), which inhabit the river-basins of tropical Africa, spawn also in the wet season in July and August.® In the Dipnoan, Ceratodus, of Australia the principal time for spawning is September and October, at the end of the dry 1 Herdman, ‘‘ Spawning of the Plaice,” Nature, vol. lxix., 1904. See also Wallace (W.),same volume. For information concerning the spawning seasons of different species of fish, 7’he Journal of the Marine Biological Association, the publications of the English and Scottish Fishery Boards, and the International Council for Fishery Investigation, should be consulted. These reports show that the migratory and reproductive periods of fishes are affected by the temperature, salinity, &c., of the sea. 2 Agassiz, ‘‘The Development of Lepidosteus,” Proc. Amer, Acad. Arts and Science, vol. xiv., 1878. 3 Bashford Dean, ‘‘The Early Development of Amia,” Quar. Jour. Mier. Setence, vol. xxxviii., 1895. ‘ Harrington, ‘‘The Life-Habits of Polypterus,’ American Naturalist, vol. xxxiii., 1899. 5 Budgett, ‘‘On the Breeding Habits of Some West African Fishes,” Trans. Zool. Soc., vol. xvi., 1901. B~ 18 THE PHYSIOLOGY OF REPRODUCTION season.! In the other two Dipnoans, Lepidosiren of South America and Protopterus of Africa, spawning occurs shortly after the emergence of the fish from their summer sleep. Kerr, writing of the former, says that the exact tune for breeding varies greatly from year to year in correlation with the extreme varia- bility of the climate, the swamps, which the mud-fish inhabit, sometimes remaining dry for prolonged periods.? Many fishes migrate, before the commencement of the breeding season, to localities suitable for the deposition of their eggs. Thus, certain marine fishes like the salmon, the shad, and the sturgeon ascend rivers for long distances before spawn- ing; others merely migrate to shallower water nearer shore. The eel, on the other hand, is a fresh-water fish which migrates to the sea for breeding, and deposits its eggs in deep water. Jacobi? showed that the migration of the eel is not deter- mined by the growth of the genital organs, for these do not begin to develop until the fish have reached the sea. He concluded, therefore, that eels need salt. water before the genital organs can develop. Similarly, Noel Paton* has pointed out that salmon, with their genitalia in all stages of development, are ascending the rivers throughout the whole year. Miescher,” too, has shown that salmon go practically without food so long as they are in fresh water, being nourished by the large store of material which they accumulated while they were in the sea. This observation has been confirmed by Noel Paton. Miescher and Paton have shown, further, that the gain in solid material (proteins, &c.), by the genitalia,° as the fish pass up the rivers, is met by a loss in solid material in the muscles. This transference is not brought about by anything of the nature of a degeneration taking place in the muscles; but the latter appear simply to excrete or give out the material which has been 1 Semon, Jn the Australian Bush, London, 1899. * Kerr, ‘‘The External Features in the Development of Lepidosiren paradoxa,” Phil. Trans. B., vol. cxcii., 1900. 3 Jacobi, Die Aalfrage, Berlin, 1880. 4 Paton, Fishery Board Report of Investigations on the Life History of the Salmon, Glasgow, 1898. 5 Miescher, Histochemische und Physiologische Arbeiten, vol. ii., Leipzig, 1897. 6 The gain in the genitalia is due largely to the formation of compara- tively simple proteins (protamines, histones, &c.). See Chapter VIII. THE BREEDING SEASON 19 accumulated in them. It should be noted, however, “ that the gain of solids by the genitalia is small as compared with the loss of solids by the muscle, that in fact the greater part of the solids lost from the muscles are used up for some other purpose than the building up of the genitalia.””! Paton concludes that the state of nutrition is the main factor determining migration towards the river, and that, when the salmon has accumulated a sufficiently large store of material, it returns to the rivers which were its original habitat. It does not seem possible, however, to maintain that nutrition is a determining influence in the growth of the genital glands, since these are undeveloped when the fish begin to migrate and enter upon their period of starvation. Wiltshire ? states that in some fishes, at the period of ovi- position, the lips of the genital orifice swell and become congested. This condition he regards as comparable to that which occurs during the “ heat ” period of a mammal. AMPHIBIA The intimate connection between sexual periodicity and climatic variation exhibited by many Amphibia and Reptilia, especially in temperate climates, was commented on by Spallan- zani.2 This close dependence upon environmental conditions is evidently due largely to the habits of life of these animals, many of which hibernate or show great sluggishness in cold weather ; while among Amphibia it must be associated with the further fact that, whereas most members of the group live to a great extent upon land, it is necessary for them to deposit their eggs in water. Spallanzani concludes that the reason why Amphibia are subject to a variation which is not observable in birds and Mammals is because the former, like insects, are cold-blooded, and have a comparatively small supply of internal heat to 1 Paton, loc. cit. Milroy (‘‘ Chemical Changes in the Muscles of the Herring during Reproductive Activity,” Seventh International Congress of Physiolo- gists, Heidelberg, 1907; abstract in Zeit. f. Phys. vol. xxi., 1907; and Biochem. Jour., vol. iii., 1908) has recently shown that similar changes take place in the herring, in which, however, the starvation period is briefer. 2 Wiltshire, ‘‘ The Comparative Physiology of Menstruation,” Brit. Med. Jour., 1883, 3 Spallanzani, Dissertations, vol. ii., London, 1784. 20 THE PHYSIOLOGY OF REPRODUCTION animate them when it is cold. “As therefore the exercise of their functions depends on the heat of the atmosphere, their amours will also depend upon this cause, and will, of course, be later in cold than in hot climates, and in both will vary with the season.” Spallanzani illustrates the truth of this fact by pointing out that various species of frogs and toads begin to propagate earlier in Italy than in Germany or Switzerland.1_ On the other hand he records the observation that the tree-frog and the fetid terrestrial toad were copulating in the ponds and reservoirs of Geneva in March, at a time when in Lombardy they had not yet quitted their subterranean abodes. It is interesting to note that in the frog and other Amphibia the ova are produced in winter, when the animals eat little or nothing, just as the genital organs of the salmon develop during the period of migration, when the fish have practically ceased to feed. Bles? has discussed at some length the conditions under which it is possible to induce various species of Amphibia to breed in captivity. He states that the most necessary con- dition is that the animals should be allowed to hibernate at the proper season, and in order to accomplish this they must be in thoroughly good health when the winter sets in, having passed the summer in the best circumstances in regard to light, heat, and supply of food. Bles’s observations relate more especially to the African frog, Xenopus levis, but he believes his conclusions to apply in a large degree to many other species of Amphibia. The frogs in question were kept in a “ tropical aquarium’ (that is to say, an aquarium which could be kept at a tropical temperature by regulating a heating apparatus). In the summer the temperature was maintained at about 25° C.; in December 2 2 1 In the common frog (Rana temporaria) the usual time for spawning in Middle Europe is March, earlier in warm, later in cold seasons; in southern °: countries, January or February, but in Norway not until May. Vdde Gadow, Cambridge Natural History, vol. viii, London, 1901. This book contains # quantity of valuable information concerning the breeding habits of many Amphibia and reptiles. * Bles, “The Life-History of Xenopus levis,” Trans. Roy. Soc. Edin., vol. xli., 1905. THE BREEDING SEASON 2) it was allowed to drop to 15°-16° C. during the day, and 5°-8° C. during the night. The bottom of the aquarium was covered with earth and stones, on which the weed Vallisneria thrived. The water in the aquarium was never changed. The frogs were fed daily upon small worms, or strips of liver, until they would eat no more. During winter they became lethargic, taking very little food. When the temperature rose in the spring and the days became brighter, the frogs became more active, especially the males. At this time breeding could be induced by a certain method of procedure which Bles describes as follows: “ First, the temperature of the aquarium is raised to 22° C.; and secondly, when it has become constant, a certain amount of water, say two gallons, is drawn off morning and evening, allowed to cool for twelve hours, and then run in slowly in the following manner, in order to simulate the fall of rain. The cooling vessel is raised above the level of the aquarium, and a syphon is used to run off the water. The lower end of the syphon is drawn out to a fine point, and turned up in such a way that the water rises up like from a fountain, and falls as spray into the aquarium. ... By carrying out such measures I obtained from one female, between April and July 1903, more than fifteen thousand eggs.”’ The abdomen of the female Xenopus is stated to become very much distended during the winter by the enormously enlarged ovaries. “ The three flaps surrounding the cloacal aperture are flaccid until the spring, when they become swollen and turgid, and more highly vascularised.” (Cf. the changes in the female genital organs of Mammals during the “heat’’ periods, de- scribed in the next chapters.) The male Xenopus is said to assume its nuptial characters two days after the temperature is raised to 22° C., and a very little later it becomes vocal, the voice strengthening from day to day. Copulation takes place only at night, and spawning may commence an hour afterwards ; but this does not occur unless the water is changed in the manner above described. According to Leslie! it would appear that Xenopus, in its native country, breeds only in August, 7.e. in the South African 1 Leslie, ‘‘ Notes on the Habits and Oviposition of Xenopus levis,” Proc. Zool, Soc., 1890. 22 THE PHYSIOLOGY OF REPRODUCTION spring. Bles, however, is disposed to think that Xenopus, like Discoglossus in the wild state, may breed several times during the spring and summer, since the frogs in confinement in some years spawned three times. Semper ! has shown that if axolotls are kept crowded together in small aquaria, without plants or seed, individuals which are sexually mature will not deposit ova even though the water be changed and abundant food supplied. But if they be suddenly transferred to aquaria stocked with plants, and with stones and sand on the bottom and running water, they can be induced to spawn within a few days, and may do so as often as three or four times a year. Bles states that he is able to confirm Semper’s observations upon axolotls, and that he obtained similar results by treating individuals of Triton waltlit and of Discoglossus in the same way. Annandale ? states that in the Malay Peninsula Rhacophorus leucomystax and Rana limnocharis appear to breed only after a heavy fall of rain, and he concludes that the stimulus set up by falling water is necessary before the sexual impulse can be induced. Thus there appears to be abundant evidence that breeding in mature Amphibians does not occur cyclically merely, but it takes place only in response to certain definite external stimuli. Bles remarks that if this view is correct, and assuming it to apply to other groups besides the Amphibia, it helps to explain why many animals fail to breed in captivity ; and also how it is that others (e.g. insects), in a state of nature, appear in large numbers in one year and are much less numerous in another.? It is interesting to note that among frogs and other cold- blooded Vertebrates there is a periodicity in the occurrence of their reflex responses. It has been shown that if the region * Semper, ‘‘ Ueber eine Methode Axolotl-Eier jederzeit zu erzeugen,” Zool. Anz., vol. i., 1878. See also Animal Life. * Annandale, Fasciculi Malaycnses, Zool., Part J. 1904. 3 See page 5, Chapter I. 4 The sexual posture of frogs in the act of sopulations is maintained as a spinal reflex. The tortoise is similar. The reflex is inhibited by excitation of the opticallobes. (Spallanzani, loc. cit. ; Goltz, Zeut. f. deutsch. med. Wiss., 1865-66 ; Tarchanoff, Pfliigcr’s Arch., vol. xl., 1887; Albertoni, Arch. Ital. de Biol., inl, ix., 1887). THE BREEDING SEASON 23 of the shoulder-girdle bearing the four limbs, together with the connected skin and muscles, and the three upper segments of the spinal cord, are cut out from the male frog during the breed- ing season (but not at other times), the irritation of the skin will cause a reflex, clasping movement, similar to that char- acteristic of the normal male at this period. In spring and early summer, after reviving from their winter sleep, frogs tend to be irregular in certain other of their reflex responses. MacLean has shown that in the heart of the frog, newt, and salamander, and also the eel, vagus inhibition is absent or markedly diminished at certain periods corresponding roughly to the seasons of sexual activity, but the significance of the changes is not very apparent. ReEPTILIA Reptiles which hibernate usually begin to breed shortly after the commencement of the warm weather which terminates the hibernating period, just as in the case of Amphibia. Other reptiles, which live in warm or tropical climates, also have regularly recurrent breeding seasons, in some cases extending over many months, generally in the spring and summer.? It would seem that in reptiles also, breeding only occurs in response to certain external stimuli, and that temperature is the main factor, as supposed by Spallanzani. AVES It would appear almost superfluous to cite examples of sexual periodicity from among birds. That spring and summer are the seasons when most birds pair, build their nests, and incubate their eggs, and that these processes are wont to vary slightly with the character of the season, are facts that are familiar to all. Bird-fanciers know also that the capacity of certain birds for egg-laying may be influenced by diet, and that this capacity can sometimes be increased (e.g. in the common fowl *) by the supply of suitable food. 1 MacLean, ‘‘The Action of Muscarin and Pilocarpin on the Heart of certain Vertebrates, with Observations on Sexual Changes,” Biochem. Journal, vol. iii., 1908. 2 See Gadow, loc. cit. * Wright, The New Book of Poultry, London, 1902. 24 THE PHYSIOLOGY OF REPRODUCTION With the approach of the breeding season the genital organs grow enormously until the whole oviduct reaches a state of hypertrophic turgescence. Gadow states that in the common fowl the oviduct at the period of rest is only six or seven inches long and scarcely a line wide, but that at the time of egg-laying it becomes more than two feet in length and nearly half an inch in width, thus increasing the volume about fifty times. This remarkable growth occurs annually. Gadow remarks also that the testes of the house-sparrow increase from the size of a mustard-seed to that of a small cherry, and in so doing tem- porarily displace the usual arrangement of the viscera in the body-cavity.1 3 A very large number of birds seasonally migrate, and this habit, as in the case of the migratory fish already referred to, is closely associated with the function of breeding.? Jenner? stated long ago that migration was invariably associated with an increase in size of the ovaries and testes, and that when these begin to shrink, after discharging their functions, the birds take their departure. Thus the ovaries of the cuckoo are stated to be almost atrophied in July. It would seem quite possible that the annual development of the sexual organs is the immediate stimulus which, in the individual, fixes the time for the spring migration, for it is known that in birds passing northward the ovaries and testes are well developed. (But ¢f. fishes, p. 18.) Thus wading birds, such as the sanderling shot by Mr. Hagle Clarke at Spurn Head, in May, were found by him to have their sexual organs in a very advanced state of growth. These birds were probably on their way to Greenland or Siberia. Schafer * has suggested that the migratory impulse is deter- 1 Gadow, Article on ‘‘ Reproductive Organs,” in Newton’s Dictionary of Birds, London, 1893-96. Disselhorst also (‘* Gewichts- und Volumszunahmen der mannlichen Keimdriisen,” Anat. Anz., vol. xxxii., 1908) has called attention to the enormous increase in size and weight of the testicles and ovaries in many birds (and also in some Mammals) in the breeding season. Thus, in Fringilla, the testicles may increase three-hundred-fold. ? For much of the information given here regarding migration, I am in- debted to Mr. Eagle Clarke. * Jenner, ‘Some Observations on the Migration of Birds,” Phil. Trans., Part I., 1824. * Schiifer, “On the Incidence of Daylight as a Determining Factor in Bird Migration,” Nature, November 7, 1907. THE BREEDING SEASON 25 mined by the relation of daylight to darkness, having been brought into being through the agency of natural selection, in consequence of the necessity to most birds of daylight for the procuring of food. This hypothesis explains both the northerly migration in spring and the southerly migration in autumn, since at both times the birds are travelling in the direction of increased light (or, if they start before the equinox, towards regions where they will enjoy longer daylight later in the season). The suggestion that the time of the spring migration is deter- mined in each individual by a stimulus set up by the growing genital organs is in no way opposed to Schifer’s theory, which provides an explanation of the general fact of migration. It has been noted that the northerly spring migration is far more hurried than the somewhat leisurely autumn migration in the reverse direction. Furthermore, although the north-south migratory movements are as a rule extraordinarily regular, it has been observed that the birds do not all set out together, and that the times of departure and arrival for each species may vary in any one year by several weeks. Moreover, golden plover are found migrating across Britain on their way north- ward (perhaps to Iceland) at a time when other individuals of the same species are rearing young in Britain. (The breeding season in Iceland is about a month or six weeks later than in Britain.) In view of these facts it is evident that the occurrence of the migratory movement is dependent not merely upon external or environmental influences, but also upon internal or individual ones, and, as already stated, it is not improbable that one of the factors involved is the state of development of the organs of generation. Many birds are double-brooded, having young ones not only in spring, but also in autumn before the close of the mild weather (in temperate climates). Swifts are stated to have a second brood in Southern Europe after leaving Britain in August, and the same is said to be the case with nightingales. Wiltshire ! mentions that a pair of swifts that stayed behind the others, had a brood in September, which migrated with the parent birds in October. Whether birds are single- or double-brooded probably depends to a large extent upon the duration of the 1 Wiltshire, loc. cit. 26 THE PHYSIOLOGY OF REPRODUCTION period of incubation. This period in wading birds and sea-birds is approximately double that of passerine birds ; but, within the limits of the group to which they belong, it is closely related to the size of the birds. Thus the incubation-period of the stormy petrel is thirty days; that of the starling is fifteen or sixteen days; while that of the raven (the largest passerine bird) is about nineteen days. The starling is, as a rule, almost certainly double-brooded, while the petrel and the raven are single- brooded.1 Other birds, such as the sparrow, are probably often treble-brooded. It is, of course, well known that domestication tends to increase the number of broods which a bird may produce (e.g. in pigeons and poultry). MaAmMaLia The breeding season in the Mammalia, and the variations in its periodicity, are discussed at some length in the next chapter. Here it will suffice to point out that whereas the occurrence of breeding in any one country or locality is closely connected with the climatic conditions and the periodicity of the seasons in that country, this rule does not hold invariably. For while the sheep in South Africa breeds in April and May (the South African autumn), thus following the seasons (since sheep breed ordinarily in autumn in this country), the camels in the Zoological Gardens in London experience rut in early spring, or at approximately the same time as the breeding season of the wild camels in Mongolia.? It has been already noted that some Mammals refuse to breed in captivity, while in many others the occurrence of breeding can be regulated to some extent by such factors as accommodation, heating, and feeding. Also in certain domestic animals, such as the sheep, the condition of “ heat’ can be induced more readily by the supply of additional or special kinds of food.® * Tam indebted to Mr. Eagle Clarke for certain of this information. * Heape, “The Sexual Season of Mammals,” Quar. Jour. Micr. Science, vol. xliv., 1900. ‘The black swans in the Zoological Gardens breed ‘at the same time as those in Australia. (Cf. also Timor pony, p. 51.) * Cf. birds, p. 23, and insects, p. 13. This point is referred to more fully in Chapter XIV., where the causes which influence fertility are dis- cussed. . THE BREEDING SEASON Q7 The approach of the breeding season in many animals, if not in most, is marked by a display of greater vitality, as mani- fested by an increased activity, which relates not merely to the sexual organs but to the whole metabolism of the body. This enhanced vitality is, as a rule, maintained throughout the breeding season. Thus male birds at the time of pairing are in a state of the most perfect development, and possess an enormous store of superabundant energy. Under the influence of sexual excitement they perform strange antics or rapid flights which, as Wallace remarks, probably result as much from an internal impulse to exertion as from any desire to please their mates. Such, for example, are the rapid descent of the snipe, the soaring and singing of the lark, the strange love-antics of the albatross, and the dances of the cock-of-the-rock, and of many other birds... The migratory impulse, which, as already mentioned, is closely associated with the periodic growth of the sexual organs, may also very possibly be regarded as affording evidence of increased vitality at the approach of the breeding season. Moreover, many of the secondary sexual characters, both those of the embellishing kind and others as well, are developed during only a part of the year, which is almost invariably the period of breeding. A familiar example of this correspondence between the development of secondary sexual characters and the activity of the reproductive organs is supplied by the growth of the antlers in stags. At the time of rut, which in the red-deer (Cervus elaphus) begins in September or October (see p. 48), the antlers, or branched outgrowths from the frontal bones, are completely developed, having shed their “ velvet” or covering of vascular skin. The animals during this season are in a state of constant sexual excitement, and fight one another with their antlers for the possession of the hinds.? By the end of the year the fighting and excitement have ceased, and the stags begin once more to herd together peaceably, and apart from the females. Shortly afterwards the antlers are shed. In most parts of Britain this occurs about April; but a Highland stag has been 1 Wallace (A. R.), Darwinism, London, 1890. 2 The larynx also is said to enlarge at this season, when the stag is wont to utter a loud bellowing noise. 28 THE PHYSIOLOGY OF REPRODUCTION known to drop his antlers as soon after the rutting season as December, while, on the other hand, some immature animals in the Lake District are said to carry them until May. After the shedding of the antlers new ones begin to grow from the pedicles, the growth taking place chiefly in July and August. When the new antlers have reached their full development the “ velvet” is shed (about the beginning of September). The size of the antlers, and the number of branches or “ points,” go on increasing every year throughout the reproductive period of the stag’s life and until he begins to decline with old age. In the American prongbuck (Antilocapra americana), which is unique among hollow-horned ruminants in shedding the horns every year, the shedding follows the rutting season more closely than in the stag. The rutting in this species begins in September, and lasts about six weeks. In old bucks the horns are shed in October, while the new growth is not completed until July or August in the following year.’ A secondary sexual character of a comparable kind occurs in the male salmon, in which the tip of the lower jaw, during the breeding season, is turned up and enlarged, as if to protect the fish in fighting when charged by another male.* In Polypterus, during the breeding season, the oval fin of the male becomes greatly enlarged and thickened, and has its surface thrown into folds between the fin-rays. The object of this modification is not known.4 The papille on-the hind limbs of the breeding male Lepidosiren are structures which seem to possess a special significance, since Kerr ® has shown that they probably serve as accessory organs of respiration. During the greater part of the year they are relatively inconspicuous ; but as soon as the animal is set free at the beginning of the wet season, they begin to grow with remarkable rapidity, forming slender filaments two or three inches in length and blood-red in colour from their intense vascularity. After the breeding season is over the filaments commence to atrophy, and eventually shrink to their 1 Cunningham (J. T.), Seaual Dimorphism, London, 1900. 2 Cunningham (J. T.), loc. cit. $ Darwin, Descent of Man, Popular Edition, London, 1901. 4 Budgett, loc, cit. 5 Kerr, loc. cit. THE BREEDING SEASON 29 former size, but still present for some time a distinctive ap- pearance owing to their being crowded with black pigment-cells. Whatever may be the precise purpose of this curious modifi- cation it is certain that its development is associated with reproductive activity, and so may be regarded as an expression of the intense vitality which the organism exhibits at this period. Some animals exhibit in the breeding season a particularly vivid coloration which is absent from them at other times. The case of the male dragonet (Callionymus lyra), which becomes a brilliant blue-and-yellow colour, has been discussed at some length by Cunningham, who concludes that the production of the guanin and pigment that give rise to the colour is to be connected with the intense nervous excitement which affects the fish at the time of courtship. “ Physiological processes are known to be governed largely by nervous impulses, and not merely the circulation, but the excretory activity of the skin, are known to be influenced by nervous action. Pigment and guanin are produced in the skin by the secretory or excretory activity of the living cells.”? Whatever be the precise ex- planation of this particular instance of intenser coloration, there can be no doubt that it is an indication of a more active metabolism. The brilliant colours of the male lump-sucker (Cyclopterus lumpus), and of other fish * at the time of breeding, are probably due to the same causes as in the dragonet.* 1 Cunningham (J. T.), loc. cit. 2 Cunningham (J. T.), loc. cit. * Numerous instances are given by Darwin, loc, cit., both for fishes and Amphibians, 4 The nuptial changes which occur in fishes are not necessarily in the direction of increased brilliance of coloration. Miss Newbigin describes these changes in the salmon as follows: ‘‘ When the fish comes from the sea the skin is of a bright silvery hue, while the flesh has the familiar strong pink colour. The small ovaries are of a yellow-brown colour. As the reproductive organs develop during the passage up the river, certain definite colour-changes occur. The skin loses its bright silvery colour, and, more especially in the male, becomes a ruddy-brown hue. At the same time the flesh becomes paler and paler, and in the female the rapidly growing ovaries acquire a fine orange-red colour. The testes in the male remain a creamy white. After spawning the skin tends, in both sexes, to lose its ruddy colour and to regain the bright silvery tint ; the flesh, however, remains pale until the kelt has revisited the sea” (Report of Scottish Fishery Board, 1898). Barrett-Hamilton (Proc. Camb. Phil. Soc., vol. x., 1900, and Annals and 30 THE PHYSIOLOGY OF REPRODUCTION The tail of the lyre-bird, which is shed at the end of the breeding season, not to be renewed again in the same form until the following summer, the brilliant plumage of the breeding drake, the more intense colouring of the phalarope, and many other birds during the season of courtship, are familiar instances of the same kind of phenomena.t_ The remarkable plate of horn which is developed in the upper mandible of the pelican in the breeding season, and bodily shed at the end of it, and the “ gular pouch ” in the throat of the breeding bustard, are examples of a more special kind, the existence of which, however, must be connected, either directly or indirectly, with the contem- poraneous increase of sexual activity and the enhanced vitality which accompanies it. In some animals certain glandular organs, apart from those concerned in the reproductive processes, show’a special activity at the breeding season. For example, in the swiftlets (Collocalia) the salivary glands become peculiarly active, and secrete a sub- stance which is allied to mucin, and is employed in building the edible birds’-nests of Chinese epicures.? A somewhat similar peculiarity exists in the male of the sea-stickleback (Gusterosteus spinachia), which binds together the weeds forming its nest by means of a whitish thread, secreted by the kidneys, and produced only during the breeding season. According to Mobius, as quoted by Geddes and Thomson,? the Mag. of Nat. Hist., vol. ix., 1902) draws attention to many such sexual phenomena, and more especially to those occurring in the spawning season in certain salmonoid fishes of the genus Onchorhynchus. The fish undergo extraordinary changes in colour and shape, and, since they die when spawning is accomplished, it is argued that the changes cannot have any zsthetic significance, but represent a pathological condition in which the fish become continually more feeble and eventually succumb. 1 Beebe (‘‘ Preliminary Report, on an Investigation of the Seasonal Changes of Colour in Birds,” Amer. Nat., vol. xlii., 1908) describes an experi- ment in which certain tanagers and bobolinks, which had been prevented from breeding, were kept throughout the winter in a darkened chamber with a somewhat increased food-supply. As a consequence the nuptial plumage was retained until the spring, when the birds were returned to normal conditions. They shortly afterwards moulted. The breeding plumage was then renewed, so that in this case the dull winter plumage was never acquired, * Geddes and Thomson, Evolution of Sex, Revised Edition, London, 1901. 3 Geddes and Thomson, loc. cit. THE BREEDING SEASON 31 secretion is semi-pathological in nature, being caused by the mechanical pressure of the enlarged testes upon the kidneys. The male gets rid of the thread-like secretion by rubbing itself against objects, and thus, by an almost mechanical process, the weaving habit is supposed to have become evolved. During the breeding season the anal scent-glands of snakes are said to be actively functional, but not at other times. A similar fact is stated about the submaxillary glands of crocodiles, and the cloacal glands of tortoises and other reptiles! The secretions of these glands, like the musk glands of Mammals, no doubt serve the purpose of enabling the sexes to detect one another’s presence more easily. (See p. 241.) The periodicity which is such a marked feature of animal life in temperate climates has been discussed at some length by Semper.” This author concludes that the phenomenon in question is dependent on the severe extremes of summer and winter temperature to which the animals are exposed. ‘‘ Every individual requires a certain duration of life to achieve its in- dividual development from the egg to sexual maturity and full growth; the length of time requisite for this is very various, and, above all, bears no proportion to the size attained... . This length of time, which we may generally designate as the period of individual growth, is not alike even for all the in- dividuals of the same species; on the contrary, it depends on the co-operation of so many different factors that it must necessarily vary considerably. Now, if from any cause the period of individual growth, say of the salmon, became changed in consequence of the slower development of the embryo in the egg or of the young larve, most or all the young salmon thus affected would die in our climate, because the greater heat of spring is injurious to them at that stage.” In a similar way it may be argued that the periodicity of the breeding season, no less than the rate of growth, is governed by the necessities of the young. No doubt this is true to a large extent, yet at the - same time it is equally evident, as has been shown above in numerous instances, that this periodicity is greatly affected by 1 Owen, Anatomy of Vertebrates, vol. i., London, 1866. Laycock, Nervous Diseases of Women, London, 1840. 2 Semper, Animal Life, London. 1881 32 THE PHYSIOLOGY OF REPRODUCTION climatic and environmental changes, and even by stimuli of a more particular nature (cf. frogs, p. 20). But this power, which all animals in some degree possess, of responding to altered con- ditions, may none the less have arisen primarily to meet the re- quirements of the next generation ; or, to speak more accurately, that those animals which breed at a certain particular season (or in response to certain conditions which prevail at that season) have the advantage in being able to produce a new generation to which this capacity to respond similarly will be transmitted. In other words, the restriction of the breeding habit to certain seasons may have been brought about under the influence of natural selection to meet the necessities of the offspring. Heape, however, has raised the objection’ that this view is inapplicable to the Mammalia, in which there is a period of gestation of greatly varying length in the different species. If the theory were correct, why, he asks, do some bats experience a breeding season in the autumn, and not produce young until the following June, although only two months are required for the development of the embryo in these animals; why do roe- deer in Germany breed in autumn, while the embryo does not develop beyond the segmentation stage until the following spring ; and why does the seal take eleven or twelve months for gestation when a large dog requires only nine weeks? Heape believes that the recurrence of the breeding season is governed directly by climatic, individual, and maternal influences,” 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 favour- able time of the year.” I cannot altogether concur in Heape’s view of this question. For it seems to me by no means improbable that whereas the necessities of the offspring, under changed environmental con- ditions, may sometimes have been provided for by modifications 1 Heape, ‘‘ The Sexual Season of Mammals,” Quar. Jour. Micr. Science, vol. xliv., 1900. ? Under the heading of “individual influences” Heape includes special nervous, vascular, and secretory peculiarities of the individual and its habits of life. The length of the gestation and lactation periods he calls ‘‘ maternal influences.” THE BREEDING SEASON 33 in the rate of development or length of gestation, yet in other cases a similar result may have been effected by alterations in the season of breeding. The mere fact that breeding in any one species occurs, as a rule, periodically at a time which is on the whole well suited to the requirements of perpetuating the race, is itself presumptive evidence that the periodicity of the breeding season is controlled (through natural selection) by the needs of the next generation. Further, the breeding season having been fixed at one period in the history of the species, the same season would probably be retained (in the absence of disturbing factors) by the descendants of that species under the directive influence of heredity. This view is in no way opposed to the doctrine that the sexual capacity is developed in the individual in response to definite stimuli, which are largely environmental and often seasonal. The occurrence of a succession of “ heat ’’ periods within the limits of a single breeding season no doubt arose in consequence of the increased opportunity afforded thereby for successful copulation. The number and frequency of the “ heat” periods under these circumstances are affected by the conditions under which an animal lives in just the same kind of way as the periodicity of the breeding season is affected, as will be shown in the succeeding chapter on the cestrous cycle in the Mammalia. Concerning the immediate cause of “ heat,’ and the nature of the mechanism by which it is brought about, something will be said later (Chapter IX.). The origin of the breeding season is a wider question. For its complete solution, as pointed out by Heape, a comparative study of the sexual phenomena in the lower animals is essential, while, as already remarked, sufficient data for a comprehensive treatment of this subject do not at present exist. That the breeding season occurs in some animals “as the result of a stimulus which may be effected through the ali- mentary canal is demonstrated by the effect upon ewes of certain stimulating foods.” “That 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 c 34 THE PHYSIOLOGY OF REPRODUCTION 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 it is [frequently] associated with nutrition, and that it is a stimulus gradually collected is indicated by the increased frequency of the [breeding] season among domesticated mammals as compared with nearly allied species in the wild state. “ That it is manifested by hypertrophy and 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 they do is to show that the sexual instinct is seasonal, and that nutrition, whether affected by external or internal factors, plays an important part in its manifestation.” 4 The last proposition may be expressed even more generally in the statement, already formulated, that generative activity in animals occurs only as a result of definite stimuli, which are partly external and partly internal; while the precise nature of the necessary stimuli varies considerably in the different kinds of animals, according to the species, and still more according to the group to which the species belong. 1 Heape, loc. cit. It should be remembered, however, that many animals, such as the salmon, have their breeding season after prolonged fasts. See above. (Cf. also the fur-seal, p. 60.) CHAPTER II THE (STROUS CYCLE IN THE MAMMALIA ‘‘Omne adeo genus in terris hominumque ferarumque Et genus zquoreum, pecudes, pictaeque volucres In furias ignemque ruunt: amor omnibus idem.” —VIRGIL, Georg. iii. In describing the sexual processes of the Mammalia, and the variations in the periodicity of breeding which occur in the different groups, I have employed the terminology originally proposed by Heape,! and afterwards adopted by me,? in giving an account of these phenomena in the sheep and other animals. The terms used may now be defined. The term sexual season is used. by Heape to designate the particular time or times of the year at which the sexual organs exhibit a special activity. It is, in fact, employed in practically the same sense as that in which the expression “ breeding season ” is used in the previous chapter. Heape suggests that it is better to adopt the latter term to denote “the whole of that consecutive period during which any male or female mammal is concerned in the production of the young,” since the expression is often used to include the period of pregnancy or even the period of lactation. The sexual season is the season during which copulation takes place, but this only occurs at certain still more restricted times, the periods of “ cestrus ” (defined below). The male sexual season, when there is one, is called the rutting season ; but in many species the male animals 1 Heape, ‘‘ The Sexual Season.” Quar. Jour. Micr. Science, vol. xliv., 1900. 2 Marshall, ‘‘ The Gistrous Cycle and the Formation of the Corpus Luteum in the Sheep,” Pil. Trans. B., vol. cxcvi., 1903, “The Gstrous Cycle in the Common Ferret,” Quar. Jour. Mier. Science, vol. xlviii., 1904. See also Marshall and Jolly, ‘Contributions to the Physiology of Mammalian Repro- duction: Part I. The @strous Cycle in the Dog,” Phil. Trans. B., vol. cxeviii., 1905. 35 36 THE PHYSIOLOGY OF REPRODUCTION are capable of copulating at any time, whereas in the females this function is restricted to definite periods. The non-breeding season or period of rest in a female Mammal, when the generative organs are quiescent (at least relatively) and the uterus is normal and comparatively anemic, and the animal shows no disposition to seek out a mate, is called by Heape the Av estrous period or simply the Ara@3trum. This period is generally considerably prolonged, and in many Mammals occupies the greater part of the year. Its close marks the beginning of the sexual season. The first part of the sexual season is occupied by the Pro- estrum. This period is characterised by marked changes in the generative organs, the uterus becoming congested, while in the later stages there is often a flow of blood from the external opening of the vagina. The procestrum is the period often re- ferred to by breeders as the time when an animal is “ coming on heat,” or “‘ coming in season.” The next period, Zstrus, or strum (as it is sometimes called), ‘‘marks the climax of the process; it is the special period of desire in the female ; it is during estrus, and only at that time, that the female is willing to receive the male, and fruitful coition rendered possible in most, if not in all, Mammals.” + The periods of procestrum and cestrus are commonly referred to together as the “ heat” or “ brunst ” period, and sometimes as the period of “rut,” ? and no attempt is then made to dis- tinguish the time occupied by “coming in season,” and the time at which the female is ready to receive the male. This failure to distinguish the two periods (procestrum and cestrus) has led to much confusion, especially in regard to the nature of the relation between “ heat ” in the lower Mammals and menstrua- tion in the human female. As was first pointed out by Heape, it is the procestrum alone, and not the entire “ heat” period which is the physiological homologue of menstruation. This is a point which will be dealt with more fully in the next chapter of this book. If conception takes place as a result of coition during cestrus, 1 Heape, loc. cit. * The term “rut” is used by Heape in the case of the male only, the “rutting season,” as stated above, being the male sexual season. THE @STROUS CYCLE IN THE MAMMALIA 37 this period is followed by gestation ;! gestation in its turn, after a short puerperium or period of recovery, is followed by nursing or lactation, and the latter is succeeded by another ancestrum at the close of the breeding season.? If, on the other hand, conception does not occur during cestrus, the latter is succeeded by a short Metewstrum, during which the activity of the generative system subsides and the organs gradually resume the normal condition. In some animals, such as the dog, the metcestrous period is followed by a prolonged period of rest or ancestrum. In others, such as the rat or the rabbit, the metcestrum may be succeeded by only a short interval of quiescence.. This short interval, which sometimes lasts for only a few days, is called the Diestrum. This in turn is followed by another procestrous period, and so the cycle is repeated until the sexual season is over. Such a cycle (consisting of a succession of the four periods, procestrum, cestrus, metcestrum, and dicestrum) is known as the Dicestrous cycle. The number of dicestrous cycles in one sexual season depends upon the occurrence or non-occurrence of successful coition during cestrus. Thus, if conception takes place during the first cestrous period of the season, there can be no repetition of the cycle, at any rate until after parturition. The cycle may then be repeated. If conception does not occur at any oestrus during the sexual season, the final metcestrous period is succeeded by a prolonged ancestrous or non-breeding period. This is eventually followed by another procestrum, marking the commencement of a new sexual season. The complete cycle of events is called the Cistrous cycle. The number of dicestrous cycles which can occur in a female Mammal in the absence of the male, or in the absence of successful coition, depends upon specific and individual differences. Thus in some animals, such as the Scotch black-faced sheep in the 1 There is evidence that “heat” may occur abnormally during gestation. This phenomenon has been observed in dogs, cows, horses, and other animals (see p. 51). Coition during pregnancy may result in superfcetation (see p. 159), and may tend to occur periodically at times corresponding to what would have been the regular heat periods if the animal had remained non-pregnant. 2 In some animals parturition is followed almost immediately by another procestrum and cestrus, in spite of lactation. 38 THE PHYSIOLOGY OF REPRODUCTION Highlands, this number is usually limited to two. In many Rodents, on the other hand, there may be six or seven, or even more recurrences of the cycle within the limits of a single sexual season. Animals in which the cestrus does not recur during the sexual season, Heape has called Moncestrous animals. Those in which there is a recurrence of the dicestrous cycle during a single season, have been designated Polycestrous animals. The polycestrous condition may be regarded as a device (using teleological language) to increase the reproductive powers by providing more frequent opportunities for successful coition. But as to what factors are actually involved in bringing about the rhythmic recurrence of the cycle is a question which must at present be left open. The differences in sexual periodicity in both moncestrous and polvcestrous Mammals, the differences in the duration of the sexual season in polycestrous Mammals, the great variation which occurs even in closely allied forms or even within the limits of a single species, and the effects of domestication and climate upon sexual and reproductive capacity are points which will be considered in describing the various types of breeding phenomena which exist in the different groups. As Heape says, “the complication into which an otherwise simple story is thrown is due . . . to variation in the quiescent period.”” The two varieties of the quiescent period (ancestrum and dicestrum) “ are homologous, the one is a modification of the other; and the modification is no doubt related to an increased or decreased power of reproduction. At the same time, for the purposes of the present chapter, “the difference between them [must be regarded as] essential, for their relation to the sexual season renders it necessary to discriminate clearly between them.” MonorrEeMATA Little is known concerning the breeding habits of the platypus and the echidna, which represent this order, the lowest of the Mammalia. Semon’ states that they breed only once a year, 1 Semon, In the Australian Bush, English Edition, London, 1899. See also Sixta, ‘Wie junge Ornithorhynchi die Milch ihrer Mutter saugen,” Zool. Anz., vol. xxii., 1899, THE CESTROUS CYCLE IN THE MAMMALIA 39 and that in Echidna, as a general rule, only a single egg is impregnated and developed at a time. After the egg is laid (for Monotremes, as is well known, differ from all other Mammals in being oviparous) the mother stows it away in her pouch. This is always well developed at the sexual season, after which it disappears, not to appear again until the ap- proach of the next sexual season. Semon states that, although the pouch is first visible in the embryo, it is thereafter lost to sight until the beginning of the first procestrum. MarsuPrsLia It would appear probable that most Marsupials breed once annually, but some are said to do so more frequently. Semon ! says that in the native Australian “bear” (Phascolarctus cinereus), on the Burnett, the sexual season begins at the end of October. Since he failed to find pregnant females until the middle or end of November, it would seem that the sexual season probably extends for three or four weeks. The males at this time experience: a rutting season, during which they cry loudly, more frequently in the evening and night, but also during the day. The gestation, as in all Marsupials, is extremely short, the young being transferred at a very early stage of development to the mother’s pouch, as in the case of Echidna? The kangaroos in the Zoological Society’s Gardens in London are stated to display sexual excitement in September, and also in April. At such times a slight flow of mucus, which may be tinged with a little blood, has been observed passing from the aperture of the vagina.? It would appear, therefore, that kangaroos may breed twice a year. Unfortunately, there is no positive information available as to whether cestrus recurs during the same sexual season. 1 Semon, loc. cit. 2 In the bandicoot (Perameles) the young are nourished by an allantoic placenta as in the higher Mammals. (See p. 384.) This is exceptional among Marsupials. 3 Wiltshire, ‘The Comparative Physiology of Menstruation,” Brit, Med. Jour., 1883. 40 THE PHYSIOLOGY OF REPRODUCTION RopENTIA There can be little doubt that the great majority of Rodents are polycestrous. Most of them, so far as is known, have one annual breeding season, which may, under favourable conditions, extend over several months. Thus the rat (Mus decumanus) and mouse (M. musculus) are known to experience a recurrence of the dicestrous cycle in the absence of the male, while, if pregnancy occurs, a new “heat” period very rapidly succeeds parturition. In a state of semi-domestication M. rattus and M. decumanus have, in my experience, a fairly regular breed- ing season from about the end of January until the end of May. During this period the majority of mature females are either pregnant or suckling their young (that is, of course, among females which have been allowed to run freely with males). Pregnancy may occur at other times of the year, but is not nearly so common. The duration of the dicestrous cycle in the rat is said to be about ten days ;1 the period of gestation is approximately three weeks. Heape states that M. minutus and M. sylvaticus are also probably polycestrous. The bank vole (Arvicola glareolus) is almost certainly polycestrous, since it can become pregnant immediately after parturition at certain times of the year. The same condition no doubt exists in the field vole (A. agrestis), which breeds in Britain from January to October.? According to Lataste,? Eliomys quercinus, Gerbillus hertipes, Dipodillus campestris, D. simont, Meriones shawi, and M. longi- frons are also polycestrous. The length of the dicestrous cycle in all these animals, as observed by the same investigator, is usually about ten days, as in the common rat. In the wild condition in Britain, according to Heape, re- current dicestrous cycles last ‘‘ about three months, probably, in Arvicola agrestis ; from four to six months, probably, in Mus minutus ; about nine months in Mus rattus ; and even longer, perhaps, in Mus musculus and M. decumanus.” From my own experience with the two latter species in captivity, I am disposed 1 Heape, loc. cit. * Millais, British Mammals, vol. ii., London, 1905. 3 Lataste, Recherches de Zooéthique sur les Mammiféres del’ ordre des Rongeurs, Bordeaux, 1887. THE CGESTROUS CYCLE IN THE MAMMALIA 41 to believe that Heape has overstated the duration of the sexual season in these animals in a state of nature. The breeding season in the wild rabbit (Lepus cuniculus) in this country generally lasts from about February to May, but may be continued for longer. In the domesticated breeds it sometimes lasts nearly the whole year if the circumstances be favourable in regard to warmth and food supply. Heape says that five or six months only is the usual duration of the period during which dicestrous cycles recur in the domestic rabbit, and that if cestrus is experienced in winter it may occur inde- pendently of the possibility of pregnancy. The duration of the dicestrous cycle varies considerably. “While some individuals 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.”! In Lepus variabilis recurrent dicestrous cycles are probably continued for about two months. The squirrel (Sciwrus vulgaris) in Britain, according to Heape, is probably moncestrous ; but this animal, in Southern Europe and Algiers, according to Lataste, is apparently polycestrous. In Britain squirrels breed early in the year, and sometimes have a second litter in August. It is difficult to determine the length of the procestrum and cestrus in Rodents, since the external changes which characterise these conditions are comparatively slight. Heape says that the procestrum in the rabbit lasts, probably, from one to four days. At this time the vulva tends to become swollen and purple in colour, but there is no external bleeding. The same may be said of the rat and the guinea-pig; but, in the experience of the writer, it is generally impossible to detect the procestrous condition in either of these animals with absolute certainty. Qistrus probably lasts for about a day. Lataste? states that external bleeding occurs during the “heat” periods of Pachyuromys duprasi, Dipodillus simom, and Meriones shawi. The guinea-pig (Cavia porcellus) in captivity can become pregnant at any season, but more frequently in the summer than in the winter. “‘ Heat” rapidly succeeds parturition, as 1 Heape, loc. cit. ? Lataste, loc. cit. 42 THE PHYSIOLOGY OF REPRODUCTION in the case of so many other Rodents.1_ The period of gestation is about sixty-two days, an unusually long time for so small an animal, being more than twice as long as the gestation period of the rabbit. As a result the newly born guinea-pig is well advanced in development, and able to feed for itself, instead of being dependent on its mother’s milk. In most male Rodents the testes undergo a periodic increase in size and descend into the sessile scrotum at the beginning of the season of rut, after which they become smaller again, and are withdrawn into the peritoneal cavity. In the Leporide, however, and in some other species, the testes are not so re- tracted, but remain throughout the year in the scrotal sacs.? UNGULATA This order contains several examples of animals which are almost certainly moneestrous in a state of nature, but are polycestrous in captivity or under domestication. In the latter case the increase in sexual capacity appears to be due partly to the inherited effects of domestication, and partly to the direct influence of a more favourable environment. For example, the sheep presents a complete gradation from the apparently moncestrous condition of some wild species to the extreme degree of polycestrum, which is reached by certain of the more domesticated breeds.? The Barbary wild sheep (Ovis tragelaphus) in the Zoological Society’s Gardens is monestrous, breeding only once annually. The same is stated to be the case with the Burrhel sheep (0. burrhel), although the moufflon (0. musimon) in captivity may experience two or more recurrent dicestrous cycles in an annual sexual season.” It would seem, however, from the account given by Lydekker® of the breeding habits of O. musimon, as 1 Sobotta, “ Uber die Bildung des Corpus Luteum beim Meerschweinchen,” Anat. Hefte, vol. xxxii., 1906. 2 Owen, On the Anatomy of Vertebrates, vol. iii., London, 1868. * Marshall, ‘The Cistrous Cycle, &c., in the Sheep,’ Phil. Trans. B., vol. cxevi., 1903. 4 Heape, loc. cit. ° I am indebted to Mr. F. E. Beddard, Prosector of the Zoological Society, for this information. § Lydekker, Wild Oxen, Sheep, and Gcats of All Lands, London, 18£8. haltathe tn cet, THE GESTROUS CYCLE IN THE MAMMALIA 48 well as O. wgnei, O. ammon, and O. canadensis, that these sheep in their wild condition are probably moneestrous, for their annual sexual season is of short duration, and occurs with great regularity. Similarly it may be inferred from Prjewalsky’s statements } that O. poli, O. burrhel, and O. argali are moneestrous and breed once a year. Among wild sheep generally the sexual season occurs as a rule in autumn, but it may vary with the locality or climate. Thus with O. vignei in the Punjab, the sheep begin to breed in September, whereas, with the same species in Astor, the sexual season must be considerably later, since the young in the latter district are produced about the beginning of June.” Scotch black-faced sheep in the Highlands experience two. dicestrous cycles, each of three weeks’ duration, so that the annual sexual season for these animals lasts six weeks. In the Lowlands the sheep of this breed may have at least three re- current dicestrous cycles in the absence of the ram, while flock- masters inform me that, under unusually favourable conditions, there may be as many as five or six, the duration of each cycle varying from about thirteen to eighteen days. It can hardly be doubted that of the two conditions of the Scotch black- faced sheep that of the Highland ewes is the more natural, for sheep, in their wild state, are essentially mountain animals, being almost entirely confined to mountain districts in the Holarctic region, their range only just extending across the border into the far warmer Oriental region. “The immense mountain ranges of Central Asia, the Pamir, and Thian-Shan of Turkestan may be looked upon as the centre of their habitat.” 3 The sexual season in hill sheep in Great Britain is ordinarily from about the middle of November until the end of the year. Under exceptional circumstances individuals may experience cestrus at other seasons, such as in April after an early abortion in the winter. In other British breeds the sexual season is earlier. Thus Hampshire Down sheep are often “ tupped ” in | Prjewalsky, Mongolia, the Tangut Country, and the Solitudes of Northern Tibet (Morgan’s Translation), London, 1876. 2 Lydekker, loc. cit. 3 Flower and Lydekker, Mammals Living and Extinct, London, 1891. 44 THE PHYSIOLOGY OF REPRODUCTION the summer, but they do not, as a rule, breed more than once a year. The Limestone sheep of Westmorland and Derbyshire, and the Dorset Horn sheep of the South of England, are the only British sheep which are ordinarily capable of breeding more than once annually. With the former the general lambing season is from the middle of February to the middle of March, but lambs are often born earlier. The ewes sometimes receive the ram very early when suckling the lambs, so that a second crop of lambs is born in August. This increase in the sexual capacity is especially noteworthy in view of the fact that Lime- stone sheep are classed as a mountain breed which thrives best on dry heaths or bare hill pastures. In Dorset Horn sheep lambs are frequently produced twice a year, but the practice is discouraged as it is said to deteriorate the ewes. With this breed cestrus may continue to recur (in the absence of the ram) from the autumn sexual season (when the sheep are ordinarily tupped) onwards until the following spring. With many foreign breeds lambs are born twice yearly. Thus Mr. Annandale informs me that the horned sheep which run half wild in Patani, in the Malay Peninsula, normally have lambs twice a year. It would appear also that among the indigenous sheep of India, which are scarcely ever supplied with any artificial or other food, green or dry, beyond what they can pick up at the pasture ground, lambs may be born three times in two years, and that there are no definite seasons for Jambing.? Among the Merino sheep in Cape Colony the sexual season is April (the autumn month, corresponding to October in this country), but some sheep come “in season” earlier. At high altitudes, however, where the sheep subsist entirely upon the natural produce of the veldt, the sexual season is May, or a month later than the usual time in Cape Colony. On the other hand, in the low country below the second range of mountains, there are two seasons for “ tupping,” and lambs are produced twice a year. Among the Merinos in Argentina there are also two breeding seasons within the year. Probably the maximum amount of sexual activity experi- » Shortt, A Manual of Indian Cattle and Sheep, 3rd Edition, Madras, 1889. eee eeeeeee THE GESTROUS CYCLE IN THE MAMMALIA 45 enced by any sheep is that reached by certain Australian Merinos which are described as being able to breed all the year round, a fact which implies, in the absence of gestation, an unbroken series of dicestrous cycles. The report of the Chief Inspector of Stock for New South Wales divides the time of lambing into six periods which embrace the entire year.! That the great variability in sexual activity which the sheep exhibits is dependent largely upon differences in food supply and climate cannot be doubted, for the black-faced sheep in Scotland, and the Merinos in Cape Colony afford direct evidence that this is the case. Indeed, the effect of the environment on the recurrence of breeding was noted long ago by Aristotle,? who observes that ‘in some places where the weather is warm and fine, and food is abundant,” sheep may have lambs twice a year. The result of flushing (or the practice of stimulating the generative system by supplying extra food or better pasture, and thereby hastening the approach of the sexual season and increasing the fertility) is further evidence of the effect of good nourishment upon the sexual and reproductive powers. On the other hand, there can be no question that the varying degrees of breeding activity are in part racial characteristics, as is shown, for example, by the Dorset Horn sheep in the south of England, and still more evidently by the Limestone sheep of Westmor- land and Derbyshire. But that an increase in the duration (or more frequent recurrence) of the sexual season is not necessarily a highly artificial condition or the result of special attention in regard to food supply, &c., on the part of the flock-master, is shown by such a condition occurring among the indigenous sheep of India and the half-wild sheep of Patani. The duration of the dicestrous cycle in black-faced sheep, as already mentioned, is from about. thirteen to twenty-one days, the variation appearing to depend partly upon the nature of the country in which they live. In other breeds the cycle may be said to vary within approximately the same limits. Lllen- 1 Wallace (R.), Farming Industries of Cape Colony, London, 1876 ; The Rural Economy and Agriculture of Australia and New Zealand, London, 1891; Argentine Shows and Live Stock, Edinburgh, 1904. 2 Aristotle, History of Anima/s (Crosswell’s Translation), Bohn’s Library, London, 1862, 46 THE PHYSIOLOGY OF REPRODUCTION berger, however, gives from twenty to thirty days as the length of this interval. The procestrum and cestrus together do not as a rule occupy more than two or three days, and cestrus alone may last for only a few hours. The external signs of the procestrum are comparatively slight in sheep. The vulva is usually somewhat congested, and there is often a flow of mucus from the external generative aperture, but blood is seldom seen. Owing to the extreme shortness of the “ heat ” period the mucous flow may continue during the cestrous and metcestrous periods. The internal changes are briefly described in the succeeding chapter. The only external indication of cestrus is that afforded by the behaviour of the ewes. At this time they tend to follow the ram, and display a general restlessness of demeanour. The period of gestation is twenty-one or twenty- two weeks. Nathusius’ observations show that it is fairly constant within the limits of particular breeds.? The cestrous cycle in the sheep, and its great variability, have been discussed at some length, since this animal is pro- bably typical of most Ungulata in the way in which its generative system is affected by different conditions of life, while the facts about other Ungulates are not so perfectly known. The effect of changed conditions upon the sheep’s fertility, ¢.e. upon its capacity to bear young (as distinguished from mere sexual capacity), is a subject which is dealt with more fully in a future chapter (Chapter XIV.). The wild goat, like the wild sheep, has a very restricted sexual season,* while, according to Low, the domesticated goat experiences cestrus at very frequent periods.4 A similar statement may be made about cattle, for Heape® says that, whereas wild cattle in captivity are capable of re- production at any time of the year, and experience a remark- able increase in the recurrence of their dicestrous cycles, we are led to infer from the limited calving season among * Ellenberger, Vergleichende Physiologie der Haussaiigethiere, vol. ii. Berlin, 1892. * Nathusius, ‘‘ Ueber einen auffallenden Racenunterschied in der Tyiichtig- keitsdauer der Schafe,”’ Zool. Garten, Jahrg. 3, 1862. 3 Lydekker, loc. cit. “ Low, The Domesticated Animals, London, 1845. ® Heape, loc. cit. THE GESTROUS CYCLE IN THE MAMMALIA 47 similar animals in the wild state that the sexual periods are likewise restricted. Raciborsky! says that in the more domestic types of cattle the cows receive the bull more frequently than in the wilder breeds. Ellenberger ? states that among domestic cattle the dicestrous cycle varies from about two to four weeks, but Schmidt * has shown that the differences may be much greater. Wallace* says that cestrus recurs in summer every nineteenth day, but in winter it may not recur oftener than every twentieth or every twenty-first day. Usually the cow seeks the bull again four or five weeks after calving. Shortt,> however, states that in India this does not occur until after six or nine months. Blood is not infrequent in the ex- ternal procestrous discharge of cows and heifers. Hmrys-Roberts® has described the internal generative organs of a procestrous cow as containing a watery secretion tinged with blood. The secretion was found to contain far less mucin than during the anoestrous period.’ The period of gestation in cattle is about nine months, but it is slightly variable. According to Heape, who has collected evidence from various authorities, the ibex, markhor, barasingha, and Hemitragus jerulaicus in Cashmir, as well as the American bison, black- tailed deer in Montana, red-deer, fallow-deer, and roe-deer,® and 1 Raciborsky, Tra/té de Menstruation, Paris. 2 Ellenberger, loc. cit. 5 Schmidt, ‘‘ Beitrige zur Physiologie der Brunst beim Rinde,” Disserta- tion, Ziirich, Miinchen, 1902. 4 Wallace (R.), loc. cit. race Shortt, A Manual of Indian Cattle and Sheep, 3rd Edition, Madras, 6 Emrys-Roberts, ‘‘ A Further Note on the Nutrition of the Early Embryo, &c..” Proc. Roy. Soc. B., vol. 1xxx., 1908. ” According to Emrys-Roberts, the profuse mucinous secretion during the procestrum in the Mammalia is derived, not from the body of the uterus, but from the cervix and vagina. ® There has been some controversy regarding the breeding season and period of gestation in roe-deer. According to Bischoff (EZntwicklungsgeschichte des Rehcs, Giessen, 1854) rut occurs in early autumn, but the embryo is not developed beyond the stage of segmentation in the following spring. Groh- mann (Sport in the Alps, Edinburgh, 1904) says that rut is experienced in July and the beginning of August, but that there is a “false rut” in November. Observations on roe-deer in Vienna showed that the period of gestation is ten months; for seven females which were served by one 48 THE PHYSIOLOGY OF REPRODUCTION several antelopes are all probably moneestrous in the wild state. This is rendered not unlikely from the limited sexual and calving seasons which these animals are known to experience, but it is by no means certain. “The American bison experiences a sexual season from some time in July until some time in August. [Catlin says August and September are the months when they breed; see below.] In the Cashmir ibex it persists during parts of November and December. In the markhor and Hemitragus jerulaicus in Cashmir it occurs in December, while in the barasingha in that country, from September 20th to November 20th, it has been observed. . . . In Scotland the red- deer’s sexual season lasts three weeks, during September and October, according to Cameron ;! while in this country [England] 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 in captivity three weeks is the usual period which intervenes between two cestri in such animals, and the extreme probability that individual females do not experience cestrus at exactly the same time, predispose one to believe that they are moneestrous in the wild buck in July 1862, gave birth each to two young in the following May. It would appear probable, therefore, that the ovum lies dormant during the early months of gestation. Grohmann suggests that the “false rut” in November may have a quickening influence on the ovum, and so cause it to develop. 1 Millais says (vol. iii. 1906) that the actual time of rut depends much on the season. September 28, in Scotland, is called “the day of roaring.” Sir 8. M. Wilson (Field, October 8, 1904), however, reports a case of a stag which roared during the whole summer in Kinveachy Forest, Boat of Garten, in 1904. Stags eat little or nothing during the rutting season, and lose weight rapidly. During the first days of roaring they are said to suck up a mixture of peat and water (Millais, Joc. cit.). ® Millais says (loc. cit ) that the fallow-deer in England ruts in October. The necks of the big bucks swell greatly during the first week, and the animals become more and more unsettled until about the 25th, when the first calls are heard. The actual rut is short as a rule. The doe drops her calf about the beginning of June, and rarely two or three are born at a time. Sometimes, however, the females may come in season at irregular times, and drop calves in any of the months after June and even as late as November. THE CESTROUS CYCLE IN THE MAMMALIA 49 state ; but, if the limit of time for coition is three weeks, there is still just time for the females to undergo two dicestrous cycles, and it is this possibility which prevents positive assertion on the matter. “Among captive animals, not more than two dicestrous cycles have been observed in the gnu during one sexual season. Gazella dorcas has two or three; the girafie about three ; while the eland, nylghau, and water-buck 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.” 1 Heape states also that with red-deer in the Zoological Gardens there is a very extensive series of dicestrous cycles, and that with wapiti deer in captivity the possibility of pregnancy at any season is only prevented by the fact that the male does not rut during the casting and growth of the antlers. The males of many of the other species referred to experience a definite rutting season, like the stag in Britain. As already mentioned, the male camels in the Zoological Gardens in London experience rut in early spring, or at the same time as the sexual season of the female camels in Mongolia. The period of gestation in the camel is thirteen months, so that in this animal, as in the walrus among carnivores, the recurrence of the sexual season is delayed by pregnancy, and conception cannot take place oftener than once in two years.2. The same is the case with the wild yak in the deserts of Tibet,® and also, in all probability, with the musk-ox in Greenland.* The sexual season in many Ruminants is a period of in- tense excitement, especially in those cases in which the males experience a definite rut. (See above, p. 27, in Chapter I.) Thus, Catlin,® referring to the American bisons, says: ‘‘ The running season, which is in August and September, is the time 1 Heape, loc. cit. 2 Swayne, Seventeen Trips through Somaliland, London, 1895. 3 Prjewalsky, Joc. cit. 4 Lydekker, Joc. cit. > Catlin, North American Indians, vol. i., 2nd Edition, London, 1841. D 50 THE PHYSIOLOGY OF REPRODUCTION when they congregate into such masses in some places as literally to blacken the prairies for miles together. It is no uncommon thing at this season, at these gatherings, to see several thousands in a mass, eddying and wheeling about under a cloud of dust, which is raised by the bulls as they are pawing in the dirt or engaged in desperate combats, as they constantly are, plunging and butting at each other in the most furious manner. In these scenes, the males are continually following the females, and the whole mass are in a constant motion; and all bellowing (or ‘ roaring ’) in deep and hollow sounds which, mingled together, seem, at the distance of a mile or two, like the noise of distant thunder.” That the antlers are the fighting weapons in stags, and that their growth is associated with the advent of the sexual season, after which time they are cast off, are facts which have been. already referred to. The effects of castration upon the growth of the antlers are described in a later chapter (p. 305). Passing to the non-ruminating Ungulata, we find that the wild sow has only one annual sexual season. It is not certain whether this consists of more than a single cestrous cycle. Under domestication, however, the sow is polycestrous, and may take the boar five weeks after parturition. The duration of the dicestrous cycle is from two to four weeks, according to Fleming.* The period of gestation is about four months. Litters are usually produced only in spring and autumn; but by weaning the young early (or partially weaning them), and feeding the mother liberally, it is possible to get five litters in two years. A sanguineo-mucous flow has been observed issuing from the genital aperture during the procestrum. At the same time the vulva is distinctly swollen. Wiltshire * states that in the hippopotamus in captivity a condition of cestrus may be experienced at regular monthly intervals. This animal has been known to breed in Zoological Gardens. The mare is polycestrous, the normal dicestrous cycle being about three weeks and the cestrous period a week, though its 1 Fleming, Veterinary Obstetrics, London, 1878. 2 Wiltshire, Joc. cit. See also Ellenberger, loc. cit., and Wallace (B.), Farm Live-Stock of Great Britain, 4th Edition London. 1907. THE QGSTROUS CYCLE IN THE MAMMALIA 51 actual length may vary by three or four days! The sexual season in the absence of the stallion extends throughout the spring and early summer months, and is generally longest in the more domesticated breeds. Professor Ewart informs me that in a pony imported from Timor, which is in the Southern Hemisphere, cestrus was experienced in the autumn, or at the same time as the spring in Timor (cf. camels, p. 49). The period of gestation in the mare is eleven months, and “ heat” recurs eleven days after parturition. This is called the “ foal heat.” Certain mares are irregular in the recurrence of the “heat ” periods, and, in some, “ foal heat ’’ does not occur until seventeen days after parturition instead of the usual eleven days. In exceptional cases a mare, like a cow, may conceive at the “foal heat’ and yet take the horse three weeks later, just as though she had failed to become pregnant.? Heape states that, very exceptionally, mares are moneestrous. Blood has been observed in the mare’s procestrous discharge, but it is not generally present. The genitalia, however, are always swollen and congested, and a glutinous secretion is generally emitted from them. The clitoris and vulva often undergo a succession of spasmodic movements, preceded by the discharge of small quantities of urine. Suckling mares tend to fail in their milk supply, and the quality of the milk appears to undergo some kind of change, as it is frequently the case that foals during the heat periods of their dams suffer from relaxation of the bowels or even acute diarrhoea. In mares which are not suckling the mammary gland becomes congested and increases in size during the heat. At the same time some mares de- velop great excitability, and kick and squeal, becoming dangerous to approach and impossible to drive. There is, however, great variation, for other animals may pass through the “heat” period without exhibiting any well-marked signs of their con- dition, which in a few instances can only be determined by the behaviour of the mare towards the stallion.’ 1 Ewart found that in Equus prjewalsky, cestrus lasted a week. 2 Wallace, loc. cit. Professor Ewart informs me that pregnant mares do not necessarily abort as a result of taking the horse at the third, sixth, or even ninth week of gestation. 3 Wortley Axe, ‘‘The Mare and the Foal,” Jour. of the Royal Agric. Soc., 3rd Series. vol. ix., 1898. Ewart (‘‘The Development of the Horse,” to be 52 THE PHYSIOLOGY OF REPRODUCTION The elephant in captivity is said to be polycestrous, but I can find no record of the duration of the dicestrous cycle. Since pregnancy is very prolonged (twenty months), the sexual season cannot occur more than once in two years; that is, if the animals breed. The elephant in the Zoological Gardens in London is stated to have persistent cestrus probably for three or four days. CETACEA Little is definitely known about the periodicity of breeding in Cetacea. According to Millais,! the right whale brings forth in March in every other year, the young being suckled for about twelve months. The humpbacked whales, blue whales, and sperm whales appear to have no regular time for breeding, but Millais says the young of the humpbacked whales are generally born sometime during the summer. Haldane’s records,? which appear to refer to several different whales, show that foetuses varying in length from six inches to sixteen feet were found in animals captured at the Scottish whaling stations in the summer of 1904. This great variation seems to imply that there is no regular season at which whales copulate, and that very possibly these animals are polycestrous. Lillie ® states that two specimens of Balenoptera musculus were taken off the west of Ireland on July 31, 1909, and that one contained a foetus of one foot in length, while the other had a foetus of five and a half feet in length. Lillie says also that several female rorquals having foetuses of different sizes were captured within a short time of published in Quar. Jour. Micr. Science, says that the period of cestrus in mares tends to be shorter the later in the season, and when the food becomes less plentiful and less nutritious all external signs of cestrus disappear. Under favourable conditions, however, mares may become pregnant in winter. Ewart gives the following as the periods of gestation in various Equide :— Asses and zebras, 358 to 385 days; Prjewalsky’s horse, 356 to 359 days; Celtic pony, 334 to 338 days. Incoarse-headed types of horse it is about the same as in Prjewalsky’s horse, but in the finer breeds the period is the same as in the Celtic pony. In abnormal cases pregnancy may be unduly pro- longed in mares as in other animals, a mare occasionally going twelve months in foal instead of eleven. 1 Millais, The Mammals of Great Britain, vol. iii, London, 1906. * Haldane, “ Whaling,” &c., Annals of Scottish Nat. Hist., April, 1908. ® Lillie, ‘‘ Observations on the Anatomy and General Biology of some Members of the larger Cetacea,” MS. still unpublished. THE GESTROUS CYCLE IN THE MAMMALIA 53 one another. These observations, therefore, are in a general way confirmatory of those of Haldane. According to Guldberg and Nansen,' the porpoise copulates at any time between June and October, the period of gestation being ten months or longer. The white-sided dolphin is said to copulate in late summer, pregnancy being about ten months, and the white-beaked dolphin is thought to be similar.? Humpbacked whales and other Cetacea have been described as indulging in amorous antics at the breeding time, rubbing against one another and patting one another with their long fins. CARNIVORA In the female of the dog the average duration of the complete estrous cycle is six months, there being two annual “ heat” periods, typically in the spring and in the autumn. It follows, therefore, that the bitch is moncestrous. Bitches be- longing to the smaller breeds tend to come “on heat” more frequently than those of the larger varieties. Thus, in Irish terriers, the cycle may recur after four months, though in this breed six months is the more ordinary time. On the other hand, in Great Danes the duration of the cestrous cycle is often as much as eight months. It would appear that in those cases where “heat” recurs as often as every four months, this is only when pregnancy is prevented, for more than two litters of pups are seldom if ever produced in a year. Stonehenge ® says that there is much individual variability in the periodicity of the cycle, and that “heat” may recur at any interval from four up to eleven months, but that six, five, and four months are the most usual periods. Each bitch as a rule has her own peculiar period to which she remains constant, unless systema- tically prevented from breeding, in which case the periods tend to recur irregularly or even cease altogether.6 It has been observed also that the recurrence of the sexual season tends to 1 Guldberg and Nansen, ‘‘On the Structure and Development of the Whale,” Bergen, 1904. 2 Millais, Joc. cit. 3 Ibid. 4 Marshall and Jolly, doc. cit. 5 Stonehenge, The Dog in Health and Disease, 4th Edition, London, 1887. 5 Heape, loc. cit. 54 THE PHYSIOLOGY OF REPRODUCTION become irregular with advancing age, and this irrespectively of whether or not the animal is permitted to become pregnant. The periodicity depends also to some extent upon climate, for in Danish Greenland the dogs usually breed only once a year.? The procestrum in the bitch is characterised externally by the vulva being swollen and moistened with mucus, and by the existence, usually, but not absolutely invariably, of a flow of blood from the aperture of the vagina. The length of the procestrum is about ten days. The sanguineous discharge generally ceases at the commencement of cestrus, which may last for another week or ten days. Heape states that the winter cestrus in some breeds does not last so long as the summer cestrus. In certain individuals a relatively slight mucous or sanguineo-mucous flow takes place during the period of cestrus, and may even be continued beyond it, but this is exceptional. Stonehenge states that a bitch will not, as a rule, receive the dog until external bleeding has sub- sided, and that the most favourable time for successful coition is about the eleventh day of “heat” (in other words, at the beginning of the period of cestrus). This statement is fully borne out by dog-breeders. The external changes which occur during “heat” are accompanied by changes in the metabolism, for Potthast,? working on the nitrogen metabolism of the bitch, records a slight retention of nitrogen during the “heat” period. A similar result was obtained by Hagemann,* who states that the retention is followed by a loss of nitrogen after copulation. These results should be compared with those recorded for menstruating women (see p. 68). The histological changes which take place in the uterus during the cestrous cycle are described in the next chapter. The period of gestation in the dog varies from fifty-nine to sixty-three days. With dogs belonging to the smaller breeds the period is often somewhat less than with large dogs. The 1 Rink, Danish Greenland, London, 1877. ae Potthast, ‘‘Kenntniss des Hiweissumsatzes,” Dissertation, Leipzig, * Hagemann, ‘‘ Kiweissumsatz im tierisch Organismus,” Dissertation, Erlangen, 1891. Cf. also Schérndorff, ‘‘ Einfluss der Schilddriise auf den Stoffwechsel,” Pfliiger’s Arch., vol. lxvii., 1897. THE GESTROUS CYCLE IN THE MAMMALIA 55 period of lactation is very variable in duration, and may extend until the commencement of the next procestrum. The wild dog of South America (Canis azare), according to Rengger,! breeds only in winter, and therefore but once a year. The same is said to be the case with the wolf and the fox in their wild state; but these animals, in the Zoological Gardens in London, experience two annual “heat” periods like the dog.2 The wolves in the Dublin Gardens, how- ever, are stated to have only one annual sexual season when permitted to breed; otherwise they come “in heat” more frequently, but are always moncestrous.? The period of gestation in the wolf and fox is approximately the same as in the dog, 7.e. about two calendar months. Bischoff * refers to the fact that the sexual season of the fox is affected by the nature of the country which it inhabits, foxes which live at high altitudes breeding later than those residing on the plains. Millais® says that fox-cubs in most parts of Britain are not born until the end of March or beginning of April, whereas, in the south of England, they are often pro- duced as early as January. The Cape hunting-dog (Lycaon pictus) has been known to have bred in captivity on several occasions, and notably in the Gardens at Dublin, where six litters were produced from a single pair between January 1896 and January 1900. The first three litters were born in January, the fourth in November 1898, the fifth in May 1899, and the sixth in January 1900. Cunningham writes: “It is not easy to offer a satisfactory explanation of the irregularity of the fourth and fifth litters. I am inclined to believe, however, in the absence of definite information on this point obtained from the animals in a state of nature, that the lycaon breeds only once a year, and that the irregularity noticeable in the fourth and fifth litters is due 1 Rengger, Naturgeschichte d. Satigethiere von Paraguay, Basel, 1830. * Heape, loc. cit. 3 For the information regarding the breeding of the animals in the Royal Zoological Society’s Gardens, Dublin, I am indebted to the Jate Professor D. J. Cunningham and Dr. R. F. Scharf. (See Marshall and Jolly, doc. cit.) 4 Bischoff, ‘‘ Ueber die Rauhzeit des Fuchses und die erste Entwicklung seines Kies,” Sitz. der Math.-phys., Wien, Classe vom 13 Juni, vol. ii., 1863. 5 Millais, loc. cit. 56 THE PHYSIOLOGY OF REPRODUCTION to a tendency on the part of the Dublin specimens to adapt themselves to the climatic conditions of Ireland. At the same time it should be mentioned that certain indications were ob- served in connection with the demeanour of the parents towards each other which seemed to indicate that the sexual instinct was excited at more than one period of the year.” The period of gestation was ascertained to be about eighty days, or nearly three weeks longer than in the domestic dog. “ As might be ex- pected, the young when they are born are more lusty and more advanced in development than new-born puppies of the dog.” On one occasion, when the litter produced was unusually large, the gestation period was lengthened to eighty-six days.1 The female of the domestic cat generally breeds two or three times a year. According to Spallanzani® the “ heat” periods occur in February, June, and October, but there can be no doubt that many individuals breed at other times, and that there is great variation.? Heape* says that there may be no less than four sexual seasons within a year, but this can only be when the cats are not allowed to become pregnant. The usual number of litters, in my experience, is two, in typical cases in spring and autumn as in the dog. Heape states also that feral cats breed only once a year. The domestic cat is polycestrous, and may experience a long succession of dicestrous cycles in one sexual season, each dicestrous cycle lasting about fourteen days and sometimes less. The period of gestation is about nine weeks. Millais ® says it is uncertain whether the wild cat has one * Cunningham (D. J.), ‘‘ Cape Hunting Dogs (Lycaon pictus) in the Gardens of the Royal Zoological Society of Ireland,” Proc. Roy. Soc. Edin., vol. xxv., 1905. 2 Spallanzani, Dissertations, vol. ii., London, 1784. * Marshall and Jolly, loc. cit. I have known a cat experience cestrus regularly at intervals of about a fortnight from December until the following August, but such a long succession of dicestrous cycles is probably unusual. 4 Heape, loc. cit. 5 Heape, loc. cit. Mr. W. O. Backhouse informs me that in his experience with Siamese cats the females, if the kittens are destroyed or birth is premature, come on heat regularly about eight days after parturition. This probably occurs in other breeds, at any rate in spring and summer. ° Tam much indebted to Mr. A. H. Cocks for supplying me with interest- ing information concerning various Carnivora in captivity. THE (ESTROUS CYCLE IN THE MAMMALIA 57 or two annual breeding seasons. The probability is that there is only one (in March), the young being born in May ; but Millais records that he has seen young wild cats, which could not have been more than forty days old, killed in Scotland in October. Cocks, in a letter quoted by Millais, says that he has received wild cats which, judging from their size, were probably born in August or September, and that in captivity he has observed a female experience “heat ” during the summer. ‘‘ Many years, when owing to the death of the young, or the fact that the pair had not bred together in the spring, I have kept male and female together all summer, but they showed no inclination to breed.” In a more recent letter to the author Mr. Cocks states that the old female wild cat in his possession came “ in season ”’ and received the male in the autumn of 1904, after the death of the kittens which were born earlier in the same year. The animal, however, failed to become pregnant. In the experience of this observer the commonest month for wild kittens is May, but the range of dates in his collection varies from April 20 to July 22. The period of gestation was ascertained to be sixty-eight days. The period of cestrus was observed to last for five days, or about the same time as in the domestic cat. The male wild cat has a definite season of rut (like the stag), and calls loudly and incessantly, making far more noise than the female cat. This information is interesting, since the males of most Carnivora, so far as is known, do not experience anything of the nature of a recurrent rutting season, although many individuals show indication of increased sexual activity at some times more than at others. So far as I am aware, nothing of the nature of a rutting season is ever known in the males of the domestic cat, dog, or ferret, all of which seem-to be capable of coition at any period of the year. On the other hand, the males of certain seals appear to possess a season of rut at the same time as the sexual season in the females. Little is known definitely regarding the breeding habits of the larger Felide in their wild state, beyond the fact that they probably agree in having a single annual sexual season. In captivity certain of them, at any rate, are polycestrous. Thus, 1 I am indebted to Mr. Cocks for information regarding the breeding habits of the wild cat. 58 THE PHYSIOLOGY OF REPRODUCTION in the lioness cestrus has been known to recur at intervals of three weeks until the animal became pregnant, while the period of cestrus may itself last a week.! Further, the lioness may experience three or four sexual seasons in the year, as in the domestic cat, this having been observed to occur in the lioness in the Dublin Zoological Gardens when copulation had not been successful, or when the animals were not permitted to breed. If allowed to become pregnant the loness at Dublin may still experience two sexual seasons, and have two litters of cubs within the year. The puma in the Dublin Gardens is stated to have one sexual season annually if breeding, or two if there is no gestation. The larger Felide as a rule breed com- paratively freely in confinement, some places, such as the Dublin Gardens, being famous for successful lion breeding. The period of gestation in the lioness is from fifteen to sixteen weeks; that of the tigress is about twenty-two weeks; while the puma goes with young for fifteen weeks. Most species of bears, both in their wild state and in confine- ment, are moncestrous and have one annual sexual season. The grizzly bear, however, according to Somerset,” bears young only once in two years. The bears in the Zoological Gardens at Dublin, on the other hand, may experience more than one annual sexual season if pregnancy does not occur. The period of gestation in the brown bear is seven months; in the grizzly bear it is probably longer. Heape states that with the bears in the Zoological Gardens in London cestrus may be experienced for two or three months continuously ; but this condition, as he points out, is unnatural and probably an effect: of confinement, for though coition can occur, it does not, as a rule, result in pregnancy. The ferret, which is a domesticated variety of the polecat, is moncestrous, but may have as many as three annual sexual seasons,® which, however, instead of being distributed at regular intervals throughout the year, occur only in the spring and summer, the autumn and winter being occupied usually by a prolonged ancestrous period. This tendency towards a con- 1 See Marshall and Jolly, Joc. cit. * Somerset. Quoted by Heape, loc. cit. * Carnegie, Ferrets ‘and Ferreting, London. THE CESTROUS CYCLE IN THE MAMMALIA 59 centration of sexual seasons during one part of the year may be considered as an approach to a condition of polycestrum ; for, if the cestrous periods were to recur at still shorter intervals than is actually the case, they could be regarded as forming so many dicestrous cycles in one sexual season. So far as I am aware, the ferret does not experience cestrus more than twice annually if allowed to breed. The polecat is also moncestrous, but breeds only once a year. Mr. Cocks informs me that in captivity the young of this animal are generally born in the first half of June, and that the gestation period, as in the ferret, is about forty days. The stoat, weasel, and pine-marten, in their wild state, are almost certainly moncestrous and breed once a year. In the last-mentioned animal Cocks1 found that a single cestrus may last a fortnight. The stoat and weasel do not appear to have been bred in captivity. The otter in a state of nature breeds only once a twelvemonth (in winter, as a rule, but young may be born at any season according to Cocks). In captivity, how- ever, cestrus may recur at regular monthly intervals all the year round.” The various species of seals are in all probability moncestrous, and have one litter of young annually. Some species show an almost perfect rhythmic regularity in the recurrence of their breeding season. Thus, in the case of the harp seal in the north- east. of Newfoundland, and also in Greenland, according to Millais,? the pups are born each year between March 8th and 10th. 1 Cocks, ‘‘ Note on the Gestation of the Pine-Marten,” Proc. Zool. Soc., 1900. 2 Cocks, ‘‘ Note on the Breeding of the Otter,’ Proc. Zool. Soc., 1881. Mr. Cocks’ subsequent experience concerning which he has been kind enough to write to me, confirms the conclusion that there is no ancestrous period in the otter in captivity. There has been some controversy regarding the breeding of the badger. According to Meale-Waldo the period of gestation is between four and five months (‘The Badger: its Period of Gestation,” Zoologist, 1894), but according to Cocks (*‘ The Gestation of the Badger,” Zoologist, 1903, 1904), this period may be anything between under five and over fifteen months, for although the sexual season may apparently occur at any time of the year, the young are invariably born within a period limited to six weeks. This extraordinary conclusion is based on a number of observations. Fries (‘‘ Uber die Fortpflanzung von Meles taxus,” Zool. Anz., vol, iii., 1880) describes the badger’s ovum as undergoing a resting stage during which development is at a standstill (cf. roe-deer, p. 47). 3 Millais, loc. cit, 60 THE PHYSIOLOGY OF REPRODUCTION Farther north, however, at Jan Mayen, they are not born until about March 23rd or 24th. Turner’s notes! on the breeding habits of seals also point to the conclusion that the sexual season with these animals is restricted to regular periods of com- paratively short duration, so that it may probably be assumed that seals are moncestrous. The males of seals, as already remarked, experience rut at the time of the female sexual season. Whether the male generative organs are functional (e.g. whether the testes produce sperms) at other times does not appear to be known. It is of interest to note that in many species the rut is experienced during a period of complete fasting. Thus it is stated that the male fur seal, after coming to land, may live for over a hundred days without taking food, and that during this period he is constantly engaged in struggles with other males, finally leaving the shore in a state of extreme emaciation. The walrus affords an example of a Mammal which bears young only once in three years. Parturition takes place about May or June, and the sexual season recurs about two years subsequently. Thus the nursing or lactation period extends for nearly two years, while gestation lasts about one year.” INSECTIVORA The majority of the animals in this order are almost certainly polycestrous, but comparatively little is known con- cerning their breeding habits. The shrew in this country may be found breeding in any month from April until November, so that it is practically certain that this animal is polycestrous, and may have two litters, if not three litters in a year. It is ex- tremely probable also that the water-shrew breeds twice a year. In the hedgehog in this country, litters are born at the end of May or June, and in August or September.? In Germany it is said that the breeding season extends from March until July.! + Turner, ‘‘On the Placentation of Seals,” Trans. Roy. Soc. Edin., vol. xxvii, 1875. 2 Millais, Joc. cit. * Millais, The Mammals of Great Britain and Ireland, vol. i., London, 1904. ‘Van Herwerden, ‘Beitrag zur Kenntniss des menstruellen Cyklus,” Monatsschr. f. Geburtshilfe und Gynak., vol. xxiv., 1906. THE GSTROUS CYCLE IN THE MAMMALIA 61 The period of gestation in the hedgehog is not more than one month. The Malayan hedgehogs Gymnura and Hylomys are stated to experience an uninterrupted polycestrum. In the mole a great development of the male generative organs begins to take place at the end of January, culminating at the end of March. Previous to the end of January it is a matter of great difficulty to distinguish the males from the females without having recourse to dissection. The testicles lie on each side of the urinary bladder within the peritoneal cavity. In March they are protruded into sacs, which look like a con- tinuation of the peritoneal cavity beneath the base of the tail. Meanwhile the seminiferous tubules within the testicles undergo enlargement, and cells are proliferated, which give origin to the spermatozoa. The prostatic glands, which begin to increase in size in February, acquire enormous dimensions, and conceal the urinary bladder at the end of March 1 (cf. hedgehog, p. 238). At the beginning of the breeding season the male moles fight one another with great ferocity, and one is often killed. Pairing takes place at the end of March, or in April, or some- times as late as early May. A second litter of moles may be born later in the year, but this fact has not been definitely proved.” It would appear that in some Insectivores the procestrum may be comparatively severe, for in Tupaia javanica Stratz > has described a “‘ menstrual ”’ blood-clot which contained pieces of desquamated epithelium. CHIROPTERA As will be explained more fully in a future chapter, some species of bats appear to be exceptional in that the season of cestrus does not synchronise with the period of ' Owen, loc. cit. The same authority states that in the Cape mole (Chryso- chloris) he found the testes near the kidneys, but that the vasa deferentia had a convoluted course, which showed that they underwent periodic movements. Owen also describes the vesiculz seminales in the hedgehog as growing to an enormous size at the season of rut. 2 Millais, loc. cit, See also Adams, “ A Contribution to our Knowledge of the Mole,” Manchester Lit. and Phil. Soc, Mem., 1902. * Stratz, Der geschlechtsreife Saiigethiereierstock, Haag, 1898. 62 THE PHYSIOLOGY OF REPRODUCTION ovulation. It has been shown by Benecke,’ Himer,? van Beneden,? and Salvi, that whereas copulation may occur in the autumn, the ova are not fertilised until after the winter hibernation, the spermatozoa in the meantime lying dormant. Salvi,4 however, describes the bats in the Grotta dell’ Inferno, near Sassari, as copulating also in the spring, but it is suggested that coition at this season may only take place among those females which have failed to become inseminated effectively in the previous autumn.’ It does not appear to be known whether | the polycestrous condition ever occurs in bats. It is stated that a “ menstrual” (procestrous) flow has been observed in the flying fox (Pteropus).® PRIMATES Lemurs.—Among Lemuroids, Stratz’ has shown that in Tarsius spectrum there is a sanguineous procestrous discharge. almost as concentrated as in monkeys. This is presumably followed by an cestrous period. It is stated also that Tarsius experiences an uninterrupted series of dicestrous cycles (i.e. a condition of continuous polycestrum); but that, whereas con- ception is possible at any time of the year, breeding occurs more frequently in October and November than at other seasons.® Monkeys.—The essential similarity between the procestrum in the lower Mammalia and menstruation in monkeys will be made clear in the next chapter, when the histological changes which occur in the uterus are described. The consideration of the sub- ject, however, is somewhat complicated by the fact pointed out by Heape ° that, whereas monkeys may have a continuous series 1 Benecke, ‘‘ Ueber Reifung und Befruchtung des Eies bei den Fleder- maiisen,” Zool, Anz., vol. ii., 1879. 2 Eimer, ‘‘ Ueber die Fortpflanzung der Fledermaiise,”’ Zool. Anz., vol. ii. 1879. 3 Van Beneden, ‘‘ Observations sur la Maturation, la Fécondation, et la Segmentation de l’ceuf chez les Cheiroptéres, Arch. de Biol., vol. i., 1880. ‘ Salvi, ‘‘ Osservazioni sopra ’Accoppiamento dei Chirotteri nostrani,” Atti della Societa Toscana di Scienze Naturali, vol. xii., 1901. 5 Duval, ‘‘ Etudes sur l’Embryologie des Cheiroptéres,” Premiére Partie, Paris, 1899. § Wiltshire, loc. cit. 7 Stratz, loc. cit. 8 Van Herwerden, loc. cit. ® Heape, loc. cit. THE CESTROUS CYCLE IN THE MAMMALIA 63 of dicestrous cycles usually at regular monthly intervals, they are not necessarily capable of breeding at every heat period. Thus there is evidence that in the gorilla and chimpanzee in West Africa there is a special sexual season,! and Heape ? has shown that the same can be said of Semnopithecus entellus and Macacus rhesus in India, but that the exact time for breeding varies in the different localities. Thus in Simla Macacus rhesus copulates about October, and gives birth to young about August or September in the following year, whereas on the plains around Muttra it seems probable that March is the usual month when young are born. However, Mr. Sanyal, the Superintendent of the Zoological Gardens in Calcutta, expressed the opinion that M. rhesus can breed at all times of the year. On the other hand, it has been shown by van Herwerden * that Cercocebus in the Island of Banha breeds only, as a rule, in the late summer or early autumn. Heape* states that in the Moor macce in the Gardens in London there is definite cestrus which always occurs after the cessation of the menstrual discharge, and persists for two or three days, and Ellis ® has shown that this is also probably the case with the orang utan as well as with various monkeys. Pocock ® has given some interesting details concerning the phenomena which attend the menstrual process in various monkeys and baboons in the Zoological Society’s Gardens. He states that the females of many species at about the time of menstruation exhibit extreme inflammation of the naked area surrounding the genital and anal orifices. An inflammatory swelling was noticed in various species of Cercocebus, and Papio and in Macacus nemestrinus," but not in Cercopithecus, or in 1 Winwood Reade, Savage Africa, London. Mohrike, Das Ausland, 1872. Garner, Gorillas and Chimpanzees, 1896. * Heape, “ The Menstruation of Semnopithecus entellus,” Phil. Trans. B., vol. clxxxv,, 1894. ‘The Menstruation and Ovulation of Macacus rhesus.” Phil. Trans. B,, vol. clxxxviii., 1897. * Van Herwerden, loc. cit. 4 Heape, ‘‘ The Sexual Season,” &c. 5 Havelock Ellis, Psychology of Sex, vol, ii., Philadelphia, 1900. ® Pocock, ‘* Notes upon Menstruation, Gestation, and Parturition of some Monkeys that have lived in the Society’s Gardens,” Proc. Zool. Soc., 1906. ? Similar observations had been previously described in Cercopithecus, Papio, and other species by certain of the older naturalists. See St. Hilaire and Cuvier, Hist. Nat. des Mammiferes, 1819-35. 64 THE PHYSIOLOGY OF REPRODUCTION certain other species of Macacus including M. rhesus. Heape, however, states that in menstruating specimens of M. rhesus observed by him, and M. cynomolgus, the skin of the buttocks became swollen and red or purple in colour, as well as the skin of the abdomen, the inside of the thighs, and the under surface of the tail, while the skin of the face tended to become flushed or blotched with red; at the same time the nipples and vulva were congested. Menstrual hemorrhage has been recorded in many monkeys and baboons, but there appears to be consider- able variability in its extent. Pocock says: “In baboons it may or may not take place, and may be great or little in amount, It has been noticed to occur in some profusion in a female of Macacus sinicus, and not to occur appreciably in a female of the closely allied species, M. fascicularis. Obviously, therefore, it cannot be associated with the inflammatory swelling of the genito-anal region [since no swelling was apparent in either of these two species]; and it is hardly likely to have a specific value in taxonomy. Perhaps the nearest guess that can at present be made is the surmise that it is dependent on the con- stitution or health of the individual.’’ Heape noticed that in M. rhesus the menstrual discharge lasted for from three to five days. Pocock records that in a Chacma baboon (Papio porcarius) hemorrhage continued for about four days. In both animals the phenomenon was truly “menstrual ” (7.e. of monthly occurrence). Pocock records the interesting fact that whereas the swelling of the inflammatory area commences at about the same time as the hemorrhage, it does not reach its full size until several days after the discharge is over. It soon afterwards begins to shrink, and in about another two weeks has disappeared, so that the female at a distance is indistinguishable from the male. After a few days’ rest inflammation again sets in, and the process is repeated. Pocock suggests that this sub-caudal swelling may serve the purpose of apprising the male (at a distance) as to when the female is “ on heat,” and it is to be noted that it is at its maximum after menstruation is over (as just mentioned), and so presumably therefore during a definite period of cestrus. The question as to the correspondence in time between the THE CESTROUS CYCLE IN THE MAMMALIA 65 processes of menstruation and ovulation is discussed in a later chapter. Little igs definitely known concerning the length of the gestation period in the various apes and monkeys. Pocock’s observations show that in Macacus nemestrinus this period is between six and seven months. Blandford ! states his belief that about seven months is the usual period for the genus Macacus. Sanydl, according to information recorded by Sclater,? found that a female of Cercopithecus cynosurus in the Zoological Gardens, Calcutta, carried her young for seven months. Gestation in the Quadrumana is dealt with at some length by Breschet,? who cites many of the older observations. He shows that the question as to the duration of the period is com- plicated by the fact that monkeys, unlike the majority of Mammals, may copulate at other times than the breeding season, and that they are said occasionally to experience men- struation during pregnancy. Man.— As is well known, menstruation recurs normally in the non-pregnant human female at intervals of from twenty-eight to thirty days. The exceptions to this general rule are, however, very numerous, and have often been noticed. Thus the interval may be extended to five weeks, or be abbreviated to two weeks without any derangement to the general health. “In one hundred women, sixty-one [were found] to menstruate every month, twenty-eight every three weeks, ten at uncertain in- tervals, and one, a healthy woman aged twenty-three years, every fortnight.” 4 The duration and amount of the discharge may also vary considerably both in different women and in the same woman at different times. It is stated, also, that the periodicity of menstruation depends partly on the climatic conditions, and that women in Lapland 1 Blandford, The Fauna of British India, vol. i., London, 1888. * Sclater, Mammals of South Africa, London. 3 Breschet, ‘‘ Recherches anatomiques et physiologiques sur la Gestation des Quadrumanes,” Mémoires de l Acad. des Sciences, vol. xix., 1845. 4 Laycock, loc. cit., and Havelock Ellis, doc. cit. There is in some cases a tendency for the cycle to become divided up into two cycles, separated by the so-called ‘‘ Mittelschmerz,” or inter-menstrual pain, which is occasion- ally accompanied by a sanguineous discharge. (Halliday Croom, “ Mittel- schmerz,” Trans. Edin. Obstet, Soc., vol. xxi., 1896). E 66 THE PHYSIOLOGY OF REPRODUCTION and Greenland menstruate less frequently, whereas in certain low and hot countries the catamenia may recur every three weeks.} Further, the regularity with which the menstrual periods occur is liable to be disturbed by environmental changes. Thus, it is stated that change of residence, or foreign travel, without otherwise affecting the health, may bring about amenorrhcea or a temporary cessation of menstruation.? Such an effect is, no doubt, comparable to the well-known influence of captivity or change of environment in arresting the sexual functions of many animals. The commonest time for the continuance of the menstrual flow is said to be about three or four days in this country, but it may last for as long as eight days, or, on the other hand, for only a few hours without disturbance of health. It usually begins gradually, becoming most profuse about the second or third day, and then diminishes.? The total amount of blood lost has been variously estimated at from two to four ounces. In hot climates the quantity is greater than in cold; and it is said to be increased by luxurious living, and also by abnormal mental stimulation. The character of the menstrual discharge and its source of origin can best be considered in describing the histology of the uterus during the cestrous and menstrual cycles (see Chapter III.). The monthly development of the uterine mucous membrane which precedes the menstrual discharge is often accompanied by a fulness of the breasts which begins to disappear after the commencement of the flow. Swelling of the thyroid and parotid glands, and tonsils, as well as congestion of the skin and a tendency towards the formation of pigment, are also » Matthews Duncan, “Sterility in Women,” Brit. Med. Jour., 1883 ; and Laycock, loc. cit. 2 Wiltshire, loc. cit. ® Galabin, 4 Manual of Midwifery, 6th Edition, London, 1904. The age at which menstruation begins varies in different countries, being earlier in warm climates than in cold ones. In our own country the first menstrua- tion does not usually occur before the age of fourteen or fifteen, while the menopause (or period when menstruation ceases) begins about the age of forty-five. (See p. 672.) Kennedy (Edin. Med. Jour., vol. xxvii., 1882), how- ever, has reported a case of a woman who continued to menstruate after giving birth to a child at the age of sixty-three. 100 26 o LEL21814161617) 8 jo 110) 11/12/18 “6 14 16 1627 18 10 D THE G&ESTROUS CYCLE IN THE MAMMALIA 67 known to occur.! The voice also is liable to be affected at the menstrual periods, and the skin and breath sometimes have a peculiar odour. Mental depression may exist, and be accom- panied by nervous pathological phenomena. According to the upholders of the “ Wellenbewegung ” hypothesis * the reproductive life of the human female consists of a succession of wave-like periods which follow the monthly cycle. Thus, according to Stevenson,® the curve of temperature G wi ecese eee wi esese esene eee 20) 21} 22 3} 24 | 26) 26/27) 28) Fig 1.—Diagram illustrating the ‘ Wellenbewegung” hypothesis. The curve AB represents the varying intensity of the vital processes during the twenty-eight days of the menstrual cycle. The numbers between ‘mand n represent the days occupied by menstruation. (From Sellheim.) is above the mean line for about half the month, when it rises to half a degree above the mean. It falls below the mean line just before the onset of menstruation, during which it remains about half a degree below. Similar results were obtained by 1 See p. 350, Chapter IX. ? Godman, “‘ The Cyclical Theory of Menstruation,” Amer. Jour. Obstet., vol. xi., 1878. Reinl, ‘‘ Die Wellenbewegung des Lebensprozesses des Weibes,” Volkmann's Sammlung klin. Vortrége, No. 273. Ott, ‘‘ Les lois de la périodicité de la fonction physiologique dans Yorganisme féminine,” Nouvelles Arch, d’ Obstet. et de Gynéc., 1890. 3 Stevenson, ‘‘On the Menstrual Wave,” Amer. Jour. Obstet., vol. xv., 1882. 68 THE PHYSIOLOGY OF REPRODUCTION Reinl, Ott, and Giles,} but Vicarelli ? and certain other authors have recorded an increased temperature during menstruation.® Zuntz,* however, as a result of more recent experiments, says that there is a regular lowering of the temperature throughout the menstrual period, after which it rises to the normal. Stevenson states also that the curve of urea excretion follows a similar course to the temperature curve, and that, speaking generally, there is an increase in metabolism coincident with the time of development of the uterine mucosa. There is, however, no doubt much truth in von Noorden’s criticism ® that the “menstrual wave ” hypothesis has given occasion to many pre- mature conclusions regarding the behaviour of the metabolism. Schroder,® who investigated the nitrogen metabolism, found a retention of nitrogen immediately before and during menstrua- tion (cf., Potthast, &c., for dogs, p. 54), but other investigators have obtained somewhat different results.’ Zuntz has shown from numerous experiments that, contrary to the conclusions of other authors, there is no evidence of a constant variation in the respiratory exchange during the menstrual cycle. Mosher ® states that there is a fall of blood pressure at the time of menstruation. Zuntz° records a diminution in the pulse rate. Sfameni '° states that there is a decrease in the quantity of hemoglobin in the blood during menstruation. He says also that the number of blood corpuscles increases in the days imme- diately preceding the hemorrhage, but is diminished during it.” 1 Giles, ‘‘ The Cyclical or Wave Theory,” &c., Trans. Obstet. Soc., London, vol. xxxix., 1897, * Vicarelli, ‘La température del’utérus dans ses diverses conditions physiologiques,” Arch. Ital. de Biol., vol. xxxii.. 1899. 5 Sfameni, ‘‘ Influence de Ja menstruation sur la quantité d’hémoglobine.” Arch. Ital. de Biol., vol. xxxii., 1899. ‘ Zuntz (L.), ‘* Einfluss der Ovarien auf den Stoffwechsel,” Arch. f. Gyndk., vol. lxxviii., 1906. 5 Von Noorden, Metabolism and Practical Medicine (English Translation), vol. i., London, 1907. * Schroder, ‘: Untersuchungen iiber den Stoffwechsel waibrend der Men- struation,” Zeitschr. f. klin. Medicin, vol. xxv., 1894. 7 See von Noorden. loc. cit. * Mosher, ‘‘ Blood-pressure during Menstruation,” Johns Hopkins Hospital Bulletin, 1901. ® Zuntz, loc. cit. 10 Sfameni, loc. cit. 11 Of. Carnot and Deflandre, “‘ Variations du nombre des Hématies chez la Femme pendant la période menstruelle,” C. R: dela Soc. de Biol , vol. lxvi., 1909. THE GE&STROUS CYCLE IN THE MAMMALIA 69 Birnbaum and Osten ! state that in the blood of menstruating women coagulation is retarded. This statement is based on experiments made by adding fibrinogen to menstrual blood serum. Blair Bell? states that in connection with menstruation there is a marked drop in the calcium content of the systemic blood, and that this is most marked just before bleeding begins. This is correlated with an excretion of calcium salts in the menstrual discharge, an examination of which revealed the presence of a considerable quantity of calcium, both free and within the leucocytes (see p. 87). This excretion of calcium during menstruation is regarded by Blair Bell as connected phylogenetically with the process of egg-formation by birds and other lower Vertebrates. According to Martin,? and certain other writers, the human female often experiences a distinct post-menstrual cestrus, at which sexual desire is greater than at other times; so that, although conception can occur throughout the inter-menstrual periods, it would seem probable that originally coition was restricted to definite periods of cestrus following menstrual or procestrous periods in women as in the females of other Mammalia. On this point Heape writes as follows :—* This special time for cestrus in the human female has very fre- quently been denied, and, no doubt, modern 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, I am convinced, still marked.” * Heape has also given a brief résumé of the evidence that primitive Man resembled the lower Primates in having a definite sexual season. The evidence is based largely upon the works of 1 Birnbaum and Osten, ‘‘ Untersuchungen iiber die Gerinnung des Blutes wahrend der Menstruation,”’ Arch. f. Gyndk,. vol. 1xxx., 1906. ? Blair Bell, ‘‘ Menstruation and its Relation to the Calcium Metabolism,” Proc. Roy. Soc. Med., July 1908. * Martin, ‘‘The Physiology and Histology of Ovulation, Menstruation, and Fertilisation,” Hirst’s System of Obstetrics, vol. i., London, 1888. ‘ Heape, loc. cit. 70 THE PHYSIOLOGY OF REPRODUCTION Ploss! and Westermarck,? the latter of whom goes somewhat fully into the subject in a chapter on ““ A Human Pairing Season in Primitive Times,” to which the reader is referred for further references on this subject.? It has been shown that there is a more or less restricted season for breeding among certain of the North American Indians, among certain tribes in Hindustan, among many of the native Australians, among the Esquimaux, among the natives of the Andaman Islands, as well as among certain other of the more primitive races of mankind. The season seems generally to occur in the spring, but this is not invariably so. Annandale and Robinson? state that among the Semang or aboriginal tribes of the Siamese State of Jalor, children are generally born only in March, or immediately after the wet season, a fact which appears to imply that there is a regular sexual season in June. Further evidence of the existence of a primitive sexual season in Man is furnished by the records of the annual feasts which the ancients indulged in—usually in the spring—and which Frazer ° has shown to be represented in modern European countries by the May-queen festivals, and other similar customs that have survived into our own time. It is well known that the ancient festivals among the civilised peoples of the past were times of great sexual licence, and so in all probability were similar in origin to the licentious feasts and dances of various savage races at the present day. Their anthropological significance and the intimate association between them and the idea of reproduction are discussed at great length by Frazer in his book entitled The Golden Bough. There is, moreover, evidence of a human pairing season in the higher birth-rate which occurs at certain seasons in various countries at the present day. Ploss has collected statistics illustrating this fact in Russia, France, Italy, and Germany, 1 Ploss, Das Wetb, Leipzig, 1895. * Westermarck, The History of Human Marriage, London, 1891. 3 See also Havelock Ellis, loc. cit. 4 Annandale and Robinson, Fasciculi Malayenses : Anthropology, Part I., 1903. 5 Frazer, The Golden Bough, 2nd Edition, London, 1900. THE GéSTROUS CYCLE IN THE MAMMALIA 71 and Haycraft + has shown that there are indications of a similar condition existing in Scotland. On this subject Mayo-Smith * writes as follows: “The largest number [of births] almost always falls in the month of February . . . corresponding to con- ceptions in May and June. . . . Observations tend to show the largest number of conceptions in Sweden falling in June; in Holland and France, in May—June; in Spain, Austria, and Italy, in May ; in Greece, in April. That is, the farther south, the earlier the spring and the earlier the conceptions.” Other facts of a like kind are recorded by Westermarck, who concludes that primitive Man had an innate tendency towards increased powers of reproduction at the end of spring or beginning of summer, and that this tendency became variously modified under the influence of natural selection in the different human races which subsequently arose.? Finally, it may be pointed out that Westermarck’s conclusion —which seems a very probable one in view of the evidence which he and others have collected—is in no way invalidated by the fact that the human female experiences normally an uninterrupted succession of dicestrous (i.e. menstrual) cycles ; for, as already shown, a similar condition is known to exist in several at least of the lower Primates, with which there is also evidence that in a state of nature the breeding functions are restricted to particular seasons of the year.* 1 Haycraft, ‘‘On some Physiological Results of Temperature Variations,” Trans. Roy. Soc. Edin., vol. xxix., 1880. 2 Mayo-Smith, Statistics and Sociology, vol. i., New York, 1895. Cf. also van Herwerden, Joc. cit. 3 Mayo-Smith (Joc. cit.) points out that sexual periodicity in civilised Man is much obscured by social influences. ‘ One great social influence is the time of marriage. Marriage tends to accumulate about the social festivities of Christmas time, and in Catholic countries especially in the period just before Lent.” He suggests that in agricultural districts the concentration about Christmas is due to the leisure following the labours of the autumn. ‘In cities the births are more evenly distributed, showing that artificial life has overcome the influence of seasons and particular occupations.” 4 That is to say that, whereas menstruation goes on at regular intervals all the year round, the procestrous or menstrual periods are only followed during the breeding season by cestri at; which it is possible for conception to occur. There are some indications that the sexual instinct among males is also periodic, both in the lower Primates and in the human subject, but the periodicity is not so marked as among females. Havelock Ellis (Joc. cit.) has 72 THE PHYSIOLOGY OF REPRODUCTION Whether the monestrous or the polyestrous condition is the more primitive is a question which cannot at present be decided. The fact that polycestrum is secondarily acquired among many animals may perhaps be regarded as evidence that moneestrum is the more primitive of the two conditions ; for, as already shown, there are numerous instances of Mammals which are almost certainly moneestrous in their wild state, but which have inde- pendently assumed a condition of polycestrum under the more luxurious influences of domestication. Thus, while the sheep, the sow, and the cat are almost certainly moncestrous in a state of nature, the domesticated breeds of these animals show a varying degree of polycestrum which appears to depend largely upon the extent to which domestication has been carried as well as upon food and the influences of the surroundings. On the other hand, the existence of the continuous polycestrum in tropical climates among such primitive Mammals as the Insectivores, and the common occurrence of varying degrees of polycestrum among the Rodents, not only in captivity but also in the wild state, point to the possibility that polycestrum may in reality be the more primitive condition, and one which can easily be reverted to under the influence of a favourable en- vironment. The main purpose of polycestrum (to use teleological lan- guage) is no doubt, as already remarked, to provide increased opportunity for coition, and so to promote the fecundity of the race. But it must be remembered that cestrus is not necessarily associated with ovulation, and consequently the explanation just given of the polycestrous habit is not of universal application. This is a point which will be referred to again in dealing with ovulation. It is of course possible, however, that the poly- cestrous condition, having once been acquired, might in certain circumstances be perpetuated in spite of its inutility. Before concluding the present chapter it remains for me to allude briefly to the effect of maternal influences on the cestrous cycle. These, as pointed out by Heape, may or may not com- discussed this question at some length, adducing evidence of a sexual rhythm in men. See especially appendix to Ellis’s work by Perry-Coste, who shows that there may be a tendency towards rhythmic regularity in the sexual functions as manifested especially in the recurrence of seminal emissions. THE GESTROUS CYCLE IN THE MAMMALIA 73 pletely disorganise the recurrence of the sexual season. In such animals as the dog they do not do so, because the dog is mon- cestrous, and has, as a rule, only two sexual seasons annually, so that the ancestrous period considerably exceeds in length the period of gestation. In large animals such as the camel, on the other hand, where the gestation period extends for thirteen months, the recurrence of the sexual season is post- poned by pregnancy for a whole year. Again, in small animals like the rat, gestation only prevents the recurrence of cestrus, reducing the number of dicestrous cycles, but not interfering with the recurrence of the sexual season. “ But whenever gestation occurs it encroaches upon, if it does not entirely absorb, the ancestrum; that is to say, it reduces the period during which the generative organs would lie fallow if the sexual season were a barren one. Thus in the case of a 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 begins. A reproductive sexual season, however, results in a period of eleven months’ gestation, interfering not only with the di- cestrous cycles which would have recurred if conception had not taken place, but also absorbing practically the whole of the ancestrum.” + The duration of the gestation period is intimately connected not only with the size of the body, but also with the stage of development at which the young are born.” It is longest in the large terrestrial and gigantic aquatic Mammals (Ungulata and Cetacea), which live amid favourable conditions of nourishment. With these animals the young are so far advanced in develop- ment at the time of birth that they are able to follow the mother about, and to a certain extent shift for themselves. In Carnivores and Rodents the period of pregnancy is relatively shorter, and the young are often born naked, and with unopened eyes, and con- sequently are absolutely helpless for a considerable time after birth. The gestation period is shortest in the aplacental Mammals (Monotremata and Marsupialia), in which the young are born at a very early stage and transferred to a pouch 1 Heape, loc. cit. 2 Sedgwick, Studént’s Text-book of Zoology, vol. ii., London, 1905. 74 THE PHYSIOLOGY OF REPRODUCTION formed by cutaneous folds in the vaginal region. In Mono- tremes the young are hatched from eggs which, after being laid, are deposited in the pouch. The question as to what are the precise factors which de- termine the length of the gestation period has already been referred to in the first chapter, where it was pointed out that both the duration of pregnancy and the time of the year at which breeding occurs are necessarily controlled by natural selection, acting in the interests of the next generation. The effects of lactation upon the recurrence of cestrus vary widely, and are often different among individuals belonging to the same species. Thus, although the mare as a general rule is capable of becoming pregnant while suckling, in some individuals the sexual season is postponed, the mares only becoming pregnant once in two years. The return of menstruation during lactation in women has been dealt with recently by Heil,! and Dingwall Fordyce.? Heil, who had studied the conditions of two hundred nursing mothers, expresses the belief that the occurrence of menstruation and not the condition of amenorrhcea is the normal state during lactation, but that menstruation is not so frequent in the later lactations as during the earlier ones. Fordyce has reached similar conclusions, finding that menstruation occurred during lactation in forty per cent. of the cases in which suckling was performed, while in ninety-two per cent. of the cases its return was within nine months of parturition, and that menstrua- tion during lactation was commoner with the earlier than with the later lactations, showing that age is an important factor. The histological changes which occur in the internal gene- rative organs of various Mammalia during the estrous cycle are described at some length in the succeeding chapters. * Heil, ‘‘ Laktation und Menstruation,” Monatsschr. f. Geburtsh, u. Gyndk., vol. xxiv., 1906. 2 Fordyce, ‘‘ An Investigation into the Complications and Disabilities of prolonged Lactation.” Being an extension of papers published in The Lancet, Part I., 1906, The Brit. Med. Jouwr., Part I., 1906, and The Brit. Jour. of Children’s Diseases, 1906. Gellhorn (‘Abnormal Mammary Secretion,” Jour. Amer. Med. Assoc., Nov. 21, 1908) mentions a case of an ape (Cercopithecus) in which menstruation always disappeared during profuse lactation, but reappeared as soon as the mammary secretion ceased or became markedly decreased. CHAPTER III THE CHANGES THAT OCCUR IN THE NON-PREGNANT UTERUS DURING THE CSTROUS CYCLE “ Menstruation is like the red flag outside an auction sale; it shows that something is going on inside.’—MaTTHEWS Duncan. For full descriptions of the morphology of the uterus in the different mammalian orders, reference may be made to the text-books on human, comparative, and veterinary anatomy. But before passing on to describe the changes which occur in the histology of the uterus during the menstrual cycle, it may not be out of place to remind the reader of the general structural relations of the generative organs in the human female. The two ovaries, the structure of which is described in the next chapter, are situated one on each side of the pelvis, and are connected with the posterior layer of the broad ligament of the uterus. In connection with each ovary is a Fallopian tube or oviduct, which opens into the peritoneal cavity about an inch from the ovary.!. Surrounding the orifice is a fringe of irregular processes or fimbrie, which, when expanded, assist in directing the ovum in its passage into the tube. The tubes are about four inches long, and terminate at the superior angles of the uterus, with the cavity of which they are in continuation. They are surrounded by an external serous coat derived from the peritoneum, a muscular coat containing both longitudinal and circular fibres, and an internal mucous membrane, which is highly vascular and is lined within by a ciliated epithelium. 1A vestigial structure lying transversely between the ovary and the Fallopian tube on either side is called the parovarium or epodphoron, or organ of Rosenmiiller, or sometimes the duct of Gartner. It consists of a few scattered tubules, with no aperture. It is the homologue of the epi- didymis of the male. Vestiges of structure corresponding to the organ of Giraldés are also sometimes found in the vicinity of the parovarium, but nearer to the uterus. These have a called the parodphoron. 76 THE PHYSIOLOGY OF REPRODUCTION The human uterus consists of two parts, the corpus or body of the uterus, and the cervix or neck, which opens into the vagina. The body of the uterus contains the following layers, which correspond with those of the Fallopian tubes: (1) A serous layer; (2) a thick muscular layer, consisting of three more or less blended sub-layers ; and (3) a still thicker layer, known as the mucous membrane or mucosa (sometimes called the endo- Fic. 2.—Transverse section through Fallopian tube, showing folded epithelium and muscular coat. metrium), which is composed of a connective tissue containing spindle-shaped cells, and is lined by a ciliated epithelium bounding the uterine cavity. The mucosa contains numerous tubular glands, which open out into the cavity of the uterus and are covered by an epithelial layer, these being continuous with the epithelium of the surface. The sub-epithelial mucosa, which is sometimes called the uterine stroma, contains also a number of blood-vessels and lymph spaces. The vessels are branches of the ovarian and uterine arteries and veins. The CHANGES IN THE NON-PREGNANT UTERUS 177 uterus is also supplied by nerves which are referred to in a future chapter (p. 527). In many of the lower Mammals the uterus is represented by two tubes, called the horns of the uterus or uterine cornua, which may unite posteriorly to form the corpus, or may, on the other hand, open separately into the vagina. The arrangement Fig. 3.—Section of a cornu of a rabbit’s uterus. 8, Serous layer ; 7m, longitudinal muscle fibres ; em, circular muscle fibres ; a, areolar tissue with large blood-vessels ; #m, muscularis mucose ; 21, mucosa, (From Schafer.) of the different layers in each of the cornua is essentially similar to that presented by the corpus uteri in the human species. The neck or cervix uteri, which is narrower than the rest of the organ, opens into the vagina by a transverse aperture known as the os. The vagina is the broad passage from the uterus to the exterior. Its walls contain both longitudinally and circularly arranged muscle fibres. Internally it is lined 78 THE PHYSIOLOGY OF REPRODUCTION by a stratified scaly epithelium, surrounded by erectile tissue. The entrance to the vagina from the exterior is guarded by a thin fold of mucous membrane, which usually becomes _per- forated at the first coition. This structure, which is called the hymen, is peculiar to the human race.* The vulva comprises the female generative organs which are visible externally. These include: the mons veneris, the aA oko ba J j *& i y a 3 ihe ° ; a : You weet § fe A 3 * Neo a lle * et : Fig. 4.—Cross-section through cervical canal of human uterus. ‘(From Williams’ Obstetrics. Appleton & Co.) labia majora and minora, and the clitoris. The last-mentioned structure is a small erectile organ, which is homologous with the penis.” Tue CycLe in Man In giving -an account of the changes which take place in the uterus during the menstrual cycle of the human female, it will be convenient to adopt the scheme of classification employed by Milnes Marshall* in his work on Vertebrate 1 The significance or function of the hymen is not certainly known. Metchnikoff (The Nature of Man, English Edition, London, 1903) suggests that it may have been useful in the earlier history of the race, when sexual intercourse probably occurred at an early age, before the reproductive organs were mature. Under such circumstances the hymen, instead of being a | barrier, may have facilitated successful coitus, Metchnikoff supposes the aperture to have become gradually dilated by repeated intercourse without being torn, until it admitted of the entrance of the adult male organ. * The outer part of the vagina into which the female urethra opens is often called the vestibule or urogenital sinus. 3 Milnes Marshall, Vertebrate Embryology, London, 1893. CHANGES IN THE NON-PREGNANT UTERUS 79 Embryology. This classification, as will be seen later, is iden- tical with that adopted by Heape! in describing the menstrual Fig. 5.—Section through wall of vagina (upper part) of monkey. a, epithelium ; 6, sub-mucous layer; c, lymphatic gland; d, nerve; e, Pacinian body ; /, fat cells. 1 Heape, ‘The Menstruation of Semnopithecus,” &c., Phil. Trans., B., vol. clxxxv., 1894, and vol. clxxxviii., 1897. A similar classification has been adopted by Minot (Human Embryology, 1892), who divides the menstrual process into (1) Tumefaction; (2) Menstruation; and (3) Restoration of the mucosa. ’ 80 THE PHYSIOLOGY OF REPRODUCTION changes of monkeys. The cycle is divided into four stages, as follows :— (1) The Constructive Stage. (2) The Destructive Stage. (3) The Stage of Repair. (4) The Stage of Quiescence. The last stage may conveniently be considered first. The Stage of Quiescence.—The normal condition of the human endometrium has been described by Webster, to whose account the reader is referred. This author calls special attention to the following points: (1) The thickness of the mucosa is not uniform, but varies considerably. (2) The epithelial cells which line the mucosa, and also those which line the glands, show differences in shape and size, and in the position of the nuclei. (3) The epithelial cells lining the glands are, as a rule, larger than the superficial cells. (4) The interglandular connective tissue or stroma is mainly embryonic in nature, and consists of a nucleated protoplasmic reticulum, containing every stage of transformation into the more differentiated spindle-shaped cells. (5) The stroma nearest the surface is for the most part arranged parallel to it, the cells immediately below the epithelium forming a kind of basement-membrane. (6) The superficial portion of the mucosa is supplied only by capillaries. (7) The line of junction of mucosa and muscle-wall is irregular, and there is no special muscularis mucose. The Constructive Stage-—During this stage the stroma of the uterus undergoes a process of growth. This is brought about partly by cell division, partly (according to Engelmann?) by an increase in intercellular substance, and partly by an enlarge- ment of the glands and blood-vessels. According to Lipes,? this stage commences as soon as the process of regeneration (following the preceding menstrual period) is completed, which is about eighteen days after the cessation of the previous flow. ‘‘ During the stage of regeneration the cells of the stroma } Webster, Human Placentation, Chicago, 1901. ® Engelmann, ‘‘ The Mucous Membrane of the Uterus,”’ &c., Amer. Jour. Obstet., vol. viii., 1875. 5 Lipes, ‘‘A Study of the Changes occurring in the Endometrium during the Menstrual Cycle,” Albany Medical Annals, vol. xxv.. 1904. Ss CHANGES IN THE NON-PREGNANT UTERUS 81 lay over each other rather thickly, but now become pressed apart, particularly in the outer third of the mucosa. The protoplasm of these cells becomes compressed, and the pro- Fic. 6.—Section through wall of vagina (lower part) of monkey. a, epithelium lining cavity ; b, sub-mucous layer; ¢, muscular layer ; d, d’, nerve ganglia; e, artery ; f, fat cells. jections by which they are bound together are either greatly lengthened or completely separated.” The capillaries of the mucous membrane become congested (Fig. 7), and a serous or F 82 THE PHYSIOLOGY OF REPRODUCTION sanguineo-serous exudate infiltrates into the stroma. The enlargement of the vessels continues, but does not become very pronounced until shortly before the stage of destruction which may be said to mark the beginning of menstruation proper. Lipes also describes an increase in the size of the glands of the mucous membrane, which he supposes to be due to the collection of the secretion of the gland-cells. This mucus-like Fic. 7.—Section through mucosa of human uterus showing pre-menstrual congestion. (From Sellheim.) product of the gland-cells is said to give them a distinctly granular appearance. “The gland-cells become uniformly swollen and take stains more evenly, and their nuclei are more widely separated as a result of the imcrease in the volume of the protoplasm, and are uniformly more round in comparison with the oval nuclei, which are seen in the regeneration period.” Westphalen? has pointed out that the nuclei, which are situated near the base of the cell as a rule, appear in the middle of the cell at the beginning of the stage of pre-menstrual swelling. 1 Westphalen, “Zur Physiologie des Menstruation,” Arch. 7. Gyndk., vol. lii., 1896. CHANGES IN THE NON-PREGNANT UTERUS 83 As a consequence of these changes the mucosa becomes con- siderably increased in thickness. Thus, if a woman who had been menstruating regularly dies shortly before the expected approach of a menstrual period, the thickness of the mucous membrane is often as much as one-sixth of an inch at its thickest part, as compared with a thickness of from one-tenth to one- twentieth of an inch in women who died within ten days after the cessation of the flow.t Leopold? has described a growth so considerable that the uterine cavity, prior to the stage of bleeding, becomes almost completely obliterated. It should be mentioned, however, that according to some authors the amount of pre-menstrual growth in the uterine mucosa is very slight, while Oliver ? seems to be doubtful whether any growth occurs at all, stating that he has made an examina- tion of uteri at various pre-menstrual and menstrual stages, and has failed to find any evidence of changes in the mucosa tissue apart from those directly associated with the phenomena of bleeding. Westphalen’s view appears to be similar; for, according to this observer, there is no multiplication of nuclei during this stage, the pre-menstrual swelling being brought about entirely by the serous saturation of the stroma. The Destructive Stage—At the close of the constructive period the blood leaves the capillaries and becomes extra- vasated freely in the stroma, but there has been some dispute as to how this process is effected. It has been suggested that the blood transudes through the walls of unruptured capillaries under the influence of congestion, or that permanent openings exist from the vessels into the uterine glands, these being closed normally by muscular contraction ;* but the belief now generally held is that, whereas the walls of many of the congested vessels break down under pressure, and so freely admit of the exit of the blood corpuscles into the mucosa tissue, hemorrhage also takes place partly by diapedesis. Engelmann,° Williams,® and 1 Galabin, 4 Manual of Midwifery, 6th Edition, London, 1904. * Leopold, ‘‘ Untersuchungen iiber Menstruation und Ovulation,” Arch. J. Gyndk., vol. xxi., 1883. 4 Oliver, ‘Menstruation: its Nerve Origin,” Jour. Anat. and Phys.. vol. xxi, 1887. 4 Galabin, Joc. cit. 5 Engelmann, Joc. cit. § Williams (Sir J.); ‘The Mucous Membrane of the Body of the Uterus,” Obstet. Jour, Gt. Britain vols. iii. and v.. 1875 1877, 84 THE PHYSIOLOGY OF REPRODUCTION others have ascribed the breaking down of the vessel-walls to fatty degeneration, but this has been denied by Méricke,* and more recently by Findley,? while Leopold has described the appearance of the fatty degeneration as a result rather than a cause of hemorrhage. After the extravasation of blood, the corpuscles tend to become aggregated in lacune which lie beneath the superficial Fig. 8.—Section through mucosa of human uterus showing extravasation of blood. (From Sellheim.) epithelium. These lacune are the sub-epithelial hematomata of Gebhard,? according to whom the epithelium becomes lifted almost bodily from its bed, the space between it and the stroma being filled with blood. Gebhard concludes that the blood eventually reaches the uterine cavity by being forced between 1 Moricke, “Die Uterusschleimhaut in der verschiedenen Altersperioden und zur Zeit der Menstruation.” Zeitsch. f. Geburtshiilfe u. ('yndk., vol. vii., 1882. 2 Findley, ‘Anatomy of the Menstruating Uterus,” Amer. Jour. Obstet., vol, xlv., 1902. 3 Gebhard, “ Ueber das Verhalten der Uterusschleimhaut bei der Men- struation,” Verhand d. Gesells. f. Geb. uw. Gyn. zu Berlin, Zeitsch. f. Geb. u. Gyno vol. xxxii., 1895. CHANGES IN THE NON-PREGNANT UTERUS 85 the epithelial cells, or that a larger exit is provided by certain of the cells being carried bodily away. Gebhard also believes that bleeding may take place into the lumina of the glands. Christ} states that when the menstrual flow is very profuse there is a considerable loss of surface epithelium, but that in other cases the removal of epithelium is slight. This author has also described bleeding into the glands. (Fig. 9.) Very contradictory statements have been made regarding the extent to which denudation takes place during menstruation. Williams (Sir J.), von Kahlden,? and others among the older writers, expressed the belief that a large part, if not the whole, of the uterine mucous membrane was destroyed. This view, as will be seen later, has been partially confirmed for monkeys by Heape. It has been pointed out, however, by Whitridge Williams,* that the older writers made their observations upon uteri which had undergone post-mortem changes. The pre- ponderance of recent opinion appears to be that destruction of the mucous membrane is, as a rule, confined to the epithelium, and that this is only partially removed. Among those who have accumulated evidence in support of this conclusion are Gebhard, Strassmann,* Westphalen, Findley, Whitridge Williams, and Lipes. De Sinety,® Méricke, and Oliver appear to uphold the opinion that even the superficial epithelium remains practically intact. Mandl,° Maerdervort,’ and also Champneys ® have made the exceedingly likely suggestion that the extent to which the mucosa is destroyed varies within wide limits in different individuals or even in the same individuals at different periods of life. 1 Christ, “Das Verhalten der Uterusschleimhaut wihrend der Menstrua- tion,” Inorg. Dissert., Giessen, 1892. 2 Von Kahlden, * Ueber das Verhalten der Uterusschleimhaut wahrend und nach der Menstruation,” Hegar’s Festschrift, Stuttgart, 1889. 3 Whitridge Williams, Obstetrics, London and New York, 1904. 4 Strassmann, “ Beitrage zur Lehre von der Ovulation, Menstruation, und Conception,” Arch. f. Gyndk., vol. lii., 1896. 5 De Sinety, “Recherches sur la muqueuse utérine pendant la menstrua- tion,” Annales de Gyncec., 1881. 5 Mandl, “Beitrag zur Frage des Verhaltens der Uterusmucosa wihrend der Menstruation,” Arch. f. Gyndk., vol. lii., 1896. 7 Maerdervort, “ Die normale und menstruirende Gebirmutterschleimhaut,”’ Inorg. Dissert., Freiburg, 1895. 8 Champneys, “On Painful Menstruation,” Harveian Lectures, 1890. 86 THE PHYSIOLOGY OF REPRODUCTION Minot,! and Martin,? agree in supposing that the superficial layers of the mucosa degenerate after the blood has passed out, so that the bleeding is in no sense the consequence of the destruction. According to Martin, fatty degeneration plays a distinct part in causing the destruction. Lipes has shown that the amount of destruction is related to the character of the hemorrhage. If the congestion is rapid and the amount of extravasated blood large, the denudation Fig. 9 —Section through mucosa of human uterus showing sub-epithelial hematomata *. (From Sellheim.) is comparatively extensive ; but if the hemorrhage is slight, and takes place chiefly by diapedesis, then the loss of tissue is practically nz. Lipes adds that in none of the cases examined by him were there enough epithelial cells in the discharge to suggest a complete loss of epithelium. Galabin states that in addition to uterine and vaginal epithelial cells being found in the discharge, shreds of tissue can frequently be detected showing the structure of uterine stroma. Heape® ' Minot, loc. cit. * Martin, “ The Physiology of Ovulation, Menstruation, and Fertilisation,” Hirst’s Obstetrics, vol. i. 1888. “® Heape, “The Menstruation and Ovulation of Monkeys and the Human Female,” Trans. Obstet. Soc., vol. xl., 1899. CHANGES IN THE NON-PREGNANT UTERUS 87 also has detected stroma tissue in the menstrual discharge of the human female. This clearly shows that destruction is not always confined to the epithelial layer. The blood poured out into the uterine cavity, and thence to the exterior, does not usually clot, unless the amount be excessive. This is due to the fact that the blood is considerably diluted with mucus derived from the uterine glands. The glandular activity is accompanied by an emigration of leucocytes which, according to Blair Bell,1 are engaged in secreting calcium com- pounds (see p. 69). The relative proportion of blood to mucus as Gis O ge ZC LE Fig. 10.—Section through mucosa of menstruating human uterus showing bleeding into the cavity *. (From Sellheim.) in the fluid is usually said to increase from the commencement of menstruation, until the discharge reaches its maximum, after which it goes on diminishing until the flow ceases. The Stage of Repair.—This corresponds to Gebhard’s period of post-menstrual involution. After the flow has ceased, or even a short time before it has quite ceased, regeneration of the uterine mucosa begins. According to Westphalen,’ profuse karyokinesis takes place in the tissue of the mucosa, which once more increases in thickness, whereas Heape, as will be seen later, describes a shrinkage as occurring in the regenerative 1 Blair Bell, ‘‘ Menstruation and its Relation to the Calcium Metabolism,” Proc. Roy. Soc. Med., July 1908. ? Westphalen, loc. cit. 88 THE PHYSIOLOGY OF REPRODUCTION stage in monkeys. Wyder,! who believed in the partial destruc- tion of the uterine stroma, concluded that this was restored by a hyperplasia of cells in the interglandular tissue of the deeper layers of the mucous membrane, and that the lost epl- thelium was regenerated from the epithelium of the glands. Similar views have been held by other writers. Those authorities who hold that the destruction is practi- cally confined to the epithelium believe that the lost cells are ¥rq. 11.—Section through the human uterus during the recuperation stage. (From Sellheim.) replaced by multiplication of the remaining cells. Mandl, for example, describes various stages of mitotic division in the cells of the epithelium at this stage. But this author is of opinion that the epithelia of the glands assist in the process of renewal. Gebhard describes the epithelium, which had been lifted from its bed by the blood in the hematomata, as sinking back to its former position, such cells as were lost being regenerated by multiplication of the others. The restoration of the mucosa is accompanied by a decrease 1 Whitridge Williams, Joc. cit. CHANGES IN THE NON-PREGNANT UTERUS 89 in the size of the blood-vessels, and an absorption of the blood which remains extravasated in the stroma. As to how the blood is absorbed has not been determined in the human female. This is a question which will be discussed in considering the regeneration stage in monkeys and in the lower Mammals. It is stated that new capillaries are formed after the close of the destruction. The average length of the normal menstrual cycle, as already mentioned, is twenty-eight days. Of these about five are occupied by the pre-menstrual swelling, four by menstruation, and probably about seven by the regeneration process, leaving not more than twelve days for the period of quiescence.! There can be no doubt, however, that the length of the respective stages must vary according to the extent of the destruction and the amount of tissue which it is necessary to replace. According to Westphalen,? the regenerative process may last for as long as eighteen days, or until the commencement of the succeeding pre-menstrual swelling.® Tue CycLte In Monkeys The histology of the menstrual cycle in Semnopithecus entellus and Macacus rhesus has been very fully studied by Heape.t Previously to Heape’s work, Bland Sutton ® had paid some attention to the histology of the menstrual process in Macacus rhesus, but without entering into great detail. More recently van Herwerden ® has given an account of the cyclical changes of the uterus in Cercocebus cynomolgus. ' Whitridge Williams, loc. cit. ° Westphalen, loc. cit. 5 For further references to the subject of menstruation in the human female the following authors may be consulted: Steinhaus, ‘‘ Menstruation und Ovulation,” Leipzig, 1890; Heape, Phil. Trans. B., vols. clxxxv. and clxxxviii., 1894 and 1897; Gebhard, ‘‘ Die Menstruation,” Veit’s Handbuch der Gynik., vol. iii., 1898. For an account of the various pathological changes which are known to occur in the human uterus, see Macgregor, A Contribution to the Pathology of the Endometrium, Edinburgh, 1905. 4 Heape, loc. cit. » Bland Sutton, “Menstruation in Monkeys,” Brit. Gynee. Jour., vol. ii., 1880. 6 Van Herwerden, “Bijdrage tot de Kennis von den Menstrueelen Cyclus,” Tijdschrift d. Ned. Dierk. Vereen., vol. x., 1906. 90 THE PHYSIOLOGY OF REPRODUCTION Heape has divided the cycle into the following four periods and eight stages :— (~ A. Period of Rest. Stage I. The Resting Stage. : : {35 Il. The Growth of Stroma. | Bi Rertadial Saroyrih lL; III. The Increase of Vessels. | 9 IV. The Breaking Down of : Vessels, 5 V. The Formation of Lacune. C. Period of Degeneration. VII. The Formation of the 55 VI. The Rupture of Lacune. Menstrual Clot. L D. Period of Recuperation. ,, WIII. The Recuperation Stage. Heape’s account may now be briefly summarised. I. The Resting Stage—The epithelial layer of the uterine mucosa consists of a single row of cubical or columnar cells. The outer border is clearly defined, but on the inner side the protoplasm of the epithelium is continuous with that of the sub-epithelial mucosa or stroma tissue. The surface epithelium is continuous with that of the glands, but the latter rest on a basement-membrane which separates them from the inter- glandular stroma. The stroma contains round nuclei embedded in a network of protoplasm, with fine, delicate processes in which granules may be seen. In Semnopithecus fibrils running fan-wise were observed in the deeper parts of the stroma, but these were not seen in Macacus. Multiplication of cells was not noticed at this stage, either in the epithelium or in the stroma. The vessels in the mucosa are small. A few arteries occur in the deeper portion, but only thin-walled capillaries in the more superficial part ; the latter, however, are fairly numerous. II. The Growth of Stroma.—The nuclei of the more superficial part of the stroma undergo a great increase, the division being amitotic in character, at least so far as could be seen. As a consequence the mucosa in its upper third becomes considerably swelled (hyperplasia), but in the deeper portion there is no change in the tissue. Owing to the effects of pressure the nuclei become elongated or fusiform. Division occurs either by fragmentation or by the nucleus simply splitting into two. The growth in the upper part of the stroma is associated with an increase in the size of the blood-vessels in the deeper part. CHANGES IN THE NON-PREGNANT UTERUS 91 The superficial epithelium, and also the epithelium of the glands, remain practically unchanged. TI. The Increase of Vessels.—Owing to the continued swelling of the stroma the nuclei in the superficial portion are packed less densely, the lining epithelium becoming simultaneously stretched. The glands tend to become wider. Hyperplasia of the vessels occurs below the epithelium, the surface of the mucosa appearing flushed. At the same time leucocytes become more numerous within the vessels. There is no change in the constitution of the deeper portion of the stroma. IV. The Breaking Down of Vessels——The whole of the mucosa, including the epithelium, stroma, and vessel-walls, under- . goes pronounced hypertrophy, and in the superficial region the congested capillaries break down and their contents become extravasated through the stroma. Fatty degeneration was not observed by Heape, who is disposed to think that the degeneration is of the amyloid or hyaline type. The leucocytes were noticed to be increased decidedly in number, but they were only de- tected outside of the blood-vessels in the superficial stroma, where the vessel-walls had given way. Diapedesis of corpuscles was nowhere observed. The nuclei of the stroma become larger and more rounded, and exhibit a nuclear network and deeply staining nucleoli. The glands increase in size, becoming longer ; their lumina are wide, and an active process of secretion is taking place. Superficially the mucosa appears very markedly flushed. V. The Formation of Lacune.—aAt this stage the extravasated blood corpuscles collect in lacune which are situated in the loose stroma tissue which lies below the epithelium. These lacune are clearly identical with the sub-epithelial hematomata of Gebhard. The dense stroma tissue, characteristic of an early stage, still persists in places, but is now of rare occurrence. All the superficial vessels have by this time broken down, but those in the deeper tissue remain intact. Neither leucocytes nor red corpuscles are to be found free in the deeper tissue of the stroma. The condition of the glands is the same as in the preceding stage, but there is evidence of degenerative changes in certain of the stroma nuclei, and also in some of the free leucocytes. VI. The Rupture of Lacune.—The superficial stroma and 92 THE PHYSIOLOGY OF REPRODUCTION epithelium shrivel up at this stage, and, as a consequence, the blood contained in the lacune is poured into the uterine cavity. The lacune are very often close to the glands, so that when a lacuna ruptures, a whole gland may be carried away in the blood stream. The lacune have no regular inner wall, but in some places the processes of the stroma were observed to combine together to form a kind of wall which appeared to resist the further encroachment of blood corpuscles in the stroma tissue. Leucocytes are very numerous (usually in the close neighbour- hood of the ruptured vessels), some of them being described as mononuclear, and some as having two, three, or four nuclei (products of division). The proportion of leucocytes to red corpuscles was found to be 2 per cent. of the former to 98 per cent. of the latter in unruptured vessels full of blood, while in ruptured vessels, from which blood had escaped, the percentage of leucocytes was noted to be as high as 18:75. Heape does not state, however, that basophil or eosinophil cells occur, such as have been described in the uterus of the dog at a corresponding stage in the cycle. Degenerative changes were noted in many of the epithelial cells, and also in some of the stroma cells, certain of which were seen scattered beneath the remains of the epithelial lming. The stroma below the lacune was observed to contain normal as well as shrivelled tissue, but the deeper parts’ appeared to undergo very little alteration. VII. The Formation of the Menstrual Clot.—At this stage Heape describes “‘ a severe, devastating, periodic action.” The entire superficial epithelium, portions of the glands or even a whole gland, and a part of the stroma, with broken-down blood- vessels and corpuscles, are torn bodily away, “ leaving behind a ragged wreck of tissue, torn glands, ruptured vessels, jagged edges of stroma, and masses of blood corpuscles, which it would seem hardly possible to heal satisfactorily without the aid of surgical treatment.” Heape is in no doubt as to the extent of the denudation, differing thus from those writers referred to above, who believe that the destructive process in the human female does not extend beyond certain portions of the superficial epithelium. The cast-cff mucous membrane is termed by Heape the mucosa menstrualis. The deeper tissue undergoes no change, the blood-vessels therein being still possessed of com- CHANGES IN THE NON-PREGNANT UTERUS 93 plete walls, but these are larger and more numerous than before. There is no extravasated blood in this region. The proportion of leucocytes in the vessels was observed to be about three per cent. of the corpuscles present, while those on the surface were estimated to comprise about 2°5 per cent. of the total number of corpuscles. Heape ascribes this comparative equalisa- tion to the fact that the ruptured vessels to which the leucocytes adhered in the earlier stages, are themselves cast off, and their contents mingled with the extravasated blood. The supply of leucocytes in the vessels, however, is well maintained. The menstrual discharge is described as consisting of (1) a viscid, stringy, opaque white fluid derived partly from the blood serum and partly from the secretion of the uterine glands, containing numerous small granules which have their origin in the broken-down plasmodium of the uterine mucosa ; (2) red blood corpuscles; (3) masses of stroma tissue and epithelium, both from the lining of the uterine cavity and from the glands, and squamous epithelium from the vagina; and (4) leucocytes together with isolated nuclei of broken-down epithelial and stroma cells. The menstrual clot is composed very similarly, containing a mass of corpuscles together with fragments of uterine tissue. It is expelled at the end of men- struation after remaining some time in the uterine cavity. VIII. The Recuperation Stage—The changes which occur during this stage are described by Heape as consisting of five processes, as follows :— (1) The re-formation of the epithelium. (2) The reduction of the blood supply. (83) The formation of new and mecuperstion of old blood-vessels. (4) The changes which take place in the stroma. (5) The behaviour of the leucocytes. (1) The new epithelium is formed, according to Heape, partly from the epithelium of the glands, but partly from the underlying stroma. The latter is described as a tissue of very primitive characteristics, and the re-formation of the epithelium is re- garded as a specialisation of cells belonging to a layer which, in the embryo, gave rise in the same way to similar epithelial 94 THE PHYSIOLOGY OF REPRODUCTION cells (that is to say, on this view, what takes place after men- struation is merely a repetition of a process which occurs in the embryo). The new epithelial cells, which are at first flattened, gradually become cubical. Heape’s account is thus completely at variance with the descriptions of those authors who hold that in: the human female the epithelium is renewed entirely from the torn edges of the old epithelium. MHeape states that the process of re-formation commences before the expulsion of the menstrual clot, and even before the cessation of the flow of blood into the uterine cavity. (2) There is still an escape of blood as long as the menstrual clot lies within the uterine cavity, but after its expulsion the flow is checked. Heape suggests that the contractions of the uterus which serve to expel the clot may assist in stopping the escape of blood. Probably, also, the growth of the new epithelium helps to stop the hemorrhage. After the growth of the new vessels the flow of blood entirely ceases. (3) At the commencement of this stage many of the ex- travasated blood corpuscles are seen lying in intercellular spaces in the stroma. These corpuscles, according to Heape, are drawn again into the circulatory system by becoming enclosed within newly formed capillaries. Heape describes the process as follows: “‘ The protoplasm of the cells bounding these [blood- containing] spaces flattens out, the nuclei of the cells becoming also flattened and elongated, and numerous fine capillary vessels are thus formed, continuous with the deeper parts of the mucosa with large pre-existing capillaries, and so with the circulatory system. “These fine capillaries exist only temporarily. When the blood corpuscles are again drawn into the circulation, and when the mucosa has shrunk again into its resting condition, the fine capillaries are no longer seen; but during the time in which the reclaiming process goes on they exist in very large numbers.” It should be added that this description of the formation of vessels in the uterine mucosa of Semnopithecus and Macacus is in opposition to the usual view regarding the growth of new vessels, which are ordinarily supposed to be only capable of developing as off-shoots from pre-existing ones. \" Heape also describes a recuperation of the old blood-vessels. CHANGES IN THE NON-PREGNANT UTERUS 95 The nuclei which were hypertrophied become reduced in size, and the swollen protoplasm becomes contracted. In this way the vessels are reduced once more to their normal size. (4) The changes in the cells of the stroma are described as being similar to those in the cells which form the walls of the hypertrophied vessels, the large nuclei and swollen protoplasm giving place to compact nuclei and fine thread-like processes of protoplasm. The multiplication of the stroma nuclei still goes on to a limited extent, but is not nearly so frequent. The tissue is very open during the early stages of recuperation, but gradually becomes drawn together. As a result the whole stroma is reduced considerably in bulk. (5) The extravasated leucocytes, like the red corpuscles, are said to be returned into the circulatory system by means of the newly formed vessels. Heape says that isolated wandering leucocytes are very rare indeed at this stage, and he makes no mention of basophil or eosinophil cells, such as have recently been described in the uterus of the dog. The actual proportion of leucocytes within the vessels is said to be greater than at any other period in the cycle, as many as fifty per cent. having been observed in certain of the vessels. With regard to the function of the leucocytes Heape: suggests that in cases of suppressed menstruation they might play an important part, but that in normal menstruation “they seem to have been induced to appear on the scene in such numbers, unnecessarily ; the casting away of the menstrual mucosa, together with all noxious material, and the clean healing of the wounded surface, rendering their protective presence unnecessary.” At the same time Heape points out that the presence of the leucocytes in the vessels is evidence of the existence therein of a noxious substance which is not present in the surrounding tissue, and he supposes that this irritant may be got rid of completely in the flow of blood. Menstruation in Macacus has also been studied by Bland Sutton,! according to whom the sanguineous discharge is slight. Sutton found no evidence of destruction of the uterine mucosa, not even of the epithelium, but the uterus was distinctly con- gested, and there was an escape of blood into the cavity. It 1 Bland Sutton, ‘‘ Menstruation in Monkeys,” Brit. Gynec. Jour., vol. ii. 1880. 96 THE PHYSIOLOGY OF REPRODUCTION should be noted, however, that Sutton’s investigation was upon monkeys in this country, whereas Heape’s observations relate to Indian animals, and that in Pocock’s experience,’ menstruation does not, as a rule, occur in Macacus rhesus in the Zoological Gardens. But it would appear also from this author’s observa- tions that the severity of the menstrual process in monkeys may vary within as wide limits as it is said to do in the human female. The changes which occur throughout the menstrual cycle in Cercocebus cynomolgus have been studied in some detail by van Herwerden,? who begins by classifying the material in two groups. In group A are included those animals in which, at the time of killing, the uterus was relatively small and menstrua- tion was correspondingly slight. In group B are placed those monkeys which, on being killed, showed comparatively large well-developed uteri, and in which the menstrual process was characterised by some degree of severity. Van Herwerden is of opinion that the individuals included in the first category were animals killed during the non-breeding season, while those be- longing to group B were specimens killed at the breeding season, when the generative organs were in a state of greater activity. The complete menstrual cycle in Cercocebus is divided into the following periods and stages :— I. Inter-menstrual period. ; 1. Increase of superficial stroma elements, Tl Fre-menstraal period © 1, siicht swelling of mucosa, 1. Increasing hyperemia. 2, Rupture of capillaries. 3. Formation of lacune. TUL, ‘Metsteaal pared _ | 4. Degeneration of epithelium and stroma elements. 5. Rupture of lacune and tearing off of degenerate tissue. 6. Beginning of regeneration. IV. Post-menstrual period. Tt will be seen from this scheme of classification that the changes recorded by van Herwerden as occurring in the menstrual cycle of Cercocebus are very similar to those described 1 Pocock, “ Notes upon Menstruation,” &c¢., Proc. Zool. Soc., 1906, 2? Van Herwerden, loc. cit. CHANGES IN THE NON-PREGNANT UTERUS 97 by Heape in Semnopithecus and Macacus. Both authors agree in stating that the superficial portion of the mucosa is denuded during the destruction period, differing thus from Bland Sutton and those writers on human menstruation (referred to above) who maintain that the denudation only involves certain portions of the superficial epithelium. Van Herwerden states that the menstrual changes are less marked in the reyion of the fundus uteri. The chief differences between van Herwerden’s account and that of Heape are as follows :— According to the former the stroma cells increase mitotically, and not by simple division or fragmentation as supposed by Heape. The epithelium is described as being renewed from the glandular epithelium in Cercocebus, and not in part from the subjacent stroma, as it is said to do in Semnopithecus and Macacus. Van Herwerden says that, so far as was observed, the walls of new vessels were not formed during recuperation from stroma, cells, as has been described by Heape. Van Herwerden states that Cercocebus may experience cestrus after menstruation is over. Presumably, therefore, cestrus occurs contemporaneously with the recuperation process in the uterus. Tue CycLe IN Lemurs As already mentioned, Stratz! has called attention to the procestrous changes which take place in the uterus of Tarsius spectrum, but the process has been studied more closely by van Herwerden.2 This author describes the following changes :— (1) There is a swelling of the glands which is closely followed by mitotic division among a large number of the epithelial cells. Hyperamia then sets in; but the congestion is localised to certain places, and is not diffused over the entire mucous mem- brane. Afterwards blood becomes extravasated in the stroma tissue, the corpuscles being aggregated in the more superficial parts—that is to say, in the vicinity of the epithelium. It was 1 Stratz, Der geschlechtsreife Satiycthiereierstock, Haag, 1898. 2 Van Herwerden, loc. cit. G 98 THE PHYSIOLOGY OF REPRODUCTION noticed that certain corpuscles were taken up by leucocytes, and transported tothe uterine cavity. Others were carried along in close association with epithelial cells, both from the superficial layer and from the glands. It would appear that destruction of the epithelium does not occur to any extent, and that the bleeding is not severe. This would seem to constitute the chief difference between the procestrous changes in Tarsius, and the corresponding changes in monkeys. The periodicity of the sexual phenomena in Tarsius spectrum has already been referred to. THE CycLe IN INSECTIVORA The changes which occur in the internal generative organs during the cycle in Tupara javanica, and in the aberrant In- sectivore, Galeopithecus volans, have received some slight attention. Stratz+ has described the existence of a blood-clot and a “menstrual” flow in Tupaia, and records the presence of desquamated epithelial cells in the blood-clot. Van Herwerden,? however, states that the individuals which Stratz examined were in the puerperal stage, and that, although Tupaza can ex- perience “heat” and become pregnant at this time, trust- worthy conclusions regarding the severity of the procestrous changes cannot be drawn from such specimens. That there was considerable bleeding van Herwerden admits. Nothing is known about the periodicity of the changes in Tupaia. In Galeopithecus van Herwerden describes uterine hyper- emia during the procestrum. In the superficial mucosa numerous highly congested capillaries were noticed. In the later stages blood was found extravasated in the stroma, some of it being collected in spaces which were probably comparable to the sub-epithelial heematomata described by Gebhard in the menstruating human female. In the superficial epithelium spots were detected where a few of the cells had been removed. Bleeding did not appear to be localised to any particular area in the uterus. 1 Stratz, loc. cit. 2 Van Herwerden, loc. cit. CHANGES IN THE NON-PREGNANT UTERUS 99 Van Herwerden is certain that the changes observed could not be ascribed to a puerperal condition, as in the case of Tupaia, but must have been the result of a normal procestrum. The periodicity of the changes is unknown. Tue CYCLE IN CARNIVORES The histological changes in the non-pregnant uterus have been studied in the dog! and in the ferret.2 The periods into which the uterine cycle is divided are identical with those adopted by Heape for the monkey :— (1) Period of rest . ; ; : Ancestrum. (2) Period of growth and congestion (3) Period of destruction ‘< (4) Period of recuperation ‘ Procestrum. (Estrus. j Metcestrum. It is seen that cestrus, or the time of desire, begins normally about the close of the period of destruction. With the ferret it may be very prolonged, extending until the end of the recuperation period, or even considerably beyond it. Conse- quently there may be no metcestrum (strictly speaking) with the ferret, since the period during which copulation can occur is liable to persist until the uterus has reached the resting stage. (1) Period of Rest.—The uterine mucosa in both the dog and the ferret is bounded at the surface by an epithelium consisting of a single row of columnar or cubical cells, and is continuous with that of the glands. The stroma is a connective tissue, containing numerous fusiform cells. Blood-vessels of small size are fairly common. Leucocytes do not appear to occur in the mucosa outside of the vessels. Pigment is not present at this stage, at least ordinarily. (2) Period of Growth and Congestion—The mucosa at this period becomes slightly thickened, and tends to be more compact. This is effected by cell divisions, but mitoses have not been * Marshall, and Jolly, “‘ Contributions to the Physiology of Mammalian Reproduction: Part I. The (&strous Cycle in the Dog,” Phil. Trans., B, vol. excviii., 1905. ? Marshall, «‘ The @strous Cycle in the Common Ferret,” Quar. Jour. Mier. Sei. vol. xlviii., 1904. 100 THE PHYSIOLOGY OF REPRODUCTION observed. Retterer,1 who has contributed a short account of the changes in the bitch’s uterus, describes the mucosa as growing to three or four times its normal thickness, but this observation has not been confirmed. The growth is accompanied by en- largement and congestion of the capillaries, which at the, same time become more numerous.? The vessels in the surrounding muscular tissue also tend to enlarge. The epithelium undergoes Fie. 12.—Section through procestrous uterine mucosa of dog, showing congested vessels between the glands. (From Marshall and Jolly.) no material change so far as seen. In the case of the ferret the uterine cavity is described as becoming markedly reduced in size, while the glands are stated to undergo an appreciable swelling accompanied by an increased secretory activity. (3) Period of Destruction.—The walls of the stretched blood- vessels break down, and red corpuscles, accompanied by 1 Retterer, ‘Sur les Modifications de la Muquenuse Utérine 2 Epoque du Rut,” C. R. de la Soe, de Biol., vol. iv , 1892. 2 Cf. Retterer, loc. cit.; also Keiffer, ‘La Formation Glandulaire de PUterus,” Annales de la Soc. Medico-Chirurg. de Brabant. 1899; and Bonnet, ‘* Beitriige zur Embryologie des Hundes,” Anat. Hefte, vol. xx., 1902. CHANGES IN THE NON-PREGNANT UTERUS 101 leucocytes, become extravasated throughout the stroma. Some of the vessels, however, remain intact. The breaking down of vessels appears to occur fairly uniformly throughout the stroma instead of being restricted to any particular portion. The extravasated blood for the most part collects immediately below the superficial epithelium, but it is not aggregated in large lacuna-like spaces, such as Heape has described in the monkey. Fic. 13.—Section through procestrous uterine mucosa of dog (From Marshall and Jolly.) ex, bl., Extravasated blood corpuscles ; polym., polymorph ; sec., cells probably indicating secretory activity. : These “ sub-epithelial hamatomata ” have beén noticed espe- cially in the procestrous bitch. The walls of the vessels in the muscular layers do not give way. Eventually the extravasated blood corpuscles (or, at any rate, the majority of them) make their way into the cavity of the uterus, and thence to the vagina, where external bleeding is observed. This is especially noticeable in the case of the bitch, with which, as already mentioned, external bleeding may last for as long as ten days. The bleeding is accompanied by an increase in the mucous secretion. At about the same stage 102 THE PHYSIOLOGY OF REPRODUCTION goblet-shaped cells are frequently observable in the glandular epithelium, and it is suggested that these are in some way con- nected with the secretory activity of the glands. It is probable that destruction of the superficial epithelium occurs normally to a greater or less extent both in the bitch and in the ferret. Epithelial cells have been observed lying free in the uterine cavity, while, in some sections, places have been noticed where the stroma presented a raw edge, having been stripped of its epithelial covering. In the bitch a layer of flattened stroma cells may sometimes be seen in close attach- ment to the epithelium during the process of denudation. In the ferret it would appear that the destruction may occasionally be severer, but it is thought that this is exceptional. It has been pointed out, however, that a comparison between the thickness of the uterine wall (and conversely the size of the uterine cavity) in ferrets lailled at the commencement of the recuperation period and during the period of rest, is very sug- gestive of a definite removal of stroma as well as of epithelium in the process of destruction. Polymorph leucocytes have been observed in abundance at this stage in the bitch’s uterus, both in the stroma and also in the cavity, and large mononuclear leucocytes (hyaline cor- puscles), containing pigment derived doubtless from the ex- travasated blood, have also been seen to occur. Large cells, with faintly staining nuclei of very considerable size and con- spicuous nucleoli, have been noticed at rare intervals lying in spaces in the stroma tissue of the procestrous bitch. The origin and significance of these cells are not known. There is no blood-clot formed in the uterus, either in the bitch or in the ferret. (4) Period of Recuperation.—The new epithelium in the bitch is first seen as a layer of flattened cells which bear a resemblance to the cells of the stroma. Its manner of formation is an open question, but it would seem probable that it is derived mainly, if not entirely, from the remaining cells of the old epithelium, or from those of the glands. It is just possible, however, that in certain places the epithelium may be renewed from the underlying stroma tissue, as is said by Heape (but not by van Herwerden) to be the case in the monkey. CHANGES IN THE NON-PREGNANT UTERUS 103 During the earlier stages of recuperation a variable, and often a large, number of red blood corpuscles remain scattered in the stroma, chiefly in the part nearest the surface. At a later stage extravasated corpuscles are no longer seen in any quantity, while numerous new vessels appear to have been formed, presumably from pre-existing vessels. Polymorphs are no longer common in the bitch’s mucosa tissue, but leucocytes of other varieties are a characteristic Oo 4.3 7 eB 2Ole = bl. v. pig. Fie. 14.—Section through edge of mucosa of dog during an early stage of recuperation. (From Marshall and Jolly.) bl. v., blood-vessel ; ep., epithelium in process of renewal ; piy., pigment ; polym., polymorph. feature. The following kinds have been observed: (1) Coarsely granular eosinophil cells, with lobed nuclei. These occur in the blood in cases of trichinosis, bronchial asthma, sarcoma, osteomalacia, skin diseases, and other affections, but are rare under ordinary conditions. (2) Basophil cells, with simple nuclei and containing coarse granules, but never any pigment. The number of granules varies, and in some of the cells is very small. These basophil cells are evidently similar to the mast cells of Ehrlich, and the plasma cells of Unna. Mast 104 ‘THE PHYSIOLOGY OF REPRODUCTION cells are said to be often found in inflammatory areas, and are: described as occurring in the stroma tissue of tumours in asso- ciation with plasma cells, and also in the peripheral circulation in cases of lymphatic and myeloid leucemia. They are especially numerous during the recuperation period of the bitch’s uterus, and it is suggested that they must in some unknown way be functionally connected with that process. Fig. 15.—Section through portion of mucosa of dog during the recupera- tion period, (From Marshall and Jolly.) bas., basophil cell; eos., eosinophil cell ; mon., mononuclear leucocyte ; polym., polymorphs ; str., stroma cell, (3) Large mononuclear leucocytes (hyaline corpuscles or macro- cytes), containing blood-pigment which gives the Prussian-blue reaction. Since pigment formation and ingestion by leucocytes are of frequent occurrence in the bitch’s uterus at about this stage, it is probable that this is the fate of the great majority of the extravasated red corpuscles. It is possible, however, as suggested in the paper from which this account is taken, that a relatively small proportion may make their way CHANGES IN THE NON-PREGNANT UTERUS 105 into the lymphatics, and so re-enter the circulation. Pigment formation has not been observed in the ferret. At a late stage in recuperation the stroma tissue tends to become denser, and also to increase in thickness (ferret), until the whole uterus once more acquires its normal condition. If copulation has taken place, spermatozoa in great numbers Fic. 16.—Section through mucosa of dog during a late stage of recupera- tion. (From Marshall and Jolly.) bl. v., blood-vessel; sp., spermatozoa in cavity of gland. may be observed in the deeper portions of the uterine glands, as well as along the edges of the uterine cavity. Tue Cycitr in Ropents Comparatively little attention has been paid to the uterine changes in Rodents. In the rabbit it has been noticed that the uterus is swollen and congested during “heat,” and the same observation has been made in the marmot 106 THE PHYSIOLOGY OF REPRODUCTION (Spermophilus citillus).1_ Lataste? has described procestrous growth and congestion in the uterus of several .Muride, and this is stated to be followed by a sanguineous dis- charge from the original opening. Lataste has also described desquamation of the uterine epithelium, but he appears to regard this process as taking place independently of “ heat.” More recently Konigstein * has recorded cyclical changes in Fic. 17.—Section through portion of procestrous uterine mucosa of rabbit showing glandular activity. (From Blair Bell, in Proc. Roy. Soc. Medicine.) several Rodents (rat, guinea-pig, &c.), and has described procestrous desquamation of the uterine epithelium, followed by recuperation. The degenerative changes are accompanied ' Rejsek, ‘‘ Anheftung (Implantation) des Sdugethieres an die Uteruswand, insbesondere des Hies von Spermophilus citillus,” Arch. f. Mikr. Anat., vol. lxiii., 1904. * Lataste, Recherches de Zoéthique sur les Mammiferes de Uordre des Rongeurs, Bordeaux, 1887. * Konigstein, ‘* Die Verinderungen der Genitalschleimhaut wahrend der Graviditaét und Brunst bei einigen Nagern,” Pfliiger’s Arch., vol. cxix., 1907. CHANGES IN THE NON-PREGNANT UTERUS 107 by a secretion of mucus, and there is a marked leucocytosis over the entire generative tract. Desquamation of epithelium also occurs in the vagina. Furthermore, emigration of leucocytes between the epithelium of the glands, accompanied by great glandular activity, has been observed by Blair Bell! in the procestrous uterus of the rabbit. THE CycLe IN UNGULATES The uterine changes have been worked out most fully in the case of the sheep.2. They relate chiefly to the blood-vessels, and are grouped according to four periods as in the case of the monkey, the dog, and the ferret, referred to above. (1) Period of Rest.—The histological characters of the uterus during this period are those of an organ In a state of quiescence. Protoplasmic processes can be seen passing from certain of the stroma nuclei, but these, though denser in some places than in others, show little evidence of division. Dark brown or black pigment may be present in considerable quantities, especially in the region subjacent to the epithelium, both in the cotyledonary papille and (more frequently) between them and round their bases. Such pigment has not been observed in yearling sheep (i.e. in sheep less than a year old); neither does it appear to occur, as a rule, during the ancestrum, but only during the dicestrous interval. (2) Period of Growth—The nuclei in the stroma multiply, and the mucosa increases slightly in thickness. The epithelium, however, appears to remain unaffected. The blood-vessels in- crease both in size and number, producing uterine congestion. These changes occur both in the cotyledonary papille and in the intervening tissue around the bases of the papille. (3) Period of Destruction.—The congestion is followed in most cases by the breaking down of some of the vessels. Very fre- quently the first extravasation takes place from vessels situated immediately below certain parts of the stroma where the nuclei are most thickly distributed. Leucocytes are extravasated ! Blair Bell, loc. cit. ? Marshall, ‘The Cistrous Cycle and the Formation of the Corpus Luteum in the Sheep,” Phil. Trans., B., vol. cxcvi., 1903. 108 THE PHYSIOLOGY OF REPRODUCTION along with the red corpuscles, but there is no evidence of the existence of wandering cells apart from those which are derived apparently from the broken-down vessels. The blood tends to collect below the epithelium. Bleeding into the uterine cavity may occur, but is not invariable. A few epithelial cells are sometimes torn off (presumably in places where blood is poured out into the cavity), but destruction even to this extent does not necessarily take place. Denudation of the stroma has never been observed. It would seem that the severity of the pro- cestrous process tends to diminish with each successive dicestrous cycle in the breeding season, and that sometimes in a late procestrum the period of destruction is never reached, the congested vessels subsiding without undergoing rupture. Bleed- ing, when it does occur, appears to be more frequent in the cotyledonary papillae than between them, and is commoner in the large papille than in the smaller ones. Kazzander + appears to have been the first to detect ex- travasated blood in the sheep’s mucosa. Subsequently Bonnet ? has noted uterine bleeding in various Ruminants, as well as in the mare and sow, and Kolster? has made similar observations (cf. also Emrys-Roberts, see p. 47). Ewart also has described procestrous extravasation and the presence of hematoidin crystals in the uterus of the mare. Glandular activity during heat was also noted.* (4) Pertod of recuperation.—The sheep’s procestrum may be said to end with the period of destruction, the entire process probably lasting for not longer than one or two days, its exact duration depending upon its severity. (Estrus itself, which occurs during the beginning of the period of recuperation, some- times occupies only a few hours. In those places where bleeding into the cavity took place in the preceding period the epithelium is renewed, apparently 1 Kazzander, ‘“ Uber die Pigmentation der Uterinschleimhaut des Schafes,” Arch. f. Mikr, Anat., vol. xxxvi., 1890. * Bonnet, article in Ellenberger’s Vergleichende Physiologie des Hausstéuge- thiere, vol. ii., Berlin, 1892. Cf. also Ellenberger's article in same volume. * Kolster, “ Weitere Beitrige zur Kenntniss der Embryotrophe bei Indeci- dunten,” Anat. Hefte, vol. xx., 1902. 4 Ewart, “The Development of the Horse,” Quar. Jour. Micr. Science, (not yet published). CHANGES IN THE NON-PREGNANT UTERUS 109 from the edges of the adjoining epithelium which had not suffered destruction. In this way the re-formation of the epithelium is sufficiently accounted for, since, as already re- marked, only a very inconsiderable number of cells is removed during the sheep’s procestrum. Congestion of the stroma gradually diminishes, and the Fig. 18.—Section through portion of uterine mucosa of sheep showing black pigment (pig.) formed from extravasated blood. mucosa as a whole undergoes a slight shrinkage. It would appear that a few new capillaries are formed, but there is no evidence that any of the extravasated corpuscles are gathered up afresh into the circulatory system. On the other hand, there are ample indications that all those corpuscles which remain in the tissue become transformed into pigment, as originally concluded by Bonnet. According to this investigator, the extravasation takes place in the deeper mucosa, and the 1 Bonnet, ‘‘ Ueber Melanose der Uterinschleimhaut,” &c., Deutche Zeitsch. f. Thiermedizin, vol. v., 1880, and vol. vii., 1882. “‘ Beitrige zum Embryologie der Wiederkauer,” &c., Arch. f. Anat. u. Phys., Anat. Abth., 1884. 110 THE PHYSIOLOGY OF REPRODUCTION derivatives of the corpuscles are carried in the form of pigment to the more superficial area by wandering cells. Kazzander,1 however, does not admit the agency of leucocytes ; but the most recent observations support Bonnet’s conclusions, excepting that (as previously stated) the extravasation which takes place during the destruction period is in the superficial mucosa rather than in the deeper tissue. Thus, although leucocytes are pro- bably involved in the process of pigment formation, there is no need to assume that they carry the extravasated corpuscles to the region where pigment is most abundant. Sometimes the interior of the uterus appears superficially to be perfectly black with pigment, but in such cases the pigment is, no doubt, de- rived from blood which had been extravasated during a series of procestrous periods, and not merely during the most recent one. Assheton? states that the pigment so formed is subsequently disposed of. A consideration of the facts set forth in this chapter should leave one in no doubt regarding the essential similarity between the menstrual cycle in the Primates, and the cestrous cycle in the lower Mammalia. Those who have denied that there is any correspondence between “heat ”’ and menstruation * have laid stress upon the assertion that whereas “heat” in the lower animals is the time for coition, this act, as a general rule, is not performed during menstruation. But, as was first pointed out by Heape, it is the procestrum alone and not the entire “ heat period ” (a term used generally to include both procestrum and cestrus) which is the physiological homologue of menstruation ; and, moreover, the latter process in many of the Primates is succeeded by a regular post-menstrual cestrus. The physiological identity of the procestrum with menstrua- tion should always be kept in view in considering the cause and nature of the phenomena, since, as will be seen later, many strange errors have been committed, and wrong conclusions 1 Kazzander, loc. cit. ® Assheton, ‘The Morphology of the Ungulate Placenta,’ Phil. Trans. B., vol. excviii., 1906. 3 Beard, in The Span of Gestation and the Cause of Birth (Jena, 1897), says, “very little is required in disproof” of this correspondence. CHANGES IN THE NON-PREGNANT UTERUS 11] arrived at, through failure to realise the unity of the two pro- cesses. It has been shown further that although the changes which occur in the uterus during the cycle present a striking similarity in the various mammalian types in which they have been studied, yet there is a considerable amount of variation in the severity and duration of the procestrous phenomena. The extent of the congestion, and the destruction which usually succeeds it, are greatest, as a rule, in the highest Mammals, and comparatively slight in the Rodentia and Ungulata. The histology of the cycle in the lowest Mammals has never been worked out, but, as already mentioned in the preceding chapter, vaginal bleeding has been noticed in Marsupials. The purpose or meaning of the procestrum, and the factors which contribute to its occurrence, will be considered as fully as the present knowledge of the subject permits, after the changes which take place in the ovaries have been dealt with, in a future chapter of this work. It may be at once stated, however, that most authorities are now agreed that the menstrual process is in some sense a preparation for the attachment of an ovum to the wall of the uterus, but opinions differ as to the precise nature of the preparation. On the other hand, it is evident that the changes involved in menstruation are not absolutely essential, since there are records of pregnancy occurring in individuals who had never experienced menstruation. Moreover, there is evidence that the procestrous discharge may be not only of no utility to the organism, but may even become injurious, as in the more severe cases of menstruation among women. In view of these facts it may be caHed in question whether the procestrous changes in the uterus should not be regarded merely as the result of a wave of disturbance which ushers in the period of desire, and is of the nature of a consequence rather than a purpose. This is in accord with Metchnikoff’s suggestion,' that the catamenia in women is essentially a “ disharmony ” of organisation, which has been brought about as the result of modifications acquired recently in the history of the species. If this is so, a similar explanation must be adopted in the case of 1 Metchnikoff, The Nature of Man, Mitchell’s Translation, London 1903. 112 THE PHYSIOLOGY OF REPRODUCTION those animals which experience an especially severe procestrum. According to such a view as this the phenomena of menstruation must be looked upon as belonging to the borderland of pathology. In this connection the large number of leucocytes which attend the menstrual process, some of them clearly phagocytic in function, is not altogether unsuggestive. CHAPTER IV CHANGES IN THE OVARY—OOGENESIS—GROWTH OF FOL- LICLES—OVULATION—FORMATION OF CORPORA LUTEA AND ATRETIC FOLLICLES—THE SIGNIFICANCE OF THE PROGSTROUS CHANGES IN THE UTERUS “The newest freak of the Fallopian tubes and their fimbriz, and the very latest news from the ovisac and the corpora lutea._—JoHN BRown, Hore Subsecivee. DEVELOPMENT OF OVARY AND OOGENESIS Tur animal egg is a large spheroidal cell consisting of external protoplasm or cytoplasm, a nucleus or germinal vesicle, and a nucleolus or germinal spot.t_ Within the cytoplasm is a mass of . food material or yolk (sometimes known as deutoplasm), the quantity of which varies slightly in different Mammalia, and is very considerable in birds and certain other animals. The unfertilised ovum differs from the male germ-cell or spermatozoén in its devoting itself mainly to the storage of food-substance and accumulation of potential energy, for it is incapable of active movement. The metabolic processes of the ovum, therefore, are almost entirely constructive, while those of the spermatozoon are largely destructive. The function of the ovum is to con- jugate with the spermatozoén, and subsequently, by a lengthy process of cell division, to give rise to a new individual. The mammalian ovary,? or organ in which the ova are pro- duced, is composed of a stroma of fibrous connective tissue, which contains some plain muscular fibres (especially in the neighbourhood of the attachment to the broad ligament) as well as numerous blood-vessels. The surface is lined by a layer of columnar epithelial cells. Within are a number of 1 A centrosome has been described as present in the ova of some animals. For a detailed description of the ovum in different forms see Wilson, The Cell in Development and Inheritance, 2nd Edition. New York, 1900. * See also Stratz, Der geschlechtsreife Sdugethtiereterstock, Haag, 1898. 113 H 114 THE PHYSIOLOGY OF REPRODUCTION vesicles of various sizes, each with an ovum, surrounded by an epithelium. These are called Graafian follicles. Certain other structures, consisting of very large yellow-coloured cells en- closed by a branching network of connective tissue, are also often found. These are the corpora lutea or discharged follicles to be described more fullv later. The stroma contains, further, a varying number of epitheloid interstitial cells. In order to gain a proper understanding of the structural Le oa 7) S ness a WY = = 4 DM, % Yi ye : PG Fic. 19.—Section through ovary of cat. (From Schrén.) 1, Outer surface; 1’, attached border; 2, fibrous central stroma; 3, peri- pheral stroma; 4, blood-vessels; 5, young follicles; 6, 7, 8, 9, and 9/, larger developing follicles; 10, corpus luteum. and functional relations of the different parts of the ovary, it is necessary to make some study of its developmental history. Pfliiger! appears to have been the first to regard the ova? and epithelial cells of the Graafian follicles as originating either in the form of ingrowths simulating tubular glands, or as solid columns of cells from that embryonic layer which Waldeyer afterwards designated the germinal epithelium. The tubular ingrowths had already been noticed by Valentin,? who, however, ' Pfliiger, Ueber die Kiersticke der Stiugethiere und des Menschen, Leipzig, 1867. nits mammalian ovum was discovered by von Baer (Ueber Entwicke- lungsgeschichte der Thiere-Beobachtung und Reflexion, vol. i., Kénigsberg, 1828). In 1861 Gegenbaur showed that the vertebrate ovum was a single cell. 3 Valentin, ‘‘ Ueber die Entwickelung der Follikel in dem Hierstocke der Saugethiere,” Miiller’s Arch,, 1838. CHANGES IN THE OVARY Fic. 20,—Section through ovary of adult dog. (From Waldeyer.) u, germinal epithelium ; 6, remains of egg tubes; c, small follicles ; d, more advanced follicle ; e, discus proligerus and ovum; f, second ovum (a rare occurrence); g, theca externa of follicle; h, theca interna; ‘, membrana granulosa; k, degenerate follicle; 7, blood-vessels; m, tubes of parovarium; y, involuted germinal epithelium; z, transition from germinal to peritoneal epithelium. failed to recognise their connection with the germinal epithelium. Later observers, however, did not confirm the tubular origin of the ovary. To Waldeyer belongs the credit of first recognising the true nature and significance of the process of egg formation, an 116 THE PHYSIOLOGY OF REPRODUCTION account of which was published in his famous monograph Eierstock und Ei. He found that in the chick, on the fourth day of development, the ccelomic epithelium which covers the inner surface of the Wolffian body became differentiated from the tissue surrounding it, the cells being relatively large and cuboidal in shape. A little later he observed that the cells had multiplied to such an extent as to give rise to a distinct elevation. In this way the germinal epithelium was formed, and this marked the site of the future ovary. The mesoblast underlying the germinal epithelium is described as growing upwards among the cells of the latter, and so giving rise to the Obstetrics, Appleton & Co.) G.E., germinal epithelium; 8., stroma. appearance of those germinal ingrowths or “ egg-tubes,” which were described by Pfliiger. The cells of the germinal epithelium are thus divided by mesoblast into clusters of “ egg-nests’’ which contain the pri- mordial ova, as Waldeyer has shown. As a result of this process two zones of tissue are formed in the future ovary. The outer or cortical zone consists of clusters of cells derived from the germinal epithelium, with mesoblastic processes in between them. The inner or medullary zone is composed at first entirely of mesoblast, which gives rise to the vascular tissue and stroma of the ovary. The majority of investigators, including Balfour,? Schafer,’ 1 Waldeyer, Lierstock und Ei, Leipzig, 1870. ? Balfour, “Structure and Development of the Vertebrate Ovary,” Quar. Jour. Micr. Science, vol, xviii., 1878. 3 Schafer, ‘On the Structure of the Immature Ovarian Ovum,” &c., Proc. Roy. Soc., vol. xxx., 1880. CHANGES IN THE OVARY 117 Nagel,! and van Winiwarter,? have followed Waldeyer in suppos- ing that the follicular epithelial cells (which form the innermost layer of the wall of the Graafian follicle) are derived like the ova from the germinal epithelium. Schafer described appearances indicating the possibility of the innermost layer of follicular Fia. 22.—Cortex of pig embryo, showing germinal epithelium, Pfluger’s tubes with ova in various stages of development. (From Williams’ Obstetrics, Appleton & Co.) epithelium being derived from the ovum itself ; but, as he himself pointed out, this view does not involve any morphological ab- surdity if the ova and follicle-cells have a common origin. Balfour described protoplasmic masses of embryonic ova in which the cells appeared to be united together in such a way as to suggest 1 Nagel, ‘«‘ Das menschliche Ei,” Arch. f. Mikr. Anat., vol. xxxi., 1888. 2? Van Winiwarter, ‘“‘ Recherches sur l’Ovogenése,” &c., Arch. de Biol., vol. xvii., 1901, 118. THE PHYSIOLOGY OF REPRODUCTION that one ovum might undergo development at the expense of the others. Somewhat similar appearances have been observed in the bat’s ovary by van Beneden,' who regarded them as syncitia from which both ova and follicular epithelial cells took origin. On the other hand, Kélliker believed that the follicle-cells arose from the epithelium of the Wolffian body, while Foulis,? Schron,? Wendeler,* and Clark,® expressing the opinion that the follicle-cells are derived from the mesoblast, have also dissented from this the more usual view. Clark, in support of his theory, has pointed out that the cells which immediately surround the primordal follicles are often spindle-shaped and similar in ap- pearance to many of the stroma cells, and further, that the primordal ova in the early stages of development are often apparently in direct contact with connective tissue which obviously had been derived from the embryonic mesoblast. Most authorities, however (including the more recent in- vestigators), are of opinion that the follicular epithelial cells, in common with the ova, are derived from the germinal epithelium. Further, Miss Lane-Claypon ® has recently shown that the epithelioid interstitial cells 7 which (in addition to the connective tissue and plain muscle-fibres) are contained in the ovarian stroma in all probability arise also from the original germinal epithelium. The changes involved in the production of ova have been fully investigated by van Winiwarter® in the rabbit. These 1 Van Beneden and Julin, ‘‘ Observations sur la Maturation.” &c., Arch. de Biol., vol. i., 1880. * Foulis, “The Development of the Ova,” &c., Jour. Anat. and Phys. vol. xiii., 1876. * Schrén, “ Beitrag zur Kenntniss der Anatomie und Physiologie des Eierstocks der Siugethiere,”’ Zeitsch, f. wissensch. Zool., vol. xii., 1863. 4 Wendeler, -- Entwickelungsgeschichte und Physiologie der Hiersticke,” Martin’s Die Krankheiten des Eierstocks und Nebeneierstocks, Leipzig. 1899. 5 Clark, “The Origin, Growth, and Fate of the Corpus Luteum,”’ Johns Hopkins Hospital Reports, vol. vii.. 1898. ° Lane-Claypon, ‘‘ On the Origin and Life History of the Interstitial Cells of the Ovary of the Rabbit,” Proc. Roy. Soc., B., vol. lxxvii., 1905. ” For a comparative account of the interstitial substance in the ovaries of various mammals, with references tothe literature, see Fraenkel, ‘“‘ Vergleichende Histologische Untersuchungen iiber das Vorkommen driisiger Formationen im Interstitiellen Eierstocksgewebe,” Arch. f. Gyndk., vol. lxxv., 1906. 8 Van Winiwarter, “Recherches sur l’Ovogenése de l’'Organogenése de l’Ovaire des Mammiféres,” Arch. de Biol., vol. xvii., 1900. CHANGES IN THE OVARY 119 - changes which chiefly concern the chromatin of the nucleus may be summarised as follows :— I. Early changes: (a) Protobroque cells, Variety a—The Fig. 23.—Various stages in the development of the Graafian follicle of the rabbit. (From Schafer.) A, from young rabbit showing Pfliiger’s egg-tubes ; B, C, D, E, successive later stages, nuclei are granular in appearance, the chromatin is arranged irregularly, and there is no reticulum. These are the original 120 THE PHYSIOLOGY OF REPRODUCTION germinal epithelial nuclei. (b) Protobroque cells, Variety b.— The cells belonging to Variety a divide, and give rise to more cells of the same kind, as well as to protobroque cells of the 6 variety. In the latter the nuclei are less granular, and contain Early ovogenetic stage. Leptotenic stage. Fig, 24.—Developing ova from ovary two days before birth. (After Lane-Claypon.) a certain number of fine chromatin filaments. (c) Deutobroque cells.—The protobroque cells of the b variety likewise divide, and give rise to more protobroque cells, similar to themselves, and also to deutobroque cells. These latter are larger in size, ite i Early. Synaptenic stage. Late. Fig. 25.—Developing ova from ovary about one day before birth. (After Lane-Claypon.) and contain’ nuclei with the chromatin arranged in the form of a reticulum. II. Later changes: (a) Leptotenic stage—Certain of the deutobroque nuclei become gradually differentiated, the chromatin during the leptotenic stage passing through a process in which it breaks up into fine filaments; these are distributed CHANGES IN THE OVARY 121 over the nuclear region. (6) Synaptenic stage.—The filaments become congregated together in the form of a lump, or dark mass, heaped up at one side of the nuclear region. (ce) Pachytenic Pachytenic stage. Fic. 26.—Developing ova from ovary one day after birth. (After Lane-Claypon.) stage—The nuclear filaments again become unwound, and spread themselves out over the whole nuclear region ; they are, however, considerably coarser than in the earlier stages. (2) Diplotenic stage.—The chromatin strands split along their Diplotenic nucleus three Dictyate nucleus seven days after birth. days after birth. Fic. 27.—Developing ova. (After Lane-Claypon.) whole length, and the two halves of each strand at first lie in pairs near to one another. (e) Dictyate stage——The split strands pass away from one another, and the chromatin generally becomes distributed once more throughout the nuclear region in the form of a reticulum. 122 'THE PHYSIOLOGY OF REPRODUCTION The nucleus or germinal vesicle of the primordial ovum thus produced then enters upon a long period of rest, the changes involved in odgenesis having been completed.t Some of the deutobroque cells, instead of passing through the transformations above described, rest for a time and subse- quently undergo retrogressive changes, becoming converted, according to Miss Lane-Claypon, either into follicular epithelial cells or into interstitial cells. “ Every cell of the germinal epithelium is probably a potential ovum, relatively very few remaining in the protobroque state, although some may still be seen at the periphery in ovaries of the eighteenth day [of gesta- tion in the rabbit]. Incomparably the greater part pass into the deutobroque state, preparatory, doubtless, to the formation of ova. All cannot become ova, for the other forms of cell are necessary for the maintenance of the ovarian functions; pos- sibly, therefore, only the most robust cells, and those which are most conveniently situated for obtaining nourishment, undergo the ovogenetic changes. This suggestion would seem to be borne out by the fact that many more of the central cells, which ‘are nearer the food supply, undergo ovogenesis, than of the peripheral ones. The rest of the cells which are not able, for one cause or another, to undergo these changes, appear to remain quiescent for a while, until finally they regress, and pass into a condition of subserviency to the needs of those which have become ova. Both follicle-cells and interstitial cells are, however, still potential ova. They have passed through the initial stages, and only need enlargement and nuclear transformations in order to become ova should the appropriate stimulus be given (as will be described below, p- 160). This chance is not given to the follicle-cells. As soon as the follicle begins to grow they multiply rapidly, and 1 For an account of the minute structure of the Mammalian egg, together with a résumé of the literature, see van der Stricht, ‘‘ La Structure de l’@uf des Mammiferes,” Part I., Arch. de Biol., vol. xxi., 1904; Part II., Bull. de Acad. Royale de Médecine de Belgique, Bruxelles, 1905; Part III., Bruxelles, 1909. Fora general account of the egg and the phenomena of odgenesis in the different groups of animals, both Vertebrate and Invertebrate, with a complete bibliography, see Waldeyer, ‘‘ Die Geschlechtszellen,” in Hertwig’s Handbuch der Entwicklungslehre der Wirbeltiere, vol. i., Jena, 1903; also Wilson, The Cell in Development and Inheritance, 2nd Edition, New York, 1900. CHANGES IN THE OVARY 123 probably provide, by their [partial] disintegration, the follicular secretion upon which the ovum feeds and grows.” ! The description given above of the origin of the follicle and interstitial cells applies especially to the rabbit. Miss Lane- Claypon has also investigated their developmental history in the rat,’ and expresses belief that in this animal also they are 0h : AYP a, Ga O Fig. 28.—Ovary at birth, showing primordial follicles. 300. (From Williams’ Odstetrics, Appleton & Co.) derived from the germinal epithelium by a similar process of differentiation. Both follicular epithelial cells and interstitial cells are stated to pass through identically the same stages, but the latter are said to remain grouped together in the spaces between the follicles instead of arranging themselves around the diplotenic nuclei of the developing ova. + Lane-Claypon, loc. cit. ? Lane-Claypon, ‘On Ovogenesis and the Formation of the Interstitial Cells of the Ovary,” Jour. Obstet. and Gynec., vol. xi., 1907. 124 THE PHYSIOLOGY OF REPRODUCTION Thus it appears that the ova, the follicular epithelial cells, and most probably also the interstitial cells, are all derived from the germinal epithelium by processes involving changes in the nuclear chromatin ; but that, whereas these changes are similar in the case of the follicle and interstitial cells, those undergone by the developing ova are more extensive and show a greater complexity. The significance of the common origin of these different ovarian elements will be more apparent when we consider the views which are held regarding the further development and the probable functional importance of these cells. It should be mentioned, however, that Allen! and Sainmont,? working on the organogenesis of the ovary in the rabbit and the cat respectively, have come to the conclusion that the ovarian interstitial cells have a connective tissue origin, but these in- vestigators do not appear to have traced the successive stages of cellular development with the same completeness as Miss Lane- Claypon. Sainmont is of opinion that they have a trophic function, a suggestion which was first made by Pfliiger.* There would seem to be no doubt that the developing ova in the immature ovary subsist and grow at the expense of the surrounding tissue. Thus protoplasmic masses, formed by the aggregation of very young ova, have been described by Balfour,* who made the suggestion that one ovum may develop at the cost of the others. These aggregations of ova were noticed in the ovary of the foetal rabbit at about the sixteenth day of pregnancy. A day or two previously the ova were observed to be separate. Miss Lane-Claypon, who confirms the observa- tion, is of opinion that Balfour’s suggestion was right, and that the ova which disappear serve ultimately as food-stuff for the 1 Allen, “The Embryonic Development of the Ovary and Testis of the Mammals,” Amer. Jour. of Anat., vol. iii., 1904. Allen describes the inter- stitial cells in a three-months-old rabbit as being derived from certain cells in the thecz interne of degenerate follicles, The cells are said to lose their walls, become irregular in shape, and undergo a rapid process of amitotic division, after which they become transformed into typical interstitial cells. 2 Sainmont,‘ Recherches relatives & ’organogendse du Testicule et l’Ovaire chez le Chat ” Arch. de Biol. vol. xxii.. 1905. ° Pfliiger, Ueber die Kiersticke der Stiugethiere und des Menschen, Leipzig. 1863. 4 Balfour, lov. cit. CHANGES IN THE OVARY 125 one ovum whose condition happens to be the most vigorous. “This cannibalism on the part of the young ovum is not sur- prising, if the life of an ovum be considered. It is really but the normal condition of the cell at all its stages of development ; it grows and fattens at the expense of other cells. In the young ovary, it is starting its first stage of growth and must devour other cells; later on, during the growth of the follicle, it lives upon the follicle-cells, and later still, when, after fertilisa- tion, the [term] ovum in its extended sense refers to the young foetus, [this latter] ives on the material provided by the cells of the maternal organism.” + MATURATION AND OVULATION The youngest and smallest Graafian follicles lie near the surface of the ovary, but pass inwards as they increase in size. The large, mature follicles, however, come to lie just below the surface from which they begin to protrude visibly at the ap- proach of the breeding season. During the procestrum one or more follicles (the number varying in different animals, accord- ing to the size of the litter) may generally be seen showing a very considerable protrusion, while in some animals, such as the sow, the appearance of the ovary at this time is not dissimilar to a bunch of grapes. A large Graafian follicle in a mature ovary contains the following parts: Forming the outermost part of the wall and in continuity with the ovarian stroma is. the theca externa, which is a layer of somewhat fibrous connective tissue. Within this is the theca interna, which is less fibrous. The two thece are only slightly modified ovarian stroma. Within the theca interna is the epithelial wall, which, in the very young follicles, consists of a single layer of cells immediately surrounding the ovum. These, as already mentioned, multiply rapidly (by mitotic division) and give rise to a layer many cells deep, which, as the follicle increases in size, becomes divided into two layers, 1 Lane-Claypon, ‘‘On Ovogenesis,” &c., loc. cit. That one ovum may de- velop at the expense of others is particularly well shown in Hydra, Tubularia, and certain other Cclenterates. The nuclei of the ingested ova continue to be easily recognisable even during the early segmentation stages of the developing egg. 126 THE PHYSIOLOGY OF REPRODUCTION the membrana granulosa lining the follicle, and the discus proligerus surrounding the ovum. The innermost cells of the discus rest upon a thick, transparent, radially striated membrane with a granular outer border. This is the zona radiata or zona pellucida. The striated appearance is due to the presence of fine canals. Within the zona, and immediately enclosing the ovum, another very thin membrane can sometimes be made out. This is the vitelline membrane. The membrana granulosa and discus proligerus are united by one or more strands of follicular epithelial cells. A viscid fluid, containing protein matter, collects between them and becomes gradually increased in quantity .as the follicle continues to grow.! The liquor folliculi begins to form in the developing rat’s ovary at about the ninth day of pregnancy.? Miss Lane-Claypon suggests that the kary- olytic changes which occur in the nuclei of the follicular epithelial cells may have some connection with the Fre. 29.—Young odcyte or Origin of the liquor. She states, how- egg surrounded by a ever, that in the process of formation single layer of follicular oF the liquor folliculi in the adult epithelial cells. (From i 7 van der Stricht.) ovary, the follicle cells appear simply to disintegrate and dissolve without showing the phenomena of karyolysis. On the other hand Honoré,’ who has investigated the subject in the case of the rabbit, concludes that the liquor folliculi is secreted by the follicle cells, without their undergoing destruction (or that, if this occur, it is immaterial to the process of liquor formation), in the same way as the urine is secreted by the epithelium of the renal 1 Occasionally a Graafian follicle may contain more than one ovum, but this is abnormal. Such follicles have been described as occurring in the rabbit’s ovary by Honoré (‘‘ Recherches sur l’Ovarie du Lapin,” Arch. de Biol., vol. xvii. 1901), and in the dog’s ovary by Smyth (‘‘ An Unusual Graafian Follicle,” Biol. Bull., vol. xiv., 1908). The latter writer states that one follicle contained seven ova, He shows that the tendency to produce multiple ova may be hereditary, and that it is apparently correlated with a high fertility. 2 Lane-Claypon, loc. cit. 3 Honoré, ‘‘ Recherches sur l’Ovarie du Lapin,” Arch. de Biol., vol. xvi., 1900. CHANGES IN THE OVARY 127 tubules. In support of this view Honoré points out that there are no indications of degeneration or destruction of the follicular epithelial cells of the ripe follicles during cestrus, and moreover, that these cells are retained in the follicle at the time of ovula- tion, giving rise subsequently to the luteal cells of the corpus luteum. It would appear possible, however, that the liquor folliculi is formed partly by the secretory activity, and partly Fia. 30.—Young human Graafian follicle. The cavity contains the liquor folliculi. (From Sellheim.) by destruction of the follicle cells, just as, according to one view, milk is derived from both the secretion and the disintegra- tion of the cells of the mammary gland (see p. 560). Heape! states that during the growth of the ovum nour- ishment is supplied to it by the aid of the discus proligerus, for fine protoplasmic processes may be seen passing from the cells of this layer and projecting into radiating canals in the zona which encloses the ovum, being in contact with the vitelline membrane. 1 Heape, ‘‘The Development of the Mole,” Quar. Jour. Mier. Science, vol. xxvi., 1886. 128 THE PHYSIOLOGY OF REPRODUCTION Immediately after copulation, and therefore during cestrus, the cells of the discus proligerus (in the rabbit) begin to with- draw radially, and eventually remain attached to the zona radiata by the extremely thin strands just referred to. At the same time the ovum itself withdraws somewhat from the zona, leaving a narrow circular space. These processes occupy some Fic. 31.—Human ovum at termination of growth period. (After van der Stricht.) Yolk granules, vacuoles, and fat drops are seen. hours. About nine hours after copulation, when the supply of nourishment has been entirely cut off, the two polar bodies are formed, and the ovum becomes mature. The essential facts about the maturation process were first ascertained by van Beneden? in Ascaris, and were afterwards 1 Heape, ‘‘ Ovulation and Degeneration of Ova in the Rabbit,” Proc. Roy. Soc., B., vol. lxxvi., 1905. 2 Van Beneden, “Recherches sur la Maturation de I’Ciuf,” Arch. de Biol., vol, iv., 1883. CHANGES IN THE OVARY 129 studied more fully by Boveri! In recent years Montgomery ” has elucidated the process still further by showing that prior to the formation of the first polar body the chromatin filaments Fig. 32.—Human ovum examined fresh in the liquor folliculi. (From Waldeyer.) The ovum shows yolk granules in the centre surrounding the nucleus (with its nucleolus) and a clearer peripheral portion. It is enclosed by follicular epithelial cells. ‘ Boveri, ‘‘ Zellenstudien,” Jenaische Zeitsch., vol. xxi., 1887. * Montgomery, ‘‘ Some Observations and Considerations upon the Matura- tion Phenomena of the Germ Cells,” Biol. Bull., vol. vi., 1904. The references to Montgomery’s earlier memoirs dealing with the same subject are given in this paper. 130 THE PHYSIOLOGY OF REPRODUCTION or chromosomes of the cell nucleus conjugate together in pairs, and that in all probability one member of each pair is a de- scendant of a chromosome derived from the father, while the other member is descended from a corresponding maternal chromosome.t The possible significance of this conjugation of chromosomes is referred to on a later page (p. 196). In the subsequent maturation division the chromosomes again separate.” The changes involved in the formation of the first polar body - are in most respects similar to those of ordinary cell division. The centrosome, which lies in the cytoplasm, divides, and the two daughter centrosomes thus produced travel to opposite sides of the nucleus. In the meantime, the latter forms a spindle composed of the chromosomes, the nuclear membrane having disappeared. Each centrosome becomes surrounded by a system of rays, and in this way the attraction spheres are formed. The chromosomes next arrange themselves equatorially between the attraction spheres, each one having now split into two parts. Half of these migrate towards each centrosome, and the nucleus becomes divided. One of the daughter nuclei, together with a thin investment of protoplasm, is extruded from the ovum. This is the first polar body, which is therefore a product of unequal cell division. Subsequently to extrusion it sometimes divides into two. After the formation of the first polar body, the ovum again divides in the same unequal fashion, and the second polar body is formed and extruded. The polar bodies undergo degeneration. Meanwhile the nucleus of the ovum once more becomes surrounded by a membrane and enters upon a resting stage. The process of formation of the second polar body differs from that of the first in that the chromosomes do not undergo splitting. Consequently the nucleus of the mature ovum con- 1 The observations of this author, together with those of Sutton, McClung, Wilson, &c., point to the conclusion that all the nuclei in the somatic cells contain two parallel series of chromosomes (paternal and maternal). * In the reduction process each pair of fused chromosomes becomes divided into a group of four bodies united by linin threads. These are the tetrads or ‘‘vierergruppen.” It follows that the number of tetrads in any particular species is always one-half the number of somatic chromosomes. Thus, if the somatic cells contain sixteen chromosomes, the number of tetrads formed is eight, while, as shown in the text, the number of chromosomes in the mature germ cells (after reduction) is also eight. CHANGES IN THE OVARY 131 tains only half the original number of chromosomes. This number varies in the different species, but is constant in each.! In Man it is twenty-four, so that in the mature human ovum there are only twelve chromosomes.? As will be shown in the next chapter, the spermatozoa, or male germ cells, undergo a similar process of maturation, the conjugating cells containing only half the number of chromosomes characteristic of the species, just as in the case of the conjugating ova. It has been sup- posed, therefore, that the reduction in the number of chromo- somes is a preparation on the part of the germ cells for their subsequent union, and a means by which the number of chromosomes is held constant in each species. The discovery that the nuclei of the conjugating cells contain only half the number of chromosomes possessed by the soma or body cells was made originally by van Beneden. It has since been extended to so many animals and plants that it may probably be regarded as a general law of development.’ It is commonly believed that the chromatin material is the substance which has the potentialities of development, and which plays the principal part in perpetuating the hereditary structure and qualities of the particular animal or plant, but there is no real proof that this is the case (see p. 199 below). The maturation phenomena may take place within the ovary prior to the discharge of the egg, or they may be postponed until after ovulation has occurred. In the rabbit, as has been 1 Van Winiwarter, however, states that in the rabbit the number varies from thirty-six to eighty, but is generally about forty-two (Arch. de Biol., vol. xvi., 1900). 2 Duesberg, ‘‘ Sur le Nombre chromosomes chez VHomme,” Anat. Anz., vol. xxviii., 1906. * For details of the process in various forms of life see Wilson, The Cell, 2nd Edition, New York, 1900. See also Doncaster, ‘On the Matura- tion of the Unfertilised Egg, &c., in the Tenthredinidez,” Quar. Jour. Micr. Science, vol. xlix., 1906; “ Gametogenesis, &c.,” Quar. Jour. Mier. Science, vol, li., 1907. Doncaster shows that in the sawflies there are two types cf maturation process, in one of which there is no reduction. It is probable that only the reduced eggs are capable of fertilisation. In other cases, however, the ova are able to undergo parthenogenetic reproduction without forming polar bodies. See Hewitt, ‘‘The Cytological Aspect of Partheno- genesis in Insects,” Manchester Memoirs, vol. 1x., 1906; Doncaster, ‘‘ Animal Parthenogenesis,”’ Science Progress, vol. iii. (July) 1908. These papers contain further references. 1382 THE PHYSIOLOGY OF REPRODUCTION shown already,’ the polar bodies are formed while the ovum is still in the ovary, but not until after the occurrence of copulation. In the case of the mouse, Sobotta 2 came to the conclusion that the first polar spindle is suppressed, and that the second polar body might be formed during the passage of the ovum down the Fallopian tube. Gerlach * describes the second polar body as being in some instances suppressed after the entry of the spermatozoon in fertilisation, the second polar spindle degenerat- ing within the egg. Kirkham,’ however, states that the matura- tion of the mouse’s ovum is in no way exceptional, the process involving the formation of two polar bodies as in most other animals. The first polar body is extruded in the ovary, while the second is given off in the Fallopian tube immediately after fertilisation by a spermatozo6n.5 Rubaschkin * has shown that the maturation processes in the guinea-pig are similar. In both the guinea-pig and the mouse, ova which are retained in the ovary, and also those which are discharged and fail to become fertilised, undergo degeneration with the second polar spindle within them. The maturation phenomena in the bat (Vesperugo noctula) have been investigated by van der Stricht, who has published a 1 Heape, loc. cit. * Sobotta, ‘Die Befruchtung und Furchung des Eies der Maus,” Arch. SF. Mikr. Anat., vol. xlv., 1895. ’ Gerlach, Ueber die Bildung der Richtungskérper bei Mus musculus, Wiesbaden, 1906. 4 Kirkham, ‘‘The Maturation of the Mouse Egg,’ Biol, Bull., vol. xii., 1907; and “The Maturation of the Egg of the White Mouse,” Trans. Con- necticut Acad, Arts and Sciences, vol. xiii., 1907. > Sobotta (“‘ Die Bildung der Richtungskérper bei der Maus,” Anat. Hefte, vol. xxxv., 1907), in a further paper, expresses himself doubtful as to whether two polar bodies are really discharged in all cases in the maturation process of the mouse’s ovum. His own observations lead him to conclude that two polar bodies are discharged in not more than one-fifth of the total number of maturations, only one polar body being formed in the great majority of cases. Lams and Doorme (‘‘ Nouvelles Recherches sur Ja Maturation et la Fécondation de l’Giuf des Mammifores,” Arch. de Biol., vol. xxiii., 1907) state that they found two polar bodies expelled in forty-four cases out of forty-eight, the first being always smaller than the second. ® Rubaschkin, ‘Ueber die Reifungs- und Befruchtungsprocesse des Meerschweincheneies,” Anat. Hefte, vol. xxix., 1905. CHANGES IN THE OVARY 133 series of papers on the subject.! This observer states that there are always two polar bodies formed. The first is extruded in the ovary. The second spindle is formed at about the ovulat- ing stage, and the second polar body is discharged in the interior of the Fallopian tube. The first body is formed in February or March, or sometimes later, according to the temperature.” It would seem that in the case of the mole the two polar bodies are discharged while the ovum is still retained within the ovary.’ In the pigeon it has been shown that the polar bodies are given off while the ovum is passing down the glandular portion of the oviduct and after the entrance of the spermatozoon. The first polar spindle, however, is formed in the ovarian egg ; but it is not definitely known at what stage fertilisation occurs, excepting that it is previous to the time when the egg is clasped by the oviducal funnel. In the frog the polar bodies are extruded after ovulation has taken place, but the egg is not set free until it has reached a certain stage of maturation, which is preparatory to the dis- charge of the first polar body. The nucleus undergoes a change, and, in place of being large and watery, consists of a small mass of chromatic substance lying in the protoplasm. An achromatic spindle is developed, and the chromatin becomes arranged in the form of granules at the equator of the spindle. The nuclear membrane disappears with the large watery nucleus. The ova in this condition pass into the oviducts.* In certain Invertebrates (Nematodes, Annelids, and Gastero- pods) it has been noticed that the occurrence of the maturation * Van der Stricht, ‘‘ La Ponte ovarique,” &c., Bull. de l’Acad. Roy. de Méd. de Belgique, 1901. Une Anomalie trés intéressante concernant le Développement Mun Huf de Mammifere, Gand, 1904. ‘Les Mitoses de Maturation de uf de Chauve-Souris,” Mémoire présenté au VIII® Congres de l'Assoc. des Anato- mistes, Nancy, 1906. 2 Van der Stricht says (La Structure de V@uf des Mammiferes, Bruxelles, 1909) that he has seen twenty-two ova at the stage of the second polar spindle within the ovary and twenty-seven at the same stage outside of the ovary, the dates varying in each case from the end of February to the end of April. 5 Heape, “ The Development of the-Mole,” Quar. Jour. Mier. Science,vol. XXVi., 1886. 4 Morgan, The Development of the Frog’s Egg, New York, 1897. 134 THE PHYSIOLOGY OF REPRODUCTION phenomena depends upon the act of fertilisation. For example, in the Japanese Palolo-worm, a marine Polychet Annelid, Izuka ! has shown that the first polar body is discharged (after certain preparatory changes) one hour after fertilisation by a spermatozoén, and that the second polar body is extruded fifteen or twenty minutes later. In other animals (eg. Amphiozus), one maturation process takes place before, the other during the entrance of the spermatozoon.? It would appear from these facts that the maturation pro- cesses in many animals only take place as a result of a specific stimulus which may be induced by the act of copulation, or may be caused only by the entry of the spermatozoon into the proto- plasm of the ovum. It would seem, on the other hand, that in some animals maturation takes place independently of any stimulus at such time as the follicle has attained to a sufficient degree of ripeness or after it has discharged its ovum.? Tt has already been shown incidentally that the processes of maturation and ovulation are intimately associated, and that the latter, like the former, is in many animals dependent for its occurrence upon a definite physiological stimulus. The Graafian follicle may rupture when the egg has reached a certain degree of maturity, or it may require the additional stimulus of sexual intercourse before ovulation can be induced. In the rabbit ovulation takes place about ten hours after coition.4 The ovum, which is entirely free from follicular epithelial cells, is discharged into the infundibulum which at this time closely invests the ovary. The discharged ovum is incapable of assimilating nutriment unless it becomes fertilised, 1 Izuka, ‘‘Observations on the Japanese Palolo,” Jour. of the Coll. of Science, University of Tokyo, vol. xvii., 1903. 2 See Przibram, Embryogeny, English Translation, Cambridge, 1908. 3 The chemistry of the maturation process is discussed by Mathews («A Contribution to the Chemistry of Cell Division, Maturation and Fertilisa- tion,” Amer. Jour. of Phys., vol. xviii., 1907). This author describes the maturation of the egg of Asterias as being inaugurated by the dissolution of the nuclear membrane. If oxygen is withheld the mature egg soon dies. It is believed that an ‘‘ oxidase” escapes from the nucleus into the cytoplasm on the rupture of the nucleus. The astral radiations disappear if oxygen is withdrawn, but reappear if oxygen is readmitted. It is concluded that the astral figures are the product of three substances: (1) centriole substance; (2) oxidase ; and (3) oxygen. 4 Heape, loc. cit. CHANGES IN THE OVARY 135 and if fertilisation is not effected it undergoes degeneration. | Heape found that ovulation could not be induced by artificial insemination, nor by any means other than sexual intercourse, and moreover, that intercourse was a sufficient stimulus, even when the progress of the spermatozoa from the vagina into the uterus was artificially stopped, provided that there was no interference with the vascular supply to the ovaries. It is stated by Weil! that ovulation may take place inde- pendently of coition in rabbits which have given birth to young just previously, and Iwanoff,? in confirmation of this statement, records experiments in which pregnancy was induced in rabbits by the artificial injection of seminal fluid shortly after par- turition. In the mouse,? the rat, and the guinea-pig,> ovulation occurs spontaneously during “ heat,’ and generally, if not invariably, during cestrus. In the dog ovulation takes place independently of coition » after external bleeding has been going on for some days, or when it is almost or quite over ; in other words, it occurs during ceestrus and not during the procestrum, or at any rate not during the early stages of the procestrum.® It is probable that the sow also ovulates during cestrus and not during the procestrum, since it is stated that sows are most successfully served on the second or third day of “heat.’’ Coition, if it occurs earlier, is frequently not followed by conception.” From Hausmann’s description it would seem that ovulation does not take place prior to coition, but this statement has not been confirmed.® ‘ Weil, ‘‘ Beitrige zur Kenntniss der Befruchtung und Entwickelung des Kanincheneies,” Wien Med. Jahrbuch, 1873. 2 Iwanoff, ‘‘ La Fonction des Vésicles séminales et de la Glande pros- tatique,” Jour. de Phys. et de Path. Geén., vol. ii., 1900. 3 Sobotta, loc. cit. ‘ Tafani, ‘‘La Fécondation et la Segmentation studieés dans les Giufs des Rattes,” Arch. Ital. de Biol., vol. ii., 1889. 5 Rubaschkin, loc. cit. § Marshall and Jolly, ‘Contributions to the Physiology of Mammalian Reproduction: Part I. The Cstrous Cycle in the Dog,” Phil. Trans., B., vol. excviii., 1905. 7 Wallace (R.), Farm Live Stock of Great Britain, 4th Edition, London, 1907. 8 Hausmann, Ueber die Zeugung und Entstehung des wahren weiblichen Lies, &c., Hanover, 1840. 136 THE PHYSIOLOGY OF REPRODUCTION In the ferret ovulation occurs during cestrus, but postpone- ment of coition may bring about the degeneration of the ripe follicles, since they do not always discharge spontaneously.? Artificial insemination, followed by pregnancy, has been successfully performed on mares, donkeys, and cows.” Conse- quently it may be concluded that these animals ovulate inde- pendently of coition. According to Ewart,? ovulation in the mare very often does not occur until near the end of the cestrous period. It has been shown also that the sheep ovulates spontaneously at each of the earlier heat periods of the sexual season, but that there are reasons for believing that during the later periods the stimulating power at the disposal of the ewes may be so reduced that without coition it is incapable of causing ovulation. There is also evidence that when coition occurs at the beginning of an cestrous period, it may provide a stimulus inducing ovula- tion to take place a few hours earlier than it otherwise would ; in other words, that if ovulation has not already occurred during an oestrus, the stimulus set up by coition may hasten the rupture of the follicle4 Recently Iwanoff has succeeded in inducing pregnancy in sheep by artificial insemination. (See p. 183.) There can be little doubt that in the great majority of Mammals ovulation, as a general 1 rule, occurs regularly during cestrus. In certain bats, however, « copulation i is performed during the autumn, whereas ovulation is postponed until the following spring, the animals in the meantime hibernating, while the spermatozoa are stored up in the uterus (see p. 177). The ovary in the winter months (during the hibernating period) is said to be in a state of quiescence, and the exact time for * Marshall, ‘‘The (strous Cycle in the Common Ferret,” Quar. Jour. Mier, Sei., vol. xlviii., 1904. * Heape, ‘The Artificial Insemination of Mammals,” Proc. Roy. Soc., vol. lxi., 1897. 3 Ewart, ‘‘ The Development of the Horse,” MS. 4 Marshall, “ The Gistrous Cycle and the Formation of the Corpus Luteum in the Sheep,” Phil. Trans., B., vol. excvi., 1903. 5 Benecke, ‘‘ Ueber Reifung und Befruchtung des Eies bei den Fleder- miiusen,” Zool. Anz., vol. ii, 1879. Eimer, ‘Ueber die Fortpflanzung der Fledermiuse,” Zool. Anz., vol. ii., 1879. Van Beneden and Julin, ‘‘ Observa- tions sur la Maturation, la Férondation, et la Segmentation de l’iuf.chez les Cheiroptéres,” Arch. de Biol., vol. i., 1880. CHANGES IN THE OVARY 137 maturation and ovulation depend upon the temperature of the early months of the year, occurring generally in February or March, but sometimes as late as April! Ovulation takes place some days or even weeks after the formation of the first polar body. It would appear, then, that in bats the follicles can discharge spontaneously under the influence of appropriate seasonal stimuli, and without even the occurrence of cestrus.? There has been a considerable amount of controversy re- garding the periods at which ovulation occurs in the Primates, the question being discussed at some length in three papers by Heape.? This author has shown that ovulation and_menstrua- tion are not associated in monkeys (at any rate not necessarily), and that whereas, in both monkeys and the human species, menstruation may occur periodically all the year round, in monkeys there is a limited season for conception and ovulation ; while in civilised woman this period is not limited to any par- ticular time of the year, although there is evidence that primi- tively man agreed with the lower Primates in having a definite sexual season (during which ovulation occurred). (See p. 71.) Van Herwerden* has adduced further evidence which shows that there is no apparent connection between ovulation and menstruation, either in monkeys or in the aberrant lemur, Tarsius spectrum. It would seem probable, however, in view of Pocock’s observations ® upon the occurrence of a pronounced post-menstrual cestrus in certain monkeys in the Zoological Gardens, that ovulation may take place at this period (that is, at the close of menstruation). ~ In the case of the human female there is still a great diver- gence of opinion in regard to the usual time for the discharge 1 Van der Stricht, ‘‘ L’Atrésie ovulaire,” &c., Verhand d. Anat. Gesell. in Bonn, 1901. “ Les Mitoses de Maturation,” &c., Nancy, 1906. 2 In some Invertebrata which undergo cyclical changes it has been shown that ovulation occurs only at certain intervals depending upon the general condition of the organism. Thus in the females of certain Crustacea ovula- tion regularly follows the moult and cannot precede it.—Science (New Series), vol, xxv. (Feb. 1907). 3 Heape, Phil. Trans., B., vol. clxxxv., 1894, and vol. clxxxviii., 1897. Trans. Obstet. Soc., vol. x1., 1898. 4 Van Herwerden, ‘‘ Bijdrage tot de Kennis van den Menstruellen Cyclus,” Tijdschr. d. Ned. Dierk. Vereen, vol. x., 1906. 5 Pocock, ‘‘ Notes upon Menstruation,” &c., Proc. Zool. Soc., 1906. \ \ 138 THE PHYSIOLOGY OF REPRODUCTION of the ova. Some authors express the belief that ovulation occurs before menstruation, others that it takes place during that process, and others again that it follows menstruation. Hergesell +_has lately adduced evidence which, in his opinion, points to the conclusion that ovulation precedes menstruation, but the occurrence of corpora lutea of uncertain age in the ovary cannot be regarded as supplying definite proof. There are reasons, on the other hand, for concluding that, primitively at any rate, the most usual period for ovulation in the human female was during a definite cestrus following a procestrum, as in many of the lower Mammals; for the period of most acute sexual feeling is generally just after the close of the men- strual period (see p. 69), while, according to Raciborsky, this is also the commonest season for fertile coition.2 Moreover, the facts narrated by Bryce and Teacher, in a recent memoir on the early development and embedding of the human ovum, render it extremely probable that the ovum described had been discharged shortly after the cessation of the last men- struation.® With regard to the question as to whether any special stimulus is necessary to induce ovulation in women, Oliver * is of opinion that whereas it sometimes may occur spontaneously, it is more than probable that it “ may be and often is accelerated by coitus,” since at this time there is “an increased determina- tion of blood to the whole genital tract.” 5 (a Hexpasétl, ‘‘Das zeitliche Verhalten der Ovulation zur Menstruation,” Inaug. Diss., Leipzig, 1905. 2 Raciborsky, Z'raité de Menstruation, Paris. 3 Bryce and Teacher, Contribution to the Study of the Early Development and Embedding of the Human Ovum, Glasgow, 1908. 4 Oliver, ‘‘ A Study of Fertilisation with Reference to the Occurrence of Ectopic Pregnancy,” Edin. Med. Jour., vol. liv., 1902. .§ Pregnancy, and therefore ovulation, have been known to take place before the onset of menstruation. Pregnancy may also occur during amenor- rheea (e.g. at the commencement of the menopause) and during the lactation period, when menstruation is often in abeyance. Again, it is stated that ovulation has been noted during infancy, before any of the other indications of puberty have been observed (Webster, ‘‘ The Biological Basis of Menstrua- tion,” Montreal Medical Journal, April 1897). Further, it will be shown below (p. 348) that the ovaries can maintain their normal functions after the removal of the uterus, It would seem, therefore, that ovulation may occur spontaneously in women, and is not necessarily connected with either men- CHANGES IN THE OVARY 139 This suggestion receives some support from an experiment by Clark,’ who caused the rupture of a Graafian follicle artificially in a freshly removed ovary by injecting carminz gelatine into the vessels and so raising the ovarian blood pressure. The causes which determine the rupture of the Graafian follicle are also discussed by Heape,? who is of opinion that this is brought about in the rabbit by the stimulation of erectile tissue, and not simply as the result of internal pressure arising from increased vascularity or a greater quantity of liquor folliculi.* In this animal the process must be due to a nervous reflex, in- duced by the act of copulation. As has been shown above, in those animals in which the ova are discharged spontaneously, this usually occurs during cestrus, and not during the procestrum when the congestion of the generative tract is at its height. Harper’s experiments 4 on the fertilisation of the pigeon’s egg elucidate the question somewhat further. This author writes as follows: ‘When a pair [of pigeons] ready for mating is put together, egg-laying ordinarily ensues at the end of a rather definite period, at the least eight days. The female functions are held in abeyance till the proper stimulus is received from a mate.> The maturing of the egg is so exclusively a female function that it seems odd at first thought that an apparent exception should occur to the rule. Of course, we know that struation, cestrus, or coitus. On the other hand, there is evidence that ovulation is intimately associated with the occurrence of the sexual orgasm in certain instances. Thus Galabin records a case of a woman who married under the age of twenty, and lived in married life with two husbands in succession, and who, when she had passed the age of forty, experienced the sexual orgasm in coitus for the first time, and from that day dated her first and only pregnancy (Manual of Midwifery, 6th Edition, London, 1904). The orgasm (which is characterised by the erection of the clitoris, accompanied by certain sensations) is not necessary for conception, for pregnancy often occurs in women who are “ impotent.” ; 1 Clark, “ The Origin, Development, and Degeneration of the Blood- Vessels of the Human Ovary, ” Johns Hopkins Hospital Reports, vol. ix., 1900. 2 Heape, ‘‘ Ovulation,” &c., Proc. Roy. Soc., B., vol. Ixxvi., 1905. 5 It has been suggested that the follicle may rupture as a result of the breaking down of the blood-vessels in its wall, and the consequently increased pressure due to the bleeding into the cavity. See Heape. 4 Harper, ‘‘The Fertilisation and Early Development of the Pigeon’s Egg,” Amer. Jour. of Anat., vol. iii., 1904. 5 In the common fowl, and probably in most other birds, ovulation takes place independently of the male. 140 THE PHYSIOLOGY OF REPRODUCTION the final maturation of the egg, or the giving off of the polar bodies, awaits in most animals the act of fertilisation. But here the effect is produced upon the egg by the entrance of sperms. How mating and the act of copulation [which is re- peated at frequent intervals every day at this time] could in- fluence the ripening of the egg in the ovary is another problem. In this connection the curious fact must be mentioned that two female pigeons placed in confinement may both take to laying eggs. The function of ovulation is in a state of tension, so to speak, that requires only a slight stimulus, ‘ mental ’ apparently in this case, to set the mechanism to working. At any rate, it is impossible to regard the presence of sperm in the oviduct as an essential element of the stimulus to ovulation, although it may have an important influence in the normal case. Our attention is directed to the various and complex instincts of the male which come under the head of courtship, both before and after mating is effected, as furnishing a part of the stimulus to the female reproductive organs.” Harper pro- ceeds to describe a curious habit which is common among pigeons before copulating. The male bird regurgitates some secretion in its throat, and this is taken up by the bill of the female in much the same manner as the young take their food. ‘Tt is easy to see that here may be one of the sources of in- direct stimulation to the female reproductive organs.” Spallanzani 1 found that whereas the female fire-bellied toad could lay its eggs in the absence of the male, the female fetid toad, if isolated, retained its eggs in the ovaries. The common frog is capable of spontaneous oviposition, at least in some cases.” The exact nature of the mechanism by means of which the discharged ova in the human female are made to pass into the aperture of the oviduct is not certainly known. Rouget? be- lieved that the fimbriated end of the Fallopian tube erected and partially enclosed the ovary. Kehrer* suggested that the 1 Spallanzani, Dissertations, English Translation, London, 1784. 2 Morgan, The Development of the Frog's Egg, New York, 1897. ® Rouget, ‘‘ Recherches sur les Organes Erectiles de la Femme,” Jour. de la Phys., vol. i., 1858. 4 Kehrer, “Die Zusammenziehungen des Weiblichen Genitalcanals,” Beitriige zur Vergleich. und Exper. Geburtskunde, 1864. CHANGES IN THE OVARY 141 ovum was shot into the open fimbriz in the act of ejaculation. The motion of the cilia, which line the fimbriated end as well as the interior of the tube, no doubt serve to set up a current which assists in directing the ova. Gerhardt,! who has paid some attention to the question, concludes that in Man and many other Primates a number of factors co-operate to secure the entry of the discharged ovum into the tube. These factors include the erectibility of the fimbrie, the muscular movements of the same, the ciliary currents on the fimbrize and tube, and the configuration of the ovarian surface. In other orders of Mammals the process is brought about in various ways. In Monotremes, Marsupials, and Cetaceans the entrance to the tube is relatively large as compared with the size of ‘the ovary. In certain other animals a portion of the peritoneum is used as a common envelope for the ovary and the end of the tube. Thus in the dog and ferret the ovary is enclosed in a sac communicating with the cavity of the tube, so that the discharged ova can scarcely fail to effect an entrance into the uterus. There can be little doubt, however, that in the majority of animals ciliary movement plays an important part in directing the course of the expelled ova. Nussbaum? has described the eggs of the frog as being carried into the mouths of the oviducts by the motion of the cilia of the ccelomic epithelium. These cilia are said to drive in a forward direction any small bodies lying free in the ccelom. Harper states that in the pigeon the egg is clasped by the oviduct, which at this time displays active peristaltic contrac- tions, as if in the act of swallowing the egg. There is evidence, however, that ova which are discharged from one ovary do not always pass into the oviduct on the corresponding side. For example, instances have been known of animals with a bicornuate uterus becoming pregnant in the uterine horn on the side opposite to that on which the ovary had discharged (as indicated by the presence of a newly 1 Gerhardt, ‘‘ Studien iiber den Geschlechtsapparat der Weiblichen Siuge- thiere: I. Die Ueberleitung des Eies in die Tuben,” Jenaische Zeitschr., vol. xxxix., 1905. 2 Nussbaum, “Zur Mechanik der Eiablage bei Rana fusca,” Arch. f. Mikr. Anat., vol. xlvi., 1895. 3 Harper, loc. cit. 142 THE PHYSIOLOGY OF REPRODUCTION formed corpus luteum). Moreover, it has been recorded that animals from which one ovary had been removed have become pregnant in both horns of the uterus, an observation which clearly shows that the ova which are discharged from one ovary may travel across the peritoneal cavity and enter into the Fallopian tube on the other side of the body. In certain abnormal cases the ovum escapes altogether into the peritoneal cavity, and never finds its way into either ovi- duct. If the ovum becomes fertilised, as sometimes happens, the condition known as ectopic or extra-uterine gestation may result ; that is to say, the embryo which is formed may become attached to some part of the wall of the body cavity and there undergo development. Ectopic or extra-uterine pregnancy has been known to occur in the domestic animals as well as in the human subject.t- Thus Gofton? has recently described a case of a cat which was pregnant with six kittens, one in the normal position in the uterus, and the other five in the abdominal cavity. The foetal envelopes of the abdominal embryos were attached by a sort of placenta to the parietal peritoneum and to the omentum, and one had also an extensive attachment to the fundus of the stomach. All the embryos were well developed and apparently normal. Moreover, Dr. Blair Bell has informed me of a case of primary abdominal pregnancy in a rabbit owned by him. There were four well-developed foetuses. Tue FoRMATION OF THE Corpus LuTEUM After the discharge of the ovum from the ovary the ruptured Graafian follicle undergoes a series of changes which result in the formation of the structure known as the corpus luteum. The fully formed corpus luteum consists of large cells con- taining a yellow pigment, the luteal cells, separated from one another by an anastomosis of connective tissue which is seen to branch inwards from the surrounding ovarian stroma, and 1 See the text-books on Midwifery, and for further details, The Journal of Obstetrics and Gynecology, vol. x., December 1906, which number is entirely devoted to the subject of extra-uterine pregnancy. Ovarian pregnancies, in which the spermatozoa have entered newly ruptured follicles, are also known. * Gofton, ‘Ectopic Gestation in a Cat,” Royal Dick Coll. Mag., vol. i., 1906. CHANGES IN THE OVARY 143 to form a central plug in which there are no luteal cells. This connective tissue contains numerous blood-vessels, so that the fully developed corpus luteum is a highly vascular structure. Three hypotheses have been put forward regarding the manner of formation of the corpus luteum. That of Paterson,} who supposed it to be derived from the blood coagulum left in the cavity of the Graafian follicle after its discharge, gained few or no adherents. The other two theories, those of von Baer ? and Bischoff,? on the other hand, have each received consider- able support. Von Baer regarded the corpus luteum as an entirely con- nective tissue structure, in the origin of which the follicular epithelium had no share; while Bischoff concluded that the luteal cells were formed by the hypertrophy of the epithelial cells of the undischarged Graafian follicle. Among the‘principal supporters of Von Baer’s view appear the names of Leuckart, His, Kolliker, Slavjansky, Gegenbaur, Benckiser, Schottlinder, and Minot. Those who have adopted the alternative theory of Bischoff include Pfliiger, Waldeyer, Call and Exner, Beigel and Schulin.4 To Sobotta® belongs the credit of being the first to deal systematically with the question, and, with the publication of his papers on the corpus luteum in the mouse, the controversy entered upon a new phase. In Sobotta’s investigation the material employed was collected upon a definite plan, the animals being killed at known intervals after coition, in re- ference to the occurrence of which the period of ovulation had been previously determined. In this way there was obtained a large series of corpora lutea representing successive stages of development. The investigation resulted in confirming Bischoff’s ' Paterson, “ Observations on Corpora Lutea,” Ldinburgh Med. and Surg. Jour., 1840. 3 Von Baer, De Ovi Mammalium et Hominis Genesi Epistola, Lipsie, 1827. ® Bischoff, Entwickelungsgeschichte des Kanincheneics, Braunschweig, 1842. 4 For an account of the older literature of the subject see Sobotta, “ Uber die Entstehung des Corpus Luteum der Saugethiere,” Merkel and Bonnet’s Ergebnisse der Anat. u. Entwick., vol. viii., 1899. 5 Sobotta, “ Uber-die Bildung des Corpus Luteum bei der Maus,” Anat. Anz., vol. x., 1895; and Arch. f. Mikr. Anat., vol. xlvii., 1896. 144 THE PHYSIOLOGY OF REPRODUCTION view that the luteal cells are the much hypertrophied epithelial cells of the undischarged follicle, the connective tissue network being derived from the inner layer of the theca. Sobotta de- scribes the outer theca as taking no share in the ingrowth, while the theca interna is stated to become entirely spent in the formation of the inter-epithelial anastomosis. The hyper- trophy of the epithelial cells is said to be of the nature of a simple enlargement, unaccompanied by division. Sobotta’s conclusions in regard to the development of the corpus luteum in the mouse were subsequently confirmed by wi SNS i SESS \ ath Fic. 33.—Recently ruptured follicle of mouse, (From Sobotta.) fe, follicular epithelium or membrana granulosa (somewhat hyper- trophied) ; th, theca interna; a, ingrowth from same. him in a further investigation carried out on similar lines on the corpus luteum in the rabbit.1 Moreover, Stratz? published de- scriptions of certain stages of corpus luteum formation in Tarsius, Tupaa, and Sorex, and these agree in essential particulars with those given by Sobotta; while Honoré,’ also working on the rabbit, differed only in concluding that the inter-epithelial network is derived in part from the theca externa, and not exclusively from the theca interna, and that the latter is not entirely exhausted by the ingrowth, some part of it still 1 Sobotta, “Uber die Bildung des Corpus Luteum beim Kaninchen.” Anat. Hefte, vol. viii., 1897. . * Stratz, Der Geschlechtsreife Stiugethiereierstock, Haag, 1898. 3 Honoré, ‘‘ Recherches sur l’Ovaire du Lapin,” Arch. de Biol., vol. xvi., 1900. CHANGES IN THE OVARY 145 remaining to form a layer within the outer theca in the fully formed corpus luteum. On the other hand, several investigators have expressed doubts regarding Sobotta’s conclusions, and some have adopted the theory originally formulated by von Baer that the luteal cells arise from the connective tissue sheath of the follicle, the follicular epithelium being either entirely discharged along with the ovum or else being partially discharged and partially de- generating im situ. Amongst those who have adopted this view are Nagel,’ who investigated the human corpus luteum ; Fig. 34,—Early stage in formation of corpus luteum of mouse. (From Sobotta,) 1, developing luteal cells; e, germinal epithelium. Clark,2, who contributed an account of the formation of the corpus luteum in the sow and in the human subject ; Doering,? who also worked upon the sow, and claimed to have confirmed Clark’s account; and Biihler,* Wendeler,® 1 Nagel, ‘‘ Die Weiblichen Geschlechtsorgane,” Bardeleben’s Handbuch der Anatomie des Menschen, vol. vii., Jena, 1896. “Uber neuere Arbeiten auf dem Gebiete der Anatomie der weiblichen Geschlechtsorgane,” Merkel and Bonnet’s Ergebnisse d. Anat. u. Entwick, vol. viii., 1899. * Clark, ‘‘ Ursprung, Wachstum, und Ende des Corpus Luteum,”’ Arch. f. Anat. u. Phys., Anat. Abth., 1898 ; Johns Hopkins Hospital Reports, vol. vii., 1899. 3 Doering, ‘ Beitrag zur Streitfrage tiber die Bildung des Corpus Luteum,” Anat. Anz., vol. xvi., 1899. 4 Biihler, ‘“ Entwickelungsstadien Menschlichen Corpora Lutea,” Verhand. d. Anat. Cesell., in Pavia, 1900. 5 Wendeler, Martin’s Die Krankheiten der Eierstocke und Nebeneierstocke. K 146 THE PHYSIOLOGY OF REPRODUCTION and Stoéckel,1 who have examined and described developing human corpora lutea. Moreover, His,” Kolliker,? and Paladino 4 have reiterated their adherence to von Baer’s hypothesis since the publication of Sobotta’s work. It is remarkable, however, that none of the supporters of this hypothesis appear to have examined the growing corpus luteum in all its stages of development, while in the case of several of the accounts it is not clear whether the structures described were not in reality atretic follicles—that is to say, Fic. 35.—Late stage in formation of corpus luteum of mouse. (From Sobotta.) Thecal ingrowths are numerous. The cavity of the follicle is not yet filled in. follicles which had undergone degenerative changes without ever being discharged. Thus, the words used in a description given by Clark seem to indicate that this author was dealing with the degenerative epithelial cells of an atretic follicle. It seems not impossible also that the young human “ corpus luteum” de- scribed by Doering was a degenerate follicle ; while Kélliker’s opinion that the corpus luteum is an entirely connective tissue structure appears to have been founded on the assumption that 1 Stickel,‘* Ueber die Cystiche Degeneration der Ovarien bei Blasenmole,” Sep. Abdruck aus der Festschrift fiir Fritsch. 2 His, Discussion, Verhand. d. Anat. Gesell., in Tiibingen, 1899. * Kolliker, ‘‘ Ueber Corpora Lutea Atretica bei Sdugethieren,” Verhand. d. Anat. Gesell., in Kiel, 1898. 4 Paladino, ‘‘Per la Dibuttata Questione sulla Esenza de] Corpo Luteo,’’ Anat. Anz., vol. xviii., 1900. CHANGES IN THE OVARY 147 the changes exhibited by discharged follicles and retrogressive undischarged follicles are identical in character. It is to be noted further that in the investigations of all those writers who have upheld the connective tissue hypothesis, the ages of the developing corpora lutea were unknown, the material having been collected in no case by Sobotta’s method of killing the animals at successive intervals after coition. In 1901, after the publication of the papers referred to above, Fig. 36.—Corpus luteum of mouse fully formed. (From Sobotta.) Theluteal tissue is vascularised and the central cavity filled in with connective tissue. the present writer issued a preliminary account! of an experi- mental inquiry upon the formation of the corpus luteum in the sheep. In this inquiry the animals were killed at successive intervals after coition, or (in cases where coition did not or was not known to occur) after cestrus was observed. The result of this investigation was to confirm Bischoff’s hypothesis in all 1 Marshall, ‘‘ Preliminary Communication on the M@strous Cycle and the Formation of the Corpus Luteum in the Sheep,” Proc. Roy. Soc., vol. 1xviii., 1901. The full paper was afterwards published in the Phil. Trans., B., vol. cxcvi., 1903. 148 THE PHYSIOLOGY OF REPRODUCTION essential particulars. The sheep, however, was found to present some differences from the mouse (as investigated by Sobotta) in regard to the origin of the connective tissue network of the corpus luteum, this being discovered to originate partly from the theca externa, and not merely from the theca interna. It was found also that the cells of the follicular epithelium con- tinued to undergo mitotic division after the rupture of the follicle, but not with the same frequency as previously. The theca interna was stated to become entirely spent in the growth of the connective tissue network. Four days after cestrus the discharged follicle was found. to have acquired all the char- acteristics of the fully developed corpus luteum, the luteal cells, as seen in section, being at least six times as large as the original epithelial cells. In the same year as the publication of the paper referred to above, on the sheep’s corpus luteum, van der Stricht! gave an account of the discharged follicle in bats belonging to the genera Vesperugo, Vespertiho, and Placotus. This was also confirmatory of the conclusion that the follicle cells hypertrophy and give rise to luteal cells, but mitotic division among these cells was also seen to occur. Van der Stricht calls attention to the appearance of fatty particles at a very early stage in the history of the luteal cells. A point of greater importance is that van der Stricht found that, whereas the majority of the luteal cells are derived from the follicular epithelium, a certain relatively small pro- portion of them are developed out of interstitial cells in the inner theca of the connective tissue sheath. This observation lends additional interest to Miss Lane-Claypon’s statement that the follicle and interstitial cells have an identical origin, since both are derived from the germinal epithelium, and pass through a similar series of changes.? The structure of the ovary, and the cyclical changes which it 1 Van der Stricht, ‘La Rupture du Follicule Ovarique et l Histogéndse du Corps Jaune,” C. R. del’ Assoc. des Anatomistes, 3rd Session, Lyon, 1901. ‘La Ponte Ovarique,” &c., Bull. del’ Acad. Roy. de Médecine Belgique, 1901. 2 Marshall, ‘The Development of the Corpus Luteum: a Review,” Quar. Jour. Mier. Science, vol. xlix., 1905. Miss Lane-Claypon’s discovery that the follicular epithelial and interstitial cells are probably equipotential may per- haps help to elucidate some of the discrepancies between the accounts by various authors of the formation of the corpus luteum. CHANGES IN THE OVARY 149 undergoes in the case of the “marsupial cat” (Dasyurus viverrmus), have been investigated by Sandes,! who shows that the mode of formation of the corpus luteum in Marsupials is essentially similar to what it is in the Eutheria. The theca interna follicul is shown to be rudimentary in Dasyurus, a circumstance which rendered it especially easy to follow the subsequent changes undergone by this layer. Sandes describes the follicular epithelium as undergoing so great an hypertrophy prior to the thecal ingrowth as sometimes almost to fill the cavity of the discharged follicle, so that there could be no possi- bility of confusing the epithelial with the connective tissue cells.” The formation of the corpus luteum in the rabbit has been further studied by Cohn,* while the same process in the marmot has formed the subject of an investigation by Volker. Both authors agree in supporting Bischoff. Volker finds that the theca externa takes a share in the connective tissue ingrowth, while the theca interna does not become exhausted in the process. Jankowski,® however, has arrived at totally different conclu- sions, and adopts the view that the luteal cells are modified connective tissue cells. The material employed in this research appears to have consisted of a miscellaneous collection of sows’ and guinea-pigs’ ovaries obtained without any attempt at syste- 1 Sandes, “The Corpus Luteum of Dasyurus Viverrinus,” Proc. Linnean Soc., New South Wales, vol. xxviii., 1903. * Through the kindness of Professor J. P. Hill I have been permitted to examine sections in his possession of the corpus luteum of the Monotreme Ornithorhynchus paradoxus, These sections show much hypertrophied and apparently fully developed luteal cells, but no trace of any ingrowth from the connective tissue wall of the corpus luteum. 3 Cohn, ‘‘Zur Histologie und Histogenesis des Corpus Luteum und des Interstitiellen Ovarialgewebes,” Arch. f. Mikr. Anat., vol. 1xii., 1903. 4 Volker, ‘“‘ Uber die Histogenese Corporis Lutei bei den Ziesel (Spermo- philus citillus),’’ Bull. Internat. Acad. Sci. (Médicine), Prague, 1904. 5 Jankowski, ‘‘ Beitrag zur Entstehung des Corpus Luteum der Sauge- thiere,” Arch. f. Mikr. Anat., vol. xliv., 1904. Williams (Obstetrics, New York, 1904) takes up the same position as Jankowski, partly on the ground that ‘the membrana granulosa presents extensive degenerative changes, and is usually cast off in great part at the time of rupture,” and partly because certain cells of the theca interna come to resemble luteal cells prior to ovula- tion. The former statement is far from proved, and the latter cannot be regarded as conclusive (see text). Cf. also Seitz, ‘‘ Die Fullikelatresie,” Arch. Ff. Gynik., vol. lxxvii., 1906. 150 THE PHYSIOLOGY OF REPRODUCTION matic investigation, so that the ages of the corpora lutea were unknown. Jankowski bases his opinion largely on the appear- ance of cells resembling luteal cells in the theca interna of the undischarged follicle. It would seem possible that these were interstitial cells, and so probably potentially equivalent to follicle cells (as supposed on independent grounds by van der Stricht and Miss Lane-Claypon). Sobotta,! however, and also Loeb,? have subsequently in-. vestigated the formation of the corpus luteum in the guinea-pig, and find that it is substantially the same as in the mouse, the rabbit, and the sheep. The results of those investigators who agree in adopting Bischoff’s theory of the mode of formation of the corpus luteum may be summarised as follows :—The luteal cells represent the epithelial cells of the undischarged Graafian follicle. These, after rupture, undergo a great hypertrophy, which may be accompanied in the earlier stages by mitotic division, but only to a relatively slight extent (Ovis, Vesperugo, &c.). Meanwhile the thickness of the wall of the discharged follicle is further increased by an ingrowth of connective tissue, which eventually forms an anastomosis of cells, generally fusiform in shape, be- tween the hypertrophying follicular epithelial cells. This con- nective tissue ingrowth is either derived from the theca interna alone (Mus, Cavia, Tarsius, Tupaia, Sorex, Dasyurus, Vesperugo, &c.), or it may arise from both the theca interna and the theca externa (Lepus, Ovis, Spermophilus). The theca interna may become entirely spent in this process (Mus, Cavia, Tarsius, Tupaia, Sorex, Ovis, Dasyurus), or certain strands of this layer may still remain and line the outside edge of the follicle after it has become transformed into a fully developed corpus luteum (Lepus, Spermophilus, Vesperugo). In some animals the inter- stitial cells of the theca interna may develop into luteal cells in just the same manner as the follicular epithelial cells (Vesperugo, &c.). The cavity of the discharged follicle becomes filled in eventually by the further ingrowth of connective tissue, which forms a central plug. 1 Sobotta, “ Uber die Bildung des Corpus Luteum beim Meerschweinchen,” Anat. Hefte, vol. xxxii., 1906. 2 Loeb (L.), “Uber die Entwicklung des Corpus Luteum beim Meer- schweinchen,” Anat. Anz., vol, xxviii., 1906. CHANGES IN THE OVARY 151 The changes undergone by the discharged follicle have also been studied in certain of the lower Vertebrates. Giacomini,! who has investigated the subject in birds, amphibians, and, more particularly, Elasmobranch fishes, describes an hyper- trophy of the follicular epithelium consequent upon ovulation. The discharged follicle of Mylobatis is described and figured as a glandular body in which the enlarged epithelium is pene- trated by an extensive ingrowth of connective tissue and blood- vessels. Wallace? gives a somewhat similar account of the spent follicles in the fishes Zoarces and Spinax. In the latter especially there is a pronounced hypertrophic enlargement of the follicle cells, associated with thecal ingrowths arrayed in a radial manner. Lucien? hag described corpora lutea in the reptiles Anguis and Seps, in which there is a simple hypertrophy of the follicular epithelium unaccompanied by mitotic division. Similar structures in reptiles have also been observed by Mingazzini,* who believes them to be identical with mammalian corpora lutea. On the other hand Bihler,®? who investigated the ovaries of Cyclostomes and certain Teleosteans, was unable to find any hypertrophy of the wall of the spent follicle, and Cunningham,® also writing on Teleosteans, arrived at the same result as Biihler. However, it is evident that the epithelial theory of the origin of the corpus luteum receives confirmation from those members of the lower Vertebrata in which there is a follicular enlargement following ovulation. The mammalian corpus luteum may contain a central clot composed of blood derived from the vessels of the follicular wall which gave way at the time of ovulation. In this case the blood-clot becomes gradually absorbed along with the remainder 1 Giacomini, ‘‘Contributo all ‘Istologia dell’ Ovario dei Selaci,”’ Ricerca Lab. di Anat. Normale della Roy. Univ. di Roma, vol. v., 1896. * Wallace (W.), ‘Observations on Ovarian Ova, &c.,” Quar. Jour. Mier. Science, vol. xlvii., 1903. 3 Lucien, ‘‘Note préliminaire sur les premiéres Phases de la Formation des Corps Jaune chez certains Reptiles,” C. R. de Soc. de Biol., vol. lv., 1903. 4 Mingazzini, “Corpi Lutei verie falsi da Rettili,” Ricerca Lab. di Anat. Normale della Roy. Univ. di Roma, vol. iii., 1893. 5 Biihler, ‘‘ Riickbildung der Eifollikel bei Wirbelthieren,” Morph. Jahr. ‘ vol, xxx., 1902. ® Cunningham (J. T.), “ On the Histology of the Ovary and of the Ovarian Ova in certain Marine Fishes,” Quar. Jour. Micr. Science, vol. x],, 1897, 152 THE PHYSIOLOGY OF REPRODUCTION of the liquor folliculi. On the other hand, there may be practically no hemorrhage, or the discharged blood may be expelled to the exterior of the ovary (with the greater part of the liquor), remain- ing as a small clot upon the surface.t_ It would seem probable that the vessels burst as an effect of the released tension conse- quent upon the rupture of the follicle ; but, as already mentioned, it has been suggested that possibly the latter process may itself vecur as the result of the pouring out of blood into the cavity. During the early stages of formation of the sheep’s corpus luteum leucocytes of the polymorph variety have been observed in great abundance, but in the later stages they disappear, some of them undergoing degeneration. These leucocytes are not extravasated, but wander inwards with the growing strands of connective tissue.” Their occurrence should probably be associated with the necessity to dispose of the blood-clot when such is present. The ingrowth of connective tissue commences a very short time after ovulation, and in the sheep may be seen very dis- tinctly as early as im the seven-hour stage of development. Blood-vessels are carried inwards with the connective tissue, and these undergo multiplication, so that the corpus luteum is a highly vascular structure. If the discharged ovum fails to become fertilised the corpus goes on growing for a short time and then degenerates, so that, in the case of the human female, two months after ovulation it is reduced to the condition of an insignificant cicatrix. In the smaller animals it disappears after a considerably shorter time. If, on the other hand, conception succeeds ovulation, the corpus luteum continues to increase in size until almost the middle of pregnancy, and in the human female attains to a diameter of nearly an inch in length. The large size of the completely developed corpus luteum is the more remarkable in that it results to so large an extent from the simple hypertrophy of certain of its constituent cells. 1 Jt is sometimes stated that the hemoglobin of the blood-clot is trans- formed into the yellow pigment (known as lutein) which gives the luteal cells their characteristic colour; but this is obviously incorrect, since there may be no blood-clot in the follicle, whereas the luteal cells always contain lutein. » Marshall, Phil. Trans., loc. cit. CHANGES IN THE OVARY 153 The wonderful property which these cells possess of enlarging within a very short time of ovulation is seemingly without a parallel in the physiology of the Vertebrata, and it becomes additionally interesting in view of the almost certain fact that the cells, from which the luteal cells develop, are derived, like the ova, from the original germinal epithelium. During the later part of pregnancy the corpus luteum becomes Fie. 37.—Section through old corpus luteum. (From Sellheim.) C, connective tissue ; L, luteal tissue. reduced in size, the luteal cells degenerating, losing their yellow colour, and eventually (at least in some cases) appearing to become transformed into cells resembling, if not identical with, the ovarian interstitial cells referred to above (see p. 148).1 At the end of pregnancy the human corpus luteum has a diameter not exceeding half-an-inch in length. 1 Schafer, Essentials of Histology, 7th Edition, London, 1907. The similarity between the luteal and interstitial cells has also been remarked upon by Allen, loc. cit. 154 THE PHYSIOLOGY OF REPRODUCTION : The corpus luteum of pregnancy is sometimes distinguished from the structure formed when pregnancy does not supervene after ovulation, the latter being called the false corpus luteum,? or corpus luteum of menstruation ; but it is obvious that the two bodies are identical in the early stages, and otherwise essentially similar.2- Moreover, according to Ancel and Bouin,? in animals like the rabbit, which do not ovulate spontaneously during cestrus, these two kinds of corpora lutea are identical throughout. In such animals interstitial cells are believed to replace func- tionally the “ periodic corpus luteum.” The hypotheses which have been put forward regarding the function of the corpus luteum, and the possible part which this organ plays in the metabolism of pregnancy, will be discussed at some length in a future chapter. (For chemistry of corpus luteum see p. 263.) ; THe ATRETIC FOLLICLE It has been already mentioned that the rabbit, the ferret, and certain other animals do not necessarily ovulate during cestrus in the absence of the male. The follicles, instead of bursting, undergo degeneration (atresia) with their contained ova. Heape 4 has shown that the congested vessels in the wall of the follicle may rupture and pour blood into the cavity, where it forms a clot surrounding the degenerating ovum. The brilliant, suffused red appearance of many of the rabbit’s follicles during the early stages of degeneration is said to result from internal bleeding. The first rush of blood into the cavity washes away the epithelium from the wall of the follicle, at the same time dis- integrating the theca interna. Bleeding, however, does not necessarily occur at all. In section the cavity of the degenerate follicle appears, during the early stages, to be bounded by the theca externa, while the ovum may be seen as a shrunken object no longer enclosed by a discus proligerus.5 Heape ® 1 Or corpus luteum spurium. ® The retrogressive changes are similar in both kinds of corpora lutea. * Ancel and Bouin, ‘Sur les Homologies et la Significance des Glandes a Sécrétion interne de ]’Ovaire,” C. R. de la Soc. de Biol., vol. lxvi., 1909. 4 Heape, ‘Ovulation, &c.,” Proc. Roy. Soc., B., vol. 1xxvi., 1905. 5 Marshall, “The Cistrous Cycle in the Common Ferret,” Quar. Jour. Mier. Science, vol. xlviii., 1904. 8 Heape, loc. cit. . CHANGES IN THE OVARY 155 states that the contents of the follicle are gradually absorbed through the agency of ingrowing parenchyma cells and leuco- cytes. The cavity is eventually filled in by the ingrowth of normal ovarian tissue. The following characteristics serve to distinguish the de- generate or atretic follicle (sometimes called the corpus luteum atreticum) from the true corpus luteum: (1) There is no indi- cation of any rupture to the exterior. (2) The ovum, being retained in the follicle, loses its regularly circular shape, becomes Fie, 38.—Section through follicle in early stage of degeneration. (From Sellheim.) The ovum and follicular epithelium are in process of atrophy. shrivelled, and gradually disappears altogether. (3) The follicular epithelium, instead of hypertrophying, degenerates, the chromatic substance at one stage often appearing in the form of fine points in the cytoplasm, and much smaller than nuclei. Subsequently the remains of the cells become unrecognisable, finally disappear- ing altogether. (4) The connective-tissue wall does not prolife- rate to form a network among the epithelial cells, and there is generally no ingrowth from the thece until the epithelial cells are in an advanced state of degeneration or have altogether dis- appeared. The earliest indication of atretic change is usually 156 THE PHYSIOLOGY OF REPRODUCTION seen in the chromatolytic changes in the epithelium. Afterwards the theca interna degenerates, and then the ovum and zona pellucida. It should be mentioned, however, that the presence of a degenerate ovum cannot, by itself, be regarded as an absolute indication of follicular atresia, since Sobotta! has recorded in- stances of rupture in the mouse and in the rabbit in which the ova were accidentally retained within the cavity of the follicle, the latter nevertheless forming an otherwise typical corpus luteum; and van der Stricht? has described a similar case of retention in Vesperugo, in which part of the follicle was de- generate while another part possessed the characteristic structure of a corpus luteum. Degeneration may set in at all stages in the development of a follicle, and not merely in the fully formed follicle which has failed to rupture. Loeb* has described follicular atresia as being common in guinea-pigs of less than six months old. The degenerative changes which such follicles pass through have been studied in various Mammalia (chiefly rabbits, cavies, and other Rodents) by Schulin,t Flemming,’ Schottlinder,® Henneguy,’ Janosik,® Kolliker,® van der Stricht,!° Seitz,1! Loeb, 1 Sobotta, loc. cit, 2 Van der Stricht, Une Anomalie intéressante de Formation de Corps Jaune, Gand, 1901. 3 Loeb (L.), ‘‘ Uber hypertrophische Sag bei der Follikelatresie,” Arch. f. Mikr. Anat., vol. lxv., 1905. * Schulin, ‘Zar Morphologie des Ovariums,” Arch. f. Mikr. Anat., vol. xix., 1881. 5 Flemming, ‘‘ Ueber die Bildung von Richtungsfiguren in Siiugethieren beim Untergang Graafschen Follikel,” Arch. f. Anat. u. Phys., Anat. Abth., 1885. 6 Schottlinder, ‘‘ Beitrag zur Kenntniss der Follikelatresie,” &c., Arch. f. Mikr, Anat., vol. xxxvii., 1891. ‘“‘ Ueber den Graafschen Follikel,” &c., Arch. J. Mikr, Anat., vol. xli., 1893. 7 Henneguy, ‘Recherches sur l’Atrésie des Follicules de Graaf,” &c., Jour. deVAnat. et de la Phys., vol. xxx., 1894. 8 Janosik, ‘‘Die Atrophie der Follikel,” Arch. f. Mikr. Anat., vol. xlviii,, 1896. 9 Kélliker, “ Uber Corpora Lutea Atretica bei Siugethieren,” Verhand. d. Anat. Gesell., in Kiel, 1898. 10 Van der Stricht, “L’Atrésie Ovulaire,” &c., Verhand. d. Anat. Gesell., in Bonn, 1901. 11 Seitz, ‘Die Follikelatresie wihrend der Schwangerschaft,” &c., Arch. f. Gynak., vol. Ixxvii., 1906. CHANGES IN THE OVARY 157 and certain other writers, whose results are for the most part in general agreement. Schulin, and also Janosik, appear to regard the follicular epithelial cells as being converted into leucocytes, which they undoubtedly resemble when undergoing degeneration. Flemming, on the other hand, denies the existence of leucocytes, pointing out Misses Fig. 39.—Section through follicle in late stage of degeneration. (From Sellheim.) The cavity is in process of being filled by an ingrowth of tissue from the wall. The ovum has disappeared. that none exist in the theca, and Schottlander clearly distin- tinguishes degenerating epithelial cells from leucocytes. More recently, however, Dubuisson ! has stated that in the sparrow the follicle cells may multiply and act as phagocytes to the yolk of the degenerating ovum, which becomes filled with them. Afterwards they are said to migrate, leaving nothing but connective tissue which fills in the cavity of the follicle. A 1 Dubuisson, ‘ Contribution » Etude du Vitellus,” Arch. de Zool. Expér., vol. v., 5th series, 1906. yy. ye 158 THE PHYSIOLOGY OF REPRODUCTION similar process is described as occurring in certain reptiles. Perez also has recorded the phagocytic absorption of ova by follicle cells in the ovary of the fasting newt. Schottlainder states that atresia can occur by fatty degenera- tion as well as by chromatolysis. Flemming and others have described nuclear spindles in the ova of follicles in an early stage of atresia, thus showing that these had reached maturity before degeneration set in. Atretic follicles may shrivel up rapidly, or continue for a time in a cystic condition. In the latter case the cavity remains filled with fluid. Kolker has shown that certain of the cells in the theca interna of cystic follicles may undergo a process of hypertrophy ; and the same fact has been noticed by Seitz, who calls these cells “ theca lutein cells” owing to their resemblance to the cells of the corpus luteum. Seitz found these cells only during pregnancy. Heape ? has shown that in the rabbit two kinds of degenera- tion prevail. In the one kind the changes first affect the follicle and then the ovum, as described above. In the other the ovum is first affected and the follicle afterwards. Heape interprets the latter change as evidence that the ovum is not capable of assimilating the nourishment supplied to it. Atresia is commonly stated to occur most frequently during pregnancy, but it may occur at other times.? Thus Sandes * has shown that in Dasyurus, as soon as the corpus luteum is formed, the surrounding follicles which were previously in various stages of active development begin to undergo atrophy. The process begins in the follicles in closest proximity to the newly formed corpus luteum, and is continued during pregnancy in the other follicles in ever-widening circles. Sandes suggests that this occurs as a result of mechanical pressure due to the growth of the corpus luteum, or is in some way effected by the internal secretion which the latter organ is supposed to elaborate. Heape ® states that in the case of the rabbit, if the buck is with- 1 Perez, ‘‘Sur la Résorption phagocytaire des Ovules,” &c., Procés- Verbaua de la Soc. des Sciences de Bordeaux, 1903. 2 Heape, loc. cit. 3 Marshall, ‘“‘The istrous Cycle, &c., in the Sheep,” Phil, Trans., B., vol. excvi., 1903. 4 Sandes, loc. cit. 5 Heape, loc. cit. CHANGES IN THE OVARY 159 held from a doe during several consecutive cestrous periods, not merely the majority of the older follicles degenerate, but also many of the younger ones, so that the animal is liable to become sterile during the remainder of the breeding season.} There can be little doubt that the more usual cause of de- generation in immature follicles is lack of sufficient nutriment, or of nutriment of the requisite kind. It is usually to be observed in under-fed animals, or in animals living under unsuitable con- ditions, but it also occurs in very fat animals. Ewart states that follicular degeneration tends to occur in mares leading a semi-wild life in winter.2. Probably it is least common in animals which are in a good thriving condition, but further investigation is urgently needed before these points can be decided. SUPERF@TATION In the majority of Mammals, as in Dasyurus, there can be little doubt that the presence of the corpus luteum tends to produce follicular degeneration, or at any rate to inhibit matura- tion. In the mare, however, Ewart has shown that degeneration does not generally take place during early pregnancy, so that if a mare aborts (a common occurrence with this animal) ripe ova are available for fertilisation, and pregnancy can be started anew without delay.® If ovulation takes place during pregnancy, and if, owing to the occurrence of coition (see p. 51) the ova become fertilised, the phenomenon of superfcetation may take place—that is to say, foetuses of different ages may be present in the same uterus —but this condition is of course abnormal, though it has been known to occur in several animals. Thus, Mr. W. O. Backhouse has informed me of a case of a cat which experienced heat and underwent coition after being pregnant for six weeks, and three weeks later produced five kittens, four of which were of the normal size and were obviously born at full time (dating from the heat period prior to the beginning of pregnancy), whereas 1 Cf. Dubreuil and Regaud (C. RB. de la Soc. de Biol., vol. lxvii., 1909), who say that absence of sexual intercourse causes hemorrhage in the follicles. 2 Ewart, loc, cit. 3 Ibid. 160 THE PHYSIOLOGY OF REPRODUCTION the other kitten was very small, and apparently about three weeks developed. FoRMATION OF OvA It is usually stated that all the ova which are to be de- veloped in the ovary exist in it at the time of birth, and that a considerable proportion of these undergo atrophy before puberty. Thus, the number of ova in the ovary at birth has been estimated at 100,000, of which it is supposed that not more than 30,000 remain at puberty.+ Miss Lane-Claypon,? however, has described the formation of ° ova, resembling primordial ova, from interstitial cells during adult life. These cells are shown to increase markedly in size, their length being often almost doubled. In addition to their becoming enlarged, certain of the interstitial cells near the periphery undergo further changes during the later stages of pregnancy. The cells appear to pass outwards and become cut off by connective tissue, and in many cases almost reach the surface of the ovary. This process begins in the rabbit at about the twentieth day of pregnancy. A little later some of the cells appear to be multi-nucleated, and it is suggested that these are formed by the fusion of the same number of inter- stitial cells as there are nuclei. The nuclei then degenerate with the exception of one, and the inference is drawn that the latter lives and grows at the expense of the others in just the same way as Balfour concluded that one developing ovum in the immature ovary might be nourished by the surrounding ova which were undergoing degeneration. In the ovary of a rabbit whose time of parturition had nearly arrived, the interstitial cells were observed to have undergone further changes identical with those taking place in the deuto- broque cells of a young ovary during the period of odgenesis (see above, p. 120). The leptotenic stage is rapidly passed through and the nucleus enters upon the synaptenic condition, which 1 Galabin, A Manual of Midwifery, 6th Edition, London, 1904. Accord- ing to another calculation the human ovary at the age of seventeen contains 17,600 ova (Heyse, Arch. f. Gyndk., vol. liii., 1893), of which only 400 become mature (Henle, Handbuch dev Anatomie, 1873). 2 Lane-Claypon, ‘‘On the Origin and Life-History of the Interstitial Cells in the Ovary in the Rabbit,” Proc. Roy. Soc., B., vol. lxxvii., 1905. CHANGES IN THE OVARY 161 extends over a somewhat longer time. The massing of the chromatin into a lump having been completed, it again becomes spread out and rearranged, and the pachytenic stage is entered upon. The chromatin filaments during this stage are markedly thicker and more bulky. It is followed by a not very typical diplotenic stage, in which the duality of the filaments is said to be not well shown. In the next stage—the dictyate stage— the nucleolus becomes very definite, and the chromatin is arranged more or less over the entire nuclear area, which is now of considerable dimensions. “There can be... not much doubt that the changes taking place are identical with those seen in the young ovary, which lead to ovogenesis, and there- fore it would appear that ovogenesis also takes place in the adult animal during pregnancy.” 1 Thus it would seem that the interstitial cells, which, like the ova, are almost certainly derived from the germinal epithelium, are actually potential ova, being capable of developing into true ova when the appropriate stimulus is given. This stimulus is provided by pregnancy, at which period they undergo enlarge- ment so as to exceed the size of a primordial ovum, and in addition pass through the same series of nuclear transformations as those which characterise embryonic odgenesis.” THE SIGNIFICANCE OF THE PRo@esTROUS CHANGES Having discussed the conditions under which the Graafian follicles ripen and discharge in various species of the class Mammalia, we are now in a position to consider more fully the significance of the uterine changes with which ovulation is frequently associated. Many obstetricians have adopted the view that the de- generation stage of menstruation in the human female is of the nature of an undoing of a preparation (represented by the 1 Lane-Claypon, loc. cit. * For an account of the interstitial tissue of the ovary in various animals, see Fraenkel. See also Cesa-Bianchi, who states that the interstitial ovarian gland in hibernating animals undergoes a great development in spring and summer, but is much reduced in winter. He also comments on the close resemblance between luteal and interstitial cells. (‘‘ Vergleichende histo- logische Untersuchungen iiber das Vorkommen driisiger Formationen im interstitiellen Hierstockgewebe,”’ Arch. f. Gyndk., vol. 1xxv., 1906.) L 162 THE PHYSIOLOGY OF REPRODUCTION previous growth stage) for an ovum which failed to become fertilised (or even to be released from the ovary). This theory was originally put forward by Sigismund, and was subsequently accepted by His.2 It has been summarised in the well-known dictum that ‘‘ women menstruate because they do not conceive.” It has been shown above, however, that menstruation in the Primates is the physiological homologue of the procestrum in the lower Mammalia, and that ovulation in the latter occurs usually, so far as is known, during cestrus, or at any rate not until after the commencement of the destruction stage of the procestrum. Consequently Sigismund’s theory becomes untenable. Loewenthal * advanced the somewhat similar theory that the monthly bleeding is actually brought about by the death of the ovum in the uterus, the “ decidua” of menstruation being pro- duced by the embedding therein of the unfertilised egg. No evidence has been adduced in support of this view, which is evidently open to the same objection as Sigismund’s hypothesis. A further modification of the same theory has been ad- vanced by Beard,‘ who expresses the belief that the process of menstruation is of the nature of an “abortion of something prepared for an egg given off at or after the close of the pre- ceding menstruation, and [that] it takes place because this egg has escaped fertilisation.” “Prior to the appearance of the menses the uterus has formed a decidua, which is regarded as equivalent to that which would arise when a fertilised egg be- came affixed to the uterus.” This theory also, if it is to be entertained at all, necessitates the assumption that there is no correspondence between the procestrum in the lower Mammalia and menstruation in the Primates, since the degeneration stage of the procestrum in the dog or ferret, for instance, can hardly be of the nature of an abortion of something prepared for an ovum which was discharged at the preceding “ heat period ” many months before. The difficulty is further increased for those animals which experience cestrus only once a year, or even 1 Sigismund, ‘‘Ideen tiber das Wesen der Menstruation,” Berliner Klin. Wochenschr., 1871. 2 His, Anatomie Menschlicher Embryonen, 1880. 3 Loewenthal, ‘‘ Eine neue Deutung des Menstruationsprocesses,” Arch. f. Gynik., vol. xxiv., 1884. 4 Beard, The Span of Gestation and the Cause of Birth, Jena, 1897. CHANGES IN THE OVARY 163 less often, for it is improbable that they ovulate more frequently than they come “on heat.’ Beard, however, denies that there is any correspondence between “ the heat or rut of Mammals” and menstruation in the higher forms, saying that very little is required in disproof of the supposed relation. The theory that the whole procestrous process, including both the degeneration and the recuperation stages, is of the nature of a preparation + on the part of the uterus for the reception of a fertilised ovum is not opposed to any of the known facts. The process is sometimes viewed as a kind of surgical “ freshening ”’ of the uterus, whereby the ovum can be safely attached to the mucosa during the healing stage. It is possible, however, that the changing of the uterine tissue is not the least important part of the process. Emrys-Roberts? has made the further suggestion that the secretion of the uterine glands, together with the blood and other products of procestrous destruction, may serve to provide a rich pabulum on which to nourish the embryo during the earliest days of pregnancy. In opposition to these theories it may be urged that pregnancy has been known to take place in women who have never menstruated, and that it may occur during periods of amenorrhcea, or during the lactation period, when menstruation is sometimes in abeyance. Such cases, however, are the exception, and it must not be inferred that because the procestrous function can occasionally be dispensed with without inducing a condition of sterility, it normally plays no part in the physiology of generation. It has been pointed out, however, that the severity of the menstrual process in women is occasionally so great as to be positively injurious, and that such cases evidently belong to the category of constitutional disharmonies which Metchnikoff * 1 Kundrat and Engelmann, ‘‘ Untersuchungen tiber die Uterusschleim- haut,” Stricker’s Med. Jahr., 1873. Lawson Tait, Diseases of Women, 1889. For a further discussion of some of the theories regarding the purpose of menstruation see Heape, ‘The Menstruation of Semnopithecus entellus,” Phil. Trans. B., vol. clxxxv., 1894. ? Emrys-Roberts, ‘‘A Preliminary Note upon the Question of the Nutri- tion of the Early Embryo,” Proc. Roy. Soc. B., vol. 1xxvi., 1905. ® Metchnikoff, The Nature of Man, London, 1903. 164 THE PHYSIOLOGY OF REPRODUCTION has shown to be so common in the organs and functions of the generative system. Geddes and Thomson! also have called attention to the pathological character of menstruation, as evidenced not only by the pain which frequently accompanies the process, and the local and constitutional disorders by which it is often attended, but by the general systemic disturbance which always occurs synchronously with it. These authors interpret the discharge as a means of disposing of the anabolic surplus which is con- sumed during pregnancy by the developing embryo. A similar view is adopted by Webster,” who associates the introduction of menstruation (as distinguished from the procestrum of the lower animals) with a diminished fertility. Reference has already been made to the “ Wellenbewegung ” or “wave” hypothesis regarding the nature of menstruation (see p. 67). The physiological cause of the procestrum, and the probable part played by the ovaries in this connection, will be discussed at some length in a later chapter. 1 Geddes and Thomson, Yhe Evolution of Sex, Revised Edition, London, 1901. 2 Webster, ‘‘ The Biological Basis of Menstruation,” Montreal Med. Jour., April 1897. CHAPTER V SPERMATOGENESIS—INSEMINATION ‘ Denique per maria ac montis fluviosque rapacis Frondiferasque domos avium camposque virentis, Omnibus incutiens blandum per pectora amorem Efficis ut cupide generatim seecla propagent.” —LUCRETIUS. THE spermatozoa, or reproductive cells of the male, were ob- served as far back as the year 1677, when Hamm, who was a pupil of Leeuwenhoek, directed the latter’s attention to them. Leeuwenhoek, however, did not understand the significance of what he saw. Spallanzani! was the first to show that the presence of spermatozoa in the semen was an essential factor in fertilisation, since the filtered fluid was found to be impotent. Subsequently Kolliker * discovered that the sperms arise from the cells of the testis, and Barry * observed the conjugation of sperm and ovum in the rabbit. Van Beneden’s discovery that the nuclei of the conjugat- ing cells—both ova and spermatozoa—contain only half the number of chromosomes that they had originally has been referred to in the preceding chapter, where the maturation phenomena in the ovum have been briefly outlined ? (p. 130). The four products of division formed at the completion of re- duction in the male differ from those in the female in that each of them is a functional conjugating cell. Before describing the reduction process in detail it will be well to give a short account of the structure of the testis.® 1 Spallanzani, Dissertations, English T:anslation, vol. ii., London, 1784. 2 Kélliker, Beitriige zur Kenntniss der Geschlechtsverhdltnisse, &c., Berlin, 1841, 3 Barry (M.), ‘‘ Spermatozoa observed within the Mammiferous Ovum,” Pail. Trans., 1843. 4 For accounts of the history of the chief discoveries relating to the spermatozoa, fertilisation, &c., see Thomson, The Science of Life, London, 1899, and Geddes and Thomson, The Evolution of Sex, 2nd Edition, London, 1901. 5 See Barry (D. T.), ‘‘The Morphology of the Testis,” Jour. of Anat. and Phys., vol. xliv., 1910. 165 166 THE PHYSIOLOGY OF REPRODUCTION This organ is enclosed within a fibrous capsule, the tunica albuginea, which is very rich in lymphatics. It is covered by a layer of serous epithelium reflected from the tunica vaginalis. Posteriorly the capsule is prolonged into the interior of the testis in the form of a mass of fibrous tissue (the mediastinum testis). Certain other fibrous processes or trabecule also pro- a b i [ : \ SN e D) on Fie. 40.--Section through human testis and epididymis. (After Bohm and von Davidoff, from Schiifer.) a, glandular substance divided into lobules by septa of connective tissue ; b, tunica albuginea; ce, part of epididymis; d, rete testis; e, body of epididymis; f, mediastinum ; g, sections through commencing portion of vas deferens. ject inwards from the capsule, and divide the glandular substance into lobules. The efferent ducts of the testis (vasa efferentia) open into a single convoluted tube situated at the posterior margin of the organ and attached to the mediastinum. This is the epididymis. Its lower extremity is prolonged into a thick-walled muscular tube (the vas deferens) which is the SPERMATOGENESIS —INSEMINATION . 16% passage of exit for the seminal fluid or sperm-containing secretion. The glandular substance of the testis is composed of the con- — Fig. 41.—Section through testis of monkey. a, seminiferous tubules; }, interstitial tissue ; c, rete testis; d, vasa efferentia ; e, vas deferens ; f, tunica albuginea. voluted seminiferous tubules, two or three of which join together to form a straight tubule which passes into the body of the mediastinum. The straight tubules within the mediastinum 168 THE PHYSIOLOGY OF REPRODUCTION unite in their turn, giving rise to a network of vessels called the rete testis. From the rete the vasa efferentia are given off. Between the tubules is a loose connective tissue containing a number of yellow epithelioid interstitial cells. The connective tissue also contains numerous lymphatics and blood-vessels (branches of the spermatic artery). The nerves of the testis are derived from the sympathetic system, but a few filaments come from the hypogastric plexus. In embryonic development the tubules arise from the primitive germinal epithelium. According to Allen? the inter- stitial cells are derived from connective tissue. The straight tubules, and the tubules of the rete, are lined by a single layer of cubical or flattened epithelium without a base- ment membrane. The seminiferous tubules, on the other hand, contain several layers of epithelial cells supported by a thick basement membrane. The layer nearest the membrane con- sists of clear cubical cells, a few of which show evidence of division. These are the spermatogonia. Certain of the epithelial cells between the spermatogonia are enlarged, and project among the more internal cells in association with de- veloping sperms. These are the cells of Sertoli. On the inside of the spermatogonia are certain larger cells, known as sperma- tocytes. These are products of division of spermatogonia, each of which on dividing into two gives rise to a cell like itself, and another cell, which grows larger, passes into the second layer, and becomes a spermatocyte. The spermatids, which in some seminiferous tubules lie on the inside of the spermatocytes, are the double products of division of the latter. The spermatids so formed may be seen as small cells with spherical nuclei, and forming irregular clumps on the inner surface of the tubule. Often, however, the spermatids are elongated, being partially converted into spermatozoa. As this process of transformation proceeds, the developing sperms become arranged in little groups. Associated with each group is a foot-cell, or a cell of Sertoli, which probably serves as a 1 Allen, ‘‘The Embryonic Development of the Ovary and Testis,” Amer. Jour. of Anat., vol. iii., 1904. As already mentioned, Allen regards the in- terstitial cells of the ovary as being developed from connective tissue, thus differing from Miss Lane-Claypon. SPERMA‘TOGENESIS—INSEMINATION 169 support and as a means of conveying nourishment to the growing spermatozoa.! The tails of the latter at this stage project freely into the cavity of the tubule, and a little later the sper- matozoa shift bodily forward and become completely liberated. Fig. 42.—Section through portion of two seminiferous tubules in testis of rat. a, basement membrane; b, spermatogonium; c, spermatocyte; d, sper- matozoa in cavity of tubule; ¢, interstitial tissue containing vessels. ' Merkel, ‘Die Stiitzellen des Menschlichen Hodens,” Miiller’s Archiv, 1871. Brown, ‘‘On Spermatogenesis in the Rat,” Quar. Jour. Micr. Science, vol. xxv.,1885. Bende, ‘“ Untersuchungen iiber den Bau den Funktioniren den Samenkaniilchens einiger Siiugethiere,” Arch. f. Mikr. Anat., vol. xxx., 1887. 170 THE PHYSIOLOGY OF REPRODUCTION According to Loisel,! the orientation of the sperms in the testis is due to a secretion from the cells of Sertoli, together with Fic. 43.—A cell of Sertoli with which the spermatids (three of which are shown) are beginning to be connected—human. (After Bramman, from Schafer.) The cell contains globules of nutritive substance and similar smaller globules are seen in the spermatids. Fig. 44,—Diagram illustrating the cycle of phases in spermatogenesis. (From Schafer.) a, spermatogonia (seen dividing at 6); a’, a”, Sertoli cells; 6, spermatocytes (seen dividing at 5); c, spermatids; s’, parts of spermatids which dis- appear when spermatozoa are fully formed; s, seminal granules. 1 Loisel, ‘‘Facteurs de la Forme et de la Fasciculisation des Spermies dans les Testicules,” Jour. de l’Anat. et de la Phys., vol, xlii., 1906. SPERMATOGENESIS—INSEMINATION 171 certain of the other cells in the parietal layer of the seminiferous epithelium. In male animals which have a rutting season spermato- genesis occurs only at this time. At other seasons of the year the testes remain in a quiescent condition! The periodic activity of the testis is usually correlated with a great increase in the size of that organ (see pp. 24 and 61). Spermatogonium. Odgonium. Proliferation period. Growth period. Maturation period. Fig, 45.—Scheme of spermatogenesis and oogenesis. (After Boveri.) The changes which occur in spermatogenesis may be sum- marised as follows: (1) A spermatogonium divides into two, one product of division passing into the second layer of the seminal epithelium and becoming a spermatocyte. (2) A 1 In some animals the renewal of activity in the testes is associated with the descent of these organs from their position in the abdominal cavity through the inguinal canal and into a cutaneous fold. This is transformed into the scrotum, which lies behind the penis (except in Marsupials, where it is in front). In many Mammals the descent takes place at an early age and is permanent. In others (most Rodents, Insectivores, and bats) the testes are withdrawn into the abdominal cavity after the breeding season is over. This is effected by the cremaster muscle. 172 THE PHYSIOLOGY OF REPRODUCTION spermatocyte, or mother-cell, divides. (3) A product of division of a spermatocyte divides, giving rise to a spermatid, the number of chromosomes becoming reduced during this process to one- half the previous number. Subsequently the spermatid elongates, the nucleus becomes shifted to one end, and the spermatozodn which is formed in this way is set free. The process is con- tinually going on in the seminiferous tubules of the testis, suc- cessive crops of spermatozoa being from time to time produced. The various stages of development may generally be observed in the same testis, or even within the limits of a single tubule. It is supposed that the reduction in the number of the chromosomes is a preparation of the conjugating cells for their subsequent union in fertilisation, and is a means by which this number is held constant in the species (see p. 131).1 In those animals in which reproduction is normally effected without the intervention of a spermatozodn (parthenogenesis) the ovum may discharge only one polar body instead of two. STRUCTURE OF SPERMATOZOA A fully developed human spermatozoon consists of a flattened egg-shaped head, a short cylindrical body or middle- piece, and a long delicate vibratile tail. Lying anterior to the head is a small apical body, or achrosome, which in some animals bears a little barb-like projection by means of which the sper- matozoon bores its way into the ovum. The tail of the sperm consists of an axial filament surrounded by a protoplasmic envelope, which becomes very thin or disappears altogether at the extremity, leaving a short naked end-piece. The axial filament passes anteriorly through the middle-piece, and ends in a small knob (the end-knob) at the base of the head. Ballowitz ? has shown that the axial filament is composed of a number of parallel fibrille, like a muscular fibre. 1 For an account of the process of spermatogenesis in different animals and plants, and a discussion of the phenomena described, see Wilson, The Cell in Development and Inheritance, 2nd Edition, London, 1900. In this work the theories of Weismann and others are dealt with, and a full account of the literature is given. 2 Ballowitz, ‘‘ Untersuchungen iiber die Struktur der Spermatozoen,” Arch. f. Mikr, Anat., vol. xxxii., 1888, and vol. xxxvi., 1890; Zeitschr. f. wiss Zool., vol. 1x., 1890, and vol. lii., 1891. SPERMATOGENESIS—INSEMINATION 173 Schweigger-Seidel + and La Valette St. George ? were the first to prove, independently but almost simultaneously, that the Fie. 46.—Human spermatozoa on the flat and in profile. (After Bramman, from Schifer.) x 2500. Those on the right have adhering protoplasm. The tail is only partly shown in the two seen in profile. * Schweigger-Seidel, «« Uber die Samenkorperchen und ihre Entwickelung,” Arch. f. Mikr. Anat., vol. i., 1865. 2 La Valette St. George, ‘‘ Uber die Genese der Samenkérper,” Arch. f. Mikr. Anat., vol. i., 1865. 174 THE PHYSIOLOGY OF REPRODUCTION spermatozoon has the essential characteristics of a complete cell. The head contains the nuclear material, which is surrounded by a thin layer of cytoplasm. The end-knob is said to represent the centrosome. Spermatozoa, conforming with more or less closeness to the type described above, occur in the greater majority of multi- cellular animals from the Coelenterata up to Mammals. In Pisces, and also in Echinoderms, the general resemblance is very distinct, but in other forms of life there is more diversity in the form assumed by the spermatozoa. “ The head (nucleus) may be spherical, lance-shaped, rod-shaped, spirally twisted, hook-shaped, hood- shaped, or drawn out into a long filament; and it is often divided into an anterior or a posterior piece of different staining capacity, as is the case with many birds and Mammals. The achrosome sometimes appears to be wanting, eg. in some fishes. When Fiq.47._Human sperma- present, it is sometimes a minute tozoa(x 1000). (After rounded knob, sometimes a sharp stylet, Retzius, from Scha- : : fer.) and in some cases terminates in a sharp ee er barb-spur by which the spermatozoon ap- the flat; b, head; c, pears to penetrate the ovum (Triton).” 1 middle-piece ; d, tail; The middle-piece also shows considerable e, end-piece of tail, variability. It may be spherical, cylin- described as a dis" ayical, or flattened against the nucleus ; tinct part by Retzius, ? ’ sometimes it is of great length, and sometimes it passes insensibly into the flagellum or tail. The latter, in some insects and fishes, gives attachment to a mem- branous fin. The end of the axial filament, as already mentioned, is sometimes left naked, giving rise to the end-piece. The tadpole-like shape is not an essential characteristic of the spermatozo6n, for in certain Arthropods and Nematodes there is no flagellum, and the sperms are consequently incapable of spontaneous movement. In the daphnid Polyphemus the 1 Wilson, loc. cit. SPERMATOGENESIS—INSEMIN ATION 1%5 sperms are said to be amceboid. In some crustacean sperma- tozoa there are a number of radiating spine-like processes which seem to take the place of the flagellum. “ + In other animals, and notably in the gasteropod mollusc Paludina, there are two kinds of spermatozoa. In this animal one is of the usual type, whereas the other is larger and worm- shaped, with a tuft of cilia at one end. The smaller variety alone is said to be functional. The size of the sperm varies greatly in different animals. In Man its length is about -05 millimetres or a 300th of an inch, Fig. 48.—Different forms of spermatozoa from different species of animals, as follows :— a, bat; b & c, frog; d, finch; e, ram; f & g, boar; h, jelly-fish; i, monkey; k, round worm; J, crab. (From Verworn.) . the head and the middle-piece being each about ‘005 millimetres long. It is obvious that the sperm contributes comparatively little material to the fertilised ovum, being provided with only suffi- cient protoplasmic substance to form a locomotive apparatus by means of which it gains access to the ovum. The pre- dominantly destructive metabolism of the spermatozoén as con- trasted with the ovum has been strongly emphasised by Geddes and Thomson,? who believe it to exemplify those katabolic 1 For further details of the structure of various kinds of sperms see Wilson, loc. cit.; also Ballowitz’s papers just referred to, and Retzius’ Biologische Untersuchungen, vols. xi., xii., and xiii, Stockholm and Jena. The latter contains numerous Jarge plates with figures of spermatozoa. 2 Geddes and Thomson, The Evolution of Sex, Revised Edition, London, 1901. ° 176 THE PHYSIOLOGY OF REPRODUCTION phenomena which, according to their view, are usually associated with the male sex. SeMINAL FLvIp The semen serves as the mechanical medium in which the spermatozoa move. It is possible also that it has a nutritive function. It is secreted by the seminiferous tubules. It is milky in appearance, and has a characteristic smell. When ejected the seminal fluid is mixed with the secretions of the accessory glands (prostate, &c.), which render it still more milky. On standing it tends to become gelatinous. According to Lode,’ the specific gravity of semen is between 1-027 and 1-046. The number of spermatozoa which exist in normal human semen is subject to much variation. Lode? has shown that it diminishes almost to zero after a number of successive emissions, but increases again after an interval of several days. The average number is given as 60,000 per cubic centimetre. The number of sperms present in the ejected seminal fluid of the dog was also found to be greater at the end of an interval in which there were no emissions, but it did not continue to increase after more than eight or ten days. In a normal emission of semen (Man) Lode calculates that there are about 226,000,000 spermatozoa, but that the number may vary from zero to 551,000,000. The spermatozoa which are not ejaculated degenerate. The tails break off, and undergo a gradual liquefaction. The end products are ultimately absorbed by the epithelial cells of the seminal vesicles, and perhaps by the cells of the vasa de- ferentia or of the testis itself. According to Perez,® the sperma- tozoa of male newts which are kept apart from females are absorbed by phagocytes.* MovEMENTS OF SPERMATOZOA When the spermatozoa are in the testis they are inactive, but they begin to move rapidly as soon as they are ejected in the 1 Lode, ‘Untersuchungen tiber die Zahlen- und Regenerationsverhaltnisse der Spermatozoiden bei Hund und Mensch,” Pfliiger’s Arch., vol. 1., 1891. 2 Lode calculates that about 339,385,500,000 spermatozoa must be pro- duced in man between the ages of twenty-five and fifty-five. 3 Perez, ‘“ Résorption phagocytaire des Spermatozoides,” Proces-Verbaux de la Soc. des Sciences de Bordeaux, 1904. 4 The chemistry of the spermatozéon and semen is dealt with in Chapter VIII. SPERMATOGENESIS—INSEMINATION 177 seminal fluid. The rate at which they progress has been estimated at 3°6 millimetres per minute.1 Bischoff? found spermatozoa at the top of the oviduct in the rabbit nine or ten hours after coition. It is probable that the ejected spermatozoa continue to undergo movement, as a general rule, so long as they retain their vitality, the rate of movement becoming gradually diminished and ceasing altogether shortly before death. In bats, however, during the period of hibernation the sperms become quiescent without dying, their vigour being restored in the spring when they conjugate with the ova? It is exceedingly probable also that in the spotted viviparous salamander and the other animals referred to below (p. 186), in Fig. 49.—Diagram illustrating wave-like movement of swimming spermatozoon. (From Nagel.) which the male cells retain their vitality for long periods, these must at such times remain quiescent, for otherwise their store of energy would soon become exhausted. The spermatozoa swim by means of their tails. The move- ment is represented in the accompanying figure (taken from Nagel), which shows the successive positions assumed by the sperm in a state of locomotion. A wave of movement first makes its appearance in the forepart of the tail, and then rapidly travels backwards to the end, to be succeeded by a fresh wave which follows the same course. It would seem that the driving 1 Lott, Anatomie und Physiologie des Cervix Uteri, Erlangen, 1871. Ac- cording to Adolphi (‘‘Ueber das Verhalten von Schlungenspermien in strémender Flussigkeiten,” Anat. Anz., vol. xxix., 1906), the spermatozoa of the adder swim at the rate of 50 u. to 80 mu. per second. ? Bischoff, Die Entwickelung des Kaninchen-Eies, Giessen, 1842 5 See p. 186, / 4 Nagel, Handbuch der Physiologie des Menschen, vol. ii., Braunschweig, 1906. M 178 THE PHYSIOLOGY OF REPRODUCTION force is located a little behind the head. The head itself does not appear to be concerned in the movements of locomotion. The movements of spermatozoa have probably been studied most closely in Insecta and Echinodermata. Buller‘ says that the sperms of the Echinoidea in a drop of sea-water (or the medium in which they are normally discharged) swim spirally, so long as they do not come into contact with the surface. The spirals may be so steep that the sperms appear to move almost in a straight line, in which case progression across the field of the microscope is relatively rapid. In other cases the incline of the spiral is so slight that the spermatozoa swim almost in circles, and consequently move forward across the microscopic field with great slowness. Every gradation between these two extremes was observed, but the more active sperms generally swam in the steeper spirals. Dewitz? has shown that when the spermatozoa of the cock- roach are put into 0°6 per cent. solution of sodium chloride, and placed between two surfaces, such as those of a slide and a cover-glass, they collect after a short time, partly upon the upper surface of the slide and partly upon the lower surface of the cover-glass. In these positions they describe circles with their tails, the rotation being invariably counter-clockwise. The bulk of the liquid remains free from spermatozoa, the latter adhering to the glass surfaces after having once reached them. If a ball be placed in the fluid, its surface is soon sought by the spermatozoa.’ Verworn has described this phenomenon under the name of “ barotaxis,” and states that it is caused by pressure acting unequally on different sides of the spermatozoon. It is said to be of great importance in the process of fertilisation, and probably assists the spermatozo6n in entering the micropyle 1 Buller, ‘‘Is Chemotaxis a Factor in the Fertilisation of the Eggs of Animals?” Quar. Jour. Micr. Science, vol. xlvi., 1902. 2 Dewitz, ‘‘Ueber Gesetzmiissigkeit in der Ortsveriinderung der Sper- matozoen,” &c., Pliiger’s Archiv, vol. xxxviii., 1886. Rotation by spermatozoa seems to have been recorded first by Eimer, ‘t Untersuchungen iiber den Bau und die Bewegung der Samenfaden,” Verhand d. Phys. Med. Gesel. zur Wiirzburg, vol. vi., 1874. _ 3 Ballowitz, ‘‘ Untersuchungen iiber die Struktur der Spermatozoen,” &c., Zeitschr. f. Zool., vol. i., 1890. SPERMATOGENESIS—INSEMINATION 179 of the ovum. Dewitz’s observations were subsequently con- firmed by Ballowitz.? Counter-clockwise rotation upon surfaces was first recorded for the spermatozoa of Echinoderms by Dungern,? who. dis- covered the phenomenon in Spherechinus and Arbacia. About the same time Buller,* who has described the manner of rotation more fully, observed its occurrence in the sperms of various other Echinoderms, and particularly in those of Echinus: “ When a spermatozoén comes in contact with a glass surface, unless it becomes immediately fixed to the glass [it] begins to make characteristic circular revolutions upon it. If the cover- glass be supported by pieces of another cover-glass, and the upper surface of the drop in contact with it be carefully focussed, it is seen that all the spermatozoa which are not attached by their heads, but are moving there, are revolving from the observer's point of view in clock-wise direction. If the lower surface of the drop in contact with the slide be examined, a reverse rotation—the counter-clockwise—is seen to be the rule. In both cases, therefore, if the surfaces be regarded from the point of view of the spermatozoa, the rotation is always in one direction—namely, the counter-clockwise.”’ The head is the only visible part of the rotating spermatozoén. This moves rapidly round in a circle, which in the case of Echinus is slightly less than 0:05 millimetres (or the length of a spermatozoon) in diameter. A normally rotating sperm of Spherechinus was observed to make 109 circles around one point in ninety seconds. The rate of movement of the head is calculated to be about 0°12 millimetres per second, or 7:2 milli- metres per minute. The characteristic rotation may likewise take place upon surfaces which are bounded by air (instead of glass), and it has been observed also upon the outer surface of the gelatinous layer of the ova of Echinus. Buller concludes, therefore, that the nature of the surface is not an important factor in the process. ' Verworn, General Physiology, Lee’s Translation from the second German Edition, London, 1899. * Ballowitz, loc. cit. * Dungern, ‘‘ Die Ursachen der Specietat bei der Befruchtung,” Zentralbl. JF. Physiol,, vol. xv., 1901. 4 Dungern, loc cit. 180 THE PHYSIOLOGY OF REPRODUCTION Ballowitz expresses the opinion that the circles described by insects’ sperms are simply the modified spirals made by the free-swimming cells. Buller thinks that this view, which pro- vides a purely mechanical explanation, is also probably correct for the spermatozoa of Echinoderms. Since counter-clockwise rotation upon surfaces has been - observed in the spermatozoa of two groups as widely separate as the Insecta and the Echinodermata, it would seem probable, as Buller remarks, that it will be found to occur in other animals. The spermatozoa of Mammals, in traversing the female passages after copulation, make their way upward towards the ovaries in opposition to downward currents set up by the cilia of the lining epithelia. Kraft has shown that when rabbits’ spermatozoa, in a state of feeble motion, are placed upon the inner wall of the oviduct, their movements become more vigorous and they swim against the current which the cilia pro- duce. Roth? also has succeeded in experimentally illustrating the same fact. It is commonly stated that in Man the passage of the sperma- tozoa from the vagina inwards is assisted by a contraction of the muscular wall of the uterus, which compresses the cavity of that organ into which the sperms are drawn when relaxation takes place. The contraction of the uterus is said to be a reflex action resulting from copulation. It has also been sug- gested that, during copulation, a mucous plug which is ordinarily contained in the cervix may be temporarily and partially ex- pelled into the vagina and afterwards withdrawn with the spermatozoa adhering to it.4 So also Heape ° has shown that in the rabbit the passage of the spermatozoa into the uterus is probably assisted by a sucking 1 Kraft, ‘Zur Physiologie des Flimmerepithels bei Wirbelthieren,” Phliiger’s Archiv, vol. xlvii., 1890. 2 Roth, ‘‘ Ueber das Verhalten beweglicher Mikroorganismen in strémender Flissigkeit,” Deutsche med. Wochenschrift, vol. xix., 1893. Verworn (loc. cit.) describes this property of spermatozoa under the name of rheotaxis, which, he says, is a special kind of barotaxis. See also Adolphi, ‘‘ Die Spermatozoen der Siugethiere schwimmen gegen den Strom,” Anat. Anz., vol. xxvi., 1905. ® See Beck, ‘‘ How Do the Spermatozoa enter the Uterus?” Amer. Jour. of Obstet., vol. viii., 1875. 4 See Williams, Obstetrics, New York, 1904. 5 Heape, ‘‘ ‘The Artificial Insemination of Mares,” Veterinarian, 1898. SPERMATOGENESIS—INSEMINATION 181 action on the part of the latter organ. The os uteri, which is situated above the ventral wall of the vagina, was observed to dip down into the seminal fluid at the bottom of the vagina, and then to be withdrawn again in conjunction with a peristaltic contraction of the uterus. These movements were repeated at intervals. Moreover, it was found that the sucking action could be induced artificially by stimulating the erectile tissue of the vulva. It is probable, however, that the spermatozoa, after once entering the uterus, proceed to their destination un- assisted, and that the direction of their movement is deter- mined by the capacity they possess to respond to the stimuli set up by opposing currents. Moreover, pregnancy has been known to follow imperfect coition in Man, so that there can be no doubt that under certain circumstances the spermatozoa are capable of passing inward by their own unaided efforts. INSEMINATION _ The act of copulation results in the introduction of seminal fluid through the generative aperture of the female. The mechanism by which this is effected in the higher animals is described in a future chapter, where the functions of the acces- sory male organs are dealt with. The introduction of the fluid into the female generative passages is known as insemination (as distinguished from impregnation, which is the term used in reference to the female when fertilisation takes place 1). It is obvious that in those animals which ovulate spon- taneously during the cestrus periods it should be possible to induce pregnancy at such times by the artificial introduction of spermatozoa into the vagina or into the uterus. That this could actually be effected was probably first demonstrated by Spallanzani,? though there is evidence that the practice of artificial insemination was not unknown to the Arabs many centuries ago.? The following is a description of Spallanzani’s 1 That is to say, the animal is inseminated when the spermatozoa are introduced, and it is impregnated when the ovum becomes fertilised by a sperm. See Heape, “The Artificial Insemination of Mammals,” Proc. Roy. Soc., vol. lxi., 1897. * Spallanzani, Dissertations, vol. ii, London, 1784. 3 Gautier, Le Fécondation artificielle, &c., Paris, 1889. a4 v 182 THE PHYSIOLOGY OF REPRODUCTION original experiment, as quoted from a contemporary English translation :— “T chose a bitch spaniel of moderate size which had before had whelps. Suspecting, from certain appearances, that she would soon be in heat, I confined her in an apartment, where she continued a long time, as will be seen below. For greater security, that she might never be let loose, I fed her myself, and kept the key the whole time. On the thirteenth day she began to show evident signs of being in heat; the external parts of generation were tumid, and a thin stream of blood flowed from them. On the twenty-third day she seemed fit for the admission of the male, and I attempted to fecundate her artificially in the following manner. A young dog of the same breed furnished me, by a spontaneous emission, with nineteen grains of seed, which were immediately injected into the matrix, by means of a small syringe introduced into the vagina. As the natural heat of the seed of animals of warm blood may be a condition necessary to render fecundation efficacious, I had taken care to give the syringe the degree of heat which man and dogs are found to possess, which is about 30° [or between 99° and 100° Fahrenheit]. Two days after the injection, the bitch went off her heat, and in twenty days her belly appeared swollen, which induced me to set her at liberty on the twenty-sixth. Mean- while the swelling of the belly increased; and sixty-two days after the injection of the seed, the bitch brought forth three lively whelps, two male and one female, resembling in colour and shape not the bitch only, but the dog also from which the seed had been taken. Thus did I succeed in fecundating this quadruped ; and I can truly say, that I never received greater pleasure upon any occasion, since I first cultivated experi- mental philosophy.” Spallanzani also records a similar experiment by Pierre Rossi, in which a dog was impregnated by artificial means. Considerable success has been obtained in recent years in ex- periments on the artificial insemination of dogs. Gautier ! refers to a case in which pregnancy was induced by this means. Albrecht ? 1 Gautier, loc. cit. 2 Albrecht, ‘‘Kiinstliche Befruchtung,” Wochenschr. f. Thierheilkunde und Viehzucht, Jahrg. xxxix. SPERMATOGENESIS—INSEMINATION 183 and Plonnis? have also described experiments in which they successfully inseminated dogs by artificial methods (see p. 611). Heape? has recorded a series of experiments carried out by Sir Everett Millais on the artificial insemination of Basset hounds. The present writer has succeeded in inducing pregnancy by this method in a Dandie Dinmont terrier. More- over, there are numerous cases on record in which dogs have been successfully inseminated artificially as a means of overcoming certain forms of barrenness (see p. 611). The method adopted in all these experiments was substantially the same as that em- ployed by Spallanzani. Artificial insemination is now also practised on mares, donkeys, and cows, and usually with the object of remedying sterility. In thoroughbred mares especially it has proved of great service, having been the means of preserving for breeding purposes many valuable animals which otherwise would have been discarded.? Iwanoff * has described experiments in which pregnancy was induced in rabbits and guinea-pigs by the artificial injection of testicular fluid into the female generative passages. The same investigator states that he induced hybridisation between a male rat and a female mouse by artificially inseminating the latter (see p. 611, Chapter XIV.). He has shown, further, that the spermatozoa retain their vitality sufficiently long to admit of their being employed successfully in artificial insemination if they are kept in solutions of various salts (sodium chloride, sodium carbonate, &c.) or in serum instead of in the secretions of the accessory generative glands. Hunter appears to have been the first to practise arti- 1 Plonnis, ‘‘ Kiinstliche Befruchtung einer Hiinden,” &c., Inaug. Dissert., Rostock, 1876. 2 Heape, loc. cit. 5 For references to particular experiments see Heape, ‘‘The Artificial Insemination of Mares,” Veterinarian, 1898; also a booklet published by Huish (The Cause and Remedy of Sterility in Mares, Cows, and Bitches, London, 4th Edition, 1899), in which a large number of cases are described in which artificial insemination was successfully carried out; also Iwanoff, “De la Feécondation Artificielle chez les Mammiféres,” Arch. des Sciences Biologiques, vol. xii., 1907. The last-mentioned paper contains an account of a very large series of experiments on horses, cows, and sheep, with a full description of the practical methods employed, and a very complete account of the literature of the subject. 4 Iwanoff, ‘La Fonction des Vésicules séminales,” &c,, Jour. de Phys. et de Path. gen., vol. ii, 1900, 184 THE PHYSIOLOGY OF REPRODUCTION ficial insemination upon a woman (previously sterile), but it has since been successfully adopted by various medical men, the method being to inject the spermatozoa through the os into the cavity of the uterus (see p. 609). With those animals whose ova are normally fertilised outside the body, artificial insemination is a still simpler process. Spallanzani was the first to show that the eggs of various species of Amphibia could be fertilised by the application of fluid obtained from the testes or seminal vesicles of the male, and that the frogs and newts which were generated by this means in no way differed from those produced in nature. Spallanzani was also successful in artificially fecundating the eggs of the silk-worm moth. Artificial impregnation of fish ova was first employed by Jacobi,? and the method which he adopted is practically the same as that habitually practised at the present day for stocking water-courses with fish. The vitality of the spermatozoén appears to vary widely in the different species of animals. Leeuwenhoek,? and subsequently Prévost and Dumas,’ state that they found moving sperms in the internal genital organs of female rabbits and dogs eight days after coition. Bonnet * says that he observed motionless sperms, which, therefore, were probably dead, but had not yet undergone disintegration, in a bitch seventeen and a half days after coition. In a series of experiments upon the longevity of the spermatozoon in the rabbit, it was found that these cells can survive in the vasa deferentia for at least ten days after the removal of the testes, but that they die before the end of thirteen days.® Spallanzani ° cites the fact that a hen can lay fertilised eggs twenty days after impregnation by a cock. 1 Home, “ An Account of the Dissection of an Hermaphrodite Dog,” Phil. Trans., 1799. 2 See Giinther, Introduction to the Study of Fishes, Edinburgh, 1880. 3 See Waldeyer’s article in Hertwig’s Handbuch der Entwicklungslehre, Jena, 1903. 4 Bonnet, ‘‘Giebt es bei Wirbelthieren Parthenogenesis,” Merkel und Bonnet’s Ergebnisse d. Anat. u. Entwick, vol. ix., 1900. 5 Marshall and Jolly, ‘‘Contributions to the Physiology of Mammalian Reproduction : The Gistrous Cycle in the Dog,” Phil. Trans. B., vol. cxeviii., 1905. § Spallanzani, loc. cit, SPERM ATOGENESIS—INSEMINATION 185 Strassmann ! has recorded a case in which human spermatozoa survived in the female generative passages for a week after coition. Bossi? refers to a similar instance where the sperms lived for over twelve days. In another case described by Diibrssen,? living spermatozoa were found in a woman who stated that coition had not been experienced for three and a half weeks. In many species of bats, as already mentioned, copulation takes place in autumn and ovulation in the following spring, so that the spermatozoa retain their vitality while stored up in the uterus during the hibernating period. Sperms obtained from the females at this time are dormant, but regain their vitality on the application of warmth.* The spermatozoa of some warm-blooded animals will stand considerable variation in temperature and still retain their vitality. Thus they have been known to live for many hours at ordinary room temperature ; but, undoubtedly, ejected sperms tend to survive longest if kept at body temperature. Heape ° states that some seminal fluid of a dog was sent to him by post in a glass tube, and on being examined eighteen hours after it was obtained, fully half the spermatozoa were found to be active and vigorous, while increased warmth stimulated to activity those which showed signs of sluggishness but did not revive the remainder. In the experience of the writer, horses’ spermatozoa die more easily if exposed to cold. Chelchowski,* in describing the methods adopted in the artificial insemination of mares, lays stress upon the necessity of keeping the seminal Auid warm, and states that, if this is done, it is possible to keep the sperms alive for twenty hours. The case of bats, which has been referred to above, has a | parallel in certain cold-blooded animals. Thus, according to ' Strassmann, Lehrbuch der gerichtlichen Mediz'n, 1895. 2 Bossi, ‘ Etude Clinique et Expérimentale de )’ Epoque la plus favorable a la Fécondution de la Femme,” Rivista di O*stet. e Ginecol., 1891. 3 Dihrssen, ‘‘ Lebendige Spermatozoen in der Tube,” Central. f. Gyndak., 1893. ; * See Eimer and other references given on page 136. ° Heape, loc. c't. ® Chelchowski, Die Ster.litat des Pferdes, Wien, 1894. 186 THE PHYSIOLOGY OF REPRODUCTION Rollinat,! in snakes belonging to the species Tropidonotus viperinus the females are usually inseminated in the autumn, whereas the eggs are not laid until the beginning of the following summer. Also in the case of the spotted viviparous salamander (Salamander maculosa), after the birth of the young, which occurs about the month of May, a new batch of ova pass into the oviducts and are fertilised (prior to the commencement of the sexual season) by spermatozoa which were introduced in the July of the previous year, and thereafter stored in the uterus.” It is obvious that in both these cases the spermatozoa retain their vitality in the female for periods of many months. In animals like the earthworm, in which the spermatozoa are stored in special reservoirs known as spermathece, it is probable that they retain their vitality for long periods. Lang * has shown that the sperms may live for three years in the vesicule seminales of snails. The extreme longevity possessed by the male cells of some insects is still more remarkable. Von Siebold* states that the spermatozoa of bees may survive for four or five years. Moreover, queen ants have been known to lay fertile ova thirteen years after the last intercourse with a male. 1 Rollinat, “Sur l’Accouplement des Ophidiens ala Fin de lEté et au Commencement de l’Automne,” Bull. Zool. Soc. France, vol. xxiii., 1898. * Sedgwick, Student's Teat-Book of Zoology, vol. ii, London, 1905. 3 Lang, ‘‘ Uber Vorversuche zu Untersuchungen iiber die Varietaéten- bildungen von Helix hortensis Miiller and Helix nemoralis L.,” Festschr. zum siebz‘gsten Geburtstage von Ernst Haeckel, Jena, 1904. 4 Von Siebold, ‘‘ Fernere Beobachtungen iiber die Spermatozoen Wirbel- loser Tiere,” Miiller’s Archiv, 1837. CHAPTER VI FERTILISATION * Although it be a known thing subscribed by all, that the foetus assumes its origin and birth from the male and female, and consequently that the egge is produced by the cock and henne, and the chicken out of the egge, yet neither the schools of physicians nor Aristotle’s discerning brain have disclosed the manner how the cock and its seed doth mint and coine the chicken out of the egge.” HARVEY. ALTHOUGH much progress has been effected, and many new facts have been discovered, since Harvey wrote his famous dis- sertation on “‘ The Efficient Cause of the Chicken,” the actual nature of the process whereby the ovum, after being discharged from the ovary, is endowed with a new vitality through union with a spermatozcon, is a problem the solution of which is still far from complete. In 1843 Martin Barry,! as already mentioned, first observed the union of the spermatozodn and ovum in the rabbit, and a little later Newport ? recorded its occurrence in the frog ; -but it was not until the last quarter of the nineteenth century that the significance of the process was realised. It was largely through the work of Hertwig, Strasburger, and van Beneden that most biologists came to believe that the union of the nuclei of the gametes was the essential act in the process of conjugation. The more recent investigations of Boveri and others do not, however, entirely support this conclusion. As already described, the head of the spermatozo6n represents the nucleus, and contains the chromatin material. When the sperm penetrates into the substance of the ovum the tail be- comes absorbed, but the head remains as the male pronucleus. The matured nucleus of the ovum, or female pronucleus (the two polar bodies having been discharged), passes towards the * Barry, “Spermatozoa Observed within the Mammiferous Ovum,” Phil. Trans., 1843. ? Newport, “‘On the Impregnation of the Ovum in the Amphibia,” Phil. Trans., 1851. 187 188 THE PHYSIOLOGY OF REPRODUCTION centre of the cell, where it unites with the male pronucleus which generally becomes somewhat enlarged. The middle- piece of the spermatozoon also enters the egg, and, according to Boveri,! induces the formation of a centrosome, which, after the completion of fertilisation, initiates the process of cell division. Fiq. 50.—Successive stages in the fertilisation of an ovum of Echinus esculentus, showing the entrance of the spermatozodn. (From Bryce.) Cytoplasmic filaments arrange themselves around the centro- some in the form of a star, the sperm-aster, which accompanies the male pronucleus, and afterwards comes to lie alongside of 1 Boveri, Zellen Studien IV., Ueber die Natur der Centrosomen, Jena, 1901. Jenkinson, ‘‘ Observations on the Maturation and Fertilisation of the Egg of the Axolotl,” Quar. Jour. Micr. Science, vol. xlviii., 1904, has re- cently stated that the middle-piece of the spermatozoén, after forming the centre of the sperm-sphere and sperm-aster, completely disappears, and that the centrosome is formed from the sperm-nucleus at a later stage. (The sperm-sphere is the clear area which forms in the ovum round the head and middle-piece of the spermatozoon shortly after its entrance.) FERTILISATION 189 the segmentation nucleus (as the nucleus formed by the union of the two pronuclei is called). In the segmentation nucleus the normal number of chromosomes characteristic of the species is once more restored. The odsperm, or zygote, produced in this way is the starting-point of a long series of cell divisions which culminate in the formation of a new, completely developed individual. Jenkinson, who has carried out a series of experiments in- tended to elucidate the physical processes occurring in fertilisa- tion, draws the conclusion that the structures which appear in the ovum are produced under the influence of the middle-piece Fig. 51.—Three stages in the conjugation of male and female nucleus in the fertilisation process of Echinus. (From Bryce.) and centrosome. He supposes these bodies to possess the power of withdrawing water from the cytoplasm, of swelling up and dissolving in the water so absorbed, and then giving off radial outgrowths which precipitate the proteins of the cell, and so produce the fertilisation spindle. Jenkinson lays some stress on the fact that a watery fluid collects in vacuoles in the centre of the sperm-sphere of the axolotl, and regards the presence of this fluid as evidence that the sperm introduces a hydroscopic substance into the ovum. In confirmation of this the experi- ments show that a hydroscopic particle is capable of giving rise to an astral structure in a colloid solution.! Boveri and others have proved experimentally that portions of unfertilised Echinoderm ova, without egg nuclei, may develop 1 Jenkinson, loc. cit. Further references are given in this paper. 1909 THE PHYSIOLOGY OF REPRODUCTION normally after the addition of spermatozoa, while Driesch has shown that if such ova are deprived of their envelopes by shaking, and are then divided into fragments some of which contain no nuclei, the latter are capable of being ferti- lised a second time. It is clear, therefore, that in such cases the union of nuclei is not essential for the development of the ovum. In those ova which are surrounded by a membrane it is probable that the fertilising spermatozoén bores its way through pb. at any point (Mammals and Am- phibians). In other cases there is a small aperture in the wall of the ovum ; this is called the micropyle ‘(some Pisces and Insecta). Some eggs, however, are naked, so that the sperms may effect an entrance anywhere on the surface (some Echinoderms and Ccelenterates), or there may be funnel-shaped depres- sions on the egg’s periphery (certain hydromedusz). ? Fia. 52.—Fertilisation process In the majority of animals only in bat’s ovum, (After van one spermatozoén normally enters ee eeney the ovum, but in some (certain p-b., polar bodies ; o.n.,nucleus ingects, elasmobranch fishes, reptiles, of ovum: s. n., nucleus of spermatozodn, earthworm, lamprey, axolotl,? &c.), several may effect an entrance. The latter condition is called Polyspermy. Only one sperm- nucleus conjugates with the ovum-nucleus; the others as a general rule undergo degeneration, but in a few cases (elasmobranchs and reptiles) they are said to divide, forming accessory nuclei whose ultimate fate is unknown. In those animals in which only one sperm normally enters the egg, pathological polyspermy may occasionally occur. In such cases each sperm centrosome may give rise to a sperm-aster. The 1 For references to the original papers, which are somewhat numerous, see Przibram, Embryogeny, English Translation, Cambridge, 1908. 2 Wilson, The Cell, &c., 2nd Edition, New York, 1900. 3 Jenkinson, loc. cit. Further references are given in this paper. FERTILISATION 191 eggs which are fertilised in this way either do not divide at all or go on dividing irregularly for a short time and then perish.' It is supposed that the entrance of supernumerary sperms is prevented normally either by some mechanical means, such as the development of a membrane formed after the penetration of the first sperm, or else by a change in the chemical constitu- tion of the ovum, occurring as the immediate result of fertilisa- tion.2 Thus, the brothers Hertwig * showed that in the case of eggs the vitality of which had been reduced artificially (e.g. by poisons), the vitelline membrane was formed so slowly after the entrance of the first spermatozodn that others also were able to make their way into the egg cytoplasm. On the other hand, the ova of many animals in which no membrane is formed seem to possess the capacity of resisting the entry of supernumerary spermatozoa, and the same is apparently the case with those ova which have a membrane before fertilisation, this membrane being penetrated by only a single sperm. Loeb * has recently suggested that polyspermy may be prevented by an alteration in the surface tension of the egg after the entrance of the spermatozoon. In the Mammalia fertilisation takes place usually in the upper part of the Fallopian tube. Tue Herepirary Errects oF FERTILISATION The attempts that have been made to interpret the nature and essence of sexual reproduction may be ranged under two heads, representing the two chief theories that have been elaborated (with some modifications by their respective ad- herents) to explain the observed phenomena.® According to 1 Wilson, loc. cét. 2 Farmer, “On the Structural Constituents of the Nucleus,” &c., Croonian Lecture, Proc. Roy. Soc, B., vol. \xxix., 1907. 5 Hertwig, O. and R., ‘‘ Beitrage zur Kenntniss der Bildung, Befruchtung und Teilung des tierischen Eies,”” Morph. Jahr., vols. ii. and iii., 1887. + Loeb, The Dynamics of Living Matter, New York, 1906. 5 For accounts of the various theories which have been put forward con- cerning the nature of fertilisation, see Wilson, loc. cit., Geddes and Thomson, The Evolution of Sex, 2nd Edition, London, 1901; Weismann, The Evolution Theory, English Translation, London, 1904; and Lock, Variation, &c., London, 1906. Further references are given in these works. 192 THE PHYSIOLOGY OF REPRODUCTION one hypothesis, conjugation of the gametes results in a re- juvenescence which is essential for the perpetuation of the race (see p. 212). According to the second theory, which is not necessarily antagonistic to the first, gametic union is a source of variation.! The latter theory may now be briefly considered. A full discussion of the hereditary effects of fertilisation is, however, beyond the scope of the present work. The doctrine that conjugation is a source of variation was first promulgated at the beginning of the last century by Treviranus. Subsequently Brooks? adopted the same idea, and Weismann made it the basis of his famous theory of heredity.’ “Sexual reproduction is well known to consist in the fusion of two contrasted reproductive cells, or perhaps even in the fusion of their nuclei alone. These reproductive cells contain the germinal material or germ-plasm, and this again, in its specific molecular structure, is the bearer of the hereditary tendencies of the organisms from which the reproductive cells originate. Thus, in sexual reproduction, two hereditary tendencies are in a sense intermingled. In this mingling I see the cause of the hereditary individual characteristics ; and in the production of these characters, the task of sexual reproduction. It has to supply the material for the individual differences from which selection produces new species.” Weismann supposes the nuclear chromatin of the cell to consist of a large number of self-propagating vital units which he calls biophors. These biophors he believes to be grouped 1 A third theory, which has never obtained any great support among biologists, suggests that the purpose of sexual reproduction may be to prevent variation, and so preserve specific uniformity. According to this view the sexual process, although continually creating new variations, is also con- stantly obliterating them by tending to produce individuals possessing the mean of their parents’ characters. ‘This theory, which is the converse of the second theory referred to in the text, has received the support of the Hertwigs. In this connection it may be remarked that variability is quite as great among non-sexual parthenogenetic animals as among those which are reproduced sexually. This fact is difficult to explain if we adopt the theory that the purpose of gametic union is to induce variability. Moreover, Enriques (“ La Con- iugazione e il differenziamento sessuale negli Infusori,”’ Arch. f. Protisten- kunde, vol. ix., 1907), as a result of a series of experiments upon conjugation in Infusoria, has adopted a similar view to that of the Hertwigs. 2 Brooks, The Law of Heredity, Baltimore, 1883. 3 Weismann, The Germ Plasm, English Translation, London, 1893. FERTILISATION 193 together to form more complex units, named determinants, which represent the separate parts of the organism. The de- terminants are supposed to be aggregated together to com- prise units of a still higher order, known as ids. These are identified with the chromatin granules. Every part of the organism (or every character that it possesses) is believed to be represented in an id. Moreover, Weismann assurhes that the ids vary slightly in related individuals, the differences in the ids corresponding with the variations in the species. Lastly, the ids are said to be arrayed in linear series so as to form idants. Weismann identifies these with the chromosomes. It follows, therefore, that each chromosome represents a particular group of slightly differing germ-plasms. The purpose of variation, as expressed in the terms of this theory, is to produce new com- binations of heritable variations by the mixture of different ids. And since the number of chromosomes, and consequently the number of ids, is doubled as a result of the conjugating process, the complexity of the chromatin would become in- definitely increased if there were no periodic reduction. But this, according to Weismann, is provided against in the matura- tion process of the gametes, when the quantity of chromatin in the cells becomes reduced by one-half, as described in the preceding chapters. The reduced number of chromosomes is supposed to contain all the primary constituents of each of the two parents. And what is more, according to this theory, every gamete con- tains ids which are derived, not only from both the parents, but also from the ancestors, all the immediate ancestors being represented. Weismann’s theory of the nature of fertilisation was ac- cepted by many biologists as a working hypothesis, until the disinterment of Mendel’s discovery about ten years ago. The confirmation of this discovery by numerous workers in different fields has led to a revision of many of Weismann’s conceptions. The original experiments of Mendel ! were upon hybridisation 1 Mendel, ‘‘ Versuche iiber Pflanzen Hybriden,” Verh. natur. f. Ver., in Briinn, vol. iv., 1865. Reprinted in English in Mendel’s Principles of Heredity (Bateson), Cambridge, 1909. Mendel’s work was rediscovered and confirmed by de Vries, Correns, and Tchermak in 1900, and subsequently N 194 THE PHYSIOLOGY OF REPRODUCTION in peas, the two parent varieties initially selected differing from each other in one particular character. The hybrids produced by crossing were all similar superficially, and resembled one of the parents in the character in question, which was therefore called the dominant character, the other character being known as recessive. When the hybrids were crossed among themselves, approximately one half of the offspring were found to be identical with their hybrid parents (dominant hybrids), one quarter resembled one of the original varieties (the grandparent with the dominant character), while the remaining quarter were like the other pure variety (the grandparent with the recessive character). Consequently the pure dominants and the dominant hybrids resembled one another outwardly, but they differed in their capacity to transmit the characteristics in question, since the pure dominants alone were capable of always breeding true. The recessives also invariably bred true. Mendel drew the conclusion that in the hybrid the gametes (both male and female) were of two kinds, which were respectively identical with the two kinds represented by the gametes of the original pure varieties. The differentiation of gametes carrying different characters is the essential principle in Mendel’s theory, the existence of dominant and recessive characters, though often observable, being by no means universal. Another example, taken from the work of Bateson and Punnett, will be sufficient to elucidate further the Mendelian conception of gametic differentiation. Breeders of blue Anda- lusian fowls have always recognised the practical impossibility of obtaining a pure strain of this breed. However carefully the birds are selected they invariably produce two sorts of “wasters,” some being pure black, and some white with irre- gular black marks or splashes. Bateson and Punnett were the first to supply the explanation. They found that, on breeding from a large number of blue Andalusian fowls, on an average half of the offspring were blue like the parents, a quarter were black, and a quarter were “splashed-white.” They conse- by Bateson and a large number of other workers. Fora general account of the Mendelian theory, and numerous references to the literature of the subject, see Bateson, loc. c.t.; also Bateson, Saunders, Punnett, and Hurst, &c., in Reports to the Evolution Committee of the Royal Society, Parts I., I1., III., IV. and V., 1202, 1905, 1£06, and 1909. FERTILISATION 195 quently drew the conclusion that the mechanism of inheritance in the Andalusian fowl is comparable to what Mendel supposed to exist in his hybrid peas. The gametes of the breed, according to this hypothesis, instead of being all similar and carrying the blue character (as one would suppose on Weismann’s theory), are of two different kinds, those of the one kind being bearers of the black character, and those of the other being bearers of the splashed-white character. Such gametes, uniting by chance when the fowls mate together, give rise to three kinds of off- spring, one black-white (becoming blue, actually, like the parents), one black-black, and one white-white, these ap- pearing (on an average) in the proportion of 2: 1:1 according to the law of probability. In this particular case of Mendelian inheritance, neither of the two alternative parent characters (i.e. neither black nor splashed-white) is dominant and neither is recessive. Why black-bearing gametes uniting with white- bearing gametes should give rise to blue individuals the Mendelian theory does not attempt to explain. The importance of Mendel’s discovery lies in the fact that it forms the basis of a theory whereby variability can be dis- cussed in terms of the conjugating cells themselves, and not merely in terms of the resulting zygotes. Moreover, it is a theory which has been found to be applicable to a very wide class of facts. There are reasons for supposing that sex is a Mendelian phenomenon; that is to say, that the ova and spermatozoa are themselves sexual entities prior to conjugation (see p. 633). It still remains to be proved, however, that the principles underlying Mendel’s theory are applicable to all forms of inheritance.1 It has been mentioned that on Weismann’s hypothesis every gamete contains ids representing both its parents and all its immediate ancestors. On the other hand, according to the Mendelian theory, although all the essential characters of the organism are represented in each germ cell, the Mendelian characters, or allelomorphs as they are called, are each repre- sented by paternal or maternal ids only, and not by both, while the immediate ancestors have no representation at all. 1 Cf. Darbishire, ‘‘Recent Advances in Animal Breeding,” Royal Horti- cultural Society’s Report of the Conference on Genetics, London, 1907. 196 THE PHYSIOLOGY OF REPRODUCTION It has been supposed that the chromatin granules (which Weismann identified with the ids) are the carriers of the Mendelian allelomorphs, and that when these fuse together during the conjugation of the chromosomes which precedes the process of reduction (see p. 130), there is an exchange of allelomorphs between the chromosomes. If this interpretation is correct, it is simply a matter of chance whether an _allelo- morph remains in the chromosome which originally contained it, or becomes transferred to the other chromosome of the con- jugating pair. And since each of the two chromosomes passes into a different product of cell division, the allelomorphs would become distributed in precisely the kind of way that the Mendelian theory postulates. The Mendelian investigators have shown that by experimental breeding it is apparently possible to superimpose certain char- acters belonging originally to one kind of individual, upon different characters belonging to another kind, thus creating new combinations of characters. Thus it is claimed that by starting with two individuals, each possessing two unit or allelomorphic characters, which we may call A and X (associated together in one individual) and B and Y (associated in the other), it is possible in two generations to produce new individuals in which the combinations are interchanged, A being associated with Y, and B with X. It has been claimed also, that, in spite of the new combinations, each of the original separate unit characters can be preserved in a state of complete purity, and without in any way affecting, or being affected by, the characters upon which they have been superimposed. By resorting to such methods, it has been thought possible to build up, little by little, entirely fresh types of organisms, possessing new com- binations of pure characters, which previously existed only in different individuals. It remains to be considered how far this conception of an organism as an individual capable of description in terms of unit characters (each of which can be transmitted pure) is in harmony with modern physiological theory, or justified by experimental investigation. In the first place, it may be pointed out that the entire 1 Lock, loc. cit. FERTILISATION 197 trend of physiological research in recent years has been to show that the correlation that exists even between remote parts of the body is often extraordinarily close, and that in all proba- bility there is not an organ or structure that is not dependent in its growth and activity upon chemical substances, elaborated by other and sometimes distant parts of the body, and carried thence in the circulating blood. Thus a change in the whole metabolism, producing palpable modification in whole groups of characters, may be induced experimentally in the individual, by interfering with or removing one particular organ. This is well shown in the various kinds of correlation existing between the organs of internal secretion. Again, a change in the environment may directly affect the metabolism, and so influence all the characters of the body. To the physiologist, therefore, a so-called unit character cannot readily be regarded as some- thing represented by a substance located originally in a chromo- some or chromomere. Such a view, as Verworn! remarks, is “too morphologically conceived.” It is more in keeping with the physiological view of life to regard the characters of the individual as manifestations of a particular kind of metabolism, which is itself partly the outcome of environmental influences, and partly the developmental result of the sort of metabolism that existed in the germ cells from which the organism was derived. According to this view, it is clear that the presence of any one characteristic may exert an influence upon many, if not upon all, the other characteristics, and that, even in heredity, one cannot hope to alter any single organ or structure without affecting, in some slight degree at any rate, all, or nearly all, the other parts of the body. It may be argued, therefore, in criticism of the Mendelian conception of unit characters, that it takes little or no account of the metabolism of the organism as a whole. Thus it has been shown that in the case of presence or absence of hair pigment (which has been regarded as a simple example of alternate characters, such as can be superimposed experimentally upon other characters in the course of two generations), there is a pronounced correlation between albinism and other characteristics of the body, these characteristics depending for their existence upon a common metabolism. 1 Verworn, loc. cit. 198 THE PHYSIOLOGY OF REPRODUCTION Moreover, the difficulty experienced by Wood } in superimposing the complete hornlessness of Suffolk sheep upon the white face of the Dorset horns, is probably another example of the physio- logical correlation subsisting between different, and apparently unconnected, structures. Originally, this case was regarded as one of simple superposition, and Bateson ? describes the hornless character as having been transmitted “ pure,” but subsequently many of the so-called hornless sheep were found to have grown scurs. The explanation which I tentatively suggest is, that the character of pure hornlessness was somehow or other incompatible with the pure white-faced character, these two characters being ordinarily indications of two sorts of metabolism, in just the same kind of way as the beef-producing quality and the milk-producing quality seem to be to some extent incompatible in cattle. I am inclined to go further, and to suspect that many of the other Mendelian cases, when examined more critically, will show that no one character can be superimposed upon another, in experimental breeding, without altering, though perhaps only very slightly, the character upon which it has been superimposed. It is only when the amount of alteration is minimal that the transmission of pure characters is apparent, according to Mendelian expectation; but experimental evidence has shown that there are considerable numbers of such cases. It is a legitimate field of work for the biometrical school of biology to determine by statistical methods the extent to which varia- tion occurs as a result of attempted superposition of characters which in their “ pure” state are physiologically incompatible. Furthermore, a latent character may be regarded as one, the outward manifestation of which is incompatible with the existing kind of metabolism, but which is capable of reappearance as soon as the conditions become favourable. But because it is helpful to assume that latent characters are present in some 1 Wood, ‘‘The Inheritance of Horns and Face-Colour in Sheep,” Jour. Agric. Science, vol. iii., 1909. 2 Bateson, Mendel’s Principles of Heredity, Cambridge, 1909. No doubt, however, it is arguable that the scurs themselves represent unit char- acters, and that if the scurs are of different kinds, these also represent unit characters (which have hitherto somehow remained ‘‘latent”), and that if they occur with different degrees of development, these again are unit characters. And so on, FERTILISATION 199 manner in the animal organisation, it is not legitimate to suppose that they are definitely located in the nuclei of germ cells or in any other definite parts or structures.! Moreover, it should be remembered that there is no ex- perimental proof that the chromosomes of the gametes are the physical basis of inheritance. The only definite evidence in support of this supposition appears to be Boveri’s experiment, in which he fertilised a non-nucleated ovum of one species of sea-urchin with the spermatozodn of another species.2 The resulting pluteus or larva was purely paternal in its characters. Boveri concluded, therefore, that this result was due to the introduced nucleus, the maternal cytoplasm having no deter- mining effect upon the offspring, but merely supplying the material upon which the sperm operated.’ Seeliger,* Morgan,® and others have objected to Boveri’s conclusion on the ground that larve arising from cross-fertilisation show an unusually wide range of variation. Moreover, Godlewsky ® has recently carried out an experiment in which he fertilised a non-nucleated portion of a sea-urchin’s egg with the spermatozoon of a crinoid, and obtained, as a result, a larva of the maternal type. This experiment seems to nullify Boveri’s conclusion. Hickson has remarked that if it be true that the chromosomes are the sole carriers of heredity it seems to be necessary to be- lieve in the individuality of the chromosomes ; that is to say, 1 The attempt to locate latent characters of organisms in particular parts of the germ cells should perhaps be regarded as a survival from a time when all kinds of qualities, abstract or otherwise, were supposed to reside in definitely restricted positions, ‘‘ Compare Phenology. The centres in the nervous system are not comparable, since these are to be regarded as parts of mechanisms for controlling different functions. The centres preside over the respective functions, but the functions themselves are not located in the centres.” 2 Boveri, ‘‘Ein Geschlechtlich erzeugter Organismus ohne Miitterliche Eigenschaften,” S. B. d. Ges. f. Morph. u. Phys., Miinchen, vol. v., 1889. 3 The nuclei of such larva have been shown to possess only half the normal number of chromosomes ; see Morgan, ‘‘ The Fertilisation of Non- nucleated Fragments of Echinoderm Eggs,” Arch. f. Entwick.-Mechanik, vol, ii., 1895. 4 Seeliger, ‘‘Giebt es Geschlechtlicherzeugte Organismen ohne Miitter- liche Eigenschaften?” Arch. f. Entwick,-Mechanik, vol. i., 1894. 5 Morgan, loc. cit. See also Wilson, loc. cit. ® Godlewsky, “ Untersuchungen iiber die Bastardierung der Echiniden und Crinoiden-Familie,” Arch. f. Entwick,-Mechanik, vol. xx., 1906. 200 THE PHYSIOLOGY OF REPRODUCTION that the chromosomes seen at the poles of the spindle at the termination of mitosis are individually identical with those seen at the equator of the spindle at the next mitosis. He points out, further, that there is distinct evidence that this is not the case in certain Protozoa and Ccelenterata. Again, Hickson has called attention to the long duration of the period of conjugation in Infusoria (Heterokaryota), remarking that this is difficult to explain if we accept the view that the cyto- plasm of the conjugating cells is not concerned with the trans- mission of hereditary characters.} Verworn, in‘ the criticism referred to above, has objected on more general but scarcely less substantial grounds to the doctrine that the hereditary transmission of parental char- acteristics is mediated by the transference of nuclear substance only. “The physiological mode of thought will hardly be able to adapt itself to the idea of a single hereditary substance, which is localised somewhere in the cell, and transferred in reproduction. A substance that is to convey the characteristics of a cell to its descendants, before all else must be capable of life, ¢.e. must have a metabolism, and this is impossible without a connection with other substances necessary to cell-metabolism, i.e. without the integrity of all essential cell-constituents. The designation of a single cell-constituent as the specially differentiated bearer of heredity is wholly un- justified ; the cell protoplasm is of exactly the same value in this respect as the nucleus, and we must constantly return to the fact that in all living nature no instance is known in which a complete cell possessing nucleus and protoplasm does not always mediate hereditary transmission. The character of every cell is determined by its peculiar metabolism. Hence, if the peculiarities of a cell are to be transmitted, its characteristic metabolism must be transmitted ; this is only conceivable when nuclear substance and protoplasm, with their metabolic relations, are transferred to the daughter-cells. This is true of the sexual reproduction of the higher animals, as well as of the asexual 1 Hickson, “The Physical Basis of Inheritance,” British Assoc. Reports, Leicester Meeting, 1907, and Trans. Manchester Micr. Soc.,1907. See also Fick, ‘‘ Vererbungsfragen Reduktions und Chromosomen hypothesen Bastard- regeln,” Merkel und Bonnet's Ergeb. f. Anat. u. Phys., vol. xvi., 1906. FERTILISATION 201 reproduction of unicellular organisms ; in-the former, however, the metabolism of one cell, the spermatozoon, is by the process of fertilisation combined with that of another cell, the ovum, into a single resultant, the metabolism of the offspring that arises from the fertilised ovum; the offspring hence possesses the characters of the two parents.” ! In view of the considerations set forth above it must be admitted that the question as to the respective parts played by the nucleus and the cytoplasm in hereditary transmission remains as yet unsolved. TELEGONY It used to be supposed that the spermatozoa of an animal on being introduced into a female of the same kind, besides fertilising the ripe ova and producing young, were capable of exercising a permanent influence over the mother, and so trans- mitting certain of their characters, not only to their own immediate offspring, but to the future offspring of the mother by another sire. This phenomenon,” in which many practical breeders still believe, was called Telegony or Infection, and the female was said to be “ infected ” by the previous sire. The classical example, and one in which Darwin? himself believed, of the supposed influence of a previous sire upon the future ofispring, is the case of Lord Morton’s quagga, which was stated to have infected an Arab mare, so that she subse- quently produced two striped colts by a black Arab horse. In recent years Ewart * has repeated the experiment, employing a 1 Verworn, loc. cit, Cf. Farmer (loc. c’t.), who regards the chromo- ‘somes of the nucleus as representing primordia, which are responsible for the appearance of the hereditary characters, but need to be supple- mented by specific exciting substances which determine what particular potential character shall actually develop. ? The phenomenon was explained by supposing that the young, while still a utero, in some way affected the mother, and this influence was further transmitted to the subsequent offspring. It will be seen that this explanation assumes the possibility of the inheritance of acquired characters of which there is little or no evidence. For recent reviews of this ques- tion see Morgan, Experimental Zoology, New York, 1907; and Thomson, Heredity, London, 1907. 3 Darwin, The Variation of Animals and Plants under Domestication, Popular Edition, vol. i., London, 1905. 4 Ewart, The Penycuik Experiments, London, 1899. 202 THE PHYSIOLOGY OF REPRODUCTION Burchell’s zebra and a number of different mares. These ex- periments were supplemented by others in which animals of various kinds were used. As a result of his investigations he has come to the conclusion that there is no evidence for the existence of Telegony. A microscopic examination of the structure of the hairs of the subsequent foals bred by Pro- fessor Ewart provided further negative evidence.t' Minot,? also, in a series of experiments upon guinea-pigs, found no indication of any telegonic influence. Moreover, Karl Pearson,’ as a result of an extensive statistical inquiry, was unable to discover any evidence of telegony in Man. On GAMETIC SELECTION AND THE CONDITIONS FAVOURABLE FOR THE OCCURRENCE OF FERTILISATION It is a well-known fact in biology that, as a general rule, conjugation occurs most readily between gametes belonging to the same kind of organism. There are innumerable cases, however, in which the spermatozoa of one species are capable of fertilising the ova of another, and so initiating development. The resulting embryo in such cases may grow into a mature hybrid offspring which is not infrequently sterile (a fact which will be referred to again later), or, on the other hand, owing to some mutual incompatibility in the respective modes of growth inherited from the two parent forms, the embryo may survive for a short time and then perish. Cross-fertilisation can usually be induced most easily among closely related species or among varieties belonging to the same species. Thus, the different varieties of the frog, Rana fusca, intercross as readily with one another as each variety fertilises its own ova. On the other hand, the gametes of two species as widely separate as the frog, Rana fusca, and the salamander, Triton alpestris, have been known to conjugate, but the fertilised eggs so produced divided irregularly and consequently 1 Marshall, ‘‘On Hair in the Equidz,’ Proc. Roy. Soc. Edin., vol. xxiii., 901. : "2 Minot, ‘‘An Experiment with Telegony,” British Assoc. Reports, Cam- bridge Meeting, 1904. 3 Pearson, The Grammar of Science, 2nd Edition, London, 1900. FERTILISATION 203 failed to develop.1. In some cases (e.g. the two species of frogs, R. fusca and R. arvalis) cross-fertilisation can take place in one direction, but not in the reverse. Pfliiger explained this result by supposing it to be due to peculiarities in the shape or structure of the spermatozoa, those which have the thinnest or most pointed heads being described as more successful in inducing cross-fertilisation than those with large stout heads.? This explanation, while seeming to account for certain individual instances, cannot be applied to all cases of cross-sterility. Bataillon * has described experiments in which he fertilised the eggs of Pelodytes and Bufo with the spermatozoa of Triton alpestris, and obtained some degree of success, for the eggs in each case underwent an irregular segmentation before they perished. The spermatozoa underwent degeneration after con- jugating, so that the chromatin of the fertilised ova was derived entirely from the female pronucleus. The experiments, there- fore, afford additional proof that spermatozoa in conjugating with ova perform a function altogether apart from amphimixis (or the introduction of fresh chromatin substance as a source of variation), and that this function is the initiation of de- velopment. Among the Mammalia, as is well known, cross-fertilisation between nearly allied species commonly occurs. The resulting hybrid may be either sterile (eg. the mule) or fertile (e.g. the hybrid offspring of the bull and American bison). There is no evidence that more widely separated species of Mammals can be induced to have hybrid offspring. Spallanzani,* by artificially inseminating an cestrous bitch with the spermatozoa of a cat, attempted such an experiment, but without a positive result. A number of investigators have effected cross-fertilisation between various kinds of Echinoderms. Vernon,® who experi- 1 Pfliiger, ‘‘Die Bastardzeugung bei den Batrachiern,’ Pfliiger’s Arch., vol. xxix., 1882. ? Pfliiger and Smith, ‘‘ Untersuchungen iiber Bastardierung der Anuren Batrachier,” &c., Pfliig:r’s Archiv, vol, xxxii., 1883. 3 Bataillon, ‘‘ Impregnation et Fécondation,” C. R. de ? Acad. des Sciences, vol. exlii., 1906. * Spallanzani, Dissertations, English Translation, vol. ii., London, 1784. 5 Vernon, ‘“‘The Relation between the Hybrid and Parent Forms of Echinoid Larve,” Phil. Trans. B., vol. cxc., 1898. 204 THE PHYSIOLOGY OF REPRODUCTION mented with forty-nine different combinations, obtained results which were more or less successful in thirty-seven. In some of these, however, development did not proceed beyond the blastula stage. Vernon attempted to show that the capacity of the animal to transmit its characters to its hybrid offspring depended upon the condition of ripeness or staleness of its gametes at the time of fertilisation. Thus, the spermatozoa of the sea-urchin, Strongylocentrotus, were supposed to grow more and more “ prepotent ’’ as they became more and more mature. Doncaster,} however, has described further experiments which seem to indicate that the variation in the form of the hybrids obtained by Vernon was really due to differences in the temperature of the water. Loeb? discovered that cross-fertilisation of the eggs of Strongylocentrotus by the spermatozoa of various species of starfish could be effected by adding sodium carbonate or sodium hydroxide to the sea-water in just sufficient quantity to render it slightly alkaline. Under these conditions as many as fifty per cent. of the Strongylocentrotus eggs could be fertilised by Asterias spermatozoa, whereas in normal sea-water cross- fertilisation between these two Echinoderms only occurs very exceptionally. What the nature of the change is whereby the alkaline sea-water enables the sperm to fertilise the ova does not appear to be known. It has been observed that the addition of the alkali increases the motive-power of the sperms, but the same result is brought about by bicarbonate of sodium, without augmenting their capacity to cross-fertilise. Loeb suggests that the entrance of the spermatozoon into the interior of the egg- 1 Doncaster, ‘‘ Experiments in Hybridisation,’ Phil. Trans. B., vol. excvi., 1903. MacBride (‘‘Some Points in the Development of Ophiothrix fragilis,” Proc, Roy. Soc. B., vol. lxxix., 1907) has recently shown that the immature (ovarian) ova of the Ophiuroid, Ophiothriz, may be fertilised, but that the subsequent development is abnormal, segmentation resulting in a morula instead of a blastula, while at the stage at which the archenteron is formed, there is a tongue of cells projecting into its lumen. It appears, therefore, that the stage of maturity at which ova are fertilised may affect their embryonic development if not their hereditary characteristics. 2 Loeb, “‘ Ueber die Befruchtung von Seeigeleiern durch Seesternsamen,” Phliiiger’s Archiv, vol. xcix., 1903. ‘‘ Weitere Versuche iiber heterogene Hybridisation bei Echinodermen,” Pfliiger’s Archiv, vol. civ., 1904. See also translation of the latter, as well as other papers, in the University of California Publications, Physiology, vols. i. and ii., 1902-4, FERTILISATION 205 protoplasm may be due to surface-tension forces, and that the conditions for this process may depend upon the surface tension between the spermatozoén and the sea-water becoming greater than the sum of the surface tensions between the sea-water and the egg, and the spermatozoén and the egg. Loeb remarks, further, that the fertilisation of Strongylocentrotus eggs by sperms of the same species can best be accomplished in normal sea-water, and with this observation he associates the fact that the mobility of the Strongylocentrotus sperms is diminished by the alkaline water.! While suggesting that restrictions to the power of cross- fertilisation may be due to differences in surface tension, Loeb admits that the evidence seems to show that the capacity to conjugate is to some extent at least specific. Attempts were made to fertilise the eggs of sea-urchins with the spermatozoa of Annelids and Molluscs, but these experiments were without success. Very recently, however, Kupelweiser? reports that he has been successful in fertilising Strongylocentrotus ova with the spermatozoa of the mussel (Mytilus), and that the products developed into gastrule. Dr. A. T. Masterman tells me that, in certain cases, hybridisa- tion among fishes may be induced more readily in the absence of opportunity for normal fertilisation, that is to say, for fertilisa- tion of ova by spermatozoa of the same species. If such ova are present, the spermatozoa tend to conjugate with them rather than with ova belonging to a different but closely allied species. It would appear, therefore, that the spermatozoa exhibit an elective affinity for ova belonging to the same species as them- selves. This has been shown especially in hybridisation experi- ments between brill and turbot.® That assortative mating amongst gametes occurs generally as the result of a preferential tendency possessed by them towards conjugating with other gametes bearing similar characters to 1 Loeb, The Dynamics of Living Matter, New York, 1906. ? Kupelweiser, ‘‘ Versuche iiber Entwickelungserregung und Membran- bildung bei Seeigeleiern durch Mollusksperma,” Biol. Centrabl., vol. xxvi., 1906. 3 M‘Intosh and Masterman, Life History and Development of the Food Fishes, and articles in the Reports of the Scottish Fishery Boards, 9th Rep., Pt. III., 10th Rep., Pt. III., and 13th Rep., Pt. ITI. 206 THE PHYSIOLOGY OF REPRODUCTION their own, and that the comparative scarcity of hybrids in a state of nature is very largely the result of this selective action, are facts with which many of the older naturalists were familiar. With reference to the various species of plants belonging to the family Composite, Darwin wrote as follows :— “There can be no doubt that if the pollen of all these species could be simultaneously or successively placed on the stigma of any one species, this would elect with unerring certainty its own pollen. This elective capacity is all the more wonderful as it must have been acquired since the many species of this great group of plants branched off from a common progenitor.” Romanes,! who quotes this passage, remarks that “ Darwin is here speaking of ‘elective affinity ’ in its fully developed form, as absolute cross-sterility between fully differentiated species. But we meet with all lower degrees of cross-infertility sometimes between ‘incipient species,’ or permanent varieties, and at other times between closely allied species. It is then-known as ‘ prepotency ’? of the pollen belonging to the same variety or species over the pollen of another variety or species, when both sets of pollen are applied to the same stigma. Although in the absence of the prepotent pollen the less potent will fertilise the seed, yet, such is the appetency for the more appropriate pollen, that even if this be applied to the stigma some considerable time after the other, it will outstrip or overcome the other in fertilising the ovules, and therefore produce the same result on the next generation as if it had been applied to the mother plant without any admixture of the less potent pollen, although in some cases such incipient degrees of cross-infertility are further shown by the number or quality of the seeds being fewer or inferior.” i It would appear, however, that when the aggregate vitality ' Romanes, Darwin and After Darwin, vol. iii., London, 1897. See also Darwin, Animals and Plants, London, 1875, and Cross- and Self-Fertilisation in Plants, London, 1876. 2 The term ‘‘Prepotency”’ is here used in a different sense to that in which it is usually employed by zoologists, according to whom it means the greater capacity of one parent, as compared with the other, to transmit its characters to its offspring ; thus, instead of both parents transmitting their characters equally, one may be ‘‘prepotent” over the other, (Cf. the Mendelian term ‘dominant,’ which has a more precise signification ; see p. 194.) FERTILISATION 207 of the ova and spermatozoa is reduced below a certain point, assortative mating as a result of affinity between gametes bearing similar characters no longer occurs. It thus happens that a reduction of vitality is frequently correlated with an increased tendency towards cross-fertilisation, which, on this view, is a source of renewal of vitality. This theory was adopted to ex- plain certain phenomena of cross-fertilisation occurring among plants, by Fritz Miiller, who wrote as follows :— “Every plant requires for the production of the strongest possible and most prolific progeny, a certain amount of difference between male and female elements which unite. Fertility is diminished as well when this degree is too low (in relatives too closely allied) as when it is too high (in those too little related).” And, further, “ species which are wholly sterile with pollen of the same stock, and even with pollen of nearly allied stocks, will generally be fertilised very readily by the pollen of another species. The self-sterile species of the genus Abwtilon, which are, on the other hand, so much inclined to hybridisation, afford a good example of this theory, which appears to be con- firmed also by Lobelia, Passiflora, and Oncidiwm.” } Castle ? found that the eggs of the hermaphrodite Ascidian, Ciona intestinalts, could not, as a rule, be fertilised by spermatozoa derived from the same individual, while they could be fertilised readily with the spermatozoa of another individual. This rule, however, was not without exceptions, for in some cases as many as fifty per cent. of the eggs of one Ciona could be fertilised with sperms of the same individual, although this was very unusual. Morgan, who confirmed Castle’s observations, states that the failure to conjugate is due to the inability of the sperms to enter the eggs. If the sperm succeeds in entering, as in the exceptional cases, the fertilised egg develops normally. Morgan found, further, that if the sperms are stimulated to greater activity by alcohol, ether, ammonia, or certain salt solutions, self-fertilisation may in some cases be induced. In another Ascidian, Cynthia partita, Morgan observed that self-fertilisa- 1 Miiller, “Investigations respecting the Fertilisation of Abwtilon,” English Translation in American Natural.st, vol. viii., 1874. 2 Castle, ‘ The Early Embryology of Ciona intestinalis,” Bull. Mus. Comp. Zool., vol. xxvii., 1896. 208 THE PHYSIOLOGY OF REPRODUCTION tion frequently occurs, but that the eggs in this species also are most usually fertilised by spermatozoa from another individual.’ It is well known that the fertility of animals which are much in-bred is often reduced, but this is by no means invariably the case.2. Thoroughbred horses are notoriously in-bred, and it is interesting to note that one of the earlier reports of the Royal Commission on Horse-breeding states that no less that forty per cent. of the thoroughbred mares in this country fail to have foals each year. This relatively large amount of sterility is probably due to a variety of causes, and not entirely to the results of in-breeding. Low ? has recorded an experiment on the effect of in-breeding in fox-hounds. The particular strain is described as having perished completely. Low states also that similar experiments have been performed upon pigs, and, as a consequence, the litters became diminished in size and frequency, while difficulty was often experienced in rearing those which were produced. Von Guaita,* and Bos, in describing the effects of in- breeding in mice and rats respectively, have recorded a steady decrease of fertility in successive generations. Castle and his collaborators,® as a result of an investigation upon the same question in the pumice-fly (Drosophila am- pelophila), have come to the conclusion that in-breeding tends to reduce the fertility to a slight extent, whereas cross-breeding has a contrary effect. The diminished fertility of in-bred animals may be due partly to a decrease in the supply of mature ova correlated with 1 Morgan, ‘‘Self-Fertilisation induced by Artificial Means,” Jour. of Exper. Zool., vol. i., 1904. ‘‘Some Further Experiments on Self-Fertilisation in Ciona,” Biol. Bull., vol. viii., 1905. 2 The results of in-breeding are discussed at some length by Darwin, Variation of Animals and Plants, vol. ii., Popular Edition, London, 1905. For a recent review of the subject see Morgan, Haperimental Zoology, New York, 1907. 3 Low, The Domesticated Animals of Great Britain, London, 1845. 4 Von Guaita, ‘‘ Versuche mit Kreuzungen von verschiedenen Rassen der Hausmaus,” Ber. d. Naturf. Gesell., Freiburg, vol. x., 1898. 5 Bos, “Untersuchungen ueber die Folgen der Zucht in engster Blutver- wandtschaft,” Biol. Centralbl., vol. xiv., 1894. 5 Castle, Carpenter, Clark, Mast, and Barrows, ‘‘ The Effects of In-breeding, &c., upon the Fertility and Variability of Droscphila,’ Proc. Amer. Acad. of Arts and Sciences, vol. xli., 1906. FERTILISATION 209 a general want of vigour. It seems probable, however, that it also results from failure on the part of the gametes to conju- gate, since the productiveness of in-bred animals can often be increased by cross-breeding with other varieties. (See p. 601.) Heape+ states that Dorset Horn sheep, when served by rams of their own breed, show a greater tendency towards barrenness than when served by Hampshire Down rams. It is possible that what in this case appears to be barrenness is in reality very early abortion, the in-bred embryos tending to die at an early stage and to be absorbed in utero, thus escaping observation. It seems not unlikely, however, that, in the absence of cross-breeding, there is sometimes an insufficiency of vitality at the very outset, the elective affinity of the gametes being too feeble to induce conjugation. Some years ago the writer carried out an experiment upon a bitch belonging to the Dandie Dinmont variety, which is known to be very in-bred. Seminal fluid was obtained from a pure-bred Dandie Dinmont dog, and also from an obviously mongrel terrier of unknown ancestry. The semen from the two dogs was examined microscopically, and in each case was found to be rich in sperms, which so far as seen were all moving and in a vigorous condition. Approximately equal quantities of each sample of semen were then mixed together in a glass tube. After a further examination of the mixture, when it was observed that all the sperms were still active, the fluid was injected into a pure-bred Dandie Dinmont bitch, which was distantly related to the Dandie Dinmont dog. Previously to the experiment the bitch had been kept apart from other dogs, and this restriction was continued so long as she showed signs of cestrus. Fifty-nine days after the injection the bitch littered four pups, which closely resembled one another. Of these one died early, but the other three grew into mongrels which some- what resembled the terrier sire, so that there can be little doubt that all four pups were mongrels. No stress should be laid upon the result of a single experiment ; but the evidence, such as it was, was indicative of a selective tendency, consequent upon a reduced vitality, on the part of the ova of the in-bred 1 Heape, ‘‘ Abortion, Barrenness, and Fertility in Sheep,’ Jour. Royal Agric. Soc., vol. x., 1899. oO 210 THE PHYSIOLOGY OF REPRODUCTION animal to conjugate with dissimilar rather than with related spermatozoa. Professor Ewart has informed the writer of a case in which a Dandie Dinmont bitch in his possession copulated with a dog belonging to the same breed, and two days subsequently had intercourse with a Scotch terrier. In due time the bitch littered three pups, and of these only one was a pure-bred Dandie Dinmont, while the other two were half-bred Scotch terriers, in spite of the fact that the Dandie Dinmont dog copulated two days earlier than’ the Scotch terrier. This case may be regarded as to some extent confirmatory of the experi- ment described above.! Doncaster,? in describing his experiments on Echinoid hybridisation, states “that cross-fertilisation is assisted by conditions which tend to reduce the vitality of the eggs.” This artificial reduction of vitality could be accomplished either by warming the eggs, or by shaking them, or by keeping them for several hours, or by placing them for from one to two hours in diluted sea-water, the last method being the most uniformly conducive to the occurrence of cross-fertilisation. There is some evidence, therefore, that a reduction of vigour among the gametes, whether occurring naturally as a consequence of in- breeding or produced artificially as in Doncaster’s experi- ments, may lead to a similar result, since both conditions may bring about an increased tendency towards the union of dissimilar gametes. On another view, the tendency towards 1 Seeing that an assortative mating of gametes can probably occur between the ova of one individual and the spermatozoa derived from different individuals, whether as a result of gametic similarity or reduction of vitality, it is not improbable that gametic selection also sometimes takes place when various gametes of a single individual are bearers of different characters, in the manner postulated by the Mendelian theory. Such a preferential mating, if it exists, would of course obscure the evidence of that very gametic segregation, the probable existence of which, in other cases, is in- ferred from the numerical proportions in which the different sorts of zygotes or offspring are produced; for if there is an assortative mating among the gametes, it is obvious that the offspring would no longer be produced in definite Mendelian proportions, since these depend upon the chance unions of gametes. According to this view, prepotency may perhaps be interpreted as the tendency of the gametes of an individual to conjugate with other gametes bearing similar hereditary characters. 2 Doncaster, loc. cit. FERTILISATION 211 cross-fertilisation in Doncaster’s experiments may be looked upon as evidence of a diminished power of resistance, on the part of the ova, to the entrance of foreign ler conse- quent upon a reduced vitality in the ova.! Further evidence upon this question is afforded by ee the Protozoa. (See also pp. 601-604.) CoNJUGATION IN THE PRoTozoA The phenomenon of conjugation in the Protozoa possesses a special interest, inasmuch as it is undoubtedly the forerunner of fertilisation in the Metazoa. It is clear, therefore, that a complete understanding of the changes which attend the former process cannot fail to throw great light on the nature and signi- ficance of gametic union in multicellular organisms. In the different groups of Protozoa all gradations are to be found between conjugation in the general sense (¢.¢., the union, either temporary or permanent, of two similar unicellular organisms), and a process identical with metazoan fertilisation. Thus, in the peritrichous Ciliata there is a pronounced sex differentiation in the size and activity of the gametes, which clearly correspond to ova and spermatozoa. Even the matura- tion phenomena, which play so important a part in the develop- mental history of the metazoan gametes, are represented in some sort by comparable processes which have been observed in certain Protozoa.2. There can be no doubt, therefore, as to the. essential similarity of conjugation in unicellular organisms and fertilisation in multicellular ones. Raymond Pearl,? as a result of a biometrical study of the process of conjugation in Parame@xvwm caudatum, has arrived 1 It may be mentioned also that Loeb has shown that, whereas mature starfish eggs soon die if fertilisation is prevented, eggs in which maturation is artificially hindered through lack of oxygen or the addition of an acid to the sea-water, remain alive much longer than when allowed to become mature. (Loeb, “ Maturation, Natural Death, and the Prolongation of the Life of Unfertilised Starfish Eggs,” &c., Biol. Bull., vol. iii, 1902.) It would appear therefore that the mature eggs have suffered a loss of vitality which ordinarily can only be increased by the act of fertilisation. 2 See Enriques, loc. cit. 3 Pearl, “A Biometrical Study of Conjugation in Paramecium,” Biome- treka, vol. v., 1907. 212 THE PHYSIOLOGY OF REPRODUCTION at the conclusion that in this protozoén there is a definite tendency for like individuals to mate with like, since there is a considerable degree of homogamic correlation both between the lengths of the conjugant pairs and also between their breadths. Evidence is presented to show that the homogamic correlation arises through’ the necessity for the anterior ends and mouths of the two individuals to “ fit”’ reasonably well in the act of successful conjugation. If this is so, the necessity for assortative mating in Paramecium is purely mechanical, and the principle involved is not of general application to other gametic organisms. Pearl states, also, that there is no evidence that conjugation tends to produce increased variability in ex-conjugants. On the contrary, there are indications that conjugation tends to restrict the existing variability induced by environmental in- fluences ; or, in other words, to preserve a relative stability of type. This conclusion is antagonistic to Weismann’s hypothesis referred to above. (See footnote 1, p, 192.) As already mentioned, the reproductive processes in the Protozoa, like those in the Metazoa, tend to run in cycles, each cycle beginning and ending with an act of conjugation. Maupas’ observations showed that in various genera of In- fusoria (Paramecium, Stylonychia, &c.) a long period, during which the animals multiply by simple cell division, is succeeded by a period when conjugation is of very common occurrence. This marks the commencement of a new cycle, being physio- logically comparable to the period of sexual maturity in multi- cellular organisms. If conjugation were prevented from occur- ring, the individuals gradually ceased to divide and underwent changes which invariably led to death. As a result of these experiments, Maupas arrived at the conclusion that the purpose of conjugation is to counteract the tendency towards senile degeneration, and to bring about a rejuvenescence or renewal of vitality. Maupas’ observations have been confirmed by Joukowsky ? 1 Maupas, ‘‘ Recherches expérimentales sur la Multiplication des Infusories Ciliés,” Arch. de Zool. Exp. et Gen., vol. vi., 1888. “Le Régennissement Karyogamique chez les Ciliés,” Arch. de Zool. Exp, et Gen., vol. vii., 1889. 2 Joukowsky, ‘‘Beitrige zur Frage nach den Bedingungen der Ver- mehrung und des Kintrittes der Konjugation bei den Ciliaten,” Verh. Nat. Med. Ver., Heidelberg, vol. xxvi., 1898. FERTILISATION 213 and Simpson,! and more particularly by Calkins.2 The last investigator found, further, that the periodic seasons of “ de- pression” or loss of vitality which invariably occurred if conjugation were prevented, and which normally resulted in the cessation of cell division and ultimately in death, could be tided over and the race carried through further cycles of activity by having recourse to artificial stimuli in the medium surrounding the culture. In a series of experiments, which Calkins conducted for twenty-three months with a single race of Paramecium, it was found that periodic reductions of vitality occurred at intervals of about six months. At such times the race under cultivation would have died out entirely had it not been for the application of stimuli in the form of extracts of various food substances (beef, pancreas, brain, &c.). With the assistance of these restoratives, on three separate occasions, this particular race of Paramecium was carried through four cycles of activity and 742 generations without the occurrence of con- jugation. It thus appears that a change in the environment may result in a rejuvenescence of the race. As a consequence of these experiments, Calkins has sug- gested that the purpose of conjugation may be to bring about the union of individuals which have lived in different environ- ments, and so to produce a renewal of vitality in the same kind of way as a change in the environment itself. Calkins differs from Maupas in stating that diverse ancestry is not essential in order that conjugation may occur, since he obtained as large a percentage of successful endogamous as exogamous pairings, and carried one endogamous ex-conjugant through 379 generations. On the other hand, there is some evidence that conjugation does not result in rejuvenescence when both gametes have lived for a long time in the same medium, so that their chemical composition is too similar.® ' Simpson (J. Y.), ‘‘Observations on Binary Fission in the Life-History of the Ciliata,” Proc. Roy. Soc, Edin., vol. xxiii., 1901. * Calkins, ‘‘Studies on the Life-History of Protozoa,” IV., Jour. of Exp. Zool., vol. i., 1804. (References to earlier papers are here given. Seealso Biol. Bull., vol. xi., 1906.) 3 Cull, ‘‘ Rejuvenescence as a Result of Conjugation,” Jour. of Exp. Zool., vol. iv., 1907. Blackman (‘The Nature of Fertilisation,’ British Assoc. Reports, York Meeting, 1906) is of opinion that the rejuvenescence theory of fertilisation is difficult to apply generally in view of the large number of 214 THE PHYSIOLOGY OF REPRODUCTION According to Enriques,! however, conjugation in Colpoda steini only takes place under certain environmental conditions (e.g.if the layer of the water is not thicker than two millimetres) and does not occur at all if the conditions of life are stationary, the infusorians going on multiplying indefinitely and the number of divisions from the last conjugation making no difference.? According to Woodruff,? on the other hand, a varied environment seemed to obviate the necessity for conjugation in Paramacium. It may seem a far cry from the Ciliate Infusorian to the British thoroughbred horse, yet there is evidence that here also an in-bred and relatively infertile race may be rejuvenated through access to new surroundings. Allison, referring to blood stock of British origin, born in Australia and New Zealand, writes as follows: “ We can draw from these, not only strains of blood which we have lost, but horses and mares, born again, so to speak, and admirably suited to strengthen and regenerate our home stock.” 4 The same result is said to have been achieved in the descendants of British horses (especially hackneys) imported into Argentina. The case of the Porto Santo rabbits and that of the goats of Juan Fernandez, which are cited by Huth ® as evidence that in-breeding is harmless, may perhaps be similarly explained. THE SUPPOSED CHEMOTACTIC PROPERTIES OF SPERMATOZOA AND THEIR RELATION TO THE PHENOMENA OF FERTILISATION Tt has been suggested that the spermatozodn is attracted towards the ovum by a chemotactic action which the metabolic products of the latter are able to exert upon the former. plants in which the fusing cells or nuclei are closely related. The force of this objection must be admitted. If, however, the conjugating cells have been subjected to slightly different environmental influences, this near relationship is not necessarily a difficulty. 1 Enriques, loc. cit. 2 Tf water from a culture in which conjugation is ‘‘ epidemic” be added to a normal culture, it is stated to induce conjugation. Conversely, if water from a normal culture is added to a ‘‘ conjugation culture,” it inhibits it. 3 Woodruff, ‘‘The Life Cycle of Paramecium when Subjected in Varied Environment,” Jour. of Exp. Zool., vol. xlii., 1908. 1 Allison, The British Thoroughbred Horse, London, 1901. 5 Wallace (R.), Argentine Shows and Livestock, Edinburgh, 1904. Cf. also Darwin, Animals and Plants, London, 1905. 6 Huth, The Marriage of Near Kin, 2nd Edition, London, 1887. FERTILISATION 215 Pfeffer’s experiments ' upon the spermatozoa of ferns are usually cited as evidence of this view. Pfeffer observed that malic acid, when put into a capillary tube with one end open and placed in a drop of liquid con- taining fern spermatozoa, has a strong attractive influence upon these organisms, causing them to swim in large numbers into the opening of the tube. He concluded, therefore, that it is the malic acid in the archegonium of the fern’s ovum which causes the approach of the spermatozoa. According to Strasburger,? the ova of the Fucacexe also possess chemotactic properties, attracting the spermatozoa from a distance equal to about two diameters of an ovum. Bordet,® however, who likewise experimented upon the Fucacez, obtained no evidence of chemotactic attraction, but he found, on the other hand, that the sperms were very sensitive to contact. Jennings,* in the course of his experiments on the behaviour of the Protozoa, has shown that these organisms will tend to collect in a drop of acid placed in water. This is due to the fact that, whereas no reaction takes place when the individuals pass from water to acid, there is a distinct reaction in passing in the reverse direction. All the organisms which enter the drop of acid remain there, and consequently they accumulate, but this is not due to any attractive influence on the part of the drop. It is of course possible that Pfeffer’s observations on the sup- posed attraction possessed by malic acid for the spermatozoa of ferns is susceptible of a similar explanation. Buller,> who has discussed the question at some length and has performed numerous experiments, states that, so far as he is aware, not a single case is known where chemotaxis plays a part in the fertilisation of the ova of animals. 1 Pfeffer, ‘‘ Locomotorische Richtungsbewegungen durch chemische Reize,” Untersuchungen aus. d. Bot. Inst. zur Tiibingen, ‘vol. i, 1884. 2 Strasburger, Das botan. Prakticum, Berlin, 1887. 3 Bordet, “Contribution a Etude de I’'Irritabilité des Spermatozoides chez les Fuccacées,”” Bull. de l’ Acad. Belgique, vol. xxxvii., 1894. 4 Jennings, ‘Studies of Reactions to Stimuli in Unicellular Organisms, Amer. Jour. of Phys., vol. xxi., 1897. 5 Buller, “Is Chemotaxis a Factor in the Fertilisation of the Eggs of Animals?” Quar. Jour. Micr. Science, vol. xlvi., 1902. 216 THE PHYSIOLOGY OF REPRODUCTION ARTIFICIAL AIDS TO FERTILISATION It has been already recorded that cross-fertilisation between certain species of Echinoderms can be effected by having re- course to physico-chemical methods. It is not surprising, there- fore, that fertilisation between individuals belonging to the same species can be assisted, or caused to take place more frequently, in the presence of certain substances artificially added. Thus, according to Roux, frog’s eggs can be fertilised more readily by adding saline solution to the water in which they are deposited. Wilson says that in the case of the mollusc Patella, a larger number of eggs can be fertilised if potash solution is added.t Dungern? states that the activity of the spermatozoa in the sea-urchin can be increased in the presence of substances extracted from the ova. Similarly it is said that normal prostatic secretion has an exciting action on mammalian spermatozoa (p. 236). Furthermore, Torelle and Morgan? have shown that the immature spermatozoa of starfish can be stimulated, and fertilisation can be induced, by adding ether and various salt solutions to the sea-water. ARTIFICIAL PARTHENOGENESIS The fact that the ova of various kinds of organisms are capable under certain circumstances of segmenting and de- veloping into new individuals without the intervention of male germ-cells, has been already referred to. In such animals as the Aphide this method of reproduction appears to be called forth by certain conditions of temperature and moisture. In other forms of life the necessary factors for the occurrence of parthenogenesis are not so evident, but the fact of its existence has been known from early times.* In many animals parthenogenesis has been observed to occur ' For further information on this subject, with references to literature, see Przibram, Embryogeny, English Translation, Cambridge, 1908 ; and Jenkinson, Experimental Embryology, Oxford, 1909. 2 Dungern, ‘‘Neue Versuche zur Physiologie der Befruchtung,” Zeitschr. f. allgem. Phys., vol. i, 1902. 3 Morgan, Experimental Zoology, New York, 1907. 4 See footnote, p. 131. FERTILISATION ait occasionally, ‘although it may never have become a confirmed physiological habit. The silkworm moth (Bombyx mori) affords an example of this phenomenon. In the higher animals also it has been shown that unfertilised eggs may very abnormally start to segment without any obvious source of stimulus. Janosik ! has recorded segmentation in the ovarian ova of Mammals, but it is doubtful whether such cases should be regarded as truly parthenogenetic in nature. Tichomiroff ? showed that the unfertilised eggs of the silk- worm moth, which, as just mentioned, is occasionally partheno- genetic, can be caused to develop in greatly increased numbers by rubbing them lightly with a brush, or by dipping them for about two minutes in strong sulphuric acid, and then washing them. Perez* subsequently made some similar observations, noting also that normal parthenogenetic development was commonest in those individuals which were most robust. Richard Hertwig * was the first to show that if the ova of various Echinoderms are treated with certain reagents, and then restored to normal sea-water, they will frequently display signs of segmentation. The particular reagent originally employed by Hertwig was a 0:1 per cent. solution of sulphate of strychnine. Not long afterwards Mead ® observed that the eggs of the marine Annelid, Cha@topterus, which ordinarily become mature only after the entrance of the spermatozoa, could be induced to throw out their polar bodies by adding potassium chloride to the sea-water in which they were placed. Morgan ® found that an addition of sodium chloride to sea- water containing ova of sea-urchins caused these to form astro- spheres, while, if the ova were afterwards transferred to ordinary 1 Janosik, ‘‘Die Atrophie der Follikel,” &c., Arch. f. Mikr. Anat., vol. xlviii., 1896. 2 'Tichomiroff, ‘‘ Die kiinstliche Parthenogenese bei Insekten,” Arch. f. Anat, in Phys., Phys. Abth., Suppl., 1886. 3 Perez, “Des Effets des Actions mécaniques sur le Développement des Ciufs non-fécondé,” &c., Procés-Verbaux de la Soc. des Sciences de Bordeaux, 1896-97. ‘ Hertwig, ‘‘ Ueber Befruchtung und Conjugation,” Verhandl. der Deutsch. Zool. Gesellsch., 1892. 5 Mead, Lectures delivered at Wood’s Holl, Boston, 1898. 5 Morgan, ‘‘ The Action of Salt Solutions on the Unfertilised and Fertilised Ova of Arbacia,” &c., Arch. f. Entwick.-Mech., vol. iii., 1896, and vol. viii., 1899. 218 THE PHYSIOLOGY OF REPRODUCTION sea-water, they sometimes proceeded to segment. The latter process, however, was not normal, since the ova that had been subjected to this treatment became transformed into masses of minute granules, and, instead of acquiring cilia and giving rise to embryonic individuals, they underwent a process of disintegration. To Loeb belongs the credit of having done more than any other worker to elucidate the physico-chemical aspects of the phenomena of fertilisation. Loeb was the first definitely to succeed in producing plutei from the unfertilised eggs of the sea-urchin. His original method was to expose the eggs for about two hours to sea-water in which the degree of concentra- tion had been raised by about forty or fifty per cent. This effect could be produced by the addition of sodium chloride, but it was found to be immaterial what particular substance was employed to raise the concentration, so long as it was one which did not act injuriously on the eggs. The ova were afterwards restored to normal sea-water, when they began to undergo segmentation and subsequently developed into normal plutei. Loeb was able to show, further, that the parthenogenetic development of the ova in such cases was brought about by a loss of water. Thus, when the concentration of the sea-water was less than forty per cent., some of the ova of the sea-urchin Arbacia could be induced to develop, even though they were allowed to remain in the hypertonic solution. By adopting similar methods a like result could be effected for the other species of sea-urchin, and also in the case of the starfish Asterias jorbesi ; but it was necessary, as a general rule, to restore the ova to normal sea- water, as the continuance of abnormal conditions, although it might not hinder segmentation, usually arrested the further course of development.1 It was found, however, that osmotic fertilisation differed in several respects from fertilisation by a spermatozoon. Firstly, the ova fertilised by the former method began to seg- 1 Loeb (J.), ‘‘On the Nature of the Process of Fertilization,” &c., Amer. Jour. of Phys., vol. iii., 1899. ‘‘On the Artificial Production of Normal Larvee from the Unfertilised Eggs of the Sea-Urchin (Arbacia),” Amer. Jour. of Phys., vol. iii., 1900. ‘‘ On Artificial Parthenogenesis in Sea-Urchins,” Science, vol. xi., 1900. ‘‘ Further Experiments on Artificial Parthenogenesis,” &c., Amer. Jour. of Phys., vol. iv., 1900. These papers are reprinted in Loeb’s Studies in General Physiology, vol. ii., Chicago, 1905. FERTILISATION 219 ment without developing a membrane such as is invariably formed in normal eggs shortly after the entrance of the sper- matozoa. Secondly, the rate of development in the artificially fertilised eggs was considerably slower than in the eggs fertilised by spermatozoa. Thirdly, the larve arising from osmotic parthenogenesis, as soon as they began to swim, did so at the bottom of the dish in which they were placed, instead of rising to the surface of the water like normal larve. It was found also that the percentage of eggs which could be induced to develop by the osmotic process was invariably very much smaller than the percentage of normally fertilised eggs which underwent development. The consideration of these differences led Loeb to conclude that the spermatozoén in normal fertilisa- tion carried into the ovum not one, but several substances or conditions, each of which was responsible for a part only of the normal characteristics of the process; and that, in order to imitate successfully the action of the sperm, it would be necessary to combine two or more artificial methods. When the eggs of Strongylocentrotus purpuratus were put into 50 cubic centimetres of sea-water to which 3 c.c. of a .deci- normal solution of a fatty acid had been added, and were left in this water for about a minute, and were then transferred to ordinary sea-water, they were observed to form membranes. It was also noticed that the eggs underwent internal changes characteristic of nuclear division, but they were rarely seen to segment. Subsequently they began to disintegrate, and after twenty-four hours were nearly all dead. If, however, the ova, after they had formed a membrane, were deposited in sea- water which had been rendered hypertonic by adding 15 c.c. of sodium chloride solution of two and a half times the normal concentration, to 100 c.c. of sea-water, all or nearly all the eggs could be induced to develop. Furthermore, the rate of de- velopment was practically the same as that of normally fertilised’ eggs, a large percentage of the blastule looked normal and rose to the surface of the water, and the plutei which developed showed the usual degree of vitality. The brothers Hertwig! had previously discovered that sea- 1 Hertwig (O. and R.), Untersuchungen zur Morphologie und Physiologie der Zelle, Jena, 1887. 220 THE PHYSIOLOGY OF REPRODUCTION water saturated with chloroform induced the unfertilised eggs of the sea-urchin to develop membranes. Herbst more recently showed that benzol, toluol, creosote, or oil of cloves produced a similar effect. Loeb ? found that amylene and various other hydrocarbons and acids also called forth membrane forma- tion, and that eggs which were subjected to these methods could be made to segment by subsequent treatment with hyper- tonic sea-water in the way described. The substances which called forth membrane formation can be divided into two groups, the first consisting of hydrocarbons and certain sub- stitute products, and the second being comprised of certain acids. Loeb states also that the order in which the two agencies are employed is of vital consequence, for if the eggs are sub- jected to the membrane-forming solution after being placed in the hypertonic sea-water instead of before, they develop a membrane, but shortly afterwards disintegrate. As a result of this series of experiments he concludes that the process of membrane formation is an essential and not a secondary pheno- menon.®? He makes the further suggestion that membrane formation is brought about by a kind of secretory process, due to the squeezing out under pressure of a liquid substance from the interior of the ovum 4 (ef. Jenkinson, p. 189). According to this view the excretion of the fluid is the essential feature, while the actual formation of the membrane is probably only a secondary mechanical effect of the sudden secretion. In the case of the starfish it was found that the process of artificial membrane formation was alone sufficient to induce parthenogenetic development without any further treatment with hypertonic sea-water. This observation is connected by Loeb with the fact that starfish eggs are sometimes able to develop in the absence of any external cause or agency. 1 Herbst, ‘‘Uber die kiinstliche Hervorragung von Dottermembranen,” &c., Biol. Centralbl., vol. xiii., 1893. 2 Loeb, The Dynamics of Living Matter, New York, 1906. This work contains further references. ‘‘On an Improved Method of Parthenogenesis,” Univ. of California Publications : Physiology, vol. ii., Berkeley, 1904. 3 It was found, however, that in the case of the starfish a very small number of eggs could develop without first forming a membrane, and that this number could be increased by transitorily treating the eggs with acidulated sea-water. See below. 4 Loeb, ‘Ueber die Natur der Lésungen,” &c., Pfliiger’s Arch., vol. ciii., 1904. FERTILISATION 221 Parthenogenetic development of starfish eggs has been produced also by mechanical agitation ;+ but it is possible, as Loeb ob- serves, that the diffusion of carbonic dioxide, or some other gas, into or from the eggs may be the real exciting cause.” Loeb found also that the unfertilised eggs of the Annelid, Chetopterus, could be made to develop into swimming larve by adding a small quantity of a soluble potassium salt to the sea-water in which they were placed.? The same result could be brought about by the addition of hydrochloric acid. The eggs appeared to undergo development, as far as the trochophore stage, but without segmenting. Lillie, however, found that the nuclear divisions were abnormal, and that the apparent trochophore larve were not typical, being in reality merely “ciliated structures which were far behind the real larve in organisation. But Bullot > showed that in another Annelid, Ophelia, ova fertilised by hypertonic sea-water underwent a regular segmentation. Loeb has shown that the ova of limpets (Acmea and Lottia) could be artificially fertilised by the combined action of fatty acid and hypertonic sea-water. This method also had the effect of hastening maturation, since ova which could not be fertilised by spermatozoa could be made to develop into larvee by the artificial treatment. It was found, further, that matura- tion could be induced by the action of alkaline sea-water, and that ova which were treated in this way could be fertilised by spermatozoa or artificially fertilised.® Bataillon’? states that the unfertilised eggs of the lamprey, and also those of the frog, can be made to undergo segmentation 1 Mathews, “Artificial Parthenogenesis produced by Mechanical Agitation,” Amer. Jour. of Phys., vol. vi., 1901. 2 Loeb, The Dynamics of Living Matter, New York, 1906. 3 Loeb, “Experiments on Artificial Parthenogenesis in Annelids,” &c. Amcr, Jour. of Phys., vol. iv., 1901. 4 Lillie, ‘ Differentiation without Cleavage in the Egg of the Annelid, Chetopterus pergamentaceus,” Arch. f. Entwick.-Mechanik, vol. xiv., 1902. 5 Bullot, ‘Artificial Parthenogenesis and Regular Segmentation in an Annelid (Ophelia), Arch. f. Entwick.-Mcchanik, vol. xviii., 1904. 6 Loeb, Univ. of California Publications : Physiology, Berkeley, vol. i., 1903, and vol. iii., 1905. 7 Bataillon, ‘Nouveaux Essais de Parthénogénése expérimentale chez les Vertébrés inférieurs (Rana fusca et Petromyzon planeri”), Arch. f. Entwick.- Mechanik, vol. xviii., 1904. a3 222 THE PHYSIOLOGY OF REPRODUCTION as far as the morula stage by depositing them in a salt solution of such a concentration that they lose water. Sugar solutions were also found to be effective." Various experiments have been tried with the object of finding out whether ova could be fertilised by substances arti- ficially extracted from spermatozoa, but so far without any positive result. Thus Gies attempted to obtain an enzyme from spermatozoa, with a view to seeing if such a substance would exert any influence on the unfertilised ovum, but his experiments lent no support to the idea.? Pizon’s + experiments on the same question were also negative in result. (See p, 299.) Loeb® has discussed at some length the question as to whether any idea can be formed regarding the nature of the action of the spermatozoén in causing the ovum to develop. He states his belief that “the essential effect of the sperma- tozoon consists in the transformation of part of the proto- plasmic or reserve material in the egg into the specific nuclein or chromatin substance of the nucleus. In each nuclear division one half of the mass of each original chromosome goes into the nucleus of each of the two resulting cells. But during the resting period which elapses until these nuclei are ready to divide again, each chromosome grows to its original size, and then a new division occurs. It is quite possible that the oxygen which is required for the process of cell division is needed for the synthesis of nuclein or chromatin substance. The fact that the rate of development is influenced by temperature, in much the same way as are chemical reactions, supports the idea given above that the essential feature of fertilisation consists in the starting or the acceleration of a chemical reaction which is going on steadily in the egg. Loeb was disposed to conclude, therefore, that the spermatozodn acts as a positive catalyser, but further evidence has led him to reject this idea as im- probable. He points out that, if it were correct, normal sea- 1 Loeb, Joc. cit. 2 See Loeb, The Dynamics of Living Matter, New York, 1906. 3 Gies, ‘‘Do Spermatozoa contain Enzyme having the Power of causing Development of Mature Ova?” Amer. Jour. of Phys., vol. vi., 1901. 4 Pizon, ‘ Recherches sur une prétendue Ovulase des Spermatozoides,” C. R. de l Acad. des Sciences, vol. cxli., 1905. 5 Loeb (J.), loc. cit. FERTILISATION 223, urchin eggs should segment if kept for a sufficiently long period, and that it ought to be possible to induce segmentation by applying heat, since heat is known to accelerate chemical re- actions, but neither of these results could be obtained. He then suggests the possibility that the spermatozodn, in conjugating with the ovum, removes from the latter a negative catalyser or condition whose existence in the ovum somehow inhibits the process of development. This suggestion seems to provide an explanation of the secretory phenomena, which, on Loeb’s hypothesis, are the cause of the membrane formation. “ Finally, we may be able to understand a fact which [has been] observed in the eggs of a starfish, and which has not yet. been mentioned, when the eggs of Asterina or Asterias are allowed to ripen, they will die within a few hours unless they develop either spontaneously or through the influence of sperms or some of the above-mentioned agencies. The disintegration which leads to the death of the non-developing egg is obviously due to an oxidation, since I found that the same eggs when kept in the absence of oxygen will not disintegrate. We know that oxygen is an absolute prerequisite for the development of the fertilised egg ” [but this statement is disputed by Delage]. The fact that oxygen is a poison for the mature but non- developing egg shows that the chemical processes which occur in the unfertilised, non-developing egg must be altogether different from those which go on in the developing egg of the star-fish.? * Loeh, loc. cit. See also “The Toxicity of Atmospheric Oxygen for the Eggs of the Sea-Urchin after the Process of Membrane Formation”; ‘‘On the Necessity of the Presence of Free Oxygen in the Hypertonic Sea-water for the Production of Artificial Parthenogenesis”’ ; ‘‘ On the Counteraction of the Toxic Effect of Hypertonic Solutions upon the Fertilised and Unfertilised Egg of the Sea-Urchin by lack of Oxygen,” Univ. of California Publ cations : Physiology, vol. iii, 1906. See also ‘“‘Versuche tber den Chemischen Charakter des Befruchtungsvorgangs,” Biochem. Zeitschr., vol. i., 1906. “Weitere Beobachtungen iiber den Einfluss der Befruchtung und der Zahl der Zellkerne auf die Sdurebildung im Ei,” Biochem. Zeitschr., vol. ii. 1906 ; “Uber die Superposition von kiinstlichen Parthenogenese und Samenbefruch- tung in derselber Ei,” Arc. f. Entwick.-Mechanik, vol. xxiii., 1907 ; ‘* Uber die allgemeinen Methoden der kiinstlichen Parthenogenese,” Pfliiyer’s Arch., vol. cxviii, 1907; and other papers in the same volume. The following papers also deal with artificial parthenogenesis in various animals: Delage, C. R. de VAcail. des ‘Sciences, vol. cxxxv., 1902 (describing fertilisation by 2294 THE PHYSIOLOGY OF REPRODUCTION Loeb’s general conclusion is that the phenomenon of fertilisa- tion (as studied in the sea-urchin, the star-fish, Lottia, Polynoe and Sipunculids) consists essentially, firstly, in a liquefaction or hydrolysis (or both) of certain fatty compounds in the ovum, and secondly, in an initiation in the right direction of a new process of oxidation. These changes which occur in the fertilised egg lead to the synthesis of nuclein material from the protoplasm. According to this view, the process of astrosphere formation is not the direct effect of the act of fertilisation, but is a secondary consequence of the new chemical changes which are brought about by the entrance of the spermatozoén.? Delage,? however, has recently adduced experimental evidence, some of which is opposed to Loeb’s interpretation of the observed phenomena. This investigator has shown that anesthetisation with carbon dioxide during maturation): and C. R. de? Acad. des Sciences, vol. cxli., 1906 (describing fertilisation with various salt solu- tions) ; Treadwell, “ Notes on the Nature of Artificial Parthenogenesis in the Egg of Patella obscura, Biol. Bull., vol. iii., 1902 ; Scott, “ Morphology of the Parthenogenetic Development of Amphitrite,” Jour. of Exper. Zool., vol. iii., 1906 ; Lefevre, * Artificial Parthenogenesis in Thalassema mellita,” Jour. of Exper. Zool., vol. iv., 1907; Kostanecki, ‘‘ Zur Morphologie der kiinstlichen parthenogenetischen Entwicklung bei Mactra,” Arch. f. Mikr, Anat., vol. lxxii., 1908. See also Mathews, whose paper has been already referred to (Chapter IV. p. 134, ‘A Contribution to the Chemistry of Cell Division, Maturation, and Fertilisation,” Amer. Jour. of Phys., vol. xviii., 1907). This author lays stress on the part played by the centriole, and suggests ‘‘ that the various methods employed to produce artificial parthenogenesis do not do so by their direct physical action on the cell, but indirectly by producing in one way or another active centriole substance in the cell cytoplasm, or by causing its discharge from the nucleus.” 1 Loeb, ‘‘ The Chemical Character of the Process of Fertilisation and its bearing upon the Theory of Life Phenomena.’’—Address before the Interna- tional Congress of Zoologists, Boston, 1907, Univ. of California Publications, vol. iii., 1907. 2 Since this was written, Loeb has elaborated his theory further in an important work recently published, in which full references are given ( Die chemische Entwicklungserregung des tierischen Eies, Berlin, 1909). Membrane formation is regarded as an essential factor in normal fertilisation, and is of the nature of a cytolysis of the egg, for all cytolytic agents produce it. Normally the fertilisation membrane is brought about by a lysin carried in by the sperm, which also carries another substance that serves to coun- teract the evil effects of membrane formation. See p. 301, Chapter VIII, where the subject is discussed further. 3 Delage, ‘“‘Les Vrais Facteurs de la Parthénogénése Expérimentale,” Arch. de Zool. Expér. et Gen., vol. vii., 1908. FERTILISATION 225 it is possible artificially to fertilise sea-urchins’ eggs by treating them with solutions of tannin and ammonia. He had already formed the conception that the essential facts of cell division could be resolved into a succession of processes involving coagulation and liquefaction. The formation of the vitelline membrane is said to be essentially a coagulative process (and also possibly the formation of the centrosome and of the nuclear spindle), and the dissolution of the nuclear membrane and certain of the accompanying events are regarded as evidence _ of liquefaction. These considerations led Delage to employ tannin as an agent for inducing coagulation, and ammonia for causing liquefaction. Tannate of ammonia was found to pro- duce a similar effect, but this is explained by Delage on the assumption that, since tannin is a feeble acid and ammonia is a feeble base, the ammonium tannate becomes dissociated, so that the acid function (which brings about coagulation) and the alkaline function (which causes liquefaction) may be sup- posed to co-exist in the solution, and so separately to exert an influence on different parts of the egg. By adopting the above- described method, Delage succeeded in artificially fertilising ova, so that they developed into complete sea-urchins, but it is curious to note that the symmetry of these individuals was liable to be abnormal, one of them being hexameral instead of pentameral. Delage also obtained successful results by using carbon dioxide and other agents, and star-fishes’ eggs as well as sea-urchins’ were successfully fertilised. Furthermore, certain of the experiments seem to indicate that the presence of oxygen is not a necessary factor (as supposed by Loeb), since development could be induced after practically all the oxygen present had been eliminated. It is, of course, obvious that Loeb’s interpretation of the observed phenomena of fertilisation among the Metazoa is inapplicable to the process of gametic union in the Protozoa, in which the conjugating units are often apparently similar and equipotential, and the same objection may be offered to Delage’s theory. It is possible, however, that conjugation in the Protozoa, while presenting an essential similarity to fertilisa- tion in the Metazoa, initiates a series of chemical processes of a relatively simpler kind. Moreover, the theory that the changes P 2296 THE PHYSIOLOGY OF REPRODUCTION consequent upon gametic union are the result of a catalytic chemical reaction is in no way opposed to the vaguer physio- logical conception that the object of the process is to secure a rejuvenescence of vital substance without which the race cannot be perpetuated. The cytological changes which occur in artificially fertilised ova have’ been dealt with at considerable length by Wilson, to whose paper ! the reader is referred. It is shown that the ovum of the sea-urchin, under an appropriate stimulus, is able to construct the complete mechanism of mitotic cell division without the importation of a sperm-centrosome, but beyond this a multitude of aberrations are exhibited. The number of chromosomes is one-half that occurring in normally fertilised eggs, being in the sea-urchin eighteen instead of thirty-six. The cen- trosomes are primarily formed de nove. According to Delage,’ however, the number of chromosomes in artificially fertilised sea-urchins becomes eventually restored to the normal by a process of auto-regulation. 1 Wilson, ‘‘ Experimental Studies in Cytology: I. A Cytological Study of Artificial Parthenogenesis in Sea-Urchin Eggs,” Arch. f. Entwick.-Mechanik, vol. xii., 1901. For an account of the cytological phenomena in normal parthenogenetic eggs, especially in insects, see Hewitt, ‘‘ Cytological Aspects of Parthenogenesis in Insects,’ Memoirs and Proc. Manchester Literary and Philosophical Soc., vol. 1., 1906. 2 Delage, ‘‘Ktudes expérimentales sur la Maturation Cytoplasmique chez les Echinodermes,” Arch. de Zool, Hxpér. et. Gén., vol. ix.,1901. Cf. also Tennent and Hogue, ‘‘ Studies on the Development of the Starfish Egg,” Jour. of Exp. Zool., vol. iii., 1906. CHAPTER VII THE ACCESSORY REPRODUCTIVE ORGANS OF THE MALE AND THE MECHANISMS CONCERNED IN INSEMINATION “Mais, par ce moyen de propagation seminale, demeure es enfans ce qu’estoit de perdu es parens et es nepveux ce que dépérissoit es enfans, et ainsi successivement.”—RABELAIS. A BRIEF description of the mammalian testis has already been given in a chapter on the physiology of the spermatozoén (p. 166). It remains, however, to state what is known regarding the functional relations of the accessory male organs, and to refer incidentally to the homologous structures in the female. After traversing the tubules of the rete testis the spermatozoa, swimming in the seminal fluid, make their way into the vasa efferentia, which open into the canal of the epididymis. The vasa efferentia in Man are about twenty in number. Before passing into the epididymis they become convoluted, forming the coni vasculosi. Both the vasa efferentia and the tube of the epididymis contain smooth muscular fibres in their walls. They are lined internally by columnar epithelial cells provided with long cilia, which assist the muscles in expelling the semen. Passing away from the epididymis, and in continuation with its canal, is the vas deferens, which is nearly two feet long in the human subject, and has an average diameter of about one- tenth of an inch. It possesses a plain muscular wall, consisting of an outer layer of longitudinal, a middle of circular, and an inner of longitudinal muscles. On the inside of the muscles there is a mucous coat lined by a columnar epithelium, which is not ciliated.1 1 Arising from the lower part of the epididymis, or from the vas deferens close to its commencement, is a long narrow diverticulum which ends blindly. This is the vas aberrans. It is probably a vestigial structure. A few small convoluted tubes, situated near the head of the epididymis and representing vestiges of part of the Wolffian body, are called the paradidymis or organ of Giraldés. The innervation of the vas deferens is described below in dealing with the process of ejaculation. 227 228 THE PHYSIOLOGY OF REPRODUCTION A branch from one of the vesical arteries accompanies the vas deferens, and eventually enters the testis, where it anas- tomoses with the spermatic artery. The vas deferens, near its termination, becomes sacculated, and in this region is known as the ampulla of Henle. In the walls of the ampulla there are Fic. 53.—Passage of convoluted seminiferous tubules (a) into straight tubules, and of these into rete testis (c), (after Mihalkowicz, from Schafer) ; }, fibrous stroma continued from mediastinum. a number of small tubular glands, which doubtless supply some portion of the ejected fluid. : Disselhorst 1 believes that the ampulla acts as a seminal reservoir (a function which has also been assigned to the vesicule seminales, as described below), and states that he has * Disselhorst, “ Ausfiihrapparat und Anhangsdriisen der Mannlichen Geschlechtsorgane,” Oppel’s Lehrbuch der V rgleichenden Mikroscopischen Anatomie der Wirbeltiere, vol. iv., Jena, 1904. & & &b MALE ACCESSORY REPRODUCTIVE ORGANS 229 found spermatozoa stored up in little pockets in the walls of this structure in animals during the rutting time. He suggests, further, that there is a relation between the state of develop- ment of the ampulla and the time occupied by copulation. When the organ is small or absent, as in dogs, cats, and boars, the coition is a slow process, but when the ampulla is large and Tig, 54.—Transverse section through the tube of the epididymis. (After Szymonowicz, from Schafer.) u, blood-vessel; 6, circular muscle fibres; c, epithelium. well-developed, as in horses and sheep, the coitus occupies a relatively short time. The vas deferens on either side unites with the terminating portion of the corresponding seminal vesicle to form the ejacu- latory duct. ‘The two ejaculatory ducts, after traversing thé prostate, open into the floor of the urethra by small slit-like apertures. Their function is to convey to the urethra the fluid contained in the seminal vesicles and in the vasa deferentia. 230 THE PHYSIOLOGY OF REPRODUCTION The coats of the ejaculatory ducts are relatively thin. The lining epithelium is similar to that of the vas deferens. The urethra, which serves as the common channel for both urine and seminal fluid, is lined by a columnar epithelium resting on a vascular corium. The latter is surrounded by submucous tissue containing two layers of muscular fibres, the inner being arranged longitudinally, and the outer circularly. The Fig. 55.—Transverse section through commencement of vas deferens. (After Klein, from Schafer.) a, epithelium ; 6, mucous membrane; c, d, ¢, inner, middle, and outer layers of muscular coat ; f, internal cremaster muscle; g, blood-vessel. urethra in man is usually described as consisting of three divisions, the prostatic, the membranous, and the spongy portions. Of these the membranous portion comprises that part of the urethra between the apex of the prostate and the bulb of the corpus spongiosum, to be described below. Opening medially into the prostatic portion of the urethra, between the two ejaculatory ducts, is the aperture of the uterus masculinus, or organ of Weber, which is the homologue of the vagina and MALE ACCESSORY REPRODUCTIVE ORGANS 231 uterus in the female. This vesicle, which is a small cul-de-sac, and in Man hes hidden by the prostate, is probably almost or quite functionless, but it has a few very small glands which open into its cavity. In some animals—such as the goat, for example—it is of comparatively large dimensions, the upper part being divided into two horns. In connection with it is a structure corresponding to the hymen of the female. On the floor of the prostatic portion of the urethra is an elevation of the mucous membrane and underlying tissue, known as the crista urethra or caput gallinaginis. This eminence (which con- tains erectile tissue) serves when distended with blood to prevent the semen from passing backwards to the bladder, and mingling with the urine in the process of emission. It is assisted in this function by the contraction of the sphincter of the bladder. The urethra in the female corresponds to that part of the male urethra which is anterior to the openings of the ejaculatory ducts. It is lined with a stratified scaly epithelium, like that of the vagina into which it opens. Communicating with the female urethra are two complex tubular glands known as the glands of Skene. Their ducts open very close to the urethral aperture. Tue VESICULZ SEMINALES The seminal vesicles are offshoots from the lower ends of the vasa deferentia. They consist in Man of coiled tubes, about five inches long, into which several diverticula sometimes open. The structure of the vesicles is similar to that of the sacculated part of the vas deferens, but the muscular layers are relatively thinner. There has been some dispute as to the chief function of the seminal vesicles. According to one view, they serve mainly as receptacles for the spermatozoa before ejaculation. Most authorities, however, are disposed to lay greatest stress upon their secretory function. Rehfisch1 has shown that if fluids are injected into the 1 Rehfisch, ‘‘Neuere Untersuchungen iiber die Physiologie der Samen- blasen,” Deutsche med. Wochenschr., vol. xxii., 1896. 232 =3'THE PHYSIOLOGY OF REPRODUCTION testicular end of the vas deferens, they first enter the seminal vesicle and afterwards pass out through the urethra. He concludes that the vesicule serve the double purpose of secretory glands and reservoirs for the semen. Misuraca’ states that in dogs and cats, which have no seminal vesicles,” the sper- matozoa disappear from the male passages from five to seven days after castration, whereas in guinea-pigs, in which the vesicles are well developed, sperms may be found alive as long as twenty days after the removal of the testes. This is regarded as evidence that the seminal vesicles function as receptacles for the spermatozoa. Moreover, Meckel*® stated that he found sperms in the vesicule of the mole in the month of February (z.e. during the breeding season); and Seubert* recorded a similar observation about the hedgehog in August (also in the breeding season) (cf p. 60). Disselhorst,> however, throws some doubt on these observations. That the vesicule may undergo periodic enlargement in animals which have a rutting season is, however, an unquestionable fact. As evidence that the vesicule seminales are undoubtedly secretory glands, Lode ® showed that in young animals, in which one of the testes had been removed, the corresponding vesicula continued to grow, and became filled with its characteristic fluid. It was evident, therefore, that the fluid must have been secreted in the vesicula in question, since it could not have been derived from the testis of the other side. (The effects of complete castration on the growth and activity of the vesi- culz seminales are briefly referred to below.) Stilling? and ? Misuraca, ‘‘Sopra un importante questione relativa alla castrazione,” Rivista sperimentale di Freniatria, vol. xv., 1890. ° Seminal vesicles are absent not only in dogs and cats, but in many other Carnivora, and also in Cetacea and Ruminantia. They are also wanting in rabbits, but are present in the vast majority of Rodentia (Owen, Comparative Anatomy, vol. iii., London, 1868). 3 Meckel, Beitrage zur Vergleichende Anatomie: I. Ueber die Mannlichen Geschlechtstetle des Maulwurfs, 1809. 4 Seubert, ‘‘Symbolum ad Erinacei europxi anatomen,” Inaug. Dissert., Bonn, 1841. 5 Disselhorst, loc. cit. * Lode, ‘‘ Experimentelle Beitriige zur Physiologie der Samenblasen,” Sttzungsber. d. kais, Acad. d. Wissenschaft in Wien, vol. civ., 1895. 7 Stilling, ‘‘ Beobachtungen iiber die Functionen der Prostata und tiber die Entstehungen prostatischer Concremente,” Virchow’s Archiv, vol. xcviii., 1884. MALE ACCESSORY REPRODUCTIVE ORGANS 233 Akutsu! state that the epithelial cells of the vesiculz seminales change their character according to whether they are in a state of rest or activity. In the former condition they are larger and contain more plasma substance. Kolster? has described desquamation of epithelial cells in the seminal vesicles of the elk (Cervus alces). The secretion is formed apparently in considerable quantity. Its character and composition vary somewhat in different Mammals. In Man it is gelatinous, and consists chiefly of lobulins.? It has been investigated in Rodents by Sobotta,* : gated ts by Sobotta, Rauther,® and others, who describe it as a white or yellowish- white gelatinous fluid, which becomes almost solid after ejacu- lation. This capacity to clot is supposed by Landwehr ® to be due to the presence of fibrinogen, 27 per cent. of which was found to be present. Calcium, however, could not be dis- covered. Camus and Gley ’ state the clotting is brought about by a specific ferment (which they call vesiculase) in the prostatic secretion. (See p. 237.) The clotting of the fluid, after its entrance into the female passages in Rodents, prevents the escape of the spermatozoa and so helps to ensure fertilisation. This fact was first dis- covered by Lataste,* who speaks of the “ bouchon vaginal ” formed by the solidified secretion of the vesicule. Similar ob- servations have been made by Leuckart® and others. The 1 Akutsu, ‘‘ Mikroscopische Untersuchung der Secretionsvorgange in den Samenblasen,” Pfliiger’s Archiv, vol. xcvi., 1903. Further references are given in this paper. 2 Kolster, ‘‘ Ueber einen eigenartigen Prozess in den Samenblasen von Cervus alces,’’ Arch. f. Mikr. Anat., vol. 1x., 1902. 3 Firbringer, ‘‘Die Stérungen des Geschlechtsfunktion des Menschen,’ Nothnagel’s Pathologie und Therapie, vol. xix., 1895. * Sobotta, ‘‘ Die Befruchtung und Furchung des Eies der Maus,” Arch. f. Mikr. Anat., vol. xlv., 1895. 5 Rauther, ‘‘ Ueber den Genitalapparat einiger Nager und Insektivoren,”’ &c., Jenaische Zeitsch. f. Naturwissenschaft, vol. xxxvii., 1903. § Landwehr, ‘‘ Ueber den Hiweisskérper (fibrinogene substanz) der Vesicula seminalis der Meerschweinchen,” Pfliiger’s Archiv, vol. xxiii., 1880. 7 Camus and Gley, “‘ Note sur quelques faits relatifs & l’énzyme prostatique (vésiculase) et sur la fonction des glandes vésiculaires,” C. R. de Soc. de Biol., vol. iv. (10th series), 1897. § Lataste, ‘Sur le bouchon vaginal des Rongeurs,” Zool, Anz., vol. vi., 1883. ® Leuckart, Zur Morphologie und Anatomie der Geschlechtsorgane. Gottin- gen, 1847, 234 THE PHYSIOLOGY OF REPRODUCTION “ bouchon vaginal ” is said to remain in situ for several hours, and then to become softened and fall out. Tarchanoff ! has suggested that in the frog the filling of the seminal vesicles serves to excite sexual feeling in the male during the breeding season, but certain other observations have been made which seem to disprove this (or at any rate to show that it is not universally true). Thus, in some animals, it is known that sexual desire exists before the seminal vesicles become full. Moreover, Steinach? found that rats, whose seminal vesicles had been removed, still retained their desire for copulation although their fertility was diminished. That the spermatozoa possess complete functional activity before they can be in any way influenced’ by the secretion of seminal vesicles has been conclusively shown by Iwanoff,? who induced pregnancy artificially in rabbits, guinea-pigs, and other animals, by injecting into the female passages fluid obtained directly from the epididymis, and mixed with a 5 per cent. solution of sodium carbonate. The diminished fertility in Steinach’s rats, after the removal of the vesicule, was probably due to the absence of formation of the “ bouchon vaginal,” as has been suggested by Rauther.* It would seem probable that, in the majority of animals which possess vesicule seminales, the secretion of these glands serves to dilute the semen, and so assists in providing a fluid medium for the transference of the spermatozoa. Exner® has suggested that the seminal vesicles may have the function of absorbing the seminal fluid which is not ejaculated, but there is little evidence that this is the case. Lode ® found that in castrated bulls, horses, and guinea-pigs, the glandular epithelium of the vesicles atrophied, but the con- 1 Tarchanoff, ‘‘ Zur Physiologie des Geschlechtsapparates des Frosches,” Phliger’s Archiv, vol. xl., 1887. ® Steinach, ‘ Untersuchungen zur Vergleichenden Physiologie der Miinn- lichen Geschlechtsorgane,” &c., Pfliger’s Archiv, vol. lvi., 1894. * Iwanoff, “ La Fonction des Vésicles seminales et la Glande prostatique,” Jour. de Phys. et de Path, Gen., vol. ii., 1900. 4 Rauther, loc. cit. 5 Exner, ‘‘ Physiologie der Minnlichen Geschlechtsfunktionen,” Frisch and Zuckenhandl, Handbuch der Urologie, 1903. 8 Lode, loc. cit. MALE ACCESSORY REPRODUCTIVE ORGANS 235 nective tissue underwent hyperplasia. Gruber’ and Pelikann ? observed that in castrated men the glands atrophied, but became filled with a kind of mucous liquid. Tue Prostate GLAND The prostate in Man and other Mammals is a tubular gland which surrounds the urethra at the base of the bladder, and opens into it by a number of small ducts situated close to the Fig. 56.—Section through part of human prostate. (After Heitzmann, from Schafer.) C, concretions, often found in old subjects; F, epithelium ; M, muscular tissue. apertures of the ejaculatory ducts. It is usually described as consisting of three lobes, two lateral and one median, the former comprising the chief mass of the organ. Associated with the glandular substance is a considerable quantity of plain muscular tissue. The prostate is provided with lymph-vessels and blood- vessels. The arteries arise from the vesical, hemorrhoidal, and 1 Gruber, “Untersuchung einiger Organe eines Castraten,” Miiller’s Archiv, 1847. 2 Pelikann, Gerichtl.-mediz. Unters. iiber d. Skopz-ntwm in Russland, Giessen, 1876. 236 THE PHYSIOLOGY OF REPRODUCTION pudic arteries. The veins communicate with the dorsal vein of the penis and with the internal iliac vein. The innervation of the gland is described below in dealing with the mechanism of ejaculation (p. 258). The prostatic secretion is a viscid, slightly acid liquid (sometimes neutral or even alkaline), containing proteins and salts... (See p. 287.) The characteristic smell of the ejected seminal fluid is said to be partly due to the prostate secretion, which also contributes to the formation of Bottcher’s crystals described below (p. 285). De Bonis ? describes the epithelial cells of the dog’s prostate as containing a small number of granules. When these have been formed in sufficient quantity, so as almost to fill the cell, its wall ruptures and the granules pass out into the lumen of the gland. This occurs especially during coitus. After the dis- charge of the granules fresh ones are formed in the cells of the gland. Little is definitely known regarding the function of the prostate beyond the fact that it contributes additional fluid to the semen. It may, perhaps, assist in providing the spermatozoa with nutriment.2 There is some evidence, however, that it exercises a stimulating influence upon the movements of the spermatozoa.* Steinach observed that prostatic fluid, when added to normal saline solution, kept the spermatozoa in active movement for a longer period than saline solution alone. Steinach also found that rats in which the prostate gland, together with the seminal vesicles, was extirpated, were ab- solutely sterile,® but this may have been due to failure to form a “bouchon vaginal” in the female. As already mentioned 1 Poehl, Die Physiol.-chem. Grundlage der Spermintheorie, St. Petersburg, 1898; Fiirbringer, Die Stérungen der Geschlechtsfunktion des Mannes, Wien, 1895; Berliner klin. Wochenschrift, vol. xxiii., 1886. 2 De Bonis, ‘‘ Uber die Sekretionserscheinungen in den Driisenzellen der Prostata,” Arch. f. Anat. u. Phys., Anat. Abth., 1907. ; * It has been suggested also that the prostate is a sphincter of the bladder, but this is rendered unlikely by its absence in the female. It is more probable that it serves to cleanse the urethra of urine before copulation. 4 Fiirbringer, loc. cit. Kolliker, “ Physiologische Studien iiber die Samen- fliissigkeit,” Zettschr. f. wiss. Zool., vol. vii., 1856. 5 Extirpation of the vesicule seminales alone produced only partial sterility (see p. 234). MALE ACCESSORY REPRODUCTIVE ORGANS 237 , (p. 233), the clotting which causes the formation of the “ bouchon’ in Rodents is believed by Camus and Gley! to be due to a fer- ment (“ vesiculase ’) which is present in the prostatic fluid. The removal of the prostate in Steinach’s experiments had no effect in diminishing sexual desire. Walker? has also adduced experimental evidence pointing a, tubular alveolus lined with epithelium; b, alveolus containing concretion in lumen; c, bundle of muscular fibres in connective tissue ; d, blood- vessels in stroma. to the conclusion that the prostatic fluid of the dog stimulates the sperms to more active movement. Iwanoff’s experiments? (see p. 234), however, show that spermatozoa which have never come into contact with prostatic 1 Camus and Gley, loc. cit. 2 Walker (G.), “‘ Beitrag zur Kenntniss der Anatomie und Physiologie der Prostata beim Hunde,” Arch. f. Anat. u. Phys., Anat. Abth., 1899. 3 Iwanoff, loc. cit. 238 ‘THE PHYSIOLOGY OF REPRODUCTION secretion possess full functional activity, and are capable of fertilising ova successfully. Serralach and Parés’ have adduced evidence indicating that the prostate is an internally secreting gland which controls the testicular functions, and regulates the process of ejaculation. It is stated that if the prostate is removed spermatozoa are no longer produced in the testis, and that the secretory activity of the accessory genital glands ceases. These changes, however, can be prevented by the administration of glycerine extracts of prostate gland. The experiments were upon dogs. The most obvious criticism of Serralach and Parés’ view is that it is unlikely, on phylogenetic grounds, that the functional activity of the essential organ of reproduction should depend on the presence of an accessory gland of comparatively recent evolu- tionary development. On the other hand, it is arguable that the prostate may originally have formed part of the testis, and sub- sequently have become differentiated as a separate organ in the course of phylogeny. Reference may be made in this con- nection to the somewhat similar theory, which certain gyneco- logists have held, that the ovarian functions are dependent on an internal secretion arising in the uterus, whereas the most recent experimental evidence proves clearly that this is not the case (see p. 345). Griffiths * has shown that the prostate glands in the hedgehog and the mole undergo definite cyclical changes which are cor- related with changes in the functional activity of the testes (cf. p. 232). In the quiescent state the prostate is composed of a.few tubules lined by small, flattened, epithelial cells, which . are at this time incapable of producing a secretion. With the approach of the breeding season the tubules grow much larger and the epithelial cells become columnar. During rut the prostate gland is a mass of tortuous tubules, and has grown to many times the size of the quiescent organ. The tubules are described as being filled with coagulated mucus, containing a number of small round cells resembling leucocytes ; while the epithelial cells are said to show numerous mucigenous granules, > Serralach and Parss, ‘‘ Quelques données sur la Physiologie de la Prostate et du Testicule,” C. R. de la Soc. Biol., vol. 1xiii., 1908. * Griffiths, ‘‘ Observations on the Function of the Prostate Gland in Man and the.Lower Animals,” Jour. of Anat. and Phys., vol. xxiv., 1890. MALE ACCESSORY REPRODUCTIVE ORGANS 239 especially in the inner or lumen half, but also, though less markedly, in the outer half of each cell (¢f. de Bonis’ description of the dog’s prostate referred to above). The prostatic secretion is expelled into the urethra during the sexual act by the contraction of the sheath of non-striped muscle which surrounds each tubule throughout its entire length. It has been shown in both Man and animals that the growth of the prostate is dependent upon the growth of the testes, since it remains of small size until the time of puberty, when the generative system reaches its full development. In those ab- normal cases in which testicular growth is arrested, the prostate remains in a condition of rudimentary development. Moreover, it has been shown that the prostate in Man normally undergoes atrophy in old age (see p. 676), or as a result of castration, becoming transformed after a few years into a mass of fibrous connective tissue containing a small number of scattered muscle fibres in a state of degeneration. It has been found also that the prostatic tubules disappear almost entirely in castrated animals, and what is left of the epithelium completely loses its secretory function ? (cf. p. 303). De Bonis’ experiments, however, seem to show that the administration of prostatic extract to castrated dogs may lead to a renewal of activity and to the formation of fresh granules in the secretory cells, but this result could not be obtained by employing testicular extract. CowPErR’s GLANDS Cowper’s glands are situated near the anterior end of the urethra. They are a pair of small tubulo-racemose glands, and communicate with the urethra by two ducts, apertures of which 1 See also Griffiths, “Observations on the Anatomy of the Prostate,” Jour. of Anat. and Phys., vol. xxiii., 1889. For the comparative anatomy of the prostate, see Oudemans’ Die Accessorischen Geschlechtsdriisen der Stiugethiere, Haarlem, 1892. According to this authority, the hedgehog has two pairs of prostates, The homologies of these glands in Insectivores still seem to be obscure. See below, under Cowper’s glands, 2 Griffiths, loc. cit. Cf. also Griffiths, ‘‘ The Condition of the Testes and Prostate Gland in Eunuchoid Persons,” Jour, of Anat. and Phys., vol. xxviii, 1893 ; Walker (G.),‘‘ Experimenta] Injection of Testicular Fluid to prevent the Atrophy of the Prostate Gland after the Removal of the Testes,” Johns Hopkins Hospital Bull., vol. xi., 1900; Wallace (Cuthbert), ‘‘ Prostatic Enlarge- ment,” London, 1907 ; de Bonis, oc. cit. 240 THE PHYSIOLOGY OF REPRODUCTION (in the human subject) are about two inches below the openings of the vasa deferentia. The lobules of the glands are surrounded by a firm investing membrane which contains muscular tissue. They are lined internally by a secretory epithelium. The significance of the viscous secretion which these glands produce is still unknown. It has been suggested that it serves to cleanse the urethra of urine or semen. Since it is poured out in considerable quantity during coitus, and appears sometimes to precede the ejaculation of the actual semen, it is not im- possible that the secretion of these glands may possess the special function of ridding the urethra of all traces of urine preparatory to the passage of the spermatozoa. The glands of Littré or Morgagni, which beset the whole lining membrane of the urethra, except near the external orifice, probably serve the same purpose as Cowper’s glands. (Cf prostate, footnote *, p. 236.) According to Nagel,’ Cowper’s glands are of the normal dimensions in castrated men, and consequently should not be regarded as purely sexual organs. On the other hand, Schneidemiihl,?, whom Nagel quotes, says that in animals they atrophy after castration. Griffiths® describes these glands in the hedgehog and the mole as undergoing periodic changes similar to those of the prostate glands. In the hedge- hog the secretion is abundant during the summer (2.e. in the breeding season), and possesses a disagreeable and penetrating odour. According to Gley,* the secretion in this animal contains a ferment which causes the fluid of the vesicule seminales to clot, so that Cowper’s glands in the hedgehog are the physio- logical equivalent of the prostate gland in the Rodentia.’ 1 Nagel, “ Physiologie der Mannlichen Geschlechtsorgane,” Nagel’s Hand- buch der Physiologie des Menschen,” vol. ii., Braunschweig, 1906. * Schneidemiihl, ‘‘Vergleichende Anatomische Untersuchungen itiber denfeineren Bau der Cowperschen Driise,” Deutsche Zeitschr. f. Tiermedizin, vol. vi., 1883. 5 Griffiths, ‘“‘ Observations on the Function of the Prostate Gland,” &c., Jour, of Anat. and Phys., vol. xxiv., 1890. 4 Gley, ‘‘Réle les Glandes génitales accessoires dans la Reproduction,” Nel primo Centenario dalla Morte di Lazzaro Spallanzani Acad. Sci. e Straniert, 1899. 5 It should be mentioned that very considerable doubt has been thrown on the homology of what are often called Cowper’s glands (those presumably referred to by Gley and Griffiths) in the hedgehog with the glands known by that name in other Mammals. According to Leydig (“ Zur Anatomie der MALE ACCESSORY REPRODUCTIVE ORGANS 241 Furthermore, Stilling’* states that the epithelium of Cowper’s glands undergoes definite histological changes which depend upon the occurrence of coitus.” Corresponding to Cowper’s glands in the male there are in the female a pair of small glands situated one on each side of the vagina. These are the glands of Bartholini or Duverney. Their ducts open out on to the vulva, on the sides of the vaginal orifice. These glands secrete a viscid fluid which helps to moisten and lubricate the surface of the vulva. In addition to the accessory male glands described above, there are, in many animals, other glands (perineal, inguinal, and preputial) which are probably sexual, inasmuch as they are believed to serve as means of attraction between the sexes during the breeding season.? Most of these glands emit secre- tions of a musky odour, which in the vast majority of cases is peculiar to the male, and very often to the male during the rutting season only. Amongst the animals in which this pecu- liarity occurs are the musk deer and other kinds of deer and antelopes, the musk rat, the hamster, and many other Rodentia Minnlichen Geschlechtsorgane und Analdriisen der Siugethiere,” Zedtschr. f. wiss, Zool., vol. ii., 1850), Cowper’s glands in the hedgehog are in reality repre- sented by a pair of glands embedded in the urethral muscle (cf. Oudemans, loc. cit.). The so-called Cowper's: glands, which, as mentioned above, undergo marked cyclical changes, are situated outside the pelvis close to the ischial tuberosity and the base of the penis (Linton, ‘‘ A Contribution to the Histology of the so-called Cowper’s Glands of the Hedgehog,” Anat. Anz., vol. xxxi., 1907). In the absence of embryological evidence, Linton appears to regard these glands as sui generis. ‘They are shown by this author to be composed of two distinct kinds of secreting acini, one lined by a single layer of columnar epithelial cells, and the other by many layers of polyhedral cells. Both kinds secrete a considerable quantity of fluid, containing circular bodies which are believed to be the nuclei of disin- tegrated cells, though no cells in process of disintegration could be found in the single-layered type of acinus. ! Stilling, ‘ Uber die Cowperschen Driisen,” Virchow’s Arch., vol. c., 1885. 2? For an exhaustive account of the minute anatomy of the accessory glands and ducts of the male reproductive system in the different groups of Vertebrata, with full references to the literature, see Disselhorst in Oppel’s Lehrbuch, loc. cit. 3 Tiedemann, Comparative Physiology, English Translation, London, 1834; Grosz, ‘‘ Beitrage zur Anatomie der Geschlechtsdriisen der Insektivoren und Nager,” Arch. f. Mikr, Anat., vol. Ixvi., 1905. See also description of prepuce (p. 242). Q 242 THE PHYSIOLOGY OF REPRODUCTION and Insectivora. The temporal gland of the elephant is also stated to emit a sexual secretion, especially in the male during rut. Tue CopuLatory ORGAN The penis is the intromittent organ of copulation. Besides serving to conduct the urine to the exterior through the channel of the urethra, it has the further function of conveying the semen into the genital passages of the female. This latter function is dependent upon its power of erection under the influence of sexual excitement. The erectile tissue of the penis is contained chiefly in three tracts, the two corpora cavernosa, which are situated one on each side and are united in the middle line, and the smaller corpus spongiosum, which is placed inferiorly and surrounds the urethral passage. The corpora cavernosa are enclosed by an invest- ment, containing plain muscle fibres, numerous well-developed elastic fibres, as well as bundles of white fibres. Trabecule pass inwards from the fibrous sheath and cross the cavities of the cavernous bodies, dividing them into interstices which are filled with venous blood, being, in fact, greatly enlarged vessels. The corpus spongiosum is similar in structure, but its fibrous framework is not so well developed. The canal of the urethra is surrounded by plain muscle fibres. Muscular tissue is also present in the external coat of the spongy body, and in the trabeculae. At their proximal ends the three corpora are enlarged into bulbs. Those of the cavernous bodies are covered by the ischio-cavernosi muscles (or erectores penis), while the bulb of the spongy body is surrounded by the bulbo-cavernosus muscle (or ejaculator urine). At its distal end the corpus spongiosum becomes enlarged, forming the glans penis, which is identical in structure with the rest of the body. The integument of the penis in the region of the glans be- comes doubled in a loose fold. This is the prepuce or foreskin. Numerous sebaceous glands are present near the free margin of the prepuce. These glands emit an odoriferous secretion which in some animals is especially marked during the season of rut.’ 1 Courant, “ Uber die Priputialdriisen des Kaninchens und iiber Verander- ungen derselben in der Brunstzeit,” Arch. f. Mikr. Anat., vol. lxii., 1903. MALE ACCESSORY REPRODUCTIVE ORGANS 243 The penis is very sensitive to external stimulation, its surface being beset with simple and compound end-bulbs and Pacinian corpuscles, especially in the region of the glans. Its innervation is described below. The arteries of the penis are the internal pudic arteries and the dorsal artery. Some of the arterial branches project into the intertrabecular spaces of the corpora cavernosa, and — Cc. ——-—-: Vv. Vz. TA, = Ss -- A, Com. - Az = N. Tun. Tr. - Te. Sube. - =F, Vere 3 --—Te Subf. Corp. x fie ff. Spong. ——— on Fig. 58.—Transverse section through adult human penis. x3. (After Eberth, from Nagel.) A., artery; C., cutis; Com., communication between the two corpora cavernosa ; Corp. Spong., corpus spongiosum; F., fascia; N., nerves ; 8., septum; 7, A., tunica albuginea; Te. Subc., tela subcutanea penis; Te. Subf., tela subfascialis ; Tun., tunica dartos penis; T'r., trabeculz of corpus cavernosum; U., urethra; V., veins. : form coiled dilated vessels which are known as the helicine arteries. In most cases the arteries are said. to open into the venous spaces, through the intervention of capillaries, but a few of the smaller arteries are stated to communicate directly with the cavernous veins. The blood is carried away by two sets of veins, the one set uniting to form the dorsal vein, and the other communicating with the prostatic plexus and the pudendal veins. 244 THE PHYSIOLOGY OF REPRODUCTION When the venous spaces in the erectile tissue are distended with blood the organ erects, becoming hard and rigid in con- dition. It is this power of erection which enables the penis to function as an intromittent organ during copulation. The above description applies more especially to the copulatory organ in Man. In the other groups of Mammals it has essentially the same structure, but presents sundry modifications in the different orders! In the Monotremata, Fia. 59,—Section through erectile tissue. (After Cadiat, from Schafer.) a, trabeculz ; b, venous spaces ; c, muscular fibres cut across. however, there is no corpus spongiosum.’ In some Mammals (Carnivora and Rodentia) the penis is provided with a 1 For an account of the structure of the copulatory organ in the various groups of Vertebrates, with notes on the different modes of copulation and bibliography, see Gerhardt, “ Morphologische und biologische Studien iiber die Kopulationsorgane der Saugethiere,’’ Jenaische Zeitschr. f. Naturwissen- schaft, vol. xxxix., 1905. 2 The penis of the Monotreme is perforated by a canal, through which the semen passes but not the urine. When in a relaxed state the organ lies in a little pouch in the floor of the cloaca, from which it projects when erected. The cloaca is the single common chamber through which the faces and urine pass to the exterior, as in birds and reptiles. In birds the penis is either altogether absent or else is rudimentary (Crax, Crypturus, Lamel- lirostres, Ratitze), Disselhorst, ‘‘ Gewichts- und Volumszunahme der miannlichen Keimdriisen,” &c., Zool. Anz., vol. xxxii., 1908, MALE ACCESSORY REPRODUCTIVE ORGANS 245 Fie. 60.—Part of transverse section through penis of monkey. u, erectile tissue ; b, urethra ; c, artery; d, nerve; e, Pacinian body ; f, fold of epithelium ; g, surface epithelium. 246 THE PHYSIOLOGY OF REPRODUCTION cartilaginous or bony support, the os penis, which is developed especially in the region of the glans. It is particularly large in the walrus. In the Cetacea the penis is often of enormous size (six feet in length in some species), and terminates in a point, but is otherwise normal. It can be withdrawn into the body when not being used. In copulation, whales apply their ventral surfaces to one another. , In most Rodents and Marsupials the penis in the relaxed state is withdrawn within an eversible fold of skin which con- stitutes a dermal sac. When the penis is erected this sac is everted, and forms its outer integument. Cole has described the structure of the intromittent sac in the male guinea-pig, which appears to be typical of many other Rodents.1 Dorsal to the urethral aperture when the penis is withdrawn, and ventral to it when it is everted, is seen the entrance to the intromittent sac. Lying in the cavity of the sac are two horny styles. Two dorsal longitudinal folds are also noticeable. These are the backward prolongations of the lateral lips of the urethral aperture, the ventral lip consisting of corpus spongiosum and separating the aperture of the urethra from that of the sac. Attached to the base of the sac are two retractor organs which consist of elastic fibres and erectile tissue, and are connected at their other extremities with the integument of the penis. The eversion of the sac is brought about by the erection of the two longitudinal folds referred to above. The whole of the sac is composed largely of erectile tissue, but the tissue of the longitudinal folds is even more highly erectile than the rest of the sac. The entire structure is provided with a very rich nerve supply. When the penis is erect, and the sac everted, the two horny styles are protruded externally to a considerable length. Moreover, both the sac and the surface of the glans are covered with sharp spine-like structures, while in some species of Caviidee they are provided also with two sharp horny saws which are appended to the sides of the penis farther back. There can be little doubt that the purpose of this unique con- trivance is to act as an exciting organ on the sexual structures of the female. * Cole, ‘On the Structure and Morphology of the Intromittent Sac of the Male Guinea-pig,” Jour. of Anat. and Phys., vol. xxxii., 1898. MALE ACCESSORY REPRODUCTIVE ORGANS 247 In another rodent, the marmot, according to Gilbert? the skin which covers the os penis becomes torn away during the tutting season, so that the bone projects freely beyond the end of the glans and is then used as a stimulating organ. Structures which project from the penis, and are probably employed as sexual irritants, are also found in the rhinoceros, the tapir, and certain other animals. In the cat the glans is beset with callous retroverted papille, which no doubt serve the same function. They are present also in the lion and tiger, but are of smaller size.? Perhaps the most curious modifications presented by the mammalian organ of copulation are those found in certain species of Ruminants. In the sheep, the gazelle, the giraffe, and a number of antelopes, there is a long filiform process Fig. 61.—Distal end of ram’s penis, as seen from the left side, showing glans and filiform appendage. The prepuce is folded back. Slightly reduced. attached to the end of the organ and traversed by the urethral passage. In some forms the process arises medially (the penis being symmetrical); but in others, such as the sheep, it is attached to the left side of the organ, the distal end of which appears to have undergone some sort of torsion.? The urethra opens to the exterior at the extreme end of the filiform ap- pendage. This structure—which has been investigated, especially in the case of the sheep 4—is composed largely of erectile tissue which surrounds the urethra, and may be regarded as an ex- tension of the corpus spongiosum. Outside the erectile tissue is a well-marked muscular layer which lies next to the integument. The process is supported by a pair of fibro-cartilage bodies, 1 Gilbert, ‘‘ Das Os priapi der Saéugethiere,”” Morph. Jahrbuch, vol. xviii. * Owen, On the Anatomy of Vertebrates, vol. iii., London, 1868. 3 Garrod, ‘‘ Notes on the Osteology and Visceral Anatomy of Ruminants,”’ Proc. Zool. Soc., vol. xlv., 1877. 4 Nicolas, ‘Sur l’Appareil Copulateur du Bélier,” Jour. de l’Anat, et la Phys., vol. xxiii, 1887. Marshall, ‘‘The Copulatory Organ in the Sheep,” Anat. Anz., vol. xx., 1901. 248 THE PHYSIOLOGY OF REPRODUCTION placed one on each side of the urethra and extending throughout - the whole length of the structure. The fact that the filiform prolongation is an erectile organ points to the conclusion that its function is insertion into the os uteri during copulation. An examination of the uterus in the sheep shows that the os, when open, is fully large enough to admit of the entrance of the distal portion of the penis in the region of the glans. If the extreme distal end does so enter, the filiform process must extend into the cavity as far, or pe Muse. \ Fibr. Cart Fic. 62.—Transverse section through filiform appendage of ram, about a quarter its length from the tip. x45. Bl. V., blood-vessels; Ep. Ur., epithelium surrounding urethral cavity ; Fibr. Cart., fibro-cartilage; Int.. integument; Musc., muscular layer; Ur., urethra, nearly as far, as the junction of the relatively short corpus uteri with the two cornua. That the appendage functions in the manner described seems additionally probable in view of the fact, to which sheep-breeders attest, that if the process is cut off the ram is rendered barren. Professor Robert Wallace informs me that it used to be a regular practice, for the pro- tection of ewes while being driven south from the Highlands of Scotland, to cut off the filiform appendage from the rams to prevent them from impregnating the ewes on the way, this method of inducing sterility proving quite as effective as removal of the testicles. MALE ACCESSORY REPRODUCTIVE ORGANS 249 In the bull, the musk ox, and some other Ruminants the filiform process is vestigial. Gl. Fibr. Cart. Fig. 63.—Transverse section through the middle of the glans penis of the ram. x45. Corp. Cav., corpus cavernosum ; Fibr. Cart., fibro-cartilage ; Gl., erectile tissue of glans; Jnt., integument; Ur., urethra. The penis in the male mammal is represented in the female by the diminutive clitoris. This organ, however, is not traversed by the urethra (at least in the majority of animals). 250 THE PHYSIOLOGY OF REPRODUCTION On the other hand, the corpora cavernosa and the glans are represented by homologous structures. The clitoris, like the penis, contains very numerous sensory nerve endings * and under- goes erection during sexual congress. The relation between the clitoris and the uro-genital canal is closer in some Mammals than in others. In some species (e.g. the capybara among the Rodents, and Tupaia among Insectivores) the clitoris is of considerable size, and is grooved along its under surface in relation to the upper wall of the urethra. In other animals (eg. Arvicola, Talpa, and Stenops) the groove on the under surface of the elongated clitoris is converted by the coalescence of its margins into a tube, which Fig. 64.—Distal end of bull’s penis as seen from left side, showing glans and urethral papilla representing vestigial filiform appendage. The prepuce is folded back. About two-thirds natural size. constitutes the urethral portion of the uro-genital canal. Further, in the female of the spotted hyena (H. crocuta), the whole of the uro-genital canal, beyond the apertures of the ducts of Bartholini’s glands, is prolonged forward to the ex- tremity of the clitoris and terminates in a similar manner to that of the urethra of the male. In this animal, therefore, the vagina is completely absent, the os uteri opening directly into the uro-genital canal, which is elongated and tubular in form as in the male. A somewhat similar condition has been known to occur abnormally in the human female.? + Worthmann,‘‘ Beitrage zur Kenntniss der Nervenausbreitung in Clitoris und Vagina,” Arch. f. Mikr. Anat., vol. xviii. 2 Watson (M.), ‘* The Homology of the Sexual Organs illustrated by Com- parative Anatomy and Pathology,” Jour. of Anat. and Phys., vol. xiv., 1879. MALE ACCESSORY REPRODUCTIVE ORGANS 251 THe MrEcHANISMS OF ERECTION, EJACULATION, AND RETRACTION. The erection of the penis is brought about mainly by the dilatation of its blood-vessels. First of all the bulbous (proximal) part of the organ increases in size, and then the swelling extends throughout the cavernous bodies, and eventually to the glans. If the penis is cut across when in a state of re- laxation only a small quantity of venous blood exudes from the wound ; but if the same operation is performed during erection, the blood flow is enormously increased, while simultaneously becoming bright and arterial in colour.1 Francois-Franck,? observed a corresponding rise in the arterial and venous tension. He found also that the organ in the process of erection became very considerably swollen in size before the increase in the blood pressure had extended to the veins. Lovén? showed that the veins in the penis are traversed by five times as much blood during erection as they are in a state of repose. The same investigator found that, whereas the ordinary arterial pressure in the penis is about half that of the carotid, during erection it rose to three-fifths that of the carotid. The increase in the amount of blood in the organ is accompanied by a rise of temperature.* : There can be no doubt that the erection of the penis is brought about partly through the contraction of the ischio- cavernosus (or erector penis) and bulbo-cavernosus muscles, certain of the fibres of which pass over the efferent vessels, and so arrest the outward flow of blood.’ The result of this contraction 1 Eckhard, ‘‘ Untersuchungen iiber d. Erektion d. Penis beim Hunde,” Bettr. zur Anat. und Phys., vol. iii., Giessen, 1863. 2 Francois-Franck, ‘‘ Recherches sur |’Innervation Vaso-motrice du Pénis,” Arch. de Phys., 1895. 3 Lovén, Berichte iiber die Verhandlungen der Kénigl. Sdchs. Gesell. zu Leipzig, vol. viii., 1866. Nikolsky, ‘‘ Ein Beitrag zur Physiologie des Nervi erigentes,” Arch. f. Anat. u. Phys., Phys. Abth., 1879. 4 Retterer, Article on ‘‘ Erection,” in Richet’s Dictionnaire de Physiologie, vol. v., 1902. 5 De Graaf (Regner), De Virorum Organis Generationi Inservientibus, Geneva, 1785. Giinther, Untersuchungen und Erfahrungen aus dem Gebiete der Anatomie, vol. i., Hanover, 1837. Kobelt, De Appareil du Sens Génital des Deux Sexes, Strasbourg, 1851. For further references, see Retterer, loc. cit. 252 THE PHYSIOLOGY OF REPRODUCTION is, that whereas the blood can freely enter the dilated vascular spaces of the penis, its exit is retarded, while this leads to a further distension of the vessels, the venous outlets of which become still more compressed. Although the muscular mechanism of the penis unques- tionably assists in the erection of that organ, it is equally clear that it is incapable by itself of causing that phenomenon, since erection cannot be induced by ligaturing the efferent veins. Moreover, the penis can be made to erect in animals in which the muscular mechanism has been paralysed by the injection of curari, but the erection in such cases is incomplete. It is stated also that the smooth or unstriated muscle fibres, which are scattered throughout the trabecular framework of the corpora, participate in the process of erection, but there has been some disagreement as to the precise part they play. Kolliker* suggested that their action is temporarily inhibited, and that the relaxation of the trabecule, which consequently follows, permits the vascular spaces to distend. According to Valentin,? these muscles contract, and in so doing cause a dilatation of the walls of the vessels, which thereby increase in volume. Langley and Anderson’s observations, which support Kolliker’s suggestion, are described below in giving an account of the nervous mechanisms of erection and retraction. It is obvious, however, that in those cases in which the penis remains erected for a considerable time a constant circulation must be maintained through both the afferent and the efferent vessels of the organ. In some animals (dog, cat, horse, hedgehog), but not in the rabbit or Man, the penis possesses an accessory muscle. This is called the retractor penis. It consists of a thin band of longi- tudinally arranged, unstriated fibres, inserted at the attach- ment of the prepuce, and continued backwards in the middle line over the ventral surface of the corpus spongiosum to the bulbous part of the urethra, where it divides into two halves which separate on either side of the anus. Some of the fibres are continuous with a portion of the bulbo-cavernosus of the same side, while others are connected with the wall of the urethra. 1 Kolliker, Verhandl. der Wirzburger Phys. Med. Gesell., vol. ii, 1851. 2 Valentin, Lehrbuch der Physiologie, vol. ii., 1844. 22 wee MALE ACCESSORY REPRODUCTIVE ORGANS 253 When it contracts it causes a marked dorsal curvature of the penis." Although the sexual orgasm is usually accompanied by a high degree of mental excitement, it is essentially a reflex action, and can take place when all connection with the brain is severed by transection of the spinal cord. It is generally believed that the centre for erection lies in the lumbo-sacral region of the cord.2 Numerous experiments have been recorded which prove conclusively that it is not situated in the upper part of the cord or in the brain. Thus, Goltz? showed that transection of the spinal cord above the lumbar region did not destroy the reflex. Brachet * also has recorded the occurrence of ejaculation under a similar condition. According to Miiller,’ only the lower part of the cord need be retained in order to preserve the erection reflex, since this is still present after the complete destruction of the cord in the whole of the lumbar and the upper part of the sacral region. Miiller was able to induce erection in a dog, which had undergone this operation, by rubbing the surface of the penis. It is known, however, that erection (and even ejaculation) 1 Langley and Anderson, ‘‘ The Innervation of the Pelvic and Adjoining Viscera: Part III, The External Generative Organs,” Jour. of Phys., vol. xix., 1895. The retractor muscle is remarkable for its sensitiveness to changes of temperature, and at the same time for being unusually tenacious of life. It can be cut out of the body and preserved in blood serum, in a cool place, for days at a time, and afterwards, on warming, will relax and undergo spontaneous contractions. Ata temperature of 40° C. it is quite placid; but, on cooling slightly, it will shorten, and not infrequently enter into a series of slow rhythmic contractions. If cooled to 15° C: it will contract to about one quarter of its original length. (Sertoli, ‘‘Contribution & la Physiologie Générale des Muscles lisses,” Arch. Ital. de Biol., vol. iii., 1883 ; Gruenhagen, “Das Thermotonometer,” Pfliiger’s Arch., vol. xxxiii., 1884. See also Fletcher, ‘Preliminary Note on the Motor and Inhibitory Nerve-Endings in Smooth Muscle,” Proc. Phys. Soc., Jour. of Phys., vol. xxii., 1898.) 2 See Onuf, ‘“‘Notes on the Arrangement and Function of the Cell Groups in the Sacral Region of the Spinal Cord,” Jour. of Nervous and Mental Diseases, 1899. 3 Goltz, ‘Ueber das Centrum der Erectionsnerven,” Pfliiger’s Arch., vol. vii., 1873. See also Goltz and Frensberg, ‘‘ Ueber die Functionen des Lendenmarks des Hundes,”’ Pfliiger’s Arch., vol. viii., 1874. 4 Brachet, Recherches expérimentales sur les Fonctions du Systeme Nerveux Ganglionaire, Paris, 1839. 5 Miiller, ‘“ Klinische und Experimentelle Studien iiber die Innervation der Blase,” &c., Deutsche Zettschr. f. Nervenheilk., vol. xxi., 1902. 254 THE PHYSIOLOGY OF REPRODUCTION can also be induced voluntarily by stimuli conveyed from the brain (7.e. by sexual emotion). It is interesting to note, there- fore, that Budge * and Eckhard” were able to cause the penis to erect by electrical stimulation of the cervical cord, the pons, and the crura cerebri. The same result was obtained by Pussep by exciting a definite region in the cerebral cortex. In this case erection was followed by ejaculation.® It is stated also that hanging and decapitation in Man are sometimes followed by erection.4 According to Spina,° who experimented on the guinea-pig, section of the spinal cord, near the last costo-vertebral articulation, is invariably suc- ceeded by erection and ejaculation. There are certain facts which seem to show that the higher nerve centres exercise an inhibitory influence over the sexual processes. Thus, Retterer® states that it is easier to induce erection by external irritation in a dog whose spinal cord has been cut through, than in a normal animal. Eckhard” was the first to show that the penis in the dog could be induced to erect experimentally by the stimulation of certain nerves which he called the nervi erigentes. These nerves, which are truly vaso-dilator, were found in the dog to arise from the 1st and 2nd sacral nerves, and in some cases from the 3rd sacral nerve also. Gaskell® showed that in the rabbit the erector fibres leave the spinal cord by the anterior (and not by the posterior) roots of the 2nd and 3rd sacral nerves. Morat ® also } Budge, ‘“‘ Ueber das Centrum genitospinale des Nervus sympatheticus,” Virchow’s Archiv, vol. xv., 1858. 2 Eckhard, loc. cit. 5 Pussep, “Ueber die Gehirnzentren der Peniserektion und des Samenergusses,” Inaug.-Dissert., St. Petersburg, 1902. Abstract in Le Physiologiste Russe, vol. iii., 1904. 4 Gotz, ‘Uber Erektion und Ejaculation bei Erhingten,” Inaug.-Diss., Berlin, 1898. ® Spina, ‘‘Experimentelle Beitrige zu der Lehre von der Erektion und Ejaculation,” Wiener Med. Blitter, 1897. ® Retterer, Article ‘‘ Erection,” in Richet’s Dictionnaire de Physiologie, vol. v., Paris, 1902. 7 Eckhard, loc. cit. * Gaskell, ‘On the Structure, Distribution, and Function of the Nerves which Innervate the Visceral and Vascular Systems,” Jour. of Phys., vol. vii., 1886. ° Morat, ‘‘Les Nerfs Vaso-dilatateurs et la Loi de Majendie,” Arch. de Phys., 1890. MALE ACCESSORY REPRODUCTIVE ORGANS 255 found that in the dog these fibres are contained only in the anterior roots of the lst and 2nd sacral nerves. The corresponding parts in the female are similarly in- nervated. Thus, Langley’ has described stimulation of the sacral nerves in the vertebral canal of the rabbit as producing dilatation and flushing of the vulva. These effects were most marked on exciting the 3rd and 4th sacral nérves. The stimu- lation of the 1st and 2nd sacral nerves, on the other hand, generally produced contraction and pallor. Langley obtained similar results in experiments on the male rabbit, the stimulation of the sacral nerves causing either protrusion and flushing of the penis, or else retraction and pallor. Nikolski? had previously stated that, on stimulating the anterior ramus of the nervus erigens (or the ramus from the Ist sacral) in the dog, he obtained a vaso-constrictor instead of a vaso-dilator effect, thus differing from Eckhard and other investigators. Sherrington * found that in the male monkey excitation of the 2nd and 3rd sacral nerves produced moderate erection, and that of the Ist sacral only slight erection. In the female monkey the effects of stimulating the 3rd sacral were usually greater than in the case of the 2nd, while the 1st sacral produced no certain effects. Similar results were observed in experimenting on the cat, but in this animal stimulation of the 1st sacral nerve appears to have had a more marked effect. Frangois-Franck * found that the anterior ramus from the Ist sacral, was capable of causing both vaso-constriction and vaso-dilatation. This investigator noticed further that both effects could be produced by stimulating the hypogastric nerves, but that the vaso-dilator action was more pronounced. Budge * also described erector action from the hypogastrics in the rabbit. Langley and Anderson,® however, were unable 1 Langley, ‘‘The Innervation of the Pelvic Viscera,” Proc. Phys. Soc., Jour, of Phys., vol. xii., 1891. 2 Nikolski, loc. cit. 3 Sherrington, ‘‘ Notes on the Arrangement of some Motor Fibres in the Lumbo-Sacral Plexus,” Jour. of Phys., vol. xiii., 1892. 4 Francois-Franck, loc. cit. 5 Budge, loc. cit. 6 Langley and Anderson, “The Innervation of the Pelvic and Adjoining Viscera,” Jour. of Phys., vol. xix., 1895. 256 THE PHYSIOLOGY OF REPRODUCTION to confirm this statement, but they found that the hypogastrics sometimes contained constrictor fibres for the external gene- rative organs. They state that they could discover no satisfactory evidence of the presence of vaso-dilator fibres in any of the upper or lumbar set of nerves. It would appear, therefore, that the vaso-dilator function is probably confined to the lower or sacral set of nerves. Following Langley and Anderson’s description, the fibres from the sacral set of nerves may be divided into two groups or classes, the visceral and the somatic. Stimulation of the visceral fibres (which run in the nervi erigentes) produces dilator effects on the vessels of the penis (and vulva), as already de- scribed. It also causes inhibition of the unstriated muscles of the penis, the retractor muscle of the penis (when present), and the unstriped muscles of the vulva (in the female). The somatic sacral nerves send motor branches to the ischio-cavernosus and bulbo-cavernosus muscles, as well as to the constrictor urethree or deeper muscular stratum of the perineum. In the female they innervate the erector clitoridis, which represents the ischio- cavernosus, and the sphincter vagine, which embraces the lower end of the vagina, and is the homologue of the bulbo- cavernosus. The sacral nerves, as far as Langley and Anderson ' were able to determine, send no visceral fibres by their somatic branches. The same investigators found that stimulation of the upper or lumbar set of nerves produced strong contraction of the vessels of the penis,? as well as contraction of the retractor muscle, and of the other unstriated muscles of the penis, prepuce, and scrotum (dog, cat, and rabbit). The penis underwent marked retraction as a result of the excitation. Stimulation of the 2nd lumbar nerves in the cat generally produced a slight but distinct. action on the external generative organs. The 3rd, 4th, and 5th lumbar nerves in many cases had a strong action, but the 6th had no action. The Ist lumbar and 13th thoracic were found to have a slight action. In the dog stimu- ' Langley and Anderson, loc, cit. ®? Vaso-constrictor fibres for the penis were first found by Eckhard (loc. cit.) in the nervus dorsalis penis. MALE ACCESSORY REPRODUCTIVE ORGANS 257 lation of the 5th lumbar nerve had no effect upon the generative organs, but the lst lumbar was observed to have a distinct action, and also the 13th and 12th thoracic. In the rabbit no effect was produced by stimulating the 1st lumbar nerve. The 2nd lumbar had a slight action occasionally, but the 3rd, 4th, and 5th lumbar nerves always had an effect which was more or less pronounced. The fibres from the lumbar nerves run in the white rami communicantes to the sympathetic chain, where they take two routes. (a) The majority of the fibres take the course of the pudic nerves (nervi pudendi). They follow the sympathetic chain to the sacral ganglia, from which fibres are given off, and these run in the grey rami communicantes to the sacral nerves. Their further course is by way of the pudic nerves (7.e. in the somatic branches), none apparently running in the nervi erigentes (z.e. to the visceral branches). (b) The second of the courses taken by the lumbar nerve fibres is that by the pelvic plexus. Only a relatively small number, however, take this route. Most of them run in the hypogastric nerves, but a few may join the plexus from the lower lumbar or upper sacral sympathetic chain, or from the aortic plexus. Of these latter, some may join the first root of the nervus erigens, and ‘proceed with it to the pelvic plexus.* It has already been mentioned that the clitoris in the female, like the penis, undergoes erection during coitus. The same is the case with the other parts of the vulva which contain erectile tissue. The friction which is set up between these structures and the glans of the penis causes a reflex discharge of motor impulses in both the female and the male. In the female the uterus undergoes a series of peristaltic contractions, by means of which the semen is sucked into its cavity (see p. 180). More- over, Bartholini’s glands show an increased activity and pour out a viscid secretion. In the male, the sexual impulses cul- minate in the emission of the semen. This is brought about by a series of muscular contractions, which probably begin in the walls of the vasa efferentia and pass to the canal of the epididymis, and thence along the vas deferens on either side. The vesicule seminales contract simultaneously, expelling their 1 Langley and Anderson, loc. czt. R 258 THE PHYSIOLOGY OF REPRODUCTION contents into the vasa, and the mixed fluid passes out through the ejaculatory ducts into the prostatic portion of the urethra. The prostatic muscles also contract, and probably assist in forcing the semen along the urethra, while at the same time | expelling the secretion of the prostate glands. Entrance to the bladder is prevented by the erection of the crista urethre, assisted by the contraction of the sphincter of the bladder, as already mentioned. The final discharge is brought about by the rhythmical contractions of the bulbo-cavernosus and ischio- cavernosus muscles, which have the effect of emptying the canal from behind forwards, and so ejecting the semen, mixed with the various glandular secretions, into the vaginal passage of the female. The innervation of the muscles of the penis has already been described. The secretory cells of Cowper’s glands receive branches from the pudic nerves. The prostate is innervated by fibres coming both from the nervi erigentes and from the hypogastric nerves. The former are purely motor, whereas the latter are both motor and secretory. Eckhard * found that stimulation of the nervi erigentes in the dog caused the expulsion of the prostatic secretion into the urethra. Loeb? obtained contraction of the prostatic vesicles by excitation of-the hypogastric nerves. Mislawsky and Bormann * confirmed both these observations, and found also that stimulation of the hypogastrics, while inducing the muscles to contract, at the same time promoted secretory activity in the glandular cells, the secretion continuing so long as the stimula- tion was kept up.* Fogge also states that he found hypogastric stimulation to produce contraction of the prostatic muscles.® 1 Hekhard, loc. cit. 2 Loeb (A.), ‘‘ Beitriige zur Bewegung des Samenleiters,” Inaug.-Dissert., Giessen, 1866. 3 Mislawsky and Bormann, “ Die Secretionsnerven der Prostata,” Zentralbl. f. Phys., vol. xii., 1898. * Timofeew has described end-bulbs in the prostate, testis, and other male genital organs. Some of these are of a peculiar kind, and are in connection with two nerve-fibres (“ Zur Kenntnis der Nervenendigungen in den Mannlichen Geschlechtsorganen der Siuger,” Anat. Anz., vol. ix., 1894). 5 Fogge, ‘On the Innervation of the Urinary Passage in the Dog,” Jour. of Phys., vol. xxviii. , 1902. MALE ACCESSORY REPRODUCTIVE ORGANS 259 Akutsu * has shown that the vesicule seminales in the guinea- pig receive fibres (motor as well as secretory) by the hypogastric nerves. The fibres leave the spinal cord in the 2nd, 3rd, and 4th lumbar nerves. Budge ? showed that it was possible to induce contraction of the vasa deferentia by stimulating the spinal cord at the level of the 4th lumbar vertebra. He observed also that contraction could be caused by stimulating one of the sympathetic ganglia, apparently the inferior mesenteric.® According to Rémy,’ stimulation of a small ganglion situated Fig. 65.—End-bulb in prostate. (After Timofeew, from Nagel.) a, thick medullated nerve fibre; 6, fine medullated nerve fibre. on the inferior vena cava at the level of the renal veins in the guinea-pig produced a sudden ejaculation. Loeb ® states that he was able to induce contraction of the vasa deferentia by stimulating the hypogastric nerves. Langley * found that most of the efferent fibres for the vasa deferentia traversed the sympathetic in the region of the 4th, 5th, and 6th lumbar ganglia, so that presumably they chiefly arose from the 3rd, 4th, and 5th lumbar nerves. Sherrington ’ observed that in the macaque monkey (Macacus rhesus), the 1 Akutsu, ‘‘ Beitrige zur Kenntniss der Innervation der Samenblase beim Meerschweinchen,” Pfliiger’s Archiv, vol. xcvi., 1903. 2 Budge, loc. cit. 3 Langley and Anderson, loc, cit. + Rémy, ‘ Nerfs éjaculateurs,” Jour. de l’Anat. et de la Phys., vol. xxii., 886 5 Loeb, loc. cie. § Langley, loc. cit. ? Sherrington, loc, cit. 260 THE PHYSIOLOGY OF REPRODUCTION 2nd and 3rd lumbar nerves, and in the cat, the 3rd and 4th lumbars, contained motor fibres for the vasa deferentia. The fibres giving this result could be found outside the spinal cord in the genito-crural nerve. The contraction of the vasa was of a slow and peristaltic kind, and did not cease immediately the stimulus was withdrawn." Langley and Anderson, as a result of an extensive series of experiments, conclude that the internal generative organs of the cat and rabbit are supplied by fibres running out by the anterior roots of the 3rd, 4th, and 5th lumbar nerves, and sometimes also the 2nd. These fibres pass through the sympathetic to the inferior mesenteric ganglia, and’ continue their course by the hypogastric nerves. Stimulation of these fibres in the cat and the rabbit caused strong contraction of the whole musculature of the vasa deferentia and uterus masculinus (which Langley and Anderson regard as the physiological homologue of the vesiculee seminales in these animals). The vas deferens in con- tracting was observed to become from one to three centimetres shorter, so that there could be no doubt that the longitudinal muscular coat took part in the process. The contraction was strong enough to cause emission of semen from the aperture of the penis. It would appear, therefore, that ejaculation occurred without erection. In the dog, in which the longitudinal muscle layer is not well developed, the contraction of the vas deferens, on excitation of the upper lumbar nerves, was not nearly so pronounced. Langley and Anderson found that stimulation of the sacral nerves had no effect on the internal generative organs. These * There has been some disagreement as to whether the vas deferens under- goes true peristaltic movement. According to Budge (Joc. cit.) this does occur in the rabbit and cat. Fick confirmed Budge for these animals (‘‘ Ueber das Vas deferens,” Miiller’s Archiv, 1856), but found no peristalsis in the dog (cf. Langley and Anderson for the dog). On the other hand, Loeb (loc. cit.) could discern no peristaltic movement in the vas deferens of the rabbit, but only a powerful contraction. Nagel, who has more recently investigated the question, states that the vas deferens in the rabbit does not undergo a true peristaltic movement, but a simple quick contraction which suffices for -the emptying the tube (‘‘ Contractilitét und Rarzburkeit des Samenleiters,” Verhandl, d. Phys. Gesell. zu Berlin ; Arch. f. Anat. u. Phys., Phys. Abth., 1905, Suppl. See also Nagel, Handbuch der Phys, des Menschen, vol. ii., Braunschweig. 1906). MALE ACCESSORY REPRODUCTIVE ORGANS 26] are innervated exclusively from the lumbar nerves, as above described.* In view of the facts which have been related, it would appear that ejaculation is a reflex act of some complexity involving Fic. 66.—Diagram illustrating innervation of internal genital organs of male cat. (From Nagel.) H., hypogastric nerve; Ur., ureter; V. D., vas deferens ; II. III. IV., branches arising from 2nd, 3rd, and 4th lumbar nerves. more than one centre in the spinal cord. The centre for the final expulsion of the semen must be the same as that for erec- tion, since the muscular mechanisms concerned are to a large extent identical in each case. The centre presiding over the internal generative organs is apparently in the lumbar spinal 1 Langley and Anderson, loc. cit, 262 THE PHYSIOLOGY OF REPRODUCTION cord. As already mentioned, Brachet observed ejaculation after all connection with the higher centres had been cut off. The centripetal nerves for the ejaculatory reflex are the sensory nerves of the penis, the stimulation of the glans being particu- larly effective.’ Erection has been observed to occur in animals which were castrated late in life, sexual desire in such cases being to some extent retained. It has been shown, however, that erection cannot be induced experimentally in animals which have been castrated prior to puberty ; or, at any rate, that it is far more difficult to -cause erection in such animals. Thus, in three experiments carried out by the writer, in conjunction with Professor Sutherland Simpson,” it was found impossible to induce erection by stimulating the nervi erigentes in three cats which were castrated when about half grown and afterwards allowed to reach their full size. It is possible, therefore, that in such animals the muscular apparatus of the penis fails to develop sufficiently to admit of erection occurring, but it would seem unlikely that the nervous mechanism is impaired. If erection is due mainly to an inhibition of the vaso-motors of the penis, as is ordinarily supposed, there would seem to be no theoretical reason why it should not be possible to bring about that process experimentally in castrated animals. It is conceivable, there- fore, that the process of erection is after all a more complex phenomenon than is generally believed, but our experiments throw no further light on the mechanism of that process. 1 For further references to the literature of the nervous mechanism of erection and ejaculation, see Bechterew, Die Funktionen der Nervencentra, Weinberg’s German Translation, vol. i., Jena, 1908. * Simpson and Marshall, ‘‘On the Effect of Stimulating the Nervi Erigentes in Castrated Animals,” Quar. Jour. Exper. Phys., vol. i., 1908. * CHAPTER VIII' THE BIOCHEMISTRY OF THE SEXUAL ORGANS “ Nous sommes dans un de ces chateaux des légendes allemandes ot les murs sont formés de milliers de fioles qui contiennent les 4mes des hommes qui vont naitre. Nous sommes dans le séjour de la vie qui précéde la vie.”—Maerreruinck, La Vie des Abeilles. THe Female GENERATIVE ORGANS Mammals In Mammals very little is known concerning the chemistry of the female generative organs. The difficulty experienced in obtaining material has rendered impossible a chemical investiga- tion of the ovum itself. The fluid contained in the Graafian follicles of the cow is stated to be of a serous nature. From the corpora lutea of the same animal amorphous and crystalline pigments have been isolated, both of which belong to the class of substances called lipochromes or luteins.2 These pigments are also found in other sites, e.g. in adipose tissue, in serum, in the retina, and in milk. Similar substances have been isolated from plants, e.g. the crystalline caroten which constitutes the colouring matter of carrots and tomatoes. The luteins are not related to blood pigment, and although hematoidin may be found in corpora lutea, especially when they are fresh, the existence of the luteins appears to be quite independent of the presence of blood pigments. The luteins contain carbon, hydrogen, and oxygen, and have a yellowish or reddish colour. Exposed to light they undergo oxidation. They are soluble in alcohol, ether, and chloroform, and in that respect resemble fats, from which they differ, however, in their resistance towards alkalies. With 1 By William Cramer. 2 Piccolo and Lieben, ‘‘ Studi nel corpo luteo della vacca,” Giorn. sc. natur. ed econ., vol. ii., 1866. Kiihne and Ayres, ‘‘ On the Stable Colours of the Retina,” Journal of Physiology, vol. i., 1878. 263 264 THE PHYSIOLOGY OF REPRODUCTION strong nitric acid and sulphuric acid they give a blue colour. Their solutions in alcohol, ether, or chloroform are further characterised by the absorption-spectrum,’ which shows two bands in the blue part of the spectrum (between the lines F and G). Observations concerning the chemistry of human ovaries have been made chiefly in cettain pathological conditions of these organs. Various protein substances have been isolated from the fluid contents of ovarian cysts. In the case of cysts due to a dilatation of the Graafian follicles the contents were found to be identical with other serous liquids. From cystic tumours of the ovaries, the contents of which may be either watery or gelatinous, a number of protein compounds have been isolated, which, on hydrolysis, all yield a considerable quantity of a re- ducing substance—glucosamine—and therefore belong to the group of glycoproteins. Hammarsten? isolated a substance, called by him Pseudomucin, which did not coagulate on heating and was not precipitated by acetic acid. On hydrolysis it, yielded 30 per cent. glucosamine. Pfannenstiel * isolated from ovarian colloid another mucoid substance, Pseudomucin 8, a gelatinous mass which was insoluble in acetic acid and water, but was dissolved by dilute alkali. These substances are formed by the activity of the cells lining the cysts. Birds Our knowledge of the chemistry of the ovum is derived almost entirely from investigations on the hen’s egg. The average weight of an egg is 40-60 grm., half of this being the weight of the white of the egg, while the yolk weighs 12-18 grm. and the shell 5-8 grm. The egg-shell contains chiefly calcium carbonate. During development the egg-shell loses calcium, which goes to the building up of the structures of the developing embryo.t In 1 Thudichum, “Uber das Lutein und die Spektren gelbgefarbter organ- ischer Substanzen,” Centralblatt f. d. med. Wissenschaft, 1869, vol. vii. * Hammarsten, ‘‘Metalbumin und Paralbumin,” Zeitschr. f. physiol. Chemie, vol. vi., 1882. . ° Pfannenstiel, ‘Uber die Pseudomucine der cystischen Ovarienge- schwiilste,” Arch. f. Gynekologie, vol. xxxviii. 4 Vaughan, ‘‘ Estimation of Lime in the Shell and in the Interior of the Egg before and after Incubation,” Journal of Physiology, vol. i., 1878. BIOCHEMISTRY OF THE SEXUAL ORGANS 265 some species the shell is coloured by pigments, which are pro- bably derivatives of the bile pigments.’ The shell membrane consists of a substance belonging to the group of the keratins. It is very rich in sulphur (about 4 per cent. S.), and, on hydrolysis, yields a relatively large amount of cystin (see p. 276). The chief constituents of the white and the yolk of the egg are water, proteins, fats, and phosphorised fats, while carbo- hydrates as such are almost entirely absent. The proportion in which these constituents are present in the white and in the yolk of the egg differs, as will be seen from the following table giving the total composition of both these parts. | White of Egg. Yolk of Egg. — | Per Cent. | Per Cent. Water é : , 85-88 47°19 Protein : i ‘i 13:0 15°63 Fat. : : a é 0°3 22°84 Phosphorised fat, calculated | ) ; : as Lecithin 1 ee sl a Cholesterin , ‘ 3 on 1°75 Reducing sugar . ou 5 trace ; Inorganic salts . ‘ ant o7 0°96 Ash... | 461 291 Another important difference in the composition of the white and the yolk of the egg is to be found in the relative quantities of the inorganic constituents as they are present in the dry residue,? both as in organic salts and inorganic com- bination. 100 parts of Dry Contain— Residue of K,0. Na,O. CaO. MgO. Fe,0;. PO; Cl. White ofegg . 144 145 O13 013 000 020 1:32 Yolk ofegg . O27 O17 O88 O06 0024 1190 0:35 1 Krukenberg, ‘‘ Farbstoffe der Vogeleierschalen,” Verhandlungen d. Phys, Med. Gesellschaft, Wiirzburg, vol. xvii., 1883. 2 Bunge, ‘Der Kalk und Eisengehalt unserer Nahrung,” Zeitschrift f. Biologie, vol. xlv., 1904, p. 532. 266 THE PHYSIOLOGY OF REPRODUCTION It will be seen that the yolk is distinguished by the presence of iron which is almost completely absent in the white, and by its richness in phosphorus. Although the percentage of iron present in the yolk is very small, it is nevertheless greater than in almost any other animal or vegetable food-stuff. As a rule the proportions in which the inorganic elements are present are given in terms of percentages of the ash. Such a table,’ which perhaps brings out more clearly the difference between the white and the yolk of the egg, may be given here :— 100 parts of the Contain— Ash of K,0. Na,O. CaO. MgO. Fe,0;. P,0; SiO, Cl. White ofegg 31°41 3157 278 2°79 0°57 471 1:06 28°82 Yolk ofegg . 929 5:87 13:04 2:13 165 = 65°46 0°86 1:95 There are, of course, slight variations between different eggs in the amount of mineral constituents present in the ash. It is possible that there are such variations even in the eggs laid by one and the same bird at different periods. Systematic investi- gations on this point have been made only with reference to the iron. These observations show that more iron is present in eggs laid in spring than in eggs laid by the same bird in autumn, the amounts varying from 0.0129 per cent. Fe,0, to 0:0086 per cent. Fe,O,, the maximum found being 00167 per cent. Fe,0,. (The percentage is calculated for the dried yolk.) This fact probably explainsthe very exaggerated statements which have been made concerning the production of eggs rich in iron by keeping hens on a diet rich in iron. The careful observations of Hartung ® show that there is indeed a distinct effect produced by such a diet, provided that it is given over a prolonged period —two months or more. But the effect of such a diet is limited, and does not go beyond the physiological maximum. The percentage of iron present in eggs laid under these conditions remains fairly constant, and is about equal to the maximum found under normal conditions, namely 0:0165 per cent. Fe,0., so that the seasonal diminution which normally appears is prevented. } Albu and Neuberg, Physiologie und Pathologie des Mineralstoffwechsels Berlin, 1906, p. 241. ® Hartung, ‘‘Der Eisengehalt des Hiihnereies,” Zeitschrift fir Biologie, vol. xliii., 1902. BIOCHEMISTRY OF 'THE SEXUAL ORGANS 267 The phosphoric acid constitutes more than half of the ash of the yolk, and it is interesting to note that both the phosphorus and the iron which are destined to enter into the composition of some of the most important constituents of the cell, such as nucleoproteins, hemoglobin, lipoids, &c., are already present in organic combination. The phosphorus is contained in the phosphorised fats, which constitute about 11 per cent. of the yolk, and partly in the phosphoprotein vitellin, which also contains iron. The phosphorised fats are obtained by extracting the yolk, which has previously been freed from water, with cold ether, and precipitating the ethereal extracts with acetone. The precipitate contains the phosphorised fats, while the acetone solution contains the cholesterin which has been extracted together with the phosphorised fats. After all the ether-soluble phosphorised fats have been removed by the ether, further extraction with cold alcohol will remove other phosphorised fats from the yolk. The precipitate obtained from the ethereal extract by acetone has often been called lecithin, the name given to the simplest and best-known phosphorised fat. But the recent work of Erlandsen,! and of Thierfelder and Stern,? has shown, what in the case of nervous tissue had been recognised long ago by Gamgee and by Thudichum, that there are a great number of phosphorised fats very similar to lecithin and very difficult to separate from each other. These substances, accompanied always by cholesterin, are widely distributed through the organic world. In fact they are present in every cell, and in almost every animal fluid. This fact alone is sufficient to in- dicate that the phosphorised fats and cholesterin must fulfil an important function in the life of the cell. What this function is has not yet been clearly recognised. We know that anesthetics such as chloroform, and toxins such as snake-venom, exert their action on the cell by virtue of the power of the phosphorised fats to absorb these substances. 1 Erlandsen, ‘‘ Untersuchungen iiber die lecithinartigen Substanzen des Herzmuskels,” Zeitschrift f. physiol. Chemie, vol. li., 1906. 2 Thierfelder and Stern, ‘‘ Uber die Phosphatide des Eigelbs,” Zeitschrift Ff. physiol, Chemie, vol. liii., 1907. 268 THE PHYSIOLOGY OF REPRODUCTION One may therefore venture the suggestion that lecithin and its allies have a similar function with regard to other substances affecting the life of the cell under normal conditions. Some experiments of the writer,’ carried out in 1908, suggest that these phosphorised fats may act as oxygen-carriers, and that they may thus fulfil an important function in cell-respiration. A similar view has been put forward recently on purely theoretical grounds by Mansfeld.? However that may be, there can be little doubt that in the egg which contains an exceptionally large amount of phos- phorised fats these substances have to fulfil a different function. Phosphorus enters into the composition of many cell consti- tuents, for instance, the complex protein substances found in the nuclei of cells, the so-called nucleoproteins, so that the assimilation of phosphorus is an important factor in the growth of an organism. Feeding experiments on Man and on animals have made it probable that phosphorus in organic combinations is better assimilated than phosphorus which is given in the form of inorganic phosphates. In birds the yolk of the egg fulfils a function similar to that of the milk in Mammals; both supply the offspring with the material necessary for its growth. We thus find that both the yolk and the milk are not only rich in phosphorus, but that most of the phosphorus is present in organic combination, as casein and nuclein in the latter, and as vitellin and phosphorised fats in the former. We also find that during incubation the vitellin disappears and the phosphorised fats diminish, so that, at the twentieth day, their quantity is reduced by one half.? It is, of course, 1 Unpublished observations. It was found that watery emulsions of egg- lecithin absorbed much more oxygen than water alone or watery solutions of proteins, and that such a lecithin-emulsion sometimes greatly accelerated the oxidation of hydriodic acid by the oxygen of the air. The results ob- tained were, however, very variable. 2 Mansfeld, ‘‘ Narkose und Sauerstoffmangel,” Pfliiger’s Archiv, vol. cxxix., 1909. 3 Merconitzki, ‘ Die quantitativen Veranderungen des Lecithins im enstehenden Organismus,” Russky Wratsch, 1907, quoted from Biochemisches Centralblatt, vol. vi., 1907.. Plimmer and Scott, “The Transformations in the Phosphorus Compounds in the Hen’s Egg during Development,” Jour. of Physiology, vol. xxxviii., 1909. BIOCHEMISTRY OF THE SEXUAL ORGANS 269 clear that the formation of nucleoproteins cannot account for this enormous consumption of phosphorised fats. Some of these substances reappear in the embryo. A proportion of them contributes to the formation of bones, which contain a con- siderable amount of inorganic phosphates. Part reappears in the foetal tissues as phosphorised fats, especially in the nervous tissue, which is very rich in these substances. That portion of the phosphorised fats which is transformed into inorganic phosphates, may at the same time fulfil another very im- portant function by the oxidation of the fat group in their molecule. It will be shown below that the development of the embryo is intimately associated with, and perhaps de- pendent upon, the transformation of chemical energy into heat. This transformation is brought about by the oxidation of certain organic substances, which are different in the different classes of Vertebrates. It will be shown also that in birds the chemical energy is furnished by fats, and it is very probable that the phosphorised fats furnish at the same time material for the formation of the tissues of the embryo and fat as a source of chemical energy. It is interesting to note that a similar double function has been assigned to glycogen in the case of the developing rabbit.* Of the cholesterin about one-third disappears during incubation. The phosphorus which enters into the composition of nucleo- protein is bound up therein in the form of phosphoric acid, ‘combined with purine bases and pentoses (see p. 294). Neither nucleoprotein nor pentoses are present in the fresh egg, and purine bases are present only in very small amounts. The fact that during development these substances rapidly increase in amount, indicates therefore that a synthesis of nucleoprotein from the reserve material of the egg (proteins and phosphorised fats) takes place during development. The purine bases found in the embryo are essentially the same as those found in the adult organism.’ 1 Lochhead and Cramer, ‘‘ The Glycogenic Changes in the Placenta and Foetus of the Pregnant Rabbit,” Proc. Roy. Soc., Series B., vol. 1xxx., 1908. 2 Kossel, ‘‘ Weitere Beitriige zur Chemie des Zellkernes,” Zeztschrift fiir Physiologische Chemie, vol. x., 1886. Mendel and Leavenworth, ‘“ Chemical Studies on Growth: VI.Changes in the Purine- Pentose- and Cholesterol-Content of the Developing Egg,” American Journal of Physiology, vol. xxi., 1898. 270 THE PHYSIOLOGY OF REPRODUCTION Of the phosphorised fats of the yolk, lecithin is the simplest and best-known representative. Like all fats, it is an ether compound of glycerine and fatty acids, such as stearic, palmitic, and oleic acid, and is, like all fats, soluble in alcohol and ether. With water it swells up and forms a colloidal solution. It is distinguished by the presence in its molecule of one molecule of phosphoric acid to which one molecule of an organic nitro- genous base, choline, is attached. If boiled with baryta water it is decomposed into glycerophosphoric acid, fatty acids, and choline. Lecithin forms loose compounds with proteins, the so-called lecithalbumins, of which vitellin is probably one. Vitellin is an ill-defined compound between lecithin and a protein substance which itself contains about 1 per cent. phosphorus. It is insoluble in water, but soluble in dilute solutions of neutral salts, behaving in that respect like a globulin. On peptic digestion a pseudonuclein, rich in phosphorus, is formed from the protein part of vitellin. . This pseudonuclein contains also a relatively large amount of iron in organic com- bination, and it is this substance which is responsible for the presence of iron in the yolk of the egg. According to Bunge,! this substance plays an important part in the formation of hemoglobin in the chick. It is the precursor of hemoglobin, and has, therefore, been called by him hematogen. It contains 5:19 per cent. P., and 0:29 per cent. Fe. Recently Plimmer 2 has isolated from egg-yolk another protein, livetin, soluble in water and containing 0-1 per cent. phosphorus. Two different fats have been isolated from the yolk—the one solid, rich in palmitic acid ; the other fluid, containing equal parts of palmitic and oleic acids. A small amount of stearic acid is also present in both fats. The composition of the fat is influenced by the food, the fat of the food passing into the yolk in the same kind of way as it passes into the fat deposits of the adult organism.® The food has also an influence upon the colour of the yolk, 1 Bunge, ‘‘Uber die Assimilation des Eisens,” Zedtschr. f. physiolog Chemie, 1884, vol. ix. ® Aders Plimmer, ‘‘The Proteins of Egg-Yolk,” Journal Chemical Soc., 1908. * Henriques and Hansen, “ Uber den Ubergang des Nahrungsfettes in das Hiihnerei,” Skandin. Arch. f. Physiologie, vol. xiv., 1903. BIOCHEMISTRY OF THE SEXUAL ORGANS 27] which is due to luteins. Feeding with grains produces a light yellow yolk, a dark yellow yolk results if grass and herbs are given, while feeding with worms leads to the production of an even darker reddish yolk. What the changes are in the colour- ing matter of the yolk has not yet been ascertained.’ During the development of the chick a considerable portion of the fat disappears. In other words, a certain amount of chemical energy, which in the fresh egg is present in the form of fat, disappears. Liebermann ? has shown, for instance, that of 5-4 grm. of fat present in a fresh egg only 2°7 grm. can be recovered when the chick is hatched. The fate of the chemical energy which has thus disappeared has been accounted for completely by the observations of Bohr and Hasselbalch,? which are the most exact and comprehensive investigations on the subject of the metabolism of the embryo. They showed that the respiratory quotient of the developing egg—that is, the ratio of the amount of CO, excreted to the amount of O, absorbed—is 0°71. Such a quotient indicates the oxidation of fat. From the amount of CO, excreted during a given period it is possible to calculate the amount of fat oxidised during that period. Under ordinary conditions the oxidation of fat produces heat which can be determined experimentally. By calculating from the amount of fat oxidised during de- velopment the amount of heat which would be generated under ordinary conditions, and by actually determining at the same ; time the amount of heat given off by the developing egg, Bohr _. i “4 and Hasselbalch found during a period of twelve days :— ee ca _ The amount of heat calculated from the amount of fat oxidised . . ‘ : A . 12°11 Cal. The amount of heat actually given off : i . 12°16 Cal. This remarkable agreement in so complicated an experiment —which is a triumph of the experimental skill of the observers * For the morphological distribution of the constituents of the yolk, see Waldeyer, ‘‘ Die Geschlechtszellen,” in Hertwig’s Handbuch der Entwicklungs- lehre der Wirbeltiere, vol. i., Jena, 1903. 2 Liebermann, “ Embryochemische Untersuchungen,” Pfliiger’s Archiv, vol. xliii., 1888. : Bohrand Hasselbalch, ‘‘ Uber die Wirmeproduktion und den Stoffwechsel des Embryo,” Skandinavisches Arch. f. Physiologie, vol. xiv., 1903. 272 THE PHYSIOLOGY OF REPRODUCTION —shows clearly that fat is the almost exclusive source of the chemical energy which is used up during development. Another very important conclusion can be drawn from these observa- tions, namely, that all the chemical energy which disappears during development reappears in the form of heat. None is transformed in an unknown way into energy of a different kind, or transferred to the developing embryo. The intensity of the metabolic changes which take place during development, and which can be expressed by the amount of CO, excreted, is very great.’ Calculated for the same unit of weight of the animal, it is as great in the embryo as it is in the adult animal, and may even exceed it. This is the case not only in birds, but also in Mammals. These changes are intimately bound up with the development of the embryo. Exposure to cold, which delays development, also diminishes the excretion of carbonic acid.2 Experiments on the eggs of cold-blooded animals ? show that those conditions which favour development, such as high temperature, also lead to an increase in the CO, excretion. The same problem has been attacked in a different way by Tangl.4 He determined, by means of a calorimeter, the heat produced by the combustion of eggs at different stages of their development. There is a gradual diminution of the caloric value as development goes on, indicating that chemical energy is used up in the process of development. In the case of the chick the difference between the caloric value of the fresh egg and that of the developed chicken is 16 calories. These 16 calories represent the chemical energy which has been used up for what Tangl calls the ‘‘ work of development.” But smce Bohr’s work has shown that the chemical energy which disappears during development is completely transformed into heat, it would be better to replace the 1 Bohr and Hasselbalch, “ Uber die Kohlensaéureproduktion des Hiihner- embryos,” Skandinav. Arch. f. Physiologie, vol. x., 1900. 2 Pembrey, ‘‘On the Response of the Chick, before and after Hatching, to Changes in External Temperature,’ Journal of Physiology, vol. xxvii., 1894. ® Bohr, “ Uber den respiratorischen Stoffwechsel beim Embryo kaltbliitiger Tiere,” Skandinav. Arch. f. Physiologie, vol. xv., 1904. 4 Tangl, “‘ Beitrige zur Energetik der Ontogenese : I. Die Entwicklungs- arbeit im Vogelei,” Pfliiger’s Archiv, vol. xciii., 1903 ; vol. cxi., 1908, BIOCHEMISTRY OF THE SEXUAL ORGANS 273 term “work of development” by the term “energy of development. The nature of the substances which by their oxidation furnish the “energy of development” is different in the different classes of animals. In birds it is furnished, as we have seen, by the oxidation of fats, and possibly also of the fat group of phosphorised fats. In Mammals in which de- velopment proceeds in utero, and there is a constant exchange of material between the mother and the foetus, the investigation of these problems is more difficult, owing to the complexity of the conditions: Investigations on the respiratory quotient of the embryo in pregnant guinea-pigs and rabbits’ indicate that there is an oxidation of carbohydrate material, and systematic chemical investigations of the placenta and foetus of pregnant rabbits? have shown that there is a constant and regular dis- appearance of glycogen from the placenta, which reappears only partly as such in the embryonic tissues. It can there- fore be concluded that in these animals glycogen furnishes at least part of the “energy of development.” But it is doubtful whether this conclusion can be applied to all the Mammals, since, in the case of the cow and of the sheep, for instance, very little glycogen is found in the placenta. In reptiles * also the chemical energy used up during de- velopment is furnished mainly by carbohydrates. Similar observations have been made on the eggs of fishes,* where the energy of development was found to be very small. In all these cases the chemical energy used up in the process of development has been found to be furnished either by fats or by carbohydrates. No conclusive evidence has as yet been obtained that the store of nitrogenous substances is used for that purpose. 1 Bohr, ‘‘ Der respiratorische Stoffwechsel des Siugethierembryos,” Skan- dinav, Arch. f. Physiologie, vol. x., 1900. 2 Lochhead and Cramer, ‘‘The Glycogenic Changes in the Placenta and Foetus of the Pregnant Rabbit,” Proc. Roy. Soc,, Series B., vol. 1xxx., 1908, . 263. : 3 Bohr, “ Uber den respiratorischen Stoffwechsel beim Embryo kaltblitiger Tiere,” loc. cit. zr 4 Tangl and Farkas, “ Beitrige zur Kenntniss der Ontogenese: IV. Uber den Stoff u. Energieumsatz im bebriiteten Forellenei,” Pfliiger’s Archiv, vol. civ., 1904. 8 274 THE PHYSIOLOGY OF REPRODUCTION Liebermann records a loss of nitrogenous substances in his analysis of hens’ eggs at various stages of development ; but as Hasselbalch ' pointed out, this loss is accounted for by the egg- membrane, which is left behind when the chick is hatched, and which was not included in Liebermann’s analysis. Reference has already been made to nitrogenous consti- tuents of the yolk : the two phosphoproteins vitellin and livetin. The other protein substances of the white of the egg can be distinguished according to their reactions as albumens, globulins, and a substance behaving like a peptone in so far as it is not coagulated by heat and not precipitated by ammonium sulphate or by hydrochloric and acetic acids. According to the investiga- tions of Morner,’ this substance is a true glucoprotein and belongs to the mucoid substances. It has, therefore, received the name Ovomucoid. On boiling with hydrochloric acid it yields 34 per cent. of glucosamine.* The amount of ovomucoid present in the white of the egg is about 10 per cent. of the proteins; 6 per cent. of the proteins belong to the globulin group, the remainder being the albumens. All the proteins of the white of the egg, not only the ovomucoid, are exceptionally rich in the carbo- hydrate radicle, and on boiling with dilute hydrochloric acid yield considerable quantities of glucosamine. The albumens and globulins contain about 10 per cent. of glucosamine. This explains perhaps the almost complete absence of carbohydrates in the egg. It acquires further significance from the fact that the developing tissues of the embryo are very rich in mucin, a protein containing considerable quantities of glucosamine. The globulin fraction of the egg-white has not yet been studied in detail. It is probable that it is a mixture of several globulins. The investigation of the albumen fraction has been greatly facilitated by the work of Hofmeister * and Hopkins,’? which 1 Hasselbalch, “Uber den respiratorischen Stoffwechsel des Hiihner- embryos,” Skandinav, Arch. f. Physiologie, vol. x., 1900. 2 Morner, “ Uber die im Hiihnereiweiss in reichlicher Menge vorkommende Mucinsubstanz,”’ Zeitschr. f. physiol. Chemie, vol. xviii. 3 Quoted from Ergebnisse der Physiologie, vol. i., Part I. * Hofmeister, “ Uber Krystallisation des Eialbumins,” Zeitschrift fiir physiolog. Chemie, vol. xiv., 1890, and vol. xvi., 1892. 5 Hopkins and Pinkus, ‘‘ Observations on the Crystallisation of Proteids,” Journal of Physiology, vol. xxiii., 1898. BIOCHEMISTRY OF THE SEXUAL ORGANS 275 has made it possible to obtain part of the albumen fraction in a crystallised form. In this way Osborne and Campbell’ have isolated two different albumens, the crystallisable “ ovalbumen ” and the non-crystallisable “ conalbumen.” Possibly even these two substances are mixtures of albumens, for Bondzinski and Zoja” claim to have isolated from the crystallisable ovalbumen several albumens by means of fractionate crystallisation. Crystalline egg albumen contains 0°13 per cent. phosphorus,® and is therefore another source of phosphorus in organic combination. The white of the eggs of some Insessores has the peculiar property of forming a transparent fluorescent jelly when it is coagulated by heat.* The name“ Tata-eggwhite,” has been given to this substance. This phenomenon is probably due to the presence of a relatively large amount of basic salts in the white of the egg, since the white of a hen’s egg will also coagulate to a transparent jelly if the egg has been kept for a few days in 10 per cent. caustic potash. Further insight into the composition of some of the proteins of the egg has been gained by means of the methods devised within recent years by E. Fischer and by Kossel, for the study of the constitution of the protein substances. By boiling with hydrochloric acid the proteins are split into the constituent amino acids and diamino acids, which are then determined as nearly quantitatively as possible.° In the results given in tabular form on p. 276, the figures represent percentages, those under “ total ’’ indicating the per- centage recovered in the form of amino acids or diamino acids. The absence of any one constituent is indicated by 0, the presence without quantitative estimation by +. while — indicates that 1 Osborne and Campbell, Journ. Americ, Chem. Soc,, vol. xxii., 1900. ? Bondzinski and Zoja, ‘ Tiber die fraktionierte Krystallisation des Eieralbumins,” Zeitschrift f. phys. Chemie, vol. xix., 1894. 8 Willcock and Hardy, ‘‘ Preliminary Note upon the Presence of Phosphorus in Crystalline Egg Albumin,” Proc. Cambridge Philosophical Soc., 1907. 4 Tarchanoff, ‘‘ Uber die Verschiedenheiten des Hiereiweisses bei befiedert geborenen (Nestfliichten) und bei nakt geborenen (Nesthocker) Vogeln,” Pfliiger’s Archiv, vol. xxxi., 1883. Tarchanoff, “ Uber Hiihnereier mit durchsichtigem Eiweiss,” Phliiger’s Archiv, vol, xxxix., 1883. 5 For fuller reference see Plimmer, The Chemical Constitution of the Proteins, London, 1908, in the series of Monographs on Biochemistry ; and Abderhalden, Lehrbuch der Physiologischen Chemie, 2 Auflage, 1909. 276 THE PHYSIOLOGY OF REPRODUCTION investigations as to the presence or absence of a particular constituent have not been made. Hoe stbumen atee Keratin from ( - Mesueleear lien Vitellin Egg Membrane d Pregl) (Hughounenq).| (Abderhalden pita ey ; and oe Per Cent. Per Cent. Per Cent. Glycine . F F 0 <0°5 39 Alanine. ‘ 21 <0°5 35 Valine . ‘ A - 15 11 Leucine . : 61 68 74 Phenylalanine 4:4 o7 - Tyrosine , 1-1 2°0 - Serine. * 4 — <05 - Cystine . 03 - 76 Proline . : A 2°3 <0°5 40 Oxyproline . : = = - Aspartic acid 15 0-7 11 Glutamic acid 80 10 81 Tryptophane. —. + a - Diami [Arginine 2°15 1:0 - eda 1 ERSMIE 9°14 1:2 = acids. | Histidine = 21 = Total 30°1 190 36:7 With regard to the question of the presence of ferments and their significance we are on very difficult ground. We must here clearly distinguish between endo-enzymes and _ secreted enzymes. The endo-enzymes comprise all those enzymes which are so closely bound up with the protoplasm that they can be isolated only after the cell has been destroyed. Their sphere of activity is therefore limited to the inside of the cell. Such endo-enzymes are present in every organ, and have also been found in the egg,’ producing proteolysis and lipolysis. But since such endo-enzymes are present in many, if not in all cells, no special significance can be attached to their presence in the eggs. The presence in the egg of secreted ferments analogous to the ferments which can be obtained by simple extraction from the digestive glands of the adult animal, would allow of more definite conclusions. The presence of such ferments 1 Wohlgemuth, ‘' Uber das Vorkommen von Fermenten im Hihnerei,” Festschrift fiir Salkowski, 1904. BIOCHEMISTRY OF THE SEXUAL ORGANS 277 has as yet not been proved with certainty, although the diastatic action of egg yolk observed by Miiller and Masuyama * points to the presence of a diastase analogous to the ptyalin of the saliva. Lower Vertebrates The covering of the eggs of the lower Vertebrates is either of the nature of a keratin, a scleroprotein rich in sulphur, similar to the membrane of birds’ eggs, or it is a mucoid substance. In reptiles, like Calotes jubatus and Crocodilus biporcatus, and in Elasmobranchs, like Raja and Scyllium, the membrane is stated to consist of a keratin.” In the membrane of the eggs of Tropi- donotus,® the British grass snake, a substance has been found which is free from sulphur and resembles the elastin which constitutes the elastic fibres of mammalian connective tissue. A similar substance is stated to occur in the egg-membrane of Mustelus levis.’ But these data are very scanty and hardly convincing. In Amphibians like the frog the membrane has been found to consist of pure mucin.’ In Teleostean fishes it has been investigated in the case of the perch,® and found to be of the nature of a mucin.. It would be interesting to find out by systematic investigations, such as those of Pregl? and Buchtala,® whether the chemical nature of the substances protecting the egg varies with the different zoological classes, or whether it is dependent upon external circumstances representing perhaps a case of chemical adaptation. 1 Miller and Masuyama, ‘Uber ein diastatisches Ferment im Hiihnerei,” Zeitschr, f. Biologie, vol. xxxix., 1900. : * Krukenberg, Vergleichende Phystolugische Studien: II. Rethe, 1 Abtet- lung, 1882. Neumeister, ‘‘ Uber die Eischalenhaéute von Fchidna und der Wirbeltiere im allgemeinen,” Zettschr. f. Biologie, vol. xiii., 1895. 3 Hilger, “‘ Ueber die Chemischen Bestandteile des Reptilieneis” ; Berichte der deutschen chem. Gesellschaft, vol. vi., 1873. 4 Krukenberg, loc. cit., 2 Abtet?ung, 1882. 5 Giacosa, ‘‘ Etudes sur la Composition chimique de l’Ciuf et de ses En- veloppes chez la Grenouille commune,” Zettschr. f. phys. Chemie, vol. vii., 1883. 6 Hammarsten, ‘‘ Chemie des Fischeies,” Skandinav, Arch. f. Physiologie, vol, xvii., 1905. 7 Pregl, ‘‘ Uber die Hihaute von Scylliwm stellare und ihre Abbauprodukte,” Zeitschr. f. phys. Chemie, vol. lvi., 1908. 8 Buchtala, ibid. 278 THE PHYSIOLOGY OF REPRODUCTION The investigations of Hammarsten brought to light the in- teresting fact that a chemical change takes place in the cover of the eggs during ripening. The immature eggs swell with water, and a mucilaginous solution of mucus is formed, from which the mucin may b: precipitated by the addition of acetic acid. If mature eggs are treated with water they do not swell. The water dissolves out the contents of the egg and the empty covers of the eggs remain, and can be transformed into mucin by weak alkali. During the ripening of the eggs there is there- fore a change from mucin to mucinogen. The composition of the eggs of fishes is essentially the same as that of birds’ eggs. The organic constituents consist chiefly of protein, fats, and phosphorised fats, with some cholesterin. The following analysis of the ash of caviar’ gives an idea of the composition of the ash of the eggs of fishes :— Total Ash. . K,O. Na,0. CaO. Fe,0,. P.O; Cl. 7°70 per cent.. 3°33 30°77 5°02 0°22 10°55 = 47-44 In the egg the protein is present in the form of a phospho- protein. Valenciennes and Frémy, who were the first to isolate this substance, called it Ichthulin. Later Walther showed that this substance very closely resembles the vitellin present in birds’ eggs. On peptic digestion it yields an iron containing pseudonuclein. A similar substance containing phosphorus and iron was isolated from the eggs of the salmon by Noel Paton, from cods’ eggs by Levene, and from perches’ eggs by Ham- marsten.” The statement by Walther that ichthulin, on boiling with mineral acids, splits off a reducing sugar and differs in this respect from vitellin has not been confirmed by the later workers. Ichthulin is probably identical with the crystalline material observed in the eggs of the tortoise, the frog, the shark, and other fishes, which is known morphologically under the name of yolk-spherules or “ Dotterplittchen.”” The unripe eggs of the perch are embedded in a fluid from which a protein of the nature of a globulin has been isolated. This protein received 1 Albu and Neuberg, Mineralstoffwechsel, p. 241. * Hammarsten, “ Chemie des Fischeies,” Skandinav. Arch, f. Physiologie, vol. xvii., 1905. This paper contains a detailed review of previous work done on this subject. BIOCHEMISTRY OF THE SEXUAL ORGANS 279 ‘ the name “ percaglobulin.”? It is rich in sulphur, and is pre- cipitated by weak hydrochloric acid. It has an astringent taste, and possesses the remarkable property of forming pre- cipitates with some glucoproteins such as ovomucoid, and with polysaccharides such as glycogen and starch. This substance could not be found when the eggs were mature, and does not appear to be present in the ovaries of other fishes. Very important and interesting results have been obtained by systematic chemical examinations of the muscles and ovaries of the salmon” and of the herring? at different seasons. Extensive chemical changes take place in these animals during the period of their reproductive activity. The reproductive organs develop at the expense of the muscles, which diminish in weight. This is best seen in the case of the salmon, since this animal does not take any nourishment during its passage up the rivers. In the case of the herring the conditions are not quite so simple, because the herring feeds until spawning occurs, although less food is taken in the later months. In the case of the salmon, then, the ovaries are built up from material contained in the muscle. The most marked change in the muscle during that period is a loss of fat, with which the muscles are loaded when the salmon leaves the sea. The protein constituents of the muscle also diminish, but not to the same extent as the fat. There is, further, a disappearance of the inorganic phosphates of the muscle. From these substances the ovaries build up their essential constituents—the phospho- protein ichthulin and the phosphorised fats. The source of the choline which is contained in the phosphorised fats is not yet clear. This formation by the ovaries of phosphorised fats out of fats and inorganic phosphates points to the important function which these organic phosphorus compounds have to fulfil in the developing organism (see above). Not all the fat which disappears from the muscles reappears 1 Morner, ‘‘ Percaglobulin ein charakteristischer Eiweisskorper aus dem Ovarium des Barsches,” Zeitschrift fiir physiolog. Chemie, vol. xl. 2 Miescher, Histochemische und physiologische Arbeiten. Noel Paton and others, ‘‘ Report of Investigations on the Life-History of the Salmon in Fresh Water,” Report to the Fishery Board for Scotland, 1898. % Milroy, “ Changes in the Chemical Composition of the Herring during the Reproductive Period,” Biochemical Journal, vol. iii., 1908, p. 366. 280 THE PHYSIOLOGY OF REPRODUCTION in the ovaries as phosphorised fats. A portion of it serves as a source of energy for the animal. The same applies to part of the protein of the muscle. The iron contained in organic combination in the ichthulin of the ova is derived partly from the muscle and partly also from the blood. Together with the accumulation of fat in the muscles there is a storing of a lipochrome, the characteristic pink pigment of the flesh of the salmon. During its sojourn in the river this pigment disappears in part from the muscles and is transferred with the fat to the ova. This pink pigment is probably formed from another yellow pigment, which is also present in the salmon, and which is widely distributed in the animal kingdom, always closely associated with fat. It is possible that the ingestion and deposition of fat containing this yellow pigment are re- sponsible for the formation of the pink pigment. Invertebrates The chemical composition of the eggs of Invertebrates does not appear to be essentially different from that of the Vertebrate eggs. The covering of the egg, which is often stated to be chitin, has been investigated by Tichomiroff* in the egg of Bombyx mort. He found it to be a protein body rich in sulphur, and similar to the keratin substances of which the membrane of the hen’s egg is composed. The covering of the eggs of a cephalopod—the cuttlefish—was investigated by von Fiirth.” These eggs are united by their capsules, which are often coloured black by pigment, and form what are popularly known as “sea-grapes.” The covering or capsule is secreted by two “nidamental glands,” which open into the oviduct, and it is interesting to note that the substance secreted by these sexual glands is a mucoid substance very similar to the pseudomucin found in cysts of the human ovary (see Mammals, p. 264). The protein substances in the eggs of Invertebrates have not been closely investigated. Vitellin is said to occur. * Tichomiroff, ‘‘ Chemische Studien iiber die Entwicklung der Insekten- eier,” Zettschr. f. phys. Chemie, vol. ix., 1885. 2 Von Firth, “‘ Uber Glycoproteide niedarer Tiere,’ Hofmeister's Bettrdge, vol, i., 1901, BIOCHEMISTRY OF THE SEXUAL ORGANS 281 The eggs of insects are comparatively rich in phosphorised fats. By extraction with alcohol and ether, Dubois’ isolated from locusts’ eggs a yellowish oil containing 1°92 per cent. phosphorus. Glycogen, purine bases, and cholesterin have been found in the eggs of Bombyx. The changes which take place during incubation, in the chemical composition of these eggs, have been investigated by Tichomiroff.” The following table shows that a considerable amount of purine bases are formed during incubation. At the same time the fat and glycogen diminish in amount, while the cholesterin remains practically unchanged and the phosphorised fats in- crease slightly in amount. Before After Incubation. | Incubation. Per Cent. Per Cent. Purine bases . , x 0:02 02 Glycogen : 4 : : 1:98 0°74 Present in ( Fat ‘ ‘ 8:08 437 Ethereal J Phosphorised fat . 1:04 174 Extract |Cholesterin . : 0°40 0°35 On the whole the: changes are similar to those observed in hens’ eggs, except that glycogen is present in considerable quantities in the egg and disappears during development as well as the fat, while the phosphorised fats are apparently not utilised as a source of chemical energy. The “‘ energy of development ” is very considerable, and, calculated as a percentage of the chemical energy contained in the whole egg, is as great as in the case of the developing hen’s egg.® The pigments have been studied especially in the eggs of Crustacea. From the eggs of Maja squinado, Maly * isolated 1 Dubois, ‘Sur Vhuile d’Giufs d’ la Sauterelle d’Algerie (Acridiwm plerinum),” Comptes Rendus, vol. cxvi., 1893. 2 Tichomiroff, loc. cit. 3 Farkas, ‘‘ Uber den Energieumsatz des Seidenspinners wihrend der Entwicklung im Ei u. wahrend der Metamorphose,” Pfliiger’s Archiv, vol, xeviii., 1903. See Appendix to this Chapter, p. 302. 4 Maly, “Uber die Dotterpigmente,” Berichte der Akademie der Wissen- schaften, in Wien, vol, lxxxiii., 1881. 282 THE PHYSIOLOGY OF REPRODUCTION two pigments—a red pigment, Vitellorubin, which is extremely sensitive to light, and a yellow pigment, Vitellolutein. These pigments belong to the lipochromes, which have been men- tioned above. Krukenberg’ has examined the pigments of a number of other Invertebrates. All. these lipochromes have characteristic absorption spectra. The lipochromes of Maja are of special interest, because a similar pigment, Tetronerythrin, has been found in the blood of Maja and other Crustacea. The amount present in the blood shows considerable variation. According to Heim ® it is com- pletely absent in the blood of the male, and appears in the blood of the female during ovulation. At this period also the ovaries, which usually have a yellowish or whitish colour, become first bright yellow and then red. In Heim’s® view this lipochrome is not formed in the ovary but in some other organ of the body, and passes at the period of ovulation into the blood, which carries it to the ovaries. The same author, together with Abelous,* has proved the existence of some ferments in watery and glycerine extracts of the eggs of various crustacea. A diastatic, a tryptic, and an inverting ferment were found. They are stated to increase in strength during the maturation of the ovum. THE Mate GENERATIVE ORGANS The Semen The semen, 2.e. the fluid discharged by an ejaculation, is the secretory product of the testis, epididymis, vesicule seminales, prostate and Littré’s glands. In Man it is a thick, viscous, yellowish, opalescent fluid, which after ejaculation solidifies at first and afterwards becomes fluid again. It has a peculiar smell, which becomes even more noticeable on heating. 1 Krukenberg, Vergleichende phystologische Studien: II. Reihe, 3 Abteilung, 1882, p. 6. ? Heim, ‘‘Sur les Pigments des (iufs des Crustacés,” Comptes Rendus Soc. Biol,, vol. xliv., 1892, p. 467. 5 Heim, Etudes sur le Sang des Crustacés, Paris, 1892. * Abelous and Heim, “ Sur les Ferments des (Eufs des Crustacés,” Compt. Rend. Soc. Biol., vol. xliii., 1891, p. 273. BIOCHEMISTRY OF THE SEXUAL ORGANS 283 Its reaction is alkaline. Its specific gravity les between 1:02 and 1°04. The amount discharged in an ejaculation is given differently by different authors, and probably varies with different individuals, and even with the same individual at different times. From the figures given in the literature 5 grammes may be taken to be the average amount.’ According to Slowtzoff,? human semen consists roughly of 90 per cent. water and 10 per cent. solids, which, on incineration, yield about 1 per cent. of ash. The solids contain 2°3 per cent. of proteins, of which a nucleoprotein, traces of albumen and mucin, and an albumose-like substance have been identified. The quantitative relation of the various solids in 100 parts of fresh semen can be seen in the following table :— Average Values. Per Cent. Water. , : ¥ - . : 3 . 90°32 Dry residue ‘ ; ‘ . ; ; . 9°68 Inorganic salts. . ; : - ‘ - 0°90 Organic material ‘ : : : . 8°78 Ether soluble matter . F : - . . O17 Extractives soluble in alcohol and water . . ll Protein substances ; ; ‘ 3 ‘ . 2:09 In the ash K, Na, Ca, Mg, P, Fe, and 8S have been found. The quantitative analysis of the ash reveals a remarkably large amount, of calcium and phosphoric acid—about 20 per cent. Ca and 30 per cent. P,O,. The amount of calcium excreted in one ejaculation is, therefore, about 0:01 grm., and exceeds that contained in an equal quantity of lime-water. Analyses of the semen of other Mammals do not appear to have been made, but it is unlikely that there are any essential differences. Since during the breeding season about fifty sheep are servéd by one ram, it is evident that a profound change must take place in the meta- bolism of phosphorus and calcium during that period. Is it 1 Acton, Functions and Disorders of the Reproductive Organs, 3rd Edition, London, 1862. Lode, ‘‘ Untersuchungen iiber die Zahlen und Regenerations Verhiltnisse der Spermatozoiden bei Hund und Mensch,” Pfliiger’s Archiv, vol, 1., 1891. Mantegazza, Gaz. Med. Ital., Lombardia, 1866, quoted from Lode. 2 Slowtzoff, ‘Zur Chemie des menschlichen Sperma,” Zeitschrift f. phys. Chemie, vol. xxxv., 1902. 284. THE PHYSIOLOGY OF REPRODUCTION not possible that the effects which are usually ascribed to a hypothetical “ internal secretion” of the testis are-partly due to such a direct connection with the metabolism of the body ? The nature of the influence which the sexual glands exert upon the metabolism of the body is very complex, and has not yet been fully cleared up. Various observers have obtained very contradictory results. Since this subject will be dealt with in another chapter, we will refer to it here only in so far as it has any bearing on the calcium and phosphorus metabolism. On this point there is conclusive evidence of a morphological nature both for the male and for the female organism. Castra- tion leads to a marked increase in the growth of the long bones. This fact, which is due to a retardation of the process of endo- chondral ossification taking place in these bones, accounts for the increase in stature of eunuchs and of castrated animals (see p.306), Similar evidence, although of a more complex character, is afforded in the case of the female by the relationship which undoubtedly exists between the ovaries and osteomalacia, a disease consisting mainly in a decalcification of the bones. It is produced probably by an abnormal function of the ovaries, since removal of the ovaries markedly improves, and sometimes cures, this condition (see p. 353). In pregnancy and parturition there is what one might call a “ physiological osteomalacia ” of the pelvic bones; and the activity of the mammary gland during lactation must necessarily bring about an increased calcium meta- bolism, since milk contains a very large amount of this element. The organic substances in the semen may be divided into two groups. If the semen is examined microscopically it is found that it contains, on the one hand, cellular elements—viz. the spermatozoa and lymphocytes, partly in a state of de- generation ; on the other hand, organic material which is partly amorphous and partly crystalline. The amorphous material consists of :— 1. Fine albuminous granules intermixed with a few fat globules and pigmented granules. 2. Small globules of about half the size of a red blood- corpuscle consisting of a lipoid substance. 3. Oval amyloid bodies composed of concentric layers. These are, however, not invariably found. BIOCHEMISTRY OF THE SEXUAL ORGANS 285 4. The so-called “ sympexions”’ of Robin, oval concrements of a wax-like substance, the nature of which is not known.’ The crystalline substances appear only when the semen is inspissated. They present various forms—prisms, rosettes, &c., —-and are sometimes called “ Béttcher’s spermine crystals.” They are insoluble in alcohol, ether, and chloroform, soluble in hot water, in formol, dilute alkalies and alkali carbonates, and in dilute acids. They are coloured black by a solution of iodine in potassium iodide (Florence’s reagent). Like many ammonium-bases spermine gives a characteristic colour reac- tion with alloxan.” On evaporating a solution of spermine to which a saturated solution of alloxan has been added, a red colour appears, which changes into violet on the addition of alkali. The spermine crystals are not identical, as was formerly believed, with the crystals found in the blood of leuceemic patients (“ Zenker’s crystals ’’), or with the ‘ Charcot- Leyden crystals’? which occur in the sputum of asthmatic persons. Their chemical nature is still a matter of doubt. According to Schreiner, they are the phosphate of an organic base spermine, C,H,N, which Ladenburg and Abel * believed to be Aethylenimin C,H,NH. This is disputed, however, by Majert and Schmidt, who ascribe to the base the formula C,H,,N,, and by Poehl,* who has attributed very remarkable properties to this substance. According to Poehl, spermine is possessed of marked pharma- cological properties, and has a powerful influence on the meta- bolism. It is recommended by Poehl as a valuable therapeutic agent. His statements have not been confirmed by other ob- servers—for example Dixon *—and his views are now not generally accepted. 1 Cohen, “ Die krystallinischen Bildungen des mannlichen Genitaltraktus,” Centralblatt f. allg. Pathologie u. pathol. Anatomie, vol. x., 1899. (This paper gives a very complete bibliography.) 2 Poehl, ‘Weitere Mitteilungen iiber Spermin,” Berliner klin. Wochen- schrift, 1891. 3 Ladenburg and Abel, ‘ Uber das Aethylenimin,” Ber. der deutschen chem, Gesellschaft, vol. xxi., 1888. 4 Poehl, Die Physiologisch-Chemischen Grundlagen der Spermintherapie, Petersburg, 1898. 5 Dixon, ‘‘ The Composition and Action of Orchitic Extracts,” Journal of Physiology, vol. xxvi., 1901. 286 THE PHYSIOLOGY OF REPRODUCTION Choline, which gives the sarhe reactions as spermine with iodine and alloxan, has also been stated to occur in the semen. The various glands of the genital tract contribute to the formation of the semen in the following way :— The spermatozoa are formed in the testis, which secretes an albuminous fluid as the medium in which the spermatozoa move about. Crystals smaller than the crystals of spermine- phosphate have been observed by Lubarsch* in the tubules of the testis. They are insoluble in formol and 50 per cent. acetic acid, and swell up under the action of alkali. Other crystalloid rod-like formations in the interstitial cells have been described by Reinke*® and von Bardeleben.* The nature of these crystals, which have been found so far only in human testes, is unknown. Amyloid bodies, which are coloured blue with difficulty by iodine, have been observed by Dareste. The secretion of the epididymis has not been chemically investigated. The vesicule seminales secrete a substance of a protein nature. Both these secretions have a faintly alkaline reaction. In the guinea-pig the protein substance secreted by the vesicule seminales clots if brought in contact with blood. This property is perhaps a means whereby fertilisation is ensured, since in the guinea-pig coitus may take place immediately after the termination of the previous pregnancy, when the uterus is still widely dilated. This unfavourable condition is compensated for by the formation of a clot brought about by the action of the semen on the blood which is still present in the uterus.* The prostate gland secretes an opaque fluid having a faintly acid reaction (which may become neutral or alkaline in in- 1 Lubarsch, “Uber das Vorkommen Krystallinischer und Krystalloider Bildungen in den Zellen des Menschlichen Hodens,” Vérchow’s Archiv, vol. cxlv., 1896. 2 Reinke, “ Beitriige zur Histologie des Menschen,” Archiv f. mikroskop. Anatomie, vol. xlvii., 1896. ° Bardeleben, ‘ Beitrige zur Histologie des Hodens und zur Spermato- genese beim Menschen,” Archiv f. Anatomie u. Physiologie, Anatomische Abteilung, Supplement, 1897. 4 Landwehr, ‘Uber den Eiweisskérper der vesicula seminalis der Meer- schweinchen,” Pfliiger’s Archiv, vol. xxiii., 1880. BIOCHEMISTRY OF THE SEXUAL ORGANS 287 flammatory conditions of the prostate). It contains spermine,' which, when brought together with the phosphates secreted by other genital glands, forms the characteristic ““ Béttcher’s crystals.” The secretion of the prostate also contains the substance which gives the characteristic smell to the ejaculated semen, the lecithin-like globules, and a protein substance. The state- ment that this protein is an albumose is probably not correct, since albumoses have never been found to occur in a living cell. Camus and Gley” found in the prostatic secretion of some animals a ferment, vesiculase, which has the property of coagulating the fluid in the vesicule seminales. The presence of this ferment in the ejaculated semen produces the formation of a coagulum. This ferment appears to have the function of ensuring fertilisation, since it occurs only in those species where the contact between male and female is of very short duration. (See p. 233.) Cowper’s glands secrete a stringy mucinous substance. If a solution of iodine in potassium iodide is added to semen, brown crystals are formed (Florence’s reaction). This reaction is common to many substances belonging to the group of organic ammonium bases. One of the best-known members of this group is choline, which forms part of the lecithin molecule, and is, therefore, a constituent of almost every animal cell. Pro- bably the reaction is not due to spermine, as Florence * states, but to choline, as Bocarius? believes, since other secretions and tissue extracts which do not contain spermine give the same reaction. Another reaction for semen, which is much more specific, has been discovered by Barberio. By the addition of picric acid, fine rhombic or needle-shaped crystals are formed. It is doubtful which substance is responsible for this reaction. The 1 Wirbringer, ‘Die Stérungen der Geschlechtsfunktion des Menschen” ; in Nothnagel, Pathologie u. Therapie., vol. xix., Part III., 1895. : 2 Camus and Gley, ‘Action Coagulante du Liquide Prostatique sur le Contenu des Vésicules Séminales,” Comptes Rendus, vol. cxxiii., 1896. 3 Florence, ‘‘Du Sperme et des Taches du Sperme,” Archives d’ Anthro- pologie Criminale, vol. xi., 1896 ; vol. xii., 1897. 4 Bocarius, ‘“ Zur Kenntniss der Substanz welche die Bildung von Florence- chen Krystallen bedingt,” Zeitschrift f. phystologische Chemie, vol. xxxiv., 1902. 288 THE PHYSIOLOGY OF REPRODUCTION observations of Littlejohn and Pirie’ show that the substance which forms the crystalline picrate is secreted by the prostate and by Cowper’s glands, and, further, that this substance appears to be specific for human semen, since a negative result is ob- tained with the semen of monkeys, rabbits, and rats. Tur CHEMISTRY OF THE SPERMATOZOON * Owing to the brilliant work of Miescher,® which has been continued by Kossel* and his pupils, our knowledge of the chemistry of the spermatozodn is more complete than that of any other cell. Thanks to the intelligent generosity of the head of a large fishery concern in Bale, Miescher obtained a liberal supply of the milt of the salmon, the sexual organs of which develop during the passage up the Rhine. By controlling his mechanical manipulations by means of histological observations Miescher was able to investigate separately the different morphological elements of the spermatozoa. The tails of the spermatozoa are very rich in phosphorised fats, and contain besides a typical protein, cholesterin, and fat, in the following proportions :— Proteins. A : . . 41:90 per cent. Phosphorised fats. : . 31°83 45 Cholesterin, fats , : . 26°27 3 Similar conditions were found to exist in the case of other fishes and in the case of the ox. The heads were found to contain only traces of fat, lecithin and cholesterin, and to be composed almost entirely of a substance very rich in phosphorus. This on further investigation proved to be a combination of a basic substance, very rich in nitrogen, which Miescher called 1 Littlejohn and Pirie, ‘‘ The Micro-Chemical Tests for Semen,” Edin. Med, Jour., 1908. (This paper contains references to the-literature.) 2 For a detailed account of this subject and the literature see Burrian, “Chemie der Spermatozoen, I.,” in Ergebnisse der Physiologie, vol. iii., 1£04, and ‘‘Chemie der Spérmatozoen, II.,” in Ergebnisse der Physiologie, vol. v., 1906. 3 Miescher, Histochemische und Physiologische Arbeiten. Gesammelt und Herausgegeben von Seinen Freunden, vol. ii., Leipzig, 1897. 4 Kossel, ‘‘ Uber die einfachsten Eiweisskérper,” Biochemisches Centralblait, vol. v., 1906-7, Part I. BIOCHEMISTRY OF THE SEXUAL ORGANS 289 protamine, and a substance rich in phosphorus, having the nature of an acid and belonging to the group of substances known as nucleinic acids, which occur in the nuclei of somatic cells in combination with protein substances as the so-called nucleoproteins. The comparative chemical investigations of Kossel showed, that while the nucleinic acid radicle present in the spermatozoa of various species of fishes shows only very little variation, the basic part is different for each species. It has, therefore, been found convenient to distinguish these basic substances by separate names, derived from the Latin names of the species of the fish in which they occur. The basic substance of the head of the spermatozo6n of the salmon is salmine, that of the herring clupeine, and so on. Since they have certain general chemical and physical characters in common they have been classed together in a group, which has received the name “ Pro- tamine,” which was originally used by Miescher to denote the basic substance in the spermatozoa of the salmon. The protamines are strongly basic substances which absorb carbonic acid from the air. They are soluble in water, insoluble in alcohol and ether ; not coagulable by heat ; free from sulphur. They are very rich in nitrogen, the percentage amount varying from 33 per cent. to 25 per cent., while that of an albumen or globulin is about 16 per cent. They give a strong biuret re- action. Like other proteins, they are precipitated by tannic acid, phosphotungstic acid, picric acid, and ferrocyanic acid ; but while the proteins are precipitated by these reagents in acid solution only, the protamines, by virtue of their basic character, form a precipitate with these reagents even in alkaline solution. They form compounds with the salts of the heavy metals (copper, mercury, silver, platinum). The protamines combine with many other protein substances in neutral or faintly alkaline solution, so that a precipitate is formed if, for example, a solution of protamine is added to a solution of caseinogen.* If injected into an animal they have a strongly toxic action, even if small doses are given.” 1 Hunter (A.), “Uber die Verbindungen der Protamine mit anderen Hiweiss-kérpern,” Zeitschrift f. phys. Chemie, vol. liii. 1907. 2 Thompson, “ Die physiologische Wirkung der Protamine,” Zeztschrift f. physiol. Chemie, vol. xxix., 1899. T 290 THE PHYSIOLOGY OF REPRODUCTION Although differing in many respects from the protein sub- stances, the protamines have been shown by Kossel to have a constitution so similar to that of the proteins that they are now considered to represent one group of the protein substances. The study of the products of hydrolytic decomposition shows that while in the case of the typical proteins, such as the proteins of muscle, of milk, or of the serum, the nitrogen is bound up in the form of a great many different substances, e.g. tyrosine, leucine, alanine, glycine, cystine, &c., of which as many as fifteen have been isolated, the protamine molecule is composed of only a few constituent substances. And, further, while in the case of the typical proteins the main bulk of the substance obtained on hydrolysis belongs to the monoamino acids, the protamines are composed largely of the diamino acids: arginine, lysine, and histidine, which, from their basic nature and the fact that they contain six carbon atoms, have received the name “ hexone- bases.” Of these the most important one is arginine, which, on boiling with baryta, is decomposed into urea and diamino- valerianic acid (ornithin), and has the structure— NH, NH, | | NH=C -NH- CH, - CH, - CH,— CH - COOH In salmine, for instance, eight-ninths of the nitrogen is bound up as arginine, while the remainder of the nitrogen is present in the form of monoamino acids, viz., serine, monoaminovalerianic acid and proline, in the following proportions: 10 molecules of arginine +2 molecules of serine+2 molecules of proline +1 molecule of aminovalerianic acid. Similar relations are found to exist in the case of scombrine and clupeine. In both these protamines eight-ninths of the total nitrogen is present in the form of arginine, which is combined with alanine and proline in the case of scombrine, and with alanine, proline, serine, and aminovalerianic acid in the case of clupeine. Since eight-ninths of the nitrogen of these three protamines is present in the form of arginine, and since arginine contains four nitrogen atoms, while the amino acids with which it is combined contain only one nitrogen atom, it follows that in BIOCHEMISTRY OF THE SEXUAL ORGANS 291 these three protamines the number of arginine molecules must be twice as great as the total number of monoamino acid molecules present in the protamine molecule. The investigations of Kossel and Pringle ' have shown that substances can be obtained by partial hydrolysis of these protamines, the so-called “ protones,’’ which represent inter- mediate decomposition products between these protamines and the amino acid units of which the protamines are built up, and that these protones again contain eight-ninths of their total nitrogen in the form of arginine. It follows, then, that the molecules of salmine, scombrine, and clupeine have a symmetrical structure, and are built up of molecular complexes containing always twice as many arginine molecules as monoamino acid molecules. In other protamines the amount of arginine is smaller, while lysine is found to be present. At the same time the number of monoamino acids bound up in the protamine molecule increases so that the different protamines exhibit varying degrees of complexity. Ammonia and certain mono- amino acids (glycocoll, phenylalanine, glutaminic acid, aspartic acid, the sulphur-containing cystine) are never present. In the case of some fishes—e.g. Gadus morrhua,” Lota vulgaris * —the basic substances isolated from the spermatozoa differ essentially from the protamines, and in character more resemble the typical proteins. Their nitrogen content varies between 16 per cent. and 18 per cent. On hydrolysis the yield of diamino acids is very much smaller than in the case of the protamines. Only 30 to 40 per cent. of diamino acids, among which arginine again preponderates, are obtained. Accordingly they are not so strongly basic as the protamines. They contain cystine. They are precipitated by ammonia, a reaction which the protamines do not give. They resemble in their be- haviour substances which have been isolated from the nuclei of somatic cells, eg. the blood corpuscles of the fowl, the 1 Kossel and Pringle, ‘‘ Uber Protamine und Histone,” Zeitschrift f. phys. Chemie, vol. xlix., 1906. 2 Kossel and Kutscher, ‘‘ Beitrige zur Kenntniss der Eiweisskérper,” Zeitschr. f. phys. Chemie, vol. xxxi., 1900. 3 Ehrstrém, ‘‘ Uber ein neues Histon aus Fischsperma,” Zeitschrift f. phys, Chemie, vol. xxxii., 1901. 292 THE PHYSIOLOGY OF REPRODUCTION thymus, &c., and which form another class of the protein sub- stances, to which the name histone has been given, In their properties and their composition these substances, therefore, take a place between the typical proteins and the protamines. The substance isolated from the spermatozoa of the carp, cyprinine (or rather the two cyprinines, since two slightly different substances have been isolated), is on the border-line between the protamines and the histones. The cyprinines do not contain any cystine, they are not precipitated by ammonia, and only about 35 per cent. of their total nitrogen is present in the form of diamino acids, mainly as lysine in the one of the two cyprinines.* The chemical differences which exist between the spermatozoa of the different species and orders do not show any connection with the zoological relationship. The significance of the presence of histones in the spermatozoa of some fishes becomes more apparent if the development of the sexual organs is considered. It was Miescher who pointed out that in the salmon the sexual organs develop at the expense of the muscular system and that the salmine deposited in the testis during the breeding season must be derived from the proteins of the muscle, since the fish does not take any food during that period. A com- parison between the amount of arginine present in salmine, and that present in the muscle of the salmon shows ”® that all the arginine deposited as salmine during the breeding season can be accounted for by the arginine which becomes available by the involution of the muscular elements. This result would suggest that the formation of salmine is not due to a profound chemical alteration of the various con- stituents of the muscle-proteins, transforming the divers sub- stances intu arginine, but rather to a gradual enrichment in arginine of the muscle protein by the splitting off of a number of the other constituent substances. 1 Kossel and Dakin, ‘“‘ Beitrag zum System der einfachsten Eiweisskorper,” Zeitschrift f. phys. Chemie, vol. xl., 1904. ? Kossel, ‘‘Einige Bemerkungen iiber die Bildung der Protamine im Thierkérper,” Zettschrift fiir physiologische Chemie, vol. xliv., 1905. Weiss, ‘Untersuchungen tiber die Bildung des Lachs-Protamins,” Zeitschrift fiir phystologische Chemie, vol. lii., 1907. BIOCHEMISTRY OF THE SEXUAL ORGANS 293 The investigation of the unripe spermatozoa of the salmon * and of the mackerel * has shown indeed that instead of a pro- tamine a histone is present, i.e. a substance which represents the transition stage between the typical proteins and the protamines. It would appear, therefore, that in the fishes the chemical processes which lead to the formation of the spermatozoa consist of a rearrangement of the constituents of the proteins of somatic tissue, so that a gradual accumulation of the basic substances rich in nitrogen takes place. This change leads at first to the formation of histones, and in some species stops here. In the majority of cases the change proceeds to the formation of sub- stances belonging to the protamines. In the case of some Invertebrates (Arbacia pustulosa,* Spherechinus granularis*) the spermatozoa have been in- vestigated and histones have been found to be present. Of the higher Vertebrates, the spermatozoa of the frog, the cock, the boar, and the bull have been examined,° but neither protamines nor histones were found. The acid substance isolated from the spermatozoa, the nucleic acid, does not show any great variation in the different species and classes of animals. It is, in fact, very similar to the nucleic acid present in the nuclei of somatic cells, and is probably identical with the nucleic acid prepared from the thymus. These nucleic acids do not belong to the proteins, but they: exist in the cell always in combination with proteins as nucleins or as nucleoproteins, according to the amount of protein present in the combination. The nucleic acids are dry, pulverulent, white substances of a decidedly acid character, containing 9 to 10 per cent. of 1 Miescher, ‘‘ Physiologisch-Chemische Untersuchungen tiber die Lachs- milch,” Histochemische Arbeiten, Archiv f. Experimentelle Pathologie u. Pharmakologie, vol. xxxvii., 1896-1897. 2 Bang (I.), “Studien iiber Histon,” Zeitschrift f. physiolog. Chemie, vol, xxvii, 1899. 3 Mathews, “ Zur Chemie der Spermatozoen,” Zetischrift f. phys. Chemie, vol. xxiii., 1897. 4 Kossel, “Uber die einfachsten Eiweisskérper,” Biochemisches Cen- tralblatt, vol. v., 1906-7. 5 Miescher, loc. cit., ‘‘Die Spermatozoen einiger Wirbelthiere,” Histo- chemische Arbeiten ; Mathews, loc. cit. 294 THE PHYSIOLOGY OF REPRODUCTION phosphorus, not easily soluble in cold water, but readily dis- solved by alkalies or ammonia. They are precipitated from their solutions by mineral acids and by alcohol. They form insoluble salts with the heavy metals and with barium, calcium, and strontium. If pure, they do not give the colour reactions for proteins. They rotate polarised light to the right. A solution of nucleic acid, acidified with acetic acid, gives a precipitate with protein solutions. By boiling the watery solutions the nucleic acids are partially decomposed.’ Complete hydrolysis is brought about by treatment with hot acids. The main products of hydrolysis which are thus obtained can be grouped under five headings :— 1. Phosphoric acid. 2. Levulinic acid, a substance formed by the oxidation of carbohydrates, and indicating the presence of a hexose (some nucleic acids contain a pentose). 3. Derivatives of purine— (1) N=CH (6) (2)HC © (5)-NH Cee (3) N-C (4)-N (9)7 @) namely— Adenine=6 — Aminopurine ; Hypoxanthine=6—Oxypurine ; Guanine =2 Amino—6 Oxypurine ; Xanthine=2—6 Dioxypurine. Of these only adenine and guanine are present as such in the nucleic acid molecule, while hypoxanthine and xanthine are formed from them in the process of hydrolysis by a secondary reaction. 4. Derivatives of pyrimidine— (1) | =CH (6) (2)HC CH) (3) N-du (4) namely— Cytosine=6 Amino —2 Oxypyrimidine Uracil = 2-6 — Dioxypyrimidine Thymine=5 Methyl —2-6 Dioxypyrimidine (Methyl-Uracil). Yor literature for nucleic acid see Steudel, * Nucleine, Nucleinséuren und ihre Spaltungsprodukte,” Biochemisches Centralblatt, vol. vi., 1907; also Burrian, loc. cit.; Levene, Zeitschr. f. phys. Chemie, vols, xxxii. to 1., Biochem, Zeitschr., vols. iy., v., and ix. BIOCHEMISTRY OF THE SEXUAL ORGANS 295 Of these cytosine and thymine are present as such in the nucleic acid molecule, while uracil is formed from cytosine by a secondary reaction in the process of the splitting up of the nucleic acid. Reference has already been made to the fact that in the salmon the material for the growth of the testis is supplied by the muscle undergoing atrophy. The analogy existing between the glycophosphoric acid which forms the “ skeleton ” of the nucleic acid, and the glycerophosphoric acid which forms the skeleton of phosphorised fats, suggests that the glycerophosphoric acid present in the muscle as phosphorised fat furnishes the material from which the glycophosphoric acid bound up in the testis as the nucleic acid is formed. This view is supported by the fact’ that, during the period of the growth of the testis, the blood of the salmon is exceptionally rich in phosphorised fats, and that the tail of the spermatozoén is also very rich in phosphorised fats. It would appear that these substances, after having been transported to the testis, are there built up partly into the nucleus of the spermatozodn, while part remains accumulated in the tail of the spermatozoon as reserve material. The origin of the purine and pyrimidine derivatives which form part of the nucleic acid molecule is as yet obscure. In the case of the developing ovum it has been shown (see p. 269) that.the living cell has the power of synthesising these sub- stances. But the substances which supply the material for their formation, and the reactions which lead to it, have not yet been revealed. The substances detailed above represent all the constituent parts of the nucleic acid molecule, so that it is possible to recon- stitute the nucleic acid from the products of its decomposition. According to Steudel,? the process of hydrolysis may be expressed by the following equation :— CyHyN1,09P, + 4H,O =C,H,N;,0 + C,H,N, + C;H NO, +C,H,N,0 Nucleic acid. Guanine. Adenine. Thymine. Cytosine. +CyHOsoPy. 1 Miescher, loc. cit. 2 Steudel, ‘Die Zusammensetzung der Nukleinséuren aus Thymus u. aus Heringsperma,” Zeitschr. f. phys. Chemie, vol. liii., 1907. 296 ‘THE PHYSIOLOGY OF REPRODUCTION The non-nitrogenous part is split up further according to the following equation :— CoH 40552, +4H,0 + 20 = 4C,H,,0, + 4HPO;. Hexose Metaphosphoric sugar. acid. In other words, the “ skeleton ” of the nucleic acid molecule is formed by four molecules of metaphosphoric acid combined with four molecules of a sugar:* a tetraglyco-metaphosphoric acid, similar to the glycerophosphoric acid which forms the “skeleton *’ of phosphorised fats. In the nucleic acid molecule this glycophosphoric acid is combined with four different nitro- genous substances, of which two are pyrimidine derivatives and two are purine derivatives.” It is an interesting fact that while nucleic acid prepared from ripe spermatozoa does not contain pentoses, these sub- stances are stated to be present in the nucleic acid of the testis of the bull,? which represents the acid constituent of the nuclei of the sexual element in the various stages of their development. Since the statement of the presence of a pentose in the nucleic acid from the testis of the bull is based only on the preparation of an osazone, further investigation on this point and analytical data are necessary before it can be accepted. The observations of Miescher * allowed of a quantitative esti- mation of the amount of nucleic acid and protamine present in the head of the spermatozoa of the salmon after the fat had been removed. 60:5 per cent. of nucleic acid was found to be combined with 35:5 per cent. of salmine, so that 96 per cent. of the head of the spermatozoon consists of protamine nucleate. This protamine nucleate is, however, not of the same nature in different parts of the head, the outer layer containing a basic nucleate rich in protamine, while the inner portion is composed of an acid nucleate poorer in protamine. 1 The sodium-salt of a tetraphosphoric acid can be prepared by fusing together the sodium metaphosphate and pyrophosphate (Kraut and Uelsmann, Liebig’s Annalen, vol. cxviii., 1861). The organic derivatives of this base have not yet been studied. 2 For a slightly different view of the constitution of nucleic acid, see Burrian in Ergebnisse dcr Physiologie, vol. v., loc. cit. * Steudel, ‘Uber die Kohlenhydratgruppe in der Nukleinsaure,” Zeit- schrift f. physiolog. Chemie, vol. lvi., 1908. 4 Miescher, Histochemische Arbeiten. BIOCHEMISTRY OF THE SEXUAL ORGANS 297 The same quantitative relations have been shown to exist in the spermatozoa of the herring,’ and similar conditions may be assumed to exist in the case of the spermatozoa of other animals, the only difference being the nature of the protein molecule which is combined with the nucleic acid. It is a protamine or a histone in the case of the fishes, but a typical protein in the case of the higher Vertebrates.” Of the remaining 4 per cent. about one half consists of in- organic salts, mainly calcium phosphate and calcium carbonate, while the other half consists of an organic substance, the com- position of which has not yet been recognised. The most important fact known about it is that it contains 0°12 per cent. iron in organic combination. The presence of iron can be recognised only after incineration. To this iron-containing organic substance Burrian*® applies the name “ Karyogen,” a word originally coined by Miescher to designate the residue which he obtained after what Schmiedeberg’s * calculations showed to be an incomplete extraction of the protamine and nucleic acid from the heads of the spermatozoa of the salmon. Since Macallum*® was able to demonstrate by means of a microchemical method the presence of iron in the chromatin of the nuclei of cells, it seems possible that the ‘‘ Karyogen ” represents the chromatin substance of the spermatozo6n. The chemical analysis of the spermatozodn is therefore complete. It shows that the tail’ is very rich in phosphorised fats which are accompanied by cholesterin, fats, and a typical protein. The head consists almost entirely (96 per cent.) of a substance—a nucleoprotein—one component of which is constant for the different species and classes—the nucleic 1 Bendix and Elstein, ‘‘ Uber den Pentosengehalt tierischer und mensch- licher Organe,” Zetischrift f. allgem. Physiologie, vol. ii., 1902. 2 Mathews, “Zur Chemie der Spermatozoen,” Zettschrift f. phys. Chemie, vol, xxiii., 1897. 3 Burrian, Ergebnisse der Phystologi-, vol. v., 1906. “ Miescher, “Physiologisch-chemische Untersuchungen tiber die Lachs- milch, nach den hinterlassenen Aufzeichnungen u. Versuchsprotokollen des Autors bearbeitet u. herausgegeben von O. Schmiedeberg,” Arch. f. Experi- mentelle Pathologie u. Pharmakologie, vol. xxxvii., 1896, and in Histochemische u. Physiologische Arbeiten von Miescher. 5 Macallum, “On the Demonstration of the Presence of Iron in Chromatin by Microchemical Methods,” Proc. Roy. Soc., vol. 1., 1892. 298 THE PHYSIOLOGY OF REPRODUCTION acid. The other more or less basic component varies widely for the different classes of Vertebrates, and shows minor variations for the different species in any one class. Besides this nucleoprotein, another organic substance, containing iron in organic combination, is present in very small amounts. It is perhaps natural that attempts should have been made to associate these different substances with the functions of the spermatozodn. But such speculations are hardly justifiable until our knowledge of the nucleus of the ovum is as complete as it is in the case of the male nucleus. At present we know practically nothing of the chemical composition of the nucleus of the ovum. Nor is it likely—and Miescher himself clearly recognised this—that the intricate processes which are con- nected with fertilisation and heredity are directly dependent upon such crude chemical facts as the percentage of arginine or serine, or the composition of nucleic acid. We are on safer ground when we consider the head of the spermatozooén simply as a typical nucleus, and when we draw deductions from the chemical composition of the nuclear material of the spermatozo6n, as to the functions of the nucleus generally. It is a very suggestive fact that the nucleus—that is to say, that part of the cell which is pre-eminently concerned in the new formation of living material—is distinguished by the presence of pyrimidine and purine derivatives, substances rich in nitrogen, which are arranged in a chain of alternating C and N atoms.* In the spermatozo6n, where the nuclear function finds its most pronounced expression, we find, at least in the case of the fishes, a further concentration of such groups with alternat- ing C and N atoms. For, besides the pyrimidine and purine derivatives of the nucleic acid part, there is also present the basic protamine part. As has been explained above, this part is composed largely of arginine, which, as the formula given on p. 290 shows, contains the group— NH, | NH=C-NH-CH,-... ‘ Kossel, “ Einige Bemerkungen iiber die Bildung der Protamine im Thierk6rper,” Zettschrift f. phys. Chemie, vol. xliv., 1905. BIOCHEMISTRY OF THE SEXUAL ORGANS 299 These facts suggest that this special arrangement of alternating Cand N atoms is the chemical expression of the specific function of the nucleus, and that this arrangement plays a special part in bringing about the chemical processes which lead to growth and to the new formation of living matter. In the case of the other organic compound present in every nucleus, which contains iron in organic combination, the evidence that it plays an active part in the synthetic functions of the nucleus is even more suggestive. It was shown by Spitzer that the oxidising enzymes which are present in every cell are localised in the ircn-containing constituent of the nucleus, and Loeb coneludes that the nucleus must be regarded as the essential respiratory or oxidising organ of the cell. Oxidation processes are generally supposed to be necessary only for the transformation of chemical energy into heat and mechanical work. But they are, according to Loeb, equally necessary for other more important and more general vital processes, t.e. growth and cell division, which come to a stand- still in the absence of oxygen. As a tule, cell division follows upon the formation of nuclear material, especially chromatin material, from the protoplasm of the cell. If we accept Schmiedeberg’s * view that in the living cell synthetic processes may occur through the intervention of oxygen, we may conclude that the oxygen which is required for the process of cell division is probably needed for the synthesis of this nuclear material, and, since the iron-containing organic compound present in the nucleus has the power of bringing about oxidations, it would follow that the synthetic functions of the nucleus are dependent upon this compound. It must, however, be understood that these considerations are still very hypothetical, and that other biologists 4 deny that the nucleus is the respiratory or oxidising centre of the cell. The power possessed by the spermatozo6n of bringing about segmentation of the ovum has been attributed by some authors 1 Spitzer, ‘‘ Die Bedeutung gewisser Nukleoproteide ftir die oxydative Leistung der Zelle,” Pfliiger’s Archiv, vol. lxvii., 1897. 2 Loeb, Dynamics of Living Matter, New York, 1906. 3 Schmiedeberg, “‘ Uber Oxydationen und Synthesen im Thierkérper,” Archiv f. experimentelle Pathologie u. Pharmakologie, vol. xiv., 1881. 4 See Verworn, Allgemeine Physiologie, 1909. 300 THE PHYSIOLOGY OF REPRODUCTION to the action of ferments present in the spermatozoén. Pidri’ claimed to have extracted from the spermatozoa of Stron- gylocentrotus lividus and Echinus esculentus a ferment, “ ovulase,” which induced segmentation of mature ova. Similar observa- tions were made by Dubois? on Echinus, and by Winkler * on Spherechinus granulosis and Arbacia pustulosa. The evidence on which these authors base their conclusion is, however, not very convincing, and the searching criticism to which their observations were subjected by Gies,* who repeated their ex- periments, tends to show that their results were due to other factors. Gies was unable to extract either from spermatozoa or from fertilised ova any enzyme or zymogen capable of causing development in mature ova of the same species. Similarly Cremer *® was unable to bring about fertilisation by means of the press-juice obtained from spermatozoa (see p. 222). Wolfgang Ostwald® has determined the amounts of oxidising ferments present in the ovaries and testes of toads, frogs, and newts. The watery extracts of these organs had the power of decomposing hydrogen peroxide with the formation of water and oxygen, and of oxidising guaiaconic acid to guaiacum blue, so that a blue colour appeared when these extracts were added to an emulsion of guaiac resin. These reactions indicate the presence of a catalase and of a peroxidase in the extracts of the sexual glands. Such ferments are present in many, if not all, organs and tissue fluids, but a special significance is attri- buted by Ostwald to their presence in the ova and spermatozoa, because he found the spermatozoa to contain more catalase and more peroxidase than the ova, and because the activity 1 Piéri, ‘‘ Un Nouveau Ferment soluble: l'Ovulase,” Archives de Zoologie Expérimentale et Générale, vol. xxix., 1899. 2 Dubois, ‘Sur la Spermase et l’Ovulase,” Comptes Rendus de la Société de Biologie, vol. lii., 1900. 3 Winkler (H.), ‘‘ Uber die Furchung unbefruchteter Eier unter der Ein- wirkung von Extraktiostoffen a. d. Spermata,” Nachrichten der kgl. Gesell- schaft der Wissenschaften zu Gottingen, Mathemat.-Phys. Klasse, 1900. 4 Gies, ‘‘ Do Spermatozoa contain an Enzyme having the Power of Causing Development of Mature Ova?” American Journal of Physiology, vol. vi., 1901. 5 Quoted from Loeb, Dynamics of Living Matter. 6 Wolfgang Ostwald, “Uber das Vorkommen von oxydativen Fermenten in den reifen Geschlechtszellen von Amphibien und iiber die Rolle dieser Fermente bei den Vorgingen der Entwicklungserregung,” Biochemische Zeitschrift, vol. vi., 1907. BIOCHEMISTRY OF THE SEXUAL ORGANS 301 of these ferments—especially the peroxidase—is increased when the extracts of ova are mixed with the extracts of spermatozoa. The development of the ovum after fertilisation is, according to Ostwald, due to this activation of the oxidising ferments inducing a chemical synthesis of nuclein substances, which form a localised coagulum of a definite orientation, namely, the astrosphere. According to the view of Fischer and Ostwald,1 which is, however, not accepted by other workers,” the forma- tion of the astrosphere initiates cell-division, and therefore the development of the egg. A very ingenious theory of the chemical mechanism of ferti- lisation has been put forward recently by Loeb,? as the result of his work on artificial parthenogenesis. According to Loeb, the development of the mature ovum is dependent upon two processes. It is initiated by a cytolysis affecting the periphery of the cell. This process, which is accompanied by the formation of a ferti- lisation membrane, can be induced by any agent having a cyto- lytic action, such as heat, ether, fatty acids, saponin, or the serum of an animal of a different species. If this initial cytolysis is allowed to proceed unchecked, the eggs, although they may begin to divide, eventually undergo complete cytolysis. If, on the other hand, the initial cytolysis is inhibited by suitable means, such as treatment with potassium cyanide or immersion in hypertonic sea-water containing oxygen, the eggs will develop in the same way as if they had been fertilised by a spermatozo6n. If it be admitted that artificial parthenogenesis represents the conditions governing fertilisation by a spermatozodn, then it follows that a spermatozodn should contain two substances, namely, a cytolysin, and a substance inhibiting the initial cyto- lysis. The presence in the spermatozoon of a cytolysin can indeed be proved. Extracts of the testis of a cock, or the dead semen (killed by heating) of a starfish or a mollusc, will induce the initial process of cytolysis in the eggs of a sea-urchin. The dead semen of a sea-urchin, however, is quite inactive against the eggs of a sea-urchin. This is in agreement with our knowledge of 1 Fischer and Ostwald, “Zur Physikalisch-Chemischen Theorie der Befruchtung,” Pfliiger’s Archiv, vol. cvi., 1905. 2 See, for instance, Burrian, loc. cit. 3 Jacques Loeb, Die chemische Entwicklungserregung des tierischen Etes, Berlin, 1909. 302 THE PHYSIOLOGY OF REPRODUCTION the actions of cytolysins generally. The cytolysins present normally in the serum or the cells of one animal are always inactive against the cells of animals of the same species, and act only against cells of animals of a different species. The explana- tion of this fact is to be found, according to Loeb, in the diminished permeability of the cells of one species towards the cytolysins produced by the cells of animals of the same species, the so-called auto-cytolysins. Similarly the ovum of an animal is not permeable to the cytolysins contained in the spermatozodn of an animal of the same species. In order to bring about the development of the mature ovum the auto-cytolysin must be carried bodily into the egg. And that is the function of the motile spermatozo6n. APPENDIX? More recent experiments on different insects 2 have confirmed the fact that in these animals, as in birds, the main source of the energy which is used up during development is fat. No nitrogen is lost, but some of the protein material undergoes partial oxidation, to uric acid, and may thus contribute to the “energy of development.” Whether the glycogen which disappears during development serves as a source of energy is doubtful. The chitin which is deposited in the cuticle of insects is a compound built up mainly of carbohydrate-groups, and it seems likely that these carbohydrate-groups are derived from the glycogen, which thus contributes to the formation of the cuticle. It is interesting to note that glycogen appears to fulfil a similar function in the developing rabbit, where it also contributes to the building up of the growing tissues. It appears indeed to be a general law that carbohydrate material is essential for growth. 1 See p. 281. 2 Farkas, loc. cit.; Weinland, Zeitschr. f. Biologie, vol. xlvii., 1905; vol. xlviii., 1907; vol. li., 1908; vol. lif, 1909; Tangl, Pfliger’s Archiv, vol. cxxx., 1909. 3 Lochhead and Cramer, loc, cit. CHAPTER IX THE TESTICLE AND THE OVARY AS ORGANS OF INTERNAL SECRETION “Da muss sich manches Rithsel lésen, Doch manches Rathsel kniipft sich auch.” —GOETHE, THE principal evidence supporting the theory that the ovary and testicle are organs of internal secretion is derived from the ~ experimental study of the effects produced, firstly, by removing these organs, and, secondly, by transplanting them to abnormal positions in the body. Experiments of such a kind clearly — demonstrate the influence of the ovary and testicle upon the growth and development of the other generative organs, and upon many of the secondary sexual characters. They indicate, moreover, thatthe nature of this influence is chemical rather than nervous. Certain further evidence, which is less satis- factory in character, has been obtained from experiments on the injection of ovarian and testicular extracts. Tue CORRELATION BETWEEN THE TESTIS AND THE OTHER MALE ORGANS AND CHARACTERS It has already been recorded (p. 239) that the removal of the testes in adult life brings about a gradual atrophy of the prostate gland. It has also been shown that this operation, if performed prior to puberty, prevents the development of the prostate, whereas division of the vas deferens and the abolition of sperm production have no arresting influence. One-sided castration produces no effect, the retention of a single testis being sufficient to maintain the functional activity of both ‘ Wallace (C ), “ Prostatic Enlargement,” London, 1907. It is shown also that vasotomy has no influence on the growth and activity of the prostate. 303 304 THE PHYSIOLOGY OF REPRODUCTION prostate glands. Similiarly it has been stated that Cowper’s glands are probably dependent upon testicular influence for their growth and activity (p. 240). More remarkable is the close correlation that exists between the testes and the secondary sexual characters of the male—that is to say, those characters which are found only in the male sex, but are not directly connected with the organs of generation. Thus, it is notorious that castration before puberty in man prevents the growth of hair on the face, arrests the development of the male chest and pelvis, and preserves the high-pitched voice of boyhood by hindering the growth of the larynx, while at the same time it exercises a marked influence over the mental characteristics.’ It is equally well known that at the time of puberty, when the testes begin to assume their functional activity, there is a corresponding development of the secondary sexual characters, both in Man and in a large number of animals. This correlation appears to be still closer in those animals in which the increased testicular activity that takes place in the breeding season is associated with a periodic development of other sexual characters. Thus, in the male elephant the glands on the side of the face emit a musky secretion during rut.? Darwin,* in elaborating his theory of sexual selection, collected together numerous examples of secondary sexual differences occurring in animals of various kinds. More recently Cunningham, in a work upon Sexual Dimorphism, has cited a number of further cases,‘ in many of which the structural 1 According to Hikmet and Regnault (‘‘ Les Eunuques de Constantinople,” Bull. et Mém. de la Soc. d’ Anthropologie de Paris, vol. ii., 5th series, 1906), the eunuchs of Constantinople have the following mental characteristics :— They are avaricious, illogical, obstinate (7.e. cannot change their ideas), have no judgment, accept information without proof; are not cruel, but fond of children and animals ; are faithful in their affections, but have no courage ; their mental activity is very slight, and they are extremely fanatical. Senility is premature, but the teeth are kept solid and white. For skeletal differences in eunuchs, see below. 2 Cf. page 305. 3 Darwin, The Descent of Man, Popular Edition, London. 4 Cunningham (J.T.), Sexual Dimorphism in the Animal Kingdom, London, 1900; “The Heredity of Secondary Sexual Characters in Relation to Hor- nones,” Arch. f, Entwick. Mech., vol. xxvi., 1908. See also Hegar, Korrelationem der Keimdriisen und Geschlechtsbestimmung, 1893 ; and Selheim, “ Zur Lehre von den sekundiren Geschlechtscharakteren,” Bettriige zu Geburish. u. Gyndk., vol. i., 1898. ORGANS OF INTERNAL SECRETION 305 peculiarities in question are shown to be closely correlated with the essential organs of reproduction. The effects of castration in the stag, for example, are dis- cussed at some length by Cunningham, Morgan,’ and other writers. If the testes are removed in quite immature animals the antlers never develop, even the knobs failing to make an appearance. If castration is performed in stags whose antlers have just commenced to develop, these remain covered by skin, forming the so-called peruke antlers, which are not shed or renewed. If the operation is carried out after the complete development of the antlers, these are shed prematurely and are replaced in the next season by incomplete antlers with a tendency towards peruke formation, and these, on being thrown off, are not renewed. Partial castration in the immature stag is said to result ina weaker horn formation ; but the effect is general, and shows no restriction to the side on which the testis is wanting.” The results of castration in the fallow deer have been in- vestigated by Fowler,* who summarises his results under five headings :—(1) Complete castration at birth limits the horn formation to the development of single dugs; (2) Castra- tion in mature life tends to produce asymmetry in the growth of the horns; (3) The antlers of castrated deer are often shed prematurely if the operation is performed after they have lost the velvet, but antlers which have grown after castration may be retained for over two years; (4) Incomplete castration shortly after birth is followed by a weak development of the antlers, which are otherwise normal; (5) One-sided castration may result in the abnormal or incomplete’ development of one antler, the other antler being nearly normal. The last point would seem to require confirmation. In the prong-buck (Antilocapra americana), which is the 1 Morgan, Experimental Zoology, New York, 1907. 2 These statements are based chiefly upon the results of Caton’s experi- ments with Wapiti and Canadian deer (Caton, Antelope and Deer of America, 2nd Edition, New York, 1881. See also Holdich, ‘‘ Exhibition of Antlers of Deer showing Arrest of Development due to Castration”), Proc. Zool. Soc,, 1905. Some further examples of sexual correlation are given in Chapter I. of this work, and Morgan, loc cit. Dr. Seligmann informs me that stags which fail to grow antlers (7.e. occasional “ sports”) have well-developed testicles. 3 Fowler, ‘‘ Notes on Some Specimens of Antlers of the Fallow Deer,” &c., Proc, Zool, Soc., 1894. U 306 THE PHYSIOLOGY OF REPRODUCTION only hollow-horned Ruminant that periodically sheds its horns, the effects of castration are also quite distinct. The horns, instead of rising vertically as in normal individuals, curve forwards from the roots, and then bend downwards and backwards so as to terminate in incurved points in the close vicinity of the eyes. The anterior tine is almost completely suppressed. The horn-sheath is never shed, and as a consequence a com- posite sheath is developed, and this seems to go on growing as long as new sheaths are formed from the horn-core.* It is interesting to note that in the eland, in which both sexes possess horns, the development of these structures is not appreciably affected by castration.” A similar statement may be made about horned cattle, in which (in common with other cattle) castration in early life produces changes in the general proportions of the body. In the sheep, also, castration during immaturity brings about changes in the bodily conformation. Thus, in breeds in which the males only are horned, the skulls of the wethers may resembles the females rather than the males.1 Differences in the form of the body have also been noted in eunuchs and other castrated animals. Thus, the bones of the limbs tend to be longer than the normal, producing a condition of gigantism. This is due to an arrest in the ossification of the epiphyses (which is one of the effects of castration). The same phenomena have been described in castrated guinea-pigs, oxen, capons, and various animals.? It is well known that caponisation or the removal of the 1 Pocock, ‘‘ The Effects of Castration on the Horns of the Prong-buck,” Proc, Zool. Soc., 1905. It is to be noted that horns are occasionally present in the female prong-buck. 2 Seligmann, “ Exhibition of a Skull of a Domestic Sheep which had been Castrated when Young,” Proc. Zool. Soc., 1906. Changes in conformation as a result of early castration have also been described in other animals. 3 Lannois and Roy, “ Des Relations qui existent entre 1’Etat des Glandes génitales males et le Développement du Squelette’’; and Poncet, “De l'Influence de la Castration sur le Développement du Squelette,” C. R. dela Soc. de Biol., vol. lv., 1902. See also Pittard, C. R. del’ Acad. des Sciences, vol. cxxxix., 1904), who gives statistics showing that there is often an increase in size in eunuchs, especially in the legs. For accounts of other anatomical differences in eunuchoid persons, see Duckworth, Jour. of Anat, and Phys., vol. xli., 1906, and Tandler and Gross (Arch. f. Entwick.-Mech., vol. xxvii., 1909). The latter authors discuss the general effects of castration on the organism. ORGANS OF INTERNAL SECRETION 307 testes in fowls arrests the development of the comb and spurs and other secondary male characters which are normally present in the cock. Other instances of the effects of castration are briefly referred to by Darwin.? Secondary sexual characters, however, are not always correlated with the essential organs of reproduction. For example, castration in the horse does not arrest the develop- ment of the withers—the gelding, in this respect, resembling the stallion rather than the mare, in which the withers are lower.” In Arthropods the correlation between the secondary sexual characters and the generative glands appears to be far less close than it is among Vertebrates. Thus, Oudemans * showed that the removal of the testes from the male caterpillar of Ocneria dispar had no influence on the development of the secondary male characters, these being normal. Kellogg * performed a similar experiment on the caterpillar of the silkworm moth and obtained a like result. Crampton ° grafted the heads of cater- pillars of one sex upon the bodies of individuals of the opposite sex, and found that the generative organs had no influence upon the development of the secondary sexual characters of the transplanted heads. Moreover, Meisenheimer® found that in caterpillars artificially made hermaphrodite (by transplanting ovaries into males or testes into females) the original males always developed into butterflies with typical secondary male characters in spite of the fact that living ovaries were present, while the original females always developed into normal female butterflies. The sexual instincts were also unmodified by the presence of the grafted gonads. In spider crabs attacked by Sacculina the gonads disappear, 1 Darwin, loc. cit. Selheim (Bettriige zur Geburtshiilfe und Gyndak., vol. i., 1898, and vol. ii., 1899), states that there is an increase in the size of the skull, pelvis, and leg-bones in castrated cocks. 2 Wallace, Farm Live-Stock of Great Britain, 4th Edition, London, 1907, 3 Oudemans, “ Falter aus Castriten Raupen,’’ Zool. Jahrbiicher, vol. xii., 1899, ‘ Kellogg, ‘Influence of the Primary Reproductive Organs on the Second- ary Sexual Characters,” Jour. of Exper. Zool., vol. i., 1904. 5 Crampton, “‘An Experimental Study upon Lepidoptera,” Arch. f. Entwick,.-Mechanik, vol. vii., 1898. § Meisenheimer, Haxperimentelle Studien zur Soma- und Geschlechts- Diferenzierung, Part I., Jena, 1909. 308 THE PHYSIOLOGY OF REPRODUCTION and in the total absence of the testis secondary sexual characters of the female type are found in a large percentage of cases ; but this change in the direction of the opposite sex may set in prior to the complete disappearance of the testes. The change is manifested in the appearance of the egg-bearing abdominal sac appendages, which have no representatives in the male.! Potts states that-in the hermit crab infected by a similar Pelto- gaster, the modifications of the male which occur are of the same type, and are maintained after the atrophy of the testis, and cannot be necessarily consequent on the presence of a secretion of the testis.” In both these cases it is suggested that the modifications which take place are brought about independently by changes in the general metabolism. In the male common shore crab it was found that the testis underwent very little diminution after infection by Sacculina, but that the male approximated to the female type. The change, however, was less marked than in the cases referred to above, in which parasitic castration was almost or quite complete.’ It would appear, therefore, that whereas many of the secondary sexual characters are closely associated with the presence of the genital glands, there are others which develop independently of any influence from the organs of reproduction. Brown-Séquard * seems to have been the first definitely to put forward the view that the testis exercises its influence upon the metabolism through an internal secretion elaborated by it. He based his conclusion to a large extent upon the beneficial effects which he believed to accrue from the administration of testicular extracts. These extracts were supposed to possess invigorating properties, and could be usefully employed in cases of deficiency of testicular substance, or in old age, when the testes lose their functional activity. It is not unlikely that 1 Smith (Geoffrey), ‘‘ Rhizocephala, Faunaand Flora of the Gulf of Naples,” Monograph xaiv., Berlin, 1906. 2 Potts, ‘‘ The Modification of the Sexual Characters of the Hermit Crab, caused by the Parasite Peltogaster,”’ Quar, Jour. Micr. Sci., vol. 1., 1806; and “Some Phenomena Associated with Parasitism,” Parasitology, vol. ii., 1909. 3 Potts, ‘‘ Observations on the Changes in the Common Shore Crab caused by Sacculina,” Proc, Camb. Phil. Soc., vol. xv., 1909. 4 Brown-Séquard, ‘‘Du Rédle physiologique et thérapeutique d’un Suc extrait de Testicules,” Arch. de Phys., 1889. ORGANS OF INTERNAL SECRETION 309 some of the effects which Brown-Séquard attributed to the use of the extract were in reality due to suggestion. Poehl* claims to have prepared from the testis a substance having the chemical composition represented by the formula C,H,,N,. He believes this substance, which he calls spermine, to be the active principle of Brown-Séquard’s testicular extract, stating that it has a beneficial influence over the metabolism of the body and acts as a physiological tonic. (See p. 285.) Zoth,? and also Pregel,? state that they have obtained evidence by ergographic records of the stimulating action of testicular extracts upon the neuro-muscular apparatus in the human subject. They are of opinion that the injection of such extracts results in a decrease of nervous and muscular fatigue, and at the same time diminishes the subjective fatigue sensations. The composition and physiological properties of testicular extract have also been investigated by Dixon,* who found it to contain proteins, organic substances unaltered by boiling, and inorganic salts. Nucleoproteim was especially plentiful. In- jection into the circulation caused a fall of blood pressure due chiefly to cardiac inhibition, but no very striking or interesting results. Walker ° appears to be dubious about the efficacy of testicular medication, stating that the injection of fluid extract into castrated dogs had no effect in arresting the atrophy of the prostate gland (cf de Bonis, see Chapter VII., p. 239). It is possible, however, that the “ active principle ” of the testicular secretion was destroyed in the preparation of the extract, and 1 Poehl, “ Weitere Mitteilungen iiber Spermin,” Berliner kin. Wochen- schrift, 1891. 2 Zoth, ‘Zwei ergographische Versuchsreihen tiber die Wirkung orchi- tischen Extractes,” Pfliiger’s Archiv, vol. lxii., 1896. 3 Pregel, ‘‘Zwei weitere ergographische Versuchsreihen,” &c., Pfliiger’s Archiv, vol. 1xii., 1896. ; 4 Dixon, ‘‘A Note on the Action of Poehl’s Spermine,” Jour. of Phys., vol. xxv., 1900 ; ‘‘ The Composition and Action of Orchitic Extracts,” Jour, of Phys., vol. xxvi., 1901. According to Hervieux, the interstitial gland of the testis contains a ferment which splits neutral fats, and converts dextrin, maltose, and glycogen into glucose but has no action on lactose (C. R. de la Soc, Biol., vol. 1x., 1906). 5 Walker (G.), ‘‘ Experimental Injection of Testicular Fluid,” &c., Johns Hopkins Hospital Bulletin, vol. xi., 1900. 310 THE PHYSIOLOGY OF REPRODUCTION that the constant administration of fresh testicular substance might have led to a different result. Bouin and Ancel } have shown in the horse and other animals that when the vasa deferentia are ligatured the spermatogenetic tissue of the testis ceases to be functional and gradually under- goes degeneration, while the interstitial cells remain unaffected. They point out, further, that those cells have a distinctly glandular appearance, and that their presence suffices for the development of the secondary sexual characters. Consequently they draw the conclusion that the testis is an organ producing an internal secretion which is elaborated by the interstitial cells and not by the spermatogenic tissue. These investigators state, further,” as a result of a series of experiments upon guinea-pigs, that the subcutaneous injection of extract prepared from the interstitial tissue of the testis arrests the effects which castration otherwise would produce upon the rest of the generative system and upon the skeleton.* Their results, therefore, differ from those of Walker. In another paper Bouin and Ancel* state that the injection of similarly prepared testicular extract in guinea-pigs tends to promote growth. In the horse they found that the development of the interstitial gland substance of the adult coincided with the first occurrence of spermatogenesis ; but that there was also a foetal interstitial gland, which disappeared at the end: of gestation, and a slightly developed gland composed of xanthochrome cells, which was only found in the immature animal.® 1 Bouin and Ancel, ‘‘ Recherches sur les Cellules interstitielles du Testicule des Mammiféres,” Arch. de Zool, Hxpér., vol. i., 4th series, 1903. 2 Bouin and Ancel, ‘‘ Action de l'’Extrait de Glande interstitielle du Testicule,” &c., C. R. de ? Acad. des Sciences, vol. cxlii., 1906. 3 Castration in early life, as already mentioned, is said to lead to a prolonged retention of the cartilaginous unions between the bones, especially in those of the limbs. 4 Bouin and Ancel, ‘‘Sur l’Effet des Injections de l’ Extrait de Glande interstitielles du Testicule sur la Croissance,” C, R. de la Soc, de Biol., vol. lxi., 1906. 5 Bouin and Ancel, ‘‘ La Glande interstitielle du Testicule chez le Cheval,” Arch, de Zool. Hxpér., vol. iii., 4th series, 1605. According to Lécaillon the interstitial tissue in the mole’s testis is functionally active during the breeding season, when the testis is sixty-four times larger than during the resting period. (‘‘ Sur les Cellules interstitielles du Testicule de la Taupe con- sidérées en dehors de la Période de Reproduction,” C, R. de la Soc, de Biol., vol, lxvi., 1909). ORGANS OF INTERNAL SECRETION 311 Shattock and Seligmann * also have performed experiments on the results of occluding the vasa deferentia in Herdwick rams and in fowls. The animals operated upon acquired full secondary characters. The authors suppose, therefore, that the development of these characters is not brought about by meta- bolic changes induced by a nervous reflex arising from the function of sperm ejaculation. Foges ® has described the effect of removing the testes of fowls and transplanting them to abnormal positions in the body cavity. In the successful experiments it was found that the presence of functional transplanted testes exercised the same influence over the development of the secondary sexual characters as testes growing in the normal position, and that the appearance of “capon” characters was averted, the comb, wattle, spurs, &c., being developed as in uncastrated cocks. Foges concludes that the testes are organs of in- ternal secretion, and control the development of the male characters. Shattock and Seligmann have also described the effects of testicular transplantation and incomplete caponisation in fowls. In certain cases the testes are stated to have broken up during the operation, so that minute fragments were retained, some- times being left in the normal position, and sometimes becoming dislocated and attached to the adjacent viscera or to the ab- dominal wall. Although these pieces of testicular substance continued to produce spermatozoa, they were virtually ductless glands. In such cases the secondary sexual characters of the cock developed to a varying extent which seemed to depend upon the amount of testicular substance left behind. “ One must regard the external character of maleness as a quantity which varies proportionately with the amount of gland tissue present.” 1 Shattock and Seligmann, “ Observations upon the Acquirement of Secondary Sexual Characters, indicating the Formation of an Internal Secre- tion by the Testicle,” Proc. Roy. Soc., vol. Ixxiii., 1904. The sanfe investi- gators also attempted to obtain further evidence by grafting together two cocks, one castrated and the other normal, but these experiments were unfortunately a failure, one of the birds always dying after a short time. Trans. Path. Soc., vol. xlvi., 1905. 2 Foges, “Zur Lehre der secundiren Geschlechtscharaktere,” Pfliger’s Archiv, vol, xciii., 1903. 312 THE PHYSIOLOGY OF REPRODUCTION According to Loewy,’ the injection of testicular substance into young capons causes the development of normal male skeletal characters, as well as a better growth of the comb, &c. Furthermore, Walker 2 states that, in two experiments in which he injected saline extract of cocks’ testicles into two hens daily for several months, the combs and wattles grew in size and became more brightly coloured, reaching a maximum in five months. When the injections were discontinued, the combs and wattles underwent shrinkage and eventually became reduced almost to their original condition. These experiments are of interest, but they would seem to require confirmation before the conclusion can definitely be drawn that the testicular extract exerted an influence upon the sexual characters of the hens, since the combs and wattles of fowls are normally subject to periodic growth which may vary with the individual. It is stated that an imperfectly descended testicle (i.e. a testicle which has failed to descend properly from the abdominal cavity into the scrotal sac) in Man, notwithstanding the fact that it may be without any spermatogenic function, is never- theless of the greatest benefit to its possessor in virtue of its influence over the metabolism. ‘The secondary sexual characters are a far more exact measure of the value of the testicular tissues than are the presence of spermatozoa in the external secretion. It may almost be said that a man’s male plumage is in direct proportion to the weight or amount of testicular tissue present.” ® Perhaps the most conclusive evidence so far adduced in support of the theory that the testis produces an internal secre- tion is that supplied by Nussbaum * as a result of his experi- ments upon frogs. At the approach of the breeding season there is formed in the male frog a thickened pad of skin on the first digit of each fore limb associated with an increased muscular 1 Loewy, ‘‘Neuere Untersuchungen zur Physiologie der Geschlechts- organe,”” Ergebnisse der Phys., vol. ii., 1903. 2 Walker (C. E.) ‘‘ The Influence of the Testis upon the Secondary Sexual Characters of Fowls,” Proc. Roy. Soc. Med., vol. i., 1908. 3 Corner, Diseases of the Male Generative Organs, Oxford, 1907. See also McAdam Eccles, The Imperfectly Descended Testis, London, 1903. 4 Nussbaum, ‘‘ Innere Sekretion und Nerveneinfiuss,’’ Merkel and Bonnet, Ergeb, der Anat. und Entwick., vol. xv., 1905. ORGANS OF INTERNAL SECRETION 313 development in the fore arm. This modification is preparatory to the act of copulation, when the male frog uses its arms in embracing the female, and so assists in pressing out the eggs from the oviduct (see p. 22). If the male frog be castrated, the pad is not formed and the muscles fail to develop. Nuss- baum found that, if pieces of testis from another frog were grafted into the dorsal lymph sac of a frog previously castrated, the secondary sexual characters of the latter developed just as in a normal frog. The transplanted testes, however, after exerting their influence in the way described, underwent a gradual ab- sorption. Nussbaum states, further, that when the nerves supplying the first digit were severed, the pad did not develop, this opera- tion being performed on a normal frog. Similarly if the nerves supplying the clasping muscle of the fore arm were severed, the enlargement did not occur. He concludes, therefore, that the internal secretion formed in the testis has a specific action upon certain local groups of ganglion cells, and that the nerves passing from these to the fore arm and digit convey a stimulus which induces the growth of the muscle and that of the thickened pad. In support of the view that the testis exerts its influence upon the metabolism (at least partially) through the medium of the nervous system, Nussbaum cites an observation of Weber, according to whom an hermaphrodite finch, having an ovary on one side of the body and a testis on the other, showed the charac- teristic female coloration on the ovarian side and the male plumage on the side of the testis. Nussbaum’s conclusion has been controverted by Pfliiger,’ who points out that in other cases the apparent effect of section of nerves is due to loss of sensibility in the parts affected, in con- sequence of which the tissues are not guarded from injury, and further, that the secondary sexual characters of animals are usually arranged symmetrically. The effect produced by one- sided castration is general rather than local, and the operation has little or no influence in destroying the symmetry of the sexual characteristics (¢f., however, Fowler’s statement about fallow deer, which appears to be exceptional). It is probable, therefore, 1 Pfliger, ‘‘Ob die Entwicklung der sekundaren Geschlechts-charaktere vom Nervensystem abhangt?”’ Pfliiger’s Archiv, vol. cxvi., 1907. 314 THE PHYSIOLOGY OF REPRODUCTION that Pfliiger is correct in supposing that the internal secretion of the testis acts as a direct stimulus upon the cells of the frog’s arm, and so induces the development of the sexual pad and the hypertrophy of the muscle.’ There is some evidence to show that, after one-sided castration, the remaining testis is capable of undergoing a compensating hypertrophy.? If this is so, it affords an additional indication that the testis is an organ of internal secretion. THE CORRELATION BETWEEN THE OVARY AND THE OTHER FEMALE ORGANS AND CHARACTERS It has long been known that the ovary, like the testis, exerts a profound influence over the metabolism, and that the ex- tirpation of this organ, no less than castration in the male, leads to very distinct results. In the human female double ovariotomy, if carried out before puberty, besides preventing the onset of puberty and the occurrence of menstruation, produces noticeable effects on the general form and appearance, as may be seen in adult women in semi-barbarous parts of Asia, where the natives perform this operation upon young girls. Such women are said to be devoid of many of the characteristics of their sex, and in certain cases to present resemblances to men. In some female animals, also, the removal or incomplete de- velopment of the ovaries has been said to lead to the appearance of male characters. For example, Rérig * records three cases in which female deer possessed horns, and were found upon exami- nation to show abnormalities in the ovaries. Darwin ‘also states that female deer have been known to acquire horns in old age.® 1 See also Nussbaum, ‘‘ Hoden und Brunstorgane,” &c., Pfliiger’s Arch., vol. cxxvi., 1909. For further references to the literature of testicular transplantation, see Boruttau, ‘‘ Innere Sekretion,’ Nagel’s Handbuch der Physiologie des Menschen, Braunschweig, 1906. 2 Ribbert, ‘‘ Beitrage zur kompensatorischen Hypertrophie,” &c., Arch. f. Entwick.-Mechanik, vol. i., 1894. 3 Rorig, ‘‘ Ueber Geweihentwickelung,” &c., Arch. f. Entwick.-Meéchanik, vol. x., 1900. 4 Darwin, Variation in Animals and Plants, Popular Edition, London, 1905. 5 Smith (F.) (Veterinary Physiology, 3rd Edition, London, 1907) states that female cats, whose ovaries have been removed while young, acquire a head of ORGANS OF INTERNAL SECRETION 315 Better instances of this kind of phenomenon have been recorded from among poultry, game birds, and ducks, which, on growing senile, have been observed to acquire some of the secondary male characters. Darwin! refers to the case of a duck which, when ten years old, assumed the plumage of the drake. He also mentions an instance of a hen which in old age acquired the secondary sexual characters of the cock. Hunter ® described a case of a hen pheasant which had male plumage correlated with an abnormal ovary, and many other such instances have been recorded. Gurney ®* states that the assumption of male plumage is frequently (but not invariably) associated with barrenness in female gallinaceous birds but not as a rule in passerine birds. The phenomenon has been observed in black grouse,-capercaillie, wild duck, widgeon, merganser, and various other species belonging to different orders. On the other hand, Gurney records instances of a hen chaffinch with male plumage and an unlaid egg, a hen redstart with male plumage and a number of developing eggs, as well as similar cases of hen pheasants. The male plumage may be only tem- porarily assumed. Further examples of the assumption of male plumage by hen birds are recorded by Shattock and Seligmamn,4 who describe the phenomenon under the name of allopterotism. Some of these cases are regarded as of the nature of partial hermaphroditism. It would appear possible that the secondary male characters are normally latent in the female, and that the ovaries exert an inhibitory influence over their development. On the male type (with well-developed tissues in the jowl, the exact converse occurring in castrated males), Herbst, who also discusses this question (Formative Reize in der Tierischen Ontogenese, Leipzig, 1901), expresses the belief that the gonads in either sex exercise a definite inhibitory influence, preventing the appearance of the secondary sexual characters of the opposite sex. 1 Darwin, loc. cit. ° Hunter, * Account of an Extraordinary Pheasant,” Phil. Trans., vol. lxx., 1780. 3 Gurney, “ On the Occasional Assumption of Male Plumage by Female Birds,” Ibis, vol. vi., 5th series, 1888. 4 Shattock and Seligmann, An Example of True Hermaphroditism in the Common Fowl, with Remarks on the Phenomena of Allopterotism,” Trans. Path, Soc., vol. lvii., 1906. ‘‘An Example of Incomplete Glandular Hermaphroditism in the Domestic Fowl,” Proc. Roy. Soc. Med., Path. Section vol. i. (November), 1907. 316 THE PHYSIOLOGY OF REPRODUCTION the other hand, there is no clear evidence that castration in the male animal leads to the assumption of female characters, ex- cepting in a negative sense (7.e. excepting in so far as it inhibits the development of male characters). The operation of complete ovariotomy is impracticable in birds owing to the diffuse condition of the ovary and the close proximity of the vena cava, and in de-sexing pullets (or con- verting them into “ poullardes ’’) the usual practice is to remove a portion of the oviduct or destroy in some other way its func- tional relation with the ovary.!_ This operation is believed to favour growth and fattening, but the result may be due simply to the fact that the albumen and the other products of oviducal secretion are no longer produced. According to Brandt,? the absence of a functional oviduct may be correlated with male characters and a normal ovary, this being stated to be the case in Ruticilla phanicurus, but such a fact seems on the face of it unlikely excepting on the assumption that a partial hermaphroditism existed. Ovariotomy performed subsequently to puberty in women produces less marked results than when carried out in early life. The most noticeable effect is the cessation of menstruation, and this is sometimes accompanied by an atrophy of the breasts and a tendency towards obesity. Most authorities are agreed that the uterus undergoes atrophy after the removal of the ovaries in adult life, and that castration in children and young animals arrests the development of the uterus.? These results are usually ascribed to the absence of ovarian influence, though a few authors seem disposed to dissent from this view (see below, p. 345). Thus, Hofmeir 4 and Benkiser 5 _1 Wright, The New Book of Poultry, London, 1902. Laycock, Nervous Diseases of Women, London, 1840. 2 Brandt, ‘‘ Anatomisches und Allgemeines iiber die sogenannte Hahnen- fedrigkeit und iiber anderweitige Geschlechtsanomalien bei Végeln,” Zeitschr. Sf. wiss. Zool., vol. xlviii., 1889. 3 Kehrer, Bettrage zur Klin. und Exper. Geburtskunde, Giessen, 1877. Hegar, Die Kastration der Frauen, Leipzig, 1878. Selheim, ‘ Die Physiologie der Weiblichen Genitalien,’ Nagel’s Handbuch der Physiologie des Menschen, vol. ii., Braunschweig, 1906. This article contains further references. 4 Hofmeir, “ Ernahrung und Riickbildungsvorginge bei Abdominal- tumoren,” Zettsch. f. Geburtsh. u. Gyndk., vol. v. 5 Benkiser, Verhandl, d. Deutsch. Gesell. f. Gynak., Fourth Congress, 1891. ORGANS OF INTERNAL SECRETION 317 ascribe the degenerative changes to an insufficiency in the blood supply consequent upon the operation of removal, while Sokoloff * and Buys and Vandervelte ? have supposed these changes to be due to a severance of nerves passing to the uterus. In a series of experiments performed recently ? upon the effects of ovariotomy in rabbits, it was found that the extent to which the degenerative process was carried was roughly proportional to the time which had elapsed between the opera- tion and the killing of the animal. After an interval of six and a half months the uterus was found to be in a condition of pro- nounced fibrosis and to contain no glands. The epithelium was much attenuated, and the muscle fibres were broken up. A few small capillaries, however, could still be seen in the stroma. The Fallopian tubes also underwent atrophy. In other experiments in which the ovaries were removed from very young immature rabbits, which were killed after they had grown up, it was found that the uteri, although they had undergone slight development, were quite infantile, being no larger than those of rats. The Fallopian tubes were affected similarly. In all these experiments great care was taken to avoid interference with the blood supply to the uterus, the uterine branches of the pelvic vessels and the anastomotic branch of the ovarian artery being left: uninjured. Furthermore, in certain other cases in which hysterectomy was performed instead of ovariotomy, and which, therefore, may be regarded as con- trols to the first series of experiments, the extirpation of the uterus had no arresting influence on the growth and nutrition of the ovaries (see p. 348). Other and more conclusive evidence in support of the theory that the ovary is an organ of internal secretion is supplied by the results of various attempts to transplant ovaries. The cases of Hose Olney Gules cad Eke Bis Gaal ovaries from one woman to another, are described below in discussing the causes of the menstrual function (p. 331). 1 Sokoloff, ‘‘ Ueber den Einfluss der Ovarienextirpation auf Structur- verinderungen des Uterus,” Arch. f. Gyndk., vol. li., 1896. ? Buys and Vandervelte, ‘‘ Recherches Expérimeéntales sur les lésions consécutives & l’Ovariotomie Double,” Arch. Ital. de Biol., vol. xxi., 1894. 3 Carmichael and Marshall, ‘‘ The Correlation of the Ovarian and Uterine Functions,” Proc. Roy. Soc. B., vol. lxxix., 1907. 318 THE PHYSIOLOGY OF REPRODUCTION Knauer? has described experiments upon rabbits in which he removed the ovaries from the normal position and grafted them upon the mesometrium or between the fascia and the muscle of the abdominal wall. He found that they could be successfully implanted on both peritoneum and muscle, but that some portion of the grafted ovary invariably died. The Fia. 67.—Transverse section through rabbit’s uterus after ovariotomy, showing degenerative changes. (From Blair Bell, British Medical Journal and Trans, Royal Society of Medicine, ) rest, however, remained functionally active, and continued to produce ova which were capable of being fertilised. Knauer states that whereas castration in female rabbits produced a premature menopause, the uterus undergoing atrophy, this result was prevented by a successfully transplanted ovary. Knauer also experimented upon dogs and obtained similar results. 1 Knauer, “‘ Die Ovarien-Transplantation, Experimentelle, Studie,” Arch. f. Gyndk., vol. 1x., 1900. ORGANS OF INTERNAL SECRETION 319 Grigorieff," Ribbert,? and Rubinstein * carried out experi- ments upon rabbits which confirmed those of Knauer, the ovaries being transplanted in various abnormal positions. Grigorieff also records two cases in which ovaries were success- fully transplanted from one individual to another (heteroplastic transplantation). Ribbert found, in his experiments, that Fic. 68.—Transverse section through bitch’s uterus 9} months after ovariotomy. (From Blair Bell, British Medical Journal and Trans. Royal Society of Medicine.) during the first month after transplantation the peripheral part of the grafted ovary remained unaltered, but the central part became transformed into connective tissue. At a later period, however, the central portion was again found to contain follicles. This fact is attributed to the conditions of increased nutrition which Ribbert supposed to prevail when the ovaries had been 1 Grigorieff, ‘‘ Die Schwangerschaft bei Transplantation der Eierstécke,” Central, f. Gyndk., vol. xxi., 1897. 2 Ribbert, “ Uber Transplantation von Ovarien, Hoden, und Mamma,” Arch. f. Entwick.-Mechanik, vol. vii., 1898. ® Rubinstein, ‘‘Extirpation beiden Ovarien,” St. Petersburg Mediz. Wochenschr., 1899. AIM 320 THE PHYSIOLOGY OF REPRODUCTION transplanted for a sufficiently long ‘period to admit of their having acquired better vascular connections. Halban+ found that the uterus and mammary glands of guinea-pigs from which the ovaries had been removed shortly after birth, remained undeveloped; but, if the ovaries were removed from the normal position and grafted underneath the skin, the other generative organs developed normally. Limon,? working upon rabbits, grafted ovaries beneath the muscle layers of the abdominal wall and on to the peritoneum of the same individuals. The follicles showed a tendency to degenerate, but the interstitial cells, after a short period of starvation, subsequently recuperated and acquired a con- dition of perfect vitality. Limon states that he found no sign of atrophy in the uterus after the transplantation of the ovaries to an abnormal position. . Carmichael * has recorded some success from experiments in ' Halban, ‘Ueber den Einfluss der Ovarien auf die Entwickelung des Genitales,”’ Monatschr. f. Geburtsh. u. Gyndk., vol. xii., 1900. 2 Limon, “ Observations sur l’Etat de la Glande Interstilielle dans les Ovaries Transplantés,” Jour, de Phys, et de Path. Gén., vol. xvi., 1904. 3 Carmichael, “The Possibilities of Ovarian Grafting in the Human Subject,” &c., Jour. of Obstet. and Gynec., March, 1907. Ovarian trans- plantation in different species of animals has also been carried out by Herlitzka (‘‘ Recherches sur la Transplantation des Ovaries,” Arch, Ital. de Biol., vol, xxxiv., 1900), Fok (‘‘ La Graffe des Ovaries en Relation avec Quelques Questions de Biologie,” Arch. Ital. de Biol., vol. xxxiv., 1900), Schultz (‘‘ Transplantation der Ovarien auf Mannliche Tiere,” Central. f. All. Path. u. Path, Anat., vol. xi., 1900), Guthrie (‘Successful Ovarian Transplantation in Fowls,” Internat. Congress of Phys., Heidelberg, 1907, Abstract in Zett. f. Phys., vol. xxi., 1907; ‘‘ Further Results of Transplantation of Ovaries in Chickens,” Jour. of Hxp. Zool., vol. v., 1908). Schultz and other investigators, without reference to the ovarian secretion theory, grafted the ovaries of guinea-pigs on to the bodies of males and recorded some success. Herlitzka also grafted the ovaries of guinea-pigs on to other individuals (heteroplastic transplantion), some females and some males, Only one experiment was at all successful, the ovary being transplanted on to a female, Foa was successful with several heteroplastic grafts in rabbits, and even succeeded in inducing pregnancy in an animal with a transplanted ovary. Guthrie’s experiments were upon fowls. He states that the ova in the heteroplastically transplanted ovaries were influenced by the ‘“ foster mother” (2.e. the birds into whom they were grafted), since the offspring which resulted from fertilising these ova par- took of some of the foster-mother’s characters. For a few further references see Marshall and Jolly, ‘‘ Results of Removal and Transplantation of Ovaries,” Trans. Roy. Soc. Edin., vol. xlv., 1907, and ‘‘ Heteroplastic Transplantation,” &c., Quar. Jour. Exp. Phys., vol. i., 1908; and Sauvé, Les Greffes Ovariennes, Paris, 1909. ORGANS OF INTERNAL SECRETION 321 which the ovaries of rabbits were transplanted on to abnormal positions in the same individuals (homoplastic transplantation), but there is no evidence in those cases that the grafted ovaries had any influence in preventing the degeneration of the uterus. Fig. 69.—Section through ovary of rat after transplantation on to peritoneum, showing ovum, normal follicles, and follicles which have undergone cystic degeneration. (From Marshall and Jolly.) The present writer also, working in conjunction with Dr. Jolly,! carried out a series of experiments upon rats in order to determine whether any histological changes occurred in the 1 Marshall and Jolly, loc. cit. x 3922 THE PHYSIOLOGY OF REPRODUCTION uterus after transplanting the ovaries to new situations. Other experiments were undertaken in which the ovaries were simply removed without being transplanted. The rats were killed at Fic. 70.—Section through ovary of rat after transplantation on to peritoneum, showing corpora luteum and small follicle with ovum. (From Marshal] and Jolly.) intervals varying from one to fourteen months after the opera- tion. In the control animals pronounced fibrosis or other atrophic appearances were always found in the uterus. On the ORGANS OF INTERNAL SECRETION 323 other hand, in those animals in which ovaries had been success- fully transplanted on to abnormal positions (such as on to the ventral peritoneum or into one of the kidneys) the uterus was found undegenerated. If, however, the ovarian graft failed to Fig. 71.—Transverse section through normal uterus of rat. (Cf. Figs. 72 and 73, From Marshall and Jolly.) “take,” or was only partially successful, the uterus presented undoubted signs of degeneration. In the cases of transplanta- tion from rat to rat, as in homoplastic transplantation, uterine degeneration was found to be arrested by a successful ovarian graft. $24 'THE PHYSIOLOGY OF REPRODUCTION The successfully transplanted ovaries exhibited all the characteristic histological features of normal ovarian tissue, excepting that the germinal epithelium was invariably absorbed after the lapse of a short interval. In some cases a certain. amount of degenerative change took place, only certain ele- ments of the tissue being recog- nisable after the lapse of several months; thus, the stroma might present its normal appearance while the follicles had disap- peared, or the greater. part of the graft might be composed of luteal tissue alone. It was also observed that the successfully transplanted ovaries underwent the same cyclical changes as normal ovaries. Thus, in animals~ killed shortly before the com- mencement of the breeding season, large follicles were found in the grafts, while at a later period corpora lutea were present, showing that ovulation had occurred in the transplanted ovaries. In one case, a homo- plastic graft was found to be Vie. 72, — ‘Transverse section Normal after fourteen months, through uterus of rat after While a normal _heteroplastic ovariotomy, showing degener- graft was composed entirely pon bamasrned ae aa of healthy ovarian tissue (with Jolly.) follicles and ova) after six months. In these experiments the ovaries were grafted into the substance of the kidneys. Homoplastic transplantation was found to be more easily accomplished than heteroplastic transplantation. This result could hardly be ascribed to increased difficulties in the per- formance of the latter operation, since the technique was identical in each case. Furthermore, our successes in hetero- plastic transplantation were usually obtained in experiments ORGANS OF INTERNAL SECRETION 325 in which two rats from the same litter were known to have been employed, so that the ovaries were grafted into whole sisters, but we were not sure of the relationship in every case. Fic. 73.—Transverse section through uterus of rat after ovarian trans- plantation. The uterus is normal. (See text and cf, Figs. 71 and 72. From Marshall and Jolly.) These experiments clearly indicate that the nature of the ovarian influence is chemical rather than nervous, since the suc- cessfully grafted ovaries, while still maintaining their functions, o 326 THE PHYSIOLOGY OF REPRODUCTION had lost their normal nervous connections. It is probable, therefore, that the uterus depends for its proper nutrition upon substances secreted by the ovaries. Further evidence in support of the view that the ovary pro- duces an internal secretion is provided by the results of ovarian medication or the administration of preparations of ovarian substance for medicinal purposes. It is somewhat difficult, however, to know precisely what value to assign to this practice about which medical authorities still appear to differ. Brown- Séquard* seems to have been the first to employ ovarian ex- tracts medicinally. He supposed them to produce similar effects to those brought about -by testicular extracts, but they did not appear to be so powerful. Since Brown-Séquard’s time ovarian preparations have been used medicinally in a large number of cases with more or less successful results. The fresh ovaries are themselves taken, or ovarian tissue is given in the form of fluid or powder (ovarine, odphorine, ovigenine, &c.). The fresh ovaries or ovarian powder are eaten, but the fluid can be administered either by the mouth, by the rectum, or b ie aie adon Nes te or Geeta ae to have met with considerable success in cases of amenorrhea, chlorosis, and menopause troubles, both natural and_post- operative. Some physicians, however, report only a very moderate or doubtful success, while a few state that the results are nearly always unsatisfactory.? The method of administering the extract by the mouth is open to the criticism that the “‘ active principle ” of the ovarian secretion may be altered in the meta- bolic processes of digestion. Moreover, it is by no means certain that the ‘‘ active principle ” may not be destroyed in the manu- facture of the preparations. Again, it is not unlikely that the effects of ovarian medication may depend, not only upon the method of preparing the extracts, but also upon the condition of the ovaries from which the extracts are made, and it would seem unreasonable to expect to obtain uniform results from the indiscriminate usage of ovaries in different stages of cyclical 1 Brown-Séquard, ‘Des Effets produits chez Homme par des Injec- tions,” &c., C. BR. de la Soc, de Biol., 1889. 2 For references to the literature of ovarian medication, see Andrews, ‘Internal Secretion of the Ovary,” Jour. of Obstet. and Gyn., vol. v., 1904. in- ot 3 ORGANS OF INTERNAL SECRETION th prominent follicles like those from or ovaries with corpora lutea like those of ovaries wi activity (e.4. “on heat,” animals ws sat (ay = Reg 4. into the tissue of which an ovary (From Marshall and Jolly, Quart. Jour. of 's kidney, Fic. 74.—Section through rat’ had been transplanted. Experimental Physiology.) ar, artery; cl., corpus luteum; g.f., Graafian follicle ; gl., glomerulus of zone of 2,46, ’ renal tubule granulation tissue between ovarian tissue and tissue of kidney. kidney ; ov.st., ovarian stroma; 7.t, 328 THE PHYSIOLOGY OF REPRODUCTION pregnant animals, or ovaries in a state of relative quiescence like those of ancestrous animals). The effects of ovarian medication are discussed at some length in a memoir by Bestion de Camboulas, who describes a large number of experiments upon dogs, rabbits, and guinea- pigs, as well as a series of clinical observations. Experiments were performed on male animals as well as on female ones. The lethal injection of ovarian extract was found to be about twice as much in non-pregnant females as in males or pregnant females. With non-toxic doses the females gained weight, but the males lost weight. The lesions discovered after lethal doses were congestion of the viscera, and minute hemorrhages in the dorsal and lumbar regions of the spinal cord. Bestion also administered ovarian extract to his patients, and states that he obtained distinctly beneficial results. Menopause troubles are described as either disappearing altogether or becoming much ameliorated, while rapid improvement was observed in cases of chlorosis and amenorrhcea. Bestion says that ovarian extract should never be administered. to pregnant women, since it causes such grave results when given to pregnant animals. Jentzner and Beuttner® found that the subcutaneous in- jection of ovarian extract in castrated animals did not supply the place of living ovarian substance, and Mr. Carmichael and the present writer * experienced a similar result after making a series of intra-peritoneal injections of commercial extract, the uterine atrophy which followed ovariotomy being in no degree diminished. It has been shown that the ovary possesses considerable capacity for regenerating tissue after partial removal, and also that if one ovary is extirpated the remaining one may undergo an apparent increase in size, which is probably of the nature of a compensatory hypertrophy. These facts may perhaps be re- garded as supplying some further evidence that the ovary is an organ of internal secretion * (c/. the testis, p. 314). 1 Bestion de Camboulas, “‘ Le Suc Ovarien,” Paris, 1898. ? Jentzner and Beuttner, ‘ Experimentelle Untersuchungen zur Frage der Castratinsatrophie,”’ Zetischr. f. Geburtsh. u. Gyndk., vol. xlii., 1900. 3 Carmichael and Marshall, loc, cit. 4 Carmichael and Marshall, ‘‘ On the Occurrence of Compensatory Hyper- trophy in the Ovary,” Jour. of Phys., vol. xxxvi., 1908. ORGANS OF INTERNAL SECRETION 329 According to Loisel,’ the ovary fulfils a purifying function in the organism, absorbing injurious products which are excreted with the ova or absorbed as internal secretions. This theory seems to have little experimental basis at present. Tue Factors WHICH DETERMINE THE OCCURRENCE or Heat aND MENSTRUATION Pfliiger * advanced the theory that menstruation is brought \ about by a nervous reflex, owing its origin to the pressure of the growing Graafian follicles upon the nerve endings in the ovary. _ This view received some support from Strassmann,? who claimed to have induced “ heat ’’ in animals by injecting gelatine into their ovaries, and so producing intra-ovarian pressure. Elizabeth Winterhalter’s 4 alleged discovery of a sympathetic ganglion in the ovary also tended to support this theory ; but Von Herff * discredited her description, which, so far, has re- ceived no confirmation. Goltz ® showed that heat in animals is not brought about by a cerebral or spinal reflex. In one experiment the spinal cord of a bitch was transected in the lumbar region ; normal procestrum, followed by cestrus and conception, occurred as usual, but copulation was unaccompanied by sensation, though the animal showed a marked inclination towards the dog. In another experiment the lumbar part of the spinal cord was completely removed without interfering with the cyclical * Loisel, ‘‘ Les Poisons des Glandes génitales,” C. R. de la Soc. de Biol., vol. lv., 1903; vol. lvi., 1904; and vol. lvii., 1904. 2 Phliiger, Uber die Bedeutung und Ursache der Menstruation, Berlin’ 1865. ® Strassmann, Lehrbuch der gerichtlichen Medizin, 1895. + Winterhalter, ‘‘ Ein Sympathisches Ganglion im Menschlichen Ovarium’,, Arch. f. Gyniik., vol. li., 1896. 5 Von Herff, ‘‘Giebt es ein Sympathisches Ganglion im Menschlichen Ovarium,” Arch. f. Gyndk., vol. li., 1896. For information upon the innerva- tion of the ovary, see Von Herff, ‘‘ Uber den feineren Verlauf der Nerven im Hierstock,” Zettschr. f. Geb. u. Gynak., vol. xxiv., 1893. ® Goltz, ‘‘Ueber den Einfluss des Nervensystems auf die Vorginge wihrend der Schwangerschaft und des Gebarakts,” Pjliiger’s Archiv, vol. ix., 1874. Goltz and Ewald, ‘‘ Der Hand mit verkiirztem Riickenmark,” Pfliiger’s Archiv, vol. lxiii., 1896. 330 THE PHYSIOLOGY OF REPRODUCTION recurrence of procestrum and cestrus. Moreover, Sherrington,’ after transecting the spinal cord of a bitch in the cervical region, and headwards of the connection between the sympathetic system and the cord, observed that heat of normal duration and character continued to recur in the animal so operated upon. The case, described by Brachet,” of a woman suffering from paraplegia in the lower part of the body and legs, but who conceived and became pregnant, may also be cited. There are other facts which indicate that menstruation is not caused by a nervous reflex set up by ovulation or by the pressure of the growing follicles. Gynecologists have pointed ‘out that in the human subject ovulation and menstruation are not necessarily associated, and Heape* has shown that the ovaries of menstruating monkeys do not always contain follicles in a state approaching ripeness. But whereas the evidence is clear that heat and menstruation are not brought about by nervous reflexes arising from the ovary, it is equally obvious that these processes are dependent upon some ovarian influence. For, if the ovaries are removed, heat and menstruation no longer take place. Some authors, however, have denied this, and cases have been cited of the occurrence of menstruation after surgical ovariotomy. For example, three cases have recently been described by Doran,* in each of which the two ovaries were believed to have been removed, although menstruation recurred at irregular intervals after the operation. Further cases have lately been reported by Blair Bell *® and other writers. It seems probable that these exceptional cases are to be explained on the supposition that the extirpation of ovarian substance was not quite complete, and that the tissue which remained behind underwent hypertrophy subsequently to the operation. That 1 Sherrington, The Integrative Action of the Nervous System, London, 1906. 2 Brachet, Recherches, 2nd Edition, Paris, 1837. 3 Heape, ‘The Menstruation and Ovulation of Macacus rhesus,” Phil. Trans. B., vol. clxxxviii., 1897. 4 Doran, ‘‘ Sub-total Hysterectomy for Fibroids,’ Lancet, Part II., November, 1905. 5 Blair Bell, ‘ Preliminary Note on a New Theory of Female Generative Activity,” Liverpool Medico-Chirurgical Journal, July 1906. ORGANS OF INTERNAL SECRETION 331 this is the true interpretation is rendered the more probable in view of the cases referred to by Gordon,’ Doran,” Meredith,® and others, in which pregnancy occurred after the supposed removal of both ovaries (see also, p. 343). Doran # also records a large series of cases in which menstruation entirely ceased after ovariotomy.° Morris * gives an account of a woman aged twenty, who suffered from amenorrheea, her uterus being infantile. He states that he transplanted on to her fundus uteri an ovary which he obtained from another woman, aged thirty. The transplantation is said to have been successful, inducing men- truation after two months. In another case Morris” states that he transplanted an ovary into a woman whose own ovaries had been previously removed, and that the graft was so far successful that conception, followed by a normal pregnancy, occurred as a result. It has been suggested, however, that in this case a portion of the woman’s original ovary may have been left behind, and that this accounted for the pregnancy (cf. p. 343). Glass ® describes a case of a patient who was suffer- ing from menopause troubles due to the extirpation of the ovaries. After the transplantation of an ovary from another woman had been effected, the patient was gradually restored to health and menstruation was renewed. Dudley * mentions a case in which a double pyosalpinx was removed, and the right 1 Gordon, ‘‘Two Pregnancies following the Removal of Both Tubes and Ovaries,” Trans. Amer. Gynec. Soc., vol. xxi., 1896. 2 Doran, ‘‘ Pregnancy after the Removal of Both Ovaries,” Jour. Obstet. and Gynec., vol. ii., 1902. 3 Meredith, ‘‘ Pregnancy after Removal of Both Ovaries,” Brit. Med. Jour,, Part I., 1904. 4 Doran, ‘‘ Sub-total Hysterectomy for Fibroids,” Lancet, Part II., Nov. 1905. 5 The continuance of menstruation after the removal of two ovaries may be due to the presence of accessory ovaries which are occasionally known to exist. § Morris, ‘‘ The Ovarian Graft,” New York Med. Jour., 1895. 7 Morris, ‘‘A Case of Heteroplastic Ovarian Grafting followed by Pregnancy,” &c., New York Med. Jour., vol. lxix., 1906. 8 Glass, ‘‘An Experiment in Transplantation of the Entire Human Ovary,’ Medical News, 1899. ® Dudley, ‘‘ Uber Intra-uterine Implantation des Ovariums,” Internat. Gyn. Congress, Amsterdam, 1899. Re acide page? 332 THE PHYSIOLOGY OF REPRODUCTION ovary implanted on the fundus uteri. The patient menstruated regularly afterwards. Again, in a case recorded by Cramer of Bonn,' the ovary of a woman suffering from osteomalacia was extirpated and transplanted into a second woman whose genital organs were much atrophied. As a result of the graft the genital organs of the woman in whom the ovary was trans- planted became normal, menstruation started once more, and the breasts secreted colostrum. In none of these cases, how- ever, is there any record of post-mortem evidence showing that the transplanted ovaries had become successfully attached. Halban? states that he found in monkeys that, whereas menstruation ceased after double ovariotomy, it recurred again after ovarian transplantation, even though the ovary was grafted in a position different from the normal one. Those cases already referred to, in which atrophy of the uterus took place after the removal of the ovaries, also indicate the dependence of the menstrual and procestrous functions upon the presence of ovarian tissue, since normal heat could not occur if the uterus were in a condition of fibrotic degeneration, while certain of Knauer’s experiments * afford evidence that heat can be experienced by animals in which the ovaries are transplanted to abnormal positions. Veterinarians are generally agreed that heat does not occur in dogs whose ovaries have been extirpated. Moreover, ovariotomy is sometimes practised on mares in order to prevent cestrus, and so suppress the vicious symptoms which are liable to render the animals periodically unworkable.* Dr. Jolly and the author * have shown, further, that normal procestrum, followed by cestrus, can occur in dogs which only possess transplanted ovaries, thus confirming the observations of Knauer and Halban. In the experiments in question the animals’ own ovaries were removed, and a few weeks later the 1 Cramer (H.), “ Transplantation menschlicher Ovarien,”’ Miinchen. med. Wochenschr., 1906. 2 Halban, “Uber den Einfluss der Ovarien auf die Entwickelung des Genitales,” Siz.-Ber. Akad. Wissenschaft, Wien, vol. cx., 1901. 3 Knauer, loc, cit. 4 Hobday, ‘‘Ovariotomy of Troublesome Mares,” Veterinary Jour., New Series, vol. xiii., April 1906. Reproduction: Part II. The Ovary as an Organ of Internal Secretion,” Phil, << 5 Marshall and Jolly, ‘‘ Contributions to the Physiology of Mammalian Trans., B., vol. cxcviii., 1905. ORGANS OF INTERNAL SECRETION 333 ovaries obtained from other dogs were grafted in abnormal positions (e.g. between the abdominal muscular layers or on the ventral border of the peritoneal cavity). The grafts seem to have become attached, and to have survived for a sufficiently long period to exercise an influence over the generative system ; but they eventually underwent considerable fibrous degenera- tion, as the post-mortem evidence afterwards showed. As a result of these experiments it may probably be con- cluded that the enhanced activity which the ovaries exhibit during the final stages of follicular development is accompanied by metabolic changes which result in an increase in the pro- duction of the ovarian secretion, and that this phenomenon is the main factor in the periodic recurrence of heat and menstrua- tion.t It has been observed that, not only are the internal and external generative organs affected at these periods, but there is also a distinct hypertrophy of the breasts, and this, as Miss Lane-Claypon and Starling * have pointed out, is pro- bably due also to an increase in the ovarian metabolism.* There is a certain amount of direct evidence that heat and menstruation are brought about by an internal secretion elaborated by the ovaries. It has been found that the injection of fresh ovarian extract obtained from animals which are “ on heat ” may produce in ancestrous animals a transient congestion of the external generative organs resembling that of the normal procestrous condition.t Miss Lane-Claypon and Starling also 1 As already pointed out, menstruation and ovulation are not necessarily associated. It is probable, however, that the ovarian metabolism is increased at the menstrual periods, although there may not always be any follicles present in a sufficiently mature condition to admit of ovulation occurring in the cestrous periods which normally follow them. 2 Lane-Claypon and Starling, »» An Experimental Inquiry into the Factors which Determine the Growth and Activity of the Mammary Glands,” Proc. Roy. Soc., B., vol. lxxvii., 1906. 3 According to Pearl and Surface (“The Nature of the Stimulus which causes a Shell to be formed on a Bird’s Egg,” Science, New Series, vol. xxix., 1909), the stimulus which excites the activity of the shell-secreting glands in the fowl’s oviduct is mechanical, being brought about by a strictly local reflex. The shape of the egg is determined by the muscular activity of the cells of the oviduct (Pearl, ‘‘Studies on the Physiology of Reproduction in the Domestic Fowl: I. Regulation in the Morphogenetic Activity of the Oviduct,” Jour. of Exp. Zool., vol. vi., 1909). 4 Marshall and Jolly, loc, cit. Ke 334 THE PHYSIOLOGY OF REPRODUCTION have described congestion in the uterus after the injection of ovarian extract ; but, in their experiments, the ovaries employed were those of pregnant animals. Further evidence that the procestrous and cestrous conditions are produced by substances circulating in the blood, but not necessarily elaborated in the ovaries, is supplied by certain facts recorded by Halban.t This author affirms that the milk of suckling sows is affected during the periods of heat, in conse- quence of which the young are liable to develop unhealthy symptoms. In a similar way the milk of women is said to be affected during menstruation. Moreover, according to Youatt,” cows can be brought “on heat ”’ artificially by feeding them on milk supplied from other cows which are in that con- dition, Heape * has suggested that heat may be due to a “ generative _ ferment ”’ which he supposes to be periodically present. in the— blood. At the same time he is of opinion that a hypothetical substance called “ gonadin,” which is secreted by the generative glands, is also an essential factor. The precise relation in which gonadin and the generative ferment are supposed to stand to one another is not at present clear, but there is no in- consistency between a belief in their existence and the views which are adopted here. Assuming that heat and menstruation are brought about, either directly or indirectly, through a stimulus depending upon _7 the secretory activity of the ovary, it is still an open_question _ _as_to_what part of the organ is con concerned. in_the_ process. ~ Fraenkel # has supposed that the secretion in _question is supplied by the corpus luteum. This conclusion is based upon nine cases in which the corpus luteum was destroyed by the cautery, and in eight of which the next menstrual period was missed. In the remaining case it is supposed that the secretion responsible for producing menstruation had already been formed in sufficient quantity and passed into the circulation at the time of the cauterisation. Fraenkel’s theory, however, is disproved by the 1 Halban, loc. cit, 2 Youatt, “Cattle, London, 1835. 3 Heape, “ Ovulation and Degeneration of Ova in the Rabbit,”’ Proc, Roy, Soc., B., vol. lxxvi., 1905. 4 Fraenkel, ‘‘Die Function des Corpus Luteum,” Arch. f. Gyndak., vol, lxviii., 1903. ORGANS OF INTERNAL SECRETION 335 fact that ovulation in most Mammals does not occur until cestrus, or, at any rate, until the end of the procestrum (see p. 135), and consequently corpora lutea are not present in the ovaries (for the corpora lutea dating from one cestrus do not always persist until the next cestrus, which may be many months after- wards). Heape’s observations’ on the absence of corpora lutea in menstruating monkeys:-may be again cited in this con- nection. Moreover, Ries* has reported a case of a woman with whom menstruation occurred normally after an operation in which an oozing corpus luteum, which was a source of hemorrhage in the peritoneal cavity, had been peeled out. It should be mentioned that Fraenkel’s views on menstruation are part of a general theory which is discussed more fully below (p. 338). Seeing that the corpus luteum is not responsible for inducing menstruation, it becomes necessary to conclude that either the follicular epithelial cells or the interstitial cells of the ovarian stroma (or both of these) are concerned in bringing about the process (see p. 124). It has already been shown that the breeding season, and consequently the recurrence of the cestrous cycle, are controlled to a great extent by the general environmental conditions, since these affect the physical state of the body (Chapters I. and II.). This is particularly well seen in certain of the domestic animals, in which “ heat’? may be caused to recur more fre- quently by the supply of special kinds of stimulating foods (p. 599). It would appear, therefore, that the metabolic activity of the ovaries is increased by these methods, and that the prob- lematical internal secretion is elaborated in greater quantity. Lastly, it must not be forgotten that, whereas it is exceedingly probable that the procestrous changes of the uterus are brought about by a specific excitant or hormone ® arising in the ovaries, 1 Heape, “ The Menstruation and Ovulation of Macacus rhesus,” Phil. Trans., B., clxxxviii., 1897. 2 Ries, ‘‘ A Contribution to the Function of the Corpus Luteum,” Amer. Jour. Obstet., vol. xlix., 1904. ° Starling has proposed the term hormone (from the Greek, opyaw, I excite or arouse) for such internal secretions or excitants of a chemical nature. Thus, secretin, or the internal secretion of the duodenum, which excites pancreatic secretion, is a hormone. See Starling, “The Chemical Cor- / relation of the Functions of the Body,” Croonian Lectures, London, 1905 ; also Lane-Claypon and Starling, loc. cit, (| ee 336 THE PHYSIOLOGY OF REPRODUCTION little or nothing is known concerning the source of that dis- turbed state of the nervous metabolism, the existence of which during cestrus is so plainly manifested in the display of sexual feeling. Tue FUNCTION OF THE Corpus LUTEUM Various theories have been’ put forward to explain the formation and presence of the corpus luteum. According to one view, which is still sometimes taught, the development of this structure is merely a result of the excessive vascularisation which characterises the entire internal generative tract during the period of pregnancy. Very little consideration of the actual facts is needed to convince one of the inadequacy of this ex- planation. The blood supply to the generative organs is greatest during the later stages of pregnancy, when the corpus luteum is becoming diminished in size. Moreover, the rapid hyper- trophy of the luteal cells takes place independently of pregnancy during the very early stages of development at a time when there is no appreciable congestion of the genital organs. Ac- cording to another theory, the corpus luteum is of the nature of a stop-gap, whose purpose is to preserve the cortical circula- tion of the ovary by preventing an excessive formation of scar-tissue.* Prenant? seems to have been the first to suggest that the corpus luteum was a ductless gland. He supposed it to produce an internal secretion which exercised an influence over the general metabolism in the manner attributed to the internal ovarian secretion. The phenomenon of chlorosis was explained as being due to the absence of this secretion. Prenant supposed also that the corpus luteum had the further function of pre- venting ovulation during pregnancy or between the cestrous periods. This theory was supported by Regaud and Policard,? who 1 Clark, ‘‘ Ursprung, Wachstum, und Ende des Corpus Luteum,” Arch, f. Anat. u. Phys., Anat, Abth., 1898. Whitridge Williams, Obstetrics, New York, 1903. 2 Prenant, ‘‘La Valeur Morphologique du Corps Jaune,” Rev. Gén. des Sciences, 1898. 3 Regaud and Policard, ‘‘ Fonction Glandulaire de l'Epithelium Ovarique chez la Chienne,” C. R. de Soc. de Biol., vol. liii., 1901. ORGANS OF INTERNAL SECRETION 337 stated that, by means of special methods of staining, droplets of a secretory substance could be detected in the cells of the corpus luteum of the hedgehog. Beard * independently suggested that the corpus luteum is a contrivance to suppress ovulation during pregnancy, while he supposed it to degenerate before parturition in order to admit of ovulation occurring immediately afterwards. It must be pointed out, however, that in many Mammals, if not in the majority, the breeding season does not recur until after an ancestrous period, which is often of considerable duration, and that it is extremely improbable that ovulation occurs during this period. Beard’s theory has been adopted by Sandes,? who investi- gated the corpus luteum of the marsupial cat (Dasyurus viver- rinus, see p. 149). This author states that in Dasyurus, as in most other Mammals, the corpus luteum disappears towards the end of the lactation period, when the next cestrus is ap- proaching, and the follicles are beginning to grow in preparation for the ensuing ovulation. He says, further, that as soon as the corpus luteum is formed, the ova in the surrounding follicles, which were up to that time in various stages of active de- velopment, begin to undergo atrophy. This atrophy com- mences in the follicles in closest proximity to the newly formed corpus luteum, and is continued in the surrounding follicles in ever-widening circles. Sandes suggests, that this result is brought about by mechanical pressure, or is due to the internal secretion of the corpus luteum, if it has one. Without in any way disputing the accuracy of the facts which Sandes describes, it is difficult to understand what advantage is gained by a mechanism having a not more important object than that of securing the degeneration of the surplus ova within the ovary instead of externally to it, and it is not easy to see how, ac- cording to the usually accepted doctrines of utility and natural selection, an organ having such a purposeless function could ever have been developed at all. Gustav Born was the first to suggest that the function of 1 Beard, The Span of Gestation and the Cause of Birth, Jena, 1897. 2 Sandes, “The Corpus Luteum of Dasyurus viverrinus,” Proc. Linnean Soc., New South Wales, vol. xxviii., 1903. Y 3838 THE PHYSIOLOGY OF REPRODUCTION the corpus luteum might be to provide an internal secretion which assisted in the attachment of the embryo to the uterine mucosa. Unable to undertake the investigation himself, he~ persuaded Ludwig Fraenkel to put his theory to an experi- mental test. For this purpose a series of experiments upon rabbits was proceeded with, the ovaries being removed at intervals varying from one to six days after the occurrence of coition, the period of gestation in this animal being thirty days. The rabbits were afterwards killed, when it was found that the extirpation of the ovaries had prevented the fixation of the embryos, or had caused these to be aborted. In other cases the corpora lutea are described as having been burnt out by the electric cautery without destroying the rest of the ovaries, and these experiments led to a similar result. Control experi- ments were performed by removing one ovary while leaving the other, and by destroying some of the corpora lutea but not all, and in the majority of these cases the animals produced young. The experiments resulted, therefore, in supporting the view that there is an intimate connection between the presence of the corpus luteum and the occurrence of pregnancy, and that this connection is in a certain sense one of cause and effect. Apart from the experimental evidence, Fraenkel adduces certain other facts which tend to support the theory that the corpus luteum is an organ of internal secretion. He points out that its general structure is eminently suggestive of its being a ductless gland, since it is formed mainly of large epitheloid cells surrounded by a network of capillaries and arranged in regular rows or columns not unlike those of the cortex of the supra-renal body. Moreover, the increase in the size of the corpus luteum, until it becomes larger than a Graafian follicle, seems inexplicable on any other view. This unusual capacity for growth is clearly out of all proportion to that of the rest of the ovary, and it is pointed out, further, that when the corpus luteum is most hyperemic, the other part of the ovary is unusually anemic, while towards the end of pregnancy, when the increase in the blood supply to the generative organs 1 Fraenkel and Cohn, ‘‘ Experimentelle Untersuchungen tiber den Einfluss des Corpus Luteum auf die Insertion des Hies,” Anat, Anz., vol. xx., 1901; Fraenkel. loc. cit. ORGANS OF INTERNAL SECRETION 339 is at its height, the corpus luteum is often reduced to little more than a scar. Fraenkel also lays some stress on the discovery that the luteal cells are derived from the follicular epithelium and not from the connective tissue of the stroma. Furthermore, he observes that whereas many cases have been recorded in which double ovariotomy was performed during pregnancy without interfering with the further course of development, in none of these, so far as he is aware, was the operation conducted in the early weeks. Fraenkel observes also that in non-placental Mammals (Marsupials and Monotremes) the corpus luteum is rudimentary or does not exist at all. Sandes,1 who has carefully described the formation of the corpus luteum im the marsupial cat, points out that this is erroneous, and says that there is a large corpus luteum in the members of both these groups. It should be remembered, however, that in Marsupials the embryo is nourished by a “ yolk-sac placenta,’’ while in at least one genus (Perameles) a definite allantoic placenta exists. In Monotremes there is a pronounced hypertrophy of the follicular epithelium following upon ovulation, but the corpus luteum is not normal in this group, since there appears to be no ingrowth of con- nective tissue or blood-vessels from the follicular wall (see p. 149). A similar objection, that might be raised in opposition to Fraenkel’s hypothesis, is that structures resembling corpora lutea have been found in the ovaries of certain of the lower Vertebrates (see p. 151). This resemblance relates chiefly to the hypertrophy of the cells of the follicular epithelium after the discharge of the ova. Such an objection is not to be regarded as a serious one, for there is nothing improbable in the sup- position that rudimentary corpora lutea, providing probably some sort of secretion, should have been developed before the acquirement of the function, which, according to Fraenkel’s hypothesis, is possessed by the fully formed structure which characterises the placental Mammalia. Fraenkel has also pointed out, as an argument in favour of his theory, that in ectopic or extra-uterine pregnancy the uterus undergoes the usual changes although there is no ovum in the uterine cavity. It is clear, therefore, that the changes do 1 Sandes, loc, cit. a 340 THE PHYSIOLOGY OF REPRODUCTION not occur simply as a consequence of the presence of the ovum. It is also pointed out that in normal pregnancy the uterine changes commence before the ovum enters the uterus. Again, the theory that the corpus luteum is responsible for the attachment and early development of the embryo receives some support from those cases in which pathological conditions in the embryo have been found associated with pathological conditions in the corpus luteum.’ Thus lutein cysts are frequently found in apparent correlation with chorionepi- theliomata. Fraenkel’s general conclusions regarding the functions of the corpus luteum may be summarised as follows: The corpus luteum is a ductless gland which is renewed every four weeks during reproductive life in the . human female, and at different intervals in the various lower Mammals. Strictly speaking, there is only one corpus luteum which represents the ovarian organ of internal secretion, and is regenerated periodically in slightly different positions in the ovaries. Its function is to control the nutrition of the uterus from puberty until the meno- pause, to. prevent ‘it from lapsing into the infantile condition o: or undergoing — atrophy, and_to _ prepare its mucous membrane — for the maintenance of the ovum. If the ovum | be. fertilised, the corpus luteum is responsible for Maintaining the raised nutrition of the uterus during the first part of gestation. If the ovim be unfertilised it merely produces the hyperemia of menstruation, and then undergoes degeneration until it is renewed in a fresh position. Since the corpus luteum is, par excellence, the ovarian gland, “lutein” or the extract of this organ, and not preparations of the entire ovary, should be employed for the purposes of ovarian medication. Reasons have already been given for concluding that this extended theory of the meaning and function of the corpus luteum is untenable (p. 334). The fact that in a very large number of animals, heat, and presumably, therefore, ovulation, occur at infrequent intervals does not support it, while it has been shown that, in some animals at any rate, ovulation does 1 Cf. Malcolm Campbell, ‘‘ Pathological Condition of the Ovaries as a Possible Factor in the Etiology of Uterine Fibroids,” Scottish Med. and Surg. Jour., vol. xvi., 1905, ORGANS OF INTERNAL SECRETION $41 not take place until cestrus, and consequently that at the time of the procestrous hyperemia there are no corpora lutea present in the ovary. These facts, however, are in no way opposed to that part of Fraenkel’s theory which assigns to the corpus luteum the function of governing the fixation of the ovum and helping to maintain its nutrition during the first stages of pregnancy. Dr. Jolly and the author * have carried out a series of experi- ments upon dogs and rats in which the ovaries were extir- pated at different stages during pregnancy, as in Fraenkel’s experiments upon rabbits. In the experiments on dogs, ovariotomy was performed at intervals ranging from three days to four weeks after impregnation. The pregnancy was dis- continued in every case excepting one, in which a portion of the tight ovary which contained the degenerate remains of two undoubted corpora lutea were found post mortem, three days after parturition, when the dog was killed. In this experiment ovariotomy was performed three days after copulation, and parturition occurred fifty days subsequently. Only a single pup was produced, and birth was premature. The pup died after being suckled normally for three days. The ovaries were also removed from a large number of rats, most of which were in early stages of pregnancy. Pregnancy was continued in no case in which ovariotomy was performed during the first six days. In other cases, in which the ovaries were removed at periods varying from the sixth day until near the end of pregnancy, the young were produced normally at full time.’ Control experiments were also carried out in which the ab- dominal cavity was opened up during an early stage of pregnancy and the ovaries were cauterised, or in which one ovary was re- moved and not the other, and in these experiments the course of pregnancy was not interfered with. We purposely refrained from attempting to extirpate the corpora lutea only while leaving the rest of the ovary, as it appeared to us to be practically impossible to destroy the whole of the luteal tissue 1 Marshall and Jolly, loc. cit. 2 In our paper the period of gestation in the rat was wrongly computed at twenty-eight days. It is in reality about twenty-one days. 3 Cf. Carmichael and Marshall, loc. cit. 342 THE PHYSIOLOGY OF REPRODUCTION without injuring the entire organ. The ovaries during pregnancy consist very largely of corpora lutea, and any attempt in a relatively small animal to discriminate between luteal tissue and stroma, while the ovary was lying in its normal position in the body cavity, seemed in our judgment to be impracticable. It will be seen that our experiments on the results of ovari- otomy during pregnancy fully confirm those of Fraenkel. It must be pointed out, however, that there is no evidence that the corpus luteum governs the fixation of the embryo in any other than the indirect sense implied in the supposition that the secretion elaborated by that organ acts as a stimulus which excites the uterine mucosa to undergo the necessary hypertrophy. In this general sense, also, it is probably true that the luteal secretion (or, at any rate, the secretion of the ovary) assists in nourishing the embryo during the first stages of pregnancy, since there is every reason for concluding that it helps to maintain the raised nutrition of the uterus. It has been shown that the presence of the ovaries is not essential for the con- tinuance of pregnancy in the later stages, when the corpora lutea are in process of degeneration. It would seem not un- likely, therefore, that the atrophic changes (fibrosis) which take place in the decidua serotina, or maternal placenta, in the later part of the gestation period are directly correlated with the degeneration of the corpus luteum.* Cases have been recorded by Essen-Miller,? Graefe,? and Flatau,* in which pregnancy was not interrupted by double ovariotomy in women when performed in the early stages of pregnancy. These cases are undoubtedly very exceptional, and it seems legitimate to conclude that a small portion of an ovary, probably containing luteal tissue, was left behind acci- 1 It has been suggested that the corpus luteum contributes an essential factor in the nourishment of the embryo through the trophoblast, and that it consequently ceases to be functional in the later part of pregnancy when the trophoblast is superseded by the allantoic placenta. See Andrews, loc, cit. 2 Essen-MOller, ‘‘ Doppelseitige Ovariotomie im Anfange der Schwanger- schaft,” Central. f. Gyndk , vol. xxviii., 1904. 3 Graefe, ‘‘Zur Ovariotomie in der Schwangerschaft,” Zedtschr. f. Geb. u. Gynik., vol. lvi., 1905. + Flatau, ‘‘ Ueber Ovariotomie wahrend der Schwangerschaft,’’ Arch. f. Gyndak., vol. lxxxii., 1907, ORGANS OF INTERNAL SECRETION 343 dentally at the time of the operation. So able and experienced an operator as Bland Sutton! has recently testified to the extraordinary difficulty experienced in removing the whole of the ovarian tissue in ovariotomy, and the distinguished French obstetrician, Lucas-Champonnitre,? has expressed himself in the same sense, so that there is nothing unreasonable in the assump- tion that the operation of removal is sometimes incomplete when performed on pregnant women. Daels * has recently recorded a large series of experiments upon guinea-pigs and rats in which he found that bilateral castration invariably interrupted the course of pregnancy during rather more than the first half of its duration. In control experiments portions of mesentery or other tissue, or only one ovary instead of both, were extirpated, and in these cases the pregnancy was continued. Furthermore, Kleinhaus and Schenk * found that destruction of the corpora lutea of rabbits, after the ninth day of gestation, did not necessarily pro- duce abortion, but that the same operation at an earlier period invariably brought the gestation to a premature end. According to Ancel and Bouin,’ the rabbit’s uterus undergoes growth, vascularisation, and muscular hypertrophy after ovula- tion even although the ova are not fertilised (e.g. owing to the A./ ¢ vasa deferentia of the male having been cut). These changes are said to be followed by regression, which sets in after the thirteenth day. According to Ancel and Bouin, therefore, there is a close parallelism between the growth and regression of | the corpus luteum and a series of cyclical changes which take ; place in the uterus. There is also said to be a parallelism” 1 Bland Sutton, ‘A Clinical Lecture on the Value and Fate of Belated Ovaries,” Medical Press, vol. cxxxv. (July 31) 1907. 2 Lucas-Champonniere, ‘‘ Sur une Observation de Graffe Ovarienne Suivie de Grossesse,” Jour. de Méd. et de Chirurgie Pratiques, vol. 1xxviii. (May) 1907. 3 Daels, ‘On the Relations between the Ovaries and the Uterus,” Surgery Gynecology and Obstetrics, vol. vi., 1908. 4 Kleinhaus and Schenk, ‘‘ Experimentales zur Frage nach der Funktion des Corpus Luteum,” Zeitschr. f. Geb. u. Gyndk., vol. 1xi., 1907. 5 Ancel and Bouin, “ Sur la Fonction des Corps jaunes,” C. R. de la Soc. de Biol., vol. lxvi., 1909; ‘tLe Développement de la Glande Mammaire pendant la Gestation est determing par le Corps jaune,” C. R, de la Soc. de Biol., vol. lxvii., 1909. 344 THE PHYSIOLOGY. OF REPRODUCTION between the development of the corpus luteum and the growth of the mammary gland in the rabbit." Dubreuil and Regaud,? however, as a result of further ex- periments, are very doubtful whether the corpus luteum has any influence over the non-gravid uterus. On the other hand, the observations of Niskoubina ? tend to confirm those of Ancel and Bouin. According to Loeb,’ deciduomata (7.e., nodules having the structure of decidua) can be produced experimentally in the uterine mucosa of the guinea-pig by making a number of trans- verse and longitudinal cuts so as to break the continuity of the tissue. The nodules originate through a proliferation of the interglandular connective tissue. Loeb states further that this can only happen during a certain definite period after the occur- rence of copulation or heat. The changes cannot be induced on the first day after heat, nor after the tenth day, but deciduomata are readily formed between the fourth and eighth days. The uterus is therefore most responsive when freshly formed corpora lutea are present in the ovaries. The changes were not excited by the presence of ova in the uterus, since they took place when the lower part of that organ was ligatured off so as to prevent the passage of the ova. On the other hand, if the ovaries were extirpated deciduomata could not be produced. If the corpora lutea were as far as possible burnt out of the ovaries by the electric cautery, deciduomata were not generally produced ; but owing to the difficulty of properly performing these experiments, the results were not quite conclusive. Lastly, when pieces of uterus were transplanted into the subcutaneous tissue, deciduo- mata were formed in the grafted pieces. It is concluded, there- fore, that the ovaries at certain periods after ovulation (and probably the corpora lutea) elaborate a predisposing substance 1 Ancel and Bouin, loc. cit. 2 Dubreuil and Regaud, “Sur les Relations fonctionelles des Corps jaunes avec l’Uterus non gravidé,” I. II. III. and IV., C. RB. de la Soc, de Biol., vol. lxvii., 1909. See also earlier papers in vol. lxv., 1908, and vol. Ixvi., 1909. 3 Niskoubina, “Recherches expérimentales sur la Fonction des Corps jaunes,” C. R, de la Soc, de Biol., vol. lxvi., 1909. 4 Loeb (L.), “ The Production of Deciduomata, and the Relation between the Ovaries and the Formation of the Decidua,” Jour. Amer. Med. Assoc., vol. 1], (June 6), 1908. Medical Record, vol. Ixxvii. (June 25), 1910. ORGANS OF INTERNAL SECRETION 345 in the presence of which indifferent stimuli (traumatisms), may produce deciduomata. It has been shown that the uterine mucosa undergoes atrophy after the complete removal of the ovaries, and it seems hardly probable that this process can be arrested by the presence of a fertilised ovum in the early stages of pregnancy. On the other hand, it js scarcely conceivable that an ovum could become attached to a uterine mucous membrane which was in process of degenerating. It would appear, however, that in the latter half or two-thirds of pregnancy, when the uterus has already undergone great hypertrophy, the presence of the ovaries may be dispensed with.1 Furthermore, it has just been mentioned that the maternal placenta undergoes a partial degeneration in the later stages of embryonic development. Miss Lane-Claypon 2 has shown that the interstitial cells of the ovarian stroma undergo an increase in size during the period of gestation, but this increase is not so great as that of the luteal cells. Consequently, she suggests that these cells also may produce a secretion of the nature postulated for the cells of the corpus luteum. If this is so, the circumstance that the interstitial cells do not hypertrophy to the same extent as the luteal cells may perhaps be ascribed to the different conditions of mechanical pressure existing in the ovarian stroma. Tue SuprposeD INTERNAL SECRETION OF THE UTERUS Although the bulk of evidence obtained clinically points to the conclusion that the uterine functions fall into abeyance after the extirpation of the ovaries, while the relatively few exceptions to this rule are probably to be explained on the sup- position of incomplete removal, some surgeons and gynecologists have adopted the view that the uterus is capable of functional activity independently of the ovaries. A few writers have even gone further, and have affirmed the belief that the ovarian functions themselves are dependent upon uterine influence. 1 It has yet to be proved, however, that the further course of development is absolutely normal after ovariotomy in the later part of pregnancy. ? Lane-Claypon, “On the Origin and Life-History of the Interstitial Cells of the Ovary of the Rabbit,” Proc. Roy. Soc., B., vol. lxxvii., 1905. IX 346 THE PHYSIOLOGY OF REPRODUCTION Zweifel and Abel,’ in describing the after-histories of cases of hysterectomy, stated that, in their experience, when the whole of the uterus was removed, entire atrophy of the ovaries always followed, so that menopause symptoms set in similar to those occurring after ovariotomy. In those cases, however, in which a portion of the uterine mucous membrane was con- served, menstruation continued and there were no menopause symptoms. Consequently, these surgeons have advocated the operation of sub-total hysterectomy wherever possible in pre- ference to complete removal, believing that the functional activity of the ovary is in some way dependent on the presence of the uterus. Doran,’ in tracing the after-histories of sixty cases of sub- total hysterectomy, is disposed to concur with Zweifel and Abel in advising that the uterus should be removed above the cervix. In support of this contention he cites two cases in which menstruation persisted after the removal of the body of the uterus, the cervix being left behind. Mandl and Biirger,? in a monograph dealing with the sub- ject, express the belief that in those cases in which the ovaries are conserved after hysterectomy there is a gradual cessation of function on the part of these organs, resulting from their degeneration. Holzbach,* on the other hand, states that as a rule the ovaries do not atrophy after hysterectomy, and that, when such de- generation does occur, it is probably due to interference with the nervous connections consequent upon the operation of removal. Blair Bell ® has suggested that menstruation is brought about by an internal secretion of the uterus, while he supposes ovula- tion to depend on the circulation of this secretion, which he calls “ uterine.” 1 Zweifel, ‘‘ Deutsche Gesellschaft fiir Gynakologie in Berlin,” Zentral. f. Gyndk., No. 21, 1899. Abel, ‘‘ Dauererfolge der Zweifelschen Myomek- tomie,” Arch. f. Gyndk., vol. lvii., 1899. 2 Doran, ‘‘Sub-total Hysterectomy for Fibroids,” Lancet, Part II., November 1905. 3 Mandl and Biirger, Die Biologische Bedeutung der EHiersticke nach Entfernung der Gebdrmutter, Leipzig, 1904. 4 Holzbach, ‘‘ Ueber die Function der nach Totalextirpation des Uterus zurickgelassen Ovarien,” Arch, f. Gyndk., vol. lxxx., 1906. 5 Blair Bell, loc. cit. ORGANS OF INTERNAL SECRETION 347 Bond * has put forward the view that the ovarian secretion is influenced by a saline secretion from the ancestrous uterus, the two, however, acting antagonistically to one another, so that the prevention of the uterine secretion by hysterectomy favours the hypertrophy of the ovaries. Bond’s view, therefore, is diametrically opposed to that of Blair Bell. Bond records two experiments on the results of hysterectomy in rabbits. In one the entire uterus was removed and the animal killed after five months. Both ovaries were found to be normal. In the other experiment the left uterine cornua only was extirpated, and the rabbit was killed after five months. In this case also the ovaries showed no signs of degeneration. As a result of these experiments Bond affirms that the pre- vention of the saline secretion of the uterine mucosa by previous hysterectomy favours the overgrowth of luteal tissue in the ovary. Stress has been laid by various writers upon the well-known fact that whereas the corpora lutea of the ovary continue to grow for a considerable period of time if pregnancy supervenes after ovulation, this hypertrophy soon ceases in the absence of pregnancy. Bond records an experiment upon a rabbit in which one of the ovaries, after transplantation in an abnormal position, was found to contain a somewhat aberrant “‘ corpus luteum of pregnancy” in association with a gravid uterus. Such observations are regarded by him as supplying evidence of an internal uterine secretion acting on the ovaries and so exciting a growth of luteal tissue. This secretion is supposed by Bond to be quite different from the saline fluid elaborated by the ancestrous uterus.” It must be remembered, however, that pregnancy produces a profound influence over the entire organism, and not merely over the ovaries. Certain other authors, such as Loewenthal,? have suggested theories which imply a dependence on the part of the ovaries upon some function of the uterus; but, excepting for the two experiments of Bond referred to above, and a series of * Bond, ‘‘Some Points in Uterine and Ovarian Physiology and Pathology in Rabbits,” British Med. Jour., Part II., July 1906. 2 Bond, “Certain Undescribed Features in the Secretory Activity of the Uterus and Fallopian Tubes,” Jour. Phys., vol. xxii., 1898. > Loewenthal, ‘‘Eine neue Deutung des Menstruationprocess,” Arch. f. Gyndk., vol. xxiv., 1884. 348 THE PHYSIOLOGY OF REPRODUCTION experiments undertaken by the author in collaboration with Mr. Carmichael,’ no systematic investigation ever appears to have been attempted upon the effects of hysterectomy. In our experiments we removed the uterus, either entirely or leaving only the cervix, from a number of very young immature rabbits. The animals were killed after they had become fully grown—in some cases not until ten months after the operation. In every experiment the ovaries were found to have developed normally. In some cases also copulation was observed on the rabbits being put with the buck. Many of the ovaries contained typical corpora lutea, showing that ovulation had taken place. Also in four experiments on fully grown rats hysterectomy was performed, and the animals were killed several months subsequently. The ovaries in no instance showed any indications of atrophy. On the other hand, marked uterine degeneration was observed in rats after the removal of the ovaries for shorter periods of time.” As a result of these experiments, it may be concluded. that the growth | and development of the ovaries is in no way de- pendent upon n the presence of the uterus. Such a conclusion is no doubt opposed by some of the clinical evidence, but it is one which was to be expected on phylogenetic grounds, since the uterus is an organ which came into existence comparatively recently in the course of vertebrate evolution, whereas the ovary is common to all Metazoa. It is possible, in those surgical cases in which the ovaries underwent atrophy after the removal of the uterus, that this was due to vascular interference.? 1 Carmichael and Marshall, Proc. Roy. Soc., loc. cit, 2 Marshall and Jolly, ‘‘Results of Removal and Transplantation of Ovaries,” Trans. Roy. Soc, Edin., vol. xlv., 1907. 3 Boston has recorded four cases of women where the uterus was con- genitally absent, but in whom the development of the breasts and other changes relating to puberty excepting menstruation were experienced. Sentiment, sexual desire, and sexual sensation are stated to have been normal in each case (‘Absence of the Uterus in Three Sisters and Two Cousins,” Lancet, Part I., Jan. 1907). It may also be mentioned that Sellheim found that removal of the oviducts in pheasants does not result in « shrivelling up of the ovaries and the assumption of secondary male characters as has been stated (Zeit. f. Gyndk., 1904, No. 24). It has not been determined whether the generative organs (apart from the uterus) undergo the character- istic procestrous changes after hysterectomy, since these changes are com- paratively slight and difficult to detect in rabbits. ORGANS OF INTERNAL SECRETION 349 Tue CORRELATION BETWEEN THE GENERATIVE ORGANS AND THE DucTLESS GLANDS Noel Paton* and Henderson? have shown that there is a reciprocal relation between the thymus and the testis, each checking the growth of the other. This conclusion is based on a series of observations on cattle and guinea-pigs. In the former it was found that castration delayed the onset of the atrophy of the thymus, for the average weight of that organ in bulls up to three and a quarter years old was considerably less than that in oxen. In guinea-pigs Paton found that, in those animals in which the thymus was removed at a time prior to the normal period of atrophy for that organ, there was an in- crease in the growth of the testis. On the other hand, Soli? states that extirpation of the thymus, carried out in young rabbits, guinea-pigs, and fowls, caused inhibition of testicular development, and sometimes even complete arrest of growth by that organ. Fichera * observed a constant hypertrophy of the pituitary body (hypophysis) in capons, oxen, buffaloes, and rabbits, cas- trated in early life—that is to say, an increase in weight by that organ as compared with the pituitary glands of other animals of the same kind, weight, and age. The increase in weight was associated with a rich blood supply, and an increase in the number of eosinophyl cells. These observations are confirmed for young dogs by Cimorini,° who states that the changes in the pituitary were similar to those occurring after removal of the thyroids. According to Pepere,® there is probably no specific hypertrophy of the hypophysis in relation to the extirpation of any particular 1 Paton, ‘The Relationship of the Thymus to the Sexual Organs,” Jour. of Phys., vol. xxxii., 1904. 2 Henderson, “On the Relationship of the Thymus to the Sexual Organs,” Jour, of Phys., vol. xxxi., 1904. 3 Soli, ‘Contribution & la Connaissance de la Formation du Thymus chez le Poulet et chez quelques Mammiféres,” Arch, Ital. de Biol., vol. 1xii., 1909, 4 Fichera, “Sulla ipertrofia della glandula Pituitaria consecutiva cas- trazione,”’ Policlinico, vol. xii., 1905. 5 Cimorini, ‘‘Sur l’'Hypertrophie de YHypophyse cérébrale chez les Animaux thyréoidectomisés,” Arch. Ital. de Biol., vol. xlviii., 1907. § Pepere, “Sur les Modifications de Structure du Tissu Parathyroidien normal et accessoire (thymique) en rapport avec sa Fonction vicariante,” Arch, de Méd, Expér., vol. xx., 1908. 350 THE PHYSIOLOGY OF REPRODUCTION ductless gland in the organism, but that the reaction of the cellular elements, though varying in response to different con- ditions, shows also many characters referable to a common cause. It has been shown further that in cases of giantism and acromegaly, in which the pituitary body is enlarged, the sexual organs may be very imperfectly formed.1 Thus, the uterus is often infantile, the ovaries are rudimentary, or the penis is ill-developed. (See also final footnote, p. 356.) It is well known that there is a correlation between the sexual organs and the thyroids. These glands undergo enlarge- ment during menstruation and pregnancy in women, and Freund 2 has shown that similar changes occur during the heat periods of many of the lower mammals. He has pointed out further, that swelling of the thyroid, at the time of puberty, often leads to goitre, and that this disease commonly begins at a period of menstruation. These facts are cited by Gaskell? as evidence of a special connection between the thyroid and the sexual organs —the former being held to represent the uterus of the scorpion. Alquier and Thauveny ¢ state that after the partial or complete removal of the thyroids and parathyroids menstruation and conception are very infrequent, but this result may be due to the general metabolic disturbance arising from the absence of the glands. There is some evidence of a correlation existing between the sexual organs and the supra-renals. Thus Gottschau® states that in rabbits, changes occur in these organs during pregnancy, the outer zone of the cortex becoming twice its normal thickness, whereas the medulla is said to become thinner. Similarly, Stilling ° states that in frogs during the pairing time, the medulla 1 Woods Hutchinson, ‘‘ The Pituitary Gland as a Factor in Acromegaly and Giantism,” New York Med, Jour., 1900. ? Freund, ‘Die Beziehungen der Schilddriise zu den weiblichen Ge- schlechtsorganen,” Deutsche Zeitsch. f. Chir., vol. xviii., 1883. 3 Gaskell, The Origin of Vertebrates, London, 1908. 4 Alquier and Thauveny, ‘Etat de l'Ovaire de Chiennes ayant lExtirpa- tion partielle ou totale de l’Appareil Thyro-Parathyroidien,” C. R. de la Soc, de Biol., vol. lxvi., 1910. 5 Gottschau, ‘‘ Ueber Nebennieren der Saiigethiere,” &c., Sitz.-Ber, d. phys. med. Gesell, zu Wurzburg, vol. xvii.—xviii., 1882. ® Stilling, “‘Zur Anatomie der Nebennieren,” Arch. f. Mikr. Anat., vol, lii., 1898. ORGANS OF INTERNAL SECRETION 351 disappears, while characteristic cells known as “‘ summer cells ” become developed. Bulloch and Sequeira‘! state that in cases of children with carcinomata of the supra-renals, this is asso- ciated with premature development of the genital organs and the accessory generative glands. GENERAL CONCLUSIONS REGARDING THE INTERNAL SECRETIONS OF THE OVARY aND THE TESTIS It will be convenient at this point to summarise the con- clusions which have been tentatively arrived at concerning the nature and purpose of the internal secretions of the ovary and the testis. The mammalian ovary, in addition to its odgenetic function, is an organ elaborating a chemical substance or substances which react on the general metabolism and control the nutrition of the uterus. The secretion is probably produced by the cells of the follicular epithelium, or by the interstitial cells of the stroma, or, perhaps, by both combined.? It is formed in greater or less quantity at all times, but is produced in increased abundance at certain recurrent periods, when it brings about those conditions of growth and hyperemia which characterise the procestrous processes. It is at these periods also, in typical cases, that the follicles become mature. After ovulation, which occurs during cestrus, the secretory cells of the ovary show still greater activity, and become converted by a process of simple | hypertrophy into the luteal cells of the corpus luteum. If the - ovum is fertilised, these cells continue to increase in size until nearly mid-pregnancy (or, in some animals, a somewhat earlier period), when they exhibit signs of degeneration. If pregnancy 1 Bulloch and Sequeira, “On the Relation of the Supra-renal Capsules to the Sexual Organs,” Trans. Path. Soc., vol. lvi., 1905. 2 Limon (loc. czt.) suggested, as a result of his experiments in grafting, that the ovarian secretion is elaborated by the interstitial cells. It should here be remembered that the follicular epithelial and interstitial cells are almost certainly identical by origin, and so probably similar potentially (p. 124), and that both of these cellular elements have been described as taking part in the formation of the corpus luteum (p. 148); and also, that those interstitial cells which do not form part of the corpus luteum have been stated to undergo an independent hypertrophy during pregnancy (p. 345). 3852 THE PHYSIOLOGY OF REPRODUCTION does not supervene, the luteal cells begin to degenerate at a much earlier period and without attaining their full development. The pronounced hypertrophy of the follicular epithelial and interstitial cells, which takes place at the beginning of pregnancy, is directly correlated with a nearly simultaneous hypertrophy on the part of the uterine wall. The corpus luteum, therefore, is to be regarded as an essential factor in maintaining the raised nutrition of the uterus during the earlier stages of the period of gestation. When the later part of this period is reached, the ovarian secretion has probably been already formed in sufficient quantity to prevent the uterus from lapsing into the normal condition until the end of pregnancy. It is to be noted, how- ever, that fibrous degeneration has been described in the maternal placenta in the later stages of its existence. Thus the ovaries pass through a series of cyclical changes which are directly correlated with those undergone by the uterus. Moreover, the uterus atrophies after ovariotomy. It seems probable that this close co-ordination between the ovarian and uterine functions arose very gradually in evolu- tionary history, and it may be that in the aplacental mammals we have in existence at the present day an intermediate stage in the development of this relation. Starling’ has suggested that the internal secretions, or hormones generally, arose at first as products of ordinary metabolic activity in certain particular tissues, and that the evolution of the various cases of chemical correlation between different organs in the body came into existence, not by the production on the part of certain tissues of special substances acting as chemical messengers, but by the acquisition of a specific sensibility on the part of other functionally related tissues. It is no doubt possible that the chemical co-ordination of the ovarian and uterine activities arose partly in this way ; but, on the other hand, the definite character of certain of the cyclical changes which take place in the ovary, and particularly those which relate to the formation of the corpus luteum, points to the conclusion that the secretory function of the ovary has been perfected, or at any rate, has undergone great development in the phylogenetic history of the 1 Starling, ‘‘The Chemical Co-ordination of the Activities of the Body,” Science Progress, vol. i. (April) 1907. ORGANS OF INTERNAL SECRETION 353 Mammalia, though it no doubt existed previously in a minor degree. substance acting as a chemical excitant, nothing is definitely known, but the composition of the corpus luteum (which is different from that of the rest of the ovary) indicates that the formation of this structure is accompanied by a change in the nature of the ovarian secretion. Lastly, it is possible that the influence of the ovary upon the metabolism is due partly to this organ being excretory as well as secretory in function, but there is no evidence that this is actually the case. The fact that the testis is an organ of internal secretion seems now to be definitely proved. This secretion is probably formed throughout the entire reproductive period of an animal’s life ; but, in those animals which experience a periodic rut, it is no doubt at this season that the testicular hormone is produced in greatest abundance. The development of the prostate and the secondary sexual characters, not to mention the growth of the testes themselves, is convincing evidence that this is the case. Tue Errects oF CASTRATION UPON THE GENERAL METABOLISM Tn view of the facts referred to above it is almost self-evident that castration must exercise some influence upon the general metabolism of the body since it produces such marked effects upon the primary and secondary sexual characters. Moreover, it is commonly asserted that the removal of the reproductive glands causes a tendency towards obesity both in Man and animals, but it is not quite clear whether this occurs as a direct or an indirect consequence of castration. The deposition of fat which is sometimes seen to take place after the menopause may be regarded as further evidence of a connection between the functional ovaries and the general metabolism. The existence of such a functional correlation is shown more clearly by the effects of ovariotomy upon the bone disease known as osteomalacia.1 The ovaries undoubtedly exert a 4 In one case of osteomalacia Krénig removed the ovaries and trans- planted them on to the peritoneum. The result was immediately beneficial ; Z 354 THE PHYSIOLOGY OF REPRODUCTION marked influence over the phosphorus metabolism, and the improvement which sets in after the removal of these organs in cases of osteomalacia is apparently brought about by a re- tention of the earthy phosphates whereby the skeletal tissues acquire their normal rigidity. Unfortunately, the experimental work which has so far been done upon the phosphorus meta- bolism in normal and castrated animals is too contradictory to admit of the deduction of any conclusions that are calculated to throw light upon the phenomena of osteomalacia." The protein metabolism of castrated animals has been in- vestigated by Liithje,” who records no changes as a consequence of the removal of the generative.glands. Certain other in- vestigators, as a result of shorter series of experiments, have obtained trifling effects, sometimes showing a slight increase in the nitrogenous output and sometimes a diminution.* Experiments upon the respiratory exchange have been almost equally inconclusive, and have so far failed to show any constant alteration as a consequence of castration. This question is discussed at some length by van Noorden,* who calls attention to the necessity for distinguishing whether the total daily metabolism, which in some cases has been shown to become diminished after castration, does so in consequence of a variation in temperament (or greater tendency towards physical repose), or whether the oxidation of the resting cell (z.e. the fundamental metabolism) is reduced. He is disposed to believe that the marked diminution in the respiratory ex- change which has been observed in some animals after castration is probably due to a greater indolence, and is, therefore, an indirect result. Moreover, he points out that, in the case of but with the return of menstruation, which followed after about two months, the symptoms of the disease are said to have reasserted themselves (Stuttgart Medical Congress, Zeit. f. Gynak., 1996). See also Fraenkel, ‘‘ Ovarialan- tikorper und Osteomalacia,” Miinch, Med. Wochenschr., No. 25, 1908. 1 Van Noorden, Metabolism and Practical Medicine, English Edition, edited by Walker Hall, vol. i., London, 1907. According to Wallart, “Ueber das Verhalten der interstiellen Eierstocksdriise bei Osteomalacia,” Zedtsch. f. Geb. und Gyndk., vol. 1xi., 1908, osteomalacia is correlated with an increase of the interstitial cells in the ovary. 2 Liithje, ‘“‘ Ueber die Kastration und ihre Folgen,” Hxperim. Archiv, vol. xlviii., 1902, and vol. 1., 1903. 8 Van Noorden, loc. cit. 4 Ibid. ORGANS OF INTERNAL SECRETION 355 Liithje’s castrated dogs, which did not exhibit any change from their normal habits and movements, there was no diminu- tion in the gaseous exchange as compared with control animals. Loewy and Richter,’ however, have arrived at different conclusions, finding pronounced reduction in the respiratory metabolism of castrated dogs of both sexes. Furthermore, these investigators found that after feeding the female animals upon ovarian substances there was a great increase in the metabolism, a castrated bitch showing an increase of from 30 to 50 per cent. above the normal values observed before the operation. Testicular substance had no influence upon any of the castrated animals, while normal animals did not react at all either to ovarian or to testicular extracts. Loewy and Richter suggest that the ovaries produce a specific substance which promotes oxidation in the body. Zuntz* has investigated the gaseous metabolism in four castrated women, and found that it lay within the limits of the normal. It is to be noted that neither of these women showed any tendency to corpulence. These observations support the view that when castrated animals show a reduction in the respiratory exchange, this is an indirect effect resulting from greater indolence of disposition. Oa this view also, the tendency towards a deposition of fat on the part of many castrated animals is to be attributed to the same cause. Dr. Cramer,’ working in conjunction with the author, has lately investigated the respiratory metabolism of a number of rats whose ovaries had been removed some time previously, and in these animals it was found that the gaseous exchange lay within the limits of the normal, thus confirming Zuntz’s experience with castrated women. It is possible, however, that the results of castration were obscured by other factors. In this investigation the apparatus employed by Haldane and Priestley was used in preference to that of Zuntz. We did not observe any marked tendency to deposition of fat in the castrated rats. 1 Loewy and Richter, ‘‘Sexual-Funktion und Stoffwechsel,” Arch. f. Phys., Supplement, 1899. 2 Zuntz, ‘‘Gaswechsel bei Kastrierten Frauen,’’ Verhandl. d. Gyndk. Gesell,, Berlin, 1904. See also Deutsch. Zeitschr. f. Chir., vol. 65, 1908. 5 Cramer and Marshall. MS. unpublished. 356 ‘THE PHYSIOLOGY OF REPRODUCTION Furthermore, it is to be noted that, according to Magnus- Levy and Falk, the period of puberty in boys and girls is not associated with any increase in the gaseous metabolism. Certain further experiments upon the effects of administer- ing ovarian extract may also be referred to here. Neumann and Vas” record losses of nitrogen, phosphorus pentoxide, and calcium monoxide after injecting glycerine extract of ovary subcutaneously. Loewy ® and Neumann found no change in the nitrogen metabolism in castrated animals after administering ovarian extracts, but Neumann observed a loss of phosphorus pentoxide and calcium monoxide in the feces. Certain other less satisfactory experiments, dealing with more or less con- tradictory observations, are briefly referred to by van Noorden. The influence of castration upon the blood has formed the subject of a research by Breuer and Seiler,t who employed bitches whose ovaries were removed shortly after puberty. They record marked diminution in the hemoglobin and the red cells.® In concluding this brief summary of the recorded results of castration upon the metabolism, the necessity for further in- vestigation must be emphasised, since it is hardly possible that the totality of the effects produced is of as slight a nature as the experimental evidence at present seems to indicate.® 1 Magnus-Levy and Falk, ‘‘ Lungengaswechsel des Menschen,” Arch. f. Phys., Supplement, 1899. 2 Neumann and Vas, “Einfluss der Ovariumpraparate auf den Stoff- wechsel,” Monatsschr. f. Geburtsh. u. Gyndk., vol. xv., 1902. 3 Loewy, ‘‘Ueber den Einfluss des Oophorins,” Berl. klin. Wochenschr., 1899. 4 Breuer and Seiler, “ Einfluss der Kastration auf den Blutbefund weib- licher Tiere,” Hxperim. Archiv, vol. 1., 1903. 5 It has also been stated that castration may improve the quality of the milk (Oceanu and Babes, “Les Effets Physiologiques de l’Ovariotomie chez la Chévre,” C. R. de l Acad, des Sciences, vol. cxl., 1905). For some account of the effects of disease in the ovaries and other reproductive organs upon the rest of the body, see Wilson, ‘The Reciprocal Relations between the Affections of the Uterus and its Appendages upon the Rest of the Body,” (Lancet, Part II., Nov. 1906). Further references are given in this paper. 6 For the effects of hypophysectomy see Crowe, Cushing, and Homans, ‘‘ Experimental Hypophysectomy”’ (Johns Hopkins Hosp. Bull., vol. xxi., May 1910). ‘These investigators found that partial removal of the anterior lobe caused hypoplasia of the generative organs in adult dogs, but persistent infantilism if operated on before puberty. CHAPTER X* FETAL NUTRITION: THE PLACENTA “Birth .. . is commonly considered as the point at which we begin to live. More truly it is the point at which we leave off knowing how to live... . Not but what before birth there have been unsettled convictions (more’s the pity) with not a few.”—SAMUEL BUTLER. PART I THE PLACENTA AS AN ORGAN OF NUTRITION J. Historican Survey Tue mammalian ovum, in all except the Monotremata, is small and does not contain a sufficient supply of nutriment for the developing embryo. It is retained for a longer or shorter period in the uterus, where, by special modifications of the uterine mucosa and a part of the ovum, the placenta is formed, and a transmission of nutriment from the mother to the embryo is made possible. The changes in the maternal and embryonic tissues vary greatly in the several orders, and even in groups of the same order, but in all they are sufficiently complicated to render their explanation a matter of great difficulty. It is doubtful if any anatomical structure has given rise to keener or more prolonged controversies than the placenta. We owe to Harvey” the conception of the placenta as an organ elaborating from the maternal blood the aliment necessary for the growth and development of the foetus. He was the first to reject the “ subtleties and fanciful conjectures ” on embryonic development, and to advocate and practise direct and diligent observation. But for a century after his death the placenta received little attention. With the introduction of the micro- scope the attention of biologists was directed towards the origin and development of the embryo, and it was then that the ovarian vesicles and spermatozoa were first observed. 1 By James Lochhead. ? Harvey, The Generation of Animals, London, 1651. 357 358 THE PHYSIOLOGY OF REPRODUCTION In the second half of the eighteenth century were pub- lished the researches of John and William Hunter on the human placenta, important not only in themselves, but as destined to set agoing the vast amount of work done in the first half of the nineteenth century. John Hunter’ stated that the maternal blood circulated through the placenta, and this view, which, according to Waldeyer,? had formerly been held by Vater and Noortwyk, though the latter at least believed in the com- munication of the maternal and fcetal circulations, was sup- ported by the subsequent dissection of injected placente by John Hunter and his brother. The statement of the former that “the blood of the placenta is detached from the common circulation of the mother, moves through the placenta, and is then returned back into the circulation of the mother,” gave rise later to a considerable amount of discussion. They showed that the decidua was uterine and not foetal, and the decidua reflexa was first figured in one of William Hunter’s plates.? It is remarkable that John Hunter did not recognise the placenta as the organ of foetal respiration. A century before, Mayow * had declared that the placenta functioned as a fcetal lung, the umbilical vessels taking up the nitro-aerial gas (oxygen) and carrying it to the foetus. This view was adopted by Ray,° who compared the villi lying in the maternal sinuses to the gills of a fish in the water. The first to take up Priestley’s discovery of oxygen, and state definitely that it was oxygen that went constantly from mother to foetus, and whose absence caused foetal asphyxia, was Girtanner ° in 1794. But all doubt was not removed till, in 1874, the spectroscopic bands of oxy- heemoglobin were demonstrated in the umbilical vein of a guinea- pig by Albert Schmidt, a pupil of Preyer.® The work of the brothers Hunter was carried on by Weber, Goodsir, Coste, Eschricht, Reid, and others. Of the many investigations, none had such an important influence as the 1 J. Hunter, Observations on Certain Parts of the Animal Economy, Edit. by Palmer, vol. iv. Z Waldeyer, ““Bemerkungen tiber den Bau der Menschen- und Affen- placenta,” Arch. f. mikr, Anat., vol. xxxv., 1890. 3 W. Hunter, Anatomy of the Human Gravid Uterus, Birmingham, 1777. + Mayow, Tractus Tertius de Respiratione Fetus in Utero, 1674. 5 Ray, The Wisdom of God in the Creation, 12th Edit., 1754. 8 See Preyer’s Specielle Physiologie des Embryo, 1883. FETAL NUTRITION: THE PLACENTA = 359 researches of Goodsir.’ He first studied the placental cells with regard to their function. His predecessors had spoken in the vaguest terms of the passage of nutriment from mother to fcetus, but Goodsir had definite ideas. He described the villi as having two covering layers of cells, an external system belonging to the decidua, and an internal belonging to the chorion. As to their function, he says: “ The external cells separate from the blood of the mother the matter destined for the blood of the foetus, they are secreting ; the internal cells absorb the matter secreted by the agency of the external cells.” Thus we have the active part of placental metabolism referred for the first time to the cells of the villi. The importance of the intervillous spaces for foetal nutrition was first emphasised by Weber,” and they were the subject of close attention. The Hunterian doctrine that in the human placenta they contained blood was not yet established, and their mode of development gave rise to a long-continued con- troversy. John Hunter considered them outwith the maternal vascular system, and his view was supported by Owen,? Kolliker,* and Farre.®? Weber and Reid® held that the spaces were bounded by a thin maternal membrane, and Goodsir described two layers of maternal tissue between the blood in the sinuses and the vessels of the villi. The investigation of the intervillous spaces and _ the epithelial investment of the villi was carried on by Turner, Ercolani, Langhans, and many others. Turner’ and Waldeyer looked on the intervillous spaces as dilated maternal capillaries ; but while Turner held that the villi, at least in part, pene- trated their endothelium, Waldeyer supposed that they pushed the endothelium before them, and so got a covering of this 1 Goodsir, Anatomical and Pathological Observations, Edinburgh, 1845. 2 See Wagner’s Elements of Physiology, translated by Willis, London, 1841. 3 See Note in John Hunter's Collected Works, Edit. by Palmer, vol. iv. 4 Kolliker, Entwicklungsgeschichte, 1861, 1884, &c. ® See Tod’s Cyclopedia, Article ‘‘ Uterus,” 1858. * Reid, ‘‘On the Anatomical Relations of the Blood-Vessels of the Mother to those of the Fetus in the Human Species,” Edinburgh Medical and Surgical Journal, vol. lv., 1841. 7 Turner, ‘*Some General Observations on the Placenta,” &c., Journal of Anatomy and Physiology, vol. xi., 1877. 360 THE PHYSIOLOGY OF REPRODUCTION maternal layer. Langhans! regarded the spaces as formed by that part of the lumen of the uterus which lay between the surface of the mucosa and the chorion, and thought that the villi by eroding vessels came to be bathed in extravasations of maternal blood. Klebs? considered them to be lymph-spaces, and therefore extra-vascular ; and Jassinsky * described them as being formed by the penetration of the villi into the maternal glands, whose epithelium came to clothe the villi externally. Now it has been proved from the examination of early ova that the intervillous spaces are entirely foetal and are formed in the epiblast. The investigations of Langhans proved to be the turning- point in the controversy regarding the investment of the villi. He showed that it consisted in the earlier stages of pregnancy of a double covering, a deep layer of cells (Langhans’ layer), and superficially a mass of “ canalised fibrin.” The presence of fibrin had been noted by Weber and several of his successors ; Winkler * proved it to be a constant phenomenon, and gave it the name “ Schlussplatte ”’ ; but it was Langhans who first de- scribed its relations, and suggested its probable origin from the foetal epiblast. The cellular layer, according to Langhans, was mesoblastic. Kastschenko® first described both layers as epiblastic, and showed that the outer layer was a syncytium or mass of nucleated protoplasm without cell-boundaries. Such investigations led to the feeling that the structure of the placenta could only be understood by tracing its development from very early periods of gestation. Hence the search for and examina- tion of young human ova were stimulated, and the study of the uterine condition in age-series of pregnant animals was begun. Up to this time the chief controversies had raged around the human placenta. Comparative placentation had engaged the 1 Langhans, ‘‘ Untersuchungen tiber die menschliche Placenta,” Arch. f. Anat. u. Physiol., anat. Abth., 1877. 2 Klebs (E.), ‘‘ Zur vergleichende Anatomie der Placenta,” Arch. f. mikr. Anat., vol. xxxvii., 1891. 3 Jassinsky, ‘‘Zur Lehre iiber die Struktur der Placenta,” Virchow’s Arch., vol. xl., 1867. + Winkler (F. N.), ‘‘Zur Kenntnis der menschlichen Placenta,” Arch, f. Gynik., vol. iv., 1872. 5 Kastschenko, ‘‘Das menschliche Chorionepithel und dessen Rolle bei der Histogenese der Placenta,” Arch. f, Anat. u. Phys., anat. Abth., 1885. FQ:TAL NUTRITION: THE PLACENTA = 361 attention of few morphologists, among whom Turner, the “grand-master of placental research ” (Hubrecht +), was facile princeps. But within recent years investigations have been carried out on many orders of placental mammals. Of these the most important are the researches of Duval and Hubrecht, which have established that the discoid placenta is essentially “a maternal hemorrhage encysted by foetal elements.” II. Structure AnD FuNcTIONS OF THE EPITHELIAL INVESTMENT OF THE VILLI The cellular layer of the villi is a temporary structure, and disappears to a great extent comparatively early in pregnancy. It is generally looked on as the mother zone of the outer syncytial layer. Strahl® states, however, that in one of the new-world apes it is not present at a stage as early as that of Peters’ human ovum, though a thick syncytial layer is present. Processes of it precede the mesoblastic outgrowths in the formation of the villi, and by a special proliferation of the cells at the tips of the villi, the “ Zellsiulen ” of Langhans, an attachment to the decidua is effected. While present, the cellular layer les in the path by which the nutriment for the foetus is carried to the villous capillaries, but it is not known whether it exerts any metabolic influence. Peters has suggested, without any very definite evidence, that it may have a coagulating action on maternal blood, necessitating the interposition of the syncytial layer. The syncytium is more permanent. In the earliest human ovum yet examined it already constitutes a considerable mass, and a similar thickening over the whole or part of the circum- ference of the blastocyst occurs early in all the Deciduata. Where a decidua reflexa exists, the early proliferation appears to be related to the excavation of the cavity in which the ovum lies. In discoid placentz the mass is vacuolated, and maternal blood is contained in the lacune. In the later stages of pregnancy it forms an attenuated membrane over the villi, and may wholly 1 Hubrecht, ‘‘The Placentation of Hrinaceus europeus,” Quar. Jour. Mier, Sci., vol. xxx., 1889. 2 Strahl, “Ueber Placentarsyncytien,” Anat, Anz., vol. xxix., Ergiinz- ungsch,, 1906. 362 THE PHYSIOLOGY OF REPRODUCTION disappear at parts. The nuclei are numerous, and most of the authorities agree on the absence of mitoses, some holding that they divide directly, others that they have lost the power of division. The protoplasm has a foam-like structure, and in Man it is condensed superficially to form a layer which bears the ‘« Biirstenbesatz ” or striated border (Fig. 75). This consists, as seen in fixed specimens, of a series of fine striae running per- pendicularly to the surface, and its structure and function have been much discussed since it was first described by Minot.’ Fie. 75.—Part of an early human chorionic villus. (From Hofbauer’s Biologie der menschlichen Plazenta, Braumiiller.) b, Biirstenbesatz with basal corpuscles ; s, syncytium ; 7, Langhans’ layer, one cell dividing mitotically (/’). Some have denied its existence during life, and ascribed it wholly to the method of preparation. But Hofbauer? has shown that the fresher a specimen is when obtained, the easier it is to demonstrate the strie by methods of staining, and, therefore, it is probably a vital structure. Kastschenko looked on the strie as fine hairs which projected from the surface of the cells, and by their vibrations created a stream in the maternal blood of the intervillous spaces. In specimens stained with iron-hematoxylin, knobs may be seen at the bases—basal corpuscles or blepharoblasts—and they may constitute the 1 Minot, “‘ Uterus and Embryo,” Jour. of Morphol., vol. xi., 1889. 2 Hofbauer, Biologie der menschlichen Plazenta, Leipzig, 1905. FETAL NUTRITION: THE PLACENTA — 363 motor centre for the ciliary beats. But no movements have yet been observed, and von Lenhossék! calls them “stereozilien,’ or stationary cilia, suggesting that they may help to break down vessel-walls during the burrowing of the syncytium into the serotina. Sometimes they appear not to project free on the surface but to lie in the superficial stratum ; then lighter and darker strie alternate, and it is this appearance which has led to the name “ striated edge.” Bonnet? in- geniously remarks that it proves the foetal origin of the syncytium, because, if it were uterine, the free edge would be formed by the bases of maternal cells, and they could not possess a “ Biirsten- besatz.”” The same appearance has been noted in intestinal epithelium, but its significance is unknown. In the placenta Graf v. Spee ® attributes the appearance to the teasing out of the surface of the protoplasm, and looks on it as evidence of a strong flow of fluid through the syncytium. It has also been suggested that the thin rods may be hollow and act as pores by which nutriment may enter the syncytium, or by which a secretion of the syncytium may pour out in order to prepare the constituents of the maternal blood for their transference to the foetus. It is still undecided whether the syncytium possesses amceboid motility. V. Lenhossék examined a human ovum several minutes after its removal from the uterus and observed, as has already been stated, no ciliary movements; but he con- sidered it not improbable that the syncytium underwent changes of form. Hofbauer tried unsuccessfully to demonstrate such movements in a specimen examined immediately after its removal, The core in young villi consists of a matrix, homogeneous or delicately fibrillated. In it are placed the blood-vessels and connective-tissue corpuscles with long branching processes, which form a network in the matrix, and probably provide a series of lymph-channels. Kastschenko also described special 1 VY. Lenhossék, Verhandl. d. anat. Kongresses in Halle, 1902. See Centralbl. f. Gynik., 1904, Nr. 7. 2 Bonnet, ‘‘ Uber Syncytien,” &c., Monatsschr. f. Geburtsh. u. Gynak., vol, xviii., 1903. 3 Graf v. Spee, ‘‘Neue Beobachtungen iiber sehr frithe Entwickelungs- stufen des menschlichen Eies,” Arch. f. Anat. u. Phys., anat. Abth,, 1896. 364 THE PHYSIOLOGY OF REPRODUCTION cells, with large nuclei, which he took to be wandering cells. But Lenhossék proved that they existed before leucocytes or lymph-cells appeared, and must therefore be formed in the villi and derived from mesoblastic cells. Hofbauer has observed them also in the lumen of the foetal vessels, and suggests a possible transformation to leucocytes. Our ideas upon the function of syncytia are largely based on the investigations of His :* “‘ They are not really specific tissue structures, but tissue conditions requiring definite phases of protoplasmic vitality. They occur along with a high degree of activity—with increased absorption and action on material— as well as with increased motility. Favourable conditions of nutrition form the fundamental condition for the existence of syncytia, and such conditions are certainly well offered in the uterus.” At the present time the syncytium is regarded as of the highest importance in foetal nutrition. Strahl? and Heinricius,? noting its gradual and progressive diminution as pregnancy advanced, supposed that it formed a part of the nutriment for the embryo, but this idea has not been adopted. The general theory is that it is essential in maintaining the interchange of material between mother and foetus. The sub- stances necessary for the building up of the foetal body may be divided into two groups—diffusible and non-diffusible. The passage of the former can be explained by physical laws, but it is different with the non-diffusible or colloid substances. This is a difficulty which does not belong to the placenta alone, but to every organ of the body, and authorities are divided between two theories, the mechanical and the vital. The supporters of the mechanical theory hold that all the processes occurring in the placenta are possible by the laws of filtration and osmosis, and they have carried out numerous experiments to prove that substances in solution may pass across the placenta in both directions. Others, paying special attention to the nature of the barrier formed by the epithelial covering of the villi, 1 His, “‘ Die Umschliessung der menschl. Frucht wahrend der frithesten Zeit der Schwangerschaft,” Arch. f. Anat. u. Phys., anat. Abth., 1897. 2 Strahl, ‘‘Der Bau der Hundeplacenta,”’ Arch. f. Anat. u. Phys., anat. Abth., 1890. 3 Heinricius, ‘‘ Ueber die Entwicklung und Struktur der Placenta beim Hunde,” Arch. f. mikr. Anat., vol. xxxiii., 1889. FQ:TAL NUTRITION: THE PLACENTA — 365 deny that by such physical processes the non-diffusible sub- stances with large molecules, e.g. hemoglobin and other blood proteins, can be absorbed by the syncytium. They postulate a vital action on the part of the cells, by which the necessary material is selected by the syncytium, and altered to a form in which it may be transmitted to the foetal circulation. It is not yet settled whether the activity of the syncytium is due to a phagocytic power or to an enzyme action. There is a third theory regarding the transmission of nutritive material, from the mother to the foetus, viz. by the actual passage of maternal leucocytes, charged with nutriment, from the one circulation to the other. This theory was first ad- vocated by Rauber * as the result of microscopic investigations, and he instanced, as further evidence in its favour, the greater number of leucocytes in the blood of the umbilical vein than in that of the artery. This view, which explained satisfactorily the passage of non-diffusible materials, subsequently received wide support. Thus Wiener® said: “It may be held as nearly without doubt that leucocytes cross from the maternal to the foetal blood,” and Preyer * considered the passage of leucocytes “indisputable.” The first objection was raised in a paper by Paterson.* Init he recorded three cases of pregnancy com- plicated by leucocythemia in the mother, and stated that the infants appeared quite normal and healthy, and their blood was of the usual colour and not white like the mothers’. These results were corroborated in similar cases by Cameron ® and Sanger,® who actually counted the foetal leucocytes and found no increase. These observations, and the inability of subse- quent investigators to demonstrate healthy leucocytes in the tissues intervening between the maternal and fcetal blood, have led to the abandonment of Rauber’s theory. 1 Rauber, Ueber den Ursprung der Milch und die Erndéhrung der Frucht im allgemeinen, Leipzig, 1879. Also Zool. Anz., No. 70. ; ® Wiener, ‘‘ Die Ernaéhrung des Fétus,” Samml. Klin. Vortrdge, No. 290. 3 Preyer, Specielle Physiologie des Embryo, 1883. « Paterson, ‘Cases of Acute Leucocythemia in connection with Preg- nancy,” Edinburgh Med. Jour., 1870. 5 Cameron, “ The Influence of Leuceemia upon Pregnancy,” Internat. Jour. of the Med. Sc., 1888. 8 Sanger, ‘‘ Ueber Leukiimie bei Schwangeren und angeborene Leukimie,” Arch. f. Gyndk,, vol. xxxiii., 1888. 366 THE PHYSIOLOGY OF REPRODUCTION But though maternal leucocytes do not pass as such straight into the foetal blood, they may be important in another way. In Ruminants, Bonnet? has drawn attention to the enormous number of degenerated leucocytes in the uterine milk, and demonstrated their absorption by the ectoderm, and similar observations have been recorded in Carnivores. In these orders leucocytes undoubtedly form a part of the embryonic nutriment. In the rest of the deciduate Mammals they seem to play a less important part. III. Tat Decipua In the uterine mucosa during pregnancy the most noticeable change occurs in the interglandular tissue of discoid placentie, in which decidual cells are formed. Various opinions have been held regarding their origin. Langhans, Hennig,’ and others held that they were enlarged and modified leucocytes, but they could not support their theory by direct observation. Overlach * and Frommel* described them as modified glandular cells, but there is no doubt that the true origin is, as Creighton ° first suggested, from the interglandular tissue of the mucosa. This consists of connective tissue of an embryonic type, which allows of a rapid transformation of its cellular elements. Masquelin and Swaen ® demonstrated this mode of origin in Rodents, and were supported by Minot, and Hart and Gulland.’ Leopold’s studies of early ova showed that the same origin was most probable in Man, and Peters described in the mucosa next the ovum connective tissue cells undergoing a decidual transformation. Their first appearance in the superficial layers 1 Bonnet, “« Uber Embryotrophe,” Deuts. med. Woch., 1899. ° Hennig, Studien iiber den Bau der menschlichen Placenta, &c., Leipzig, 1872. Overlach, ‘‘Die pseudomenstruirende Mucosa Uteri nach akuter Phos- phorvergiftung,” Arch. f. mikr. Anat., vol. xxxv., 1885. 4 Frommel, “ Beitrag zur Frage der Wachstumsrichtung der Placenta,” Zeits. f. Geburtsh, u. Gyndk., vol. xxxvi. 5 Creighton, ‘‘ The Formation of the Placenta in the Guinea-pig,” Jour. of Anat. and Phys., vol. xii., 1878. 5 Masquelin and Swaen, ‘‘ Premiéres phases du développement du placenta chez le lapin,”’ Bull. de ? Acad. roy. de Belg., 1879. 7 Hart and Gulland, “On the Structure of the Human Placenta,” &c., Labor. Rep., Roy, Coll. of Phys., Edinburgh, vol. iv., 1892. FaQTAL NUTRITION: THE PLACENTA = 367 of the mucosa has suggested a stimulus for their formation arising from the product of conception.’ The study of early human specimens has effectually disproved Ercolani’s? idea that the uterine mucosa was first entirely destroyed by the developing ovum, and then replaced by decidual tissue formed from the cells of the vessel walls. Such an endothelial pro- liferation does, however, occur in certain animals, e.g. hedgehog (Hubrecht ?) and bat (Nolf*), and probably in ectopic gestation in Man. The rapid increase in the size and number of the decidual cells, together with the dilatation of the blood-vessels, leads to a great increase in the thickness of the serotina. At a certain stage it reaches its full development, and then gradually diminishes till, at the end of gestation, it forms only a thin layer, and even disappears entirely at parts so that the villi impinge on the muscular wall. Individual decidual cells have probably a short life-history. Even at a comparatively early period many of them are found in various stages of hyaline degeneration, giving rise in part to the layers of fibrin, and as pregnancy advances there is a gradual extension of the fibrinous change. The degeneration of the decidual tissue would seem to be due to the influence of the foetal epiblast, as in Man it occurs much earlier and more abundantly in the serotina and reflexa than in the vera (Webster *). Its gradual diminution during pregnancy in- dicates an absorption of the decidua. That maternal tissues do not play a large part in this absorption is probable from the small number of leucocytes and the absence of lymph-channels in the neighbourhood of the fibrinous masses. At the same 1 Under abnormal conditions the formation of decidual cells occurs even although no ovum is present in the uterus, ¢.g. in tubal pregnancy in the human female. Whether this indicates a chemical stimulus from the ovum, or perhaps from the corpus luteum, effected through the blood-stream, is not yet known (see p. 491). ? Ercolani, ‘Sulla unita del tipo anatomico della placenta,” Mem. dell’ Accad. di Bologna, 1876. 3 Hubrecht, ‘‘The Placentation of EHrinaceus europeus,” Quar. Jour. Micr, Science, vol. xxx., 1889. 4 Nolf, “‘ Modifications de la muqueuse utérine pendant la gestation chez le murin,” Arch. de Biol., vol. xiv., 1896. 5 Webster, Human Placentation, Chicago, 1901. 368 THE PHYSIOLOGY OF REPRODUCTION time, specialised decidual cells, which have the power of de- stroying the rest of the decidual tissue, have been described in the hedgehog,! rat, and other animals. But it is now generally accepted that the foetal ectoderm from the earliest stages of pregnancy is able to disintegrate the cells with which it comes in contact, and to absorb the degenerate products. To that part of the foetal epiblast which is thus adapted for the ac- quirement of embryonic nutriment the name of trophoblast has been given by Hubrecht. Along with the gradual absorption of the degenerated parts of the decidua, and the great increase in the extent of the serotinal surface as pregnancy advances, there is probably a continued formation of new decidual elements. Pfannenstiel attributes the new formation to the peri-vascular tissue, and Webster to groups of active cells, the “ Ersatz-zellen ” of Klein,’ found here and there in the mucosa. Whatever their origin is, we may see, even in the shed placenta at full time, well-formed and apparently healthy decidual elements as well as the fibrinous masses containing cellular fragments. Within recent years there has been a tendency to belittle the importance of the connective tissue elements of the placenta. This has been largely due to the wider acceptance of the foetal origin of the syncytium, and to the conception of the placenta as a maternal hemorrhage circumscribed by foetal structures. But the same idea has been encouraged by some who look on the syncytium as maternal, and they adduce as evidence the obvious degeneration in the decidua during the greater part of pregnancy. Pfannenstiel maintains that decidual cells aré, from the begin- ning, degeneration forms of the connective tissue cells and are of use only as pabulum to be absorbed by the ovum. But during the whole of pregnancy, as mentioned above, there exist in the placenta decidual cells which, in their appearance and staining properties, show no resemblance to degenerated cells. From their abundance and great specialisation they have in all likeli- hood definite functions to perform. Their first formation dates 1 In a later memoir Hubrecht assigns to these cells, the deciduofracts of the hedgehog, an origin from the outer layer of the trophoblast. See foot-note, p. 470. 2 Klein, ‘‘ Entwicklung und Riickbildung d. Decidua,” Zetts. f. Geburtsh. u. Gyndk., vol, xxii. FaETAL NUTRITION: THE PLACENTA — 369 from the destruction of the surface epithelium when the blasto- cyst comes in contact with the connective tissue, and the earliest to appear are in the neighbourhood of the ovum. Their position and general appearance in different orders suggested to Turner a maternal reaction against the advance of the parasitic ovum, and the same idea has been forced on different observers. Fothergill’ speaks of the decidua preventing the injurious in- vasion of the uterine wall by the foetal elements. Chipman’s? figures on the placenta of the rabbit show that the ectoplacenta advances more rapidly where it encounters a vessel than where it lies against decidual cells. Wade and Watson * have noted its resemblance to young granulation tissue in the mucosa of the Fallopian tube in an early ectopic pregnancy. Bryce and Teacher,* in their description of the youngest human ovum yet examined, say: “ The decidua formation is a process of a con- servative nature, by which, during the early months of pregnancy, the activities of the trophoblast are limited and controlled until such time as placentation is complete.” Whether or not the decidua forms the protection to the mother, there is increasing evidence that the trophoblast does not invade the decidua to the extent supposed by the older authorities. This was first emphasised by Hubrecht in the hedgehog, and has more recently been advocated by Webster, and by Bryce and Teacher, in Man. Hoffmann * and Ahlfeld ® considered the decidua to be of the nature of a diffuse gland whose cells secreted a nutritive juice for the wants of the foetus. They stated that they could demonstrate such a secretion in the “ intervillous ” spaces formed by the separation of the decidual cells; but their observa- tions have been discounted by the investigations of Werth,’ 1 Fothergill, “‘ Decidual Cells,” Edinb. Med. Jour., vol. v., 1899. » Chipman, ‘ Observations on the Placenta of the Rabbit,” &c., Edinb. Roy. Coll. of Physic. Labor. Rep., vol. viii., 1903. 3 Wade and Watson (B. P.), ‘“‘The Anatomy and Histology of an Early Tubal Gestation,” Jour. of Obstet. and Gynec. of the Brit. Emp., 1908. 4 Bryce and Teacher, Contributions to the Study of the Karly Development and Imbedding of the Human Ovum, Glasgow, 1908. 5 Hoffmann, ‘‘Sicherer Nachweis der sogennanten Uterinmilch beim Menschen,” Zetts. f. Geburtsh. u. Gyndk., vol. viii., 1882. 8 Ahlfeld, Berichte u. Arbeiten aus der geburtsh. Klinik zu Chessen, Leipzig, 1883. 7 Werth, “Beitrage zur Anatomie, Physiologie, und Pathologie der menschlichen Schwangerschaft,” Arch. f. Gyndk., vol. xxii. 2A 370 THE PHYSIOLOGY OF REPRODUCTION who showed that the spherical globules described by Hoffmann were never present in the fresh placenta, but appeared only after its separation, and probably consisted of droplets exuded by the dying chorionic epithelium. It may be mentioned here that the “ boules,”’ described by Nattan-Larrier* as an internal secretion of the syncytium, have been thought by many to be a post-mortem appearance. In Rodents the decidual cells have an important and definite part to play in synthesising and storing glycogen as a supply of carbohydrate for the foetus. In Man also the decidual cells contain glycogen at an early period. Fat globules infiltrate the decidual cells of various animals at a stage when there is no question of a fatty degeneration taking place in the cells. Finally, the cells appear to have the power of ingesting and decomposing erythrocytes, but their relations to the iron- metabolism of the foetus require further study. PART II THE FIRST STAGES OF PREGNANCY: PLACENTAL CLASSIFICATION I. Toe Ovartan Ovum Wuite still in the ovary, the ovum obtains the necessary nutri- ment by means not yet discovered. In the Graafian follicle it is surrounded by the zona pellucida and externally the corona radiata. The origin of the zona pellucida has been variously described. According to some authorities it is the thickened outer edge of the ovum itself, a true vitelline membrane, but it is more probably a deposit from the cells of the corona radiata.” Its structure is almost homogeneous, but with the highest powers of the microscope fine striae are seen running from without inwards. Their appearance indicates the possibility that they are pores or delicate canals by which protoplasmic processes of the cells of the corona radiata, or a secretion of 1 Nattan-Larrier, ‘‘ Fonction sécrétoire du placenta,’ Comp. Rend. de U Acad. de Sc., vol. lii., 1900. ? Te. the discus proligerus, or innermost layer of follicular epithelium. FQ:TAL NUTRITION: THE PLACENTA = 37] these cells, may reach the ovum and nourish it (see p. 127). Whatever the source of the food-supply of the ovum is, it not only increases in size until it is ripe for deliverance, but stores in its protoplasm yolk granules, the deutoplasm of Beneden, which increase in number as the ovum approaches maturity. The granules vary in size and number in different species, and also in their position. They may be mingled uniformly through the cytoplasm, or be collected at the marginal zone (sheep), or at the periphery of the central zone (Man). During the earliest stages of segmentation, when perhaps food is not readily acces- sible, or a specialised form of nutriment is required, the granules are used up. II. Tue Fertinisep Ovum AND ITS CovERINGS When the ovum leaves the ovary it carries with it the zona pellucida and cells of the corona radiata. After fertilisation, which most probably occurs in all animals at the outer end of the oviduct or Fallopian tube, the cells disappear and are re- placed in some species by a homogeneous sticky layer of albuminous material. According to Robinson,’ it is derived in part from the disintegrated cells of the corona radiata, but most of it seems to be obtained from the secretion of the tubal and later of the uterine glands.” It is covered by villous tufts, which led to its designation as prochorion by Hensen. But the tufts are merely casts of the gland-ducts, due to the coagulation of the secretion by the use of reagents. The investment formed by the two layers around the ovum is very thick in Marsupials. In Ungulates it forms a thin coat, which disappears at a comparatively early stage in the pig, sheep, and deer. In the last named, according to Bischoff, there is no albumen layer. In Carnivores there is invariably a firm coat of zona pellucida or albumen layer, or both, which persists, in the dog and ferret at least, till the appearance of the primitive streak and the commencement of the formation of the mesoderm 1 Robinson, ‘‘On the Early Stages of Development of Mammalian Ova, and on the Formation of the Placenta,” Hunterian Lectures, Jour. of Anat. and Physiol., vol. xxxviii., 1904. 2 Bonnet, ‘‘ Ueber das Prochorion der Hundekeimblase,” Anat. Anz.. vol. xiii., 1897. 372 THE PHYSIOLOGY OF REPRODUCTION (Robinson). In Rodents there are differences. In the rabbit (Fig. 76) the albuminous layer is well-marked while the fertilised ovum is still in the Fallopian tube; on the fourth day, when the uterus is reached, it rapidly thins but remains up to the eighth day (Assheton!). In the rat the covering disappears early—usually about the eight-cell stage. In the mole the 1 Fig. 76.—Early blastocyst of the rabbit. (From Hertwig’s Entwicklungs- geschichte des Menschen und der Wirbelthiere : by permission of Gustav Fischer.) u, albumen layer ; zp, zona pellucida ; ¢, trophoblast ; sc, segmentation cavity; ec, mass of embryo cells. covering is thick, and, according to Heape,” the albumen layer is applied in the uterus and not in the Fallopian tube. It per- sists, as in the shrew, till the embryonic ectoderm appears on the surface of the ovum. In the hedgehog and bat it dis- appears before the blastocyst is formed, and in Tupata javanica it may be already absent in the two-cell stage. Little is known of it in the Primates ; in the earliest ovum investigated, 1 Assheton, “The Attachment of the Mammalian Embryo to the Walls of the Uterus,” Quar. Jour, Micr. Sci., vol. xxxvii., 1895. 2 Heape, ‘‘The Development of the Mole (Talpa europea),” &c., Quar. Jour, Micr. Sci., vol. xxiii., 1883. FETAL NUTRITION: THE PLACENTA 373 the four-cell stage of Macacus nemestrinus, it had already dis- appeared. . With regard to its functions, there is little doubt that the degenerating cells of the corona radiata, and later the albumen layer, serve as food for the growing mass of the ovum in the Fallopian tube and uterus. In the investment in the mouse, Jenkinson * found nutritive substances—fat, and probably also protein matter. In addition, Bonnet has adduced strong evidence to show that it is absorbed by the ectoderm of the blastodermic vesicle. In the rabbit the albumen layer forms a tough, strong membrane enclosing at the end of the third day the solid morula. Within the mass of cells a cavity develops and rapidly increases by diffusion inwards of fluid. “It is hardly conceivable that the delicate cells could cause expansion of the tough albuminous wall. Rather the osmotic current is more inwards than outwards, either simple or more probably assisted by the vital activity of the cells’ (Assheton). Heape had previously pointed out that the increasing fluid must be secreted into the interior of the blastocyst under considerable pressure, as the vesicle remains spherical and extends the uterine walls before it. Once inside, the fluid exerts a greater or less hydrostatic pressure, which is counteracted by the albumen layer, and the rupture of the vesicle is prevented. At the beginning of the cavity formation in the morula, the cells are not yet pressed on by the investment. Later the vesicle in- creases in size, and the outer cells are pressed and flattened. At the same time the albumen layer is thinned, and is soon hardly perceptible. Finally it ruptures, and immediately after- wards the blastodermic vesicle is flaccid, apparently from injury to its wall. Besides its nutritive and protective function, the investing layer may prevent the contact of the external cells of the blasto- dermic vesicle with the cells of the uterus. Only when it has disappeared is fusion of the maternal and fetal elements possible. Robinson has followed out this idea in different Mammals. He suggests that in those animals (Carnivores, rabbit) in which the embryonic ectoderm reaches the surface, 1 Jenkinson, ‘Observations on the Physiology and Histology of the Placenta of the Mouse,” Tijd. Nederl. Dierk., Ver. ii., Dl. 7. 374 THE PHYSIOLOGY OF REPRODUCTION the albumen layer prevents contact with the uterine wall till differentiation of the ectodermal cells has taken place to such an extent that they are no longer disposed to fuse with the uterine tissues. In those in which the embryonic ectoderm never reaches the surface (mouse, guinea-pig, hedgehog, bat, probably Primates), the investment disappears before the blastula is attained. With the disappearance of the zona, the developing ovum lies naked in the Fallopian tube or the uterus. It takes some time to complete the journey along the tube—about eighty hours in the rabbit, and a little longer in the sheep. For a further period it remains unattached in the uterine cavity, and then, by processes which vary in different orders, it obtains attachment—loose in Marsupials and firmer in the other orders. At first each blastomere is nourished separately ; but when the blastocyst is formed, the greater part of its outer layer is set aside to look after the nutrition of the whole, and takes no share in the formation of the embryo or amnion. To that part Hubrecht gave the name of trophoblast, and the term has been generally accepted. Already, before the embryo is elaborated, provision is in this way made for its maintenance. II. Tue Urertne Mucosa While the ovum is still in the oviduct, no obvious changes occur in the uterus itself. In the sheep, Assheton ' detected no difference except an increase in the number of the leucocytes. There was no sign of activity in the uterine glands or blood- vessels. When the ovum reaches the uterus changes begin— dilatation of blood-vessels and lymphatics, widening and in- creased tortuosity of glands, disappearance of cilia from the surface epithelium. The whole mucosa is soft and cedematous, and there may even be a transudation of lymph into the uterine cavity, which is mingled with the glandular secretion to form a supply of nutriment for the ovum before attachment. Great 1 Assheton, “The Morphology of the Ungulate Placenta,” &c., Phil. Trans, Roy. Soc., London, Ser. B., vol. cxeviii., 1906. FCETAL NUTRITION: THE PLACENTA = 375 differences, however, occur, and it is more convenient to de- scribe the changes in the uterine mucosa in each order. IV. PLacentaL CLASsIFICATION At the outset we are beset with the difficulty of grouping Mammals in such a way as to show how the variations in the anatomy and physiology of the placenta have been evolved. Well-marked differences, such as occur in other organs and serve to differentiate Mammals into certain orders, are not always to be observed in their placente. In widely diverging groups there may be striking similarities in placentation, while great differences may exist in closely related types. On this account the most satisfactory, and indeed the only possible, classification of Mammals for our purpose is one based on their placental characters. Such a classification was introduced by Huxley * in 1864. He divided Mammals into two great sections according as their placentee were non-deciduate or deciduate.” In Deciduates the substance of the mucosa undergoes rapid growth and textural modification to form decidual tissue, and the maternal and fcetal parts of the placenta become firmly united. In Non-deciduates there is no formation of decidual tissue, and at parturition the foetal villi are simply drawn out like the fingers from a glove, no vascular substance from the mother being thrown off. In a later publication? Huxley attempted to arrange all Mammals in one or other division. The Deciduata are classed in two groups according to the external appearance of the placenta, which is either zonary, as in Carnivora, Amphibia, and Proboscidea ; or discoid, as in Rodentia, Insectivora, Cheiroptera, Lemuride, Simiade, and Primates. The Non-deciduata are the Ungulata and Cetacea. The Sirenia and Edentata offer diffi- culties. Of the latter, Manis has a diffuse placenta, Bradypus a poly-cotyledonary, and Orycteropus a discoid and deciduate 1 Huxley, The Elements of Comparative Anatomy, London. 2 Thirty years earlier Weber had suggested a similar division into caducous and non-caducous ; but his terms, although accepted by von Baer and Eschricht, were displaced by those of Huxley. 3 Huxley, Introduction to the Classification of Mammals, London, 1869. 376 THE PHYSIOLOGY OF REPRODUCTION placenta. One of the Sirenia, the dugong, which possesses a zonary but not deciduate placenta, illustrates a type not re- presented at all in Huxley’s classification. No maternal tissue is lost at birth ; but, in addition, part of the foetal tissue remains attached to the uterus and is absorbed (Turner *). The placenta of the mole is not shed at birth, but becomes gradually absorbed by the mother. For such Hubrecht? suggested the term contra-deciduate. The classification of Strahl? does not promise to be any more satisfactory. He divides Mammals into two groups, one having a “ Halbplacenta’’ and the other a “ Vollplacenta.” In the former no maternal vessels are opened and the connec- tion is less intimate, while in the latter hemorrhages occur during pregnancy. But in a physiological sense, the half placenta is certainly as efficient an organ of nutrition as the whole placenta. In view of the recent work on the placenta, it is obvious that Huxley’s classification fails in taking no account of the trophoblast, the most active constituent of the placenta, and in laying too much stress on the differences at birth, 7.e. on the shedding of an organ which is of no more use, and may be con- sidered as physiologically dead. Moreover, it would appear that in many of the deciduate Mammals almost no maternal tissue except blood is lost at birth, and maternal blood is also lost in the non-deciduate sheep. A perfect classification must take account of the structure and behaviour of the trophoblast during the whole course, or at least the earlier part, of pregnancy. Without it a clear insight into the processes which regulate foetal nutrition cannot be obtained. Robinson * and Assheton ° have recently made efforts in this direction, the former em- phasising the methods of attachment of the trophoblast to the uterus, and the latter the anatomical condition of the tropho- 1 Turner, ‘‘On the Placentation of Halicore Dugong,’ Trans. Roy. Soc. Edin., vol. xxxv., 1889. 2 Hubrecht, ‘‘ Spolia Nemoris,” Quar. Jour. Micr. Sct., vol, xxxvi., 1894. 3 See Hertwig, Entwicklungsgeschichte des Menschen und der Wirbelthiere, 1906. 4 Robinson, ‘‘ Hunterian Lectures,” loc. cit. 5 Assheton, ‘‘The Morphology of the Ungulate Placenta,’ Phil. Trans. Roy. Soc., London, Ser. B., vol. cxcviii., 1906. ie, FATAL NUTRITION: THE PLACENTA = 377 blast at the time of its first attachment. Hubrecht, on the basis of Huxley’s statement that Insectivora are among the most archaic of Mammals, has investigated several members of this order as showing probably the most ancient type of placenta, and thus affording a starting-point for a classification. Accord- ing to Huxley, the least differentiated types, the hedgehogs and Gymnura, occupy a central position, while shrews show resemblances to Rodents, and Tupate to lemurs; moles and Galeopitheci vary in other directions, while the whole order shows more general relationships to Carnivores and Ungulates. But at present these relationships are not understood. It seems impossible to trace any connection between the placenta of the sheep, in which there is no circulation of maternal blood in the foetal parts of the placenta but the foetus is nourished by uterine milk, and that of the hedgehog, in which maternal blood circulates in the trophoblastic lacune and forms the main source of nutriment. At present, we must be content with a review of the pro- cesses occurring in several Mammals which have been more particularly investigated, without straining to find how such processes have arisen in the course of placental evolution." PART III THE FETAL MEMBRANES, THE YOLK-SAC, AND THE PLACENTA I. GeneraL Anatomy oF THE FataL MEMBRANES So far no reference has been made to the part played by the mesoblast in the nutrition of the embryo. The placenta has been described as an organ consisting of maternal and fcetal elements—of modified uterine mucosa, and trophoblast which ' Throughout this chapter, the arrangement of the mammalian orders is more in accordance with the older views of placental classification, but an attempt has been made to emphasise the trophoblastic characteristics. Since it was written, an important memoir has been published by Hubrecht (“Early Ontogenetic Phenomena in Mammals,” Quar. Jour. Micr. Sci., 1908), in which he follows out, in more detail than previously, his ideas regarding the phylogeny of the placenta. 378 THE PHYSIOLOGY OF REPRODUCTION absorbs nutritive material from the mucosa and from the maternal blood. The nutriment serves in part for the nutrition of the trophoblast itself, and in part for the growth and de- velopment of the embryo. In the earliest stages there are as yet no embryonic vessels, and the nutriment is, transmitted from cell to cell. But as the embryo increases in size and its requirements grow in proportion, such a path becomes in- adequate, and a vascular channel is developed in connection with the two foetal membranes—the yolk-sac or umbilical vesicle, and the allantois. The mammalian yolk-sac has only a secondary importance for the nutrition of the embryo. The blastodermic vesicle at an early stage of development is divided into an embryonic and a non-embryonic area. The latter is the yolk-sac which gradually becomes folded off from the embryo. Its relations are the same as those of the yolk-sac in Sauropsida, but the contents are an albuminous fluid instead of yolk. It is com- monly believed that the placental Mammals are descended from ancestors in which the ovum had a large supply of yolk, but that, when the fertilised ovum found a new supply of food in the uterus, the yolk was reduced and ultimately disappeared. At the same time the envelopes, which were developed under the influence of the vitelline contents, have been preserved and modified in different ways to aid uterine nutrition.+ In the early stages the development proceeds, as in birds and reptiles, with the gradual extension of the hypoblast round the wall of the blastocyst, which thus becomes didermic. The mesoblast grows out between the epiblast and hypoblast, starting at the embryonic area and gradually extending for a variable distance round the wall of the blastocyst. Near the embryo appears the area vasculosa, in which blood-vessels and blood are developed from the cells of the mesoblast, while at the same time the embryo begins to be folded off from the yolk-sac by anterior and posterior folds. The area gradually extends further and further round. Its outer boundary is marked by the sinus termunalis which communicates with the vitelline veins. The blood is brought from the dorsal aorte by a 1 According to Hubrecht’s views, the mammalian ovum is not descended from the ovum of Sauropsida. FATAL NUTRITION: THE PLACENTA = 379 series of lateral vitelline branches. These arteries break up into a deeper arterial network, from which the blood is collected into the sinus terminalis and the superficial venous network, and in this way reaches the vitelline veins and so passes to the heart. During the spread of the mesoblast, it splits into an external layer or somatopleur, and an internal layer or splanchnopleur. The former is non-vascular and adheres to the inner aspect of the trophoblast, forming with it the diplo-trophoblast, and the splanchnopleur is applied externally to the hypoblastic wall of the yolk-sac. By the splitting a space is formed between the two layers. This is the eatra-embryonic ca@lom, which thus intervenes over a larger or smaller area between the diplo-tropho- blast and the yolk-sac. While the above changes are taking place, the allantois grows out (on the tenth day in the rabbit) from the hind-gut as a vesicle lined by hypoblast, and covered externally by a layer of splanchnopleur. In some Mammals the cavity of the allantois is not continued beyond the body-wall of the embryo, the extra-embryonic portion consisting of a solid rod of mesoblast. In all orders below the Primates, however, it projects free for a time into the ccelom, and later fuses, except in the Marsupials, with the whole or part of the outer wall of the blastocyst. In the allantoic mesoblast many vessels are developed, and branches extend into the projections which form the cores of the villi. The blood is brought by two allantoic arteries continued from the terminal bifurcation of the dorsal aorta, and returned by one, or more rarely two, allantoic veins. “While the placenta is being developed, the folding off of the embryo from the yolk-sac becomes more complete, and the yolk-sac remains connected with the ileal region of the in- testine by a narrow stalk, the vitelline duct. While the true splanchnic stalk of the yolk-sac is becoming narrow, a somatic stalk connecting the amnion with the walls of the embryo is also formed, and closely envelops the stalk both of the allantois and yolk-sac. The somatic stalk, together with its contents, is known as the umbilical cord” (Balfour’). The yolk-sac atrophies completely in some, but in others it is only removed at birth. 1 Balfour, Comparative Embryology, London, 1881. 380 THE PHYSIOLOGY OF REPRODUCTION Il. Tue Nurririve ImporTANcE oF THE YOLK-SAC When the blastodermic vesicle becomes adherent to, or sinks into, the uterine mucosa, the wall of the yolk-sac in some orders becomes intimately related to the uterine mucosa and is nourished by it. Even in the non-mammalian Vertebrata the latter condition has been observed. In the Lacertilia the yolk-sac absorbs nutriment from the uterus through the porous shell. In Mustelus levis the embryos lie in a fluid derived from the surface secretion and a lymphoid transudate of the uterine mucosa. It passes through the porous shell to reach the yolk-sac (Brinkmann 1). In Seps chalcides, a reptile, the insufficient supply of yolk is added to by a uterine secretion containing degenerated cells and blood derivatives, the outer layer of the blastocyst being distinctly phagocytic (Giacomini ”). But in the Sauropsida no union takes place between the maternal tissues and the foetal membranes, and so in one order of Mammals, the Ornithodelphia,? where the young de- velop outside the body. In all the other orders the wall of the yolk-sac comes into relation with the uterine wall over a greater or less area, depending on the extent to which the mesoblast, spreading round the wall of the blastocyst, splits into two layers. In the non-mammalian Vertebrates, the mesoblast and the ceelom extend completely round and the yolk-sac is entirely separated from the surface layer; so in the sheep and Man. In others (e.g. the rabbit) the ccelom does not spread so far. It still remains to consider the path by which the nutriment is conveyed to the embryo. In partial extension of the area vasculosa, the wall of the yolk-sac consists of three parts, each with different relations (see Fig. 77) :—(1) The non-vascular part, with a two-layered wall of epiblast and hypoblast; (2) the vascular part, where the mesoblast is unsplit, e.g. in the opossum —the mesoblast splits in its entire extent in the rabbit ; (3) the part opposite the ccelom. In all three parts the trophoblast is 1 Brinkmann, ‘‘ Histologie, Histogenese und Bedeutung der Mucosa Uteri einiger Viviparer Haie und Rochen,” Mitt. a. d. Zool. Stat. ~. Neapel., vol. xvi., 1903. 2 Giacomini, ‘‘ Ueber die Entwicklung von Seps Chalcides,” Anat. Anz., vol. vi., 1891. 3 Or Monotremata. FETAL NUTRITION: THE PLACENTA — 381 bathed by the uterine secretion after the disappearance of the prochorion. In the non-vascular part it is probably trans- mitted through the hypoblast cells to the yolk-sac, whence, in turn, it reaches the embryo either by the vitelline vessels or the developing alimentary canal. In the vascular part the same may occur, or the nutriment may be conveyed to the embryo directly by the vessels of the area vasculosa. It is in this region that the fcetal circulation is brought close to the maternal, and gaseous exchanges may be effected. Opposite the ccelom Fig. 77.—Diagram to illustrate the three parts of the wall of the yolk-sac in the rabbit. (From Minot’s Human Embryology, by permission of William Wood & Co.) Al., allantois; Apl., area placentalis; Ec., ectoderm; Mes., mesoderm ; Ent., extra-embryonic entoderm ; Ca., celom; £n., entodermic cavity of the embryo; Pro.A, proamnion. the trophoblast is lined by a thin layer of non-vascular somato- pleur, through which transference of material to the ccelomic cavity is possible. This part is subsequently connected with the embryo by the allantoic vessels. When the yolk-sac is entirely separated from the outer wall, nutritive substances may also be transmitted to the ccelomic cavity and then to the embryo or yolk-sac. The nutritive importance of the yolk-sac may now be con- sidered in greater detail in several orders of Mammals. Marsuprats.—In the opossum the mesoblast spreads about half-way round the wall of the blastocyst, but it does not split 382. THE PHYSIOLOGY OF REPRODUCTION over its whole extent. Hence the ccelom is small, and corre- spondingly the separation of the yolk-sac and trophoblast is insignificant (Fig. 78). The allantois grows out into the ccelom only to impinge on and invaginate the wall of the yolk- sac. It never comes in contact with the outer wall of the blastocyst. The part of the wall where the mesoblast is unsplit is thrown into folds which fit into corresponding furrows of the mucosa. Hence an avillous yolk-sac placenta is formed (Selenka +). The nutrition in the uterus is very primitive. Fie. 78.—Diagram of an opossum embryo and its appendages. (From Minot.) All, allantois; Yk, cavity of yolk-sac; Caw, celom; Am, amnion; Pro.am, pro-amnion; mb, embryo; Ec, ectoderm; nt, entoderm; mes, mesoderm ; s.f, sinus terminalis ; Cho, chorion (diplo-trophoblast). The ova contain a comparatively large supply of yolk granules for the initial stages of development. As they travel along the oviduct and into the uterus, they are invested with a thick nutritive layer, derived from the secretion of the tubal and uterine glands. Later the embryos are also nourished by the primitive placental structures for a period short in duration, but long enough to allow of the differentiation of their main organs and systems. In the mucosa the surface epithelium remains intact. The only change is an cedema of the layers, and the sole nutritive material is a watery fluid, composed of 1 Selenka, Studzen iiber die Entwicklungsgeschichte der Thiere, Wiesbaden. FQTAL NUTRITION: THE PLACENTA — 383 glandular secretion and a lymph transudate almost devoid of cells. It is absorbed by the trophoblast cells, which here and there enlarge to enormous “ Nahrzellen”’ and so increase the absorbing surface. After eight days the food supply becomes inadequate for the developing embryos, and they are transferred to the pouch and nourished by the mammary secretion. Fig. 79.—Diagram showing the arrangement of the fcetal membranes in Dasyurus. (From Hill, ‘‘On the Foetal Membranes, Placentation and Parturition of the Native Cat (Dasyurus viverrinus),” Anat, Anzeig., vol. xviii., 1900. amn., trunk amnion; all, allantois; bil.omph, bilaminar omphalopleur ; ch, chorion (diplo-trophoblast); ede, extra-embryonic splanchnocele ; proa, proamnion ; proa.l, posterior limit of proamnion; s.¢, sinus ter- minalis ; vasc.omph. vascular omphalopleur ; y.c, cavity of yolk-sac ; y.8, yolk-stalk ; y.spl, invaginated yolk-sac splanchnopleur: the ectoderm is represented by a thin line, the entoderm by a dotted line, and the mesoderm by a thick line. In Dasywrus the allantois is vascular over a small area and comes in contact with the diplo-trophoblast (Fig. 79). But the allantoic "vessels degenerate rapidly and completely, and the allantois again lies free in the ccelom. In the region of the area vasculosa the wall of the yolk-sac adheres to the uterine epithelium, and, as in the opossum, forms a simple yolk-sac 384 THE PHYSIOLOGY OF REPRODUCTION placenta. The superficial capillaries of the mucosa, which are slightly dilated, are separated from the vitelline vessels by the uterine epithelium and a thin layer of foetal ectoderm. ‘Through the two layers the gaseous exchange probably takes place. Beyond the sinus terminalis, the non-vascular part of the wall unites over an annular zone with the uterine epithelium by enlarged ectodermal cells. These syncytial “ Nahrzellen ” are phagocytic, and enclose fragments of epithelium and superficial capillaries. Maternal blood is effused and lies in a space between the ectoderm and entoderm, whence it is transmitted to the cavity of the yolk-sac and serves for nutriment (Hill'). The gestation period is about eight days, as in the opossum. In Perameles the placental structures are better developed (Hill*). Before the attachment of the blastocyst, the uterine mucosa undergoes preliminary changes. The capillaries in- crease in size and new vessels are formed ; the interglandular tissue is composed of a loose network of anastomosing cells and the inter-spaces are filled with lymph, the glands increase in length and diameter, and the cells of the surface epithelium lose their boundaries, and fuse to form a syncytium analogous to the symplasma of higher forms (see p. 414). Opposite the ccelom, the blastocyst becomes attached to a discoidal area of the uterine symplasma by means of enlarged ectodermal cells, and later its wall is vascularised by the allantois. Outside the disc, the part corresponding to the area vasculosa is also attached by an annular zone, and a yolk-sac placenta is formed. The non-vascular part of the wall is bathed by the uterine fluid as in the opossum (Fig. 80). In the discoid area a functional allantoic placenta is de- veloped. The ectodermal giant-cells, like the early tropho- blastic proliferation in Man, disappear, and the allantoic vessels become firmly attached to the symplasma into which the maternal vessels penetrate. A regular interlocking of maternal and foetal tissues is produced, and the two systems of blood- vessels are separated at the most by a thin layer of symplasma. 1 Hill, “On the Foetal Membranes, &c., of the Native Cat (Dasyurus viverrinus),”’ Anat, Anz., vol. xviii., 1900. 2 Hill, ‘The Placentation of Perameles,” Quar. Jour. Mier. Sci., vol. xl., 1898. FETAL NUTRITION: THE PLACENTA — 385 It is not yet determined whether the yolk-sac placenta is functional till birth. According to Hill the wall probably breaks up before the end of pregnancy. The allantoic placenta, on the other hand, remains active, and at the time of birth some bil omph —y'spl. Fig. 80.—Diagram showing arrangement of fcetal membranes in Perameles. (From Hill, ‘The Placentation of Perameles,” Quar. Jour. Mier. Sci., vol. xl., 1897.) amn, amnion ; all.c, allantoic cavity ; all.mes, allanto-chorionic mesenchyme ; all.s, allantoic stalk; bil omph, bilaminar omphalopleur; ch., marginal zone of true chorion around the allanto-chorionic area; cde, extra- embryonic ccelom; cée.w, inner or chorionic wall of allantois; proa.r, persistent remnant of proamnion; st, sinus terminalis; vasc.omph, vascular omphalopleur ; y.c, yolk-sac cavity ; y.spl., invaginated yolk- sac splanchnopleur; ectoderm represented by thin line, mesoderm by dotted line, entoderm by thick line. maternal tissue is shed, while part of the foetal tissue is left behind. The gestation period is about eight days. The allantois in Perameles is of greater importance than in the opossum or Dasyurus ; but, relatively to the yolk-sac, it plays a small part in the nutrition of the embryo, as evidenced 2B 386 THE PHYSIOLOGY OF REPRODUCTION by the fact that the vitelline vein is thrice as large as the allantoic vein. Uneutata.—In the sheep the blastocyst elongates early, and contains at one part the thickened embryonic area or shield (Fig. 81). From it the mesoderm reaches out on all sides. As it spreads between the epiblast and hypoblast, the ccelom is de- veloped in it. By the thirteenth day one-third of the circum- ference is surrounded by ccelom, and in this area the yolk-sac is separated from the outer wall. At the seventeenth day the separation of the yolk-sac is complete all round (Bonnet ’). It continues, however, to grow pari passu with the blastodermic vesicle, and is gradually pushed to one side by the enlargement hat Fic. 81.—Elongated blastocyst of sheep at thirteenth day of pregnancy. (From Hertwig’s Entwicklungsgeschichte des Menschen und der Wirbelthiere, by permission of Gustav Fischer.) bl, blastocyst ; E, embryonic shield. of the cclom. At the twenty-fifth day it is reduced to a solid rod of cells with a few blood-vessels on its outer surface (Fig. 82), and it disappears before the end of pregnancy (Assheton ?). The allantois grows out into the ccelom very early and expands with extraordinary rapidity, occupying most of the cavity of the blastodermic vesicle. Its further developments are de- scribed later (p. 397). Hence in the sheep, and in the pig and cow, in which the conditions are similar, the yolk-sac is func- tional only from the first appearance of the vessels in the area vasculosa till about the twentieth day of pregnancy. Carnivora.—The mesoblast and ccelom extend completely round the blastocyst, and the vitelline circulation is active 1 Bonnet, ‘‘ Beitrage zur Embryologie der Wiederkauer,” Arch. f. Anat. u. Physiol., 1889. 2 Assheton, ‘* The Morphology of the Ungulate Placenta,’ Phil. Trans. Roy, Soc., London, Ser. B., vol. excviii., 1906. bE FETAL NUTRITION: THE PLACENTA = 387 only in the early stages. In the dog the yolk-sac is large and extends at first to the end of the citron-shaped ovum (Fig. 97). According to Bischoff! it persists till birth, but this is denied by Duval.? The allantois grows out on the dorsal side of the embryo, and fuses with the diplo-trophoblast over a small discoidal area. Later, as the cavity of the allantois en- larges, it adheres to the whole of the blastocyst wall except the poles. Subsequently the zone of adhesion is reduced in extent (see p. £13). Prozoscip—a and Hyrax.— The elephant and the aberrant genus Hyrax have at full-time, like the Carnivores, a zonary placenta, but little is known regarding the development of the foetal mem- branes. Assheton® has recently given an account of two early embryos of Hyrax. In the younger, the yolk-sac occupied about three- quarters of the surface of the blastocyst, and the allantois the temaining quarter, the ovum pos- sibly being wholly embedded in the uterine mucosa. The yolk-sac was covered with a network of vessels, and the head of the embryo dipped into it. It was Fig. 82—Transverse section through the blastocyst of the sheep at the twenty-fifth day. (From Assheton, ‘‘‘The Mor- phology of the Ungulate Placenta,” Phil: Trans. Roy. Soc., London, Ser. B., vol. excviii., 1906.) A., allantois; AS, splanchno- pleur of allantois; A.V, allan- toic blood-vessel; C, ccelom ; V, commencing folds from which villi spring; Y, solid yolk-sac. invested externally with a mass of trophoblastic cells, honey- combed with spaces and filled with maternal blood, but no villi were developed. In the second embryo the yolk-sac was 1 Bischoff, Entwickelungsgeschichte der Sdugethiere und des Menschen, 1842, 2 Duval, ‘‘ Le Placenta des Carnassiers,” Jour. de l’ Anat. et de la Phys., 1893. 3 Assheton, Phil. Trans. Roy. Soc., London, loc, cit. 388 THE PHYSIOLOGY OF REPRODUCTION much reduced, and was “ presumably enveloped by the allantois.” It had previously been shown by Turner that the yolk-sac disap- peared at an early period. Ropent1a.—In Rodents the conditions are entirely different. The mesoblast never extends, in the rabbit, rat, or mouse, completely round the ovum, and the yolk-sac hypoblast remains long in contact with the trophoblast, and carries on the nutrition of the embryo till the tardily formed allantoic placenta is de- veloped. Regarding the partial extension of the mesoblast, Minot’ says: “That it represents a modified condition is Fia. 83.—Blastodermic vesicle of the rabbit. (Minot. ) ce, celom ; Cho, chorion (diplo-trophoblast); Yk, yolk-sac; mes, mesoderm ; v.t, vena terminalis ; Ent, entoderm ; Ec, ectoderm. evident, since in all non-mammalian Vertebrates both mesoderm and coelom extend completely round the yolk. Hence the com- plete separation of the yolk-sac in Man and the sheep is nearer the ancestral type than the relations of the extra-embryonic germ-layers to one another in the rabbit and opossum.” In the rabbit, the mesoblast begins to spread out from the embryonic region about the end of the first week of gestation, and it gradually reaches half-way round the circumference of the blastocyst. It splits into two layers over its whole extent, and it is limited below by the sinus terminalis (Fig. 83). The lower half of the yolk-sac is non-vascular, and its wall of hypoblast is closely invested by trophoblast. Later the yolk-sac begins to 1 Minot, Human Embryology, Boston, 1892. FQETAL NUTRITION: THE PLACENTA = 389 shrink, taking a mushroom shape, and its vascular half comes against the non-vascular half (Fig. 84). The specially large coelomic space, thus left by the shrinking of the vesicle, is filled with fluid through which the allantois extends to reach the part of the wall not covered by the yolk-sac. Hence at this stage the whole wall of the blastocyst is vascularised, one half by the vitelline and the other half by the allantoic vessels. From an investigation of the early stages in the mouse and Fic. 84 —Diagram of the blastodermic vesicle of the rabbit in longitudinal section. (From Hertwig’s Hntwicklungsgeschichte des Menschen und der Wirbelthiere.) e, embryo; a, amnion; al, allantois with blood-vessels; fd, vascular layer of mushroom-shaped ‘yolk- sac; d.s, cavity of yolk-sac; s.t, sinus terminalis ; r, large space filled with fluid. rat, Robinson ? attaches much importance to the yolk-sac in providing for the nutrition of the embryo. On the seventh day the yolk-sac is large, and becomes invaginated with the inver- sion of the germinal layers (see p. 438). Outside its thin wall lies extravasated maternal blood, which is absorbed into the cavity. Over a large area, the wall of the yolk-sac becomes villous with a covering of columnar hypoblast. Over a small 1 Hertwig, Entwicklungsgeschichte des Menschen und der Wirbelthiere, 1906. 2 Robinson, ‘t The Nutritive Importance of the Yolk-Sac,” Jour. of Anat. and Phys., vol. xxvi., 1892. 390 THE PHYSIOLOGY OF REPRODUCTION area the trophoblast is thickened and maternal blood circulates in its spaces. But the allantois has not yet come in contact with it, and the blood “ must serve only for the nutriment of the trophoblast itself.” At the eleventh day the trophoblast is vascularised by the allantoic vessels, by which the nutriment is now transmitted as well as by the vitelline vessels in the yolk- villi. Then the yolk-sac becomes less important. The circula- tion in the decidua reflexa, which surrounds it, decreases and ceases altogether on the sixteenth day, and the wall of the yolk-sac becomes thin and bloodless. “At the same time numerous diverticula grow out from the entodermal sinus into the hilum of the allantoic placenta, and these may still absorb nutriment though they are more probably excretory.” Later the outer wall of the invaginated yolk-sac undergoes atrophy and completely disappears. The remains of the yolk-sac cavity are in this way bathed in the uterine fluids. At the same time the villi of the inner wall increase in size and complexity, but whether they absorb the fluids or are entirely excretory is uncertain. In the spiny mouse (Acomys caharinus), Assheton 1 found in a well-advanced pregnancy that the yolk-sac was still extremely vascular, and covered with a columnar-celled epithelium which was much folded. The blood-vessels lay in the folds, and so approached closely to the placenta. The yolk-sac was firmly attached to the placenta over the peripheral area, but not so closely as described above for the rat and common mouse. In the spiny mouse the folds do not become involved in the placental tissues. InsEctivora.—In the hedgehog, the yolk-sac forms a placenta which nourishes the embryo until the mesoblast splits into two layers and the allantoic placenta is formed. At a very early stage the epiblastic wall of the blastocyst has spaces in which maternal blood appears. As the mesoblast spreads out in a single layer, the area vasculosa develops, and its branches, contained in mesoblastic warts and ridges, interlock with the adjacent trophoblast to form yolk-villi (Fig. 85). The yolk- 1 Assheton, ‘On the Fetus and Placenta of the Spiny Mouse,” Proc. Zool, Soc., London, 1905, vol. ii. FQ:TAL NUTRITION: THE PLACENTA — 391 sac or omphaloidean placenta reaches its full development at the time when the allantois comes in contact with the tropho- blast (see p. 451). Then the yolk-sac is gradually separated from the wall, more and more of its villi being peeled out from the trophoblast as the separation increases. The vitelline circulation at the same time diminishes, though it never ceases entirely (Hubrecht *). _ Allantoidean region of trophosphere Omphaloidean region of trophosphere Uterine Decidua reflexa lumen a Fig. 85.—Diagram to illustrate the foetal membranes of Erinaceus. (From Hubrecht’s ‘The Placentation of Hrinaceus europeus,” Quar. Jour. Micr. Sci., vol. xxx., 1889.) In the shrew, the yolk-sac adheres by a zonary strip to lateral cushions of proliferated mucosa, but the resulting yolk- sac placenta is avillous (Hubrecht 2). The trophoblast is again thickened, and in its spaces maternal blood appears, but at a later date than in the hedgehog. The maternal blood is bodily 1 Hubrecht, ‘‘The Placentation of Erinaceus europaeus,” Quar. Jour. Micr. Sci., vol. xxx., 1889. 2 Hubrecht, ‘The Placentation of the Shrew,” Quar. Jour, Micr. Sci., vol. xxxv., 1894. 392 'THE PHYSIOLOGY OF REPRODUCTION absorbed, and at the same time the yolk-sac contains a charac- teristic yellowish-green, glassy coagulum with granules in it. Later the mucosal cushions disappear and the adjacent tropho- blast thins (see p. 454). In the mole a simple yolk-sac placenta persists throughout pregnancy (Robinson '). Unlike the hedgehog and the shrew, in which the gland lumina are plugged by the trophoblastic syncytium, there is in the mole a copious glandular secretion containing degenerated cells, which is absorbed by the tropho- blast (see p. 456). Tupata javanica differs from the other Insectivora in having a temporary yolk-sac placenta formed in the same situation as the allantoic placenta subsequently occupies (see p. 458). The same occurs in the bat (p. 462). PrimaTes.—In monkeys, old- and new-world, there is no decidua reflexa, and a portion of the trophoblast is in contact with the uterine fluids. But even in Selenka’s earliest specimens of monkeys and apes, the yolk-sac is a small, closed sac attached to the ventral surface of the embryonic area, and is entirely separated from the trophoblast. The embryonic area is con- nected with the inner surface of the chorion by a short stalk of mesoderm, in which the vessels run. In the youngest human ovum yet examined, the yolk-sac is also a small, closed vesicle, separated from the trophoblast by a single thick layer of mesoblast (Fig. 86). The splitting of the mesoblast occurs very early, even before the appearance of the primitive streak, and the ccelom spreads round the whole circum- ference of the ovum. The earliest vessels appear on the under surface of the sac, and gradually extend over its upper pole, until the whole sphere is covered by a vascular network. The vessels are in direct continuity with vessels which develop in the connecting-stalk (see p. 463), and through them with the vessels of the chorion by a vascular loop, the sinus ensiformis of Eternod (Bryce *). This communication appears to exist before any vessels appear in the embryo itself. From the third week onwards, saccular dilatations of the entodermal lining of 1 Robinson, Hunterian Lect., loc. cit. 2 See Quain’s Anat., vol. i., Part I., 1908. FQ:TAL NUTRITION: THE PLACENTA = 393 the yolk-sac are produced, and from their walls solid masses of cells are budded off, resembling liver-tissue in its simplest form and perhaps functioning as such (von Spee’). The sac grows up to the end of the fourth week. It is then pear-shaped, and Fig. 86.— Hypothetical section of the human ovum embedded in the decidua, somewhat younger than Peters’ ovum. The trophoblast is greatly thiekened, and lined with mesoderm, which surrounds also the embryonic rudiment, with its yolk-sac and amnio-embryonic cavity (T. H. Bryce in Quain’s Anatomy). The embryonic rudiment is proportionally on too large a scale. is united to the intestine by a long neck in which the cavity is obliterated. The vesicle persists throughout pregnancy. Little is known of its contents; at the end of pregnancy it contains variable quantities of fatty substances and _ carbonates (Schultze *), 1 See Quain’s Anatomy, vol. i., Part I., 1908. ? Schultze, ‘‘ Ueber die Embryonalhiillen und die Placenta der Siugethiere und des Menschen,” Sttzwngsb. d. Wiirzburger physik.-med, Gesell., 1896. 394 ‘THE PHYSIOLOGY OF REPRODUCTION TI. Tue Puacenta in INDECIDUATA In the placental Mammals, an attachment takes place be- tween maternal and fcetal tissues in the uterus, and the tropho- blast is vascularised, except in the Primates, by the allantois. The method of attachment varies in different orders, and sometimes in different groups of an order. In the Indeciduata, Fig. 87.—Portion of the injected chorion of the pig. The figure shows a minute circular spot, b, enclosed by a vascular ring from which villous ridges (r, r) radiate (Turner). (From Balfour's Comparative Embryology, vol. ii, By permission of Messrs. Macmillan & Co., Ltd.) however, the first attachment is always obtained by an appost- tion of the trophoblast to the surface of the mucosa. Uneuata : Pig.—In the pig the blastocysts are spherical till the tenth day. Then they rapidly elongate, and by the four- teenth day they fill the whole length of the uterus. Subsequently they obtain a greater surface of contact by a series of concer- tina-like foldings (Assheton '), which fit between ridges of the uterine mucosa. The ridges are inter-glandular in position 1 Assheton, Phil. Trans., loc. cit. FQ@:TAL NUTRITION: THE PLACENTA = 395 (Fig. 87), radiating from small circular spots, twenty or thirty to the square inch, which represent the gland-mouths (Turner ’). It is usually stated that the uterine surface epithelium remains intact ; but Assheton has recently proved that it shows signs of degeneration as early as the eighth day, and at the eighteenth day is reduced to a thin layer. Three days later, however, it again appears normal and is formed of long columnar cells, to the ends of which the trophoblast fits closely, sending proto- Bly Fig. 88.—Section through the wall of the uterus and the blastocyst of the pig at the twentieth day of pregnancy (Assheton). mes, mesoblast ; Bl.v, fetal vessel ; Z'r, trophoblast ; Lp, long columnar epithelium. of uterine surface. plasmic processes between the cells (Fig. 88). These processes may even reach past the epithelium to the underlying layer of dilated capillaries (Robinson), and absorb nutritive material or effect gaseous exchanges. The trophoblast is single-layered throughout, and, after the first three weeks, forms a syncytium. Internally to it lies the mesoblast, which in the main follows its ridges and furrows, but occasionally bridges across a fold. It is vascularised by the vessels of the allantois, which completely surrounds the embryo. The gland-mouths lie along the course of the vessels (Assheton). No formation of villi takes place, and the attachment never 1 Turner, Lectures on the Comparative Anatomy of the Placenta, Edinburgh, 1876. 396 THE PHYSIOLOGY OF REPRODUCTION goes beyond the stage of apposition except for the proto- plasmic extensions of the trophoblast (Fig. 89). The uterine mucosa contains no special cotyledonary areas such as are found in the sheep and cow. The surface epithelium, though it shows the degenerative changes already referred to, is apparently never completely destroyed. The glandular epithelium does not at any time show signs of de- generation. It secretes actively during the early stages, and probably during the whole of pregnancy. As in the sheep and one of the lemurs (Galago agisymbanus), the glandular orifices Fig. 89.—Diagram representing a stage in the formation of the placenta of the pig. (From Robinson, ‘‘Hunterian Lectures,” Jour. Anat. and Phys., vol. xxxviii., 1904.) UM, uterine muscle; MB, maternal blood-vessel; UG, uterine glands ; UE, uterine epithelium ; FE, fcetal ectoderm; FM, foetal mesoderm. are covered by domes of trophoblastic cells, which absorb the secretion and transmit it as nutriment for the developing embryo by the allantoic vessels. The sub-epithelial tissue is gelatinous, and early in pregnancy it begins to increase in thickness by a widening of the lymphatics and blood-vessels and a new formation of capillaries. The constituents of the nutriment provided for the embryos are referred to later (see p. 400). Mare.—In the mare the details of placental development are not yet known. In the early stages the blastodermic vesicle is attached to the uterine mucosa by the trophoblast covering the lower pole of the ovum, and the attachment is aided by the formation of delicate, nearly parallel ridges (Ewart '). Villi are 2 Ewart, Critical Period in the Development of the Horse, London, 1897. FQ:TAL NUTRITION: THE PLACENTA 397 formed in the allantoic region, and they fit into crypts which are probably lined with maternal epithelium. Between the foetal and maternal tissues in the crypt is a space filled with secretion. The lymphatic system of the mucosa is enormously developed (Kolster +). Sheep.—tIn the sheep and cow the poly-cotyledonary type of placenta is found. The form is determined by the presence from an early period, and independently of pregnancy, of numerous prominences or cotyledonary burrs, which project as thickened knobs of the sub-epithelial tissue into the uterine lumen. During pregnancy they form connections with localised proliferations of the trophoblast. The burrs vary in number from fifty or sixty in the sheep to five or six in the roe-deer. The ova of the sheep reach the uterus four or five days after coitus, and the blastodermic vesicles remain free till the seven- teenth day. Then the attachment to the mucosal surface begins, and it is completed by the thirtieth day (Assheton). After the ninth day, when the prochorion ruptures, the tropho- blast comes in contact with the uterine epithelium. Apparently, as the result of this, the absorption of nutriment is easier, and the blastodermic vesicle increases rapidly in size so as to fill the uterine horn, or both horns if only one embryo is present. Certain changes occur in the mucosa before attachment. The leucocytes, which in the non-pregnant uterus are situated at the base of the lining epithelium, increase in number and penetrate between the epithelial cells. The glandular sacs, situated at the junction of the branches with the main ducts, expand greatly and actively secrete. It is generally held that the surface epithelium is not destroyed, but Assheton has shown that on the cotyledonary burrs it is distinctly degenerated by the seventeenth day, and he has also brought forward strong evidence that it is not subsequently regenerated, but is re- placed by binucleate cells of the foetal ectoderm. In the cotyledonary areas of the trophoblast, villi are de- veloped as buds of epiblast, which afterwards contain cores of mesoblast with branches of the allantoic vessels (Fig. 90). They 1 Kolster, ‘“‘ Die Embryotrophe placentarer Siiuger, mit besonderer Beriick- sichtigung der Stute,” Anat. Hefte, vol. xviii., 1902. 398 THE PHYSIOLOGY OF REPRODUCTION fit into depressions or crypts on the surface of the cotyledons, increase in length, and branch in different directions. Whether they literally grow into the maternal tissues either mechanically or by a phagocytic action is uncertain.’ It seems more likely that very little, if any, further penetration occurs, but that the sub-epithelial tissue swells and keeps pace with the villi as they increase in length. The crypts, if their lining cells really belong to the foetal ectoderm, are not secretory, and there is no free space, such as is described in the mare, between them and the villi. The sub-epithelial tissue is represented in the non- herd Be au wee - 4 SORE pte SS aah aaa, lent + cam og. Soc NS wh ge aie Fic. 90,—Section through the uterine and embryonic parts of a cotyledon of the sheep at the twentieth day of pregnancy. Folds in the tropho- blast fitting into sulci of the cotyledonary burr. (Assheton.) mes, mesoblast ; tr, trophoblast ; ws, degenerated uterine epithelium ; str, uterine stroma. pregnant uterus by a thin layer of dense connective tissue, with localised thickenings in the burrs. With the onset of pregnancy occur an infiltration of lymph between the more superficial cells of the sub-epithelial layer, and an increase in the number and size of the blood-capillaries and lymphatics. Thus the layer becomes spongy and swells up around the foetal vill, producing the cotyledonary interdigitation. At the fundus of the crypts the lining cells become syncytial. At the apices of the inter-crypt columns lacune of maternal blood are formed by repeated small hemorrhages from the superficial capillaries (Fig. 91). 1 At this stage Assheton did not observe any actual engulfment of cells, but considered that nutriment might be transmitted by fine processes of the binucleate cells which united with similar processes of the connective tissue cells of the mucosa. FQTAL NUTRITION: THE PLACENTA 399 In the inter-cotyledonary area, the epithelium, whether or not it degenerates over large areas in the early stages as Assheton supposes, is later healthy and vigorous. There is no formation of a spongy layer in the sub-epithelial tissue as in the burrs. But a great change occurs in the glands, which are wholly inter-cotyledonary in position. They increase in length and complexity, and secrete actively. Towards the end of mY Tr Ic. Fic. 91.—Section through the base of a fcetal villus and the apices of two inter-crypt columns. Sheep. The surfaces of the columns are traversed by large blood-vessels which later rupture and form the blood-extravasa- tions. (Assheton.) Tr, trophoblast dipping into crypt; Jc, inter-crypt column; m.v, maternal blood-vessel. pregnancy, however, the greater part of the uterine glands is destroyed, but the surface epithelium still secretes. At the upper end of each horn the wall of the blastocyst forms a crumpled structureless membrane with no trace of nuclei, while the uterine mucosa in this region is thrown into folds and covered with a high columnar epithelium which is very active. The secretion is apparently transmitted by transfusion through the membranous wall, and is found inside the sac. At full- 400 THE PHYSIOLOGY OF REPRODUCTION time this part of the mucosa shows signs of great degenera- tion, resembling the pulpe diffluente of Duval in the guinea-pig (Assheton). The inter-glandular cells also hypertrophy like the connective tissue cells of Rodents. The inter-cotyledonary trophoblast is avillous in the sheep and cow. In the giraffe, however, there are rows and clusters of villi in addition to the cotyledonary villi. The development and structure of the placenta of the sheep have been described at some length because the formation of the special nutriment for the foetus has received close atten- tion in that animal.* Cow.—In the cow (Fig. 92) the placenta has essentially the same form as in the sheep, but the interlocking is not so firm. On separation of the maternal and foetal parts of the cotyledons, the former are found to comprise the larger part. In the fully developed sheep’s placenta the foetal parts constitute the main mass of the cotyledon. The various stages of develop- ment have not been completely investigated, but one other difference has been noted, viz. the absence of lacunze of maternal blood at the bases of the villi (Ledermann °). The Uterine Milk The existence of a nutritive juice in the uterus of Ruminants during pregnancy has been recognised since the days of Harvey. He spoke of an albuminous fluid, which might be squeezed out from the cotyledons’ of the placenta, as a source of nutriment for the foetus. As to its origin, he says in one of his Letters : “It might be transported by the uterine arteries and distilled into the uterus.” The fluid was first called uterine milk by Needham in 1667. Haller described it as a secretion of the utricular glands, and this view was supported by Bischoff, Sharpey, and others, who considered it the immediate store of ’ For the above account of the development and structure of the sheep’s placenta, we are largely indebted to the important memoir of Assheton. Differing in many respects from previous descriptions, it alone brings forward evidence that the Ungulate placenta may be ‘‘ secondarily simplified” i in Hubrecht’s sense (see Quar. Jour. Micr. Sci., 1908). 2 Ledermann, ‘‘ Ueber den Bau der Cctyledonen im Uterus von Bos,” &c. Inaug.-Diss., Berlin, 1903. FQ:TAL NUTRITION: THE PLACENTA 401 foetal nutriment. It was analysed by Gamgee,’ who showed that the fluid contained a large amount of protein and fat and some salts, and was thus well adapted for nutrition. But Haller’s view of its origin was not accepted by Turner ” and Ercolani.*? Turner showed that during pregnancy new crypts were formed in the cotyledons, and he supposed that Fig. 92.—Columnar trophoblast-cells from the base of a fcetal villus of the placenta of the cow at the third month of pregnancy, to show phago- cytosis. (From Jenkinson’s ‘ Notes on the Histology and Physiology of the Placenta in Ungulata,” Proc, Zool. Soc,, London, vol. i., 1906.) the uterine milk represented the secretion of these crypts. Ercolani went even further and stated that such a secretion existed in all placente, but Turner was strongly opposed to this: “That such a fluid (uterine milk) is produced in all placentee, where utricular glands or follicles continue to secrete during the whole period of placental formation, is very probable. + Gamgee, ‘On the Chemistry and Physiology of the Milky Fluid found in the Placental Cotyledons of Ruminants,” Brit. and For. Med.-Chir. Review, 1864. * Turner, ‘The Placentation of the Sloths,” Jour. of Anat. and Phys., vol. viii., 1874. 3 Ercolani, ‘Sull’ unita del tipo anatomico della placenta,” Mem. dell Accad. di Bologna, 1876. 2c 402 THE PHYSIOLOGY OF REPRODUCTION But in the placente: of the sloth, the apes, and the human female, where an unusual development of the maternal blood- vessels into larger sinuses takes place, a modification in the anatomical structure is produced which seems to render the -presence of such a secretion unnecessary. The nutritive changes in all probability take place directly between the maternal and foetal blood.” More recent investigations have thrown fresh light on the origin, composition, and absorption of uterine milk. It must be recognised that, even before the onset of pregnancy, changes occur in the uterus which are important for the nourishment of an embryo developing later. Shortly before the first cestrous period, the mucosa “‘ matures” by the formation of the richly cellular sub-epithelial layer of connective tissue already re- ferred to (see p. 398). Among Indeciduates it is specially well marked in the cotyledonary types. With the first procestrum the mucous membrane becomes cedematous, and the super- ficial capillaries are dilated. Many of them rupture and give rise to miliary hemorrhages, which later undergo changes such as occur in hemorrhages elsewhere. Whether the changes are caused by an enzyme action on the part of the leucocytes is uncertain ; but in any case the white corpuscles take up the pigmented products of disintegration, and then arrange them- selves in a row, or in groups, close under the surface epithelium in the manner described in an earlier chapter (Chap. III. p. 109). Some of the leucocytes contain unaltered hemoglobin, as is shown by the characteristic reaction with eosin ; others contain derivatives of it, in which iron may often be demonstrated. With the onset of pregnancy these cells wander out between the epithelial cells, and mingle with the secretion lying in the uterine cavity. This secretion is poured out by the superficial and glandular epithelium, which becomes more active at the be- ginning of pregnancy with the increased flow of blood and lymph through the mucosa. It forms the more fluid part of the uterine milk in which the formed constituents lie. It is necessarily found only in the extra-cotyledonary regions since no glands exist in the burrs. Besides the intracellular pigments, there is another source of iron, though in widely varying amounts. In all placental ® e FETAL NUTRITION: THE PLACENTA = 403 Mammals a greater or less amount of maternal blood is in direct contact with the trophoblast. In the pig and mare it is re- stricted to individual red blood corpuscles, which find their way to the surface and mingle with the gland secretion. In the ass Strahl’ has found blood in greater amount, forming small effusions. In the sheep its presence has often been noted by Tafani,? Bonnet,’ and others. The position of the extravasa- tions in the placenta has been already referred to (see p. 398). In the cow they are apparently not a constant phenomenon, the supply being often restricted, as in the mare, to a few single erythrocytes. In the deer, blood is effused into the glands, but no extravasations take place in the cotyledons. Here the whole of the maternal part of the ‘burr appears to be digested and absorbed by the trophoblast. The greater activity of the foetal ectoderm in the deer is also shown by the destruction of the epithelium over the whole surface of the uterus (Strahl *). In addition to blood, the uterine milk contains fat in large quantities. Before pregnancy it may be demonstrated in the sub-epithelial leucocytes which later migrate to the surface. Fat globules are also contained in large amount in. the epithelial cells of the surface and glands. According to Bonnet, it cannot be considered as a fatty degeneration because the cells are otherwise healthy ; it is rather a fatty infiltration, the epithelium secreting it from the lymph or blood-plasma, storing it and later giving it off to the uterine milk. Kolster * has described a process by means of which cellular elements are added to the “ Embryotrophe.”® The gland 1 Strahl, see Hertwig’s Handb. d. vergl. u. exp. Entwickelungsg. d. Wirbelthiere, 1902. 2 Tafani, “‘Sulle Condizioni utero-placentari della Vita Fetale,” Arch. della Scuola d’ Anat.-Path., Firenze, 1886. 3 Bonnet, ‘‘ Ueber Embryotrophe,” Deut. Med. Woch., 1899. 4 Strahl, ‘‘ Ueber die Semiplacenta multiplex von Cervus elaphus ’’ Anat. Hefte, H. xciii., 1906. 5 Kolster, ‘‘Die Embryotrophe placentarer Sduger,”’ &c., Anat. Hefte, vols. xviii. and xix., 1902 and 1903. § Objections have been raised to the term “uterine milk ’’ because the fluid contains cellular elements, pigment granules, &c., which are not present in the mammary secretion. Bonnet and his followers have employed the convenient term ‘‘Embryotrophe,” but it must be noted that in the sheep it forms the nutriment long after the embryonic stage of the developing ovum is past. The two terms are used indiscriminately in this chapter. 404 THE PHYSIOLOGY OF REPRODUCTION epithelium proliferates so strongly that the cells cannot find room in the wall, and tracts of them are invaginated into the lumen. Later the cellular projections, sometimes along with some of the underlying connective tissue as in the mare, are cut off and added to the embryotrophe (Fig. 93). Traces of glycogen may be extracted from both the maternal and foetal parts of the cotyledons, but it is too small in amount to be demonstrated histologically. It is also present in small amounts in the extra-cotyledonary areas—in the uterine epithelium both superficial and glandular in the cow, in the sub-epithelial connective tissue in the sheep, and in the uterine milk (Jenkinson '). Large quantities of glycogen are stored in the plaques amniotiques, localised masses of cells on the internal surface of the amnion, and later on the umbilical cord. In the calf embryo the plaques reach their full development about the sixth month, and then gradually atrophy. It is obvious that the uterine milk must contain many elements which have not been mentioned individually. The product of conception requires numerous other substances for its development besides protein, fat, carbohydrate, and iron. Organic phosphorus compounds are furnished by the nuclei of cells, and these may also contain iron. In general the fixation of mineral elements is sight at the beginning of pregnancy, but becomes active towards the end. But the requirements vary at different periods of pregnancy. For example, sodium decreases and calcium increases with the replacement of cartilage by bone, and potassium increases with the increased manu- facture of red blood corpuscles. These and many other sub- stances are present in uterine milk though not demonstrated histologically. Either they have been dissolved by the fixative, or have remained unstained by the methods hitherto employed. One other constituent has been described by various ob- servers, but its composition and significance are unknown. Besides the leucocytes that contain pigment granules and fat, others are filled with rod-like bodies, the “ Uterinstabchen ” of Bonnet.” Later they appear in the uterine milk. Rods have 1 Jenkinson, ‘‘Notes on the Histology and Physiology of the Placenta in Vertebrata,’ Proc. Zool. Soc., London, 1906, vol. i. 2 Bonnet, “‘Beitrage zur Embryologie der Wiederkauer gewonnen am Schafe,”’ Arch. f. anat. u. Phys., anat. Abth., 1884. FQ@:TAL NUTRITION: THE PLACENTA = 405 also been described in the trophoblast of the rabbit by Beneden, and in the uterine mucosa by Schmidt,! who stated Fig. 93.—First stage of cellular secretion in the placenta of the cow. Invagination of glandular epithelium and some of the underlying con- nective tissue, (From Kolster, ‘‘ Die Embryotrophe placentarer Sduger,” Anat, Hefte, vols, xviii. and xix., 1902-3.) that they were composed of calcium oxalate. In Ruminants they are found in enormous numbers, but whether they form * Quoted by Bonnet, “ Ueber Embryotrophe,” Minch. med. Woch., 1899. y s 406 THE PHYSIOLOGY OF REPRODUCTION a supply of calcium for the foetus is not known (Fig. 95). There is at present no evidence that they are “ protein crystals,’ a name sometimes applied to them. The uterine milk has thus the following constituents—the secretion of the superficial and glandular epithelium, perhaps mingled with lymph transuded from the cedematous mucosa ; leucocytes containing hemoglobin derivatives, fat globules, and “ Stiibchen ”; glycogen ; tracts of glandular epithelium set free by a process of “ cellular secretion’; red blood corpuscles and their derivatives ; connective-tissue elements; salts, &c., which are in solution and not recognisable by ordinary histological methods. While lying free in the uterine cavity, the uterine milk under- goes changes which consist largely in a disintegration of its cellular elements. The leucocytes degenerate and their cyto- plasm, with the pigment granules, fat globules, and “ Stabchen,” is set free. The tracts of glandular epithelium are also trans- formed into a mass of débris, and their contents lie free in the embryotrophe. The red blood corpuscles may be ingested almost unaltered by the trophoblast, or they may first be laked, and the hemoglobin may be absorbed as such, or undergo changes before absorption. According to Jenkinson, hemo- globin is broken up into an iron-containing and an iron-free part. The former is carried away by the foetal blood-vessels and stored in large quantities, principally in the foetal liver, as a re- serve for use during lactation. The iron-free part is deposited in the cells as a pigment, occurring in such amount as to give, especially in the later stages of pregnancy, a deep brown colour to the foetal cotyledons. It collects at the apices of the villi, and its presence suggests that the cotyledons are actively en- gaged in excretion (Assheton). The histological changes in the red blood corpuscles absorbed by the trophoblast have been described by Jenkinson. They are engulfed by amceboid pro- cesses of the cells, and gradually become paler in colour and irregular in outline; often they clump together. Gradually yellowish-brown granules are deposited on the surface of the included cells, and this process continues till the whole is con- verted into a dark brown mass. Bonnet called the granules hematoidin crystals, but Jenkinson was unable to demonstrate FETAL NUTRITION: THE PLACENTA 407 this pigment in alcoholic extracts of the placenta. He found two other pigments, one absorbing a small part of the violet end of the spectrum, and the other showing two absorption bands, which differed slightly from those of oxyhemoglobin in neutral solution and of hematoporphyrin in acid solution. This pig- ment is obviously a hemoglobin derivative, and from it bilirubin may be formed. It is present in the sheep and. cow during pregnancy, but not in the virgin uterus of the sheep. A similar yellowish-brown pigment occurs in the crypts and the tissues outside them, and also, according to Assheton, in the maternal blood-stream. It is not yet possible to explain the exact significance of these changes. The iron-free pigment is appa- rently a waste product, and the iron-containing part is stored in the foetal organs. Whether the foetus subsequently synthesises part of the organic iron compound into hemoglobin, or absorbs minute quantities of hemoglobin as such, according to its re- quirements, is unknown. The cotyledonary and inter-cotyledonary parts of the placenta present differences both anatomically and physiologically. In the inter-cotyledonary region are the glands, and here only are found the gland-secretion and the “cellular” secretion. In the cotyledonary parts the glands are absent. Here the vill are formed, and they effect an attachment to the mucosa by the greater activity of the trophoblast. Assheton has suggested that this hyper-activity may be stimulated by the absence of glands and consequently of uterine milk in the cotyledons, the foetal ectoderm attacking the mucous membrane more vigorously in order to obtain food. The blood effusions are also cotyle- donary, and the eosin and iron reactions are obtainable in the adjacent trophoblast, and not at other places. Finally, it is probable that the exchange of oxygen and carbonic dioxide is carried out in the cotyledons. Here the maternal capillaries are more dilated than outside the burrs, and they come close up to the surface, some of them even impinging on. the lining membrane of the crypts. Between them and the allantoic vessels in the villi intervene only a small amount of mesoblast, the cellular trophoblast, and the lining of the crypts which, according to Assheton, corresponds to the plasmodiblast of the bat. In the inter-cotyledonary regions, on the other hand, the 408 'THE PHYSIOLOGY OF REPRODUCTION foetal vessels are related to the orifices of the glands, and appear to be concerned principally with the absorption of their secre- tion. As already mentioned, the villi may also be concerned with the excretion of waste products of hemoglobin. Bonnet was the first to show that the trophoblast in Ruminants was actively phagocytic and absorbed the consti- tuents of the uterine milk (Fig. 94). He demonstrated the presence of fat-globules, hemoglobin and its derivatives, de- generated leucocytes and “ Stabchen ” (Fig. 95)—in short, all the histologi- cally demonstrable constituents of the embryotrophe —in the trophoblast. Many, if not all, of the cellular ele- ments are partially degenerated before absorption. The appearances suggest an enzyme action on the part of the : trophoblast, and perhaps also the Fig. 94.—Ingestion and dis- leucocytes, but no proteolytic or ti She ig a. Se lipolytic enzyme is contained in y A aoe glycerin extracts of the maternal blast of the sheep. (From Jenkinson’s “ Notes onthe or foetal part of the cotyledon. yee ae TE on After their absorption, the disin- co} e acenta 1n ngu- s . dig? Phen, Boul Soe, tegration of the cellular constituents London, vol. i., 1906.) is completed in the trophoblast, and they are no longer recognisable as individual elements. Their products are transmitted to the foetal vessels, though they may first be elaborated in the trophoblast into a form or forms suitable for the use of the embryo in the development of its various organs. LemuromEs.—Many of the lemurs have a simple avillous diffuse placenta, as Turner? first pointed out in specimens from Madagascar. Hubrecht has investigated two others found in the East Indies—Tarsius* and Nycticebus.? The latter has also a diffuse placenta. Villi develop over the whole of the 1 Turner, ‘‘On the Placentation of the Lemurs,’ Phil. Trans. Roy. Soc., London, vol. clxvi., 1876. 2 Hubrecht, “Ueber die Entwicklung des Placenta von Tarsius,” &c., Internat, Congr. of Zool., Cambridge, 1898. 3 Hubrecht, “‘Spolia Nemoris,’’ Quar. Jour. Micr. Sci., vol. xxxvi., 1895. FQETAL NUTRITION: THE PLACENTA = 409 chorion, and fit into vascular crypts in the uterine mucosa from which they are easily retracted at birth. The epithelium (Assheton. ) mes, mesoblast ; 7'r, trophoblast containing “ Stabchen” (st); J'r.D, binucleate trophoblast cells ; Hp, uterine epithelium undergoing absorption by the trophoblast ; V, vacuolated cell Fig. 95.—Absorption of “ Stiébchen” by the trophoblast of the sheep. of the crypts persists as in the cow, and the “ osmotic inter- change takes place through two cell-layers of different origin, and of different physiological significance (phylogenetically). 410 THE PHYSIOLOGY OF REPRODUCTION Tarsius approaches more closely to the Insectivora and Primates. The trophoblast proliferates and penetrates into the mucosa, and maternal blood circulates in its spaces. The mesoblast grows profusely, and forms with the trophoblast a true chorion in Hubrecht’s restricted sense. The placenta is discoid. In Galago agisymbanus, Strahl * has shown that a layer of secretion lies between the uterus and the ovum from the beginning of pregnancy. It is absorbed by the ectoderm, the cells of which are vesiculated over the gland orifices. Many blood extravasa- tions occur in the connective tissue of the mucosa, and the red blood corpuscles undergo changes as in the sheep, the glandular cells and embryotrophe containing granules which give an iron reaction. Turner? had previously noted in lemurs the intense brown staining of the glands from effused blood. Ceracea, Epentata, and Strenta.—The details of placental development and the constitution of the embryotrophe are unknown. IV. Tae Pracenta In Decipuata In the Deciduata three modes of attachment between embryo and mother are found: Centric, in which the blastocyst rests in the cavity of the uterus, attains a large size, and comes in con- tact with the wall over its whole circumference ; Excentric, in which the blastocyst remains small and lodges in a furrow of the uterine mucosa, and later a decidua reflexa is formed ; Interstitial, in which the small blastocyst attacks the mucosa at one point and reaches the connective tissue. In this form also a decidua reflexa is formed. In the neighbourhood of the attachment the mucosa de- generates, but the connective tissue cells usually enlarge to form decidual cells before degeneration sets in. The capillaries dilate and come in contact with the trophoblast. The mucosa interlocks so closely with the foetal villi that the two tissues cannot be separated without injury. 1 Strahl, ‘“‘Die Verarbeitung von Blutextravasaten durch Uterindriisen,” Anat, Anzeig., vol. xvi., 1899. 2 Turner, ‘‘The Placentation of Lemurs,” Jour. of Anat. and Phys., vol. xii, 1878. FATAL NUTRITION: THE PLACENTA 411 CarnivorA.—The Carnivora are characterised by a zonary form of deciduate placenta. The following account of its development refers particularly to the dog and cat, which have been most frequently investigated. The gestation period in the cat is about sixty-three days, and in the dog fifty-eight to sixty-two days. In both the ovum takes a comparatively long time to traverse the oviduct. On reaching the uterus the blastocyst is covered by a thick prochorion which prevents adhesion for a considerable period. The mucosa is matured, as in Ungulates, at the first pro- jestrum by the development of a well-differentiated sub- epithelial cellular layer, and of the glands and crypts (see p. 398). The crypts provide an increase of superficies and of secreting epithelium, and are later concerned in the attachment of the ovum. They have been recognised by all the authorities with the exception of Robinson,’ who states that he can find no evidence that any of the crypts are other than the ducts of the uterine glands. At the first and each succeeding procestrum there is a marked hypéremia of the mucosa, and from the rupture of some of the superficial capillaries miliary hemorrhages occur (see Chap. III.). At the beginning of pregnancy, blood effusions are found close under the surface of the mucous membrane, but bleeding into the uterine cavity, which took place during the procestrum, has entirely ceased. The epithelium of the surface glands and crypts is swollen and pervaded with minute fat-globules in the dog (Bonnet?) and cat (Melissenos*). The glands widen quickly into “chambers,” and tracts of their proliferated epithelium are invaginated, and often obliterate the lumen. The widening of the glands and crypts makes the deep layer spongy. The capillaries increase and form practically the whole of the sub-epithelial layer. Immediately below it lies the layer of glandular ducts which are obliterated by débris 1 Robinson, Hunterian Lectures, Jour. of Anat.and Phys., vol. xxxvili., 1904, 2 Bonnet, “ Beitrige zur Embryologie des Hundes,” Anat. Hefte, vol. xx., 1902. 3 Melissenos, “Ueber die Fettkérnchen und ihre Bedeutung in der Placenta bei den Nagern und der Katze,” Arch. f. mikr. Anat., vol. lxvii., 1906. THE PHYSIOLOGY OF REPRODUCTION 412 resulting from the degeneration of the proliferated epithelial Between it and the spongy layer is the compact layer, cells. In it the glands are also formed from the sub-epithelial layer. Fia. 96.—The uterine mucosa of the dog about the twenty-third day of (From Duval’s ‘ Le Placenta des Carnassiers,” Journ. de ? Anat, et de la Phys., 1893.) pregnancy. detritus ; g, glands of compact layer; Sp, dilated glands of spongy mes, mesoblast; tr, trophoblast; v, capillary layer; d, layer of glandular layer. FATAL NUTRITION: THE PLACENTA = 413 not so widely dilated and the connective tissue is more abundant (Fig. 96). The embryotrophe at this stage differs from that in Un- gulates. The glandular secretion is less fluid, perhaps because the lymph transudate is less abundant (Kolster’). It sur- rounds the ovum to form the prochorion or “ Gallertschicht,” and is, according to Bonnet,” absorbed by the trophoblast. When the prochorion disappears, the foetal ectoderm already has proliferated over a broad zone of the citron-shaped ovum (Fig. 97), to form villosities which attack the surface of the mucosa, and obtain an attachment to it—-about the twentieth Fic. 97.—Ovum with zonary band of villi. (From Hertwig’s Entwicklungs- geschichte des Menschen und der Wirbelthiere, by permission of Gustav Fischer.) day in the dog (Duval*) and the twelfth day in the cat (Robinson). Vascular processes of the allantois grow into the centre of the trophoblastic vill, first over a limited discoid area, and later over the whole zone as the allantois spreads round the wall. Hence the rudimentary placenta is discoid, and the completed placenta zonary. In procuring attachment to the uterus many of the villi project into glands and crypts. According to Strahl,* the epithelium lining the ducts and the surface of the uterine cavity 1 Kolster, “Ueber die Zusammensetzung der Embryotrophe der Wir- belthiere,” Hrgebn. d. Anat., vol. xvi., 1906. 2 Bonnet, ‘‘ Ueber das ‘ Prochorion’ des Hundekeimblase,” Anat. Anzeig., vol. xiii., 1897. 3 Duval, ‘“‘ Le Placenta des Carnassiers,”’ Journ. de l Anat, et de la Phys., 1893. 4 Strahl, ‘Die histologischen Verdnderungen d. Uterusepithel. in d. Raubthierplacenta,” Arch. f. Anat. u. Phys., Supplement, 1890. 414 THE PHYSIOLOGY OF REPRODUCTION is then transformed into a syncytium and invests the villi externally. Heinricius! is of opinion that the epithelium dis- appears, and the syncytium is formed by the uterine connective tissue. But it is now generally recognised that the syncytium is trophoblastic. It has been proved by Strahl himself, and by Duval, that many of the villi obtain attachment at parts of the surface where there are no gland openings or crypts, and pene- trate into the substance of the mucosa. Before the disappear- ance of the epithelium, the cells lose their outlines and form a homogeneous mass of protoplasm with fragmented nuclei. This degenerated tissue ought not, as Bonnet? emphasised, to be known as syncytium, which represents an active protoplasmic condition (see p. 864). The name which he suggested, symplasma, is very convenient and is used here. It is not only the surface epithelium which forms asymplasma. The glandular epithelium, the connective tissue cells, and extravasated blood may also give tise to a symplasma which may be designated glandular, con-. nective tissue, and hematogenous respectively. All are formed to a large extent in the placenta of Carnivores, and their resem- blance to the trophoblastic syncytium has led to much confusion. After the destruction of the epithelium, the villi penetrate into the deeper tissues of the mucosa by gradually absorbing the symplasmata, and branch to form secondary and _ tertiary villi. When the ectoderm reaches the capillary layer, it sends out protoplasmic processes which encircle the dilated vessels. The trophoblast on the sides of the villi becomes syncytial, but retains its cellular character at the tips. Internally the villi contain vascular cores of mesoblast. Hence is formed the angioplasmode of Duval—a continuous layer of foetal vascular villi, clad with syncytium, penetrating everywhere into the capillary layer, and leading to a disappearance of all the maternal tissues except the vessels (Fig. 98). By the epithelial arcades at the tips, the layer of villi rests on the sheet of glandular © detritus and the compact layer, which in turn form a symplasma and undergo absorption. Thus the foetal structures reach the 1 Heinricius, ‘‘ Ueber die Entwicklung und Struktur der Placenta beim Hunde,” Arch. f. mikr. Anat., vol. xxxiii., 1889. 2 Bonnet, ‘‘ Ueber Syncytien, Plasmodien und Symplasma,”’ &c., Monats- schr. f. Geburtsh. u. Gyndk., vol. xviii., 1903. FETAL NUTRITION: THE PLACENTA 415 spongy layer, in which the glandular culs-de-sac have expanded to form large cavities separated by partitions, the mesenteriform lamelle. Gradually the roof of this layer is also absorbed by Fic. 98.—The angioplasmode of the dog at the thirtieth day of pregnancy. (From Duval’s “Le Placenta des Carnassiers,” Journ de l’ Anat, et de la Phys., 1893.) ms, mesoblast ; ¢r, trophoblast ; ae, ectodermic arcades; d, layer of glandular detritus. the trophoblast, and the ectodermal arcades at the tips of the villi gain a permanent attachment to the mesenteriform lamelle. At the same time, by the further branching and penetration 416 THE PHYSIOLOGY OF REPRODUCTION of the foetal mesoderm in the angioplasmode, the tissue is broken up into a series of labyrinthine lamelle, which consist of a network of maternal vessels clothed on each side by syncytial trophoblast. The meshes of the network are penetrated by the vessels of the villi. In this way, according to Duval, the labyrinth is formed. In it the maternal and the fcetal blood are separated by the endothelium of the uterine capillaries, a cellular layer (considered foetal by Duval and maternal by Heinricius) which later disappears, the syncytium, mesoblast, and foetal capillary walls. At places, however, the villi come directly in contact with maternal blood, especially at the “ green border ” of the placenta, which forms a characteristic appearance in some of the Carnivora. In all the members of the order, larger or smaller maternal hemorrhages occur at an early period after the attachment of the blastodermic vesicle. The effusions vary in size and position. In the dog they occur regularly along the margins of the placental zone, and form the bordure verte; in addition smaller hemor- thages take place into the substance of the placenta, and form the “ green pockets,” which may be isolated or joined to the green border by bridges (Fig. 99). In the cat, the hemorrhages occur in irregular positions and do not assume the green colour typical of the dog. Indications of a green border are present in the earlier stages, but not in the completed placenta. In the otter and badger, the effusion takes the form of a large blood- pouch, filled with a great variety of blood derivatives. In the ferret the conditions are similar; the main effusion occurs at the anti-mesometrial border of the uterus, and divides the zone into two lateral discs. According to Robinson, it lifts the trophoblast from the decidua, and forces it in the form of irre- gular pouches towards the interior of the ovum. Strahl and Bonnet also state that the blood is effused between the mucosa and the blastodermic vesicle, and thus is contained in spaces whose walls are maternal on the one side and foetal on the other. According to Duval the blood-spaces are entirely lined by trophoblast, and with the advance of the villi other and larger hemorrhages occur, coalescing to form the green border and islands. In either case the trophoblast is in direct contact with maternal blood. There the wall of the blastodermic FQ:TAL NUTRITION: THE PLACENTA 417 vesicle is avillous but strongly folded, the ends of the ectodermal cells are expanded like clubs, and their protoplasm becomes coarsely reticular. Into the meshes the constituents of the green pulpy mass, unaltered erythrocytes and hemoglobin or its derivatives, are absorbed by phagocytosis. From the preceding account, it is clear that certain re- Bee + ree peers *S gamicde san Sagecae POOF? Fig. 99.—The labyrinth and the green border of the placenta of the dog at the fortieth day of pregnancy. To the right are two lobules of the angioplasmode which have reached the stage of complexity of the labyrinthine lamelle: to the left is the green border, the cavities of which, normally filled with blood, are indicated by a cross. (From Duval’s “ Le Placenta des Carnassiers,” Journ. de l’ Anat, et de la Phys., 1893.) 1, 2, and 3, basal lamellz of the green border; 4, basal lamella of lobule of labyrinth, semblances and certain differences exist between Carnivora and Ungulata in the composition of the embryotrophe. The most notable difference in the zonary placenta is the absence of the large amount of milky fluid which arises in the sheep from the glandular secretion and the transudation of lymph. In Carnivora the gland secretion is less important. Though the deep parts of the glands which lie in the glandular layer may 2D 418 ‘THE PHYSIOLOGY OF REPRODUCTION secrete, the epithelium of the more superficial parts proliferates, and then degenerates and loses its secretory function ; finally it forms a symplasma which plugs up the lumen of the glands. On the other hand, the amount of nutriment furnished directly from the maternal blood is increased. It is found in the extravasations already described, and as individual blood corpuscles and droplets of hemoglobin or its derivatives in the lumina of glands. Leucocytes are found during the whole of pregnancy, but in less abundance than in the sheep. They do not act to the same extent as store-houses of fat, but some of them, the siderophores, contain granules which give an iron reaction. In the course of pregnancy they disappear com- paratively early, with the exception of a few in the deep glandular layer. Fat is found in the intact epithelium of the glands, and in the lumen after desquamation of the cells. It appears in the epithelium partly as an infiltration and partly as a degeneration product of the protoplasm. In the Carnivora, the foetal ectoderm of the zonular band of attachment attacks the uterine mucosa more strongly than in the Ungulata. As a result, the maternal tissues, with the exception of the septa containing the placental vessels, disappear down to the middle of the spongy layer, and the tissue which is destroyed serves as pabulum for the developing embryo. Van der Brock’ suggests that the general cedema of the uterine mucosa may lead, as elsewhere, to its malnutrition and de- generation, and thus it may fall an easy prey to the trophoblast. Others maintain that the degeneration is brought about by a trophoblastic influence, perhaps of the nature of an enzyme action. The result is a transformation of all the elements to a symplasma. In the cat the connective tissue cells may form large decidual cells before their final destruction. As in the Indeciduates, there is strong histological evidence that the trophoblast is actively phagocytic, and takes up, as it meets them, the constituents of the prochorion, and later the degenerated tissues and extravasated blood. In the neighbour- hood of the extravasations active absorption is indicated by the 1 Van der Brock, ‘‘ Die Eihii!len und die Placenta von Phoca vitulina,”’ Petrus Camper, D. ii. Quoted by Kolster (Hrgebn. d. Anat., vol. xvi., 1906). FQ@:ITAL NUTRITION: THE PLACENTA 419 change in shape of the trophoblast cells and by their pigmen- tation. In the mesoblast of the villi and its vessels no trace is found of any of the formed elements of the embryotrophe, a proof that they undergo further transformation in the tropho- blast after absorption. The interchange of oxygen and carbonic dioxide apparently occurs in the labyrinth, as in the cotyledons of the sheep. Here only is the foetal circulation brought into close proximity with circulating maternal blood. Other fcetal waste products are probably also got rid of in the labyrinth. Nolf’ suggests that the excretory products may be responsible for the degeneration of the maternal tissues into a symplasma. In how far the other substances necessary for the growth of the embryo are taken up respectively from the circulating blood by purely physical or physiologically selective processes, and from the extravasated blood effusions by direct phagocytosis, is not known. ProgoscipEA.—In the elephant, the allantois is large and vesicular. Short villi are developed over a large area of the blastodermic vesicle. They lodge in pre-existing depressions in the uterine wall, but the trophoblast is inactive and does not attack the maternal tissues (Assheton ”). Over a zonary area, however, the villi are much longer, and, penetrating deeply into the maternal tissues, they form a large mass of tissue in the meshes of which maternal blood circulates. Hence the zonary placenta differs from that of Carnivores and resembles that of Insectivores, in which, however, the maternal blood circulates in trophoblastic spaces before the advent of foetal capillaries. Though no red blood corpuscles appear to be absorbed as such by the trophoblast, there is evidence of an active absorp- tion of hemoglobin derivatives, the presence of iron compounds being easily demonstrated, especially in the cores of the villi 1 Nolf, “Etude des modifications de la muqueuse utérine pendant la gestation chez le murin,”’ Arch, de Biol., vol. xiv., 1896. 2 Assheton, ‘The Morphology of the Ungulate Placenta, with Remarks on the Elephant and Hyrax,” Phil. Trans. Roy, Soc., London, Ser. B., vol. cxcviii., 1906. 420 "THE PHYSIOLOGY OF REPRODUCTION and the walls of the foetal capillaries. In the syncytial tropho- blast, however, the Prussian-blue test is negative (see p. 486). At birth the long villi are left in situ and absorbed by the maternal tissues. Hyrax.—As in the elephant, the placenta of Hyrax has been studied only in isolated specimens, and its development is not known. According to Assheton,’ the trophoblast is probably thickened all round the wall of the blastocyst, as in the hedge- hog and Man, but there is no appearance of a decidua reflexa. Maternal blood is carried directly to the foetal side of the tropho- blast, where it is close to the foetal vessels, and so may provide nutriment. It then trickles back through a complicated system of lacune in the trophoblast. The placenta is at first diffuse and later zonary. In the mucosa of the placental area the glands disappear early, and a great increase in the inter-glandular stroma occurs, as in Rodents.” Ropgentia.—Among the Rodents there are variations in the mode of attachment. It is centric in the rabbit, excentric in the mouse and rat, and interstitial in the guinea-pig. In all the ultimate form of the placenta is discoid. It was in Rodents that the proliferation and vascularisation of the trophoblast were first described by Selenka.*? Later Duval * gave a fuller account of the earlier stages, and Hubrecht discovered the same conditions in other orders. Rabbit.—The fertilised ovum of the rabbit, clothed by the prochorion, reaches the uterus at the beginning of the fourth day after coitus. At first it has no fixed position; but by the 1 Assheton, loc. cit, 2 Hubrecht (Quar. Jour. of Micr. Science, 1908) draws attention to the peculiar position of Hyraz. It has many archaic peculiarities, and has been placed near Rodents, elephants, and Ungulates by different authors. Yet its placental characters resemble those of the hedgehog and Man. This he takes as strong evidence that the type of placenta found in Hyraz, the hedgehog, and Man, diverges less widely from the primitive type than the placenta of Ungulates and Rodents. 3 Selenka, Keimblétter und Primitivorgane der Maus, 1883. 4 Duval, “‘ Le Placenta des Rongeurs,” Journ. de l’ Anat. et de la Phys., 1889-92. FQ@TAL NUTRITION: THE PLACENTA 421 seventh day, when the blastocyst is about five millimetres in diameter, the prochorion hes so closely on the surface of the uterus that it fixes the ovum. At the end of the eighth day the prochorion ruptures, and the blastodermic vesicle probably collapses at the same time by injury to its wall. The “mature” uterine mucous membrane of the non- pregnant rabbit already shows specialised structures, which are of importance for the attachment and nutrition of a future embryo. These consist of symmetrical pairs of longitudinal folds, first described by Hollard,? and subsequently named by Minot :? Fig. 100.—Transverse section of a four days’ gestation sac of the rabbit. The mucosa is differentiated into six definite folds. The two folds nearest the mesometrium are the largest and mark the site of placental attachment. (From Chipman’s ‘‘The Placenta of the Rabbit,” Labor, Rep,, Roy. Coll. Physic., Edinburgh, vol. viii., 1903.) p, p’, placental folds ; , n’, peri-placental folds; v, 0’, ob-placental folds. placental folds, the largest, situated one on each side of the groove corresponding to the insertion of the mesometrium ; ob-placental folds, the smallest, opposite the mesometrium ; peri-placental folds, intermediate in position and size (Fig. 100). Each fold is divided by transverse fissures into rectangular areas, the coussinets of Hollard. At the onset of pregnancy two of these areas on the placental folds, placed one on either side of the mesometrial groove, hypertrophy and form the maternal part of the future discoid placenta (Bischoff *), which is thus 1 See Hertwig’s Entwicklungsgeschichte des Menschen und der Wirbelthiere, 1906. 2 Hollard, ‘‘Recherche sur le Placenta des Rongeurs, Sciences Naturelles, 1863. 3 Minot, ‘‘ Die Placenta des Kaninchens,” Biol. Centralbl., vol. x., 1890. 4 Bischoff, Entwickelung des Kaninchen-Hies, Braunschweig, 1842. ” Annales des 422 THE PHYSIOLOGY OF REPRODUCTION bi-lobed (Fig. 101). The folds of the mucosa are essentially increased areas of the mucosal connective tissue, but they differ from the cotyledons of Ruminants in having glands. On the entrance of a fertilised ovum into the uterus, the folds, especially the ob-placental, become shortened, and a localised actual cavity appears which is occupied by the blasto- cyst. At the same time there is a marked hyperplasia of the cellular connective tissue of the placental and peri-placental folds, leading to a thickening of their bases (Chipman '). By the Fiq. 101.—Transverse section of a seven days’ gestation sac of the rabbit (Chipman). The placental folds (coussinets) are large (a); the muscular walls of the sac are thin. sixth day, the capillaries are also increased in these regions. In the ob-placental folds appear enormous giant-cells, derived by a process of “degenerative hypertrophy’ from the epithelium of the surface and glands. They persist till the fourteenth day, and are probably absorbed by the trophoblast overlying the yolk-sac. In the placental lobes the epithelial 1 Chipman, ‘‘ Observations on the Placenta of the Rabbit, with Special Reference to the Presence of Glycogen, Fat and Iron,” Laboratory Reports, Roy. Coll. Phys., Edinburgh, vol. viii, 1903. The development of the placenta is carefully traced in a complete age-series of pregnant rabbits and admirably figured by many photo-micrographs. The account as given here is based mainly on Chipman’s monograph, but the phraseology is some- times changed. FQITAL NUTRITION: THE PLACENTA 423 cells proliferate and fill up the superficial culs-de-sac of the mucous membrane. The glands are as yet unchanged, and the increased blood supply leads to a free secretion which is usually considered to be added to the albumen-layer, and then to be absorbed by the trophoblast. There is no appreciable transudation of lymph such as occurs in Ruminants. As the blastodermic vesicle grows, it presses against the folds and levels them. Hence at the time of attachment the surfaces of the placental lobes are nearly regular. The covering epithelium again returns to normal, but the active proliferation of the connective tissue cells is continued to form the placental cotyledons. At the same time the trophoblast proliferates in concentric areas on either side of the embryonic rudiment, which is placed opposite the groove between the placental cushions. Here the ovum is generally said to gain its first attachment, the ob-placental lobes having by this time dis- appeared,” Where the maternal and foetal tissues are in contact, the surface epithelium shows a form of degeneration similar to the epithelial symplasma of the zonary placenta—fusion of cells and fragmentation of nuclei. It is attacked by the thickened, horseshoe-shaped trophoblast, the ectoplacenta of Duval, and its edge presents microscopically a “ bitten or corroded ap- pearance.” This phagocytic or chemical action leads later to the complete disappearance of the epithelium, so that the trophoblast comes in contact with the connective tissue of the uterus. The glands are dilated, and their proliferated endo- thelium forms a symplasma which blocks the lumina. At these places the trophoblast advances more quickly, as if the resistance was weaker, and the line of attachment is undulating (Fig. 102). The dips thus correspond to the gland orifices and represent the beginnings of the future villi. The blood-vessels are large and numerous and have no adventitia, z.e. they are wholly capillaries. But the more deeply placed of them acquire an adventitia, the perivascular sheath (Masquelin and 1 Assheton (Quar. Jour. Micr. Sci., vol. xxxvii., 1895) states that the trophoblast shows papillary thickenings over the ob-placental and _ peri- placental lobes, and that by them the ovum obtains the first attachment over its lower pole. 424 THE PHYSIOLOGY OF REPRODUCTION Swaen 1). It is formed of one or two layers of large connective tissue cells which represent the first appearance of the decidual cells. After the destruction of the superficial and glandular epithelium, the trophoblast advances into the interglandular tissue, the cells of which degenerate in turn and are absorbed. The advance is most rapid where a capillary is met with. Fig. 102.—Thickened ectoderm (ectoplacenta) in the rabbit, attached to placental lobe and dipping more deeply at the position of the glands. (Chipman ) ec, foetal ectoderm ; J, line of attachment of ectoderm; d, fcetal ectoderm dipping into placental gland ; g, terminal cul-de-sac of placental gland. The mucous membrane is now differentiated into two zones, the intermediary region and the region of the uterine sinuses (Duval). The intermediary region lies superficially. It is closely packed with fusiform stroma cells and capillaries with thin perivascular sheaths of wninucleate decidual cells. “It suggests a reaction of the maternal placenta to the ‘ parasitic’ ‘ Masquelin and Swaen, ‘‘ Développement du placenta maternel chez le lapin,” Bull. de Vv Acad. Roy. de Belg., 1879. FQ'TAL NUTRITION: THE PLACENTA = 425 foetal placenta ” (Chipman ; see also p. 369). By the influence of the trophoblast the decidual cells increase in size and become multinucleate (Maximow'). They lose their _peri- vascular position and pervade the whole of the region. In their formation all traces of the gland ducts are lost, the cells of the latter appearing to serve as pabulum for the decidual cells. In the region of the uterine sinuses the blood-vessels dilate to form large spaces, and the decidual cells remain uninucleate till a considerably later period. The junction between the two zones is marked by the blind ends of the glands, which are filled with degenerated epithelium. In section each appears as an island of glandular symplasma. At the tenth day the allantois joins the outer wall of the blastocyst over the site of the future placenta. The trophoblast of this region is differentiated into two layers, the plasmodiblast and the underlying cytoblast. The latter disappears before the end of pregnancy. Processes of vascular mesoblast invade the trophoblast at intervals, and break it up into columns. At the same time the foetal tissues continue to advance and surround maternal capillaries, the endothelium of which they replace. In the zonary placenta of Carnivora the trophoblast surrounds the vessels without destroying the endothelium. In the rabbit the ectodermal processes are hollow tubes which surround the vessels ; they are closed on the foetal side and open on the maternal side. Their cavity is filled with maternal blood, and externally lies the cytoblast and vascular mesoblast. Such are the “villi.” Subsequently the arrangement becomes more complex, each hollow column being divided up into a series of hollow tubes parallel to the original column, and each tube in turn forming a series of hollow tubules. At each division the thickness of foetal tissue between the maternal blood in the axis and the foetal vessels decreases, till finally there is only a film of trophoblast and the vascular wall. At places the trophoblast even is wanting, and the foetal endothelium alone intervenes between the two blood-streams. The endothelium of the maternal capillaries frequently ruptures just before it is overtaken by the ectoderm, and irre- 1 Maximow, ‘‘ Zur Kenntnis des feineren Baues der Kaninchen-Placenta,”’ Arch. f. mikr. Anat., vol. li., 1897. See also ibid., vol. lvi., 1900. 426 THE PHYSIOLOGY OF REPRODUCTION gular blood extravasations are formed, and later surrounded by trophoblast. In the deeper layers of the intermediary region, according to Chipman, capillary hemorrhages occur more slowly, and give rise to a fibrinous tissue with red and white blood corpuscles scattered through it. This is similar to the hematogenous symplasma of Bonnet. It gradually increases in amount, and extends to the region of the uterine sinuses. While the foetal ectoderm advances along the vessels, it remains stationary at the non-vascular parts. Hence there is an interlocking of maternal and fcetal tissues, and peninsule of multinucleate cells come to le between the projections of the trophoblast. At the same time the intermediary region de- creases in thickness, and the ectoderm reaches the superficial sinuses of the deeper zone. Here the uninucleate decidual cells again become multinucleate, apparently at the expense of the blood symplasma, in the same manner as formerly at the ex- pense of the glandular symplasma. The sinuses enlarge, and their walls proliferate into several layers of degenerated cells, which after mid-term are gradually replaced by lamine of fibrin. At a later period the intermediary zone still further de- creases in thickness, and the multinucleate cells gradually “melt to form a granular detritus” (Duval). At the end of pregnancy the maternal placenta consists almost entirely of blood and blood symplasma, except for a thin rim of tissue containing blood-sinuses at the zone of separation. The gesta- tion period is thirty days. As compared with the placenta of Carnivora, it is obvious that the dilatation of maternal vessels is much more marked in the rabbit, and throughout the placenta the maternal blood is in direct contact with the trophoblast, and not only at the border or round a blood-pouch. The blood is not degenerated to a sufficient extent to exhibit the varieties of pigmentation found in the zonary placenta. Chipman does not state whether the maternal blood circulates in the trophoblastic tubes, but Maximow* says that it does. Similarly Duval says: “ The maternal blood circulates from the foetal extremity towards the * Maximow, “Die ersten Entwicklungsstadien der Kaninchenplacenta,” Arch. f. mikr. Anat., vol. lvi., 1990, FETAL NUTRITION: THE PLACENTA 427 maternal extremity of a lobule” (z.e. the series of tubules de- rived from one tube). According to Masius,’ “the maternal blood circulates in an ectodermal mass of foetal origin.” Herein lies a great difference between the placente of Rodents and Carnivores or Ungulates. In the sheep the main nutriment is furnished by the glands ; the maternal blood which is in contact with foetal ectoderm is stationary and small in amount, and serves chiefly as a supply of iron; the exchange of gases takes place through foetal and maternal tissues. In the dog the gland secretion is less important ; the blood is again stationary and restricted to certain situations, and it shows markedly degenerative appearances, but it is greater in amount, and probably furnishes other substances besides iron for the foetus ; in the angioplasmode the maternal blood circulates and here the exchange of gases is effected, but again both maternal and foetal tissues intervene between the two blood-systems. In the rabbit the glandular secretion is still less important after attach- ment, and even the blind ends do not secrete ; throughout the placenta there is normal circulating maternal blood in direct contact with foetal tissues, and it serves both as nutriment and for the exchange of gases. In addition, there are stationary blood extravasations which are engulfed by the trophoblast, but they are subsidiary. Both in the dog and the rabbit there is a marked formation of symplasma which may be connected, as Bonnet suggested for the dog and Maximow for the rabbit, with the slowing of the circulation in the placenta, or may be the result of a trophoblastic influence.: In the placenta of the rabbit there is one other difference which marks it off from the placenta of Carnivores and links it with Insectivores and Man—the connective tissue cells of the mucosa form decidual cells. They assist to an important degree in the preparation of nutriment for the embryo. They exercise a phagocytic action on the neighbouring degenerated maternal tissues, glandular remnants and fibrin, and so attain their greatest development, while at the same time they become store-houses of foetal nutriment. At a later period they de- generate and are absorbed by the trophoblast. Their possible 1 Masius, ‘‘De la Genése du Placenta chez le Lapin,” Arch. de, Biol., 1889, 428 THE PHYSIOLOGY OF REPRODUCTION function as a protection against the attack of the foetal ectoderm has already been mentioned. At the end of pregnancy their defence is no longer required, as the trophoblast has also lost its activity. Iron Metabolism.—The decidual cells are concerned in the metabolism of iron, fat, and glycogen for the foetus. In the rabbit, as contrasted with Ruminants, the ingestion of healthy or degenerated erythrocytes probably does not occur. Though Maximow states that they are “present in the plasmodium,” they appear to be im the plasmodium only as the isolated penin- sule of decidual cells are in it, ¢.e. they lie in spaces surrounded by trophoblast. Whether hemoglobin as such, or its more immediate derivatives in the form of organic iron compounds are absorbed has not been investigated, but Chipman has shown that inorganic iron compounds are present, and their distribution speaks for their absorption by the trophoblast. The compounds appear as blue-black granules in sections stained with a weak watery solution of hematoxylin. At the fourteenth day they are present in the foetal mesoblast, especially where it approaches the decidua. They increase in size and number for a few days and then diminish, but some are still seen at the end of preg- nancy. A few granules appear in the trophoblast between the sixteenth and twentieth days (Fig. 103). From the sixteenth day they are also found in an increasing number of the decidual cells which lie close to the fcetal placenta; after the twenty- fourth day, when the cells degenerate, the granules are no longer discrete, but there are irregular blue-black patches up to the end of pregnancy. : Such isolated data cannot be accurately interpreted. The fact that the deposits in the three tissues are always situated in apposition to each other speaks for their absorption by the foetal tissues; on the other hand, a very small number of granules are present in the trophoblast, and only for a few days. It is possible that organic iron compounds, not shown by the hematoxylin stain, are absorbed and broken up, and later appear as granules in the mesoderm. Their further course to the foetal liver, in which they are stored, has not been traced. It is to be noted that the iron compounds are not only derived from hemoglobin. They may also represent degeneration pro- ducts of the nucleoproteins. FOETAL NUTRITION: THE PLACENTA = 429 Hubrecht * has suggested that erythrocytes may be manu- factured in the decidual cells, and their iron-containing granules may thus be utilised (see p. 494). Fat Metabolism.—Regarding the presence of fat in the Fie. 103.--Iron granules in the placenta of the rabbit at the eighteenth day of pregnancy. (Chipman. ) a, iron granules in mesoblast; 6, iron granules in multinucleate decidual cells ; g, iron granules in ectodermal tubules, 1 Hubrecht, ‘“‘Ueber die Entwicklung der Placenta von Tarsius und Tupaja,” Internat, Congr. of Zool., Cambridge, 1898, 430 THE PHYSIOLOGY OF REPRODUCTION placenta of the rabbit, a few observations have been made by Eden,’ Maximow, and Masius. Chipman has investigated the subject in greater detail, but he draws no conclusions from the histological data. In reality, the study of fat in the placenta is rendered difficult by its occurrence both as an infiltration and in the degeneration of cells. Fat is found in the foetal viscera, liver, heart, and mid-gut, before the allantoic circulation is established. At this time, the tenth day, the vitelline circulation is at its height, and the fat probably reaches the embryo by its vessels, as it is also found in the hypoblast of the area vasculosa. It may be de- rived from the absorption by the trophoblast of fat-droplets contained in the giant-cells of the peri-placental folds. As the vitelline circulation diminishes, the fat disappears from the embryonic viscera, and does not reappear till four or five days after the establishment of the allantoic circulation. During this interval fat is present in the extra-placental wall of the blasto- cyst, but it probably arises by a degeneration of its cellular protoplasm. In the foetal placenta, fat is never found in the mesoblast or capillary walls, but it occurs in the trophoblast, especially where it is in contact with maternal blood or decidua. It in- creases from the twelfth to the sixteenth day, then it decreases, and a week later disappears altogether. In the maternal placenta fat first appears in the decidual cells which are nearest the trophoblast. They show no sign of degeneration at this time, and they probably secrete the fat globules. After increasing for a few days, it diminishes with the atrophy of the decidual cells, and finally appears as fatty débris. Fat is also present in the proliferating endothelium, and later in the fibrin lamine of the uterine sinuses. In the new-born foetus the main store of fat is contained in the subcutaneous tissue. It is remarkable that it does not appear in this situation till the greater part of the fat has dis- appeared. from the placenta. It is either transmitted to the foetus in a form which does not reduce osmic acid, or formed in the foetus itself from other substances. At birth the foetal 1 Eden, ‘‘The Occurrence of Nutritive Fat in the Human Placenta,” Proc. Roy. Soc., London, vol. lx., 1896. FETAL NUTRITION: THE PLACENTA 431 viscera, especially the liver, have a considerable store of fat which increases during suckling. Glycogen Metabolism.—The presence of glycogen in the placenta of the rabbit was discovered by Claude Bernard? in 1859. He showed its increase and subsequent decrease during pregnancy, and concluded from his observations that the placenta carried out for the foetus, in the first half of intra- uterine life, the glycogenic function subsequently assumed by the foetal liver. Godet* described two areas of glycogen-con- taining cells, one immediately underlying the foetal villi, the other in the deeper part of the placenta. Maximow investigated these cells at different stages of pregnancy ; he found glycogen in the decidual cells of the vascular sheaths at the eighth day, gradually increasing in amount and playing an important part in the nourishment of the trophoblast. In the later stages glycogen disappeared and the decidual tissue was transformed into polygonal multinucleate cells rich in fat. Chipman recorded detailed observations in a more complete age-series from the eighth day to the end of gestation. He showed that glycogen was always present in the maternal part of the placenta, but never in the foetal. Occurring in the decidual cells of both zones, it increased and reached a maximum between the twelfth and sixteenth days (Fig. 104); then it steadily diminished, and in the last week only a few granules were found scattered in the conglomerate masses of decidual cells. At the zone of separa- tion, however, glycogen granules were still contained in decidual cells. Chipman also examined the foetal liver. In it he found that glycogen appeared at the twenty-second day, and increased rapidly and steadily in amount till the end of pregnancy. These results have for the most part been corroborated by chemical analyses carried out by the writer, working in colla- boration with Dr. W. Cramer.*? They determined quantitatively the glycogen of the maternal placenta, foetal liver, and remainder * Bernard, “Sur une nouvelle fonction du placenta,’’ Comp. Rend, Acad. Sci., Paris, 1859. 2 Godet, ‘Recherches sur la structure intime du placenta du lapin,” Dissert. Inaug. a la Fac. de Méd, de Berne, Neuveville, 1877. 3 Lochhead and Cramer, ‘The Glycogenic Changes in the Placenta and the Foetus of the Pregnant Rabbit,” Proc. Roy. Soc., London, B, vol. 1xxx., 1908, 432 THE PHYSIOLOGY OF REPRODUCTION of the foetal body in an age-series of pregnant rabbits from the fourteenth day to the end of pregnancy. The maternal placenta } Sp ir TS Fic. 104.—Glycogenic areas of the rabbit’s p'acenta at the twelfth day of pregnancy. (Chipman.) fp, fetal placenta, containing no glycogen ; ir, intermediary region; re, region of uterine sinuses ; ss, uterine sinuses with perivascular sheaths of uninucleate cells rich in glycogen; g, glycogen granules in multi- nucleate cells; m, muscular wall immediately above which, at a later date, the zone of separation, containing glycogenic decidual cells, is differentiated. was separated mechanically from the foetal placenta, and each was investigated separately. The maternal part includes the two glycogenic areas, the region of the uterine sinuses and the FETAL NUTRITION: THE PLACENTA 433 zone of separation. The foetal part includes the peninsule of decidual tissue which form the intermediary zone ; the glycogen contained in it belongs wholly to these peninsule and represents the fraction most intimately related to the trophoblast. It may on that account be termed the proximal glycogen, while that of the maternal part is the distal glycogen. On the fourteenth day the distal glycogen forms over 4 per cent. of the weight of the maternal part, and it gradually increases till the eighteenth day, when it forms 5°5 per cent. ; it remains nearly constant till the twenty-second day, and then there is a continuous decrease each day till the end of pregnancy. On the day before labour it amounts to slightly over 1 per cent., and practically the whole of it is situated at the zone of separation. This last is probably not destined for the foetus. The variations in the proximal glycogen are similar. At the ‘twenty-ninth day there is no glycogen left in the intermediary region, In the foetal liver traces of glycogen are present at the eighteenth day, though none can be demonstrated histologi- cally till four days later. Up to the twenty-fourth day the percentage gradually increases, but is still very small. Next day it rises for the first time above the glycogen percentage in the rest of the foetal body, and then there is a rapid increase til], on the twenty-ninth day, half of the foetal glycogen is stored in the liver. Hence it may be concluded that, although the liver contains glycogen in the earlier stages, a change occurs at the twenty-fifth day of pregnancy. Only then does it store more than its proportion of glycogen by weight, and thus may be said to be capable of carrying on the glycogenic function for the foetus. Before that date the only store of glycogen avail- able is contained in the maternal placenta. “The glycogen metabolism of the placenta and fcetus shows a regular suc- cession of changes which proceed almost regardless of external conditions, and which are independent to a great extent of the glycogen metabolism of the mother ” (Lochhead and Cramer). There can be little doubt that the glycogen stored in the decidual cells is absorbed by the trophoblast. It is situated in the maternal peninsule which are surrounded by fcetal tissue, and it gradually decreases in amount while it increases in the 25 434 THE PHYSIOLOGY OF REPRODUCTION foetus. That none can be demonstrated in the trophoblast may be due to a transformation into sugar before it is absorbed. Glycerine extracts of both the maternal and the foetal part of the placenta possess an enzyme which has a powerful hydrolytic action on glycogen. On the other hand, the enzyme action is markedly weaker, or absent altogether, in the placentz of Ruminants, in which the glycogenic changes are known to be insignificant. It is not easy to determine why such a complex mechanism is necessary if, as is stated by Cohnstein and Zuntz,’ glucose passes from the maternal to the foetal circulation by diffusion. But these investigators have only proved that it diffuses when a hyperglycemia exists in the mother. Under similar con- ditions glucose passes into the urine and liquor amnii in Man, but it does not pass normally.” Hence it has not been proved that the sugar of the maternal blood is diffused unchanged through the trophoblast. It is more probable that the trans- ference of sugar is not effected by a purely physical process, since the serum of the foetal rabbit contains levulose, while the serum of the mother has none (Paton, Kerr, and Watson °). Between the glycogen metabolism and the growth of the foetus there is a distinct relationship, which probably depends directly on the uses to which glycogen is put. Part of it is accounted for by the intense carbohydrate metabolism which proceeds in the foetus (Bohr*). The glycogen, which is thus katabolised, furnishes thereby the energy necessary for the formation of new tissues, the “ Entwicklungsarbeit ” of Tangl.® The question arises whether glycogen also performs anabolic 1 Cohnstein and Zuntz, ‘‘ Weitere Untersuchungen zur Physiologie der Saugetierfotus,”’ Pfliger’s Arch., vol. xlii., 1888. 2 Even in the hyperglycemia of diabetes the figures do not support the theory of the mere diffusion of glucose. Offergeld found 0°8 per cent. of sugar in the maternal blood, and 2°2 per cent. in the fcetal blood in diabetic coma (“‘ Ueber das Vorkommen von Kohlehydraten im Fruchtwasser bei Diabetes,”’ Zeit. f. Geb. u. Gyndk., vol. li.). 3 Paton, Kerr, and Watson (B. P.), “‘On the Source of the Amniotic and Allantoic Fluids in Mammals,” Trans, Roy. Soc, Edinburgh, vol. xlvi., 1907. ‘ Bohr, “‘ Die respiratorische Stoffwechsel des Séugetierembryos,”’ Skand. Arch. f. Phys., vol. x., 1900. See also vol. xv., 1904. 5 Tangl, “Beitrage zur Energetik der Ontogenese,” Pfliiger’s Arch., vol. xciii., 1903. FQ@ITAL NUTRITION: THE PLACENTA 435 functions in the development of the foetus. ‘“‘ The absence of glycogen from some of the growing fcetal tissues, and the fact that many of the tissues in which it is present do not contain even as much as the adult ones, leave little doubt that a definite formative power cannot be attributed to glycogen as such. On the other hand, the scarcity of glycogen in embryonic tissues does not necessarily justify the conclusion that glycogen does not take part in the building up of the tissues. It is well known that embryonic tissues are rich in mucin, which contains a large amount of a carbohydrate group in its molecule. Although glycogen as such has no formative power, it may yield one of the “ Bausteine ” for the building up of the main protein body of foetal tissues. In this connection it is interesting to consider the conditions in the hen’s egg, which contains in itself the material of which the embryo is built up. In the ovum carbo- hydrate as such is practically absent. At the same time all the protein substances of the white of egg are distinguished by the presence of a large amount of glucosamine in their molecule. Here the carbohydrate group has entered into the protein molecule, and correspondingly there is a scarcity of free carbohydrate.” ? Protein Metabolism.—lIn so far as the influence of the tropho- blast on proteins has been investigated in the placenta of the rabbit, it may be considered here. It is generally accepted that colloid substances with large molecules, which are not adapted for diffusion, require a preliminary transformation, by which the size of the molecules is decreased before they can be taken up by the foetal ectoderm. But the actual observations are against such a general statement. In the sheep the trophoblast can absorb not only hemoglobin, a colloid, without any preliminary transformation, but even enormously larger masses of proto- plasm in the form of cells. On the other hand, such hydrolysed products of albumen as albumoses and peptone are not present in the fresh placenta, nor can any extra-cellular proteolytic enzyme be extracted.2 Hence there is no evidence of a placental 1 Compare Emrys-Roberts, ‘‘ A Further Note on the Nutrition of the Early Embryo, with Special Reference to the Chick,’’ Proc. Roy. Soc,, London, B., vol. lxxx., 1908. * Lochhead and Cramer, loc, cit. 5 Lochhead, “On the Transmission of Nitrogenous Compounds from Mother to Foetus,” Trans. Obstet, Soc,, Edinburgh, vol. xxxiii., 1907-8. 436 THE PHYSIOLOGY OF REPRODUCTION digestion of proteins before their absorption by the trophoblast. Further it has been shown, by means of the precipitin reaction, that if egg-albumen is injected into the mother some of it passes unchanged to the foetus (Ascoli). On the other hand, the proteins of ox-serum cannot be recognised in the foetal blood, even when a considerable quantity is injected.? The reason appears to be that the proteins of ox-serum resemble more closely the normal serum proteins of the rabbit and are meta- bolised by the trophoblast, while ege-aloumen cannot be utilised, and is passed on to the foetal circulation unchanged. Hence it is probable that the normal proteins of the serum are also transformed by the trophoblast into a form suitable for the foetus. The exact nature of the transformation is unknown, but it is not comparable with the hydrolytic processes which occur in the intestine. Respiration.—According to Bohr,* the foetal rabbit absorbs slightly more oxygen and gives off slightly more carbonic acid per kilogram per hour than the mother. Hence the intensity of the metabolic reactions is slightly greater in foetal life. This is directly opposed to the views held by Pfliiger on theoretical grounds, and by Cohnstein and Zuntz* from their experimental results. The second result of Bohr’s experiments has been already mentioned, viz. that in that part of the metabolism which is evidenced by the respiratory exchange, the energy arises from carbohydrates. He supposes that the energy liberated by the combustions, which in the adult is dissipated largely under the form of heat radiated and water evaporated from the surface of the body, is in the foetus used for the in- crease and maintenance of the newly formed tissues; in other words, “the reactions of synthesis, which are so numerous during development, are endothermic or heat-absorbing, and they borrow the heat from other simultaneous exothermic actions,” ° in this case the oxidation of carbohydrates. 1 Ascoli, ‘‘Passiert Eiweiss die placentare Scheidewand?”’ Zeit. f. phys. Chem., vol. xxxvi., 1902. This has been confirmed by the writer and Dr. W. Cramer (see reference, note 3, p. 435). 2 Lochhead, loc. cit. 3 Bohr, loc, cit. * Cohnstein and Zuntz, ‘‘ Untersuchungen tiber das Blut, den Kreislauf und die Atmung der Siugetierfétus,” Pfliiger’s Arch., vol. xxxiv., 1884. 5 See Richet’s Dictionnaire de Physiologie, vol. vi., Article ‘“‘ Foetus.” FQ:TAL NUTRITION: THE PLACENTA § 437 Mouse.—The fertilised ova of the mouse reach the uterine cavity on the third day, and segmentation is completed one day later. The zona pellucida has by this time disappeared, and fixation of the ovum to the uterus can be quickly attained. Each blastocyst comes to rest in an anti-mesometrial groove. At first spherical, it becomes ovoid on the sixth day, with the long axis perpendicular to the long axis of the uterus. One pole is turned towards the mesometrium and is composed of several layers of cells, while the opposite pole is single-layered. It is nourished by the glandular secretion, and perhaps also by a transudate, in which, however, leucocytes are not present. The connective tissue of the mucosa shows a thickening at the point where a blastocyst rests. The epithelium degenerates as the result of contact with the foetal ectoderm (Duval), or of pressure by the proliferated connective tissue cells which interferes with the nutrition of the epithelium (Burckhard °). More probably it is not mechanical, as the change begins first at the mouth of the groove, i.e. at the point of first contact with the ovum (Kolster*). In the cells the chromatin clumps on the inner surface of the nuclear membrane, the cell boundaries disappear, and a symplasma is formed which later becomes broken up into nuclear and cellular fragments. Fat globules, which are present in the epithelium of the non-pregnant uterus, are found in the detritus and also in the foetal ectoderm. With the destruction of the epithelium appears the first sign of decidual formation. The connective tissue cells increase in size and displace the glands; the capillaries dilate irregularly, and at places form sinuses. On the sixth day, the ectoplacental cone is formed by a pro- liferation of the ectoderm at the mesometrial pole of the blasto- cyst. It plugs the opening between the crypt and the lumen of the uterus. At the same time the lips of the crypt are gradually brought nearer to each other by the swelling of the tissues, and at the end of the seventh day they fuse and cover 1 Duval, “Le Placenta des Rongeurs,” Journ. de l’ Anat, et de la Phys., 1891. ? Burckhard, ‘“‘ Die Implantation des Eies der Maus in die Uterinschleim- haut,” Arch. f. mtkr. Anat., vol. lvii., 1901. 3 Kolster, “Zur Kenntnis der Embryotrophe beim Vorhandensein einer Decidua Capsularis,”’ Anat, Hefte, vol. xxii. THE PHYSIOLOGY OF REPRODUCTION the ectoplacenta. In this way the ovum is completely shut off in a decidual cavity, the “ Eikammer,” from the uterine lumen. The roof of the chamber forms the primary decidua reflexa, and it is gradually thickened by a decidual deposit. In it new blood-vessels are developed, and they form a specially rich vascular network. By this time the blastocyst has become tubular in shape, and it shows an inversion of the germinal layers (Fig. 105). In the earlier stage a cavity appears in the inner mass of cells. The roof of the cavity becomes thickened to form the “Trager” or ecto - placental cone, which is at first cylindrical and later conical, with its base resting on the mesometrial pole 438 Fig. 105.—Inversion of the germinal layers in the blastodermic vesicle of the mouse. The trophoblast becomes greatly thickened and invaginated, pushing the for- mative epiblast before it. The whole blastocyst assumes a tubular shape, and the hypoblast appears to be external to the epiblast. Trophoblast represented by con- tinuous black lines or masses: entoderm by interrupted lines: embryonic ectoderm by epithelial cells. (T. H. Bryce, in Quain’s Anatomy, Longmans.) the ectoplacenta which communicate with the surface. of the ovum. By its inward growth, it shoves before it the floor of the inner mass consist- ing of epiblast and hypoblast. In this way an invagination is produced in the tube with the epiblast internal to the hypo- blast. Hence the germinal layers are said to be inverted. Blood is regularly found in the implantation cavity. It completely surrounds the ovum, and reaches irregular spaces in At this time, however, there are no foetal vessels near the cone, and the blood in its meshes may be of use only for its own nutrition. On the other hand, the thin trophoblast of the wall of the invaginated yolk-sac is partly vascularised by vitelline vessels, by means of which the nutriment absorbed from the blood effusion may reach the embryo, or be stored in the yolk-sac. In the trophoblast itself the hemoglobin of laked corpuscles and its derivatives are FETAL NUTRITION: THE PLACENTA = 439 present (Jenkinson *), and the contents of the umbilical vesicle are “not yolk, but another nutritive substance which the ovum, in the absence of yolk, takes from the maternal tissues, viz. hemoglobin ” (Sobotta ”). The decidual cavity is at first small and ovoid, and has a thick wall. As it grows, the lumen of the uterus is obliterated, and at its point of contact with the mesometrial wall the epi- thelium of the latter disappears. Thereafter the two layers fuse, and at the point of fusion the placenta is developed. The lumen of the uterus is later re-established, as in the guinea-pig (see Fig. 110), at the floor of the decidual cavity. Hence the primary decidua reflexa forms the serotina, and a secondary reflexa is formed, which is recognisable till the twentieth day of pregnancy. The increase in size of the implantation cavity is accom- panied by a thinning of its wall. According to Duval this is a mechanical process, since the cells do not increase in number, but it is probably more complicated. On the inner surface of the decidua giant-cells appear around the ovum, and they are phagocytic (Fig. 106). Duval stated that each was derived from a cell of the foetal ectodermal wall of the yolk-sac, and later from a cell of the ectoplacental cone. As they increase in number, they form a distinct layer, two to five cells in depth, between the yolk-sac and the wall of the implantation cavity, and some wander into the decidua and lie singly or in groups. In their interior degenerating leucocytes are frequently seen. Sobotta also stated that they were foetal in origin, and helped to fix the ovum and erode maternal capillaries. More recently Kolster has brought forward evidence from their histological appearance that they are transformed decidual cells, and this is strongly supported by Disse’s investigations on the field-mouse,* in which the giant-cells are found before the ovum has become embedded, and the first to appear are at an appreciable dis- tance beneath the surface epithelium. A second series of 1 Jenkinson, ‘‘Observations on the Histology and Physiology of the Placenta of the Mouse,” Tijd. Nederl, Dierk., Ver. ii., Dl. vii. 2 Sobotta, “Die Entwicklung der Maus,” Arch. f. mtkr. Anat., vol. lzi., 1903. 3 Disse, ‘‘ Die Vergrésserung der Eikammer bei der Feldmaus,” Arch. f. mikr. Anat., vol. lxviii., 1906. 440 THE PHYSIOLOGY OF REPRODUCTION smaller size appears later in the lumen and wall of the implanta- tion cavity. Jenkinson also recognised two groups, but assigned Fie. 106.—Longitudinal section of the implantation cavity of the field- mouse about the eighth day of pregnancy. (From Disse’s “Die Vergrésserung der Kikammer bei der Feldmaus (Arvicola arvalis),” Arch. f. mikr. Anat., vol. lxviii., 1906.) p.l., placental pole ; mph, macrophages or giant-cells ; sym, uterine symplasma ; /, blood lacuna. to them different origins, foetal in the “ Eikammer” and maternal in the decidua. All authorities agree that they are phagocytic. The tissue FETAL NUTRITION: THE PLACENTA 441 around them undergoes fatty degeneration, and in their interior may be seen remnants of connective tissue and endothelial cells and fat-globules. Many capillaries are ruptured, and red and white blood corpuscles are also absorbed. Such an absorption of maternal tissue by the giant-cells leads to an increase in the size of the implantation cavity and a thinning of its wall (Disse). In spite of their abundant supply of nutriment, their life-history is short. No cell- divisions occur, and soon they degenerate. Their contents are absorbed by the trophoblast, and their protoplasm shrinks to form a rim around the nucleus. Later still their remnants are also absorbed. The allantois in the mouse is a solid mass of mesoderm with no entodermal cavity. Growing out from the posterior end of the embryo, it projects into the extra-embryonic ccelom, and on the eleventh day fuses with the mesoblast of the ectoplacental cone. After this the ovum again becomes spherical. The circu- lation in the decidua reflexa diminishes, and gradually more and more of the nutriment is conveyed to the embryo by the allantoic vessels. At the same time the allantoic trophoblast increases in thickness, and its lacunee become more numerous and complicated. Into its mass, in which the circulation of maternal blood is now established, the vascular mesoblast pro- jects at intervals, and breaks it up into segments. The glands take no part in the formation of the placenta. Their ducts do not even act as guides to the advancing edge of the trophoblast, as in the rabbit. They are completely displaced by the rapid formation of decidual tissue, and their remnants are absorbed by the giant-cells. Hence the embryotrophe contains no glandular secretion. At this time the nutritional conditions are essentially the same as in the rabbit. The trophoblast shows two layers, plasmodiblast and cytoblast, which intervene, along with mesoblastic cells and the walls of the villous capillaries, between the two blood-streams. The subsequent changes are all in the way of producing an increased surface of contact with maternal blood, and lessening the thickness of tissue between it and the foetal circulation. In the mouse the decidual cells contain glycogen. According 442 THE PHYSIOLOGY OF REPRODUCTION to Driessen, its distribution in the placenta of the white mouse before mid-term is the same as in the rabbit. It is in great abundance in the decidual cells, especially in the boundary layer between the maternal and fcetal tissues. No glycogen is found in the maternal endothelium, or in the fetal placenta. Jenkinson ® has studied the distribution of glycogen throughout the whole period of gestation in the mouse. It appears first in the cells which overlie the ectoplacenta, and increases in amount till the twelfth day, when the mesoblastic processes are just beginning to project into the trophoblast. Then the decidual cells are disintegrated and the glycogen granules are mixed with the detritus. Hence the life-history of the maternal glycogenic tissue is shorter than in the rabbit. But in the mouse glycogen again makes its appearance in the trophoblast which is most directly in contact with the maternal blood, ae. the part not penetrated by the allantoic capillaries. It lies in oblong ectodermal cells, which gradually encroach on and occupy the space previously occupied by the maternal glyco- genic cells down to the muscularis. Here the glycogen remains till the end of gestation.® According to Kolster, a considerable amount of fat appears in the decidua, in which the connective tissue and endothelial cells undergo a fatty degeneration in the proximity of the giant cells. No observations have been made regarding the meta- bolism of iron-containing substances. Guinea-Pig—In the guinea-pig the ovum is again com- pletely surrounded by decidua. Reichert * was the first to notice that the ovum lay in a special cavity, “a little nest.” Bischoff * stated that the nest was only temporary, and the ovum again appeared in the uterine cavity, only that part of the 1 Driessen, ‘‘ Ueber Glykogen in der Placenta,” Arch. f. Gyndk., vol. 1xxxii., 1907. 2 Jenkinson, loc. cit. See also Brit. Med. Jour., 1904. ’ Whether the differences in the distribution of the placental glycogen in the rabbit and the mouse during the later stages of pregnancy exist in reality, or depend only on differences of interpretation, requires further investigation. 4 Reichert, ‘‘ Ueber die Bildung der hinfalligen Haute der Gebirmutter,”’ Miiller’s Arch., 1848. 5 Bischoff, Entwicklung des Meerschweinchens, 1852. FETAL NUTRITION: THE PLACENTA = 443 nest remaining which formed the placenta. After a long interval this was proved to be wrong by Reichert ! and Hensen.” The fertilised ovum reaches the uterus as a morula or early blastocyst, surrounded by the zona radiata. On the seventh day the zona disappears and embedding begins, but even before this, according to von Spee,® the ovum is fixed by processes which extend from the cells of the implantation pole through the zona and come into direct metabolic relationship with the epithelial cells. As in the mouse, the blastocyst remains small, 1 Fig. 107.—Longitudinal section of the uterus and implantation cavity of the guinea-pig. (From Duval’s ‘‘Le Placenta des Rongeurs,” Journ. de UV Anat. et de la Phys., 1892.) mes, mesometrial border ; gi, uterine glands ; J, uterine lumen ; bl, blastodermic vesicle. about one-tenth of a millimetre in diameter. At its point of contact with the mucosa, the epithelium is rapidly eroded, and absorbed along with its fat globules by the foetal ectoderm. At the same time changes occur in the deeper layers. In the non- pregnant uterus two layers are present, a sub-epithelial layer of embryonic connective tissue cells interrupted only by capillaries and glands, and a deeper, more reticulate layer. Before the ninth day of pregnancy, no very marked changes occur in the 1 Reichert, ‘‘Beitrage zur Entwicklungsgeschichte des Meerschweinchens,” Abhandl, d. Akad, d. Wissensch. zu Berlin, 1861. 2 Hensen, “‘ Beobachtungen tiber die Befruchtung und Entwicklung des Kaninchens und Meerschweinchens,”’ Zeit. f. Anat. u. Entwick., vol. i., 1866. 3 Von Spee, ‘Die Implantation des Meerschweincheneies in die Uterus- wand,” Zeit. f. Morphol. u. Anthropol., vol. iii, 1901. 444 THE PHYSIOLOGY OF REPRODUCTION mucosa. Some of the cells show mitoses, the blood-vessels are full, and a few red blood corpuscles may lie between the cells, and also in the foetal ectoderm. During the penetration of the epithelium by the trophoblast, some of the superficial connective tissue cells enlarge. Their nuclei stain more deeply, and the protoplasm of adjacent cells fuses to form a symplasma. The degenerated tissue in its immediate neighbourhood is absorbed by the ectoderm, and the blastocyst thus comes to lie in the substance of the mucosa (Fig. 107). According to von Spee, the destruction of uterine tissue is effected entirely by a biochemical process; there is no evidence of absorption of formed elements by phagocy- tosis. Fiqa. 108.—Blastodermic vesicle of the guinea-pig, showing inversion of the germinal layers. The blastocyst is tubular, and the formative cell-mass is invaginated as in the mouse, but the thickened trophoblast is not invaginated to so great an extent as in Fig. 105, and the connection between them is lost. Hence the roof of the amnio-embryonic cavity is inde- pendent of the trophoblast. (T. H. Bryce in Quain’s Anatomy, Longmans.) Round the periphery of the necrotic zone lies a thick layer of large foetal cells, the two together forming the “ Implan- tationshof.” Later the sym- plasma degenerates further. The nuclei shrink and_ lose their chromatin, and the proto- plasm becomes fibrillated and granular. Vacuolations appear in the mass, and coalesce to form a space round the ovum filled with clear fluid. In this way the implantation cavity is excavated till it is limited externally by the large cells. Outside it the decidual cells around the vessels survive, while the rest are transformed to a symplasma and absorbed. Hence the wall is sinuous. The dips are, however, filled up in part by newly formed tissue resembling granulation tissue. It encapsules the necrotic zone, and may be looked on, as in the rabbit, as a defence against the advancing ectoderm (see p. 369). By this time the ovum has become tubular, with its long axis perpendicular to the long axis of the uterus. It exhibits, FQTAL NUTRITION: THE PLACENTA = 445 as in the mouse, an inversion of the germinal layers, but in the guinea-pig the amnio-embryonic vesicle is closed and separates the thickened trophoblast from the embryonic ectoderm (Fig. 108). With the growth of the blastodermic vesicle, the roof of the implantation cavity projects into the lumen of the uterus, and in time obliterates it by coming in contact and fusing, at the tenth day, with the mesometrial mucosa (Fig. 109). Here also the cellular tissue has developed at the expense of the glands, and the surface epithelium disappears. At the fifteenth mes Fig. 109.—Implantation cavity of the guinea-pig. (Duval.) mes, mesometrial border ; /, uterine lumen. day the lumen reappears anti-mesometrially (Fig. 110). Thus a secondary decidua reflexa arises which rapidly thins and be- comes vacuolated in its inner half by a loss of tissue. The cause of the tissue excavation is uncertain ; it may be brought about by the large cells which, according to von Spee, are foetal and form a third layer of the trophoblast outside the plasmodiblast, and the disintegrated products are probably absorbed by the ovum. At the same time the vessels which penetrate the necrotic zone are opened, and blood is effused into the implanta- tion cavity. The placenta develops, as in the mouse, mesometrially. The 446 THE PHYSIOLOGY OF REPRODUCTION allantois consists of a tubular passage in the body wall and a solid extra-embryonic stalk of mesoderm. It projects into the celom and gradually extends, and becomes applied to the mesoblast underlying the thickened part of the trophoblast, in the spaces of which a circulation of maternal blood is established. The trophoblast continues to attack and absorb maternal tissue and blood, and to advance more deeply into the decidua, while at the same time it is penetrated on the embryonic side by out- Fig. 110.—Implantation cavity of the guinea-pig. (Duval.) mes, mesometrial (placental) border ; J, lumen of uterus, re-established anti- mesometrially ; d.r., decidua reflexa; all, allantois ; am, amnion. growths of mesoblast containing branches of the allantoic vessels. The tissues intervening between the maternal and foetal blood-streams are entirely foetal; they gradually thin with the progress of gestation and the continued branching of the mesodermal villi. Glycogen is contained in the decidual cells, but its variations have not yet been investigated. It is of interest historically that oxyhemoglobin was demonstrated first in the umbilical vein of a foetal guinea-pig by Schmidt." The amounts of oxygen 1 Schmidt, ‘“ Sauerstoffhimoglobin in F6tusherzblut,” Cent. f. d. med, Wiss., 1874, No. xlvi. FETAL NUTRITION: THE PLACENTA § 447 absorbed and carbonic dioxide excreted are the same, weight for weight, as in the foetal rabbit (Bohr), InsEcTIVORA.—The importance ascribed to the placentation in Insectivora has already been referred to (see p. 377). The hedgehog, shrew, mole, and Tupaia have been most fully. in- vestigated. Hedgehog.—In the hedgehog (Erinaceus ewropeus), the zona pellucida disappears early, before the expansion of the hypo- blast, which, as in Man, forms a closed vesicle. The chronology of embedding is not yet known. In the earliest stage examined by Hubrecht,* the blastocyst was 0°22 of a millimetre in diameter. The outer wall was several layers thick all round its circum- ference, and spaces were already present in it. At a slightly later stage, the blastocyst grows rapidly and the epiblast is re- duced to a single layer, with numerous villiform processes at intervals, except for a thickened knob which represents the future germinal area. Even now the name érophoblast may be given to the single layer of epiblast with its projections, ex- cluding the thickened knob which is formative and gives rise to the embryonic ectoderm and the lining of the amniotic cavity. The mesoblast, as yet one-layered, which extends between the trophoblast and hypoblast, consists of an attenuated somatic part which forms with the trophoblast the dzplo-trophoblast,* and a splanchnic part which forms blood-vessels and blood. The early blastocyst comes to rest, as in the mouse, in an anti-mesometrial furrow of the mucosa. It is not yet deter- mined whether any changes occur previously in the uterus; but at least, soon after the blastocyst has taken up its position, there is a great cell-proliferation in the stroma of the floor and walls of the furrow, not perivascular as in the rabbit, but sub- epithelial. Along with this decidual formation, the lumina of the glands are closed, and their epithelium gradually disappears, perhaps by the influence of the trophoblast. The capillaries are distended and new vessels are formed. This distension is at 1 Hubrecht, ‘The Placentation of Erinaceus europeus,” Quar. Jour. Micr. Sci., vol. xxx., 1889. 2 Hubrecht restricts the term chorion to Tarsius (a lemur), monkeys, apes, and Man. 448 THE PHYSIOLOGY OF REPRODUCTION first most marked in the lips and sides of the groove, and small superficial hemorrhages occur, which detach the epithelium at places. The tissue fluids also exude, and, along with the blood and desquamated epithelium, form a coagulum around the’ ovum. Part of it shuts off the entrance of the furrow from the uterine cavity. The epithelium of the crypt, after a preliminary prolifera- tion such as Robinson describes in the mouse and rat, degenerates Fig. 111.—The allantoidean diplo-trophoblast of Hrinaceus, (From Hubrecht’s “The Placentation of Hrinaceus europeus,” Quar. Jour. Micr, Sci., vol. xxx., 1889.) Tr.S., trophospongia; Z'7,, trophoblast; F.L., layer of fusiform cells; Sp., spaces in trophoblast ; M.Som., thin layer of somatic mesoblast. entirely, part being stripped off by extravasated blood and part yielding to the influence of the foetal ectoderm. Its remnants and the other constituents of the coagulum probably furnish pabulum for the ovum. The development of the de- cidua proceeds rapidly, and the swollen lips of the groove fuse together to complete the implantation cavity. The trophoblast is now in contact with decidual tissue, of which the innermost zone consists of a stratified layer of fusiform cells, best marked in the FATAL NUTRITION: THE PLACENTA = 449 allantoic region (Fig. 111). Whether they are maternal or foetal in origin is not yet determined. They persist for a time, but disappear when the endothelial proliferation occurs. Around the groove, the tissue becomes looser by an increase in the size of the newly formed blood-spaces. The endothelium lining them is swollen and deep, and the cells bulge into the lumen. Near the ovum the endothelium proliferates and forms an enormous cell-mass, the trophospongia,! interposed between the blastocyst and the unaltered decidua. The trophoblast with its lacune, and the trophospongia with large blood-sinuses together form the trophosphere, which, along with the maternal blood, represents an effective nutritional arrangement for the embryo before the vitelline or allantoic circulation is estab- lished (Fig. 112). Many of the blood-spaces are ruptured, and the blood pours out into the lacune of the tropho- blast, and circulates through them before returning into the maternal veins. At this stage the trophospongia is separated from the external decidua by rows of fusiform cells. As in the mouse, in which, however, the trophospongia is derived from connective tissue cells instead of endothelium, giant-cells appear. They lie between the trophospongia and the fusiform cells, and they are first seen at the time of the appearance of the embryonic mesoblast. In their interior are contained fragments of red blood corpuscles and decidual cells. Hence they are called deciduofracts by Hubrecht (Fig. 113). Externally the circular layers of fusiform cells form sheaths round some of the endothelium-lined vessels. The line of union between the giant-cells and the external decidua is irregular, and the decidual tissue is fibrillar and reticulate. These appear- ances indicate an erosion and absorption of the maternal tissue. The deciduofracts are probably derived from the maternal trophospongia (Hubrecht?). After a short life-history they dwindle and are themselves absorbed. 1 “The trophospongia is a maternal cell-proliferation specially intended for the fixation of the blastocyst. It shows a different histological evolution in different genera’ (Hubrecht). * Hubrecht now considers that the deciduofracts are of fcetal origin, and represent the outermost layer of the trophoblast. See p. 470, footnote. Also compare Graf v. Spee’s description of the trophoblast of the guinea-pig (see p. 444), and Bryce and Teacher’s of that of Man (see p. 469). 2F 450 THE PHYSIOLOGY OF REPRODUCTION With the changes in the mucosa, changes also take place in the trophoblast. After the thinning already mentioned, its cells increase in number. They grow in strands, leaving spaces between them like the meshes of a net, and in the spaces maternal blood circulates. In this respect the hedgehog differs 3 ae - 5 ae é sy Eo fae vee a Pg fe o/s V8 Trs. “ae 2 = 9. E ‘a << HY Cw Nee wae ‘olite v4 i AEP v5 eg Fig. 112.—Section in situ of the ovum of Hrinaceus (Hubrecht). Hy., hypoblast; T'r., trophoblast; sp., spaces in the trophoblast, communi- cating with the maternal blood-spaces (M.Sp.); D., decidua; Trs., trophospongia. from the Rodents, in which the proliferation of the trophoblast is confined to the allantoic region. In the hedgehog the pro- liferation occurs even in the omphaloidean region, which is vascularised by the area vasculosa. Here the vacuolated trophoblast is gradually interlocked with vascular processes of the mesoblast, and yolk-vili, containing branches of the vitel- line vessels, are developed. The omphaloidean placenta thus FQ:TAL NUTRITION: THE PLACENTA 451 formed embraces about one-half of the circumference of the blastodermic vesicle. With the union of the allantois and diplo- trophoblast, the circulation in the decidua reflexa decreases, and it and the trophoblast in contact with it become membra- naceous. They project into the uterine cavity and obliterate its lumen by meeting, but not fusing with, the mesometrial part of the uterine mucosa. As in the bat, the circulation in the yolk-sac never ceases entirely during pregnancy. The changes in the allantoidean trophoblast are of the same ef Pen I i ing Fra. 113.—The extension of the yolk-sac against the lacunar trophoblast in Erinaceus (Hubrecht). The yolk-sac is to the left of the figure, and its villi (Vi.) and blood-vessels (B.V.) are well seen. Tr., trophoblast; Trs., trophospongia; Df., layer of deciduofracts; D., decidua, of which the inner layer (D’) has assumed a more reticulate aspect; Sp., spaces in trophoblast. kind, but they occur later. It occupies a discoid area as in Rodents, but it is on the anti-mesometrial side, 7.e. the primary decidua reflexa is permanent. The lacunar spaces in it are more complicated than in the omphaloidean trophoblast, and their walls bulge towards the embryo and interlock with vascular projections of the allantois. Hence the villi have a complete trophoblastic covering. The extremity of each villus is attached to the maternal decidua by strands of trophoblastic cells. The allantoidean trophospongia develops like the omphaloidean, but 452 THE PHYSIOLOGY OF REPRODUCTION it retains its thickness later in pregnancy. The deciduofracts remain distinct to the end, though they partly degenerate. Hence it is probable that during the whole, or nearly the whole, of pregnancy they exercise a phagocytic action on the maternal Fig. 114.—Transverse section through the uterus of Sorex at a stage when the blastocysts are still in the oviducts. The coiled uterine glands (Gl.) are massed together in the anti-mesometrial regions. The uterine lumen (U) is more or less J-shaped. (From Hubrecht’s ‘‘The Placentation of the Shrew,” Quar, Jour. Micr. Sci., vol. xxxv., 1894.) B.V., blood-vessels ; ¢c.m., circular muscle ; /.m., longitudinal muscle. tissues, and store nutriment which they give up to the embryo in a way as yet unknown. Shrew.—In the shrew (Hubrecht ') the method of embedding is centric, and no decidua reflexa is formed. The yolk-sac pla- centa is not so well developed as in the hedgehog. The attachment of the blastocyst is modified, as in Ruminants, 1 Hubrecht, “The Placentation of the Shrew,” Quar. Jour. Micr. Sci., vol. xxxv., 1894. FQETAL NUTRITION: THE PLACENTA 453 by special characteristics of the uterine mucosa. They differ from the cotyledonary burrs, however, in being proliferations of the surface epithelium. Before the fertilised ova reach the uterus, there are variations in thickness in the mucosa. It is thin at the mesometrial and anti-mesometrial sections, but thickened over the sides to form two cushions, in which the blood-vessels are more numerous. No glands are present near the mesometrium. They are collected on the opposite surface and open into a longitudinal anti-mesometrial groove (Fig. 114). Fig. 115.—Part of the anti-mesometrial wall of the uterus of Sorex (Hubrecht). The proliferated epithelium is arranged in a radial fashion, and later it forms a secondary crypt (Cr.), when the uterine epithelium (U.E£.) gives way over it. : When the blastocysts reach the uterus, further changes take place. Both the lateral regions increase in thickness by the proliferation of connective tissue cells and the formation of new vessels, while the anti-mesometrial part is widened out into a concave bell-shaped surface into which the glands open. Then the epithelium proliferates, first in the lateral cushions and later in the concave area. In the former the proliferation reaches a thickness of twelve to eighteen cells, and the new elements pass in among the cells and vessels of the deeper layers. In the allantoidean region, the bell-shaped area, the proliferation also leads to a thick epithelial layer with vascular channels between the cells. At intervals, however, the cells are 454 THE PHYSIOLOGY OF REPRODUCTION arranged radially like a fan, and later the internal parts of the cells break away and leave a crypt. No crypts are formed in the lateral cushions (Fig. 115). Over the special areas of the mucosa the trophoblast thickens. It comes in contact first with the lateral cushions by a zonary strip against which the vessels of the area vasculosa spread out. The cell-outlines in the epithelium of the cushions are lost, and a symplasma is formed. At the same time the trophoblast be- comes syncytial, is fused to the uterine symplasma, and absorbs part of it. Some of the intercellular channels are opened, and the maternal blood thus begins to circulate in the syncytial lacunee. At the same time a deeper cell layer, corresponding to the cytoblast of the bat, appears in the trophoblast, but it is never so well marked as in the allantoidean region. In this way the avillous yolk-sac placenta is formed (see also p. 391), and it functions for a time. Soon retrogressive changes appear, resulting in the absorption of the omphaloidean syncytium and epithelial thickenings (Fig. 116). The disappearance is ap- parently brought about by a newly formed annular proliferation of the trophoblast above the non-placental part, and the de- generated products of the thickened uterine epithelium and of a blood extravasate, which constantly exists between the annulus and the epithelium, are absorbed and transmitted through the hypoblast to the yolk-sac. From it the vessels of the area vasculosa, which at this time reach their full development, carry the nutriment to the developing embryo. The allantoidean trophoblast is applied against the bell- shaped proliferation on the anti-mesometrial side of the uterus, and is fixed by projections which sink into the newly formed crypts. After destroying their epithelial lining, the projections erode capillaries, and the maternal blood circulates in the syncytial lacune as in the omphaloidean trophoblast. The cytoblast follows the plasmodial projections, and later the trophoblastic villi are vascularised by the allantoic vessels. Subsequently the plasmodiblast thickens to a considerable extent, and in it the mesoblastic villi continue to branch and form secondary and tertiary vili. There is no penetration on their part into the decidual tissue between the crypts, but the maternal part of the placenta as a whole is gradually absorbed FQETAL NUTRITION: THE PLACENTA = 455 by the plasmodiblast, and is replaced by foetal elements. In the ripe placenta the only maternal constituent is blood, except a Fia. 116.—Uterus and embryo of Sorex (Hubrecht). a,T., allantoidean trophoblast with knobs entering the epithelial crypts (Cr.); am., amnion ; all., free knob projecting into the extra-embryonic cclom (Z.ec.); a.v., area vasculosa ; an’, embryonic cells which grow downwards from the upper rim of the trophoblastic annulus (tr.an.), and adhere against the maternal tissue ; np.7'., non-placental trophoblast ; GL, glands; M., mesometrium. thin discoid sheet of nuclear remnants next the muscularis. The glands are not penetrated by vascular villi. In the early stages they are plugged by syncytium and later disappear. 456 THE PHYSIOLOGY OF REPRODUCTION Mole.—The method of embedding is centric. A simple yolk-sac placenta exists for a time. The allantoic placenta is discoid and is placed anti-mesometrially. The glandular secretion is of importance for the nourishment of the developing foetus during the greater part of pregnancy (Strahl,? Vernhout ”). At the beginning of pregnancy the mucosa shows variations in its different parts. Near the mesometrium, for about one- third of the circumference of the lumen, the glandular layer is thin. Anti-mesometrially the muscular layer is not so well developed, but superficially to the glands there is a proliferation of connective tissue cells, through which the ducts run to open into the lumen. The first attachment is in this region. The uterine horns show a series of small swellings where the ova are present. The blastocysts grow to a comparatively large size, and completely fill up the lumen. By their further growth, the epithelium near the mesometrium is flattened and replaced by trophoblastic cells, which do not penetrate into the connective tissue or form villi. Hence the yolk-sac placenta is is of a simple type ; it persists throughout pregnancy. On the opposite side the decidual formation proceeds, and the mucosa becomes thicker. In its substance a rich network of blood-capillaries is developed. The epithelial cells lose their boundaries and form a symplasma. According to Strahl this remains, and forms the syncytial covering of the future villi, but Vernhout has shown that the trophoblast proliferates and forms a layer of epithelioid cells which penetrate into the epithelium and absorb and gradually replace it. Over each gland-opening the trophoblast forms a dome as in Ruminants (Fig. 117). In the placental region the glandular epithelium is not changed, and around each opening a small area of the surrounding uterine epithelium persists. In the cavity between a gland-orifice and its trophoblastic cap les a dark secretion, pigmented by admixture with extravasated blood, and the cap is similarly pigmented. Hence the secretion is probably absorbed by the foetal ectoderm throughout the greater part of pregnancy during which the glands remain. After the disappearance of the surface ? Strahl, ‘‘ Veber den Bau der Placenta von Talpa europea,” Anat. Anz., vol, v., 1890. 2 Vernhout, ‘‘ Ueber die Placenta des Maulwurfs,” Anat. H. efte, vol. v.,1894. FQETAL NUTRITION: THE PLACENTA § 457 epithelium at the point of connection with the blastocyst, the plasmodiblast penetrates into the connective tissue layer which forms a symplasma. It is followed by the cytoblast and the allantoic villi. In the syncytium the circulating maternal Fig. 117.—Orifice of a uterine gland of the mole with trophoblastic dome. (From Vernhout’s ‘‘Ueber die Placenta des Maulwurfs,” Anat. Hefte, vol. v., 1894.) : m., uterine mucous membrane ; ue., uterine epithelium ; pl., plasmodiblast ; cy., cytoblast ; g.s., gland secretion. blood provides for the exchange of gases, and supplements the nutriment supplied by the glandular secretion. Tupaia.—In Tupata javanica also, the placentation is modi- fied by the characteristics of the uterine mucosa. Hubrecht? 1 Hubrecht, ‘‘ Ueber die Entwicklung der Placenta von Tarsius und Tupaja,”’ Internat. Congr. of Zool., Cambridge, 1898. 458 THE PHYSIOLOGY OF REPRODUCTION has shown that two specialised areas, the “ Haftflecke,” exist before the attachment of the trophoblast. They le one on each side, about midway between the mesometrial and anti-mesometrial regions, and are recognised by the ab- sence of glandular ducts. The deeper parts of the glands persist till the end of pregnancy, but none open on the modified areas. The uterine epithelium again disappears at the points of contact with the blastocyst over the “ Haftflecke.” There the trophoblast becomes thickened, and its cells enlarge and pene- trate between the epithelial cells, which fuse to form a sym- plasma. This is quickly absorbed by the trophoblast, which continues to thicken, and now shows two layers, plasmodiblast and cytoblast. The outer layer fuses so closely with the de- cidual tissue as to be indistinguishable from it. The capillaries dilate and new vessels are formed, especially in the layers next the ovum. When their endothelium is destroyed, maternal blood enters the trophoblastic lacune and soon circulates through them. The inter-vascular connective tissue cells pro- liferate and form the trophospongia. The decidual layers outside it become fibrillar, and soon are extremely attenuated. The trophospongia remains longer, but finally it also thins, and at the end of pregnancy there is only a thin rim of maternal tissue left. Over the “ Haftflecke ” the trophoblast is first vascularised by the vitelline vessels, and a temporary yolk-sac placenta is formed. Later the allantois displaces the yolk-sac, and its vessels vascularise the same part of the trophoblast (Fig. 118). “The permanent placenta replaces the omphalic placenta both physiologically and topographically ”’ (Hubrecht). In this respect Tupaia differs from the hedgehog and the shrew. Centetes—A peculiar form of placentation has been de- scribed by Strahl? in the tenrec (Centetes ecaudatus). A large effusion of maternal blood destroys the centre of the allantoic placenta, and leaves only a peripheral ring. Round the margin 1 Strahl, ‘‘ Beitrage zur vergleichenden Anatomie der Placenta,’’ Abh. Senckenberg Naturf.-Ges.,1905. See also Rolleston, ‘‘On the Placental Structures of the Tenrec (Centetes ecaudatus),”’ &c., Trans. Zool, Soc., London, vol. v., 1863. FQ:TAL NUTRITION: THE PLACENTA 459 of the ring runs a deep groove which is crossed by branches of the allantoic vessels to reach an epithelial ridge of cells. CHEIROPTERA.—The mode of embedding in the bat is centric, and the allantoic placenta is discoid. Before segmentation is completed, the fertilised ovum reaches the uterus and invariably enters the right cornu (Ercolani'). The zona pellucida is already thinned and soon disappears, the spherical blastodermic vesicle lying free in the uterine cavity. At the beginning of gestation, according to: van Beneden,? 1 H y.8. Fig. 118.—Replacement of omphaloidean by allantoidean placenta in Tupaia. (From Hubrecht’s “‘ Ueber die Entwicklung der Placenta von Tarsius und T'upaja,” Internat, Congr. of Zool., Cambridge, 1898.) m.v., mesodermic villi; T'r., trophoblast; Ta., trophospongia; All., allantois: y.8., yolk-sac. the mucosa is composed of a richly cellular connective tissue, covered by a non-ciliated epithelium. Of the glands some are simple tubes, and others divide dichotomously. None open on the mesometrial aspect where the blastocyst later becomes fixed. There also the cellular tissue is not so thick. Before fixation of the blastocyst, important changes occur 1 Ercolani, ‘‘ Nuove ricerche sulla placenta nei pesci cartilaginosi e nei mammiferi,” Mem. dell’ Accad. d. Sc. dell’ Institut. di Bologna, vol. x., 1879. 2 V. Beneden, ‘‘ De la formation et de la constitution du placenta chez le murin,’’ Comp. Rend. de la Soc. de Biol., vol. v., 1888. 460 THE PHYSIOLOGY OF REPRODUCTION in the mucosa. The sub-epithelial connective tissue cells pro- liferate and form a distinct compact zone. All the capillaries dilate, even before the disappearance of the zona pellucida, and give off many new branches. The tissue fluids are increased, and a serous fluid is transuded and forms, with the glandular secretion, a coagulum around the ovum (Van der Stricht *). On the mesometrial side, the trophoblast thickens around the formative cell mass, and absorbs the surface epithelium. At the opposite pole the cells are flattened, and they also dis- appear. The ftetal ectoderm, which thus comes in contact with the connective tissue, is composed of two layers at the embryonic pole, the plasmodiblast, and, internally to it, the cytoblast. At the non-embryonic or anti-mesometrial pole the plasmodiblast is absent. The decidua also differs at the two poles. Opposite the non-embryonic pole, the cells remain epithelioid and undergo little change. Where they come in contact with the tropho- blast, they show a tendency to necrose. At the placental pole the deeper layers are also composed of epithelioid cells, but superficially the capillaries continue to dilate and make the layer spongy. The cells between them are in active division, but next the plasmodiblast they degenerate. This layer forms the couche paraplacentaire of Nolf? (Fig. 119). At the placental margin it thins out and disappears. Beneath the epithelioid layer in both areas the cells are drawn out and pseudo-fibrous. The conditions for nutrition resemble those in the very early human ovum, the trophoblast lying against a non-vascular detritus-zone. But in the bat there is strong evidence of phagocytosis. The epiblastic protoplasm, where it is in contact with dead tissue, is “crammed with irregular granules, some fatty and others coloured brown with safranin”’ (Nolf). The mouths of the glands opening at the non-embryonic pole are filled with débris, and their epithelium is degenerated and desquamated. As previously mentioned, no gland-ducts are present in the couche paraplacentaire. The blind ends of the 1 Van der Stricht, ‘‘La fixation de l’ceuf de chauve-souris h l’intérieur de Vutérus,” Verh. d. anat. Gesell., 13 Vers., Tiibingen, 1899. 2 Nolf, “Etude des modifications de la muqueuse utérine pendant la gestation chexle murin,” Arch. de Biol., vol. xiv., 1896. FETAL NUTRITION: THE PLACENTA 461 glands are, however, distended with secretion, and_ their epithelium is normal. Next a change occurs such as Hubrecht described in the hedgehog (see p. 449). The endothelium of some of the vessels in the paraplacental layer proliferates irregularly round the hae - ee Swe ae eS: 3° <2 oe As ane ° be) of =, o 2 ee oe O48 Pa eee \ Fig. 119.—The placenta of the bat. (From Nolf’s “ Etude des modifications de la muqueuse utérine pendant la gestation chez le murin,” Arch. de Biol., vol. xiv., 1896.) m., muscularis ; a., unaltered mucosa; C.ep., epithelial layer ; gl., glands ; C.pp., paraplacental layer with blood-spaces (b.); Art., artery running towards trophoblast ; Ve., vein; Z'r., trophoblast with lacune; V2. all., allantoic villi. lumen, and degenerates. In the bat, according to Nolf, the vessels in which the change occurs are the venous capillaries, in which the blood, returning from the placenta charged with foetal excretory products, stagnates and produces the hyper- plasia’ and simultaneous degeneration. Hubrecht, however, 462 THE PHYSIOLOGY OF REPRODUCTION states that an endothelial proliferation occurs in arterial and venous capillaries alike in the hedgehog. At the embryonic pole the plasmodiblast undergoes a marked thickening. It gradually replaces the superficial de- cidual cells, and surrounds the vessels as in the rabbit. Then it attacks the endothelial sheath and replaces it, so that lacune of maternal blood come to be surrounded by feetal tissue. At the same time the cytoblast sends out cellular buds, which project into the plasmodial mass. Under the cytoblast is the double layer of mesoblast, the thin somatopleur, and the splanchno- pleur in which the area vasculosa is developed. A yoll-sac placenta is thus formed in the same region as is subsequently occupied by the allantoic placenta. Nutritive exchanges be- tween maternal and fcetal blood are now possible. In the further development of the placenta there is very little or no penetration of maternal tissue by the trophoblast (Duval*). Degenerative changes occur in the cells of the epithelioid layer in the placental hemisphere. They lose their outlines, and form a symplasma which is absorbed by the ad- jacent cells of the couche paraplacentaire (Nolf). Superficially the paraplacental layer remains until the end of pregnancy. The blind ends of the glands are still distended, but their epithelium degenerates and is cast off into the lumen. In the non-placental trophoblast, retrogressive changes also occur. Its cells lose their phagocytic power and contain no granules. In the placental area, as already mentioned, the allantois replaces the yolk-sac. The “ villi”’ resemble the tubes of the rabbit. They form a series of arches whose meshes are occupied by allantoic vessels; there are no villi hanging free. As the placenta develops, the thickness of the arches sur- rounding maternal blood is reduced, and the two blood-streams lie close together. The cytoblast almost entirely disappears. Pteropus edulis—In Pteropus the placenta is attached to a large mushroom-shaped outgrowth of the uterine wall which grows nearly round the ovum to form a decidua capsularis. As pregnancy advances, the outer wall of the bell-shaped decidual 1 Duval, “Etude sur VPembryologie des Cheiroptéres,”’ Journ. de l’ Anat. et de la Phys., 1895-97. FQ:TAL NUTRITION: THE PLACENTA 463 mass is pressed against the uterine surface and fuses with it. In this way the completed placenta is discoid (Gohre 1). Primatrs.—The order of the Primates includes monkeys, apes, and Man. Hubrecht also includes Tarsius, a lemur (see p. 410). Owing to the difficulties of securing material for investigation, many details regarding the early stages of development of the foetal membranes and placenta are yet unknown. . From the researches of Turner, it is known that the placenta- tion is in general the same throughout the order, except for differences in the size and form of the villi, and in the structure of the decidua. On the other hand, the Primates are distin- guished from all other placental Mammals in that they do not form an allantoic placenta. Notwithstanding the variations in the degree of its development, in all the orders previously considered the allantois projected free into the extra-embryonic colom before it was united with the wall of the blastodermic vesicle. In the Primates and Tarsius the embryo is attached from the beginning to the wall of the blastocyst by the ‘ Bauch- stiel ”’ or ‘“‘ Haftstiel,” a mesodermal connecting-stalk first ob- served by His? in human embryos. The allantois appears very early as a recess of the posterior wall of the yolk-sac before the formation of the hind-gut. It never projects free into the colom, but is contained as a narrow tube in the “ Bauchstiel ”’ without reaching at any time the wall of the blastocyst (Fig. 120). The trophoblast is in this way vascularised directly, and a chorionic instead of an allantoic placenta is formed. For this reason Hubrecht has suggested that the term chorion should be restricted to the Primates. Minot ° strongly supported the views of His. He went even further, and stated that the placenta was also chorionic in Carnivora, Rodentia, Insectivora, and Cheirop- tera, but his views have not been generally accepted. Re- garding the modification in Primates, Hubrecht * says: “ Once 1 Gdhre, ‘“‘Dottersack und Placenta des Kalong (Pteropus edulis),”’ Studien iiber Entwicklungsgeschichte der Thiere, Selenka, vol. v., 1892. 2 His, Anatomie menschlicher Embryonen, 1. 3 Minot, Human Embryology, Boston, 1892. 4 See Robinson’s ‘‘ Hunterian Lectures,” Journ. of Anat. and Phys., vol. xxxviii., 1904. 464 THE PHYSIOLOGY OF REPRODUCTION the embryonic circulation has found the shortest route towards the trophoblast by way of the ‘ventral stalk,’ trophoblastic lacune, with their profusion of maternal blood, which have been there from the very earliest periods of development, are exquisitely situated for rendering this new adaptation highly advantageous. And while in the ancestral forms of the Primates both yolk-sac and allantois largely drew upon the trophoblastic source, these embryonic organs come to be dispensed with to a very great extent in their more highly developed descendants who come to use that trophoblastic source along a more direct, a shorter, and an earlier established route.” Fie, 120.—Median longitudinal section of an early human ovum, 0°4 mm. in length. (From Quain’s Anatomy, Longmans. ) e.ec., embryonic ectoderm ; ch., chorion; ec., ectoderm ; mes., mesoderm ; all,, allantois ; c.s., connecting stalk ; a4., amnion; y.s., yolk-sac. In old-world monkeys there is no decidua capsularis. The trophoblast thickens over two discoid areas on the blastocyst, and the thickenings form a primary placenta on the dorsal surface, and a smaller secondary placenta on the opposite aspect. Hence two groups of chorionic villi are developed. No unattached blastocyst has yet been obtained. In the youngest specimen of an old-world monkey, Semnopithecus. nasicus, the ovum was attached to the surface of the uterus by large villous processes with mesoblastic cores at the bases. The trophoblast consisted of two layers, the cytoblast, which was much thickened at the tips of the mesoblastic cores, and, externally to it, a syncytium which was blended at the apices with maternal decidua. Over the non-villous chorion, syncytium FG:TAL NUTRITION: THE PLACENTA 465 was absent (Selenka). Spaces, which are in direct com- munication with maternal capillaries, are present in the syncytium. The most notable characteristic in the decidua is the presence of a glandular secretion in the embryotrophe. In the non-placental area the glands are dilated and open into the uterine cavity, many of them close to the peripheral villi. Hence their secretion may reach the trophoblastic lacune. In the placental region they are also dilated, but their superficial parts are closed and appear to degenerate early. In the decidua le nests of epithelioid cells, the origin of which is uncertain. The new-world monkeys, like the old-world, have no de- cidua capsularis, and the placenta is formed as a single disc. In the anthropoid apes, on the other hand, the ovum is lodged in an implantation cavity, and so is covered by a reflexa. The whole circumference of the trophoblast thickens and develops villi, but later they disappear except over a discoid area, the decidua serotina. In the earlier stages two main groups of villi are present, as in the old-world monkeys, while the rest of the chorion is covered with smaller villi. In Selenka’s youngest specimen, the ovum was completely enclosed by decidual tissue, and there was no evidence to show whether the mode of embedding was excentric or interstitial. The surface of the ovum was separated from the decidua by a series of intercommunicating spaces, the intervillous spaces, which contained lymph. In other words, Selenka looks on the intervillous space in apes as a space lying between maternal and fcetal tissues, in which villi are suspended. Tn Man also the villi are at first diffuse, and later restricted to a discoid area, the placenta being again developed in the decidua serotina. The ovum probably reaches the uterus still enclosed in the zona pellucida, and lies free until the end of the first week, but this stage has never been observed. The uterine mucosa, as in other orders, is matured about the time of puberty (Bjérken- heim’), and then consists of embryonic connective tissue cells, ‘separated from the surface epithelium by a layer of flattened cells, The intercellular spaces are filled with lymph, and they 1 Bjorkenheim, ‘‘ Zur Kenntnis der Schleimhaut im Uterovaginalkanal des Weibes in den verschiedenen Altersperioden,” Anat. Hefte, H. cv., 1907. 2G 466 THE PHYSIOLOGY OF REPRODUCTION drain into lymphatic vessels in the outer half of the mucosa, where also the arterioles and venules lie. All the blood-vessels in the inner half are capillaries. In all probability the fertilised ovum, during its sojourn in the Fallopian tube and while it lies free in the uterine cavity, does not influence the structure of the mucosa, and may implant itself at any period during the cestrous cycle (Bryce and Teacher*). But under the abnormal conditions in a tubal pregnancy, the uterine mucosa undergoes a decidual change although no fertilised ovum is embedded in it. In all the early specimens the ovum was completely en- closed in the uterine mucosa, and the actual process of em- bedding has not yet been observed. John Hunter considered that the ovum reached the uterus from the Fallopian tube under the mucous membrane, and so had a decidua reflexa, while at a later stage the mucosa developed underneath it; hence the term decidua serotina. Sharpey supposed that the enclosure was effected by circumvallation, t.e. by a growth round the ovum of two folds of mucosal tissue, which fused and formed the decidua capsularis. But v. Spee® discovered a different mode of embedding in the guinea-pig, and later stated that it was the same in Man, viz. a destruction of the superficial epithelium, and the implantation of the ovum in the cellular substance of the mucous membrane. This view has received considerable support from the researches of v. Heukelom,* Peters,* Bryce and Teacher, and others. At the same time it must be borne in mind that His,° in describing an early human ovum in 1897, stated that the implantation cavity was lined with epithelium, and thus represented a part of the uterine lumen shut off by the growth of decidual folds. At the time of embedding, segmentation has probably 1 Bryce and Teacher, The Karly Imbedding and Development of the Human Ovum, Glasgow, 1908. 2 V. Spee, ‘‘Neue Beobachtungen iiber sehr friihe Entwicklungsstufen des menschlichen Hies,” Arch. f. Anat. u. Phys., anat. Abth., 1896. 3 V. Heukelom, ‘‘ Ueber die menschliche Placentation,” Arch. f. Anat. u. Phys., anat. Abth., 1898. * Peters, Ueber die Hinbettung des menschlichen Hies, Leipzig u. Wien, 1899. 5 His, ‘‘Die Umschliessung des menschlichen Frucht wiahrend der friihesten Zeit der Schwangerschaft,” Arch. f. Anat. u. Phys., anat. Abth., 1897. FETAL NUTRITION: THE PLACENTA 467 finished and the ovum is in the condition of the early blastocyst. Its epiblastic wall disintegrates the epithelium, the subjacent cells, and a few capillaries at the point of contact. Hence the blastocyst comes to lie in the connective tissue of the mucosa, which completely surrounds it, except at the point of entrance of the ovum. Here there is a gap in the tissue, the “ Gewebspilz,” filled up at first by a blood-clot which afterwards becomes fibrinous (Peters), and later by decidual tissue (Kollmann ?). In Peters’ ovum the gap was four-fifths of a millimetre in diameter, and in Bryce and Teacher’s a tenth of a millimetre. The size of the ovum when it becomes embedded is probably, according to the last-named authors, a fifth of a millimetre. When the hypoblast of the early blastocyst is differentiated, it does not apparently line the wall of the blastocyst, but forms a small vesicle. Very early, even before the appearance of the primitive streak, a marked proliferation of mesoblast occurs (Fig. 121). In the youngest ovum its cells filled the space between the wall of the blastocyst and the small amniotic and hypoblastic vesicles. In the ovum described by Leopold,’ it was already split by the “ Haftstiel ” into two parts, which enclosed the ccelom and were continuous with each other (Fig. 122). The outer wall of the blastocyst, the foetal ectoderm or trophoblast which anchors the ovum in the mucosa, is thickened all round its circumference, and even in the earliest specimen contained vacuoles into some of which maternal blood had penetrated. In this thick spongy layer Bryce and Teacher found no cell-outlines anywhere. Hence the transformation to syncytium is not due, as Peters supposed, to the contact with maternal blood. Under the syncytium is the cellular layer, corresponding to the cytoblast of Beneden. Its cells are in a state of active division, and they appear later to lose their outlines and merge into the syncytium. The growth of the latter from the mother-zone of cytoblast occurs, not as a solid mass, but in strands forming primitive syncytial villi (Fig. 123). Into the syncytium project outgrowths of the cytoblast, forming the cellular villi of Peters and Leopold. In the * Kollmann, ‘‘Die menschlichen Eier von 6 Millimeter Grodsse,” Arch. f. Anat. u. Phys., anat. Abth., 1879. 2 Leopold, ‘‘ Demonstration eines sehr jungen menschlichen Hies,” Arbetten aus d. Kénigl. Frauenklinik in Dresden, Leipzig, 1906. Nz. pl. cyt. pe. cyt, pl. Nz, 468 THE PHYSIOLOGY OF REPRODUCTION youngest ovum the formation of these buds was just commencing, and, according to Bryce and Teacher, they tended to grow out not so much into the strands of trophoblast as into the spaces ©: ° Sg 3B i. a A i) ‘| a o [ay B a i Po 3 a > fas. a N ta y i co) ~ i oe a , and embedded therein are th (From Bryce and Teacher's Early Development pl. -trophoblast , masses of vacuolating plasmodium pl. Fic. 121.—Diagram of the earliest human ovum hitherto described cyto-trophoblast ; pl., plasmodi nd; cap., capillary; pl’ cap. of the Human Ovum, Maclehose.) zone of decidua; gl., gla blastocyst is completely filled with mesoblast invading capillaries. embryonic and entodermic vesicles. p.e., point of entrance; cyt., between them. Later still, mesoblastic processes penetrate into the cellular buds and complete the vascular chorionic villi. Round the blastodermic vesicle is a zone of degenerated tissue, the “ Detrituszone”’ (Fig. 124). It is uncertain whether it is formed by the influence of the trophoblast or maternal elements. (09 ¥ IaUs0y ‘uornpUIINIg UnlUNF S.1a4sqaA wor) *(prodoeT 104j3e) Vxopol puv VUIZOIOS LAPIOIP 9} 07 TOLV[aI UT UMOYS ST UNAO agT “(Avp YIWEEqzy 94} Jnoge oq 0} pjodoery fq paaarjaq) AouvuSoad yo yred Aqrea oq} UT suIEqn ayy Jo [[VAX 9q} YSno1q, GoIo9g—'BZT “OI 469 Brvce and ( e likely maternal ”’ a aH Zz. S O a = a Baumm, ‘‘Gewichtsverinderungen der Schwangeren,”’ &c., Inaug.- Dissert., Miinchen, 1887. * Zacharjewsky, ‘‘ Ueber den Stickstoffwechsel waibrend der letzten Tage der Schwangerschaft,” &c., Zettschr. f. Biol., vol. xxx., 1894. a1 498 "CHE PHYSIOLOGY OF REPRODUCTION total metabolism by the alteration in weight. Thus Bar and Daunay ! discovered no increase of weight in a pregnant dog, though it had retained 5:24 grammes nitrogen, equal to 170 grammes flesh. Such a discrepancy may be easily ex- plained, for example, by a loss of water. In Man the physio- logical variation in the water-content’ is as much as 2 kilo. Hence it is necessary to obtain a more accurate measure, and for this purpose to investigate separately the metabolism of various substances, proteins, carbohydrates, fats, minerals, salts, and oxygen. The available data are as yet too meagre to demonstrate the good and the bad conditions of nutrition, but they indicate the paths along which future investigations may prove of value. C. The Protein Metabolism in Pregnancy a. The Absorption of Proteins by the Mother—According to Kehrer,? the gastric functions are slightly below normal in the human female during pregnancy. Free hydrochloric acid and pepsin are each decreased by a third. At the same time the intestinal functions appear to be sufficiently active for the satisfactory absorption of nutriment. The absorption of flesh does not show any characteristic change in the dog during pregnancy. If decreased, it is due to pathological conditions, and diarrhcea and vomiting are present (Bar and Daunay). Ver Heke? states that the absorption of nitrogen decreases in the second half of pregnancy in the rabbit, but he ascribes the change to mechanical conditions. Maurel 4 is of opinion that a gradual decrease in the nitrogen intake occurs throughout pregnancy in the guinea-pig, but at the beginning the intake is above the non-pregnant level. Zacharjewsky found that only 4 to 6 per cent. of the nitrogen was un- 1 Bar and Daunay, “Bilan des échanges azotés pendant la grossesse,” Journ, de Phys. et de Path., vol. vii., 1905. 2 Kehrer, Die physiologischen und pathologischen Beziehungen der weib- lichen Sexualorgane zum Tractus intestinalis, Berlin, 1905. 3 Ver Eeke, Lots des échanges nutritifs pendant la gestation, Bruxelles, 1901. * Maurel, ‘‘Des dépenses albuminoides pendant la grossesse chez le cobaye,” Comp. Rend. Soc. Biol,, vol. 1xi., 1907. CHANGES IN THE MATERNAL ORGANISM 499 absorbed by the human female in the last two weeks of pregnancy, and Slemons* found 7 per cent. and 3 per cent. in a primipara and a multipara respectively at the same period. b. The Daily Requirement of Protein for the Fetus.—The only measure we possess of the extra protein required in pregnancy is the amount deposited in the foetus and adnexa, the growing uterus, and mamme. But this gives too low a figure, since one gramme of tissue-protein requires more than one gramme of food-protein for its manufacture. In addition, though we are dealing with a period when anabolic processes are at a maximum in the new organism, we are bound to assume that the cardiac, hepatic, and other activities of the foetus, and the rhythmic con- tractions of the uterus entail a certain loss of protein from wear and tear. What these extra requirements amount to is un- known, or whether protein substances play any part in the provision of energy for the work of organisation.” The amount of nitrogenous material deposited in the human foetus during the last stages of pregnancy has been calculated. Michel ? estimates it at 56°69 grm. of nitrogen in two months, or slightly under 1 grm. per day. Magnus-Levy’s figures are some- what lower—50 grm. in the last hundred days, or 0:5 grm. per day. This represents only 3 grm. of protein, and when added to the daily deposition in the placenta, uterus, and mamme, it still remains inconsiderable. c. The Nitrogen Balance in Pregnancy.s—According to the earlier investigators, a special economy of protein exists during pregnancy. As Repreff® puts it, anabolic processes are in- 1 Slemons, ‘ Metabolism during Pregnancy, Labour, and Puerperium,”’ Johns Hopkins Hosp. Rep., vol. xii., 1904. 2 In so far as the work of organisation is carried out by the mammalian foetus and not by the mother, the energy is probably supplied by the com- bustion of carbohydrates alone (see p. 518). 5 Michel, ‘Sur la composition chimique de l’embryon et du feetus humain,” Comp, Rend, Soc. Biol., vol. li., 1899. 4 See also v. Noorden’s Metabolism and Practical Medicine, vol. i., Sect. IV. D., English Translation, 1907. 5 Repreff, ‘‘De l’influence de la gestation sur les échanges materiels,” Russ, Dissert., 1888, Quoted by Slemons, loc, cit, 500 THE PHYSIOLOGY OF REPRODUCTION creased and katabolic processes decreased in pregnancy in dogs, rabbits, and guinea-pigs. Hagemann’s! investigations in the dog form the first ac- curate observations of the nitrogen balance during the whole course of pregnancy. He set himself to solve the question whether the new organism was formed from the food, or at the expense of the maternal tissues. From the first experiment he concluded that, even on a diet rich in nitrogen, there was a loss of protein to the mother at the end of pregnancy. While 33:583 grm. nitrogen were retained, the young contained at birth 7-445 grm. This left a balance of 26128 grm. for the extra needs of the mother, which, he says, was nearly all required for the formation of the foetuses (calculated at 16:6 grm.) and placente (8°7 grm.). The additional nitrogen required for the growth of the uterus and mammez must have been derived from the maternal tissues. Hence the pregnancy resulted in a loss to the mother. Similarly in lactation 34-056 grm. nitrogen were retained, and the calculated excretion in the milk was 76 grm.—a loss of 41-944 grm. nitrogen. It is doubtful if such a conclusion is warranted, but the figures have been given in some detail to illustrate some of the difficulties to be overcome in carrying out the investigation. Many troubles have been experienced in trying to keep the animals on a constant diet, and, in addition, the increasing size of the uterus may prove a mechanical difficulty and impede the intestinal activity (Ver Eeke *). Hagemann failed to obtain the shed placentee, which were eaten by the mother animal. Hence the estimate of 8-7 grm. nitrogen lost by them during pregnancy and labour is arbitrary, and is, according to Bar and Daunay,* much too high. On these and other grounds—there is a period of thirteen days during the pregnancy for which no data are given—the calculations for pregnancy considered as a unit are open to objection. 1 Hagemann, ‘‘ Ueber Eiweissumsatz wahrend der Schwangerschaft und Laktation,” Arch, f. Anat. u. Phys., phys. Abth., 1890; also Inaug. Diss., Erlangen, 1891. 2 Ver Eeke, Lots des échanges nutritifs pendant la gestation, Bruxelles, 1901. * Bar and Daunay, ‘‘ Bilan des échanges azotés pendant la grossesse,” Journ, de Phys. et de Path., vol. vii., 1905. CHANGES IN THE MATERNAL ORGANISM 501 On one point the results are of value. Hagemann states that the period of gestation may be divided into two parts. In the first, which lasts in his experiment for the first month of pregnancy, there is a continuous loss of nitrogen to the mother each day. In the second, there is a storage of nitrogen which is used in the growth of the product of conception. In Ver Eeke’s experiments, nineteen in all, in the rabbit, two phases were also frequently observed, but the results varied widely. In some there was a positive balance throughout, and in others a negative balance now at one time and now at another. In the greater number the same diet was administered before and after pregnancy and during its whole course. The amount of protein did not far exceed the minimal requirement for the maintenance of nitrogenous equilibrium. Similarly variable results were obtained by Jagerroos} in the dog.? In his Experiment IT., in which the nitrogen content of the food was high and the diet was pure flesh, there was a positive balance each week except the second, 27°9 grm. nitrogen in all being retained during pregnancy. In Experiment III., also on a diet of flesh but containing only 5-97 grm. nitrogen per day, a negative balance occurred only in the fifth and sixth weeks ; but when the weight of the foetuses and adnexa, and a serious loss of nitrogen soon after labour were deducted, there was a final loss to the mother of more than 6 grm. of protein. In the last experiment the diet consisted of 60 grm. of flesh and 100 grm. of sugar, which was just sufficient to maintain nitrogenous equilibrium.’ It was maintained for the first few days of pregnancy, and then a loss of nitrogen occurred each week throughout the whole course of gestation except the third. In summing up the result of the three investigations, we must still leave it undecided whether an increased katabolism of pro- tein is characteristic of pregnancy as a whole, or is entirely de- pendent on the diet. Hagemann’s dictum that gestation entails a sacrifice of protein on the part of the maternal organism is 1 Jagerroos, ‘“ Der Eiweiss-, Phosphor-, und Salzumsatz wahrend der Gravi- ditat,” Arch. f. Gynék., vol. Ixvii., 1903. * Jagerroos and Ver Eeke failed to secure the shed placente. 3 Calculated over two days only. 502 THE PHYSIOLOGY OF REPRODUCTION still unproven. Such is undoubtedly the case on a minimal protein diet ; but, with a greater allowance of nitrogen, the con- clusions of Hagemann and the others are not borne out by the more recent researches of Bar and Daunay. They fed three pregnant bitches on a constant diet of bread, water, fat, beef, and salt, and estimated the nitrogen of the urine and feces at regular intervals. They took precautions to secure the young and the after-births, and were able to determine accurately their nitrogenous content. In the three animals, as in two observed by Jagerroos, the period of gestation was triphasic. There were first a period of retention of nitrogen, then a balance or very slight loss, and finally a retention increasing with the progress of gestation. Further, there was over all a gain of nitrogen in two dogs at the conclusion of labour. Hence they conclude that pregnancy in a healthy animal, with a rational and sufficient diet, does not necessitate a drain on her stock of nitrogen to satisfy the needs of the foetus. Jagerroos showed that, on a minimal protein diet, the nitrogenous equilibrium was disturbed by the onset of pregnancy. The loss of nitrogen began during the first week after conception, when the fertilised ova were still in the oviduct or had just reached the uterine cavity. At this stage the daily fixation of nitrogenous substances in the young blastocyst is too small in amount to affect per se the nitrogenous equilibrium. At the same time there is an appreciable daily loss of nitrogen which must be derived from the maternal tissues. It is permissible to assume a relationship between the two facts, and argue that the presence of the young blastocyst leads in some way to an increased katabolism of protein.1 The daily loss of tissue is maintained for a longer or shorter period during pregnancy, according as the nitrogenous content of the diet is near the minimum or more abundant. But, even on a comparatively tich protein diet, it is generally accepted by the investigators that a negative balance occurs for a considerable period, that it then disappears, and is replaced by a positive balance lasting 1 It must, however, be kept in mind that the corpus luteum is undergoing active changes at this period. As already stated, it is not known whether the ovum or the corpus luteum provides the stimulus for the changes referred to, or whether both of these are concerned (see p. 504). CHANGES IN THE MATERNAL ORGANISM 503 till the end of pregnancy.’ In other words, during the period in which the needs of the embryo are small the amount of protein katabolised is not counterbalanced by the food protein, and the maternal tissues suffer loss ; in the later period, although the daily amount of nitrogen fixed by the new organism is con- siderably greater, the excreted nitrogen is more than counter- balanced by the food nitrogen, and the maternal tissues gain, or at least do not lose to such an extent as formerly. In the human female, in whom investigations have been conducted only in the last few weeks of pregnancy, a retention of nitrogen has been invariably found. According to Zacharjewsky,? it amounted to a gain of 0873 grm. per diem in primipare and 5°05 grm. in multipare. On a diet usually containing less than 20 grm. nitrogen per day, Bar and Daunay observed an average retention of 6°54 grm. in three primipare for eleven days in the last month of pregnancy, a figure far exceeding that ob- tained in the same women on the same diet a considerable time after pregnancy.? What is the reason for the increased katabolism of nitrogenous substances during the earlier stages of pregnancy? Hagemann says: “In the transformation of maternal proteins into the proteins of the growing uterus, embryos, and mammary glands, some of the nitrogen-containing complexes of the molecules lose their specific character, cannot be built up in the new protein molecule, and are excreted in the urine.” Ver Eeke suggests that the loss of maternal blood may hasten protein katabolism, and its reconstitution entail a sacrifice of nitrogenous substances on the part of the mother. But it is not enough to say that the loss of nitrogen is due to the inability of the cells to build up protein synthetically, since no loss occurs on a sufficient diet in the later stages of pregnancy, although the synthesis of new tissue then reaches a maximum. Ver Heke also states that the greater katabolism in proportion to weight in growing than in 1 Recently corroborated in the dog by Murlin (‘‘ Protein Metabolism in Development,” Amer. Journ. of Phys., vol. xxiii., 1908-9). * Zacharjewsky, ‘‘Ueber den Stickstoffwechsel wahrend der letzten Tage der Schwangerschaft,” Zettschr. f. Biol., vol. xxx., 1894. * During the puerperium, the low diet administered to women entails a loss of nitrogen to the maternal organism. Very variable times have been noted in different cases before nitrogenous equilibrium was restored. 504 THE PHYSIOLOGY OF REPRODUCTION grown animals may result in a negative nitrogen balance. But in every other instance growth is associated, not with a loss, but with a retention of nitrogen. The conditions are too com- plex to admit of such a simple explanation. With the onset of pregnancy certain parts of a grown organism —uterus, mamme, &c.—are suddenly stimulated to growth. At the same time a new organism is to undergo development. Concurrently with these phenomena of grow: h, a negative nitrogen balance occurs in the first half of pregnancy; that is to say, pregnancy produces a change in the protein metabolism. In the second half of pregnancy, growth is associated with a re- tention of nitrogen by the mother. In other words, the con- ditions which come into existence at the b- ginning of gestation, and lead to a negative nitrogen balance, alter during its course. That growth proceeds along with a loss of nitrogen is note- worthy. Jt is at variance with the conditions found in all other instances of physiological growth, with which, however, the growth of certain organs in pregnancy cannot be compared, since it alone occurs in a grown mammal. It is conceivable that this phenomenon in itself is sufficient to disturb the protein metabolism. As was previously mentioned, it is not known whether the stimulus for the changes during pregnancy is derived from the fertilised ovum itself, the corpus luteum, or some other less obvious factor. It has been experimentally proved that the corpus luteum is essential in the early, but not in the later stages.’ Its development dates from the period of conception, and its activity lasts until the middle of pregnancy, after which it undergoes structural and functional degeneration. Hence the period of its activity corresponds with the period of the negative nitrogen balance in the mother. Hagemann’s observa- tion of a similar nitrogen balance at a certain phase of the cestrous cycle when corpora lutea are also developed, though no ovum is fertilised, would seem to favour the view that the loss of nitrogen is in some way connected with the changes in the ovary. Like the corpus luteum, the trophoblast undergoes a marked change during pregnancy. In the early stages it forms the special organ of nutrition for the embryo, and in addition to ! Marshall and Jolly, loc. cit. (see pp. 336-345, 351, and 491). CHANGES IN THE MATERNAL ORGANISM = 505 absorbing nutriment it probably elaborates it into a form suit- able for its incorporation in the new tissues. It is to this activity that we may have to lo.k for an explanation of the negative nitrogen balance at the beginning of pregnancy. In the later stages the ectodermal covering of the villi loses its vitality, and seems to act more as a semi-permeable membrane (see p. 488). The cells of the new. organism are now more fully differentiated, and are capable of carrying on their own metabolic functions. d. The Nitrogen Excretion during Preqnancy.—The total nitrogen excreted during the later stages of pregnancy is decreased in amount. It again rises distinctly in the puerperium (Boni,’ Slemons*). The urea nitrogen was stated to be normal in amount by v. Winckel? and Zacharjewsky, but more recent observations prove that it is diminished in proportion to the total nitrogen. According to Matthews,‘ it may fall below 13 grm. per day without any signs of insufficiency.» The ammonia nitrogen, which is of interest in connection with the question of acidosis in pregnancy, is relatively increased, but at present no proof is forthcoming that it is absolutely higher than in the non-pregnant state. The relative increase is due to the decrease in the total nitrogen (Slemons, Matthews). In eclampsia, Zweifel ® has frequently observed an increase of the ammonia nitrogen to 10 per cent. or more of the total, and, associated with it, the presence of an organic acid in the urine. The acidosis, at least in a certain number of the cases, is the result of the eclamptic seizures. Further investigations of the conditions when no fits have occurred are necessary before any constant association of an acidosis with the disease can be affirmed. The uric acid excretion is within physiological limits. The ? Boni, ‘1 corpi purinici nelle urine delle gravide e delle puerpere,”’ Ann. di Ost. e Gin., 1906. ® Slemons, ‘‘ Metabolism during Pregnancy,” &c., Johns Hopkins Hosp. Rep., vol. xii., 1904. 3 V. Winckel, Studien uber den Stoffwechsel, &c., Rostock, 1865. ‘ Matthews, “‘ The Urine in Normal Pregnancy,” Amer. Journ. Med. Sc., vol. cxxxi., 1906. 5 There are, however, wide physiological variations according to the N-content of the diet. 5 Zweifel, ‘‘ Die Eklampsie,”’ Arch. f. Gyndk., vol. lxxii., 1904. 506 THE PHYSIOLOGY OF REPRODUCTION figures given by Zacharjewsky are 0-603 grm. per day in primi- pare, and 0-531 grm. in multipare. Boni states that it is almost normal in amount, but his figures are considerably lower than the average given by Magnus-Levy for a mixed diet.1 Boni observed a diminution in the purine bases which varied between 4-7 and 6'8 per cent.” V. Leersum ? states that in 40 per cent. of pregnant women on the usual hospital diet, the amino-acid nitrogen amounts to over 10 per cent. of the total nitrogen, whereas it varies between 2-7 and 7-7 per cent. in the non-pregnant. The maximum is usually reached before birth, and there is a decrease later. Sometimes the maximum does not occur till after birth, but the acids may then be derived from the involution of the uterus. The results, according to this investigator, argue for a dis- turbance of the liver even in apparently normal pregnancies, its power of splitting off ammonia from and oxidising the amino- acids being impaired.* The albuminuria of pregnancy in the human female is not strictly physiological. Regarding its frequency very varying figures have been given, ranging from 5 per cent. to 60 per cent. It appears in the second half of pregnancy, gradually increases up to the time of birth, and quickly decreases in the puerperium. In 50 per cent. of the cases it has already disappeared on the fourth day after labour. The protein is of renal origin, and in a typical case amounts to 0°01 to 0-05 per cent. That it is not due to mechanical pressure on the renal vessels or ureter, or to increased intra-abdominal pressure, seems certain. Nor has any definite proof been given of the influence of a toxin arising in the foetus, and causing degeneration of the renal epithelium. Veit ® 1 As uric acid is derived in part from the nucleins of the food, no conclusions can be drawn from its estimation on an unknown diet. 2 The average value is 8 per cent. on a mixed diet. * Vv. Leersum, “ Die Ausscheidung von Aminosduren wahrend der Schwang- erschaft,” Biochem. Zettschr., 1908; Fest. f. Hamburger. 4 It has not yet been proved that the liver is the only organ which possesses this function. The placenta itself is stated to contain a desamidase (Savaré, ‘“‘ Zur Kenntnis der Fermente der Placenta,” Hofmeister’s Beittr., vol. ix., 1907; see also p. 482), hence the increase in amino-acid nitrogen may be due to a disturbance of placental function. 5 Veit, ‘‘Ueber Albuminurie in der Schwangerschaft,” Berlin. klin. Woch., 1902. CHANGES IN THE MATERNAL ORGANISM 507 explains it by his hypothesis of the presence of placental con- stituents in the maternal circulation. Metabolic investigations in pregnancy complicated by albuminuria show nothing charac- teristic (Magnus-Levy '). A special constituent of the urine may be found during the puerperium. Though called peptone (Fischel?), it really con- sists of deutero-albumuses which arise from the involution, ae. autolysis, of the uterus (Langstein and Neubauer 3). As with similar proteins introduced subcutaneously, the organism has not the power of splitting them up, and they are excreted un- changed. Fischel stated that peptonuria might also occur in pregnancy; but this was disproved by Thomson,* who also showed that a puerperal peptonuria did not regularly exist. Ehrstrém * regards it as a certain indication of fever and sepsis, the peptone being contained in the leucocytes of the purulent lochia. As a result of the involution of the uterus, creatin may also appear in the urine. Murlin ® kept a dog on a creatin-free diet during the last week of pregnancy. The creatinin output was constant, but creatin appeared two days before parturition. It reached a maximum five days after labour—the period when the involution processes reach their height. D. The Carbohydrate Metabolism in Pregnancy a. The Absorption of Carbohydrates by the Mother.—The starch digestion is said to be retarded in the stomach during pregnancy (Kehrer”). Little is known regarding the absorp- tion of carbohydrates, but there is evidence of a tendency to 1 Magnus-Levy, see v. Noorden, loc. cit. 2 Fischel, ‘‘ Peptongehalt der Lochien,” Arch. f. Gynak., vols. xxiv. and xxvi. 3 Langstein and Neubauer, “ Autolyse des puerperalen Uterus,” Miinch. med. Woch., 1902. 4 Thomson (H.), ‘‘ Ueber Peptonurie in der Schwangerschaft und im Wochenbett,”’ Deutsche med. Woch., 1889. 5 Ehrstrém, ‘“ Puerperale Peptonurie,” Arch. f. Gyndk., vol. Ixiii., 1901. § Murlin, “ Protein Metabolism in Development,” Amer. Journ. of Phys., vol. xxiii., 1908-9. 7 Kehrer, Die. physiologischen und pathologischen Beziehungen der Weiblichen Sexualorgane zum Tractus Intestinalis, Berlin, 1905. 508 THE PHYSIOLOGY OF REPRODUCTION abortion in certain animals on a diet containing them in excess (see p. 495). b. Carbohydrates of the Maternal Organism.—Lactose may appear in the blood in pregnancy as well as during the lactation period. Levulose is not present in the serum of a healthy animal; but it is normally present in the allantoic fluid of the cow (Giirber and Griinbaum *), and in the blood-serum of the foetal rabbit, cow, and sheep (Paton 2). Whether it is the only monosaccharide present has not yet been determined, but it is in sufficient amount to render the serum levo-rotatory. The glycogen store of the liver is stated to be increased in pregnancy in the dog (Burlando 3), in the guinea-pig (Maurel *), and in the human female (Charrin and Guillemont*). There is no increase in the rabbit. The placenta contains glycogen in varying amounts. It is found only in traces in Ruminants, but in great amount in Rodents (see Chap. X., p. 431). It occurs also at the margin of the zonary placenta in Carnivores, and in the human placenta. In many species it has not yet been investi- gated. In the foetus, the feature of the glycogen is not its high percentage, but its almost universal distribution in the de- veloping tissues.® It has been shown by Bohr that the energy in the mammalian foetus is supplied by the combustion of carbohydrates (see p. 518), and by the wide distribution of 1 Girber and Griinbaum, ‘‘ Ueber das Vorkommen von Livulose im Fruchtwasser,” Minch. med. Woch., 1904. 2 Paton, Watson (B. P.), and Kerr, “On the Source of the Amniotic and Allantoic Fluids in Mammals,” Trans. Roy. Soc. Edin., vol. xlvi., 1907. The proof that the carbohydrate is levulose rests on the levo-rotation of the plane of polarised light and the ketone reaction. Doubts have recently been expressed regarding the sufficiency of these two tests. 3 Burlando, ‘‘ Behaviour of Hepatic Glycogen during Menstruation, Pregnancy, Puerperium, and Lactation Period,” Arch. Ital. di Ginec., 1906. 4 Maurel, ‘Des dépenses albuminvides pendant la grossesse chez le cobaye,” Comp. Rend. Soc. Biol., vol. 1xi., 1907. 5 Charrin and Guillemont, ‘‘ Physiologie pathologique de la Grossesse,”’ Comp. Rend. Soc. de Biol., 1899. 8 Gierke, ‘‘ Glycogen in der Morphologie des Zellstoffwechsels,’’ Habili- tationsschrift, Freiburg, 1905. See also Lochhead and Cramer (‘‘The Glycogenic Changes in the Placenta and the Foetus of the Pregnant Rabbit,” Proc. Roy. Soc., London, Ser. B., vol. Ixxx., 1908), from whose memoir the Table is copied. CHANGES IN THE MATERNAL ORGANISM 509 glycogen an available supply is procured in every part of the foetal body in which the work of organisation is proceeding. c. The Daily Requirement of Carbohydrate for the Fetus.— Some idea can be obtained of the daily requirements of glycogen for the foetus of the rabbit in the second half of pregnancy. The appended table gives the amount of glycogen contained in the unborn young from the eighteenth day of gestation till the day before parturition :— Average Weight | Average Amount Num Gestation, | ofeach Fetus |" of Glycogen | “Pgtnses, | -Giyeogen. 18 0:89 0018 8 0144 20 2°32 “0050 6 0300 21 3°28 0080 5 0400 22 4:13 0103 4 0412 23 7-20 0203 8 1624 24 9°75 *0346 6 2076 25 20°23 ‘0808 v “5656 26 11°24 ‘0257 5 "1285 27 32°84 1418 3 “4254 28 32:07 2017 6 1:2102 29 26°67 1199 9 1:0791 Taste to show the fcetal * weight and amount of fcetal glycogen in the second half of pregnancy (rabbit). In the animal killed at the twenty-sixth day, the pregnancy was abnormal, one foetus being dead and the others badly developed. In the last also the foetuses were unusually small. The table shows that 1:2 grm. of glycogen are deposited between the eighteenth and the twenty-eighth day, or about 0:2 grm. per foetus. Hence the average daily deposition is 0-02 grm. per foetus. In the later stages the rate of deposition increases out of proportion. This is due to the assumption of its glycogenic function by the foetal liver. The amount of carbohydrate oxidised each day can be calculated from Bohr’s figures. The oxygen consumption for a foetus weighing 30 grm. is 0-14 c.cm. per minute. This is sufficient to oxidise 0-00017 grm. of sugar, or 0-245 grm. per day, which is equal to 0:227 grm. of glycogen. Hence for six foetuses, the average number, 1:362 grm. are required for combustion each day. Jn addition, an average of 0°3 grm. of glycogen is deposited 510 THE PHYSIOLOGY OF REPRODUCTION in them daily near the end of pregnancy. Hence the total daily requirement for the unborn young at this stage is 1-662 grm. of glycogen. A small additional amount of carbohydrate is re- quired for the daily increasing blood-serum, for the liquor amnii in the rabbit, and for the manufacture of mucin and other glycoproteins. d. Excretion of Carbohydrates in Pregnancy : Glycosuria and Lactosuria. Blot? was the first to postulate the occurrence of a “physiological glycosuria” in pregnancy. Kirsten * found sugar in the urine in the majority of cases of pregnancy and labour, and regularly in the puerperium. Hofmeister * first discussed the relationship of the glycosuria to milk secre- tion, and proved that the sugar excreted in the puerperium was lactose.* The sugar is in extremely small amounts, but above the normal. Lemaire *® found 0-003 to 0:009 per cent., and Brocard * an upper limit of 0-01 per cent. Zacharjewsky,’ however, observed no increase in the reducing power of the urine on an ordinary diet during the last weeks of pregnancy. The first definite increase comes with the appearance of lactose in the urine after birth, though it may also be excreted a few days before birth. It is more evident when the milk is not utilised and becomes re-absorbed, but it rarely exceeds 0:3 per cent.® Extirpation of the mammary glands immediately stops the lactosuria,’ and, if carried out in pregnancy, prevents it. 1 Blot, ‘De la glycosurie physiologique chez les femmes en couches,” &c., Comp. Rend. Soc. Biol,, vol. xliii., 1856. 2 Kirsten, ‘° Ueber das Vorkommen von Zucker im Harn der Schwangeren,”’ Monatsschr. f. Geburtsh. u. Frauenkrankh., vol. ix., 1857. 3 Hofmeister, ‘‘ Ueber Laktosurie,” Zettschr. f. phys. Chem., vol. i., 1877. * Corroborated by Kaltenbach (‘‘ Die Laktosurie der Wdochnerinnen,” Zettschr. f. Geburtsh. u, Gyndk., vol. iv.) and many others, 5 Lemaire, ‘‘ Ueber das Vorkommen von Milchzucker,” Zeitschr. f. phys. Chem., vol. xxi., 1895. § Brocard, ‘‘ La Glycosurie de la Grossesse,”’ Thése de Paris, 1898. 7 Zacharjewsky, loc. cit., Zeitschr, f. Biol., vol. xxx., 1894. 8 The inability of the organism to oxidise lactose was demonstrated by Voit (‘‘ Verhalten der Zuckerarten im menschlichen Organismus,” Deut, Arch. f. klin. Med., vol. lviii., 1897). ® Sinéty, ‘‘ Urine of Guinea-Pigs in Puerperium,”’ Comp. Rend. Soc, Biol., vol. 1. 10 V. Noorden, loc. cit., vol. i. (see also pp. 571-573). CHANGES IN THE MATERNAL ORGANISM 511 The glycosuria of pregnancy has been ascribed to a diminished glycolysis (Brocard), and to hepatic inadequacy (Cristalli +), without sufficient evidence. The greater tendency to ali- mentary glycosuria in pregnancy was upheld by Lanz.? He frequently observed it after the administration of 100 grm. of glucose. On the other hand, Payer’s* careful experiments showed an assimilation limit of 130 grm. of glucose, which is not subnormal, the excess being very rapidly excreted. Hence. it must be left unsettled whether a more ready saturation of the maternal organism may be brought about in pregnancy, and whether this is related to an increased storage of carbohydrate at this time. E. The Metabolism of Fats in Pregnancy a. The Absorption of Fats by the Mother.—The absorption of fats from the intestine is increased during pregnancy (Ferroni *), the neutral fats, fatty acids, cholesterin, and soaps contained in the feces being all decreased towards the end of the gestation period. This is the time when the subcutaneous tissues of the foetus receive an abundant supply. They rapidly reach the normal level in the puerperium. There is a corre- sponding increase of fat in the maternal blood in the dog and guinea-pig, and the excess disappears after parturition (Capaldi °). b. Fat of the Maternal Organism.—According to Miotti,® the liver cells contain a continuously increasing amount of fat, first in the central parts of the lobule and later throughout. He looks on it as a fatty infiltration, and concludes that an increased fat formation takes place during pregnancy. 1 Cristalli, Ricerche sulla presenza dello zuchero nelle orine delle donne gravide e puerpere, Naples, 1900. ? Lanz, “ Ueber alimentiire Glykosurie bei Graviden,” Wien. med. Presse, 1895. ° Payer, “ Einfluss des Zuckers auf den Stoffwechsel der Schwangeren,” Monatsschr. f. Geburtsh, u. Gyndk., vol. x 4 ¥Ferroni, ‘I grassi neutri . . . delle gravide e delle puerpere sane,” Ann. di Ost. e Ginec., 1905. 5 Capaldi, ‘‘Sul contenuto di grasso del sangue nella gravidanza e nel puerperio,” Ann, di Ost. e Ginec., 1905. ° Miotti, ‘‘Contributo allo studio istologico de fegato durante la gravi- danza,” Ann, di Ost. e Ginec., 1900. 512 THE PHYSIOLOGY OF REPRODUCTION In the placenta there is evidence of a transmission of fat to the product of conception. Even in the early stages of preg- nancy the cells of the uterine mucosa are infiltrated with fat, and the trophoblast is pervaded with fat globules. In Ungu- lates a large amount of fat is contained in the uterine milk (see p. 403). In those mammalian orders, in which the tropho- blast is directly bathed by maternal blood, the fat dissolved in it forms a second available supply. There is no reason to doubt an active transference of fat from the mother, or to assume that a transformation from carbohydrates or proteins is necessary. c. The Daily Requirement of Fat for the Fotus—The daily requirement of fat varies very considerably during pregnancy, and especially towards the end, when the subcutaneous fat of the foetus is deposited. Fehling? found 0°5 per cent. of fat in the human foetus at the fourth month, over 4 per cent. at the eighth, and 9 per cent. at the ninth month. d. Origin of the Fetal Fat.—As to its origin, Thiemich 2 states that it is not derived from the alimentary fat of the mother, since after feeding a dog in two successive pregnancies on widely different fats, palmin and linseed oil, he could determine no difference in the constitution of the foetal fat. Oshima * comes to the same conclusion from his investigations on the number of ultra-microscopic particles in the blood of cats, rabbits, and guinea-pigs. He states that the number is dependent on the stage of development, and independent of the condition of the mother’s blood—for example, when a great increase is produced by rich fat-feeding. Capaldi, on the other hand, states that the percentage of fat is the same in the maternal and foetal blood, at least at the end of pregnancy. Some feeding experiments carried out by Hofbauer* agree with this. He administered coco-nut oil® to three pregnant guinea-pigs, and demon- 1 Fehling, “‘Beitrige zur Physiologie des placentaren Stoffverkehrs,” Arch. f. Gynik., vol. xi., 1877. 2 Thiemich, ‘‘ Ueber die Herkunft des f6talen Fettes, Centralbl. f. Phys., vol, xii., 1898. ® Oshima, ‘‘Ueber das Vorkommen von ultra-mikroscopischen Teilchen im fétalen Blute,” Cenétralbl. f. Phys., vol. xxi., 1907. 4 Hofbauer, Biologie der menschlichen Plazenta, Wien and Leipzig, 1905. 5 It consists essentially of the triglycerides of laurinic and myristinic acids with a very small quantity of tripalmitin. CHANGES IN THE MATERNAL ORGANISM 513 strated laurinic acid in considerable amount in the foetuses. Hence the fat of the food, or at least one of its fatty acids, had been transmitted across the placenta. But any conclusions based on the introduction of a foreign fat must be guarded. In the foetus, fat is present in many of the tissues in a state of fine division. Its wide-spread distribution and its amount, probably equal at least to that of glycogen, are a characteristic of foetal life; but its significance is not obvious if, as Bohr states, it is not a source of energy. Guillot } showed that it did become a source of energy immediately after birth. He found 12 per cent. of fat in the lungs of foetuses dying during labour, and only 6 per cent. after several hours’ respiration. Fat may have anabolic functions to perform in the building up of the foetal body, e.g. in the synthesis of lecithin. e. The Excretion of Fat Derivatives in Pregnancy.—The primary product is oxybutyric acid. This, by oxidation, is transformed to aceto-acetic acid, which in turn gives rise to acetone by the loss of carbon dioxide from the molecule. Little is known regarding the excretion of aceto-acetic acid and oxy- butyric acid in apparently normal pregnancies, though in patho- logical cases of persistent vomiting, with a high degree of inanition, the latter may often appear (Kraus ”). This is to be expected. In general, if the amount of oxybutyric acid is small, acetone alone appears in the urine; if in greater amount diacetic acid may also be present, and, if greater still, all three may be excreted.? That acetonuria exists in pregnancy is certain, but in the majority of cases it does not pass the physiological limit (Stolz *). If it is in greater abundance, some special factor must be at work. It is not enough to say that its presence is always due to the exclusion of carbohydrates in varying degrees from the metabolism,* leading to a lowered oxidation of fats by the ? Guillot, quoted in Richet’s Dictionnaire de Physiologie, Article “ Foetus.” * Kraus, quoted in v. Winckel’s Handbuch der Geburtshilfe, vol. i., H. 1. 3 See v. Noorden, loc. cit., vol. i. 4 Stolz, ‘‘Die Acetonurie in der Schwangerschaft,’’ Arch. f. Gyndk., vol. lxv. 5 Wolfe (“The Chemistry of Toxemias in Pregnancy,” New York Med. Journ., 1906) states that there is no connection between acetone compounds in the urine and the essential features of hyperemesis gravidarum, a condi- tion in which there is pre-eminently a deficient absorption of carbohydrates. 2K 514 THE PHYSIOLOGY OF REPRODUCTION cells of the body. When no change is made in the ordinary diet, when no signs of dyspepsia are present and no glycosuria exists, we are not justified in assuming a withdrawal of carbohy- drates from the metabolism. Rather is it related to the aceton- uria arising after chloroform and ether narcosis (Beesly)* or in febrile conditions—that is, it is toxic in origin. It has, however, still to be discovered whether the acetonuria of pregnancy is associated, as the acetonuria of narcosis ? and of fever (Regnard * and Geppert *), with a diminished alkalinity of the blood. F. The Metabolism of Metals and Salts in Pregnancy Little is known regarding the metabolism of the individual metals and salts. The fixation of mineral elements is slight at the beginning, but becomes active towards’ the end of pregnancy. From first to last, about a hundred grammes are transferred from the mother to the human foetus. With a few exceptions, the mineral salts are approximately in the same proportion throughout pregnancy. The exceptions are sodium, potassium, and calcium, of which sodium decreases and calcium increases with the replacement of cartilage by bone, and potassium increases with the increased manufacture of red blood corpuscles (Hugouneng °). a. Iron.—Part at least of the iron for the foetus is derived from the hemoglobin of the maternal organism. In the poly-cotyledonary placenta of Ruminants and the zonary placenta of Carnivores, the disintegration of red blood corpuscles has been demonstrated. There .is less certainty regarding the actual ingestion of the red cells by the syncytium of the discoid placenta, 1 Beesly, ‘‘ Post-Anzsthetic Acetonuria,” Brit. Med. Journ., 1906. 2 Beesly and Milne, unpublished paper. 3 Regnard, Combustions respiratoires, 1879. 4 Geppert, ‘‘ Die Gase des arteriellen Blutes im Fieber,’’ Zeitschr, f. klin. Med., vol. ii. 5 Hugounenq, ‘‘Recherches sur la statique des éléments minéraux et particuligrement du fer chez le foetus humain,” Comp. Rend. Soc, Biol., llth series, vol. i. 1889. * It is doubtful whether haemoglobin is an ‘ organised ” protein, hence its disintegration does not, as might be supposed, afford proof of the trans- mission of maternal tissue protein to the foetus. CHANGES IN THE MATERNAL ORGANISM 515 though it has been described by Peters in an early human ovum. But in all placenta yet investigated, iron-containing granules have been observed in the trophoblast. The possible sources are hemoglobin, which is in part absorbed as such by the tropho- blast in Man (Bonnet 2), nucleoprotein, and the reserve iron of the mother. Nuclein is the only iron-containing constituent of yolk of egg, and must serve for the manufacture of hemoglobin in the developing chick. It is also known that in the adult organism nucleoprotein is a better source of iron for hemoglobin than any inorganic or other organic compound hitherto ad- ministered by the mouth.* Hence it is not difficult to conceive that the same process may occur in the foetus. But whether it is the food nucleoproteins or the organised nuclein bodies of the maternal organism that are utilised, is unknown.* With regard to the reserve iron of the mother, it is stated by Charrin * that the store in the spleen is reduced during pregnancy. In the foetus iron is required for the synthesis of hemoglobin (see p. 480) and nucleoproteins.* Large amounts of iron are also stored in the liver and other organs. According to Bunge’s” law, this forms a reserve which is drawn on after birth to make up for the deficiency-of the iron in the milk. Thus the liver of a rabbit contains 18 mg. of iron per 100 grm. body-weight at birth, and only 3-2 mg. twenty-four days later. According to Veit and Scholten,® the villi can dissolve intact red cells of the circulating blood, just as the solution of erythro- 1 See Chap. X., p. 479. 2 See Chap. X., p. 480. 3 V. Noorden, loc. cit., vol. i., p. 78. 4 As the purine bases of the urine are stated to be decreased in pregnancy (see p. 506), the maternal nucleins are probably not a source of iron for the foetus to any appreciable extent. 5 Charrin, ‘‘ Physiologie pathologique de la grossesse,” Comp, Rend. Soc. de Biol., 1899. 8 The nucleoproteins of the foetal placenta in the sheep differ in their chemical constitution from those of the maternal placenta. They are probably synthesised in the ovum from lower complexes, in the same way as the nucleoproteins of the chick embryo are built up though the egg contains no purine bases. 7 Bunge, ‘‘ Weitere Untersuchungen iiber die Aufnahme des Hisens in den Organismus des Siuglings,” Zeitschr. f. phys. Chem., vols. xvi. and xvii., 1892-3. : 8 Veit and Scholten, ‘‘ Synzytiolyse and Haemolyse,” Zettschr. f. Geburtsh. u. Gyndk., vol. xlix. 516 THE PHYSIOLOGY OF REPRODUCTION cytes can be produced by placental extracts. As a result of this, hemoglobinemia may occur in pregnancy. Wychgel?* observed it in eight out of twenty-three pregnancies, and the condition occurs more frequently still in eclampsia. At present, however, it is not yet generally accepted that an erythrotoxin is formed by the syncytium, though Bonnet” has shown histo- logically that a destruction of red cells probably takes place during life. He noticed on the surface of the villi “ perfect and damaged erythrocytes in all stages of degeneration, clumping and solution.” So Hofbauer found, by adding neutral-red to the chorionic villi of two fresh two-months’ placentz teased in saline, that many of the blood corpuscles showed red dots indicating degeneration. b. Calcitwm.—The source of the foetal calcium is still un- settled. According to Drennan,? it is derived from the circulat- ing blood and not from the tissues of the mother, but he adduces no strong evidence. It is well known that the teeth are apt to become brittle in pregnancy from a decrease in calcium fluoride * and a deficiency in enamel formation. Evidence of a special drain on calcium is also found in puerperal osteomalacia, which occurs in poor people who presumably have an insufficient supply of calcium in their diet. c. Phosphates and Sulphates.—It has been generally found that the phosphoric acid excretion runs parallel to the nitrogen (V. Eeke,® Schrader °). Jagerroos,> however, showed an equili- brium between intake and output in a pregnant dog which showed a distinct loss of nitrogen. According to Schrader, the excretion of sulphates is parallel to that of nitrogen. 1 Wychgel, “Untersuchungen tiber das Pigment der Haut und der Urin wabrend der Schwangerschaft,” Zeits. f. Geburtsh. u. Gyndk., vol. xlvii. 2 Bonnet, quoted by Hofbauer (Biologie der menschlichen Plazenta, Wien und Leipzig, 1905). 3 Drennan, ‘‘The Abstraction of Calcium Salts from the Mother’s Blood by the Foetus,” New York Medic. Journ., vol. lxxxvii. 4 Terrier, ‘‘ De l’Influence de la Grossesse sur les Dents,” Thése de Paris, 1899. 5 V. Heke, Jagerroos; see pp. 500 and 501 for references. 8 Schrader, ‘‘Stoffwechsel wa&hrend der Schwangerschaft,” Arch. f. Gyndk., vol. x., 1900. CHANGES IN THE MATERNAL ORGANISM 517 d. Chlorides—The first estimations of the chlorides of the urine in pregnancy indicated no variation from the non- pregnant level (Winckel*). Repeated investigations have been carried out since the discovery that a retention of chlorides may occur in nephritis and lead to cedema (Widal *). Biancardi * stated that cedemas in pregnancy were sometimes due to the same cause, and might be cured by decreasing the chlorides of the food. Next Cramer * affirmed that all cases of hydrops graviditatis without albuminuria were due to a re- tention of sodium chloride ; and Boni, whose careful investiga- tions of the urine in pregnancy have already been referred to, found that the chlorine excretion was decreased, and remained low during the puerperium. Along with this there is a retention of water to maintain osmotic balance. Normally 90 to 100 per cent. of the water taken in is excreted in the urine, but the percentage fell to 72 per cent. in a primipara, 53 per cent. in a multipara, and 48 per cent. in a twin pregnancy (Slemons *). Such a retention did not occur in a woman who was later delivered of dead twins, 93 per cent. of the water being excreted in the urine. Birnbaum’s ® results are not in agreement with the others. He states that a retention of chlorides occurs only in the nephritis of pregnancy, and not in normal pregnancy or in hydrops without albuminuria. In the blood-serum the chlorides were 0:1740 per cent. and 0°1775 per cent. in two cases, and 0:1733 per cent. in a non-pregnant woman. G. Respiratory Exchange during Pregnancy Modifications in the respiratory exchange arise from the alterations in the maternal organism, and from the requirements 1 Winckel, Studien iiber Stoffwechsel, &c., Rostock, 1865. 2 Widal, ‘‘ La cure de déchloruration dans le mal de Bright,” Arch, Génér., vol. cxciii., 1904. 3 Biancardi, ‘‘ Sulla cura declorurante nelle nefriti e nelle albuminurie nel campo ostetrico,” Ann, di Ost, e Ginec., 1905. 4 Cramer, ‘‘Chlornatrium-Entziehung bei Hydrops Graviditatis,” Monats- schrift f. Geburtsh. u. Gyndk., vol. xxiii. 5 Slemons, ‘‘ Metabolism during Pregnancy, Labour, and Puerperium,” Johns Hopkins Hosp, Rep., vol. xii., 1904. § Birnbaum, ‘‘ Excretion of Chlorides during Pregnancy,” Arch. f. Gynak., vol, lxxxiii., 1907. 518 THE PHYSIOLOGY OF REPRODUCTION of the product of conception. To a certain extent diffusion of oxygen takes place from mother to foetus, as it has been proved, by experiments in asphyxia of the mother, that the direction in which oxygen goes across the placenta depends on the tension. Whether there is also a gas-secretion by the trophoblast is unknown. With regard to the foetus, Pfliiger argued on theoretical grounds that the oxidation processes were inconsiderable, and the oxygen intake small. This was confirmed experimentally by Cohnstein and Zuntz.1 More recently, however, Bohr? has shown by more convincing experiments that in the later stages of pregnancy the foetal guinea-pig consumes at least as much oxygen as the mother. The actual figures which he ob- tained were 462 c.cm. for the mother and 509 c.cm. for the foetus per kilo per hour. He has also shown that the foetal respiratory quotient is unity, indicating that carbohydrates are the source of energy. The same has been found in new-born puppies before suckling (Murlin *). It is well to remember that Bohr’s experiments refer only to the foetus in the later stages of de- velopment, and that they entirely leave out of account the placental metabolism.* The high consumption of energy in the foetus, which differs from the adult in losing little heat by radiation from the skin surface and lungs, must be due to the intensive growth of the embryo (see Chap. X., p. 434). 1 Cohnstein and Zuntz, ‘‘ Untersuchungen iiber das Blut, den Kreislauf, und die Atmung beim Saugetierf6tus,” Pfliiger’s Arch., vol. xxxiv., 1884. 2 Bohr, ‘‘ Der Respiratorische Stoffwechsel des Sdugetierembryos,” Skand, Arch. f. Phys., vol. x., 1900. 3 Marlin, ‘‘ Protein Metabolism in Development,” Amer. Journ. of Phys., vol. xxiii., 1908-9. 4 In the later stages there is a wide distribution of glycogen throughout the tissues of the foetus, and the fcetal liver has assumed its glycogenic function. It is scarcely justifiable to extend Bohr’s results to the early stages of pregnancy, when the placenta probably takes a leading part in embryonic development. It may be that at that time also glycogen is the source of energy for the placenta in Rodents, but it cannot be so in Ruminants. In their placentz glycogen is found only in traces, while fat is in consider- able amount. Hence we cannot assume that the energy is derived from the combustion of carbohydrates until experimental evidence has been obtained. CHANGES IN THE MATERNAL ORGANISM 519 It is possible, though not yet proved, that, in addition to carbonic acid, incompletely oxidised substances may be brought to the placenta from the foetus and oxidised there or in the mother (Bohr?). Such a hypothesis lies at the foundation of the theory that certain pathological conditions in pregnancy are due to the circulation of toxins manufactured in the product of conception. With regard to the total energy exchange, the results of Magnus-Levy,? F. Muller,? and E. Zuntz* tend to show that in the human pregnancy no decrease in metabolism occurs, the metabolic changes being at least as active in the foetus as in the mother. In one experiment Levy found a progressive increase in the oxygen intake during pregnancy, but he does not lay too much stress on the figures,> as in all the others no increase in the gaseous exchange per kilo was established. Even in the third month there was a marked increase. The weight increased from 1084 to 111-4 kilo, and the oxygen intake from 302 to 320 c.cm. per minute, 7.e. from 2°79 to 2°88 c.cm. per kilo per minute. With such figures we must conclude that the early stages of pregnancy have had a favourable influence on the growth of the mother animal, and at the same time have led to a more energetic metabolism.® 1 Bohr, Nagel’s Handbuch der Physiologie, ‘‘ Respiration.” ? Magnus-Levy, ‘ Stoffwechsel und Néhrungsbedarf in der Schwanger- schaft,” Vortrag, Zeitschr. f. Geburtsh. u. Gyndk., vol. lii.; also v. Noorden, loc. ctt., vol. i. 3 F, Miiller, ‘‘ Diskussion zum Vortrag von Magnus-Levy,”’ see v. Noorden, loc. cit., vol. i. 4. Zuntz, “ Der Stoffaustausch zwischen Mutter und Frucht,’’ Hrgebn. d, Phys., 1908. 5 The older investigations of Oddi and Vicarelli (‘‘ Influence de la gros- sesse sur l’échange respiratoire,” Arch. ital. de Biol., vol. xv., 1891), showed a progressive increase in the consumption of oxygen during the last third of pregnancy ‘in rats; but Magnus-Levy raises the objection that the movements of the animals were not restricted. § Such a result is in conformity with those obtained in rats soon after inoculation with malignant new growths ; Cramer (W.), ‘‘ The Gaseous Meta- bolism in Rats inoculated with Malignant New Growths,” 3rd Scient. Rep., Imperial Cancer Research Fund, London, 1908). Magnus-Levy’s exceptional result may, however, be due to the fact that the woman under observation had not yet completed her growth. 520 THE PHYSIOLOGY OF REPRODUCTION Tl]. Tue Cuances in THE MATERNAL TISSUES DURING PREGNANCY The changes in the ovaries, the mammez, and the mucous membrane of the uterus are dealt with elsewhere. To the changes in some of the other organs, a brief consideration is here given. a. The Blood.—Ehrlich’s* statement that pregnancy does not appreciably alter the number of the red blood corpuscles has been more or less firmly established by Ingerslev,? Dubner,* Bernhard * and others in Man, by Spiegelberg and Gscheidlen * in the dog, and by Cohnstein® in the sheep. Their investi- gations have upset the older theory of a hydremia of pregnancy. There is evidence of a slight increase of hemoglobin (Payer,’ Fehling,® Winckelmann,* Wild *), especially towards the end of pregnancy. The number of leucocytes increases during pregnancy, and there is a further rise during the act of parturition (Nasse,” Lebedeff,” Rieder). The leucocytosis is referred by some to 1 Ehrlich, ‘‘ Die Andémien,”’ in Nothnagel’s Spezielle Pathologie. 2 Ingerslev, ‘‘ Ueber die Menge der roten Blutkérperchen bei Schwangeren,”’ Centralbl. f. Gyndk., 1879. 3 Dubner, “ Untersuchungen iiber den Hiimoglobingehalt des Blutes,” &c., Minch. med. Woch., 1890. 4 Bernhard, ‘‘ Untersuchungen tiber Hamoglobingehalt und Blutkérper- chenzahl in der letzten Zeit der Schwangerschaft,” Minch. med. Woch., 1892. 5 Spiegelberg and Gscheidlen, ‘“ Untersuchungen tiber die Blutmenge trachtiger Hunde,” Arch. f. Geburtsh. u. Gyndk., vol. iv. ® Cohnstein, ‘‘ Blutveranderungen wahrend der Schwangerschaft,” Pfliiger’s Arch., vol. xxxiv., 1884. 7 Payer, vide v. Winckel’s Handbuch der Geburtshiilfe, vol. i., H. 1. 8 Fehling, ‘‘ Ueber Blutbeschaffenheit,” &c., Arch. f. Gyndk., vol. xxviii., 1886. ® Winckelmann, ‘‘Ha&moglobin-Bestimmungen bei Schwangeren und Wochnerinnen, Inaug. Diss., Heidelberg, 1888. 10 Wild, ‘‘ Untersuchungen tiber den Hamoglobingehalt und die Anzahl der roten und weissen Blutkérperchen bei Schwangeren,” Arch. f. Gyndk., vol. liii. 11 Nasse, Das Blut, Bonn, 1836. 12 Lebedeff, quoted in v. Winckel’s Handbuch der Geburtshiilfe., vol.i., H. 1. 18 Rieder, Bettrige zur Kenntnis der Leukocytose und verwandter Zu- stande des Blutes, Leipzig, 1892, CHANGES IN THE MATERNAL ORGANISM 521 the lymphoid tissue of the endometrium, and by others to an increase in the groups of lymphatic glands in the neighbourhood of the genital apparatus. According to Spiegelberg and Gscheidlen, the total amount of blood is increased during pregnancy in the dog from 7°8 per cent. to 9 per cent. of the body-weight. There is no essential difference in the specific gravity (Nasse, Blumreich’). The observations on the alkalinity of the blood are few and con- tradictory. Lebedeff states that it is increased, and similarly Blumreich, who investigated the blood of pregnant rabbits and women. The alkalinity quickly returned to the normal level. On the other hand, Payer’s estimations of the “diffusible ” alkali, i.e. alkali not combined with protein, of defibrinated blood give values slightly below the non- pregnant level. The molecular concentration of the blood shows no change during pregnancy. b. The Heart and Circulation.—Older authorities stated that a true hypertrophy of the heart occurred during pregnancy, and was caused by the increased length and size of the uterine vessels, the placental circulation, and the compression of the aorta by the gravid uterus. Experiments showed, however, that the uterine vessels did not offer a resistance which required an increase in the work of the heart (Engstrém *), while the compression of the abdominal aorta and the introduction of large quantities of fluid into the abdominal cavity produced no change which could be detected from the pulse (Heinricius *). The controversy has been a long one, but it does not properly belong to this article. The present-day opinion of the cardiac modifications in the human female may be summed up as follows: Tendency to dilatation, especially of the right heart, and to some compensatory hypertrophy. The frequent em- barrassment of the right ventricle, even in the early stages of pregnancy, is marked by the occurrence of shortness of breath 1 Blumreich, ‘‘Der Einfluss der Graviditét auf die Blutalkalescenz,” Arch. f. Gyndk., vol. lix., 1899. 2 Engstrém, ‘‘L’Influence de la grossesse sur la circulation,” Arch, de Gyn., 1886, vol. ii. 3 Heinricius, Haperimentelle und klinische Untersuchungen iiber Circula- tionsverhalten der Mutter und der Frucht, Helsingfors, 1889. 522 THE PHYSIOLOGY OF REPRODUCTION and palpitation and by changes in the rate and rhythm of the heart. An increased area of dullness to the right of the sternum can usually be made out, but it is mainly due to the abnormally transverse position of the heart, and to its greater contact with the anterior wall of the chest (v. Winckel *). It has been suggested that the increased work of the heart, which leads in many cases to the dilatation of its chambers and perhaps to some compensatory hypertrophy, is due to an increased peripheral resistance from the presence of a vaso-~ constricting substance in the blood.’ In excess it may cause anuria and eclampsia (Nicholson %). The blood-pressure is not affected in normal pregnancy, but is always raised in labour as a result of the uterine con- tractions. After parturition the pressure falls, but rises again on the third day of the puerperium. Varices of the lower extremities and external genitals are frequent in human pregnancy. They are due mainly to the increased intra-abdominal pressure and the stretching of the abdominal wall. Secondary thromboses are common in the puerperium. c. The Ductless Glands—There is regularly a swelling of the thyroid gland in pregnancy (Tait *), which consists of a simple hypertrophy, and not a vascular engorgement or cystic change (Freund *). It has been shown experimentally in cats that a 1 V. Winckel, loc. cit., vol. i, H. 1. This has been clearly established by radiograms of the thorax in pregnancy. 2 The origin of this substance, if such exists, is still unknown. The investigation of extracts of the placenta by the writer, in conjunction with Dr. W. Cramer, proved that this organ contained no blood-pressure raising substance. The substances extracted by Dixon and Taylor (‘On the Physio- logical Action of the Placenta,’ Proc, Roy. Soc, of Med., London, vol. i., 1908) from the placenta and observed to have an adrenalin-like action, were subsequently shown to arise in the course of putrefaction (see Rosenheim, Journ, of Phys., 1909). ® Nicholson, ‘‘The Maternal Heart in Pregnancy,” Brit, Med. Journ., 1904, part ii. 4 Tait, ‘‘ Enlargement of the Thyroid Body in Pregnancy,” Obstet. Journ., 1875. 5 Freund, “Ueber die Beziehung der Schilddriise,” &c., Deuts, Zeitschr. f. Chir., vol. xxxi., 1890. CHANGES IN THE MATERNAL ORGANISM — 523 remnant of the gland, which is sufficient to maintain health in the non-pregnant state, is insufficient after the onset of preg- nancy (Lange *). An increased suprarenal secretion in pregnancy has also been suggested, the effect of which on the blood pressure is normally balanced by the increased thyroid secretion (Nicholson *). But experimental evidence seems to show that the blood-pressure raising action of the suprarenals is entirely independent of the thyroid gland (Pick and Pineles *). d. The Skin.—The cause of the increased pigmentation of the skin in pregnancy is little understood. It has been looked on as a simple deposit of pigment, as the result of infection with the microsporon furfur, the cause of pityriasis versicolor which not infrequently attacks pregnant women, and as a subcutaneous hamorrhage.* Jeannin® first suggested that it was derived from hemoglobin set free by the solution of red blood corpuscles. According to Veit® the hemolysis may be produced by the circulation of syncytial elements in the blood. The presence of iron in the pigment, though strongly denied by Truzzi,’ has recently been demonstrated by Wychgel.® He associates its presence with the frequent occurrence of hemoglobinuria in pregnancy. V. Firth and Schneider’s suggestion that the pigment is derived from tyrosin by the action of a placental tyrosinase is mentioned elsewhere (Chap. X., p. 481). An abnormal development of the hair of the face and body 1 Lange, ‘Die Beziehungen der Schilddriise zur Schwangerschaft,” Zettschr. f. Geburtsh. u. Gyndk., vol. x1., 1899. 2 Nicholson, ‘‘ Physiological Changes in the Maternal Organism during Pregnancy,” Trans, Obstet. Soc. Edinburgh, vol. xxxi., 1905-6. 3 Pick and Pineles, ‘‘ Beziehung der Schilddriise zur physiol. Wirkung des Adrenalins,” Biochem. Zettschr., vol. xii., 1908. 4 See v. Winckel’s Handbuch der Geburtshiilfe, vol. i. H. 1. ® Jeannin, ‘‘Observations pour servir & histoire du masque des femmes enceintes,” Gaz. Hebdom., 1868. 6 Veit and Scholten, ‘‘ Synzytiolyse und Hamolyse,” Zeitschr. f. Geburtsh. u. Gyndk., vol. xlix., 1903. 7 Truzzi, ‘‘ Ueber die Genese der Hyperchromie der Haut in der Gravi- ditat,” Monatsschr. f, Geburtsh., vol. xi., 1898. 8 Wychgel, ‘‘ Untersuchungen tiber das Pigment der Haut und den Urin wihrend der Schwangerschaft,”’ Zettschr. f. Geburtsh. u. Gyndk., vol. xlvii. 524 THE PHYSIOLOGY OF REPRODUCTION is occasionally seen in pregnancy (Slocum,’ Halban*). Under the name of dermographismus, Freund * describes a phenomenon, often met with in pregnancy, similar to the tache cérébrale of meningitis and other nervous affections. It may be elicited even in the early stages of gestation, and is best shown by stroking the skin over the sternum or fundus uteri. e. The Mamme.—tThe growth of the mammary glands is brought about by the development of new vesicles, the widening of existing blood-channels, and the formation of new vessels.* ‘Even in the first half of pregnancy, and sometimes in the first weeks, the mamme contain colostrum, a milky fluid composed of proteins, albumen, globulin, and casein, the carbohydrate lactose, fat, free fatty acids, lecithin, cholesterin, free glycero-phosphoric acid, and urea (Winterstein and Stickler °). 1 Slocum, ‘‘ Hair Development in Pregnancy,” New York Med. Rec., 1875. ? Halban, ‘Zur Frage der Gravidititshypertrichose,’ Wien, klin. Woch., 1907. 5 Freund, ‘‘ Die Haut bei Schwangeren,” Verhandl. d. vi. deutsch. Der- matologen-Kongr. zu Strassburg. 4 See Chapter XIII. 5 Winterstein and Stickler, ‘‘Die chemische Zusammensetzung des Colostrums,”’ Zettschr. f. phys. Chem., vol. xlvii., 1906. CHAPTER XII THE INNERVATION OF THE FEMALE GENERATIVE ORGANS—UTERINE CONTRACTION—PARTURITION—THE PUERPERAL STATE “ Birth is the end of that time when we really knew our business, and the beginning of the days wherein we know not what we would do, or do,”— SAMUEL BUTLER. THE innervation of the generative organs of the male was dealt with at some length in an earlier part of this work. It remains in the present chapter to describe the nerve supply to the female generative system, and more particularly to the uterus, since this is the organ which is especially concerned in the process of parturition. But before giving an account of the innervation of the internal organs, the nerve supply to the vulva and clitoris may be briefly dealt with. Tue INNERVATION OF THE EXTERNAL GENERATIVE ORGANS The external generative organs in the female are similarly innervated to those of the male (p. 254 e¢ seq.). Langley and Anderson’ found that stimulation of the first five lumbar nerves in the cat, or the third, fourth, and fifth lumbar nerves in the rabbit, produced the same effects as in the male excepting that they were less pronounced. The effects were (1) Pallor of the clitoris and of the mucous membrane of the vulva, accompanied by slight retraction of the clitoris, (2) Contraction of the vulva, and (3) Contraction of the muscles of the adjoining skin, drawing the vulva dorsally towards the rectum. Langley,? and subsequently Langley and Anderson,® found 1 Langley and Anderson, ‘‘ The Innervation of the Pelvic and Adjoining Viscera,” Jour. of Phys., vol. xix., 1895. 2 Langley, ‘‘ The Innervation of the Pelvic Viscera,” Proc. Phys. Soc., Jour. of Phys., vol. xii., 1891. 3 Langley and Anderson, loc. cit. 525 526 THE PHYSIOLOGY OF REPRODUCTION that two groups of effects, which were antagonistic to one another, could be produced by stimulating the sacral set of nerves in the vertebral canal, but that, as in the male, only those fibres which exercised an inhibitory influence run from the spinal cord in the sacral nerve roots. The inhibitory effects produced were (1) Flushing of the vulva and clitoris, (2) Dilata- tion of the vulva, and (3) Relaxation of the skin muscles sur- rounding the vulva. The visceral motor effects were the same as those produced by the lumbar set of nerves as described above. Besides these effects, contraction was induced in the external sphincter of the vagina and in the striated genital muscles. Tur INNERVATION OF THE OVARIES The ovary is innervated from the sympathetic plexus ac- companying the ovarian artery and from the plexus associated with the ovarian branch of the uterine artery. It is generally supposed that the nerve fibres, which are non-medullated, are merely vascular in function. The fact that ovulation in some animals only occurs as a consequence of coition, and then takes place at a definite time afterwards, points to the conclusion that the follicles discharge in response to a stimulus conveyed to the ovary by its nerves (see p. 134). It has been suggested that the rupture is due to the stimulation of erectile tissue.” Nerve fibres have been described in the tissue immediately surrounding the follicles, and have even been traced as far as the follicular epithelium. 1 Von Herff, ‘‘ Ueber den feineren Verlauf der Nerven im Eierstocke des Menschens,” Zettschr. f. Geburt. u. Gyndk., vol. xxiv., 1892. Gawronsky, “Ueber Verbreitung und Endigungen der Nerven in den weiblichen Geni- talien,” Arch. f. Gyndk., vol. xlvii., 1894. Kallius, ‘‘ Nervendigungen in Driisen d. Eiersticke,’’ Merkel and Bonnet’s Ergeb. d. Anat. u. Entwick., vol. iv., 1895. Mandl, “ Ueber Anordnung und Endigungsweise der Nerven im Ovarium,” Arch. f. Gyndak., vol. xlviii., 1894-5. Vallet, ‘‘ Nerfs d’Ovarie,” &c., Thesis, Paris, 1900. Abel and McIlroy, “ Nerves of the Ovary,” Phys. Soc., June 5th, 1909. See also references on p. 329. 2 Rouget, ‘‘ Recherches sur les Organes Erectiles de la Femme,’’ Jour. de la Phys., vol. i., 1858. THE FEMALE GENERATIVE ORGANS 527 Tue INNERVATION OF THE UTERUS AND VAGINA AND THE MEcHANISM OF UTERINE CONTRACTION It is well known that the onset of parturition is manifested by rhythmically repeated contractions of the uterus which constitute the “labour pains.” But although the contractions are most pronounced at this period, observations on animals have shown that even in a virgin uterus rhythmical movements may occur. Kehrer ' showed long ago that a uterus separated from the body is capable of undergoing contractions if kept moist, and at the normal body temperature. More recently Helme,” Kurdinowski,? Franz,* and others have confirmed Kehrer’s observation, thus proving that the movements are not dependent on impulses received from the central nervous system. Those investigators showed that the excised uterus may undergo regular contractions for a prolonged period if placed in a warm bath of normal saline solution or on having its vessels perfused with Locke’s solution. According to Franz the excised virgin uterus exhibits no spontaneous contractions, but Helme and Kurdinowski state that they may occur, but that they are much weaker than those taking place during and after pregnancy. The movements of the uterus have lately been more fully investigated by Cushny,°® who has carried out a large number of experiments upon rabbits and other animals. This author states that in virgins the unexcised uterus may remain motion- less for a long time, but that after manipulation or exposure to air rhythmic contractions are often developed. He is disposed to believe, therefore, that the virgin uterus in the intact animal " Kehrer, ‘‘Zusammenziehungen der glatten Genitalmuskelatur,” &c., Bettrage zur Vergl. u. Exper. Geburtskunde, 1867. * Helme, ‘Contributions to the Physiology of the Uterus and the Phy- siological Action of Drugs upon it,” Reports of the Laboratory of the Royal College of Physicians, Edinburgh, vol. iii., 1891. 3 Kurdinowski, “‘ Physiologische und pharmakologische Versuche an der isolirten Gebarmutter,” Arch. f. Anat. u. Phys., phys. Abth. (supplement) 1904, 4 Franz, “Studien zur Physiologie des Uterus,” Zeitschr. f. Geburt. u. Gyndak., vol. liii., 1904. 5 Cushny, “On the Movements of the Uterus,” Jour. of Phys., vol. xxxv. 1906. 528 THE PHYSIOLOGY OF REPRODUCTION undergoes no spontaneous movements. In animals in a state of “heat,” and during and after pregnancy, spontaneous con- tractions could generally be discerned from the first, and the author is doubtful if the organ ever resumes its original inert condition after it has once been pregnant. In some cases the movements seemed to occur almost simultaneously throughout the entire organ, but in others the circular muscle fibre con- tracted independently of the longitudinal, and vice versa. Mechanical or electrical stimulation caused very powerful contractions, but these were elicited more easily in the pregnant than in the virgin uterus, while the increased irritability was found to persist after pregnancy was over. Helme stated that a shutting off of the blood-supply in the excised and perfused uterus of the sheep brought about con- traction. Kurdinowski, on the other hand, found that in the intact animal the opposite effect was produced. Cushny’s experiments for the most part confirm those of Kurdinowski, but clamping the aorta in the cat led to conflicting results, since in two cases it was succeeded by relaxation and in three by contraction. No reason could be assigned for this diver- gence, It has long been known that uterine contractions can be induced by nervous stimulation. Thus Serres' showed that irritation of the spinal cord in the lumbar region excited the uterus to contract, and later investigators have obtained similar results. Rohrig* showed that asphyxia which may bring about uterine contractions (and abortion m the preg- nant condition) cannot do so if the lumbar cord is destroyed. Frankenhauser* and Ké6rner® discovered that the efferent nerve fibres left the lumbar region of the spinal cord, and after traversing the sympathetic, the inferior mesenteric ganglia and 1 Serres, Anatomie Comparée du Cervea, 1824. 2 Budge, ‘‘ Ueber das Centrum genitospinale des Nervus sympatheticus,” Virchow’s Archiv, vol. xv., 1858. Riemann, ‘‘Einige Bemerkungen itiber die Innervation der Gebarmutter,” Arch. f. Gyndk., vol, ii., 1871. 8 Rohrig, ‘‘Experimentelle Untersuchungen iiber die Physiologie der Uterusbewegung,” Virchow’s Archiv, vol. Ixxvi., 1879. 4 Frankenhauser, ‘‘ Die Bewegungsnerven der Gebarmutter,” Jenaische Zettschr. f. Med., vol. i., 1864. > Korner, Studien d. Phys. Instituts zu Breslau, 1865. THE FEMALE GENERATIVE ORGANS — 529 the aortic plexus, made their way to the uterus. Langley * found that the majority passed to this organ by way of the sympathetic in the region of the fourth, fifth, and sixth lumbar ganglia, so that they probably arise from the third, fourth, and fifth spinal nerves. Subsequently Langley and Anderson * showed that stimulation of the second, third, fourth, and fifth lumbar nerves (in cats and rabbits) causes pallor and con- traction of the Fallopian tubes, uterus, or vagina, but that stimulation of the first and sixth lumbar nerves produces no effect. They state that the efferent fibres are motor for the muscular walls and vaso-constrictor for the small arteries. The effect on the uterus and vagina was found to vary with the state of the uterus in regard to parturition. Langley and Anderson state that the sacral nerves send neither motor nor inhibitory fibres to any of the internal generative organs, thus differing from Kehrer, Korner, and others, who say that they obtained contraction of the uterus on stimulating these nerves. Keiffer * also independently investigated the innervation of the uterus, and the results obtained by exciting various nerves, his observations agreeing for the most part with those of Langley and Anderson. Cushny, in the paper already referred to, has described at some length the effects of hypogastric stimulation, which pro- duced in the rabbit powerful contraction of the whole uterus irrespective of its condition in regard to the occurrence of pregnancy. If the stimulation was prolonged for more than fifteen seconds the organ remained in a state of extreme con- traction (tetanus uteri), but oscillations soon began again, and a gradual relaxation followed. Cushny shows also that the hypogastric contains inhibitory fibres, and in one exceptional case (a pregnant rabbit) stimulation of this nerve induced pure inhibition, the uterus ceasing to contract at all. Moreover, in the virgin cat the effect of hypogastric stimulation was in- hibitory, the organ undergoing relaxation. On the other hand, in the cat during pregnancy, or as a general rule after pregnancy, hypogastric stimulation led to strong and immediate contraction 1 Langley, loc. cit. ? Langley and Anderson, loc, cit. ® Keiffer, Recherches sur la Physiologie de l’ Utérus, Bruxelles, 1896. 2L 530 THE PHYSIOLOGY OF REPRODUCTION just as in the rabbit. It is supposed, therefore, that the in- hibitory fibres prevail in the virgin, but that during and after pregnancy the action of the motor fibres conceals their presence.’ Fellner? states that the “nervi erigentes”’ are motor for the longitudinal muscles of the uterus and for the circular muscles of the cervix, but are inhibitory for the circular muscles of the uterus and the longitudinal muscles of the cervix. According to the same author the hypogastric nerves are motor for the circular muscles of the corpus uteri and for the longitudinal muscles of the cervix, but are inhibitory for the longitudinal muscles of the uterus and for the circular muscles of the cervix. Dembo * has described a peripheral nerve centre for the uterus in the upper part of the anterior wall of the vagina in the rabbit. Stimulation of this centre produced a very dis- tinct contraction of both uterine cornua. According to Jacob * there is an inhibitory centre for uterine contraction situated in the medulla oblongata. This assertion is based on experiments upon rabbits, in which it was found 1 Cushny deals also with the action of various drugs on the uterus, and for an account of this subject the reader is referred to his paper (loc, cit.). See also Dale, ‘‘On Some Physiological Actions of Ergot,” Jour. of Phys., vol. xxxiv., 1906. The effects of temperature upon uterine contraction were first described by Runge (M.) (“Die Wirkung hoher und neidriger Tempera- turen auf den Uterus,” Arch. f. Gyndk., vol. xiii., 1878), who found that hot water caused increased contraction followed by paralysis, while cold water pro- duced tetanus, Helme (loc. cit.) obtained results which were mostly similar. Kurdinowski also found that cold excited contraction to tetanus, and that long-continued mechanical stimulation produced exhaustion. Asphyxia did not cause contraction, and experimental anzemia had no effect. ? Fellner, ‘‘ Ueber die Bewegungen und Hemmungsnerven des Uterus,” Arch, f. Gyndak., vol. Ixxx., 1906. Labhardt (‘‘ Das Verhalten der Nerven in der Substanz des Uterus,” Arch. f. Gyndk., vol. 1xxx., 1906) describes an extensive system of nerves in the uterus of Man and of the rabbit, the main trunks lying between the middle layer of muscles and giving off intra- fascicular bundles. Keiffer (Bull. Soc. d’Obstét , Paris, 1908, Nos. 2 and 3) describes sympathetic ganglia in the uterine and vaginal walls in the course of the large nerves coming from the hypogastric plexus. % Dembo, ‘‘Zur Frage iiber die Unabhingigkeit der Kontraktinen der Gebarmutter von dem Cerebrospinalnervensystem,’? Abstract in Biol. Cen- tralbl., vol. iv., 1885. (The original is in Russian.) + Jacob, ‘‘ Ueber die Rhythmischen Bewegungen des Kaninchenuterus,” Verhandl. der Phys. Gesell, zu Berlin, Anat. f. Anat. u. Phys., phys. Abth., 1884. THE FEMALE GENERATIVE ORGANS 531 that stimulation of the medulla caused the movements of the uterus to cease. Moreover, it is to some extent borne out by the fact that the “ pains” of labour can often be inhibited by emotions and other contemporary actions of the central nervous system (see below, p. 539). It is well known that uterine contraction can be induced by the presence of a foreign body in the uterus, by injections into the rectum, by the application of the child to the breast, and by various other means. According to Kurdinowski’ the sensation of any violent pain may cause uterine contraction in animals, and the organ may respond to remote stimulation (e.g. in the ears). These observations alone are sufficient to show that the contraction is often a reflex act. The experimental evidence cited above shows no less clearly that the controlling centre is in the lumbar portion of the spinal cord. Nevertheless there are many indications, as just mentioned, that the move- ments of the uterus can be brought under the influence of a higher centre situated in the brain. On the other hand, the fact that rhythmical contractions can continue to occur in the absence of all nervous connections is a certain proof that they are primarily independent of the nervous system, although normally they are to a large extent influenced by it. It must be concluded, therefore, that the power to contract and relax rhythmically is an inherent property of the muscular tissue of the uterus. The question as to the nature of the mechanism involved in uterine contraction is inseparably connected with the further problem concerning the part played by nervous influence in controlling the course of parturition. This subject is dealt with below (p. 537). THe NormaL Course OF PARTURITION IN THE Human FEMALE The increased size of the foetus, together with the accumula- tion of the amniotic fluid, causes. the uterus towards the end of pregnancy to become considerably distended. The enlarge- ’ Kurdinowski, “‘ Ueber die Reflectorische Wechsel beziehung zwischen der Briistdriisen und dem Uterus,” Arch. f. Gyndk., vol. 1xxxi., 1907. 582 THE PHYSIOLOGY OF REPRODUCTION ment is still further increased by the growth of the uterine wall itself. Partly as a consequence of this enlargement the waves of contraction which were present at the beginning of pregnancy, or even previously, as above described, become much more marked, but are still unaccompanied by painful sensation. With the onset of labour, however, these uncon- scious painless contractions are replaced by others of increasing intensity, and in the human subject distinctly affecting con- sciousness and giving rise to severe suffering. These are the “Jabour pains” which bring about the dilatation of the cervix uteri and lead to the expulsion of the child followed by the placenta. At the commencement of labour the contractions do not occur oftener than once every half or quarter of an hour, but they soon become more frequent, and recur eventually at in- tervals of two or three minutes. Their average duration is about a minute, though actual pain is experienced for a shorter time. Polaillon ? and Schutz * have shown from tracings that the period of increase occupies the main portion of the “ pain,” its acme being of short duration. In animals possessing bi- cornuate uteri the contractions are said to be peristaltic in nature, but this is not so evident in the case of the human subject. Williams * has discussed the question as to the amount of force exerted at each “ pain ” in a woman during delivery. He states that the expenditure of energy necessary to restrain the head of the child as it emerges from the vulva is represented by not more than fifty pounds, although the obstetrician some- times finds it impossible to hold it back at the acme of the pain. Schutz ° made an attempt to arrive at a more exact estimation by inserting into the uterus a rubber bag connected with a mercury manometer. He found that whereas the intra-uterine pressure between the contractions was represented by a column 1 Williams, Obstetrics, London, 1904. * Polaillon, Recherches sur la Physiologie de l'Utérus Gravide, Paris, 1880. 3 Schutz, ‘‘ Ueber die Formen der Wehenerven und iiber die Peristaltik des Menschlichen Uterus,” Arch. f. Gyndk., vol. xxvii., 1886. 4 Williams, loc. cit. 5 Schutz, ‘‘ Ueber die Entwickelung der Kraft des Uterus in Verlaufe der Geburt,” Verhandl. d. Deutsch. Gesell. fiir Gyndk., 1895. THE FEMALE GENERATIVE ORGANS — 533 of mercury of twenty millimetres, during the pains it rose to a height of from eighty to two hundred and fifty millimetres. This difference is calculated to represent a force of from eight and a half to twenty-seven and a half pounds. The clinical course of labour and the muscular forces con- cerned in the process are fully dealt with in the text-books on Midwifery,! and it is not proposed in the present work to devote more than a very brief space to the consideration of this subject. It is customary to divide the period of labour into three stages. The first stage is characterised by the dilatation of the cervix and os uteri. Galabin gives the following account of the mechanical processes which take place in the uterus during this stage of labour:—‘ There are three elements in the mechanism of dilatation of the cervix and os; first, the mechanical stretching by the bag of membranes; secondly, the contraction of the longitudinal fibres of the uterus, which draw the cervix open; and thirdly, the physiological relaxation of the circular fibres, which [is always associated] with the con- traction of the body of the uterus. It follows from the principles of mechanics that the effect of any given. pressure within the bag of membranes in producing a tension of the edge, either of the internal or external os, is directly proportional to the diameter of the os, and therefore vanishes when the os is very small. Hence, if the os is closed to begin with, some dilatation by the stretching influence of the longitudinal fibres must have taken place before the mechanism of dilatation by the bag of membranes or parts of the foetus can come into play. The mechanical action of the dilating part, as it is pressed into the cervix, is that of a wedge; a fluid and uniform wedge, in the case of the bag of membranes ; a solid and irregular wedge, in the case of the head or other part of the foetus. It follows that the effect produced by the wedge varies according to the acute- ness of its angle at the points where it is in contact with the edge of the os. . . . It follows that the dilating force vanishes when there is no projection, and becomes greater the more complete 1 See Williams, loc. cit. Galabin, Manual of Midwifery, 6th Edition, London, 1904, and the other text-books on the subject. See also Sellheim, “ Die Physiologie der Weiblichen Geschlechtsorgane,” Nagel’s Handbuch der Physiologie des Menschen, vol. ii., Braunschweig, 1906. 534 THE PHYSIOLOGY OF REPRODUCTION is the projection. It follows also that it becomes progressively more and more effective in proportion to the degree of dilatation which has already been produced.” ? The second stage, which has been called the expulsive stage, may be said to include the period from the complete dilatation of the os uteri to the delivery of the foetus. When the os has become fully expanded, and the membranes have ruptured, there is generally a short lull in the pains of labour. At the end of the lull the contractions of the uterus begin to recur with increasing vigour and frequency, while the abdominal muscles which are brought into play for the first time exert on the uterus an additional extrinsic force similar to that exerted on the rectum during defecation. These abdominal contrac- tions are synchronous with those of the uterus, and therefore, like them, tend to occur rhythmically. At the commencement of the process the patient is able to some extent to control the contractions by an effort of the will, but later on they are quite involuntary. The combined effect of the contractions is to drive the child, usually head foremost, through the vagina and then out through the vulva, these however playing a purely passive part in the act of expulsion. Sometimes the membranes do not rupture before birth, and the child is born surrounded by a “ caul.” ‘The third stage of labour comprises the expulsion of the placenta. After the delivery of the child the uterus ceases to contract for a longer or shorter period, at the end of which its activity is renewed once more. At this time the placenta becomes completely separated from the wall of the uterus, and passes into the upper part of the vagina. It is expelled thence through the action of the muscles of the abdomen. During this stage there is almost invariably a certain amount of hemorrhage, which is represented in normal cases by from three to four hundred cubic centimetres of blood. The duration of labour shows considerable variation, but is generally longer in primiparous women (t.e., those who have never borne children before) than in multiparous ones. The average for the former is rather more than eighteen hours, the three stages respectively occupying sixteen, two, and from a 1 Galabin, loc, cit. THE FEMALE GENERATIVE ORGANS — 535 quarter to half-an-hour. The average for multiparous women is twelve hours, eleven of which are occupied by the first, and one by the second stage. The duration of labour in primiparous women depends also upon age, being usually more prolonged in elderly subjects. PARTURITION IN OTHER MAMMALIA In animals the process of delivery varies somewhat in the different animals. In the horse the foetus, which has been lying on its back during intra-uterine life, preparatory to birth Fig. 131.—The first stage in the revolution of the equine fetus. The os is dilated by the membranes, which have not yet ruptured. (After Franck, From Smith’s Veterinary Physiology, Baillitre, Tindall & Cox.) changes on to its side and afterwards assumes the upright position, with its muzzle and forelegs in the direction of the pelvis. Dilatation of the passage follows, and the foal is de- livered head first. In the cow and sheep the movements which occur are essentially similar. It is stated that the alteration in the position of the foetus is not brought about by its own movements but by the uterine contractions. The revolution of the foetus prior to birth in the mare and cow is apparently re- sponsible for the torsion of the neck of the uterus and vagina which often occurs in these animals. Parturition in the mare is accompanied by a complete separation of the chorion from the uterine wall. As a conse- 536 THE PHYSIOLOGY OF REPRODUCTION quence of this fact any difficulty experienced in delivery usually causes the death of the foal. In Ruminants, on the other hand, the separation of the cotyledons takes place very gradually, so that the connection between the maternal and fcetal circula- tion is maintained to some extent until the last. In these animals the process of parturition may last for hours. In the mare, on the contrary, delivery is usually effected very rapidly.’ The foetal membranes may be expelled with the young or be Fig. 132.—The Foal in the normal position for delivery, the revolution being completed and the membranes ruptured. (After Franck. From Smith’s Veterinary Phystolcgy, Bailligre, Tindall & Cox.) retained until a little later, when the uterus recovers its power and then expels them. In animals such as the rat, in which multiple conception is the rule, the “ presentation” of the young at birth may be either “ breech” or ‘‘ head.” The foetuses tend to be expelled irregularly, some being discharged along with the placenta, while others are born separately.” 1 Smith, Veterinary Physiology, 3rd Edition, London, 1907. Fleming, Veterinary Obstetrics, London, 1878. See also Wortley Axe, ‘‘The Mare and Foal,” Jour. Royal Agric. Soc., 3rd Series, vol. ix., 1898, and Leeney, “The Lambing Pen,” Jour, Royal Agric. Soc., 8rd Series, vol. vii., 1896. * Brumpt, ‘‘ Parturition chez le Rat blanc,” Bull. Soc, Zool., France, vol. xxxii., 1907. The loosening of the placenta and other changes in Tupaia are described by van Herwerden, “ Die puerperalen Vorginge in der Mucosa uteri von Tupaia javanica,” Anat. Hefte, vol. xxxii., 1907. THE FEMALE GENERATIVE ORGANS = 537 THE Nervous MEcHANISM OF PARTURITION Parturition may be considered as being normally a reflex act, the centre of which is situated in the lumbar region of the spinal cord. On the other hand, it has been shown from experi- ments upon animals that the transmission of impulses through the cord is not absolutely essential to the occurrence of par- turition. Simpson (Sir James) * removed the spinal cord from the first dorsal vertebra downwards from a number of sows a few days before parturition was due. Some of the animals died as a result of the operation, but in others parturition proceeded normally, excepting that in each case the last foetus of the series was not born. “The uterine contractions proceeding from fundus to cervix were sufficient to expel the foetuses from the uterus; and each foetus as it came into the vagina was thence extruded by the force transmitted from the foetus behind it; but when the last foetus came into the vagina it remained there, because ‘there was nothing to transmit the uterine ex- pulsive force, while the vaginal and abdominal muscles, being under the influence of the spinal nerves, had been rendered powerless by the removal of the spinal cord.” Riemann ? states that after the destruction of the cord of a cat from the third dorsal vertebra downwards the animal gave birth to a kitten two days subsequently, shortly before its death. Rein *® describes experiments upon rabbits in which -he severed the uterus from all nervous connection with the cerebro- spinal system, and found afterwards that the mechanism of labour was not destroyed. Furthermore, Oser and Schlesinger,’ as a result of experi- mental evidence, state that parturition can occur in animals after the severance of the sympathetic nerves which pass to the uterus, but it is difficult to understand how this operation 1 Simpson, Selected Obstetric Works, edited by W. H. Black, Edinburgh, 1871. 2 Riemann, ‘‘Einige Bemerkungen iiber die Innervation der Gebiir- mutter,” Arch. f. Gyndk., vol. ii, 1871. 3 Rein, ‘Beitrag zur Lehre von der Innervation des Uterus,” Pfliiger’s Archiv, vol. xxiii. 4 Oser and Schlesinger, ‘‘ Experimentelle Untersuchungen tiber Uterus- bewegungen,” Stricker’s Med. Jahrbiicher, 1872. 588 THE PHYSIOLOGY OF REPRODUCTION could have been made complete without interfering with the blood supply to that organ. More recently, Goltz and Ewald * have described an experi- ment in which they completely exsected the spinal cord of a bitch from the mid-dorsal region downwards, and found that after the operation the animal experienced normal “ heat,” became pregnant, and in due course produced a litter of pups. Kruiger and Offergeld? have also shown that parturition is possible after destruction of the cord. Goltz had already shown * that parturition could occur after the transection of the spinal cord in the dorsal region, and consequently after all connection with the higher centres had been cut off. (See pp. 490—491.) The last-mentioned fact is also demonstrated in the various cases In which parturition has proceeded normally in women suffering from paraplegia from the level of the mid-dorsal part of the spinal cord downwards. Routh ‘ has recorded several such cases, and in all of them labour set in and proceeded regularly (or almost regularly), but without sensation. In Routh’s own patient the injury was in the dorsal region of the cord, which was completely disorganised at the seat of the fracture of the spine, as the post-mortem evidence showed. In the lumbo- sacral region, however, there were a large number of cells which were normal in appearance, so that it could not be contended that the centre for parturition had been destroyed. Routh also refers to Brachet’s case,> which he states is the only one re- corded in which the spinal lesion was apparently in the lumbar region of the cord. In this case the uterus failed to make the normal contractions, and the child was eventually extracted with forceps. The placenta also had to be removed by hand. 1 Goltz and Ewald, ‘‘ Der Hund mit verkiirztem Riickenmark,” Pfliiger’s Archiv, vol. lxiii., 1896. 2 Kruiger and Offergeld, ‘‘Der Vorgang von Zeugung, Schwangerschaft, Geburt, und Wochenbett an der ausgeschalteten Gebirmutter,” Arch. f. Gynik., vol, lxxxiii., 1908. 5 Goltz, “Ueber den Einfluss des Nervensystems auf die Vorgange wahrend der Schwangerschaft und des Gebarakts,” Pflager’s Archiv, vol. ix., 1874. 4 Routh, ‘Parturition during Paraplegia,” Trans. Obstet. Soc., Lond., vol. xxxix., 1898. 5 Brachet, Recherches, 2nd Edition, Paris, 1837. THE FEMALE GENERATIVE ORGANS 539 It is clear, therefore, that a spinal lesion in the lumbar region may result in materially weakening the action of the uterus, and so may hinder the normal course of labour. On the other hand, in those cases in which the lesion was in the dorsal part of the cord, the possibility of spinal reflexes in the lumbar region could not be excluded.’ The following general conclusions regarding the nervous mechanism of parturition are based largely on those of Routh. (1) The act of parturition is partly automatic and partly reflex, these actions corresponding in the main to the first and second stages of labour respectively, the spinal reflexes usually com- mencing as soon as the membranes have ruptured. (2) Direct communication with the brain is not essential for the proper co-ordination of uterine action, but the brain appears to exercise a controlling influence of some kind. Thus, emotions often become a hindrance to the progress of parturition. It would seem possible that this inhibition of uterine contractions is brought about by an inhibition of a centre in the brain (see above, p. 530). (3) Direct communication between the uterus and the lumbar region of the cord, is generally essential for the occurrence of those rhythmical contractions which take place during the progress of normal labour. There is experi- mental evidence upon animals, however, that the uterus is some- times able automatically to expel its contents, at least as far as the relaxed portion of the genital cord, even when entirely deprived of all spinal influence.” CHANGES IN THE MATERNAL ORGANISM The influence of parturition upon the metabolism of the maternal organism is dealt with by Sellheim.* There is a 1 Routh also discusses post-mortem parturition, but points out that in most of those cases where it occurred, the expulsion of the foetus was caused by increased abdominal pressure due to putrefactive gaseous distension during a condition of muscular relaxation. There are some facts which go to prove that uterine contractility and retraction may continue or even commence after death, possibly resulting from the movements of the imprisoned child. 2 For further references to the literature of the nervous mechanism of parturition, see Bechterew, Die Funktionen der Nervencentra, Weinberg’s German translation, vol. i., Jena, 1908. 3 Sellheim, loc, cit. 540 THE PHYSIOLOGY OF REPRODUCTION slight rise of temperature during the process, and the pulse rate is also affected, being much quicker during the pains, but slower between them, the difference amounting to as much as thitty- six beats a minute. The blood shows a marked leucocytosis, and the blood pressure is higher. Urine is secreted in smaller quantities, and is liable to contain traces of renal epithelium, red and white blood corpuscles, and albumen. THE Cause oF BIRTH Foster in his Text-book of Physiology’ has written as follows: “‘ We may be said to be in the dark as to why the uterus, after remaining for months subject only to futile contrac- tions, is suddenly thrown into powerful and efficient action, and within it may be a few hours, or even less, gets rid of the burden which it has borne with such tolerance for so long a time. None of the various hypotheses which have been put forward can be considered as satisfactory. We can only say that labour is the culminating point of a series of events, and must come sooner or later, though its immediate advent may sometimes be decided by accident.’” What Foster wrote about this question is still true to-day, for no real progress has been made towards the solution of the physiological problem as to the immediate cause of parturition. Williams * has classified the various theories which have been formulated under eleven heads. These may now be briefly considered in the order adopted by him. (1) The increasing irritability of the uterus, as manifested by its greater tendency to respond to stimulation in the later stages of gestation, is probably a factor in determining the time of birth. As already described, the uterine contractions towards the close of pregnancy are not only more frequent, but they are also much more intense. This growing irritability is no doubt to be directly associated with the increase in the size of the foetus. (2) It is suggested that the mere distension of the uterus must, after a certain point, lead to a reaction, when the organ 1 Foster, Text-Book of Physiology, 5th edition, vol. iv., London, 1891. 2 Williams, loc. cit. THE FEMALE GENERATIVE ORGANS 541 attempts to reduce itself to its former size, and so expels its contents, This idea receives some support from the fact that twin pregnancies and hydramnios (or the presence of an excessive quantity of liquor amnii) often result: in premature labour. (3) It has been supposed from early times onwards that parturition might be brought about through the pressure of the foetus producing a gradual dilatation of the cervix. Williams, however, has pointed out that this condition of the cervix cannot be the sole factor, since in a certain number of cases, especially in twin pregnancies, a pronounced dilatation has been known to occur for a considerable period prior to the onset of labour. (4) Keilmann,’ working upon the bat, came to the conclusion that the onset of labour was caused by the increasing pressure set up by the lower distended portion of the pregnant uterus (the lower uterine segment) upon the surrounding nerve ganglia. Supposing this conclusion to be correct as applied to the bat, it is not quite clear that it is equally applicable to the human female and to other animals. (5) Simpson 2 and others were of opinion that the “ pains ” of labour were the indirect result of a partial separation of foetus and decidua, brought about by the fatty degeneration of the latter in the last stages of pregnancy, so that the foetus became virtually converted into a foreign body, which caused the uterus to respond accordingly. It is no doubt true that part of the maternal placenta undergoes degenerative changes towards the end of pregnancy, but there is no evidence that this by itself is sufficient to cause a separation of the foetus from the uterine wall. (6) There is no evidence in support of the theory that the exciting cause of parturition is an accumulation of carbon dioxide in the blood, beyond the fact demonstrated by Brown- Séquard,*® Keiffer,* and others, that uterine contractions can be induced experimentally by this means. 1 Keilmann, ‘‘ Zur Klérung der Cervixfrage,”’ Zedtschr. f. Geb. u. Gynik., vol. xxii., 1891. 2 Simpson, loc. cit. 3 Brown-Séquard, Experimental Researches, English translation, London, 1853. 4 Keiffer, loc. cit. 542 THE PHYSIOLOGY OF REPRODUCTION (7) Spiegelberg? put forward the theory that parturition was brought about through the action of substances secreted by the foetus and passed into the maternal blood. These hypo- thetical substances, which appear to have been comparable to Starling’s hormones, were supposed to act on the uterine centre in the spinal cord. Spiegelberg suggested, further, that the ex- citing substances were elaborated as a result of an insufh- ciency of nutrition, and were an indication that the mature foetus required other sustenance than that supplied to it through the placenta. This theory appears to be devoid of all experimental basis, but it is not opposed by any of the known facts. (8) Tyler Smith,’ Minot,? Beard * and others have held the view that there is a connection between parturition and men- struation, the two processes being physiologically homologous. According to this theory, there is an increased tendency towards uterine contractions at the periods at which menstruation would occur if the condition were not one of pregnancy. Thus Tyler Smith says that there is in all women a greater tendency to abort at the times represented by the catamenial periods. According to Minot, the menstrual and gravitidal changes follow the same cycle of events, the pregnant uterus passing through a prolonged and intensified “ menstrual cycle.” Consequently, it is probable that there is a common cause for the ending of the series (the casting off of the superficial part of the mucosa in both cases). This theory has been further elaborated by Beard, who has arrived at the conclusion that parturition takes place at the time it does in order that a new ovulation may be carried into effect. This author lays great stress upon the rhythmical character of the sexual processes, and points out in support of his theory that “heat ” and ovulation frequently ensue shortly after parturition. That this does not happen in many animals has been already shown in the second chapter of 1 Spiegelberg, ‘‘ Die Dauer der Geburt,”” Lehrbuch der Geburtshilfe, vol. ii. 1891. * Tyler Smith, Parturition and the Principles and Practice of Obstetrics, London, 1849, 5 Minot, “ Uterus and Embryo,” Jour. of Morph., vol. ii., 1889. “Human Embryology.” * Beard, The Span of Gestation and the Cause of Birth, Jena, 1897. THE FEMALE GENERATIVE ORGANS — 543 this work.1 Moreover, Beard’s theory makes no attempt to explain why parturition should occur in some animals at the close of one particular ovulation interval (e.g. in the human species at the close of the tenth), and in other animals at the termination of a different one (that is to say, no explanation is given of the variation in the number of ovulation intervals which are comprised in the period of gestation in different animals). It cannot be said, therefore, that Beard’s hypothesis as to the time occupied by gestation and the cause of birth is an adequate one. (9) Various writers, such as Geyl,? have laid some stress upon the belief that parturition occurs in women at a tim> which has proved, after long ages, to be the most suitable for the perpetuation of the race. A similar statement might of course be made about any other existing species of mammal, for it is only another way of stating the generally accepted belief that parturition, like all other natural phenomena in the animal world, is under the control of natural selection. In support of this contention, as applied to the human species, it has been pointed out that when labour takes place after an abnormally prolonged gestation, it frequently results in dead children, while; on the other hand, premature labour results in puny, ill-developed children, who often perish in early life. (10) Eden,? and also Williams, have pointed out “ that the frequent occurrence of infarct formation [1.e. a certain kind of degenerative change] in the placenta at term must be regarded as evidence of its senility, and that this change is analogous to the obliteration and atrophy of the chorion leve at an earlier period. Where these changes are marked the nutrition of the foetus must be interfered with, and it is possible that certain of its metabolic products may result in stimulation of the uterine centre.””* This theory should be compared with that. advanced by Spiegelberg (see above). 1 Beard holds that ovulation takes place shortly after parturition in all Mammals, This is not the case in any moncestrous animals which have a prolonged ancestrous period. * Geyl, ‘Ueber die Ursache des Geburtseintrittes,”’ Arch. f. Gynik., vol. xvii., 1881. ’ Eden, ‘A Study of the Human Placenta,” Jour. of Path. and Bacteriol., vol. iv., 1897. 4 Williams, loc. cit. 544 ‘THE PHYSIOLOGY OF REPRODUCTION (11) Lastly, Williams calls attention to the fact that ex- cessive physical fatigue, sudden jars or violence, mental emotion, fright, &c., may lead to the termination of gestation in women. Similarly, it is well known that circumstances of a like nature may induce abortion in animals. Williams remarks that in all probability the onset of labour in most cases is due to a combination of a number of the above-mentioned causes. The main objection to all the theories which have so far been advanced is that they take no account of the complexity of the problem. An hypothesis may be fairly adequate as a general explanation of the duration of gestation, while at the same time taking no account of the immediate cause of birth. Thus, it is no doubt true that the time of parturition is determined largely by the necessities of the offspring, but this conclusion provides no sort of ex- planation as to why it is that the pains of labour in any one particular species generally commence at a certain fixed stage of development, and it remains for us to assume that it is one of the inherent properties of the uterus in the species in question that they should do so. Even on this assumption it is im- possible to avoid concluding that there must be some definite exciting cause, such as that postulated by Spiegelberg. PROLONGED GESTATION The duration of gestation in any one species usually varies within quite narrow limits, but under exceptional circumstances it may continue for an abnormally long period. Thus, Williams ! records a case of a woman with whom pregnancy extended for over eleven lunar months after the cessation of menstruation, instead of the usual ten lunar months (7.e. about 280 days). In this case typical labour pains were experienced at the end of the tenth month, but these subsided after a short time, and were not renewed until four weeks later, when they resulted in parturition. The same woman became pregnant a second time, when the period of pregnancy was again prolonged until the end of the eleventh month after the last menstruation. The children on each occasion were abnormally large and heavy 1 Williams, loc, cit. THE FEMALE GENERATIVE ORGANS = 545 at birth. Allen’ has recently recorded a number of further cases of prolonged gestation in women, the longest time chronicled being 334 days. It is stated that inertia of the uterus (due to fatty degeneration) is frequently associated with prolonged gestation; but the occurrence of the latter is no doubt often brought about by other causes which are at present unknown. Cases of prolonged gestation have been observed also among animals. Professor Ewart has informed the writer of a mare in his possession in which the period of gestation was extended to twelve months instead of the usual eleven. Other cases of prolonged gestation in mares, and also in cows, have been re- corded by Tessier 2? and Franck-Albrecht-Goring,*? and appear to be not uncommon. No satisfactory reason has been sug- gested to account for such cases. According to Pinard* prolonged gestation may occur in Rodents (Dipodillus simont, Meriones shawi, M. longifrons, Mus musculus, &c.), as a result of suckling a large litter produced just previously to a second gestation, the development of the young during the latter being arrested by a relative insufficiency of nourishment. In some cases the period of gestation was half as long again as the normal duration. Tue PUERPERIUM In multiparous women the uterus continues to contract and relax at more or less regular intervals after the expulsion of the placenta which marks the termination of the third stage of labour. The contractions which occur at this period give rise to the sensations commonly known as the “ after-pains.”” These may last several days, but are not generally very severe after the first day. They are particularly liable to occur when the child in Allen (L. M.), ‘‘ Prolonged Gestation,” Amer. Jour. of Obstet., vol. lv., 2 Tessier, ‘Recherches sur la Durée de la Gestation,” &c., Mém. de l’ Acad. des Sciences, Paris, 1817. * ¥ranck-Albrecht-Géring, “Die Trachtigkeitsdauer,’ Thiertirztliche Ge- burtshiilfe, vol. iv., 1901. + Pinard, Article ‘Gestation,’ Richet’s Dictionnaire de Physiologie, vol. vii., Paris, 1905. 2M 546 THE PHYSIOLOGY OF REPRODUCTION is put to the breast, a fact which seems to indicate a nervous connection between the uterus and the mammary glands. In primiparous women the tonicity of the puerperal uterus is usually greater than in multiparous ones, so that the uterus is capable of remaining during this period in a state of almost uninterrupted retraction unless blood clots or other foreign bodies are present in the cavity, in which case the organ under- goes movements in attempting to expel them. This tonic retraction of the uterus is an important factor in closing the blood sinuses, and so preventing bleeding. If, owing to any circumstance, the normal contraction and retraction of the uterus are interfered with, post-partum hemorrhage is liable to occur. This is not infrequently the case with white women who have migrated to the tropics, or with ill-nourished women in the slums, in whom, owing apparently to an inefficiency in the uterine nerve supply, the organ tends to become inert.’ It follows from what has been said that multiparous women are more liable to post-partum hemorrhage than primiparous ones.” According to Longridge the anzemic condition of the normal puerperal uterus is due partly to the effacement of the ovarian and uterine arteries which occurs when the uterus contracts. “ The reality of this occurrence is supported by an observation which can be made in many cases of Cesarian section ; in this operation it is noticed that as long as the uterus remains outside the abdomen it tends to bleed, but that as soon as it is dropped back bleeding ceases. It is not the warmth of the abdominal cavity that checks the bleeding, since it may continue when the uterus is wrapped in warm towels outside the abdomen. But the mere fact of pulling up the uterus opens out the concertina, as it were, and allows blood to flow through the arteries. If the bladder is full at the end of labour, the uterus is pushed 1 Longridge, The Puerperiwm, London, 1906. ® Longridge has pointed out, however, that the amount of post-partum discharge in multipara: is not as a rule in proportion to the severity of the “after-pains,” and consequently that the latter cannot be ascribed simply to defective retraction on the part of the uterus. He suggests, therefore, that the ‘‘ after-pains” in multipars are largely due to the uterus suffering from cramp resulting from the excessive exertion involved in dis- charging the child, THE FEMALE GENERATIVE ORGANS = 547 upwards, and slight loss may continue until the water is drawn off. As soon as the uterus is allowed to nestle down into its normal position the bleeding stops.” + The puerperal vaginal discharge is known technically as the lochia. It varies considerably in amount in different individuals, and changes in character as the puerperium proceeds, ceasing altogether about the middle of the third week. For the first few days it consists almost entirely of blood, which makes its way from the raw surface of the uterus and from lacerations caused during delivery. This is the lochia rubra. After three or four days it becomes paler, owing to the dilution of the sanguineous discharge by mucous secretion. This is called the lochia serosa. During the next three days the normal colour of the lochia is brown. This change (from pale pink to.brown) is due to the fact that the normal acidity of the vaginal secretion has by this time become re-established. Longridge suggests that the brown colour is probably the result of the formation of some such compound as acid hematin. After about the tenth day the lochia assumes a whitish or yellowish-white colour, owing to the admixture of leucocytes and the cessation of the blood flow. It is then known as the lochia alba. In many cases, however, traces of blood may be observed for weeks, but the lochia alba consists mainly of secretions from the vagina and cervix, together with leucocytes, a few epithelial cells, fragments of decidual tissue, and crystals of cholesterin. Micro-organisms are also present in the discharge, but recent investigations have shown that the lochia obtained directly from the uterine cavity does not contain bacteria, excepting in cases where the uterus is the seat of infectious processes.” The average quantity of the discharge has been computed by Gassner * at 1485 cubic centimetres, or about 50 ounces. Giles * estimated it as 10 ounces (or considerably less than Gassner’s ‘ Brock (Practitioner, January 1908) has recently expressed the opinion that puerperal bleeding is chiefly venous, pointing out that the discharge is usually very dark in colour. ® Krénig, Bakteriologie des Genitalkanales, &c., Leipzig, 1907. * Gassner, ‘‘ Ueber die Veriinderungen des Kérpergewichtes bei Schwang- eren, Gebirenden, und Wéchnerinnen,” Monatsschr. f. Geburtskunde, vol. xv., 1862. 4 Giles, ‘‘ On the Lochia,” Trans. Obstet. Soc., vol. xxxv., 1897. 548 THE PHYSIOLOGY OF REPRODUCTION estimation), and found further that in women who were accustomed to bleed freely at the menstrual periods the amount of the lochial discharge was beyond the average. According to Gassner, the discharge is generally less in women who suckle. The uterus after delivery becomes rapidly reduced in size. This process is. known as the involution of the uterus; it is completely effected in from five to eight weeks, the greatest reduction taking place in the first few days. Thus the freshly delivered uterus weighs on an average 1000 grams (or about 2 pounds), a week later it weighs only half that amount, at the close of the second week 375 grammes, and at the end of the puerperal period as little as 60 grammes (or about 2 ounces). Its decrease in size is such that by the tenth day after parturition the organ is once more confined to the cavity of the pelvis proper, and cannot be felt above the symphysis. The process of uterine involution is the result chiefly of changes occurring in the muscle walls.1. The size of the in- dividual cells becomes very markedly diminished, but there is little or no reduction in their number. Fatty degeneration does not take place in the muscular tissue. It is stated that the retraction of the muscle fibres produces a compression of the vessels, and that the comparatively anemic condition of the puerperal uterus, especially in the earlier stages, is due to this cause. Subsequently the uterus becomes more vascular again. The remains of the decidua which are not expelled at partu- rition undergo degeneration and are discharged in the lochia, leaving only the fundi of the glands and a certain amount of con- nective tissue from which the uterine stroma is renewed. The epithelium is re-formed from that of the glands, as shown by Friedlander,” Kundrat and Engelmann,’ Leopold,’ Krénig,> 1 The account given of the changes in the uterus during the puerperium is based largely on that given by Williams (Obstetrics, New York, 1904). See also Sellheim, “Das Wochenbett,” in Nagel’s Handbuch der Physiologie des Menschen, vol. ii., Braunschweig, 1906, where further references are given. 2 Friedlander, Physiologische und Anatomische Untersuchungen iiber den Uterus, Leipzig, 1870. 3 Kundrat and Engelmann, “ Untersuchungen tiber die Uterusschleim- haut,” Stricker’s Med. Jahrbuch, 1873. 4 Leopold, Studien iiber die Uterusschleimhaut, &c., Berlin, 1878. 5 Kronig, ‘“‘ Beitrag zum anatomischen Verhalten der Schleimhaut der Cervix und des Uterus,” &c., Arch. f. Gyndk., vol. 1xiii., 1901. THE FEMALE GENERATIVE ORGANS — 549 and others.’ Excepting in the position of the placenta, the new epithelium is completely regenerated by the end of the sixth week after delivery. The placental area at the end of parturition is marked by the presence of thrombosed vessels. It is raised above the general surface of the uterine wall, and is irregular in shape. It very soon diminishes in size, its diameter being not more than two centimetres long at the end of the puerperal period, although its former position may be detected as an area slightly stained by blood pigment for several months after delivery. Williams states that in the last month of pregnancy some of the sinuses at the placental area undergo thrombosis, but that this process becomes much more marked after the completion of labour, although many of the sinuses are simply compressed by the contracting uterine muscles without ever becoming thrombosed.?, The thrombi are eventually converted into ordinary connective tissue by a cellular proliferation from the lining membrane of the vessels. While this change is in progress the lining membrane presents a folded appearance somewhat resembling a typical developing corpus luteum. This is especially well seen about the fourth week after parturi- tion, but even up to the end of a year the convoluted appearance is still sometimes discernible.* The lumina of the arteries become reduced in size, but the thickening of their walls, which takes place during pregnancy, is an alteration of a more permanent character. This histological change affords a means of discriminating between a virgin and a parous uterus. The cervix uteri remains for some time after delivery as a soft, flaccid structure with lacerated edges, but it gradually undergoes involution, the lumen becoming narrower. The vagina takes about the same time to recover as the uterus. 1 Leusden, assuming the syncytial tissue of the deciduum to be of maternal origin, has suggested that it may assist in giving rise to the new epithelium (‘Ueber die Serotinalen Riesenzellen,” &c., Zettschr. f. Geb. und Gyndk., vol. xxxvi., 1897). 2 According to Longridge (see below in the text), thrombosis is of little or no importance in assisting the hemostasis of normal labour. 3 Williams (Sir J.), “Changes in the Uterus,” &c., Trans. Obstet. Soc., vol. xx., 1878. See also Helme, “Histological Observations,” &c., Trans. Roy. Soc, Edin., vol. xxxv., 1890. 550 THE PHYSIOLOGY OF REPRODUCTION After a first delivery its outlet remains permanently wider than before. The ruge reappear about the third week. The place of the hymen is taken by numerous small tags of tissue which become transformed into the caruncule myrtiformes. The condition of the labia majora and labia minora is generally flabby and atrophic as contrasted with that exist- ing in virgin women. The characteristic changes which occur in the breasts in connection ' with the secretion of milk are described Fia. 133.—Virginal exter- in the next chapter. : nal os (human), (From The quantity of urine passed during Williams’ Obstetrics, the first two days of the puerperium is SES) generally above the average. The urine frequently contains sugar, which may be either glucose or lactose. In the latter case it is generally believed that the sugar has been absorbed into the circulation from the changed mammary glands. When glycosuria occurs, it is probably comparable to post-opera- tive glycosuria (see p. 510 and pp. 571-573). Albumen may also be present in the urine in the first days of the puerperium. It is stated further that there is an increase in the amount of acetone ! (see also p. 507). As mentioned above, a marked leuco- cytosis occurs during labour. According to Hofbauer,” this becomes still more pronounced during the first twelve hours of the puerperium, after which Fic. 134.—Parous exter- the number of leucocytes in the blood nal os (human). (From falls again and in a short time becomes Earth eR lala : Appleton & Co.) normal. Henderson * states that on the fifth day the average number of leucocytes per cubic millimetre is 12,000, whereas immediately after parturition it is 21,000, as + Scholten, ‘‘ Ueber Puerperale Acetonurie,” Hegar’s Bettrdge zur Geb. und Gyndk., vol. iii., 1900. * Hofbauer, “Zur Physiologie des Puerperiums,’”’ Monatsschr. f. Geburt. und Gyndk., vol. v., 1897. * Henderson, ‘Observations on the Maternal Blood at Term and during the Puerperium,”’ Jour. of Obstet. and Gynecc., vol. i., 1902. THE FEMALE GENERATIVE ORGANS 551 compared with about 8000 in a normal woman. It is stated that there is a diminution in the number of red corpuscles during the first days of the puerperium, a circumstance which is commonly ascribed to the loss of blood at delivery and the lochial discharge. It is also said that the amount of hemoglobin is reduced, and that there is a relative increase in the quantity of fibrin and serum. Experiments show, however, that there is no appreciable shortening in the coagulation-time of the blood, such as has been supposed to account for the thrombosis of the sinuses.’ The pulse rate during the early days of the puerperium is usually stated to be somewhat below the normal, but according to Longridge such cases are unusual. Williams? says that the pulse is slowest on the second or third day, after which it becomes quicker, resuming its normal rate after about ten days. The temperature is ordinarily normal during the puerperium, the old idea that the commencement of milk secretion was associated with a rise of temperature having apparently no basis in fact, excepting in cases of infection. Little attention has been paid to the changes which occur during the puerperal period in animals. Strahl has shown * that the Mammalia with so-called full placenta (commonly called Deciduata) can be arranged under three groups according to the process of puerperal involution of the uterus. In the first group, to which Man and monkeys belong the epithelium is absent from the mucosa, and requires, therefore, to be re-formed in the manner described above. In the second group the placenta is spread out over the inside of the uterus as in the first group, but in addition to this the inside of the organ is covered by a layer of epithelium. This arrangement is found in Carnivores. In the Rodents we often meet with the third form ; here, towards the end of gestation, not only is the womb covered. with cell- tissue, but this epithelium also runs from the fiwbrie night underneath the placenta, undermining it till it is finally only adhering to the walls of the uterus by a slender cord carrying 1 Longridge, loc. cit. 2 Williams (Whitridge), doc. cit. 3 Strahl, ‘‘The Process of Involution of the Mucous Membrane of the Uterus of Tarsius spectrum after Parturition,’ Proc, Section of Sciences, Koninklijke Akademie van Wetenschappen te Amsterdam, vol. vi., 1904. 552 THE PHYSIOLOGY OF REPRODUCTION the vessels. It is evident, therefore, that the uteri of the second and third groups will resume relatively quickly their non- puerperal appearance. The principal changes that occur are the reduction of the surface epithelium, both by the casting off of superfluous parts and by the changing of larger cells into smaller ones, the advance of new epithelium to cover places that were bare,! and the reduction and consolidation of the connective tissue. The latter process is effected by the cells becoming more compact, as in the bitch, or by a reduction in the amount of inter-cellular substance, as in the hedgehog.” The puerperal changes in Tarsius are said to resemble those of Rodents.® Excepting in those animals which belong to the first group mentioned the lochial discharge is either very slight or absent altogether. The changes which take place in connection with the forma- tion of milk in animals are described in the next chapter. 1 Duval, ‘‘De la Régénération de YEpithélium des Corne utérine aprés la Parturition,” C. R, de la Soc. de Biol., vol. ii., Series 9, 1890. ® Strahl, ‘‘The Uterus of Erinaceus europeus after Parturition,” Proc. Sect. Sciences, Kon. Akad. Wet. Amsterdam, vol. viii., 1906. 3 For the puerperal changes in Tupaia see von Herwerden, loc. cit. CHAPTER XIII LACTATION “Nune femina queque, Cum peperit, dulci repletur lacte, quod omnis Impetus in mammas convertitur ille alimenti.” —LUcRETIUvS. THE possession of mammary glands is an essentially mammalian character. Their function is to provide nourishment for the newly born young. They are present in both sexes, but are usually functional in the female only. Their number and position vary considerably in different species. There may be only a single pair (Man), or as many as eleven pairs (Centetes). The number in any particular species usually bears a relation to the normal size of the litter, or to the requirements of the newly born offspring. Thus in the guinea-pig, in which the young are born in an advanced state of development, and can feed without being suckled, there are only two mammary glands, while in the rabbit, in which the newly born young are naked and help- less and the gestation period is far shorter, there are seven or eight mamme. In animals which possess a number of mammary glands, these are usually arranged in two nearly parallel rows along the ventral side of the thorax and abdomen. In other cases they are restricted to the thorax (Primates, excepting some lemurs, Cheiroptera, Sirenia, elephants, sloths); while in others again they are confined to the inguinal region (Un- gulates, Cetaceans). Tn the cow and other Ungulates the mamme are contained within a definite milk-bag or udder, which is surrounded by a fibrous envelope and is suspended below the abdomen. The udder is provided with milk cisterns or galactophorous sinuses into which the ducts of the gland open and convey the milk from the secretory acini. Each sinus communicates with the exterior by a teat, there being four teats in a cow, corresponding 553 554 THE PHYSIOLOGY OF REPRODUCTION to the four mammary glands (and sinuses) commonly called the four “‘ quarters.” One quarter may run dry without the others. There is a fibrous di ision consisting of yellow elastic tissue between the two lateral halves of the cow’s udder, but not between the anterior and posterior parts. In the sheep there are only two glands (lateral halves), sinuses, and teats (occasionally four), and the mare is similar excepting that there may be two or even four sinuses opening into one teat. In Monotremes the mammary glands are stated to be modified sweat glands, whereas in other mammalian orders they are commonly regarded as representing sebaceous glands.’ In Monotremes alone there are no teats, the orifices of the glands being mere scattered pores in the skin, the exuding milk prob- ably passing along the hairs, which in this region are arranged in bunches. In Echidna the orifices open into two depressions which have been called the mammary pockets.” Teats, which are present in all other orders of Mammals, are of two kinds. In one kind the skin in the region of the gland becomes raised up in a circular rim, and in this way gives rise to a tubular teat or nipple, into the base of which the ducts of the gland open. This form of teat occurs in Carnivora and Ungulata. In the other kind of teat the gland itself is raised into a papilla, as in Man and other Primates, in Rodents and in Marsupials. The use of the teats is to facilitate the process of sucking. In the Cetacea, however, where the action of sucking is incompatible with the sub- aqueous life of these animals, the ducts of the mammary glands are enlarged into reservoirs (somewhat similar to the galacto- phorous sinuses of Ungulates), from which the milk is ejected into the mouths of the young by means of a compressor muscle.* ’ Brouha and certain other authorities regard the mammary glands in all the Mammalia as modified sweat glands (‘‘ Recherches sur les Diverses Phases du Développement et de l’ Activité de la Mamelle,” Arch. de Biol., vol. xxi., 1905. This paper contains many references). Eggelung regards the mam- mary glands either as homologous with sweat glands, or else as organs which are sui generis being. derived independently from the primitive merocrine skin-gland (‘‘ Ueber den wicktiges Stadium in der Entwickelung der mensch- lichen Milchdriise,” Anat. Anz., vol. xxiv., 1904). 2 Wiedersheim, Comparative Anatomy of Vertebrates, Parker’s transla- tion, 2nd Edition, London, 1897. 3 Flower and Lydekker, An Introduction to the Study of Mammals. London, 1891. LACTATION 555 In the male mammal, as just mentioned, the mamme do not usually function, though milk is occasionally produced in Man at birth and at puberty, and more rarely at other times. Male goats and sheep have been known to yield milk exceptionally, and the same is also said to be the case with male rats! (see p. 584). STRUCTURE OF THE MAMMARY GLANDS The mammary glands are composed typically of a number of lobes, which are themselves divisible into lobules. Each lobule consists of connective tissue in which the convoluted ducts of the gland are bound together. If these ducts are traced backwards they are seen to arise from groups of secretory alveoli. If they are traced forwards they are found to unite together to form the lactiferous ducts, which in the human subject are from fifteen to twenty in number, and open to the | exterior by minute apertures through the teat. The lactiferous | ducts at their point of origin from the lobular ducts are provided with reservoirs in which the milk collects during the periods of | glandular activity (¢.e. during lactation). These reservoirs in some animals are of a very considerable size (e.g. whales, as _ described above). The duct walls consist of areolar tissue containing some unstriated muscle fibres. They are lined internally by short columnar epithelial cells which become flattened in the proximity of the nipple. A quantity of fat generally covers the surface of the gland, excepting the nipple. This fat is connected both with the skin in front and with the glandular tissue behind. Like the latter it is lobulated by processes of areolar tissue. The nipple also is formed of areolar tissue with unstriated muscle fibres. It is richly supplied with vessels which give it an erectile structure. The glandular tissue also is plentifully supplied with vessels, which vary in size according to the condition of the gland. The glands in Man are innervated by branches from the anterior and lateral intercostal cutaneous nerves. Sensitive papille are present on the surface of the nipple, and around it there is a small area of skin, on which the ducts of little secretory glands open to the exterior. ’ Wiedersheim, loc. cit. 556 ‘THE PHYSIOLOGY OF REPRODUCTION In the secretory cells of the lactating mammary gland an active and a resting condition can be distinguished. In the latter the lumina of the alveoli are wide, and the cells of the lining epithelium form a single flat layer with centrally situated nuclei. In the active condition the epithelial cells are long and columnar, and project into the lumina, and some of them have two nuclei. In these cells numbers of granules and globules accumulate, = BES Fiq@. 135.—Section of mammary gland of woman. after de Sinéty.) a, lobule of gland ; 6, acini lined by cubical epithelium ; c, duct; t, connective tissue. the former being probably of a protein nature, and the latter of a fatty composition. Gradually the alveoli become charged with a fluid containing detached cells and fatty globules. The detached cells are usually filled with granules, staining with osmic acid and seemingly identical with the colostrum corpuscles which have been observed to occur in milk in the first few days after parturition, and occasionally also at other times. ‘These colostrum corpuscles have been seen to exhibit amceboid move- ments, and so are probably leucocytes which have wandered into the lumina of the alveoli. The secretory fluid also con- 1 Schafer, “The Mechanism of the Secretion of Milk,” Tezt-book of Physiology, vol. i., Edinburgh, 1898. LACTATION 557 tains cells which are supposed to have been detached from the epithelium, but, as will be seen presently, there is some doubt regarding this point. The alveoli secrete milk during lactation, not merely while suckling is going on, but also at other times, so that milk tends to collect in the ducts and especially in the reservoirs. It has Fic. 136.—Section of mammary gland (human) during lactation (highly magnified). u, acini; b, duct. been calculated that the udders of a cow could not contain the quantity of milk which can be obtained from them at one milking, so that in such cases at least it seems certain that the process of secretion must be carried on during the time that the milk is being drawn. Furthermore, the milk which is drawn latest has been shown to have a different composition from that which is first obtained, the proportion of solids to liquids undergoing an increase as the process of milking is continued. This, how- 558 THE PHYSIOLOGY OF REPRODUCTION ever, is believed to be due partly to the larger globules of fat meeting with greater resistance in passing through the ducts and so being retained until the end of milking. Lehmann’ has recorded an experiment in which a solution of sulphin- digotate of sodium was injected into a vein of a goat which (From Schafer, after von Ebner.) a, a’, a”, alveoli variously cut and distended by secretion ; g, g’, com- mencing ducts ; 7, connective tissue. was immediately afterwards milked. By the time the udders had been almost completely emptied, a blue tinge appeared in the milk. After an interval of about an hour and a half the animal was again milked, when it was found that the injected sulphindigotate had penetrated in sufficient quantity to render the milk quite blue. Three different hypotheses have been put forward regarding 1 Lehmann, “Beitrige zur Physiologie der Milchbildung,” Dze land- wirthschaftlichen Versuchs-Stationen, vol. xxxiii., 1887. LACTATION 559 the manner in which the substances of which the milk is formed pass out from the secretory cells. According to one view, the cells themselves break loose and become disintegrated, setting free their contents in the alveoli of the gland, just as in the case of the sebaceous glands. Another theory states that the cells simply excrete the substances into the alveolar lumina without becoming detached or destroyed themselves, as with the submaxillary mucous gland. According to the third hypothesis the mammary gland in its mode of activity occupies a position midway between the Frq@. 138.—Section through an alveolus with fat drops in cells. (From Schafer, after von Ebner.) e, cells of alveolus ; &, cells of basement membrane (m) ; 7, connective tissue. sebaceous and submaxillary glands; some of the cells simply discharging their contents into the lumina, while with others, the central part of the cell, containing a degenerate daughter nucleus, breaks away and becomes disintegrated, leaving the basal portion still in position. It has already been mentioned that the mammary glands of all Mammals, with the exception of the Monotremes, are usually regarded as being of the nature of modified sebaceous glands. It was partly on account of this belief that certain of the older writers held the view that the secretion of milk was the result of a fatty degeneration leading to a complete disintegration of the secretory cells of the mammary gland.' According to this 1 Virchow, Die Cellular-Pathologie, Berlin, 1871. 560 THE PHYSIOLOGY OF REPRODUCTION theory the colostrum corpuscles were the detached epithelial cells. In opposition to this theory, it has been pointed out that there is no evidence of the extensive cell multiplication, such as would be required in order to supply the large number of cells which, according to this hypothesis, would necessarily become detached. Heidenhain’ has shown that if this theory is correct, the cells of the gland must be completely renewed as often as five times in one day in order to provide the solid constituents of the secretion. The second of the above-mentioned theories receives con- siderable support from the circumstance that it has the analogy of the great majority of secretory glands.? Moreover, the recent investigation of Bertkau * points strongly to the conclusion that any appearances of disintegration which the secretory cells possess is due to imperfect fixation. This author states that he found no necrobiosis of any kind in these cells, and he believes that milk formation is a purely secretory process. The colostrum corpuscles, according to those who hold this view, are of the nature of wandering leucocytes. The third theory was first suggested by Langer, and has since been adopted, with various slight modifications, by Heidenhain,* Steinhaus,® and Brouha® and others. According to their view the cells of the gland lengthen out, so that their ends come to project freely into the lumina of the alveoli. The projecting portions then undergo a process of disintegration before or after becoming detached, and the cell substance passes into solution to form the albuminous and carbohydrate constitu- ents of the milk. The fat droplets which collect in the disintegrat- ing part of the cell give rise to the milk fat. The basal portions of the cell remain in position without being detached, and subse- quently develop fresh processes, which in their turn become 1 Heidenhain, ‘‘ Die Milchabsonderung,” Hermann’s Handbuch der Phy- stologte, vol. iv., 1883. 2 Schafer, loc. cit. 3 Bertkau, ‘‘ Kin Beitrag zur Anatomie und Physiologie der Milchdriise,” Anat. Anz., vol. xxx., 1907. 4 Heidenhain, loc. cit. 5 Steinhaus, ‘‘ Die Morphologie der Milchabsonderung,” Arch. f. Anat. u. Phys., Phys. Abth,, Suppl., 1892. § Brouha’s paper (loc. cit.) contains a full account of the literature. LACTATION 561 disintegrated. It is believed, however, that some cells simply discharge their fat droplets and other contents into the lumina, while otherwise remaining intact.’ Steinhaus states that mitotic division of the cell nuclei in the actively secreting mammary glands is of frequent occur- rence, and that the daughter nuclei which lie in the outer portions of the cells degenerate and share in the general process of dis- sociation. Szabé* also records the occurrence of two or more nuclei in the same cell during lactation, and similar evidence of nuclear division has been observed by others. Moreover, it is argued that this view is in no way inconsistent with the generally accepted homology between the mammary and sebaceous glands, since it is easy to understand how, in the course of evolutionary development, the mode of secretion in the glands in question might have undergone an alteration, whereby the process of disintegration in the actively secreting cells became gradually lessened as the character of the secretion changed. On the other hand, if we suppose that the cells of the mammary gland merely extrude their secreted materials without undergoing any histological disintegration, it is more difficult to uphold the homology in question. Lastly, it should be mentioned that those who, like Steinhaus, support the theory of partial disintegration, do not regard the colostrum corpuscles as detached epithelial cells, as Heidenhain did, but agree with those who uphold the purely secretory theory in supposing the corpuscles to be of the nature of “mast cells,’ or basophil leucocytes which have wandered inward from the connective tissue of the gland, as already described, and have made their way into the lumina of the alveoli.? 1 Brouha, loc. cit.; also ‘‘Les Phénomenés histologiques de la Sécrétion lactée,” Anat. Anz., vol. xxvii. 2 Szabé, ‘‘Die Milchdriise im Ruhezustande und wahrend ihrer Thitig- keit,” Arch. f. Anat. u. Phys., anat, Abth., 1896. 3 For references to further literature upon the physiology of milk forma- tion see Basch, “Die Physiologie der Milchabsonderung,”’ Hirgeb. des Phys., 1903, Jahrg. See also the following for references to the histology :— Bizzorzero and Ottolanghi, «« Histologie der Milchdriise,” Merkel and Bonnet’s Ergeb. d. Anat. u. Entwick., vol. ix., 1900, and von Ebner, “Von der Ge- schlechtsorganen,” Kélliker’s Handbuch der Gewebelehre des Menschen,vol. iii., 1902. 2N 562 THE PHYSIOLOGY OF REPRODUCTION Ture Composition AND Properties oF MILK Milk is essentially an emulsion, its white appearance being caused by the reflection of the innumerable fat globules which it contains in suspension. These globules, which are from ‘0015 to 005 millimetres in diameter, tend to float chiefly at the top, where they help to form the cream, or that part of the fluid which is richest in fatty constituents. The specific gravity of both human and cow’s milk is from about 1-028 to 1-034." When the cream is skimmed off the specific gravity of course rises. It is not proposed in the present work to deal more than very briefly with the composition and properties of milk in different animals.? Human milk and cow’s milk have been most fully investigated, and it will suffice in this place to give a short account of their respective constituents. The average composition of cow’s milk as compared with human milk is as follows :— Cow's. Human. Water ¢ . 7 : ‘ . 883 88°8 Proteins . ‘ : 3 : . 30 1:0 Fats . 5 ‘ é , 4 ‘ 3°5 35 Carbohydrates . : 2 : e 4°5 65 Salts . ; A 3 d : ‘ 0-7 0-2 100°0 1000 The proteins of milk are caseinogen, lactalbumen, and lacto- globulin. Of these caseinogen is the most important. This is the substance which is acted on by the ferment of rennet, pro- ducing the well-known clotting or curding of milk, when the caseinogen is converted into whey albumen and insoluble casein. Lactoglobulin and lactalbumen are only present in small quantities. The fats of milk, which occur in small globules as just de- scribed, are olein, palmatin, and stearin, with small quantities of butyrin, capronin, and other fats of lower composition. Lecithin. and cholesterin are also present in small amounts, at 1 Halliburton, ‘‘The Chemical Constituents of the Body and Food,” Schifer’s Text-book of Physiology, vol. i., Edinburgh, 1898. 2 See Halliburton, loc. cit., and Schafer. LACTATION 563 any rate in cow’s milk. The percentage of volatile fatty acids is less in human than in cow’s milk. Lactose or milk-sugar is the carbohydrate of milk, but other carbohydrates (animal gum, dextrin, &c.), have also been stated to occur. Lactose under the influence of certain micro-organisms becomes converted into lactic acid, which causes the souring of milk, Milk is rich in calcium and potassium salts (especially in calcium phosphate), but magnesium, sodium, and other salts (chiefly chlorides) are also present in small quantities. The amount of iron in human milk is very slight, while in cow’s milk it is practically absent altogether. Bunge* has pointed out that whereas the inorganic salts in milk are present in different proportions from those found in the blood plasma, these proportions are almost identical with those occurring in the young animal. He supposes this similarity to indicate an adaptation to the needs of the young. This point is illustrated in the following table, which gives the respective amounts of mineral constituents present in a hundred parts of ash of (1) the young pup; (2) dog’s milk, and (3) dog’s serum. (1) Young (2) Dogs (3) Dog’s Pup. Milk. Serum. KO . 2... BS 10°7 24 NaO . . . . 88 61 52'1 CaO. . é » 358 34-4 21 MgO. . . . 16 1s. 05 FeOy 5 . . « O84 0-14 0-12 PO, . . . . 398 37°5 59 Cl : i . = 7:3 12°4 47°6 Small quantities of oxygen, nitrogen, and carbon dioxide gases have been found in solution both in human and in cow’s milk. 1 Bunge, Lehrbuch der Physiologische und Pathologische Chemie, Leipzig, 1887, and various original papers. C/. Abderhalden, ‘“‘ Die Beziehungen der Wachsthumsgeschwindigkeit der Siuglinge zur Zusammensetzung der Milch,” &e., Zettschr. f. Phys. Chem., vol. xxvi,, 1899, and other papers by the same author in the same journal (vols. xxvi. and xxvii.). For further references see Lusk, The Science of Nutrition, Philadelphia, 1906. It is stated also that the rennin of the stomach is specifically adapted for the coagulation of the casein produced by the female of the same race. 564 THE PHYSIOLOGY OF REPRODUCTION The chief difference in the composition of cow’s milk as compared with human milk is the relatively high percentage of proteins, fats, and salts, and the correspondingly low percentage of lactose present in cow’s milk. Colostrum is the milk which is secreted during the first two or three days after parturition. It contains less caseinogen than ordinary milk, but considerable quantities of albumen and globulin enter into its composition. It coagulates on boiling. The characteristic colostrum corpuscles have already been described. The mammary glands of newly born animals sometimes secrete small quantities of what is popularly called “ witches’ milk.” This secretion contains most of the constituents of normal milk, but the solid substances are usually less in amount. It has an alkaline reaction.’ THe INFLUENCE oF DIET AND OTHER FACTORS ON THE CoMPOSITION AND YIELD oF MILK The composition of the milk in any one species is subject to some amount of variation, which is due to various causes. Thus, the differences in the composition of cow’s milk are said to depend on the following factors: (1) The breed, (2) The advance in the period of lactation, (3) The season of the year, (4) The length of the interval between the times of milking, (5) The occurrence of sexual excitement, (6) Situation and climate, (7) Meteorological changes, and (8) The character of the food.* These factors may now be briefly discussed. 1 For fuller information about the constituents and properties of milk, with tables of composition for different animals, and numerous references to the literature, see Halliburton, loc. cit. See also Raudnitz, «‘ Bestandteile, Eigenschaften und Veranderungen der Milch,”’ Ergeb. der Phys.. 1903, Jahrg. 2, where certain later papers are referred to ; and Abderhalden, loc. cit. ° Crowther, Milk Investigations at Garford, Leeds, 1904. Droop Rich- mond, ‘‘The Composition of Milk,’ Analyst, vol. xxxi., 1906. Lauder, “The Variation in the Composition of Milk,” Bulletin XI. issued by the Edinburgh and East of Scotland College of Agriculture, 1906. Crowther, “« The Chemical Composition of Butter,” Trans. Highland and Agric. Soc., vol. xix., 1907. Gilchrist and Jones, “ Dairy Investigations in the North-East of England,” Trans. Highland and Agric. Soc., vol. xviii., 1906, and vol. xix., 1907. LACTATION 565 That the yield and composition of the milk varies in the different breeds is generally admitted. Thus Jersey cows yield a larger proportion of butter fat than Ayrshires. But of all the factors enumerated above, diet is perhaps the most important. The richest and al:o the most abundant supply of milk is usually yielded when the food supply is liberal. As a result of giving food rich in protein substances, the milk supply tends to contain a larger quantity of protein, sugar, and fat (especially the latter). Schafer has pointed out, however, that because an excess of a particular organic principle in the food causes an increase of certain constituents in the milk, it must not be supposed that these constituents are necessarily formed directly from such material, “for the effect may be produced indirectly by the functions of the gland-cells becoming modified, according to the nature of the pabulum they are receiving. Looked at in this light, certain substances may be said to stimulate the cells of the glands to increased activity in all directions, tending to the production of a larger quantity of milk rich in all kinds of sol d constituents ; whilst other substances may be looked upon as stimulating the cells in a special manner, tending to the increased production of certain only of the constituents of the milk.” ! According to Crowther’s researches on cows, change from a highly nitrogenous diet to one relatively poor in nitrogen causes secretion of a greater quantity of milk, but there is a decrease in the fat content, this being more pronounced in the morning than in the evening milk. A change in the reverse direction effected an improvement in the quality of the milk. Concen- trated food given either in the morning or evening tended to increase the fat content of the morning milk, but had little or no effect upon the evening milk. These alterations were found to persist without appreciable diminution for fully five weeks after the change of treatment. There are a number of preparations in the market, known as galactagogues, which are said to increase the flow of milk in women, but, according to Williams, any virtue which they possess is due largely to the quantity of fluid which is taken + Schiifer, loc. cit. There is evidence also that an abnormal diet during and previous to pregnancy may arrest the normal mammary development. See Watson (B. P.), ‘The Effect of a Meat Diet on Fertility and Lactation,” Proc. Roy. Soc. Edin., vol, xxvii., 1907. 566 THE PHYSIOLOGY OF REPRODUCTION with them. It is stated also that certain particular foodstuffs have a very appreciable effect upon the quantity and quality of milk in cows. Thus bean-meal is said to increase the flow of really good milk, unless it is given in immoderate quantities. Brewers’ and distillers’ grains are likewise described as having a beneficial influence upon the milk supply, but if given too freely they tend to injure the breeding capacity, and in conse- quence are most used in town dairies where the cows are not bred from.2, Many substances ingested by the mother pass unaltered into the milk. It is well known that certain foods (e.g. turnips) cause an unpleasant taste or smell in the milk of cows to which they are supplied. Lehmann’s experiment, in which sodium sulphindigotate was injected into the veins of a goat, and shortly afterwards made its appearance in the milk, has been already referred to (p. 558). So also it has been found that immunity from disease may be acquired by young animals being suckled by a female which had previously become immune, the antibody to the disease being absorbed in the ingested milk. It is generally recognised that the nature of the surroundings has an influence over the mammary secretion. For example, the composition of the fat in the milk of cows varies with the condition of the animals. Circumstances tending to cause discomfort usually lower the proportion of volatile acids present in the butter-fat, but the variation in the composition is very irregular, and appears to depend partly upon the nervous temperament of the cow. Extremes of heat and cold are said to produce a decrease in the percentage of volatile acids, a fact which has been put forward as an explanation of the general poorness in these compounds of butters from Siberia and other cold climates. Unseasonable and inclement weather is believed to have a similar influence.? In women exercise in the open air may not infrequently increase the flow of milk. Nervous and mental influences or any cause which affects the general metabolism may so change the character of the secretion in women as to make it no longer fit 1 Williams, Obstetrics, London, 1904. % Wallace (R.), Farm Live Stock of Great Britain, 4th Edition, Edinburgh, 1907. 3 Crowther, loc, cit. LACTATION 567 for the child. Violent emotion or shock have been known to lead to the complete suppression of the mammary secretion.’ The employment of certain drugs also influences it. Thus atropine, if given in sufficient quantities, stops the secretion altogether, or if supplied in smaller amounts causes the milk to become more concentrated. The occurrence of menstruation in women, or of heat in certain animals, may have a deleterious influence upon the milk, and so upon the offspring (see p. 334). In the case of cows, estrus generally has a marked effect on the milk-yield, which as a rule shows at first a perceptible diminution, followed usually at the next milking by a yield well above the average. The fat content is generally at first considerably reduced, but at the following milking is sometimes abnormally high, or may be still abnormally low. On the two or three days preceding the outward manifestations of heat, the fat content tends to be decidedly above the average. Castration is stated to have a beneficial effect upon goat’s milk, relieving it of the characteristic hircine odour, increasing the quantity of butter, casein, and phosphoric acid (though decreasing the lactose present), and producing a greater and more long-continued secretion.2 The removal of the ovaries in cows may also tend to improve the quality of the milk, rendering it richer than when the animals have been some months pregnant.* The advance of lactation may be accompanied by changes both in the amount and in the composition of the mammary secretion, but the changes vary greatly in different individuals. In cows, the milk fat secreted in the first few days after parturi- tion is poor in volatile acids, but it tends to improve rapidly during the first few months, the improvement being maintained until near the close of the lactation period, z.e. in most cases near the approach of the next parturition.* 1 Williams, loc. ctt. * Oceanu and Babes, ‘‘Les Effets Physiologiques de 1l’Ovariotomie,” C. R. de V Acad. des Sciences, vol. cxl., 1905. 3 Wallace, loc. cit. 4 In cows which are ‘drying off,” the percentage of volatile acids in the butter fat is very low. See Crowther, loc. cit. 568 THE PHYSIOLOGY OF REPRODUCTION Tue DuRATION OF LACTATION The duration of the lactation or nursing period in the different species of animals is governed mainly by the needs of the young. In such animals as the guinea-pig, in which the young are born in a sufficiently advanced state of development that they are able to fend for themselves, the length of the lacta- tion period is relatively short and inconstant, while in other animals, belonging to the same order of Mammals, the young are born helpless, and are dependent for some weeks upon their mother’s milk. In the larger animals the period of nursing is of course Jonger, but in them also its average duration appears to depend largely upon the ne¢essities of the offspring. The natural period of lactation in the cow is between nine and ten months, allowing for an interval of from two to three months to prepare for the next milking period. The duration of the period in any given animal depends to some extent upon such factors as diet and general treatment as described above, but there is much individual variation. Some cows continue to give milk until the next calving, but without a rest they are liable to yield a less abundant supply in the succeeding year." It follows that a new gestation period in the cow has no arresting influence over the mammary secretion. Cows which have been castrated during lactation may yield milk for years without any cessation, and thus give on the aggregate a larger supply than cows which calve annually in the ordinary way. It is well known that constant milking acts as a stimulus to the secretory activity, and that cows which are not milked soon “run dry.” In the human female a year may be regarded as the normal period of nursing, any longer time involving what is known as hyperlactation. The practice of hyperlactation is said to be common, but it is to be deprecated in the interests of the infant.” It would appear that if continuous suckling is encouraged, the 1 Wallace, loc. ctt. 2 Dingwall Fordyce, ‘‘An Investigation into the Complications and Disabilities of Prolonged Lactation,” &c., an extension of papers published in the Lancet, the British Medical Journal, and the British Journal of Children’s Diseases, 1906. LACTATION 569 supply of milk in strong, healthy women may last almost inde- finitely. As already mentioned, menstruation not infrequently commences to recur during the lactation period, and the latter may overlap gestation until within a short time of delivery. Tur Discuarce oF MILK The discharge of the milk from the lactiferous ducts which occurs during sucking is due partly to the direct mechanical pressure, and partly to the action of the muscular tissue which is present in the walls of the ducts and in the nipple. The muscular mechanism appears to be stimulated reflexly by the action of sucking. The contraction of the muscles in the nipple causes this structure to stiffen, and it is suggested that this action has the effect of keeping open the orifices of the ducts, and thus permitting the free outflow of milk. It is probable also that the discharge of the secretion is assisted in some degree by the swelling of the entire mammary gland resulting from a reflex dilatation of the vessels; but if the secretory process is very active, and the ducts are heavily charged, the flow of milk may take place almost automatically, and with hardly any external stimulus. THE FoRMATION OF THE ORGANIC CoNnSTITUENTS OF MILK The principal organic constituents of milk are peculiar to the secretion, a fact which shows that they are elaborated in the mammary glands themselves, and not elsewhere in the body. It is stated, however, that a relatively small amount of caseinogen is present in the secretion of the sebaceous glands, from which, as already remarked, itis commonly supposed that the mammary glands ® have been derived in the course of evolution. Nothing appears to be definitely known regarding the method of forma- tion of the caseinogen of milk,® but it has been suggested that it is derived from the degenerate nuclei of the gland cells. 1 Schafer, loc. cit. ® Neumeister, Lehrbuch der physiologischen Chemie, vol. ii., Jena, 1895. * Thierfelder, ‘‘Zur Physiologie der Milchbildung,” Pfliger’s Archiv, vol, xxxii,, 1883. 570 THE PHYSIOLOGY OF REPRODUCTION The precise method by which the milk fat is formed is like- wise unknown. It may be derived from protein material, the change being effected in the cells of the gland, or some of it may possibly have its source in fat which has already been formed elsewhere, and carried to the mammary glands in the blood or lymph. There is no reason for supposing that the cells of the glands do not possess, in common with most other tissues, the power to elaborate fat. On the other hand, there is definite his- tological evidence that they have this capacity (see above, p. 560). Moreover, the special composition of the milk fat seems to be by itself conclusive evidence that it is constructed within the mammary glands. The suggestion has been made that the leucocytes which migrate through the epithelium and make their way into the secretory fluid may help to bring fatty globules into it,! but there seems no necessity for assuming that this is the case. The fat formation which takes place in the cells of the lacteal glands in the process of milk manufacture has been compared with the fatty degeneration which occurs in other tissues, milk being nothing more than an emulsion of the fat of butter in a solution of salts, proteins, and sugar. “ What occurs as a normal process in the cells of the lacteal glands occurs under pathological conditions in much greater extent in very various tissues, and leads almost always to incurable and fatal losses, since as a rule no reparation is made by the younger cells.” 2 “ The production of milk,” says Virchow,? “in the brain instead of in the lacteal glands, constitutes a form of brain softening. The same process that in the one place affords the happiest and sweetest results, in another induces a painful and bitter wound.” It has already been mentioned, however, that the fat of milk has a special composition of its own, so that too much stress must not be laid upon a resemblance between the secretion of milk and the pathological formation of other fluid substances in different parts of the body. The mode of formation of the sugar of milk has been the 1 Michaelis, ‘‘Beitrage zur Kenntniss der Milchsecretion,’ Arch. f. Mikr. Anat., vol. xxi., 1898. 2 Verworn, General Physiology, Lee’s Translation from the second German edition, London, 1899. 3 Virchow, loc. cit. LACTATION 571 subject of some controversy. Bert 1 supposed that it was formed from glucose which was absorbed by the cells of the mammary gland from the circulating blood. The glucose, according to this view, was manufactured in the liver, or, at any rate, elsewhere than in the mammary gland. Bert based his hypothesis upon two experiments in which the glands were removed from goats which afterwards became pregnant. The urine of each animal was tested during pregnancy to see if any reducing agent was present, but no such substance could be found prior to the birth of the kid. On the other hand, for several days after parturition a substance which reduced cupric sulphate was dis- covered in each case. Bert concluded that this was glucose. He supposed further that the reducing body present in the urine of the two goats represented glucose which in normal animals would have been converted into lactose in the mammary glands. The experiments were afterwards repeated by Moore and Parker,” who operated likewise upon two goats, and obtained results which were the direct opposite of those of Bert. These authors consequently concluded that the complete process of lactose formation takes place in the cells of the mammary glands. The question was subsequently reopened by Porcher,*® who also repeated Bert’s original experiment on a goat. After par- turition in the operated animal, an intense glycosuria is said to have occurred, the phenylhydrazine test showing that the substance present in the urine was glucose, and not lactose or some other reducing body. Porcher also removed the mammary glands from four goats and one cow during lactation, and for a few hours after the operation obtained marked glycosuria. As a result of those experiments, taken in conjunction with those of Bert, he concluded that the truth of the latter’s theory was established beyond all doubt. More recently the writer, working in conjunction with Dr. 1 Bert, ‘‘Sur l’Origine du Sucre du Lait,” C. R. de Acad. des Sciences, vol. lxxxviii., 1884. ? Moore and Parker, ‘‘ A Study of the Effects of Complete Removal of the Mammary Glands in Relationship to Lactose Formation,” Amer. Jour. of Phys., vol. iv., 1900. ® Porcher, ‘‘Sur l’Origine du Lactose,” C. R. de l’Acad. des Sciences, vol. cxxxviii,, 1904. ‘De la Lactosurie,” Monographies Cliniques, Paris, 1906, 572 THE PHYSIOLOGY OF REPRODUCTION Kirkness,! carried out a series of experiments upon guinea-pigs. The mammary glands were removed prior to pregnancy (four cases) or during pregnancy (one case). The urine was tested for sugar both before and after parturition, but none was found in any of the experiments. Other experiments showed that glycosuria may occur after parturition in normal unoperated animals, but that it does not do so invariably.?, When glycos- uria does so take place, its occurrence is probably comparable to post-operative glycosuria, the cause of which is not under- stood. The glycosuria observed by Porcher after the removal of the mammary glands during lactation may perhaps be explained as an ordinary post-operative effect, and cannot be cited as proof of Bert’s hypothesis. According to Thierfelder ® and Landwehr,* a formation of lactose may take place if pieces of fresh mammary tissue are kept in normal salt solution at body temperature. The lactose is said to be formed from a precursor which Landwehr identified as “animal gum ” or carbohydrate of low reducing power. According to Foi, there is a diminution of glucose in the venous blood coming from the mammary glands, but the amount of glucose and other carbohydrates present in the blood during lactation is no greater than in normal blood.° Muntz*® has put forward the view that the lactose of the mammary secretion is formed by the union of glucose, the normal sugar of the organism, with galactose, which is 1 Marshall and Kirkness, “ On the Formation of Lactose,” Biochem. Jour., vol. ii., 1906. 2 Puerperal glycosuria and lactosuria have been described in women in a number of cases. Lactosuria is also stated to occur not infrequently in the late stages of pregnancy both in women and animals, the lactose in such cases being presumably derived from the mammary glands by a process of absorp- tion. See Hofmeister, ‘‘ Ueber Laktosurie,” Zedtsch. f. Phys. Chemie, vol. i., 1877; Porcher, De la Lactosurie, 1906 ; and ‘‘L’Origine du Lactose,” Arch. Internat. de Phys., vol. viii., 1909. See also p. 510. 3 Thierfelder, ‘‘Zur Physiologie der Milchbildung,” Pfliiger’s Archiv, vol. xxxii., 1883. 4 Landwehr, “Ueber die Bedeutung des tierischen Gummis,’’ Pfliiger’s Archiv, vol. xl., 1887. ’ 5 Fou, ‘Sul’ Origine del Lattosio del Latte,” Arch, die Fis., vol. v., 1908. ® Muntz, ‘‘Sur )’Existence des Eléments du Sucre de Lait dans les Plantes,” Annales de Chim. et de Phys., vol. x. LACTATION 573 supposed to be derived directly by hydrolysis from certain polysaccharide substances introduced in the food. It is pointed out further, that such substances are present in plants which form the normal diet of certain animals. It would appear, however, that there is no direct evidence that lactose is actually formed in this way. Moreover, this theory can scarcely be applied to carnivorous animals, as Porcher + has pointed out. There is, therefore, but little evidence that lactose is ela- borated in the mammary glands from any closely related carbo- hydrate precursor carried thither from elsewhere in the body. It is of course obvious that this sugar must be derived ultimately from compounds contained in the food, and it would seem not improbable that it is manufactured partly from protein sub- stances, and not merely from other carbohydrates. Tue NorMAL GROWTH OF THE MAMMARY GLANDS The growth of the mammary glands in the rabbit has been described by Miss Lane-Claypon and Starling, from whose paper the following account is taken.? In the virgin animal of about eight to twelve months old mammary tissue cannot ordinarily be detected with the naked eye, but in stained preparations of the connective tissue sur- rounding the nipple, it is possible to see the ducts which com- prise the gland. These are generally restricted to an area of not more than one centimetre broad. Sections show that the gland at this stage consists entirely of ducts which are lined with a single layer of flattened epithelium, and end blindly. No traces of alveoli are to be seen in the gland. By the fifth day after conception a marked change has taken place in the gland, which now appears, on reflecting the skin from the abdomen, as a clearly differentiated pink area, circular in shape, and surrounding the position of each nipple. The diameter of this area is from about two to three centimetres. 1 Porcher, “Sur la Physiologie de la Mamelle,” Jour. de Méd. Vet. de UV Ecole de Lyon, Sept. 30, 1905. ? Lane-Claypon and Starling, “An Experimental Inquiry into the Factors which Determine the Growth and Activity of the Mammary Glands,” Proc. Roy. Soc., B., vol. lxxvii., 1906. See also Brouha, loc. cit. 574 THE PHYSIOLOGY OF REPRODUCTION Sections through the gland show that it still consists entirely of ducts, but that these are in a state of active proliferation. The epithelial lining no longer consists of a single cellular layer, but is two or three cells deep, while the individual cells are more swollen than those of the virgin gland, and mitotic figures are commonly seen. The mammary gland now grows rapidly, so that on about Fig. 139.—Section of developing mammary gland of horse. (From Schafer, after Hamburger.) 8, sebaceous glands ; v, blood-vessels, the ninth day after conception, on reflecting the skin from the abdomen, the entire surface is found to be covered with a layer of glandular tissue, the margins of the individual glands being practically contiguous, each of them having a diameter of from five to eight centimetres. Sections show that the formation of alveoli (i.e. definite secretory structures) has begun at this period, especially at the periphery, where the gland is generally somewhat thicker than in other parts. From this stage onwards the growth of the ducts and the LACTATION 575 formation of alveoli proceed rapidly, so that by the twenty- fifth day of pregnancy the whole surface of the abdomen has become covered by mammary gland tissue, which may be half a centimetre thick. This tissue is seen in sections to consist for the most part of alveoli, in the-cells of which fat globules are in process of formation. From about the ninth day onwards to the twenty-fifth it Fic. 140.—Section of mammary gland (human) showing developing alveoli. (From Schifer, after von Ebner.) b, connective tissue ; d, undeveloped alveoli; d’, partially developed alveoli; g, blood-vessel ; m, portion of duct. is usually possible to squeeze a watery fluid from the nipples. During the last days of pregnancy this fluid assumes the char- acteristics of normal milk, so that by the time of parturition, which occurs in the rabbit on the thirtieth day after conception, the glands are full of milk. The multiparous rabbit differs from the virgin in pos- sessing ready-formed alveoli at the beginning of pregnancy. 576 THE PHYSIOLOGY OF REPRODUCTION Consequently the amount of mammary growth during the gestation period of the multiparous animal is relatively less. The changes which take place in the human female and in other animals during pregnancy are in a general way similar to those occurring in the rabbit. In women after the second. month the breasts are said to offer a nodular sensation on palpa- tion, this being due to the hypertrophy of the mammary alveoli. The nipples also enlarge, and at the same time become more erectile and pigmented, while the areola surmounting the nipple becomes broader and pigmented also, in dark individuals being often almost black. The hypertrophy of the sebaceous glands in the areola results in the formation of the so-called glands of Montgomery, which appear as small round elevations. As already mentioned, during the later months of pregnancy the thin yellowish fluid known as colostrum can generally be expressed from the nipples. The mammary glands are said to undergo growth at puberty, and there can be no doubt that a slight hypertrophy generally takes place in connection with each period of procestrum and cestrus. These changes must be ascribed to ovarian influence, which, as has already been shown, is probably responsible for the changes which occur at such times in the other generative organs. Professor J. P. Hill informs me that in certain Marsupials the amount of mammary growth occurring at each ovulation period is so marked as to render it difficult to distinguish such animals from pregnant ones. Gellhorn! refers to a case of a woman who had abnormal mammary glands with seven nipples in the neighbourhood of the mons veneris, and who yielded milk at each menstrual period. Other similar cases have been recorded. This phenomenon is, of course, contrary to the more usual tendency for menstruation to be in abeyance during lactation. Tue FactoRS WHICH ARE CONCERNED IN THE PROCESS oF Mammary GRrowTH It has just been mentioned that the mammary glands in the female begin to undergo enlargement at the period of puberty in correlation with the increase in ovarian activity. In Man 1 Gellhorn, “Abnormal Mammary Secretion,” Jour. Amer. Med. Assoc., Nov. 21, 1908. LACTATION 577 the difference between the glands in the two sexes is first mani- fested at this time. The slight hypertrophy which occurs in connection with each procestrous period has been referred to, while the great: growth which the glands undergo during preg- nancy has also been described. It would appear, therefore, that the stimulus to mammary growth, which arises originally in the ovary, is afterwards derived from the developing embryo. This view is supported by the fact, which has been established experimentally, that mammary development succeeded by lactation after parturition can occur in animals whose ovaries have been extirpated at about mid-pregnancy or even at a slightly earlier period. It was formerly supposed that the connection between the growth of the mammary glands and that of the embryo in the uterus was a nervous one—that is to say, that the hypertrophy of the glands was determined reflexly through the central nervous system. There is now, however, abundant evidence that such is not the case. This is shown, for example, by the experiment performed by Goltz and Ewald,* which has already been referred to in considering the factors concerned in parturition. The lumbo-sacral part of the spinal cord was completely exsected in a pregnant bitch, so that all possible connection between the mammary glands and pelvic organs through the nervous system was destroyed. Pregnancy was accompanied as usual by mammary development, and after parturition, lactation occurred normally. Routh’s case,? in which normal lactation took place in a woman with complete paraplegia below the level of the sixth dorsal vertebra, has also been referred to (p. 538). Moreover, it has been shown by Eckhard ® that after complete severance of the nerves (branches of the external sper- matic) passing to the mammary gland, the activity of the latter, and consequently the supply of milk, are in no way affected.* 1 See pages 490 and 538. * Routh, ‘‘ Parturition during Paraplegia, with Cases,” T'rans. Obstet. Soc. vol. xxxix., 1897, 5 Eckhard, Bettrage zur Anat. u. Phys., vol. i., Giessen, 1855. 4 Eckhard’s experiments have been repeated by others with somewhat contradictory results (see Basch, loc. cit.); Rébrig (‘‘ Experimentelle Unter- suchungen iiber die Physiologie der Milchabsonderung,” Virchow’s Archiv, vol. lxvii., 1876) found that the external spermatic nerve contained 20 578 THE PHYSIOLOGY OF REPRODUCTION Further evidence in support of the conclusion that the con- nection between mammary and foetal growth is not nervous in character is supplied by those experiments in which portions of gland were successfully transplanted to abnormal positions in the body. Thus in an experiment on a guinea-pig Ribbert?} grafted mammary tissue from the normal position to the neigh- bourhood of one of the ears. Notwithstanding the fact that the transplanted gland had lost its normal nervous connections, it underwent enlargement during a subsequent pregnancy, and afterwards secreted milk. Pfister” states that he performed a similar experiment on a rabbit, and obtained a similar result. The inference is, therefore, that the relation between the growth of the mammary glands and the development of the foetus in the uterus is chemical in nature. As Miss Lane-Claypon and Starling have pointed out, the phenomenon of fertilisation succeeded by foetal growth involves the occurrence of changes in the ovaries and in the uterus (both in the muscle and in the mucous membrane), as well as the forma- vasomotor fibres for the vessels of the mammary gland, and that these affected its secretory activity by controlling the blood supply. Mironow (‘‘ De l'Influence du Systtme Nerveux des Glandes Mammaires,” Arch. des Sciences Biol, de St, Petersbourg, vol. iii., 1894) states that artificial stimulation causes a reduction in the quantity of secretion. He states further that whereas section of the external spermatic on one side has no effect on the secretion, section on both sides diminishes it, but that the diminution only comes on gradually after a number of days. After complete severance of all the nerves in pregnant animals the glands may continue to grow and yield milk after parturition. Basch (loc. cit.) states that extirpation of the celiac ganglion or transection of the spermatic nerve does, not inhibit the secretory process, but increases the number of colostrum corpuscles. There is abundant evidence of a general kind that the central nervous system in some way exerts an influence on the mammary gland. Thus the effects of nervous shock in altering or inhibiting milk secretion in women are well known. Moreover, the occurrence of uterine contractions on putting the child to the breast, and so stimulating the nipples, is evidence of a neryous connection. It would seem probable, therefore, that though the mammary gland is essentially an automatic organ, the connection of which with the generative organs is through the vascular rather than the nervous system, yet it is under the regulating control of the latter by means of secretory or vasomotor fibres, 1 Ribbert, ‘‘ Veber Transplantation von Ovarium, Hoden und Mamma,” Arch. f. Entwick.-Mechanik, vol. vii., 1898. 2 Pfister, ‘“‘ Ueber die reflektorischen Beziehungen zwischen Mamme und Genitalia muliebria,” Bettrdge zur Geb. und Gyndk., vol. v., 1901. LACTATION 579 tion of an organ of complicated structure—the placenta—the function of which is to nourish the developing young. The question arose, therefore, as to whether the foetus or either of the above-mentioned organs was not the direct source of formation of a hormone or chemical excitant which, after circulating in the blood stream, acted as a stimulus to mammary growth. It has been shown that the ovaries of rats can be removed at, any time during the second half of pregnancy (or somewhat earlier) without interfering with the course of foetal develop- ment or mammary growth, and, moreover, that lactation may take place normally after the ovaries have been thus extirpated.* It is evident, therefore, that though the ovaries may represent the original source of the stimulus necessary for mammary hypertrophy, they are not essential for the continuance of the process, and exercise no sort of control over the final stages which precede the secretion of milk.? Furthermore, it has been shown that the mammary glands undergo normal development in cases of extra-uterine foetation in which the growth of the uterus is relatively small. This observation clearly indicates that the source of the stimulus in question is not to be sought in the hypertrophied uterus. A consideration of these and other facts led Miss Lane-Claypon and Starling to the conclusion that one or other of the products of conception (7.e. either the foetus or placenta), or possibly both, were the seats of origin of the specific chemical stimulus which brought about mammary growth. Halban ® had already formed the opinion, chiefly on clinical grounds, that the specific stimulus arose mainly in the chorionic villi and placenta. More recently Ancel and Bo-in have laid stress on the close parallelism between the development and regression of the cor- pora lutea and mammary glands respectively in the rabbit. Marshall and Jolly, ‘‘ Contributions,” &c., Phil. Trans., B., vol. excviii., 1905. ° Gf. Foges, ‘‘ Beitriige zu der Beziehung von Mamma und Genitale,” Wien, klin. Woch., 1908, No. 5. Griinbaum (Deut. med. Wochenschr., 1907, No. 20) has shown that mammary secretion may also occur after hysterectomy. 5 Halban, ‘ Die innere Sekretion von Ovarium und Placenta und ihre Bedeutung fiir die Function der Milchdriise,” Arch. f. @yndk., vol. 1xxv., 1905. 580 THE PHYSIOLOGY OF REPRODUCTION This parallelism is said to exist even in the absence of pregnancy.' Miss Lane-Claypon and Starling appear to have been the first to deal with the problem experimentally. In an initial series of experiments they injected extracts or emulsions of ovaries obtained from pregnant rabbits into other rabbits either sub- cutaneously or intraperitoneally. In two further series of experiments rabbits were injected with uterine and placental emulsions or extracts. In no case, however, did the injections produce any effect on the mammary glands, although in certain of the experiments in which ovarian or uterine substance was employed, marked swelling and congestion of the uterus were afterwards observed. The effect of injecting foetal extract was next tried, and this led to definite positive results. When repeatedly injected into female rabbits the extract was found to produce a genuine development of the mammary glands which simulated the normal growth which occurs during pregnancy. In one case a virgin rabbit received fifteen injections of extract made from many embryos of the same species. The injections were spread over a fortnight, at the end of which the rabbit was killed. It was found that a secretory fluid could be expressed from the nipples, and that on reflecting the abdominal skin all the mammary glands had grown to the size which is ordinarily reached in a rabbit about eight days pregnant. In another rabbit which received twenty-four injections, spread over five and a half weeks, the effects produced were still more marked. Further experiments showed that boiled extract was as effective as unboiled, and the conclusion is therefore drawn that in all probability the specific secretion or hormone is capable of with- standing boiling. It was shown also that the substance in question could be obtained equally well from different parts of the foetus, that it passes through a Berkefeld filter, and that it is not retained to any appreciable extent by the kieselgur in Buchner’s method for extracting cell juices. Fod states that extract of ox foetus, when injected into rabbits, produced development of the mammary glands. He concludes, therefore, that the stimulating substance which causes mammary 1 See page 343. LACTATION 581 growth is not specific—z.e. not peculiar to any one kind of mammal. Fo’ says also that if the extract is heated to 110° the active substance is destroyed, and no result is produced by injection." Tur FACTORS WHICH ARE CONCERNED IN THE COMMENCE- MENT OF MAMMARY SECRETION ‘Since the growth of the mammary glands was apparently due to a specific chemical stimulus arising in the foetus, it was natural to suppose that the beginning of the actual secretory process which marks the cessation of growth was caused by the removal of this stimulus—in other words, by the expulsion of the foetus. In this connection it is interesting to note that abortion or premature labour is often followed by the appearance of milk in the breasts. The idea that lactation is due to the removal of an inhibition appears to have been entertained first by Hildebrandt, who put forward the suggestion that the developing embryo exerts an influence whereby the cells of the mammary gland are protected from those autolytic disintegrative processes which are supposed to occur during active secretion. That the act of secretion is to be ascribed to autolytic processes of the gland, is, according to Miss Lane-Claypon and Starling, highly improbable, and there is no evidence that the autolysis of the gland cells would give rise to the specific constituents which characterise milk. Halban * has put forward the view that the specific stimulus for mammary development arises in the placenta, while the active secretion of the mammary glands is determined by the expulsion or death of the placenta.* Keiffer,>5 on the other hand, has entertained the contrary conception, that the secretion of milk is due to a ferment elaborated in the placenta and trans- 1 Fon, ‘‘Sui Fattori che determinano |’Accrescimento e la Funzione della Ghiandola Mammaria,”’ Arch. di Fis., vol. v., 1908. ®? Hildebrandt, “ Die Lehre von der Milchbildung,’’ Hofmeister’s Bcttrage, vol. v., 1904. 3 Halban, loc. cit. 4 He points out that in cases of abortion the secretion of milk may not begin until some days after the death of the child. This he believes to be due to the circumstance that the placenta remained alive during the interval. * Keiffer, ‘Recherches sur Anatomie et la Physiologie de la Mamelle,”’ Bull. de la Soc. Belge de Gyn. et d’Obstét., 1901-2. 582 THE PHYSIOLOGY OF REPRODUCTION ferred to the maternal circulation at the time of birth. These theories are based mainly on clinical evidence of a somewhat questionable value. Miss Lane-Claypon and Starling have shown that after multi- parous rabbits are injected with foetal extract milk is secreted by the glands. This result is explained as follows: “The multi- parous rabbit differs from a virgin rabbit in possessing ready- formed alveoli, z.e. secretory structures. On the theory which we have adopted, the circulation of the mammary hormone should. diminish any secretion in these alveoli, and should cause growth. In all our experiments at least twenty-four hours elapsed between each two injections. It is probable that the hormone was rapidly absorbed from the injection, and was therefore present in the blood of the animal only for a certain fraction, say a few hours, out of the twenty-four. While it was circulating it should cause building up of the secreting cells. Directly, however, it ceased to circulate, the cells would enter into dissimulative activity resulting in secretion. By our injections, therefore, we are not able to imitate the continuous stimulus of pregnancy. We are rather producing each day a pregnancy of a few hours followed by a parturition. These factors should therefore result in the production of milk in any animals possessing the structures (i.e. the alveoli) which are capable of secreting milk, and would therefore account for the secretion of milk observed by us in all the cases where multiparous rabbits were the objects of our experiment.” It has been shown that in the foetus itself there is an increased growth of the mammary glands during the last part of pregnancy, while it is well known that a secretion is often formed in the glands of the newly born. Halban has explained this secretion as the result of removal of the inhibitory influence— that is to say, it is due to the same circumstance as the secretion in the mother. Miss Lane-Claypon and Starling point out that the complete change which occurs in the environment of the newly born animal must induce equally profound changes in the metabolism, and there is consequently no difficulty about the conclusion that the formation of the mammary hormone ceases with the commencement of extra-uterine life. The general conclusions reached by these authors may be LACTATION 583 ~ summarised as follows: The anabolic changes associated with the growth of the mammary glands are due to the assimilatory efiects of a hormone elaborated in the fcetus and carried thence through the placenta by the foetal and maternal circula- tion. The removal of this stimulus produces those katabolic changes which are involved in the breaking down of the built-up tissues and the consequent formation of milk.1 CRITICISMS There are certain objections to be urged against these con- clusions, which, however, are not claimed by the authors to be as yet firmly established. Thus in certain animals the period of lactation may continue for an almost indefinitely long time, so that it would appear as if the katabolic processes involved in milk-secretion were out of all proportion to the anabolic pro- cesses concerned in the building up of the gland tissue. For example, it is stated that in castrated cows the mammary glands may remain perpetually active for years and years so long as milking is regularly continued (see p. 568). Moreover, in some animals (e.g. mares) a secretion of milk may be induced artificially as a result of a mechanical stimulus set up by repeated attempts at milking. In one instance known to the writer. a mare which had never had a foal could be made to yield milk at any time for years. It would seem probable, however, that in such cases there must have been an original tendency to secrete, and that this tendency was merely augmented by the emptying of the galactophorous ducts. This is in accordance with the view that the emptying of the ducts during normal suckling constitutes a physiological stimulus which acts on the gland cells, either directly or by means of a reflex. Heape * has pointed out as an objection to Starling’s theory of the foetal hormone that virgin bitches are frequently known to produce milk, and that the quantity secreted may even be sufficient to admit of their rearing pups. He also refers to a statement by 1-According to Fo& (loc. cit.) fetal extract has no inhibitory influence on mammary secretion. * Heape, ‘ The Source of the Stimulus which causes the Development of , the Mammary Gl Gland and the Secretion of ‘Milk, ,” Proc. Phys..Soc., Jour. of J Phys., vol. xxxiv., 19060 ay 584 THE PHYSIOLOGY OF REPRODUCTION Tegetmeier and Sutherland! that mules may yield milk in sufficient abundance to rear a foal. He concludes, therefore, that the source of the stimulus which excites the development of the mammary glands is to be sought in the ovary rather than in the foetus. Instances have also been recorded by Knott? and others, in which males have secreted milk, thus showing that mammary development is not necessarily even a female function; but such cases are at all events exceedingly rare.? Knott mentions cases in which suckling occurred in a bull, a male goat, a wether, and in men. He also cites instances of virgin girls who were nurses secreting copious supplies of milk as a consequence of allowing infants to suck their nipples; and thus he supports Heape’s objection to the foetal hormone theory. Gellhorn ‘ cites similar cases, including one of a virgin monkey (Cercopithecus). Another case is mentioned of a woman who suckled children un- interruptedly for forty-seven years, and in her eighty-first year had a moderate but regular supply of milk,® thus showing that mammary secretion may continue exceptionally for long after the menopause, and presumably, therefore, in the absence of any sort of stimulus from the generative organs. This observation further supports the idea referred to above, that normal suckling acts by itself as a physiological stimulus for mammary secretion. A more forcible objection to the theory of the foetal hormone is supplied by the Monotremata, which are the lowest order of Mammalia. These animals are oviparous, the developing embryo being contained in an egg, which does not enter into any sort of connection with the uterine wall. Halban,® however, has made the suggestion, which is quoted by Miss Lane-Claypon and Starling, that since the embryo goes on increasing in size during its passage down the female generative tract, and since the shell of the egg is porous, it is not impossible that substances may diffuse outward from the embryo and be absorbed by the uterine mucous membrane,and so be carried into the maternal circulation. 1 Tegetmeier and Sutherland, Horses, Asses, Zebras, Mules, and Mule Breeding, London, 1895. 2 Knott, ‘Abnormal Lactation,” &c., American Medicine, vol. ii. (new series, June), 1907. Cf. Wiedersheim (see p. 555). 3 The occasional occurrence of milk secretion in the newly born, both males and females, is well known. 4 Gellhorn, loc. cit. 5 Knott, loc. cit. 5 Halban, loc. cit. LACTATION 585 Miss Lane-Claypon and Starling, however, do not contend that the foetus is the sole source of the stimulus for mammary development. On the other hand, they specially mention that the growth of the mammary glands which occurs at puberty, for instance, can only be attributed to ovarian influence, since it does not take place if the ovaries have been previously re- moved. It isnot improbable, therefore, that an ovarian stimulus is also responsible for initiating the growth of the glands in Monotremes, while Hill’s observations on certain Marsupials afford a clear indication that such is the case in these animals (see p. 576). APPENDIX Lombroso and Bolaffio’ have described an experiment in which two female rats were grafted together so that their re- spective circulatory systems were presumably united. Subse- quently to their union they each became pregnant, but at different times. They afterwards produced young, one pre- maturely, and the other at full term. The mammary glands of each underwent the characteristic changes, but they occurred independently and not synchronously. The authors cite this result as evidence against the foetal hormone theory. Moreover, as a result of this and another similar experiment, they conclude that parturition is not induced by a chemical excitant circulating in the blood (see p. 542). On the other hand, in the case of the Bohemian pygopagous twins, Rosa-Josepha, the mammary glands of both are de- scribed as having been similarly and simultaneously affected by the pregnancy of Rosa, who bore a healthy boy on April 17, 1910. Milk was afterwards secreted by the breasts of Josepha as well as of Rosa, although Josepha had never conceived.? * Lombroso and Bolaffio, ‘‘La Parabiosi e la Questione dei Fattori che determinano la Fuz Funzione mammaria e l’Insorgenza del travaglio di parto,” ltt della Soc. Ital. di Obstet, e Gin., vol. xv., 1909. 2 British Med. Jour., Part IJ., May 28, 1910. The twins are described as being united posteriorly by 4 common sacrum, but the iliac bones are separate. There is a common anus, perineum, clitoris, and meatus urinarius, but the labia majora are double. The urethra is single for an inch above the meatus, but then it bifurcates. The ureters are normal. The desire to micturate is said to be distinct, but not the desire to defecate. CHAPTER XIV FERTILITY ‘“*Nam multum harmonize veneris diferre videntur. Atque alias alii complent magis ex aliisque, Succipiunt aliz pondus magis inque gravescunt. Atque in eo refert quo victu vita colatur.”—LUCRETIUS. TuE rate of propagation in any species of animal depends not only upon the average number of young born in each litter, but also upon the frequency of recurrence of the sexual season and the duration of the reproductive period in the animal’s life. The frequency of recurrence of the sexual season—that is to say, the cestrous cycle—in different species of Mammals has been discussed at some length in an early chapter of this work. In the present chapter it remains to consider a little more closely some of the causes which control this periodicity and the factors which affect, fertility. Theduration of the reproductive period of ananimal’sexistence extends in most cases from a time when that animal has almost reached its full size until the beginning of senescence, so that the normal period of generative activity in the individuals of any given species bears a definite relation to their average length of life. In the male the sexual maturity is usually reached later than in the female. Moreover, in the male there is no definite ending of the reproductive period, since in Man, for example, the power of producing spermatozoa continues in a gradually diminishing degree even in extreme old age, whereas in the female, on the other hand, the climacteric marks the cessation of generative activity (see below, p. 672). Broadly speaking, the average number of young produced in a litter in any species of Mammal is inversely proportional to the average size of the animals belonging to that species. Thus, in most species of Ungulates twins are the exception rather than the rule; and there are seldom more than two young produced at a time even in sheep and goats, which show a greater degree of fertility than most Ungulates. The sow, however, is 586 FERTILITY 587 exceptional in having very large litters, as many as seventeen young being sometimes born. On the other hand, in small Mammals such as Rodents large litters are the rule; the rat, for example, being known occasionally to bear as many as sixteen or even twenty young; but the Cheiroptera, or bats, are remark- able for their relative infertility, only one young one ordinarily being produced at a time, although the common bat is no larger than the mouse. Generally speaking, only one young one is produced in those animals in which the period of gestation exceeds six months. The number of teats characteristic of the species also affords an approximate indication of the average size of the litter. “ Among women, the birth of twins occurs once in about eighty deliveries. Triplets, quadruplets, quintuplets, and even higher figures, are occasionally observed; they are very un- common, and the rarity is progressive with the number. The normal or ordinary rule in woman is to bear one child at a time ; and the next most frequent condition is temporary or persistent sterility—two points in which she signally differs from what is generally believed [of animals].’’1 Veit’s statistics? for 13,000,000 births in Prussia showed that twins were produced once in 89 cases, triplets once in 7910, and quadruplets only once in 371,125 cases. There is some evidence also that the frequency of occurrence of multiple pregnancy in women depends upon the race or climate, and that it is commoner in cold than im warm countries.? Herbert Spencer * elaborated a theory whereby he explained the relative degrees of fertility in the different races of men and animals. According to this theory the power to sustain individual life and the power to produce new individuals are inversely proportional, a conclusion which is summarised in the generalisa- tion that Individuation and Genesis vary inversely. When there is an abundant food supply and a favourable environment, 1 Matthews Duncan, Fecundity, Fertility, Sterility, and Allied Topics, Edinburgh, 1866. 2 Veit, “Beitrige zur geburtshiilflichen Statistik,” Monatsschr. f. Geb., vol. vi., 1855. 3 For further statistics and references see Williams, Obstetrics, New York, 1904. 4 Spencer, Principles of Biology, revised edition, vol. ii., London, 1899. 588 THE PHYSIOLOGY OF REPRODUCTION and the necessary expenditure of energy is relatively slight, the cost of Individuation is much reduced, and the rate of Genesis is correspondingly increased ; in other words, there is a high degree of fertility. Spencer cited the Boers, the Kaffirs, and the French Canadians as examples of fertile races in which the rate of increase is associated with a nutrition that is greatly in excess of the expenditure. Conversely, he concluded that a relative increase of expenditure leaving a diminished surplus reduces the degree of fertility, and in support of this statement adduced evidence that bodily labour tends to make women less prolific, since the reproductive age is said to be reached a year later by women of the labouring class than by middle-class women. Spencer applied his generalisation to animals as well as to Man, and attempted to explain thereby the average contrast between the fertility of birds and Mammals. “Comparing the large with the large and the small with the small, we see that creatures which continually go through the muscular exertion of sustaining themselves in the air and propelling themselves rapidly through it, are less prolific than creatures of equal weights which go through the smaller exertion of moving about over solid surfaces. Predatory birds have fewer young ones than predatory Mammals of approximately the same sizes. If we compare rooks with rats, or finches with mice, we find like differences. And these differences are greater than at first appears. For whereas among Mammals a mother is able, unaided, to bear and suckle and rear half-way to maturity a brood that probably weighs more in proportion than does the brood of a bird; a bird, or at least a bird that flies much, is unable to do this. Both parents have to help; and this indi- cates that the margin for reproduction in each adult individual is smaller.” Spencer cites numerous instances from among both birds and Mammals illustrating the effects of different degrees of activity upon fertility. The hare and the rabbit, for example, are closely allied species, “ similar in their diet, but unlike in their expenditures for locomotion. The relatively inert rabbit has six young ones in a litter, and four litters a year; while the relatively active hare has but two to five in a litter. That is not all. The rabbit begins to breed at six months old; but a FERTILITY 589 year elapses before the hare begins to breed. These two factors compounded result in a difference of fertility far greater than can be ascribed to unlikeness of the two creatures in size.” Furthermore, Spencer refers to the case of the bat, which has been already mentioned as being abnormally unprolific in proportion to its size. The relatively low rate of multiplication is of course ascribed to a relatively high rate of expenditure resulting from the habit of flying. In a similar way Spencer explains such well-known facts as that hens cease to lay when they begin to moult. ‘‘ While they are expending so much in producing new clothing, they have nothing to expend for producing eggs.” There can be little doubt that Spencer’s generalisation is in the main true, but it is equally certain that it cannot be applied indiscriminately to explain the relative degrees of fertility in all animals, and consequently it must not be pressed too far. Some of the more special factors which control fertility are referred to below, and it is evident that many (though not all) of these fall within the scope of Spencer’s generalisation. The rate of increase as distinguished from the rate of repro- duction (in any given species) depends upon a large number of factors, of which the rate of reproduction is only one. Errect oF AGE Matthews Duncan? has discussed at some length the varia- tion which occurs in the fertility of women according to their age. He adduces statistical evidence showing that the fertility of the female population increases gradually from the commence- ment of the child-bearing period of life until about the age of thirty, and then it gradually declines. He shows also that the fertility is much greater before the climax is reached (at thirty years) than after it is passed. These conclusions, however, apply merely to the actual productiveness (i.e. the number of births), as opposed to the capability of bearing children, which Duncan designates the fecundity. By eliminating from his calculations all women not living in married life, Duncan arrives at the following conclusions, which are based on statistics showing the 1 Duncan, loc. cit. 590 THE PHYSIOLOGY OF REPRODUCTION productiveness of wives:! (1) “That the initial fecundity of women gradually waxes to a climax, and then gradually wanes ” ; (2) ‘‘ That initial fecundity is very high from twenty to thirty- four years of age’; and (3) “ That the climax of initial fecundity is probably about the age of twenty-five years.” The fecundity of the average individual woman may be described, therefore, as forming a wave which, starting from sterility, rises somewhat rapidly to its highest point, and then gradually falls again to sterility. There can be no doubt that animals as a general rule tend to follow a similar law. A dog generally has fewer puppies in its first litters than afterwards, while in its declining years there is a diminution until sterility is reached once more. The same is said to be the case with the bear, the elk, and other animals,? but there are obviously many individual exceptions. Geyelin ® gives the following table showing the fertility of the domestic fowl at different ages :— First year after hatching 15 to 20 | Sixth year after hatching 50 to 60 Second ‘i fs . 100 ,, 120 | Seventh _,, i . 35 ,, 40 Third 3 $s 120 ,, 1385 | Highth __,, - . 15 ,, 20 Fourth 3 a . 100 ,,115 | Ninth a 55 . I ,, 10 Fifth 5 3 . 60 ,, 80 Furthermore Minot * observed that in guinea-pigs the size of the litters increased with age during the first sixteen months of their lives. Errects oF ENVIRONMENT AND NUTRITION That the generative system in animals is peculiarly susceptible to changed conditions of existence has been recognised from early days. Thus Aristotle® commented on the increased fertility of sheep in a favourable environment. In more recent 1 It is, of course, obvious that it is impossible to determine statistically the real “fecundity’’ (using the term as defined by Duncan) in view especially of the practice of volitional interference with conception (see below, p. 621). 2 Duncan, loc. cit. 3 Geyelin, Poultry-Breeding in a Commercial Point of View, London, 1865. 4 Minot, ‘‘Senescence and Rejuvenation,’ Amer. Jour. of Phys., vol. xii., 1891. 5 Aristotle, History of Animals, Bohn’s Library, London. FERTILITY 591 times Buffon,! among others, remarked on the fact that domestic animals breed oftener and produce larger litters of young than wild animals belonging to the same species; and Darwin, who made the same observation, attributed the increased fertility of the former to a long habituation to a regular and copious food supply without the labour of seeking for it. “‘ It is notorious how frequently cats and dogs breed, and how many young they produce at birth. The wild rabbit is said to breed four times yearly, and to produce each time at most six young; the tame rabbit breeds six or seven times yearly, producing each time from four to eleven young. . . . The ferret, though so closely confined, is more prolific than its supposed wild prototype [the polecat]. The wild sow is remarkably prolific ; she often breeds twice in the year, and bears from four to eight, and sometimes even twelve, young; but the domestic sow regularly breeds twice a year, and would breed oftener if permitted ; and a sow that produces less than eight at birth ‘is worth little, and the sooner she is fattened for the butcher the better.’ The amount of food affects the fertility of the same individual; thus sheep which on mountains never produce more than one lamb at birth, when brought down to lowland pastures frequently bear twins. The difference apparently is not due to the cold of the higher land, for sheep and other domestic animals are said to be extremely prolific in Lapland.” 2 Darwin remarks that birds afford still better evidence of increased fertility resulting from domestication. Thus, in its natural state the female of Gallus bankiva, the wild representative of the common fowl, lays only from six to ten eggs; the wild duck lays from five to ten eggs, as compared with eighty or a hundred produced by the domestic duck in the course. of the year. Similarly, the turkey, the goose, and the pigeon are more fertile in the domestic state, though this is not the case with the pea-fowl. Among plants also there are countless instances of increased fertility as a consequence of cultivation? 1 Buffon, Histoire Naturelle, Paris, 1802. * Darwin, The Variation of Animals and Plants under Domestication, Popular Edition, vol. ii., London, 1905. * Cf. also Spencer (Joc. cit.), who discusses this question at some length in connection with his generalisation that Individuation and Genesis vary Inversely, See above, p. 587. 592 'THE PHYSIOLOGY OF REPRODUCTION On the other hand, it is well known that wild animals, when removed from their natural conditions and brought into captivity, often become partly or completely sterile. Darwin discusses this phenomenon at some length, and cites numerous cases from different groups of animals and birds. The Indian elephant, for example, seldom breeds in captivity, although kept in a perfectly healthy condition and in its native country. On the other hand, most members of the Suide are known to breed in menageries and zoological gardens, while many Ruminants breed readily in climates widely different from their own. Carnivorous animals breed somewhat less freely in confinement, and show considerable variation in different places. The Canide tend to be more fertile than the Felidee, while the members of the bear group breed less easily. Rodents as a general rule fail to breed after being brought into captivity, but there are several exceptions. Monkeys also when kept in con- finement only rarely have young ones. Many of these animals, however, although failing to conceive, are known to copulate freely. This is especially the case with captive bears and monkeys, in which the typical phenomena of procestrum and cestrus occur. It would seem probable that the sterility under these circum- stances results from a failure to ovulate, due possibly to an absence of ripe follicles in the ovaries. Among birds, members of the hawk group very seldom breed in captivity. The graminivorous birds show considerable variation, some, like the canary, breeding freely in aviaries (although it was some time before it became fully fertile), while others, like the finches, only occasionally reproduce their kind when kept in confinement. Gallinaceous birds, on the other hand, show an unusual capacity to breed in captivity, and the same is the case with pigeons, ducks, and geese. Certain kinds of gulls also are known to breed readily when kept in open spaces in zoological gardens. As pointed out by Darwin, there is other evidence that changed conditions of life may induce a disturbance of the sexual functions. Thus when conception does occur under confinement, the offspring are sometimes born dead or ill-formed, or otherwise show signs of insufficiency of nourishment. The mother’s milk may fail, indicating an interference with those FERTILITY 593 factors which control the mammary metabolism. Moreover, in animals which are characterised by a periodic growth of the secondary sexual characters, these sometimes fail to make their appearance. The male linnet in captivity does not assume its characteristic crimson breast, or the male bunting (Emberiza passerina) the black colour on its head. Other birds, such as a pytrhula and an oriole, may acquire the appearance of the hen, while a falcon (Falco albidus) has been observed to lose its adult plumage.! These facts seem to show that the generative meta- bolism may be so altered by changed conditions of existence as to induce not merely a state of sterility, but also an interference with the secretory activity of the essential organs of reproduction.? Darwin says: “ We feel at first naturally inclined to attribute [such results] to loss of health, or at least to loss of vigour ; but this view can hardly be admitted when we reflect how healthy, long-lived, and vigorous many animals are under captivity, such as parrots, and hawks when used for hawking, chetahs when used for hunting, and elephants. The reproductive organs themselves are not diseased;? and the diseases from which animals in menageries usually perish are not those which in any way affect their fertility. The failure of animals to breed under confinement has been sometimes attributed exclusively to a failure in their sexual instincts. This may occasionally come into play, but there is no obvious reason why this instinct should be especially liable to be affected with perfectly tamed animals, except, indeed, indirectly through the reproductive system itself being disturbed. Moreover, numerous cases have been given of animals which couple freely under confinement, but never conceive ; or, if they conceive and produce young, these are fewer in number than is natural to the species.... Change of climate cannot be the cause of the loss of fertility, for whilst 1 Darwin, loc. cit. 2 The relation between the gonads and the secondary sexual characters, and the apparent dependence of the latter upon the secretory activity of the former, are discussed in Chapter IX. * Few observations have been made upon the condition of the gonads in animals in captivity, but Branca (‘‘ Recherches sur le Testicule et les Voies spermatiques dans Lémuriens en captivité,” Jour. de ’ Anat, et la Phys., vol. xl., 1904) states that in captive lemurs he could find no spermatozoa in the testicles. 2P 594 THE PHYSIOLOGY OF REPRODUCTION many animals imported into Europe from extremely different climates breed freely, many others when confined in their native land are sterile. Change of food cannot be the chief cause; for ostriches, ducks, and many other animals, which must have undergone a great change in this respect, breed freely. Carnivorous birds when confined are extremely sterile, whilst most carnivorous Mammals, except plantigrades, are moderately fertile. Nor can the amount of food be the cause ; for a sufficient supply will certainly be given to valuable animals ; and there is no reason to suppose that much more food would be given to them than to our choice domestic productions which retain their full fertility. Lastly, we may infer from the case of the elephant, chetah, various hawks, and of many animals which are allowed to lead an almost free life in their native land, that want of exercise is not the sole cause.” Darwin shows also that close confinement by itself does not necessarily cause sterility, since such animals as the rabbit and ferret breed freely in cramped hutches. The general conclusion reached is that “any change in the habits of life, whatever these habits may be, if great enough, tends to affect in an inexplicable manner the powers of reproduction. The result depends more on the constitution of the species than on the nature of the change ; for certain whole groups are affected more than others; but exceptions always occur, for some species in the most fertile . groups refuse to breed, and some in the most sterile groups breed freely.” In support of these conclusions Darwin shows further that domesticated animals also under new conditions occasionally show signs of lessened fertility, and that animals such as the canary, which now breed readily in a state of captivity, were formerly often sterile. Bles’ observations,! to which reference has already been made (p. 20), seem to have a bearing on this question. This observer, who has kept various kinds of Amphibia in captivity, has shown that axolotls can only be induced to breed under certain special environmental conditions. By feeding them copiously in summer and allowing them to hibernate in winter, 1 Bles, ‘“‘The Life-History of Xenopus levis,” Trans. Roy. Soc. Edinburgh, vol. xli., 1906. FERTILITY 595 and then suddenly transferring them to an aquarium stocked with growing plants and provided with running water, these animals could be induced to spawn within a few days. (Cf. also Annandale’s observations referred to on p. 22.) Bles draws the conclusion that the difficulty so often experienced in inducing Amphibians to breed in a state of captivity is not due to toxic influence on the gonads resulting from the confinement, but must rather be ascribed to the absence of the necessary external stimuli without which the generative organs of animals are incapable of properly discharging their functions. Bles suggests that this view may help to explain why some animals (e.g. insects) make their appearance in great numbers in one year, and are comparatively scarce in another. In animals which as a general rule breed freely in a state of domestication or under confinement, it is probable that nutrition plays the chief part (though by no means the sole part) in re- gulating the capacity to produce offspring. That an insufficient or markedly abnormal diet must affect this power is almost self-evident, and Chalmers Watson + has shown that sterility is a common condition among caged rats when fed exclusively upon meat. It is also certain that an excessive quantity of nutriment is likewise prejudicial to the proper discharge of the reproductive functions. No better example could be given of the way in which overfeeding results in a condition of sterility than that of the barren Shire mares, which in recent years have been a striking feature at agricultural shows in England. Some foods are said to induce sterility more easily than others. Sugar, molasses, and linseed are noted for having this effect when given to cattle, but they are often used to prepare beasts for show or sale, since they produce a good coat of hair and cause a deposit of fat. Very fat animals do not come in season so often, and consequently cattle “settle better and feed faster as they become what the butchers designate ‘fat ripe.’’? In such animals there can be no doubt that the ovarian metabolism is abnormal, for the author has often found large quantities of bright orange-coloured lipochrome in the interstitial tissue 1 Campbell and Watson, ‘‘ The Minute Structure of the Uterus of the Rat,” &c., Proc. Phys. Soc., Jour, of Phys., vol. xxxiv., 1906. * 596 THE PHYSIOLOGY OF REPRODUCTION of the ovaries of fat cows and heifers. A low condition, especially if associated with exposure to wet and cold, as in the case of cattle wintered in the open air, or of cows which have suckled a large calf or more than one calf, is also a common cause of temporary barrenness.!. Certain other more special causes of sterility are referred to briefly below (p. 606). A few years ago the Royal Agricultural Society of England instituted an inquiry into the subject of fertility in sheep. The investigation was conducted by Heape, at whose instigation it was carried out. In the report? which was subsequently pub- lished a comparative account is given of the fertility of various breeds of sheep chiefly in the south of England in the season 1899. The most fertile breed was the Wensleydale, in which six flocks, consisting of a total of 319 ewes, produced a percentage of 177-43 lambs. The effects of locality are discussed, and there is an accumulation of evidence indicating that the character of the district is not without influence on the fertility of the breed. Thus, Lincoln sheep run on the wolds, Shropshire sheep on a subsoil of new red sandstone, and Hampshire sheep, which are not run upon chalk downs, are shown to be associated statistically with a relatively high percentage of infertility. The report shows further that the fertility of a flock depends greatly upon its management, that the quality and quantity of the food supplied affect the condition of the sheep, and so influence their power to breed, that some seasons are more favourable to fertility than others, and that sheep-stained pasture (or pasture on which sheep have run for some considerable time previously) is detrimental to breeding stock. The present writer has shown® that in Scotch Blackfaced, Cheviot, and other Scottish sheep the normal percentage of ova discharged at any single cestrous period is not appreciably in excess of the usual percentage of births at the lambing season. 1 Wallace (R.), Farm Live Stock of Great Britain, 4th Edition, Edinburgh, 1907. 2 Heape, ‘‘ Abortion, Barrenness, and Fertility in Sheep,” Jour. Roy. Agric. Soc., vol. x., 1899. See also Heape, “Note on the Fertility of Different Breeds of Sheep,” &c., Proc. Roy. Soc., vol. lxiv., 1899. 3 Marshall, ‘‘The Qistrous Cycle and the Formation of the Corpus Luteum in the Sheep,” Phsl. Trans., B., vol. cxcvi., 1903. FERTILITY 597 It would seem probable, therefore, that a scarcity of twin births at lambing time is the direct consequence of an abnormally low number of ripe follicles in the ovary at tupping time (i.e. during the sexual season). A low percentage of twins is generally associated with barrenness, a fact which is recognised by flock- masters, and which is proved very clearly by Heape’s statistics. And since ewes which are constitutionally barren are a rarity, there can be little doubt that infertility among sheep is due ordinarily to an absence or great scarcity of follicles available for ovulation at tupping time. Scarcity of mature follicles must itself result either from a retardation in follicular development or from an unusual tendency towards follicular degeneration whether occurring shortly before the sexual season or at some previous period in the animal’s lifetime. Atretic or degenerate follicles are by no means un- common in sheeps’ ovaries, the process of atresia appearing to set in most commonly in follicles which have reached a size varying from about one-eighth to one-half the dimensions of the mature follicle. It may set in, however, at practically any stage of development and probably in the so-called primordial follicle (see p. 156). There can be little doubt that an excessive follicular degeneration results usually from an insufficiency of stimulating power at the disposal of the ewe. That a relative scarcity of ripe follicles in sheeps’ ovaries at the sexual season is due to retardation of development is a conclusion which is based on inference rather than observation, for little is known regarding the actual rate of growth of the Graafian follicle. Nevertheless, there is every reason for sup- posing that the processes of growth and maturation can be very largely influenced both by insufficiency of food supply on the one hand and by artificial stimulation on the other. This fact has been recognised for years past by certain individual flockmasters who have consistently practised the methods of “flushing ” or artificially stimulating their ewes by means of an extra supply of special food at the approach of the tupping season, but no precise records of the effects of this process had been published until lately, when the Highland and Agricultural Society of Scotland undertook an investigation upon this subject. 598 ‘THE PHYSIOLOGY OF REPRODUCTION In the report which has since been issued,1 and which contains the lambing statistics for various flocks of Scottish sheep for the years 1905, 1906, and 1907, it is shown that the percentage of lambs born was, as a general rule, highest among sheep which had been subjected to a process of artificial stimulation. The method adopted was to feed the ewes upon turnips, oats, maize, dried grains, or other additional food at the tupping time and for about three weeks previously, while maintaining them upon grass only during the greater part of the year. Some flocks, however, received a limited supply of extra food (generally turnips) during gestation, and especially during the later part of this period. The additional supply of turnips, which are specially rich in carbohydrate material, was found to be in no way detrimental to fertility, but rather the reverse, when accompanied by other food (pasture), and so not taken in excess. The statistics show that in the flocks treated in the way described, the percentage of lambs per ewes? was almost invariably in excess of the average percentage for flocks which received no special treatment, while the percentage of barren ewes was usually also less in the specially fed flocks. In some cases the number of lambs per ewes in the flushed flocks was nearly 200 per cent. Among flocks belonging to the same breeds (Border Leicester or half-bred Border Leicester) which received no sort of special treatment, the average proportion of lambs per ewes was between 150 and 160 per cent., while flocks which were run upon superior pasture at the approach of the sexual season, without being otherwise specially fed, generally produced a slightly larger percentage of lambs. The twins appear almost invariably to have been born early during lambing, thus showing that the generative activity of the ewes tends to be greatest at the commencement of the sexual season. It has proved more difficult to obtain definite information concerning the effects of flushing in one year upon the fertility of the ewes in subsequent seasons. The more usual experience of flockmasters seems to be that flushing is not in any way prejudicial to breeding stock unless it is overdone, the object 1 Marshall, ‘Fertility in Scottish Sheep,” Trans. Highland and Agric. Soc., vol. xx., 1908. See also Proc. Roy. Soc., B., vol. lxxvii., 1905. 2 That is to say, the number of lambs per 100 ewes. FERTILITY 599 of the process being to get the animals in an improving condition without permitting them to put on too much fat. If the artificial feeding is excessive and the sheep are forced to depend for the remainder of the year upon a mere sustenance diet, it is easy to understand that they would tend to deteriorate, and their subsequent fertility become impaired, owing probably to a higher frequency of follicular degeneration. It is seemingly for such a reason that some flockmasters regard the practice of flushing as one altogether to be deprecated. There is some evidence, however, that if sheep are specially fed in one season, the process must be repeated in the next, and that if this is omitted the sheep tend to be less fertile than if they had never been subjected to flushing. j It has already been mentioned (p. 335) that the practice of flushing tends to hasten the sexual season, the sheep coming “on heat” sooner than they would otherwise. The result must be ascribed to a general increase in the ovarian meta- bolism consequent upon the stimulating power of the special food supply. Conversely, it has been shown that in ewes which are poorly fed the sexual season is often retarded, and the fertility of the flock reduced. So also the occurrence of a snow- storm, or other unfavourable climatic condition, occurring during tupping time will cause a corresponding scarcity of twin births in the following lambing season. There can be little doubt, therefore, that the conditions which exist during tupping time are largely responsible for controlling the fertility of the flock, and that favourable conditions tend to promote the more rapid growth and maturation of the follicles in the ovary, and cause a greater number to discharge their ova during the cestrous periods. It would appear also that the condition of the ewe is a far more important factor in determining the number of twin births than that of the ram ; but it is obvious that the number of ewes which one ram can serve successfully must depend upon the degree of vigour possessed by the latter. Sixty ewes to one ram is about the usual proportion allowed. 1 It is said that a good stallion should be able to serve eighty mares in one season, and get on an average forty to fifty foals. See Wallace, loc. cit. The reproductive capacity of the male animal is almost invariably far greater than that of the female, 600 THE PHYSIOLOGY OF REPRODUCTION «., PRoLonceD LacTaTIon It has been recorded that the continuance of lactation commonly exerts an inhibitory influence on menstruation in women and on heat in animals, though this is very far from being invariable (see p. 74). There can be no doubt that in the case of sows, for example, early weaning is conducive to a more frequent recurrence of cestrus and an increased number of litters (see p. 50). In a similar way long-continued lactation is believed to reduce the fecundity of women, who sometimes refrain from weaning their babies in the belief that by so doing they are less liable to become pregnant again. Moreover, Haddon’s observations’ upon the Eastern Islanders of the Torres Straits show that with these people also prolonged nursing tends to reduce the size of the families, and that a single lactation may be continued for three years. EFFECT oF Drugs There is little evidence as to the effects of drugs upon egg- or sperm-production, but innumerable substances have been recommended as cures for impotence.? Cantharides and various other drugs are said to produce sexual excitement, but this result is probably due simply to the increased flow of blood to the generative organs which these substances induce? Wallace says that the practice adopted by some grooms of giving cantharides to stallions is strongly to be deprecated. Bloch is disposed to recommend the use of phosphorus and strychnine in the treat- ment of impotence in men, but the most favourable results have been obtained by yohimbine, an alkaloid prepared from the bark of a West African tree. Bloch mentions several cases where, in his own experience, treatment by yohimbine has been entirely successful, and there are numerous others on record. Many 1 Haddon, Reports of the Cambridge Anthropological Expedition to Torres Straits, vol. vi., Cambridge, 1908. * For the distinction between sterility and impotence see below (p. 606). 3 Bloch, The Sexual Life of our Time, English Translation, London, 1908. FERTILITY 601 veterinarians also have testified to the powerful aphrodisiac action of yohimbine, stating further that it is capable of inducing a condition of heat in domestic animals and acting as an effective remedy for certain kinds of sterility. Daels'! found that yohimbine when administered to dogs produced hyperemia of the generative organs, followed by mucous and sanguineous discharge, but not true heat. Dr. Cramer and the present writer ? have made similar observations. We first administered 0-005 grams of yohimbine twice daily for nearly a fortnight to each of two ancestrous bitches, the drug being swallowed in the form of tablets. Marked congestion of the generative organs followed. On treating rabbits with yohim- bine the vulva and the uterine mucosa became excessively hyperemic, the entire generative tract being affected to some extent. The ovaries were much overgrown by luteal tissue, and degenerate follicles which are generallyso common in rabbits’ ovaries. were relatively scarce. “It seems extremely probable, therefore, that yohimbine, by preserving a constant and rich supply of blood, and consequently of nutriment, to the ovaries, may arrest the normal process of follicular degeneration, and so be the means of bringing a larger number of follicles to maturity than would otherwise be the case, thereby tending to increase the fertility.” There was some evidence also that yohimbine may promote mammary development and the secretion of milk. Errects oF In-BREEDING AND Cross-BREEDING The fact that in-breeding may result in a reduced fertility has been already discussed in dealing with the significance of the fertilisation process (pp. 207-214). It was then pointed out that a tendency towards sterility is often associated with a con- stitutional loss of vigour. In the same place it was mentioned further that cross fertilisation between organisms which are allied but belong to different strains often results in an increased 1 Daels, ‘‘On the Relation between the Ovaries and the Uterus,” Surgery Gynecology and Obstetrics, vol. vi. (Feb.), 1908. * Cramer and Marshall, ‘‘ Preliminary Note on the Action of Yohimbine on the Generative System,” Jour. Econ. Biol., vol. iii., 1908. 602 THE PHYSIOLOGY OF REPRODUCTION fertility,! but that cross fertilisation between different species is frequently difficult to accomplish while there is every gradua- tion between a mere disinclination towards gametic union and complete cross sterility. The differences in fertility between varieties and species when crossed are discussed at some length by Darwin,? who summarises his general conclusions under seven heads. Firstly, the laws governing hybridisation in plants and animals are practically identical. Secondly, there are all degrees of cross infertility. “Thirdly, the degree of sterility of a first cross between two species does not always run strictly parallel with that of their hybrid offspring. Many cases are known of species which can be crossed with ease, but yield hybrids excessively sterile ; and conversely some which can be crossed with great difficulty, but produce fairly fertile hybrids. This is an inex- plicable fact on the view that species have been specially endowed with mutual sterility in order to keep them distinct.” Fourthly, the degree of sterility is often different in the two sorts of reciprocal crosses between the same species, and hybrids produced from reciprocal crosses sometimes differ in their degree of sterility. “‘ Fifthly, the degree of sterility of first crosses and of hybrids runs, to a certain extent, parallel with the general or systematic affinity of the forms which are united. For species belonging to distinct genera can rarely, and those belonging to distinct families can never, be crossed. The parallelism is, however, far from complete; for a multitude of closely allied species will not unite, or unite with extreme difficulty, whilst other species, widely different from one another, can be crossed with perfect facility. Nor does the difficulty depend on ordinary constitutional differences, for annual and perennial plants, deciduous and evergreen trees, plants flowering at different seasons, inhabiting different stations, and naturally living under the most opposite climates, can often be crossed with ease. The difficulty or facility depends exclusively on the ’ Frazer has shown that this fact is probably the biological basis for the practice of exogamic marriages originally adopted by primitive races of mankind and perpetuated under the influence of natural selection (Totemism and Exogamy, London, 1910). 2 Darwin, loc. cit. See also Origin of Species, 6th Edition, London, 1872. FERTILITY 603 sexual constitution of the species which are crossed; or on their elective affinity.” Sixthly, cross sterility between species may depend possibly in certain cases upon distinct causes, such as deterioration due to unnatural conditions to which the hybrid embryo may be exposed in the uterus, egg, or seed of the mother. “Seventhly, hybrids and mongrels present, with the one great exception of fertility, the most striking accordance in all other respects ; namely, in the laws of their resemblance to their two parents, in their tendency to reversion, in their variability, and in being absorbed through repeated crosses by either parent form.’ It is obvious, however, that this last conclusion requires some modification in the light of recent Mendelian research. Darwin maintains further that the cross fertility which exists between the different varieties of various species of domesticated animals, in spite of their great divergence in external appearance, is the direct effect of domestication which eliminates the tendency towards mutual sterility. In this way “the domesticated descendants of species, which in their natural state would have been in some degree sterile when. crossed, become perfectly fertile together.” Both Darwin and Wallace lay stress upon the apparent existence of a parallelism between crossing and change of conditions in so far as these affect the power to reproduce. “Slight changes of conditions and a slight amount of crossing, are beneficial; while extreme changes, and crosses between individuals too far removed in structure or constitution, are injurious.” + Furthermore, domestic animals are less susceptible to the influences of changed conditions of existence than wild animals, a fact which finds a parallel in the absence of sterility between domesticated varieties of the same species. Wallace has cited several cases in which it has been shown that hybrids between distinct species are fertile inter se. Such cases are the hybrids between the domestic and Chinese geese, those between the Indian humped and common cattle, and the various hybrids between the different species of the genus Canis. A recently recorded case of a fertile hybrid between a lion and a jaguar may also be cited. These and other observations 1 Wallace (A. R.), Darwinism, London, 1897. 604 THE PHYSIOLOGY OF REPRODUCTION show that sterility among hybrids between closely allied species, although usual, is very far from being universal.! Similar cases have been recorded from among plants. The cause of sterility in hybrid organisms is still to a large extent an open question. In some cases the generative organs are atrophied or imperfectly developed, while in most, if not all sterile hybrids, the gametes are not developed. For example, Iwanoff? states that hybrids between the horse and the zebra do not possess spermatozoa. It has been suggested that the sterility is due to irregularities in the mechanics of division in the germ cells. “ When we recall that at one stage in the development of the germ cells there may be a pairing and subsequent fusion of the maternal and paternal chromosomes, we can readily imagine that any differ- ences in their behaviour at this time might lead to disastrous results.” § INHERITANCE OF FERTILITY That fertility is a racial characteristic, and consequently is capable of hereditary transmission, is a fact that is generally accepted. Among sheep, for example, some breeds, like the Dorset Horns, the Hampshire Downs, and the Limestones, are notoriously prolific, while other varieties, like the Scotch Black- faced, are relatively infertile* Furthermore, there is a con- siderable amount of evidence that in each breed there are particular strains of related individuals which have a higher degree of fertility than the average, and that flockmasters, by breeding from twin ewes and employing the services of twin rams, have been able permanently to increase the fertility of their stock.® 1 See Suchetet, “ Problémes Hybridologiques,” Jour. de ? Anat. et la Phys., vol. xxxili., 1897 ; Dewar and Finn, The Making of Species, London, 1909. 2 Iwanoff, “ Untersuchungen tiber die Unfruchtbarkeit von Zebrdiden,”’ Biol, Cent., vol. xxv., 1905. ‘‘Dela Fécondation Artificielle chez les Mammi- féres,” Arch. des Sciences Biologiques, vol. xii., 1907. 3 Morgan, Experimental Zoology, New York, 1907. 4 The Leicester breed of sheep is characterised by a relatively low fertility, and this is said to be due to the preference that was shown to large single lambs at the time when high prices ruled, and the consequent discarding of ewes which bore twins. See Wallace (R.), loc. cit. 5 Marshall, “ Fertility in Scottish Sheep,” Trans. Highland and Agric. Soc., vol. xx., 1908. FERTILITY 605 The inheritance of fertility in Man and also in thoroughbred horses has been investigated statistically by Karl Pearson and his biometrical collaborators,! to whose memoir the reader is referred for a full discussion of the mathematical details and the conclusions which are arrived at. It is there shown, among other facts, that the woman inherits fertility equally through the male and female lines. Among thoroughbred race-horses the fecundity was first ascertained (7.e. the ratio of foals surviving to be yearlings to the total number of foals possible under the given conditions), and the following general conclusions were afterwards reached :—(1) Fecundity is inherited between dam and daughter, and (2) Fecundity is also inherited through the male line, 1.e. the sire hands down to his daughter a portion of the fertility of his dam. Thus fecundity, which is, of course, a latent character in the male, was measured for a horse and for his sire, and was found to be strongly inherited. More recently Rommel and Phillips? have shown mathe- matically that there is an actual correlation between the size of the litter in two successive generations of Poland China sows, the productiveness being a character which is transmitted from mother and daughter. On the other hand Pearson * from studying Weldon’s records of mice-breeding experiments, failed to find a sensible parental correlation in regard to the size of the litters. Furthermore, Pearl and Surface,’ as a result of a statistical investigation on egg-production in Barred Plymouth Rock fowls, carried on over nine years, found no evidence of the inheritance of fecundity. For this particular breed at any rate the capacity for egg-pro- ducing could not be increased by selective breeding, but tended 1 Pearson, Lee, and Bramley-Moore, ‘‘ Mathematical Contributions to the Theory of Evolution: VI., Genetic (Reproductive) Selection, Inheritance of Fertility,” &c., Phil. Trans., A., vol. cxcii., 1899. * Rommel and Phillips, ‘“‘Inheritance in the Female Line of Size of Litter in Poland China Sows,’’ Proc. Amer. Phil. Soc., vol. xlv., 1907. ® Pearson, ‘‘On Heredity in Mice, from the Records of the late W. F. R. Weldon,” Biometrika, vol. v., 1907. ‘ Pearl and Surface, ‘‘Data on the Inheritance of Fecundity obtained from the Records of Egg Production,” &c., Maine Agric. Exp. Station, Bulletin No. 166; Maine, 1909. Pearl, ‘‘A Biometrical Study of Egg Pro- duction in the Domestic Fowl,” U. S. Dep. of Agric., Bureau of Animal Industry, Bulletin No. 110; Washington, 1909. 606 THE PHYSIOLOGY OF REPRODUCTION rather to diminish, though the last result may have been due to slight environmental changes. It is possible that fertility, like other characteristics, cannot be increased indefinitely by selective breeding, but that when once the limit existing in the strain has been reached, artificial selection is powerless to effect an improvement. CERTAIN CaUsES OF STERILITY A detailed account of the various pathological conditions which are capable of inducing sterility is outside the scope of this work, The medical publications dealing with the subject form a very considerable literature,’ while the causes of sterility in animals are discussed, though somewhat unsatisfactorily, in many of the veterinary text-books. It may not be out of place, however, to refer briefly to certain of the conditions which are known. to induce sterility in Man and also in animals. In the case of the male an incapacity to procreate is due either to impotence (.e. inability to perform the sexual act), or to sterility (using the term in the more restricted sense, implying an absence of spermatozoa). Impotence may result from (1) absence of sexual desire, (2) absence of the power of erection and consequent intromission, (3) absence of the power of ejaculating the seminal fluid into the vagina, and (4) absence of the ability to experience pleasure during the act of coition, and at the time of the emission of the semen.? Or, according to another classification, the causation of impotence may be either anatomical, physiological, pathological, or psychological. Among the anatomical causes may be mentioned defects and deformities in the penis. The physiological and pathological causes include incomplete erections, premature ejaculations, diseases of the brain and spinal cord (and more particularly of the centres for the performance of the sexual act), besides such diseases as albuminuria or prolonged diabetes. The psycho- logical causes include fear, repugnance, want of confidence, &c.° 1 Miiller (P.), Die Unfruchtbarkeit der Ehe, Stuttgart, 1885. This work contains a bibliography. 2 Hammond, Sexual Impotence in the Male, New York, 1883. 3 Corner, Diseases of the Male Generative Organs, London, 1907. FERTILITY 607 Complete sterility, 7.e. inability to procreate owing to the absence of fertile semen, is due to various causes, and may be either congenital or acquired. Congenital sterility occurs when the testicles are never developed, or are so imperfectly de- veloped that they fail to produce ripe spermatozoa. In cases of incomplete descent of the testicles fertility is rare, but it may exist for a short time as in young men from twenty to twenty- three years of age. Acquired sterility results from the various diseases to which the generative organs are subject, such as tubercle, syphilis, attacks of inflammation, urethral stricture, epididymitis, prostatic enlargement or diminution, &c.1 A more special cause of sterility in men is one which operates in the case of workers with radium or the Réntgen rays. Several years ago Albers-Schénberg? noticed that the X-rays induced sterility in guinea-pigs and rabbits, but without interfering with the sexual potency. These observations have been confirmed by other investigators,? who have shown, further, that the azoéspermia is due to the degeneration of the cells lining the seminal canals. In men it has been proved that mere presence. in an X-ray atmosphere incidental to radiography sooner or later causes a condition of complete sterility, but without any apparent diminution of sexual potency. As Gordon observes, for those working in an X-ray atmosphere adequate protection for all parts of the body not directly exposed for examination or treatment is indispensable, but, on the other hand, the X-rays afford a convenient, painless, and harmless method of inducing sterility, in cases in which it is desirable to effect this result.° 1 Corner, loc, cit, ® Albers-Schénberg, ‘‘Ueber eine bisher unbekannte Wirkung der Réntgen- strahlen auf den Organismus der Tiere,” Muiinchener med. Wochenschr., No. 43, 1903. 5 See Gordon, “Diseases caused by Physical Agents,” Osler’s System of Medicine, vol. i., London, 1907. See also Regaud and ‘Dubreuil, ** Action des Rayons de Réntgen sur la Testicule de la Lapin,” C. R. de la Soc, de Biol., vol. 1xiii., 1907. ‘ Brown and Osgood, ‘‘ X-Rays and Sterility,” Amer. Jour. of Surgery, vol. xviii. (April), 1905. 5 Gordon, loc. cit. It has been shown also that the Roéntgen rays may induce degeneration of the follicles, corpora lutea, and interstitial cells in the ovaries and cause sterility in the female. See Bouin, Ancel, and Villemin (C. R. de la Soc, de Biol., vol. 1xi., 1906), Bergomié and Trabondeau (C. R. dela Soc, de Biol., vol. lxii., 1907), and Specht (Arch. f. Gyndk., vol. 1xxviii. 1907). ” 608 THE PHYSIOLOGY OF REPRODUCTION The various causes of sterility in women are discussed at considerable length by Kelly,! as well as by other writers? on gynecology. Kelly mentions the following conditions as likely to be found associated with sterility: Gonorrhceal infection of Skene’s or Bartholin’s gland, stricture of the vagina or cervix, the presence of a uterine polyp, a uterine fibroid tumour, a parovarian cyst, or a nodular salpingitis (from gonorrhoea or tuberculosis), atresia of the uterine tube (from inflammation), and the existence of ovarian adhesions. These, and other causes of sterility, and the methods of treatment to be adopted, are fully dealt with by Kelly. Sterility in animals, as in Man, is brought about by a variety of causes,? some of which are incurable, but others, such as constriction of the os uteri, are capable of treatment. In the case of cattle great difficulty is often experienced in getting the cows to breed after attacks of contagious abortion, and this is said to be due to an acid condition of the vaginal mucous membrane. In order to remedy this, injections of dilute solu- tions of bicarbonate of soda are employed and are found to be effective. Others recommend that the uterus should be injected with solutions of perchloride of mercury.* Sterility in mares and cows and other animals is often due to structural or functional defects in the vagina, os uteri, or cervix. These may sometimes be overcome by resorting to artificial insemination, the methods of which are described below.5 Furthermore, sterility among cows may be contagious owing to the disease known as infectious granular vaginitis, which is primarily an acute inflammation of the vulva and vagina. It is 1 Kelly, Medical Gynecology, London, 1908. 2 See especially Duncan, Sterility in Women, London, 1884, and Miller, loc. cit, Duncan states his opinion that probably ten per cent. of the marriages in Great Britain are sterile. 3 Fleming, Text-book of Veterinary Obstetrics, London, 1878. 4 Wallace (R.), loc. cit. According to Knowles (“Sterility of Mares and Cows,” Amer, Veterinary Review), “ sub-acute and chronic cervical hyperemia are probably the most frequent and fruitful causes of temporary sterility, due in an astonishingly large number of instances to continually recurring abortions.” 5 Constriction of the os uteri in cows may often be remedied by the employment of a large probe followed by the finger, or better still by a specially devised instrument known as a dilator. See Wallace (R.), loc. cit. FERTILITY 609 commonly communicated by a contaminated bull in which the penis and sheath are affected. Similarly a bull may become diseased by serving an infected cow, and in this way vaginitis may spread through an entire herd. During recent years con- tagious sterility has been very common in Switzerland and Germany, and there is evidence of its existence in England. Antiseptic disinfection is useful, but experience has shown that even when treated infectious vagin tis often runs a prolonged course. Nevertheless, a complete cure usually takes place after some months, this recovery being indicated by the cessation of the muco-p-rulent discharge and the recurrence at normal intervals of the cestrous periods.' Deficient, excessive, or unfavourable nutrition, change of environment, in-breeding, &c., as sources of infertility, have been already discussed. -ARTIFICIAL INSEMINATION AS A MEANS OF OVER- COMING STERILITY Artificial insemination as a means of overcoming certain forms of sterility has been employed by various medical men from Hunter’s time downwards. In the case treated by Hunter himself,? the husband of the woman experimented upon was affected with hypospadias. The semen was injected into the vagina, conception followed, and a child was afterwards born. Sims? recorded a case of a woman who suffered from dysmenorrhcea and a deformed uterus, and who had been married for nine years without having children. Artificial in- semination was resorted to, pregnancy ensued, and a child was born in due time. Numerous other cases are cited by Heape * and Iwanoff,® to whose papers the reader is referred for biblio- graphies of the subject. 1 McFadyean, “Sterility in Cows,’ Jour. Royal Agric. Soc., vol. Ixx., 1909. 2 This case is described by Home, Phil. Trans. 1799. (See p. 189, Chapter V.) 3 Sims, Notes Cliniques sur la Chirurgie Utérine, Paris, 1866. 4 Heape, “The Artificial Insemination of Mammals,” &c., Proc, Roy. Soe., vol. lxi., 1897. 5 Iwanoff, ‘‘De la Fécondation artificielle chez les Mammiféres,” Arch. des Sciences Biologiques, vol. xii., 1907. 2Q 610 THE PHYSIOLOGY OF REPRODUCTION The method adopted by gynecologists who have practised artificial insemination is to inject seminal fluid into the uterus by means of a syringe, the fluid in most cases being obtained from the vagina of the same individual shortly after coitus. In this way it has been found possible to overcome such structural defects as constriction or undue rigidity of the cervix or hypertrophy of the lips of the external os uteri. By modify- ing the method by which the semen is obtained, it has proved possible to induce pregnancy in cases of abnormal vaginal secretion where the spermatozoa are ordinarily killed before they can effect an entrance into the uterus, and in other cases where there is an inability on the part of the vagina to retain the semen after coitus. Artificial insemination has frequently been practised on mares with a view to overcoming certain forms of sterility, and considerable success has been attained. ‘“‘Such defects as flexion or constriction of the canal of the cervix; rigidity of the cervix; hypertrophy of the lips of the external os, and the formation of false membranes which may effectually close the orifice ; inability to retain spermatozoa in the vagina, owing to abnormal shortness of the organ or to violent muscular con- traction after coitus; a want of sufficient muscular power ; abnormal structure or size of the cervix or os uteri, which pre- vent the free action of the functions of the cervix ; occlusion of the os owing to spasmodic contraction of the muscles of the cervix during coitus ; abnormal or excessive vaginal secretions, which may kill or deleteriously affect the spermatozoa, &c., may be overcome by artificial insemination.”1 Heape, and more recently Iwanoff,? have cited numerous cases in which mares have been got in foal successfully by artificial insemination. : The actual methods employed are described by these writers. The most usual plan is to allow the stallion to serve the mare in the ordinary way, and then, immediately afterwards, to insert 1 Heape, “The Artificial Insemination of Mares,” Veterinarian, 1898. 2 Iwanoff, loc. cit. This important memoir, besides containing descrip- tions of the author’s own experiments, gives a very full account of the literature of artificial insemination. 3 See also a booklet edited and published by Huish, The Cause and Remedy for Sterility in Mare, Cows, and Bitches, London. FERTILITY 611 a sytinge into the vagina, and draw up into it some of the seminal fluid which is caused to collect in a depression or pocket made in the vaginal floor by the pressure of the finger tips. The same mare can then be inseminated by injecting the fluid so obtained into the uterine cavity, or the semen can be utilised for impregnating other mares. Another method is to collect the semen in gelatine capsules which are placed in the vagina before coitus, and then, when they have been filled, to close their lids and insert them in the interior of the uterus, where the heat of the body gradually melts the gelatine and sets free the spermatozoa. By such means as this several mares may be impregnated as a result of one service by a stallion. In some cases pieces of sponge have been employed instead of gelatine capsules. In transferring semen from one animal to another it is of considerable importance to preserve a moderate degree of warmth; otherwise the spermatozoa are liable to die as a result of exposure before injection has been effected. Artificial insemination has been of considerable use also in remedying sterility in cows as well as in dogs.1 Several investigators by employing artificial insemination have been successful in getting crosses between animals be- longing to varieties in which the disparity in size is so great that coitus between them is difficult or impossible. Thus, Plénnis? in 1876 successfully inseminated a lap-dog with the semen of a setter, and obtained a pup which in most of its points resembled its father. Allbrecht? performed a similar experi- ment and obtained a similar result. More recently Heape 4 has described some experiments carried out by Millais, in which bloodhounds were inseminated with spermatozoa obtained from Basset hounds (a much smaller breed), litters of cross-bred pups being produced. Iwanoff * has recorded an experiment in which he successfully inseminated a white mouse with the spermatozoa of a white rat. 1 See Huish, loc. cit. ® Plénnis, « Kiinstliche Befruchtung einer Hiinden,” &c., Inaug.-Dissert., Rostock, 1876. q * Allbrecht, “ Kiinstliche Befruchtung,” Wochenschr. f. Thierheilkunde und Viehzucht, Jahrg. xxxix. 4 Heape, ‘The Artificial Insemination of Mammals,” Proc. Roy. Soc., vol. 1xi., 1897. 5 Iwanoff, loc. cit. 612 THE PHYSIOLOGY OF REPRODUCTION Two hybrid young ones were produced after a pregnancy lasting twenty-seven days. They were intermediate in size between rats and mice. This is the first record of a cross being obtained between two species so different in size as the rat and the mouse, coitus between them being practically impossible. Furthermore, Iwanoff has successfully employed artificial insemination to obtain hybrids between horses and zebras (a cross which is often difficult to get by the normal method owing to the liability of the animals to refuse service). ABORTION Abortion is often an important factor in determining a low fertility, but its frequency of occurrence shows a considerable range of variation. With women the frequency of abortion to birth at full term is said to be from one in five to one in ten.1 According to the records of Franz? for the maternity hospital at Halle, the per- centage of cases in which abortion occurred was 15-4. Williams ? expresses the opinion that in ordinary private practice every fifth or sixth pregnancy usually ends in abortion, and that the percentage would be considerably increased if one reckoned the early cases in which there is a profuse loss of blood following a retardation of the menstrual period, the actual fact of abortion being often obscured. Excepting in the case of sheep, there are no satisfactory data on which to estimate the frequency of abortion among the different kinds of domestic animals, but there can be no doubt that it is of common occurrence, and that it occasions much loss to breeders. For various varieties of English sheep Heape * found that the percentage of abortion experienced by 300 flock- masters varied from nothing to 23°75, while the percentage for 85,878 ewes was 2°39. The statistics showed that Dorset Horn and Lincoln breeds suffered most from abortion, the losses from 1 Kelly, loc. cit. 2 Franz, ‘‘ Zur Lehre des Aborts,” Hegar’s Bettrcige, vol. i., 1898. 3 Williams, loc. cit. 4 Heape, “Abortion, Barrenness, and Fertility in Sheep,” Jour. Royal Agric. Soc., vol. x., 1899. FERTILITY 613 this cause being respectively 4°11 per cent. and 4 percent. The Southdown breed were found to occupy an intermediate position (the percentage of abortion being 2:86 per cent.), while the other breeds investigated showed a smaller percentage of abortion. Among Scottish breeds the percentage of aborting ewes does not generally exceed 2 per cent., as far as could be ascertained ; but with Blackfaced ewes it may be as much as five, or even a considerably higher number, as a consequence of any special adverse circumstance. It is possible, however, that the per- centages of abortion are actually somewhat higher than they appear, since its occurrence during the early stages of pregnancy is not readily detected, and consequently some of the ewes which were entered in the statistical returns as barren may in reality have aborted. Among cattle in Great Britain the frequency of abortion, according to Heape,? is not less than ten per cent. of the total number of animals selected for breeding, and there can be no doubt that in certain districts it is often very much higher, especially where contagious or epidemic abortion occurs. Heape states further that from ten to twelve per cent. of abortion is not unusual in herds in which no contagious abortion is proved to exist. There are no data available on which to compute the fre- quency of occurrence of abortion among horses, but the ex- perience of breeders shows that the losses arising from this cause are very considerable, and that they are greatest amongst the better-bred animals. One of the earlier reports of the Royal Commission on Horse-Breeding stated that in this country in any given year no less than forty per cent. of the mares chosen for breeding fail to produce foals, but to what extent this result is due to sterility or how far it may be ascribed to abortion does not appear to have been ascertained. The causes of abortion are diverse, and may be mechanical, psychological, physiological, or pathological. Deliberate abor- tion among civilised European nations is a criminal offence punishable by law, but nevertheless is not infrequently carried ! Marshall, ‘Fertility in Scottish Sheep,” Trans. Highland and Agric. Soc., vol. xx., 1908. * Heape, The Breeding Industry, Cambridge, 1906. 614 THE PHYSIOLOGY OF REPRODUCTION out. In Oriental countries and among savages abortion is practised more openly. The more usual means are drugs (ergot, ethereal oil of juniper, yew, turpentine, camph r, cantharides, aloes, &c.),' but none of these are infallible, and owing to their toxic properties their use is often accompanied by danger. Haddon? says that among the Eastern I landers of the Torres Straits abortion is procured by the leaves of the shore convol- vulus and certain other plants. Also the old women give the younger women young leaves of the argerarger (Callicarpa sp.), a large tree with inedible fruit, and bok, a large shrub. When a woman’s body is saturated with the j ice from the leaves, she is believed to be proof against fecundity, and can indulge in sexual intercourse without fear of becoming pregnant. Pro- bably the toxic substances introduced cause abortion at very early stages of pregnancy, or even inhibit pregnancy at the \ery outset. Abortion is sometimes procured by purely mechanical means—-e.g. blows, massage, hot injections,? carrying heavy loads, &c. But although mechanical and psychological influ- ences, both voluntary and involuntary, play a part in bringing about abortion, they are probably less frequently concerned in the process than pathological conditions existing either in the embryo or in the maternal organism. Among the causes of abortion in women Kelly ® mentions hemorrhage of the chorion, imperfect vascularisation of the amnion, hydatiform degeneration of the chorion, circulatory disturbances caused by heart lesions in the mother, various infections of the mother (notably syphilis), psychic disturbances, and excessive cohabitation, acute poisoning (by alcohol, phos- phorus, lead, &c.), and various diseases of the generative organs, such as endometritis, decidual inflammation, polypoid thicken- ing, &c. It is stated that the excitability of the nerve centres which control the movements of the uterus and the tendency to uterine congestion are greatest at the epochs which would have been menstrual periods if pregnancy had not occurred, and consequently that abortion is especially common at these 1 Bloch, loc cit. 2 Haddon, loc. cit. 3 Bloch, loc. cit. 4 Haddon, loc. cit. 5 Kelly, loc. cit. See also Oliver, ‘‘The Determinants of Abortion,” Brit. Med. Jour., November 30, 1907. FERTILITY 615 dates! The membranes are usually cast off with the foetus, but the decidua is said in some cases to remain, and to regenerate a normal uterine mucosa. The expulsion of the foetus and membranes is accompanied by “ pains” comparable to those occurring in normal parturition, the two processes having a general similarity, which is closer if abortion takes place in the later part of pregnancy. There is generally also a considerable loss of blood. After the expulsion the hemorrhage and pains cease, and a process of puerperal involution sets in. In horses abortion is probably most frequent during the period from the sixth to the ninth week of pregnancy. This is explained by Ewart? as being due to the fact that about this time the embryo loses its primitive attachment to the uterus before acquiring its more permanent connection by means of the allantoic villi, which are only beginning to be numerous. The yolk sac, which in the marsupial is the organ of foetal nourishment throughout the whole of pregnancy, in the case of the horse ceases to provide a sufficient supply at about the end of the seventh week; but the horse embryo, instead of being born at this period, like the marsupial, acquires new and more efficient structures in the allantoic villi. “ At the end of the third week of gestation, when the reproductive system passes through one of its periods of general excitement, about one- fourth of the embryonic sac probably adheres to the uterus ; but at the end of the sixth week, when another wave of dis- turbance arrives, all the grappling structures are at one pole. Hence there is probably more chance of the embryo ‘ slipping ’ at the end of the sixth than at the end of the third week. About the end of the seventh week the supply of nourishment by means of the yolk sac is coming to an end, and there is perhaps still about this time an hereditary tendency for the embryo to escape. Unless the new and more permanent nutritive apparatus is provided, unless a countless number of villi rapidly sprout out from the allantois, the embryo will die from starvation during the eighth week, and in a few days be discharged. It may therefore be taken for granted that there is a certain amount 1 Galabin, Manual of Midwifery, 6th Edition, London, 1904. 2 Ewart, A Critical Period in the Development of the Horse, London, 1897. 616 THE PHYSIOLOGY OF REPRODUCTION of danger at the end of the third and sixth weeks, but that the most critical period is about the end of the seventh or beginning of the eighth week; for unless the villi appear in time, and succeed in coming into sufficiently intimate relation with the uterine vessels, the developmental process is of necessity for ever arrested.” ! Ewart discusses briefly the external conditions and circum- stances which are likely to lead to abortion, and provides some useful practical hints as to the best way to treat mares in order to prevent them from “ slipping foal.” He remarks that the horse is a peculiarly high-strung, nervous animal, and is easily affected by sudden changes in its surroundings, especially during the breeding season. Such changes are, no doubt, often re- sponsible for setting up disturbances in the nervous system, and so inducing abortion, more particularly at that period of development at which the fixation of the embryo to the uterine wall is relatively insecure. Abortion in cows is said to be commonest during the first month of pregnancy. According to Wallace? the usual causes are the following: (1) Eating ergotised grass; (2) injury due to horning by other cattle, hunting by dogs, or shaking and bruising in travelling, &c.; (3) physical strain, resulting from walking over too soft land, &c.; (4) very cold or foul water, or frozen turnips, &c.; (5) superpurgation, whether occurring naturally or as a consequence of dosing by physic ; (6) contagion from other cows affected by epidemic abortion. This is said to be the commonest and at the same time the most dangerous cause of abortion. Bang* has shown that contagious, epidemic, or epizojtic abortion in cattle is due to a specific bacillus which he has been able to isolate and cultivate in oxygenated glycerine-bouillon or serum-gelatine agar. The germ causes the formation of a brownish-yellow exudate between the chorion and the mucous 1 Ewart, loc. ct. ? Wallace (R.), loc. cit. Wallace states that after abortion in cattle the placenta adheres to the cotyledons, and should be removed artificially ; otherwise it is liable to undergo a process of rotting, sometimes resulting in septicemia and death. 3 Bang (B.), ‘‘ Infectious Abortion in Cattle,” Nat. Vet. Soc., Liverpool, July 25, 1906. FERTILITY 617 membrane of the uterus, and more particularly around the cotyledons, but the affected area may be considerably greater.' The chief mode of entrance is the vagina (especially during copulation when the contagion is introduced by the bull’s penis”), but Bang has shown experimentally that the germs may be carried to the seat of the disease by the blood after intravascular injection, and furthermore that they can be absorbed through the alimentary canal. Thus, after administering some bouillon culture to a cow, the placenta was found covered with typical exudate rich in bacilli. There is some experimental evidence that cows may acquire immunity to the disease, at least tempo- rarily. Investigations show also that mares, sheep, goats, dogs, and guinea-pigs may be infected with the bacillus experimentally, but in all probability the disease is ordinarily confined to cattle. The abortion microbe is stated to be oval or rod-shaped, between one and two microns in length, and non-motile. It sometimes occurs singly, but in many places the bacilli are collected in dense groups or colonies. The microbe associated with akortion out- breaks in sheep is said to be a vibrio and therefore totally different. It has been isolated and used experimentally to infect pregnant ewes. Pregnant cows, however, cannot be infected by it. The external use of antiseptics is said to prevent the spread of contagious abortion by means of disinfection, and this is the treatment prescribed by the Board of Agriculture.® The causes of abortion in sheep are dealt with at some length by Heape in the paper already referred to.* Statistical evidence shows that an excessive proportion of shearling ewes in a flock is associated with a relatively high percentage of abortion, and that ewes of particular breeds in certain districts, or run on certain subsoils, are more liable to abortion than the average for the breed in question. Thus Lincoln sheep run on the Wolds suffer much more from abortion than sheep of the same breed in other districts. The Southdown and Hampshire Down 1 Report of the Departmental Committee appointed by the Board of Agriculture and Fisheries to inquire into Epizoétic Abortion, London, 1909. 2 According to the Report referred to above, nothing more than a quite subsidiary réle in the spread of the disease can now be referred to the bull. 3 Board of Agriculture Leaflet, No. 108, 1904. ‘ Heape, ‘‘ Abortion, Barrenness, and Fertility in Sheep,” Jour. Royal Agric. Soc., vol. x., 1899. 618 THE PHYSIOLOGY OF REPRODUCTION statistics show that a heavy rainfall during gestation is associated with a high degree of abortion. Over-exertion (as from jumping ditches), fright (from strange dogs or shooting), are usually credited with producing abortion in sheep, but Heape remarks that such causes are not truly responsible unless the ewes are in a susceptible condition. The main conclusion reached is that the food and the resulting condition of the ewes are the principal factors which influence the percentage of abortion. Unsuitable food, causing indigestion or other ailments, and poor food, re- sulting in bad nutrition, are held to be mainly responsible. Heape states, however, that it is not the kind of food so much as the condition of the food which is most liable to be at fault, while the schedules show clearly that a poor condition of ewes during gestation is associated with a relatively high percentage of abortion. “ Sheep-stained”’ pasture (i.e. pasture grown with the aid of sheep manure or on which sheep have been run for a considerable time previously) is credited with causing abortion, and there is strong evidence in support of this view in cases where rank or over-stimulated growth results.1 As already noted, the Dorset Horn and Lincoln breeds of sheep suffer most from abortion.? In the case of the former this may result partly from inbreeding, since Dorset Horn ewes served by Hampshire Down rams are less liable to “ slip lamb ”’ than those served by rams of their own breed. It is possible, therefore, that the abortion may be due to a want of vitality on the part of the developing embryo, the cross-bred young possessing a superior vigour. Abortion among Lincoln sheep has been known to reach thirty, forty, or even fifty per cent., and so to assume an epidemic form. Wortley Axe,? who reported on an outbreak of abortion among the Lincolnshire flocks in the season of 1882-83, was disposed to attribute it to debility, arising largely from foot-rot and exposure to cold winds and 1 Abortion in sheep may result from more exceptional causes. Thus it is recorded that a large proportion of a certain flock of Cheviot ewes slipped lamb after a gale which blew down a number of Scotch fir-trees, the abortion resulting, in the owner’s opinion, from the animals eating the branches and bark. See Marshall, loc. cit. 2 Heape, loc. cit. 3 Wortley Axe, ‘‘Outbreak of Abortion and Premature Birth in the Ewe Flocks of Lincolnshire during the Winter and Spring of 1882-83,” Jour. Royal Agric. Soc., vol. xxi., 1885. FERTILITY 619 heavy continuous rains, as well as to the feeding of the ewes on unripe watery roots and unwholesome, filth-laden shells. Heape has suggested that abortion on the Wolds arises partly from the practice of unduly crowding the ewes on turnip fields. As already mentioned, a bacillus has been isolated from outbreaks of abortion in ewes, and has been used to infect other ewes for experimental purposes in the laboratory. Tue INCREASE OF FERTILITY, A PROBLEM OF PRACTICAL BREEDING Heape ! has shown from statistical evidence that the amount of money invested in live stock in this country cannot be com- puted at very much less than £450,000,000, and this sum does not include the enormous capital spent on buildings, land, vehicles, and various accessories. The annual export of live stock from Great Britain in recent years has been tending steadily to increase, until it has reached a total value of £1,750,000. It is clear, therefore, that in this country the breeding industry occupies a position of no inconsiderable importance, and that the scientific study of the problems of breeding possesses a great national interest. Foremost among these problems is that which concerns itself with the factors that control fertility. Despite its comparative prosperity, it is evident that the breeding industry suffers annually from no inappreciable loss. Allusion has been made to the losses sustained by breeders owing to the occurrence of abortion in domestic animals. Sterility, whether persistent or temporary, is responsible for a greater reduction of profit. The prevalent barrenness among the better class of Shire mares has been already referred to, while incapacity to breed is perhaps still commoner among thoroughbreds. As already mentioned, the Royal Commission on Horse-Breeding found that no less than forty per cent. of the mares chosen for breeding in any given year failed to produce ofispring.2 Moreover, there is evidence that in certain districts 1 Heape, The Breeding Industry, Cambridge, 1906. 2 Owing probably to a combination of circumstances, the number of foals dropped in this country in recent years has shown a tendency to decrease. This fact has called forth serious comment in many quarters, and attention 620 THE PHYSIOLOGY OF REPRODUCTION of India this percentage is still higher.t Among cattle the average loss from sterility and abortion (together with mortality of calves) is estimated by Heape ”* to be at least fifteen per cent., while it is shown in the report (already referred to) issued by the Royal Agricultural Society on fertility in English sheep for the year 1899, that the proportion of sterile ewes was 4°71 per cent. out of a total number of 96,520, and this percentage does not include the ewes which aborted (see p. 612). In view of these facts, it is obvious, as Heape has pointed out, that any means by which sterility in domestic animals can be checked and their capacity to bear young increased, must be possessed of great commercial value. Tue Birtu-Rate 1In Man It is now more than a century ago since Malthus * advanced his famous proposition that whereas population tends to in- crease in geometrical ratio, the means of subsistence increase only in arithmetical proportion. As a consequence of the acceptance of that doctrine, the political economists of the early Victorian period tended to see in over-population the most fruitful source of pauperism, disease, and crime, and the cause of increasing congestion in the future. That Malthus’ predictions have not been verified is a matter of common knowledge, and the problem before the modern economist is not how to place a check on population generally, but rather how to secure that future generations shall be sufficiently recruited from that section of the population which is industrially capable. There is abundant evidence that in most civilised countries at the present time the birth-rate (that is, the proportion of the children born to the population) is tending to decrease, while in some countries the actual population is diminishing. This decline in the birth-rate has been made the subject of has been drawn to the urgent need for practical proposals on the subject with a view to maintaining the horse supply of the country and arresting a state of things which, if it continues, must be a source of danger. 1 Ewart, loc. cit. 2 Heape, loc. cit. 3 Malthus, An Essay on the Principles of Population, 7th edition, London, 1872. FERTILITY 621 statistical inquiries by Newsholme and Stevenson,! and Udny Yule.2 These writers have shown that the observed fall is not simply a consequence of changes in the ages of the people, or in the proportion of married to single women, for allowing for such alterations as have occurred, the number of births per 100,000 of the population in England and Wales, for example, has dropped from 3236 in 1861 to 2729 in 1901. The decline in the birth-rate (so far as England and Wales are concerned) is not appreciably greater in the towns than in the rural districts. It is, however, especially marked in places inhabited by the servant-keeping class.2 It appears to be greatest in those sections of the population which give evidence of the exercise of thrift and foresight, for Heron * has shown that the more cultured, prosperous, and healthy classes are producing fewer children than those belonging to a lower social status. There is no evidence that this decline in the birth-rate is due to an increase of sterility, for congenital unavoidable sterility in either sex is rare.> The inference is, therefore, that the decline is principally, if not entirely, the result of deliberate volition in the regulation of the married state. Direct evidence that this inference is correct is provided by the Fabian Society, whose report ® indicates that the practice of limitation prevails with at least one-half, if not three-fourths, of all the married people of Great Britain. The statistics collected from other countries point in a similar direction.? This is noticeably the case for New South Wales, Victoria, and New Zealand among the British Colonies, and for France among Continental nations. Indications pointing unmistakably in the same direction are to be observed in the United States, Germany (especially Saxony, and certain of the big cities) as well as in Belgium and Italy. 1 Newsholme and Stevenson, ‘‘ The Decline of Human Fertility in the United Kingdom,” &c., Jour. Royal Statis. Soc., 1906. ® Yule, ‘On the Changes in the Marriage and Birth-Rates,” &c., Jour. Roy. Statis. Soc., 1906. 3 Sidney Webb, ‘‘ The Decline in the Birth-Rate,” Fabian Society Tract, London, 1907. 4 Heron, “On the Relation of Fertility in Man to Social Status,” &c., Drapers’ Company Memoir, London, 1906. 5 Kelly, loc. cit, 6 Sidney Webb, loc. cit. 7 Newsholme and Stevenson, loc, cit. 622 'THE PHYSIOLOGY OF REPRODUCTION The German rural population are apparently still unaffected, while the British and Irish Catholics are almost so, since any regulation of the married state is forbidden by their religion, but in other Catholic countries this prohibition does not appear to be so strongly insisted on, and is often altogether ignored. To the political economist of sixty years ago this decline in the production of children would have been regarded as the fulfilment of an aspiration, but the modern economist takes a different view. He believes that a mere limitation of numbers cannot be a factor in the improvement of social conditions, and the student of Eugenics never tires of urging that the real danger before society is not over-multiplication, but multiplica- tion of the unfit. As Sidney Webb has said: “ Modern civilisa- tion is faced by two awkward facts; the production of children is rapidly declining, and this decline is not uniform, but char- acteristic of the more prudent, foreseeing, and restrained members of the community. . . . The question is whether we shall be able to turn round with sufficient sharpness and in time. For we have unconsciously based so much of our social policy—so many of our habits, traditions, prejudices, and beliefs—on the assumption that the growth of population is always to be reckoned with, and even feared, that a genuine realisation of the contrary position will involve great changes. There are thousands of men thinking themselves educated citizens to-day to whose whole system of social and economic beliefs the dis- covery will be as subversive as was that announced by Copernicus. We may at last understand what the modern economist means when he tells us that the most valuable of the year’s crops, as it is the most costly, is not the wheat harvest or the lambing, but the year’s quota of adolescent young men and women enlisted in the productive service of the community ; and that the due proportion and best possible care of this particular product is of far greater consequence to the nation, than any other of its occupations.” ! 1 Sidney Webb, loc. cit. Cf. also Whetham, The Family and the Nation, London, 1909. CHAPTER XV THE FACTORS WHICH DETERMINE SEX “ What was a question once is a question still”’—Bacon. A work upon the Physiology of Reproduction would be incom- plete without some reference to the problem of sex-determina- tion, and: some account of the more recent attempts which have been made towards its solution. A résumé of some of the more important papers and memoirs is given by Morgan in his work on Experimental Zoology,) and the reader is referred to this volume for further references and fuller information in regard to certain of the points discussed. It is hoped, however, that the present summary may prove useful if only as a supple- ment to Morgan’s discussion, since certain important papers dealing with sex-determination and containing an account of experimental investigations have been published since the appearance of Morgan’s volume, and these papers I have en- deavoured to summarise here. Moreover, some of the more recent observations, and more particularly those relating to “parasitic castration,’ have necessitated a further revision of the conclusions previously arrived at. Reproduction in organisms may occur by simple fission or budding, in which case it is said to be asexual, or it may involve the union of two conjugating cells, which in Metazoa and Meta- phyta are specially differentiated for the purpose, and are known as ova and spermatozoa. In some animals these two types of cell are produced by the same individual, which is then said to be hermaphrodite or moncecious, but such a condition is rare or absent altogether among the highest forms of life. In the vast majority of animals there are two sexes—that is to say, two kinds of sexual individuals, the male and the female, whose ? Morgan, Experimental Zoology, New York, 1907. See also Geddes and Thomson, The Evolution of Sex, Revised Edition, Londor, 1904, and Thomson, Heredity, London, 1908. 623 624. THE PHYSIOLOGY OF REPRODUCTION respective functions are to produce spermatozoa and ova. This condition is described as dicecious. Again, in a relatively small number of animals, of which the bee is a familiar example, there are three kinds of individuals, perfect females, imperfect females, and males. In a few insects there are even more than three kinds. Lastly, in certain of the lower animals the females can reproduce ova which are capable of developing into adult in- dividuals without conjugating with spermatozoa. This method of reproduction is described as parthenogenetic (see p. 216). Among dicecious animals the two sexual individuals are generally produced in approximately equal numbers. Thus, in Man the number of male births is only slightly in excess of the number of female births, the proportion varying very slightly in different countries,! while in those races in which the numerical proportion of the two sexes among the adult population is very unequal, inequality is due to a higher death-rate of children belonging to one sex. Thus among the Todas the pronounced preponderance of males over females results from the practice of female infanticide.? Theories of sex determination may be conveniently arranged under three headings :—(1) Those in which it is assumed that the sexual condition of the individual is determined subsequently to fertilisation and during embryonic or larval life; (2) those which assume that sex is established either at the moment of fertilisation or prior to fertilisation ; and (3) those which limit sex-determination to no particular period, or which definitely assert that sex may be established at different periods of development in different animals. (1) THEORIES WHICH ASSUME THAT SEX-DETERMINATION TAKES PLACE SUBSEQUENTLY TO FERTILISATION In tadpoles sex is apparently indeterminate until a rela- tively late stage of development, but it is said to be established at the time of metamorphosis. Born,? and subsequently 1 Bodio, ‘‘ Movimento della Populazione,” Confront Internazionali, 1895. 2 Punnett, ‘‘On the Proportion of the Sexes among the Todas,” Proc. Camb. Phil. Soc., vol. xii., 1904. 3 Born, ‘‘ Experimentelle Untersuchungen ueber die Entstehung der Geschlechtsunterschiede,” Breslauer drztliche Zett,, 1881. THE FACTORS WHICH DETERMINE SEX 625 Yung * and certain other investigators, have adduced evidence in support of the view that the sex is determined by the quantity and quality of the food supply. Thus they claimed that they could produce an excess of females by feeding the tadpoles upon a meat or fish diet. The conclusions of these authors, however, are hardly borne out by more recent researches, for Cuénot’s experiments,” conducted on similar lines to those of Born and Yung, show a preponderance of males among tadpoles which were fed upon animal food, and an approximate numerical equality among those which received an exclusively. vegetable diet. Moreover, the method adopted by Born for ascertaining the sex of the individual tadpoles during the period of meta- morphosis seems to have been unsatisfactory, since it was based on the assumption that the ovary is always larger than the testicle, whereas this is not invariably the case. It is stated also that frogs’ eggs from certain localities yield a higher per- centage of females than those from other localities, and conse- quently that a disproportion of the sexes may exist under normal conditions, but this fact in itself does not show that sex is not determined by nutritive or other environmental influences, but may point to a directly opposite conclusion. But, as Morgan points out, if the natural disproportion between the two sexes is great, errors may easily creep into the experimental results. Lastly, King’s observations relating to sex-determination in Amphibians provide no evidence that-either food or temperature are factors in this process.4 The experiments of Treat® and other observers who at- tempted to show that the sex of caterpillars could be determined artificially by regulating the supply of food may be disregarded, since it has since been shown that the sex in those animals is already established at the time of hatching, while it is 1 Yung, ‘De 1l’Influence de la Nature des Aliments sur la Sexualité,” C. R. de V Acad. des Sciences., vol. xciii., 1881. : ? Cuénot, “ Sur la Détermination du Sexe chez les Animaux,” Bull, Sci. de France et Belg., vol. xxxii., 1899. 3 Morgan, loc. cit. 4 King, “Food as a Factor in the Determination of Sex in Amphibians,” Biol, Bull., vol. xvi., 1909. ‘Temperature as a Factor,” &c., Biol, Bull., vol. xviii., 1910. 5 Treat, ‘‘Controlling Sex in Butterflies,” American Naturalist, vol. vii., 1873. 2k 626 THE PHYSIOLOGY OF REPRODUCTION improbable in the cases described that it could have been reversed after having been differentiated. Furthermore, experi- ments by Briggs 1 and other investigators have failed to support the hypothesis that the proportion of the sexes can be altered by modifying the diet, while Kellogg? has shown that in the case of the silkworm moth, sex is definitely determined as early as immediately after the first larval moulting, this conclusion being based on an examination of the rudimentary reproductive glands. According to Cuénot® the essential organs of reproduction in the maggots of flies are not differentiated into ovaries or testicles until a late period of larval development. There was a possibility, therefore, that in these animals the sex could be modified by the conditions of nutriment or other external factors. Cuénot found, however, that the proportion of the sexes was not materially affected by the supply of nourishment, although the maggots were fed upon different kinds of food, some being given brain, suet, and a little meat, some a large supply of putrefying flesh, while others were relatively starved. Among bees and other hymenopterous insects the nutriment appears to be the main factor determining the difference be- tween the two kinds of females (workers and queens). A worker larva can be made to develop into a queen by supplying “royal food,” that is, food which is given to young queens. In the worker the female generative organs never fully develop, but royal diet stimulates these organs to grow so that the larve become queens. A partially developed worker may be made partially fertile by supplying it with some of the jelly obtained from a royal cell. The following table shows the relative com- position of the solid food given to workers and queens : 4—- Solid Food. Workers. Queens. Nitrogenous . : ; 51:21 45-14 Fatty . : i F 6°84 13°55 Glucose . : - : 27°65 20°39 This table shows that the quantity of fatty material supplied 1 Briggs, ‘‘ Notes on the Influence of Food in Determining the Sexes of Insects,” Trans. Entom. Soc., London, vol. i., 1871. 2 Kellogg, ‘‘ Notes on Insect Bionomics,” Jour. of Exper. Zool., vol. i., 1904. 3 Cuénot, loc. cit. * Geddes and Thomson, loc. cit. THE FACTORS WHICH DETERMINE SEX 627 to the developing queens is very nearly double that given to the workers. There is no evidence that drone larve can be converted into females by a supply of royal or other food, so that the case of bees can scarcely be regarded as affording a real instance of sex being determined by conditions of nutrition, since workers are true females whose reproductive organs and other sexual char- acteristics have failed to develop owing to an insufficiency of stimulating food. The case of white ants or termites is probably comparable, though considerably more complicated, since the different kinds of sexual individuals are more numerous. The young may develop into workers, soldiers, or royal substitutes, and the latter may be further transformed into fully fertile or “ royal ” individuals, while both sexes (i.e. males and females) are represented in each of these forms. Grassi’s observations ! point strongly to the conclusion that these different kinds of indivi- duals are developed from similar eggs under different condi- tions of nutrition which is supplied to the young by the older members of the community ; but here again there is no evidence that males can be converted into females or females into males. Rolph? has described a series of observations on the pro- duction of males and females in Nematus ventricosus, a species of wasp. These observations show that the percentage of females in broods of larve reared from fertilised ova steadily increased from June to August and then proceeded to diminish. “We may conclude without scruple, that the production of females from fertilised ova increases with the temperature and with the food supply (Assimilationsleistung), and de- creases as these diminish.” Certain further experiments with unfertilised ova of the same species seem to show that “ the more abundant the metabolism (Stoffwechsel) and the nutrition, the greater the tendency to the production of females.” In the normal condition males only were produced as a result of 1 Grassi and Sandias, ‘‘ The Condition and Development of the Society of Termites,” Quar. Jour. Micr. Science, vols, xxxix. and xl., 1896-97. 2 Rolph, Biologische Probleme, Leipzig, 1884. * Translated by Geddes and Thomson. 628 THE PHYSIOLOGY OF REPRODUCTION parthenogenetic development, but the superior nutrition is believed to have led to the production of females. The fact that in certain Crustacea a condition of herma- phroditism can be induced by an external cause acting on a sexually differentiated individual is discussed below in dealing with latent characters. (2) THEORIES WHICH ASSUME THAT SEX-DETERMINATION TAKES PLACE AT THE TIME OF FERTILISATION OR PREVIOUSLY TO FERTILISATION Effect of Fertilisation—While it seems certain that queen and worker bees are developed from fertilised eggs under different conditions of nutrition, the conclusion is now fairly established that drones or male bees arise parthenogenetically from unfertilised eggs. If this view is correct, it clearly follows that in bees the differentiation into female and male individuals is brought about by the occurrence or non-occurrence of fertilisa- tion. This theory of sex-determination in the bee was first formulated by Dzierzon,) and has since been accepted by Weismann ? and many other biologists, although some writers, such as Beard,® deny the conclusion that fertilisation is capable of exercising any such influence. In support of his contention Beard quotes an observation by Weismann and Petrunkewitsch, showing that a drone egg may occasionally undergo fertilisation. He also refers to the results obtained by “ bastardising ’ hives of bees through the intro- duction of Italian queens into colonies of German workers and drones, or of German queens into Italian swarms. In such a bastard hive Dzierzon found a drone which appeared to be a cross between a German and an Italian bee, and which conse- quently afforded evidence of a drone egg having been fertilised. This result led Dzierzon temporarily to doubt the truth of his 1 Dzierzon, “Uber die Befruchtung der Kénigin,” Hichstadt Bienen- Zeitung, vol. i., 1845. 2 Weismann, ‘‘ Ueber die Parthenogenese der Bienen,” Anat. Anz., vol. v. 1900. 3 Beard, “The Determination of Sex in Animal Development,’ Zool. Jahrb., vol. xvi., 1902. 4 Von Siebold, Wahre Parthenogenesis bei Schmetterlingen und Bienen, Leipzig, 1856. THE FACTORS WHICH DETERMINE SEX 629 hypothesis, but he subsequently accepted the interpretation of von Siebold, who suggested that the queen which had given rise to the apparently bastard drone was herself of impure descent, and that in reality the egg had not been fertilised. A further exceptional case has been recorded by Perez,1 who found that a considerable number of male bees produced by an Italian queen which had been fertilised by a French drone appeared to be of mixed blood. This result, which is admittedly unusual, has been explained by Sanson ? as due to “ reversion,” while it has also been pointed out that the hybrid drones may conceivably have arisen from hybrid workers which sometimes lay eggs, and further that male bees are often very variable in their characters. Hither of these explanations would appear to be possible. Moreover, the later observations of Petrunkewitsch,! showing that sperm nuclei are not found in drone eggs whereas they are commonly met with in worker eggs, supply an important confirmation of Dzierzon’s hypothesis. Attempts to extend this hypothesis to other hymenopterous insects have not been so satisfactory, though it seems, as a general rule, to hold good for ants. There are instances cn record, however, in which worker ants have developed from parthenogenetic ova, and other exceptional cases have been stated to occur.® Among the Tenthredinide or sawflies also the unfertilised eggs commonly develop into males, but this is by no means invariable. Thus in some forms fertile parthenogenetic females only have. been known to arise for many generations in suc- cession without the appearance of males.® 1 Perez, ‘‘Mémoire sur Ja Ponte de l’Abeille reine et la Théorie de Dzierzon,” Annales des Sciences Nat., vol. v., 1878. ? Sanson, ‘‘ Note sur la Parthénogénése chez les Abeilles,” Annales des Sctences Nat., vol. v., 1878. 3 Morgan, loc, cit. 4 Petrunkewitsch, ‘‘Die Richtungsk6rper und ihr Schicksal im befruch- teten und unbefruchteten Bienenei,’’ Zool. Jahrb., vol. xiv., 1901. ‘‘ Das Schicksal der Richtungsk6rper im Drohnenei,” Zool. Jahrb., vol. xvii., 1902. 5 Wheeler, ‘‘The Origin of Female and Worker Ants from the Eggs of Parthenogenetic Workers,” Science, vol. xviii., 1903. ® Doncaster, ‘‘On the Maturation of the Unfertilised Egg and the Fate of the Polar Bodies in the Tenthredinide,” Quar. Jour. Micr. Science, vol, xlix., 1906, 630 THE PHYSIOLOGY OF REPRODUCTION In the parthenogenetic Rotifer, Hydatina, Maupas’ has adduced strong evidence that if the parthenogenetic male eggs are fertilised they are thereby converted into “ winter” eggs which give rise solely to females. If this is so (and Maupas’s conclusions are now generally accepted), it is a clear instance of fertilisation altering the sex of the individual. It is stated, however, that impregnation has no effect unless it is performed during the first few hours after hatching. Certain writers have adopted the view that sex in animals generally is regulated by the time at which fertilisation takes place, that is to say, by the condition of the germ cells. Thus, Thury ? and subsequently Diising* expressed the opinion that an egg which is fertilised shortly after ovulation usually de- velops into a female, and that an older egg tends to produce a male. Thury claimed that he could regulate the sexes in cattle by allowing coitus only at the beginning or at the end of the cestrous periods, an early coitus being supposed to result in the birth of a female, and a late coitus in the production of a male, but other investigators have failed to establish Thury’s conclusions. Influence of Nutrition Schenk * also has elaborated a highly speculative theory which supposes sex to be determined by the relative degree of “ripeness” or “ unripeness ” of the ovum ; but the term “ unripeness ” is here used to imply a condition consequent upon incompleteness of nutrition, while “ ripeness ” is held to result from a more favourable state of nutrition. “ Ripe ” ova are supposed to develop into males, and “ unripe ” ones into females. The presence of sugar in the urine is evidence of an incomplete metabolism, and hence is regarded by Schenk as implying a condition likely to result in the birth of females. By supplying women with a highly nitrogenous diet, which 1 Maupas, “Sur la Multiplication et la Fécondation de 1’Hydatina senta,” C. R. del’ Acad, des Sci., vol. cxi., 1890. ‘‘Sur la Fécondation de V’Hydatina senta,” C. R. de l’Acad. des Sct., vol. cxi., 1890. ‘Sur la Déterminisme de la Sexualité chez Hydatina senta,” C. R. de [ Acad. des Sci., vol. cxiii., 1891. 2 Thury, Ueber das Gesetz der Erzeugung der Geschlechter, Leipzig, 1863. 3 Diising, ‘‘ Die Regulierung des Geschlechtsverhaltnisses bei der Vermeh- rung,” &c., Jenaische Zeitschr., vol. xvii., 1884. 4 Schenk, The Determination of Sex, English Translation, London, 1898. THE FACTORS WHICH DETERMINE SEX 631 prevented the elimination of sugar in the urine and made the metabolism more complete, Schenk claimed that he could ripen the ova, and so increase the chances of male offspring. Influence of Environment.—It has long been known that parthenogenesis is the normal method of reproduction among plant-lice or Aphides during the months of summer, successive generations of individuals arising in this way, but that with the approach of autumn males make their appearance and repro- duction then becomes sexual. If, however, the Aphides be kept in an environment of artificial warmth, and at the same time are supplied with abundant food, the succession of partheno- genetic females may be caused to continue for years without the appearance of the sexual form. It is to be noted that the sexual and parthenogenetic females are not identical, and also that the same female may give rise to parthenogenetic and sexual offspring, or to males and females, or to only one sex. Moreover, Stevens has shown that male and female embryos may be produced practically simultaneously by the same in- dividual. It is maintained therefore by this writer that “ the changes in sex usually attributed to changes in external con- ditions are really a change from the parthenogenetic to the sexual mode of reproduction. The life cycle is often very com- plicated, and in some species of Aphides there is evidence that the environment (e.g. the trees on which they live) rather than the temperature is responsible for the development of the sexual forms.t : Many of the lower Crustacea undergo a somewhat similar alternation of generations. For example, the water-flea (Daphnia), after reproducing parthenogenetically during the summer time, deposits eggs which give rise to sexual forms at the commencement of autumn, and the female after impreg- nation lays the winter eggs from which the new brood arises. This result is generally supposed to be brought about by the conditions of temperature or nutrition; but Weismann,” as a consequence of numerous experiments and observations, has 1 Balbiani, ‘‘ Le Phylloxera du Chéne et le Phylloxera de la Vigne,” &c., Mém. & V?Acad. des Sci., vol. xxviii., 1884. Stevens, ‘Studies on the Germ Cells of Aphids,” Carnegie Institution Publications, Washington, 1906. * Weismann, “‘Beitrige zur Naturgeschichte den Daphniden,” Zettsch. f. wiss. Zoologie, vols. xxvii,, xxviii., xxx., and xxxiii., 1876-79. 632 THE PHYSIOLOGY OF REPRODUCTION cast doubts upon this view, believing rather that the animal has been so constituted by natural selection that it tends spon- taneously to reproduce sexually in the appropriate season, and that it does so to a large degree irrespectively of the actually existing conditions. More recently Issakowitsch ' has carried out an investigation upon another daphnid, Simocephalus, from which he has been able to show that differences in tem- perature may determine the mode of reproduction, but that this result is effected indirectly by the change of temperature altering the conditions of nutrition. Unfavourable conditions tend to the production of sexual forms, and favourable ones to the parthenogenetic method of generation. The same individual female may give rise either to sexual or parthenogenetic offspring, the conditions which exist in the ovary appearing to determine what kind of egg will develop. In the Rotifer Hydatina senta there are at least two kinds of females, which are distinguished by the kinds of eggs that they lay—(1) thelytokous females, which produce other females parthenogenetically, and (2) arrenotokous females, which pro- duce males parthenogenetically. The second kind of female may also produce fertilised eggs. Furthermore, the thelyto- kous females may give rise either to arrenotokous females or to more thelytokous females, and the proportion of arreno- tokous females so produced is hable to considerable variation. Maupas* has sought to connect this variation with differences in temperature, and Nussbaum? with differences in nutri- tion, but neither conclusion has been satisfactorily established. The question has been reinvestigated by Punnett, who has carried out a number of further experiments. In one of these a strain which had hitherto appeared to be purely thelytokous was subjected to considerable fluctuations of temperature. The rate of reproduction was much retarded, but in the subsequent generations which were produced no arrenotokous females could 1 Issakowitsch, ‘‘Geschlechtsbestimmende Ursachen bei den Daphiden,” Biol. Centralbl., vol. xxv., 1905. 2 Maupas, loc. cit. * Nussbaum, “Die Entstehung des Geschlechtes bei Hydatina senta,”’ Arch. f. Mikr, Anat., vol. xlix., 1897. 4 Punnett, ‘“‘Sex-determination in Hydatina,” Proc. Roy. Soc., B., vol, Ixxviii., 1906. THE FACTORS WHICH DETERMINE: SEX 633 be found. Starvation experiments were undertaken, and in these also thelytokous females which had hitherto “ bred true” continued to do so. Punnett concludes that neither temperature nor nutrition has any influence in determining the production of arrenotokous females. On the contrary, it is the property of certain females to produce arrenotokous females in a definite ratio, and the property of others to produce none. Theorves which assume that the Gametes are themselves Secual. —Many biologists have entertained the conception that the gametes are themselves sexual, and a number of facts have been adduced which give very strong support to this idea. Some of these have already been mentioned, but probably the strongest evidence in favour of this generalisation is that relating to the existence of sexually differentiated spermatozoa. It has been known for a long time that two kinds of sperm exist in the snail Paludina, a hair-like form and a worm-like form, but it is commonly believed that only: the former is func- tional. Dimorphic spermatozoa have also been discovered in various other animals, but the differences between the two kinds vary greatly.1 Henking ? made the discovery that in the bug, Pyrrhocoris, half of the spermatozoa differ from the other half in possessing an additional chromosome. . McClung® was the first to suggest that the difference between the two sorts of spermatozoa in this insect was connected with sex-determination, and that those which contained the accessory chromosome produced males and that those without it produced females. The last assumption has, however, proved to be incorrect, since Wilson * found that 1 A list of species in which dimorphic forms of spermatozoa have ‘been recorded (down to 1902) is given by Beard, loc. cit. ? Henking, ‘‘ Untersuchungen ueber die ersten Entwicklungsvorginge in den Eien der Insekten,” Zettschr. f. wiss. Zool., vol. xlix., 1890, and vol. li., 1891. 3 McClung, “The Accessory Chromosome Sex Determinant,” Biol, Bull., vol. iii., 1902. : 4 Wilson, ‘‘ Studies on Chromosomes,” Jour. of Exp. Zool., vols. ii. and ili., 1905-6; vol. vi., 1909. ‘‘ Note on the Chromosome Groups of Metapodius and Banusa,” Biol. Bull., vol. xii., 1907 ; ‘‘ The Supernumerary Chromosomes of Hemiptera,” Science, vol. xxvi., 1907; see also Stevens, ‘‘ Studies in Spermatogenesis,” Part I., 1905, and Part II., 1906, Carnegie Institution 634 THE PHYSIOLOGY OF REPRODUCTION in this and other forms the female and not the male contains an additional chromosome in its somatic cells. It is almost certain also that the ova have one more chromosome than one half of the sperms have, and the same number as that possessed by the sperms which contain the additional chromosome. Consequently the latter are supposed to produce females and the former males. For example, in Anasa tristis the somatic cells of the male contain twenty-one chromosomes, whereas those of the female contain twenty-two. Half of the spermatozoa are supposed to contain eleven chromosomes, the other half having only ten. The ova are believed to all resemble one another in containing eleven chromosomes. It is concluded, therefore, that the spermatozoa possessing the smaller number give rise to males, while those with eleven chromosomes produce females.* Payne 2 has recently shown that in Galgulus oculatus there are two sorts of spermatozoa possessing respectively sixteen and nineteen chromosomes, whereas the eggs are uniform in containing nineteen chromosomes. Furthermore, the females are believed to have three more chromosomes than the males (z.e. thirty-eight as compared with thirty-five). It is evident therefore that the sexual differences of the chromosomes, even in the same order of animals, do not conform to a single numerical rule, but at present it would appear that where there is a difference in the number it is always the female which has more chromosomes than the male. That two sorts of spermatozoa (one with an additional chromosome) may exist in other animals besides insects has Publications, Washington. In these papers dimorphic spermatozoa (one kind containing one smaller chromosome or lacking one chromosome) are described for various species of Orthoptera, Coleoptera, Hemiptera and Lepidoptera. 1 Miss Foote and Strobell (‘‘ A Study of Chromosomes in the Spermato- genesis of Anasa tristis,” Amer. Jour. of Anat., vol. vii. 1907), as a result of an investigation withsmear preparations instead of sections, find no evidence of a persisting accessory chromosome in Anasa tristis, and believe that the body described as such by Wilson is a plasmosome and not a chromosome. 2 Payne, ‘On the Sexual Differences in the Chromosome Groups in Galgulus oculatus,” Biol. Bull., vol. xiv., 1908. Correns also has shown that in some plants there are two classes of male germ cells, and that these are produced in equal numbers (Die Bestimmung und Vererbung des Geschlechtes nach neuen Versuchen mit hiheren Pflanzen, Berlin, 1907). THE FACTORS WHICH DETERMINE SEX 635 been shown by Guyer,! who has investigated the matter for the chicken and guinea-fowl.? (See footnote’, p. 657.) The manner in which the spermatozodn with the accessory chromosome (or chromosomes) produces a female is still an open question. It is often supposed that the accessories are themselves the carriers of those hereditary characters which distinguish the female sex, but it may be that the result is due simply to the greater amount of chromatin carried into the egg in the process of fertilisation. “ The result,” as Morgan remarks, “is similar to that of the bee, in the sense that the fertilised egg contains more chromosomes than the unfertilised, and produces in consequence the female.* In the absence of all knowledge as to how the greater quantity of chromatin produces a female, one is tempted to assume that the result is reached through assimi- lative changes that take place in the early cells, and there is some evidence in favour of the view that one of the main functions of the chromatin is tocarry on the assimilative processes in the cells.” Morgan has shown further that in Phylloxera, in which all the fertilised ova become females, the “male” spermatozoa are rudimentary.* The theory that there are two kinds of sexually differentiated. ova has also been advanced. In support of this contention it has been pointed out that in Hydatina senta, Phylloxera, and Dinophilus apatris, there are two sizes of eggs, and that in each case the large eggs produce females and the small ones males. It is not clear, however, whether the size determines the sex, or the sex controls the size, but Beard says: “ As the size of the egg will naturally be attained during the odgenesis, it would seem to follow, that here the destination of the odgonium must 1 Guyer, ‘‘The Spermatogenesis of the Domestic Chicken,” Anat. Anz., vol. xxxiv., 1909; “ Guinea-fowl,”’ Anat, Anz., vol. xxxiv., 1909. 2 So also in the Nematode Heterakis and probably also in Ascaris (see Boveri and Gulick, Arch. f. Zellforsch, vol. iv., 1909). 3 It is said that in the process of spermatogenesis in the drone one of the maturation divisions is suppressed, a fact which suggests that only half the normal number of chromosomes is present in the cells (Meves, Arch. f. Mtkr. Anat., vol. 1xx., 1907). 4 Morgan, “The Production of two Kinds of Spermatozoa in Phyl- lowerus,” &c., Proc, Soc. Exp. Biol. and Med., vol. v., 1908; “Sex De- termination and Parthenogenesis in Phyllowera and Aphids,’ Science, vol, xxix., 1909. 636 THE PHYSIOLOGY OF REPRODUCTION be determined prior to the final phenomena of the reduction and of the ripening, for these latter would not appear to possess any influence on the size of the egg itself.” ! Beard states that the eggs of the skate, Raja batis, are likewise of two kinds. It is also pointed out in support of Beard’s view that according to von Ihering? embryos which are found in one chorion (and which are supposed, therefore, to have arisen from one ovum) in the Edentate Praopus hybridus, are invariably of one sex, and that “ double monsters ” in Man are of the same sex, while Marchal? states that in the chalcid fly (Ageniaspis fuseicollis) in which a chain of embryos takes origin from a single egg, these embryos are all of one sex. (See footnote *, p. 657.) Beard asserts that sex is determined solely in the egg, and that in those animals in which there are two kinds of spermatozoa one kind is always functionless. This theory is clearly opposed by the facts discovered by Wilson regarding the spermatozoa of many insects, and by the case of the bee and other forms in which sex is determined by fertilisation. It must be pointed out, however, that, according to Morgan, in the parthenogenetic Phyllozera, the egg has the power of determining sex by regu- lating the number of its chromosomes in the same kind of way as has been shown in the case of other insects for the spermatozo6n.* The view has also been entertained that there is a relation between the position of the ovary and the sex of the ova. Thus, according to Rumley Dawson,* the ova produced by the right ovary become males, and those produced by the left become females. This theory is believed to be applicable especially to Man, and is based on clinical evidence and on a supposed alterna- tion of the sexes of the eggs discharged at the ovulation periods. It clearly cannot apply to birds, in which the left ovary only is functional, and King® has shown experimentally that it is 1 Beard, loc, cit. 2 Von Ihering, ‘‘ Ueber Generations-wechsel bei Siugethieren,” Biol. Centralbl., vol. vi., 1886. 5 Marchal, ‘‘Recherches sur la Biologie et le Développement des Hymenoptéres parasites,” Arch. de la Zool. Expér. et Gén., vol. ii., 1904. 4 Morgan, Proc. Soc. Exp. Biol, and Med., loc. cit. 5 Dawson, The Causation of Sex, London, 1909. 6 King, ‘‘Studies on Sex Determination in Amphibians,” Biol. Bull, vol, xvi., 1909. = THE FACTORS WHICH DETERMINE SEX = 637 inapplicable to Amphibians. The alternative theory that sex depends on the position of the testis from which the fertilising spermatozo6n was derived has been negatived by Copeman? as a result of an experimental investigation upon rats. Castle’s Theory.— Bateson * was the first to suggest that the Mendelian laws are applicable to sex-heredity. This suggestion has been elaborated by Castle * into a theory which is based on the idea that sex is determined during the process of maturation, when the male and female gametes are believed to undergo differentiation. Thus, in the case of the ovum, the male or female element is supposed to be ejected in one of the polar bodies, while a similar process is thought to occur in spermato- genesis, excepting that in the latter case all the products of division become functional gametes. According to this hypo- thesis the ordinary sexual individual is regarded as comparable to a Mendelian hybrid. It is clear, however, that the ordinary Mendelian interpretation requires modification if it is to be applied to the phenomena of sex, since hermaphrodite in- dividuals do not occur in accordance with the usual formula which assumes a gametic segregation and three kinds of conjugation according to the law of probabilities :— Spermatozoa . 50 per cent. male +50 per cent. female, Ova : . 50 per cent. male+50 per cent. female. Result after cingisuatunt ; 25 per cent. mm.+50 per cent. mf.+25 per cent. ff, If this result actually happened, hermaphrodite individuals (mf.) would be twice as common as individuals belonging to either sex. Castle assumes, therefore, that male spermatozoa are capable of conjugating with female ova only, and that female spermatozoa can conjugate with male ova only. The actual determination of sex in the zygote is supposed to depend upon whether the male or female character is dominant. Dominance, according to this theory, in dicecious forms, is 1 Copeman, “Sex Determination,” Phys. Soc., May, 1908. 2 Bateson, Report to the Evolution Committee of the Royal Society, I., 1902, 3 Castle, ‘‘ The Heredity of Sex,” Bulletin of the Museum of Comparative Zoology, Harvard, vol. x1., 1903. 6388 THE PHYSIOLOGY OF REPRODUCTION possessed sometimes by the male character and sometimes by the female. No zygotic individual is of either sex purely, for the characters of the recessive sex (whether it be male or female) are latent, as has been shown both anatomically and experi- mentally.' In parthenogenetic animals, however, the female character always dominates over the male whenever the characters of both sexes are present together. In such species, all the fertilised ova are female, those unfertilised ova which are formed without the segregation of the sex characters are also female, while male individuals only develop from un- fertilised ova from which the female character has been eliminated. “The segregation of sex characters takes place in most parthenogenetic animals, and doubtless in dicecious animals also, at the second maturation division (the ‘reduction division ’) of the egg, and probably at a corresponding stage in spermatogenesis. For (1) eggs which develop without ferti- lisation and without undergoing a second maturation divi- sion contain both the male and female characters, the former recessive, the latter dominant; but (2) in normally partheno- genetic species, eggs which, after undergoing a second matura- tion division, develop without fertilisation, are always male (except in the gall-wasp, Rhodites). In such species the female character regularly passes into the second polar cell, the male character remaining in the egg. In dicecious animals, on the other hand, either sex character may remain in the egg after maturation.” , In Hydatina senta only a single division occurs in the matura- tion of the male eggs, and this is held to be comparable to the second maturation division of other parthenogenetic forms, and in it a segregation of sex characters is believed to take place. In the case of the female parthenogenetic ovum no maturation division occurs. The parthenogenetic egg of the gall-wasp (Rhodites rose) undergoes two maturation divisions, but apparently without segregation taking place in either of them, for no reduction occurs (at least normally), the nucleus of the ovarian egg, the three polar nuclei, and the nuclei of the mature egg being alike in each containing nine chromosomes. * Evidence that this is so is given below (p. 652 et seq.). ‘THE FACTORS WHICH DETERMINE SEX 639 The offspring are almost invariably females. Castle concludes that in those rare instances in which males are produced a reduction of chromosomes probably takes place, the dominant female character being then eliminated. Experiments by Doncaster and Others——Important evidence has lately been obtained by Doncaster as a result of breeding experiments with certain Lepidoptera. He has shown that in the moth Abraxas grossulariata, there is a rare variety, which penerally occurs only in the female sex. This variety, which is called A. grossulariata lacticolor, is a Mendelian recessive, so that when crossed with an ordinary grossulariata male, the offspring are all typical, the lacticolor variety disappearing. Experimental crossings yielded the following results :— (1) Lact. 9 x gross. $ gave males and females all gross. (2) Heterozygous? ? x heterozygous ¢ gave gross. g, gross. @, and lact. ¢. (3) Lact. 9 x heterozygous g gave all four possible forms (gross. ¢ ,lact. ¢, gross. , and lact. ? ), the lacticolor males being the first ever seen. (4) Heterozygous ? x lact. ¢ gave gross. g and lact. 9. (5) Lact. 9 x lact. g gave lact. ¢ and lact. ?. (6) Wild gross. ? x lact. ¢ gave gross. ¢ and lact, ?. It is shown, therefore, that males of the lacticolor variety can be produced by mating lacticolor females with heterozygous males (i.e. with males obtained by crossing the two original varieties, and so presumably bearing two sorts of gametes), but that the converse mating (4) results in offspring which are either grossulariata males or lacticolor females. Further- more, whereas lacticolor females, mated with wild grossulariata 1 Doncaster, ‘Recent Work on Determination of Sex,” British Associa- tion Report, Dublin Meeting, 1908. See also Punnett and Bateson, “The Heredity of Sex,” Science, vol. xxvii., 1908. ? The term heterozygote has been given by Bateson to offspring result- ing from the union of dissimilar gametes. Such organisms, according to the Mendelian theory, produce more than one sort of gamete (see p. 194). Homozygotes are formed by the union of similar gametes, and produce gametes of one kind. Thus, homozygotes, as regards sex, are believed to produce gametes bearing one sex character only (either male or female) ; whereas heterozygotes, as regards sex, are supposed to give rise to both male-bearing and female-bearing gametes. 640 THE PHYSIOLOGY OF REPRODUCTION males (1) produce offspring which are of both sexes, but all of the grossulariata variety, the converse cross (6) yields grossu- lariata males and lacticolor females. It is concluded, therefore, that the wild and presumably pure grossulariata females are heterozygous for sex, femaleness being dominant and maleness a homozygous recessive character. All the females are be- lieved to produce male-bearing and female-bearing gametes in equal numbers, whereas all the males appear to produce only male-bearing spermatozoa. According to this view, in gameto- genesis there is a repulsion between the female determinant and the grossulariata determinant, so that each gamete can be the bearer of one or other of these two characters, but not of both. The results obtained by Miss Durham in her experiments on cinnamon canaries are explicable on a similar hypothesis. When a cinnamon male was mated with a green female, the female offspring were cinnamon and the males green; but when a cinnamon female was paired with a green male, all the offspring of both sexes were green.’ Where, however, a green cock of the second generation (the F, generation produced by crossing) was mated with a cinnamon hen, both green and cinnamon birds of both sexes were produced ; but when a green cock of the second (F,) generation was crossed with a green hen the resulting male birds were all green, but the females were of both types. A more complex case of a like kind has been brought to light by Bateson and Punnett in their investigation on the heredity of the black pigmentation of the silky fowl in its crosses with brown Leghorns and other fowls with light shanks. Here two allelomorphic characters, in addition to the two sex determinants, are concerned, but Bateson and Punnett state that the facts point very clearly to some such solution as that indicated by Doncaster’s experiments with Abraxas. They suggest further that whereas in Vertebrates it is probable that the female is heterozygous as regards sex (the production of secondary male characters in castrated females supporting this view), the work of Potts and Smith (see p. 308) on parasitic castration in Crustacea points to the converse conclusion that in these animals the male is heterozygous, assuming definite 1 Durham, Report to the Evolution Committee of the Royal Society, IV., London, 1908. Cf. p. 637. THE FACTORS WHICH DETERMINE SEX 641 female characters after the destruction of the testicles, while in the female, castration merely arrests development.! Liegler’s Theory—Ziegler? has put forward a theory which assumes that the chromosomes which are derived from a grand- parental female tend to produce a female, and that those de- rived from a grandparental male tend to give rise to a male. Ziegler points out that the parental chromosomes as such cannot determine the sex, since these are equal in number. He there- fore assumes that the grandparental chromosomes are the directing factor, and consequently that sex is a matter of chance depending on the result of the reduction division during matura- tion—that is to say, upon which member of a pair of homologous chromosomes goes to one pole of the spindle and which to the other. Jf the number of chromosomes derived from the male grandparent is greatest, the sex will be male, and if the chromosomes from the female grandparent are most numerous the offspring will be a female. Ziegler’s theory has been ad- versely criticised by Morgan, who writes as follows :—“‘On Ziegler’s theory of sex it is evident that whenever the reduced number of chromosomes is even, there may occur an exact balance of grand- mother and grandfather chromosomes, hence the child can have no sex at all... . It seems improbable that the equal balance of the maternal and paternal chromosomes could be counter- balanced by the presence of chromosomes derived from the grandparents, especially since these have also been contained in one or the other parent whose sex, on the theory, should have in- fluenced them to acquire the character of that parent. These and other difficulties make Ziegler’s hypothesis very improbable.” ® Heape’s Views.-Heape* has recently expressed the belief “that while each ovum and spermatozoén in the generative glands contains within itself sex, which is probably determined by the laws of heredity, the proportion of those male and female ova and spermatozoa which are developed and set free { For further discussion see Bateson, Mendel’s Principles, Cambridge, 1909. ; * Ziegler, Der Vererbungslehre in der Biologie, Jena, 1905. * Morgan, loc. cit. See also ‘‘Ziegler’s Theory of Sex Determination and an Alternative Point of View,” Science, vol. xxii., 1905. ey Heape, ‘‘ Note on the Proportion of the Sexes in Dogs,” Proc, Camb. Phil. Soc., vol. xiv., 1907. 28 642 THE PHYSIOLOGY OF REPRODUCTION from the generative glands may be regulated by selective action, exerted in accordance with the resultant of a variety of extraneous forces. If this be true, the proportion of living male and female ova and spermatozoa which are freed from the generative glands, and the proportion of the sexes of the off- spring which result therefrom, will thus be influenced.” A similar suggestion had been made by Schultze! and also by Morgan.” Heape is of opinion, however, that just as there is evidence that adult animals are never purely male or female,’ so it is probable that the sexual products (7.e. the gametes) are them- selves similarly constituted. According to this view, an ovum or a spermatozodn may possess dominant male or female characters as the case may be, and recessive characters of the opposite sex. ‘In such cases the possibility of infinite grada- tions of sexual differentiation in an individual would be vastly increased, and from the point of view of heredity, such complex conditions carry with them factors of the highest importance.” Ova and spermatozoa in which the characters of one sex are dominant are referred to as being male and female, and Castle’s conclusion is accepted, that an ovum of one sex must always be fertilised by a spermatozo6n of the opposite sex, but whether the sex of the adult is determined by the ovum or by the spermatozo6n is a question which is left open, as it may admit of a different answer for different species of animals, or even for different individuals. Heape says, however, that even if that be so, the sex of the ovum must be regarded as bearing a regular relation to the sex of the embryo as surely as if it con- ferred its own sex. “On this assumption a female parent producing ova of one sex only will give birth to embryos of one sex, unless the male parent possesses no spermatozoa of the opposite sex wherewith to fertilise it, in which case the union will be barren. Diising * claimed that the statistical results he obtained from a study of 1 See below (p. 652 et seq.). 2 Morgan, loc. cit. 3 Cf. Castle (see above, p. 638). Evidence on this point, including some of that adduced by Heape, is cited below in dealing with hermaphroditism and the latency of sexual characters. 4 Diising, loc. cit. THE FACTORS WHICH DETERMINE SEX 643 the mating of thoroughbred horses indicated the dominant influence of the male parent on the sex of the offspring. Any sire that usually produces spermatozoa of one sex only can be fertile, as a rule, only with mares which produce ova of the other sex, and to such an extent he determines the proportion of the sexes of the offspring for which he is responsible ; but where the sperm of both sexes is uniformly produced, the sire must be fertile with all mares producing ova, and as only one ovum is produced by each mare, the responsibility for the sex of the ofispring then lies solely with the female parent.” The opinion is expressed that much of the evidence cited to show the dominating influence of the male parent on the off- spring produced may be explained on this view; “ while statistically the father might be shown to be responsible, physio- logically the mother controls the governing influence.” It is assumed that in normal cases both sexes of ova and spermatozoa are probably produced in the gonads in equal quantities, and that in those females which shed all their ova the proportion of the sexes in the offspring is, in all likelihood, determined by. Mendelian laws. But it is pointed out that in many animals only a small proportion of the ova formed in the ovary ever reach maturity, the remainder undergoing de- generation and ultimately absorption (see p. 156). It is inferred, therefore, that the proportion of the sexes among the ova which survive and are discharged must depend directly upon the causes which lead to the degeneration of some ovarian ova and the continued development of others. On this view it is held that the ova are subject to the same law of natural selection as other organisms, and that in some cases the male ova are best fitted to survive, and in other cases the female ones. Heape* has shown further that in the ovary of the rabbit two kinds of degeneration prevail, and that in one kind it is the follicle which first begins to undergo atretic changes, and that in the other kind it is the ovum that is earliest affected. The former condition is regarded as evidence that the available supply of nutriment is insufficient for the maintenance of all the ova.in the ovary, while the latter is interpreted to mean that 1 Heape, ‘Ovulation and Degeneration of Ova in the Rabbit,” Proc. Roy. Soc., B., vol. xxvi,, 1905. ae 644 THE PHYSIOLOGY OF REPRODUCTION the ovum, for one reason or another, is unable to assimilate the nutriment provided for it. It is possible, therefore, that nutrition may in this way exercise a selective action as regards sex. In this connection it is interesting to note that, according to Issakowitsch,! the nutritive conditions prevailing in the ovary of the daphnid Simocephalus are determinative as to the kind of egg which will develop (i.e. whether it will be a parthenogenetic or a “ winter” egg), and that the two kinds of eggs are stated to arise in different parts of the ovary. More- over, Heape suggests that the marked difference between the death-rate of men and women during famines,” for example, may be reproduced among male and female ova in the ovary when that organ is subjected to conditions of a homologous kind. Heape’s general conclusions are summarised as follows :— “ (1) That through the medium of nutrition supplied to the ovary, either by the quantity or by the quality of that nutrition, either by its direct effect upon the ovarian ova or by its indirect effect, a variation in the proportion of the sexes of the ova pro- duced, and therefore of the young born, is effected in all animals in which the ripening of the ovarian ova is subject to selective action ; (2) That when no selective action occurs in the ovary the proportion of the sexes of ovarian ova produced is governed by laws of heredity.” Having arrived at these conclusions, Heape next adduces evidence that certain external forces may affect the proportion of the sexes in dogs. It is shown that amongst greyhounds conception during the period from August to November is most favourable to the production of males under the conditions of breeding at present practised, and this result is attributed to a selective action on the ova produced at this time. There is evidence also that among dachshunds and Basset hounds the seasons affect the proportions of the males and females born. The bloodhound returns seem to show that an excessive production of males is associated with inbreeding. Further, there is statistical evidence that a higher proportion of males is produced in the larger litters, that the larger dogs produce the 1 Issakowitsch, loc. cit. 2 Mclvor, Madras Census Reports, 1883. THE FACTORS WHICH DETERMINE SEX 645 larger litters, and consequently that the larger breeds have a racial tendency to produce an excess of dog pups. Lastly, the schedule returns strongly support the popular belief that there is a tendency to prolonged gestation when the embryo is of the male sex. In a further paper + Heape discusses the apparent influence of extraneous forces on the proportion of the sexes in two aviaries of canaries, kept under different conditions. One aviary was kept at a regular temperature during the breeding season ; it was comparatively well lighted, and the sun had access to it. On the other hand, the birds did not receive specially rich nutri- tion. The other aviary was kept in a room facing north and east, and the temperature was allowed to vary considerably during the breeding time, but the birds were always fed with a plentiful supply of rich food. In the former of the two cases nesting, hatching, and moulting took place earlier, only about half the percentage of loss was experienced, and from the nests in which all the eggs were hatched, the percentage of males produced was more than three times that which was obtained from the other aviary, in which the environmental conditions were less favourable. The results obtained in each case could not be ascribed to the particular strains of canaries, since an interchange of birds between the aviaries was not followed by any material alteration in the proportion of the sexes in the two environments. It is concluded, therefore, that the ova were subject to a selective action on which depended the proportional differences produced. “As a rule in nature the climatic forces which stimulate the activity of the generative functions are also associated with a plentiful supply of food ; the conditions which excite the one ensure the supply of the other. Among domesticated animals living in the open air, on the other hand, any forcing of the breeding time is brought about by special feeding. In neither case are the results obtained comparable to those we have now before us, where both the quality and the quantity of the food supplied is regulated entirely independently of the other causes 1 Heape, “Note on the Influence of Extraneous Forces upon the Pro- portion of the Sexes Produced by Canaries.” Proc. Camb. Phil. Soc., vol. xiv., 1907, 646 THE PHYSIOLOGY OF REPRODUCTION which stimulate the activity of the generative system. It is to this peculiar combination I attribute the regularity of the remarkable differences shown in these aviaries.”’ In a still later paper! Heape shows that there is evidence of the influence of extraneous forces upon the proportion of the sexes produced by the white and coloured peoples of Cuba. Illegitimate unions were found to give rise to a larger propor- tion of females, and it is concluded that in this class of union there is an exceptionally active metabolism of the mother which favourably affects the development of those ovarian ova which give rise to female offspring. Heape suggests further that much of the evidence that has been collected in regard to the influence of nutrition and other environmental causes upon the proportions of the sexes, although it may be disregarded from the point of view from which it was put forward (since it is commonly assumed that the conditions directly determine the sex of the embryo), may yet be well worthy of attention from the standpoint adopted by him. Some of this evidence is briefly referred to below. (3) THEORIES WHICH LIMIT SEX-DETERMINATION TO NO PARTICULAR PERIOD OF DEVELOPMENT, OR WHICH ASSERT THAT SEX MAY BE ESTABLISHED AT DIFFERENT PERIODS. Influence of Age of Parent.—Hofacker ? and Sadler * arrived independently at the conclusion that the sex of the offspring depends on the relative ages of the parents—that when the father is the oldest more male births occur, and similarly when the mother is the oldest there tends to be a preponderance of females. This hypothesis, which is known as Hofacker and Sadler’s Law, has been both confirmed and contradicted,‘ but the most recent statistical investigation® on the causes con- 1 Heape, ‘‘The Proportion of the Sexes Produced by Whites and Coloured Peoples in Cuba,” Phil. Trans., B., vol. cc., 1909. 2 Hofacker, Ueber die Higenschaften welche sich bet Menschen und Thieren auf die Nachkommen vererben, Titbingen, 1828, 3 Sadler, The Law of Population, London, 1830. 4 Geddes and Thomson, loc. cit. ® Newcomb, “A Statistical Inquiry into the Probability of Causes of the Production of Sex in Human Offspring,” Carnegie Institution Publications, THE FACTORS WHICH DETERMINE SEX 647 trolling sex in Man lends no support to it. Moreover, Schultze’s experimental investigation 1 on the sexes produced by mice of different ages has led likewise to a negative result.” Influence of Parental Vigour or Superiority.—Considerable importance has been attached by breeders and others, and notably by Starkweather,® to the comparative vigour or con- dition of the parents as a factor in sex determination. Ac- cording to Starkweather, the superior parent tends to produce the opposite sex. This theory has been accepted by Allison, who believes it to be applicable to thoroughbred horses. It is obvious, however, that in attempting to apply Starkweather’s hypothesis much depends on the signification to be attached to the term “ superiority,” and for this, if for no other reason, the theory is unsatisfactory. Furthermore, Schultze® has shown that long-continued or strained reproduction in female mice has no effect on the proportion of the sexes produced. The results of experiments on the effects of inbreeding were also indefinite or contradictory. Influence of Nourishment—Of the various external factors which have been supposed to have direct influence in determin- ing sex, nourishment seems to have found more favour than any other. In some cases this factor is supposed to act upon the developing embryo or larva (see p. 624), and so to determine its sex, while in other cases it is concluded that sex is established at an earlier period. Geddes and Thomson have elaborated the idea that favour- able nutritive conditions tend towards the production of females, and unfavourable ones towards the development of males, and certain of the evidence referred to above (p. 624) has been cited Washington, 1904. Newcomb states that the first-born child of any mother is more likely to be a boy in the proportion of about eight to seven. 1 Schultze, ‘‘Zur Frage von den geschlechts-bildenden Ursachen,” Arch. f. Mikr, Anat., vol. Ixiii., 1903. 2 This theory, and that which follows, should possibly be included among those which assume that sex is settled at fertilisation ; for if sex is determined by the age of the parents, it seems to follow that no event occurring during embryonic life can alter it. This point, however, does not appear to have been raised by the authors of the theory. 3 Starkweather, The Law of Sex, London, 1883. 4 Allison, The British Thoroughbred Horse, London, 1901. 5 Schultze, loc. cit. 648 THE PHYSIOLOGY OF REPRODUCTION by them in support of this hypothesis. The normal female metabolism is said to be relatively anabolic, while the greater activity of the male is held to indicate a preponderance of kata- bolic conditions. Consequently the generalisation is reached that abundant or rich nutrition (or any other favourable circum- stance) tends to induce an anabolic habit, and so favours the development of females; and conversely, that deficiency of the necessary food supply (or any adverse circumstance) leads to a katabolic condition of life, and so causes the production of males. According to this idea, the organism is at first “ sexually in- different,” the sex becoming established at varying periods of development in different animals according to the circumstances. Thomson has recently admitted that some of the evidence which was formerly adduced in support of this view has since been invalidated, and that it seems being proved more and more that sex is fixed in the fertilised ovum or earlier, and consequently that subsequent conditions of nutrition can play no part in determining the relative proportion of males and females. But Thomson is still disposed to lay stress on the connection between sex and metabolism, believing that the determinants for each of the sexual characteristics (both male and. female) are present in all ova and in all sperms, and that their liberation or latency depends on a bias towards egg- production or sperm- production. The so-called contrasted peculiarities of the two sexes are due in certain cases “ to in- ternal physiological conditions which give the same primordium two different expressions, much less different than they seem.” ! Statistics of human births have been brought forward in support of the view that the proportion of the sexes varies with the conditions of nutrition. It has been pointed out that in France the proportion of births of boys and girls is 104-5 to 100 for the upper classes (which are presumably best nourished) and 115 to 100 for the lower classes (who are more poorly fed). In the Almanack of Gotha the proportion recorded is 105 boys to 100 girls, while for Russian peasants this proportion is 114 to 100. Among the nobility of Sweden statistics show a proportion of 98 male to 100 female births, but that given for the Swedish clergy is 108°6 boys to 100 girls.2 There is therefore some ' Thomson, Heredity, London, 1908. 2 See Morgan, loc. cit. THE FACTORS WHICH DETERMINE SEX 649 slight evidence that the percentage of female births is a little higher among those classes which are best nourished or subject to more favourable circumstances, but the differences are very small. ‘ Punnett * has examined the statistics collected in the official census of the county of London for the year 1901, with a view to determining the relative proportions of the sexes amongst different classes of society. The following is his summary and conclusion :— “Tf the population of London be divided into three portions exhibiting graduated poverty, it is found that the proportion of male to female infants produced [or rather which have sur- vived] is lowest in the poorest portion, highest in the wealthiest portion, and intermediate in the intermediate portion. The proportion of males is highest of all in a number of births taken from Burke’s Peerage, where the nutrition may be supposed to be of the best. From this alternative conclusions may be drawn: that either more favourable conditions of nutrition (1) may result in a large proportion of male births [a conclusion which is contrary to that indicated in the returns mentioned above, but which nevertheless appears to be warranted at first sight], or (2) may have no effect on the proportion of the sexes, or (3) may even result in a relative preponderance of female births, but that in the last two cases the effect is masked by other factors which affect unequally the different strata of society. Such factors are shown to exist in a differential infant mortality, a differential birth-rate, and probably also in a differential marriage-age. These factors all tend to diminish the proportion of males in the poorer portions of the population, and consequently render the first of the above alternative con- clusions improbable. Whether the second or third of the other possible conclusions is to be accepted must remain doubtful so long as we are not in a position to estimate the quantitative effect of the factors given above. From the necessarily rough estimate which he has been able to form, the writer’s opinion is that their combined effect would not be sufficiently great to mask a preponderance of female births due to better nutrition, 1 Punnett, ‘On Nutrition and Sex-Determination in Man,” Proc. Camb. Phil. Soc., vol. xii., 1903. 650 THE PHYSIOLOGY OF REPRODUCTION and consequently he is inclined to believe that in man, at any rate, the determination of sex is independent of parental nutrition. In any case its influence can be but small.” Cuénot’s experiments! upon rats, in which some were fed mainly on bread and others were fed upon an abundant supply of different kinds of food, yielded no evidence of a preponderance of one sex among the better-nourished individuals. Lastly, in Schultze’s experiments? on mice, in which one lot was starved and other lots were variously nourished upon different kinds of foods, there is no evidence that sex-determina- tion is regulated by nutrition. Schultze and Morgan conclude that if nutrition really in- fluences the proportion of the sexes, it is probable that it does so indirectly by eliminating one or the other kind of egg. This suggestion has been further elaborated by Heape, as described above (p. 641). Newcomb’s Statistical Investigation —Newcomb,? as a result of an investigation into the statistics of multiple births, has come to the conclusion that sex is established at different periods of development in different cases. He shows that there is a tendency among human offspring for twins to be of the same sex, a fact which he regards as supplying a “ practically con- clusive negation of the theory of completely determined sex in the original germs.” His conclusion appears to be that sex is established by “ accidental causes,” the nature of which is at present unknown, and that in the case of twins the sex- determining factors act similarly on both children, and so tend towards a uniformity of sex. But he omits to mention the probability that some twin embryos arise from a single ovum, a fact which would account for their sexual identity on the assumption that sex is already determined in the germ cell. HERMAPHRODITISM AND SEXUAL LATENCY Organisms which combine within themselves the essential characters of both sexes are said to be hermaphrodite. True hermaphrodites produce both ova and spermatozoa, but there 1 Cuénot, loc. cit. 2 Schultze, loc. cit. 3 Newcomb, loc. cit. THE FACTORS WHICH DETERMINE SEX _ 651 are all gradations between true and partial hermaphroditism (in which the essential organs of reproduction are not involved), and between the latter and the completely unisexual condition, in which the characters of the other sex are either latent or absent altogether. Complete hermaphroditism is the normal state in many groups of invertebrate animals (many sponges, ccelenterates, and worms, and some molluscs and crustaceans). In some forms the male and female sexual elements do not exist contemporaneously, but are called forth separately by different environmental con- ditions or are associated with particular phases in the repro- ductive cycle (see Chapter I.). In such cases the fact that the animal is hermaphrodite is liable to be obscured. Among vertebrate animals true hermaphroditism is rare, though its casual occurrence has been recorded even in Mammalia, and is said to be comparatively frequent in certain species of Amphibia.t According to Castle ? the true hermaphrodite is a sex mosaic, the alternative sexual characters existing side by side without dominance of either, and passing (without segregation) into the gametes. Dicecious individuals are supposed to result ordinarily from a union of gametes in which one sex is dominant and the other recessive, so that no one individual is purely either male or female. The occurrence of partial hermaphroditism may be held to be an expression of an incomplete dominance of the characters of one sex. Partial hermaphroditism is usually said to occur when only one kind of gonad is developed (either testis or ovary) in conjunction with accessory generative organs characteristic of 1 See Geddes and Thomson, loc. cit. Curtis, ‘‘ Studies on the Physiology of Reproduction in the Domestic Fowl” (Biol. Bull,, vol. xvii., 1909). Pearl and Surface have described a case of an hermaphrodite fowl which had a testis on one side and an ovary on the other. The accessory organs were likewise unilaterally arranged, Externally it was an antero-posterior gynandromorph, having male characters in front but female body characters. Cf. Weber's finch (p. 313), which was a lateral gynandromorph. Such gynandromorphs are not uncommon among some insects (Hymenoptera). See also Shattock and Seligmann’s papers quoted on p. 315. For an exhaustive account of the question of hermaphroditism in Man, with a full discussion of the evidence, see von Neugebaur, Hermaphroditismus beim Menschen, Leipzig, 1908. 2 Castile, loc, cit. 652 THE PHYSIOLOGY OF REPRODUCTION both sexes. Such cases are by no means uncommon even among the higher animals. The so-called “ Free-Martins” among cattle have been held to be examples of incomplete herma- phroditism. According to Berry Hart, however, the Free- Martin is in reality a sterile bull which is co-twin of a normal fertile bull. Among animals which are usually regarded as purely dicecious there are many instances of vestigial or even of func- tional sexual organs characteristic of one sex being present normally in individuals of the opposite sex. The mammary glands and teats of the male mammal, and the clitoris of the female are examples of such organs. A more striking case is that of the pipe fish (S¢phostoma floride), in which the male possesses a marsupium which acts functionally as a placenta.” Such cases as these have led Castle, Heape, and others to conclude that all animals and plants are potentially herma- phrodite, inasmuch as they contain the characters of both sexes, although ordinarily the characters of one sex only are developed, while those of the other are either latent or im- perfectly developed. Castle has cited cases from among plants in which the characters of one sex can be induced to appear by the artificial destruction of those of the other. Examples of the same kind of - 1 Berry Hart, “The Structure of the Reproductive Organs of the Free- Martin, with a Theory of the Significance of the Abnormality,’’ Proc, Roy. Soc. Edin., vol. xxx., 1910. The Free-Martin has also been regarded as a sterile cow born co-twin with a potent bull. In most cases a vagina and rudimentary uterus have been described, but vesicule seminales and other male organs are also stated commonly to occur. Berry Hart bases his explanation of the occurrence of Free-Martins upon his recently elaborated theory of sex. (Mendelian Action on Differentiated Sex, Edinburgh, 1909.) According to this theory, sex is determined by a ‘‘sex-gamete” which may be either male or female. There are also male and female ‘‘non- sex gametes,” which unite with the “sex-gametes” but are non-potent in determining sex. A female sex-gamete uniting with a male non-sex gamete gives rise to a female zygote, and conversely. Moreover, according to Hart, a Free-Martin with a potent bull twin is the result of a division of a male zygote, so that the somatic determinants are equally divided, but the gametic determinants unequally divided, the potent going to the one twin, the potent bull, and the non-potent to the Free-Martin. ? Gudger, ‘‘The Breeding Habits and the Segmentation of the Egg of the Pipe-Fish, Siphostoma Floridx,” Proc. U. S. Nat, Mus., vol. xxix., 1905. THE FACTORS WHICH DETERMINE SEX 653 phenomenon are supplied by certain animals. Thus Potts * bas shown that in the male Hermit Crab ova make their appearance in the testes, and the secondary sexual characters become modi- fied in the direction of the female as a consequence of the animal being affected by the parasite Peltogaster. Similar changes occur in a number of other animals belonging to widely different groups, but they are especially common in the Crustacea. Smith, who has paid considerable attention to this subject,” explains the phenomenon by assuming that the males, in order to cope with the drain on the system caused by the parasites, have to increase their vegetative activity, and that they do this by suppressing their male organisations and calling into play the female ones, which they possess in a latent condition. In further support of this view, Orton has shown that in the mollusc Crepidula fornicata also the males under certain conditions may change into females, thus showing that they have the poten- tialities of both sexes.3 Further evidence in support of the view that each sex is latent in the other is afforded by the well-known fact that the characters of one sex can be transmitted through the other. For example, Darwin states that the gamecock can transmit his superiority in courage and vigour through his female offspring to his male grandchildren, while with Man it is believed that diseases such as hydrocele, which are necessarily restricted to the male sex, can be handed on through female children to a future generation.* Again, it is well known to cattle-breeders that a bull which is descended from a good milking stock can transmit this quality to his female offspring. Smith has laid much stress on the relation between sex and metabolism, inasmuch as changes in the latter are capable under certain circumstances of calling forth the characters of the 1 Potts, ‘‘ The Modification of the Sexual Characters of the Hermit Crab caused by the Parasite Peltogaster,’ Quar. Jour. Micr. Science, vol. 1. 1906. (See p. 308, Chapter IX.) 2 Smith (G.), ‘‘Sex in the Crustacea,” &c., British Association Report, Leicester Meeting, 1907; “‘ Studies in the Experimental Analysis of Sex,” Quar, Jour, Micr, Science, vols. liv. and lv., 1910. (See p. 658.) ® Orton, ‘‘On the Occurrence of Protandric Hermaphroditism in the Molluse Crepidula fornicata,” Proc. Roy. Soc., B., vol. 1xxxi., 1909. ‘ Darwin, The Variation of Animals and Plants, vol. ii, Popular Edition, London, 1905. 654 THE PHYSIOLOGY OF REPRODUCTION opposite sex. In this connection it is important to note that the removal of the testes in the male is believed in certain instances to lead to the development of the secondary female characters, and that conversely the extirpation of the ovaries in the female is said sometimes to cause the assumption of the male characters (see p. 314). Moreover, Darwin and others have shown that female birds (e.g. poultry, pheasants, ducks) in old age, when the ovaries are no longer functional, or in cases where these organs are diseased or have been injured by shot, some- times acquire the secondary sexual characters of the male. So also, Wallace } states that aged mares tend to assume the arched neck characteristic of the stallion. Conversely, cases are re- corded in which characters and habits ordinarily confined to the female are assumed by the castrated male. Thus Darwin states that capons have been known to incubate eggs and bring up chickens, and that sterile male hybrids between the pheasant and the fowl may act in a similar manner. Such cases as these are evidence of the latency of characters belonging to the recessive sex in individuals of the other sex. Furthermore, in studying the sexual pathology of youth and old age, there are a number of well-ascertained facts that point in a similar direction. Weininger* has elaborated the idea that just as there may be an “ Idioplasm ” that is the bearer of the specific characters and exists in all the cells of a multicellular animal, so also there may be two sexual modes in which this idioplasm can appear, namely an “ Arrhenoplasm” or male plasm, and a “Thelyplasm ” or female plasm. He maintains further that every metazoon cell (and not merely every reproductive cell) has a sexuality lying somewhere between arrhenoplasm and thelyplasm, but that the actual degree of maleness or femaleness varies in the different groups of cells of which the animal is built up. Moreover, the different parts of the organism are supposed: to possess their own sexual determinants, which are believed to be stable from their earliest embryonic foundation. Weininger makes no suggestion as to what it is that determines 1 Wallace, Farm Live-Stock of Great Britain, 4th Edition, Edinburgh 1907. 2 Weininger, Sex and Character, English Translation, London, 1906. THE FACTORS WHICH DETERMINE SEX = 655 the differentiation of the original protoplasm into arrhenoplasm and thelyplasm, but his idea, though somewhat too morpholo- gically conceived, is useful if only because it emphasises the fact that male and female characters coexist (though they are very unequally represented) in most if not in all dicecious in- dividuals—that is to say, that such individuals are rarely, if ever, wholly male or wholly female. “ There may be conceived,” he tells us, “for every cell all conditions, from complete masculinity through stages of diminishing masculinity to its complete absence and the consequent presence of uniform femininity.” Weininger draws special attention to the gradations in sexual characters which exist among men and women. There are many men, he remarks, with a poor growth of beard and a weak muscular development, who are otherwise typically males; and so also there are women with ill-developed breasts who in other respects are typical females. There exist all transitional forms from the most masculine male to the most effeminate male, and on the other side, from the Sapphist and the virago to the most feminine female ; but in Man the characters of one sex are always dominant, though the degree of dominance varies through considerable limits. On this view, the phenomena of so-called sexual inversion and homosexuality, which are ordinarily regarded as purely pathological, are in reality psycho- logical manifestations of special characters belonging to the recessive sex.) It is usual to regard the sex of an animal as being contributed by the essential reproductive organs, while the effect of re- moving these organs points to the conclusion that they exercise by means of their internal secretions a very powerful influence over the entire organism and more particularly over those char- acters the development of which is ordinarily correlated with 1 For further information see Krafft-Ebing, Psychopathia Sexualis, Stuttgart, 1882; Havelock Ellis, Studies in the Psychology of Sex: Sexual Inversion, Philadelphia, 1901; Forel, The Sexual Question, English Transla- tion, London, 1908; and Bloch, The Sexual Life of our Tim’, English Translation, London, 1908. For a discussion on the distinctions between men and women, see Manouvrier, ‘‘ Conclusions générales sur ]’Anthropologie des Sexes et Applications sociales,” Rev. de l’ Ecole d’ Anthropologie de Paris, 1909. 656 THE PHYSIOLOGY OF REPRODUCTION sexual potency. But it has been shown that castration, while tending in certain cases to favour the development of characters belonging to the opposite sex, results frequently in a distinctive sexual type, as the experiments of Sellheim and others have shown. Moreover, in certain forms of life (e.g. insects) the secondary sexual characters are developed independently of the essential organs of reproduction (see p. 307), the sexual characteristics of the different tissues, although clearly correlated to a large extent in most individuals, being independent of one another when once they have been laid down in embryonic life. This fact is demonstrated by Crampton’s experiment in grafting the heads of caterpillars from individuals of one sex on to those of the other sex. It would appear possible, therefore, that in exceptional in- dividuals, whose sex has been assigned to them on account of the presence of testicles or ovaries, the sexual complement is to be found actually on their own side of the sexual line—that is to say, on the side on which they are reckoned, although in reality they may belong to the other." In the terms of Weininger’s hypothesis, such individuals would be regarded as possessing more arrhenoplasm than thelyplasm (or conversely), although the particular kind of plasma that predominates in the soma is unrepresented in the organs of generation. Lastly, Weininger’s theory helps to explain why it is that transplantation of gonads on animals of the opposite sex is usually attended by failure, a fact which has been noted by Ribbert and others, including the present writer. The internal secretions of the ovaries or testicles, on this view, are operative only in an appropriate environment of thelyplasm or arrheno- plasm, or, to speak physiologically, in the existence of a re- sponsive metabolism, and without this their influence on the organism is ineffective, even though they succeed in becoming attached. In criticism of Weininger’s morphological hypothesis, it must be pointed out again that there is no real evidence that any sort of character, whether sexual or otherwise, is at any time definitely located in a special kind of material or plasma (not even in the accessory chromosome, since this probably 1 Weininger, loc. cit. THE FACTORS WHICH DETERMINE SEX 657 is merely one factor in a complex system of causes), and that the physiological mode of thought requires one to associate the characters of an organism with its particular metabolism and not with any special sort of cell substance.* GENERAL CONCLUSIONS If it be true that all individuals are potentially bisexual (one of the two sexes being recessive or latent excepting in hermaphrodites), and that changed circumstances, leading to a changed metabolism, may, in exceptional cases, even in adult life, cause the development of the recessive characteristics (as in the case of the Crustaceans mentioned above), it would seem extremely probable that the dominance of one set of sexual characters over the other may be determined in some cases at an early stage of development in response to a stimulus which may be either internal or external. The observations which Smith and others have made upon certain Crustaceans point even to the possibility that sex may be reversed after it has once been established. It seems certain that sex is not determined by the same factors in all cases, neither is it determined at the same period of development. It may well be that some gametes have an initial tendency to give rise to males and others to give rise to females, and to this extent it is probably legitimate to speak of male and female ova or male and female spermatozoa.” More- over, the conclusion is probably correct that these are developed (at least generally) in simple Mendelian ratios. But it is also probable that no gamete is either purely male or purely female, and itis possible that in some the two kinds of sexual determi- nants or tendencies are about equally represented. 1 The presence of a certain kind of cell substance must of course influence the metabolism, but the extent of its influence will depend upon other factors, and may vary with different external conditions. * Bateson and Punnett suggest that in some forms of life (e.g. Verte- brates) the ova are the sexually differentiated gametes, and that in other organisms (e.g. Crustaceans) the sexual differentiation occurs among the spermatozoa, Guyer’s cytological observations, however (p. 635), seem to show that male Vertebrates may be sexually heterozygous. Moreover, Baltzer’s cytological observations seem to show that among sea-urchins there may be two kinds of eggs (Arch. f. Zellforsch., vol. iv., 1909). 2T 658 THE PHYSIOLOGY OF REPRODUCTION When once we admit the existence of latent (7.e. recessive) sexual characters in individuals in which the characters of one sex are dominant, and that under certain circumstances those of the latent sex can develop at the expense of the dominant ones, in response to appropriate physiological stimuli, we are compelled to acknowledge also that the sex of the future individual is not always predetermined in the gametes or even in the fertilised ovum, but may be called into being at a later stage of life. Such an admission is of course opposed to some extent to the modern tendency to believe that sex is fixed irrevocably in the fertilised ovum or in the gametes before fertilisation ; but while there is evidence amounting to proof that this is the case in some forms of life, it does not necessarily follow that it is true of all metazo6n animals, or even that it is uniformly so of the particular species which have been investigated. On the other hand, many of the facts enumerated above point to the con- clusion that the sex of the future organism is determined in different cases by different factors and at different stages of development—either in the unfertilised gamete, or at the moment of fertilisation, or in the early embryo, while the effects of castration indicate that an alteration in the metabolism, even in comparatively late life, may initiate changes in the direction of the opposite sex.’ APPENDIX Braem? has described an experiment in which he divided in half a mature female of the annelid, Uphryotrocha puerilis. The head portion after some weeks regenerated and produced spermatozoa, but the ova almost disappeared. There was no sign of hermaphroditism at the outset, and Braem regards the case as one of change of sex resulting from altered conditions. In a recent paper Potts* has adduced evidence that in certain hermaphrodite Nematodes, in Rhabdoccel Turbellarians and in Rhizo- cephala the monecious condition has arisen through the sperms developing in the ovaries in gradually increasing numbers in successive generations. Smith‘ states that in the male of Inachus affected by Sacculina the assumption of adult female characters is due to the formation of a yolk substance (or female generative substance) similar to that normally elaborated in the ovaries. 1 Such changes are notoriously more difficult to effect after puberty than before it. 2 Braem, Anat, Anz., vol. xxxiii., 1908. 3 Potts, Quar. Jour. Mier. Science, vol. lv., 1910. 4 Smith, Quar. Jour. Micr. Science, vol. lv., 1910. CHAPTER XVI PHASES IN THE LIFE OF THE INDIVIDUAL—THE DURATION OF LIFE AND THE CAUSE OF DEATH “Tabroy yap 1Bavr’ dvdpa cai mpéo By Oaveiv ;”—EvRIPipss, A lcestis, THE physiological life of the metazo6n individual begins with the union of sperm and ovum, and the organism thus formed thence- forth proceeds to grow. As has been said by Verworn,} there is an essential similarity between reproduction and growth, both processes consisting of an increase of living substance. “The difference between that which is usually termed growth in the narrow sense and the phenomenon of reproduction consists only in the fact that in the former case the newly-formed living substance remains in constant connection with the original organism and helps to increase its volume; while in the latter case a part of the substance separates itself from the original organism, either, as in most cases, being set entirely free, or, as in the increase of tissue-cells, being separated merely by a partition-wall and remaining in place.” Among the more highly organised Protozoa there are various transitional stages between these two conditions. Growth, like reproduction, involves cell division. As the mass of living substance increases, the cells must multiply, for every cell has assigned to it a limit in size beyond which it cannot pass. Cell division goes on, though with gradually decreasing frequency throughout practically the whole of life ; tissue formation continues, but from an early period of de- velopment onwards there is a progressive diminution in the power of growth. Increase in the number of cells is, how- ever, specially characteristic of the embryonic period. In the later stages of development growth occurs largely through cell enlargement and the deposition of intercellular substance. 1 Verworn, General Physiology, Lee’s Translation, London, 1899. 659 660 THE PHYSIOLOGY OF REPRODUCTION Minot has compared the growth of the body to a man building a wall! ‘‘He begins at first with great energy, full of vigour ; the wall goes up rapidly ; and as the labour continues, fatigue comes into play. Moreover, the wall grows higher, and it takes more effort and time to carry the material up to the top of the wall, and to continue to raise its height, and so, as the wall grows higher and higher, it grows more slowly and ever more slowly, because the obstacles to be overcome have in- creased. with the very height of the wall itself. So it seems with the increase of the organism, and with the increase of our development, the obstacles to our growth increase.” According to Minot, the explanation of this phenomenon must be sought in the differentiation of the protoplasm, which goes on growing with an ever-increasing complexity as the cells of the body multiply. It has just been mentioned that every cell has assigned to it a definite limit in size beyond which it cannot go. Boveri? has enunciated the general law that the process of cell division is regulated by the proportion of chromatin material to cyto- plasm, and that it comes to a standstill when the ratio of the mass of chromosomes to that of the cells in any given tissue or organ reaches a certain definite point. Furthermore, it is stated that the size of the cells in any given tissue after active cell multiplication has ceased, bears a definite relation to the original mass of chromatin contained in the fertilised egg.’ Thus it is pointed out that the mesenchyme cells of the embryo developed from the artificially fertilised sea-urchin’s egg are only half the size of those of the embryo which has been pro- duced by normal fertilisation, for although the parthenogenetic and normally fertilised eggs are equal in size at the commence- ment of segmentation, the latter possess initially twice as much nuclear substance as the former.* The fact that cell division ceases when the ratio of the mass 1 Minot, ‘The Problem of Age, Growth, and Death,” Popular Science Monthly, vol. 1xxi., 1907; reprinted London, 1908. 2 Boveri, Zellen-Studien, Part V., Jena, 1905. * Robertson, ‘On the Normal Rate of Growth of an Individual and its Biochemical Significance,” Arch. f. Entwick.-Mech., vols. xxv. and xxvi., 1908. 4 Driesch, ‘‘ Uber das Mesenchym yon unharmonisch zusammengesetzten Keimen der Echiniden,” Arch. f. Hntwick.-Mech., vol. xix., 1905. PHASES IN THE LIFE OF THE INDIVIDUAL 661 of chromosomes in the nuclei of an egg (or of a tissue or organ) to that of the surrounding protoplasm reaches a certain definite limit, is regarded by Loeb! as evidence that this ratio is deter- mined by the laws of mass action and chemical equilibrium. He says further that if this conclusion is correct the synthesis of nuclein compounds, from their protoplasmic constituents, must be a reversible process. The fertilisation of an ovum is immediately succeeded by an enormous synthesis of nuclear material. In the cellular division which follows, each new nucleus is of the same size as the parent nucleus. From this fact Loeb? concludes that the nucleus itself, or one of its constituents, acts as a catalyser in the synthesis of nuclein in the fertilised ovum. Robertson,’ quoting partly from Loeb, writes as follows :— If the mass of the original fertilisation-nucleus be m, the mass of nuclear material increases during the first segmentation period to 2m, during the next to 4m, and so on in geometrical progression. The duration of the various periods of segmentation, however, matters very little. Hence in the first unit of time after the beginning of cell division, a mass m of nuclear material is formed, in the second a mass 2m, in the third a mass 4m, and so on; thus the velocity of the synthesis increases with lapse of time and with the mass of nuclear material already formed. This is a characteristic of that class of reactions known as autocatalytic, in which one of the products of the reaction, or, in this case, one of the con- stituents of the nucleus, accelerates the reaction. During the process outlined above, an emphatic disproportion between nuclear and protoplasmic material has been established. As the nuclear synthesis becomes slower, however, the disproportion tends to adjust itself until, finally, the growth of the organism consists almost entirely of the growth of protoplasmic material and in the final re-establishment of the equilibrium between cytoplasm and nuclear material.” Robertson has investigated mathematically the quantitative 1 Loeb, The Dynamics of Living Matter, New York, 1906. 2 Loeb, ‘‘ Weitere Beobachtungen iiber den Einfluss der Befruchtung,” &c., Bio, Chem. Zeitsch., vol. ii., 1906. ‘The Chemical Character of the Process of Fertilisation and its Bearing on the Theory of Life Phenomena,” Seventh Internat, Congress, Boston, Univ. of California Publications, vol. iii., 1907. 3 Robertson, loc. cit. 662 THE PHYSIOLOGY OF REPRODUCTION relations which exist between the amount of growth and the time of growth. He concludes that there are two or more growth cycles representing autocatalytic processes which make up the total growth of an individual. In Man there are three maxima of rate of growth, representing three phases or growth cycles. One of these is intra-uterine, but it is probable that this is not quite complete at birth. The second growth cycle seems to attain its maximum annual increment at about the fifth year, since the increment in weight at that age, as deduced from an investigation on growth in English boys, considerably exceeds the annual increments for the years immediately follow- ing. A third maximum in yearly increments occurs in males at about the sixteenth year, that is, at about the time of puberty. In the rat, according to Donaldson,’ there are two intra-uterine growth cycles, while there is only a single well-defined extra- uterine cycle. Robertson suggests that the first growth cycle in Mammals represents the course of the autocatalytic synthesis of the nuclear substance, that the third cycle represents the period during which cytoplasmic material is built up, while the second growth cycle is intermediate, representing a time when both synthetic processes go on contemporaneously. GROWTH OF THE BoDy BEFORE BirtTH Minot ® has recorded the results of weighing embryo rabbits at different stages of development with a view to determining their rate of growth. The results showed that in the period from the ninth to the fifteenth day the young rabbit adds on an average 704 per cent. to its weight daily, and that in the period from the fifteenth to the twentieth day, the average daily addition is only 212 per cent. It may be assumed, therefore, that in younger embryos (before the ninth day) there is an increase of over a thousand per day. Minot estimates that over 98 per cent. of the original power of growth of the rabbit or the chick has been lost at the time of birth or hatching, and that a similar fact is equally true of Man. “ We start out at birth certainly with * Donaldson, ‘‘ A Comparison of the White Rat with Man in respect to the Growth of the Entire Body,” Boas Anniversary Volume, Anthropological Papers, New York, 1906. ? Minot, loc. cit. PHASES IN THE LIFE OF THE INDIVIDUAL 663 less than two per cent. of the original growth power with which we were endowed. Over 98 per cent. of the loss is accomplished before birth—less than two per cent. after birth.” The accom- 600%, 500% Becentiage 400% Rikb. 300% 200% 100% N L MONTHS O s) 2 3 4 53.6 7 6 9 10 Fic. 141.—(From C. 8. Minot’s Problem of Age, Growth, and Death, G. §. Putnam & Sons, and John Murray.) panying diagram represents roughly the rate of growth in Man before birth. The time intervals correspond to the ten lunar months of gestation. The rate of increase in the first three ad 664 THE PHYSIOLOGY OF REPRODUCTION months is not indicated, since there are no statistical data on which to found any knowledge, but from the third month onwards there are a few records available. The diagram shows that from the third to the fourth month the increase in growth is 600 per cent., after which it quickly drops until, during the last month of pregnancy, it is barely twenty per cent. GRowtTH oF THE Bopy AFTER BirTH The rate of growth from birth to maturity has been in- vestigated most fully by Minot? in the case of the guinea-pig. Pecentage Incuments. Inales. pL 256 M 23 29 3538 45 60 18 90 10S 120 135 150 165 180 195 2odays 24) Fig. 142,—(From Minot’s Problem of Age, Growth, and Death, G. 8. Putnam & Sons, and John Murray.) When this animal is born it is far advanced in development, the period of gestation being unusually long. Immediately after birth there is a lessening in the power of growth, a fact which Minot ascribes to the physiological shock from which the organism suffers as a consequence of being born. After two or three days, however, the young are fully recovered, and are capable of adding over five per cent. to their weight in a single day. By the time they are seventeen days old they are only able to add four per cent. to their weight, and by the time they are twenty-four days old, less than two per cent. When they have been born forty-five days, they can add only a little 1 Minot, ‘‘ Growth and Senescence,” Jour. of Phys., vol. xii., 1891. “ Age, Growth, and Death,” Popular Science Monthly, vol. 1xxi., 1907. Ra PHASES IN THE LIFE OF THE INDIVIDUAL 665 over one per cent. to their weight ; when ninety days old, less than one per cent., and still less as they grow older, until when about a year old they attain their full size. The curves in the accompanying diagrams show the daily percentage increments in weight in male and female guinea-pigs respectively, as ascer- tained by Minot. It is seen that the curve for the females is very similar to that for the males. Both show an early period of rapid decline in which the rate of growth is quickly diminish- ing, followed by a period of slight decline in which the curve is still falling, but very much more gradually. (Figs. 142 and 143.) ES Percentage Increments, Females i 3 29 33 45 60 75 90 105 120 135 150 165 180 195 210 days 24h Fig. 143.—(From Minot’s Problem of Age, Growth, and Death, G.8. Putnam & Sons, and John Murray.) Minot has also investigated the rate of growth in the rabbit and in the chicken. The young rabbit, as is well known, is born in a very immature state of development after a relatively short gestation period. Correlated with this fact, it was found that the male rabbit four days after birth is capable of adding over seventeen per cent. to its weight in a single day. From that time the percentage increment drops very rapidly, so that at an age of twenty-three days the rabbit can only add a little over six per cent. After about the fifty-fifth day the decline in the growth rate, which has hitherto been rapid, becomes more gradual. In the case of the chicken, Minot’s results were in a general way similar, but the rate of growth on the first day it could be measured was a nine per cent. addition to the weight, 666 THE PHYSIOLOGY OF REPRODUCTION while the change from the initial rapid decline to the subsequent slow decline was more gradual than in the other two animals. | Percentage Incremonts Leabbets 03 8 131823283338 55 72 1065 \s0days = 270] Fic, 144,—(From Minot’s Problem of Age, Growth, and Death, G. 8. Putnam & Sons, and John Murray.) The mean weight of the foal at birth is said to be 112 pounds. During the first three months the average daily increase is PHASES IN THE LIFE OF THE INDIVIDUAL 667 2:2 pounds ; from three up to six months it is 1:3 pounds; and from six months up to three years 07 pound. It is said that 15 td Pe.centage Increments Rabbits Females 13 (2 Ul 10 9 7 4 2 | } 03 8 1318232833 5 z Ls 5 80 1063 180 daya 270 Fig. 145.—(From Minot’s Problem of Age, Growth, and Death, G. 8. Putnam & Sons, and John Murray.) probably many horses continue to grow until they are six years old. 1 Smith (F.), Veterinary Phystology, 3rd Edition, London, 1907. 668 THE PHYSIOLOGY OF REPRODUCTION The calf at birth weighs about 77 pounds, and the average daily increase during the first two years is 15 pounds. _ With the sheep the increase is greater, for a young lamb in ten days can add fifty per cent. to its original weight, and can double it at the end of the first month, and treble it at the end of the second. In pigs, however, the increase is even more rapid, for a young pig can add twenty per cent. to its original weight by the end of the first week, and up to the end of the first year can add an average daily increase of 0-44 pound. In Man growth is most rapid during the first year of life, ts z 8 | Percentage Incuments Chick. Mates 7 | A 5 4 3 2 I 0358 131822 263338 «6 36 66 77 ~~90 106 130 (eidayd 3a2 Fic. 146.—(From Minot’s Problem of Age, Growth, and Death, G. 8. Putnam & Sons, and John Murray.) when a child is able to increase its weight by 200 per cent. For the second year this percentage drops to twenty, and for subse- quent years up to about the age of thirteen, it fluctuates around ten, showing a gradual tendency to decrease (but cf. Robertson, quoted on p. 662). After this there is a distinct increase in the percentage increment representing the prepubertal and pubertal growth. Then there is a further decline in the power of growth, which gradually diminishes. The prepubertal growth of girls usually precedes that of boys, so that between the ages of twelve and fifteen girls are often heavier and taller than boys. Boys grow most rapidly at sixteen, girls at thirteen or fourteen. Boys attain their full height at from twenty-three to twenty- PHASES IN THE LIFE OF THE INDIVIDUAL 669 five years of age; girls at twenty or twenty-one. In both sexes the weight of the body tends to increase until about the fiftieth year or somewhat later, owing to an accumulation of fat, but there are of course very many exceptions.! That good nourishment and a healthy environment favour growth is a fact recognised by all. So also systematic exercise has been found to increase both the weight and the height,? and it has been shown further that well-developed children are more efficient mentally and take better places at school than ill-developed and badly-nourished ones.* “ Perncentage Increments Chick, Females (peat 0346 131822 28333846 56.66 77 90 106 130 W7days 342 Fig. 147.—(From Minot’s Problem of Age, Growth, and Death, G. S. Putnam & Sons, and John Murray.) In horses and other domestic animals the effects of feeding on growth and general development are remarkable. Thus it is said that a highly-fed thoroughbred at two years old is “furnished ” and looks as old as an ordinary horse at four years old.* 1 See Minot, Popular Science Monthly, vol. lxxi., 1907. Minot states that his calculations are based on data supplied by Professor Donaldson. See also Lee, Article ‘‘Reproduction,” in Howell’s American Text-Book of Physiology, 2nd Edition, London, 1900. 2 Beyer, “The Influence of Exercise upon Growth,” Jour. of Exper. Medicine, vol. i., 1896. 3 Porter, ‘The Physical Basis of Precocity and Dulness,” Trans. Acad. of Science, St. Louis, vol. vi., 1893. 4 Smith, loc. cit. 670 THE PHYSIOLOGY OF REPRODUCTION The various other external factors that influence growth in animals of different kinds are discussed by Morgan in his recent work on Experimental Zoology,’ to which the reader is referred for an account of the literature of the subject. PUBERTY Puberty, or the period at which the organism becomes sexually mature, is marked by the occurrence of those con- stitutional changes whereby the two sexes become fully dif- ferentiated. It is at this period that the secondary sexual characters first become conspicuous, and the essential organs of reproduction undergo a great increase in size,” while in those animals in which during immaturity the testicles remain within the body cavity, it is at puberty that these organs first descend into the scrotal sacs. The puberty acceleration in growth which takes place in Man has been already referred to. This change is accompanied, as is well known, by alterations in the general proportions, associated with an increase of strength, a deepening of the voice and a growth of hair on the face and other parts of the body. In temperate climates puberty begins in boys at about the fourteenth or fifteenth year; in tropical countries it is usually a few years earlier. It is at this period that ripe spermatozoa first make their appearance in the seminal fluid, which is henceforward secreted in considerable quantity. In women puberty occurs at a slightly earlier age than in the male sex. The constitutional changes characterising this period take place more suddenly in the female, the girl almost at once becoming a woman, whereas the boy is several years before he develops into a man. Moreover, the onset of puberty in the girl is marked more precisely by the coming of menstruation, which may make its appearance in temperate climates in the thirteenth year. At about the same time the pelvis widens, and the other characteristic anatomical changes take place ; the subcutaneous layer of fat, the development of which assists so largely in giving the body its graceful contour, is deposited ; ‘ Morgan, Experimental Zoology, New York, 1907. 2 Disselhorst, ‘‘Gewichts- und Volumszunahme der minnlichen Keim- driisen,” &c., Anat. Anz., vol. xxxii., 1908. PHASES IN THE LIFE OF THE INDIVIDUAL 671 while the internal generative organs enlarge and ripe ova are produced by the ovary.1 In both sexes the purely physical changes of puberty are accompanied by psychical ones which are no less pronounced. Both kinds of change are dependent largely, if not entirely, upon the functional development of the generative glands. In animals the general nature of the change which sets in at puberty is similar to that occurring in the human species, and the secondary sexual characters often appear for the first time at this phase of life. Excepting in the case of the domestic animals, little is definitely known concerning the respective ages at which the different species become mature. Most fillies come in use when two years old, and all by the time they are three. Cows may come on heat when a year old, but it is best to postpone service until three months later. A good deal depends on nutrition, but even starved and backward cows will receive the bull when fifteen months old. Sows will receive the boar when eight months old, and sometimes two months earlier. Sheep will breed at the age of six months (that is to say, lambs born in the spring will breed in the following autumn), but the practice is to be deprecated in the interests both of the ewes themselves and of their lambs. Dogs will breed when about ten months old or even earlier (sometimes seven), but the larger kinds do not breed so soon. Cats are similar. Rodents may breed when still younger, but whether they do so or not depends upon the season of the year and other conditions of environment and nutrition. 1 Runge (E.), however (‘‘ Beitrag zur Anatomie der Ovarien Neugeborener und Kinder von der Pubertitzeit,” Arch. f. Gyndk., vol. 1xxx., 1906), states that growing follicles are by no means uncommon in ovaries of young children. In the first year of life he found follicles of considerable size, and in the second year still larger ones, some having a diameter of 135 p. In the third year degenerate follicles were also found. During this and the following years there was a progressive increase in the size of certain of the follicles until the ovaries became scarcely distinguishable from those of adults excepting for their smaller size. Runge states further that in one instance he found a corpus luteum in an ovary of a recently born child, but this must be regarded as very exceptional. As a result of his observations, Runge concludes that follicular maturation sets in during infancy and not at puberty. Ovaries of human embryos showed growing follicles only in very rare instances. 672 THE PHYSIOLOGY OF REPRODUCTION THE MENOPAUSE In the male sex (as already mentioned) there is no definite age at which the reproductive functions cease. In the female, on the other hand, the close of the reproductive period is far more definite, and it is this change in the human female which constitutes the menopause or climacteric. The essential pheno- menon of the menopause, therefore, is the permanent arrest of all the functions connected with reproduction. It is the in- version of the developmental process of puberty, and marks the termination of active sexual life. In temperate climates it almost always takes place between the ages of forty and fifty, and most usually at about the age of forty-five.’ In warm countries it has a tendency to be earlier, and in colder ones later. It is usually earlier among the labouring classes, and also in cases in which puberty was early. The actual duration of the period when menopause symptoms occur varies from about three to five years. The symptoms of the menopause may be referred to two stages—(1) a stage of menstrual irregularity, and (2) a post- cessation stage, during which various systemic disturbances are wont to occur. During the latter period especially the organic functions are irregular. Palpitation, dyspepsia, sweating, and vasomotor changes are not infrequent, and hysteria and other psychic disturbances sometimes occur, accompanied by neuralgia, rheumatism, and various disorders. The changes which take place in the lower Mammals have not been studied, but they can hardly be so great as those which occur in women. The anatomical and physiological basis of the menopause is, as already indicated, the atrophy of the reproductive organs. The following are the changes which take place in women :— (1) Senile changes in the ovary: (a) Atrophy, induration, and shrinkage to the size of the rudimentary ovary; (b) disappear- ance of Graafian follicles and cessation of ovarian functions. (2) Senile changes in the Fallopian tubes: (a) shortening and narrowing, often accompanied by obliteration of the lumen ; (5) destruction of the epithelial cells. ? For further details see Kelly, Medical Gynecology, London, 1908. PHASES IN THE LIFE OF THE INDIVIDUAL 673 (3) Senile changes in the uterus: (a) Atrophy of the entire organ, which may be reduced to a hard, wedge-shaped body, one quarter the size of the functional organ; (6) in many cases closure of the internal os, or of the external os, or complete obliteration of the canal; (c) consequent secretions producing Fiq. 148,—Section through ovary of woman of fifty-six, showing degeneration of follicles and sclerosis of connective tissues. (From Sellheim.) pyometra or hydrometra, due to the locking up of the secretions ; (d) in some cases the disappearance of the vaginal portion, making the upper part of the vagina continuous with the uterine canal ; (e) degeneration of the muscular and glandular elements ; and (f) cessation of menstruation. (4) Senile changes in the vagina: (a) shortening, narrowing, and loss of elasticity; (b) loss of pavement epithelium, and 2U 674 THE PHYSIOLOGY OF REPRODUCTION substitution of a hard surface containing cicatricial tissue ; and (c) contraction of the entrance to the vagina. (5) Senile changes in the vulva: (a) great contraction and loss of elasticity, (b) destruction of glands and follicles, and (c) cutaneous surface becoming dry and scaly. (6) Senile changes in the mammary glands: (a) loss of Fia. 149.—Section through uterine mucous membrane of woman of sixty. (From Sellheim.) gl. glands. glandular elements and cessation of function ; and (6) shrinkage due to atrophic loss, which, however, is sometimes compensated for by a deposition of fat.’ Other changes, depending probably on the degeneration of the ovaries, are the assumption of certain of the secondary male characters. These are apparently more marked in some animals * Dudley, The Principles and Practice of Gynecology, 4th Edition, London, 1905. Fora further account of the atrophic changes in the uterus and other generative organs, see Sellheim. PHASES IN THE LIFE OF THE INDIVIDUAL 675 than they are in the human species, and have already been mentioned in dealing with the internal ovarian secretions (p. 314). SENESCENCE As age advances, in addition to the menopause changes which relate more especially to the cessation of the female generative functions, atrophic changes of one sort or another take place in both sexes throughout practically the entire system. The internal spongy structure of the bones is dissolved away, so that they are left with only a hard external shell and conse- quently become brittle. The teeth decay and drop out. The Fie. 150.—Section through vaginal mucous membrane of woman of sixty-one. (From Sellheim.) muscles shrink in volume, the actual fibres of which they are composed becoming smaller in size and fewer in number. The arterial walls lose their elasticity and undergo sclerosis, a characteristic which is so constant that it has given rise to the well-known dictum that “a man is as old as his arteries.” The tendons and ligaments also become calcified, and there is a consequent shrinkage of stature. The size of the liver and other viscera undergoes diminution, but the kidney and heart retain their size; in fact the heart is usually slightly enlarged in old age, but this apparent hypertrophy is not associated with an accession of power but with an increased feebleness, and the pulse, in order to compensate for the weakness of the enlarged heart, beats more quickly, the normal rate of seventy- 676 THE PHYSIOLOGY OF REPRODUCTION two beats per minute rising to seventy-nine or eighty. The rate of respiration also rises slightly, and the vital capacity of the lungs diminishes. Moreover, the amount of carbon dioxide and urine which are excreted becomes less. The pigment in the hair undergoes absorption, the hair turning grey or white. The adipose tissue beneath the skin disappears, especially in ad- vanced old age, but fatty degeneration of muscle or glandular tissue is not infrequent. In the male sex the prostate gland undergoes atrophy, or in some cases a pathological hypertrophy, which is said to be the cause of frequent penile erections. It has been shown also that the brain decreases in size in old age. The shrinkage begins soon after maturity, and then continues almost steadily to the very end of life.’ Handmann ? has published the following statistical results, which are based on measurements carried out at the Pathological Institute at Leipzig :— Weight of Brain. Age. Male. Female. 46 . é . - 1215 grams. 1194 grams. 7-14 . : : . 1376 ,, 1229, 15-49. ‘ : - 1372 ,, 1249 50-84 . . : - 1332 ,, 1196, The decrease in brain weight is accompanied by a diminution in the thickness of the cortex and in the number of tangential fibres present in it. These changes are associated on the psychical side with a gradual mental failure—loss of memory, decrease in the power of original thought and in the assimilation of new ideas, and general decline of mental activity. Moreover, the reaction time is lengthened, the sense organs lose their delicacy, and in the eye the power of accommodation is largely lost. The minute cellular changes in the tissues are no less pro- nounced. These also are in the direction of atrophy. There is a general shrinkage in the protoplasm of the cells, but especially in the nuclei, so that the relative amount of cytoplasmic to nuclear substance becomes increased in old age. The nucleoli 1 Minot, loc. cit. 2 Handmann, “ Uber das Hirngewicht des Menschen,” Arch. f. Anat. u, Phys., anat,, Abth., 1906. PHASES IN THE LIFE OF THE INDIVIDUAL 677 also tend to disappear. Hodge? has made a comparison of the changes in the cells of the first cervical ganglion with the follow- ing result :— Nucleolt observable Volume of Nucleus. in Nucleus. At birth é - 100 per cent. In 53 per cent. At 92 years . . 642, si 5 iss Thus the nucleoli are often apparently quite absent in extreme old age. The nuclei, besides becoming smaller, grow irregular Fig. 151.—Group of nerve cells from the first cervical ganglion of a child at birth. (After Hodge, from Minot’s Age, Growth, and Death, G. 8. Putnam & Sons, and John Murray.) in shape, and in the cytoplasm there is a deposition of pigment granules. _ Senescence in men is said to commence at about the age of fifty,? but it is obvious that no definite limit can be assigned to the period, since in some of the organs changes which are in their nature degenerative begin quite early in life. Spermatozoa continue to be produced even in quite ad- vanced old age, and instances have been recorded of men of 1 Hodge, ‘‘Die Nervenzelle bei der Geburt und beim Tode an Alter- schwiche,” Anat. Anz., vol. ix., 1894. 2 Lee, loc. cit. 678 THE PHYSIOLOGY OF REPRODUCTION 94, 96, and even 103 in whose semen active sperms were found.! There can be no doubt, however, that the spermatozoa are produced in far less abundance in old age. In women the period of senescence is usually reckoned from the menopause. It is difficult to form any accurate comparison between the phases of life of men and those of animals, partly because so Fig. 152.—Group of nerve cells from the first cervical ganglion of a man of ninety-two. (After Hodge, from Minot’s Age, Growth, and Death, G. 8. Putnam & Sons, and John Murray.) C, ©, cells still intact, but shrunken and loaded with pigment ; c, ¢, cells which have disintegrated. little is known regarding the conditions of natural senescence and death in animals. Smith? remarks that few horses live long enough to show much sign of arterial degeneration ; the work they perform is the chief cause of their rapid decay, for their legs wear out before their bodies: but, apart from this, degenerative changes in the teeth, and more particularly the wearing away of the molars, prevent many horses from reaching 1 Cooper, The Sexual Disabiliti2s of Man, &c., London, 1908. % Smith, loc, cit, PHASES IN THE LIFE OF THE INDIVIDUAT. 679 a real old age. Blaine? has drawn the following comparison between the age of a horse and that of a man :—“ The first five years of a horse may be considered as equivalent to the first twenty years of a man; thus, a horse of five years may be comparatively considered as old as a man of twenty; a horse of ten years as a man of forty; a horse of fifteen as a man of fifty ; a horse of twenty as a man of sixty; of twenty-five as a man of seventy ; of thirty as a man of eighty ; and of thirty- five as a man of ninety.” Tue Duration or LIFE AND THE CAUSE oF DEATH Weismann, in a famous essay on the duration of life,? and Metchnikoff in his book of optimistic studies,? have dealt.at some length, but from different standpoints, with the factors which determine longevity in the animal kingdom. That the duration of life in the various races of animals is very variable, and that, whereas some species are remarkably long-lived, others die after a relatively brief existence, are facts that are known to all. Both Weismann and Metchnikoff cite numerous instances of longevity among animals, some of the more extreme of which may be mentioned here. A sea-anemone belonging to the species Actinia mesembryan- themum is known to have lived for sixty-six years, and to have produced young, though in smaller numbers than formerly, at the age of fifty-eight. Another sea-anemone of the species Sagartia troglodytes, lived to be fifty years old.t Certain marine Mollusca are said to live for as many as a hundred years. Among insects there is an extraordinary variability in the duration of life, some living in a condition of maturity for only a few days or even hours, while others (certain Hemiptera) are believed to survive for as many as seventeen years. Moreover, the duration of life is sometimes very different in the two sexes, 1 Blaine, Encyclopedia of Rural Sports, London, 1858. 2 Weismann, ‘The Duration of Life,” English Translation, in Essays upon Heredity, &c., 2nd Edition, Oxford, 1891. 3 Metchnikoff, The Prolongation of Lif, English Translation, London, 1907. 4 Ashworth and Annandale, ‘On Some Aged Specimens of Sagartia,” Proc. Roy. Soc., Edin., vol. xxv., 1904. 680 THE PHYSIOLOGY OF REPRODUCTION the queen ant being known to live for several years (in one case for fifteen years), whereas the male ant survives for only a few weeks. Among fish, pike and carp are usually said to attain to great ages and even to live for centuries, but there are few accurate data. Among reptiles, crocodiles and tortoises are known to have long lives, a tortoise from the Galapagos Islands being stated to have lived for 175 years. The length of life in birds has been discussed by Gurney,’ Fic. 153.—Land tortoise (Testudo mauritanico), aged at least eighty-six, belonging to M. Elie Metchnikoff. (From Metchnikoff’s “‘ The Prolongation of Life,” by permission of Mr W. Hei ) who cites several examples of great longevity, but the more usual duration of life is from fifteen to twenty years. Canaries are stated to have attained to twenty years of age, a herring gull to forty-four, an imperial eagle to fifty-six, a heron to sixty, an eagle owl to sixty-eight, a raven to sixty-nine, a swan to seventy, and a goose to eighty. Metchnikoff records a case of-a parrot which lived for eighty-two years. Mammals on the average appear to have considerably shorter lives than birds. According to Weismann, whales live for some hundreds of years, but it is difficult to see how this can be 1 Gurney, ‘‘On the Comparative Ages to which Birds Live,” Ibza, vol. v., 1899. PHASES IN THE LIFE OF THE INDIVIDUAL 681 more than an assumption. There can be little doubt that the great age assigned by some of the older writers to elephants is mythical, and probably 150 years is almost the maximum ever attained. Horses in rare cases have reached forty years, cattle somewhat over thirty, and sheep over twenty years. A dog is said to have lived for thirty-four years, but twenty is usually regarded as a great age for this animal. Cats have been Fig. 154.—Lonk sheep, aged eighteen years, with her last lamb. This sheep, which belonged to Mr. William Peel of Knowlemere Manor, Clitheroe, lived to be twenty-one years. It had thirty-five lambs, nine of which were triplets.1 known to live to be twenty-one and even twenty-three, but no greater ages appear to have been recorded. Many instances are on record of extraordinary longevity among men and women, but perhaps the most trustworthy is the famous case of Thomas Parr, described by Harvey in the Philosophical Transactions of the Royal Society.’ His death is + Tam indebted to my friend Mr. W. Ralph Peel, of Trinity College, Cambridge, for this photograph (taken by his sister, Miss Peel), and for the information which accompanied it. 2 Harvey, ‘‘ Anatomical Account of Thomas Parr,” Phil. Trans., vol. iii., 1700. A portrait of Parr painted by van Dyck may be seen in the Royal Gallery at Dresden. 682 THE PHYSIOLOGY OF REPRODUCTION said to have been due to the change in his mode of life, resulting from his migration from Shropshire to London, “ where he fed high and drunk plentifully of the best wines.” “He died after he had outlived nine princes, in the tenth year of the tenth of them, at the age of one hundred and fifty-two years and nine months.” As to what factors determine the average duration of life in different species is a problem about which there has been much speculation. Weismann has elaborated a theory which asserts that living matter was originally immortal, mortality first arising in correlation with cellular differentiation. On this view the Protozoa are potentially immortal,’ natural death occurring only among multicellular organisms. The protoplasm of the latter is shown to be of two kinds—germplasm, which is capable of propagating itself indefinitely under suitable conditions like the protoplasm of unicellular organisms, and somatoplasm, which composes the rest of the body and is subject to natural death. The life of the somatic cells was at first limited to one generation, but afterwards in the higher Metazoa was extended to many generations, and the life of the organism was lengthened to a corresponding degree. Such a restriction went on hand in hand with a differentiation of the parts of the organism into somatic and reproductive cells, in accordance with the principle of the physiological division of labour, and this process of differentiation was controlled by natural selection. ‘‘ Death itself,” says Weismann,’ “and the longer or shorter duration of life both depend entirely on adaptation. Death is not an essential attribute of living matter; it is neither necessarily associated with reproduction, nor a necessary consequence of it.” According to this theory, therefore, the phenomena of senescence and death, as exhibited by all the cells of the body with the exception of the germ cells, are secondary properties which have been preserved in multicellular organisms by natural selection, because they are of direct advantage in the propaga- tion of the species. An indefinite prolongation of the life of the organism after the age of reproduction had been passed would * This question, about which there has been much controversy, is referred to in Chapter VI. (pp. 212-14). ? Weismann, “ Life and Death,” Essays, vol. i., 2nd Edition, Oxford, 1891. PHASES IN THE LIFE OF THE INDIVIDUAL 683 be of no value or utility to the race, but rather a disadvantage, since it would tend to retard the evolution of more perfectly adapted forms of life. Furthermore, according to Weismann, longevity, although depending ultimately upon the physiological properties of the cells, is capable of adaptation to the conditions of existence, and consequently is influenced by natural selection just in the same way as other specific characters are. Perhaps the most cogent criticism of Weismann’s doctrine of immortality is that of Verworn, who writes as follows :—‘ The conception of living substance as immortal will be accepted by scarcely any one who bears in mind the characteristic peculiarity of living substance, viz., that it continually decomposes, or, in other words, dies. There is no living substance that, so long as it is living at all, is not continually decomposing in some parts, while being regenerated in others. No living molecule is spared this decomposition: .the latter, however, does not seize upon all molecules at the same time; while one is decomposing, another is being constructed, and so on. One living particle affords the conditions for the origin of another or several others, but itself dies. The particles newly formed in turn give rise to others, and, likewise, die. In this manner living substance is continually dying, without life itself becoming extinct.” 4 From this standpoint, therefore, there can be no question of any kind of living substance being truly immortal. The whole conception of a possible immortality arises from a confusion of ideas. Minot,? on the other hand, has elaborated a theory of senescence which may be regarded as an extension of that of Weismann. Like the latter, he seems to assume that death is not a universal accompaniment of life, and that natural death has been acquired in the course of evolutionary development. He proceeds to define senescence as an increase in the differentiation of the protoplasm. During the early periods of life the young material is produced, and the proto- plasm is undifferentiated. During the later stages of existence cell differentiation goes on, and the organism gradually becomes old. When the cells acquire the faculty of passing beyond the 1 Verworn, General Physiology, Lee’s Translation from the second German Edition, London, 1899. 2 Minot, loc. cit. 684 THE PHYSIOLOGY OF REPRODUCTION simple stage to the more complete organisation, they lose some- thing of their vitality, of their power of growth, and of their possibilities of perpetuation. Just as senescence depends upon the increase and differentiation of the cytoplasm, so, conversely, rejuvenation depends upon the increase of the nuclear material ; and consequently the alternation of the two phases of the life cycle (the early brief one when the young material is formed, and the later prolonged one when the process of differentiation is going on) is due to an alternation in the proportions of nucleus and protoplasm. In criticism of this theory, it may be urged that it is in reality nothing more than a descriptive account of a general type of cellular change, and that it provides no sort of explanation as to why this type of change occurs, nor how it is that differentiation is apparently correlated with a reduction of vitality leading eventually to death. Metchnikofi has laid great stress on the idea that natural death is a rare phenomenon, at least among the higher animals. That death with Man is frequently, if not generally, caused by disease or accident is a fact about which there can be no disagree- ment, and Karl Pearson! has worked out statistically the chances of death occurring in the different phases of human life. “‘ We have five ages of man,” he says, ‘‘ corresponding to the periods of infancy, childhood, youth, maturity or middle age, and senility or old age. In each of these periods we see a perfectly chance distribution of mortality centring at a given age and tacking off on either side according to a perfectly clear mathe- matical law.” It was found also that the curve of mortality, as deduced from a study of the deaths per annum of a thousand persons born in the same year, “ starts very high in infancy, falls to its least value at thirteen or fourteen years with only 236 deaths. It then slowly increases till it reaches a maximum in the seventy-second year of life, and falls more rapidly than it rose, till scarcely two isolated stragglers of the thousand reach ninety-one.” It is‘clear, therefore, that death from old age is far from being the rule in the human species, but according to Metchnikoff it seldom occurs at all.? ' Pearson, The Chances of Death, &c., vol. i., London, 1897. ® Metchnikoff, loc. cit.; and The Nature of Man, Mitchell’s Translation, London, 1903. PHASES IN THE LIFE OF THE INDIVIDUAL 685 This biologist finds it impossible to accept the view that the high mortality observable between the ages of seventy and seventy-five indicates a natural limit to human life at about this period. Centenarians, he points out, are not really very rare, and he cites many cases of extreme old age, including that of Thomas Parr referred to above. Real old age, we are told, is associated with an instinct for death which is as natural as is the instinct for sleep. Metchnikoff therefore answers in an emphatic negative the question asked by Admetus in Euripides’ Alcestis, “Is it the same thing for an old man as for a young man to die?” The fact that the instinct for death seems so rarely to exist is regarded as evidence that true senility is a comparatively infrequent phenomenon. According to Metchnikoff, senescence is not brought about simply as the result of arrest of the reproductive powers of the cells. The whitening of hair in old age is due to the destructive action of phagocytes which remove the pigment. Moreover, hairs become old and white without ceasing to grow. Metchnikoff believes also that atrophy of the brain is due to the destruction of the higher nerve cells by neuronophags, and that there are many other devouring cells which are adrift in the tissues of aged men and animals and cause the destruction of other cells of the higher type. The testes, however, appear to have the power to resist these phagocytes, and with this power is corre- lated the fact that spermatozoa are often produced even in ad- vanced old age. Metchnikoff’s theory as to the cause of death is that it is due to the poisoning of the tissues and to the damage done by phagocytes to those parts of the body affected by the toxic action. He believed further that in Man and certain of the animals this process of poisoning is brought about by fer- mentation set up by microbial action in the large intestine. The toxic substances produced by the intestinal fermentation are supposed to enter the system and poison it, the result being that the vitality of the tissues is lowered, so that they are less able to resist the action of devouring phagocytes. The presence of lactic acid in the intestine is believed to arrest the process of fermentation. Metchnikoff recommends, therefore, the regular drinking of sour milk as a means of destroying the microbes in the intestine in the hope of prolonging life. 686 THE PHYSIOLOGY OF REPRODUCTION The term ‘ Death” is employed in two separate senses ; it may mean the death of the whole body, 7.e. somatic death (this being the sense in which it is ordinarily used), or it may be applied to the death of the individual tissues, some of which remain alive for many hours after the body as a whole is said to be dead. The death of the body as a whole usually occurs suddenly. As Michael Foster says :—‘‘ Were the animal frame not the complicated machine we have seen it to be, death might come as a simple and gradual dissolution, the ‘ sans everything ’ being the last stage of the successive loss of fundamental powers. As it is, however, death is always more or less violent; the machine comes to an end by reason of the disorder caused by the breaking down of one of its parts. Life ceases not because the molecular powers of the whole body slacken and are lost, but because a weakness in one or other part of the machinery throws its whole working out of gear.’’? The synchronous disturbance of two or more of the bodily functions, such as is wont to occur in old age, may destroy that co-ordination of the various vital activities, without which life cannot continue. The stoppage of the heart’s beat is the ordinary criterion of death, and this is a true conception, because the cessation of the heart’s movements implies the arrest of the circulation of the blood and the consequent starvation of the tissues of the body. The tissues do not die simultaneously, for as already described, some cells of the body are in process of disintegration through the whole of life. After somatic death, the cells which make up the nervous system usually die very rapidly. The same is true of the gland cells; but the muscles may remain sensitive to external influences for many hours. In animals it has been shown that the heart itself after removal from the body, if kept under suitable conditions and perfused with an artificial fluid resembling blood serum, may continue to live and undergo rhythmical contractions for a considerable time. In the process of death-stiffening, or rigor mortis, the muscles once more con- tract spontaneously, and not till this has happened is their life utterly extinguished. Rigor mortis is brought about by the coagulation of the muscle plasma within the cells. It begins * Foster, Textbook of Phystology, Part IV., 5th Edition, London, 1891. PHASES IN THE LIFE OF THE INDIVIDUAL 687 at periods varying from half-an-hour to thirty hours after somatic death, and it continues for an average of about thirty hours. Certain cells may even live for some time after rigor mortis has passed. This is notably the case with the ciliated epithelial cells of the inner surface of the respiratory passages, and with the white corpuscles of the blood. Sooner or later, however, every part of the organism perishes, putrefactive changes set in, and the entire substance of the body passes once more to that “dust ” out of which its vital activities enabled it to build itself up in the progress of individual life. INDEX [Names of authors are printed in Clarendon type, specific names in Italics. ] A Abderhalden, 563 sq. Abel and Mellroy, 526 Abelous, 282 | Abortion, 612 sqq. Abraxas grossulariata, 639 Acmea, 221 Acomys caharinus, 390 Actinia mesembryanthemum, 8 sq., 679 Acton, 283 Adolphi, 177 Agassiz, 17 Ageniaspis fuscicollis, 636 Ahifeld, 369, 497 Akutsu, 233, 259 Albatross, 27 Albers-Schénberg, 607 Albertoni, 22 Albu and Neuberg, 266, 278 Alcyonium digitatum, 9 Allbrecht, 182, 611 Allen, B. M., 124, 153, 168 —— L. M., 545 Allison, 214, 647 Alquier and Thauveny, 350 Amia, 17 Amphibia, breeding season of, 19 sgg.; insemination in, 184 ; fertilisation in, 190; fertility of, 594 sq.; sex-determination in, 625, 637, 651 Amphioxus lanceolatus, 16 Anasa tristis, 634 Ancel and Bouin, 154, 343, 579 Anderson. See Langley and Anderson Anguis, 151 Annandale, 7, 22, 44 Annandale and Robinson, 70 Annelida, breeding season of, 10 sq. ; 133, 205, 221 Ancestrum defined, 36 Anopheles, 13 Ant, sex-determination in, 629 ; age of, 680 Antelope, 48, 241, 247 Antilocapra americana, 28, 305 “39 Ape, cestrous cycle in, 63 sqq. ; foetal nutrition in, 392, 463 sqq. Apfelstedt and Aschoff, 478 Aphide, 11 sq., 216, 631 Arbacia, 179, 218 Arbacia pustulosa, 293, 300 Aristotle, 590 Arthropoda, breeding season of, 11 ; spermatozoa of, 174; 307 Arvicola, 250 Arvicola agrestis, 40 Arvicola glareolus, 40 Ascaris, 128 Ascidians, fertilisation of, 207 Ascoli, 436, 481 Ashworth, 8 sq. Ashworth and Annandale, 679 Ass, 403 Assheton, 110, fcetal nutrition, 372 sqq., 376, 386 sg., 390, 394 sq., 397 sqq., 406 sg., 419 sg., 423, 487 Astacus fluviatilis, 11 Asterias, 134 n., 204, 220 sq., 223 qd. a Asterias forbesii, 218 Asterina, 223 Atretic follicle, 154 sqq. Aves, breeding season of, 23 sqq. See also Birds Axe, Wortley, 51, 536, 618 Axis, cestrous cycle in, 49 Axolotl, 22, 189 sq., 594 B Backhouse, 159 Badger, gestation of, 59 n.; 416 Baer, von, 143, 145 sq., 375 Balbiani, 631 Balenoptera musculus, 52 Balfour, 116 sg., 124, 160, 379 Ballo witz, 172, 175, 178, 179 sq. Bang, B., 616 sq. —— I, 293 Bar and Daunay, 498, 500, 502 sq. Barasingha, 47 sq. 2X 690 Barberio, 287 Bardeleben, von, 286 Barrett-Hamilton, 29 Barrows, 208 Barry, D. T., 165 M., 165, 187 Basch, 561, 577, 578 Basso, 481 Bat, breeding season of, 32 ; cestrous eycle in, 61 sg.: maturation in, 132; ovulation in, 135, 185 ; 367, 374, 392, 407, 494; parturition in, 541; fertility of, 587, 589 Bataillon, 203, 221 Bateson, 194, 198, 637, 639 sqq., 657 Baumm, 497 Bear, breeding season of, 58; fer- tility of, 590, 592 Beard, 110, 162 sq., 337, 542 sq., 628, 633, 635 sq. Bechterew, 262, 539 Beck, 180 Beddard, 42 Bee, 186; 626 sqq. Beebe, 30 Beesly, 514 Beesly and Milne, 514 Bell, Blair, 69, 87, 142, 330, 346 Bende, 169 Bendix and Elstein, 297 Beneden, van, Cheiroptera, 62, 118 ; maturation, 128, 131, 136, 165, 187 ; 371, 405, 459 sq., 467 Beneke, 62, 136 Benkiser, 316 Bergell and Liepmann, 481 Bergomié and Trabondeau, 607 Bernard, 431 Bernhard, 520 Bert, 571 Bertkau, 560 Bestion de Camboulas, 328 Beyer, 669 Bianeardi, 517 Birds, female generative organs in, 264 sqq. ; 315 sg. ; foetal nutrition in, 485 ; breeding of, in captivity, 592 sqq.; hermaphroditism in, 654; age of, 680 Birnbaum, 517 Birnbaum and Osten, 69 Birth-rate, 620 sqq. Bischoff, 47, 55; corpus luteum, 143, 147, 149 sqg.; 177; placenta, 371, 387, 400, 421, 442 Bison, 47 sqq. Bizzorzero and Ottolanghi, 561 Bjorkenheim, 465 sex-determination in, INDEX Blackman, 213 Blaine, 679 Blandford, 65 Bles, 5, 20, 22, 594 sq. Bloch, 600, 614, 635 Blood, changes in, during pregnancy, 520 sq. : Blot, 510 Blumreich, 521 Bocarius, 287 Bodio, 624 Bohr, 272 sq., 434, 436, 486, 491 aq., 508, 512, 518 ag. Bohr and Hasselbalch, 271 sq. Bolaffio, 585 Bombyx mort. Bond, 347 sq. Bondzinski and Zoja, 275 Boni, 505 sq. Bonnet, 100, 108 sqg., 184; placenta, 363, 366, 371, 373, 386, 403 sqq., 411, 413 sqq., 426 sg., 476 sq., 480 ; 515 sq. See also Merkel and Bonnet Born, 624 sq. —— Gustav, 337 Boruttau, 314 Bos, 208 Bossi, 185 Boston, 348 Bottazzi, 481 Bouin and Ancel, 154, 310, 343 Bouin, Ancel, and Villemin, 607 Bourne, 10 Boveri, 129, 187 sqq., 199, 660 Brachet, 253, 262, 330, 490, 538 Bradypus, 375 Braem, 658 Branea, 593 Brandt, 316 Breeding season, 4-35 Breschet, 65 Breuer and Seiler, 356 Bridge, 16 Briggs, 626 Brill, 205 Brinkmann, 380 Broeard, 510 sq. Brock, 547 Brock, van der, 418 Brooks, 192 Brouha, 554, 560 sq., 573 Brown, 169 Brown and Osgood, 607 Brown-Séquard, 308 sq., 326, 541 Brumpt, 536 ** Brunst,”’ 36 Bryee, 138, 392 Bryce and Teacher, 369, 449, 466 sqq., 471, 474, 479 See Silkworm moth INDEX Buccinum undatum, 14 Budge, 254 sq., 259 sq., 528 Budgett, 17, 28 Buffalo, 349 Buffon, 591 Bufo, 203 Bihler, 145, 151 Buller, 178 sqq., 215 Bulloch and Sequeira, 351 Bullot, 221 Bunge, 265, 270, 480, 515, 563 Burchell’s zebra, 202 Burekhard, 437 Burlando, 508 Burrian, 288, 296, 297 Bustard, 30 Buys and Vandervelte, 317 Cc Calf, growth of, 668 Calkins, 6, 7, 213 Callionymus lyra, 29 Calotes jubatus, 277 Camel, rut in, 26, 49 Cameron, 48, 365 Campbell, Malcolm, 340, 595 Camus and Gley, .233, 237, 287 Canary, breeding of, in captivity, 592 ; 640, 680 Canis azarae, 55 Capaldi, 511 sq. Capercaillie, 315 Capon, 306, 312, 349, 654 Capybara, 250 Carmichael, 320 Carmichael and Marshall, 317, 328, 341, 348 Camegie, 58 Carnivora, cestrous cycle in, 53 sqq.; uterine cycle in, 99 sqq. ; fetal nutrition in, 386 sg., 411 sqq., 485; puerperium in, 551; lactation in, 554; fertility of, 592; 594 Carnot and Deflandre, 68 Carp, 292 Carpenter, 208 Castle, 207 sq., 637, 639, 642, 651 sq. Castration, chap. ix. passim, in Man, 303 ; stag, 305; sheep, &c., 306 ; arthropods, 307; fowl, 311 sg.; frog, 313; effect of, on general metabolism, 353 sqq., 656 Cat, cstrous cycle in, 56 sq.; superfeetation in, 159; acces- sory reproductive organs in, 229, 232, 247, 252, 255 sg., 260, 262; foetal nutrition in, 411, 413, 416, 418; pregnancy in, 512, 523; 691 525; female generative organs in, 525, 528 sq., 537; fertility of, 591; growth in, 671; age at- tained by, 681 Caterpillar, 307, 625 Catlin, 48 eg. Caton, 305 Cattle, cestrous cycle in, 46 sq., 334; effects of castration on, 306, 349; abortion in, 613; hermaphroditism in, 652; hered- ity in, 653; age in, 681 Cavia, 150 Cavia porcellus, 41 Caviar, 278 Centetes, 553 Centetes ecaudatus, 458 Cephalochordata, breeding season of, 16 Ceratocephale os wat, 11 Ceratodus, 17 Cercocebus, 63, 96 sq. Cercocebus’ cynomolgus, 89, 96 Cercopithecus, 63, 74 n., 584 Cercopithecus cynosurus, 65 Cervus alces, 233 Cervus elaphus, 27 Cesa-Bianchi, 161 Cetacea, cestrous cycle in, 52 sq. ; 141, 246, 375; lactation in, 553 sqq. Chadwick, 15 Cheetopterus, 217, 221 Chaffinch, 315 Champneys, 85 Charrin, 515 Charrin and Goupil, 481 sq. Charrin and Guillemont, 508 Cheiroptera, cestrous cycle in, 61 sq.; foetal nutrition in, 459-463 ; lactation in, 553 ; fertility in, 587 Chelchowski, 185 Chermes, 12 Chicken, growth in, 665 Child, 10 Chimpanzee, cestrous cycle in, 63 Chipman, 369, 422, 425 sq., 428, 430 sq., 487 Christ, 85 Chrysochloris, 61 n. Cimorini, 349 Ciona intestinalis, 207 Clark, 118, 139, 145 sq., 208, 336 Clarke, Eagle, 24, 26 Cock-of-the-rock, 27 Cocks, 56, 57, 59 Cod, 278 Ceelenterata, breeding season of, 7; 125 n. ; spermatozoa of, 174, 190 ; 200 692 Cohen, 285 Cohn, 149 Cohnstein, 520 Cohnstein and Zuntz, 518 Cole, 246 Collocalia, 30 Colpoda steini, 7, 214 Cook, 14 Cooper, 678 Copeman, 637 Copulatory organ, 242 sqq. Corner, 312, 606 sq. Corpus luteum, formation of, 142 sqq. ; false, 154; 334 sq.; func- tion of, 336 sq., 491, 502 n. Correns, 193, 634 Coste, 358 Courant, 242 Cow, ovulation in, 1365 183; foetal nutrition in, 386, 396 sq., 400, 403 sq., 407; pregnancy in, 487, 495, 508; parturition in, 535; lacta- tion in, 553 sq., 557, 568, 571, 583; composition of milk of, 562 sqq.; fertility of, 596, 608 sq. ; artificial insemination of, 611; abortion in, 616 sg.; growth of, 668, 671. Sce also Cattle Cowper’s glands, 239 sqq. Crab, 307 sq., 653 Cramer, A., 478 — H., 332, 491, 517 chap. viii, 355, 431, See also Loehhead and Cramer and Marshall and Cramer —— W., and Marshall, 601 Crampton, 307, 656 Creighton, 366 Cremer, 300 Crepidula fornicata, 653 Cristalli, 511 Crocodile, 31 Crocodilus biporcatus, 277 Croom, Halliday, 65 Cross-breeding, 202-11 effects of, 601 sqq. Crowe, Cushing, and Homans, 356 Crowther, 564 sqq. Crustacea, ovulation in, 137 n.; 281 sqg.; parasitic castration in, 640 ; 653 Cryptorhynchus gravis, 13 Ctenophora, 9 Cuckoo, 24 Cuénot, 625 sq., 650 Culicide, 13 Cull, 213 Cunningham, D. J., 55 434, 436, passim ; INDEX Cunningham J. T., 28, 29, 151, 304 sq. Curtis, 651 3 Cushing, 356 Cushny, 527 sqq. Cuttlefish, 280 Cyclopterus lumpus, 29 Cynthia partita, 207 D Daels, 343, 601 Dale, 530 Dandie Dinmont, 183, 209 sq. Daphnia, 631 Darbishire, 195 Dareste, 286 Darwin, 5, 28, 29, 201, 206, 208, 304, 307, 314 sg., 591 sqqg., 602 sq., 653 sq. Dastre, 478 Dasyurus, 150, 158 sq., 383, 385 Dasyurus viverrinus, 149, 337 Dawson, 636 Dean, Bashford, 17 Death, 682 sqq. Death’s-Head hawk moths, 13 De Bonis, 236, 239. Decidua, and fetal nutrition, 366 8qq- Deer, 32, 47 sg., 241; effects of castration on, 305, 313; feetal nutrition in, 371, 397, 403 De Graaf, 251 Delage, 223 sqq. Dembo, 530 De Sinéty, 85 De Vries, 193 Dewar and Finn, 604 Dewitz, 178 sq. Dinophilus apatris, 635 Diestrous cycle, defined, 37 Dicestrum, defined, 37 Diplozoin paradoxum, 10 Dipodillus campestris, 40 Dipodillus simoni, 40, 41, 545 Discoglossus, 22 Disse, 439, 441 a 24, 228, 232, 241, 244, 0 Dixon, 285, 309 Doering, 145 sq. Dog, gestation of, 32; cycle in, 37, 53 sqq., 99 sqq., 329; ovulation in, 135, 141; artificial insemination of, 182 sq., 203, 611; in-breeding in, 208 sqq-; accessory reproductive organs in, 229, 232, 236, 238 sq., 252 sqq., 256, 260; castration of, cestrous INDEX 309, 355 ; 349 ; influence of ovary in, 318, 328 sg., 332 sg., 341; ovum of, 371; fcetal nutrition in, 387, 411, 413, 416, 427; pregnancy in, 490, 498, 500 sqq., 507 sq., 511 sqg., 520; parturition in, 5883; 552; lactation in, 563, 583; fertility of, 590 sg., 601; sex in, 644 aq. ; 671 Dolphin, breeding period of, 53 Donaldson, 662 Doncaster, 131, 204, 210 sq., 629, 639 sq. Donkey, ovulation in, 136 ; 183 Doran, 330 sq., 346 Drennan, 516 Driesch, 190, 660 Driessen, 442, 478 Droop-Richmond, 564 Drosophila ampelophila, 208 Dubner, 520 Dubois, 281, 300 Dubreuil and Regaud, 159, 344 Dubuisson, 157 Duck, 315; fertility of, 591 sq. Duckworth, 306 Ductless glands, 336; correlation between generative organs and, 349 sg.; during pregnancy, 522 aq. Dudley, 331, 674 Duesberg, 131 Dugong, 376 Diihrssen, 185 Dumas, 184 ers Matthews, 66, 587, 589 sq., Dungern, 179, 216 Durham, 640 Diising, 630, 642 Duval, 62, 361, 387, 400, 413 sq., 416, 420, 423 sqg., 426, 437, 439, 462, 483, 552 Dzierzon, 628 sq. E Earthworm, 186, 190 Ebner, von, 561 Echidna, cestrous cycle in, 38 sq. ; lactation in, 554 Echinodermata, ‘breeding season of, 15 sq. : spermatozoa of, 174, 178, sqq-, 190; cross-fertilisation of, 203 sqg., 210 sq.; partheno- genesis in, 216-226 passim Echinoidea, 178 Echinus, 179, 300 Echinus acutus, 16 Echinus esculentus, 15, 300 693 Echinus microtuberculatus, 16 Eckhard, 251, 254 sqq., 577 Eden, 430, 478, 543 Eel, 18, 23 Eggelung, 554 Ehrlich, 520 Ehrstrém, 291, 507 Eimer, 62 Ejaculation, mechanism of, 251 sqq. Eland, cestrous cycle in, 49; 306 ! lasmobranchs, 16, 190, 277 Elephant, cestrous cycle in, 52 ; 242, 304; foetal nutrition in, 419 sq. ; lactation in, 553; fertility of, 592; age attained by, 681 Eliomys quercinus, 40 Ellenberger, 45-6, 47, 50 aes Havelock, 63, 65, 70, 71, 55 Emberiza passerina, 593 Embryotrophe, defined, 403 n. Empide, 13 Emrys-Roberts, 47, 163, 435 Engelmann, 80, 83. See also Kun- drat and Engelmann Engstrém, 521 Enriques, 192, 214 Equus prjewalskii, 51 Ercolani, 359, 367, 401, 459 Erection, mechanism of, 251 sqq. Erlandsen, 267 Esehricht, 358, 375 Essen-Moller, 342 Eunice fucata, 11 Eunice viridis, 11 Eutheria, 149 Ewart, 51, 108, 136, 159, 201 sq., 210, 396, 545, 615 sq., 620 Exner, 234 F Faico albidus, 593 Farkas, 281, 302. and Farkas Farmer, 191, 201 Farre, 359 Fehling, 512, 520 Fellner, 530 Ferret, 57; breeding period of, 58 sq.; oestrous cycle of, 99 sqq. ; ovulation in, 136, 141, 154; ovum in, 371; 416; fertility of, 591, 594 Ferroni, 481, 511 Fertilisation, chap. vi., 371; and sex-determination, 628 sqq. Fertility, chap. xiv., 586 Fichera, 349 Fick, 200, 260 Finch, breeding of, in captivity, 592 See also Tangl 694 Findley, 84 sg. Finn, 604 Fisehel, 507 Fischer, 275 Fischer and Ostwald, 301 Fish, 184; biochemistry of eggs of, 277 sqq.: age attained by, 680 Flatau, 342 Fleming, 536, 608 Flemming, 156 sqq. Fletcher, 253 Flies, sex-determination in maggots of, 626 Florence, 287 Flower, 43 Flower and Lydekker, 554 Foa, 320, 572, 580 sqg., 583 Foetal membranes, 377 sqq. Foges, 311, 579 Fogge, 258 Foote and Strobell, 634 Fordyce, Dingwall, 74, 568 Forel, 655 —. Foster, 540, 686 Fothergill, 369 Foulis, 118 Fowl, oviduct of, 24, 333; ovula- tion in, 139 n.; 184; Andalusian, 194 sg.; biochemistry of the sexual organs of, 264 sqqg.; 311 sq, 315, 320 n., 349; foetal nutrition in, 485, 485, 487; fertility of, 589, 590, 605 ; hered- ity in, 640; hermaphroditism in, 651 n., 654 Fowler, 305 Fox, breeding season of, 55 Fraenkel, 118, 161, 334, 338 sqq., 353 Fraenkel and Cohn, 338 Franck-Albrecht-Goring, 545 Francois-Franck, 251, 255 Frankenhauser, 528 Franz, 527, 612 Frazer, 70, 602 Free-Martin, 652 Freund, 350, 493, 522, 524 Friedlander, 548 Fries, 59 n. Frog, breeding season of, 20 sqq. ; maturation in, 133; oviposition in, 140, 141; insemination in, 184; fertilisation in, 187, 216, 221; 234, 277, 278, 300; experi- ments on testes of, 312 sgq., 350. See also under Rana Frommel, 366, 494 Firbringer, 236, 287 Firth, von, 280 Firth, von, and Schneider, 481 INDEX G Gadow, 20, 23, 24 Gadus morrhua, 291 Galabin, 66, 83, 86, 139, 160, 533 sq., 615 Galago agisymbanus, 396, 410 Galeopithecus, 377 Galeopithecus volans, 98 Galgulus oculatus, 634 Gallus bankiva, 591 Gamecock, 653 Gametic selection, 202 sqq. Gamgee, 267, 401 Garner, 63 Garrod, 247 Gaskell, 254, 350 Gassner, 497, 547 sq. Gasteropods, 133 Gautier, 181 sq. Gawronsky, 526 ? Gayal, cestrous cycle in, 49 Gazella dorcas, 49 Gazelle, 247 Gebhard, 84 sg., 87 sq., 89 Geddes and Thomson, 30, 164, 165, 175, 191, 628, 626 sq., 646 sq., 651 Gellhorn, 74, 576, 584 Geppert, 514 Gerbillus hertipes, 40 Gerhardt, 141, 244 Gerlach, 132 Gestation in Mammalia, 32 ; guinea- » pig, 42; sheep, 46; cattle, 47; camel, 49; sow, 50; mare, 51; elephant, 52; dog, 54; wolf, 55; fox, 7b. ; Cape hunting dog, 2b. ; domestic cat, 56; wild cat, 57; lioness, 58; tigress, 7b. ; puma, ib.; bear, 7b.; badger, 59 n.; walrus, 60; hedgehog, 61; apes and monkeys, 65; duration of, 73 sq., 544 sq. Geyelin, 590 Geyl, 543 Giacomini, 151, 380 Giacosa, 277 Gierke, 508 Gies, 222, 300 Gilbert, 247 Gilchrist and Jones, 564 Giles, 68, 547 Giraffe, cestrous cycle in, 49, 247, 400 Girtanner, 358 Glass, 331 Gley, 240. See also Camus and Gley Gnu, cestrous cycle of, 49 INDEX Goat, cestrous cycle in, 64; in- breeding in, 214; 231; lactation in, 555, 558, 567, 571 sq., 584 Godet, 431 Godlewsky, 199 Godman, 67 Gofton, 142 Gohre, 463 Goltz, 22, 253, 329, 490, 538 Goltz and Ewald, 329, 490, 538, 577 Goodsir, 358 sq. Goose, fertility of, 591 sq. Gordon, 331, 607 Gorilla, cestrous cycle in, 63 Gottschalk, 477 Gottschau, 350 Graefe, von, 342 Grassi, 627 Grassi and Sandias, 627 Griffiths, 238, 240 Grigorieff, 319 Grohmann, 48 Gross, 306 Grouse, 315 Gruber, 235 Gruenhagen, 253 Grimbaum, 579. and Griinbaum Guaita, von, 208 Gudger, 652 Guillot, 513 Guinea-fowl, 635 Guinea-pig, maturation in, 132 ; ovulation in, 135; 150, 156; arti- ficial insemination of, 183, 234 ; male accessory reproductive organs in, 232, 234, 236; 273, 286; castration in, 306, 310, 349; ovariotomy in, 320, 343; 328, 349; foetal nutrition in, 374, 400, 439, 442-7, 466; lacta- tion in, 568, 578; fertility of, 590, 607; growth in, 664 sq. Guldberg and Nansen, 53 Gull, breeding of, in captivity, 592 Giinther, 184, 251 Giirber and Grimbaum, 508 Gumey, 315, 680 Gusterosteus spinachia, 30 Guthrie, 320 Guyer, 635, 657 Gymnura, 61, 377 See also Giirber H Haddon, 600, 614 Hagemann, 54, 500 sqq., 504 Halban, 320, 332, 334, 492, 524, 579, 581 sq. 695 Haldane, 52 Haller, 400 sg. Halliburton, 562, 564 Hamm, 165 Hammarsten, 264, 277, 278 Hammond, 606 Hamster, 241 Handmann, 676 Hare, 588 Harper, 139 sqq. Harrington, 17 Hart, Berry, 652 Hart and Gulland, 366 Hartung, 266 Harvey, 187, 357, 400, 681 Hasselbalch, 274. See also Bohr and Hasselbalch Hausmann, 135 Hayeraft, 71 Heape, 26, 32 sqg.; the cestrous eycle, chap. ii., passim, 79, 85 sqq., 89-97 passim: the ovary, 127, 133-9, 154, 158, 163; in- semination, 180-5 passim, 609 sgq.; 209, 330, 334 sg.; placenta, 372 sq.; 495, 583 sq., 596 sq., 617 sqq.; sex-determination, 641-6 “* Heat,” 26, chap. ii., passim ; and menstruation, 110, 329 sqqg. ; and ovulation, 135; cause of, 329 Hedgehog, breeding season of, 60 8q., 238; 240, 252, 337; foetal nutrition in, 367 sqg., 374, 377, 390 sqg., 420, 447-452, 469; 552 Hegar, 304 Heidenhain, 560 sq. Heil, 74 Heim, 282 Heinricius, 364, 414, 416, 521 Helme, 527 sq., 530, 549 Hemitragus jerulaicus, 47, 48 Henderson, 349, 550 Henking, 633 Henneguy, 156 Hennig, 366 Henriques and Hansen, 270 Hensen, 371, 443 Herbst, 220, 315 Herdman, 17 Herff, von, 329, 526 Hergesell, 138 Herlitzka, 320 Hermaphroditism, 650 sqq. Heron, 621 Herring, 279, 297 Hertwig, 187, 191, 217, 219, 376, 389 Herwerden, van, 60, 62, 63, 89, 96 sqq., 137, 536 696 Heukelom, von, 466, 470, 473 Hewitt, 13, 131, 226 Hickson, 199 sq. Hikmet and Regnault, 304 Hildebrandt, 491, 581 Hilger, 277 Hill, 149, 384 sq., 576, 585 His, 143, 146, 162, 364, 463, 466 Hobday, 332 Hodge, 677 Hofacker, 646 Hofbauer, 362 sqg., 479 sqq., 486, 489, 512, 516, 550 Hoffmann, 369 sq. Hofmeir, 316 Hofmeister, 274, 510, 572 Hogue, 226 Holdich, 305 Hollard, 421 Holophytum, 9 Holzbach, 346 Homans, 356 Home, 189, 609 Honoré, 126 sq., 144 Hopkins and Pinkus, 274 Horse, 229, 234, 252; offect of castration on, 307, 310; fertility of, 599 n., 604 sq.; 612; sex- determination in, 643; growth in, 666 sqg., 669, 671; age at- tained by, 681. See also Mare Howlett, 13 Hubrecht, placenta, 361, 367 sqq., 376 sqq., 391-486 passim, 494 Hugouneng, 514 Huish, 183, 610 sq. Hunter, A., 289 —— John, 184, 315, 358 sg., 466, 609 — William, 358 Hurst, 194 Hutchinson, Woods, 350 Huth, 214 Huxley, 375 sqq. Hybrids, fertility of, 603 sg. ; 612 Hydatina, 630 Hydatina senta, 632, 635, 638 Hydra orientalis, 7 Hydromedusz, 190 Hyena, 250 Hylomys, 61 Hyrax, 387, 420 Ibex, 47 sq. Thering, von, 636 In-breeding, 208 sq. ; 601 sqq. Infusoria, 6, 200 effects of, INDEX Ingerslev, 520 Insecta, spermatozoa of, 178, 190 Insectivora, cestrous cycle in, 60 sq.; foetal nutrition in, 390 sqq., 447-459 Insemination, artificial, 609, sqq. , Issako witsch, 632, 644 Iwanoff, 135 sq., 183, 234, 237, 604, 609 sq., 612 Izuka, 11, 134 181 sqq., Jacob, 530 Jacobi, 18, 184 Jagerroos, 484, 501, 516 Jankowski, 149 sq. Janosik, 156 sq., 217 Jassinsky, 360 Jeannin, 523 Jenkinson, 188 sqq., 220, 373, 404, 406, 439 sq., 442, 487 Jenner, 24 Jennings, 215 Jentzner and Beuthner, 328 Joukowsky, 212 Julin, 118 K Kahlden, von, 85 Kallius, 526 Kaltenbaech, 510 Kangaroo, 39 Kastschenko, 360, 362 sg., 475 Kazzander, 108, 110 Kehrer, 140, 316, 498, 507, 527 Keiffer, 100, 529 sg., 541, 581 Keilmann, 541 Kellogg, 307, 626 Kelly, 608, 614, 621, 672 Kennedy, 66 Kerr, 18, 28 King, 625, 636 Kirkham, 132 Kirsten, 510 Klebs, E., 360 — G., 8 Klein, 368, 478 Kleinhaus and Schenk, 343 Knauer, 318 sg., 332 Knott, 584 Kobelt, 251 Kdlliker, 118, 143, 146, 156, 158, 165, 236, 252, 359, 561 Kollmann, 467, 494 Kolster, 108, 233, 397, 403, 413, 437, 439, 442 Korner, 528 INDEX Kossel, 269, 275, 288 sqg., 292, 293, 298 Kossel and Dakin, 292 Kossel and Kutscher, 291 Kossel and Pringle, 291 Kostanecki, 224 Krafft-Ebing, 655 Kraft, 180 Kraus, 513 Kronig, 353, 548 Kruieger and Offergeld, 490, 538 Krukenberg, 265, 277, 282 Kiihne and Ayres, 243 Kundrat and Engelmann, 163, 548 Kupel weiser, 205 Kurdino wski, 527 sq., 530 sq. Kworostansky, 479 L Lacertilia, 380 Lactation, and the cestrous cycle, 74; and pregnancy, 138 n., chap. xiii. ; and fertility, 600 Ladenburg and Abel, 285 Lamprey, 190, 221 Landwehr, 233, 286, 572 Lane-Claypon, 118, 122 sqqg., 148, 150, 160 sq., 168, 344 Lane-Claypon and Starling, 333, 573, 578 sqq. Lang, 186 Lange, 523 Langer, 560 Langhans, 359 sqq., 366, 477 Langley, 255, 259, 525, 529 Langley and Anderson, 252 sq., 255 sqq., 259, 260 sg., 525, 529 Langstein and Neubauer, 507 Lannois and Roy, 306 Lanz, 511 Lark, 27 Lataste, 41, 106, 233 Lauder, 564 La Valette St. George, 173 Layeock, 31, 65, 66, 316 Leathes, 482 Lebedeff, 520 sq. Lécaillon, 310 Ledermann, 400 Lee, 669, 677 Leeney, 536 Leersum, 506 Leeuwenhoek, 165, 184 Lefévre, 224 Lefroy, 13 Lehmann, 558, 566 Lemaire, 510 Lemur, cestrous cycle in, 62, 97 sg. : 697 ovulation in, 137; foetal nutri- tion in, 377, 396, 410; fertility of, in captivity, 593 n. Lemuroidea, foetal nutrition 408 sqq. Lenhossék, von, 363 sq. Leopold, 83 sg., 366, 467, 548 Lepidoptera, 13, 639 Lepidosiren, 18, 28 Lepidosteus, 17 Lepus, 150 Lepus cuniculus. Sce Rabbit Lepus variabilis, 41 Leslie, 21 Leuckart, 233 Leusden, 549 Levene, 278, 294 Leydig, 240 Liebermann, 271, 274 Liepmann, 493 Lillie, 52, 221 Limnea, 14 Limon, 320, 351 Linnet, 593 Linton, 241 Lion, 247 Lioness, cestrous cycle in, 58 Lipes, 80, 82, 85 sq. Littlejohn and Pirie, 288 Littorina, 14, 15 Lo Bianco, 14, 16 Lochhead, chap. x., 435 sq. Lochhead and Cramer, 269, 273, 302, 431, 433, 435, 496, 508 Lock, 191, 196 Lode, 176, 232, 234, 283 Loeb, A., 258 —— Jacques, 191, 204 sq., 218 sqq., 299 sq., 301 sq., 661 — L., 150, 156, 344 Loewenthal, 162, 347 Loewy, 312, 356 Loewy and Richter, 355 Loisel, 170, 329 Lombroso and Bolaffio, 585 Longridge, 546 sq., 549, 551 Lota vulgaris, 291 Lott, 177 Lottia, 221, 224 Lovén, 251 Low, 46, 208 Lubarseh, 286 Lucas-Champonniére, 343 Lucien, 151 Lusk, 563 Liithje, 354 sq. Lycaon pictus, 55 sq. Lydekker, 42, 43, 46. Flower and Lydekker Lyre-bird, 30 in, See also 698 M Macacus cynomolgus, 64 Macacus fascicularis, 64 Macacus nemestrinus, 63, 65, 373 Macacus rhesus, 63 sq., 89 sqq-, 96, 259 Macacus sinicus, 64 Macallum, 297 Maebride, 204 McClung, 130, 633 McFadyean, 609 Maegregor, 89 M‘Intosh and Masterman, 205 Mellroy, 526 Mclvor, 644 Mackerel, 293 MacLean, 23 Maerdervort, 85 Magnus-Levy, 497, 499, 506 sq., 519 Magnus-Levy and Falk, 356 Maja, 282 Maja squinado, 281 Majert and Schmidt, 285 Malthus, 620 Maly, 281 Mammalia, breeding season of, 26 sqq.; cestrous cycle in, chap. ii.; spermatozoa of, 174; ferti- lisation in, 190 sq., 203; female generative organs in, 263 sq., 273 ; placental classification of, 375 sqq. Man, cestrous cycle in, 65 sqq.; menstrual cycle in, 75 sqq., 161 sqg., 334; ovulation in, 137 sqq. ; spermatozoa in, 172 sqq.; artificial insemination in, 184, 609; accessory reproductive organs in, chap. vii. ; castration in, 304; ovariotomy in, 314, 316 sq., 330 sqq. ; foetal nutrition in, 371, 380, 384, 388, 392, 402, 463-483 passim, 487; changes in the maternal organism during preg- nancy in, chap. xi. passim; innervation of female generative organs in, 525 sqq.; parturition in, 531 sqqg.; prolonged gestation in, 544 sg.; puerperium in, 545 sqq.; lactation in, 553, 562, 566 sqq.; fertility in, chap. xiv. passim; sex-determination in, 636 sqq. ; 653, 655 ; growth in, 662 sqq., 668 sg. ; puberty in, 670 sq. ; menopause in, 672 sqq.; sene - cence in, 675 sqqg.; age attained by, 681 sg. Mandl, 85, 88, 526 Mandl and Birger, 346 Manis, 375 INDEX Manouvrier, 655 Mansfeld, 268 Marchal, 636 Mare, cestrous cycle of, 50 sg. ; ovulation in, 136; 159; artificial insemination of, 183, 185, 610 aq. ; telegony in, 201 sg. ; in-breeding in, 208, 214; ovariotomy in, 332 ; foetal nutrition in, 396 sq., 403 sq. ; parturition in, 535 sq. ; ges- tation in, 545; lactation in, 554, 583; fertility of, 595, 605; abortion in, 613, 615 sqq., 619, 654 Markhor, 47 sq. Marmot, cestrous cycle in, 105 sg. ; corpus luteum in, 149, 247 Marshall, F. H. A., the estrous cycle, 35, 42, 99, 136; the corpus luteum, 147, 148, 152; 154, 202, 247, 268; fcetal nutrition, 431, 436; fertility, 595 sq., 598, 604, 613, 618. See also Carmichael and Mar- shall; Cramer and Marshall ; and Simpson and Marshall. Marshall, F. H. A., and Cramer, 495 Marshall, F. H. A., and Jolly, 35, 53, 56, 58, 99, 135, 184, 320, 321, 332, 341, 348, 491, 504, 579 Marshall, F. H. A., and Kirkness, 572 Milnes, 78 Marsupialia, cestrous cycle in, 39; 141, 149, 246; corpus luteum in, 339; foetal nutrition in, 381 sqq. ; lactation in, 554; mammary glands in, 576 Martin, 69, 86 Masius, 427, 430 Masquelin and Swaen, 366, 423-4, 494 Mast, 208 Masterman,16,205. See also M‘Intosh and Masterman Matthes, 480 ss Matthews, 134, 224, 293, 297, 505 Maturation, 125 sqg.; rabbit, 131; mouse, 132; guinea-pig, 7b. ; bat, ib.; mole, 133; pigeon, 12.; frog, 1b. ; Invertebrates, 133-4 Maupas, 212 sq., 630, 632 Maurel, 498, 508 Maximow, 425 sqq., 430 sq. Mayo-Smith, 71 Mayow, 358 Mead, 217 Meade-Woldo, 59 Meckel, 232 Meisenheimer, 307 INDEX Mendel, 193 sqq. Mendel and Leavenworth, 269 Menopause, 353, 672 sqq. Menstruation, in Primates, 62 sqq. ; in Man, 65 sqq., 75 sqq., 161 sqq. ; and lactation, 74, 334, 569; and “ heat,” 329 sqg.; 346, 350 Mereonitski, 268 Meredith, 331 Merganser, 315 Meriones longifrons, 40, 545 Meriones shawi, 40, 41, 545 * Merkel, 169 Merkel and Bonnet, 526, 561 Merletti, 481 Merttens, 473, 478 Metaphyta, 7 Metazoa, breeding season of, 7 Metehnikoff, 78, 111, 163, 679 sq., 684 aq. Metcestrum, defined, 37 Michaelis, 570 Michel, 499 Miescher, 18, 279, 288 sq., 292 sq., 295 sqq. Milk, uterine, 400 sqg. ; composi- tion and properties of human and cow’s, 562 sgq.; influence of diet, &c., on yield of, 564 sqq. ; discharge of, 569; formation of organic constituents of, 569 sqq. Millais, 48, 52, 53, 55 sq., 59 sqq., 183 Milroy, 19, 279 Mingazzini, 151 Minot, 79, 86, 202; fcetal nutri- tion, 362, 366, 388, 421, 463 ; 542, 590 ; growth, 660, 662, 664 sqq., 676, 683 Miotti, 511 Mironow, 578 Misuraca, 232 Mislawsky and Bormann, 258 Mobius, 30 Mohrike, 63 Mole, breeding season of, 61; maturation in, 133; accessory reproductive organs in, 232, 238, 240; ovum in, 372; foetal nu- trition in, 376 sg.; 392, 456-7, 485 Mollusca, breeding season of, 13 sqq., 205 Monkeys, cestrous cycle in, 62 sq. ; menstrual cycle in, 89, 335; ovulation in, 137, 330 ; 255 ; fcetal nutrition in, 392, 463 sqq.; fer- tility of, 592 Moneestrous, definition of, 38 Monotremata, oestrous cycle in, 38 699 sq., 141; 244; corpus luteum in, 339 ; 357; lactation in, 554, 584 Montgomery, 129 Moore and Parker, 571 Morat, 254 ~ Morgan, 8, 12, 140, 199; fertilisa- tion, 207, 208, 216 sq. ; 305, 604; sex-determination, 623, 625, 635 sq., 641 sq., 648, 670 Moricke, 84 ag. Morner, 274, 279 Morris, 331 Mosher, 68 Mouse, 40; ovulation in, 135; 156; artificial insemination of, 183 ; 373 sq., 389; foetal nutrition in, 420, 437-442, 449, 494 ; 545, 605, 611; sex in, 647, 650 Mule, 203, 584 Miiller, A., 253 — F,, 519 —-— Fritz, 207 —— P., 606 Miiller and Masuyama, 277 Muntz, 572 Murlin, 503, 507, 518 Mus, 150 Mus decumanus. See Rat Mus minutus, 40 Mus musculus. Mus rattus, 40 Mus sylvaticus, 40 Musk deer, 241 Musk ox, 49, 249 Musk rat, 241 Mustelus levis, 277, 380 Myliobatis, 151 Mytilus, 205 ‘See Mouse N Nagel, 117, 145, 177, 240, 260, 533 Nasse, 520 sq. Nathusius, 46 Nattan-Larrier, 370, 492 Needham, 400 Nematodes, 133, 174 Nematus ventricosus, 627 Nemertea, breeding season of, 10 Neugebaur, 651 Neumann and Vas, 356 Neumeister, 277, 569 Newbigin, 29 Newcomb, 646, 650 Newport, 187 Newsholme and Stevenson, 621 Newt, 23, 184, 300 Nicholson, 522 sq. Nicolas, 247 Nightingale, 25 700 Nikolski, 255 Niskoubina, 344 Nitabuch, 477 Nolf, 367, 419, 460 sqq. Noorden, von, 68, 354, 356, 497, 510, 513, 515 Nudibranchs, 14 Nussbaum, 141, 312 sqg., 632 Nycticebus, 408 Nylghau, cestrous cycle in, 49 ie) Oceanu and Babes, 356, 567 Ocneria dispar, 307 Oddi and Vicarelli, 519 Gstrus or Gistrum, defined, 36 Cistrous cycle, chap. ii., 335 Offergeld. Sce Kruieger and Offer- geld Oliver, 83, 85, 138, 614 Onchorhynchus, 30 n. Onuf, 253 O5genesis, chap. iv. Ophelia, 221 Ophiothria fragilis, 204 n. Opossum, 385, 484 Orang-utan, cestrous cycle in, 63 Ornithodelphia, 380 . Ornithorhynchus paradoxus, 149 Orton, 653 Orycteropus, 375 Osborne and Campbell, 275 Oser and Schlesinger, 537 Oshima, 512 Ostwald, 300 sq. Ott, 67, 68 Otter, breeding season of, 59; 416 Oudemans, 239, 307 Ovariotomy, 314, 316 sqg.; and menstruation, 330 sgq. ; and preg- nancy, 341 sqq. Ovary, changes in, during the estrous cycle, chap. iv.; in- fluence of, 314 sqg.; Man, 314, 316 sg., 330 sqg.; deer, 314; poultry, 315 sg. ; rabbit, 317 sqq. ; guinea-pig, 320; rat, 321 sqq.; internal secretions of, chap. ix. passim ; innervation of, 526 Overlach, 366 Ovis, 150 Ovis ammon, 43 Ovis argali, 43 Ovis burrhel, 42 sq. Ovis canadensis, 43 Ovis musimon, 42 Ovis poli, 43 Ovis tragelaphus, 42 Ovis vignei, 43 INDEX Ovulation, 125 sqg.; rabbit, 134; mouse, 135; rat, 7b. ; guinea-pig, ib.; dog, ib.; sow, ib.; ferret, 136, mare, 7b. ; donkey, ib. ; cow, ib.; sheep, ib.; bat, 136 sg. ; Primates, 137; Man, 137 sqq. ; Invertebrata, 137 n.; and men- struation, 330, 333 n., 335 Ovum, formation of, 160 sg.; chap. x., part ii, passim; the ovarian, 370 sg.; the fertilised, 371 sqq. Owen, 31, 42, 61, 247, 359 Ox, 288, 296, 306, 349, 486 P Pachyuromys duprasi, 41 Paladino, 146 Palolo worms, 10 sq., 134 Paludina, 175, 633 Papio, 63 Papio porcarius, 64 Paramecium, 6, 212 sqq. Paramecium caudatum, 211 Parthenogenesis, 216 sqq. Parturition, 527 sqqg.; human, 531 sqqg., 538; other Mammalia, 535 sqg. ; nervous mechanism of, 537 sqq. Patella, 14, 216, 224 n. Paterson, 143, 365 Paton, Noel, 18, 19, 278 sq., 349, 496, 508 Paton, Kerr, and Watson, 434, 508 Payer, 511, 520 sq. Payne, 634 Pearl, 211 Pearl and Surface, 333, 605, 651 Pearson, Karl, 202, 605, 684 Pearson, Lee, and Bramley-Moore, Pelikann, 235 Pelodytes, 203 Pembrey, 272 Pepere, 349 Perameles, 39, 339, 384 sq. Perch, 277 sg. Perez, 158, 176, 217, 629 Peripatus, 11 Perry-Coste, 72 Peters, 361, 366, 466 sq., 469, 471, 473, 479, 515 Petrel, stormy, 26 Petrunke witsch, 628 sq. Pfannenstiel, 264, 368 Pfeffer, 215 INDEX Pfister, 578 Pfliiger, 114, 116, 124, 148, 203, 313 sg., 329, 436, 518 Pfliger and Smith, 203 Phalarope, 30 Phascolarctus cinereus, 39 Pheasant, 315 Phylloxera, 635 sq. Piccolo and Lieben, 263 Pick and Pineles, 523 Piéri, 299 Pig, 208, 371, 668. See also Sow Pigeon, maturation in, 133; ovula- tion in, 139 sgq.; fertility of 591 sq. Pinard, 545 Pine-marten, breeding season of, 59 Pisces, breeding season in, 16 sqq. ; spermatozoa in, 174; fertilisa- tion in, 190 Pittard, 306 Pizon, 222 Placenta, as an organ of nutrition, chap. x., 491 sqq. Placotus, 148 Plaice, 17 Plimmer, 270, 275 Plimmer and Scott, 268 Plénnis, 183, 611 Ploss, 70 Plover, golden, 25 Pocock, 63 sqg., 96, 137, 306 Poehl, 236, 285, 309 Polaillon, 532 Polecat, breeding season of, 59 Polynoe, 224 Polycestrous, definition of, 38 Polyphemus, 174 Polypterus, 17, 28 Polypterus bichea, 17 Polypterus laprodei, 17 Polypterus senegalis, 17 Polyspermy, 190 Poncet, 306 Porcher, 571 sqq. Porpoise, breeding period of, 53 Porter, 669 Potthast, 54 Potts, 308, 640, 653, 658 Praopus hybridus, 636 Pratt, 9 Pregel, 309 Pregnancy, 138 n., chap. x. passim ; changes in the maternal organism during, chap. xi. ; body-weight during, 497 sq. ; protein metabolism in, 498 sqq. ; carbohydrate metabolism in, 507 sqg.; metabolism of fats in, 511 sqqg.; metabolism of metals 701 and salts in, 514 sqq. ; respiratory exchange during, 517 sqq.; changes in maternal tissue during, 520 sqq. Prenant, 336 Prepotency, defined, 206 n. Prévost, 184 Preyer, 358, 365 Primates, cestrous cycle in, 62 sqqg. ; ovulation in, 137; 374; foetal nutrition in, 392 sqq., 402, 463- 482, 484; lactation in, 553 Prjewalsky, 43 Proboscidia, foetal nutrition in, 387 8q., 419 sq. Prochownick, 496 Procstrum, defined, 36; signifi- cance of changes during, 161 sqq. Prostate gland, 235 sqq. Protopterus, 18 Protozoa, breeding season of, 6 sq. ; 200; conjugation in, 211 sqq. ; immortality of, 682 Przibram, 134, 190 Pteropus, 62 Pteropus edulis, 462 Puberty, 670 sq. Puerperium, 545 sqq. Puma, cestrous cycle of, 58 Punnett, 194, 624, 632 sq., 639 sq., 649, 657 Punnett and Bateson, 639 Purpura lapillus, 14 Pussep, 254 Pyrrhocoris, 633 Q Quagga, Lord Morton’s, 201 R Rabbit, cestrous cycle in, 37, 41, 105 sqq. ; changes in the ovary of, 123, 128, 131, 134 sqg., 139, 144, 149, 154, 156, 158 sq., 160; spermatozoa of, 177, 180; artifi- cial insemination of, 183 sq., 234; fertilisation in, 187 ; in-breeding in, 214; accessory reproductive organs in, 232, 252, 254 sqq., 260; 269, 273; ovariotomy in, 317 sqq., 338; 328, 343 sq.; hysterectomy in, 347 sqg.; 349; foetal nutrition in, 369, 372 sqqg., 380, 388 sqq., 405, 420-436, 481, 483, 486 sq., 489 n.; pregnancy in, 494 sqq., 498, 500 sqg., 508, 512, 515; female generative organs in, 525, 527 sqqg.; parturition in, 537; lactation in, 553; growth of 702 mammary glands in, 573 sqq., 578 sqq.; fertility of, 588, 591, 594, 601, 607; sex in, 643; growth in, 662, 665 Raciborsky, 47, 138 Raja, 277 Raja batis, 636 Rana arvalis, 203 Rana fusca, 202 sq. Rana limnocharis, 22 Rat, cstrous cycle in, 37, 40, 105 sgq.; changes in the ovary in, 123; ovulation in, 126; 135, 183, 234, 236; influence of ovary in, 321 sqq., 341, 343; hysterec- tomy in, 348 ; 355, 368; ovum in, 372; 389, 420; parturition in, 536; lactation in, 555, 579; fertility in, 587, 595; 637; sex in, 650; growth in, 662 Rauber, 365 Raudnitz, 564 Rauther, 233 sq. Raven, 26 Ray, 358 Réaumur, 12 Redstart, 315 Regaud and Dubreuil, 607 Regaud and Policard, 336 Regnard, 514 Rehfisch, 231 Reichert, 442 sq. Reid, 358 sq. Rein, 537 Reinke, 286 Reinl, 67, 68 Rémy, 259 Rengger, 55 Repreff, 499 Reptilia, breeding season of, 23; fertilisation in, 190; 273 Retraction, mechanism of, 251 sqq. Retterer, 100, 251, 254 Retzius, 175 Rhacophorus leucomystax, 22 Rhinoceros, 247 Rhodites, 638 Ribbert, 314, 319, 578, 656 Rieder, 520 Rielander, 481 Riemann, 528, 537 Ries, 335 Rink, 54 Robertson, 660 sqq. Robinson, 371 sqqg., 376, 389, 395. 411, 413, 416 Rodentia, cestrous cycle in, 40 sqq. 232 n., 241; accessory reproduc- tive organs in, 244, 246 sq. ; foetal nutrition in, 388 sgq., 420 sqq, ; INDEX gestation in, 545; puerperium in, 551; lactation in, 554; fer- tility in, 587, 592; 671 Rohrig, 528, 577 Rolleston, 458 Rollinat, 186 Rolph, 627 Romanes, 206 Rommel and Phillips, 605 Rorig, 314 Ross, 13 n. Rossi, Pierre, experiment by, 182 Roth, 180 Rouget, 140, 526 Routh, 538 sq., 577 Roux, 216 Rubaschkin, 132, 135 Rubinstein, 319 Runge, E., 671 +» 530 Ruticilla phenicurus, 316 Rutting season, defined, 35 sq. iS) Sadler, 646 Sagartia troglodytes, 8 sq., 679 Sainmont, 124 Salamander, 23, 177 Salamander maculosa, 186 Salmon, 18 sq., 28, 31, 278 sqq., 288, 292 sq., 295 Salvi, 62 Sanderling, 24 Sandes, 149, 1558, 337, 339 Sanger; 365 Sanson, 629 Sanyal, 63 Sarcophytum, 9 Saunders, 194 Sauropsida, 378, 380 Sauvé, 320 Savare, 481 sq. Sawflies, 131 n., 629 Schafer, 24 sg., 116 sqg., 153, 556, 562, 565, 569 Scharf, 55 Schenk, 630. See also Kleinhaus and Schenk Schmidt, Albert, 358, 405, 446 » A. Schmiedeberg, 297, 299 Schmorl, 493 Schneidemiihl, 240 Schorndorff, 54 Schottlander, 156 sqq. Schrader, 516 Schreiner, 285 Sehréder, 68 INDEX Schrén, 118 Schulin, 156 sg. Schultz, 320 Schultza, 393, 642, 647, 650 Schutz, 532 Sch weigger-Seidel, 173 Sciurus vulgaris, 41 Sclater, 65 Sclerophytum, 9 Scorpion, 350 Scyllium, 277 Seal, gestation of, season of, 59 aq. Sea-urchin, 199, 225, 301. under generic names Sedgwick, 6, 73, 186 Seeliger, 199 Seitz, 149, 156, 158 Selenka, 382, 392, 420, 465 Seligmann, 305, 306. Shattock and Seligmann Semen, chemistry of, 282 sqq. Seminal fluid, 176 Semnopithecus entellus, 63, 89 sqq., 97 Semnopithecus nasicus, 464 Semon, 18, 38, 39 Semper, 10, 12, 14, 15, 22, 31 Senescence, 675 sqq. Seps, 151 Sepa chalcides, 380 Serralach and Parts, 238 Serres, 528 Sertoli, 253 Seubert, 232 Sex, determination of, chap. xv. Sfameni, 68 Shad, 18 ; Sharpey, 400, 466 Shattock and Seligmann, 311, 315 Sheep, 26; dicestrous eycle in, 37; cestrous cycle in, 42 sqq., 107 sqq. ; ovulation in, 136 ; corpus luteum in, 147 sq., 152; 183; Mendelian experiments on, 198 ; in-breeding in, 209; accessory reproductive organs in, 229, 247 sq. ; castra- tion in, 306; foetal nutrition in, 371, 376, 380, 386, 396 sq., 400, 403 sq., 407, 417, 427, 435, 484, 487; pregnancy in, 495, 508, §20; parturition in, 535; lacta- tion in, 554 eg. ; fertility in, 590 8q., 596 sqg., 604; abortion in, 612 sq., 617 sqg. ; growth of, 668 ; age attained by, 681 Sherrington, 255, 259, 330 Shortt, 44, 47 Shrew, breeding season of, 60; fetal nutrition in, 372, 377, 391 g., 452-5 32; breeding See also See also 703 Siebold, von, 186, 628 sq. Sigismund, 162 Silkworm moth, 184, 217, 280 8q-5 307, 626 Simocephalus, 632, 644 Simpson, Sir James, 537, £41 — J. Y., 213 Simpson (Sutherland) and Marshall, 262 Sims, 609 Sinéty, 510. Sve also De Sinéty Siphostoma floridee, 652 Sipunculids, 224 Strenia, 376 sq., 553 Sixta, 38 n. Skin, changes in, during pregnancy, 523 Slemons, 499, 505, 517 Slocum, 524 Sloth, 402, 553 Slo wtzoff, 283 Smith, F., 314, 678 —— Geoffrey, 308, 640, 653. 658 —— Tyler, 542 Smyth, 126 Snail, 186 Snakes, scent-glands of, 31 Snipe, 27 Sobotta, 42, 132, 143 sqq., 150, 156, 233, 439 Sokoloff, 317 Soli, 349 Somerset, 58 Sow, cestrous cycle in, 50, 334; ovulation in, 135; 145; in-breed- ing in, 208; fcetal nutrition in, 386, 394 sqq., 403, 484; partu- rition in, 537; fertility of, 586, 591, 600, 605, 671 Spallanzani, 4, 19 sq., 22, 23, 56, 140, 165, 181 sgq., 203 Sparrow, 24, 26, 157 Specht, 607 Spee, von, 363, 393, 443 sqg., 449, 466 536, 667, 669, Spencer, Herbert, 587 sqq. Spermatogenesis, chap. v. Spermatozoa, structure of, 172 sqq. ; movements of, 176 sqqg. ; chemo- tactic properties of, 214 sqq.; chemistry of, 288 sqq. Spermophilus, 150 Spherechinus, 179, 300 Spherechinus granulosus, 293, 300 Spider crab, 307 Spiegelberg, 542 sg. Spiegelberg and Gscheidlen, 520 sq. Spina, 254 Spinax, 151 704 Spitzer, 299 Sorex, 144, 150 Stag, breeding season of, 27 sq. ; effects of castration on, 305 Starfish. See Asterias Stark weather, 647 Starling, 26 Starling, 335, 352, 492. See also Lane-Claypon and Starling Steinach, 234, 236 sq. Steinhaus, 89, 560 sq. Stenops, 250 Sterility, 606 sqq. Steudel, 294, 295, 296 Stevens, 12, 631, 633 Stevenson, 67 sg. See also News- holme and Stevenson Stilling, 232, 240, 350 Stoat, breeding season of, 59 Stockel, 146 Stolz, 512 Stonehenge, 53 sq. Strahl, 361, 364, 376, 403, 410, 413 sq., 416, 456, 458, 551 sq. Strasburger, 187, 215 Strassmann, 85, 185, 329 Stratz, 61, 62, 97, 113 Stricht, van der, 122, 132, 137, 148, 150, 156, 460 : Strongylocentrotus, 204 sq. Strongylocentrotus lividus, 300 Strongylocentrotus purpuratus, 219 Sturgeon, 18 Stychostemma asensoriatum, 10 Stylonychia, 212 Stylonychia pustulata, 6 Suchetet, 604 Superfcetation, 159 sqq. Sutton, 130 Bland, 89, 95, 97, 343 Swan, 26 Swayne, 49 Swifts, 25 Symplasma, defined, 414 Szabo, 561 T Tadpole, 624 sq. Tafani, 135, 403 Tait, 163, 522 Talpa, 250 Tandler and Gross, 306 Tangl, 272, 434 Tangl and Farkas, 273, 302 Tapir, 247 Tarehanoff, 22, 234, 275 Tarsius, 144, 150; foetal nutrition in, 408, 410, 468, 494 ; 552 Tarsius spectrum, 62, 97 sq., 137, 551 n. INDEX Tchermak, 193 Teacher, 138. Teacher Tegetmeier and Sutherland, 584 Telegony, 201 sq. Teleoste, 16, 151, 277 Tennent, 226 Tenrec, 458 Tergipes, 15 Termite, 627 Terrier, 516 Tessier, 545 Testis, influence of, 303 sqqg.; in Man, 7b. ; stag, 305; fallow deer, ib. ; sheep, 306 ; horse, 307, 310 ; arthropods, 307; fowl, 311 sq. ; frog, 312 sqq.; relation between thymus and, 349 ; 353 Thiemich, 495, 512 Thierfelder, 569, 572 Thierfelder and Stern, 267 Thompson, 289 ; Thomson, J. A., 165, 201, 623, 648. See also Geddes and Thomson — H., 507 Thudichum, 264, 267 Thury, 630 Thymus, relation between testis and, 349 Tichomiroff, 217, 280 sq. Tiedemann, 241 Tiger, 247 Timofeew, 258 Toad, breeding season in, ovulation in, 140; 300 Torelle, 216 Tortoise, 22, 31, 278, 680 Treadwell, 224 Treat, 625 Trematode, 10 Treviranus, 192 Triton, 174 Triton alpestris, 202 sq. Triton waltlii, 22 Tropidonotus, 277 Tropidonotus viperinus, 186 Truzzi, 523 Tupaia, 144, 150, 250, 377, 457 aq., 494, 552 n. Tupaia javanica, 61, 98 sq., 372, 392, 457 sq. Turbot, 205 - Turner, 60, 359, 361, 369, 376, 388, 395, 401, 408, 410, 463 Twins, pygopagous, 585 See also Bryce and 20; U Ulesco-Stroganowa, 479 Ungulata, cestrous cycle in, 42 ; INDEX foetal nutrition in, 375, 386, 394 sqq., 417 sq., 484; lactation in, 553 sq. ; fertility in, 586 Uterus, structure of, 75 sqq.; changes in, during cestrous cycle, chap. iii.; significance of pro- estrous changes in, 161 sqq. ; supposed internal secretion of, 345 sqqg. ; innervation of, 527 sqq. Vv Surnames with van and von are in- dexed under name following. Valenciennes and Frémy, 278 Valentin, 114, 252 Vallet, 526 Vaughan, 264 Veit, 493 sq., 506, 523, 587 Veit and Scholten, 480, 493, 515 Ver Eeke, 498, 500 sq., 503, 516 Vernhout, 456 Vernon, 203 ag. Verworn, 178 sq., 197, 200, 299, 570, 659, 683 Vesicule seminales, 231 sqq. Vesperugo, 148, 150, 156 Vesperugo noctula, 132 Vespertilia, 148 Viearelli, 68. Vicarelli Virchow, 559, 570 Voit, 510 Volker, 149 See also Oddi and WwW Wade and Watson (B. P.), 369, 474 Waldeyer, 114 sqq., 143, 184, 271, 358 aq. Walker, C. E., 312 Walker, G., 237, 239, 309 aq. Wallace, A. R., 27, 603 —— Cuthbert, 239, 303 —— R., 17; estrous cycle, 45, 47, 50, 51; 151, 214, 248, 307, 495; lactation, 566 sgq.; fertility, 596, 599, 600, 604, 608; 616; 654 Wallart, 354 bey ae breeding season of, 49, 60; Walther, 278 : Wapiti deer, cestrous cycle in, 49; 305 n. Water-buck, cestrous cycle in, 49 Watson, M., 250 — B. P., 565. Kerr, and Watson —— Chalmers, 595 See also Paton, 705 Weasel, breeding season of, 59 Webb, Sidney, 621 sq. Weber, 313, 358 sqq., 375 Webster, 80, 138, 164, 367, 474, 476 sq. Weichardt and Opitz, 493 Weil, 135 Weininger, 654 sqq. Weinland, 302 Weismann, 172, 191, 192 sgq., 628, 631, 679 sq., 682 sq. Weiss, 292 fe We eatersenns ” hypothesis, 67, Wendeler, 118, 145 Westermarek, 70 sq. Westphalen, 82 sq., 85, 87, 89 Werth, 369 Whales, breeding period of, 52 sq. ; age of, 680 Wheeler, 629 Whetham, 622 Whitney, 7 Widal, 517 Widgeon, 315 Wiedersheim, 554 sq. Wiener, 365 Wild, 520 Willecock and Hardy, 275 Willey, 16 Williams, Whitridge, uterus, 85, 88 ; 149, 180, 336 ; female genera- tive organs, 532 sq., 540 sq., 543 sq., 548 sq., 551; 565 sqq., 587, 632 —— Sir J., 83, 549 Wilson, E. B., changes in the ovary, 118, 122, 1380, 131; spermato- genesis, 172, 174, 175 ; 190, 216, 226, 356; sex-determination, 633, 636 —— S. M., 48 Wiltshire, 19, 25, 39, 50, 62, 66 Winckel, 505, 517, 522 Winckelmann, 520 Winiwater, van, 117 sq., 131 Winkler, H., 300 —— F.N., 360 Winterhalter, 329 Winterstein and Stickler, 524 Winwood Reade, 63 Wohlgemuth, 276 Wolf, breeding season of, 55 Wolfe, 513 Wood, 198 Woodruff, 214 Worthmann, 250 Wright, 23, 316 Wyehgel, 516, 523 Wyder, 88 2 706 x Xenia hicksoni, 9 Xenopus levis, 20 sqq. Y Yak, 49 Yolk-sac, 378; nutritive ance of, 380 sqq. Yule, 621 Youatt, 334 Yung, 625 INDEX import- Z Zacharjewsky, 497 sq., 503, 505 sq., 510 Ziegler, 641 Zoarces, 151 Zoth, 309 Zuntz, L., 68, 355 —— E., 519 Zweifel, 505 Zweifel and Abel, 346 Printed by BALLANTYNE, HANSON & Co. Edinburgh & London A LIST OF WORKS ON MEDICINE, SURGERY AND GENERAL SCIENCE CONTENTS PAGE AWATOMY Gc si Re “ae ee “aw. Cee em Caer. cae 8 BACTERIOLOGY ...00 0.0 eee tee tee eee 18 BIOKOGY us, Se. Ge GAS ie coat. Sake. Gae “ae ee 8 CHEMISTRY ae te ie oi ca ae HEALTH AND HYGIENE <, 8 42. 25 68 a coe AIG INDEX i patho Oi oe ie E.R. eh. Cae ED MEDICINE ...00 0. ee eee ete BB MISCELLANEOUS ” we oe Gi. He. cee TIO MONOGRAPHS ON BIOCHEMISTRY ee, ae, at oe i at ~*~ =o : Se maietheevnes spe Sito ijt tgmned ooree eh ies Ss it Taba! Parlor jai anes hint. catangtse ica cay ites a Serra = aera Sea mak ved is SSS es at late 2 pn sem. ayn Samant Shasta, ceeeen ome GUN SEER SS ees Sees oh el —— cee ae ieee SONS or eet Ap Be pare PaLGhceeten aE NS vey Brita te! 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