-D J- ru a m o THE PHYSIOLOGY OF REPRODUCTION THE PHYSIOLOGY OF / KEPRODUCTION BY FRANCIS H. A. MARSHALL M.A. (CANTAB.), D.Sc. (EoiN.) FELLOW OP CHRIST'S COLLEGE, CAMBRIDGE, AND UNIVERSITY LECTURER IN AGRICULTURAL PHYSIOLOGY WITH A PREFACE BY PROFESSOR E. A. SCHAFER, Sc.D., LL.D., F.R.S. AND CONTRIBUTIONS BY WILLIAM CRAMER, PH.D., D.Sc. AND CHHEAD, M.A., M.D., B.Sc., F.R.C.S.E. WITH ILLUSTRATIONS LONGMANS, GREEN AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AM) CALCUTTA 1910 All rights reserved TO WALTER HEAPE, ESQ., 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. vii CONTENTS PAGE INTRODUCTION ......... 1 CHAPTER I THE BREEDIKG SEASON ......... 4 Protozoa — Coelenterata — Nemertea, &c. — Annelida — Arthropoda — Mollusca — Echinodermata — Cephalochordata — Pisces — Amphibia — Reptilia — Aves — Mammalia — Periodicity of Breeding, &c. CHAPTER II THE (ESTROUS CYCLE IN THE MAMMALIA 35 Monotremata — Marsupialia — Rodentia — Ungulata — Cetacea — Carnivora — Insectivora — Cheiroptera — Primates. CHAPTER III THE CHANGES THAT OCCUR IN THE NON-PREGNANT UTERUS DURING THE OJSTR ,US CYCLE ........ 75 The Cycle in Man — Monkeys — Lemurs — Insectivora — Carnivores — Ungulates. CHAPTER IV CHANGES IN THE OVARY OOQENESIS GROWTH OF FOLLICLES OVULATION FORMATION OF OORP RA LUTEA AND ATRETIC FOLLICLES THE SIGNIFICANCE OF THE PROO3STROUS CHANGES IN THE UTERUS . . . . . . . . .113 Dev lopment of Ovary and Oogenesis — Maturation and Ovulation — The Formation of the Corpus Luteum — The Atretic Follicle — Superf cetation — Formation of Ova — The Significance of the Prooastrous Changes. CHAPTER V SPERMATOGENESIS INSEMINATION . . . . . . .165 Structure of Spermatozoa — Seminal Fluid — Movements of Sper- matozoa— Insemination. x CONTENTS CHAPTER VI PAGE FERTILISATION . . . . . . . . . . .187 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 .... 227 The Vesiculae 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 263 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 . 303 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 FCETAL NUTRITION : THE PLACENTA ....... 357 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 II. 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 III. The Fietal Membranes, the Yolk-sac, and the Placenta — i. General Anatomy of the Fretal Membranes. — ii. The Nutri- tive Importance of the Yolk-sac (Marsupialia, Ungulata, Carnivora, Proboscidea and Hyrax, Rodentia, Insectivora, 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 Fretal Nutrition and the Placenta : A. The Plan of Placental Formation. B. 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 Source of the Materials transferred to the New Or- ganism. B. The Body-Weight during Pregnancy. C. The Protein Metabolism in Pregnancy. D. The Carbohydrate Metabolism in Pregnancy. K. 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 . . 525 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 553 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. 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, a 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. — lii. 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 CF DEATH ....... 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 .... . 689 ILLUSTRATIONS FIG. PAGE 1. Diagram illustrating the " Wellenbewegung " hypothesis . 67 2. Transverse section through Fallopian tube showing folded epithelium and muscular coat . . . . . .76 3. Se :tion of a cornu of a rabbit's uterus ..... 77 4. Cross-section through cervical canal of human uterus . . 78 5. Section through wall of vagina of monkey (upper part) . 79 6. Section through wall of vagina of monkey (lower part) . . 81 7. Se tion through mucosa of human uterus showing pre-menstrual congestion ......... 82 8. Section through mucosa of human uterus showing extravasation of blood 84 9. Section through mucosa of human uterus showing sub-epithelial haematomata ......... 86 10. Section through mucosa of human uterus showing bleeding into the cavity during menstruation ..... 87 11. Section through mucosa of human uterus during the recupera- tion stage .......... 88 12. 13. Sections through prooastrous uterine mucosa of dog . 100-101 14. Section through edge of mucosa of dog during an early stage, of recuperation . . . . . . . . . 103 15. Section through portion of mucosa of dog during recuperation period .......... 104 16. Section through portion of mucosa of dog during Iat3 stage of recuperation ......... 105 17. Section through portion of prooestrous uterine mucosa of rabbit showing glandular activity . . . . . .106 18. Section through portion of uterine mucosa of sheep, showing black pigment formed from extra vasated blood . .109 19. Section through ovary of cat . . . . . . .114 20. Section through ovary of adult dog . . . . . .115 21. Section through ovary of pig embryo . . . . .116 22. Cortex of pig embryo showing germinal epithelium, &c. . .117 23. Various stages in the development of the Graafian follicle (rabbit) 119 xiv ILLUSTRATIONS FIG. PACE 24 to 27. Developing ova from ovary 120-121 28. Ovary at birth, showing primordial follicles . . . .123 29. Young oocyte 126 30. Young human Graafian follicle . . . . . .127 31. Human ovum at termination of growth period . . .128 32. Human ovum examined fresh in the liquor folliculi . . .129 33. Recently ruptured follicle of mouse 144 34. Early stage in formation of corpus luteum of mouse . . 145 35. Late stage in formation of corpus luteum of mouse . . .146 36. Corpus luteum of mouse fully formed . . . . 147 37. Section through old corpus luteum ...... 153 38. Section through follicle in early stage of degeneration . .155 39. Section through follicle in late stage ..... 157 40. Section through human testis and epididymis . . . .166 41. Section through testis of monkey . . . . . .167 42. Section through portion of two seminiferous tubules in testis of rat 169 43. A cell of Sertoli with which the spermatids are beginning to be connected (human) ........ 170 44. Diagram illustrating the cycle of phases in spermatogenesis . ib. 45. Scheme of spermatogenesis and oogenesis . . . . .171 46. Human spermatozoa on the flat and in profile . . . .173 47. Human Spermatozoa . . . . . . . .174 48. Different forms of spermatozoa from different species of animals .......... 175 49. Diagram illustrating wave-like movement of swimming sperma- tozoon . . . . . . . . . .177 50. Successive stages in the fertilisation of an ovum of Echinus esculentus, showing the entrance of the spermatozoon . 188 51. Three stages in the conjugation of male and female nucleus (Echinus) 189 52. Fertilisation process in bat's ovum . . . . . .190 53. Passage of convoluted seminiferous tubules into straight tubules, &c 228 54. Transverse section through the tube of the epididymis . . 229 55. Transverse section through commencement of vas deferens . 230 56. Section through part of human prostate ..... 235 57. Section through prostate gland of monkey . . . .237 58. Transverse section through adult human penis . . . 243 59. Section through erectile tissue ....... 244 60. Part of transverse section through penis of monkey . . . 245 61. Distal end of ram's penis, showing glans and filiform appendage 247 62. Transverse section through filiform appendage of ram . . 248 ILLUSTRATIONS xv FIG. PAGE 63 Transverse section through middle of glans penis of rani . . 249 64. Distal end of bull's penis showing glans, £c. .... 250 65. End-bulb in prostate 259 66. Diagram illustrating innervation of genital organs of male ^ at . 261 67. Transverse section through rabbit's uterus after ovariotomy . 318 68. Transverse section through bitch's uterus 9£ months after ovariotomy . . . . . . . . .319 69. Section through ovary of rat after transplantation on to peri- toneum . . . . . . . . . .321 70. Section through ovary of rat after transplantat on on to peri- toneum - . . .322 71. Transverse section through normal uterus of rat . . . 323 72. Transverse section through uterus of rat after ovariotomy . 324 73. Transverse section through uterus after ovarian transplantation 325 74. Section through rat's kidney into the tissue of which an ovary had been transplanted . . . . . . .327 75. Part of an early human chorionic villus . . . . .362 76. Early blastocyst of rabbit 372 77. Diagram to illustrate the three parts of the wall of the yolk- sac (rabbit) .......... 381 78. Diagram of an opossum embryo and its appendages . . 382 79. Diagram showing the arrangement of foetal membranes in Dasyurus ......... 383 80. Diagram showing the arrangement of foetal membranes in Perameles . ......... 385 81. Elongated blastocyst of sheep at thirteenth day of pregnancy 386 82. Transverse section through blastocyst of sheep at twenty- fifth day 387 83. Blastodermic vesicle of rabbit ....... 388 84. Diagram of blastodermic vesicle of rabbit in longitudinal section . ....... 389 85. Diagram to illustrate foetal membranes of Erinaceus . .391 86. Hypothetical section of human ovum imbedded in decidua . 393 87 Portion of injected chorion of pig ...... 394 88. Section through wall of uterus and blastocyst of pig at twentieth day of pregnancy ........ 395 89. Diagram representing a stage in the formation of the placenta (pig) 396 90. Section through uterine and embryonic parts of a cotyledon of sheep at twentieth day of pregnancy .... 398 91. Section through base of foetal villus, &c. (sheep) . . . 399 92. Columnar trophoblast-cells from the base of foetal villus at third month of pregnancy (cow) to show phagocytosis . 401 xvi ILLUSTRATIONS FIG. PAGE 93. First stage of cellular secretion in placenta of cow . . . 405 94. Ingestion and disintegration of red blood corpuscles by tropho- blast of sheep ......... 408 95. Absorption of " Stiibchen " by trophoblast of sheep . . 409 96. The uterine mucosa of dog at about twenty-third day of pregnancy ......... 412 97. Ovum with zonary band of villi 413 9$. The angioplasmode of dog at thirtieth day of pregnancy . .415 99. The labyrinth and green border of placenta of dog at fortieth day of pregnancy . . . . . . . .417 100. Transverse section of a four days' gestation sac of rabbit . 421 101. Transverse section of a seven days' gestation sac of rabbit . 422 102. Thickened ectoderm in rabbit, attached to placental lobe . . 424 103. Iron granules in placenta of rabbit at eighteenth day of pregnancy ......... 429 104. Glycogenic areas of rabbit's placenta at twelfth day of pregnancy ......... 432 105. Inversion of germinal layers in blastodermic vesicle of mouse . 438 106. Longitudinal sections of implantation cavity of field-mouse about eighth day of pregnancy ...... 440 107. Longitudinal section of uterus and implantation cavity of guinea-pig ......... 443 108. Blastodermic vesicle of guinea-pig showing inversion of ger- minal layers ......... 444 109. Implantation cavity of guinea-pig ...... 445 110. Implantation cavity of guinea-pig ...... 446 111. Allantoidean diplo-trophoblast of Erinaceus .... 448 112. Section in situ of ovum of Erinaceus ..... 450 1 13. The extension of yolk-sac against lacunar trophoblast in Erinaceus .......... 451 114. Transverse section through uterus of Sorex at a stage when the blastocysts are still in the oviducts . . . .452 115. Part of the anto-mesometrial wall of the uterus of Sorex . . 453 116. Uterus and embryo of Sorer ....... 455 117. Orifice of uterine gland of mole with trophoblastic dome . . 457 118. Replacement of omphaloidean by allantoidean placenta . . 459 119. Placenta of bat 461 120. Median longitudinal section of an early human ovum. 0-4 mm. in length .......... 464 121. Diagram of the earliest human ovum hitherto described . . 468 122. Section through the wall of the uterus in the early part of pregnancy ......... 469 123. Section of a portion of the wall of the human blastocyst . . 470 ILLUSTRATIONS xvii FIG. PAGE 124. Section of a portion of the necrotic zone of the decidua, &c. . 471 1 25. Section through embryonic region of ovum .... 472 126. Condition of the glands at the beginning of pregnancy in Man 473 127. Median longitudinal section of embryo of 2 mm. . . . 475 128. Diagram of stage in development of human placenta . 476 129. Fat in a villus of human placenta ...... 479 130. Iron granules in a villus of the placenta in Man . . . 480 131. The first stage in the revolution of the equine foetus . . 535 132. The foal in the normal position for delivery .... 536 133. Virginal external os (human) 550 134. Parous external os (human) ib. 135. Section of mammary gland of woman ..... 556 ] 36. Section of mammary gland (human) during lactation . . 557 137. Section of mammary gland (human) in full activity . . . 558 13^. Section through an alveolus with fat drops in cells . . . 559 139. Section of developing mammary gland of horse . . . 574 140. Section of mammary gland (human) showing developing alveoli . . 575 141 to 147. Diagrams from Minot's Problem of Age, Growth, and Death 663-9 148. Section through ovary of woman of fifty-six showing degenera- tion of follicles, &c 673 149. Section through uterine mucous membrane of woman of sixty . 674 150. Section through vaginal mucous membrane of woman of sixty-one .......... 675 151. Group of nerve cells from the first cervical ganglion of a child at birth .677 152. Group of nerve cells from the first cervical ganglion of a man of ninety-two 678 153. Land tortoise aged at least eighty-six belonging to M. Elie Metchnikoff 680 154. Lonk sheep aged eighteen years, with her last lamb . . .681 ERRATA P. 51, footnote1, instead of " prjewzlsky" read " prjewalskii." P. 306, 1. 12, instead of "castration.2" read "castration.1" (that is, see footnote l instead of footnote 2). P. 306, 1. 13, instead of "about horned cattle" read "about many horned cattle." P. 306, 1. 9 from bottom, instead of " males.1 " read " males.2 " (that is, see footnote 2 instead of footnote 1). P. 316, 1. 10, before " Rulicilla" read "a specimen of." P. 355, 1. 3 from bottom, instead 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 gynaecological 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 gynaecology, 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- ologic 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 gynaecological 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 L'ochhead, 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 fo?tal 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. S. Carmichael, of the Royal Infirmary, Edin- burgh, has read the section dealing with parturition. Dr. J. H. Ash worth 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-Clay pon, 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. Kingston 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." — Ecclesiastcs iii. 1. " IT 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. 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." 1 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.2 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,1 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 metazoon ; 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° C.2 Again, Flagellate Infusoria of different kinds have been induced to conjugate by changing the temperature or increasing the density in the surrounding medium.3 Furthermore, the life-cycle of Para- mcetium 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 1 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.). 2 Sedgwick, Student's Text-Book of Zoology, vol. i., London, 1898. 3 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," Bid. 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 steini at least the occurrence of conjugation is detarmined entirely by the conditions of the surrounding medium. COELENTERATA 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,2 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.3 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 rise 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 Ash worth and Annandale 2 about the breeding habits of sea- anemones. The species Sagartia troglodytes and Actinia mesern- 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.-MecJutnik, 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 lias reached a 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. ( Willkiirliche Entwickdungsanderungcn bei Pflnnzen, 1903.) 2 Ashworth and Annandale, "Observations on some Aged Specimens of Sayartia troglodytes, and on the Duration of Life in Coelenterates," Proc. Roy. Soc. Edin., vol. xxv., 1904. THE BREEDING SEASON 9 the process every morning for a number of weeks, when the breeding season conies 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 Actinia 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 Faeroes, 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 Faeroes, 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 l that in the coral Xenia hick- soni, 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,2 who has studied the process of oogenesis 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 Alcyonidse," fferdman'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.1 NEMERTEA, &c. The breeding season and its relation to the environment have formed the subject of a careful investigation by Child 2 in the case of a small Nemertean, Stychostemma asensoriaium, 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. Egg- 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 oocytes when taken, and which are kept in clean water without food, the growth of the oocytes 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 oocytes." 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, Diplozoon paradoxum, 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.3 ANNELIDA • Certain species of Polychaet Annelids, known as the Palolo worms, exhibit a quite remarkable regularity in the periodicity of their breeding habits. During their immaturity all the Palolos 1 Bourne, "The Ctenophora," Treatise on Zoolor/y, vol. ii., London, 1900. 2 Child, "The Habits and Natural History of Stychostemma," American Naturalist, vol. xxxv., 1901. 3 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 fucatd) and the South Pacific Palolo (Eunice 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 osawai) 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, chiUy nights. It would appear also that no individual worm takes part in more than one swarming in the year.1 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.2 Also, in the Cape species of Peripatus (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.3 In the case of the hemipterous insect known as the plant- louse (Aphis), we have evidence that the mode of reproduction 1 Izuka, " Observations on the Japanese Palolo/' Jour, of the College of Science, University of Tokyo, vol. xvii., 1903. 2 Huxley, The Crayfish, London, 1880. 3 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. Reaumur, 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.1 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.2 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.3 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 repro- duction (or of the particular mode of reproduction), with 1 Semper, loc. cit. 2 Morgan, loc. cit. 3 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.2 It is interesting to note also that in the mos- quitoes and other Culicidae, 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 Empidae, 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.3 In some insects oviposition takes place long after the death of the males. Thus, Lefroy and Hewlett state that in the mango weevil (Cryptorhynchus gravis) the males die in August while the females live until the following March to lay eggs.4 MOLLUSCA 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. 2 " Report of Malaria Expedition to Nigeria," Liverpool, Trop. Med. Memoir, IV. See also Ross (Nature, vol. Ixxx., 1909), who says that females of Culex and Stegomya apparently only desire to suck blood after fertili- sation. 3 Hewlett, "Coupling of Empis" Ent. Mag., vol. xliii., 1907. * Lefroy and Hewlett, Indian Insect Life, Calcutta, 1909. 14 THE PHYSIOLOGY OF REPRODUCTION eggs.1 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 Littorina breeds all the year round.2 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.3 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 (Limncea) 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 year 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 maturita sessuale degli aniruali del golfo di Napoli." Mitth. Zool. Stat. Ncapol., 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 l 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 eggs, larvae, 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, Teryipes, have been found at all seasons, like those of Littorina on our own coasts. ECHINODERMATA 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.2 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 (E. acutus being mature in November and December, and E.microtuberculatus from September onwards).1 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 (i.e. between 5 and 7 P.M.), and never, so far as known, at any other time.2 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 rule to the spring and summer in temperate climates. In a single individual spawning may last no longer than a few weeks or even days.8 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.4 The investigations of the Marine 1 Lo Bianco, loc. cit. The spawning times of most of the Naples Kchinoderms are given in these memoirs. 2 Willey, Amphioxus and the Ancestry of the Vertebrates, New York, 1894. 3 Bridge, " Fishes," Caml. Nat. Hint., 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 l 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.2 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.3 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.4 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.5 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. Ixix., 1904. See also Wallace (W.), same volume. For information concerning the spawning seasons of different species of fish, The 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. Micr. Science, vol. xxxviii., 1895. 4 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.1 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 time 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.2 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 3 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 Pa ton 4 has pointed out that salmon, with their genitalia in all stages of development, are ascending the rivers throughout the whole year. Miescher,5 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,6 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, In l/ie 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 Jnrcxtiyations on the Life History of the .Ww,m, Glasgow, 1898. • Miescher, Hislochem^'sche und Physiologische Arbeiten, vol. ii., Leipzig, 1897. 8 The gain in the genitalia is due largely to the formation of compara- tively simple proteins (protaraines, 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 2 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.3 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. Hi., 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 2 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 kevis, 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 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. Vide Gadow, Cninlirldfjc Natural History, vol. viii., London, 1901. This book contains a quantity of valuable information concerning the breeding habits of many Amphibia and reptiles. * Bles, "The Life-History of Xenopus la-vis," Trans. Roy. Sot. Edin., vol. xli., 1905. THE BREEDING SEASON 21 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 VaUisneria 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 l it would appear that Xenopus, in its native country, breeds only in August, i.e. in the South African 1 Leslie, " Notes on the Habits and Oviposition of Xcnopus Iccvis" Proc. •Zool.Soc., 1890. 22 THE PHYSIOLOGY OF REPRODUCTION spring. Bles, however, is disposed to think that Xenopus, like Discoylossus 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 l 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 waltlii and of Discoglossus in the same way. Annandale 2 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.3 It is interesting to note that among frogs and other cold- blooded Vertebrates there is a periodicity in the occurrence of their reflex responses.4 It has been shown that if the region 1 Semper, " Ueber eine Methode Axolotl-Eier jederzeit zu erzeugen," Zool. Am., vol. i., 1878. See also Animal Life. * Annandale, Fasciculi Malaytntcs, Zool., Part I. 1904. * See page 5, Chapter I. 4 The sexual posture of frogs in the act of copulation is maintained as a spinal reflex. The tortoise is similar. The reflex is inhibited by excitation of the optical lobes. (Spallanzani, loc. cit. ; Goltz, Zcut. f. deutsch. mcd. Wist., 1865-66 ; Tarchanoff, Pflugcr's Arch., vol. xl., 1887 ; Albertoni, Arch. Hal. de Bid., vol. 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, neAvt, and salamander, and also the eel, vagus inhibition is absent or m&rkedly diminished at certain periods corresponding roughly to the seasons of sexual activity,1 but the significance of the changes is not very apparent. REPTILIA 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.2 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 3) by the supply of suitable food. 1 MacLeau, "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. 3 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 wBole 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 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.2 Jenner 3 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 cf. fishes, p. 18.) Thus wading birds, such as the sanderling shot by Mr. Eagle 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 4 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 dermannlichen 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 FringUla, the testicles may increase three-hundred-fold. 2 For much of the information given here regarding migration, I am in- debted to Mr. Eagle Clarke. 3 Jenner, " Some Observations on the Migration of Birds," Phil. Trans., Part I.. 1824. • Schafer, " 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 Schafer'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 l 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). MAMMALIA 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.2 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.3 1 I am indebted to Mr. Eagle Clarke for certain of this information. 2 Heape, "The Sexual Season of Mammals." Quar. Jour. Micv. 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.) 3 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 27 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.1 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.2 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.), Danvinism, 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.1 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.2 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.3 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 papillae on the hind limbs of the breeding male Lepidosiren are structures which seem to possess a special significance, since Kerr 5 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.), Sexunl Dimorphism, London, 1900. 1 Cunningham (J. T.), loc. cit. 3 Darwin, Descent of Man, Popular Edition, London, 1901. * Budgett, loc. cit. 3 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,1 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." 2 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 3 at the time of breeding, are probably due to the same causes as in the dragonet.4 1 Cunningham (J. T.), loc. cit. * Cunningham (J. T.), loc. cit. 3 Numerous instances are given by Darwin, loc. cit., both for fishes and Amphibians. * 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. Cainb. 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.1 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.2 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,3 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 Onchorhynehus. 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 aesthetic 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.1 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.2 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 larvae, 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 l 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,2 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. After. Science, vol. xliv., 1900. 1 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 oestrous 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." l 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.) CHARTER II THE (ESTROUS CYCLE IN THE MAMMALIA " Omne adeo genus in terris hominumque ferarumque Et genus aequoreum, pecudes, pictasque volucres In furias ignemque ruunt: amor omnibus idem." — VlRGlL, 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,1 and afterwards adopted by me,2 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 " oestrus " (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 CEstrous Cycle and the Formation of the Corpus Luteum in the Sheep," Phil. Tran*. B., vol. cxcvi., 1903. " The (Estrous Cycle in the Common Ferret," Quar. Jour. Micr. Science, vol. xlviii., 1904. See also Marshall and Jolly, " Contributions to the Physiology of Mammalian Repro- duction : Part I. The (Estrons Cycle in the Dog," Phil. Trans. B., vol. cxcviii., 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 anaemic, and the animal shows no disposition to seek out a mate, is called by Heape the Ar.aestrous period or simply the Ancestrum. 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- oestrum. 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 prooestrum 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, (Estrus, or (E 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 oestrus, 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." l The periods of prooestrum and oestrus are commonly referred to together as the " heat " or " brunst " period, and sometimes as the period of " rut," 2 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 (prooestrum and oestrus) 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 prooestrum 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 oestrus, 1 Heape, toe. cit. 2 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 (ESTROUS 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 anoastrum at the close of the breeding season.2 If, on the other hand, conception does not occur during cestrus, the latter is succeeded by a short Metcestrum, 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 Diaestrum. 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 cestrus during the sexual season, the final metcestrous period is succeeded by a prolonged ancestrous or non-breeding period. This is eventuaUy followed by another procestrum, marking the commencement of a new sexual season. The complete cycle of events is called the (Estrous 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 superfoetation (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 prooestrum and osstrus, 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 oestrus does not recur during the sexual season, Heape has called Moncestrous animals. Those in which there is a recurrence of the dio3strous cycle during a single season, have been designated Polyosstrous animals. The polyoestrous 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 polyo3strous 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 (anoestrum 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." MONOTREMATA Little is known concerning the breeding habits of the platypus and the echidna, which represent this order, the lowest of the Mammalia. Semon l 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 (ESTROUS 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 proo3strum. MARSUPIALIA It would appear probable that most Marsupials breed once annually, but some are said to do so more frequently. Semon l 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.3 It would appear, therefore, that kangaroos may breed twice a year. Unfortunately, there is no positive information available as to whether oestrus recurs during the same sexual season. 1 Semon, loc. cit. 2 In the bandicoot (Perameles) the yonng 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 RODENTIA There can be little doubt that the great majority of Rodents are polyoestrous. 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 dioestrous 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 dioestrous cycle in the rat is said to be about ten days ; x the period of gestation is approximately three weeks. Heape states that M. minutus and M. sylvaticus are also probably polyoestrous. 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.2 According to Lataste,3 Eliomys quercinus, Gerbillus hertipes, Dipodillus campestris, D. simoni, Meriones shaivi, and M. longi- frons are also polyoestrous. The length of the dioestrous 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 dioestrous 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. 2 Millais, British Mammals, vol. ii., London, 1905. 3 Lataste, Recherches de Zootthique sur let Mammifires de Vordrc des Rongeurs, Bordeaux, 1887. THE (ESTROUS 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 (Lepits 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 dioestrous cycles recur in the domestic rabbit, and that if oestrus 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 oestrus 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 (Sciurus vulgaris) in Britain, according to Heape, is probably monoestrous ; 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 oestrus 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. CEstrus probably lasts for about a day. Lataste 2 states that external bleeding occurs during the " heat " periods of Pachyuromys duprasi, Dipodillus simoni, 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. eit. 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 Leporidae, however, and in some other species, the testes are not so re- tracted, but remain throughout the year in the scrotal sacs.2 UNGULATA This order contains several examples of animals which are almost certainly moncestrous 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 polyoestrum, which is reached by certain of the more domesticated breeds.3 The Barbary wild sheep (Om tragelaphus) in the Zoological Society's Gardens is moncestrous, breeding only once annually.4 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.5 It would seem, however, from the account given by Lydekker 6 of the breeding habits of 0. musimon, as 1 Sobotta, " tiber die Bildung des Corpus Luteum beim Meerschweinchen," Anat. Hcfte, vol. xxxii., 1906. 2 Owen, On the Anatomy of Vertebrates, vol. iii., London, 1868. 3 Marshall, "The (Estrons Cycle, &c., in the Sheep," Phil. Trans. B., vol. cxcvi., 1903. 4 Heape, loc. cit. 5 I am indebted to Mr. F. E. Beddard, Prosector of the Zoological Society, for this information. 8 Lydekker, Wild Oxen, Sheep, and G(ats of All Land*, London, 18r8. THE (ESTROUS CYCLE IN THE MAMMALIA 43 well as 0. vignei, 0. ammon, and 0. canadensis, that these sheep in their wild condition are probably monoestrous, for their annual sexual season is of short duration, and occurs with great regularity. Similarly it may be inferred from Prjewalsky's statements l that 0. poli, 0. burrhel, and 0. argali are moncestrous 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 0. 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.2 Scotch black-faced sheep in the Highlands experience two dio3strous 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 oestrus 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 1 Prjewalsky, Mongolia, the Tanyut 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 oestrus 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 lambing.1 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- 1 Shortt, A Manual of Indian Cattle and Sheep, 3rd Edition, Madras, 1889. THE (ESTROUS 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 dioestrous 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.1 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,2 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 dioestrous 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. Ellen- 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 Animals (Crosswell's Translation), Bohn's Library. London, 1862. 46 THE PHYSIOLOGY OF REPRODUCTION berger,1 however, gives from twenty to thirty days as the length of this interval. The prooestrum and oestrus together do not as a rule occupy more than two or three days, and oestrus alone may last for only a few hours. The external signs of the prooestrum 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 oestrous and metoestrous periods. The internal changes are briefly described in the succeeding chapter. The only external indication of oestrus 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.2 The oestrous 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, i.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,3 while, according to Low, the domesticated goat experiences oestrus at very frequent periods.4 A similar statement may be made about cattle, for Heape 5 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 diosstrous cycles, we are led to infer from the limited calving season among 1 Ellenberger, Veryleichtndc Phy.nologie der Haussaiiyelhierc, vol. ii. Berlin, 1892. 2 Nathusius, " Ueber einen auffallenden Racenunterscbied in der Triichtig- keitsdauer der Schafe," Zool. Garten, Jahrg. 3, 1862. 3 Lydekker, loc. cit. 4 Low, The Dcmfsticated Animals, London, 1845. 5 Heape, loc. cit. THE (ESTROUS CYCLE IN THE MAMMALIA 47 similar animals in the wild state that the sexual periods are likewise restricted. Raciborsky l says that in the more domestic types of cattle the cows receive the bull more frequently than in the wilder breeds. Ellenberger 2 states that among domestic cattle the dicestrous cycle varies from about two to four weeks, but Schmidt 3 has shown that the differences may be much greater. Wallace 4 says that oestrus 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,5 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. Emrys-Roberts6 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 ancestrous period.7 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 jsrulaicus in Cashmir, as well as the American bison, black- tailed deer in Montana, red-deer, fallow-deer, and roe-deer,8 and 1 Raciborsky, Traite de Menstruation, Paris. 2 Ellenberger, loc. cit. 3 Schmidt, " Beitrage zur Physiologic der Brunst beim Rinde," Disserta- >i"n, Zurich, Miinchen, 1902. 4 Wallace (R.), loc. cit. 6 Shortt, A Manual of Indian Cattle and Sheep, 3rd Edition, Madras, 1889. 6 Emrys-Roberts, " A Further Note on the Nutrition of the Early Embryo, &c.," Proc. Roy. Soc. £., vol. Ixxx., 1908. 7 According to Emrys-Roberts, the profuse mucinous secretion during the prooestrum in the Mammalia is derived, not from the body of the uterus, but from the cervix and vagina. 8 There has been some controversy regarding the breeding season and period of gestation in roe-deer. According to Bischoff (Enticicklungsgeschichte de.g 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 monoestrous 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 ; l while in this country [England] September is the sexual month for the fallow-deer,2 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 oestri in such animals, and the extreme probability that individual females do not experience oestrus at exactly the same time, predispose one to believe that they are moncestrous 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 S. 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, loc. cit.). 3 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 dioestrous cycles, and it is this possibility which prevents positive assertion on the matter. " Among captive animals, not more than two dioestrous cycles have been observed in the gnu during one sexual season. Gazdla dorcas has two or three ; the giraffe 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 dioestrous cycles all the year round, at intervals of about three weeks." l 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,3 and also, in all probability, with the musk-ox in Greenland.4 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,5 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, 18M. 3 Prjewalsky, loc. cit. * Lydekker, loc. fit. 6 Catlin, North American Indiana, 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 oestrous cycle. Under domestication, however, the sow is poly oestrous, and may take the boar five weeks after parturition. The duration of the dicestrous cycle is from two to four weeks, according to Fleming.1 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 prooestrum. At the same time the vulva is distinctly swollen. Wiltshire 2 states that in the hippopotamus in captivity a condition of oestrus may be experienced at regular monthly intervals. This animal has been known to breed in Zoological Gardens. The mare is polycestrous, the normal dioestrous cycle being about three weeks and the cestrous period a week, though its 1 Fleming, Veterinary Obstetrics, London, 1878. 2 Wiltshire, loc. cit. See also Ellenberger, loc. cit., and Wallace (R.), Farm Live-Stock of Great Britain. 4th Edition London 1907. THE CESTROUS CYCLE IN THE MAMMALIA 51 actual length may vary by three or four days.1 The sexual season in the absence of the stallion extends throughout the spring and early summer months, and is generaUy longest in the more domesticated breeds. Professor Ewart informs me that in a pony imported from Timor, which is in the Southern Hemisphere, oestrus 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.2 Heape states that, very exceptionally, mares are moncestrous. 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.3 1 Ewart found that in Equus prjewalsky, oestrus 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 Rtnjal Ayric. 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 oestrus probably for three or four days. CETACEA Little is definitely known about the periodicity of breeding in Cetacea. According to Millais,1 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,2 which app*ear 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 3 states that two specimens of Balcenoptera 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, say« that the period of oestrus 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 oestrus disappear. Under favourable conditions, however, mares may become pregnant in winter. Ewart gives the following as the periods of gestation in various Equidse : — Asses and zebras, 358 to 385 days; Prjewalsky's horse, 356 to 359 days; Celtic pony, 334 to 338 days. In coarse- 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. 1 Haldanc. "Whaling," &c., Annals of Scottish Nat. Hist., April, 1905 3 Lillie, " Observations on the Anatomy and General Biology of some Members of the larger Cetacea," MS. still unpublished. THE (ESTROUS 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,1 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.2 Humpbacked whales and other Cetacea have been 4escribed as indulging in amorous antics at the breeding time, rubbing against one another and patting one another with their long fins.3 CARNIVORA In the female of the dog the average duration of the complete cestrous 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.4 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 5 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, loc. cit. 3 Ibid. * Marshall and Jolly, loc. cit. 5 Stonehenge, The Dog in Health and Disease, 4th Edition, London, 1887. ' 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.1 The prooestrum 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 oestrus, which may last for another week or ten days. Heape states that the winter oestrus in some breeds does not last so long as the summer oestrus. In certain individuals a relatively slight mucous or sanguineo-mucous flow takes place during the period of oestrus, 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 oestrus). 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,2 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,3 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 oestrous 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. 2 Potthast, " Kenntniss des Eiweissumsatzes," Dissertation, Leipzig, 1887. 3 Hagemann, " Eiweissumsatz im tierisch Organisnuus," Dissertation, Erlangen, 1891. Cf. also Schorndorff, " Einfluss der Schilddriise auf den Stoffwechsel," Pfliiger'8 Arch., vol. Ixvii., 1897. THE (ESTROUS CYCLE IN THE MAMMALIA 55 period of lactation is very variable in duration, and may extend until the commencement of the next prooestrum. The wild dog of South America (Canis azarce), according to Rengger,1 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.3 The period of gestation in the wolf and fox is approximately the same as in the dog, i.e. about two calendar months. Bischoff 4 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 5 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. Saiigcthiere von Paraguay, Basel, 1830. 2 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 late Professor D. J. Cunningham and Dr. R. F. Scharf. (See Marshall and Jolly, loc. cit.) 4 Bischoff, " Ueber die Rauhzeit des Fuchses und die erste Entwicklung seines Eies " Sitz. der Math.-phys., Wien, Cla-tse 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 2 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.3 Heape 4 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 polyoestrous, and may experience a long succession of dioestrous cycles in one sexual season, each dioestrous cycle lasting about fourteen days and sometimes less.5 The period of gestation is about nine weeks. Millais 6 says it is uncertain whether the wild cat has one 1 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. 3 Marshall and Jolly, l»c. cit. I have known a cat experience oestrus regularly at intervals of about a fortnight from December until the following August, but such a long succession of dioestrous cycles is probably unusual. 4 Heape, loc. cit. s Heape, loc. eit. 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. 8 I am 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 oestrus 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.1 This information is interesting, since the males of most Garni vora, 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 Fehdse 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 oestrus has been known to recur at intervals of three weeks until the animal became pregnant, while the period of oestrus may itself last a week.1 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 lioness 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 Felidae 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,2 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 oestrus 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 monoestrous, but may have as many as three annual sexual seasons,3 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, loc. cit. - Somerset. Quoted by Heape, loc. cit. 3 Carnegie, Ferrets and Ferreting, London. THE (ESTROUS 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 polyoestrum ; for, if the oestrous periods were to recur at still shorter intervals than is actually the case, they could be regarded as forming so many dices trous cycles in one sexual season. So far as I am aware, the ferret does not experience osstrus 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 Cocks l found that a single oestrus 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, oestrus may recur at regular monthly intervals all the year round.2 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,3 the pups are born each year between March 8th and 10th. 1 Cocks, " Note on the Gestationof 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 taxua," 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 l 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 qther 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.2 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.3 In Germany it is said that the breeding season extends from March until July.4 1 Tamer, "On the Placentation of Seals," Trans. Roy. Soc. Edin., vol. xxvii., 1875. 2 Millais, loc. cit. 3 Millais, The Mammals of Great Britain and Ireland, vol. i, London, 1904. * Van Herwerden, "Beitrag zur Kenntniss des menstruellen Cyklus," Monatsschr. /. Gcburtshulfe und Gynak., vol. xxiv., 1906. THE CESTROUS 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 polyoestrum. 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 l (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.2 It would appear that in some Insectivores the prooestrum may be comparatively severe, for in Tupaia javanica Stratz 3 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 oestrus does not synchronise with the period of 1 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 vesiculae 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. 3 Stratz, Der geschlechtsreife Saiiyethiereierstock, Haag, 1898. 62 THE PHYSIOLOGY OF REPRODUCTION ovulation. It has been shown by Benecke,1 Eimer,2 van Beneden,3 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.6 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 7 has shown that in Tarsius spectrum there is a sanguineous prooestrous 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.8 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 9 that, whereas monkeys may have a continuous series 1 Benecke, " Ueber Reifung und Befruchtung des Eies bei den Fleder- maiisen," Zool. An:., vol. ii., 1879. 2 Eimer, " Ueber die Fortpflanzung der Fledermaiise," Zool. Am., vol. ii. 1879. 3 Van Beneden, " Observations sur la Maturation, la Fecondation, et la Segmentation de 1'ceuf chez les Cheiropteres, Arch, de Biol.. vol. i., 1880. 4 Salvi, " Osservazioni sopra 1'Accoppiamento dei Chirotteri nostrani," Atti della Xucietd Tuscanu di 8cien~.<' \ntiii-nli . vol. xii., 1901. 5 Duval, "Etudes sur 1'Embryologie des Cheiropteres," Premiere Partie, Paris 1899. • Wiltshire, loc. cit. 7 Stratz, loc. cit. 8 Van Herwerden, loc. cit. * Heape, loc. cit. THE (ESTROUS CYCLE IN THE MAMMALIA 63 of dioestrous 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,1 and Heape 2 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 3 that Cercocebus in the Island of Banha breeds only, as a rule, in the late summer or early autumn. Heape 4 states that in the Moor maco3 in the Gardens in London there is definite oestrus which always occurs after the cessation of the menstrual discharge, and persists for two or three days, and Ellis 5 has shown that this is also probably the case with the orang utan as well as with various monkeys. Pocock 6 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. 2 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. 3 Van Herwerden, loc. cit. * Heape, " The Sexual Season," Ac. 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. 7 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 haemorrhage 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) haemorrhage continued for about four days. In both animals the phenomenon was truly " menstrual " (i.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 haemorrhage, 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 oestrus. The question as to the correspondence in time between the THE (ESTROUS CYCLE IN THE MAMMALIA 65 processes of menstruation and ovulation is discussed in a later chapter. Little is 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 l states his belief that about seven months is the usual period for the genus Macacus. Sanydl, according to information recorded by Sclater,2 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,3 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. 2 Sclater, Mammals of South Africa, London. 3 Breschet, " Recherches anatomiques et physiologiques sur la Gestation des Quadrumanes," Memoires de V Acad. des Sciences, vol. xix., 1845. 4 Laycock. loc. cit., and Havelock Ellis, loc. 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.1 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 amenorrhoea or a temporary cessation of menstruation.2 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.3 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 1 Matthews Duncan, "Sterility in Women," Brit. Med. Jour., 1883 ; and Lay cock, loc. cit. 2 Wiltshire, loc. cit. 3 Galabin, A 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. (572.) Kennedy (Ed in. 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. THE (ESTROUS CYCLE IN THE MAMMALIA 67 known to occur.1 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 2 the reproductive life of the human female consists of a succession of wave-like periods which follow the monthly cycle. Thus, according to Stevenson,3 the curve of temperature 100 75 50 25 12346678 10 20 i 21 22 23 24 25 26 27 28 Q 14 15 16 17 18 19 D 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 •in and 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. 2 Godman, "The Cyclical Theory of Menstruation," Amer. Jour. Obstet., vol. xi , 1878. Reinl, " Die Wellenbewegung des Lebensprozesses des Weibes," lrolkinann's Sammlungklin. Vurtrage, No. 273. Ott, " Leslois de la periodicite de la fonction physiologique dans 1'organisme feminine," Nwuvelles Arch. d'Obstet. et de Gynic., 1890. 3 Stevenson, "On the Menstrual Wave," Amer. Jour. Obstet., vol. xv., 1882. 68 THE PHYSIOLOGY OF REPRODUCTION Reinl, Ott, and Giles,1 but Vicarelli 2 and certain other authors have recorded an increased temperature during menstruation.3 Zuntz,4 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 5 that the " menstrual wave " hypothesis has given occasion to many pre- mature conclusions regarding the behaviour of the metabolism. Schroder,6 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.7 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 8 states that there is a fall of blood pressure at the time of menstruation. Zuntz 9 records a diminution in the pulse rate. Sfameni 10 states that there is a decrease in the quantity of haemoglobin 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.11 1 Giles, " The Cyclical or Wave Theory," &c., Trans. Obstct. .S'oc., London, vol. xxxix., 1897. 2 Vicarelli, "La temperature de 1'ut^rus dans ses diverses conditions physiologiques," Arch. Hal. de Biol., vol. xxxii.. 1899. 3 Sfameni, '• Influence cle la menstruation sur la quantity d'hemoglobine." Arch. Ital. de Biol., vol. xxxii., 1899. 4 Zuntz (L.), " Einfluss der Ovarien auf den StofFwechsel,"^rr//./. Gyniik., vol. Ixxviii., 1906. 5 Von Noorden, Metabolism and Practical Medicine (English Translation), voL i., London, 1907. ' Schroder, '• Untersuchungen iiber den Stoffwechsel wiihrend der Men- struation," Zeitschr.f. klin. Medicin, vol. xxv. 1894. 7 See von Noorden. loc. cit. 8 Mosher, " Blood -pressure during Menstruation," Johns Hopkins Hospital Bulletin, 1901. 9 Zuntz, loc. cit. I0 Sfameui, loc. cit. 11 Cf. Carnot and Deflandre, " Variations du nombre des Hematics chez la Femme pendant la pe"riode menstruelle," C. R. de la Soc. de Biol , vol. Ixvi., 1909. THE (ESTROUS CYCLE IN THE MAMMALIA 69 Birnbaum and Osten 1 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 2 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,3 and certain other writers, the human female often experiences a distinct post-menstrual oestrus, 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 oestrus 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 oestrus 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 oestrus may readily be interfered with, but the instinct is, I am convinced, still marked." 4 Heape has also given a brief resume* 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. Ixxx., 1906. '- Blair Bell, " Menstruation and its Relation to the Calcium Metabolism." Proc. Roy. Soc. Med., July 1908. 3 Martin, "The Physiology and Histology of Ovulation, Menstruation, and Fertilisation," Hirst's System of Obstetrics, vol. i., London, 1888. 4 Heape, loc. cit. 70 THE PHYSIOLOGY OF REPRODUCTION Ploss l and Westermarck,2 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.3 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 4 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 5 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 Bonfjli. 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 Weib, Leipzig, 1895. 2 Westermarck, The History of Human Marriage, London, 1891. 3 See also Havelock Ellis, loc. cil. •» Annandale and Robinson, Fasciculi Malayentes: Anthropoloytj, Part I., 1903. 8 Frazer, The'Golden Bough, 2nd Edition, London, 1900. THE (ESTROUS CYCLE IN THE MAMMALIA 71 and Haycraft l has shown that there are indications of a similar condition existing in Scotland. On this subject Mayo-Smith 2 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.3 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 dioestrous (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.4 1 Haycraffc, "On some Physiological Results of Temperature Variations," Trans. Boy. Soc. Edin., vol. xxix., 1880. * Mayo-Smith, Statistics and Sociology, vol. i., New York, 1895. Cf. also van Herwerden, loc. cit. 3 Mayo-Smith (loc. 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." * 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 (loc. cit.) has 72 THE PHYSIOLOGY OF REPRODUCTION Whether the monosstrous or the polyoestrous 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 monoestrum is the more primitive of the two conditions ; for, as already shown, there are numerous instances of Mammals which are almost certainly moncestrous 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 oestrus 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 corn- 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 sexnal functions as manifested especially in the recurrence of seminal emissions. THE (ESTROUS 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 anoestrous 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 oestrus, 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." l 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.2 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. a Sedgwick, Student'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 oestrus 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,1 and Dingwall Fordyce.2 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 cestrous cycle are described at some length in the succeeding chapters. 1 Heil, " Laktation und Menstruation," Monatsschr.f. Gcburtsh. 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. Aled. Jmir., Part I., 1906, and The Brit. Jmir. of i'1'ililren's Diseases, 1906. Gellhorn ("Abnormal Mammary Secretion," Jour. Amer. Mcd. Assoc., Nov. 21, 1908) mentions a case of an ape (Cercopithccut) 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 (ESTROUS 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.1 Surrounding the orifice is a fringe of irregular processes or fimbrise, 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. 1 A vestigial structure lying transversely between the ovary and the Fallopian tube on either side is called the parovarium or epoophoron, 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 Giraldes are also sometimes found in the vicinity of the parovarium, but nearer to the uterus. These have been called the paroophoron. 75 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- FIG. 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 77 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. s, Serous layer ; Im, longitudinal muscle fibres ; cm, circular muscle fibres ; a, areolar tissue with large blood-vessels ; mm, muscularis mucosae ; m, 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.1 The vulva comprises the female generative organs which are visible externally. These include the mons veneris, the FIG. 4. — Cross-section through cervical canal of human uterus. (From Williams' Obstetrics. Appleton & Co.) labia inajora and minora, and the clitoris. The last-mentioned structure is a small erectile organ, which is homologous with the penis.2 THE 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 3 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 1 in describing the menstrual ^ff^Sj^, i\- 9".$'. ' -s-jj/ I8F • *'.'•'.*%' .^"Safe ••"'-'.. ":' • '-••'• '-'''.-^ ••;':- .'.--•.'.•'••V--\y"-?"''^;V'--Vv;';j':-i^ ,.' >:• ' '. ^'.'' ':'.'t?^'v^'^-V^--"':- .'.. . ••.••"•• .j ••.*•';:>.->: -'x;,-: .^.;^.'--.; • '/;v'v.:v';.v'.-':;:' .' V; "'**: . • ! • "*•"•'.''.' ; '. .•!}:T5l5A^5Bw2' ;-?• ''.•-•' <•".". •[':'.•- ^- '. •'"'.>• • :•'.-:-••-" "": - ---;;•:-:"; . ;--'.V-'':-.'-'' ' ,''-^;"'^ '.-M": -'vl * •;:-.- -. /•/". .':'--.- ,:--•>.. ^S,-' FIG. 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 increase 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 l 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 Physiologic des Menstruation," Arch. /. Gynak., vol. lii., 189f». 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.1 Leopold 2 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 3 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 ; 4 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, haemorrhage also takes place partly by diapedesis. Engelmann,5 Williams,6 and 1 Galabin, A ManutJ of Midwifery, 6th Edition, London, 1904. 2 Leopold, " Untersuchungen liber Menstruation nnd Ovulation," Arch. f. t/.i/ndk., vol. xxi., 1883. 3 Oliver, "Menstruation: its Nerve Origin," Jour. Anal, and I'lii/s.. vol. xxi.. 1887. 4 Galabin, loc. <•>/. 6 Engelmann, 1m: fit. • 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 Moricke,1 and more recently by Findley,2 while Leopold has described the appearance of the fatty degeneration as a result rather than a cause of haemorrhage. After the extravasation of blood, the corpuscles tend to become aggregated in lacunae which lie beneath the superficial I'M; 8. — Section through mucosa of human uterus showing extravasation of blood. (From Sellheim.) epithelium. These lacunae are the sub-epithelial haematomata of Gebhard,3 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 Mi>ricke, "Die Uterusschleimhaut in der verschierlenen Altersperioden undzur Zeit der Menstruation " /?'V/.xv/, . /. i;rl,f Vessels. V. The Formation of Lacume. U. Fenod or Degeneration. - .„ m, T, e T VI. The Rupture of Lacunse. VII. The Formation of the Menstrual Clot. D. Period of Recuperation. „ VIII. The Recuperation Stage. Heape's account may now be briefly summarised. I. The Resting Stage. — The epithelial layer of the uterine inucosa consists of a single row of cubical or columnar cells. The outer border is clearly denned, 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. III. 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 extra vasated through the stroma. Fatty degeneration was not observed byHeape, 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 Lacunce. — At this stage the extra vasated blood corpuscles collect in lacuna? which are situated in the loose stroma tissue which lies below the epithelium. These lacunae are clearly identical with the sub-epithelial haematomata 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 Lacunce. — The superficial stroma and 92 THE PHYSIOLOGY OF REPRODUCTION epithelium shrivel up at this stage, and, as a consequence, the blood contained in the lacunae is poured into the uterine cavity. The lacunae 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 lacunas 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 lining. The stroma below the lacuna) 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-off mucous membrane is termed by Heape the mucosa menstraalis. 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 extra vasated 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. (3) The formation of new and recuperation 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 REPRODUCTIOiN 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. Heape 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 haemorrhage. 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 shculd 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. \r- 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 inucosa, 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,1 according to whom the sanguineous discharge is slight. Button 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. Gymec. Jour., vol. ii. 1880. 96 THE PHYSIOLOGY OF REPRODUCTION should be noted, however, that Button's investigation was upon monkeys in this country, whereas Heape's observations relate to Indian animals, and that in Pocock's experience,1 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,2 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. fl. Increase of superficial sti-oma elements. II. Pre-menstrual period . \ -, or , , „. , 1-2. blight swelling of mucosa. '1. Increasing hypersemia. 2. Rupture of capillaries. 3. Formation of lacume. i 4. Degeneration of epithelium and stroma III. Menstrual period . < elements. 5. Rupture of lacunfe and tearing off of degenerate tissue. .6. Beginning of regeneration. IV. Post-menstrual period. It 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. Zoo/. Soc., 1906. 2 Van Herwerden, loc. cil. 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 Button 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 region 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 Macacos, 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 osstrus after menstruation is over. Presumably, therefore, oastrus occurs contemporaneously with the recuperation process in the uterus. THE CYCLE IN LEMURS As already mentioned, Stratz l has called attention to the prooDstrous 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. Hypersemia then sets in ; but the congestion is localised to certain places, and is not diffused over the entire mucous mem- brane. Afterwards blood becomes extra vasated 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 yeschlechtsreife Sartytthiereierstock, Haag, 1 898. - Van Herwerden, loc. cit. Q 98 THE PHYSIOLOGY OF REPRODUCTION noticed that certain corpuscles were taken up by leucocytes, and transported to the 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 prooastrous 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 Tupaia javanica, and in the aberrant In- sectivore, Galeopitliecus volans, have received some slight attention. Stratz l 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,2 however, states that the individuals which Stratz examined were in the puerperal stage, and that, although Tupaia can ex- perience " heat " and become pregnant at this time, trust- worthy conclusions regarding the severity of the proosstrous 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- aemia during the prooestrum. 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 haematomata 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. oil. 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 Tujxiia, but must have been the result of a normal procestrum. The periodicity of the changes is unknown. THE CYCLE IN CARNIVORES The histological changes in the non-pregnant uterus have been studied in the dog x 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 Anoestrum. (2) Period of growth and congestion . ) Procestrum. (3) Period of destruction . > . . ( (Estrus. (4) Period or recuperation . . .-?•»«•. ( Metcestrum. It is seen that oestrus, 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 metoestrum (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 1 Marshall, and Jolly, '• Contributions to the Physiology of Mammalian Reproduction: Part I. The (Estrous Cycle in the Dog," Phil. Trans., B , vol. cxcviii., 1905. 2 Marshall, " The (Estrous Cycle in the Common Ferret," Quar. Jour. Micr. Sci. 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 niucosa 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.2 The vessels in the surrounding muscular tissue also tend to enlarge. The epithelium undergoes s-^f&Ofe , Tiff fa $fifc> •Os<«;3t •?.•. B£.->>;_ *. "? ? "^^> * *S*t<»™JgL*''*^\ ^^p^^^fe ^ Q ® ^"| .: ' ' ^ ^T,V: 55JT FIG. 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 Muqnensc Uterine ?i 1'Epoque du Rut," C. R. de la ,S'oc. dc Bid., vol. iv , 1892. 2 Cf. Retterer. loc. cit. ; also Keiffer, "La Formation Glandulaire de 1'Uterus," Annalcs dc In Soc. Mcdiw-Cliirurg. de Brabant 1899; and Bonnet, " Beitriige zur Embryologie des Huudes," Anat. Hcfte, vol. xx., 1902. CHANGES IN THE NON-PREGNANT UTERUS 101 leucocytes, become extravasated throughout the ^troma. 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. ex. bl. .© (From FIG. 13. — Section through prorestrous uterine mucosa of dog. Marshall and Jolly.) ex. bl., Extravasated blood corpuscles ; polym., polymorph ; sec., cells probably indicating secretory activity. These " sub-epithelial hsematomata " have been noticed espe- cially in the prooastrous 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 killed 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 prooestrous 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 polym. *x •*£ffci~if 9::i^ *- ep' polym. FIG. 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 ; pig. , pigment; polym., polymorpb. 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 leuca?mia. 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. polym. - sir. FIG. 15. — Section through portion of mucosa of dog during the recupera- tion period. (From Marshall and Jolly.) bat., basophil cell ; cos., 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 !-, si i, SM^ L- * : S ?,4i3fc _ Ov M.v. FIG. 16. — Section through mucosa of dog during a late stage of recupera- tion. (From Marshall and Jolly.) U. i1., blood-vessel; up., 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. THE CYCLE IN RODENTS 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 2 has described procestrous growth and congestion in the uterus of several Muridae, 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 3 has recorded cyclical changes in FIG. 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 prooestrous desquamation of the uterine epithelium, followed by recuperation. The degenerative changes are accompanied 1 Rejsek, " Anheftung (Implantation) des Siiugethieres an die Uteruswand, insbesondere des Eies von Spermophilus cititlus," Arch. f. Mikr. Anat., vol. Ixiii., a Lataste, Recherchet de Zoethique aur les Mammifercs dc I'ordrc des Rongcurs, Bordeaux, 1887. 3 Konig?tein, '-Die Veriinderungen der Genitalschleimhaut wahrend der Graviditat und Brunst bei einigen Nagern," Pftiigcr's Arch., vol. cxix., 1007. 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 papillae 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 papillae and in the intervening tissue around the bases of the papillae. (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 extra vasa ted 1 Blair Bell, loc. cit. 2 Marshall, " The (Estrous 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- oestrous process tends to diminish with each successive dioestrous 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 papillae than in the smaller ones. Kazzander l appears to have been the first to detect ex- tra vasated blood in the sheep's mucosa. Subsequently Bonnet 2 has noted uterine bleeding in various Ruminants, as well as in the mare and sow, and Kolster 3 has made similar observations (cf. also Emrys-Roberts, see p. 47). Ewart also has described procestrous extravasation and the presence of haematoidin crystals in the uterus of the mare. Glandular activity during heat was also noted.4 (4) Period 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 Uterinscbleimhaut des Schafes," Arch.f. Mikr. Anat., vol. zxxvi., 1890. 2 Bonnet, article in Ellenberger's Verylcichendc Phygiologie des Haussduyc- thifre, vol. ii., Berlin, 1892. Cf. also Ellenberger's article in same volume. 3 Kolster, " Weitere Beitriige zur Kenntniss der Embryotrophe bei Indeci- dunten," Anat. Ilefte, vol. xx., 1!IO± 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 prooestrum. Congestion of the stroma gradually diminishes, and the >v :-VyPj»v f v ysiasl '«*.- •;-v^y-v t£^?^ ... FIG. 18. — Section through portion of uterine mucosa of sheep showing black pigment (pi'j.) 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.1 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. "Beitrage zum Eiubryologie der Wiederkauer," &c., Arch. f. Atiat. u. Phys., Anut. 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 prooestrous periods, and not merely during the most recent one. Assheton 2 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 oestrous cycle in the lower Mammalia. Those who have denied that there is any correspondence between " heat " and menstruation 3 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 proo3strum alone and not the entire " heat period " (a term used generally to include both prooestrum and oestrus) which is the physiological homologue of menstruation ; and, moreover, the latter process in many of the Primates is succeeded by a regular post-menstrual oestrus. The physiological identity of the prooestrum 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. 2 Assheton, "The Morphology of the Ungulate Placenta," Phil. Trans. B., vol. cxcviii., 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 111 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 proo3strum, 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 called 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,1 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 prooestrum. 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. CHAPTEE IV CHANGES IN THE OVARY— OOGENESIS— GROWTH OF FOL- LICLES—OVULATION— FORMATION OF CORPORA LUTEA AND ATRETIC FOLLICLES— THE SIGNIFICANCE OF THE PROCESTROUS CHANGES IN THE UTERUS " The newest freak of the Fallopian tubes and their fimbriae, and the very latest news from the ovisac and the corpora Intea " — JOHN BEOWN, Hor» ,/. . „ $fc* B A ^ f i ^r^p <,. , -••' 'ff-u K; f«s . • -^n r^v^™ - »»" £ P • ;-;4, >s&%%.' •''*'• '• ' '•: Si^»'^ti\ ' •?'"''';-' •- r »f\-^^ ' fer^l //f.^ p * }• ' ^ FIG. 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. Anal., vol. xxxi., 1888. 2 Van Winiwarter, " Recherches sur 1'Ovogenese," &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,1 who regarded them as syncitia from which both ova and follicular epithelial cells took origin. On the other hand, Kolhker believed that the follicle-cells arose from the epithelium of the Wolffian body, while Foulis,2 Schron,3 Wendeler,4 and Clark,5 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-Clay pon 6 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 Winiwarter8 in the rabbit. These 1 Van Beneden and Julin, " Observations sur la Maturation." &c., Arch, de £iol.,vol. i., 1880. 2 Foulis, "The Development of the Ova," &c., Jour. Anat. and Phys., vol. xiii., 1876. 3 Schron, " Beitrag zur Kenntniss der Anatomic und Physiologic des Eierstocks der Siiugethiere," Zeitsch.f. wisscnsch. Zool., vol. xii., 18(J3. 4 Wendeler, -• Entwickelungsgeschichte und Physiologic der Eierstocke." Martin's Die Krankheiten des Eierstocks und N chewier stocks. Leipzig 1899. 6 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., #., vol. Ixxvii., 1905. 7 For a comparative account of the interstitial substance in the ovaries of various mammals, with references to the literature, see Fraenkel, " Vergleichende Histologische Untersuchungen iiber das Vorkommen driisiger Formationen im Interstitiellcn Eierstocksgewebe," Arch. f. Gynak., vol. Ixxv., 1900. 8 Van Winiwarter, " Recherches sur 1'Ovogenese de 1'Organogenese de 1'Ovaire des Mammiferes," Arch, de Bid., 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. (6) 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 b variety. In the latter the nuclei are less granular, and contain Early ovogenetic stage. Leptotenic stage. Fia. 24. — Developing ova from ovary two days before birth. (After Lane-Clay pon.) 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, 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, (c) Pachytenic Pachytenic stage. FIG. 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. (d) Diplotenic stage. — The chromatin strands split along their Diplotenic nucleus three days after birth. Dictyate nucleus seven days after birth. Fu;. 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 oogenesis having been completed.1 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 resum6 of the literature, see van der Stricht, " La Structure de 1'OEuf des Mammiferes," Part I., Arch, de Eiol., vol. xxi., 1904; Part II., Bull, de V Acad. lioyale de Medecine dc Belyique, Bruxelles, 1905; Part III., Bruxelles, 1909. For a general account of the egg and the phenomena of oogenesis in the different groups of animals, both Vertebrate and Invertebrate, with a complete bibliography, see Waldeyer, " Die Geschlechtszellen," in Hertwig's Handbuch der EntwicUungslehre 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." x 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,2 and expresses belief that in this animal also they are PIG. 28. — Ovary at birth, showing primordial follicles, x 300. Williams' Obstetrics, Appleton & Co.) (From 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. 1 Lane-Claypon, loc. cit. 2 Lane-Claypon, " On Ovogenesis and the Formation of the Interstitial Cells of the Ovary," Jour. Obstet. and Gyncec., 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 1 and Sainmont,2 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.3 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,4 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 thecse internae of degenerate follicles. The cells are said to lose their walls, become irregular in shape, and undergo a rapid process of amitotic division, afier which they become transformed into typical interstitial cells. * Sainmont, • Recherches relatives k 1'organogencse du Testicule et 1'Ovaire chez le Chat " Arch, de Biol. vol. xxii.. 1905. 3 Pfliiger, Ueber die Eicrstiklce der Sauyethiere und des Menschen, Leipzig, 18G3. 4 Balfour, loc. 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] lives on the material provided by the cells of the maternal organism." l 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 prooestrum 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 thecse 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 Coslenterates. 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.1 The liquor folliculi begins to form in the developing rat's ovary at about the ninth day of pregnancy.2 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 origin of the liquor. She states, how- ever, that in the process of formation of the liquor folliculi in the adult ovary, the follicle cells appear simply to disintegrate and dissolve without showing the phenomena of karyolysis. On the other hand Honore,3 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 Honore (" Recherches sur 1'Ovarie du Lapin," Arch, dc 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 Honore, "Recherches sur 1'Ovarie du Lapin," Arch, de Biol., vol. xvi., 1900. FIG. 29. — Young oocyte or egg surrounded by a single layer of follicular epithelial cells. (From van der Stricht.) CHANGES IN THE OVARY 127 tubules. In support of this view Honore points out that there are no indications of degeneration or destruction of the follicular epithelial cells of the ripe follicles during oestrus, 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 , i.i*c I^HH m^^^^Mi-'. - . -. FIG. 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 l 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. Micr. Science, vol. xxvi., 1886. 128 THE PHYSIOLOGY OF REPRODUCTION Immediately after copulation, and therefore during oestrus, the cells of the discus proligerus (in the rabbit) l 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 FIG. 31. — Human ovum at termination of growth period. (After van der Stricht.) Yolk grannies, 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 2 in Ascaris, and were afterwards 1 Heape, " Ovulation and Degeneration of Ova in the Rabbit," Proc. Roy. Soc., B., vol. Ixxvi., 1905. 2 Van Beneden, "Recherches sur la Maturation de 1'CEuf," Arch, de Biol., vol. iv., 1883. CHANGES IN THE OVARY studied more fully by Boveri.1 In recent years Montgomery 2 has elucidated the process still further by showing that prior to the formation of the first polar body the chromatin filaments FlG. 32. — Human ovum examined fresh in the liquor folliculi. (From Waldejer.) 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. 1 Boveri, " Zellenstudien," Jenaische Zcitsch., vol. xxi., 1887. 2 Montgomery, " Some Observations and Considerations upon the Matura- tion Phenomena of the Germ Cells," Bid. Bull., vol. vi., 1904. The references to Montgomery's earlier memoirs dealing with the same subject are given in this paper. I 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.1 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.2 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 Button, McClung, Wilson, &c., point to the conclusion that all the nuclei in the somatic cells contain two parallel series of chromosomes (paternal and maternal). 2 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.1 In Man it is twenty-four, so that in the mature human ovum there are only twelve chromosomes.2 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.3 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 1'Homme," Anat. Anz., vol. xxviii., 1900. 3 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 Tenthredinidae," Quar. Jour. Micr. Science, vol. xlix., 1906; " Gametogenesis, &c.," Quar. Jour. Micr. Science, vol. li., 1907. Doncaster shows that in the sawflies there are two types of 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. lx., 1906; Doncaster, "Animal Parthenogenesis," Science Progress, vol. iii. (July) 1908. These papers contain further references. 132 THE PHYSIOLOGY OF REPRODUCTION shown already,1 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 3 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,4 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 spermatozoon.5 Rubaschkin 6 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 noclula) have been investigated by van der Stricht, who has published a 1 Heape, loc. cit. 2 Sobotta, " Die Befruchtung und Furchung des Eies der Maus," Arch, f. Mikr. Anat., vol. xlv., 1895. 3 Gerlach, Ueber die Bildung der Richtunyskorper bci Mut 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. 5 Sobotta (" Die Bildung der Richtungskorper bei der Maus," Anat. Ifefte, 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 la Maturation et la Fecondation de 1'CEuf des Mammiferes," 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. 8 Rubaschkin, " Ueber die Reifungs- und Befrucbtungsprocesse des Meerschweincheneies," Anat. Hefte, vol. xxix., 1905. CHANGES IN THE OVARY 133 series of papers on the subject.1 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.2 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.3 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.4 In certain Invertebrates (Nematodes, Annelids, and Gastero- pods) it has been noticed that the occurrence of the maturation 1 Van der Stricht, " La Ponte ovarique," &c., Bull, de V Acad. Roy. de Med. de Belrjir/ue, 1901. Une Anomalie tr?s inttressante concernant le Developpcment d'un (Euf de Mammifere, Gand, 1904. " Les Mitoses de Maturation de 1'CEuf de Chauve-Souris," Mdmoire pnfsente au VlIIe Congres de VAssoc. des Anato- ni'ixtrs, Nancy, 190P>. 2 Van der Stricht says (La Structure de VCEuf 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. 3 Heape, " The Development of the-Mole," Quar.Jour. Micr. Sciencc,\o\. xxvi., 1886. 4 Morgan, The Development of the Frog's Eyy, New York, 1897. 134 THE PHYSIOLOGY OF REPRODUCTION phenomena depends upon the act of fertilisation. For example, in the Japanese Palolo-worm, a marine Polychset Annelid, Izuka l has shown that the first polar body is discharged (after certain preparatory changes) one hour after fertilisation by a spermatozoon, and that the second polar body is extruded fifteen or twenty minutes later. In other animals (e.g. Amphioxus), one maturation process takes place before, the other during the entrance of the spermatozoon.2 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.3 It 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, Embryogcny, 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," Arncr. Jour, of Phys., vol. xviii., 1!)07). 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. * 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 1 that ovulation may take place inde- pendently of coition in rabbits which have given birth to young just previously, and Iwanoff,2 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,3 the rat,4 and the guinea-pig,5 ovulation occurs spontaneously during " heat," and generally, if not invariably, during oestrus. 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 oestrus and not during the prooestrum, or at any rate not during the early stages of the prooestrum.6 It is probable that the sow also ovulates during oestrus and not during the prooastrum, 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.7 From Hausmann's description it would seem that ovulation does not take place prior to coition, but this statement has not been confirmed.8 1 Weil, " Beitriige zur Kenntniss der Befruchtung uud Entwickelung des Kanincheneies," Wieu Med. Jahrbuch, 1873. 2 Iwanoff, '• La Fonction des Vesicles seminales et de la Glande pros- tatique," Jour, de Phys. et de Path. Gen., vol. ii., 1900. 3 Sobotta, loc. fit. 1 Tafani, " La Fecondation et la Segmentation studied dans les (Eufs des Rattes," Arch. Ital. de £iol., vol. ii., 1889. 5 Rubaschkin, loc. fit. 6 Marshall and Jolly, " Contributions to the Physiology of Mammalian Reproduction: Part T. The CEstrous Cycle in the Dog," Phil. Trans. , B., vol. cxcviii., 1905. 7 Wallace (R.), Farm, Live Stock of Great Britain, 4th Edition, London, 1907. 8 Hausmann, Ueber die Zeuguny und Entstehung des toahrcn weiUichen Eiet, &c., Hanover, 1840. 136 THE PHYSIOLOGY OF REPRODUCTION In the ferret ovulation occurs during oestrus, but postpone- ment of coition may bring about the degeneration of the ripe follicles, since they do not always discharge spontaneously.1 Artificial insemination, followed by pregnancy, has been successfully performed on mares, donkeys, and cows.2 Conse- quently it may be concluded that these animals ovulate inde- pendently of coition. According to Ewart,3 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 follicle.4 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 rule, occurs regularly during oestrus. In certain bats, however, copulation 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).5 The ovary in the winter months (during the hibernating period) is said to be in a state of quiescence, and the exact time for 1 Marshall, "The (Estrous Cycle in the Common Ferret," Quar. Jour. Micr. Sci., vol. xlviii., 1904. * Heape, " The Artificial Insemination of Mammals," Proc. Roy. Soc., vol. Ixi., 18(J7. 3 Ewart, " The Development of the Horse," MS. 4 Marshall, " The (Estrous Cycle and the Formation of the Corpus Luteum in the Sheep," Phil. Tram., B.t vol. cxcvi., 1903. 6 Benecke, " Ueber Reifung und Befruchtung des Eies bei den Fleder- miiusen," Zod. Anz., vol. ii., 1879. Eimer, "Ueber die Fortpflanzung der Fledermause," Zool. Anz., vol. ii., 1879. Van Beneden and Julin, "Observa- tions sur la Maturation, la Ferondation, et la Segmentation de 1'CEuf chez les Cheiropteres," Arch, de Bid., 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.1 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 oestrus.2 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.3 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 4 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 5 upon the occurrence of a pronounced post-menstrual oestrus 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'Atresie 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., £., vol. clxxxv., 1894, and vol. clxxxviii., 1897. Trans. Obstet. Soc., vol. xl., 1898. 4 Van Herwerden, " Bijdrage tot de Kennis van den Menstrnellen Cyclus," Tijdschr. d. Ned. Dierk. Vereen, vol. x., 1906. 5 Pocock, " Notes upon Menstruation," &c., 1'roc. 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 1 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 oestrus 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.3 With regard to the question as to whether any special stimulus is necessary to induce ovulation in women, Oliver 4 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 1 Hergesell, "Das zeitliche Verhalten der Ovulation zur Menstruation." Inaug. Diss., Leipzig, 1905. 8 Raciborsky, Traite 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. 6 Pregnancy, and therefore ovulation, have been known to take place before the onset of menstruation. Pregnancy may also occur during amenor- rhoea (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,1 who caused the rupture of a Graafian follicle artificially in a freshly removed ovary by injecting carmina 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,2 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.3 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 oestrus, and not during the prooestrum when the congestion of the generative tract is at its height. Harper's experiments 4on 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.5 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, oestrus, 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. Foe., B., vol. Ixxvi., 1905. 3 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. 6 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. "It is easy to see that here may be one of the sources of in- direct stimulation to the female reproductive organs." Spallanzani l 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.2 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 3 be- lieved that the fimbriated end of the Fallopian tube erected and partially enclosed the ovary. Kehrer 4 suggested that the 1 Spallanzani, Dissertations, English Translation, London, 1784. 2 Morgan, The Development of the Frog's E3££&ika 11 H 'm * * ,3 ". _ » - . '- ' f ~ ^»M *-«_t -JL [*:».7/.;,rfrA-io <•-. ;...-;.' FIG. 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 Scbafer, Essentials of Ilistoloyy, 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,1 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,3 in animals like the rabbit, which do not ovulate spontaneously during oestrus, 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 oestrus 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 6 1 Or corpus luteum spurium. * The retrogressive changes are similar in both kinds of corpora lutea. 3 Ancel and Bouin, " Sur les Homologies et la Significance des Glandes ;i Secretion interne de 1'Ovaire," C. R. de la Soc. de Bid., vol. Ixvi., 1909. 4 Heape, "Ovulation, &c.," Proc. Roy. Soc., B., vol. Ixxvi., 1905. 5 Marshall, "The (Estrous Cycle in the Common Ferret," Quar. Jour. Micr. Science, vol. xlviii., 1904. ' 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 FIG. 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 thecse 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 l 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 2 has described a similar case of retention in Vesperwjo, 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 3 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,4 Flemming,5 Schottlander,6 Henneguy,7 Janosik,8 Kolliker,9 van der Stricht,10 Seitz,11 Loeb, 1 Sobotta loc. cit. * Van der Stricht, Une Anomalie interessante de Formation de Corps Jaunc, Gand, 1901. 3 Loeb (L.), " liber hypertrophische Vorgiinge bei der Follikelatresie," Arch.f. Mikr. Anat., vol. Ixv., 1905. 4 Schulin, "Zur Morphologie des Ovariums," Arch. f. Mikr. Anat., vol. xix., 1881. 5 Flemming, " Ueber die Bildung von Ilichtungsfiguren in Saugethieren beim Untergang Graafschen Follikel," Arch. f. Anat. u. Phys.,Anat. Abth., 1885. 6 Schottliinder, " Beitrag zur Kenntniss der Follikelatresie," &c., Arch. f. Mikr. Anat., vol. xxxvii., 1891. " Ueber den Graafschen Follikel," &c., Arch. f. Mikr. Anat., vol. xli., 1893. 7 Henneguy, " Recherches sur 1'Atresie des Follicules de Graaf," &c., Jour, de VAnat. ct dc la Phys., vol. xxx., IS'.M. 8 Janosik, "Die Atrophie der Follikel," A rch. f. Mikr. Aunt., vol. xlviii., 18%. ' Kolliker, " Uber Corpora Lutea Atretica bei Saugethieren," Verhand. d. Anat. Gesell., in Kiel, 1898. 10 Van der Stricht, "L'Atresie Ovukiire," &c., Verhand. d. Anat. Gesell., in Bonn, 1901. 11 Seitz, "Die Follikelatresie wiihrend 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 -I^M^Ss "^^8^ 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 l 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 k I'fitude du Vitellus," Arch, dc Zool. i'xper., vol. v., 5th series, 1906. 158 THE PHYSIOLOGY OF REPRODUCTION similar process is described as occurring in certain reptiles. Perez l also has recorded the phagocytic absorption of ova by follicle cells in the ovary of the fasting newt. Schottlander 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. Kolliker 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 2 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.3 Thus Sandes 4 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 5 states that in the case of the rabbit, if the buck is with- 1 Perez, " Sur la Resorption phagocytaire des Ovules," &c., Procis- Vtrbaux de la Soc. des Sciences de Bordeaux, 1903. 2 Heape, loc. cit. 3 Marshall, "The (Estrous Cycle. &c., in the Sheep," Phil. Trans., B., vol. cxcvi., 1903. 4 Sandes, loc. cit. s 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.1 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. StTPERFOSTATION 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.3 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. 0. 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. R. de la Soc. de Biol, vol. Ixvii., 1909), who say that absence of sexual intercourse causes haemorrhage 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.1 Miss Lane-Clay pon,2 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 oogenesis (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, Gth Edition, London, 1904. Accord- ing to another calculation the human ovary at the age of seventeen contains 17,600 ova (Heyse, Arch. f. Oynak., vol. liii., 1893), of which only 400 become mature (Henle, Handbuch der Anatomic, 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. Ix.xvii., 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." l 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 oogenesis.2 THE SIGNIFICANCE OF THE PROCESTROUS 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. 2 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 iuterstitiellen Eierstockgewebe," Arch. f. Gyndk., vol. Ixxv., 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,1 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 oestrus, or at any rate not until after the commencement of the destruction stage of the prooestrum. Consequently Sigismund's theory becomes untenable. Loewenthal 3 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,4 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 prooestrum in the lower Mammalia and menstruation in the Primates, since the degeneration stage of the prooestrum 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 oestrus only once a year, or even 1 Sigismund, " Ideen iiber das Wesen der Menstruation," Berliner Klin. Wochenschr., 1871. 2 His, Anatomic Mensehlicher Embryonen, 1880. 3 Loewenthal, " Eine neue Deutung des Menstruationsprocesses," Arch. f. Gyniik., vol. xxiv., 1884. * 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 l 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 2 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 3 1 Kundrat and Engelmann, " Uutersuchungen iiber die Uterusscbleim- haut," Strieker'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 entilltts," Phil. Trans. B., vol. clxxxv., 1894. 2 Emrys-Roberts, "A Preliminary Note upon the Question of the Nutri- tion of the Early Embryo," Proc. Roy. Soc. S., vol. Ixxvi., 1905. 3 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 1 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,2 who associates the introduction of menstruation (as distinguished from the prooestrum 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 prooestrum, 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, The Evolution of Sex, Revised Edition, London, 1901. 2 Webster, " The Biological Basis of Menstruation," Montreal Med. Jour., April 1897. CHAPTER V SPERM ATOGENESIS— INSEMINATION " Denique per maria ac mentis fluviosque rapacis Frondiferasque domos avium camposque virentis, Omnibus incutieus blandum per pectora amorem Efficis ut cupide generatim ssecla 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 l 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 2 discovered that the sperms arise from the cells of the testis, and Barry 3 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 4 (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.6 1 Spallanzani. Dissertations, English Translation, vol. ii., London, 1784. a Kolliker, Bcitriiyc zur Kenntniss dcr Cfescklcchtsvcrhaltnisse, &c., Berlin, 1841. 3 Barry (M.), " Spermatozoa observed within the MammiferousOvum,"/Vu7. 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 Piiys., 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 trabeculae also pro- FIG. 40. — Section through human testis and epididymis. (After Bohm and von DaTidoff, from Schafer.) <7, glandular substance divided into lobules by septa of connective tissue ; b, tunica albuginea; c, part of epididymis; d, rete testis; e, body of epididymis ; /, 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 SPERM ATOGENEsis— INSEMINATION 167 passage of exit for the seminal fluid or sperm-containing secretion. The glandular substance of the testis is composed of the con- d -f FIG. 41. — Section through testis of monkey. a, seminiferous tubules ; b, interstitial tissue ; c, rete testis ; rf, vasa efferentia ; e, vas deferens ; /, 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 x 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 Amit., 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. SPERMATOGENESIS— INSEMINATION 169 support and as a means of conveying nourishment to the growing spermatozoa.1 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, sperrnatogonium ; c, spermatocyte ; d, sper- matozoa in cavity of tubule ; c, interstitial tissue containing vessels. 1 Merkel, " Die Stiitzellen des Menschlicben Hodens," Muller's Archii; 1871. Brown, "On Spermatogenesis in the Rat," Quar. Jour. Micr. Science, vol. xxv., 1885. Bende, " Untersuchungen iiber den Bau den Funktioniren den Sarnenkanalchens einiger Saugethiere," Arch. f. Mikr. Anat., vol. xxx., 1887. 170 THE PHYSIOLOGY OF REPRODUCTION According to Loisel,1 the orientation of the sperms in the testis is due to a secretion from the cells of Sertoli, together with U' "N-/ FIG. 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 ; b, spermatocytes (seen dividing at 5) ; c, spermatids ; »', parts of spermatids which dis- appear when spermatozoa are fully formed ; », seminal granules. 1 Loisel, " Facteurs de la Forme et de la Fascicnlisation des Spermies dans les Testicules," Jour, de I'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.1 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. Oogonium. 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 spermatozoon 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). l In those animals in which reproduction is normally effected without the intervention of a spermatozoon (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 2 has shown that the axial filament is composed of a number of parallel fibrillae, 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 Weisniann and others are dealt with, and a full account of the literature is given. 2 Ballowitz, " Untersuchungen iiber die Struktur der Spermatozoon," Arch. f. Mikr. Anat. vol. xxxii.. 1888, and vol. xxxvi., 1890; Zeitschr. f. tpm Zool., vol. lx., 1890, and vol. lii., 1891. SPERMATOGENESIS—INSEMINATION 173 Schweigger-Seidel l and La Valette St. George 2 were the first to prove, independently but almost simultaneously, that the FIG. 46. — Human spermatozoa on the flat and in profile. (After Bramman, from Schafer. ) x 2500. Those on the right have adhering protoplasm. The tail is only partly shown in the two seen in profile. 1 Schweigger-Seidel, " liber die Samenkorperchen und ihre Entwickelung," Arch. f. Mikr. Anat., vol. i., 18(55. 2 La Valette St. George, " Dber die Genese der Samenkorper," 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 Ccelenterata 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, e.g. in some fishes. When present, it is sometimes a minute rounded knob, sometimes a sharp stylet, and in some cases terminates in a sharp barb-spur by which the spermatozoon ap- pears to penetrate the ovum (Triton)." l The middle-piece also shows considerable variability. It may be spherical, cylin- drical, or flattened against the nucleus ; sometimes it is of great length, and sometimes it passes insensibly into the flagellum or tail. The latter, in some insects and tishes, 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 spermatozoon, 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. FIG. 47. — Human sperma- tozoa ( x 1000). (After Retzius, from Scba- fer.) 1 , in profile ; 2, view on the flat ; b, head ; c, middle-piece ; d, tail ; e, end-piece of tail, described as a dis- tinct part by Retzius. SPERM ATOGENESIS— INSEMINATION 175 sperms are said to be amoeboid. 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.1 The size of the sperm varies greatly in different animals. In Man its length is about '05 millimetres or a 300th of an inch, (D Q a d 9 FIG. 48. — Different forms of spermatozoa from different species of animals, as follows : — a, bat ; b & c, frog ; d, finch ; e, ram ; / & g, boar ; /t, jelly-fish ; i, monkey ; k, round worm ; I, 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 spermatozoon as con- trasted with the ovum has been strongly emphasised by Geddes and Thomson,2 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 Untersuchunyen, vols. xi., xii., and xiii., Stockholm and Jena. The latter contains numerous large plates with figures of spermatozoa. - Geddes and Thomson, The Emlution 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 FLUID 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,1 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 2 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,3 the sperma- tozoa of male newts which are kept apart from females are absorbed by phagocytes.4 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, " Untersuchnngen iiber die Zahlen- und Regenerationsverhaltnisse der Spermatozoiden bei Hund und Mensch," Pjluger» Arch., vol. 1., 1891. 1 Lode calculates that about 339,385,500,000 spermatozoa must be pro- duced in man between the ages of twenty-five and fifty-five. * Perez, " Re"sorption pbagocytaire des Spermatozokles," Process- Vcrbaux de la Soc. dee Sciences nl«iux, 1904. * The chemistry of the spermatozoon 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 milli metres per minute.1 Bischoff 2 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.3 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),4 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, Anatomic und Physiologic des Cervix Uteri, Erlangen, 1871. Ac- cording to Adolphi ("Ueber das Verhalten von Schlnngenspermien in stromender Flussigkeiten," Anat. Anz., vol. xxix., 1906), the spermatozoa of the adder swim at the rate of 50 /*. to 80 M- per second. 2 Bischoff, Die Entwickelung des Kaninrhen-Eies, Giessen, 1842 3 See p. 136. 4 Nagel, Handbuch der Physiologic 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 l 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 2 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 vipper 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.3 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 spermatozoon 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 Gesetzmassigkeit in der Ortsveranderung der Sper- matozoen," &c., Pfliiger's Archiv, vol. xxxviii., 1886. Rotation by spermatozoa seems to have been recorded first by Eimer, " Untersuchungen uber den Bau und die Bewegung der Samenfaden," Verhand d. Phys. Med. Oesel. zur \\'iir-.hurg,\ol. vi., 1874. 3 Ballowitz, " Untersuchungen iiber die Struktur der Spermatozoen," &c., Zeitichr.f. Zool., vol. i., 1890. SPERMATOGENESIS— INSEMINATION 179 of the ovum.1 Dewitz's observations were subsequently con- firmed by Ballowitz.2 Counter-clockwise rotation upon surfaces was first recorded for the spermatozoa of Echinoderms by Dungern,3 who dis- covered the phenomenon in Spheerechinus and Arbacia. About the same time Buller,4 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 spermatozoon 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 spermatozoon. 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 Spheerechinus 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. 1 Verworn, General Physiology, Lee's Translation from the second German Edition, London, 1899. 2 Ballowitz, loc. rit. 3 Dungern, " Die Ursachen der Specietat bei der Befruchtung," Zentralbl. f. Physiol,, vol. xv., 1901. 4 Dangern, 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 l 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 2 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.3 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 5 has shown that in the rabbit the passage of the spermatozoa into the uterus is probably assisted by a sucking 1 Kraft, " Zur Physiologic des Flimmerepithels bei Wirbelthieren." Pfliiger's Archiv, vol. xlvii., 1890. * Roth, " Ueber das Verhalten beweglicher Mikroorganismen in stro'mender Fliissigkeit," Deutsche ined. 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 Spermatozoon der Saugethiere schwimmen gegen den Strom," Anat. Anz., vol. xxvi., 1905. 3 See Beck, " How Do the Spermatozoa enter the Uterus ? " Amer. Jour, of Obitet., vol. viii., 1875. * See Williams, Obstetric*, New York, 1904. 8 Heape, "The Artificial Insemination of Mares," Veterinarian, 1898. SPERM ATOGENES IS— 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 l). It is obvious that in those animals which ovulate spon- taneously during the oestrus 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,2 though there is evidence that the practice of artificial insemination was not unknown to the Arabs many centuries ago.3 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. Ixi., 1897. 2 Spallanzani, Dissertations, vol. ii., London, 1784. 3 Gautier, Le Fecondation artificielle, &c., Paris, 1889. 182 THE PHYSIOLOGY OF REPRODUCTION original experiment, as quoted from a contemporary English translation : — " I 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 1 refers to a case in which pregnancy was induced by this means. Albrecht 2 1 Gautier, loc. cit. 2 Albrecht, "Kiinstliche Befruchtung," Wocfienschr. f. Thierheilkuiide und Viehzucht, Jahrg. xxxir. SPERMATOGENESIS — INSEMINATION 183 and Plonnis * have also described experiments in which they successfully inseminated dogs by artificial methods (see p. 611). Heape 2 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.3 Iwanoff 4 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. 3 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, Cmcs, and Bitflux, 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 Fecondation Artificielle chez les Mammiferes," 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 Vesicules scminales," &c., Jmir. de Phys. ct de Path, gen., vol. ii., 1900. 184 THE PHYSIOLOGY OF REPRODUCTION ficial insemination upon a woman (previously sterile),1 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,2 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 spermatozoon appears to vary widely in the different species of animals. Leeuwenhoek,3 and subsequently Prevost and . Dumas,3 state that they found moving sperms in the internal genital organs of female rabbits and dogs eight days after coition. Bonnet 4 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.6 Spallanzani 6 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," I'hil. Tram., 1799. 2 See Giinther, Introduction to the Study of Fixhcs, Edinburgh, 1880. 3 See Waldeyer's article in Hertwig's Handbuch der k'ntu-wklungslehrc, Jena, 1903. 4 Bonnet, "Giebt es bei Wirbelthieren Parthenogenesis," Merkcl und Bonnet's Ergebniese d, Anat. u. Entumk, vol. ix., 1900. 8 Marshall and Jolly, "Contributions to the Physiology of Mammalian Reproduction : The (Estrous Cycle in the Dog," Phil. Trans. B., vol. cxcviii., 1905. 6 Spallanzani, loc. cit. SPERMATOGENESIS— INSEMINATION 185 Strassmann 1 has recorded a case in which human spermatozoa survived in the female generative passages for a week after coition. Bossi 2 refers to a similar instance where the sperms lived for over twelve days. In another rase described by Diihrssen,3 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.4 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 5 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,6 in describing the methods adopted in the artificial insemination of mares, lays stress upon the necessity of keeping the seminal fluid 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 1 Strassmann, Lehrbuch der gerichtlichen Med'z'n, 1895. 2 Bossi, " Etude Clinique et Expe"rimentale de 1'Epoque la plus favorable h la Fe"cond;ition de la Femme," Rivwta di O ' stet. e Ginecol., 1891. 3 Dithrssen, "Lebendige Spermatozoon in der Tube," Central* I. f. Gyndk., 1893. 4 See Eimer and other references given on page 136. 5 Heape, loc. c '(. 8 Chelchowski, Die Ster.litat den Pferdes, Wien, 1894. 186 THE PHYSIOLOGY OF REPRODUCTION Rollinat,1 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 maculesa), 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.2 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 spermathecse, it is probable that they retain their vitality for long periods. Lang 3 has shown that the sperms may live for three years in the vesiculse seminales of snails. The extreme longevity possessed by the male cells of some insects is still more remarkable. Von Siebold 4 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 1'Accouplement des Ophidiens a la Fin dc 1'Ete et au Commencement de 1'Automne," Bull. ZooL Soc. France, vol. xxiii.. 1898. 2 Sedgwick, Student's Text-Book of Zoology, vol. ii., London, 1905. 3 Lang, " tiber Vorversuche zu Untersuchungen iiber die Varietaten- bildungen von Helix hortensis Miiller and Helix nemoralis L.," Festschr. zum siebz 'gaten Oeburtatage von Ernst Haeckel, Jena, 1904. 4 Von Siebold, " Fernere Beobachtungen iiber die Spermatozoon Wirbel- loser Tiere," Mailer'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 spermatozoon, is a problem the solution of which is still far from complete. In 1843 Martin Barry,1 as already mentioned, first observed the union of the spermatozoon and ovum in the rabbit, and a little later Newport 2 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 spermatozoon 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 1 Barry, "Spermatozoa Observed within the Mammiferous Ovum," Phil. Trans., 1843. 2 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,1 induces the formation of a centrosome, which, after the completion of fertilisation, initiates the process of cell division. FIG. 50. — Successive stages in the fertilisation of an ovum of -Echinus esculentus, showing the entrance of the spermatozoon. (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 Studicn IV., Ucber die Natur dcr 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 spermatozoon, 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 oosperm, 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.1 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. 190 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.1 In those ova which are surrounded by a membrane it is probable that the fertilising spermatozoon bores its way through p.b. 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 Coelenterates), or there may be funnel-shaped depres- sions on the egg's periphery (certain hydromedusse). 2 FIG. 52. — Fertilisation process In the majority of animals only in bat's ovum. (After van one spermatozoon normally enters der Stricht. ) , •> -, • , , • the ovum, but in some (certain p. b polar bodies ; o. n., nucleus insects elasmobranch fishes, reptiles, of ovum: *. n., nucleus of . , , . earthworm, lamprey, axolotl, &c.), several may effect an entrance. spermatozoon. 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. * 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.1 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 3 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 spermatozoon 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 4 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. THE HEREDITARY EFFECTS 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.5 According to 1 Wilson, toe. cit. 2 Farmer, "On the Structural Constituents of the Nucleus," &c., Croonian Lect-irc, Proc. Roy. Soc. B., vol. Ixxix., 1907. 3 Hertwig, O. and R., " Beitrage zur Kenntniss der Bildung, Befruchtung und Teilung des tierischen Eies," Morph. Jahr., vols. ii. and iii., 1887.' 4 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, he. cit., Geddes and Thomson, Tlie Evolution of Sex, 2nd Edition, London, 1901 ; Weismann, The Evolution Thcoi-y, 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.1 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 2 adopted the same idea, and Weismann made it the basis of his famous theory of heredity.3 " 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- knnde, 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. * 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 assumes 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 l were upon hybridisation 1 Mendel, "Versuche uber Pflanzen Hybriden," Verh. natur. /. Ver., in Briinn, vol. iv., 1865. Reprinted in English in Mendel's Principles of Heredity (Bate^on), 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 game tic 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. For a 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 Report* to the Evolution Committee of the Royal Society, PaYts I., II., III., IV. and V.. 1?02, 1905, UOG, 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 ah1 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.1 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, toe. 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 l 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 canrfot 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 dep'ending for their existence upon a common metabolism. 1 Verworn, loc. cit. 198 THE PHYSIOLOGY OF REPRODUCTION Moreover, the difficulty experienced by Wood l 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 2 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, Mtndcl'g Principles of I/rrrdity, Cambridge, 1909. No doubt, however, it is arguable that the scurs themselves represent unit char- acters, and that if the scnrs 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.1 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 spermatozoon 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.3 Seeliger,4 Morgan,5 and others have objected to Boveri's conclusion on the ground that larvae arising from cross-fertilisation show an unusually wide range of variation. Moreover, Godlewsky 6 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. Gea. f. Morph. u. Phys., Miinchen, vol. v., 1889. 3 The nuclei of such larvae 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. 6 Morgan, Zoo. cit. See also Wilson, foe. 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 Coelenterata. 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.1 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, i.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. Pfiys., 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." l 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,2 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 3 himself believed, of the supposed influence of a previous sire upon the future offspring, 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 4 has repeated the experiment, employing a 1 Verworn, loc. cit. Cf. Farmer (toe. o'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. 2 The phenomenon was explained by supposing that the young, while still in 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. THE PHYSIOLOGY OF REPRODUCTION Bun-hell'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.1 Minot,2 also, in a series of experiments upon guinea-pigs, found no indication of any telegenic influence. Moreover, Karl Pearson,3 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 FOB 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 Jusca, 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 Equidae," Proc. Roy. Soc. Edin., vol. xxiii., 1901. - Minot, "An Experiment with Telegony," British Aasoc. Report*, Cam- bridge Meeting, 1904. ' 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.2 This explanation, while seeming to account for certain individual instances, cannot be applied to all cases of cross-sterility. Bataillon 3 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 (e.g. 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,4 by artificially inseminating an oestrous 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,5 who experi- 1 Pfliiger, " Die Bastardzeugung bei den Batrachiern," Pjlwjer'a Arch., vol. xxix., 1882. 1 Pfliiger and Smith, " Untersuchungen iiber Bastardierung der Anuren Batrachier," &c., Pfliig(r's Archiv, vol. xxxii., 1883. 3 Bataillon, " Impregnation et Fecondation," C. R.de I'Acad. deg Sciences, vol. cxlii., 1906. * Spallanzani, Dissertations, English Translation, vol. ii., London, 1784. 5 Vernon, " The Relation between the Hybrid and Parent Forms of Echinoid Larvae," 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, Strong ylocenlrotus, were supposed to grow more and more " prepotent " as they became more and more mature. Doncaster,1 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 2 discovered that cress-fertilisation of the eggs of Slronyylocenlrotus 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 Strong ylocentrotus 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. cxcvi., 1903. MacBride ("Some Points in the Development of Ophiothrix fruyilis," Proc. Roy. Soc. B.,\o\. Ixxix.. 1907) has recently shown that the immature (ovarian) ova of the Ophiuroid, Ophiothrix, 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," Pjluger's Archiv, vol. xcix., 1903. " Weitere Versuche iiber heterogene Hybridisation bei Echinodermen," Pjluger'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 spermatozoon and the sea-water becoming greater than the sum of the surface tensions between the sea-water and the egg, and the spermatozoon 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.1 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 2 reports that he has been successful in fertilising Strongylocentrotus ova with the spermatozoa of the mussel (Mytilus), and that the products developed into gastrulae. 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.3 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. III. 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,1 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 ' 2 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." It would appear, however, that when the aggregate vitality 1 Romanes, Darwin and After Darwin, vol. iii., London, 1897. See also Darwin, 1 n'mmlx and Plants, London, 1875, and Cross- and Self-Fertilisation in Plants, London, 1876. a 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 Abutilon, 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 Oncidium." 1 Castle 2 found that the eggs of the hermaphrodite Ascidian, Cionaintestinalis, 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 dona 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 Abutilon," English Translation in American Natural'st, vol. viii., 1874. 2 Castle, " The Early Embryology of Ciona intestinalis," Bull. Mutt. Comp. Zoo/., 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.1 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 3 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,4 and Bos,5 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,6 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. Butt., vol. viii., 1905. 2 The results of in-breeding are discussed at some length by Darwin, Variation of Animals and Plant*, vol. ii., Popular Edition, London, 1905. For a recent review of the subject see Morgan, Experimental 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. Qesell., Freiburg, vol. x., 1898. 6 Bos, " Untersuchungen ueber die Folgen der Zucht in engsterBlutver- wandtschaft," Biol. Centralbl., vol. xiv., 1894. • Castle, Carpenter, Clark, Mast, and Barrows, " The Effects of In-breeding, Ac., upon the Fertility and Variability of Drosophila ," 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 l 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. O 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.1 Doncaster,2 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 zygoles 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 heieditary characters. * 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 spermatozoa, conse- quent upon a reduced vitality in the ova.1 Further evidence upon this question is afforded by studying 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 (i.e., 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,3 as a result of a biometrical study of the process of conjugation in Paramceiium 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., 11)02) 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. * See Enriques, loc. cit. 3 Pearl, " A Biometrical Study of Conjugation in Paramcecium," Blotne- treka, vol. v., 1907. 212 THE PHYSIOLOGY OF REPRODUCTION at the conclusion that in this protozoon there is a definite tendency for like individuals to mate with like, since there is a considerable degree of homogainic correlation both between the lengths of the conjugant pairs and also between their breadths. Evidence is presented to show that the homogainic correlation arises through1 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 Paramoecium 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 (Paramoecium, 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.1 Maupas' observations have been confirmed by Joukowsky 2 1 Maupas, " Recherchesexperimentales sur la Multiplication des Infusories CilieV' Arch, de Zool. Exp. et Gen., vol. vi., 1888. " Le Regennissement Karyogamique chez les Cilie"s," Arch, de Zool. Exp. et Gen., vol. vii., 1889. 2 Joukowsky, " Beitrage zur Frage nach den Bedingungen der Ver- mehrung und des Eintrittes der Konjugation bei den Ciliaten," Verh. Nat. Med. Ver., Heidelberg, vol. xxvi., 1898. FERTILISATION 213 and Simpson,1 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 Pammaecium, 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 Paramcecium 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 land 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.3 1 Simpson (J. Y.), "Observations on Binary Fission in the Life-History of the Ciliata," Proc. Roy. Soc. Edin., vol. xxiii., 1901. 2 Calkins, "Studies on the Life-History of Protozoa," I V., Jour, of Exp. Zool., vol. i. , 15'04. (References to earlier papers are here given. See also 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,1 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.2 According to Woodruff,3 on the other hand, a varied environment seemed to obviate the necessity for conjugation in Paramcecium. 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.5 The case of the Porto Santo rabbits and that of the goats of Juan Fernandez, which are cited by Huth 6 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 It has been suggested that the spermatozoon 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 teen subjected to slightly different environmental influences, this near relationship is not necessarily a difficulty. 1 Enriques, loc. cit. 2 If 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. a Woodruff, "The Life Cycle of Paramaecium when Subjected in Varied Environment," Jour, of Exp. Zoo!., vol. xlii., 1908. 4 Allison, The British Thoroughbred Horse, London, 1901. 5 Wallace (R.), Argentine Shows and Livestock, Edinburgh, 1904. Cf. also Darwin, Animals and Plants, London, 1905. • Huth, The Marriage of Near Kin, 2nd Edition, London, 1887. FERTILISATION 215 Pfeffer's experiments l 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,2 the ova of the Fucacese also possess chemotactic properties, attracting the spermatozoa from a distance equal to about two diameters of an ovum. Bordet,3 however, who likewise experimented upon the Fucaceae, obtained no evidence of chemotactic attraction, but he found, on the other hand, that the sperms were very sensitive to contact. Jennings,4 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,5 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," Untersuchungcn aus. d. Bot. Inst. zur Tubingen, vol. i., 1884. 2 Strasburger, Das botan. Prakticum, Berlin, 1887. 3 Bordet, " Contribution a l'6tude de 1'Irritabilite des Spermatozoides chez les Fuccacdes," Bull, de VAcad. Belgique, vol. xxxvii., 1894. 4 Jennings, " Studies of Reactions to Stimuli in Unicellular Organisms, Amcr. 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.1 Dungern 2 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 3 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 Aphidae 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.4 In many animals parthenogenesis has been observed to occur 1 For further information on this subject, with references to literature, see Przibram, Embryogeny, English Translation, Cambridge, 1908 ; and Jenkinson, Experimental Embryology, Oxford, 1909. * Dungern, " Neue Versuche zur Physiologic der Befruchtung," Zeitschr. f. 'I'lgem. Phys., vol. i., 1902. * Morgan, Experimental Zoology, New York, 1907. * See footnote, p. 131. FERTILISATION 217 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 l 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 2 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 3 subsequently made some similar observations, noting also that normal parthenogenetic development was commonest in those individuals which were most robust. Richard Hertwig 4 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 O'l per cent, solution of sulphate of strychnine. Not long afterwards Mead 5 observed that the eggs of the marine Annelid, Chcetopterug, 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 6 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 Partbenogenese bei Insekten," Arch, f. Anat. inPhys., Phys. Abth., Suppl., 1886. 3 Perez, " Des Effets des Actions mecaniques sur le Developpement des (Eufs non-feconde"," &c., Procvs-Vcrbaux de la Soc. des Sciences de Bordeaux, 1896-97. 4 Hertwig, " Ueber Befruchtung und Conjugation," Verhandl. der Deutsch. Zool. GeseUsch., 1892. 5 Mead, Lectures delivered at Wood's Holl, Boston, 1898. 6 Morgan,' " The Action of Salt Solutions on the Unfertilised and Fertilised Ova of Arbacia," &c., Arch.f. Entucick.-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 jwbesii ; 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. Hi., 1899. "On the Artificial Production of Normal Larvae from the Unfertilised Eggs of the Sea-Urchin (Arbacia)," Amer. Jour, of Phys., vol. iii., 1900. " On Artificial Parthenogenesis in Sea-Urchins," Sciince, vol. xi., 1900. "Further Experiments on Artificial Parthenogenesis," &c., Amir. Jour, of Phys., vol. iv., 1900. These papers are reprinted in Loeb's Studict 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 larvae 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 larva?. 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 spermatozoon 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 Strongylocenlrotus 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 blastulae looked normal and rose to the surface of the water, and the plutei which developed showed the usual degree of vitality. The brothers Hertwig l had previously discovered that sea- 1 Hertwig (O. and R.), Untersvchungen zur Morphologic und Physiologic der ZeUe, Jena, 1887. 220 THE PHYSIOLOGY OF REPRODUCTION water saturated with chloroform induced the unfertilised eggs of the sea-urchin to develop membranes. Herbst l 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.3 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 (cf. 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 Hervorraguug von Dottermembranen," &c., Biol. Centralbl., vol. xiii., 1893. * 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. * 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 Losungen," &c.,Pftuger'a Arch. , vol. ciii., 1904. FERTILISATION 221 Parthenogenetic development of starfish eggs has been produced also by mechanical agitation ; 1 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.2 Loeb found also that the unfertilised eggs of the Annelid, Clicetopterus, could be made to develop into swimming larvae by adding a small quantity of a soluble potassium salt to the sea-water in which they were placed.3 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,4 however, found that the nuclear divisions were abnormal, and that the apparent trochophore larvae were not typical, being in reality merely " ciliated structures " which were far behind the real larvae in organisation. But Bullot 5 showed that in another Annelid, Ophelia, ova fertilised by hypertonic sea- water underwent a regular segmentation. Loeb has shown that the ova of limpets (Acmoea and Lottid) 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 larvae 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.6 Bataillon 7 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. ofPhys., vol. vi., 1901. 2 Loeb, The Dynamics of Living Matter, New York, 1906. 3 Loeb, "Experiments on Artificial Parthenogenesis in Annelids," &c. Anur. Jour, of Phys., vol. iv., 1901. 4 Lillie, " Differentiation without Cleavage in the Egg of the Annelid, Chcetopterus pergamentaceus," Arch. f. Entwick.-Mechanik, vol. xiv., 1902. 5 Bullot, " Artificial Parthenogenesis and Regular Segmentation in an Annelid (Ophelia)," Arch. f. Entwick.-Mtchanik, vol. xviii., 1904. 6 Loeb, Univ. of California Publications : Physiology, Berkeley, vol. i., 1903, and vol. iii., 1905. 7 Bataillon, " Nouveaux Essais de Parthenogenese experimental chez les Vertebres inferienrs (Rana fiiftca et Petromyzon pluneri "), Arch. f. Entwick.- Mechanik, vol. xviii., 1904. 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.1 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.2 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.3 Pizon's 4 experiments on the same question were also negative in result. (See p. 299.) Loeb 5 has discussed at some length the question as to whether any idea can be formed regarding the nature of the action of the spermatozoon 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 spermatozoon 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, loc. cit, 2 Sec 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 pr^tendue Ovulase des Spermatozoides," C. R. de VAcad. des Sciences, vol. cxli., 1905. 8 Loeb ( J. ), he. 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 spermatozoon, 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.1 1 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'catlons : Physiology, vol. iii., 1906. See also "Versuche iiber den Chemischen Charakter des Befruchtungsvorgangs," Biochem. Zeitschr., vol. i., 1906. " Weitere Beobachtungen iiber den Einfluss der Befruchtung und der Zahl der Zellkerne auf die Saurebildung im Ei," Biochem. Zeitxchr., vol. ii. 1906 ; " Uber die Superposition von kiinstlichenParthenogenese und Samenbefruch- tung in derselber Ei," Arc\. f. Entwick.-Mechanik, vol. xxiii., 1907 ; " Uber die allgemeinen Methoden der kiinstlichen Parthenogenese," Pfliijer'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 VAcad. des Sciences, vol. cxxxv., 1902 (describing fertilisation by 224 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.1 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 spermatozoon.2 Delage,3 however, has recently adduced experimental evidence, some of which is opposed to Loeb's interpretation of the observed phenomena. This investigator has shown that ansesthetisation with carbon dioxide during maturation) : and C. R. dc V 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. Hi., 1902 ; Scott, " Morphology of the Parthenogenetic Development of Amphitrite," Jour, of Exper. Zool., vol. iii., 1906 ; Lefevre, " Artificial Parthenogenesis in Thalassema mcllita," Jour, of Exper. Zool., vol. iv., 1907 ; Kostanecki, " Zur Morphologie der kiinstlichen pafthenogenetischen Entwicklung bei Mactra," Arch. f. Mikr. Anat., vol. Ixxii., 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. 1 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 dcs ticrischen Eics, 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 Parthe"nogenese Experimentale," Arch, de Zool. Exper. et Gen., vol. vii., 1908. FERTILISATION 226 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 226 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 l 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 novo. According to Delage,2 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, "Etudes experimentales sur la Maturation Cytoplasmique chez les Echinodermes," Arth. de Zool. Exper. et. Q(n.,vo\. 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 seininale, demeure es enfans ce qu'estoit de perdu es parens et es nepveux ce que de"perissoit 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 spermatozoon (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 Wolftian body, are called the paradidymis or organ of Giraldes. 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 f/ FIG. 53. — Passage of convoluted seminiferous tubules (a) into straight tubules, and of these into rete testis (r), (after Mihalkowicz, from Schafer) ; b, fibrous stroma continued from mediastinum. a number of small tubular glands, which doubtless supply some portion of the ejected fluid. Disselhorst l believes that the ampulla acts as a seminal reservoir (a function which has also been assigned to the vesiculae seminales, as described below), and states that he has 1 Disselhorst, " Ausfiihrapparat und Anhangsdriisen der Mannlichen Geschlftchtsorgane," Oppel's Lehrbuch der V rgleichenden Mikroecopischen Anatomie der Wirbeltiere, vol. iv., Jena, 1904. 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 FIG. 54. — Transverse section through the tube of the epididymis. (After Szymonowicz, from Schafer.) a, 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 the 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 Schiifer.) a, epithelium ; 6, mucous membrane ; rt d, e, inner, middle, and outer layers of muscular coat ; /, internal cremaster muscle; {/, 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 lies 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. THE VESICUL^E 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. Rehfisch l has shown that if fluids are injected into the 1 Kehfisch, " Neuere Untersnchungen iiber die Physiologic der Samen- blasen," Deutsche med. Wochenachr., vol. xxii., 1896. 232 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 vesiculae serve the double purpose of secretory glands and reservoirs for the semen. Misuraca l states that in dogs and cats, which have no seminal vesicles,2 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 3 stated that he found sperms in the vesiculae of the mole in the month of February (i.e. during the breeding season) ; and Seubert 4 recorded a similar observation about the hedgehog in August (also in the breeding season) (cf. p. 60). Disselhorst,5 however, throws some doubt on these observations. That the vesiculae may undergo periodic enlargement in animals which have a rutting season is, however, an unquestionable fact. As evidence that the vesiculae seminales are undoubtedly secretory glands, Lode 6 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- culae seminales are briefly referred to below.) Stilling 7 and 1 Misuraca, " Sopra un importante questione relativa alia castrazione," Rimata sperimentale di Freniatria, vol. xv., 1890. 2 Seminal vesicles are absent not only in dogs and cats, but in raany 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 M&nnlichen jleschlechtsteile des Maulwurfs, 1809. 4 Seubert, " Symbolum ad Erinacei europsei anatomen," Inaug. Dissert., Bonn, 1841. 5 Disselhorst, loc. cit. * Lode, " Experimentelle Beitriige zur Physiologic der Samenblasen," Sitzungsber. d. kais. Acad. d. Wissenschaft in Wien, vol. civ., 1895. 7 Stilling, " Beobachtungen liber die Functionen der Prostata und liber die Entstehungenprostatischer Concremente," Virchow'g Archiv, vol.xcviii., 1884. MALE ACCESSORY REPRODUCTIVE ORGANS 233 Akutsu l state that the epithelial cells of the vesiculae 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 2 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 globulins.3 It has been investigated in Rodents by Sobotta,4 Rauther,5 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 6 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 7 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,8 who speaks of the " bouchon vaginal " formed by the solidified secretion of the vesiculae. Similar ob- servations have been made by Leuckart 9 and others. The 1 Akutsu, " Mikroscopische Untersuchung der Secretionsvorgange in den Samenblasen," Pfluger'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. lx., 1902. 3 Fiirbringer, "Die Storungen des Geschlechtsfunktion des Menschen," Nothnagel's Pathologic 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. Natururissenschaft, vol. xxxvii., 1903. * Landwehr, " Ueber den Eiweisskorper (fibrinogene substanz) der Vesicula seminalis der Meerschweinchen," Pfluger's Archiv, vol. xxiii., 1880. 7 Camus and Gley, " Note sur quelques faits relatifs a 1'enzyme prostatique (vesiculase) et sur la fonction des glandes vesiculaires," C. R. de Soc. de Biol., vol. iv. (10th series), 1897. 8 Lataste, " Sur le bouchon vaginal des Rongeurs," Zool. Am., vol. vi., 1883. ' Leuckart, Zur Morphologic und Anatomic der Geschlechteorgane, 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 l has suggested that in the frog the rilling 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 2 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,3 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 vesicul®, was probably due to the absence of formation of the " bouchon vaginal," as has been suggested by Rauther.4 It would seem probable that, in the majority of animals which possess vesiculae 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 5 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 6 found that in castrated bulls, horses, and guinea-pigs, the glandular epithelium of the vesicles atrophied, but the con- 1 Tarchanoff, " Zur Physiologic des Geschlechtsapparates des Frosches," Pfluger'a Archiv, vol. xl., 1887. 1 Steinacb, " Untersuchnngen zur Vergleichenden Physiologic der Mann- lichen Geschlechtsorgane," &c., Pfliiger's Archiv, vol. Ivi., 1894. * Iwanoff, " La Fonction des Vesicles seminales et la Glande prostatique," Jour, de Phya. et de Path. Gen., vol. ii., 1900. 4 Rauther, toe. cit. * Exner, " Physiologic der Miinnlichen Geschlechtsf unktionen," Frisch and Zuckenhandl, Handbuch der Uroloyie, 1903. 8 Lode, toe. cit. MALE ACCESSORY REPRODUCTIVE ORGANS 235 nective tissue underwent hyperplasia. Gruber l and Pelikann * observed that in castrated men the glands atrophied, but became filled with a kind of mucous liquid. THE 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 ihrough part of human prostate. (After Heitzmann, from Schafer.) C, concreticns, often found in old subjects ; E, 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, haemorrhoidal, and 1 Gmber, " Untersuchung einiger Organe eines Castraten," Mailer's Archiv, 1847. 8 Pelikann, Qerichtl.-mediz. Unters. iiber d. Skopz-ntum 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.1 (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 2 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.3 There is some evidence, however, that it exercises a stimulating influence upon the movements of the spermatozoa.4 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,5 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 Spennintheorie, St. Petersburg, 1898 ; Fiirbringer, Die Stijrungen der Geschlechtsfunktion des Mannes, Wien, 1895; Berliner klin. Wochetwchrift, vol. xxiii., 1886. 2 De Bonis, " Dber 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, lac. cit. Kolliker, "Physiologische Studien liber die Samen- fliissigkeit," Zeitechr. f. wiss. Zool., vol. vii., 1856. 6 Extirpation of the vesiculae 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 1 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 2 has also adduced experimental evidence pointing ^-i.: %&*% ") ::~:-':'';.. •;..v . '••••••..•.. ..-* ^»%. ^•.J IV FIG. 57. — Section through prostate gland of monkey. a, tubular alveolus lined with epithelium ; 6, alveolus containing concretion in lumen ; r, bundle of muscular fibres iu connective tissue ; rf, blood- vessels in stroma. to the conclusion that the prostatic fluid of the dog stimulates the sperms to more active movement. IwanofF s experiments 3 (see p. 234), however, show that spermatozoa which have never come into contact with prostatic 1 Camus and Gley, loc. cit. • Walker (G.). " Beitrag zur Kenntniss der Auatomie und Physiologic der Prostata beim Hunde," Arch. f. Anat. u. Phya., Anat. Abth., 1899. * Iwanoff, toe. cit. 238 THE PHYSIOLOGY OF REPRODUCTION secretion possess full functional activity, and are capable of fertilising ova successfully. Serralach and Pares 1 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 Pares' 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 gynaeco- 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 2 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, 1 Serralach and Pares, " Quelques donnees sur la Physiologic de la Prostate et du Testicule," C. R. de la Soc. Biol., vol. Ixiii., 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 (cf. de Bonis' description of the dog's prostate referred to above).1 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 2 (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. COWPER'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 Phye., vol. xxiii., 1889. For the comparative anatomy of the prostate, see Oudemans' Die Acceasorischen Oeschlechtsdrusen 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 he obscure. See below, under Cowper's glands. 2 Griffiths, toe. cit. Cf. also Griffiths, " The Condition of the Testes and Prostate Gland in Eunuchoid Persons," Jour, of Anat. and Phya., vol. xxviii., 1893 ; Walker (G.)," Experimental 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, toe. 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 Littre 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 3, p. 236.) According to Nagel,1 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,2 whom Nagel quotes, says that in animals they atrophy after castration. Griffiths 3 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 (i.e. in the breeding season), and possesses a disagreeable and penetrating odour. According to Gley,4 the secretion in this animal contains a ferment which causes the fluid of the vesiculse seminales to clot, so that Cowper's glands in the hedgehog are the physio- logical equivalent of the prostate gland in the Rodentia.5 1 Nagel, " Physiologie der Miinnlichen Geschlechtsorgane," NageVa Hand- buck der Physiologie des Menschen," vol. ii., Braunschweig, 1906. 2 Schneidemiihl, " Vergleichende Anatomische Untersuchungen iiber denfeineren Bau der Cowperschen Druse," Deutsche Zeitschr. f. Tiermedizin, vol. vi., 1883. * Griffiths, " Observations on the Function of the Prostate Gland," &c., Jour, of Anal, and Phys., vol. xxiv., 1890. 4 Gley, "Role les Glandes genitales accessoires dans la Reproduction," Nel primo Centenario dalla Morte di Lazzaro Spallanzani Acad. Sci. e Stranieri, 1899. 8 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 l states that the epithelium of Cowper's glands undergoes definite histological changes which depend upon the occurrence of coitus.2 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 (perinea!, 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.3- 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 Munnlichen Geschlechtsorgane und Analdriisen der Siiugethiere," Zeitschr. 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. Am., 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. 1 Stilling, " Uber die Cowperschen Driisen," Virchow'a Arch., vol. c., 1885. 2 For an exhaustive account of the minute anatomy of the accessor}' 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 Fsehr'ouch, loc. cit. 3 Tiedemann, Comparative Physiology, English Translation, London, 1834 ; Grosz, " Beitrage zur Anatomic der Geschlechtsdriisen der Insektivoren und Nager," Arch. f. Mikr. Anat., vol. Ixvi., 1905. See also description of prepuce (p. 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. THE 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. Trabeculae 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 urinae). 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 1 Courant, " Uber die Praputialdriisen des Kaninchens und iiber Verander- ungen derselben in der Brunstzeit," Arch. f. Mikr. Anat., vol. Ixii., 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 Corp. Spong. U. A. FIG. 58. — Transverse section through adult human penis, x 3. (After Eberth, from Nagel.) A., artery; C., cntis ; Com., communication between the two corpora cavernosa ; Corp. Spong., corpus spongiosum ; F., fascia ; N., nerves ; .S'., septum; T. A., tunica albuginea ; Te. Subc., tela subcutanea penis; Te. Subf., tela subfascialis ; Tun., tunica dartos penis; Tr., trabeculae of corpus cavernosum ; U., urethra ; F., 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.1 In the Monotremata, Fio. 59. — Section through erectile tissue. (After Cadiat, from Schafer.) a, trabeculse ; b, venous spaces ; c, muscular fibres cut across. however, there is no corpus spongiosum.2 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 biologisfihe 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 faeces and urine pass to the exterior, as in birds and reptiles. In birds the penis is either altogether absent or else is "rudimentary (Crax, Cryptums, Lamel- lirostres, Ratitae), Disselhorst, " Gewichts- und Volumszunahmedermannlichen Keimdriisen," &c., Zoo/. Am., vol. xxxii., 1908. I i.'l'/ ' ^fr- •fc'".'"^ :.'•? •"'.•' •i-'f-' ~ ."' .,.''.'>•.. .'."/!'--*!• ^ Cv>. fiP. *Vff*--' ' FIG. 60. — Part of transverse section through penis of monkey. a, erectile tissue ; b, urethra ; c, artery ; d, nerve ; e , Pacinian body ; /, 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 Caviidae 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. 1 Cole, " On the Structure and Morphology of the Intromittent Sac of the Male Guinea-pig," Jour, of Anat. and Phya., 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 rutting 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 retro verted papilla?, which no doubt serve the same function. They are present also in the lion and tiger, but are of smaller size.2 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.3 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 Saugethiere," Morph. Jahrbuch, vol. xviii. 2 Owen, On the Anatomy of Vertebrate*, vol. iii., London, 1868. 3 Garrod, "Notes on the Osteology and Visceral Anatomy of Ruminants," Proc. Zool. Soc., vol. xlv., 1877. 4 Nicolas, "Sur 1'Appareil Copulateur du Be"lier," Jour, de VAnat. et la Phys., vol. xxiii., 1887. Marshall, "The Copulatory Organ in the Sheep," Anat. Am., vol. xx., 1901. 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 Fib> Cart •). Ur FIG. 62. — Transverse section through filiform appendage of ram, about a quarter its length from the tip. x 45. Bl. V., blood-vessels; Ep. Ur., epithelium surrounding urethral cavity; Fibr. Cart., fibre-cartilage ; Int.. integument; MIMC., 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. Gt. Fibr. Cart — Corp. COP. Int. Fibr. Cart. Fibr. Cart. FIG. 63.— Transverse section through the middle of the glans penis of the ram. x 45. Corp. Cav., corpus cavernosum ; Fibr. Cart., fibre-cartilage ; Gl., erectile tissue of glans ; Int., 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 l 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 (e.g. 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.2 1 Worthmann/'Beitriige zur Kcnntniss der Nervenausbreitung in Clitoris und Vagina," Arch. f. Mikr. Anat., vol. Ixviii. 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 MECHANISMS 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 Fran9ois-Franck,2 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. Loven 3 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.4 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.5 The result of this contraction 1 Eckhard, " Untersuchungen iiber d. Erektion d. Penis beim Hunde," Beitr. zur Anat. und Phys., vol. iii., Giessen, 1863. 2 Fra^ois-Franck, " Rechercb.es sur 1'Innervation Vaso-motrice du Penis," Arch, de Phys., 1895. 3 Loven, Berichte iiber die Verhandlungen der Kdnigl. Sachs. Qesell. zu Leipzig, vol. viii., 1866. Nikolsky, " Ein Beitrag zur Physiologie des Nervi erigentes," Arch. f. Anat. u. Phys., Phys. Abth., 1879. * Retterer, Article on " Erection," in Richet's Dictionnaire de Physiologie, vol. v., 1902. 5 De Graaf (Regner), De Virorum Organia Generationi Inservientibus, Geneva, 1785. Giinther, Untersuchungen und Erfahrungen aus dem Gebiete der Anatomie, vol. i., Hanover, 1837. Kobelt, De I'Appareil du Sens Genital des Deux Sexes, Strasbourg, 1851. For further references, see Retterer, toe. 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 1 suggested that their action is temporarily inhibited, and that the relaxation of the trabeculae, which consequently follows, permits the vascular spaces to distend. According to Valentin,2 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 Wurzburger Phys. Med. GeseU., vol. ii., 1851. * Valentin, Lehrbuch der Physiologic, vol. ii., 1844. MALE ACCESSORY REPRODUCTIVE ORGANS 253 When it contracts it causes a marked dorsal curvature of the penis.1 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 3 showed that transection of the spinal cord above the lumbar region did not destroy the reflex. Brachet 4 also has recorded the occurrence of ejaculation under a similar condition. According to Miiller,5 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. At a 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 h, la Physiologic Gdnerale des Muscles lisses," Arch. Ital. de Biol., vol. iii., 1883 ; Gruenhagen, " Das Thermotonometer," PJluger'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.) 8 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," PJluger's Arch., vol. vii., 1873. See also Goltz and Frensberg, "Ueber die Functionen des Lendenmarks des Hnndes," PJluger's Arch., vol. viii., 1874. 4 Brachet, Recherches experimentales sur les Ponctions du Systeme Nerreux Ganglionaire, Paris, 1839. 8 Miiller, " Klinische und Experimentelle Studien iiber die Innervation der Blase," &c., Deutsche Zeitschr. f. Nervenheilk., vol. xxi., 1902. 254 THE PHYSIOLOGY OF REPRODUCTION can also be induced voluntarily by stimuli conveyed from the brain (i.e. by sexual emotion). It is interesting to note, there- fore, that Budge l and Eckhard 2 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.3 It is stated also that hanging and decapitation in Man are sometimes followed by erection.4 According to Spina,5 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, Retterer6 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 7 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 8 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 9 also 1 Budge, " Ueber das Centrum genitospinale des Nervus sympatheticus," Virchow's Archiv, vol. xv., 1858. 2 Eckhard, loc. cit. 3 Pussep, " Ueber die Gehirnzentren der Peniserektion and des Samenergusses," Inaug. -Dissert., St. Petersburg, 1902. Abstract in Le Physiologists Russe, vol. iii., 1904. 4 Gotz, ' tiber Erektion und Ejaculation bei Erhiingten," Tnaug.-Diss., Berlin, 1898. 6 Spina, " Experimentelle Beitrage zu der Lehre von der Erektion und Ejaculation," Wiener Med. Blatter, 1897. 8 Retterer, Article " Erection," in Richet's Dictionnaire de Physiologic, vol. v., Paris, 1902. 7 Eckhard, loc. cit. 8 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 1st and 2nd sacral nerves. The corresponding parts in the female are similarly in- nervated. Thus, Langley l 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 nerves. 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 2 had previously stated that, on stimulating the anterior ramus of the nervus erigens (or the ramus from the 1st sacral) in the dog, he obtained a vaso-constrictor instead of a vaso-dilator effect, thus differing from Eckhard and other investigators. Sherrington 3 found that in the male monkey excitation of the 2nd and 3rd sacral nerves produced moderate erection, and that of the 1st 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. Fran9ois-Franck 4 found that the anterior ramus from the 1st 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 5 also described erector action from the hypogastrics in the rabbit. Langley and Anderson,8 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. * Fran<;ois-Franck, loc. cit. 5 Budge, loc. cit. 6 Langley and Anderson, "The Innervation of the Pelvic and Adjoining Viscera," Jour, of Phya., 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-cavernosiis and bulbo-cavernosus muscles, as well as to the constrictor urethrae or deeper muscular stratum of the perineum. In the female they innervate the erector clitoridis, which represents the ischio- cavernosus, and the sphincter vaginae, 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,2 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 1st lumbar and 13th thoracic were found to have a slight action. In the dog stimu- 1 Langley and Anderson, loc. cit. 1 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 1st 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 3rcl, 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 (i.e. in the somatic branches), none apparently running in the nervi erigentes (i.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.1 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 vesiculse seminales contract simultaneously, expelling their 1 Langley and Anderson, loc. cit. 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 urethrse, 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 1 found that stimulation of the nervi erigentes in the dog caused the expulsion of the prostatic secretion into the urethra. Loeb 2 obtained contraction of the prostatic vesicles by excitation of the hypogastric nerves. Mislawsky and Bormann 3 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.4 Fogge also states that he found hypogastric stimulation -to produce contraction of the prostatic muscles.5 1 Eckhard, toe. cit. * Loeb (A.), "Beitrage zur Bewegung des Samenleiters," Inaug. -Dissert., Giessen, 1866. 3 Mislawsky and Bormann, " Die Secretionsnerven der Prostata," Zentralbl. f. Phya., vol. xii., 1898. 4 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 M tin n lichen Geschlechtsorganen der Sauger," Anat. Am., vol. ix., 1894). 8 Fogge, " On the Innervation of the Urinary Passage in the Dog." Jour. ofPhys.. vol. xxviii., 1902. MALE ACCESSORY REPRODUCTIVE ORGANS 259 Akutsu l has shown that the vesiculae 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.3 According to Remy,4 stimulation of a small ganglion situated FIG. 65. — End-bulb in prostate. (After Timofeew, from Nagel.) a, thick medullated nerve fibre ; b, 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 5 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 7 observed that in the macaque monkey (Macacus rhesus), the 1 Akutsu, " Beitrage zur Kenntniss der Innervation der Samenblase beim Meerschweinchen," Pfliiger'a Archiv, vol. xcvi., 1903. 2 Budge, loc. cit. 3 Langley and Anderson, loc. cit. 4 Remy, " Nerfs ejaculateurs," Jour, de VAnat. et de la Phys., vol. xxii., 886 8 Loeb, loc. cit. 8 Langley, loc. cit. 7 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.1 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 vesiculae 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 1 There has been some disagreement as to whether the vas deferens under- goes true peristaltic movement. According to Budge (loc. cit. ) this does occur in the rabbit and cat. Fick confirmed Budge for these animals (" Ueber das Vas deferens," Mutter's Archiv, 185(5), but found no peristalsis in the dog (cf. Langley and Anderson for the dog). On the other hand, Loeb (toe. 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 (•' Contractilitat nnd 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 ORGAN'S 261 are innervated exclusively from the lumbar nerves, as above described.1 In view of the facts which have been related, it would appear that ejaculation is a reflex act of some complexity involving V.D. in. FIG. 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.1 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,2 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. 2 Simpson and Marshall, " On the Effect of Stimulating the Nervi Erigentes in Castrated Animals," Quar. Jour. Exper. Phya., vol. i., 1908. CHAPTER VIII1 THE BIOCHEMISTRY OF THE SEXUAL ORGANS " Nous sommes dans un de ces chateaux des legendes allemandes ou les murs sont formes de milliers de fioles qui contiennent les ames des hommes qui vont naitre. Nous sommes dans le sejour de la vie qui precede la vie." — MAETERLINCK, 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 hsematoidin 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. ec. 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,1 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 certain 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 2 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 3 isolated from ovarian colloid another mucoid substance, Pseudomucin (3, 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.4 In 1 Thudichum, " Uber das Lutein und die Spektren gelbgefarbter organ- iscber Substanzen," Centralblatt f. d. mcd. Wissenschaft, 1869, vol. vii. 1 Hammarsten, " Metalbumin und Paralbumin," Zeitachr. f. physiol. Chemie, vol. vi., 1882. 3 Pfannenstiel, " Uber die Pseudomucine der cystischen Ovarienge- schwiilste," Arch. f. GyncBkologie, 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.1 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 85-88 47-19 Protein 13-0 15-63 Fat . 0-3 22-84 Phosphorised fat,calculatec as Lecithin trace 10-72 Cholesterin » 1-75 Reducing sugar trace Inorganic salts . 0-7 0-96 Ash 4-61 2-91 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,2 both as in organic salts and inorganic com- bination. 100 parts of Dry Contain — Residue of " K20. Na2O. CaO. MgO. Fe2O; White of egg . 1-44 1'45 0'13 0'13 000 0-27 0-17 0-38 0-06 0'024 0-20 190 CL 1-32 0-35 1 Krukenberg, " Farbstoffe der Vogeleierscbalen," Verhandlungen d. Phys. Med. Gesellschaft, Wiirzburg, vol. xvii., 1883. 2 Bunge, " Der Kalk und Eisengehalt unserer Nahrung," Zeitschrift /. Biologic, 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,1 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 K20. Na2O. CaO. MgO. Fe203. P206. Si02. Cl. White of egg 31'41 31'57 2'78 2-79 0'57 4'71 1'06 28'82 Yolk of egg. 9-29 5-87 13'04 2'13 1-65 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. Fe203 to 0'0086 per cent. Fe203, the maximum found being 0'0167 per cent. Fe203. (The percentage is calculated for the dried yolk.) This fact probably explains the 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 2 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. Fe203, so that the seasonal diminution which normally appears is prevented. 1 Alba and Neuberg, Physiologic und Pathologie des Mineralstoffwechsela Berlin, 1906, p. 241. 2 Hartung, "Der Eisengehalt des Huhnereies," Zeitschrift fur Biologic, 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, haemoglobin, 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,1 and of Thierfelder and Stern,2 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 anaesthetics 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. * Thierfelder and Stern, " Uber die Phosphatide des Eigelbs," Zeitschrift f. phyaiol. 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,1 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.2 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.3 It is, of course, 1 Unpublished observations. It was found (hat 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. * Mansfeld, " Narkoseund Sauerstoffmangel," Pftii'jcr'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.1 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.2 1 Lochhead and Cramer, " The Glycogenic Changes in the Placenta and Foetus of the Pregnant Rabbit," Proc. Roy. Soc., Series B., vol. Ixxx., 1908. * Kossel, " Weitere Beitriige zur Chemie des Zellkernes," Zeitschrift fur Physiologiache Chemie, vol. x., 1886. Mendel and Leavenworth, "Chemical Studies on Growth: Vl.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,1 this substance plays an important part in the formation of haemoglobin in the chick. It is the precursor of haemoglobin, and has, therefore, been called by him haematogen. It contains 5- 19 per cent. P., and 0'29 per cent. Fe. Recenth* Plimmer 2 has isolated from egg-yolk another protein, livetin, soluble in water and containing (H 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.3 The food has also an influence upon the colour of the yolk, 1 Bunge, "Uber die Assimilation des Eisens," Zeitschr. f. physiolog Chemie, 1884, vol. ix. * Aders Plimmer, "The Proteins of Egg- Yolk," Journal Chemical Soc., 1908. 3 Henriques and Hansen, " Uber den Ubergang des Nahrungsfettes in das Huhnerei," Skandin. Arch. f. Phyinologie, vol. xiv., 1903. BIOCHEMISTRY OF THE SEXUAL ORGANS 271 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.1 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 2 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,3 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 C02 excreted to the amount of 02 absorbed — is 0'71. Such a quotient indicates the oxidation of fat. From the amount of C02 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 and Hasselbalch found during a period of twelve days :— The amount of heat calculated from the amount of fat oxidised 12'11 Gal. The amount of heat actually given off . . . 12'16 Cal. This remarkable agreement in so complicated an experiment —which is a triumph of the experimental skill of the observers 1 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," PJluger's Archiv, vol. xliii., 1888. s Bohr and Hasselbalch, " Uber die Wiirmeproduktion und den Stoffwechsel des Embryo," Skandinavisches Arch. f. Physiologic, 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 C02 excreted, is very great.1 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 3 show that those conditions which favour development, such as high temperature, also lead to an increase in the C02 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 since 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 Kohlensaureproduktion des Hiihner- embryos," Skandinav. Arch. f. Physiologic, 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. 3 Bohr, " Uber den respiratorischen Stoffwechsel beim Embryo kaltbliitiger Tiere," Skandinav. Arch. f. Physiologic, vol. xv., 1904. 4 Tangl, " Beitriige zar Energetik der Ontogenese : I. Die Entwicklungs- arbeit im Vogelei," PjHiger'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 l indicate that there is an oxidation of carbohydrate material, and systematic chemical investigations of the placenta and foetus of pregnant rabbits 2 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 3 also the chemical energy used up during de- velopment is furnished mainly by carbohydrates. Similar observations have been made on the eggs of fishes,4 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 Stoffwecbsel des Saugethierembryos," Skan- flinar. Arch.f. Physiologic, 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. Ixxx., 1908, p. 263. 3 Bohr, " tiber den respiratorischen Stoff wechsel beim Embryo kaltblutiger Tiere," toe. cit. 4 Tangl and Farkas, "Beitrage zur Kenntniss der Ontogenese : IV. Uber den Stoff u. Energieumsatz im bebriiteten Forellenei," Pfliiger's Archiv, vol. civ., 1904. S 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 l 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,2 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.3 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 4 and Hopkins,5 which 1 Hasselbalcb, " Uber den respiratorischen Stoffwechsel ties Hiihner- embryos," Skandinav. Arch. f. Physiologic, vol. x., 1900. * Morner, " Uber die im Huhnereiweiss in reichlicher Menge vorkoramende Mucinsubstanz," Zeitschr. f. physiol. Chemie, vol. xviiL 3 Quoted from Ergebnisse der Physiologic, vol. i. , Part I. 4 Hofmeister, " Uber Krystallisation des Eialbumins," Zeitschrift fiir physiolog. Chemie, vol. xiv., 1890, and vol. xvi., 1892. 8 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 l 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 2 claim to have isolated from the crystallisable ovalbumen several albumens by means of fractionate crystallisation. Crystalline egg albumen contains 0'13 per cent, phosphorus,3 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.4 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.5 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. 2 Bondzinski and Zoja, " Tiber die fraktionierte Krystallisation des Eieralbumins," Zeitechrift f. phya. Chemie, vol. xix., 1894. s Willcock and Hardy, " Preliminary Note upon the Presence of Phosphorus in Crystalline Egg Albumin," Proc. Cambridge Philosophical Soc., 1907. 4 Tarchanoff, " Uberdie Verschiedenheiten des Eiereiweisses beibefiedert geborenen (Nestfliichten) und bei nakt geborenen (Nesthocker) Vogeln," Pfluger's Archiv, vol. xxxi., 1883. Tarchanoff, " Uber Hiihnereier mit durchsichtigem Eiweiss," Pjtuger's Archil', 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. Egg Albumen (Abderhalden and Pregl). Vitellin (Hughounenq). Keratin from Egg Membrane (Abderhalden and Ebstein). Per Cent. Per Cent. Per Cent. Glycine . 0 <0'5 3-9 Alanine . 2-1 <0'5 3-5 Valine . - 1-5 1-1 Leucine . 6-1 6-8 7-4 Phenylalaniiu 4.4 0-7 - Tyrosine 1-1 2-0 - Serine — <0'5 - Cystine . 0-3 - 7-6 Proline . 2-3 <0'5 4-0 Oxyproline - - _ Aspartic acid 1-5 0-7 1-1 Glutamic acid 80 i-o 8-1 Tryptophane . + - - TX- • fAreinine Diammo Lvfine . aclds- lllistidine 2-15 2-14 1-0 1-2 2-1 - Total . 30-1 19-0 367 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,1 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 Hiihnerei," Festschrift fiir Salkowaki, 1904. has as yet not been proved with certainty, although the diastatic action of egg yolk observed by Miiller and Masuyama l 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.2 In the membrane of the eggs of Tropi- donotus,3 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 Icevis.* But these data are very scanty and hardly convincing. In Amphibians like the frog the membrane has been found to consist of pure mucin.5 In Teleostean fishes it has been investigated in the case of the perch,6 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 7 and Buchtala,8 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 Miiller and Masuyama, " liber ein diastatiscb.es Ferment im Hiihnerei," Zeitschr. f. Biologic, vol. xxxix., 1900. 2 Krukenberg, Vergleichende Physiologiache Sttutien : II. Reihe, 1 Abtei- lung, 1882. Neumeister, " liber die Eischalenhaute von Echidna und der Wirbeltiere im allgemeinen," Zeitschr. f. Biologic, vol. xiii., 1895. 3 Hilger, " Ueber die Chemischen Bestandteile des Reptilieneis " ; Bcrichte der deutschen chcm. Gesellschaft, vol. vi., 1873. 4 Krukenberg, loc. cit., 2 Abteilung, 1882. 5 Giacosa, " Etudes sur la Composition chimique de 1'OEuf et de ses En- veloppes chez la Grenouille commune," Zeitschr. f. phys. Chemie, vol. vii., 1883. 6 Hammarsten, " Chemie des Fischeies," Skandinav. Arch. f. Physiologic, vol. xvii., 1905. 7 Pregl, " Uber die Eihaute von Scyllium stellare und ibre Abbauprodukte," Zeitschr. f. phys. Chemie, vol. Ivi., 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 bi 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 l gives an idea of the composition of the ash of the eggs of fishes : — Total Ash . . K20. Na20. CaO. Fe2O3. P206. 01. 7-70 per cent. . 3'33 3077 5'02 0'22 10'55 47'44 In the egg the protein is present in the form of a phospho- protein. Valenciennes and Fremy, 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.2 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 " Dotterplattchen." 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, Mineralslo/wecheel, p. 241. 1 Hammarsten, "Chemie des Fischeies," Skandinav. Arch. f. Physiologic, 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." l 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 2 and of the herring 3 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 fur phyaiolog. Chemie, vol. xl. 2 Miescher, Histochemiache 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. 3 Milroy, " Changes in the Chemical Composition of the Herring during the Reproductive Period," Biochemical Journal, vol. iii., 1908, p. 366. 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 l in the egg of Bombyx mori. 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.2 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. 1 Tichomiroff, " Chemische Studien iiber die Entwicklung der Insekten- eier," Zeitschr. f. phys. Chemie, vol. ix., ] 885. * Von Fiirth, " Uber Glycoproteide niederer Tiere," Hofmeister's Beitrdge, 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 l 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 Bonibyx. The changes which take place during incubation, in the chemical composition of these eggs, have been investigated by Tichomiroff.2 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 . 0-02 0-2 Glycogen 1-98 0-74 Present in ( Fat 8-08 437 Ethereal J Phosphorised fat Extract [Cholesterin . 1-04 0-40 1-74 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.3 The pigments have been studied especially in the eggs of Crustacea. From the eggs of Maja squinado, Maly 4 isolated 1 Dubois, " Sur 1'huile d'CEufs d' la Sauterelle d' Algeria (Acridium pzlerinum)" Comptes Rcndiv), vol. cxvi., 1893. 2 Tichomiroff, loc. cit. 3 Farkas, " Uber den Energieumsatz des Seidenspinners wahrend der Entwicklung im Ei u. wahrend der Metamorphose," Pjluger's Archiv, vol. xcviii., 1903. See Appendix to this Chapter, p. 302. 4 Maly, " liber die Dotterpigmente," Berichte der Akademie der Wiasen- schaften, in Wien, vol. Ixxxiii., 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 l 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 2 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 3 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,4 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 MALE GENERATIVE ORGANS The Semen The semen, i.e. the fluid discharged by an ejaculation, is the secretory product of the testis, epididymis, vesiculas seminales, prostate and Littre'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 physiologische Studien : II. Reihe, 3 Abteilung, 1882, p. 6. 2 Heim, "Sur les Pigments des (Eufsdes Crustace's," Comptes RendusSoc. Biol., vol. xliv., 1892, p. 467. 3 Heim, Eludes sur le Sang des Crustaces, Paris, 1892. 4 Abelous and Heim, " Surles Ferments des (Eufs des Crustaces," Compt. Rend. Soc. Biol., vol. xliii., 1891, p. 273. BIOCHEMISTRY OF THE SEXUAL ORGANS 283 Its reaction is alkaline. Its specific gravity lies between 1'02 and T04. 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.1 According to Slowtzoff,2 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 90'32 Dry residue 9'68 Inorganic salts 0'90 Organic material . . . . . . 8'78 Ether soluble matter O17 Extractives soluble in alcohol and water . . 6'11 Protein substances 2*09 In the ash K, Na, Ca, Mg, P, Fe, and S 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. P205. The amount of calcium excreted in one ejaculation is, therefore, about O'Ol 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 served 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 and Regenerations Verhaltnisse der Spermatozoiden bei Hund und Mensch," Pjiuger's Archiv, vol. 1., 1891. Mantegazza, Gaz. Med. Ital,, Lombardia, 1866, quoted from Lode. 2 Slowtzoff, "Zur Chemie des menschlichen Sperma," Zeitschrift f, phye. 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.1 The crystalline substances appear only when the semen is inspissated. They present various forms — prisms, rosettes, &c., — and are sometimes called " Bottcher'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.2 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 leucaBmic 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, C2H5N, which Ladenburg and Abel 3 believed to be Aethylenimin C2H4NH. This is disputed, however, by Majert and Schmidt, who ascribe to the base the formula C5H14N2, and by Poehl,4 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 5 — and his views are now not generally accepted. 1 Cohen, " Die krystallinischen Bildungen ties mannlichen Genitaltraktus," Cenlralfjlatt f. allg. Pathologic u. pathol. Anatomic, vol. x., 1899. (This paper gives a very complete bibliography.) 2 Poehl, " Weitere Mitteilungen iiber Spermin," Berlinir klin. Wochen- schrift, 1891. 3 Ladenburg and Abel, " ttber das Aethylenimin," Her. der deutschen chem. Oesellschaft, 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 same 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, )vhich 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 l 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 2 and von Bardeleben.3 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 vesiculee 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 vesiculse 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 sernen on the blood which is still present in the uterus.4 The prostate gland secretes an opaque fluid having a faintly acid reaction (which may become neutral or alkaline in in- 1 Lubarsch, " tiber das Vorkommen Krystallinischer und Krystalloider Bildangen in den Zellen des Menschlichen Hodens," Virchow's Archiv, vol. cxlv., 1896. 2 Reinke, " Beitrage zur Histologie des Menschen," Archiv f, mikroskop. Anatomie, vol. xlvii., 1896. 3 Bardeleben, " Beitrage zur Histologie des Hodens und zur Spermato- genese beim Menschen," Archiv f. Anatomic u. Physiologic, Anatomische Abteiluny, Supplement, 1897. 4 Landwehr, " Uber den Eiweisskorper der vesicula seminalis der Meer- schweinchen," PJluger'a Archiv, vol. xxiii., 1880. BIOCHEMISTRY OF THE SEXUAL ORGANS 287 flammatory conditions of the prostate). It contains spermine,1 which, when brought together with the phosphates secreted by other genital glands, forms the characteristic " Bottcher'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 2 found in the prostatic secretion of some animals a ferment, vesiculase, which has the property of coagulating the fluid in the vesiculae 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 3 states, but to choline, as Bocarius4 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 Fiirbringer, " Die Storungen der Geschlechtsfunktion des Menschen " ; in Nothnagel, Pathologic u. Therapie., vol. xix., Part III., 1895. 2 Camus and Gley, " Action Coagulante du Liquide Prostatique sur le Contenu des Vesicules Seminales," Comptes Rtndus, vol. cxxiii., 1896. 3 Florence, " Du Sperme et des Taches du Sperme," Archives d'Anthro- pologie Criminate, vol. xi., 1896 ; vol. xii., 1897. 4 Bocarius, " Zur Kenntniss der Substanz welche die Bildung von Florence- chen Krystallen bedingt," Zeitschriftf. phyeiologische Chemie,vol. xxxiv., 1902. 288 THE PHYSIOLOGY OF REPRODUCTION observations of Littlejohn and Pirie l 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. THE CHEMISTRY OF THE SPERMATOZOON 2 Owing to the brilliant work of Miescher,3 which has been continued by Kossel 4 and his pupils, our knowledge of the chemistry of the spermatozoon 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 41 '90 per cent. Phosphorised fats . . . 31 '83 „ Cholesterin, fats . . . 26'27 „ 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 Littlejobn and Pirie, "The Micro-Chemical Tests for Semen," Ellin. Med. Jour., 1908. (This paper contains references to the literature.) * For a detailed account of this subject and the literature see Burrian, " Chemie der Spermatozoen, I.," in Ergebnisse der Physiologic, vol. iii., 1904, and "Chemie der Spermatozoen, II.," in Ergebniaae der Physiologic, vol. v., 1906. 3 Miescher, Histochemische und Physiologische Arbeiten. Qeaammelt und Herausgegeben von Seinen Freunden, vol. ii., Leipzig, 1897. 4 Kossel, " tiber dieeinfachsten Eiweisskorper," Biochemiachea Centralblatt , 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 spermatozoon 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.1 If injected into an animal they have a strongly toxic action, even if small doses are given.2 1 Hunter (A.), " Uber die Verbindungen der Protamine mit anderen Eiweiss-korpern," Zeitachrift f. phys. Chemie, vol. liii. 1907. 2 Thompson, " Die physiologische Wirkung der Protamine," Zeitachrift f. phyaiol. 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 — NH2 NH2 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, monoamino valerianic 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 l 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 wdgaris 3 — 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 IS 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, e.g. the blood corpuscles of the fowl, the 1 Kossel and Pringle, " tiber Protamine und Histone," Zeitechrift f. phys. Chemie, vol. xlix., 1906. 2 Kossel and Kutscher, " Beitrage zur Kenntniss der Eiweisskorper," Zeitschr.f. phya. Chemie, vol. xxxi., 1900. 3 Ehrstrom, " Uber ein neues Histon aus Fi.schsperma." 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.1 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 2 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 into 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," Zeitechrifl f. phya. Chemie, vol. xl., 1904. 2 Kossel, " Einige Bemerkungen iiber die Bildung der Protamine im Thierkorper," Zeitachrift fur physiologische Chemie, vol. xliv., 1905. Weiss, " Untersuchungen iiber die Bildung des Lachs-Protamins," Zeitschrift fiir phyaiologische Chemie, vol. Hi., 1907. BIOCHEMISTRY OF THE SEXUAL ORGANS 293 The investigation of the unripe spermatozoa of the salmon l and of the mackerel 2 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? Sphcerechinus 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,5 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 iiber die Lachs- milch," Histochemische Arbeiten, Archiv f. Experimentclle Pathologic u. Pharmakologie, vol. xxxvii., 1896-1897. 2 Bang (I.), "Studien iiber Histon," Zeitschrift f. physiolog. Chemie, vol. xxvii., 1899. 3 Mathews, " Zur Chemie der Spermatozoon," Zeitschrift f. phys. Chemie, vol. xxiii., 1897. * Kossel, " Uber die einfachsten Eiweisskorper," Biochemisches Cen- tralblatt, vol. v., 1906-7. 8 Miescher, loc. cit., "Die Spermatozoon 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.1 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. Laevulinic 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 C (5)-NH(7)\ I! II >CH (8) (3) N-C (4)-N (9)^ namely — Adenine = 6 - Aminopurine ; Hypoxanthine = 6 - Oxypurine ; Guanine = 2 Ainino-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) N = CH(6) ! I (2) HC CH (5) II II (3) N-CH(4) namely — Cytosine = 6 Amino-2 Oxypyrimidine Uracil = 2 - 6 - Dioxypyriniidine Thymine = 5 Methyl -2 -6 Dioxypyriniidine (Methyl-Uracil). 1 For literature for nucleic acid see Steudel, " Nucleine, Nucleinsjiuren und ihre Spaltungsprodukte," Biochemiachea Centralblatt,vo\. vi.,1907; also Burrian, lac. cit. ; Levene, Zeitechr.f. phys. Chemie, vols. xxxii. to 1., Biochem. Zeitschr., vols. iv., 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 l 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 spermatozoon 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 spermatozoon, 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,2 the process of hydrolysis may be expressed by the following equation : — C43H67N1603oP4 + 4H20 = C5H5N50 + C?H5N5 + C5H6N2O2 + C4H6N3O Nucleic acid. Guanine. Adenine. Thymine. Cytosine. + C24H.MO30P4. 1 Miescher, loc. cit. 2 Steudel, " Die Zusammensetzung der Nukleinsauren 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 :— C24H44O30P4 + 4H20 + 20 = 4C6H1206 + 4HPO3. 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 : l 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.2 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,3 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 4 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. 6O5 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'a 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 Ergebnisae d£?/.: ••• :'-'i-/:-^ ; '^: . ' •"-, " • ••'• Flo. 70.— Section through ovary of rat after transplantation on to peritoneum, showing corpora luteum and small follicle with ovum. (From Marshall 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. 324 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 normal after fourteen months, while a normal heteroplastic graft was composed entirely of healthy ovarian tissue (with 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 FlO. 72. — Transverse section through uterus of rat after ovariotomy, showing degener- ative changes. (Cf. Figs. 71 and 73. From Marshall and Jolly.) 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. X>. -v .: ''^;r';too;-^-0^F;^..%;;g::o .•fkK:-, %w 'bA ^ -^ ^ -"O :|| ...1:^ ; '" ;^ 2T-.^: •.*';v"^- ••'••'• C5; - - - FlG. 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, 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- Sequard 1 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-Sequard'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, oophorine, ovigenine, &c.). The fresh ovaries or ovarian powder are eaten, but the fluid can be administered either by the mouth, by the rectum, or by hypodermic injection. These methods of treatment are said to have met with considerable success in cases of amenorrhcea, 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.2 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-S&juard, " Des Effets produits chez 1'Homme par des Injec- tions," kc., (7. R. 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. ORGANS OF INTERNAL SECRETION 327 activity (e.q. ovaries with prominent follicles like those from animals " on heat," or ovaries with corpora lutea like those of c.l '•.•-• FIG. 74. — Section through rat's kidney, into the tissue of which an ovary had been transplanted. (From Marshall and Jolly, Quart. Jour, of Experimental Physiology.) ar, artery; c.l., corpus luteum ; g.f. , Graafian follicle; yl., glomerulus of kidney; ov.st., ovarian stroma ; r.t., renal tubule; z.".t., zone of granulation tissue between ovarian tissue and tissue of kidney. 328 THE PHYSIOLOGY OF REPRODUCTION pregnant animals, or ovaries in a state of relative quiescence like those of anosstrous animals). The effects of ovarian medication are discussed at some length in a memoir by Bestion de Camboulas,1 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 haemorrhages 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 2 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 3 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 4 (cf. the testis, p. 314). 1 Bestion de Camboulas, " Le Sue Ovarien," Paris, 1898. * Jentzner and Beuttner, " Experimentelle Untersuchungen zur Frage der Castratinsatrophie," Zeitschr. f. Ofburtsh. u. Oyndk., vol. xlii., 1900. * Carmichael and Marshall, toe. 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,1 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. THE FACTORS WHICH DETERMINE THE OCCURRENCE OF HEAT AND MENSTRUATION Pfliiger 2 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,3 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 5 discredited her description, which, so far, has re- ceived no confirmation. Goltz 6 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 oestrus 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 1 Loisel, " Les Poisons des Glandes genitales," C. R. de la Soc. de Biol., vol. lv., 1903 ; vol. Ivi., 1904 ; and vol. Ivii., 1904. 2 Pfliiger, Uber die Bediutung und Ursache der Menstruation, Berlin' 1865. 3 Strassmann, Lckrbuch der gcrichtticken Medizin, 1895. 4 Winterhalter, " Ein Sympathisches Ganglion im Menschlichen Ovarium',, Arch.f. Gynak., vol. li., 1896. 5 Von Herff, " Giebt es ein Sympathisches Ganglion im Menschlichen Ovarium," Arch.f. Gyniik., vol. li., 1896. For information upon the innerva- tion of the ovary, see Von Herff, " liber den feineren Verlauf der Nerven im Eierstock," Zeitschr. f. Geb. u. Gynrik., vol. xxiv., 1893. 8 Goltz, " Ueber den Einfluss des Nervensystems auf die Vorgange wahrend der Schwangerschaft und des Gebarakts," Pfliiger's Archiv, vol. ix., 1874. Goltz and Ewald, " Der Hand mit verkiirztem Riickenmark," Pfliiger'a Archiv, vol. Ixiii., 1896. 330 THE PHYSIOLOGY OF REPRODUCTION recurrence of procestrum and oestrus. Moreover, Sherrington,1 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,2 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. Gynaecologists have pointed out that in the human subject ovulation and menstruation are not necessarily associated, and Heape 3 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,4 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 5 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 Inttyrativc Action of the Nervous System, London, 190C. 2 Brachet, Recherche*, 2nd Edition, Paris, 1837. * Heape, "The Menstruation and Ovulation of Macacua 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 190(5. ORGANS OF INTERNAL SECRETION 331 this is the true interpretation is rendered the more probable in view of the cases referred to by Gordon,1 Doran,2 Meredith,3 and others, in which pregnancy occurred after the supposed removal of both ovaries (see also, p. 343). Doran 4 also records a large series of cases in which menstruation entirely ceased after ovariotomy.5 Morris 6 gives an account of a woman aged twenty, who suffered from amenorrhoea, 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 7 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 8 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 9 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. Oyncec. Soc., vol. xxi., 1896. 2 Doran, "Pregnancy after the Removal of Both Ovaries," Jour. Obstet. and Oyncec., vol. ii., 1902. 3 Meredith, "Pregnancy after Removal of Both Ovaries," Brit. Med. Jour., Parti., 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. 6 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. Ixix., 1906. 8 Glass, "An Experiment in Transplantation of the Entire Human Ovary," Medical News, 1899. 9 Dudley, " tJber Intra-uterine Implantation des Ovariums," Internal. Gyn. Congress, Amsterdam, 1899. THE PHYSIOLOGY OF REPRODUCTION ovary implanted on the fundus uteri. The patient menstruated regularly afterwards. Again, in a case recorded by Cramer of Bonn,1 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 2 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 prooestrous 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 3 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 O3strus, and so suppress the vicious symptoms which are liable to render the animals periodically unworkable.4 Dr. Jolly and the author 5 have shown, further, that normal prooestrum, followed by oestrus, 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., 190(>. * Halban, " Uber den Einfluss der Ovarien auf die Entwickelung des Genitules," Silz.-Ber. Akad. Wisaenschaft, Wien, vol. ex., 1'JOl. 3 Knauer, foe. cit. 4 Hobday, " Ovariotomy of Troublesome Mares," Veterinary Jour., New Series, vol. xiii., April 1906. 6 Marshall and Jolly, " Contributions to the Physiology of Mammalian Reproduction: Part II. The Ovary as an Organ of Internal Secretion," Phil. 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.1 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 2 have pointed out, is pro- bably due also to an increase in the ovarian metabolism.3 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 anoestrous animals a transient congestion of the external generative organs resembling that of the normal procestrous condition.4 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 oestrous 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. 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 proosstrous and oestrous conditions are produced by substances circulating in the blood, but not necessarily elaborated in the ovaries, is supplied by certain facts recorded by Halban.1 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,2 cows can be brought " on heat " artificially by feeding them on milk supplied from other cows which are in that con- dition. Heape 3 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 the secretory activity of the ovary, it is still an open question as to what part of the organ is concerned in the process. Fraenkel 4 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, he. cit. * Youatt, Cattle, London, 1835. * Heape, " Ovulation and Degeneration of Ova in the Rabbit," Proc. Roy. Soc., B., vol. Ixxvi., 1905. < Fraenkel, "Die Function des Corpus Luteum," Arch. f. Oyndk., vol. Ixviii., 1903. ORGANS OF INTERNAL SECRETION 335 fact that ovulation in most Mammals does not occur until oestrus, or, at any rate, until the end of the prooestrum (see p. 135), and consequently corpora lutea are not present in the ovaries (for the corpora lutea dating from one oestrus do not always persist until the next oestrus, which may be many months after- wards). Heape's observations l on the absence of corpora lutea in menstruating monkeys may be again cited in this con- nection. Moreover, Ries 2 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 haemorrhage 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 oestrous 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 prooestrous changes of the uterus are brought about by a specific excitant or hormone 3 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. Obatet., vol. xlix., 1904. 3 Starling lias proposed the term hormone (from the Greek, 6p/j.au, 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. 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 oestrus is so plainly manifested in the display of sexual feeling. THE 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.1 Prenant 2 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 oestrous periods. This theory was supported by Regaud and Policard,3 who 1 Clark, " Ursprung, Wachstum, und Ende des Corpus Luteum," Arch, f. Anat. u. Phy*., Anat. Abth., 1898. Whitridge Williams, Obstetrics, New York, 1903. ••: Prenant, " La Valeur Morphologique da Corps Jaune," Rev. Gen. des Sciences, 1896. » Regaud and Policard, " Fonction Glandulaire de 1'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 anoestrous 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.2 who investi- gated the corpus luteum of the marsupial cat (Dasyurus vicer- 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 oestrus 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 Oestation 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 3JJ8 THE PHYSIOLOGY OF REPRODUCTION the corpus luteuni 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 hyperaamic, the other part of the ovary is unusually anaemic, while towards the end of pregnancy, when the increase in the blood supply to the generative organs 1 Krarnkol and Cohn, " Experimentelle Untersuchungen iiber den Einfluss des Corpus Luteuni auf die Insertion des Eies," 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 in 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 s 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. 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.1 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 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 ovum be unfertilised it merely produces the hyperaemia of menstruation, and then undergoes degeneration until it is renewed in a fresh position. Since the corpus luteum is, par cjxellence, 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 Fibroid.*," Scottish Med. and Surg. Jour., vol. xvi., 1905. ORGANS OF INTERNAL SECRETION 341 not take place until oestrus, and consequently that at the time of the prooestrous hypersemia 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 l 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 right ovary which contained the degenerate remains of two1 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.2 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.3 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.1 Cases have been recorded by Essen-Moller,2 Graefe,3 and Flatau,4 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./. Oyndk , vol. xxviii., 1904. 3 Graefe, "Zur Ovariotomie in der Schwangerschaft," Zeitechr.f. Oeb. u. Gyndk., vol. Ivi.. 1905. * Flatau, " Ueber Ovariotomie wahrend der Schwangerschaft," Arch. f. Oyndk., vol. l.xxxii., 1907. ORGANS OF INTERNAL SECRETION 343 dentally at the time of the operation. So able and experienced an operator as Bland Sutton 1 has recently testified to the extraordinary difficulty experienced in removing the whole of the ovarian tissue in ovariotomy, and the distinguished French obstetrician, Lucas-Champonniere,2 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 3 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 4 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,5 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 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-Champonnicre, " Sur une Observation de Graffe Ovarienne Suivie de Grossesse," Jour, de Med. et de Chirurgie Pratiques, vol. Ixxviii. (May) 1907. 3 Daels, " On the Relations between the Ovaries and the Uterus," Surgery Oyncecology and Obstetrics, vol. vi., 1908. 4 Kleinhaus and Schenk, " Experimentales zur Frage nach der Funktion des Corpus Luteum," Zcitschr. f. Oeb. u. Gynak., vol. Ixi., 1907. 5 Ancel and Bouin, " Sur la Fonction des Corps jaunes," C. R. de la Soc. de BioL, vol. Ixvi., 1909 ; " Le DeVeloppement de la Glande Mammaire pendant la Gestation est determine par le Corps jaune," C. R, de la Soc. de BioL, vol. Ixvii., 1909. 344 THE PHYSIOLOGY OF REPRODUCTION between the development of the corpus luteum and the growth of the mammary gland in the rabbit.1 Dubreuil and Regaud,2 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 3 tend to confirm those of Ancel and Bouin. According to Loeb,4 deciduomata (i.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 jauiu;s avec 1'Uterus non gravidc," I. II. III. and IV., C. R. de la Soc. de BioL, vol. Ixvii., 1909. See also earlier papers in vol. Ixv., 1908, and vol. Ixvi., 1909. 3 Niskoubina, " Recherches exp<5rimentales sur la Fonction des Corps jaunes," (7. R. de la Soc. de Biol., vol. Ixvi., 1909. 4 Loeb (L.), "The Production of Deciduomata, and the Relation between the Ovaries and the Formation of the Decidua," Jour. Amer. Med. Aseoc., 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 is 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. THE SUPPOSED 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 gynaecologists 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. 2 Lane-Claypon, "On the Origin and Life-History of the Interstitial Cells of the Ovary of the Rabbit," Proc. Boy. Soc., B., vol. Ixxvii., 1905. 346 THE PHYSIOLOGY OF REPRODUCTION Zweifel and Abel,1 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,2 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,3 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,4 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 5 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 fur Gyniikologie in Berlin," Zentral. /. Gi/nnk., No. 21, 1899. Abel, " Dauererfolge der Zweifelschen Myomek- tomie," Arch.f. Gynrik., vol. Ivii., 1899. 2 Doran, "Sub-total Hysterectomy for Fibroids," Lancet, Part II., November 1905. 3 Mandl and Burger, Die Biokgische Bedeutung der Eierstocke nach Entfernung der Gebdrmutter, Leipzig, 1904. 4 Holzbach, " Ueber die Function der nach Totalextirpation des Uterus zunickgelassen Ovarien," Arch.f. Gyndk., vol. Ixxx., 1906. 5 Blair Bell, toe. 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 anrestrous uterus.2 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,3 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 1 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. 3 Loewenthal, "Eine neue Deutung des Menstruationprocess," Arch. f. Qyndk., vol. xxiv., 1884. 348 THE PHYSIOLOGY OF REPRODUCTION experiments undertaken by the author in collaboration with Mr. Carmichael,1 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.2 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 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.3 1 Carmichael and Marshall, Proc. Roy. Soc., loc. cit. - 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 a shrivelling up of the ovaries and the assumption of secondary male characters as has been stated (Zeit. f. Qyniik., 1904, No. 24). It has not been determined whether the generative organs (apart from the uterus) undergo the character- istic prooestrous changes after hysterectomy, since these changes are com- paratively slight and difficult to detect in rabbits. ORGANS OF INTERNAL SECRETION 349 THE CORRELATION BETWEEN THE GENERATIVE ORGANS AND THE DUCTLESS GLANDS Noel Paton l and Henderson 2 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 3 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 4 observed a constant hypertrophy of the pituitary body (hypophysis) in capons, oxen, buffaloes, and rabbits, cas- trated in early lift — 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,5 who states that the changes in the pituitary were similar to those occurring after removal of the thyroids. According to Pepere,6 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 Phytt., vol. xxxii., 1904. 2 Henderson, "On the Relationship of the Thymus to the Sexual Organs," Jour, of Phys., vol. xxxi., 1904. 3 Soli, "Contribution h, la Connaissance rle la Formation du Thymus chez le Poulet et chez quelques Mammiferes," Arch. Ital. de BioL, vol. Ixii., 1909. * Fichera, " Sulla ipertroSa della glandula Pituitaria consecutiva cas- trazione," Policlinico, vol. xii., 1905. 6 Cimorini, " Sur 1'Hypertrophie de PHypophyse ceVebrale chez les Animaux thyrdoidectomise's," Arch. Ital. de BioL, vol. xlviii., 1907. 8 Pepere, " Sur les Modifications de Structure du Tissu Parathyroidien normal et accessoire (thymique) en rapport avec sa Fonction vicariante," Arch, de Med. Exper., 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 3 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 4 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 5 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 6 states that in frogs during the pairing time, the medulla Hutchinson, "The Pituitary Gland as a Factor in Acromegaly :ui'l Giantism," New York Med. Jour., 1900. * Freund, " Die Beziehungen dcr Schilddriise zu den weiblichen Ge- schlechtsorganen," Deutsche Zeitach. f. Chir., vol. xviii., 1883. 3 Gaskell, The Origin of Vertebrates, London, 1908. * Alquier and Thauveny, "^tat de 1'Ovaire de Chiennes ayant PExtirpa- tion partielle ou totale de 1'Appareil Thyro-Parathyroidien," C. R. de la Soc. de Biol., vol. Ixvi., 1910. s Gottschau, " Ueber Nebennieren der Saiigethiere," &c., Sitz.-Ber. d. •it. med. Ge*ell. 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 l 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 oogenetic 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.2 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 hyperaemia which characterise the proosstrous processes. It is at these periods also, in typical cases, that the follicles become mature. After ovulation, which occurs during oestrus, 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. Ivi., 1905. 2 Limon (loc. cit.) 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 luteura have been stated to undergo an independent hypertrophy during pregnancy (p. 345). 352 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 l 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. As to whether the ovary elaborates more than one specific 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. THE EFFECTS OF CASTRATION UPON THE GENERAL METABOLISM In 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 1 In one case of osteomalacia Kro'nig 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.1 The protein metabolism of castrated animals has been in- vestigated by Liithje,2 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.3 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,4 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 (i.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. Oynak., 1996). See also Fraenkel, " Ovarialan- tikorper und Osteomalacia," Munch. Med. Wochenschr., No. 25, 1908. 1 Van Noorden, Metabolism and Practiced Medicine, English Edition, edited by Walker Hall, vol. i., London, 1907. According to Wallart, " Ueber das Verhalten der interstiellen Eierstocksdriise bei Osteomalacia," Zeitftch. f. Qeb. und Gyntik., vol. Ixi., 1908, osteomalacia is correlated with an increase of the interstitial cells in the ovary. a Liithje, " Ueber die Kastration und ihre Folgen," Experim. Archiv, vol. xlviii., 1902, and vol. 1., 1903. * Van Noorden, foe. cit. * 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,1 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 2 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. On 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,3 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. Qynak. Gesell., Berlin, 1904. See also Deutsch. Zeitschr. f. Chir., vol. 65, 1908. 3 Cramer and Marshall. MS. unpublished. 356 THE PHYSIOLOGY OF REPRODUCTION Furthermore, it is to be noted that, according to Magnus- Levy and Falk,1 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 2 record losses of nitrogen, phosphorus pentoxide, and calcium monoxide after injecting glycerine extract of ovary subcutaneously. Loewy 3 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 faeces. 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,4 who employed bitches whose ovaries were removed shortly after puberty. They record marked diminution in the haemoglobin and the red cells.5 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.6 1 Magnus-Levy and Falk, " Lungengaswechsel des Menschen," Arch. f. Phys., Supplement, 1899. 2 Neumann and Vas, "Einfluss der Ovariumpraparate auf den Stoff- wechsel," Monatsachr. f. Geburtsh. u. Gyru'ik., vol. xv., 1902. 3 Loewy, "Ueber den Einfluss des Oophorins," Berl. klin. Wochcnschr., 1899. •» Breuer and Seiler, " Einfluss der Kastration auf den Blutbefund weib- licher Tiere," Experim. Archiv, vol. 1., 1903. 8 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 Chevre," C. R. de I'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," (iMncet, Part II., Nov. 1906). Further references are given in this paper. 6 For the effects of hypophysectomy see Crowe, Gushing, and Homans, "Experimental Hypophysectomy" (Johns Hopkins Hasp. 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. CHAFIER X1 FtETAL 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 I. HISTORICAL SURVEY THE 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 2 the conception of the placenta as an organ elaborating from the maternal blood the aliment necessary for the growth and development of the fcetus. 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. 2 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 l stated that the maternal blood circulated through the placenta, and this view, which, according to Waldeyer,2 had formerly been held by Vater and Noortwyk, though the latter at least believed in the com- munication of the maternal and foetal circulations, was sup- ported by the subsequent dissection of injected placentae 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.3 It is remarkable that John Hunter did not recognise the placenta as the organ of foetal respiration. A century before, Mayow 4 had declared that the placenta functioned as a foetal lung, the umbilical vessels taking up the nitro-aerial gas (oxygen) and carrying it to the foetus. This view was adopted by Ray,5 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 6 in 1794. But all doubt was not removed till, in 1874, the spectroscopic bands of oxy- haemoglobin were demonstrated in the umbilical vein of a guinea- pig by Albert Schmidt, a pupil of Preyer.6 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. 2 Waldeyer, " Bemerkungen iiber den Bau der Menscben- und Affen- placenta," Arch. f. mikr. Anat., vol. xxxv., 1890. 3 W. Hunter, Anatomy of the Human Gravid Uterus, Birmingham, 1777. 4 Mayow, Tractus Tertius de Respiratione Fostus in Utero, 1674. 5 Ray, The Wisdom of God in the Creation, 12th Edit., 1754. • See Preyer's Speciette Physiologic des Embryo, 1883. FCETAL NUTRITION: THE PLACENTA 359 researches of Goodsir.1 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 foetus, 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 fcetal nutrition was first emphasised by Weber,2 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,3 Kolliker,4 and Farre.5 Weber and Reid 6 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 7 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, Entvncklungsgeschichte, 1861, 1884, &c. 5 See Tod's Cyclop axlia, Article " Uterus," 1858. 6 Reid, " On the Anatomical Relations of the Blood- Vessels of the Mother to those of the Foetus 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 l 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 2 considered them to be lymph-spaces, and therefore extra-vascular ; and Jassinsky 3 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 4 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 5 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 iiber die menschliche Placenta," Arch, f. Anal. 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. 4 Winkler (F. N.), "Zur Kenntnis der menschlichen Placenta," Arch. f. Gynak., vol. iv., 1872. 6 Kastschenko, "Das menschlicbe Chorionepithel und dessen Rolle bei der Histogenese der Placenta," Arch. f. Anat. u. Phys., anat. Abth., 1885. FCETAL NUTRITION: THE PLACENTA 361 attention of few morphologists, among whom Turner, the " grand-master of placental research " (Hubrecht 1), 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 haemorrhage 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 2 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 " Zellsaulen " of Langhans, an attachment to the decidua is effected. While present, the cellular layer lies 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 placenta the mass is vacuolated, and maternal blood is contained in the lacuna?. In the later stages of pregnancy it forms an attenuated membrane over the villi, and may wholly 1 Hubrecht, "The Placentation of Erinaceus europceus," Quar. Jour. Micr. Set., vol. xxx., 1889. 8 Strahl, " Ueber Placentarsyncytien," Anat. Am., 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.1 ~b sl I' j ## ** ?* «, ,* & OS* .. V 5, 9 - * FIG. 75. — Part of an early human chorionic villns. (From Hofbauer's Biologic der menschlichen Plazenta, Braumiiller.) b, Biirstenbesatz with basal corpuscles ; «, syncytium ; /, Langhans' layer, one cell dividing mitotically (V). Some have denied its existence during life, and ascribed it wholly to the method of preparation. But Hofbauer 2 has shown that the fresher a specimen is when obtained, the easier it is to demonstrate the striae by methods of staining, and, therefore, it is probably a vital structure. Kastschenko looked on the striae 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-haematoxylin, 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, Biologic der menschlichen Plazenta, Leipzig, 1905. F(ETAL NUTRITION: THE PLACENTA 363 motor centre for the ciliary beats. But no movements have yet been observed, and von Lenhossek 1 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 he in the superficial stratum ; then lighter and darker striae alternate, and it is this appearance which has led to the name " striated edge." Bonnet 2 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. Spec 3 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 amoeboid motility. V. Lenhossek 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 V. Lenhossek, Verhandl. d. anal. Kongresses in Halle, 1902. See Centralbl. f. Gynak., 1904, Nr. 7. 2 Bonnet, " tJber Syncytien," &c., Monatsschr. /. Geburteh. u. Oynnk., vol. xviii., 1903. 3 Graf v. Spee, "Neue Beobachtungen iiber sehr friihe Entwickelungs- stufen des menschlichen Eies," Arch. f. Anat. u. Phya., anat. Abth., 1896. 364 THE PHYSIOLOGY OF REPRODUCTION cells, with large nuclei, which he took to be wandering cells. But Lenhossek 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 festal 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 2 and Heinricius,3 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 Umscbliessung der menschl. Frucht wabrend der f ruhesten Zeit der Schwangerschaft," Arch.f. Anat. u. Phys., anat. Abth., 1897. - Strabl, "Der Bau der Hundeplacenta," Arch.f. Anat. u. Phya., anat. Abth., 1890. 3 Heinricius, •' Ueber die Entwicklung und Struktur der Placenta beim Hunde,".4rcA. /. mikr. Anat., vol. xxxiii., 1889. FCETAL NUTRITION: THE PLACENTA 365 deny that by such physical processes the non-diffusible sub- stances with large molecules, e.g. haemoglobin 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 2 said : "It may be held as nearly without doubt that leucocytes cross from the maternal to the foetal blood," and Preyer 3 considered the passage of leucocytes " indisputable." The first objection was raised in a paper by Paterson.4 In it he recorded three cases of pregnancy com- plicated by leucocythaemia 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 5 and Sanger,6 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 foetal blood, have led to the abandonment of Rauber's theory. 1 Rauber, Ueber den Ursprung der Milch und die Ernahrung der Frucht ini , f.i-tal plauonta, containing no glycogeu ; ir, intermediary region ; re, region of uterine sinuses; as, uterine sinuses with pcrhascular sheaths of uninucleate cells rich in glycogen ; •» piiC^ . . . ~ - •>* \*£./ --£~-'^~— Sp. M.Som. FIG. 111. — The allantoidean diplo-trophoblast of Erinaceus. (From Hubrecht's "The Placentation of Erinaceus europceus" Quar. Jour. After. Sci., vol. xxx., 1889.) Tr.S., trophospongia ; Tr., 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 Tr.S. F.L. FCETAL 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,1 interposed between the blastocyst and the unaltered decidua. The trophoblast with its lacunae, 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 lacunae 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 2). 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). 2 Hubrecht now considers that the deciduofracts are of fostal 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 Ily , Trs. FIG. 112.— Section in situ of the ovum of Erinaceua (Hubrecht). Hy., hypoblast; Tr., trophoblast; sp., spaces in the trophoblast, communi- cating with the maternal blood-spaces (M.Sp.) ; D., decidua ; Trs., tropbospongia. 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-villi, containing branches of the vitel- line vessels, are developed. The omphaloidean placenta thus FCETAL 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 Tr. Trs. Df. C AvTt '•**.< * **,.'.* • i f . i 23 '•'• y^^f1" \ Sl>~\ • . '• •'[••/--,' Y», V f r>f. FIG. 113. — The extension of the yolk-sac against the lacunar trophoblast in Erinaceiis (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, i.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 I. in. i.l. n.v. - — u.v 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 ^-shaped. (From Hubrecht's "The Placentation of the Shrew," Quar. Jour. Micr. Sci., vol. xxxv., 1894.) B. V., blood-vessels ; c.m., circular muscle ; /.MI., longitudinal muscle. tissues, and store nutriment which they give up to the embryo in a way as yet unknown. Shrew. — In the shrew (Hubrecht l) 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. FCETAL 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 (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 lacunae. 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 lacunae 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 villi. 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 FCETAL 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 Cr. GI: np.T ' M. FIG. 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 conlom (E.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.T., non-placental trophoblast; OL, 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,1 Vernhout 2). 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 lies 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 1 Strahl, " Ueber den Ban der Placenta von Talpa europea" Anat. Am., vol. TM 1890. 2 Vernhout, •• Ueber die Placenta des Maulwurfs," Anat. Hefte, vol. v.,1894. FCETAL 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 gs. 771 FIG. 117. — Orifice of a uterine gland of the mole with trophoblastic dome. (From Vernhout's "Ueber die Placenta des Maulwurfs," Anat. Hefle, vol. v., 1894.) »»., uterine mucous membrane ; ue., uterine epithelium ; pi., plasmodiblast ; cy., cytoblast ; ^vv &$7- ^fi : '&(^r?'':''-\ VJall FIG. 119.— The placenta of the bat. (From Nolf's " Etude des modifications de la muqueuse uterine pendant la gestation chez le murin," Arch, de Biol., vol. xiv., 1896.) m., mnscularis ; a., unaltered mucosa; C.ep., epithelial layer; gl., glands; C.pp., paraplacental layer with blood-spaces (6.) ; Art., artery running towards trophoblast ; VP., vein ; 2V., trophoblast with lacuna? ; VU. nil.. 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 fcetal 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 lacuna? of maternal blood come to be surrounded by foetal 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 yolk-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 1). 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 he close together. The cytoblast almost entirely disappears. Pteropus edidis. — 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 Doval, "iStude sur 1'embryologie des Cheiroptdres," Journ. de I' Anal. etdela Phys.t 1895-97. F(ETAL NUTRITION: THE PLACENTA 463 mass is pressed against the uterine surface and fuses with it. In this way the completed placenta is discoid (Gohre *). PRIMATES. — 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 ccelom 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 2 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 ccelom, 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 chori&n should be restricted to the Primates. Minot 3 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 4 says : " Once 1 Gohre, " Dottersack und Placenta des Kalong (Pteropus edulis)," Studien iiber Enturicklungsgeschichte der Thiere, Selenka, vol. v., 1892. 2 His, Anatomie menschlicher Embryonen, I. 3 Minot, Human Embryology, Boston, 1892. * See Robinson's " Hunterian Lectures," Journ. of Anat. and Phy*., 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 lacunae, 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." -ch. FIG. 120. — Median longitudinal section of an early human ovum, 0*4 mm. in length. (From Quoin's Anatomy, Longmans. ) c.cc., embryonic ectoderm ; ch., chorion ; ec., ectoderm ; mes., mesoderm ; all., allantois ; r.s., connecting stalk ; a., 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 RETAL 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 embryo trophe. 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 lacunae. In the placental region they are also dilated, but their superficial parts are closed and appear to degenerate early. In the decidua he 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 foetal tissues, in which villi are suspended. In 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 (Bjorken- heim 1), 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. ffefte, 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 1). 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 serotinq. Sharpey supposed that the enclosure was effected by circumvallation, i.e. by a growth round the ovum of two folds of mucosal tissue, which fused and formed the decidua capsularis. But v. Spee 2 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,3 Peters,4 Bryce and Teacher, and others. At the same time it must be borne in mind that His,5 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 Early Imbedding and Development of the Human Ovum, Glasgow, 1908. 2 V. Spee, "Neue Beobachtungen iiber sehr friihe Entwicklungsstufen des raenschlichen Eies," Arch. f. Anat. u. Phys., anat. Abth., 1896. 3 V. Heukelom, " Ueber die menscblicbe Placentation," Arch. f. Anat. u. Phys., anat. Abth., 1898. * Peters, Ueber die Einbettung dea menachlichen Eies, Leipzig u. Wien, 1899. 6 His, "Die Umschliessung des menschlicben Frucht wahrend der friihesten Zeit der Schwangerschaft," Arch. f. Anat. u. Phys., anat. Abth., 1897. FCETAL 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,2 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 1 Kollmann, "Die menschlichen Eier von 6 Millimeter Grosse," Arch, f. Anat. u. Phys., anal. Abth., 1879. 1 Leopold, " Demonstration eines sehr jungen menschlichen Eies," Arbeiten aus d. Konigl. Frauenklinik in Dresden, Leipzig, 1906. 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 between them. I^ater 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. FCETAI, NUTRITION: THE PLACENTA 469 At its inner edge, and within its spaces, are numerous large mononuclear cells which are " more likely maternal " (Bryce and Teacher). Peters also mentioned the presence of many large cells, and compared them to the deciduofracts of the hedgehog. 470 THE PHYSIOLOGY OF REPRODUCTION V. Heukelom described the cellular layer outside the syncytium as foetal, and derived from Langhans' layer.1 Whatever their FIG. 123. — Section of a portion of the wall of the human blastocyst. (Bryce and Teacher.) C!/*M cyto-trophoblast ; dec., decidua ; end., endothelium of maternal capillary ; pi., plasrnodium ; nz., necrotic zone of decidua. 1 Much uncertainty still exists regarding the origin of these large cells in Man and other animals. In the mouse, Duval and Sobotta consider them f(jetal, Kolster and Disse maternal, and Jenkinson both foetal and maternal. In the guinea-pig, v. Spec states that they are fcetal. In the hedgehog they were first described by Hubrecht as maternal, and later as fu'tal. In Man, as stated above, the same doubt exists whether the trophoblast con- sists of two layers, cytoblast and plasmodiblast, or possesses a third layer composed of large cells, and forming the advance guard in attacking the uterine mucous membrane and enlarging the " Eikammer." FCETAL NUTRITION: THE PLACENTA 471 origin, the mononuclear cells in Man appear to be engaged in disintegrating mucosal tissue, and producing a zone of coagula- tion necrosis, i.e, a symplasma, around the trophoblast. But they differ from similarly situated, cells in lower animals, e.g. the mouse, in showing no evidence of ingestion of formed tissue- elements. Fici. 124. — Section of a portion of the necrotic zone of the decidua, and of the layer of large cells ou its inner aspect. (Bryce and Teacher.) nz., necrotic zone ; me., large cells in various stages of degeneration ; cav., blood- filled implantation cavity. In the youngest ova no space exists between the trophoblast and the wall of the implantation cavity (Fig. 125). In later specimens a space is formed, apparently by the absorption of the debris of the necrotic zone. How this excavation is brought about is uncertain. According to Peters, the trophoblast may exercise a phagocytic action. Bryce and Teacher, however, found 472 THE PHYSIOLOGY OF REPRODUCTION no evidence of such a process, and inclined to the opinion that the material was dissolved by an enzyme before its absorption. In the trophoblast they found that some of the vacuoles were not yet filled with maternal blood, but contained a granular coagulum which might, when liberated, have a digestive activity. In either case, the extensive proliferation of the trophoblast •;• FIG. 125. — Section through embryonic region of ovum (after Peters). (From C. Webster's Human Placentation.) E. Sch., embryonic epiblast ; Ent., embryonic hypoblast ; Mcs., mesoblast ; D.S., umbilical vesicle ; A.H., amniotic cavity ; Ekt., chorionic epiblast ; >'/'., space. appears to provide for the absorption of the necrosed tissue around it, as well as for the flow of maternal blood into its lacunae by the erosion of superficial capillaries. These two objects accomplished, the greater part of the trophoblastic pro- liferation disappears. Immediately after the excavation of the cavity the decidual formation begins. Before this stage, the changes resemble those that take place during the menstrual period. The vessels are FCETAL NUTRITION: THE PLACP^NTA 473 dilated, and blood extravasations occur between th3 cells and into the lumen. The tissue is oedematous and spongy, and the swollen cells often appear to be floating free in a fluid (v. Heukelom). These changes are especially marked near the ovum, and they give rise to an elevation which marks the resting-place of an early blastocyst. The mucosa is differentiated into a superficial layer, the compacta, and a deeper layer, the spotujiosa, in which are the enlarged middle portions of the glands, arterioles, venules, and lymphatics. In the compacta the connective tissue cells undergo active division, and they enlarge to form the decidual cells (Fig. 126). Before the excavation of the " Eikammer " they are probably not found, though Peters described the com- mencement of a decidual change before that stage. In Merttens' l ovum large decidual cells were found, many of them fusiform and lying parallel to the surface. The decidual change arises first in the connective tissue cells near the ovum, and later it ex- tends more deeply in the FIG. 126.— Condition of the glands at the beginning of pregnancy in Man (after Kundrat and Engel- niann). (From Quoin's Anatomy, Longmans.) c, compact layer near free surface of decidua: the glands are here some- what enlarged, but not very tor- tuous, and the mucous membrane is rendered compact by the hyper- trophy of the interglandular tissue; sp., spongy layer containing the middle portion of the glands greatly enlarged and tortuous, producing a spongy condition in the mucous membrane ; d, deepest portion of glands, elongated and tortuous, but not much enlarged; w.,muscularis. compacta. There is no special perivascular development as 1 Merttens, " Beitrage zur normalen und pathologischen Anatomic der menschlichen Placenta," Zeitschr. f. Qeburteh.u. Gynak., vols. xxx. and xxxi., 1894-5. 474 THE PHYSIOLOGY OF REPRODUCTION in the rabbit, and no endothelial proliferation as in the hedge- hog and bat, though the latter may occasionally occur in tubal pregnancy (Webster 1). The capillaries dilate to sinuses, and new vessels are also formed in the compacts,. Many of them are opened by the trophoblast and perhaps by the mononuclear cells, and gradually more and more blood is effused into the trophoblastic lacunae. In them it does not clot, the syncytium acting as an endothelium, but at a certain stage the blood begins to circulate and continues to do so throughout pregnancy. The gland-ducts are destroyed in the necrotic zone. In the underlying compact zone they are found dilated in the serotina and base of the reflexa, but even in Bryce and Teacher's ovum the epithelium showed signs of degeneration and desquamation. With the formation of the space between the ovum and the decidua, a permanent attachment of the two structures is brought about. The development of the villi has already been traced up to the stage when they consisted of simple stalks of mesoblast with a double ectodermal covering. In the core are developed capillary vessels which are continuous with the vessels of the " Haftstiel," and later with those of the umbilical cord. After the excavation of the necrotic zone, some of the stalks reach the decidual surface and attach the ovum to it. At first the attached ends of these primary villi are plasmodial, but later the cytoblast proliferates and forms thick rounded masses, the " Zellsaulen," over which the syncytium disappears. This forms the permanent attachment between the villi and the de- cidual surface,. The spaces between the stalks form the primary intervillous space, which is thus entirely in the plasmodiblast. The primary villi form buds of their three layers which develop into secondary villi. Of these some may also become attached to the decidua, while others hang free in the intervillous space. By a similar process other villi are also developed, till the whole system becomes branched like a tree (Fig. 127). At first they are equally distributed over the chorion, but the villi in relation to the reflexa do not branch so much, and even at the end of the 1 Webster, Human Placentation, Chicago, 1901. Wade and Watson (Journ. of Obstet. and Oynec. of Brit. Emp., 1908) also state that in tubal pregnancy some of the decidual cells are formed from endothelium. FCETAL NUTRITION: THE PLACENTA 475 first month they are fewer in number than over the serotina (Kastschenko l). When the blood-supply to the reflexa is re- duced, the villi in relation to it degenerate, and are compressed between the chorion and the apposed decidua reflexa and vera. Over the serotina they continue to branch and form the foetal 'e.g. p.s. -all. -Ent. FIG. 127. — Median longitudinal section of an embryo of 2 mm. (von Spec). (From Quain's Anatomy, Longmans.) v., villus ; c.v., core of villus; mes., mesoderm ; c.s., connecting stalk; p.s., primitive streak; all., allantois ; y.s., yolk-sac; Ent., entoderm ; ves., vessels; h., heart ; n.p., notochordal plate ; a., amnion. part of the placenta, which is essentially a mass of foetal villi between which maternal blood circulates. By the " Haftzotten " the spongy mass is attached to the decidual surface. The attached ends may excavate the decidua to some extent, but there is no great degree of penetration (Fig. 128). 1 Kastschenko, " Das menschliche Chorionepithel und desscn Rolle bei der Histogenese des Placenta," Arch.f. Anat. u. Phya., anat. Abth., 1885. 476 THE PHYSIOLOGY OF REPRODUCTION As pregnancy advances, marked degenerative changes occur in the maternal and foetal parts of the placenta. The most notable change in the villi is the gradual disappearance of the cytoblast, the mother-zone of the syncytium. Even the " Zellsaulen " tend to disappear from the tips of the villi, and their connective tissue comes in contact with the decidua. Fibrinous changes are frequent in the remnants of the cytoblast FIG. 128. — Diagram of stage in the development of the human placenta (T. H. Bryce in Quoin's Anatomy, Longmans). The " Haftzotten " are attached to the surface of the decidua. The mesodermic processes are everywhere covered by a single layer of cells (Langhans' layer) and a lamella of syncytium. b., attachment of a villus ; mes., mesoderm ; vcs.t vessels going to villi ; ay., syncytium; L.I., Langhans' layer; a., cross-section of a villus; dec., decidua ; ccr., maternal capillary. and in the mesoblast. The syncytium becomes very thin, and occasionally tracts of it are stripped off. The decidua serotina, after reaching its full development during the third month, is gradually thinned out. This may be partly due to the stretching of the tissue by the increasing growth of the uterine contents, but it would seem also to depend on conditions of malnutrition caused by the blood-stasis (Bonnet), and the choking of the lymphatics by the decidual development (Webster). The resulting degeneration takes the form of a FCETAL NUTRITION: THE PLACENTA 477 coagulation necrosis or symplasma, as shown by the " Fibrin- streifen," which are comparable to the fibrinous deposits in the rabbit's placenta. The layers of fibrin in the serotina were first described by Nitabuch.1 They may be seen as early as the sixth week, and even earlier in the reflexa (Webster). They gradually extend more deeply into the substance of the decidua, and also occur in the vessel walls. They are, however, most marked on the surface, at or near the junction of the maternal and foetal tissues. That they are due to the influence of the ovum is highly probable from their absence in the vera. Whether the symplasma is formed from the blood or the decidua, or both, is not known. It is probably absorbed by the villous ectoderm during the greater part of pregnancy. According to Webster, there may be a new formation of de- cidual tissue during pregnancy, from irregularly distributed groups of active cells which are present at all periods in the maternal part of the placenta (see p. 368). The uterine glands take no part in the formation of the placenta. By the sixth week their superficial parts are largely obliterated, and the deeper parts degenerated. At a later stage, only a few blind ends are seen next the muscular layer. Though their epithelium offers a considerable degree of resistance, and is visible for a long time, its secretory power is probably lost very early. According to Gottschalk,2 the glandular epithelium undergoes a fatty degeneration, but Bonnet 3 states that the change is a hyaline one. In the vera the glands increase in size and secrete actively for a time. Their secretion is found as a milky fluid in the uterine cavity. Glycogen. — Glycogen is present in the early stages of preg- nancy. Langhans 4 demonstrated it in the decidual cells, in the cellular proliferations of the trophoblast at the tips of the villi, and in the mesoblast. It was absent in the canalised fibrin and 1 Nitabuch, " Beitriige zur Kenntnis der menschlichen Placenta," Inaug.- Dissert., Bonn, 1887. 2 Gottschalk, " Weitere Studien viber die Entwickluug der menschlichen Placenta," Arch. f. Gynak., vol. xl., 1891. 3 Bonnet, "Ueber Syncytien," &c. , Monateschr. f. Oeburtsh. u. Oyniik., vol. xviii., 1903. 4 Langhans, " Ueber Glykogen in pathologischen Neubildungen und den menschlichen Eihiiuten," Virchow's Arch., vol. cxx., 1890. 478 THE PHYSIOLOGY OF REPRODUCTION Langhans' layer. Merttens l also found it in the decidua near the ovum. Driessen 2 states that it is present in the superficial and glandular epithelium of the uterus in the first month of pregnancy ; around the ovum " in cells of doubtful origin," glycogen is plentiful, but absent in the deeper parts of the de- cidua ; in the villi it is not found in the syncytium and Langhans' layer, but is present in the cell-islands at the tips of the villi, and occasionally in the mesoblast. The total amount is, how- ever, much smaller than in Rodents, and represents only about 0'08 per cent, by weight (Cramer 3). Fat. — Fat was first described in the human placenta by Apfelstedt and Aschoff.4 They found it during the second month of pregnancy in the syncytium and Langhans' layer, and in the decidual cells near the villi. Eden 5 found fat in the perinuclear protoplasm of the syncytium, and in Langhans' layer and the stroma of the villi. It is also present in the capillary walls (Dastre 6). The appearances suggested to Eden that " the placenta appears to be a storehouse of nutritive fat just as is the liver." Minute discrete droplets were also present in the decidual cells, and by the sixth month they had increased in number. At full time the serotina still contained fat, but "it is doubtful whether now it is a physiological deposit, as the serotina shows many degenerative changes." At the same time, a fatty degeneration of the decidua is probably pathological and not a constant phenomenon (Klein 7), and the fat globules in the early stages represent an infiltration of fat into the decidual cells from the maternal blood. From the absence of fat in the more superficial parts of the 1 Merttens, " Beitrage zur normalen und pathologischen Anatomic der menschlichen Placenta," Zeit. f. Geb. u. Gynak., vols. xxx. and xxxi., 1894-5. * Driessen, " Ueber Glykogen in der Placenta," Arch. f. Oyniik., vol. Ixxxii., 1907. s Cramer (A.), " Beitrage zur Kenntnis des Glykogens," Zeitschr. f. Biol. vol. xxiv. 4 Apfelstedt and Aschoff, " Ueber bosartige Tumoren der Chorionzotten," Arch. f. Gyndk., 1896. * Eden, "The Occurrence of Nutritive Fat in the Human Placenta," Proc. li'ifj. .S'oc., London, vol. lx., 1896. 8 See Ricbet's Dictionnaire de Physiologic, vol. vi., Article "Foetus." 7 Klein, " Entwicklung und Riickbilduug der Decidua," Zeitschr. f. Qeburtah. u. Gyndk., vol. xxii. FCETAL NUTRITION: THE PLACENTA 479 syncytium, Hofbauer l suggests that it may be split up into fatty acids and glycerine before absorption, and then re-synthesised by the foetal placenta (Fig. 129). Thence it is carried by the blood in a soluble form, and is again deposited in droplets in the heart, liver, lungs, alimentary tract, and spleen of the foetus. In the later months of pregnancy there is a considerable deposit of fat in the subcutaneous tissue. fs FIG. 129. — Fat in a villas of the human placenta. (From Hofbauer's Biologic der menschlichen Plazenta, Braumiiller.) fa., fat globules in deeper layers of syncytium ; /.*'., fat in syncytium between Langhans' cells ; fb., fat in mesoblast ; fv., fat in vacuolated cell. Iron. — In Man, Peters found evidence of the presence of red blood corpuscles in the trophoblast of the early ovum, and Ulesco-Stroganowa 2 states that they are also present in the syncytium in later stages. This has been disputed by Kworostansky 3 and Hofbauer, who maintain that the corpuscles are first dissolved. More recently Bryce and Teacher found no evidence of the ingestion cf red blood corpuscles by the tropho- blast, while Bonnet4 has shown that the syncytium gives the eosin- 1 Hofbauer, Grundzuge einer Biologic der menschlichen Plazenta, Leipzig, 1905. 2 Ulesco-Stroganowa, " Beitrage zur Lelire vom mikroskopischen Bau der Placenta," Monateschr. f. Oeburtsh. u. Qynak., vol. iii. 3 Kworostansky, " Ueber Anatomie und Pathologic der Placenta," Arch, f. Oyndk., vol. Ixx. 4 Bonnet, quoted by Hofbauer, loc. cit. 480 THE PHYSIOLOGY OF REPRODUCTION reaction of haemoglobin at the points where it comes in contact with extravasated blood. It has been stated that placental extracts produce haemolysis in vitro (Veit and Scholten 1), but whether a similar action takes place in the body is unknown. Iron-containing compounds are also found in the villi. Using the method of Hall, which demonstrates iron in loose organic compounds, Hofbauer found none such in the superficial layers of the syncytium, but an increasing number of granules were present in the deeper parts. In the mesoblast they again decreased in number, and were altogether absent near the capillary walls (Fig. 130). He suggests that at first the haemoglobin derivatives are in too firm combination to take on the stain, then they are further broken down and stained granules appear, and later they are again synthesised into non-stainable compounds which reach the foetal circulation. Such changes were char- acteristic of the first half of pregnancy. In the second half the iron-reaction of the villi was " extraordinarily slight." Iron is stored in the liver and other foetal organs. According to Bunge,2 it diminishes rapidly after birth, and he supposes that it compensates for the insufficient amount of iron contained in the mammary secretion. Albumen. — The transmission of albumen to the foetus of the rabbit has already been referred to (see p. 435). In the human placenta attention has been chiefly directed to the investigation of the decomposition products of proteins. Matthes 3 and FIG. 130.— Iron granules in a villas of the pla- centa in Man. (From Hofbauer's Bioloyie der menscfilichen Pla- zenta, Braumiiller.) 1 Veit and Scholten, "Synzytiolyse uncl Hamolyse," Zeitschr. f. Geburtsh. M. Gyndk., vol. xlix., 1903. a Bunge, " Ueber die Aufnahme des Eisens in den Organismus des Sauglings," Zeit. f. phys. Chem., vol. xvii., 1893. ' Matthes, "Ueber Autolyse der Placenta," Cenlralbl. f. Gyndk., 1901. FCETAL NUTRITION: THE PLACENTA 481 Hofbauer state that albumoses are present in the placenta, but this is doubtful. In watery extracts Rielander l demonstrated purine bases, uracil and choline, and in the autolysed placenta leucine and tyrosine have been found (Basso 2). It is generally held that such results prove an active metabolism of protein in the foetal placenta. Ferments. — Various enzymes have been investigated in the placenta. They may be grouped according to the chemical nature of the actions which they produce : — Hydrolijtic Reactions. — A proteolytic enzyme was found by Ascoli,3 and subsequently by Merletti,4 Bergell and Liepmann,5 Savare,6 and others. Bottazzi 7 states that placental tissue can transform glycogen into maltose, and a similar action is strongly produced by glycerine extracts of the maternal and foetal placenta of the rabbit (see p. 434). Savare holds that the transformation of glycogen to sugar is due to the blood ; but the fact that extracts of the ungulate placentae, which also contain blood, do not possess the same power, forces us to conclude that the enzyme activity in the rabbit and Man depends on the placental tissue. No lipolytic enzyme is present in the placenta (Charrin and Goupil 8). Oxidation Reactions. — The oxidation of aromatic aldehydes by the placenta has been obtained by Hofbauer and by Ferroni,9 not by Savare or Charrin and Goupil. V. Furth and Schneider10 state that tyrosine is oxidised by contact with the placenta, 1 Rielander, " Ein Beitrag zur Chemie der Placenta," Centralbl. f. (lyna\\, 1907. 2 Basso, " Ueber Autolyse der Placenta," Arch. f. Gynak., vol. Ixxvi. 3 Ascoli, " Passiert Eiweiss die placentare Scheidewand ? " Zeitachr. f. phys. Chemie, vol. xxxvi., 1902. 4 Merletti, " Ricercht; e studi intorno ai poteri selettivi del' epitelio dei villi coriali," Rasa. d'Oat. e. Ginec., 1903. 5 Bergell and Liepmann, "Ueber die in der Placenta enthaltenen Fermente," Miinch. med. Woch., 1905. 6 Savare, " Zur Kenntnis der Fermente der Placenta," Hofmeiatera Beitrdge, vol. ix., 1907. 7 Bottazzi, "Placental Activity," Boll, dell* R. Accod. med. Genova, vol. xviii. 8 Charrin et Goupil, " Physiologic du Placenta," Comp. Rend, de VAcad. dea Sciences ; vol. cxli., 1905 ; also vol. cxlii., 1906. 9 FeiToni, " L'eterolisi utero-placentare," Ann. di Oat. e Ginec., 1905. 10 V. Furth and Schneider, " Ueber tierische Tyrosinasen nnd ibre Bezie- hungen zur Pigmeutbildung," Hofmeiater'a Btitriige, vol. i. 2H 482 THE PHYSIOLOGY OF REPRODUCTION resulting in the production of a dark pigment, and they have suggested that this reaction may be related to the special pig- mentation of pregnancy. Removal of amino-groups from amino-acids. — Savare states that the placenta transforms the NH2 group of amino-acids into ammonia by means of a special ferment, a desamidase. Decomposition of peroxides. — This reaction may be produced by enzymes, the so-called indirect oxidases, and is sometimes regarded as the means by which oxidation changes are re- stricted to the appropriate parts of the body, and secluded, for instance, from the blood (Leathes *). The guaiacol reaction, by which a colourless solution of guaiacol becomes red, takes place, according to Charrin and Goupil, when hydrogen peroxide is present ; in other words, placental tissue decomposes the peroxide, and the nascent oxygen oxidises guaiacol. Hofbauer, however, says that the presence of hydrogen peroxide is not required, i.e. that the placenta acts as a direct oxldase. Decomposition of glucose. — No glycolytic ferment is present in the placenta.2 A few ferment actions still remain — e.g. the removal of urea from arginin, the decomposition of uric acid, and the oxidation of purine bases — which have not yet been investigated in the placenta. V. GENERAL CONSIDERATIONS OF FCETAL NUTRITION AND THE PLACENTA A. The Plan of Placental Formation The problems of foetal nutrition are not new problems. They deal with the assimilation of organic and inorganic substances, and their incorporation in the developing tissues. These phenomena are made up of a series of chemical changes which must be studied individually before we can hope to understand the final sum which constitutes foetal metabolism, or the dis- turbances which constitute fcetal disease. Set in the path 1 Leathes, Problem* in Animal Metabolism, London, 1!)07. * It cannot yet be held as proved that glycolysis by ferment action occurs at all in animals. FCETAL NUTRITION: THE PLACENTA 483 traversed by the materials on their way to the new organism is the placenta, a complex organ composed of specialised maternal elements and newly developed foetal elements. Among the Monodelphia no uniform plan is observable in the formation of the placenta, nor is it possible to trace each step in its evolution. But Duval's conception of this temporary organ as a maternal haemorrhage surrounded by foetal elements, and Hubrecht's discovery of such a type of placenta in a mammalian order which is among the most archaic, lead to a change in the ideas of placental classification. We can no longer depend on the shape of the placenta, or the characteristics of the after-birth, for an understanding of its morphological or physiological features. Rather must we go back to the phenomena to be observed in the uterine fixation of the blastocyst, and even earlier in the preparation for that fixation. At this stage we find two constant features, one maternal and the other festal. The maternal change consists of an epithelial, connective tissue or endothelial proliferation, the trophospongia, which is " specially intended for the fixation of the blastocyst." Ac- cording to Hubrecht, it degenerates into a symplasma when the fixation is accomplished and the foetal elements are in contact with circulating maternal blood. But its degeneration is not completed at that stage. Though individual cells may die, other cells are formed and take their place, at least in Man, throughout the greater part of pregnancy. Moreover, the cells have other functions to perform. Whether or not they act as a defence against the excessive penetration of the trophoblast, they continue in the rabbit to exercise the glycogenic function for the developing organism till the hepatic cells have attained the power, and there is reason to believe that they play a part in the iron metabolism of the fetus. The embryonic preparation is the proliferation of the whole or part of the extra-embryonic ectoderm, the trophoblast, in the spaces of which maternal blood circulates. The outer layer is plasmodial, and thus resembles the maternal symplasma in histological appearance, but differs from it in being a live tissue while the other is dying or dead. The fusion of the trophoblast and trophospongia constitutes the placenta, which is perfected by an increase in the number and size of the trophoblastic 484 THE PHYSIOLOGY OF REPRODUCTION lacunae, and in the amount of maternal blood in contact with it. The above description does not, however, fit the placenta of Ungulates, for in them the trophoblast is not permeated by maternal blood. If the Insectivore placenta represents the primitive type, or is nearer to it than any other at present existing, we must assume that the Ungulate placenta, differing more widely from the original type, has lost this characteristic. Further, the placenta of the pig must have undergone a greater degree of modification than that of the sheep. In other words, the old ideas of placental evolution, based on the researches of Turner and others, must be literally reversed. The Primates must stand with the Insectivores near the primitive type, while the sheep and pig are near the opposite end, where some of the Didelphia are placed. Such considerations as these must inevitably come up for discussion in all future investigations. B. The Nature of the Trophoblastic Activity During the period of gestation, the mother organism is concerned with the provision of material for the growth and development of the fertilised ovum and the new-born young. Does the material provided for the ovum, and secured for it by the trophoblast, come from the maternal tissues or from the food supply ? There is no doubt that in insufficient nutrition the foetus draws on the tissues of the mother (Jagerroos 1), and a study of comparative placentation goes far to prove that this is a normal process in some orders. It is obvious that such occurs in the earliest stages. In all orders, before fixation of the blastocyst to the uterine mucosa, the degenerating ovarian cells which surround the extruded ovum form a store of nutriment. In some animals, however, such as the opossum, in which no attachment of the blastocyst can be said to occur, and the sheep, in which the attachment is long delayed, this nutriment is added to by the secretion of the uterine glands. In the so- called Deciduate orders, fixation is effected by a phagocytic or chemical action on the part of the trophoblast, and the 1 Jagerroos, " Der Eiweiss-, Phosphor-, und Salzumsatz wahrend der Graviditat," Arch. f. Gyrak., vol. IxviL FCETAL NUTRITION: THE PLACENTA 485 destroyed maternal tissue again seems to serve as food for the blastocyst. After fixation, differences appear in the various orders. In Ruminants a special nutritive secretion, the uterine milk, is elaborated in the inter-cotyledonary areas. This secretion con- tains cellular elements of maternal tissue, particularly leucocytes and glandular epithelium, which are ingested and dissolved by the trophoblast during the whole period of gestation. In addition, extravasations of maternal blood or individual cor- puscles occur in all, and the erythrocytes are also taken up and dissolved. In such orders maternal tissue elements are normally used for the foetus throughout pregnancy. Among the Deciduata, however, with the exception of the mole, in which the glandular secretion is maintained, the maternal blood may be considered to be the only source of foetal nutriment when the allantoic or chorionic placenta is developed.1 In them the trophoblast resembles a sponge saturated with slowly circulating blood, and its large superficies is admirably adapted for the acquisition of the various materials required for the foetus. In what form do these materials exist in the blood ? Are they simply the substances absorbed from the food by way of the intestine (see also Chap. XL, p. 495), or are they more highly elaborated ? In other words, in the formation of the new organism are the syntheses carried out by the fertilised ovum itself, and it must be remembered that thia includes the trophoblast, or are the new tissue-elements trans- ferred ready-made from the mother ? The limitations of biological chemistry force us to approach this problem indirectly. Differential analyses of special constituents of the blood, as the proteins, in the non-pregnant and pregnant animal are not yet possible. In the first place, a brief consideration of the development of the chick embryo is sufficient to prove the high degree of activity vested in the ovum of birds. The special proteins and other tissue-elements are not pre-formed, but are elaborated by a series of katabolic and anabolic processes which are carried 1 The Carnivora, in which the trophoblast is not in contact with circu- lating maternal blood, occupy a special position among the Deciduata, and are not considered above. 486 THE PHYSIOLOGY OF REPRODUCTION out by the ovum itself. There is no reason to believe that the mammalian ovum, after acquiring the property of intra-uterine development, has lost its metabolic activity.1 In addition, we possess positive evidence of metabolic activity in the mammalian ovum. The results of Bohr's in- vestigations on the respiratory exchange of the foetus (see p. 436) mean nothing if they do not afford proof of this. As a large amount of energy is generated, while, at the same time, practically none is dissipated as heat evaporated or radiated from the surface or lungs, the unavoidable conclusion is that the foetus itself carries out the work of organisation, and utilises the energy for its fulfilment. When we come to consider individual substances, we obtain further evidence of activity, at least in the extra-embryonic ectoderm or trophoblast. In no order of Mammals has the transmission of haemoglobin as such from mother to foetus been demonstrated. Even if it is absorbed as such by the tropho- blast, it undergoes changes of such a nature that the iron- containing part of the molecule is less firmly bound. In all animals in which special investigations have been made, such loose organic compounds of iron have been observed. In this connection, reference may once more be made to Hofbauer's statement that the histological appearances argue not only for a decomposition of maternal haemoglobin in the syncytium, but also for a synthesis of its derivatives into organic compounds in which the iron is more firmly bound (see p. 480). The trophoblast probably acts also on simpler proteins. If ox-serum is injected into a pregnant rabbit, its proteins cannot be detected by the biological reaction in the serum of the foetus. It may be that the trophoblast rejects them altogether, but this is unlikely, since molecules of egg-albumen are absorbed and transferred to the foetus (see p. 436). In all probability the proteins of ox-serum are katabolised in the villi, and, as a result, the constitution of the precipitable substance is interfered with, and the precipitin reaction is negative. The 1 If Hubrecht's view is correct, that the mammalian ovum is older than the ovum of birds (see "Early Ontogenetic Phenomena in Mammals," Quar. Jour. Mi<-r. N( •/.. 1908), the sentence ought to read: "There is no reason to believe that the fertilised ovum of birds acquired its metabolic activities only after the loss of viviparity." FCETAL NUTRITION: THE PLACENTA 4-87 existence of an intra-cellular proteolytic enzyme l and de- composition products of the proteins in the placenta also point to the occurrence of a trophoblastic metabolism of proteins. The carbohydrates undergo changes which appear to be the result of trophoblastic activity. In the rabbit, the glycogen which is " swallowed " along with the decidual cells by the plasmodium (Chipman) is not found as glycogen. A hydrolytic transformation to sugar probably takes place (see p. 434). In addition the foetal serum contains Isevulose, which must be formed in some part of the fertilised ovum, since it is absent in the mother. Fats may also be transformed by the trophoblast (see Chap. XI., p. 512). It is generally supposed that many syntheses occur in the fertilised ovum, though direct evidence is difficult to obtain in Mammals. In the chick haemoglobin is synthesised, and the same almost certainly occurs in Man and other animals, part of the synthesis being effected by the trophoblast (see p. 480). The nucleoproteins of the foetal cotyledons in the sheep appear to be formed there, since they differ in composition from the nucleo- proteins of the cotyledonary burrs. The glycoprotein mucin is a characteristic constituent of the inter-cellular ground- substance of the whole foetal organism, and is apparently built up by the ovum.2 The chondroproteins, a special group of glycoproteins, which yield on hydrolysis proteins and the carbohydrate-containing chondroitin-sulphuric acid, are also found chiefly in the foetus as constituents of the cartilage and tendons. A consideration of these and similar facts leads us to believe that the new organism owes its development in large part to 1 The enzyme has been found only in the human placenta. It is desirable that its presence in the trophoblast should be established, and this can only be done in such animals as the sheep and rabbit, in which the foetal placenta can be detached from the maternal, and investigated separately. As was previously mentioned, the placenta contains no extra-cellular proteolytic enzyme. * In the placenta of the cow, Jenkinson has described cells resembling goblet-cells in the lining of the cotyledonary crypts, and ascribes to them a maternal origin (Proc. Zool. Soc., London, vol. i., 1906). They may supply mucin to the uterine milk, and so to the trophoblast. According to Assheton, these lining cells are trophoblastic in the sheep. 488 THE PHYSIOLOGY OF REPRODUCTION the energy generated in it and by it from the combustion of substances supplied by the mother, and to a series of active metabolic changes by means of which these substances are transformed into living protoplasm. Whether the nutritive materials are derived from the food or tissues of the mother is of secondary importance. What is essential is that the fertilised ovum obtains certain organic and inorganic compounds and a supply of oxygen to carry out its work of organisation, just as in the first period of extra-uterine life the growth and develop- ment of the new being progress by its own activities, so long as it is furnished with the proper materials. The special organ of embryonic nutrition is the trophoblast, and evidences of its katabolic activities have been described in various orders of Mammals. But in addition to procuring fixation of the blastocyst to the uterine mucosa, and absorbing and katabolising the food for itself and the embryonic portion of the ovum, it seems also to possess anabolic functions, at least in the earlier periods of pregnancy. Already developed in the blastocyst stage, it is active and functional for a con- siderable time. But in the later stages, it exhibits in all orders of Mammals a degree of morphological degeneration which is incompatible with the maintenance of its early physiological activity. It is further to be noted that its condition varies inversely with the food requirements of the embryo. When the daily requirements for the new organism are almost infinitesimal, the trophoblast is well developed. But as the daily transmission of nutriment increases, the trophoblast, which is now repre- sented by the ectodermal covering of the villi, gradually and progressively degenerates. At the end of pregnancy the cyto- blast, the mother zone of the plasmodiblast, is reduced to a few scattered groups of cells, while the plasmodial layer itself is no thicker than an endot helium, and may be altogether absent over long stretches of the villi. At this stage it is impossible to believe that the syncytium has any vital functions to perform. Indeed, we know that it has none, because the foetus, if pre- maturely born, is able to maintain life without its aid. Hence it seems likely that in the later stages the extra-embryonic ectoderm, though allowing a greater amount of material to pass to the foetus each day, acts merely as a semi-permeable FCETAL NUTRITION: THE PLACENTA 489 membrane, and has lost all, or nearly all, its physiological activity.1 What is the difference in the early stages of pregnancy, when the trophoblast is morphologically well-developed ? We believe that at that time the extra-embryonic ectoderm has less to do with the quantity, and more with the quality, of the material transferred to the new organism. It does not act merely by the physical laws of diffusion and osmosis. At this stage the cells of the ovum have not yet departed widely from a general type, and the active trophoblast would seem to spare the embryonic cells much of the work of the elaboration of the food-materials, and thus conserve their energies for their own multiplication and differentiation. As the cells gradually depart further and in different directions from the original type, each cell requires to expend less energy on its own specialisation ; at the same time the nutritive wants become more varied, and each cell requires to expend more energy on the synthesis of its individual protoplasm. As the duties of selection and anabolism are more and more taken up by the cells themselves, the trophoblast has a less important part to play, and it undergoes a gradual process of degeneration.2 1 Hofbauer's observations on the haemoglobin metabolism, already quoted (see p. 480), furnish concrete evidence of such a change in the trophoblast. In the first half of pregnancy the syncytium breaks down the maternal haemoglobin, and subsequently builds it up in part for the foetus. But in the second half, though a greater daily supply of organic iron is required for the formation of haemoglobin and other purposes (see p. 515), the amount of loosely bound iron-compounds in the villi is " extraordinarily small." The only explanation is that the larger molecules of the more firmly combined iron- compounds are not attacked and broken down so strongly by the syncytium, but are passed on to the foetal circulation. 2 A similar change occurs in the decidual cells of the rabbit. In the first periods of their existence, they synthesise and store a large quantity of glycogen. In the last week, the cells of the foetal liver assume their glyco- genic function, apparently absorbing the carbohydrate from the foetal blood as it returns from the placenta, and the decidual cells degenerate with the loss of their function. CHAPTER XI " We cannot reason with our cells, for they know so much more than we do that they cannot understand us ; but though we cannot reason with them, we can find out what they have been most accustomed to, and what therefore they are most likely to expect ; we can see that they get this, as far as it is in our power to give it them, and may then generally leave the rest to them." — SAMUEL BUTLKR. I. THE STIMULUS FOR THE MATERNAL CHANGES THE anatomical and physiological changes which occur in the maternal organism during pregnancy are manifold. They affect not only the generative system, but the body in general. They are associated with the supply of nutriment and energy for the formation of a new organism in the uterus, and the preparation for its maintenance in the succeeding period. What constitutes the original stimulus for the changes that occur in pregnancy remains still outside our ken. At least the influence of the cerebrum is not all-important, as is shown by the occurrence of normal pregnancy and lactation in women suffering from paraplegia (Brachet,2 Kruieger and Offergeld 3). Similarly, transection of the spinal cord in the lumbar region has no effect on pregnancy in the dog (Goltz 4). Further, Goltz and Ewald 5 have proved the absence of any spinal reflex influence in the dog by removing the entire lumbar cord without disturbing the onset and progress of pregnancy. Kruieger and Offergeld state, as the result of numerous experi- ments, that the central nervous system has no influence, and the 1 By James Lochhead. 2 Brachet, Recherchea, 2nd Edition, Paris, 1837. 3 Kruieger and Offurgeld, "Der Vorgang von Zeugung, Schwanger- schaft," &c., Arch.f. Oyndk., vol. Ixxxiii., 1908. 4 Goltz, " Ueber den Einfluss des Nervensystems auf die Vorgiinge wahrend der Schwangerschaft," &c., PJtiiger'a Arch., vol. ix., 1874. * Goltz and Ewald, " Der Hund mit verkiirztem Riickenmark," Pfliiger'a Arch., vol. IxiiL, 1896. 490 CHANGES IN THE MATERNAL ORGANISM 491 sympathetic system has an effect only in so far as it modifies the circulatory conditions. The only change observed, after destruction of the lumbar cord, was a prolongation of the act of parturition, due to an absence of pain and the consequent loss of the reflex contractions of the abdominal muscles. The most important nervous elements for the uterus are contained in the uterine, paracervical, and paravaginal ganglia, but their excitability for external stimuli gradually decreases during pregnancy and is lost at the end. We are thus forced to conclude that the phenomena of pregnancy and parturition are brought about by chemical stimuli acting through the blood-stream. The hormone or hormones may arise in the corpus luteum, which is essential for the progress of pregnancy, at least in the early stages (Marshall and Jolly *). Evidence is also forthcoming that the mammary secretion is due to an ovarian influence in certain cases. For instance, secretion may occur in virgin women who are the subjects of ovarian tumours, and in virgin bitches. Cramer 2 has recorded a case in which the transplantation of ovaries into a woman, whose genital organs were much atrophied, led to a secre- tion of colostrum.3 On the other hand, removal of the ovaries at the middle of pregnancy does not interfere with the second half of the period of gestation, or with labour and lactation.1 The presence of the placenta may modify the normal meta- bolism in various ways. It is set in the path traversed by the formative material on its way to the embryo, and by the waste products excreted by the embryo. The form in which the materials required by the product of conception reach the placenta is still obscure. The protein may be merely the " circulating protein " found in the non-pregnant condition, or more highly elaborated. The diffusion of the blood-sugar to the foetus is disputable,4 and the form of the fats is unknown. Of the waste products carbonic acid, which, according to Bohr,5 1 Marshall and Jolly, "The Ovary as an Organ of Internal Secretion," Phil. Trans., Roy. Soc., London, B., vol. cxcviii., 1905. 2 Cramer (H.), "Transplantation menschlicher Ovarien," Munch, med. Woch., 1906. 3 With regard to the existence of an ovarian stimulus, see also Hilde- brandt (Hofmeister's Beitrage, vol. v., 1904). * See Chap. X., p. 434. 5 Bohr, " Der respiratorische Stoffwechsel des Saugetierembryo," Skand. Arch. d. Phya., vol. x., 1900 ; also vol. xv., 1904. 492 THE PHYSIOLOGY OF REPRODUCTION results entirely from the combustion of carbohydrates in the mammalian foetus, is excreted into the maternal circulation through the placenta. With regard to a wastage in the protein metabolism, a certain loss is bound to occur in the transforma- tion of " circulating " or " fixed " maternal proteins into foetal tissue proteins ; and in addition, incompletely oxidised substances may possibly be transmitted to the placenta and oxidised there or in the mother (Bohr *). The question of urea formation by the foetal liver or the trophoblast is still uninvestigated, and no proof exists of the excretion of urea otherwise than into the liquor amnii. Nor does its presence in the amniotic fluid necessitate an oxidation of protein ; it may be split off, as in the adult, by a simple hydrolytic cleavage. At present we must be content with assuming the possibility of modifications in the maternal blood from the presence of fcetal nutritive and waste materials. Hitherto the investigations have been largely con- fined to human pregnancies, in which individual differences are at a maximum, and the application of the experimental method is restricted. Hence our knowledge of the chemical changes in the blood is very limited. Its composition may, in addition, be modified by the activities of the placenta itself. Several theories have been put forward in support of the view that this organ acts as an internally secreting gland. Nattan- Larrier 2 goes so far as to state that the secretion can be demonstrated in the form of globules, lying on the surface of the villi, but these arise in the post-mortem degeneration of the tissue. Of the same nature are the products of the placenta, which have a blood-pressure raising action. Extracts of the fresh organ have no pressor effects, nor do they increase uterine contractions.3 Halban 4 considers that the placenta secretes a hormone which stimulates the growth of the mam- mary gland and the secretion oi milk. Starling 5 states, on the 1 Bohr, see Nagel's Handbuch der Physiologic, " Respiration," vol. i., H. i. 2 Nattan-Larrier, "Fonction Secretaire du Placenta," Comp. Rend. Soc. I'.i'iL. vol. lii., 1900. s gee foot-note 2, p. 522. 4 Halban, "Die innere Secretion von Ovarium nnd Placenta, und ihre Bedeutung fur die Function der Milchdriise," Arch. f. Gyndk., vol. Ixxv., 1905. 5 Starling, "Chemical Correlations of the Functions of the Body," Croonian Led., Lancet, 1905. CHANGES IN THE MATERNAL ORGANISM 493 other hand, that the hormone is contained in the tissues of the fetus.1 By its activity during pregnancy, it leads to a pro- liferation of the mammary tissue, while the cessation of the stimulus after parturition brings on the secretion of milk. According to Liepmann,2 the maternal blood contains a special protein, elaborated by the placenta, which may be re- cognised by the biological reaction, and Freund 3 states that the precipitable substance is present in the urine of pregnant women. Others have been unable to find such a substance either in the blood or urine (see Weichardt and Opitz 4). Veit's 5 theory is also sub judice. Taking up Schmorl's 6 discovery that emboli of placental cells may be found in organs of the mother in eclampsia, he extends it to normal pregnancy, and postulates that syncytial fragments and even whole villi pass regularly into the maternal circulation. There they give rise to an anti-body, a syncytiolysin 'which itself dissolves the circulating syncytium. He also seeks to explain, by the activity of the lysin, the absorption of haemoglobin and other proteins from the inter villous space by the villi, the pigmentation of the skin and Vaginal mucous membrane from superficial emboli, and the phenomena of telegony from the circulation of elements derived in part from the paternal side.7 1 It is conceivable that both views are right, since the main mass of the placenta is as much a part of the fertilised ovum as the fcrtus itself. In future investigations, the better recognition of the composite structure of the placenta is desirable. In many animals it is possible to separate the maternal and fcetal tissues with considerable accuracy, and any effect ob- tained from one or other part can be definitely ascribed to the modified uterine mucous membrane, or to the extra-embryonic part of the ovum. 2 Liepmann, " Ueber ein fiir monsehliche Plazenta spezifisches Serum," Dent. med. Woch., 1902, 1903. 3 Freund, " Beitrage zur Biologic der Schwangerschaft," Vortr. aiif. vulose 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 l), 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 Isevo-rotatory. The glycogen store of the liver is stated to be increased in pregnancy in the dog (Burlando 3), in the guinea-pig (Maurel 4), and in the human female (Charrin and Guillemont 5). 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.6 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 Giirber and Griinbaum, " Ueber das Vorkommcn von Lavulose im Fruchtwasser," Munch, 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 laevulose rests on the laevo-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, " DCS ddpenses albuminoides pendant la grosscsse chez le cobaye," Comp. Rend. Soc. Biol., vol. Ixi., 1907. 5 Charrin and Guillemont, " Physiologic pathologique de la Grossesse," Comp. Rend. Soc. de BioL, 1899. • Gierke, "Glycogen in der Morphologic des Zellstoffwechsels," Habili- tationaschrift, 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 Foetus. — 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 : — Day of Gestation. Average Weight of each Foetus in Grammes. Average Amount of Glycogen per Foetus. Number of Foetuses. Total Amount of Glycogen. 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 7 •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 TABLE to show the foetal weight and amount of foetal 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 T2 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 O02 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, T362 grm. are required for combustion each day. In 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 T662 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 l was the first to postulate the occurrence of a " physiological glycosuria " in pregnancy. Kirsten 2 found sugar in the urine in the majority of cases of pregnancy and labour, and regularly in the puerperium. Hofmeister 3 first discussed the relationship of the glycosuria to milk secre- tion, and proved that the sugar excreted in the puerperium was lactose.4 The sugar is in extremely small amounts, but above the normal. Lemaire 5 found 0*003 to 0'009 per cent., and Brocard 6 an upper limit of O'Ol per cent. Zacharjewsky,7 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.8 Extirpation of the mammary glands immediately stops the lactosuria,9 and, if carried out in pregnancy, prevents it.10 1 Blot, " De la glycosurie physiologique chez les femmes en couches," Ac., Comp. Rend. Soc. Biol., vol. xliii., 1856. * Kirsten, '• Ueber das Vorkommen von Zucker im Harn der Schwangeren," Monatsachr. f. Qeburtsh. u. Frauenkrankh., vol. ix., 1857. 3 Hofmeister, " Ueber Laktosurie," Zeitschr.f. phys. Chem., vol. i., 1877. 4 Corroborated by Kaltenbach (" Die Laktosurie der Wochnerinnen," Zeitschr. f. Qeburtsh. u. Gynak., vol. iv.) and many others. 8 Lemaire, " Ueber das Vorkommen von Milchzucker," Zeitschr. f. phys. Chem., vol. xxi., 1895. * Brocard, " La Glycosurie de la Grossesse," Thise 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. Iviii., 1897). * Sinely, " 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.2 He frequently observed it after the administration of 100 grm. of glucose. On the other hand, Payer's 3 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 4), the neutral fats, fatty acids, cholesterin, and soaps contained in the faeces 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 5). b. Fat of the Maternal Organism. — According to Miotti,6 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 alimentare Glykosurie bei Graviden," Wien. med. Preaae, 1895. 3 Payer, " Einfluss des Zuckers auf den Stoff wechsel der Schwangeren," Monatsechr. f. Qeburtah. u. Gyniik., vol. x 4 Ferroni, " I grassi neutri . . . delle gravide e delle puerpere sane," Ann. di Oat. e Qinec., 1905. 6 Capaldi, "Sal contenuto di grasso del sangue nella gravidanza e nel puerperio," Ann. di Oat. e Qinec., 1905. 6 Miotti, "Contribute allo studio istologico de fegato durante la gravi- danza," Ann. di Oat. e Qinec., 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 Foetus. — 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 l 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 Fatal 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 3 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 4 agree with this. He administered coco-nut oil 5 to three pregnant guinea-pigs, and demon- 1 Fehling, " Beitrage zur Physiologic des placentaren Stoffverkehrs," Arch.f. Gyndk., vol. xi., 1877. 2 Thiemich, " Ueber die Herkunft des fotalen Fettes, Centralbl. f. Phys., vol. xii., 1898. 3 Oshima, " Ueber das Vorkommen von ultra-mikroscopischen Teilchen im fotalen Blute," Centralbl. f. Phys., vol. xxi., 1907. 4 Hofbauer, Biologie der menschlichen Plazenta, Wien and Leipzig, 1905. 8 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 fcetal life ; but its significance is not obvious if, as Bohr states, it is not a source of energy. Guillot l 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 fcetal 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 2). 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 maybe excreted.3 That acetonuria exists in pregnancy is certain, but in the majority of cases it does not pass the physiological limit (Stolz 4). 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,5 leading to a lowered oxidation of fats by the 1 Guillot, quoted in Richet's Dictionnaire dt Physiologie, Article " Foetus." 2 Kraus, quoted in v. Winckel's Handbuch der Qeburtehillfe, vol. i., H. 1. 3 See v. Noorden, loc. cit., vol. i. 4 Stolz, "Die Acetonurie in der Schwangerschaft," Arch. f. Oyndk., vol. Ixv. 5 Wolfe ("The Chemistry of Toxaemias 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) l 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 2 and of fever (Regnard 3 and Geppert 4), 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 (Hugounenq 5). a. Iron, — Part at least of the iron for the foetus is derived from the haemoglobin of the maternal organism.6 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-Anaesthetic Acetonuria," Brit. Med. Journ., 1906. * Beesly and Milne, unpublished paper. 3 Regnard, Combustion* respiratoires, 1879. * Geppert, "Die Gase des arteriellen Blutes im Fieber," Zeitschr. f. klin. Med,, vol. ii. 5 Hugonnenq, "Recherches sur la statique des 61ements mineraux et purticulierement du fer chez le fcetus 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.1 But in all placentae yet investigated, iron-containing granules have been observed in the trophoblast. The possible sources are haemoglobin, 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 haemoglobin in the developing chick. It is also known that in the adult organism nucleoprotein is a better source of iron for haemoglobin than any inorganic or other organic compound hitherto ad- ministered by the mouth.3 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.4 With regard to the reserve iron of the mother, it is stated by Charrin 5 that the store in the spleen is reduced during pregnancy. In the foetus iron is required for the synthesis of haemoglobin (see p. 480) and nucleoproteins.6 Large amounts of iron are also stored in the liver and other organs. According to Bunge's 7 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,8 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. 6 Charrin, " Physiologie pathologique de la grossesse," Comp. Rend. Soc. de Biol., 1899. 6 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 Anfnahme des Eisens in den Organismus des Sauglings," Zeitschr. f. phya. Chem., vols. xvi. and xvii., 1892-3. 8 Veit and Scholten, " Synzytiolyse and Haemolyse," Zeitschr. f. Qeburteh. u. Oyndk., vol. xlix. 516 THE PHYSIOLOGY OF REPRODUCTION cytes can be produced by placet! tal extracts. As a result of this, hsemoglobinaemia may occur in pregnancy. Wychgel l 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 2 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 ah1 stages of degeneration, clumping and solution." So Hofbauer found, by adding neutral-red to the chorionic villi of two fresh two-months' placentae teased in saline, that many of the blood corpuscles showed red dots indicating degeneration. b. Calcium. — The source of the foetal calcium is still un- settled. According to Drennan,3 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 4 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,5 Schrader 6). Jagerroos,5 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, " Untersnchungen iiber das Pigment der Haufc und dor Urin wiihrend der Schwangerschaft," Zcits. f. Oeburtsh. u. Qyndk., vol. xlvii. 2 Bonnet, quoted by Hofbauer (Biologic der menscMichen Plazenta, Wien und Leipzig, 1905). 3 Drennan, " The Abstraction of Calcium Salts from the Mother's Blood by the Fretus," New York Medic. Journ., vol. Ixxxvii. * Terrier, " DC 1'Influence de la Grossessc sur les Dents," Th&se de Paris, 1899. 5 V. Eeke, Jagerroos ; see pp. 500 and 501 for references. 6 Schrader, "Stoffwechsel wahrend der Schwangerschaft," Arch. f. Oyndk., 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 1). Repeated investigations have been carried out since the discovery that a retention of chlorides may occur in nephritis and lead to oedema (Widal 2). Biancardi 3 stated that osdemas in pregnancy were sometimes due to the same cause, and might be cured by decreasing the chlorides of the food. Next Cramer 4 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 (Siemens 5). 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 6 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 01740 per cent, and 0-1775 per cent, in two cases, and 0*1733 per cent, in a non-pregnant woman. G. Respiratory Excfiange 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 do dechloruration dans le mal dc Bright," Arch. Gener., vol. cxciii., 1904. 3 Biancardi, "Sulla cura dcclorurante nelle nefriti e nolle albuminurie ncl campo ostetrico," Ann. di Oet. e Ginec., 1905. * Cramer, "Chlornatrium-Entziehung bei Hydrops Graviditatis," Monals- schriftf. Geburtsh. u. Gyndk., vol. xxiii. s Siemens, "Metabolism during Pregnancy, Labour, and Puerperium," Johns Hopkins Hosp. Rep., vol. xii., 1904. 6 Birnbaum, " Excretion of Chlorides during Pregnancy," Arch. f. Gyndk., vol. Ixxxiii., 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, Bohr2 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 3). 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.4 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, and die Atmung beira Saugetierf otus, " Pfluger's Arch., vol. xxxiv., 1884. 2 Bohr, "Der Respiratorische Stoffwechsel des Saugetierembryos," Skand. Arch.f. Phys., vol. x., 15100. 3 Mnrlin, "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 foetal 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 placentae 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 1). 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,2 F. Muller,3 and E. Zuntz 4 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,5 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 108'4 to 111 '4 kilo, and the oxygen intake from 302 to 320 c.cm. per minute, i.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.6 1 Bohr, Nagel's Handbuch der Physiologic, " Respiration." 2 Magnus-Levy, " Stoffwechsel und Nahrungsbedarf in der Schwanger- schaft," Vortrag, Zeilschr. f. Geburhh. u. Oyndk., vol. lii. ; also v. Noorden, loc. cit., vol. i. 3 F. Muller, " Diskussion zura Vortrag von Magnus-Levy," see v. Noorden, loc. cit., vol. i. * E. Zuntz, " Der Stoffaustausch zwischen Mutter und Frucht," Ergebn. d. Phya., 1908. 5 The older investigations of Oddi and Vicarelli (" Influence do la gros- sesse sur 1'echange 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. 6 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. ]{., 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 III. THE CHANGES IN THE MATERNAL TISSUES DURING PREGNANCY The changes in the ovaries, the mammae, 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,2 Dubner,3 Bernhard 4 and others in Man, by Spiegelberg and Gscheidlen 5 in the dog, and by Cohnstein 6 in the sheep. Their investi- gations have upset the older theory of a hydrsemia of pregnancy. There is evidence of a slight increase of haemoglobin (Payer,7 Fehling,8 Winckelmann,9 Wild 10), 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,11 LebedefT,12 Rieder 1S). The leucocytosis is referred by some to 1 Ehrlich, " Die Anamien," in Nothnagel's Spezielle Pathologic. 2 Ingerslev, " Ueber die Menge der roten Blutkorperchen bei Schwangeren," Centralbl.f. Oyndk., 1879. 3 Dubner, " Untersuchungen iiber den Hamoglobingehalt des Blutes," &c., Munch, med. Woch., 1890. 4 Bernhard, " Untersuchungen iiber Hamoglobingehalt und Blutkorper- chenzahl in der letzten Zeit der Schwangerschaft," Munch, med. Woch., 1892. 6 Spiegelberg and Gscheidlen, " Untersuchungen iiber die Blutmenge trachtiger Hunde," Arch. f. Gsburtsh. u. Oyndk., vol. iv. • Cohnstein," Blutveranderungen wahrendderSchwangerschaft,"P/?fl<7er'« Arch., vol. xxxiv., 1884. 7 Payer, vide v. Winckel's Handbuch der Ocburtehiilfe , vol. i., H. 1. 8 Fehling, " Ueber Blutbeschaffenheit," &c., Arch. f. Oyndk., vol. xxviii., 1886. • Winckelmann, " Hamoglobin-Bestimmungen bei Schwangeren und Wochnerinnen, Inaug. Dies., Heidelberg, 1888. 10 Wild, " Untersuchungen iiber den Hamoglobingehalt und die Anzahl der roten und weissen Blutkorperchen bei Schwangeren," Arch. f. Oyndk., vol. liii. 11 Nasse, Das Blut, Bonn, 1836. 12 Lebedeff, quoted in v. Winckel's Handbuchder Oeburtshulfe., vol. i., H. 1. 11 Rieder, Beitrage zur Kenntnis der Lcukocytose und verwandter Zu- atande dee 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 1). 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. 6. 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 (Engstrom 2), 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 3). 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 Graviditat auf die Blutalkalesccnz," Arch. f. Gynak., vol. lix., 1899. 2 Engstrom, " L'Influence de la grossessc sur la circulation," Arch, de Oyn., 1886, vol. ii. 3 Heinricius, Experimentclle und klinische Untersuchungen iiber CircuUt- tionsverha.lt/en der Mutter und der Frucht, Hclsingfors, 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.2 In excess it may cause anuria and eclampsia (Nicholson 3). 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 4), which consists of a simple hypertrophy, and not a vascular engorgement or cystic change (Freund 5). It has been shown experimentally in cats that a 1 V. Winckel, toe. cit., vol. i., H. 1. This has been clearly established by radiograms of the thorax in pregnancy. - 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 Phye., 1909). 3 Nicholson, "The Maternal Heart in Pregnancy," Brit. Med. Journ., 1904, part ii. 4 Tait, " Enlargement of the Thyroid Body in Pregnancy," Obstet. Journ., 1875. » Freund, " Ueber die Beziehung der Schilddriise," &c., Deute. Zeitechr. 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 1). 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 2). 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 3). 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 haemorrhage.4 Jeannin 5 first suggested that it was derived from haemoglobin set free by the solution of red blood corpuscles. According to Veit 8 the haemolysis may be produced by the circulation of syncytial elements in the blood. The presence of iron in the pigment, though strongly denied by Truzzi,7 has recently been demonstrated by Wychgel.8 He associates its presence with the frequent occurrence of hsemoglobinuria in pregnancy. V. Fiirth 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 Beziehnngen der Schilddriise zur Schwangerschaft," Zeitschr. f. Geburtsh. u. Gyndk., vol. xl., 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. Zeitschr., vol. xii., 1908. 4 See v. Winckel's Handbuch der Oeburtshulfe, vol. i. H. 1. 5 Jeannin, "Observations pour servir ii 1'histoire du masque des femmes enceintes," Qaz. Hebdom., 1868. 8 Veit and Scholten, " Synzytiolyse und Hamolyse," Zeitschr. f. Qcburtsh. u. Gyndk., vol. xlix., 1903. 7 Truzzi, " Ueber die Genese der Hyperchromie der Haut in der Gravi- ditat," Monatsschr. f. Oeburtsh., vol. xi., 1898. 8 Wychgel, " Untersuchungen iiber das Pigment der Hant und den Urin wahrend der Schwangerschaft," Zeitschr. f. Oeburtsh. u. Qanak., vol. xlvii. 524 THE PHYSIOLOGY OF REPRODUCTION is occasionally seen in pregnancy (Slocum,1 Halban 2). Under the name of dermographismus, Freund 3 describes a phenomenon, often met with in pregnancy, similar to the tache cdrtbrale 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 Mammce. — The 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.4 Even in the first half of pregnancy, and sometimes in the first weeks, the mammae 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 5). 1 Slocum, " Hair Development in Pregnancy," New York Med. Rec., 1875. * Halban, " Zur Frage der Graviditatshypertrichose," Wien. klin. Woch., 1907. 3 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," Zeitschr.f. phys. Chem., vol. xlvii., 1906. CHARTER 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 BUTLEH. 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. THE INNERVATION OF THE EXTERNAL GENERATIVE ORGANS The external generative organs in the female are similarly innervated to those of the male (p. 254 et seq.). Langley and Anderson l 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,2 and subsequently Langley and Anderson,3 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. ofPhya., vol. xii., 1891. 3 Langley and Anderson, loc. cit. 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. THE 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.1 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.2 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," Zeitftchr. f. Oeburt. u. Oyndk,, vol. xxiv., 1892. Gawronsky, " Ueber Verbreitung und Endigungen der Nerven in den weiblichen Geni- t.-ilii'M," Arch. f. Q /rtiik., vol. xlvii., 1894. Kallius, " Nervendigungen in Driisen d. Eierstocke," Merkel and Bonnet's Ergeb. d. Anat. u. Entwick., vol. iv., 1895. Mandl, " Ueber Anordnung und Endigungsweise der Nerven im Ovarium," Arch. f. Oyndk., vol. xlviii., 1894-5. Vallet, " Nerfs d'Ovarie," &c., Thesis, Paris, 1900. Abel and Mcllroy, " 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 THE 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 l 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,2 Kurdinowski,3 Franz,4 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,5 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 1 Kehrer, " Zusammenziebungen der glatten Genitalmuskelatur," Ac., Beitrdge zur Vergl. u. Exper. Qeburtskunde, 18(57. 1 Helme, " Contributions to the Physiology of the Uterus and the Phy- siological Action of Drugs upon it," RejwrtB of the. Laboratory of the Royal College of Physicians, Edinburgh, vol. iii., 1891. 3 Kurdinowski, " Physiologische und pharmakologische Verauchc an der isolirten Gebiirmutter," Arch. f. Anat. u. Phy*., phy*. Abth. (supplement) 1904. 4 Franz, "Studien zur Physiologic des Uterus," Zeitschr. f. Oeburt. u. Gt/nak., vol. liii., 1904. 5 Cushny, " On the Movements of the Uterus," Jour, of Phya., 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 l showed that irritation of the spinal cord in the lumbar region excited the uterus to contract, and later investigators have obtained similar results.2 Rohrig 3 showed that asphyxia which may bring about uterine contractions (and abortion in the preg- nant condition) cannot do so if the lumbar cord is destroyed. Frankenhauser 4 and Korner 5 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, Anatomic Compare" du Cervea, 1824. 1 Budge, " Ueber das Centrum genitospinalc des Nervns sympatheticus," Virchow's Arckiv, vol. xv., 1858. Riemann, "Einige Eemerkungen iiber die Innervation der Gebarmutter," Arch.f. Gynak., vol. ii., 1871. 3 Rohrig, " Experimentelle Untersuchungen iiber die Physiologic der Uterusbewegung," Virchow's Archiv, vol. Ixxvi., 1879. 4 Frankenhauser, " Die Bewegungsnerven der Gebarmntter," Jenaische Zeitachr. f. Meet., vol. i., 1864. 8 Korner, Studien d. Phye. Institute zu Breslau, 1865. THE FEMALE GENERATIVE ORGANS 529 the aortic plexus, made their way to the uterus. Langley i 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 2 showed that stimulation of the second, third, fourth, and fifth lumbar nerves (iri 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 3 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 (tetamis 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. 2 Langley and Anderson, loc. cit. 8 Keiffer, Recherches sur la Physiologic de V Uterus, 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.1 Fellner 2 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 3 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 4 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 (toe. cit.). See also Dale, " On Some Physiological Actions of Ergot," Jour, of Phya., 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. Qyntik., vol. xiii., 1878), who found that hot water caused increased contraction followed by paralysis, while cold water pro- duced tetanus. Helme (toe. 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 anaemia had no effect. 2 Fellner, " Ueber die Bewegungen und Hemmungsnerven des Uterus," Arch.f. Qyntik., vol. Ixxx., 1906. Labhardt (" Das Verhalten der Nerven in der Substanz des Uterus," Arch.f. Qyntik., vol. Ixxx., 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'Obatet , 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. 3 Dembo, " Zur Frage iiber die Unabhangigkeit 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 Phya. Geeell. zu Berlin, Anat. f. Anat. u. Phya., phya. 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 l 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- 1 Kurdinowski, " Ueber die Reflectorische Wecbsel beziehung zwischen der Briistdriisen und dem Uterns," Arch. f. Qyniik., vol. Ixxxi., 1907. 532 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 " labour 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.1 Polaillon 8 and Schutz 3 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 4 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 6 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. 2 Polaillon, Recherches sur la Physiologic de V Uterus Gravide, Paris, 1880. 3 Schutz, " Ueber die Formen der Wehenerven und iiber die Peristaltik des Menschlichen Uterus," Arch. f. Gyru'ik., vol. xxvii., 1886. * Williams, loc. tit, 6 Schutz, " Ueber die Entwickelung der Kraft des Uterus in Verlaufe der Geburt," Verhandl. d. Deutsch. Qeae.ll. fur Gyncik., 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,1 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, toe. cit. Galabin, Manual of Midwifery, 6th Edition, London, 1904, and the other text-books on the subject. Sec also Sellheim, " Die Physiologic der Weiblichen Geschlechtsorgane," Nagcl's Handbuch der Physiologic 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 defsecation. 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 haemorrhage, 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 (i.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, foe. 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 fnetus. The os is dilated by the membranes, which have not yet ruptured. (After Franck. From Smith's Veterinary Physiology, Bailliere, 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- THK 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 foetal 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.1 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 Physiolcgy, Bailliere, 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.2 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., 3rd Series, vol. vii., 1896. * Brumpt. " Parturition chez le Rat blanc," Butt. Soc. Zool., France, vol. xxxii., 1907. The loosening of the placenta and other changes in Tupaia are described by van Herwerden, " Die puerperalen Vorgiinge 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) l 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 2 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 3 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,4 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. Qyncik., vol. ii., 1871. 3 Rein, " Beitrag zur Lehre von der Innervation des Uterus," PJHi>i>-r'x Archiv, vol. xxiii. •» Oser and Schlesinger, " Experimentelle Untersuchungen iiber Uterus- bewegungen," Strieker's Med. Jahrbticher, 1872. 538 THE PHYSIOLOGY OF REPRODUCTION could have been made complete without interfering with the blood supply to that organ. More recently, Goltz and Ewald l 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 2 have also shown that parturition is possible after destruction of the cord. Goltz had already shown 3 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 4 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,5 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 rait verkiirztem Riickenmark," Pjliiger's Archiv, vol. Ixiii., 1896. 2 Kruiger and Offergeld, " Der Vorgang von Zeugung, Schwangerschaft, Geburt, und Wochenbett an der ausgeschalteten Gebarmutter," Arch. f. Qyniik., vol. Ixxxiii., 1908. 3 Goltz, " Ueber den Einfluss des Nervensystems auf die Vorgange wahrend der Schwangerschaft und des Gebarakts," Pfluyer'a Archiv, vol. ix,, 1874. 4 Routh, "Parturition during Paraplegia," Trans. Obatet. Soc., Lond., vol. xxxix., 1898. * 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.1 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.2 CHANGES IN THE MATERNAL ORGANISM The influence of parturition upon the metabolism of the maternal organism is dealt with by Sellheim.3 There is a i 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. * For further references to the literature of the nervous mechanism of parturition, see Bechterew, Die Funktionen der Nerveneentra, Weinberg's German translation, vol. i., Jena, 1908. 3 Sellheim, toe. tit. 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 thirty- 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 l 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 2 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. 1 Williams, loc. tit. 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,1 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 a£ 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- Sequard,3 Keiffer,4 and others, that uterine contractions can be induced experimentally by this means. i Keilmann, " Znr Klarung der Cervixfrage," Zeitschr f. Oeb. H. vol. xxii., 1891. * Simpson, loc. tit. 3 Brown-Sequard, Experimental Researched, English translation, London, 1853. * Keiffer, loc. cit. 542 THE PHYSIOLOGY OF REPRODUCTION (7) Spiegelberg l 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 insuffi- 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,2 Minot,3 Beard 4 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," Lehrbuchder Qeburtshulfe, vol. ii. 1891. 1 Tyler Smith, Parturition and the Principles and Practice of Obstetrics, London, 1849. 3 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,2 have laid some stress upon the belief that parturition occurs in women at a tima 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,3 and also Williams, have pointed out " that the frequent occurrence of infarct formation [i.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 laeve 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 anoestrous period. * Geyl, "Ueber die Ursache des Geburtseintrittes," Arch. f. Oynak., vol. xvii., 1881. 3 Eden, " A Study of the Human Placenta," Jour, of Path, and Bacterial., vol. iv., 1897. 4 Williams, loc. tit. 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 l 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 (i.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 l 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-Gdring,3 and appear to be not uncommon. No satisfactory reason has been sug- gested to account for such cases. According to Pinard 4 prolonged gestation may occur in Rodents (Dipodillus simoni, 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. THE 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 1 Allen (L. M.), "Prolonged Gestation," Amer. Jour, of Obntct., vol. lv., 1907. 2 Tessier, "Recberches sur la Dur6e de la Gestation," &c., Mim. de VAcad. des Sciences, Paris, 1817. :| Franck-Albrecht-Goring, " Die Trachtigkeitsdauer," Thieriirztliche Oe- burtshulfe, vol. iv., 1901. ••Pinard, Article "Gestation," Ricbet's LHctionnaire de Physiologic, 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 haemorrhage 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.1 It follows from what has been said that multiparous women are more liable to post-partum haemorrhage than primiparous ones.2 According to Longridge the anaemic 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 Caesarian 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 Puerperium, London, 1906. 2 Longridge has pointed out, however, that the amount of post-partum discharge in multipane 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 multipart 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 hsematin. 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.2 The average quantity of the discharge has been computed by Gassner 3 at 1485 cubic centimetres, or about 50 ounces. Giles 4 estimated it as 10| ounces (or considerably less than Gassner's 1 Brock (I'ractitioner, January 1908) has recently expressed the opinion that puerperal bleeding is chiefly venous, pointing out that the discharge is usually very dark in colour. 2 Kronig, Bakteriologie des Genttalkanaleg, &c.. Leipzig, 1907. 3 Gassner, "Ueber die Veranderungen des Korpergewichtes bei Schwang- eren, Gebarenden, und Wochnerinnen," Monatsschr. f. Qeburtskunde , 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,2 Kundrat and Engelmann,3 I^eopold,4 Kronig,5 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 Physiologic den Menschen, vol. ii., Braunschweig, 1906, where further references are given. 2 Friedlander, Physiologische und Anatomische Untersuchungen iiber den Uterus, Leipzig, 1870. s Kundrat and Engelmann, " Untersuchungen iiber die Uterusschleim- haut," Strieker's Med. Jahrbuch, 1873. * Leopold, Studien iiber die Uterusschleimhaut, &c., Berlin, 1878. » Kronig, " Beitrag zum anatomischen Verhalten der Schleimbaut der Cervix und des Uterus," &c., Arch. f. Oyndk., vol. Ixiii., 1901. THE FEMALE GENERATIVE ORGANS 549 and others.1 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.2 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.3 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 syncy tial 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., Zeitschr. f. Oeb. und Qynhk., vol. xxxvi., 1897). - According to Longridge (see below in the text), thrombosis is of little or no importance in assisting the hzemostasis of normal labour. 3 Williams (Sir J.), "Changes in the Uterus," &c., Tran*. Obstct. Soc., vol. xx., 1878. See also Helme, "Histological Observations," &c., Trans. Roy. Soc. Edin., vol. xxxv., 1890. 550 THE PHYSIOLOGY OF REPRODUCTION FIG. 133.— Virginal exter- nal os (human). (From Williams' Obstetrics, Appleton & Co. ) After a first delivery its outlet remains permanently wider than before. The rugae reappear about the third week. The place of the hymen is taken by numerous small tags of tissue which become transformed into the carunculae 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 in the next chapter. The quantity of urine passed during the first two days of the puerperium is 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 l (see also p. 507). As mentioned above, a marked leuco- cytosis occurs during labour. According to Hofbauer,2 this becomes still more pronounced during the first twelve hours of the puerperium, after which the number of leucocytes in the blood falls again and in a short time becomes normal. Henderson 3 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 1 Scholten, "Ueber Puerperale Acetonurie," Hegar's Beitrriye ~ur Ocb. und Oynak., vol. iii., 1900. * Hofbauer, "Zur Physiologic des Puerperiums," Monatsachr. /. Oeburt. und Oi/nak., vol. v., 1897. 3 Henderson, " Observations on the Maternal Blood at Term and during the Puerperium," Jour, of Obstet. and Gyncec., vol. i., 1902. FIG. 134. — Parous exter- nal os (human). (From Williams' Obstetrics, Appleton & Co.) 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 haemoglobin 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.1 The pulse rate during the early days of the puerperium is usually stated to be somewhat below the normal, but according to Longridge such cages are unusual. Williams 2 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 3 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 firrbriae right 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), loc. cit. 3 Strahl, " The Process of Involution of the Mucous Membrane of the Uterus of Tarsius spectrum after Parturition," Proc. Section of Sciences, Koninklijkc 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,1 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.2 The puerperal changes in Tarsius are said to resemble those of Rodents.3 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 Regeneration de 1'Epitheliura des Corne uterine apres la Parturition," C. R. de la Soc. de Biol., vol. ii., Series 9, 1890. 2 Strabl, "The Uterus of Erinaceus europceus 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 " Nunc femina quseque, Cum peperit, dulci repletur lacte, quod omnis Impetus in mammas convertitur ille alimenti." — LUCRETIDS. 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 mammae. 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). In the cow and other Ungulates the mammae 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.1 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.2 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.3 1 Brouha and certain other authorities regard the mammary glands in all the Mammalia as modified sweat glands (" Recherches sur les Diverses Phases da Developpement et de 1' Activity 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 eui generis being derived independently from the primitive merocrine skin-gland (" Ueber den wicktiges Stadium in der Entwickelung der mensch- lichen Milchdruse," Anat. Am., vol. xxiv., 1904). 2 Wiedersheim, Comparative Anatomy of Vertebrates, Parker's transla- tion, 2nd Edition, London, 1897. 3 Flower and Lydekker, An Introduction 5-9 Cl 7-3 12-4 17-t; 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. Cf. Abderhalden, " Die Beziehungen der Wachsthumsgeschwindigkeit der Sauglinge zur Zusammensetzung der Milch." &c., Zeitschr. 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 casein ogen 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.1 THE INFLUENCE OP 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.2 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 Abdcrhalden, 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 also 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." l 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 1 Schafer, 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.1 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.3 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, Obstetric*, London, 1904. '2 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.1 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, oestrus 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.- 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.3 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, i.e. in most cases near the approach of the next parturition.4 1 Williams, toe. cit. 2 Oceanu and Babes, " Les Effets Physiologiques de 1'Ovariotomie," C. R. de VAcad. des Sciences, vol. cxl., 1905. :1 Wallace, foe. cit. •i In cows which are " drying off," the percentage of volatile acids in the butter fat is very low. See Crowther, toe. cit. 568 THE PHYSIOLOGY OF REPRODUCTION . THE 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 longer, but in them also its average duration appears to depend largely upon the necessities 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.1 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.2 It would appear that if continuous suckling is encouraged, the 1 Wallace, loc. cit. * 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. THE DISCHARGE 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.1 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 CONSTITUENTS 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, it is commonly supposed that the mammary glands 2 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,3 but it has been suggested that it is derived from the degenerate nuclei of the gland cells. 1 Schafer, loc. cit. 2 Neumeister, Lehrbuch der physiologischen Chemie, vol. ii., Jena, 1895. 3 Thierfelder, " Zur Physiologic der Milchbildung," Pfluger'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,1 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,3 " 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 x 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,2 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,3 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 1'Origine du Sucre du Lait," C. R. de I'Acad. dea Sciences, vol. Ixxxviii., 1884. 2 Moore and Parker, " A Study of the Effects of Complete Removal of the Mammary Glands in Relationship to Lactose Formation," Amcr. Jour, of Phya., vol. iv., 1900. 3 Porcher, "Sur 1'Origine du Lactose," C. R. de VAcod. des Sciences, vol. cxxxviii., 1904. "De la Lactosurie," Monographiea Cliniques, Paris, 1906. 572 THE PHYSIOLOGY OF REPRODUCTION Kirkness,1 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.2 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 3 and Landwehr,4 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 Foa, 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.5 Muntz 6 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," Zeitech.f. Phys. Chemie, vol. i., 1877 ; Porcher, De la Lactoaurie, 1906 ; and " L'Origine du Lactose," Arch. Internal, de Phys., vol. viii., 1909. See also p. 510. 3 Thierfelder, "Zur Physiologic der Milchbildung," Pfluger's Archiv, vol. xxxii., 1883. 4 Landwehr, "Ueber die Bedeutung des tierischen Gummis," Pftiiger's Archiv, vol. xl., 1887. 6 Foa, " Sail' Origine del Lattosio del Latte," Arch, die Fie., vol. v., 1908. 6 Muntz, "Sur 1'Existence des Elements du Sucre de Lait dans les Plantes," Annales de Chim. et de Phya., 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 1 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. THE 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.2 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 Physiologic de la Mamelle," Jour, de Med. Vet. de I'^cole de Lyon, Sept. 30, 1905. 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. Ixxvii., 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.) ft, 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 FIG. 140. — Section of mammary gland (human) showing developing alveoli. (From Schafer, after von Ebner.) b, connective tissue ; ri, undeveloped alveoli ; d', partially developed alveoli ; ery outset. Abortion is sometimes procured by purely mechanical means— e.g. blows, massage, hot injections,3 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 5 mentions haemorrhage 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 i Bloch, toe cit. 2 Haddon, toe. cit. 3 Bloch, toe. cit. * Haddon, toe. cit. 6 Kelly, toe. cit. See also Oliver, " The Determinants of Abortion," Brit. Med. Jour., November 30, 1907. FERTILITY 615 dates.1 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 haemorrhage 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 2 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." l 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 2 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 3 has shown that contagious, epidemic, or epizo itic 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 a'gar. The germ causes the formation of a brownish-yellow exudate between the chorion and the mucous 1 Ewart, loc. cit. 1 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 septicaemia 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.1 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 abortion 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.3 The causes of abortion in sheep are dealt with at some length by Heape in the paper already referred to.4 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 Epizootic Abortion, London, 1909. * According to the Report referred to above, nothing more than a quite subsidiary r6le 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.2 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,3 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. THE INCREASE OF FERTILITY, A PROBLEM OF PRACTICAL BREEDING Heape x 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 offspring.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.1 Among cattle the average loss from sterility and abortion (together with mortality of calves) is estimated by Heape 2 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. THE BIRTH-RATE IN MAN , It is now more than a century ago since Malthus 3 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, foe. cit. 2 Heape, loc. cit. 3 Malthns, An Essay on the Principles of Population, 7th edition, London, 1872. FERTILITY 621 statistical inquiries by Newsholme and Stevenson,1 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.3 It appears to be greatest in those sections of the population which give evidence of the exercise of thrift and foresight, for Heron 4 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.5 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 6 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.7 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. 2 Yule, " On the Changes in the Marriage and Birth-Rates," &c., Jour. Roy. Statia. Soc., 1906. 8 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, toe. cit. e Sidney Webb, toe. cit. 7 Newsholme and Stevenson, foe. 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." l 1 Sidney Webb, toe. cit. Cf. also Whetham, The Family and the Nation, London, 1909. CHAFIER 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 resume 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 monoecious, 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 1 Morgan, Experimental Zoology, New York, 1907. See also Geddes and Thomson, The Evolution of Sex, Revised Edition, Londor, 1904, and Thomson, Heredity, London, 1908. 628 624 THE PHYSIOLOGY OF REPRODUCTION respective functions are to produce spermatozoa and ova. This condition is described as dioecious. Again, in a relatively small number of animals, of which the bee is a familiar example, there are three lands 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 dioecious 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,1 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.2 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,3 and subsequently 1 Bodio, " Movimento della Populazione," Confronti Internazionali, 1895. * 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 tirztiiche Zeit., 1881. THE FACTORS WHICH DETERMINE SEX 625 Yung l 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 Cuenot's experiments,2 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.3 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 5 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 1'Influence de la Nature des Aliments sur la Sexualite"," C. R. de VAcad. des Sciences., vol. xciii., 1881. 2 Cue'not, " Sur la Determination 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., fiiol. Hull., vol. xviii., 1910. 5 Treat, " Controlling Sex in Butterflies," American Naturalist, vol. vii., 1873. 2R 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 2 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 Cuenot 3 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. Cuenot 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 larvae 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 . . . Fatty .... Glucose .... 51-21 6-84 27-65 45-14 13-55 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," Trana. Entom. Soc-., London, vol. i., 1871. 2 Kellogg, " Notes on Insect Bionomics," Jour, of Exper. Zool., vol. i., 1904. 3 Cuenot, Joe. ctV. * Geddes and Thomson, lor. 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 larvae 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 l 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 2 has described a series of observations on the pro- duction of males and females in Nemalus ventricosus, a species of wasp. These observations show that the percentage of females in broods of larvae 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." 3 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. 3 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 E/ect 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,1 and has since been accepted by Weismann 2 and many other biologists, although some writers, such as Beard,3 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.4 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, " tiber die Befruchtung der Konigin," Eichstadt 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 bet 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 2 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.3 Either of these explanations would appear to be possible. Moreover, the later observations of Petrunkewitsch,4 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 en record, however, in which worker ants have developed from parthenogenetic ova, and other exceptional cases have been stated to occur.5 Among the Tenthredinidae 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.6 1 Perez, " Memoire sur la Ponte de PAbeille reine et la Theorie de Dzierzon," Annales des Sciences Nat., vol. v., 1878. 2 Sanson, " Note sur la Parthdnogenese chez les Abeill^es," Annales des Sciences Nat., vol. v., 1878. 3 Morgan, toe. cit. 4 Petrunkewitsch, " Die Richtungskorper und ihr Schicksal im befruch- teten und unbefruchteten Bienenei," Zool. Jahrb., vol. xiv., 1901. " Das Schicksal der Richtungskorper im Drohnenei," Zool. Jahrb., vol. xvii., 1902. 8 Wheeler, " The Origin of Female and Worker Ants from the Eggs of Parthenogenetic Workers," Science, vol. xviii., 1903. 8 Doncaster, " On the Maturation of the Unfertilised Egg and the Fat« of the Polar Bodies in the Tenthredinidce," Quar. Jour. Micr. Science, vol. xlix., 1906. 630 THE PHYSIOLOGY OF REPRODUCTION In the parthenogenetic Rotifer, Hydatina, Maupas l 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 2 and subsequently Diising 3 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 4 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, •« §ur la Multiplication et la Fe"condation de 1'Hydatina senta," C, R. de VAcad. des Sci., vol. cxi., 18£0. " Sur la Fecondation de 1'Hydatina senta," C. R. de VAcad. des Sci., vol. cxi., 1890. "Sur la D&erminisme de la Sexualitd chez Hydatina senta," C. R. de VAcad. des Set., vol. cxiii., 1891. * Thury, Ueber das Geselz der Erzeugung der Geschlechter, Leipzig, 1863. 3 Diising, " Die Regulierung des Geschlechtsverhaltnissesbei der Vermeh- rung," &c., Jenaische Zeitschr., vol. xvii., 1884. • 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.1 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,2 as a consequence of numerous experiments and observations, has 1 Balbiani, " Le Phylloxera du Chene et le Phylloxera de la Vigne," &c., Mem. A VAcad. des Sci., vol. xxviii., 1884. Stevens, " Studies on the Germ Cells of Aphids," Carnegie Institution Publications, Washington, 1906. - Weismann, " Beitrage zur Naturgeschichte den Daphniden," Zeitoch. f. wise. Zooloyie, vols. xxvii., xxviii., xxx., and xxxiii., 1876-79. (>32 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 l 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 liable to considerable variation. Maupas 2 has sought to connect this variation with differences in temperature, and Nussbaum 3 with differences in nutri- tion, but neither conclusion has been satisfactorily established. The question has been reinvestigated by Punnett,4 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. * Maupas, foe. cit. 3 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. Theories which assume that the Gametes are themselves Sexual. — 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 2 made the discovery that in the bug, Pyrrhocoris, half of the spermatozoa differ from the other half in possessing an additional chromosome. McClung 3 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 4 found that 1 A list of species in which dimorphic forms of spermatozoa have been recorded (down to 1902) is given by Beard, loc. n't. 2 Henking, " Untersuchungen ueber die ersten Entwicklungsvorgange in den Eien der Insekten," Zeitachr. f. wise. Zoo/., vol. xlix., 1890, and vol. li., 1891. 3 McClung, "The Accessory Chromosome Sex Determinant," Biol. Bull., vol. iii., 1902. * Wilson, " Studies on Chromosomes," Jour, of Exp. Zool., vols. ii. and iii., 1905-6 ; vol. vi., 1909. " Note on the Chromosome Groups of Metapodius and Banuaa," 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.1 Payne 2 has recently shown that in Galqulus 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 (i.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 trislis," Amer. Jour, of Anat., vol. vii., 1907), as a result of an investigation with smear preparations instead of sections, find no evidence of a persisting accessory chromosome in Anasa trislis, 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 (Jeschlechtes nach neuen Versuchen mit hoheren Pflanzen, Berlin, 1907). THE FACTORS WHICH DETERMINE SEX 635 been shown by Guyer,1 who has investigated the matter for the chicken and guinea-fowl.2 (See footnote2, p. 657.) The manner in which the spermatozoon 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.3 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 to carry 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.4 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 oogenesis, it would seem to follow, that here the destination of the oogonium 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 Heteraki* and probably also in Ancaii* (see Boveri and Gulick, Arch.f. ZeUforacli, vol. iv., 1909). 3 It is said that in the process of spennatogenesis 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. M >l. /. Anat., vol. Ixx., 1907). 4 Morgan, "The Production of two Kinds of Spermatozoa in /'/////- loxcru*," &c., Proc. Soc. Exp. Biol. and Med., vol. v., 1908 ; " Sex De- termination and Parthenogenesis in Phylloxera 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." l 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 2 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 3 states that in the chalcid fly (Ageniaspis fuscicollis) in which a chain of embryos takes origin from a single egg, these embryos are all of one sex. (See footnote 2, 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 land 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 Phylloxera, 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 spermatozoon.4 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,6 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 King6 has shown experimentally that it is 1 Beard, loc. cit. * Von Ihering, " Ueber Generations-wechsel bei Siiugethieren," Biol. Centralbl., vol. vi., 1886. 3 Marchal, " Recherches sur la Biologie et le Developpement des Hymenopteres parasites," Arch, de la Zool. Exper. et Gen., vol. ii., 1904. * Morgan, Proc. Soc. Exp. Biol. and Med., loc. cit. 5 Dawson, The Causation of Sex, London, 1909. * 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 spermatozoon was derived has been negatived by Copeman l as a result of an experimental investigation upon rats. Castle's Theory. — Bateson 2 was the first to suggest that the Mendelian laws are applicable to sex-heredity. This suggestion has been elaborated by Castle 3 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 tkis 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 ) 2f) cent mm + ^ cent mf + 25 cent ff> conjugation \ 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 dioecious forms, is 1 Copeman, " Sex Determination," Phys. Soc., May, 1908. 2 Bateson, Report to the Evolution Committee of the Royal Society. I., 1902. 8 Castle, " The Heredity of Sex," Bulletin of the Museum of Comparative Zoology, Harvard, vol. xl., 1903. 638 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 anatomicaUy and experi- mentally.1 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 dioecious 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 dioecious 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 rosa) 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. 1 Evidence that this is so is given below (p. 652 tt 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 l as a result of breeding experiments with certain Lepidoptera. He has shown that in the moth Abraxas grossulariata, there is a rare variety, which generally 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 g4-oss. (2) Heterozygous 2 9 x heterozygous £ gave gross. ^ , gross. 9 , and lact. 9 . (3) Lact. 9 * heterozygous £ gave all four possible forms (gross. £ , lact. $ , gross. 9 > and lact. 9 ),the lacticolor males being the first ever seen. (4) Heterozygous 9 * lact. <£ gave gross. ^ and lact. 9 • (5) Lact. 9 x lact- c? gave lact. £ and lact. 9 • (6) Wild gross. 9 x lact. £ gave gross. £ and lact. 9 • 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. 2 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.1 Where, however, a green cock of the second generation (the FX 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 (Fx) 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.1 Ziegkr's Theory. — Ziegler2 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 divis'on 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. If 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." 3 Heape's Views. — Heape 4 has recently expressed the belief " that while each ovum and spermatozoon 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 1 For further discussion see Bateson, Mendel' 8 Principles, Cambridge, 1909. 2 Ziegler, Der Vererbungslehre in der Biologie, Jena, 1905. 3 Morgan, loc. cit. See also "Ziegler's Theory of Sex Determination and an Alternative Point of View," Science, vol. xxii., 1905. •* Heape, " Note on the Proportion of the Sexes in Dogs," Proc. Camb. Phil. Soc., vol. xiv., 1907. 2s 64-2 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 l and also by Morgan.2 Heape is of opinion, however, that just as there is evidence that adult animals are never purely male or female,3 so it is probable that the sexual products (i.e. the gametes) are them- selves similarly constituted. According to this view, an ovum or a spermatozoon 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 spermatozoon of the opposite sex, but whether the sex of the adult is determined by the ovum or by the spermatozoon 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. Diising4 claimed that the statistical results he obtained from a study of 1 See below (p. 652 et seg.). 1 Morgan, loc. cit. 3 Gf. 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 offspring 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 l 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. Ixxvi., 1905. 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,1 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,2 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 l 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. 6'oe., 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 1 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 2 and Sadler 3 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,4 but the most recent statistical investigation B 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. 1 Hofacker, Ueber die Eigenschaften welche sich bei Menschen und Thieren aufdie Nachkommen vererben, Tubingen, 1828. 1 Sadler, The Law of Population, London, 1830. 4 Geddes and Thomson, loc. cit. 8 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 l on the sexes produced by mice of different ages has led likewise to a negative result.2 Influence of Parental Vigour or Superiority. — Considerable importance has been attached by breeders and others, and notably by Starkweather,3 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,4 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 5 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." l 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 1 Thomson, Heredity, London, 1908. 2 See Morgan, toe. 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 : — " If 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." Cuenot's experiments 1 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 2 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,3 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. HEKMAPHRODITISM 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 Cuenot, loc. cit. a Schultze, toe. 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, coelenterates, 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.1 According to Castle 2 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. Dioecious 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 (Hymfnoptera). See also S hat took 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, Hermaphroditiemu* beim Mentchen, Leipzig, 1908. * Castle, 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.1 Among animals which are usually regarded as purely dioecious 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 (Siphostoma florida.'), in which the male possesses a marsupium which acts functionally as a placenta.2 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 vesiculae 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. 1 Gudger, " The Breeding Habits and the Segmentation of the Egg of the Pipe-Fish, Siphoetoma Florida;," Proc. U. S. Nat. Mus., vol. xxix., 1905. THE FACTORS WHICH DETERMINE SEX 653 phenomenon are supplied by certain animals. Thus Potts * has 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,2 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.4 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. i;.",*., 3 Orton, "On the Occurrence of Protandric Hermaphroditism in the Mollusc Crepidula fornicata," Proc. Roy. Soc., B., vol. Ixxxi., 1909. 4 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 l 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 2 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 thely plasm, 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 dioecious 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 Sipphist 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.1 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, Paychopathii Sexualis, Stuttgart, 1882; Havelock Ellis, Studi°s in the Psychology of Sex: Sexual Inversiyn, 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 generates sur 1'Anthropologie des Sexes et Applications sociales," Rev. de I'Acole d1 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.1 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, toe. 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.1 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.2 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 it is 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. 2 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 (i.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 metazoon 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.1 APPENDIX Braem 2 has described an experiment in which he divided in half a mature female of the annelid, Ophnjotrocha puerilis. The head portion after some weeks regenerated arid 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 Potts3 has adduced evidence that in certain hermaphrodite Nematodes, in Rhabdocoal Turbellarians and in Rhizo- cephala the monoecious 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. Am., vol. xxxiii., 1908. 3 Potts, Quar. Jour. Micr. Sciznce, vol. lv., 1910. 4 Smith, Quar. Jour. Micr. Science, vol. lv., 1910. CHAPTEE XVI PHASES IN THE LIFE OF THE INDIVIDUAL— THE DURATION OF LIFE AND THE CAUSE OF DEATH "Ta.vrbi> yap fiftaur' tiv&pa. /cat Trpf^">s>v. ^** '*;§/ . ''<£-£ • • ' . ' /. ,-Y.j( . " . 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. S. Putnam & Sons, and John Murray.) C, C, cells still intact, but shrunken and loaded with pigment ; c, c, cells which have disintegrated. little is known regarding the conditions of natural senescence and death in animals. Smith 2 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 Disabilities of Man, &c., London, 1908. 2 Smith, loc. cit. PHASES IN THE LIFE OF THE INDIVIDUAL 679 a real old age. Elaine l 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." THE DURATION OF LIFE AND THE CAUSE OF DEATH Weismann, in a famous essay on the duration of life,2 and Metchnikoff in his book of optimistic studies,3 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.4 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, Encyclopaedia of Rural Sports, London, 1858. * 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,1 FlG. 153. — Land tortoise (Testudo mauritanico), aged at least eighty-six, belonging to M. Elie Metchnikoff. (From Metchniko/'s " The Prolongation of Life," by permission of Mr W. Heinemann.) 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," Ibia, 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.2 His death is 1 I am 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,1 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,2 " 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 1 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." l 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,2 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, toe. 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 m 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. Metchnikoff 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 l 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.2 1 Pearson, The Chances of Death, &c., vol. i., London, 1897. 8 Metchnikoff, toe. 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' Alccstis, "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. MetchnikofT'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, i.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 o'f 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 1 Foster, Textbook of Physiology, 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 Jtalics.] Abderhalden, 563 sq. Abel and Mcllroy, 526 Abelous, 282 Abortion, 612 sqq. Abraxas grossulariata, 639 Acmaea, 221 Acomys caharinus, 390 Actinia mesembryanthemum, 8 sq., 679 Acton, 283 Adolphi, 177 Agassiz, 17 Ageniaspis fuscicollis, 636 Ahlfeld, 369, 497 Akutsu, 233, 259 Albatross, 27 Albers-Schonberg, 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 sqq. ; insemination in, 184 ; fertilisation in, 190 ; fertility of, 594 sq. ; sex-determination in, 625, 637, 651 Amphioxus lanceolatus, 16 Anasa tristis, 634 Ancel and Bouln, 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 de6ned, 36 Anopheles, 13 Ant, sex-determination in, 629 ; age of, 680 Antelope, 48, 241, 247 Antilocapra americana, 28, 305 Ape, O2strous cycle in, 63 sqq. ; foetal nutrition in, 392, 463 sqq. Apfelstedt and Aschoff, 478 Aphid*, 11 sq., 216, 631 Arbacia, 179, 218 Arbacia pustulosa, 293, 300 Aristotle, 590 Arthropoda, breeding season of , 1 1 ; spermatozoa of, 174 ; 307 Arvicola, 250 Arvicola agrestis, 40 Arvicola qlareolus, 40 Ascaris, 128 Ascidians, fertilisation of, 207 Ascoli, 436, 481 Ashworth, 8 sq. Ash worth and Annandale, 679 Ass, 403 Assheton, 110, foetal nutrition, 372 sqq., 376, 386 sq., 390, 394 sq., 397 sqq., 406 sq., 419 sq., 423, 487 Astacus jtuviatilis, 11 Asterias, 134 n., 204, 220 sq., 223 sqq. Asterias forbesii, 218 Asterina, 223 Atretic follicle, 154 sqq. Aves, breeding season of, 23 sqq. See also Birds Axe, Wortley, 51, 536, 618 Axis, osstrous cycle in, 49 Axolotl, 22, 189 sq., 694 B Backhouse, 159 Badger, gestation of, 59 n. ; 416 Baer, von, 143, 145 sq., 375 Balbiani, 631 Balenoptera muaculus, 52 Balfour, 116 sq., 124, 160, 379 Ballowit*, 172, 175, 178, 179 «?. Bang, B., 616 sq. - I., 293 Bar and Daunay, 498, 500, 502 sq. Barasingha, 47 sq. 2x f>90 INDEX 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 ; oestrous cycle in, 61 aq. : maturation in, 132; ovulation in, 135, 185 ; 367, 374, 392, 407, 494; parturition in, 541 ; fertility of, 587, 589 Bat a- 11 on. 203, 221 Bateson, 194, 198, 637, 639 gqq., 657 Baumm, 497 Bear, breeding season of, 58 ; fer- tility of, 590, 592 Beard, 110, 162 aq., 337, 542 sq., 628, 633, 635 aq. Bechterew, 262, 539 Beck, 180 Beddard, 42 Bee, 186 ; sex-determination in, 626 aqq. 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, 459s?., 467 Beneke, 62, 136 Benkiser, 316 Bergell and Liepmann, 481 Bergomie and Trabondeau, 607 Bernard, 431 Bernhard, 520 Bert, 571 Bertkau, 560 Bestion de Camboulas, 328 Beyer, 669 Biancardi, 517 Birds, female generative organs in, 264 aqq. ; 315 aq. ; foetal nutrition in, 485 ; breeding of, in captivity, 592 aqq. ; hermaphroditism in, 654 ; age of, 680 Birnbaum, 517 Birnbaum and Osten, 69 Birth-rate, 620 aqq. Bischoff, 47, 55 ; corpus luteum, 143, 147, 149 aq.; 177 ; placenta, 371, 387, 400, 421, 442 Bison, 47 aqq. Bizzorzero and Ottolanghi, 561 Bjbrkenheim, 465 Black m an, 213 Blaine, 679 Blandford, 65 Bles, 5, 20, 22, 594 aq. Bloch, 600, 614, 655 Blood, changes in, during pregnancy, 520 aq. Blot, 510 Blumreich, 521 Bocarius, 287 Bodio, 624 Bohr, 272 aq., 434, 436, 486, 491 aq., 508, 512, 518 aq. Bohr and Hasselbalch, 271 .---/. Bolaflio, 585 Bombyx mori. See Silkworm moth Bond, 347 aq. Bondzinski and Zoja, 275 Boni, 505 aq. Bonnet, 100, 108 aqq., 184 ; placenta, 363, 366, 371, 373, 386, 403 aqq., 411, 413 aqq., 426 aq., 476 aq., 480 ; 515 aq. See also Merkel and Bonnet Born, 624 aq. 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 aqq., 199, 660 Brachet, 253, 262, 330, 490, 538 Brodypua, 375 Braem, 658 Branca, 593 Brandt, 316 Breeding season, 4-35 Breschet, 65 Breuer and Seller, 356 Bridge, 16 Briggs, 626 Brill, 205 Brinkmann, 380 Brocard, 510 aq. Brock, 547 Brock, van der, 418 Brooks, 192 Brouha, 554, 560 aq., 573 Brown, 169 Brown and Osgood, 607 Brown-Sequard, 308 aq., 326, 541 Brumpt, 536 " Brunst," 36 Bryce, 138, 392 Bryce and Teacher, 369, 449, 466 aqq., 471, 474, 479 INDEX JBuccinum undatum, 14 Budge, 254 eg., 259 sq., 528 Budgett, 17, 28 Buffalo, 349 Buff on, 591 Bufo, 203 Buhler, 145, 151 Buller, 178 sgg., 215 Bulloch and Sequeira, 351 Bullot, 221 Bunge, 265, 270, 480, 515, 563 Burcheirs zebra, 202 Burckhard, 437 Burlando, 508 Burrian, 288, 296, 297 Bustard, 30 Buys and Vandervelte, 317 C Calf, growth of, 668 Calkins, 6, 7, 213 Callionymus lyra, 29 Calotes jtibatua, 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 azarce, 55 Capaldi. 511 *'/. Capercaillie, 315 Capon, 306, 312, 349, 654 Capybara, 250 Carmichael, 320 Carmichael and Marshall, 317, 328, 341, 348 Carnegie, 58 Carnivora, oestrous cycle in, 53 sgg. • uterine cycle in, 99 sgg. ; foetal nutrition in, 386 sg., 411 sgg., 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 sg. Castration, chap. ix. passim, in Man, 303 ; stag, 305 ; sheop, Ac., 306 ; arthropods, 307; fowl, 311 sq. • frog, 313 ; effect of, on general metabolism, 353 sgg., 656 Cat, cestrous cycle in, 56 sg. ; superfo3tation 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 ; 525 ; female generative organs in, 525, 528 sg., 537 ; fertility of, 591 ; growth in, 671 ; age at- tained by, 681 Caterpillar, 307, 625 Catlin, 48 sg. Caton, 305 Cattle, oestrous cycle in, 46 sg., 334 ; effects oi 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 CeratocephaleoHiuai, 11 Ceratodus, 17 Cercocebus, 63, 96 sg. Cercocebus cynotnolgus, 89, 96 CercopUhecus, 63, 74 n., 584 Cercopithecus cynosurus, 65 Cervus alces, 233 Cervus elaphus, 27 Cesa-Bianchi, 161 Cetacea, oestrous cycle in, 52 sg. ; 141, 246, 375 ; lactation in, 553 sgg. Chad wick, 15 Chiitopterus, 217, 221 Chaffinch, 315 Champneys, 85 Charrin, 515 Charrin and Goupil, 481 sg. Charrin and Guillemont, 508 Cheiroptera, oestrous cycle in, 61 sg. : foetal nutrition in, 459—463 ; lactation in, 553 ; fertility in, 587 Chelchowski, 185 Chermes, 12 Chicken, growth in, 665 Child, 10 Chimpanzee, oestrous cycle in, 63 Chipman, 369, 422, 425 sg., 428, 430 sg., 487 Christ, 85 ChrysocfUoris, 61 n. Cimorini, 349 Ciona intestina'is, 207 Clark, 118, 139, 145 sg., 208, 336 Clarke, Eagle, 24, 26 Cock-of-the-rock, 27 Cocks, 56, 57, 59 Cod, 278 Coelenterata, breeding season of, 7 ; 125 n. ; spermatozoa of, 174, 190 ; 200 692 INDEX 436, Cohen, 285 Cohn, 149 Cohnstein, 520 Cohnstein and Zuntz, 434, 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, 136; 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 sq. ; growth of, 668, 671. See also Cattle Cowper's glands, 239 sqq. Crab, 307 sq., 653 Cramer, A., 478 - H., 332, 491, 517 - W., chap, viii., 355, 431, 436, 519. See also Lochhead 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 biporcattis, 277 Groom, Halliday, 65 Cross-breeding, 202-11 passim; effects of, 601 sqq. Crowe, Gushing, and Ho mans, 356 Crowther, 564 sqq. Crustacea, ovulation in, 137 n. ; 281 sq. ; parasitic castration in, 640; 653 Cryptorhynchus gravis, 13 Ctenophora, 9 Cuckoo, 24 Cuenot, 625 sq., 650 Culicidae, 13 Cull, 213 Cunningham, D. J., 55 Cunningham J. T., 28, 29, 151, 304 sq. Curtis, 651 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 sq., 591 sqq.. 602 *'/., 653 ••"/• Dastre, 478 Dasyurtis, 150, 158 sq., 383, 385 Dasyurus viverrinus, 149, 337 Dawson, 636 Dean, Bash ford, 17 Death, 682 sqq. Death's-Head hawk moths, 13 De Bonis, 236, 239 Decidua, and fretal nutrition, 366 sqq. Deer, 32, 47 sq., 241 ; effects of castration on, 305, 313 ; foetal nutrition in, 371, 397, 403 De Graaf, 251 Delage, 223 sqq. Dembo, 530 De Sinety, 85 De Vries, 193 Dewar and Finn, 604 Dewitz, 178 sq. Dinophilus apatris, 635 Dioestrous cycle, defined, 37 Dio38trum, defined, 37 Diplozoon paradoxum, 10 Dipodillus campestris, 40 Dipodillus simoni, 40, 41, 545 Discoglossus, 22 Disse, 439, 441 Disselhorst, 24, 228, 232, 241, 244, 670 Dixon, 285, 309 Doering, 145 sq. Dog, gestation of, 32 ; oestrous 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, INDEX 309, 355 ; 349 ; influence of ovary in, 318, 328 sq., 332 sq., 341 ; ovum of, 371 ; foetal nutrition in, 387, 411, 413, 416, 427 ; pregnancy in, 490, 498, 500 aqq., 507 sq., 511 aq., 520 ; parturition in, 538 ; 552 ; lactation in, 563, 583 ; fertility of, 590 aq., 601 ; sex in, 644 aq. ; 671 Dolphin, breeding period of, 53 Donaldson, 662 Doncaster, 131, 204, 210 aq., 629, 639 aq. Donkey, ovulation in, 136 ; 183 Doran, 330 aq., 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 aq. Duckworth, 306 Ductless glands, 336 ; correlation between generative organs and, 349 aq. ; during pregnancy, 522 sq. Dudley, 331, 674 Duesberg, 131 Dugong, 376 Diihrssen, 185 Dumas, 184 Duncan, Matthews, 06, 587, 589 aq., 608 Dungern, 179, 216 Durham, 640 Dusing, 630, 642 Duval, 62, 361, 387, 400, 413 sq., 416, 420, 423 aq., 426, 437, 439, 462, 483, 552 Dzierzon, 628 aq. Earthworm, 186, 190 Ebner, von, 561 Echidna, oestrous cycle in, 38 sq. ; lactation in, 554 Echinodermata, breeding season of, 15 sq. ; spermatozoa of, 174, 178, sqq., 190 ; cross-fertilisation of, 203 sqq., 210 sq. ; partheno- genesis in, 216-226 passim Echinoidea, 178 Echinus, 179, 300 Echinus acutus, 16 Echinus esculentus, 16, 300 Echinus microtuberculotus, Ifi Eckhard, 251, 254 aqq., 577 Eden, 430, 478, 543 Eel, 18, 23 Eggelung, 554 Ehrlich, 520 Ehrstrom, 291, 507 Eimer, 62 Ejaculation, mechanism of, 251 aqq. Eland, oestrous cycle in, 49 ; 306 I lasmobianchs, 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 Ellis, Havelock, 63, 65, 70, 71, 655 Emberiza passerina, 593 Embryotrophe, defined, 403 n. Empidae, 13 Emrys-Roberts, 47, 163, 435 Engelmann, 80, 83. See also Kun- drat and Engelmann Engstrom, 521 Enriques, 192, 214 Equus prjewalskii, 51 Ercolani, 359, 367, 401, 459 Erection, mechanism of, 251 sqq. Erlandsen, 267 Eschricht, 358, 375 Essen-Mbller, 342 Eunice fucata, 11 Eunice viridis, 1 1 Eutheria, 149 Ewart, 51, 108, 136, 159, 201 sq., 210, 396, 545, 615 sq., 620 Exner, 234 F Falco albidus, 593 Farkas, 281, 302. See also Tangl 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 Pick, 200, 260 Finch, breeding of, in captivity, 592 694 INDEX Findley, 84 aq. Finn, 604 Fischel, 507 Fischer, 275 Fischer and Ostwald, 301 Fish, 184 ; biochemistry of eggs of, 277 eqq. : age attained by, 680 Flatau, 342 Fleming, 536, 608 Flemming, 156 aqq. Fletcher, 253 Flies, sex-determination in maggots of, 626 Florence, 287 Flower, 43 Flower and Lydekker, 554 Foa, 320, 572, 580 aq., 583 Foetal membranes, 377 aqq. Foges, 311, 579 Fogge, 258 Foote and Strobell, 634 Fordyce, Dingwall, 74, 568 Forel, 655 Foster, 540, 686 Fothergill, 369 Fouiis, 118 Fowl, oviduct of, 24, 333 ; ovula- tion in, 139 n. ; 184 ; Andalusian, 194 aq. ; biochemistry of the sexual organs of, 264 sqq. ; 311 aq., 315, 320 n., 349; foatal nutrition in, 435, 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 aqq., 353 Fraenkel and Conn, 338 Franck-Albreeht-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 aqq. ; 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 sqq., 350. See olao under Rana Frommel, 366, 494 Fiirbringer, 236, 287 Furth, von, 280 Fiirth, von, and Schneider, 481 G Gadow, 20, 23, 24 Godua morrhua, 291 Galabin, 66, 83, 86, 139, 160, 533 aq., 615 Galogo agisymbanua, 396, 410 GoleopUhecuz, 377 Qaleopithecua volana, 98 Golgulua oculatua, 634 Gallus bankiva, 591 Gamecock, 653 Gametic selection, 202 aqq. Gamgee, 267, 401 Garner, 63 Garrod, 247 Gaskell, 254, 350 Gassner, 497, 547 aq. Gasteropods, 133 Gautier, 181 aq. Gawronsky, 526 ' Gayal, a-strous cycle in, 49 Gazella dorcas, 49 Gazelle, 247 Gebhard, 84 aq., 87 aq., 89 Geddes and Thomson, 30, 164, 165, 175, 191, 623, 626 aq., 646 aq., 651 Gellhorn, 74, 576, 584 Geppert, 514 Gerbillua hertipea, 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, ib. ; Cape hunting dog, ib. ; domestic cat, 56 ; wild cat, 57 ; lioness, 58 ; tigress, ib. ; puma, ib. ; bear, ib. ; badger, 59 n. ; walrus, 60 ; hedgehog, 61 ; apes and monkeys, 65 ; duration of, 73 aq., 544 aq. Geyelin, 590 Geyl, 543 Giacomini, 151, 380 Giacosa, 277 Gierke, 508 Gies, 222, 300 Gilbert, 247 Gilchrist and Jones, 564 Giles, 68, 547 Giraffe, oestrous cycle in, 49, 247, 400 Girtanner, 358 Glass, 331 Gley, 240. See aUo Camus and Gley Gnu, oestrous cycle of, 49 INDEX 695 Goat, cestrous cycle in, 64 ; in- breeding in, 214; 231; lactation in, 555, 558, 567, 571 aq., 584 Godet, 431 Godlewsky, 199 Godman, 67 Gofton, 142 Gbhre, 463 Goltz, 22, 253, 329, 490, 538 Goltz and Ewald, 329, 490, 538, 577 Goodslr, 358 aq. Goose, fertility of, 591 sq. Gordon, 331, 607 Gorilla, oestrous cycle in, 63 Gottschalk, 477 Gottschau, 350 Graefe, von, 342 Grassi, 627 Grass! and Sandias, 627 Griffiths, 238, 240 Grigorieff, 319 Grohmann, 48 Gross, 306 Grouse, 315 Gruber, 235 Gruenhagen, 253 Griinbaum, 579. See also Gurber 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 Gurber and Griinbaum, 508 Gurney, 315, 680 Gusterosteus spinachia, 30 Guthrie, 320 Guyer, 635, 657 Oymnura, 61, 377 11 Haddon, 600, 614 Hagemann, 54, 500 sqq., 604 Halban, 320, 332, 334, 492, 524, 579, 581 sq. Haldane, 52 Haller, 400 sq. Halliburton, 562, 564 Hamm, 165 Hammarsten, 264, 277, 278 Hammond, 606 Hamster, 241 Handmann, 676 Hare, 588 Harper, 139 .-/'/., 259, 260 aq., 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 Laycock, 31, 65, 66, 316 Leathes, 482 Lebedeff, 520 -/. Lecaillon. 310 Ledermann, 400 Lee, 669, 677 Leeney, 536 Leersum, 506 Leeuwenhoek, 165, 184 Lefevre, 224 Lefroy, 13 Lehmann, 558, 566 Lemaire, 510 Lemur, oestrous cycle in, 62, 97 aq. : ovulation in, 137 ; foetal nutri- tion in, 377, 396, 410 ; fertility of, in captivity, 593 n. Lemuroidea, foetal nutrition in, 408 aqq. Lenhossek, von, 363 aq. Leopold, 83 aq., 366, 467, 548 Lepidoptera, 13, 639 Lepidosiren, 18, 28 Lepidoateua, 17 Lepua, 150 Lepua cuniculua. See Rabbit Lepua variobilia, 41 Leslie, 21 Leuckart, 233 Leusden, 549 Levene, 278, 294 Leydig, 240 Liebermann, 271, 274 Liepmann, 493 Lillie, 52, 221 Limnrra, 14 Llmon, 320, 351 Linnet, 593 Linton, 241 Lion, 247 Lioness, oestrous cycle in, 58 Lipes, 80, 82, 85 aq. Littlejphn and Pirie, 288 Littorina, 14, 15 Lo Bianco, 14, 16 Lochhead, chap, x., 435 aq. 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 aq., 218 aqq., 299 aq., 301 aq., 661 — L., 150, 156, 344 Loe wen thai, 162, 347 Loewy, 312, 356 Loewy and Richter, 355 Loisel, 170, 329 Lombroso and Bolallio, 585 Longridge, 546 aq., 549, 551 Lota vulgar ia, 291 Lott, 177 Lottia, 221, 224 Loven, 251 Low, 46, 208 Lubarsch, 286 Lucas-Champonniere, 343 Lucien, 151 Lusk, 563 Luthje, 354 aq. Lycaon pictua, 55 aq. Lydekker, 42, 43, 46. See alao Flower and Lydekker Lyre-bird, 30 698 INDEX 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 Macbride, 204 McClung, 130, 633 McFadyean, 609 Macgregor, 89 M'Intosh and Master man, 205 Mcllroy, 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. ; oestrous cycle in, chap, ii. ; spermatozoa of, 174 ; ferti- lisation in, 190 sq., 203 ; female generative organs in, 263 sq., 273 ; placental classification of, 375 aqq. Man, oestrous cycle in, 65 sqq. ; menstrual cycle in, 76 sqq., 161 sqq., 334 ; ovulation in, 137 sqq. ; spermatozoa in, 112 sqq.; artificial insemination in, 184, 609 ; accessory reproductive organs in, chap. vii. ; castration in, 304; ovariotomy in, 314, 316 aq., 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 sqq. ; prolonged gestation in, 544 sq. ; 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 sq. ; puberty in, 670 sq. ; menopause in, 672 sqq. ; sene - cence in, 675 sqq. ; age attained by, 681 sq. Maiidl, 85, 88, 526 Mandl and Burger, 346 Mania, 375 Manouvrier, 655 Mansfeld, 268 Marchal, 636 Mare, oestrous cycle of, 50 sq. ; ovulation in, 136 ; 159 ; artificial insemination of , 183, 185, 610 sq. ; telegony in, 201 sq. ; 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 sq. ; corpus luteum in, 149, 247 Marshall, F. H. A., the oestrous cycle, 35, 42, 99, 136 ; the corpus luteum, 147, 148, 152 ; 154, 202, 247, 268; foetal 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, FT 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 Matthews, 134, 224, 293, 297, 505 Maturation, 125 sqq. ; rabbit, 131 ; mouse, 132 ; guinea-pig, ib. ; bat, ib. ; mole, 133 ; pigeon, ib. ; frog, ib. ; Invertebrates, 133-4 Maupas, 212 sq., 630, 632 Maurel, 498, 508 Maximo W, 425 sqq., 430 sq. Mayo-Smith, 71 Mayow, 358 Mead, 217 Meade-Woldo, 59 Meckel, 232 Meisenheimer, 307 INDEX 699 Mendel, 193 aqq. Mendel and Leaven worth, 269 Menopause, 353, 672 aqq. Menstruation, in Primates, 62 aqq. ; in Man, 65 sqq., 75 aqq., 161 aqq. ; and lactation, 74, 334, 569 ; and " heat," 329 8qq. ; 346, 350 Merconitski, 268 Meredith, 331 Merganser, 315 Merionea longifrona, 40, 545 Meriones ahawi, 40, 41, 545 Merkel, 169 Merkel and Bonnet, 526, 561 Merletti, 481 Merttens, 473, 478 Metaphyta, 7 Metazoa breeding season of, 7 Metennikoff, 78, 111, 163, 679 aq., 684 aq. Metoestrum, denned, 37 Michaelis, 570 Michel, 499 Miescher, 18, 279, 288 aq., 292 aq.. 295 aqq. Milk, uterine, 400 aqq. ; composi- tion and properties of human and cow's, 562 aqq. ; influence of diet, &c., on yield of, 564 aqq. ; discharge of, 569 ; formation of organic constituents of, 569 aqq. Millais, 48, 52, 53, 55 aq., 59 aqq., 183 Milroy, 19, 279 Mingazzini, 151 Minot, 79, 86, 202 ; foetal 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 ; foatal nu- trition in, 376 aq. ; 392, 456-7, 485 Mollusca, breeding season of, 13 aqq., 205 Monkeys, cestrous cycle in, 62 aq. ; menstrual cycle in, 89, 335 ; ovulation in, 137, 330 ; 255 ; foetal nutrition in, 392, 463 aqq. ; for-" tility of, 592 Monoestrous, definition of, 38 Monotremata, oestrous cycle in, 38 aq., 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 «?. ; 305, 604; sex-determination, 623, 625, 635 aq., 641 aq., 648, 670 Moricke, 84 aq. Morner, 274, 279 Morris, 331 Mosher, 68 Mouse, 40 ; ovulation in, 135 ; 156 ; artificial insemination of, 183 ; 373 aq., 389; fostal 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 Mua, 150 Mua decumanua. See Rat Mua minutua, 40 Mua muaculua. See Mouse Mua rottua, 40 Mua aylvoticua, 40 Musk deer, 241 Musk ox, 49, 249 Musk rat, 241 Muatelua Icevia, 277, 380 Myliobotia, 151 Mytilua, 205 N Nagel, 117, 145, 177, 240, 260, 533 Nasse, 520 aq. Nathusius, 46 Nattan-Larrier, 370, 492 Needham, 400 Nematodes, 133, 174 Nemotua ventricoaua, 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 aq. Nicolas, 247 Nightingale, 25 700 INDEX Nlkolski, 255 Niskoubina, 344 Nitabuch, 477 Nolf, 367, 419, 460 sqq. Noorden, von, 68, 354, 356, 497, 510, 513, 515 Nudibranchs, 14 Nussbaum, 141, 312 sq., 632 Nycticebus, 408 Nylghau, oestrous cycle in, 49 0 Oceanu and Babes, 356, 567 Ocneria dispar, 307 Odd! and vicarelli, 519 CEstrus or CEstrum, defined, 36 (Estrous cycle, chap, ii., 335 OffergeW. " S« Kruieger and Offer- geld Oliver, 83, 85, 138, 614 Onchorhynchus, 30 n. Onuf, 253 CXigenesis, chap. iv. Ophelia, 221 Ophiothrix fragilia, 204 n. Opossum, 385, 484 Orang-utan, n-strous cycle in, 63 Ornithodelphia, 380 Ornithorhynchns parodoxus, 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 sqq. ; and menstruation, 330 sqq. ; and preg- nancy, 341 sqq. Ovary, changes in, during the oastrous cycle, chap. iv. ; in- fluence of, 314 sqq. ; Man, 314, 316 sq., 330 sqq. ; deer, 314 ; poultry, 315 aq. ; rabbit, SIT 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 tragdaphus, 42 Ovis vignei, 43 Ovulation, 125 sqq. ; rabbit, 134 ; mouse, 135 ; rat, ib. ; guinea-pig, ib. ; dog, ib. ; sow, ib. ; ferret, 136, mare, ib. ; donkey, ib. ; cow, ib. ; sheep, ib. ; bat, 136 sq. ; Primates, 137 ; Man, 137 sqq. ; Invertebrata, 137 n. ; and men- struation, 330, 333 n., 335 Ovum, formation of, 160 sq. ; chap, x., part ii., passim ; the ovarian, 370 sq. ; the fertilised, 371 sqq. Owen, 31, 42, 61, 247, 359 Ox, 288, 296, 306, 349, 486 Pachyuromys duprasi, 41 Paladino, 146 Palolo worms, 10 sq., 134 Paludina, 175, 633 Papio, 63 Papio porcarius, 64 Paramoecium, 6, 212 sqq. Paramcecium caudatum, 211 Parthenogenesis, 216 sqq. Parturition, 527 sqq. ; human, 531 sqq., 538 ; other Mammalia, 535 sqq. ; 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 Bra mley- Moore, 605 Peel, 681 Pelican, 30 Pelikann, 235 Pelodytes, 203 Pembrey, 272 Pepere, 349 Perameles, 39, 339, 384 sq. Perch, 277 sq. 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 .-•'/. Pfannenstiel, 264, 368 Pfeffer, 215 INDEX 701 Pfister, 578 Pfluger, 114, 116, 124, 143, 203, 313 sq., 329, 436, 518 Pfluger and Smith, 203 Phalarope, 30 Phascolarctus cinereus, 39 Pheasant, 315 Phylloxera, 635 sq. Piccolo and Lieben, 263 Pick and Pineles, 523 Fieri 299 Pig, 208, 371, 668. See also Sow Pigeon, maturation in, 133 ; ovula- tion in, 139 sqq. ; 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 Pldnnis, 183, 611 Ploss, 70 Plover, golden, 25 Pocock, 63 sqq., 96, 137, 306 Poehl, 236, 285, 309 Polaillon, 532 Polecat, breeding season of, 59 Polynoe, 224 Polyoestrous, 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 sqq. ; metabolism of fats in, 511 sqq. ; metabolism of metals and salts in, 614 sqq. ; respiratory exchange during, 517 sqq. ; changes in maternal tissue during, 520 sqq. Prenant, 336 Prepotency, defined, 206 n. Prevost, 184 Preyer, 358, 365 Primates, oestrous cycle in, 62 sqq. ; ovulation in, 137 ; 374 ; foeta! nutrition in, 392 sqq., 402, 463- 482, 484 ; lactation in, 553 Prjewalsky, 43 Proboscidia, fostal nutrition in, 387 sq., 419 sq. Prochownick, 496 Prooestrum, 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 aqq. ; immortality of, 682 Przibram, 134, 190 Pteropus, 62 Pteropus edulis, 462 Puberty, 670 sq. Puerperium, 545 sqq. Puma, oestrous cycle of, 58 Punnett, 194, 624, 632 sq., 639 sq., 649, 657 Punnett and Bateson, 639 Purpura lapillus, 14 Pussep, 254 Pyrrhocoris, 633 Quagga, Lord Morton's, 201 R Rabbit, o?strous cycle in, 37, 41, 105 sqq. ; changes in the ovary of, 123, 128, 131, 134 sq., 139, 144, 149, 154, 166, 158 sq., 160 ; spermatozoa of, 177, 180; artifi- cial insemination of, 183 .-•/.. 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 sq. ; 349 ; foetal nutrition in, 369, 372 sqq., 380, 388 sqq., 405, 420-436, 481, 483, 486 sq.t 489 n. ; pregnancy in, 494 sqq., 498, 500 sq., 508, 512, 515; female generative organs in, 525, 527 sqq. ; parturition in, 637 ; lactation in, 553 ; growth of 702 INDEX mammary glands in, 573 sqq., 578 egg. ; 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 limnocharia, 22 Rat, oestrous cycle in, 37, 40, 105 aqq. ; changes in the ovary in, 123 ; ovulatioh 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 Reaumur, 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 Remy, 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 Rhacophorua 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 sqq., 376, 389, 395 411, 413, 416 Rodentia, oestrous cycle in, 40 aqq. 232 n., 241 ; accessory reproduc- tive organs in, 244, 246 sq. ; foetal nutrition in, 388 sqq., 420 sqq, ; gestation in, 645 ; 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 - M., 530 Ruticilla phcenicurus, 316 Rutting season, defined, 35 sq. S Sadler, 646 Sagartia troglodytes, 8 sq., 679 Sainmont, 121 Salamander, 23, 177 Salamander maculosa, 186 Salmon, 18 sq., 28, 31, 278 sqq., 288, 292 sq., 295 Salvi, 62 Sander] ing, 24 Sandes, 149, 158, 337, 339 Sanger, 365 Sanson, 629 Sanyal, 63 Sarcophytum, 9 Saunders, 194 Sauropsida, 378, 380 Sauve, 320 Savare, 481 sq. Sawflies, 131 n., 629 Schafer, 24 sq., 116 sq., 153, 556, 562, 565, 569 Scharf, 55 Schenk, 630. See also Kleinhaus and Schenk Schmidt, Albert, 358, 405, 446 , H., 47 Schmiedeberg, 297, 299 Schmorl, 493 Schneidemiihl, 240 Schorndorff, 54 Sehottlander, 156 sqq. Schrader, 516 Schreiner, 281 Schroder, 68 INDEX 703 Schron, 118 Schulin, 156 sq. Schultz, 320 Schultza, 393, 642, 647, 650 Schutz, 532 Schweigger-Seidel. 173 Sciurus vulgar is, 41 Sclater, 65 Sclerophytum, 9 Scorpion, 350 Scyllium, 277 Seal, gestation of, 32 ; breeding season of, 59 sq. Sea-urchin, 199, 225, 301. See al#o under generic names Sedgwick. 6. 73, 186 Seeliger, 199 Seitz, 149, 156, 158 Selenka, 382, 392, 420. 465 Seligmann, 305, 306. See also Shattock and Seligmann Semen, chemistry of, 282 sqq. Seminal fluid, 176 Semnopithecus entellus, 63, 89 sqq., 97 Semnopitfiecus nasicus, 464 Semon, 18, 38, 39 Semper, 10, 12, 14, 15, 22, 31 Senescence, 675 sqq. Seps, 151 Seps chalcides, 380 Serraiach and Pares, 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 ; dioestrous cycle in, 37 ; oestrous 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 sq. ; fertility in, 590 sq., 596 sqq., 604 ; abortion in, 612 sq., 617 sqq. ; growth of, 668 ; age attained bv, 681 Sherrington, 255/259, 330 Shortt, 44, 47 Shrew, breeding season of, 60 ; foetal nutrition in, 372, 377, 391 sq., 452-5 Siebold, von, 186, 628 *-/. Sigismund, 162 Silkworm moth, 184, 217, 280 sq., 307, 626 Simocephalus, 632, 644 Simpson, Sir James, 537, ." 1 1 - J. Y., 213 Simpson (Sutherland) and Marshall, 262 Sims, 609 SinSty, 510. S»e also De Sin6ty Siphostoma floridrr, 652 Sipunculids, 224 Sirenia, 376 sq., 553 Sixta, 38 n. Skin, changes in, during pregnancy, 523 Siemens, 499, 505, 517 Slocum, 524 Sloth, 402, 553 Slowtzoff, 283 Smith, F., 314, 536, 667, 669, 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 SoU, 349 Somerset, 58 Sow, oestrous cycle in, 50, 334 ; ovulation in, 135 ; 145 ; in-breed- ing in, 208 ; foetal 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 sqq., 203 Sparrow, 24, 26, 157 Specht, 607 Spee, von, 363, 393, 443 sqq., 449, 466 Spencer, Herbert, 587 sqq. Spermatogenesis, chap. v. Spermatozoa, structure of, 1 72 sqq. ; movements of, 176 sqq. ; chemo- tactic properties of, 214 sqq. ; chemistry of, 288 sqq. Spemwphilus, 150 Sphcerechinus, 179, 300 SphoErechinus granulosus, 293, 300 Spider crab, 307 Spiegelberg, 542 sq. Spiegelberg and Gscheidlen, 520 sq. Spina, 254 Spinax, 151 704 INDEX Spitzer, 299 Sorex, 144, 150 Stag, breeding season of, 27 sq. ; effects of castration on, 305 Starfish. See Aaterias Starkweather, 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. Steudelj 294, 295, 296 Stevens, 12, 631, 633 Stevenson, 67 sq. See also News- holme and Stevenson Stilling, 232, 240, 350 Stoat, breeding season of, 59 Stbckel, 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 Hindus, 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 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 Tarchanoff, 22, 234, 275 Tarsius, 144, 150; foetal nutrition in, 408, 410, 463, 494 ; 552 Tarsius spectrum, 62, 97 sq., 137, 551 n. Tchermak, 193 Teacher, 138. See also Bryce and 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 sqq. ; in Man, ib. ; 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, 20 ; 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 ualtlii, 22 Tropidonotus, 277 Tropidonotus viper inus, 186 TruzzI, 523 Tupaia, 144, 150, 250, 377, 457 sq., 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 U Ulesco-Stroganowa, 479 Ungulata, oestrous cycle in, 42 ; INDEX 705 foetal nutrition in, 375, 386, 394 sqq., 417 sq., 484 ; lactation in, 553 aq. ; fertility in, 586 Uterus, structure of, 75 sqq. ; changes in, during cestrous cycle, chap. iii. ; significance of pro- oestrous changes in, 161 sqq. ; supposed internal secretion of, 345 aqq. ; innervation of, 527 aqq. Surnames with van and von are in- dexed under name following. Valenciennes and Fremy, 278 Valentin, 114, 252 Vallet, 526 Vaughan, 264 Veit, 493 aq., 506, 523, 587 Veit and Scholten, 480, 493, 515 Ver Eeke, 498, 500 sq., 503, 516 Vernhout, 456 Vernon, 203 aq. Verworn, 178 aq., 197, 200, 299, 570, 659, 683 Vesiculae seminales, 231 sqq. Vesperugo, 148, 150, 156 Veaperugo noctula, 132 Veapertilia, 148 Vicarelli, 68. See also Oddi and Vicarelli Virchow, 559, 570 Voit, 510 Volker, 149 W 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 ; cestrous cycle, 45, 47, 50, 51; 151, 214, 248, 307, 495; lactation, 566 sqq. ; fertility, 596, 599, 600, 604, 608; lili'i; 654 Wallart, 354 Walrus, breeding season of, 49, 60 ; 246 ' Walther, 278 Wapiti deer, oestrous cycle in, 49 ; 305 n. Water-buck, oestrous cycle in, 49 Watson, M., 250 - B. P., 565. See also Paton, Kerr, and Watson - Chalmers, 595 I Weasel, breeding season of, 59 Webb, Sidney, 621 aq. Weber, 313, 358 sqq., 375 Webster, 80, 138, 164, 367, 474, 476 aq. Weichardt and Opitz, 493 Weil, 135 Weininger, 654 aqq. Weinland, 302 Weismann, 172, 191, 192 aqq., 628, 631, 679 aq., 682 sq. Weiss, 292 " Wellenbewegung " hypothesis, 67, 164 Wendeler, 118, 145 Westermarck, 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 aq. Wiener, 365 Wild, 520 Willcock 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, 113, 122, 130, 131; spermato- genesis, 172, 174, 175 ; 190, 1'lii. 226, 356 ; sex-determination, 633, 636 S. M., 48 Wiltshire, 19, 25, 39, 50, 62, 66 Winckel, 505, 517, 522 Winckelmann, 520 Wini water, van, 117 sq., 131 Winkler, H., :{<><> F. N., 360 Winterhalter, 329 Winterstein and Stickler, •".-' I Win wood Reade, >••'. Wohlgemuth, 276 Wolf, breeding season of, 65 Wolfe, 513 Wood, 198 Woodruff, 214 Worthmann, 250 Wright, 23, 316 Wychgel, 516, 523 Wyder, 88 2Y 706 INDEX x Xenia hicksoni, 9 Xenopus lavis.ZO sqq. Zacharjewsky, 497 sq., 503, 505 sq. Y Ziegler, 641 Yak, 49 Zoarces, 151 Yolk-sac, 378 ; nutritive import- Zoth, 309 ance of, 380 sqq. Zuntz, L., 68, 355 Yule, 621 - E., 519 Youatt, 334 Yung, 625 Zweifel, 505 Zweifel and Abel, 346 I'rilitetl by I'.AI.I.AXTYNK, HANSON & Co. Kiliiiliurgh & London A LIST OF WORKS ON MEDICINE, SURGERY AND GENERAL SCIENCE CONTENTS PAGE ANATOMY 3 BACTERIOLOGY 18 BIOLOGY 13 CHEMISTRY 20 HEALTH AND HYGIENE 16 INDEX 2 MEDICINE ... 3 MISCELLANEOUS 10 MONOGRAPHS ON BIOCHEMISTRY 24 OPTICS 19 PHOTOGRAPHY 19 PHYSIOLOGY 13 PROCEEDINGS OF THE ROYAL SOCIETY OF MEDICINE ... 12 SURGERY 3 TEXT-BOOKS OF PHYSICAL CHEMISTRY 23 VETERINARY MEDICINE 12 ZOOLOGY 13 LONGMANS GREEN & CO. 39 PATERNOSTER ROW LONDON EC FOURTH AVE. & THIRTIETH ST. NEW YORK 8 HORNBY ROAD BOMBAY 303 BOWBAZAR STREET CALCUTTA 1910 INDEX. Abney's Photography 19 Armitage's A History of Chemistry 20 Armstrong's Simple Carbohydrates and the Glucosides 24 Arrhenius's Text-book of Electro-Chemistry 20 Theories of Chemistry so Ashby's Health in the Nursery ... >... 16 Notes on Physiology "... 13 and Wright's The Diseases of Children 3 Bain and Edgecombe's Harrogate Waters... 3 Baly's Spectroscopy 19, 23 Barnetfs Making of the Body 13 Bayliss' Nature of Enzyme Action 24 Beddard's Elementary Practical Zoology ... 13 Bell's Principles of Gynaecology 4 Bennett's Abdominal Hernia 3 On the Use of Massage 3 On Varix : Its Causes and Treatment 3 Recurrent Effusion into the Knee- joint after Injury 3 Treatment of Simple Fractures ... 3 Varicose Veins 3 Bidgood's Practical Elementary Biology ... 13 Bose's Comparative Electro-Physiology ... 13 Plant Response 13 Response in Living and Non-Living 13 Macalister's Zoology of the Invertebrate Animals Brodie's Essentials of Physiology Buck-ton's Health in the House Bull's Hints to Mothers... 13 18 16 Maternal Management of Children ... 16 Bunge's Organic Chemistry for Medical Students ... ... ... ... ... 20 Buttenvorth's Manual of Household Work 16 Cabot's Clinical Examination of the Blood... 4 Chapman's The Foraminifera ... ... ... 13 Charities Register and Digest 10 Cheyne and Burghard's Manual of Surgical Treatment 4 Coats' Manual of Pathology 5 Cooke's Aphorisms in Applied Anatomy ... 5 Tablets of Anatomy 5 Corfield's Laws of Health 16 Creighton's Economics ot the Household ... 16 Crookes' Methods in Chemical Analysis ... 20 Curtis' Practical Bacteriology 18 Dakin's Handbook of Midwifery ... ... 5 Desch's Metallography 23 Dickson's The Bone Marrow ... ... ... 5 Donnan's Thermodynamics 23 Drude's Theory of Optics 19 Ellis' Outlines of Bacteriology 18 Findlay's Phase Rule and its Application ... 23 Physical Chemistry 20 Practical Physical Chemistry 20 Fitzwygram's Horses and Stables 12 Fowler and Godlee's Diseases of the Lungs 6 Frankland's Bacteria in Daily Life 18 Friend's Theory of Valency 23 Furneaux's Human Physiology :4 Practical Hygiene 16 Gaskell's Th« Origin of the Vertebrates ... 10 Glazebrook's Physical Optics 19 Goadby's Mycology of the Mouth 18 Godfrey's Elementary Chemistry 20 Goodsall and Miles' Diseases of the Anus and Rectum 6 Gray's Anatomy, Descriptive and Applied ... 6 Halliburtpn's The Essentials of Chemical Physiology 14 Hanson's and Dodgson's Intermediate Course of Laboratory Work in Chemistry 20 Harden's Alcoholic Fermentation ... ... 24 Hardy's Colloids 24 Hare's The Food Factor in Disease 6 Hayes' Training and Horse Management ... 12 Hobart's Medical Language of St. Luke ... 10 Hopfs Human Species ... ... ... ... 10 Hopkins' Development and Present Position of Biological Chemistry 24 Hudson and Gosse's The Rptifera 14 Influence of Heredity on Disease Inquiry into the Phenomena attending Death by Drowning n James's Ball Games and Breathing F.xercises 16 King's College Hospital Cooking Recipes ... n Klocker's Fermentation Organisms 18 Leathes' The Fats 24 Lehfeldt's Electro-Chemistry 23 Ling's The Polysaccharides 24 Lloyd and Bigelow's Teaching of Biology ... 14 Luff's Text-book of Forensic Medicine ... 7 Macalister's Systematic Zoology of the Vertebrate Animals . 14 Vertebrate Animals ... Macdougall's Elementary Plant Physiology Text-book of Plant Physiology Mees' Atlas of Absorption Spectra Mellor's Chemical Statics and Dynamics ... Mendele'effs Principles of Chemistry Meyer's Outlines of Theoretical Chemistry Monographs on Bi chemistry Moon's Relation of Medicine to Philosophy Moore's Elementary Physiology Morgan's Animal Biology Muir's Course of Practical Chemistry Newth's Chemical Lecture Experiments Elementary Practical Chemistry Manual of Chemical Analysis... Smaller Chemical Analysis Text-book of Inorganic Chemistry... Notter and Firth's Hygiene 17 Practical Domestic Hygiene 17 Osborne's Vegetable Proteins 24 Ostwald's Principles of Chemistry 21 Paget's Memoirs and Letters n Perkin's Methods of Electro-Chemistry ... 21 Qualitative Chemical Analysis ... 21 Pettigrew's Design in Nature n Plimmer's Constitution of the Proteins ... 24 Pollok's Practical Spectographic Analysis 19, 23 Poole's Cookery for the Diabetic n Poore's Colonial and Camp Sanitation Essays on Rural Hygiene The Dwelling House The Earth in Relation to Contagia Porter's Sanitary Law School Hygiene Price and Twiss' Organic Chemistry Probyn-Williams' The Administration of Anaesthetics 7 Proceedings of the Royal Society of Medicine 12 Quain's Dictionary of Medicine 7 Elements of Anatomy (loth Edition)... 8 (nth Edition)... 9 Radclifle and Sinnatt's Practical Organic Chemistry 21 Raffety's Science of Radio Activity n Reynolds' Experimental Chemistry 21 Robinson's Health of our Children in the Colonies 17 Schafer's Essentials of Histology 9 Practical Physiology 15 Schryver's Characters of the Proteins ... 24 Sheppard and Mees' Photographic Process... 19 Sheppard's Actinochemistry 23 Smale and Colyer's Diseases and Injuries of the Teeth 9 Smiles' Chemical Constitutions and Physical Properties 23 Smith and Hall's Teaching of Chemistry and Physics in Secondary School ... 21 Handbook for Midwives o 12 Steel's Diseases of the Ox Sheep Stevenson's Wounds in War 10 Stewart's Physical and Inorganic Chemistry 22 Recent Advances in Organic Chemistry 22 Stereochemistry 23 Sutherland-Gower's Cleanliness versus Cor- ruption ii Symington and Rankin's Atlas of Skiagrams 10 Text- Books of Physical Chemistry Thomsen's Thermochemistry ... Thornton's Elementary Biology Practical Physiology Human Physiology Thorpe's Dictionary of Applied Chemistry... 22 Tilden's Chemical Philosophy 22 Practical Chemistry 22 Progress of Scientific Chemistry ... 22 Vanderpoel's Colour Problems ... ... 19 Waller's Introduction to Human Physiology 15 Watt's Dictionary of Chemistry 22 West's How to Nurse Sick Children 17 Weston's Detection of Carbon Compounds... 22 Whiteley's Chemical Calculations 22 Organic Chemistry Williams' Rhinology 10 Wilsmore's Electro-Chemistry 23 Wright's Optical Projection 19 Youatt's The Dog 12 The Horse 12 Young's Stoichiometry , ... 23 MEDICINE, SURGERY, ANATOMY, ETC. ASHBY AND WRIGHT. THE DISEASES OF CHILDKEN, MEDICAL AND SUKGICAL. By HENRY ASHBY, M.D. Lond., F.R.C.P., late Physician to the Manchester Children's Hospital ; and G. A. WRIGHT, B.A., M.B. Oxon., F.R.C.S. Eng., Surgeon to the Manchester Royal Infirmary ; Consulting Surgeon to the Manchester Child- ren's Hospital. With 15 Plates (1 Coloured) and 241 Illustrations in the Text. Fifth Edition. Thoroughly Revised, 1905. 8vo, 21s. net. BAIN AND EDGECOMBE. THE PHYSIOLOGY AND THEEAPEUTICS OF THE HAEEOGATE WATEES, BATHS, AND CLIMATE APPLIED TO THE TEEAT- MENT OF CHEONIC DISEASE. By WILLIAM BAIN, M.D., M.R.C.P., and WILFBID EDGECOMBE, M.D. 8vo, 7s. 6d. net. BENNETT.— WORKS by Sir WILLIAM H. BENNETT, K.C.V.O., F.R.C.S., Surgeon to St. George's Hospital. EECUEEENT EFFUSION INTO THE KNEE-JOINT AFTEE INJUEY, WITH ESPECIAL EEFEEENCE TO INTEENAL DEEANGEMENT, COMMONLY CALLED SLIPPED CAE- TILAGE : an Analysis of 750 Cases. A Clinical Lecture delivered at St. George's Hospital. With 13 Illustrations. 8vo, 3s. 6d. CLINICAL LECTUEES ON VAEICOSE VEINS OF THE LOWEE EXTEEMITIES. With 3 Plates. 8vo,6s. CLINICAL LECTUEES ON ABDOMINAL HEENIA : chiefly in relation to Treatment, including the Radical Cure. With 12 Diagrams in the Text. 8vo, 8s. 6d. ON VAEIX, ITS CAUSES AND TEEATMENT, WITH ESPECIAL EEFEEENCE TO THEOMBOSIS. 8vo, 3s. 6d. LECTUEE ON THE USE OF MASSAGE AND EAELY MOVEMENTS IN EECENT FEACTUEES AND OTHEB COMMON SUEGICAL INJUEIES : SPEAINS AND THEIE CONSEQUENCES : EIGIDITY OF THE SPINE, AND THE MANAGEMENT OF STIFF JOINTS GENEEALLY. With 23 Illustrations. 8vo, 6.s. THE PEESENT POSITION OF THE TEEATMENT OF SIMPLE FEACTUEES OF THE LIMBS : an Address delivered to the British Medical Association. To which is appended a Summary of the Opinions and Practice of about 300 Surgeons. 8vo, 2s. 6d. 4 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. MEDICINE, SURGERY, ANATOMY, ETC.— continued. BELL. THE PRINCIPLES OF GYNAECOLOGY. By w. BLAIR BELL, B.S., M.D., Assistant Gynaecological Surgeon, Eoyal Infirmary, Liverpool. With Illustrations. 8vo. A concise, yet complete" account of the development, anatomy and physiology of the female genital organs. The methods of physical examination are fully described. The diseases of the special organs and the allied morbid conditions are discussed, special attention being paid to the pathology which is illustrated by numerous photomicrographs and drawings of actual specimens, each of which is carefully described. CABOT. A GUIDE TO THE CLINICAL EXAMINATION OF THE BLOOD FOR DIAGNOSTIC PURPOSES. By RICHARD C. CABOT, M.D., Physician to Out-Patients, Massachusetts General Hospital. With 3 Coloured Plates and 28 Illus. in Text. 8vo, 16s. CHEYNE AND BURGHARD. A MANUAL OF SURGICAL TREATMENT. By Sir W. WATSON CHEYNE, Bart., C.B., M.B., F.R.C.S., P.R.S., D.Sc., Professor of Clinical Surgery in King's College, London ; Surgeon to King's College Hospital, and the Children's Hospital, Paddington Green, etc.; and F. F. BURGHARD, M.D. and M.S. Lond., F.R.C.S., Teacher of Practical Surgery in King's College, London ; Surgeon to King's College Hospital, and the Children's Hospital, Paddington Green, etc. PART I. The treatment of General Surgical Diseases, including inflam- mation, suppuration, ulceration, gangrene, wounds and their compli- cations, infective diseases and tum- ours; the administration of anaesthe- tics. With 66 Illustrations. Royal 8vo, 9s. net. PART II. The treatment of the Surgical Affections of the Tissues, including the skin and subcutaneous tissues, the nails, the lymphatic vessels and glands, the fasciae, bursae, muscles, tendonsand tendon-sheaths, nerves, arteries and veins ; deformities. With 141 Illustrations. Royal 8vo, 12s. net. PART III. The treatment of the Surgical Affections of the Bones. Ampu- tations. With 100 Illustrations. Royal 8vo, 10s. 6d. net. PART IV. The treatment of the Surgical Affections of the Joints (including excisions) and the spine. With 138 Illustrations. Royal 8vo, 12s. net. PABT V. The treatment of the Surgical Affections of the head, face, jaws, lips, larynx and trachea ; and the Intrinsic Diseases of the nose, ear and larynx, by H. LAMBERT LACK, M.D. (Lond.), F.R.C.S., Surgeon to the Hospital for Diseases of the Throat, Golden Square, and to the Throat and Ear Department, the Children's Hospital, Paddington Green. With 145 Illustrations. Royal 8vo, 15s. net. PART VI. — Section 1. The Surgical Affections of the tongue and floor of the mouth, the pharynx, neck, oesophagus, stomach and intestines. With an Appendix on the Examin- ation of the Blood in Surgical Condition. By W. ESTE EMERY, M.D., D.Sc. (Lond.). With 124 Illustrations. Royal 8vo, 15s. net. Section 2. The Surgical Affections of the rectum, the liver, pancreas and spleen, and genito-urinary organs, the breast and the thorax. With 113 Illustrations. Royal 8vo, 18s. net. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 5 MEDICINE, SURGERY, ANATOMY, ETC.— continued. COATS. A MANUAL OF PATHOLOGY. By JOSEPH COATS, M.D., late Professor of Pathology in the University of Glasgow. Fifth Edition, 1903. Revised throughout and Edited by LEWIS R. SUTHER- LAND, M.D., Professor of Pathology, University of St. Andrews. With 729 Illustrations and 2 Coloured Plates. 8vo, 28s. net. COOKE. — WORKS by THOMAS COOKE, F.P.C.S. Eng., B.A., B.Sc., M.D. Paris, late Senior Assistant Surgeon to the Westminster Hospital. TABLETS OF ANATOMY. Being a Synopsis of demonstrations given in the Westminster Hospital Medical School. Eleventh Edition in three Parts, thoroughly brought up to date, and with over 700 Illustrations from all the best sources, British and Foreign. Post 4to. Part I. The Bones, 7s. 6d. net ; Part II. Limbs, Abdomen, Pelvis, 10s. 6d. net ; Part III. Head and Neck, Thorax, Brain, 10s. 6d. net. APHOEISMS IN APPLIED ANATOMY AND OPERATIVE SURGERY. Including 100 Typical viva voce Questions on Surface Marking, etc. Crown 8vo, 3s. 6d. DAKIN. A HANDBOOK OF MIDWIFERY. By WILLIAM RAD- FORD DAKIN, M.D., F.R.C.P., Obstetric Physician and Lecturer on Midwifery at St. George's Hospital, Examiner in Midwifery and Diseases of Women on the Conjoint Board of the Royal Colleges of Physicians and Surgeons in England, etc. With 400 Illustrations. Large crown 8vo, 18s. DICKSON. THE BONE-MARROW : a Cytological Study. Forming an Introduction to the Normal and Pathological Histology of the Tissue, more especially with regard to Blood Formation, Blood Destruction, etc. Together with a short account of the Reactions and Degenerations of the Tissue in Disease. By W. E. CARNEGIE DICKSON, M.D., B.Sc. Edin., F.R.C.P. Edin., Lecturer on Pathological Bacteriology and Senior Assistant to the Professor of Pathology in the University of Edinburgh ; Assistant Pathologist to the Edinburgh Royal Infirmary. With 12 Coloured Plates and 51 Micro- Photographs by Richard Muir. Medium 4to, £2 2s. net. 6 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. MEDICINE, SURGERY, ANATOMY, ETC.— continued. FOWLER AND GODLEE. THE DISEASES OF THE LUNGS. By JAMES KINGSTON FOWLER, M.A., M.D., F.R.C.P., Physician to the Middlesex Hospital and to the Hospital for Consumption and Diseases of the Chest, Brompton, etc. ; and RICKMAN JOHN GODLEE, M.S., F.R.C.S., Honorary Surgeon-in-Ordinary to His Majesty, Fellow and Professor of Clinical Surgery, University College, London, etc. With 160 Illustrations. 8vo, 25s. GOODSALL AND MILES. DISEASES OF THE ANUS AND RECTUM. By D. H. GOODSALL, F.R.C.S., late Senior Surgeon Metropolitan Hospital, Senior Surgeon St. Mark's Hospital ; and W. ERNEST MILES, F.R.C.S., Assistant Surgeon to the Cancer Hospital, Surgeon (out-patients) to the Gordon Hospital, etc. (In Two Parts). PART I. — Anatomy of the Ano-rectal Region — General Diagnosis — Abscess — Ano-rectal Fistula — Recto-urethral, Recto-vesical and Recto-vaginal Fistulse — Sinus over the Sacro-coccygeal Articulation — Fissure — Haemorr- hoids (External and Internal). With 91 Illustrations. 8vo, 7s. 6d. net. PART II. — Prolapse of the Rectum — Invagination of the Rectum — Ulceration — Stricture of the Anus and of the Rectum — Malignant Growths of the Anus and Rectum — Benign Tumours of the Anus and Rectum — Foreign Bodies in the Rectum — Pruritus Ani — Syphilis of the Anus and Rectum. With 44 Illustrations. 8vo, 6s. net. GRAY. ANATOMY, DESCRIPTIVE AND APPLIED. By HENRY GRAY, F.R.S., late Lecturer on Anatomy at St. George's Hospital Medical School. Seventeenth Edition. Edited by ROBERT HOWDEN, M.A., M.B., C.M., Professor of Anatomy in the University of Durham. Notes on Applied Anatomy, revised by A. J. JEX-BLAKE, M.A.. M.B., M.R.C.P., Assistant Physician to St. George's Hospital; and W. FEDDE FEDDEN, M.S., F.R.C.S., Assistant Surgeon and Lecturer on Surgical Anatomy, St. George's Hospital. With 1,032 Illustrations. Royal 8vo, 32s. net. HARE. THE FOOD FACTOR IN DISEASE : Being an investiga- tion into the humoral causation, meaning, mechanism and rational treat- ment, preventive and curative, of the Paroxysmal Neuroses (migraine, asthma, angina pectoris, epilepsy, etc.), bilious attacks, gout, catarrhal and other affections, high blood-pressure, circulatory, renal and other degenerations. By FRANCIS HARE, M.D., late Consulting Physician to the Brisbane General Hospital ; Visiting Physician at the Diamantina Hospital for Chronic Diseases, Brisbane ; Inspector-General of Hospitals for Queensland. 2 vols. Medium 8vo, 30s. net. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 7 MEDICINE, SURGERY, ANATOMY, ETC.— continued. INFLUENCE OF HEEEDITY ON DISEASE (THE), WITH SPECIAL EEFEEENCE TO TUBEECTTLOSIS, CANCEE AND DISEASES OF THE NEEVOUS SYSTEM. A Dis- cussion opened by SIB WILLIAM S. CHURCH, Bt., K.C.B., M.D., SIB WILLIAM R. GOWERS, M.D., F.R.S. (Diseases of the Nervous System), ARTHUR LATHAM, M.D. (Tuberculosis), and E. F. BASHFORD, M.D. (Cancer). [From the Proceedings of the Royal Society of Medicine, 1909, Vol. II., No. 3.] 4to, 4s. 6d. net. LUFF. TEXT - BOOK OF FOEENSIC MEDICINE AND TOXICOLOGY. By ARTHUR P. LUFF, M.D., B.Sc. Lond., Physician in Charge of Out-Patients and Lecturer on Medical Jurisprudence and Toxicology in St. Mary's Hospital ; Examiner in Forensic Medicine in the University of London ; External Examiner in Forensic Medicine in the Victoria University ; Official Analyst to the Home Office. With 13 full- page Plates (1 in colours) and 33 Illustrations in the Text. 2 vols., Crown 8vo, 24s. PROBYN-WILLIAMS. A PEACTICAL GUIDE TO THE ADMIN ISTEATION OF ANAESTHETICS. By R. J. PROBYN-WILLIAMS, M.D., Senior Anaesthetist and Instructor in Anaesthetics at the London Hospital, etc. With 44 Illustrations. Crown 8vo, 4s. 6d. net. QUAIN. QUAIN'S (SiR EICHAED) DICTIONAEY OF MEDI- CINE. By Various Writers. Edited by H. MONTAGUE MURRAY, M.D., F.R.C.P., Joint Lecturer on Medicine, Charing Cross Medical School, and Physician to Charing Cross Hospital, and to the Victoria Hospital for Children, Chelsea ; Examiner in Medicine to the University of London. Assisted by JOHN HAROLD, M.B., B.Cn., B.A.O., Physician to St. John's and St. Elizabeth's Hospital, and Demonstrator of Medicine at Charing Cross Medical School, and W. CECIL BOSANQUET, M.A., M.D., F.R.C.P., Assistant Physician, Charing Cross Hospital, etc. Third and Cheaper Edition, largely Rewritten, and Revised throughout. With 21 Plates (14 in Colour) and numerous Illustrations in the Text. 8vo, 21s. net., buckram. 8 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. MEDICINE, SURGERY, ANATOMY, 'ETC.— continued. QUAIN. QUAIN'S (JONES) ELEMENTS OF ANATOMY. The TENTH EDITION. Edited by EDWARD ALBERT SCHAFER, F.R.S., Professor of Physiology in the University of Edinburgh ; and GEORGE DANCER THANE, Professor of Anatomy in University College, London. %* The several parts of this work form COMPLETE TEXT-BOOKS OF THEIB RESPECTIVE SUBJECTS. They can be obtained separately as follows : — VOL. L, PABT I. EMBEYOLOGY. By E. A. SCHAFER, F.R.S. With 200 Illustrations. Royal 8vo, 9s. VOL. L, PART II. GENEEAL ANATOMY OE HISTOLOGY. By E. A. SCHAFER, F.R.S. With 491 Illustrations. Royal 8vo. [Out of print. VOL. II., PART I. OSTEOLOGY— AETHEOLOGY. By G. D. THANE. With 224 Illustrations. Royal 8vo, 11s. VOL. II., PART II. MYOLOGY— ANGEIOLOGY. By G. D. THANE. With 199 Illustrations. Royal 8vo, 16s. VOL. III., Part I. THE SPINAL COED AND BEAIN. By E. A. SCHAFER, F.R.S. With 139 Illustrations. Royal 8vo, 12s. Qd. VOL. III., PART II. THE NEEVES. By G. D. THANE. With 102 Illustrations. Royal 8vo, 9s. VOL. III., PART III. THE OEGANS OF THE SENSES. By E. A. SCHAFER, F.R.S. With 178 Illustrations. Royal 8vo, 9s. VOL. III., PART IV. SPLANCHNOLOGY. By E. A. SCHAFER, F.R.S., and JOHNSON SYMINGTON, M.U. With 337 Illustrations. Royal 8vo, 16s. APPENDIX. SUPEEFICIAL AND SUEGICAL ANATOMY. By Professor G. D. THANE and Professor R. J. GODLEE, M.S. With 29 Illustrations. Royal Svo, 6s. 6d. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 9 MEDICINE, SURGERY, ANATOMY, ETC.— continued. QUAIN. QUAIN'S ELEMENTS OF ANATOMY. The ELEVENTH EDITION. Edited by EDWARD ALBERT SCHAFER, F.R.S., Professor of Physiology and Histology in the University of Edinburgh ; JOHNSON SYMINGTON, M.D., F.R.S., Professor of Anatomy in Queen's College, Belfast ; and THOMAS HASTIE BRYCE, M.A., M.D., Regius Professor of Anatomy in the University of Glasgow. IN FOUR VOLUMES. Royal 8vo. VOL. I. EMBEYOLOGY. By T. H. BRYCE, M.A., M.D. Illustrated by more than 300 Engravings, many of which are coloured. 10s. 6d. net. VOL. III. NEUEOLOGY. By E. A. SCHAFER and J. SYMINGTON. Part I. Containing the General Structure of the Nervous System and the Structure of the Brain and Spinal Cord. With 361 Illustrations, many of which are coloured. 15s. net. Part II. Containing the Descriptive Anatomy of the Peripheral Nerves and of the Organs of Special Sense. With 321 Illustrations, many of which are coloured. 15s. net. %* The other Volumes are in preparation. This work has been completely re-edited and brought up to date. The volumes will comprise respectively Embryology; General and Visceral Anatomy ; the Nervous System and Sense Organs ; and the Bones, Ligaments, Muscles, and Blood-vessels. Each volume will be complete in itself, and will serve as a text-book for the particular subject or subjects with which it deals. Thus the first volume is intended to form a com- plete text-book of Human Embryology, the second a text-book of His- tology and Visceral Anatomy, the third a text-book of Neurology, the fourth dealing with the systems which are not included in the second and third volumes. SCHAFER. THE ESSENTIALS OF HISTOLOGY: Descriptive and Practical. For the Use of Students. By E. A. SCHAFER, F.R.S., Professor of Physiology in the University of Edinburgh. With 553 Illustra- tions some of which are Coloured. Seventh Edition, 1907. 8vo, 10s. 6d. net. SMALE AND COLYER. DISEASES AND INJUEIES OF THE TEETH, including Pathology and Treatment. By MORTON SMALE, M.R.C.S., L.S.A., L.D.S., Dental Surgeon to St. Mary's Hospital, Consulting Dental Surgeon, Dental Hospital of London, etc. ; and J. F. COLYER, L.R.C.P., M.R.C.S., L.D.S., Dental Surgeon to Charing Cross Hospital and to the Dental Hospital of London, Dean of the School, Dental Hospital of London. Second Edition Revised and Enlarged by J. F. COLYER. With 645 Illustrations. Large Crown 8vo, 21s. net. SMITH. THE HANDBOOK FOE MID WIVES. By HENRY FLY SMITH, 'B. A., M.B., Oxon., M.R.C.S. Second Edition. With 41 Woodcuts. Crown 8vo, 5s. 10 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. MEDICINE, SURGERY, ANATOMY, ETC.— continued. STEVENSON. WOUNDS IN WAE : the Mechanism of their Production and their Treatment. By Surgeon-General W. F. STEVENSON, C.B. (Army Medical Staff), B.A., M.B., M.Ch. Dublin University; Professor of Military Surgery, Royal Army Medical College, London. With 127 Illustrations. 8vo, 15s. net. SYMINGTON AND RANKIN. AN ATLAS OF SKIAGKAMS, ILLUSTEATING THE DEVELOPMENT OF THE TEETH. With Explanatory Text, By JOHNS JN SYMINGTON, M.D., F.R.S., Professor of Anatomy, Queen's College, Belfast; and J. C. RANKIN, M.D., Physician in charge of the Electrical Department, Royal Victoria Hospital, Belfast. With ]2 Plates. Demy 4to. 10s. 6d. net. WILLIAMS. RHINOLOGY : a Text-book of Diseases of the Nose and the Nasal Accessory Sinuses. By PATRICK WATSON WILLIAMS, M.D. (London). With 3 Coloured Plates and 44 Black and White Plates (of which 26 are Stereoscopic) and 140 Illustrations in the Text. 8vo, 12s. 6d. net. With Stereoscope, 15s. net. MISCELLANEOUS. ANNUAL CHARITIES REGISTER AND DIGEST : being a Classi- fied Register of Charities in or available for the Metropolis, together with a Digest of Information respecting the Legal, Voluntary, and other Means for the Prevention and Relief of Distress and the Improvement of the Condition of the Poor. With an elaborate Index, and an Introduction, "How to Help Cases of Distress". By C. S. LOCH, Secretary to the Council of the Charity Organisation Society, London. 8vo, 5s. net. CASK ELL. THE ORIGIN OF VERTEBRATES. By WALTER H. GASKELL, M.A., M.D. (Camb.), LL.D. (Edinburgh and McGill Univ., Montreal), F.R.S., Fellow of Trinity Hall and University Lecturer in Physiology, Cambridge. With 168 Illustrations. 8vo, 21s. net. HOBART. THE MEDICAL LANGUAGE OF ST. LUKE. By the Rev. WILLIAM KIRK HOBART, LL.D. 8vo, 16s. HOPF. THE HUMAN SPECIES : CONSIDERED FROM THE STANDPOINTS OF COMPARATIVE ANATOMY, PHYSI- OLOGY, PATHOLOGY AND BACTERIOLOGY. By Dr. LUDWIG HOPF. Authorised English Translation. With 7 Plates and 217 Illustrations in the Text. 8vo, 10s. 6d. net. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 11 MISCELLANEOUS— continued. INQUIRY (AN) INTO THE PHENOMENA ATTENDING DEATH BY DEOWNING AND THE MEANS OF PRO- MOTING RESUSCITATION IN THE APPARENTLY DROWNED. Report of a Committee appointed by the Royal Medical and Chirurgical Society. With 2 Diagrams and 26 Plates. 8vo, 5s. net. KING'S COLLEGE HOSPITAL BOOK OF COOKING RECIPES : being a Collection of Recipes contributed by Friends of the Hospital and Published in aid of the Fund for the Removal of King's College Hospital to South London. Crown 8vo, Is. net. MOON. THE RELATION OF MEDICINE TO PHILOSOPHY. By R. O. MOON, M.A., M.D. (Oxon.), F.R.C.P., Physician to the National Hospital for Diseases of the Heart, etc. Crown 8vo, 4s. 6rf. net. PAGET. MEMOIRS AND LETTERS OF SIR JAMES PAGET, Bart., F.R.S., Sergeant-Surgeon to Her late Majesty Queen Victoria. Edited by STEPHEN PAGET, F.R.C.S. With Portrait. 8vo, 6s. net. PETTIGREW. DESIGN IN NATURE : Illustrated by Spiral and other Arrangements in the Inorganic and Organic Kingdoms as exemplified in Matter, Force, Life, Growth, Rhythms, etc., especially in Crystals, Plants, and Animals. With Examples selected from the Reproductive, Alimentary, Respiratory, Circulatory, Nervous, Muscular, Osseous, Loco motory, and other Systems of Animals. By J. BELL PETTIGREW, M.D., LL.D., F.R.S., F.R.C.P. ; Laureate of the Institute of France ; late Chandos Professor of Anatomy and Medicine in the University, St. Andrews; Fellow of the Royal Botanical, Medico- Chirurgical, Royal Medical. Literary and Philosophical, Harveian and other Societies. Illustrated by nearly 2,000 Figures, largely original and from nature. In 3 vols. 4to. 63s. net. POOLE. COOKERY FOR THE DIABETIC. By W. H. and Mrs. POOLE. With Preface by Dr. PAVY. Fcap. 8vo, 2s. Gd. RAFFETY. AN INTRODUCTION TO THE SCIENCE OF RADIO-ACTIVITY. By CHARLES W. RAFFETY. With 27 Illustrations. Crown 8vo. 4s. 6d. net. SUTHERLAND-GOWER. CLEANLINESS VEBSUS COR- RUPTION. By Lord RONALD SUTHERLAND-GONYKK. With 11 Illustrations. Crown 8vo, paper covers, 6d. .1 pica fur the mwv yenrral adujdion of cremation for human 12 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. THE PROCEEDINGS OF THE ROYAL SOCIETY OF MEDICINE. The Royal Society of Medicine was formed in June, 1907, by the amalgamation of the following London Medical Societies : — The Royal Medical and Chirurgical Society. The Pathological Society. The Epidemiological Society. The Odontological Society of Great Britain. The Obstetrical Society. The Clinical Society. The Dermatological Society. The British Gynaecological Society. The Neurological Society. The British Laryngological, Rhinologi. cal, and Otological Association. The Laryngological Society. The Dermatological Society of Great Britain and Ireland. The Otological Society of the United Kingdom. The British Electro-therapeutic Society. The Therapeutical Society. The " Proceedings " of the Royal Society of Medicine are published monthly from November to July inclusive. Tlie numbers contain the papers of, and the discussions read at each of the Sections during the previous month, and are so arranged that each Section can, if desired, be detached and bound separately at tlit end of the year. The Annual Subscription is £3 3s. net, which may be paid through any bookseller. The price of each montMy number is 7s* 6d. net. VETERINARY MEDICINE, ETC. FITZWYGRAM. HOESES AND STABLES. By Lieutenant- General Sir P. PITZWYGRAM, Bart. With 56 pages of Illustrations. 8vo, 3s. net. HAYES. TEAINING AND HOUSE MANAGEMENT IN INDIA. With Hindustanee Vocabulary. By M. HORACE HAYES, P.R.C.V.S. (late Captain, "The Buffs"). With Portrait. Crown 8vo, 8s. net. STEEL— WORKS by JOHN HENRY STEEL, F.R.C.V.S., F.Z.S., A.V.D., late Professor of Veterinary Science and Principal of Bombay Veterinary College. A TREATISE ON THE DISEASES OF THE OX ; being a Manual of Bovine Pathology. Especially adapted for the use of Veterinary Practitioners and Students. With 2 Plates and 117 Woodcuts. 8vo, 15s. A TREATISE ON THE DISEASES OF THE SHEEP ; being a Manual of Ovine Pathology for the use of Veterinary Practitioners and Students. With Coloured Plate and 99 Woodcuts. 8vo, 12s. YOUATT.- WORKS by WILLIAM YOU ATT. THE HORSE. Revised and Enlarged by W. WATSON, M.R.C.V.S. With 52 Wood Engravings. 8vo, 7s. 6d. JJHE DOG. Revised and Enlarged. With 33 Wood Engravings. 8vo, Gs. MESSRS. LONGMANS' WORKS ON MEDtdNE, SfrRGERf, E?C. 13 PHYSIOLOGY, BIOLOGY, ZOOLOGY, ETC. ASH BY. NOTES ON PHYSIOLOGY FOR THE USE OF STUDENTS PREPARING FOR EXAMINATION. By HENRY ASHBY, M.D. (Lond.), F.R.C.P., late Physician to the General Hospital for Sick Children, Manchester ; Lecturer and Examiner in Diseases of Children in the Victoria University. Revised by HUGH T. ASHBY, B.A., M.B., B.C. (Camb.), M.R.C.P. (Lond.). With 148 Illus- trations. 18mo, 5s. BARNETT. THE MAKING OF THE BODY: a Children's Book on Anatomy and Physiology. By Mrs. S. A. BARNETT. With 113 Illustrations. Crown 8vo, Is. 9d. BEDDARD. ELEMENTARY PRACTICAL ZOOLOGY. By FRANK E. BEDDARD, M.A. (Oxon.). With 93 Illustrations. Crown 8vo, 2a. 6d. BIDGOOD. A COURSE OF PRACTICAL ELEMENTARY BIOLOGY. By JOHN BIDGOOD, B.Sc., F.L.S. With 226 Illustra- tions. Crown 8vo, 4s. 6d. BOSE.—WORKS fy JAGADIS CHUNDER BOSS, M.A. (Cantab.), D.Sc. (Lond.), Professor, Presidency College, Calcutta. RESPONSE IN THE LIVING AND NON-LIVING. With 117 Illustrations. 8vo, 10s. 6d. PLANT RESPONSE AS A MEANS OF PHYSIOLOGICAL INVESTIGATION. With 278 Illustrations. 8vo, 21s. COMPARATIVE ELECTRO-PHYSIOLOGY: A PHYSICO- PHYSIOLOGICAL STUDY. With 406 Illustrations and Classi- fied List of 321 new Experiments. 8vo, 15s. net. BRODIE. THE ESSENTIALS OF EXPERIMENTAL PHY- SIOLOGY. For the use of Students. By T. G. BRODIE, M.D., Lecturer on Physiology, St. Thomas's Hospital Medical School. With 2 Plates and 177 Illustrations in the Text. Crown 8vo, 6s. 6d. CHAPMAN, THE FORAMINIFERA : an Introduction to the Study of the Protozoa. By FREDERICK CHAPMAN, A.L.S., F.R.M.S. With 14 Plates and 42 Illustrations in the Text. 8vo, 9s. net. 14 MESSRS. LONGMANS' 1&ORKS ON MEDICINE, SURGERY, ETC. PHYSIOLOGY, BIOLOGY, ZOOLOGY, ETC.— continued. FURNEAUX, HUMAN PHYSIOLOGY. By w. FURNEAUX, F.R.G.S. With 223 Illustrations. Crown 8vo, 2s. 6d. HALLIBURTON. THE ESSENTIALS OF CHEMICAL PHY- SIOLOGY. For the Use of Students. By W. D. HALLIBURTON, LL.D., M.D., F.R.S., F.R.C.P., Professor of Physiology in King's College, London. With 71 Illustrations. 8vo, 4s. 6d. net. HUDSON AND GOSSE. THE EOTIFEEA OE "WHEEL ANIMALCULES ". By C. T. HUDSON, LL.D., and P. H. GOSSE, F.R.S. With 30 Coloured and 4 Uncoloured Plates. In 6 Parts. 4to, price 10s. 6d. each; Supplement, 12s. 6d. Complete in Two Volumes, with Supplement, 4to, £4 4s. *,* The Plates in the Supplement contain figures of almost all the Foreign Species, as well as of the British Species, that have been discovered since the original publication of Vols. I. and II. LLOYD AND BIGELOW. THE TEACHING OF BIOLOGY IN THE SECONDAEY SCHOOL. By FRANCIS E. LLOYD, A.M., and MAURICE A. BIGELOW, Ph.D., Professors in Teachers' College, Columbia University. Crown 8vo, 6s. net. MACALISTER.— WORKS by ALEXANDER MA&ALISTER, M.D. AN INTEODUCTION TO THE SYSTEMATIC ZOOLOGY AND MOEPHOLOGY OF VEETEBEATE ANIMALS. With 41 Diagrams. 8vo, 10s. 6d. ZOOLOGY OF THE INVEETEBEATE ANIMALS, with 77 Diagrams. Fcp. 8vo, la. Gd. ZOpLOGY OF THE VEETEBEATE ANIMALS, with 59 Diagrams. Fcp. 8vo, Is. Gd. MACDOUGALL.— WORKS by]>ANIEL TREMBLY MACDOUGALL, I'h.ii. TEXT-BOOK OF PLANT PHYSIOLOGY, with 159 lilustra- tions. 8vo, 7s. 6d. net. ELEMENTAEY PLANT PHYSIOLOGY, with 108 illustrations. Crown 8vo, 3s. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 15 PHYSIOLOGY, BIOLOGY, ZOOLOGY, ETC.— continued. MOORE. ELEMENTAEY PHYSIOLOGY AND ANATOMY. By BENJAMIN MOORE, D.Sc., Professor of Bio-Chemistry in the University of Liverpool. With 125 Illustrations. Crown 8vo, 3s. 6d. MORGAN. ANIMAL BIOLOGY. An Elementary Text-Book. By C. LLOYD MORGAN, F.R.S., Principal of University College, Bristol. With numerous Illustrations. Crown 8vo, 8s. 6d. SCHAFER. DIEECTIONS FOR CLASS WOEK IN PEAC- TICAL PHYSIOLOGY: Elementary Physiology of Muscle and Nerve and of the Vascular and Nervous Systems. By E. A. SCHAFER, LL.D., F.R.S., Professor of Physiology in the University of Edinburgh. With 48 Diagrams. 8vo, 3s. net. THORNTON.— WORKS by JOHN THORNTON, M.A. HUMAN PHYSIOLOGY. With 284 Illustrations, some of which are Coloured. Crown 8vo, 6s. ELEMENTAEY BIOLOGY, Descriptive and Experimental. With numerous Illustrations. Crown Svo, 3s. 6d. ELEMENTAEY PEACTICAL PHYSIOLOGY. With 178 Illus- trations (6 of which are Coloured). Crown Svo, 3s. 6d. WALLER. AN INTEODUCTION TO HUMAN PHYSIOLOGY. By AUGUSTUS D. WALLER, M.D., F.R.S., Hon. LL.D. Edin., Lec- turer on Physiology at St. Mary's Hospital Medical School, London ; late External Examiner at the Victorian University. With 314 Illustrations. 8vo, 18s. 16 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. HEALTH AND HYGIENE, ETC. ASH BY. HEALTH IN THE NUESEEY. By HENRY ASHBY, M.D., F.R.C.P., Physician to the General Hospital for Sick Children, Manchester ; Lecturer and Examiner in Diseases of Children in the Victoria University. With 25 Illustrations. Crown 8vo, 3s. net. BUCKTON. HEALTH IN THE HOUSE. By Mrs. c. M. BUCKTON. With 41 Woodcuts and Diagrams. Crown 8vo, 2s. BULL.— WOEK& by THOMAS BULL, M.D. Thoroughly Revised by ROBERT W. PARKER, M.R.C.S. Eng. HINTS TO MOTHEES ON THE MANAGEMENT OF THEIE HEALTH DUEING THE PEEIOD OF PEEGNANCY, AND HINTS ON NUESING. Fcp. 8vo, sewed, Is. 6d. ; cloth, gilt edges, 2s. net. THE MATEENAL MANAGEMENT OF CHILDEEN IN HEALTH AND DISEASE. Fcp. 8vo, sewed, Is. 6d. ; cloth, gilt edges, 2s. net. BUTTERWORTH. MANUAL OF HOUSEHOLD WOEK AND MANAGEMENT. By ANNIE BUTTERWORTH. Crown 8vo, 2s. 6d. COR FIELD, THE LAWS OF HEALTH. By w. H. CORFIELD, M.A., M.D. Fcp. 8vo, Is. 6d. CREIGHTON. THE ECONOMICS OF THE HOUSEHOLD. Six Lectures given at the London School of Economics during the Winter of 1906. By LOUISE CREIGHTON. Crown 8vo, Is. 4d. FURNEAUX. ELEMENTAEY PEACTICAL HYGIENE. Sec- tion I. By WILLIAM S. FURNEAUX. With 146 Illustrations. Crown 8vo, 2s. 6d. JAMES. BALL GAMES AND BEEATHING EXEECISES. By ALICE R. JAMES. With Preface by HARRY CAMPBELL, M.D., B.S. (London), F.R.C.P. With 17 Illustrations. Crown 8vo, Is. 6d. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY. ETC. 17 HEALTH AND HYGIENE, ETC.— continued. NOTTER AND FIRTH.— WORKS byj. LANE NOTTER, M.A. M D and li. H. FIRTH, F.R.C.S. HYGIENE. With 99 Illustrations. Crown 8vo, 4s. 6d. PEACTICAL DOMESTIC HYGIENE, with 84 illustrations Crown 8vo, 2s. 6d. POORE.— WORKS by GEORGE VIVIAN POORE, M.D., F.R.C.P THE EAETH IN EELATION TO THE PEESEEVATION AND DESTEUCTION OF CONTAGIA : being the Milroy Lectures delivered at the Royal College of Physicians in 1899, together with other Papers on Sanitation. 13 Illustrations. Crown 8vo, 5s. ESSAYS ON EUEAL HYGIENE. With 12 Illustrations. Crown 8vo, 6s. 6d. THE DWELLING HOUSE. With 36 Illustrations. Crown 8vo, 3s. 6d. COLONIAL AND CAMP SANITATION. With n Illustrations Crown 8vo, 2s. net. PORTER.— WORKS by CHARLES PORTER, M.D., B.Sc., M.R.C.P. (/;///«.). SCHOOL HYGIENE AND THE LAWS OF HEALTH : a Text- Book for Teachers and Students in Training. With 121 Illustrations. Crown 8vo, 3s. 6d. SANITAEY LAW IN QUESTION AND ANSWEE. Crown 8vo. This book is primarily intended to assist candidates for Diplomas in Public Health and the certificates of the various examining bodies grant- ing qualifications to Sanitary Inspectors, in their study of the Sanitary Laws of England and Wales. As many of the queries in the book are such as have to be dealt with almost daily in practice, the volume should prove of value also to those already in the Public Health Service, as a reference book and guide to Sanitary Legislation. ROBINSON. THE HEALTH OF OUE CHILDEEN IN THE COLONIES : a Book for Mothers. By LILIAN AUSTEN ROBIN- SON, M.D. Crown 8vo, 2s. 6d. net. WEST, HOW TO NUESE SICK CHILDEEN. By CHARLES WEST, M.D., Founder of and late Physician to the Hospital for Sick Children, Great Ormond Street, London. With Preface by GEORGE F. STILL, M.D., Physician to the Hospital for Sick Children, Great Ormond Street. Crown 8vo, Is. net. 18 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. BACTERIOLOGY, ETC. CURTIS. THE ESSENTIALS OF PEACTICAL BACTEEI- OLOG Y : an Elementary Laboratory Work for Students and Practitioners. By H. J. CURTIS, B.S. and M.D. Lond., F.R.C.S., formerly Surgeon to the North-Eastern Hospital for Children ; Assistant Surgeon, Royal Hospital for Children and Women, Waterloo Road ; Surgical Registrar and Assistant to the Professor of Pathology, University College, London. With 133 Illustrations. 8vo, 9s. ELLIS, OUTLINES OF BACTEEIOLOGY (Technical and Agri- cultural). By DAVID ELLIS, Ph.D. (Marburg), D.Sc. (London), •F.R.S.E., Lecturer in Bacteriology and Botany to the Glasgow and West of Scotland Technical College, Glasgow. With 134 Illustrations. 8vo, 7s. 6d. net. FRANKLAND. BACTEEIA IN DAILY LIFE. By Mrs. PERCY PRANKLAND, F.R.M.S. Crown 8vo, 5s. net. GOADBY. THE MYCOLOGY OF THE MOUTH: A TEXT- BOOK OF OEAL BACTEEIA. By KENNETH W. GOADBY, L.D.S. Eng., D.P.H. Camb., L.R.C.P., M.R.C.S., Bacteriologist and Lecturer on Bacteriology, National Dental Hospital, etc. With 82 Illustrations. 8vo, 8s. 6d. net. KLOCKER. FERMENTATION OEGANISMS. A Laboratory Handbook. By ALB. KLOCKER, Assistant in the Carlsberg Laboratory, Copenhagen. Translated from the German by G. E. ALLAN, B.Sc., Lecturer in the University of Birmingham, and J. H. MILLAR, F.I.C., formerly Lecturer in the British School of Malting and Brewing, and revised by the Author. With 146 Illustrations. 8vo, 12s. net. MESSES. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 19 OPTICS, PHOTOGRAPHY, ETC. ABNEY, A TREATISE ON PHOTOGRAPHY. By Sir WILLIAM DE WIVELESLIE ABNEY, K.C.B., F.R.S. With 134 Illustrations. Crown 8vo, 5s. BALY.— SPECTROSCOPY. By E. C. C. BALY, F.I.C., Lecturer on Spectroscopy and Assistant Professor of Chemistry, University College, London. With 163 Illustrations. Crown 8vo, 10s. 6d. DRUDE. THE THEORY OF OPTICS. By PAUL DRUDE, Pro- fessor of Physics at the University of Giessen. Translated from the German by C. RIBORG MANN and ROBERT A. MILLIKAN, Professors of Physics at the University of Chicago. With 110 Diagrams. 8vo, 15s. net. GLAZEBROOK. PHYSICAL OPTICS. By R. T. GLAZEBROOK, M.A., F.R.S. With 183 Woodcuts of Apparatus, etc. Crown 8vo, 6s. MEES. AN ATLAS OF ABSORPTION SPECTRA. By C. E. KENNETH MEES, D.Sc. Crown Svo, 6s. net. POLLOK. PRACTICAL SPECTROGRAPHIC ANALYSIS. By J. H. POLLOK, D.Sc. Crown Svo. SHEPPARD AND MEES. INVESTIGATION ON THE THEORY OF THE PHOTOGRAPHIC PROCESS. By S. E. SHEPPARD, D.Sc. (Lond.), 1851 Exhibition Scholar of University College, London, and C. E. KENNETH MEES, D.Sc. (Lond.). With 65 Illustrations and Diagrams. Crown Svo, 6s. 6d. net. VANDERPOEL. COLOUR PROBLEMS: A Practical Manual for the Lay Student of Colour. By EMILY NOYES VANDERPOEL. With 117 Plates in Colour. Square Svo, 21s. net. WRIGHT. OPTICAL PROJECTION : A Treatise on the Use of the Lantern in Exhibition and Scientific Demonstration. By LEWIS WRIGHT, Author of " Light : a Course of Experimental Optics ". With 243 Illustrations. Crown Svo, 6s. 20 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. CHEMISTRY, ETC. ARMITAGE, A HISTOEY OF CHEMISTEY. By F. P. ARMITAGE, M.A., F.C.S. Crown 8vo, 6s. ARRHENIUS.— WORKS by SVANTE ARRHENIUS, Director of the Sobel Institute, Stockholm. THEOETES OF CHEMISTEY: being Lectures delivered at the University of California, in Berkeley. Edited by T. SLATER PRICE, D.Sc., Ph.D., F.I.C. 8vo, 5s. 6d. net. A TEXT-BOOK OF ELEGTEO - CHEMISTEY. Translated from the German Edition by JOHN McCRAE, Ph.D. With 58 Illustra- tions. 8vo, 9s. &d. net. BUNGE. TEXT-BOOK OF OEGANIC CHEMISTEY FOE MEDICAL STUDENTS. By Dr. G. VON BUNGE, Professor of Physiology in the University of Basel. Translated by R. H. ADERS PLIMMER, D.Sc. 8vo, 6s. net. CROOKES. SELECT METHODS IN CHEMICAL ANALYSIS (chiefly inorganic). By Sir W. CROOKES, F.R.S. With 68 Illustrations. 8vo, 21s. net. FINDLAY.— WORKS by ALEX. FINDLAY, M.A., Ph.D., D.Sc. PHYSICAL CHEMISTEY AND ITS APPLICATIONS IN MEDICAL AND BIOLOGICAL SCIENCE. Being a Course of Seven Lectures delivered in the University of Birmingham. Royal 8vo, 2s. net. PEACTICAL PHYSICAL CHEMISTEY With 92 Illustrations. Crown 8vo, 4s. 6d. GODFREY. ELEMENTAEY CHEMISTEY. By HOLLIS GOD- FREY, Head of the Department of Science, Girls' High School of Prac- tical Arts, Boston, Mass. With numerous Illustrations. Crown 8vo, 4s. 6V/. net. HANSON AND DODGSON. AN INTEEMEDIATE COUESE OF LABOEATOKY WOEK IN CHEMISTEY. By EDWARD KENNETH HANSON, M.A. (Cant.), F.I.C., Teachers' Diploma (Lond.) ; Lecturer in Chemistry, University College, Reading ; Lecturer to the Cambridge University Local Lecture Syndicate, and JOHN WALLIS DODGSON, B.Sc. (Lond.) ; Director of Evening Classes and Lecturer in Chemistry, University College, Reading. With Illustrations. 8vo, 3s. 6d. MENDELEEFF. THE PEINCIPLES OF CHEMISTEY. By D. MENDELfiEFF. Translated from the Russian (Seventh Edition) by GEORGE KAMENSKY, A.R.S.M., and Edited by THOMAS H. POPE, B.Sc., F.I.C. With 110 Illustrations. 2 vols. 8vo, 32s. net. MEYER. OUTLINES OF THEOEETICAL CHEMISTEY. By LOTHAR MEYER. Translated by Professors P. PHILLIPS BED- SON, D.Sc., and W. CARLETON WILLIAMS, B.Sc. 8vo, 9s. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 21 CHEMISTRY, ETC.— continued. MUIR. A COUESE OF PEACTICAL CHEMISTRY. By M. M. P. MUIR, M.A. Part I. Elementary. Cr. 8vo, 4s. 6d. Part II. Intermediate. Cr. 8vo, 4s. 6d. NEWTH.— WORKS by G. S. NEWTH, F.I.C., F.C.S. CHEMICAL LECTURE EXPERIMENTS. With 230 Illustra- tions. Crown Svo, 6s. MANUAL OF CHEMICAL ANALYSIS, QUALITATIVE AND QUANTITATIVE. With 102 Illustrations. Crown Svo, 6s. 6d. SMALLER CHEMICAL ANALYSIS. Crown 8vo, 2*. A TEXT-BOOK OF INORGANIC CHEMISTRY. With 15 Illustrations. Crown Svo, 6s. 6d. ELEMENTARY PRACTICAL CHEMISTRY. With 108 Illustra- tions and 254 Experiments. Crown Svo, 2s. 6d. OSTWALD. THE FUNDAMENTAL PRINCIPLES OF CHEMISTRY. An Introduction to all Text-Books of Chemistry. By WILHELM OSTWALD. Authorised Translation by HARRY W. MORSE. Svo, 7s. 6d. net. PERK IN.— WORK* by F. MOLLWO PEUKIN, Ph.D. QUALITATIVE CHEMICAL ANALYSIS (ORGANIC AND INORGANIC). With 15 Illustrations and Spectrum Plate. Svo, 4s- PRACTICAL METHODS OF ELECTRO-CHEMISTRY. 8vo, 6s. net. PRICE AND TWISS. A COURSE OF PRACTICAL ORGANIC CHEMISTRY. By T. SLATER PRICE, D.Sc., Ph.D., F.I.C., Head of the Chemical Department of the Birmingham Municipal Technical School, and D. F. TWISS, M.Sc., A.I.C., Lecturer in Chemistry at the Birmingham Municipal Technical School. Svo, 3s. 6d. RADCLIFFE AND SINNATT. A SYSTEMATIC COURSE OF PRACTICAL ORGANIC CHEMISTRY. By LIONEL GUY RAD- CLIFFE, F.C.S. With the assistance of FRANK STURDY SINNATT, F.C.S. Svo, 4s. 6d. REYNOLDS. EXPERIMENTAL CHEMISTRY for Junior students. By J. EMERSON REYNOLDS, M.D., F.R.S. Fcap. Svo, with numerous Illustrations. PABT I.— Introductory, Is. 6d. PART III. — Metals and Allied Bodies, 3s. 6d. PABT II. — Non-Metals, 2s. 6d. PABT IV. — CJiemistry of Carbon Compounds, 4s. SMITH AND HALL. THE TEACHING OF CHEMISTRY AND PHYSICS IN THE SECONDARY SCHOOL. By ALEX- ANDER SMITH, B.Sc., Ph.D., Associate Professor of Chemistry in the University of Chicago, and EDWIN H. HALL, Ph.D.. Professor of Physics in Harvard University. With 21 Woodcuts, Bibliographies, and Index. Crown Svo, Gs. net. 22 MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. CHEMISTRY, ETC.— continued. STEWART.— WORKS by A. W. STEWART, D.Sc. EECENT ADVANCES IN ORGANIC CHEMISTRY, with an Introduction by J. NORMAN COLLIE, Ph.D., XjL.D., F.R.S., Pro- fessor of Organic Chemistry in University College, London. 8vo, 7s. 6d. RECENT ADVANCES IN PHYSICAL AND INORGANIC CHEMISTRY. With an Introduction by Sir WILLIAM RAMSAY, K.C.B., F.R.S. 8vo, 7s. 6rf. net. THORPE. A DICTIONARY OF APPLIED CHEMISTRY. By Sir T. E. THORPE, C.B., D.Sc. Viet., Ph.D., F.R.S., Principal of Government Laboratory, London. Assisted by Eminent Contributors. 3 vols. 8vo. Vols. I. and II., £2 2s. each (Postage, 3s. 4d.) ; Vol. III., £3 3s. TILDEN.— Works by Sir WILLIAM A. TILDEN, D.Sc. London, F.R.S. A SHORT HISTORY OF THE PROGRESS OF SCIENTIFIC CHEMISTRY IN OUR OWN TIMES. Crown 8vo, 5s. net. INTRODUCTION TO THE STUDY OF CHEMICAL PHILO- SOPHY. The Principles of Theoretical and Systematic Chemistry. With 5 Illustrations. Crown 8vo, 5s. With ANSWERS to Problems. Crown 8vo, 5s. 6d. PRACTICAL CHEMISTRY. The Principles of Qualitative Analysis. Fcp. 8vo, Is. 6d. WATTS' DICTIONARY OF CHEMISTRY. Revised and entirely Re-written by H. FORSTER MORLEY, M.A., D.Sc., Fellow of, and lately Assistant- Professor of Chemistry in, University College, London ; and M. M. PATTISON MUIR, M.A., F.R.S.E., Fellow and Prelector in Chemistry of Gonville and Caius College, Cambridge. Assisted by Eminent Contributors. 4 vols. 8vo, £5 net. WESTON. A SCHEME FOR THE DETECTION OF THE MORE COMMON CLASSES OF CARBON COMPOUNDS. By FRANK E. WESTON, B.Sc., London (First Class Honours), F.C.S., Lecturer in Chemistry at the Polytechnic, Regent Street, W. 8vo, 2s. WHITELEY. — W.IKKS >>n 11. L. Whiteley, F.I.C., Principal of the Muidi-ijxd Science School, West Bromwich. CHEMICAL CALCULATIONS. With Explanatory Notes, Problems, and Answers, specially adapted for use in Colleges and Science Schools. With a Preface by Professor F. CLOWES, D.Sc. (Lond.), F.I.C. Crown 8vo, 2s. ORGANIC CHEMISTRY : the Fatty Compounds. With 45 Illustra- tions. Crown 8vo, 3s. 6d. MESSRS. LONGMANS' WORKS ON MEDICINE, SURGERY, ETC. 23 TEXT.BOOKS OF PHYSICAL CHEMISTRY. Edited by Sir WILLIAM RAMSAY, K.C.B., F.R.S., D.Sc. Crown 8vo. STOICHIOMETEY. By SYDNEY YOUNG, D.Sc., F.R.S., Professor o Chemistry in the University of Dublin ; together with AN INTRODUC- TION TO THE STUDY OF PHYSICAL CHEMISTRY, by SIB WILLIAM RAMSAY, K.C.B., F.R.S., Editor of the Series. Is. 6d. CHEMICAL STATICS AND DYNAMICS, INCLUDING THE THEOKIES OF CHEMICAL CHANGE, CATALYSIS, AND EXPLOSIONS. By J. W. MELLOR, D.Sc., B.Sc. 7s. 6d. THE PHASE EULE AND ITS APPLICATIONS. By ALEX. FINDLAY, M.A., Ph.D., D.Sc., Lecturer and Demonstrator in Chemistry, University of Birmingham. With 134 Figures in the Text. 5s. SPECTEOSCOPY. By E. C. C. BALY, F.I.C., Lecturer on Spectroscopy and Assistant Professor of Chemistry, University College, London. With 163 Illustrations. 10s. 6d. THEEMOCHEMISTEY. By JULIUS THOMSEN, Emeritus Professor of Chemistry in the University of Copenhagen. Translated by KATHARINE A. BURKE, B.Sc. (Lond.), Assistant in the Department of Chemistry, University College, London. 9s. ELECTEO-CHEMISTEY. PAET I.— GENEEAL THEOEY. By R. A. LEHFELDT, D.Sc., Transvaal University College, Johannes- burg. Including a Chapter on the Relation of Chemical Constitution to Conductivity, by T. S. MOORE, B.A., B.Sc., Lecturer in the University of Birmingham. 5s. ELECTEO-CHEMISTEY. PAET II.— APPLICATIONS TO ELECTEOLYSIS, PEIMAEY AND SECONDAEY BAT- TEEIES, ETC. By N. T. M. WILSMORE, D.Sc. [In Reparation. STEEEOCHEMISTEY. By A. W. STEWART, D.Sc., Carnegie Research Fellow. With 87 Illustrations. 10s. 6d. THE THEOEY OF VALENCY. By J. NEWTON FRIEND, Ph.D. (Wiirz), M.Sc. (Birmingham). 5s. METALLOGEAPHY. By CECIL H. DESCH, D.Sc. (Lond.), Ph.D. (Wurzb.) ; Graham Young Lecturer in Metallurgical Chemistry in the University of Glasgow. With 14 Plates and 108 Diagrams in the Text. 9s. THE EELATIONS BETWEEN CHEMICAL CONSTITUTION AND SOME PHYSICAL PEOPEETIES. By SAMUEL SMILES, D.Sc., Fellow of University College, and Assistant Professor of Organic Chemistry at University College, London University. THEEMODYNAMICS. By F. G. DONNAN, M.A., Ph.D. [In Reparation. ACTINOCHEMISTEY. By S. E. SHEPPARD, D.Sc. [In preparation. PEACTICAL SPECTEOGRAPHIC ANALYSIS. By J. H. POLLOK, D.Sc. [In preparation. MESSRS. LOXGMANS' WORKS ON MEDICINE, SURGERY, ETC. MONOGRAPHS ON BIOCHEMISTRY. Edited by R. H. ADEBS PLIMMEB, D.Sc.. and F. GOWLAND HOPKINS, D.Sc., F.R.S. Boyal 8vo. In these volumes un attempt is being made to make the subject of Bio- chemistry more accessible by issuing a series of monographs upon the various chapters of the subject, each independent of and yet dependent upon the others, so that from time to time, as new material and the demand therefor necessitate, a new edition of each monograph can be issued without reissuing the whole series. The expenses of publication and the expense to the purchaser will thus be diminished, and by a moderate outlay it will be possible to obtain a full account of any particular subject as nearly current as possible. THE DEVELOPMENT AND PEESENT POSITION OF BIO- LOGICAL CHEMISTEY. By F. GOWLAND HOPKINS, M.A., M.B., D.Sc., F.R.S. [In preparation. THE NATUKE OP ENZYME ACTION. By w. M. BAYLISS, D.Sc., F.R.S., Assistant Professor of Physiology, University College, London. 3s. net. THE CHEMICAL CONSTITUTION OF THE PEOTEINS. By R. H. ADERS PLIMMEB, D.Sc., Assistant Professor of Physiological Chemistry, University College, London. In 2 Parts. Part 1, 3s. net ; Part 2, 2s. 6d. net. THE GENEEAL CHAEACTEES OF THE PEOTEINS. By S. B. SCHBYVER, D.Sc., Ph.D., Lecturer on Physiological Chemistry, University College, London. 2s. 6d. net. THE VEGETABLE PEOTEINS. By THOMAS B. OSBORNE, Ph.D., Research Chemist in the Connecticut Agricultural Experiment Station, New Haven, Connecticut ; Research Associate of the Carnegie Institution of Washington, D.C. 3s. 6d. net. THE SIMPLE CAEBOHYDEATES AND THE GLUCOSIDES. By E. FRANKLAND ARMSTRONG, D.Sc., Ph.D., Associate of the City and Guilds of London Institute. 3s. 6d. net. THE FATS. By J. B. LEATHES, D.Sc. [In the press. THE POLYSACCHAEIDES. By ARTHUR R. LING, F.I.C. [In preparation. COLLOIDS. By W. B. HARDY, M.A., F.R.S. [In preparation. ALCOHOLIC FEEMENTATION. By H. HARDEN, D.Sc., F.R.S. [In preparation. II.— 5,000— A. v. p.— iv/1910.