The Eggs of Mammals (1936) 1
Chapter I Introduction
The behavior of mammahan eggs from the time of their genesis in the ovary to their implantation in the uterus is the subject matter of this book. The attempt has been made to include experimental investigations of the growth and development of ova rather than morphological descriptions. This is not an easy task, because an acute morphologist may make deductions about the nature of his material which are far more illuminating than those of an eager but inexpert experimenter. Furthermore, except for certain notable investigations of ovarian dynamics, there has been no extensive inquiry into the physiology of living mammalian ova. It has been tacitly assumed, for example, that the reactions involved in the activation of non-mammalian ova occur also in mammalian eggs. Until quite recently no attempt has been made to test even this assumption. Since the middle of the last century a controversy has raged about the possibility of ovarian parthenogenesis. Almost every observer of mammalian ovaries has contributed an opinion, but no one has tried to see if ovarian eggs can be induced to develop parthenogenetically. Experimentation has lagged presumably because of the difficulty of handling living ova.
It is interesting to note that the discovery of the mamimalian egg by von Baer in 1827 led initially to extensive observations of living ova. At first the exact morphology of the egg and its membranes was a matter of some debate (see Wagner, 1836; Jones, 1837, 1838, 1885; Barry, 1838; Bischoff, 1842). Following Barry's (1839) initial observation of cytoplasmic cleavage there ensued a long series of observations on the developmental history of fertilized eggs. Attention gradually shifted from living eggs to fixed specimens, chiefly employed for the determination of the exact cytology of fertilization and the histological changes occurring during differentiation. This resulted in the publication of numerous detailed descriptions of the early embryology in various classes of mammals (Bischoff, 1845, 1852, 1854; Bonnet, 1884, 1891; Caldwell, 1887; Hartman, 1916, 1919; Heape, 1883, 1886; Hensen, 1876; Hill, 1910, 1918; Hill and Tribe, 1924; Huber, 1915; Hubrecht, 1912; Jenkinson, 1900, 1913; Keibel, 1888, 1894, 1899, 1901, 1902; Lams and Doorme, 1908; Lams, 1910, 1913, 1924; Melissinos, 1907; Minot, 1889; van Oordt, 1921; Reichert, 1861; Rein, 1883; Robinson, 1892; Sakurai, 1906; Selenka, 1883, 1884, 1887; Sobotta, 1893, 1895; Tafani, 1889; Van Beneden, 1875, 1880, 1899, 1911, 1912; Van Beneden and Julin, 1880; Weil, 1873; Wilson and Hill, 1907). The hving egg was neglected presumably because no technique was developed for preserving it intact in vitro long enough for any extensive experimentation to be performed. Nor did the possibility of experimental manipulation of ova in vivo receive more than passing attention (see Grusdew, 1896; Novak and Eisinger, 1923).
Since the pubhcation of Stockard and Papanicolou's (1917) and Long and Evans' (1922) exhaustive accounts of the oestrus cycle of the guinea pig and rat respectively, a new era in the study of sexual physiology has been initiated. Enormous strides have been made in the discovery and purification of the hormones regulating the activities of the genital tracts of mammals. The ovarian control of the various phases of the sex cycles in the female has received exhaustive attention, and the control of gonad function by the anterior pituitary has been investigated in detail. Despite the enormous accumulation of data on the endocrine regulation of the ovarian and oviduct environment of ova, the ova themselves have received relatively little attention. The study of the hormonal control of ovarian function has centered upon the relation of hormone activity to the development of follicle and corpus luteum. The ovary has been largely considered as a sort of diphasic machine geared for hormone production by certain specialized follicle components. Its primary function as a producer of gametes has been relatively neglected. The endocrine control of the proliferative, secretory and contractile activities of the oviducts themselves is known in detail, and it is tacitly recognized that all these activities have as their end and aim the nutrition and protection of the developing egg. Yet the exact nature of the dependence of the ovum upon these activities is still problematical. We are now provided with the sort of knowledge that should certainly make profitable in vivo experimentation with eggs.
Brachet (1912, 1913) did indeed take advantage of the development of a tissue culture technique in order to investigate a specific stage of development in rabbit ova. But neither the availability of the technique nor Brachet 's suggestive discourse led to any acti\^e investigation until. 1929 when Lewis and Gregory published their account of the cinematography of rabbit ova developing in culture. Since then a number of workers associated with Lewis (Gregory, 1930; Squier, 1932; Lewis and Hartman, 1933; Lewis and Wright, 1935) have conducted a fairly intensive examination of living ova, chiefly with the object of culturing fertilized eggs. In addition to these investigations and similar work undertaken by Nicholas and his coworkers (Nicholas and Rudnick, 1933, 1934; Defrise, 1933), the physiological properties of developing ova have been examined from quite different angles. So there exists a measurable body of work of recent origin which is properly experimental. Wherever possible the factual data of this work have been presented in the hope that these, speaking for themselves, may stand side by side with any interpretation herein presented.
It is the earnest belief of the writer that these experimental inquiries represent a small fraction of the work that should and will be done. The enormous variety and richness of mammalian material that is available and untapped should provide an extraordinary temptation to exploitation now that a beginning has been made in the development of technical facilities for the manipulation of this material. I emphasize that only a beginning has been made. This book is a beginning.
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- The Eggs of Mammals (1936): Introduction | The Origin of the Definitive Ova | The Growth of the Ovum | The Development and Atresia of Full-Grown Ova and the Problem of Ovarian Parthenogenesis | Methods Employed in the Experimental Manipulation of Mammalian Ova | The Tubal History of Unfertilized Eggs | Fertilization and Cleavage | The Activation of Unfertilized Eggs | The Growth and Implantation of the Blastodermic Vesicle | Summary and Recapitulation | Bibliography | Figures | Historic Disclaimer
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