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. 



