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." ^ 



Thus it would seem that the interstitial cells, which, hke 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.^ 



The Significance of the Prooestrous Changes 



Having discussed the conditions under which the Graafian 

 folhcles ripen and discharge in various species of the class 

 Mammaha, 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 



' Lane- Clay pon, foe. cit. 



" For an account of the interstitial tissue of the ovary in various animals, 

 see Fraenkel. See also Cesa-Bianchi, who states that the interstitial ovarian 

 gland in hibernating animals undergoes a great development in spring and 

 summer, but is much reduced in winter. He also comments on the close 

 resemblance between luteal and interstitial cells. (" Vergleichende histo- 

 logisohe Untersuchungen iiber das Vorkommen driisiger Formationen im 

 interstitiellen Eierstockgewebe," Arch. f. Oynak., vol. Ixxv., 1906.) 



L 



