CHANGES IN THE OVARY 155 



Formation of Ova 



It is usually stated that all the ova which are to be developed 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, 

 pf which it is supposed that not more than 30,000 remain at puberty.^ 



Miss Lane-Claypon,^ however, has described the formation of ova, 

 resembling primordial ova, from interstitial cells during adult life. 

 These cells are shown to increase markedly hi 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 oif 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 interstitial 

 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 deutobroque 

 cells of a young ovary during the period of oogenesis (see above, 

 p. 116). The leptotenic stage is rapidly passed through and the 

 nucleus enters upon the synaptenic condition, which 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 pachytenie 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 



> Galabin, A Manual of Midmifery, 6th Edition, London, 1904. According 

 to another calculation the human ovary at the age of seventeen contams 17,600 

 ova (Heyse, Aroh. f. Qyndh., vol. liii., 189.3), of which only 400 become mature 

 (Heine, Handbuch der Anatomie, 187.3). 



2 Lane-Claypon, " On the Origin and Life-History of the Interstitial Cells in 

 the Ovary in the Eabbit," Proc. Roy. Soc, B., vol. Ixxvii., 1905. 



