562 THE STRUCTURE AND DEVELOPMENT 



to the time and completeness of the disappearance, of the out- 

 lines marking the separate cells, and although, so far as can be 

 gathered from my specimens, the rule is that the outlines of 

 the primitive ova with modified nuclei soon become indistinct, 

 yet in one of my best preserved ovaries very large nests 

 with modified nuclei are present in which the outline of each 

 ovum is as distinct as during the period before the nuclei 

 undergo these peculiar changes (PI. 24, fig. 12). In the same 

 ovary other nests are present in which the outlines of the indi- 

 vidual ova are no longer visible. The section represented on 

 PI. 24, fig. 2, is fairly average as to the disappearance of the 

 outlines of the individual ova. 



It is clear from the above statements, that in the first in- 

 stance the nests are produced by the coalescence of several 

 primitive ova into a single mass or syncytium ; though of course, 

 the several separate ova of a nest may originally, as Semper 

 believes, have arisen from the division of a single ovum. In any 

 case there can be no doubt that the nests of separate ova in- 

 crease in size as development proceeds ; a phenomenon which 

 is more reasonably explained on the view that the ova divide, 

 than on the view that they continue to be freshly formed. The 

 same holds true for the nests of nuclei and this, as well as other 

 facts, appears to me to render it probable that the nests grow 

 by division of the nuclei without corresponding division of the 

 protoplasmic matrix. 1 cannot, however, definitely prove this 

 point owing to 'my having found nests, with distinct outlines to 

 the ova, as large as any without such outlines. 



The nests are situated for the most part near the surface of 

 the germinal epithelium. The smaller ones are frequently 

 spherical, but the larger are irregular in form. The former are 

 about O'O5 mm. in diameter; the latter reach O'l mm. Scat- 

 tered generally, and especially in the deeper layers, and at the 

 edges of the germinal epithelium, are still unmodified or only 

 slightly modified primitive ova. These unmodified primitive 

 ova are aggregated in masses, but in these masses the outlines 

 of each ovum, though perhaps less clear than in the earlier 

 period, are still distinct. 



When the embryo reaches a length of seven centimetres, and 

 even in still younger embryos, further changes are observable. 



