24 ART. 5. — N. YATSU : 



nucleus is vesicular and stains less intensely than cytoplasm, as if 

 it were quite devoid of chromatic substance. 



In young ova the nucleolus is single hut in older ovarian 

 ova there appear accessory nucleoli (a. nl.) which are usually 

 found closely apposed to the principal nucleolus (p. nl.) (PI. II., 

 Figs. 28, 29 a, c). But sometimes they detach themselves from 

 the principal one (PI. II., Fig. 29 b). The accessory nucleolus 

 is not always spherical, in some cases assuming an irregular 

 outline (PI. IL, Fig. 29 b). The two kinds of nucleoli can easily 

 be differentiated by gentian violet, the principal one staining 

 darker than the accessory, as is shown in the figures (PI. IL, 

 Figs. 28, 29). Consequently it seems that the accessory nucleoli 

 are less dense than the principal. In the Testicardines the pre- 

 sence of two kinds of nucleoli is clearly figured by van Bem- 

 melen ('83), but he says nothing about it. Vogt and Jung 

 ('88) mention that often two nucleoli are present. The supporting 

 substance (Stützsubstanz) of the ileo-parietal band is found as a 

 thin membrane between two layers of ova (PI. IL, Figs. 27, 28). 

 This membrane Beyer ('86) neither mentions nor figures. At 

 some places the membrane increases in thickness and gives a 

 vacuolated appearance (PI. IL, Fig. 30). 



Even in the region where ova are developed cells are of 

 course not all converted into them. The follicle of the ovum is 

 formed at the expense of interstitial cells, which become extremely 

 flattened, so that their presence is perceived only by their compact 

 and spindle-shaped nuclei (PI. IL, Fig. 28). Of the cells which 

 have started to become ova, some lying pressed between two ad- 

 jacent ova are arrested in their early development and remain small. 

 That these degenerating ova take a hematoxylin stain more readily 

 than others, shows that they are at the beginning of yolk-formation. 



