60 



REPRODUCTIVE SYSTEM OF THE ADULT FROG 



which is found to one side of the nucleus, and around which gather 

 the granules or yolk platelets. The chromatin filaments become achro- 

 matic and the nucleoli increase in number, by fragmentation, and 

 become more chromatic. Many of the nucleoli, which are concen- 

 trations of nucleo-protein, pass through the nuclear membrane into 

 the surrounding cytoplasm during this period. It is not clear whether 

 this occurs through further fragmentation of the nucleoli into particles 

 of microscopic or sub-microscopic size, and then their ejection 

 through the nuclear membrane. It may occur by the loss of identity 

 (and chromatic properties) by possible chemical change and sub- 

 sequent diffusion of the liquid form through the membrane to be 



1= 



J 



100-^ 



The entire set of chromosomes of Rana lemporaria. The 1 3 pairs of chromo- 

 somes in this species are remarkably like those of other species of Rana. They 

 are seen in stage 6. (Q) Four ring-shaped pairs. (R) Four medium-sized pairs. 

 (S) Three longest (super) pairs. (T) Two short T-shaped pairs. (Courtesy, 

 W. R. Duryee, 1950, Ann. N. Y. Acad. ScL, 50, Art. 8.) 



