34 



PHYSIOLOGY 



both morphologically and chemically, namely, the chromatin filaments, 

 which are most directly concerned. This assumption receives support 

 from the changes which have been observed to occur in these filaments 

 during various phases of nutritive activity of the cell. The staining 

 powers of chromatin are in direct proportion to the amount of nuclein 

 it contains. In the eggs of the shark it has been shown that the chromo- 

 somes undergo characteristic changes during the entire growing period 



* 8 ** t ' J ^^iX*wX 



FIG. 12. Chromosomes of the germinal vesicle in the shark Pristiurus, at different 



periods, drawn to the same scale. (RUCKERT.) 



A. At the period of maximal size and minimal staining-capacity (egg 3 mm. in 

 diameter). B. Later period (egg 13 mm. in diameter). C. At the close of ovarian 

 life, of minimal size and maximal staining -power. 



of the egg. At first they are small and stain deeply with ordinary 

 nuclear dyes, but during the period of growth they undergo a great 

 increase in size and at the same time lose their staining capacity,* 

 their surface being increased by the development of long threads 

 which grow out in every direction from the central axis. As the egg 

 approaches its full size, the chromosomes diminish in size and are 

 finally reduced to minute intensely staining bodies which take part 

 in the first division of the egg preparatory to its fertilisation (Fig. 12). 

 We must conclude that whereas the processes of destructive meta- 

 bolism or dissimilation, which determine the activity of the cell, have 

 * Biickert, cited by Wilson, 



