The Cellular Basis 



141 



and even photographed, while in the living condition. The peri- 

 pheral layer of protoplasm is yellow and it gathers at the lower 

 pole of the egg, where the sperm enters, forming a yellow cap 



FIG. 45. SUCCESSIVE STAGES IN THE CLEAVAGE OF THE EGG OF A MOLLUSK 

 (Crepidula), showing the separateness of the male and female chromo- 

 somes ( $ ch, 9 ch) and of the male and female halves of each nucleus 

 ($N, 



