The Cellular Basis 

 1P.S. 



143 



FIG. 46. SECTIONS OF THE EGG OF Styela, showing maturation, fertiliza- 

 tion and early cleavage. I PS., First polar spindle, p.b., Polar bodies ; 

 $ N, sperm nucleus, %N, egg nucleus. />./., peripheral layer of yellow pro- 

 toplasm. Cr., Crescent of yellow protoplasm. A Zt A s , Anterior cells, 

 B 3 , B z Posterior cells of the 4-cell stage. In i the sperm nucleus and cen- 



