236 



FERTILIZATION 

 DEUTOPLASM 



PERIVITELLiN E 



Fig. 118. Fertilization in the guinea pig. (After Lams, Arch. Biol., Paris, 28, figures 

 slightly modified.) (A) Spindle of first maturation division. (B) Second maturation 

 division completed; head of sperm in cytoplasm beginning to swell. (C) Sperm pro- 

 nucleus, with tail still attached, greatly enlarged; female pronucleus small. (D) Pronuclei 

 ready to fuse; chromatin material (chromosomes) evident within. (E) First cleavage 

 spindle. (F) First cleavage completed. Observe deutoplasmic and cytoplasmic globules 

 which have been exuded into the space between the blastomeres and the zona pellucida. 

 (G) Four-cell cleavage stage. Observe that the zona pellucida encloses the four blasto- 

 meres and the cytoplasmic globules which have been exuded. The zona functions to 

 keep the entire mass intact. 



the emission of fluid is present in the amphibia and the egg thus is enabled 

 to revolve within a relatively thick vitelline membrane. The latter membrane 

 expands gradually during development, and is associated intimately with the 

 surrounding jelly membranes secreted by the oviduct. In the reptiles and birds, 

 the separation of the egg from the vitelline membrane or zona radiata and 



