CHAPTER VII 

 FERTILIZATION AND CLEAVAGE 



The events occurring at fertilization in the fallopian tubes 

 have been subject to detailed examination chiefly in poly- 

 ovular mammals, e.g., the rabbit, rat, mouse, ferret, etc. 

 In all cases the sperm surround the ova embedded in the 

 mass of follicle cells, and penetrate to the ova causing the 

 follicle cells to fall away at the 

 same time. That the sperm 

 swarm present in the tubes is 

 actively responsible for the fall- 

 ing away of the follicle cell 

 mass is abundantly evident from 

 numerous recent observations of 

 fertilization in the rabbit (Pincus, 

 1930; Yamane, 1930, 1935; 

 Pincus and Enzmann, 1932, 

 1935). As described previously 

 rabbit ova in does mated to 

 sterile bucks begin to separate 

 out of the follicle cell mass by 16 



hours after copulation at the earliest, and the process is 

 normally completed between the 17th and 19th hours. 

 In fertile matings free ova have been observed as early as 

 113/^ hours after coitus, and all ova are invariably free 

 by the 14th hour. Furthermore, when freshly o\ailated 

 ova from sterile matings are placed in vitro with sperm 

 suspensions there is a rapid dispersion of the surrounding 

 follicle cells which does not occur in control cultures of ova 

 in sperm-free media. Similar phenomena have been observed 

 by Gilchrist and Pincus (1932) in the rat (Figures 23 to 25) 

 and by Pincus (unpublished observations) in the mouse. 



75 



Fig. 23, Rat ovum recov- 

 ered from the tubes at 16 

 hours after a sterile mating. 

 Note surrounding folUcle cells. 

 (From the Anatomical Record.) 



