MANIPULATION OF EGGS 115 



more acceptable explanation than the operation of chemotaxis is 

 simply that the resistance ofFered by the densely-packed, radially- 

 arranged follicle cells around the eggs tends to detain spermatozoa 

 there (Braden, 196 1). Another recent inquiry into the problem was 

 that of Schwartz, Brooks and Zinsser (1958), who noted that human 

 spermatozoa suspended in a neutral medium on a slide tended to 

 congregate in regions in which had been deposited fluids from 

 follicles or ovarian cysts, or hen egg-white ; they concluded that the 

 effect was caused by chemotaxis since the motility of the sperma- 

 tozoa in these regions was increased and this would tend to coun- 

 teract any trapping action. 



An influence of a different kind exerted by eggs on spermatozoa 

 is that described by Bishop and Tyler (1956) ; they maintained that 

 a substance akin to the fertilizin of sea-urchin and other invertebrate 

 eggs diffuses from the zona pellucida and reacts with spermatozoa 

 in such a way as to increase their tendency to become attached to 

 surfaces by their heads. In slide preparations, the effect is seen in the 

 greater frequency of head-to-head agglutination of spermatozoa 

 nearer the eggs than of those further away. In nature, the action 

 of this 'fertilizin' could be responsible for attachment of spermatozoa 

 to the surface of the zona pellucida, preparatory to their penetration 

 of this membrane. The agent was detected in association with the 

 oocytes and freshly ovulated eggs of rabbit, mouse and cow, and 

 the reaction with spermatozoa was largely species specific. The 

 agent did not appear to be released by rabbit eggs that had acquired 

 mucin coats — presumably, it could not diffuse through the mucin 

 layer and this conforms with Bishop and Tyler's suggestion that it 

 may be a glycoprotein. 



The term 'fertilizin' is used also by Thibault and Dauzier (i960) 

 for an agent with a somewhat different action. In the course of 

 experiments on the fertilization of rabbit eggs in vitro (p. 122), these 

 authors noted that both the proportion of eggs developing pro- 

 nuclei and the number of spermatozoa entering eggs were increased 

 if the eggs were held in vitro for 2 to 4 hr before the addition of 

 spermatozoa. An even greater improvement was achieved by 

 washing the eggs before semination. On the other hand, good 

 results could be had with freshly recovered eggs if the spermatozoa 

 used were obtained by removing the undiluted uterine fluid of a 

 mated animal instead of flushing the uterus with an artificial 

 medium, which was the procedure normally followed. Thibault 



