THE BIOLOGY OF THE CELL SURFACE 



of the female's body, as those of echinoderms other than 

 sea-urchins, of worms, of molluscs, of ascidians and of 

 vertebrates may retain their fertilization-capacity for 

 hours. 



With one exception species of animal eggs undergo no 

 change in maturation whilst the fertilizable condition per- 

 sists but remain unless fertilized until death in that stage 

 in which fertilization normally occurs. Eggs of the genus, 

 Asterias, (starfish) make the exception, as pointed out. 

 When normally laid by the females, these eggs are in the 

 stage of the breaking-down germinal vesicle, their normal 

 stage for fertilization. The steadily accumulating evidence 

 to show that in normal conditions for breeding the males 

 and females of starfishes closely congregate prior to the 

 shedding of spermatozoa and eggs also indicates that the 

 optimum stage for fertilization is that found in the eggs 

 when shed. But if shed eggs or those removed from an 

 ovary with their germinal vesicles intact are brought into 

 normal sea-water without spermatozoa, they may undergo 

 complete maturation. Such eggs fertilized during stages 

 of first maturation develop normally; thereafter, fertiliza- 

 tion-capacity steadily falls off. After complete maturation 

 only low percentages both of fertilization and of subsequent 

 development are obtained and are highly abnormal. 



The Abbe Spallanzani made interesting observations on 

 the duration of the fertilizability of frog's eggs after deposi- 

 tion. Sobotta points out that fertilization of the eggs of 

 Amphioxus succeeds best when the eggs exude from the 

 female into sea-water containing spermatozoa; whereas the 

 addition of spermatozoa to eggs already in sea-water tends 

 to result in abnormal fertilization — an observation indi- 

 cating the short duration of fertilizability in this tg^. 

 Fertilization of the eggs of a fish, the wall-eyed pike, drops 

 from 40 per cent, for the eggs that have lain in water for 

 two minutes to zero per cent, for eggs that have been in 



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