THE BIOLOGY OF THE CELL SURFACE 



The fertilizable condition in animal eggs arises suddenly. 

 Delage' demonstrated that with break-down of the germinal 

 vesicle the Qgg of a starfish undergoes a change which ren- 

 ders it fertilizable, a finding which I have confirmed in the 

 same and in two other species of the same genus, Asterias. 

 Further, not only are these eggs unfertilizable while the 

 germinal vesicle is intact; attachment and entrance of the 

 spermatozoa during this stage actually inhibit completely 

 the break-down of the germinal vesicle. Other eggs which 

 normally are extruded into the sea-water in the stage of 

 intact germinal vesicle are fertilizable only after its disrup- 

 tion, an event which occupies a few minutes. 



The fertilizable condition can not, however, in all eggs 

 be correlated with break-down of the germinal vesicle, since, 

 as we have seen, eggs like that of Nereis, for example, and 

 of many other animals, are fertilizable only in the germinal 

 vesicle stage. The egg of Nereis offers another example of 

 the sudden onset of fertilizability. This is shown by the 

 following: Eggs of this worm are Jiormally shed when the 

 animals are in the so-called heteronereis phase, i.e., when 

 during a period of full-moon they swim actively at the sur- 

 face of the sea, at which time all the eggs are in the optimum 

 fertilizable condition. Now I have reared in the laboratory 

 to the heteronereis phase many of these worms which had 

 been collected while immature (i.e., in the nereid phase). 

 On five successive days before full-moon I have inseminated 

 eggs removed from these worms without obtaining develop- 

 ment despite the fact that under the microscope the eggs 

 resembled fertilizable ova.- On the day of full-moon, eggs 

 taken from the same animal, from which others had been 

 removed during previous days and inseminated without 



^ Delage, igoia. 



~ If a fully ripe female {one in the sztumming stage) be punctured 

 all of her eggs are usually extruded. After the same degree of 

 puncture of an immature female only fetv eggs exude from the site of 

 injury. 



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