FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 7 



much easier to handle: the endoplasmic outflow is more readily 

 followed. 



With a little care one may induce flow of endoplasm through 

 the cortex. The naked endoplasm rounds up and in appearance 

 is like the remaining part of the egg. But the endoplasm does not 

 fertilize; it fails to react with sperm. 



Here, again, eggs of Arbacia give comparable results. 



While my observations were under way in 1918, Dr. Robert 

 Chambers informed me that by the method of microdissection he 

 was able to remove the cortex from the egg of the starfish (Lillie, 

 '19). Such eggs are incapable of fertilization. Portions of the 

 egg with cortical material, on the other hand, readily fertilize. 



We may conclude from these observations that certain forms of 

 treatment so alter the cortex as to facilitate endoplasmic outflow. 

 By such treatment the fertilization capacity of the egg is not lost; 

 it is, however, localized in only that part of the egg enclosed by 

 cortical material. It thus follows that the inner substance of the 

 egg is non-fertilizable in fertilized eggs not because of progressive 

 centripetal changes set up at the cortex on insemination, but be- 

 cause the endoplasm is inherently non-fertilizable. Again, it is 

 not necessary to postulate that the development of fragments from 

 uninseminated eggs following fertilization may be due to the pres- 

 ence of some nuclear material of the egg (cf. Boveri). If the 

 interpretation of the observations here reported be correct, frag- 

 ments of uninseminated eggs, whether nucleated or not, are ferti- 

 lizable if they possess cortical material. The egg cortex is thus 

 necessary for the fertilization-reaction. 



IV. 



In any attempt at defining fertilization we must consider several 

 facts. 



In the first place, animal ova vary with respect to the stage in 

 their development in which they are fertilized. Thus some reach 

 the fertilizable condition before the germinal vesicle breaks down, 

 others in the mesophase of the first maturation* still others during 

 the second maturation, and many after maturation is complete. 

 Starfish eggs may be fertilized at any time from the dissolution of 

 the germinal vesicle to a short time after complete maturation. 



