FERTILIZATION-REACTION IN ECHINARACHNIUS PARMA. 297 



3. The activated egg is an egg that has lost its fertilizin. The 

 evidence of Lillie, Moore, and Just on this point working with 

 two species of echinids and with Nereis shows very clearly that 

 once activated, as shown by membrane production, the egg ceases 

 to secrete fertilizin. Apparently, this loss is coincident with acti- 

 vation representing a neutralization of fertilizin with antifer- 

 tilizin in the egg cortex. 



We find these results, then, in the fully activated egg: (i) 

 inability to respond to insemination, (2) the presence of a mem- 

 brane widely separated from the vitellus which has arisen as the 

 result of a cortical liquefaction, and (3) the absence of fertilizin. 

 In the case of the sperm activated egg, the normal cleavage and 

 development follow insemination; but in the butyric activated 

 egg without hypertonic treatment, after a longer or shorter resi- 

 dence in sea-water cytolysis and death result. 



Comparison with the over-exposed egg yields many dissim- 

 ilarities. 



1. The over-exposed egg is capable of insemination. Though 

 it would appear Loeb failed to get such eggs to fertilize, the ob- 

 servations of Herbst, Moore, and Just seem to show that for a 

 time at least after exposure these eggs will respond to insemina- 

 tion, albeit development is far from normal. 



2. These eggs never form membranes on insemination. 



In my judgment this failure to form a membrane after insemi- 

 nation is due to the loss of the membrane or membrane sub- 

 stance through too long exposure to the acid. I interpret the 

 transparent jelly-like peripheral layer of these eggs to be not a 

 swollen membrane but the cortex itself which swells as the re- 

 sult of the injurious action of the acid after loss of the mem- 

 brane. This cortical change is the most striking characteristic 

 of the over-exposed egg. In the activated egg, the cortex lique- 

 fies, pushes the membrane off and so brings about the formation 

 of the perivitelline space ; but in the over-exposed egg this cortex 

 thickens. 



3. The over-exposed egg, an egg still capable of fertilization, 

 secretes fertilizin. On this point the studies of Moore admit no 

 doubt. The over-exposed egg is not an activated egg. 



As with the butyric acid activated egg without hypertonic 



