I 



FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 49 



July 26, August 4 and August 6. Eggs after 35 seconds ex- 

 posure showed 100 per cent, membranes but failed to develop 

 following insemination whether freed of membranes or not. 



Early in the season eggs were found that failed to form a 

 single membrane subsequent to optimum butyric treatment. 

 Such eggs on insemination never developed. Eggs inhibited 

 by the body fluid may not form membranes; if they be insemi- 

 nated they do not form membranes or otherwise develop. Such 

 eggs have undergone cortical changes but membrane formation 

 is suppressed. In serum eggs the suppression usually is not 

 complete: the membrane thickens and remains stuck to the egg. 



Moore working with Arbacia found that those eggs that form 

 butyric membranes do not develop after insemination though 

 the sperm may penetrate. Whether under similar conditions 

 sperm enter the eggs of Echinarachnius I am unable to say. 

 Mere penetration, however, in no wise affects our position. 

 Development does not depend on sperm penetration simply; 

 development begins with certain cortical changes which having 

 been initiated by agents other than the sperm inhibit action by 

 superimposed sperm. 



C. Summary of Part III. 



We may summarize the results of this section as follows: 

 Butyric acid eggs with membranes respond best to hypertonic 

 sea-water giving development that closely simulates the normal. 

 Eggs with butyric membranes cannot be fertilized though the 

 membranes be removed. These facts indicate that cortical 

 activation is complete. 



IV. DISCUSSION. 



i. Workers generally appreciate how capricious is the response 

 of eggs to agents that initiate development. Often the procedure 

 of a given experiment may be repeated with altogether different 

 results. Hence we conclude that the varying "physiological 

 condition" of the eggs is responsible for our results. Study of 

 fertilization in Echinarachnius (Just, 'IQ&) shows that this 

 physiological condition depends on the presence of fertilizin: 

 eggs that have a high fertilizin index show a high per cent, of 



