FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 45 



(r) July 8. Eggs shaken from ovaries into butyric mixture 

 gave the following results: 



Exposure in seconds 20 25 30 35 40 45 50 55 



Per cent, of membranes 33 38 34 48 31 20 17 o 



All contracted membranes. 



(d) Experiments of August 4 and 6. Serum eggs form no 

 membranes after butyric acid exposure. 



In (d) the cortical changes that are responsible for membrane 

 formation were probably complete (see beyond). The actual 

 lifting off of the membrane is not a sine qua non of activation. 

 (See Just, '196. Loeb, '15, discusses this point apropos certain 

 observations of Brachet.) 



Heilbrunn found that in Arbacia eggs membrane elevation by 

 acid is inhibited by Arbacia blood. 



C. Summary of Part II. 



Summarizing we find that butyric acid in sea-water activates 

 Echinarachnius eggs if they are in best physiological condition; 

 slight washing will not impair their capacity to respond to the 

 acid but long washing will. The body fluid inhibits membrane 

 elevation. 



III. ANALYSIS OF BUTYRIC ACID ACTIVATION. 

 If membrane elevation is a sign of complete activation those 

 eggs exposed for optimum length of time to sea-water with 

 butyric acid in optimum concentration should respond best to 

 subsequent hypertonic treatment. Moreover, activation by 

 butyric if complete as in fertilization should inhibit fertilization. 

 The present section deals with the analysis of butyric acid activa- 

 tion and contains the evidence that shows that such activation 

 is complete. 



A. Effect of Hypertonic Sea-water on Butyric Treated Eggs. 

 Butyric acid acting along on Echinarachnius eggs (at least for 

 exposures employed which were up to 16 minutes) never induces 

 cleavage. But after butyric activation hypertonic sea-w T ater 

 causes cleavage 62 per cent, in one case which is scarcely to 

 be distinguished from the normal; such eggs form gastrulae and 



