42 E. E. JUST. 



These citations are sufficient, I think, to show that there is a 

 very definite optimum exposure between rather narrow limits 

 for the activation of Echinarachnius eggs by the mixture of 

 butyric acid and sea-water employed. But if the eggs are ex- 

 posed to higher concentrations of butryic acid even for a shorter 

 time they do not form full rounded membranes that stand off 

 from the cortex but thick membranes adhering closely to the 

 cytoplasm. Thus, on July 6, eggs exposed to 3 c.c. of n/io 

 butyric acid plus 50 c.c. of sea-water and those exposed to 3.5 

 c.c. of the acid plus 50 c.c. of sea-water for 20 seconds each gave 

 one hundred per cent, of these thick contracted membranes. 

 These membranes are entirely different from the so-called "fer- 

 tilization membranes" got with lower concentrations of butyric 

 used. Apparently, Loeb obtained the same results with Arbacia 

 eggs.. Speaking of the effect of butyric on this egg he says: 

 "When transferred to sea-water, they did not form a conspicuous 

 fertilization membrane as did the eggs of S. purpuratus under 

 the same circumstances, but only a fine gelatinous layer which 

 was not easily visible" (page 71). 



On shaking some time after removal from butryic sea-water 

 full membranes partially collapse; contracted membranes on 

 shaking break and the eggs give off buds. These buds show 

 extreme variations in size. Butyric treatment alone (at least 

 for the longest exposure tried, sixteen minutes) never gives 

 cleavage. The eggs never go beyond the monaster stage. 



B. Condition of the Eggs as a Factor in the Response to Activation 







by Butyric Acid. 



Without exception my best results with Echinarachnius eggs 

 have been obtained with dry shed eggs i. e., eggs deposited by 

 the animals in clean dry watch glasses. It is not always prac- 

 ticable to wait until the animals shed; I, therefore, proceed as 

 follows: The animals are washed in sea-water then in running 

 tap-water, shaken dry and placed aboral side down after a slight 

 cut around the peristome which usually suffices to induce shed- 

 ding; 1 such eggs are scarcely inferior to normally shed eggs. In 



1 Great care was exercised to keep everything sterile. On only one occasion 

 was an egg found in the two cell stage in the control not more certainly than one 

 in three or four hundred eggs, but the experiment was discarded. 



