24 FRANK R. LILLIE. 



considerably from Loeb's account and they are therefore re- 

 corded for the purpose of clearing up the apparent flat contra- 

 diction between the results of Loeb on Strongylocentrotus pur- 

 puratus and of Moore and Just on other forms. 



The conditions of activation by butyric acid should first be re- 

 called. It is convenient to proceed from a standard concentra- 

 tion of butyric acid, and accordingly the strength used by Loeb 

 was adopted for all the experiments, viz : 2.8 c.c. N/io butyric 

 acid -f- 5 c - c - sea-water. Membranes are not formed in butyric 

 acid, but only after transfer of the eggs to sea-water. The 

 optimum time of exposure to butyric acid for membrane forma- 

 tion in sea-water is a function of temperature ; a series of de- 

 terminations showed the following approximate optimum ex- 

 posures: 15 C, 110-120 seconds; 17, 90 seconds; 20, 80 

 seconds ; 24.5, 40 seconds ; 30, 18 seconds. It is therefore very 

 important that the temperature of any given experiment should 

 be known ; the temperature of the experiments recorded here was 

 always close to 16 C. The optimum time of exposure is also 

 rather narrowly limited at any temperature. Thus in one experi- 

 ment where 105 seconds was optimum, 90 seconds was too short 

 and 120 seconds too long for optimum results. 



The concentration of the butyric acid to which the eggs are 

 exposed is another vital factor; therefore in adding the eggs to 

 the butyric acid the same amount of sea-water should be carried 

 over with them each time; in my experiments this was 2.5 c.c.' 

 The membrane reaction after transfer to sea-water depends on 

 removal of the action of the butyric acid ; it is therefore im- 

 portant not to carry over too much butyric acid in making this 

 transfer; the transfers were therefore made uniformly to TOO c.c. 

 sea-water and not more than 2.5 c.c. of the butyric acid solution 

 was carried over. The eggs were not fertilized in this sea-water, 

 but from 2 to 5 drops were transferred to 10 c.c. of fresh sea- 

 water in a Syracuse watch crystal in which the inseminations 

 were made ; thus the butyric acid was reduced to a negligible 

 quantity in the insemination. 



Considerable variations in temperature or of conditions of 

 transfer to or from the butyric acid will produce considerable 



