568 FRANK R. LILLIE 



inhibitor might remain in the blood after the gonads were emptied. 

 Thus the mere fact that an individual with small gonads had 

 much inhibitor in its blood would not prove that the gonads had 

 little to do with the formation of the inhibitor, for there would be 

 no way of telling whether the reduction of the gonads was recent 

 or not. 



The considerations that led to the adoption of the above 

 hypothesis are (1) that the condition of the gonads is the most 

 variable thing in the summer sea-urchins, which coincides well 

 with the variability of the amount of the inhibitor; (2) in general, 

 the fluctuation through the season of periods of maturity of 

 the sea-urchins coincides very well with the fluctuations in the 

 amount of the inhibitor. Thus the animals were in very fine 

 breeding condition during the first three weeks of July when 

 the first tests showing abundance of the inhibitor in the blood, 

 were made. They were in very poor condition then for about 

 10 days up to about August 2, when the individual tests were 

 made showing such surprising decrease of the inhibitor. On 

 August 6 when the material became better again, the inhibiting 

 effect of the blood was stronger once more. (3) Although it 

 was difficult, as said, in the individual tests to correlate the 

 amount of the inhibitor with the condition of the animals, yet 

 especially in the case of the females, those with large gonads 

 appeared to have a large amount of inhibitor present. Thus 

 females 28, 29, 30 and 32 were all ripe females that shed eggs 

 when inverted after opening, in a watch crystal, whereas females 

 31, 33, 34, 35 and 36 were all individuals with medium size ovaries 

 that shed no eggs when similarly inverted. Female 8, on the 

 other hand, had small ovaries, shed no eggs, and yet possessed 

 much inhibitor in its blood. 



The conditions that determine the amount of inhibitor in the 

 blood are thus a matter for more careful investigation. It may 

 be possible to regulate the quantity experimentally by injection 

 of fertilizin or of entire eggs. This merely indicates a possible 

 method of approaching the problem. 



I spent a great deal of time in endeavoring to meet the possible 

 objection that the inhibiting action of the blood might be due to 



