566 FEANK R. LILLIE 



While the experiments cited give effects only of mixed blood 

 from the two sexes, and the blood of the males alone, other experi- 

 ments, not so complete in all details, showed that females contain 

 the inhibitor in their blood at least to the same degree as the males. 

 If there is any sexual difference it is in favor of the females. The 

 blood of the males was used in many tests alone because there was 

 danger, in opening the females, of wounding the ovaries and so 

 getting fertilizin into the blood, which as shown beyond, greatly 

 modifies the results. There was of course the danger in using 

 blood frdm males of getting spermatozoa from wounded testes, 

 but as the eggs were in any case to be fertilized the result could 

 hardly be affected by this ; some control experiments showed that 

 this was a rare occurrence in any event. 



Individual variability in the amount of the inhibitor present 

 in the blood being indicated in these experiments, a special study 

 was made of this factor in order to test its extent, and if possible 

 to correlate it with the condition of the animals. The individual 

 tests were as follows (table 9) : the columns give the percentage 

 of egg's segmented after 2 to 3 hoiu-s. All the fertilizations of 

 July 28 were made with a single sperm suspension and a single 

 lot of eggs; similarly for each succeeding date. The various num- 

 bers therefore act as controls on one another. In all, a great 

 excess of sperm was used. The counts were carefully made and 

 checked by my assistant. Miss Brockett. 



These tests of bloods of individuals bring out very extreme 

 individual differences in the content of fertilization inhibitor in 

 the blood, ranging in fact all the way from no inhibition to absolute 

 inhibition of fertilization. But it is not easy to correlate the 

 variations with the conditions of the individuals. The general 

 hypothesis that I have been led to adopt, provisionally at least, 

 is that the quantity of the inhibitor in any individual blood is 

 related to the size and degree af maturity of the gonads. It would 

 seem to be a very simple matter to determine whether this is or 

 is not the case. However, in the first place,, after the beginning 

 of the season there are practically no animals with immature 

 gonads to test, and in the second place, if the hypothesis were 

 correct, it would be impossible to know in advance how long the 



