236 FRANK R. LILLIE. 



because a parallel control series, in which the same quantities 

 of the same lot of eggs were first placed in the same quantities 

 of sea-water and sufficient of the original i per cent, sperm 

 suspension added to make similar sperm dilutions, showed over 

 95 per cent, cleavage in each case, and actually 99 per cent, in 

 No. 8 of the control where the sperm dilution was 1/1200 per cent. 

 As a further control it may be added that eggs which fail to 

 fertilize in such relatively concentrated sperm suspensions may 

 all be fertilized by the subsequent addition of a trace of perfectly 

 fresh sperm. 



The type of experiment just cited was the first undertaken, 

 and for a time it seemed to offer an almost insoluble problem, 

 though the real explanation turned out to be extremely simple. 

 I have twenty curves from similar experiments, fourteen of which 

 run out absolutely from the third to the twelfth place on the 

 scale {i. e., from 1/8 per cent, to 1/4096 per cent.) ; in the remain- 

 ing 6 (as in the curve just given) the dilutions were not carried 

 far enough to reach the zero point, but they agree in principle 

 with the others. 



A number of control experiments demonstrated the relative 

 lack of significance of the actual sperm concentrations. As one 

 of these I may mention experiment C of August 3. In this case 

 a series of sperm dilutions in powers of 4 was made from i per 

 cent. The proportion of eggs fertilized ran off to i per cent, at 

 1/4^ (1/2^") and to o at 1/4.^ = 1/4096 per cent. But one drop 

 of a 0.1 per cent, suspension of the original i per cent, sperm 

 added to eggs in 200 c.c. sea-water fertilized 94 per cent, of them 

 (control for sperm). Thus the control fertilized almost perfectly 

 at 1/60,000 per cent, dilution, whereas the fifth member of the 

 series of dilutions 1/2^° (1/1024 per cent, sperm) fertilized only 

 I per cent. The actual concentration of the sperm is thus not the 

 most significant thing. 



This is also brought out strikingly in the following experiment 

 (August 14). A series of half sperm dilutions was made as usual 

 (Series A) 2 c.c. in each dish; to a second series (series B) of 

 dishes was added 2 c.c. sea-water each and 4 drops of an egg- 

 suspension. The numbers of series B were then inseminated by 

 one drop each of sperm from the corresponding number of A , thus 



