STUDIES OF FERTILIZATION, 



243 



added at 9.47, that is, 17 minutes after the i per cent, sperm was 

 prepared. Twenty-eight minutes later (10.15 A.M.) two drops 

 of the same egg suspension were added to series B. The only 

 difference between series A and B is the time factor. The per- 

 centages of cleavages were counted for both series, and the plotted 

 results given the curves. Considerable loss of fertilizing power 



012345 6 789 10 II 



90 

 80 

 70 

 60 

 so 

 40 

 30 



■ 



Curve 4. 



has occurred in series B as compared with series A . Now, if we 

 compare these time intervals with those given in Table II. we 

 see that, in the curve of series B the last number, which is a 

 1/2^^ or 1/2048 per cent, sperm suspension, loses its fertilizing 

 power completely in 36 minutes {i. e., from 9.39.30 to 10.15.30) 

 which corresponds very well with the rate of loss of fertilizing 

 power in a 1/2400 per cent, sperm suspension. This agreement 

 is rather closer than usual ; in some cases the series of 3^ dilutions 

 ran out at higher concentrations in about the same time; but 

 in no case, I think, did they require more time. This suggests 

 some possible stimulating effect of the successive changes which 

 causes the spermatozoa to lose their fertilizing power more 

 rapidly than under the time factor alone. 



Gemmill (1900) observed that the duration of vitality of 

 spermatozoa of sea-urchins and limpets tested by their move- 

 ments or by the fertilizing capacity, varies greatly " according to 

 the amount of sperm used in proportion to the volume of sea- 



