238 FRANK R. LILLIE. 



could not be examined, the whole number must have been at 

 least double ; in No. 8 of the series, an average of five spermatozoa 

 was counted with each egg; in No. 9 an average of 1.2; No. 10, 

 1.4; No. II, 0.9. Similar counts were made in other cases. 

 But in fertihzations under optimum conditions all of the eggs 

 may fertilize in dilutions of sperm so great that it is almost 

 impossible to find spermatozoa in the jelly of the eggs. (2) 

 The spermatozoa are active and the eggs readily fertilizable in 

 such a series as the above. Repeated observations were made 

 on this point; which would be tedious to relate in detail. 



It may be noted that in the fertilization under optimum condi- 

 tions the eggs were first placed in sea-water, and given quantities 

 of sperm then added ; whereas in the experiments with successive ' 

 dilutions eggs were added to sperm suspensions already made up. 

 This suggested that the order of adding eggs and sperm might 

 be of significance in some way. However, this does not appear 

 to be the case. 



The possibility remained that the repeated handling of the 

 sperm in successive dilutions decreased their motility. Micro- 

 scopical examination did not confirm this idea; and subsequent 

 experiments disproved it, as the fundamental factor at least. 



Thus it would appear that the only real difference between the 

 optimum and minimum conditions of the fertilizing power of 

 sperm dilutions is a time factor; under what I have called the 

 optimum conditions the final dilution is made from a relatively 

 concentrated sperm suspension in the presence of eggs ; but under 

 the conditions of successive dilutions time elaspses before the 

 eggs are added. 



Thus in Curve 2 the preparation of the series of sperm dilutions 

 from the original i per cent, suspension occupied 22 minutes 

 before the eggs were added. In Curve i, on the other hand, 

 less than a minute elasped from the time of preparing the i/ioo 

 per cent, and i/iooo per cent, sperm suspensions used in the 

 last four determinations to the time of their use in inseminating 

 (see p. 234) ; and the final dilution was made in the presence of 

 the eggs. 



The time factor is the real explanation as will be shown im- 

 mediately. But at first sight it did not seem a very probable 



