248 FRANK R. LILLIE. 



more concentrated suspensions;^ the relative freedom from CO2 

 and other sperm excreta should favor a longer continuation of 

 their motility in the dilute suspensions rather than the reverse. 



{d) Moreover, in general the results of recent fertilization 

 studies such as the antagonistic action of sperm suspensions 

 of different phyla, inhibition of fertilization in the presence 

 of blood of the species, or in the absence of certain ions (Loeb, 

 '14), or again the sterility in certain self-fertilizations, and finally 

 the inability of spermatozoa to penetrate fertilized eggs, unite 

 in demonstrating the relative lack of significance of motility 

 as such. 



We come therefore to the conclusion that the individual spermatozoa 

 in suspension tend to lose their fertilizing material, so that an 

 increasing proportion of these spermatozoa become absolutely in- 

 effective whatever their motility. This conclusion is in agreement 

 with all the data of the foregoing experiments, and seems to 

 be the only one competent to explain the results. 



The following questions arise: (i) Whether the loss of this 

 substance by the sperm is a mere process of diffusion or an active 

 secretion? (2) Can the substance be recovered from the fluid 

 of the suspension, or can its presence in the fluid be demonstrated 

 in any way? 



As regards the first question: In the case of the ova we know 

 that the external jelly-covering is loaded with sperm-agglutinat- 

 ing substance which diffuses into the sea-water continuously. 

 It is theoretically possible, at least, to apply a similar conception 

 to the spermatozoon, although no such covering is demonstrable. 

 The more rapid loss of fertilizing power in the greater dilutions 

 would be consistent with this interpretation. From this point 

 of view we would have to regard the sperm head as covered 

 superficially with a layer of fertilizing material, like the phos- 

 phorus on a match. Such a conception is by no means im- 

 possible. On the other hand the fact that dilutions reached- by 

 a series of successive half-dilutions from i per cent, lose their 



1 Gemmill (1900) observed the same phenomenon and concluded that the more 

 rapid exhaustion of spermatozoa in dilute suspensions is due to dilution of a 

 hypothetical nutritive medium which keeps the spermatozoa of concentrated sus- 

 pensions in a vigorous condition. This explanation comes back to the principle 

 of loss of motility, so far as it relates to fertilizing power. 



