STUDIES OF FERTILIZATION, 249 



fertilizing power more rapidly than the same dilutions made in 

 one stroke, indicates that successive stimulation hastens the 

 loss, which therefore appears more in the nature of a secretion 

 or a discharge than mere diffusion. The source of the substance 

 must ultimately be the sperm cell itself, and it is quite possible 

 that, as in the case of the egg, there is both a superficial layer 

 and an internal supply. 



It must be admitted that the data are inadequate to answer this 

 problem. The statement of the problem can therefore serve 

 only to bring out the resemblance between the spermatozoon 

 and the ovum in respect to the existence of a fertilizing substance 

 in each, the fertilizin in the case of the ovum and the sperm 

 receptors in the case of the spermatozoon, and also the possible 

 resemblance in respect to the disposition of the substances in 

 each. It certainly is an interesting parallelism that both cells 

 contain a substance necessary to fertilization, which may be 

 lost in the sea-water. 



The most interesting and crucial question of course concerns 

 the possibility of detecting this lost substance in the fluids of the 

 suspensions. If such a substance actually occurs in the fluid it 

 should have the property of fertilizing ova; unless it can be 

 detected by this property, we have no other indicator for it. 

 So far I have not been able to make even a beginning on this 

 problem. As is well known a number of experimenters have 

 attempted without success to derive a fertilizing medium from 

 spermatozoa. It has been suggested by Loeb that the reason 

 for the failure to secure an extract of spermatozoa that will 

 fertilize is that the motile power of the spermatozoon is needed 

 to carry the effective substance into the egg. But it may equally 

 well be that the methods hitherto employed have been too brutal ; 

 the substance may well be too labile to withstand extraction 

 by ether, etc. 



My results strongly suggest, if they do not prove, that such a 

 substance must be present in the fluid of sperm suspensions of 

 Arbacia, and they therefore suggest other methods for securing 

 it for testing. We must bear in mind that it can form only 

 an extremely small proportion of the entire spermatozoon, as 

 proved by morphological considerations alone, and that it must 



