kStudies of fertilization 549 



principles as factors in the union. Chemotaxis has fallen into 

 disrepute; and the theory that the spermatozoon bores into the 

 egg has been rejected by several observers. 



If chemotaxis is concerned in the union of ovum and spermato- 

 zoon the medium in which fertilization operates must contain the 

 substance concerned. In the case of the eggs of Nereis and Arba- 

 cia, therefore, the hypothetical substance which attracts the 

 spermatozoa must exist in sea-water which has been in contact 

 with fertilizable eggs; and it must be possible to obtain a sufficient 

 concentration of the substance in question in sea-water to demon- 

 strate its presence by reaction of the spermatozoa, because, ex 

 hyp., the substance exists in effective amounts in the sea- water 

 surrounding the eggs. If it were mipossible to demonstrate the 

 presence of an agent to which spermatozoa of the same species are 

 positively chemotactic by such means the theory of chemotaxis 

 would have to be abandoned. However, the presence of such a 

 substance is readily demonstrated both in Nereis and Arbacia. 



In the second place, if the union of the ovum and spermatozoon 

 after they have come in contact operates not mechanically, but 

 through some bio-chemical reaction between spermatozoon and 

 o\aim, the sea-water in which eggs have been standing should 

 contain a substance also capable of reaction with the sperm, which 

 should be an efficient indicator for it. 



I was guided by some such ideas as these in the series of experi- 

 ments which follow, and which showed at the very first trials that 

 sea-water which has stood with fertilizable eggs of Nereis or 

 Arbacia contains a substance to which the spermatozoa of the 

 same species are positively chemotactic, and also a substance 

 which agglutinates the spermatozoa of its own species. It may 

 be that one substance is concerned in both reactions, but it is 

 more probable that two are present. It is perhaps worth empha- 

 sizing here, for this is the fact that struck me at the start, that the 

 sea-water which has stood over eggs^ combines both the effects of 



^ To avoid the frequent repetition of such a circumlocution we may call sea- 

 water, which has contained eggs and is charged with their emanation, egg sea- 

 water; and the concentration of the substance in the sea-water may be expressed 

 by writing the relative bulks of eggs and sea-water as a fraction. Thus 'egg sea- 

 water 1/3' would indicate that the bulk of eggs was one-third the volume of the 

 sea-water. Time is also a factor in the concentration, of course. 



