STUDIES OF FERTILIZATION 585 



already in the egg as shown by the fact that the rate of develop- 

 ment is not increased by superposing fertilization on partheno- 

 genesis or by polyspermic fertilization. 



The evidence for the existence of a fertilizing lysin in the sperm 

 is thus entirely analogical and would apply equally well to the 

 conception that the sperm causes membrane formation by acti- 

 vating a substance in the egg, which would make the first part 

 of Loeb's theory of fertilization consistent with the last part. 

 Direct evidence is lacking for the lysin theory, but the whole series 

 of facts described in this paper is direct evidence for the existence 

 of the fertilizing substance in the ovum. We have obtained it 

 in sea-water solution and we have studied its effects both on the 

 spermatozoon and on the ovum and have found it to answer to 

 all the necessary requirements. If the conclusions are accepted, 

 we can hardly continue to believe in the existence of the hypotheti- 

 cal sperm-carried lysin. 



But apart from this consideration, the lysin theory exhibits 

 certain featm*es of inadequacy. In the first place the failure of 

 attempts to isolate such a substance from spermatozoa and obtain 

 fertihzation can be explained, as Loeb has pointed out, on the 

 assumption that, though presumably present in sperm extracts, 

 it lacks power of penetration in the isolated condition and needs 

 the penetrative power of the living spermatozoon to carry it 

 through the egg membrane. A similar assumption would have 

 to be made with reference to the sperm receptors in my theory; 

 so that this lacuna is not peculiar to the lysin theory. 



In the second place the lysin theory affords no explanation 

 whatever of the non-fertilizable condition of fertilized eggs. If 

 membrane formation is the result of a superficial cytolysis pro- 

 duced directly by a lysin carried by the sperm and checked by 

 operation of a second spermatic substance effective after pene- 

 tration of the spermatozoon, what is to prevent a second cytolysis 

 by a second insemination? There is nothing in the lysin theory 

 that affords the least explanation of this universal phenomenon; 

 even concentrated sperm suspensions do not refertilize or exert 

 a 'cytolytic' effect on fertilized eggs. 



Loeb has noted that it is impossible to ascribe the increase of 

 rate of oxidation after fertilization to the introduction of a cata- 



