66 WITHIN AND WITHOUT 



the ovum it causes some alteration in the surface 

 membrane of the latter which, amongst other 

 things, prevents the entrance of further sper- 

 matozoa. Loeb thinks that in causing this 

 alteration it sets up the segmentation of the ovum. 

 That there is a close connection between the 

 two events seems undoubted ; that they are in 

 relation of cause and effect seems likely. It is 

 quite evident that an artificial stimulus can in 

 certain cases set up segmentation, but never can 

 it cause the fertilisation of the ovum. It may very 

 likely produce the same change in the membrane 

 that is caused by the entrance of the spermatozoon 

 under normal circumstances membrane forma- 

 tion may be necessarily coincident with the 

 liberation in the egg of some zymose which arises 

 from a pre-existent zymogen. But we are still 

 some way off any assurance that the main object 

 of the spermatozoon in inducing the development 

 of the egg is this surface alteration. It may be 

 the initial effect ; very probably it is ; but since 

 the main function of the spermatozoon must 

 be the introduction of germplasm from the male 

 parent, it is too much for anyone to ask us to 

 believe that its main function is concerned with 

 surface alteration. . 



Loeb argues that the change in the surface 

 membrane is of a chemical character, and that no 

 doubt may be correct ; but even if we allow him 

 every scientific fact, or surmise, he is still, as in 

 the other cases with which we have dealt, miles 

 away from any real explanation. He is still 

 inside his chemico-physical explanation to begin 



