218 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



Another hypothetical suggestion is that the fertilization 

 membrane is preformed in the unfertilized egg and is merely 

 the peripheral film of protoplasm which is lifted up from 

 the egg through the swelling and liquefaction of some protein 

 lying underneath in the cortical layer of the egg. When lifted 

 up from the egg the preformed membrane undergoes a modifica- 

 tion; it becomes thicker and tougher. The objection has been 

 raised that no such surface film is visible in the unfertilized egg, 

 but this objection is not valid, since the surface films which 

 form on the principle of Thomson-Gibbs are beneath the limit 

 of visibility. This fact also meets the objection of Moore, 1 

 that after shaking unfertilized eggs into fragments, each frag- 

 ment can still form a fertilization membrane upon the entrance 

 of a spermatozoon, since each fragment is bound to have at its 

 surface such a film. But we are now in the realm of mere 

 hypotheses to which it is not worth while to devote much space. 



1 Moore, University of California Publications, Physiology, IV, 89, 1912. 



