Artificial Parthenogenesis 



97 



or certain annelids, the surface of the egg undergoes 

 a change which is called membrane formation; and 

 which consists in the appearance of a fine membrane 

 around the egg, separated from the latter by a liquid 

 (Figs. 4 and 5). O. and R. Hertwig and Herbst had 



Fig. 4 Pig. 5 



Fig. 4. Unfertilized egg surrounded by spermatozoa (whose 



■flagellum is omitted in the drawing). 

 Fig. 5. The same egg after a spermatozoon has entered. The 



fertilization membrane is separated from the egg by a clear 



space. 



observed that such a membrane could be produced in 

 an unfertilized egg if the latter was put into chloroform 

 or xylol, but such eggs perished at once. It was gene- 

 rally assumed, moreover, that the process of membrane 

 formation was of no significance in the phenomenon of 

 fertilization, except perhaps that the fertilization mem- 

 brane guarded the fertilized egg against a further 

 invasion by sperm. However, since the fertilized egg 

 is protected against this possibility by other means 

 the membrane is hardly needed for such a purpose. 



