294 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



The fertilization of the eggs of the sea-urchin with the sperm 

 of molluscs and annelids by Kupelwieser and by Godlewski 

 (see chap, xxii) did not lead to any normal larvae and cannot 

 therefore be utilized for this problem. The writer's experiments 

 on the cross between S. franciscanus ? and Chlorostoma $ 

 (a mollusc) gave maternal plutei. 



2. It can be stated as a general fact that the rate of cleavage 

 in hybrid eggs is exactly like the rate found in the development 

 of eggs fertilized with sperm of their own species. The writer 

 found this to be true for sea-urchin eggs fertilized with the 

 sperm of starfish. Moenkhaus measured the rate of segmen- 

 tation in hybrid fish eggs and found that the rate for the first 

 cleavages is determined by the egg. 1 The egg of Ctenolabrus 

 segments about forty minutes after impregnation with sperm 

 of its own kind, while the egg of Batrachus tau, if fertilized with 

 the sperm of the same species, segments after about eight hours. 

 If the egg of Batrachus be fertilized with the sperm of Ctenolabrus 

 it also does not segment until after eight hours. 2 I have 

 repeated these experiments in a number of fish hybrids and 

 confirmed Moenkhaus' results. This fact proves again what we 

 stated in a previous chapter, that the spermatozoon does not 

 start the development by carrying an enzyme or catalyzer into 

 the egg, which the latter needs in order to develop, but causes the 

 development by altering the surface layer of the egg. If the seg- 

 mentation of the egg were caused by an enzyme carried into the 

 egg by a spermatozoon, the rate of cleavage of slowly develop- 

 ing eggs should be accelerated by a spermatozoon of a species 

 developing at a faster rate. The egg, however, behaves exactly as 

 we should expect from the fact that the spermatozoon removes 

 only certain obstacles for the development of the egg, but does 

 not cause its segmentation by carrying an activating enzyme. 



1 Moenkhaus, Am. Jour. Anat., 115. 29, 1904. 



- The acceleration of segmentation which Newman observed in the egg of 

 Fundulus majalis fertilized by the sperm of Fundulus heteroditus is too small to 

 influence our conclusions. 



