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 8S. franciscanus 2 and Chlorostoma 2 
(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. 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 fasterrate. 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., lYf, 29, 1904. 
2The acceleration of segmentation which Newman observed in the egg of 
Fundulus majalis fertilized by the sperm of Fundulus heteroclitus is too small to 
influence our conclusions. 
