ARTIFICIAL PARTHENOGENESIS AND HEREDITY 299 
a suppression of the paternal influence. The disturbance is 
the same in practically all the heterogeneous hybrids. I have 
also produced the crosses between Ctenolabrus 4 and Fundulus 
heterochitus 2 and between Stenotomus ¢ and Fundulus 
heteroclitus 2. The result was about similar to the one 
described here. In all cases there was a consumption of yolk, 
development of an embryo, of pigment, of a heart beat, of eyes, 
lenses, ears, fins; but, with rare exceptions, there was no circula- 
tion. The number of relatively good embryos was very large 
in the cross between Fundulus heterochitus 9 and Menidia ¢ 
(where about 90 per cent formed embryos that lived for about 
a month); it was much smaller in the cross between Fundulus 
heteroclitus @ and Ctenolabrus . One word should be said 
in regard to the development of the head in these embryos. 
In later stages it is often abnormally small in comparison with 
the body. The reason for this is that, although at first the 
head of these heterogeneous hybrids develops normally, sooner 
or later its development stops and often phenomena of degenera- 
tion set in, especially in the eyes. The body of such larvae, 
however, continues to grow. 
All these hybrid larvae between Fundulus 2 and Menidia ¢ 
were in reality pure breeds, namely Fundulus heterocltus 
larvae whose development was retarded through some inter- 
ference with the normal chemical reactions in the egg; and the 
abnormalities described were in no way hybrid characters. 
This is proved by the fact that the writer was able to obtain 
similar larvae by putting the eggs of the Fundulus fertilized 
with Fundulus sperm under abnormal conditions. 
All the facts known about heterogeneous hybridization point 
to one conclusion: namely, that in these cases fertilization 1s 
really a case of artificial parthenogenesis. 
4. Bataillon had observed that if the eggs of toads are 
fertilized with the sperm of frogs the eggs die very early without 
giving rise to tadpoles. G. Hertwig, however, found that if the 
