PAKTHKNOCKNKSIS AND HKKKIMTY 299 



a suppression of the paternal inflnenee. The disturbanee is 

 the same in practically all the heterogeneous hybrids. I have 

 also produced the crosses between Ctenolahnis * and Fumluliix 

 heteroclitus ? and between ,S7rm>/o/////.x <3 and Fundulu* 

 heteroclitus $. 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 eye-, 

 lenses, ears, fins; but, with rare exceptions, there was no circula- 

 tion. The number of relatively good embryos was very lar^e 

 in the cross between Fundulus heteroclitus ? 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 $ and Menidia 6 

 were in reality pure breeds, namely Fundulus heteroclitus 

 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 is 

 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 



