HEREDITY IN HETEROGENEOUS HYBRIDS / 



rate of chemical reactions will be found and the outcome will be 

 pathological embryos and very likely a suppression of the paternal 

 influence. The disturbance is the same in practically all the heter- 

 ogeneous hybrids. I have also produced the crosses between 

 Ctenolabrus d" and Fundulus heteroclitus 9 and between Stenoto- 

 musc?- and Fundulus heteroclitus 9 . In all cases the result was 

 about similar to the one described here. Tn 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 

 about which we are to speak later, there was no circulation. The 

 number of relatively good embryos was very large in the cross be- 

 tween Fundulus heteroclitus 9 and Menidiac? (where about 90 per 

 cent formed embryos that lived for about a month) ; it was much 

 smaller in the cross between Fundulus heterochtus 9 with Cteno- 

 labrus cf . One word should be said in regard to the development 

 of- the head in these embryos. In later stages it is often abnor- 

 mally 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 degeneration set in, especially in the eyes. 

 The body of such larvae however continues to grow. 



5. From what was said before, I reached the conclusion, that 

 these hybrid larvae between Fundulus 9 and Menidia d" were 

 in reality pure breeds, namely Fundulus heteroclitus larvae whose 

 development was retarded through some interference with the ' 

 normal chemical reactions in the egg; and that the abnormalities 

 described were in no way hybrid characters. It occurred to me 

 that it might be possible to produce similar larvae from pure breeds 

 of heteroclitus eggs, if the latter were compelled to develop under 

 an abnormal chemical condition. For this purpose the following 

 experiment was made. Eggs of Fundulus heteroclitus were put 

 immediately after fertilization into closed Erlenmayer flasks, each 

 of which contained 50 cc. of sea water to which various amounts 

 of a 0.01 per cent solution of NaCN were added, from to 10 cc. 

 The eggs remained in these solutions about a month. In the 

 mixture of 2 cc. 0.01 per cent NaCN and 50 cc. of sea water, em- 

 bryos were found which in every way resembled the hybrids 



