32 The Chromatin in the Development of Hybrids 



defined. An egg or embryo obtained by using Fundulus heteroclitus 

 as the female, is designated as the Fundulus egg, embryo or hybrid, as 

 the case may be. The reciprocal, with Menidia notata as the female, 

 will then be a Menidia egg, embryo or hybrid. A normal egg, embryo 

 or cross is one in which both parents belong to the same species, in 

 distinction from a hybrid egg or embryo in which the two parents belong 

 to different species. 



IV. Fertilization. 



1. Fundulus lieteroditus, female, and Menidia notata, male. 



The cross in which Fundulus heteroclitus was used as the female was 

 made ten times. In three of the experiments the males had died before 

 the milt was taken. In one of these the male had been dead for an 

 hour but the milt was normally white and the results of the experiments 

 could not be told from those in which the males were alive and vigorous. 



The per cent of eggs impregnated was not determined for all the 

 ten experiments. In all the experiments, however, it was considerably 

 above 50 per cent. Below are given the per cents based on actual count 

 of four experiments. The per cents in these range from 70 to 93. 



Experiment No. 24b 87 per cent. 



" 25b 80 



" " 29b 93 " 



"120 70 



Of the eggs impregnated, approximately 50 per cent in each experi- 

 ment were normally impregnated, the remainder were, with a very few 

 exceptions, disperic. 



2. Menidia notata, female, Fundulus liet^roclitus, male. 



The cross in which Menidia notata M'as used as the female was made 

 8 times. Two of .these experiments were made at Cold Spring Harbor 

 during the summer of 1898, and the remaining six at Woods Holl two 

 years later. The results obtained at the two places were not the same. 

 At the former place the per cent of eggs impregnated was very small, 

 namely 14, while at the latter place the impregnation was nearly perfect, 

 96 per cent. The difference may be due to the fact that at Cold Spring 

 the mother fish had to be transported for half a mile in a bucket, so 

 that they were dead or almost so by the time that the eggs were procured. 

 The experiments at Woods Hole were, on the other hand, carried on 

 under the most favorable circumstances ; the mother fish being alive 



