356 



DESCKIPTiON OF CROSSES. 



In the following detailed description of the various crosses only such 

 details are included as seemed valuable. Certain of the crosses were kept 

 under observation much more closely thau others, and these are more 

 completely considered. It seemed desirable, however, to list the other 

 ci'osses made, giving brief notes when such seemed worth while. A com- 

 Xjlete list of all the crosses made is included in Table 9. 

 Fundulus heterocUttis, female, 



X 



Menidia nutata, male. 



This cross was made more frequently and studied more completely 

 than any of the others. A description of the chromosomal behavior has been 

 published by the writer ('94). I included there also a brief description of 

 the development. For the sake of completeness this may be incorporated 

 here. The percentage of eggs fertilized varies from 70 to 93. Actual counts 

 were not made in all the experiments. The percentages in four determina- 

 tions were as follows : 



Experiment 24b 87 per cent. 



25b 80 " " 



24b 93" " 



126 70" " 



Of the eggs impregnated, approximately 50 per cent, are quite constantly 

 dispermic. Very few are polyspermic so far as can be ascertained by the 

 mode of cleavage. The dispermic eggs never go further than to the close 

 of cleavage. The normally impregnated eggs go through the cleavage 

 stages in a perfectly normal fashion. This is true both for the form and the 

 rhythm of cleavage. In the following table is given a comparison of a lot 

 of hybrid eggs with a lot of normals. The eggs were taken from the same 

 female, fertilized at the same moment and kept under similar conditions. 

 The observations were made at the same time on both lots of eggs and the 

 stage at which each w^as found was recorded as accurately as possible. 



