356 
DESCRIPTION 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 than others, and these are more 
completely considered. It seemed desirable, however, to list the other 
crosses made, giving brief notes when such seemed worth while. A com- 
plete list of all the crosses made is included in Table 9. 
Fundulus heteroclitus, female, 
x 
Menidia notata, 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 98. Actual counts 
were not made in all the experiments. The percentages in four determina- 
tions were as follows: 
Experiment 24b............ a Mteted yt hes 87 per cent. 
oe 25b. ; ae “Wars BhaeeOO es a ee 
= 24b. “ : Be er Gee IER) ole 
“s 126 F ; Bei (Uae 
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 was found was recorded as accurately as possible. 
