HEREDITY OF PIGMENTATION 157 
number though stillremaining in the vicinity of the embryo. After 
a few days their number again decreased markedly, apparently by 
incorporation within the embryo, so that they could only be found 
in a small proportion of the eggs, and in these not more than two 
or three cells to each yolk sac. There is no doubt then, that, so 
far as the number of these cells is concerned, there is a well marked 
Mendelian dominance, but as it is almost impossible to count them 
accurately I cannot be sure that in the hybrids the number of red 
yolk chromatophores is not slightly less than in pure F. heteroclitus. 
An examination of the red yolk chromatophores in the four 
forms for size showed that the chromatophores of F. majalis 
were usually much smaller than those of any of the other forms; 
but that these cells in the F. majalis egg hybrid were slightly 
smaller and in the F. heteroclitus egg hybrid considerably smaller 
than in the pure F. heteroclitus (compare figs. 13 and 14; 15, 
16, and 17; 18 and 19; 20 and 21; 22 and 23). As in most cases 
where the hybrids showed a condition intermediate between 
those of the two pure species it was the F. heteroclitus egg hybrid 
which was most like the pure F. heteroclitus; this case in which 
the F. majalis egg hybrids were most like the pure F. heteroclitus 
deserves special emphasis. 
In shape the red yolk chromatophores of both hybrids approxi- 
mated closely to the dominant condition of the pure F. hetero- 
clitus. When they first appeared, these chromatophores in all 
four forms had about the shape of the red yolk chromatophore 
in fig. 13. In the pure F. majalis the red yolk chromatophores 
even at the period of their maximum complexity (fig. 17) did not 
progress far beyond this early shape; while the chromatophores 
of the three other became much larger and more complex. The 
F’. heteroclitus egg hybrids usually had red yolk chromatophores 
of exactly the same shape as the pure F. heteroclitus (compare 
figs. 18 and 19, 20 and 21, 22 and 23). The F. majalis egg hy- 
brids also in many cases had cells of exactly the same shape and 
almost the same size, as those of the pure F. heteroclitus. In 
some cases, however, the processes of these cells in the hybrids 
were fewer and the central body less extensive (fig. 9). 
