168 FRANK W. BANCROFT 
and they all have developed from three to six or seven trans- 
verse black bands due both to an increased number of chromato- 
phores and an increased expansion of the chromatophores in the 
region of the bands. Between the bands there are at present 
usually not more than one black chromatophore to the scale, while 
in the more pronounced bands there may be as many as four 
or five chromatophores to the scale. The present appearance of 
the fish is much like that of the females of F. heteroclitus shortly 
after the breeding season, when indistinct transverse dark bands 
may be seen. 
CHARACTERS OTHER THAN THOSE OF PIGMENTATION 
As regards the rate of the development of the embryo my obser- 
vations confirm those of Newman on most points. The devel- 
opment of the F. heteroclitus egg hybrid was slower than that of - 
its maternal parent; and the development of the F. majalis egg 
hybrid, during the early stages was faster than that of the pure 
F. majalis. After hatching the F. heteroclitus egg hybrid seemed 
more vigorous and grew faster under like conditions than either 
of the pure forms. 
The failure of the F. majalis egg hybrids to develop well during 
the later stages seemed to depend primarily upon the poor diges- 
tion of the yolk in this form. The first considerable difference 
that could be seen between the pure F. majalis and the F. majalis 
egg hybrid was that in the hybrid the yolk was not digested away 
from under the embryo as rapidly as in the pure form. A result 
of this appeared to be that, when the heart was forming, the vesicle ’ 
underneath the embryo was very shallow and the normal anterior 
curvature of the head did not take place (compare figs. 28 and 
29). These two factors seemed to be responsible for the fact that 
when the heart first began to beat in the hybrid it was closely 
pressed to the ventral side of the embryo (fig. 28) and did not 
extend across the vesicle making an angle of nearly 90° with the 
embryo as in the pure form (fig. 29). Consequently from the 
very first the heart in the hybrid was much stretched and on the 
next day when the circulation had become established the heart 
