HEREDITY OF PIGMENTATION 169 
in the hybrid was much longer, narrower, and less efficient than 
in the pure form. In the hybrid the heart never did get over 
this initial handicap but was stretched farther as development 
proceeded until finally shortly before the embryos died it had 
assumed the appearance shown in fig. 30, and at each beat was 
propelling only a very small amount of blood through the vessels. 
It seems then that a slight retardation in the digestion of the yolk 
led to such an increase in the distance between the points of 
attachment of the heart to yolk sac and embryo, that the heart 
could not grow fast enough to catch up, but remained permanently 
disabled. 
SUMMARY 
1. While it had been generally assumed that in hybrid embryos 
the inheritance was either maternal or paternal, Loeb, King and 
Moore have ealled attention to the fact that for the hybrid sea- 
urchin embryo we find dominance of individual characters as in 
the adult. For Fundulus hybrids Newman found a dominance of 
a few individual characters, but usually found the characters inter- 
mediate between those of the two parent species. In this study, 
which is concerned mainly with the pigment characters of Fun- 
dulus heteroclitus, F. majalis, and their hybrids, dominance of 
individual characters has been found in most cases, as in the fol- 
lowing characters: 
a. The character—presence of many large red yolk chromato- 
phores (F. heteroclitus condition) is dominant over the charac- 
ter—presence of few small red yolk chromatophores (F. majalis 
condition). 
_ b. The size and shape of the black yolk chromatophores of 
F. heteroclitus is dominant over the size and shape of these same 
cells characteristic of F. majalis. 
c. The presence of a first crop of head chromatophores appear- 
ing before the majority of the head chromatophores (I. hetero- 
clitus condition) is dominant over the absence of this crop of 
head chromatophores (F. majalis condition). 
d. The presence of red chromatophores along the lateral line 
at hatching time, or shortly before it (F. heteroclitus condition) 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, No. 2 
