MODES OF INHERITANCE IN HYBRIDS 475 



characters depending upon rate of development are not really 

 mattei:s of inheritance at all but matters primarily of physio- 

 logical chemistry. For example, although F. heteroclitus devel- 

 ops at a higher rate of speed than F. diaphanus, both reciprocal 

 crosses have a higher rate than the pure bred strains. There is 

 no intermediate condition here and therefore no blended inher- 

 itance. Similarly, when we make reciprocal crosses between 

 Cyprinodon and any species of Fundulus we find a marked retar- 

 dation in developmental rate in both crosses, whereas if rate is a 

 matter of inheritance we would expect the Fundulus egg hybrid 

 to inherit from the Cyprinodon father a markedly accelerated 

 rate. I am inclined to believe, on the basis of evidence now 

 available, that it will be found generally true that in crosses 

 between very closely related species the rate of development will he 

 accelerated, while those between distantly related species development 

 will be retarded, but not necessarily in direct proportion to the hetero- 

 geneity of the cross. 



These are the considerations that have led me to modify my 

 former views and to conclude that, although foreign sperm may 

 materially alter the rate of early development, it plays no role in the 

 heredity of the organism until embryonic differentiation is well under 

 way. 



INHERITANCE OF PIGMENT CHARACTERS IN FUNDULUS HYBRIDS 



1. A STATEMENT CONCERNING PIGMENT CHARACTERS IN FUNDULUS 



SPECIES 



The study of the inheritance of pigment characters in the va- 

 rious crosses is a complex and very difficult one, involving as it 

 does a consideration of the development, time relations and dis- 

 tributions of several distinct types of chromatophores, each with 

 its peculiar specific characters. In order to simplify the issue 

 as far as possible I have endeavored in most cases to limit my de- 

 scriptions to the definitive conditions of these cells as they appear 

 in the young larvae or, in the cases of non-hatching hybrids, in 

 embryos of a stage of differentiation equivalent to that of the 

 pure bred larvae selected for study. 



