MODES OF INHERITANCE IN HYBRIDS 451 



tending to show that in practically all characters examined the 

 hybrids reared in the laboratory are strictly intermediate between 

 those of the parent species. This is true for such matters as 

 numbers of scales in a row, numbers of fin-rays, numbers of 

 teeth, and other integral variates. Characters involving dimen- 

 sions show a similar blending between the two species. No men- 

 tion is made of the discovery of any type of inheritance sugges- 

 tive of Mendelian dominance. 



In addition to the crosses mentioned above Kammerer made 

 a number of heterogenic crosses between teleost species, the 

 results of which led him to conclude that the degree of success 

 in the development of hybrids depends not upon the closeness 

 of relationship of the parent species but upon their similarity 

 of habitat. The fallacy of this conclusion is evident in view of 

 the success of Moenkhaus and the writer in cross fertilizing prac- 

 tically any two species of teleosts. 



The first attempt to follow in detail the development of teleost 

 hybrids was made by the writer (Newman '08). This paper 

 dealt exclusively with the reciprocal hybrids between Fundulus 

 heteroclitus and Fundulus majalis. The former species develops 

 nearly twice as rapidly as \he latter and the reciprocal hybrids 

 both have a developmental time rate intermediate between those 

 of the parent species, though more nearly like that of the egg 

 than that of the sperm species. All characters involving the 

 time factor show blended inheritance, but many characters not 

 dependent on the time factor were shown to exhibit more or less 

 typical Mendelian dominance. Some of the dominant characters 

 noted were as follows: F. heteroclitus type of chromatophore 

 dominant over that of F. majalis; size of young on hatching 

 or at the time of maximum development that of F. heterocli- 

 tus in both reciprocal crosses; the rate of cleavage nearly pure 

 maternal; the viability of young hybrid larvae, when capable of 

 hatching, equal to or greater than that of the more viable species, 

 F. heteroclitus; resistance to lack of oxygen or presence of carbon 

 dioxid of F. heteroclitus egg hybrid as great or greater than that 

 of the more resistant species; susceptibility to these reagents 

 greater in F. majalis egg hybrids than in the more susceptible 



