MODES OF INHERITANCE IN HYBRIDS 487 



2. Harm Jul versus heneficial effects of foreign sperm 



The effects of foreign sperm are not always deleterious nor 

 is it true that cross fertilization always results in a retardation 

 or interruption of early development, as Moenkhaus maintains. 

 In fact the sperm of a closely related species may, and actually 

 does in three out of six Fundulus crosses, definitely accelerate 

 development from the very beginning, and produces a hybrid larva 

 more viable and capable of growing faster than those of either 

 parent species. The idea of Moenkhaus then, that foreign sperm 

 plays a role equivalent to that of foreign blood in transfusion 

 experiments, is out of accord with these facts, for there is nothing 

 equivalent to the injurious hemolytic effects of foreign blood in 

 crosses where the sperms of closely related species are used. On 

 the contrary, an effect is produced akin to the well-known 

 stimulating effects of crossbreeding strains in practical animal 

 husbandry. 



3. Phylogenetic relationship of parent species and developmental 



success of hybrids 



The idea expressed by Moenkhaus that success in the develop- 

 ment of teleost crosses is a function of the phylogenetic relation- 

 ship of the parent species breaks down in view of two sets of facts : 



a. There is a marked difference between the developmental 

 success of reciprocal hybrids. The parents are the same in both, 

 hence factors other than that of phylogenetic relationship must 

 underlie this different degree of success in development. 



b. The data given in this paper, and by Moenkhaus himself, 

 prove that success in development of hybrids produced by cross- 

 ing different orders of teleosts is not seldom greater than that 

 attained by hybrids between different families of the same order, 

 or even between different genera of the same family. 



Kammerer endeavors to show that success in crossing depends 

 on similarity of habitat, but in these experiments of mine a 

 fresh water and a marine species give the most normal develop- 

 ment, while two marine species give unsuccessful crosses. The 



