MODES OF INHERITANCE IN HYBRIDS 455 



6. If the heart is formed, although it pumps no blood, the embryo 

 may remain aMve for a considerable period, yolk absorption taking 

 place to a varying degree. If the heart handles blood and the blood 

 vessels are differentiated, the embryo is likely to develop to the point 

 of hatching. 



7. The numerous abnormalities appearing in the hybrid embryos are 

 due to a deterioration in the developmental processes, resulting prob- 

 ably from the poisonous action of the sex products upon each other. 



8. The success of the hybrids, i.e., the stage to which a given hybrid 

 will develop, is correlated with the nearness of relationship of the two 

 species used. 



9. The mixing of unrelated sex products is looked upon as analogous 

 to the transfusion of unrelated bloods, the more distantly related the 

 two species concerned the greater their toxicity. 



For the most part the results of Moenkhaus confirm the earlier 

 results of Appellof and extend the horizon of our knowledge of 

 the field in question. I am unable, however, to accept any of 

 the last six conclusions listed above, and will present my reason 

 for thus dissenting after presenting my new results. 



Bancroft ('12) has made the most recent contribution to the 

 literature on the hybridization of teleosts. He repeated the ex- 

 periments published by the present writer in 1908, intercrossing 

 Fundulus heteroclitus and F, majalis, paying especial attention 

 to the heredity of pigmentation. The avowed object of the 

 experiments was to reexamine the hybrids ''from the Mendelian 

 and physiological points of view." Bancroft confirms my obser- 

 vations and in most points agrees with my conclusions. In his 

 search for evidences of Mendelian dominance he overlooks many 

 intermediate conditions. In one instance he attempts to explain 

 what had seemed to me a perfect case of blended inheritance 

 as the result of the interaction of two separate unit factors. He 

 confirms my results and conclusions very exactly when he con- 

 cludes that "in general, characters connected with rate of devel- 

 opment show blended heredity and it may be that such charac- 

 ters are so intimately associated with extra-nuclear substances 

 such as the yolk that complete dominance is not obtained." 



It is noteworthy, in view of Moenkhaus's statement ' ' that any 

 effect of the strange sperm upon the rate of development shows 

 itself by slowing the process of development regardless of whether 



