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THE AMERICAN NATURALIST [Vol. XLIII 



in the first generation some spotted mice. This result I have 

 also repeatedly obtained. It remains to be discovered what 

 relation exists between the white of such mice and the white of 

 common spotted mice, for in these the spotting disappears in 

 the first generation. It appears that the white mice with black 

 eyes are derived from spotted mice in which the spotting has 

 been carried so far that pigment remains in the eyes alone. If 

 these mice are only extremes of the spotted conditions the results 

 seem to indicate that a recessive character has been changed 

 to a partially dominant one. Perhaps one might say that 

 physiologically it has become stronger. On the other hand, these 

 black-eyed white mice may have arisen not from extremes of 

 ordinary spotted mice but from a different relation between 

 black and white. It is interesting, however, to note that in rats 

 the recessive spotted coat also partially dominates in the first 

 generation. 



Cuenot has shown that ordinary spotted mice behave towards 

 mice with uniform coats as a simple recessive, appearing in the 

 second generation as 1 to 3. But I have found in practise that 

 it is almost impossible to give an exact classification of the mice 

 in the F 2 generation. In some individuals there may be only 

 a small white tip to the tail, or only a few hairs may be white. 

 Whether to classify such mice as dominant or recessive is largely 

 arbitrary. White hairs not infrequently appear in mice that 

 seem to be uniform in color. I find them quite abundant in 

 wild black rats (Mus rattus) . In man they appear in old age, 

 and in horses when the skin is injured, etc. These considera- 

 tions raise the question whether the problem may not after all 

 be physiological, the result being due to the activity of the cells 

 rather than to the absence of factors in the sense in which that 

 term is ordinarily used in Mendelian hypotheses. If so, the 

 entire result may be one of physiological activity rather than 

 one of presence and absence of factors in a morphological sense. 



The inheritance of the yellow color in mice has been a stand- 

 ing puzzle. Cuenot attempted to explain the facts on the as- 

 sumption that a yellow bearing sperm can not fertilize an egg 

 bearing this color, but can fertilize any other sort of egg. In 

 other words selective fertilization takes place. Hence every 

 yellow individual contains latent another color ; it is yellow be- 

 cause yellow " dominates " (?) the other colors. But if selective 

 fertilization can take place in regard to the individual characters 



