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THE AMEBIC AX N AT U BALI ST [Vol.LII 



tures. It is more than possible, likewise, that the hybridi- 

 zation of such diverse strains was the disturbing element 

 that led to the loss or modification of a ' 'gene." The 

 latter possibility is strengthened by a consideration of 

 the Hagedoorns's waltzing rats and abnormalities of coat 

 color. But this is a very different view from the hypothe- 

 sis that ''the new types were already given in the geno- 

 type of the . . . species crossed." 



2. Yellow gambeli 



The five normally colored progeny of a single pair of 

 normally colored Peromyscus manicuJatus fjcnnbeU (La 

 Jolla race) became the parents of 21 offspring, of which 

 14 were normally colored and 7 were of a peculiar yel- 

 lowish-brown color. These "mutants," which I have 

 called "yellows," are of a shade not very far removed 

 from Ridgway's "clay color." They are considerably 

 darker than some, at least, of the yellow races of Mus 

 musculus. Microscopic examination of the hair of these 

 aberrant gambeli shows that it is closely similar to that 

 found upon the more highly colored parts of P. m. sono- 

 riensis. In comparison with normal specimens of its sub- 

 species the mutant strain is found to have a larger num- 

 ber of the yellow-banded hairs, in proportion to those 

 which are black throughout their entire length. The 

 latter type of hair is, however, by no means wanting. In 

 the second place, the yellow zone of each hair, on the col- 

 ored parts of the body, occupies, on the average, a con- 

 siderably larger proportion of its length. On the mid- 

 ventral surface, the basal, plumbeous zone is quite lacking, 

 the hairs being entirely white. Besides the differences 

 stated, I can not be certain of any hair characters which 

 distinguish this type of sports from the normal stock. 

 Moreover, the eyes, ears, tail, etc., carry a normal amount 

 of black pigment. 



It is to be noted that these "yellow" mice, unlike the 

 "partial albinos," are not distinguished by any types of 

 hair which are lacking in normal individuals. * We may, 

 however, very justly regard the yellow condition as having 

 arisen through "discontinuous variation." Though due 



