6 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



Jackson. During the academic year 1903-1904, Mr. R. C. Kibbey has 

 given me valuable assistance in the breeding experiments, and Mr. 

 A. D. Howard in the study of the hair pigments. 



EXPERIMENTS WITH GUINEA-PIGS. 

 HEREDITY OF COAT COLOR. 



In the coat of many mammals there occur two or more distinct pig- 

 ments associated together in the same individual hair, and according 

 as one or the other of these predominates in particular regions of the 

 hair or of the body, a distinct " ticking" of the hair is produced, or a 

 color-pattern of the body. Familiar examples of " ticked" or parti- 

 colored hairs are those of mice, squirrels, and foxes. Body color-pat- 

 terns of the sort mentioned occur in cats, tigers, leopards and the like. 



In mice Bateson ( : 03)* has shown that there occur three different 

 pigments black, chocolate, and yellow. In the wild mouse all these 

 pigments occur together in the same individual hair, but in fancy mice 

 the pigments may occur singly or combined in pairs, when they pro- 

 duce the color varieties most sought by fanciers. Bateson's observa- 

 tions have been confirmed by Allen ( :O4). 



COAT OF THE WILD CAVY. 



In wild guinea-pigs (or cavies) occur the same three pigments as in 

 mice, viz, black, chocolate, and yellow. A skin of a young Cavia aperea 

 Linn, from Brazil, which lies before me, shows a coloration similar 

 to that of the " agouti " variety of the domesticated guinea-pig. On 

 the back and sides of the body the ordinary hairs have a tip, about 2 

 mm. long, of a deep brownish-black color. Below this comes a yellow 

 band of about the same length. The rest of the hair appears black, 

 but is less heavily pigmented than the tip, and grows lighter toward 

 its base, which is of a dull leaden color. Microscopic examination 

 shows that the medulla of the hair, throughout its length, contains fine 

 pigment granules of an intense black color, and associated with them 

 others of a chocolate-brown color. The former are much more 

 numerous than the latter, and both are much less abundant toward the 

 base of the hair than at its tip. The cortex of the h'air contains 

 throughout the greater part of its length, where it is relatively thin, only 

 some chocolate pigment with a very little black. But in the distal part 

 of the hair the cortex is much thicker and more heavily pigmented. 

 Its terminal 2 mm. has the combination of chocolate and black already 

 described, but in the region just proximal to this it contains only bright 

 yellow pigment, which produces the yellow ticking of the coat. 



The longer, so-called contour hairs, found on the back and sides of 

 The figures in parentheses refer to the Bibliography, p. 77. 



