CROSSES OF CAVIA CUTLERI. 13 



CROSSES OF CAVIA CUTLERI MALES WITH GUINEA-PIG FEMALES. 



Crosses have been made only between male Cavia cutleri and female 

 guinea-pigs. The reciprocal cross was not undertaken, because the 

 number of cutleri females on hand at any one time has been insufficient 

 and because it seemed probable that a cross with the much larger 

 guinea-pig would be fatal to the cutleri females because of the probable 

 large size of the hybrid offspring. Two races of guinea-pigs were 

 employed in the crosses, these being the purest races available, the 

 genetic properties of which had been long and thoroughly tested. 



The race most extensively used may be called race C. It consisted 

 of "brown-eyed cream" individuals or of albinos borne by brown-eyed 

 cream parents. The results of crosses of colored and albino individuals 

 of race C will be described separately. The other race may be called 

 race B. It consisted of intensely black-pigmented individuals or of 

 albinos produced by such black individuals. The results of crosses with 

 the two sorts of individuals will be described separately. A cutleri male 

 bred in captivity (cf 78) was mated with black females of race B, and 

 produced 9 F : young, all colored like C. cutleri, but darker, the ticking 

 of the fur being brick red or yellow instead of creamy white as in cutleri. 



Albino females of race B were mated with the same cutleri male 

 (d"78) or with cf 114, another cutleri male reared in captivity, or else 

 with cf 4 or cf 8, which were original cutleri males caught wild. Such 

 matings produced 39 F x young, all with the same (golden agouti) type 

 of coloration as the young produced by the black mothers. 



Females of race C were mated only with the two wild-caught cutleri 

 males (r?4 and c?8). The cream-colored mothers of race C produced 

 34 young, all golden agouti in color like the young derived from race B 

 crosses, but much lighter. They were, however, darker in color than 

 C. cutleri, the agouti ticking being yellow or reddish, not creamy white 

 as in cutleri. (See plate 3.) Albino females of race C produced by the 

 cutleri males 14 young, indistinguishable in appearance from the young 

 produced by their cream-colored sisters. 



The Fi hybrids, whose total number was 96, were all vigorous and 

 large, their adult size nearly or quite equaling that of guinea-pigs. 

 They grew with great rapidity and have proved fully fertile inter se. 

 In wildness and ferocity they are intermediate between the parent races. 



COLOR INHERITANCE AMONG THE F 2 HYBRIDS. 



(a) CROSS 9 ALBINO (RACE B)Xc? CUTLERI. 



By breeding inter se certain of the F : hybrids, from the cross 9 

 albino, race B, X cf cutleri there has been produced a second (or F 2 ) 

 generation of hybrids, which number 75 individuals. As regards color, 

 disregarding minor differences of intensity of pigmentation, these 

 hybrids fall into three classes: golden agouti, black, and albino. Of the 



