26 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



INTERCROSSING OF DIFFERENT PIGMENT TYPES. 

 Intercrossing of elementary pigment types other than albino results 

 not in perfect dominance of one and complete disappearance (recessive- 

 ness) of the other, but in coexistence of the two in the offspring, though 

 one pigment character from its nature may be much more in evidence 

 than the other. Thus black animals mated with red ones ordinarily 

 produce black offspring, though of a shade different from that of the 

 black parent, the more intense black pigment masking to a great extent 

 the presence of red. True Mendelian dominance, then, is wanting in 

 such crosses; nevertheless the other Mendelian principle, segregation, 

 is here realized. 



THE AGOUTI TYPE. 



An agouti animal, as we have seen, is one which bears the three pig- 

 ments black, chocolate, and red-yellow in a particular regional distri- 

 bution on the same hair. It is the original or wild type of pigmentation 

 and might be expected to show superior potency in crosses. My ex- 

 periments, which, however, are far from complete, indicate that this 

 type of pigmentation as transmitted in the gametes of a wild animal 

 really is potent over other types. Thus, a male Cavia aperea, which 

 was captured wild in southern Brazil, has produced by two different 

 domesticated albino females (neither of which was of agouti-colored 

 parentage) 15 young, all agouti-colored, but in some cases at least of a 

 somewhat lighter shade than the wild parent. I can not speak very 

 emphatically as to the exact shade of pigmentation in several cases, 

 because all but four of the hybrids were born dead, and their coats have 

 been examined as yet only in a wet condition. This matter will be 

 discussed more fully in a subsequent paper. 



The agouti type of pigmentation, when borne by gametes of a domes- 

 ticated guinea-pig, likewise shows a strong tendency to dominate over 

 other types of pigmentation, the only possible exception thus far ob- 

 served being black. 



Agouti x agouti. It goes without saying that pure agoutis, like 

 pure* animals of any other type, breed true. Thus, agouti $ 2017 

 mated with agouti 9 $ 2019 and 2021 produced 6 young, all of the same 

 (golden) agouti type as the parents. 



Agouti x black. Agouti 9 2018 mated with black cf 2053 (known 

 by test to be pure) produced 3 young, of which one was an agouti, the 

 other two black. This outcome indicates that the black type of pig- 

 mentation may in some cases at least have equal potency with the 



* The term pure is here used, as throughout this paper, in the Mendelian sense, 

 referring to the character of the gametes which an animal forms. Thus a pure 

 agouti animal is one which forms gametes all of which transmit the agouti type 

 of pigmentation. 



