16 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



sented them as evidence of Mendelism in a species cross, when the 

 criticism on alternative inheritance in species crosses was first made. 

 Possibly it was the lack of numbers in his experiments, but surely, as 

 far as they go, the results are quite conclusive on this, as well as some 

 other points. 



All I wild hybrids recorded in table 2 were heterozygous in agouti, 

 for they were the result of matings between wild agouti males and 

 non-agouti females. The agouti which they bore came from one defi- 

 nite source, the wild strain. Tables 1 to 12 deal with both tame and 

 wild agouti as one. This method of procedure is followed because 

 both wild and tame agouti have many common characteristics. The 

 discussion of their differences is reserved for tables 13 to 15. 



It has been proven that agouti obtained from the wild is dominant 

 over the non-agouti condition in the tame. Therefore a number of 

 matings were made to investigate the reciprocal cross, in which tame 

 agouti guinea-pig males were mated to wild hybrid females. Two 

 homozygous agouti majes (cfl961 and cf2157) were mated to 10 dif- 

 ferent I" wild females (table 3) ; 3 of these females were heterozygous 

 in wild agouti, and the rest were non-agouti animals; the 27 young 

 obtained were all agouti, like the father. These young should be of 

 two zygotic classes; those produced by the 3 agouti females should 

 half of them be homozygous and the remainder heterozygous agouti 

 animals, whereas all the young from the 7 non-agouti females should be 

 heterozj^gous. Both zygotic classes were produced ; for in testing the 

 offspring of the 3 heterozygous females, one female (580) was found to 

 be heterozj'^gous, and one female and one fertile male (9 485 and cf 506) 

 were found to be homozygous. But the offspring of the 7 non-agouti 

 females used were invariably heterozygous. The result of these matings 

 shows that agouti obtained from either wild or tame is dominant to 

 non-agouti, whether this latter condition is derived from tame females 

 (table 2) or from hybrids (table 3). 



The matings indicated in table 4 corroborate this view. In this 

 experiment 5 different ^ wild hybrids were used. The hybrids were 

 the result of matings calculated to produce homozygous agouti by 

 crossing females of the wild agouti type with males of the tame agouti 

 type. These 5 agouti hybrids showed their homozygous character 

 by producing 21 offspring, all agouti. Their gametes evidently carry 

 agouti in all cases, although this agouti was derived from two very 

 different sources, the wild and the tame. When such gametes are 

 formed they are presumably of two types, one bearing wild agouti 

 and one bearing tame agouti; and when they meet gametes without 

 agouti, the zygote formed produces an agouti animal, the agouti being 

 theoretically in one case like the wild and in the other like the tame. 

 The numbers are small, but quite conclusive; for not only were all the 

 offspring agouti, but among them occurred agouti individuals of two 



