C. rufescens 6 



C. porcellus 53 



§ wild hybrids. ... 13 



J wild hybrids .... 44 



I wild hybrids. . . . 133 



A; wild hybrids 189 



Total 438 



GROWTH AND MORPHOLOGICAL CHARACTERS. 73 



No satisfactory measure of the sutures could be found and, therefore, 

 camera-lucida tracings were made of the nasal-frontal suture in all 

 available skulls. The original data are pre- 

 sented directly in figures 42 to 47. Draw- 

 ings were made as shown in the table here- 

 with. 



Fifty-three camera lucida drawings of this 

 suture in the guinea-pig are given in figure 

 42. Several hundred skulls were examined, 

 but no cases were found which could be con- 

 fused with the wild (fig. 43). There is a 

 range of variability in the tame; but in 



general the suture may be described as forming nearly a transverse line. 

 Only 6 C. rufescens sutures are shown. We do not know whether the 

 vn\d is very variable or not. Nor do we know that the wild males used 

 in the crosses were pure for such a character. When the wild males were 

 mated with tame females, the ^ wild (fig. 44) showed the effect of the 

 wild parent. None of the 13 ^ wild were truncate, but all v/ere M- 

 shaped. 



The ^ wild females were mated to guinea-pig males. Their \ wild 

 offspring were very variable. Forty-four of these showed a range of 

 forms from those like the \ wild to forms just like the tame (see 

 fig. 45) . It may mean that there was a rearrangement of factors, and 

 the tame form segregated out in this F2 generation, as one might 

 expect on the basis of several incompletely dominant factors. 



The \ wild females were mated with guinea-pigs to produce the 

 \ wild, and these in turn were mated to guinea-pigs to produce the 

 yV wild. The \ wild (fig. 46) and iV wild (fig. 47) presented a wide 

 range of forms. This was to be expected, for the hybrid females used 

 as dams were of many very different types. No series of guinea-pigs, 

 to my knowledge, ever showed such a range as these hybrids. 



If the wild form is regarded as dominant, then the perfectly truncate 

 forms which segregated out in the F2 (or \ v/ild) might be expected 

 to breed true when mated back to the recessive guinea-pig. This was 

 not found to be the case; for some of these female hybrids with per- 

 fectly truncate sutures had offspring showing M-shaped sutures. 

 In other words, those F2 individuals which appeared to be recessive 

 often gave M-shaped sutures in the F3 generation. It is difficult 

 to say whether or not this was due to the interaction of complementary 

 factors. The number of offspring from each F2 female was necessarily 

 small. Some bred true to the recessive truncate form, others did not. 



The frontal-parietal suture of the wild was also apparently dominant 

 in the Fi. The F2 generation was variable, giving some segregates 

 like the tame (see figs. 12, 13, 14, 17, 18, 19, 32, and 33). 



