No. 580] 



NOTES AND LITERATURE 



253 



found to be sterile but the F x females were fertile, and the line 

 was continued only by crossing- these females with guinea-pig 

 males. Thus with each succeeding generation there was a reduc- 

 tion in the amount of wild blood and the author refers to his 

 hybrids as one half wild, or F„ one fourth wild or F 2 , etc. 



As to the inheritance of coat color, the tame agouti coat is 

 dominant over the wild agouti. These two types segregate and 

 are allelomorphic to each other. Each is also allelomorphic to 

 its absence. Detlefsen finds that there is a constant relation be- 

 tween back color and belly color, but this condition is not due to 

 separate factors because they can not be transmitted independ- 

 ently. The two types of tame and wild agouti, he thinks, are 

 perhaps comparable with the types of gray mice described by 

 Cuenot and Morgan, viz., gray-bellied and light- (or white-) 

 bellied agouti. In crosses with non-agouti, the wild agouti type 

 is dominant over black and over red, as in domestic guinea-pig>. 

 After back-crossing the wild agouti colored hybrids with non- 

 agouti for several generations, it is found that the agouti factor 

 is modified, producing a darker coat, in some eases almost black, 

 the ticking being faintly seen only on the belly. Roughness of 

 coat is imperfectly dominant over smooth eoat. In later genera- 



In respect to growth and vigor, the Fj hybrids were heavier at 

 all ages than the guinea-pig parents, and were more vigorous 

 than either parent. These F 1 individuals were crossed with 

 guinea-pigs and gave young which were smaller than the F 1 ani- 

 mals in every way, and in size resembled the guinea-pig parent. 

 The variability of the wild stock in weight and vigor is unknown, 

 but guinea-pigs are remarkably uniform in both respects. In 

 morphological characters, the M-shaped nasal-frontal suture of 

 the wild species is dominant over the truncated nasal suture of. 

 the domestic form. The truncated suture reappears in the sec- 

 ond generation but does not breed true. As to skull shape, the 

 wild has a pointed head and the tame species a round one. In 

 F x a blending occurs, and in later generations the wild pointed 

 head disappears. In the wild cavy a narrow indenture is pres- 

 ent on the outer surface of the last upper molar — a character 

 held to be of much importance by systematists. In F, this in- 



tions was lost. 



