INHERITANCE OF DILUTION. 77 



white and yellow spotting respectively. S int+ and 2 int- mean 

 hereditary constitutions which intensify or dilute, respectively, the 

 color associated with a given array of Mendelian factors. 2 + and S - 

 in the rough column have a similar meaning with respect to the rough 

 character. SR means the presence of roughness of a different kind 

 from that analyzed. Where a factor occurs only rarely in a stock, it 

 is inclosed in parentheses. 



PROBLEMS. 



The inheritance of the discontinuous color variations which are known 

 in guinea-pigs has been solved by previous work. After each factor 

 variation from the wild type (Cavia cutleri) in the definitions of the 

 factors the principal papers on the subject are given. The writer has 

 been concerned mainly with an analysis of inheritance in the contin- 

 uous series of variations by which each of the intense colors red, 

 brown, and black grade into dilute colors and ultimately white. A 

 second group of problems concerns the variations in the amount of 

 yellow ticking in agoutis. The writer has worked with the agouti 

 patterns of Cavia cutleri, C. rufescens hybrids, and tame guinea-pigs. 

 The inheritance of variations in the rough coat occasionally found in 

 guinea-pigs is discussed in a later section. 



INHERITANCE OF DILUTION. 



THE RED-EYE FACTOR. 



The experiments with dilution have become closely associated with 

 experiments with certain imported South American stocks (lea, Are- 

 quipa) which are discussed in detail in Part I. A number of hitherto 

 unknown color varieties appeared in these stocks, the inheritance of 

 which could be explained by assuming the existence of a new allelo- 

 morph of albinism intermediate in effect and dominance between albin- 

 ism and its normal allelomorph. More specifically, this new factor 

 is characterized by the production of red eyes, slight dilution of black 

 in the fur, and complete inhibition of yellow pigment development. 



The writer has used animals of both the lea and Arequipa stocks in 

 experiments, with results in full agreement with those given in Part I. 

 Crosses 20-1 and 21 to 25 involve red-eye (from lea stock) without 

 also involving dilution. In cross 20-1 a pure lea male, a red-eyed 

 agouti, is crossed with intense guinea-pigs, giving young all intense. 

 This illustrates the dominance of intensity over red-eye. 



In cross 21 a pure lea intense male crossed with albinos of intense 

 stock gives both intense and red-eye young. The lea male no doubt 

 was heterozygous for red-eye, but the albinos could not possibly trans- 

 mit red-eye, as they come from a stock in which red-eye has never 

 appeared. This illustrates the apparent reversal of dominance of red- 

 eye whenever albinism is introduced into a cross. A further illus- 

 tration is given in cross 23, in which red-eye by albino of intense 



