104 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the three characters D, DR, and K, as appears from Crampe's state- 

 ment. The young of " family K" are also included, being of a similar 

 nature. 



TABLE O. 



(Based on observations of Cranipe.) 



This table is particularly instructive because it is certain that the total 

 for each generation represents the sum total of all the unions that took 

 place among the various heterozygotes of a single family. The closeness 

 with which the numbers of albinos obtained approximate the theoretical 

 ^\ is certainly remarkable. 



It will be noticed also that this table contains no class showing total 

 pigmentation, — a fact which may mean a partial change of the D character 

 through long inbreeding and association with the characters DR and R. 

 The degree of white marking among the gray-whites is of course very 

 variable, and it is assumed that in the present instance gray rats showing 

 only a few flecks of white were included with the rest, though probably 

 residting from a cross of wild gray and either partial or total albinism. 

 For Crampe states that the latter cross did sometimes give gray indi- 

 viduals with whitish feet or white tips of tail. This fact is referred to in 

 the discussion of partial albinism. 



To sum up the results of the three tables, we have, by the interbreed- 

 ing of heterozygotes, among wliich three allelomorphic characters are 



