IN RATS AND GUINEA-PIGS. 9 



to occur, those the existence of which has not yet been demonstrated being 

 W[BI], W[GI] t W[G-IH], and W[GB-I]. It is probable that more extensive 

 tests would demonstrate the existence of all the missing classes, as no special 

 search has been made for them, the demonstrations obtained being for the 

 most part incidental to other investigations. 



The fundamental assumption on which table i rests finds further justifi- 

 cation in the numerical proportions in which the various classes are observed 

 to occur, as will appear from an examination of tables 2 and 3 (pp. 35, 36). 

 In these tables are shown the theoretical Mendelian results and the actual 

 results of twenty- three different sorts of matings involving the pigments 

 and color- patterns which have been discussed in the previous pages. Table 

 2 includes only matings between pigmented animals; table 3, matings be- 

 tween a pigmented animal and an albino. Throughout both tables, it will 

 be seen, the expected Mendelian results agree quite closely with those actually 

 observed. Two animals possessing the same recessive character have in 

 no case produced offspring bearing the corresponding dominant character. 

 Further, the proportions of dominants and of recessives observed in mixed 

 lots of young agree in general quite closely with those expected. The most 

 striking deviation is an excess of black hooded young (BH) which is seen in 

 the totals for both table 2 and table 3. This, however, is not large enough 

 and does not occur with enough uniformity to warrant one in regarding it 

 as other than accidental. The totals for tables 2 and 3 combined are: 



GI GH BI BH W Total. 



Observed 69 132 130 186 168 685 



Expected 56 137.5 136 158 187 



In order of size the groups are as expected, except the last two, in case of 

 which the order is reversed. 



In addition to the experiments recorded in tables 2 and 3, the following 

 observations may be mentioned as corroborative evidence of the Mendelian 

 behavior of pigment characters, color-patterns, and albinism in rats. 



Black hooded individuals bearing white recessive, mated inter se, give 

 two classes of offspring, albinos and black hooded. These albinos have been 

 shown to bear without exception the black hooded pattern in a latent con- 

 dition. Of the black hooded offspring, there should be two classes pure 

 hooded (free from albinism) and hooded individuals bearing albinism re- 

 cessive, the latter being twice as numerous as the former. Out of 22 off- 

 spring tested, 14 had albinism recessive and 8 were pure hooded individuals. 



Matings of pure black hooded individuals with black hooded ones bearing 

 white recessive gave all black hooded offspring, 109 in number. One-half 

 of these should be pure hooded, and of the limited number tested this was 

 found to be true. 



