No. 507] BREEDING EXPERIMENTS WITH RATS 185 



slate) below instead of white. The presence of this 

 condition may dominate in some of the first hybrids. 



In addition to the points noted above it should be 

 recorded that in nearly all of the individuals, resulting 

 from a cross between a wild gray Norway rat and an 

 albino, there occurs a pure white spot or streak on the 

 belly, as other observers have recorded. The hair of 

 these spots is white to its base. This result is obviously 

 due to the incomplete dominance of the uniform coat. 

 The albino in my experiments, carried, latent, not only 

 black, but a spotted " condition, " as the second generation 

 demonstrated. The presence of this condition in the 

 hybrids of the first generation is shown to the extent of 

 the white ventral spot. This region of the body is, as 

 it were, a "weak" area in which the recessive character 

 displays itself, although elsewhere, as a rule, the spotting 

 is suppressed. The result shows that at certain points 

 in the pelage a recessive character may crop out in a 

 dominant-recessive individual. 



In the second generation gray, black, spotted gray, 

 spotted black and albinos appear, as others have already 

 shown. In the uniform gray individuals a series of types 

 occur varying from rats with white bellies, like that of 

 the wild gray rat, to those with a uniform slate-colored 

 belly. The gray color itself is subject to some variation 

 -the result depending perhaps on the condition of the 

 black present. 



