92 Experimental Zoology 



characters, spotted versus color uniform, are independent of the 

 coupled characters gray-black. Cuenot adds, therefore, a new 

 character to the formula representing the uniform color, U, 

 viz. its antagonist the spotted color, S. 



From the point of view of heredity the spotted condition is 

 peculiarly interesting, since it appears to be continually vary- 

 ing, and by suitable selection this spotted character may be 

 carried through a regular progression until the dark color may 

 almost disappear. The depigmentation begins at the tail, 

 toes, and ventral surface of the body ; more rarely there is a 

 small spot on the top of the head. This is the condition found 

 not infrequently in the wild gray mouse. Through selection 

 the caudal and ventral white areas enlarge and the latter in- 

 vades the flanks, right and left, finally meeting dorsally, pro- 

 ducing a white girdle. The white invades the muzzle, then 

 the head, where it may unite below with the ventral spot. Fi- 

 nally there remain two pigmented regions, both dorsal, one 

 anterior and one posterior. The eyes always remain black. 

 Cuenot is not sure that the development of the white may be 

 carried so far that the black totally disappears from the hair, 

 his experiments on these points not being sufficiently complete. 



Cuenot studied the problems connected with the heredity of 

 the spotted condition by making the following combinations : — 



1. Cross between spotted and uniform coat. 



2. Cross between a form much spotted (with white) and a 



form bearing the least possible amount. 



3. Cross between two forms much spotted. 

 These experiments may now be considered in turn. 



I. Cross between Spotted and Unijorm Coat. — The couple 

 uniform, U, and spotted-pigmented, 5, follow rigorously the 

 Mendehan rule of dominance with disjunction of the gametes. 

 The spotted character is dominated in the first generation by 

 uniform color. If a much- spotted mouse is crossed by one 

 uniformly colored, the offspring that result show the dominant 

 color without trace of spots. This result is all the more para- 

 doxical, because if we cross a much- spotted mouse with an 



