Xo. 571] 



PATTERN DEVELOPMENT 



,",89 



mice (Microtis). Melanism commonly results through 

 an excess of black pigment which may mask a second 

 pigment. Thus the black hairs of the black variety of 

 fancy mouse commonly contain a considerable amount of 

 chocolate pigment as well, and so of the hairs of the 

 black-appearing skunk. A black mouse thus does not 

 contain the yellow pigment, while the chocolate pigment 

 is largely masked in general view by the black. In other 

 cases it may be that black pigment alone is present. 



It is probable that many cases of dichromatism among 

 animals are explicable as similar cases in which one or 

 other of the pigments normally present becomes to a 

 greater or less degree inactive. Thus red forms of certain 

 blackish or dull-colored bats (e. g., the small Molossus of 

 Cuba) are apparently the result of the dropping out of 

 the factor for black pigment or its great reduction. The 

 red and gray phases of the screech owl (Otus asio) are 

 probably also explicable as a similar phenomenon. 



