No. 571] 



PATTERN DEVEL OPMEN T 



387 



respect they are also primitive, though in most cases I 

 venture to think this may be true. The uniformity of 

 plumage is probably a derived condition in such a species 

 as the Cuban blackbird (HoloquisccUus assimilis) in which 

 the duller colored females have yet a yellow patch at the 

 bend of the wing, a style of marking widespread among 

 allied forms. The adult males, however, have lost this 

 and are wholly black. Gadow as well as Keeler (1893) 

 conclude that among related species in which there is a 

 tendency to differentiation of the coloring the end result 

 of the stages through which the species may pass is the 

 production of a wholly black bird. In general a wholly 

 black condition is no doubt to be considered as a derived 

 rather than a primitive state among birds whereas a uni- 

 formly dull plumage of a brownish or grayish tone is 

 probably in most cases primitive. Among mammals the 

 same is probably also true, for in both the black condi- 

 tion indicates either an excessive production of the black 

 over other associated pigments, or a loss of the power to 

 produce the latter, whereas the neutral gray or brownish 

 coloring is due to a more even mixture of such pigments. 



As pointed out by Professor W. E. Castle, the " ticked" 

 pattern of the hairs of mammals is probably primitive, 

 and it is certainly very widespread. It is well illustrated, 

 for example, by the house mouse (Mns musculus) or the 

 wild guinea-pig (Cavia), in which three separate pig- 

 ments occur as granules in the individual hairs — yellow, 

 chocolate, and black. These three in their normal mix- 

 ture produce a neutral gray tint— mouse color— and an 

 examination of this type of coat usually shows that some 

 hairs are wholly black, others dark at base barred with 

 black and yellowish near the tip. 



There are two ways in which patterns may be developed 

 from a uniformly tinted covering of hair or feathers : (1) 

 by a local change in the relation of the associated pig- 

 ments so that in certain areas only one or two sorts are 

 produced instead of three, or only one ; (2) by a failure to 



