PATTERN DEVELOPMENT IN MAMMALS 

 AND BIRDS 



II 



GLOVER M. ALLEN 

 Boston Society op Natural History 



Partial Albinism in Wild Mammals 

 Partially albinistic individuals of species that normally 

 are wholly pigmented, occur frequently in a wild state, 

 and almost any large series of a given species may con- 

 tain a few. I have examined many such, in which it was 

 perfectly evident that the white mark was due to areal 

 restriction of some one or more of the primary pigment 

 areas just as described in the various domestic species. 

 It is apparent that the white markings in both are quite 

 comparable, but in species under doine-ticati.m no agency 

 seems present whereby such pied individuals are elimi- 

 nated, whereas in a wild state the sudden acquisition of a 

 large amount of white in an individual would not only 

 render him too different from his fellows, but might put 

 him at a disadvantage because of a conspicuousness to 

 which as a species he had not yet become accustomed. 



There are many other species in which, as we now see 

 them, white markings form a permanent and normal part 

 of the pattern. Among those in which these white mark- 

 ings are few or simple, it is often evident that they are 

 merely primary breaks between the pigment patches that 

 have become more or less fixed by long periods of selec- 

 tion, whether natural, sexual or otherwise. As I shall 

 endeavor to show, there are species in which a beginning 

 has already been made towards the development of a 

 pied pattern, though it has not yet become well fixed. 

 Still other species show a more complicated white and 

 pigmented pattern, the white portions of which can not 

 readily be derived from primary breaks alone. Such I 

 take to be highly developed patterns and make no attempt 



