No. 572] PATTERN DEVELOPMENT 469 



a large patch 15 X 10 mm. wide. Evidently it has not 

 yet become precisely defined in its limits, though now a 

 permanent mark of the species. 



White marks in the forehead are common among the 

 species of the Mustelidae or weasel family. A narrow 

 white median line is present in the Javan mydaus and in 

 the skunks (Mephitis) as part of the permanent pattern. 



In the badger (Taicidea) a white line is not only pres- 

 ent on the forehead, but it is often extended medially so 

 as to separate the pigment patches of both sides of the 

 body. In the New York weasel (Mustela noveboracensis) 

 of the eastern United States a few white hairs are often 

 present on the forehead, and other instances could be 

 multiplied. xVmong monkeys, a white spot on the nose is 

 present in some species of Lasiopyga, and in an allied 

 genus Rhino stigma, it is elongated vertically to form a 

 white streak. 



A yet more illuminating case is that of the Muskeget 

 Beach mouse (Microtus brace ri) a derivative of the 

 common brown meadow mouse of the New England 

 mainland. On this island of white sand otf the Massa- 

 chusetts coast, a pale variety has developed which is very 

 distinct from that of the neighboring shores. Not only 

 is it a paler race, but albinism also has begun to appear, 

 so that occasional individuals have a white fleck between 

 the ears, showing the drawing apart of the ear patches. 

 Of a series of 62 specimens in the collections of the 

 Museum of Comparative Zoology and the Boston Society 

 of Natural History, no less than 13 had such white flecks, 

 and one had in addition a white spot just in advance of 

 the shoulders, marking the line of separation between 

 neck and shoulder patches. In our studies on the hered- 

 ity of coat colors in mice, Professor Castle and I dis- 

 covered (Allen, 1904; see also Little, 1914) that the pied 

 condition is recessive in the Mendelian sense towards 

 the self colored, so that partial albinos bred to wholly 

 pigmented mice produce in the second generation, if 

 interbred, 25 per cent, of spotted young. The figures 



