No. 572] 



PATTERN DEVELOPMENT 



471 



white or whitish tip to the tail, often for one half its 

 length. A similar white tip is occasionally seen in our red 

 squirrel (S. hudsonim) as an albinistic mark, and is due, 

 of course, to the terminal restriction of the rump patches. 

 The deer of Whitby Island, Puget Sound, are said to be 

 much marked with white, and sundry marsupials of 

 Papua as well as the monotreme Zaglossus are subject to 

 white markings. In the cuscus (PseudocMrus) the pig- 

 ment is sometimes restricted to small patches and round 

 spots scattered on the back, those in the region of the 

 shoulder of a different color from those of the side and 

 rump patches. Another instance is that of the white- 

 footed mouse of Monomoy Island, Massachusetts, the 

 mid-ventral parts of which are pure white to the roots of 

 the hairs, an albinistic condition to be clearly distin- 

 guished from that in which the belly appears white, but 

 only because of the white tips to the hairs whose bases 

 are dark-pigmented. 



The restriction of the rump patches so as to produce 

 a white tail-tip is common among mammals. It is found 

 in occasional specimens of many species as t lie shrew mole 

 (Warina), Brewer's mole (Pantscalops), the meadow 

 jumping mouse (Zapus), the white-footed mouse {Pero- 

 myscus), and squirrels (Sciurus). In some it has be- 

 come developed as a permanent and characteristic mark, 

 as in the woodland jumping mouse (Xapceozapus), the 

 red fox (Vulpes), such genera as Hifd mm T/domi/s, 

 the Virginia opossum (Didelphi/s ri rginiana), the tree 

 kangaroos (Dendrolagus). In many others a pure white 

 belly is developed through ventral restriction of the 

 shoulder and side patches. 



Among ungulates the break between the ear patches 

 has been developed to form a broad white blaze from 

 forehead to nose in case of the blesbok (Damaliscus 

 albifrons) of South Africa and in related species in 

 East Africa. The chevron-mark on the forehead of cer- 

 tain antelopes is possibly a specialized development of 

 the same thing. 



