A REVISION OF THE GENUS GENN^US. 663^ 



somewhat similar grey tone has been evolved with the assistance of 

 nmch broader bars and streaks of black and white. 



The above then shows roughly how in the triangle containing 

 Assam, the Northern Shan States and Tennasserim, certain species 

 and snb-species of Pheasants have answered to the demands of evolu- 

 tion. But in addition to these which are worthy of specific and 

 sub-specific rank there are a great number of specimens in Museums 

 which shew by certain well-known signs that they are but hybrids, 

 and many others which cannot with certainty be assigned to any 

 recognized form, for every area inhabited by a species or sub- 

 species, is surrounded by another area in which the governing factors 

 are themselves intermediate, and are not sufficiently strong to 

 determine to which species or sub-species the birds inhabiting it 

 shall belong. 



Where also the change in the characteristics of a country is very 

 abrupt, in consequence of which two very different forms of 

 Pheasant closely approach one another, at this point of contact there 

 will be found a comparatively large number of specimens which are 

 the result of hybridization pure and simple rather than of the 

 gradual formation of a new sub-species. 



In the Shan States man has proved a recent additional factor in 

 the differentiation of form. He has cultivated highlands which 

 were originally under forests, but has then deserted this cultivation 

 and left behind him wide extents of grass. In some cases he has 

 thus adapted the country to s^ich birds as seek the open, and in 

 others he has driven the forest-loving birds into valleys and pockets 

 so small that the surrounding forms are gradually, by constant 

 hjT^bridization, exterminating all signs of their origin. 



This I have little dou.bt is the main cause, together with the 

 fact that here three streams of extension meet, why we find such a 

 curious medley of forms in the North-Western Shan States. 



Finally, before leaving the consideration of the genus as a whole, 

 it is necessary to emphasize two facts, first, that individual variation 

 in both species and sub-species is very great, and, secondly, that alter- 

 ations in plumage occur at every moult until the birds are two or 

 three years old. In the male birds, these variations occur princi- 

 pally in the depth of the black and tone of its gloss, the width of 

 the black and white markings, and, to a lesser degree, in their 

 disposition and character. In females the diff'erences consist 

 principally in the general tone, varying from chestnut to dull grey 

 brown, and in the breadth and darkness of the markings on the 

 lower plumage ; the tails in this sex perhaps vary more than the rest 

 of the plumage and are sometimes almost a chestnut red, some- 

 times a dull brown, and sometimes well stippled or barred with 

 darker marks. To work oat the variations and assign to each a 

 cause or an age is not possible with the material at hand, but 



