‘ie ae Dwicut, Moult of Quails and Grouse. 35 
-As some feathers, chiefly in young birds, may survive several 
periods of moult without being renewed, it follows that a recog- 
nized stage of plumage may consist of feathers developed at no 
less than two or three separate periods, and besides this the 
plumage will be modified by the wear and tear to which it has 
been exposed. ‘That there is a definite sequence of plumages 
and of moults is a fundamental fact of the greatest importance 
and goes far to explain problems of plumage which may be 
found either among the Grouse or among distantly related birds. 
The exact method of moulting in the Tetraonide has been 
understood none too well, and there are some details the signifi- 
cance of which has been quite overlooked. There are nearly 
forty species and subspecies of these birds distributed among 
ten genera accredited to North America, and although there is 
great diversity in relative size and in the patterns and colors of 
their plumage, they differ little in their moults, which conform 
quite closely to those of other birds. In an article now in press 
(Annals N. Y. Acad. Sci., XIII, 1900, pp. 1-—, pll. i-vu.), I 
have shown in considerable detail how the moult of Passerine 
species is effected, new feathers first appearing at definite central 
points in the different feather tracts or pteryle. The growth of 
new feathers spreads so that outer rows and extremities of 
tracts are normally last to be renewed. This systematic replace- 
ment, which proceeds so gradually that birds are usually not 
deprived of power of flight nor of protective feathering, is also 
apparent in the Grouse and Quails, due allowance being made 
for differences of pterylosis. These differences have been so 
exhaustively treated in a recent paper by Mr. Hubert M. Clark 
(Proc. U. S. Nat. Mus., XXI, 1898, pp. 641-653, pll. xlvii—xlix) 
that I need say nothing more upon the subject except later on 
to designate briefly the points at which new growth begins and 
the areas over which it spreads at different periods of moult. 
In my earlier study of Passerine species, extending over a 
number of years, I reached conclusions that have enabled me to 
formulate some fundamental principles governing plumage and 
moult which my later study of the Tetraonidz and other groups 
bears out in every particular. As the application of these prin- 
ciples will explain every plumage and every moult, I present 
them here before going farther. They are as follows : — 
