34 Dwicnt, Moult of Quatls and Grouse. fon 
them Arizona is but a bridge to reach their breeding and winter 
grounds, hence they are met with here only as travelers to the 
north and south. Among the summer residents I cannot say 
there was any appreciable diminution, but it did noticeably change 
the nesting habits of several of the larger Thrashers. Hereto- 
fore they had chiefly made homes in the different forms of cacti, 
and when this was broken down and destroyed they occupied 
the next round on the vegetable ladder— mesquite and palo 
verde trees and bushes. 
THE MOULT OF THE NORTH AMERICAN Z7EZ- 
RAONID4 (QUAILS, PARTRIDGES 
AND GROUSE). 
BY JONATHAN DWIGHT, JR., M. D. 
L. Fundamental Principles of Moult and of Plumage. 
In spire of all that has been written regarding the plumages 
of the Grouse and their allies variously known as the Quails, 
Partridges, Pheasants and Ptarmigans, there still is room for fur- 
ther discussion of the relations that exist between their plumages 
and their moults, from which standpoint little has hitherto been 
attempted. From the comparative study of moult in other groups 
of birds, I am convinced that this is the proper point from which 
to view the subject in order to comprehend its full significance. 
The fact that the plumage of any bird at a given time is simply 
one of a series following each other during the bird’s natural life, 
is obvious when it is remembered that each new feather grows 
from the same papilla as the old one. Plumage, which is an 
assemblage of feathers, would be very simple to understand if all 
the papilla were equally active at a period of moult, but as a 
matter of fact, individual papilla, as well as whole groups of 
them, may remain dormant and thus produce the mixed plumages 
that have been so difficult to understand in many species of birds. 
