XiV INTRODUCTION. 
lengthened enormously, and occasionally the feathers are 
highly decorated by various markings or brilliant color- 
ation. The flight is labored but rapid, and occasionally 
protracted. 
In their anatomy these birds have various peculiarities. 
The esophagus is dilated, forming the crop which re- 
ceives and moistens the food; while the gizzard, which 
is present in all save the Sage Cock, is very strong, with 
a thick, hard, interior wall. To assist this organ in grind- 
ing the food the birds are in the habit of swallowing 
small stones and other hard objects. The cceca are 
highly developed. 
The species of this order are accustomed to lay numer- 
ous eggs, to go in coveys of considerable numbers, com- 
posed at times of one or more families, and the young, 
which are at first covered with down, are able to run and 
feed as soon as hatched. The family TETRAONID&, which 
comprises the great majority of gallinaceous birds inhab- 
iting North America, contains those known as Quails, 
Partridges, and Grouse, and is represented in every por- 
tion of the world. The members differ greatly from 
each other in many particulars, and form three rather 
natural groups or subfamilies, one of which, the Per- 
dicine, or Old World Quails and Partridges, are not 
found upon the Western Hemisphere. American Par- 
tridges have certain peculiarities, more particularly 
described in the Appendix, which place them apart and 
distinguish them from their relatives across the sea, 
while certain species of Grouse have so wide a dis- 
tribution, retaining at the same time their specific 
characters, that they are found in high latitudes through- 
out the world. This can be said of but very few 
species of birds known to ornithologists at the present 
day. 
