Xvl THE STORY OF THE BIRDS. 
before flying, perhaps crawled. Had birds more than one origin 
among the reptiles? 
For Study.—Examine the skeleton of the wing of table fowl 
in connection with figure on page 138. Notice the separation and 
superposition of the breast muscles of a cooked bird. Dissect an 
English sparrow for further study. 
CuapreR IV.—Plumage was acquired by birds for warmth, 
not lightness; quickly modified for flight. Skin pores suppressed 
to preserve heat also. Hollow bones and various air spaces used 
as reservoirs of air on account of scant lungs, 
For Study.—Note heavy downs on a duck’s body, and the 
hook vanes on its flight quills. Observe the hollow, marrowless 
bones of table fowls. Cut windpipe of dead bird, insert tube and 
blow, noting inflation of body. 
CuaprerR V.—Plumage grows in symmetrical tracts with bare 
spaces between. Diagnostic value of this arrangement. Did 
plumage originate in patches? The pattern much subject to 
environment and habit and much modified since the beginning. 
For Study.—Examine picked poultry in market and note the 
clustering of the papille. Look at any nestling of song bird 
(canary or sparrow) and, if possible, a woodpecker or chimney 
swift. 
CuaprerR VI.—Downs are of two kinds—nestling and adult. 
The first grow in the pockets (papill@) of the latter and of the 
large feathers, and are pushed out. Downs may be degenerate 
feathers; often ornamental; sometimes powdery in_ tracts. 
Downs not usually present in bare tracts except in aquatic birds. 
Aftershafts formerly prevailed more gencrally. Joas had strictly 
double-stemmed feathers. Downs developed as needed. All 
nestlings of early birds hatched downy. Naked nestling a later 
development (see Chapter XX). 
For Study.—Note difference in downs and their arrangement 
in ducks and chickens, and the nakedness of any little bird’s 
nestling. See the aftershaft on some of the body feathers of 
common hen. Examine some down under a magnifier. 
CuaprerR VII.—The plumage is a product of the skin purely 
originating beneath the epidermis. Scales were changed to 
feathers. Barrel of feathers evidently once flat. The necessities 
of flight doubtless made them tubular and caused the vanes to 
