ANALYSIS OF THE STORY OF THE BIRDS. xxiii 
styles defined. Swimming membranes are, perhaps, rather recent 
developments. They are transient (or seasonal) now in some am- 
phibians. They speak confidently of habits. The bird’s foot is 
based on the lizard’s. Prestige of the middle front (third) toe dis- 
cussed. Peculiarity of leg bones—the fusion and stiffening of 
parts for better running. Loss of rear toe and the various tendon 
arrangements mentioned. 
For Study.—Notice feet of ducks and chickens. Dissect out 
tendons and note their uses. Observe that the very tendons are 
bony in the turkey. What does this mean? Note in the ostrich 
(at the menagerie) that for speed afoot purely almost no toes are 
needed, and that bird’s toes now are preserved for clasping and 
swimming. 
CuaprerR XX VI.—The wing, after fluttering-up flight came, was 
variously modified. Hach new need made a new shape. Ground 
haunters have usually broad, short, round, concave wings. Pen- 
guins’ wings not long used as such, perhaps. Long wings mean 
long flight. Chest muscles (quality and quantity) are compensating 
factors, however. Instances in ducks and plovers. The soaring 
wing noted. Soaring largely a matter of skill. Flight by flap- 
ping largely a matter of propelling rather than lifting after the 
bird once starts. The number, shape, length, set of the wing 
quills. 
For Study.—Make a collection of, and label such wings as fall 
in your way without special slaughter, and note shape in connec- 
tion with the bird’s flight habits. Observe difference between 
those of duck and hen, hawk and plovers, sparrow and quails. 
Place no confidence in the collection on the hats of any feminine 
assembly. They are usually trimmed to suit the wsthetics of the 
milliner, 
Cuaprer XXVII.—Birds have a definite home region and love 
it, and, in the extreme north, are driven from it by stress of weather 
and scarcity of food. They return to it in the spring. View of 
glacial theory of migration and the probability that the tendency to 
conceal nests and get apart send southern birds north. Some mi- 
grate afoot partly. but flight is the great factor of the seasonal move- 
ments. Some migrations very direct, others straggling, many day 
birds moving at night high up. Migration may change social 
habits. Coast lines, rivers, mountains, act as guiding factors. 
