INTRODUCTION. 
hii 
the form and combination of the little being ; on the fourteenth, the 
animal opens its mouth to breathe, if the shell and surrounding membrane 
be broken. The incubatory heat dilutes the white which is supposed to 
be pressed into the vessels of the chicken through the yolk, by the action 
of the air enclosed between the membrane and the albumen. In the same 
manner the yolk grows more fluid, changes to a greenish hue, and is 
absorbed by the chick, and serves for its food. It continues to increase in 
size and strength, until the time arrives when it bursts from its imprison- 
ment. This is sooner or later, according to the species to which it belongs. 
At each end of the egg is placed a small bag, containing air, which is^ 
encircled by the thin membrane that lines the shell, and this air expands 
with the heat of the parent, and affords a supply to the incipient and evi- 
dently breathing animal.*® The most capacious of the air bags lies at the 
** This is a short account of the progressive growtli of a chichen, which, as soon as it 
escapes from the shell, commences a life of activity. Those birds, wtiich remain in inactive/ 
imbecility for many days, wear a very different appearance in their reciprocal periods of ittCti- 
bation. At the time when the young of the Sparrow, of the Hawk, and numerous other kinds, 
burst from their confinement, they exhibit the picture of helpless beings. They are totally inca- 
pable of the least active exertion ; their frames are without vigour, their legs without strength, 
and their eyes without sight. Indeed, most birds are born blind. As soon as the young one 
quits the shell, a small black line may be observed across the eyelids ; the eyes are closed, but 
they, as well as the abdomen, appear of disproportionate and monstrous size. If the lids be 
forced open, the pupil and iris of the eye are obscured by a film, and overspread by a light 
mucous substance. At the end of three days, in many of the species, the little animal seems to 
peep through the lids, but it is still incapable of distinct vision. At the end of five days it 
begins to notice objects, and its power of sight is greatly increased in strength. At the time of 
their emancipation from the shell, the young of the Sparrow kinds are slightly clad in a long 
down, which is soon removed by the incipient feathers ; this down is of different colours in 
different birds 5 in the young of the green Grossbeak, it is of a pure, snowy white; in those of 
the Whinchat a rufous yellow ; in those of the Robin, and of the Hedge Sparrow, dusky ; and 
in those of the Water Hen, quite black ; in the young Hen Harrier of a faint blush colour; in 
the young Wood Pigeon, as well as in the young of the Hawk tribe, it resembles wool. Little 
black dots, scarcely discernible by the naked eye, mark the places of the quills ; a few similar 
spots are found round the rump, though some birds, such as the Goatsucker, and some others# 
xvhen they escape from their imprisonment, are nearly clad in feathers. 
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