BIRDS 173 
which enable them to replace with great rapidity the large 
supplies of oxygen necessarily used up. The breathing 
organs are not confined to the lungs. The wind-pipe leads 
to a number of air-chambers, which supply air to all parts 
of the body. The bones, too, are hollow and communicate 
with the air-chambers ; so that the air drawn into the wind- 
pipe, quickly finds its way to any part of the animal— 
hence the exceeding warmth of a bird’s blood. This 
arrangement of air-chambers and hollow bones by making 
the body more buoyant is of great service in flight. 
Habits. The Common Fowl is a ground bird, seldom 
flying unless hard pressed—it is, moreover a social bird, 
preferring to live with a number of its own kind. It 
spends most of its time in scratching up the ground in 
search of food, which consists of worms, insects, seed, and 
grain. Its feet are specially adapted for scratching, a 
statement which all whose gardens have been invaded by 
fowl will readily admit. ‘The food is picked up by means of 
its horny bill and passed into a large bag at the bottom of the 
gullet calledthe crop. Here it is softened for some time 
before passing into the stomach, where it is further ground 
up in that portion of the stomach called the gizzard. This 
is a body with thick walls, and a hard tough lining and 
contains small pieces of grit which are swallowed, in order 
to assist in the grinding process. At night the bird 
roosts on a perch, which is firmly grasped by the toes. If 
not trained to go to the nest prepared for her, the hen lays 
in a nest of her own making in some sheltered spot. The 
loud cackling cry she utters after laying is familiar to 
any poultry keeper. When the eggs are laid, she sits on 
them for twenty-one days. At the end of this time the 
chickens appear fully fledged and able to fend for them- 
selves. 
