166 NATURAL HISTORY. 
disposed to make the Pigeon tribe an order by them- 
selves. The Pigeons are very remarkable for their mode 
of feeding their young. The crop is double, forming two 
pouches, one on either side 
of the gullet, as represent- 
ed at a and 6 in Fig. 135. 
Now, while the bird is in- 
cubating, a curious change 
takes place in the crop, and 
for a special purpose. Ordi- 
narily it is thin and smooth, 
as seen at a; but when the 
bird is about to have young 
to care for, the crop be- 
comes thick and full of lit- 
tle lumps, as represented at 
6. These lumps are glands, 
that have now become en- 
larged, in order to perform 
their duty of pouring a 
milky fluid into the crop. The object of this is to soften 
the food, so that, when this is done, the bird may throw 
it up out of the crop and give it to its young. It is sin- 
gular that the same change takes place in the male bird ; 
and both parents, therefore, engage in feeding their off 
spring. The most conspicuous varieties of the domestic 
Pigeons are seen in Fig. 136 (p.167). That large Pig- 
eon, the Pouter, is able to inflate its crop with air so as 
almost to hide its head behind it, and it seems to be quite 
vain of this accomplishment. 
273. This family are found in almost every part of the 
globe, and in some they multiply to an enormous extent. 
The most remarkable in this respect is the Passenger 
Pigeon of this country. ‘The associated numbers of 
wild Pigeons,” says Nuttal, “are without any other par- 
allel in the feathered race; they can, indeed, alone be 
compared to the shoals of herrings, which, descending 
TA 
Fig. 185.—Pigeon’s Craw. 
