130 The Bird 
When we sought the extreme in the provision of saliva 
in birds, we had to refer to a swift, living in caves in 
islands of the Malay Archipelago, but to find the highest 
degree of development of crops is a much easier matter. 
In the ordinary pigeon the crop is of very great size 
and divided into two lobes. The capacity of the crop 
in some birds of this class is astonishing. AS Many as 
sixty-three acorns have been found in the crop of the 
English Wood-pigeon. If we look at the crop of a pigeon 
before its young leave the nest, we will discover a func- 
tion of this organ which would otherwise never be sus- 
pected. We know that herons and some other birds 
feed their young on fish half-digested by themselves. 
This process is known as regurgitation. If we have ever 
seen a pigeon with the beak of its young half down its 
throat, pumping something into the offspring’s mouth, 
we have probably thought that a similar habit was being 
shown,—half-digested grain taking the place of the 
heron’s fish. But such is not the case. At the time 
of the breeding season, the folds of membrane in the 
crops of both parent pigeons thicken and secrete or 
peel off in curdy cheesy masses—“pigeon’s milk” some 
call it—and this forms the food of the young birds So 
in pigeons the crop not only receives food, but at times 
provides it. 
Now for a glance at some of the oddities in the struc- 
ture of crops. The Hoatzin—a strange bird of Brazilian 
swamps—which harks back to its reptilian ancestors in 
many ways, has a very curious crop. There are strong 
muscles in its walls, the use of which, it is said, is to 
