138 The Bird 
That this is something more than an abnormal con- 
dition brought about by artificial means is proved by 
the fact that in the Orkney Islands the wild gulls feed 
in winter, spring, and summer on fish, and at this time 
are gizzardless; but in the fall they change to a diet of 
corn and develop a very respectable gizzard. So we 
see that this organ, apparently so independent in func- 
tion and individual in appearance in many birds, is in 
reality only a physiological change from the stomach 
proper. 
The history of the development of this organ may 
be traced in various living species, from the soft mem- 
branous sac of a fish-eating bird to the knot of tendons 
which forms the gizzard of certain Fruit-pigeons. These 
birds feed on nutmegs and other very hard, almost stony 
nuts, and to enable the bird to crush these, the lining of 
the gizzard is covered with several score of conical pro- 
jections, horny in consistence. These are probably the 
nearest approach to “hen’s teeth” we are likely to find. 
What a boon to a business man who indulges in a 
daily ‘“fireman’s lunch,” if his masticatory function 
could be an internal and unconscious one, as in a bird! 
A crocodile, which has so much in common with a 
bird, is provided with a gizzard, which, like that of a 
chicken, is round, muscular, and has two great side ten- 
dons, and no less than five pounds of grinding-stones 
have been found in one of these reptiles. 
Many interesting adaptations are found in the stom- 
achs of birds, made necessary by special requirements 
in the diet. As an instance of this, the snake-bird has 
