434 A HISTORY OF BIRDS 



some noteworthy and puzzling variations. Usually the inner 

 surface of such a gizzard is faced with apposed horny pads, 

 between which the food is comminuted by being ground up 

 with small stones, the pads exercising an alternate up and down 

 motion. In the Nicobar Pigeon these horny pads have become 

 ossified, while in two closely allied Fruit Pigeons yet another 

 plan has been adopted. Thus, in the Fiji Fruit Pigeon {Carpo- 

 phaga latrans) the inner lining of this organ is beset with conical 

 horny bosses, or tubercles, set closely together, while in an 

 allied species, Phenorhina goliath, this modification is carried 

 still further by ossification of the tubercles. Apparently these 

 peculiar modifications have been brought about to enable these 

 birds to digest fruits encased by an unusually hard outer coat, 

 the Carpophaga living on the fruit of a species of onocarpus 

 which bears a curious " corky " fruit of the size of a walnut. 



In the Jambu Fruit Pigeons of the Genus Ptilopus, of which 

 there are several species, the interior of the gizzard is so 

 fashioned as to form four crushing pads, arranged so that, in a 

 cross section, the cavity of the gizzard is cruciform. So far 

 no facts concerning the food of these birds have come to light 

 which enable any explanation to be given of this unique 

 arrangement. 



The Darters again, close allies of the Cormorants, present 

 peculiar modifications of the gizzarc^ all the more remarkable 

 because they differ in no respect from the Cormorants in the 

 nature of their food — living fish. In the last-named birds the 

 gizzard is that of a normal fish-eating bird, thin-walled and 

 capacious. In the Darters this is quite otherwise, and what is 

 still more remarkable is the fact that the several species of 

 Darters differ among thenjselves in the complexity of the 

 modifications in question. Thus in the American Darter {Plotus 

 anhinga), the first portion of the stomach or proventriculus is 

 peculiar in that the digestive glands thereof are gathered to- 

 gether so as to enclose a chamber into which their secretions are 

 poured, while the hinder end of the stomach, that corresponding 

 to the gizzard in other birds, is doubled back upon the central 

 portion and lined with long hair-like structures resembling 

 cocoa-nut fibre, and about half an inch long. The function of 

 this hairy mat seems to be to prevent bones and other solid 

 particles from gaining admittance into the intestine. In an 



