104 THE BIOLOGY OF BIRDS 



rigid, and a more or less firm thick skin is formed in the 

 interior of the stomach." 



It must be understood, as Semper insists, that the two 

 types of stomach are connected by inter-grades as well as 

 by modifications, and that many carnivorous birds have as 

 much gizzard as a pigeon or a hen. In the Little Grebe, the 

 Crow, the Lapwing, and the Kingfisher there is a strong 

 muscular wall and an internal, hard, brown pseudo-cuticle. 

 In the recently fledged kestrel and in some other cases there 

 is a transitory pseudo-cuticle. 



The gizzard is a legacy from reptiles, for it is well 

 developed in the crocodile. The typical features are : 

 {a) the huge development of musculature on two opposite 

 walls, numerous fibres radiating outwards from a central 

 tendinous disc ; {b) the bending of the sac upon itself so 

 that the exit into the duodenum is not far from the 

 entrance from the proventriculus ; (c) the internal lining of 

 pseudo-cuticula, really a secretion ; and (d) the presence of 

 pebbles which serve as grindstones. The contraction of 

 the muscles of the two opposite walls brings these walls 

 nearer one another, lessening the lumen of the gizzard, and 

 the stones grind the food. In the course of time they get 

 their corners rubbed off and slip down the duodenum. If 

 they are not replaced by others, the bird goes out of health. 



There are some remarkable peculiarities in gizzards. 

 Some fruit-pigeons that eat nutmegs and the like have 

 several score of hard conical projections on the pseudo- 

 cuticle. The snake-bird, Anhinga, has a sieve of hairs at 

 the duodenal end of the gizzard, which keeps fish-bones 

 and the like from going through too quickly. 



Mr. Beebe (1907, p. 140) tells how the lining of the 

 gizzard in the male hornbill is ejected, forming a bag round 

 the fruit which he has swallowed. " I'his, the male bird, 

 in his native land, doubtless takes in his beak to the tiny 

 opening of the walled-up nest and delivers into the bill of 

 his mate. How admirable a spouse this, who not only 

 seeks and provides sufficient food for his temporarily help- 

 less family, but bears it to them wrapped up in a packet 



