172 ANATOMY OF VERTEBRATES. 



into a spiral valve, analogous to that which exists in the long 

 coecum of the Hare and Rabbit. 



In the Gr alia tores the two coeca are generally short where 

 present ; they attain their greatest developement in this order in 

 the Demoiselle, where the length of each coecnm is five inches ; 

 and they are also large in the Flamingo, where they each mea- 

 sure nearly four inches, and are dilated at their extremities, pre- 

 senting with the gizzard, crop, lamellated beak, and webbed feet, 

 the nearest approach to the Anatidce of the following order. 



In the Natatores, the coeca, where they are present, vary in 

 length according to the nature of the food, being very short in 

 the fish-eating Penguin, Pelican, Gull, &c., and long in the 

 Duck, Goose, and other vegetable-feeding LamelVirostres. In 

 the Crested Grebe {Podiceps cristatus), each coecum measures 

 3-16ths of an inch in length. In the Canada Goose the coeca 

 are each nine inches in length, and in the Whitefronted Goose 

 the same parts measure severally thirteen inches. They have 

 the same length in the Black Swan. In the Wild Swan the coeca 

 measure each ten inches in length, while in the tame species they 

 are each fifteen inches long. 



As digestion may be supposed to go on less actively in the 

 somnolent, night-flying Owls, than in the high- soaring Diurnal 

 Birds of Prey, an additional complexity of the alimentary canal 

 for the purpose of retaining the chyme somewhat longer in its 

 passage, might be expected ; and the enlarged coeca of the Noc- 

 turnal Raptores afford the requisite adjustment in this case. For, 

 althouo'h the nature of the food is the same in the Owl ^ as in the 

 Hawk, yet the differences of habit of life call for corresponding 

 differences in the mechanism for its assimilation. 



In the Rasorial Order, where the nature of the food differs so 

 widely from that of the Birds of Prey, the principal modification 

 of the digestive apparatus obtains in the more complex structure 

 of the crop, proventriculus, and above all the gizzard ; but with 

 respect to the coeca, as great differences obtain in their develope- 

 ment as in the Raptores. Now these differences are explicable 

 on the same principle as has just been applied towards the eluci- 

 dation of the differences in the size of the coeca in the Raptores, 

 Where the difference in the locomotive powers is so great in the 

 Dove-tribe and the common Fowl; where the circulating and 



' The indigestible parts of the prey of the Owl do not pass into the intestine, but 

 are regularly cast or regurgitated from the stomach; the length of the ceeca cannot, 

 therefore, be accounted for on Macartney's supposition of iheir being receivers of those 

 parts. 



