324 



AVES. 



that the cceca are deficient in the greater part 

 of the Diurnal Raptores, but we have observed 

 them in the Huliatus Albicilla, Aquila Chry- 

 saetos, Astur palumbarius, and Buteo nisus. 

 They seldom exceed the length above-men- 

 tioned (g,Jig. 156), and in the Secretary Vul- 

 ture they form mere tubercles. In the Barn 

 Owl the caeca severally measure nearly two 

 inches in length, and are dilated at their blind 

 extremities; they are proportionally developed 

 in the larger Strigida. 



In the Insessores they are invariably very 

 short where present. Among the Scansoriat 

 Genera which possess the cceca, these parts 

 are found to vary in length, measuring in the 

 Cuckoo and Wattle-bird (Glaucopis), each 

 half an inch ; while in the Scythrops, or New- 

 Holland Toucan, the cceca are each two inches 

 Ions:, and moderately wide. 



In the Rasores the cceca present considerable 

 varieties. In the Pigeons (g,fg- 163) they are 

 as short as in the Insessorial order, and are 

 sometimes wanting altogether, as in the Crown- 

 pigeon. In the Guan (Penelope cristata) each 

 coecum is about three inches in length; while in 

 the Grouse each ccecum measures a yard long, 

 being thus upwards of three times the length 

 of the entire body. The internal surface of 

 these extraordinary appendages to the alimen- 

 tary canal is further increased in the Grouse by 

 being disposed in eight longitudinal folds, 

 which extend from their blind extremities to 

 within five inches of their termination in the 

 rectum. We have always found the cceca in 

 this species filled with a homogeneous pulta- 

 ceous matter without any trace of the heather 

 buds, the remains of which are abundant in the 

 fcecal matter contained in the ordinary tract of 

 the intestines. 



In the Peacock the cceca measure ach 

 about one foot in length; in the Partridge 

 about four inches ; in the common Fowl and 

 other Phasianida the cceca are each about one- 

 third the length of the body ; they commence 

 by a narrow pedicle, which extends about half 

 their length, and then they begin to dilate into 

 reservoirs for the chyme (g,fg- 157). 



In the Cursores the cceca again present very 

 different degrees of development. In the 

 Emeu they are narrow and short. In the Cas- 

 sowary they are wholly deficient; while in the 

 Ostrich they are wide and upwards of two feet 

 in length, and their secreting and absorbing 

 parietes are further increased by being pro- 

 duced into a spiral valve, analogous to that 

 which exists in the long ccecum of the Hare 

 and Rabbit. 



In the Grallatores the two cceca are gene- 

 rally short where present; they attain their 

 greatest development in this order in the De- 

 moiselle, where the length of each ccecum is 

 five inches ; and they are also large in the Fla- 

 mingo, where they each measure nearly four 

 inches, and are dilated at their extremities, 

 presenting with the gizzard, crop, lamellated 

 beak, and webbed feet, the nearest approach 

 to the Anatida of the following order. 



In the Natatores the cceca, where they are 

 present, vary in length according to the nature 

 of the food, being very short in the fish-eating 



Penguin, Pelecan, Gull, &c. and long in the 

 Duck, Goo.se, and other vegetable feeding 

 Lamellirostres. 



In the crested Grebe (Podiceps cristatus), 

 Yarrell detected two cceca, each measuring 

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

 Goose the same indefatigable observer found 

 the cceca each nine inches in length, and in 

 the White-fronted Goose the same parts mea- 

 sured 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 naturally 

 be expected; and the enlarged cceca of the 

 Nocturnal Raptores afford the requisite adjust- 

 ment in this case. For, although the nature 

 of the food is the same in the Owl* as in the 

 Hawk, yet the differences of habit of life call 

 ibr 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 cceca, as great differences obtain in their 

 development as in the Raptores. Now these 

 differences are explicable on the same prin- 

 ciple as has just been applied towards the 

 elucidation 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 respiratory systems must be so 

 actively exercised to enable the Pigeon to take 

 its daily flights and in some species their an- 

 nual migrations a less complicated intestinal 

 canal may naturally be supposed with such 

 increased energy in the animal and vital func- 

 tions to do the business of digestion, than in 

 the more sluggish and terrestrial vegetable 

 feeders; and accordingly we find that the 

 requisite complexity of the intestinal canal is 

 obtained by an increased development of the 

 ccecal processes in them, while in the Colum- 

 bidfE the cceca remain as little developed as 

 in the Insessores, which they resemble in powers 

 of flight. If we regard the cceca as excretive 

 organs, their differences in the above orders may 

 be in like manner explained by their relations 

 to the locomotive and respiratory functions. 



In the Cursores the development of cceca 

 seems to have reference to the quantity of food, 

 and the ease with which it may be obtained, 

 according to the geographical position of the 

 species. In the Cassowary, which is a native 



* 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 creca cannot, therefore, be accounted for on 

 Macartney's supposition of their being receivers of 

 those parts. 



