and Classification of Birds. *26'3 



habit of life call for corresponding differences in the mechan- 

 ism for its assimilation."* But admitting to the full extent 

 the reasonableness of this view, and its accordancy with fact, 

 in the aggregate, it should still be remembered that the ra- 

 pidly-flying, active, snowy owl, which on the wing is scarce- 

 ly distinguishable from the jer falcon, possesses cceca fully as 

 much developed as the light-flapping barn owl; while, on the 

 other hand, the lazy, smooth-sailing buzzard, the floating 

 kite, or the buoyantly-skimming harrier, presents no farther 

 developement of these appendages than the darting hawks, 

 or the impetuous far-rushing falcons, f The diurnal and 

 nocturnal Accipitres differ importantly in the skeleton, as well 

 as in other portions of the structure of the alimentary pas- 

 sage ; exhibiting no trace whatever of a gradation or transi- 

 tion from one into the other, in these rudimentary characters, 

 however they may superficially appear to do so. They con- 

 stitute, in brief, two separate sub-types of the more general 

 type of the Accipitres : and the respective amount of deve- 

 lopement of the ceeca coli, is one of many invariable charac- 

 ters proper to each. It is, as it were, a necessary accompa- 

 niment, or one of the items of the subtypical conformation. 



Throughout the Insessores, I have found that the degree of 

 developement of the cceca is thus an adjunctive character of 

 some value in indicating natural groups ; but in the Gresso- 

 res and Natatores it is of less importance.^ Of course it would 

 be idle to demonstrate to any practical naturalist, that the 

 majority of characters are thus of variable consequence in dif- 

 ferent groups. 



To sum up, we have seen that the intestine, in the pre- 

 sent sub-class, is either entirely devoid of cceca, or that these 

 appendages, being present, are either of small size, or of 

 considerable dimensions, that is to say, of the magnitude no- 

 ticeable in the owls. They are either minute, or largely de- 

 veloped, in the Accipitres ; invariably present, and of small 

 size, in the extensive division which presents the anatomy of 

 the raven ; and either absent, or considerably developed, in 

 the remainder of the sub-class : at present I know of no (nor- 

 mal) exception to these generalizations. 



The structure of the vocal organs, also, as has been alrea- 



* Cyclop. Anat. and Phys. i. 324. 



f There are even some instances of an inverse developement of cceca to 

 that required hy the theory respecting the use of these appendages, which 

 has heen quoted. Thus the skuas, (Lestris), possess them of much larger 

 size than the gulls. 



X For instance, the smew possesses only one minute ccecum, while its con- 

 geners, the other species of Merganser, have two comparatively large cceca. 



