26*2 Observations upon the Affinities 



of tail-feathers in this sub-class is a valuable, or rather per- 

 haps useful, diagnostic : for instance, in the Accipitres, and 

 in the other grand division which I have partly characterized, 

 their number is, without exception, twelve ; while, curiously 

 enough, in nearly all the genera which have been improperly 

 placed with the members of these divisions, it does not ex- 

 ceed ten. I refer to Podargus, which has been approximated 

 to the owls ; Caprimulgus, and Cgpselus, to the swallows ; 

 Upupa to the creepers or promerops group ; and the Troclii- 

 lidce to the Cinnyridoi : in all which instances this apparent- 

 ly unimportant diversity indicates distinctions of real conse- 

 quence, pervading the entire structure. It may be remarked 

 that throughout the Insessores the number of caudal feathers 

 never exceeds twelve ; which number is in no instance fallen 

 short of in the Gressores and Natatores, — save, however, in 

 two or three genera, as the grebes, which possess no tail what- 

 ever.* The Alectura accords with the grouse, and various 

 other GallinaceSy in possessing eighteen caudal feathers; 

 even this external character distinctly pointing out its appro- 

 priate systematic station.f 



But to return to the consideration of the cceca. Without 

 regarding individual deviations or monstrosities, as of suffici- 

 ent importance to mar extensive generalizations, the facts 

 that have been already stated relative to the absence or de- 

 gree of developement, of these appendages in the Insessores, 

 impart a value to the character which is thence derivable, 

 disproportionate to the influence that they exercise in the ani- 

 mal economy. It has been remarked, for instance, in refe- 

 rence to the large size of the cceca in the owl family, as com- 

 pared with the minuteness of them in the diurnal Accipitres, 

 that, — "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 alimen- 

 tary 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 

 adjustment in this case. For, although the nature of the food 

 is the same in the owls as in the hawks, yet the differences of 



* Yet the grebes have the uropygal glands considerably developed, which 

 subverts the notion that these have any necessary connexion with the tail, 

 as has been assumed from their absence, together with the part that should 

 contain them, in the Gallus ecaudatus of Temminck. 



f The poultry genera differ very remarkably in the number of tail-feathers. 

 Thus, the colins, (Ortyx) y have only twelve, the partridges fourteen, the ptar- 

 migan sixteen, and the true grouse eighteen, which I believe is the ultima- 

 tum arrived at. 



