440 A HISTORY OF BIRDS 



Osteologically the Hawks and Owls bear a most remarkable 

 likeness one to another, so much so that on this evidence alone 

 it is doubtful whether the two groups could be separated. That 

 is to say, they would be regarded simply as divergent branches 

 of a common stock. The evidence of the soft parts, however, 

 is conclusive. Without entering into minute details, it will be 

 sufficient here to mention one or two of the more important 

 characters on which the independence of the two stocks is 

 established. 



For example, Gadow has pointed out that the Ow\s{SM'^es) 

 cannot have been derived from the diurnal birds of prey {Acci- 

 pitres) since they have no ambiens muscle, although the structure 

 of the foot is practically the same as that of the Accipitres 

 which possess an ambiens. Another item in the case disproving 

 the common origin of the two types, according to the author 

 just quoted, is the fact that the Accipitres have only vestiges 

 of the cseca, or blind gut, while in the Owls the caeca are of 

 considerable size — being tubular in shape and dilated at their 

 extremities, as in the Night-jars {Caprimulgi). The existence 

 of these organs in the Owls, if derived from the Accipitres, is, 

 he contends, inexplicable, since though both being carnivorous, 

 we must suppose that the flesh diet in one case had preserved, 

 or even increased these organs, while in the other it had re- 

 duced them. But this argument loses its cogency when we 

 reflect that in the closely allied Swifts and Night-jars we have 

 a precisely parallel case. Both are insectivorous, yet the Swifts 

 have no caeca, while in the Night-jars they are largely developed. 

 Stranger still, among the Night-jars caeca are wanting in 

 the Genus Aigotheles, though the birds of this genus do not 

 differ in their diet from say Caprhmilgns, the British Night-jar, 

 where they are large and functional ! The character of the 

 convolutions of the intestine is of more importance in this 

 matter. In the Accipitres the gut is of great length, especially 

 in the case of the fish-eaters : and specialisation has taken place, 

 as Mitchell has shown, in other ways. In the Owls the gut 

 is comparatively short and primitive in the nature of its con- 

 volutions. These agree with those of the Caprimulgi^ whilst the 

 Accipitrine birds agree with the Storks in this matter. 



This marked difference in the convolution of the intestines 

 is a point of considerable interest. In the shortness of the gut 



