8488 Birds. 



prolonged os hyoides has entirely disappeared, and the tongue has 

 consequently lost its peculiar extensile power; yet in both cases the 

 characters of the sternum, the feet and the plumage show that the birds 

 are true woodpeckers, and the food and general habits remain unal- 

 tered. In like manner the bill may undergo immense changes from 

 the smallest size in some goatsuckers to the enormous horny mandibles 

 of Podargus, without at all invalidating the affinities of those birds for 

 each other ; or the long feathery tongue of the toucan may differ 

 from that of any other bird, and yet not overcome the force of the 

 anatomical and other evidence which shows that the barbets and the 

 cuckoos are their undoubted allies. 



The skeleton, therefore, and especially the sternum, offers us an 

 almost infallible guide in doubtful cases, as indicating deeper seated 

 affinities than those shown by organs which are continually modified 

 in accordance with varying conditions of existence. Another guide 

 of this kind is furnished by the e^g. This has a characteristic form 

 and colour, and a peculiar texture of surface which runs unchanged 

 through whole genera and families which are really related to each 

 other, however much they may differ in outward form and habits. 

 When, therefore, these two kinds of evidence coincide in indicating 

 an affinity, which is in other respects doubtful, they may be considered 

 as almost infallible. Now 7 , in the case of the humming birds, w r e have 

 this evidence. Their sternum and eggs resemble those of swifts much 

 more than they do those of any other birds. Nor is this by any means 

 their only likeness, for in many important points of general structure 

 the two closely agree. If any one will take a swift of the genus Col- 

 localia (the constructor of the edible nest) and also one of the eastern 

 tree swifts {Dendrochelidon cornatus), he must be struck by the 

 resemblance of these to the larger hummers in everything but the bill. 

 The small size, the immense pectoral muscles, the short and powerful 

 wing-bones and the enormously developed quills, are points of coinci- 

 dence of great importance. The Dendrochelidon also makes an 

 approach to the brilliant metallic tints of the hummers, and its long 

 white whisker-plumes, erectile crest and immensely forked tail, remind 

 us of some of the eccentricities of that wonderful group of birds. 

 Here, too, we have the first quill-feather longer than all the others, a 

 peculiarity found in no other family of Passeres but the Trochilidae and 

 the Cypselidse, which further agree in having each but ten feathers in 

 the tail. The feet also strikingly resemble each other, in both being 

 small, with very short tarsi, short and powerful toes, with short greatly 

 curved claws, a dilated sole, the hind toe and claw always shorter than 



