322 GEOGRAPHICAL ZOOLOGY. [part iv. 



generic groups being confined to limited districts ; wliile single 

 mountains, valleys, or small islands, often possess species found 

 nowhere else. It is now well ascertained that the TrochilidaB 

 are really insectivorous birds, although they also feed largely, but 

 probably never exclusively, on the nectar of flowers. Their 

 nearest allies are undoubtedly the Swifts ; but the wide gap 

 that now separates them from these, as well as the wonderful 

 variety of form and of development of plumage, that is found 

 among them, alike point to their origin, at a very remote period, 

 in the forests of the once insular Andes. There is perhaps no 

 more striking contrast of the like nature, to be found, than that 

 between the American kingfishers — confined to a few closely 

 allied forms of one Old World genus — and the American hum- 

 ming-birds with more than a hundred diversified generic forms 

 unlike everything else upon the globe ; and we can hardly 

 imagine any other cause for this difference, than a (compara- 

 tively) very recent introduction in the one case, and a very high 

 antiquity in the other. 



General Remarks on the Didribution of the Picarice. 



The very heterogeneous mass of birds forming the Order 

 Picariae, contains 25 families, 307 genera and 1,604 species. 

 This gives about 64 species to each family, while in the Passeres 

 the proportion is nearly double, or 111 species per family. 

 There are, in fact, only two very large families in the Order, 

 which happen to be the first and last in the series — Picid?e and 

 Trochilidfe. Two others — Cuculidce and Alcedinidse — are rather 

 large ; while the rest are all small, seven of them consisting 

 only of a single genus and from one to a dozen species. Only 

 one of the families — Alcedinida? — is absolutely cosmopolitan, 

 but three others are nearly so, Caprimnlgidte and Cypselidse 

 being only absent from New Zealand, and Cuculidte from the 

 Canadian sub-region of North America. Eleven families inhabit 

 the Old World only, while seven are confined to the New 

 World, only one of these — Trochilidse— being common to the 

 Neotropical and Nearctic regions. 



The Picariae are highly characteristic of tropical faunas, for 



