322 
GEOGRAPHICAL ZOOLOGY. 
[part IV. 
generic groups being confined to limited districts ; while single 
mountains, valleys, or small islands, often possess species found 
nowhere else. It is now well ascertained that the Trochilidse 
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 Distribution of the Picarice. 
The very heterogeneous mass of birds forming the Order 
Picariee, 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 — Picidae and 
Trochilidae. Two others — Cuculidee and Alcedinidae — 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 — Alcedinidae — is absolutely cosmopolitan, 
but three others are nearly so- Caprimulgidae and Cypselidee 
being only absent from New Zealand, and Cuculidae 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 — Trochilidm —being common to the 
Neotropical and Nearctic regions. 
The Picariee are highly characteristic of tropical faunas, for 
