8 ZOOLOGICAL GEOGRAPHY. [part hi. 



tirds which, though comprising nearly three-foiirths of the 

 entire class, yet presents hardly any well-marked differences 

 of structure by which it can be subdivided — the families confined 

 to America are, for the most part, more closely related to each 

 other than to the Old World gi'oups. The ten families forming 

 the group of " Formicaroid Passeres," in our arrangement (vol. 

 i, p. 94), are characterised by the absence of singing muscles in 

 the larynx, and also by an unusual development of the first primary 

 quill ; and seven of this series of families (wliich are considered 

 to be less perfectly developed than the great mass of Old World 

 passeres) are exclusively American, the three belonging to the 

 Eastern hemisphere being of small extent. Another group of 

 ten families — our " Tanagroid Passeres," are characterised by the 

 abortion or very rudimentary condition of the first quill ; and of 

 these, five are exclusively American, and have numerous genera 

 and species, while only two are non- American, and these are of 

 small extent. On the other hand the '•' Turdoid Passeres," con- 

 sisting of 23 families and comprising all the true " singing-birds," 

 is poorly represented in America ; no family being exclusively 

 Neotropical, and only three being at all fully represented in South 

 America, though they comprise the great mass of the Old World 

 passeres. These peculiarities, which group together whole series 

 of families of American birds, point to early separation and long 

 isolation, no less surely than the more remarkable structural 

 divergences presented by the Neotropical mammalia. 



In the Picarise, we have first, the toucans (Rhamphastidse) ; 

 an extraordinary and beautiful family, whose enormous gaily- 

 coloured bills and long feathered tongues, separate them widely 

 from aU other birds. The Galbulidse or jacamars, the motmots 

 (Momotidae), and the curious little todies (Todida?) of the 

 Antilles, are also isolated groups. But most remarkable of all 

 is the wonderful family of the humming-birds, which ranges 

 over all America from Tierra del Fuego to Sitka, and from the 

 level plains of the Amazon to above the snow-line on the Andes ; 

 which abounds both in genera, species, and individuals, and is 

 yet strictly confined to this continent alone ! How vast must 

 have been the time required to develop those beautiful and 



