152 
ON THE CLASSIFICATION OP BIRDS. 
perpendicular rocks or buildings with the greatest 
facility : others (^Chcctura Stev.), with less robust feet, 
are compensated for the deficiency by being furnished 
with a very stiff and pointed tail, which serves as an 
additional support, when resting in such situations. 
In the long-winged swifts of India {Macropteryai 
Swains.), all these characters are modified, and we see 
the swifts changed almost into the swallows. The two 
typical groups of the Ussirostres are thus united, and 
both may be characterised by a very short bill. The 
third group, as usual, contains three others, all exhibit- 
ing, more or less, a similar economy, but having the 
bill considerably more lengthened. 
(172.) The MeropidcF, or bee-eaters, succeed the 
swallows. This family is confined to the warm regions 
of the Old World: one species, however, the Mcrops 
apiastcr, or European bee-eater, has occasionally strayed 
to Britain. These birds annually visit Italy in flocks of I 
twenty or thirty, and may be seen skimming over the I 
vineyards and olive plantations with a flight much re- 
sembling the swallow, though more direct and less rapid : i 
their bill, however, is considerably longer and more j 
gracile j but this difference is softeneil down by the inter- | 
vention of the genus Enry^tomus, containing the swallow | 
rollers of India, Africa, and Australia, where this member 1 
is very short. To these succeed the true roOers (Con, das I 
Lin.), which arrive in Italy at the same time with the 1 
bee-eaters, and associate also in small fiocks. These two | 
genera of rollers are so indissolubly united, that nothing 1 
but the strongest prejudice in favour of a preconceived 
theory could ever have induced certain naturalists ! 
(whose labours, in other respects, have been of much ad- 
vantage to science) to have placed them in two different , 
orders. The whole structure of the roUers, their ' 
lengthened pointed wings, and their firm and often 
forked tail, at once induces the idea that they feed upon 
the wing ; while their very short legs, scarcely longer 
than their hind toe, might have shown their incapacity 
to alight and walk, like the crows, upon the ground : 
