336 ON THE OLASSIPIOATION OF BIBHS. 
in its analogies ; for this may be done by simply show- 
ing that no animal yet known that is excluded /rom the 
group has an affinity with the type equal to any of 
those that are brought within the group. Our doctrine 
of analogies may thus, to use a colloquial expression, be 
thrown overboard, and yet our group will remain just 
as natural as it was, if the chain of affinity has been 
truly and strictly followed. 
CHAP. n. 
GENEBAl HEMARKS ON THE ISSESSORIAL OR PERCHING OR- 
PER, rillMAKY DIVISIONS. — CHARAACTEKS AND ANALO- 
GIES OF THE DENTIBOSTRAL TRIBE. 
(271.) The order Insessobes, composed of the pebcii- 
iNG BIRDS, is the most numerous, and the most varied, in 
the whole circle of ornithology. It comprises, as before 
stated, all those tribes and families which (without being 
rapacious) live habitually among trees, or at least have 
nothing in their structure to show they are in the least 
degree aquatic. Their foot, in short, as the name 
denotes, is especially formed for grasping or perching ; 
a peculiarity evinced by the situation of the hinder toe, 
which is invariably placed upon the same level, or 
])lane, as those in front. Their number is generally 
four ; either placed, as in ordinary birds, three forwards 
and one backwards, or, as in the scansorial tribe, two in 
front and two behind. Tlie length of the tarsus or 
shank is always moderate, and generally very short 
in comparison to what is seen in the other orders ; and, 
as these birds never seize their prey by the claws, 
these weapons are never retractile. The perchers are 
thus distinguished from the birds of prey, properly so 
called ; while the situation of the hind toe separates them 
