TRUE AND FALSE ANALOGIES. 239 
which they would occupy in our imperfect group. Let 
us illustrate this by an example. The perching, or 
insessorial, order of birds, collectively, is a perfect 
group, because its primary divisions are all known; but 
the rapacious order is imperfect, because one of its 
primary divisions is extinct, or, at least, undiscovered. 
We say one, and not two, as is generally thought, be- 
cause the Dodo was, in our opinion, the rasorial type of 
the raptorial order. By comparing these two series, 
we shall at once see which is the missing type in that 
of the Raptores. 
Imperfect circle. Analogical Perfect circle. 
RAPTORES. characters. INSESSORES. | 
Vulturide, Notch of the Conirostres. 
bill obsolete. 
Falconide. Notch very Dentirostres. 
conspicuous. 
Strigidz ? Head very large, _Fissirostres, 
flight rapid. 
Bill long, soft. Tenuirostres. 
Didiadez. Wings very short. _Rasores. 
(295.) The structure of the Dodo is essentially that 
of a large vulture ; but, as it should represent the gallina- 
ceous birds in some one respect, we consequently find it 
possessed of very short wings. This is one of the pecu- 
liarities of all rasorial types, and is never found in those 
of the tenuirostral structure: hence we are led, by 
analogy of reasoning, to conclude that the imperfection 
of the raptorial circle consists in the tenuirostral type 
being unknown. The Raptores, in fact, when we con- 
sider its rank, is the most imperfect, as a group, in the 
whole class of birds. It is, therefore, one of the best 
which could be cited, on the present occasion, to illustrate 
an imperfect circle. 
(296.) The theory of symbolical types involves, in its 
application, another principle, from inattention to, or ig~ 
norance of, which great mistakes have arisen*, and are 
still likely to arise. In tracing the analogy between two 
* Asin Linn. Trans, vol. xvii p. 46, 
