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. ', 



Vulturidae. Notch of the Conirostres. 



bill obsolete. 

 Falconidse. Notch very Dentirostres. 



conspicuous. 

 Strigidae ? Head very large, Fissirostres. 



flight rapid. 



Bill long, soft. Tenuirostres. 



Didiadse. 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 



* As in Linn. Trans, vol. xvl p."4& 



