and Classification of Birds. 315 



from one extremity of the series, and the Cantrices, mihi, from 

 the other. It was necessary to treat, in part, of the latter im- 

 portant and vastly comprehensive group, that the exception- 

 less constancy of its numerous distinctive characters might 

 be duly appreciated, and its consequent thorough separate- 

 ness acknowledged, on the occasion of any reference or allu- 

 sion being made to it, the more especially as so many imagina- 

 ry, but un-real, or what may be termed skin-deep affinities 

 have been indicated, as connecting some of its components 

 with genera at most according, superficially, in external aspect. 



To promote this effectually, it became further requisite to 

 enter somewhat diffusely into details, relative to some of the 

 more prominent internal differential characters, the valuable 

 aid of which has rarely been sought by ornithological system- 

 atists : and the generalizations to which these investigations 

 have given rise, (all suggested by myself, from data chiefly 

 the accumulated result of my own observations, whether or 

 not others may chance to have preceded me in deducing them), 

 will tend, I hope, to shew the necessity of studying all parts 

 of an animal's structure, in order to arrive, conclusively and 

 securely, at its systematical relations. 



It devolves on me, now, to descant on the insessorial ge- 

 nera excluded from the two well-defined orders which have 

 been mentioned. They form a succession of distinct groups, 

 more or less extensive, and of various degrees of value and of 

 mutual affinity, but which do not admit of being collected in- 

 to a few separate orders, though nought can perhaps be stat- 

 ed in common of the entire series. I shall therefore bestow 

 on them, provisionally at least, the appellation Heterogenes : 

 and commence by succinctly placing them before the reader, 

 as nearly according to the order of their mutual relations as 

 I am able, reserving, for the present, a more detailed exposi- 

 tion of their characters. The elucidation of this series of 

 forms is, indeed, the more immediate object of the present 

 essay. 



I may be pardoned for repeating here, that the intestine, in 

 all these birds, is either quite devoid of coeca, or else, these 

 appendages being present, are of considerable size, pedicil- 

 late, and dilated towards the extremity, as in the owls : they 

 are absent in the majority; and present chiefly in those which 

 pass most of their time in a state of quietude. Save in the 

 parrots, there exists no craw or enlargement of the oesopha- 

 gus ; but the stomach is generally capacious, extending into 

 the abdominal portion of the cavity of the body. The par- 

 rots only, also, have more than the ordinary stemo-tracheal 

 muscles connected with the inferior larynx. 



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