470 Mr. N, A. Vigors on the JSJatural Affinities 



the Tenuirostres and Fissirostres, which for the most part confine 

 themselves to one species of food, whether animal or vegetable. 

 While the Scansores and Dentirostres, holding an intermediate 

 station between the extremes, are intermediate also in the extent 

 of their food ; fruit and berries being added to the animal food of 

 the rest in some families, and in those more particularly which 

 are contiguous to the omnivorous typical tribes. 

 / ■ The foregoing figure affords, moreover, an opportunity of ob- 

 serving some striking analogies between different groups in the 

 order. It has been remarked by the author of the " Ho7'cb Ento- 

 mologies," who was the first to exhibit the relations of nature in a 

 similar geometrical figure, and thus almost to reduce the science 

 of natural history to geometrical precision, that, in figures con- 

 structed as the above, representing a series of circles united 

 by affinities, the external groups of one circle always bear an 

 analogy to the corresponding groups of those which are conti- 

 guous*. This analogous connexion serves to point out the 

 causes of many important coincidences among the different 

 groups of the Tnsessores. It explains the reason why the Picidce 

 on the one hand, and the Trochilida and Cinnyrida on the other, 

 families otherwise totally differing in their food and habits, should 

 yet resemble each other in the common use to which they apply 

 the tongue. It explains why the Trochiliis, the Hirundo, and 

 the Caprimulgus should be assimilated in the feebleness and 

 almost uselessness of the bill ; that of the former being but a 

 sheath to defend the tongue, that of the latter but a secondary 

 fence to prevent the escape of the prey. It accounts for the cha- 

 racters of the genus Hirundo being so far transferred to the La- 



* See Horcc Entomologkee, p. 396, where the meaning of an external group is ex- 

 plained. In the foregoing diagram the Picidce, Cinnyrida:, Trochilida, Hiritndiriida, 

 CaprimulgidtB, Laniada, Merulidce, Sturnida, Corvida, and Psittacidte, are the exter- 

 nal families. They comprise, in fact, the typical groups of each tribe. 

 ... niada 



