168 TODUS. 



ho will perceive that the entire genus Tod us is too 

 distinct and peculiar to be incorporated with either 

 Rkipidura, Monacha, or Megalophus; while its re- 

 lation to this latter, and to the genus Muscicapa, is 

 so very nearly equal, that w r e can only conclude its 

 station to he intermediate. This point being settled, 

 we are next to ascertain whether Todus, as a 

 whole, constitutes a natural group; or, in other 

 words, whether this group is circular and represen- 

 tative. This question, as will presently appear, can 

 also be answered in the affirmative. Hence it fol- 

 lows, that if its sub- genera differ more among them- 

 selves than do the species which we have been 

 illustrating, our inevitable conclusion is, that these 

 latter are variations of the sub-genus, and not of the 

 genus, that they are specific modifications, and not, 

 like Conopophaga, &c., types of sub-genera. We 

 shall arrive at a similar conclusion if we argue the 

 question in another way. We have stated, in ano- 

 ther place, as one of the primary laws of natural 

 classification, that the number of circular groups, in 

 point of rank, are NINE; and that those which 

 form the ninth are sub-genera. Let us then take 

 one of the examples that have been quoted in sup- 

 port of this theory, and see how far the group, 

 which we here term a sub-genus, will agree there- 

 with. We have stated that Parus Uarmicus holds 

 precisely the same rank in the typical division, or 

 sub-genus of Parus, as does Todus platy circus in 

 our sub-genus Todus; the two birds, in fact, repre- 

 senting each other. We will therefore now see how 



