1 68 TODUS. 



ho will perceive that the entire genus Tod us is too 

 distinct and peculiar to be incorporated with either 

 llhipidura, Monacha, or Megalophug; while its re- 

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

 so very nearly equal, that we can only conclude its 

 station to be 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 liarmicus holds 

 precisely the same rank in the typical division, or 

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

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

 senting each other. We will therefore now see how 



