TODUS. 169 



many circles are to be traversed before we arrive at 

 the two which contains the birds. 



Rink of the Rank of the 



PARUS BIAK.MICUS, L. TODUS PLATYCIRCUS, Sto. 



I. Kingdom, Animalia. 1. Kingdom, Animalia. 



'2. Sult-Idnydom, Vert^brata. 2. SuL-kingdom, Vertebrata. 



3. Class. Avis. 3. Class* Avis. 



4. Order, Insessores. 4. Order, Insessores. 



5. Tribe. Dentirostres. 5. Tribe, Dentirostres. 



C>. Family, Sylviada. 6. Family, Muscicapidae. 



7. Sub-family, Parianoe. 7. Sub-family, Muscicapinse. 



8. Genus, Parus. 8. Genus, Todus. 



9. Sub-genus, Parus proper. 9. Sub-genus, Todus proper. 



Type of form, Parns biannicus. Type of form, Todus platycircus. 



We thus perceive that the genus Todus is precisely 

 of the same rank as that of Parus, and that the 

 pre-eminent typical division, or sub-genus, of each, 

 contains subordinate types of variation or of form, 

 as well marked as those of all the higher divisions ; 

 so that a sub- genus, when perfect, becomes just as 

 much a circular group as any of the eight which 

 precedes it in *he lists There is not a whit greater 

 difference between Todus viridis and Todus platy* 

 circus, than there is between Parus biarmicus and 

 Parus cceruleus. And if Todus megacephalus de- 

 serves to be ranked as a sub-genoo, so must its 

 representative Parus caudatus ; for the eoe is a 

 prototype of the other both behig at cace distin- 

 guished by their great disproportionate heads. All 

 these arguments, indeed, may be admitted; and 



