TODUS. 169 
many circles are to be traversed before we arrive at 
the two which contains the birds. 
Rank of the 
Parus Biarmicus, L. 
1. Kingdom , Animalia. 
2. Sub-kingdom, Vertebrata. 
3. Class, Avis. 
4. Older, Insessores, 
5. Tribe , Dentirostres. 
6. Family , Sylviadae. 
7. Sub-family, Parianse. 
8. Genus, Paras. 
9. Sub-genus, Parus proper. 
Rank of the 
Tod us Platycircus, Sto. 
]. Kingdom, Animalia. 
2. Sub-kingdom , Vertebrata. 
3. Class, Avis. 
4. Order , Insessores. 
5. Tribe , Dentirostres. 
6. Family, Muscicapidse. 
7. Subfamily , Muscicapin®. 
8. Genus, Todus. 
9. Sub-genus , Todus proper. 
Type of form, Parus biarmicus. 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 the list. There is not a whit greater 
difference between Todus viridis and Todus platy- 
circus, than there is between Parus liarmicus and 
Parus cceruleus. And if Todus megacephalus de- 
serves to be ranked as a sub-genes, so must its 
representative Parus caudatus ; far the ene is a 
prototype of the other — both being at cnee distin- 
guished by their great disproportionate heads. All 
these arguments, indeed, may be admitted; and 
