EXTERNAL anatomy. 
19 
passes into one that is insessorial. The parrots and the 
woodpeckers unquestionably follow each other; the one 
being typical, the other subtypical, of the scansorial tribe. 
W e should much have wished, in this place, to have 
shown how beautifully the primary orders of birds re- 
present the primary orders of insects ; but as our theory 
on the annulose animals has not yet been laid before 
the scientific world, and would require to be accompa- 
nied with ample details, in support of the novel views 
it contains, we must reserve this comparison for a sub- 
sequent volume. 
CHAP. II. 
ON THE EXTERNAL ANATOMY OF BIRDS IN REFERENCE TO THEIR 
HABITS AND ECONOMY. ON THE PARTS OP A BIRD. 
CRESTS, EYES, EARS, TONGUE, MOUTH, BILL. 
(23.) Before we enter into further details on Sys 
tematic Ornithology, let us for a while contemplate the 
different modifications of form which belong to birds 
in general ; and trace how far these variations effect corl 
responding ones in their food, habits, and economy. It 
might be thought, at first, that this inquiry should have 
preceded the exposition of the primary orders contained 
in the last chapter ; but, as we shall frequently have 
o mention the names of those types and divisions which 
nave been just explained, it is clear that our present 
disquisition would have lost half its interest, had not the 
eader been first put in possession of the meaning of 
ose terms which it is absolutely necessary for us here 
o use. The student will therefore do well to peruse 
chapter with attention, before he enters upon 
(24.) Comparative anatomy regards two distinct por- 
10ns of the structure of an animal, — its inward and its 
c 2 
