SPECIFIC CHAllACTEBS OF BIRDS. 519 
upon the subject, has endeavoured to divest himself of all 
prepossession. It is only further to be premised, that the 
Specific characters alone, not the generic, or ordinal, or clas- 
sic ones, are those which it is intended to elucidate. 
1. The characterisation of specific forms is the principal 
object of systematic arrangement. 
^. In a natural-history point of view, the characters are 
to be taken, in zoology, from obvious, consequently from 
external parts. 
3. They must be taken from permanent and essential 
organs, or circumstances. 
4. From whatever circumstances the characters of the 
more general or comprehensive divisions of a system or ar- 
rangement, as being in some measure arbitrary, maybe 
taken ; those by which specific forms are to be designated, 
must be from circumstances positive, certain, fixed, deter- 
minate, not liable to lead to misinterpretation or ambi- 
guity. 
5. Specific characters, in a logical point of view, should 
be concise, positively expressed (the negative form giving 
rise to misapprehension, and' n6t presenting an image of 
the object), direct, and perspicuous; essentially or intrin- 
sically, they should be perfectly distinctive, whether in their 
simple and individual capacity, or by comparison with 
others. 
This much being admitted, — and the exclusion of nega- 
tive characters, which is a point that may be allowed or 
not, is perhaps the only objectionable part, — I proceed, as 
proposed, to mention a few of the more generally adopted 
modes of characterising the Species of birds. 
The first and most generally, in fact universally, used 
character, is that derived from Colour, chiefly from the 
colour of tlie plumage. To characterise the different vspe- 
