AIDS AFFORDED BY ANATOMY. 171 
born of the same race, and of the same country. 
If we look to the animal world, the same results are 
apparent, more especially in all the leading systems 
on the vertebrated classes. In ornithology, par- 
ticularly, there is not a single division which has 
been mainly founded upon internal structure: so 
that, in this class, even the Régne Animal follows 
precisely the plan of the Systema Nature. Hence 
we may conclude that external characters are almost 
always preferable to those founded solely upon in- 
ternal structure; and that this conclusion is tacitly 
admitted by those who, in theory, maintain a contrary 
opinion. 
(114.) Nevertheless, it would be absurd to sup- 
pose that the internal construction of an animal is 
not deserving of great attention. This study, in 
fact, constitutes, of itself, a distinct branch of phy- 
sical science ; useful, indeed, to the zoologist, as the 
means of assisting and guiding his studies, but by 
no means so essential as is generally supposed. 
Wherever external peculiarities are sufficient to 
supply us with clear definitions, we require no other. 
It must nevertheless be remembered, that when we 
descend to the lower groups of animal life, where 
the forms become proportionally simple, we must 
then have frequent recourse to dissection; not so 
much, indeed, for the purpose of characterising such 
forms, as for that of ascertaining to which of the 
grand divisions of the animal kingdom they truly 
belong. We allude more particularly to those soft 
molluscous-like animals, confusedly put into the 
Linnean class of Worms. These stand so low in the 
scale of creation, that many of them have the aspect 
