OF FORM AND STRUCTURE. 167 
tion of a species. These considerations, again, may 
be classed under three divisions, viz. external organ- 
isation, internal anatomy, and chemical composition. 
The first of these belongs more especially to the 
zoologist, the second to the anatomist, and the third 
to the chemist: all are fit objects of enquiry; but as 
all are not equally essential to our present purpose, 
we shall confine our observations chiefly to the first. 
(109.) For the sake of simplification, the word 
form or structure may commonly be used as syno- 
nymous with external organisation. If a person, 
unacquainted with natural history, was put into an 
immense store-room, filled with all sorts of plants, 
animals, and minerals confusedly mixed together, 
and then desired to sort and separate them, he 
would, even were he a clown, begin to place the 
plants in one heap, the animals in another, and the 
minerals in a third. If, after this was done, he 
was again directed to make a more particular assort- 
ment of the animals only, he would assuredly sepa- 
rate the quadrupeds from the birds; and these, again, 
from the fishes and the serpents. No one will deny 
that this would be the natural process: and we may 
therefore infer, that external form is the chief and 
primary mode by which nature herself teaches us to 
know her productions: and that we need only de- 
scend to an examination of internal structure, when 
this resource fails, and we are obliged to enter upon 
minute and delicate investigations. But as many have 
laid an undue stress upon the importance of internal 
over external organisation, and thereby, as we con- 
ceive, embarrassed the path of the student with un- 
necessary difficulties, it may be as well to explain, 
M 4 
