$42 PRACTICAL AND SCIENTIFIC ZOOLOGY. 
sufficiently marked to render them recognisable. Whe- 
ther we term these parts of the great system of nature, 
circles, divisions, or groups, is immaterial, the three 
words, in fact, to prevent tautology, will be here consi- 
dered synonymous: the reader, however, must under- 
stand that they designate, each and all, an assemblage of 
objects, whose affinities, more or less, are circular. 
(422.) It is obvious that, in proportion to the pre- 
cision which we can attain in the determination of a 
group, so do we also give stability to all that belongs to 
it. So soon as a group, therefore, has been verified by 
the tests enumerated in the last chapter, it becomes, in 
the truest sense of the word, definite: it therefore follows, 
if we can ascertain what is the relative rank or value of 
such a group, in reference to other definite groups, we 
can then give a definite meaning to the name we bestow 
upon it. If, in short, groups are definite, the names 
indicative of their rank must be definite also, provided 
a uniformity in their nomenclature is preserved. Authors, 
indeed, are accustomed to distinguish their artificial 
groups by many of the same terms (as order, tribe, 
family, &c.) which we are about to explain ; but the 
student must remember that, unless otherwise stated 
these terms, which he will meet with in other systems, 
are merely conventional ; being founded, not upon any 
fixed plan of proceeding, but upon the mere opinion of 
the author. It is to Mr. Macleay and to his dis- 
ciples that our science is indebted for the introduction 
of this definite system of naming groups, the least ad- 
vantage of which is, that, when we now talk of a natural 
family, or a natural order*, we immediately know the 
determinate value of the group spoken of. We shall 
devote this chapter to the explanation and illustration of 
those groups whose rank or value have been ascertained ; 
and conclude with a few remarks upon species and 
their varieties. The different ranks of divisions or 
* T regret to observe, however, that very recently some of our entomolo- 
gists call their divisions by these names, without bringing forward any evi- 
dence or proof whatever that they are “ natural.’’ 
