SYSTEM OF INSECTS. 405 
the trifling difficulty occasioned sometimes by the disco- 
very of a new group, be set against the advantage of hav- 
ing only 2000 names to commit to memory instead of 
10,000 a ? But if, after all, it is judged best to name sub- 
genera, M. Savigny's excellent plan of distinguishing 
them by a plural termination would diminish the weight 
of the above objection, and might be used with advan- 
tage. 
When the component parts of any minor group differ 
from another, — for the most part in important charac- 
ters, indicating some tangible difference in their habits 
and economy, and confirmed by peculiarities in their 
larva? ; and these differences run through the whole, ex- 
cept that as usual they grow weaker as it is passing off 
to another; especially where they are striking in the 
centre or type of the group, — this is always a legitimate 
genus : but where the characters assumed are very slight, 
and nothing peculiar in its habits, economy or larva, 
warrant such distinction, it ought not to be conferred. 
vii. I must next say a word concerning species and 
varieties. A species is a natural object whose differences 
from those most nearly related to it had their origin 
when it came from the hands of its Creator; while 
those that characterize a variety, have been produced 
since that event. As we do not know the value and 
weight of the momenta by which climate, food, and other 
supposed fortuitous circumstances operate upon animal 
forms, we cannot point out any certain diagnostic by 
which in all cases a species may be distinguished from 
* See Bichcno in Linn. Trans, xv. 491. 
