22 
INSECTS IN GENERAL. 
whole sentence in English. It is also an important consideration that 
in learning the elements of any science or art, an indispensable part of 
such education is to acquire a knowledge of the more common techni- 
cal terms which properly belong to it, and which constitute its peculiar 
phraseology, and which the student will continually meet with in all 
writings upon the subject. In a work intended, like the present, for 
the common student, all unnecessary use of such , words should, of 
course, be avoided, and whenever we have found it necessary to use 
them, we have taken care, as a general rule, to explain their meaning, 
either directly or by the nature of the context. 
The student must not expect that any science can be so simplified as 
to remove all difficulties ; and especially true is this of so extensive and 
complex a science as entomology. Nor is it desirable that this should 
be done. One of the principal advantages to bo expected from the 
study of this science is the admirable mental discipline which it affords. 
The forms with which it has to deal are so numerous and diversified, 
and often, at the same time, so closely allied, that their classification 
constantly demands a minute and careful examination, and a discrimi- 
native analysis, which, regarded purely as an exercise of the mind, are 
scarcely inferior to those required by the abstract mathematics, whilst 
they possess the additional interest which naturally attaches to the 
study of living beings. 
CLASSIFICATION AND NOMENCLATURE. 
Classification in natural history has two objects in view — first, to 
show the relationship which exists between organized beings, by put- 
ting them in groups in accordance with the similarity of their charac- 
ters; and secondly, to facilitate the study of them by enabling the stu- 
dent to comprehend a great number of different but allied forms under 
a comparatively small number of general heads, and thus to afford an 
important aid to the memory. 
By nomenclature is meant the giving to these groups and the species 
which compose them distinctive names. This is necessary to enable us 
either to receive or to communicate knowledge ; and without it natural 
history could not be raised to the dignity of a science. 
In a department so extensive as that of insects a very great number 
of names, not only of species, but of the groups in which these are 
comprehended, must be necessarily introduced. It is therefore import- 
ant that the science shall not be encumbered by the creation of unneces- 
sary genera, or such as are founded upon slight and unimportant char- 
acters. It is, indeed, often difficult to determine precisely what charac- 
ters or combination of characters necessitate or justify the formation 
of a new genus, or the subdivision of an old one. No definition of the 
term genua which is universally applicable ever has been, or perhaps 
