CLASSIFICATION. 
11 
the complexity of the increasing number of recorded species led to a 
system of grouping, say, the beetles under one title, the moths and butter¬ 
flies under another, and so on, the insects most obviously similar being 
put into one group chiefly as a matter of convenience. As the subject 
grew, the morphological characters of the collected insects were utilised 
to an increasing extent, and the more the number of known insects 
increased, the more minute and detailed was this classification. When 
the evolution theory was accepted, it was evident that every scrap of 
available information would be required to give data on which to make 
a natural grouping of insects ; what was the origin of insects ? from 
what had they developed ? how far had different insects remained 
for a long period in the same condition, and how far was the evolution 
either continuing still or had it been continuous up to the recent past ? 
These were the questions to be answered, and the answer is embodied 
in the present-day system of classification which is believed to be so far 
natural that it conforms, as far as possible, to the actual developments 
of insects during the earth’s history and does represent actual relation¬ 
ships. On these terms all the members of one group are more closely 
interrelated than each one is to any other insect not in that group. 
In making this classification, there are practically three main sources 
of evidence: (1) the morphology of the insect in all its stages ; (2) the 
processes of embryological and post-embryological development; (3) 
the evidence of fossil and extinct insects. 
In the beginning, the first alone was utilised, and it is still the main 
source of information; at first superficial characters were used, then 
more detailed ones such as the structure of the trophi, finally the fuller 
evidence afforded by all parts of all stages is being utilised, though this is 
by no means near completion. The second has been utilised, but not to 
a great extent. The third has been utilised as far as it is available, but 
the geological record is scanty, and what there is, is very imperfectly 
available as yet. There is a great bulk of literature on this question, and 
it is impossible to more closely enter into the subject here. How little 
is really known can be gauged from the great changes made in the classi¬ 
fication of Ileterocera, for instance, as well as from the fact that ento¬ 
mologists have arrived at no definite conclusions which are generally 
accepted. The most diverse views prevail, and there is no standard classi¬ 
fication that is or can be universally employed even if it be admittedly 
