+ Annals Entomological Society of America |Vol. VIII, 
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“I 
Entomology is now confronted with the same condition 
which older sciences experienced and like them must become an 
exact science if it is to realize its highest development. 
Along with the improvement in accuracy and detail there 
must come at the same time a simplification through the 
elimination of the non-significant details of each department 
of entomology and a clearer recognition of the distinctness 
of these departments. 
DIAGNOSTIC ENTOMOLOGY. 
In no place is this need more clearly shown than in what 
we know as Systematic Entomology, a very utilitarian depart- 
ment concerned in the assigning of names to insects and in 
providing ‘the means whereby these insects may be identified. 
Such an entomologist is a Diagnostician. His problems are 
numerous and difficult enough, requiring the specialization 
into very restricted groups, and is rendered more difficult 
by the fact that many have confused their work with two 
very different departments — classification and descriptive 
entomology. 
Keys have been rendered unnecessarily difficult by attempts 
to make them conform in arrangement to supposed phyletic 
sequences and pages of descriptive matter in defining a new 
species seldom results in making its correct identification 
more certain and certainly makes it much more laborious. 
Keys should be arranged in a manner to best facilitate 
identification, every other consideration should be subordinated 
to this end. This principle appears to be beyond controversy. 
How it shall be applied, that is, what form tables will finally 
take, is a matter that time will decide. 
Two plans of arrangement are presented for your considera- 
tion, one based on dominance and the other on historic sequence. x 
The latter appears to be best for the species of a genus where 
the commoner forms are liable to be first described and the 
former method for larger groups which, because of the changing 
views as to what they include, can be best studied according 
to their present rather than their historic content. Keys 
constructed along these lines have proven remarkably simple 
and workable. They are particularly good for teaching 
* The paper was illustrated at this point by the keys given in the author’s 
‘“Pamilies of Insects,’’ and ‘‘ Insects of California.’’ 
