378 Annals Entomological Society of America [Vol. VIII, 
CLASSIFICATION. 
The classification of organic beings has to do with questions 
of phylogeny exclusively. No small amount of confusion 
has arisen from attempts to combine classifications and keys. 
for identification to the detriment of both. The groups recog- 
nized by both the Diagnostician and the Systematist should 
be the same, but the characters and arrangement need have 
nothing in common. The best diagnostic characters may have 
little or no phyletic significance and the phylogenetic sequence 
of groups may introduce confusion and difficulties in identi- 
fication. 
The problems of phylogeny are two, the derivation of 
groups and the coordination of groups. 
Derivation of groups to determine by a comparative study 
of the structure, substantiated wherever possible by the historic: 
sequence of the first appearance of the groups as shown by the 
geological record, the underlying principle being that the 
complex structure was derived by the specialization of simple 
structures. Two groups are supposed to have a common 
ancestor if they resemble each other in most of their characters. 
The characters by which they differ are supposed to be those 
historically responsible for the separation of the groups. Asa 
matter of fact groups are usually distinguishable by numerous 
characters, many of which are accidental or only incidentally 
coordinated with the historic basis of the segregation. The 
Systematist therefore, must search for the differentiating 
character, which may be internal or difficult of observation 
and very unsatisfactory for diagnosis, but the only one perhaps 
that gives a clue to the causes which brought about the separa- 
tion of the groups. Differentiating characters are perhaps 
always differences of kind, representing alternative possibilities 
in growth and either a new structure in the place of an older 
one, or progress in the development of a structure of which 
there may be two possible lines of growth. Some differentiations. 
involve no appreciable change in other parts of the body, 
while others are revolutionary. The former we conceive may 
frequently recur, giving us examples of parallel development. 
Many generic differences are clearly of this character. The 
more involved modifications give so many opportunities for 
variation that strict parallelism appears to be impossible. 
