SOME PROBLEMS OF TAXONOMY 
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of individuals which are at the present time delimitable, with- 
out regard for the extent of variation embraced by any one, it 
should be possible for the average worker, as well as the specialist 
with extensive resources, to become familiar with the chief units 
of any division. The next difficulty is the treatment of the sub- 
ordinate divisions of such extremely variable species as some of 
those included in Euxoa. In discussing this, although a degree 
of unwelcome complexity is thus introduced into the second part 
of this paper, it will be convenient to take up in rather intimate 
association the methods of subspecific nomenclature and the 
value of the various subdivisions. 
II. Subspecific Divisions. 
In the first topic of this paper the species concept was dis- 
cussed, with the conclusion that the term species properly desig- 
nates a natural entity consisting of a delimitable group of indi- 
viduals. This was qualified by the addition of the element of 
time, recognizing that the species of the present are in varying 
stages of evolution, and that many of them may ultimately re- 
solve themselves into more nearly ideal species. As the ideal 
species, senile forms which had run through their possible phy- 
logenetic development were mentioned. The purpose of the sec- 
ond topic is the discussion of the subdivision of the more gener- 
alized and variable species of the present, and the nomenclature 
to be applied to their subordinate parts. 
Formulating the problem as a generally applicable hypothesis, 
rather than as a specific case, let us consider the ways in which 
these variable groups have been treated. We may examine them 
as two hypothetical species, both variable. Each in its entirety 
may be regarded as a well defined '‘cross-section,’’ the first made 
up of a number of fairly definite subordinate sections and the 
second of scarcely separable subordinate components. The two 
may be likened to a cellular tissue in comparison with a syn- 
cytium. 
The first hypothesis finds many examples in existing species 
which occur in two or more forms, usually well marked. The 
early method of treating such species was to accept the form first 
named as the species and those discovered later as varieties. If 
an occasional specimen appeared showing a marked variation 
from the normal, it was, and still is, known as an aberration. 
Many of these bear names. This simple subdivision of species 
