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Indiana University Studies 
be determined only from further studies on other gall wasp 
genera and upon organisms of many diverse groups ; but mean- 
while we offer our data as illustrative of possibilities in the 
taxonomic method, and as a body of observations leading to 
what would seem to be unmistakable conclusions on the origin 
of species in this particular genus. 
THE TAXONOMIC METHOD 
The attainment of sound ends in any field of science de- 
pends on certain common fundamentals of scientific method. 
An adequate understanding of any phenomenon must await 
repeated observations of that phenomenon thruout a wide 
range of specific cases, and an interpretation of the data based 
upon a comparative study of the groups in which that phe- 
nomenon is known to appear. It is only because the nature 
of the material studied and the categorical rank of the unit 
of comparison varies considerably with the problem under 
observation that we assign each biologic question to some spe- 
cial field, recognizing that each sub-science provides the best 
means of handling particular materials and particular cate- 
gories. 
To morphology, physiology, and psychology we make cer- 
tain assignments not only because we wish to deal with par- 
ticular aspects of the organic organization, but because these 
sciences are adapted for dealing with ordinarily few species 
which may be taken to stand as types of whole orders and 
classes or phyla of plants or animals. For this reason these 
sciences contribute data on such problems as the relationships 
of the larger groups, their appearance in the geologic record, 
and their value as evidence of the processes of evolution itself. 
In genetics, on the other hand, it is the individual which is 
the category chiefly concerned, and the correlations are made 
between individuals of experimentally proved hereditary re- 
lationships. In taxonomy the data are again individual or- 
ganisms, but the comparisons employed are between such 
groups of individuals as constitute what we call species, and 
between all of the species for which we may find evidence of 
close, phylogenetic affinities. The unfolding of the complete 
record of evolution would thus appear to depend upon the 
coordination of the contributions from cytology, genetics, 
taxonomy, comparative anatomy, embryology, paleontology, 
