be determined only from further studies on other gall wasp genera and upon organisms of many diverse groups; but meanwhile 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 depends 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 phenomenon 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 special field, recognizing that each sub-science provides the best means of handling particular materials and particular categories.
To morphology, physiology, and psychology we make certain assignments not only because we wish to deal with particular 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 relationships. In taxonomy the data are again individual organisms, 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 coördination of the contributions from cytology, genetics, taxonomy, comparative anatomy, embryology, paleontology,
