THE THORAX OF THE HYMENOPTERA. By Robert Evans Snodgrass, Of the Bureau of Entomology , United States Department of Agriculture. 1. INTRODUCTION. There are always two classes of workers concerned in the scientific study of any group of animals who think that the work of the other class is properly but secondary to their own. These are the system-atists and the morphologists. In the field of entomology, how-ever, there is now a very large third class of workers who pick out as important only those phases of the subject that have some direct connection with the welfare of mankind. We need not discuss the relative merits of the three, however, because the present paper is a sufficient demonstration of the interdependence of all these branches of entomological research. To wit, the gypsy moth and the brown-tail moth have been for a number of years greatly infringing on human interests and pleasure in certain parts of New England. A most promising means of combating them is the importation and rearing of destructive Hymenopteran parasites. Students of these parasites discover that the thorax presents valuable characters for the determination and classification of species, but they are handi-capped in the use of such characters by the lack of reliable studies on the structure of the thorax among parasitic Hymenoptera in general. When, furthermore, the present writer undertook a study of the latter subject, he soon found himself necessarily involved in a gen-eral investigation of the Hymenopteran thorax, and especially of that of the lower members — the Tenthredinoidea and Siricoidea. These in turn had to be compared with the more generalized orders of insects to make sure of correct interpretations. Hence, while an unscientific person may be inclined to ask what the study of a cockroach's thorax has to do with the extermination of the gypsy moth in Massachu-setts, experience shows that no special branch of entomology can be developed properly unless based on a knowledge of the fundamental structure of insects in general. Proceedings U. S. National Museum, Vol. 39— No. 1774. 37
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