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 



