THE THORAX OF INSECTS AND THE ARTICULATION 



OF THE WINGS. 



By Robert Evans Snodgrass, 



Of the Bureau of EntomoloffU, U. »S'. Department of Agrieiilture. 



I. INTRODUCTION. 



This paper is an attempt to shoAv the unity of thoracic structure 

 that prevails throughout all the orders of insects. It is hoped that it 

 will he of special service to systematists in entomology and that it 

 will meet with approval from students of morphology. The material 

 on which the paper is based was all drawn from the U. S. National 

 Museum and the dissections have been deposited in the museum. 



The work has been done under the direction of Dr. A. D. Hopkins, 

 of the U. S. Bureau of Entomology, and has grown from an attempt 

 to determine thoracic homol-ogies in the Coleoptera, especially in the 

 family Scolytida\ It is published by the approval of Dr. L. O. 

 Howard, chief of the bureau, as a contribution from the office of 

 Forest Insect Investigations. The author is indebted to Doctor Hop- 

 kins not only for the opportunity of carrying on the Avork but also 

 for a great deal of help in doing it and for the verification of observa- 

 tions. Assistance has also been received from other members of the 

 entomological staff of the bureau, among whom are Mr. Nathan 

 Banks, Mr. A. N. Caudell, Mr. D. W. Coquillett, Mr. R. P. Currie, 

 Dr. H. G. Dyar, Mr. Otto Heidemann, Mr. E. A. Schwarz, and Mr. 

 H. S. Barber and also Mr. J. C. Crawford, of the U. S. National 

 Museum. 



Some of the drawings on the plates were used by the writer in a 

 former paper on the thorax, published in the Proceedings of the 

 Washington Entomological Society (1908), and are here reproduced 

 with the permission of the editors of that journal. 



No new theory is presented. The writer claims that the dia- 

 grams forming text figures 1 to 6 represent simply the facts. All 

 schemes of thoracic symmetry in consecutive circles are discarded 

 on the ground that they are supported only by the imagination. 



Proceedings U. S. National Museum, Vol. XXXVI— No. 1687. 



511 



