574 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



always precodcd ]\y a trachea and that in certain cases this is the most 

 prominent trachea in the wing. The tracheal trunks behind cubitus 

 are divided into two groups. The anterior he has called the anal group 

 and the posterior the axillar}^ group. The modified Redtenbacher 

 nomenclatun^ used ])y Comstock and Needham is adopted. 



From a study, extending over a period of several years, of the 

 wing-veins of the superfamily Tenthredinoidea, w^hich contains all the 

 generalized wings found in the ordei" Hymenoptera, I am convinced 

 that the homologies established for the H3^menoptera by Comstock in 

 his Manual for the Study of Insects, and farther elal)orated by Com- 

 stock and Needham, are correct, and they are accepted and followed 

 in this paper. An attempt will l)e made here to explain some details 

 of the Hymenopterous wing as exemplified b}' the Tenthredinoidea 

 and not discussed by these investigatoi-s. 



II.— GENERAL CONSIDERATIONS. 



In determining the homology of the wing-veins of insects, conclu- 

 sions are reached ])y two difJerent methods. First, by a study of the 

 ontogonv of the wing-veins, which consists of a careful examination 

 of the tracheation that precedes the veins and a comparison of it with 

 the wing- veins of the pupa and adult. As a rule, cross-veins are not 

 preceded by trachea\ so that this method, where it can be applied, is 

 of the greatest importance in determining the course and extent of the 

 principal veins and their branches. Second, by a study of the phy- 

 logeny of the wing-veins, which consists of a careful comparison of the 

 progressive modifications found in the wings of adult insects. By this 

 method, the accuracy of the results depend on the skill of the investi- 

 gator in decif)hering the record. 



It has been shown by Comstock and Needham " that an ontogenetic 

 study of the wings of the Hymenoptera is not of any value in deter- 

 mining the homology of the veins, and I can not do better than ([uote 

 their account: 



The importance of this method of study has been well shown by the residts we 

 have obtained. But we also found that in the Trichoptera there is little correlation 

 between the venation and the tracheation of the wings, a remarkable reduction of the 

 wing tracheae having taken place. A similar reduction of the tracheae of the wings 

 exists in most families of Diptera; and even when a large proportion of the trachea- 

 are retained, as in certain Asilids, they afford little aid in the determining of the 

 homologies of the wing-veins. For this reason we omitted a discussion of the 

 tracheation of the wings of Diptera. Again, in the Hymenoptera we find that 

 the courses of the trachete can not be depended upon for determining the homologies 

 of the wing-veins. But here, in the more generalized members of the order, we 

 find a very complete system of wing-trache;e, and it is, therefore, incumbent on us 

 either to point out the correspondence between the tracheee and the wing-veins, or 

 to demonstrate that such a correspondence does not exist. 



« J. H. Comstock and J. G. Needham. Amer. Nat., XXXII, 1898, pp. 421-422. 



