i 



THE WINGS OF TRICHOPTERA 



315 



There are two features of the venation of these wings that are of especial 

 interest: first, the course of cubitus in the fore wing, described above; 

 and second, the course of the second 

 anal vein of the hind wing, which 

 anastomoses with the first anal vein near 

 the base of the wing, in the same manner 

 as in Rhyacophila, described on an eariier 

 page. 



The fibula of Mnemonica (Fig. 325) is 

 identical in structure with that of Rhyaco- 

 phila (Fig. 320). It is hatchet-shaped, the 

 axillary furrow is immediateh' behind the 

 second branch of the third anal vein, and 

 the longitudinal margin is supported by the third branch of the third 

 anal vein. 



Fig. 325. — Fibula of Mnemonica sp. 



(b) THE TRACHEATIOX OF THE WINGS OF THE MICROPTERYGINA 



A study of the tracheation of the wings of Mnemonica confirms the 

 conclusions reached regarding the homologies of the wing-veins of this 

 insect and of those of Rhyacophila* 



In Figures 326 and 327 which represent the basal portion of the wings of 

 Mnemonica, the tracheae are shown in the wing-veins in so far as they can 

 be clearly distinguished in the specimen figured. 



In the fore wing, no costal trachea was found. There is a single trachea 

 in the subcosta, which is not clearly visible except in the basal fourth of the 

 vein, where it is distinct. At the base of the radius there is a single trachea, 

 but this forks just before the point where subcosta and radius diverge. At 

 about one-third of the distance from this point to the radial fork, one of 

 these two tracheae again divides. A little farther distad the other of the 

 tw^o branches divides. All four of these branches pass into the radial 

 sector. 1 am unable to find any trace of trachea Ri.f In the basal part of 

 the stem of media there is a single trachea; this divides into two a con- 

 siderable distance before the cross-vein that extends to vein Cu {p a) is 

 reached; one of the two again di\'ides a short distance beyond this cross- 

 vein; and the other divides into two a little farther on; all of these tracheae 



*I am indebted to Dr. W. T. M. Forbes for an opportunity to study a preparation 

 of the wings of a species of Mnemonica, in which the tracheae can be clearly seen in the 

 basal portions of most of the wing- veins. Dr. Forbes placed this preparation in my 

 hands with the suggestion that the tracheation of these wings indicates the necessity 

 of a modification of the commonly accepted view regarding the homologies of some of 

 the wing-veins of the Microptcrygidse. A careful study of this specimen has fully 

 confirmed Dr. Forbes' suggestion. 



fA similar forking of trachea; near the base of the wing which results in the stem of a 

 forked vein containing several parallel trachea;, one for each of its branches, occurs 

 in the Sesiidas, and in some hepialids, at least. 



