328 THE WINGS OF LEPIDOPTERA 



In several adult hepialids that I have studied the tracheae are visible in 

 the wing- veins. The results of my studies of these specimens differ in 

 some details from those reached by Dr. MacGillivray. It is quite possible 

 that these differences are due to the fact that the material studied by Dr. 

 MacGillivray had been preserved in formal and may not have been in good 

 condition. It is obviously desirable that fresh pupal wings be studied. 



The most important of the differences referred to is the fact that in all 

 cases where I have seen trachea in the wing-veins of hepialids what appears 

 to be the posterior arculus is traversed by a branch of the medial trachea, 

 which extends towards the margin of the wing in the longitudinal part of 

 the cubitus, and parallel with the cubital trachea. I am unable to explain 

 satisfactorily the presence of this trachea in this position. It may have 

 originated as an adventitious trachea ; but if so, it has become a definitive 

 part of the tracheation of the wing for it is as large as or larger than the 

 cubital trachea. It may be the trachea of the missing vein M4, which has 

 been separated from the other branches of the medial trachea. An 

 analogous splitting back of a trachea is that of trachea R4+.5 in the butter- 

 flies. I leave the problem until more data bearing on it is obtained. 



In some hepialids there is a forking of trachese near the base of the wing 

 which results in the stem of a forked vein containing several parallel 

 branches. In a wing of Sthenopis that I have examined there are two 

 tracheae in radius at the base of the wing, and these divide into four a short 

 distance beyond the humeral vein. 



The venation of the wings of hepiahds. — In the hepialids the subcosta is 

 often forked; the radius of both fore and hind wings is of the hypotheti- 

 cal primitive type ; media is reduced to a three-branched condition in both 

 fore and hind wings ; and in the fore wings veins Cu and i st A coalesce at 

 the base, as in the Trichoptera. 



The way in which media has been reduced in the hepialids is still an 

 open question. Dr. MacGillivray, as a result of his studies of tracheation 

 of Hepialus thule, reached the conclusion that the reduction is the result 

 of the coalescence of veins M^ and M4 ; but had he found the branch of the 

 medial trachea that traverses the posterior arculus he probably would have 

 reached a different conclusion. 



Comstock and Needham concluded that the reduction of media had 

 been attained by the coalescence of veins M4 and Cui, and figured the wings 

 of an abnormal Sthenopis in which the tips of veins M4 and Cui are separate 

 in the hind wing (Fig. 337), believing that this condition is atavistic. The 

 value of this evidence is seriously questioned by Dr. MacGillivray ; but the 

 presence of the trachea that traverses what appears to be the posterior 

 arculus, described above, adds weight to it. 



Until this question is more definitely settled, it will be best to omit any 

 reference to vein M4 as is done in Figure 334. 



