CHAPTER X 

 THE WINGS OF THE EPHEMERIDA 



(a) THE MORE GENERAL FEATURES OF THE WINGS OF THE EPHEMERIDA 



In the order Ephemerida or May-flies the wings are triangular in out- 

 line, and delicate in stnicture ; they are usually furnished with a consider- 

 able ntimber of intercalary veins and with many cross-veins (Fig. 212.) 



The presence of intercalary veins is correlated 

 with a corrugation of the wings by which the 

 well known fan-like form has been produced; 

 there being a remarkably perfect alternation 

 of so-called convex and concave veins. When 

 at rest, the wings are held upright; they are 

 never folded over the abdomen. No anal furrow has 

 been developed. 



In this order a marked cephalization of the flight 

 function has taken place, which has resulted in a great 

 reduction of the hind wings of all living forms. In some 

 cases {CcBuis et at.) this has gone so far that the hind 

 wings are wanting (Fig. 213); but at least one pair of 

 wings are present in all members of this order. 



In a few genera {Oligoneuria et at.) both pairs of wings 

 are furnished with but few veins. It requires only a 

 little study, however, to convince one that these genera 

 with few-veined wings are degraded and not generalized. It is in the fore 

 wings of those forms in which many wing-veins have been retained that 

 the homologies of the wing-veins are most easily determined. 



(6) THE TRACHEATION OF THE WINGS OF THE EPHEMERIDA 



Comstock and Needham ('98) made the first attempt to determine the 

 homologies of the wing-veins of May-flies by a study of the tracheation of 

 the wings. In this paper we made the following statement: 



"We have studied the tracheation of many nymphs of 

 May-flies, but with results much less satisfactory than those 

 we have reached in a study of other orders of insects with 

 many-veined wings. In all nymphs of May-flies that we have 

 examined, a greater or less reduction of the tracheae appears 

 to have taken place ; and in many of them a large proportion 

 of the longitudinal veins contain no tracheae. And, too, the 

 presence or absence of a trachea in a vein appears to have little significance. 

 As an example of this the wings of two nymphs are before the writer, in which 



(214) 



Fig. 212. — 

 A May-fly. 



Fig. 213.— 

 Can is. 



