CHAPTER XI r 

 THE WINGS OF THE PLECOPTERA 



(a) THE MORE GENERAL FEATURES OF THE WIXGS OF THE PLECOPTERA 



The members of this order have four membranous wings (Fig. 243). 

 In some genera the branches of the principal veins are reduced in number 



and there are comparatively few 

 cross-veins; in others, accessory veins 

 are developed and there arc many 

 cross-veins. The hind wings are a 

 little shorter than the fore wings, but 

 usually, owing to the expansion of the 

 anal area, they are considerably larger 

 than the fore wings. No organ for 

 uniting the two wings of each side 

 has been developed. When at rest 

 the ^nngs are folded over the abdo- 

 men. In a few members of the order 

 the wings of the male are greatly 

 reduced in size, and in some males 

 the wings are wanting. 



Fig. 243. — Pleronarcys dorsata. 



(b) THE TRACHEATION OF THE WINGS OF THE PLECOPTERA 



The most striking feature of the tracheation of the wings of the Plecop- 

 tera is the absence of the basal transverse trachea ; there being no connec- 

 tion between the costo-radial and the cubito-anal groups of tracheae (Fig. 

 244). This is a generalized feature, which has been observed as yet only 

 in this order, in certain cockroaches, and in some Homoptera. In each of 

 these cases, the medial trachea is a member of the costo-radial group. 



In the wings of nymphs of the Plecoptera, the cross-veins are not pre- 

 ceded by tracheae (Fig. 244). It is easy therefore to distinguish the cross- 

 veins from the other veins in this order by a study of the wings of nymphs. 

 It should be noted, however, that in certain genera, as Acroneuria and 

 Pteronarcys for example, accessory veins are developed on the front side of 

 subcosta and of the terminal portion of radius-one that are commonly called 

 cross- veins; but as these are preceded by tracheae and as the true cross- 

 veins in other parts of the wing are not preceded by tracheae in this order, 

 these are evidently accessory veins. 



In some forms, as in Pteronarcys, tracheae other than those that precede 

 the wing- veins penetrate the wings; this is especially true in the area 



(243) 



