THE GENERAL FEATURES OF WINGS 57 



The costal sclerite. — The costa does not connect with any of the axillary 

 sclerites named above ; but there is very generally at its base a more or less 

 distinct sclerite, which may be termed the costal sclerite. This is regarded 

 by Snodgrass as merely the base of the costa; but as it is frequently a dis- 

 tinct sclerite of considerable width it merits a special name. 



In the hind wings of many of the Lepidoptera, the costal sclerite forms 

 a strong support for the frenukim. This sclerite is represented, but not 

 lettered, in the figiue of the wings of Prionoxystus (Fig. 62) ; it is also very 

 prominent in the hind wing of Cacoecia (Fig. 353). 



Figures of the bases of many insect wings showing the form and position 

 of the axillaries are given by Snodgrass. 



The tuberosities of the base of the wing. — At the base of each wing in 

 most insects, there are two prominent, elevated, shoulder-like areas; these 

 were designated by Amans ('85) as the anterior tiiherosity and the posterior 

 tuberosity respectively. These tuberosities are better defined in the fore 

 wings than they are in the hind wings. 



The anterior tuberosity is at the base of the radius and the adjacent 

 veins, and the posterior tuberosity is at the base of the anal veins. The 

 posterior tuberosity is sometimes di\ndcd into two or three tuberosities, 

 corresponding to the separate anal veins. 



The cubito-anal sulcus.^ — The deep channel between the anterior and 

 the posterior tuberosities may be termed the cubito-anal sulcus. 



In most insects the cubito-anal sulcus is traversed by the basal part of a 

 wing-vein. This vein is either the cubitus, the first anal vein, or the 

 coalesced bases of these two veins, differing in different insects. In a few 

 insects, as in Corydalus, there is no vein at the bottom of the sulcus, the 

 cubitus extending along one side of it and the first anal vein along the other. 



As a rule, a vein traversing this sulcus is more or less atrophied at its 

 base. 



The corrugations of the wings. — The wings of comparatively few insects 

 present a fiat surface ; in most cases we find that the membrane of the wing 

 is throwai into a series of folds or corrugations. This corrugating of the 

 wing in some cases adds greatly to its strength; this is well-shown by the 

 wings of dragonflics; and in most orders the costal margin of the wing is 

 strengthened by a plication between the costa and the radius, this is the 

 subcostal fold. In other cases, the conjugations are the result of a folding of 

 the wing when not in use; this is well-shown in the anal area when this part 

 is broadly expanded. 



The cubito-anal fold. — There is one fold that is almost universally present 

 in the wings of insects. This fold is a continuation of the cubito-anal 

 sulcus, which usualU' extends to the margin of the wing; it may be tenned 

 the cubito-anal fold. It is in this fold that the anal furrow is developed 

 when present. 



