CHAPTER XIX 

 THE WINGS OF THE COLEOPTERA 



The members of this order have four wings; the first pair of wings, 

 which are called elytra, are greatly thickened and meet in a straight line 

 down the back (Fig. 307) ; the second pair of wings are folded beneath the 

 elytra when not in use. 



The great modifications in form and structure of the wings of the 

 Coleoptera make the study of the wing-venation of these insects a difficult 

 one. Correlated with the loss of the flight function of the elytra in the 

 course of their change to thickened protective organs, there has been a 

 reduction of their venation ; and in the case of the hind wings, the fact that 

 in most cases they are transversely folded when 

 at rest has resulted in a great modification of the 

 courses of the veins and in the formation of secon- 

 dary vein-like thickenings of the wing. 



In spite of the difficulties just referred to, the 



problem of determining the homologies of the 



wing-veins of the Coleoptera is not an insuperable 



one if use be made of the ontogenetic method of 



study. In the pupal wings, so far as they have 



1 -1.1 • • 1 . 1 Fig. "^OT. — Desmoceriis 



been exammed, the pnncipal tracheae are com- "^ palUatus 



paratively well-preserv^ed ; and a study of these 



tracheae furnishes data for detennining the homologies of the wing-veins. 



The beginning of the application of this method of study to the wings 

 of the Coleoptera was made by Comstock and Needham ('98). Our dis- 

 cussion of the matter, however, was brief and devoted largely to a demon- 

 stration of the fact that the elytra are modified wings and not the greatly 

 enlarged paraptera of the mesothorax, as was believed by Meinert ('80). 



The most conclusive evidence that we found regarding the homology 

 of the elytra was presented by their development. We traced the develop- 

 ment of the two pairs of wings in a coccinellid beetle, Hippodamia ij- 

 punctata; and found that previous to their emergence from the larv^al wing- 

 pockets, there is no appreciable difference between the fore and the hind 

 wings; after this, however, the elytra show a distinctly thicker layer of 

 h^'podermis on their dorsal side, and the thinness of the hind wings steadily 

 increases with their expansion in area. The hind wings are greatly 

 expanded at their final transformation, while the elytra are almost as large 

 in the pupa as in the imago (C. & N. '99, p. 850). 



Ftirther evidence is the fact that a very close correspondence exists 

 between the tracheation of the elytra and that of the hind wings; and what 



(297) 



