60 



THE GENERAL FEATURES OF WINGS 



Fig. 42. — Fore wing of a flower-bug 

 (Acanthiidae) ; e embolium. 



when this is present. This Hne serves as a hinge which faciUtates the fold- 

 ing of the posterior lobe of the wing under that part of the wing in front of it. 



The axillary excision. — In the 

 wings of most Diptera there is a 

 notch in the inner margin of the 

 wing near its base (Fig. 44, ae) ; this 

 has long been known as the axillary 

 excision; the application of this term 

 may be extended advantageously to 

 the notch in a similar position that 

 exists in the wings of many other insects. 



The posterior lobe. — That part of the wing lying between the axillary 

 excision and the axillary membrane at the base of the wing in the wings of 

 Diptera (Fig. 44, /) has been termed the posterior lobe. The development of 

 a posterior lobe, however, is not limited to the Diptera, a distinct posterior 

 lobe being found in the representatives of several of the orders. 



In some cases, as in those Diptera where an alula is developed, the 

 posterior lobe and the axillary membrane are distinctly differentiated ; but 

 in other cases they are not, as in the wings of Corydalus. 



The posterior lobe of the fore wings of certain insects has been specialized 

 so as to serve as an organ for uniting the fore and hind wings. Two types of 

 such an organ are defined later. 



The posterior lobe of the wing and the clavus of the Heteroptera are not 

 homologous, the clavus including a much larger part of the wing than does 

 the posterior lobe. 



The methods of uniting the two wings of each side. — It is obvious that 



a provision for ensuring the synchronous action of the fore and hind wings 



adds to their efificiency ; it is as important that the two pairs of wings should 



act as a unit as it is that the members of a boat's crew should pull together. 



In many insects 



the synchronous , "^ 



action of the wings 

 is ensured by the 

 fore wing of each side 

 overlapping the hind 

 wing. But in other 

 insects special struct- 

 ures have been devel- 

 oped which fasten 



Fig. 43. — Fore wing of a (Cicada; n f, nodal furrow. 



together the two wings of each side. Tlic different types of these struc- 

 tures have received special names. 



The hamuli. — With certain insects the costal margin of the hind wings 

 bears a row of hooks, which fasten into a corresponding fold on the inner 



