324 



THE WINGS OF LEPIDOPTERA 



Aculeatce. The introduction of these two terms in this connection is unfor- 

 tunate on account of their long and very general use in another sense in 

 works on the H^Tnenoptera. The term, fixed hairs, used by Kellogg is 

 perfectly satisfactory. 



The mode of origin and development of the fixed hairs has not been 

 studied. They may be merely elongated cuticular nodules; but Spuler 

 states that they are hollow, which indicates a different mode of origin from 

 that of the ordinary cuticular nodules. The fixed hairs are designated by 

 Marshall ('15) as the small surface hairs. 



(c) THE METHODS OF SPECIALIZATION OF THE WINGS OF THE LEPIDOPTERA 



The Lepidoptera belong to the series of orders in which the number of 

 wing-veins does not exceed that of the hypothetical primitive type, the 

 divergences from this type being the result of specialization by reduction. 



Fig. 333. — Fore wing of a pupa of Pieris rapce. 



Neither accessory nor intercalary veins are normally developed in this 

 order; and only the principal cross- veins are present. In some cases, how- 

 ever, there appear to be four anal veins, which indicates that one of the anal 

 veins is two-branched. 



That this was more generally the case in the primitive Lepidoptera than 

 it is in recent forms is shown by the fact that, although there is only one anal 

 vein in the fore wing of the adult Pieris, in the pupal wing there are three 

 anal tracheae and the third is two-branched. (Fig. 333). 



Although accessory veins are never normally present in members of 

 this order, abnormal specimens have been found, especially of hepialids, 

 in which there are extra branches on the branched veins. 



Reduction in the number of veins is of frequent occurrence, and is the 

 result cither of the coalescence of adjacent veins or of the fading out of 

 veins. Reduction by the coalescence of veins is the more usual method of 



