574 



AN INTRODUCTION TO ENTOMOLOGY 



They are so small that they can be seen only by the aid of a micro- 

 scope, and being covered by the scales they can be seen only in 

 bleached and stained or denuded wings. 



In the more generalized members of this order, the venation of 

 the wings corresponds quite closely to the hypothetical primitive 

 type. The most striking divergence from this type is the fact that 

 vein M is only three-branched. This is probably due to a coalescence 

 of veins M^ and Cui. If this is true, the vein that is commonly desig- 

 nated as vein Cui is really vein M4 plus Cui; but for the sake of 

 simplicity it seems best to designate it ordinarily as vein Cui. For a 

 detailed discussion of this problem, see "The Wing's of Insects," pp. 



334-337- 



Although the wings of Lepidoptera, except in certain specialized 

 forms, are broadly expanded, there are but few cross-veins, and nor- 

 mally no accessory veins. 



In the more specialized members of this order the number of the 

 wing-veins is reduced. This reduction is due in some cases to the 

 aLiOphy of a vein or veins, as, for example, the loss of the main stem 

 of vein M in many families ; in other cases, it is due to the coalescence 

 of adjacent veins, as, for example, the reduction of the mmiberof 

 branches of radius or of media which has taken place in many 

 members of the order. 



In many genera of this order the branches of radius of the fore wings 

 anastomose so as to form one or more closed cells ; these have been 

 termed accessory cells . 



There are several methods by which the fore and hind wings of 

 Lepidoptera are held together in flight, in order to insure their 

 synchronous action. In the suborder Jugatae the posterior lobe of 

 the fore wing functions either as a jugum (see p. 61) or as a fibula 

 (see p. 62). In most moths the wings of each side are united by a 



frenulum (see p. 61). In 

 some moths and in the 

 skippers and butterflies, 

 the humeral angle of the 

 hind wing is greatly ex- 

 panded and projects be- 

 neath the fore wing; this 

 insures the synchronous 

 action of the two wings 

 and renders a frenulum 

 unnecessarv' ; in these 

 forms, which doubtless 

 descended from frenate 

 ancestors, the frenulimi 

 has been lost. 



The frenulum when 

 well developed consists of a bunch of bristles situated at the base of 

 the costa of the hind wings, on the costal sclerite. As a rule these 

 bristles are separate in females, and consolidated into a single strong, 

 spine-like organ in males. 



Fig. 711. — Wings of Obrussa ochrefasciella, male. 

 (After Braun.) 



