4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



varies considerably throughout the order. However, the posterior 

 bridge of the tentorium is always short. 



The mouth parts of adult Lepidoptera consist of the maxillae, the 

 labium, the labrum, and the hypopharynx. The maxillae, as is well 

 known, are the most important, their galeae forming the long suc- 

 torial proboscis in those which have functional feeding mechanisms. 

 Various degrees of degeneracy may be found, until the point is 

 reached, as in the males of Thyridopteryx, where the maxillae are no 

 longer recognizable as distinct appendages. The hypopharynx of 

 moths and butterflies is incorporated in the floor of the sucking pump 



Clp 



AT' 



PoR 



PT 



Lrm-^ 



Prb — \- 



A 



Fig. I. — Structural details of the head and feeding mechanism of Argynnis 

 and Danaus. 



A, right half of head, mesal view, of Argynnis cybclle, showing endoskeleton 

 and floor of sucking pump {SP) formed by hypopharynx (Hphy). B, left 

 half of clypeus and base of left maxilla attached to parietal part of head of 

 Danaus menippe, anterior view. 



and will be described under that heading. The labrum, like the hypo- 

 pharynx, is really a part of the cranium, but since it plays a part in 

 the mechanics of feeding it may be described as a mouthpart. The 

 lateral lobes of the labrum, called the pilifers, bear against the pro- 

 boscis base, and in some butterflies the labrum is sufficiently flexible 

 to move as a unit with the proboscis base. In such cases (fig. i B) 

 the proboscis base is provided with a knob that fits against the pilifer 

 under its fringe of setae. In many moths, however, the labrum does 

 not have this function. The labium is evident only as a small triangu- 

 lar area bearing the three-segmented labial palpi. These palpi are 

 usually so placed that the coiled proboscis can be clasped between 

 them and be almost completely hidden from view. The labial palpi 



