LEPID OP TERA . 1 89 



at their ends, often appearing like clubs. The shape 

 of these organs is so constant that it usually, though 

 not always, serves as a distinguishing characteristic 

 between butterflies and moths (see p. 196), and has 

 been used to justify the name of Rhopalocera (see p. 

 212) as apphcable to this group of Lepidoptera. The 

 mouth parts first observed are the sucking-tube or 

 trunk (PL IX., Figs. 135, 136, ;;/.v'), which is usually 

 coiled hke a watch-spring, and the hairy palpi (Fig. 

 135, jc"). Looking more closely, two small, immov- 

 able, horny pieces (Fig. 136, ind^ are seen on either 

 side of the sucking-tube : these are the remnants of 

 mandibles. The trunk represents the first pair of 

 maxillae, whose palpi are small (Fig. 136, .t'). A 

 cross-section of the trunk is shown in PL IX., Fig. 138. 

 According to Mr. Burgess,^ it consists of two lateral 

 parts, each representing one maxilla. These parts 

 are convex on the outer side and concave on the 

 inner. By the union of the two concavities a com- 

 plete central tube (<:;/) is formed. The lateral parts 

 are filled with muscles (2), tracheae (//?), and nerves 

 (;//), while the central tube is hollow and opens 

 into the pharyngeal sac, the floor of which is seen in 

 PL IX., Fig. 139, hph. When the sucking-tube is 

 thrust into the corolla of a flower, the sweet fluid is 

 drawn upward by the alternate contraction and dila- 

 tation of the pharyngeal sac. PL IX., Figs. 139, 140, 

 make this subject clearer. Fig. 139 is a longitudinal 

 section of the head, giving a view of the interior of 



1 Loc. cit. See also " The Structure and Action of a Butter- 

 fly's Trunk," Amer, Nat., Vol. XIV., p. 313, 1880. 



