26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



The palpus musculature of Danaus menippe is illustrated in figure 

 12 D. Each palpus is supplied with two muscles, a levator {Iplp) and 

 a depressor (dplp). Nymphalidae usually have a pair of muscles for 

 each palpus, although the depressor is often very weak. In the Papili- 

 onidae and the Pieridae there is no depressor muscle, but the levator 

 is always well developed (fig. 12 C, E). In this case the levator arises 

 either on the sclerotized median plate (MP) of the labium, or on the 

 hypostomal bridge. 



The presence or absence of labial palpus muscles is extremely 

 variable in the other families. Pronuha yuccasella has no palpus 

 muscles, nor does an Agonopterix sp. Each palpus of Galleria inel- 

 lonella has a single large muscle. Geometridae show only a single 

 palpus muscle or none at all. In the Arctiidae there is only a single 

 muscle, usually arising on the hypostomal bridge. Sphingidae have 

 either one or two pairs of palpus muscles, commonly only one. Satur- 

 niids and other extremely degenerate groups usually lack any palpus 

 musculature, and the trembling motion of the palpi sometimes seen in 

 this family is usually caused by the remnants of the proboscis exten- 

 sors. However, BasUona imperaUs has a single muscle in each palpus, 

 as does also Malacosoma americana. 



V. SUMMARY 



1. The coiled proboscis of Lepidoptera is extended by means of 

 blood pressure created in the stipes of each maxilla. This pressure is 

 caused by three pairs of muscles, which by their contraction press the 

 stipes against the head wall. Two pairs of these muscles arise on the 

 anterior arms of the tentorium and the third pair arises on the gena. 



2. The sucking pump is a compound organ, derived from the 

 pharynx, the buccal cavity, and the cibarium. This is evidenced by 

 these facts : ( i ) true pharyngeal dilators are inserted only in the 

 posterior part of the pump; (2) muscles homologous with the com- 

 pressors of the labrum are present in some Lepidoptera; and (3) the 

 dorsal salivarium muscles arise on the pump floor, showing that the 

 hypopharynx forms at least the anterior part of the floor. 



3. There is no labial musculature except that of the palpi. There 

 are generally two pairs of palpus muscles, but in many families only 

 one pair, or none at all, may be found. 



4. The area posterior to the labial palpi is bounded by the hypos- 

 toma, the hypostomal ridge offering an insertion for the ventral inter- 

 segmental muscles. A hypostomal bridge is sometimes present. 



5. The anterior arms of the tentorium are well developed but lack 

 dorsal arms. The posterior tentorial bridge is short and weak. The 



