NO. 4 FEEDING MECHANISM OF LEPIDOPTERA SCHMITT 



25 



In the yucca moth, Pronuha yuccasella, there is a small paired fleshy 

 lobe at the distal end of the labium. The Oriental fruit moth, Grapho- 

 litha inolesta, also has a pair of minute lobes at the tip of the labium, 

 but it is improbable that these lobes have any significance. 



The labium of many moths and butterflies possesses a strong ventral 

 ridge at the distal end (figs. 11 A and 9 C, Keel). A possible function 

 of this ridge is to serve as a bearing surface for the proboscis base. 



c^? sp ji^j,^^ 



Fig. 12. — Various structural details of the head. 



A, head of Danaus menippe, as seen with dorsal wall removed. B, labium and 

 basal part of maxillae, ventral view, of Heviaris thysbe. C, labial palpus mus- 

 culature of Papiiio glauctis. D, same of Danaus menippe. E, same of Pieris 

 rapae. 



The musculature of the labium is limited to the palpi muscles. Ber- 

 lese and Burgess have figured palpus muscles arising on the tentorium, 

 but apparently did so by mistaking proboscis extensors for palpi 

 muscles. In every moth and butterfly examined by the writer there 

 were never more than two pairs of palpus muscles, and these arise 

 either on the labium itself or on the hypostomal bridge. The articula- 

 tion of the labial palpus with the head is so formed that little or no 

 blood passes out into the palpus. If the palpus of a live butterfly is 

 snipped off, it will be found that the walls of both the first and the 

 second joints are barely moist inside. This, of course, greatly lightens 

 the palpi. 



