94 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



wanting- structures. The muscular base is short and abruptly con- 

 stricted, and from this point to the tip the mandible continues as a 

 slender, strono"h^ chitinized spine having a very sharp point. This 

 structure is capable of protrusion for only about one-fourth of its 

 length, and therefore appears to be used onl}^ for piercing the outer, 

 tougher tissues of plants. The mandible in the Tubulifera is decidedly 

 shorter and more bent than is that in the Terebrantia, 



Maxillary lohes. — This pair of piercing organs has been considered 

 by the majority of writers as the mandibles, but such they surely are 

 not. Dissection shows that they are attached by a movable joint to 

 the bases of the maxilltB. Each lobe is composed of two parts: A short 

 basal, muscular arm or lever attached to the maxilla, and at the other 

 end united to the enlarged, muscular base of the spine which is very 

 slender and strongly chitinized. These spines are longer and more 

 slender than the mandible and are developed alike on each side. When 

 retracted into the mouth, the basal arm or lever extends obliquely for- 

 ward so that the lever forms an acute angle with the spine, which then 

 reaches just to the mouth, but when protruded the lever is brought 

 down toward the mouth so as to straighten this joint, and the spine is 

 thus thrust out from the mouth opening to a considerable distance. 

 As these spines are more slender and protrude farther from the mouth 

 than does the mandible, it appears probable that the latter is used to 

 start the puncture through the hard, tough outer tissues, while the 

 weaker lobes of the maxilla?, penetrating deeper through this opening, 

 reach into the inner tissues. Some writers have stated that the three 

 spines are hollow and used as suction tubes, but I have not found this 

 to be the case in the species examined. 



There is a marked difference in length of the maxillary lobes in the 

 two suborders. In the Tubulifera they are extremely long, and when 

 retracted curve far forward under the eyes, while in the Terebrantia 

 the bend of the lobes scarcely reaches beyond the transverse thickening. 

 In the Tubulifera these lobes are altogether longer than the entire head 

 and can be protruded in many species as far as the hind edge of the 

 mesosternum. 



Other mouth structures. — Attached to the inner surface of the labium 

 are certain other chitinized structures hard to describe and of uncer- 

 tain homology, but considered bj" some as an hypopharjmx. 



Larvse. — The mouth parts of the larva are much the same as those 

 of the adult, though weaker and less strongly chitinized. The chitin 

 of these structures is shed at each molt, and may then be seen con- 

 nected with the cast-off skin. 



Movements of mouth parts. — The parts forming the external wall of 

 the mouth cone are not free, being united by a membranous connection 

 along their sides. At the tip of the cone there is a small opening. It 

 thus appears that structurally these insects are incapable of biting or 



