1904] McCLENAHAN:—RHYNCOPHOROUS COLEOPTERA. 99 



within the cavity. With the beginning of metamorphosis, and the disintegration 

 of larval fat providing material for growth, and the loosening of the larval 

 cuticle allowing room for expansion, the antenna rapidly extends itself, and the 

 transi'erse wrinkling begins. Fig. 7 is from a section of the antenna of a larva in 

 an early stage of metamorphosis. The hypodermis still appears composed of 

 closely crowded elongate and compressed cells with elongate nuclei filled with 

 chromatin granules, the cell layer being thickest at the distal end. It shows 

 within more abundant fat and leucocytes, a better development of the neuroblastic 

 layer, and the beginning of the development of muscle fibres. Fig. 8 is from 

 an older larva, nearer the time of pupation, and shows the same features through- 

 out, a little better developed. Fig. 9 is from a section of the club after the 

 extension that takes place when the larval skin is cast. It shows at once the tran- 

 sition in form of the cells of the hypodermis to the peaked type, with the nucleus 

 settled down upon the chitin layer and a long internal process reaching the base- 

 ment membrane — a type entirely characteristic of such conditions of crowding 

 and subsequent extension,^ best exemplified here at the place where the extension 

 has been greatest as in the segment at the base of the club. 



The neuroblastic layer here is still better developed, and the segmentation of 

 the club is still very distinct. The further development of the antenna consists in 

 the elongation of the scape, the better differentiation of the segments of the pedicel, 

 the consolidation of those of the club, the perfecting of the articulations, and the 

 development of the abundant sense organs which are presumably associated with 

 the neuroblastic lining cell layer. 



The Question of Homologies. 



What has become of the gula, so constant in normal coleoptera ? What has 

 become of the labrum ? What are the limits of the lateral sclerites of the head ? 

 These questions have grown out of the fact that in the adult distinct sclerites are 

 not discoverable ; and the evidence derived from the development of these parts has 

 not proved as clear and complete as might have been wished. Several features of 

 the newly formed beak already alluded to (Plate VIII, fig. 10), seem to bear upon 

 these questions. The constriction at about two thirds its length marking as it does 

 internally the transition from pharynx to esophagus, probably marks also externally 

 the proper base of the mouth parts, the junction of labrum and clypeus above and of 

 labium and gula below: that is, this dilated front end probably corresponds with 

 the periphery of the mouth opening in other coleoptera. At this level there begins 



' See on the mechanics of this process, Comstock and Needham, Amer. Nat., vol. XXXIII, pp. 856-857. 



