1904] McCLEXAHAN-.—RHYNCOPHOROUS COLEOPTERA. 97 



Plate VIII, fig. 10, is a semidiagrammatic optic section of the head of a newly 

 formed pupa of Mononychus, seen from the front. It will be seen that the rostrum 

 is relatively short and broad, narrower in the middle portion than in its apical 

 third. At its tip are the crudely shaped mouth parts. The mandibles as yet show 

 no development of their pharyngeal processes. The hypopharynx is an elongate 

 ridge upon the pharyngeal floor. The salivary glands of the imago are just making 

 their appearance as little sacculated ingrowths from the floor of the mouth. Fig. 

 13 is a section of a similar but slightly older specimen, showing the cellular struc- 

 ture. Here the pharyngeal processes {m) of the mandibles are budding. The 

 upturned salivary gland is cut obliquely off, and the tubular ingrowths that will 

 constitute the adductor (/^) and adductor (/2) tendons of the mandibles are clearly 

 shown. While these are clearly ingrowths of hypodermis, and therefore quite 

 distinct in their nature from the muscle fibres inserted upon them, it is very prob- 

 able that they are being formed in the larva, and are drawn out to great length 

 pari pass uviith the extension of the beak, and maintain throughout their connection 

 with the muscle fibers in the head. The hypodermis of the mandibles and of the 

 adjacent parts of the distal end of the rostrum show the characteristic peaked cells 

 with nuclei settled down 'against the chitin, characteristic of hypodermis generally 

 when its cells have been greatly crowded and thereafter greatly stretched apart. 



Fig. II is an optic section of a somewhat older pupal head. Aside from the 

 progress seen in the development of the antennae (which will be discussed under 

 another heading), several changes are seen : the salivary glands are rapidly extend- 

 ing toward the head, one a little in advance of the other, the beak is increasing in 

 length, and the mandibles are becoming toothed. At this age the tendons, which, 

 as shown in fig. 13, are not tendonous at all, but distinctly cellular in structure, 

 begin to show that wasting away of the cells with the deposition of chitine in the 

 lumen, which will ultimately result in the disappearance of these cells altogether. 



The further progress of the development of the salivary glands will consist in 

 their prolongation backward beneath the esophagus around the sub-esophageal 

 ganglion, and up into the dorsal side of the prothorax, where they become con- 

 voluted, as seen in Plate IX, fig. 14. Figs. 16 and 17 of Plate IX are cross sections 

 of the beak in pupa and imago respectively, but taken at different levels. In fig. 

 16 the tendons have much the same appearance as the glands ; but in fig. 17 the 

 tendon that is to be, shows no cavity, but instead a central chitinous rod surrounded 

 by a thin peripheral layer of cells. The salivary glands, on the other hand, are dis- 

 tinctly glandular in both stages but distinctly more slender in the imago than in the 

 pupa, owing doubtless to their stretching out. There is another kindred structure 

 seen here also. The beak is penetrated by two tracheae which enter from the ven- 

 tral side of the prothorax as shown in figure 14, pass to the dorsal side at the base of 



