32 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



oval nuclei ; the cytoplasm ftn*ms a close network, the interspaces of 

 which contain a clear substance. 



The transition is abrupt between the gland and the duct, which ends 

 blindly (Fig. 35, dt.). The end of the duct, however, is provided with 

 many pores, which facilitate the passage of secreted fluid throuoh the 

 thick, chitinous wall of the duct. The mouth of the duct is distinctly 

 marked by ectodermal pigment, which is reflected from the wall of the 

 buccal cavity and lines the lumen of the duct for a considerable dis- 

 tance (Fig. 31, hi.). 



The pivot of the mandible (cdx.), resting in its stirrup, abuts against 

 the gland, as shown in Figure 35. This leads me to think that the lubri- 

 cation of the pivot may possibly be an incidental function of the gland. 



This pair of glands evidently corresponds to a pair described for Smyn- 

 thurus by Willem et Sabbe ('97, p. 132), who state, however, that " Les 

 conduits excreteurs des differentes cellules d'un meme cote se reunissent 

 en un canal collecteur qui, de la base de la mandibule, descend oblique- 

 ment pour se terminer dans la partie superieure de la cavite buccale, 

 dans Tangle forme par la mandibule et l'bypopharynx." In Qrchesella, 

 the gland cannot be said to open in the same place. 



Regarding the possibility of the existence of a lingual gland, I may 

 say that the base of the glossa is lined with epithelial cells which are 

 unusually large and contain large oval nuclei (Plate 1, Fig. 3). There 

 is apparently a median opening, or at least a very thin place on the 

 upper wall of the glossa (Plate 3, Fig. 23, and Plate 4, Fig. 28, of.), but 

 I have not been able to trace its relation to underlying tissues on account 

 of the extreme delicacy and brittleness of the glossa, resulting in una- 

 voidable distortions in the process, of sectioning. On the other hand, 

 the central cavity of the glossa is undoubtedly a part of the general 

 body cavity, so that the evidence in favor of the tongue being glandular 

 is at most very slight. 



The Physiology of the Mouth-Parts. 



Almost complete ignorance of the physiology of the mouth-parts has 

 been but the natural consequence of an incomplete knowledge. of their 

 anatomy. Obviously, very little can be learned by direct observation 

 or experiment ; much may be inferred, however, from the structure and 

 relations of the organs. I have already described the action of the mus- 

 cles which are concerned, and may now briefly trace the history of the 

 food until the stomach is reached. 



