TONGUE AND MOUTH PARTS. gi 



some special sense, which Wolff concludes to be 

 smell — an opinion in which I cannot agree, for 

 reasons given hereafter. The under side of the 

 mouth-opening {mo, Fig. 18) is formed by the labium, 

 or under lip {lb), which is seen to embrace a number 

 of parts, carried by its basal portion, or mentum {nit, 

 Fig. 18, or B, Plate III.). The mentum lies beneath the 

 head, and somewhat behind it, and can, within con- 

 siderable limits, be moved backwards and forwards. 

 It is strongly chitinous below, is articulated to the 

 heid by means of the sub-mentum, or lora {lo, Fig. iS, 

 01 /, B, Plate HI.), and contains the muscles {a, a, rb, 

 B Plate III.), which can draw the tongue, or ligula, 

 partly back into it, and also conveys the salivary duct 

 {sd, Fig. 1 8), which opens by a valve {sv) at the base 

 of the ligula. Otherwise the mentum has no opening, 

 is filled with blood, has nothing to do with the 

 oesophagus, or swallow, and is, of course, not tubular, 

 as Cook states. The ligula is not a continuation of 

 the mentum in front, but has its roots within the 

 latter, from which it is withdrawn by the action of 

 a muscle (the protractor lingua?), when the tongue 

 is outstretched for sucking. Attached to the mentum 

 at its front margin, and possessing at this point a 

 hinge joint, we have on each side of the ligula a 

 labial palpus {lp, Fig. 18 and Plate II.). It consists 

 of four joints, the two upper being large, the two 

 lower very small, and provided with elaborately 

 contrived feeling hairs. Outside these we find the 

 maxillae {mx, Fig. 18, and Plates II. and III.), attached 

 to the sub - mentum (the right maxilla has been 

 removed in Fig. 18), and having a chitinous portion 



