There remains for consideration the most remarkable part of the proboscis, the long, delicate, hairy organ which the bee thrusts out from the tip of the shining tube formed by the labial palps and the maxillae, described above, and which looks like a prolongation of the mentum. This organ is variously called ligula, lingua, or tongue.[13] We prefer the first of these names. According to Breithaupt and Cheshire the structure of the ligula is highly remarkable; it is a tube (filled with fluid from the body cavity), and with a groove underneath caused by a large part of the circumference of the tube being invaginated; the {16}invaginated part can be thrust out by increase of the pressure of the fluid in the tube. A portion of the wall of the invaginate part is thickened so as to form a chitinous rod. This description will suffice for present purposes, as the other parts of the mouth will be readily recognised by the aid of figure 9, A, B, C. In the exquisitely endowed South American genus _Euglossa_ (Fig. 18), the proboscis is somewhat longer than the whole of the body, so that its tip in repose projects behind the body like a sting. [Illustration: Fig. 8.—Transverse section of ligula of honey-bee, diagramatic. A, With the long sac invaginate. B, evaginate: _a_, chitinous envelope with the bases of the hairs; _b_, rod; _c_, groove of rod; _d_, lumen due in A to invagination of the rod, in B to its evagination; _n_, nerve; _tr_, trachea.] The correct nomenclature of the parts connected with the lower lip is not definitely settled, authorities not being agreed on several points. The whole of the proboscis is usually called the tongue; this, however, is admittedly an erroneous application of this term. The terminal delicate, elongate, flexible organ is by some called the tongue; but this again is wrong: the lingua in Insects is the hypopharynx; this part is developed in a peculiar manner in bees, but as it is not tongue-like in shape, the term lingua is not suitable for it, and should be dismissed altogether from the nomenclature of the bee's trophi; it is used at present in two different senses, both of which are erroneous. We see no objection to describing the flexible apical portion of the proboscis as the ligula. The lorum is probably a special part peculiar to the higher bees; according to Saunders it is not present as a specialised part in some of the primitive forms.[14] The application of the terms mentum, submentum and hypoglottis is open to the same doubts that exist with regard to them in so many other {17}Insects, and we have omitted the term hypoglottis altogether, though some may think the mentum entitled to that name.