The proboscis of the Bee is therefore more like a case of instruments than a single organ. The mandibles form a strong pair of blunt scissors. The maxillæ are used for piercing, for stiffening and protecting the base of the tongue, and when closed they form an imperfect tube outside the tongue, which, according to Hermann Müller, is probably suctorial. The labial palps are protective and sensory. Lastly, the central part, or tongue, is a split tube used for suction; it is very long, so as to penetrate deep flower-cups, and hairy, so that pollen may stick to it. When the proboscis is not in use it can be slid into the mentum (_M_), while it and the mentum together can be drawn out of the way downwards and backwards.[60] [60] An interesting account of the structure and mode of action of the Bee’s tongue is to be found in Hermann Müller’s Fertilisation of Flowers, where also the evolution of the parts is traced through a series of graduated types. [Illustration: Fig. 23.--Mouth-parts of Honey Bee.] [Illustration: Fig. 23A.--Diagram of Mouth-parts of Honey Bee.] [Illustration: Fig. 24.--Mouth-parts of Burnet Moth.] [Illustration: Fig. 24A.--Diagram of Mouth-parts of Moth.] In the singular suctorial mouth of Moths and Butterflies we observe, first of all, the great development of the maxillæ. Each forms a half-tube, which can be accurately applied to its fellow, so as to form an efficient siphon. In many species the two halves can be held together by a multitude of minute hooks.[61] At the base of each maxilla is a rudimentary palp (_Mxp_). The mandibles (_Mn_) are also rudimentary and perfectly useless. The labium, which was so important to the larva as a spinneret, has disappeared almost completely, but the labial palps (_Lp_) are large and evidently important. [61] See Newport’s figure of Vanessa atalanta (Todd’s Cyc., Art. Insecta), or Burgess on the Anatomy of the Milk-weed Butterfly, in Anniversary Mem. of Boston Soc. Nat. Hist., pl. ii., figs. 8–10 (1880). [Illustration: Fig. 25.--Mouth-parts of Gad-fly (_Tabanus_).] [Illustration: Fig. 25A.--Diagram of Mouth-parts of Gad-fly.]