230 



HARDWICKE'S SCIENCE-GOSSIP. 



The mouth of the great Stag Beetle will serve the 

 beginner as an excellent starting-point, because the 

 different organs are not only distinct, but they are 

 comparatively very large, and may all be identified 

 ■with an ordinary magnil'ying-glass, or even with the 

 naked eye. When possible, it is always well to 

 compai'e microscopic structures with those which 

 are similar, and require no optical aid. Unfortunately 

 this can seldom be done ; but in the case before us 

 no difficulty will occur in doing it. 



Kigr. 143. A portion of the Mouth of a Stag Beetle, seen from 

 above : the left mandible and tiie labrum are removed to 

 show the labium. The references as in fig-. 144. 



If a longitudinal section be made vertically 

 through the middle line of the head, each lateral 

 half will exhibit the following parts. (These are 

 seen in fig. 144.) 



Fig. 144. A vertical section of the Mouth of a Stag' Beetle 

 (Lnc'inus cerviis), with a portion of the mandible, md, re- 

 moved : nix', maxilla ; /, ligula ; lb, labium ; m, raeiitum ; 

 M, mouth-cavity; Ir, labrum ; rnx", paraglossa; /), palpus. 



The upper and lower lips (/;• and lb) bound the 

 moutli, M, above and below. Tlie upper lip, or 

 labrum {Ir), is exceedingly simple, and forms a 



mere horny cover above the mouth : it is seen to be 

 hollow and immovable. 



The lower lip is more complex ; its structure will 

 be understood, however, by the comparison of figs. 

 143 and 144. It consists of a broad plate, m, called 

 the mentum or chin : the mentum is similar to the 

 labrum, but smaller. Above this the tongue or ligula, 

 I, is seen, an insignificant organ in the Beetle, but 

 one which attains the most marvellous development 

 in the Bee. On either side of the ligula is a jointed 

 and feathered appendage, the paraglossa, or tongue- 

 sheath, m.v". The whole of these structures are 

 usually included under the term labium, although 

 the term is sometimes used for the paraglossse, 

 or tongue-iheaths, alone. 



Fig. 145. The Mandible of a Predatory Beetle. 



r The great mandibles, md, or horns, as they are 

 frequently called, flank the mouth. These are 

 organs of preiiension in many insects, in others they 

 are used for bruising or gnawing. The Stag Beetle, 

 for instance, bruises the bark of the young trees on 

 which it feeds with these jaws or mandibles, and 

 laps up the juice which exudes with its paraglossse, 

 or tongue-sheaths, mx", as well as with a second pair 

 of jointed fringed spoonlike organs, ma.-', which are 

 placed at the sides of the floor of the mouth to 

 which they are hinged. They are called maxillse, or 

 jaws, and have a lateral motion, like the mandibles. 



Fig. 146. Young Embryo of a Crayfish— references as above. 

 p', p", &.C., foot-jaws and legs. 



' It will be observed that all the; lateral or paired 

 organs have a horizontal plane of motion, and 

 this is extremely characteristic of the jaws of 

 insects, and, indeed, of all the Articulata, or those 



