PARTS OF THE MOUTH OF INSECTS. 667 



Fig. 341, a, by the small circles that beset almost their entire 

 area ; their form, which is very peculiar, can here only be made-out 

 by vertical sections ; but in many of the smaller antenna?, such as 

 those of the Bee, the cavities can be seen sideways without any 

 other trouble than that of bleaching the specimen to render it 

 more transparent.* 



519. The next point in the organization of Insects to which the 

 attention of the Microscopist may be directed, is the structure of 

 the Mouth. Here, again, we find almost infinite varieties in the 

 details of conformation; but these may be for the most part 

 reduced to a small number of types or plans, which are charac- 

 teristic of the different orders of Insects. It is among the Coleop- 

 tera, or. Beetles, that we find the several parts of which the mouth 

 is composed in their most distinct form ; for although some of 

 these parts are much more highly developed in other Insects, other 

 parts may be so much altered or so little developed as to be scarcely 

 recognizable. The Coleoptera present the typical conformation of 

 the Mandibulate mouth, which is adapted for the prehension and 

 division of solid substances; and this consists of the following 

 parts: — 1, a pair of Jaws, termed Mandibles, frequently furnished 

 with powerful Teeth, opening laterally on either side of the mouth, 

 and serving as the chief instruments of manducation ; 2, a second 

 pair of Jaws, termed Maxillce, smaller and weaker than the preced- 

 ing, beneath which they are placed, and serving to hold the food, and 

 to convey it to the back of the mouth ; 3, an upper Lip, or Labrum; 

 4, a lower Lip, or Labium; 5, one or two pairs of small jointed 

 appendages termed Palpi, attached to the Maxillae, and hence called 

 Maxillary Palpi ; 6, a pair of Labial Palpi. The labium is often 

 composed of several distinct parts ; its basal portion being dis- 

 tinguished as the Mentum or chin, and its anterior portion being 

 sometimes considerably prolonged forwards, so as to form an organ 

 which is properly designated the Ligula, but which is more com- 

 monly known as the 'Tongue,' though not really entitled to that 

 designation, the real tongue being a soft and projecting organ which 

 forms the floor of the mouth, and which is only found as a distinct 

 part in a comparatively small number of Insects, as the Cricket. — 



* See the Memoir of Dr. Hicks ' On a new Structure in the Antennae of 

 Insects,' in " Trans, of Linn. Soc," Vol. xxii., p. 147 ; and his 'Further 

 Remarks' at p. 383 of the same volume. See also the Memoir of M. 

 Lespes ' Sur l'Appareil Auditif des Insectes,' in "Ann. des Sci. Nat.," 

 Ser. 4, Zool.,Tom. ix., p. 258 ; and that of M. Claparede " Sur les pretendus 

 Organes Auditif s des Coleopteres lamellicornes et autres Insectes,' in 

 "Ann, des Sci. Nat.," Ser. 4, Zool., Tom. x., p. 236. Dr. Hicks lays great 

 stress on the ' bleaching process,' as essential to success in this investiga- 

 tion ; and he gives the following directions for performing it : — Take of 

 Chlorate of Potass a drachm, and of Water a drachm and a half ; mix 

 these in a small wide bottle containing about an ounce ; wait five minutes, 

 and then add about a drachm and a half of strong Hydrochloric Acid. 

 Chlorine is thus slowly developed ; and the mixture will retain its bleach- 

 ing power for some time. 



