EXTERNAL STRUCTURE OF INSECTS. 31 



different in different orders of insects. It is composed 

 of several pieces, more or less developed, and both 

 these separate pieces and the whole organ have been 

 variously named by various authors. It is generally 

 composed of a basal horny plate, succeeded by a 

 second horny or membranous plate, something like 

 a lip, or by a prolonged fleshy tongue-like organ ; 

 and always bears a pair of palpi, called labial palpi 

 (fig. 5, a a, and 6, //). Sometimes the whole organ 

 is called the labium or lip, sometimes only the second 

 part is so called, the first being called mentum or chin. 

 Sometimes the whole is called " lip," " tongue," " pro- 

 boscis," and so on. In the present work the whole organ 

 will generally be called by the most usual name of 

 labium, while the English words "lip," or "tongue," 

 will be applied according to the form, whether it be, as 

 in beetles, for instance, a lip-like plate, or, as in bees, a 

 fleshy projectile tongue-like instrument. In the dragon- 

 fly and the grasshopper the lining of the lip is free, and 

 forms an internal tongue something like our own. 



In the first five orders of biting insects namely, 

 those which contain the beetles, earwigs, grasshoppers, 

 dragonflies, and caddis-flies,* no important variation 

 occurs in the character of the parts of the mouth as 

 described above. In the sixth order, however, contain- 

 ing the bees and their relations, we come to the first re- 

 markable change in the form of these parts, though they 

 are still to be recognised with ease. The peculiarities 



* The caddis is included in this list for the sake of uniformity, but in 

 fact, these insects, living but a short time in the perfect state, and requir- 

 ing little or no food, have the mouth in a very rudimentary and unde- 

 veloped state. 



