...........GENERAL ZOOLOGY 



over an inch) in length, and resemble each other so closely 

 that the following description will apply nearly as well to 

 one as to another. 



External Plan of Structure. The body is made up of a 

 series of rings, called somites (Fig. 2), externally hardened by 

 a horny substance, chitin, for protection of the interior organs. 

 The somites are grouped in three clearly marked regions, 

 the head, thorax, and abdomen (Fig. 2, 1, 2-4, 5). While the 

 characteristic appearance of a ring is clearer in the abdo- 

 men than elsewhere, it is nevertheless true that the head and 

 thorax are made up of several somites, much altered and 

 pressed together. The head probably consists of at least five 

 somites, of which four bear appendages, the feelers, or anten- 

 na? (Fig. 2, 0); the jaws, or mandibles (Fig. 1, 2; Fig. 2, 8); 

 the first maxilla? (Fig. 1, 4) ; and the second maxilla* (Fig. 1, 5). 

 The thorax plainly consists of three somites, on each of which 

 is borne a pair of legs (Fig. 2, 14, 15, 10). Ten somites can with- 

 out much difficulty be distinguished in the abdomen (Fig. 2, 5). 

 The external plan upon which the locust is built is thus seen 

 to be a series of somites, of which the anterior (front) somites 

 bear jointed appendages modified for various uses. 



The Head. The short, several-jointed antennas are organs 

 of touch and of smell, and, in most insects, of hearing as well. 

 The maxillas are constructed on the plan of jaws, though 

 fitted for guiding and holding food rather than for crush- 

 ing it. Each maxilla bears a short, several-jointed " feeler," 

 or palpus (Fig. 1, 4, 5 ; Fig. 2, 9, 11). The anterior boundary of 

 the mouth is a flap-like piece, the upper lip, or labrum (Fig. 1, 1; 

 Fig. 2, 7) ; and the posterior (hind) boundary is made by the 

 union of the bases of the second maxilla (Fig. 1, 5), forming 

 a flap called the lower lip, or labium (Fig. 2, 10). 



On the sides of the head are large, oval, compound eyes 

 (Fig. 2, 12), composed externally of a number of transparent 

 divisions, facets, each of which has beneath it the necessary 



