468 ARTHEOPODA. 



end of the alimentary tract ; into the mouth empty from one to 

 four pairs of salivary glands (sp) ; at the anus are defensive anal 

 glands with their malodorous secretions of a protective character. 

 The alimentary tract with the other viscera is enveloped in the 

 fat body, a soft mass which contains, besides fat cells and connec- 

 tive tissue, concretions of uric acid. 



The nervous system (fig. 405) has the ventral cord, especially 

 in primitive forms (Apterygota, Archiptera, Orthoptera, fig. 491), 



rtg 



FIQ. 491. Viscera of male cockroach (Perip/cmefa orientalis). (Partly after Huxley.) 

 /-///, segments of thorax and corresponding legs; 1-10, abdominal segments; a, 

 anus; <(/, ventral ganglia; ap, gastric ceeca ; at, antenna; W, salivary bladder; 

 ?/, sexual opening; h, heart; fc\ crop; km, gizzard; /, labial palpus; m, stomach 

 (the arrow shows the connexion between m and km}, also maxillary palpus ; mg, 

 male genitalia ; oe, oesophagus ; oy, brain; 7-, rectum; sp, salivary gland; tg, 

 thoracic ganglia; iig, infracesophageal ganglion ; inn, Malpighian tubules. 



nnd nearly all larvse (fig. 59), long and composed of numerous 

 separate pairs of ganglia. In beetles, moths, bees (fig. 494), and 

 flies the cord is shortened and the ganglia are in part fused. The 

 brain arises by the fusion of three pairs of ganglia (proto-, deuto-, 

 and tritocerebrum), and is, especially in the adult, very complex. 

 It is connected on either side with a large optic ganglion the size 

 of which is correlated to that of the eyes. In the adult condition 

 the Hexapoda have a single pair of highly developed compound eyes 

 {figs. 407, 408), which not infrequently occupy nearly the whole 

 of the top of the head. Between and in front of these small and 

 simple ocelli, usually three in number, frequently occur, especially 

 in insects which are strong fliers. These are either lacking or 

 poorly developed in the larvae, while the compound eyes are fre- 

 quently replaced by groups of from two to six closely crowded 

 ocelli. Of other sense organs only the tactile hairs of the skin are 

 known with certainty, while similar hairs on the antennas and 

 about the mouth are supposed to be organs of smell and taste, since- 

 these senses are known to be well developed. The tympanal 

 organs of the Orthoptera are the only structures which can be with 



