468 



ARTimOPODA. 



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

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

 glands with their malodorous secretions of a jjrotective character. 

 The alimentary tract with the other viscera is enveloped in the 

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

 tive tissue, concretions of uric acid. 



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

 in primitive forms (Apterygota, Archijitera, Orthoptera, fig. 4'Jl), 



m 6g- ilg. Hff. 



Fig. 491. — Viscera of male cockroach {Periplaneta orientals). (Partly after Huxley.) 

 /-///, segments of thorax and corresponding legs; 1-10, abdominal segments: n. 

 anns ; ik], ventral ganglia; a]i, gastric ca^ca : «</, antenna; hi, salivary bladder; 

 r/, sexual opening ; /), heart ; />■' , crop ; km, gizzard ; /, labial palpus ; ni, stomach 

 (the arrow shows the connexion between */( and km ), also maxillary palpus ; >/i!j. 

 male genitalia ; Of, a^sopltagus ; '"/, l>rain ; r, rectum ; ^p, salivary gland ; tij, 

 thoracic ganglia; ng, iiifracesophageal ganglion ; vn, ]Malpighian tubules. 



and nearly all larva? (fig. 50), long and composed -of numerous 

 separtite joairs of ganglia. In beetles, moths, bees (fig. 404). 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 Ilexapoda 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 numljer, frequently occur, especially 

 in insects Avhich are strong fliiers. These are either lacking or 

 poorly devolojjcd in the larva\, while the comiiound eyes are fre- 

 quently replaced liy 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 antenna^ and 

 about the mouth are supposed to 1)0 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 



