IV. INSECTA: HEXAPODA 



409 



is the gizzard {hn, pv),ox provenlricidus, the chitinous linirg of which is 

 toothed for grinding the food. The true stomach, of entodermal origin 

 {m, cd), freciuently bears blind sacs or gastric caca (ap); in general it is 

 short and its junction with the hinder ectodermal portion, the proctodeum, 

 is marked by the entrance of the Malpighian tubules (vm) . The latter, ex- 

 cretory in function, arise from the proctodeal region. The proctodeum 

 is usually differentiated into a small intestine and a two-regional (colon 

 and rectum) large intestine. The rectum may have enlargements called 

 rectal glands. True glands, however, 

 occur only at the beginning and end of 

 the alimentary tract; from two to four 

 salivary glands {sp) empty into the 

 mouth; at the anus are defensive anal 

 glands wdth malodorous secretions of a 

 protective character. The alimentary 

 tract with the other viscera is enveloped 

 in the fat body, a soft mass which con- 

 tains, besides fat cells and connective 

 tissue, concretions of uric acid. 



The nervous system (fig. 370) has 

 the ventral cord, especially in primiti\'e 

 forms (Apterygota, Archiptera, Ortho- 

 ptera, fig. 449), and nearly all larvie (fig. 

 60), long and composed of numerous 

 separate pairs of ganglia. In beetles, 

 moths, bees (fig. 452), 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 

 colonial species, very complex. It is 

 connected on either side with a large 

 optic ganglion, the size of which is cor- 

 related to that of the eyes. In the adult 

 condition the Hexapoda have a single 

 pair of highly developed compound eyes (fig. 372), (each occasionally 

 divided into two), 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 different from the more numerous 

 simple eyes of the larvte of holometabolous insects (e.g., butterflies and 



Fig. 448. — Alimentary tract of 

 Caralnts aiiratus (from Lang, after 

 Dufour). av, anal vesicle; ad, anal 

 gland; cd, stomach with ca;ca; ed, 

 hind gat; in, ingluvies (crop); k, 

 head; oe, oesophagus; pv, proven- 

 triculus (gizzard); r, rectum; vm, 

 Malpighian tubules. 



