610 



ZOOLOGY 



SECT. 



complete oxygenation which the functional activity of the Insect 

 requires. 



The nervous system consists of a brain (Fig. 502, brn., and 

 506, br.), a sub-cesophageal pair of ganglia (infr. gang.), three thoracic 

 (Fig. 506, thor. 1, #, and 3) and six abdominal pairs of ganglia (the 

 members of each pair being united), a system of connectives uniting 

 the ganglia together, and a series of nerves given off to the various 

 parts of the body. The brain consists of a bilobed mass of nerve- 

 matter situated in the head, and divisible into two parts, anterior 

 and posterior. From the anterior part is given off on each side the 



FIG. 504. Portion of a trachea of a 

 Caterpillar. B, C, D, branches ; a, 

 cellular layer ; b, nuclei. (From Gegen- 

 baur.) 



Fia. 505. Cockroach. View of 

 the arrangement of the principal 

 trunks of the tracheal system. 

 (After Miall and Denny.) 



optic nerve passing to the eye to become expanded into an optic 

 ganglion, and from the posterior part the nerves to the antennae. 

 It is supported by a chitinous framework the tentorium. From 

 the brain there run backwards a pair of oesophageal connectives 

 (conn.), passing, one on each side of the oesophagus, downwards 

 and backwards to the sub-cesophageal ganglia. The latter, which 

 are situated between the submentum and oesophagus, give off a 

 pair of connectives, passing backwards to the first thoracic ganglia. 

 From the sub-cesophageal ganglia are given off the nerves to the 

 labrum, the mandibles, and both pairs of maxillae. The three 

 airs of thoracic and six of abdominal ganglia are connected together 



