PHYLUM ARTHROPOD A 



627 



in the sixth segment of the abdomen (aid 6 ), are larger than the 

 others, and supply the segments behind. A visceral nervous system, 

 ramifying on the anterior part of the alimentary canal, is con- 

 nected with the two cesophageal connectives by two nerves, which 

 join above the oesophagus to form a median frontal ganglion. 



The organs of special sense are the eyes, the antennae, and 

 the palpi. The eyes are compound each being made up of a 

 large number of simple elements similar to those that go to 

 make up the eye of Apus (see p. 537). The antennae and palpi, 



FIG. 498. Cockroach. View of 

 the arrangement of the principal 

 trunks of the tracheal system. 

 (After Miall and Denny.) 



FIG. 499. Cockroach. General view of the 

 nervous system, abd*, sixth abdominal gang- 

 lion ; ant. antennary nerve ; br. brain ; conn. 

 cesophageal connective ; inf. sub-cesophageal 

 ganglion ; opt. optic nerve ; thor,* thor, z thor,3 

 first, second, and third thoracic ganglia. 

 (After Miall and Denny.) 



together with the anal cerci, act as organs of touch. In addition, 

 certain setae on the antennae appear to have an olfactory function. 



Reproductive organs. In the male the testes (Fig. 500, test.), 

 are a pair of small bodies which lie in the fourth and fifth seg- 

 ments of the abdomen immediately below the terga. From these 

 a pair of delicate tubes, the vasa defercntia, lead to the mswidce 

 seminales, two tufts of whitish caeca, which together constitute 

 what is known as the " mushroom-shaped gland '' ; these open 

 into the anterior end of the ejacidatory duct (duct, ej.), an un- 



