PHYLUM ARTHROPODA 



627 



in the sixth segment of the abdomen {abd!^), 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 oesophageal connectives by two nerves, which 

 join above the oesophagus to form a median /row^a^ ganglion. 



The organs of special sense are the eyes, the antennaj, 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 antennas and palpi. 



\0 ^T <^&f.f 



Ilur1 



l/wr.2 



Fig. 498.— Cockroach. View of Pm. 499.— Cockroach. General view of the 



the arrangement of the principal 

 ti-Liuks of the tracheal system, 

 (After Miall and Denny.) 



nervous system, ahd^, sixth ahdominal gang- 

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

 cesophageal connective ; inf. sub-cesophageal 

 ganglion ; opt. optic nerve ; tlior,'^ thor,^ iliorfi 

 first, second, and third thoracic ganglia. 

 (After Miall and Denny.) 



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

 certain setse 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 deferentia, lead to the vesic^olce 

 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 ejaeulatory duct (duct, ej.), an un- 



