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 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, 



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Fio. 4!>s. Cockroach. View of Fig. 499.— Cockroach. General view of the 



the arrangement of the principal 

 trunks of the tracheal system. 

 (After Miall and Denny.) 



nervous system, aba"*, sixth abdominal gang- 

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

 oesophageal connective ; inf. sub-oesophageal 

 ganglion ; opt. optic nerve ; thor* thorp thorp 

 first, second, and third thoracic ganglia. 

 (After Miall and Denny. f~. 



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 deferentia, lead to the vesicuku 

 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 ejaculatory duct {duct, ej.), an un- 



