PHYLUM ARTHROPODA 



579 



head, and divisible into two parts, anterior and posterior. From 

 the anterior part is given off on each side the optic nerve passing 

 to the eye to become expanded into an optic ganglion, and from 

 the posterior part the nerve to the antenna?. It is supported by 

 a chitinous framework the tentorium. From the brain there run 

 backwards a pair of cesophageal connectives (conn.), passing, one on 

 each side of the oesophagus, downwards and backwards to the sub- 

 oesophageal 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 paired thoracic and six 

 abdominal ganglia are connected together into a chain by a series 

 of double connectives ; the last pair of abdominal ganglia, situated 

 in the sixth segment of the abdomen, are larger than the others, 

 and supply the segments behind. A visceral nervous system, rami- 

 fying on the anterior part of the alimentary canal, is connected 

 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 the Crayfish (see p. 513). ^ The antennae and palpi, 

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

 certain setaa on the antennae appear to hg,ye an olfactory function. 



Reproductive organs. In the male'the testes (Fig. 462, tst.), 

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

 ments of the abdomen immediately below the terga. From these 



stern? \ 



Fi<;. 4ic>. Periplaneta. Male 

 reproductive organs, lateral 

 view. duct. ej. ductus ejacula- 

 torius with mushroom-shaped 

 gland ; stern. 7, sternum of 

 seventh segment of abdomen ; 

 f< /</. 7, tergum of the same 

 segment ; test, testis. (After 

 Miall and Denny.) 



Fit;. 4(53. Periplaneta. Female re- 

 productive organs, coll. gld. colleterial 

 glands ; od. oviducts ; or. ovaries. 

 (After Miall and Denny.) 



a pair of delicate tubes, the vasa deferentia, lead to the vesiculce 

 seminales, two tufts of whitish casca, which together constitute 

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



p p 2 



