XI 



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 antennae It is supported by 

 a chitinous framework the tentorium. From the brain there run 

 backwards a pair of cesophagcal 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-oesophageal 

 ganglia are given off the nerves to the labrum, the mandibles, 

 and both pairs of -maxilla?. 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 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 antenna?, 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 antennas and palpi, 

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

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



Reproductive organs. In the male the tcstes (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 



Fio. 4i;-j. Periplaneta. Male 

 reproductive organs, lateral 

 view, ili'cf. <:j. cluctus ejacula- 

 torius with mushroom-shaped 

 gland ; slern. 7, sternum of 

 seventh segment of abdomen ; 

 ti i'ii. 7, terguni of the same 

 segment ; f< at. testis. (After 

 M lull and Denny.) 



coll. (if Id 



Fie. 403. Periplaneta. Female re- 

 productive organs, i-nii.ijlii. colleterial 



glands ; od. oviducts ; or. ovaries. 

 (After Miall and Denny.) 



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

 scminalcs, two tufts of whitish caeca, which together constitute 

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



P P 2 



