NERVOUS SYSTEM. 155 



zygooardiacs inwards, and bringing the lateral 

 teeth together in the median plane. 



Pull the cardiac and pyloric ossicles forwards and back- 

 tvards respectively tvith forceps, when the three teeth will be 

 seen to come together. 



D. The Excretory System. 



1. The kidneys, or 'green glands,' are a pair of rounded 



and somewhat flattened bodies, of a light green 

 colour, lying in the ventral part of the head, in front 

 of the mouth, 



2. The ureters are a pair of wide thin-walled sacs, lying 



one on the dorsal surface of each kidney. Each 

 ureter communicates directly with the cavity of its 

 kidney, and opens to the exterior by an aperture 

 already seen on the hinder surface of a tubercle on 

 the basal segment of the antenna. 



Inflate the ureter by hloiuing air in at its external aper- 

 ture. 



E. The Endopbragmal Skeleton. (Fig. 85, p. 148.) 



In the thorax a series of calcified plates project inwards 

 from the cuticle of the ventral surface, forming an internal 

 skeleton, which gives origin to the muscles of the legs and to 

 the powerful flexor muscles of the abdomen. 



F. The ITervous System. 



1. The central nervous system consists of a series of 

 ganglia arranged in pairs, and united by paired 

 bundles of nerve-fibres, or connectives, to form a 

 chain, which runs along the whole length of the 

 body close to the mid- ventral line. The two ganglia 

 of each pair are usually fused indistinguishably. 



a. The pre-oesophageal ganglionic mass, or ' brain,' is 

 a white mass of considerable size, situated just 

 behind and slightly above the bases of the anten- 



