EESPIEATOEY AND NERVOUS SYSTEMS 165 



b. The cells which form the organised wall of the 

 tube, and secrete the chitinous lining, are thin 

 and not easily seen till stained. 



Stain with carmine, and note the nuclei of the cells. 



Bemove small portions of muscle from the leg, of the fat- 

 body, of the salivary gland, etc., and note and examine the 

 fine tracheal tubes ramifying through them. Stain as above. 



t). The Nervous System. 



The nervous system consists of supra-oesophageal and 

 sub-cesophageal ganglia, and para-oesophageal connectives in 

 the head ; a double ventral chain in the thorax and abdomen ; 

 and a visceral nervous system in relation with the alimentary 

 canal. (Fig. 38, p. 160.) 



1. The cephalic nervous system. 



If the buccal cavity has already been exposed, a second 

 specimen will probably be necessary for the dissection of the 

 nervous system of the head. 



Fix the head, with the anterior surface upwards, by means 

 of a fine pin through the upper part of the epicranium and 

 another between the mandibles. 



Bemove the clypeus and the anterior portion of the epi- 

 cranium with scissors or the point of a scalpel, taking care 

 not to injure the ganglia, which lie close beneath the cly- 

 peus. Carefully expose and clean the following structures, 

 avoiding injury to the cephalic portion of the visceral nervous 

 system. 



a. The supra-oesophageal, or ' cerebral,' ganglia are 

 a pair of large closely apposed ganglia close to 

 the anterior surface of the head. They are sup- 

 ported by an internal chitinous framework, the 

 tentorium, 

 i. The ' hemispheres ' are the large romided upper 

 parts of the ganglia. From them arise the 

 large optic nerves, 

 ii. The antennary lobes are the smaller and lower 

 portions of the ganglia. From them the an- 

 tennary nerves arise. 



