164 THE COCKROACH 



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 or magenta, and note the nuclei of the 

 cells. 



Remove 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. 



D. The Nervous System. 



The nervous system consists of supra-oesophageal and 

 infra-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. 

 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. 



Hemove the clypeus and the anterior portion of the epi- 

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

 care not to injure the ganglia, which lie close beneath the 

 clypeus. Carefully expose and clean the following structures, 

 avoiding injury to the cephalic portion of the visceral nervous 

 system. 



a, The supra-03sophageal, or 'cerebral,' ganglia are 

 a pair of large closely apposed ganglia close to 

 the anterior surface of the head. 



i. The * hemispheres ' are the large rounded upper 



part 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 arise the 



antennary nerves. 



