72 GENERAL BIOLOGY. 



Y. Endophragmal System. 



Calcified projections from the inner side of 

 the exoskeleton of the ventral surface of the 

 thorax form an internal skeleton the endo- 

 pliragmal skeleton, which arches over a canal 

 the sternal canal. 

 To see the endophragmal system remove the thoracic 



viscera and the muscles ventral to them. 

 YI. Nervous System. 



Cut through the endophragmal system at each side 

 of the median line, thus exposing the thoracic 

 part of: 



The central nervous system, which runs the 

 whole length of the body, in the median line, 

 consisting of : 



1. The supraoesophageal or cerebral ganglia, 



dorsal to the oesophagus. Each ganglion 

 gives off nerves to the eye, to the anten- 

 nule, and to the antenna of its own side. 



2. The circumoesophageal commissure passing 



posteriorly and ventrally from the cerebral 

 ganglia around the oesophagus to the first 

 pair of : 



3. The thoracic ganglia : six pairs united by 



longitudinal commissures. 

 Follow the commissures passing posteriorly 

 from the posterior pair of thoracic ganglia, 

 and find in the abdomen : 



