184 THE BIOLOGY OF THE ANIMAL 



many in the rest of the thorax? How many in 

 the abdomen ? Compare them with those in the 

 thorax. 



Eemove all of the muscles and digestive organs 

 from the thorax and abdomen. 



I. The Nervous System. 



The principal parts of this system are the fol- 

 lowing : 



Lying on top of the oesophagus, between the 

 compound eyes, find 



1. The supra-cesoph.ageal ganglion or "brain." 



— What is its shape 1 Size ? Color ? Compare 

 with the " brain " of the lobster. 



Running from the " brain " to the eyes are 



2. The optic nerves. — What is their shape ? 



Length ? 

 Lying below the oesophagus look for 



3. The infra-oesophageal ganglion — How con- 



nected to the supra - oesophageal ganglion? 

 What is its shape ? Size ? 

 On the side of the crop are 



4. The gastric ganglia. — What is their shape? 



Size as compared with the supra- oesophageal 

 ganglion ? 



Lying on the floor of the thorax are 



5. The thoracic ganglia. — How many are there ? 



How are they connected ? What is their shape ? 

 How do they compare with the " brain " in size ? 

 Lying on the floor of the abdomen are 



6. The abdominal ganglia. — How many are 



there ? How does their number compare with 

 that of the abdominal segments ? How are 

 they connected? In what segments do they 



