108 THE FRESH- WATER CRAYFISH— THE CAPE CRAWFISH 



and the walking legs. The ganglia are connected by a double nerve cord. 

 There are six pairs of free thoracic ganglia, each pair being incompletely fused. 

 Between the fourth and fifth thoracic ganglia the double nerve cord 

 separated to form a loop through which the sternal artery passes. 



IS 



Optic nerve 



Cerebral ganglion— /- 



- -Adductor muscle 

 of Mandible 



(ophthalmic artery 

 -y -Digestive gland 

 ■ --V-Antennary artery 

 Hepatic artery 

 -Testis 

 -/-Ostium 

 -Heart 



6th Thoracic ganglion 

 -Vas deferens 



Extensor muscle 



l9t Abdominal ganglion 



T.FIexor muscles 

 of Abdomen - 



-•Intestine 



Superior abdominal 

 artery 



6th Abdominal ganglion- 



Anterior 

 visceral nerve 



- -Stomach 

 or aizzard 



Suboesophageal 

 ganglion 



1st Thoracic 

 ganglion 



Loop for 

 Sternal artery 



'Endophragmal 

 skeleton 



Intestine 



Posterior 

 visceral nerve 



Fig. 



32. —The Fresh-water Crayfish [Aataam). A. Dissection of a •maXt showing the general 

 structure ; B. the nervous system. 



Note the transverse post-oesophageal commissure immediately behind the 

 oesophagus and joining the two circum- oesophageal commissures. From the 

 supra-cesophageal ganglion a visceral nerve passes backwards to supply 

 the stomach, while from the last abdominal ganglion there arises a posterior 

 visceral nerve supplying the intestine. 



\ln Jams there are jive pairs of free thoracic ganglia, and the loop for the sternal 

 artery occurs between the third and fourth pairs.] 



