330 



PHYSIOLOGY OF THE INVERTEBRATA. 



FlG. 65. 



Nkrvous System of Astacus. 



a = brain. 6 = optic nerve, c = " collar." 



d — sub-oesophageal ganglion. 

 e ~ visceral nerve. / = posterio-lateral 



nerve. ,0-=: "hepatic" nerve. 



The stomach is turned on one side to show 



its nerves. 



glands ; to the visceral nervous 



In some C7-ustacea, such 

 as the shore-crab (Garcinvs 

 riuenas), there is a large cere- 

 bral ganglion which gives 

 off nerves to the eyes and 

 antennce ; while the ventral 

 chain of ganglia (of other 

 forms) is fused into one 

 mass (Fig. 64). From this 

 mass radiate the nerve-cords. 

 The nerve-cords connecting 

 the cerebral ganglion with 

 the nervous mass form the 

 oesophageal ring or collar. 

 There is in Carcinus a degree 

 of concentration of the gan- 

 glionic cells, greater, in some 

 respects, than in the Verte- 

 brates themselves. 



The nervous system of 

 Astacus fiuviatilis (Fig. 65, 

 and see also Fig. 13) con- 

 sists of thirteen ganglia 

 joined together by means of 

 commissures. These ganglia 

 are divided as follows : one 

 cerebral, one sub-oesopha- 

 geal, five thoracic, and six 

 abdominal ganglia. The 

 cerebral ganglion or brain 

 gives off nerves to the eyes ; 

 to the auditory organs ; to 

 the antennas ; to the cara- 

 pace in front of the cer- 

 vical suture ; to the green 

 system ; and to the sub- 



