528 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



tfEBVOCTS SYSTEM* (Pis. IV and V). 

 The nervous system of Eupagurus shows little trace 

 of the asymmetry which involves so many other parts of 

 the animal. The variations in position and size which 

 occur in the nerves supplying the opposite sides of the 

 cephalo-thorax are exhibited in any higher Crustacean, 

 but the twist of the abdomen necessarily causes a certain 

 amount of alteration of the abdominal portion of the 

 nerve-cord. There would be no reason to expect any 

 further modification in a system which is not of large 

 bulk, and whose functions are in no way altered by the 

 change in symmetry. 



The degree of concentration of the thoracic ganglia 

 is intermediate between that of the Macrura on the one 

 hand, and of the Brachyura on the other. They are not 

 disposed in a diffuse chain as are those of the Crayfish, 

 nor are they indistinguishably fused as in the common 

 Crab, but the concentration is carried to a stage in which 

 the individuality of the ganglia has been lost, while a 

 more general division into regions representing the 

 fusion of two or more ganglia is preserved. Thus the 

 central thoracic ganglion-mass can be differentiated into 

 three (or perhaps four) main portions, which respectively 

 supply the mouth parts and chelae, the first pair of 

 walking legs, the second and third pairs of legs, and the 

 fourth pair. 



The nervous system may be conveniently described 

 in three portions : the brain and its connectives, the 

 thoracic ganglion-mass, and the abdominal chain. 



The Brain or supra-oesophageal ganglion (fig. 37) is 



situated in the mid-line, under the anterior margin of 



the cephalo-thoracic shield, behind the eye-stalks and 



* For a comparative study of Decapod nervous systems see : — 

 Bouvier, Ann. des sci. nat., zool., Series 7, Vol. VII, 1889, p. 73, 



