NERVOUS SYSTEM. 199 



ing the anterior and lower part of the trunk, immediately be- 

 neath the eyes ; this lobed mass is perforated obliquely by a 

 small aperture through which the oesophagus passes to the 

 stomach. I have generally found the ganglionic spaces of 

 the columns of the scorpion, as in many insects, closely en- 

 crusted with small white lobes of adipose substance, in which 

 the oesophageal nervous collar is likewise imbedded. The in- 

 fra-oesophageal ganglia are much larger than the first pair which 

 have few and small parts to supply. This second pair of gan- 

 glia, composed of all the ganglia of the extremities (84. B. 2,) 

 is protected behind by a cartilaginous arch, through which the 

 columns pass to the third pair of ganglia, like the consolidated 

 internal arch for the nervous column in the thorax of Crustacea. 

 Numerous large nervous branches proceed backwards along the 

 inferior surface of the abdominal cavity from the infra-oesopha- 

 geal ganglia (84. B. 2,) beneath the motor and sensitive co- 

 lumns, as represented, many years ago, by Treviranus and 

 Muller, in their views of these columns in the scorpion. In 

 the short and rounded body of the spiders, the supra- and 

 infra-ossophageal ganglia form a large nervous collar around 

 the oesophagus, the inferior portion of which, as in the scor- 

 pions, forms a large lobed mass, from which all the nerves of 

 the extremities radiate. The supra-ossophageal ganglia are 

 small here also, from the imperfect development of the or- 

 gans of the senses and of mastication. The ganglia of the 

 abdomen, which are extended along the trunk separately 

 in the scorpions, are accumulated into a single mass in the 

 spiders, and placed near the anterior part of their short and 

 wide abdominal cavity. Thus the extent of concentration 

 of the nervous columns of arachnida, and the extent of dis- 

 tribution of their unsymmetrical or sympathetic system, cor- 

 respond with the high condition of the other systems in this 

 class, and while they vary in the different tribes, they ap- 

 proximate the more elevated forms to the highest insects and 

 Crustacea. 



In the numerous and diversified class of Crustacea we meet 

 with every condition of the nervous system, from that of the 

 lowest annelide, or the earliest larva state, where scarcely a 

 filament is yet perceptible in the place of the nervous columns, 

 to that concentration of the nervous ganglia around the oeso- 

 phagus, which connects the highest articulata with the mol- 



