30 PHYSIOLOGICAL SERIES. 



large oval SubcBSOphageal ganglion a composite mass from 

 which nerves an- given oil' to tin- mouth, the pedipalpi, the 

 i'our pairs of walking-legs, and the first tour segment- of 

 the abdomen. The oephalothoracic mass is united by a 



pair of delicate connectives to a chain of three abdominal 

 and four post-abdominal ganglia, all of which are trans- 

 versely concentrated hut are united by separate connective-. 

 The last abdominal anil the first three post-abdominal 

 ganglia lie severally in the segments that they innervate, 

 but the first two free abdominal ganglia are approximated to 

 the cephalothoracic mass, being respectively two segments 

 and one segment in advance of their nerve distribution. The 

 terminal ganglion of the chain lies in the 4th post-abdominal 

 segment; it supplies the 4th and 5th segments of the 

 post-abdomen and the post-anal spine. The three posterior 

 ganglia and their connectives show a marked increase in si/e 

 compared with those in front of them, correlated no doubt 

 with the great activity of the post-abdomen. 0. 0. 1297 p. 

 Blanchard, ^organisation dti Regne Animal (Arach- 

 nides), 1852, p. W. 



D. 22. A Spider (Avicularia avicularia) dissected from the dorsal 

 aspect. The central nervou< system is extremely concen- 

 trated; it lies in the middle of the cephalothorax behind 

 the mouth, encircling the horizontal part of the oesophagus 

 and extending backwards beneath the stomach. The supra- 

 OBSOphagcal part of the system i- small and feebly bilobed ; 

 it innervates the eyes and rostrum. On either side ol the 

 oesophagus it is connected to the BttboBSOpnageal mass by a 

 pair of ganglionio centre- that give otV nerves to the 

 chelicene ami vi-cera. The third and large-t part of the 

 central -y-lein lie- beneath the ( i-o|hagii< and -tomach, 

 -eparated from them by the ento-ternite ; it has an oval 

 form and is compo-ed of -i\ pair- of I'u-ed ganglionic 

 centres that repre-ent the ganglia of th<- ventral chain. 

 From thi- ma-- ner\f- are given oil' to the pedipalpi. to tin- 

 four pairs of walking-leg-, and to the abdomen. Fibrous 

 partition-, derived from the neiirilemma, penetrate to a 

 rtain extent between the -everal centres of the sub- 

 O3SOphageal ma . 0. C. 1300 A. 



Schimkewitsch, Ann. Sci. Nat., ser. 6, t, xvii. 1884, p. 15. 



