100 



NERVOUS SYSTEM OF ARTHROPODS. 



in the common Crab and its allies (fig. 36) quite close 

 to the great stellate systemic ganglion (s), into which 

 are fused the representatives of the sub-oesophageal, the 

 thoracic, and the abdominal ganglia. 



From this ganglion (fig. 38, i) 

 five principal nerves are sent off 

 on each side, " the first to the 

 pediform maxillary palpi; the 

 second to the more pediform 

 labial palpi, which are usually 

 longer than the rest of the legs, 

 and used by many Spiders rather 

 as instruments of exploration 

 than of locomotion ; the three 

 posterior nerves supply the re- 

 maining legs, which answer to 

 the thoracic legs of hexapod 

 Insects." (Owen.) 



Since the sub - oesophageal 

 ganglia are in part analogous, 

 as already stated, with the ' me- 

 dulla oblongata' of vertebrate 

 animals, their fusion with the 

 thoracic ganglia in Arachnida, 

 as well as in Myriapoda, tends, 



FIG. 38. Nervous System of a . /> 



great scorpion-iike Spider (Thdy- m a measure, to confirm the 



phonuscaudatus). (Gegenbauer, aft- r y j ew }Q\J{ by S0 me anatomists, 

 Ulanchard.) s, Cerebral ganglia ; i, ', -\' LL j. J4.1, 



great ventral ganglion, communicat- that it IS better to regard the 



ing with fiv. large nerves on each < medulla > as a prolongation of 

 side; o, eyes; p, palpi; p'-p", feet; $ * 



c. taii-iike prolongation. the spinal cord, than as an in- 



tegral part of the brain. The 



artificial line, that is, which for convenience is drawn 

 between the brain and the cord in Vertebrates, should be 

 placed at the upper rather than the lower or posterior 





