96 



THE NERVOUS SYSTEM OF ARTHROPODS. 



ganglion sends off lateral nerves to a pair ot limbs. The 

 stomato-gastric nerves are connected with the posterior 

 part of the brain or with the oesopha- 

 FiG. 3K Fig. 35. g^^j ^^j.^^g^ ^^^ ^^^^^ distribute them- 

 selves over the alimentary canal in 

 the usual manner. 



AmonsT Crustacea 



great 



differ 



ences are met with in the degree of 

 concentration of the nervous system, 

 the variations being, in the main, de- 

 pendent upon differences of external 

 form and in the arrangement of 

 locomotor appendages, in the difierent 

 representatives of the class. In some 

 of the lower terms of the series, such 

 as the Sandhopper and its allies, in 

 which the body is elongated and com- 

 posed of many almost similar seg- 

 ments, the nervous system is not very 

 different from that of many Worms. 

 In the Sandhopper, indeed, the ven- 

 /'"dLiTZZ:::^ tral cords and ganglia (fig. 34) of the 

 (Taiitrus locusia). (Grant.) two sides of tlio body are separate 



Showing separate cerebral „ ^ , , , • r> 



ganglia, each about the same "'om ouc another as they are in Ser- 



size as other ganglia situated p^J^ /fior^ 32) althouo-h the fj^anorlia 



on the separate ventral cords. ^ ^ n - ^ ^ ^ 



Fig. 35.-Neivous System are licre fcwcr 111 iiumber and much 

 more distinct. 



of Cymothoa. (Grant.) Cere- 

 bral ganglia almost wholly 

 absent from oesophageal 

 ring. Oesophageal cords dis- 

 tinct, and uniting bclowjnto 

 a single ventral cord, with 

 compound ganglia at inter- 

 vals. 



several ganglia diminishes. 



In slightly higher forms of Crus- 

 tacea, however, the two divisions of 

 the originally double ventral cord 

 always become fused together, whilst, 

 at the same time, the equality of the 

 T]ius, in such forms as the 



