96 



THE NERVOUS SYSTEM OF ARTHROPODS. 



FIG. 34. 



PIG. 35. 



ganglion sends off lateral nerves to a pair of limbs. Th0 

 stomato-gastric nerves are connected with the posterior 

 part of the brain or with the ossopha- 

 geal cords, and they distribute them- 

 selves over the alimentary canal in 

 the usual manner. 



Among 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 different 

 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 

 /fi T\\ ^fe different from that of many Worms. 

 ^ ' In the Sandhopper, indeed, the ven- 



12. 34) of the 



(Taiurus locusta). (Grant.) two sides of the body are separate 

 from one another as they are in Ser- 



size as other ganglia situated p u j a /fipr 32) although the ganglia 

 on the separate ventral cords. r , 



FIG. 35. -Nervous System are here fewer in number and much 



of Cymothoa. (Grant.) Cere- mQre Distinct. 



In slightly higher forms of Crus- 

 tacea, however, the two divisions of 

 ^he originally double ventral cord 



_ _ n i M i 



always become fused together, whilst, 

 at the same time, the equality of the 

 several ganglia diminishes. Thus, in such forms as the 



bral ganglia almost wholly 



absent from cesophageai 



a single ventral cord, with 



compound ganglia at inter- 



