j^ERYOUS SYSTEM AND GENERAL SENSATION. 



55 



of the animal series. The number of the ganglia in the simpler 

 forms of the articulata, corresponds in general to the number of 

 the ringsof thebody : butin the 

 higher groups there is often a 

 fusion of two or more ganglia 

 into one. This change is well 

 exemplified in the development 

 of insects, spiders, and crus- 

 taceans : the spinal cord of 

 the articulata, like that of the 

 vertebrata, is composed of 

 motory and sensitive columns. 

 In insects, a special nervous 

 system, the sympathetic, is dis- 

 tributed to the organs of vege- 

 tative life. The annexed figure Fig 34- _The nervous system of 

 (34) shows the distribution of Carabus nemoralis, a garden beetle, 

 the cerebro-spinal system in a The cephalic ganglia supply nerves 

 beetle, Carabus nemoralis. to the e y es > antennae, parts of the 



r& llfi Trirriprnnllnsra thp mouth, &c. ; the thoracic ganglia 

 p . in me monusca, me , neryes to the thorax> thethree 



principal centre of the nervous pairs of legs and the wings . tne ab _ 

 system surrounds the gullet, in dominal ganglia send branches to the 

 the form of a gangliated collar ; organs contained in the abdomen, 

 but it exhibits many phases of development in the different 

 classes of this sub-kingdom. In the CONCHIFERA, which are 

 acephalous, as the mussel (Mytilus edulis), distinct organs exist 

 for the ingestion of the food, respiration, and locomotion, and 

 each of these possesses ganglia, in immediate relation with the 

 function over which it presides. Hence we find 



1st. Msophageal ganglia, which surround the gullet, and re- 

 present the brain. These nerves proceed to the labial pro* 

 cesses, that serve for taste and touch. 



2nd. Branchial ganglia presiding over the respiratory func- 

 tion. From these ganglia, likewise, the muscles concerned in 

 the act of respiration, the adductors of the shell, the folds of the 

 mantle, and the intestine are supplied. 



3rd. Pedal ganglia vary with the presence or absence of a 

 foot for locomotion. The whole of these ganglia are united 

 into a nervous chain by connecting filaments. 



In the GASTEEOPODA we observe a further development o< 

 the nervous system. They possess a head; and the brain 



