114 



FUNCTIONS OF THE NERVOUS SYSTEM. 



Fig. 14. 



they ramif}?- minutely, and also to the muscles concerned in the respiratory 

 movements. (The latter, however, being a part of the general locomotive 

 apparatus, are also supplied from the principal ganglionic column.) These 

 nerves, then, which are evidently analogous to those of the gills and siphonic 

 apparatus in the Mollusca, may be regarded as corresponding with the pneu- 

 monic portion of the par vagum in Vertebrata (which is in like manner distri- 

 buted on the air-passages), and with its associated motor nerves. 



149. In comparing the nervous system of Insects with that of the higher 

 Mollusca, it will be seen that they differ more in the arrangement and in the 

 relative proportions of their parts than in their essential character. In both 

 there is a cephalic division of the ganglionic centres, in which sensibility and 

 psychical power appear to reside more particularly, if not entirely. In both 

 there is a division specially appropriated to the locomotive apparatus, differing 

 only in the multiplication of the centres in Insects, conformably with the 

 arrangement of the members they supply; and sometimes consolidated to 

 nearly the same degree. In both, also, we find a division appropriated to the 

 respiratory apparatus, in which there is a corresponding multiplicity of cen- 

 tres in the Articulata, in harmony with the universal 

 distribution of their tracheal system. And in both, as 

 Ave shall now see, there is a separate system of nerves, 

 distributed to the alimentary apparatus, and supplying 

 the organs of mastication (with the salivary glands), of 

 deglutition, and of digestion. 



150. Of the stomato-gastric system, some traces 

 may be found in nearly all the Articulated classes. 

 Thus, in the Leech, we find a minute ganglion existing 

 at the base of each of the three teeth which form the 

 mouth; these ganglia are connected together, and, to 

 the cephalic, by slender filaments ; and they seem also 

 to be in connection with other filaments, which may 

 be traced on the alimentary canal. As a specimen of 

 its highly-developed form, we shall describe that of 

 the Gryllotalpa vulgaris (common Mole-Cricket). 

 Here we find it consisting of two divisions ; one placed 

 on the median line, which may hence be called the 

 median system; the other running on each side at 

 some little distance, and heflce called the lateral sys- 

 tem. The Median system appears to originate in a 

 small ganglion, situated anteriorly and inferiorly to 

 the cephalic mass, with which it communicates by a 

 connecting branch on each side. From this ganglion, 

 nerves proceed to the walls of the buccal cavity, the 

 mandibles, &c. Its principal trunk, however, (the re- 

 current of authors,) is sent backwards beneath the 

 pharynx. The ramifications of this are distributed 

 along the resophageal tube and dorsal vessel ; whilst 

 the trunk passes downwards to the stomach, where its 

 branches inosculate with those supplied by the lateral 

 system, and seem to assist in forming a pair of small 

 ganglia, from which most of the visceral nerves radi- 

 ate. The ganglia of the Lateral system are two on 

 each side, lying behind and beneath the cephalic 

 masses . The anter i r pair are the largest, and meet on 



Stomato-gastric system of 

 GRYLLOTALPA VULGABIS; A A, 

 cephalic ganglia; a, anterior 



g ang ii a . 



with which they communicate. Posteriorly to these 



