RESPIRATORY AND STOMATO-GASTRIC SYSTEMS OF INSECTS. 



261 



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 dis- 

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



331. 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 proportion 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, differ- 

 ing 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 

 centres in the Articulata, in harmony with the universal distribution of their 

 tracheal system. And in both, as we shall now see, 



there is a separate system of nerves, distributed to the Fig. 129. 



alimentary apparatus, and supplying the organs of mas- 

 tication (with the salivary glands), of deglutition, and of 

 digestion. 



332. 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 con- 

 nection with other filaments, which maybe traced on the 

 alimentary canal. As a specimen of its highly-deve- 

 loped form, we shall describe that of the Gryllotulpa 

 vulgaris (Common Mole-Cricket). Here we find it con- 

 sisting 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 hence called the lateral system. The median sys- 

 tem appears to originate in a small ganglion, situated an- 

 teriorly and interiorly 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 recurrent of authors,) is sent backwards 

 beneath the pharynx. The ramifications of this are 

 distributed along the oesophageal tube and dorsal ves- 

 sel ; 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 radiate. The ganglia of the lateral system are 

 two on each side, lying behind and beneath the cephalic 



masses. The anterior pair are the largest, and meet on O f Gryiiotaipa vulgaris; 

 the median line, just behind the cephalic ganglia, with AA, cephalic ganglia; a, 

 which they communicate. Posteriorly to these lie the anterior median ganglion 

 second pair, which are in connection with them. Two ^^/ownwwdJftem 

 cords pass backwards on each side ; one derived from ft"faa ^."lateral ga 

 the anterior, the other from the posterior, of these gan- g i' ia; ' d , visceral ganglia. 

 glia. They run along the sides of the oesophagus and 

 dorsal vessel ; and, after inosculating with the branches of the central system, 



Stomato-gastric system 



