INSECTA. 273 



exist in the central axis of insects ; but, from the extreme minute- 

 ness of the different parts, it is not easy satisfactorily to demonstrate 

 them separately. In the larger ARTICULATA, however, as for 

 example in the CRUSTACEANS, two distinct columns of nervous 

 matter are readily detected: it will, therefore, be more convenient 

 to defer the investigation of this interesting subject until we have 

 an opportunity of describing these parts upon an enlarged scale ; 

 enough has been said at present to enable the reader to compare 

 the nervous axis of an insect with that of a lobster, and draw correct 

 conclusions from the comparison. 



(314.) The last division of the nervous apparatus, which we have 

 already mentioned as being the representative of the sympathetic 

 system, consists of two portions ; one corresponding, in distribution 

 at least, with the nervus vagus of VERTEBRATA, while the other 

 represents, apparently, the sympathetic ganglia. The nervus vagus , 

 as we shall call it, and which has been named by Swammerdam* 

 and Cuvier the recurrent nerve, arises (Jig* 122, i, b) by two roots 

 from the opposite extremities of pi ff , 122. 



the brain close to the origins of 

 the antennal nerves. The nervous 

 cords thus derived soon unite to 

 form a minute central ganglion 

 (Jig- 122, i), from which proceeds 

 a single nerve (fig. 122, /, *), 

 that runs with the gullet (/) be- 

 neath the brain, and spreads in deli- 

 cate ramifications upon the oesopha- 

 gus as far as the muscular stomach (Jig. 121, 9, 9), or to the gizzard, 

 when that organ exists. 



(315.) The Sympathetic system, properly so called, consists 

 of four small ganglia (Jig. 121, c, c, /, /), the two anterior of 

 which communicate with the brain, and with each other by 

 means of connecting filaments. These ganglia are closely applied 

 to the commencement of the resophagus, and supply it with minute 

 nerves. 



(316.) Various are the conjectures entertained by different au- 

 thors concerning the senses possessed by the members of the insect 

 world, and^ the organs subservient thereunto. The possession of 

 certain sources of perception has been alternately granted and denied, 



* Biblia Naturaj, 



