288 ANATOMY. 



stomach, but furcates shortly before this spot, and ramifies into the 

 finest threads. 



The double nervous system in these orders consists of four small 

 ganglia, which lie directly behind the brain upon the oesophagus. The 

 anterior generally somewhat larger ganglion (f. 6 8. b. b.) arises with 

 one (Coleoptera) or two (LepidopteraJ branches from one half of the 

 cerebrum, and sends outwards delicate branches about the oesophagus, 

 but inwards a branch which unites itself with the single nervous cord 

 lying between the two ganglia. The second smaller ganglion (the 

 same, 6*. &*.) stands in connexion with the first by means of a nerve of 

 communication ; it also sends off fine branches, which run along the 

 oesophagus : indeed, in the Lepidoptera, it also unites itself again with 

 the unequal cord. This last ganglion of the double system was discovered 

 at the same time by Straus Durkheim, and Brandt : the first was 

 discovered by Lyonet in the Cossus caterpillar, but its connexion with 

 the single cord escaped him. 



191. 



The double nervous system attains its most complete development in 

 the Orthoptera, namely, in Locusta and Gryllifs. In Gryllus migra- 

 torins (PI. XXXI. f. 6.), there are found immediately behind the brain, 

 upon the superior surface of the oesophagus, five different ganglia. The 

 central and smallest (6.) lies nearest the brain, in which its two halves 

 make considerable constrictions, being united on each side by means of 

 a fine branch within each hemisphere. Between these two connecting 

 branches this ganglion meets the single cord, which, coming from the 

 frontal ganglion beneath the brain, originates likewise with two arched 

 branches from the anterior side of the brain, and from the frontal 

 ganglion itself sends off delicate branches forwards. Posteriorly this 

 single nerve does not quit the central ganglion, but wholly terminates 

 in it. Two other ganglia, which lie closely to the central one (c. c.), 

 are the largest of all, and have the form of a figure of eight, and stand 

 in connexion with the central one by means of one, and with the brain 

 by means of two branches. At its posterior end two other branches 

 originate from it, the exterior of which is the longest ; both furcate, 

 the latter after it has first swollen at the point of separation into a 

 small ganglion (e.). Close to these two ganglia, we find at the lateral 

 margins of the oesophagus two other oval but somewhat smaller ones 

 (d. d.), which are connected with the central one by means of two, and 



