278 CLASS viii. 



single nerve, lying above upon the strings of the ganglionic nervous 

 system, connects each plexus with the following one. In perfect 

 Insects this system is less distinctly visible, and often is completely 

 combined with the rest of the nervous system l . 



There is found in addition still another nervous system in Insects, 

 destined especially for the organic life, which was made known in 

 part by the investigations of SWAMMERDAM and LYONET in former 

 times, and described by the last under the name of nerf recurrent 2 , 

 and to which in our century JOH. MUELLER has by his investiga- 

 tions especially directed the attention of anatomists. It has been 

 compared by him and by most modern writers to the sympathetic 

 nerve of vertebrate animals, by others to the nervus vagus. This 

 system of nerves consists of a single middle portion and of two lateral 

 portions. The single portion arises from one or more nervous 

 ganglia situated in the head, which are connected with the most 

 anterior part of the first (the cerebral) ganglion of the ganglionic 

 cord. From this single portion whilst situated in the head nerves 

 arise for the uppermost oral organs, and a thread which runs along 

 the oesophagus on the dorsal surface to the stomach, and at its 

 extremity terminates in a ganglion. In Phasma ferula BRANDT 

 saw numerous branches arising transversely, and running in arches 

 over the oesophagus and stomach to form a fine nervous net. Per- 

 haps a similar distribution may be suspected in other Insects, where 

 the extreme delicacy of the nervous branches does not permit their 

 determination. In most Insects the middle single portion is the 

 most developed ; in Gryllotalpa and Gryllus, on the contrary, the 

 lateral portions are more developed than the single and middlemost. 

 The lateral portions consist ordinarily of two pair of ganglia that 

 lie close together behind the cerebral ganglion, of which the 

 anterior is connected with the cerebral ganglion by one or two fine 

 nervous threads. From these ganglia delicate nervous branches 

 arise which run to the oesophagus whilst they are also in connexion, 

 by fine threads with the single middle nerve that runs over the 

 oesophagus 8 . 



1 Besides the authors cited comp. also especially an excellent paper on the nervous 

 system of Beetles by E. BLANCHARD, Ann. des Sc. Natur., sieme SeVie, Tom. v. 

 Zoologie, 1846, pp. 273379, PI. 815. 



2 Traite anat. de la Chen. pp. 413, 578, &c. 



3 Comp. JOH. MUELLER, Ueber ein eigenihumliches dem Nervus sympatJiicus amilnya 



