INSECTA. 



959 



has passed half-way along the oesophagus, 

 (jig- 428, H,) when it divides into two branches, 

 which pass on each side of the oesophagus as far 

 as the gizzard, (i,} where each forms a very 

 minute ganglion, from which are given a few 

 filaments to the substance of the gizzard. 



Fig. 417. 



Brain, sympathetic ganglia, and vagus nerve of 

 Lucanus cervus. 



Each nerve thus passes on to the stomach, (K,) 

 and we have succeeded in tracing it about half-way 

 along that organ, when it can be followed no far- 

 ther, being lost by minute subdivisions. As con- 

 nected also with the vagus nerve both in func- 

 tion and by analogy of distribution, is the nerve 

 which we noticed so particularly in the larva, 

 the glosso-pharyngeal, (fig. 418, F,) which is 

 remarkably distinct in Lucanus, and as in the 

 larva gives branches to the under-surface of the 

 esophagus. It is remarkable, also, that in this 

 insect each root of the vagus arises from a 

 ganglion on each side, situated below the cere- 

 bral lobes, but closely connected to them, and 

 from which ganglion the antennal nerves (D) ori- 

 ginate, and a third nerve, which is directed 

 backwards ajnong the muscles, but the course 



of which we have not yet traced, but which 

 probably is a compound nerve ; it appears to be 

 formed in part by the ganglion, (E,) and partly by 

 a portion of the cerebrum, which is united to it. 



Fig. 418. 



Under-surface of brain, S^c, of Lucanm cermu. 



The form which the frontal ganglion usually 

 assumes is nearly triangular, but in some in- 

 stances, as in Carabus monilis, it is elongated, 

 oval, lying transversely across the pharynx, but 

 in almost all the insects we have examined, ex- 

 cepting the Buprestida and some of the Or- 

 thoptera both in the larva and pupa state, as 

 in Tirnarcha, Meloe, Anthophora, and Bombus, 

 whatever be its form, the single nerve continued 

 from it has more resembled in its distributions 

 and relations the vagus than the sympathetic. 

 These are the reasons for our continuing to de- 

 scribe it as the former rather than as the latter 

 of these nerves. The fact, however, of its dis- 

 position to form ganglia in its course appears, 

 indeed, as observed by Professor Miiller,* to 

 assimilate it most in character with the sympa- 

 thetic ; but we conceive this fact to be satisfac- 

 torily explained by the anatomy of these nerves 

 in Buprestis, in which the middle or recurrent 

 nerve, although exceedingly short, is very 

 large, and is terminated by a ganglion, as in 

 the Gryllida, and from which, in Buprestis, 

 two small nerves are continued along the eso- 

 phagus, while the corresponding nerves in 

 Gryllus have become approximated to those 

 from the lateral ganglia, and assist to form the 

 long gangliated nerve at the side of the oesopha- 

 gus. The functions of the vagus and sympa- 

 thetic in insects would thus appear to be nearly 

 similar, and that, as is sometimes the case with 

 these nerves in vertebrata, as we have seen, for 

 example, in the neck of the calf, the two become 

 often closely approximated together, as noticed 

 also by Professor Miiller, in the Myxinoid 

 Fishes, in which the vagus and sympathetic 

 form only one nerve, the chief portion of which 

 is the vagus, and which is extended to the anus. 



* Muller's Archiv, No. v. 1837, Jahresbresbt, p. 

 Ixxxv. to viii. 



