958 



INSECTA. 



tary canal. Muller* had previously shewn a 

 similar arrangement of these ganglia in Gryllo- 

 talpa vulgaris, and Brandt f has since further 

 elucidated the distribution of these structures 

 in the same insects. We have ourselves re- 

 cently found a somewhat similar distribution of 

 these nerves in one of the Coleoptera, Bupres- 

 tis chrysis, in which the first of the anterior 

 lateral ganglia, on each side, besides its con- 

 nexion with the brain, gives off three distinct 

 nerves, one of which passes outwards to the 

 muscles of the oesophagus and pharynx, and 

 another inwards to unite with the great trunk 

 of the recurrent nerve, while the third passes 

 backwards for a short distance, and then forms 

 the second of the lateral ganglia, from which, 

 in like manner also, proceed three other nerves. 

 The first of these passes outwards to the sides 

 of the oesophagus, and the second inwards to 

 join a large ganglion formed at the extremity 

 of the recurrent nerve, while the third branch 

 is of considerable length and traceable for a 

 great distance along the sides of the oesophagus. 

 From the ganglion at the termination of the 

 recurrent nerve, and which most certainly be- 

 longs to this trunk, are also given off two nerves, 

 which are soon again divided, and distributed 

 along the posterior part of the oesophagus. 

 From these connexions, and the relative size 

 of the parts, it still appears to us that although 

 the sympathetic and recurrent nerves are most 

 intimately connected, and appear in certain 

 instances almost to supply the place of each 

 other, there is reason for still considering them 

 as distinct, and for describing the latter, as we 

 formerly designated it,J as the vagus. 



The vagus, or visceral nerve of Professor 

 Miiller, after arising, as in the larva, from the 

 anterior part of the base of the cerebrum, and 

 forming a ganglion on the upper surface of the 

 pharynx, always passes backwards beneath the 

 brain, along the middle line of the oesophagus. 

 We shall first describe its course in Lepidopte- 

 rous insects, and point out what we conceive to 

 be its analogies to the vagus of vertebrata. In 

 the Sphinx it originates in the perfect insect, as 

 in the larva, from the lowest part of the anterior 

 surface of the brain by two roots, one on each 

 side, which we regard as analogous to the two 

 vagi in the higher animals. Each root gives off 

 from its base a small branch to the sides of the 

 mouth, after which the two roots ascend, and 

 meeting above the pharynx, form the frontal 

 ganglion, from the anterior surface of which a 

 few nerves are given to the mouth and palate, 

 and also to the bifurcation of the dorsal vessel, 

 which, after having passed along the oesopha- 

 gus and beneath the brain, is divided in front of 

 the brain into several branches. The frontal 

 ganglion at the junction of these roots of the 

 vagus we regard as analogous to the enlarge- 

 ment on the vagus nerve in vertebrata after it 

 has passed out of the skull by the foramen la- 

 cerum posterius. From the ganglion thus 

 formed by the approximation of the two roots, 

 a single trunk passes backwards along the me- 



* Nova Acta Curios. Nat. vol. xiv. 

 t Annal. des Sciences Natur. torn. v. 

 t Phil. Trans. 1832. 



dian line, lying upon the oesophagus and be- 

 neath the dorsal vessel, and giving to both se- 

 veral branches in its course. When arrived at 

 the dilatation of the oesophagus, the air-bag or 

 crop, it first distributes a few filaments to that 

 part, and then divides into two primary 

 branches, which run along the sides of the 

 stomach, and are again subdivided and distri- 

 buted to it. Behind the brain, the vagus in the 

 Sphinx receives but one branch of communica- 

 tion on each side from the sympathetic ganglia, 

 which connexions appear to be analogous to 

 those between the vagus and sympathetic in 

 vertebrata. In passing along the median line 

 of the oesophagus, the single vagus in insects 

 is in close relation with the anterior or aortal 

 portion of the dorsal vessel, which may repre- 

 sent the two carotids of the higher animals 

 united, and thus its relation to these parts is 

 also precisely similar to that of the vagus, caro- 

 tids, and oesophagus in these animals. There is 

 a like analogy in its distribution to the anterior 

 part of the stomach, beyond the middle portion 

 of which it has never yet been traced. At its 

 point of division the single vagus nerve often 

 forms a very distinct ganglion, as in the Melb'e 

 (Jig. 416, i). This is the usual distribution in 

 a large majority of insects, more particularly 

 in the Lepidoptera, Coleoptera, Neuroptera, 



Fig. 416. 



Brain and vagus nerve of Meloe dcatricosus. 



Hymenoptera, and in many of the Orthoptera. 

 In Lucanus cervus (Jig. 417), the nerve, conti- 

 nued backwards from the frontal ganglia (a), is 

 of large size until after it has passed beneath the 

 brain, and given off a minute branch on each 

 side to the dorsal vessel and oesophagus, after 

 which it becomes on a sudden much smaller, 

 and forms a second small ganglion, (e,) which 

 is connected on each side by a single 

 branch with the sympathetic ganglia (C,) which 

 have assumed an elongated form, and are 

 greatly enlarged. After this the vagus nerve 

 is ' continued as a single trunk, (&,) until it 



