INSECT. 



This is the case in the perfect, state of the heini- 

 pterous insect, Riinalra lincaris, for a figure of which 

 the writer is personally indebted to John Anderson, 



Nervous system of Ranatra linearis. 



Esq., of Richmond, by whom a most elaborate series 

 of preparations of the nervous system throughout 

 the entire range of the animal kingdom has been 

 made, in illustration of a very valuable paper read on 

 the 23rd of April last before the Physical Section at 

 Guy's Hospital, with reference to the remarkable 

 analogies (noticed in the early part of this article), 

 exhibited by the human embryo in the various stages 

 of its passage to perfection, with the perfect state of 

 the inferior animals. We trust that this admirable 

 memoir will he shortly published. 



In the larva there are thirteen knots, corresponding 

 with the number of rings of the body; but these 

 organs, like the other internal systems, are modified 

 during the passage to the perfect state. Thus Dr. 

 Herold in his celebrated work upon the Internal 

 Anatomy of the white Garden Butterfly, ascertained 

 as the larva approached maturity, the second ganglion 

 became united with the first ; the fifth and sixth ap- 

 proach and unite; then the third and fourth ; whilst 

 in the pupa, the seventh and eighth have entirely 

 disappeared ; so that, instead of thirteen, the imago 

 possesses but eight ganglia. 



On examining the invertebrated, or rather the ex- 

 ternally vertebrated structure of an insect with that 

 of the internally vertebrated animals, we find no part 

 corresponding with the brain ; or rather the organ 

 which might be regarded as analogous thereto, and 

 which, indeed, has been called the brain, namely, 

 the ganglia of the head, are repeatedly represented 

 along the entire length of the body ; consequently it 

 has been supposed that the nervous cord of the insect 

 represents the great sympathetic nerve of the latter ; 

 although, perhaps, it would be more correct to regard 

 it rather as the spinal cord. 



The matter of which the nerves are composed is 

 a soft pulpy substance, enclosed in a simple and 

 transparent membrane. 



The first pair of ganglia is always situated in the 

 h':id of insects above the digestive canal, and is 

 furnished with nerves extending to the eyes, antennee, 

 mandibles, maxillae, and labrum. The other ganglia 



NAT. HIST. Vol.. II. 



are lodged in the thorax and abdomen, or in the 

 former alone, and similarly placed above the alimen- 

 tary canal ; the two thick nervous filaments con- 

 necting the head ganglia with the prothoracic 

 ganglia are deflexed, so as to surround the oeso- 

 phagus, forming a kind of nervous collar. From the 

 thoracic and abdomial ganglia are emitted nerves 

 which communicate with the legs, wings, and other 

 organs of the body. In the larva of the goat-moth, 

 Lyonnet counted forty-five pairs of these nerves, 

 besides two single ones, thus making a total of ninety- 

 two, which is considerably more than are found in 

 the human body ; namely, seventy-eight. 



In the vertebrated animals the nerves proceed 

 from the brain, which is enclosed in the head ; in 

 insects, on the contrary, we have seen that nerves 

 proceed from the various knots, whether belonging to 

 the head, thorax, or abdomen ; hence we might ana- 

 logically call the various ganglia and their con- 

 necting filaments an elongated brain. In the verte- 

 brated animals sensation originates in the brain; and 

 hence, from the concentration of this organ into one 

 mass (for so we may call it although divided into two 

 lobes), sensation is more concentrated, and the feel- 

 ings rendered highly acute. In insects, on the 

 contrary, owing to the want of concentration of the 

 nervous ganglia, sensation is necessarily much less 

 acute; and, as the nerves laterally emitted by one 

 ganglion generally serve for the segment of which it 

 forms a part, the connexion with the preceding or 

 subsequent ganglia being at the same time slight 

 in proportion to the slightness of the connecting 

 filaments, we are enabled satisfactorily to account 

 for the apparent want of sensation in insects, as 

 exhibited, for instance, in the cockchaft'er, which 

 will walk about, although some bird has nearly 

 emptied the body of its viscera ; or by the head or 

 abdomen of a wasp, which will continue to bite and 

 sting long after they have been separated from the 

 rest of the body ; or by the headless trunk of a male 

 mantis, which has been known to unite itself to the 

 other sex, as recorded by Dr. Smith, and quoted by 

 Kirby and Spence. Another instance is recorded by the 

 Rev. Mr. Bird, in a memoir published in the Ento- 

 mological Magazine, entitled, " On the want of 

 Analogy between the Sensations of Insects and our 

 own." " When I was young in entomology," observes 

 this kindly-hearted writer, " I wished anxiously to 

 find the quickest mode of killing an insect. Having 

 captured a pretty beetle, Malachius (Bncus, it struck 

 me that by cutting it in two at the junction of the 

 thorax and abdomen, the part which gives rise to the 

 name insect, Insectum, Evrofwv, I should kill it in a 

 moment. I took a pair of scissors and divided it ; the 

 parts fell on a piece of white paper which lay before 

 me. Far from being dead in an instant, I was grieved 

 and surprised to see the head with the two fore-legs 

 attached to it begin to run about the paper. It oc- 

 casionally stumbled, but rose again, and exhibited, if 

 I may so speak, perfect self-possession. It made for 

 the edge of the paper ; but arriving there and look- 

 ing over it, seemed to think it too precipitous, and 

 so coasted along in quest of an easier descent, which, 

 nevertheless, it did not seem able to find. This 

 coasting and searching for a convenient place of 

 descent, suited to its curtailed condition with respect 

 to legs, of which it appeared perfectly aware, occu- 

 pied the head incessantly. I regarded it with asto- 

 nishment' Here, then,' I said to myself as I watched 

 I I I 



