806 



INSECT. 



its motions, ' here lies the vitality of an insect ; the 

 body at any rate is dead ;' but in this I was quickly 

 undeceived, for in about a minute after the body had 

 fallen upon the paper, I saw the hind legs brought 

 upward, and employed in deliberately brushing and 

 cleaning the wing-cases, exactly as a house-fly may 

 be seen to clean its wings on a window pane. The 

 legs were then withdrawn, the case* raised up, and 

 true wings expanded from beneath, and all made 

 ready for flight, which, indeed, I expected to see ; 

 but the body seeming then to become aware that 

 there was no guide, the head, its former companion, 

 being in possession of the eyes, the design was aban- 

 doned, the winsrs folded up in their usual beautiful 

 manner, and the attitude of rest again assumed. This 

 whole process was repeated with perfect regularity 

 at intervals of about a minute, if I rightly remember*. 

 A more perfect act of a sentient creature could not 

 be exhibited : the head continued to run about, and 

 the body to clean and expand its wings, the one for 

 about twelve and the other for sixteen hours, their 

 energies gradually decaying, till they appeared to 

 perish, or rather to sleep. And now, I ask, which 

 was the beetle? where was the original creature? 

 had not the head and the body an equal right to be 

 taken as its representative? Is not all analogy be- 

 tween insects and ourselves destroyed by such a 

 phenomenon ?" And in the same view of the subject 

 it has been considered better to consider each nervous 

 ganglion as a separate and independent centre of 

 volition. But surely we have no authority for adopt- 

 ing such a view, the ganglia being united together, 

 and the insect constantly dying when thus divided, 

 instead of each portion forming itself into a new 

 being, like the planaria and some other iriverte- 

 brated animals. 



The nerves, as before observed, form the medium 

 whereby the notice of the various transactions of 

 the external world is conveyed to the seat of the 

 instinctive or intellectual organs. The perceptions 

 thus obtained constitute the senses, of which sight, 

 hearing, smell, taste, and touch, are those which are 

 generally allowed to prevail. Some physiologists 

 (Dr. Virey, &c.), add to these love, and the internal 

 sense of thought or instinct. 



The former of these, as a perception distinct from 

 the mere physical act of propagation, can scarcely 

 be allowed to insects. In this point of view the 

 subject cannot be discussed in a work like the 

 present. The instinctive powers of insects also appear 

 to the writer of this article to be on a very different 

 footing compared with the other senses. We shall 

 therefore defer our observations thereon to the sub- 

 seqiuMit section of this article. 



That insects possess several of the senses is certain ; 

 but the seat of these senses is not ascertained ; nei- 



.!! ^'il Apparently controverts the conclusion of Burmeister, 

 that after the separation of the nervous cord at any part, the 

 voluntary motion of the organs seated beyond the point of in- 

 cision i is lost, but that the irritability of the muscles, that is to 

 power of reaction upon external excitement, is re- 

 :d by these organs as long as life remains. We say appa- 

 rently, because when the increased size of the muscular system 

 -rto iT S . 8 U1 ! llalachius (which is a strong flier',, is con- 

 n *.< J / S - in , the sw - immin S motion of the hind legs 

 us deprived of its anterior ganglia, recorded by Bui- 



TZ3KEL 1 * T hlch the muscles of the hin d legs are very 

 hT^SLW^' the unfoldin S *"d Aiding of the wings ma 



ther can we by any possibility arrive at a certain 

 conclusion that the senses of these animals are iden- 

 tical with our own. Their entire organisation having 

 been shown to be so totally different from that of the 

 vertebrated animals ; indeed, as Mr. Mac Leay has 

 observed in the Horse Entomologies, there is no 

 reason why animals constituted upon a plan so 

 totally unlike our own, should not possess senses of 

 which we have no idea. We will, however, adopt 

 the general opinion, and speak of the senses of insects 

 as analogous to our own, the consideration of which 

 will form so many distinct sub-sections. 



a. The Sense of Sight. The eyes of insects are the 

 only organs which we can with any certainty refer to 

 the sense of which they are the seat. We have 

 already described the external structure of the eye?, 

 and ocelli or eyelets, and shall therefore now notice 

 their internal organisation, and the mode in which 

 vision is effected. On making a perpendicular incision 

 into the eye, it is found to consist of various layers ; 

 the external membrane is hard, transparent, and com- 

 posed of a multitude of hexagonal facets, each forming 

 a more or less distinct conical cylinder, running 

 towards the centre of the eye ; beneath this external 

 membrane is a layer of coloured matter, often of a 

 blackish violet hue, but sometimes green, red, or 

 banded, pierced with as many holes as there are 

 facets or pupils ; beneath this is a varnish of a black 

 colour, within which is another belt, the inclosed 

 space receiving the optic nerve, with its numberless 

 ramifications, a branch probably going to each facet. 

 The structure and functions of the eyes of insects 

 have been investigated with great accuracy by Miiller, 

 who has proved that the refractive powers of the 

 ocelli must be very great, each ray of light suffering 

 a four-fold refraction ; the first produced by the 

 convex cornea, the second by the anterior convex 

 surface of the lens, the third by the posterior convex 

 surface of the lens, and the fourth by the convex sur- 

 face of the glassy body itself; hence a very distinct 

 short sight, suitable for small objects, is possessed by 

 these eyes. In the compound eyes the effect is dif- 

 ferent, here, owing to the convexity of these eyes, and 

 the consequent obliquity of the lateral facets and their 

 cylinders, a much wider horizon must be embraced, 

 each individual facet surveying but a small space of 

 the entire field of vision, each thus contributing to the 

 perception of objects comprised within the view, those 

 rays of light only that fall in a right line upon a facet, 

 which itself forms the segment of a circle, can reach the 

 optic nerve of this facet, whereas all others are 

 withheld by the pigment which separates the indivi- 

 dual glass cases from each other, and partly circularly 

 surrounds the margin of the crystalline lens beneath 

 the cornea. According to Miiller, each nervous fila- 

 ment conveys to the bulb of the optic nerve the 

 impression of the ray which it has individually re- 

 ceived ; and as all the nervous filaments at first 

 separated by the pigment are at length united together 

 into one common and continuous bulb or nervous 

 expansion, the impression received by each filament is 

 united to those of the others in the bulb of the optic 

 nerve, and so a common and continuous image is pro- 

 duced. This author, however, further considers, that 

 rays coming from one point of a remote object will 

 illuminate throughout more than a single cone, and thus 

 to each luminous point without there will correspond 

 in the interior of the eye, not exactly a single illu- 

 minated point, but rather a little circle of diffused or 



