INSECT. 



dispersed light, and in consequence an image of but 

 little distinctness will be reproduced on the internal 

 surface or retina, the distinctness of the image increas- 

 ing in proportion as the object approaches the eye. 

 It is, however, admitted, that the distinctness of the 

 image will increase in proportion to the number of 

 facets, and the length of the cones, for the longer the 

 cones are, the more completely will all rays entering 

 them obliquely be prevented from reaching their 

 internal extremity or apex. Upon these remarks we 

 would, however, be permitted to observe, that, from 

 the fact of each facet being the segment of a circle, 

 as well as from the exceedingly minute size of the 

 pupil-like aperture of the pigmental division of each 

 facet, those rays only which fall upon the centre of 

 each facet, and pass down the axis of each cylinder, 

 can reach the nervous filaments in the centre of the 

 eve, and thus there can be no such dispersion of the 

 rays and consequent indistinctness of vision above 

 noticed. We submit this opinion with great defer- 

 ence, and because it appears to us, that in the various 

 experiments made upon this subject, due allowance 

 has not been made for the external circularity of each 

 facet of the cornea. 



Immediately in connexion with the sense of sight 

 ought to be noticed that remarkable property which 

 many insects possess of emitting a peculiar light, and 

 which, as we apprehend, should be regarded as dis- 

 played by insects with a view to its perception by the 

 eyes of their associates, just as the chirping of a 

 cricket is adduced in favour of the hearing of its 

 fellows. Amongst insects, the Lampyridce (or GLOW- 

 WORMS, which see) and the Elatendee are the only 

 families which are decidedly proved to possess this 

 faculty; although it has been asserted to prevail in the 

 Fulgoridee, and some isolated species of other groups, 

 but there is no distinct evidence of its existence in 

 these latter insect. We must, however, refer to the 

 various articles upon these families, where we have 

 dwelt more at large upon the nature and peculiarities 

 of these luminous exhibitions. 



b. The Sense of Hearing. Linnaeus describes in- 

 sects in general as "Muta nisi alio proprio instrumento, 

 sonora ; Surda stridorem setheris licet percipiant." 

 From many facts, however, it is evident that insects 

 distinguish sounds in some manner or other, although 

 the greatest uncertainty prevails amongst naturalists 

 as to the organ of this sense. Without presuming to 

 offer any opinion of our own upon a point on which 

 so muny learned physiologists are at variance, we 

 shall content ourselves with noticing the production 

 of sounds caused by insects, which has invariably 

 been employed as an argument in favour of the pos- 

 session of the sense of hearing by these animals, and 

 then allude to the opinions which have been enter- 

 tained as to its seat. 



Unlike the higher animals, insects possess no dis- 

 tinct vocal apparatus terminating in the mouth. The 

 noises made by insects may be divided into three 

 kinds, according to the mode in which they are pro- 

 duced. In the first, the sound is produced by the 

 mere friction of one part of the external integument 

 against another, whereby, when an insect is disturbed, 

 it forcibly rubs one portion of its body against another 

 in its endeavours to escape. In this manner, by the 

 friction of the prothorax against the base of the meso- 

 thorax, or the abdomen against the elytra in beetles, 

 a continuous and rather loud sound is produced. The 

 second kind of sound is produced by numerous 



flying insects, and which our bard of the Seasons has 

 alluded to in his lines, 



Yet not unpleasant is the ceaseless hum 

 To him who wanders in the woods at noon. 



The mode in which this sound is produced has been 

 endeavoured to be explained in a variety of ways. We 

 have already alluded to these opinions in our account of 

 the Halteref. and shall only add, that the experiments 

 of Burmeister and others, together with the fact that 

 bees produce as loud a sound as dipterous insects, 

 although unprovided, like the latter, with winglets 

 or halteres, seem satisfactorily to prove that it is 

 owing to the rushing of the air through the thoracic 

 spiracles that the buzzing is produced. The third 

 kind of sound is produced by a distinct modification, 

 of certain organs for their express emission. We 

 have already described these structures in the Linna-an 

 genera Gri/lliis and Cicada, which comprise the only 

 insects thus circumstanced, and which are confined to 

 the males. The death's-head moth also produces a 

 plaintive kind of cry, as described in our article upon 

 that insect. 



In many works we find the effects of other sounds 

 upon insects described, an instance of which we have 

 already recorded in our account of the great green 

 grasshopper. 



As to the organs supposed to be the means whereby 

 this sense is produced, we find that the opinions of the 

 majority of authors may be divided into those by 

 which the seat of this sense is asserted to be wholly 

 unknown, and those who consider that the antennae 

 in some way or other perform the functions of organs 

 of hearing. Other opinions have, indeed, been main- 

 tained by several other and distinguished authors. 

 Thus Treviranus described a small drum-like mem- 

 brane* on the forehead in front of the base of each 

 antennae in moths, to which nerves extend, but no 

 analogous organ has ever been discovered in other 

 tribes of insects. Miiller in like manner regarded 

 part of the chirping apparatus of the grasshopper as 

 an organ of sound ; whilst Rudolphi considered the 

 anterior salivary glands of bees as similar organs. Of 

 continental authors who have regarded the antennae 

 as analogous to ears, the most celebrated are Sulzer, 

 Scarpa, Schneider, Berkhausen, Reaumur, Bonnsdorf, 

 Cams, Strauss-Diirckheim, Oken, and Burmeister. 

 Kirby and Spence adopt the same view to a certain 

 extent, considering it probable that the primary func- 

 tion of the antennas may be something related to 

 hearing ; they further conceive that antennae, by a 

 peculiar structure, may collect notices from the atmop- 

 phere, receive pulses or vibrations, and communicate 

 them to the sensorium, which, though not precisely to 

 be called hearing, may answer the same purpose. It 

 is true that the antennas have, by other authors, been 

 regarded as the organs of smell and of touch, the 

 grounds for which we shall notice in our observ- 

 ations upon that sense. Moreover in the higher 

 Crustacea (crabs, &c.), the organs of hearing distinctly 

 exist in the shape of oval apertures, inclosing move- 

 able plates, and placed at the base of the larger 

 pairs of antenna?, a circumstance which has been con- 

 sidered as affording a strong analogy in favour of the 

 opinion that the antennas are organs of hearing. 



c. The Sense of Smell. That insects possess, in a 

 high degree, this sense, is evident to every one who 



* Did not Treviranus here mistake the ocelli for the ears > 



