THE ORGANS OF THE SENSES. 295 



flies, the Hymenoptera and Coleoptera, of a dark blue or entirely black. 

 Even in insects which possess but one pigment, the colour is not entirely 

 the same, but darker nearer the centre, brighter at its circumference in 

 the vicinity of the glass cone and lens. In some cases we discover 

 more than two layers of pigment, as, for example, in Gryllus hicro- 

 glyphicus, an exterior pale orange colour, a central bright red, and a 

 dark violet. The first and second were very thin, each thinner than 

 the lenses; the innermost entirely filled the remaining portion of the 

 eye*. 



Thus much upon the structure of the eye. We may here once more 

 repeat that this entire description is but an extract of Joh. M filler's 

 admirable treatise upon this subject, and that here merely the most 

 interesting portion of his results are stated. The subsequent labours 

 of Straus Durkheim f and Duges do not equal those of the above 

 distinguished entomotomist, nor have they been able to add many new 

 discoveries or corrections of his. 



195. 



Much obscurity still invests our knowledge of the hearing of insects. 

 G. R. Treviranus J has, indeed, discovered and described the organ of 

 hearing of the moths ; it consists of a simple thin drum, which is seated 

 at the forehead in front of the base of each antenna, and to which the 

 nerves of hearing, which are branches of the nerves of the antennae, 

 spread themselves without the intermedium of a hearing bladder filled 

 with water; but this admirable discovery of his has not been confirmed 

 in insects of other orders, for a similar organ has not yet been detected 

 in them. After him, Joh. Muller described the peculiar organ of the 

 grasshopper, which is seated on each side at the base of the abdomen ; 

 he considered it the organ of hearing, but incorrectly, as will be shown 

 below : it is more likely to be an organ of sound. Other earlier opinions, 

 for example, those of Ramdohr ||, who considered the anterior salivary 

 glands of the bees as organs of hearing, are partly, as this latter, recalled, 

 or else, as unsatisfactory, require no further notice. To these may be 

 classed Comparetti's observations of bags and passages in the heads of 



* Muller, p. 355. f Considerations General, &c., p. 40S 



+ Annalen clu Wetterau. Gesell. f. d. Ges. Naturk. Vol. i. Pt. 2. 180!>. 

 Consult his Phys. du Gesischtssinncs. p. 438. 

 || Mag. du Ges. Naturf. Berlin. 1811. 389. 



