328 THE NATURAL HISTORY 



prisms in each compound eye radiate from a common 

 centre, and are isolated from each other by a coating 

 of dark pigment, an object to be seen by the insect 

 must be in a strictly direct line with the axis of one of 

 the prisms and, as this cannot happen with the same 

 object to more than one prism on either side at a time, 

 it is not difficult to comprehend that our own vision, 

 with two eyes only, may not be more free from a 

 confusion of images than that of an insect with its 

 thousands ; and that the aggregation of so many 

 similar organs, placed at all angles, may in reality 

 have been designed as an admirable compensation for 

 their immobility. Many insects possess one, two, or 

 three simple eyes in the form of very convex lenses 

 (sometimes of unsurpassed brilliancy) fitted into the 

 central space on the head not occupied by the com- 

 pound eyes ; and it has been conjectured by Messrs. 

 Kirby and Spence that the range of vision in the 

 former is upwards, while that of the compound eyes is 

 more or less horizontal. For further details of the 

 general and particular structure of insects we cannot 

 refer to more delightful and instructive works than 

 Kirby and Spence's " Introduction to Entomology," 

 and its sequel, Westwood's " Introduction to the 

 Classification of Insects." 



We have already stated that the organs of man- 

 ducation (parts of the mouth) in beetles* are more 

 fully developed both as regards number and structural 

 character than those of other insects ; beetles, there- 

 fore, in modern systems of classification take precedence 

 of all the other orders. Their numbers are so great 

 that Stephens, in his " Manual of British Entomology," 

 published in 1839, has described upwards of three 

 thousand species ; and, without doubt, many others 

 have since then been added to the list. The Cicindelidce 



Order COLEOPTERA from the Greek Koleos, a sheath and 

 pteron, a wing wings in a sheath. Wings four ; the upper ones 

 (Elytra) corneous, without veins, and covering the under ones. 



