290 



THE MICROSCOPE. 



on either side ; above which are two jointed feelers (palpi labiales), the 

 use of which is probably for the purpose of examining the food before 

 it is taken into the mouth, and afterwards to clean the tongue. Near 

 these feelers the antennae or horns are placed, curious in form as they 

 are delicate in structure. The antennae of the male generally differ from 

 those of the female : some writers have believed them to be the organs 

 of smell or hearing ; others that they are solely intended to add to the 

 perfection of their touch or feeling, being sensible to the least motion 

 or disturbance of the air. They are amongst the most interesting and 

 distinguishing characteristics of insects ; and appear to be always em- 

 ployed for the purpose of examining every object they alight upon. 



The structure of the eye is in all creatures a most admirable piece 

 of mechanism : in none more so than in those of the insect tribe. 

 The eyes differ in each species ; varying in number, situation, figure, 

 simplicity of construction, and in colour. 



Fig. 127 represents a portion of the eye of the common fly, 

 drawn by the light of the sun upon a prepared photographic surface 

 of wood ready for the engraver, not a hne 

 being added by the hand of the draughts- 

 man. 



Fig. 128 represents a side view of the 

 eye when thrown down, and showing the 

 compound eye to be made up of a large 

 number of cylindrical tubes. 



" On examining the head of an insect, 

 we shall find a couple of protuberances, more 

 ^S- 128. Qj. jggg prominent, and situated symmetri- 



cally one on each side. Their outline at the base is for the most part 

 oval, elliptical, circular, or truncated ; while their curved surfaces are 

 spherical, spheroidal,. or pyriform. These horny, round, and naked 

 parts, seem to be the cornese of the eyes of insects ; at least they are with 

 propriety so termed, from the analogy they bear to those transparent 

 tunics in the higher classes of animals. They differ, however, from 

 these ; for when viewed by the microscope, they display a large number 

 of hexagonal facets, which constitute the medium for the admission of 

 light to as many simple eyes. Under an ordinary lens, and by re- 

 flected light, the entire surface of one of these corneas presents a beauti- 

 ful reticulation, like very fine wire gauze, with a minute papilla, or at 

 least a slight elevation, in the centre of each mesh. These are resolved, 

 however, by the aid of a compound microscope, and with a power of 

 from 80 to 100 diameters, into an almost incredible number (when 



