72 The Microscope. 



interior mechanism of an insect's eye can be examined 

 in a section, mounted in fluid; its preparation is a 

 matter of much nicety, but the outer lenses (also 

 known as " corneules") are hard and easily managed. 

 They require only to be washed at the inside with 

 water, applied by a camel's-hair brush, which removes 

 the fibres and pigment. The whole of one mass of 

 lenses can be detached with a pair of scissors, and 

 when washed, can be mounted by nicking its edges to 

 make it lie flat. It is then ready to examine with one 

 of the lower powers of the microscope, and I know no 

 more extraordinary and splendid object. It is really 

 like twelve thousand well -polished lenses, beautifully 

 precise in their hexagon forms about the front part of 

 the mass, and largest there ; while their form accom- 

 modates itself to their position near the edges. The 

 arrangement of light known as " back-ground illumi- 

 nation," shows this object in peculiar splendour. Some 

 additional apparatus is supplied for affording this sort 

 of illumination; but even without this addition, the 

 effect can be produced sufficiently for many purposes 

 by placing the lamp as low as possible, and at some 

 distance from the stage, and throwing light upwards 

 with the condensing lens placed obliquely, so that no 

 rays reach the observer's eye except those that are 

 caught by the object, which accordingly appears in 

 extreme brilliancy on a dark field of view. 



To show the experiment of the multiplied views, a 

 very small fragment of the eye will be found most 

 convenient, and different little pieces of management 

 must be used to add to the effect. It is well to have 



