MICROSCOPIC OBJECTS. 39 



excellent objects for the examination of the exact forms 

 of the parts to which they belonged. In general, they 

 are too diaphanous for mounting in Canada balsam, though 

 the exuviae of the jaws of the Spider may be displayed 

 in this way with effect. 



Eyes, Fish. — The dried globular crystalline lens in the 

 eye of a Fish, when examined by the aid of a microscope, 

 will be found to be composed of a number of concentric 

 strata or layers, somewhat resembling the coats of an 

 onion. A portion of one of these laminae, separated, 

 and placed under a microscope, magnifying 300 diame- 

 ters, will be found to consist of flat fibres or bands, aris- 

 ing from each pole of the lens and expanding towards its 

 equator, like the spaces between the meridians on the 

 artificial globe. The edges of these fibres are serrated, 

 and fit into each other like the teeth of a double rack or 

 the sutures of the human skull. Sir David Brewster, 

 who first minutely examined the structure of these lenses, 

 has accurately measured the breadth of the bands. (See 

 Phil. Trans, for 1833.) He found that a single lens, 

 y^^ths of an inch in diameter, from the eye of a codfish, 

 contained five millions of these flat fibres, and 62,500 

 millions of serratures, or teeth. They are dehghtful 

 objects, whether opaque or transparent. — Magnifying 

 power for the former 250, and for the latter 350 diame- 

 ters. 



Eyes, Insects, 8;c. — The structure, number, and form of 

 the eyes of insects may be ranked among the most curious 

 parts of natural history. The compound eyes are arranged 



