220 THE MICROSCOPIST. 



dies of fibres, and cavities containing cells. Its tissues are 

 in layers, as follows : 1. External epithelium, flat and 

 laminated. 2. Anterior basement-membrane or lamina. 

 3. True corneal tissue. 4. Membrane of Descemet or 

 Demours. 5. Endothelium with flat cells (Plate XXIY, 

 Fig. 176). The cells of corneal tissue are of two forms. 

 The first are wandering or amoeboid cells, and may be 

 seen in a freshly extirpated frog's cornea placed underside 

 up, with aqueous humor in a moist chamber, on the stage 

 of the microscope. If a small incision be made at the 

 margin of the cornea of a living frog a few hours before 

 its extraction, and vermilion, carmine, or anilin blue is 

 rubbed in, the cells which have absorbed the coloring 

 matter will be found at some distance afterwards, having 

 wandered like leucocytes or pus-cells elsewhere. Their 

 origin may be from blood or true corneal corpuscles, or 

 both. The second form, or corneal corpuscles, are im- 

 movable, flat, with branching or stellate processes. They 

 may be demonstrated by staining with chloride of gold 

 or nitrate of silver. The bundles of fibrillar substance in 

 the cornea pass in various directions, and the natural 

 cavities in it contain the corneal cells. As stated, the 

 nerves of the cornea have been traced to the external 

 epithelium, which sometimes contains- serrated (riff' or 

 stachell) cells. 



The aqueous humor is structureless, but the vitreous 

 humor is supposed to have delicate membranous septa. 

 The crystalline lens consists of a capsule inclosing a tissue 

 of fine transparent fibres or tubules, which are of epithe- 

 lial origin. These fibres are flat, and often have serrated 

 borders, especially in fishes. 



The retina, or nervous portion of the eye, is the most 

 important, as its delicacy and liability to decomposition 

 render it the most difficult object of microscopic exami- 

 nation. 



We must dismiss the popular notion of minute images 



