276 



THE MICROSCOPE AND ITS REVELATIONS. 



c, c). The gradual formation of these prolongations may be traced in 

 the pigment-cells of the Tadpole during its metamorphosis (Fig. 465). 

 Similar varieties of form are to be met-with in the pigmentary cells of 

 Fishes and small Crustacea, which also present a great variety of hues; 

 and these seem to take the color of the bottom over which the animal 

 may live, so as to serve for its concealment. 



672. The structure of the Epidermis may be examined in a variety of 

 ways. If it be removed by maceration from the true Skin, the cellular 

 nature of its under surface is at once recognized, when it is subjected to 

 a magnifying power of 200 or 300 diameters, by light transmitted 

 through it, with this surface uppermost; and if the epidermis be that of 

 a Negro or any other dark-skinned race, the pigment- cells will be very 

 distinctly seen. This under-surface of the epidermis is not flat, but 



FIG. 464 



FIG. 465. 



FIG. 466. 



Cells from Pigmentum 

 Nigrum; a, pigmentary 

 granules concealing the 

 nucleus; b, the nucleus. 



Pigment-cells from 

 tail of Tadpole: a, 

 a, simple forms of 

 recent origin; 6, ft, 

 more complex forms 

 subsequently assum- 

 ed. 



Detached Epithelium-cells; a, with 

 nuclei 6, and nucleoli c, from Mucous 

 Membrane of mouth. 



FIG. 467. 



Ciliated Epithelium; , nucleated 

 cells resting on their smaller extremi- 

 ties; 6, cilia. 



is excavated into pits and channels for the reception of the papillary 

 elevations of the true Skin; an arrangement which is shown on a large 

 scale in the thick cuticular covering of the Dog's foot, the subjacent 

 papillae being large enough to be distinctly seen (when injected) with 

 the naked eye. The cellular nature of the newly-forming layers is best 

 seen by examining a little of the soft film that is found, upon the surface 

 of the true Skin, after the more consistent layers of the cuticle have been 

 raised by a blister. The alteration which the cells of the external layers 

 have undergone, tends to obscure their character; but if any fragment of 

 epidermis be macerated for a little time in a weak solution of Soda of 

 Potass, its dry scales become softened, and are filled-out by imbibition 

 into rounded or polygonal cells. The same mode of treatment enables 

 us to make out the cellular structure in warts and corns, which are 

 epidermic growths from the surface of papillae enlarged by hypertrophy. 

 673. The Epithelium may be designated as a delicate cuticle, cover- 



