182 



THE MICROSCOPE AND ITS REVELATIONS. 



TIG. 121. 



172. Plate- Glass Cells. Where large shallow cells with flat bottoms 

 are required (as for mounting Zoophytes, small Medusa, etc.), they may 

 be made by drilling holes in pieces of plate glass of various sizes, shapes, 

 and thicknesses (Fig. 121, A), which are then cemented to glass slides with 

 marine glue. By drilling two holes at a suitable distance and cutting 

 out the piece between them, any required elongation of the cavity may 

 be obtained (B, c, D). 



173. Sunk Cells. This 

 name is given to round or oval 

 hollows excavated by grinding 

 in the substance of glass slides, 

 which, for this purpose, should 

 be thicker than ordinary. Such 

 cells have the advantage not 

 only of comparative cheapness, 

 but also of durability, as they 

 are not liable to injury by a sud- 

 den jar, such as sometimes causes 

 the detachment of a cemented 



c plate or ring. For objects whose 

 shape adapts them to the form 

 and depth of the cavity, such 

 cells will be found very conve- 

 nient; thus the Author has a 



D series of young Comatulce (Fig 

 378) thus mounted, which are 

 extremely well displayed, alike 

 on their upper and on their 

 under surfaces. It naturally 

 suggests itself as an objection 

 to the use of such cells, that the 

 concavity of their bottom must 

 so deflect the light rays, as to 

 distort or obscure the image; 

 but as the cavity is filled either 

 with water or some other liquid 

 of higher refractive power; the 

 deflection is so slight as to be 

 practically inoperative. Before 

 mounting objects in such cells, 

 the Microscopist should see that 

 their concave surfaces are free 

 from scratches or roughness. 



174. Built-up Cells. When 

 cells are required of forms or 

 dimensions not otherwise pro- 

 curable, they may be luilt up of 

 separate pieces of glass cemented 

 together. Large shallow Cells, 

 suitable for mounting Zoophytes 



Sunk Ceils. or similar flat objects, may be 



easily constructed after the 



following method: A piece of plate-glass, of a thickness that shall give 

 the desired depth to the cell, is to be cut to the dimensions of its outside 



Plate-Glass Cells. 



Eio: 122. 



