176 MICROSCOPIC ILLUSTRATIONS. 



water-tight ; and the tubes themselves may be greased 

 for the same purpose if necessary. These boxes are as useful 

 pieces of microscopic apparatus as ever were invented. 



Figure 22 represents the black ground box (an inven- 

 tion of Mr. Lister), which in the present instrument also 

 forms a stage for the single microscope, and for dis- 

 section. 



At 'n is seen its lid, of which a side view is given at 'o ; 

 at 'p, its bottom with its side view also ; its interior 

 surface is lined with black silk velvet, and so is the 

 superior surface of rhe lid ; the sides of the cone, 'q, are 

 well blacked ; at 'r is seen a disk, also covered with black 

 silk velvet, which acts along with the silver specula. 

 Its arm revolves on the top of the cone, and can be 

 removed altogether, if necessary; at its extremity is a 

 hole, in which is inserted the cradle-joint, which carries 

 a brass needle; a small piece of brass tube, stuffed with 

 cork, is affixed to one of its extremities, and to the other 

 a pair of forceps, which are represented of their full size 

 at figure 23. These are constructed as usual, except 

 that a hole is drilled through them at 's, to enable them 

 forcibly to grasp the head of a common pin. 



Figure 24 is the piece which carries the wheel of dia- 

 phragms ; 't is the plan of their under side. There should 

 be about five apertures, varying from half an inch to 

 l-10th in diameter. This apparatus screws on to any of 

 the aquatic boxes, also to the slider holder, figs. 25 and 

 26, and the false stage or black ground, figure 22, in 

 place of the bottom, 'p. It was invented by Monsieur 



