MICROSCOPIC OBJECTS. 165 



(16.) Compressor, or Crush-hocc. — Tliis is a modification 

 of the aquatic live-box. The cover or upper plate has 

 either a screw cut within it or is jointed to an arm con- 

 nected with a screw. The design of either contrivance 

 is to enable the observer to bring the upper and lower 

 plates of glass, between which the animalcules are placed, 

 in contact, and thus crush them. It is only in this way 

 that the existence of a lorica (shell) can be verified in 

 some minute infusoria, as in the family Crj^tomonadinse. 

 See ' History of Infusoria,' page 113, fig. 33. 



Note. — In whatever way the compressor, or crush- 

 box, is constructed, the upper glass must not, in its 

 approach to the lower one, have a lateral motion, but 

 only a vertical one. 



(16.) Arranging Transparent Microscopic Objects. — 

 One method for a small collection is to have a cabinet 

 with shallow drawers (twelve of them occupy a depth of 

 4;f inches) ; the most convenient width from front to 

 back being six inches. Into these shallow drawers the 

 slides containing the objects are laid flat in double rows. 

 The outer ends of the slides are made to fit into a ledge 

 in the front and back of each drawer. The inner ends of 

 the sliders meeting in the middle of the drawer are kept 

 down by a very thin slip of wood covered with velvet. 

 In this way the sliders do not shake when the cabinet 

 is moved from place to place ; every object is seen without 

 removal, and thus no loss of time is occasioned in 

 making a selection. 



Whatever plan be adopted for arranging microscopic 

 objects, it is always ad\dsable to arrange them so that 



