GLASGOW SOCIETY OF FIELD NATURALISTS. 131 



already, a tube-fitting attached to the stage into which the sub-stage 

 illumination apparatus is fixed by means of a bayonet catch, but 

 the length of this tube prevents oblique illumination by means of 

 the mirror or prisms. On the tail-piece of the microscope a large 

 mirror held by a jointed, often doubly jointed, arm can be made 

 to slide up and down. One side of the mirror is generally plane 

 and the other concave. 



Having described the essential parts of the microscope itself, 

 I will now enumerate and explain those accessories which the 

 microscopist will find useful and often indispensable. 



1. The stage or mineral forceps for holding unmounted objects, 

 such as insects, parts of plants, minerals, &c. 



2. The stage plate, which is made of glass and has a glass ledge, 

 serves for unmounted objects, especially fluids, which might 

 injure the stage if they came in contact with it. 



3. The Folyp or Zoophyte trough of ground glass, for viewing 

 Polyps, &c., in water. 



4. The live-hox, of which it is well to have various sizes. It 

 consists of a circular box fixed on a plate ail of brass and having 

 a glass bottom and a thin glass cap to slide over it. A convenient 

 form for condenser illumination is the live-box with flush glass 

 bottom. These live-boxes are used for the examination of live 

 objects such as insects, but especially for Infusorise. 



5. The compresser is an instrument consisting of two plane 

 parallel glass surfaces, which, by means of levers, screws, or wedges, 

 may be more or less approached to each other. These compressers 

 serve to apply a gradual pressure to objects whose structure can 

 be bettei-, or can only then be, seen when they are flattened out. 

 Such pressure may be applied to crush small shells, to flatten a 

 cuticle, to hold larger animalcules in the same place so that they 

 are unable to move out of the field of vision, &c. Strict parallel- 

 ism of the surfaces is most essential, especially for the examination 

 of fluids, which otherwise would be at once squeezed out in one 

 direction instead of being spread out, 



6. The frog and fish plate for examining the circulation of the 

 blood in the web of a frog's foot, or in the tail or fins of a fish, the 

 animal being wrapped in a little piece of wetted linen and tied by 

 means of threads to the plate which is then fixed on the stage. 



7. The double, triple, or quadruple object-glass carrier, or Brooke's 

 arm or double nose-piece, which screws into the nose-piece of the 



