THE MICROSCOPE IN ZOOLOGY. 175 



until quite transparent, when it may be removed, the tur- 

 pentine partially drained off, and a solution of balsam in 

 chloroform allowed to insinuate itself by capillary attrac- 

 tion. Gentle heat from a spirit-lamp will be useful at this 

 stage of the mounting. 



Small insects hardly need soaking in caustic potash, as 

 turpentine or oil of cloves will render them after awhile 

 quite transparent, and their internal organs are beautifully 

 seen in the binocular microscope. Thin sections of insects 

 are instructive, and may be made with a section-cutter by 

 first saturating the body with thick gum mucilage, and 

 then incasing in melted paraffin. 



Many insects and insect preparations are well preserved 

 in glycerin. 



The eggs of insects are often interesting objects, and 

 should be mounted in fluid. 



Wing cases of beetles are often very brilliant opaque 

 objects. Some are covered with iridescent scales, and 

 others have branching hairs. Many are improved by 

 balsam, and this may be determined by touching with 

 turpentine before mounting. 



Scales of Lepidoptefa, etc., may be exhibited in their 

 natural arrangement by mounting a small piece of wing 

 dry. If desired as test objects, a slide or thin cover, after 

 having been breathed on, may be slightly pressed on the 

 wing or body of the insect. The scales are really flattened 

 cells, analogous to the epidermic cells of higher animals. 

 Some have their walls strengthened by longitudinal ribs, 

 while others, as the Podurce, show a beaded appearance 

 under high powers from corrugation. Dr. Carpenter be- 

 lieves the exclamation marks in the scales of the latter to 

 be the most valuable test of the excellence of an objective. 



Hairs of insects are often branched or tufted. The hair 

 of the bee .shows prismatic colors if the chromatic aberra- 

 tion of the object-glass is not exactly neutralized. 



Antennae vary greatly in form, and are often useful in 



