OF MICROSCOPIC OBJECTS. 89 



The eyes of insects are sometimes allowed to dry in their 

 natural shape, and mounted as opaque objects; but generally 

 they are used as transparencies in balsam or liquid, so the 

 description of the treatment which they require will be 

 deferred to Chapter IV. 



Hairs when not too dark, are sometimes transparent 

 enough when mounted dry, but are usually mounted in 

 balsam. These will be more fully noticed in another place, 

 but there are some without which no cabinet is deemed in 

 anywise complete. Many different species of bats, English 

 and foreign, present us with hairs the form of which we 

 should never have dared to imagine without microscopic 

 aid. Other curious objects are found in the antennae 

 of crabs. You can also readily know whether you are being 

 deceived when you buy what you deem a real sealskin or 

 sable. From some of the common caterpillars I have ob- 

 tained exquisitely beautiful slides, and a kangaroo is a true 

 friend to an object-gatherer. 



The hair of the ornithorhynchus is a very curious object, 

 having a thin place in the middle of its length, and so pre- 

 senting somewhat the appearance of a flail. 



These are a few of the objects which are often mounted 

 dry, but some of them should be shown in balsam or liquid 

 also, and there is much difference of opinion as to the best 

 way of preserving others. This, however, is explained by 

 the fact, that the transparency which balsam gives, inter- 

 feres with one property of the object, and yet develops 

 another which would have remained invisible if preserved 

 dry. The only method of overcoming this difficulty is to 

 keep the object mounted in both ways, which is comparatively 

 little trouble. 



I may here mention that many prefer the lieberknhn 

 for the illumination of opaque objects; and a good back- 

 ground is gained by putting upon the under-side of the 

 slide, immediately beneath the object, a spot of black varnish, 

 which does not interfere materially with the light. 



