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 antenne 
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 lieberkuhn 
. 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. 
