PREPARATION OF MARINE ANIMALS.
347
unless they are kept very dry. Of course the great aim should
be to show, not merely the general form and colour, but also as
much as possible of the anatomical structure. To accomplish
this many different methods are necessary in the case of different
animals; but, on the whole, independent of partial dissection,
they may be classified under five divisions, viz. :—
(1.) Animals which may be dried and mounted in their natural state,
and need no special precautions to preserve their original
colour.
(2.) Those which require special treatment to retain their natural
colour.
(3.) Animals which must be stained in various ways, in order to
properly show their structure, or to make them permanently of
the true colour.
(4.) Animals which could not be properly mounted unless previously
decalcified by acids.
(5.) Those from which it is desirable to remove some of the natural or
acquired colour, in order that it may not obscure their structure.
There are indeed cases in which it is better to combine two
or more of these processes, and in describing the specimens it is
not desirable to keep strictly to the above divisions.
In the first instance my aim was to mount the animals
merely for use as lantern slides, but lately I have been en-
deavouring to so prepare them that they may be successfully
photographed. This materially increases the difficulties, since a
specimen may show extremely well in the lantern, when the
colouring is such as to make it almost impossible to produce a
good photograph.
Though nearly all the slides I propose to show were pre-
pared with material collected on the coast of Essex, they are
now exhibited merely to illustrate methods, and, it may be well
to briefly describe them in order.
The simple Ascidian, Cione intestinalis, is a good example
of an animal which needs neither staining nor special precaution
to preserve the colour. Some specimens of Sabella also give
excellent results, but when required for photographic purposes
it is well to reduce the general colour of the body by long
keeping in alcohol, and to stain the plumes, which otherwise
might be too pale, with log-wood. Small specimens of the
beautiful Medusa, Chysaora, are sometimes naturally coloured
so as to make excellent slides, though it may be necessary to
slightly tint the outline of some portions, which otherwise would