348 PREPARATION OF MARINE ANIMALS.
be invisible. The Lob-worm, Arenicola, is often much too dark
to give good results, but pale specimens, partially dissected,
show the entire structure to great advantage, the blood in the
chief vessels retaining its natural colour without sensible change.
The beautiful purple Nudibranch, Eolis, contains a pigment
easily dissolved out by Canada-balsam, but the colouring is
retained perfectly for many years, if protected by the animal
being well soaked with gum-Arabic, to which a little glycerine
has been added to prevent undue brittleness.
The Slender Spider-crab, Stenorhynchus, varies much in
different localities. Sometimes it is much too dark, but in one
year, in the Orwell, it was very pale and the shell comparatively
soft, and covered with parasites, which, however, would not
have been well seen unless somewhat stained with log-wood, so
as to be of about the natural colour. In mounting Crustacea,
the principal difficulty is to get rid of the included air, but this
may be done by carefully pricking with a sharp, fine needle,
when the specimen is in benzole.
Priapulus should be killed by fresh water, and kept in it
until it has become limp, since otherwise it contracts laterally,
and shows little of its proper character. It may also be
necessary to slightly stain it. Most excellent preparations may
be made by cutting open the body longitudinally, staining it,
and spreading it open, so as to show the internal anatomy and
the whole muscular structure.
It is difficult to prepare good specimens of Cirratulus borealis,
since they are often too dark and opaque. My best results have
been obtained by killing them in fresh water and leaving them
in it until they have swollen considerably, but are not decom-
posed. By this means they may be mounted so as to show the
remarkably convoluted intestine, and the chief blood vessels
filled with red blood. The cirri should be cut off and stained
with carmine, so as to be of the natural colour of the living
animal, and mounted on the glass after the body has been dried.
My specimens of Synapta have been obtained in the Orwell,
outside this county. I exhibit them in order to show the great
advantage of proper staining. In one specimen the animals
were kept for a considerable time in alcohol, with a somewhat
diluted solution of madder, so as to penetrate internally. By
this means the tentacles, the intestine, the ovaries, and the chief