FOR ZOOLOGICAL PURPOSES.
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bellows the bell-jar is filled with the dense fumes of the tobacco, and
the whole apparatus is left for some hours. Then the fumigation is
repeated in the evening, and the next morning an open bottle con-
taining a little chloroform is placed under the bell-jar and left there
for two or three hours. After this the anemone is usually found to
have lost its irritability, and not to contract or move when touched,
and it is finally killed and fixed in the expanded condition by a
mixture of chromic acid (1 per cent.) ten parts, pure acetic acid 100
parts. It is left in this only a few seconds, and is then transferred to
chromic acid 1/2 per cent, for a few hours, and then to alcohol. This
method would probably succeed well with Tealia crassicornis.
Hydromedusae.—The fixed branching compound forms of the
Hydrozoa such as Obelia, Sertularia, Tubularia, etc., can all be fixed
with little difficulty by pouring suddenly over them hot concentrated
sublimate solution when they are fully expanded in a small quantity
of sea water. They must then be emptied out into cold water and
washed for some time in a gentle current of the same, and then be
transferred to alcohol of increasing strengths. The small delicate
Medusas, which are derived from the fixed hydroids, are killed in
various ways. Many can be well fixed with a mixture of sublimate,
saturated solution, and acetic acid, in the proportion of two parts of the
former to one of the latter. Others are killed with acetic acid pure,
and then transferred to a mixture of alcohol and chromic acid equal
parts, in which they remain for fifteen minutes, after which they
undergo the usual treatment with alcohol.
Another reagent very useful for Medusae is chrom-osmic acid
made by mixing together chromic acid (1 per cent. solution) 100
parts, and osmic acid (1 per cent.) two parts. Our common Aurelia,
often occurring in summer in hundreds and thousands, is prepared
by placing it in this mixture for about an hour, then rinsing it in
fresh water and transferring it to weak alcohol. To avoid the flat-
tening of the medusa it may be placed when in the alcohol, um-
brella downwards, in a concave clock glass, or suspended in a loose
muslin bag. Rhizostoma and other large medusae may be prepared
in the same way, or may be killed in a mixture of three parts of
osmic acid (1 per cent.) to 100 of sea water. Specimens should
only be left in the osmic until they have acquired a light brownish
tinge, then washed in fresh water and transferred to weak alcohol.
Ctenophora.—Only Hormiphora plumosa (often called Pleuro-
brachia) and Beroc ovata occur commonly on the British coast. The