JELLYFISH.
79
temperature, the Hydra tubae become ringed, the incisions
becoming deeper until, in due time, the Strobilae, which are, of
course, the nearly severed portions of the the Hydra tuba body
itself, become incipient medusae known as Ephyrulae until, when
development has proceeded sufficiently to permit movement,
the now separate entities push each other off into the water as
Ephyrae, or baby jellyfishes, to commence life for themselves.
This is a most fascinating metamorphosis to observe. When
almost ready to break loose the Ephyrulae begin to colour
according to species, and, as before stated, variations in colour
(as regards Chrysaora) are due to light. Sometimes it will be
found that a Hydra Tuba will, at strobilation time, assume
strobilation colours. In such cases it may be taken as certain
that that Hydra Tuba will not strobilate during that season.
Strobilae once started are sometimes arrested and revert to
normal again, but this state is not of frequent occurrence, and
its cause is unknown to me.
The investigator has now reached the Ephyra stage in the
metamorphoses, and since the difficulties confronting the ordinary
man in this research are so tremendous it will almost certainly
be the last stage of "Home work," in which he will consider
himself well repaid; for the experience of seeing some hundreds
of young ephyrae together in a tank for the first time is one not
easily forgotten; they are such delicate and beautiful little
creatures.
However, work soon increases for any one living away from
the sea and away from a marine laboratory, for if the little
mites are to grow they must be fed and they will grow—
—in captivity—only on a rising temperature, and this pro-
bably applies to the seas also, as they, of course, belong
to the plankton. It is possible to identify Aurelia, Chrysaora
and Cyanea from the earliest stages, provided that Rhizostoma
(which I have never seen) does not imitate either of the species
in their characteristics. Otherwise each is different—if but
little—from the others. They are all, at first, very delicate and
most difficult to feed individually; sometimes it took me ten
minutes to feed one. No plants should be kept with them in
small jars, and all containers—unless very large—should be
round and not square, otherwise they tend to become defective
and aeration by syringe should now be avoided.