JELLYFISH. 85
no romance, in the, wresting of secrets from Nature in the form
of jelly fish.
REPRODUCTION IN SCYPHOMEDUSAE.
It would seem that as with the Actinia there is a limit to
size in Hydra Tubae, with a subsequent breaking down to
normality. This is marked in the anemones. This limit is
proved to have been attained by Hydra Tubae by: (a) budding,
(b) strobilation, i.e., the number of buds produced at a time
will depend on the size of the Hydra Tuba and the number of
ephyrulae in a strobila will depend upon the size of the Hydra
Tuba. This cannot be questioned, it seems to me. It must be
remembered that fission is unknown, normally, in Hydra Tuba,
and it seems to the writer that the original method of repro-
duction was by the "resting gemmule" (generation time 14
days) which, after the race had succeeded in evolving the medusa,
continued as the planula.9
A possible explanation of this double method may be found
in variations in temperature.
The Hydra Tuba buds and encysts at high temperatures.
It strobilates at low ones, the difference in temperatures re-
quiring, apparently, a different method.
This raises an interesting point, still to be certainly proved.
Supposing a Hydra Tuba to be placed in a situation where the
critical low temperature is never attained—will it strobilate?
The writer thinks that it will not, and that, instead, the race
will be preserved by budding alone, even in the case of Chrysaora,
and that in this postulate lies a possible explanation as to why
some species are sporadic, appearing but rarely at certain times
and in abundance at others. Cannibalism, of course, may affect
this.
If correct, this postulate would tend to show that the Hydra
tuba may be the mature, though not the final form; as is
the case with many plants which propagate by suckers
which eventually break loose from the parent plant. When
one realises that it is merely the adult breaking itself up
into parts some of the difficulty disappears.
The writer desires to express his grateful thanks to the
following friends for the very sympathetic and ungrudging
9 Cyanea planulae still sometimes encyst by the thousand—a percentage subsequently
producing Hydra Tubae.