JELLYFISH. 71
Essex Jellyfish. I write "Essex Jellyfish" because Pelagia, the
oceanic Medusa of the Irish coast, short-circuits the process of
its metamorphoses, and the form discovered by Miss Renton at
University College, and called after her, has not so far, after some
years, produced an ephyra in captivity, and there appears to be
no particular reason why it should do so in Nature. The four
forms which produce medusae off the Essex Coast are Aurelia,4
Chrysaora, Cyanea and Rhizostoma. It is also possible that Miss
Renton's "Hydra Tuba" may one day be found, since it has
been "planted" by me in a few spots in the Thames Estuary.
It is pelagic and will form—if surviving—part of the plankton.
Strangely enough to those people who enjoy the old problem of
"Which came first, the chicken or the egg?" it would appear
quite within the bounds of probability that the Medusa (Jelly-
fish), though it lays eggs, did not come first and that the "Hydra
Tuba," as with Miss Renton's form, is the true parent, but the
evolutionary cycle of a jellyfish is usually regarded as being the
following:—Medusa, ova, planula, Hydra Tuba, Strobila,
Ephyra, and so to Medusa again. The process as seen by me
over a period of nine years of very close observation is as follows:
The planulae develop from the eggs within the ovarian mem-
branes until they attain to free movement by cilia; they then
are liberated in clouds by Chrysaora directly into the water, but
are retained by Aurelia for some time in marsupia, and by
Cyanea in the voluminous folds of the manubrial curtains. I
have not been able to observe the reproduction of Rhizostoma,
so cannot comment on it. The numbers of planulae vary very
much with the species, as does also their size.
Chrysaora medusae in my experience liberated the greatest
number at one emission, an aquarium 18 inches x 11 inches x
9 inches having the front, back and sides so covered by attached
planulae that the water within could not be seen; the bottom
also was affected, since I removed 40 pieces of large nereids
from 6 inches to 2 inches in length from the tank; their pulsations
having drawn in swarms of planulae, the poison from whose
nematocysts causing the worms to break up. The Medusa was
7 inches in diameter and very beautiful.
Aurelia, so far as I have seen, does not liberate such hosts
4 This should properly be Aurellia, but custom sanctions the spelling adopted in this paper.
—Ed.