Dr. Du Plessis on a new Paludicolous Medusa. 387 
vicissitudes, has become hardened by this process j and the 
proof of this is that it may be very well preserved for -weeks 
together in the smallest bottles, with a few hundred grammes 
of the water of the canal and a few green Alga? to keep up a 
small supply of oxygen. Under these circumstances we have 
transported specimens with the greatest facility from Cette to 
Lausanne, and kept them for months without the least trouble. 
This species, being so accommodating, will be very welcome 
to those who desire to observe these animals for a long time 
in captivity. 
We are aware, indeed, that Cladonema radiatum , Duj., and 
other microscopic Medusa? also bear captivity; but these are 
creatures scarcely visible to the naked eye, whilst ours, being 
of the size of a half-franc (Swiss money), is much more suit¬ 
able for all sorts of manipulation. 
Moreover (and this is the most interesting point) it presents 
one of the clearest examples of the influence of the circumam¬ 
bient medium upon the gradual modification and, finally, 
transformation of one species into another; for certainly our 
Medusa has originated from an importation through the pool 
of Thau of the large Cosmetira jou/tctata, the form of which it 
reproduces on a small scale, repeating its whole organization 
en diminutif. 
Description. 
Form. In repose the animal resembles a little basin or 
saucer, the circumference of which is furnished with long and 
equal fringes. These fringes are the tentacles ; and the basin 
is what is called the umbrella. 
In motion (that is to say, when the animal swims by alter¬ 
nately contracting or relaxing the muscles of the umbrella) 
the form becomes that of a more or less open bell, according to 
the muscular contraction. 
At the bottom of this bell, starting from the centre of the 
cup, hangs a clapper in the form of a bottle with a quadran¬ 
gular neck. This clapper is the trunk [ manubrium ], which 
can elongate and contract, become rounded, and turn and 
bend in all directions to enable the animal to seize the ani¬ 
malcules upon which it feeds. The end of the trunk termi¬ 
nates in four angles, surmounted by a small knob or inflation. 
Even in repose it passes beyond the margin of the umbrella ; 
if is therefore longer than the depth of the bell. 
Size. Usually the bell or umbrella when spread out scarcely 
exceeds the dimensions of a half-franc or piece of 50 centimes 
(Swiss money). Very old examples, however, sometimes 
attain the size of a franc, and the young are scarcely above 
