of the Genus Equoree. 375 
So great, in short, is the density or homogeneousness of this 
substance, that the .enuvity of the canals which pass 
through it, and nourish it, must be inconceivable. When 
exposed to the atmosphere, it resolves into a colourless l- 
guid, very like common sea-water. We shall speak in an- 
other place of the peculiarities which this hquor presents, 
when we allow ij to pass to the putrid decomposition, and 
describe the results of our analysis: it is. sufficient in the 
‘mean time to observe, that this fusion of the equoree is so 
complete, that of one which weighed several kilogrammes, 
there scarcely remained upon the filter a few milligrammes 
of a membranous-like residue. 
Locomotion.—Notwithstanding the singular composition 
of their substance, the equorez, like all the other species 
of meduse, enjoy a power of contraction which is truly 
Astonishing. Always active on the.surface of the sea, we 
see them alternately locked up within themselves, and after- 
wards expand with more or less rapidity. We shall describe 
the mechanism of these motions; but let us first speak of 
the effect which they ought to, produce with respect to the 
position of the animal which executes them. 
In contracting themselves, the equorea tend to repel the 
column of water which is immediately in contact with 
the lower surface of their umbrella: by the resistance of 
the fluid and the decomposition of movement which it pro= 
duces, the zoophyte finds itself ‘in some measure projected 
in a direction contrary to that of the column of water 
displaced by the shock: it will therefore have changed 
place by a given quantity; and this quantity, every thing 
else being the same, will be in proportion to the force of 
repulsion which it will have developed. In the expansion 
which succeeds immediately after the contraction, the ani- 
mal acts on the subjacent column of water in the same 
manner; and from this second percussion there results a 
new step for it, if We may be allowed to use the ex- 
pression. 
However numerous or varied may be the motions of 
the medusz, we may nevertheless refer them all to these 
two elements, as simple as they are easy to conceive. Thus, 
if one of these animals wishes to rise from the bottom of | 
the sea to the surface, it fixes itself in a vertical position, 
strikes from bottom to top, and rises by a series of steps, 
9f, to speak less metaphorically, by a succession more or 
Jess rapid of contractions and dilatations, to the height 
which it wishes to attain. If it wishes to change the di- 
rection of its route, it inclines itself so as to make the 
Aa4 umbrella 
