ON ECHINODERMATA. 545 
tions; one comprehending the holothuriz, and the other the 
true actiniz. 
The holothuriz, which the ancients usually comprehended 
under the vague name of purgamenta maris, or of pudenda 
marina, are found, as it would seem, in every sea, the deep- 
est parts of which they most particularly inhabit, even as far 
as three hundred feet and more. It is even to this cause that 
the peculiarity seems owing, of these animals vomiting, as it 
were, their intestinal canal, in consequence of the great dif- 
ference of pressure. They more particularly remain in the 
oozy bottom, and in the anfractuosities of the rocks, where 
they fix themselves by means of sorts of cuppers, or papilli, 
from tentacula, with which certain parts of their bodies are 
provided. They can, by means of these organs, draw them- 
selves along over the submarine bodies, and thus change 
place. But it appears, that they can do so likewise, either 
by alternate flexions of the body, after the manner of worms, 
or even by filling their body with water, and shooting it 
forcibly through the anus, so as to be able to swim, assisting 
themselves with their tentacula. They feed on pretty strong 
marine animals. It is thought that they are hermaphrodites, 
and that they reproduce by internal gemmule, like the acti- 
niz, whence it has been said, that they are viviparous. Fa- 
bricius, in fact, tells us that he found in the anal part of one 
individual a young holothuria, swimming freely. 
The organization of the holothuriz had been studied by 
many anatomists, and among others, by M. Bohatsh, and by 
Vahl, but inanincomplete kind of way. M. Tiedmann, in his 
dissertation, which gained him the prize proposed by the 
Academy of Sciences in Paris, has added very considerably 
to our acquaintance with this subject. 
The species of this genus appear to be rather numerous, 
and especially so in the seas of cold countries. But they 
have been in general too ill described to be  charac- 
VOL. XII. Nn 
