ON ECHINODERMATA. 543 
the testa, are put in motion in every direction by the external 
lamina of the cutaneous envelope, which attaches itself to the 
circumference of the pad of their base, and which appears 
stronger, and more evidently muscular at the spines of the 
base of the echinus. In desiccation, it is impossible to per- 
ceive any distinct muscular fibres, and sometimes even any 
muscles, properly so called. 
These animals are all aquatic and marine. They, never- 
theless, constantly live on the sea-shore, in rocky and sandy 
places. They are very rarely found abandoned by the tide. 
It would seem, that if too much advanced to recede, they 
possess the faculty of sinking more or less deeply into the sand. 
In this case, it is easy to recognize the place where they are, 
by the existence of a small hole in the form of a funnel, which 
is remarked at the surface of the sand. They sink and recede 
considerably less when the weather is fine, than when it is 
tempestuous. 
The echinus, in locomotion, which is never very quick, 
makes use of its tentacular suckers, and its prickles, and es- 
pecially of the inferior ones. But it appears, that this cannot 
take place, except on a resistant soil. In the first case, it 
elongates as far as possible (and it is astonishing the extent 
to which it can be done) a certain number of the suckers, 
which are in the direction in which it wishes to go. It at- 
taches these strongly to some solid body, causing a vacuum 
by means of the cuppers which terminate them, after which it 
contracts them, and thus draws its body towards this point. 
By thus reiterating the same manceuvre, the echinus may, 
without doubt, advance with some degree of rapidity. In 
the second case, when it employs its prickles, it extends those 
on the side where it wishes to move, to the utmost possible 
degree. Then it lowers them, pushing itself on with those on 
the opposite side; and as it has some in all directions, it is 
evident that it can walk in all ways. In general, its progress 
