482 CLASS ECHINODERMATA. 
THE FIRST ORDER OF ACALEPH&, 
ACALEPH SIMPLICES, 
Float and swim in the waters of the sea, by means of the con- 
tractions and dilatations of their body, although their sub- 
stance is gelatinous, without any apparent fibres. ‘The sorts 
of vessels which are seen in some of them, are hollowed in the 
gelatinous substance. ‘They often come from the stomach in 
a visible manner, and do not give rise to any true circulation. 
Mepusa, L., 
Have a disk more or less convex above, similar to the head of 
a mushroom, and to which the name of wmbrella has been 
given. Its contractions and dilatations concur in producing 
the movements of the animal. ‘The edges of this umbrella, 
as well as the mouth, or the suckers, more or less prolonged 
into pedicles, which take its place, at the middle of the in- 
ferior face, are furnished with tentacula of very various forms 
and sizes. These different degrees of complication have given 
rise to very numerous divisions. 
We shall give the general name of 
MEDUSA (proper), 
To those which have a mouth under the middle of the inferior 
surface, whether simply opening on the surface, or prolonged 
into a pedicle. And among the medusa proper 
We may unite under the name of 
ALQUOREA, 
All those in which this mouth is simple and not prolonged or 
furnished with arms. 
