CHAPTER VIII. 
ACALEPH2E, OK SEA NETTLES. 
.. In nova fevt animus mutatis dicsre formas corpora.”— O vid, Met. 
The class Acalephse, from aicaXrityr], a nettle, so called from the 
stinging properties which many ot them possess, include a great 
number of radiate animals of which the Medusae are the type. They 
form the third class of Cuvier’s zoophytes. The Acaleph.se, forming 
the first order, are characterised as floating and swimming in the sea 
hy means of the contraction and dilation of their bodies, their substance 
being gelatinous, without apparent fibres. 
The great genus Medusse is characterised by having a disk, more 
° r less convex above, resembling a mushroom or expanded umbrella 
the edges of the umbrella, as well as the mouth and suckers, being 
more or less prolonged into pedicles, which take their place in the 
middle of the lower surface ; they are furnished with tentacula, varying 
iu form and size, which have given rise to many subdivisions, with 
v, 'hich we need not concern ourselves. 
The substance of the disk presents an uniform cellular appearance 
internally, but, the cellular substance being very soft, no trace of 
hbre is observable. Taken from the sea and laid upon a stone, a 
hledusa weighing fifty ounces will rapidly diminish to five or six 
Smins, sinking into a sort of deliquescence, from which Spalanzani 
c °ncluded that the sea water penetrated the organic texture of its 
s ubstance, and constituted the principal volume of the animal. Those 
Av hich have cilia round then* margins have also cellular bands running 
al °ng their bases, and most of the projectile and extensile tentacula and 
