356 SUPPLEMENT 
cartilaginous froth, composed of small cells or utricles, which 
can swell or contract at the will of the animal. M. de Blain- 
ville, however, tells us that this mass, in an individual a long 
time preserved in spirits of wine, bore a strong resemblance to 
the cellular tissue, a little gelatinous, and did not present the 
least indication of being cartilaginous. Observers are doubt- 
ful as to its point of attachment. Forskal says that it is at- 
tached to the mantle of the animal, but M. Bosc that it 
issues from the anterior part of the foot, and is extended in 
length beyond that organ. M. Cuvier, as we see in the text, 
describes it as being situated under the foot. 
The janthine inhabit the deep parts of the sea in all warm 
latitudes. When the water is calm they may be seen floating 
on its surface, with the shell underneath, and the foot and its 
vesicle just mentioned, upwards, and are sometimes in pretty 
numerous bodies. It is probable that they have no need of 
any muscular effort to maintain themselves thus on the surface 
of the water, and that the vesicles of their feet produce the 
effect of an hydrostatic bladder ; but then they must of neces- 
sity be the sport of the lightest wind or the least current, 
which is not the case with the other mollusca, which can 
swim in this manner on the water, unless we admit that the 
foot should possess some action, or at all events that its lateral 
appendages should act as fins. Be this, however, as it may, 
on the slightest appearance of danger, or cessation of calm, 
the little animal withdraws its head into its shell, contracts 
its vesicles, either by forcing them to re-enter the testa with 
its foot, if they be attached to its posterior part, or by acting 
directly upon them, if their attachment be under the foot 
itself, and in the hollow which it forms; but in whatsoever 
manner this may be done, the air of these vesicles can neither 
be absorbed nor rejected. By the diminution of its volume 
the weight of the animal is increased, and it sinks more or 
less towards the bottom of the water. Whether it can creep 
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