MOLLUSCA. 19 
py a shell, resembling in appearance that of a 
Snail, but tinged with blue (Janthina), which is 
furnished with an elaborate apparatus for swim- 
ming,— 
“ Like little wanton boys that swim on bladders.” 
To the hinder part of the foot is attached a kind of 
float, consisting of many small bladders of thin 
membrane, united in a group, and looking some- 
what like coarse froth. By means of these, the 
shell floats securely on the broad sea. 
- Another bladder-swimmer, and like the former, 
an ocean-species, 1s the Litiopa. “'This ‘is a small 
snail, born amid the gulf-weed, where it is destined 
topass the whole of its life. The foot, though 
rather narrow and short, is of the usual character, 
and, having no extra hold, the snail is apt to be 
swept off its weed; but the accident is provided 
against, for the creature, like a spider, spins a 
thread of the viscous fluid that exudes from the 
foot, to check its downward fall, and enable it to 
regain the pristine site. But suppose the shock 
has severed their connexion, or that the Litiopa 
finds it necessary to remove, from a deficiency of 
food, to a richer pasture, the thread is still made 
available to recovery or removal. In its fall, acci- 
dental or purposed, an air-bubble is emitted, pro- 
bably from the branchial cavity, which rises slowly 
through the water, and as the snail has enveloped 
it with his slime, this is drawn out into threads as 
the bubble ascends; and now, having a buoy and 
bladder whereon to climb to the surface, it waits 
suspended until that bubble comes into contact 
with the weeds that everywhere float around.” * 
* Johnston’s Conchology, p. 134. 
b 
