18 CLASS PTEROPODA. 
SECOND CLASS OF MOLLUSCA. 
THE PTEROPODA 
Swim like the cephalopoda in the waters of the sea, but can- 
not fix themselves, nor creep there, for want of feet. Their 
organs of locomotion consist only of fins, placed like wings at 
the two sides of the mouth. But small species are known, 
and few in number, all hermaphrodites. 
Cio, Lin. CLione, Pall., 
Have the body oblong, membranaceous, without a mantle; the 
head formed of two rounded tubes, from which issue small 
tentacula; two small fleshy lips and a ligula on the front of 
the mouth ; and the fins provided with a vascular net-work, 
which takes the place of gills. ‘The anus and the orifice of 
generation are under the right gill. Some authors attribute 
eyes to these animals. 
The mass of the viscera does not nearly fill the exterior en- 
velope; the stomach is broad, the intestine short, the liver 
considerable. 
The most celebrated species (Clio Borealis, L.) swarms in 
the seas of the north, and constitutes, from its abundance, 
plenty of food for the whales, though each individual is 
scarcely an inch long. 
Bruguiéres has observed one larger, and not less abundant, 
in the Indian Ocean. It is distinguished by its rose colour, 
by its emarginated tail, and its body divided by furrows into 
six lobes—Encyc. Meth. pl. des Mollusc. pl. lxxv. f. 1, 2. 
