442 
THE OCEAN WORLD. 
numerous as to colour the ocean for leagues. They are the principal 
food of whales and sea birds in high latitudes, rarely approaching the 
coast. Only one or two species have been accidentally taken on our 
shores, and those evidently driven thither by currents into which 
they have been entangled, or by tempests which have stirred the 
waters with a power beyond theirs. l>r. Leach states that in 181L 
during a tour to the Orkneys, he observed on the rocks of the Isle ot 
Staffa several mutilated specimens of Clio borealis. Some days afteL 
having borrowed a largo shrimp-net, and rowing along the coast o 
Mull when the sea, which had previously been extremely stormy, 
pad 
become calm, he succeeded in catching one alive, which is now in ^ lL ' 
British Museum. 
“ In structure,” Mr. Huxley tells us, “ the Pteropods are n>° s 
nearly related to the marine univalves, but much inferior to them- 
Their numerous ganglia are concentrated into a mass below the 
oesophagus ; they have auditory vesicles containing otolithes, and 
sensible of light and heat, and probably of odours, although at m° s 
they possess very imperfect eyes and tentacles. The true foot 1 
small or obsoleto; in Cleodera lanceolata (Pig. 310) it is combine 1 
with the fins; but in Clio it is sufficiently distinct, and consists of t"° 
elements or spirals : the superior portion of the foot supports 
operculum. The fins are developed from the sides of the mouth ° l 
neck, and are the equivalents of the side-lappets (Epipoda) of the sea 
snails. The mouth of Pneumodermon is furnished with two sup 
porting miniature suckers ; these organs have been compared to t 
dorsal arms of the cuttle-fishes; but it is doubtful whether tb® 11 
nature is the same. A more certain point of resemblance is ^ ^ 
ventral flexure of the alimentary canal, which terminates on the un 
surface near the right side of the neck. The Pteropods bare 
muscular gizzard armed with gastric teeth, a liver, a pyloric caecum, & 
contractile renal organ opening into the cavity of the mantle. 
heart consists of an auricle and a ventricle, and is essentially °P l3 ^ 0 
branchiatic, although sometimes affected by the general flexure of 
body. The venous system is extremely incomplete. The respi ra , 
organ, which is little more than a ciliated surface, is either situate*- ^ 
the extremity of the body, and unprotected by a mantle, or “ lc U ^ 0lJ 
in a branchial chamber with an opening in front. The shell w 
present is symmetrical, glassy, and translucent, consisting of 11 c 0 
