284 THE INHABITANTS OF TIE SEA. 
sparkling like the purest crystal shines with the liveliest 
colours, red, yellow, or azure. Some inhabit the coasts, where 
they creep along upon a well-developed foot, others live ir 
the deep waters, where they cling to the stems of floating 
sea-weed with a nar- 
row and _ furrowed 
foot, or swim upon 
their back, using the 
borders of the man- 
tle and of the bran- 
chie as oars. Though chiefly living in the warmer lati- 
tudes, they are found in every sea, and many interesting 
species inhabit the British waters: such as the Sea-lemon 
(Doris tuberculata), which, when its horns and starry wreath 
of branchis are concealed, bears a curious resemblance in 
size, form, colour, and warty surface to the half of a citron 
divided longitudinally; the exquisite Holis coronata, whose 
crowded clusters of branchial papille are radiant with crimson 
and cerulean tints; and the crested Antiopa, whose transparent 
breathing organs are tipped with silvery white. 
Though they have no shell to cover them, the Nudi- 
branchiata are not left defenceless to the mercy of their 
enemies. The transparency of their body is a cause of 
safety to many of them. Some conceal themselves under 
stones or among the branches of the madrepores, and some 
on coutracting cast off a part of their mantle, which they 
leave in possession of their hungry foe, while they themselves 
make their escape. 
Among the British Inferobranchiata we find the rare golden 
or orange-coloured Plewrobranchus plumula, thus named from 
its branchie projecting like a plume from between the mantle 
and foot in crawling; and among the Tectibranchiata the 
common sea-hare (Aplysia punctata), which resembles a great 
naked snail; its back opening with two wide lobes, which can be 
expanded or closed over the opening at the animal’s will. When 
open, they expose to view on the right side the finely fringed 
and lobed branchiz, seated in a deep hollow beneath a fold of 
the mantle. The uncomely creature glides along over the stones 
upon its flat fleshy foot and up the slender stems of sea-weeds 
by bringing the borders of the same locomotive apparatus to 
