SEA-HARES. 141 
also, visible pulsations in the heart ; and the mouth 
is armed with jaws, and with a spinous tongue. 
Another stage is marked by the fall of the veils, 
and by the budding forth of the anterior tentacula, 
as well as of the branchiz; and the full evolution 
of these organs completes the metamorphosis and 
entitles the animal to the privileges of maturity.* 
GENUS APLYSIA. 
Most of the characters which distinguish this 
genus liave been already enumerated in those of 
the family. The peculiarities by which it is sepa- 
rated from its fellow genera are chiefly the presence 
of an internal shell, and the position of the gill- 
plume. The latter organ assumes the form of 
complex leaflets, attached to a broad membranous 
footstalk, and concealed beneath the shell. 
The genus is truly marine; yet M. Rang has 
observed specimens of A. dolabrifera inhabiting 
marshes in the island of Bourbon, where the water 
was almost fresh, and where Neritina and Melania, 
both essentially fresh-water genera, were its com- 
panions. } 
They swim freely, by means of the large fin-like 
expansions of the mantle, which are waved with an 
undulating motion. They have been seen also 
floating at the surface, suspended like Pond-snaiis 
from the inverted foot. 
All the species, I believe, are remarkable for the 
power of pouring out, in copious profusion, a fluid 
of a brilhant purple hue, which readily diffuses 
itself through the surrounding water. I have 
already mentioned my own experience of this phe- 
_* Jchnston’s Introd. to Conchol. 373. 
