UNIVALVE MOLLUSCA. 4Itr 
of Gasteropods very numerous, both in species and in special types, 
all the species of which respire by the aid of branchiz or gills. 
The Tectibranchiata have the gills attached either to the right 
side of the body or upon the back, arranged in the form of leaflets, 
more or less divided, but not symmetrical, and nearly covered by the 
mantle. 
Some species of the genus 4f/ysia were known to the ancients 
under the name of.sea-hares (Lepus marinus), from some fancied 
resemblance to the terrestrial hare. They were objects of profound 
horror, inspired either by their singular form, or from an acrid, caustic, 
and inodorous liquid which they secrete. A magic influence was 
attributed to them; they were supposed, for instance, to have in- 
fluence over the female heart. It is not easy, however, to explain 
the evil renown acquired by an animal which is known to be gentle 
and even timid. They are naked and fat, somewhat resembling the 
Limnza in their oval, elongated form, their thickness in the dorsal 
region, and their peculiar locomotion. Their head, which is very 
indistinct, is furnished with four tentacles, the anterior two of which 
are the largest, and somewhat resemble the ears of ahare. The eyes 
are found at the base of the posterior tentacles. These characters 
are observed in Aplysia depilans (Fig. 179). Aplysia inca shows also 
the same arrangement (Fig. 180). In this family the mollusc is 
much more important from its volume than from its shell, which is 
internal, rudimentary, and horny, and is placed just over the branchial 
cavity. In Fig. 181 we have this small and thin cartilaginous shell 
as it exists in A. zvca figured. 
Species of the genus Aplysia are found nearly in every region of the 
globe, not only upon the shores of continents, but on every island 
shore. They commonly inhabit sandy and muddy shores of small 
depths, or even their rocky recesses, or under shelter of the stones 
which have fallen from the cliffs. Their eggs form great long filaments, 
which are discharged in immense numbers, and which fishermen call 
sea-worms. 
They feed upon certain alge, with which the bottom of the sea is. 
covered ; but they eat also small marine animals, such as the naked 
molluscs, annelids, and crustaceans. 
We are the less astonished to see the Aplysia so gluttonous when 
we learn how liberally Nature has accorded to them organs of masti- 
cation, trituration, and digestion. Their mouth is formed of thick 
and muscular lips ;-a very long cesophagus or gullet succeeds, and 
this cesophagus does not communicate with a single stomach, but 
with four—one enormous membranous crop, an exceedingly muscular 
