- 37 - 



this fluid. Until this day it is a^riddle how such corrosive mi- 

 neral acids can be freely produced and retained in the body 

 of these snails. 



Akin to the above animal is the Helmeted-snail or Cassis 

 of which one kind (C. sulcosa) is often found in the Aquarium. 

 In habits and frequency they resemble the Barrel-snails, and 

 are much prized for the beauty and elegance of their shells. 

 It is from the shells of many kinds of this snail that are cut 

 the well-known shell-cameos. For this purpose suitable pieces 

 are sawn out. and the exterior polished, while the interior is 

 left untouched. The relief is then worked out, use being made 

 of the different-coloured layers. 



To these shell-carrying snails is related a group of mollusks, 

 distinguished as rnollusks with hind gills, because, contrary to 

 those we have just described, their gill lies behinvd the heart. 

 They either have no shell at all, or it exists in a rudimentary 

 form, hidden in the mantle, similar to that of the naked com- 

 .mon snail (Limax). To this group belongs 



The Sea-hare (Aplysia leporina), a dark brown , rather 

 large snail , with two pair of feelers, the hinder ones , which 

 stand erect , actually resembling the ears of a hare , whence 

 the name , sea-hare. The mantle is extended into two large 

 wing-like flaps, by means of which the animal swims. Usually 

 creeping lazily among the rocks, when it wants to swim it fans 

 the above mentioned flaps until the movement raises it from 

 the ground. Once afloat, it swims well and quickly, but only 

 for a short time. When teazed, it expels not only the water 

 contained in its body, but also a beautiful violet-coloured fluid, 

 which, like the ink of the Sepia, serves as a weapon of de- 

 fence. Chemical examination proves that this colouring matter 

 has the properties of a concentrated aniline solution, and re- 

 acts in the same manner as an artifical aniline dye. The poi- 

 sonous character of the fluid seems to have been known to the 

 ancients, for Latin authors mention its being used for charms 

 und poisonous draughts, after taking which the victim suffered 

 torture until the sea-hare dies. Large snails yield about two 

 grammes of pure dry colour. 



The Aplysiae are vegetable feeders, and graze on the weed 

 at the bottom of the sea in troops. It is a pretty sight when 

 several stones overgrown with algae are brought to these snails 

 in the Aquarium. They come creeping from all sides to feed, 

 ^and in a few hours the stones are denuded of a 1 ! the vegetable 

 matter. The Aplysiae endure confinement capitally on this food, 



