Tank No. 3, 
55 
into two large wing-like flaps. They generally creep about lazily over 
the rocks; but if they want to swim, they begin to flap their "wings”, 
till they have raised themselves from the ground. Once afloat they swim 
very well and fairly fast, but not for long. When annoyed they give 
out a very beautiful violet, and also a white liquid, which serves as 
a protection like the sepia of the Cuttlefish. The ancients already 
were aware of the poisonous nature of this secretion, for their writers 
Fig. 89. Aplysia limacina, V 2 nat. size. Tank 3. 
record its use for the preparation of poisonous and magic draughts; 
those who partook of these were supposed to linger on in agonies until 
the Sea-hare died. Large specimens furnish about 30 grains weight of 
this colouring matter; recent investigations have shown it to be probably a 
true aniline dye, such as has been produced artificially only from coal-tar. 
Fig. 90. Fleurobranchus testudi- Fig. 91. Umbrella mediterranean 
narius, ^4 nat. size. Tank 3. 1/2 nat. size. Tank 3. 
The Sea-hares live on vegetable matter and graze in hundreds on the 
fields of sea-weeds. It is interesting to see them when stones covered 
with sea-weeds are brought into their tank; they creep forth from every 
corner to get at the food, and in a few hours the stones are bare. With 
the help of this food they live a long time in the Aquarium; they 
grow to considerable size and often lay their eggs in long thread-like 
masses, of yellow or violet colour, on the walls of the tank. — In tank 
No. 3 may be further observed the two flattened forms Pleurobranehus 
(Fig. 90) and Umbrella (Fig. 91). The shell of the latter is quite flat 
and the foot relatively very high. 
