80 Part second. 



ainoiiuts of tlii.s acid fluid in order to soften the linni calcareous skin 

 of the Kcliinoderms which it eats, and porliai)s also in i^elf-defence ; it 

 is still a puzzle how these strong- corrosive acids are produced hy the 

 animal and how they can be stored up. 



An interesting- animal is the Worm-shell, Vermetus (Fig-. 12')), from 

 the fact that it is not able to move about freely like the other snails, 

 l)ut is jfixed to one spot. At first sight its shells are just like the 

 calcareous tubes of Protula (see p. 66). But on closer inspection may 

 l)e recognized the head of the snail with its two short tentacles, very 

 difiVueiit from the brightly coloiired gills of the worms. These animals 

 feed on the small Crustacea and worms in their neighbourhood, and when 

 alarmed, they withdraw themselves into their txibes. To the inner wall 

 of the latter they also fix their eggs; from these free-swimming- larvje 

 are hatched, wduch afterwards fix themselves to some rock. 



Allied to the above mentioned snails is a group of Mollusks which 

 differ in having- their g-ills attached behind their heart instead of in front. 

 Tliey are devoid of a shell or only possess a very small one whicli is 

 hidden by the mantle, as in the land-slug-s. This group includes: 



The Sea-hare Aplysia (Fig-. 16), h fairly large dark-brown animal 

 with two pairs of tentacles, the posterior pair of which are carried erect 

 and are something' like the ears of a hare. The mantle is continued 

 into two lai*g-c wing-like flaps. They g-enerally creep about lazily over 

 tiie rocks; but if they want to swim, they begin to flap their «.Aving-s », 

 till th(!y have raised themselves from the ground. Once afloat they swim 

 verv well and fairlv fast, but not for long-. When annoved thev 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 the white secretion , for their writers 

 record its use for the preparation of poisonous and magic draughts; 

 those who partook of these were supposed to linger on in ag-onies until 

 the Sea-hare died. The Sea-hares live on veg-etable matter and g-raze 

 in hundreds on the fields of sea-weeds. It is interesting- to see them 

 when stones covered with sea-weeds are broui>ht into their tank ; thev 

 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 Aquariu.m; they g-row to considerable size and often lay their eggs 

 in long- thread-like masses , of yellow or violet colour , on the Avails of 

 the tank. — In tank Xr. 3 may be further observed the tAvo flattened 

 snails Pleurobranehus (Fig-. 17) and Umbrella (Fig-. 18). The shell of 

 the latter is quite flat and the foot relatiA^ely A^ery high. 



One of the finest animals belonging- to this group is Tethys 

 (Fig-. 101). Its body is white and semi-transparent, and carries an exceed- 

 ingly broad head. On both sides of the back are attached the delicate 

 transparent gills, and besides these there are large spotted appendages 

 Avhich fall ofl' very easily and Avere therefore formerly considered as para- 

 sites. This animal, like other pelagic ones, is only occasionally found in 

 the Aquarium; the fishermen scoop them up from the surface of the sea 

 Avith buckets. Thev sAvim bA^ throAving- their head first to one side and 



