ioo THE FOOD OF ANIMALS 



lodged, and prey upon jelly-fish and other floating forms with 

 which they are associated on the high seas. 



TECTIBRANCHS. So far examples have been given of thefore- 

 gilled Gastropods only, but carnivorous types are found among 

 the hind-gilled subdivision as well. The Tectibranch members 

 of the group are provided with a shell, though this may in some 

 cases be a mere plate sunk below the surface to a greater or less 

 extent. The burrowing form, Scaphander, is a good example 

 of quite a different mode of procedure from that adopted by 

 whelk, &c., for instead of boring holes in the shells of compara- 

 tively large animals, it selects for its prey small molluscs and the 

 like, which can be conveniently swallowed whole, after which they 

 are crushed by the action of a powerful gizzard armed with firm 

 calcareous plates. Similar in habit and structure are the Bubble- 

 Shells (see vol. i, p. 324); and so is one of the most abundant 

 British Tectibranchs, Philine aperta, a little white creature with 

 its delicate shell completely hidden from view, and which feeds 

 very largely upon Foraminifera. 



SEA-SLUGS (Nudibranchs). Some of the Sea-Slugs, consti- 

 tuting the shell-less Nudibranch section of the hind-gilled group, 

 are also flesh- eaters. An instance is ^Eolidia, in which the 

 body is studded with tentacle-like outgrowths, and which chiefly 

 attacks soft creatures like sea-anemones. It is not uncommon 

 between tide-marks on some parts of our coast. A related 

 genus, Glaucus, is of a beautiful blue tint, and drifts about 

 in the open sea attached to sea- weed. It preys upon jelly-fish 

 and the like. 



LUNG- SNAILS (Pulmonates). Though most of the lung-breath- 

 ing Gastropods, including the land-snails and slugs, as well as 

 some of the freshwater snails, feed upon vegetable substances, 

 there are some kinds which are exclusively carnivorous. Among 

 these may be mentioned certain slugs belonging to the genus 

 Testacella, in which there is a small cup-shaped shell borne on the 

 tip of the tail. These creatures are among the many enemies of 

 earth-worms, which they pursue underground. 



