2s8 



THE FOOD OF ANIMALS 



foreign particles, such as sand-grains, glued together by a sticky 

 secretion. A typical example is afforded by the genus Serpula 

 (fig. 466), which makes and inhabits calcareous white tubes, 

 twisted masses of which are often found adhering to rocks, 

 oyster-shells, &c. It is clear that a tube-dweller like this has to 

 make special provision for breathing and feeding, and this is here 



effected in an interesting manner. On 

 watching a living Serpula placed in a 

 vessel of sea-water the head end will 

 soon be seen to protrude. First of all 

 a sort of conical stopper (operculum), 

 which closes and protects the mouth of 

 the tube, is pushed out, and then follow 

 two brightly -coloured plume -like out- 

 growths from the head. These are 

 covered with cilia, which set up currents 

 in the surrounding water, as a result of 

 which breathing is provided for, while 

 at the same time a constant stream of 

 edible particles is directed into the mouth. 

 A common and, when expanded, very 

 attractive - looking worm {Pontaioceros 

 triqueter) that abounds on the British 

 coast, lives in a small wavy tube attached to a stone or other 

 firm body. One end of the tube tapers to a point, while the 

 aperture is overhung by a sharp projecting spine from which a 

 prominent ridge runs backwards. Equally common is a still 

 smaller tube-worm {Spirorbis), which inhabits a calcareous tube 

 coiled into a flat spiral, and adhering to brown sea-weeds or other 

 suitable objects. Other tube-dwellers will be considered when 

 animal habitations are described. 



Great interest attaches to the widely -distributed group of 

 Earth-Worms, the habits of which, so far as British species are 

 concerned, were first studied in detail by Darwin, the results 

 being embodied in his classic work on the subject. 



A number of species are native to Britain (a common sort 

 being Liimbrictis herculeus), all of which live in much the same 

 way. Examination of one of them shows the complete absence 

 of jaws, and the food chiefly consists of earth which is constantly 

 swallowed for the sake of the organic matter it contains. An 



Fig. 466. — Group of Serpulse. Two indi- 

 viduals are projecting from their tubes 



