26o 



THE FOOD OF ANIMALS 



the gut consists of a long very thin-walled intestine, which pursues 

 a spiral course to the hind end of the body, and then twines back 



upon itself to terminate upon the upper 

 side of the body not far from the front 

 j„ end (see fig. 468). It is always full 

 of sand, and siphon - worms of the 

 sort described play much the same part 

 in regard to the sand of the sea that 

 earth-worms do as regards the earth 

 covering the land. Shipley (in The Cam- 

 bridge Natii.ral History) makes the fol- 

 lowino- remarks on this head: — "The 

 rate at which the sand passes through 

 the body of Sipttncuhis is unfortunately 

 unknown, but that at any one moment 

 a considerable quantity is contained in 

 the intestine is shown by the fact that 

 the average weight of five specimens of 

 S. nudus [a large species] from Naples, 

 taken at random, was 19.0S grms., whilst 

 the average weight of sand washed out 

 of their alimentary canal was 10.03 



int: 



grms 



Fig. 468. — Dissection of Siphon-Worm 

 {Sij>?t?icjthis) 



t, Tentacles: mm and ?«'?«' w;'?K',muscles 

 which pull in front end of body, cut through; 

 ^/. gullet; iJf^. intestine; i.a. intestinal aper- 

 ture : f.r. ej:. excretory tubes ; dr. brain; 

 « c, nerve cord. 



Three groups of specialized worms 

 now claim our attention, i.e. Lamp- 

 Shells (Brachiopoda), Moss- Polypes 

 (Polyzoa), and Wheel-Animalcules (Ro- 

 tifera). All the animals included in 

 these groups are omnivorous, feeding 

 upon the minute organisms and nutritive 

 particles brought to them by ciliary cur- 

 rents (see pp. 243, 244). 



LAMP-SHELLS (Brachiopoda) 



The animals here included were once confounded with the 

 bivalve Molluscs (p. 248), chiefly because they are enclosed in a 

 shell composed of two pieces. A typical Lamp-Shell (see vol. i, 

 p. 439) is attached to some firm body, either by the substance of 

 one shell or by means of a sort of stalk projecting at one end. 

 As has already been exemplified in other groups, sedentary or 



