CHAPTER XXIII 



THE FOOD OF ANIMALS— OMNIVOROUS ANNELIDS, 

 SIPHON-WORMS, LAMP-SHELLS, MOSS-POLYPES, 

 AND WHEEL-ANIMALCULES 



SEGMENTED WORMS (Annelida) 



The Annelids include Leeches (Discophora) and Bristle- 

 Worms (Chaetopoda). The former are carnivorous, and have 

 already been dealt with (pp. 147-149), and the same is true for 

 many rapacious marine worms belonging to the latter group, as, 

 for example, the Sea-Centipede {Nereis) (pp. 146, 147). 



Omnivorous Bristle- Worms. — These comprise marine, fresh- 

 water, and terrestrial forms. The marine species include a number 

 of worms which are entirely devoid of biting structures and burrow 

 in sand or mud, which they swallow in order to extract the nutri- 

 tive animal and vegetable matter present. The same habit has 

 already been described (p. 246) for the Acorn-headed Worm 

 {Balanoglossus), one of the lowest animals having any claim to 

 be considered a member of the Vertebrata. A good example 

 of marine worms which feed in this way is the Lob -Worm 

 {Arenicold) (see vol. i, p. 430), common on British shores be- 

 tween tide -marks where mud or mud-containing sand occurs. 

 This is a good-sized cylindrical form with broad front end, and 

 may attain a length of some 8 inches. It burrows in the sand 

 to a depth of about 2 feet, eating its way through, so to speak, 

 and from time to time comes to the surface for the purpose of 

 ejecting the sand which has passed through its body. This is 

 the oriofin of the little coils of mud or sand known as "worm- 

 castings " which are commonly seen upon the shore. 



A considerable number of marine bristle-worms have given 

 up an active life and taken to live in tubes of various kinds, 

 these either consisting entirely of material exuded from the surface 

 of the body and hardened into horny or shelly substance, or of 



Vol. II. 257 49 



