POLYPES. 221 



comparative ease with which, they are reared, form 

 frequent and interesting objects of study in the 

 same miniature ocean. 



Polypes have numerous enemies in the shape of 

 worms, Crustacea, fish, water insects, etc. They 

 also devour each other when opportunity offers, 

 but it has been observed that polypes of the same 

 species cannot digest each other. 



They appear to live principally upon animal sub- 

 stances, such as small worms, infusoria, and the 

 like, with which the waters they inhabit generally 

 abound. Certain sea anemones have been seen to 

 devour small fish; in the aquarium they are fed 

 with small pieces of raw beef. 



Some polypes remain for ever attached to their 

 cells, and cannot be drawn from their polypidom 

 without being killed. Others appear capable of 

 leaving their habitation, to wander about and con- 

 struct another polypidom at some distance from the 

 old one; but this fact has not been sufficiently 

 proved. 



The most important polype, in a commercial 

 point of view, is the Coral (Corallium noUlis, L. 

 Fig. 26) ; the bright red substance of its polypidom 

 has rendered it valuable as an article of trade. 

 After pearls, coral is considered the most precious 

 production of the ocean, and on the coasts of the 

 Mediterranean it has for ages been the object of an 



