CCELENTEliA TES. 



31 



associate does not need to, for the anemone grows as he grows, and 

 furnishes him with a living house. Further, the old shell would be a 

 nuisance to the hermit after he had outgrown it, were it not for the 

 fact that the anemone, by some chemical process, gradually dissolves it. 

 Other species have other habits even more closely allied to true parasitism. 

 Thus in the summer almost every specimen of the large blue jelly-fish 

 (Cyanea) is found to have one or more anemones (Philomedusa) imbedded 

 in the tissues of the lower surface of the disc. Still other forms live 

 buried deeply in the mud, so that only the mouth and tentacles can be 

 exposed. 



It may be said in passing that all of the sea-anemones reproduce by 

 e^ss, and that in but few is there that alternation of Q-enerations which 

 has been described in the preceding pages, and which we shall meet again 

 in the worms. They also have the power of budding, and our common 

 fringed anemone may often be found with young budded from its base. 

 This budding explains some of the facts concerning the corals now to be 

 taken up. 



We can best understand the structure of the corals by first considering 

 one of the simpler forms grouped under the common name, " mushroom 



corals," — a term which is given from the fact 

 that their frequently circular outline, with the 

 radial partitions, bear a striking resemblance to 



^%Wr 



Fia. 31. — Side and top views of 

 a mushroom coral. 



Fig. 32. — Star coral (Astrxa). 



the under surface of a mushroom. These forms live free in the water, 

 resting on the bottom, and are attached only in the young state. Above 

 we described the radial partitions (the spokes of the wheel) in the common 

 anemone. In life each mushroom coral supported a polyp much like an 

 anemone, which had the power of secreting carbonate of lime ; and the 

 partitions (septa; of the coral were inserted between those of the polyp. 

 Now if a form like this were to bud, and the buds not to separate 



