SIX-RAYED POLYPS 



the Red Sea, shown in the illustration, has, immediately round the mouth, several 

 circles of delicate grasping tentacles, shaped like curly cabbage or endive leaves. 

 Below these comes a circle of numerous thick arms altogether unlike the others, 

 being rough skinned, and of a simple spindle shape, the body itself forming a thick 

 disc. All the tentacles of the sea anemones are hol- 

 low, with a fine aperture at the tip, through which, 

 when the animal contracts, the water contained in 

 the body cavity can be expelled, but in the deep- 

 sea forms these organs are very curiously modified. 

 For instance, in the genus Poly siphonia , the ten* 

 tacles are short and unsuited for catching and 

 holding prey; but the aperture at the tip is large, 

 and through it flows in water containing organic 

 detritus which can be used as food. The allied Sic- 

 yonis has sixty-four wart-like tentacles with wide 

 apertures standing in a double circle round the mouth, 

 and in Liponema the> body wall is perforated by 

 several hundred apertures leading into the digestive 

 cavity and corresponding to the tentacles. 



Although most members of the group arise as 

 single individuals from eggs, some multiply by the 

 detachment of small pieces from the pedal disc. 

 Fischer observed this process in the translucent 

 anemone (Sagartia pellucida} on the French coast. 

 The pieces detached on the twenty-third of August 

 had, by the seventh of September, developed into 

 small individuals with fifteen or sixteen tentacles. 

 Multiplication by fission seems common in several 

 species, such as 5. ignea, and always ends in pro- 

 ducing single individuals. Sea anemones some- 

 times, however, form stocks, but are then no 

 longer called Actinia but Zoantharia. Such stocks 

 are not very numerous, but some species can 

 be found on European coasts. The genus Zoan- 

 tharia, in which the separate individuals are united 

 by a creeping branching root, is distinguished from 

 Palythoa, in which the common stock resembles a 

 root-like crust, on which the polyps form irregular 

 groups of various sizes. A peculiarity common to 

 the two genera is the incorporation of hard particles 

 of the most different kinds sand, sponge spicules, 

 pieces of shell or coral into the body wall in large 

 quantities. The walls in consequence become so 

 firm that the exact form of the polyp is retained in 

 dried specimens. The species of Palythoa, although 



PARASITIC ANEMONE ^Palythoa) 



ON STAI,K OF GI.ASS-ROPE 

 SPONGE. 



(One-third natural size.) 



The holes on the body of the sponge 



are formed by anthozoans. 



