SEA-ANEMONES. 



503 



aar 



single individuals from eggs, some multiply by the detachment of small pieces from 

 the pedal disc. Fischer observed this process in the translucent anemone (Sayartia 

 pellucida) on the French coast. The pieces detached 

 on the 23rd of August had, by the 7th of September, 

 developed into small individuals with fifteen or 

 sixteen tentacles. Multiplication by fission seems 

 common in several species, such as 8. ignea, and 

 always ends in producing single individuals. Sea- 

 anemones sometimes, 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 un- 

 attractive when in spirit, are of a sulphur yellow, 

 and beautiful when alive in an extended condition. 

 The most interesting species is Palythoa fatua, 

 which is always found growing on and in one of 

 the most curious of sponges, the Japanese glass- 

 sponge (Hyalonema). Here the surface of the stalk, 

 that is above the portion embedded in the mud, is 

 covered with a warty crust belonging to this 

 Palythoa. All the specimens of this Japanese 

 sponge in European museums in 1860 had their 

 stalks overgrown with the Palythoa, while many 

 had their bodies also covered with another polyp 

 which, however, settled singly and, fortunately for 

 the sponge, did not form a sandy crust. The illustra- 

 tion represents a specimen of this beautiful glass 

 rope-sponge, its body pitted all over with holes in 

 which small Anthozoa once lived, and its stalk 

 coated with the sandy crust of the stock - forming 

 Palythoa. The former, having no skeleton, dry up 

 entirely ; no traces of them being found in dried 

 specimens of the sponge except the holes they lived in. Unlike a parasite, the 

 polyps do not feed upon the juices and soft-parts of the sponge, nor indeed do 

 they share its food, but simply settle upon the sponge and feed upon the food that 



PARASITIC ANEMONE (Palythoa) ON 

 STALK OF GLASS - ROPE SPONGE 



(^ nat. size). 



The holes on the body of the sponge 

 are formed by anthozoans. 



