042 



RADIATA. 



j^oneral inoilo of i«cproduction is by a process of hudding or gemmation, by wliich a portion of 

 tlie sub.staiicc of the creature is piislanl out and becomes a living Hydra. This takes place in 

 summer; during the winter they produce oviform granules, which remain like seeds in the water, 

 until the return of spring causes them to develop a new race of polypes. 



'riie most wonderful part of the history of these creatures is still to be told. It appears to be 

 well ascertained that they may be propagated by being cut in pieces, each piece becoming a 

 (•ompletc living animal. Trembley says : "I have opened a polype on my hand, extended it, 

 and cut the simple skin of which it is formed in every direction ; 1 liave reduced it to little 

 pieces, and, in a manner, minced it. These little pieces of skin, both those which did and those 

 which did not possess arms, became perfect polypes!" 



The Ilvdrje are exceedingly voracious, and feed only on living animals. The larvfe of insects, 

 worms, and the minute crustaceous animals which swarm in all waters, constitute their food. 

 Sometimes two polypes will seize upon the same worm, when a dispute of course ensues, which 

 occasionally ends in a very singular manner. If the weaker of the two docs not feel inclined to 

 let slip a booty for which he has perhaps been waiting with extended tentacles for several days, it 

 sometimes happens that each polype swallows the end wliich has fallen to his share, until at 

 length the worm being all gone, the mouths of the pair come into actual contact. They now 

 tiud themselves in a position of considerable difficulty, which is sometimes terminated by the 

 breaking of the worm ; but if this does not take place, the larger or stronger of the two seizes 

 upon his antagonist, and swallows him, worm and all. After a time the swallowed polype emerges 

 from his living tomb ; the worm, however, is gone ! One of the most singular circumstances con- 

 nected with the digestion of the Hydra — a digestion which is capable of dissolving creatures of far 

 higher organization than itself — is, that the creature may actually be turned inside out without 

 any derangement of its functions; the old inner surface now acts the part of a skin, while that 

 which was the outer skin adapts itself without difficulty to the performance of the work of diges- 

 tion ! 



THE SERTULARID^. 



These polypes all live in societies, each polype being inclosed in a sort of horny cup, supported 



on a branched polypidom of the same consist- 

 ence. These polypidoms are among the most 

 elegant productions of the sea, and their struc- 

 ture and formation are extremely curious. 

 Their delicate arborescent forms are con- 

 stantly to be seen attached to the sea-weeds 

 left upon the beach by the retiring waves. 

 Among the species are the beautiful IIer- 

 RiNG-BoNE, Halccium halccinum ; the Sea- 

 Fir, Scrtularia abietina ; the Sea-Hair, S. 

 operculata ; the Feun Coralline, S.fiUcida; 

 the Bottle-brush Coralline, Thn'mria 

 thuia ; the Feather Coralline, Plumu- 

 laria ])cnnatula ; the Sea-Bristle, P. seta- 

 cea, and many others — these being common 

 on the Atlantic shores. 



THE TUBULARID^. 



This family of hydroid polypes are for the 

 most part social animals, frequently possess- 

 ing a polypidom, which, however, when pres- 

 ent, is of much less firm consistence than the 

 horny framework of the Sertularida?. Tlie 

 polypes are never entirely retractile within 

 their tubes; the upper extremity is enlarged into a clavate head, surrounded by a variable nuin- 



TPBULARIA CORONATA. 



