POLYPIFEBA. 467 



lation appears to be as great as that possessed by the 

 Hydra. 1 



The great majority of the Actinozoa exhibit a structure 

 closely corresponding with that of the Actimince ; but from 

 the manner in which they grow up into compound masses 

 of associated Zooids, produced by gemmation or by fission, 

 they stand in nearly the same relation to Actinia, as the 

 compound Hydrozoa to Hydra. 



Sir John Day ell believes that Actiniae conquer their prey 

 by mere strength ; this is doubtless the case, as from 

 experience we find nothing like a stinging property be- 

 longing to the tentacles ; nor are there any poison vesicles 

 attached thereunto. The tentacles appear to be armed 

 with rows of spines, which give a clinging and slight 

 rasping sensation when the finger is thrust against them ; 

 and by the same means they are able to obtain a firm 

 hold of any smaller animal that falls within their reach. 

 Animals with a hard case or shell seem to escape from 

 their clutches without having sustained the smallest in- 

 jury. The same remarks apply to the Hydra; they have 

 neither the power to sting or benumb their prey, as 

 asserted by many authorities. It has been said that 

 certain minute organs found in polypes, and variously 

 styled thread capsules, filiferou* capsules, or urticating 

 cells, are stinging organs. This thread Agassiz likens t<? 

 a lasso thrown by the polype to secure its prey. Mr. 

 Lewes writes : " On a survey of the places where these 

 ' urticating cells' are present, I stumbled upon an unlucky 

 fact, and one likely to excite our suspicion. They aro 

 present in a few jelly-fish which urticate, in Actiniae which 

 urticate, and in all polypes, which, if they do not urticate, 



(l)The Author's aquarium affords at this time (1856) a curious illustration of 

 increase both by budding and fissuration, in a beautiful ^1. dianthus. In the firs, 

 case an offset was seen to protrude ; it resembled a small bud near the foot; thii 

 increased until it attained to a perfect animal of a considerable size, when It be- 

 came detached. In another, the animal, after having remained for several weeks 

 firmly adherent to the side of the glass, with a part of its disc out of the water, by a 

 great effort tore itself away, leaving six small pieces behind, attached to the glass. 

 For some days these pieces served only to mark so many spots, but in about a 

 week rudimentary tentacles were observed to be sprouting out from each piece, 

 which went on rapidly increasing, and ultimately six perfect animals resulted 

 therefrom. The repair of the marginal portion of the disc of the parent animal 

 was completed in a few days, and it suffered no injury whatever from its self- 

 mutilation. This furnishes a proof, if one were wanting, of the hydrozoid cha- 

 racter of this class of animals. 



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