REPORT ON THE ACTINIARIA. 133 



small or entirely wanting, gapes widely. In Polysiphonia tuherosa (565 fathoms) the 

 tentacles have become short, slightly movable, wide-mouthed tubes; in Sicyonis crassa 

 (1600 fathoms) they are small, wart-like rings, and in Polystomidium patens (1825 

 fathoms) iindPolyopis striata (2160 fathoms) the walls have almost entirely disappeared, 

 so that the terminal opening forms a fissure in the oral disk, the last remains of the 

 tentacle being represented by a circular margin surrounding the fissure, and so we come 

 finally to the genus Liponema (1875 fathoms), in which the points at which the 

 tentacles were actually placed are merely indicated by openings in the oral disk. Of 

 the twenty-one forms from 500-3000 fathoms here described, no less than six species 

 have therefore undergone modifications of the tentacles in the same sense, whilst it has 

 never been observed in a single one of the forms of the coast fauna, which greatly exceed 

 the deep-sea fauna in number. 



The view that the retrograde formation of the tentacles is connected with life in 

 greater depths is not only supported by the fact observed, that the character is limited 

 in its distribution to the deep-sea Actiniae, but also by the way in which it 

 appears in the difi"erent groups of Actinise. The six forms named in the last paragraph 

 show conditions allied to those in families of Actinise lying widely apart from one another. 

 Of the three genera united as Liponemidse, Liponema comes near the Discosomidae, as 

 its stomidia may be divided into principal and accessory stomidia ; Polystomidium patens 

 resembles the Antheadse in having an endodermal muscle and marginal spherules, and 

 Polysiphonia with its mesodermal circular muscle resembles the Paractidse, to which Par- 

 actis tuhidifera undeniably belongs. It might therefore perhajas be advisable to do away 

 with the family Liponemidse, and to distribute its members among the Discosomidae, 

 Antheadse, and Paractidse. Finally, Sicyonis crassa and Polyopis striata vary entirely 

 from other Actinia, and are at the same time forms which difi"er entii-ely one from another. 

 It is most probable that a character which appears in forms which vary so remarkably, 

 but exist under the same conditions, is the consequence of these conditions of existence. 



There is another point in the mode of life of the deep-sea Actinise which seems to me 

 to favour the transformation of the tentacles into tubes and openings. The nutriment of 

 the deep-sea animals probably consists chiefly of material which is already disintegrated, 

 and of a soft nature when obtained. The animals often ingest sand, impregnated with 

 nutriment, from which they extract what is digestible ; at least I have repeatedly found 

 the interior of the deep-sea Actinias full of mud. In such a mode of nutrition the long- 

 prehensile tentacles would not be of the same use as they are in the littoral Actinise, which 

 lie in wait for booty, whilst on the other hand it would be a decided advantage to the 

 animals to be furnished with numerous inhalent tubes and openings through which they 

 can absorb semi-liquid nourishment. This then is the advantage of the stomidia and 

 tubular tentacles. 



The retrograde formation of the tentacles is by no means the only point to be taken 



