OF THE PEOTOZOA. ACINETINA. 259 



that seen in others ; or the anterior lobed part is undefended by such a cover- 

 ing, except of a very delicate and yielding structure. Cienkowsky speaks of 

 the Acineta he examined as naked without limitary membrane (XXIII. 40). 

 Very frequently, on the other hand, the Acineta is entii^ely enclosed within 

 a stout capsule. This capsule is readily discerned when, as frequently 

 happens, the internal animal mass of the Acineta does not fill it ; or it may be 

 brought into view by the application of diluted acetic acid or alcohol, either 

 of which causes the shrinking of the contained body. In general the capsule 

 appears to be a very thin, coloiuiess, hyaline membrane ; but after the action 

 of acetic acid. Stein represents it to be, in the supposed Acineta of Ojyercularia 

 Lichtensteinii, of considerable thickness (XXIII. 22, 23). This thickening 

 is doubtless due to the action of the acid in causing the membrane to swell 

 out. With the exception of the so-called Actinojplirys Sol of Stein, and the 

 Dendrocometes, the Acinetina are attached by a stalk of varying length, 

 more commonly very short, to the body on which they live (XXIII. 17, 18, 

 22 ; XXYI. 3, 4). This stalk or pedicle is a tubular prolongation backwards 

 of the capsule itself, like which, it is hyaline and transparent. 



It is not articulated with the body of the Acineta, but expands more or 

 less abruptly into the capsule, and has a proportionately greater or less 

 infimdibuliform figure. Occasionally the stem at the upper part has trans- 

 verse rugae, and in a few instances exhibits a sort of longitudinal striae, par- 

 ticularly near its junction with the body (XXIII. 3, 4). Stein describes the 

 stem of the supposed Acineta of Ejnstylis, to be solid like that of an Ejpistylis 

 itself. Frequently the capsule is thrown into transverse folds, at times, of 

 considerable depth. There is no aperture in it ; but it is penetrated by the 

 tentacles which rise from the contained organic being. The capsule, if in 

 some specimens of considerable firmness, would seem to be in others, even 

 when thick, very yielding, — so much so as to allow great variety in figure by 

 the contractions of the contained body, as instanced by Stein in the Acineta 

 attributed to Opercidaria Lichtensteinii. The tentacles of Acinetina have not 

 the imiformity of stnicture seen in those of Actinoi^liryina. In some Acinetce 

 they closely resemble those of ActinopJirys, are long, gently tapering, and 

 capitate ; in others they form parallel tubular processes, dilated a Httle, or 

 not at all, at the extremity, and either straight or slightly curved or undu- 

 lated ; in others, again, they rather resemble bristles, appear stiff, and taper 

 to a sharp point. In the remarkable Acineta called Dendrocometes, the 

 tentacular character is entii^ely lost, and a few most bizarre branched tubular 

 processes spring from one to six points of the surface (XXX. 22, 23). Per- 

 haps these processes are homologous Avith tentacles ; yet, imlike them, they 

 seem to be formed from the capsule of the animal, into which the granular 

 contents of the interior penetrate, as into hollow tubules prolonged from the 

 surface of the organism. 



In certain Acinetina that approach Actinophrys in external characters, the 

 tentacles are equally difiused over the body. In the large ppifonn Acineta, 

 assigned by Steia to Opercularia articulata, the short slender tubular pro- 

 cesses appear chiefly marginal (XXX. 3, 4). The digitate Acineta is covered 

 by long tapering and thick processes on its dorsal convex suiface (XXIII. 

 21) ; and the Diademiform Acineta has its long setiform tentacles in twos 

 and threes at considerable inteiwals, chiefly on the margin (XXIII. 15, 16). 

 The Actinophryean Acineta of Epistylis plicatilis bears a bundle of long 

 finely capitate tentacula on each of its four lobes (XYIII. 2) ; that of 

 Vorticella nehulifera has two such bundles, — whilst the triangular Acineta, 

 with its tongue-Hke process (XXIII. 17, 18, 19), carries a large expanding 

 pencil of shorter obtuse tentacles upon each angle at its base. 



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