830 ORDER TENTACULIFERA-SUCTORIA. 



between this species and its fresh-water homotype consists of the respective modes 

 in which they are united to their loricse, and the relative portions of the cavities of 

 the same that they usually occupy. In the present type adhesion always subsists 

 between the posterior extremity of the body and the fundus of the loricae, which 

 does not obtain in A. lemnarum, and while in the last-named species the body more 

 or less completely fills the cavity of its domicile, in A. tuberosa the posterior region 

 is usually very attenuate, quadrilateral in shape, and united to the sides of the 

 lorica at each angle in such a manner that, as seen in transverse optical section, 

 the cavity of the lorica is as it were divided by four membranous septa into as 

 many vertical compartments. This structural peculiarity is well shown in the 

 drawings by M. Fraipont reproduced at PI. XLVIII. Figs. 26 and 28. The last-named 

 authority adduces as an additional point of distinction between the two forms 

 under discussion, that while in the fresh-water variety the pedicle is relatively short, 

 varying from much less to about one and a half times the length of the body, in 

 the examples of A, tuberosa he examined and figures, the pedicles measured no less 

 than four or five times such dimensions. The author is, however, disinclined to 

 accept this distinction as diagnostic, the same length to twice the length of the 

 body representing the proportions of the pedicle commonly exhibited out of a very 

 large series of examples derived from different localities as personally examined, and 

 the same proportions obtaining in the specimens originally figured by Ehrenberg. 

 Fraipont's types would thus seem to represent indeed a well-marked long-stalked 

 variety differing in the same manner as the variety A, longipes does from the normal 

 examples of Acineta mystacina. A much more reliable distinction is apparently 

 afforded by the relative dimensions of the loricae of A. tuberosa and A. lemnarum, as 

 specified in the figures quoted in their respective diagnoses, derived in each instance 

 from examples personally examined. 



The character of the endoplast in the present type, not previously recorded, was 

 clearly demonstrated by Fraipont in specimens treated with picrocarmine, and is 

 also clearly shown in specimens preserved by the author with osmic acid. Endo- 

 genous peritrichously ciliated embryos, as observed by Stein of A. lemnarum, are 

 produced singly in connection with the constriction and separation off of a fragment 

 of the endoplast. Although collected in the Channel Islands and on the Devonshire 

 coast, the most abundant development of this species was obtained by the author in 

 August 1 88 1, growing, in company with Acineta livadiana and Ophryodendron 

 sertularia, on examples of Sertularia abietina collected in the Menai Straits, 

 North Wales. 



Acineta lemnarum, Stein. 



Lorica subtriangular, compressed, widest anteriorly, tapering gradually 

 towards the posterior extremity, its walls thin and readily adapting them- 

 selves to the contour of the body ; the body soft and plastic, almost com- 

 pletely filling the cavity of the lorica, often transversely folded or puckered 

 posteriorly, but not distinctly adherent to the lorica in this region ; tentacles 

 finely capitate, forming two antero-lateral fascicles ; pedicle rarely exceed- 

 ing one and a half times the length of the body, frequently much less, 

 increasing very slightly in diameter towards its point of junction with the 

 lorica, slightly curved ; contractile vesicles two in number ; endoplast 

 ovate ; embryos peritrichous, formed singly in connection with a separation 

 off of a portion of the endoplast. Length of body 1-600" to 1-500". 



HAB. Fresh water, on Lemna and other aquatic plants. 



The author includes under the above title both the Acineta lemnarum and the so- 

 called A. tuberosa of Stein, figured in PI. III. of his earlier work, ' Die Infusionsthiere,' 

 published in the year 1854. From the typical marine Acineta tuberosa it differs 



