568 



SYSTEMATIC HISTORY OF THE INFUSOKIA. 



ble, and the leugthening and sliortening 

 of the tentacles is very slow. This 

 Acineta developes a ciliated embryo 

 which resembles the Halteria Grandi- 

 nella (Duj.). Maximmn length 1-30'". 

 Common size, diameter 1-50'" to 1-40'". 

 Aci]\t:ta diademifonnis (xxin. 15-16). 

 — Stein describes a peculiar Acineta 

 foimd upon the roots of Lemna, under 

 the name of the diadem-like Acineta. 

 Its figure is compressed, disciform, 

 transversely oval or reniform ; and it 

 is supported on its somewhat contracted 

 base by a short, thick, solid stalk, longi- 

 tudinally striated, and often marked by 

 a few transverse lines. The stem is 

 always so short that the body looks as 

 if sessile. The latter is enveloped by 

 a thick, structureless, smooth and hya- 

 line external membrane, and by a second 

 layer beneath, closely investing the ani- 

 mal mass. On the free margin of the 

 body, particularly in front, a number 

 of comparatively thick but fine-pointed 

 tentacles are disposed at slight distances 

 from one another. These, which are not 

 clearly capitate, consist of a delicate mem- 

 brane enclosing a finely granular matter, 

 and are prolongations from the special 

 membrane of the body; consequently 

 they have to perforate the outer enve- 

 lope ; and Stein leans to the opinion that 

 the latter is an excretion from the 

 former. Usually the tentacular pro- 

 cesses are very slowly retracted : how- 

 ever, when the Acineta is much disturbed, 

 the shortening takes place much more 

 rapidly, and renders them tortuous. A 

 long band-like nucleus lies across the 

 centre ; and a number of transparent 

 vesicles are disposed at equal intervals 

 around the border, like a row of pearls 

 around a diadem. At long intervals one 

 or another of these sacs is seen to vanish. 



place, like true contractile vesicles. No 

 contractions of the body are observable ; 

 it remains stiff and motionless. It pro- 

 duces a large ciliated embryo, which 

 lies transversely across it in its special 

 sac. Maximum breadth 1-14'" ; height 

 1-20'", of stem 1-100'". 



The stiff solid stem and the remarkable 

 band-like nucleus indicate, says Stein, 

 its derivation from some large species 

 of Epistylis. It is the same organism as 

 the Acineta Ferrum-eqiiinum, according 

 to Lachmann. 



A. digitata (xxiii. 21). — Under the 

 name of the fingered or digitate Acineta, 

 another variety of this class is charac- 

 terized by Stein, who failed to detect 

 the ciliated Infusorium to which, ac- 

 cording to his h}^othesis, it shoidd owe 

 its origin. It was found on some Ento- 

 mostraca, and had a stemless, patella- 

 shaped or transversely oval body, ad- 

 herent either by the whole surface in 

 apposition or by the central portion only. 

 Its upper side usually presented irregular 

 depressions and small eminences, and was 

 very often divided into an anterior and 

 posterior half by an annular constriction. 

 From the entire upper surface, or only 

 from its anterior section when the central 

 constriction is present, a number of di- 

 vergent, very thick, finger-like tentacles 

 spring, apparently without order and 

 non-retractile. No contractions of the 

 body were ^\dtnessed ; but some change 

 of outline is possible. A narrow, coiled 

 nucleus is brought into view by acetic 

 acid. The peculiar contractile vesicles 

 are wanting ; but from two to three im- 

 changeable clear spaces of dilFereut sizes 

 exist. Along with these normal speci- 

 mens, others occurred ha^dng a smooth 

 surface and no processes. Maximmn 

 width 1-30'": heig-ht 1-58'". 



and after a time to reappear in the same j 



Genus OPHRYODENDRON. — Noticed and named in Lachmann and 

 Claparede's paper in the Ann. d. Sc. Nat. 1857. No description given. 



It is said to be a very singular animal, doubtfully referable to Acinetina, 

 found parasitic on Campanularia from the Norwegian coast. One species is 

 named. 



OPHRYODENDnoN ahietinum. — Characters imdescribed. 



GROUP III.— CILIATA (p. 199 and p. 266). 



The group of the ciliated Protozoa, according to the scheme adopted, are 

 resolved into two di\-isionR : — 1, mouthless (Astoma) ; and 2, those hanng 



