OF THE ACINETIXA, 



567 



at the anterior end, wliicli is then con- 

 tracted npon it by being thrown into a 

 few longitudinal folds. The tentacles 

 proceed from the anterior sui'face of the 

 body and penetrate through certain fis- 

 sures in the capsule above, diverging 

 from the smface in a radiating manner. 

 They are long, capitate, slightly tapering 

 and retractile. The body contains a cir- 

 cular nucleus and a contractile vesicle. 

 Maximum dimensions of capsule 1-4'" in 

 height, 1-32'" in width. The minimum 

 1-24"' high, and 1-43'" wide. 



Stein puts this Aci'neta forward as one 

 of the best illustrations to be obtained of 

 the conversion of an encysted Vorticel- 

 lina into an Acineta. The Acineta he 

 identities with the A. 7nystacina (Ehr.), 

 and portrays two modes of develop- 

 ment: one by a series of ciliated em- 

 bryos, enveloped each in its own capsule, 

 given off from the surface by a sort of 

 gemmation — this process going on until 

 the whole animal mass is exhausted; 

 the other by the conversion of the whole 

 mass, simultaneously, into several elon- 

 gated-oval gi'anular germs, covered by 

 a membrane, but not ciliated. 



Vorticella microstoma. — Stein consi- 

 ders the Actinophrys Sol and Podophrya 

 Jixa (Ehr.) to be the Acinetiform re- 

 presentatives of this species of Vorti- 

 cella. In our opinion, as before expressed, 

 and which we partake in common with 

 Cienkowski and others, ■ the being de- 

 scribed by Stein imder the name Actino- 

 phrys is in fact an Acineta. It is repre- 

 sented as covered by a firm integument, 

 which frequently assumes the characters 

 of a cyst, becomes plicated around it, 

 and extended into a hollow pedicle, 

 giving it the appearance of Podoplwya. 

 Moreover, foreign substances were never 

 seen to enter its interior, as happens 

 in the true Actinophrys. The further 

 history of this Acineta has been sketched 

 in the chapter on development of CUiata 

 (p. 360 et seq.). 



V. nehxdifera. — The Acineta in Stein's 

 estimation belonging to this species of 

 Vorticella is found upon Lemna. The 

 pedicle is much longer and the body 

 more contractile, and therefore more 

 changeable in figm-e, than the Acineta 

 found on the Cyclops. When at rest, 

 their figure is more or less compressed, 

 and ovate or pear-shaped, with a pro- 

 minent angle on each side of the anterior 

 margin, from which a bimdle of radi- 

 ating retractile tentacles extends. Oval, 

 circular, and discoid forms are not mi- 

 common. The stem is elastic, curved, 



and, as a rule, lunger than the body it 

 supports, and is hollowed by a narrow 

 canal. It expands at its junction with 

 the body and then spreads over it, form- 

 ing an external sheath or capsule, except 

 in the region supporting the tentacles, 

 where it seems to be either absent or of 

 great tenuity. Beneath this is a special 

 covering of the Acineta body, entirely 

 investing it. Notwithstanding these co- 

 verings, the body is remarkable for its 

 contractility and the mutability of its 

 figure. It also enjoys a certain amoimt 

 of movement on its pedicle, bending in 

 this and that direction with a peculiar 

 jerking motion. The body contains an 

 oval nucleus, and from one to three con- 

 tractile spaces. It developes a ciliated 

 embryo. The length of the body is from 

 1-100'" to 1-20'", that of the stem not 

 above 1-10'". 



Zoothamnium affine, — The supposed 

 Acineta of this animalcule was found by 

 Stein on marine Cru-tacea — the Qam- 

 marus marinas and Sph<reroma serrata, 

 along with the Zoothamnium. It appea,rs 

 identical with the Acineta tuberosa (Ehr,). 

 It is compressed, campanulate, or p}T"i- 

 form, and has each external anterior 

 angle lobate and surmounted by a group 

 of tapering and radiant tentacula. An 

 intermediate prominence is also frequent, 

 but no tentacles spring from it. The 

 body is distinctly enclosed by a hyaline 

 elastic capsule, which is extended down- 

 wards into a tubular pedicle, and by a 

 softer membrane immediately investing 

 it. The latter becomes especially pro- 

 noimced when, as fi-equently happens, it 

 is thrown into transverse folds in its 

 narrower or posterior half dming the 

 forcible contractions of the bodv. 



to 1-24'": maximum 



more 



Length fi'om 1-63' 



of stem 1-18'". 



Carchesium pyym<sum. — Stein lat- 

 terly referred to this species an Acineta, 

 common on Cyclops, and which he at 

 first assigned to Epistylis diyitcdis. The 

 stem is very short, often with difficidty 

 perceptible, but never wanting. The 

 body is generally pyriform and com- 

 pressed; its anterior end is roimded or 

 truncate, and slightly emarginate, and 

 supports at each of its angles a bimdle 

 of tentacles. Frequently the tentacula 

 are not thus gi'ouped in two masses, but 

 occupy the whole anterior margin and 

 the sides for a short distance — a circum- 

 stance met with in smaller specimens 

 which have a circular, oval, or reniform 

 figure. The nucleus is oval and small. 

 No movements in the bodv are discerni- 



