0¥ TUE PEOTOZOA. CILIATA. 359 



bodies having the figiu'e of Acinetce, furnished with tentacles slightly move- 

 able and more or less retractile (XXYII. 17, 18, 19, 20). These Acineti- 

 form beings were noticed and figui'ed by our countryman Baker a century ago ; 

 they, moreover, did not escape the observation of Ehi'enberg, in the alHed 

 genus Oj)e7'cidaria, hut were regarded by him as parasitic animalcules. 



On another occasion, Stein met with a stem of Epistylis plicatilis bearing 

 some thirty Acinetce, diffeiing among themselves very much, both in size and 

 in their stage of development. Each was supported on a branch presenting 

 the characteristics of this species, but smaller in dimensions, and tapering 

 from the base of the Acinetiform body (where it had the usual thickness of 

 an Epistylis-stalk) to its jimction Tvdth the stem below. The length of the 

 branches also varied greatly, being in some instances not quite so much as that 

 of the body they supported, in others twice as long ; however, there was no 

 proportion between the length of the stem and the size of the body. Most 

 of the Acinetoi had a smooth siuface and no tentacula ; they were of a pyri- 

 form compressed figure, and contained a coarsely granular and homogeneous 

 substance, two or three irregularly-placed contractile spaces, and a central 

 nucleus ha\TJig either the normal horse-shoe- or an elongated oval shape. 

 Where the Acinetce had tentacles, these processes were few and small, and the 

 surface of the body thro^Ti into irregularities by its contractions ; their nuclei 

 were either round or oval. These Acinetce exhibited no movements, except 

 some slight ones affecting the tentacula. Were their anterior extremity un- 

 folded and theii- tentacles outspread, they would assume the figure presented 

 by those described in the first observations on this species, whilst the closed 

 pyi'iform bodies were precisely ahke. 



The further developmental history of this particular E_pistylis could not be 

 followed out, and to arrive at the purpose of its ^cnieto-metamorphosis, the 

 research was extended to other species. A particular form of Acineta occurs 

 in company with Episti/lis digitalis, which Stein concluded to be derived from 

 it by a similar process to that presumed in E. j^Hcatilis, although the Acinetce 

 were isolated and seated on short pedicles. At the anterior part of each 

 Acineta, amid the large granules crowding the homogeneous contents, were a 

 contractile space and, in many specimens, a mo\'ing embiyo having a cylin- 

 drical figui'e, rounded at each end and narrower in the middle, where several 

 zones of long cilia, in apparent folds of the smface, surrounded it. In ge- 

 neral characters it would, as an independent organism, be referable to the 

 genus Trichoclina, and is probably no other than the T. vonuv or T. gran- 

 clineUa, Ehi'enberg. The embryo escaped through a temporary opening, 

 which closed very speedily afterwards, leaving the animal apparently unin- 

 jiu'ed ; moreover the tentacles, which are retracted during the birth, were 

 again outstretched. The conclusion arrived at is, that the Acineta -condition 

 is specially provided to cany out embryonic development, and that in so doing 

 the Acineta gradually exhausts itself. 



Stein's fii'st impression was, that the embryo resulted from the develop- 

 ment of the entire nucleus, and that this organ was formed anew from the 

 general contents of the Acineta ; however, later researches lead him to be- 

 heve that only a portion of the nucleus is concerned in building up the em- 

 bryo. No particular season seems devoted to this Acineta -formation, since 

 Stein has observed it from the middle of March through the whole sum- 

 mer, and in fewer instances imtil December ; moreover, embryonic gene- 

 ration is not restricted to any particular size of Acineta, but occurs in all 

 except the very smallest ; nevertheless the embryo is smaller proportionably 

 to the decreasing size. Active embryos were seen in Acinetce of onlj^ ^"', 

 the germ itself being only Yko'"' 



