360 GENERAL HISTORY OF THE INFrSOElA. 



Besides the cysts and Acinetce supported on branching E2jistt/lis-iitem^, 

 Stein found others attached separately by very short stalks, or nearly sessile ; 

 these, his observations go to show, are probably derivable from the beings 

 produced by fission or gemmation, which have detached themselves from the 

 parent-stem in the strongly- contracted or partially-encysted condition, and, 

 on afterwards fixing themselves, proceeded either to complete their encysted 

 state or to assume the Acinetiform condition. 



Another set of beings Stein is disposed to introduce in the developmental 

 history of Episfiflis digitalis, in the shape of miniature branching Vorticellina. 

 The branches are dichotomously disposed, veiy slender, short, and rigid. 

 Seated at the extremity of each is a small campanulate being, with a stiff 

 bristle proceeding from each angle of the base (XXYII. 22, 23). Internally 

 they are finely granular. They exhibit slight changes of outline and jerking 

 movements upon their stalks ; they, moreover, can detach themselves and 

 swim freely away like a detached Epistylis digitalis, and may sometimes be 

 seen to affix themselves again by their base and produce a pedicle. These 

 beings, whether derived from E. digitalis or from Carchesium pygmcPAiin — 

 for they occur in company with both these animalcules, — their discoverer 

 would regard as their earliest phase of development, and believes that not 

 improbably similar miniature beings belong to all the pedicellate Vorticellina. 

 This notion involves no great stretch of the imagination ; for there is no extra- 

 ordinary metamorphosis necessary, and we may throw out the suggestion that 

 such minute Vorticellina are developed from the monadiform contents of the 

 brood-cysts. 



To take another illustration of Stein's hypothesis from the allied genus Ojjer- 

 cularia — the 0. herherina. Direct observation is wanting to identify the Aci- 

 neta as belonging to this Ojjercularia, except so far as contiguity on the same 

 filament of a plant or on the same member of a marine animal, and their frequent 

 occurrence, be allowed to have weight. Stein argues that the conversion of an 

 encysted Opercidaria into an Acineta is readily conceivable, by reason of their 

 congmity of form and the existence of intermediate phases, whilst, on the con- 

 trary, the transformation of the ciliated embryo into an Acineta, without first 

 passing through the intervening stage of an Opercidaria (a change easily 

 imagined), is a circumstance scarcely probable : on similar grounds he would 

 associate the pear-shaped Acineta, ha\ing a ramified nucleus (XXX. 3, 4), 

 with Opercularia articidata (XXX. 1), as a phase of existence interposed 

 between it and its embrj'onic stage of a free ciliated animalcule ; but his 

 developmental history of Vorticella microstoma is by far the most elaborate, 

 although much too long to present here except in abstract. 



His first step in the investigation of this species was the illustration of 

 the act of encysting (XXYII. 5 a-d) in its widest range, and the next, 

 to identify certain globular cysts, found in company with the Vorticellce, Tvith 

 the cysts of those animals. These cysts were about 4^'" in diameter ; they 

 had a clear double outhne, and contained a homogeneous, transparent, coloui'- 

 less and granular substance. In most, the characteristic band-like nucleus 

 and contractile space were ^dsible, together with, in many specimens, the in- 

 voluted cihary apparatus and oral ca\T^ty, looking, as a whole, hke a fissiu'e 

 at the anterior part of the cyst (XXYII. 7, 9). In other cysts, again, nought 

 could be discerned save the nucleus and the contractile space, sometimes di- 

 vided (XXYII. 1,8); and lastly, in others, all distinction of organs was lost, 

 the nucleus being the last to disappear (XXYII. 9). 



Stein considered, at first, those peculiar capsules to be connected with the 

 process of reproduction, and, from meeting with torn empty sacs, supposed 

 that the interior was broken up into germs which made their escape through 



