370 GENERAL HISTORY OF THE INFUSORIA. 



the abandonment of the hypothesis, the gTeatest names in microscopic science 

 having pronounced against it. 



To sum up the leading circumstances opposed to the theory in question. 

 The processes of the surface, both in variety of character and of movements, 

 are not paralleled in any known simple cell ; the same may be said of the 

 pedicles and branched stems of Vorticellina, and of the sheaths of Oplirydina : 

 the presence of a mouth, and, according to the descriptions of many excellent 

 observers, of a discharging aperture or anus, and the involution of the external 

 siu"face in the form of an alimentary tube, are facts iiTeconcileable with the 

 idea of a cell. So, likewise, the beautiful and complicated cihary apparatus 

 of the VorticeWma and Ophrydina — the existence of cells, or at least of 

 vesicles, in the interior — the reception of external matters into the general 

 cavity, where they are either entirely digested or partially or wholly extruded 

 again — and, lastly, the acti\dty, persistence, and apparently voluntary cha- 

 racter of their movements, are cii^cumstances vrithout parallel in the economy 

 of simple cells. In the face of all these discrepancies in stnictm-e and func- 

 tion between the bodies of Ciliated Protozoa and simple cells — closed sacs, 

 containing a nucleus amid their protoplasmic substance — it appears to us it 

 would be a mere visionary notion to insist upon a homology betwixt the two. 

 To conceive such a thing, the accepted idea of a cell must be set aside, and 

 replaced by so loose and general a definition as would be worthless. 



Without quoting their remarks, which is imcalled for here, the following 

 observers may, among others, be cited in opposition to the hypothesis of the 

 imicellular nature of the Cihata : viz. Leuckart, Lachmann, Claparede, Perty, 

 and Schneider. Our countryman, Mr. Busk, is, as we gathered from his lec- 

 tures, to be reckoned in the number. 



Conditions of Life. — Under this head we have to consider the habitats 

 of the Ciliata, the usual conditions imder which they live, their successive 

 appearance in liquids, the influence of heat and cold, and of chemical agents 

 upon them, and their probable duration of life. 



The majority of the Cihated Protozoa are inhabitants of fresh water; few' 

 are marine ; or perhaps it would be more correct to state that few marine 

 species are known. Cohn affirms that fresh water acts as a poison and kills 

 the marine forms (Entiv. pp. 132, 133) ; that the several genera of Entero- 

 dela (Ehr.) — Cydidium, Pmximecium, Eujplota, Oxytricha, and Yorticella — 

 occiu' in water holding organic matter in solution or decomposition ; and that 

 Stentor, Ophrydium, and Loxodes are found only where the water is pure and 

 uncontaminated with dead matter. This statement must not be taken arbi- 

 trarily ; for among the former series, specimens are constantly seen in water 

 free from appreciable organic impurities. Moreover, in all cases, the aqueous 

 medium in which the Ciliata live must contain a certain proportion of organic 

 materials (either living in the tissues of minuter organisms, or in a state of 

 transition, commencing decomposition or breaking up into mineral or dead 

 matter), from which they can derive the elements of their nutrition. 



Animalcules indeed, if we may so say, stand between the living and the 

 dead, rescuing the atomic fragments of organic matter which are ready to 

 perish and to lapse into the domain of dead matter. Thus we find them 

 constantly in infusions, either artificially made by steeping animal or, more 

 particularly, vegetable substances in water, or naturally occurring in ponds 

 and ditches containing growing aquatic plants or theii' detached portions, or 

 in the tui'fy hollows of commons and bogs. At times, indeed, the water in 

 which they occur appears to the eye almost pure, and free from extraneous 

 matters ; but a closer examination will prove it to be inhabited by multitudes 

 of monadiform existences, of minute plants, Desmidiece, Diatomece, Nostochinece, 



