278 GENERAL HISTOKY OE THE INEUSOBIA. 



stalked VorticelUe extend themselves to y^th in length. Paramecia are men- 

 tioned by Ehi'enberg from ^th to ^ ^\. ^ th in length ; and specimens of the same 

 species of VorticeUa, viz. F. microstoma, are described to vary in size between 

 2-gVo^^ ^^^ yio^^* Stein has also noticed examples of Chilodon CucuUulus 

 from 2^0^^ ^^ TTUU^^- ^ ^^®^ surprising magnitude is attained by the polypoid 

 masses of Oplirydium versatile, which range between mere microscopic globules 

 and aggregated masses the size of the fist or even of the head of a man. 



FiGUEE. — In figure the Ciliata exhibit an immense variety, but have a 

 rounded outline in all instances. The prevailing figure is oval or oblong ; but 

 some taper much at one or both ends, and acquire a spindle-, or a flask-, or a 

 club-shaped aspect, whilst others, as the VorticelUna (XXVII. 1, 2, 4, 16; 

 XXX. 1, 9, 11), present a bell-shaped or campanulate outline, and others 

 again, as Spirostommn (XXIV. 298), an elongate ribbon- or band-like one. 

 However, the best idea of the manifold forms can be gathered by inspecting 

 the subjoined plates of the Ciliated Protozoa, which render verbal description 

 imnecessary. 



The figure is determinate and constant under like phases of existence for 

 each species, although liable in the majority to very great changes by the 

 contraction and movements of the animalcules, by their contact with more 

 solid bodies, and by the introduction of food. These changes are proportionate 

 to the elasticity of the integument and to the contractile power of the contents ; 

 and hence, in several with firm integument, they are veiy limited, or not 

 possible. 



The figui^e is also much modified by the processes of multiplication and of 

 reproduction. The act of fission materially modifies it ; gemmation does so 

 to a less extent ; but the most remarkable change is caused by the encysting- 

 process, which is generally a prelude to the peculiar set of phenomena attend- 

 ing the reproduction by germs or embryos, and, according to Stein's views, 

 would seem to temdnate in actual metamorphosis or transformation of the 

 beings concerned. Indeed the Ciliata in general appear to pass thi'ough a 

 cycle of changes, each of these entaihng a distinct figure ; in other words, 

 in the historj^ of each ciliated Infusorium, there are several phases of ex- 

 istence, difi'ering from one another in form and other particulars. The history 

 of an animalcule, therefore, is comprehended in that of no one form or phase, 

 but in that of every one it normally assumes ; nevertheless it is necessary to 

 fix upon one phase, either as the most important or the most perfect, and to 

 characterize and name it, just as is done in the case of insects, which are 

 described in their most developed or " imago " condition. 



Another point to be remembered is, that the figiu'e of a specimen appears 

 diff'erent in most cases, according to the aspect in which it is viewed ; and, 

 again, there is often much diversity in shape between young beings and those 

 arrived at maturity. Perty has applied the term ' metahoUa ' to express the 

 changes of figure animalcules may assume. The figure is extremely varied 

 in Lacrymaria by its movements, and chiefiy by the lengthening or shorten- 

 ing of its elongated anterior portion or neck. This variability of form struck 

 Baker and other old observers so forcibly, that they applied the term Proteus 

 to designate the animalcule (XXIV. 274, 275). Trachelocerca (XXIV. 317- 

 319) and PMalina have a similar power of varying their outline ; and all three 

 genera are further remarkable by the manner in which their surface can be 

 thrown into transverse or even intersecting folds or plaits. 



The influence of food when swallowed in modifying the figure, Ehrenberg 

 particularly illustrated in his Enchehjs Farcimen (XXVIII. group 64). This 

 animalcule devours others nearly as large as itself, and, to efiect this, Avidcly 

 dilates its mouth, and so becomes shorter and broader ; and as during the 



