288 GENERAL HISTORY OF THE INFUSORIA. 



along the margin of animalcules, on eminences and in depressions and other 

 particular parts ; such Lachmann would name " ciliary bristlesJ' In Tricho- 

 dina Pediculus (XXIX. 17), Stein describes a ciixle of uncini supported on a 

 cartilaginous or corneous ring, and extenial to this a yellowish membrane of 

 comeoiLS consistence and extraordinary flexibility, with closely-placed striae 

 across it. On a lateral "vdew of the animalcule, this membrane is seen to rise 

 round the circlet of uncini like a raised rim (XXIX. 17/). 



LOCOMOTIYE AND FlXED FoEMS OF THE CiLIATA. VARIETIES OF LoCOilOTION. 



Transitory Power of Locomotion among the Attached Genera. Pedicle 

 Single and Branched. Varied Outline of Ramified Stems. Structure of 

 Stem. Contractile Stems. Rigid Stems. — The Ciliata, with respect to the 

 function of locomotion, present themselves under two groups, — one compre- 

 hending those genera which at all periods of their existence can move from 

 place to place at will, the other embracing aU those which under ordinary 

 conditions are attached by means of a stem or pedicle, of greater or less length. 



The foimer — the locomotive group — includes the larger number of genera, 

 in aU. of which the cilia are more or less generally dLstributed over the entii-e 

 body. Theii' swimming movements are especially due to the cilia, but may be 

 aided by other tegumentaiy processes, by setae, styles, or uncini, and lq several 

 instances by the general figure of the body. It is rare that swimming is a 

 simple onward movement ; on the contrary, it is usually attended with a 

 rotarv motion about the long — seldom the short — axis of the body ; and when 

 the animalcule is considerably elongated, it becomes undulating, as m an eel. 

 In the case of Spirostomiim (XXIV. 297, 298), the elongated ribbon-like 

 figiu'e is particularly favourable to rapid writhing motion. In short, as before 

 intimated, the developement of the body to a greater extent in one or more 

 parts, so as to form processes, or the constriction of a portion, reducing it 

 to the dimensions of a member, or the lengthening of the entire animal into 

 a band-like or ligulate figure is made subservient to the piu'pose of locomo- 

 tion, and imparts to it a more or less special character. Moreover, the loco- 

 motive Ciliata have the power of altering the direction of their movements, 

 and wiU often retrace their course, and this frequently without tiu-ning them- 

 selves round in order to advance the same extremity foremost. 



The simple movement of swimming is common to all the Ciliata ; but in 

 the case of those furnished with setae and uncini, a creeping or crawling 

 motion is superadded, as, for example, in ^iylonychki (XXVIII. 10), Himan- 

 tophorus, Euphtes, and Kerona (XXV. '622, 328, 347, 353). In several 

 of these examples we find one side of the body covered T\ath a more resistant 

 integument or shield, whilst the locomotive uncini or setae are disposed 

 along the other, just as in the case of a myriapodous insect, and supply a 

 locomotive apparatus whereby the animalcules can nm, with much activity, 

 over the surface of an Alga or other solid body, or climb it without difficulty. 

 The movements of the setae, in creeping, are not independent Hke those of 

 vibratile cilia, but are produced by the contraction of the substance into 

 which theu' bases are fixed. 



Every microscopist has observed Ciliata suddenly arrest their course and as 

 quickly reverse it. This phenomenon Pert}^ calls ' diastrophy,' and asserts 

 (op. cit. p. 122) that this change in movement is accompanied by such a 

 transition, that not only does the posterior extremity become, for the time, the 

 anterior, but it also acquires the size and appearance of the latter. There is, 

 in his language, an actual polar reversion of the organism. This peculiarity is 

 observed among the swimming, but not among the creeping Protozoa, which 

 always advance with the anterior end first. When Paramecium versutum or 

 P. leiicas becomes diastrophied, its figure elongates and changes to cylindrical 



