OF THE PROTOZOA. CILIATA . 289 



— the present anterior portion (fonnerly the posterior) grows thicker, whilst 

 the opposite end becomes somewhat more pointed. For a few seconds the animal 

 swims about, revolving at the same time upon its long axis, and after sud- 

 denly making a tiu'n, reassumes its regular form and its usual movements. 

 It is singular that the cilia of the reversed anterior cxtremit}^ acquii'e a greater 

 length and strength, and act with increased \agour, whilst those at the oppo- 

 site end become inconspicuous and passive. Dming diastrophy, moreover, 

 rotation upon its long axis is particularly rapid. Perty illustrates this pecu- 

 liar act of diastrophy in many other species, of which we may mention Para- 

 mecium Colpoda, Colpoda Ren, Coleps hirtus, Oxytriclia PeUioneJla, (fcc. 



A very indifferent conception can be formed of the energetic ever- varying 

 movements of the Ciliata by any attempted descriptions of their manner 

 and dii'ection. One method is combined with or rapidly exchanged for an- 

 other ; and we see the little beings not simply swimming, but revolving and 

 curving on themselves in a marvellous and beautiful manner, to be appre- 

 ciated only by observation. 



Could we imagine the existence of a will, or of a power of control, in 

 such tiny creatures, we should say that ciliary motion is at its bidding ; we 

 see it incessantly varying in. the same individual, both in activity and power, 

 at one moment urging on the moving atom at full force, at another merely 

 revolving it rapidly, at another slackened and presently stopped. These va- 

 riations, too, appear not fortuitous, but directed to certain ends — to the pro- 

 curing of food, to the avoiding of an obstacle, or to the escape from an enemy. 

 Yet, on the one hand, the belief in the need of a special organization for the 

 manifestation of volition, and, on the other, the observation of very similar 

 movements in the ciliated cells of higher animals when detached and free in 

 water, in the Phytozoa and in the spores and filiform cells of plants — are 

 circiunstances which make us hesitate in attributing such phenomena to 

 any other than purely physical forces. 



"There is no sufficient reason," says Dr. Carpenter (' The Microscope,' p. 

 476), " to regard such actions as indicative of a wonderful adaptation, on the 

 part of these simple ciliated cells, to a kind of life which enables them to go 

 in quest of their own nutriment, and to introduce it, when obtained, into the 

 interior of their bodies." 



Prof. Owen remarks, in his lectures on the Comparative Anatomy and Phy- 

 siology of the Invertebrated Animals (1843), p. 19, — " If you watch the 

 motions of the Polygastric Infusoria, you will perceive they avoid obstacles 

 to their progress, rarely jostle one another ; yet it is difficult to detect any 

 definite cause or object of their movements." Further on, he writes — " The 

 motions of the Polygastrica have appeared to me, long watching them for indi- 

 cations of volition, to be in general of the nature of respiratoiy acts, rather than 

 attempts to obtain food or avoid danger. Very seldom can they be constraed as 

 voluntaiy, but seem rather to be automatic — governed by the influence of sti- 

 muli Ts-ithin or without the body, not felt, but reflected upon the contractile 

 fibre — and therefore are motions which never tire. "We may thus explain 

 the fact which Ehrenberg relates (not without an expression of surprise), 

 namely, that at whatever period of the night he examined the living Infu- 

 soria, he invariably foimd them moving as actively as in the day-time ; in 

 short, it seemed to him that these little beings never slept." 



Turning now to the fixed Ciliata, we perceive that the true VorticeUina, 

 not invested by an external sheath, arrange themselves under two sections, 

 according as the stem is flexible and contractile, or non-contractile and almost 

 or completely inflexible. The geniLS VorticeUa is the type of the contractile 

 group, and Epistylh that of the non-contractile and inflexible. The stem 



