286 GENERAL HISTORY OF THE INFUSORIA. 



of uniform length. In Coleps (XXIV. 284), the lorica is divided into a mul- 

 titude of minute facettes bj intercurrent lines or sulci, and the cilia are placed 

 at the points of their intersection. In Colpoda Cucidlulus (XXIX. 35, 36, 37), 

 the cilia are much longer at the anterior prolonged extremit}^, the lip, just 

 as in Chilodon ; but there is besides, in the deep sulcus where the mouth is 

 found, a dense pencil of long and strong cilia (XXIX. 37), which Ehrenberg 

 mistook for a solid process of the body, and called the " tongue." From this 

 fasciculus or bundle, a row of long cilia is, moreover, seen to extend backwards 

 to the posterior extremity (XXIX. 37). 



Other groups of Ciliated Protozoa have the cilia confined, more or less strictly, 

 to one part or organ of the body, — a circumstance exemplified in the Vortl- 

 cellina and Ophrydina (XXX. 1, 2, 5, 9 ; XXIX. 1, 3, 4, 5). This Hmita- 

 tion, as contrasted with the general diffasion of cilia, imphes an advance in 

 the scheme of organization, and is attended by the constniction of a special 

 apparatus about the head of the animalcules. Thus, in the families named, 

 the rule is that the anterior extremity is bounded by an evident, mostly thick- 

 ened margin, either curved or straight — the "peristom " — crowned with vibra- 

 tile cilia and complicated by an internal, usually extensile, ciliated disk or 

 rotary organ (XXX. 1, 2, 9 a, 29 «), the whole apparatus recalling the stnic- 

 ture of the rotary organ of the Rotatoria. The cilia appertaining to the pe- 

 ristom and disk are highly developed and strong, although, instead of ser\dng 

 for locomotion, they only subserve the processes of nutrition and aeration or 

 respiration, by reason of the fixed condition of the animalcules possessing them. 



Another peculiarity of the ciliar}- apparatus of the Vorticellina and Opliry- 

 dina is that it is retractile (XXX. 6 a), or can be involuted and withdi-awn 

 into the interior of the animal (XXX. 13), and the peristom closed completely, 

 and contracted sometimes so far as to di-aw in a part of the wall around it, 

 and not leave a single ciKum visible externally (XXX. 11b, 31, 33). When 

 thus retracted, the ciHated organ appears like an internal, irregular-sigmoid, 

 contracted cavity or fissure, with the cilia closely packed together and scarcely 

 distinguishable (XXVII. 5 a, b ; XXX. 11 b). The retraction of the ciliary 

 wreaths, which takes place very rapidly, is caused by the presence of sur- 

 rounding objects in the immediate vicinity of the animal, by their contact 

 with it, by any shocks it may feel, and by the presence of noxious matters in 

 the water. On the removal of such and similar causes of annoyance, the ex- 

 tension of the delicate apparatus follows ; this act, however, is less rapid than 

 that of retraction, and may be arrested at any point. 



A more permanent withdrawal of the rotary apparatus, in the families 

 named, occurs when the process of self- division is about to proceed (XXVII. 3 ; 

 XXVIII. 18), and also when the animalcule prepares to enter into the en- 

 cysted condition (XXVII. 5, 7). 



The disappearance of ciHa is witnessed not only in Vorticellina and Ophry- 

 dina when the process of encysting takes place, but is a general phenomenon 

 among ciliated organisms under the same circumstances ; yet it would appear 

 that in some cases, even when an animalcule has surrounded itself with a 

 cyst, its cilia are not actually lost, but only withdrawn from view, — a fact 

 adverted to by Stein in his account of Chilodon Cucidlulus, which at times, 

 after encysting itself and developing one or more Hving germs within the 

 cyst, has been seen to renew its original appearance, to regain its cilia upon 

 its surface, and, after rotating for a while within the sac, to burst at length 

 through it and escape (XXIX. 55, 58). Moreover many observers have 

 asserted the fact that an animalcule may, soon after encysting itself, be set 

 free by rupturing the cyst by pressure, and then reassume its previous ciliated 

 and active condition. Nevertheless the act of encvsting, when advanced to 



