252 INFUSORIA CILIATA. 



deposit in men, mentions no fewer than three species of Trichomonas, 

 which are respectively described under the names of T. elongata, 

 T. caudata, and T. flagellata. 



Order II. CILIATA. 



Stein, " Der Organismus der Infusionsthiere : " Abth. i., 1859; Abth. ii., Leipzig, 1867. 



Infusoria with numerous cilia, which are never confined to the 

 immediate neighbourhood of the mouth, but either cover the whole body 

 or are disposed in greater numbers, and in more regular groups on the 

 anterior portion, or on the ventral sarface. The body-parenchyma 

 exhibits, as a rule, a distinct differentiation into a cortical layer and 

 central mass, and usually contains a nucleus and accessory nucleus. 

 When a mouth is present there is also an anus. 



This division contains the larger and more highly developed 

 Infusorians, the properly typical forms with respect to which what 

 we have before remarked in regard to reproduction and multiplication 

 primarily and specially holds good. 



Although agreeing in certain essential conditions, the Ciliata show 

 manifold differences in the details of structure, not only in the above- 

 mentioned ciliary apparatus, but in form and habit, and especially 

 in the mode of motion. Some have attempted to turn these differ- 

 ences to account by dividing the Ciliata 1 again into a number of sub- 

 orders. Thus they distinguish in the first place a group " Holotricha," 

 so called because the generally flattened and oval body is covered 

 throughout its whole extent by a thick coating of short cilia. In the 

 group " Heterotricha " there is, in addition to this covering of cilia, a 

 peculiar modification of the oral region, which develops by flattening or 

 by excavation into a larger and smaller peristome. This peristome is 

 sometimes indicated even in the Holotricha, but in the Heterotricha 

 it is always distinguished by one of its edges being furnished with a 

 longer or shorter, and sometimes spiral, row of strong cilia, which 

 can be traced as far as the mouth aperture. In the so-called 

 " Peritricha " this per'istoniial region surrounds the whole anterior 

 end of the body, which thus possesses a complete girdle of cilia, and 

 can also be retracted to a greater or less extent into the other portion 

 of the body. In individual members of this group an aboral girdle 

 of cilia occurs, in addition to the cilia of the peristoniial region, while 

 the former uniform ciliated coat is completely absent. The body has 

 besides a cylindrical form, so that the structure appears somewhat 



1 The altogether unciliated adult Suetoria, or Acinetans, are not taken into account, 

 as they never appear as parasites in the Vertebrata. 



