Vrotozoa and Rot'ifera at Ilacana, III. '60l 



variable in shape. The endoplasm and ectoplasm are "well 

 differentiated. From the anterior end of the body projects a 

 long slender flagellum, just below which is the mouth opening. 

 Near the base of the flagellum is the red stigma, sometimes 

 called the eye-spot. A little behind this pigment spot is the 

 contractile vacuole. This empties into a sort of vestibule. 

 The posterior extremity of the body is, in some species, pro- 

 longed into a short spine-like process. A large nucleus is 

 present. The endoplasm usually contains anuml)er of starch 

 bodies. 



The order T)inoji(igellat(ii\\c\\!i(\.Q^ Pcridinlum and Ceratinin, 

 which have a hard covering or shell of modified cellulose. 

 Contractile vacuole and nucleus are present. There are two 

 flagella ; one extending out in front of the animal, while the 

 other encircles the body and lies in an equatorial groove. 



The members of the class Infusoria have more or less of 

 the surface of the body covered with fine cilia. These are 

 permanently present in the subclass Clliata, but in the sub- 

 class Snctoria are found only in the young. In the holotri- 

 chous Ciliata they are comparatively uniform, and usually 

 invest the entire body surface. By some authors these forms 

 are all grouped under the name Iloloiricha. A large part 

 of them, however, constitute a group sufficiently distinct 

 from all other Ciliata to be ranked as a separate order, the 

 Gymnostomata. The mouth is naked, and closed except when 

 in use, the ^food being swallowed. In the remaining Ciliata, 

 constituting the order Trichostomata, the mouth usually 

 remains open, and the food is swept into it by the action of 

 cilia or undulating membrane. 



The holotrichous Trichostomata form the suborder Aspiro- 

 trieha, which is Avell represented by Paramecium aurelia, the 

 slipiDer animalcule. Its body is elongate, pointed posteriorly, 

 and rounded and slightly narrower anteriorly. The entire 

 surface is covered with tine cilia. On the ventral surface is 

 an anterior oblique groove, at the posterior end of which the 

 oral opening is situated. The nucleus is large. Two con- 

 tractile vacuoles are present, which usually assume a stellate 

 appearance upon contracting The ectoplasm or cuticula is 



