PROTOZOA: INFUSORIA. 



95 



which is by no means free from difficulties the " nucleus " of 

 the Infusorian animalcules really corresponds with the struc- 

 ture known by the same name in an 

 ordinary animal or vegetable cell. 



The Infusoria may be divided 

 into three orders viz., Suctoria, 

 Ciliata, and Flagellata of which the 

 second comprises the majority of 

 the members of the class, and alone 

 requires much consideration. 



I. ORDER CILIATA. This order 

 comprises those Infusoria in which the 

 otiter layer of the body is more or less 

 abundantly furnished with vibratile 

 cilia, which serve either for locomotion 

 or for the procuring of food. Besides 

 cilia, properly so called, some of the 

 ciliated Infusoria are provided with 

 styles or jointed bristles, which are 

 movable, and subserve locomotion ; 

 whilst others have little hooks or 

 uncini, with which they can attach 

 themselves to foreign bodies. As 

 types of the order, Paramcecium and 

 Vorticella may be selected, the former 

 being free, whilst the latter is per- 

 manently fixed in its adult condition. 



Paramcecium (figs. 31 and 32) is a 

 slipper-shaped animalcule, composed 

 externally of a structureless trans- 

 parent pellicle the " cuticle " 

 which is lined by a layer of firm and 

 consistent sarcode, which is termed 

 the "cortical layer," or the "paren- 

 chyma of the body," this in turn pas- 

 sing into a central mass of softer and 

 more diffluent sarcode, known as the 

 " chyme- mass," or " endoplasm." 

 The cuticle is merely the structure- 

 less hardened external lamina of the 

 " cortical layer," and it may in some 

 cases form a regular protective sheath 

 ( Vaginicola), a horny shell ( Codon- 

 ella\ or even a reticulated siliceous 

 envelope (as in Dictyocysta\ Beneath 



'ig. 31. Paramaechun, viewed 

 dorsally, and greatly magnified. 

 m Mouth ; m to g Gullet ; a 

 Anus ; cv' and cv The contractile 

 vesicles; I, II, III, Canals pro- 

 ceeding from the anterior con- 

 tractile vesicle ; n Nucleus ; i> 

 Large cilia bounding the depres- 

 sion ("vestibule") leading to the 

 mouth. The arrows indicate the 

 course in which the particles of 

 food circulate in the semi-fluid 

 protoplasm of the interior of the 

 body. (After James-Clark.) 



