PROTOZOA : INFUSORIA. 



77 



the fact that the members of the class are often developed in 

 organic infusions. 



The Infusoria, or Stomatode Protozoa, maybe defined as Pro- 

 tozoa which are mostly provided with a mouth and rudimentary 

 digestive cavity, which do not possess the power of emitting pseu- 

 dopodia, but which are furnished with vibratile cilia, or with 

 contractile filaments. They are mostly microscopic in size, and 

 their bodies usually consist of three distinct layers. 



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 outer 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, Paramos- 

 cium and Vorticella may be selected, the former being free, 

 whilst the latter is permanently fixed in its adult condition. 



Paramctcium (fig. 14, c] is a slipper-shaped animalcule, com- 

 posed externally of a structureless transparent pellicle the 



Fig. 14. Morphology of Infusoria ; a Epistylis, a stalked Infusorian ; b A single 

 calyx of the same greatly magnified, showing the ciliated disc which protrudes at 

 will, and the ciliated internal cavity into which the particles of food are received. 

 In the substance of the body are the contractile vesicle and smaller food-vactioles. 

 c Diagrammatic representation of Paramceciurn, showing the funnel-shaped gullet, 

 the nucleus and nucleolus, food-vacuoles, and two contractile vesicles, d Aspidisca. 

 lynceus : e Peranema globulosa, a flagellate Infusorian. 



" cuticle " which is lined by a layer of firm and consistent sar- 

 code, which is termed the " cortical layer," or the " parenchyma 



