THE INFUSORIA 



435 



N 



plete turns, pass down into the vestibule, at the bottom of which 

 is the mouth, leading into a short oesophagus (Fig. 183, m, ORS.}. The 

 vestibule, into which the faeces and the excretions of the contractile 

 vacuoles are evacuated, forms a sort of cloaca, combining, as it 

 were, the functions of a stomodseum and a proctodaeum. 



The body of a ciliate Infusorian is composed of ectoplasm and 

 endoplasm, the first of these two regions being highly differentiated 

 and complex in structure. The surface of the entire body is clothed 

 by a pellicle (Fig. 185, p.) the most superficial differentiation of the 

 ectoplasm usually in the form of a thin, delicate membrane, which 

 is sometimes, however, greatly thickened to form a cuirass or 

 lorica. In addition to the mouth and anal pore already men- 

 tioned, the pellicle is perforated 

 by the openings of the contractile 

 vacuoles, one or more in number. 

 The cilia also pass through the 

 pellicle. 



Beneath the pellicle the ecto- 

 plasm, in its full development, 

 may be differentiated into four 

 layers, which, however, are not all 

 of them invariably present. The 

 most external layer of the ecto- 

 plasm is the so-called alveolar layer 

 (Fig. 185, al.}, consisting of the 

 outermost stratum of the alveoli 

 of the protoplasmic framework, 

 which take a regular arrangement, 

 the walls between contiguous 

 alveoli being disposed vertically 

 to the pellicle, thus giving the 

 appearance of a radially-striated 

 layer. Within the alveolar layer 

 is found commonly a protoplasmic zone containing small, spindle- 

 shaped bodies the so-called trichocysts (Fig. 185, tm.) from which a 

 long, stiff thread is discharged upon suitable stimulation. Within the 

 trichocyst-layer comes a contractile layer, containing myonemes 

 which run primitively beneath, or parallel to, the rows of cilia at 

 the surface. The cilia themselves take origin from basal granules 

 placed externally to, or between, the myonemes, and pass to the 

 exterior between the alveoli of the alveolar layer. The most 

 internal stratum of the ectoplasm is a spongy protoplasmic zone 

 traversed by irregular spaces and channels containing fluid, and 

 representing an excretory layer. The liquid from this region drains 

 into the contractile vacuole or vacuoles. The smaller channels 



FIG. 184. ChUodon cucullidus. o, 

 Mouth ; ph., pharynx surrounded 

 by a supporting apparatus of rods ; 

 N, macronucleus ; c.v., c.v., con- 

 tractile vacuoles ; an., anus, tem- 

 porarily visible during the extrusion 

 of fsecal matter (ex.). After Stein. 



