286 PROTOZOA chap. 



Each of the organisms which we have studied in this 

 and the two previous chapters consists of a single cell — or 

 in the case of Carchesium and Epistylis of a colony of cells 

 to a large extent independent of one another. They are 

 therefore placed in the lowest primary division of the animal 

 kingdom — the phylum Protozoa (p. 220). This phylum is 

 subdivided into a number of classes, examples of certain of 

 which we have examined. Those in which, like the Amoeba, 

 the amoeboid form is predominant constitute the class 

 Rhizopoda : those in which, like the Monads and Euglenas 

 (Flagellata), the flagellate form is predominant are often 

 included with the ciliated forms (Ciliata) — such as Para- 

 moecium, Opalina and Vorticella — in a single class, the 

 Infusoria. 



The animals above the Protozoa are classed, as we have 

 seen, in a number of different phyla, but as they are all 

 multicellular they are often spoken of collectively as the 

 Metazoa, one of the simplest of which we must next 

 examine. 



PRACTICAL DIRECTIONS. 



Faramoeciam. — Spread a little cotton-wool on a slide over a drop 

 of water containing Paramcecia, in order to entangle them in its meshes, 

 and put on a cover-glass. Examine first with the low power and then 

 with the high power. Note — 



1. The elongated form of the ^animal ; its anterior (more rounded) 

 and posterior (more pointed) end ; its flattened dorsal and ventral 

 surfaces ; and its buccal groove and mouth, on the ventral surface. 



2. The active movements, due to the cilia covering the body. 



3. The marked distinctioh between cortex and medulla. 



4. The characters of the elastic cortex : — [a) the superficial cuticle, 

 and deeper striated layer ; [b) the cilia arising from the deeper layer, 

 and projecting through the cuticle ; (c) the trichocysts — small oval sacs, 

 imbedded in the deeper layer ; (rf) the two spherical contractile vacuoles, 

 situated in the deeper layer on the dorsal side : note that canals radiate 



