Glass 2. Infusoria. 



95 



Under the term Flagellata is included a lai-ge number of diverse unicellular 

 animals, which are all, characterised by the possession of a single powerful 

 ■flageUum. These organisms 



do not, however, constitute A B 



a natural division : some of 

 them seem to be most closely 

 allied to the Infusoria, and in 

 any case undoubtedly belong 

 to the Animal Kingdom. 

 Others are certainly vege- 

 table organisms, provided 

 with chlorophyll (c/. p. 81), 

 whilst yet others are of very 

 doubtful position. Among 

 the Flagellates possessing 

 animal characters may be 

 mentioned the M o n a - 

 dinidse, small organisms 

 provided with one or several 

 flagella at the anterior end, 

 ocoui-ring in vast numbers 

 in decaying substances and 

 in the alimentary canal of 

 various animals ; some 

 species are invariably pre- 

 sent in the stomach of the Ruminants, the oscum of the Pig, the rectum of 

 Frogs and Toads ; whilst some have been found in the alimentary canal of Man. 



Fig. 54. Various Monadidas. A Cercomonas 

 muscw (from the duodenum of the house-fly) . B Bodo 

 ovatus, C JSexamita rostrata. c contractile vacuole, 

 n nucleus. — After Stein. 



Class 3. Gregarinida. 



The Gregarines which are, without exceptioiij parasitic, are, like 

 the Infusoria, unable to protrude pseudopodia, but are distinguished 

 from these, amongst other things, by the absence of cilia. The 

 unicellular body is usually, although not always, surrounded by a 

 definite coat : the protoplasm is usually divided into two layers, 

 the inner granular and the outer clearer, not, however, sharply 



Kg. 55. Diagrammatic figure of a Gregarine. 1 a single individual, 2 two conjugating 

 individuals, 3 two such encysted, 4 the same, completely fused, 5 they have divided into 

 spores, 6 within the spores falciform young are formed, 7 — 9 a spore at various stages of 

 devetopment strongly magnified. — Orig. 



