PROTOZOA 



CLASS 5. Infusoria 



The name of this group is derived from the fact that 

 the animals composing it are almost always found in 

 infusions of vegetable substance. 

 The characteristic feature of the 

 group is the presence of fine, hair- 

 like protrusions of the body sub- 

 stance, which more or less com- 

 pletely cover the animal, and which 

 are called cilia. These are perma- 

 nent structures in some forms 

 (Ciliata), but are found only in the 

 young condition of others (Tenta- 

 culiferd), the adults developing -ten- 

 tacles (Fig. 12). Their bodies show 

 a great variety of shapes, spherical, 

 flattened, oval, cylindrical, conical, 

 and so on. Some live as indepen- 

 dent organisms, as Paramecium 

 (Fig. 9); others 

 are sedentary, 

 being attached 

 by a stalk, as 



Vorticella (Fig. n); the trumpet 

 animal (Stentor) can attach itself at 

 will. Epistylis forms branching col- 

 onies. In some colonies the mem- 

 bers are all alike in structure and 

 function (Carchesium), while in 

 others (Zoothamnium) the members 

 which capture the food for the 

 FIG. .- Paramecium in colony are plainly different in shape, 

 the process of fission: m, s j ze an( ^ structure from those which 



mouth ; cv, contractile 



vacuoie;,macronucieus; produce the new colonies, the latter 



', micronucleus. Much , 111 i 11 



magnified. being mouthless, larger, and capable 



FIG. 9. Paramecium, c, 

 cilia ; g, gullet ; f, food 

 vacuole ; t, trichocysts ; 

 cv, contractile vacuole ; 

 m, macronucleus ; n, mi- 

 cronucleus. Much mag- 

 nified. 



