INFUSORIA 



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CLASS IV. INFUSORIA 



The fourth class of protozoans is the Infuso'ria, of which 

 the Paramcecium, or "slipper animalcule," is a type (Fig. 2). 

 It is somewhat cylindric in form and is surrounded by a cuticle 

 perforated with minute openings, through which the proto- 

 plasm projects in the form of short hair-like structures, called 

 cilia, which are the organs of locomotion. 

 On the ventral surface of the Paramcecium 

 is a groove which runs backward and 

 inward into a short tube or gullet. Both 

 the tube and the gullet are lined with 

 vibrating cilia which cause currents of 

 water. These currents carry the food into 

 the inner end of the gullet, where it is 

 pushed by occasional constrictions into the 

 soft endoplasm and carried about in its 

 movements as a food vacuole. The un- 

 digested particles are cast out at a fixed 

 point in the cell wall, but it is not per- 

 manently open, so it is not easily recog- 

 nized. The Paramcecium is supplied with 

 two coiled threads which may be used 

 as organs of defense. The Paramcecium 

 has two nuclei, one, the macronucleus, 

 supposed to be the seat of all vital func- 

 tions, and the other, the micronucleus, 

 which controls the reproduction. The 

 Paramcecium reproduces by fission, both 

 nuclei being divided, but conjugation 

 also is manifested. In conjugation, 

 two Paramcecia unite temporarily, ex- 

 change a portion of the micronuclei, 



and perform other processes ; they then separate, and continue 

 more actively the process of transverse division or fission. 



While these examples are only a few of the thousands of 

 species and of the countless myriads of individuals of proto- 

 zoans, yet, if carefully studied, they teach many things. 



Protoplasm. — Living protoplasm is the active substance of all 

 living organisms. All the forces or conditions which tend to 





Fig. 2. — Parojiioe- 

 cium aurelia. In the 

 center may be seen 

 one of the nuclei, and 

 at each end a contrac- 

 tile vacuole. (After 

 Verworn.) 



