INFUSORIA 



CLASS IV. INFUSORIA 



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

 the raramopchmi, or "sUpper animalcule," is a type (Fig. 2). 

 1 1 is somewhat cyUndric in form and is surrounded by a cuticle 

 perforated with minute openings, through 

 which the protoplasm projects in the form 

 of short hair-like structures, called cilia, 

 which are the organs of locomotion. 

 On the ventral surface of the Paramoecium 

 is a groove which runs backward and 

 inward into a short tube or gullet. Both 

 the tube and the gullet are lined with 

 vibrating ciha 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 Paramoecium is supplied with 

 two coiled threads which may be used 

 as organs of defense. The Paramoecium 

 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 

 Paramoecium reproduces by fission, both 

 nuclei being divided, but conjugation 

 also is manifested. In conjugation, 

 two Paramoecia 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. 



Fig. 2. 

 cixim canddtiini, 

 the ventral side, sliow- 

 ing the vestibule en 

 face; arrows inside the 

 body indicate the di- 

 rection of protoi)lasinic 

 currents; thoseoutside, 

 the direction of water 

 currents caused by the 

 ciha. c.v, Contractile 

 vacuoles;/./', food vac- 

 uoles; ir.r, water vacu- 

 oles; ///, inoutii; tunc, 

 macronucleus; tnic, mi- 

 cronucleus; 6P, esopha- 

 gus; ;;, vestibule. The 

 anterior end is directed 

 upward. (Sedgwick 

 and Wilson.) 



