CHAPTER XXX. 



CILOPHORA. 



Paramaecium Caudatum. This is the most common infusor- 

 ian met with in stagnant water. Its 

 length varies from 120 to 325^1. The 

 cell is spindle-shaped with a deep oral 

 groove which takes a spiral course on 

 one side of the body. The surface is 

 thickly set with active cilia. Food par- 

 ticles are swept into the oral groove, 

 enter the cytoplasm at its bottom and 

 circulate in the cell within food vac- 

 uoles. Near the center of the cell is 

 a large macronucleus and near it a 

 smaller micronucleus. Multiplication 

 takes place by simple longitudinal or 

 oblique division. 



Conjugation is isogamic. The simi- 

 lar conjugating cells adhere to each 

 other, the micronuclei divide twice and 

 three of the four nuclei thus produced 

 disintegrate, as does also the macro- 

 nucleus. The remaining micronucleus 

 divides into two and one of these passes 

 into the other conjugating cell in ex- 

 change for a similar element. The 

 newly acquired element unites with the 

 element which remained behind to form 

 the new nucleus. The new nucleus di- 

 vides three times in succession to form 

 28 433 



FIG. 208. Paramcecium 

 caudatum. K, Macronucleus; 

 NK, micronucleus; C, gullet; 

 N, food vacuoles; CV, contrac- 

 tile vacuoles. (After Doflein.} 



