THE ANIMAL KINGDOM 



383 



the prevention of death in Protozoa is due less to the environ- 

 ment than to the nature of the organism — in the case of 

 Paramecium, to the process of endomixis. 



Order 2. Heterotrichida. Membranelles about the oral zone. 

 Cilia uniform over the rest of the body. 



Example: Stentor, common in fresh water (Fig. 216, A). 



Order 3. Oligotrichida. Cilia limited almost entirely to the 

 oral zone. 



Fig. 215. — Diagram of the nuclear changes in Paramecium aurelia during 

 endomixis. A, typical nuclear condition; B, degeneration of macronucleus 

 and first division of micronuclei; C, second division of micronuleci; D, degenera- 

 tion of six of the eight micronuclei; E, cell division; F, first reconstruction division 

 of micronuclei; G, second reconstruction division; H, transformation of two 

 micronuclei into two maeronuclei; I, division of micronuclei and cell division; 

 J, two complete new individuals. (After Woodruff, Foundation of Biology, 

 copyright. The Macmillan Company. By permission.) 



Example: Halteria, a fresh-water form that moves in leaps 

 by means of cirri. 

 Order 4. Hypotrichida. A flattened body, as a rule with cilia, 

 cirri, and membranelles on the ventral surface. 

 Example: Stylonychia (Fig. 216, D). 

 Order 5. Peritrichida. Cylindrical or cup-shaped body, usually 

 free of cilia except in the adoral zone; and usually provided with 

 a contractile stalk. 



Examples: Vorticella (Fig. 216, C); Carchesium, a branched 

 colonial form. 



