48 MANUAL OF ZOOLOGY sect, i 



conjugation. In this very remarkable and characteristic 

 process two Paramoecia become applied by their ventral 

 faces, but do not fuse ; their meganuclei break up and dis- 

 appear, and an interchange of the substance of the micro- 

 nuclei of the two conjugating individuals takes place, with 

 the result that each develops a new meganucleus, and a 

 new micronucleus, partly formed of the substance of its own 

 micronucleus, partly that of the other Paramoecium. 



The possession of cilia is the distinctive feature of the class 

 Infusoria among the Protozoa. But in one section of the 

 class — the order Tentaeulifera — cilia are only present in 

 the young, their place in the adult being taken by append- 

 ages known as tentacles. The form of the body in the 

 Infusoria (Fig. 19) is very varied; it may be globular, 

 ovoid (7), kidney-shaped (2), trumpet-shaped (j), vase- 

 shaped (9), produced into a long, flexible, neck- like pro- 

 cess (5), or into large paired lappets (6), flattened from 

 above downwards, or elongated and divided into a series 

 of segments. Most are free-swimming, but many are fixed, 

 usually by means of a slender stalk (p). 



The arrangement of the cilia also varies greatly. Some, 

 like Paramoecium, have small cilia of uniform character 

 distributed over the entire surface. Others have different 

 kinds of cilia on different parts of the surface, while in 

 others the cilia are entirely confined to certain regions. 

 An instance of the latter arrangement is the common 

 stalked form Vorticella, with its allies such as Epistylis (9), 

 in which the cilia are confined to the free extremity. These 

 cilia produce rapid currents, and the Epistylis, says Stokes, 

 select from them anything they may want, and let the rest 

 sweep by. In another group, again, the body, which is of 

 flattened shape, bears on its dorsal surface a small number 

 of very fine motionless cilia, while on its ventral the cilia are 



