50 MANUAL OF ZOOLOGY SECT. 



very strong, and are modified into the shape of hooks, bris- 

 tles, or plates with fringed ends. The hooks and plates do 

 not vibrate rhythmically like ordinary cilia, but are moved 

 as a whole at the will of the animal, such Infusoria being 

 able, in addition to swimming freely through the water, 

 to clamber by the aid of these specially modified cilia over 

 the surface of weeds, etc. Tentacles may be present in 

 addition to cilia (14), and a number of other exceptional 

 modifications (10-13) occur which cannot be specially re- 

 ferred to here. 



In addition to cilia, many genera possess delicate sheets 

 of protoplasm, or undulating membranes (u. mb) in connec- 

 tion with the peristome. These contract so as to pro- 

 duce a wave-like movement which aids in the ingestion 

 of food. 



The tentacles, which, in the Tentaculifera (Fig. 20), take 

 the place of cilia in the adult, are elongated cylindrical 

 structures, capable of protrusion and retraction, and having 

 the distal end expanded into a sucker. The tentacle is 

 practically tubular, the core consisting of a semi-fluid proto- 

 plasm, while the outer part is tolerably firm. Infusoria and 

 other organisms are caught by the tentacles, the cuticle of 

 the prey is pierced or dissolved where the sucker touches 

 it, and the semi-fluid protoplasm can then be seen flowing 

 down the tentacle into the body of the captor. A single 

 tentacle alone may be present (j>), or the tentacle may be 

 branched (4), the extremity of each of the branches being 

 suctorial. In some forms (j") the tentacles are devoid of 

 sucker-like extremities, and can be moved about actively to 

 catch the prey. 



The meganucleus is often ovoid, as in Paramcecium. In 

 other cases it may be long and band-like (Fig. 19, j, 

 mg. nu}, horseshoe-shaped (p), very long and constricted 



