flattened, they have the ciha confined almost entirely 

 to the flat undersurface, on which they creep about 

 in a characteristic jerky manner. The cilia do not 

 beat but are fused into a number of stout projections 

 that act like little legs. The upper surface is convex 

 and has only a few stiff sensory bristles. Well known 

 are Oxytricha, Stylonychia, and Eiiploies, as well as 

 Kerona, a curious little commensal that crawls about 

 on the outer surface of hydras. 



THE PERITRICHS 



The peritrichs typically are bell-shaped or vase- 

 shaped forms that live attached by a long, spirally 

 contractile stalk, and that have no cilia except those 

 on the feeding disk that occupies the broad end of 

 the bell. The cilia occur in circlets, and cling loosely 

 to each other to form a kind of continuous undu- 

 lating membrane that sweeps food particles into the 

 mouth. When the animal is feeding the bell is held 

 aloft, fully expanded, and the ciliary membrane 

 sweeps in bacteria by creating a whirlpool or vortex, 

 which suggested the name of the common genus, 

 Vorticella. At the least alarm the stalk contracts like 

 a coiled spring and the contractile bell folds its edge 



over the cilia. Any bell can develop a girdle of cilia, 

 break loose, and swim away to a better neighbor- 

 hood. When vorticellas conjugate, one of the mem- 

 bers is of very different size. Vorticella grows singly 

 or in dense clusters; and Epistylis is colonial, with 

 stalks that are noncontractile. Both occur in marine 

 waters but are most familiar from fresh waters ev- 

 erywhere, for they form whitish patches on sub- 

 merged sticks and stones and in some streams are 

 found springing from the body of almost every 

 aquatic insect or crustacean. Carchesium colonies, 

 in which the individuals contract their stalks inde- 

 pendently, grow nearly V^s. of an inch long on the 

 underside of sticks and stones in fresh-water streams. 

 Zootluinmiiiin is like Carchesium except that there is 

 a single branching system of contractile fibers, so 

 that the whole colony contracts at one time. A freely 

 moving peritrich is Trichodina. often seen moving 

 about on the bodies of hydras by means of a posterior 

 circlet of cilia. The round squat body has a concave 

 undersurface bearing a horny ring, usually with 

 curved hooks, by which it clings to the hydra and 

 also to a variety of other aquatic hosts such as 

 sponges, flatworms, frog tadpoles, other amphibians, 

 and fish. 



The Suctorians 



( Class Suctoria ) 



In Stylunijcliia, many of the cilia are fused in groups 

 and are stout organs, easy to see as the animals move 

 about on them. Stylonychia is flattened, with definite 

 upper and lower surfaces. (General Biological Sup- 

 ply House, Chicago) 



The suctorians have staked out a new claim in the 

 protozoan world, and established a whole new class 

 of animals, through their development of long, 

 sucking tentacles that enable them to capture and 

 feed on prey without either moving about or produc- 

 ing feeding currents. Though obviously derived from 

 ciliates, the adult suctorians have been able to dis- 

 pense with cilia altogether. Only the young are cili- 

 ated, and this helps them to move a little distance 

 before settling down and competing for food with 

 their parents, who live attached by a stalk to vegeta- 

 tion, to other animals, or to any solid object in fresh 

 and salt waters everywhere. Tokophrya has a long, 

 noncontractile stalk that holds aloft a club-shaped 

 body. From the free end of the club it rigidly extends 

 a number of very long and slender hollow tentacles, 

 knobbed at their tips. When a ciliate sails unaware 

 into one of these tentacles it is seized and held fast 

 by a number of tentacles, while from three to ten of 

 the hollow tubes in some way penetrate the surface 

 covering and suck up the protoplasm. About fifteen 

 minutes suffice for sucking dry a euplotes. The vic- 

 tim may thrash about and struggle mightily to escape, 

 but it rarely does, even though held by only a few 

 delicate-appearing tentacles. A specialist on sucto- 

 rians watched many trapped paramecia in their 

 death struggles without ever seeing one extrude trich- 



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