456 



THE PROTOZOA 



stalked forms the body is raised up from the point of attachment 

 on a straight, non-contractile stalk of secreted substance, similar to 

 that of many Vorticellids, and the animal as a whole may resemble 

 in its general contours an Epistylis or other Vorticellid (Figs. 10, 

 190). Collin (877) finds that the stalk consists of a sheath, a cor- 

 tical layer thickest at the base, and a medullary substance stratified 

 longitudinally to the longitudinal axis. The base of the stalk rests 

 on a cushion of secreted substance the portion which is first 

 formed, and which is produced by a special organ of the larva 

 comparable to the scopula (p. 441) of the Vorticellids. 



The body is often protected by a secreted house or theca, con- 



FIG. 190. A, Podophrya mollis ; B, Tocoplirya quadripartite, two specimens 

 attached to the stalk of Epistylis plicatilis ; C, Podophrya fixa, two specimens 

 conjugating. After Saville Kent. 



tinuous with the stalk in the pedunculate forms. In AstropJirya 

 arenaria the house is built up of foreign particles of various sizes 

 (Aweriiizew). As in the attached ciliates, colonies may be formed 

 of considerable size and extent, and of various forms. The non- 

 pedunculate genus Dendrosoma produces spreading colonies, which 

 bear a considerable resemblance to a polyp-colony. 



The characteristic tentacles are stiff protoplasmic processes con- 

 sisting of a parietal layer of ectoplasm in the form of a tube en- 

 closing a canal containing fluid. The apex of the tentacle usually 

 terminates in a sucker-like knob ; suctorial tentacles (" Saugten- 



