FLAGELLATE AND CILIATE PROTOZOA 239 



possess well-defined pseudopodia, and the flagella of these forms have 

 the appearance of permanent, specialized pseudopodia endowed 

 with the power of vibration. The interchanging of pseudopodia 

 and flagella has been referred to in the case of Vampyrella under 

 Sarcodina. The origin of the flagellum has been traced in some 

 forms to the region of the nucleus, which may be considered as 

 evidence in favor of its homology with the axial supports of 

 pseudopodia. 



Cilia, which are the conspicuous and for diagnosis the special struc- 

 tural feature of the ciliates, as contrasted with flagella, are short, 

 hair-like processes. They arise from the ectoplasm, not origina- 

 ting from the deeper regions of the body as do flagella. Cilia may 

 be evenly distributed over the surface of the animal or restricted 

 to certain regions or zones. Often fusion of cilia takes place form- 

 ing vibrating membranelles or large bristle-like cirri or setae. By 

 tufts of cilia certain forms may be temporarily attached to supports. 

 Suctoria, in transition from the embryonic stages to the adult, lose 

 the covering of cilia which is replaced by hollow tentacles, capable 

 of extension and retraction. The tentacles may be pointed or dis- 

 tinctly capitate, the prey being pierced by them and its protoplasm 

 drawn through the hollow tubules into the body of the suctorian. 



In Mastigophora and Infusoria the protoplasm is similar in 

 structure to that of lower Protozoa, being alveolar in character. 

 However, in these groups, the protoplasmic contents of the body 

 are not arranged in zones to the extent found in Sarcodina. Great 

 variation exists in the consistency of the body both in flagellates 

 and in ciliates. In some the body is soft and flexible, the ectoplasm 

 permitting rapid changes in shape or even the formation of pseud- 

 opodia; others are enclosed by inflexible membranes, sheaths, or 

 well-defined plates. Cup-like loricae are sometimes developed, 

 to the inner surface of which the animal may be fixed, from which 

 it may project, and into which it may retract. In a few of the 

 flagellates a delicate collar is formed about the base of the flagellum. 

 The collar is very transparent, variable in size, and capable of being 

 retracted into the body protoplasm like a pseudopodium. 



Many flagellates and ciliates are free swimming, while some may 

 be temporarily fixed by cilia or flagella or by the adherence of a 



