. The Protozoa. Protozoa. THE INFUSORIA 183 runs around the peristome connecting the series,' and possibly form- ing a nervous organ (Delage, '96; Moore, '93). The undulating membranes, finally, which are almost always con- fined to the oral region, and like the membranelles chiefly concerned with food-taking, have probably a similar origin, although the con- nection with the cilia is less apparent. They are frequently, as in the Hypotrichida, placed deep in the vestibule, but in many forms they are confined to the pharynx itself, as in many of the Holo- trichida. In addition to cilia, membran
. The Protozoa. Protozoa. THE INFUSORIA 183 runs around the peristome connecting the series,' and possibly form- ing a nervous organ (Delage, '96; Moore, '93). The undulating membranes, finally, which are almost always con- fined to the oral region, and like the membranelles chiefly concerned with food-taking, have probably a similar origin, although the con- nection with the cilia is less apparent. They are frequently, as in the Hypotrichida, placed deep in the vestibule, but in many forms they are confined to the pharynx itself, as in many of the Holo- trichida. In addition to cilia, membranelles, and membranes, the ectoplasm has other modifications, such as pseudopodia { Stentor) and tenta- cles. The pseudopodia are used for anchoring the animal, and are produced at the posterior end by the so-called foot-disk (Johnson, '93). The cortical plasm gives rise to these processes, and also to the peculiar tentacle-like appendages found in some forms. In Actinobo- lus (Fig. 100) these pseudopodial tentacles are particularly well known through the complete study made by Entz ('82). Here the threads pass out between the cilia and not infrequently reach a length of twice or even three times the body diameter. The threads are of nearly uni- form thickness, with blunt or slightly knobbed ends (Entz). These tentacles, while occasion- ally stiff and unyielding, can be shortened or lengthened, or drawn into the body in a manner surprisingly suggestive of pseudo- podia, while the protective and offensive func- tion is shown by the presence of trichocysts at their extremities. Similar tentacles are found in Mesodinium and Ileonema (see Fig. 115). While the ectoplasm is devoted to the functions of motion and irri- tability, the endoplasm is charged with digestion and reproduction. Thus the membranelles and membranes are important in creating the current which brings the food particles ; the trichocysts are occasion- ally developed as food-killing organs, and these, with the mo
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