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 {e.g. 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 mouth, 

 vestibule, and pharynx, are ectoplasmic in origin. 



While all these special modifications are developed for the pur- 

 pose of food-getting, the endoplasm, with its digestive processes, 

 shows but little advance, so far as can be made out, over the already 

 complicated endoplasm in the less highly organized forms. Simi- 

 lar food substances are treated in similar gastric vacuoles, and the 

 products of assimilation are carried about in the plasm by similar 

 cyclosis, while indigestible remains are excreted in the same way. 

 The Protozoa thus offer in the most striking manner an example of 



Fig. 99. — Urorentrum tuibo- 

 O. F. M. [BUTSCHLI.] 



