196 



THE PROTOZOA 



are all hollow. The function of the endoplasm, according to Biitschli, 

 differs in the styliform and the capitate tentacles. In the latter, the 

 prey is retained by the sucking disk at the extremity while the endo- 

 plasm within the tube meantime works up and down like a pump- 

 piston, and a vacuum being thus formed, the cuticle of the prey 

 is burst, and the fluid endoplasm flows down the tentacle canal to 

 the endoplasm of the captor, where it is digested. 



Such an explanation of the action of these tentacles is regarded 

 by most observers as extremely doubtful. Delage finds no motion in 

 the endoplasm during feeding, save in the rhythmic pulsations of the 

 contractile vacuole, an organoid which Eismond ('90) believed is the 

 cause of the suction. The excretion of water from the vacuole, he 

 argued, creates a semi-vacuum in the protoplasm, and the pressure 



Fig. 108. Tentacles of Suctoria. [R. HERTWIG.] 

 A. Different types of styliform or piercing tentacles. B. Capitate and piercing tentacles. 



from without forces food or loose particles, etc., through the tentacle 

 openings to the endoplasm. This explanation, although somewhat 

 fanciful, is certainly as plausible as the principle of the pump, but 

 the matter must remain for the present as one of the many unsolved 

 problems connected with this group. In some cases (Tric/iophrya 

 angulata) the tentacles are apparently unnecessary for food-taking, 

 as Dangeard ('90) found that particles are occasionally engulfed, as 

 in the Rhizopoda, at any point of the naked body. 



In the styliform tentacles, on the other hand, the sharp points 

 pierce the membrane of the prey, while the endoplasm contained 

 within the tentacle possibly flows into the prey, whose endoplasm is 

 digested in situ. In some cases they appear to have a paralyzing 

 effect upon other forms, and ciliates coming in contact with them 

 have been seen to stop their movements as though stunned. 



