154 



BIOLOGY OF THE PROTOZOA 



The tentacle, then, with prey attached, is withdrawn entirely into 

 the body, the Halteria is worked around to the mouth and swal- 

 lowed (Fig. 81). 



In Didinium nasvtum the proboscis bears a peculiar protrusible 

 plug or tongue of protoplasm termed the "seizing organ" by Thon 

 (1905) and Prandtl (1907) (Fig. 89, 8). A zone of trichocyst-like 

 fibrils lies near the extremity of this plug and when certain types of 

 ciliates, preferably Paramecium, are struck by Didinium the plug, 

 with trichocysts, is shot out penetrating the cortex of the prey and 

 paral;\'zing it. While this process takes place too rapidly to be 

 seen the results show that it must have taken place for, after striking 

 and anchoring in the Paramecium, the seizing organ with prey 



Fig. 81. — Actinobolus radians St. (After Moody.) 



attached is retracted and the prey, often larger than the captor, 

 is swallowed whole (Fig. 89). No satisfactory explanation of this 

 phenomenon has yet been given. 



Still another type of cortical organs is illustrated by the various 

 kinds of tentacles of the Suctoria. Some of these are constructed 

 for piercing, while others are hollow, forming sucking tubes through 

 which food is taken into the body. They are evidently provided 

 with some type of poison for active ciliates, coming in contact with 

 these tentacles, become suddenl,\' quiet and remain so while the 

 suctorial tentacles penetrate the cortex and suck out the endoplasm 

 of the prey which can be followed through the feeding tubes to the 

 endoplasm of the captor (Maupas, 1883). Like the tentacles of 



