DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 163 



In Didinium nasutum the proboscis bears a peculiar protrusible 

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

 (1905) and Prandtl (1907) (Fig. 98, p. 187). A zoneof 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 penetrates the cortex of the prey, paralyzing 

 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 attached 

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

 whole (Fig. 98, p. 187). No satisfactory explanation of this phenom- 

 enon has yet been given. 



Fig. 91. — Actinobolina radians St. (After Moody.) 



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 suddenly 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 

 Actinobolina radians, these suctorial tentacles are retractile, but 

 again there is no satisfactory explanation of their activity and no 

 description or mention of specialized motile apparatus. 



