MORPHOLOGY AND TAXONOMY OF THE INFUSORIA 475 



seated by Paramecium, Frontonia and other related forms, there 

 appears to be no toxic action connected with the trichocysts, the 

 threads affording protection by the formation of a net-like weft 

 about the organism. In other cases, however, there is considerable 

 evidence of toxic action and in such types the long threads are not 

 formed. Visscher (1923) has described such toxic action on the 

 part of the trichocysts of Dileptus, and the sudden paralysis of 

 Halteria grandinella upon coming in contact with a tentacle of 

 Actinobolina is interpreted as due to the toxic action of the minute 

 trichocyst at the extremity of the tentacle (Calkins, Moody). In 

 Didinium nasutum there is a zone of rods quite independent of the 



Fro. 195. — Nassvla anna (C) and details of basket (.-1, B), after Butschli. 



pharyngeal trichites and interpreted as trichocysts near the extrem- 

 ity of the seizing organ of this voracious animal (Fig. 98, p. 1ST). 

 A Paramecium jabbed by this proboscis in one of the vigorous 

 darts of Didinium is immediately paralyzed and the poisoning is 

 attributed to the trichocyst material. While this interpretation is 

 plausible it cannot be regarded as proved, and it must be admitted 

 that the protoplasm itself may carry the toxic substance. Thus 

 in the Suctoria a ciliate or other small organism is similarly par- 

 alyzed upon coming in contact with an outstretched tentacle in 

 which no trichocysts can be demonstrated. 



Pharyngeal baskets are characteristic of the Chlamydodontidae 

 where they form conspicuous oral armatures (Fig. 195). The 



