SPECIAL MORPHOLOGY AND TAXONOMY OF INFUSORIA 365 



Metaplastids are numerous and widely distributed. Of these 

 trichites, trichocysts and "pharyngeal baskets" are the most charac- 

 teristic. Trichites are elongate slender rods usually surrounding 

 the mouth in gymnostomes and are 

 generally interpreted as organs of sup- 

 port or protection. They are not 

 limited to the oral region, however, 

 and in some forms provide a protec- 

 tive cuirass about the posterior region 

 {Strombidium) . The oral trichites are 

 numerous and closely applied and in 

 some cases form a continuous and 

 smooth tube extending deep in the 

 endoplasm (some Nassidas, Odhodon, 

 etc.). Trichocysts are shorter and 

 more conspicuous; formed in the 

 endoplasm they assume a tangential 

 position in the cortex and may cover 

 the entire surface {Parameciuin, Fig. 

 156, Frontonia, etc.) or may be limited 

 to certain regions (Dileptus proboscis, 

 Fig. 157)). In a moving Adlnoholus 

 thex are arranged as in Paramecium, 

 but in a quiescent individual each 

 trichocyst is carried out at the end 

 of a long tentacle which this interest- 

 ing ciliate has the power to protrude 

 for feeding purposes (Fig. 81, p. 154). 



The function of the trichocysts is 

 still in dispute (Visscher, 1923)."^ The 

 substance of a trichocyst may be shot 

 out in the form of a long thread which 

 hardens on contact with water. In 

 such forms, represented by Parame- 

 cium, 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 



Fig. 157. 



Dileptus gigas, with 

 beaded macronucleiis and twisted 

 proboscis. (Original.) 



