I_|.O J- PAUL VISSCHER. 



I 



method of staining " intra vitam," which demonstrates so clearly 

 the poisonous threads of the nematocysts of the common fresh- 

 water hydra, was also tried, but gave only negative results. 



We would maintain, then, that the contents of the trichocysts of 

 this organism do not have a morphological structure after they are 

 discharged, such as the trichocysts of Paramccium and Frontonia 

 have. It would appear that the trichocysts of Dilcptus are more 

 like elongated sacs of toxic fluid, which collapse upon discharging 

 the fluid. 



If it is true that these structures found in the proboscis of 

 Dileptus are bags rilled with a poisonous fluid, it is evident that the 

 term trichocyst (hair-sack) is not exactly applicable, and in order 

 to be more exact the term toxicyst (poison-sack) might be em- 

 ployed. 



C. SUMMARY OF OBSERVATIONS ON TRICHOCYSTS. 



The foregoing observations and experiments show that the 

 trichocysts of Dileptus are the structures which this organism em- 

 ploys in capturing food. They have the power to paralyze some 

 organisms, to bring about the cytolysis of others, and to cause a 

 vigorous reaction in almost all infusoria. Organisms like Para- 

 mecium and Frontonia are probably protected against the ordinary 

 attacks of Dilcptus by their own protective trichocysts. Organ- 

 isms like Euplotcs, which are provided with a lorica, form another 

 class of infusorians which appear to be protected against the tricho- 

 cysts of Dilcptus. Certain species of Stylonychia are known to 

 possess a heavy cuticle resembling a lorica, and it is perhaps for 

 this reason that these organisms were but rarely observed to fall 

 prey to Dileptus. The great majority of ciliates seem to fall prey 

 to Dilcptus, either owing to the paralyzing effect of its trichocysts 

 or to the cytolytic action of these structures. 



6. THE MECHANISM OF SELECTION OF FOOD IN DILEPTUS. 



There appear to be two distinct mechanisms by which selection 

 of food is brought about in Dilcptus. fi) The rejection of in- 

 organic particles, as shown in Tables I., II. , and III., is evidently 

 due to the effect of the physiological state, which serves to prevent 

 the organism from ingesting more. (2) The purely chemical and 



