FEEDING REACTIONS IN DILEPTUS GIGAS. 



physical properties of the trichocysts of Dilcptus seem to determine 

 very largely the nature of the food which this organism ingests. 

 If the trichocysts are able to bring about cytolysis of the proto- 

 plasm of an organism, or even to completely paralyze it for a time, 

 that organism is " selected " as food. This relation between the 

 protoplasm of the prey and the trichocysts of Dilcptus is the im- 

 portant factor in determining whether or not Dilcptus " selects " it 

 as food. 



In Dileptus the former mechanism seems to play but a small role. 

 Because of its natural habits this ciliate deals almost exclusively 

 with living organisms. As previously stated, Dilcptus thrives only 

 in " relatively pure " and quiet water in which there are but few 

 inorganic particles in suspension. Its habit of continually swim- 

 ming serves admirably to keep it off the substratum, and we can 

 readily comprehend that motile organisms are almost the only sub- 

 stances from which it has normally to select. \Ye can safely con- 

 clude that much of the power of selection of food in Dilcptus 

 resides in the peculiar properties of its trichocysts. 



7. SUMMARY. 



1. Dilcptus gigas normally feeds on living organisms, but under 

 certain conditions it ingests inanimate particles. 



2. It discriminates between living organisms and inanimate sub- 

 stances, ingesting the former in large amounts, while the latter are 

 only sparingly ingested. 



3. Dileptus selects from among different kinds of organisms, 

 eating some with great readiness, while others are rarely ingested. 



4. It captures its prey by means of trichocysts which either 

 paralyze the prey, e.g., Euglena, or bring about cytolysis of all or 

 part of the protoplasm of the prey, e.g., Colpidium and Stcntor. 



5. The trichocysts are probably of a liquid nature, highly toxic, 

 with specific cytolytic properties. 



6. The trichocysts of Dilcptus are used for the purpose of 

 capturing food. 



7. Selection of food in Dilcptus depends on two factors : (a) 

 The physiological state of the organism itself, which appears to 

 determine whether a substance shall be ingested in large or small 

 amounts, and (b) the chemical properties of its trichocysts, which 



