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J. PAUL VISSCHER. 



not capture all organisms, but selects from among the different 

 kinds of living organisms in accordance with the grouping shown. 

 The basis for this grouping will be more readily understood after 

 presenting a few observations on the mechanics of feeding and the 

 function of the trichocysts. 



4. OBSERVATIONS ON THE MECHANISM OF FEEDING. 



Many detailed observations were made on the mechanics of the 

 feeding process in Dilcptus in the hope of ascertaining the nature 

 of the power of choice which Dilcptus has been shown to possess. 

 A few of them, illustrating the various factors involved in the 

 feeding process, are described below. 



A. Euglcna. 



In making observations on the capture and ingestion of Euglena, 

 a single starved dileptus was isolated in a minute drop of water 

 on a glass slide. To this another small drop containing many 

 euglense was added. The reactions were observed under a magni- 

 fication of about 350 diameters. In numerous observations it was 

 found that whenever a euglena came in contact with any part of 

 the oral surface of the proboscis of the dileptus, it at once become 

 motionless (Fig. 2, a), and remained so for a longer or shorter 



FIG. 2. Diagrammatic sketches illustrating the process of feeding. A-F ' , 

 successive stages in process of ingesting Euglena. e, euglena paralyzed by 

 trichocysts; m, mouth; in', mouth with protruding lips (/) ; e', euglena being 

 engulfed ; e" ' , euglena in food vacuole. 



