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J. PAUL VISSCHER. 



at a distance at least equal to their own length. Sometimes as 

 many as two or three of these ciliates were seen to gather around 

 and attack a single rotifer. In these attacks the dilepti usually 

 failed to capture the rotifers. Only in one instance was a rotifer 

 actually observed to be captured and eaten. Although the feeding 

 process rarely culminated successfully, this experiment afforded 

 observations which are very instructive, as the following indicate. 

 In these observations each dileptus was continuously swinging 

 its proboscis back and forth, and at the same time revolving on its 

 longitudinal axis. Thus it struck the rotifers, now with the aboral 

 side, now with the oral side of the proboscis, and the corresponding 

 differences in the reactions of the rotifers were most striking. 

 The rotifer in question is one which attaches itself quite securely 

 to the wall of the dish. It also elongates and contracts from time 

 to time without changing its location. When the aboral side of 



FIG. 3. Sketches illustrating the effect of Dileptus on rotifers. A-H, suc- 

 cessive stages. Note differential effect, as seen by degree of subsequent con- 

 traction, of contact with aboral surface of proboscis as seen in A and B, and 

 of contact with oral surface of proboscis as seen in C and D. For further 

 explanation see text. 



the proboscis of a dileptus came in contact with an elongated rotifer 

 it contracted but slightly (Fig. 3, B), if at all, but when the oral 

 surface of the proboscis struck the rotifer it contracted completely 



