FEEDING REACTIONS IN DILEPTUS GIGAS. 



129 



and vigorously, and often remained thus contracted for some little 

 time (Fig. 3, D). The hungry little ciliates still persisted and an 

 occasional individual was sometimes seen to succeed in getting the 

 head of an attached rotifer far into its oral opening (Fig. 3, F), 

 but a sudden contraction on the part of the attached rotifer in- 

 variably resulted in freeing the captive. 



Thus when a rotifer comes in contact with the oral surface of 

 the proboscis of a dileptus its reaction is extremely vigorous, while 

 if the aboral surface of the proboscis touches the same rotifer 

 little, if any, reaction is observed. The reaction resulting from 

 contact with the aboral surface of the proboscis is just such as 

 would be expected from a sight mechanical stimulus, but the vio- 

 lent reaction observed whenever the oral surface comes in contact 

 with the rotifer is clearly of an entirely different nature. This 

 difference must be in some way related to the difference between 

 the oral and aboral surfaces of the proboscis. The essential dif- 

 ference between these two is the fact that the former contains 

 trichocysts, while the latter does not. The difference in the reac- 

 tion is probably, therefore, related to the action of the trichocysts. 



C. COLPIDIUM. 



The observations on Colpidiwn, like those on Euglena described 

 above, were made under high magnification. In one of the many 

 experiments two starved dilepti were isolated in a single drop of 

 water and a smaller drop containing numerous specimens of Col- 

 pidium was added. The latter were so numerous that they were 

 continually coming in contact with various parts of the dilepti. 

 Some, consequently, frequently came in contact with the oral sur- 

 face of the prpboscis, as well as with various regions of the surface 

 of the body. It was very apparent that those which came in con- 

 tact with the oral surface of the proboscis were the only ones seri- 

 ously affected. Whenever a Colpidiuni came in contact with this 

 surface of the proboscis it at once became motionless and remained 

 so for a very brief interval (Fig. 4, A, a). Then it suddenly 

 became very active and swam away rapidly. Very often, how- 

 ever, with only a part of its body, for the part which came in 

 contact with the proboscis bulged out and seemed to increase in 

 volume, somewhat comparable to that which takes place when water 

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