J- PAUL VISSCHER. 



continually shrinks in size, and unless it escapes before it is 'too 

 badly injured it dies. 



The trichocysts of Dileptus evidently affect the ectoplasm of 

 S tent or and, as in the case of Colpidium previously described, 

 result in a cytolytic action on the surface of the prey at the point 

 of contact. This results in an outflowing of the inner protoplasm 

 until the injured surface can again gelate in some manner, resulting 

 in a new " pellicle." 



If the observations just described are made under high magnifi- 

 cation, it can be seen that the proboscis of dileptus never comes in 

 actual contact with the body of the stentor. They are always 

 separated by a space, at least equal to the sum of the lengths of 

 their respective cilia. This would lead to the conclusion that the 

 trichocysts of Dileptus are discharged through some little dis- 

 tance that is, they are thrown out with some force. 



c. Effect of Trichocysts on Paramecium aurelia. 



Dileptus is normally unable to injure Paramecium aurelia in any 

 way, but in one experiment several paramecia were seriously in- 

 jured by two dilepti. In two instances, which were carefully ob- 

 served, the paramecia appeared to be completely paralyzed, al- 

 though only momentarily, immediately upon coming in contact with 

 the oral surface of the proboscis. When the proboscis touched 

 the paramecia they reacted vigorously and swam away, but not 

 before they were injured. It was observed that they became much 

 deformed soon after the attack, doubling on the point that had been 

 injured to such an extent that they assumed the form of a horse 

 shoe. One of these paramecia was attacked a second time while 

 in this semi-quiescent condition and was successfully engulfed. 

 The other one was isolated on a hollow ground slide and after about 

 an hour began to swim about, gradually losing its deformity. On 

 the following day it appeared to be normal. The ectoplasmic pelli- 

 cle of Paramecium aurelia is probably of such a nature that it 

 prevents any cytolytic action resulting from the trichocysts. The 

 injurious effect of these structures seems to be due to the produc- 

 tion of a definite wound at the point of contact. 



