FEEDING REACTIONS IN DILEPTUS GIGAS. 133 



latent period shows characteristic signs of injury. The violent 

 contraction of the rotifers on every occasion when they come in 

 contact with that portion of Dileptus provided with trichocysts 

 gives definite signs of their effect. The observations on Colpidium 

 show that the trichocysts not only paralyze this organism, but pro- 

 duce a cytolytic effect upon the protoplasm of the prey. 



The following observations are presented in order to show more 

 specifically the precise manner in which these trichocysts function. 



a. Effect of Trichocysts on Paramecium bursana. 



In making observations . on the action of the trichocysts of 

 Dileptus on Paramecium bursaria, a single starved dileptus was 

 isolated and added to a small drop of water on a slide containing 

 four specimens of Paramecium bursana. Nearly all the water 

 was then drawn off, after which a cover-glass ringed with vaseline 

 was applied. Two of the paramecia were lost, but the remaining 

 two and the dileptus were confined in so small an amount of water 

 and were so much compressed that they could move only very 

 slowly, and never more than their own length from the others. 

 Consequently all reactions could be observed very accurately. The 

 dileptus, although so compressed that it was more than three times 

 its normal width, continued to rotate on its longitudinal axis and 

 its proboscis was consequently thrown from one side to the other. 

 On several occasions the posterior end of the dileptus came in 

 contact with one of the paramecia, making small indentations in it 

 without any noticeable reaction on the part of the latter. When, 

 however, it slowly reversed its position and the oral surface of the 

 proboscis came in contact with the paramecium, a sudden discharge 

 of trichocysts from the paramecium was observed, so dense as to 

 force the dileptus away. The latter continued to rotate slowly, all 

 the time removing the barrier of trichocysts by means of its ciliary 

 action. The next time only the aboral surface of the proboscis 

 came in contact with the paramecium and no reaction resulted. 

 The third time the proboscis struck the paramecium it was at a 

 slightly different spot and another discharge of trichocysts resulted 

 from the latter. After some little time this again was cleared 

 away, and a fourth attack occurred at about the same spot as the 

 first, this time with an entirely different result. The paramecium 



