IO2 S. O. MAST. 



escapes, leaving a portion of the ectosarc with the enemy, which 

 the latter proceeds to swallow. 



I am not certain as to how soon Didinium is able to make a 

 second attack, but from all appearances it can do so in the course 

 of a few minutes. On May I, a specimen of Frontonia leucas ( ?) 

 was put into a drop of water on a slide containing numerous 

 Didinia which had not been fed during the preceding two days. 

 This specimen was attacked 58 times before it finally died, 40.5 

 minutes after it was put in. A piece was taken out of the 

 creature at every attack. The wounds thus made immediately 

 closed and the animal swam about as though nothing had hap- 

 pened, but it of course became smaller and smaller, until when 

 it finally burst and died there remained but a minute mass of 

 protoplasm nearly spherical in form, with a diameter nor more 

 than one tenth as great as the original length of the specimen. 

 Four other individuals studied the same day were killed in a 

 much shorter time. They lived after the first attack respectively 

 6, 7, 10 and 12 minutes. But later, June 9, a specimen lived 

 for nearly two hours after the first attack, and was seized literally 

 hundreds of times by small Didinia during this period. 



I am well aware that the results of all these observations do not 

 prove conclusively that Didininin does not poison its prey, for it 

 may be said that the very fact that a piece remains attached to 

 the seizing organ every time that an animal which has been 

 attacked escapes, saves the animal from being poisoned by pre- 

 venting any toxic substances from entering the remaining portion 

 of the body. This,' however, does not apply to the case where 

 the victim remains alive for some time with Didinium fastened 

 to it. As stated above, one specimen lived more than four min- 

 utes under such conditions. 



Let us now briefly consider the evidence in favor of the view 

 that noxious fluid is used by Didinium in capturing its food. 

 This view has its foundation in the apparent sudden paralysis 

 and death of the organism captured, described by Balbiani, 

 Maupas and others. Thon, however, presents other evidence sup- 

 porting this view. He writes as follows (1905, p. 296) : " Dass 

 das Plasma des Stranges auf den Korper der Beute atzend ein- 

 wirkt. sehen wir wie an lebenden Tieren so auch besonders an 



