r 1 6 s. o. MAST. 



1. There is no doubt about the fact that these creatures are 

 frequently seen rapidly rotating on the long axis with the anterior 

 end against objects of all sorts, but I feel very certain that this 

 reaction has nothing to do with the process of capturing food, 

 for I have repeatedly seen specimens which had just swallowed 

 a Parameciwn performing this very act. As a matter of fact, 

 after having swallowed its prey Didinium ordinarily swims down 

 and when it comes in contact with the bottom it remains there 

 rotating on its axis, so that shortly after feeding one can fre- 

 quently see many of them with the anterior end against the 

 bottom, spinning much like miniature tops. Specimens which 

 had just been fed were also repeatedly seen swimming 

 about in contact with each other, sometimes as many as five 

 or six in series, like a string of beads, each one apparently 

 trying to seize the one in front of it. 



One never, or rarely at least, sees this reaction in specimens 

 which have been without food. Such specimens immediately 

 respond with the motor reaction when they come in contact with 

 an object. They appear to be darting about in every direction 

 in wildest confusion, never coming to rest until they are actually 

 attached to their prey. This attachment, as previously stated 

 (p. 104), takes place at the very instant the Didinium strikes the 

 surface to which it becomes fastened and never after having 

 been in contact for some time apparently boring into the surface. 

 The boring reaction may then be considered to be due to inac- 

 tivity. Didinium responds in this way when the threshold of 

 stimulation is increased to such an extent that contact no longer 

 induces the avoiding reaction. 



2. The size and the activity of the organisms are important 

 factors in the general process of feeding, but they have nothing 

 to do with the question as to the cause of the attachment of the 

 seizing organ, for it readily adheres to Frontonia which are 

 much larger than Paramecia and it does not adhere to Euglencc 

 and specimens of Spirostonmm, which are much smaller. 



3. The character of the outer surface seems to be the con- 

 trolling factor in determining the possibility of the attachment of 

 the seizing organ and this, together with the trichocysts and the 

 size and activity of the organism, determines whether or not it 



