REACTIONS OF DIDINIUM NASUTUM. I I/ 



can escape the attack of Didiniiiin. I am inclined to believe that 

 the chemical composition as well as the physical constitution ha. 

 to do with this process, that it is not merely the toughness of the 

 integument but also the chemical composition of this covering 

 that prevents the seizing organ from sticking. One thing is 

 certain: it does not stick to the surface of any of the forms 

 mentioned under group I (p. 113), and surely the outer covering 

 of some of these, e. g., O.rytrica, Englcna, etc., is no tougher than 

 that of Paramecium or Vorticella. 



Is the conclusion of Jennings that Didinia try all objects and 

 feed on any they can master, valid? I think there can be no 

 doubt but that it is. This conclusion, however, has nothing to 

 do with the question of conscious choice. Neither does the fact 

 that the apparent choice has been explained mechanically show 

 that Didinium is devoid of consciousness. For all that is known 

 to the contrary, Didinium may be aware of the difference between 

 different organisms. It may have certain sensations when it 

 comes in contact with one surface and others when it comes in 

 contact with another. I am not assuming that this organism is 

 conscious, nor am I assuming that it is not. The question as to 

 consciousness in this creature is open and should be left open 

 until we have much more evidence bearing on it than we now 

 have. 



SUMMARY. 



1. When Didinium comes in contact with an object, it usually 

 responds with the avoiding reaction. In this response it always 

 turns tow r ard the same side, in spite of the fact that it is prac- 

 tically radially symmetrical. 



2. It feeds entirely upon living organisms, principally Para- 

 mecium, but it has been known to devour also Colpoda, Col- 

 pidium, Frontonia and Vorticella. It captures these organisms 

 by accidentally coming in contact with them in swimming about 

 at random. The prey is held by means of the seizing organ, 

 which in some way adheres to the surface when the contact is 

 made. 



3. There are no trichocysts discharged by the Didinia, they 

 come from the victims ; neither is the seizing organ thrust out at 



