112 S. O. MAST. 



being deeply impressed with the complexity of its structure, as 

 well as with its unique habits. The differentiation of the seizing 

 organ with its highly specialized function is remarkable in an 

 organism consisting of a single cell. It shows what we are 

 coming to realize more and more fully as the Protozoa are 

 subjected to more detailed study; namely, that many cells are 

 exceedingly complicated. 



AMOUNT AND KIND OF FOOD. 



The number of Parainecia devoured by a Didinimn in a day 

 depends, of course, upon the size of the Parainecia. In all the 

 experiments on this subject the Parainecia were between one 

 and two times as large as the Didinia. Usually Didinia which 

 had been without food for at least a day were selected and put 

 with Parainecia. Then after they had swallowed one, they were 

 isolated and later returned from time to time. In this way it 

 was found that they take a Paraineciwn about every three hours 

 and divide two or three times in twenty-four hours. None of 

 the experiments on feeding were, however, continued for more 

 than twelve hours. It is therefore impossible to say that the 

 Didinia would feed at the rate mentioned for longer periods. 



Didinia which have swallowed a Paraniecinin are, as already 

 stated, frequently very irregular in form, owing to unsymmetrical 

 extension of the body-wall (Fig. 17). As digestion proceeds, 

 such specimens gradually become symmetrical again. I have fre- 

 quently seen these ciliates capture prey when they were so 

 gorged that they were still very much distorted. This shows 

 that the seizing organ returns to the anterior end of the body 

 long before the creature engulfed is fully digested. 



The amount of food that Didinia eat depends upon the tem- 

 perature and various other conditions. Under most favorable 

 conditions they consume relatively enormous quantities. If 

 they should take a Paramecium, averaging one and one half 

 times their own size, every three hours, as the experiments 

 described above indicate, in twenty-four hours they would con- 

 sume a mass of substance having a volume twelve times as great 

 as their own. I know of no other creatures that even approach 

 these in their feeding capacity. 



