18 E. J. LUND 



These results from individuals are therefore strictly comparable 

 and in accord with those obtained when a large number are 

 tested at one time (table 1). 



Now, in order to explain the cause of the change in reaction 

 the suggestion might be offered that Bursaria shows a decrease 

 in the rate of feeding because of the decrease in the amount of 

 space in the body which food can occupy. This is undoubtedly 

 true to some extent in those individuals which do not stop feed- 

 ing until the cell becomes distorted by the comparatively immense 

 mass of food. So far as the volume capacity of a normal indi- 

 vidual of Bursaria is concerned, hundreds of observations have 

 shown me beyond doubt that this may frequently be as much 

 as twenty-five to thirty grains. Nevertheless, reversal of the cilia 

 always takes place sooner or later. But the suggestion evidently 

 does not apply to those individuals which show a change in the 

 reaction when only a few grains have been eaten, for it seems 

 impossible to understand how there could be a difference of as 

 much as twenty grains of fresh yolk (table 2) in two normal 

 individuals of equal size, when the cells are under exactly the 

 same conditions, if this result were not due to a difference in the 

 physiological state of the cells. Change in feeding was caused 

 by the periodic reversal of the cilia and the reversal of the cilia 

 in turn in some manner initiated or caused by a stimulus from 

 the food already eaten, for it seems most natural to suppose 

 that the stimulus originated from the change produced by the 

 food mass in the interior of the cytoplasm. The most definite 

 evidence that the change is due to stimulus from the eaten food 

 is found in the radical change in the action of the cilia of the 

 feeding mechanism. 



If such fed individuals as those in table 3 are left in tap water 

 free from food they may again eat yolk after digestion is par- 

 tially or wholly completed, and again show a similar decrease 

 in the rate of feeding, that is, a reversal of the oral cilia. The 

 total quantity which will be eaten may be greater than that 

 eaten at the previous feeding; but it usually is less, or often none 

 at all. 



