20 E. J. LUND 



not the object of the above experiments: they are onl}- here 

 considered for the purpose of demonstrating the existence of 

 these conditions, the fact of change within them and especially 

 in this connection their role in the external phenomena of feeding 

 and food selection in Bursaria, and how they may affect the 

 results which will be given in the following pages. 



EXTERNAL RELATIONS OF THE FEEDING PROCESS 

 1. Effects of external factors on feeding 



a. Concentration of the food supply. The rate of feeding is 

 within comparatively wide limits not dependant upon the con- 

 centration of the yolk suspension, provided it is not too low. 

 This may be illustrated from one out of a series of experiments. 

 The time of feeding was reduced to five minutes for the purpose 

 of bringing out the effect of difference in the concentration more 

 strongly If the animals had been left in the suspensions twenty 

 minutes (the usual time of feeding;- cf. table 3) the difference 

 would have been less marked, especially with material which 

 shows a high rate of feeding. • 



I Experiment 1} Material from a healthy culture was starved twenty- 

 four hours in tap water. All were perfectly normal and active. The 

 experiment was carried out in 8 cc. stender dishes. The concentration 

 in dish 5 was 8 times that in dish A. Twenty individuals were placed 

 in each dish. The results from trial number 2 represent more nearly 

 the ideal because these two suspensions were kept uniformly distrib- 

 uted during the five minutes feeding, and the individuals were picked 

 out alternately by fives. Both trials, however, express equally well 

 the proportional effect of concentration, namely, 1 to 2, as compared 

 to the proportion of concentration, 1 to 8^ (table 4). 



The concentrations used in the experiment are approximately 

 represented by figure 3. 



* The experiments given in this paper are numbered in regular order for the 

 convenience of the reader, and do not represent the actual order. Only a small 

 number "of the experiments actually carried out are given. 



^ In all the experiments considered in this paper, where the concentration 

 plays a part, the concentration was intermediate between those used in this 

 experiment (fig. 3). 



