RELATION OF BURSARIA TO FOOD 19 



The process of feeding in Bursaria shows it to be a function- 

 ally equilibrating system in its behavior towards food and the 

 condition of its equilibrium at any particular time constitutes 

 the physiological state which the cell is in, so far as its relation 

 to food is concerned. The changes in the increase or decrease 

 in the quantity of food eaten in successive meals and the increase 

 or decrease in the rate of feeding might be discussed in the 

 psychological terms 'hunger and 'satiation;' but it is evident 

 that the simpler terms quantity and rate express the facts of 

 experiment, while any attempt at definitely determining whether 

 the changes in quantity and rate are the same or different from 

 'hunger' and 'satiation' will obviously lead nowhere. Hence it 

 seems better to use the terms, rate and quantity, which have a 

 clear and quantitative meaning. 



3. Other causes of individual variation 



Bursaria at times closes up its oral apparatus. This may take 

 place to such an extent that the opening is smaller than the 

 food particles and then the latter can of course not be eaten. 

 This condition can readily be observed under the binocular and 

 it can always be determined beforehand whether closure has 

 taken place to such an extent that the organisms can not feed. 

 Other minor accidental individual variations are also present to 

 some extent. These may be partly due to the difference in the 

 size of the grains of yolk eaten. Sometimes when an individual 

 is weak, owing to prolonged starving or for some other reason, 

 two or three grains may become stuck in the oral pouch and this 

 prevents feeding until the animal succeeds in throwing them 

 out or by other means they become loosened. The material 

 used was always examined beforehand to make sure that it was 

 in a healthy condition so that these accidental conditions play 

 no part in the final results of the experiments described. 



Such a series of experiments as the forego ng do not show us 

 specifically what these complex conditions are which have been 

 cloaked in the phrase 'physiological states.' This however is 



