GENERAL SUMMARY AND CONCLUDING REMARKS 



occasionally three, but the first one as a rule receives the 

 larger share of food and ejects the faces, which are thereupon 

 swallowed by the parent or carried away and dropped some 

 distance from the nest. Does the parent bird remember which 

 of its young it fed at the last visit, or is the process in this 

 respect a haphazard one ? My interpretation is simple enough 

 though not altogether free from the possibility of criticism ; it 

 relieves the parent of all responsibility but at the same time 

 leaves nothing to chance. I regard the sensation of hunger 

 as the guiding factor. According to the strength of this 

 sensation the young bird is active in stretching up its neck 

 and in struggling towards its parent, and on the average the 

 more active individual is the one that secures the food. There 

 is therefore no need for the parent to remember to which of 

 its offspring it attended on the last occasion ; its business is 

 to place the food in the nearest open throat ; the rest is done 

 for it. But, it may be said, is not hesitation shown by the 

 parents as they stand upon the side of the nest and contemplate 

 their offspring before finally parting with the larva they are 

 carrying ? Certainly, I reply ; but is not their behaviour 

 related to that of their offspring ? Do they not hesitate only 

 because the young hesitate also as the time draws nigh for 

 sleep and response is therefore weak ? I think we can explain 

 it thus : we must regard the parents and offspring not as 

 separate units, but as a biologically determined whole within 

 which the sequence of activities forms a complete circle. The 

 young bird that is hungry is the more active in stretching up 

 its neck and thus has a greater chance of securing food. 

 Having received it, it proceeds to eject the fceces, which are 

 carried away by the parent. Hunger being temporarily ap- 

 peased, it lies in the bottom of the nest taking but little heed 

 of the parent returning with a fresh supply, and though it 

 may open its mouth, yet the persistent striving towards some 

 end is manifestly absent; digestion however proceeds apace, 

 the hunger sensation once more asserts itself, response becomes 

 increasingly active, and in time it receives a further supply. 



17 2 



