GENERAL SUMMARY AND CONCLUDING REMARKS 



the necessary food, affording protection from cold and from 

 enemies, and attending to the sanitation of the nest as 

 efficiently and rapidly as possible. If then the faces, instead 

 of being enclosed in this envelope, were ejected in smaller 

 pieces, as is occasionally done even now, what would be the 

 result ? Some part of the parents' duty must perforce be 

 neglected ; either the young must receive insufficient nourish- 

 ment, or the nest must become contaminated, or the nestlings 

 must suffer from exposure. The lessening as far as possible 

 of the risk which thus threatens the fragile offspring is, I 

 believe, the biological end for which this envelope has been 

 evolved. But no matter how perfect the system which has 

 been organically built up, the species will not benefit unless 

 the parents, either by the aid of their intelligence, or through 

 acquired experience, or by instinct, are able to take advantage 

 of the special facility for removal which is thus afforded them. 

 I believe that their ability to do so is due to racial preparation. 

 The experiments with small leaves placed in the nest, referred 

 to in the life of the Whitethroat, seem to point to an impulse 

 of considerable strength to remove anything of a foreign 

 nature. For if in place of instinct we fall back upon intelli- 

 gence, ought we to find leaves carefully picked up and carried 

 away and even efforts made, not without some success, to 

 swallow them ? Should we not rather anticipate some small 

 measure of discrimination ? The leaf experiments however do 

 not constitute conclusive evidence in favour of something 

 congenital as opposed to something acquired through ex- 

 perience ; let us therefore consider the position of a young bird 

 carrying out its parental functions for the first time. How is 

 it to gain its experience ? Only, I suppose, by trial and error. 

 But during the process of learning by trial and error what is to 

 happen to the offspring ? They must be the sufferers ; it is upon 

 them that the initial blunders of an inexperienced parent will 

 recoil, and it is upon them that the future of the race must 

 depend. 



How can we account for the parallel development of the 



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