THE WORLD OF LIVING ORGANISMS 163 



birds in such a way as to secure that these shall take over the 

 care of the young. 



This is not a case of an effect on our human mark-organs ; 

 these are not deceived in the least, for at the first glance we 

 can pick out the cuckoo's egg. But song-birds are completely 

 taken in, and proceed to care for the changeling. This gives 

 us a really reliable means of defining the sensed-world of 

 song-birds. 



We may readily admit that inter-adjustment between the 

 cuckoo and the song-bird is perfect in so far as it concerns 

 the cuckoo ; but we shall the more strenuously deny that it 

 spells perfection for the song-bird. 



Here again we come upon a question that we have already 

 touched ; and we must make up our minds about it before 

 we proceed with our discussion of inter-adjustments. 



PERFECTION 



We go on now to speak of a problern that is especially 

 important in the fimction-circle of the enemy, when attacker 

 and attacked come face to face. We may assert that, in all 

 such cases, perfection is not attained, at least by one of the 

 antagonists, for the one that is defeated shows, by the very 

 fact of its defeat, that it was imperfectly equipped for the 

 fight. Even when both appear quite remarkably well 

 equipped for battle, and are perfectly fitted into the enemy- 

 circle as regards their effectors, this inter-adjustment must 

 be imperfect for one of the two parties, if that is worsted. 



If even in such cases the inter-adjustment, though 

 apparently in conformity with plan, is really imperfect, 

 then the plan of Nature is not perfect ; and we have a right 

 to be incredulous concerning the perfection of the framework 

 of animals in general. This seems to justify the view that 

 Nature is full of imperfection. The plan of Nature de- 



