92 HABITS OF WORMS. Chap. IT. 



are led by instinct to plug up their burrows ; 

 and it might have been expected that they 

 would have been led by instinct how best 

 to act in each particular case, independently 

 of intelligence. We see how difficult it is to 

 judge whether intelligence comes into play, 

 for even plants might sometimes be thought 

 to be thus directed; for instance when dis- 

 placed leaves re-direct their upper surfaces 

 towards the light by extremely complicated 

 movements and by the shortest course. With 

 animals, actions appearing due to intelligence 

 may be performed through inherited habit 

 without any intelligence, although aborigin- 

 ally thus acquired. Or the habit may have 

 been acquired through the preservation and 

 inheritance of beneficial variations of some 

 other habit ; and in this case the new habit 

 will have been acquired independently of 

 intelligence throughout the whole course 

 of its development. There is no a priori 

 improbability in worms having acquired 

 special instincts through either of these two 

 latter means. Nevertheless it is incredible 

 that instincts should have been developed 

 in reference to objects, such as the leaves or 



