62 Life and Immortality. 



plugging-up process may undoubtedly serve for all these 

 purposes. Whatever the motive may be, it seems that worms 

 much dislike leaving the mouths of their burrows open, yet, 

 nevertheless, they will reopen them at night, whether or not 

 they are able afterwards to close them. 



Considerable intelligence is shown by worms in their man- 

 ner of plugging up their burrows. If man had to plug up 

 a cylindrical hole with such objects as leaves, petioles or 

 twigs, he would push them in by their pointed ends, but if 

 these were thin relatively to the size of the hole, he would 

 probably insert some by their broader ends. Intelligence 

 would certainly be his guide in such a case. But how 

 worms would drag leaves into their burrows, whether by 

 their tips, bases, or middle parts, has been a matter of interest 

 to many. Darwin, who experimented upon the subject, 

 found it especially desirable to experiment with plants not 

 natives to his country, for he conceived that although the 

 habit of dragging leaves into their burrows is undoubtedly 

 instinctive with worms, yet instinct could not teach them 

 how to act in the case of leaves about which their progeni- 

 tors knew nothing. Did they act solely through instinct, or 

 an unvarying inherited impulse, they would draw all kinds 

 of leaves into their burrows in the same manner. Having 

 no such definite instinct, chance might be expected to deter- 

 mine whether the tip, base, or middle might be seized. If 

 the worm in each case first tries many different methods, 

 and follows that alone which proves possible or the most 

 easy, then both instinct and chance are ruled out of the 

 solution of the question. But to act in this manner, and to 

 try different methods, makes what in man would be called 

 intelligent action. 



Three species of pine-leaves are mentioned by Darwin as 

 being regularly drawn into the mouths of worm-burrows on 

 the gravel-walk in his garden. These leaves consist of two 

 needles, which are united to a common base, and it is by this 

 point that they are almost invariably drawn into the burrows. 



