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. 
