712 THE AMKHIC.W XATl^RALIST [Vol. XLI 



and there over the ground, each tuft so tightly and completely 

 filling a burrow that one might at first suppose that children at play 

 had deftly thrust leaves into all the earthworms' burrows. 



It was this strong instinct to plug up its burrows which Darwin 

 seized upon as a means of enquiry into the mental powers of the 

 earthworm. Scattering triangles of paper over the ground he 

 judged from the way in which these triangles were used by the 

 worm in plugging its burrows that it distinguished between angles 

 of different acuteness and probably exercised something akin to 

 reasoning. In his classic work on the earthworm Darwin does not 

 refer to the possible collection of seeds, though he discusses the 

 plugging instinct at considerable length. He says, — "Worms 

 seize leaves and other objects not only to serve as food, but for 

 plugging up the mouths of their burrows; and this is one of their 

 strongest instincts. Leaves and petioles of many kinds, some 

 flower peduncles, often decayed twigs of trees, bits of paper, 

 feathers, tufts of wool, and horse hairs are dragged into their 



burrows for this purpose They often, or generally, fill in the 



interstices between the drawn-in leaves with moist, viscid earth 

 ejected from their bodies; and thus the mouths of their burrows 



are securely plugged When worms cannot obtain leaves, 



petioles, sticks, etc., with which to plug up the mouths of their bur- 

 rows, they often protect them by little heaps of stones; and such 

 heaps of smooth, rounded pebbles may frequently be seen on 

 gravel walks " Darwin was inclined to think that one advan- 

 tage gained by the earthworms in plugging up their burrows lay in 

 the protection gained from cold night air, from animal enemies, 

 and less probably from rain. 



Whatever the utility of this instinct, it is carried out with so great 

 a variety of objects, that it was not surprising to find earthworms 

 plugging their burrows with the dry, flat fruits of the maple tree. 

 On May 30th the ground under several large silver iiiaj)le trees in 

 Druid Hill Park was thickly sprinkled with ihv yellow key-fruit, 

 or samaras, that had fallen from these trees, and it was quite 

 noticeable that in many places these fruits were gathered together 

 in little heaps. Each collection of seeds contained form twelve 

 to fifty, some lying loose, others more or less buried in the earth. 

 One of the larger heaps when lifted up filled a hand nearly full. 



