VI ANNELIDA 75 



procedure, apparently necessitated here by the dry hard 

 nature of the fallen leaves vifhich form a large part of their 

 food, especially during the autumn months. 



At other times of the year, or in spots vrhere leaves are 

 scarce, worms seem to subsist almost entirely on the nourish- 

 ment they obtain from the soil which they swallow. Most 

 surface soil contains many minute spores, ova, seeds, larvae, 

 and small living or dead creatures, all of which come as " grist " 

 to the earthworm's " mill," for any necessary grinding of the 

 food takes place in the hard-walled muscular " gizzard," an 

 enlargement of the alimentary canal corresponding to a 

 stomach, lying within segments 16 to 20 of the body. When 

 a worm is feeding in this way, the " castings " on the surface 

 are very numerous, whilst, where leaf food is plentiful, the 

 castings are fewer and less conspicuous. 

 The Plug- Besides obtaining leaves for food during the 

 ging of the night, worms often actively exert themselves in 

 Burrows, pluggj^g up tjje mouth of their burrows with 

 leaf-stalks, leaves, or even small stones ; the rustling of the 

 dry leaves as they are drawn over the ground is sometimes 

 distinctly audible ; this is most noticeable in the autumn or 

 early winter, and the habit is probably chiefly a protection 

 against cold ; in the summer, too, it lessens the danger of 

 the burrows becoming too dry during the hot days, and also 

 excludes certain enemies of the worm, such as parasitic flies, 

 which might enter the burrow from above. 



A most interesting account of the way in which the leaves 

 are pulled into the burrows is given by Charles Darwin 

 in his book. Vegetable Mould and Earthworms. From his 

 numerous observations and experiments on this point, Darwin 

 concluded that worms show a certain degree of intelligence in 

 their mode of action, for a leaf is not drawn in by whichever 

 side happens to be nearest, but only after having been care- 

 fully felt over by the sensitive head end of the worm's body. 

 It is then nearly always seized by its narrowest part, which 

 is usually, but not invariably, the apex of the leaf, and so 

 the leaves are used in the most easy and effective way as a 

 plug for the burrow. Often leaves are used to line the mouth 

 of the burrow to a depth of several inches, possibly to protect 

 the body of the worm from becoming unduly chilled by con- 

 tinual contact with the cold damp earth. Darwin describes 



