CH. l] EARTHWORMS AND LEECHES 3 



of the burrow unobserved. Here however they are not 

 secure from all attack, for the quick ears of the thrush 

 and other birds enable them to detect the slightest 

 movement and, with a quick plunge of the beak, to seize 

 and, after a brief tug-of-war, to extract the worm from its 

 refuge. Frequently the well-known worm-castings are 

 thrown up on the surface, and when this is so, leaves are 

 not, as a rule, drawn into the burrows, the heap of 

 castings serving the purpose. 



The burrow is made partly by the awl-like tapering 

 anterior end pushing aside the earth on all sides, and 

 partly by the actual swallowing of the earth as the worm 

 advances, so that the animal literally eats its way into the 

 soil. The organic material in the swallowed soil serves as 

 food, and the residue in a state of very fine division passes 

 out at the anus, and is used either to form the above- 

 mentioned castings or as a lining to the burrow, especially 

 where this passes through hard, coarse earth. 



Perfectly healthy worms seldom leave their burrows 

 completely except perhaps -after very heavy rain. The 

 majority of those so frequently found travelling over 

 the surface of roads and paths after rain are infected 

 by the larvae of parasitic flies and doomed to die. On 

 warm, moist evenings, however, worms may be seen in 

 hundreds lying stretched on the surface of the ground 

 with only the broad flattened posterior end remaining 

 in the burrow. Here we see one of the uses of this 

 modification in the shape of the hinder segments of the 

 body : their greater width enables them to obtain a firm 

 purchase on both sides of the burrow, and thus the worm 



12 



