74 INTRODUCTION TO ZOOLOGY CHAP. 



running longitudinally, which by their contraction cause the 

 body to shorten and thicken. 



Earthworms live in burrows that run down 

 Burrow a ^ m ost perpendicularly into the earth. These, 

 in very dry or cold weather, may penetrate to a 

 depth of 6 or 7 feet, but usually end at about 18 to 20 

 inches below the surface. The burrow is made, if in soft 

 soil, mainly by the mere pushing of the body through the 

 earth, the thin tapering head end being inserted into some 

 tiny crevice, and then the crevice enlarged by the swelling of 

 the body ; the habit of earthworms of swallowing soil aids 

 also in the making of the burrow, especially in very compact 

 soil. If the earth contains any organic matter this is absorbed 

 as food, and the remaining soil is usually ejected at the surface 

 of the ground from the end of the body, forming the well- 

 known " worm-castings." Sometimes some of the soil, as it 

 is ejected, is pressed by the flattened tail against the sides of 

 the burrow, and, adhering there in a thin layer, it makes a 

 smooth, firm lining to the burrow, which is kept lubricated by 

 a slimy substance secreted by the skin, and by the liquid that 

 at times exudes from small pores along the back. This 

 liquid is said to be antiseptic and to protect the worm 

 from any harmful bacteria in the soil. 



The worms live in these burrows, rarely leaving them, 

 except after very heavy rain, when they are said to desert 

 them entirely, and to make fresh burrows. During the day- 

 time they remain hidden, but at night they are very active, 

 coming almost entirely out of their retreats, the tail just 

 being kept in the mouth of the burrow so that at the 

 slightest alarm a dart can quickly be made back into 

 shelter. It is at this time that they obtain their supply of 

 leaf food. They move the exposed ends of their 

 bodies over the ground all around until they touch 

 some desirable object, such as a fallen leaf or flower. This 

 they seize between upper and lower lip, and by a sucking 

 action of the mouth the leaf is held and then drawn down 

 into the burrow to a depth of two or three inches. There it 

 is moistened with an alkaline fluid secreted by the skin, 

 which discolours and softens it, acting on the starchy and 

 proteid contents of the leaf, so that they are actually partially 

 digested before being taken into the soft mouth, an unusual 



