III. 



THE EARTHWORM {Liwtbricus terrestris). 



The Earthworm is to be found wherever damp earth is 

 accessible, no matter how hard or stony the surface; the 

 presence of moisture is indispensable to its existence. Into 

 this earth it burrows, excavating a tubular habitation to 

 which it repairs during the day time, emerging at night to 

 seek food and to work, or at early morning to reproduce its 

 species. It remains within the burrow throughout both the 

 winter and the dry summer seasons. 



The interior of the burrow is smooth and frequently lined 

 with minute stones ; its mouth is often surrounded with 

 "castings" and plugged with leaves drawn in by the animal 

 itself, or covered, as with a lid, by stones sometimes of 

 relatively great weight and size. 



The body of the worm is fairly uniform in dimensions 

 throughout; it is bilaterally symmetrical, both mouth and 

 anus being situated at opposite ends. The metameric 

 symmetry such as was seen in the abdomen of the Crayfish, 

 is here common to the whole body, which can no longer be 

 subdivided into well-marked regions. It is constricted 

 externally into a number of repetitional segments or somites^ 

 of which there may be, in a sexually mature animal, as few 

 as 68 or considerably more than 200. For each of these 

 somites there is a similar repetitional series of certain of the 

 internal organs. Each somite is subdivided externally into 



