56 



Chapter V. 

 THE EAETHWOEM. Lumbricus terrestris. 



The earthworm lives in burrows in moist earth, through 

 which it makes its way by alternate elongation and contrac- 

 tion of its body, aided by small stiff setae projecting from its 

 surface. 



It is a pinkish worm about six inches long, cylindrical in 

 front, flattened posteriorly. Its food consists of organic 

 matter derived chiefly from the soil, which it swallows in 

 enormous quantities. The worm is hermaphrodite, and lays 

 its eggs in a chitinous cocoon, which also contains packets of 

 spermatozoa and an albuminous fluid. 



The body is marked by transverse grooves dividing it into 

 annuli, of which there are about one hundred and fifty. This 

 external annulation corresponds with an internal segmentation, 

 the body-cavity being divided into chambers by transverse 

 septa, which are placed opposite the external grooves. Nearly 

 all the organs exhibit a corresponding segmental arrangement, 

 there being one pair of nephridia and one pair of nerve-ganglia 

 in each segment or somite throughout the greater part of the 

 animal's length, and the blood-vessels, muscles, and setffi being 

 also disposed segmentally. 



Several species of Lumbricus occur in this country. These 

 differ from one another in the position and arrangement of 

 certain of the reproductive organs, and in other minor points. 

 The following description, taken from the largest of the 

 commoner species, will however apply with but slight altera- 

 tions to any of the others. 



The worm is most conveniently killed by dropping it into 

 spirit for a few minutes before dissection. 



