CHAPTER XVII 



THE CH^TOPODA— THE COMMON EARTHWORM— 

 LUMBRICOS HERCULEUS 



Earthworms, belonging to many different species, are very 

 common in all parts of the world. The commonest English 

 species, Lumbricus herculeus, lives in burrows in the surface 

 soil. The mouths of the burrows are marked by the well- 

 known worm-castings, and their upper parts are lined by 

 leaves which the worms have dragged down into their holes. 

 Earthworms, as Darwin has shown, are important agents in 

 the formation of vegetable mould, and a full account of their 

 habits will be found in his admirable memoir on the subject.* 

 But before studying the habits of earthworms it will be 

 desirable to gain a knowledge of the structure of these 

 animals. 



A full-grown specimen of Lumbricus herculeus is about seven 

 inches long, and nearly circular in section except in the 

 posterior region, where the body is flattened dorso-ventrally. 

 The worm always progresses with one of its surfaces applied 

 to the ground ; this is therefore the ventral surface, the oppo- 

 site side being the dorsal surface. Furthermore, it always 

 travels with one end, the anterior end, foremost, so we can 

 recognise anterior and posterior ends, dorsal and ventral 

 surfaces, right and left sides. At the anterior end of the 

 body there is no distinct head, but a small conical projection 

 called the prostomium. Below and behind the prostomium, 

 on the ventral surface, is a crescentic opening, the mouth, 

 destitute of jaws and other appendages, and at the posterior 

 extremity of the body is a circular terminal opening, the vent 

 or anus. The whole body is divided by a series of transverse 

 furrows into a number of rings, called segments or somites, 

 and we shall see that this external segmentation of the body 

 corresponds to a definite internal segmentation. As certain 



* "The Formation of Vegetable Mould through the Action of Enrth- 

 worms," by Charles Darwin. London. J. Murray, 1881. 



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