i:^S EARTHWORMS. PHYLUM ANNELIDA 



and constantly supplied with a fine ' top dressing ', which may 

 be as much as 25 tons per acre per annum. Organic matter is 

 converted into a useful form and amalgamated with the earth, 

 and the latter is made easier of penetration by the roots of plants. 



ProstomLum.^ 

 penstomium 



A. 



Opening of 

 Oviduct. 



Opening of 

 vos deferens 



Spermatic 

 groove ■ 



Mouth 



Frost omium 

 Peristomium 



Clite/lum 



Lateral chaetae. 



Fig. 109. — A, The first three segments of an earthworm, Ltimbricus terrestris, 

 ventral ; B, the same, dorsal showing the epilobous condition ; C, the 

 first three segments of Allolobophora, dorsal (tanylobous) ; D, Lumbricus 

 terrestris, ventrolateral ; E (after Grove), worms' in coition. In B-E the 

 numbers refer to the segments. 



The only species which form worm casts in this country are 

 Allolobophora longa and A. nocturna ; the others void their faeces 

 below the surtace and so are of less importance in agriculture. 



EXTERNAL FEATURES 



One of the commoner English earthworms is Lumbricus terrestris 

 (Fig. 109). The body of this animal is roughly cylindrical, but 



