314 



NATUEAl HISTOET. 



little bristly points which all look backward. There are 

 four pairs of them on each segment. It is on account of 

 these that, while you can pass the finger readily on the 

 worm backward, you can feel resistance on attempting 

 to pass it forward. There are two sets of muscles en- 

 gaged in the movement of the worm — the one longi- 

 tudinal, which, on contracting, short- 

 en the worm ; and the other circu- 

 lar, which make the body smaller 

 and longer when they contract. In 

 Fig. 248 is a representation of an 

 Earthworm at a, and at 6 a few seg- 

 ments magn^d, so as to shoAv the 

 bristles pofirting backward. The 

 egg of thfe Worm is curiously con- 

 structed, havfcg a valve at one end, 

 as seen at c.fnAt d the young worm 

 has opened the valve, and is coming 

 out. These worms are of great serv- 

 ice to the- farmer and gardener in 

 loosening the earth below the reach 

 of the spade and the plow. " It has 

 been lately shown," says Carpenter, 

 " that they will even add to the depth 

 of soil, covering barien tracts with 

 a layer of productive mould. Thus, 

 in fields which have been overspread 

 with lime, burned marl, or cinders, 

 these substances are in time covered 

 with finely-divided soil, well adapted to the support of 

 vegetation. That this result — which is commonly at- 

 tributed to the ' working down' of the materials in 

 question — is really due to the action of the Earthworms, 

 appenrs from tlie fact that in the soil tlius formed large 

 numbers of ' worm-casts' may be distinguished. These 

 are produced by the digestive process of the worms, 

 which take into their intestinal canal a large quantity of 



Fig. 248 Lumbricus Ter- 



restris, or Earthivonu. 



