314 NATURAL HISTORY. 
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 b a few seg- 
ments magnified, sd as to show the 
bristles pointing backward. The 
egg of the Worm is curiously con- 
structed, having a vaive at one end, 
i as seen atc. At d the young worm 
has opened the valve, and is coming 
out. These worms are of great sery- 
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 barren tracts with 
a layer of productive mould. Thus, 
in fields which have been overspread 
Fig. 248.—_Lumbricus Ter. With lime, burned marl, or cinders, 
testris, or Earthworm. — 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, 
appears from the fact that in the soil thus 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 
