THE EARTHWORM AND HIS WORK. 153 
home, crawling - over very difficult roads and even 
scaling perpendicular walls. The controlling mechan¬ 
ism for these movements lies in a small brain situated 
above the oesophagus and hence sometimes called the 
supracesophageal ganglion, and in a series of ganglia 
lying under the alimentary canal, a pair in each seg¬ 
ment. These ganglia are connected with each other 
and with the brain by nerves, and branches ramify from 
them to all parts of the body. This arrangement of 
nerve-masses along the ventral portion of the body is 
decidedly advantageous to a crawling animal, giving 
him constant information concerning the ground over 
which he travels. 
Locomotion in the earthworm is accomplished by 
the use of three sets of muscles under the control of his 
nervous system. One set of muscular fibres runs 
lengthwise of the body, another surrounds each ring, 
and a third layer sends its fibres diagonally across the 
segments. When an earthworm wishes to go forward 
he fixes his setae in the ground in such a way that his 
body cannot move backward, but will easily move for¬ 
ward. If, now, his body is already extended its full 
length, he contracts his longitudinal muscles, thus 
shortening his body and making it much thicker. He 
then contracts the circular muscles surrounding the 
segments, elongating the body and making it much 
smaller in circumference. Since the setae prevent the 
body from going backward, it must move forward. The 
setae are curved near the end to make them more useful 
in holding the body in place. The diagonal muscles 
are used in moving the body from side to side. 
The Usefulness of the Earthworm. In spite of his 
apparent insignificance the earthworm is the farmer’s 
loyal friend. He is a ploughman of ancient lineage 
and his work is most efficient. He brings to the sur¬ 
face fresh subsoil to replace the exhausted layer which 
the farmer has been cultivating. He grinds up organic 
matter and leaves it finely powdered in his castings for 
