The Formation of Vegetable Mould Through the Action of Worms | Page 6

of the ground without
being torn into pieces. {11} During the day they remain in their
burrows, except at the pairing season, when those which inhabit
adjoining burrows expose the greater part of their bodies for an hour or
two in the early morning. Sick individuals, which are generally affected
by the parasitic larvae of a fly, must also be excepted, as they wander
about during the day and die on the surface. After heavy rain

succeeding dry weather, an astonishing number of dead worms may
sometimes be seen lying on the ground. Mr. Galton informs me that on
one such occasion (March, 1881), the dead worms averaged one for
every two and a half paces in length on a walk in Hyde Park, four paces
in width. He counted no less than 45 dead worms in one place in a
length of sixteen paces. From the facts above given, it is not probable
that these worms could have been drowned, and if they had been
drowned they would have perished in their burrows. I believe that they
were already sick, and that their deaths were merely hastened by the
ground being flooded.
It has often been said that under ordinary circumstances healthy worms
never, or very rarely, completely leave their burrows at night; but this is
an error, as White of Selborne long ago knew. In the morning, after
there has been heavy rain, the film of mud or of very fine sand over
gravel-walks is often plainly marked with their tracks. I have noticed
this from August to May, both months included, and it probably occurs
during the two remaining months of the year when they are wet. On
these occasions, very few dead worms could anywhere be seen. On
January 31, 1881, after a long- continued and unusually severe frost
with much snow, as soon as a thaw set in, the walks were marked with
innumerable tracks. On one occasion, five tracks were counted crossing
a space of only an inch square. They could sometimes be traced either
to or from the mouths of the burrows in the gravel-walks, for distances
between 2 or 3 up to 15 yards. I have never seen two tracks leading to
the same burrow; nor is it likely, from what we shall presently see of
their sense-organs, that a worm could find its way back to its burrow
after having once left it. They apparently leave their burrows on a
voyage of discovery, and thus they find new sites to inhabit.
Morren states {12} that worms often lie for hours almost motionless
close beneath the mouths of their burrows. I have occasionally noticed
the same fact with worms kept in pots in the house; so that by looking
down into their burrows, their heads could just be seen. If the ejected
earth or rubbish over the burrows be suddenly removed, the end of the
worm's body may very often be seen rapidly retreating. This habit of
lying near the surface leads to their destruction to an immense extent.

Every morning during certain seasons of the year, the thrushes and
blackbirds on all the lawns throughout the country draw out of their
holes an astonishing number of worms, and this they could not do,
unless they lay close to the surface. It is not probable that worms
behave in this manner for the sake of breathing fresh air, for we have
seen that they can live for a long time under water. I believe that they
lie near the surface for the sake of warmth, especially in the morning;
and we shall hereafter find that they often coat the mouths of their
burrows with leaves, apparently to prevent their bodies from coming
into close contact with the cold damp earth. It is said that they
completely close their burrows during the winter.
Structure.--A few remarks must be made on this subject. The body of a
large worm consists of from 100 to 200 almost cylindrical rings or
segments, each furnished with minute bristles. The muscular system is
well developed. Worms can crawl backwards as well as forwards, and
by the aid of their affixed tails can retreat with extraordinary rapidity
into their burrows. The mouth is situated at the anterior end of the body,
and is provided with a little projection (lobe or lip, as it has been
variously called) which is used for prehension. Internally, behind the
mouth, there is a strong pharynx, shown in the accompanying diagram
(Fig. 1) which is pushed forwards when the animal eats, and this part
corresponds, according to Perrier, with the protrudable trunk or
proboscis of other annelids. The pharynx leads into the oesophagus, on
each side of which in the lower part there are three pairs of large glands,
which secrete a surprising amount of carbonate