The Formation of Vegetable Mould Through the Action of Worms | Page 7

of lime. These
calciferous glands are highly remarkable, for nothing like them is
known in any other animal. Their use will be discussed when we treat
of the digestive process. In most of the species, the oesophagus is
enlarged into a crop in front of the gizzard. This latter organ is lined
with a smooth thick chitinous membrane, and is surrounded by weak
longitudinal, but powerful transverse muscles. Perrier saw these
muscles in energetic action; and, as he remarks, the trituration of the
food must be chiefly effected by this organ, for worms possess no jaws
or teeth of any kind. Grains of sand and small stones, from the 1/20 to a
little more than the 1/10 inch in diameter, may generally be found in
their gizzards and intestines. As it is certain that worms swallow many

little stones, independently of those swallowed while excavating their
burrows, it is probable that they serve, like mill-stones, to triturate their
food. The gizzard opens into the intestine, which runs in a straight
course to the vent at the posterior end of the body. The intestine
presents a remarkable structure, the typhlosolis, or, as the old
anatomists called it, an intestine within an intestine; and Claparede {13}
has shown that this consists of a deep longitudinal involution of the
walls of the intestine, by which means an extensive absorbent surface is
gained.
The circulatory system is well developed. Worms breathe by their skin,
as they do not possess any special respiratory organs. The two sexes are
united in the same individual, but two individuals pair together. The
nervous system is fairly well developed; and the two almost confluent
cerebral ganglia are situated very near to the anterior end of the body.
Senses.--Worms are destitute of eyes, and at first I thought that they
were quite insensible to light; for those kept in confinement were
repeatedly observed by the aid of a candle, and others out of doors by
the aid of a lantern, yet they were rarely alarmed, although extremely
timid animals. Other persons have found no difficulty in observing
worms at night by the same means. {14}
Hoffmeister, however, states {15} that worms, with the exception of a
few individuals, are extremely sensitive to light; but he admits that in
most cases a certain time is requisite for its action. These statements led
me to watch on many successive nights worms kept in pots, which
were protected from currents of air by means of glass plates. The pots
were approached very gently, in order that no vibration of the floor
should be caused. When under these circumstances worms were
illuminated by a bull's-eye lantern having slides of dark red and blue
glass, which intercepted so much light that they could be seen only
with some difficulty, they were not at all affected by this amount of
light, however long they were exposed to it. The light, as far as I could
judge, was brighter than that from the full moon. Its colour apparently
made no difference in the result. When they were illuminated by a
candle, or even by a bright paraffin lamp, they were not usually

affected at first. Nor were they when the light was alternately admitted
and shut off. Sometimes, however, they behaved very differently, for as
soon as the light fell on them, they withdrew into their burrows with
almost instantaneous rapidity. This occurred perhaps once out of a
dozen times. When they did not withdraw instantly, they often raised
the anterior tapering ends of their bodies from the ground, as if their
attention was aroused or as if surprise was felt; or they moved their
bodies from side to side as if feeling for some object. They appeared
distressed by the light; but I doubt whether this was really the case, for
on two occasions after withdrawing slowly, they remained for a long
time with their anterior extremities protruding a little from the mouths
of their burrows, in which position they were ready for instant and
complete withdrawal.
When the light from a candle was concentrated by means of a large lens
on the anterior extremity, they generally withdrew instantly; but this
concentrated light failed to act perhaps once out of half a dozen trials.
The light was on one occasion concentrated on a worm lying beneath
water in a saucer, and it instantly withdrew into its burrow. In all cases
the duration of the light, unless extremely feeble, made a great
difference in the result; for worms left exposed before a paraffin lamp
or a candle invariably retreated into their burrows within from five to
fifteen minutes; and if in the evening the pots were illuminated before
the worms had come out of their burrows, they failed to appear.
From the foregoing facts it is evident that light