the formation of vegetable mould-第3章
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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 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 affects worms by
its intensity and by its duration。 It is only the anterior
extremity of the body； where the cerebral ganglia lie； which is
affected by light； as Hoffmeister asserts； and as I observed on
many occasions。 If this part is shaded； other parts of the body
may be fully illuminated； and no effect will be produced。 As these
animals have no eyes； we must suppose that the light passes through
their skins； and in some manner excites their cerebral ganglia。 It
appeared at first probable that the different manner in which they
were affected on different occasions might be explained； either by
the degree of extension of their skin and its consequent
transparency； or by some particular incident of the light； but I
could discover no such relation。 One thing was manifest； namely；
that when worms were employed in dragging leaves into their burrows
or in eating them； and even during the short intervals whilst they
rested from their work； they either did not perceive the light or
were regardless of it； and this occurred even when the light was
concentrated on them through a large lens。 So； again； whilst they
are paired； they will remain for an hour or two out of their
burrows； fully exposed to the morning light； but it appears from
what Hoffmeister says that a light will occasionally cause paired
individuals to separate。
When a worm is suddenly illuminated and dashes like a rabbit into
its burrowto use the expression employed by a friendwe are at
first led to look at the action as a reflex one。 The irritation of
the cerebral ganglia appears to cause certain muscles to contract
in an inevitable manner； independently of the will or consciousness
of the animal； as if it were an automaton。 But the different
effect which a light produced on different occasions； and
especially the fact that a worm when in any way employed and in the
intervals of such employment； whatever set of muscles and ganglia
may then have been brought into play； is often regardless of light；
are opposed to the view of the sudden withdrawal being a simple
reflex action。 With the higher animals； when close attention to
some object leads to the disregard of the impressions which other
objects must be producing on them； we attribute this to their
attention being then absorbed； and attention implies the presence
of a mind。 Every sportsman knows that he can approach animals
whilst they are grazing； fighting or courting； much more easily
than at other times。 The state； also； of the nervous system of the
higher animals differs much at different times； for instance； a
horse is much more readily st
