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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 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； mad