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animals； or to the soil being occasionally manured by the droppings
from animals； I do not know。 ｛9｝ On such grassy paths worm…
castings may often be seen。 On a heath in Surrey； which was
carefully examined； there were only a few castings on these paths；
where they were much inclined； but on the more level parts； where a
bed of fine earth had been washed down from the steeper parts and
had accumulated to a thickness of a few inches； worm…castings
abounded。 These spots seemed to be overstocked with worms； so that
they had been compelled to spread to a distance of a few feet from
the grassy paths； and here their castings had been thrown up among
the heath； but beyond this limit； not a single casting could be
found。 A layer； though a thin one； of fine earth； which probably
long retains some moisture； is in all cases； as I believe；
necessary for their existence； and the mere compression of the soil
appears to be in some degree favourable to them； for they often
abound in old gravel walks； and in foot…paths across fields。
Beneath large trees few castings can be found during certain
seasons of the year； and this is apparently due to the moisture
having been sucked out of the ground by the innumerable roots of
the trees； for such places may be seen covered with castings after
the heavy autumnal rains。 Although most coppices and woods support
many worms； yet in a forest of tall and ancient beech…trees in
Knole Park； where the ground beneath was bare of all vegetation；
not a single casting could be found over wide spaces； even during
the autumn。 Nevertheless； castings were abundant on some grass…
covered glades and indentations which penetrated this forest。 On
the mountains of North Wales and on the Alps； worms； as I have been
informed； are in most places rare； and this may perhaps be due to
the close proximity of the subjacent rocks； into which worms cannot
burrow during the winter so as to escape being frozen。 Dr。
McIntosh； however； found worm…castings at a height of 1500 feet on
Schiehallion in Scotland。 They are numerous on some hills near
Turin at from 2000 to 3000 feet above the sea； and at a great
altitude on the Nilgiri Mountains in South India and on the
Himalaya。
Earth…worms must be considered as terrestrial animals； though they
are still in one sense semi…aquatic； like the other members of the
great class of annelids to which they belong。 M。 Perrier found
that their exposure to the dry air of a room for only a single
night was fatal to them。 On the other hand he kept several large
worms alive for nearly four months； completely submerged in water。
｛10｝ During the summer when the ground is dry； they penetrate to a
considerable depth and cease to work； as they do during the winter
when the ground is frozen。 Worms are nocturnal in their habits；
and at night may be seen crawling about in large numbers； but
usually with their tails still inserted in their burrows。 By the
expansion of this part of their bodies； and with the help of the
short； slightly reflexed bristles； with which their bodies are
armed； they hold so fast that they can seldom be dragged out 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 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 circul