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excretion； but secondarily serves to neutralise the acids generated
during the digestive process。
Earth…worms are distributed throughout the world under the form of
a few genera； which externally are closely similar to one another。
The British species of Lumbricus have never been carefully
monographed； but we may judge of their probable number from those
inhabiting neighbouring countries。 In Scandinavia there are eight
species； according to Eisen； ｛7｝ but two of these rarely burrow in
the ground； and one inhabits very wet places or even lives under
the water。 We are here concerned only with the kinds which bring
up earth to the surface in the form of castings。 Hoffmeister says
that the species in Germany are not well known； but gives the same
number as Eisen； together with some strongly marked varieties。 ｛8｝
Earth…worms abound in England in many different stations。 Their
castings may be seen in extraordinary numbers on commons and chalk…
downs； so as almost to cover the whole surface； where the soil is
poor and the grass short and thin。 But they are almost or quite as
numerous in some of the London parks； where the grass grows well
and the soil appears rich。 Even on the same field worms are much
more frequent in some places than in others； without any visible
difference in the nature of the soil。 They abound in paved court…
yards close to houses； and an instance will be given in which they
had burrowed through the floor of a very damp cellar。 I have seen
worms in black peat in a boggy field； but they are extremely rare；
or quite absent in the drier； brown； fibrous peat； which is so much
valued by gardeners。 On dry； sandy or gravelly tracks； where heath
with some gorse； ferns； coarse grass； moss and lichens alone grow；
hardly any worms can be found。 But in many parts of England；
wherever a path crosses a heath； its surface becomes covered with a
fine short sward。 Whether this change of vegetation is due to the
taller plants being killed by the occasional trampling of man and
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