按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
drawn in by or near the apex。 The petioles of the Clematis could
certainly have been drawn in with equal ease by the base and apex；
yet three times and in certain cases five times as many were drawn
in by the apex as by the base。 It might have been thought that the
foot…stalks of leaves would have tempted the worms as a convenient
handle； yet they are not largely used； except when the base of the
blade is narrower than the apex。 A large number of the petioles of
the ash are drawn in by the base； but this part serves the worms as
food。 In the case of pine…leaves worms plainly show that they at
least do not seize the leaf by chance； but their choice does not
appear to be determined by the divergence of the two needles； and
the consequent advantage or necessity of drawing them into their
burrows by the base。 With respect to the triangles of paper； those
which had been drawn in by the apex rarely had their bases creased
or dirty； and this shows that the worms had not often first tried
to drag them in by this end。
If worms are able to judge； either before drawing or after having
drawn an object close to the mouths of their burrows； how best to
drag it in； they must acquire some notion of its general shape。
This they probably acquire by touching it in many places with the
anterior extremity of their bodies； which serves as a tactile
organ。 It may be well to remember how perfect the sense of touch
becomes in a man when born blind and deaf； as are worms。 If worms
have the power of acquiring some notion； however rude； of the shape
of an object and of their burrows； as seems to be the case； they
deserve to be called intelligent； for they then act in nearly the
same manner as would a man under similar circumstances。
To sum up； as chance does not determine the manner in which objects
are drawn into the burrows； and as the existence of specialized
instincts for each particular case cannot be admitted； the first
and most natural supposition is that worms try all methods until
they at last succeed； but many appearances are opposed to such a
supposition。 One alternative alone is left； namely； that worms；
although standing low in the scale of organization； possess some
degree of intelligence。 This will strike every one as very
improbable； but it may be doubted whether we know enough about the
nervous system of the lower animals to justify our natural distrust
of such a conclusion。 With respect to the small size of the
cerebral ganglia； we should remember what a mass of inherited
knowledge； with some power of adapting means to an end； is crowded
into the minute brain of a worker…ant。
Means by which worms excavate their burrows。This is effected in
two ways； by pushing away the earth on all sides； and by swallowing
it。 In the former case； the worm inserts the stretched out and
attenuated anterior extremity of its body into any little crevice；
or hole； and then； as Perrier remarks； ｛36｝ the pharynx is pushed
forwards into this part； which consequently swells and pushes away
the earth on all sides。 The anterior extremity thus serves as a
wedge。 It also serves； as we have before seen； for prehension and
suction； and as a tactile organ。 A worm was placed on loose mould；
and it buried itself in between two and three minutes。 On another
occasion four worms disappeared in 15 minutes between the sides of
the pot and the earth； which had been moderately pressed down。 On
a third occasion three large worms and a small one were placed on
loose mould well mixed with fine sand and firmly pressed down； and
they all disappeared； except the tail of one； in 35 minutes。 On a
fourth occasion six large worms were placed on argillaceous mud
mixed with sand firmly pressed down； and they disappeared； except
the extreme tips of the tails of two of them； in 40 minutes。 In
none of these cases； did the worms swallow； as far as could be
seen； any earth。 They generally entered the ground close to the
sides of the pot。
A pot was next filled with very fine ferruginous sand； which was
pressed down； well watered； and thus rendered extremely compact。 A
large worm left on the surface did not succeed in penetrating it
for some hours； and did not bury itself completely until 25 hrs。 40
min。 had elapsed。 This was effected by the sand being swallowed；
as was evident by the large quantity ejected from the vent； long
before the whole body had disappeared。 Castings of a similar
nature continued to be ejected from the burrow during the whole of
the following day。
As doubts have been expressed by some writers whether worms ever
swallow earth solely for the sake of making their burrows； some
additional cases may be given。 A mass of fine reddish sand； 23
inches in thickness； left on the ground for nearly two years； had
been penetrated in many places by worms； and their castings
consisted partly of the reddish sand and partly of black earth
brought up from beneath the mass。 This sand had been dug up from a
considerable depth； and was of so poor a nature that weeds could
not grow on it。 It is therefore highly improbable that it should
have been swallowed by the worms as food。 Again in a field near my
house the castings frequently consist of almost pure chalk； which
lies at only a little depth beneath the surface； and here again it
is very improbable that the chalk should have been swallowed for
the sake of the very little organic matter which could have
percolated into it from the poor overlying pasture。 Lastly； a
casting thrown up through the concrete and decayed mortar between
the tiles； with which the now ruined aisle of Beaulieu Abbey had
formerly been paved； was washed； so that the coarser matter alone
was left。 This consisted of grains of quartz； micaceous slate；
other rocks； and bricks or tiles； many of them from 1/20 to 1/10
inch in diameter。 No one will suppose that these grains were
swallowed as food； yet they formed more than half of the casting；
for they weighed 19 grains； the whole casting having weighed 33
grains。 Whenever a worm burrows to a depth of some feet in
undisturbed compact ground； it must form its passage by swallowing
the earth； for it is incredible that the ground could yield on all
sides to the pressure of the pharynx when pushed forwards within
the worm's body。
That worms swallow a larger quantity of earth for the sake of
extracting any nutritious matter which it may contain than for
making their burrows； appears to me certain。 But as this old
belief has been doubted by so high an authority as Claparede；
evidence in its favour must be given in some detail。 There is no a
priori improbability in such a belief； for besides other annelids；
especially the Arenicola marina； which throws up such a profusion
of castings on our tidal sands； and which it is believed thus
subsists； there are animals belonging to the most distinct classes；
which do not burrow； but habitually swallow large quantities of
sand； namely； the molluscan Onchidium and many Echinoderms。 ｛37｝
If earth were swallowed only when worms deepened their burrow