SUBTERRANEAN LIGHT-GIVERS.
In wandering through the fields in early morning, we often see little
heaps of newly disturbed earth, and occasionally catch glimpses of
reddish or pink bodies quickly withdrawing into little tunnels in the
sod. These are the earthworms, considered the humblest of all animals;
yet, as insignificant as they seem, they are among the most valuable
aids to the agriculturist.
We may appreciate this by selecting a field at random in a good
producing country, making a section down through the earth for several
feet, when, if carefully done, we shall find innumerable tunnels formed
by the worms, leading here, there, and everywhere. In fact, the upper
crust of the earth is an endless maze of streets, lanes, and avenues. A
naturalist has even attempted to calculate the number of these little
workers, and has come to the conclusion that they average one hundred
thousand to the acre; and in especially rich ground in New Zealand it
was estimated that there were three hundred and forty-eight thousand,
four hundred and eighty in a single acre. This vast body of worms is
continually at work, boring this way and that, coming to the surface
during the night, and retreating to greater depths during the day;
and it is at once evident that their tunnels constitute a system
of irrigation and ventilation for the upper crust. In other words,
rain, instead of running off, enters the holes, and so penetrates the
earth, thus being held for a longer time. Air also finds its way below
the surface; so that the homes of the little creatures constitute
storehouses for moisture.
But this is a very small part of the work accomplished. The worms are
in league with the farmer; are, in fact, his unappreciated assistants,
upon whose endeavors depends much of the success of his crops. They are
continually swallowing the earth, and depositing it at the surface, and
working it over and over. If I should ask my young readers to estimate
the quantity of earth brought to the surface in a single acre in a
year, I fear they would not place the amount as high as Mr. Darwin, who
states that the vegetable mould thus transported in some places amounts
to ten tons an acre. Think of it! If your ten-acre farm is in one of
these favored localities, these silent workers, say to the number of
a million, have ploughed up about one hundred tons of earth for you,
giving you a fine top dressing.
The worms not only carry all this material to the surface, but they
drag vast quantities of leaves and other matter down, that serve to
enrich the soil and render it capable of producing larger crops. They
cover up seeds and other objects to a remarkable extent; and a flat
rock set upon the ground will soon become buried, through their means.
Some of the most interesting parts of Roman villas found in England
have been, according to Darwin, preserved in this way; the worms
undermining them, and gradually heaping soil over the walks and slabs,
until finally, aided by other causes, they disappeared beneath the
ground.
The earthworms of Australia attain a large size,--sometimes several
feet in length,--and have been seen climbing trees. Some casts found
in India are a foot in length. The worms evidently live in complete
darkness; but it is known that at certain times, and under certain
conditions, they are luminous: so that a state of things may exist
under the ground of which we have no conception, and the tunnels of
these little creatures may be brightly illumined. We have never been so
fortunate as to observe their phosphorescence, but Dr. Phipson says, “I
distinctly remember witnessing, when a child, the phosphorescence of
the earthworm. The light appeared connected with the mucus that covered
the animal’s body.” And other naturalists have observed the light under
certain conditions.
If they possess this property to a greater extent than we are now aware
of, it must be a fatal gift, as the sharp little eyes of the mole,
though not remarkable for their powers of observation, would probably
catch the faintest gleam. These animals are continually upon the
forage; and their appetites can be imagined from an actual experiment,
which showed that two moles devoured in nine days 341 grubs, 193
earthworms, 25 caterpillars, and a mouse,--skin, bones, and all!
In the ocean depths we find that the marine worms, which constitute in
the beauty of their appearance a magnificent assemblage, tunnel the
upper crust of the bottom. Some years ago the moat or ditch surrounding
Fort Jefferson, Fla., was pumped out, leaving a space nearly half a
mile in extent, high and dry, which abounded in specimens that would
have delighted the eyes of a specialist in any branch. Over this spot
we had often, as a lad, enjoyed the venturesome fun of riding upon
the backs of the great sea-turtles, kept there for the commissaries’
use, had fished in every nook and corner, and now the opportunity was
presented for penetrating below the surface of the bottom.
Some little digging showed, that, for a foot or more from the surface,
the sand and mud was fairly alive with a variety of worms, numerous
to an extraordinary extent, and in many cases beautiful beyond
description. This condition of things is true, to a greater or less
extent, in many localities; the worms retiring to the mud and other
retreats during the day, at night venturing out, and even swimming at
the surface.
If we take a drop of water from any ditch or pond, or even from the
stem of a flower that has been standing in a vase, and place it under a
microscope of even ordinary power, we shall find that it is a world of
itself; a vast ocean, in fact, to the many forms that live there. Chief
among these drop inhabitants, we notice numbers of little creatures
that attract attention immediately. They resemble tall hats without
brims, or crystal bags with fringed edges. And that they are busy
bodies is at once evident, as they swim along at a wonderful rate of
speed, eating as they go, keeping their fringes or _cilia_, which
appear like so many arms, in perpetual motion; now bumping against each
other, forcing their way among crowds of different animals, and always
appearing full of life and energy.
These little creatures, invisible to the naked eye, are minute worms,
or Rotifers; and among them we find some interesting light-givers. The
_Synachata_ is one; and others described by Ehrenberg, the largest
being about one-eighth of a line in size, present a striking appearance
under the glass in a dark room,--the little bags, seemingly at a white
heat, darting about in every direction.
As small as are these wonderful creatures, they are well worthy of
study; and even those not interested in natural history will find that
the stems of their flowers, or the water in the vase, contain more
wonders than they had dreamed of,--a single drop that can be lifted
upon a pin-head being sufficient for the purpose.
The little hat-like form, _Hydatina senta_, already referred to, is
remarkable for the rapidity of its increase. The eggs are laid or
deposited within a few hours of the time they are first seen within
the transparent parent, and twelve hours later the young break
from the shell and appear; so that in a comparatively few days the
descendants of a single animal might possibly far exceed the population
of the United States. The larger worms are with hardly any exception
ornamented in some remarkable way, and in many the splendors of their
decorations must be seen to be appreciated. The radiating coronets
of _Serpulæ_[30] are of the most delicate and beautiful description,
abounding in bands and markings of striking hues. _Pectinaria_ has upon
its head a pair of combs that might be burnished gold; while _Eunicedæ_
and _Nereidæ_[31] have equally resplendent decorations.
These charms of color, and they are of great variety, are seen
by day; but at night many of these creatures assume the gift of
phosphorescence, adding to the long list of marine light-givers that
have been previously referred to. In four other families[32] are found
the most beautiful light-givers of the group. Assuming that we have a
certain species of the first mentioned in the aquarium, we may prepare
for an extraordinary display. It is now snugly coiled up under a
stone, perhaps fast asleep, and giving no evidence of its wondrous
gift. Now touch it with the narrow handle of the dip-net, and a seeming
electric spark is given out. But there is no electricity here: the
light is a phosphorescent protest, and rapidly passes from scale to
scale, until the whole animal stands out like a vivid shield of light
against the bottom, glowing with the mysterious flame.
If the worm is greatly disturbed, we are presented with a unique method
of protection. Upon feeling the blow or attack, the light becomes
intense, and flashes quickly from segment to segment, and along all
the series of _elytra_; and, as the animal darts away, one or more of
the scales become disconnected and are left behind, a luminous spot,
to attract the attention of a possible follower, while the worm itself
escapes.
Nearly all the phosphorescent worms are rapid swimmers, and noted
for their agile movements; and, as their scales are very readily
disconnected, we may imagine in some cases a worm darting off and
leaving a shower of sparks behind. In these worms the light is usually
green.
We have seen that one of the deep-sea Crustaceans has phosphorescent
bands upon its feet; and in the _Syllidæ_, a family which contains
some remarkable worms, we find that the luminosity is confined to the
under surface of the feet. In _Chætopterus_[33] a bright flashing
light is emitted from the posterior feet, while a far more brilliant
one glows at a point on the dorsum between the lateral wings of the
tenth segment. The mucus of the animals appears to be the seat of
the luminosity, and not only encircles the worm with an aureola of
phosphorescence, but pervades the surrounding water with a rich bluish
purple light, so vivid and brilliant that the medium in which the
light-giver lives seems to have ignited, and to be slowly consuming its
dependents.
[Illustration:
PLATE VII.
BURROW OF PHOLAS.
SEA PEN. (_Pennatula._)]
It has been noticed, according to W. C. McIntosh, that an odor
accompanies this display, resembling somewhat that produced by
phosphorus in combustion. We have noticed that many worms have a
peculiar odor when handled, though not quite of this character.
The most brilliant of all these light-givers is _Polycirrus_, which
emits over its entire surface a vivid pale-bluish light, marking it as
one of the most beautiful of its kind; while _Sagitta_ and many more
add to the wonders in this generally considered uninteresting group of
animals.[34]