represented in the beds of the lias and oolite, and sparingly in the
white chalk; and are named respectively Pentacrinus asteria, L., and
P. mülleri, Oersted. The first of these has been known in Europe
since the year 1755, when a specimen was brought to Paris from the
island of Martinique, and described by Guettard in the Memoirs of
the Royal Academy of Sciences. For the next hundred years an example
turned up now and then from the Antilles.
Pentacrinus asteria may be taken as the type of its order; I will
therefore describe it briefly. The animal consists of two well-marked
portions, a stem and a head. The stem, which is often from 40 to 60
centimetres in length, consists of a series of flattened calcareous
joints; it may be snapped over at the point of junction between
any two of these joints, and by slipping the point of a penknife
into the next suture a single joint may be removed entire. The
joint has a hole in the centre, through which one might pass a fine
needle. This hole forms part of a canal filled during life with a
gelatinous nutrient matter which runs through the whole length of
the stem, branches in a complicated way through the plates of the
cup, and finally passes through the axis of each of the joints of the
arms, and of the ultimate pinnules which fringe them. On the upper
and lower surfaces of the stem-joint there is a very graceful and
characteristic figure of five radiating oval leaf-like spaces, each
space surrounded by a border of minute alternate ridges and grooves.
The ridges of the upper surface of a joint fit into the grooves of
the lower surface of the joint above it; so that, though from being
made up of many joints the stem admits of a certain amount of motion,
that motion is very limited.
As the border of each star-like figure exactly fits the border of
the star above and below, the five leaflets within the border are
likewise placed directly one above the other. Within these leaflets
the limy matter which makes up the great bulk of the joint is more
loosely arranged than it is outside, and five oval bands of strong
fibres pass in the interspaces right through the joints, from joint
to joint, from one end of the stem to the other. These fibrous bands
give the column great strength. It is by no means easily broken even
when dead and dry. They also, by their elasticity, admit a certain
amount of passive motion. There are no muscles between the joints
of the stem, so that the animal does not appear to be able to move
its stalk at will. It is probably only gently waved by the tides and
currents, and by the movements of its own arms.
In Pentacrinus asteria about every seventeenth joint of the lower
mature part of the stem is a little deeper or thicker than the
others, and bears a whorl of five long tendrils or cirri. These
tendrils have no true muscles; they have, however, some power of
contracting round resisting objects which they touch, and there are
often star-fishes and other sea animals entangled among them.
Near the head the cirri become shorter and smaller, and their whorls
closer. At the top of the stem five little calcareous lumps like
buttons stand out from the projecting ridges, and upon these and upon
the upper part of the stem the cup which holds the viscera of the
animal is placed.
All the ordinary joints of the arms are provided with muscles
producing various motions, and binding the joints firmly together. If
one of the arms get entangled, or fall into the jaws or claws of an
enemy, by a jerk the star-fish can at once get rid of the embarrassed
arm; and as all this group have a wonderful power of reproducing lost
parts, the arm is soon restored.
Unfortunately, most of the examples of Pentacrinus asteria hitherto
procured have had the soft parts destroyed and the disk more or less
injured. One specimen, however, in my possession is quite perfect.
The body is covered above by a membrane closely tessellated with
irregularly formed flat plates. The mouth is a rounded opening of
considerable size in the centre of the disk, and opens into a stomach
passing into a short curved intestine which ends in a long excretory
tube--the so-called “proboscis” of the fossil crinoids--which rises
from the surface of the disk near the mouth. From the mouth five deep
grooves, bordered on either side by small square plates, run out to
the edge of the disk, and are continuous with the grooves on the
upper surface of the arms and pinnules, while in the angles between
them five thickened masses of the mailing of the disk surround the
mouth like valves. These were at first supposed to answer the purpose
of teeth. The crinoids, however, are not predatory animals. Their
nutrition is effected in a very gentle manner. The grooves of the
pinnules and arms are richly ciliated. The crinoid expands its arms
like the petals of a full-blown flower, and a current of sea-water
bearing organic matter in solution and suspension is carried by the
cilia along the brachial and radial grooves to the mouth. In the
stomach and intestine the water is exhausted of assimilable matter,
and the length and direction of the excretory proboscis prevent the
exhausted water from returning at once into the ciliated passages.
Two other fixed crinoids were dredged from the _Porcupine_, and these
must be referred to the Apiocrinidæ, which differ from all other
sections of the order in the structure of the upper part of the stem.
The Apiocrinidæ attained their maximum during the Jurassic period,
when they were represented by many fine species of the genera
Apiocrinus and Millericrinus. The chalk genus Bourguetticrinus shows
many symptoms of degeneracy. Rhizocrinus loffotensis, M. Sars, was
discovered in the year 1864, at a depth of about 300 fathoms, off the
Lofoten Islands, by G. O. Sars, a son of the celebrated Professor
of Natural History in the University of Christiania, by whom it was
described in the year 1868. It is obviously a form of the Apiocrinidæ
still more degraded than Bourguetticrinus, which it closely resembles.
The genus Bathycrinus must also be referred to the Apiocrinidæ, since
the lower portion of the head consists of a gradually expanding
funnel-shaped piece, which seems to be composed of coalesced upper
stem-joints. The stem of Bathycrinus gracilis is long and delicate;
in one example of a stem alone, which came up in the same haul with
the one nearly perfect specimen which was procured, it was 90 mm. in
length.
The general distribution of the deep-sea Asteridea has already been
referred to. Perhaps the most obvious peculiarity which they present
is the great preponderance of the genera Astrogonium, Archaster,
Astropecten, and their allies. Genera belonging to other groups do
not apparently become less numerous, for species of Asteracanthion,
Cribrella, Asteriscus, and Ophidiaster are as abundant as they are at
lesser depths; but as we go down new species with tessellated mailing
on the disk and massive marginal plates seem to be perpetually added.
Of the twenty-six Echinoderms dredged from the _Porcupine_,
seven--Porocidaris purpurata, Phormosoma placenta, Calveria hystrix,
C. fenestrata, Neolampas rostellatus, Pourtalesia jeffreysi, and
P. phiale--are forms which have been for the first time brought to
light during deep-sea dredging operations, whether on this or on
the other side of the Atlantic. There seems little doubt that these
must be referred to the abyssal fauna, upon whose confines we are
now only beginning to encroach. Three of the most remarkable generic
forms--Calveria, Neolampas, and Pourtalesia--have been found by
Alexander Agassiz among the results of the deep dredging operations
of Count Pourtales in the Strait of Florida, showing a wide lateral
distribution, while even a deeper interest attaches to the fact that
while one family type, the Echinothuridæ, has been hitherto only
known in a fossil state, the entire group finds nearer allies in the
extinct faunæ of the chalk or of the earlier Tertiaries than in that
of the present period.
Many of the mollusca from the deep water have hitherto been found
only in the northern portions of the area examined, and are generally
allied to northern forms.
The abyssal mollusca are by no means devoid of color, though, as
a rule, they are paler than those from shallow water. Neither are
the abyssal mollusca universally destitute of eyes. A new species
of Pleurotoma from 2,090 fathoms had a pair of well-developed eyes
on short foot-stalks; and a Fusus from 1,207 fathoms was similarly
provided. The presence of organs of sight at these great depths
leaves little room to doubt that light must reach even these abysses
from some source. From many considerations it can scarcely be
sunlight. The whole of the light beyond a certain depth might be due
to phosphorescence, which is certainly very general, particularly
among the larvæ and young of deep-sea animals.
“THE MIMIC FIRES OF OCEAN”
--G. CLARKE NUTTALL
Nature dazzles the eye of man with many wonderful phenomena, but
perhaps never more so than when she turns the gloomy night waters of
the sea into a sheet of silvery fire. At these times every movement
of the wave, every cleavage of the water by oar or prow, reveals
in its dark depths a hidden fire which scintillates and sparkles
with weird and mysterious light. The spectacle is one of absolute
fascination, for the Spirit of Enchantment rests upon the waters and
reality becomes fairyland.
The ancients, keenly alive to a sense of the supernatural, saw in
this luminosity a manifestation of some unknown power, and wondered;
the ignorant read in it a portent of judgment and terror; while
in all ages the curious and the searchers after knowledge have
speculated as to its cause. But just as Nature has invested its
appearance with a halo of mystery, so she has also wrapped in much
obscurity its immediate cause; and thus, though in the course of
centuries varying suggestions have been put forward, nothing with any
finality about it has been arrived at. It was asserted truly that
certain fishes were luminous; sharks have glowed and shone, shoals of
herrings, pilchards, or mackerel have been moving masses of light,
and the fish drawn out of the water have lain in great shining heaps,
the glow of which vanished as they dried and died.
Many writers have described the passages of ships through such
shoals--the sheet of moving flames--the beautiful pale greenish
elf-light that the fish exhibited; while poets have apostrophized
the “mimic fires of ocean” and the “lightnings of the wave,” and
scientists and naturalists have in turn tried to account for their
power of luminosity. Some have attributed it to the presence of
certain substances of a fatty nature excreted by the fish and
adhering to the surface of their bodies; others have declared that
it is due to a subtle power of the fish itself--a form in which the
energy of life shows itself under certain conditions, just as this
energy may be exhibited in heat, or motion, or electricity; others,
again, have ascribed it to direct absorption and transmission of the
light of the sun, and so on. Many theories have been elaborated, but
none convincingly.
But now, it is asserted, the secret is laid bare.
It is wonderful how many secrets the searching light of the
Nineteenth Century is claiming to reveal.
It is only lately that any very serious effort has been made to study
this phenomenon, but the research has been abundantly rewarded, for
it is now pretty certain that the luminosity is due to the presence
in the water of various kinds of bacteria.
Now, bacteria are the very smallest living organisms of which we
have cognizance. Millions of them can lie on a penny; therefore, to
produce the gleaming appearance recognized by us as phosphorescence,
they must be present in numbers too enormous even to contemplate with
our finite minds. It would be immeasurably easier to reckon with the
stars for multitude than with these phosphorescent bacteria. They are
colorless, rod-like bodies, only known to us in the land revealed
by the highest powers of the microscope, and careful comparison
shows minor differences among them. For instance, some of them are
capable of independent motion--we can hardly call it swimming--others
are non-motile, some are inclosed in a jelly-like covering, others
are without this sheath. Their power of motion is probably due to
excessively fine hairs at their extremities, which, moving to and fro
in the water, act the part of oars. These cilia have not been found
in all forms of bacteria which move, but their presence is inferred,
since every advance in the study of motile forms increases the number
of bacteria which are seen to possess them.
These light-producing bacteria are known as photo-bacteria, and so
far some half-dozen varieties have been distinguished and named.
The names in such cases are usually either given from the locality
of their appearance (thus, photo-bacterium Balticum, found in
the Baltic), from their discoverer (for example, photo-bacterium
Fischeri, after Professor Fischer), or from some striking attribute
(to wit, photo-bacterium phosphorescens, the commonest light-giving
species).
A Dutchman named Beyerinck has made a special study of these
photo-bacteria, and has experimented with them in a great number
of ways to determine, if possible, why they should thus become
illuminated, and if the light plays any notable part in their
life-history; but his results are, seemingly, all more or less of
a negative nature. He can not find that it has any very important
function. The breathing of these tiny organisms is not, apparently,
in any way bound up with it; their nutrition, growth, and development
go on quite well even if they are placed under such conditions that
their luminosity is arrested; in no way, indeed, is it a vital
process. It only seems to depend on the food which the bacteria feed
upon and the presence of oxygen. Given suitable food and plenty of
fresh air, and they exhibit their characteristic light; deprive them
of one or the other and they no longer shine.
This knowledge helps us to understand, then, the phenomenon of
phosphorescence. It is visible only at night because in the full
glare of day the greater light overpowers the lesser; it is visible
at certain times and seasons because the conditions are such as to
evoke it. And what is favorable for the lighting up of a single
bacterium is favorable for all; hence the myriad multitudes of
infinitesimal units, each set glowing with its tiny light, are
sufficient in the sum total to put a whole ocean aflame.
It would, of course, be presumptuous, and doubtless erroneous,
to say that all the phosphorescence of the sea is due solely to
photo-bacteria; it can only be asserted in the present state of our
knowledge that they are certainly responsible for a great share of
it. But this wonder of nature must now be regarded as yet another
instance of the mighty results accomplished through the agency of the
smallest of living things.
THE JELLY-FISH AND OTHER HYDROZOA
--P. MARTIN DUNCAN
If anybody were asked to name the commonest objects on a sandy or
pebbly seashore, the reply would be--sea-weed, crabs, limpets, a
stranded jelly-fish, looking like so much blubber, and a sea-gull
flying overhead. The first three things really belong to the shore;
the bird is a visitor that is looking after food, and the large,
turned-upside-down, basin-shaped, jelly-looking mass is a waif from
the ocean. If one of these stranded jelly-fish is looked at, as it
lies on the sand, its shape appears to be something like that of
an umbrella without the stick. It is thick, however, and has some
curious markings about its surface and inside. Even something like
a fringe of thick hairs may be detected around the edge. On trying
to take it up or turn it over, the fingers go into it, so readily
does the animal tear; but on getting the umbrella on its back,
the underneath part is seen to be made up, in the middle, of some
projections slightly more solid than the rest of the body; and if put
between them, the finger passes through a sort of tube into a cavity
in the body, which is the stomach.
Some of these jelly-fish, or Medusæ, as they are called, are pounds
in weight; but after a while only a shred of membrane-looking stuff
remains, the water which makes up nearly all the animal having
drained away. It is evident that the large Medusæ grow from small
ones, and that there are many kinds of them, some of which are always
small. A great jelly-fish, two feet across, was once a little one,
leading exactly the same life. They grow, and to grow they must have
nourishment; they are never still, and their muscles, transparent as
they may be, have to be nourished, or their strength would soon give
way. They require not only food, but also air in the water, so that
they consume it, and make its oxygen gas of use to them. They seek
the light in a remarkable manner, and get out of the way of things
very gracefully, and their motions are rhythmical, like the ticks of
a clock, in succession. Have they nerves and eyes? Science answers in
the affirmative. These creatures, consisting of a vast proportion of
sea-water, breathe, digest, and feed. More than this, they produce
young; and if they are pale in color, bluish, or roseate in hue
during the day, they are the glory of the deep during the night; and
each one is a globe of light, the luminousness being the result of
the action of the mysterious energy of life upon matter.
Many of the jelly-fish found on the shores dead and injured are
eighteen inches across, and it is not uncommon to see one swimming
freely whose body is larger than that. Yet in spite of this size, and
of the gifts of the creature, it has one of the shortest of lives,
and it is born, grown, and dead between the spring and the winter.
[Illustration: Typical Radiolaria
1, Rhizosphæra; 2, Sphærozoum; 3, Actinomma; 4, Lithomespilus; 5,
Ommatocampe; 6, Carpocaium; 7, Challengeron; 8, Heliosphæra; 9,
Clathrocyclas; 10, Dictyophimus]
On examining a large jelly-fish, it will be noticed to have not only
four round bodies on the top, round the centre, and the four lobes
hanging down beneath, but that the edges of the body are not quite
round, but are notched, so as to make eight lobes to it. And if a
little care be taken, marks can be seen on the under part of the
body, from the round centre spots to each of the eight splits in the
disk; and a magnifying-glass shows a little substance there which
feels gritty, and is sometimes colored. Other branching tube-marks
pass from the midst of the body to the edge of the umbrella, and a
tube runs all round the edge. The tubes communicate in the midst of
the body with a cavity, into which the finger can pass between
the four under lobes--the stomach--and the digested matters pass
into them to nourish the creature. Around the disk or umbrella, and
outside the circular tube, is the fringe of hairs which have, to a
certain extent, to do with the capture of prey. Each consists of a
filmy substance, in which are fixed thread-cells, not very unlike
those of the sea-anemone, but they have longer barbs and sharper
thorns stretching out from them. Any violence or irritation causes
the thread to shoot forth and to injure. The rest of the body of the
Medusa is covered with an excessively thin skin, which has movable
cilia upon it. It is supposed, and with some reason--for nervous
threads and bodies have been found on the disk, close to the gritty
bodies especially--that these last are eyes, or ears, or both. The
nerves supply the muscles that move the umbrella, and cause it to
expand and contract, and the muscles are remarkable, for some are not
simple contracting fibres all made of one piece, as in the Anemone
tribe.
The jelly-fish, when in full vigor and weighing many pounds, must
catch and eat much, and the manner in which this is done is by no
means perfectly understood. The food is digested, and the results
are taken from the stomach into the numerous tubes in the body,
where they nourish the tissues. The movements of the animal and its
extremely delicate membranes enable much water to come in contact
with it, and it breathes by that means, for there are no special
gills or lungs.
The four round spots on the top of the body, sometimes white and
sometimes red in color, are spaces in the body, and they open into
the central stomach. The circles of these chambers are lined with
ciliate membrane, and in some places it is arranged in folds, and
in them the eggs or ova form. Little oval or roundish things, like
pins’ heads are they: they burst forth and pass out of the stomach,
and then through the canal into the four lobes hanging down like
pouting lips. Here they rest a while until a little grown, and they
start out on their journey of life in the autumn time as little oval
or long things made up of cells, the outside ones having movable
hairs also on them. Totally unlike the parent, the tiny offspring
floats off with the tide and does a little work in moving itself
with its hairy covering. Sooner or later this minute thing, which
is called a planula, settles on a stone or piece of sea-weed, and
begins to grow. First of all its outer skin is formed into a hollow
on the top, a kind of basin-shaped cavity being produced. This is the
future stomach. Then some little projections grow around the hollow,
and stick out in the water like so many rays, and they increase in
number and length very rapidly. Under this shape the creature has
been described as a hydra or a polype, and it really resembles a
small sea-anemone with very long and slender tentacles. But the
internal anatomy differs. The creature is all stomach and tentacles,
and it grows by catching small prey. All the elaborate tissues of
the jelly-fish are absent and the creature can not move. It is this
curious condition of life that brings the jelly-fish tribe within
notice of a seashore observer, for those little hydras live in some
places at low-water mark. The knowledge that the hydra was the
child of the jelly-fish was obtained many years ago by a Scotch and
by a Scandinavian naturalist. It was known that some small kinds of
jelly-fish which were kept in sea-water in an aquarium disappeared
altogether in the late autumn. Then it was noticed that there were
many very small things with tentacles, on the sides of the glass,
which had not been noticed before. And at last the curious discovery
was made that these hydras or planulas reproduced jelly-fish the
next year. This is a very strange story, and the course of nature’s
proceeding is, that when food has become scarce and the boisterous
waves would become fatal to the delicate Medusa, it shall lay eggs
which produce creatures that can settle down out of the way of the
rush of water, and that require but little food. Then in the next
year when food is in plenty, the progeny separate into jelly-fish
like the parent. The hydras or progeny have no power of laying
eggs; they digest and produce the creature that shall lay eggs.
The Scandinavian naturalists and Germans called this “alternate
generation,” and named the hydra the nurse of the jelly-fishes.
This is the method by which most of the jelly-fish, which may be
occasionally seen stranded on the coast, were produced; but there are
some whose planulas do not settle down, but are always free swimmers,
and they divide into Medusæ in the sea.