observed appearances, in its great size, its laminated and acervuline
forms, and in its canal system and tubulation, are not only in
conformity with those of other Foraminifera, but such as might be
expected in a very ancient form of that group.
6. Indications exist of other organic bodies in the limestones
containing Eozoon, and also of the Eozoon being preserved not only in
reefs but in drifted fragmental beds as in the case of modern corals.
7. Similar organic structures have been found in the Laurentian
limestones of Massachusetts, New York, Brazil,[45] and also in those
of various parts of Europe, and Dr. Gümbel has found an additional
species in rocks succeeding the Laurentian.
[Footnote 45: Fragmental; specimens from J. A. Derby, Esq.]
8. The manner in which the structures of Eozoon are effected by the
faulting, development of crystals, mineral veins, and other effects of
disturbance and metamorphism in the containing rocks, is precisely that
which might be expected on the supposition that it is of organic origin.
9. The exertions of several active and able opponents have failed to
show how, otherwise than by organic agency, such structures as those
of Eozoon can be formed, except on the supposition of pseudo-morphism
and replacement, which must be regarded as chemically extravagant,
and which would equally impugn the validity of all fossils determined
by microscopic structure. In like manner all comparisons of these
structures with dendritic and other imitative forms have signally
failed, in the opinion of those best qualified to judge.
Another and perhaps simpler way of putting the case is the
following:--Only four general modes of accounting for the existence
of Eozoon have been proposed. The first is that of Professors King
and Rowney, who regard the chambers and canals filled with serpentine
as arising from the erosion or partial dissolving away of serpentine
and its replacement by calcite. The objections to this are conclusive.
It does not explain the fine tubulation, which has to be separately
accounted for by confounding it, contrary to the observed facts,
with the veins of fibrous serpentine which actually pass through
cracks in the fossil. Such replacement is in the highest degree
unlikely on chemical grounds, and there is no evidence of it in the
numerous serpentine grains, nodules, and bands in the Laurentian
limestones. On the other hand, the opposite replacement, that of
limestone by serpentine, seems to have occurred. The mechanical
difficulties in accounting for the delicate canals on this theory are
also insurmountable. Finally, it does not account for the specimens
preserved in pyroxene and other silicates, and in dolomite and calcite.
A second mode of accounting for the facts is that the Eozoon forms are
merely peculiar concretions. But this fails to account for their great
difference from the other serpentine concretions in the same beds, and
for their regularity of plan and the delicacy of their structure, and
also for minerals of different kinds entering into their composition,
and still presenting precisely the same forms and structures. The third
is that first suggested, I think, by Jullien, and later by Gregory and
Lavis, that the forms are merely banded alternations of calcite with
silicious minerals similar to those observed at the junction of igneous
rocks and limestones. To this it may be replied that there is really
only an apparent resemblance, which, on careful examination, proves
to be illusory; that it does not account for the canals and tubuli,
and that studies of such banded rocks from several regions have been
made by competent observers, who have distinguished these from the
Laurentian Eozoon. The only remaining theory is that of the filling
of cavities by infiltration with serpentine. This accords with the
fact that such infiltration by minerals akin to serpentine exists in
fossils in later rocks. It also accords with the known aqueous origin
of the serpentine nodules and bands, the veins of fibrous serpentine,
and the other minerals found filling the cavities of Eozoon. Even the
pyroxene has been shown by Hunt to exist in the Laurentian in veins
of aqueous origin. The only difficulty existing on this view is how
a calcite skeleton with such chambers, canals, and tubuli could be
formed; and this is solved by the discovery that all these facts
correspond precisely with those to be found in the shells of modern
oceanic Foraminifera. The existence, then, of Eozoon, its structure,
and its relations to the containing rocks and minerals being admitted,
no rational explanation of its origin seems at present possible other
than that advocated in the preceding pages.
If the reader will now turn to the figures in the illustration on the
opposite page (Fig. 59), he will find a selection of examples bearing
on the above arguments and objections. Fig. 1 represents a portion of a
very thin slice of a specimen traversed by veins of fibrous serpentine
or chrysotile, and having the calcite of the walls more broken by
cleavage planes than usual. The portion selected shows a part of one
of the chambers filled with serpentine, which presents the usual
curdled aspect almost impossible to represent in a drawing (_s_). It
is traversed by a branching vein of chrysotile (_s′_), which, where
cut precisely parallel to its fibres, shows clear fine cross lines,
indicating the sides of its constituent prisms, and where the plane of
section has passed obliquely to its fibres, has a curiously stippled or
frowsy appearance.
[Illustration: Fig. 59.--_Figures of various Structures and States of
Preservation._
Fig. 1.--Portion of two laminæ and intervening serpentine, with
chrysotile vein. (_a_) Proper wall tubulated. (_b_) Intermediate
skeleton, with large canals. (_c_) Openings of small chamberlets
filled with serpentine. (_s_) Serpentine filling chamber. (_s¹_)
Vein of chrysotile, showing its difference from the proper wall.
Fig. 2.--Junction of a canal and the proper wall. Lettering as in
Fig. 1.
Fig. 3.--Proper wall shifted by a fault, and more recent chrysotile
vein not faulted. Lettering as in Fig. 1.
Fig. 4.--Large and small canals filled with dolomite.
Fig. 5.--Abnormally thick portion of intermediate skeleton, with
large tubes and small canals filled with dolomite.
]
On either side of the serpentine band is the nummuline or proper wall,
showing under a low power a milky appearance, which, with a higher
power, becomes resolved into a tissue of the most beautiful parallel
threads, representing the filling of its tubuli. Nothing can be more
distinct than the appearances presented by this wall and a chrysotile
vein, under every variety of magnifying power and illumination; and all
who have had an opportunity of examining my specimens have expressed
astonishment that appearances so dissimilar should have been confounded
with each other. On the lower side two indentations are seen in the
proper wall (_c_). These are connected with the openings into small
subordinate chamberlets, one of which is in part included in the
thickness of the slice. At the upper and lower parts of the figure
are seen portions of the intermediate skeleton traversed by canals,
which in the lower part are very large, though from the analogy of
other specimens it is probable that they have in their interstices,
and at their branching extremities, minute canaliculi not visible in
this slice. Fig. 2, from the same specimen, shows the termination of
one of the canals against the proper wall, its end expanding into a
wide disc of sarcode on the surface of the wall, as may be seen in
similar structures in modern Foraminifera. In this specimen the canals
are beautifully smooth and cylindrical, but they sometimes present a
knotted or jointed appearance, especially in specimens decalcified
by acids, in which perhaps some erosion has taken place. They are
also occasionally fringed with minute crystals, especially in those
specimens in which the calcite has been partially replaced with other
minerals. Fig. 3 shows an example of faulting of the proper wall, an
appearance not infrequently observed; and it also shows a vein of
chrysotile crossing the line of fault, and not itself affected by it--a
clear evidence of its posterior origin. Figs. 4 and 5 are examples of
specimens having the canals filled with dolomite, and showing extremely
fine canals in the interstices of the others: an appearance observed
only in the thicker parts of the skeleton, and when these are very well
preserved. These dolomitized portions require some precautions for
their observation, either in slices or decalcified specimens, but when
properly managed they show the structures in very great perfection. The
specimen in Fig. 5 is from an abnormally thick portion of intermediate
skeleton, having unusually thick canals, and referred to in a previous
chapter. Such additional peculiarities and specialties might be
multiplied to any extent from the numerous prepared specimens now in
our collections.
One object which I have in view in thus minutely directing attention
to these illustrations, is to show the nature of the misapprehensions
which may occur in examining specimens of this kind, and at the same
time the certainty which may be attained when proper precautions are
taken. I may add that such structures as those referred to are best
seen in extremely thin slices, and that the observer must not expect
that every specimen will exhibit them equally well. It is only by
preparing and examining many specimens that the best results can be
obtained. It often happens that one specimen is required to show well
one part of the structures, and a different one to show another; and
previous to actual trial, it is not easy to say which portion of the
structures any particular fragment will show most clearly. This renders
it somewhat difficult to supply one's friends with specimens. Really
good slices can be prepared only from the best material and by skilled
manipulators; imperfect slices may only mislead; and rough specimens
may not be properly prepared by persons unaccustomed to the work, or
if so prepared, may not turn out satisfactory, or may not be skilfully
examined. One slice heated in the grinding may show nothing but
cleavage in the calcite layers, while an adjoining one more carefully
prepared may show beautiful canals. These difficulties, however, Eozoon
shares with other specimens in micro-geology, and I have experienced
similar disappointments in the case of fossil wood.
In conclusion of this part of the subject, and referring to the notes
appended to this work for some further details, I would express the
hope that those who have hitherto opposed the interpretation of Eozoon
as organic, and to whose ability and honesty of purpose I willingly
bear testimony, will find themselves enabled to acknowledge at least
the reasonable probability of that interpretation of these remarkable
forms and structures.
_THE ORIGIN OF LIFE_
X
_THE ORIGIN OF LIFE_
The thoughts suggested to the philosophical naturalist by the
contemplation of the dawn of life on our planet are necessarily many
and exciting, and the subject has in it the materials for enabling the
general reader better to judge of some of the theories of the origin of
life agitated in our time. Let us then put Eozoon into the witness-box,
and try to elicit its testimony as to the beginnings of life; supposing
for the moment that it is really an animal, and not a mere pretender;
though even in that case, it might serve to represent the first animal,
whatever it may have been.
Looking down from the elevation of our physiological and mental
superiority, it is difficult to realize the exact conditions in which
life exists in creatures so simple as the Protozoa. There may perhaps
be higher intelligences that find it equally difficult to realize how
life and reason can manifest themselves in such poor houses of clay
as those we inhabit. But placing ourselves near to these creatures,
and entering as it were into sympathy with them, we can understand
something of their powers and feelings. In the first place, it is
plain that they can vigorously, if roughly, exercise those mechanical,
chemical, and vegetative powers of life which are characteristic of
the animal. They can seize, swallow, digest, and assimilate food; and,
employing its albuminous parts in nourishing their tissues, can burn
away the rest in processes akin to our respiration, or reject it from
their system. Like us, they can subsist only on food which the plant
has previously produced; for in this world, from the beginning of time,
the plant has been the only organism which could use the solar light
and heat as forces to enable it to turn the dead elements of matter
into living, growing tissues, and into organic compounds capable of
nourishing the animal. Like us, the Protozoa expend the food which
they have assimilated in the production of animal force, and in doing
so cause it to be oxidized, or burnt away, and resolved again into
dead matter. It is true that we have much more complicated apparatus
for performing these functions, but it does not follow that this gives
us much real superiority, except relatively to the more difficult
conditions of our existence. The gourmand who enjoys his dinner may
have no more pleasure in the act than the Amœba which swallows a
Diatom; and for all that the man knows of the subsequent processes to
which the food is subjected, his interior might be a mass of jelly,
with extemporised vacuoles, like that of his humble fellow-animal. The
workman or the athlete has bones and muscles of vastly complicated
structure, but to him the muscular act is as simple and unconscious a
process as the sending out of a pseudopod to a Protozoon. The clay is
after all the same, and there may be as much credit to the artist in
making a simple organism with varied powers, as a more complex frame
for doing nicer work. It is a weakness of humanity to plume itself on
advantages not of its own making, and to treat its superior gifts as
if they were the result of its own endeavours. The truculent traveller
who illustrated his boast of superiority over the Indian by comparing
his rifle with the bow and arrows of the savage, was well answered by
the question, "Can you make a rifle?" and when he had to answer, "No,"
by the rejoinder, "Then I am at least better than you, for I can make
my bow and arrows." The Amœba or the Eozoon is probably no more than
we its own creator; but if it could produce itself out of vegetable
matter, or out of inorganic substances, it might claim in so far a
higher place in the scale of being than we; and as it is, it can assert
equal powers of digestion, assimilation, and motion, with much less of
bodily mechanism.
In order that we may feel, a complicated apparatus of nerves and
brain-cells has to be constructed and set to work; but the Protozoon,
without any distinct brain, is all brain, and its sensation is simply
direct. Thus vision in these creatures is probably performed in a rough
way by any part of their transparent bodies, and taste and smell are
no doubt in the same case. Whether they have any perception of sound
as distinct from the mere vibrations ascertained by touch, we do not
know. Here also we are not far removed above the Protozoa, especially
those of us to whom touch, seeing, and hearing are mere feelings,
without thought or knowledge of the apparatus employed. We might so far
as well be Amœbas. As we rise higher we meet with more differences.
Yet it is evident that our gelatinous fellow-being can feel pain,
dread danger, desire possessions, enjoy pleasure, and in a simple,
unconscious way entertain many of the appetites and passions that
affect ourselves. The wonder is that with so little of organization it
can do so much. Yet, perhaps, life can manifest itself in a broader
and more intense way where there is little organization; and a highly
strung and complex organism is not so much a necessary condition of
a higher life as a mere means of better adapting it to its present
surroundings. Those philosophies which identify the thinking mind with
the material organism, must seem outrageous blunders to an Amœba on
the one hand, or to an angel on the other, could either be enabled to
understand them; which, however, is not very probable, as they are too
intimately bound up with the mere prejudices incident to the present
condition of our humanity. In any case, the Protozoa teach us how much
of animal function may be fulfilled by a very simple organism, and warn
us against the fallacy that creatures of this simple structure are
necessarily nearer to inorganic matter, and more easily developed from
it than beings of more complex mould.
A similar lesson is taught by the complexity of their skeletons. We
speak in a crude, unscientific way of these animals accumulating
calcareous matter, and building up reefs of limestone. We must,
however, bear in mind that they are as dependent on their food for
the materials of their skeletons as we are, and that their crusts
grow in the interior of the sarcode just as our bones do within our
bodies. The provision even for nourishing the interior of the skeleton
by tubuli and canals is in principle similar to that involved in the
Haversian canals, cells, and canalicules of bone. The Protozoon of
course knows neither more nor less of this than the average Englishman.
It is altogether a matter of unconscious growth. The process in
the Protozoa strikes some minds, however, as the more wonderful of
the two. It is, says an eminent modern physiologist, a matter of
"profound significance" that this "particle of jelly [the sarcode
of a Foramlnifer] is capable of guiding physical forces in such a
manner as to give rise to these exquisite and almost mathematically
arranged structures." Respecting the structures themselves, there is
no exaggeration in this. No arch or dome framed by human skill is more
perfect in beauty or in the realization of mechanical ideas than the
tests of some Foraminifera, and none is so complete and wonderful in
its internal structure. The particle of jelly, however, is a figure of
speech. The body of the humblest Foramlnifer is much more than this.
It is an organism with divers parts, as we have already seen in a
previous chapter, and It is endowed with the mysterious forces of life
which in it guide the physical forces, just as they do in building
up phosphate of lime in our bones, or indeed just as the will of the
architect does in building a palace. The profound significance which
this has, reaches beyond the domain of the physical and vital, even to
the spiritual. It clings to all our conceptions of living things: quite
as much, for example, to the evolution of an animal, with all its parts
from a one-celled germ, or to the connection of brain-cells with the
manifestations of intelligence. Viewed in this way, we may share with
the author of the sentence I have quoted his feeling of veneration in
the presence of this great wonder of animal life, "burning, and not
consumed," nay, building up, and that in many and beautiful forms. We
may realize it most of all in the presence of the organism which was
perhaps the first to manifest on our planet these marvellous powers.
We must, however, here, also, beware of that credulity which makes too
many thinkers limit their conceptions altogether to physical force
in matters of this kind. The merely materialistic physiologist is
really in no better position than the savage who quails before the
thunderstorm, or rejoices in the solar warmth, and seeing no force or
power beyond, fancies himself in the immediate presence of his God. In
Eozoon we must discern not only a mass of jelly, but a being endowed
with that higher vital force which surpasses vegetable life and also
physical and chemical forces; and in this animal energy we must see an
emanation from a Will higher than our own, ruling vitality itself; and
this not merely to the end of constructing the skeleton of a Protozoon,
but of elaborating all the wonderful developments of life that were to
follow in succeeding ages, and with reference to which the production
and growth of this creature were initial steps. It is this mystery of
design which really constitutes the "profound significance" of the
foraminiferal skeleton.
Another phenomenon of animality forced upon our notice by the Protozoa
is that of the conditions of life in animals not individual, as we
are, but aggregative and accumulative in indefinite masses. What, for
instance, the relations to each other of the Polyps, growing together
in a coral mass, of the separate parts of a Sponge, or the separate
cells of a Foraminifer, or of the sarcode mass of an indefinitely
spread out Cryptozoon. In the case of the Polyps, we may believe that
there is special sensation in the tentacles and oral opening of each
individual, and that each may experience hunger when in want, or
satisfaction when it is filled with food, and that injuries to one part
of the mass may indirectly affect other parts, but that the nutrition
of the whole mass may be as much unfelt by the individual Polyps as
the processes going on in our own bones are by us. So in the case of
a large Sponge or Foraminifer, there may be some special sensation in
individual cells, pseudopods, or segments, and the general sensation
may be very limited, while unconscious living powers pervade the whole.
In this matter of aggregation of animals we have thus various grades.
The Foraminifers and Sponges present us with the simplest of all, and
that which most resembles the aggregation of buds in the plant. The
Polyps and complex Bryozoons present a higher and more specialized
type; and though the bilateral symmetry which obtains in the higher
animals is of a different nature, it still at least reminds us of that
multiplication of similar parts which we see in the lower grades of
being. It is worthy of notice here that the lower animals which show
aggregative tendencies present but imperfect indications, or none
at all, of bilateral symmetry. Their bodies, like those of plants,
are for the most part built up around a central axis, or they show
tendencies to spiral modes of growth.
It is this composite sort of life which is connected with the main
geological function of the Foraminifer. While active sensation,
appetite, and enjoyment pervade the pseudopods and external sarcode
of the mass, the hard skeleton common to the whole is growing within;
and in this way the calcareous matter is gradually removed from
the sea-water, and built up in solid reefs, or in piles of loose
foraminiferal shells. Thus it is the aggregative or common life,
alike in Foraminifers as in Corals, that tends most powerfully to the
accumulation of calcareous matter; and those creatures whose life is
of this complex character are best suited to be world-builders, since
the result of their growth is not merely a cemetery of their osseous
remains, but a huge communistic edifice, to which multitudes of lives
have contributed, and in which successive generations take up their
abode on the remains of their ancestors. This process, so potent in the
progress of the earth's geological history, began, as far as we know,
with Eozoon.
Whether, then, in questioning our proto-foraminifer, we have reference
to the vital functions of its gelatinous sarcode, to the complexity and
beauty of its calcareous test, or to its capacity for effecting great
material results through the union of individuals, we perceive that we
have to do, not with a low condition of those powers which we designate
life, but with the manifestation of those powers through the means of a
simple organism; and this in a degree of perfection which we, from our
point of view, would have in the first instance supposed impossible.