PEDIGREE AND HISTORY OF THE KINGDOM OF THE PROTISTA.
Special Mode of Carrying out the Theory of Descent in the
Natural System of Organisms.—Construction of Pedigrees.—Descent
of all Many-Celled from Single-Celled Organisms.—Descent of
Cells from Monera.—Meaning of Organic Tribes, or Phyla.—Number
of the Tribes in the Animal and Vegetable Kingdoms.—The
Monophyletic Hypothesis of Descent, or the Hypothesis of one
Common Progenitor, and the Polyphyletic Hypothesis of Descent,
or the Hypothesis of Many Progenitors.—The Kingdom of Protista,
or Primæval Beings.—Eight Classes of the Protista
Kingdom.—Monera, Amœbæ, or Protoplastæ.—Whip-swimmers, or
Flagellata.—Ciliated-balls, or Catallacta.—Labyrinth-streamers,
or Labyrinthuleæ.—Flint-cells, or Diatomeæ.—Mucous-moulds, or
Myxomycetes.—Root-footers (Rhizopoda).—Remarks on the General
Natural History of the Protista: Their Vital Phenomena,
Chemical Composition, and Formation (Individuality and
Fundamental Form).—Phylogeny of the Protista Kingdom
By a careful comparison of the individual and the palæontological
development, as also by the comparative anatomy of organisms, by the
comparative examination of their fully developed structural
characteristics, we arrive at the knowledge of the degrees of their
different structural relationships. By this, however, we at the same
time obtain an insight into their true _blood relationship_, which,
according to the Theory of Descent, is the real reason of the structural
relationship. Hence by collecting, comparing, and employing the
empirical results of embryology, palæontology, and anatomy for
supplementing each other, we arrive at an approximate knowledge of “the
Natural System,” which, according to our views, is the _pedigree_ of
organisms. It is true that our human knowledge, in all things
fragmentary, is especially so in this case, on account of the extreme
incompleteness and defectiveness of the records of creation. However, we
must not allow this to discourage us, or to deter us from undertaking
this highest problem of biology. Let us rather see how far it may even
now be possible, in spite of the imperfect state of our embryological,
palæontological, and anatomical knowledge, to establish a probable
scheme of the genealogical relationships of organisms.
Darwin in his book gives us no answer to these special questions of the
Theory of Descent; at the conclusion he only expresses his conjecture
“that animals have descended from at most only four or five progenitors,
and plants from an equal or less number.” But as these few aboriginal
forms still show traces of relationship, and as the animal and vegetable
kingdoms are connected by intermediate transitional forms, he arrives
afterwards at the opinion “that probably all the organic beings which
have ever lived on the earth have descended from some one primordial
form, into which life was first breathed by the Creator.” Like Darwin,
all other adherents of the Theory of Descent have only treated it in a
general way, and not made the attempt to carry it out specially, and to
treat the “Natural System” actually as the pedigree of organisms. If,
therefore, we venture upon this difficult undertaking, we must take up
independent ground.
Four years ago I set up a number of hypothetical genealogies for the
larger groups of organisms in the systematic introduction to my General
History of Development (Gen. Morph. vol. ii.), and thereby, in fact,
made the first attempt actually to construct the pedigrees of organisms
in the manner required by the theory of development. I was quite
conscious of the extreme difficulty of the task, and as I undertook it
in spite of all discouraging obstacles, I claim no more than the merit
of having made the first attempt and given a stimulus for other and
better attempts. Probably most zoologists and botanists were but little
satisfied with this beginning, and least so in reference to the special
domain in which each one is specially at work. However, it is certainly
in this case much easier to blame than to produce something better, and
what best proves the immense difficulty of this infinitely complicated
task is the fact that no naturalist has as yet supplied the place of my
pedigrees by better ones. But, like all other scientific hypotheses
which serve to explain facts, my genealogical hypotheses may claim to be
taken into consideration until they are replaced by better ones.
I hope that this replacement will very soon take place; and I wish for
nothing more than that my first attempt may induce very many naturalists
to establish more accurate pedigrees for the individual groups, at least
in the special domain of the animal and vegetable kingdom which happens
to be well known to one or other of them. By numerous attempts of this
kind our genealogical knowledge, in the course of time, will slowly
advance and approach more towards perfection, although it can with
certainty be foreseen that we shall never arrive at a complete
pedigree. We lack, and shall ever lack, the indispensable
palæontological foundations. The most ancient records will ever remain
sealed to us, for reasons which have been previously mentioned. The most
ancient organisms which arose by spontaneous generation—the original
parents of all subsequent organisms—must necessarily be supposed to have
been Monera—simple, soft, albuminous lumps, without structure, without
any definite forms, and entirely without any hard and formed parts. They
and their next offspring were consequently not in any way capable of
being preserved in a petrified condition. But we also lack, for reasons
discussed in detail in the preceding chapter, by far the greater portion
of the innumerable palæontological documents, which are really requisite
for a safe reconstruction of the history of animal tribes, or phylogeny,
and for the true knowledge of the pedigree of organisms. If we,
therefore, in spite of this, venture to undertake their hypothetical
construction, we must chiefly depend for guidance on the two other
series of records which most essentially supplement the palæontological
archives. These are ontogeny and comparative anatomy.
If thoughtfully and carefully we consult these most valuable records, we
at once perceive what is exceedingly significant, namely, that by far
the greater number of organisms, especially all higher animals and
plants, are composed of a great number of cells, and that they originate
out of an egg, and that this egg, in animals as well as in plants, is a
single, perfectly simple cell—a little lump of albuminous constitution,
in which another albuminous corpuscle, the cell-kernel, is enclosed.
This cell containing its kernel grows and becomes enlarged. By division
it forms an accumulation of cells, and out of these, by division of
labour (as has previously been described), there arise the numberless
different forms which are presented to us in the fully developed animal
and vegetable species. This immensely important process—which we may
follow step by step, with our own eyes, any day in the embryological
development of any animal or vegetable individual, and which as a rule
is by no means considered with the reverence it deserves—informs us more
surely and completely than all petrifactions could do as to the original
palæontological development of all many-celled organisms, that is, of
all higher animals and plants. For as ontogeny, or the embryological
development of every single individual, is essentially only a
recapitulation of phylogeny, or the palæontological development of its
chain of ancestors, we may at once, with full assurance, draw the simple
and important conclusion, that _all many-celled animals and plants were
originally derived from single-celled organisms_. The primæval ancestors
of man, as well as of all other animals, and of all plants composed of
many cells, were simple cells living isolated. This invaluable secret of
the organic pedigree is revealed to us with infallible certainty by the
egg of animals, and by the true egg-cell of plants. When the opponents
of the Theory of Descent assert it to be miraculous and inconceivable
that an exceedingly complicated many-celled organism could, in the
course of time, have proceeded from a simple single-celled organism, we
at once reply that we may see this incredible miracle at any moment, and
follow it with our own eyes. For the embryology of animals and plants
visibly presents to our eyes in the shortest space of time the same
process as that which has taken place in the origin of the whole tribe
during the course of enormous periods of time.
Upon the ground of embryological records, therefore, we can with full
assurance maintain that all many-celled, as well as single-celled,
organisms are originally descended from simple cells; connected with
this, of course, is the conclusion that the most ancient root of the
animal and vegetable kingdom was common to both. For the different
primæval “original cells” out of which the few different main groups or
tribes have developed, only acquired their differences after a time, and
were descended from a common “primæval cell.” But where did those few
“original cells,” or the one primæval cell, come from? For the answer to
this fundamental genealogical question we must return to the theory of
plastids and the hypothesis of spontaneous generation which we have
already discussed (vol. i. p. 327).
As was then shown, we cannot imagine _cells_ to have arisen by
spontaneous generation, but only _Monera_, those primæval creatures of
the simplest kind conceivable, like the still living Protamœbæ,
Protomyxæ, etc. (vol. i. p. 186, Fig. 1). Only such corpuscules of mucus
without component parts—whose whole albuminous body is as homogeneous in
itself as an inorganic crystal, but which nevertheless fulfills the two
organic fundamental functions of nutrition and propagation—could have
directly arisen out of inorganic matter by autogeny at the beginning (we
may suppose) of the Laurentian period. While some Monera remained at the
original simple stage of formation, others gradually developed into
cells by the inner kernel of the albuminous mass becoming separated from
the external cell-substance. In others, by differentiation of the
outermost layer of the cell-substance, an external covering (membrane,
or skin) was formed round simple cytods (without kernel), as well as
round naked cells (containing a kernel). By these two processes of
separation in the simple primæval mucus of the Moneron body, by the
formation of a kernel in the interior and a covering on the outer
surface of the mass of plasma, there arose out of the original most
simple cytods, or Monera, those four different species of plastids, or
individuals, of the first order, from which, by differentiation and
combination, all other organisms could afterwards develop themselves.
(Compare vol. i. p. 347.)
The question now forces itself upon us, Are all organic cytods and
cells, and consequently also those “original cells” which we previously
considered to be the primary parents of the few great main groups of the
animal and vegetable kingdoms, descended from a single original form of
Moneron, or were there several different organic primary forms, each
traceable to a peculiar independent species of Moneron which originated
by spontaneous generation? In other words, _Is the whole organic world
of a common origin, or does it owe its origin to several acts of
spontaneous generation?_ This fundamental question of genealogy seems at
first sight to be of exceeding importance. But on a more accurate
examination, we shall soon see that this is not the case, and that it is
in reality a matter of very subordinate importance.
Let us now pass on to examine and clearly limit our conception of an
_organic tribe_. By _tribe_, or _phylum_, we understand all those
organisms of whose blood relationship and descent from a common primary
form there can be no doubt, or whose relationship, at least, is most
probable from anatomical reasons, as well as from reasons founded on
historical development. Our tribes, or phyla, according to this idea,
essentially coincide with those few “great classes,” or “main classes,”
of which Darwin also thinks that each contains only organisms related by
blood, and of which, both in the animal and in the vegetable kingdoms,
he only assumes either four or five. In the animal kingdom these tribes
would essentially coincide with those four, five, or six main divisions
which zoologists, since Bär and Cuvier, have distinguished as “main
forms, general plans, branches, or sub-kingdoms” of the animal kingdom.
(Compare vol. i. p. 53.) Bär and Cuvier distinguished only four of them,
namely:—1. The vertebrate animals (Vertebrata); 2. The articulated
animals (Articulata); 3. The molluscous animals (Mollusca); and 4. The
radiated animals (Radiata). At present six are generally distinguished,
since the tribe of the articulated animals is divided into two tribes,
those possessing articulated feet (Arthropoda), and the worms (Vermes);
and in like manner the tribe of radiated animals is subdivided into the
two tribes of the star animals (Echinodermata) and the animal-plants
(Zoophyta). Within each of these six tribes, all the included animals,
in spite of great variety in external form and inner structure,
nevertheless possess such numerous and important characteristics in
common, that there can be no doubt of their blood relationship. The same
applies also to the six great main classes which modern botany
distinguishes in the vegetable kingdom, namely:—1. Flowering plants
(Phanerogamia); 2. Ferns (Filicinæ); 3. Mosses (Muscinæ); 4. Lichens
(Lichenes); 5. Fungi (Fungi); and 6. Water-weeds (Algæ). The last three
groups, again, show such close relations to one another, that by the
name of “Thallus plants” they may be contrasted with the three first
main classes, and consequently the number of phyla, or main groups, of
the vegetable kingdom may be reduced to the number of four. Mosses and
ferns may likewise be comprised as “Prothallus plants” (Prothallophyta),
and thereby the number of plant tribes reduced to three—Flowering
plants, Prothallus plants, and Thallus plants.
Very important facts in the anatomy and the history of development, both
in the animal and vegetable kingdoms, support the supposition that even
these few main classes or tribes are connected at their roots, that is,
that the lowest and most ancient primary forms of all three are related
by blood to one another. Nay, by a further examination we are obliged to
go still a step further, and to agree with Darwin’s supposition, that
even the two pedigrees of the animal and vegetable kingdom are connected
at their lowest roots, and that the lowest and most ancient animals and
plants are derived from a single common primary creature. According to
our view, this common primæval organism can have been nothing but a
Moneron which took its origin by spontaneous generation.
In the mean time we shall at all events be acting cautiously if we avoid
this last step, and assume true blood relationship only within each
tribe, or phylum, where it has been undeniably and surely established by
facts in comparative anatomy, ontogeny, and phylogeny. But we may here
point to the fact that two different fundamental forms of genealogical
hypothesis are possible, and that all the different investigations of
the Theory of Descent in relation to the origin of organic groups of
forms will, in future, tend more and more in one or the other of these
directions. The unitary, or _monophyletic_, hypothesis of descent will
endeavour to trace the first origin of all individual groups of
organisms, as well as their totality, to a single common species of
Moneron which originated by spontaneous generation (vol. i. p. 343). The
multiple, or _polyphyletic_, hypothesis of descent, on the other hand,
will assume that several different species of Monera have arisen by
spontaneous generation, and that these gave rise to several different
main classes (tribes, or phyla) (vol. i. p. 348). The apparently great
contrast between these two hypotheses is in reality of very little
importance. For both the monophyletic and the polyphyletic hypothesis of
descent must necessarily go back to the Monera as the most ancient root
of the one or of the many organic tribes. But as the whole body of a
Moneron consists only of a simple, formless mass, without component
particles, made up of a single albuminous combination of carbon, it
follows that the differences of the different Monera can only be of a
chemical nature, and can only consist in a different atomic composition
of that mucous albuminous combination. But these subtle and complicated
differences of mixture of the infinitely manifold combinations of
albumen are not appreciable by the rude and imperfect means of human
observation and are, consequently, at present of no further interest to
the task we have in hand.
The question of the monophyletic or polyphyletic origin will constantly
recur within each individual tribe, where the origin of a smaller or of
a larger group is discussed. In the vegetable kingdom, for example, some
botanists will be inclined to derive all flowering plants from a single
form of fern, while others will prefer the idea that several different
groups of Phanerogama have sprung from several different groups of
ferns. In like manner, in the animal kingdom, some zoologists will be
more in favour of the supposition that all placental animals are derived
from a single pouched animal; others will be more in favour of the
opposite supposition, that several different groups of placental animals
have proceeded from several different pouched animals. In regard to the
human race itself, some will prefer to derive it from a single form of
ape, while others will be more inclined to the idea that several
different races of men have arisen, independently of one another, out of
several different species of ape. Without here expressing our opinion in
favour of either the one or the other conception, we must, nevertheless,
remark that in general _the monophyletic hypothesis of descent deserves
to be preferred to the polyphyletic hypothesis of descent_. In
accordance with the chorological proposition of a single “centre of
creation” or of a single primæval home for most species (which has
already been discussed), we may be permitted to assume that the original
form of every larger or smaller natural group only originated _once_ in
the course of time, and only in _one part_ of the earth. We may safely
assume this simple original root, that is, the monophyletic origin, in
the case of all the more highly developed groups of the animal and
vegetable kingdoms. (Compare vol. i. p. 353.) But it is very possible
that the more complete Theory of Descent of the future will involve the
polyphyletic origin of very many of the low and imperfect groups of the
two organic kingdoms.
For these reasons I consider it best, in the mean time, to adopt the
_monophyletic hypothesis of descent_ both for the animal and for the
vegetable kingdom. Accordingly, the above-mentioned six tribes, or
phyla, of the animal kingdom must be connected at their lowest root,
and likewise the three or six main classes, or phyla, of the vegetable
kingdom must be traced to a common and most ancient original form. How
the connection of these tribes is to be conceived I shall explain in the
succeeding chapters. But before proceeding to this, we must occupy
ourselves with a very remarkable group of organisms, which cannot
without artificial constraint be assigned either to the pedigree of the
vegetable or to that of the animal kingdom. These interesting and
important organisms are the _primary creatures_, or _Protista_.
All organisms which we comprise under the name of Protista show in their
external form, in their inner structure, and in all their vital
phenomena, such a remarkable mixture of animal and vegetable properties,
that they cannot with perfect justice be assigned either to the animal
or to the vegetable kingdom; and for more than twenty years an endless
and fruitless dispute has been carried on as to whether they are to be
assigned to this or that kingdom. Most of Protista are so small that
they can scarcely, if at all, be perceived with the naked eye. Hence the
majority of them have only become known during the last fifty years,
since by the help of the improved and general use of the microscope
these minute organisms have been more frequently observed and more
accurately examined. However, no sooner were they better known than
endless disputes arose about their real nature and their position in the
natural system of organisms. Many of these doubtful primary creatures
botanists defined as animals, and zoologists as plants; neither of the
two would own them. Others, again, were declared by botanists to be
plants, and by zoologists to be animals; each claimed them. These
contradictions are not altogether caused by our imperfect knowledge of
the Protista, but in reality by their true nature. Indeed, most Protista
present such a confused mixture of several animal and vegetable
characteristics, that each investigator may arbitrarily assign them
either to the animal or vegetable kingdom. Accordingly as he defines
these two kingdoms, and as he looks upon this or that characteristic as
determining the animal or vegetable nature, he will assign the
individual classes of Protista in one case to the animal and in another
to the vegetable kingdom. But this systematic difficulty has become an
inextricable knot by the fact that all more recent investigations on the
lowest organisms have completely effaced, or at least destroyed, the
sharp boundary between the animal and vegetable kingdom which had
hitherto existed, and to such a degree that its restoration is possible
only by means of a completely artificial definition of the two kingdoms.
But this definition could not be made so as to apply to many of the
Protista.
For this and other reasons it is, in the mean time, best to exclude the
doubtful beings from the animal as well as from the vegetable kingdom,
and to comprise them in a third organic kingdom standing midway between
the two others. This intermediate kingdom I have established as the
_Kingdom of the Primary Creatures_ (Protista), when discussing general
anatomy in the first volume of my General Morphology, pp. 191-238. In my
Monograph of the Monera,(15) I have recently treated of this kingdom,
having somewhat changed its limits, and given it a more accurate
definition. Of independent classes of the kingdom Protista, we may at
present distinguish the following:—
1. The still living Monera; 2. The Amœboidea, or Protoplasts; 3. The
Whip-swimmers, or Flagellata; 4. The Flimmer-balls, or Catallacta; 5.
The Tram-weavers, or Labyrinthuleæ; 6. The Flint-cells, or Diatomeæ; 7.
The Slime-moulds, or Myxomycetes; 8. The Ray-streamers, or Rhizopoda.
The most important groups at present distinguishable in these eight
classes of Protista are named in the systematic table on p. 51. Probably
the number of these Protista will be considerably increased in future
days by the progressive investigations of the ontogeny of the simplest
forms of life, which have only lately been carried on with any great
zeal. With most of the classes named we have become intimately
acquainted only during the last ten years. The exceedingly interesting
Monera and Labyrinthuleæ, as also the Catallacta, were indeed discovered
only a few years ago. It is probable also that very numerous groups of
Protista have died out in earlier periods, without having left any
fossil remains, owing to the very soft nature of their bodies. We might
add to the Protista from the still living lowest groups of organisms—the
Fungi; and in so doing should make a very large addition to its domain.
Provisionally we shall leave them among plants, though many naturalists
have separated them altogether from the vegetable kingdom.
_The pedigree of the kingdom Protista_ is still enveloped in the
greatest obscurity. The peculiar combination of animal and vegetable
properties, the indifferent and uncertain character of their relations
of forms and vital phenomena, together with a number of several very
peculiar features which separate most of the subordinate classes sharply
from the others, at present baffle every attempt distinctly to make out
their blood relationships with one another, or with the lowest animals
on the one hand, and with the lowest plants on the other hand. It is not
improbable that the classes specified, and many other unknown classes of
Protista, represent quite independent organic tribes, or phyla, each of
which has independently developed from one, perhaps from various, Monera
which have arisen by spontaneous generation. If we do not agree to this
polyphyletic hypothesis of descent, and prefer the monophyletic
hypothesis of the blood relationship of all organisms, we shall have to
Look upon the different classes of protista as the lower small
off-shoots of the root, springing from the same simple monera root, out
of which arose the two mighty and many-branched pedigrees of the animal
kingdom on the one hand, and of the vegetable kingdom on the other.
(compare pp. 74, 75.) before i enter into this difficult question more
accurately, it will be appropriate to premise something further as to
the contents of the classes of protista given on the next page, and
their general natural history.
SYSTEMATIC SURVEY
_Of the Larger and Smaller Groups of the Kingdom Protista._
----------------+--------------------+------------------+-----------------
_Classes of | _Systematic Name | _Orders of | _A name of a
the Protista | of the Classes_. | Families of the | Genus
Kingdom._ | | Classes._ | as an example._
----------------+--------------------+------------------+-----------------
{ 1. Gymnomonera Protogenes
1. MONERS Monera { 2. Lepomonera Protomyxa
{ 1. Gymnamœbæ Amœba
2. PROTOPLASTS Amœboida { 2. Leptamœbæ Arcella
{ 3. Gregarinæ Monocystis
{ 1. Nudiflagellata Euglena
3. WHIP-SWIMMERS Flagellata { 2. Cilioflagellata Peridinium
4. FLIMMER-BALLS Catallacta 1. Catallacta Magosphæra
5. TRAM-WEAVERS Labyrinthuleæ 1. Labyrinthuleæ Labyrinthula
{ 1. Striata Navicula
6. FLINT-CELLS Diatomea { 2. Vittata Tabellaria
{ 3. Areolata Coscinodiscus
{ 1. Physareæ Æthalium
7. SLIME-MOULDS Myxomycetes { 2. Stemoniteæ Stemonitis
{ 3. Trichiaceæ Arcyria
{ 4. Lycogaleæ Reticularia
{ I. Acyttaria { 1. Monothalamia Gromia
{ { 2. Polythalamia Nummulina
8. RAY-STREAMERS {
OR RHIZOPODS. { II. Heliozoa 1. Heliozoa Actinosphærium
(Root-feet) {
{ { 1. Monocyttaria Cyrtidosphæra
{ III. Radiolaria { 2. Polycyttaria Collosphæra
[Illustration: FIG. 8.—Protamœba primitiva, a fresh-water Moneron, much
enlarged. _A._ The entire Moneron with its form-changing processes. _B._
It begins to divide itself into two halves. _C._ The division of the two
halves is completed, and each now represents an independent individual.]
It will perhaps seem strange that I should here again begin with the
remarkable _Monera_ as the first class of the Protista kingdom, as I of
course look upon them as the most ancient primary forms of all organisms
without exception. Still, what are we otherwise to do with the _still
living Monera_? We know nothing of their palæontological origin, we know
nothing of any of their relations to lower animals or plants, and we
know nothing of their possible capability of developing into higher
organisms. The simple and homogeneous little lump of slime or mucus
which constitutes their entire body (Fig. 8) is the most ancient and
original form of animal as well as of vegetable plastids. Hence it would
evidently be just as arbitrary and unreasonable to assign them to the
animal as it would be to assign them to the vegetable kingdom. In any
case we shall for the present be acting more cautiously and critically
if we comprise the still living Monera—whose number and distribution is
probably very great—as a special and independent class, contrasting them
with the other classes of the kingdom Protista, as well as with the
animal kingdom. Morphologically considered, the Monera—on account of the
perfect homogeneity of the albuminous substance of their bodies, on
account of their utter want of heterogeneous particles—are more closely
connected with anorgana than with organisms, and evidently form the
transition between the inorganic and organic world of bodies, as is
necessitated by the hypothesis of spontaneous generation. I have
described and given illustrations of the forms and vital phenomena of
the still living Monera (Protamœba, Protogenes, Protomyxa, etc.) in my
Monograph of the Monera,(15) and have briefly mentioned the most
important facts in the eighth chapter (vol. i. pp. 183-187). Therefore,
only by way of a specimen, I here repeat the drawing of the fresh-water
Protamœba (Fig. 8). The history of the life of an orange-red _Protomyxa
adrantiaca_, which I observed at Lanzerote, one of the Canary Islands,
is given in Plate I. (see its explanation in the Appendix). Besides
this, I here add a drawing of the form of Bathybius, that remarkable
Moneron discovered by Huxley, which lives in the greatest depths of the
sea in the shape of naked lumps of protoplasm and reticular mucus (vol.
i. p. 344).
[Illustration: FIG. 9.—Bathybius Hæckelii, the “creature of primæval
slime,” from the greatest depths of the sea. The figure, which is
greatly magnified, only shows that form of the Bathybius which consists
of a naked network of protoplasm, without the discoliths and cyatholiths
which are found in other forms of the same Moneron, and which perhaps
may be considered as the products of its secretion.]
The _Amœbæ_ of the present day, and the organisms most closely connected
with them, _Arcellidæ_ and _Gregarinæ_, which we here unite as a second
class of Protista under the name of _Amœboidea_ (Protoplasta), present
no fewer genealogical difficulties than the Monera. These primary
creatures are at present usually placed in the animal kingdom without
its in reality being understood why. For simple naked cells—that is,
shell-less plastids with a kernel—occur as well among real plants as
real animals. The generative cells, for example, in many Algæ (spores
and eggs) exist for a longer or shorter time in water in the form of
naked cells with a kernel, which cannot be distinguished at all from the
naked eggs of many animals (for example, those of the Siphonophorous
Medusæ). (Compare the figure of a naked egg of a bladder-wrack in
Chapter xvii. p. 90.) In reality every naked simple cell, whether it
proceeds from an animal or vegetable body, cannot be distinguished from
an independent Amœba. For an Amœba is nothing but a simple primary cell,
a naked little lump of cell-matter, or plasma, containing a kernel. The
contractility of this plasma, which the free Amœba shows in stretching
out and drawing in its changing processes, is a general vital property
of the organic plasma of all animal as well as of all vegetable
plastids. When a freely moving Amœba, which perpetually changes its
form, passes into a state of rest, it draws itself together into the
form of a globule, and surrounds itself with a secreted membrane. It can
then be as little distinguished from an animal egg as from a simple
globular vegetable cell (Fig. 10 _A_).
[Illustration: FIG. 10.—Amœba sphærococcus, greatly magnified. A
fresh-water Amœba without a contractile vacuole. _A._ The enclosed Amœba
in the state of a globular lump of plasma (_c_) enclosing a kernel and a
kernel-speck (_a_). The simple cell is surrounded by a cyst, or cell
membrane (_d_). _B._ The free Amœba, which has burst and left the cyst,
or cell-membrane. _C._ It begins to divide by its kernel parting into
two kernels, and the cell-substance between the two contracting. _D._
The division is completed, and the cell-substance has entirely separated
into two bodies. (_Da_ and _Db_).]
Naked cells, with kernels, like those represented in Fig. 10 _B_, which
are continuously changing, stretching out and drawing in formless,
finger-like processes, and which are on this account called amœboid, are
found frequently and widely dispersed in fresh water and in the sea;
nay, are even found creeping on land. They take their food in the same
way as was previously described in the case of the Protamœba (vol. i. p.
186). Their propagation by division can sometimes be observed. (Fig. 10
_C_, _D_.) I have described the processes in an earlier chapter (vol. i.
p. 187). Many of these formless Amœbæ have lately been recognized as the
early stages of development of other Protista (especially the
Myxomycetæ), or as the freed cells of lower animals and plants. The
colourless blood-cells of animals, for example, those of human blood,
cannot be distinguished from Amœbæ. They, like the latter, can receive
solid corpuscles into their interior, as I was the first to show by
feeding them with finely divided colouring matters (Gen. Morph. i. 271).
However, other Amœbæ (like the one given in Fig. 10) seem to be
independent “good species,” since they propagate themselves unchanged
throughout many generations. Besides the real, or _naked_, Amœbæ
(Gymnamœbæ), we also find widely diffused in fresh water _case-bearing_
Amœbæ (Lepamœbæ), whose naked plasma body is _partially_ protected by a
more or less solid shell (Arcella), sometimes even by a case (Difflugia)
composed of small stones. Lastly, we frequently find in the body of many
lower animals parasitic Amœbæ (Gregarinæ), which, adapting themselves to
a parasitic life, have surrounded their plasma-body with a delicate
closed membrane.
The simple naked Amœbæ are, next to the Monera, the most important of
all organisms to the whole science of biology, and especially to general
genealogy. For it is evident that the Amœbæ originally arose out of
simple Monera (Protamœbæ), by the important process of segregation
taking place in their homogeneous viscid body—the differentiation of an
inner kernel from the surrounding plasma. By this means the great
progress from a simple cytod (without kernel) into a real cell (with
kernel) was accomplished (compare Fig. 8 _A_ and Fig. 10 _B_). As some
of these cells at an early stage encased themselves by secreting a
hardened membrane, they formed the first vegetable cells, while others,
remaining naked, developed into the first aggregates of animal cells.
The presence or absence of an encircling hard membrane forms the most
important, although by no means the entire, difference of form between
animal and vegetable cells. As vegetable cells even at an early stage
enclose themselves within their hard, thick, and solid cellular shell,
like that of the Amœbæ in a state of rest (Fig. 10 _A_), they remain
more independent and less accessible to the influences of the outer
world than are the soft animal cells, which are in most cases naked, or
merely covered by a thin pliable membrane. But in consequence of this
the vegetable cells cannot combine, as do the animal cells, for the
construction of higher and composite fibrous tracts, for example, the
nervous and muscular tissues. It is probable that, in the case of the
most ancient single-celled organisms, there must have developed at an
early stage the very important difference in the animal and vegetable
mode of receiving food. The most ancient single-celled animals, being
naked cells, could admit solid particles into the interior of their soft
bodies, as do the Amœbæ (Fig. 10 _B_) and the colourless blood-cells;
whereas the most ancient single-celled plants encased by their membranes
were no longer able to do this, and could admit through it only fluid
nutrition (by means of diffusion).
[Illustration: FIG. 11.—A single Whip-swimmer (Euglena striata), greatly
magnified. Above a thread-like lashing whip is visible; in the centre
the round cellular kernel, with its kernel speck.]
The _Whip-swimmers_ (Flagellata), which we consider as a third class of
the kingdom Protista, are of no less doubtful nature than the Amœbæ.
They often show as close and important relations to the vegetable as to
the animal kingdom. Some Flagellata at an early stage, when freely
moving about, cannot be distinguished from real plants, especially from
the spores of many Algæ; whereas others are directly allied to real
animals, namely, to the fringed Infusoria (Ciliata). The Flagellata are
simple cells which live in fresh or salt water, either singly or united
in colonies. The characteristic part of their body is a very movable
simple or compound whip-like appendage (whip, or flagellum) by means of
which they actively swim about in the water. This class is divided into
two orders. Among the fringed whip-swimmers (Cilioflagellata) there
exists, in addition to the long whip, a short fringe of vibrating hairs,
which is wanting in the unfringed whip-swimmers (Nudoflagellata). To the
former belong the flint-shelled yellow Peridinia, which are largely
active in causing the phosphorescence of the sea; to the latter belong
the green Euglenæ, immense masses of which frequently make our ponds in
spring quite green.
[Illustration: FIG. 12.—The Norwegian Flimmer-ball (Magosphæra planula)
swimming by means of its vibratile fringes, as seen from the surface.]
A very remarkable new form of Protista, which I have named
_Flimmer-ball_ (Magosphæra), I discovered only three years ago (in
September, 1869), on the Norwegian coast (Fig. 12), and have more
accurately described in my Biological Studies(15) (p. 137, Plate V.).
Off the island of Gis-oe, near Bergen, I found swimming about, on the
surface of the sea, extremely neat little balls composed of a number
(between thirty and forty) of fringed pear-shaped cells, the pointed
ends of which were united in the centre like radii. After a time the
ball dissolved. The individual cells swarmed about independently in the
water like fringed Infusoria, or Ciliata. These afterwards sank to the
bottom, drew their fringes into their bodies, and gradually changed into
the form of creeping Amœbæ (like Fig 10 _B_). These last afterwards
encased themselves (as in Fig. 10 _A_), and then divided by repeated
halvings into a large number of cells (exactly as in the case of the
cleavage of the egg, Fig. 6, vol. i. p. 299). The cells became covered
with vibratile hairs, broke through the case enclosing them, and now
again swam about in the shape of a fringed ball (Fig. 12). This
wonderful organism, which sometimes appears like a simple Amœba,
sometimes as a single fringed cell, sometimes as a many-celled fringed
ball, can evidently be classed with none of the other Protista, and must
be considered as the representative of a new independent group. As this
group stands midway between several Protista, and links them together,
it may bear the name of _Mediator_, or _Catallacta_.
[Illustration: FIG. 13.—Labyrinthula macrocystis (much enlarged). Below
is a large group of accumulated cells, one of which, on the left, is
separating itself; above are two single cells which are gliding along
the threads of the retiform labyrinth which form their “tramways.”]
The Protista of the fifth class, the _Tram-weavers_, or _Labyrinthuleæ_,
are of a no less puzzling nature; they were lately discovered by
Cienkowski on piles in sea water (Fig. 13). They are spindle-shaped
cells, mostly of a yellow-ochre colour, which are sometimes united into
a dense mass, sometimes move about in a very peculiar way. They form, in
a manner not yet explained, a retiform frame of entangled threads
(compared to a labyrinth), and on the dense filamentous “tramways” of
this frame they glide about. From the shape of the cells of the
Labyrinthuleæ we might consider them as the simplest plants, from their
motion as the simplest animals, but in reality they are neither animals
nor plants.
[Illustration: FIG. 14.—Navicula hippocampus (greatly magnified). In the
middle of the cell the cell-kernel (nucleus) is visible, together with
its kernel speck (nucleolus).]
The _Flint-cells_ (Diatomeæ), a sixth class of Protista, are perhaps the
most closely related to the Labyrinthuleæ. These primary creatures—which
at present are generally considered as plants, although some celebrated
naturalists still look upon them as animals—inhabit the sea and fresh
waters in immense masses, and offer an endless variety of the most
elegant forms. They are mostly small microscopic cells, which either
live singly (Fig. 14), or united in great numbers, and occur either
attached to objects, or glide and creep about in a peculiar manner.
Their soft cell-substance, which is of a characteristic brownish yellow
colour, is always enclosed by a solid and hard flinty shell, possessing
the neatest and most varied forms. This flinty covering is open to the
exterior only by one or two slits, through which the enclosed soft
plasma-body communicates with the outer world. The flinty cases are
found petrified in masses, and many rocks—for example, the Tripoli slate
polish, the Swedish mountain meal, etc.,—are in a great measure composed
of them.
A seventh class of Protista is formed by the remarkable _Slime-moulds_
(Myxomycetes). They were formerly universally considered as plants, as
real Fungi, until ten years ago the botanist De Bary, by discovering
their ontogeny, proved them to be quite distinct from Fungi, and rather
to be akin to the lower animals. The mature body is a roundish bladder,
often several inches in size, filled with fine spore-dust and soft
flakes (Fig. 15), as in the case of the well-known puff-balls
(Gastromycetes). However, the characteristic cellular threads, or hyphæ,
of a real fungus do not arise from the germinal corpuscles, or spores,
of the Myxomycetes, but merely naked masses of plasma, or cells, which
at first swim about in the form of Flagellata (Fig. 11), afterwards
creep about like the Amœbæ (Fig. 10 _B_), and finally combine with
others of the same kind to form large masses of “slime,” or “plasmodia.”
Out of these, again, there arises, by-and-by, the bladder-shaped
fruit-body. Many of my readers probably know one of these plasmodia, the
Æthalium septicum, which in summer forms a beautiful yellow mass of soft
mucus, often several feet in breadth, known by the name of “tan
flowers,” and penetrates tan-heaps and tan-beds. At an early stage these
slimy, freely-creeping Myxomycetes, which live for the most part in damp
forests, upon decaying vegetable substances, bark of trees, etc., are
with equal justice or injustice declared by zoologists to be animals,
while in the mature, bladder-shaped condition of fructification they are
by botanists defined as plants.
[Illustration: FIG. 15.—A stalked fruit-body (spore-bladder, filled with
spores) of one of the Myxomycetes (Physarum albipes) not much enlarged.]
The nature of the _Ray-streamers_ (Rhizopoda), the eighth class of the
kingdom Protista, is equally obscure. These remarkable organisms have
peopled the sea from the most ancient times of the organic history of
the earth, in an immense variety of forms, sometimes creeping at the
bottom of the sea, sometimes swimming on the surface. Only very few live
in fresh water (Gromia, Actinosphærium). Most of them possess solid
calcareous or flinty shells of an extremely beautiful construction,
which can be perfectly preserved in a fossil state. They have frequently
accumulated in such huge numbers as to form mountain masses, although
the single individuals are very small, and often scarcely visible, or
completely invisible to the naked eye. A very few attain the diameter
of a few lines, or even as much as a couple of inches. The name which
the class bears is given because thousands of exceedingly fine threads
of protoplasm radiate from the entire surface of their naked slimy body;
these rays are quasi-feet, or pseudopodia, which branch off like roots
(whence the term Rhizopoda, signifying root-footed), unite like nets,
and are observed continually to change form, as in the case of the
simpler plasmic feet of the Amœboidea, or Protoplasts. These
ever-changing little pseudo-feet serve both for locomotion and for
taking food.
The class of the Rhizopoda is divided into three different legions, viz.
the chamber-shells, or Acyttaria, the sun-animalcules, or Heliozoa, and
the basket-shells, or Radiolaria. The _Chamber-shells_ (Acyttaria)
constitute the first and lowest of these three legions; for the whole of
their soft body consists merely of simple mucous or slimy cell-matter,
or protoplasm, which has not differentiated into cells. However, in
spite of this most primitive nature of body, most of the Acyttaria
secrete a solid shell composed of calcareous earth, which presents a
great variety of exquisite forms. In the more ancient and more simple
Acyttaria this shell is a simple chamber, bell-shaped, tubular, or like
the shell of a snail, from the mouth of which a bundle of plasmic
threads issues. In contrast to these _single-chambered forms_
(Monothalamia), the _many-chambered forms_ (Polythalamia)—to which the
great majority of the Acyttaria belong—possess a house, which is
composed in an artistic manner of numerous chambers. These chambers
sometimes lie in a row one behind the other, sometimes in concentric
circles or spirals, in the form of a ring round a central point, and
then frequently one above another in many tiers, like the boxes of an
amphitheatre. This formation, for example, is found in the nummulites,
whose calcareous shells, of the size of a lentil, have accumulated to
the number of millions, and form whole mountains on the shores of the
Mediterranean. The stones of which some of the Egyptian pyramids are
built consist of such nummulitic limestone. In most cases the chambers
of the shells of the Polythalamia are wound round one another in a
spiral line. The chambers are connected with one another by passages and
doors, like rooms of a large palace, and are generally open towards the
outside by numerous little windows, out of which the plasmic body can
stream or strain forth its little pseudo-feet, or rays of slime, which
are always changing form. But in spite of the exceedingly complicated
and elegant structure of this calcareous labyrinth, in spite of the
endless variety in the structure and the decoration of its numerous
chambers, and in spite of the regularity and elegance of their
execution, the whole of this artistic palace is found to be the secreted
product of a perfectly formless, slimy mass, devoid of any component
parts! Verily, if the whole of the recent anatomy of animal and
vegetable textures did not support our theory of plastids, if all its
important results did not unanimously corroborate the fact that the
whole miracle of vital phenomena and vital forms is traceable to the
active agency of the formless albuminous combinations of protoplasm, the
Polythalamia alone would secure the triumph of that theory. For we may
here at any moment, by means of the microscope, point out the wonderful
fact, first established by Dujardin and Max Schulze, that the formless
mucus of the soft plasma-body, this true “matter of life,” is able to
secrete the neatest, most regular, and most complicated structures. This
secretive skill is simply a result of _inherited adaptation_, and by it
we learn to understand how this same “primæval slime”—this same
protoplasm—can produce in the bodies of animals and plants the most
different and most complicated cellular forms.
It is, moreover, a matter of special interest that the most ancient
organism, the remains of which are found in a petrified condition,
belongs to the Polythalamia. This organism is the “Canadian Life’s-dawn”
(_Eozoon canadense_), which has already been mentioned, and which was
found a few years ago in the Ottawa formation (in the deepest strata of
the Laurentian system), on the Ottawa river in Canada. If we expected to
find organic remains at all in these most ancient deposits of the
primordial period, we should certainly look for such of the most simple
Protista as are covered with a solid shell, and in the organization of
which the difference between animal and plant is as yet not indicated.
We know of but few species of the _Sun-animalcules_ (Heliozoa), the
second class of the Rhizopoda. One species is very frequently found in
our fresh waters. It was observed even in the last century by a
clergyman in Dantzig, Eichhorn by name, and it has been called after
him, Actinosphærium Eichhornii. To the naked eye it appears as a
gelatinous grey globule of mucus, about the size of a pin’s head.
Looking at it through the microscope, we see hundreds or thousands of
fine mucous threads radiating from the central plasma body, and perceive
that the inner layer of its cell-substance is different from the outer
layer, which forms a bladder-like membrane. In consequence of its
structure, this, the little sun-animalcule, although wanting a shell,
really rises above the structureless Acyttaria, and forms the transition
from these to the Radiolaria. The genus Cystophrys is of a nature akin
to it.
The _Basket-shells_ (Radiolaria) form the third and last class of the
Rhizopoda. Their lower forms are closely allied to the Heliozoa and
Acyttaria, whereas their higher forms rise far above them. They are
essentially distinguished from both by the fact that the central part of
their body is composed of many cells, and surrounded by a solid
membrane. This closed “central capsule,” generally of a globular shape,
is covered by a mucous layer of plasma, out of which there radiate on
all sides thousands of exceedingly fine threads, the branching and
confluent so-called pseudopodia. Between these are scattered numerous
yellow cells of unknown function, containing grains of starch. Most
Radiolaria are characterized by a highly developed skeleton, which
consists of flint, and displays a wonderful richness of the neatest and
most curious forms. Sometimes this flinty skeleton forms a simple
trellice-work ball (Fig. 16 _s_), sometimes a marvellous system of
several concentric trelliced balls, encased in one another, and
connected by radial staves. In most cases delicate spikes, which are
frequently branched like a tree, radiate from the surface of the balls.
In other cases the whole skeleton consists of only one flinty star, and
is then generally composed of twenty staves, distributed according to
definite mathematical laws, and united in a common central point. The
skeletons of other Radiolaria again form symmetrical many-chambered
structures, as in the case of the Polythalamia. Perhaps no other group
of organisms develop in the formation of their skeletons such an amount
of various fundamental forms, such geometrical regularity, and such
elegant architecture. Most of the forms as yet discovered, I have given
in the atlas accompanying my Monograph of the Radiolaria.(23) Here I
shall only give as an example the picture of one of the simplest forms,
the _Cyrtidosphæra echinoides_ of Nice. The skeleton in this case
consists only of a simple trelliced ball (_s_), with short radial spikes
(_a_), which loosely surround the central capsule (_c_). Out of the
mucous covering, enclosing the latter, radiate a great number of
delicate little pseudopodia (_p_), which are partly drawn back
underneath the shell, and fused into a lumpy mass of mucus. Between
these are scattered a number of yellow cells (_l_).
[Illustration: FIG. 16.—Cyrtidosphæra echinoides, 400 times enlarged.
_c._ Globular central capsule. _s._ Basket-work of the perforated flinty
shell. _a._ Radial spikes, which radiate from the latter. _p._ The
pseudo-feet radiating from the mucous covering surrounding the central
capsule. _l._ Yellow globular cells, scattered between the latter,
containing grains of starch.]
Most Acyttaria live only at the bottom of the sea, on stones and
seaweeds, or creep about in sand and mud by means of their pseudopodia,
but most Radiolaria swim on the surface of the sea by means of long
pseudopodia extending in all directions. They live together there in
immense numbers, but are mostly so small that they have been almost
completely overlooked, and have only become accurately known during the
last fourteen years. Certain Radiolaria living in communities
(Polycyttaria) form gelatinous lumps of some lines in diameter. On the
other hand, most of those living isolated (Monocyttaria) are invisible
to the naked eye; but still their petrified shells are found accumulated
in such masses that in many places they form entire mountains; for
example, the Nicobar Islands in the Indian Archipelago, and the Island
of Barbadoes in the Antilles.
As most readers are probably but little acquainted with the eight
classes of the Protista just mentioned, I shall now add some further
general observations on their natural history. The great majority of all
Protista live in the sea, some swimming freely on the surface, some
creeping at the bottom, and others attached to stones, shells, plants,
etc. Many species of Protista also live in fresh water, but only a very
small number on dry land (for example, Myxomycetes and some
Protoplasta). Most of them can be seen only through the microscope,
except when millions of individuals are found accumulated. Only a few of
them attain a diameter of some lines, or as much as an inch. What they
lack in size of body they make up for by producing astonishing numbers
of individuals, and they very considerably influence in this way the
economy of nature. The imperishable remains of dead Protista, for
instance, the flinty shells of the Diatomeæ and Radiolaria and the
calcareous shells of the Acyttaria, often form large rock masses.
In regard to their _vital phenomena_, especially those of nutrition and
propagation, some Protista are more allied to plants, others more to
animals. Both in their mode of taking food and in the chemical changes
of their living substance, they sometimes more resemble the lower
animals, at others the lower plants. _Free locomotion_ is possessed by
many Protista, while others are without it; but this does not constitute
a characteristic distinction, as we know of undoubted animals which
entirely lack free locomotion, and of genuine plants which possess it.
All Protista have a _soul_—that is to say, are “animate”—as well as all
animals and all plants. The soul’s activity in the Protista manifests
itself in their _irritability_, that is, in the movements and other
changes which take place in consequence of mechanical, electrical, and
chemical irritation of their contractile protoplasm. Consciousness and
the capability of will and thought are probably wanting in all Protista.
However, the same qualities are in the same degree also wanting in many
of the lower animals, whereas many of the higher animals in these
respects are scarcely inferior to the lower races of human beings. In
the Protista, as in all other organisms, the activities of the soul are
traceable to molecular motions in the protoplasm.
The most important _physiological characteristic_ of the kingdom
Protista lies in the exclusively _non-sexual propagation_ of all the
organisms belonging to it. The higher animals and plants multiply almost
exclusively in a sexual manner. The lower animals and plants multiply
also, in many cases, in a non-sexual manner, by division, the formation
of buds, the formation of germs, etc. But sexual propagation almost
always exists by the side of it, and often regularly alternates with it
in succeeding generations (Metagenesis, vol. i. p. 206). All Protista,
on the other hand, propagate themselves exclusively in a non-sexual
manner, and in fact, the distinction of the two sexes among them has not
been effected—there are neither male nor female Protista.
The Protista in regard to their vital phenomena stand midway between
animals and plants, that is to say, between their lowest forms; and the
same must be said in regard to the _chemical composition_ of their
bodies. One of the most important distinctions between the chemical
composition of animal and vegetable bodies consists in the
characteristic formation of the skeleton. The skeleton, or the solid
scaffolding of the body in most genuine plants, consists of a substance
called cellulose, devoid of nitrogen, but secreted by the nitrogenous
cell-substance, or protoplasm. In most genuine animals, on the other
hand, the skeleton generally consists either of nitrogenous combinations
(chitin, etc.) or of calcareous earth. In this respect some Protista are
more like plants, others more like animals. In many of them the skeleton
is principally or entirely formed of calcareous earth, which is met with
both in animal and vegetable bodies. But the active vital substance in
all cases is the mucous protoplasm.
In regard to the _form_ of the Protista, it is to be remarked that the
_individuality_ of their body almost always remains at an extremely low
stage of development. Very many Protista remain for life simple plastids
or individuals of the first order. Others, indeed, form colonies or
republics of plastids by the union of several individuals. But even
these higher individuals of the second order, formed by the combination
of simple plastids, for the most part remain at a very low stage of
development. The members of such communities among the Protista remain
very similar one to another, and never, or only in a slight degree,
commence a division of labour, and are consequently as little able to
render their community fit for higher functions as are, for example, the
savages of Australia. The community of the plastids remains in most
cases very loose, and each single plastid retains in a great measure its
own individual independence.
A second structural characteristic, which next to their low stage of
individuality especially distinguishes the Protista, is the low stage of
development of their stereometrical fundamental forms. As I have shown
in my theory of fundamental forms (in the fourth book of the General
Morphology), a definite geometrical fundamental form can be pointed out
in most organisms, both in the general form of the body and in the form
of the individual parts. This ideal fundamental form, or type, which is
determined by the number, position, combination, and differentiation of
the component parts, stands in just the same relation to the _real_
organic form as the ideal geometrical fundamental form of crystals does
to their imperfect _real_ form. In most bodies and parts of the bodies
of animals and plants this fundamental form is a pyramid. It is a
regular pyramid in the so-called “regular radiate” forms, and an
irregular pyramid in the more highly differentiated, so-called
“bilaterally symmetrical” forms. (Compare the plates in the first volume
of my General Morphology, pp. 556-558.) Among the Protista this
pyramidal type, which prevails in the animal and vegetable kingdom, is
on the whole rare, and instead of it we have either quite irregular
(amorphous) or more simple, regular geometrical types; especially
frequent are the sphere, the cylinder, the ellipsoid, the spheroid, the
double cone, the cone, the regular polygon (tetrahedron, hexahedron,
octahedron, dodecahedron, icosahedron), etc. All the fundamental forms
of the pro-morphological system, which are of a low rank in that system,
prevail in the Protista. However, in many Protista there occur also the
higher, regular, and bilateral types, fundamental forms which
predominate in the animal and vegetable kingdoms. In this respect some
of the Protista are frequently more closely allied to animals (as the
Acyttaria), others more so to plants (as the Radiolaria).
With regard to the _palæontological development of the kingdom
Protista_, we may form various, but necessarily very unsafe,
genealogical hypotheses. Perhaps the individual classes of the kingdom
are independent tribes, or phyla, which have developed independently of
one another and independently of the animal and the vegetable kingdoms.
Even if we adopt the monophyletic hypothesis of descent, and maintain a
common origin from a single form of Moneron for all organisms, without
exception, which ever have lived and still live upon the earth, even in
this case the connection of the neutral Protista on the one hand with
the vegetable kingdom, and on the other hand with the animal kingdom,
must be considered as very vague. We must regard them (compare p. 74) as
lower off-shoots which have developed directly out of the root of the
great double-branched organic pedigree, or perhaps out of the lowest
tribe of Protista, which may be supposed to have shot up midway between
the two diverging high and vigorous trunks of the animal and vegetable
kingdoms. The individual classes of the Protista, whether they are more
closely connected at their roots in groups, or only form a loose bunch
of root offsets, must in this case be regarded as having nothing to do
either with the diverging groups of organisms belonging to the animal
kingdom on the right, or to the vegetable kingdom on the left. They must
be supposed to have retained the original simple character of the common
primæval living thing more than have genuine animals and genuine plants.
But if we adopt the polyphyletic hypothesis of descent, we have to
imagine a number of organic tribes, or phyla, which all shoot up by
spontaneous generation out of the same ground, by the side of and
independent of one another. (Compare p. 75.) In that case numbers of
different Monera must have arisen by spontaneous generation whose
differences would depend only upon slight, to us imperceptible,
differences in their chemical composition, and consequently upon
differences in their capability of development. A small number of Monera
would then have given origin to the animal kingdom, and, again, a small
number would have produced the vegetable kingdom. Between these two
groups, however, there would have developed, independently of them, a
large number of independent tribes, which have remained at a lower stage
of organization, and which have neither developed into genuine plants
nor into genuine animals.
A safe means of deciding between the monophyletic and polyphyletic
hypotheses is as yet quite impossible, considering the imperfect state
of our phylogenetic knowledge. The different groups of Protista, and
those lowest forms of the animal kingdom and of the vegetable kingdom
which are scarcely distinguishable from the Protista, show such a close
connection with one another and such a confused mixture of
characteristics, that at present any systematic division and arrangement
of the groups of forms seem more or less artificial and forced. Hence
the attempt here offered must be regarded as entirely provisional. But
the more deeply we penetrate into the genealogical secrets of this
obscure domain of inquiry, the more probable appears the idea that the
vegetable kingdom and the animal kingdom are each of independent origin,
and that midway between these two great pedigrees a number of other
independent small groups of organisms have arisen by repeated acts of
spontaneous generation, which on account of their indifferent neutral
character, and in consequence of their mixture of animal and vegetable
properties, may lay claim to the designation of independent Protista.
II. III.
=Vegetable Kingdom= =Animal Kingdom=
Plantæ _Animalia_
/--------^----------\ /-------------------------------^------------\
Flowering Plants Vertebrate Animals
_Phanerogamia_ _Vertebrata_
| \-----v-------/
| |
| |
| Articulated Animals |
| _Arthropoda_ |
| \-----v------/ |
| | |
| | |
| Star-fishes | | Molluscous Animals
Ferns _Echinoderma_ | | _Mollusca_
_Filicinæ_ \-----v------/ | | \-----v------/
| | | | |
| | | | |
| | | | |
| | | | |
Mosses \-------------------v---------------/
_Muscinæ_ Lichens Worms
| _Lichenes_ _Vermes_
| | |
| | |
| | Animal-trees |
| | _Zoophytes_ |
—— Fungi | |
_Algæ_ _Fungi_ | |
| | | |
| | | |
\-------v-----/ \-----v---/
=Neutral=
=Primæval Plants= =Primæval Creatures= =Primæval Animals=
Protophyta Protista Protozoa
\-----v------/ \-----v------/ \-----v------/
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Vegetable Monera Neutral Monera Animal Monera
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=Archigonic Monera=
(Pieces of Protoplasm which have originated by Spontaneous Generation)
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POLYPHYLETIC PEDIGREE.
II. I. III.
=Vegetable= =Protista= =Animal=
=Kingdom= =Kingdom= =Kingdom=
Vegetabilia Protista Animalia
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| /-----------------------------------^--------------------------------\ |
| Slime-moulds, |
| or |
| Mucous Fungi Ray-streamers |
| _Myxomycetes_ _Rhizopoda_ |
| \-----v------/ \-----v------/ |
| | | |
| | Flint-cells | Flimmer-balls |
| | _Diatomæ_ | _Catallacta_ |
| | \-----v------/ | \-----v------/ |
| | | | | |
| | | Whip-swimmers | | |
| | | _Flagellata_ | | |
| | | \-----v------/ | | |
| | | | | | |
| | | Tram-weavers | | | |
| | | _Labyrinthulea_ | | | |
| | | \-----v------/ | | | |
| | | | | | | |
| | | | Amœbæ, | | | =Primæval=
=Primæval Plants= | | | or | | | =Animals=
Protophyta | | | Protoplasta | | | Protozoa
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=Vegetable= | | | =Neutral= | | | =Animal=
=Monera= | | | =Monera= | | | =Monera=
| | | | | | † | † † | † |
† | | † | | † | | † | | | | † | |† | †
|† | † | †| | † | |† | † | | | | |†| | | ||† | † |†
||† | |† | || | | | || | |† | |†| | |||†| | |||† | | ||
†|||† | †||† | ||† | †|† | ||† | ||† | ||| | ||||| | |||| | |†||†
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N.B.—The lines marked with a † indicate extinct tribes of Protista,
which have arisen independently by repeated acts of Spontaneous Generation.
Thus, if we assume one entirely independent trunk for the vegetable
kingdom, and a second for the animal kingdom, we may set up a number of
independent stems of Protista, each of which has developed, quite
independently of other stems and trunks, from a special archigonic form
of Monera. In order to make this relation more clear, we may imagine the
whole world of organisms as an immense meadow which is partially
withered, and upon which two many-branched and mighty trees are
standing, likewise partially withered. The two great trees represent the
animal and vegetable kingdoms, their fresh and still green branches the
living animals and plants; the dead branches with withered leaves
represent the extinct groups. The withered grass of the meadow
corresponds to the numerous extinct tribes, and the few stalks, still
green, to the still living phyla of the kingdom Protista. But the common
soil of the meadow, from which all have sprung up, is primæval by
protoplasm.