JEAN BAPTISTE DE MONET, CHEVALIER DE LAMARCK, was born on
August 1, 1744, in Picardy, where his father owned land. Originally
educated for the Church, he soon enlisted, and distinguished himself
in active service. Owing to an accident affecting his health, the
young Lieutenant gave up the military career, and, without means,
studied medicine and natural sciences at Paris. In 1778 appeared his
'Flore française.' In 1793 he was appointed to a Chair of Zoology at
the newly-formed Musée d'Histoire Naturelle. He had the misfortune to
become gradually blind, and the last years of his life were spent amid
straitened circumstances. He died in 1829.
In 1794 Lamarck divided the whole animal kingdom into vertebrate and
invertebrate animals, and founded successively the groups of Crustacea,
Arachnida, Annelida, and Radiata. Between 1816 and 1822 he published
his celebrated 'Histoire naturelle des Animaux sans Vertèbres.'
His most famous work is the 'Philosophie zoologique,' 1809.
Assuming the spontaneous origin of life, he propounded the doctrine
that all animals and plants have arisen from low forms through
incessant modifications and changes. In this respect he was in absolute
opposition to Cuvier, who upheld the immutability of species, and did
his best by absolute silence to suppress the spread of the new doctrine.
Lamarck has explained his views of transformism chiefly in the seventh
chapter of the first volume of his 'Philosophie zoologique.'
Organisms strive to accommodate or adapt themselves to new
circumstances, or to satisfy new requirements--_e.g._, climate, mode
of procuring food, escape from enemies. The continued function of
parts of an organism changes the old and produces new organs. The
acquirements are inherited by the offspring, and thus are produced the
more complicated from simpler organisms. Continued disuse brings about
degeneration and ultimate loss of an organ.
Lamarck consequently sees in the adaptability, or power of adaptation,
which he assumes for all living matter the ultimate cause of variation;
and, as he was certainly the first to point out that acquired
characters are inherited by the progeny, he has given a working
explanation of Evolution.
But his doctrine did not spread--partly because he was misunderstood.
His theory, that a new want, by making itself felt, exacts from the
animal new exertions, perhaps from parts hitherto not used, until the
want is satisfied--this way of putting it sounds too teleological
to explain the yearned-for change in a mechanical or natural way.
Moreover, many of his examples lacked the exact basis of experiment
and observation necessary for their acceptance. Witness that of the
neck of the giraffe,--a never-failing source of ridicule to men who
cannot see the deeper purpose underlying the well-meant attempt at
an explanation, which failed from want of complete knowledge of the
intricate circumstances.
However, the theory of transformism was, so to speak, in the air;
and various authors have written on the subject, filling the gap
between Lamarck and Darwin, especially Goethe, Treviranus, Leopold
von Buch, and Herbert Spencer. But it is Darwin's immortal merit to
have opened our eyes by his theory of natural selection, which is, at
least, the first attempt to explain some of the causes and incidents
of organic Evolution in a natural mechanical way. Moreover, he was
the first clearly to express the fundamental principles of the theory
of descent, to elaborate what had been at best a general sketch of an
ill-defined problem, and to enter into detail, supported by a host
of painstaking observations, the making of which had taken him half a
lifetime. Darwin, without going further than cursorily into the causes
of variation, argued as follows: We know that variations do occur
in every kind of living creatures. Some of these variations lead to
something, while others do not. An enormously greater number of animals
and plants are born than reach maturity and can in their turn continue
the race. What is the regulating factor? His answer is, The struggle
for existence--in other words, the weeding out of the less fit, or
rather of the owners of those variations which are not so well adapted
to their surroundings.
For 'adapted' we had better read 'adaptable,' because a variation which
does not answer, which cannot be made use of, or, still more notably,
is a hindrance or disadvantage, does not become an adapted feature.
There is often a confusion between adaptation as an accomplished
fact, a feature, or resultant condition, and adaptation as the mode
of fitting the organism to, or making the best of, the prevailing
surroundings or circumstances.
ÉTIENNE GEOFFROY SAINT-HILAIRE was born in 1772 at Étampes,
Seine-et-Oise. He was originally brought up for the Church; but when
already ordained he attended lectures on natural science and medicine
in Paris. He managed to get the place of assistant in the Musée
d'Histoire Naturelle; he became Professor of Zoology in 1793, and took
the opportunity of encouraging young Cuvier. Later he became Professor
of Zoology of the Faculté des Sciences, and in 1818 he published his
remarkable 'Philosophie anatomique.' He died in 1844.
He had conceived the 'unity of organic composition,' meaning that there
is only one plan of construction,--the same principle, but varied in
its accessory parts. In 1830, when Geoffroy proceeded to apply to the
Invertebrata his views as to the uniformity of animal composition,
he found a vigorous opponent in Cuvier. Geoffroy, like Goethe, held
that there is in Nature a law of compensation, or balancing of growth,
so that if one organ take on an excess of development, it is at the
expense of another part; and he maintained that, since Nature takes no
sudden leaps, even organs which are superfluous in any given species,
if they have played an important part in other species of the same
family, are retained as rudiments, which testify to the permanence
of the general plan of creation. It was his conviction that, owing
to the conditions of life, the same forms had _not_ been perpetuated
since the origin of all things, although it was not his belief that
existing species were becoming modified. Cuvier, on the other hand,
maintained the absolute invariability of species, which, he declared,
had been created with regard to the circumstances in which they were
placed, each organ contrived with a view to the function it had
to fulfil,--thus putting the effect for the cause ('Encyclopædia
Britannica,' 9th edition, vol. xxi., p. 171).
GEORGE CUVIER was born in 1769 at Montbéliard, in the department of
Doubs, which at that time belonged to Württemberg. He was educated at
Stuttgart, and studied political economy. While acting as private tutor
to a French family in France he followed his favourite pursuit, the
study of natural sciences. Geoffroy Saint-Hilaire heard of him, and
appointed him assistant in the department of comparative anatomy in the
Musée d'Histoire Naturelle. In 1799 he was elected Professor of Natural
History at the Collège de France, and soon after he became Perpetual
Secretary of the Institut National. In 1831, a year before his death,
Louis Philippe raised him to the rank of a peer of France.
Cuvier was the first to indicate the true principle upon which the
natural classification of animals should be based--namely, their
structure. It is the study of the anatomy of the creatures and their
comparison which affords the only sound basis of a classification.
The work which had the greatest influence upon the scientific public
is his 'Règne animal distribué d'après son Organisation,' 1817. The
system which he propounded in this book gradually came to have almost
world-wide fame, and, in spite of its many obvious deficiencies, still
lingers in some of our most recent text-books.
A standard work is his 'Leçons d'Anatomie comparée,' and, in truth, he
is the founder of that kind of comparative anatomy which was brought
to such a high state by his pupil, the late Sir Richard Owen. Cuvier
discovered the law of 'correlation of growth,' and was the first to
apply this law to the reconstruction of animals from fragments: see his
monumental work entitled 'Recherches sur les Ossemens fossiles,' 1812.
Cuvier, however, as a strict matter-of-fact man, was incapable of
appreciating the speculative conclusions which were drawn by his
contemporaries Saint-Hilaire and Lamarck. On the contrary, he firmly
stuck to the doctrine of the immutability of species; and, in order to
account for the existence of animals whose kind exists no longer, he
invented the famous doctrine of successive cataclysms.
KARL ERNST VON BAER was born in 1792 in Esthonia, studied at Dorpat
and then at Würzburg, where Döllinger introduced him to comparative
anatomy. For a few years he was a _Privat-docent_ at Berlin; then he
went to Königsberg as Professor of Zoology and Embryology. In 1834
he became an Academician at St. Petersburg, where for many years he
was occupied with the most varied studies, chiefly geographical and
ethnological. The last years of his long, active life he spent in
contemplative retirement on his paternal estate, and he died at Dorpat
in 1876.
While still at Würzburg he induced his friend Pander, a young man
of means, to study the development of the chick; and Pander was the
first to start the theory of the germinal layers from which all the
organs arise. Baer, however, continued these researches in Königsberg,
and after nine years' labour produced his epoch-making work, 'Ueber
Entwicklungsgeschichte der Thiere: Beobachtung und Reflexion,'
Königsberg, 1828. Nine years later he completed the second volume.
He established upon a firm basis the theory of the germinal layers,
and by further 'reflexions' arrived at the elucidation of some of the
most fundamental laws of biology. For example, in the first volume
he made the following prophetic statement: 'Perhaps all animals are
alike, and nothing but hollow globes at their earliest developmental
beginning. The farther back we trace their development, the more
resemblance we find in the most different creatures. And this leads to
the question whether at the beginning of their development all animals
are essentially alike, and referable to one common ancestral form.
Considering that the "germ" (which at a certain stage appears in the
shape of a hollow globe or bag) is the undeveloped animal itself, we
are not without reason for assuming that the common fundamental form is
that of a simple vesicle, from which every animal is evolved, not only
theoretically, but historically.'
This statement is all the more wonderful when we consider that the
cells, the all-composing individual units, were not discovered until
ten years later.
In 1829 Baer discovered the human egg, and later the chorda dorsalis.
In an address delivered in 1834, entitled 'The Most Universal Law
of Nature in all Development,' he explained that only from a most
superficial point of view can the various species be looked upon as
permanent and immutable types; that, on the contrary, they can be
nothing but passing stages, or series of stages, of development, which
have been evolved by transformation out of common ancestral forms.
JOHANNES MUELLER, born at Coblenz in 1801, established himself
as _Privat-docent_ at Bonn, where in 1830 he became Professor of
Physiology. In 1833 he accepted the Chair of Anatomy and Physiology at
Berlin, where he died in 1858.
He was one of the most distinguished physiologists and comparative
anatomists. By summarizing the labours and discoveries already made in
the field of physiology, by reducing them to order, and abstracting the
general principles, he became the founder of modern physiology. But
he was scarcely less distinguished by his researches in comparative
anatomy. His 'Vergleichende Anatomie der Myxinoiden,' in _Abhandlungen
der Berliner Akademie_, 1835-45, and 'Ueber die Grenzen der Ganoiden'
(_ibid._, 1846), are standard works of lasting value.
Mueller exercised a stimulative influence as a teacher. Many well-known
men--such as Helmholtz, Gegenbaur, Bruecke the physiologist, Guenther
the zoologist, Virchow the pathologist, Koelliker and Haeckel--have
been his pupils.
RUDOLPH VIRCHOW was born in 1821 at Schievelbein, a small
town in Eastern Pomerania. He studied medicine in Berlin as a pupil
of Johannes Mueller, and went in 1849 to Würzburg, where, under the
influence of Koelliker, and Leydig the pathologist, he laid the
foundation of an entirely new branch of medical science--that of
'cellular pathology.' Since 1856 he has filled the principal Chair of
Pathology at Berlin. In 1892 he received the Copley medal of the Royal
Society.
'His contributions to the study of morbid anatomy have thrown light
upon the diseases of every part of the body; but the broad and
philosophical view he has taken of the processes of pathology has
done more than his most brilliant observations to make the science of
disease.
'In pathology, strictly so called, his two great achievements--the
detection of the cellular activity which lies at the bottom of
all morbid as well as normal physiological processes, and the
classification of the important group of new growths on a natural
histological basis--have each of them not only made an epoch in
medicine, but have also been the occasion of fresh extension of science
by other labourers' (Proc. Royal Soc., 1892).
Virchow has not confined himself to medicine. He takes the keenest
interest in anthropology and ethnology, on which subjects he has
contributed many papers. Together with his colleagues Helmholtz the
physicist, and Du Bois Reymond the physiologist, he has taken a leading
place in the spreading of natural science; but, unfortunately, he
did not take to the doctrine of Evolution, and for the last thirty
years has been its declared antagonist, rarely missing an opportunity
of denouncing everything but descriptive anatomy and zoology as the
unsound speculations of dreamers. This has on more than one occasion
brought him into sharp conflict with Haeckel. His activity is
astonishing, especially if it be remembered that Virchow has for many
years been one of the most conspicuous leaders of the Progressists and
Radicals in the German Parliament and Berlin town-council.
EDWARD DRINKER COPE was born at Philadelphia, Pa. After studying at
several Continental Universities, especially at Heidelberg, he became
first Professor of Natural Science at Haverford College, and later
Professor of Geology and Mineralogy. He died at an early age in 1897.
As a member of various geological expeditions and other surveys, he
explored chiefly Kansas, Wyoming, and Colorado; and he published many
most suggestive papers on the fossil vertebrate fauna of North America,
and on classification especially of Amphibia and Reptiles.
Among works of a more general philosophical scope may be mentioned 'The
Origin of the Fittest,' 1887, and his latest work, 'The Primary Factors
of Organic Evolution,' 1896.
ALBERT VON KOELLIKER, born in 1817, became Professor of Anatomy at
Würzburg. His earlier studies and discoveries contributed considerably
to the systematic development of the cell theory. In 1844 he observed
the division and further multiplication of the original egg cell. Next
year he showed the continuity between nerve cells and nerve fibres in
the Vertebrata; later, that the non-striped or smooth muscular tissue
is composed of cellular elements. He demonstrated that the Gregarinæ
are unicellular creatures. In 1852 he went with his younger friend
Gegenbaur to Messina, where he studied especially the development
of the Cephalopoda (cuttlefishes and allies); and he produced a
magnificent work on Alcyonaria, Medusæ, and other allied forms. He
elucidated the development of the vertebral column, especially with
reference to the notochord.
In 1848 he founded, together with Th. von Siebold, the famous
_Zeitschrift für wissenschaftliche Zoologie_.
A standard work on mammalian embryology is his 'Entwicklungsgeschichte
des Menschen und der höheren Thiere,' a text-book of which the second
edition appeared in 1879.
At the anniversary meeting of 1897 he received the Copley medal, the
highest honour which the Royal Society can bestow.
CARL GEGENBAUR was born on August 21, 1826, in Bavaria. He studied
medicine and kindred subjects in Würzburg, and as a pupil of Johannes
Mueller in Berlin.
In 1852 he went with Koelliker to Messina to study the structure and
development of the marine fauna. Important papers on Siphonophora,
Echinoderms, Pteropoda, and, later, Hydrozoa and Mollusca, were the
result. Soon after his return he was offered the chair of Anatomy at
Jena, and at this retired spot he produced his most important works,
devoting himself more and more to the study of the Vertebrata. Since
1875 he has held the Chair of Anatomy at Heidelberg.
In 1859 he published his 'Principles of Comparative Anatomy'; but in
1870 he remodelled it completely, the theory of descent being the
guiding principle. These 'Grundzüge' were followed by a somewhat more
condensed 'Grundriss,' the second edition of which was published
in 1878, and has been translated into French and English. In the
meantime he had broken new ground by the development and treatment of
certain problems concerning the composition and origin of the limbs,
the shoulder-girdle and the skull, researches which are embodied in
his 'Untersuchungen zur vergleichenden Anatomie der Wirbelthiere,'
1864-65-72.
In 1883 he brought out a text-book on human anatomy. This also marked
a new epoch, because for the first time, not only the nomenclature,
but also the general treatment of human anatomy, was put upon a firm
comparative anatomical basis. The success of this work is indicated by
the fact that it reached the sixth edition in 1897.
Lastly, in 1898, appeared the first volume of what may be called his
crowning work, 'Vergleichende Anatomie der Wirbelthiere.'
Gegenbaur is universally recognised, not only as the greatest living
comparative anatomist, but also as the founder of the modern side of
this science, by having based it on the theory of descent.
In 1896 he received from the Royal Society the Copley medal 'for
his pre-eminence in the science of comparative anatomy or animal
morphology.'
His marvellously powerful influence as a teacher and investigator has
made Heidelberg a centre whence many pupils have spread his teaching,
and above all his method of research.
ERNST HEINRICH HAECKEL was born on February 16, 1834, at Potsdam. He
carried out his academical studies alternately at Berlin and Würzburg,
attracted by such men as Johannes Mueller, Koelliker, and Virchow.
For years he was undecided what his career should be, whether that
of botanist, collector, or geographical traveller. Certainly that of
medicine attracted him least, although in deference to his father's
wishes he qualified and settled down for a year's practice in Berlin.
As he himself has told us, he might perhaps have proved rather
successful as a physician, to judge from the fact that he did not lose
a single patient. But 'I had only three patients all told, and the
reason of this is perhaps that I had given on my plate the hours of
consultation as from 5 to 6 _a.m._'
During the year 1859 he travelled as medical man and artist in Sicily.
In 1861 he was induced by Gegenbaur, whose acquaintance he had made in
Würzburg, to establish himself as a _Privat-docent_ for comparative
anatomy in Jena. And there he has remained ever since, filling the
Chair of Zoology, and having declined several much more tempting offers
from the Universities of Würzburg, Vienna, Strassburg, and Bonn.
Within one year, 1865, he wrote the two volumes of his 'Generelle
Morphologie der Organismen,' as he himself relates, in order to master
his sorrow over the loss of his first wife. But he broke down, and went
to the Canaries to recruit health and strength. The 'Morphologie,'
which has long been out of print,[25] made scarcely any impression. It
was ignored, probably because he had placed the old-fashioned study of
zoology and morphology upon a thoroughly Darwinistic basis.
[25] That this great work is now comparatively rare, although still
in the second-hand market, may perhaps be urged in excuse of the
fact of so many attempts made by many authors, both professional and
amateur, to find fault with or to explain the principles of adaptation,
variation, heredity, cænogenesis, phylogeny, etc., in complete
ignorance that all these and many more fundamental questions were fully
discussed more than thirty years ago in the 'Generelle Morphologie.'
On the advice of his friend Gegenbaur, he gave a more popularly
written abstract of his 'Generelle Morphologie'--in fact, the
substance of a series of his lectures--in the shape of his 'Natürliche
Schöpfungsgeschichte.' This 'History of Natural Creation,' which
in 1898 has reached the ninth edition (first edition translated
into English in 1873), had the desired effect. So also had his
'Anthropogenie oder Entwicklungsgeschichte des Menschen,' the fourth
edition of which appeared in 1891.
It was a lucky coincidence that Haeckel had just finished his
preliminary academical studies, was entirely at leisure, and
undetermined to which branch of natural science he should devote his
genius, when Darwin's great work was given to the world. Haeckel
embraced the new doctrine fervently, and, as Huxley was doing in
England, he spread it and fought for it with ever-increasing vigour in
Germany.
With marvellous vigour and quickness of perception he applied the
principles of Evolution or the theory of descent to the whole organic
world, and not only opened entirely new vistas for the study of
morphology, but also worked them out and fixed them. He was the first
to draw up pedigrees of the various larger groups of animals and
plants, filling the gaps by fossils or with hypothetical forms (the
necessary existence of which he arrived at by logical deductions);
and thus he reconstructed the first universal pedigree, a gigantic
ancestral tree, from the simple unicellular Amoeba to Man. Of course
these pedigrees were entirely provisional, as he himself has over and
over again avowed; but they are, nevertheless, the ideal which all
systematists and morphologists working upon the basis of Evolution have
since been seeking to establish.
Naturally he was vigorously attacked, not only by anti-Darwinians,
or rather anti-Evolutionists, but also by many of those who, having
accepted the principle of transformism, ought to have known better.
Perhaps they thought they did know better. Imperfections or mistakes in
details of the grand attempt,--and these, naturally, were many,--were
singled out as samples of the whole, which was ridiculed as the romance
of a dreamer.
In the end, however, this hostility, narrow-minded and unfair in
many respects, has done good to the cause. There has arisen an
ever-increasing school of workers in favour of the new doctrine. Owing
to renewed research, criticism, corrections in all directions, we
now know considerably more about natural classification (and this is
pedigree) than when Haeckel first opened out the whole problem.
Owing to his fearless mode of exposition, regardless of the indignant
wrath which the new doctrine aroused in certain ecclesiastical
quarters, Haeckel bore the brunt of almost endless attacks, and had to
write polemical essays. The result has been that friend and foe alike
are now working on the lines which he has laid down; most of the ideas
which he was the first to conceive, and to formulate by inventing a
scientific terminology for them, have become important branches, or
even disciplines, of the science.
Most morphologists of the younger generations now take these terms
for granted, without remembering the name of their founder. It is,
therefore, perhaps not quite superfluous to mention some of them:
_Phylum_, or stem, the sum total of all those organisms which have
probably descended from one common lower form. He distinguished eight
such phyla--Protozoa, Coelenterata, Helminthes or Vermes, Tunicata,
Mollusca, Articulata, and Vertebrata. The phyla are more or less
analogous to 'super-classes,' large branches or 'circles,' or principal
groups of other zoologists.
_Phylogeny_, the history of the development of these various phyla,
classes, orders, families, and species.
_Ontogeny_, the history or study of the development of the individual,
generally called embryology. In reality the scope of embryology
is the ontogenetic study of the various species, and this branch
of developmental study alone can be checked by direct, 'exact'
observation, for the simple reason that the individuals alone are
entities, while the species, genera, families, etc., are abstract ideas.
The _ontogenesis of any given living organism is a short, condensed
recapitulation of its ancestral history or of its phylogenesis_. This
is Haeckel's 'fundamental biogenetic law.'
A complete proof of the phylogeny of any creature would be given by
the preservation of an unbroken series of all its fossil ancestors.
Such a series will in most cases, for obvious reasons, always remain a
desideratum. In a few cases, however, the desideratum is nearly met:
for example, the ancestral line of the one-toed digitigrade horse from
a four-or five-toed plantigrade and still very generalized Ungulate is
approaching completion.
Phylogenetic study has to rely upon other help. This is afforded by
comparative anatomy and by the study of ontogeny. If the latter were
a faithful, unbroken recapitulation of all the stages through which
the ancestors have passed, the whole matter would be very simple; but
we know for certain that in the individual development many stages
are left out (or, rather, are hurried through, and are so condensed
by short-cuts being taken that we cannot observe them), while other
features which have been introduced obscure, and occasionally modify
beyond recognition, the original course.
Again, the sequence of the appearance of the various organs is
frequently upset (_heterochronism_). Some organs are accelerated in
their development, while others, which we know to be phylogenetically
older, are retarded in making their reappearance in the embryo.
These disturbing or distorting newly introduced features or factors
show themselves chiefly in connection with the embryonic conditions of
growth--for example, yolk-sac, placenta, amnion. They all come within
the category of _cænogenesis_: they are cænogenetic, while the true,
undisturbed recapitulation is _palingenetic_.
Lastly, some features, so-called rudimentary or vestigial organs,
instead of disappearing, are most tenacious in their recurrence,
while others of originally fundamental importance scarcely leave
recognisable traces, and are, so to speak, only hinted at during the
embryonic growth of the creature we happen to study. Hence arises the
philosophical study of 'Dysteleology.'
Among other terms invented by Haeckel, and now in general use, are
_Metamere_, _Metamerism_, _Coelom_, _Gonochorism_, _Gastrula_,
_Metazoa_, _Gnathostomata_, _Acrania_, _Craniota_, and _Amniota_.
Hitherto we have dealt with his general work only, a résumé of which
he gave for many years in a course of thirty lectures before an
audience composed of 'all sorts and conditions of men.' Students of
biology and of medicine side by side with theologians, incipient and
ordained, jurists, political economists, and philosophers, crowded his
lecture-room during the 'seventies to hear the master explaining the
'natural history of creation' or the mysteries of anthropogenesis.
Another course of eighty lectures during the winter semester was, and
still is, devoted to a systematic treatment of zoology, while practical
classes are reserved for the more select.
His winning personality and fascinating eloquence, combined with a
clear and concise delivery, have gained the enthusiastic admiration of
many a student who went to the quiet University town in order to learn
with his own ears and eyes.
_List of Separate Publications by Professor Haeckel._
'Biologische Studien. I.: Studien ueber die Moneren und andere
Protisten.' Leipzig, 1870 (out of print). He was the first to
make observations on the natural history of the Monera, living
bits of protoplasm, devoid even of a nucleus--_e.g._, _Protogenes
primordialis_, _Protomyxa aurantiaca_.
'Monographie der Radiolarien.' Berlin, 1862-88. With 171 plates.
'Entwicklungsgeschichte der Siphonophoren.' Utrecht, 1869.
'Plankton-Studien. Vergleichende Untersuchungen ueber die Bedeutung und
Zusammensetzung der pelagischen Fauna und Flora.' Jena, 1880.
'Metagenesis und Hypogenesis von Aurelia aurita.' Jena, 1881.
'Monographie der Geryoniden oder Ruesselquallen.' Leipzig, 1865.
'Generelle Morphologie der Organismen.' 2 vols. Berlin, 1866.
'Anthropogenie oder Entwicklungsgeschichte des Menschen,' 1874; 4th
edition, 1891.
'Natuerliche Schoepfungs-Geschichte.' 2 vols. Berlin, 1st edition,
1868; 9th edition, 1898. This work has been translated into most
European languages (the first edition in English, under the title
'Natural History of Creation' in 1873; the eighth in 1892).
'Monographie der Kalkschwaemme.' 3 vols. Berlin, 1872 (out of print).
With the subtitle, 'An Attempt to solve analytically the Problem of
the Origin of Species.' In this work, illustrated by sixty plates, he
showed that the Calcispongia are individually so yielding, so adaptive
to external influences, that it is practically impossible to break up
the whole group into anything like satisfactory species or genera.
According to predilection, we can distinguish either 1 genus with only
3 species, or 3, 21, 43 genera, with 21, 111, 181, or 289 species
respectively.
In this work, in 1872, Haeckel established the homology of the two
primary layers, ecto- and endoderm, throughout the Metazoa. The attempt
to do the same for the four secondary layers, as made in the second
part of his 'Gastræa-theory,' failed. It caused an enormous amount of
research, hitherto without a satisfactory solution of the problem.
'Studien zur Gastræa-Theorie.' Jena, 1874. The transformation of
the single primitive egg-cell by cleavage into a globular mass of
cells (Morula)--which latter, becoming hollow (and then known as the
Blastula), turns ultimately by invagination or by delamination into
the Gastrula--is a series of processes which applies to all Metazoa.
The Gastrula is, therefore, the ancestral form of the Metazoa; and the
Gastræa-theory, founded by Haeckel, throws light, on the one hand, upon
the mystery of the phyletic connection of the various animal groups,
while, on the other hand, it connects the Metazoa, or multicellular
organisms, with the lowest Protozoa. We come to this conclusion
becaues the Gastrula arises from and passes through stages which exist as
independent, permanent organisms among the Protozoa.
Needless to say this Gastræa-theory has been violently attacked in
detail, with the result that various modifications of the Gastrula,
until then undreamed of, have become known.
'Monographie der Medusen.' Jena, 1879-81. With 72 coloured plates.
'Reports on the Scientific Results of the Voyage of H.M.S.
_Challenger_.' With 230 plates:
1. Deep-sea Medusæ. 1881.
2. Radiolaria. 1887.
3. Siphonophoræ. 1888.
4. Deep-sea Keratosa. 1889.
A short holiday spent on the coasts of the Red Sea produced the volume
'Arabische Korallen' (Berlin, 1876); and a longer trip to Ceylon has
been described in 'Indische Reisebriefe,' of which the third edition
appeared in 1893. The English translation (1883) is entitled 'A Visit
to Ceylon.'
'Monism as connecting Religion and Science: the Confession of Faith of
a Man of Science.' 1894.
Haeckels latest work is the 'Systematische Phylogenie' (Berlin, 1896),
three volumes dealing with Protistæ and Plants, Invertebrata and
Vertebrata. They contain the author's views on the natural system of
the organic world, both living and extinct. Notable in the work are
the many reconstructions of ancestral forms which, provided Evolution
is true, must have existed--hypothetical until they, or something like
them, are found in a fossil state. Everybody who works systematically,
and upon the basis of Evolution, does, sometimes unconsciously,
reconstruct such links, although he may perhaps not see the necessity,
or have the courage to fix his vision, by assigning to it all those
attributes or characters which are indicated by deductions from
comparative anatomy, palæontology, and embryology.