THE GERMAN TRANSCENDENTALISTS
To complete our historical survey of the morphology of the early 19th
century we have now to turn back some way and consider the curious
development of morphological thought in Germany under the influence of
the _Philosophy of Nature_. We have already seen many of these notions
foreshadowed by Goethe, who had considerable affinity with the
transcendentalists, but the full development of transcendental habits of
thought comes a little later than the bulk of Goethe's scientific work,
and owes more to Kielmeyer and Oken than to Goethe himself.
A great wave of transcendentalism seems to have passed over biological
thought in the early 19th century, arising mainly in Germany, but
powerfully affecting, as we have seen, the thought of Geoffroy and his
followers. Many ideas were common to the French and German schools of
transcendental anatomy, the fundamental conception that there exists a
unique plan of structure, the idea of the scale of beings, the notion of
the parallelism between the development of the individual and the
evolution of the race. It is difficult to disentangle the part played by
each school and to determine which should have the credit for particular
theories and discoveries. The philosophy seems to have come chiefly from
Germany, the science from France. It must be borne in mind that German
comparative anatomy was largely derivative from French, that the Paris
Museum was the acknowledged anatomical centre, and that Cuvier was its
acknowledged head.
It is probably correct to say that the credit mainly belongs to the
German transcendental school for the law of the parallelism between the
stages of individual development and the stages of the scale of beings,
and the theory of the repetition or multiplication of parts within the
individual. The vertebral theory of the skull is a particular
application of the second of these generalisations.
The law of parallelism[141] seems to have been expressed first by
Kielmeyer (1793),[142] who gave to it a physiological form, saying that
the human embryo shows at first a purely vegetative life, then becomes
like the lower animals, which move but have no sensation, and finally
reaches the level of the animals that both feel and move.
The idea was next taught by Autenrieth in 1797.[143]
Oken (1779-1851) in his early tract _Die Zeugung_ (1805), and in his
_Lehrbuch der Naturphilosophie_ (1809-11) elaborated the thought, and
taught that every animal in its development passes through the classes
immediately below it. "During its development the animal passes through
all stages of the animal kingdom. The foetus is a representation of all
animal classes in time."[144] The Insect, for example, is at first Worm,
next Crab, then a perfect volant animal with limbs, a Fly (_ibid._, p.
542).
As Nature is "the representation of the individual activities of the
spirit," so the animal kingdom is the representation of the activities
or organs of man. The animal kingdom is therefore "a dismemberment of
the highest animal, _i.e._, of Man" (p. 494). Now "animals are gradually
perfected, entirely like the single animal body, by adding organ unto
organ"--the way of evolution is the way of development. Hence "animals
are only the persistent foetal stages or conditions of Man," who is the
microcosm, and contains within himself all the animal kingdom.
Oken was himself a careful student of embryology; von Baer[145] speaks of
his work (published in Oken and Kieser, _Beitraege zur vergleichenden
Zoologie, Anatomie und Physiologie_, 2 pts., 1806-7) as forming the
turning-point in our understanding of the mammalian ovum. He had
accordingly actually observed a resemblance in certain details of
structure between the human foetus and the lower animals; but the
peculiar form which the law took in his hands was a consequence of his
hazy philosophy. He saw the relation of teratological to foetal
structure, for he affirmed that "malformations are only persistent
foetal conditions" (p. 492).
The idea of comparing the embryo of higher animals with the adult of
lower was widely spread at this time among German zoologists. We find,
for example, in Tiedemann's brilliant little textbook[146] the statement
that "Every animal, before reaching its full development, passes through
the stage of organisation of one or more classes lower in the scale, or,
every animal begins its metamorphosis with the simplest organisation"
(p. 57).
Thus the higher animals begin life as a kind of fluid animal jelly which
resembles the substance of a polyp; the young mammal, like the lower
Vertebrates, has only a simple circulation, and, like them, lives in
water (the amniotic fluid); the frog is first like a worm, then develops
gills and becomes like a fish (p. 57). In his work on the anatomy of the
brain,[147] Tiedemann established the homology of the optic lobes in birds
by comparing them with foetal corpora quadrigemina in man (see Serres,
_Ann. Sci. nat._, xii., p. 112).
J. F. Meckel, in 1811, devoted a long essay to a detailed proof of the
parallelism between the embryonic states of the higher animals and the
permanent states of the lower animals. In a previous memoir in the same
collection[148] (i., 1, 1808) he had made some comparisons of this kind in
dealing with the development of the human foetus; in this memoir (ii.,
1, 1811) he brings together all the facts which seem to prove the
parallelism.
His collection of facts is a very heterogeneous one; he mingles
morphological with physiological analogies, and makes the most
far-fetched comparisons between organs belonging to animals of the most
diverse groups. He compares, for instance, the placenta with the gills
of fish, of molluscs and of worms, homologising the cotyledons with the
separate tufts of gills in _Tethys, Scyllaea_ and _Arenicola_(p. 26).
This is purely a physiological analogy. He compares the closed anus of
the early human embryo with the permanent absence of an anus in
Coelentera, and the embryo's lack of teeth with the absence of teeth in
many reptiles and fish, in birds, and in many Cetacea (p. 46).[149] These
are merely chance resemblances of no morphological importance. He
considers bladderworms as animals which have never escaped from their
amnion, and _Volvox_ as not having developed beyond the level of an egg
(p. 7). He lays much stress upon likeness of shape and of relative size,
comparing, for instance, the large multilobate liver of the human foetus
with the many-lobed liver of lower Vertebrates and of Invertebrates. In
general he shows himself, in his comparisons, lacking in morphological
insight.
His treatment of the vascular system affords perhaps the best example of
his method (pp. 8-25). The simplest form of heart is the simple tubular
organ in insects, and it is under this form that the heart first appears
in the developing chick. The bent form of the embryonic heart recalls
the heart of spiders; it lies at first free, as in the mollusc _Anomia_.
The heart consists at first of one chamber only, recalling the
one-chambered heart of Crustacea. A little later three chambers are
developed, the auricle, ventricle, and aortic bulb; at this stage there
is a resemblance to the heart of fish and amphibia. At the end of the
fourth day the auricle becomes divided into two, affording a parallel
with the adult heart of many reptiles.
In his large text-book of a somewhat later date, the _System der
vergleichenden Anatomie_ (i., 1821), he works out the idea again and
gives to it a much wider theoretic sweep, hinting that the development
of the individual is a repetition of the evolutionary history of the
race. Meckel was a timid believer in evolution. He thought it quite
possible that much of the variety of animal form was due to a process of
evolution caused by forces inherent in the organism. "The
transformations," he writes, "which have determined the most remarkable
changes in the number and development of the instruments of organisation
are incontestably much more the consequence of the tendency, inherent in
organic matter, which leads it insensibly to rise to higher states of
organisation, passing through a series of intermediate states."[150]
His final enunciation of the law of parallelism in this same volume
shows that he considered the development of the individual to be due to
the same forces that rule evolution. "The development of the individual
organism obeys the same laws as the development of the whole animal
series; that is to say, the higher animal, in its gradual evolution,
essentially passes through the permanent organic stages which lie below
it; a circumstance which allows us to assume a close analogy between the
differences which exist between the diverse stages of development, and
between each of the animal classes" (p. 514).
He was not, of course, able fully to prove his contention that the lower
animals are the embryos of the higher, and we gather from the following
passage that he could maintain it only in a somewhat modified form. "It
is certain," he writes, "that if a given organ shows in the embryo of a
higher animal a given form, identical with that shown throughout life by
an animal belonging to a lower class, the embryo, in respect of this
portion of its economy, belongs to the class in question" (p. 535). The
embryo of a Vertebrate might at a certain stage of development, be
called a mollusc, if for instance, it had the heart of a mollusc.
He admits, too, that the highest animal of all does not pass through in
his development the entire animal series. But the embryo of man always
and necessarily passes through many animal stages, at least as regards
its single organs and organ-systems, and this is enough in Meckel's eyes
to justify the law of parallelism (p. 535).
In his excellent discussion of teratology Meckel points out how the idea
of parallelism throws light upon certain abnormalities which are found
to be normal in other (lower) forms (p. 556).[151]
We may refer to one other statement of the law of parallelism--by K. G.
Carus in his _Lehrbuch der vergleichenden Anatomie_ (Leipzig, 1834). The
standpoint is again that of _Naturphilosophie_. It is a general law of
Nature, Carus thinks, that the higher formations include the lower; thus
the animal includes the vegetable, for it possesses the "vegetative" as
well as the "animal" organs. So it is, too, by a rational necessity that
the development of a perfect animal repeats the series of antecedent
formations.
As we have said, the main credit for the enunciation of the law of
parallelism belongs to the German transcendental school; but the law
owes much also to Serres, who, with Meckel, worked out its implications.
It might for convenience, and in order to distinguish it from the laws
later enunciated by von Baer and Haeckel, be called the law of
Meckel-Serres.
Under the "theory of the repetition or multiplication of parts within
the organism" may be included, first, generalisations on the serial
homology of parts, and second, more or less confused attempts to
demonstrate that the whole organisation is repeated in certain of the
parts. The recognition of serial homologies constituted a real advance
in morphology; the "philosophical" idea of the repetition of the whole
in the parts led to many absurdities. It led Oken to assert that in the
head the whole trunk is repeated, that the upper jaw corresponds to the
arms, the lower to the legs, that in each jaw the same bony divisions
exist as in the limbs, the teeth, for instance, corresponding to the
claws (_loc. cit._, p. 408). It led him to distinguish "two animals" in
every body--the cephalic and the sexual animal. Each of these has its
own organs; thus "in the perfect animal there are two intestinal systems
thoroughly distinct from each other, two intestines which belong to two
different animals, the sexual and cephalic animal, or the plant and the
animal" (p. 382). The intestine of the sexual animal is the large
intestine; the lungs of the sexual animal are the kidneys, its glottis
is the urethra, its mouth the anus. So, too, the mouth is the stomach of
the head. On another line of thought the sternum is a ventral vertebral
column. Limbs are connate ribs, the digits indicating the number of ribs
included (_cf._ Duges, _supra_, p. 88).
J. F. Meckel[152] discusses "homologies" of this kind in the thorough and
pedestrian way so characteristic of him. Not only, he says, are the
right and left halves of the body comparable with one another, but also
the upper and the lower, the dividing line being drawn at the level of
the diaphragm. The lumbar complex corresponds to the skull, the anus to
the mouth, the urino-genital opening to the nasal opening; in general,
the urino-genital system corresponds to the respiratory, the kidneys to
the lungs, the ureters to bronchi, the testes and ovaries to the thymus
(he had observed the physiological relation between the development of
the thymus and the state of the genital organs), the prostate and the
uterus to the thyroid gland, and the penis and clitoris to the tongue.
The fore-limbs and girdle correspond in detail with the hind limbs and
the pelvis--a point already worked out by Vicq d'Azyr; the dorsal and
ventral halves of the body are likewise comparable in some respects, the
sternum, for example, answering in the arrangement of its bones, muscles
and arteries to the vertebral column. The skeleton of each member is in
some respects a repetition of the vertebral column.
His brother, D. A. Meckel,[153] worked out an elaborate comparison between
the alimentary canal and the genital organs, basing the legitimacy of
the comparison upon early embryological relations and upon the state of
things in Coelentera, where genital and digestive organs occupy the same
cavity. In his view the uterus corresponded to the stomach, the vagina
to the oesophagus, the fallopian tubes to the intestine, and so on.
The vertebral theory of the skull took its origin from the same habit of
thought. As part of the wider idea of the metameric repetition of parts
it had some scientific worth, but the theory was pushed too far, and the
facts were twisted to suit it. Among annulate animals the theory of
repetition found ample scope; Oken was able to compare with justice the
jaws of crabs and insects with their other limbs, as Savigny did later
in a more scientific way. Among Vertebrates the application of the
theory of serial repetition was not so obvious, except in the case of
the vertebrae. Goethe seems to have been the first to hit upon the idea
that the skull is composed of a number of vertebrae, serially homologous
with those of the vertebral column. He tells us that the idea flashed
into his mind when contemplating in the Jewish cemetery at Venice a
dried sheep's skull. The discovery was made in 1790, but not published
till 1820.[154]
The idea seems to have been taught by Kielmeyer, one of the earliest of
the "philosophers of nature," but it was not published by him.
In a book (_Cours d'Etudes medicales_), published in 1803, Burdin
assimilated the skull to the vertebral column.
Oken, in an inaugural dissertation (Programm) _Ueber die Bedeutung der
Schaedelknochen_,[155] published in 1807, gave to the theory its necessary
development. Autenrieth, also in 1807,[156] distinguishing separate
ganglia in the brain, was not far from the hypothesis that each of these
ganglia must have its separate vertebra.
In 1808 Dumeril read a paper to the Academie des Sciences in which he
compared the skull to a gigantic vertebra, basing his hypothesis on the
similarity existing between the crests and depressions on the hinder
part of the skull and those on the posterior surfaces of the vertebrae.
After Oken's work the vertebral theory was taken up generally by both
the German and the French anatomists. Spix published in 1815 a large
volume on the skull, entitled _Cephalogenesis_, distinguishing (as Oken
did at first) three cranial vertebrae. Bojanus in his _Anatome testudinis
europaeae_ (1819), and in a series of papers in _Isis_ (1817-1819, and
1821) established the existence of a fourth cranial vertebra, and this
was accepted by Oken in the later editions of his _Lehrbuch_. Meckel and
Carus among the Germans, de Blainville and E. Geoffroy among the French,
contributed to the development of the theory. In England the theory was
championed particularly by Richard Owen.
It was one thing to assert in a moment of inspiration that the skull was
composed of modified vertebrae; it was quite another to demonstrate the
relation of the separate bones of the skull to the supposed vertebrae.
Upon this much uncertainty reigned; there was not even unanimity as to
the number of vertebrae to be distinguished. Goethe found six vertebrae in
the skull; Spix, and at first Oken, three only, Geoffroy seven; the
accepted orthodox number seems to have been four (Bojanus, Oken, Owen).
As an example of the method of treatment adopted we may take Oken's
matured account of the composition of the cranial vertebrae, as given in
the English translation of his _Lehrbuch_. "To a perfect vertebra," he
says, "belong at least five pieces, namely, the body, in front the two
ribs, behind the two arches or spinous processes" (p. 370). In the
cervical vertebrae the transverse processes represent the ribs. The skull
consists of four vertebrae, the occipital, the parietal, the frontal and
the nasal, or, named after the sense with which each is associated, the
auditory, the lingual, the ocular and the olfactory. The "bodies" of
these vertebrae are the body of the occipital (basioccipital), the two
bodies of the sphenoid (basi- and pre-sphenoid), and the vomer. The
transverse processes of each are the condyles of the occipitals
(exoccipitals), the alae of the two sphenoids (alisphenoids and
orbitosphenoids) and the lateral surfaces of the vomer. The arches or
spinous processes are the occipital crest, the parietals, the frontals,
and the nasals.
The cranium is thus composed of four rings of bone, each composed of the
typical elements of a vertebra.
The arbitrary nature of the comparison is obvious enough. As Cuvier
pointed out in the posthumous edition of his _Lecons_, it is only the
occipital segment that shows any real analogy with a vertebra--an
analogy which Cuvier ascribed to similarity of function. He admitted a
faint resemblance of the parietal segment to a vertebra:--"The body of
the sphenoid does indeed look like a repetition of the basioccipital,
but having a different function it takes on another form, especially
above, by reason of its posterior clinoid apophyses."[157] He denied the
resemblance of the frontal and nasal "vertebrae" to true vertebrae,
pointing out that both parietals and frontals are bones specially
developed for the purpose of roofing over and protecting the cerebrum.
A very curious development was given to the vertebral theory by K. G.
Carus, who seems to have taken as his text a saying of Oken's, that the
whole skeleton is only a repeated vertebra.[158] His system is worthy of
some consideration, for he tries to work out a geometry of the
skeleton.[160]
His method of deduction is a good example of pure _Naturphilosophie_.
Life, he says, is the development of something determinate from
something indeterminate. A finite indeterminate thing, that is, a
liquid, must take a spherical form if it is to exist as an individual.
Hence the sphere is the prototype of every organic body. Development
takes place by antagonism, by polarity, typically by the division and
multiplication of the sphere. In the course of development the sphere
may change, by expansion into an egg-shaped body, or by contraction into
a crystalline form, the changes due to expansion being typical of living
things, those due to contraction being typical of dead. At the surface
of the primitive living sphere is developed the protective
_dermatoskeleton_, which naturally takes the shape of a hollow sphere;
round the digestive cavity which is formed in the living sphere is
developed the _splanchnoskeleton_; round the nervous system (which is,
as it were, the animal within the animal) is developed the
_neuroskeleton_. All skeletal formations belong to one or other of these
systems.
Carus defines his aim to be the discovery of the inner law which
presides over the formation of the skeleton throughout the animal
kingdom; he desires to know "how such and such a formation is realised
in virtue of the eternal laws of reason" (iii., p. 93). Here we touch
the kernel of _Naturphilosophie_--the search for rational laws which are
active in Nature; the discontent with merely empirical laws.
The thesis which Carus sustains is that all forms of skeleton, whether
of dermatoskeleton, splanchnoskeleton, or neuroskeleton, can be deduced
from the hollow sphere, which is the primary form of any skeleton
whatsoever (p. 95). That means, put empirically, that every skeleton can
be represented schematically by a number of hollow spheres, suitably
modified in shape, and suitably arranged. The chief modification in
shape exhibited by bones is one which is intermediate between the
organic and the crystalline series of modifications of the sphere. The
organic modifications are bounded by curved lines, the crystalline by
straight; the intermediate partly by curved and partly by straight
lines. They are the dicone (the shape of a diabolo) and the cylinder.
These forms must necessarily be of importance for the skeleton, which is
intermediate between the organic and the inorganic. "The dicone embodies
the real significance of the bone," writes Carus. Each dicone and
cylinder composing the skeleton is called by Carus a vertebra.
We may expect then all skeletons to be composed of spheres, cylinders
and dicones in diverse arrangements. Nature being infinite, all the
possible types of arrangement of these elements must exist in the test
or skeleton of some animal, living, fossil, or to come (p. 127). One
conceives easily what the main types of skeleton must be. In some
animals, _e.g._, sea-urchins, the skeleton is a simple sphere; in
others, _e.g._, starfish, secondary rows of spheres radiate out from a
central sphere or ring; in annulate animals the skeleton consists of a
row of partially fused spheres.
In Vertebrates the arrangement is more complex. There are first the
protovertebral rings of the dermatoskeleton, these being principally the
ribs, limb-girdles, and jaws. Round the central nervous system are
developed the deutovertebral rings of the neuroskeleton (vertebrae in the
ordinary sense). The apophyses and bodies of the vertebrae, and the bones
of the members[160] are composed of columns of tritovertebrae, or vertebrae
of the third order. Thus the whole vertebrate skeleton is a particular
arrangement of vertebrae, which in their turn are modifications of the
primary hollow sphere.
The German transcendentalists were more or less contemporary with E.
Geoffroy, and no doubt influenced him, especially in his later years, as
they certainly did his follower Serres. Oken indeed wrote, in a note[161]
appended to Geoffroy's paper on the vertebral column of insects, that
"Mr Geoffroy [_sic_] is without a doubt the first to introduce in France
_Naturphilosophie_ into comparative anatomy, that is to say, that
philosophy one of whose doctrines it is to seek after the
_signification_ of organs in the scale of organised beings." This is,
however, an exaggeration, for Geoffroy was primarily a morphologist,
whereas the morphology of the German transcendentalists was only a
side-issue of their _Naturphilosophie_.
Geoffroy, on his part, exercised some influence on the
transcendentalists. He asserts[162] indeed that Spix got some of the ideas
published in the _Cephalogenesis_ (1815) from attending his course of
lectures in 1809. It is certainly the case that Spix published before
Geoffroy the view that the opercular bones are homologous with the
ear-ossicles, adopting, however, a different homology for the separate
bones.[163]
Some speculations seem to have been common to both schools--for
instance, the law of Meckel-Serres, the vertebral theory of the skull,
and the recognition of serial homology in the appendages of Arthropods
(Savigny, Oken). Latreille and Duges, as well as Serres, clearly show in
their theoretical views the influence of Oken and the other
transcendentalists. Geoffroy's principle of connections and law of
compensation were recognised by some at least of the Germans.
But whatever his actual historical relations may have been with the
German school, Geoffroy was vastly their superior in the matter of pure
morphology. He alone brought to clear consciousness the principles on
which a pure morphology could be based: the Germans were transcendental
philosophers first, and morphologists after.
One understands from this how J. F. Meckel, who was in some ways the
leading comparative anatomist in Germany at this time, could be at once
a transcendentalist and an opponent of Geoffroy. Meckel had a curiously
eclectic mind. A disciple of Cuvier, having studied in 1804-6 the rich
collections at the Museum in Paris, the translator of Cuvier's _Lecons
d'anatomie comparee_, he earned for himself the title of the "German
Cuvier," partly through the publication of his comprehensive textbook
(_System der vergl. Anatomie_, 5 vols.), partly by his extensive and
many-sided research work, partly by his authoritative teaching. His
_System_ shows in almost every page of its theoretical part the
influence of Cuvier; and it is through having assimilated Cuvier's
teaching as to the importance of function that Meckel combats Geoffroy's
law of connections, at least in its rigorous form. He submits that the
connections of bones and muscles must change in relation to functional
requirements. He rejects Geoffroy's theory of the vertebrate nature of
Articulates. Generally throughout his work the functional point of view
is well to the fore.
Yet at heart Meckel was a transcendentalist of the German school. His
vagaries on the subject of "homologues" leave no doubt about that, and,
in spite of Cuvier, he believed, though not very firmly, in the
existence of one single type of structure.
A Cuverian by training, his lack of morphological sense threw him into
the ranks of the transcendentalists, to whom perhaps he belonged by
nature.
[141] For a full account, see Kohlbrugge, _Zool. Annalen_,
xxxviii., 1911.
[142] _Rede ueber das Verhaeltnis der organischen Kraefte_,
Stuttgart u. Tuebingen, 1793 (1814). See Radl, _loc.
cit._, i., p. 261; ii., p. 57.
[143] _Supplem. ad historiam embryonis_, Tuebingen, 1797.
[144] _Lehrbuch der Naturphilosophie_, Eng. trans., p.
491, 1847.
[145] _Ueber Entwickelungsgeschichte der Thiere_, i., p.
xvii., 1828.
[146] _Zoologie_, Landshut, i., 1808.
[147] _Anatomie u. Bildungsgeschichte des Gehirns im Foetus
des Menschen_, Nuernberg, 1816.
[148] _Beytraege zur vergleichende Anatomie_, Leipzig, i.,
1808-9, ii., 1811-2.
[149] Cetacea were generally considered at this time to be
mammals of low organisation.
[150] From the French trans., which appeared under the
title _Traite gen. d'Anat. comparee_, i., p. 449, 1828.
[151] _Cf._ Geoffroy (_supra_, p. 70).
[152] _Beytraege_, ii., 2, 1812. Also in his _System d.
vergl. Anat._, i., 1821.
[153] In J. F. Meckel's _Beytraege_, ii.
[154] _Zur Morphologie_, i., 2, p. 250, 1820; and ii., 2,
pp. 122-4, 1824.
[155] See translation, giving the gist of this paper, in
Huxley's _Lectures on the Elements of Comparative
Anatomy_, pp. 282-6, London, 1864.
[156] Reil's _Archiv. f. Physiol._, vii., 1807.
[157] _Lecons d'anatomie comparee_, 3rd ed., Brussels
reprint, i., p. 414, 1836.
[158] In his Programm, _U. d. Bedeut. d. Schaedelknochen_,
1807.
[159] _Traite elementaire d'anatomie comparee_ (French
trans.), vol. iii., Paris, 1835. First developed in his
volume _Von den Ur-Theilen des Knochen und
Schalen-Gerustes_, Leipzig, 1828.
[160] Dutrochet in 1821 had tried to prove that the bones
of the members belong to the type of the vertebra--the
dicone.
[161] _Isis_, pp. 552-9, 1820 (2).
[162] _Mem. Mus. d'Hist. nat._, ix., 1822.
[163] Cuvier and Valenciennes, _Hist. nat. Poissons_, i.,
p. 311, f.n.