Form and Function

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Geoffroy's morphological units or materials of organisation were in the
case of the skeleton--with which his researches principally deal--the
single bones. But the interesting point is that he sought his
skeleton-units in the embryo, and considered each separate centre of
ossification as a separate bone. Coalescence of bones originally
separate is one of the most usual events in development, and it is an
occurrence which, more than any other, tends to obscure homologies.
Because of its coalescence with the maxillaries, the intermaxillary in
man was not discovered until Vicq d'Azyr and Goethe found it separate in
the embryo. Apparently quite independently of Goethe, Geoffroy hit upon
this plan of seeking in the embryo the primary elements or materials of
organisation. In an early paper on the skull of Vertebrates,[113] where he
is concerned with showing that each bone of the fish's skull has its
homologue in the skull of higher Vertebrates, he is faced with the
difficulty that the skull of the fish has more bones than the skull of
higher Vertebrates. "Having had the inspiration," he writes, "to reckon
as many bones as there are distinct centres of ossification, and having
made a consistent trial of this method, I have been able to appreciate
the correctness of the idea: fish, in their earliest stages, are in the
same conditions relatively to their development as the foetuses of
mammals, and hence bear out the theory" (p. 344). So, too, in dealing
with the homologies of the sternal elements (_supra_, p. 57) he treats
as separate bones the "annexes" of the sternum in birds, though these
are separate only in the young.

If the same materials of organisation are present in all animals, and if
they are arranged always in the same positions relatively to one
another, how does it come about that animal forms are so varied, what
explanation can be offered of the diversities of organic structure?
Geoffroy's main answer to this question is his _Loi de balancement_. The
law was enunciated by him already in 1807.[114] We take the following
quotation, which represents his thought most nearly, from the _Cours de
l'histoire naturelle des Mammiferes_ (1829). "According to our manner of
regarding the organisation of mammals, there is only a single animal
modified by the inverse reciprocal variation of all or some of its
parts. Now, from the fact that there is only one single general animal,
it follows that for each section of its components or for each of its
organs there is available only a given quantity of formative materials.
Now suppose that the distribution of these materials has not been made
in such a way as to ensure an exact equilibrium between all the parts
concerned, one organ will get more than its share, another less. My law
of the compensation of organs is founded on these principles" (i.,
_Lecon_ 16, p. 12). "The atrophy of one organ turns to the profit of
another; and the reason why this cannot be otherwise is simple, it is
because there is not an unlimited supply of the substance required for
each special purpose."[115] The nutritive material available is limited
for each species; if one part gets more than its share the other parts
must get less--that is all the law means. As an example, take the
minuteness of the episternals and xiphisternals in birds, as contrasted
with the huge size of the entosternal. "The minuteness of the
episternals and xiphisternals might be imputed to this gigantic piece
diverting to its own profit the nutritive fluid, since the bigger it is
the smaller these are."[116]

One has constantly to remember in dealing with Geoffroy's theories that
he was not an evolutionist, but purely a morphologist. It is therefore,
perhaps, to ask too much to require of him an explanation of the causes
of diversity. The morphologist describes, classifies, generalises; he
does not seek for causes. But we must leave this question aside in order
to discuss how far Geoffroy's theory of the unity of plan and
composition fits the facts. As Geoffroy himself admitted on several
occasions, his theory was an _a priori_ one, a theory hit upon by hasty
induction, then erected into a principle and imposed upon the facts. No
more than Goethe did he extract his principle from a sufficient mass of
data.

Now he found his theory to be in its pure form unworkable; he found, for
example, that the skeleton of fishes could not be compared directly,
bone for bone, with the skeleton of higher Vertebrates; he had to admit
differences of position of whole sets of organs in the two groups, he
had to admit various _metastases_, before he could bring the skeleton of
fish into line. And these metastases are due to functional
requirements--for example, the forward position of sternum and thoracic
organs in fish is an adaptation to swimming.

So he does not so much demonstrate the unity of plan of whole organisms
as the unity of plan of particular corresponding parts of them. Thus he
does not prove or attempt to prove that Articulates are in all points
like Vertebrates, but simply that their skeleton is built upon the same
plan as that of Vertebrates. The rest of the organs, while still
comparable with the organs of Vertebrates, stand in different relations
to the skeleton. An Articulate therefore, on his own showing, is not,
_as a whole_, built upon the same general structural plan as a
Vertebrate.

Further, he does not always remain true to his principles, for he does
not establish homologies of parts entirely by their connections but
sometimes by their functions as well. Thus the sternum, or rather the
complex of sternal elements, is defined and discovered in particular
cases not by its connections only but also by its functions. The
framework of the gills is homologised part by part with the framework of
the lungs, not because the relations of the framework to the rest of the
skeleton are the same in fish and air-breathing Vertebrates, but simply
because gills are considered the equivalents of lungs--a comparison
which is purely physiological.

Even with these concessions to the functional view of living things,
Geoffroy was unable to make good his contention that all animals are
built upon the same plan. His arguments failed to carry conviction to
his contemporaries, and Cuvier in particular subjected them to
destructive, and indeed final, criticism.

The paper, already referred to, in which Cuvier disposed of the
transcendentalists' comparison of Cephalopods and Vertebrates is of
great significance, for it states in the clearest way the radical
opposition between the functional and the formal attitudes to living
things.

Cuvier points out that if by unity of composition is meant identity,
then the statement that all animals show the same composition is simply
not true--compare a polyp with a man!--on the other hand, if by unity is
meant simply resemblance or homology, the statement is true within
certain limits, but it has been employed as a principle since the days
of Aristotle, and the theory of unity of composition is original only in
so far as it is false. He admits, however, that Geoffroy has seized upon
many hidden homologies, especially by his valuable discovery of the
importance of foetal structure. In all this Cuvier is undoubtedly right.
Unity of plan and composition, as Geoffroy conceived it, simply does not
exist. Cuvier goes on to say that this principle of Geoffroy's, in the
greatly modified form in which it can be accepted, and has been accepted
from the dawn of zoology, is not the sole and unique principle of the
science. On the contrary, it is merely a subordinate principle,
subordinate to a higher and more fruitful principle, that, namely, of
the conditions of existence, of the adaptation (_convenance_) of the
parts, of the co-ordination of the parts for the role which the animal
is to play in Nature. "That is the true philosophical principle," he
says, "whence may be deduced the possibility of certain resemblances,
the impossibility of certain others; it is the rational principle from
which follows the principle of the unity of plan and composition, and in
which at the same time it finds those limits, which some would like to
disregard" (p. 248).

Geoffroy's position is the direct contrary. He holds that the principle
of the unity of plan and composition is the true base of natural
history,[117] and that this unity limits the possible transformations of
the organism. Thus, speaking of the influence of the respiratory medium,
he says, "All the same this influence of the external world, if it has
ever become a cause which disturbed organisation, must necessarily have
been confined within fairly narrow limits; animals must have opposed to
it certain conditions inherent to their nature, the existence of the
same materials composing them, and a manifest tendency to resemble one
another, and to reproduce invariably the same primordial type."[118] Unity
of plan and composition is, on this view, prior to adaptation and limits
adaptation. Cuvier's view, on the contrary, is that the necessity of
functional and ecological adaptation accounts for the repetition of the
same types of structure. There are, of all the possible combinations of
organs, only a few viable types--those whose structure is adapted to
their life. Therefore it is reasonable that these few types should be
repeated in innumerable exemplars. One must remember, in order to
appreciate Cuvier's view, that he was not obsessed, as we are, by the
idea of evolution.

Cuvier thought in terms of organs, not in terms of "materials of
organisation." He held that the resemblances between the organs of one
class of animals and the organs of another were due to the similarity of
their functions. "Let us conclude, then, that if there are resemblances
between the organs of fish and those of other classes, it is only in the
measure that there is a resemblance between their functions."[119] There
are only a few kinds of organs, each adapted for a particular function,
and these organs are necessarily repeated from class to class.--"As the
animal kingdom has received only a limited number of organs, it is
inevitable that some at least of these organs should be common to
several classes."[120]

Geoffroy thought in terms of "materials," of parts of indefinite
function, parts which might take on any function. He insists upon the
necessity of disregarding function when tracing out the unity of
composition. He considers, in direct opposition to Cuvier's
interpretation of structural resemblance as due to similarity of
function, that unity of composition is the primary fact, and similarity
of function subsidiary. In his reply in the _Mammiferes_ (1829) to
Cuvier's criticisms in the _Histoire naturelle des Poissons_ (1828), he
insists on the necessity of excluding function from consideration in any
truly philosophical treatment of comparative anatomy (Discours prel., p.
25). Cuvier held that function determined structure, or at least that
the necessity of adaptation ruled the transformations of form. Geoffroy
considered that structure determined function, that changes of
structure, however they might arise, caused changes of function.
"Animals," he writes, "have no habits but those that result from the
structure of their organs; if the latter varies, there vary in the same
manner all their springs of action, all their faculties and all their
actions."[121]

Again, "a vegetarian regime is imposed upon the Quadrumana by their
possession of a somewhat ample stomach, and intestines of moderate
length."[122] The hand of the bat has become so modified as to constrain
the bat to live in the air.[123]

The best example of Geoffroy's insistence upon the priority of structure
to function, and so of his purely morphological attitude, is perhaps his
interpretation, already alluded to, of the appendages of Articulates.
The segments of the Articulate are, he says, the equivalents of the
bodies of the vertebrae of higher forms. Now "from the circumstance that
the vertebra is external, it results that the ribs must be so too; and,
as it is impossible that organs of such a size can remain passive and
absolutely functionless, these great arms, hanging there continually at
the disposition of the animal, are pressed into the service of
progression, and become its efficient instruments."[124] The ribs become
locomotory appendages.

We may compare the similar thought that the ear ossicles are simply
opercular bones reduced and turned to other uses.

Geoffroy could not but recognise the correlation of structure to
function, for this is a fact which imposes itself upon every observer.
He recognised also correlation between functions, as when he pointed out
the connection between increased respiration and enhanced muscular
activity in birds.[125] He interpreted structure at times in terms of
function, the short, strong clavicle of the mole as an adaptation to
digging, the keeled sternum of birds as an adaptation to flying, and so
on. But we may say that his whole tendency was to disregard function, to
look upon it as subsidiary. He protests against arguing from function
and habits to structure, as an "abuse of final causes."[126] He was not so
convinced as Cuvier was of the all-importance of functional correlation;
in this view he was probably confirmed by his work on teratology. It did
not surprise him that Insects, in which lungs, heart and circulation
have disappeared(!), should yet have a skeleton built upon the same plan
as the skeleton of Vertebrates, which possess these organs; the
correlation of organ-systems is not so close as to prevent this.[127] So
too, although the other organs of the insect are all inside the body of
the vertebrae, they are yet comparable with the organs of Vertebrates.[128]
The existence of rudimentary organs also seemed to him an argument
against too strict a correlation of parts.

The contrast between the teleological attitude, with its insistence upon
the priority of function to structure, and the morphological attitude,
with its conviction of the priority of structure to function, is one of
the most fundamental in biology.

Cuvier and Geoffroy are the greatest representatives of these opposing
views. Which of them is right? Is there nothing more in the unity and
diversity of organic forms than the results of functional adaptation, or
is Geoffroy right in insisting upon an element of unity which cannot be
explained in terms of adaptation? If there be an irreducible element of
unity, is there any truth in Geoffroy's suggestion that this unity
results from a power which is exercised in the world of atoms where are
elements of inalterable character?[129]

The problem as Geoffroy and Cuvier understood it was not an evolutionary
one. But the problem exists unchanged for the evolutionist, and
evolution-theory is essentially an attempt to solve it in the one
direction or the other. Theories such as Darwin's, which assume a random
variation which is not primarily a response to environmental changes,
answer the problem in Geoffroy's sense. Theories such as Lamarck's,
which postulate an active responsive self-adaptation of the organism,
are essentially a continuation and completing of Cuvier's thought.

[86] "Memoire sur les rapports naturels des makis,"
_Magasin Encyclopedique_, vii.

[87] Discours preliminaire, pp. xv.-xxiv.

[88] _Etudes progressives d'un Naturaliste_, p. 50,
Paris, 1835.

[89] _Philosophie Anatomique_., i., Introduction, p. 1.

[90] "Sur une colonne vertebrale et ses cotes dans les
insectes apiropodes," (_Acad. Sci._, Feb. 12, 1820).
Printed in _Isis_, pp. 527-52, 1820 (2).

[91] "Sur l'organisation des insectes," p. 458. _Isis_,
pp. 452-62, 1820 (2).

[92] _Mem. Mus. d'Hist. nat._, ix., pp. 89-119, Pls.
v-vii.

[93] _Sur l'organisation des insectes_, p. 459.

[94] _Isis_, p. 549.

[95] Published in _Ann. Sci. Nat._, xix., pp. 241-59,
1830.

[96] _Cf._ Aristotle (_supra_, p. 10).

[97] For an account of the controversy reference may be
made to I. Geoffroy St Hilaire, _Vie Travaux et Doctrine
scientifique d'Etienne Geoffroy St Hilaire_, Paris,
1847; also Semper, _Arb. zool. zoot. Instit. Wuerzburg_,
iii., 1876-7, K. E. von Baer, _Lebensgeschichte Cuviers_,
ed. L. Stieda, 1897, and J. Kohlbrugge, in _Zoolog.
Annalen_, v., pp. 143-95. 1913.

[98] "Recherches sur l'organisation des Gavials," _Mem.
Mus. d'Hist. nat._, xii., 1825.

[99] _Mem. Mus. d'Hist. nat._, xvii., pp. 209-29.

[100] _Mem. Acad. Sci._, xii., pp. 63-92, 1833.

[101] _Mem. Acad. Sci._, xii., pp. 43-61, 1833.

[102] Geoffroy's French style is at times incredibly bad,
and more or less literal translations of his sentences
are apt to read queerly!

[103] _Mem. Mus. d'Hist. nat._, xiii., p. 289, 1826.

[104] _Mem. Mus. d'Hist. nat._, xviii., p. 221, 1828. His
teratological work is important, and is chiefly
contained in the second volume of the _Philosophie
anatomique_.

[105] _Phil. anat._, i., p. 449.

[106] _Mem. Acad. Sci._, xii., p. 82, 1833.

[107] _Mem. Mus. d'Hist. nat._, ix., p. 101, 1822.

[108] _Cours de l'histoire naturelle des Mammiferes_, i.,
Lecon 3, p. 13, 1829.

[109] _Etudes progressives d'un Naturaliste_, p. 59, f.n.,
Paris, 1835.

[110] _Phil. Anat._, i., p. 444.

[111] _Ann. Mus. d'Hist. nat._, x., p. 344, 1807.

[112] _Isis_, p. 534, 1820 (2).

[113] _Ann. Mus. d'Hist. nat._, x., pp. 342-65, 1807.

[114] _loc. cit._, x., p. 343.

[115] _Phil. anat._, i., 450, f.n. _Cf._ Aristotle
(_supra_, p. 11).

[116] _Loc. cit._, p. 136.

[117] _Mammiferes_, i., Discours prel., p. 18.

[118] _Phil. anat._, i., p. 208.

[119] Cuvier and Valenciennes, _Hist. nat. Poissons_, i.,
p. 550, 1828.

[120] Cuvier and Valenciennes, _loc. cit._, p. 544.

[121] _Mammiferes_, i., _Lecon_ 4, p. 17.

[122] _Loc. cit._, _Lecon_ 5, p. 8.

[123] _Loc. cit._, _Lecon_ 13, p. 6.

[124] _Isis_, p. 539, 1820 (2).

[125] _Mammiferes_, i., _Lecon_ 4, p. 6.

[126] _Mammiferes_, Discours prel., p. 7.

[127] _Isis_, p. 460, 1820 (2).

[128] _Mem. Mus. d'Hist. nat._, ix., p. 102, 1822.

[129] _Mem. Acad. Sci._., xii., p. 76, 1833.

CHAPTER VI

THE FOLLOWERS OF ETIENNE GEOFFROY SAINT-HILAIRE

Geoffroy's theories were not generally accepted by his contemporaries,
but his methods had considerable influence, especially in France, where
many made essays in pure morphology.

His chief follower was Serres, who is mentioned indeed in the
_Philosophie anatomique_ as a fellow-worker. Serres was primarily a
medical anatomist; his interest lay in human anatomy and embryology,
normal and pathological.

His best early work was an _Anatomie comparee du cerveau_ (1824-26),
which met with a flattering reception from Cuvier.[130] He laid great
stress upon the development of the brain and spinal cord in the
different classes, and was quick to point out analogies not only between
adult but also between embryonic structures. He paid much attention to
cases of correlation, and noted a great many; he observed, for instance,
a constant relation between the development of the spinal cord and of
the corpora quadrigemina, and between the size of the corpora
quadrigemina and the volume of the optic nerves and eyes. In this the
influence of Cuvier is unmistakable.

Serres' early theoretical views are to be found in a series of papers in
the _Annales des Sciences naturelles_,[131] under the general title
_Recherches d'Anatomie transcendante, sur les Lois de l'Organogenie
appliquees a l'anatomie pathologique_, also published separately. We
follow these papers in our expose of Serres' doctrine, reserving for a
future chapter (Chap. XII.) the consideration of his matured views of
thirty years later.

In the first of them he points out how neither position nor function has
proved altogether sufficient to establish homologies. In the early days
anatomists were guided by form; when form failed them, they traced an
organ in its changes throughout the series of animals by considering its
function. This method was satisfactory enough as regards the organs of
the nutritive life. But in the organs of the life of relation, in the
nervous system, the functions of the parts were difficult to discover,
and their form very changeful. Hence a new principle was required, and
Serres found it in the thought which he probably owed to the German
transcendentalists (see Chap. VII.), that the permanent structure of the
lower animals could be compared with phases in the development of the
higher, and particularly of man, or, as he put it, that comparative
anatomy was often only a fixed and permanent anthropogeny, and
anthropogeny a fugitive and transitory comparative anatomy (xi., p.
106).

"In rising towards the first formations," he writes, "transcendental
anatomy recognised that one and the same organ, however complicated its
definitive form might be, repeated in its transitory states the organic
simplicities of the lower classes. Thus the primitive heart of birds was
first of all a canal, then a pocket or single cavity, then finally the
complex organ of the class. Comparative anatomy was thus seen to be
repeated and reproduced by embryogeny" (xii., p. 85).

His explanation of the fact of repetition is that, "in animals belonging
to the lower classes the _formative force_, whatever it may be, has a
less energetic impulsion than in the higher animals, and hence the
organs pass through only a part of the transformations which those of
the higher forms undergo; and it is for this reason that they show
permanently the organic dispositions which are only transitory in the
embryo of man and the higher Vertebrates. Hence these double aortas,
these double venae cavae which one observes more or less constantly among
reptiles" (xxi., p. 48).

The number of stages in embryogeny is proportionate to the complexity of
the adult; the younger the embryo the simpler its organs--such is the
general formula of the relation between the embryo and the adult. But
here in Serres' doctrine of parallelism a complication enters. He
observed that embryonic organs did not always develop in a piece, by
simple growth, but often were formed by the union of separately formed
parts or layers. Thus the kidney in man is formed by the fusion of a
number of "little kidneys," and the spinal cord reaches its full
development by the laying down of successive layers within it. He was
greatly impressed with this fact, which, as a convinced believer in
epigenesis, he used with great effect against the preformistic theories.
"This method of isolated formation," he wrote, "is noticed in early
stages in the thyroid, the liver, the heart, the aorta, the intestinal
canal, the womb, the prostate, the clitoris, and the penis" (xi., p.
69). So, too, in the development of the skeleton, ossification proceeds
from separate centres, foramina are formed by the fusion of separate
bones round them. In his memoir, _Lois d'Osteogenie_ (1819), Serres
established several laws of ossification based upon this principle of
separate formation.[132]

How is the fact of multiple formation to be reconciled with the
principle of repetition, according to which organs are simplest in the
early embryo and in the lower animals? But observation shows that, as a
rule, the further down the scale you go the more divided organs
become--the more numerous the bones of the skull, for example. There is
thus a parallel between multiple formation of organs in the embryos of
the higher Vertebrates and their subdivided state in the lower. Take,
for example, the kidney. In the genus _Felis_, and in birds, each kidney
has two lobes, in the elephant four, in the otter ten, in the ox twelve
to fourteen. The human kidney in its development starts with about a
dozen lobes, and the number diminishes as the kidney grows. Thus the
permanent state of the kidney in the animals mentioned is reproduced by
the stages of its development in man (xii., p. 126).

So, too, at the second or third month the uterus of the human embryo is
bicornuate, and afterwards passes through stages comparable to the adult
and permanent uterus of rodents, ruminants, and carnivores. There is
indeed a time in the development of the human embryo when it resembles
in many of its organs the adult stage of various lower animals. It is
about this time that it possesses a tail.

We note that Serres' theory of parallelism applies, strictly speaking,
only to organs, not to organisms, although he, too, readily fell into
the error of supposing that the organisation of an embryo could be
compared as a whole with the adult organisation of an animal lower in
the scale. Thus he wrote in one of his later papers[133]--"As our
researches have made clear, an animal high in the organic scale only
reaches this rank by passing through all the intermediate states which
separate it from the animals placed below it. Man only becomes man after
traversing transitional organisatory states which assimilate him first
to fish, then to reptiles, then to birds and mammals." Serres was not
altogether free from the besetting sin of the transcendentalists--hasty
generalisation.

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