Joseph Jacobs (coll. & ed.) - "English Fairy Tales"

John Wood Campbell - "Invaders from the Infinite"

Frank E. Smedley - "Frank Fairlegh"

Sir Rabindranath Tagore - "Glimpses of Bengal"

Annual Bibliography of Commonwealth Literature 2007
This paper argues that discourses of love in Ghanaian market literature for youth offer a view into complex negotiations of agency and empowerment. Drawing on Deborah Durham's notion of youth as "social `shifters'" and Francis Nyamnjoh's conception of the "interconnectedness" of agency, I take Ghanaian market literature as one specific case of how African literature for youth foregrounds questions of continuity and change as African societies enter into increasingly complex global relations. In this literature for youth, received notions of love, often constructed out of impressions from American pop and hip hop music, carry new notions of agency that compete with existing "domesticated" forms. Authors like Ike Tandoh and Evelyn Tay employ discourses of love to offer youth alternative avenues for empowerment in a context of socio-economic disenfranchizement. In a creative process of "straddling", this writing both reveals and reproduces the contradictions that obtain in youth configurations of agency.

Form and Function

E >> E. S. (Edward Stuart) Russell >> Form and Function




This recognition of the parallelism between comparative anatomy and
embryology is, of course, the kernel of the Meckel-Serres law. For
Gegenbaur it had a very definite evolutionary meaning--he subscribed to
the evolutionary form of it, the biogenetic law. How near his conception
of the relation between ontogeny and phylogeny came to the old
Meckel-Serres law may be gauged from the following passage, taken from a
later work:--"Ontogeny thus represents, to a certain degree,
palaeontological development abbreviated or epitomised. The stages which
are passed through by higher organisms in their ontogeny correspond to
stages which are maintained in others as the definitive organisation.
These embryonic stages may accordingly be explained by comparing them
with the mature stages of lower organisms, since we regard them as forms
inherited from ancestors belonging to such lower stages"[382] (p. 6).

It is worth noting that in Gegenbaur's opinion comparative anatomy was
prior in importance to embryology, that embryology could hardly exist as
an independent science, since it must seek the interpretation of its
facts always in the facts of comparative anatomy (_Grundzuege_, pp. 7-8).

While Gegenbaur was at one with all "pure" morphologists, whether
evolutionary or pre-evolutionary, in minimising as far as possible the
importance of function in the study of form, he was too cautious and
sober a thinker not to recognise the immense part which function really
plays. Thus he classified organs, according to their function, into
those that established relations with the external world and those that
had to do with nutrition and reproduction, very much as Bichat had done
before him.

Like Darwin, Haeckel and most evolutionists, he interpreted the
homological resemblances of animals as being due to heredity, their
differences as due to adaptation,[383] but he did not adopt Haeckel's
crude and shallow definition of these terms. For Gegenbaur heredity was
a convenient expression for the fact of transmission, and was not
explained offhand as the mere mechanical result of a certain material
structure handed down from germ to germ. Adaptation he defined in a way
which took the fullest account of function, and was as far as possible
removed from Haeckel's definition of it as the direct mechanical effect
of the environment upon the organism. "The organism is altered," writes
Gegenbaur, "according to the conditions which influence it. The
consequent _Adaptations_ are to be regarded as gradual, but steadily
progressive, changes in the organisation, which are striven after during
the individual life of the organism, preserved by transmission in a
series of generations, and further developed by means of natural
selection. What has been gained by the ancestor becomes the heritage of
the descendant. Adaptation and Transmission are thus alternately
effective, the former representing the modifying, the latter the
conservative principle.... Adaptation is commenced by a change in the
function of organs, so that the _physiological relations_ of organs play
the most important part in it. Since adaptation is merely the material
expression of this change of function, the modification of the function
as much as its expression is to be regarded as a gradual process. In
Adaptation, the closest connection between the function and the
structure of an organ is thus indicated. Physiological functions govern,
in a certain sense, structure; and so far what is morphological is
subordinated to what is physiological" (_Elements_, pp. 8-9). Gegenbaur
recognised also that morphological differentiation depended largely on
the physiological division of labour (_Grundzuege_, p. 49).

It is clear that Gegenbaur realised vividly the importance of function,
and in this respect, as in others, he is far beyond Haeckel. The same
thing comes out markedly in his treatment of correlation. Haeckel had no
slightest feeling for the true meaning of correlation. For him, as for
Darwin, it reduced itself to a law of correlative variation, according
to which "actual adaptation not only changes those parts of the organism
which are directly affected by its influence, but other parts also, not
directly affected by it."[384] Such "correlative adaptation" was due to
nutrition being a "connected, centralised activity."

Gegenbaur, on the contrary, had a firm grasp of the Cuvierian
conception, and expressed it in unmistakable terms. "As indeed follows
from the conception of life as the harmonious expression of a sum of
phenomena rigorously determining one another, no activity of an organ
can in reality be thought of as existing for itself. Each kind of
function (_Verrichtung_) presupposes a series of other functions, and
accordingly every organ must possess close relations with, and be
dependent on, all the others" (_Grundzuege_, p. 71). The organism must be
regarded as an individual whole which is as much conditioned by its
parts as one part is conditioned by the others. For an understanding of
correlation a knowledge of functions, and of the functional relations of
the organism to its environment, is clearly indispensable.

Gegenbaur's morphological system was out-and-out evolutionary. "The most
important part of the business of comparative anatomy," in Gegenbaur's
eyes, "is to find indications of genetic connection in the organisation
of the animal body" (_Elements_, p. 67).

The most important clue to discovering this genetic connection is of
course that given by homology; it is indeed the main principle of
evolutionary morphology that what is common in organisation is due to
common descent, what is divergent is due to adaptation. "Homology ...
corresponds to the hypothetical genetic relationship. In the more or the
less clear homology, we have the expression of the more or less intimate
degree of relationship. Blood-relationship becomes dubious exactly in
proportion as the proof of homologies is uncertain" (_Elements_, p. 63).

It is worth noting that while Gegenbaur agrees with Haeckel generally
that morphological relationships are really genealogical, that, for
instance, each phylum has its ancestral form, he enters a caution
against too hastily assuming the existence of a genetic relation between
two forms on the basis of the comparison of one or two organs. "In
treating comparative anatomy from the genealogical standpoint required
by the evolution-theory," he writes, "we have to take into consideration
the fact that the connections can almost never be discovered in the real
genealogically related objects, for we have almost always to do with the
divergent members of an evolutionary series. We derive, for instance,
the circulatory system of insects from that of Crustacea ... but there
exists neither a form that leads directly from Crustacea to insects nor
any organisatory state (_Organisationszustand_), which as such shows the
transition. Even when one point of organisation can be denoted as
transitional, numerous other points prevent us from regarding the whole
organism strictly in the same light" (_Grundzuege_, p. 75). The real
ancestral forms cannot, as a rule, be discovered among living species,
nor often as extinct. "When we arrange allied forms in series by means
of comparison, and seek to derive the more complex from the simpler, we
recognise in the lower and simpler forms only similarities with the
ancestral form, which remains essentially hypothetical" (p. 75).

The facts of development, Gegenbaur goes on to say, help us out greatly
in our search for ancestral forms, for the early stages in the ontogeny
of a highly organised animal give us some idea of the organisation of
its original ancestor. Characters common to the early ontogeny of all
the members of a large group are particularly important in this respect
(_cf._ von Baer's law).

Gegenbaur distinguishes homologous or morphologically equivalent
structures from such as are analogous or physiologically equivalent,
just as did Owen and the older anatomists. Like von Baer he recognises
homologies, as a rule, only within the type.

He contributed, however, to the common stock a useful analysis of the
concept of homology, and established certain classes and degrees of it.
He distinguished first between general and special homology, in quite a
different sense from Owen.

General homology, in Gegenbaur's sense, relates to resemblances of
organs within the organism, and includes four kinds of resemblance,
homotypy, homodynamy, homonomy and homonymy. Right and left organs are
homotypic, metameric organs are homodynamic; homonomy is the relation
exemplified by fin-rays or fingers, which are arranged with reference to
a transverse axis of the body; homonymy is a sort of metamerism in
secondary parts (not the main axis) of the body, and is shown by the
various divisions of the appendages (_Grundzuege_, p. 80).

Special homology, on the other hand, relates to resemblances between
organs in different animals. The interesting thing is that Gegenbaur
defines it genetically. Special homology is the name we give "to the
relations which obtain between two organs which have had a common
origin, and which have also a common embryonic history" (_Elements_, p.
64). This is his definition; but, in practice, Gegenbaur establishes
homologies by comparison just as the older anatomists did, and infers
common descent from homology, not homology from common descent.

"Special homology," he continues, "must be again separated into
sub-divisions, according as the organs dealt with are essentially
unchanged in their morphological characters, or are altered by the
addition or removal of parts" (p. 65). In the former case the homology
is said to be "complete," in the latter "incomplete." Thus the bones of
the upper arm are completely homologous throughout all vertebrate
classes from Amphibia upwards, while the heart of a fish is incompletely
homologous with the heart of a mammal.

Independently of Gegenbaur, Sir E. Ray Lankester proposed in 1870 a
genetic definition of homology.[385] He proposed, indeed, to do away with
the term homology altogether, on the ground that it included many
resemblances which were obviously not due to common descent--as, for
instance, the resemblance of metameres. So, too, organs which were
homologous in the ordinary sense, as the heart of birds and mammals,
might have arisen separately in evolution. He proposed, therefore, that
"structures which are genetically related, in so far as they have a
single representative in a common ancestor," should be called
_homogenous_(p. 36). All other resemblances were to be called
_homoplastic_. "Homoplasy includes all cases of close resemblance of
form which are not traceable to homogeny, all details of agreement not
homogenous, in structures which are broadly homogenous, as well as in
structures having no genetic affinity" (p. 41). Serial homology, for
instance, was a case of homoplasy.

The term "analogy" was to be retained for cases of functional
resemblance, whether homogenetic or not.

The attempt was an interesting one, but most morphologists wisely
adhered to the old concept of homology, in spite of Lankester's
declaration that this belonged to an older "Platonic" philosophy, and
ought to be superseded by a term more consonant with the new philosophy
of evolution.

[366] _Generelle Morphologie der Organismen. Allgemeine
Grundzuege der organischen Formenwissenschaft, mechanisch
begruendet durch die von Ch. Darwin reformierte
Descendenztheorie_. Berlin, 1866. Reprinted in part as
_Prinzipien der generellen Morphologie der Organismen_.
Berlin, 1906.

[367] He mentions as his predecessors in this field,
Bronn, J. Mueller, Burmeister, and G. Jaeger.

[368] In _Grundriss einer Allgemeinen Naturgeschichte der
Radiolarien_, Berlin, 1887, and _Kunstformen der Natur_,
Suppl. Heft, Leipzig.

[369] Haeckel had an intense admiration for Goethe's
morphological work. It is a curious coincidence that the
work of Goethe, Oken and Haeckel was closely associated
with the town of Jena.

[370] But he himself would not admit this! See _Gen.
Morph._, ii., p. 11.

[371] _Fuer Darwin_, 1864. Eng. trans, by Dallas as _Facts
and Arguments for Darwin_, London, 1869.

[372] The bion is the physiological, as the morphon is the
morphological, individual.

[373] See Vogt, _Embryologie des Salmones_, p. 259, 1842,
and _supra_, p. 230.

[374] _An Essay on Classification_, London, 1859.

[375] It was hinted at by Tiedemann. "It is clear that,
proceeding from the earlier to the more recent strata, a
gradation in fossil forms can be established from the
simplest organised animals, the polyps, up to the most
complex, the mammals, and that accordingly the animal
kingdom as a whole has its developmental periods just
like the single individual organism. The species and
genera which have become extinct during the evolutionary
process may be compared with the organs which disappear
during the development of the individual animal" (p. 73,
1808).

[376] _The History of Creation_, vol. i., p. 310, 1876.
Translation of the _Natuerliche
Schoepfungsgeschichte_, 1868.

[377] _Cf._ a parallel passage from Serres, _supra_, p.
82.

[378] _Jenaische Zeitschrift_, ix., pp. 402-508, 1875.

[379] _Loc. cit._, ix., p. 409.

[380] _Untersuchungen zur vergl. Anatomie d.
Wirbelthiere_, Leipzig, i., 1864; ii., 1865; and iii.,
1872.

[381] "U. d. Biologie in Jena waehrend des 19
Jahrhunderts," _Jenaische Zeitschrift_, xxxix., pp.
713-26, 1905.

[382] _Grundriss der vergl. Anatomie_, 1874, 2nd ed.,
1878. Trans. by F. Jeffrey Bell, revised by E. Ray
Lankester, as _Elements of Comparative Anatomy_, London,
1878.

[383] "This theory (evolution) shows that what was
formerly called 'structural plan' or 'type' is the sum
of the dispositions (_Einrichtungen_) of the animal
organisation which are perpetuated by heredity, while it
explains the modifications of these dispositions as
adaptive states. Heredity and adaptation are thus the
two important factors through which both the unity and
the variety of organisation can be understood"
(_Grundzuege_, p. 19).

[384] _History of Creation_, i., pp. 241-2.

[385] "On the use of the term Homology in Modern Zoology,
and the distinction between Homogenetic and Homoplastic
agreements," _Ann. Mag. Nat. Hist._ (4), vi., pp. 35-43,
1870.




CHAPTER XV

EARLY THEORIES ON THE ORIGIN OF VERTEBRATES


Haeckel and Gegenbaur set the fashion for phylogenetic speculation, and
up to the middle 'eighties, when the voice of the sceptics began to make
itself heard, the chief concern of the younger morphologists was the
construction of genealogical trees. The period from about 1865 to 1885
might well be called the second speculative or transcendental period of
morphology, differing only from the first period of transcendentalism by
the greater bulk of its positive achievement. It must be remembered that
the later workers (at least towards the end of this period) had immense
advantages over their predecessors in the matter of equipment and
technique; they possessed well-fitted laboratories in the university
towns and by the sea; they had at their command perfected microscopes
and microtomes; while the whole new technique of microscopical anatomy
with its endless variety of stains and reagents made it possible for the
tyro to confirm in a day what von Baer and Mueller had taken weeks of
painful endeavour to discover.[386] But the democratisation of morphology
which followed upon the facilitation of its means of research left an
evil heritage of detailed and unintelligent work to counterbalance the
very great and real advances which technical improvements alone rendered
possible.

This period of rapid development, which set in soon after the coming of
evolution and multiplied the concrete facts of morphology an
hundredfold, may for our present purpose be conveniently divided into
two somewhat overlapping periods, of which the second may be said to
begin with the enunciation by Haeckel of his Gastraea theory. Within the
first period fall the evolutionary speculations associated with the
names of Kowalevsky, Dohrn, Semper, and others; the characteristic of
the second period is the preponderating influence exercised upon
phylogenetic speculations by the germ-layer doctrine in its two main
evolutionary developments, the Gastraea and Coelom theories.

In the first period we might again distinguish two main tendencies,
according as speculations were based mainly upon anatomical or mainly
upon embryological considerations, and it so happens that these two
tendencies are very well illustrated by the various theories as to the
origin of Vertebrates which began to appear towards the 'seventies. We
shall accordingly, in this chapter, consider very briefly the history of
the earlier views on the phylogeny of the vertebrate stock.

In the early days, before the other claimants to the dignity of
ancestral form to the Vertebrates--_Balanoglossus_, Nemertines and the
rest--had put in an appearance, there were two main views on the
subject, one upheld by Haeckel, Kowalevsky and others, to the effect
that the proximate ancestor of Vertebrates was a form somewhat
resembling the ascidian tadpole, the other supported principally by
Dohrn and Semper that Vertebrates and Arthropods traced their descent to
a common segmented annelid or pro-annelid ancestor. The former view is
historically prior, and arose directly out of the brilliant
embryological investigations of A. Kowalevsky, who proved himself to be
a worthy successor of the great comparative embryologist Rathke. His
work was indeed a true continuation of Rathke's. It was not directly
inspired by evolution, though it supplied much useful confirmation of
the theory--you may read Kowalevsky's earlier memoirs and not realise
that they were written several years after the publication of the
_Origin of Species_.

His first paper of evolutionary importance was a note in Russian on the
development of Amphioxus, published in 1865. This subject was followed
up in two papers which appeared in 1867[387] and 1877.[388] In his
papers on Amphioxus Kowalevsky made out the main features in the
development of this primitive form, and showed that the chief organs
were formed in essentially the same way as in Vertebrates; he described
the formation of the archenteron by invagination, the appearance of the
medullary folds, which coalesced to form the neural canal, the formation
of the notochord and of the gill-slits. At first he made the mistake of
supposing that the body-cavity arose from the segmentation-cavity, but
in his later paper he rightly surmised that it was formed from the
cavities of the "primitive vertebrae," or mesodermal segments. The origin
of the notochord from the endoderm was also not made out by Kowalevsky
in his paper of 1867.

Although many important details remained to be discovered by later
investigators,[389] Kowalevsky's work at once made the development of
Amphioxus the key to vertebrate embryology, the typical ontogeny with
which all others could be compared.

Meanwhile, in 1866 and 1871, Kowalevsky had communicated memoirs of even
greater interest,[390] in which he showed that the simple Ascidians
developed in an extraordinarily similar way to Amphioxus and hence to
Vertebrates in general. His proof that Ascidians also develop on the
vertebrate type aroused great interest at the time, and was naturally
acclaimed by the evolutionists as a striking piece of evidence in favour
of their doctrine. The systematic position of the Ascidians was at that
time quite uncertain; they were grouped, as a rule, with the Mollusca,
and certainly no one suspected that their well-known tailed larvae, first
seen by Savigny, showed any but the most superficial analogy with the
tadpoles of Amphibia. Kowalevsky's papers put a different complexion on
the matter. In the first of them he showed how the nervous system of the
simple Ascidian developed from ectodermal folds just as it did in
Amphioxus and Vertebrates, how gill-slits were formed in the walls of
the pharynx, and how there existed in the ascidian larva a structure
which in position and mode of development was the strict homologue of
the vertebrate notochord. In his second paper he entered into much more
detail, and published some excellent figures, often reproduced since
(see Fig. 13), but the proof of the affinity between Vertebrates and
Ascidians was in all essentials complete in his paper of 1866.

[Illustration: FIG. 13.--Development of the Ascidian Larva. (After
Kowalevsky.)]

Kowalevsky's results were accepted by Haeckel, Gegenbaur, Darwin,[391]
and many others as conclusive evidence of the origin of Vertebrates
from a form resembling the ascidian tadpole; they were extended and
amplified by Kupffer[392] in 1870, later by van Beneden and Julin[393]
and numerous other workers; they were adversely criticised by
Metschnikoff[394] and von Baer,[395] as well as by H. de
Lacaze-Duthiers and A. Giard.[396] Lacaze-Duthiers and von Baer both
held fast to the old view that Ascidians were directly comparable with
Lamellibranch molluscs; they denied the homology of the ascidian
nervous system with that of Vertebrates, von Baer being at great pains
to show that the ascidian nerve-centre was really ventral in position.
He pointed out also that the "notochord" was confined to the tail of
the ascidian larva. Giard's attitude was by no means so
uncompromising, and the criticisms he passed on the Kowalevsky theory
are both subtle and instructive. He admits that there exists a real
homology between, for instance, the notochord of Vertebrates and that
of Ascidians. "But," he adds, "it is too often forgotten that homology
does not necessarily mean an immediate common origin or close
relationship. There exist, doubtless, homologies of great atavistic
importance--I consider as such, for example, the formation of the
cavity of Rusconi [the archenteron] in Ascidians and lower
Vertebrates. But there are also adaptive and purely analogical
homologies, such as the interdigital palmation of aquatic birds,
amphibians and mammals. These are not purely analogous organs, for
they can be superposed one on another, which is not the case with
simply analogous structures (the bat's wing, for example, cannot be
superposed on the bird's wing); they are homologous formations,
resulting from the adaptation of the same fundamental organs to
identical functions. Such is, in my opinion, the nature of the
homology existing between the tail of the ascidian tadpole and that of
Amphioxus or of young amphibians. The ascidian larva, having no cilia
and being necessarily motile, requires for the insertion of its
muscles or contractile organs ... a central flexible axis, a true
chorda dorsalis analogous to that of Vertebrates" (pp. 278-9). This
point of view is strengthened by the fact that in _Molgula_, studied
by Lacaze-Duthiers, the embryo is practically stationary, and forms no
notochord, nor ever develops sense-organs in the cerebral vesicle.

Giard's general conclusion is that "the true homology with Vertebrates
ceases after the formation of the cavity of Rusconi and the medullary
groove: the homologies established by Kowalevsky for the notochord and
the relations of the digestive tube and nervous systems are not
atavistic, but adaptive, homologies" (p. 282). There is accordingly no
close genetic relationship between Ascidians and Vertebrates.

Giard's criticisms did not avail to check the vogue of the new theory,
which soon became an accepted article of faith in most morphological
circles.[397] The fall of the Ascidians from their larval high estate
provided the text for many a Darwinian sermon.

Some years after the genetic relationship of Ascidians and Vertebrates
had been established, a rival theory of the origin of Vertebrates made
its appearance--a theory which was practically a rehabilitation in a
somewhat altered form of the old Geoffroyan conception that Vertebrates
are Arthropods walking on their backs. This was the so-called Annelid
theory of Dohrn and Semper. Both Dohrn and Semper started out from the
fact that Annelids and Vertebrates are alike segmented animals, and it
was an essential part of their theory that this resemblance was due to
descent from a common segmented ancestor. Both laid great stress on the
fact that the main organs in Vertebrates are arranged in the same way as
in an Annelid lying on its back, the nervous system being uppermost, the
alimentary system coming next, and below this the vascular.

Dohrn's earlier views are contained in the fascinating little book
published in 1875, which bears the title _Der Ursprung der Wirbelthiere
und das Princip des Functionswechsel_ (Leipzig). He followed this up by
a long series of studies on vertebrate anatomy and embryology,[398] in
which he modified his views in certain details. We shall confine our
attention to the first sketch of his theory.

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