of all organic beings from form to form--a transmutation _en masse_ of
the whole--so that to any one among them they would all appear
stationary. Such a view is utterly opposed to the greater number of
zoological and palæontological facts, and to all the necessities of the
Darwinian hypothesis. One species, either with little inherent capacity
for variation, or so circumstanced that such variation as may have
occurred in different individuals has never been accumulated by
selection, may remain without alteration for ages, while other species
differently constituted or circumstanced may have undergone vast
transmutations during the same period. In fact, the derivative
hypothesis is not a theory of things long ago; it is not a curious
speculation into the beginnings of the present condition of things. It
may be appealed to every day in the solution of constantly occurring
problems in morphology.
I will give an example from the subject of our present course. There is
in Australia an animal, the koala (_Phascolarctos cinereus_), rather
larger than a cat, but having more the aspect of a small bear (Fig. 1).
It is covered with a soft woolly fur, and lives entirely among the
boughs of trees, on the leaves of which it feeds. Its tail is a mere
rudiment. Its feet are admirably adapted for grasping the branches on
which it climbs. The hind feet especially are remarkably modified for
this end, being very broad, and having a strong prehensile or opposable
inner toe or hallux, like a thumb. The skeleton of that foot is very
singular (see Fig. 2). The hallux is stout, and placed nearly at a right
angle with the other toes. The next two digits are rather slender,
placed close together, and in the living animal are united almost to the
claws in a common integument. The two outer toes are free and much
stouter than the others, the fourth especially so.
Now, a naturalist of the last century would have looked upon this foot
simply as a piece of machinery beautifully
[Illustration: FIG. 1.--The Koala (_Phascolarctos cinereus_). From
_Gould’s Mammals of Australia_.]
adapted for the particular work it had to perform in the animal’s life.
He would have pointed to the broad palm, the
[Illustration: FIG. 2.--Skeleton of the hind foot of the Koala
(_Phascolarctos cinereus_).]
opposable great toe, and would doubtless, if a worthy representative of
his school, have developed some ingenious theory to show that the
smaller size of the second and third toes, and that being wrapped up to
their ends in skin, added to the efficiency of the foot as a climbing
organ, though indeed he might be at a loss to say why the American
opossums, of precisely similar habits, and with similarly opposable
great toes, have all their other four toes free and equal.
[Illustration: FIG. 3.--Skeleton of the hind foot of the Virginian
Opossum (_Didelphys Virginiana_).]
The philosophical naturalist of the second of the types that I have
sketched out, in investigating this structure, will institute a careful
comparison between the foot of the koala and that of other animals
belonging to the same group.
Among the marsupial animals of Australia, few are so well known as the
kangaroo. Like the koala, it is a vegetable feeder, and these two forms
have some dental and other structural characters in common. But the mode
of progression, and the limbs which effect this, offer the greatest
possible contrast.
In the kangaroo the hind legs are disproportionately large. The foot
especially is long and narrow, and at first sight appears composed of a
single large toe. Its motion along the ground consists of a series of
leaps or hops effected entirely by these powerful hind limbs. On looking
more closely at the foot (see Fig. 4), it will be seen that the first
digit or hallux is entirely wanting, but the other four toes are present
with their complete number of phalanges. The fourth is immensely
developed, the fifth moderately so, but the second and third are reduced
to the most slender rudiments, and are so united in life by a common
integument, that they look like a single toe with a double claw.
Now, here are two feet as unlike as possible in their functions--the one
formed for rapidly hopping along over the arid plains, the other for
slowly and securely climbing among the boughs of the forests--yet
presenting a deep-seated resemblance in a character not found in the
feet of any other known mammal except the immediate allies of these two.
We may call this “conformity to type” without getting much nearer to an
explanation of the phenomenon. Perhaps it is safest to rest at this
stage.
[Illustration: FIG. 4.--Skeleton of the hind foot of the kangaroo
(_Macropus major_).]
But is it not powerfully suggestive--I will not say more, for, of
course, by itself it cannot be considered as a proof--of true
relationship, of inheritance from a common ancestor? We can easily see
that in some manner the great preponderance of the one toe in the
kangaroo, and the reduction of the others, would be advantageous in its
mode of progression, reducing the foot to a narrow spring-board as it
were; and we can see that this attenuation of the second and third toes,
after the first had quite disappeared, might be a stage in the direction
of their total disappearance. But while this was taking place, let us
suppose that one branch of the family took to climbing trees (I must not
enter fully into all that might be supposed on this subject, as I am
merely introducing this as an example of the mode in which morphological
problems are illustrated by these general views), and the variations in
a particular direction, tending towards better climbing, were preserved
and accumulated on the Darwinian hypothesis, the hallux (a common part
in all mammals, only in abeyance when not wanted) was redeveloped in a
form best adapted for its actual purposes, the other digits gradually
resuming their normal condition; these two, however, still preserving
strong reminiscences of the ancestral state.[24]
It is certainly significant that all the Australian vegetable-feeding
climbing opossums have feet constructed on this type, one that is
similar to that of the kangaroos of the same country, while the American
opossums, further removed geographically, and therefore, in all
probability, in actual relationship, with feet functionally the same,
show no trace of this deep-seated structural peculiarity--a peculiarity
most important for the consideration of the philosophical anatomist, as
it evidently depends on some more far-reaching cause than mere
adaptation to purpose.
* * * * *
In considering a little more fully the application of such views to the
study of morphology, I must say a few words on _classification_. It was
felt at the very outset of the study of natural history that without
some system of classification the subject was little more than a
hopeless chaotic confusion. The first instinct of a zoologist is to
arrange in some sort of order the multitudinous objects with which he
has to deal. In the beginning of science, with little sound knowledge,
such classifications were often mere arbitrary arrangements, founded on
some easily accessible peculiarities, and forming nothing more than a
means by which the distinction between certain objects and certain other
objects could be grasped by the mind of the founder and communicated to
others. Classifications based on such characters became so general, and
were often so carelessly and ignorantly put together, that they
threatened to bring the whole system into disrepute; whereas I have
little hesitation in saying that, in reality, _classification_ is one of
the, if not the, most important aims and ends of the study of
morphology. It is the best contribution which we can make towards the
solution of the great biological problem, for a true classification,
viewed by the light of the derivative hypothesis, is nothing more or
less than an expression of the actual amount of affinity between
different objects. An order, a family, or a genus is no longer a group
of animals linked together by some arbitrarily selected characters, but
a group supposed to have been descended from a common ancestor, and to
have become, by whatever process, gradually differentiated from other
groups of animals.[25]
As in such groups, when once established, there can be no crossing with
other groups (as in human families, to which they are sometimes
compared), all the resemblances which are found between members of
different groups must either be characters inherited from the common
ancestor, perhaps lost through many generations and reappearing at a
subsequent period by the process of “reversion,” or they must be
characters having merely _analogical_ resemblances--_i.e._ characters
developed by variation, but which, owing to similarity of conditions of
existence or other causes, have become similar to each other.
To discriminate between these two classes of characters,--namely, those
that are essential and fundamental, or, in the language of one school,
are dependent on conformity to type, or, according to the derivative
hypothesis, are inherited from remote ancestors, and those that are
modifications to suit the conditions of existence to which the animal
is exposed, or, in other words, adaptive characters,--is a constantly
recurring problem to the systematic morphologist; and the difficulties
that encompass the solution of this problem are the main causes of the
little progress hitherto made towards a general agreement as to
classification otherwise than in the main groups. Let me illustrate this
point by a single and, as it happens, by no means difficult example.
[Illustration: FIG. 5.--The Thylacine (_Thylacinus cynocephalus_). From
Wolf’s _Zoological Sketches_.]
You have before you the skeletons of two animals very similar in their
general or superficial characters--one is the common dog, the other the
carnivorous marsupial, the thylacine, sometimes called “Tasmanian wolf.”
These animals, when wild, have very similar habits. You will see that,
in the general characters of the skeleton, the structure of the limbs,
and the arrangement of the teeth, a remarkable similarity prevails. You
might easily conclude that these animals were related. They were,
indeed, formerly placed near together by systematists.
Now, if I place by the dog another well-known animal, a sheep, you will
see that in many characters of its bones, its feet, its teeth, etc., it
differs far more from the dog than the latter does from the thylacine.
Yet zoologists affirm, without the slightest hesitation, that the sheep
and the dog are far more nearly related to each other than either is to
the thylacine. This assertion is founded on a discrimination of the
essential from the adaptive characters. The dog and the sheep belong to
one great branch of the mammalian class, although they represent
different stocks of that branch. The thylacine belongs to another
primary branch, but in that branch it has taken the place, functionally,
of the dog in the other; its organs have become adapted to perform the
same work.[26]
It has been asserted, in a recent very able pamphlet by an anonymous
writer, “On the Difficulties of the Theory of Natural Selection,”[27]
“that on the theory of ‘natural selection’ it is all but impossible,
such are the probabilities against it, that identical structures should
have arisen independently. Yet many structures undeniably exist which,
to all appearance, must have so arisen.” And the “remarkable identity of
structure between certain of the teeth of the large predatory marsupial,
the thylacine, or Tasmanian wolf, and those of the common dog,” is cited
as a case in point. Now, though I am fully willing to admit difficulties
in the theory, quite inexplicable with our present knowledge, as many
almost as the author quoted, I cannot see this one in the same light. It
appears to me that the probabilities, instead of being against the
independent origin of such similar structures (erroneously called
_identical_) as those just mentioned, are exceedingly in their favour. I
cannot in the least see why a marsupial animal should not be carnivorous
and predaceous as well as a placental animal, and if so, why its teeth
should not have come to possess the general attributes essential to
animals of such habits--namely, large, pointed, recurved fangs at each
of the anterior angles of the jaw; the teeth between them much reduced,
so as not to interfere with the piercing and holding action of the
canines; the molars more or less scissor-shaped. These are plainly
adaptive characters, and whatever process has produced them in the one
case is just as likely to have produced them in the other--I might
almost say, must have produced them in the other. So far, however, are
the teeth of the thylacine and the dog from being essentially
“identical,” that in numerous non-adaptive and non-functional
characters, as the number of the incisors, premolars, and molars, the
mode of succession, and the minute structure (all which will be spoken
of at a later period of the course), they widely differ, the dog
conforming in all these points with the ordinary placental mammals, the
thylacine with the remaining marsupials. Such characters, underlying, in
large groups of animals, the various modifications in relation to use,
cannot be too diligently sought out as the true landmarks to guide our
steps through the intricacies that beset our path in tracing affinities.
[Illustration: FIG. 6.--Skull of Thylacine.]
[Illustration: FIG. 7.--Skull of Shepherd’s Dog.]
Another valuable guiding principle in morphological studies is this. It
is a remark of Gegenbaur’s, in his valuable work “On the Structure of
the _Carpus_ and _Tarsus_,” but it must have occurred to any one who has
given much thought to these problems. When we wish to discover the
distinguishing characters between different organisms, it is necessary
to examine them in their most fully developed condition. If, on the
other hand, our object is to trace their resemblance, their intimate
relationships, we must study them in their early embryonic stages. By
these methods we can do much to separate what is secondary or superadded
from what is fundamental or essential in the character of an animal. The
farther back we can carry our researches, the more prominent do the
characters, common to the whole group to which the animal belongs,
become. The more completely mature the specimen, the more do the special
characters of the species or even of the individual predominate.
* * * * *
It is not my province in these lectures to indulge much in speculations.
Indeed, as students of morphology, we are as yet little in a position to
do so. I shall not say much more even on the general views to which I
have lately referred, for I feel that the acquisition of a sound basis
of fact to work with is what is, at present, most needed in comparative
anatomy. The difficulties which beset the beginner, and indeed the more
advanced student, in this subject are very great. As regards the branch
to which I propose more particularly to direct your attention, the
anatomy of the class Mammalia, which, we might suppose, was better
worked out than any other, the information to be found in books is
scattered, fragmentary, unequal, and often untrustworthy; even good
elementary treatises are wanting, much more anything like an exhaustive
work. Moreover, our museum--superior as I believe it to be to any other
of the kind--is, as yet, far from adequate to supply the knowledge
frequently sought for in it.
In considering the special subject for these lectures, I have often
thought that the greatest permanent benefit would be conferred on our
science by collecting together in a systematic form all the available
information upon limited groups of the animal kingdom, supplementing, as
far as possible, the deficiencies of knowledge by fresh observations,
and illustrating the subject by a complete series of preparations. At
the present day it is only by working out a definite branch of limited
extent monographically, that any solid advances in detailed knowledge
can be attained. Courses of lectures on this principle, especially if
they were published so as to reach a wider circle of students than this
theatre is apt to contain, may do much to _advance_ knowledge; but, on
the other hand, they might do less than more elementary lectures, giving
a general outline of a larger variety of topics, to _diffuse_ knowledge,
for it is probable that they would be attractive to only a limited
number of auditors or of readers.
I think it therefore advisable, in the first course I have the honour of
addressing to you, to confine my subject to a survey of the structure of
the animals of the highest class of organised beings; and I think that
this will prove of the greater importance and interest to the audience
assembled here, because it may be presumed that all have already either
commenced or completed the acquisition of a knowledge of the structural
anatomy of one, the most elevated member, of that class. I propose,
therefore, to take human anatomy as a point of departure, and, presuming
on your acquaintance with its details, shall refer only to some of its
general outlines, and shall point out the deviations from and
resemblance to the mammalian structure as we know it in man, in
descending throughout the series of animals composing the class.
I trust that some further interest may be given thereby to the daily
work of the student of our profession. Human anatomy is too often
learned as a mere collection of hard names applied to a complicated
network of structures, the form, position, and relation of which have to
be got up, probably to be forgotten soon afterwards. It might, however,
be made a far more attractive and useful subject if taught by the light
of a wider morphology. But I am afraid that very little of our
anatomical teaching, either by books or lectures, is of this class at
present. If any comparative anatomy is introduced, instead of
enlightening and illustrating the subject, it often only adds another
load to the already over-burdened memory--for instance, after the usual
dry, detailed and technical description of the part treated of, a
disquisition is added on what is called its “transcendental” anatomy,
extremely incomprehensible to most minds, and consisting chiefly in the
imposition of a new set of names to parts of which the student has just
succeeded in mastering the old ones.
All this ought to be reversed; the essential nature of the part in
question, as deduced from comparative anatomy, should be first announced
with a glance at its principal modifications; then its special
characters as seen in man will be a subject of intelligent interest. I
know from experience that after studying and teaching human anatomy for
many years on the ordinary methods, there were many parts the meaning
and nature of which I never understood until I began to dissect animals;
and increase of knowledge in this direction constantly throws light on
apparently unmeaning or incomprehensible parts of human structure.
One word more by way of introduction. I began with the mention of my
immediate predecessor in this chair. To him I must once again return.
The subject matter of the present course will embrace many points
treated of by him, more or less fully, in some of his lectures delivered
in this theatre, and many on which I have had the advantage of his
conversation and counsel. His teaching has entered so deeply into, and
mingled so closely with, observations and reflections that may have
suggested themselves in the course of my work in the museum, that in
many cases it would be difficult to trace the sources of information
that I may have to impart, and I may, perhaps, appear guilty of
appropriating what should belong to another. Let me acknowledge then,
once for all, how deeply I am indebted to Professor Huxley, not only for
the information conveyed in the public manner of lectures and books, but
also for the generous way in which, on all occasions, his time, his
knowledge, his thoughts, have been freely given to me. And I say this
the more willingly, because I know that I am but one of many whose
labours have been lightened, whose efforts have been stimulated, whose
difficulties have been smoothed, by his encouragement and support, by
his candid and judicious criticism, and by the example of his often
self-sacrificing devotion to the advancement of scientific truth.
I also desire, in conclusion, Mr. President, to take this opportunity of
publicly expressing the obligations which I, as well as numbers of
others, feel towards you and your predecessors in that chair, as well as
to the former and present members of the Council of the College,
individually and collectively, for the immense aid that you have given
to the progress of philosophical biology in this country, and I may say,
in the whole world, by the maintenance and augmentation of John Hunter’s
Museum. An epoch of revolution appears to be at hand in our profession,
which may lead to a material alteration in the respective positions and
opportunities of the various corporate bodies. Whatever changes may take
place, the College of Surgeons will always look back with satisfaction
to the fact that, for the first seventy years of the century, when these
studies were less appreciated than they are now, or will be hereafter,
it has, with scanty aid from the national resources, cherished the
growth of a truly national institution, the benefits of which are not
confined to any one class or profession, but are freely open to the
whole community. I can say, moreover, with perfect assurance, speaking
both from my own experience and from knowledge of the history of the
museum, as recorded in its archives, that any deficiencies which exist
in the condition of the collection, any needs which it does not supply,
must be due to other causes than want of encouragement to the officers
of the establishment, or want of liberality in supplying the requisite
funds, on the part of the Council of the College.
IX
RECENT ADVANCES IN NATURAL SCIENCE IN RELATION TO THE CHRISTIAN
FAITH[28]
I have been requested by the Subjects Committee of the Congress to place
before you a brief statement of some of the advances which have recently
been made in natural science, with a view to open a discussion upon
their relations, real or supposed, to religious belief. The particular
advances which, as I am given to understand, were especially in the
minds of the Committee in proposing this question, are those which have
resulted in the more or less general adoption by scientific men of the
view of the sequence of events which have taken place and are still
taking place in the universe, to which the term “evolution” is now
commonly applied.
All that is embraced by this term, the various realms of nature in which
its manifestations are traced, the various shades of meaning attached to
it by different persons, would constitute far too large and complex a
subject to be treated of in the time to which addresses to this meeting
are wisely restricted. I will therefore select for special consideration
the only point in the application of the theory upon which I can speak
with any practical knowledge--one which is, however, in the eyes of many
of very vital interest. It is the one, at all events, which at the
present moment attracts most attention; the new ideas upon it being
received with enthusiasm by some, and with distrust, if not with
abhorrence, by others.
The doctrine of continuity, or of direct relation of event to some
preceding event according to a natural and orderly sequence is now
generally recognised in the inorganic world; and although the modern
expansion of this doctrine as applied to the living inhabitants of the
earth appears to many so startling, and has met with so much opposition,
it is, in a more restricted application, a very old and widespread
article of scientific as well as of popular faith.