Facts and Arguments for Darwin
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Fritz Muller >> Facts and Arguments for Darwin
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FACTS AND ARGUMENTS
FOR
DARWIN.
BY FRITZ MULLER.
WITH ADDITIONS BY THE AUTHOR.
TRANSLATED FROM THE GERMAN
BY W.S. DALLAS, F.L.S.,
ASSISTANT SECRETARY TO THE GEOLOGICAL SOCIETY OF LONDON.
WITH ILLUSTRATIONS.
LONDON:
JOHN MURRAY, ALBEMARLE STREET.
1869.
MR. DARWIN'S WORKS.
A NATURALIST'S VOYAGE ROUND THE WORLD; BEING A JOURNAL OF RESEARCHES
INTO THE NATURAL HISTORY AND GEOLOGY OF COUNTRIES VISITED. Post 8vo. 9
shillings.
THE ORIGIN OF SPECIES, BY MEANS OF NATURAL SELECTION; OR, THE
PRESERVATION OF FAVOURED RACES IN THE STRUGGLE FOR LIFE. WOODCUTS. Post
8vo. 15 shillings.
THE VARIOUS CONTRIVANCES BY WHICH BRITISH AND FOREIGN ORCHIDS ARE
FERTILISED BY INSECTS, AND ON THE GOOD EFFECTS OF INTERCROSSING.
Woodcuts, Post 8vo. 9 shillings.
THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION. Illustrations.
2 volumes, 8vo. 28 shillings.
TRANSLATOR'S PREFACE.
My principal reason for undertaking the translation of Dr. Fritz
Muller's admirable work on the Crustacea, entitled 'Fur Darwin,' was
that it was still, although published as long ago as 1864, and highly
esteemed by the author's scientific countrymen, absolutely unknown to a
great number of English naturalists, including some who have occupied
themselves more or less specially with the subjects of which it treats.
It possesses a value quite independent of its reference to Darwinism,
due to the number of highly interesting and important facts in the
natural history and particularly the developmental history of the
Crustacea, which its distinguished author, himself an unwearied and
original investigator of these matters, has brought together in it. To a
considerable section of English naturalists the tone adopted by the
author in speaking of one of the greatest of their number will be a
source of much gratification.
In granting his permission for the translation of his little book, Dr.
Fritz Muller kindly offered to send some emendations and additions to
certain parts of it. His notes included many corrections of printers'
errors, some of which would have proved unintelligible without his aid,
some small additions and notes which have been inserted in their proper
places, and two longer pieces, one forming a footnote near the close of
Chapter 11, the other at the end of Chapter 12, describing the probable
mode of evolution of the Rhizocephala from the Cirripedia.
Of the execution of the translation I will say but little. My chief
object in this, as in other cases, has been to furnish, as nearly as
possible, a literal version of the original, regarding mere elegance of
expression as of secondary importance in a scientific work. As much of
Dr. Muller's German does not submit itself to such treatment very
readily, I must beg his and the reader's indulgence for any
imperfections arising from this cause.
W.S.D.
LONDON, 15TH FEBRUARY, 1869.
AUTHOR'S PREFACE.
It is not the purpose of the following pages to discuss once more the
arguments deduced for and against Darwin's theory of the origin of
species, or to weigh them one against the other. Their object is simply
to indicate a few facts favourable to this theory, collected upon the
same South American ground, on which, as Darwin tells us, the idea first
occurred to him of devoting his attention to "the origin of
species,--that mystery of mysteries."
It is only by the accumulation of new and valuable material that the
controversy will gradually be brought into a state fit for final
decision, and this appears to be for the present of more importance than
a repeated analysis of what is already before us. Moreover, it is but
fair to leave it to Darwin himself at first to beat off the attacks of
his opponents from the splendid structure which he has raised with such
a master-hand.
F.M.
DESTERRO, 7TH SEPTEMBER, 1863.
CONTENTS.
CHAPTER 1. INTRODUCTORY.
CHAPTER 2. THE SPECIES OF MELITA.
CHAPTER 3. MORPHOLOGY OF CRUSTACEA.
CHAPTER 4. SEXUAL PECULIARITIES AND DIMORPHISM.
CHAPTER 5. RESPIRATION IN LAND CRABS.
CHAPTER 6. STRUCTURE OF THE HEART IN EDRIOPHTHALMA.
CHAPTER 7. DEVELOPMENTAL HISTORY OF PODOPHTHALMA.
CHAPTER 8. DEVELOPMENTAL HISTORY OF EDRIOPHTHALMA.
CHAPTER 9. DEVELOPMENTAL HISTORY OF ENTOMOSTRACA,
CIRRIPEDES, AND RHIZOCEPHALA.
CHAPTER 10. ON THE PRINCIPLES OF CLASSIFICATION.
CHAPTER 11. ON THE PROGRESS OF EVOLUTION.
CHAPTER 12. PROGRESS OF EVOLUTION IN CRUSTACEA.
HISTORY OF CRUSTACEA.
CHAPTER 1. INTRODUCTORY.
When I had read Charles Darwin's book 'On the Origin of Species,' it
seemed to me that there was one mode, and that perhaps the most certain,
of testing the correctness of the views developed in it, namely, to
attempt apply them as specially as possible to some particular group of
animals. such an attempt to establish a genealogical tree, whether for
the families of a class, the genera of a large family, or for the
species of an extensive genus, and to produce pictures as complete and
intelligible as possible of the common ancestors of the various smaller
and larger circles, might furnish a result in three different ways.
1. In the first place, Darwin's suppositions when thus applied might
lead to irreconcilable and contradictory conclusions, from which the
erroneousness of the suppositions might be inferred. If Darwin's
opinions are false, it was to be expected that contradictions would
accompany their detailed application at every step, and that these, by
their cumulative force, would entirely destroy the suppositions from
which they proceeded, even though the deductions derived from each
particular case might possess little of the unconditional nature of
mathematical proof.
2. Secondly, the attempt might be successful to a greater or less
extent. If it was possible upon the foundation and with the aid of the
Darwinian theory, to show in what sequence the various smaller and
larger circles had separated from the common fundamental form and from
each other, in what sequence they had acquired the peculiarities which
now characterise them, and what transformations they had undergone in
the lapse of ages,--if the establishment of such a genealogical tree, of
a primitive history of the group under consideration, free from internal
contradictions, was possible,--then this conception, the more completely
it took up all the species within itself, and the more deeply it enabled
us to descend into the details of their structure, must in the same
proportion bear in itself the warrant of its truth, and the more
convincingly prove that the foundation upon which it is built is no
loose sand, and that it is more than merely "an intellectual dream."
3. In the third place, however, it was possible, and this could not but
appear, prima facie, the most probable case, that the attempt might be
frustrated by the difficulties standing in its way, without settling the
question, either way, in a perfectly satisfactory manner. But if it were
only possible in this way to arrive for oneself at a moderately certain
independent judgment upon a matter affecting the highest questions so
deeply, even this alone could not but be esteemed a great gain.
Having determined to make the attempt, I had in the first place to
decide upon some particular class. The choice was necessarily limited to
those the chief forms of which were easily to be obtained alive in some
abundance. The Crabs and Macrurous Crustacea, the Stomapoda, the
Diastylidae, the Amphipoda and Isopoda, the Ostracoda and Daphnidae, the
Copepoda and Parasita, the Cirripedes and Rhizocephala of our coast,
representing the class of Crustacea with the deficiency only of the
Phyllopoda and Xiphosura, furnished a long and varied, and at the same
time intimately connected series, such as was at my command in no other
class. But even independently of this circumstance the selection of the
Crustacea could hardly have been doubtful. Nowhere else, as has already
been indicated by various writers, is the temptation stronger to give to
the expressions "relationship, production from a common fundamental
form," and the like, more than a mere figurative signification, than in
the case of the lower Crustacea. Among the parasitic Crustacea,
especially, everybody has long been accustomed to speak, in a manner
scarcely admitting of a figurative meaning, of their arrest of
development by parasitism, as if the transformation of species were a
matter of course. It would certainly never appear to any one to be a
pastime worthy of the Deity, to amuse himself with the contrivance of
these marvellous cripplings, and so they were supposed to have fallen by
their own fault, like Adam, from their previous state of perfection.
That a great part of the larger and smaller groups into which this class
is divided, might be regarded as satisfactorily established, was a
further advantage not to be undervalued; whilst in two other classes
with which I was familiar, namely, the Annelida and Acalephae, all the
attempted arrangements could only be considered preliminary revisions.
These undisplaceable groups, like the sharply marked forms of the hard,
many-jointed dermal framework, were not only important as safe starting
points and supports, but were also of the highest value as inflexible
barriers in a problem in which, from its very nature, fancy must freely
unfold her wings.
When I thus began to study our Crustacea more closely from this new
stand-point of the Darwinian theory,--when I attempted to bring their
arrangements into the form of a geological tree, and to form some idea
of the probable structure of their ancestors,--I speedily saw (as indeed
I expected) that it would require years of preliminary work before the
essential problem could be seriously handled. The extant systematic
works generally laid more weight upon the characters separating the
genera, families and orders, than upon those which unite the members of
each group, and consequently often furnished but little employable
material. But above all things a thorough knowledge of development was
indispensable, and every one knows how imperfect is our present
knowledge of this subject. The existing deficiencies were the more
difficult to supply, because, as Van Beneden remarks with regard to the
Decapoda, from the often incredible difference in the development of the
most nearly allied forms, these must be separately studied--usually
family by family, and frequently genus by genus--nay, sometimes, as in
the case of Peneus, even species by species; and because these
investigations, in themselves troublesome and tedious, often depend for
their success upon a lucky chance.
But although the satisfactory completion of the "Genealogical tree of
the Crustacea" appeared to be an undertaking for which the strength and
life of an individual would hardly suffice, even under more favourable
circumstances than could be presented by a distant island, far removed
from the great market of scientific life, far from libraries and
museums--nevertheless its practicability became daily less doubtful in
my eyes, and fresh observations daily made me more favourably inclined
towards the Darwinian theory.
In determining to state the arguments which I derived from the
consideration of our Crustacea in favour of Darwin's views, and which
(together with more general considerations and observations in other
departments), essentially aided in making the correctness of those views
seem more and more palpable to me, I am chiefly influenced by an
expression of Darwin's: "Whoever," says he ('Origin of Species' page
482), "is led to believe that species are mutable, will do a good
service by conscientiously expressing his conviction." To the desire
expressed in these words I respond, for my own part, with the more
pleasure, as this furnishes me with an opportunity of publicly giving
expression in words to the thanks which I feel most deeply to be due
from me to Darwin for the instructions and suggestions for which I am so
deeply indebted to his book. Accordingly I throw this sand-grain with
confidence into the scale against "the load of prejudice by which this
subject is overwhelmed," without troubling myself as to whether the
priests of orthodox science will reckon me amongst dreamers and children
in knowledge of the laws of nature.
CHAPTER 2. THE SPECIES OF MELITA.
A false supposition, when the consequences proceeding from it are
followed further and further, will sooner or later lead to absurdities
and palpable contradictions. During the period of tormenting doubt--and
this was by no means a short one--when the pointer of the scales
oscillated before me in perfect uncertainty between the pro and the con,
and when any fact leading to a quick decision would have been most
welcome to me, I took no small pains to detect some such contradictions
among the inferences as to the class of Crustacea furnished by the
Darwinian theory. But I found none, either then, or subsequently. Those
which I thought I had found were dispelled on closer consideration, or
actually became converted into supports for Darwin's theory.
Nor, so far as I am aware, have any of the NECESSARY consequences of
Darwin's hypotheses been proved by any one else, to stand in clear and
irreconcilable contradiction. And yet, as the most profound students of
the animal kingdom are amongst Darwin's opponents, it would seem that it
ought to have been an easy matter for them to crush him long since
beneath a mass of absurd and contradictory inferences, if any such were
to be drawn from his theory. To this want of demonstrated contradictions
I think we may ascribe just the same importance in Darwin's favour, that
his opponents have attributed to the absence of demonstrated
intermediate forms between the species of the various strata of the
earth. Independently of the reasons which Darwin gives for the
preservation of such intermediate forms being only exceptional, this
last mentioned circumstance will not be regarded as of very great
significance by any one who has traced the development of an animal upon
larvae fished from the sea, and had to seek in vain for months, and even
years, for those transitional forms, which he nevertheless knew to be
swarming around him in thousands.
A few examples may show how contradictions might come forth as necessary
results of the Darwinian hypotheses.
It seems to be a necessity for all crabs which remain for a long time
out of the water (but why is of no consequence to us here), that air
shall penetrate from behind into the branchial cavity. Now these crabs,
which have become more or less estranged from the water, belong to the
most different families--the Raninidae (Ranina), Eriphinae (Eriphia
gonagra), Grapsoidae (Aratus, Sesarma, etc.), Ocypodidae (Gelasimus,
Ocypoda), etc., and the separation of these families must doubtless be
referred to a much earlier period than the habit of leaving the water
displayed by some of their members. The arrangements connected with
aerial respiration, therefore, could not be inherited from a common
ancestor, and could scarcely be accordant in their construction. If
there were any such accordance not referable to accidental resemblance
among them, it would have to be laid in the scale as evidence against
the correctness of Darwin's views. I shall show hereafter how in this
case the result, far from presenting such contradictions, was rather in
the most complete harmony with what might be predicted from Darwin's
theory.
(FIGURE 1. Melita exilii n. sp., male, enlarged five times. The large
branchial lamellae are seen projecting between the legs.)
A second example.--We are already acquainted with four species of Melita
(M. valida, setipes, anisochir, and Fresnelii), and I can add a fifth
(Figure 1), in which the second pair of feet bears upon one side a small
hand of the usual structure, and on the other an enormous clasp-forceps.
This want of symmetry is something so unusual among the Amphipoda, and
the structure of the clasp-forceps differs so much from what is seen
elsewhere in this order, and agrees so closely in the five species, that
one must unhesitatingly regard them as having sprung from common
ancestors belonging to them alone among known species. But one of these
species, M. Fresnelii, discovered by Savigny, in Egypt, is said to want
the secondary flagellum of the anterior antennae, which occurs in the
others. From the trustworthiness of all Savigny's works there can
scarcely be a doubt as to the correctness of this statement. Now, if the
presence or absence of the secondary flagellum possessed the
significance of a distinctive generic character, which is usually
ascribed to it, or if there were other important differences between
Melita Fresnelii and the other species above-mentioned, which would make
it seem natural to separate M. Fresnelii as a distinct genus, and to
leave the others united with the rest of the species of Melita--that is
to say, in the sense of the Darwinian theory, if we assume that all the
other Melitae possessed common ancestors, which were not at the same
time the ancestors of M. Fresnelii--this would stand in contradiction to
the conclusion, derived from the structure of the clasp-forceps, that M.
Fresnelii and the four other species above-mentioned possessed common
ancestors, which were not also the ancestors of the remaining species of
Melita. It would follow:--
1. From the structure of the clasp-forceps: that M. exilii, etc. and M.
Fresnelii would branch off together from a stem which branches off from
M. palmata.
2. From the presence or absence of the secondary flagellum: that M.
palmata, etc. and M. exilii, etc. would branch off together from a stem
which branches off from M. Fresnelii.
As, in the first case, among the Crabs, a typical agreement of
arrangements produced independently of each other would have been a very
suspicious circumstance for Darwin's theory, so also, in the second,
would any difference more profound than that of very nearly allied
species. Now it seems to me that the secondary flagellum can by no means
furnish a reason for doubting the close relationship of M. Fresnelii to
M. exilii, etc., which is indicated by the peculiar structure of the
unpaired clasp-forceps. In the first place we must consider the
possibility that the secondary flagellum, which is not always easy to
detect, may only have been overlooked by Savigny, as indeed Spence Bate
supposes to have been the case. If it is really deficient it must be
remarked that I have found it in species of the genera Leucothoe,
Cyrtophium and Amphilochus, in which genera it was missed by Savigny,
Dana and Spence Bate--that a species proved by the form of the Epimera
(Coxae Sp. B.) of the caudal feet (uropoda Westw.), etc., to be a true
Amphithoe* possesses it (* I accept this and all the other genera of
Amphipoda here mentioned, with the limits given to them by Spence Bate
('Catalogue of Amphipodous Crustacea').)--that in many species of
Cerapus it is reduced to a scarcely perceptible rudiment--nay, that it
is sometimes present in youth and disappears (although perhaps not
without leaving some trace) at maturity, as was found by Spence Bate to
be the case in Acanthonotus Owenii and Atylus carinatus, and I can
affirm with regard to an Atylus of these seas, remarkable for its
plumose branchiae--and that from all this, at the present day when the
increasing number of known Amphipoda and the splitting of them into
numerous genera thereby induced, compels us to descend to very minute
distinctive characters, we must nevertheless hesitate before employing
the secondary flagellum as a generic character. The case of Melita
Fresnelii therefore cannot excite any doubts as to Darwin's theory.
CHAPTER 3. MORPHOLOGY OF CRUSTACEA--NAUPLIUS-LARVAE.
If the absence of contradictions among the inferences deduced from them
for a narrow and consequently easily surveyed department must prepossess
us in favour of Darwin's views, it must be welcomed as a positive
triumph of his theory if far-reaching conclusions founded upon it should
SUBSEQUENTLY be confirmed by facts, the existence of which science, in
its previous state, by no means allowed us to suspect. From many results
of this kind upon which I could report, I select as examples, two, which
were of particular importance to me, and relate to discoveries the great
significance of which in the morphology and classification of the
Crustacea will not be denied even by the opponents of Darwin.
Considerations upon the developmental history of the Crustacea had led
me to the conclusion that, if the higher and lower Crustacea were at all
derivable from common progenitors, the former also must once have passed
through Nauplius-like conditions. Soon afterwards I discovered
Naupliiform larvae of Shrimps ('Archiv fur Naturgeschichte' 1860 1 page
8), and I must admit that this discovery gave me the first decided turn
in Darwin's favour.
(FIGURE 2. Tanais dubius (?) Kr. female, magnified 25 times, showing the
orifice of entrance (x) into the cavity overarched by the carapace, in
which an appendage of the second pair of maxillae (f) plays. On four
feet (i, k, l, m) are the rudiments of the lamellae which subsequently
form the brood-cavity.)
The similar number of segments* occurring in the Crabs and Macrura,
Amphipoda and Isopoda, in which the last seven segments are always
different from the preceding ones in the appendages with which they are
furnished, could only be regarded as an inheritance from the same
ancestors.
(* Like Claus I do not regard the eyes of the Crustacea as limbs, and
therefore admit no ocular segment; on the other hand I count in the
median piece of the tail, to which the character of a segment is often
denied. In opposition to its interpretation as a segment of the body,
only the want of limbs can be cited; in its favour we have the relation
of the intestine, which usually opens in this piece, and sometimes even
traverses its whole length, as in Microdeutopus and some other
Amphipoda. In Microdeutopus, as Spence Bate has already pointed out, one
is even led to regard small processes of this tubular caudal piece as
rudimentary members. Bell also ('British Stalk-eyed Crustacea' page 20),
states that he observed limbs of the last segment in Palaemon serratus
in the form of small moveable points.
The attempt has often been made to divide the body of the higher
Crustacea into small sections composed of equal numbers of segments,
these sections consisting of 3, 5 or 7 segments. None of these attempts
has ever met with general acceptance; my own investigations lead me to a
conception which nearly approaches Van Beneden's. I assume four sections
of 5 segments each--the primitive body, the fore-body, the hind-body,
and the middle-body. The primitive body includes the segments which the
naupliiform larva brings with it out of the egg; it is afterwards
divided, by the younger sections which become developed in its middle,
into the head and tail. To this primitive body belong the two pairs of
antennae, the mandibles and the caudal feet ("posterior pair of
pleopoda," Sp. B.). Even in the mature animal the fact that these
terminal sections belong to one another is sometimes betrayed by the
resemblance of their appendages, especially that of the outer branch of
the caudal feet, with the outer branch (the so-called scale) of the
second pair of antennae. Like the antennae, the caudal feet may also
become the bearers of high sensorial apparatus, as is shown by the ear
of Mysis.
The sequence of the sections of the body in order of time seems
originally to have been, that first the fore-body, then the hind-body,
and finally the middle-body was formed. The fore-body appears, in the
adult animal, to be entirely or partially amalgamated with the head; its
appendages (siagonopoda Westw.) are all or in part serviceable for the
reception of food, and generally sharply distinguished from those of the
following group. The segments of the middle-body seem always to put
forth limbs immediately after their own appearance, whilst the segments
of the hind-body often remain destitute of feet through long portions of
the larval life or even throughout life (as in many female Diastylidae),
a reason, among many others, for not, as is usual, regarding the
middle-body of the Crustacea as equivalent to the constantly footless
abdomen of Insects. The appendages of the middle-body (pereiopoda) seem
never, even in their youngest form, to possess two equal branches, a
peculiarity which usually characterises the appendages of the hind-body.
This is a circumstance which renders very doubtful the equivalence of
the middle-body of the Malacostraca with the section of the body which
in the Copepoda bears the swimming feet and in the Cirripedia the cirri.
The comprehension of the feet of the hind-body and tail in a single
group (as "fausses pattes abdominales," or as "pleopoda") seems not to
be justifiable. When there is a metamorphosis, they are probably always
produced at different periods, and they are almost always quite
different in structure and function. Even in the Amphipoda, in which the
caudal feet usually resemble in appearance the last two pairs of
abdominal feet, they are in general distinguished by some sort of
peculiarity, and whilst the abdominal feet are reproduced in wearisome
uniformity throughout the entire order, the caudal feet are, as is
well-known, amongst the most variable parts of the Amphipoda.)
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