The Science and Philosophy of the Organism

TION OF MORPHOG

alue and Pros

orphogenetic differentiations had to be solved first, before any problem of causality pro

introductory chapter an analysis of the distribution of morphogenetic potencies.

lement in the future actual course of this development, whether it be undisturbed or disturbed in any way; it is, so to say, the actual, the real fate of our element, that we take in account. I have proposed to call this real fate of each embryonic part in this very definite line of morphogenesis its prospective value ("prospective Bedeut

ate of each of those elements. With the aid of our two artificial concepts we are now able to formulate our introductory question thus: Is the prospective potency of each embryonic part fully given b

ses; that the potency of the first four blastomeres of the egg of the sea-urchin, for instance, has a far wider range than is shown by what each of them actually pe

special reference to it: there are more morphogenetic possibilities in each part than the observation of the normal development can reve

analytical interest, leaving to the concept of prospective value the second place only. For that each embryonic part actually has a certain prospective value, a specified actual fate in every single case of ontogeny, is clear from itself and does not affirm more than the reality of morphogenetic cases in general; but that the prospective value of the

case just what happens and nothing else? In these words indeed we may state the chief problem of our science, at least

stage, if at all, is there an absolutely equal distribution of the potencies over all the elements of the germ? When such an equal distribution has ceased to exist at a certain stage, what are then the relations between t

a little formal, and, so to say, academical at the outset.

ies of the

may produce a whole organism. We may add that the swimming blastula, consisting of about one thousand cells, when cut in two quite at random, in a plane coincident with, or at least passing near, its polar axis, may form two fully develop

xperimentally determined depends on the position of that cell in the whole, if the "whole" is put into relation with any fixed

e value, the actual fate of a cell, will change, whenever its position in the whole is different.26 The "whole" may be related to any three axes drawn through the normal undisturbed egg, on the hypot

f Elementary Or

This experiment will easily lead to a few new concepts, which we shall want later on, and will serve, on the other hand, as a basis of explanation for some r

ittle organisms developed from the parts: the ectoderm is formed in the typical manner in the parts, and so is the endoderm; everything is proportionate and only smaller than in the normal case. So we have at once the important results, that, as in the blastu

e Starfish

ted along the main axis or at rig

larva, "B

esults by a process of regulation f

e "Bipinnaria," de

f of the larva is separated from the lower by an equatorial section, you will get a complete larva only from that part which bears the "Anlage" of the endoderm, while the other half will proceed in morphogenesis very well

mmarise both our

different potencies compared one with the other. And the same relation is found to hold for all cases of what we call ele

Potencies: Primary a

potency" a few words of further analytical explan

m with respect to the ectoderm is not of the same kind as its diversity in respect to the blastoderm. The potency of the endoderm and that of the ectoderm are both specialised in their typical manner, but compared with the potency of the blastoderm they may be said not only to be specialised but also to be re

rm layers. We shall call this sort of immediate potency explicit, and then we see at once that, with regard to their explicit potencies, there are only differences among the prospective potencies of the elementary organs; but with respect to the im

ept. We are dealing only with primary potencies in our present considerations, i.e. with potencies which lie at the root of true embryology, not with those serving to regulate disturbances of the organisation. It is true, we have in some way disturbed the development of our sea-urchin's egg in order to study it; more than that, it would have been impossible to study it

to "secondary regulation" phenomena. At present it must be enough to say that in speaking of the restriction of the implicit potencies in for

n of Maturation in the Li

al forms has taught us. We know from our historical sketch that there are some very important aberrations from the type, to which the Echinus germ belongs,27 i.e. the type with an equal distribution of the potencies over all the blastomeres. We know not only that in cas

germ of the echinoderms and the molluscs to remain where it is, and not to be elucidated any further? Then there would be rather important differences among the germs of different animals, at least with regard to the degree of the specification of their cleavage cells, or if we as

proved this hypothesis. Conklin showed, several years ago, that certain intracellular migrations and rearrangements of material do happen in the first stages of ovogenesis in certain cases, but it is to E. B. Wilson28 that science owes a proper and definitive elucidation of the whole subject. Wilson's researches, pursued not only by descriptive methods,29 but also by means of analytical experiment, led him to the highly important discovery that the eggs of several fo

is not with fertilisation that morphogenesis begins,

f the egg-protoplasm to mere differences in the time of the beginning of real morphogenesis. What occurs in some eggs, as in those of Echinus, at the time of the definite formation of the germ layers, leading to a specification and restriction of their prospectiv

organisation of the germ and their bearing

cture of Protopla

" or better, "fragmental" development of isolated blastomeres in which a certain embryonic organ is wanting on account of its specific morphogenetic material being absent, and those cases in which the "fragmental" embryo lacks complete "halves" or "quarters" with regard to general symmetry on account of the symmetry of its intimate structure being irregularly disturbed. This logical difference has not always received the attention which it undoubtedly deserves. Our hypothetical intimate structure in itself is, of cou

of the Concep

oes not prejudice anything; we have said, it is true, that limitations of potencies may be due to the presence of specific parts of organisation in some cases; that, at least, they may be connected therewith; but we have not determined at all what a prospective potency really is, what the term really is to signi

ANS" OF MO

e "conditions" in this connection, as the latter would not cover the whole field. It is in quite an unpretentious and merely descriptive sense

Elementary Mean

ow the very foundation of these elementary processes themselves lies in the elementary functions of the organism as far as they result in the for

al change or by physical separation, the latter by the aid of changes in surface tension. B

entary means of morphogenesis. We shall only select from the whole a few t

plies as much. It would be possible to understand each of these single acts in morphogenesis as well as anything, and yet to be as far from understa

constituents of the structure in the organisms, as is the case in the well-known inorganic foams, but two fluids, which do not mix with one another. One general law holds for all arrangements of this kind: the so-called law of least surfaces, expressed by the words that the sum of all surfaces existing is a minimum; and it again is a consequence of this law, if discussed mathematically, that four lines will always meet in one point and three planes in one line. This feature, together with a certain law about the relation of the angles meeting in one line to the size of the bubbles, is realised most clearly in many structures of organic tissues, and makes it highly probable, at least in some cases, that capillarity is a

d by the physically conditioned arrangement of protoplasmatic or cellular elements, and some phenomena

ounts for the Specific! Capillarity gives us not the least clue to it. As the organic substance, at least in many cases, is a fluid, it must of course follow the general laws of hy

called by Roux "correlation of masses," though this author originally intended to express by this term o

rst seems to be the result of mechanical pressure may afterwards be found to be an active process of growth, and what at first seems to be a full effect

hysiological processes. But all these processes are only means of the organism, and can never do more than furnish the general type of events. They do

logical character, that is, which nobody claims to understand physically at present

Osmotic pressure, of course, plays an important part both in the growth of the body-cavities and in simple cellular extension. We repeat the caution against believing too much to be explained by this phenomenon: it is the organism which by the secretion of osmotic subs

er the chief lines of organisation are laid out; it is only the formation

hich it does not occur at all, and there have also become known many cases of morphogenesis in higher animals, mostly of the type of regulation, in which cellular division is almost or wholly wanting. Therefore, cellular division cannot be the tr

tained by T. H. Morgan, I was able to show that in all the small but whole larvae, reared from isolated blastomeres, the size of the cells remains normal, only their number being reduced; and Boveri has shown most clearly that it is always the size of the nucleus-more correctly,

nal Means of

re, and so we may glance at some of the most impor

um. For the germ, as for the adult, there exists not only a minimum but also a maximum limit of all the necessary factors of th

ding to the increase of intensity of the agent. The acceleration of development by heat has been shown to follow the law of the acceleration

orphogenesis proper, and therefore may be left out of account here: we must, however, lay great stress on the general fact that the

e no knowledge whatever how this happens. We at present are only able to ascertain what must necessarily be accomplished in the medium, in order that normal morphogenesis may

of sea-water upon the development of the sea-urchin. If we select the most important of Herbst's results, we must in the first place say a few words on the part taken by lime or calcium, not only in establishing specific features of form, but in rendering individual morphogenesis possible at all. Herbst has found that in sea-water which is deprived of calcium the cleavage cells and many

d to keep them together afterwards. Thus, if for instance you want to study the development of isolated cells of the eight-cell stage, you will leave the egg in the artificial mixture containing no calcium until the third cleavage, which leads from the four- to the eight-cell stage, is finished. The single eight cells brought back to normal sea-water at this point will give you the eight embryos you wa

in other terms, sulphur salts present in the water, in order that the germs may acquire their pigments and their bilateral symmetry. This is indeed a very important result, though it cannot be said to be properly understood. It is a fact that in water wi

pment.38 I cannot describe fully here how the so-called "lithium larva" originates; let me only mention that its endoderm is formed outside instead of inside, that it is far too large, that there is a spherical mass between the ectodermal and the endodermal part of the germ, that a radial symmetry is established in place of the normal bilateralism, that no skeleton exists, and that the mesenchyme cells are placed in a quite abnormal position. All these features, though abnormal, are typic

ATIVE CAUSE

inition

most disputed of all categories; many modern scientists, particularly in physics, try to avoid the concept of cause altogether, and to replace it by mere functional depe

mplete, for we have the concept of the acting "cause" in our Ego and are forced to search for applications of it in Natur

l the constellations necessary for its start are accomplished, must still take place in order that the event may actually occur? Let us see what would follow from such a use of the word causality. We here have an animal germ in a certain stage, say a larva of Echinus, which is just about to form the intestine; all the internal conditions are fulfilled, and there is also a certain temperature, a certain salinity, and so on, but there is no oxygen in the water: the intestine; of course, will not grow in such a state

ine which appears, while at another time it is the lens of the eye? We might very well, but we already have our term for this sort of cause, which is nothing else than our prospective potency applied to that element

o has its specific and typical place in the whole-its locality. Therefore we shall call the "cause" of a single morphogenetic proc

s now acquire a clear and definite meaning: potency is the real basis of the specific character of every act in morphogenesis, and "means," including conditions, are the sum of all

that general type which usually is called a stimulus or "Ausl?sung," to use the untranslatable Ger

f Formative and

calls "formative and directive stimuli"40 but also some important discoveries on this s

etic formations are to arise; in hydroids also we know that these factors of the medium may be at work41 as morphogenetic causes, though

not only the place of the effect, but also part of its specification. The galls of plants are the most typical organogenetic results of such stimuli. The potenc

t between the single parts of animal germs, each of these parts being in some respect external to every other; and, indeed, it might have been expected already a priori, that such formative relations between the parts of an animal embryo must exist, after all we have learned about the chief lines of early embryology. If differentiation does no

y be determined by the typical character of other parts, and that real morphogenetic characters can be the result of some such relation; a sort of "chemotropism" or "chemotaxis" may be at work here. Herbst himself has discussed theoretically several cases of organogenesis in which the action of directive stimuli is very probable. What has become actually known by experiment is n

he arms of the so-called pluteus of the sea-urchin are in formative dependence on the skeleton-no skeleton, no arms; so many skeleton primordia,42 in abnormal cases,

the same in another case, which, after having been hypothetically stated by Herbst on the basis of pathological data, was proved experimentally by Spemann. The lens of the eye of certain Amphibia is formed of their skin in response to a formative stimulus pr

nce of parts may also

the optic ganglion is present, but that an antenna will arise in their place if this ganglion has also been removed. There must in th

he nervous communications have been disturbed. But in other animals there is no such influence; and in yet others, as for instance, in Planarians, it must seem doubtful at present whether the morphogenetic influence of th

ructure are concerned. This again would bring us to the problem of so-called "polarity" in general, and to the "inversion" of polarity, that is to a phenomenon well known in plants and in many hydroids and worms, viz., that morphogenetic processes, especially of the type of restitutions, occur differently, according as their point of origin

etermination of sex,44 according to the latest researches, seems to depend on cytological events occurring in the very earliest embryonic stages, say even before ontogeny, and not on formative

PHOGENETIC

d with some morphogenetic interactions among the parts of a developing embryo; and, indee

opment of each embryonic part depends on the

elf-differentiation" to denote this phenomenon, and we admit that this term may be conveniently used for the purpose, if only it can be kept in mind that its sense is always relative, and that it is also negative. Suppose a part, A, shows the phenomenon of self-differentiation: this means that the furth

ntestine is present at all (Fig. 10); but ectoderm and endoderm both are formatively dependent on the intimate and the material organisation of the blastoderm. It further seems from the most recent experiments t

eus-larva of

side (by means of raising the temperature); but the

spite of this relative morphogenetic independence of embryonic parts, the resulting organism is one whole in organisation and in function, some sort of harmony of constellation, as it may properly be styled, must be said to be one of the most fundamental characters of

ormative causes may always find something upon which to act, and that those parts which contain the potencies for the next ontogenetic stage may properly receive the stimuli awaking these potencies: otherwise there would be no typical

ction, and so we may state, as the latest result of our analytical theory of development up

RESTIT

re disturbances of its organisation, and it certainly is to be regarded as one of the chief problems of analytical morphogenesis to discover the specific and real stimulus which calls forth the restoring proces

encies and on Secondary Morpho

ive type, and that their distribution may be most various and quite independent of all the potencies for the primary processes of ontogeny pr

traction on the part of specific localities of the ectoderm in spite of a very abnormal original position enforced upon them by experiment. In these cases we speak of primary regulations or restitutions; disturbances are neutralised by the very nature of the process in questio

s to form our special study in the next chapter. In all other cases restoration processes start from specific localities; if they occur on the site of the wound which caused the disturbance, we speak of regeneration; if they occur at some distance from the wound, we call them adventitious processes. Besides these three types of processes of restitution there may be mentioned a fourth one

hese processes may be said to be "complex." It is a complicated series of events, a proper morphogenesis in itself, for which the potency has to

distribution of complex potencies are reserve

s or means, occur again. But of course we cannot enter into these problems a second time, and may only say that, especially in regeneration proper, the specific type of the regenera

li of Res

imulus50 that calls forth processes of restitution; or, in other

elf, we might probably at first be inclined to advocate the doctrine that the removing of some obstacles might in fact be the stimulus to the process of restoration; but, even then, why is it that just what is wanted grows out? Why is there not only growth, but specific growth, growth followed by specificati

es larger after the other has been removed, or when pruning of almost all the leaves of a tree leads to the rest becoming larger, it certainly must fail to explain the fact that in other cases true new formations may arise in order to restore a damaged part, or that the latter may be regenerated in its proper way. For merely quantitative differences in the mixture of the blood or of the nourishing sap in plants can never be a sufficient reason for the highly typical and qualitative structure of newly-formed res

n as regards its rate, to occur quite irrespectively of the animal being fed or not.54 There could hardly be a

of legs and tails in Amphibia, of the head in Planarians, of the root-tip in plants and in some other cases. Here it has always been a disturbance of the normal connection of some parts with the rest of the organism which proved to be the reason of the new formation. This shows that something to do with the communication among parts is at least connected with restitution, and this communication may go on either by the unknown action of specific tissues or by the aid

e is not a simple homogeneous act, for which one special material might account, but is a very complicated work in itse

rtain ground of what may be called the newest and most up-to-date branch of the physiology of form. No doubt, there will be something discovered some d

entered into our discussion. The same idea may be said to have entered it alread

licit and less hypothetical form. Let us see whether our analytical theory of development is in fact