The Science and Philosophy of the Organism

" and "Ep

ORY OF

g a theory of heredity, and that is true inasmuch as problems of inheritance proper have been the starting-point of all his hypothetic speculations, and also form in some respect the most valuable part of them. But, rightly understood, Weismann's theory consists of two in

from generation to generation as the basis of heredity, another part of it is disintegrated during the individual development, and directs development by being disintegrated. The expression, "part" of the structure, first calls for some explanati

plexes of elements of the organisation, but to the chief relations of symmetry; the first cleavage, for instance, may separate the right and the left part of the structure, the second one its upper and lower parts, and after the third or equatorial cleavage all the principal eighths of our minute organisation are divided off: for the minute organisation, it must now be ad

ken up into its elements, and these elements, which may be chemical c

growth of that chick in miniature, but what really is supposed to be present in the egg is nevertheless a something that in all its parts corresponds to all the parts of the chick, only under a somewhat different aspect, while all the relations of the parts of the one correspond to the relations of the parts of the other. Indee

s we know, manifoldness in the visible sense is produced, but that epigenesis can never form the foundation of a real morphogenetic theory: theoretically one pre-existing manifoldness is transformed into the other. An epigen

ght, it seems to me, to speak of a dogmatic

ing ontogeny. But these difficulties were not absolute: they could be overcome: indeed, Weismann assumes, that in certain specific cases-and he regarded all cases of restoration of a destroyed organisation as due to specific properties of the subjects, originated by roundabout variations and natural selection-that

very closely resembles the hypothesis of Weismann. According to Roux a minute ultimate structure is present in the

logical investigation on mentioning Roux's name: we are leaving hypothetic construction, at

ENTAL M

st the physiology of form as an exact separate science was almost wholly forgotten. At least that was the state of affairs as regards zoological biology; botanists, it must be granted, have never lost the historical continuity to such a degree; botany has never ce

ogy to be the mathematical derivation of the adult form from the distribution of growth in the germ. To Alexander Goette12 we owe another set of analytical considerations about ontogeny. Newport, as early as 1850, and in later years Pflüger and Rauber, carried out experiments on the eggs of the frog, which may truly be called anticipatory of what was to follow. But it was Wilhel

d. I feel the more obliged to do so, because later on I shall have to contradict not only many of his positive statements but also most of his theoretical views. He himself has latel

now that experiment, by its method of isolating the single constituents of complicated phenomena, is the principal aid in the discovery of

OF WILH

he supposed that there exists a very complicated structure in the germ, and that nuclear division leads to the disinte

have been worked out into the doctrine of so-called "cell-lineages," typical cleavage cells were found to correspond to typical organs. Was not that a strong support for a theory which regarded cellular division as the principal means of differentiation? It is true, the close relations between cleavage and symmetry did not e

astomeres of the frog's egg after the full accomplishment of its first cleavage, and then watched the development of the surviving cell. A typical half-embryo was seen to emerge-an organism indeed, which w

here is a very complicated structure which promotes ontogeny by its disintegration, carried out during the

h. Certainly some sort of "evolutio" is proved by rearing half the frog from half the egg. But is anything proved, is there anything discovered at all ab

ecame still m

S ON THE EGG O

that the eggs of the common sea-urchin (Echinus microtuberculatus) are able to stand well all sorts of rough treatment, and that, in particular, when broken into pieces by shaking, their fragments will survive and continue to segment. I took advantage of t

lf of the normal ones. The stage, for instance, which corresponded to the normal sixteen-cell stage, and which, of course, in my subjects was built up of eight elements only, showed two micromeres, two ma

rical germ bent together a little, as if it were about to form a whole sphere of smaller size, and, indeed, the next morning a whole diminutive blastula was swimming about. I was so much convinced that I should get Roux's morphogenetical result in all its features that,

hole gastrula on my dish the next morning, differing only by its small size from a normal one; an

ation of Experi

al gastrula and

ught to result from one of the first two blastomeres,

whole gastrula and pluteu

ge as in his case, but then it had become a whole organism by a simple process of rearrangement of its ma

to two different halves, and not even the protoplasm of the egg could be said to have been divided by the first cleavage furrow into unequal parts, as the postulate of the strict theory of so-called "evolutio" had been. T

e of the first four blastomeres together result in an absolutely perfect organism, I went on to follow up separately one of the two fundamental problems which had

e type of the cleavage-stages without any damage to the resulting organism. There may be no micromeres at the sixteen-cell stage, or they may appear as early as in

divisions began to occur at right angles to their former direction, as soon as the pressure ceased. By letting the pressure be at work for different times I therefore, of course, had it quite in my power to obtain cleavage types just as I wanted to get them. If, for instance, I kept the eggs under pressure until the eight-cell stage was complete, I got a plate of eight cells one beside the other, instead of two rings, of four

to say, every nucleus has got quite different neighbours if compared with the "normal" case. If that makes no difference, then there cannot exist any close relation between the single nuclear divisions and organogenesis at all, and the conclusion we have drawn more provisionally from the whole development of isolated blastomeres has been extended and proved in the most perfect manner. There ought to result a morphogenetic cha

ure-experimen

avage stages, consisting

ied by exerting pressure until the ei

gg of annelids (E. B. Wilson), my pressure experi

RUCTURE OF THE PRO

l we know about the whole development of isolated blastomeres seems to show tha

rge the hypothesis that there existed, that there must exist, a sort of intimate structure in the egg, including polarity and bilaterality as the chief features of its symmetry, a structure which belongs to every smallest element of the egg, and which might be imagined by analogy under the form of elementary magnets.19 This hypothetic structure could have its seat in the protoplasm only. In the egg of echinoderms it would be capable of such a quick rearrangement after bei

ctenophore egg behave like parts of the whole and result in a half-organisation like the frog's germ does. Chun had not laid much stress on his discovery, which now, of course, from the new points of view, became a very important one. We first repeated Chun's experiment and obtained his results, with the sole exception that there was a tendency of the endoderm of the half-larva of Bero? to become more than "half." But that was not wh

nts there was all of the nuclear material, but there were defects on one side of the protoplasm of

lled one of the first two blastomeres, as was done in the original experiment of Roux, was able to bring the surviving one to a half or to a whole development according as it was undisturbed or turned. There cannot be any doubt that in both of these cases, it is the possibility of a rearrangement of protoplasm, offered by the turning over, which allows the isolated blastomere to develop as a whole. The regulation

tructure; the development is whole, in spite of disturbances, if the intimate structure became whole first. We may describe the "wholeness," "halfness," or "quarterness" of our hypothetic structure in a mathematical way, by using three axes, at right angles to one another, as the base of orientation. To each of these, x, y, and z, a certain specific state with regard to the symmetrical relations corresponds; thence it follows that, if there are wanting all those parts of t

he intimate Regulation of Prot

inal structure is only present as "half" in the beginning, say only on the right (+y) side. Development then becomes "half," if the intimate

eral symmetry of themselves and of their isolated parts, and another sort of possible structure of the egg-protoplasm which we now shall have to consider, and which, at the first glance, seems to form a serious difficulty to our statements, as far at l

IES OF ORGANISATIO

rities of the different parts of the protoplasm could account for such relations of special cleavage cells to special organs. I advocated this view as early as in 1894, and it was proved two years later by Crampton, a pupil of Wilson's, in some very fine experiments performed on the germ of a certain mollusc.22 The egg of this form contains a special sort of protoplasm near its vegetative pole, and this part of it is separated at each of the first two segmentations by a sort of pseudo-cleavage, leading to stages of three and five separated masses instead of two and four, the supernumera

sc Dentalium (aft

three different kinds of

ne "pseudo-cell," the yolk-sac, which contains no

HE FIRST PERIOD OF "

he new science of physiology of form, a period devoted almost exclusively to the problem whether the theory of nuclear

of manifoldness," not only with regard to visibility but in a more profound meaning. But some sort of pre-formation had also been proved to exist, and this pre-formation, or, if you like, this restricted evolution, was found to be of two different kinds. First an intimate organisation of the protoplasm, spoken of as its polarity and bilaterality, was discovered

full regulation of the intimate structure of isolated blastomeres to a new whole, has been proved to exist in the highest degree in the eggs of all echinoderms, medusae, nemertines, Amphioxus, fishes, and in one class of the Amphibia (the Urodela); it is facultative only among the other class of Amphibia, the Anura, and seems to be only partly developed or to be wanting altogether among ctenophora, ascidia, annelids, and mollusca. Peculiarities in the organisation of specific parts o

in the physical consistency of their protoplasm.23 But all differences in specific organisation must remain as they are for t

ay with the systematic position of the animals exhibiting them; for, strange as it would be if there were two utterly different kinds of morphogenesis, it would be still more strange if there

LTS CONCERNIN

heir origin from typically localised points of the body in every case; each time they occur a certain well-defined part of the body is charged with the restoration of the lost parts. To explain such cases Weismann's hypothesis was quite adequate, at least in a logical sense. But at present, as we shall discuss more fully in another chapter, we know of some very widespread forms of restitution, in which what is to be done for a replacement of the lost is not entrusted to one typical part of the body in every case, but in which the whole of the morphogenetic action to be performed is transferred in its single parts to the sing

l pass on to ou

system, in which each part will be, or at least will try to be, in its proper place and in relation with every other part. Our analytical work will give us ample opportunity of mentioning many important topics of so-called general physiology also, ir