The Biological Problem of To-day

tiating. Proof of this fundamental assumption may be sought in vain in Weismann's writings. I

then goes on to ask whether or no the pieces of hereditary material that make up the chromatin-tree of an organism are like each other or different. 'It can easily be shown,' the answer runs, 'that the latter must be the case.' For 'the chromatin is in a condition to

ubt. When once it is established that the morphoplasm of each cell is controlled, and its character decided, by the idioplasm of the nucleus, the regular c

me to follow from this, as a logical necessity, that the hereditary substance of the egg-cell, which contains all the hereditary tendencies of the species, does not transmit them in toto to the segmentation cells, but separates them into various combinations,

ontain different kinds of protoplasm. There are other possibilities to be reckoned with. Weismann himself knows that there is no logical necessity for the conclusion, for he himself suggests another possibility in the following: 'If we wished to assume that the whole of the determinants of the germplasm are supplied to all the cells of the entog

n other places he has attempted to represent as a n

on and development. He attributes to certain series of cells, in addition to the active rudiments controlling the normal cha

n higher animals and plants. Why should Nature, who always manages with economy, indulge in the luxury of always providing all the cells of the body with the whole of the determinants of the germplasm, if a sing

heir nuclear matter, we have at once a new and important decision to make. Does the nuclear matter in the different cells, that has arisen by division from the nuclear matter of the

of the egg-cell and must increase as development proceeds; for otherwise the different products of the division of the egg-cell could not give rise to entirely different hereditary tendencies. This is, however, the case.' Weismann represents to himself that[11] 'the changes of the idioplasm dep

perpetual casting loose of rudiments, of such a kind that at each division there is caused a complete rearrangement and unequal division of these rudiments. In the one case, the inner forces produce a reciprocal, coherent bond between the numerous rudiments; in the other case, permit change of their position and relations to one another, and this not only once but in orderly, definite fashion, different in each of many successive divisions, so that the id comes to possess a completely altered architecture. 'Each id

pend upon the physical nature of the idioplasm; that is to say, nothing at all about the causes w

r no the occurrence of differentiating division of the nucleus in the organic world is

f structural growth due to external interferences (heteromorphosis); (5) A number of physiological indications that cells and tissues, in additio

FACTS.-UNICEL

cellular organisms the hereditary mass should be split into two unequal components and be bestowed unequally upon the daughter-cells. All research shows that unicellular fungi, alg?, infusoria, and so forth, in dividing, transmit specific characters so strongly and in detail so minute that their descendants, a million generations off, resemble them in every respect. No one has doubted

the substance that is the bearer of specific characters, to the hereditary mass; besides that, a unicellular organism contains other substances, substances that change from time to time during its life. Many

l tentacles. It reproduces by giving rise to many little buds, ciliated on the upper surface like free-swimming, hypotrichous infusoria. These, in appearance, are quite unlike the parent organism, and

cular fibrils. After conjugation they encyst, the nucleus divides, and they break up into numerous peculiarly-shaped boat-like structures, (pseudonavicell?), whi

s clear that the infusoria-like vagrant young of the Acinetan, and the sickle-shaped embryos of the Gregarine possess it, although for some time they

test contradictions. For the supposition that the nucleus is the hereditary mass transmitting the characters of the species necessitates the conclusion, in the case of unicellular forms, that the hereditary mass remains in possession of all the rudiments of the cell while it passes through the various phases of its cycle of development. Ot

TS.-THE LOWER MULTI

s from an egg, and in turn gives rise to an egg, and so on in unending sequence. But the succeeding stages of the sequence are so exceedingly dissimilar in appearance that the question how one step of the series turns into the next, and, above all, the question how the similarity of organisms, separated by the egg-stage, can be transmitted through the egg-stage, form the deepest

and other simple creatures. In them cells arise by division from the egg or from the spore, and become united into an individual of a higher rank; these cells resemble

lls, in which each part retains the qualities of the egg from which it arose by doubling divisio

ng of the slime-fungi (Myxomycetes), with their peculiar formation of reproductive bodies; of the 'acellular plants,' which in some cases closely resemble multicellular species in their formation of leaf and root, an

to be found. It would be inconsistent with his theory of the germplasm had somatic cells contained germplasm as their idioplasm, even when the soma first came into existence. The phyletic origin of the somatic cells depended directly upon an unequal separation of the d

o body. Take the closely-allied creatures Pandorina morum and Volvox globator, which Weismann himself brings forward as i

or we are concerned here not with the interpretation of individual cases, but with the principles involved in the question, and, therefore, w

OMENA OF REPRODUCTION AND REGE

ubling division-that is, of division in which the germinal substance is handed on to every pa

rise to a bud; the bud grows out into a shoot, ultimately producing flowers and genital products. Such happens both in parts of the plant above the

cutting little pieces from a willow, an experimenter may cause the production from slips of thousands of willow-trees, each with all the characters of the species, so that there must have been contained in ea

vellina lepadiformis), may give rise to buds in many places, and these grow up into the perfect hydroid, bryozoon, or ascidian. There must, then, be contained in the cell

brought into a solution of its own salt. A Hydra, from which the oral disc and tentacles have been cut off, a Nais deprived of its head or of its tail, a snail of which a tentacle with its terminal eye has been amputated, will reproduce the lost parts, sometimes in a very short time. The cells lying at the wounded spot begin to bud, producing a layer or lump, the cells

he spinal cord with its ganglia and nerves, in the other case, the numerous, differently-shaped, skeletal pieces of the hand or foot, with their appropriate muscles and nerves. The regeneration, moreover, is in strict conformity with the characters of the species concerned. Thus, from the facts of regeneration also, we must infer

S.-THE PHENOMENA OF

rphosis perhaps bear most strongly in favour of my conception, a

gans on parts of the organism where such do not occur normally, or the power to replace lost parts by parts unsimilar to them in form a

rgans not normal to that part of the twig, while shoots will rise from the upper end. Moreover, either end of the slip may be made the root portion, and it is clear, therefore, that in every small area there are cell-groups present able to bear roots or shoots ac

and male and female genital organs on the lower surface, i.e., on that turned from the light. But the experimente

es of cells which grow into organs of definite form and of complex structure. The galls, moreover, differ widely, in correspondence with the specific stimulus which was their initial cause, and with the specific substan

he germ. I, also, consider them witnesses against Weismann's germplasm. They teach us that the cells of the plant-body may serve purposes quite different from those arranged for in the course of develo

other instructive ki

lanted in moist earth, bear rootlets identical with those of the normal plant. As the roots of all woody plants are able to bear adventitious buds, De Vries thinks

lly upon many lower animals, among which were

her hand, a heteromorphosis may be produced by modifying the experiment as follows: Both root and head must be cut from the stem; if the lopped piece of the stem be stuck in the sand of the aquariu

lit, where the experimenter had prevented coalescent growth. These buds gave rise to inner and outer tentacles, and an oral disc was produced. Thus,

oral aperture, surrounded by tentacles, has appeare

sembling those surrounding the mouth have appeared

provided with numerous, simple eye-spots. Loeb, in a series of experiments, made incisions either into the inhalent or the exhalent tube; after a time eye-spots appeared round the edges of the cut; then the margin of

gin, were made in different parts of the bodies and in different directions. Thus, again, we have an indication that there are present i

ithout, manifest themselves in abnormal formation of organs in abnormal situations. Save that they are in abnormal situation, the induced organs conform to the specific type in all respects, and indicate that all the cells of an organism contain, as the result of doubling division, the characters of germinal rudiments of th

avage of the egg. I have in mind those experiments by Driesch, Wilson, and myself, in which the first cells of the embryonic history were induced to form

had relative positions quite different from the normal. As, notwithstanding this, the distorted eggs developed into normal plutei larv?, Driesch inferred that the cell material composing the earliest cells of echinoids is equivalent in all the cells, and that the cells may be pushed over one another like a hea

great a number of "supplemental hypotheses," how many "accessory determinants," would be required to make specification

's egg has the poles different, and so has a definite orientation. Weismann and Roux themselves have used t

germplasm. As, moreover, in many of these animals-e.g., in the frog-the division of the ovum into the two first embryonic cells indicates a separation of the body into right and left halves, it follows that the id of germplasm itself posses

ryo respectively, but also the differentiating and elaborating forces for these, so that on the destruction of one cell, the other can give rise only to one lateral half of the embryo (hemiembryo lateralis). Roux, th

tributed. The nuclei indicated by the same numbers have the same descent in all the diagrams. All the eggs are viewed from the animal pole. A.

cally or horizontally placed glass-plates. In the first case they were flattened in the dorsoventral direction, i.e., the axis passing through the animal and vegetative pole was shortened;

he nuclei after normal cleavage; B, the same, when the egg was pressed between horizontally-arranged paralle

division lay one above the other, the cells of the lower layer are distinguished in the figure by shading. In the three diagrams the nuclei are numbered so that the re

descent, and therefore, according to the theory of Roux and Weismann, have

ee processes of division, of which two are

e to the left; 4 and 6 to the right of the second cleavage-plane, which, according to Roux's hypothesis, corresponds to the median-pla

ision there is no agreeme

yers, in B2 in a single layer. The nuclei 8, 10, 12, and 14, which compose the upper layer in A2, form the middle of the disc in B2; and

rm the right side of the mass, here form a dorsal layer with nuclei 7, 8, 12, 11, forming a ventral layer. In the fourth cycle of di

cal form to a cylinder or to a disc produces a method of division completely different, so far as the nuclei are related to each other in a genealogical tree. In the one and t

t qualities in the nuclei-qualities according to which the masses of protoplasm surrounding them become different and definite parts of the embryo-what a pretty set of malfor

gmentation of the egg. In the cases of an echinoid and of amphioxus (Fig. 4) they succeeded in shaking apart the first two and the fi

nd Fractional Ga

r Wil

rtificially separated, (B) from the two-celled stage, (C) from the fo

tained by shaking apart the segmentation spheres, were even more interesting, as they were performed upon amphioxus, a more highly-organized animal. He reared gastrul? and older embryos with notochord and nerve-tube, whic

ad been destroyed, Chabry obtained, in the case of an ascidian, and I obtained, in the common frog, embryos with notochord and nerve-plate. These developed directly

ording to whether they remain bound with each other into a whole or are separated and develop by themselves. In the former case, each forms only one-half (in some cases only a fourth) of the whole. In the latt

pothesis, which, from the spirit of his theory, could be none other than this: each of the first cleavage-cells, in addition to its specific part of the hereditary mass, the part that controls its normal course of development,

es with the chief axis of the future embryo, may assume different relations to the first segmentation-plane, sometimes coinciding with that, sometimes making a right or an acute angle with it. It is c

ayer of the egg. According to the position of these two invaginations, which may be regarded as crystallisation-points for the formation of the future embryo, the cells of the germinal disc will be drawn into the process of development, and, falling into groups, will build

so as to distort the normal course of deve

y placed glass plates. I then inverted them, so that the vegetative pole came to lie uppermost. In spite of

s very different, and perhaps depended on the tightness of the constriction. Some became greatly elongated, and had developed so that the thread surrounded the dorsal nerve-cord. In other cases the dorsally-placed organs arose only from one-half of the sand-glass-shaped embr

and of the triton, the cell-material, separated at the first cleavage, was tu

was very much bent outwards. In consequence of this the cleft of the blastopore lay between the normal blastopore-lip and the everted border of the other lip. When the notochord

sion; he must extend it to the thousands of embryonic cells that arise by division up to the time for the appearance of the nerve-tube and notochord. T

S.-PHENOMENA OF VEG

ew that all the cells of an individual, of any species, are alike, and are to be

microscopical investigation one cannot distinguish the tendons, nerves, bones, and cartilages of a dog from the corresponding tissues in a horse. So far as their special use in the organism goes, one might interchange the corresponding parts in these two mammals. A tendon from the do

ession to which I have alluded has arisen because we do not bear in mind that each tissue, each part of an organ, each cell, possesses, in addition to its obvious characters, very many characters that are invisible to us. Such characters are inherent in the tissue-cells b

re wonderfully alike in all the mammalia; in many cases we could not distinguish between those of different animals. But, becau

ble microscopical characters, the tissues and organic parts are in possession of more general characters, identical in all the differently-specialised tissues of a single organism; but we m

and so bring about a firm and lasting union between the two. In a short time the corresponding tissues of the parts broug

ar less on the conjunction of obviously appropriate parts than upon characters unrecognisable by us, such as deep-seated kinship between the parts, and the specific characters of their cells; while in the case of individuals of the same species two p

that the same condition of things occurs as when, in ordinary fertilisation, sexual cells from different varieties, or species, are united. In both cases

c constitutional differences. Frequently union will not take place between plants most near akin in classification, most alike in external characters; while it will occur between plants most different in out

ace only with difficulty, although the apple is a close kinsman and belongs to the same genus. On the other hand, most of them graft easily upon the quince, although t

finity, that is to say, the relationship between the egg-cell and the pollen of two species, and the rela

y. The twig and the stem begin to unite, but, sooner or later, disturbances occur, and complete destruction results. According to V?chting, in the case of some Crucifer? the disturbances are as follows: the twig begins to form roots at its lower end, and these grow into the stem of the host. Through them the twig uses as food the juices and salts of the stem, refusing to unite with the stem so as to form a single individual. As V?chting says, this formation of roots simply is an attempt on

th A and B. Thus, an intermediary between the two disharmonic forms is made, and by such an arrangement a single functional individual is produced from p

ther cases, the alien spermatozoon may penetrate the egg and unite with its nucleus, making, however, an unsatisfactory combination in various degrees of infertility. Sometimes the fertilised egg divides only a few times

transplantation of animal tissues is

pplied the upper end of one to the lower end of the other. In one case he was rewarded by the occurrence of complete union; for, after a few days, on feeding the upper end with a worm, it was passed on into the lo

and by several investigators. I shall mention only the older results of

ning a supply of blood from vessels which grew out into it from the surrounding connective tissue in which it was embedded. In a short time lamell? of bone were formed by the layer of osteoblasts, so that a small plate of bone was formed under the skin. This, however, proved always but a temporary structure, for, being formed in an inappropriate spot, and,

l. In a few days circulation of blood was established in the pieces of the tails, by union with vessels from the connective tissue in which they were embedded. Muscles and nerves degenerated, but the other tissues, bones, cartila

ersa), either extensive suppuration took place, and the piece was extruded, while sometimes the subject of the experiment died; or, after a less turbulent course, the alien piece was absorbed. The continuance of life and growth

e transplantation was from one individual to another of the same species, or to another part of the same individual. Beresowsky transplanted pieces of fr

'We have always found,' says Ponfick, summing up the results of the investigation, 'not only that blood of another species acts in strong doses as a poison, and in weaker or smaller doses is harmful, but that (and this seems to me my most important result) in every case the blood-corpuscles are destroyed almost completely, probably quite completely.' In a very few minutes, in the case of disharmonic kinds of blood, the

d happens the more slowly the more nearly the animals are allied.' 'Thus, in doubtful cases, experiments on transfusion might settle degrees of relationship. Between individuals of the same species transfusion is a complete success; when the species are closely allied, the transfused blood disappears only very gradually, and large quantities may be transf

ieve, although there might be drawn from literature contradictory results-in which, however, I cannot feel confident-I am prepared to extend a conclusion to the animal kingdom that is better supported in botany: the conclusion that the cells and tissues

ONCLUSIONS IN TH

cells multiply only by doubling division. First comes the fundamental circumstance that single-celled organisms exhib

ence of budding in almost any part of the body, are easily intelligible if every cell, like the egg-cell, has been formed by doubling division, a

th at different stages, as these showed that the separate cells which arose by division were not predestined u

e cells and tissues of an organism possess, in addition to their patent microscopica

-division has a double aspect. According to Weismann, this is possible, because the egg contains many, sometimes as many as a hundred, ids, each of which is a combination representing the species. Weismann believes that in an egg, while it is preparing for its first division, the ids are arranged in two groups-an active army and a reserve army. By differentiating division the active army is broken up into the divisions, brigades, and regiments of determinants appro

to endow every cell with accessory germplasm to prepare it for unforeseen events. This, however, would sterilize the other part of the theory, the doctrine of determinants, and the mechanism of development dependent on a rigid architecture of the germplasm. Consider the confusion that would arise when the deploying of the active army was disarranged by external influences, now in one fashion, now in another, if the reserve army, with its store of latent rudiments, had to come to the help of the broken pieces. What would compel the rudiments disposed to activity accor

n attaches the greatest importance to the distinction. The twofold nature of the process of development is a cardinal point

as they alone serve for the starting of new generations of development. The somatic cells, on the other hand, are endowed only with fragments of germplasm, and hence they are incapable of preserving the specie

e subject to death, unless the conditions necessary to their further development have occurred in time. But under such conditions other cell-complexes may have death averted from them, as, for instance, when a slip cut from a willow-tree is planted. Thirdly, the reproductive cells are derived from the egg-cell just in the same way as other tissue cells are derived from it. Like tissue cells in multicellular organisms, they arise by the specialisation of material separated from the egg-cell, a

but this happens in the case of all specialised cells, such as muscle, liver, kidney, and bone cells. The conception of special germ-tracks has no more significance than there would be in

indivisibility. This, at least, was the view of the old philosophers, who have defined the idea of immortality. Thus says Leibnitz in his Theodice: 'I hold that the souls which on

e are subject to destruction by external agents, the separate individuals are mortal. The unicellular organism is not immortal in itself, but only in as much as it may give rise to other organisms. In this way Weismann comes in conflict with the idea of individuality, and is compelled to transform his conception. For he says 'that among unicellular organisms there are not individuals separated from each other in the sense of time, but that each living being is separated into parts so far as space is considered, but is contin

sum of all the individuals arising from it, all the individuals of the same species

the course of a defence in which, however, he did not intend to give up the standpoint he had taken; he wishes to imply, by the immortality of unicellular or

anic material, depends upon the continual formation and eventual destruction of newly-formed material, but in no way implies the continuous existence of the organised material in a state of organisation. From this point of view, the immortality of unice

hat cannot be bridged. The continuity of the process of development depends upon the power of the cells to grow and to divide, and has already been set forth in the sayings-Omnis cellula e