The History of Biological Theories

whole theory. Hartmann introduced the idea of the 'unconscious' ; this represented Schopenhauer's 'will' plus 'idea'. He considered this the fundamental cause of all action. Starting from Man's conscious actions, he shows that, beyond the realm of consciousness, there are many other actions which do not differ from these in essence, and which, like the conscious ones, possess an ideal content. He points to the development of the embryo, to the heal- ing of wounds, to the phenomena of instinct, to reflex actions ; these are all analogous to Man's conscious actions, and yet are unconscious.

Hartmann partially agrees with the materialists, for he considers that the atom is the foundation of all reality ; yet he assures those who believe in a soul that the psychic is not the result of the material, but is just as fundamental as is matter. He praises the endeavours of the scientists to get rid of such vague ideas as 'vital force' and 'life urge', for 'science should only seek for mechanical causes'. But the 'vital force' which he has banished from science he introduces into metaphysics, calling it 'will', and supposes that it controls all change. In regard to Darwinism, Hart- mann's attitude was also one of attempted reconciliation between science and philosophy. He approved of Darwin's fundamental idea. He had a considerable knowledge of biological literature, and could follow the criticisms of a Kolliker, a Wigand, a Nageli, and an Eimer. Aided by these, he formulated a very discerning criticism of Darwin- ism, totally rejecting the idea of a blind mechanism. 'The struggle for existence and natural selection are but labourers in the service of the idea. They perform the menial services in the realization of the idea, the shaping and fitting into place of the stones, which have been measured out by the Great Architect, and appropriately chosen for their destined place in His great building.'

Von Hartmann believes that the organism is governed by an inner law of development, a law of correlation. Natural selection, sexual selection, and so on, are merely so many external factors aiding this development. Teleo- Von Hartmann's biology was adversely criticized by the scientists ; his metaphysics could hardly be favourably re- ceived by the Darwinists who considered that one of their greatest services had been to free the world of metaphysics. Schmidt, the Darwinist, and Wigand, the idealist, both found fault with his philosophy because it faced both ways. Displeased with these criticisms, Hartmann himself pub- lished an anonymous criticism of his own views, which was favourably commented upon by such Darwinists as Haeckel, Seidlitz, Schmidt, and du Prel.

Many and varying theories are included under the name of Neo-Lamarckianism. The name is often applied to writers whose scientific achievements have been concerned with very different subject-matter, but who incidentally express themselves favourable to Lamarck's theory, in whole or in part. Thus some biologists are called Lamarck- ians simply because they hold that the function comes before the organ. Among these are the French physio- logist Marey, and Roux, the originator of developmental mechanics. Others are called disciples of Lamarck merely because they have held that the organism possesses a direct power of adapting itself to its surroundings. Warming, Wettstein, Sachs, Pfeffer, Henslow, and Wagner, among botanists, Haacke, the zoologist, Roule, the embryologist, Roux, Rabl, and Semper, the anatomists, Koken and Jaeckel, the palaeontologists, belong to this group.

Another group have been called Lamarckians because they believe in the inheritance of acquired characters. Among these are Strasburger, Haeckel, Herbert Spencer, Brown-Sequard, Giard, Perrier, Packard, Semper, Kasso- witz, Romanes, and others. Ehis History of the Inductive Sciences, Whewell had ready pointed out that, as the plant is comparatively- simple in structure, the development of botany has always been more direct and less dramatic than that of zoology. Botanical theory has always been in advance of zoological. The zoologists, on the other hand, have, in the diversity of animal structure, a more varied material to consider. They therefore tend to imbue their theories with a deeper mean- ing and to investigate their significance more completely.

Systematic biology, for example, begins with Linnaeus's study of plants; Cuvier added to it by his study of animal anatomy. Morphology, as a theoretical science, began with Goethe's observations on metamorphosis among plants; it received a more plastic content from zoological considerations of analogy and homology. Schleiden^ a botanist, introduced genetic philosophy into Germany; Haeckel, the zoologist, gave this both breadth and depth. The same phenomenon has repeated itself in the downfall of genetic ideas. Sachs, the botanist, was the first who called for experimental work; in the hands of Roux and Driesch the experimental method was raised to the dignity of a scientific philosophy.

The influence of Darwinism on botany was similar to its influence on zoology. It inspired botanical studies of the cell, and theories of invisible oodies in the protoplasm; mechanical explanations of cell division; theories of here- dity, &c. The type of work that was being done in those times is indicated by the names of Wigand, Nageli, Sachs, Celakovsky, and Strasburger. Of these Wigand was the most conservative. He re- mained true to pre-Darwinian conceptions, and rejected the new ideas a limine. Celakovsky, always a morphologist, never entirely freed himself from the ideas of Braun and his school, but he accepted evolution. Strasburger believed in the new ideas whole-heartedly, and assisted in the working

out of new theories of the cell. Nageli was a Darwinist, but he was in favour of a more physiological view of evolution, and in this Sachs agreed with him. Some botanists indulged in a great many phylogenetic specula- tions Strasburger and Sachs, for example. Even to-day such discussions are in favour with some (e. g. Scott, the palaeobotanist), but they have never become as important in botany as in zoology. The botanists soon began to depart from orthodox Darwinism. We see this in their preference for the idea of the polyphyletic origin of plants, and also in the great importance they have attached to physiology. In the nineteenth century a deep rift de- veloped between animal morphology and animal physio- logy. This rift was never so wide in botany, for the diversity of plant forms is not as striking or as characteristic as are the forms of animals ; it is function rather than form that is of interest. The leaf of a dicotyledon is very similar to that of a monocotyledon or of a vascular cryptogam, and even among the mosses and algae structures occur which are very like leaves both structurally and functionally, and like them subserve assimilation, trans- piration, and respiration. Among animals, on the other hand, function is subservient to form, as may be seen in the differences between the organs of locomotion in mammals, fishes, molluscs, echinoderms, medusae, and infusoria. In all these groups it is the form that stands forth. The form changes very strikingly from group to group, while the functions remain analogous.

This difference between animals and plants has deter- mined the course of development of modern botany and of zoology. The effect of Darwinism was to turn zoology into a study of morphology, strongly tinged with phylo- geny, a study of the parts of bodies to which definite functions were ascribed. Botanists, from the beginning, emphasized the fact that the physiological function deter- mines the form. Sachs introduced this idea. He believed in the theory of evolution, but he was no upholder of the old academic morphology. With Schleiden and

he was firmly convinced that the principal aim of scientific research should be to discover the causal connexions between phenomena. Following this idea out logically, he was less concerned with history than with the actual cause of structure, believing that this was partly due to in- ternal organization, partly to the action of the environment on the plant. Sachs saw that the effect of the environ- ment could be determined by experiment. Structures called forth by environment he called Mechanomorphoses ; examples of these are the various leaf-like structures seen in the algae, the mosses, and in the higher plants. These are due to the action of light. Among mechanomorphoses von Sachs distinguished between 'photomorphoses', 'bary- morphoses', and so on.

Other botanists followed the same line of thought as von Sachs, and endeavoured to determine by experiment how structures can vary as the result of alterations in the environment. Schwendener turned his attention to the mathematical view of spiral phyllotaxy (1878), and suggested that the spiral arrangement is due to the alter- nating pressure of the embryonic organs on the growing point. Vochting succeeded in making the plant develop roots, leaves, scales, and other organs in predetermined positions. The results of these researches led him to attack both the preformation theory and the theory of the germ-plasm (1878). Pfeffer, the physiologist, evolved a system of plant physiology (1897) independently of Darwinism, on the basis of his ideas about energy and assimilation. Klebs and Goebel continued this experi- mental work. Goebel was the chief member of this non- morphological school; he even rejected the belief, re- tained by Sachs, that there are given inner organizations, and that adaptations are imposed upon these. Sachs regarded such an organization as something existing for itself, and quite independent of external influences ; he quoted as examples of these heterospory and the seed habit. Goebel thought physiology all-important, and called his physiological botany 'Organography' (1898).

During the period when idealism was the popular philo- sophy, a contrast was drawn between morphology and physiology, the latter being the study of function, the former the study of form, which was independent of function. Goebel regarded this division as unnatural, since the structure always determines the function to a very large extent, while, on the other hand, function is con- stantly influencing structure. The plant is built up of organs that is, of tools formed each for a definite task which must be studied in relation to their functions. The Darwinists suggested that morphology should be included in physiology, but they did not follow up this suggestion ; in practice they remained absorbed in morphology. Seek- ing always for the story of the evolution of plants, they were dominated by forms, which they arranged in evolutionary sequences. These phylogenetic trees do not explain why evolution thus progressed, but are rather like those series of abstract forms put together by the older morphologists though now held to represent the history of their evolution.

'We do not deny the importance of these questions of phylogeny,' wrote Goebel, 'but the results which have hitherto been obtained by the study of this subject are more like the products of poetic imagination than of an inquiry which calls for stringent proof' (1905). Further, he does not doubt 'that the results of the older morphologists were based on a surer foundation than are the modern speculations about primitive forms'. These were Goebel's reasons for introducing his new science of organography. Evolution remained his guiding star, but he did not deal with the history of the evolution of organisms ; instead he discussed the origin and develop- ment of the various organs. His method is experimental, his aim the discovery of the immediate cause of the forms of organs.

Goebel explains his views as to the metamorphosis of the leaf thus. Goethe and his contemporaries thought that there exists some ideal of a leaf, some thought-out scheme. The various types of leaf foliage leaves, stamens, petals, scale leaves, &c. are concrete manifestations of that ideal. Phylogenists arranged these forms in a series, which they regarded as having an historical significance; from the foliage leaf the petal, and later the stamen, had been evolved. Goebel himself does not believe in the existence of an 'ideal' of a leaf; all that exist are actual leaf forms. These resemble each other, not because they are embodi- ments of one general plan, nor because one has been evolved from the other, but because the one form can arise from the other here and now. The scale leaf which arises in place of the green foliage leaf in the maple tree is a leaf, for in early embryonic life it arises as does the foliage leaf. The effect of a change of function is that some parts of this leaf primordium are suppressed, while other parts develop. A type of leaf is thus produced, which resembles the other in broad outline, though differing in its detailed structure. From the same embryonic beginning very different structures may be developed. The cause of this difference is different function.

Thus Goebel enunciates a genetic view of living organ- isms, in place of a more formal one. He denies that morphology can be an independent science. 'By Morpho- logy we mean', he writes, 'that which cannot yet be explained by physiology.' Goebel's ideas are worthy of notice for several reasons. They express, in its most extreme form, that physio- logical conception which is so fashionable to-day. They represent the final working out of the idea first introduced by Darwin, that the form is the result of the manner of life. They are an absolute antithesis to the morphological point of view. Goebel's views are related to those of Aristotle, morphological ideas are nearer to those of Plato.

Finally, his phrase 'to understand physiologically' is interesting. With these words the Darwinists had dismissed everything that could not be explained but only described. While the Darwinists 'explained' everything by means of phylogeny and the mechanics of the atom, Goebel's ex- planations were always physiological. ONE of the most fundamental problems of biology is that of individuality. Leibniz pointed this out, and placed the individual as the indivisible and unchangeable monad in the centre of his system. Not without reason he contrasted his philosophy with the mechanistic philosophy of Descartes, and he attached great importance to the activity of living organisms.

From quite ancient times the idea of individuality has indeed been bound up very closely with the idea of the organism. There are, it is true, 'individua' in inorganic nature things which are indivisible, which cannot be divided without altering their nature as a stone, a mole- cule, a machine. Divided, these lose their original charac- ter the stone loses its form, the molecule its chemical composition, the machine its usefulness. But the in- dividuality of an organism is of a higher order ; it reveals itself in its development, in the structure of its body, in its food, in its reaction to the influences of the external world, in psychical matters in short, in the whole moving pageant of life. Further, the organism reproduces itself, i.e. it periodically repeats itself, and finally it consists of a hierarchy of more lowly individuals, intimately bound together. An earthworm represents a complete unit both in space and time ; it has form and structure, is composed of heterogeneous parts put together according to a definite plan. Its development follows a definite sequence in time it begins with the egg, passes through a series of forms, and finally dies. It is an individual. This individuality recurs periodically, for it lays eggs, from which new in- dividuals arise. The earthworm is further composed of lower orders of individuals of body segments, of organs, cells, &c. Finally, its individuality is manifested in its ability to avoid certain dangers, its ability to regenerate

lost body-parts, its power to co-ordinate its movements to a definite end. In the early nineteenth century many morphologists dealt with this question of individuality. Alexander Braun (1849-50) ended his discussion of the problem of meta- morphosis in plants thus: the simplest individual plant is the cell. This renews its youth by division, and may re- main at the same level of individuality, or may raise itself to a higher level ; in a Phanerogam, for example, it may form the shoot, i. e. a portion of the stem, with the leaves appertaining thereto. The individual plant is formed out of as many subordinate individuals as it has leaves. In some^ plants various stages in the individual life occur in definite sequence. The bean germinates, and from the seed there develops an individual with cotyledonary leaves ; this gives rise to a series of 'foliage leaf individuals ; from the leaf axils a third series of individuals arises the in- florescence axes and their bracts ; these in turn produce the last and most highly developed individuals the flowers.

Braun looked for some analogy in the animal world to this hierarchy of individuals in the plant world. He found it in the alternating generations discovered by Steenstrup (1842) among the Coelenterata. A free-swimming larva produces a coral-like colony, which represents the first stage in individuality, and from this are budded off free- swimming sexually mature Medusae (jelly-fish), as the second stage. Leuckart (1851) attached importance to the analogy between plant metamorphosis and the structure of the Siphonophora. These latter have gelatinous bodies which consist of many less highly organized individuals, which are all formed on the same plan but very different in external appearance, for one is constructed for the taking in of food, another for reproduction, a third for move- ment, and so on.

Another idea arises from this study of individuality. Each organism is an individual, because its characters are specific ; it is no mere aggregate of qualities ; these are so interdependent, that, given one, we can deduce all the others. Look at a cat, for example. Everything about it tells us that it is a nocturnal predatory animal which pounces on its prey its eyes, its movable claws, its soft tread, its habits, which it reveals even when a kitten. The brain must be constructed to regulate its characteristic movements, the teeth to grasp its prey, the digestive system to assimilate a fleshy diet. Everything must work together harmoniously. We know, or at least we have some conception of, what gives point to the cat's whole harmonious organization. We guess, too, that the essential characteristic of the body of the swallow is the power of easy flight; that the structure of the whale's body is explained when we consider that it inhabits the sea. In other cases the essential character of an animal cannot be so easily visualized; nevertheless we see that every organism has a certain individuality. The giraffe seems to suggest length by its whole body, by its head, its tongue, its neck, its feet, its curved back ; the segmented insect has not only a segmented body, but segmented feet, segmented feelers yes, even segmented eyes.

Considerations of this kind were very natural to pre- Darwinian science. Cuvier, Geoffroy, Goethe, Jussieu, and De Candolle expressed ideas similar to the above about animal form. Speculations of this nature were very com- monly applied to Man; they called him an intelligent being, an ethical, religious, and social animal, and showed how much his intelligence had affected his bodily structure ; for not only is his brain the servant of his intellect, but his hand, his foot, his eye, his upright position, all these are connected with his high destiny. Cuvier gave concrete expression to this idea of individuality. The fact that to each type of head there corresponds a special type of trunk, and to this again a special form of limb, he called 'correlation of form'. Following this conception, he de- duced the structure of the whole body from single bones of extinct animals. Goethe and Geoffroy held very similar views.

The idea of individuality found no support in Darwin- ism ; fundamental principles of that philosophy were, that natural objects only differ quantitatively from each other, and that each organism is merely the expression of the sum of its qualities. The essence of the conception of individu- ality, on the other hand, is that it is qualitative, and that the parts of each individual are pictured as woven to- gether into a uniform whole. Haeckel was in this respect still influenced by the older morphological conceptions, and he retained the word 'individuality' in biology if not the idea. He was like the morphologists in that he only considered the in- dividuality which is revealed by bodily structure. He certainly distinguished between the morphological and physiological individual. He defined the latter as 'a single organic body, occupying a definite volume, limited in all directions and indivisible'.

This might lead us to believe that he placed the physio- logical individual above the morphological. But the very fact that he seeks to define the nature of the physiological individual through its form shows that he attached much more importance to facts of structure, and we find that he did not investigate this physiological individuality further. His ideas about individuality were based on the facts of morphology, and he suggests that it presents the following stages. The cell, the organ, the antimere (a lateral organ of a bilaterally symmetrical body, as, for example, the hand, the left eye), the metamere (one segment of a body which is divided into segments lengthwise), the person, the Cormus. Of all these the only one that has any real claim to be called an individual is the single cell, and in recent times even its reputation for individuality has waned together with that of atoms, protein molecules, and various hypothetical living 'units'.

There were many text-book discussions of this subject of individuality, but these had no real influence on bio- logical thought. To-day the prevalent views on the subject are those of Haeckel. We follow him in presenting the following degrees of individuality, although it is not possible to draw any sharp boundary between them. 2. Multicellular organisms, which are subdivided into cell colonies, coenocytia and metazoa. The first include groups of cells, in which each cell is able to live inde- pendently and to produce a new colony, e. g. Volvox. The coenocytes are formed of groups of cells, in which the boundaries between the individual cells can no longer be traced. The Metazoa are multicellular organisms with definite internal structure, and showing cell differentiation.

3. Persons are formed either by the loose union of similar individuals (Corals) or the closer union of structurally different individuals (Siphonophora). Some philosophers make another group societies to include individuals of separate heredity who are held together by spiritual ties. Tonnies distinguishes between communities when the individuals composing the group are descended from the same parents, and societies when this is not the case. Spe- cial cases of the union of several individuals are furnished by the phenomena of symbiosis. This is specially seen in lichens plant individuals composed of two organisms only held together by their method of life ; the organisms are an alga and a fungus, and each of these is capable of independent existence. Other examples are furnished by certain types of parasitism, where two individuals form one complete whole ; and by a whole series of other phenomena, where two independent organisms of quite different origin adopt a mode of life which makes them dependent on one another.

The problem of segmentation, as seen in the body of the earthworm, claimed the attention of the evolutionary morphologists. Animals were divided into the unseg- mented animals, like the worm ascaris and the mussel, in which no important part of the body is repeated, and the segmented; these were further subdivided into various groups : segmentation one organ is repeated; this is seen in the worm Gordius and in Chiton (a gastropod). In the latter only the shell reveals segmentation, in the former it is seen in the nervous system. This type of segmentation is called Pseudometamerism.

(V) The body of the tape-worm is made up of many similar segments, all capable of independent life, and of a first segment called the head, which has a special structure unlike that of the others. Nevertheless, a series of such segments is required to form one tape-worm. This type of segmentation is called Strobilation. The name is derived from the strobilia the larvae of certain Medusae. A cup-like larva divides, at right angles to its vertical axis, into segments which, having arisen by budding, become separated from the larva, and develop into free-swimming sexually-mature Medusae. In the tape-worm new seg- ments are also formed by budding from the head.

(c) An example of true segmentation is exhibited by the annelid worms. In these the body consists of segments, each one of which forms a fairly complete unit, but there are a finite and definite number of such segments ; in this respect these worms differ from the tape-worm. (d) A still higher stage in metameric segmentation is seen in the differentiated (heteronymous) segmentation of insects. Head, thorax, and abdomen are formed from similar segments, but head segments differ from those of the thorax and these again from those of the abdomen.

(e) The highest stage of all is seen in the vertebrates. Their bodies are, it is true, segmented, as we may see in the backbone ; yet the adult body forms so unified a whole that this segmentation is hardly noticeable. Geoffroy and his school began to ask what is the meaning of this metameric segmentation. The followers of Darwin gave a genetic explanation; they asked which type of segmentation was the more primitive, which the more advanced, and then formulated their theory of its evolu- tion. Some thought that metameric segmentation began in the Strobilia, others believed that the most primitive

type is seen in the pseudometamerism of the simpler worms. When Darwinian morphology became dis- credited the interest in this fascinating morphological problem vanished. At the same time there was a revival of interest in the problem of organic individuality. If we concentrate our attention upon the purpose of the organism we are inevitably led to feel that it is harmonious, all its organs working together for one end. Studying the problem of regeneration we find that, within the fully formed organism, there is an active principle which is capable of renewing the structure that has been destroyed ; and, when we turn to the philosophical question of the influence of the soul on structure and mode of life, we seem to see in the organism a unity which transcends the limits of time and space.