BIOLOGY, the science of organisms, an inquiry into the na ture, continuance and evolution of life. The term may also be used comprehensively to include botany, zoology, bacteriology (qq.v.), protistology and the other special sciences that have to do with particular kinds of living creatures. Thus in Herbert Spencer's classification of the general concrete sciences, biology occupies a central place, with its foundations in chemistry and physics, and leading on to psychology and sociology. This is a convenient classification, particularly useful in emphasizing the central position of biology ; but there is something to be said in favour of a classification simpler still. It is practically impossible to separate chemistry and physics, and it is inviting fallacy to separate biology and psychology. Thus it may be simpler to recognize three great orders of facts :—(1) the domain of things, entirely describable (in their present occurrence) in terms of mat ter and energy, i.e., in terms of protons, electrons and radiations or ether-waves; (2) the realm of organisms, from microbes to mammals, whose activities require for their description certain concepts or categories, which transcend those of mechanism; and (3) the kingdom of man, in which the units are not individuals, but societary forms with a continued tradition. For these three orders of facts, the terms cosmosphere, biosphere and sociosphere have been suggested, with the corresponding sciences—chemo physics, biology (or bio-psychology) and sociology. In any case, there is value in the elementary, yet fundamental, idea, that the domain of things encloses and interpenetrates the realm of organ isms, and that the kingdom of man is within the larger rubric of organism. Within the immense ellipse of the cosmosphere is the minute ellipse of the known biosphere, and within that again the still more minute sociosphere. When man domesticates ani mals he is taking part of the biosphere into his kingdom; and similarly he acts on the cosmosphere in gigantic operations such as a Panama Canal. When earthworms make soil, or green plants make oxygen, the biosphere cuts into the cosmosphere ; and into the sociosphere when bacilli cause plagues or the forest closes in on the village. So the cosmosphere irradiates both the realm of organisms and the kingdom of man, it may be killing in the light ning flash or invigorating in the sunshine. It is impossible to read either human history or the ascent of life without the assistance of the climatologist.
Biology may be used, then, in a comprehensive way to include all the special sciences that deal with different parts of the biosphere ; but the stricter usage, which began with Treviranus and Lamarck, is in reference to the study of the larger or deeper questions that apply to all sorts of living creatures. In this sense the biologist inquires into the nature of the particular kind of ac tivity that we call "life" (q.v.). A third usage, common in Ger many, is as an equivalent for bionomics or ecology or ethology. This is indefensible and should be discontinued.
(2) . But the study of structure leads to the grouping together of organisms that resemble one another in their fundamental archi tecture. Morphology points the way to Taxonomy or classifica tion, and that in different grades—species, genus, family, order, class and phylum. This is not merely for the sake of convenience, it is based on the discovery of deep-seated resemblances in struc ture and development, homologies. Classification aims at being an expression of actual relationships or affiliations between the different types. In most cases, this end is still remote.
(3). The obverse of morphology is Physiology (q.v.), the study of activity or function. The morphologist is concerned with statical relations, the physiologist with dynamical, but the two aspects are obviously complementary. Symmetry, e.g. radial or bilateral symmetry, has to be correlated with the animal's manner of living; the structure of the heart must be studied in the light of its function; and, on the other side, physiology has to analyse a re sultant into the components that are contributed by the individual parts. And as the history of morphology has been a persistently deepening analysis, so physiology has passed from the study of the intact organism's activities, to inquire into the working of the organs, the tissues, the cells and even of the particles in the living matter itself.
(4)• Conventional physiology restricts itself in the main to the activities of the individual, especially the everyday animal functions of contractility, irritability, nutrition, respiration and excretion, and the corresponding functions in plants. But in the study of the reproductive function it is necessary to pass beyond the individual, and thus there arises what has been called "the higher physiology," the study of habits and inter-relations. This corresponds to a large extent to the old Natural History, now called Ecology (q.v.). What are the dynamic relations between parents and offspring, between the members of a family, a herd, a community or an association? What linkages bind one kind of organism to another, it may be in the quest for food, or in the avoidance of enemies, or in the continuance of the race, as in the part insects play in pollinating flowers, or the part birds play in distributing seeds? In ordinary respiration there is a give and take between the individual organism and the immediate environ ment ; and this is obviously a question of ordinary physiology. But the swaying balance between the insects and the flowers of a given district, or between the rodents and the vegetation, or between the vegetarian and the carnivorous animals, is a problem of ecology.
So far then four sub-sciences have been recognized,—mor phology and taxonomy, physiology and ecology; and these may be arranged (after Patrick Geddes) as tables on the following page'.
(5). A fifth clear-cut question inquiries into the individual development, and the answer is Embryology (q.v.). In so far as this consists in describing the structure of successive stages in the individual Becoming, it is a morphological study, and might well be called embryography. But of recent years the inquiry has 'This scheme applies to multicellular organisms and needs modifica tion for others.
closure of the individual development. Palaeontology should be more than palaeontography,—an anatomy of fossils ; it fails of its ambition unless it also does something to reveal the great events in the historical advancement of life. Palaeontology describes as far as possible the gradations from one species to another, the connecting links between distinct types, the pre sumed affiliation of a class, and even the origin of a particular association of organisms. Thus there may be distinguished a palaeontology of species, of types, of classes, of phyla and of associations. With the last may be included an inquiry into geographical distribution, i.e., as to how different regions have come to possess similar or dissimilar faunas and floras. In essence palaeontology is a description of the stages by which organisms have come to be as they are.
If embryology and palaeontology are linked under the rubric historical, since both describe processes of Becoming or Genesis, individual and racial, the following schema may be useful.
become more and more physiological, seeking to analyse the con ditions of growth, the play of stimuli, the influence of one part on another, and so forth. This study is often called Develop mental Mechanics (Entwicklungsmec.hanik) or Developmental Physiology ; and some would separate it off from embryography, just as physiology is separated from anatomy or morphology. The term embryology, which would unite the morphological with the physiological analysis of development, must not be taken too literally ; for the word "embryo" refers strictly to the stages before the developing organism gets free from the egg-shell or egg-envelope, whereas the science has also to do with the later stages such as larva and young creature. Indeed it may be sug gested that the science of development should logically include the biological study of adolescence and maturity, of the repro ductive period and of senescence. It is a study of the organism in its time-relations. It is an analysis of the course or trajectory of the individual life, though for practical purposes it is restricted to the period before the "finished form" is attained. Embryology may be subdivided like anatomy and physiology. Thus organo genesis is concerned with the development of organs, and histo genesis with the development of tissues. Even deeper is the diffi cult problem of the division of labour which gives rise to different types of cells—nervous, contractile, glandular, skeletal and so forth. The central problem is how the inherited organization of living matter comes to be differentiated yet integrated.
(6) . When the biologist asks how the tadpole becomes a frog, he is an embryologist ; but to the question whence came the race of amphibians, the answer is Palaeontology (q.v.). In other words, embryology has to do with individual development (ontogeny), palaeontology, with racial evolution (phylogeny). The main material of the palaeontologist is of course to be found in the fossils in the rocks, but in his task of reconstructing the past and disclosing the advance of life through the geological ages, he may be able to utilize hints afforded by the comparative anatomist's study of the extant, and by the embryologist's dis (7 and 8). Huxley applied the useful term Aetiology to the study of the factors that have operated in the process of organic evolution. It is one thing to state that birds evolved from an extinct stock of reptiles; it is another thing to be able to indicate, by analogy from the present day, what factors were at work in this notable emergence. Here is included much of the study, in part experimental, of variation and heredity (qq.v.), selection and isolation. Aetiology is the study of the causes of phylogeny; it might be pardonable to call it a scientific philosophy of the history of organisms. P. Geddes has suggested that it may be useful to make a separate division for the study of the causes of ontogeny, an inquiry into the factors operative in individual development, not racial evolution. This would include the general part of physiological embryology, the whole question of the plastic influ ence of the environment on the individual, and much of what is now called genetics, a term suggested by W. Bateson for the science of heredity and variation. The whole diagram may now be put together.
Taxonomic.—The ambition of many a post-Darwinian tax onomist was to make a genealogical tree, showing the relationships of the phyla, classes and orders—an entirely legitimate ambition when there are sufficient data. But most genealogical trees have crumbled in parts; and it must be admitted that we know very little that is certain in regard to the origins of the chief phyla, such as Vertebrata, Nlollusca, Arthropoda or Annelida. More is known in regard to classes, but while all zoologists are agreed, since Huxley's day, that birds are affiliated to some extinct reptilian stock, there is no certainty in regard to the precise pedigree. Yet in regard to more detailed questions, such as the classification of birds and fishes, insects and spiders, Echinoderma and Coelente rata, much progress has been made. It seems, at first sight, strange that the taxonomists should be puzzling still over the old question : What is a species? But the inquiry has deepened (see SPECIES). Thus there has been a disclosure of specificity—i.e., of the cyto logical, biochemical, even habitudinal individuality or idiosyncrasy of any species worthy of the name. Probably every "good species" has its own protein. Then there is the discovery, for plants in particular, that a series of species believed to be nearly related on account of macroscopic resemblances, may show a regular progression in the number of their chromosomes, e.g., in a series of four species of rose, the chromosomes are 14, 28, 42 and 56 respectively. Thirdly there is the experimental attack on the species-problem, which is throwing some light on the puzzling inter-specific discontinuity and frequent sterility. It is becoming clear, however, that in many cases at least, the term species is only a convenient label, and that species are usually not sharply marked off in time and often not in space.
Physiological.—The aspect of the science has been profoundly changed by a series of modern discoveries. Thus, as has been pointed out already, to the integration effected by the nervous sys tem and by the common medium of the blood, there has to be added the specific biochemical integration due to the regulatory hormones. Similarly the modern account of the movement of the sap in a tree has become, on the one hand, simpler, because of a clearer understanding of the rOle of the water-columns in the wood cells and wood-vessels, and, on the other hand, subtler, through a recognition of the probable influence of hormones in the vessels of the bast. Modern biology has been profoundly affected by some understanding of the significance of the colloidal state, of semi permeable membranes, of substances in the form of films. Some progress has been made towards a better understanding of fer ments or enzymes, which play an important part in vital processes. In short, biochemistry is exerting a transforming influence in biology, as is illustrated in the article COLOURS OF ANIMALS.
Since the contraction of muscle fibres enables most animals to move about, and also secures in the majority the circulation of the blood and the passage of the food down the alimentary canal, it is one of the most important processes in the animal body. It is not yet more than partially understood, but it has become much more intelligible within recent years. The researches of Fletcher and Hopkins have shown that the stimulation of the muscle fibre is associated with the liberation of lactic acid which in some way or other induces a physical change in the fibre, namely contrac tion. Thus we can understand better why there must be a rein statement of the lactic acid or its chemical precursor into the fibre if it is to continue effective ; and there are interesting theories which suggest how the restitution of lactic acid may be effected. Part of it seems to be burnt up to supply the energy to reinstate the remainder. We cannot do more than touch the subject, but it is a good illustration of the way in which chemistry and physics are being applied to the elucidation of an everyday func tion. One cannot expect an understanding of the whole process to be easy ; for, as Sir Charles Sherrington has put it, "The en gineer would find it difficult to make a motive machine out of white of egg, some dissolved salts and a thin membrane, which is practically what nature has done in the exquisite artifice of the muscle fibre !" The physiology of reproduction (q.v.) in animals has been much influenced by the modern study of hormones (q.v.). From glandular tissue entangled within the reproductive organs or gonads, essentially germ-cell-producing, hormones pass into the blood and are distributed throughout the body, activating adoles cent changes in their manifold expression. The male frog's swollen first finger, the courting adornment of many cock-birds, and the antlers of stags are familiar instances of masculine pecu liarities, instigated by the reproductive hormones. In many cases the female includes in her inheritance the factors of masculine characters, but these lie latent, because the liberating stimulus is absent, or because they are inhibited by an antagonistic female hormone with an opposite influence. This explains how a duck from which the ovary has been removed may at the next moult put on the brighter livery of the drake, and assume some of his ways as well. Crowing hens and egg-laying cocks are no longer hopeless puzzles. Not less important are the hormones associated with the female reproductive organs in mammals, for they pre pare the mother for the development of the offspring in the uterus and for its demands for milk after it is born. Very inter esting lights are being shed on the intimacy of the ante-natal partnership between the mother and the unborn offspring. For it has been discovered that there is a passage of regulatory hormones from the mother to the developing offspring, and also a passage of hormones from the offspring to the mother, which contribute to her health. Thus there is a literal symbiosis, correcting the old ugly idea of "the foetal parasite." The male organism is essentially a sperm-producer, the female an egg-producer; and there are some animals, such as sea-urchins in which the sexes are so closely alike that they cannot be distin guished without a microscopic or a very experienced inspection of the reproductive organs. What lies behind this essential difference between males and females remains obscure (see SEx), it finds expression in two microscopically indistinguishable threads of a mould, as well as in the staring contrast between peacock and pea hen. There are, as we have mentioned, differences in the sex hormones, but may there not be some deep constitutional di chotomy leading to this difference? Again, there may be a differ ence in the chromosomes, as when the female has in every cell of the body one more chromosome than the male (woman having 48 and man 47), but what is there in the presence of an extra chromosome to account for all the contrasts between the sexes? Thus some biologists have sought to discover physiological differ ences between the sexes, and we take this as an instance of a modern inquiry. It has long been known that males and females may differ in constitutional details, as in the number of red blood-corpuscles and the proportionate amount of haemoglobin. Here, for instance, man is numerically superior to woman. The developing grub of a worker hive-bee has, as regards fat and glyco gen, a chemical composition markedly different from that of a grub that is developing into a drone. In many cases the blood of a caterpillar that is developing into a female butterfly is greenish, while that of its neighbour that is developing into a male is light yellow or colourless. This points to a difference in the chemical routine or metabolism of the body.
In 1889 P. Geddes and J. A. Thomson suggested in The Evolu tion of Sex that the fundamental sex-difference behind all the minor contrasts was in the ratio of anabolic to katabolic biochemi cal processes, A/K in the female being always greater than a/k in the male ; and of this theory there has been some experi mental and much observational confirmation. A germ-cell whose rate and rhythm of metabolism (measured, for instance, in pigeon's eggs by Oscar Riddle) inclines to a large A/K ratio, will tend to develop into an egg-producing female, with the ex pression of feminine characters. Conversely, a germ-cell whose a/k ratio tends to be much smaller, will tend to develop into a sperm-producing male, with the expression of masculine characters. And if it should be asked why there should be these alternatives in the A/K ratio, the answer is that this is a universal variational dichotomy, comparable to low gear and high gear. It finds ex pression in the contrast between ovum and spermatozoon as cell types ; between plants and animals as sub-kingdoms ; between Sporozoa and Infusorians as sub-phyla; between reptiles and birds, as classes; between hydroid and medusoid as phases in one life-history, and so with thousands of bifurcations on the path of life. It is often illustrated by variations, of lizards for instance, within a species. It may also be recalled that one and the same organism may in the course of its life change normally from one sex to another, as is illustrated by the hagfish, Myxine glutinosa.
In 1923 Manoiloff described a chemical test that enabled him with notable success to tell whether a sample of blood had been taken from a male or from a female animal. To a diluted half transparent emulsion of blood in salt solution he added, drop by drop, a succession of reagents. After the treatment the emulsion of blood from a male was colourless ; that from a female was coloured. Out of 53o tests Manoiloff had about 96% right answers, and two of his students had 97 and 92% of successes. Many others, however, have been much less fortunate, and the dis crepancies are puzzling. As the chlorophyll-green of plants and the haemoglobin of animals are regarded by many biochemists as nearly allied pigments, Manoiloff turned his attention to some of the dioecious plants, such as willow, poplar and dog's mercury. In Manoiloff's hands the sex-test worked almost as well for the plants as for the animals, but some other investigators have not had this experience.
Distinctive of this generation has been the study of reflex actions (see PSYCHOLOGY, COMPARATIVE). In the familiar knee jerk, when a sharp tap below the joint of a crossed leg sends the foot up into the air, the mechanical stimulus leads to a thrill along sensory nerve-fibres to the spinal cord ; the nervous pulse—still so much of a puzzle—passes to connecting or tive cells and thence to motor nerve-cells, both in the spinal cord. Thence, along motor nerve-fibres, orders come to the muscles, commanding them, as we say, to contract. The brain is not required at all. A pre-arranged linkage of sensory, associative, and motor spinal neurons is sufficient in itself, with, of course, the muscle-cells to give effect to the motor orders. What occurs is called by the physiologists an "unconditioned reflex," and it is one of the commonest occurrences, both in man and beast. When we shut our eyes at the approach of a missile, or when we low what touches the back of our mouth, we are illustrating various forms of the unconditioned reflex, some more complicated than others. So is it when a sea-anemone closes its tentacles on a piece of food, when a crab amputates a badly damaged leg, when an earthworm jerks itself into its hole if the ground vibrates under a blackbird's. footsteps, when a plaice puts on the colour of sand on which it has come to rest, when a nestling opens its mouth at the touch of food in its mother's bill—these are illustrations of unconditioned reflexes; and the animal world is full of them. It is characteristic of unconditioned reflexes that they are inborn, that they do not require to be learned, that they are shared by all members of the species, and that they are often quite inde pendent of the brain for their performance. It should be noted, however, that even in the case of a very simple unconditioned reflex like the knee-jerk, a message goes to the brain to report the occurrence. Moreover, the brain is sometimes able to sup press the normal reaction, as in the case of criminals tried by Oriental ordeals, such as the swallowing of dry rice, which is almost impossible if fear inhibits the flow of saliva.
But the modern development of this line of inquiry which we wish to take as an illustration of physiological progress is I. Pavlov's study of "conditioned reflexes." If a dog is shown a piece of flesh its mouth waters. If a whistle is always sounded when the flesh is shown to the dog, an association is gradually formed between the sound and the prospect of a meal. This association or enregistration may become so strong that the dog's mouth will water when the animal hears the whistle, al though there is no flesh in sight. The flow of saliva in the dog's mouth illustrates a "conditioned reflex," and the strength of the reaction can be measured by the amount of saliva secreted. It seems likely that in the everyday early life of animals many of these conditioned reflexes are established, and this is to the na turalist the particular interest of Pavlov's experiments. The established associations work rapidly and are probably life-saving as well as time-saving. A wild animal, such as a lion, will react rapidly to a sound or sight in connection with which a reflex has been established, whereas it may not be in the least perturbed by a much more obvious, but unfamiliar, source of danger, such as the arrival of a motor-car against the wind. The conditioned reflex, though usually based on some much older unconditioned reflex, is always built up in the experience of the individual; and, as in mankind, so among the higher animals, there may be some appre ciation of the meaning of the connection.
Ecological.—Ecology (q.v.) is the study of life as it is lived in nature, where the circle of each individual's interests is inter sected by many other circles—such as kindred, members of the same species, competitors, deadly enemies, parasites, symbions, and so forth. Ecology is concerned with inter-relations and linkages, with ways of living, with adjustments to space and time. Thus it includes the study of numbers and dispersal, of migration and other seasonal reactions. Ordinary physiology is concerned with the internal economy of the individual body, but ecology has to do with external relations. The transition from in dividual physiology to ecology is in the study of reproduction, for that leads from organism to organisms. A few illustrations may be given of the lines of modern ecological investigation.
The leaf-cutter ants cut off segments of leaf from certain trees and carry them to their underground nest, where they are chewed into a green paste, used as the culture-medium for a particular kind of mould not found anywhere else. This mould forms the exclusive food of the leaf-cutters in their subterranean life. When the queen leaves the nest on her nuptial flight, thereafter to start a new community, she takes with her in a little depression be neath her mouth a sample of the mould, which she plants out as soon as her brood of workers have collected leaves and made a soil of green paste. Naturalists have been long admiringly fa miliar with the parental care exhibited by many insects, but did anyone suspect the extraordinary nutritive exchange common among social wasps between the nurses and the grubs, and also illustrated among ants and termites? Sometimes the mother wasps, but oftener the step-mothers or workers, feed the grubs in their cells with the chewed flesh of insects, the jaw-apparatus of the larvae being poorly developed. But when the meal is supplied, and sometimes in defect of it, the larva exudes from its mouth a drop of sweet elixir which is greedily licked off. The demand for this luxury may be somewhat coercive, and the elixir is appreciated and may be obtained by the drones, as well as by the queen and the workers (see SOCIAL INSECTS). As the sweet juice is secreted only by the young larval wasps, the ex change or "trophallaxis" tends towards the establishment of a ménage in which throughout the season there are continual relays of young ones. The luxury seems to have become almost a necessity.
Instances of symbiosis have multiplied greatly within recent years, plant within plant, plant within animal, animal within ani mal. The last is best illustrated by the highly specialized Infuso rians whose sole habitat is the intestine of wood-eating termites, where they do something that is indispensable to the food. By raising the temperature it is possible to kill off the Infusorians without harming the termites, whereupon the insects die, being unable to make anything of the wood. But they can be rescued by introducing a fresh supply of Infusorians. Another remarkable symbiosis is illustrated by some luminous cuttlefishes that shine with a light produced by nests of harmless luminous bacteria, like those familiar on drying fish.
The disclosures of the ecologists are warnings against taking simple views of things. Some beetles that bore in growing wood have no symbionts in their food-canal, but on the walls of their tunnels they grow a mould that yields what is called "ambrosia." The fungus collects, concentrates and prepares the sap, and in some cases it has been proved that the beetles do not eat the wood or sap as such, but depend entirely on. the ambrosia. The fungus does not seem to form spores or other elements specialized for propagation, so it is probable that the beetles infect a new tree with surplus vegetative ambrosia cells which have passed out undigested from the food-canal. Ecology makes life more com plex. Thus the much-studied life of the hive-bee has been compli cated by the disclosure of the nectar-dance and pollen-dance on the honeycomb, in which a worker-bee gives her sisters a clue to treasure-trove. Similarly there is the discovery of the graduated quasi-apprenticeship of the worker through a succession of in stinctively discharged duties, and there is the punctilious study of homing. To take the last, Wolf has shown that the homing depends partly on visible landmarks that have been learned, partly on the odour of the hive, and partly on a "sense of direction," which has its seat on the antennae, and is remotely comparable to the sense associated with man's semicircular canals. By the antennae the bee is able to record movements until it begins to "lose count." When bees are fed for the nonce at a point 15o yards due north of the hive, a captured one released from its box flies at once southwards. But if the captive is carried in the box 15o yards due east of the hive and then released, it flies again due south. When it has covered 15o yards (judging the distance to ten yards!) it begins to hesitate, apparently made aware that it is quite wrong. It then proceeds to circle around until it finds the hive by sight and scent. Our illustrations have perhaps been within too narrow a range, for ecology has to do with associations and communities, families and pairs, thrust and parry with the environment and with the seasons, trading with time and traffick ing with circumstance, migrations and trekkings, outgoings and incomings, and, of course, with plants as much as with animals.
Embryological.—The old-fashioned morphological embryog raphy has largely given place to experimental and physiological studies of development; but the description of the stages in a life-history can never cease to be an integral part of biology. Johann Schmidt's masterly elucidation of the larval development of the common eel has much interest even for the general biologist, and Leiper's discovery of the story of Bilharzia is notable in itself as well as in its practical applications. Of recent years there has been no more striking achievement than Isabella Gordon's description of the building up of the sea-urchin's test, from a few sclerites in the early free-swimming larva to the elaborate edifice of the adult. Notable advances have rewarded the applications of physiological methods and ideas to embryology (q.v.). There has been a fruitful study of the regulative and "organizing" influence of one part on another during development, of the role of hor mones in controlling the rate and rhythm of developmental changes, of the significance of certain environmental factors and of chemical substances in the food. The studies of Julian Huxley and others on dedifferentiation and regeneration (qq.v.) well illus trate the modern movement, and the experiments of Spemann are outstanding. A few particular discoveries may be mentioned to give more concreteness to the picture. (a) In many cases (even in frogs), it is possible to induce the normal development of eggs without there being any fertilization (see FERTILIZATION). (b) Many experiments show that a part of an egg may be as good as the whole. A larva may be reared from a fertilized fragment of an Echinoid egg, or from one of the first four cells into which the ovum of Amphioxus divides. (c) In certain cases, as in Ctenophores and Tunicates, it is possible to prove that there are specific organ-forming substances in an egg, whose removal is followed by some particular defect in the developing organism. (d) A portion of the optic vesicle of a tadpole grafted under the skin of the larva in an entirely irrelevant place, such as the side, will induce in the cells of the epidermis the formation of a lens, which is the normal function of the optic vesicle in its proper place. (e) If the newly fertilized eggs of the American minnow (Fundulus) are exposed for a few hours to a temperature a little above freezing point, a percentage will develop into blind larvae. This experiment shows that the blindness of certain cave fishes need not necessarily be ascribed to the darkness. (f) If the developing eggs of the same fish are subjected to various reagents, such as butyric acid, there result numerous strange monstrosities in eyes and ears, nostrils and mouth, even in heart and fins. The chemical intrusion seems to dislocate and partially dissolve the germinal material, especially towards the head end. This may throw some light even on mammalian monstrosities, for butyric acid sometimes appears in higher animals as the result of some disturbance in the carbohydrate metabolism. A consequent poison ing of the mammalian mother's constitution might result, through the placenta, in monstrosities in the early embryo. (g) If the larva of the blind newt Proteus be reared in the laboratory under red light, the developing eye, which is normally arrested in the darkness of the caves, increases in size, reaches the surface of the head, and may continue its development even to the extent of becoming functional. The reason for the red light is that in white light the skin of the larva becomes darkly pigmented, and shuts off the stimulus from the developing eye. (h) According to Baltzer's account of the development of the green worm Bonellia, notable for its extraordinary sexual dimorphism, those free swimming larvae that settle down on the floor of the sea develop into large females with a body an inch or two in length and a flexible food-capturing proboscis which may be a foot long. But those that settle down on the proboscis of a full-grown female, and proceed to absorb the skin-secretion, have their development inhibited, and become pigmy males ! Those larvae that Baltzer helped to attach themselves to the proboscis of a full-grown female, but left attached for a very short time, subsequently de veloped into almost perfect females. Those that he left attached for a long time became the ordinary pygmy males with much simplified structure, which live parasitically in the female. But those left for intermediate intervals of time showed various stages of inter-sex.
There is more than verbal progress in the recognition that em bryology cannot be limited to the study of the very young animal. It is plain that the larval, as well as the embryonic, stages must be included, and all the difficult phenomena of metamorphosis. But one cannot logically exclude such strange dis-organizations and re-differentiations as are involved, for instance, in the "brown body" of many Polyzoa. The changes of adolescence cannot be separated off from their antecedents, and thus the broader view of embryology will include the study of the whole organism in its time-relations, even those of senescence. The work of Child on Senescence and Rejuvenescence is significant of the broadened modern outlook. It is biologically interesting to compare the life histories of different types, for they sometimes differ from one another in the relative length of the various arcs on the life-curve. Thus some, like Peripatus and the elephant, have a prolonged embryonic period ; others, like the lamprey, show a lengthened out larval phase ; others have a long adolescence, like the elephant again; and so on. Some, like eels, die abruptly after reproduction, while others continue parental for many years, like Golden Eagles. Some, like Mound Birds, practically telescope the whole youthful period; others, e.g., many fishes, continue steadily growing throughout life. These elongations and telescopings of arcs on the life-curve are undoubtedly adaptive in many cases to par ticular conditions of environment and seasons. They suggest the occurrence of what may be called "temporal variations"; and these in higher animals may be correlated with endocrinal pecu liarities.
Palaeontological.—The modern advance in palaeontology may be dated from the work of Waldemar Kowalevsky (1874) who devoted himself to a reconstruction of the life of fossil ungulates. He sought to relate his fossils not only to their extinct ancestors and extant descendants, but to their own habits and to their par ticular environments, both climatic and animate. The distinctive note in the outstanding palaeontological studies of recent years is the reconstruction of the life of the past. The palaeobotanist joins with his zoological colleague, and both take counsel with the geologist and with the climatologist. A further aspect of modern palaeontology is the way in which it has filled in gaps and given us continuous series of fossils.
Aetiological.—The origin of the new remains one of the central problems of biology, but some steps of essential importance have been made since Darwin's day. (I). There is evidence of the frequency of discontinuous variations or mutations, and these illustrate Mendelian inheritance. (2). There is no doubt that many—some would say a//--visible and somatic variations are due to germinal permutations, combinations and changes. (3). In some cases it is certain that the germinal "factors" or "genes," corresponding to particular mutations, and to all or many of the discrete non-blending "unit characters" of the organism, lie in longitudinal order in the chromosomes of the nuclei of the germ cell. In the fruit-fly Drosophila there are known to be about 7,5oo of these "factors"; and their topography has been provisionally mapped out. In the history of the germ-cells there are ample opportunities for their shuffling, which might, and no doubt does result in new patterns. (4). Some experiments show that deeply saturating environmental, nutritional and functional peculiarities —including X-ray radiations—may incite germinal changes. (5). Just as a periodic scrapping and re-organization (endomixis) occurs normally in some species of slipper animalcule, so there may be re-arrangements and re-organizations in the complex nucleus of a germ-cell, which, after all, must be intensely alive. (6). There is strong palaeontological and a little experimental evidence that variations are sometimes definite or orthogenic, i.e., occurring consistently in a particular direction. In other words, a variation may be congruent with what has been already en registered in the organization of the creature. As a particular illustration we may refer to Erwin Baur's study of mutations in snapdragons, Antirrhinum majus and its relatives. The garden races are continually exhibiting mutations, small in amount, but crisp and brusque in character, and transmissible in their entirety in Mendelian fashion. There seems no doubt that they are ex pressions of slight germinal changes in the hereditary factors.
Various evolutionists who admit the reality of mutations have been inclined to depreciate their importance on the ground that they tend towards monstrosities and represent a weakening of germinal vigour. This may be true in some cases, e.g. in fancy goldfishes or waltzing mice, but it is certainly not true of Baur's small mutations in snapdragons, for these are generally well within the limits of healthy normality. They find expression not only in the flower and its colour, but in many parts and characters of the plants. Sometimes the new departures suggest an enhancement of vigour, as in a deeper green in the leaves. In any case, there is rarely any hint of the pathological. In most cases the mutants seem to have taken a small step further along the direction which marks the parental race. After 20 years of investigation of the garden races and wild species of snapdragon, Baur has come to the conclusion that in many cases their distinguishing character istics are due to the summation of small mutations such as are of everyday occurrence in the garden. In natural conditions the summation may be put to the credit of natural selection, which sifted the new tentatives in reference to the diverse and changeful conditions of locality and climate. This is a characteristically Darwinian conclusion, for Darwin thought much more of the creeping than of the leaping of the eternal Proteus of life. But whereas Darwin was vague in regard to his raw material of "small variations," Baur is very precise in regard to his "small muta tions," except as regards their cause. While Baur confirms Dar win's belief in the cumulative importance of small changes, which might be called evolution-jerks or quanta, he is far from saying that these furnish the whole of the raw material of progress. On the contrary, while he lays chief emphasis on minute changes in the hereditary factors or genes,—changes which occur abundantly even in "pure lines" (all descended from one parent),—he admits that new departures may arise from the crossing of different strains with different sets of factors. But the existence of these different strains depends in snapdragons on the previous summing up of small, mutations. The large transilient variations or freaks, which attract the gardener's eye, can be continued by careful cultivation, but they tend to be eliminated by natural selection as too extreme. The small mutations count for most. It may be noted that, in contrast to roses and some other organisms, the number of chromosomes does not change, being eight in all the species studied.
As regards heredity, the modern position has been profoundly altered (I) by the re-discovery (19oo) of Mendelian inheritance, (2) by Weismann's concept of germinal continuity, and (3) by the use of statistical methods. While there are some puzzling phenomena, there is at present no conclusiveness in the evidence adduced in support of the transmission of individually acquired somatic modifications, even to a slight degree. But there is a clearer recognition of the fact that the expression of a character in the course of development is always the resultant of two com ponents—the hereditary "nature" and the environmental, nutri tional, and functional "nurture." There have been several violent reactions from the characteristically Darwinian theory of natural selection, but they do not appear to be well-informed. Darwin anticipated the criticism that natural selection does not account for the material to be sifted; he was careful to distinguish other forms of selection besides the immediate lethal elimination of the relatively less fit; he laid stress on the survival value of such non-competitive endeavours as parental care and mutual aid; he laid emphasis on the correlation of variations, as explaining how an incipient new departure, too minute to be of appreciable value, might be carried in the wake of a large and important variation with which it is correlated. Since Darwin's day it has become clearer that natural selection operates in relation to a system of inter-relations—the web of life—already established, a fact which explains how the difference between Shibboleth and Sibboleth may have survival value. It has also become clearer that organisms sometimes take part in their own evolution by playing the hand of hereditary cards with which they have been endowed. It is true that the environment often selects organisms, but it is also true that the organism sometimes selects its environment. Since Darwin's day there have been a few actual proofs of natural selec tion at work, as in the case of Weldon's crabs and Cesnola's mantises.
Increased attention has been paid to the effect of isolation in its varied forms—geographical, habitudinal, temporal and tem peramental—for isolation tends to inbreeding or endogamy, which stabilizes a stock or species, whereas outbreeding or exogamy pro motes variability, sometimes almost like an epidemic. There *can be little doubt that alternations of inbreeding and outbreeding have meant much in evolution. Careful experiments have shown that inbreeding may be long continued in a vigorous stock without any deterioration, the prejudice against it being due to the mis take of supposing that the not infrequent disclosure of recessive defects in the course of inbreeding is due to the consanguinity as such.
As an alternative grouping it may be suggested that the biologist has to do with Organisms, Functionings and Environments, using each term in the plural, and "functionings" rather than "func tions" on the ground that the everyday functions that secure the continuance of the living creature cannot be separated from the organism without leaving a false abstraction.
Organisms may be studied statically (anatomy, etc.) or dynami cally (physiology, etc.), and in their time-relations (from embry onic development to senescence). Functionings include all the ongoings and operations of the organisms (ecology). The study of environments includes the whole staging of life, animate as well as inanimate, and that is also to be studied in its time relations, both seasonal and secular. At every point the evolution ary question may be raised, in regard to each of the three sides: By what steps and by what factors did these organisms, func tionings and environments come to be as they are? This removes the awkwardness of having aetiology as a separate sub-section, and of separating the anatomy and physiology of the embryo or larva from the anatomy and physiology of the adult. If the sides of the triangle, a cross-section of "the biological prism," be pictured as convex, the inner surface may represent the psychical, mental or subjective aspect (clearly present in many organisms and functionings and in at least the higher reaches of the animal part of the environment), while the outer surface may represent the protoplasmic, bodily or objective aspect. The correspondence of the biological co-ordinates, Organisms, Functionings and En vironments, with the sociological analogues, Folk, Work and Place, is obvious.