herent and indefinite, there arises the coherent and definite. But a coherent whole made up of definite parts definitely combined, must exhibit more definitely combined changes than a whole made up of parts that are neither definite in themselves nor in their combination. Hence, if living bodies display more than other bodies this structural definiteness, then, definiteness of combination must be a characteristic of the changes constituting Life; and must also distinguish the vital changes of higher organisms from those of lower organ- isms. Finally, however, we discovered that all these peculiarities are subordinate to the one fundamental pecu- liarity, that vital changes take place in correspondence with external co- existences and sequences; and that the highest possible Life is reached, when there is some inner relation of actions fitted to meet every outer relation of actions by which the organism can be affected. But this conception of the highest possible Life, is in perfect harmony with the con- ception, before arrived at, of the ultimate limit of Evolution. When treating of equilibration as exhibited in organic phenomena {First Principles, |§ 133, 134), it was pointed out, that the continual tendency is towards the establishment of a balance between inner and outer changes. It was shown that " the final structural arrangements must be such as will meet all the forces acting on the aggregate, by equivalent antagonistic forces,'^ and that " the maintenance of such a moving equilibrium " as an organism displays, *•' requires the habitual genesis of internal forces correspond- ing in number, directions, and amounts, to the external incident forces — as many inner functions, single or com- bined, as there are single or combined outer actions to be met." It was shown, too, that the relations among concep- tions and ideas, are ever in progress towards a better balance between mental actions and those actions in the environment to which conduct must be adjusted. So that that main- tenance of a correspondence between inner and outer rela- tions, which we have here found to constitute Life, and the THE LIFE VAKTES AS THE CORRESPONDENCE. 93 perfection of whicli is the perfection of Life, answers com- pletely to that state of organic moving equilibrium which we saw arises in the course of Evolution, and tends ever to become more complete.
There is much significance in this complete parallelism. That two inquiries starting from different points and carried on in different ways, should lead to conclusions so entirely harmonizing with each other, cannot fail further to confirm these conclusions; if further confirmation of them be needed.
CHAPTER YII.
THE SCOPE OF BIOLOGY.
§ 37. "We are now in a position to map-out the boundaries and divisions of our subject. Grouping together the general results arrived at in the first three chapters, and joining with them the results which the last three chapters have brought us to, we shall be prepared to comprehend the science of Biology as a whole; and to see how its truths may best be classified.
In the chapters treating of Organic Matter, the Actions of Forces on it, and its Eeactions on Forces, the generalizations reached were these: — that organic matter is specially sensi- tive to surrounding agencies; that in consequence of the extreme instability of the compounds it contains, minute dis- turbances can cause in it large amounts of re- distribution; and that during the fall of its unstably-arranged atoms into stable arrangements, there are given out proportionately large amounts of motion. We saw that organic matter is so constituted, that small incident actions are capable of initiat- ing great reactions — setting up extensive structural modifica- tions, and liberating large quantities of power. In the chapters just concluded, the changes of which Life is made up, were shown to be so adjusted as to balance outer changes. And the general process of the adjustment we found resolves itself into this; that if in the environment there are any related actions, A and B, by which the or- THE SCOrK OF IIIOLOGY. 95 ganism is affected, then if A produces in the organism some change a, there follows in the organism some change h, fitted in time, direction, and amount to meet the action B — a change which is often required to be much larger than its antecedent. Mark, now, the relation between these two final results. On the one hand, for the maintenance of that correspondence between inner and outer actions which constitutes Life, an organism must be susceptible to small changes from small external forces (as in sensation), and must be able to initiate large changes in opposition to large external forces (as in muscular action). On the other hand, organic matter is at once extremely sensitive to disturbing agencies of all kinds, and is capable of suddenly evolving motion in great amounts. That is to say, the constitution of organic matter specially adapts it to receive and produce the internal changes required to balance external changes.
This being the general character of the vital Functions, and of the Matter in which they are performed, the science of Biology becomes an account of all the phenomena attend- ant on the performance of such Functions by such Matter — an account of all the conditions, concomitants, and conse- quences, under the various circumstances fallen into by living bodies. If all the functional phenomena which living bodies present, are, as we have concluded, incidents in the main- tenance of a correspondence between inner and outer ac- tions; and if all the structural phenomena ^vhich living bodies present, are direct or indirect concomitants of func- tional phenomena; then the entire Science of Life, must con- sist in a detailed interpretation of all these functional and structural phenomena in their relations to the phenomena of the environment. Immediately or mediately, proximately or remotely, every trait exhibited by organic bodies, as distinguished from inorganic bodies, must be referable to this continuous adjustment between their actions and the actions going on around them. Such being the extent and nature of our subject-matter, it may be thus divided.
96 THE DATA OF BIOLOGY.
1. An account of tlie structural phenomena presented by organisms. And this subdivides into: — a. The structural phenomena presented by individual organisms. h. The structural phenomena presented by successions of organisms.
2. An account of the functional phenomena which or- ganisms present. And this, too, admits of sub- division into: — a. The functional phenomena of individual organisms. h. The functional phenomena of successions of organisms.
3. An account of the actions of Structure on Function, and the re- actions of Function on Structure. And like the others, this is divisible into: — a. The actions and re-actions as exhibited in individual organisms. h. The actions and re-actions as exhibited in successions of organisms.
4. An account of the phenomena attending the production of successions of organisms: in other words — the phenomena of Genesis.
There is, indeed, another mode of grouping the facts of Biology, with which all are familiar. According as they are facts of animal or vegetal life, they may be classed under the heads of Zoology and Botany. But this di- vision, though convenient and indeed necessary for practi- cal purposes, is one that does not here concern us. Dealing with organic structures and functions in connexion with their causes, conditions, concomitants, and consequences, Biology cannot divide itself into Animal-Biology and Vege- tal-Biology; since the same fundamental classes of phe- nomena are common to both. Recognizing this familiar distinction only as much as convenience obliges us to do, let us now pass on to consider, more in detail, the classification of biologic phenomena, above set down in its leading outlines.
§ 38. The facts of structure which an individual or- THE SCOPE OF BIOLOGY. 97 ganism exhibits, are of two chief kinds. In order of con- spicuousness, though not in order of time, there come first those ultimate arrangements of parts which characterize the organism in its mature state — an account of which, commonly called Anatomy, is more properly called Morphology. And second, there come those successive modifications through which the organism passes in its development from the germ to the adult form— an account of which is called Embryology.
The facts of structure which any succession of individual organisms exhibits, admit of similar classification. On the one hand, we have those inner and outer differences of shape, that are liable to arise between the adult members of suc- cessive generations descended from a common stock — differ- ences which, though usually not marked between adjacent generations, may in course of many generations become great. And on the other hand, we have those developmental modi- fications through which such modifications of the descended forms are reached.
The interpretation of structure, as exhibited in individual organisms and successions of organisms, is aided by two sub- sidiary divisions of biologic inquiry, named Comparative Anatomy (properly Comparative Morphology) and Compara- tive Embryology. These cannot properly be regarded as in themselves parts of Biology; since the facts embraced under them are not substantive phenomena, but are simply inci- dental to substantive phenomena. All the facts of structural Biology are comprehended under the two foregoing sub- divisions; and the comparison of these facts as presented in different classes of organisms, is simply a method of inter- preting the real relations and dependencies of the facts compared.
Nevertheless, though Comparative Morphology and Com- parative Embryology do not disclose additional series of con- crete or special facts, they lead to the establishment of certain abstract or general facts. By them it is made manifest that underneath the superficial differences of groups and classes 98 THE DATA OF BIOLOGY.
and types of organisms, there are hidden fundamental simi- larities; and that the courses of development in such groups and classes and types, though in many respects divergent, are in some essential respects, coincident. The wide truths thus disclosed, come under the heads of General Morphology and General Embryology.
By contrasting the structures of organisms, there is also achieved that grouping of the like and separation of the unlike, called Classification. First by observation of ex- ternal characters; second by observation of internal charac- ters; and third by observation of the phases of development; it is ascertained what organisms are most similar in all particulars; what organisms are like each other in every important attribute; what organisms have common primor- dial characters. Whence there finally results such an ar- rangement of organisms, that if certain structural attributes of any one be given, its other structural attributes may be empirically predicted; and which prepares the way for that interpretation of their relations and genesis, which forms an important part of rational Biology.
§ 39. The second main division of Biology, above de- scribed as embracing the functional phenomena of organisms, is that which is in part signified by Physiology: the remain- der being what we distinguish as Psychology. Both of these fall into subdivisions that may best be treated separ- ately. That part of Physiology w^hich is concerned with the molecular changes going on in organisms, is known as Organic Chemistry. An account of the modes in which the force generated in organisms by chemical change, is trans- formed into other forces, and made to work the various or- gans that carry on the functions of Life, comes under the head of Organic Physics. Psychology, which is mainly concerned with the adjustment of vital actions to actions in the environment (in contrast with Physiology, which is mainly concerned with vital actions apart from THE SCOPE OF lUOLOGY. 99 actions in the environment) consists of two quite distinct por- tions. Objective Psychology deals with those functions of the nervo-muscular apparatus by which such organisms as possess it, are enabled to adjust inner to outer relations; and includes also, the study of the same functions as externally manifested in conduct. Subjective Psychology deals with the sensations, perception's, ideas, emotions, and volitions that are the direct or indirect concomitants of this visible adjustment of inner to outer relations — considers these several kinds of conscious- ness in their genesis, and their connexions of co-existence and succession. Consciousness under its different modes and forms, being a subject-matter radically distinct in nature from the subject-matter of Biology in general; and the method of self- analysis, by which alone the laws of dependence among changes of consciousness can be found, being a method un- paralleled by anything in the rest of Biology; we are obliged to regard Subjective Psychology as a separate study —not absolutely, of course, but relatively to the mind of each student. And since it would be very inconvenient to dis- sociate Objective Psychology from Subjective Psychology, we are practically compelled to deal with the two as forming an independent sub-science, to be treated apart from the lower diA^sions of Biology.
Obviously, the functional phenomena presented in succes- sions of organisms, similarly divide into physiological and psychological. Under the physiological, come the modifications of bodily actions that arise in the course of generations, as concomitants of structural modifications; and these may be modifications, qualitative or quantitative, in the molecular changes classed as chemical, or in the organic actions classed as physical, or in both. Under the psychological, come the qualitative and quantitative modifica- tions of instincts, feelings, conceptions, and mental changes in general, that occur in creatures having more or less intelligence, when certain of their conditions are changed. This, like the preceding department of Psychology, has in 100 THE DATA OF BIOLOGY.
the abstract two different aspects — the objective and the sub- jective. Practically, however, the objective, which deals with these mental modifications as exhibited in the changing habits and abilities of successive generations of creatures, is the only one that admits of scientific investigation; since the corresponding alterations in consciousness, cannot be im- mediately known to any but the subjects of them. Evidently, convenience requires us to class this part of Psychology along with the other parts, in a distinct sub-science.
Light is thrown on functions, as well as on structures, by comparing organisms of different kinds. Comparative Physiology and Comparative Psychology, are the names given to those collections of facts respecting the homologies and analogies, bodily and mental, that are brought to light by this kind of inquiry. These classified observations concern- ing likenesses and differences of functions, are helpers to interpret functions in their essential natures and relations. Hence Comparative Physiology and Comparative Psychology are names of methods, rather than names of true subdivisions of Biology.
Here, however, as before, the comparison of special truths, besides facilitating their interpretation, brings to light certain general truths. Contrasting bodily and mental functions as exhibited in various orders of organisms, shows that there exists, more or less extensively, a community of processes and methods. Hence result two groups of abstract proposi- tions, constituting General Physiology and General Psy- chology.
§ 40. In these various divisions and sub- divisions of the first two great departments of Biology, the phenomena of Structure are considered separately from the phenomena of Function, so far as separate treatment of them is possible. The third great department of Biology deals with them in their necessary connexions. It comprehends the determin- THE SCOPE OF inOLOGY. 101 ation of functions by structures, and the determination of structures by functions.
As displayed in individual organisms, the action of struc- tures on functions is to be studied, not only in the broad and familiar fact that the general kind of life an organism leads is necessitated by the main characters of its organization, but in the more special and less conspicuous fact, that between members of the same species, minor differences of structure lead to minor differences of power to perform certain kinds of action, and of tendency to perform such kinds of action. Conversely, under the re- actions of function on structure as displayed in individual organisms, come the facts showing that functions, when fulfilled to their normal extents, main- tain integrit}^ of structure in their respective organs; and that within certain limits, the increase of functions is followed by such structural changes in their respective organs, as enables the organs to discharge better their extra functions.
Inquiry into the action of structure on function as dis- played in successions of organisms, introduces us to such phenomena as Mr Darwin's "Origin of Species" deals with. In this category come all proofs of the general truth, that when an individual is enabled by a certain structural pecu- liarity, to perform better than others of its species some advantageous action; and when it bequeaths more or less of its structural peculiarity to descendants, among whom those which have it most markedly, are best able to thrive and propagate; there arises through this continuous action of structure on function, a visibly modified type of structure, having a more or less distinct function. In the correlative class of facts, which come under the category of re- actions of function on structure as exhibited in successions of organisms, are to be placed all those modifications of struc- ture which arise in races, when changes of conditions entail changes in the balance of their functions. Here is to be studied the way in w^hich altered function externally necessi- 102 THE DATA OF BIOLOGY.
tated, works, by re-action, altered structure; and how in succeed- ing generations, this altered structure may be made continu- ally more marked by this altered function. Though logically distinct, these two sub-divisions of biologic inquiry cannot in practice be carried on apart. A speciality of struc- ture which leads to an excess of function in any direction, is, by the perpetual re-action of function, rendered ever more decided. A speciality of function, by calling forth a corre- sponding speciality of structure, produces an increasingly efficient discharge of such function. Whichever of the two initiates the change, there goes on between them an unceas- ing action and re-action, producing in them co-ordinate modifications.
§ 41. The fourth great division of Biology, comprehend- ing the phenomena of Gfenesis, may be conveniently separated into three sub-divisions.
Under the first, comes a description of all the special modes whereby the multiplication of organisms is carried on; which modes range themselves under the two chief heads of sexual and asexual. An account of Sexual Multiplication in- cludes the various methods by which germs and ova are fertilized, and by which, after fertilization, they are furnished with the materials, and maintained in the conditions, needful for their development. An account of Asexual Multiplica- tion includes the various methods by which, from the same fertilized germ or ovum, there are produced many organisms that are partially or totally independent of each other.
The second of these sub-divisions deals with the phenomena of Genesis in the abstract. It takes for its subject-matter, such general questions as — What is the end subserved by the union of sperm-cell and germ -cell? Why cannot all multi- plication be carried on after the asexual method? What are the laws of hereditary transmission? What are the causes of variation?
The third sub-division is devoted to still more abstract THE SCOPE OF BIOLOGY. 103 aspects of the plienomcna. Recognizing the general facts of multiplication, without reference to their modes or immediate causes, it concerns itself simply with the different rates of multiplication in different kinds of organisms, and different individuals of the same kind.. Generalizing the numerous contrasts and variations of fertility, it seeks a rationale of them in their relations to other organic phenomena.
§ 42. Such appears to be the natural arrangement of divisions and sub-divisions which Biology presents, when re- garded from the highest point of view, as the Science of Life — the science which has for its subject-matter, the cor- respondence of organic relations, with the relations amid which organisms exist. This, however, is a classification of the parts of Biology when fully developed; rather than a classification of the parts of Biology as it now stands. Several of the sub-divisions above named have no recognized existence; and sundry of the others are in quite rudimentary states. It is therefore impossible now to fill in, even in the roughest way, more than a part of the outlines here sketched.
Our course of inquiry being thus in great measure de- termined by the present state of knowledge, we are com- pelled to follow an order widely different from this ideal one. It will be necessary first to give an account of those empiri- cal generalizations which naturalists and physiologists have established: arranging them rather with a view to facility of comprehension than to logical sequence; and append- ing to those which admit of it, such deductive interpreta- tions as First Principles furnish us with. Having done this, we shall be the better prepared for dealing with the lead- ing truths of Biology, in connexion with the doctrine of Evolution.
\' VI PART II.
THE INDUCTIONS OF BIOLOGY.
§ 43. Perhaps the widest and most familiar induction of Biology, is that organisms grow. While, however, this is a characteristic so habitually and markedly displayed by plants and animals, as to be carelessly thought peculiar to them, it is really not so. Under appropriate conditions, increase of size takes place in inorganic aggregates, as well as in organic aggregates. Crystals grow; and often far more rapidly than living bodies. Where the requisite materials are supplied in the requisite forms, growth may be witnessed in non-crystal- line masses: instance the fungus-like accumulation of carbon that takes place on the wick of an unsnufFed candle. On an immensely larger scale, we have growth in geologic formations: the slow accumulation of deposited sediment into a stratum, is not distinguishable from growth in its widest acceptation. And if we go back to the genesis of celestial bodies, assuming them to have arisen by Evolution, these, too, must have gradually passed into their concrete shapes through processes of growth. Growth is indeed a concomi- tant of Evolution; and if Evolution of one kind or other is universal, growth is universal — universal, that is, in the sense that all aggregates display it in some way at some period.
The essential community of nature between organic growth and inorganic growth, is, however, most clearly seen 108 THE INDUCTIONS OF BIOLOGY.
on observing that they both result in the same way. The segregation of different kinds of detritus from each other, as well as from the water carrying them, and their aggregation into distinct strata, is but an instance of a universal tend- ency towards the union of like units and the parting of un- like units (First Principles, § 123). The deposit of a crystal from a solution, is a differentiation of the previously mixed atoms; and an integration of one class of atoms into a solid body, and the other class into a liquid solvent. Is not the growth of an organism a substantially similar process? Around a plant there exist certain elements that are like the elements which form its substance; and its increase of size is effected by continually integrating these surrounding like elements with itself. Nor does the animal fundament- ally differ in this respect from the plant or the crystal. Its food is a portion of the environing matter, that contains some compound atoms like some of the compound atoms constitut- ing its tissues; and either through simple imbibition or through digestion, the animal eventually integrates with it- self, units like those of which it is built up, and leaves behind the unlike units. To prevent misconception, it may be well to point out that growth, as here defined, must be distinguished from certain apparent and real augmentations of bulk which simulate it. Thus, the long, white potato- shoots thrown out in the dark, are produced at the expense of the substances which the tuber contains: they illustrate not the accumulation of organic matter, but simply its re- arrangement. Certain animal- embryos, again, during their early stages, increase considerably in size without assimilating any solids from the environment; and they do this by | absorbing the surrounding water. Even in the highest organisms, as in children, there appears sometimes to occur ^ a rapid gain in dimensions, that does not truly measure the added quantity of organic matter; but is in part due to changes analogous to those just named. Alterations of this riROwrir. 109 IvincI must not be confounded with that growth, properly so called, of which we have here to treat.
The next general fact to be noted respecting organic growth, is, that it has limits. Here there appears to be a distinction between organic and inorganic growth; but this distinction is by no means definite. Though that aggrega- tion of inanimate matter which simple attraction produces, may go on without end; yet there appears to be an end to that more definite kind of aggregation which results from polar attraction. Different elements and compounds, habitu- ally form crystals more or less unlike in their sizes; and each seems to have a size that is not usually exceeded without a tendency arising to form new crystals rather than, to increase the old. On looking at the organic kingdom as a whole, we see that the limits between which growth ranges, are very wide apart. At the one extreme, we have monads so minute as to be rendered but imperfectly visible by micro- scopes of the highest power; and at the other extreme, w^e have trees of 300 feet high, and animals of 100 feet long. It is true that though in one sense this contrast may be legitimately drawn, yet in another sense it may not; since these largest organisms are made by the combination of units that are individual^ like the smallest. A single plant of the genus Protococcus, is of the same structure as one of the many cells united together to form the thallus of some higher Alga, or the leaf of a phaenogam. Each separate shoot of a phgenogam is usually the bearer of many leaves. And a tree is an assemblage of numerous united shoots. One of these great teleophytes is thus an ag- gregate of aggregates of aggregates of units, which sever- ally resemble protophytes in their sizes and structures; and a like building up is traceable throughout a consider- able part of the animal kingdom. Even, however, when we bear in mind this qualification, and make our com- parisons between organisms of the same degree of compo- 110 THE INDUCTIONS OF BIOLOGY.
sition, we still find the limit of growth to have a great range. The smallest branched flowering plant is extremely insignificant by the side of a forest tree; and there is an enormious difference in bulk between the least and the great- est mammal. But on comparing members of the same species, we discover the limit of growth to be much less vari- able. Among the Protozoa and Protophyta, each kind has a tolerably constant adult size; and among the most complex organisms, the differences between those of the same kind that have reached maturity, are usually not very great. The compound plants do, indeed, sometimes present marked contrasts between stunted and well- grown individuals; but the higher animals diverge but inconsiderably from the average standards of their species.
On surveying the facts with a view of empirically general- izing the causes of these differences, we are soon made aware that by variously combining and conflicting with each other, these causes produce great irregularities of result. It be- comes manifest that no one of them can be traced to its. consequences, unqualified by the rest. Hence the several statements contained in the following paragraphs, must be taken as subject to mutual modification.