specific peculiarities. Shall we regard all the growing axes thus resulting from slips and grafts and buds, as parts of one individual, or as distinct individuals? If a strawberry- plant sends out runners carrying buds at their ends, which strike root and grow into independent plants, that separate from the original one by decay of the runners, must we not say that they possess separate individualities; and yet if we do this, are we not at a loss to say when their separate individu- alities were established, unless we admit that each bud was from the beginning an individual? Commenting on such perplexities, Schleiden says — " Much has been written and disputed concerning the conception of the individual, with- out, however, elucidating the subject, principally owing to the misconception that still exists as to the origin of the con- ception. Now the individual is no conception, but the mere subjective comprehension of an actual object, presented to us under some given specific conception, and on this latter it alone depends whether the object is or is not an individual. Under the specific conception of the solar system, ours is an individual: in relation to the specific conception of a planet- ary body, it is an aggregate of many individuals." * * * **I think, however, that looking at the indubitable facts already mentioned, and the relations treated of in the course of these considerations, it will appear most advantageous and most useful, in a scientific point of view, to consider the vegetable cell as the general type of the plant (simple plant of the first order). Under this conception, Protococcus and other plants consisting of only one cell, and the spore and pollen- granule, will appear as individuals. Such individuals may, however, again, with a partial renunciation of their in- dividual independence, combine under definite laws into definite forms (somewhat as the individual animals do in the globe of the Volvox globator*). These again appear empiri- cally as individual beings, under a conception of a species * It is now generally agreed that the Volvox globator is a plant.
INDIVIDUALITY. 203 (simple plants of the second order) derived from the form of the normal connexion of the elementary individuals. But we cannot stop here, since nature herself combines these in- dividuals, under a definite form, into larger associations, whence we draw the third conception of the plant, from a connexion, as it were, of the second power (compound plants — plants of the third order). The simple plant proceeding from the combination of the elementary individuals is then termed a bud [gemma) j in the composition of plants of the third order."
The animal kingdom presents still greater difficulties. When, from sundry points on the body of a common polype, there bud-out young polypes, which, after acquiring mouths and tentacles and closing up the communications between their stomachs and the stomach of the parent, finally separate from the parent; we may with propriety regard them as dis- tinct individuals. But when, in the allied compound Hydro- zoa, we find that these young polypes continue permanently connected with the parent; and when, by this continuous budding-out, there is presently produced a tree-like aggre- gation, having a common alimentary canal into which the digestive ca^dty of each polype opens; it is no longer so clear that these little sacs furnished with mouths and tenta- cles, are severally to be regarded as distinct individuals. We cannot deny a certain individuality to the polypedom. And on discovering that some of the buds, instead of unfolding in the same manner as the rest, are transformed into capsules in which eggs are developed — on discovering that certain of the incipient polypes thus become wholly dependent on the aggregate for their nutrition, and discharge functions which have nothing to do with their own maintenance, we have still clearer proof that the individualities of the members are partially merged in the individuality of the group. Other organisms belonging to the same order, display still more decidedly this transition from simple individualities to a com- plex individuality. In the Diphyes there is a special modifi- 204 THE INDUCTIONS OF BIOLOGY.
cation of one or more members of the polypedom into a swimming apparatus, which, by its rhythmical contractions, propels itself through the water, drawing the polypedom after it. And in the more differentiated Physalia, various organs result- from the metamorphosis of parts that are the homo- logues of individual polypes. In this last instance, the in- dividuality of the aggregate is so predominant, that the individualities of the members are practically lost. This combination of individualities in such way as to produce a composite individual, meets us in other forms among the ascidian molluscs. While in some of these, as in the ClaveUnay the animals associated are but little subordinated to the community they form; in others, as in the BotryllidcB, they are so fused into a rounded mass, as to present the appearance of a single animal with several mouths and stomachs.
On the hypothesis of Evolution, perplexities of this nature are just such as we might anticipate. If Life in general, com- menced with minute and simple forms, like those out of which all individual organisms, however complex, now originate; and if the transitions from these primordial units to organisms made up of groups of such units, and to higher organisms made up of groups of such groups, took place by degrees; it is clear that individualities of the first and simplest order, would merge gradually in those of a larger and more complex order, and, these again in others of an order having still greater bulk and organization; and that hence it would be impossible to say where the lower indivi- dualities ceased, and the higher individualities commenced.
§ 73. To meet these difficulties, it has been proposed that the whole product of a single fertilized germ, shall be re- garded as a single individual: whether such whole product be organized into one mass, or whether it be organized into many masses, that are partially or completely separate. It is urged that whether the development of the fertilized germ INDIVIDUALITY. 205 INDIVIDUALITY. 205 be continuous or discontinuous (§ 50) is a matter of secondary importance; that the totality of living tissue to which the fertilized germ gives rise in any one case, is the equivalent of the totality to which it gives rise in any other case; and that we must recognize this equivalence, whether such totality of living tissue takes a concrete or a discrete arrangement. In pursuance of this view, a zoological individual is consti- tuted either by any such single animal as a mammal or bird, which may properly claim the title of a zooUy or by any such group of animals as the numerous Mediisce that have been developed from the same Qg^i which are to be severally dis- tinguished as zooids.
Admitting it to be very desirable that there should be words for expressing these relations and this equivalence, it may still be objected, that to apply the word individual to a number of separate living bodies, is inconvenient: conflicting so much, as it does, with the ordinary conception which this word suggests. It seems a questionable use of language to say that the countless masses of Aiiacharis Alsmastrum, which, within these few years, have grown up in our rivers, canals, and ponds, are all parts of one individual; and yet as this plant does not seed in England, these countless masses, having arisen by discontinuous development, must be so regarded, if we accept the above definition.
It may be contended, too, that while it does violence to our established way of thinking, this mode of interpreting the facts is not without its difficulties — smaller, perhaps, than those it escapes, but still considerable. Something seems to be gained by restricting the application of the title individual, to organisms which, being in all respects fully developed, possess the power of producing their kind after the ordinary sexual method; and denying this title to those incomplete organisms which have not this power. But the definition does not really establish this distinction for us. On the one hand, we have cases in which, as in the working bee, the whole of the germ-product is aggregated into a single 206 THE INDUCTIONS OF BIOLOGY.
organism; and yet, though an individual according to the definition, this organism has no power of reproducing its kind. On the other hand, we have cases like that of the perfect ApJiides, where the organism is but an infinitesimal part of the germ-product; and yet has that completeness required for sexual reproduction. Moreover, if we adopt the prop^osed view, we find ourselves committed to the anomalous position, that among many orders of animals, there are no concrete individuals at all. If the individual is consti- tuted by the whole germ-product, whether continuously or discontinuously developed, then, not only must individuality be denied to each of the imperfect Aphides, but also to each of the perfect males and females; since no one of them is more than a minute fraction of the total germ- product. And yet further, it might be urged with some show of reason, that if the conception of individuality involves the conception of completeness; then, an organism which possesses an independent power of reproducing itself, being more complete than an organism in which this power is dependent on the aid of another organism, is more in- dividual.
§ 74. There is, indeed, as already implied, no definition of individuality that is unobjectionable. All we can do is to make the best practicable compromise.
As applied either to an animate or an inanimate object, the word individual ordinarily connotes union among the parts of the object, and separateness from other objects. This fundamental element in the conception of individuality, we cannot with propriety ignore in the biological application of the word. That which we call an individual plant or animal, must, therefore, be some concrete whole, and not a discrete whole. If, however, we say that each concrete living whole is to be regarded as an individual, we are still met by the question — What constitutes a concrete living whole? A young organism arising by internal or external INDIVIDUALITY.
gemmation from a parent organism, passes gradually from a state in whicli it is an indistinguishable part of the parent organism, to a state in which it is a separate organism of like structure with the parent. At what stage does it become an individual? And if its individuality be conceded only when it completely separates from the parent, must we deny in- dividuality to all organisms thus produced, w^hich permanently retain their connexions with their parents? Or again, what must we say of the Hectocotylus, which is an arm of the Cuttle-fish that undergoes a special development, and then detaching itself, lives independently for a considerable period? And what must we say of that larval Echinus, which is left to move about awhile after being robbed of its viscera by the young Echinus developed within it?
To answer such questions, we must revert to the definition of Life. The distinction between individual in its biological sense, and individual in its more general sense, must consist in the manifestation of Life, properly so called. Life we have seen to be, '^ the definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external co-existences and sequences." Hence, a biolo- gical individual is any concrete whole having a structure which enables it, when placed in appropriate conditions, to continuously adjust its internal relations to external relations, so as to maintain the equilibrium of its functions. In pursuance of this conception, we must consider as individuals, all those wholly or partially independent organized masses, which arise by multicentral and multiaxial development that is either continuous or discontinuous (§ 50). We must accord the title to each separate aphis, each polype of a polypedom, each bud or shoot of a flowering plant, whether it detaches itself as a bulbil or remains attached as a branch.
By thus interpreting the facts, we do not, indeed, avoid all anomalies. While, among flowering plants, the power of in- dependent growth and development, is usually possessed only by shoots or axes; yet, in some cases, as in that of the Begonia- 208 THE INDUCTIONS OF BIOLOGY.
leaf awhile since mentioned, the appendage of an axis, or even a small fragment of such appendage, is capable of initiating and carrying on the functions of life; and in other cases, as shown by M. K^audin in the Drosera intermedia^ yo^^g plants are occasionally developed from the surfaces of leaves, while still connected with the parent plant. Nor among forms like the compound Hydrozoa, does the definition enable us to decide where the line is to be drawn between the individuality of the group and the individualities of the members — merging into each other, as these do, in different degrees. But, as before said, such difficulties must necessa- rily present themselves, if organic forms have arisen by in- sensible gradations. We must be content with a course which commits us to the smallest number of incongruities; and this course is, to consider as an individual, any centre or axis that is capable of independently carrying on that con- tinuous adjustment of inner to outer relations which consti- tutes Life.
CIIAPTEE YII.
GENESIS.
§ 75. Having concluded what constitutes an individual, we are in a position to deal with the multiplication of in- dividuals. For this, the title Genesis is here chosen, as being the most comprehensive title — the least specialized in its meaning. By some biologists. Generation has been used to signify one method of multiplication, and Reproduction to signify another method; and each of these words has been thus rendered in some degree unfit to signify multiplication in general.
Here the reader is indirectly introduced to the fact, that the production of new organisms is carried on in fundament- ally unlike ways. Up to quite recent times, it was believed, even by naturalists, that all the various processes of multipli- cation observable in different kinds of organisms, have one essential character in common: it was supposed that in every species, the successive generations are alike. It has now been proved, hoAvever, that in plants, and in numerous animals, the successive generations are not alike; that from one generation there proceeds another whose members differ more or less in structure from their parents; that these produce others like themselves, or like their parents, or like neither; but that eventually, the original form re-appears. Instead of there being, as in the cases most familiar to us, a constant recurrence of the same form, there is a cyclical recurrence of 14 210 THE INDUCTIONS OF BIOLOGY.
the same form. These two distinct processes of multiplication, may be aptlj^ termed homogenesis and heterogenesisJ* Under these heads let us consider them more closely.
The kind of genesis, once supposed to be universal, in which the successive generations are alike, is always sexual genesis; or, as it has been otherwise called — gamogenesis. In every species of organism which multiplies by homogenesis, each generation consists of males and females; and from the fertilized germs they produce, the next generation of similar males and females arises. This method of propagation is further distinguished by the peculiarity, that each fertilized germ gives rise to but one individual — the product of de- velopment is always organized round one axis, and not round several axes. Between the different kinds of homogenesis, the most marked contrast, and the only one which need here detain us, is that between the oviparous and the viviparous. The oviparous kind is that in which the fertil- ized germ is detached from the parent, before it has undergone any considerable development. The viviparous kind is that in which development is considerably advanced, or almost completed, before final detachment takes place. This distinction is, however, not a sharply- defined one: there are transitions between the oviparous and the viviparous processes. In ovo- viviparous genesis, there is an internal incubation; and though the young are in this case finally detached from the parent in the shape of eggs, they do not leave the parent's body until after they have assumed something like the parental form. Looking around, we find that homogenesis is universal among the Verteh'cita: there is no known vertebrate animal but what arises from a fertilized germ, and unites into its single indi- viduality the whole products of this fertilized germ. In * Unfortunately the word Jieterogemsis, has been already used as a synonyme for " spontaneous generation." Save by those few who believe in " spontaneous generation," however, little objection will be felt to using the word in a sense that seems much more appropriate.
GENESIS.
GENESIS.
the mammals or highest Vcrtchrata, this homogcnesis is in every case viviparous; in. birds it is uniformly oviparous; and in reptiles and fishes, it is always essentially oviparous, though there are cases, of the kind above referred to, in which viviparity is simulated. Passing to the Invertebrata, we find oviparous homogenesis universal among the Arach- nida (except the Scorpions, which are ovo-viviparous); universal among the higher Crustacea, but not among the lower; extremely general, though not universal, among Insects; and universal among the higher Mollusca, though not among the lower. Along with extreme inferiority among animals, we find homogenesis to be the exception rather than the rule; and in the vegetal kingdom, there appear to be no cases, save those of a few aberrant parasites like the Raffle siacece J in which the centre or axis which arises from a fertilized germ, becomes the immediate producer of fertilized germs.
germs.
Where propagation is carried on by heterogenesis, or is characterized by unlikeness of the successive generations, there is always asexual genesis with occasionally-recurring sexual genesis; in other words — agamogenesis interrupted more or less frequently by gamogenesis. If we set out with a generation of perfect males and females; then, from their ova or seeds, there arise individuals that are neither males nor females, but that produce the next generation from buds. By this method of multiplication, many individuals originate from a single fertilized germ: the product of development is organized round more than one centre or axis. The simplest form of heterogenesis is that seen in uniaxial plants. If, as we find ourselves obliged to do, we regard each separate shoot or axis of growth, as a dis- tinct individual; then, in uniaxial plants, the successive in- dividuals are not represented by the series A, A, A, A, &c., like those resulting from homogenesis; but they are repre- sented by the series A, B, A, B, A, B, &c. For in plants which were before classed as uniaxial (§ 50), and which may 212 THE INDUCl'IONS OF BIOLOGY.
be conyeniently so distinguished from other plants, the axis which shoots up from the seed, and substantially constitutes the plant, does not itself flower and bear seed; but gives lateral origin to flowering, or seed -bearing, axes. Though in uni- axial plants, the fructifying apparatus appears to be at the end of the primary, vertical axis; yet dissection shows that, morphologically considered, each fructifying axis is usually an offspring from the primary axis. There arises from the seed, a sexless individual, from which spring by gemmation, in- dividuals having reproductive organs; and from these there result fertilized germs or seeds, that give rise to sexless individuals. That is to say, gamogenesis and agamogenesis alternate: the peculiarity being, that the sexual individu- als arise from the sexless ones by continuous development. The Salpce show us an allied form of heterogenesis in the animal kingdom. Individuals developed from fertilized ova, instead of themselves producing fertilized ova, produce, by gemmation, strings of individuals; from which fertilized ova again originate. In multiaxial plants, we have a succession of generations represented by the series A, B, B, B, &c.. A, B, B, B, &c. Supposing A to be a flowering axis, or sexual individual; then, from any fertilized germ it casts off", there grows up a sexless individual, B; from this there bud-out other sexless individuals, B; and so on for generations more or less numerous; until at length, from some of these sexless individuals, there bud-out seed-bearing individuals of the original form A. Branched herbs, shrubs, and trees, exhibit this form of heterogenesis: the successive generations of sexless individuals thus produced, being in most cases continuously developed, or aggregated into a compound individual; but being in some cases dis- continuously developed. Among animals, a kind of hetero- genesis represented by the same succession of letters, occurs in such compound polypes as the Scrtularia; and in those of the Hi/drozoa which assume alternately the poly- poid form, and the form of the Medusa: the chief differences GENESIS. 213 GENESIS. 213 presented by these groups, arising from the fact that the successive generations of sexless individuals produced by budding, are in some cases continuously developed, and in others discontinuously developed; and from the fact that, in some cases, the sexual individuals give off their fertilized germs while still growing on the parent-polypedom, but in other cases, not until after leaving the parent-polypedom and undergoing further development. Where, as in all the foregoing kinds of agamogenesis, the new individuals bud-out, not from any specialized reproductive organs, but from unspecialized parts of the parent; the process has been named, by Prof. Owen, metagenesis. In most instances, the individuals thus produced, grow from the outsides of the parents — the metagenesis is external. But there is also a kind of metagenesis which we may distinguish as internal. Certain entozoa of the genus Distomaj exhibit it. From the Gg^ of a Dlstoma, there results a rudely- formed creature known to naturalists as the ^' King's-yellow worm.'' Gradu- ally as this increases in size, the greater part of its inner substance is transformed into young animals called Cercarice (which are the larvae of Distomata); until at length, it becomes little more than a living sac, full of living offspring. In the Dlstoma pacljicay the brood of young animals thus arising by internal gemmation, are not Cercarice, but are of the same form as their parent: themselves becoming the producers of Cercarice after the same manner, at a subsequent period. So that sometimes the succession of forms is repre- sented by the series A, B, A, B, &c.; and sometimes by the series A, B, B, A, B, B, &c. Both cases, however, exemplify internal metagenesis, in contrast with the several kinds of external metagenesis described above. That agamogenesis which is carried on in a reproductive organ — either a true ovarium or the homologue of one — has been called, by Prof. Owen, parthenogenesis. In his work published under this title, he embraced those cases in which the buds arising in the pseud- ovarium, are not ova in the full sense of the 214 THE INDUCTIONS OF BIOLOGY.
word; but rather, as they have since been called by Prof. Huxley, pseud-ova. Yon Siebold and other naturalists, have hence applied the term parthenogenesis to a narrower class of cases. Perhaps it would be best to distinguish this process, which is intermediate between metagenesis and parthenogenesis, by the term jJ5ewc^o-j:'ar^7i<?yio^^;2^S2S. It is the process familiarly exemplified in the Aphides. Here, from the fertilized eggs laid by perfect females, there grow up imperfect females, in the pseud-ovaria of which there are developed pseud-ova; and these, rapidly assuming the organization of other imperfect females, are born vivi- parously. From this second generation of imperfect females, there by and by arises, in the same manner, a third genera- tion, of the same kind; and so on for many generations: the series being thus symbolized by the letters A, B, B, B, B, B, &c., A. Respecting this kind of heterogenesis, it should be added, that in animals, as in plants, the number of genera- tions of sexless individuals produced before the re-appearance of sexual ones, is indefinite; both in the sense that in the same species it may go on to a greater or less extent accord- ing to circumstances, and in the sense that among the generations of individuals proceeding from the same fertilized germ, a recurrence of sexual individuals takes place earlier in some of the diverging lines of multiplication than in others. In trees we see that on some branches, flower-bearing axes arise while other branches are still producing only leaf-bearing axes; and in the successive generations of Aphides, a parallel truth has been observed. Lastly has to be set down,