The hypothesis of physiological units, then, remains outstanding. For cauline buds imply that throughout the plant-tissue, where not unduly differentiated, the local physiological units have a power of arranging themselves into the structure of the species.
But this hypothesis, too, as it now stands, is inadequate. Under the form thus far given to it, it fails to explain some accompanying facts. For if the branch just instanced as producing a cauline bud be cut off and its end stuck in the ground, or if it be bent down and a portion of it covered with earth, there will grow from it rootlets and presently roots. The same portion of tissue which otherwise would have produced a shoot with all its appendages, constituting an individual, now produces only a special part of an individual.
§ 97c. Certain kindred facts of animal development may now be considered. Similar insufficiencies are disclosed.
The often-cited reproduction of a crab's lost claw or a lizard's tail, Mr. Darwin thought explicable by his hypothesis of diffused gemmules, representing all organs or their component cells. But though, after simple amputation, regrowth of the proximate part of the tail is conceivable as hence resulting, it is not easy to understand how the remoter part, the components of which are now absent from the organism, can arise afresh from gemmules no longer originated in due proportion. Prof. Weismann's hypothesis, again, implies that there must exist at the place of separation, a ready-provided supply of determinants, previously latent, able to reproduce the missing tail in all its details—nay, even to do this several times over: a strong supposition! The hypothesis of physiological units, as set forth in preceding chapters, appears less incompetent: reproduction of the lost part would seem to be a normal result of the proclivity towards the form of the entire organism. But now what are we to say when, instead of being cut off transversely, the tail is divided longitudinally and each half becomes a complete tail? What are we to say when, if these two tails are similarly dealt with, the halves again complete themselves; and so until as many as sixteen tails have been formed? Here the hypothesis of physiological units appears to fail utterly; for the tendency it implies is to complete the specific form, by reproducing a single tail only.
Various annulose animals display anomalies of development difficult to explain on any hypothesis. We have creatures like the fresh-water Nais which, though it has advanced structures, including a vascular system, branchiæ, and a nervous cord ending with cephalic ganglia, nevertheless shows us an ability like that of the Hydra to reproduce the whole from a small part: nearly forty pieces into which a Nais was cut having severally grown into complete animals. Again we have, in the order Polychætæ, types like Myrianida, in which by longitudinal budding a string of individuals, sometimes numbering even thirty, severally develop certain segments into heads, while increasing their segments in number. In yet other types there occurs not longitudinal gemmation only, but lateral gemmation: a segment will send out sideways a bud which presently becomes a complete worm. Once more, Syllis ramosa is a species in which the individual worms growing from lateral buds, while remaining attached to the parent, themselves give origin to buds; and so produce a branched aggregate of worms. How shall we explain the reparative and reproductive powers thus exemplified? It seems undeniable that each portion has an ability to produce, according to circumstances, the whole creature or a missing part of the creature. When we read of Sir J. Dalyell that he "cut a Dasychone into three pieces; the hindermost produced a head, the anterior piece developed an anus, and the middle portion formed both a head and a tail" we are not furnished with an explanation by the hypothesis of gemmules or by the hypothesis of determinants; for we cannot arbitrarily assume that wherever a missing organ has to be produced there exists the needful supply of gemmules or of determinants representing that organ. The hypothesis that physiological units have everywhere a proclivity towards the organic form of the species, appears more congruous with the facts; but even this does not cover the cases in which a new worm grows from a lateral bud. The tendency to complete the individual structure might be expected rather to restrain this breaking of the lines of complete structure.
Still less explicable in any way thus far proposed are certain remedial actions seen in animals. An example of them was furnished in [§ 67], where "false joints" were described—joints formed at places where the ends of a broken bone, failing to unite, remain moveable one upon the other. According to the character of the habitual motions there results a rudely formed hinge-joint or a ball-and-socket joint, either having the various constituent parts—periosteum, fibrous tissue, capsule, ligaments. Now Mr. Darwin's hypothesis, contemplating only normal structures, fails to account for this formation of an abnormal structure. Neither can we ascribe this local development to determinants: there were no appropriate ones in the germ-plasm, since no such structure was provided for. Nor does the hypothesis of physiological units, as presented in preceding chapters, yield an interpretation. These could have no other tendency than to restore the normal form of the limb, and might be expected to oppose the genesis of these new parts.
Thus we have to seek, if not another hypothesis, then some such qualification of an existing hypothesis as will harmonize it with various exceptional phenomena.
§ 97d. In Part II of the Principles of Sociology, published in 1876, will be found elaborated in detail that analogy between individual organization and social organization which was briefly sketched out in an essay on "The Social Organism" published in 1860. In §§ 241-3 a parallel is drawn between the developments of the sustaining systems of the two; and it is pointed out how, in the one case as in the other, the components—here organic units and there citizens—have their activities and arrangements mainly settled by local conditions. One leading example is that the parts constituting the alimentary canal, while jointly fitted to the nature of the food, are severally adapted to the successive stages at which the food arrives in its progress; and that in an analogous way the industries carried on by peoples forming different parts of a society, are primarily determined by the natures of things around—agriculture, pastoral and arable, special manufactures and minings, ship-building and fishing: the respective groups falling into fit combinations and becoming partially modified to suit their work. The implication is that while the organization of a society as a whole depends on the characters of its units, in such way that by some types of men despotisms are always evolved while by other types there are evolved forms of government partially free—forms which repeat themselves in colonies—there is, on the other hand, in every case a local power of developing appropriate structures. And it might have been pointed out that similarly in types of creatures not showing much consolidation, as the Annelida, many of the component divisions, largely independent in their vitalities, are but little affected in their structures by the entire aggregate.
My purpose at that time being the elucidation of sociological truths, it did not concern me to carry further the biological half of this comparison. Otherwise there might have been named the case in which a supernumerary finger, beginning to bud out, completes itself as a local organ with bones, muscles, skin, nail, etc., in defiance of central control: even repeating itself when cut off. There might also have been instanced the above-named formation of a false joint with its appurtenances. For the implication in both cases is that a local group of units, determined by circumstances towards a certain structure, coerces its individual units into that structure.
Now let us contemplate the essential fact in the analogy. The men in an Australian mining-camp, as M. Pierre Leroy Beaulieu points out, fall into Anglo-Saxon usages different from those which would characterize a French mining-camp. Emigrants to a far West settlement in America quickly establish post-office, bank, hotel, newspaper, and other urban institutions. We are thus shown that along with certain traits leading to a general type of social organization, there go traits which independently produce fit local organizations. Individuals are led into occupations and official posts, often quite new to them, by the wants of those around—are now influenced and now coerced into social arrangements which, as shown perhaps by gambling saloons, by shootings at sight, and by lynchings, are scarcely at all affected by the central government. Now the physiological units in each species appear to have a similar combination of capacities. Besides their general proclivity towards the specific organization, they show us abilities to organize themselves locally; and these abilities are in some cases displayed in defiance of the general control, as in the supernumerary finger or the false joint. Apparently each physiological unit, while having in a manner the whole organism as the structure which, along with the rest, it tends to form, has also an aptitude to take part in forming any local structure, and to assume its place in that structure under the influence of adjacent physiological units.