If against all this it be urged that such a combination of structures and forces and processes is inconceivably involved, then the reply is that so astonishing a transformation as that which an unfolding organism displays cannot possibly be effected by simple agencies.
§ 97g. But now let it be confessed that none of these hypotheses serves to render the phenomena really intelligible; and that probably no hypothesis which can be framed will do this. Many problems beyond those which embryology presents have to be solved; and no solution is furnished.
What are we to say of the familiar fact that certain small organs which, with the approach to maturity, become active, entail changes of structure in remote parts—that after the testes have undergone certain final developments, the hairs on the chin grow and the voice deepens? It has been contended that certain concomitant modifications in the fluids throughout the body may produce correlated sexual traits; and there is proof that in many of the lower animals the period of sexual activity is accompanied by a special bodily state—sometimes such that the flesh becomes unwholesome and even poisonous. But a change of this kind can hardly account for a structural change in the vocal organs in Man. No hypothesis of gemmules or determinants or physiological units enables us to understand how removal of the testes prevents those developments of the larynx and vocal cords which take place if they remain.
The inadequacy of our explanations we at once see in presence of a structure like a peacock's tail-feather. Mr. Darwin's hypothesis is that all parts of every organ are continually giving off gemmules, which are consequently everywhere present in their due proportions. But a completed feather is an inanimate product and, once formed, can add to the circulating fluids no gemmules representing all its parts. If we follow Prof. Weismann we are led into an astounding supposition. He admits that every variable part must have a special determinant, and that this results in the assumption of over two hundred thousand for the four wings of a butterfly. Let us ask what must happen in the case of a peacock's feather. On looking at the eye near its end, we see that the minute processes on the edge of each lateral thread must have been in some way exactly adjusted, in colour and position, so as to fall into line with the processes on adjacent threads: otherwise the symmetrical arrangement of coloured rings would be impossible. Each of these processes, then, being an independent variable, must have had its particular determinant. Now there are about 300 threads on the shaft of a large feather, and each of them bears on the average 1,600 processes, making for the whole feather 480,000 of these processes. For one feather alone there must have been 480,000 determinants, and for the whole tail many millions. And these, along with the determinants for the detailed parts of all the other feathers, and for the variable components of all organs forming the body at large, must have been contained in the microscopic head of a spermatozoon! Hardly a credible supposition. Nor is it easy to see how we are helped by the hypothesis of constitutional units. Take the feather in its budding state and ask how the group of such units, alike in structure and perpetually multiplying while the unfolding goes on, can be supposed by their mutual actions so to affect one another as eventually to produce the symmetrically-adjusted processes which constitute the terminal eye. Imagination, whatever licence may be given, utterly fails us.
At last then we are obliged to admit that the actual organizing process transcends conception. It is not enough to say that we cannot know it; we must say that we cannot even conceive it. And this is just the conclusion which might have been drawn before contemplating the facts. For if, as we saw in the chapter on "The Dynamic Element in Life," it is impossible for us to understand the nature of this element—if even the ordinary manifestations of it which a living body yields from moment to moment are at bottom incomprehensible; then, still more incomprehensible must be that astonishing manifestation of it which we have in the initiation and unfolding of a new organism.
Thus all we can do is to find some way of symbolizing the process so as to enable us most conveniently to generalize its phenomena; and the only reason for adopting the hypothesis of physiological units or constitutional units is that it best serves this purpose.
CHAPTER XI.
CLASSIFICATION.
§ 98. That orderly arrangement of objects called Classification has two purposes, which, though not absolutely distinct, are distinct in great part. It may be employed to facilitate identification, or it may be employed to organize our knowledge. If a librarian places his books in the alphabetical succession of the author's names, he places them in such way that any particular book may easily be found, but not in such way that books of a given nature stand together. When, otherwise, he makes a distribution of books according to their subjects, he neglects various superficial similarities and distinctions, and groups them according to certain primary and secondary and tertiary attributes, which severally imply many other attributes—groups them so that any one volume being inspected, the general characters of all the neighbouring volumes may be inferred. He puts together in one great division all works on History; in another all Biographical works; in another all works that treat of Science; in another Voyages and Travels; and so on. Each of his great groups he separates into sub-groups; as when he puts different kinds of Literature under the heads of Fiction, Poetry, and the Drama. In some cases he makes sub-sub-groups; as when, having divided his Scientific treatises into abstract and concrete, putting in the one Logic and Mathematics and in the other Physics, Astronomy, Geology, Chemistry, Physiology, &c.; he goes on to sub-divide his books on Physics, into those which treat of Mechanical Motion, those which treat of Heat, those which treat of Light, of Electricity, of Magnetism.
Between these two modes of classification note the essential distinctions. Arrangement according to any single conspicuous attribute is comparatively easy, and is the first that suggests itself: a child may place books in the order of their sizes, or according to the styles of their bindings. But arrangement according to combinations of attributes which, though fundamental, are not conspicuous, requires analysis; and does not suggest itself till analysis has made some progress. Even when aided by the information which the author gives on his title page, it requires considerable knowledge to classify rightly an essay on Polarization; and in the absence of a title page it requires much more knowledge. Again, classification by a single attribute, which the objects possess in different degrees, may be more or less serial, or linear. Books may be put in the order of their dates, in single file; or if they are grouped as works in one volume, works in two volumes, works in three volumes, &c., the groups may be placed in an ascending succession. But groups severally formed of things distinguished by some common attribute which implies many other attributes, do not admit of serial arrangement. You cannot rationally say either that Historical Works should come before Biographical Works, or Biographical Works before Historical Works; nor of the sub-divisions of creative Literature, into Fiction, Poetry, and the Drama, can you give a good reason why any one should take precedence of the others.