Certain other experiments point in the same direction. Cut a hydra into equal halves and each half will form a complete animal. The lower half forms a new top, with mouth and tentacles; the upper half, a new base. Cut the other hydra a hair's-breadth farther up. The same layer of cells which in the first animal formed the lower exposed surface of the upper half now forms the upper exposed surface of the lower half. And with this change of position it has changed its line of development; it will now give rise to a new upper half, not a base as before. The same experiment can be tried on certain worms with similar results, only head and tail differ far more than top and base of hydra. Difference in the position of cells has made vast difference in their line of development. Now in both embryo and adult there must be some directing influence guiding these cells. What is it?
An army is more than a mob of individuals; it is individuals plus organization, discipline, authority. A republic is not square miles of territory and thousands or millions of inhabitants. It is these plus organization, central government. Webster claimed that the central government was, and had to be, before the states. The organism cannot exist without its parts; it has a very real existence in and through them. It can coerce them. The state may be an abstraction, but it is one against which it is usually fatal to rebel, and which can say to a citizen, Go and be hanged, and he straightway mounts the scaffold. Now these are analogies and prove nothing. But in so far as they throw light on the essential idea of an organism, they may aid us in gaining a right view of our "cell republic."
Says Whitman in a very interesting article on the "Inadequacy of the Cell-Theory": "That organization precedes cell-formation and regulates it, rather than the reverse, is a conclusion that forces itself upon us from many sides." "The structure which we see in a cell-mosaic is something superadded to organization, not itself the foundation of organization. Comparative embryology reminds us at every turn that the organism dominates cell-formation, using for the same purpose one, several, or many cells, massing its material and directing its movements, and shaping its organs as if cells did not exist, or as if they existed only in complete subordination to its will, if I may so speak. The organization of the egg is carried forward to the adult as an unbroken physiological unity, or individuality, through all modifications and transformations." And Wilson, Whitman, Hertwig, and others urge "that the organism as a whole controls the formative processes going on in each part" of the embryo. And many years ago Huxley wrote, "They (the cells) are no more the producers of the vital phenomena than the shells scattered along the sea-beach are the instruments by which the gravitative force of the moon acts upon the ocean. Like these, the cells mark only where the vital tides have been, and how they have acted."[17]
"Interaction of cells" can help us but little. For how can neighboring cells direct others placed in a new position? The expression, if not positively misleading and untrue, is at the best only a restatement of fact. It certainly offers no explanation. Flood-tide is not due to the interaction of particles of water, though this may influence the form of the waves.
The centre of control is therefore not to be sought in individual cells, whether germ-cells or somatic, but in the organism. And it is the whole organism, one and indivisible, which controls in germ, embryo, and adult, in egg and owl. This individuality, or whatever you will call it, impresses itself upon developing somatic cells, moulding them into appropriate organs, and upon germ-cells in process of formation, moulding them so that they may continue its sway. The muscle, modified by use or disuse, is a better expression of the individuality of its possessor, and the same individuality moulds similarly and simultaneously the germ-cells. Both are different expressions or manifestations of the same individuality. Only slowly does the individuality mould the muscles and nerves of the adult body to its use. Still more slow may be the moulding of the still more refractory germ-plasm, if such there be. But the moulding process goes on parallel in the two cases.
But Weismann's argument rests not merely upon any difficulty or impossibility of the transmissibility of acquired characteristics. His argument is rather that all facts can be better explained by his theory without postulating or accepting such transmission, cases of which have never been absolutely proven. But the question is not whether his theory offers a possible explanation of the facts, but whether it is the most probable explanation of all the facts. No one would deny, I think, that the continuity of the germ-plasm offers the best and most natural explanation of heredity; and that variations could be produced by the influence on the germ-plasm of external conditions seems entirely probable.
But when we consider the aggregation of these variations in a process of evolution, his theory seems unsatisfactory. We have already seen that what we commonly call a variation involves not one change, but a series of changes, each term of which is necessary. Muscle, nerve, and ganglion must all vary simultaneously and correspondingly. Correlation and combination are just as essential as variation. And evolution often demands the disappearance of less fit structures just as much as the advance of the fittest. Says Osborne, "It is misleading to base our theory of evolution and heredity solely upon entire organs; in the hand and foot we have numerous cases of muscles in close contiguity, one steadily developing, the other degenerating." Weismann offers the explanation that "if the average amount of food which an animal can assimilate every day remains constant for a considerable time, it follows that a strong influx toward one organ must be accompanied by a drain upon others, and this tendency will increase, from generation to generation, in proportion to the development of the growing organ, which is favored by natural selection in its increased blood-supply, etc.; while the operation of natural selection has also determined the organ which can bear a corresponding loss without detriment to the organism as a whole."[18]
Here again natural selection of individuals, not the diminished supply of nutriment, has to determine which of many muscles shall be poorly fed and which favored. But natural selection can favor special organs only indirectly through the individuals which possess such organs. Variation is fortuitous, and there is nothing, except natural selection, to combine or direct them. And, I think, we have already seen that any theory which neglects or excludes such directing and combining agencies must be unsatisfactory and inadequate. Weismann has promised us an explanation of correlation of variation in accordance with his theory; and if such an explanation can be made, it would remove one of the strongest objections. But for the present the objection has very great weight.
Furthermore, as Osborne has insisted, linear variations, or variations proceeding along certain single and well-marked lines, would seem inexplicable by, if not fatal to, Weismann's theory. And yet Osborne, Cope, and others have shown that the teeth of mammals have developed steadily along well-marked lines. They have apparently not resulted at all by selection from a host of fortuitous variations.
Says Osborne in his "Cartwright Lectures"[19]: "It is evident that use and disuse characterize all the centres of evolution; that changes of structure are slowly following on changes of function or habit. In eight independent regions of evolution in the human body there are upward of twenty developing organs, upward of thirty degenerating organs." Now this parallelism, through a long series of generations, between the evolution of organs, their advance or degeneration, and the use or disuse of these same organs, that is, of the habits of the individual, is certainly of great significance. It must have an explanation; and the most natural one would seem to be the transmission of the effects of use and disuse.