The Science and Philosophy of the Organism

by Hans Driesch

The figures will serve to show you a little more concretely what has been described. The head of Tubularia consists of a sort of broad base with a thin proboscis upon it, both bearing a large number of tentacles; these tentacles are the first things to be seen as primordia (“Anlagen”) in the process of restitution. You notice two rings of longitudinal lines inside the stem; the lines will become walls and then will separate from the stem until they are only connected with it at their basal ends; the new tentacles are ready as soon as that has happened, and a process of growth at the end will serve to drive the new head out of the so-called perisarc or horny skeleton, which surrounds the stem. By comparing the two figures, 12 e, and g, you easily find out that the absolute lengths of the two tentacle rings are very different, and that both are in proportion[60] to the actual size of the stem (Fig. 12).

Fig. 12.—Tubularia.

a.	Diagram of the “Hydranth,” with its short and long tentacles.
b.	Restitution of a new hydranth inside the perisarc (p).
c.	The same—later stage; the tentacles are complete; the whole hydranth will be driven out of the perisarc by a process of growth that occurs at the locality marked ↑.
d.	A stem of Tubularia cut either at a1b1 or at a2b2 or at a1c.
e.	Position of tentacles in the piece cut at a1b1.
f.	Position of tentacles in the piece cut at a2b2 which is equal in length to a1b1.
g.	Position of tentacles in the piece cut at a1c, which is half as long as a1b1.

So we find our formula p.v. (X) = f(s, l, E) very well illustrated in Tubularia. The formula indeed may help us to predict, in any case, where a certain part of the polyp’s organisation is to originate, at least if we know all that is included under our letter E, i.e. the normal proportion of our form. Of course such prediction would not have much practical importance in all our cases of morphogenesis, but nevertheless I should like to state here that it is possible; for many scientific authors of recent times have urged the opinion that prediction of, and domination over, what will happen, can be the only true aims of sciences at all. I myself judge these aims to be of second or third-rate importance only, but, if they may be reached by what our purely theoretical study teaches, so much the better.

Fig. 13.—Clavellina.

a.	Diagram of the normal animal: E and J = openings; K = branchial apparatus; D = intestine; M = stomach; H = heart.
b.	The isolated branchial apparatus.
c-e.	Different stages of reduction of the branchial apparatus.
f.	The new whole little ascidian.

Another very typical case of a morphogenetic system of the harmonious type is supplied by the phenomena of restoration in the ascidian Clavellina. I cannot fully describe the organisation of this form (Fig. 13a), and it must suffice to say that it is very complicated, consisting of two very different chief parts, the branchial apparatus and the so-called intestinal sac; if these two parts of the body of Clavellina are separated one from the other, each may regenerate the other in the typical way, by budding processes from the wound. But, as to the branchial apparatus, there may happen something very different: it may lose almost all of its organisation and become a small white sphere, consisting only of epithelia corresponding to the germ-layers, and of mesenchyme between them, and then, after a certain period of rest, a new organisation will appear. Now this new organisation is not that of a branchial apparatus but represents a very small but complete ascidian (Fig. 13). Such a fact certainly seems to be very important, not to say very surprising; but still another phenomena may be demonstrated on the animal which seems to be even more important. You first isolate the branchial apparatus from the other part of the body, and then you cut it in two, in whatever direction you please. Provided they survive and do not die, as indeed many of them do, the pieces obtained by this operation will each lose their organisation, as did the whole branchial apparatus, and then will each acquire another one, and this new organisation is also that of a complete little Clavellina. So we see that not only is the branchial apparatus of our animal capable of being transformed into a whole animal by the co-operative work of all its parts, but even each part of it may be transformed into a small whole, and it is quite at our disposal how large this part shall be, and what sort of a fragment of the original branchial apparatus it shall represent.