then, to prevent a slow and lasting manifestation, in a viscous medium such as a protoplasmic organism, of phenomena which appear and disappear with prodigious rapidity in a more mobile liquid. Nor is there anything peculiar in the ãsplashã itself; it is simply a convenient method of setting up certain motions or currents, and producing certain surface-forms, in a liquid medium,ãor even in such an extremely imperfect fluid as is represented (in another series of experiments) by a bed of sand. Accordingly, we have a large range of possible conditions under which the organism might conceivably display conôÙfiôÙgurôÙaôÙtions analogous to, or identical with, those which Mr Worthington has shewn us how to exhibit by one particular experimental method.
To one who has watched the potter at his wheel, it is plain that the potterãs thumb, like the glass-blowerãs blast of air, depends for its efficacy upon the physical properties of the medium on which it operates, which for the time being is essentially a fluid. The cup and the saucer, like the tube and the bulb, display (in their simple and primitive forms) beautiful surfaces of equiôÙlibôÙrium as manifested under certain limiting conditions. They are neither more nor less than glorified ãsplashes,ã formed slowly, under conditions of restraint which enhance or reveal their mathôÙeôÙmatôÙiôÙcal symmetry. We have seen, and we shall see again before we are done, that the art of the glass-blower is full of lessons for the naturalist as also for the physicist: illustrating as it does the development of a host of mathôÙeôÙmatôÙiôÙcal conôÙfiôÙgurôÙaôÙtions and organic conformations which depend essentially on the establishment of a constant and uniform pressure within a closed elastic shell or fluid envelope. In like manner the potterãs art illustrates the somewhat obscurer and more complex problems (scarcely less frequent in biology) of a figure of equiôÙlibôÙrium which is an open surface, or solid, of revolution. It is clear, at the same time, that the two series of problems are closely akin; for the {239} glass-blower can make most things that the potter makes, by cutting off portions of his hollow ware. And besides, when this fails, and the glass-blower, ceasing to blow, begins to use his rod to trim the sides or turn the edges of wineglass or of beaker, he is merely borrowing a trick from the craft of the potter.
It would be venturesome indeed to extend our comparison with these liquid surface-tension phenomena from the cup or calycle of the hydrozoon to the little hydroid polype within: and yet I feel convinced that there is something to be learned by such a comparison, though not without much detailed consideration and mathôÙeôÙmatôÙiôÙcal study of the surfaces concerned. The cylindrical body of the tiny polype, the jet-like row of tentacles, the beaded annulations which these tentacles exhibit, the web-like film which sometimes (when they stand a little way apart) conjoins their bases, the thin annular film of tissue which surrounds the little organismãs mouth, and the manner in which this annular ãperistomeã contracts32, like a shrinking soap-bubble, to close the aperture, are every one