[157] Child, C. M., "Die physiologische Isolation von Teilen des Organismus," Roux's _Vorträge und Aufsätze_, Leipzig, 1911.
4. The phenomena of regeneration in _Cerianthus membranaceus_, a sea anemone, can be easily understood from the experiments on Tubularians, if we imagine the body wall of _Cerianthus_ to consist of a series of longitudinal elements running parallel to the axis of symmetry of the animal from the tentacles to the foot. The number of these elements may be supposed to correspond to the number of tentacles in the outer row of the normal animal. Each such element behaves like a Tubularian, with this difference, however, that the elements in _Cerianthus_ are more strongly polarized than in _Tubularia_, and that each one is able to form a tentacle at its oral pole only. This fact can be nicely illustrated in the following way: if a square or oblong piece (_a b c d_, Fig. 24) be cut from the body wall of a _Cerianthus_ in such a way that one side, _a c_, of the oblong is parallel to the longitudinal axis of the animal, tentacles will grow on one of the four sides only; namely, on the side _a b_.[158] (Fig. 25.) The other three free edges are not able to produce tentacles. If an incision be made in the body wall of a _Cerianthus_, tentacles will grow on the lower edge of the incision (Fig. 26).
[158] Loeb, J., "Untersuchungen zur physiologischen Morphologie der Tiere."
The writer tried whether or not by tying a ligature around the middle of a piece of an Actinian this polarity could be suppressed; but the experiments did not succeed, inasmuch as the cells compressed by the ligature died, and were liquefied through bacterial action so that the pieces in front and behind the ligature fell apart. It is therefore impossible to decide whether or not a current or a flow of substances in a certain direction through these elements is responsible for this polarity, though this may be possible. The writer found, however, that one condition is necessary for the growth and regeneration of tentacles which also plays a rôle in the corresponding phenomena in plants, namely turgidity. The tentacles of _Cerianthus_ are hollow cylinders closed at the tip, and by liquid being pressed into them they can be stretched and appear turgid. If, however, an incision is made in the body, the tentacles above the incision can no longer be stretched out. In one experiment the oral disk of a _Cerianthus_ was cut off; very soon new tentacles began to grow at the top, and after having reached a certain size, an incision was made in the animal. The tentacles above the incision collapsed in consequence and ceased to grow, while growth of the others continued. On the lower edge of the incision new tentacles began to grow.