. Comparative physiology of the brain and comparative psychology. Brain; Psychology, Comparative. ON ACTINIANS 59. FORCED BY GRAVITATION TO PUSH ITSELF THROUGH THE NET THREE TIMES (a, b, AND c). See text. incision be made in the middle of a Cerianthus which almost but not quite separates the two halves, and the animal be placed immediately after the operation on a wire net, the foot works itself into one of the meshes up as far as the incision and assumes a vertical position. The oral piece, on the con- trary, from the place of incision to the head, usu- ally remains lying hori- FIG. 15. ACTIN
. Comparative physiology of the brain and comparative psychology. Brain; Psychology, Comparative. ON ACTINIANS 59. FORCED BY GRAVITATION TO PUSH ITSELF THROUGH THE NET THREE TIMES (a, b, AND c). See text. incision be made in the middle of a Cerianthus which almost but not quite separates the two halves, and the animal be placed immediately after the operation on a wire net, the foot works itself into one of the meshes up as far as the incision and assumes a vertical position. The oral piece, on the con- trary, from the place of incision to the head, usu- ally remains lying hori- FIG. 15. ACTINIAN THAT HAS BEEN zontally on the net. This shows that the foot pos- sesses geotropic irritabil- ity. But if the Actinian be divided transversely we see that the head-piece as well as the tail-piece pushes itself through the meshes, although not so frequently. While an Actinian that is suspended vertically in a test-tube or in a mesh of a wire net seldom retains this position longer than two days, it remains indefinitely in the sand after burrowing. In addition to gravita- tion, some other stimulus must hold it there. I be- lieve that it is the contact-stimulus of the sand. I called this kind of irritability stereotropism, and have shown that in a series of animals it determines their habits. Positive geotropism and positive stereotrop- ism cause the Cerianthi to burrow in the sand vert- ically, and the positive stereotropism keeps them permanently in the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Loeb, Jacques, 1859-1924. New York, G. P. Putman's Sons; [etc. , etc. ]
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