. The elementary nervous system. Nervous system; Nervous system -- Coelenterata. 26 THE ELEMENTARY NERVOUS SYSTEM due not to changes in the activity of the choanocytes but to other causes. Some sponges, such as the fingered form Stylotella, appear, when out of water, to be more or less shrivelled or contracted and under other circumstances to be plump and well rounded-out. The differences, which, for rea- sons to be mentioned pres- ently, are known not to be due to the simple physical loss of fluid, are apparently depen- dent upon a general contractil- ity of the whole flesh of the sponge whic
. The elementary nervous system. Nervous system; Nervous system -- Coelenterata. 26 THE ELEMENTARY NERVOUS SYSTEM due not to changes in the activity of the choanocytes but to other causes. Some sponges, such as the fingered form Stylotella, appear, when out of water, to be more or less shrivelled or contracted and under other circumstances to be plump and well rounded-out. The differences, which, for rea- sons to be mentioned pres- ently, are known not to be due to the simple physical loss of fluid, are apparently depen- dent upon a general contractil- ity of the whole flesh of the sponge which, though slight, may nevertheless enable the sponge to change its form somewhat. Aristotle in the fourteenth chapter of his fifth book on the history of animals makes the interesting state- ment that the sponge is sup- posed to possess sensation because it contracts if it per- ceives anv movement to tear • it up and it does the same when the winds and waves are so violent that they might loosen it from its attachment. He further adds in his characteristic way that the natives of Torona dispute this. The idea that the common flesh of the sponge is con- tractile is not without modem support. Merejkowsky (1878) stated that if the sponge Suberites is so placed that it is partly out of water, it will curve the body until it is under water as much as possible, and if the body is then. Fio. 4.—Diagram of the canal sys- tem of a calcareous sponge (modified Haeckel). The innumerable superfi- cial pores receive water from the exte- rior, as shown by the arrows on the sides; the osculum at the apex dis- charges water to 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 Parker, George Howard, 1864-1955. Philadelphia, London J. B. Lippincott Company
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