. The elementary nervous system . died (Fig. 21), a stimulus applied to the pedal edge of the column will call forth a contraction of the oral disc even more readily than when it is applied to the portion of the column that is on, the oral side of the circular in- cision. Hence it must be admitted that there are trans- mission tracts that lead from the ectoderm of the pedal edge of the column directly through to the longitudinal muscles of the mes- enteries irrespective of such con- nections as may exist in the oesophagus. The same conclusion can be drawn from what is seen in prep- arations fr
. The elementary nervous system . died (Fig. 21), a stimulus applied to the pedal edge of the column will call forth a contraction of the oral disc even more readily than when it is applied to the portion of the column that is on, the oral side of the circular in- cision. Hence it must be admitted that there are trans- mission tracts that lead from the ectoderm of the pedal edge of the column directly through to the longitudinal muscles of the mes- enteries irrespective of such con- nections as may exist in the oesophagus. The same conclusion can be drawn from what is seen in prep- arations from which the whole oral disc has been cut off. On stimulating the pedal edge of such a preparation the portions of the longitudinal muscles of the mesenteries still remaining in the animal contract vigor- ously, showing that there is not only a direct connection between the ectoderm of the pedal edge of the column and the longitudinal muscles of the mesenteries, but that the oral disc, believed by the Hertwigs to contain a central- ized portion of the nervous system of the actinian, is in no way essential to the reaction noted. The belief that the oral disc does not contain an essential nervous center has already been vigorously set forth by Jordan (1908). If the column of a large sea-anemone with a pedal disc 10 centimeters or more in diameter is cut through in an oblong outline, 4 centimeters by 2 centimeters, a super- ficial piece of the column results that is attached to the rest of the animal only through its mesenteries (Fig. 22). FIG. 21.—Metndium with its column wall completely girdled by a cut that passes at all points en- tirely through the wall. Stimulus applied at z.
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Keywords: ., bookpublisherphiladelphialondonjblipp, booksubjectnervoussystem
