. The elementary nervous system. Nervous system; Nervous system -- Coelenterata. NEUROID TRANSMISSION 67 animals the swimming plates form eight well-defined rows that extend from the aboral pole toward, if not ac- tually to, the oral pole. The effective stroke of each plate is in the aboral direction, thus carrying the animal through the water with its mouth forward. The wave of ciliary action, however, sweeps over each row from its aboral to its oral end and thus takes a course the reverse of that indi- cated by the effective stroke. Hence it may be concluded that the effective stroke and the
. The elementary nervous system. Nervous system; Nervous system -- Coelenterata. NEUROID TRANSMISSION 67 animals the swimming plates form eight well-defined rows that extend from the aboral pole toward, if not ac- tually to, the oral pole. The effective stroke of each plate is in the aboral direction, thus carrying the animal through the water with its mouth forward. The wave of ciliary action, however, sweeps over each row from its aboral to its oral end and thus takes a course the reverse of that indi- cated by the effective stroke. Hence it may be concluded that the effective stroke and the wave of ciliary action are inde- pendent factors; for though they usually agree in direction they may be directly opposed as in the example just given. The regularity with which one cilium beats after another, the coordinated metachronism of the series, is the feature of the ciliated epithelia that most recalls nervous control and that requires explana- tion. It might be supposed that this regularity was due to the mechanical influence of a given cilium on the one next following and so forth. Thus if cilium A begins to beat, it will strike toward cilium B, which on being struck will thus be called into action and by a similar process excite C and so on. This operation, at least so far as the effective stroke is concerned, is not unlike that seen in the successive toppling over of a row of bricks each on end where the fall of the first brick knocks over the second and so on. Although this explanation finds an easy application to the usual form of ciliary beat in which the effective. Fio. 15.—Side view of the cteno- phore Mnemiopsis leidyi. Of the eight rows of swimming plates four are shown, two long ones and two short. All start from the aboral pole o and converge on the oral pole 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 r
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