STUDIES ON THE PHYSIOLOGY OF THE NERVOUS SYSTEM OF CASSIOPEA XAMACHANA.
In this paper are gathered the results of several distinct lines of experimentation, all of which have this in common—that they deal with some phase of the physiology of the nervous system of Cassiopea and represent portions of a general program of research on the nervous system of the lower animals. On account of its ability to live under adverse conditions and to withstand practically any type of operation, Cassiopea is an especially favorable form for experimentation and has been used as a subject for many researches. On regeneration by Stockard, Zeleny, and Goldfarb; for the study of pulsation, rate of nerve-conduction, effect of starvation, etc., by Mayer; on chemical com position and chemical changes during starvation by Hatai; on reaction to temperature, permeability, and nerve-conduction by Harvey, and the researches herein recorded by the author.
In very few types of animals, where the recognizable activities are entirely under the control of nerve-centers, can all these structures be removed without causing death, or at least serious injuries which will render abnormal practically all physiological activities. Among the Scyphomeduste, Cassiopea, in common with many other Rhizostonate, is distinguished for the density of its mesoglcea, but it stands preemi nent as a laboratory marine animal because of the fact that its normal habitat, being in shallow lagoons of relatively stagnant water, fits it especially for the adverse environment encountered under experimental conditions in laboratory aquaria. The sense-organs (nerve-centers), because of their position around the periphery of the disk, can be removed with very little injury to any of the other tissues of the body.
Since, also, these structures are equally spaced around the circum ference of the disk, any portion of the body can, by the appropriate operation, be deprived of its normal nerve-supply, while retaining its other relations undisturbed. Then, too, the rapidity with which the centers are replaced by the regeneration of normally functioning new ones permits experimenting on any given area of tissues, first without and later under the influence of nervous impulses.
In studying regeneration in Cassiopea I found that the rhopalia exert a decided influence on the rate of regeneration, which is most marked in the early stages of any experiments, and that this influence was in the major part independent of muscular activity. The observa
tions were, therefore, extended to involve other factors as the basis of comparison, since it seemed evident that the influence on regeneration must be in some manner exerted through fundamental metabolic activity, which might be expected to be measurable on some other basis than the rate of regeneration. These expectations were fulfilled when either the general metabolism, as measured by total production, the loss of weight during starvation, or the changes in the rate of nerve conduction in response to changes in temperature, was used as the standard of comparison.
The same types of operations were used in experiments on regenera tion, general metabolism, loss of weight during starvation, and the influence of the sense-organs on the change in rate of nerve-conduction in response to changes in temperature, so that the results obtained by use of these distinct standards of measurement are directly comparable.
The experiments on the influence of the nerve-centers on the loss of weight during starvation, on account of the operations employed, necessarily involved regeneration at the same time, and in some instances this factor was measured as well as that for which the experiments were primarily carried out. Conversely the experiments on regeneration, since only the disks were used, were carried out on starving medusas and the decrease in both area and weight of the half disks was often recorded for these experiments. While both these factors (i. e. regeneration and decrease in size and weight) were involved in the experiments on the rate of nerve-conduction, each experiment extended over so short a period of time that no measurements of the amount of regeneration were possible, and the loss of weight, while actually small, was entirely in accord with the results obtained from the more extended experiments. Thus the high rates of pulsation brought about by nerve-conduction, independent of the rhopalia, tended especially to emphasize the inadequacy of differences in motor activity as the explanation of difference in rate of metabolism as expressed by loss of weight.