In spite of this lack of completeness in our knowledge of the nature of the nervous system of Cassiopea, it should be emphasized that, through whatever morphological mechanism it may be exercised, the trophic influence of the sense-organs is a constant factor in the normal metabolic activity. Without these impulses, even while muscular activity is far above normal, all the measurable metabolic activities except that of the motor system are maintained at a considerably lower level than when under the control of the sense-organs, by which muscular activity is held at a much lower rate than that at which these tissues are capable of maintaining a constant activity for long periods.
Summary.
(1) The experiments with entire disks, when the rates of regenera tion of specimens on which the sense-organs remained are compared with those of specimens from which all sense-organs are removed, are inconclusive because of wide differences in physiological activity between different individuals.
(2) When we compare the insulated halves of a disk, on one of which the sense-organs remain, while all of them have been removed from the other half, it is found that the half-disk with sense-organs always regenerates most rapidly. This is especially noticeable in the early stages of regeneration. The difference in rate falls gradually through out the course of an experiment (table 1 and fig. 6).
(3) When disks prepared as in the experiments mentioned in the previous paragraph are allowed to regenerate in sea-water plus 15 parts 0.6 m the regeneration is at first more rapid from the half on which the sense-organs come under the influence of the anesthetic, and from that time on the rate of regeneration is practically equal from halves (table 2 and fig. 7).
(4) When all the sense-organs are removed from a disk and the halves insulated, muscular activity may be maintained in one half by forming an endless labyrinth of the subumbrella tissue and initiating a circuit wave of contraction by induction shocks. Under these condi tions the regeneration is faster from the activated than from the inactive half-disk. The difference is, however, not nearly so great as when the sense-organs are removed from only one of the insulated halves of a disk (table 3 and fig. 8).
(5) Comparison of rates of regeneration of the halves of a disk, one half of which retains its sense-organs, while a circuit wave of contrac tion is maintained in the muscles of the other half, shows that the half-disk the muscles of which are contracting under the control of the sense-organs regenerates faster, although the rate of pulsation of the activated half is more than 3 times that of the former (table 4 and fig. 9).
(6) The influence of the nervous system on the earlier stages of regeneration has been noted by several earlier investigators, but apparently no importance has been attached to it. • (7) These experiments indicate that the rate of regeneration is simply one expression of the general metabolic activity of an animal, and as such is subject to the influence of the nerve-centers, as are many other functional activities.
(8) When a normal medusa, a regenerating medusa, a medusa disk, or half-disk is kept in water free from food material, the loss in weight follows a curve of the formula y = w(1 — a)x. Here y = the weight for any given day, w = original weight, x = number of days of starvation, and a is a constant, the "coefficient of negative metabolism." The value of a will differ under different experimental conditions, but all observed instances agree closely with the expectations.
(9) The greater part of the loss in weight appears to be shown by the mesoglcea, which undergoes marked histological changes during the course of starvation.
(10) As in regeneration experiments, the greatest metabolic activity is shown by the active specimens, the least by the inactive, while the activated individuals stand in an intermediate position, being closest to the one in which muscular activity is entirely suppressed. (Table 9, and figures 10, 11, and 12.) (11) Specimens as prepared for the previous experiments were kept for various periods in closed jars of sea-water, each containing about 1,200 c.c. The amount of given off was ascertained by determining the hydrogen ion concentration of this water at the beginning and end of each experiment. The volume of necessary to bring about the observed change was determined by adding known volumes of this gas to 1,200 c.c. of sea-water, as shown in figure 13.
(12) While the rate of pulsation of the activated half-disks was gen erally more than 3 times that of the active half of the same disk, the amount of given off in respiration from the activated specimen was never more, and almost always considerably less, than that from the active specimens of any pair of half-disks. In general the results from this type of experiment are in perfect accord with those obtained from those recorded in sections I and II, where the standard of measure ment was a component part of that used in the respiration experiments.