Physiology and histology of the Cubomedusæ / including Dr. F.S. Conant's notes on the physiology

by E. W. Berger

Many of the observations on these forms relate to the rate of pulsation. In an Aurelia, following the removal of a lithocyst, there was a pause followed by pulsations. In about two minutes rhythmic pulsations were renewed. Four minutes after the operation there were nineteen pulsations to the half minute, while twenty minutes after there were only nine, and these in groups of six and three. The normal rate of pulsation was twenty-five to the half minute.

Polyclonia behaved much in the same manner as Aurelia. Upon the removal of lithocyst pulsations continued, but in groups with short pauses. The normal rate of pulsation was twenty-seven to the half minute, while three minutes after the operation it was seventeen, and eleven minutes after, fifteen to the half minute. The tissue connected with a removed lithocyst gave contractions. Placing a Polyclonia in fresh sea-water more than doubled the rate of pulsation, which, however, soon fell to the normal rate, and lower in one instance. In small individuals the rhythm is decidedly more rapid than in those of larger size. The few observations on this point would seem to show that it is in inverse proportion to the squares of the diameters of the bells.

The removal of a single oral arm or of the whole eight, in Polyclonia, had much the same effect as the removal of a lithocyst: there was a decided slowing of the rate of pulsation, while the immediate effect of cutting was an acceleration or a return to near the normal rate. About a day later this same animal had quite regained its normal rate of pulsation and continued to live over two weeks. A long latent period followed the cutting of an arm, before the stimulation of cutting manifested itself.

An Aurelia, with all its lithocysts removed, still gave spontaneous and coördinated contractions after allowing time for recovery from the operation. This was the result in one instance, while in several others only a few contractions were observed. Removal of the sixteen marginal bodies (lithocysts) in a Cassiopœa produced paralysis for a time but recovery soon followed. A Polyclonia with its entire margin removed was paralyzed but had so far recovered in a day as to be able, at intervals, to give spontaneous pulsations.

The removed margin of a Polyclonia pulsated vigorously. This margin was then split so as to make a ring within a ring but connected at one point by a small bridge of tissue. The waves of contraction, which always originated on the ring with the lithocysts, passed the bridge to the inner ring quite as Romanes experienced. The outer ring was next split so as to separate the exumbral portion from the subumbral, when it was found that the contractions always originated from the latter. Seven days after its removal, this same margin was still alive and pulsating vigorously, and broken-off pieces of the subumbral portion were pulsating by themselves. Fifteen of the ganglia were removed. It was then found that while most of the pulsations originated at the remaining ganglion, now and then contractions originated in other parts where no ganglion remained. Two days later this margin was still alive with contractions originating as often from other parts as from the ganglion. A similar observation was made on a margin of Cassiopœa.

A Polyclonia with the eight lithocysts of one side removed, to compare with a normal one, gave no evidence of affected coördination.

An oral lobe from an Aurelia could give contractions some minutes after removal.

In another Aurelia a circular cut was made about the base of the oral lobes through the epithelium of the subumbrella. The animal could pulsate well enough but coördination seemed a little affected, while in another one with a like cut but semicircular, no effect was noticed.

These results on the removal of the lithocysts (and margin in Polyclonia) in Aurelia, Polyclonia and Cassiopœa agree quite with those on Charybdea and, of course, also with Romanes’ and Eimer’s results as to paralysis and recovery following the removal of the lithocysts, or margin, in Aurelia, Cyanea, etc. I recall no similar observations, however, on removing a single lithocyst, and the question of an explanation for the slowing of the rhythm thus brought about arises. Romanes gives as an explanation for the slowing of the rhythm (Aurelia, Cyanea, etc.) following the temporary acceleration upon removing the manubrium or a portion from the center of the bell, as due to a lack of an afferent stimulating influence upon the ganglia from the excised tissue. May a similar explanation not serve to explain the slowing following the removal of a single lithocyst, above noted? The removed lithocyst could no longer give its efferent stimulus to the remaining ganglia nor to the tissue, so that the former would have a weaker stimulating influence, in consequence of which the latter (the contractile tissue) would be deprived of a part of the original stimulus of the remaining ganglia as also of that of the removed ganglion. The whole would thus result in giving to the contractile tissue a weaker stimulus, which, again, would require longer and greater recovery on the part of the tissue in order to be set off by the stimulus at hand. This explanation is given on the basis of Romanes’ theory of rhythmic contraction previously explained.

Of course, it may be suggested that the musculature had lost tonus, due to the lack of influence of the removed ganglion (lithocyst), in consequence of which there was a lowering of irritability on the part of the contractile tissue. This would require a greater summation of stimulating influence (Ganglionic theory of contraction) on the part of the remaining ganglia to set it off. Again, the loss of irritability on the part of the contractile tissue may have been due to a lack of nutritive influence from the removed ganglion.