Researches, 1890-[1909] (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1901 Excerpt: ...of marginal sense-organs to pulsate constantly and regularly in sea-water; and if such disks be pinched or lifted out of water or otherwise disturbed the amplitude of their pulsations becomes suddenly increased, while the rate remains practically constant. In normal uninjured Medusae both rate and amplitude increase, but as we shall see, disks without sense-organs pulsate at the maximum rate at which their tissue is capable of transmitting the wave of pulsation, and they can therefore exhibit "excitement" only by an increase in amplitude. It is worthy of note that if the forceps used to stimulate the Medusa be made to seize upon only a small area of tissue, the Medusa will not respond, but on bringing a larger area between the forceps the response is sudden and violent. In this connection it will be recalled that Romanes showed that the bell of Sarsia, when deprived of its margin, will respond to mechanical shocks by pulsations, each stimulus usually giving rise to one or two pulsations, and this is also true of the paralyzed disk of Cassiopea. We must conclude that the presence of marginal sense-organs is not necessary for the display of that sudden increase in activity which we have called "excitement," and that this response may come from many or all parts of the undifferentiated tissue of the sub-umbrella. a Fig. i. Fig. 2. Romanes showed that in Aurelia annular cuts separating the margin from the center of the disk caused the rhythm to become slower, and he was led to suspect (1885, p. 163) that a stimulus of an afferent character emanates from all parts of the sensory surfaces of the sub-umbrella to the marginal sense-organs, although of this he had no direct proof. I think we can prove that this is the case in Cassiopea, for if we...