. The Cambridge natural history. Zoology. 446 ECHINODERMATA ASTEROIDEA of physiological experiment, and so Starfish have been favourite " corpora vilia " with many physiologists. The light-perceiving function of the eye is easily demon- strated. If a number of Starfish be put into a dark tank which is illuminated only by a narrow beam of light they will be found after an interval to have collected in the space reached by the beam of ' If all the median tentacles but one be removed this will still be the case; if, however, they are all removed the Starfish will exhibit indiffer
. The Cambridge natural history. Zoology. 446 ECHINODERMATA ASTEROIDEA of physiological experiment, and so Starfish have been favourite " corpora vilia " with many physiologists. The light-perceiving function of the eye is easily demon- strated. If a number of Starfish be put into a dark tank which is illuminated only by a narrow beam of light they will be found after an interval to have collected in the space reached by the beam of ' If all the median tentacles but one be removed this will still be the case; if, however, they are all removed the Starfish will exhibit indifference to the light. If the under sur- face of a Starfish be irritated by an electric shock or a hot needle, or a drop of acid, the tube - feet of the affected area will be strongly retracted, and this irritation will be carried by the pedal nerves to the radial nerve- cord, with the re- sult that finally all the tube-feet in the groove will be retracted and the groove closed by the action of the transverse muscle connecting each ambulacral ossicle with its fellow. If, on the other hand, the back of a Starfish be irritated this may produce a contraction of the tube-feet if the irritation be strong, but this will be followed by active alternate expansions and contractions, in a word, by endeavours to move. Preyer- by suspending a Starfish ventral surface upward, by. MB Fig. 193.—A, longitadinal section of a single eye-pit of Asterias. , Nucleus of supporting cell; , niicleus of visual cell; , visual rod. B, view of the terminal tentacle showing the eye-pits scattered over it. (After Pfeffer.) ' Romanes," Jellyfisli, Starfish, and Sea Urchins," Intern. Scientific Series, 1885, pp. 320, 321 ; Preyer, " Bewegungen von Stelleriden," Mitth. Zool. Slat. Neapcl, vii. 1886-87, p. 22. = Preyer, loc. cit. p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appea
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