TRACHYMEDUS.E — GONIONEMUS. 347 



at one small opening; and under these conditions coordinated movements were made when 

 the animals were stimulated. Apparently also some spontaneous movements were executed, 

 but this is uncertain. 



It appears from the works of Hargitt and of Morgan that the power of regeneration is 

 slight in Gonionemus, but the bell heals over by bending in and the cut edges fuse, thus reform- 

 ing the medusa shape. In some instances after the bell-margin has been removed, the ten- 

 tacles, lithocysts, and velum do not regenerate, but the bell-margin bends upward and inward, 

 and the bell-opening becomes smaller and smaller, so that finally the bell assumes a balloon 

 shape, the outer surface of the balloon being the subumbrella (see Hargitt, 1899, p. 43, figs. 

 13 to 16). I have observed a similar phenomenon in Cassiopea under similar conditions. 

 The regenerative activity in Gonionemus is mainly effected at the expense of the intact portions 

 of the body proper, and although new manubria, tentacles, velum, lithocysts, or radial-canals 

 may regenerate, this power is not possessed to any marked degree in comparison with the 

 somewhat remarkable ability in the medusa to reform the shape of the medusa body through 

 mere coalescence and healing of cut edges (see Morgan, 1899). 



Yerkes, Yerkes and Ayers,and Morse have studied the reactions of Gonionemus to external 

 stimuli, with a view to discover the effects these reactions may have upon the normal habits 

 of the medusa. The peculiar "turning-over reaction" which ensues when the medusa reaches 

 the surface has been well described by Perkins. Yerkes believes that this turning reaction is 

 due, in part at least, to the effect of the strong light at the surface of the water. Yerkes states, 

 however, that this reaction may take place in the dark, and that therefore, while light is a 

 contributary cause to the turning reaction, it is not a necessary or a sole cause. Morse, 1906, 

 denies that light is an important factor in causing the turning reaction; neither is this turning 

 due to the effect of the oxygen of the air, or of lack of oxygen, for the reaction takes place when 

 the medusa swims upward and reaches the surface, even when the surface of the water is 

 covered by vapor of NH^Cl, held in suspension in water vapor. On the other hand no reversal 

 takes place if the medusae swim upward against a film of olive oil, or against a horizontal 

 glass plate. The reversal takes place even if half of the velum be removed. Morse does not 

 attempt to define the cause for the reaction, but merely states that it is a "normal reaction." 

 Light may or may not exert a directive influence upon the medusa, but this question is 

 still in dispute; Morse claims that there is no directive influence in light, but Yerkes states 

 that if the medusa has been in weak light then brilliant illumination of one side of the bell 

 brings about movement toward the region of lower illumination. Both observers agree that 

 if the medusae be placed in an aquarium one portion of which is brilliantly lighted and another 

 dark or shaded, that the greater number of the medusae will soon be found in a relatively 

 quiescent state in the shaded portion of the aquarium. Morse claims that this is due simply 

 to the fact that the medusae swim in all directions through the lighted region, and if by accident 

 they enter the shadow they cease swimming and sink passively to the bottom, thus being 

 "trapped" in the shaded area. Yerkes on the other hand claims that Gonionemus definitely 

 turns from the region of strong stimulation toward the shaded portion of the aquarium. There 

 are other important matters in dispute between these observers, for the study of which the 

 reader is referred to their papers cited above. 



Yerkes and Ayers found that the reaction time to ordinary daylight is 7 seconds, to sun- 

 light only 5.5, and for weak daylight 9.4 seconds. The reaction time to electrical stimuli 

 ranges from 6 to 20 seconds, according to the intensity of the stimulus and the place stimulated. 

 The reaction time is shorter when the radial-canals are stimulated than it is when the inter- 

 radial regions are stimulated. The reaction time to photic stimuli ranges from I to 10 seconds, 

 the subumbrella being more sensitive to effects of light than the exumbrella. Medusae at 

 rest react to light as do those already in movement (Morse, 1907). 



The tentacles in the radii of the radial-canals are apparently more sensitive than are the 

 other tentacles. When cut away from the bell the tentacles soon tire and their reactions become 

 weak. Murbach, 1907, finds that the general subumbrella epithelial tissue, not exclusively 

 the marginal papillae, is responsive to light-stimulation. 



Loeb, 1900, 1905, 1906, has carried out studies upon the influence of the various salts of 

 sea-water in maintaining or inhibiting pulsation in Gonionemus murbachii. He finds that if 

 we cut away the margin of the bell the center does not pulsate spontaneously in sea-water. 



