160 



Papers from the Department of Marine Biology. 



constant temperature, the resulting rate of pulsation might follow Van't 

 Hoff's law more closely than when the entire disks were subjected 

 to the change in temperature, or the rate of pulsation — nerve-conduc- 

 tion — of activated disks under similar conditions was measured. Such 

 experiments showed, however, that the results from this cause were 

 in no essential different when either a single sense-organ, an ''active" 

 disk, or activated disk were subjected to the changes in temperature. 

 All my later experiments 

 were therefore confined to 

 those in which active and 

 activated halves of the 

 same medusa disk were 

 subjected to the tempera- 

 ture changes at the same 

 time in order to determine 

 the influence of sense- 

 organs upon the response 

 to changes in temperature. 

 The prepared half-disks 

 were placed in a 4-liter jar 

 of fresh sea-water which 

 was in turn contained in 

 a 20-liter jar of fresh water 

 supported on a copper tray 

 filled with water. The 

 water surrounding the 

 inner jar was cooled by 

 the addition of ice or 

 heated by the flame of a small alcohol lamp so that a change of 1° 

 in the temperature of the sea-water was obtained in 15 minutes. The 

 activity of the medusa) was sufficient to agitate the water to such an 

 extent that at no time could a difference of 0.1° C. be detected in the 

 temperature of any two portions of the contents of the jar. 



In beginning any experiment the temperature was lowered to the 

 desired starting-point and then raised until either the desired upper 

 limit was reached or continued until the disks became inactive. On 

 being cooled below 20° C. the activated specmiens often ceased 

 pulsating and could not again be aroused to steady pulsation by the 

 application of repeated sthnuli until the temperature had been raised 

 to about 22° C. From 23° to 33° C. the increase in rate of pulsation 

 for activated specimens followed a right line (fig. 14) and within that 

 limit the rate was nearly doubled. The active half-disks, over the 

 same range of temperature, gave generally a smaller increase in rate 

 and the change in rate was always more erratic than that shown by 

 those deprived of their sense-organs. (Fig. 14.) 



5 



cc-CO- 



:ddcd to I200 cci-ca-water 



Fig. 15. — Showing change in hydrogen-ion concentra- 

 tion when a known volume of carbon dioxide is 

 added to 1,200 c.c. of Tortugas sea-water. 



