136 Papers from the Department of Marine Biology. 



closure of the open circle in disk 36, table 1, was complete in 2 days, 

 while 5 days were necessary to complete the closure in specimen 30, 

 table 1. Had the latter been the active disk and the former the in- 

 active disk of a pair compared in an experiment with entire disks, the 

 conclusion that an inactive disk sometimes regenerates more rapidly 

 than an active one could not have been avoided. 



EXPERIMENTS WITH ANESTHETICS. 



In the previously described experiments it was shown that the 

 active half of a medusa disk prepared as shown in figures 3 and 5 

 has a higher rate of regeneration than does the inactive half of the 

 same specimen. While this point is clearly shown in all the experi- 

 ments of the two types just mentioned, the results obtained by this 

 method throw no light upon the nature of the control exercised by the 

 marginal sense-organs as to whether it is exerted through the higher 

 metabolism brought about by muscular activity or through some other 

 less apparent metabolic process under the control of the sense-organs. 



Two other types of experiments were undertaken to ascertain the 

 nature of the nervous control. In the first set of experiments (type 3) 

 disks prepared with insulated active and inactive halves (fig. 3) were 

 allowed to regenerate in sea-water to which 15 per cent by volume of 

 0.6 m MgSO 4 had been added. In this solution the disks will live for 

 an indefinite time and will for several hours retain the capacity to 

 regain their normal activity within a few moments after being returned 

 to fresh sea-water. Mayer (op. cit.) has shown that the effect of the 

 magnesium in a weak MgSO 4 solution in sea-water is for a time confined 

 almost entirely to the muscular tissues, while the nervous network is 

 still capable of transmitting the impulse necessary for pulsation over 

 an area submerged in the magnesium solution where no contraction 

 of the muscles could be observed. When kept in the magnesium 

 sea-water for a prolonged period the sense-organs become incapable of 

 giving rise to the stimulus necessary for normal pulsation long before 

 the nervous network loses its capacity for transmitting such a stimulus, 

 so that a ring cut from a medusa disk and activated by a circuit wave 

 of contraction will show by an indicator strip in sea-water (Mayer, 

 loc. cit., page 122) the transmission of the nervous impulse for some time 

 after a ring retaining its sense-organs is no longer able to activate its 

 indicator strip. 



When medusa disks prepared with insulated active and inactive 

 halves are put into the magnesium sea-water they lose their power of 

 muscular movement within a few moments. Usually all of the disks 

 float on the surface of the new solution for 20 to 30 minutes before 

 they become adjusted to the abnormally dense medium; at the end of 

 this period they settle to the bottom of the jar and remain completely 

 relaxed throughout the experiment. 



