128 



Papers from the Department of Marine Biology. 



tion of the half-disks did away with the folding of the disks at the point 

 where the insulating strips were removed, which often interfered with 

 accurate measurement of the regenerated tissue. (These series will be 

 referred to as the "active" and "inactive" series.) 



In the second type of experiments normal disks or half-disks were 

 compared with others from which all sense-organs had been removed, 

 but in which the subumbrella muscles had been activated by electrical 

 stimulation. In entire half-disks, from which the central portion has 

 been removed, a circuit wave of contraction may be initiated by induc- 

 tion shocks and maintained for as many as 1 1 days unless interrupted 

 by some strong stimulus (Mayer, op. cit.', Harvey, 1911). 



When half-disks were employed it was necessary to make two 

 incisions through the muscles and nerves in such a manner that an 

 endless labyrinth of these tissues would be formed (fig. 4), in which the 

 circuit wave of contraction could be maintained. 



FIG. 4. A medusa prepared for comparison of activated and inactive half-disks. All the sense- 

 organs have been removed from both halves, while in the subumbrella tissues of one of them 

 an endless labyrinth has been formed in which a circuit wave of contraction will be main- 

 tained as soon as it has been initiated by induction shocks. 



FIG. 5. A medusa prepared for the comparison of active and activated half-disks. 



These series will be referred to as the "active and activated" series. 



In the third type of experiments "activated" specimens prepared in 

 the manner just described were compared with "inactive" specimens 

 (fig. 5). 



In all instances where active and activated specimens were compared 

 it was observed that the pulsation-rate of the activated specimens was 

 at first about 3 times as great as that of the active specimens. The 

 difference in rate became progressively greater for about the first 24 

 hours, both on account of an actual increase in that of the activated as 

 well as a decrease in the rate of those with sense-organs intact, until 

 at the end of this time the activated specimen was often pulsating 10 

 times as rapidly as its mate. If an entire disk or unmutilated half 

 disk were used as the active specimen of any pair its pulsations 

 appeared to be much more vigorous than its mate, in the muscles of 

 which a circuit wave of contraction was maintained, because the bell- 



