614 
ZOOLOGY: L. R. CARY 
These results, while confirming the previous observations that a half- 
disk under the control of the rhopalia regenerates faster than its com- 
panion half-disk from which these organs have been removed, were 
not sufficient, because of a lack of knowledge of the differential action 
of the magnesium ions on the several tissues involved, to determine 
whether the factor of muscular activity was or was not concerned in 
the initial difference in rate of regeneration. Fortunately another type 
of operation made known by Mayer ('06) makes it possible to determine 
the influence of muscular activity in a half-disk from which the rhopalia 
have been removed. When a series of cuts are made in the subumbrella 
tissues of a half-disk in such a manner that an endless labyrinth of 
tissue is formed, an entrapped wave of contraction can be initiated by 
an induction shock. This contraction wave will traverse the labyrinth 
of tissue for days before the muscles 
are overcome by fatigue so that the 
regeneration of new tissue to fill the 
open center of the disk will be com- 
pleted before the contractions cease. 
When the two insulated halves of a 
disk, from which all of the rhopalia 
have been removed while in the sub- 
umbrella tissues of one of them a 
circuit wave of contraction is main- 
tained, are compared the actively 
contracting half -disk shows a slightly 
higher rate of regeneration than the 
inactive half. The difference in the 
rapidity of regeneration of the two 
halves in these experiments, as is 
shown by comparing curves B and C, figure 1, is not nearly as great as 
when a half-disk without rhopalia is compared with one on which the 
rhopalia remain (curves A and C, figure 1). When the fact that the rate 
of pulsation of a half-disk contracting under the influence of an entrap- 
ped wave is on the average more than three times the normal rate for a 
disk of the same size is taken into account it is at once apparent that 
some factor other than muscular activity must be the most important 
influence in determining the rate of regeneration. Added confirmation 
of this conclusion is obtained when the rates of regeneration of two insu- 
lated half-disks are compared, one of which is contracting normally under 
the influence of its rhopalia while an entrapped wave of contraction is 
maintained in the subumbrella tissues of the other (curves A and B, 
tXKT. OF flECrNERATION IN DAYZ. 
FIG. 2.— COMPARATIVE RATES OF RE- 
GENERATION OF SPECIMENS IN MAG- 
NESIUM SOLUTION. SOLID LINE HALF- 
DISKS WITH SENSE ORGANS ATTACHED. 
BROKEN LINE HALF-DISKS WITHOUT 
SENSE ORGANS. 
