ZOOLOGY: L. R. GARY 
613 
cal characteristics of the two halves of any disk would at the start of 
an experiment be identical, and the pulsations of the half on which the 
rhopaha remained were sufficiently strong to move the inactive half 
about in the water and thus reduce to a very small amount any differ- 
ence in aeration. 
In every instance where the rates of regeneration of the two halves of 
a medusa disk under these experimental conditions were compared it 
was found that the active half — i.e., the half on which the rhopalia 
remained — regenerated at a more rapid rate than the inactive half. 
The results of two such series of experiments in which the insulated 
halves of 40 disks were compared are shown in curves A and B, figure 1. 
The proportion between the amounts of tissue regenerated each day, 
when that from the inactive half is taken as the unit was respectively: 
first day, 1 : 1.53; second day, 1 : 1.44; third 
day, 1 : 1.41; fourth day, 1 : 1.38; and for 
the fifth day, 1 : 1.39. 
Although the results from the experiments 
just described show conclusively that each 
half-disk on which the sense-organs were 
present regenerated faster than its com- 
panion half-disk without sense-organs, no 
evidence was afforded respecting the nature 
of the influencing factors. Since the muscu- 
lar activity was the most striking difference 
between the two half-disks in this type of 
experiment other operations were undertaken 
to eliminate this factor. When disks with 
insulated active and inactive halves are put 
into a solution made up of 85 parts sea water 
and 15 parts 0.6 m MgS04 the activity first 
of the muscles, then of the rhopalia, and 
finally of the conducting portion of the nerv- 
ous system is entirely suppressed. Under these experimental conditions 
the rate of regeneration of both half-disks becomes very much lowered. 
For the first few hours the half-disk on which the rhopaHa remain regen- 
erates faster, but after the full effect of the magnesium has become 
established the rate is the same for both halves. 
As shown in the curves in figure 2 which represents the results of the 
comparison of the halves of 40 disks the difference in rate of regenera- 
tion is apparent only during the period before the rhopalia had come 
completely under the influence of the anesthetic. 
TIME OF RECENERaTIOW in DilVS. 
FIG. 1.— COMPARATIVE RATES 
OF REGENERATION OF SPECI- 
MENS IN SEA WATER. A. HALF- 
DISKS WITH SENSE ORGANS 
ATTACHED. B. HALF-DISKS 
ACTIVATED WITH CIRCUIT 
WAVE OF CONTRACTION. C. 
HALF-DISKS WITHOUT SENSE 
ORGANS (INACTIVE). 
