ACTIVITIES OF COLONIAL ANIMALS 487 
whole organ, so the peduncle of Renilla may be looked upon as 
the pace-maker for the Renilla colony. Thus the peristaltic 
wave that passes over Renilla has a most striking resemblance 
to the wave of contraction that sweeps through the cardiac muscle 
of the vertebrate. 
Although the wave of rachidial peristalsis passes from one part 
to another of the rachis of Renilla so long as there is organic 
continuity, it can be easily interrupted by anesthesia. If the 
edge of the rachis of a Renilla on which peristaltic waves are run- 
ning is covered with crystals of magnesium sulphate, in a short 
time the waves pass around this region as they do around an 
incision. If a rachis is cut transversely so that the peduncular 
portion is connected with the apical portion by only a narrow 
bridge of tissue over which the peristaltic waves pass and this 
bridge is then covered with crystals of magnesium sulphate (fig. 
7), in a few minutes the waves cease to pass across the bridge. 
On transferring such a preparation to pure sea-water, the bridge 
will within half an hour or so again transmit waves. Ifa Renilla 
is cut lengthwise on its principal axis so that the halves are con- 
nected only by the distal part of the peduncle, the halves, as 
already stated, will exhibit synchronous waves, which obviously 
have a common starting-point in the distal portion of the pedun- 
cle. If, now, the halves of the split peduncle are spread apart 
and crystals of magnesium sulphate are applied to one of these 
arms (fig. 8), the synchronism of the two halves of the rachis 
soon disappears, showing that one of them, that on the anes- 
thetized arm is no longer under the control of the original 
peduncular center. On washing off the anesthetic and return- 
ing such a preparation to pure sea-water, synchronism in the 
peristaltic waves begins to reappear in about twenty minutes 
and is fully reestablished in thirty-five minutes. Magnesium 
sulphate is an effective temporary means of checking the waves 
of rachidial peristalsis. 
I have been no more successful in exciting artificially rachidial 
peristalsis than I have been in inducing peduncular peristalsis. 
If a dozen contracted Renillas are set aside in as many bowls of 
sea-water and time is given them for partial distention, a number 
