ACTIVITIES OF COLONIAL ANIMALS Sit 
Renilla they are represented not only by the peduncle, but by 
the rachis, the contained nerve-net, and like parts. Such super- 
organs give a unity to a colony that would be entirely unexpressed 
in the individuals of which it is composed. 
SUMMARY 
1. Renilla shows two forms of peristalsis: peduncular, with 
waves running distally over the peduncle, and rachidial, with 
waves running in the opposite direction over both peduncle and 
rachis. 
2. In ordinary peduncular peristalsis the waves occurred once 
every 36 seconds; the time of passage of the waves averaged 
27.4 seconds with an average period of rest between waves of 
8.6 seconds. The wave progressed over the peduncle at the rate 
of 1.1 mm. per second. 
3. Peduncular waves have been seen on excised peduncles. 
4. Peduncular peristalsis is primarily concerned with sinking 
the peduncle into the sand and thus anchoring the animal. It is 
also the means of bringing about a complete withdrawal of the 
animal under the sand and of a certain amount of locomotion. 
It is secondarily concerned with the distribution of fluid within 
the animal during distention. 
5. In rachidial peristalsis the waves occurred once in about 
every 130 seconds; the time of passage of the wave averaged 
about 115 seconds, with an average period of rest between waves 
of 15 seconds. The waves progressed over the colony at the 
rate of 1.2 mm. per second. 
6. Rachidial waves will pass around any number or variety of 
incisions in the colony so long as organic continuity is maintained. 
7. Separate pieces of Renilla show rachidial waves. When 
these pieces are from symmetrical regions, they agree in rate; 
when they are not, the rates are different; the rate is most rapid 
in the peduncle and least so in that part of the rachis farthest 
from the peduncle. The peduncle is the pacemaker for the 
system of rachidial waves. 
8. Rachidial waves are temporarily checked by magnesium 
sulphate. 
