476 G. H. PARKER 
shorten to one-fourth of what was its distended length. If Renil- 
las in a state of contraction are placed in a basin of quiet sea- 
water, in a short time the peduncles of many of them will show 
peristaltic waves, which begin not far from the region where the 
peduncle is attached to the rachis and proceed over the length 
of the peduncle to its distal end (pl. 1, figs. 1 to 4). These are 
the waves of peduncular paristalsis (Parker, 719). 
Such waves, of which never more than one at a time is seen on 
the peduncle, pass over that structure with considerable fre- 
quency. ‘Thus in a Renilla, that may be taken to represent the 
normal state, ten waves passed over the peduncle in 360 seconds, 
hence at the rate of one wave every 36 seconds. The periods 
occupied by the actual passage of the waves varied from 26 to 
28 seconds, and averaged 27.4 seconds; therefore the average 
resting period for the peduncle as a whole was 8.6 seconds, the 
difference between 36 and 27.4 seconds. ‘The distance traversed 
on the peduncle by one of these waves was about 30 mm., and 
as this distance was covered on the average in 27.4 seconds, it 
follows that the average rate of progress for the wave over the 
peduncle was a little less than 1.1 mm. per second. This deter- 
mination applies to animals in sea-water at a temperature of 
23°C. Attempts to ascertain the influence of change of temper- 
ature upon this rate were unsuccessful, for colonies of Renilla 
that were put into sea-water much warmer or much colder than 
what was normal for them never showed peduncular peristalsis 
clearly enough to allow of measurement. 
Peduncular waves can be seen on excised peduncles, though 
from the fact that these are not distended with water the waves 
are less conspicuous than when they are seen in normally attached 
peduncles. They arise in the severed peduncles at less frequent 
intervals and with less regularity than in the attached ones. 
Thus in a severed peduncle they occurred at intervals varying 
from 110 to 400 seconds instead of every 36 seconds. Because of 
the collapsed state of such preparations, the moment of their 
beginning and ending could not be determined with accuracy, 
hence it is impossible to state their rate under such circumstances. 
So far as could be judged by the eye, however, the waves traversed 
