ACTIVITIES OF COLONIAL ANIMALS 477 
the severed, collapsed peduncles about as fast as they did the 
distended ones. As a rule, peristalsis is not to be observed on 
peduncles that have been ligated in a distended condition and 
then cut from the colony. Apparently this procedure inhibits 
the movement: In an exceptional case, however, a distended 
severed peduncle showed peristaltic waves at the rate twelve 
in 15 minutes or one in 75 seconds, about half as fast as the nor- 
mal rate, though much more rapid than in the case of severed, 
collapsed peduncles. 
If a contracted Renilla is placed in a shallow aquarium of sea- 
water that is partly filled with sand, it will usually quickly show 
peduncular peristalsis and, directing its peduncle downward, it 
will soon anchor itself in the sand by means of this structure. 
The peduncular waves running from the attached end to the tip 
of the peduncle give rise to alternate enlargements and contrac- 
tions, especially of the distal portion of the peduncle, precisely 
the kind of movement that is appropriate for burying this struc- 
ture in the sand It is therefore probable that this form of peri- 
stalsis is primarily concerned with the process of sinking the 
peduncle into the substrate and thereby anchoring the Renilla. 
It is to be noticed, however, that contracted Renillas as soon as 
they commence to show peduncular peristalsis not only begin to 
anchor themselves, but also start to distend. This occurs even 
when the animal is in a glass basin of sea-water without sand 
and is thus unable to sink its peduncle. When I first had the 
opportunity of studying living Renillas, in 1916, I observed the 
distention of colonies at the same time that peduncular peristal- 
sis was in progress, and as these two processes were invariably 
associated in the few specimens that I had to work with at that 
time, I concluded that peduncular peristalsis was an operation 
by which the colony became filled with water, and not one con- 
cerned with anchorage. Since then I have had the opportunity 
of experimenting on a much larger number of individuals and 
I have seen specimens of Renilla in which the peduncles have 
been ligated and cut off fill themselves with sea-water This 
observation shows that the peduncle is not essential to this oper- 
ation, as I once believed, and it is my opinion at present that 
