478 G. H. PARKER 
peduncular peristalsis has to do primarily with sinking the pedun- 
cle into the sand and that it is only incidentally concerned with 
pressure relations in the interior of Renilla whereby distention 
is accomplished. Individuals that are undergoing inflation very 
commonly show peduncular peristalsis and inflate more rapidly 
than those in which the peduncles are quiescent. I, therefore, 
believe that peduncular peristalsis is ‘an aid in this process, but 
I am convinced that I was mistaken in my first opinion that this 
operation is essential to inflation. Inflation apparently depends 
primarily upon the currents of water generated in the lateral 
siphonozodids, currents that, as I have pointed out elsewhere 
(Parker, ’20), are without doubt ciliary in origin. 
Peduncular peristalsis is one of the commonest movements in 
Renilla. If a dozen specimens are made to contract and empty 
themselves of their contained water and are then placed in a 
glass vessel of sea-water, within a quarter of an hour half of 
them perhaps will show peduncular peristalsis. If those showing 
peristalsis are moved or otherwise disturbed, their activities 
immediately cease, to begin again only after an interval of quies- 
cence. The operation is, therefore, one freely open to external 
influences, and yet I have never been able to find any means of 
exciting it artificially beyond that of causing a colony to dis- 
charge its contained water and then allowing it to refill. While 
this is going on peduncular peristalsis is likely to take place. 
Wilson (’83, p. 783) has called attention to the fact that in 
the young of R. reniformis a peristaltic wave can often be seen 
passing over the colony from the end at which the rachis is 
forming to the tip of the peduncle. Each wave results in a 
forward projection of the peduncle, which thus enables the ani- 
mal to creep in that direction. The same he says is true of the 
adults. This statement I can confirm for R. amethystina, for 
the adults of this species not only anchor and eventually bury 
themselves in the sand by means of peduncular peristalsis, but 
they will also slowly plow through the substrate by this means. 
In the first instance of this kind that I observed the Renilla was 
in sea-water in a shallow aquarium whose bottom was covered 
with a few inches of sand. The animal when discovered was 
