362 G. H. PARKER 
Sufficient facts have now been brought together to allow the 
formation of a reasonable hypothesis as to the course of the 
water through the Renilla colony. (In a resting expanded Re- 
nilla water is entering the animal through the innumerable pores 
of its lateral siphonozodéids (fig. A).) This water enters in conse- 
quence of the ciliary action of these zodids. It fills the open 
spaces of the rachis and from time to time escapes to the exterior 
by passing either directly through the minute pores of the rachis 
tissue into the superior canal and out of the axial pore or indi- 
rectly by passing down the inferior canal of the peduncle to its 
—_ 
Fig. A Diagram of a median section of the rachis (R) of Renilla and of the 
peduncle (P) showing lateral siphonozodids (L), autozodids (A), inferior 
canal (J), superior canal (S), and pore of the median siphonozcéids (MW). The 
direction of the current of water in a resting individual is shown by the 
arrows. 
distal half where it may pass freely over into the superior canal 
and thence to the axial pore and out. Of these two outward 
courses that through the peduncle is much the freer and probably 
the more usual one to be followed. 
An indication of the relative freedom of these two courses, 
as well as a check on the correctness of the hypothesis just ad- 
vanced, may be gathered from the following experiments. If the 
peduncle of a fully distended Renilla be tied off tightly in the 
region where it emerges from the rachis, the animal will contract 
its musculature vigorously, but its volume will remain almost 
