MEMBRANIPORA. 329 
It is oblong, placed between the base of two of the arms, 
and attached to the tentacular rng. Round the opening at 
the top there is a play of cilia, and it is lined with cilia. 
Mr. Hincks had long made this organ the subject of inves- 
tigation, and at length he was rewarded by the following 
discoveries. ‘‘ Specimens of the zoophyte were procured 
in spring, in which the cercarig of Dr. Farre—filamentous 
bodies which are found swimming in the visceral cavity in 
many species of Bryozoa—were present in great abundance. 
In one of these polypes I observed a mass of these cercaria 
wriggling upward from the lower part of the visceral cavity ; 
and each filament, when it reached the base of the organ 
before referred to, was drawn into it and carried through 
it by the action of the cilia lining the interior, and then 
ejected and borne off by the tentacular currents. This ex- 
pulsion went on for three or four minutes, during which 
time the filaments were streaming up incessantly from below. 
After a while a single filament only made its appearance 
occasionally, and at last none were to be seen.” 
Dr. Farre having observed the cercarie in Alcyonium, 
“drifting rapidly to the upper part of the visceral cavity,” 
adds, “it would appear from this that there is some external 
communication with the cavity of the body.” Mr. Hincks 
