EXPERIMENTAL OBSERVATIONS ON PENNATULIDS. 457 
tlie whole into a tank of sea-water, so as to entail as little 
diffusion of liquids as possible. 
After an interval of two hours the colony was examined in 
fresh sea- water, when it was found that the coloured fluid had 
been absorbed by a single pore only. This proved to be the 
basal ventral aperture of the large ventral canal (fig. 3a, 
B.V.Ap.). Carmine particles were still observed in the act 
of extrusion in considei’able quantity from the basal, dorsal, 
and other apertures. 
This experiment indicates the simultaneous presence of 
an inhalent current into the ventral canal, and several 
“exhalent” currents, the principal one being from the large 
dorsal canal to the exterior (fig. 3). 
It is by no means proved that such conditions always 
prevail. It is very probable that under certain conditions the 
currents may be entirely inhalent or entirely exhalent; the 
direction of the current is doubtless dependent upon the 
individual requirements of the colony and responsive to 
stimuli from within. This matter is further discussed on pp. 
470 and 471 . 
The stalk of a second specimen of Pterooides spinosum 
was placed in a narrow-necked vessel as before, but the 
vessel contained in this instance finely powdered particles of 
carmine. After several hours had elapsed the stalk of the 
colony was opened and examined, but no trace of carmine 
was observed in any of the canals. 'I’lie currents during the 
experiment may have been entirely exhalent, but there seems 
sotne evidence for the supposition that the colony has the 
power to some extent of filtering the sea-water as it enters 
the canals basally. AYe have reason to believe that such 
is not always the case, for in other Pennatulids particles of 
earthy foreign matter are frequently observed in the large 
canals near the base of the stalk (cf. Pennatula rubra, 
as indicated in Plate 26, fig. 1). 
On the third day specimen No. 1, which still remained 
apparently healthy and responsive to stimulation, was injected 
with a solution of methylene blue from the ventral canal about 
