EXPEUIMEKTAL OBSERVATIONS ON PENNATULIDS. 477 
this portion of the colony is also seen and also its extrusion from the 
basal apertures (B.D.Ap. and B.V.Ap.) of the dorsal and ventral 
canals. The brownish mass (M.) of earth-like matter, which appears to be 
deposited on the vertical septum, may represent an aggregation of 
foi’eign matter sucked in by the sea pen, or waste matter on the point 
of extrusion. In this genus the ventral canal extends to the base of 
the stalk. The four canals of the stalk are shown in ci’oss-section. The 
dorsal canal (D.C.) is the largest, and contains in this region the two 
smaller lateral canals (L.C.), between which the basal end of the axis 
(Ax.) is shown by transparency of the walls of the canals. 
Fig. 2.- — Pennatula rubra. Basal vein of the termination of the 
stalk after injection with carmine particles and a solution of methylene 
blue as in fig. 1 ; x 7. The two large apertures (B.D.Ap. and B.V.Ap.) 
of the dorsal and ventral canals are shoum. Six other apertures are 
also indicated, whicli only became perceptible after injection. Of these, 
two are in close i^roximity to the large dorsal and ventral apertiu'es and 
the othei' four definitely arranged to form the four corners of a square 
(Ap.^„^^). The solid particles were exj^elled from the large apertures 
of the dorsal and ventral canals, and the methylene blue solution 
from the other six ; occasionally solid particles and coloured liquid 
were expelled from a common pore (L.Ap.i.). 
Fig. 3. — Pterceides spinosum. («) Drawing of the basal jDortion of 
the stalk from the left side of a living specimen twenty-four hours after 
an injection of caimine and methylene blue, as in fig. 1 ; x 3. Numerous 
apertures are indicated which before the experiment were impercejjtible 
to the naked eye, from which issued streams of methylene blue solution, 
indicated in the dniwing. Carmine particles are also shown in a state 
of extrusion. The arrows indicate the direction of the currents. An 
inhalent cuiTent into the ventral canal was revealed by a prolonged 
immersion of the base of the stalk in methylene blue solution. It is 
possible that the direction of the currents may be reversed or otherwise 
on occasion, (h) The base of the same colony after fixing with formalin 
solution. The contraction of the axial tissues has caused an invagination 
of the basal portion of the stalk, giving the appearance of a single pore 
at the base {F.Ap>.). This appears to be the usual condition in preserved 
specimens, and the apparent presence of a single pore has given rise to 
considerable difference of opinion in the past as to the presence or other- 
wise of a so-called mouth in this region. 
Fig. 4. — Pennatula phosphorea. Drawing of the base of the 
stalk showing inhalent and exhalent apertures; X 30. The two 
apertures in close proximity to the basal, dorsal and ventral apertiu’es 
in the species “ rubra ” were not observed in this species. 
Fig. 5. — Pennatula rubra. Drawing of the dorsal surface of the 
