EXPERIMENTAL ORSERVATIONS ON PENNATULIDS. 481 
like movement in the cavity of the dorsal canal when the mnscula- 
ture contracts. This would give an impetus in an upward direction 
to the ciuTents entering at the basal apertures. As in other genera 
the musculature of the body-wall is less well developed near the 
base, its ^jlace being occiipied by the spongy hydrostatic tissue, 
which is abundantly supplied with canals having numerous apertm’es 
into the lumen of the canals and also to the exterior (fig. 3). In living 
specimens this portion of the stalk is often considerably dilated. In the 
drawing numerous apertures (Ap.) are indicated, which are arranged in 
two vertical rows, one on the left the other on the right of the drawing, 
between the insertion of the muscular fibres of the muscular apparatus 
controlling the axis, which establish communications between the lumen 
of the large canals and the canal of the spongy tissue lining the body- 
wall. 
Fig. 1.5. — -Pteroeides caledonicum. Dissection of the upper 
poi’tion of the rachis from the dorsal sitrface exposing the lumen of 
the dorsal canal (D.C.) to show the musculature conti’olling the ajDical 
portion of the axis, which is slightly twisted spirally when the muscles 
are contracted, as indicated in the drawing; X 1^. The corresponding 
twist of the basal portion of the axis in this genus is indicated in fig. 14. 
The musculature and thickness of the body-wall is moie jjronounced in 
this specimen than in that of the species Pt. griseum (fig. 14). 
