180 
EDITH ^r. MUSfHIAVE. 
l)ecomes delicate and meiubranons in character. In the specimen 
represented in the drawing the slender, needle-like, hut slightly flexible 
axis (Ax.), supported by the axial sheath (Ax. S.), does not extend down 
to the base of the stalk as is usually the case in this genus (Marshall, 
p. 56). A close similarity exists between Pennatula and Virgularia 
in the musculature (31. A. A.) controlling the movements of the axis. 
Fig. 13. — Pennatula rubra. Dissection of the stalk from the 
dorsal surface exposing the lumen of the dorsal canal ; X 2. The stalk 
is shorter and of comparative greater thickness than in Virgularia 
(fig. 12), but it is very similar in constitution. In Pennatula the four 
large canals of the stalk are shorter and broader, and the musculature 
controlling the axis less strongly developed. Pennatula appears to be 
less sensitive to contact, and therefore less contractile than Virgularia. 
In the drawing the vertical septum is seen to extend to the extreme base 
of the stalk, so that the ventral canal is equal in length in this region to 
the doi’sal canal (compare Pterceides [fig. 14], Anthoptilum [fig. 
10], etc.). The transverse muscular tissue (T.3I.F.) of the body-wall in 
the neighbourhood of the insertion of the musculature controlling the 
axis is strongly developed to give the necessary additional support. 
The thickening of muscular tissue in this region is more strongly 
marked in P. naresi and P. borealis. In this respect Pennatula 
approaches Pterceides. 
Fig. 14. — Pterceides griseum var. longispinosum. Dissection 
of the stalk from the dorsal surface exposing the lumen of the dorsal 
canal ; X 1|-. The musculature of the body-wall is very pronoimced in 
this genus. The thickened zone in the upper portion of the stalk is due 
in this genus to an extraordinary development of a si^hincter muscle 
(Sph.3I.), in which I’espect it apparently dilfers from all other genera. 
The fibres of the sphincter run almost transversely, and are attached on 
the inner side to the axial sheath and on the outer side to the body- wall. 
This powerful muscle has probably a double function — it may assist in 
the support of the axis, but its chief function seems to be that of con- 
trolling the dilatations and contractions of the stalk, and therefore 
materially assists in regulating the quantity of fluids within the canals. 
At the base of the sphincter muscle are powerful muscle-bands 
(M.B.), which are connected with the axial sheath and body-wall, and 
in addition assist in supporting and controlling the extremely power- 
ful muscular apparatus (31. A. A.) governing the action of the axis 
(Ax.). The calcai'eous axis with its accompanying muscular sheath 
is slightly twisted spirally at its apical and basal termination (fig. 15). 
The whole conformation of the stalk seems to indicate that it is 
specially adapted as a boring organ, working, in this instance, in a 
screw-like fashion, and a’so as a pump woi'king with a slightly piston- 
