4(36 
EDITH M. MUSGRAYE, 
internal transverse musculature, which assumes the form of an 
extremely powerful “sphincter muscle” (fig. 14, Sph.^I.), 
whose dense and numerous fibres are attached internally to 
the integument of the axis and externally to the body-wall, 
where a slightly increased development of the musculature 
has arisen in that region to support this extraordinary 
development of muscular tissue. 
Between the attachment of the muscular fibres to the body- 
Avall are the numerous apertures {Ap.) of the canals of the 
spongy tissue. 
The chief function of the “Sphincter muscles” is 
obviously that of dilating and contracting the diameter of 
the stalk in the region immediatel}^ inferior to the rachis, and 
thereby opening and closing the lumen of the canals. It 
may therefore be regarded ‘ as a very important factor in 
instituting and maintaining the circulation of fluids within 
the colony. This matter is further discussed on p. 473. 
It apparently also serves as a double fulcrum in supporting 
the axis in a vertical position (p. 468), and assists also in the 
support of the “oblique musculature” of the stalk, with 
which it doubtless acts in conjunction (fig. 14), p. 470. 
4'he Axis. 
The axis of Pennatulids is usually mainly calcareous; but 
in Pteroeides it is not wholly so, but contains in addition a 
considerable proportion of dense,hard, horn-like matter, which, 
owing to its insolubility in acid and other solutions, renders 
the cutting of satisfactory sections an extremely difficult and 
patience-exhausting task. In all cases the axis is enveloped 
in a sheath-like integument (figs. 11, 12, 13), delicate and 
membranous in smaller forms (e. g. Pennatula phos- 
phor e a), but usually extremely tough and of considerable 
density in robust types (Anthoptilum and Pteroeides). 
The axis varies according to the magnitude and density of 
the colony in length, breadth and thickness. In Pennatula 
phosphorea it is remarkable for its exceeding tenuity. In 
