408 
EDITH M. MUSGEAYE. 
The Musculature of the Axis. 
In all Pennatnlids possessing a calcareous axis, with 
apparently the exception of Virgularia,^ in which the apical 
portion of the rachis is generally missing in captured speci- 
mens, the axis is supported and its movements manipulated 
by two series of muscles : 
The apical musculature in the rachis, which supports 
the upper and apical portions of the axis, and the oblique 
musculature in the stalk, which supports the lower and 
basal portions. 
The concerted action of the two series of muscles would 
extend and contract the axis superiorly and interiorly. Their 
probable function is discussed later. 
In Ptero3ides the axis is further supported by the powerful 
“sphincter muscle’^ of the stalk (fig. 14, S 2 ^h.M.) and by two 
strong muscle-bands to which are attached certain fibres of 
the inferior portion of the sphincter muscle, and numerous 
strong muscle-fibres of the superior portion of the oblique 
musculature (fig. 14, M.B.). 
The apical musculature of the axis is most powerfully 
developed in Pteroeides (fig. 15), in which the whole of the 
apical portion of the axis is enveloped in a muscular sheath, 
from which jiroceed numerous stout and tough fibres which 
run obliquely downwards and are attached to the tissues 
lining the bod}'-wall. In the retracted condition they are 
lightly twisted in a spiral (fig. 15). This spiral twist was 
also indicated, but to a less degree in a dissection of Penna- 
tula phosphorea. 
The chief function of this musculature is obviously that of 
’ This curious and apparently general mutilation of specimens of 
Virgularia, so frequently commented upon by writers, is believed by 
J ungersen to be due to natural causes, and not, as was generally believed, 
to accident. He attributes the absence of the upper leaves and apical 
portion of the rachis to a gradual dying off and atrophy of the older 
apical portion of the colony. 
