190 Prof. M‘Intosh’s Notes from the 
The filaments taper from base to apex, and end in a some- 
what long non-ciliated process contaiming a blood-vessel 
and which in life projects beyond the pinne, though in the 
preparations the long terminal pinnz extend even beyond 1t. 
The pinne are long throughout, and are richly ciliated. 
No skeletogenous elements are present in these or in the 
filaments, which, however, have a band of muscular fibres 
passing from the base to the tip, but they do not appear to 
enter the terminal process. ‘he entire branchial system, 
indeed, is eminently contractile and under voluntary control. 
The cilia on the pinne are large and long, and appear to be 
under the control of the animal, since they remain quiescent 
for a time and then commence to vibrate rapidly. The 
branchiz on the approach of danger are shortened, grouped 
together, and drawn in, the operculum following and closing 
the tube. The pinne havea dotted aspect from the grouping 
of the cilia in tufts, though this may only be apparent ; 
moreover, the movement of each pinna is independent of the 
others, so that it bends downward, jerks inward, and per- 
forms various motions with celerity and accuracy. ‘The 
wall is composed of firm mucoid (hypodermic) cells and a 
greenish blood-vessel occurs in the centre, the fluid therein 
being devoid of corpuscles. In contraction the pinne are, 
by their muscular elements, only slightly shortened and 
narrowed, so that when the branchial apparatus is again 
unfolded the elastic nature of the tissues readily restores 
them to the former size. 
The operculum is funnel- or vase-shaped, hollow at the 
tip, and gradually dilating from the stalk upward. The 
distal plate is calcareous (effervescing under HCl) and the 
muscular fibres pass from the pedicle to the eularged oper- 
cular region, in which they spread out in a fan-like manner 
to be attached to the distal cup. No trace of a central 
cavity exists in this form, though a calcareous mass occurs 
in the centre below the operculum, and its shape differs from 
that in the developing young of other forms. 
When removed from its tube the anterior region of the 
body is pale, but the rest is of a pale grass-green. It is 
widest anteriorly, and tapers posteriorly to a bluntly conical 
tail, a rounded papilla being on each side of the anus. The 
anterior region has four pairs of bristle-bundles, whilst the 
posterior region consists of nineteen or twenty segments. No 
cilia were observed on the anterior region, but they occurred 
dorsally on the swollen greenish posterior region, and were 
vigorous toward the tail—indeed, by far the greater part of 
the body is supplied with cilia. 
