SPIRORBIS GRANULATUS. 403 
(J. G. J.). The species is probably widely distributed in foreign waters, especially in the 
north, but it would be unsafe to specify without careful re-examination. 
The branchiee (Plate CX XXIII, fig. 12a) are pale, or reddish at the base, ten in number, 
and the cuticle of the filaments is thin, so that the hypodermic elements form the main support. 
The filaments taper from base to apex, and end in a somewhat long non-ciliated process 
(Plate CX XII, fig. 7a), containing a blood-vessel, and which in life projects beyond the pinne, 
though in the preparations these extend even beyond it. The pinnz 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. The entire branchial system, mdeed, is eminently 
contractile and under voluntary control. The cilia on the pinne are large and long, and 
also appear to be under the control of the animal, smce 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 pimne have a 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 mward and performs 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 (Plate CX XXIII, fig. 12) is funnel- or vase-shaped, hollow, like a saucer, 
at the distal end, 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 enlarged 
opercular 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 forms with opercular develop- 
ment. Frequently around the edge of the operculum is a fringe of delicate filamentous alge, 
stalked and thecate Infusoria and other organisms. When viewed laterally the opercular 
plate is thin. 
When removed from its tube, the anterior region of the body is pale, or reddish, but the 
rest 1s of a pale grass-ereen. 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 three 
pairs of bristle-bundles, whilst the posterior region consists of nineteen to twenty segments. 
No cilia were observed on the anterior region, but they occurred dorsally on the swollen 
ereenish posterior region, and were vigorous toward the tail; indeed, by far the greater 
part of the body is supplied with cilia. 
The alimentary canal is richly ciliated, and thus the contained cells and granules are 
kept in active motion—a stream of them proceeding posteriorly, and, it may be, escaping 
by a rupture of the body-wall. The intestine contains much dark mud, carried in by ciliary 
action, amidst which are many diatoms and other organic particles, spicules of sponges, 
and a considerable quantity of sand. ‘The intestinal canal is enlarged immediately behind 
the anterior region, and such may represent the stomach, which is muscular, tough, and 
221 
