60 
pide and the display of its organs, in a way which no needle 
of the anatomist can ever be expected to imitate. 
A feature, however, of great interest in the structure of the 
polypide of Rhabdopleura was very satisfactorily made out 
from my specimens. This consists in a remarkable shield-like 
organ (fig. 2 b ) , which is borne on the convex edge of the body 
of the lophophore. It lies outside of the tentacular crown, the 
haemal side of which it covers and conceals, at least in the 
contracted state in which the polypides necessarily existed 
in my specimens. It is of a somewhat pyramidal form, and 
might be taken for a very large and peculiarly developed 
epistome, were it not that its position, lying as it does to the 
haemal side of the mouth instead of lying between the mouth 
and anus, as well as the phenomena of development to be 
presently described, oppose themselves to this view of its 
homologies. 
It may be that the continuity of the tentacular series 
is interrupted at the base of the shield. The parts, however, 
are at this spot so completely hidden by the shield that an 
examination of living specimens will be necessary, in order 
to enable us to say with certainty whether this be really the 
case, or whether the tentacles pass uninterruptedly round 
the lophophore, as in other hippocrepian forms. In either 
case the shield lies entirely outside of the tentacular series. 
As in other hippocrepians, no gizzard is here developed in 
the alimentary tract. 
From the anal side of the alimentary canal at some dis- 
tance above the fundus of the stomach, a flexible cord, the 
“funiculus” (fig. 1 c, c, c, fig. 2 d, d), passes backwards 
until it reaches the rod to which it then becomes attached. 
The flexibility of the funiculus contrasts with the rigidity of 
the rod ; and during life it must have freely yielded to the 
motions of the polypide in the acts of exsertion and retraction. 
Indeed, its extensibility must be very great in order to allow 
of the exsertion of the polypide from the extremity of the 
tube. It is accompanied by a long fasciculus of muscular fibres 
(fig. 2 d'), which is attached to the chitinous rod at the point 
which gives attachment to the funiculus ; and at the point 
where this is attached to the body of the polypide it divides 
into two bands, one passing along the right side, and the other 
along the left side of the body, to be attached, each at its own 
side, to the pharynx below the lophophore. These fibres 
constitute the great retractive muscles of the polypide. 
But besides conducting the retractor muscles to their 
point of attachment to the rod, the funiculus usually pre- 
sents a series of dilatations. A greater or less number of 
