396 Prof. J. Reid on the Anatomy and 
the hinge-process is not unfrequently found in the position into 
which it is brought by the action of the elevator muscle. These 
muscular fibres present no transverse strie, can contract and relax 
with rapidity, and become shorter and thicker during their con- 
traction. ‘The movements of the body upon the polypidom are 
effected by the pedicle, and are as follows:—Suppose it to be 
attached to one of the edges of the polypidom, and the concave 
or upper surface to be looking upwards in the line of the long 
axes of the cells, it can turn “Slow ly outwards over the edge of 
the polypidom until its concave surface looks directly outerward, 
and it then returns to its former place: it may also turn in- 
wards until the concave surface looks across the cells. This 
movement being suspended, it exhibits at intervals a nodding 
motion, the concave and convex surfaces being alternately de- 
pressed towards the anterior surface of the polypidom. When 
the concave surface is carried downwards, the hinge-process is 
slightly separated from the body; but when the convex surface 
is depressed, it 1s again approximated. These last movements 
of the hinge-process are probably in a great measure mechanical, 
and occasioned by it rubbing over the surface of the polypidom 
during the downward motion of the concave surface. The pedi- 
cle consists of two parts: a posterior and dense portion which is 
attached to the internal surface of the inferior edge of the pro- 
cess of the polypidom to which it is fixed, and passes inwards 
through the inferior aperture in the concave surface of the body 
to be inserted into the lower part of the imternal surface of the 
convex surface of the body; and an anterior portion, more trans- 
lucent and less dense, which is prolonged downwards into the 
process, and forwards to the middle aperture in the concave sur- 
face of the body and the attached end of the hinge-process. In 
the noddmg movements when the convex surface is moved down- 
wards, the ‘posterior edge of the pedicle contracts and becomes 
bent so as to form an acute angle; and it relaxes while the con- 
cave surface of the body is moved downwards, resembling the 
contractile movements of the stalks in Pedicellina echinata. 1 
have never had an opportunity of observing the changes in the 
pedicle durmg the other movements of the body under a high 
magnifying power, as this can only be done under certain condi- 
tions not easily to be obtained. ‘The anterior portion of the 
pedicle has more of the appearance of a membranous than a con- 
tractile structure, and contains several small nucleated cells. A 
similar structure is found in the upper chamber of the body, 
and is prolonged through the upper aperture in the concave sur- 
face into the hinge-process. I have not been successful in ob- 
serving contractile movements in this structure, if it really pos- 
sesses this function, and I believe that it is more connected with the 
