438 THE DEPTHS OF THE SEA. [ CHAP. IX, 
amount of passive motion. There are no muscles 
between the joints of the stem, so that the animal 
does not appear to be able to move its stalk at will. 
It is probably only gently waved by the tides and 
currents, and by the movements of its own arms. 
In Pentacrinus asteria about every seventeenth 
joint of the lower mature part of the stem is a little 
deeper or thicker than the others, and bears a whorl 
of five long tendrils or cirri. The stem is, even 
near the base, slightly pentagonal in section, and 
it becomes more markedly so towards the head. 
The cirri start from shallow grooves between the 
projecting angles of the pentagon, so that they are 
ranged in five straight rows up and down the stem. 
The cirri are made up of about thirty-six to thirty- 
seven short joints; they start straight out from the 
stem rigid and stiff, but at the end they usually 
curve downwards, and the last joint is sharp and 
clawlike. These tendrils have no true muscles; 
they have, however, some power of contracting round 
resisting objects which they touch, and there are 
often star-fishes and other sea-animals entangled 
among them. The specimen figured has thus be- 
come the temporary abode of a very elegant species 
of Asteroporpa. 
Near the head the cirri become shorter and 
smaller, and their whorls closer. The reason of 
this is that the stem grows immediately below the 
head, and the cirrus-bearing joints are formed in 
this position, the intermediate joints being produced 
afterwards below and above each cirrated joint,— 
which they gradually separate from the one on either 
side of it, till the number of seventeen or eighteen 
