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 balow and above each cirrated joint, 

 which they gradually separate from the one on either 

 side of it, till the number of seventeen or eighteen 



