CRINOIDS. 



146 



true muscles, they seem to have some power of contracting around resisting objects 

 which they touch. The cirri become smaller and closer together near the head, for 

 each cirrus-bearing joint develops immedi- 

 ately below the calyx, and the joints which 

 separate the cirrus-bearing joints from each 

 other develop afterwards. 



In P. asteria the arms divide a second 

 time about six arm-joints above the first 

 bifurcation, and again bifurcate seven or 

 eight joints farther, the bifurcations repeat- 

 ing themselves somewhat irregularly imtil 

 each of the primary arms has divided into 

 twent}- or thirty branches, making more than 

 a hundred arms iu all. 



P. wi/ville-thoinsoni, foimd upon the 

 coast of Portugal, has the cirri separated 

 by thirty to thirty-five joints. The num- 

 ber of arms is not (Miustant, because iu 

 some cases the third radials bear one or 

 two simple arms, while in others there is 

 a third bifurcation. 



Some examples of P. mullei'i, and all of 

 ,P. ipyville-thomsoni, that were dredged by 

 Mr. Jeffreys, showed by the smooth and 

 rounded terminal joint of the stem, by the 

 shortness of the lower cirri, and by the 

 small number of joints in the lower inter- 

 nodes between tlie cirri, that they must 

 have for a long time been free, and Sir 

 Wyville Thomson states his belief that 

 the latter species lives loosely rooted in 

 the soft mud, and can change its place at 

 pleasure by swimming with its pinnated 

 ai'ms. 



P. maclearianits, dredged near the coast 

 of Brazil, has a peculiar style of arm-divi- 

 sion. Each of the ten primary arms stand- 

 ing upon the radial auxiliaries, gives off 

 two secondary arms close to its base, so 

 that there would be in all thirty arms, were 

 the arrangement absolutely regular. The 

 arms are very robust, and the joints have 

 a tendency to widen in the middle of the 

 arm. Each arm has about seventy joints. 

 The cirrus-bearing joints of the stem are 

 very short, and much inflated with round, bead-like knobs, and there are only two 

 very thin plates between the nodes. Su' W. Thomson believes that this form floats 

 about unattached. 



VOL. I. —10 



Fig. 128. — Peutamnue asteria. 



