CRINOIDEM. 



267 



a rose with five petals. At the base of the stem of this animal-plant, 

 in many of the Crinoideee, we find a sort of spreading root, which is 

 implanted in the rocks, and is capable of growing by itself, and 

 of nourishing the stem. 



The root and stem of the fixed Encrinites seem to indicate that 

 the animal can only live with the head erect. Their normal condition 

 is thus quite different from that of any other of the Echinoderms, 

 almost all of which keep their mouths invariably directed downwards. 



Fentacrinus and Rhizocnnus are chiefly found on rocky beds, or 

 in the midst of banks of corals, at great depths. There, firmly fixed 

 by their roots, their long stems raise themselves vertically; then, 

 with expanded calyx and long-spreading arms, they wait for the prey 

 which passes within their reach in order to seize it. 



The Fenfacritius caput Medusce has, as we have said, been fished 

 up from great depths in the Antilles. It is borne upon a stem of 

 from eighteen to twenty inches in height, terminating in long movable 

 arms, the internal surface of which bears the ambulacral feet. In 

 the middle of the arms is a mouth, and at the side the orifice for the 

 expulsion of the digested residuum. 



The Crinoidese are not, however, all like the two species which 

 have been referred to. There is an entire section of the animals belong- 

 ing to this class, namely, the Comatulidce, which are fixed in their early 

 days, but separate themselves from the rooted stem in their adult 

 age, and, throwing oft" the bonds imposed in their youth, live freely, 

 swimming through the water, or clinging to mussel or oyster banks. 

 Species of the genus Comatula are found in the seas of both hemi- 

 spheres. Their bodies are flat — large calcareous plates form a cuirass 

 upon their backs — presenting, besides, cirri composed of numerous 

 curling joints, the last of Avhich terminates in a hook. The ventral 

 ■surface presents two orifices : the one in the centre corresponding to 

 a mouth, the other evidently intended for the discharge of the pro- 

 ducts of digestion. This animal is provided with five arms, which 

 diverge directly from the centre plate or cuirass. The branches of 

 these aims have a double row of ambulacral feet, in the centre of 

 which is the ambulacral groove, properly so-called. The feet are 

 clothed with vibratile cilia over their whole surface. These cilia 

 guide the current which drives the substances on which the animal 

 feeds — such as the organic spores of sea-weeds and microscopical 

 animalcules floating in the sea — towards its mouth. 



The movements of these curious creatures are very slow, their 

 only object being to catch the bodies of anmials and marine plants, 

 ■ox, by extendmg or contracting their arms, to feel their way through 



