10.'^ 



IXVEETEBRATE ANIMALS. 



When young, the ComaUda is so different in appearance from the 

 adult, that it was originally described as a distinct animal. It con- 

 sists now of a little cup-%haped disc with ten radiating arms above, 



produced by the splitting into 

 two of five primary rays, and 

 furnished inferiorly with a 

 little flexible column or stalk 

 composed of a number of cal- 

 careous joints. By this jointed ' 

 stem the body is at this period 

 of life fixed to sea - weeds 

 or other submarine objects. 

 When sufficiently mature, 

 however, the body drops off 

 its stalk, and then only re- 

 quires to grow in size to 

 become a fully developed 

 Comatida. 



The stalked condition which 

 we have just seen to constitute 

 a merely temporary stage in 

 the life -history of Comatida 

 is, on the other hand, the per- 

 manent state of parts in all the 

 " Stone - lilies " and in most 

 other fossil Crinoidea, and in 

 a few living foi-ms. Of the 

 living stalked Ciinoids the 

 ones with which naturalists 

 have been longest acquainted 

 are the species of Pentaorinus, 

 from the seas of the West 

 Indies. Recently a number of' 

 stalked Crinoids have been 

 obtained from great depths in 

 the sea, showing (hat these 

 ancient types still survive, 

 though in much diminished 

 numbers. One of the most 

 interesting of these deep-sea 

 Crinoids is the little Rhiiocrinus lofotensis (fig. 67), which seems 

 to be distributed over the whole of the deeper portions of the 

 North Atlantic. 



Fig. 67. — Rhizocrinus lofotensis, a living 

 stalked Crinoid (after Wyville Thomson), 

 four times tlie natural size, a Stem ; b 

 Cup ; c c Anns. 



