II4 INVERTEBRATE ANIMALS. 
itself. When fully grown (fig. 46, a) it presents no small super- 
ficial resemblance to some of the Ophiuroddea. When young 
(fig. 46, 4) the.Comatuda is so different in appearance from the 
adult, that it was originally described as a distinct animal. It 
consists now of a little cup-shaped 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 calcareous 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 requires to grow in 
size to become a fully-developed Comazula. 
The stalked condition which we have just seen to constitute 
a merely temporary stage in the life-history of the Comatula is, 
on the other hand, the permanent state of parts in all the “stone- 
lilies” and other fossil Cyzzozdea, and in a few living forms. 
Of these recent species, one of the most remarkable is one which 
has been recently discovered in the Atlantic and North Seas, 
and which has been described under the name of RAdzocrinus 
lofotensts, This curious species (fig. 47) consists of a little 
thread-like jointed stem supporting a calcareous cup, from which 
proceed five branched and jointed arms; 
and the stalked condition is here perma- 
nently retained during life. 
ORDERS V. AND VI. CySTOIDEA AND 
BLASTOIDEA.—These orders merely require 
to be mentioned here, as all the forms in- 
cluded in them are extinct, and are unre- 
iy presented at the present day by living 
ay species, In both, the body is enclosed in 
[5 a kind of box formed by jointed cal- 
= careous plates (fig. 48), and it was in most 
é \ cases permanently fixed to the sea-bottom 
sa oia eset by a jointed stalk or column, The arms, 
which form so conspicuous a feature in 
the true Crinotdea, were either absent or very rudimentary. 
Both orders are most closely allied to the Crinoddea, and they 
constitute probably the least highly developed sections of the 
whole class of the Echinodermata. 
