458 CRIN01DEA. COMATULA. 



of spines or scales. The Ophiurce are much more active in their 

 habits than are the Asterias. Their rays seem very flexible ; and 

 by the contraction of their envelope, they may be moved in all 

 directions. Thus they are able to swim and to walk with con- 

 siderable facility ; as well as to exercise considerable power in 

 obtaining their prey. 



1016. To the Order Stellerida, also, belong the very interest- 

 ing family of Crinoidea ; in which we find some important 

 differences in organisation. This family, which was formerly 

 much more abundant than at present, receives its name from the 

 lily-like form which several of its members present (Fig. 607). 

 The greater part of them, instead of moving freely where they 

 will, are attached, during a portion or the whole of their lives, 

 by a peduncle, or footstalk, to some solid body. And all of them 

 seem to possess two orifices to the digestive cavity. Of this 

 family the Comatula is the most abundant example ; and as its 

 organisation is better understood than that of any other genus, 

 our notion of the character of the group is principally derived from 

 it. In general form, the Comatula does not depart widely from 

 some of the animals just described. The star-like aspect is still 

 regularly preserved ; and the mouth is in the centre of what 

 must yet be regarded as the under surface of the body. The 

 viscera are contained in the central disk, which is composed of 

 numerous polygonal plates. The arms arising from this disk are 

 five in number; but they speedily subdivide, each usually 

 separating into four. These are composed of a number of calca- 

 reous pieces, solid and nearly cylindrical, which are inclosed in 

 a living flesh of greater thickness than the integuments of the 

 Asterice. Thus we have seen the rays, which in the Asterias 

 contained the principal part of the animal, first deprived of the 

 prolongation of the stomach, and then losing their cavity alto- 

 gether, so as to become mere locomotive appendages to the 

 central disk. To the skeleton of the arms, we find that jointed 

 lateral appendages, of a similar structure, are attached ; and these 

 also are clothed with the fleshy integument which secretes them. 

 Between these lateral appendages is a slight furrow, occupied by 

 papillse, which are furnished with vibratile cilia ; and it appears 



