126 
STRUCTURE OF ECHINODERMATA. 
of a great number of pieces, very regularly arranged and 
united together (fig. 69, e); but these pieces are for the most 
Fig. 67. —Holothuria. 
part only repetitions of one another; and the different 
portions have not that variety of uses which we see in higher 
animals. With the exception of 
the tribe of Encrinites or lily-like 
animals (fig. 68), of which there are 
very few now existing, but which 
were very abundant in former ages, 
all the animals belonging to this 
class are unattached, and are capa¬ 
ble of moving freely from place to 
place. Their motions are very 
sluggish, however, and are princi¬ 
pally effected by means of an im¬ 
mense number of minute tubular feet 
(fig. 68, c ), furnished with suckers 
at their extremities, which can be 
projected from almost any part of 
the body. These are seen in rows 
on the under side of each arm of 
the Star-fish; they are put forth 
through rows of very minute aper¬ 
tures in the shell of the Sea- 
Urchin (commonly termed the Sea- 
Fig. 68 .—Encrinite. 
