98 LIFE, IN ITS LOWER FORMS. 
occasion to notice, — all present the same structure, which 
is thus eminently characteristic of the class, — a transpa- 
rent, hard, brittle, crystalline deposit, hollowed into num- 
berless isolated cells. These cells are sometimes so nume- 
rous that the solid matter is reduced to a scries of slender 
bridges and attenuated pillars, when, though the beauty 
is much enhanced, the fragility is in proportion. 
It is interesting also to observe the flexibility which is 
imparted to the long rays of the Brittle-star. Though 
composed of rigid and fragile plates, a wonderful flexibility 
is afforded to it by their number and arrangement ; and 
whoever has watched, either by its native sea-shore, or in 
the tiny mimic ocean which the marine aquarium furnishes, 
one of these animals twining over the shells aud stones 
that lie on the bottom, as it pursues its rapid but devious 
course, must have been struck with the precision and ease 
with which these plaited organs, all bristling over with 
points and spines, catch hold of projections, and drag the 
body along, in much the same manner as a man would do 
if reduced to a prone position, and if all his limbs were 
arms. 
Perhaps our readers think we have made small progress 
in our travels from the Feather-star to the Sea-urchin ; 
still there is an advance ; and in our next chapter we hope 
to shew that the journey is not so long as might be sup- 
posed. 
