RADIATA,. 505 
were gradually withdrawn, but those of the other rays 
were not in the least affected by it. 
Like the other radiata, these animals breathe by means 
of a kind of branchiae or gills, which consist of a fringed 
substance extended along each ray, and communicating 
with the stomach. These all unite under a small circular 
and striated operculum, or cover, which may be observed 
on the back. 
THE SEA-URCHIN. (Echinus.) 
THIS animal, which lodges in the cavities of rocks just 
beneath low-water mark, on most of the British coasts, 
is nearly of a globular shape, not much unlike that of 
an orange, having its shell marked into ten partitions, 
with rows of projections like beads, which divide it. On 
the outside of the shell there are a great number of 
sharp, moveable spines, of a dull violet and greenish 
colour, curiously articulated, like balls and sockets, with 
tubercles on the surface, and connected by strong liga- 
ments to the skin or epidermis with which the shell is 
covered. The mouth is situated in the under-part, and is 
armed with five strong and sharpened teeth. The animal can 
move from place to place by means of its contractile 
tubular feet and its spines ; but its movements are slow 
and laborious. So tenacious are the Sea-urchins of the 
vital principle, that the ancients, according to Appian, 
believed that the body retained life even when cut to 
pieces. 
Sea-urchins, who their native armour boast, 
All stuck with spikes, prefer the sandy coast. 
Should you with knives their prickly bodies wound, 
Still the crude morsels pant upon the ground ; 
You may e'en then, when motion seems no more, 
Departing sense and fleeting life restore. 
z 
