STARFISHES, URCHINS AND SEA-CUCUMBERS 59 
centre of the under side is the mouth with its five white teeth pro- 
vided with powerful muscles which enable them to grind the vege- 
table food upon which the sea urchin lives. The mouth leads into 
a coiled intestine which opens by a pore at the summit of the 
body. Around this opening im the areas devoid of spines, are five 
little pores which are the openings. of the reproductive system. 
In summer the eggs are cast out through these pores, and float 
in the water where they rapidly develop into little translucent 
larvee with reddish spots, and provided with eight long processes 
which are rendered straight and rigid by calcareous rods. After 
swimming about, and devouring small creatures for several weeks 
the sea urchin suddenly develops in the posterior end of the larva, 
most of the body of which is absorbed and withers away in a few 
hours, leaving, upon the bottom, a minute globular sea urchin not 
larger than a pin’s head. 
The Green Sea Urchin, (Strongylocentrotus drobachiensis, Fig. 
25), is found in the deep waters of Long Island Sound but north of 
Cape Cod it occurs in shallow tide-pools, and on the Maine coast it 
literally covers the rocks. It extends into the Arctic Ocean, and is 
found on the north Pacific coast. It may be at once recognized by 
its resemblance to a greenish chestnut bur. The body is flatter 
than a hemisphere, about two inches in diameter and densely cov- 
ered with sharp pointed spines not more than three-eighths of an 
inch long. In some individuals these spines are tipped with dull 
violet. In addition to the spines, there are also a large number of 
little pincers mounted upon rod-like bases. These are used for the 
removal, or retention, of refuse material which may fall upon the 
sea urchin. The five double rows of long, slender, tube-feet allow 
the animal to cling to the rocks over which it slowly glides in search 
of the algw, and small organisms upon which it feeds. It often 
covers itself with bits of seaweed and other fragments. 
The Stinging Urchin, (Diadema setosum), is abundant along 
the Florida coast and in the West Indies, where it is often seen in 
clusters upon the sandy bottoms. These urchins are velvety black, 
about four inches in diameter, and are covered with sharp pointed 
black spines, some of which are fully four inches long. These 
spines wave rapidly about upon the approach of an enemy, and if 
the urchin be seized, they penetrate the skin of the attacking per- 
son and break off, inflicting a most painful sting. 
