340 NATURAL HISTORY. 
ering of the Turtle. Ifit were not for this arrangement 
the animal would be obliged to leave its shell occasion- 
ally, and have, like the Lobster, a new covering formed. 
590. The Echini (plural of Echinus) are generally found 
on sandy shores. Here they make hollows with their 
spines, and in them lie in wait for their prey. As they 
do this they let their tubular feet play about, and when 
any Mollusk or Crustacean happens to hit a sucker, it is 
at once captured, many suckers taking hold of it, and 
passing it to the mouth to be crushed, and thrust into 
the stomach. 
591. Many of these animals have a powerful and com- 
plex masticating apparatus. It consists of five hard, 
sharp teeth, worked by strong muscles. These teeth are 
attached to bony jaws, and the whole apparatus has twen- 
ty-five pieces, moved by thirty-five distinct muscles. It is 
a powerful mill, reducing to fragments the Crustacea and 
Mollusks which the tentacula capture and force into it. 
592. The most singular of all the facts in regard to the 
Echini is the mode of their development. There comes 
out of the egg an animal covered with cilia, and by the 
waving movement of these, it swims freely about in the 
water. At first it is globular, but it soon acquires a py- 
ramidal form, having a stomach opening below. At the 
same time there are formed four slender, bony rods in 
the four angles of the pyramid, meeting together at the 
top. There are some cross-pieces, also, on the sides of 
the pyramid, connecting the rods together. All this 
time the animal is moving about by means of the cilia, 
which are all over its outside. It is a sort of pyramidal 
tent sailing about. Inside of this the real animal is at 
length formed, and, at the same time, the tent-portion of 
the original animal wastes away. The stomach of the 
animal that comes out of the egg is the only part which 
remains through all this metamorphosis. 
593. There are two orders of the Echinoderms which 
are quite aberrant. One is that of the Crinoidea, which 
