340 NATURAL HISTORY. 



ering of the Turtle. If it 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 



