36 MECHANICAL FUNCTIONS. 



denotes a mass of these animals, and polype, a single 

 animal. 



20. This order embraces many species of very simple 

 animals, chiefly inhabiting salt water. Some of them are 

 exceedingly minute, while others are several inches in 

 length. 



21. Each of these curious animals is formed of a tube, 

 attached by its lower end to some solid substance, the 

 upper end being surrounded by a number of flexible 

 fibres, or arms, called tentacula. These tentacula radi- 

 ate from a common centre, in the midst of which is the 

 mouth of the animal. A single polype is represented 

 by Fig. 3. The tentacula are eight in number, Fig- 3. 

 but in some species are much more numerous. 



The arrangement of these, on the margin of the 

 mouths of the animals, bears a considerable re- 

 semblance to a flower with radiating petals, as 

 the daisy and aster. 



22. Polypi for the most part reside in cells, or 



tubes, composed of horny or alcareous matter, in the 

 form of sheaths, which enclose the body of the animal, 

 leaving the tentacula and mouths free for action above 

 their margins. Sometimes these tubes are joined to- 

 gether endwise, like the branches of a Fl ; 4 - 

 tree, leaving lateral apertures for the pro- 

 tusion of the tentacula of each animal, 

 as shown by Fig. 4. In this figure each 

 bundle of radiating fibrils along the 

 branches represents the tentacula of a 

 polype. 



23. The well-known marine substance 

 called coral is the product of the la- 

 bors of certain species of these indus- 

 trious animals. A great number of 



species are perpetually employed in the construction of 

 different varieties of this substance. Coral is composed 

 of calcareous particles, with a portion of animal, and 

 occasionally coloring matter elaborated into a solid, or 

 porous form, by these animals. 



What does polype mean? Polypus? Polypi? Describe a polype? 

 What are teutacula? What common flowers do these animals resemble ? 

 What does Fig. 4 represent? 



