182 THE BOTTOM OF THE SEA. 



perfection it may be compared to a tree. MariDe 

 plants are generally attached to it, and at its ex- 

 tremities are stalks analogous to those of flowers. 



One entire family of polyps is remarkable for its 

 attachment to a common stalk, which is capable of 

 supporting the colony without fixing itself to the 

 bottom of the sea. The foot buries itself in the 

 nmd or sand, or, better still, the polypier floats in 

 the water. This is the family of pennatulae, of which 

 we will mention only three examples — the pennatula, 

 the virgularia, and the veretillum. 



The virgularia has a rough resemblance to a pen. 

 The polypier is in the form of a cylinder split length- 

 wise. The principal stem does not itself bear any 

 polypi, but the}' are attached, like blossoms, to the 

 short lateral branches which proceed from the stem 

 at equal distances from the top of the polypier almost 

 to its other extremity. 



The Pennatula s^inosa (fig. 32) is destitute ot 

 polyps over the greater part of its surface. They are 

 arranged to the right and left of a large stem, upon 

 fan-like brandies. The foot, which serves to fix 

 the polypier in the sand, is shaped like the hilt of a 

 8 word. 



In the Veretillum cynomorium (fig. 33) the polypi 

 are arranged with great regularity over the greater 

 part of the polypier. They are inserted directly iu 



