MICROSCOrE AT THE SEA-STDE. 71 



been called stinging hairs, as seen at a, figure 1 46. 

 If we suppose several of these hydras placed in 

 little cups upon a common branch or stem, we 

 should have a Sertularia, or such an animal as is 

 represented at Figure 147, Plate 5. These polyps 

 are very common on all our sea-shores ; and the 

 branches and cups are often cast up on the shore, 

 and regarded by the uninstructed as sea- weeds. 

 The branches and cups are called the polypidoms of 

 the animal, and assume a great variety of forms. 

 When the cups are fixed on ringed stalks, they 

 constitute the genus Campamdaria, seen at figure 

 148, plate 5. These cups are often objects of great 

 beauty, as in those of CamjMmdaria volubilis, 

 figured in 149. It is the polypidom which consti- 

 tutes the coral in the family of polyps, producing 

 the masses of carbonate of lime which sometimes 

 cover the bottom of the ocean and form reefs in the 

 sea. In one family of polyps, known as sea-fans 

 {Gorgonia), which are calcareous, the fleshy mass 

 covering the horny polypidom contains spicula of 

 various forms, which are beautiful objects under the 

 Microscope. These spicula are seen at figure 150, 

 plate 5. The red coral of commerce is another 

 interesting form of these polypidoms. In some 

 families of these polyps, as in the campanularidse 

 and the corynidae, the young, before they arrive 

 at their mature stage, assume the forms of minute 

 medusae or jelly-fishes. These are exceedingly 

 beautiful objects for microscopic observation. 



Another family of animals common enough in 

 the sea, are the star-fishes and sea-eggs {Echinoder- 

 mata). Although not themselves microscopic, 

 certain parts of their structure present very in- 

 teresting objects for examination. If a section is 

 made of one of the spines of the common echinus, 

 or sea-egg, it presents under a low power a beau- 



