52 A HALF-HOUR WITH THE 



iu water. The water must be first decanted from 

 the coarser particles of chalk, and in subsequent 

 deposits the foraminifera will be found. They may 

 be obtained from dry sand in which they are con- 

 tained, by throwing the sand into water, when the 

 sand will sink and the foraminifera will swim on 

 the surface, and may be skimmed off. They are 

 best examined as opaque objects. 



The family of polyps will next command atten- 

 tion. One of the most simple forms of this family 

 is found in ponds and rivers, and is called the 

 fresh-water polyp or hydra (Fig. 144, PL 5). It 

 may be easily observed adhering to plants with the 

 naked eye, and needs only a low power with trans- 

 mitted light, to observe it accurately. Its body is 

 cup- shaped, surmounted with eight long tentacles, 

 which it has the power of retracting. It produces 

 young ones by the process of budding, and the 

 buds may be often seen protruding from the side 

 of their parents. It is very tenacious of life, and 

 may be cut into several pieces, and each part will 

 grow into a new hydra. These, with many other 

 polyps and the jelly-fish, have their flesh filled 

 with little hair-like bodies, which, from their pro- 

 perty of stinging in some species, have been called 

 stinging-hairs (a). If we suppose several of these 

 hydras placed in little cups upon a common branch 

 or stem, we shall have a Sertidaria (Fig. 145, PI. 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. Such polyps assume a variety of forms. 

 When the cups are fixed on hinged stalks, they 

 constitute the genus Campanularia (Fig. 146, PL 5). 

 These cups are often objects of great beauty, as in 

 those of Campanularia volubilis (Fig. 147, PL 5). 

 The branches or skeletons on which these polyps 



