256 NATURE-STUDY 



structure. Both are protected with a calcareous shell pro- 

 vided with knobs or spines. When the animal is killed the 

 fleshy parts decay, leaving the shell, and this is all that we 

 see in the specimens often found in the homes as curios. 



The Coral Polyp, being of so much importance in geography 

 and geology, should not be omitted. It is one of the lower 

 animals that in its fixed growth is almost plant-like. Essen- 

 tially this animal is a little fleshy sac, with an orifice or mouth 

 at the top, which is surrounded by a number of arms or ten- 

 tacles. These arms wave about in the water and draw minute 

 animals into the mouth. The coral polyp forms a hard 

 deposit of lime carbonate in the lower part of its body-wall, 

 and this is what remains after the death of the creature. It 

 is this part which is used for ornaments, and which builds 

 up great coral reefs and islands in the sea. Many large rock 

 areas in the earth are made of coral limestone deposited in 

 some former age. The branching of corals is due to the fact 

 that these animals have the power of producing buds on 

 their sides, which develop into other polyps and remain con- 

 nected with the parent animal. 



Show pictures of the coral polyp, diagrams to show its 

 structure; and pieces of coral skeleton of various kinds. The 

 coral polyp is appropriately studied in connection with Florida, 

 or the islands of Polynesia, in geography. 



In our fresh-water lakes and streams we have an animal 

 that resembles the coral in many respects, except that it forms 

 no skeleton. This is the Hydra, which may often be seen in 

 aquaria attached to the sides. If one of these can be found 

 it should be used to illustrate the general appearance and 

 habits of the coral. 



Another very low animal, also of fixed location, is the 



