Test both kinds of sponges by dropping a bit of each into weak acid, and noting the results. Also burn a bit of each and notice the odor. _Questions._ 1. What is the shape of a simple sponge? What enables a mass of cells to retain such a definite shape? 2. What seems to be the composition of the skeletons? Why is one type of skeleton rigid and the other elastic? 3. Since sponges are attached for most of their lives to stationary objects, suggest means for obtaining food and oxygen, and for getting rid of waste matter. 4. Although individual cells are sensitive, a sponge as a whole is not. What connection has this fact with the fact that sponges are stationary? 5. Compare simple and complex sponges. _Suggested drawings._ a. A view of a simple sponge. Label everything shown. b. A diagram of a simple sponge split in halves. Show by arrows the path followed by the water as it passes through the sponge. c. A few spicules. d. A few fibers. Summary of Important Points in the Study of Sponges 1. What are two functions of the spicules or fibers? 2. What are at least two of the functions of the endoderm cells? 3. What can you suggest as functions for the ectoderm cells? 4. In what cases do cells show "team work" in accomplishing an object? 5. What degree of specialization is indicated by the fact that the cells may exchange positions and functions? 6. What work can any single cell of a sponge do? Compare the work done by such a cell with that done by a paramecium. 7. What work can a whole sponge do? Compare that with the work done by a paramecium. Review and Library Exercise on Sponges 1. What are the distinguishing characteristics of Porifera? 2. Sponges were once supposed to be plants. In what respect are they plant-like? What made students finally class them as animals? 3. How do sponges reproduce? How are they distributed to new locations? 4. Where, as to depth of water, do most sponges grow? Where, as to oceans? Where, as to latitude? 5. What are some of the difficulties which confront a stationary animal? How are they overcome? 6. To what class of sponges do the "toilet" sponges belong? Why? 7. What conditions are necessary for toilet sponges to thrive? Where are the best ones found? Where are they most numerous? How are they collected? How are they prepared for market? 8. What is man able to do toward raising good sponges for market? 9. Using reference books and museum specimens, describe some especially odd sponges. 3. A STUDY OF CŒLENTERATES _To show cells working together more definitely than in Sponges_ A Study of Hydra _Materials._