1. What is the shape of a simple sponge? What enables a ma.s.s 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 pa.s.ses 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 cla.s.s 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 lat.i.tude?
5. What are some of the difficulties which confront a stationary animal? How are they overcome?
6. To what cla.s.s 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 CLENTERATES
_To show cells working together more definitely than in Sponges_
A Study of Hydra
_Materials._
Living hydras in permanent aquaria, undisturbed. Living hydras in small aquaria, _i.e._ tumblers, test tubes, watch gla.s.ses, etc., with pieces of water weed and if possible some of the microscopic animals found in water where hydras are abundant. If kept cool, hydras may live several days in such aquaria. Permanent slides of hydras; some whole, some in sections, and some showing the organs of reproduction.
_Definitions._
_Proximal end_, the end by which an animal is attached to an object.
_Distal end_, the end opposite the proximal end.
_Tentacles_, slender projections around the distal end.
_Mouth_, the opening through the distal end, into the central cavity.
_Bud_, a small hydra or other clenterate growing out from the wall of the parent.
_Mesoglea_, a thin, gluey part.i.tion, without wandering cells, between the ectoderm and the endoderm.
_Nettle cells_, very small cells, chiefly in the tentacles, easily identified in permanent preparations as clear cells with small hairs
projecting from them. See text-books for details of their structure.
_Spermary_, the region or organ where the sperm cells are formed.
_Ovary_, the region or organ where the egg cells are formed.
_Clenterates_ (hollow bowels), sac-shaped animals, the digestive tract having only one opening; the body wall is of two layers.