How To Study Living Animals


Comparative Study of Cœlenterates
Materials.

Various cœlenterates, such as hydroids, hydro-medusæ, jellyfishes, sea anemones, corals, sea fans, etc herunterladen. Since nearly all the cœlenterates except hydras are marine forms, these will usually have to be dead specimens, preserved in formalin or alcohol, or put up as permanent preparations for the microscope herunterladen.

Definitions.

Colony,

as used in this group, a number of individuals descended by budding from an original one, and remaining connected microsoft office kostenlos downloaden vollversion deutsch chip.

Polyp,

an individual cœlenterate; one of the individuals in a colony.

Observations.

1. How large is an individual specimen in the form you are studying? If the form is colonial, how large is the colony or portion of a colony you are studying? Estimate the number of individuals in it. Is the colony free-swimming or attached? If attached, to what is it usually fastened?

2. Compare the individual you are studying with a hydra, as to size and shape of the body, the location of the mouth, and the size, number, and arrangement of the tentacles.

3. Is there a skeleton? If so, describe it. What appears to be its use? In corals, notice the radiating partitions.

4. Has the specimen any nettle cells? If so, where are they located?

5. Are all the polyps of the colony alike? If not, how many kinds are there? How do they differ?

What is each kind best fitted to do? What is the probable result of this differentiation?

6. What kinds of reproduction, if any, does the specimen you are studying show?

Find out from books what other forms of reproduction are sometimes used by this animal.

Suggested drawings.

a. At least one drawing of each cœlenterate you study.

Summary of the Comparative Study of Cœlenterates

1. How may polyps in colonial forms differ from polyps which live singly?

2. What variations in methods of reproduction are shown in this group?

3. Which of the polyps you have studied shows the greatest differentiation? In what ways?

4. What characteristic do you find common to all the cœlenterates you have studied?