How To Study Living Animals


The Mouth and the Gills of the Fish
Materials.

The same materials as those used in the preceding exercise may be used here herunterladen.

Directions.

The mouth, its structure and its action, can be seen by pulling the upper jaw upward and forward until the mouth and the gill chambers open fully herunterladen. Examine the structure and action of the jaws, the tongue, the throat, and the teeth on each jaw and on the roof of the mouth.

Investigate the breathing apparatus from the throat side and from the exterior, noting the number, form, and structure of the gills, their attachment and their protection microsoft office kostenlos downloaden vollversion deutsch chip.

The mouth may be kept open by a short splinter or a ball of paper.

The pupil should identify the following structures:—

1. Gill,

an organ for breathing the air dissolved in water.

2. Gill arch,

an arch of bone or cartilage supporting the gills.

3. Gill filaments,

fringe-like structures attached to the gill arches, forming the gills.

4. Gill raker,

lateral projections from the gill arches.

5. Gill-slits,

openings between the gill arches for the passage of water.

6. Operculum,

the flap-like covering of the gills on each side of the head.

Questions.

1. Compared with the size of its body, how wide can the fish open its mouth? What do you infer as to the size of its “bite”?

2. Are the jaws rigidly affixed to the skull? Why should they be so attached, or why not?

3. Of how many pieces is the upper jaw composed? the under jaw?

4. Where are the teeth? Judging from their form, size, and situation, what do you think must be their use?

5. Do you think the tongue is used to assist in mastication? in tasting? in speech? in swallowing?

6. How many gills are there, and where are they situated? How are they attached? Which one is not free from the body throughout its length?

7. What probably causes the color of the gill filaments? What is there in their number and texture which fits them for their function?

8. What is the direction of the water current through the gill chamber? Of what use are the gill rakers?

9. How are the gills protected?

Summary.

Write a complete account of how the fish eats and how it breathes.

Suggested drawings.

a. A front view of the fish’s face, with the mouth fully open.

b. A side view, as above.

c. A ventral view of the head, with both gill-chambers wide open and the gills separated from each other. Indicate currents by arrows.

d. A single gill.