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.
  1. A front view of the fish's face, with the mouth fully open.
  2. A side view, as above.
  3. A ventral view of the head, with both gill-chambers wide open and the gills separated from each other. Indicate currents by arrows.
  4. A single gill.
The Alimentary Canal and the Circulatory System of the Fish
Materials.

Small fresh fish, shallow pans or dishes of water, forceps, and scissors.