1. Drawings to show the pond snail in various positions in the aquarium.
  2. A drawing of the slug.
  3. At least three different types of snail shell.
Summary.
  1. In what respects does a snail show resemblance to a clam?
  2. What are the chief points of difference?
  3. What reasons can you suggest for the better development of the sense organs?
  4. What advantage has a snail over a clam in the matter of getting food?
  5. How does the shell of the snail compare with that of the clam as an organ for protection?

3. THE SQUID—A TYPE OF MOLLUSCA

To show the Effect of a Much Reduced or Rudimentary Skeleton

Materials.

Small squids, and a few large specimens for comparison and dissection.

Definitions.

Cephalopoda, the name of the class to which the squid belongs. Caudal fin, a horizontal structure at the posterior end of the squid. Chromatophores, irregular cells in the mantle which give color to the squid. Exhalent siphon, a funnel or tube opening on the ventral side just below the base of the arms or tentacles. Pen, a remnant of an exoskeleton imbedded in the mantle along the dorsal side. Ink sac, a sac containing a dark, sticky liquid which may be thrown out through the funnel into the water. The opening is near the inner opening of the funnel.

Observations.