2. Identify the head and mouth of the snail. Watch the snail feeding and examine the mouth of the snail with a lens. What do you notice? If your aquarium in which the pond snail is living has a green coating (algæ) on the side, describe its appearance after the snail has been crawling up and down over it. Explain. 3. How many tentacles has a pond snail? a land snail? Where are the eyes located in each case? What movements of the tentacles do you notice? What is their purpose? 4. How does the rate of locomotion of the snail compare with that of the clam? Find out if the snail can creep backwards or on the surface of the water. Does there seem to be any tendency for the snail to go up and down the sides of the aquaria vertically rather than to the right or left? 5. What does a snail do when disturbed? What is gained by this action? 6. Search for pond snail's eggs on the side of the aquaria. Lift up the bits of cabbage on which the slugs are feeding and search for eggs. Describe what you find in each case, noting the size, appearance, and whether the eggs are laid singly or in masses. 7. Find the breathing pore. Describe its position and appearance. 8. Contrast the various types of shells, and note with care in what respects they differ. Holding the shell with the aperture toward you and the spire pointing up, determine whether each shell has the aperture on the right (right-handed shell) or on the left (left-handed shell). Is the right-handed or the left-handed shell more common? 9. (Optional) By means of some book in the laboratory, determine the scientific name of each of the snails found in the various aquaria in the laboratory. _Suggested drawings._ a. Drawings to show the pond snail in various positions in the aquarium. b. A drawing of the slug. c. 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.