Page:First course in biology (IA firstcourseinbio00bailrich).pdf/344

 Why is a smooth shell suited to a clam and a rough shell suited to an oyster? Why are the turns of a snail's shell so small near the center?

Why does the mussel have no use for head, eyes, or projecting feelers? In what position of the valves of a mussel is the hinge ligament in a stretched condition? How does the shape of the mussel's gills insure that the water current and blood current are brought in close contact?

The three classes of mollusks are: the pelecypoda (hatchet-footed); gastropoda (stomach-footed); and cephalopoda (head-footed). Give an example of each class.

Comparison of Mollusks

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+==========+==========+==========         |    |     |  +++ Shell     |          |          | +++ Head     |          |          | +++ Body     |          |          | +++ Foot     |          |          | +++ Gills    |          |          | +++ Eyes     |          |          |

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+==========+==========+==========

Comparative Review.—(To occupy an entire page in notebook.)

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+===========+========+========+=========+=========           ||  ||| +-+++-+-            |           |        |        |         | Bilateral   |           |        |        |         | or radiate |           |        |        |         | +-+++-+- Appendages |           |        |        |         | for        |           |        |        |         | locomotion |           |        |        |         | +-+++-+- Names of   |           |        |        |         | divisions  |           |        |        |         | of body    |           |        |        |         | +-+++-+- Organs and |           |        |        |         | method of  |           |        |        |         | breathing  |           |        |        |         | +-+++-+-           |           |        |        |         | Locomotion  |           |        |        |         | |          |        |        |         |

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+===========+========+========+=========+=========