Materials

■ safety goggles

■ live earthworm

■ medicine dropper

■ black paper or piece of cardboard

■ fluorescent lamp

■ 3% aqueous ammonia solution

■ thermometer

■ stopwatch or clock with second hand

■ 2 plastic tubs for water baths

Background

1. How does an earthworm benefit from cephalization?

2. Describe how gases enter and exit an earthworm's body.

water from a medicine dropper to prevent the worm from drying out.

2. Observe the behavior of the earthworm for a few minutes. Identify the earthworm's anterior and posterior ends by watching it move in the pan. As the worm crawls around in the pan, it will lead with its anterior end.

3. Locate the earthworm's clitellum. Is the clitellum closer to the anterior end or the posterior end? What is the function of the clitellum?

4. Identify the earthworm's dorsal and ventral surfaces by gently rolling the worm over. The dorsal surface will be on top after the worm rights itself.

5. Pick up the earthworm, and feel its skin with your fingers. One surface of the earthworm should feel slightly rougher than the other. The roughness is due to the hairlike setae that project from the earthworm's skin. On which surface are the setae located? Use a hand lens to examine the setae up close.

6. Return the earthworm to the pan, and use the hand lens to find a thick purple line running along the dorsal surface of the worm. This line is the dorsal blood vessel. Does the earthworm have an open or a closed circulatory system?

7. Draw a picture of the earthworm, and label its anterior and posterior ends, dorsal and ventral surfaces, clitellum, setae, and dorsal blood vessel.

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