EXTERNAL STRUCTURE :

Examine the external surface of the earthworm closely. Notice the CLITELLUM, a smooth swollen area toward the anterior end of the worm. Feel the bristles called SETAE along the ventral side. Note the PROSTOMIUM or "upper lip".
 

INTERNAL STRUCTURE:

Place a paper towel and a worm in a dissecting pan. Beginning toward the posterior end, make a cut in the dorsal side of the worm. Be careful to lift the skin away from the organs underneath. Use your scissors to cut all the way to the anterior end.

You may want to pin the worm in place to make the cutting easier. Expose the body organs by spreading the body walls apart. Pin the skin back by breaking the SEPTA (membranes that separate the segments) with a pin.

The body cavity exposed is called the COELOM. Beginning at the anterior end, trace the digestive system and label the parts on the drawing. Locate the following parts:
 

PHARYNX - Segments 2-5

ESOPHAGUS - Segments 6-15

CROP - Segments 15-16

GIZZARD - Segments 17-18

INTESTINE - Segments 20 to end
 

Notice the DORSAL BLOOD VESSEL running along the dorsal survace of the intestine. Trace it anteriorly to the AORTIC ARCHES located in segments 7-11.
 

Notice also the reproductive organs. The SEMINAL VESICLES are the most conspicuous male reproductive organs, located in segments 9-12. The TESTES, located in segments 10-11, cannot usually be seen.
 

The female organs called SEMINAL RECEPTACLES are located in segments 9 and 10. The OVARIES are located in the septum between segments 12 and 13, and may be too difficult to find.
 

The BRAIN is located on the dorsal side of the body in the third segment. It is connected by two nerves to the VENTRAL NERVE CORD which runs down the ventral side of the body. Locate the GANGLIA, swollen nerve centers on the nerve cord in each segment.
 

The NEPHRIDIA, small white tubules, can sometimes be seen in the segments. These tubules remove nitrogenous wastes as our kidneys do.
 

When you have located all of these structures and are confident that you know them well enough to identify them on a test, you may throw the worm away, wash out the pan, and CLEAN UP YOUR AREA!