by Liz LaRosa

www.middleschoolscience.com

Objectives:

• To learn the external and internal anatomy of the earthworm.
• To understand the structure and function of external and internal organs.
• To know the digestive, circulatory, reproductive and nervous system.
• To calculate statistical data on earthworm length and segmentation.

1. Predict the # of segments in your earthworm. _______
2. Does the # of segments relate to the age of the earthworm? ______

1. Obtain a plastic bag and write your name, lab partner, and class period on it.
2. Make a sketch of your earthworm in Figure 1. The ventral side is flatter than the dorsal, label them plus : anterior, posterior, clitellum, mouth, anus.
3. Look at the ventral side of the earthworm with the magnifying lens, look for the oviducts, which hold the eggs, open on the fourteenth segment. The sperm ducts open on the fifteenth. Record in Figure 2
4. Count the number of segments on your earthworm, record in Table 1.
5. Record the length of your earthworm in cm in Table 1.
6. Record how many segments between the mouth and the clitellum in Table 1.
7. Run your fingers along the sides of the worm, towards the ventral side, you will feel bristles called Setae.
8. Pin your earthworm, ventral side down, through the anterior and posterior regions.

Figure 1: Sketch of Earthworm Dorsal side up. Label all parts.

Figure 2: Sketch of Earthworm, Ventral side up. Label all parts.

Table 1: Table of External Earthworm Anatomy

Figure 3: Stem and Leaf of Earthworm segments

Procedure: READ ALL DIRECTIONS CAREFULLY!

1. Turn your tray so that the posterior end faces 12 noon.
2. Take you scalpel and CAREFULLY make an incision towards the anterior end of the worm. DO NOT PRESS TOO HARD OR CUT DEEPLY! Only cut through the skin.
3. As you cut, pin the flaps of skin open, angle the pins on a 45 degree angle away from the worm.
4. Continue making the incision past the clitellum towards the anterior end of the worm.
5. Turn your earthworm so that the anterior end is at noon again.
6. Make a sketch of your open worm from the mouth to the clitellum in Figure 4.
7. Starting at the anterior end, locate and label the following parts in Figure 4: Brain, Pharynx, Esophagus, Crop, 5 Aortic Arches, Gizzard, Intestines.
8. Using the scalpel and dissection needle, remove the crop and gizzard, and intestines. Look for the Ventral Nerve Cord and Blood Vessel.
9. Cut open the crop and gizzard, and intestines and examine the contents.

 

Figure 4: Internal Anatomy of Earthworm, Dorsal side up. Label all parts.

Table 2: Summary Data Table for # of Earthworm Segments.

1. Were you correct in your PreLab predictions?
2. Why would the earthworm have bristles (setae) on the outside of its body? How is it used?
3. Discuss one part of the external anatomy that was interesting to you. Same for internal anatomy.
4. What did you find inside the crop, gizzard and intestines?
5. What was the median # of segments for the earthworm? Use data from Table 2.
6. You are responsible for knowing the parts of the worm in BOLD for this lab!