Earthworm Dissection Lab

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.

Directions: Using pages 79-82 in your INB, write a lab report with the following sections.

Title – Earthworm Dissection Lab

Introduction – Write a 7 sentence introduction. You decide what kind of information is appropriate for this section.

Materials – gloves, goggles, apron, earthworm, dissection pan, dissection tool kit, magnifying glass, paper towel

Procedure – After reading the following procedures, cut and paste them into your INB.

External Anatomy

1. Go back to the sketch you made of the external anatomy of the earthworm on page 76. Use that to help you identify the ventral side (flatter), the dorsal side, plus: anterior, posterior, clitellum, mouth, and anus.

2. Count the number of segments on your earthworm, record in a data table labeled Table 1.

3. Record the length of your earthworm in cm in Table 1. 4. Record how many segments between the mouth and the clitellum in Table 1. 5. 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 these two structures on the external anatomy sketch you made on page 76.

6. Run your fingers along the sides of the worm, towards the ventral side, you will feel bristles called Setae.

7. Pin your earthworm, ventral side down, through the anterior and posterior regions.

Earthworm Dissection Lab

Internal Anatomy

1. Turn your tray so that the posterior end faces 12 noon. 2. Take your 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. Go back to the sketch of the internal worm anatomy on INB page 76. Starting

at the anterior end, locate and label the following parts: Brain, Pharynx, Esophagus, Crop, 5 Aortic Arches, Gizzard, Intestines.

7. Using the scalpel and dissection needle, remove the crop and gizzard, and intestines. Look for the Ventral Nerve Cord and Blood Vessel.

8. Cut open the crop and gizzard, and intestines and examine the contents. Record your observations in Table 1.

Data Table –Create an appropriate data table and label it Table 1 (you may need to go back and reread the procedures so you will know what kind of data you’ll be collecting).

Analysis – Cut and paste these questions into your INB. Leave room to answer them after the lab.

1. Why would the earthworm have bristles (setae) on the outside of its body? How is it used?

2. Discuss one part of the external anatomy that was interesting to you. Same for internal anatomy.

3. What did you find inside the crop, gizzard and intestines? 4. You are responsible for knowing the parts of the worm in BOLD for this lab!

Conclusion – Describe what you did, what you saw, and what you learned.