Materials Included In Kit

Additional Materials Required

Safety Precautions

Protective latex gloves, chemical-resistant aprons and protective eyewear are dissection necessities. Quality dissection tools that are sharp and free of rust should be provided. Routine procedures for inspecting dissection tools should be instituted. (Dull and dirty scissors, scalpels or blades are much more dangerous than sharp, clean ones!) Student laboratory directions should include the proper techniques for using specified dissection instruments as well as how to dispose of sharps. Appropriate dissection pans and table protection should be provided at each workstation. Common-sense rules relative to jewelry, nails, hair length, etc., should be reviewed in terms of student personal safety during dissection work. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Preserved and live specimens may be disposed of following Flinn Suggested Method for Type III biological materials and Flinn Suggested Method for Type IV biological materials, respectively, in the Biological Waste Disposal Section of your current Flinn Scientific Catalog/Reference Manual.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of three. This laboratory activity can reasonably be completed in two 50-minute class periods.
• The color overhead transparency of the Earthworm Structures Worksheet may be used by the instructor to help guide the students in filling in their black and white copy of the worksheet, if desired.
• Be sensitive of any student who may be put under physical stress when using preserved materials.
• Monitor students for any signs of illness during dissection.
• Properly mount dissection specimens to the dissecting pan or tray. Do not dissect a specimen while holding it.
• Handle scalpels, razor blades and other sharp instruments with care.
• Cut away from the body and away from other students.
• Do not use excessive force when working with sharp instruments. Use scissors instead of scalpels wherever possible.
• Students should be cautioned to never ingest specimen parts.
• Students should not be allowed to remove specimens or specimen parts from the classroom.
• All dissection parts should remain within the dissecting pan.
• Properly dispose of dissected materials.
• Store specimens in accordance with directions and chemical storage safety rules.
• Dissections may be done by the instructor or by individual student groups.
• Have a culturing setup ready for the earthworms before their arrival. Upon arrival, keep the cultures out of direct sunlight and in the coolest area (40–60 °F) of the classroom or stockroom. As long as the earthworms are kept above freezing, they will thrive and reproduce. Temperatures over 60 °F will slow reproduction, and temperatures over 80 °F may be fatal to worm cultures.

Teacher Tips

• Earthworms will thrive in any sturdy, leak-proof wooden, plastic or glass container. Styrofoam^® coolers also work well. A container 30 x 30 x 45 cm in size will house up to 100 earthworms. Fill to a level of at least 10 cm of a lightly moistened, loamy soil that doesn’t have a lot of sand or clay in it. Mix it with some decomposing leaves or other organic material. Additional leaves should be placed on top of the culture soil. Earthworms eat decaying organic matter, which is primarily supplied by the decaying leaves. Add a few pinches of crumbled bread or cornmeal to the top of the soil approximately every three weeks. Soil should be changed every six months if the worms are being cultured long-term.

• When setting up an earthworm culture, test the soil for appropriate moisture content by squeezing a small amount together. If the soil stays clumped, but does not leave a water residue, the moisture level is appropriate for culturing worms. If the soil falls apart, water needs to be added. If the soil is very wet, allow it dry in sunlight for a few hours.
• Live earthworms will create an initial high level of energy in the laboratory. After the initial, predictable reactions, students become totally interested in observing live earthworms.
• Individual student cultures containing 2–3 earthworms can be housed in plastic pencil boxes, plastic margarine, cottage cheese containers or Styrofoam cups.
• Earthworms are also a good food source for many larger classroom animals, such as amphibians, reptiles, crayfish, birds and certain species of fish.
• An extension or extra project following the movement activity is to have students use common materials to build working models of a moving earthworm. Extremely imaginative models are likely to result from this assignment.
• The sequence of movements in a worm goes something like this:
  1. Circular muscles contract (while longitudinal ones relax) squeezing the body walls inward. This “squeezes” the body wall and forces the body to get “longer” kind of like squeezing a balloon.
  2. During this circular muscle contraction the setae are retracted and there is little friction to prevent the body from elongating out over the moving surface (ground).
  3. When the worm is fully extended, the circular muscles relax (the setae on the anterior end become extended providing a grip on the surface) while the longitudinal muscles contract. As the setae on the extended, anterior end of the worm grip the surface, the contraction of the longitudinal muscles “pull” up the posterior end of the worm.
  4. The contraction and relaxation of the two sets of opposing muscles in a coordinated and alternating pattern causes the worm to “pull” itself along from one place to another. The coordinated cycle of opposing muscles contracting and relaxing is repeated over and over again.

Sample Data

A

1. Epidermis
2. Circular muscles
3. Longitudinal muscles
4. Setae
5. Dorsal porus
6. Alimentary canal
7. Typhlosole
8. Coelomic cavity
9. Dorsal vessel
10. Ventral vessel
11. Ventral nerve cord
12. Nephridia
13. Heart

B and C

7. Intestine

9. Dorsal blood vessel
10. Ventral blood vessel
11. Nerve cord
12. Nephridium

14. Gizzard
15. Crop
16. Seminal vesicles
17. Seminal receptacles
18. Heart
19. Esophagus
20. Pharynx
21. Mouth
22. Supra-esophageal ganglion
23. Testis
24. Sperm funnel
25. Vas deferens
26. Ovary
27. Egg sac
28. Oviduct
29. Opening of oviduct
30. Opening of vas deferens
31. Segment
32. Spermatozoa
33. Funnel of nephridium

Introduction

Have you ever wondered how earthworms move, breathe, eat and reproduce? The following activities will help you answer these questions and more as you delve deeper into the world of the earthworm.

Concepts

• Classification

• Digestion
• Earthworm structures
• Reproduction
• Movement

Background

Classification

Earthworms are classified as animals belonging to the order Oligochaeta, class Chaetopoda, phylum Annelidia. This phylum contains more than 1,800 different species of earthworms, which are grouped into five families. The most common worms in North America belong to the family Lumbricidae, which has about 220 species. Earthworms range from a few millimeters long to over 3 feet, but most common species are only a few inches long. Lumbriculus terrestris is the most common and well-known earthworm and is the specimen that will be studied in this activity.

Structures

The earthworm, while somewhat primitive, has well developed nervous, digestive, circulatory, muscular and reproductive systems. The most obvious external feature of the earthworm is the multiple segmentation of the body. An earthworm, on average, has 150 segments. The first section of the earthworm is the anterior or head region. This section consists of the mouth and the prostomium—a lobe that serves as a covering for the mouth and as a wedge to force open cracks in the soil through which the earthworm may crawl. The worm swallows soil (which includes decomposing organic particles) and plant litter (in or on the soil) through its mouth. The mouth leads to a muscular pharynx. Food is then passed on by muscular contractions in the pharynx through the esophagus to the crop where it is temporarily stored. The crop opens into a thick-walled gizzard where the food is ground up. It is then passed on to the intestine where digestive fluids release amino acids, sugars and other small organic molecules from the organic food particles. The molecules are then absorbed through the intestinal membranes and are utilized for energy and cell synthesis. Solid waste particles are passed out of the worm through the anus.

The circulatory system of the earthworm is a closed system where the blood circulates within a series of blood vessels. The major vessels of the earthworm’s circulatory system include the dorsal longitudinal vessel on top of the digestive tract and the ventral blood vessel lying below. These two vessels are connected to each other by a number of other vessels that pass around the digestive tract. The five pair of the vessels around segments 7 to 11 (remember, segment 1 begins at the anterior end) of the worm represent the aortic arches which function similar to hearts. The pulsation of the aortic arches causes circulation of the blood in the worm.

The nervous system of the earthworm consists of a ventral nerve cord, which runs the entire length of the worm on the lower, inner surface and the cerebral ganglia. The cerebral ganglia is found at the anterior end of the ventral nerve cord and passes around the pharynx where it enlarges and forms two swellings. The cerebral ganglia is considered as the worm’s primitive brain.

Earthworms lack specialized breathing organs. Respiratory exchange occurs through the body surface.

Earthworms are usually not self-mating although they are hermaphroditic—each individual possesses both male and female reproductive organs. A mutual exchange of sperm occurs between two worms during mating. Sperm cells are released from seminal vesicles and shared in seminal receptacles of the opposite worm. Mature sperm and egg cells and nutritive fluid are then deposited in cocoons produced by the clitellum, the girdle-like structure near the anterior end of the worm. The eggs are fertilized by the sperm cells within the cocoon, which then slips off the worm and is deposited in or on the soil. The eggs hatch after about three weeks. Each cocoon will produce anywhere from two to twenty worms (an average of four per cocoon).

Movement

As earthworms move, they aerate and enrich the soil. This enrichment and aeration greatly increases the yield and quality of crop growth in farmers’ fields. It has been estimated that an acre of “high quality” soil may contain over 50,000 earthworms.

Materials

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. If you are performing the earthworm dissection, follow all safety rules provided by the instructor. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Dissecting

Use your textbook, local library or the Internet to label all of the structures on the Earthworm Structures Worksheet.

1. Obtain a dissection tray, scalpel, dissecting pins, forceps, probe and a preserved earthworm.
2. Place the preserved earthworm in the dissection tray.
3. Place a pin through the prostomium. Place another pin through the anus (see Figure 1).

4. Using forceps, lift the dorsal skin of the earthworm. Cut a slit at the base of the forceps, insert scissors and cut a line, slightly off-center, through to the anus (see Figure 2). Note: Be careful to cut only as deep as the skin to avoid damage to the internal organs.

5. Beginning at the anal end, hold the body wall with forceps and, using a scalpel, cut through the septa on both sides of the intestine. Cut to 1" from the clitellum (see Figure 3).

6. Pin the body wall to the dissection tray as shown in Figure 4.

7. Using scissors, cut through the clitellum all the way to the prostomium (anterior portion of the earthworm) (see Figure 5).

8. Pin the body wall to the dissection tray as shown in Figure 6.

9. Refer to the completed Earthworm Structures Worksheet and identify as many structures as possible of the dissected earthworm.

Movement

1. Obtain a live earthworm.
2. Place the earthworm in a large, flat container, such as a dissection pan, lined with wet paper towels.
3. Observe the earthworm carefully as it moves across the bottom of the container on the paper towel.
4. Discuss the movement of the worm, and write a preliminary explanation for how you think an earthworm moves from one place to another.
5. Dissect a preserved earthworm (as discussed in the Dissection section), if not done already.
6. Locate the muscles on the inside of the body wall. They will appear as a layer of whitish tissue against the body wall.
7. Use forceps to pick into the whitish material on the inside of the body wall. Note that it is fibrous and that the fiber runs longitudinally along the length of the body.
8. Gradually pick your way through this thick layer until a layer of fibers is found that runs transversely around the body. Observe that the earthworm has two sets of muscles—one set running the length of the body (longitudinal muscles) and one set running around the body (circular muscles).
9. Feel the surface of the live worm. Also, feel the “bristles” along the dorsal and ventral surfaces of the anterior part of the worm. These bristle-like structures are called setae (sing. seta).
10. Read the following list of facts:

1. Muscles only contract (shorten) and relax (return to original length), they do not 

   expand or get longer.

2. Circular muscles around the earthworm can contract and squeeze the body.

3. Circular muscles around the earthworm can relax (returning the body to its original “fatness”).

4. Longitudinal muscles can contract and shorten the length of the body of the earthworm.

5. Longitudinal muscles can relax, returning the worm to its original length.

6. Setae (bristles) provide friction on a crawling surface.

7. Setae are retracted during circular muscle contraction.

8. Setae are extended when circular muscles are relaxed.

11. Describe in as much detail as possible the sequence of events that can explain how an earthworm can move from one place to another.
12. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10749_Student1.pdf