Kenwood Academy High School



Earthworm Dissection

Earthworms are important helpers in the garden or field! Their tunneling mixes up the soil and brings rich soil to the surface. You can observe the organs of these tiny creatures by dissecting a preserved earthworm.

Observation: External Anatomy

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1. Find the anterior (front) end of the earthworm by locating the fleshy bump over its mouth, called the prostomium. The posterior (back) end has a small hole where solid waste is expelled, called the anus. The length of the worm is made up of many tiny segments, each separated by a thin wall called a septum.

2. About one-third of the way back from the mouth you should see a thicker and smoother section of the worm. This is called the clitellum, and it is involved in reproduction.

3. Notice that the earthworm has a rounded dorsal (back) surface and a flatter ventral (belly) surface. Usually the dorsal surface is darker than the ventral surface (though sometimes this is obscured in the preservation process). Lightly rub your finger along the ventral side toward the posterior end of the worm. You should feel a roughness caused by tiny bristles called setae. Using a magnifying glass, try to see the setae.

4. With your magnifying glass look for tiny pores on each segment. Liquid wastes are expelled through these pores. Near the front end of the worm you should see some larger pores that can be easily seen without magnification. These are genital pores and are important in reproduction.

Dissection: Internal Anatomy

1. Lay the worm on your dissecting tray with its dorsal side facing up. Use dissection pins to secure each end on the tray. Start your dissection about an inch posterior to the clitellum. Lift up the skin with a pair of forceps and snip an opening with a pair of dissecting scissors. Insert the scissors into the opening and cut in a straight line all the way up through the mouth. Go slowly and be sure to cut just the skin--if you go too deep you may damage the internal organs.

2. Using the forceps and dissection pins, carefully pull apart the two flaps of skin and pin them flat on the tray. (You may need to drag a pin along the inside of the skin to sever the septum walls to make it easier to spread the skin.)

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3. Look at the labeled picture to help you find the following features:

• Pharynx: This is the light-colored organ just inside the mouth. Its muscular contractions pass food on down to the esophagus.

• Hearts (or "aortic arches"): Behind the pharynx are five dark loops wrapped around the esophagus. These are the blood vessels that serve as the hearts of the worm.

• Dorsal blood vessel: This is a dark line extending from the hearts over the top of the crop.

• Crop: Food from the esophagus is temporarily stored in the crop.

• Gizzard: Food comes from the crop into the gizzard, where it is ground up.

• Intestine: The intestine is the long tube extending from the gizzard all the way to the anus. Food is digested and absorbed here.

• Reproductive organs: The light colored tissue above and around the hearts are seminal vesicles. Other reproductive parts appear as small white organs on the ventral side of the hearts.

• Ventral Nerve Cord: With your forceps, gently push aside the intestine to view the long white nerve cord running along the length of the worm beneath it.

4. Finish cutting the rest of the worm open from the first incision through to the anus. Observe how the intestine and ventral nerve cord both continue through the entire length of the worm.

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Frog Dissection:

Objective:

To observe the internal and external structures of a frog.

Materials:

• safety goggles, gloves, and a lab apron

• forceps

• preserved frog

• dissecting pins (6–10)

• dissecting tray and paper towels

• plastic storage bag and twist tie

• scissors

• marking pen

• dissecting needle

Procedure: 

1. Put on safety goggles, gloves, and a lab apron.      

2. Place a frog on a dissection tray. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes, as shown in the diagram below. Male frogs are also usually smaller than female frogs. Observe several frogs to see the difference between males and females.

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3.  Use the diagram below to locate and identify the external features of the head. Find the mouth, external nares, tympani, eyes, and nictitating membranes.

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4. Turn the frog on its back and pin down the legs. Cut the hinges of the mouth and open it wide. Use the diagram below to locate and identify the structures inside the mouth. Use a probe to help find each part: the vomerine teeth, the maxillary teeth, the internal nares, the tongue, the openings to the Eustachian tubes, the esophagus, the pharynx, and the slit-like glottis.

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5. Look for the opening to the frog’s cloaca, located between the hind legs. Use forceps to lift the skin and use scissors to cut along the center of the body from the cloaca to the lip. Turn back the skin, cut toward the side at each leg, and pin the skin flat. The diagram above shows how to make these cuts

6. Lift and cut through the muscles and breast bone to open up the body cavity. If your frog is a female, the abdominal cavity may be filled with dark-colored eggs. If so, remove the eggs on one side so you can see the organs underlying them.

7. Use the diagram below to locate and identify the organs of the digestive system: esophagus, stomach, small intestine, large intestine, cloaca, liver, gallbladder, and pancreas.

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Crawfish Dissection:

Objective:

To observe the internal and external structures of a crawfish.

1. Put on safety goggles.   You may use gloves if you want.

2. Using one hand to hold the crayfish dorsal side up in the dissecting tray, use scissors to carefully cut through the back of the carapace along dissection cut line 1,  as shown in the diagram below. Cut along the indentations that separate the thoracic portion of the carapace into three regions. Start the cut at the posterior edges of the carapace, and extend it along both sides in the cephalic region.

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3. Use forceps to carefully lift away the carapace. Be careful not to pull the carapace away too quickly. Such action would disturb or tear the underlying structures.

4. Place the specimen on its side, with the head facing left, as shown in the diagram below. Using scissors, start cutting at the base of cut line 1. Cut along the side of the crayfish, as illustrated by cut line 2. Extend the cut line forward toward the rostrum (at the top of the head).

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5. Use forceps to carefully lift away the remaining parts of the carapace, exposing the underlying gills and other organs.

6. Use the diagram below to locate and identify the organs of the digestive system. Locate the maxillae that pass the pieces of food into the mouth. The food travels down the short esophagus into the stomach. Locate the digestive gland, which produces digestive substances and from which the absorption of nutrients occurs. Undigested material passes into the intestine. Observe that the intestine is attached to the lobed stomach. The undigested material is eliminated from the anus.

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7. Use the diagram below to locate and identify the organs of the respiratory system. Locate the gills, which are featherlike structures found underneath the carapace and attached to the chelipeds and walking legs. A constant flow of blood to the gills releases carbon dioxide and picks up oxygen.

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8. Use the diagram of the internal anatomy of the crayfish to locate and identify the organs of the circulatory system. Locate the dorsal tubular heart and several arteries. The crayfish has an open circulatory system in which the blood flows from arteries into sinuses, or spaces, in tissues. The blood flows over the gills before returning to the heart.

9. Use the same diagram to locate and identify the organs of the nervous system. Find the ventral nerve cord. Locate a ganglion, one of the enlargements of the ventral nerve cord. Locate the dorsal brain, which is located just behind the compound eyes. Note the two large nerves that lead from the brain, around the esophagus, and join the ventral nerve cord.

10. Use the same diagram to locate and identify the organs of the excretory system. The blood carries cellular wastes to the disk-like green glands. Locate these organs just in front of the stomach. The green glands excrete waste through pores at the base of each antenna.

11. Use the diagram once again to locate and identify the organs of the reproductive system. The animal shown in the diagram is a male crayfish. If your specimen is a male, locate the testis. The testis is the long, white organ under the heart and a bit forward. The sperm ducts that carry sperm from the testis open at the fifth walking leg. If your specimen is a female, locate the bi-lobed ovary. It is in the same relative position as the testis, but the ovary appears as a large, reddish mass under the heart. Then locate the short oviducts that extend from near the center of each side of the ovary and open at the third walking leg. Exchange your specimen with a nearby classmate who has a crayfish of the opposite sex. Then study its reproductive system.

12. Dispose of your materials according to the directions from your teacher.

13. Clean up your work area and wash your hands before leaving the lab

Starfish Dissection:

Objective:

To observe the internal and external structures of a starfish.

Materials:

Preserved starfish, dissecting pan, scissors, scalpel, forceps, T-pins, pencil, lab apron, safety glasses

Procedure (Aboral Surface):

1. Obtain a preserved starfish and rinse off any preservative with water.

2. Place the starfish in the dissecting pan with its dorsal or aboral (top) surface upward.

3. Observe the starfish and determine  its symmetry.

4. Locate the central disc in the center of the starfish. Count and record the number of arms or rays the starfish has.

5. Locate the small, round hard plate called the madreporite on top of the central disc. Water enters through this into the water vascular system. Label the central disc, arms, and madreporite on Figure 1.

6. Feel the upper surface of the starfish for spines. These spines protect the starfish and are part of their internal skeleton. Label these on figure 1.

7. Look at the tip of each arm and find the eyespot. Label this on Figure 1.

Figure 1 -Aboral Surface

Procedure (Oral Surface):

7. Turn the starfish over to its ventral or oral surface (underside).

8. Locate the mouth in the center of the central disc. Find the ring of oral spines surrounding the mouth. Label these  on figure 2.

9. Find the groove that extends down the underside of each arm. This is called the ambulacral groove. Label this on figure 2.

10. Feel the numerous, soft tube feet inside each groove. these are part of the water vascular system & aid in movement and feeding. Label these on Figure 2.

Figure 2 - Oral Surface

Procedure (Internal anatomy):

11. With the starfish's aboral surface facing you, cut off the tip of a ray. Cut along lines a, b, and c (Figure 3) and then remove this flap of skin.

Figure 3 - Cuts in Arm

12. Inside each arm, locate two long digestive glands called the pyloric caeca. These make enzymes to digest food in the stomach. Label these in Figure 4.

13. Cut a circular flap of skin from the central disc. (You will have to also cut around the madreporite in order to remove this flap.) Observe the stomach under the central disc. Label this on Figure 4.

14. Remove the pyloric caeca from the dissected ray. Find the gonads (testes or ovaries) underneath. These may be small if the starfish is NOT in breeding season. Label these on figure 4. Remove these to see the rest of the water vascular system.

15. Cut off the tip of a ray to observe the parts of the tube feet. Find the zipper-like ridge that extends the length of the ray. The tube feet are attached to these.

16. Locate the bulb-like top of a tube foot called the ampulla. This sac works like the top of an eyedropper to create suction. The bottom of the tube foot is a sucker. Label these in Figure 4.

17. Embedded in the soft body wall are skeletal plates called ossicles. Locate these and label them in Figure 4.

Figure 4 - Starfish Digestive & Reproductive Systems

18. Running down the center of each arm is a lateral canal to which tube feet are attached. Label this in Figure 5.

19. In the central disc the five lateral canals connect to a circular canal called the ring canal. Find this canal & label it on figure 5.

20. A short, canal called the stone canal leads from the ring canal to the madreporite where water enters. Find this canal & label the stone canal & madreporite on Figure 5.

21. Draw an arrow on Figure 5 tracing the path that water takes when it enters & moves through the starfish.

Figure 5 - Water Vascular System

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Mollusk Dissection:

Objective

To study the internal and external anatomy of a bivalve mollusk.

Materials

Dissecting pan, dissecting kit, screwdriver, lab apron, plastic gloves, safety glasses, preserved clam

Procedure

1. Put on your lab apron, safety glasses, and plastic gloves.

2. Place a clam in a dissecting tray and identify the anterior and posterior ends of the clam as well as the dorsal, ventral, & lateral surfaces. Figure 1

Figure 1

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3. Locate the umbo, the bump at the anterior end of the valve. This is the oldest part of the clam shell. Find the hinge ligament which hinges the valves together and observe the growth rings.

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4. Turn the calm with its dorsal side down and insert a screwdriver between the ventral edges of the valves. Carefully work the tip of the screwdriver between the valves so you do not jab your hand.

5. Turn the screwdriver so that the valves are about a centimeter apart. Leave the tip of the screwdriver between the valves and place the clam in the pan with the left valve up.

6. Locate the adductor muscles. With your blade pointing toward the dorsal edge, slide your scalpel between the upper valve & the top tissue layer. Cut down through the anterior adductor muscle, cutting as close to the shell as possible.

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7. Repeat step 6 in cutting the posterior adductor muscle. Figure 2

Figure 2

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8. Bend the left valve back so it lies flat in the tray.

9. Run your fingers along the outside and the inside of the left valve and compare the texture of the two surfaces.

10. Examine the inner dorsal edges of both valves near the umbo and locate the toothlike projections. Close the valves & notice how the toothlike projections interlock.

11. Locate the muscle "scars" on the inner surface of the left valve. The adductor muscles were attached here to hold the clam closed.

12. Identify the mantle, the tissue that lines both valves & covers the soft body of the clam. Find the mantle cavity, the space inside the mantle.

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13. Locate two openings on the posterior end of the clam. The more ventral opening is the incurrent siphon that carries water into the clam and the more dorsal opening is the excurrent siphon where wastes & water leave.

14. With scissors, carefully cut away the half of the mantle that lined the left valve. After removing this part  of the mantle, you can see the gills, respiratory structures.

15. Observe the muscular foot of the clam, which is ventral to the gills. Note the hatchet shape of the foot used to burrow into mud or sand.

16. Locate the palps, flaplike structures that surround & guide food into the clam's mouth. The palps are anterior to the gills & ventral to the anterior adductor muscle. Beneath the palps, find the mouth.

Figure 3

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17. With scissors, cut off the ventral portion of the foot. Use the scalpel to carefully cut the muscle at the top of the foot into right and left halves.

18. Carefully peel away the muscle layer to view the internal organs.

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19. Locate the spongy, yellowish reproductive organs.

20. Ventral to the umbo, find the digestive gland, a greenish structure that surrounds the stomach.

21. Locate the long, coiled intestine extending from the stomach. 

22. Follow the intestine through the calm. Find the area near the dorsal surface  that the intestine passes through called the pericardial area. Find the clam's heart in this area.

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23. Continue following the intestine toward the posterior end of the clam. Find the anus just behind the posterior adductor muscle.

24. Use your probe to trace the path of food & wastes from the incurrent siphon through the clam to the excurrent siphon.

25. Answer the questions on your lab report & label the diagrams of the internal structures of the clam. Also, use arrows on the clam diagram to trace the pathway of food as it travels to the clam's stomach. Continue the arrows showing wastes leaving through the anus.

Grasshopper Dissection:

Objective:

Identify & label the internal & external anatomy of a grasshopper.

Materials:

Lab apron, gloves, eyeglasses, dissecting pan, dissecting kit with forceps & scalpel, t-pins, magnifying glass, preserved grasshopper, paper, pencil.

Procedure (External Anatomy): Examine the entire grasshopper and identify the major subdivisions and parts of the body.  

1. Obtain a preserved grasshopper & rinse off any preservative with water. Place grasshopper in the dissecting pan.

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2. Observe that the body of the grasshopper is divided into 3 regions --- the head, the thorax, and abdomen. Label these on Figure 2.

3. Examine the head and locate the following parts:

HEAD

Antennae (two, slender appendages)

Compound eyes (2, large lateral)

Ocelli (or simple eyes) - 3, small, between compound eyes

Mouth parts - Labrum (upper lip), mandibles (jaws) below the labrum, maxillae located behind the mandibles to help cut & hold food, and the lower lip or labium

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|          1. Labrum |         4. Labium |

|          2. Mandibles |         5. Maxillary Palps |

|          3. Labial Palps |         6. Maxillae |

|          7. compound eye |         8. ocelli |

 

4. Label the mouthparts, eyes, and antenna on Figure 1.

5. Using forceps, remove each of the appendages from the head, and attached them to table 1.

6. Examine the following appendages on the thorax (middle section of the grasshopper's body):

      THORAX

     Legs (first 2 pairs are for walking & the last pair are for jumping)

     Wings (forewings have a leathery appearance & protect the hind wings)

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7. Using forceps, remove one of the walking legs and identify these parts --- the coxa connects the femur (the thickest part of the leg) to the grasshopper's body; a slender, spiny tibia connects the femur to the tarsal segments (lowest part of the leg). Label these on Figure 2.

8. Remove a jumping leg and attach the walking leg & jumping leg to Table 1.

9. Raise both pairs of wings and locate the first abdominal segment.

10. Locate the tympanic membrane or eardrum on the first abdominal segment. Label this on Figure 2.

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11. Using a magnifying glass, locate the spiracles or tiny pores for respiration on each side of the abdominal segments.  Label these on Figure 2.

12. Determine if your grasshopper is a male or female by looking at the end of the abdomen. Females have a tapered abdomen that ends in a pointed egg laying tube called the ovipositor. Male have a more rounded abdomen that turns upward.

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13. Label the ovipositor on Figure 2.

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ABDOMEN

Spiracles (small openings on the side of somites or body segments)

Auditory Organs (two located laterally on the 1st body somite or segment)

Ovipositor (on female)

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