Grasshopper Dissection

Insects are the largest and the most diverse group of animals on Earth. To study all the different types of insects would be more than a lifetime task. However, if you chose one insect to study as a representative, the grasshopper would be a good choice. Like other arthropods, grasshoppers have jointed appendages and a segmented body that is surrounded by an exoskeleton. The grasshopper's body is typical of an insect. It is divided into three distinct regions: the head, the thorax, and the abdomen. Three pairs of legs attach to the thorax. The legs of insects are usually adapted for some special activity such as digging, swimming or crawling. The grasshopper's legs are adapted for the activity after which it was named--hopping. Two pairs of wings also are attached to the thorax, making this body segment specially designed for locomotion. The head of a grasshopper bears a pair of compound eyes, simple eyes, a pair of antennae, and specialized mouthparts. In this investigation, you will study the external and internal structures of the grasshopper and investigate features common to the insect class.

OBJECTIVES:
1. Identify and label the external structures of a grasshopper.
2. Identify the mouthparts of a grasshopper and describe the function of each.
3.Describe the structure and adaptations of the grasshopper's legs. Identify and label the internal organs of a grasshopper and explain their functions.

MATERIALS:
Preserved grasshopper, dissecting tray, forceps, dissecting microscope, probe, 6 dissecting pins, medicine dropper, scissors, beaker (150-mL)

PRELAB:
1. Read the instructions for the investigation and answer Prelab questions 1 through 4.
2. Rinse the specimen in clear water.
3. Obtain a preserved grasshopper and place it in a dissecting tray dorsal side up. Identify the head, thorax, and abdomen.
4. On the head, locate the pair of antennae and the pair of compound eyes. Use a the dissecting microscope to observe the three simple eyes. Find the two pairs of palps which extend from the mouthparts.
5. On the thorax, locate the two pairs of wings. Compare the front or fore-wings to the rear or hind wings. Answer Prelab question 5.
6. Study the three pairs of legs on your grasshopper. Using scissors and forceps. remove one of the front legs. Identify each of the five parts on the leg you just removed. Answer Prelab question 6.
7. On the first segment of the abdomen, find the large, oval tympanum. Locate the spiracles in the lateral walls of the abdomen. Answer Prelab question 7.
8. In males, the end of the abdomen is blunt and somewhat rounded. In females, the abdomen ends in a four-pronged, egg-laying structure called the ovipositor. Determine whether your specimen is male or female. Answer Prelab question 8.
9. Make a drawing of the external parts of the grasshopper and label the external features of the grasshopper. Answer Prelab question 9.
10. Look closely at the mouthparts of the grasshopper with the dissecting microscope. Using forceps, carefully remove the mouthparts from the preserved grasshopper. Answer Prelab question10.
12. Using scissors, remove both pairs of wings and all remaining legs from your grasshopper.
13. Cut along the middle of each side of the grasshopper with the scissors. Each incision should begin at the anterior edge of the thorax and extend through the last segment of the abdomen.
14. Carefully lift the dorsal part of the exoskeleton. Use your probe to separate the exoskeleton from the tissues beneath it.
15. With dissecting pins, fasten the rest of the body wall to the dissecting tray.
16. With forceps, remove the stringy muscle tissue covering the internal organs. Be careful not to remove the dorsal blood vessel and the heart. You should now be able to see the internal organs.
17. Obtain some tap water in a beaker. With a medicine dropper, cover the organs with water to prevent them from drying out.
18. In the thoracic area, find a large, saclike structure. The posterior part of this organ is the gizzard and the anterior part is the crop. With your probe, gently press down on the crop and the gizzard and compare the way they feel. Answer Investigation questions 1 and 2.
19. Anterior to the crop, follow the short esophagus which opens into the mouth. Locate the small salivary glands which lie beneath the crop.
20. Just posterior to the gizzard, find the fingerlike projections called the gastric caeca. They are attached at the junction between the gizzard and the stomach. Answer Investigation question 3 and 4.
21. Locate the saclike stomach, often called the midgut, just behind the gizzard. Follow the stomach posteriorly and find the narrow, tubelike intestine. The intestine ends in a muscular structure called the rectum which eliminates wastes through the anus.
22. Find the Malphigian tubules, the threadlike tubes attached to the point where the stomach meets the intestine, Label the Malphigian tubules on your drawing. Answer Investigation question 7.
23. In the abdominal area, locate the tiny, whitish-colored tubes called the trachea. Note where they attach to the inside and the outside of the body wall. Answer Investigation question 8.
24. Find the threadlike dorsal aorta in the middle of the dorsal surface on top of the internal organs. Follow the aorta into the abdomen and identify the heart, which looks like bulges in the aorta.
25. Locate the reproductive structures dorsal to the stomach and the intestine. Include these structures in your drawing and label them "testes" or "ovaries" depending on the sex of your specimen.
26. With scissors, cut the digestive tract anterior to the crop and posterior to the rectum. Remove the digestive structures to see the nervous system.
27. On the inner surface of the ventral body wall, find the double, threadlike, ventral nerve cord. Identify the ganglia, the swellings in the nerve cord.
28. Trace the nerve cord toward the head to find the brain, located between the compound eyes.
29. After you have studied the grasshopper, dispose of it. Thoroughly wash and dry your dissecting tools and tray.
30. Before you leave the laboratory, wash your hands thoroughly with soap and water.

PRELAB QUESTIONS:
1. Why are scissors used rather than a scalpel to open the body wall of the grasshopper?
2. Name the body segments of a typical insect.
3. What common structures can be found on the head of the grasshopper and most insects?
4. What structures are attached to the thorax of the grasshopper?
5. Compare the structure of the two pairs of wings. Based on their structure, what do you think is the job of each wing?
6. Are the three pairs of legs identical? Explain your answer and describe for what you think each type of leg is adapted.
7. What is a spiracle?
8. What is the sex of your grasshopper? Explain how you can tell.
9. Name the five major sensory organs of the grasshopper and describe the function of each organ.
10.Describe the function of each mouthpart listed: a. labrum, b. mandible, c. maxillac, d. labium

OBSERVATIONS AND DATA:
1. Compare the muscularity of the crop and the gizzard.
2. How does the structure of the crop and the gizzard make each suitable for its function?
3. What is the role of the gastric caeca?
4. Which is larger, the gizzard or the stomach. In which one do you think food remains the longest?
5. In the grasshopper, where is food digested and absorbed into the bloodstream?
6. What happens in the intestine?
7. How do the Malphigian tubules function as organs of excretion?.
8. Explain how the grasshopper is adapted for moving large amounts of air into its body.
9. Describe the circulatory system of a grasshopper.

ANALYSIS AND CONCLUSIONS:
1. Summarize the main characteristics of insects, these will be the criteria on your phylum chart.
2. Compare the grasshopper with the crab. Which characteristics make the grasshopper well adapted for its life on dry land?