Part I: Grasshopper Dissection

(A) External anatomy of the grasshopper.

1. Place a preserved grasshopper in a dissecting pan. From observations and using pre-lab research material identify the main characteristics of the class Insecta (question 1) on the data sheet.

2. Use your hand lens or dissecting microscope to examine your specimen more carefully. Using pre-lab research material answer questions 2-3 on the data sheet. Locate and label the parts listed below onto the grasshopper diagram on the data sheet (figure 1): Use researched material from pre-lab as a reference. (add any other parts that you may have found but are not on this list)

abdomen - the segmented tail area of a grasshopper, which contains the heart, reproductive organs, and most of the digestive system
antennae - like all insects, grasshoppers have 2 segmented antennae that sense touch and odors
compound eye - grasshoppers have 2 faceted eyes made up of many hexagonal lenses
head - the head is at the front end of the grasshopper's body and is the location of the brain, the two compound eyes, the mouth parts, and the points of attachment of its two antennae.
jumping legs -the long, hindmost pair of the grasshopper's six legs

palps - long, segmented mouth parts (under the jaws) that grasp the food
spiracles - a series of holes located along both sides of the abdomen; they are used for breathing
thorax - the middle area of the grasshopper's body - where the legs and wings are attached
walking legs - the four, short front legs that are used for walking
forewing & hindwing - grasshoppers have two long wings, used for flying.

Ovipositor -female reproductive structure

mandibles - the jaws, located near the tip of the head, by the palps; the jaws crush the food

3. Examine the mouthparts of the grasshopper to see how they are adapted to feeding on grass. Use the hand lens or dissecting microscope. Carefully remove each mouthpart with a forceps (may also require scissors), Compare the mouthparts to those in the figure below. Record your conclusions about your observations in questions 4-8 on the data sheet.

(B) Internal anatomy of the grasshopper.

Read the directions carefully before beginning your dissection. The organs you are to find are indicated in boldface.

4. First, remove the three left legs. Insert the point of your scissors under the dorsal surface of the last abdominal segment. Being careful not to cut underlying organs, make an incision just to the left of the mid-dorsal line. Continue the cut through the thorax. Then, cut down the left side to the ventral surface in front of the thorax. Make another lateral cut on the left side between the next-to-the-last and the last abdominal segments. Make a ventral cut on the underside connecting the last two cuts.

5. With the forceps, pull down the left side and look for the large dorsal blood vessel (“heart”).

6. Now, use your scalpel to cut the muscles close to the exoskeleton as you slowly remove the left side of the insect’s abdomen and thorax. Locate the finely branched tracheae going to the spiracles.

7. Insert the point of the scissors at the back of the head and cut through the exoskeleton over the top of the head between the left antenna and left eye. Extend this incision to the mouth. Use the forceps and scalpel to remove the exoskeleton on the left side of the head. Locate the dorsal ganglion (“brain”). You may be able to identify a large, whitish nerve passing from the dorsal ganglion around the esophagus to the ventral ganglion. Follow the ventral nerve cord posteriorly and compare your observations to pre-lab research references. You should locate several ganglia in your specimen. Label these observed items on figure 2.

8. Cut away the tissue to expose the digestive tract along the length of the animal. From the posterior end of the esophagus, the digestive tract enlarges into a crop. Posterior to the crop, the wall of the digestive tract becomes muscular and is the gizzard. Notice that the gizzard and the stomach (mid gut) are separated by a narrowing of the digestive tract. Also observe that many gastric caeca are attached here. Label these observed items on figure 2.

9. Posteriorly, another narrowing separates the stomach from the intestine. Identify the many long, thin, malpighia tubules attached at this point. Note the narrow colon posterior to the intestine. The digestive tube enlarges to form the rectum. Here, wastes are concentrated before passing out through the anus. Label these observed items on figure 2.

10. Note the ovary in the female or the testes in the male. Label both of these items on figure 2. Answer question 9-12 on the data sheet. (Check to make sure all items are labeled on figure 2 the internal grasshopper diagram)

Part II: Crayfish Dissection

(A) External Anatomy Procedure:

1. Place a crayfish in your dissection try. Notice that the body of the crayfish is divided into two distinct regions: the cephalothorax and the abdomen. Observe the carapace covering the cephalothorax. The abdomen ends in a reduced abdominal segment called the telson. Label these observed items on figure 3.

2. Notice the cervical groove that marks the division between the head and the thorax. Observe that the carapace extends forward. This forms a horny beak called the rostrum. Notice the location of the eyes. Answer question 1-2 on the data sheet. Label these observed items on figure 3.

3. The most anterior appendages are the branched antennules. Locate the antennae, which are attached to the head, posterior to the antennules. On the data sheet describe the structure of the antennules and antennae (no.3). Label these observed items on figure 3.

4. Observe the mouthparts of the crayfish. On the data sheet describe how the mouthparts move (no.4).

5. The thorax has 8 pairs of appendages. Three pairs are maxillipeds and are used in handling food. Five pairs are legs. Try to identify all 8 pairs. Compare the maxillipeds to the walking legs. Notice that the first pair of legs is well-developed chelipeds. The next four pairs of legs are called walking legs. On the data sheet compare the maxillipeds, chelipeds and walking legs (no.5). Label these observed items on figure 3.

6. Arrange your crayfish so you can observe the ventral surface of the abdomen. The abdominal appendages of the crayfish are called swimmerets. In the female the first pair of swimmerets are small. In the male the first two pairs are modified for transferring sperm. Determine the sex of your crayfish and record it on the data sheet (no.6). Label these observed items on figure 3.

7. The sixth pair of swimmerets are enlarged to form the uropods. The uropods and the telson form the powerful tail fin used in backward swimming. Find the anal opening on the ventral side of the telson. Label these observed items on figure 3.

8. Label any other external anatomy items that have not been labeled using pre-lab information on figure 3.

(B) Internal Dissection of the Crayfish

9. Locate the carapace of the crayfish. Insert your dissection scissors under the posterior edge of the carapace at the mid-dorsal line, and cut forward to the head segment. Then cut ventrally toward the walking legs, so that one side of the posterior carapace can be removed to create a “window”. Locate the grayish structures located underneath the carapace “window” section you have removed. Use your blunt probe to tease the structure apart. Answer question 7 on the data sheet.

10. Using your scissors remove the structure located in step 9. Using your Pre-lab research (diagrams) as a guide, carefully locate the gonads (reproductive structure), heart, and stomach of the crayfish. On the data sheet (no. 8) give a description of what you found. Label these observed items on figure 4.

11. Cut along the dorsal midline of the abdomen to the telson. Peel the abdominal segments back to expose the internal anatomy. Locate the intestine and muscles contained in the abdomen. Note your observations on the data sheet (no. 9). Label these observed items on figure 4.

12. Examine the compound eye of the crayfish under a dissecting microscope. Answer question 10 on the data sheet. Label these observed items on figure 3.

13. Using the information from the pre-lab research, label all other internal structures on the crayfish diagram figure 4.

14. Complete the table located on the data sheet (number 11) as follows: (1) List each type of major appendage on a crayfish: (2) Tell whether each type of appendage is attached to the head, thorax, or abdomen: (3) Briefly describe the function of each type of appendage.

15. When you have finished with your specimens make sure to wrap them in paper towels and dispose of them properly. Clean your lab station and replace all lab tools were they belong.