Name _____________________________________ Lab 5: Insect Anatomy ☺ Rationale: We have reviewed the arthropods and orders of insects, and, in the process, used various morphological (structural) terms. Now, we need to more thoroughly examine the external and internal anatomy of the largest group of animals! We're hoping that you won't find this lab overly "icky" since you will likely be handling, and perhaps even dissecting, insects! You are not required to do the dissections, but we will provide you with the opportunity to do so. You might find that you really have the talents of a heart or eye surgeon! We prefer to use freshly killed insect specimens for dissections because the internal organs have distinctive colors which are lost when the animals are preserved. We will be a humane as possible, but we will be killing the insects before the dissections. We usually do this by quickly freezing them or using a standard insect killing bottle. In any case, please let us know if you have religious or ethical issues so we can accommodate your needs! External Anatomy (the Grasshopper) Please work in groups of 2 to 4 depending on your laboratory instructor's instructions (we need to pair folks with at least one person willing to dissect). We have captured and preserved grasshoppers by injecting them with alcohol. This expands the abdomens (so you can observe the external claspers and/or ovipositor) and legs. Look at the grasshopper from the top (dorsal), side (lateral) and underside (ventral) to get a general idea of where the head, thorax, and abdominal segments begin and end. HEAD: 1. Locate the following structures of the head – compound eyes, ocelli, antennae. 2. Draw or sketch below a picture of the grasshopper head with the main structures identified. (This is just to help you study; remember that your TA is not an artist, so your drawing abilities are not judged. ☺) 1 3. With a razor blade, slice off the head where it joins the prothorax (you should be able to slide the razor blade through the soft tissues that join the head and thorax). 4. With the front of the head facing you, take your finger and nail lift up the front flap (the labrum) and tear it off. Place this on the 3x5 card provided. This will expose the mandibles. 5. Pull each mandible out by pushing them sideways (away from the head) until they break out of the head capsule. Look at the two mandibles under the microscope. Are they bilaterally symmetrical (meaning, is each mandible a mirror image of the other)? Place each mandible on the card below the labrum. The maxillae should now be exposed. 6. Pull each maxilla out, being careful to not destroy the toothed, flap and palp subsegments. Again, place these on the card below the mandibles. Look under the microscope at the tips of the palps. What do you see? 7. Finally, pull the back flap (the labium) backwards from the head capsule, keeping their palps intact. If you have done this correctly, you will have the head capsule with a strange peg‐
shaped projection coming down where the mandibles and maxillae were. This is the hypopharynx and it is an extension from the floor of the foregut. This structure is covered with chemoreceptors. What would this be in humans? THORAX: 1. From one side, pull a front wing forward and tear it off at the base. Now pull the underlying hind wing off and expand it. Place on a 3X5 card with the mouthparts. Are the wings the same size and shape? ______________________________________ How many longitudinal veins (veins that are parallel to the front wing margin) would you estimate are in the front wing? _____________________________________________ The hind wing? __________________________________________________________ 2. Carefully cut off the front, middle and hind legs on one side being sure to get their bases. Identify the – coxa, trochantor, femur, tibia and tarsus of each leg. Which two are alike? _____________________________________________________ What is different about the hind leg? ________________________________________ How many tarsomeres are present? _________________________________________ What are the structures at the tip of the tarsus? _______________________________ 2 3. With the wings and legs gone on one side of the grasshopper, you can now see the spiracles on the thoracic segments. Look at these under a microscope. Describe what their openings look like below: ABDOMEN: 1. Observe the grasshopper carcass from the side where you removed the wings and legs. You should easily see an oval to bean‐shaped structure where the abdomen joins onto the thorax. This is the tympanum. What does this do? 2. How many segments of the abdomen can you observe? (Hint, count the spiracles and add another segment as the last segment doesn't have spiracles.) 3. The tip of the grasshopper abdomen has a pair of short, spike‐like cerci. Below the cerci is the anus and genital structures. Look around at other students' grasshoppers and see if they have the abdomen ending in the same structure. Some (the larger ones) will have two pairs of pointed, hard structures (the ovipositor) while others will have the abdomen ending in a rounded or bulbous knob (male genitalia and claspers). WINGS: 1. Your instructors will have a live cockroach with one of its wings spread out on a microscope slide and under a compound scope. Look through the scope and see if you can see blood cells moving through the wing veins. Are insect wing veins the same as your veins? ____________________________________ How does the blood move through the wing veins? _______________________________ Internal Anatomy (American cockroach) GUTS!: 1. One of your instructors will dissect a cockroach. When we go through the back (dorsal) area, what structure would be destroyed? _______________________________________ 3 You'll have to see the dorsal vessel pumping under a separate demonstration! Once we dissect the cockroach and lay it out in a dissecting pan, you will need to observe the following: foregut, gastric caecae, proventriculus, midgut, hind gut, Malpighian tubules, fat body, tracheal trunks, ovaries or testes. 2. Look at the tracheal trunks under a microscope. Why are they silvery white? The tracheal trunks will appear to have many small rings. What are these rings? 3. Describe the function of the following structures. Proventriculus ________________________________________________________ Malpighian Tubules ____________________________________________________ Fat Body _____________________________________________________________ DORSAL VESSEL: 1. We will restrain a cockroach with its wings spread so that you can see the dorsal area of the thorax and abdomen. Look to see if you can see a darker line running down the middle of the back that seems to get smaller and larger. This is the dorsal vessel pumping! 2. Where does the dorsal vessel get the blood, and where does the dorsal vessel pump the blood? 3. What are the functions of the insect blood? 4. What is a function of human blood that is not a function of insect blood? Instructor sign out: _____________________________________________________________ ☺ 4