Determine which internal and external structures you want to identify. List those structures in your lab notebook. Decide if you want to use your identification list as a checklist, or if you want to draw these structures in your notebook.
Put on gloves and lay the crayfish on its back, or dorsal side, in the dissection pan. Use your anatomical guide to identify your desired external structures. Lay the crayfish on its side and repeat.
Place the crayfish on its abdomen, or ventral side. Use your anatomical diagram to find the carapace, or shell. Carefully insert the point of your scissors under the carapace at the at the back of the cephalothorax, or body, where it meets the tail.
Cut a straight line up the center of the carapace to the rostrum, or forehead. Make the cut extend past the eyes. This effectively cuts the shell into two halves.
Insert the scissor tip under the side of the carapace, just behind the eyes. Cut straight across. Gently lift the two halves of carapace off the crayfish, exposing the internal organs of the celphalothorax. Use the magnifying glass to identify smaller structures. Use the tip of your scissors or a toothpick to push overlying structures out of the way to view those underneath, if needed.
Lay the crayfish on its abdomen, or ventral side. Insert the scissor tip under the center edge of the tail shell and cut a straight line down to the telson, or middle tail flipper. Spread open the shell with your fingers to view the tail's internal organs.
Wash the tray, scissors and dissection area thoroughly. Wrap the crayfish in newspaper and dispose of it in an outdoor trash receptacle, along with the gloves and pencil.