Internal Insect Anatomy

Transcription

1 EEB Lab 4 (Internal insect anatomy) 1 Internal Insect Anatomy During today's lab we will look at the internal anatomy of Gromphadorhina portentosa, a tropical, Madagascan cockroach. Dissection of several organ systems will be performed on one cockroach, so throughout your study of the digestive tract take care not to damage other internal structures/organs unnecessarily. I. Alimentary canal Cut off the legs and wings of the roach close to the body and then place the specimen, dorsal side up, in a dissecting dish. Fasten the specimen to the wax through the sides of the pronotal disc and edges of abdominal terminus. Insert the scissors (or the blade) beneath the posterior edge of the seventh (approximately) abdominal tergite, about 1/2 or 3/4 of the way between the mid-dorsal line of the insect and the sides of the body; cut the terga forward on each side of the body, being careful not to cut into the organs beneath. Continue cutting as far forward as the posterior margin of the metathorax. Lift the terga with forceps, carefully severing any adhering tissue or organs as you work your way toward the anterior end of the abdomen. Carefully remove the uppermost tracheae, muscles, fat body, and assorted debris so as to expose the digestive system: including esophagus, crop, gizzard (proventriculus), midgut caeca, midgut, Malpighian tubules, cardiac and pyloric sphincters, ileum and rectum of hindgut, etc. When you have cleared the extraneous parts from the abdomen, remove the broad prothoracic notum by inserting a scalpel or razor underneath it, cutting as close to the notum as possible. Cut the other thoracic terga as you did the abdominal ones, and remove enough of the thoracic muscles and tracheae to expose anterior portions of the alimentary canal. The Malpighian tubules or excretory organs are closely associated with the hindgut, and their secretory products (that are secreted into the tubule lumen) enter this part of the alimentary tract, usually just behind the pyloric sphincter. Make a drawing of the entire alimentary canal and excretion system and label the following elements: foregut pharynx esophagus crop proventriculus midgut gastric caeca (singular = gastric caecum) ventriculus (stomach)

2 EEB Lab 4 (Internal insect anatomy) 2 hindgut colon rectum rectal pads anus excretion system Malpighian tubules II. The nervous system The specimen of G. portentosa used in the previous exercise will be used here. Cut away laterally remaining portions of the abdominal tergites to facilitate dissection and viewing. Carefully remove the digestive tract, tracheae, etc., from the abdominal cavity, until you expose the paired ventral nerve cord and ganglia (use care as they are often very inconspicuous, fine, and translucent). Continue this dissection into the thorax; note that part of the exoskeleton projects into the meso- and metathorax in places these are phragmata and the furca, one of the apodemes. Remove tissue down to the paired ventral nerve cord it is delicate and easily damaged you may want to take a look at the demo dissection before proceeding. Make a drawing of the nervous system and indicate the following elements: subesophageal ganglion (if visible) prothoracic ganglion mesothoracic ganglion metathoracic ganglion abdominal ganglia connective nerves Again, use the drawings in this handout as a reference only.

3 EEB Lab 4 (Internal insect anatomy) 3 Dorsal view of Periplaneta americana showing the alimentary canal and nervous system III. Circulatory system Examine the preparations of the circulatory system of G. portentosa. Note the heart, aorta, and associated alary (aliform) muscles. These muscles should be visible attached to the dorsal diaphragm of the insect's body, nearly pressed against the inner surface of the dorsal integument (tergum). Watch for any peristaltic contractions of the heart, traveling from back to front. Try to locate a pair of ostia (watch for particulate matter in the saline solution being sucked in through these incurrent valves of the aorta/heart). Make sure you can locate the following structures: heart, dorsal diaphragm, ostia.

4 EEB Lab 4 (Internal insect anatomy) 4 Ventral view of Periplaneta americana showing the circulatory system IV. Respiratory system Locate the tracheal air sacs, together with the major lateral and dorsal longitudinal connectives of the tracheal system (the tracheal trunks). You may remove most of the internal organs that you see without fear of damaging much of the respiratory system. Be very careful as you near the dorsal diaphragm just below the heart ("above" the heart in this ventral view). Clear out fat body tissues, etc., to reveal the network of tracheal tubes and sacs. Make a schematic drawing and indicate: mesothoracic spiracle metathoracic spiracle abdominal spiracle lateral tracheal trunks dorsal tracheal trunks transverse connectives (commisures).

5 EEB Lab 4 (Internal insect anatomy) 5 Dorsal view of an insect showing the respiratory system