Digestive System of Cockroach or Grasshopper
Alimentary Canal: It is a tubular structure, extending from the mouth to the anus and comprises the foregut, the midgut and the hindgut.
1. Foregut / Stomodaeum: It is the part of alimentary canal anterior to the gastric cecae and comprises of-
i. Pharynx: It is a anterior most narrow part in the head region between mouth and oesophagus.
ii. Oesophagus: It is the part between the pharynx and the crop running through the neck.
iii. Crop: It is the thin walled, swollen and extensible posterior part of oesophagus for storing the food.
iv. Gizzard or Proventriculus: It is a conical, muscular chamber used for grinding and filtering the food. It consist six heavily sclerotized teeth (denticles).
2. Midgut or Mesenteron: It is a short tube and is marked by the gastric caecae at the anterior border and the insertion of malpighian tubules posterior. It is the part where the digestion and absorption of food takes place.
Gastric Cecae: These are also called hepatic cease or enteric cecae. They are blind tubes, in cockroach eight in numbers. It’s proximal end open at the beginning of the midgut. It increases the surface area of midgut which facilitates digestion and absorption of food.
3. Hindgut / Proctodaeum: It is the posterior portion between the midgut and anus.
1. Ileum: It is a short anterior portion.
2. Colon: It is corrugated middle portion.
3. Rectum: Enlarged globular terminal portion and bears six rectal papillae (pads) for reabsorption of water and essential ions from the faeces.
Malpighian tubules: Fine yellowish bodies (tubules) are the malpighian tubules which are 80-100 in number, arranged in 8 to 10 groups behind Mesenteron. They are excretory organs.
Salivary Glands: These are pair of the glandular structures (acini) and a pair of reservoirs. The salivary glands are present on the sides of the crop. Each gland has a separate duct. The ducts of the glands unite and form a common salivary instruction fro dissection.
Alimentary Canal: Kill the cockroach with the help of chloroform (do not inhale the gas which is poisonous). Cut the wings and legs from their bases. Give the lateral cuts in the region of abdomen in order to separate the terga from the sterna with the help of scissor. Keep the cockroach in wax dish in its natural position. Fix the cockroach by inserting one pin through the head (labrum) and second through the last abdominal segment. Pour sufficient water (submerge the specimen) in wax dish. Remove the pronotum by separating from underlying tissues.
Remove abdominal terga from behind forward with the help of forceps. Also remove meso and metanotum carefully. Use fresh water for cleaning and separating the fat bodies, tracheae and muscles with the help of forceps and observe the coiled part of alimentary canal. Take alimentary canal outside carefully and pin down on the left side of the wax-dish.
Salivary Glands and their Mounting: Lift up the crop and observe the salivary glands in its both sides, above the alimentary canal in the thoracic region. Cut open the neck and the head in the median line, above the alimentary canal and up to the pin in the head. Lift up the crop, separate the glands from the crop and observe the ducts running from the salivary glands. Cut off the ventral nerve cord, which crosses the ducts of the glands and the glands along with ducts. Mount it in glycerin and observe under dissecting microscope.