Q.Describe the digestive system of the cockroach with the help of a labelled diagram.

The cockroach's alimentary canal is a straight tube of three developmentally distinct regions — foregut, midgut and hindgut — each specialised for storage/grinding, enzymatic digestion/absorption, and water reabsorption/egestion respectively.

Overview: The cockroach's digestive (alimentary) canal runs the length of the body and is divisible into three regions of different embryonic origin.

1. Foregut (Stomodaeum) — ectodermal, lined with cuticle:

• Mouth, opening into a small buccal cavity.
• Pharynx, a short muscular tube that aids swallowing.
• Oesophagus, a narrow tube conducting food backward.
• Crop, a large thin-walled sac used for the temporary storage of ingested food.
• Gizzard (proventriculus), a muscular chamber lined internally with strong chitinous teeth/ridges that grind and triturate food into fine particles before it passes to the midgut; it also has a valve preventing regurgitation of partially digested food from the midgut.

2. Midgut (Mesenteron) — endodermal, the main site of digestion and absorption:

• A short tube not lined by cuticle, so digestive enzymes and absorption occur here directly across the epithelium.
• At its anterior end arise 6–8 finger-like blind projections called gastric (hepatic) caeca, which greatly increase the surface area and secrete digestive enzymes that act on the food, aiding both digestion and absorption of nutrients.

3. Hindgut (Proctodaeum) — ectodermal, lined with cuticle:

• Ileum — a narrow anterior part of the hindgut.
• Colon — a wider, longer region, where reabsorption of water and some ions occurs, concentrating the waste.
• Rectum — the terminal, dilated region where faecal matter is further consolidated (efficient water reabsorption to conserve water, an adaptation for terrestrial life).
• Anus — the opening through which faeces (frass) are egested.

Associated glandular structures:

• Salivary glands (a pair, bilobed, located in the thorax): secrete saliva containing amylase, delivered via ducts to a reservoir and then into the salivarium near the base of the hypopharynx, aiding preliminary digestion of starch.

• Malpighian tubules open at the junction of midgut and hindgut; though primarily excretory (not digestive), they are anatomically associated with this region of the gut.

The digestive system of the cockroach (Periplaneta americana) is a straight alimentary canal differentiated into foregut, midgut and hindgut, assisted by salivary glands and gastric caeca, adapted for handling and digesting solid, omnivorous food.

Description of the digestive system (in place of a hand-drawn figure, since no image can be produced here — the labelled parts below are exactly what such a diagram would show):

A. Foregut (stomodaeum) — ectodermal, lined by cuticle:

• Mouth: Opens between the mouthparts (mandibles, maxillae, labium) on the head.
• Buccal cavity: Just behind the mouth; receives saliva from the salivary glands via the salivarium.
• Pharynx and oesophagus: A short pharynx leads into a narrow, tubular oesophagus carrying food to the crop.
• Crop: A large, thin-walled sac-like dilation used for temporary storage of food.
• Gizzard (proventriculus): A muscular, thick-walled chamber lined internally with six chitinous teeth/plates that grind and triturate food into fine particles before it passes into the midgut; it also acts as a filter.

B. Midgut (mesenteron) — endodermal, glandular:

• A short, narrow tube where actual chemical digestion and absorption of food occurs.
• At its junction with the foregut arise 6-8 finger-like blind tubules called gastric (hepatic) caeca, which secrete digestive enzymes and increase the surface area for absorption.
• The midgut epithelium secretes a delicate, permeable peritrophic membrane enveloping the food mass, protecting the gut wall from abrasion.

C. Hindgut (proctodaeum) — ectodermal, lined by cuticle:

• Ileum: A narrow tube continuing from the midgut; numerous thread-like Malpighian tubules (excretory organs) open at the junction of midgut and hindgut, pouring nitrogenous waste into the gut.
• Colon: A wider, longer tube following the ileum.
• Rectum: The terminal, dilated part bearing internal projections called rectal papillae/pads, which reabsorb water and salts from the undigested residue, helping conserve water.
• Anus: The terminal opening through which faecal pellets (largely dry, owing to water reabsorption) are egested.

Associated glands: A pair of salivary glands (with salivary reservoirs) lie in the thorax and pour saliva, containing amylase, into the buccal cavity through a common salivary duct opening at the salivarium, initiating digestion of starch.