Q.Describe the external head structure of the cockroach with the help of a labelled diagram.

The cockroach has biting-and-chewing mouthparts made of the labrum, a pair of mandibles, a pair of maxillae (with palps), the labium (with palps) and a central hypopharynx.

(Diagram: draw the mouthparts separated out and labelled - the labrum at the top; below it the pair of toothed mandibles; then the pair of maxillae, each showing cardo, stipes, lacinia, galea and the 5-segmented maxillary palp; the labium at the bottom showing submentum, mentum, prementum and the labial palps; and the median hypopharynx in the centre.)

The mouthparts of Periplaneta americana are of the BITING and CHEWING (mandibulate) type, consisting of:

1. Labrum (upper lip):

• A broad flap forming the upper covering of the mouth; helps hold the food.

2. Mandibles (a pair):

• Hard, thick, jaw-like structures with toothed inner (grinding) margins; they cut and grind (masticate) the food, moving sideways.

3. Maxillae (a pair):

• Each consists of a basal cardo and stipes, bearing an inner toothed lacinia, an outer hood-like galea, and a 5-segmented MAXILLARY PALP.

• They hold the food, push it towards the mandibles and bear sensory palps for tasting.

4. Labium (lower lip):

• Formed by the fusion of the second maxillae; consists of submentum, mentum and prementum, and bears a pair of 3-segmented LABIAL PALPS. It forms the lower lip / floor of the mouth.

5. Hypopharynx (lingua):

• A median, tongue-like structure in the centre of the mouth cavity; the salivary duct opens near its base. It helps in tasting and mixing food with saliva.

Cockroach mouthparts are of the biting-and-chewing type, made up of the labrum, a pair of mandibles, a pair of maxillae, the labium, and the hypopharynx.

Note: this answer describes and labels each part of the mouthparts in detail, since a hand-drawn figure cannot be rendered here - use this description to draw and label the diagram.

The mouthparts of Periplaneta americana (cockroach) lie in a ventral cavity called the gnathal/buccal cavity, bounded above by the clypeus and are of the primitive biting and chewing type. From outside inward, the parts are:

1. Labrum - a broad, flap-like structure attached to the clypeus, forming the upper lip; it covers the mouthparts from above and helps hold food in place during feeding.

2. Mandibles (a pair) - strong, dark-coloured, heavily sclerotised jaws lying just behind the labrum. Their inner (medial) edges bear cutting/crushing teeth, and they work side-to-side to bite and crush food.

3. Maxillae (a pair) - lie behind the mandibles; each maxilla consists of a basal cardo and stipes, which bear an inner toothed lacinia and an outer soft galea (both used to hold/manipulate food), plus a segmented, sensory maxillary palp (5-segmented) used to test/taste food.

4. Labium - formed by fusion of the second pair of maxillae, forming the lower lip; it consists of a basal postmentum and prementum, the prementum bearing a pair of 3-segmented labial palps (sensory) and an apical ligula, itself divided into an inner pair of glossae and an outer pair of paraglossae, which help push food into the mouth.

5. Hypopharynx - a median, tongue-like lobe lying between the mandibles/maxillae and the labium, in the floor of the buccal cavity; the common salivary duct opens near its base, and it bears taste receptors, aiding both salivation and taste.

Together these parts allow the cockroach to bite off, hold, manipulate, taste, moisten (with saliva) and push food into the pharynx - characteristic of a generalized chewing insect mouthpart.

The cockroach has biting-and-chewing mouthparts made of the labrum, a pair of mandibles, a pair of maxillae (with palps), the labium (with palps) and a central hypopharynx.

(Diagram: draw the mouthparts separated out and labelled - the labrum at the top; below it the pair of toothed mandibles; then the pair of maxillae, each showing cardo, stipes, lacinia, galea and the 5-segmented maxillary palp; the labium at the bottom showing submentum, mentum, prementum and the labial palps; and the median hypopharynx in the centre.)

The mouthparts of Periplaneta americana are of the BITING and CHEWING (mandibulate) type. They consist of the following parts:

1. Labrum (upper lip):

• A broad flap that forms the upper covering of the mouth; it helps hold the food.

2. Mandibles (a pair):

• Hard, thick, jaw-like structures with toothed inner (grinding) margins; they cut and grind (masticate) the food. They move sideways.

3. Maxillae (a pair):

• Each maxilla consists of a basal cardo and stipes, bearing an inner lacinia (with teeth), an outer hood-like galea, and a 5-segmented MAXILLARY PALP.

• They hold the food, push it towards the mandibles and bear sensory palps for tasting.

4. Labium (lower lip):

• Formed by the fusion of the second maxillae; consists of submentum, mentum and prementum, and bears a pair of 3-segmented LABIAL PALPS. It forms the floor/lower lip of the mouth.

5. Hypopharynx (lingua):

• A median, tongue-like structure in the centre of the mouth cavity; the salivary duct opens near its base. It helps in tasting and mixing food with saliva.

Cockroach mouthparts are hypognathous and of the primitive biting-chewing type, made up of the labrum, mandibles, maxillae, labium and hypopharynx, each with a specific role in seizing and processing food, as shown in the labelled diagram above.

Mouthparts of the cockroach (Periplaneta americana) — biting and chewing type, hypognathous (directed ventrally):

1. Labrum (upper lip): A broad, flap-like structure attached to the clypeus, forming the anterior/upper boundary of the mouth; it helps hold food in place during feeding.
2. Mandibles (a pair): Strong, heavily sclerotised, dark, triangular jaws with toothed/serrated inner (chewing) margins; they are the principal organs for biting and crushing/grinding food, moving side to side (unlike vertical jaws).
3. Maxillae (a pair): Located just behind the mandibles, each maxilla is a jointed appendage bearing:
   • Cardo and Stipes — basal segments attaching the maxilla to the head.
   • Galea — an outer soft, hood-like lobe.
   • Lacinia — an inner, more sclerotised, spine-tipped lobe used to hold and manipulate food.
   • Maxillary palp — a long, segmented (5-segmented), sensory feeler used for tasting/testing food.
4. Labium (lower lip): Formed by the fusion of the second (posterior) pair of maxillae; it forms the floor of the mouth and bears a pair of segmented labial palps (sensory) plus lobes (glossae and paraglossae) that help manipulate food.
5. Hypopharynx: A median, tongue-like lobe lying within the space enclosed by the other mouthparts, arising from the floor of the mouth cavity; the salivary duct opens near its base, so it plays a role in channelling saliva onto the food and aids in swallowing.

Functional summary: Food is seized and held by the labrum and maxillae, cut/crushed by the mandibles, tasted/manipulated further by the maxillary and labial palps, mixed with saliva delivered via the hypopharynx, and passed into the buccal cavity for swallowing — a well-coordinated set of mouthparts typical of chewing insects.