Chewing and Biting Type (e.g. Cockroach)
Insect feed on plants and animals in diverse ways and their mouthparts have become modified for these purposes. They are mainly two types viz. Mandibulate (feeding mainly on solid food) and Haustellate (feeding mainly on liquid food).
Chewing & Biting Type: The basic and most primitive type of mouthparts present in grasshopper, cockroach and beetles. In order of appearance, from anterior to posterior, chewing mouthparts consists of a single labrum (upper lip). A singly structure, the hypopharynx (tongue like organ) is located centrally. The inner surface of the labrum is referred to as the epipharynx, an area frequently membranous and inconspicuous.
i. Labrum: It is a flap like bilobed structure attached to the clypeus by an articular membrane. It helps to guide the food into the mouth and also holds the food in position so that mandibles can act on it. Epipharynx is identified as a swollen area of the ventral surface of the labrum, which is an organ of taste.
ii. Mandibles: They are also called as primary or true jaws and concerned with chewing and grinding the food. They are hinged to the cranium by anterior and posterior articulations. They have transverse movement produced by abductor (outer) and adductor (inner) muscles. They are heavily sclerotized and are toothed o their inner border. Distal teeth are sharply pointed and area called incisors or cutting teeth. The proximal teeth are called molar or grinding teeth.
iii. Maxillae: They are called as secondary jaws or accessory jaws. The basal segment, known as the cardo, joins the maxilla to the head. This is joined to the central body of maxilla, the stipes. On the outer side of the stipes is a more or less distance sclerite known as the palpifer to which the palpus is attached. Antennae like five segmented Palpi, bears tactile hairs and also probably organs of smell or taste. On the distal end of the stipes there are two lobes. The outer lobe is called galea and the inner lobe lacinia which is toothed. May be employed for grasping/cutting/chewing food. Whenever these two distinct lobes are fused together to form a single lobe (e.g. Coleopterous larvae) it is termed as Mala.
iv. Labium: It closes the mouth cavity from below or behind. It is informed by fusion of two primitive segmented apopendages like maxillae. It consists of three median sclerites viz. submentum (large basal sclerite), mentum (middle sclerite) and prementum (apical sclerite). On the lateral side of the prementum, there are two small lateral sclerites called palpiger bearing seven segmented labial Palpi. Distally prementum bears two pairs of lobes. The outer pair is called paraglossae and inner pair glossae. Both pairs when fused together to form a median lobe (e.g. Grasshopper), it is termed as Ligula.
Instructions for the Dissection:
Hold the head capsule between the thumb and the index-finger and gently press it. All the components of mouthparts will be seen distinctly. Remove labrum, right & left mandibles, right & left maxillae, hypopharynx and labium and mount them in a drop of glycerin on a slide. Place a cover slip over it and examine under a microscope.