Mouth part of Periplaneta americana.

Mouthparts

Mouth parts are head appendages surrounding the mouth. The appendages around the mouth consist the mouth parts which are chewing or biting or mandibulate type.They consist of the labrum or upper lip, a pair of mandibles, a pair of maxillae, the labium or lower lip and the hypopharynx. Mouth parts of cockroach have remained unspecialised due to the omnivorous habit. They enable cockroach to bite and the hard stuff, consume soft stuff and lap up liquids.

1. Labrum.

It is a membranous flat lobe suspended below the clypeus.Labrum or upper lip is the appendages of a 3rd head segment.It is a broad, and obligate plate, movable due to the muscle inserted on its base.It lies in the front of the mouth as the upper lip.On its ventral surface, many sensory setae are situated which are possibly gustato receptors. Fused on the inner surface of the labrum is a thin membranous plate, called the epipharynx. Labrum overlaps the toothed portion of mandibles.

2. Mandibles.

These are appendages of 4th head segments. These are small, triangular, and strongly sclerotized in structure and are suspended with the side of the head capsule and articulate by means of a condyle with the gena of the same side.They have a ball and socket attachment with the head. Each mandible is stout, heavily sclerotized heaving teeth-like cutting plates at its inner edge. On its upper inner edge is a softer prostheca.

The inner margin of the mandibles are jaws used for the crushing and the cutting the food. The mandible is movable with the help of adductor and abductor sets of muscle. The contraction of the adductor muscle brings the mandibles closer so that their teeth are inter-fitted and in this position the food is broken down into small fragments. Then the abductor muscles contract and the mandibles get separated from each other. So, the cutting and the chewing of food is affected by the alternate contraction and the relaxation of these muscles. Both the mandibles show horizontal sidewise movements brought about by the action of adductor and abductor muscles.

3. Maxillae.

These are the appendages of the 5^th segments of the head and known as the first pair of maxillae. These are two, one on either side of the head capsule behind the mandible. They are also attached to the head capsule by muscles and each of them consists of podomeres.Each maxilla as a basal protopodite heaving cardo and stipes podomeres bent at right angle to each other.The cardo joins the maxilla with the head capsule. The stripes possess three processes.

1. Inner lacuna which is sclerotized with a pair of sharp denticles and a blunt lacinula.
2. The outer long surface of stripes arises a five-jointed maxillary palp representing the exopodite, at the base of which is a small sclerite called the palpifer.
3. Middle galea which acts as blood for lacinula.

The maxillae are also used for the cleaning the antennae, palps and front legs.Both maxillae act as accessory jaws. The maxillae hold food by the claws of the lacuna and bring it to the mandibles for mastication.

4. Labium.

The Labium is called also as lower lip. It is the appendages of the 6^th head segments.It is lying behind the mouth and represents the second pair of maxillae which have fused together into one. It has a proximal postmentum divided into a large submentum and a small poorly sclerotized mentum.The distal part of the labium is a paired structure resembling a pair of maxillae united at their bases, it consists of premium below the mentum and on each side, it has 3 jointed labial palps, at the base of each palp is a small sclerite, the palpiger. Between the labial palps are four labels, two median and the smaller glossae and the outer and the larger paraglossae. The labial palps sensory and the labium does not take the active part in feeding, but the glossae and the paraglossae together called the ligula prevents the loss of food particles from the mandibles. The first and the third segments on the head has no appendages.The terminal part of the palp is covered thickly with sensory setae.

5. Hypopharynx.

It is a median somewhat cylinder structure also known as a line.Its distal end bears two comb-like plates, the super lingua. The common salivary duct opens at its front end. It lies between the maxillae and above the labium.

Walking legs.

There are three pairs of walking legs, one pair attached ventrally to the sternum of each of prothorax, mesothorax, and metathorax and called for, mid and the hind leg. All these 3 pairs of walking legs are similar and they help the cockroach in its cursorial habit. Each leg consists of five segments a large basal coxa articulating with the thoracic segment between the pleuron and sternum. Coxa is followed by a smaller trochanter which is freely movable on the coxa but is fixed to the next segment, the femur which is long and broad; this is followed by a long uniformly thick tibia which spurs; the last segment is a tarsus having five movable joints or podomeres or tarsomeres which have bristles, and their lower side has soft adhesive pads, the planulae.The arolium is an adhesive organ holding on the smooth surfaces.The last tarsomere of the tarsus is often referred to as pretarsus and it terminates in two curved claws or units. Between the claws is a soft hollow lobe, the arolium has small bristles.

Wings.

The wings are of two pairs. The first pair arises from mesothorax and the second pair rises from metathorax. In wings reach up to the tip of the abdomen in the female and a little beyond in male cockroach.

. The wings are two types

1.. Forewings.

These are also known as mesothoracic . Forewings are highly sclerotized. These are dark, narrow, opaque and leathery in texture.They are not used for the fight but serve to protect the findings at rest.Hence, they are known as elytra, wing covers or time.

2. Hindwings.

These are also known as metathoracic. These are broad, transparent, thin , delicate, and used in flight, and these are folded below the tegmina when at rest.Movements are due to special muscles attached to wing bases and working at a very high speed.

The wings are formed as outgrowths of the integument from between the notum and pleuron. Each wing of cockroach consists of two numerous layers of cuticle enclosing tubular veins or nervous which contains blood in every stage. Chitin thickens around trachea to form veins or nervures that strengthen the wings. Veins are strongly criticised and enclose a small trachea. The cockroach has a poorly developed set of wing muscles yet it can fly fairly well.

In flight the wings are stretched horizontally , the anterior margins of the wings remain rigid but the rest of the wings moves downwards, it is curved, upwards, it is bent downwards. Hence, by becoming defeated the wings encounter pressure from behind which propels the insect through the air.A longitudinal dorsal muscle lying below the terga raises the terga by which the wings move down. A tergosterol muscle running from the tergum to the sternum on each side of the thorax pulls the tergum down by which the wings are raised up.

Reference.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

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