STRUCTURAL ORGANISATION IN ANIMALS

 

COCKROACH :

Morphology :

• Adults cockroach Periplaneta americana are about 34-53 cm long with wings that extended beyond the tip of the abdomen.
• Segmented body distinguished into head, thorax and abdomen.
• Entire body is covered by external chitinous exoskeleton.
• Each segment has hardened plates called sclerites (dorsal tergites, ventral sternites).
• Successive sclerites are joined by flexible articular membrane (arthrodial membrane)

Head :

• Head is formed by fusion of six segments, with flexible neck.
• The head bears a pair of compound eye, a pair of antennae.
• Antennae have sensory receptors.
• Head bears appendages meant for biting and chewing types of mouth parts.
• The mouth parts consists of:
  • A labrum (upper lip)
  • A pair of mandibles.
  • A pair of maxillae
  • A labium (lower lip)
  • A median flexible lobe acting as tongue (hypopharynx).

Thorax :

• Thorax consists of three parts – prothorax, mesothorax and metathorax.
• Each thoracic segment bears a pair of walking legs.
• First pair of wings arises from mesothorax and second pair from metathorax.
• The hind wings are transparent, membranous meant for flying.

Abdomen :

• The abdomen consists of 10 segments.
• In female the 7th segment is boat shaped and along with 9th and 10th segment it forms the broad or genital pouch.
• Genital pouch contains female gonopore, spermathecal pores and collateral glands.
• In male the genital pouch bounded dorsally by 9th and 10th terga and ventrally by the 9th sternum.
• Male bears a pair of anal style, absent in female.
• Anal cerci present in both sexes in 10th segment.

ANATOMY :

Digestive system :

• Alimentary canal divided into three regions; foregut, midgut and hindgut.
• The mouth opens into short pharynx leading to oesophagus.
• Oesophagus opens into a sac like crop, which store food.
• Crop is followed by gizzard or proventriculus.
• Gizzard contains chitinous teeth for grinding the food.
• The entire fore gut is lined by cuticle.
• A ring of 6-8 blind tubules called hepatic or gastric caecae present at the junction of foregut and midgut, which secretes digestive juices.
• Midgut is long tube like structure.
• At the junction of midgut and hindgut, another ring of 100-150 yellow coloured thin filamentous Malpighian tubules are present.
• Malpighian tubules are meant for excretion from haemolymph.
• The hindgut is broader and differentiated into ileum, colon and rectum.

Blood vascular system:

• Blood vascular system is open type.
• Blood vessels are poorly developed and open into space called haemocoel.
• Visceral organs located in the haemocoel and bathed in blood called haemolymph.
• The haemolymph composed of colourless plasma and haemocytes.
• Heart is elongated multichambered, funnel shaped with ostia.
• Blood enter into the heart through ostia and is pumped anteriorly into the sinuses.
• The haemocoel differentiated into three sinuses;
  • Pericardial sinus.
  • Perivisceral sinus.
  • Perineural sinus.

Respiratory system :

• The respiratory system consists of a network of trachea.
• Trachea opens to outside by 10 pairs of small holes called spiracles on lateral side of the body.
• Trachea gives rise to branching tubes called tracheal tubes which subdivided into tracheoles.
• Opening of spiracles regulated by valves.
• Movement of air takes place by diffusion and directly to the body cell.

Excretion:

• Excretion is performed by malpighian tubules.
• Each tubule is lined by glandular and ciliated cells.
• They absorb nitrogenous wastes from the haemocoel and converted into uric acid and poured into the hindgut.
• Hence cockroach is uricotelic in nature.
• Nephrocytes and uricose glands also assist in excretion.

Nervous system:

• Consists of a series of segmentally arranged ganglia joined by paired longitudinal double ventral nerve cord.
• Three ganglia lie in thorax and six in the abdomen.
• Head contain a bit of nervous system.
• The brain is represented by supra-oesophageal ganglion which innervates the compound eye and antennae.
• The sense organs are antennae, eyes maxillary palps, labial palps, anal cerci etc.
• Each compound eye consists of about 2000 hexagonal ommatidia.
• Each ommatidium forms a part of the image, called mosaic vision.

 

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
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