2. External Morphology of an Insect

External Morphology of an Insect








EXTERNAL MORPHOLOGY OF AN INSECT
 Eg. Grass hopper

The insect body is grouped into three distinct regions or tagmata (Singular: Tagma) namely head, thorax and abdomen. This segmentation of the body into functional unit is called tagmosis. 
Head
ü This anterior tagma is composed of five sclerites namely vertex, frons, clypeus, gena and occiput that are joined by “sutures”.
ü  The head capsule is called as “cranium” and strengthened by a set of invagination of cuticle called tentorium.
ü  Head is a centre for sensing and feeding.
ü  Head consists of a pair of antenna, a pair of compound eyes, three simple eyes and mouth parts.  Head is connected to the thorax through the neck or cervix. 



Thorax:
ü  This is the middle tagma which is divided into three segments namely prothorax, mesothorax and metathorax.
ü  Meso- and meta-thorax bears two pairs of wings (forewing and hind wing) and are called pterothorax.
ü  Each segment consists of a pair of legs namely fore legs (prothorax) middle legs (mesothorax) and hind legs (metathorax).
ü  It is the centre for locomotion. 
Abdomen:
ü  It is the largest, eleven segmented (Uromers) posterior tagma.
ü  Eleventh segment, being reduced and divided into three lobes namely a dorsal epiproct and a pair of paraproct that surround the anus.
ü  The terminal segments may bear a pair of cerci.
ü  Spiracles are present on each side of the first eight abdominal segments.
ü  8th and 9th segments bear the genital structure , hence are known as genital segments. Female egg laying organ (ovipositor) is present in 8th and 9th segment while male genitalia present in 9th segment.
Abdomen is the centre for reproduction.


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