Insect

Subclass: Apterygota

Morphology and development

Insects range in size from less than a millimeter

Related Topics:
Walkingstick - Exoskeleton - Chitin - Thorax - Abdomen - Antennae - Compound eye - Six - Excretory

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Insects have a complete digestive system. That is, their digestive system consists basically of a tube that runs from mouth to anus, contrasting with the incomplete digestive systems found in many simpler invertebrates. The excretory system consists of Malpighian tubules for the removal of nitrogenous wastes and the hindgut for osmoregulation. At the end of the hindgut, insects are able to reabsorb water along with potassium and sodium ions. Therefore, insects don't usually excrete water with their feces, a fact which allows them to store water in the body. This process of reabsorption enables them to withstand hot, dry environments.

Related Topics:
Malpighian tubule - Osmoregulation

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[[Image:robal.png|left|350px|thumb|Insect anatomy

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A- Head   B- Thorax   C- Abdomen

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1. antenna

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2. ocelli (lower)

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3. ocelli (upper)

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4. compound eye

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5. brain (cerebral ganglia)

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6. prothorax

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7. dorsal artery

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8. tracheal tubes (trunk with spiracle)

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9. mesothorax

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10. metathorax

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11. first wing

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12. second wing

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13. mid-gut (stomach)

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14. heart

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15. ovary

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16. hind-gut (intestine, rectum & anus)

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17. anus

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18. vagina

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19. nerve chord (abdominal ganglia)

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20. Malpighian tubes

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21. pillow

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22. claws

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23. tarsus

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24. tibia

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25. femur

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26. trochanter

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27. fore-gut (crop, gizzard)

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28. thoracic ganglion

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29. coxa

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30. salivary gland

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31. subesophageal ganglion

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32. mouthparts]]

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Most insects have two pairs of wings located on the second and third thoracic segments. Insects are the only invertebrate group to have developed flight, and this has played an important part in their success. The winged insects, and their secondarily wingless relatives, make up the subclass Pterygota. Insect flight is not very well understood, relying heavily on turbulent atmospheric effects. In more primitive insects it tends to rely heavily on direct flight muscles, which act upon the wing structure. More advanced flyers, which make up the Neoptera, generally have wings that can be folded over their back, keeping them out of the way when not in use. In these insects, the wings are powered mainly by indirect flight muscles that move the wings by stressing the thorax wall. These muscles are able to contract when stretched without nervous impulses, allowing the wings to beat much faster than would be otherwise possible.

Related Topics:
Pterygota - Neoptera

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Insects use tracheal respiration in order to transport oxygen through their bodies. Openings on the surface of the body called spiracles lead to the tubular tracheal system. Air reaches internal tissues via this system of branching trachea. The circulatory system of insects, like that of other arthropods, is open: the heart pumps the hemolymph through arteries to open spaces surrounding the internal organs; when the heart relaxes, the hemolymph seeps back into the heart.

Related Topics:
Trachea - Spiracle - Circulatory system - Hemolymph

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Insects hatch from eggs, and undergo a series of moults as they develop and grow in size. This manner of growth is necessitated by the exoskeleton. Moulting is a process by which the individual escapes the confines of the exoskeleton in order to increase in size, then grows a new outer covering. In most types of insects, the young, called nymphs, are basically similar in form to the adults (an example is the grasshopper), though wings are not developed until the adult stage. This is called incomplete metamorphosis. Complete metamorphosis distinguishes the Endopterygota, which includes many of the most successful insect groups. In these species, an egg hatches to produce a larva, which is generally worm-like in form. The larva grows and eventually becomes a pupa, a stage sealed within a cocoon or chrysalis in some species. In the pupal stage, the insect undergoes considerable change in form to emerge as an adult, or imago. Butterflies are an example of an insect that undergoes complete metamorphosis.

Related Topics:
Eggs - Moult - Metamorphosis - Endopterygota - Larva - Pupa - Cocoon - Chrysalis - Imago

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