General Features Of The Insect Body Plan

In contrast to the various life habits and life histories, the insect body plan is quite uniform with its basic body plan (see Figure 21.1).

The body is composed of three parts—head, thorax, and abdomen—and covered with a chitinuous cuticle of varying thickness. Three pairs of legs and, in winged insects, two pairs of wings, are attached to the thorax.

The central nervous system consists of a supraesopha-geal and a subesophageal ganglion in the head and a rope ladder-like ventral nerve cord. The supraesophageal ganglion or brain is the most complex part of the nervous system. It includes the optic center, areas of behavioral regulation and centers of integrative learning. The alimentary canal consists of three parts. It begins, behind the mouth, with an ectodermic foregut or stomodeum with pharynx and stomach, followed by the entodermic midgut or mesodeum, which is the main region of digestion. An ectodermic hind gut or

Corpus allatum (endocrine gland)

Corpus cardiacum (neurohemalorgan)

Compound eye

Oesophagus Aorta "heart" (dorsal vessel)

Malpighian tubules

Supraoesophageal ganglion

Suboesophageal ganglion

Hind gut

Corpus allatum (endocrine gland)

Corpus cardiacum (neurohemalorgan)

Compound eye

Malpighian tubules

Hind gut

Suboesophageal ganglion

Spermatheca

Dorsal diaphragma

Aorta "heart" Dorsal longitu-

(dorsal vessel) dinal muscles

Fat body

Malpighian tubules

Stigma (tracheal opening)

Tracheal trunc

Dorsal diaphragma

Aorta "heart" Dorsal longitu-

(dorsal vessel) dinal muscles

Malpighian tubules

Fat body

Mid gut

Ovarioles

Vental nerve cord

Ventral longitudinal muscles

Figure 21.1. Basic body plan of an insect: (a) lateral view of the female insect body (fat body omitted); (b) lateral view of the male insect abdomen; (c) cross section of the female insect abdomen. (All charts modified after Weber, 1966)

Spermatheca

Accessory gland

Mid gut

Trachea (cross section)

Blood cells

Ventral diaphragma

Accessory gland

Ejaculatory duct

Vental nerve cord

Ovarioles

Ventral longitudinal muscles

Figure 21.1. Basic body plan of an insect: (a) lateral view of the female insect body (fat body omitted); (b) lateral view of the male insect abdomen; (c) cross section of the female insect abdomen. (All charts modified after Weber, 1966)

b c proctodeum opens into the anus. The excretory system consisting of the malpighian tubules is connected to the proctodeum.

The blood circulation system of insects is an open system; their body fluid—hemolymph—is therefore comparable to a mix of extracellular fluid ("lymph") and blood in animals with closed circulatory systems. The respiratory system is separated from the circulatory system. Tracheae that start with spiracles transport the respiratory gases. There are no respiratory proteins, and the distribution of oxygen and carbon dioxide is achieved by diffusion.

The body cavity is filled with the prominent fat body. This is not simply a storage organ like the white fat of vertebrates. It is very active metabolically, most comparable to the liver of vertebrates.

The male sex organs consist of the paired testes accompanied with glands for accessory fluids. The female ovaries are composed of a varying number of ovarioles and adjacent parts (e.g., spermatheca).

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