Insects and crustaceans
Activation hormone
regulates the function of other endocrine glands
when there is a lack of AH, the development of insects stops
it stimulates pair of the glands in the prothorax to produce ecdysone and pair of
glands near the brain to produce juvenile hormone
Ecdysone (Fig. 1)
produced by insects and crustaceans; promotes growth and controls moulting
Juvenile hormone (Fig. 1)
regulates many aspects of insect physiology, such as development, reproduction,
diapause, etc.
it ensures the growth of larva, at the end of larval stadium JH stops to produce and
that is a signal for insect moulting
it helps for production of eggs in female
Figure 1: Posterior–dorsal view of insect neuroendocrine system. The corpora allata (ca)
produce juvenile hormone which, together with the steroid ecdysone produced and
released by the prothoracic gland (ptg), control growth and molting.
Mollusks
The best-established endocrine organs in mollusks, the optic glands (Fig. 2), occur in the
octopus and squid. They are a pair of small structures, found near the brain, that produce
a substance which causes gonadal maturation. The optic glands in turn are regulated by
inhibitory nerves from the brain. There is also some evidence that a portion of the
nervous system (the pleural ganglia) may secrete a hormone that affects water balance.
Removal of the pleural ganglia from a freshwater snail results in swelling of the animal
due to the influx of water.
Figure 2: Dorsal view of crustacean brain and neuroendocrine system. X-organ’ (X)
found in the optic lobe. The Y-gland (Y) produces ecdysone and represents a homolog of
the insect prothoracic gland; likewise, the mandibular organ (mo) secretes methyl
farnesoate which is chemically and functionally similar to insect juvenile hormone.