Mollusks
The best-established endocrine organs in mollusks, the optic glands, 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.