Lever and his associates (1961 a, b) after conducting the experiments on freshwater pulmonate snail Limnaea stagnalis, observed that hormones are responsible for water and salt, balance in these in vertebrates which regulate in accordance with environmental demands.
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According to Kamemoto (1964) these hormones are secreted in the brain particularly in earthworms. Pleural glands of adult snails are also said to control the water and salt balance.
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In vertebrates the hormones which control the osmoregulation are the arginine vasotocin and vasopressin from the posterior pituitary (according to Gorbman and Bern, 5962) and aldosterone from adrenal cortex.
Their regulation operates at the level of the surface membranes (gills, integument, urinary bladder), at the level of the kidney and also on the special glands of extra renal salt excretion (gills, orbital glands, rectal glands etc.).
The hormonal regulation of water and salt balance is an integrated process dependent on the co-operative action of many hormones.
For example, amphibian skin is said to be responsive to hormones of posterior pituitary (arginine vasotocin and vasopressin in the presence of aldosterone of adrenal cortex (Chesier Jones, 1957).
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Besides these above mentioned hormones, there are also other factors which have indirect effect on the water and salt balance.
These are thyroid hormone (thyroxine) and parathyroid hormones (parathormone and paracalcitonin) (Hickman, 1959 ; Maity and Green, 1963).
In some fishes caudal neurosecretory system is also involved in the regulation of salt and water balance as it secretes active neurosecretions (Enami, 1959; Takasugi and Bern, 1962; Maetz el al., 1964).
The pineal apparatus is also believed to control water and salt balance (Gorbman and Bern, 1962).