The protocerebrum sends neurosecretory axons to the corpora- cardiaca that are located just posterior to the brain.
The corpora- cardiaca are neurohaemal organs, somewhat comparable to the neurohypophysis of vertebrates except that they also contain neurosecretory cells.
Axons from the corpora cardiaca and from the supraoesophageal ganglia are sent to the corpora allata which are also paired structures in most insects.
Corpora allata appear to have intrinsic non-nervous secretory cells as well as termini and hence are true endocrine glands of non-nervous tissue origin.
The corpora cardiaca are responsible for the control of the heart, they secrete an orthodiphenol which activates the heart indirectly by causing pericardial cells so release a heart accelerating substance (Davey, 1961 ; Cameron, 1963).
Corpora allata, on the other hand form a fat soluble juvenile hormone which has not been identified chemically, but which has specific developmental actions in retarding the apperance of adult characteristics. This hormone with ecdysone (secretion of ecdysially gland) also controls the moulting.
The principal endocrine organ of insects, as distinct from neurosecretory structures, is the prothoracic or thoracic gland, variously known in arthropods as the moult gland and in crustaceans as the Y-organ or ventral gland.
It is also known as ecdysial gland. It is a gland of non-nervous origin and is supplied with nerves originating from neurosecretory cells of the brain.
It exists in a pair. This gland secretes a hormone called ecdyson first isolated from insects and crustaceans by Karlson 1954 and Butenandt in Germany. It is steroid in nature and causes moulting with metamorphosis.