Evidence for moulting active substances in isolated prothoracic glands and oenocytes during the 5th instar ofBombyx mori.

The content of moulting hormones has been determined in homogenates of isolated prothoracic glands and oenocytes during the 5th instar of the silkworm,Bombyx mori by means of the Calliphora bioassay.Prothoracic glands show variable activity in the production of moulting hormones, reaching a maximum near the end of the larval period. Comparable activities, but at higher levels, could be demonstrated in oenocytes. Controls with doubled quantities of tissue produced in a proportionate reaction in the bioassay. Fat bodies were inactive.Prothoracic glands and oenocytes incubated together resulted in a slower pupation index than would be expected from the sum of single determinations of oenocytes and prothoracic glands. This is explained by the ability of prothoracic glands to build conjugates of ecdysones.