Nymph of cockroach emerge out from ootheca. A nymph resembles to adult in general structure but lacks the wings and mature reproductive organs.
Instar a large stage in the development of insects (larval instar, nymphal instar). Period between two moults in insects is termed stadium.
In periplaneta americana the nymph grows by moulting about 13 times to reach the adult from blatta orientalis moults 6 times.
Metamorphosis is regulated by two hormones, ecdysone secreted by prothoracic glands and juvenile hormone secreted by corpora allata.