From the literature on onthogenesis it is concluded, that male genitalia with two pairs of appendices must be considered primitive. The male genitalia of a number of species from three families (Cossidae, Saturniidae, Brahmaeidae) in which the male genitalia comprise two pair of appendices, valvae and valvellae, were dissected. The results are compared to earlier studies of species of Lithosiinae (Arctidae). It is concluded, that morphologically must be distinguished between two types of intromittant organ, or phallos, viz. aedoeagus and pseudaedoeagus.