Internal gravity waves are present in both the ocean and atmosphere. The oceanic gravity wave power spectra have been modeled semi-empirically by Garrett and Munk (1972, 1975) and shown to have ''universal'' properties. Their model seems to be useful also for atmospheric waves. Recently a similitude type of ''saturation'' model for vertical wave number horizontal velocity fluctuation spectra has met with empirical support in the atmosphere. The present paper employs a further similitude argument related to ''cascade'' properties which would apply to the frequency and horizontal wave number spectra. Testable consequences are exhibited. If validated the model would provide useful insight into the physics of these waves.