The evidence is noted that (1) a flux density limited complete sample of X-ray emitting BL Lac type sources is now available from Schwartz and Ku (1983), that (2) the radio through X-ray emission of BL Lac type sources is most easily interpreted as nonthermal emission from a relativistically boosted jet pointed close to the line of sight and that (3) all galaxies identified with BL Lacs are of giant elliptical type. From this, a space density of the parent population of BL Lacs is derived, elliptical galaxies with relativistically boosted jets not generally pointed at the observer. This space density is remarkably close to that of bright elliptical galaxies and suggests that these galaxies constitute the parent population for BL Lacs.