Discussion Do whitefish have epibranchial organs Diverticu- lae are certainly present in the same place as epi branchial organs, but are these small sacs epibranchial organs NELsoN (1967) mentioned the difficulty in answering this question in Alosa and tabulated other species with small, large or absent epibranchial organs. No definitions were, however given of "small" and "large", and he obviously missed the vestigial epibranchial organs of some fishes, e.g. in the Pristigasterinae (BERTMAE et al., 1970). In order to decide if the diverticulae are epibranchial organs rudimentary or vestigial, one has to study the com parative anatomy and function of these organs and associated structures. Comparative anatomical investigations have shown that the epibranchial organs are always supported by and attached to, the enlarged E4 bones and that the latter are fused to small cartilaginous E5 elements (NELsON, 1967 BERTMAR et al., 1970). Since Coregonus iavaretus has diverticulae supported by such modified structures (Fig. 1) we have concluded that the divertic, ulae are epibranchial organs and that predecessors of the species must have had large epibranchial organs, which later became reduced when the fishes no longer