Title Reflexions sur la valeur des donnees embryologiques pour la morphologie. - The present paper contains some notes on the morphological value of embryological data. As an example, a critical discussion is given of the influence of embryological data on the interpretation of the gnathosoma. At the hand of a series of examples from other groups of animais, the inadequacy is demonstrated of embryological data as an only base for .conclusions in the field of morphology, especially on homology. The embryonic development is characterized as a complicated network of ascendant, descendant and vertical evolutions. It is pointed out that this network can only be analysed by comparison of numerous cases from different groups (an analysis of which it is still unknovvn whether it will arrive at a synthesis of evolution) .