ABSTRACT
The phylogenetic significance of the characters of developmental stages in animals and plants has been the subject of much recent controversy, in which the issues have been bedevilled by dogmas and counter-dogmas. An important factor working against the manifestation of proper recapitulation in the animal kingdom has been the widespread tendency toward accelerated development, often correlated with the development of more yolky eggs. This chapter outlines the phylogenetic systematist considering information about the developmental stages of his organisms needs to answer two main questions. The first is, to what extent are the special features of the immature stages recapitulatory, reflecting former adult conditions? The second, to what extent are the non-recapitulatory, 'caenogenetic' features of the young stages phylogenetically and taxonomically significant in their own right? The early developmental stages of freshwater eels manifest, in their physiological adaptations to marine life, an element of ontogenetic recapitulation.
