ABSTRACT
Early development in animals is guided by the RNA reserves of the egg (see Davidson, 1986 for a review), and therefore variations in eggs might correlate with changes in their patterns of early development. Frogs are organisms especially suitable for analyzing the relationship of oogenesis to development, because many frog species have evolved distinctive changes to avoid or diminish their period of aquatic dependence (Lamotte and Lescure, 1977; Duellman and Trueb, 1986). The analysis of the developmental adaptations that accompany the modes of frog reproduction, however, is hindered by the fact that the best investigated frogs, such as Xenopus laevis or Rana pipiens, have aquatic reproduction and similar modes of oogenesis and early development, although the former is in a family considered to be primitive (Pipidae), with adult specializations for an extreme aquatic life-style, whereas the latter is in an advanced family (Ranidae), with more pronounced terrestrial adaptations in the adult (Table 1). The modes of reproduction found in the 21 living families of frogs is shown in Table 1. The traditional order of anuran classification has been maintained in Table 1, but the higher taxa are not given. In an ancient and diverse group, such as the anurans, there might be many cases of similarity due to derived features, and the current knowledge of many characters and their evolutionary change does not allow the reconstruction of the anuran phylogeny (Duellman and Trueb, 1986).
