Embryology of Dolphins: Staging and Ageing of Embryos and Fetuses of Some Cetaceans (Advances in Anatomy, Embryology and Cell Biology, 157)

Comparative embryology has been neglected in the past decades. In our opinion the decreased interest has been caused by the fact that the time factor has not suffficiently been respected. Therefore we used the Stageing and Ageing Method (Sterba 1995) to determine the ontogenetic age of embryos and to state the time tables and time relations of various ontogenetic events. We examined 167 embryos and fetuses of four dolphin species (collection Dr. Senckenbergische Anatomie, Franfurt am Main). The study of intrauterine development and growth while consistently respecting the time factor enabled us to determine the time course of organogenesis of all organ systems. The resulting comparison with other mammals detected the time lag in ossification, retardation of odontogeny, the time of the origin and development of the fluke, dorsal fin and flipper, etc. We believe the Stageing and Ageing Method serves for a much more efficient evaluation of existing embryological collections which very often contain embryos of unknown age. The rapid development of molecular biology and genetics has led to renewed interest in embryology, comparative embryology, and studies of the relations between ontogeny and phylogeny. In fact, genes have been identified which are involved in the formation of shapes and structures, and it is becoming apparent that their primary morphological expressions are conspicuously similar in different species. The primarily identical shapes do not become diversified until advanced individualization of embryos, and it is here that it is possible to employ the knowledge of comparative embryology, the branch of science engaged in the study of the development and differentiation of tridimensional structures in different animal groups. However, comparative embryology has been neglected during the past decades, as its development has appeared to have been completed. In our opinion, the decreased interest in comparative embryology has been caused by the fact that often the time factor was not or could not be respected. In fact, in the case of embryos of wild animals even their ontogenetic age and sometimes the duration of intrauterine development are unknown.

The study of intrauterine development and growth while consistently respecting the time factor enabled the authors to determine the time course of organogenesis of all organ systems. The resulting comparison with other mammals detected the time lag in ossification, retardation of odontogeny, the time of the origin and development of the fluke, dorsal fin and flipper, etc. The authors believe the Staging and Ageing Method serves for much more efficient evaluation of existing embryological collections which very often contain embryos of unknown age.

Sex differences are observed in various physiological, behavioral, and psychic functions, including reproductive behavior, aggres­ sion, emotions, and cognition. The existence of sex differences in functions of the central nervous system has suggested that there are also morphological sex differences. Content: Front Matter....Pages I-X Introduction....Pages 1-8 Aims of this Study....Pages 9-9 Material....Pages 11-17 Methods....Pages 19-44 Results....Pages 45-121 Discussion....Pages 123-125 Back Matter....Pages 127-133