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.