Te overall body plan of the organism is laid down during oogenesis, and in early embryogenesis. In many types of eggs some specific factors (determinants) are symmetrically deposited within these cells what results thereafter in differential mitoses of embryos. The overall body plan of embryo results from a hierarchy and spatially self-limiting activations of fairly universal classes of genes coding some transcription factors essential for pattern formation in different types of embryos, and from activations of genes controlling the geometry of cleavage. Implementation of instructions concerning the emergence of the body plan specificies the main anteroposterior and dorso-ventral reference axes and the proportional assessment of the primary regionalization of embryos. Two kinds of mechanisms creating positional information are presented: 1) based on cross-talks of signalling pathways either among particular cells within the embryos, or between the embryo and adjacent somatic cells of the ovary, and 2) based on mechanism polarising and orienting mitoses. The emergence of positional information within the embryos is discussed in terms of appearance of gradients of morphogens, the primary embryonal induction, lateral inhibition and mechanisms of segmentation. The recent idea of evolution of homeotic genes by their tandem duplications and diversification is summarized, that results in combinatory networks of the homeotic genes, monitoring specification of the body parts.