|Beschreibung:||Pattern formation, morphogenetic movements and extensive processes of cell proliferation and differentiation are hallmarks of embryogenesis. Yet freshwater Hydra undergoes all these processes in adult asexual state, and was traditionaly considered to be a constant embryonic model. However, we have previously demonstrated that the timing of expression of regulatory genes differs significantly between in embryos and during patterning events in the asexual polyps. In this thesis the result of an unbiased search for genes upregulated during embryonic development in contrast to adult morphogenetic events is presented. Sequencing of the subtracted cDNA library yielded 76 clusters and 12 singletons, and many of these clusters and singletons represented putative novel genes. A homologue of the conserved Polycomb group regulatory gene Embryonic Ectoderm Development was cloned in this experiment and characterized in detail. It turned to be the earliest known marker of the multipotent interstitial stem cells, and allowed to trace their origin to the endoderm of the embryo.