The terms embryonic and adult stem cells are explained. Previous studies on identification, description and isolation of the embryonic stem cells in different invertebrate groups are briefly summarized. Most invertebrates, which reproduce asexually have retained the embryonic stem cells in their adult body. A hypothesis is proposed for the possible exclusion of embryonic stem cells and thereby asexual mode of reproduction by the coelom in arthropods and molluscs. This hypothesis attempts to establish a correlation between the presence of haemocoelom and the absence of embryonic stem cells and the consequent nonoccurrence of asexual reproduction in arthropods and molluscs. Most invertebrates reproduce sexually but may switch over to asexual mode of reproduction, when need arises owing to biotic factors, e.g. very high density1 or abiotic factors, e.g. water quality parameters2. The presence of embryonic stem cells is obligatorily required to facilitate the asexual reproduction, as in sponges, cnidarians, turbellarians, clitellates and echinodermates.
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