Stem cells are found in epithelia and embryonic mesenchyme of connective tissue. Each structure originates from a different germ layer&colon; the ectoderm, endoderm and mesenchyme. The mesoderm forms mesenchyme, mesothelium, non-epithelial blood cells and coelomocytes. In utero, the epithelium and underlying mesenchyme interact to form hair follicles. Hepatic stellate cells are derived from mesenchyme. Like other cells of connective tissue, fibroblasts are derived from primitive mesenchyme. The choroid plexus is formed from ependymal cells and vascular mesenchyme. The mesenchyme above the meninges undergoes intramembranous ossification forming the neurocranium. Osteoblasts/osteocytes develop in mesenchyme. The gonadal ridge initially consists mainly of mesenchyme and cells of underlying mesonephric origin. Important to the sea urchin blastula is the ingression of the primary mesenchyme. Several different cells from the mesenchyme can give rise to sex-cord or stromal tumors. The importance of mesenchyme-to-epithelial signaling is to maintain AMHR-II expression in the mesenchyme. Neural mesenchyme forms soon after primary mesenchyme formation. Furthermore, dorsal mesenchyme surrounding the presumptive esophagus form the muscular crura of the diaphragm.