develops from ends during starts during intermediate mesoderm pronephric mesenchyme XAO:0000264 pronephric primordium pronephric bulge xenopus_anatomy pronephric anlage UBERON:0005721 Portion of tissue that consists of the mesenchymal precursor to the pronephric kidney and that begins to separate from the intermediate mesoderm at NF stage 21 and epithelializes by NF stage 30. mesenchyme NF stage 21 NF stage 29 and 30