 electron microscop studi wolffian len regener adult newt chang morpholog cell regen tissu transform pigment epithelium iri len adult newt trituru viridescen studi ultrathin section electron microscop addit quantit analys electron micrograph perform cell normal iri character abund melanin granul extens smooth-- surfac endoplasm reticulum irregular indent nuclear membran len remov visibl chang detect nuclei mediodors iri cell involv increas number primari nucleoli nuclei enlarg spheric promin nucleoli appear nucleoli distinguish normal nucleoli presenc granular cortex surround fibrou core pigment granul complet extrud intercellular space subsequ leucocyt endoplasm reticulum disintegr gradual final disappear increas ribosom cytoplasm cytoplasm matrix acquir fibrou element 50 wide low densiti correspond natur main compon normal len cell chang transform cell discuss 