Hans Spemann demonstrated nuclear equivalence using:
Hans Spemann tested nuclear equivalence by constricting newt Triturus taeniatus embryos with baby hair ligature until two compartments connected by narrow cytoplasmic bridge, allowing nuclei to cross. Newt embryos tolerate slow cleavage, large blastomeres and pliability making technique feasible, unlike smaller frog or sea urchin eggs. He demonstrated each half with a nucleus developed into normal larva, supporting totipotency. Salamander similar but newt preferred historically. These newt experiments laid foundation for organizer discovery and later somatic cell nuclear transfer concepts and cloning principles.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Spemann's nuclear equivalence experiments using newt embryos.