How did urodele embryos come into prominence as a model system?

Experimental studies on amphibian embryos started mainly in Germany during the last two decades of the 19th century. At first, urodele amphibians were used much less frequently than anurans. At that time, embryological studies on urodeles were mostly descriptive and comparative. In Germany, Spemann (1900)--immediately followed by Harrison in the United States--began extensive studies on the newt egg and early embryo. Those studies finally led to the prominence of urodele embryos in general experimental embryology during the period 1920-1950. Milestones of that era are described and the main researchers are indicated.