Hans Spemann

The held texts cite Spemann's 1918 paper series on the determination of the first organ rudiments in the amphibian embryo². Child used it, with Mangold's 1920 work, as evidence about the region in front of the dorsal lip of the blastopore¹. Child said this region helps form the head nervous system. His passage says it develops independently of other parts after a certain stage. It breaks off while saying that the region also governs how other parts develop¹.

Child's bibliography also lists a 1921 paper by Spemann. Its title describes producing animal chimaeras by embryonic transplantation between two newt species, Triton cristatus and Triton taeniatus³. The held passage gives only the title. It does not say what was measured or found. It shows that Spemann's transplant work was known to Child by 1924.

Rádl wrote that Spemann returned to the problem of developmental mechanics after the war. In this account Spemann and pupils tried to revive Roux's ideas. They sought to show that the embryo holds specific centres which control how organs differentiate⁴⁵. Durant and colleagues, writing on planarian regeneration, place Spemann's organizer concept in a line of historical gradient models. They list it alongside Child's gradient model and Wolpert's positional information theory⁶.