The Occurrence of the Evocator in Organisms Which Possess no Nerve Cord

Abstract

1. Tissue from Hydra viridis, boiled in water for ½-1 min. and then implanted into the blastocoele of young newt gastrulae, evocates the formation of neural tissue, in the best cases of definite neural tubes. 2. Since Hydra possesses no nerve cord, the evocator which it contains cannot perform, during development, any function similar to that of the evocator in the amphibian egg. 3. It is pointed out that it would probably be impossible to distinguish between a substance which actually contained the evocator and one which could unmask the evocator which is known to be contained in the amphibian gastrula ectoderm. The substances and tissues which have hitherto been taken to be themselves evocating (including Hydra tissue) may therefore be agents which unmask the evocator already present.