Contributions to the Physiology of Form Generation in the Development of the Sea Urchin

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Abstract
A survey of the gradient hypothesis as the term is used by workers on echinoderm development is given. The methods of modifying the development of form by treatment of the embryos with certain chemicals are analyzed for the purpose of ascertaining whether modifications are due to specific, formed materials or to metabolic processes modified by them. Animalization of vegetal parts of the embryo by SO4 deficiency and their restoration by treatment with Li+ indicate that the vegetative principle is extended by Li+ rather than that it is formed by it. Further evidence is given that the animal principle is associated with the metabolic processes and that a causal relationship exists between inhibition of respiration and the animal principle. The reduction patterns shown by embryos up to the late blastuJa must be directly associated with the metabolic processes. A close relationship between the origin of the dorso-ventral axis and the animal and vegetal principles is also indicated.