Abstract
It appears that the initial steps up to the [sea urchin] blastula stage are independent of the quality of the nuclear substance, even though it is essential that the nuclear substance be of a kind capable of existing in the egg. The necessity for particular chromosomes becomes apparent first with the formation of the primary mesenchyme and from then on shows up in all processes as far as development can be observed. . . . With respect to those characters in which we are able to recognize individual variations, the nuclear substance and not the cyte plasmic cell substance imposes its specific character on the developing trait. . . . Earlier stages, for which according to our results, specific chromosomes are not necessary, demonstrate a purely maternal character. . . . I would like to ascribe to the cytoplasm of the sea urchin egg only the initial and simplest properties responsible for differentiation. . . it provides the most general basic form, the framework within which all specific details are filled in by the nucleus.
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