Stockard has shown that, not only do anesthetics arrest the development of the intra-embryonic blood vessels in the embryos of Fundulus, at an early ontogenetic stage, but in such a manner that no doubt can now exist that, under normal conditions, these vessels are formed in situ by a concrescence of independent and discontinuous anlagen, and that their endothelium is derived directly from intra-embryonic mesenchymal cells.
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