Paper - The futility of the human yolk sac

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Lewis FT. The futility of the human yolk sac. (1922) Science 55 (No. 1427): 478.

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This historic 1922 letter by Frederic Thomas Lewis (1875—1951) was commenting on a recent paper by Arey.

Arey LB. Direct proof of the monozygotic origin of human identical twins. (1922) Anat. Rec. : 245- .

Modern Notes: yolk sac

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The Futility of the Human Yolk Sac

Frederick Thomas Lewis
Frederick Thomas Lewis (1875-1951)

The Futility Of The Human Yolk Sac

Science (May 5, 1922) - Discussion and Correspondence

by Frederick Thomas Lewis

In the current issue of the Anatomical Record, Professor Arey publishes a brief but very interesting contribution (No. 90) from the Anatomical Laboratory of Northwestern University. He describes a human chorion containing two embryos, of 11.5 and 12 mm. respectively, one of which has a yolk sac, and the other has none—that is, none was found, and sections of the umbilical cord showed no trace of a yolk stalk. Hence the broad conclusion is drawn that “the human yolk sac is a vestige unessential to growth or differentiation (including vasculogenesis).” It is stated that one of these embryos “received all, or essentially all, the cells destined to form a yolk sac” and that’ “the total absence of a yolk sac in one embryo, which is otherwise normal in every way, further demonstrates conclusively that this organ is not essential to the growth of an embryo or to the proper differentiation of its parts; indeed, the embryo in question is slightly larger than its twin.”

Since from the days of Wolff the yolk sae has been regarded as the source of the intestinal tract, and in young human embryos is seen to be the organ from which the allantoic duct and the digestive tube proceed, the startling nature of this conclusion becomes apparent. But it is universally recognized that the yolk sac does its work in early stages, and though the sac usually persists as a functionless rudiment until birth, its duct normally becomes parted through atrophy in embryos younger than the one under consideration. Does Dr. Arey’s case indicate anything more than the precocious obliteration of the stalk of an organ no less essential than the placenta, likewise cast off after its very vital functions have been performed?

If the question is raised, Where then is the yolk sae in Dr. Arey’s case? his own studies furnish a plausible answer, since in another specimen he has described a single sac with two stalks, each leading to a separate embryo. Under such circumstances, the early obliteration of one of the stalks would give rise to the conditions observed in the second case, and this possibility must be eliminated before accepting the proposed conclusion. In reading the account of a human embryo without a yolk sae, we recall Bentham’s incredulous comment, “I am very glad, my dear sir, that you saw that, for had I seen it myself, I wouldn’t have believed it.”

Frederick T. Lewis

Harvard Medical School,

Boston, Massachusetts

Cite this page: Hill, M.A. (2024, May 25) Embryology Paper - The futility of the human yolk sac. Retrieved from

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