XXVI.—Observations on the Early Development of the Human Embryo

Abstract

This memoir is based upon the study of three normal human embryos belonging to the period of development preceding the cleavage of the paraxial mesoderm into the primitive segments, as well as of certain abnormal specimens of the same early period which have yielded valuable corroborative data, but will not be described in detail. Well-preserved specimens belonging to these early stages are very rare, and our knowledge has been, and can only be, built up from the detailed descriptions of isolated cases by the individual observers into whose hands they happen to fall.