. Quain's elements of anatomy . vertebral divisions are visible; so, the upperdivision of the blastoderm ; sf, the lower division, wherethey have been cut away from the peripheral parts. Some part of the difficulty now mentioned hasarisen from the observations of A. Eauber (No. 101),who in 1875 detected the presence, in addition to twoother layers of the blastodenn in the rabbit, of a thinlayer of flat cells closely adherent to the outer surface,which he found to have only a temporary existence,and gradually to disappear in the course of the de-velopment of the other layers. Lieberkiihn a fewy
. Quain's elements of anatomy . vertebral divisions are visible; so, the upperdivision of the blastoderm ; sf, the lower division, wherethey have been cut away from the peripheral parts. Some part of the difficulty now mentioned hasarisen from the observations of A. Eauber (No. 101),who in 1875 detected the presence, in addition to twoother layers of the blastodenn in the rabbit, of a thinlayer of flat cells closely adherent to the outer surface,which he found to have only a temporary existence,and gradually to disappear in the course of the de-velopment of the other layers. Lieberkiihn a fewyears later (No. 104) showed that the outer layer offlat cells described by Rauber, which form the wholeof the outer covering of the blastodermic vesicleresulting from the primary segmentation, is not theprincipal source of the permanent epiblast, but that that layer as well as thehypoblast or lower layer are the product of differentiation of the cells whichform the internal mass of segmentation, spheres or yolk-rest. Fig.
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