An introduction to the study of embryology / by Alfred C. Haddon.

  • Haddon, Alfred C. (Alfred Cort), 1855-1940.
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to the study of embryology / by Alfred C. Haddon. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    spot where tlie epiblast and hypoblast pass into each other, and it is difficult to say which layer has the larger share in its formation; if either, it is perhaps the epiblast. The formation of the mesoblast in the Lamprey is, according to Calberla, practically identical with that in the Newt; in some Fig. 6o.—Late Gastrula Stage of Lampkey. [After Scott.] A. Median longitudinal vertical section. B. Section to one side of A. The relation of the hypoblast to the mesoblast is more clearly seen in fig. 6i. a. archenteron (mesenteron); bp. blastopore; ep. epiblast; hy. hypoblast of mesenteron, axial hypoblast in A. ; m. paired mesoblast; m' ventral unpaired mesoblast; y.hy. yolk-hypoblast. respects it is simpler than in the latter, owing to less food-yolk being present in the ovum. The position of the paired mesoblast is clearly shown in figs. 60 and 61. The two latero-dorsal sheets extend from the lip of the blastopore some distance forwards, but Fig. 61.—Transverse Sections through the Upper Portions of Two Embryo Lampreys (Petroruyzon plaiieri). [After Calberla.] A. Same stage as fig. 63. B. Later stnge. a. archenteron ; ax.hy. axial (notochordal) hypoblast; ep. epiblast; hy. (diges- tive) hypoblast; vi, mesoblast; n.k. neural keel; n.p. neural plate; y.h. yolk- hypoblust. they have not yet acquired any lateral or rather ventral extension ; dorsally they are separated from one another by the axial hypo- blast (figs. 60, A, and 61, a). According to Scott, a single layer of mesoblast (fig. 60, m') surrounds the lateral and ventral surface of the yolk-hypoblast