_am._ Amnion. _ch._ Notochord. _ch´._ Notochordal thickening of hypoblast.
_ep._ Epiblast. _hy._ Hypoblast. _m.g._ Medullary groove. _me.p._
Mesoblastic plate. _ne._ Neurenteric canal (blastopore). _pr._ Primitive
streak.
SERIES A. Sections through an embryo shortly after the formation of the
medullary groove. x 120[4].
Footnote 4: The spaces between the layers in these sections are
due to the action of the hardening reagent.]
Fig. 1. Section through the trunk of the embryo.
Figs. 2-5. Sections through the neurenteric canal.
Fig. B. Surface view of a somewhat older embryo than that from which Series
A is taken. x 30.
SERIES B. Sections through the embryo represented in Fig. B. x 120.
Fig. 1. Section through the trunk of the embryo.
Figs. 2, 3. Sections through the hind end of the medullary groove.
Fig. 4. Section through the neurenteric canal.
Fig. 5. Section through the primitive streak.
Fig. C. Surface view of a somewhat older embryo than that represented in
Fig. B. x 30.