Mosaic and Regulation Phenomena during the Early Formation of the Chick Blastoderm
(a): Schematic representation of the oblique hemisectioning of an unincubated chicken blastoderm in which the sickle horn and half median part of the Rauber’s sickle (indicated by double interrupted lines) and endophyll were surgically removed on the same side. SH, top of the remaining sickle horn region (in green) extending far cranially; RS, remaining Rauber’s sickle half and E, remaining half endophyll; CMZ, caudal marginal zone; CGW, caudal germ wall; L, unoperated left side of the blastoderm. (b): Unincubated chicken blastoderm (operated according to the schematic representation in Figure 13(a)) at the start of the culture period; a graphite particle (arrowhead) is placed on the sectioned median part of Rauber’s sickle. E, left half of endophyll sheet localized in the concavity of left half of Rauber’s sickle of the unoperated side. Bar = 2 mm. (c): The same blastoderm after 7 hours of culture: a densification with primitive streak (arrowhead) formation parallel with the cut edge is observed. Bar = 2 mm. (d): Living somite embryo developed in the blastoderm of Figure 13(c), after 31 hours of culture; arrow indicates a beating denser round mass (corresponding to the left primary heart tube as visible in sections) just cranial from the anterior intestinal portal (arrowhead) at the left side; bar = 1 mm. (e): The same blastoderm after fixation and in toto staining with Unna; the area vasculosa (AVA) lies caudally and laterally from the embryo proper. AVI, area vitellina interna. At the right side no area vasculosa has formed due to the total absence of Rauber’s sickle material in this side. Bar = 2 mm. (f): Section through the heart region of the embryo seen in Figure 13(d) shows unilaterally (at left side of the embryo) a hemi-pericardial cavity (P); arrowhead indicates the epimyocard; H, unilateral heart tube; G, foregut; S, somite-like material and intermediary mesoderm (IM) splitting into parietopleura and splanchnopleura. Harris hematoxylin-eosin. Bar = 100 μm.
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