Location of fluorescent descendants of cells from region A and B at stage HH8.

<p>(<b>A–B</b>) Bright field and fluorescent images of labelled embryo at stage HH8 and HH8⁺ showing the location of fluorescently labelled cells. Descendants from region A are labelled with DiI (red) and descendants from region B are labelled with DiO (green). White arrow heads in (<b>A</b>) mark where the intestinal portals are situated. At HH8 cells from region A were located in the intermediate mesoderm and head mesenchyme, whilst cells from region B were located in the intestinal portals and in the heart forming region. (<b>B</b><b><i>i</i></b><b>–B</b><b><i>iv</i></b>) Sections of embryo in (<b>B</b>) demonstrated that cells from region A (red) were located in the cranial paraxial mesoderm (CPM) and cells from region B (green) were located in the splanchnic mesoderm (SpM). (<b>B</b><b><i>i</i></b><b>–B</b><b><i>iii</i></b>) Colour channels of sections have been separated into DiI/red on the left hand side panels and DiO/green on the right hand side panels for clearer observation of cell location. (<b>C</b>) Labelled cells from region B were also observed in the dorsomedial region of the splanchnic mesoderm, marked with an oval (n = 10). (<b>D</b>) DiI labelled descendants of cells from a region of the primitive streak just caudal to the limits of region B were located in the extraembryonic mesoderm (red cells), (n = 21). Scale bars = 50 µm.