A triangular dorsal structure, consi dered to be the gastrocoel roof plate(grp),was located in the primitive gus, and was exposed to the cavity of the gastrocoel (Fig.12.12C).The grp ijncluded the ventral surface the notochord and paraxial mesoderm,and was bordered by the ateral endodermal crests(lec).The grp is illustrated for E.call stomma(Figs.12D)