Fig. 3

Early lithium exposure leads to excess shield formation and aberrant morphogenesis. (A-D) Animal pole views of 6 h embryos. Arrowheads mark the location and presumptive direction of migration of regions of the germ ring having embryonic shield morphology. (A) Control embryo. The shield appears as an anterior thickening of the germ ring and occupies a 30° arc. (B) Lithiumized embryo, broadened shield. A single thickening at the germ ring subtends a 90° arc. (C) Lithiumized embryo, supernumerary shields. (D) Lithiumized embryo, radialized shield. (E-H) Lateral views of 12.5 h embryos. Anterior is to the left in each panel. The blastopore in each embryo is indicated by an arrowhead. (E) Control embryo. Seven somites have formed, and the tailbud, which is just caudal of the blastopore, has not yet extended off the yolk. (F) Lithiumized embryo. A large mass of segmented tissue extends posteriorly, with the blastopore located at its terminus. (G) Lithiumized embryo. The large posterior extension is unsegmented. (H) Lithiumized embryo. The blastopore has closed onto and bisected the yolk, and the extruded portion of the yolk is partially covered by posteriorly extending cellular material.