An Analysis of the Postgastrula Differentiation of the Hypomere

Since the publication of earlier papers (Finnegan, 1953, 1955) the investigation of the capacity of the salamander hypomeric mesoderm for histogenesis under a variety of experimental conditions has continued. It is perhaps prudent at this time to initiate a series of reports with results obtained from in vitro experiments which were designed to gain some insight into the roles of competence, tissue mass, and endodermal influence relative to hypomeric differentiation in Ambystoma . This portion of the mesoderm is destined to undergo its differentiation far removed from the dorsal axial influences of the chorda-mesoderm but with its inner (splanchnic) material in rather intimate association with the endoderm, a tissue known to be determined at an early age and metabolically active, two conditions which lead one to suspect it of inductor potentialities (Nieuwkoop, 1947; Copenhaver, 1955).