Studies in the Dynamics of Histogenesis. Ii. Tension of Differential Growtii as a Stimulus to Myogenesis in Tike Esophagus. by Eben

Facts presented, for the first time, in a previous publication by the writer (1919-20) prove that the developing descending colon of the pig embryo possesses two zones of differential growth which by their interaction mutually influence each other during the formation period. The inner epithelial tube is the dominant, most active region of growth. I t presents numerous mitotic figures which pursue a path cephalad, primarily, in the manner of a left-handed helix. The outer mesenchymal zone is less active in growth and early in development is composed of a uniform mass of undifferentiated cells. The inner, rapidly growing, epithelial tube practically revolves due to the rapid spiral growth of its cells. With subsequent growth an apparent ring (this is qualified apparent for in reality a close spiral is formed) of smooth muscle myoblasts appears gradually near the periphery of the vortex. This position taken by the inner, close spiral, smooth muscle coat at some distance from the epithelial tube is dependent upon an optimum tension. The attitude heretofore taken by embryologists eliminated the search for the underlying cause of the first formed, inner, muscle coat The theory of self-differentiation excluded interpretation as regards myogenesis. A certain mesenchymal cell, regardless of position, was considered as destined to become a myoblast. This highly differentiated tissue is now considered to self-dextelop, for so called muscle-forming elements have been identified in the