Relations Between Temperature Sensitivity and Morphogenesis in Tetrahymena pyriformis GL*

SYNOPSIS. The division delay responses of Tetrahymena (“set‐back” curves) which result from heat shocks of the type used in synchronizing studies have been examined in logarithmic and synchronized T. pyriformis GL. The curves indicate an increasing sensitivity to heat shocks with increasing cell age, a sudden sharp increase just prior to the “transition point” and a loss of sensitivity at the transition point. A correlated study of morphogenesis in the synchronous generation suggests that the sudden increase in thermal sensitivity before the transition point is due to a dedifferentiation and redifferentiation of the developing oral primordium which can be induced at this time. The results also suggest that the “stabilization” of the primordium which follows the transition point may occur at more than one developmental stage, i.e., is not stage‐specific. It is suggested that stabilization may therefore be due to conditions lying outside the primordium.