Appearance of Accessory “Organizers” in Overripe Eggs of the Frog. ∗

Abstract

The author has described 1 the condition of overripeness that develops in frog eggs if fertilization is delayed 3 to 5 days after ovulation. Among the abnormalities of embryonic development that follow, one of the most striking is the frequent appearance of reduplications. In the early gastrulation stage instead of the normal upper blastopore lip of limited extent and regular curvature there often appear long and irregular clefts and folds in the equatorial region. Attempts at gastrulation become visible not only on one side but all around the whole circumference of the embryo. As time progresses multiple blastopores and multiple gastrulation lead to the development of twin embryos. As we have pointed out previously, 1 this effect indicates that overripeness has brought about 2 concomitant changes in the embryos. First, the physiological correlations by which an embryo develops as a balanced organism are impaired. These correlations largely rest on inhibitory functions by which established “organizers” (inductors) suppress either the formation or the effective functioning of competing organizers. Secondly, “organizers” appear in lateral and ventral regions of embryos, where normally they never occur. We have described this as self-differentiation or merogenesis of physiologically isolated parts. The mechanism of this formation of secondary organizers remained a complete puzzle until the recent discovery of Holtfreter 2 that material from the ventral region of an early embryo which has no inductive qualities in living condition, acquires such potencies after being killed by heat, dryness, etc. We are inclined now to assume that the possibility to develop into organizer is inherent to any part of the embryo, probably even to every cell. The inhibitors that suppress their realization are destroyed by such factors as heat and dryness but also by the process of overripeness.