Lens Induction in the Salamander (Amblystoma punctatum) with Special Reference to Conditions in Experimentally Produced Cyclopia *

It has long been known that the early optic vesicle and cup are much concerned with the growth and differentiation of the lens in the vertebrate eye. Le Cron"2 first demonstrated this fact when he isolated the lens-forming cells in Amblystoma embryos at various early stages in development by merely removing the underlying optic anlage. His experiments showed that the longer the lens epithelium was associated with the optic vesicle or cup the better was the final development of the lens. Therefore, as the developing lens presses deeper into the early forming optic cup, it is clear that the relationship is more significant than mere contact between the two tissues. The effects of the lens-eye association can be demonstrated even later in development, as shown by Harrison"' and one of the authors"8 in experimental studies on lens and eye size. The close association by contact between the lens and eye-forming cells, however, starts very early. That this contact is very important was first shown by Lewis'4 '5 and later by Spemann,'7 Mangold,'" and others. In some forms of amphibians they showed that the optic vesicle induces the overlying ectoderm, in some unexplainable way, to form a lens, even if the ectoderm was transplanted from some place on the body wall. Strong evidence has been accumulating that the time at which this induction first begins to take place, and the period over which it extends, varies in the different species. If an experiment on an early stage in eye development fails to reveal the existence of induction capacity of the eye at that time, it has often been found that the period has not yet been reached or that it has passed. A further search then usually reveals the moment at which induction takes place. Spemann17 and Mangold'"