Factors Controlling Lens Regeneration from the Dorsal Iris in the Adult Triturus viridescens Eye. ∗

When the adult eye of Triturus viridescens is transplanted 1 , 2 or its blood supply is temporarily lost 3 the lens degenerates along with most of the retina. In these cases a new lens is developed from the dorsal pupillary margin of the iris such as follows simple lensectomy. 3 , 4 This phenomenon of lens replacement is largely, if not exclusively, confined in the vertebrates to the Triturus group of salamanders 5 , 6 , 7 where the lens appears to be less resistant to injury than in other forms. 5 , 8 An extensive study is being made by the author in search for the factors which govern this phenomenon. Some of the findings can be summarized at this time.

Slight injuries to the fully developed lens in the adult eye of Triturus viridescens cause it to degenerate. Injuries to the dorsal iris produced by mechanical stretching and incisions radiating from the pupillary margin neither prevent nor favor lens regeneration. Such injuries heal readily. Only the presence of the normal lens prevents a new one from forming. This was shown by means of a successful pipette method of removing and reimplanting the lens in the adult eye without injury.

If a piece of the dorsal iris from a normal eye or from one lensectomized 6 or 7 days earlier is transplanted to a freshly lensectomized host eye, a new lens will develop from the graft. If, however, such grafts are placed in an eye possessing a normal lens, the latter sharply inhibits lens regeneration in all cases. Even in those grafts where the implanted iris was allowed to initiate early preparation 7 for lens regeneration through delay before transplantation, only a rare case showed at best a feeble, short-lived attempt to progress further before it was permanently arrested. The presence of the normal lens of the host eye apparently exerts an early effect upon the lens-forming capacity of the implanted iris.