RESIDUAL CORNEA AND THE DEGENERATE EYE OF THE CRYPTOPHTHALMIC TYPHLOTRITON-SPELAEUS

The cave-dwelling Typhlotriton spelaeus larvas live in daylight. The l arvas undergo a metamorphosis when the thyroxin level (T3 and T4) incr eases. They leave aquatic life for terrestrial and subterranean aphoti c life. The larval eyes are normal and show good vision response to te sts. On the contrary, in the oldest larva and the adult, the eyes are small with poor vision or no vision at all. The lens can disappear but in any case the eyelids grow over the eye. The retinal degeneration t akes place during and after metamorphosis. The admitted statement that ''after metamorphosis . . . the developing lids close over the eye an d invade the cornea'' is not confirmed concerning the invasion, becaus e it is now evident that the eyelids separate spatially from the resid ual cornea. Consequently, the fibroblasts of the eyelids are not able to invade the corneal stroma. In fact, the periocular tissues do not i nvade the cornea but invade the eyelids' tissues. We are able to confi rm that the development of the larval eyes is complete and apparently normal. After metamorphosis, the eyes decrease in size. The cornea ''s inks'' with the eye into orbit tissues. The eyelids cover the eye and are themselves replaced by a supraocular skin. This fits the descripti on of the human cryptophthalmia. We also demonstrate that even in the degenerate eye the residual cornea retains the main structure of a nor mal salamander cornea. The preservation of the endothelium and of the Descemet membrane is exceptional in blind cave-dwelling vertebrates be cause in the other degenerate corneas the edema of the stroma depends on the spatial disjunction of the underepithelial stroma and the supra endothelial stroma. Perhaps, the, very advanced development of the eye and the late start of the degenerative processes could explain the re lative preservation of the cornea. Thus, the arguments put forward ten d to prove that the thyroxinic metamorphosis sets off the growth and f usion of the eyelids but that the eye degeneration is related to hered itary processes.