REPAIRS AND REGENERATION 103 



made upon the eyes of the larvae of the triton or The newt's 

 waternewt by Wollff. 1 This observer removed eye 

 the crystalline lens from the eyes of triton larvae, 

 performing upon them, in fact, the operation known 

 as " couching" in cases of cataract. He found 

 that the animal was capable of regenerating its 

 lens and did regenerate it in a few weeks. Some- 

 times it happened that a fragment of the old lens 

 had been left behind and in these cases it was from 

 this that the new one grew, a state of affairs which 

 one- can well understand. But in other cases a 

 most remarkable state of affairs came under notice, 

 for the new lens was reconstructed from the 

 epithelium of the border of the iris, that is to say 

 the coloured curtain, which in our eyes is blue or 

 grey or brown. To the ordinary reader this will 

 not seem more remarkable than any of the phen- 

 omena which have been already narrated and per- 

 haps less remarkable than some of them, but to 

 the embryologist it is a truly wonderful thing. 



The lens and the iris are originally formed from 

 wholly different layers of the developing embryo, 

 so that when a new lens is formed from the iris 

 it is being made not only in a way but from a 

 material in which and from which no lens ever 

 was made before so far as we know or indeed can 

 imagine. Hence this experiment shows the re- 

 1 Arch. f. EntwickL-Mech. d. Organismen, bd. i., 1895. 



