168 VITALISM AND SCHOLASTICISM 



A further remarkable experiment has been 

 made upon the eyes of the larvae of the Triton 

 or waternewt by Wolff.* This observer re- 

 e newt's move( j 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 regene- 

 rate it in a few weeks. Sometimes 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 phennomena which have been al- 

 ready narrated and perhaps 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 is is being made not only in a way 

 but from a material in which and from which 



* Arch. /. Entwicld.-Mech. d. Organismen, bd. i., 1895. 



