556 THE AMERICAN NATURALIST [Vol. LVI 



and definite statements can not yet be made. The foun- 

 dation for the statement that eyes severed from their 

 connection with the brain are not able to regain sight 

 seems to lie in the fact that the optic nerve in mammals, 

 when the eyes are left movable by their proper muscles, 

 can not find its way to a connection with any nerve center, 

 and then degenerates with the other parts of the eye. It 

 seems that the regenerating ends of the optic nerve fibers 

 coming from the retina are carried to and fro by each 

 rolling of the eye and thus fail to connect wath the central 

 stump of the nerve. In contrast to this sheering of the 

 fibers in eyes left attached to the orbit after severing of 

 the nerve, the nerve fibers in autophoric replantation 

 reach their goal before the muscles have grown together 

 and become movable again. It must be emphasized that 

 our method involves no injury to the nerve besides a clean 

 cut, and also that Boeke in Amsterdam has been able to 

 obtain results in nerve regeneration far exceeding those 

 of previous experimenters by avoiding suturing or other- 

 wise ill-treating the nerves. 



.V second opportunity for autophoric replantation is 

 afforded in the vertebrate eye by the lens. It is well 

 known that this part of the eye is derived ontogenetically 

 from an invagination pinching off from the outer layer 

 of ectoderm. The lens of cold-blooded vertebrates, espe- 

 cially urodeles, is capable of regeneration and is easily 

 extracted as a whole, and when it is replanted again into 

 its former place, it fits well into the lens-sac. At my sug- 

 gestion Berthold Wiesner has applied the method of 

 autophoric replantation to the lens of fish and amphibia; 

 the results show that replanted lenses can clear up again 

 and restore normal eyesight to their bearer. In mam- 

 mals analogous experiments have not yet succeeded, 

 perhaps because in the rat, the only available mammals 

 for the present, conditions are unfavorable in respect to 

 the relative size of lens, cornea and eyeball. In other 

 forms, as in man, where the lens relative to the size of 

 the eye is much smaller, replantation should succeed, as 



