554 THE AMERICAN NATURALIST [Vol. LVI 



replanted eyes, which had again regained their function, 

 has been made by Professor Walter Kolmer, of the Physi- 

 ological Institute, University of Vienna, and the re-in- 

 growth of the severed optic nerve-fibers into the optic 

 thalamus is beyond doubt. Professor Kolmer, as all 

 other authorities, to whom the animals with functioning 

 replanted eyes were show, stated that they would 

 scarcely have believed the fact, without having them- 

 selves seen and tested it. Some oculists even refused to 

 believe what they saw, taking refuge in far-fetched ex- 

 planations for the absolutely normal behavior of the rats 

 and for the connection of retina and brain in anatomical 

 and microscopical preparations. But is the restoration 

 of function in the vertebrate eye really in contradiction 

 to the facts known to us concerning the regeneration in 

 this animal type? If we resort to our theory of regen- 

 eration as accelerated growth, moving on the same lines 

 as normal ditTerentiation, and waning with higher spe- 

 cialization, it is necessary to inquire into the normal de- 

 velopment of the eye and optic nerve, before answering 

 this question. The vertebrate eye grows from multiple 

 origins, the nervous elements being derived from a fold 

 of the central nervous system (brain). It is generally 

 believed that the nerves of the brain grow in centrifugal 

 direction and are incapable of regeneration, as one does 

 not observ^e regeneration-cones at the peripheral end of 

 sectioned central nerves as a rule. Ramon y Cajal, on the 

 other hand, thinks that this inability to regenerate is 

 only a consequence of secondary difficulties, regeneration 

 at least commencing when the right nurture is given: 

 this may be accomplished by inserting degenerating 

 nerve-pieces into the pathway of the sectioned nerve. At 

 any rate there would be but little chance of quick and suf- 

 ficient regeneration, if the eye depended on the nerve 

 growing into it from the brain. Fortunately, as is well 

 known, the fibers of the optic nerve in ontogeny grow 



