Experiments on Lens in Amblystoma. 199 



always takes place perpendicular to the conductor. Bok has called 

 attention to the fact that in the living organism the nerve fibers 

 grow out from the spinal cord perpendicular to the long fiber paths 

 growing down from the brain stem. Kappers has tried to explain 

 this as a galvanotropic phenomenon. To this observation, an 

 interesting analogy is thus found in tissue cultures. 



The hypothesis of Kappers, as the main result of this author's 

 work on "neurobiotaxis," that electrical forces are determining 

 factors in the outgrowth and distribution of the different constitu- 

 ents of the nervous system, has been proved to be a fact in pieces 

 of the central nervous system of the chick cultured in vitro. 



As several authors (Hyde, Mathews, PfefTer) have pointed 

 out, electrical currents flow in developing organisms. The 

 currents successfully employed in our experiments correspond in 

 range in electromotive force with those found in various embryos. 

 From this it may be concluded that electrical forces play a role 

 in the formative processes in morphogenesis. 



106 (1566) 



Experiments on the lens in amblystoma. 



By Ross G. Harrison. 



[From the Osborn Zoological Laboratory, Yale University, 

 New Haven, Conn.] 



The embryo of Amblystoma punctatum has been reported as 

 one of those in which the ectoderm normally giving rise to the 

 lens is dependent upon the continued influence of the optic vesicle 

 to effect its differentiation. 1 It was surprising, therefore, to 

 find that in certain experiments, directed toward the study of the 

 gills, lenses developed from the proper ectoderm when transplanted 

 to regions far from the eye. 



There are obviously two ways of testing the independence of 

 lens differentiation: one is to take away the eye rudiment as has 

 been done in previous experiments (Spemann, Lewis, Le Cron) ; 

 the other is to transplant the lens-forming ectoderm to another 



1 Wilbur L. Le Cron, "Experiments on the Origin and Differentiation of the 

 Lens in Amblystoma," Am. Journ. Anat., 1906-7, VI. 



