HISTOGENESIS OF THE RETINA IN AMBLY- 

 STOMA AND NECTURUS. 



F. MALL. 



The various researches during the last fifty years on nerve 

 cells and nerve fibers give us a very clear insight into the 

 real meaning of the latter. Shortly after the cell-doctrine was 

 propounded by Schwann, a series of studies were made upon 

 the nerve fibers, the most prominent of which were those of 

 Remak and of Helmholtz. Both of these observers showed 

 that the nerve fiber is a prolongation of a nerve cell, although 

 their studies were not upon cerebro-spinal nerves. About 

 fifteen years later Deiters showed that the same held true 

 for these nerves also, and from this time on histologists and 

 physiologists accepted the discovery of the above investiga- 

 tors. 



With these discoveries clearly in mind, and with the knowl- 

 edge that the whole nervous system is ectodermal in its origin, 

 it is no wonder that His's attention was constantly directed to 

 the ganglion cell as the only originator of the nerve fiber. The 

 growth of the nerve fiber had already been followed by Kolli- 

 ker in the tadpole's tail, but this did not prove that the fiber 

 arises from the ganglion cell. While investigations were being 

 made to show that the nerve fiber is a direct continuation of a 

 cell, a number of others were being made to show that a group 

 of cells participate in the formation of a single axis cylinder; 

 and it is remarkable that some of these are being published 

 even at the present day. His was soon able, by direct observa- 

 tion, to show that, in its development, the fiber arises from a 

 cell and then grows to its point of destination. Studies in 

 nerve regeneration indicate that the same must be true. His's 

 observations were immediately confirmed by Ramon y Cajal, 

 who stained nerve fibers while they were developing by means 

 of staining with a modification of Golgi's method. In addition 

 to these two methods we have also Ehrlich's, and, by these 



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