MORPHOLOGY OF EYE MUSCLE NERVES 21 



from special cells, which, as actual 'nerve cells' — that is, as 

 neurofibril-forming cells — are intercalated in the path of the 

 nerve fibers and which push their differentiated product into 

 the interior of the muscle cell or gland cell as well as into the 

 ganglion cell. This doctrine, which conceives of the ganghon 

 cell and the nerve cell as entirely distinct kinds of cells has been 

 also supported by Bethe ('00-'07). According to Bethe the 

 neurilemma cells are the 'nerve cells' in the Apathy sense of the 

 word. That is to say, they are the cells which have formed the 

 neurofibrils and persist as sheath cells. 



Held attempts ('09) to reconcile the divergent views of nerve 

 histogenesis, finding something of truth in them all. In_ common 

 with Hensen he emphasizes the importance of protoplasmic paths 

 which furnish material for the growing nerve; agrees with the 

 Hertwig brothers that these may be secondarily formed by in- 

 different cells, and supports the Kupffer-Bidder theory in hold- 

 ing that the neurofibrils are the product of the neuroblast through 

 a process of centrifugal growth. While his observations seem 

 to support the process theory in most details, he denies the 

 doctrine of free outgrowth of nerve fibers. 



None of these hypotheses of nerve histogenesis has been aban- 

 doned entirely by partisan supporters. With the introduction 

 of special nerve methods the confusion has seemed to increase 

 rather than to diminish, so that there is not a single result of 

 the most recent investigation which is not directly opposed by 

 another. The chief problem raised by Apathy as to the genesis 

 of the neurofibrils, has not yet been solved; and the more impor- 

 tant question of how muscle and nerve become connected seems 

 as far from solution as ever. Relief from conflict of opinion 

 has not fgllowed recourse to experimental morphological methods 

 as is shown by the divergence in the views regarding neuro- 

 genesis held by Harrison ('03, '04) and Braus ('05). While the 

 former supports the process theory, the latter thinks that his 

 results confirm the Hensen or Hertwig hypothesis of predeter- 

 mined paths for the growing nerves. 



• Upon the answer to the question, whether or not nerve and 

 muscle are primarily connected, depends, in large measure, not 



