MORPHOLOGY OF EYE MUSCLE NERVES 27 



careful study of the earlier stages in the differentiation of the 

 somite and of the 'protoplasmic bridges.' A study of those 

 earlier stages when protoplasmic connections are formed might 

 have convinced him that Dohrn, Froriep and Neal have stated 

 the facts correctly. That Paton had neglected the study of the 

 genesis of these bridges is evident from his failure to recognize 

 the sclerotome in his sections. For had he been thoroughly 

 familiar with the earlier stages, when the 'protoplasmic bridges' 

 first appear, he would have seen the formation of the sclerotome 

 associated with the development of the bridges and consequently 

 would not have been led to the inference that the primitive 

 fibrils of somatic motor nerves make their first appearance within 

 the myotome. Held ('09, p. 253) has already called attention 

 to this. 



The origin of the neurofibrillae and their relation to the pro- 

 toplasmic processes which form the protoplasmic bridges will be 

 discussed in a later section of this paper in connection with the 

 problem of the genesis of these plasmodesms. This is the essen- 

 tial point of difference between the results of Paton and the 

 writer. I have regarded the medullary processes which form 

 the 'protoplasmic paths' as neuraxon processes, since the neuro- 

 fibrils are differentiated within them. These processes were 

 therefore spoken of as neuraxons and the statement was made 

 that "before the first neuraxon makes its exit from the neural 

 tube, sections show no protoplasmic connection, even of the most 

 attenuated kind, between the neural tube and the somite." Paton, 

 holding the Apathy view of the independent and exogenous ori- 

 gin of the neurofibrils recognizes no neuraxon — not even an un- 

 differentiated neuraxon — in the absence of neurofibrils. And yet, 

 as Paton has demonstrated in the case of the Rohon-Beard cells, 

 the neurofibrils become secondarily differentiated within the neu- 

 roblast and its process, which consisted primarily of undifferen- 

 tiated protoplasm. The proof that the protoplasmic bridges are 

 formed by neuraxon processes will be stated later in this paper. 



If Paton ('07, p. 556) be correct in thinking that the trochlear 

 and the oculomotorius acquire their nervous connections with 

 their muscles without the participation of plasmodesmatous 



