570 Stewart Paton 



the development of certain of the Crauial nerve nuclei, particularly 

 the large latero-ventral groui) of eells from which the Acustico- 

 facialis Springs. In Fig. 11, Piate 23, there is an arrangement 

 which I have not observed more than once or twice, where the fibrils 

 spread out over the nucleus {a). The bündle [d] divides iuto a number 

 of liner branches which spread over the nucleus forming a net 

 with very wide meshes, the tilaments agaiu reuniting to form a 

 single bündle (c) that is continued in the direction of the central 

 canal. The manner in which the ventral root bimdles frequenti}' 

 split up into liner threads, so attenuated that they soon become 

 lost to view in the surrounding structure, is also seen in this same 

 drawing. Any oue who doubts the fuuctional iniportance of the 

 neuro-reticuluin, in connection with the conductiou of nervous Im- 

 pulses, will find it exceediugly difficult to even suggest an hypothesis 

 which would explain the presence and peculiar distribution of the 

 neuro-reticulum in the ventral roots on the basis that the only pur- 

 pose it served was to form a scaffolding or supportiug substance. 

 As the process of ueurofibrillation proceeds in the various areas the 

 ])rotoplasm forming the body and processes of the neuroblasts is still 

 further ditfereutiated from the surrounding matrix. This takes place 

 rapidly in connection with the large cells of Beard. Frequently, as 

 in the case of the ventral root cells, a triangulär area with an 

 attenuated long drawn out point, capping the nucleus is the first 

 definite sign marking the formation of the true neuroblast (Stage 1, 

 Figa. 5, 6, Piate 23). Coincidentally with, or just follo wing the 

 appearance of the first fibrils in this apical part a shorter rather 

 bluut basai process is formed which gives the celi a bipolar appea- 

 rance (Stage 2, Fig. 9j. In sections that have been carefully tìxed 

 and stained so as to avoid as far as possible ali possible shrinkage 

 the short, rounded, comparati vely broad basai ]»r(»jectiou forms a 

 marked contrast to the slenderer and more pointed Prolongation ex- 

 teuding from the opposite pole. With slight variations, as far as 

 I am able to judge, ali neuroblasts in their development pass 

 through this bipolar stage. It is an extremely difficult task to 

 determine at what point the jjroeess of a given neuroblast actually 

 ends. Ali the evidence so far obtained is in favor of the view that 

 the actual celi processes are often shorter than is generally supposed 

 to bc the case. 



As the first neurofibrils seem to develope at a point lying 

 beyond the limit of the primitive processes of the neuroblasts they 



