296 
At present my researches neither confirm nor refute the obser- 
vation of DoHrn!) that “im Nasociliaris findet man auch noch in 
terminaleren Partien des Stammes echte Ganglienzellen”. The passage 
is not very precise as to the locality meant, and the phenomenon 
described by DoHRN may very easily come under the statements made 
above regarding the lateralis. 
There is no doubt whatever to my mind that the axis-cylinders 
and white substance of ScHwAnN are epiblastic products formed by 
the activity of chains of epiblastic cells. Like Donrn I regard the 
conditions met with in the lateral nerve development as decisive on 
this point. Here there can be no question of mesoblast cells becom- 
ing applied to the developing nerve in the way usually supposed 
by leading histologists such as von KÖLLIKER and His. 
Long ago I had made notes to the effect that, as the lateralis 
(and similar nerves to lateral sense organs) was formed entirely 
within the epiblast and from epiblast cells, any röle in such case 
must be denied to the mesoderm. It is gratifying to notice that 
Dourn has expressed the same opinion, and that he has made good use 
of the facts as arguments against the validity of the current doctrines. 
DoHrn’s present view of neurogenesis is simple in the extreme. 
It is briefly summarised in extra large type on page 281 of his memoir: 
“Damit haben wir das Bild eines Nerven, wie er sich typisch 
überall zeigt. Die Kerne sind die Scawann’schen Kerne, die hell- 
glänzenden Cylinder sind die Achsencylinder, das Plasma ist der 
Mutterboden der SchwAnn’schen und der später auftretenden Mark- 
scheide. Diese vier den typischen Nerven bildenden Elemente sind 
mithin ausschließliche Produkte der zur Bildung der einzelnen Nerven- 
fasern kettenartig aneinander gereihten Ektodermzellen.” 
While it would be unfair not to refer the reader to anything 
more than this summary, one may not be far wrong in assuming 
Dourn to maintain that the “plasma” of the cell plays the chief part 
in the building up of the white substance, and that the outermost 
portion of this same plasma goes to form the neurilemma. 
With Dourn I look upon the nuclei of RANviEr’s nodes (to which 
further reference will presently be made) as those of. nerve-forming 
cells, and as of epiblastic origin; though at present reserve must be 
Maintained as to the question whether or not they may be in all 
cases the nuclei of original nerve-forming cells, i. e. the progeny 
of nuclei of the original chain. For it is conceivable, and evidence 
can be produced in support of such on belief, that in some special 
1) p. 274. 
