NERVE AND PLASMODESMA 67 
3. Are neuromuscular connections effected by indifferent— 
neurilemma or glia or mesenchyma—cells or by medullary 
neuroblasts? All three questions have been discussed at length 
in papers by Paton (’07), Held (’09), and the writer (14), in 
which the voluminous literature has been reviewed. ‘The reason 
- for raising again the three questions stated above is that, while 
none of the investigators up to the present has been able to 
demonstrate neurofibrillae in the primary protoplasmic con- 
nections between the neural tube and the myotome, the writer 
has been able to discover them in preparations made by the 
Bielschowsky-Paton process. The evidence is presented in the 
five figures of this paper. The divergence in the conclusions 
reached by Paton and Held on the one hand and by the writer 
on the other are essentially the result of the capriciousness of 
special neurofibrillar stains as applied to the earlier stages of 
nerve histogenesis. Not until after some years of experimen- 
tation with the Bielschowsky method and not until after the 
publication of the 1914 paper on the morphology of the eye- 
muscle nerves did the writer succeed in staining the neuro- 
fibrillae in the plasmodesmata. The present paper is therefore 
to be considered as a supplement to the one published in 1914. 
Turning, now, to the first of the questions raised above, the 
writer can only reiterate the assertion made in earlier papers 
that in embryos of Squalus acanthias of stages previous to 4.5 
mm. there is not the slightest evidence of protoplasmic con- 
nection between neural tube and myotome. Figures 1 and 2 
of this paper reproduce faithfully the relations which obtain 
previous to the appearance of definitive nervous connection. 
These figures represent sections cut transversely- through the 
middle of a myotome where in the later stages the anlagen of the 
motor nerves make their appearance. In some preparations it 
is possible to demonstrate in the plasma-filled space between 
neural tube and myotome a minimal amount of vacuolated 
coagulable material, invisible in most preparations made by the 
usual methods of fixation and staining, and lacking the staining 
properties of cell protoplasm. The ‘Fasernetz’ of Szily (04) 
and the plasmodesmata of Paton (’07) and of Held (’09) make 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 33, NO. 1 
