OCTOPUS ARM, REGENERATION AND STRUCTURE 29 
stimulated to division by the operation, have multiplied and 
migrated into the central nerve-fiber mass. Some neuroblasts 
also originate in the layer of ganglion cells. It is hard to tell 
whether they are evolved from the glia or produced by the 
nerve cells. If the latter is the case, we may safely say that 
only the small ganglia, the so-called nude nerve nuclei, take part 
in the production of neuroblasts. These small ganglia are 
probably in a very early stage of differentiation. Therefore 
they are more like the neuroblasts than the medium-sized or 
larger ganglia. But in spite of their similarity, I would not say 
- that the small ganglia and the neuroblasts are identical. I was 
never able to discover any mitosis in the small ganglia, whereas 
the neuroblasts exhibited many cases of karyokinesis. The 
large and medium-sized ganglia do not participate in the pro- 
duction of neuroblasts. Neither a division nor a reduction of the 
protoplasm (a process which would bring them in closer relation 
with the neuroblasts) takes place. It is quite probable that 
both the glia and the small nerve cells produce the neuroblasts. 
The neuroblasts are very similar to the sarcoblasts, which makes 
it difficult to tell them apart (fig. 31). 
Fine fibers of the myelin cords grow into the second blastema, 
thus separating the neuroblasts from the sarcoblasts of the ex- 
ternally located muscle bundle. The myelin cords do not change 
their appearance very much during regeneration. They do 
not undergo such a radical change as the rest of the tissues. 
Their alteration, due to degeneration, has already been mentioned 
(p. 27), and the only change caused by regeneration was an 
increase in the number of nuclei of the sustentacular tissue. 
In consequence of this remarkable behavior, they are more 
easily and rapidly recognized in the regenerated piece than any 
of the other parts, with the exception of the epithelium, the 
main artery, and the two venae superficiales. The myelin 
cords grow into the regenerated piece, not in the form of blastema 
cells of any kind, but as a well-differentiated tissue. Many 
authors have put forth the theory that regeneration is in a large 
degree dependent on the presence of nerves. The fact that the 
myelin cords, which serve as a connection between the brain 
