NEUROBIOTAXIS 293 
In connection with the accumulation of myelin in the periph- 
ery of the axis-cylinder I wish to mention a fact which struck 
me repeatedly in the study of the cerebral commissures of ower 
animals, where (e.g., in the commissura superior habenulae of 
plagiostomes fig. 6) we frequently observe that the medullated 
fibers are arranged in the decussating bundle on the periphery of 
the non-medullated fibers. The same fact struck me often in 
the fasciculus retroflexus, especially in Arius. 
Sheldon, too, noticed this in his study of the olfactory tracts 
and centers in teleosts, and he makes the same remark with 
regard to some thalamic tracts. Whether this is to be explained 
as a repetition of the same process—an analogy—of peripheral 
accumulation of myelin in the medullary sheath, I do not venture 
to say. It seems probable, since we saw that also in another 
respect (monoaxonism and fasciculation, see above) the principle 
that holds good for an axon seems to hold good also for a col- 
lection of axons. 
Here, however, we transgress the limits of a scientific hypoth- 
esis, which, though not pretending to be more than a mere 
hypothesis, must be founded on facts. 
I would be perfectly content if this short note might stimulate 
others to think about these matters. The dynamic polarization 
of the neurone and its biologic character still require a good deal 
more light than has as yet been shed upon it, and is worth the 
attention of our best physiologists and biochemists.** 
RESUME AND CONCLUSION 
From the shiftings exhibited (phylogenetically) by the cells 
of the motor nuclei it appears that those parts of the neurone 
that receive the stimuli (dendrites and cellular body) are formed 
and directed to those stimuli trying to approach their center. 
® Sheldon, R. E. The olfactory tracts and centers in teleosts. Jour. Comp. 
Neur., vol. 22, pp. 177-339, 1912. 
°3 T have only one more remark to make. Darwin once said that plants think 
with their roots. He did not mean this in a literal sense, of course, but that 
there may be some similarities between the sensibility to certain stimuli and the 
behavior of the roots of plants (or other centers of growth) and parts of the nerv- 
ous system, chiefly the axons, does not seem so very improbable. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 3 
