264 Cc. U. ARIENS KAPPERS 
majority of stimuli proceed.2. The truth of this was soon con- 
firmed also in other parts of the cerebrum, by Tretjakoff,* 
Herrick,‘ Bartelmez,> Obenchain,é Bok, Van der Horst? and 
others. . 
I observed, however, on an increase of afferent stimuli in a 
given center, that not all the neighboring cells approach this 
center, but that only certain cells proceed to that center which 
apparently had a certain relation to it, while other cells (even 
lying nearer by) did not migrate into the direction of the increased 
sensory field, because evidently they had nothing to do with it 
and did not stand in relation to it. 
Further researches convinced me that the functional relation 
which appeared to be the condition for the approach was shown 
to be a correlation depending on simultaneity of function—of 
stimulation. 
So the abducens nucleus shifts from one center of visual co- 
ordination fibers (the f.l.p.) to another set of visual co-ordination 
fibers (the tr. tecto-bulbaris) if the latter increase; but an increase 
of the taste fibers for instance, does not have any effect upon it. 
* Later I found that a similar observation had been already made by Strasser 
(92) and by Cajal (99). Compare: Strasser, Alte und neue Probleme der Ent- 
wicklungsgeschichtlichen Forschung auf dem Gebiete des Nervensystems. 
Ergebnisse der Anatomie und Entwicklungsgeschichte, Bd. 1, 1892, p. 721. 
Cajal, Textura del sistema nerviosa del hombre y de los vertebrados, vol. I, 
1899, p. 560. See also Cajal, Algunas observacionas favorables a la teoria neuro- 
tropica. Trabajos, vol. 7, 1908, p. 63. Both, however, failed to see the corre- 
lative character in this process, and Cajal ascribes a great influence to the spon- 
gioblasts (ependyma and glia) in the secretion of attracting chemicals for the 
axones, in which I do not at all agree with him. 
> 'Tretjakoff. Das Nervensystem von Ammococtes, I]. Das Gehirn. Archiv 
f. mikrosk. Anat., Bd. 75, 1909. 
* Herrick. The morphology of the forebrain in Amphibia and Reptilia. 
Jour. Comp. Neur., vol. 20, 1910. 
° Bartelmez. Mauthner’s cell and the nucleus motorius tegmenti. Jour. 
Comp. Neur. vol. 25, 1915. 
*Obenchain (with Herrick). Notes on the anatomy of a cyclostome brain, 
Ichthyomyzon concolor. Jour. Comp. Neur. vol. 23, 1913. 
7 Van der Horst. De motorise¢he kernen en banen in de hersenen der visschen, 
hare taxonomische waarde en neurobiotactische beteekenis. See also: Tijd- 
schrift der Ned. Dierk. Vereen, 1917. 
