NEUROBIOTAXIS 263 
to classify it under the phenomena of galvanotaxis, chemo- 
taxis or other processes of taxis or tropism known at that time. 
This phenomenon of shifting is clearly shown by figures 1 and 
2, where the dorsal position of the abducens nucleus in the 
shark with its huge fasciculus longitudinalis posterior (f.l.p., 
fig. 1) strongly contrasts with the ventral position of the same 
nucleus in a bony fish (fig. 2), where the fasciculus longitudinalis 
Fig. 1 Acanthias vulgaris, showing the dorsal position of the abducens 
nucleus. /f.l.p., fasciculus longitudinalis posterior; Nuc.VI, abducens nucleus; 
N.VI, abducens nerve; 7.V/J,m., motor facialis root. After Van der Horst. 
posterior is much smaller, but where the ventral set of central 
afferent tracts which influences this cell group is much more 
strongly developed (tr. tecto-bulbares ventrales, tr.t.b.v., fig. 2). 
The first way in which I formulated this law was thus: When 
from different places stimuli proceed to a cell, its chief dendrite 
grows out and its cell-body shifts in the direction whence the 
