558 DAVIDSON BLACK 
the inability of the central nervous system in ganoids to specialize 
part passu with changed peripheral conditions. Definite evi- 
dence of this loss within the central nervous system of the 
capacity for unlimited specialization (suppression of neurobio- 
tactic activities) is to be seen in the restricted distribution of 
modern ganoids. 
Among teleosts the capacity for apparently unlimited varia- 
tions in the reflex pattern of the brain stem nuclei reaches its 
acme among the vertebrate series. Within this group the ex- 
treme specialization of any of the organs of special sense is 
followed by a corresponding amplification of the primary afferent 
nucleus or nuclei involved, together with a modification of the 
motor nuclear pattern in perfect harmony with reflex needs of 
the animal. Further, the specialization of effectors of whatever 
nature is also followed by an adequate corresponding adjust- 
ment of the reflex connections of the sensory and motor neurones 
involved. 
Thus, within the teleost group it is difficult to construct any 
generalized scheme of motor nuclear arrangement owing to the 
characteristic ability of the elements of the primary nuclei to 
react to neurobiotactic influences and to develop a pattern based 
chiefly upon peculiar specific requirements. 
