I'hcnomena of neurobiotaxis in the optic system 297 



F"igure 24, gives a reproduction of similar cells in a bony fish, Lophius 

 piscatorius where they remain in adult life. 



In the other adult vertebrates all sensory root-cells lie extrame- 

 duUary in the vertebral canal ', with the exception of the mesencopha- 

 lic V sensorv cells, which keep their position in the midbrainroof, though 

 in many mammals (rodents, ungulates), some have shifted candad along 

 their root-fibres until the level of the emergence of the root. 



Fig. 23. — Hxtramedullar posterior rootcells (spinal ganglion cellsj in a shark; 



after von Lenhossek. 



Thus \ve find a clear example of neurobiotaxis in the phylogenetic 

 evolution of the sensory root-cells. 



Studying the relations of the cochlear cells, with regard to our sub- 

 ¡ect, \ve also find shiftings, resulting from stimuli. 



In phylogenesis and in ontogénesis the ganglion cells of the Xervus 

 Cochlearis are known to be derived from the pars posterior of the ganglion 

 vestibuli or Scarpa's ganglion. They are however known to be lying 



' Why thev do not migrate further, \ve do not yet know. Perhaps they are 

 inhibeted by the intervertebral canal, which endoses them. Or they may be con- 

 fined to the n-.eeting point of the motor-and sensory root, because a part of their 

 elements belong to muscle-sensory-fibres, which at this crossing, for functional 

 neurobiotactic reasons may rctain their anatómica! connection with the motor- 

 root fibres. 



