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ALBERT KUNTZ 



zontal line represent the lengths of the embryos in mm. ; the figures 

 in the vertical line indicate the number of cells present in a given 

 length of longitudinal sections of the spinal nerves, as they appear 

 in transverse sections of the embryos, taken at random between 

 the point of union of the sensory and the motor roots and the 

 origin of the communicating rami. Embryos which seemed to 

 be most normal in their development were selected, and the curve 

 is based on the averages of ten independent counts. This curve 



Fig. 7. Diagrammatic transverse section of an embryo 9 or 10 mm. in length. 

 The arrows indicate the course and the direction of the cells migrating from the 

 neural tube and the spinal ganglia into the sympathetic anlagen. 

 ao., Aorta, c.r., Path of communicating ramus, d.n.r., Dorsal nerve-root, pv.a., 

 Anlagen of prevertebral plexuses, sp.g., Spinal ganglion, sp.n.. Spinal nerve. 

 supr., Suprarenal bodies, sy., Sympathetic trunks, v.n.r., Ventral nerve-root. 

 ir.b., Wolffian body. 



indicates that the rate of migration reaches its maximum in em- 

 bryos 9 mm. in length, and that migration practically ceases 

 when a length of 13 mm. is attained. It also indicates that a 

 relatively small but fairly constant number of cells remains in 

 the spinal nerves after migration has ceased. 



As already indicated in reviewing the literature, Kohn and Neu- 

 mayer have attempted to account for the cells giving rise to the 

 sympathetic nervous system, by local differentiation of elements 



