230 ALBERT KUNTZ 



of the "accompanying" cells arise by the mitotic division of " in- 

 different" cells along the course of migration, but these mitotic 

 figures are by no means sufficiently numerous to account for the 

 multitudes of cells which take part in the development of the 

 sympathetic trunks. Furthermore, I have observed cells along 

 the spinal nerves and the communicating rami, which, as will be 

 shown later, are neuroblasts. Such cells were recently described 

 by Cajal ('08) in the spinal nerves, and the communicating rami 

 in embryos of the chick. According to Cajal, "these neuroblasts 

 do not correspond to the neurocytes of Kohn, but to the real motor 

 cells in the neural tube." These facts are incompatible with 

 the theory of local differentiation. 



(c) Later development. — In embryos 12 mm. in length, the an- 

 lagen of the sympathetic trunks are rapidly becoming fibrous. 

 They still appear as continuous cell-columns showing little evi- 

 dence of their future segmental character. The earliest fibers 

 of the longitudinal commissures, therefore, do not grow out through 

 the inter-gangliar spaces, but the cells become aggregated into 

 distinct ganglia after the sympathetic trunks have become fibrous. 

 " Accompanying" cells are still present along the spinal nerves 

 and the communicating rami, but they are notably fewer than in 

 the preceding stages. Cells may still be observed migrating 

 from the neural tube and the spinal ganglia, but such migration 

 probably does not continue far beyond this stage. In embryos 

 over 12 mm. in length, the motor niduli are sharply limited, and 

 medullary cells are rarely seen along the fibers of the ventral nerve- 

 roots as they traverse the marginal veil. The spinal ganglia 

 are also becoming more sharpty limited distally, and cells no 

 longer become separated from them. The later development of 

 the sympathetic trunks consists in progressive changes and growth 

 of the elements already present. 



(d) Nature of migrating cells. — In his excellent work on the 

 earliest differentiations in the central nervous system, Schaper 

 ('97) made a most thorough and detailed study of the cells which 

 arise by the mitotic division of the "germinal" cells (Keimzellen) 

 of His. These cells were originally described by His as cells 



