146 Journal of Comparative Neurology. 



amphibia, however, this stage is transitory and the "pal- 

 lium," which remains throughout life the only representive 

 of the cortex in fishes, is in, the Salamander, quickly folded 

 into the interior and encroached upon by excursions of 

 cells from the striatum or proliferations from the stray 

 neuroblasts in its own substance. 



It is remarkable how differently the several parts of 

 the brain behave with reference to the development of the 

 nerve cells. The medulla, which is charged with the con- 

 trol of the vital functions, has exhausted its power of cell- 

 multiplication from the primitive neuroblasts long before 

 the archetecture of the cerebellum is nearly finished. We 

 cannot resist the belief that there are extensive migrations 

 of the growing nerve cells during the earlier development 

 periods. The appearance of the embryonic brain of a frog, 

 for example, is almost impossible to explain except upon 

 the theory that, not only are the nerve cells actively 

 sprouting forth nerve fibrils which find their way to distant 

 regions of the brain with an instinct as infallible as that of 

 a plant shoot for light, but cells are actually moving from 

 point to point in the intervals between the rapidly elongat- 

 ing epithelium cells leaving a thread behind, as a spider 

 might in its passage. Such a migration toward the 

 periphery has been described by His in the cord and we 

 have followed even more extensive migrations in the cere- 

 brum. Thus cells which arise from the epithelium reach 

 the external part of the brain and turn transversely (in 

 amphibia) and send long processes to subdivide in the 

 brain base {pes pediincitli) where they indirectly communi- 

 cate with the cerebellum. 



As already stated, the process of cell-multiplication is 

 completed much earlier in some regions than in others. 

 Thus, in fishes, after the process is practically somplete 

 elsewhere, it continues very actively in an accessory struct- 

 ure of the cerebellum known as the "volvula. " The organ 



