4o8 Jourhal of Comparative Neurology and Psychology. 



3. The nasal pit is formed by a process of invagination. 



4. At a very early period in the formation of the pit, two 

 kinds of cells are present in the olfactory membrane ; first, 

 columnar epithelial cells ; second, spherical cells, located near 

 the outer margin of the epithelum. Many of these latter cells 

 are in the process of karyokinetic division. 



5. These spherical cells develop into neuroblasts which, at 

 first, arc unipolar having only the central process developed, 

 but later those which migrate from the outer margin become 

 typical bipolar nerve cells. 



6. For the most part, the developing nerve cells retain 

 their position near the outer margin of the epithelium, but, in 

 some cases, the cell body comes to lie at a deeper level within the 

 epithelium necessitating the lengthening of the peripheral pro- 

 cess. 



7. Soon after the neuroblasts are formed cells from the 

 inner part of the nasal epitheli\mi push slightly into the meso- 

 derm. This is indicated by a waviness of the margin of the 

 epithelium, followed by distinct elevations extending towards 

 the brain wall. Among the first indications of their outpush- 

 ing, is a change in the arrangement of the nuclei of the cells of 

 the epithelium. 



8. Distinct projections extend from the epithelium into 

 the mesoderm. While these projections are chiefly cellular, 

 dissections show that they are also somewhat fibrous. 



9. A few of these cells seem to be migrating neuroblasts, 

 while the majority are evidently epithelial cells which upon be- 

 ing relieved of the pressure exerted upon them within the epi- 

 thelium, take a more rounded shape. 



10. These projections, which may now be known as cords, 

 become much longer. They converge and near the brain unite 

 to form a cellular mass, which, however, as yet, has no connec- 

 tion with the brain. 



11. At no stage have structures been observed originating 

 in the brain that may be considered to take part in the forma- 

 tion of the olfactory nerve. 



12. In still older embryos, the cellular mass, to form which 



