402 Journal of Comparative Neurology and Psychology. 



margin of that portion of the wall bordering the mesoderm 

 shows a slight waviness. Earlier stages show no indication of 

 such a condition, nor do other portions of the olfactory wall in 

 the same embryos (Figs. 8 and 9). 



/"«]f . J?. A, Section of olfactory epithelium of a swine embrj'o 9 millimeters 

 in length. A^. P., nasal pit; O. E., elevations of the olfactory epithelium- 

 X QSyi- ^1 Section through head, a portion of which ( x ) is represented by A- 

 F. B., forebrain. X 7>i- 



This waviness on the mesodermal margin of the epithe- 

 lium develops into distinct elevations. These elevations appear 

 to be caused by the pushing toward the mesoderm of the cells 

 of the epithelium. Histologically, these cells seem to be, for 

 the most part, the ordinary epithelial cells. In a few instances, 

 they resemble the germinating cells found near the outer margin 

 of the epithelium. 



Fi^. g. Section through the walls of the olfactory pit of a 12 mm. em- 

 bryo, showing at 0. E. the elevations mentioned in the text. 



The section shows also the variations in thickness of the epithelial walls. 

 X 93K- 



In earlier stages the nuclei of those cells nearest the inner 

 margin are arranged in a row at a definite distance (.00875 mm.) 

 from the inner border. See Fig. 10, A. This arrangement is 

 also to be noted in the later stages in those portions of the epi- 

 thelium away from the elevations mentioned above. 



