622 John. F. Holm 
Fig. 4 shows a sagittal section of such an embryo and an involu- 
tion can now plainly be seen; the connection with the ectoderm is 
unmistakeable and more elongated cells appear in the epithelium. 
The entire organ has now commenced to move forwards and upwards, 
but is still on the ventral side and is separated from the olfactory 
b 
Fig. 1. Sagittal serie of embryo 83 days old. Schematic drawings. Sections a—e, running from lateral 
towards middle line, Ect. ectoderm. F.B. fore brain, 01.0. olfactory organ. O.N. olfactory nerve. 
lobe by an increasing layer of mesoderm. The organ is an open, 
elongated fosse, or pit, and has not commenced to form a canal, 
but in an embryo of 83 days the beginning of this can be seen. 
Figs. a, b, ce, d, e, represent schematic drawings of a sagittal serie 
of sections, which aregiven from the lateral, towards the middle line. 
