36 SMELL, TASTE, ALLIED SENSES 



nasal epithelium must be their cells of origin, as in fact 

 was shown to be the case for the chick by Disse (1896a, 

 1897). Here the olfactory nerve-fibers have been demon- 

 strated to grow from certain olfactory epithelial cells into 

 the olfactory bulb, the epithelial cells acting in all respects 

 like neuroblasts Bedford (1904). The trigeminal fibers 



Fio. 10. Olfactory epithelium of an embryo chick (ninth day) showing olfactory cells, 

 sustentacular cells, and free-nerve endings of fibers from ganglion cells of the trigeminal 

 nerve. After Rubaschkin, 1903, Fig. 3. 



must on the other hand grow from trigeminal ganglion 

 cells into the olfactory epithelium there to terminate as 

 free-nerve endings, but of this there is at present no di- 

 rect evidence. 



9. Comparative Anatomy of Olfactory Organs. The 

 nasal organs in the lower vertebrates are very different 

 from those in man. In Amphioxus a single sensory pit 

 slightly to the left of the median dorsal line of the head 

 and connected with the anterior end of the nerve-tube is 

 assumed to be an olfactory organ. If this is so, it is prob- 

 able that this pit corresponds to the single median olf ac- 



