NERVUS TERMINALIS IN AMIA 



63 



opening to the capsule (fig. 3), although the central cavity is 

 larger than when it appeared ten hours earlier. 



At a period about six hours after hatching the olfactory nerve 

 has lengthened to one fourth the diameter of the nasal capsule 

 (fig. 4). A small increase is to be noted in the number of nuclei 

 among the fibers as they arise from the capsule. The two main 

 peripheral divisions of the olfactory nerve are more evident 

 than previously. An outer fibrous membrane covers the brain 



Fig. 3. Horizontal section of Amia 6 hours before hatching, showing anterior 

 end of the neural tube, the olfactory placode with beginning of nasal cavity, and 

 the origin of the olfactory nerve from the placode. Iron hematoxylin and eosin. 

 X 450. 



except where the olfactory fibers pierce it. A marginal zone of 

 fibers lies just inside the brain at this point, almost entirely devoid 

 of nuclei so that it does not seem possible that any nuclei are 

 migrating from the neural tube into the nerve. 



The olfactory capsules remain closed in this series of embryos 

 until about thirty hours after hatching, although slight cavities 

 are to be detected twenty-four hours earlier among the laterally 



