29-J LEIGH llo\]i| I Y. 



B. The XasaJ Region. 



The material for the grafts of the nasal region was taken from 

 chicks of thirty-six, forty-eight, and sixty hours of incubation. 

 As in the case of the eye tissues, only a few grafts were made of 

 the sixty hour material. Inasmuch as it was desired to note the 

 growth and differentiation of the nasal epithelium especially, no 

 twenty-four hour material was grafted, for at this age, the medul- 

 lary folds only are localized. 



When grafts were made of thirty-six hour chick primordia, the 

 anterior end of the head as far back as the optic vesicles was 

 transplanted. If the material was taken from an embryo of 

 forty-eight hours incubation, the tip of the head was cut away so 

 that both nasal pits were transplanted in one piece. 



A brief account of the normal development of the olfactory 

 organ based on Disse's account (1897) will form a useful intro- 

 duction to the study of the grafts of this region to be described. 

 After three days of incubation, the sensory epithelium of the 

 chick nose is represented by two thickenings of the epithelium in 

 the nasal grooves. As the embryo approaches the fourth day, 

 the epithelium becomes differentiated into columnar epithelial 

 cells and round cells, more transparent in sections stained with 

 carmine. These cells are isolated in groups which are more or less 

 distinct from each other. It is from these that the cells migrate 

 out, forming the olfactory nerve and the ganglion-like group. 

 At first a chain of cells appears to lead from the nasal epithelium 

 to the brain. As late as the sixth day, this nerve primordium 

 contains cell bodies but they are most numerous at the extremi- 

 ties. In the eight day chick, the stage which serves as the con- 

 trol for the grafts to be described below, Disse finds the nerve 

 formed and two types of cells appearing in it at rare intervals. 

 There is a pear-shaped unipolar cell, and a bipolar cell that is 

 spindle-shaped. The greater part of the nerve is composed of 

 nerve fibers. The cells are most numerous at the ends of this 

 fiber bundle. At the distal end, near the nasal epithelium, the 

 grouping of these cells and their shape led Heard (1885) to 

 describe a ganglion-like mass which Disse describes merely .1- ,i 

 group of cell bodies. Disse (confirming His, 1889) concludes that 

 the nervus olfactorius arises from certain cells of the nasal 

 epithelium and adds that it lacks a ganglionic portion. 



