THE SYRINX OF GALLUS DOMESTICUS 183 



In a stage 24 hours later (200 hours), as well as in a 212 hour 

 embryo, the epithelium shows a noteworthy characteristic. The 

 nuclei of the cells bordering upon the lumina have migrated from 

 the basal to the free ends of the cells, thus giving rise to a very 

 prominent superficial row of nuclei. Immediately beneath this 

 the other nuclei show an irregular arrangement. Although this 

 characteristic arrangement of nuclei is noticeable in the 176 hour 

 stage, it does not become very striking until the present stage is 

 reached. In this stage also a second evagination (fig. 13) ap- 

 pears in the lateral wall of each bronchus, just cephalad to the 

 one described as present in the preceding stage. At 248 hours 

 many of these evaginations may be observed in the walls of 

 both the trachea and the bronchi. In the latter they are con- 

 fined, however, to the lateral walls. 



A cross section of a 332 hour embryo shows two or three lay- 

 ers of nuclei in the epithelium, except in the region of the future 

 t5'mpanic membranes, where a single laj^er occurs. The cells 

 in these regions are cuboidal. Throughout the region of the 

 bifurcation of the trachea, a considerable number of goblet cells, 

 as well as numerous cells exhibiting a somewhat differentiated 

 clear area in their free ends, occur in the epitheUal layer nearest 

 the lumen. Numerous cilia are present on the free borders of 

 some cells. 



In a 404 hour embryo a very distinct layer of nuclei appears 

 at the very base of the epithelium. These are much smaller 

 than those found nearer the lumen. As the regions of the future 

 tympanic membranes are approached, all cells between the layer 

 of small nuclei are left to cover the membranes. These cells 

 differ from those described in the 332 hour embryo in being much 

 less cuboidal, smaller and possessing much smaller nuclei. 



The most noticeable differences between the last embryo and 

 one of 452 hours are (1) the nuclei of the cells covering the tym- 

 panic membranes have become much more flattened and in ap- 

 pearance suggest the nuclei of endothelial cells; (2) in addition 

 to individual goblet cells, small groups consisting of three or 

 n.ore eecreting cells are found in the epithelium. Each of these 

 groups is slightly invaginated, leaving a shallow pit connecting 



