Plate 19 



The cells secreting keratin to form the lining of the gizzard in a 17-day-old 

 chicken. 



Top: S, secretory granules; L, lumen of glandular pocket; M, cell 

 membrane. The arrows indicate secretion escaping from the cells be- 

 tween the villi. 



Bottom: A cell not filled with secretion granules in which particle- 

 covered membranes R, mitochondria M and Golgi apparatus can be seen; 

 S is the secretion in the lumen L. N, nucleus; NM, double nuclear 

 membrane. 



