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Figs. 11 to 15 Sections of gland tubules illustrating the process of tubule 

 formation . 



Fig. 11 Thickening of epithelium; from an embryo 47.3 mm. long (S. C. 11); 

 alum hematoxylin. X 450. 



Fig. 12 Beginning formation of outpouching and extension of lumen; from 

 an embryo 95 mm. long (H. E. C. 1882); alum cochineal. X 450. 



Fig. 13 Pinching off of new tubule by ingrowth of cells from the sides; from 

 an embryo 47.3 mm. long (S. C. 11); alum hematoxylin. X 450. 



Fig. 14a Further ingrowth of cells from the sides, showing the nuclei ar- 

 ranged tangentially with the lumina; from an embryo 95 mm. long (H. E. C. 

 1882); alum cochineal. X 450. 



