26 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



orifice of the stomach to the anus, and 6, wholly or in part all the ducts of the 

 glands opening on its free surface, and c, many gland-ducts in other regions 

 of the body, e.g., mammary, salivary, etc. The intracellular and intranuclear 

 networks are well developed, and in some cases the spongioplasm is arranged 



FIG. 23. Simple Columnar Ephithelial Cells from the Human Intestinal Mucous Membrane. 

 a, Mucous (goblet) cell; b, basement membrane; c, cuticle; d, leucocyte nucleus; e, germinating 

 cell. (Bailey.) 



in rods or longitudinal striae at one part of the cell, as in the cells of the ducts 

 of salivary glands. The protoplasm of columnar cells may be vacuolated 

 and may also contain fat or other substances seen in the form of granules. 

 Certain columnar cells transform a large part of their protoplasm into mucin, 

 goblet cells, figure 24, which is discharged by the open mouth of the goblet, leav- 



FIG. 24. 



FIG. 25. 



FIG. 24. Goblet Cells. (Klein.) 



FIG. 25. Cross- section of a Villus of the Intestine, e. Columnar epithelium with striated 

 border; g, goblet cell, with its mucus partly extruded; /, lymph-corpuscles between the epithelial 

 cells; b, basement membrane; c, sections of blood -capillaries; m, section of plain muscle fibers; 

 c.l, central lacteal. (Schafer.) 



ing only a nucleus surrounded by the remains of the protoplasm in its narrow 

 stem. This transformation is a normal process which is continually going on 

 during life, the cells themselves being supposed to regenerate into their original 

 shape. 



