THE STRUCTURE OF THE ELEMENTARY TISSUES. 



33 



In the neighborhood of the stomata the cells often "manifest indica- 

 tions of germinating. They may be either large with two or more 

 nuclei, or about half the size of the generality of cells. Germinating 

 cells of this kind or of the kind above described, are generally very 

 I granular. 



Spheroidal or glandular epithelium forms the active secreting agent 

 in the glands, the cells are usually spheroidal, but may be polyhedral 

 from mutual pressure, or even columnar; their protoplasm is generally 

 occupied by the materials which the gland secretes. 



Examples of glandular epithelium are to be found in the liver (fig. 

 24), in the secreting tubes of the kidney, and in the salivary (fig. 25) 

 and gastric glands. 



/ Columnar epithelium (fig. 28, a and b) as a single layer lines (a.) the 

 mucous membrane of the stomach and intestines, from the cardiac 



d 



Fig. 20. Fig. 27. 



Fig. 26. Columnar epithelial cells from the intestinal mucous membrane of a cat. a and 6, 

 Small cells of the lowest layer; c, superficial layer; d, goblet cells. (Cadiat.) 

 Fig. 27. Goblet cells. (Klein.) 



orifice of the stomach to the anus, and (1).) wholly or in part the ducts 

 of the glands opening on its free surface; also (c.) many gland-ducts in 

 other regions of the body, e.g., mammary, salivary, etc. 



Columnar epithelium consists of cells which are cylindrical or pris- 

 matic in form containing a large oval nucleus. They vary in size and 

 also to a certain extent in shape; the outline is often jagged and irreg- 

 ular from pressure of neighboring cells, but one end of the cell is always 

 narrower than the other, and by this narrower end the cell is as a rule 

 attached to the membrane beneath. The intracellular and intranuclear 

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

 arranged in rods or longitudinal striae at one part of the cell, generally 

 the attached border, as in some of the cells of the ducts of salivary 

 glands. 



This may also be the case with the columnar epithelial cells of the 

 alimentary canal which possess an apparently structureless layer on 

 their free surface : such a layer, appearing striated when viewed in sec- 

 tion, is termed the "striated basilar border" (fig. 28, e). 



The protoplasm of columnar cells may be vacuolated and may also 

 3 



