STRUCTURAL CHARACTERS OF ANIMAL ORGANISMS. 



45 



function performed by the epithelial tissues, namely, that of man- 

 ufacturing certain materials which, being collected by suitable 

 channels, appear as secretions. 



The active elements of glandular tissue are epithelial cells 

 whose nutrition seems to lead to the formation of specific chemical 

 products within their protoplasm. These products pass out com- 



FIG. 10. 



Section of the epiderm of the prepuce, showing the superimposed layers of cells of a 

 stratified epithelium. (Cadiat.) a. Young proliferating cells, bd. Cells advancing 

 toward surface, c. Flattened cell of horny layer. /. Basement membrane, g. Connec- 

 tive tissue. 



monly as fluids, and form various substances of great importance 

 in the economy. A gland, then, is simply a special arrangement 

 of epithelial cells, generally lining the sacks or tubes into which 

 the secretion is poured. 



The covering of epithelium is in various places found to be 

 modified in different ways, so as to suit it for the special part in 





