ii THE METAZOA 65 



the epithelium through a narrow prolongation of the cell, 

 which serves as the duct of the gland. In other cases the 

 gland is multicellular (D ), formed of a number of cells 

 of the epithelium, lining a depression or infolding, simple or 

 complex in form, of the latter. In the central cavity of 



FIG. 20. Diagram to illustrate the structure of glands. A, unicellular glands in an 

 epithelium ; B, unicellular glands lying below epithelium and communicating 

 with the surface by narrow processes (ducts) ; C, group of gland-cells ; D, group 

 of gland-cells lining a depression ; E and F, simple multicellular gland ; G, 

 branched multicellular gland. (From Lang.) 



such a gland the secretion collects to reach the surface 

 through a passage, the duct. 



The general name of connective tissues is applied to a 

 number of tissues which play a passive part in the economy 

 of the animal, connecting and supporting or protecting the 

 various organs. Sometimes connective tissue is gelatinous 

 in character, sometimes fibrous. Fat or adipose tissue is 



Man. Zool. r 



