THE METAZOA 



65 



epithelium through a narrow prolongation of the cell, which 

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

 multicellular (D, G), formed of a number of cells of the 

 epithelium, lining a depression or infolding, simple or com- 

 plex in form, of the latter. In the central cavity of such a 



Fig. 29. — 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 t simple multicellular gland; G, 

 branched multicellular gland. (From Lang.) 



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 



F 



