CHAP. VIII.] OFiGANSOF liEi^Pir.ATION AND SECHETION. 231 



and mucous glands, and complex ones in the salivary glands, the 

 pancreas, and above all, the liver. The Ibldings or subdivisions of 

 a gland arc manifestly but a convenient mode of augmenting the 

 secreting surface within a small space. Since all secretions are 



— a 





'm-^ 



Fig. lOS.— Diagram of ptfferent rop.iis of Glands, showing how the Sf.cretino Sttrface 

 may lllj auomknted, and the glandular structure erndkred wore coml'ltx by 

 Inversion or Kecession of the Surface to a greater and greater degree. 



A. Simple glands. 



0. Htraiglit tube. 

 h. S.-ic. 



i. Coiled till ic. 



B. Slightly iiioiu eomiilex fonns. 



k. Tubular. 



1. SaeexUar. 



C. Racemose or compound saccular gland 



in. The entire gland, showing its braneliing 



duct and lobular strncture. 

 1). A separated lobule, with one branch of 

 the duct (o) proceeding from it. 

 D. Coni]iound tubular gland. 

 Secreting surfaces may also be increased by 

 ]irojiH-tions and foldings dutwards, analogous 

 to these inversions and foldings inwards. 



formed from the blood, every secreting surface, and therefore every 

 gland, must be highly vascular. It is as yet quite unknown A\luit 

 causes different epithelial cells to have the power of forming such 



