154 



ANIMAL BIOLOGY 



from the intestine into which they pour their products through 

 long ducts. But, as we know, even in the latter case the glands 

 are really derivatives of the intestine — cellular areas sunk, as it 

 were, below the membrane to which they really belong — because 



Duct 



Alveoli 



Secreting Cell$ 

 Capillary Network 



Fig. 111. — Diagram of a gland, in section, together with the surrounding 

 tissues. Highly magnified. See Fig. 33. (From Hough and Sedgwick.) 



they arise during development as outpocketings of its wall: the 

 ducts being the sole remaining connection with the point of 

 origin. (Figs. Ill, 112.) 



1. Liver and Pancreas 



The largest gland in the body, the liver, and an equally im- 

 portant one, the pancreas, pour their secretions into ducts which 

 unite to form a single duct. This carries the secretions to the upper 

 part of the small intestine. The secretion of the liver, termed 

 bile, which is constantly formed but may be stored until needed 

 in the gall bladder, is a highly complex mixture of substances. 

 Some of them are waste products on their way out of the body 

 through the intestine, while others contribute to digestion by 

 cooperating with an enzyme from the pancreas. Thus bile salts 

 aid in the emulsification of fats and the absorption of fatty acids. 

 However, the liver is still more versatile, as will appear beyond. 



