202 



VERTEBRATE ANIMALS. 



is called the " small intestine " (sm). Here it is subjected to 

 the action of two other digestive fluids, called the " bile " and 

 " pancreatic juice," as well as to the fluids secreted by the 

 intestine itself. The bile is secreted by a large gland, which 

 is known as the " liver," while the pancreatic juice is produced 

 by another, termed the " pancreas," both pouring their secre- 

 tion into the upper part of the small 

 intestine. By the combined action 

 of these digestive fluids the chyme 

 is ultimately converted into a milky 

 fluid, which is called chyle, when it 

 is fit to be taken up into the blood- 

 vessels. The small intestine finally 

 opens into a tube of larger diameter, 

 which is called the " large intestine " 

 (Zm), and this opens on the surface 

 of the body by an anal aperture. In 

 the large intestine the last remain- 

 ing portions of the food which can 

 be rendered useful are absorbed into 

 the blood, the indigestible portions 

 being ultimately got rid of as use- 

 less. The fluid products of diges- 

 tion (chyle) are chiefly absorbed 

 from the intestinal canal by a set of 

 special vessels, which are present in 

 all Vertebrates, and which are called 

 the lacteals (Lat. lac, milk) from the 

 milky fluid they contain. These 

 lacteals combine to form a large 

 . *^ by which their contents are 

 Small in- ultimately added to the circulating 

 < Wood. Part of the products of di- 

 final ^portion, called the "rec- gestion are absorbed by the veins 

 which ramify on the intestinal canal, 



and which ultimately unite to form a great vessel, called the 

 " vena portse," which goes to the liver. The materials, how- 

 ever, which are taken up in this way also ultimately reach the 

 circulating blood. In this way, therefore, fresh matter is 

 being constantly added to the blood to replace the waste 

 caused by the performance of the vital functions. 



The blood is thus formed out of the materials which are 

 taken into the alimentary canal as food ; and in all the Verte- 

 brata (with one exception) it is of a red color, when viewed in 



