68 ANIMAL LIFE 



sac-like part of the canal, called the abomasum. Here 

 the process of digestion goes on. The four cacs rumen, 

 reticulum, omasum, and abomasum are called stomachs, 

 or they may be considered to be four chambers forming 

 one large stomach. In the abomasum, or digesting stom- 

 ach, digestive fluids are poured from glands lining its 

 walls, and the food becomes converted into a liquid called 

 chyle. The chyle passes from the stomach into a long, 

 narrow, tubular portion of the canal called the intestine. 

 The intestine is very long, and lies coiled in a large mass 

 in the body of the cow. The intestine is divided into 

 distinct regions, which- vary in size and in the character 

 of the inner wall. These parts of the intestine have 

 names, as duodenum, jejunum, ileum, caecum, colon, etc. 

 Part of the intestine is lined inside with fine papillae, 

 which take up the chyle (the digested food) and pass it 

 through the walls of the intestine to other special organs, 

 which pass it on to the blood, with which it becomes mixed 

 and carried by an elaborate system of tubes to all parts of 

 the body. Part of the grass taken into the alimentary 

 canal by the cow can not be digested, and must be got rid 

 of. This passes on into a final posterior part of the intes- 

 tine called the rectum, and leaves the body through the 

 anus or posterior opening of the alimentary canal. The 

 whole canal is more than twenty times as long as the body 

 of the cow ; it is composed of parts of different shape ; its 

 walls are supplied with muscles and blood-vessels ; the inner 

 lining is covered with folds, papillae, and gland cells. It is 

 altogether a highly specialized organ, a structurally com- 

 plex and elaborately functioning organ. 



Let us now examine the alimentary canal, or organ of 

 digestion, in some of the simpler animals. 



The Protozoa, or simplest animals, have no special organ 

 at all. When the surface of the body of an Amceba comes 

 into contact with an organic particle which will serve as 

 food, the surface becomes bent in at the point of its con- 



