ANIMAL FORMS 



juice. From the stomach it is made to enter the intestine, 

 and is further acted upon by fluids from the liver, the 

 pancreas, and the glands of the 

 intestines themselves. Thus 

 treated it becomes changed from 

 an insoluble state into a fluid 

 which readily penetrates the 

 coats of the digestive tract. 



Many of the organs of the 

 body are placed at a considera- 

 ble distance from the food as 

 it comes through the coats of 

 the stomach and intestine. In 

 order to supply them with the 

 necessary nourishment a distrib- 

 uting apparatus is required. 

 This is the office performed by 

 the circulatory system, for as 

 rapidly as the food penetrates 

 the walls of the digestive tract 

 it enters the blood, and by the 

 beating of the heart is driven 

 to all parts of the body, which 

 are thus continually kept in a 

 state of repair. The blood serves 

 also to remove waste substances 

 from the various structures or 

 organs of the animal body and 

 to transfer them to the kidneys, 

 skin, or lungs, which effect their 

 removal from the body. 



4. Muscular and nervous sys- 

 tems. Owing to the fact that 

 animals, as a rule, are compelled 

 to move about in search of food, we find two highly devel- 

 oped systems, the muscular and nervous, which are absent 



FIG. 2. Diagram of heart and blood- 

 vessels of the squirrel or other 

 mammal, a.o., aorta ; h, vessels 

 of head ; l.a., left auricle ; Lex., 

 vessels of lower extremities ; lg., 

 lung ; l.v., left ventricle ; p.a., 

 pulmonary artery ; p.v., pulmo- 

 nary vein ; r.a., right auricle ; 

 r.v., right ventricle ; v., vessels of 

 viscera. Arteries are represented 

 by heavy walls. 



