A Story Outline of Evolution 



There are more than 10,000 species of mammals in 

 existence at the present time, the greater number of which 

 belong to the first of the three general groups above men- 

 tioned. They are found under all possible conditions of life 

 from the equator to the poles. They have adapted their 

 bodies for habitations on the soil, in the subsoil, in trees, 

 caverns of the earth. In the air, and In both fresh and salt 

 water. Their range and distribution cover all conditions of 

 existence In a variety of adaptations to meet the conditions 

 of the environments surrounding them. They nourish their 

 young upon milk which is produced from the mammary 

 glands of the mother and from which the class is named. 

 These glands are arranged In pairs and In no animal Is the 

 number less than two with the number Increasing In propor- 

 tion to the number of young produced at each birth. Dur- 

 ing the period of gestation, these glands are developed so 

 that their secretions may furnish the proper food for the 

 delicate digestive system of the new born offspring which is 

 unable to digest the food upon which the mother lives. The 

 position of these glands Is determined by the convenience 

 they afford to the young offspring so that it may secure Its 

 nourishment with the least effort. Nature always devises 

 ways providing for the functioning of body organs with the 

 least effort. In the whales that have forsaken the land and 

 returned again to the sea, prolonged sucking would be a 

 difficult process. Nature has overcome this difficulty by 

 dilating the glands where the mother's milk is collected in 

 a reservoir around which a compressor muscle Is developed 

 and the milk Is jetted into the mouth of the baby whale with- 

 out the necessity of a continuous sucking process as is 



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