74 INTRODUCTION TO CLASSIFICATION. 



glands are aggregated into two or more masses, disposed upon 

 each side of the median line of the ventral surface of the body ; 

 and, in almost all Mammals, the aggregated ducts of each mass 

 open upon an elevation of the skin common to all the nipple 

 or teat. To this the mouth of the newly-born Mammal is 

 applied, and from it, either by suction on the part of the young, 

 or by the compressive action of a special muscle on the part of 

 the parent, the nutritive fluid makes its way into the stomach 

 of the former. 



