MAMMALS OF MINNESOTA. 17 



The ox is supposed to be derived from three ancient species 

 (Bos brachyceros, B. primigenius, B. frontosus) which have since 

 been crossed interminably. While the ox seems to have ap- 

 peared in the eastern continent, America may claim to have 

 been the birth place of the bison whose enormous herds were 

 once so characteristic a feature of our country. Bison latifrons 

 from the diluvium is the first form known. Allen believes that 

 from this species have sprung B. antiquus in America and B. 

 prisons in the old world, the precursors of the living species 

 in each. 



One group of mammals the Cetacea have left no trace in 

 the formation of Minnesota. Our knowledge of the whale is a 

 very recent acquisition and is chiefly derived from the careful 

 researches of Eschricht, Brandt, Van Beneden, Gervais and 

 Flower. Whalebone had long been an article of commerce 

 before the relation it sustained to the teeth of other mammals 

 was made out that it is, indeed, a thickened appendage to the 

 mucus membrane of the mouth, used in straining out of the 

 water the minute animals serving its owner for food. The 

 discovery that the young or f cetal bearded whale has teeth, 

 which are never cut, but are soon reabsorbed, deserves to be 

 noted here as a remarkable instance of unexpected genealogi- 

 cal testimony. We are thus informed that the present whales 

 are lineally descended from toothed whales not unlike the 

 dolphin. The cetaceans were most plentifully represented in 

 the Miocene period and at that time the two groups of whales 

 were less clearly marked. It is certain that the whalebone 

 whales are the latest members of the group historically. The 

 origin of the group is shrouded in mystery, a more or less 

 obvious similarity in certain osteological features to the 

 omnivorous hoofed animals being the only clue as yet available. 



SUB-CLASS MO^OTREMATA. 



This sub-class contains the principal orders of mammals and 

 all of those included in this work with the exception of the 

 opossum, which is the sole North American representative of 

 the sub-class Didelphia. The characters of the sub-class, so far 

 as here necessary, are the following: Development of thefcetus 

 is accomplished through the agency of a placenta'formed from 

 the allantois membrane. The mammary glands have teats. 

 There is, in the female, a single vagina. There is no cloaca. 



