VERTEBRA TA. 283 



tremes, Marsupials, and higher Mammals. The young 

 of the Metatheria are bom in a very early stage of 

 development, and are subsequently further developed 

 in the marsupium; while the young of the Butheria 

 are born in a much more advanced stage, and are 

 attached before birth to a special structure called the 

 placenta. They are therefore called Placental Mam- 

 mals. 



The orders classified under the name Eutheria 

 include the Sloths, or Edentata, Whales, or Cetacea, 

 the order including Horses, called Odd-toed Ungulates, 

 or Perissodactyla, the order including Sheep, called 

 Artiodactyla or Even-toed animals, the Elephants or 

 Proboscidea, the Eats or Rodentia, the Hedgehog 

 family, or Insectivora , the Seals or Pinnipedia, the Cats 

 and Dogs, or Carnivora, the Bats, or Cheiroptera, the 

 Lemurs, or Proswiice (ape-like animals) , and the Mon- 

 keys, or Primates, under -which, zoologically speaking, 

 is included Man. 



Each of these orders is a group distinctly defined in 

 habits, and in structure corresponding to those habits. 

 Hence the distinction which was made the basis of 

 early classifications was that of their habits regarding 

 food. Now a classification based on this stands good 

 up to a certain point, for similar food habits necessi- 

 tate some similarity in the structure of the teeth, 

 paws, etc. ; but, as we have just stated, such a simi- 

 larity may arise secondarily in animals which difi'er 

 greatly from one another in other respects, and thus 

 we have Carnivora in the widely- differing groups of 



