INTRODUCTION. XX111 



The previous remarks (page xx) will have prepared the reader for" 

 the first step in the arrangement of Mammals, viz., their division 

 into those in which the young are nourished in the maternal uterus 

 by means of a placenta, PLACENTAE MAMMALS, and those in which 

 the young foetus is expelled at a very early period, and maintained in 

 a pouch firmly attached to a nipple, IMPLACENTAL, or Marsupial 

 animals. None of these last occur in the Asiatic province, being 

 chiefly developed in the Australian region, and a few in America. 

 They have, moreover, very anomalous forms of dentition. 



Having separated the Marsupial animals, the great mass of the 

 Mammals still remains. Taking the teeth as our guide, we find a 

 large number of animals possessed of all four kinds of teeth (vide 

 page xiv) though in varying number and proportion. These are called 

 by Blyth, TYPODONTIA, i.e., animals with the typical forms of teeth 

 developed, and include Man,* Monkeys, Bats, Carnivorous animals 

 and Shrews, See., in fact all the most perfect forms of Mammals. 

 We next find a large and still more varied association of animals, of 

 inferior and more specialized organization, in which the teeth vary 

 much from the typical formation, and have rarely more than two 

 kinds of teeth developed. This group is called by Blyth, DIPLODON- 

 TIA, and includes Rats and Squirrels, Deer, Sheep and Cattle, the 

 Elephant, Pig and Horse, and the almost toothless Ant-eaters. 

 They chiefly live on vegetable matter, as the majority of the Typo- 

 dontia do on animal food. 



A third small division, comprising the Whales and Porpoises 

 &c., were called ISODONTIA by Blyth, because the teeth when present 

 are all of one kind. 



Having thus divided Placental Mammals into three great groups, 

 which can in most cases be recognized by a glance at the teeth, 

 the next step is to divide them into orders ; and first the typically- 

 toothed Mammals. On examining the hairy covering of a Monkey 

 and a Bat, it will be seen that there is only one kind of hair, no 

 underhair or wool being present. In both these animals too, the 

 penis is pendent, and not sheathed as in all other animals. As 

 Man belongs to this division, it was called PRIMATES by Linnaeus. 



* Man is excluded from the scope of the present work. 



