182 On the Classification of Mammalia. 



creation has likewise assumed a peculiar zoological character, 

 always in a direct relation with the physical characters of the 

 time and the special physical wants of the globe. 



There are two points of view to be taken into consideration 

 when investigating the introduction of life upon the surface 

 of our globe, but these we cannot discuss at length here : we 

 must limit ourselves merely to the signalizing of them. 



1. Life, from its first manifestation upon the globe, may 

 have undergone a gradual, slow, and continuous development ; 

 in which case a single and unique creation, passing through 

 divers metamorphoses to suft the wants of the globe, renew- 

 ing itself without the necessity of a special creation at the be- 

 ginning of each period, would seem the real doctrine. 



2. Life, after its first introduction on earth, might have 

 ceased at the end of each period, and at the beginning of each 

 one, a new creation called forth, purposely made to suit the 

 physical wants of the new era. Thus numerous creations 

 would have succeeded each other without any material con- 

 nection, or any genetic relationship, but physically indepen- 

 dent of each other. 



Both of these views have their defenders and opponents. 

 The choice of one or the other is of no consequence in regard 

 to the fact which we are now tracing, as soon as we can ad- 

 mit that at each period the animal kingdom was in a direct 

 relation with the physical wants of the globe. 



The physical wants of our planet went on increasing with 

 time, both in number and importance ; and the same may be 

 said of animal life. The relations of these two worlds are so 

 intimate, that the zoological subordination of the groups will 

 give us the relative physical superiority of the continents 

 above one another ; and, vice versa, the relative physical su- 

 periority of the continents will point to the zoological grada- 

 tion of the groups composing the class of mammalia. 



Now let us look at the facts. The lowest Mammalia, the 

 Monotremata, belong exclusively to Australia. Australia is 

 physically the lowest continent. Marsupialia are also limited 

 to the same continent. 



The next in grade after Monotremata are the Edentata 

 proper, which belong chiefly to South America ; the Manidae 

 and Orycteropodida? alone being African. South America 



