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bers of the same orders. These successive pairs of animals 
may, and some do, differ from one another immensely, in 
such matters as the proportions and structure of their limbs ; 
the number of their dorsal and lumbar vertebrz; the adap- 
tation of their frames to climbing, leaping, or running; the 
number and form of their teeth; and the characters of their 
skulls and of the contained brain. But, with all these dif- 
ferences, they are so closely connected in all the more im- 
portant and fundamental characters of their organization, and 
so distinctly separated by these same characters from other 
animals, that zoologists find it necessary to group them to- 
gether as members of one order. And if any new animal 
were discovered, and were found to present no greater dif- 
ference from the Kangaroo and the Opossum, for example, 
than these animals do from one another, the zoologist would 
not only be logically compelled to rank it in the same order 
with these, but he would not think of doing otherwise. 
Bearing this obvious course of zoological reasoning in 
mind, let us endeavour for a moment to disconnect our 
thinking selves from the mask of humanity; let us imagine 
ourselves scientific Saturnians, if you will, fairly acquainted 
with such animals as now inhabit the Earth, and employed in 
discussing the relations they bear to a new and singular ‘ erect 
and featherless biped,’ which some enterprising traveller, 
overcoming the difficulties of space and gravitation, has 
brought from that distant planet for our inspection, well pre- 
served, may be, inacask of rum. We should all, at once, 
agree upon placing him among the mammalian vertebrates ; 
and his lower jaw, his molars, and his brain, would leave 
no room for doubting the systematic position of the new 
genus among those mammals, whose young are nourished 
during gestation by means of a placenta, or what are called 
the ‘ placental mammals.’ 
Further, the most superficial study would at once convince 
us that, among the orders of placental mammals, neither the 
Whales nor the hoofed creatures, nor the Sloths and Ant- 
