106 INTRODUCTION. 
they be without a known prototype, we might form 
a system as philosophically admissible as our present 
knowledge will suffer, or as those already established. 
We might view the dogs residing nearest the arctic 
circle, or considered as descended from that quarter, 
and resembling wolves, as their offspring, more or 
less modified by the conditions of their being, during 
a long process of ages, and their fertile intermixture 
with other more southern species. We might take 
the more aberrant forms, whose original types we 
want, from that point in their zones where the most 
vigorous race of them is known to exist; and next 
connect, in a similar manner, the wild and domestic 
species of the tropics in the Old World, and those of 
South America, with the group of their congeners 
in that part of the New. We would in this manner 
distinguish the large wolf-headed and long-haired 
species of the north from the smaller jackal-headed 
tribes of the south; and find the species belonging 
to the mastiff race, known to degenerate alike in 
cold and hot countries, strong, numerous, and typi- 
cal in central Asia ; spreading eastward into Chinese 
Tartary and westward to Great Britain,—always in 
temperate regions ; while the long-nosed greyhound 
group, in the highest state of procreative vigour and 
serviceable activity, occupies another belt of the old 
continent centering in the Persian Taurus, west of 
Hinducoh, and spreading from China through north- 
ern India, Persia, and Arabia, including both sides 
of the Mediterranean to Morocco, and to the extre- 
mity of Europe. 
