702 
REVIEW— THE NATURALISTS LIBRARY. 
gions of the globe are so striking, that they must have attracted 
the notice even of superficial observers; and a very interesting 
question arises out of these differences, — Have they descended 
from one common stock? or must we trace them to more than one? 
and if so, how many species must we admit? These questions 
belong to the domain of natural history and physiology, and are 
particularly interesting to the veterinary student. The pheno- 
mena are capable of solution in two ways. Either different kinds 
of horses were originally created, fitted to inhabit the different 
countries wherein they were placed ; or one kind only was formed 
in the first instance, and then we account for the diversity that is 
now observable, by the agency of the various physical causes to 
which they have been subsequently exposed, and in which case 
they will only form different varieties of the same species. 
The author inclines to the former opinion, and imagines that the 
domesticated horse, in the form we now have him, never existed in 
a wild state. He considers it more probable “ that osculating forms 
existed ab initio distinct, circumstanced to accomplish certain ends, 
such as the service of man, and therefore framed so as to render 
them fusible into one species/’ He is also of opinion that great 
changes have been produced by the intermixture of hybrid blood, 
particularly in colour and covering ; and he even imagines that 
a very superior domestic animal, little inferior to our present 
horse, might be manufactured, even now, out of the quagga, the 
zebra, and the dauw. “We do not,” he says, “as yet know the 
limits of what constitutes a genus , nor have we a satisfactory defi- 
nition of species, since it is admitted that hybrids, derived even 
from assumed distinct genera, are not without the power of pro- 
creating a fertile offspring with either of the parent species, if not 
among themselves; thus implanting new forms and new charac- 
teristics in a progeny, which may again and again receive additional 
blood of the foreign stock with the more facility, since the hybrid 
conformation is already prepared for further adulteration ; and, 
notwithstanding the known tendency to sterility, obliterate specific 
distinctions, and form a homogeneous race.” 
We shall proceed to consider these opinions in a slow and hum- 
ble, but sure method of observation. 
On attempting a sketch of the natural history of any animal, our 
first efforts are necessarily directed to its immediate origin; and in 
this instance it would be particularly interesting to be enabled to 
trace the exact genealogy of one that is now become our constant 
companion and most faithful friend. The author has clearly 
shewn, that native breeds of wild horses are still found in various 
quarters of the world, most of which present one common charac- 
ter; and when, in addition to this, it can be satisfactorily shewn 
