40 Hybridity in Animals. 
ractical observers, any authenticated examples of an analogous 
ind, that may not be embraced in this memoir. 
We shall merely further premise that naturalists have differed 
as to the import of the word species, but we know of no better 
definition than that which is expressed by “separate origin and 
distinctness of race, evinced by the constant transmission of some 
characteristic peculiarity of organization.” The term race has 
been indefinitely and conveniently used in those instances in 
which it is difficult to decide whether an individual of any tribe 
of plants or animals, is a distinct species, or only a variety of 
some other species. Races are properly successions of individ- 
uals propagated from any given stock; and we agree with the 
learned. Dr. Prichard, from whom we cite these definitions, that 
when races can be proved to possess certain primordial distine- 
tions, which have been transmitted unbroken, they should be re- 
garded as true species.* 
Let us now proceed to examine the question before us, com- 
mencing with the larger mammiferous animals, and proceeding 
from these to birds, fishes, insects and plants. 
Equine Hybrids.—The common mule, the progeny of the ass 
and mare, has been familiar to man since the days of Homer . 
and it is equally well known that with this animal, the hybrid 
born, as a general rule, begins and terminates. But the result 
appears to depend much on temperature; for in the south of 
Spain, mules have often been observed to produce young; and 
M. de la Malle observes that this phenomenon is frequent in hot 
climates, in which their period of gestation is twelve months, 
ing the same as that of the mare. The same author quotes 
Be eS ae eee ee a 
. : ‘ nk. 
country they inhabit, and that collective identity of physical traits, mental and 
t meri 
one are destructive to the other; and subsequent investigations have confirmed me 
in these views. ee Crania Americana, p. 3; Crania /Egyptiaca, Pp. 37; and Dis- 
tinctive Characteristics of the Aboriginal Race of America, p. 36. 
