eles. 
SPECIES. 
the animals whose differences cannot be thus ex- 
plained, must be held to belong to separate spe- 
“Where two races of animals are distin- 
guished by any undeviating marks in such a way 
that they never will, under any circumstances, 
pass into each other, or that the progeny of either 
can never acquire the characters of the other, 
they are of distinct species, and it matters not 
how wide or how narrow be the line of discrimina- 
tion, provided that it never be broken in upon.” 
But when we come to apply these abstract rules 
to the realities of Nature, we find that they are 
not always sufficient to distinguish the mere va- 
riety from the genuine species. The difficulty is 
further increased by the circumstance that many 
varieties or races of some species differ more de- 
cidedly among themselves, than the species of 
certain genera, where the objects are very nu- 
merous. Again, the greater part of our acquisi- 
tions are imported from remote and barbarous 
countries. “A large proportion,” as Mr. Lyell ob- 
serves, “ have never even been seen alive by scien- 
tific enquirers. Instead of having specimens of 
the young, the adult, and the aged individuals of 
each sex, and possessing means of investigating 
the anatomical structure, the peculiar habits and 
instincts of each, what is usually the state of our 
information? A single specimen, perhaps, of a 
dried plant, or a stuffed bird or quadruped ; a 
shell without’the soft parts of the animal ; an 
insect in one stage of its numerous transforma- 
tions ;—these are the scanty and imperfect data 
which the naturalist possesses. Such informa- 
tion may enable us to separate species which 
stand at a considerable distance from each other ; 
but we have no right to expect any thing but 
difficulty and ambiguity, ifwe attempt from such 
imperfect opportunities to obtain distinctive 
marks for defining the characters of species 
which are closely related. When our data are so 
defective, the most acute naturalist must expect 
to be sometimes at fault, and, like a novice, to 
overlook essential points of difference, or pass 
unconsciously from one species to another.” 
Buffon established the criterion for the deter- 
mination of species in the power of producing, 
by their union, races equally fertile with them- 
selves, and this rule seemed to be confirmed by 
the experiments of John Hunter. They were of 
opinion, “that if a male and female produce an 
offspring which is prolific, the tribes to which 
the parents respectively belong are hence proved 
not to be specifically different, and whatever di- 
versities may happen to characterize them, are 
in this case to be looked upon as examples of va- 
riation. But if the third animal be unprolific, it 
is to be concluded that the races from which it is 
descended are originally separate, or of distinct 
kinds. The fact that most hybrid animals are 
wholly unprolific, would appear to be a provision 
for the attainment of this desirable end, and for 
maintaining the order and variety of Nature. 
For if such had not been the condition of these 
297 
intermediate animals, we have reason to believe 
that all the primitive distinctions would have been 
long ago totally effaced ; a universal confusion of 
species must have ensued, and there would not 
be at this day one pure and unmixed species left 
in existence. The naturalists above mentioned, 
inferring, from the apparent utility of this law, 
that it must universally prevail, obtain by means 
of it a ready method of determining on identity 
and diversity of species.” It is very clear that 
if two animals are prevented by any great dis- 
parity of organization or disposition from uniting, 
that the criterion of generation holds good to a 
certain extent. The bull and the goat, for exam- 
ple, would at once be pronounced to be distifict 
species. This rule may enable us to assert that 
two animals are not of the same species, but it 
does not always serve to discriminate between 
nearly-allied species. Hence it seems rather to 
be the first rude attempt at forming a criterion, 
than one which serves to mark out nice distinc- 
tions. The crosses among the dog, the wolf, and the 
jackal ;—between the goat and the sheep ;—the 
horse and the ass ;—the lion and the tiger, with 
the occasional appearance of fertile hybrids in 
many, and the possibility of its occurrence in 
them all, show that the converse often fails. Al- 
though animals which do not generate together 
belong to distinct species, yet it is not true that 
distinct species must not generate together, nor 
does it follow that their progeny must always be 
sterile. 
The determination of species by the property 
of producing fertile races, had previously been 
restricted by Frisch to such as generate together 
of their own accord, “von Natir mit einander 
gatten.” Those artificial unions brought about 
by restraint, artifice, or domestication, were 
wholly excluded by him. But this restriction 
renders the rule useless in practice for determin- 
ing those points where difficulties may chiefly be 
expected to arise. It is in respect to man and 
the domestic animals, or with animals brought 
from distant and uncivilized countries, that a 
rule is most required to distinguish the species 
from the mere variety. Blumenbach inquires, 
‘When will it come to pass that all nearly-allied 
animals shall be brought together from remote 
countries, so as to submit them to the requisite 
experiments,—for example, whether the chim- 
pansé, T’roglodytes niger, from the Angola coast, 
will form a fertile race with the Orang outang, 
Pithecus satyrus, from Borneo?” This is a de- 
sideratum which the general establishment of 
zoological gardens alone can supply, but in the 
meantime we must seek some other criterion, 
which shall be applicable to man and the domes- 
ticated animals, for the determination of species. 
It is here that difficulties arise in drawing the line 
between the species and the variety. ‘Tiliesius 
considers that several distinct species are con- 
founded under the name of jackal or chacal, 
Canis aureus, while both Pallas and Gulden- 
ee 
