1. The great laws of the. organized system, or with respect
to sentient beings of the animal economy, all the principal
facts which relate to the natural and vital functions, the
periods and duration of life, the economy of the sexes, the
phenomena of parturition and reproduction, are with slight
deviations resulting from external agencies, constant and
uniform in each particular species.
2. Connected with the same subject are the phenomena
relating to the mixture or blending of races, and the propagation
or sterility of hybrids. In the circumstances related
to this series of facts, it is possible that some information may
be obtained on the distinctive characters and discrimination
of species.
3. The pathological history of species and of races is a
branch of physiological history which has not been so much
investigated as its importance seems to merit. It is one at
least the consideration of which must not be omitted.
4. The -psychical endowments of particular tribes, comprehending
all their faculties of sense and perception, as well as
their instincts and propensities/their modes of action and
habits, constitute an important part of the natural history of
species. 1 These characters are, when viewed on an extensive
seale, subject to few variations: they may be said, indeed/to
display a surprising uniformity.
5. After considering what bearings the facts observed
under these different heads have on the inquiry respecting
the human family, we shall proceed to the more variable
characters of species, and to the deviations which frequently
arise in the same identical race, and constitute particular
tribes.
S e c t io n IV.— F irst Head o f the Analogical Investigation o f
Species—Laws o f the Animal Economy in Species.
Animals of the same species are subjected to nearly uniform
laws with respect to all the principal functions of the
animal economy. Among the' most constant characteristics
of species are the circumstances connected with reproduction,
the times and frequency of breeding, in mammalia,
the period of utero-gestation, and in birds that of sitting
upon eggs, the number of progeny brought forth at a time,
and the period of suckling or watching over the young. The
progress of physical developement and decay is likewise
ordained by nature to take place in each species according
to a certain rule. The periods at which individuals arrive at
adult growth, the different changes which the constitution
undergoes at particular ages, the periods of greatest vigour
and of decline, and the total duration cif life are given,
though with individual exceptions and varieties, to every
species of animals. There are exceptions and variations, but
these are within certain prescribed limits, and obey definite
laws,
On the other hand, it may be observed as a very general
fact, that animals belonging to tribes which nearly resemble
each other, but are yet specifically distinct, differ in a decided
manner with respect to the Saine particulars. y
Thus the wolf and the dog, though proximate species, differ
remarkably: as to the period of wterp*gastatiori, The *she-wolf
appears tp carry her young ninety days, while the period of
gestation in the bitch is well known tp be sixty-two or sixty-
three days the former being longer by nearly ^one-third
part than the latter. We are acquainted with no similar
deviation in the animal economy within the limits of any one
species, and it is very unlikely that such a fact will ever be
observed.
Paragraph 1.—-Of the Duration of Life in general.
The duration of life proper to each species is subject, like
other characters of the physical constitution, to individual
varieties, The peculiarities of temperament and organization
on which these individual varieties depend are, like other
analogous properties, more or less disposed to become hereditary,
and by transmission common to whole families, Indi-
* The Count de BufFon asserts that the period of utero-gestaticon of the wolf is
above pne hundred days, Am instance is reported in the fourth volijme of dje
Annals of the Museum of Natural History^ in which the gestation of the wolf was
from eighty-nine to ninety-one days.