development--and, if so, there can be no embryotic identity. "By no
change of conditions," says Dr. CLARKE, "can two ova of animals of the
same species be developed into different animal species; neither by any
provision of identical conditions can two ova of different species be
developed into animals of the same kind." If these views be right, and
we believe them to be so, there cannot be a transmutation of species
under the influence of external circumstances.

Baffled in the effort either to create species or organically to change
them, attempts have been made to approach nearer to the source of
vitality, and explain the chemical, electric, or mechanical laws by
which the vital principle is influenced. For this purpose various
hypotheses have been put forth; one is the noted conjecture of Lord
MONBODDO, that man is only an advanced development of the chimpanzee or
ourang-outang. A second explanation is that given by LAMARCK, who
surmised, and with much ingenuity attempted to prove, that one being
advanced in the course of generations into another, in consequence
merely of the experience of wants calling for the exercise of faculties
in a particular direction, by which exercise new developments of organs
took place, ending in variations sufficient to constitute new species.
In this way the swiftness of the antelope, the claws and teeth of the
lion, the trunk of the elephant, the long neck of the giraffe have been
produced, it is supposed, by a certain plastic character in the
construction of animals, operated upon for a long course of ages by the
attempts which these animals make to attain objects which their previous
organization did not place within their reach. This is what is meant by
the hypothesis of _progressive tendencies_, and which requires for its
validity not only the assumption of a mere capacity for change, but of
active principles conducive to improvement and the attainment of higher
powers and faculties. More recently ST. HILAIRE has published a paper in