adopted. And,

3. The physiologists who have made this branch of their science an
especial study, tell us, as the result of their microscopic observations,
that the embryo of the higher animals pursues a different course of
development, _from the very earliest stages_, to that of the lower
animals. It cannot be, therefore, according to the diagram that the author
presents to us, that the same germ which is nourished up to a certain
point to be fish, would, if transferred to other care and a better system
of nutrition, be nourished into a bird or a mammal. If it is to be a
mammal, it must be fashioned accordingly from the very beginning.

We will content ourselves with quoting, as our authority for these
assertions, a passage from Dr Carpenter's work on _Comparative
Physiology_; and we cite this author the more willingly, because he is
certainly not one who is himself disposed to damp the ardour of
speculation, and because the very similarity of some of his views, or
expressions, renders him, at all events, an unexceptionable witness on
this occasion.

"Allusion has been made to the correspondence which is discernible
between the transitory forms exhibited by the embryos of the higher
beings, and the permanent conditions of the lower. When this was
first observed, it was stated as a general law, that all the higher
animals, in the progress of their development, pass through a series
of forms analogous to those encountered in ascending the animal
scale. But this is not correct, for the _entire animal_ never does
exhibit such resemblance, except in a few particular cases to which
allusion has already been made, (the case of the frog, and others,
who undergo what is commonly called a metamorphosis.) And the
resemblance, or analogy, which exists between individual organs, has
no reference to their _forms_, but to their _condition_ or _grade of
development_. Thus we find the heart of the mammalia, which finally
possesses four distinct cavities, at first in the condition of a
prolonged tube, being a dilatation of the principal arterial trunk,
and resembling the dorsal vessel of the articulated classes;
subsequently it becomes shortened in relation to the rest of the
structure, and presents a greater diameter, whilst a division of its
cavity into two parts--a ventricle and an auricle--is evident, as in
fishes; a third cavity,