ion extend, when we come to microscopic
vesicles that can be discerned only by the highest magnifiers, general
similarity of outward shape is all that can be predicated of them. The
specific differences lie below this general resemblance of outward form;
we cannot discern them, but we _know_ that they must exist, and that
they are _essential_ differences, for each one of these vesicles is
invariably developed, if at all, into an individual of the species to
which its parent belongs. The germinal vesicles of a tree and a
quadruped are somewhat alike, outwardly; so, to the hen's eyes, there is
no difference between her own eggs and the duck's eggs which the
farmer's wife has put into her nest. But when she has hatched her brood,
part of them are found to be web-footed, and these, to her great
astonishment and distress, immediately take to the water. Our author
commits the same blunder as the poor hen. This want of consciousness
that he has got to the end of his tether, this inability to believe that
any difference can exist where he is not able to see it, though it is
invariably indicated by future consequent differences of the most
striking nature, is perfectly characteristic of the rash theorist in
science.

The assertion, that man's "first form _is_ that which is permanent in
the animalcule,"--even if we do not look to the potentiality of
development into a higher being, which experience shows to exist in the
human germ, but not in the infusorial,--is a positive misstatement. The
lowest monad has a mouth and means for propagating its kind, which do
not belong to the primitive ovum of any higher animal. About the
succeeding stages in the growth of the embryo our author's language is
more cautious. He only says, that they _resemble_, or _typify_, some of
the lower orders of being; and this is virtually admitting a specific
difference, and giving up his own theory for all the conditions
posterior to that of the germ. The brain and heart of the embryo
successively _resemble_ the corresponding organs in a fish, a reptile, a
bird, and a quadruped; but they are not identical, _even in outward
appearance_, with those organs. Of course, if arrested at any stage of
its growth, and prematurely born, the embryo would not be one of the
lower animals, but only something resembling it in outward shape; and
conversely, if it were possible for the birth of a bird to be delayed
till it had reached a higher stage of development in the sa