of the progress of organic life is
that the "_simplest and most primitive type under a law to which that of
like production is subordinate, gave birth to the type next above it;
that this again produced the next higher, and so on to the very
highest_, the stages of advance being in all cases very small--namely,
from one species only to another; so that the phenomenon has always been
of a modest and simple character." (p. 231.) The arguments by which the
author endeavours to prove his hypothesis may be thus compressed.

According to him foetal development is a science, illustrated by
HUNTER'S great collection of the Royal College of Surgeons, and
established by the conclusions of ST. HILAIRE and TIEDMANN. Its primary
positions are--1. That the embryos of all animals are not
distinguishably different from each other; and, 2. That those of all
animals pass through a series of phases of development, each of which is
the type or analogue of the permanent configuration of tribes inferior
to it in the scale. Higher the order of animals, the more numerous its
stages of progress. Man himself is not exempt from this law. His first
foetal form is that which is permanent in the animalcule; it next passes
through ulterior stages, resembling successively a fish, a reptile, a
bird, and the lower mammalia before it attains its specific maturity.
The period of gestation determines the species; protract it, and the
species is advanced to a higher class. This might be done by the force
of certain conditions operating upon the system of the mother. Give good
conditions and the young she produces will improve in development; give
bad conditions and it will recede. Cases of monstrous birth in the human
species are appealed to, in which the most important organs are left
imperfectly developed; the heart, for instance, having sometimes
advanced no further than the three-chambered or reptile form, while
there are instances of that organ being left in the two-chambered or
fish-like form. These defects arise from a failure of the power of
development in the mother, occasioned by misery or bad health, and they
are but the converse of those conditions that carry on species to
species. The _differences of sexes_ is the result of foetal progress
only one degree less marked than that of a change of species. Sex is
fully ascertained to be a matter of development. All beings are at one
stage of the embryotic progress _female_. A certain number of them a