e the heavy oily part remains beneath, where the lower cavity,
inclosing all the organs of mere material animal existence, is
afterwards developed. In other words, when the egg is a mere mass of
oil and albumen, not indicating as yet in any way the character of the
future animal, and discernible only by the microscope, the distinction
is indicated between the brains and the senses, between the organs of
instinct and sensation and those of mere animal functions. At that stage
of its existence, however, when the egg consists of an outer sac, an
inner sac, and a dot, its resemblance to a cell is unmistakable; and,
in fact, an egg, when forming, is nothing but a single cell. This
comparison is important, because there are both animals and plants
which, during their whole existence, consist of a single organic cell,
while others are made up of countless millions of such cells. Between
these two extremes we have all degrees, from the innumerable cells that
build up the body of the highest Vertebrate to the single-celled Worm,
and from the myriad cells of the Oak to the single-celled Alga.

But while we recognize the identity of cell-structure and egg-structure
at this point in the history of the egg, we must not forget the great
distinction between them,--namely, that, while the cells remain
component parts of the whole body, the egg separates itself and assumes
a distinct individual existence. Even now, while still microscopically
small, its individuality begins; other substances collect around it, are
absorbed into it, nourish it, serve it. Every being is a centre about
which many other things cluster and converge, and which has the power to
assimilate to itself the necessary elements of its life. Every egg is
already such a centre, differing from the cells that surround it by
no material elements, but by the principle of life in which its
individuality consists, which is to make it a new being, instead of a
fellow-cell with those that build up the body of the parent animal and
remain component parts of it. This intangible something is the subtile
element that eludes our closest analysis; it is the germ of the
immaterial principle according to which the new being is to develop. The
physical germ we see; the spiritual germ we cannot see, though we may
trace its action on the material elements through which it is expressed.

The first change in the yolk, after the formation of the Purkinjean
vesicle, is the appearance of minu