f Van Beneden's
blastopore (V.B.b.), for a point where the outer layer of cells is
incomplete over the inner, only commemorates the authorship of a
misnomer. The uniformity, or agreement, in the development of our
other vertebrate types is apparently departed from here.

{Illustration: Development Section 36.}

Section 37. As the egg develops, however, we are astonished to find
an increasing resemblance to that of the fowl. A split occurs at one
point between outer layer and inner layer cells, and the space
resulting (Y in Figure 2) is filled by an increasing amount of fluid, and
rapidly enlarges, so that presently we have the state of affairs shown
in 3, in which the inner layer cells are gathered together at one point
on the surface of the ovum, and constitute the germinal area. If, with
Hubrecht, we regard the outer layer cells as an egg membrane, there
is a curious parallelism between this egg and the fowl's the fluid Y
representing the yolk; and the inner layer cells the cells of the fowl's
germinal area.

At any rate, the subsequent development goes far to justify such a
view. The inner cells split into epi-, meso-, and hypo-blast, like the
blastoderm in the fowl; there is a primitive streak and no blastopore;
an amnion arises; the yolk sac, small and full of serous fluid, is cut off
just as the enormous yolk of the fowl is cut off; and an allantois arises
in the same way. There is no need to give special diagrams-- Figures
3, 4b, 5, and 6 of the fowl will do in all respects, except proportion, for
the development of the rabbit. The differences are such as we may
account for, not on the supposition that the rabbit's ovum never had
any yolk, but that an abundant yolk has been withdrawn from it. The
nutrition of the embryo by yolk has been superseded by some better
method. The supposition that the rabbit is descended from ancestors
which, like the birds and reptiles, laid eggs with huge quantities of
yolk, meets every circumstance of the case.

Section 38. But the allantois and yolk sac of the rabbit, though they
correspond in development, differ entirely in function from the similar
organs of the fowl. The yolk sac is of the very smallest nutritive value;
instead of being the sole source of food, its contents scarcely avail
the young rabbit at all as nourishment. Its presence in development is
difficult to account for except on the supposition, that it was once of
far greater importance. At an early stage,