development advances, becoming apparent by the simple comparison of the
figures with those on page 249.

Fig. 14.--A. Human ovum (after Kolliker). a. germinal vesicle. b.
germinal spot. B. A very early condition of Man, with yelk-sac,
allantois, and amnion (original). C. A more advanced stage (after
Kolliker), compare Fig. 13, C.

Indeed, it is very long before the body of the young human being can be
readily discriminated from that of the young puppy; but, at a tolerably
early period, the two become distinguishable by the different form of
their adjuncts, the yelk-sac and the allantois. The former, in the
Dog, becomes long and spindle-shaped, while in Man it remains
spherical; the latter, in the Dog, attains an extremely large size, and
the vascular processes which are developed from it and eventually give
rise to the formation of the placenta (taking root, as it were, in the
parental organism, so as to draw nourishment therefrom, as the root of
a tree extracts it from the soil) are arranged in an encircling zone,
while in Man, the allantois remains comparatively small, and its
vascular rootlets are eventually restricted to one disk-like spot.
Hence, while the placenta of the Dog is like a girdle, that of Man has
the cake-like form, indicated by the name of the organ.

But, exactly in those respects in which the developing Man differs from
the Dog, he resembles the ape, which, like man, has a spheroidal
yelk-sac and a discoidal--sometimes partially lobed--placenta. So that
it is only quite in the later stages of development that the young
human being presents marked differences from the young ape, while the
latter departs as much from the dog in its development, as the man
does.