It leaves
the organ in which it is formed in a similar fashion and enters the
organic chamber prepared for its reception in the same way, the
conditions of its development being in all respects the same. It has
not yet been possible (and only by some rare chance can it ever be
possible) to study the human ovum in so early a developmental stage as
that of yelk division, but there is every reason to conclude that the
changes it undergoes are identical with those exhibited by the ova of
other vertebrated animals; for the formative materials of which the
rudimentary human body is composed, in the earliest conditions in which
it has been observed, are the same as those of other animals. Some of
these earliest stages are figured below, and, as will be seen, they are
strictly comparable to the very early states of the Dog; the marvellous
correspondence between the two which is kept up, even for some time, as
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.
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