The structure which is developed by the interlacement of the vessels of
the offspring with those of the parent, and by means of which the
former is enabled to receive nourishment and to get rid of effete
matters, is termed the 'Placenta.'
It would be tedious, and it is unnecessary for my present purpose, to
trace the process of development further; suffice it to say, that, by a
long and gradual series of changes, the rudiment here depicted and
described becomes a puppy, is born, and then, by still slower and less
perceptible steps, passes into the adult Dog.
There is not much apparent resemblance between a barndoor Fowl and the
Dog who protects the farm-yard. Nevertheless the student of
development finds, not only that the chick commences its existence as
an egg, primarily identical, in all essential respects, with that of
the Dog, but that the yelk of this egg undergoes division--that the
primitive groove arises, and that the contiguous parts of the germ are
fashioned, by precisely similar methods, into a young chick, which, at
one stage of its existence, is so like the nascent Dog, that ordinary
inspection would hardly distinguish the two.
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