Watching the fashioning process stage by stage, one is forcibly
reminded of the modeller in clay. Every part, every organ, is at
first, as it were, pinched up rudely, and sketched out in the rough;
then shaped more accurately; and only, at last, receives the touches
which stamp its final character.
Thus, at length, the young puppy assumes such a form as is shown in Fig.
13, C. In this condition it has a disproportionately large head, as
dissimilar to that of a dog as the bud-like limbs are unlike his legs.
The remains of the yelk, which have not yet been applied to the
nutrition and growth of the young animal, are contained in a sac
attached to the rudimentary intestine, and termed the yelk sac, or
'umbilical vesicle.' Two membranous bags, intended to subserve
respectively the protection and nutrition of the young creature, have
been developed from the skin and from the under and hinder surface of
the body; the former, the so-called 'amnion,' is a sac filled with
fluid, which invests the whole body of the embryo, and plays the part of
a sort of water-bed for it; the other, termed the 'allantois,' grows
out, loaded with blood-vessels, from the ventral region, and eventually
applying itself to the walls of the cavity, in which the developing
organism is contained, enables these vessels to become the channel by
which the stream of nutriment, required to supply the wants of the
offspring, is furnished to it by the parent.
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