igure 13,
B), the other remains narrow, and eventually becomes the tail; the side
walls of the body are fashioned out of the downward continuation of the
walls of the groove; and from them, by and bye, grow out little buds
which, by degrees, assume the shape of limbs. 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
Figure 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.

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