blood of the fetus becomes
thus oxygenated from the passing stream of the maternal
arterial blood; exactly as is done by the gills of fish from
the stream of water, which they occasion to pass through
them.

But the chicken in the egg possesses a kind of aerial
respiration, since the extremities of its placental vessels
terminate on a membranous bag, which contains air, at the
broad end of the egg; and in this the chick in the egg
differs from the fetus in the womb, as there is in the egg no
circulating maternal blood for the insertion of the
extremities of its respiratory vessels, and in this also I
suspect that the eggs of birds differ from the spawn of fish;
which latter is immersed in water, and which has probably the
extremities of its respiratory organ inserted into the soft
membrane which covers it, and is in contact with the water.]

[Footnote: _First forms minute_, l. 297. See Additional Note
I. on Spontaneous Vitality.]

"Thus the tall Oak, the giant of the wood,
Which bears Britannia's thunders on the flood;
The Whale, unmeasured monster of the main,
The lordly Lion, monarch of the plain,
The Eagle soaring in the realms of air,
Whose eye undazzled drinks the solar glare,
Imperious man, who rules the bestial crowd,
Of language, reason, and reflection proud, 310
With brow erect who scorns this earthy sod,
And styles himself the image of his God;
Arose from rudiments of form and sense,
An embryon point, or microscopic ens!

"Now in vast shoals beneath the brineless tide,
On earth's firm crust testaceous tribes reside;
Age after age expands the peopled plain,
The tenants perish, but their cells remain;
Whence coral walls and sparry hills ascend
From pole to pole, and round the line extend. 320

[Footnote: _An embryon point_, l. 314. The arguments showing
that all vegetables and animals arose from such a small
beginning, as a living point or living fibre, are detailed in
Zoonomia, Sect. XXXIX. 4. 8. on Generation.]

[Footnote: _Brineless tide_, l. 315. As the salt of the sea
has been gradually accumulating, being washed down into it
from the recrements of animal and vegetable bodies, the sea
must orig