-fourth of the whole, is devoid of the duct. The liver
having the duct, is functional as a gland, while the spleen having no
duct, cannot serve any such function. If, in thus indicating the
function which the spleen does not possess, there appears no proof
positive of the function which it does, perhaps the truth is, that as
being the ductless portion of the whole original hepatic quantity, it
exists as a thing degenerate and functionless, for it seems that the
animal economy suffers no loss of function when deprived of it. 6thly.
In early foetal life, the left lobe of the liver touches the spleen on
the left side; but in the process of abdominal development, the two
organs become separated from each other right and left. 7thly. In
animals devoid of the spleen, the liver appears of a symmetrical shape,
both its lobes being equal; for that quantity which in other animals has
become splenic, is in the former still hepatic. 8thly. In cases of
transposition of both organs, it is the right lobe of the liver--that
nearest the spleen, now on the right side--which is the smaller of the
two lobes, proving that whichever lobe be in this condition, the spleen,
as being opposite to it, represents the minus hepatic quantity. From
these, among other facts, I infer that the spleen is the representative
of the liver on the left side, and that as such, its signification being
manifest, there exists no exception to the law of animal symmetry. "Tam
miram uniformitatem in planetarum systemate, necessario fatendum est
intelligentia et concilio fuisse effectam. Idemque dici possit de
uniformitate illa quae est in corporibus animalium. Habent videlicet
animalia pleraque omnia, bina latera, dextrum et sinistrum, forma
consimili: et in lateribus illis, a posteriore quidem corporis sui
parte, pedes binos; ab anteriori autem parte, binos armos, vel pedes,
vel alas, humeris affixos: interque humeros collum, in spinam excurrens,
cui affixum est caput; in eoque capite binas aures, binos oculos, nasum,
os et linguam; similiter posita omnia, in omnibus fere animalibus."
--Newton, Optices, sive de reflex, &c. p. 411.]

X.--The heart, though being itself the recipient, the prime mover, and
the dispenser of the blood, does not depend either for its growth,
vitality, or stimulus to action, upon the blood under these uses, but
upon the blood circulating through vessels which are derived from its
main systemic artery, and disposed in capillary ramifications