The males of oviparous animals, whether biped or quadruped, are
in all cases furnished with testicles close to the loin underneath the
midriff. With some animals the organ is whitish, in others somewhat of
a sallow hue; in all cases it is entirely enveloped with minute and
delicate veins. From each of the two testicles extends a duct, and, as
in the case of fishes, the two ducts coalesce into one above the
outlet of the residuum. This constitutes the penis, which organ in the
case of small ovipara is inconspicuous; but in the case of the
larger ovipara, as in the goose and the like, the organ becomes
quite visible just after copulation.