Again,

in all viviparous animals furnished with feet the
following properties are observed in the testicles themselves. From
the aorta there extend vein-like ducts to the head of each of the
testicles, and another two from the kidneys; these two from the
kidneys are supplied with blood, while the two from the aorta are
devoid of it. From the head of the testicle alongside of the
testicle itself is a duct, thicker and more sinewy than the other just
alluded to-a duct that bends back again at the end of the testicle
to its head;