Fishes, then, are devoid of testicles, as has been stated, and
serpents also. They are furnished, however, with two ducts connected
with the midriff and running on to either side of the backbone,
coalescing into a single duct above the outlet of the residuum, and by
'above' the outlet I mean the region near to the spine. These ducts in
the rutting season get filled with the genital fluid, and, if the
ducts be squeezed, the sperm oozes out white in colour. As to the
differences observed in male fishes of diverse species, the reader
should consult my treatise on Anatomy, and the subject will be
hereafter more fully discussed when we describe the specific character
in each case.