First,

then, we must proceed to treat of 'covering' in regard to
such animals as cover and are covered; and then after this to treat in
due order of other matters, both the exceptional and those of
general occurrence.

Those animals, then, cover and are covered in which there is a
duality of sex, and the modes of covering in such animals are not in
all cases similar nor analogous. For the red-blooded animals that
are viviparous and furnished with feet have in all cases organs
adapted for procreation, but the sexes do not in all cases come
together in like manner. Thus, opisthuretic animals copulate with a
rearward presentment, as is the case with the lion, the hare, and
the lynx; though, by the way, in the case of the hare, the female is
often observed to cover the male.