Hence if the eyes of swallows
while still young be put out they recover their sight again, for the
birds are still developing, not yet developed, when the injury is
inflicted, so that the eyes grow and sprout afresh. And in general the
production of young before they are perfect is owing to inability to
continue nourishing them, and they are born imperfect because they are
born too soon. This is plain also with seven-months children, for
since they are not perfected it often happens that even the
passages, e.g. of the ears and nostrils, are not yet opened in some of
them at birth, but only open later as they are growing, and many
such infants survive.
In man males are more often born defective than females, but in
the other animals this is not the case. The reason is that in man
the male is much superior to the female in natural heat, and so the
male foetus moves about more than the female, and on account of moving
is more liable to injury, for what is young is easily injured since it
is weak. For this same reason also the female foetus is not
perfected equally with the male in man (but they are so in the
other animals, for in them the female is not later in developing
than the male). For while within the mother the female takes longer
in developing, but after birth everything is perfected more quickly in
females than in males; I mean, for instance, puberty, the prime of
life, and old age.
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